JPH07248645A - Magnetic toner and image forming method - Google Patents

Abstract

PURPOSE:To provide a magnetic toner having a high image density and a little toner consumption and to provide an image forming method using the magnetic toner. CONSTITUTION:This magnetic toner is constituted of at least inorganic fine powder and magnetic toner grains containing a binding resin and a magnetic substance. The volume-average grain size Dv is 3mum<=Dv<6mum, and the weight- average grain size D4 is 3.5mum<=D4<=6.5m. The ratio Nr of toner grains having the grain size of 57x or below in the numeral grain size distribution is 60 numeral %<Nr<=90 numeral %, the volume variation coefficient A in the volume grain size distribution is 27.5<A<=40.0, and the weight variation coefficient Aw is 27.5<Aw<=38.0 in this magnetic toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner used in electrophotography, electrostatic recording, magnetic recording and the like, and an image forming method using the magnetic toner.

[0002]

2. Description of the Related Art Conventionally, a large number of electrophotographic methods are known. Generally, a photoconductive substance is used to form an electrical latent image on a photoconductor by various means, and then the latent image is developed with toner to form a visible image, and if necessary, transfer to paper or the like. After the toner image is transferred to the material, the toner image is fixed on the transfer material by heat, pressure or the like to obtain a copy.

In recent years, in addition to conventional copying machines, there have been many printers, facsimile machines, and the like using electrophotographic methods. Particularly in printers and facsimiles, a developing device using one-component toner is often used because it is necessary to reduce the size of the copying device.

Unlike the two-component developing system, the one-component developing system does not require carrier particles such as glass beads, iron powder, or ferrite particles, so that the developing device itself can be made compact and lightweight. Furthermore, since the two-component developing system needs to keep the toner concentration in the developer constant, an apparatus for detecting the toner concentration and supplying a required amount of toner is required. Therefore, also in this case, the developing device becomes large and heavy. Such a device is not necessary in the one-component developing system, and it is preferable because it can be made small and light.

Further, as for the printer device, the LBP printer or the LED printer has become the mainstream of the market recently, and the direction of the technology is that the conventional resolution of 240, 300 dpi becomes higher resolution of 400, 600, 800 dpi. It is coming. Therefore, the developing system is also required to have higher definition. Further, the functions of copiers are also becoming more sophisticated, and as a result, they are moving toward digitalization. In this direction, the method of forming an electrostatic charge image by a laser is mainly used, and therefore, it is also advancing toward high resolution, and here also, as in the case of a printer, a high resolution / high definition developing method is required. . For this reason, the particle size of the toner is becoming smaller, and the toner is disclosed in JP-A-1-112253, JP-A-1-191156, and JP-A-2-284158.
Japanese Patent Laid-Open No. 3-181952, Japanese Patent Laid-Open No. 4-1952
Japanese Patent No. 62048 proposes a toner having a specific particle size distribution and a small particle size.

In copying machines, there is always a demand for higher speed and stabilization. Especially for medium speed machines and high speed machines, the two-component developing method is the mainstream. This is because, with such a relatively large machine, the stability for long-term use at high speed becomes more important than the problem of the size and weight of the developing device. Generally, the toner of the two-component developer is colored with carbon black or the like, and the rest is composed of a polymer. For this reason, the toner particles are light and have no force to attach to carrier particles other than electrostatic force, which causes scattering of the developer, especially during high-speed development, resulting in stains on the lens, original glass, transport section, etc. during long-term use. May impair the stability of the. Therefore, a developer has been put into practical use in which a magnetic substance is contained in the toner to make the toner heavier and at the same time adhere to the magnetic carrier particles not only with an electrostatic force but also with a magnetic force to prevent scattering.

As described above, the magnetic toner containing the magnetic substance is becoming more and more important.

In recent years, so-called recycled paper has become the mainstream as copy paper from the viewpoint of environmental protection. However, since recycled paper has a large amount of paper powder and filler powder, problems such as cleaning failure and toner fusion are promoted by the use of recycled copy paper. These problems are small while clearing environmental problems.
This has been a problem that must be improved in order to obtain an image forming apparatus that can obtain high resolution and high definition images at light weight and low cost.

Further, with the increasing awareness of resource saving, it is required to further reduce the toner consumption amount (the amount of toner used for forming one image). Proposals for fine particle size toners have not been sufficient.

By the way, in the one-component magnetic development system, magnetic toner is chained (generally called "brush") during development.
Therefore, the resolution in the horizontal direction of the image tends to be poorer than that in the vertical direction, and the magnetic toner tends to excessively deposit on the line as compared with the solid black image, and the consumption amount of the magnetic toner tends to increase. For example, the tailing phenomenon due to the protrusion of the ears is likely to occur in the non-image portion in the latter half of the developed image, and a rough image tends to be produced as compared with the two-component developing method. Also, 400
The amount of magnetic toner on a line having a width of about μm may reach almost twice the amount of magnetic toner on a solid black image. Therefore, as a method of further improving the image reproducibility and reducing the consumption amount, it is conceivable to make the ears of the magnetic toner shorter and denser. The relationship between the magnetic strength of the magnetic toner and the shape of the spikes is also qualitatively understood as follows. That is, when the magnetic toner has a large magnetization intensity, a strong attractive force along the magnetic field direction and a strong repulsive force in the direction perpendicular to the magnetic field are generated between the magnetic toner particles. Therefore, when the magnetization intensity is high, the ears formed by the magnetic toner are long, and the ears on the toner carrier have a low density, and the individual ears are thin. On the contrary, when the magnetic toner has a low magnetization, the ears are short and the density on the toner carrier becomes dense, but the individual ears are thick and short because the binding between the magnetic toner particles is not broken. , Will be in an aggregated state. In this case, the magnetic toner particles existing inside the ears are less likely to come into contact with the surface of the toner carrying member, and thus charging failure is likely to occur. Such poorly charged magnetic toner particles cause fog on the image and deteriorate the image quality. That is, if the content of the magnetic material is the same, the finer the magnetic toner, the shorter and denser the ears. Furthermore, as the particle size of the magnetic toner becomes smaller, the amount of fine particles with a high charge amount increases and it becomes easier to fill the latent image electric field with a small amount of magnetic toner. The magnetic toner with a large amount tends to have an insufficient image density.

Further, from the viewpoint of environmental protection, the primary charging and transfer process using corona discharge, which has been conventionally used, is changed from the primary charge and transfer process using a photoconductor contact member that hardly generates ozone. It is becoming mainstream.

Specifically, in the primary charging step, a voltage is applied to a medium resistance roller or a medium resistance brush which is a charging member to bring the roller into contact with a photoconductor which is a member to be charged so that the surface of the photoconductor is predetermined. It is charged to a potential. For example, in Japanese Examined Patent Publication No. 50-13661, a roller having a core metal coated with a dielectric made of nylon or polyurethane rubber enables a low voltage to be applied when the photosensitive member is charged. Also, JP-A-63-149669
Japanese Patent Application Laid-Open No. 2-123385 and Japanese Patent Application Laid-Open No. 2-123385 also propose a contact charging method and a contact transfer method.
However, in the charging method in which the charging member is in contact, the physical and chemical action of the surface of the organic photoconductor due to the discharge generated between the charging member and the photoconductor is larger than that in the corona charging system, and particularly in the OPC photoconductor / In combination with blade cleaning, problems such as defective cleaning of the photoconductor due to deterioration of the photoconductor surface or toner fusion onto the photoconductor are likely to occur. The combination of contact charging / OPC photoreceptor / single-component developing method / contact transfer / blade cleaning makes it easy to reduce the cost and size and weight of the image forming apparatus. A magnetic toner and an image forming method which are useful in such a copying machine, a printer, a facsimile, etc. and can effectively exhibit their characteristics are desired.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic toner that solves the above-mentioned conventional problems and an image forming method using the magnetic toner.

That is, it is an object of the present invention to provide a magnetic toner that consumes less toner than ever before and an image forming method using the magnetic toner.

A further object of the present invention is to provide a high image density,
It is an object of the present invention to provide a magnetic toner capable of obtaining a sharp image even in a small spot latent image and an image forming method using the magnetic toner.

[0016]

Specifically, the present invention relates to a magnetic toner containing at least a binder resin, magnetic toner particles containing a magnetic substance, and inorganic fine powder. Volume average particle diameter Dv (μm) of 3 μm
≦ Dv <6 μm, the weight average particle size D4 (μm) is 3.5 μm ≦ D4 <6.5 μm, and the ratio Nr of the toner particles having a particle size of 5 μm or less in the number particle size distribution is 60% by number <Nr ≦ 90. % Of number, volume variation coefficient A of volume particle size distribution is 27.5 <A ≦ 40.0, and weight variation coefficient Aw is 27.5 <Aw ≦ 38.0 .

Further, according to the present invention, the magnetic toner is applied on the toner carrier with a layer thickness smaller than the closest distance (between S and D) of the toner carrier and the latent image carrier, and an alternating electric field is applied. While forming an electrostatic latent image on an electrostatic image bearing member with a magnetic toner, the image forming method includes magnetic toner particles containing at least a binder resin and a magnetic substance, and inorganic fine powder as the magnetic toner. And a volume average particle diameter Dv (μm) of the magnetic toner is 3 μm.
m ≦ Dv <6 μm, the weight average particle size D4 (μm) is 3.5 μm ≦ D4 <6.5 μm, and the ratio Nr of the toner particles having a particle size of 5 μm or less in the number particle size distribution is 60 number% <Nr ≦ 90% by number, the volume variation coefficient A of the volume particle size distribution is 27.5 <A ≦ 40.0, and the weight variation coefficient Aw is 27.5 <Aw ≦ 38.0. The present invention relates to a characteristic image forming method.

The volume variation coefficient A is obtained from the equation Sv / Dv (where Sv is the standard deviation value of the volume particle size distribution and Dv is the volume average particle diameter), and the weight variation coefficient Aw
Is calculated from the formula Sv / D ₄ [wherein, Sv represents the standard deviation value of the volume particle size distribution, and D ₄ represents the weight average particle size].

The magnetic toner of the present invention is a mixture of magnetic toner particles and at least inorganic fine powder, and in addition, organic fine powder, resin fine powder and the like having an average particle size smaller than the average particle size of the toner particles. It also includes a mixture.

Further, it is preferable that the magnetic toner particles also have the particle size distribution of the present invention.

If the variation coefficient of the volume distribution is 27.5 or less, or if the number of particles of 5 μm or less is 60% by number or less, the effect of reducing the consumption is not sufficient and the volume average particle diameter Dv (μ
m) is 6 μm or more and the weight average particle diameter D4 (μm) is 6.5 μm or more, the resolution of an isolated 1 dot of a small spot is not sufficient. At this time, if it is attempted to forcibly modify it under developing conditions or the like, line thickening and scattering easily occur. Furthermore, by having the above-mentioned particle size distribution, high productivity can be maintained even for the fine particle size magnetic toner. In addition, the coefficient of variation of volume distribution exceeds 40, or the number of particles of 5 μm or less is 9
If it exceeds 0% by number, the image density will decrease. It is preferable that 62% by number, Nr ≦ 88 by 4%, and 64% by% <Nr ≦ 86 by%. The average particle size is preferably 3.2 μm ≦ Dv ≦ 5.8 μm, 3.6 μm <
D4 ≦ 6.3 μm is preferable.

The coefficient of variation is preferably 28 <A <from the viewpoint of maintaining the image density and further improving the productivity.
38 and 28 <Aw <36 are preferable, and 29 <A <36 and 28.5 <Aw <34 are more preferable. Further, since the magnetic toner of the present invention has a small particle size and the amount of magnetic toner particles of 8 μm or more is small, even if the particle size distribution is broad within a proper range, the change in the particle size distribution in the developing device can be observed throughout the durability. Stable image density can be obtained.

In addition, the charge amount Q of the magnetic toner is related to the coefficient of variation B of the number distribution by the following condition 0.1B + 10 <| Q | ≦ 60 (Q is the friction charge amount with iron powder (μc / g)). In the formula, it is preferable that (B represents S1 / D1, D1 represents a number average particle diameter, and Sv represents a standard deviation value of the number particle diameter distribution).

More preferably, the following condition 0.1B + 20 <| Q | ≦ 55 (Q represents the triboelectric charge amount (μc / g) with iron powder) should be satisfied.

If the relationship between the charge amount Q of the magnetic toner and the coefficient of variation B of the number distribution is the following condition 0.1B + 10 ≧ | Q |, the charge amount is low and the effect of reducing the consumption amount is likely to decrease. If the condition | Q |> 60, the charge amount is too high and the density is likely to decrease.

Further, the volume ratio of particles having a particle size of 8 μm or more in the volume particle size distribution of the magnetic toner is preferably 10% by volume or less in order to reduce scattering.

The magnetic toner of the present invention achieves higher image quality by having a small particle size, and has a low consumption amount by increasing the abundance of fine powder magnetic toner particles having a high charge amount per unit weight of 5 μm or less. It was possible to prevent a decrease in concentration by achieving the above and broadening the particle size distribution.

The reason why more magnetic toner is developed in the line image area than in the solid image area is considered as follows. In the electrostatic latent image of the line image portion on the photoconductor, unlike the solid image portion, the lines of electric force are closely wrapped around the line latent image from the outside of the line latent image. Since a large amount of toner is attracted to and pressed against the latent image surface of the photoconductor, more magnetic toner is easily developed on the line latent image surface.

The magnetic toner of the present invention has a smaller weight of the magnetic toner on the line image portion than the conventional magnetic toner,
The reason why the consumption of the magnetic toner can be reduced is considered as follows.

In the one-component developing system using magnetic toner,
The magnetic toner particles are developed on the surface of the photoconductor while being aggregated to some extent. Since the magnetic toner of the present invention contains a large amount of magnetic toner particles having a high charge amount of 5 μm or less, the magnetic toner particles 1
Since the magnetic force per piece is small and it is easy to fill the latent image potential, the magnetic toner once developed in the line image part formed on the photoconductor is more than necessary, and the latent image electric force line wraps around. It is considered that the magnetic toner can be returned to the developing sleeve against the force due to, and only an appropriate amount of magnetic toner remains in the line image portion. That is, since particles of magnetic toner having a particle size of 5 μm or less have a high charge amount per unit weight, they reach the latent image on the photoreceptor faster than the magnetic toner particles having a large particle size, and the latent image is weakened in order to weaken the developing electric field. This is because other magnetic toner particles are less likely to be affected by the wraparound of lines of electric force. Also in the case of a solid black image, it is possible to increase the image density with a smaller amount by reducing the particle size of the magnetic toner, and it is expected that the consumption amount of the magnetic toner can be reduced.

Examples of the magnetic substance used in the magnetic toner of the present invention include metal oxides containing elements such as iron, cobalt, nickel, copper, magnesium, manganese, aluminum and silicon. Among them, those containing iron oxide as a main component such as triiron tetraoxide and γ-iron oxide are preferable. From the viewpoint of controlling the chargeability of the magnetic toner, the content of silicon element in the magnetic material is preferably 0.5 to 4% by weight based on the iron element. It is more preferable to contain a silicon atom. Specifically, the amount of silicon atoms present in the magnetic material up to the iron element dissolution rate of 20% is 44 to 8% of the amount of the silicon element at 100% dissolution.
It is preferably 4%. The silicon atom may be added in the form of a water-soluble silicon compound at the time of forming the magnetic substance, or may be added in the form of a silicate compound after forming the magnetic substance, filtration and drying, and may be fixed to the surface with a mix muller or the like. . The BET specific surface area by the nitrogen adsorption method of these magnetic particles is preferably ² to 30 m ² / g, and particularly preferably 3 to 28 m ² / g. Further, magnetic particles having a Mohs hardness of 5 to 7 are preferable.

The shape of the magnetic particles may be octahedron, hexahedron, sphere, acicular, scaly or the like, but octahedral, hexahedron, sphere, or irregular shape having less anisotropy is preferable.
In particular, it is preferable that the sphericity Ψ of the magnetic particles is 0.8 or more in order to increase the image density. The average particle size of the magnetic particles is preferably 0.05 to 1.0 μm, more preferably 0.1 to 0.6 μm, and particularly preferably 0.1 to 0.4 μm.

The content of magnetic particles in the magnetic toner is 30 to 200 parts by weight, preferably 60 to 200 parts by weight, and more preferably 70 to 150 parts by weight based on 100 parts by weight of the binder resin. If it is less than 30 parts by weight, it is inferior in terms of transportability, and unevenness tends to occur in the magnetic toner layer on the developer carrying member to cause image unevenness, and further, the image density tends to decrease due to increase in tribo of the magnetic toner. It was a trend. On the other hand, if the content of the magnetic particles exceeds 200 parts by weight, the fixing property tends to be problematic.

Examples of the binder resin used in the present invention include polystyrene; homopolymers of styrene substitution products such as poly-p-chlorostyrene and polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene- Vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic acid ester 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 copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer Styrene-based copolymers such as; polysalts Vinyl, phenol resin, natural modified phenol 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, coumarone indene resin, petroleum resin, etc. can be used. A crosslinked styrene resin is also a preferable binder resin.

As the comonomer for the styrene monomer of the styrene-based copolymer, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, A monocarboxylic acid having a double bond such as methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide and the like; or a substituted form thereof; maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like, and substituted products thereof; vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc .; ethylene, propylene, butylene, etc. The ethylene-based olefins, vinyl methyl ketone, vinyl ketones such as vinyl hexyl ketone, vinyl methyl ether, vinyl ethyl ether, vinyl ethers such as vinyl isobutyl ether; and the like. These vinyl monomers are used alone or in combination. Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used. An aromatic divinyl compound such as divinylbenzene, divinylnaphthalene; ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1 A carboxylic acid ester having two double bonds such as 3-butanediol dimethacrylate; a divinyl compound such as divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone; and a compound having three or more vinyl groups. Can be mentioned. These can be used alone or as a mixture.

As the binder resin of the toner used for pressure fixing, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acid, polyamide resin , And polyester resin. These are preferably used alone or in combination.

Further, it is also preferable to include the following waxes in the toner from the viewpoint of improving the releasability from the fixing member during fixing and the fixing property. Examples thereof include paraffin wax and its derivatives, microcrystalline wax and its derivatives, Fischer-Tropsch wax and its derivatives, polyolefin wax and its derivatives, carnauba wax and its derivatives, and the like. Derivatives include oxides, block copolymers with vinyl monomers, and graft modified products.

As other additives, alcohols, fatty acids, acid amides, esters, ketones, hydrogenated castor oil and its derivatives, vegetable wax, animal wax, mineral wax, petrolactam and the like can be used.

In the magnetic toner of the present invention, a charge control agent can be used by blending with the magnetic toner particles (internal addition) or by mixing with the magnetic toner particles (external addition). The charge control agent makes it possible to control the optimum charge amount according to the developing system, and particularly in the present invention, it is possible to further stabilize the balance between the particle size distribution and the charge amount. Examples of compounds that control the magnetic toner to be negatively charged include the following compounds.

For example, organic metal complexes and chelate compounds are effective, and examples thereof include monoazo metal complexes, acetylacetone metal complexes, aromatic hydroxycarboxylic acids, and aromatic dicarboxylic acid type metal complexes. Other examples include aromatic hydroxycarboxylic acids, aromatic mono- and polycarboxylic acids and their metal salts, anhydrides, esters, and phenol derivatives such as bisphenol. The following substances can be mentioned as substances that are controlled to be positively charged.

For example, modified products of nigrosine and fatty acid metal salts; quaternary ammonium salts such as tributylbenzeneammonium-1hydroxy-4-naphthosulfonate, tetrabutylammonium tetrafluoroborate, and phosphonium which is an analog thereof. Onium salts such as salts and lake pigments thereof, triphenylmethane dyes and lake pigments thereof, (as a laker, phosphotungstic acid, phosphomolybdic acid, phosphotungstic molybdic acid, tannic acid, lauric acid, gallic acid, Ferricyanide, ferrocyanide, etc.) Metal salts of higher fatty acids; Diorganotin oxides such as dibutyltin oxide, dioctyltin oxide, dicyclohexyltin oxide; Dibutyltin borate, dioctyltin borate, dicyclo Diorgano tin borate such as hexyl tin borate, and the like. These can be used alone or in combination of two or more kinds. The charge control agents described above are preferably used in the form of fine particles, and in this case, the number average particle diameter of these charge control agents is preferably 4 μm or less, more preferably 3 μm or less. When these charge control agents are internally added to the magnetic toner particles, it is preferable to use 0.1 to 20 parts by weight, particularly 0.2 to 10 parts by weight, based on 100 parts by weight of the binder resin. Further, as the coloring material which can be further added to the magnetic toner of the present invention, there are conventionally known carbon black, copper-phthalocyanine and the like.

As the inorganic fine powder contained in the magnetic toner of the present invention, known fine powders are used. However, in order to improve charge stability, developability, fluidity and storability, silica fine powder,
It is preferably selected from alumina fine powder, titania fine powder, or a complex oxide thereof. Further, it is more preferably a fine silica powder. For example, such silica fine powder is a so-called dry method produced by vapor phase oxidation of a silicon halide or an alkoxide, or a dry silica fine powder called fumed silica, and a so-called wet silica fine powder produced from alkoxide water glass or the like. Both of them can be used, but dry silica fine powder having less silanol groups on the surface and inside the silica fine powder and less production residue of Na ₂ O, SO ₃ ^2-, etc. is preferable. Further, in the case of dry silica fine powder, in the manufacturing process, for example,
By using other metal halogen compounds such as aluminum chloride and titanium chloride together with the silicon halogen compound, it is possible to obtain a composite fine powder of silica and another metal oxide, and these are also included. The inorganic fine powder used in the present invention has a specific surface area of 30 m by nitrogen adsorption measured by the BET method.
^{It is} preferably ² / g or more, particularly 50 to 400 m ² / g.

It is preferable to use 0.01 to 8 parts by weight, preferably 0.1 to 5 parts by weight of silica fine powder with respect to 100 parts by weight of the magnetic toner. In addition, the inorganic fine powder used in the present invention may contain a silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oil, a silane coupling agent, and a functional group for the purpose of hydrophobizing, controlling chargeability, etc. It is also possible and preferable to treat with a silane coupling agent, a treating agent such as an organic silicon compound, an organic titanium compound, or the like, or a combination of various treating agents.

In order to maintain a high charge amount of the magnetic toner, and achieve a low consumption amount and a high transfer rate of the magnetic toner, it is further preferable that the inorganic fine powder is treated with at least silicone oil.

The magnetic toner of the present invention may further contain other additives as long as they do not have a substantial adverse effect.
Lubricant powders such as Teflon powder, zinc stearate powder, polyvinylidene fluoride powder; cerium oxide powder,
Abrasives such as silicon carbide powder and strontium titanate powder; flowability-imparting agents such as titanium oxide powder and aluminum oxide powder; anti-caking agent; carbon black powder,
Examples of the conductivity imparting agent include zinc oxide powder and tin oxide powder. Further, a small amount of organic fine particles or inorganic fine particles having a polarity opposite to that of the magnetic toner particles can be used as the developing property improver.

A known method is used to prepare the magnetic toner of the present invention. For example, a binder such as a binder, a wax, a metal salt or a metal chain, a pigment as a colorant, a dye, a magnetic particle, a charge control agent, and other additives as necessary are mixed in a hex shell mixer, a ball mill, or the like. After sufficiently mixing with a heating roll, a kneader, a heat kneader such as an extruder to melt-knead the resin to make them compatible with each other in which the metal compound, pigment, dye, magnetic particles are dispersed or dissolved. The magnetic toner particles according to the present invention can be obtained by pulverizing and classifying after cooling and solidifying. In the classification step, it is preferable to use a multi-division classifier in terms of production efficiency.

The average particle size and particle size distribution of the magnetic toner can be measured by various methods such as Coulter Counter TA-11 type or Coulter Multisizer (manufactured by Coulter Co.). In the present invention, Coulter counter TA-
PC98 with an interface (manufactured by Nikkaki) that outputs the number distribution and volume distribution using the 11 type (manufactured by Coulter)
01 Connect a personal computer (made by NEC),
As the electrolytic solution, a 1% NaCl aqueous solution is prepared using primary sodium chloride. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As the measuring method, the electrolytic aqueous solution 100 to 150 is used.
0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) as a dispersant is added to ml, and then 2 to 20 mg of a measurement sample is added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and a particle size of 2 μm is obtained by the Coulter counter TA-II type using an aperture of 100 μm.
The volume distribution and number distribution of the magnetic toner particles are calculated by measuring the volume and number of the particles. Then, the volume-based volume average particle diameter (Dv: the median value of each channel is a representative value of the channel) and the volume variation coefficient (Sv) obtained from the volume distribution of the sample, and the number-based length average obtained from the number distribution. The particle size (D1), the length variation coefficient (S1), and the weight-based coarse powder amount (8.00 μm or more) obtained from the volume distribution and the number-based fine powder amount (5 μm or less) obtained from the number distribution are obtained.

The method for measuring the two-component tribo value of the magnetic toner in the present invention is shown below.

EFV200 / 300 (manufactured by Powdertech Co., Ltd.) was used as a carrier in an environment of 23 ° C. and 60% relative humidity, and a mixture of 9.0 g of carrier and 1.0 g of magnetic toner was mixed in polyethylene of 50 to 100 ml volume. Put in bottle and shake by hand 50 times. Then, at the bottom shown in FIG.
Metal measuring container 2 with 0 mesh screen 23
Put 1.0 to 1.2 g of the mixture in No. 2 and cover with a metal lid 24. Weigh the entire measuring container 22 at this time,
W ₁ g. Next, in the suction device (at least the part that is in contact with the measurement container 22 is an insulator), suction is performed from the suction port 27 and the air volume control valve 26 is adjusted to set the pressure of the vacuum gauge 25 to 250 mm
Let Aq. In this state, suction is performed for 1 minute to remove the magnetic toner by suction. The potential of the electrometer 29 at this time is V (volt). Here, 28 is a capacitor, and the capacitance is C (μF). The weight of the entire measuring machine after suction is weighed and is W ₂ (g). Friction charge of magnetic toner (μc /
g) is calculated by the following formula.

Triboelectric charge amount (μc / g) = CV / (W1-W2)

In the present invention, the BET specific surface area of the magnetic particles is determined by the BET multipoint method using a specific surface area measuring device Autosorb 1 (made by Yuasa Ionics) by nitrogen adsorption. The sample pretreatment was performed at a temperature of 50 ° C.
Degas for 1 hour.

In the present invention, the sphericity Ψ of magnetic particles is calculated as follows.

Sphericality Ψ = minimum length of magnetic particles (μm) / maximum length of magnetic particles (μm)

The sphericity ψ was 100 at a voltage of 100 kV using a magnetic particle sample treated with a collodion film copper mesh with a transmission electron microscope (Hitachi H-700H).
Take a picture at 00 times, and set the baking magnification to 3 times and the final magnification to 3 times.
It is assumed that 100 magnetic particles are randomly selected from the 0000 times photograph, the maximum length and the minimum length are measured, and then the average value is calculated. The average particle size of the magnetic particles is obtained by averaging the maximum lengths of the particles in the same manner.

The magnetic characteristics of the magnetic particles are values measured using a vibrating magnetometer VSM-3S-15 (manufactured by Toei Industry Co., Ltd.).

In order to obtain a high image quality, the magnetic toner of the present invention is applied on the toner carrier with a layer thickness smaller than the closest distance (between S and D) of the toner carrier and the latent image carrier. Then, it is developed in a developing process in which an alternating electric field is applied to develop.

The surface roughness of the toner carrier used in the present invention is from 0.2 to JIS center line average roughness (Ra).
It is preferably in the range of 3.5 μm.

If Ra is less than 0.2 μm, the charge amount of the magnetic toner on the toner carrier tends to be high, and the developability may decrease. When Ra exceeds 3.5 μm, unevenness in the magnetic toner coat layer on the toner carrier is likely to occur, and uneven density may occur in the image. More preferably, Ra is in the range of 0.5 to 3.0 μm.

Further, since the magnetic toner of the present invention has a high charging ability, it is preferable to control the total charge amount of the magnetic toner at the time of development, and the surface of the toner carrier used in the present invention has conductive fine particles and fine particles. It is / are preferably covered with a resin layer in which a lubricant is dispersed.

Examples of the conductive fine particles contained in the resin layer coating the surface of the toner carrier include conductive metal oxides such as carbon black, graphite and conductive zinc oxide, and metal double oxides. These are alone or 2
Used as a mixture of two or more. As the resin in which the conductive fine particles are dispersed, a phenol resin, an epoxy resin, a polyamide resin, a polyester resin, a polycarbonate resin, a polyolefin resin, a silicone resin, a fluorine resin, a styrene resin, A resin such as an acrylic resin is used. In particular, thermosetting or
Photocurable resins are preferred.

Further, the diameter (or major axis) is 20 to
A developing sleeve in which a resin layer in which conductive fine particles and / or a lubricant are dispersed is coated on a non-metallic cylinder blasted with 250 μm regular particles or irregular particles is preferable for maintaining Ra of the surface layer throughout durability.

Further, the ratio Vt / V of the peripheral speed Vt of the toner carrier to the peripheral speed V of the latent image carrier is 1.1 ≦ Vt / V ≦ 3 so that high image density and fog reduction can be achieved. It is preferable from the viewpoint.

More preferably, 1.2 ≦ Vt / V ≦ 2.
5 is good.

Further, in the magnetic toner of the present invention, the member for regulating the magnetic toner on the toner carrier is regulated by the elastic member which is in contact with the toner carrier via the toner, so that the magnetic toner is uniformly charged. From the viewpoint, it is particularly preferable.

In the present invention, it is preferable in terms of environmental protection that the charging member and the transfer member are in contact with the photoconductor so that ozone is not generated.

[0066]

EXAMPLES The present invention will be specifically described below with reference to production examples and examples, but the present invention is not limited thereto. All parts in the following formulations are parts by weight.

In FIG. 1, 100 is a photosensitive drum,
A primary charging roller 117, a developing device 140, a transfer charging roller 114, a cleaner 116, a resist roller 124, and the like are provided around it. And the photosensitive drum 10
0 is charged to, for example, −700 V by the primary charging roller 117 having the bias applying unit 133 (applied voltage is AC voltage −2.0 kVpp, DC voltage −700 Vd).
c). Then, laser light 123 is applied to the photosensitive drum 100 by the laser generator 121 to expose the photosensitive drum 100 to form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 100 has a stirring device 141, and bias applying means 131.
Is developed with a one-component magnetic toner by a developing device 140 equipped with a transfer roller 114 having a bias applying means 132 and transferred onto a transfer material (applied DC voltage 2 k
Vpp). The transfer material bearing the magnetic toner image is conveyed to the fixing device 126 by the conveyor belt 125 or the like and fixed on the transfer material. Further, the magnetic toner partially left on the photosensitive drum 100 is cleaned by the cleaning unit 116. The developing device 140 is, as shown in FIG.
A cylindrical toner carrier 102 (hereinafter referred to as a developing sleeve) made of a non-magnetic metal such as aluminum or stainless steel is disposed in the vicinity of, and a gap between the photosensitive drum 100 and the developing sleeve 102 is not shown. It is maintained at about 300 μm by a drum gap holding member or the like. A magnet roller 104 is concentrically fixed to the developing sleeve 102 in the developing sleeve. However, the developing sleeve 102 is rotatable, and the developing sleeve 102 is rotating in the forward direction with respect to the photosensitive drum. The magnet roller 104 is provided with a plurality of magnetic poles as shown in the figure. S1 is development, N1 is magnetic toner coat amount regulation, S2.
Indicates that magnetic toner is taken in / conveyed, and N2 influences prevention of magnetic toner blowout. An elastic blade 103 is provided as a member for controlling the amount of magnetic toner attached to the developing sleeve 102 and conveyed, and the amount of magnetic toner conveyed to the developing area by the contact pressure of the elastic blade 103 against the developing sleeve 102 Between sleeve photosensitive drums (S-
(Between D), the layer thickness is controlled to be smaller. In the development area,
A DC and AC developing bias is applied between the photosensitive drum 100 and the developing sleeve 102 by the bias applying means 131, and the magnetic toner on the developing sleeve flies on the photosensitive drum 100 in accordance with the electrostatic latent image to form a visible image. To form.

Example 1 Magnetic material (saturation magnetization σ S at 1 kOe s = 63 em
u / g, silicon element content rate 1.7%, average particle size 0.22μ
m, BET specific surface area 22 m ² / g, sphericity 0.90)
100 parts by weight-Styrene-butyl acrylate-butyl maleic acid half ester copolymer 100 parts by weight-Monoazo dye iron complex (negative charge control agent) 2 parts by weight-Low molecular weight polyolefin (release agent) 2 parts by weight

The above materials were mixed in a blender, and
Melted and kneaded with a twin-screw extruder heated to ℃, chilled kneaded material is coarsely crushed with a hammer mill, coarsely pulverized material is finely pulverized with a jet mill, and the obtained finely pulverized material is multi-divided using the Coanda effect. Strict classification was carried out with a classifier to obtain magnetic toner particles. 100 parts by weight of the obtained magnetic toner particles are treated with dry silica (BET specific surface area 130 m ² / BET) which has been hydrophobized with silicone oil and hexamethyldisilazane.
g) Magnetic toner A was obtained by mixing 1.5 parts by weight with a mixer. The obtained magnetic toner has a weight average particle diameter of 5.1 μm, a volume average particle diameter of 4.3 μm, a number average particle diameter of 4.0 μm, and 81 magnetic toner particles having a particle diameter of 5 μm or less. %, And 5% by volume of magnetic toner particles having a particle diameter of 8 μm or more. Further, the number variation coefficient, the volume variation coefficient, and the weight variation coefficient calculated from the particle size distribution were 31.3, 33.8, and 28.8, respectively. The charge amount Q of the magnetic toe was −47 μC / g. The physical properties are shown in Table 1.

Examples 2 to 4 and Comparative Examples 1 and 2 Black magnetic toner particles having various particle sizes and particle size distributions were obtained by controlling the classifying process by crushing the coarsely pulverized products obtained in Example 1. It was To 100 parts by weight of the obtained black magnetic toner particles, 1.3 parts by weight of dry silica fine powder subjected to hydrophobic treatment in the same manner as in Example 1 was mixed with a mixer to prepare magnetic toners B, C, D and E. (Comparative Example 1), F (Comparative Example 2)
Got Table 1 shows the physical properties of the obtained magnetic toner.

Example 5 The same procedure as in Example 1 was carried out except that 1.4 parts by weight of silica fine powder was used as the inorganic fine powder, which was made hydrophobic with hexamethyldisilazane (BET specific surface area 180 m ² / g). , Magnetic toner G was obtained.

The physical properties of the magnetic toner obtained are shown in Table 1.

Example 6 The addition amount of the hydrophobic silica fine powder (BET specific surface area 180 m ² / g) hydrophobized with dimethyldichlorosilane was 1.
A magnetic toner H having a weight average particle diameter of 5.2 μm was obtained in the same manner as in Example 1 except that the amount was 2 parts by weight. Table 1 shows the physical properties of the obtained magnetic toner.

Examples 7 and 8 Magnetic toners I and J were prepared in the same manner as in Example 1 except that hydrophobic titania, fine powder or hydrophobic alumina fine powder hydrophobized with silicone oil was used as the inorganic fine powder. Obtained. Table 1 shows the physical properties of the obtained magnetic toner.

Example 9 Saturation magnetization at 1 kOe σ S = 65 emu / g, silicon element content 0.3%, average particle size 0.19 μm, BET
A magnetic toner K was obtained in the same manner as in Example 1 except that a magnetic material having a specific surface area of 8 m ² / g and a sphericity of 0.78 was used. Table 1 shows the physical properties of the obtained magnetic toner.

Example 10 Magnetic material (saturation magnetization σ S = 60 em at 1 kOe)
u / g, silicon element content 3.1%, average particle size 0.24μ
m, BET specific surface area 26 m ² / g, sphericity 0.87)
90 parts by weight Polyester resin 100 parts by weight Chromium complex of monoazo dye (negative charge control agent) 2 parts by weight Low molecular weight polyolefin (release agent) 2 parts by weight

A magnetic toner L having a weight average particle diameter of 4.9 μm was obtained in the same manner as in Example 1 except that the above materials were used.
Table 1 shows the physical properties of the obtained magnetic toner.

[0078]

[Table 1]

Example 11 A rubber roller (diameter 12 mm, contact pressure 50 g / cm) in which conductive carbon coated with nylon resin was dispersed was used as a primary charging roller, and an OPC having a diameter of 24 mm was used as an electrostatic latent image carrier. Laser exposure (6
00 dpi, laser spot diameter 50 μm) to set the dark portion potential VD = −700 V and the light portion potential VL = −200 V. As a toner carrier, the following layer thickness is about 7 μm, J
A developing sleeve was prepared by forming a resin layer having an IS center line average roughness (Ra) of 2.2 μm on a stainless steel cylinder having a diameter of 12 mm whose surface was blasted. -Phenolic resin 100 parts-Graphite (particle size about 7 μm) 90 parts-Carbon black 10 parts

Next, the gap between the photosensitive drum and the developing sleeve (between S and D) is set to 300 μm, the developing magnetic pole is 800 gauss, the thickness of the toner regulating member is 1.0 mm, and the free length is 10.
A blade made of urethane rubber of mm was brought into contact with the blade at a linear pressure of 15 g / cm. DC bias component Vd as developing bias
c = -450V, superposed AC bias component _Vpp = 1
200V and f = 2000Hz were used.

A urethane rubber blade having a thickness of 2.0 mm and a free length of 8 mm was brought into contact with the photosensitive drum cleaning blade at a linear pressure of 25 g / cm. The process speed is 24 mm / sec, and the peripheral speed V of the developing sleeve is
The ratio Vt / V of t to the peripheral speed V of the photosensitive drum was set to 1.5, and rotation was performed in the forward direction.

Magnetic toner A of Example 1 was used as the magnetic toner.
Was used in the environment of 23 ° C. and 65% RH. As a result, as shown in Table 2, a good image having high resolution without scatter on the image was obtained. Note that the scattering was evaluated by scattering with fine fine lines related to the image quality of the graphical image, and was evaluated with scattering at a 1 dot line (laser spot diameter 50 μm), which is more likely to scatter than scattering on a character line.

The resolving power of the small-diameter isolated 1d as shown in FIG.
It was evaluated by reproducibility of ot (laser spot diameter 50 μm).

Further, the transfer rate was high and a sufficient image density was obtained.

Further, when a character pattern of 4% printing (area ratio) was printed out continuously on A4 size paper from the initial 500 sheets, and the consumption amount of the magnetic toner was obtained from the change in the weight of the magnetic toner in the developing device. It was 0.035 g / sheet. In addition, laser exposure (spot diameter 5
(0 μm), 600 dot 10dot vertical line pattern latent image (line width about 420 μm) is written at 1 cm intervals,
This was developed, transferred onto an OHP sheet made of polyethylene terephthalate, and fixed. The obtained vertical line pattern image was obtained by using a surface roughness meter Surfcoder SE-30H (manufactured by Kosaka Laboratory Ltd.) as a profile of the surface roughness of the magnetic toner on the vertical line, and from the width of this profile. The line width was calculated. As a result, the line width is 430 μm
It was confirmed that the line was reproduced with high density and clearly, and low consumption was achieved while maintaining the reproducibility of the latent image.

Comparative Example 3 The magnetic toner E of Comparative Example 1 was used as the magnetic toner, and image formation was performed under the same apparatus and conditions as in Example 11. As a result, the results shown in Table 2 were obtained, but the amount of consumption was larger than in Example 11, and the images were slightly scattered and the resolution was slightly inferior.

Comparative Example 4 As a toner carrier, JIS center line average roughness (Ra)
Image formation was carried out under the same apparatus and conditions as in Example 11 except that an aluminum cylinder having a diameter of 12 .phi., The surface of which was 1.0 .mu.m blasted, was used as the developing sleeve, and the magnetic toner E of Comparative Example 1 was used as the magnetic toner. . As a result, as shown in Table 2, the image density was low, the lines were thin, and the images were poor and scattered.

Comparative Example 5 The gap (between S and D) between the photosensitive drum and the developing sleeve was set to 50.
μm, DC bias component Vdc = − as development bias
Using only 600 V, the peripheral speed Vt of the developing sleeve and the peripheral speed V of the photosensitive member Vt / V are set to 1.0 to rotate in the forward direction,
Image formation was performed under the same apparatus and conditions as in Example 11 except that the magnetic toner F of Comparative Example 2 was used as the magnetic toner.
As a result, as shown in Table 2, the image was a large amount of consumption and scattered.

Example 12 Image formation was performed under the same apparatus and conditions as in Example 11 except that the magnetic toner B of Example 2 was used as the magnetic toner, and a good image and consumption amount were obtained. The results are shown in Table 2.

Examples 13 and 14 As the toner carrier, the layer thickness of the following constitution is about 7 μm, JIS
A resin sleeve having a center line average roughness (Ra) of 1.5 μm was formed on a stainless steel cylinder having a diameter of 12 mm, the surface of which was blasted, to prepare a developing sleeve. -Phenolic resin 100 parts-Graphite (particle size about 3 μm) 45 parts-Carbon black 5 parts

The developing sleeve, the magnetic toner C of the third embodiment and the magnetic toner D of the fourth embodiment are used as the magnetic toner, and the DC bias component Vdc =-is used as the developing bias.
500 V, AC bias component to be superimposed V _pp = −110
0 V, f = 2000 Hz, peripheral speed Vt of developing sleeve
And the peripheral speed V of the photoconductor is set to 2.0 and rotated in the forward direction, image formation is performed under the same apparatus and conditions as in Example 11, and the magnetic toner D consumes a little but is good. An image was obtained. The results are shown in Table 2.

Examples 15 and 16 Magnetic toner G of Example 5 was used as the magnetic toner, and Example 6 was used.
The ratio of using a magnetic toner H, DC bias component Vdc = -450 V as a developing bias, an AC bias component V _pp = -1300 V to be superimposed, f = a 2000 Hz, and the circumferential speed Vt of the developing sleeve and the photosensitive member peripheral speed V Image formation was performed under the same apparatus and conditions as in Example 11 except that Vt / V was set to 1.1 and rotation was performed in the forward direction, and a good image was obtained although the amount of consumption was somewhat large. The results are shown in Table 2.

Example 17 and Example 18 As magnetic toner, the magnetic toner I of Example 7 and Example 8 were used.
Image formation was performed under the same apparatus and conditions as in Example 11 except that the magnetic toner J of No. 1 was used, and a good image was obtained although the consumption amount was slightly high and the image density was slightly low. The results are shown in Table 2.

Example 19 Image formation was carried out under the same apparatus and conditions as in Example 11 except that the magnetic toner K of Example 9 was used as the magnetic toner, and the fluidity was slightly inferior, and some fog was observed on the image. However, good images and consumption were obtained. The results are shown in Table 2.

Example 20 Image formation was performed under the same apparatus and conditions as in Example 11 except that the magnetic toner L of Example 10 was used as the magnetic toner, and good images and consumption were obtained. The results are shown in Table 2.

[0096]

[Table 2]

[0097]

The volume average particle diameter Dv (μm) is 3 μm ≦ D.
v <6 μm and the weight average particle diameter D4 (μm) is 3.5.
μm ≦ D4 <6.5 μm, the ratio of particles of 5 μm or less in the number particle size distribution is more than 60% by number, the volume variation coefficient A of the volume distribution is 27.5 <A ≦ 40.0, and the weight variation coefficient Aw. Is 27.5 <Aw ≦ 38.0, by using the magnetic toner of the present invention, an excessive amount of magnetic toner is applied to the line image while maintaining high image density and latent image reproducibility. It is possible to reduce the consumption amount of the magnetic toner and to reduce the consumption amount of the magnetic toner as compared with the conventional case.

Furthermore, a high-quality and clear toner image can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view schematically showing an example of an image forming apparatus for carrying out an image forming method of the present invention.

FIG. 2 is a schematic view schematically showing a developing device.

FIG. 3 is an explanatory diagram of a circular spot pattern for evaluating resolution.

FIG. 4 is a schematic diagram of a measuring device for measuring the triboelectric charge of a powder sample.

[Explanation of symbols]

 100 electrostatic latent image carrier 114 transfer roller 117 charging roller 140 developing device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G03G 15/09 G03G 9/08 374 375 13/08 (72) Inventor Kasuya Rare Shimomaruko Ota-ku Tokyo 3-30-2 Canon Inc. (72) Inventor Masayoshi Kato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (16)

[Claims] 1. A magnetic toner comprising at least a binder resin, magnetic toner particles containing a magnetic substance, and inorganic fine powder, wherein the volume average particle diameter Dv (μm) of the magnetic toner is 3 μm ≦ Dv <6 μm. And the weight average particle diameter D4 (μ
m) is 3.5 μm ≦ D4 <6.5 μm, the ratio Nr of toner particles having a particle size of 5 μm or less in the number particle size distribution is 60 number% <Nr ≦ 90 number%, and the volume variation coefficient A of the volume particle size distribution is Is 27.5 <A ≦ 40.0, and the weight variation coefficient Aw is 27.5 <Aw ≦ 38.0. 2. The relationship between the charge amount Q of the magnetic toner and the coefficient of variation B of the number distribution is as follows: 0.1B + 10 <| Q | ≦ 60 (Q indicates the friction charge amount (μc / g) with iron powder) .) The magnetic toner according to claim 1, wherein 3. The relationship between the charge amount Q of the magnetic toner and the coefficient of variation B of the number distribution is as follows: 0.1B + 20 <| Q | ≦ 55 (Q is the friction charge amount (μc / g) with iron powder) .) The magnetic toner according to claim 1, wherein 4. The magnetic toner according to claim 1, wherein the volume ratio of the toner particles having a particle size of 8 μm or more in the volume particle size distribution of the magnetic toner is 10% by volume or less. 5. The magnetic toner according to claim 1, wherein the inorganic fine powder contained in the magnetic toner is a titania fine powder, an alumina fine powder, a silica fine powder, or a double oxide fine powder thereof. . 6. The magnetic toner according to claim 1, wherein the inorganic fine powder contained in the magnetic toner is a hydrophobic inorganic fine powder treated with at least silicone oil. 7. The sphericity Ψ of the magnetic material contained in the magnetic toner is 0.8 or more, and the content of silicon element in the magnetic material is 0.5 to 4% by weight based on the iron element. 7. The magnetic toner according to any one of 1 to 6. 8. An electrostatic image is formed by applying magnetic toner on a toner carrier with a layer thickness smaller than the closest distance (between S and D) of the toner carrier and the latent image carrier. An image forming method comprising a step of developing an electrostatic latent image formed on a carrier with a magnetic toner, wherein the magnetic toner comprises at least a binder resin, magnetic toner particles containing a magnetic substance and inorganic fine powder. A magnetic toner having a volume average particle diameter Dv (μ
m) is 3 μm ≦ Dv <6 μm, and the weight average particle diameter D4 is
(Μm) is 3.5 μm ≦ D4 <6.5 μm, and the ratio N of toner particles having a particle size of 5 μm or less in the number particle size distribution is N.
r is 60% by number <Nr ≦ 90% by number, the volume variation coefficient A of the volume particle size distribution is 27.5 <A ≦ 40.0,
An image forming method comprising using a magnetic toner having a weight variation coefficient Aw of 27.5 <Aw ≦ 38.0. 9. The relationship between the charge amount Q of the magnetic toner and the coefficient of variation B of the number distribution is as follows: 0.1B + 10 <| Q | ≦ 60 (Q indicates the friction charge amount (μc / g) with iron powder) .) Is satisfied, and the image forming method according to claim 8. 10. The relationship between the charge amount Q of the magnetic toner and the coefficient of variation B of the number distribution is as follows: 0.1B + 20 <| Q | ≦ 55 (Q indicates the friction charge amount (μc / g) with iron powder). .) Is satisfied, and the image forming method according to claim 8. 11. The image forming method according to claim 8, wherein the volume ratio of the toner particles having a particle size of 8 μm or more in the volume particle size distribution of the magnetic toner is 10% by volume or less. 12. The image forming method according to claim 8, wherein the inorganic fine powder contained in the magnetic toner is a titania fine powder, an alumina fine powder, a silica fine powder, or a double oxide fine powder thereof. Method. 13. The image forming method according to claim 8, wherein the inorganic fine powder contained in the magnetic toner is a hydrophobic inorganic fine powder treated with at least silicone oil. 14. The sphericity Ψ of the magnetic material contained in the magnetic toner is 0.8 or more, and the silicon element content of the magnetic material is 0.5 to 4 wt% based on the iron element. 14. The image forming method according to any one of 1 to 13. 15. The toner carrier comprises conductive fine powder and / or
Alternatively, the image forming method according to any one of claims 8 to 14, wherein the image forming method is coated with a resin containing lubricating fine particles. 16. The ratio Vt / V between the peripheral speed Vt of the toner carrier and the peripheral speed V of the latent image carrier is 1.1 ≦ Vt / V ≦ 3. The image forming method described.