JP2728954B2 - Magnetic toner for developing electrostatic latent images - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic toner for developing an electrostatic latent image used in an electrophotographic method, an electrostatic recording method, and the like, and particularly to an insulating magnetic toner for developing an electrostatic latent image.

(Background technology)

Conventional electrophotographic methods are described in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 (U.S. Pat. No. 3,666,363) and Japanese Patent Publication No. 43-24748 (U.S. Pat. No. 4,071,361).
Many methods are known as described in JP-A No. 2000-216, etc., but generally, a photoconductive substance is used to form an electric latent image on a photoreceptor by various means. The latent image is developed with toner to form a visible image, and if necessary, a toner image is transferred to a transfer material such as paper, and then fixed by heating, pressure, or the like to obtain a copy.

Various development methods for visualizing an electrostatic latent image using toner are also known. For example, the magnetic brush method described in U.S. Pat.No. 2,874,063, the cascade developing method described in U.S. Pat. No. 2,618,552 and 2,221,77
Numerous development methods are known, such as a powder cloud method, a fur brush development method, and a liquid development method described in the specification of Japanese Patent Application Laid-Open No. 6-204,086. Among these developing methods, in particular, a magnetic brush method, a cascade method, a liquid developing method and the like using a developer mainly composed of a toner and a carrier have been widely put to practical use. Each of these methods is an excellent method for obtaining a good image relatively stably, but has the common drawbacks relating to the two-component developer such as deterioration of the carrier and fluctuation of the mixing ratio of the toner and the carrier.

In order to avoid such disadvantages, various developing methods using a one-component developer consisting of toner alone have been proposed.
Among them, many are excellent in a method using a developer composed of toner particles having magnetism.

U.S. Pat. No. 3,909,258 proposes a method of developing using an electrically conductive magnetic toner. In this technique, a conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism therein, and is brought into contact with an electrostatic image for development. At this time, in the developing section,
A conductive path is formed by the toner particles between the surface of the recording medium and the surface of the relief, and charges are guided to the toner particles from the sleeve via the conductive path, and the toner particles form an image due to the Coulomb force between the electrostatic image and the image portion. And is developed. The developing method using the conductive magnetic toner is an excellent method that avoids the problems associated with the conventional two-component developing method.
On the other hand, since the toner is conductive, it has a disadvantage that it is difficult to electrostatically transfer the developed image from the recording medium to a final supporting member such as plain paper.

As a developing method using a high-resistance magnetic toner capable of electrostatic transfer, there is a developing method using dielectric polarization of toner particles. However, such a method is disadvantageous in that the development speed is essentially low and the density of a developed image cannot be sufficiently obtained, and is practically difficult.

As another developing method using a high-resistance magnetic toner, a method of frictionally charging toner particles due to friction between toner particles, friction between the toner particles and a sleeve or the like, and developing the toner particles by contacting the electrostatic image holding member is developed. It has been known. However, these methods have disadvantages in that the number of times of contact between the toner particles and the friction member is small and triboelectric charging is likely to be insufficient, and the charged toner particles are liable to agglomerate on the sleeve due to the strong Coulomb force between the sleeve and the sleeve. And it was practically difficult.

However, Japanese Patent Application Laid-Open No. Sho 55-18656 has proposed a new developing method which eliminates the above-mentioned disadvantages. This involves applying a very thin coating of magnetic toner on a sleeve, triboelectrically charging it, and then developing it very close to the electrostatic image. This method increases the chance of contact between the sleeve and the toner by applying the magnetic toner on the sleeve very thinly, enabling sufficient triboelectric charging,
The toner is supported by magnetic force and the magnet and toner are moved relatively to solve the aggregation of toner particles and sufficiently rub against the sleeve.The toner is supported by magnetic force and this is formed into an electrostatic image. An excellent image can be obtained, for example, by preventing development of the background fog by developing the image without facing the surface.

Today, the copying machine itself has been replaced with a conventional analog type, and a digital latent image has been made available. As a result, the latent image has been written more minutely than ever. The toner that sufficiently follows such a fine latent image must have a high-resolution developing ability. Further, since copiers are moving toward higher speeds, toners must be highly satisfied with high resolution, high speed development, and high durability.

When such a development method is used for a printer, there is a similar demand for high performance, but in terms of high durability, it is used as a computer output, so the output frequency is high, and the durability performance is stricter than that of a copier. There is.

Also, it is becoming insufficient just to make images black. In the case of a copying machine, it is particularly required that a photograph be faithfully reproduced (that is, reproduction of a halftone), and in the digital latent image system, the halftone is represented by a difference in line density, so that the line thickness is always the same. Otherwise, halftones cannot be expressed in the same way, which is a problem. Such gradation reproduction is also highly demanded especially in digital latent image printers, and it is not possible with conventional toners to always output the same halftone stably at the beginning and end of durability. You can say

Both copiers and printers have been improved to be faster, smaller and lighter. For this reason, a smaller developing device, which is the heart of image formation, is required. In particular, the developing sleeve is still rotating at a high speed at the time of development. However, if the developing sleeve is a sleeve having a smaller diameter, it must be further rotated at a higher speed. As a result, the toner on the sleeve is subjected to a strong centrifugal force, and scatters more heavily than when magnetic toner having good fluidity is used, and a small and narrow inside of the machine immediately becomes a serious problem of toner contamination. .

[Object of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic toner for developing an electrostatic latent image which has solved the above problems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic toner for developing an electrostatic latent image having a high resolution developing ability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic toner for developing an electrostatic latent image, which provides a stable image even in high-speed development and has an improved level of scattering in the apparatus.

Another object of the present invention is to provide a magnetic toner for developing an electrostatic latent image having excellent durability.

Another object of the present invention is to provide a magnetic toner for developing an electrostatic latent image having excellent gradation reproducibility.

It is another object of the present invention to provide a magnetic toner for developing an electrostatic latent image which stably provides halftone and fine line reproducibility over a long period of time.

Another object of the present invention is to provide a magnetic toner for developing an electrostatic latent image having excellent environmental stability.

[Summary of the Invention]

The present invention relates to a magnetic toner for developing an electrostatic latent image used for developing a digital latent image, wherein the magnetic toner contains a binder resin and a magnetic material, and the magnetic material has an average particle size. A magnetic toner for developing an electrostatic latent image, wherein the magnetic material surface is 0.05 to 0.2 μm, the coefficient of change in particle diameter is 25% or less, and the surface of the magnetic material is surface-treated with a surfactant. .

[Specific description of the invention]

In order to solve the above-mentioned problems, various research and improvement of the magnetic material were examined, and the average particle size was 0.05 to 0.2 μ,
When a magnetic material having a coefficient of change (%) of 25% or less was surface-treated with a surfactant and applied, various performances of the toner were remarkably improved, and it was found that such problems could be improved to a satisfactory level. .

The average particle diameter and the change coefficient (%) of the magnetic material referred to here are as follows. A photograph of a magnetic material of about 10,000 obtained by a transmission electron microscope is magnified four times to obtain a photograph of 40,000 times, and then randomly. 250 magnetic materials are selected, their diameters are measured, and a number distribution is obtained from the diameters and the numbers.

The change coefficient is obtained by calculating the standard deviation σ of the distribution, subtracting the standard deviation σ by the average value, and adding 100 to the result and expressing the result in%.

Conventionally, there has been a concern that the fineness of the magnetic material deteriorates the fixing property of the toner, causing a problem. However, it has been found that a particularly fine magnetic material in the magnetic material deteriorates the fixing property of the toner. That is, the fixing property is hardly deteriorated unless it is finer than necessary.

If the particle size of the magnetic material is less than 0.05 μm, the color of the magnetic material becomes apparently lean and is not preferable in practical use, and furthermore, the cohesive force is large and it is difficult to loosen, so the dispersibility is deteriorated, and the durability, image stability, etc. are reduced. It becomes a problem.

On the other hand, if the thickness is larger than 0.2 μm, the magnetic substance does not uniformly enter the toner, and non-uniformity increases particularly in the case of toner having a fine particle diameter.
Particularly in a low-temperature and low-humidity environment, it is difficult to stably maintain image quality, particularly halftone and fine line reproducibility for a long period of time, and it is difficult to obtain a long-term stable image especially in high-speed development. Preferably 0.07 to 0.19 μm, more preferably 0.10 to 0.18 μm,
More preferably 0.12 to 0.18 μm, more preferably 0.1 to 0.18 μm.
12 to 0.16 μm. If the change coefficient is larger than 25%, the fixability may be deteriorated, and the image quality may fluctuate in long-term durability, and the fine line reproducibility also becomes a problem. In addition, the image density may decrease due to durability in a low temperature and low humidity environment. This is considered to be a problem related to the dispersion of the magnetic material.
The coefficient of change is preferably 24% or less, more preferably 23% or less, more preferably 22% or less,
More preferably, it is at most 20%.

In printers and high-speed machines using digital latent images,
The reason that the toner using the conventional magnetic material cannot follow the developing ability of the toner is that it is difficult for the toner using the conventional magnetic material to include the magnetic material uniformly in the toner particles, particularly in the fine particle diameter. It is considered that a large amount of toner particles having fine particle diameters having various performances may cause a broad charge amount distribution of the toner.

The bulk density of the magnetic material is preferably 0.35 g / cc or more,
More preferably, it is 0.40 g / cc, further 0.50 g / cc, further 0.60 g / cc, further 0.70 g / cc. In particular, the particle diameter of the magnetic material is 0.2 μm or less, further 0.18 μm
If it is less than m, the magnetic material tends to contain air between particles, so that a higher bulk density is preferable for dispersion.

In magnetic toner, simply average particle size is 0.05-0.2μ
When a magnetic substance having a coefficient of change (%) of 25% or less is contained, the fluidity of the classified product for toner is remarkably improved as compared with the related art. This is because the amount of the magnetic substance contained in each magnetic toner particle of the classified product used as the magnetic toner is homogenized, and the number of the magnetic substance that comes out on the surface of the toner particle is increased, so that the triboelectric charging of the toner particles is performed. It is considered that the amount is homogenized and electrostatic aggregation of the toner particles is loosened. If the fluidity of the toner particles is remarkably improved in this way, on the contrary, there is a tendency that toner scattering inside the copying machine is less likely to be bad. For high-speed machines that have been considered in the past, even if they have sufficient performance for practical use, especially for high-speed machines, we intend to develop even faster models in the future. There is also a tendency to reduce the sleeve diameter, which is becoming a problem.

When such a magnetic material is surface-treated with a surfactant, the fluidity of the classified toner product is appropriately suppressed, and the scattering is improved even with a faster high-speed machine or a machine using a smaller-diameter sleeve, which is sufficient for practical use. It becomes the amount of scattering.

Polystyrene and poly-p-
Homopolymers of styrene and its substituted products such as chlorostyrene, polyvinyl toluene, styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer and copolymers thereof: styrene-methyl acrylate copolymer,
Styrene-ethyl acrylate copolymer, copolymer of styrene and acrylate such as styrene-n-butyl acrylate copolymer; styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, Copolymer of styrene and methacrylate such as styrene-n-butyl methacrylate copolymer; multi-component copolymer of styrene and acrylate and methacrylate; other styrene-acrylonitrile copolymer, styrene-vinyl Methyl-ter copolymer, styrene-butadiene copolymer, styrene-vinyl methyl ketone copolymer, styrene-acrylonitrile-indene copolymer,
Styrene-based copolymers of styrene such as styrene-maleic acid ester copolymer and other vinyl monomers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid , Phenolic resins, aliphatic or alicyclic hydrocarbon resins, petroleum resins, chlorinated paraffins and the like can be used alone or in combination.

In particular, as a binder resin for the toner subjected to the pressure fixing method, low-molecular-weight polyethylene, low-molecular-weight polypropylene,
Ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, higher fatty acid, polyamide resin, polyester resin and the like can be used alone or in combination.

More desirable results can be obtained when the polymer, copolymer, or polymer blend used contains a vinyl aromatic or acrylic monomer represented by styrene in an amount of 40% by weight or more.

Any appropriate pigment or dye may be used in combination with the magnetic material according to the present invention in the toner. For example, there are known dyes and pigments such as carbon black, phthalocyanine blue, gun blue, quinacridone, and benzidine yellow.

Examples of the magnetic material include ferromagnetic elements such as iron, cobalt, and nickel, and alloys and compounds of iron, cobalt, nickel, and manganese such as magnetite, hematite, and ferrite, and other ferromagnetic alloys.

Among these magnetic materials, magnetite will be described.

The magnetite is prepared by mixing a ferrous salt solution and an alkaline aqueous solution to form a suspension containing ferrous hydroxide having a temperature of 70 to 100 ° C. and a pH of 10 or more, and then passing an oxygen-containing gas through the suspension. It is obtained by doing. The shape of the magnetite particles may be hexahedral, octahedral, or tetrahedral polyhedral particles, depending on the generation conditions.

As the alkaline aqueous solution, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide and hydroxides of alkaline earth metals such as magnesium hydroxide and calcium hydroxide can be used.

Produced when a water-soluble silicate such as sodium silicate or potassium silicate (0.1 to 2.0% by weight in terms of SiO _{2 based on the} generated magnetite particles) is present in a suspension containing ferrous hydroxide. This is preferable because the distribution of magnetite can be further improved.

When an oxygen-containing gas is passed while heating a suspension containing ferrous hydroxide obtained by mixing an aqueous alkaline solution and an aqueous ferrous salt solution at a temperature of 70 to 100 ° C and a pH of 10 or more, the particle size is fine and the particle size distribution is small. Are also sharp, ie, magnetite particles having a small coefficient of change are obtained.

Next, the synthesis of magnetite used in the present invention will be described in detail with reference to experimental examples.

Experimental Example 1 A bubble oxidation type reaction tower having a diameter of 35 cm and an internal volume of 50 was used as a reactor. Ferrous sulfate aqueous solution containing 1.75 mol / Fe 2 ⁺ 20
, 4N sodium hydroxide aqueous solution 18, water 4, and 18.9 g of sodium silicate (No. 3) (28.55 wt% of SiO ₂ ) (corresponding to 0.23 wt% in terms of SiO ₂ with respect to generated magnetite) At a temperature of 88 ° C and pH of 12.5, 42 Fe (O
H) A suspension containing ₂ was prepared.

The above-mentioned suspension containing Fe (OH) ₂ is added at a temperature of 90 ° C. per minute.
A black precipitate was produced by bubbling 100 air through for 120 minutes. The produced particles were washed with water, separated by filtration, dried and pulverized by a conventional method.
Observation of the obtained magnetite particle powder with an electron microscope revealed that the powder had an octahedral shape with an average particle size of 0.16 μm and a change coefficient of 18%. This is magnetite A. Of the above reaction conditions, except for changing the Fe ²⁺ concentration, temperature, pH, the amount of sodium silicate added and the temperature of the oxidation conditions, and the amount of air when producing a suspension containing ferrous hydroxide, Magnetites B, C,..., E were obtained under the same conditions as in Experimental Example-1. Table 1 summarizes the reaction conditions, the average particle size of the generated magnetite, and the coefficient of change.

As the surfactant used for the surface treatment of the magnetic material, any appropriate surfactant can be used.

For example, surfactants include anionic surfactants (carboxylates, sulfates, sulfonates, phosphates), cationic surfactants (amine salts, quaternary ammonium salts), amphoteric surfactants Agents (amino acid type, betaine type) and nonionic surfactants (polyethylene glycol type, polyhydric alcohol type).

As a method of treating a magnetic substance with a surfactant, a method in which a surfactant is added to a magnetic substance slurry, dried with a spray drier, and surface treated is added. Surface treatment by removing water by adding a surfactant during the mixing operation of the constituent materials before melt-kneading during the production of the toner, and the like, and a surface treatment may be used. Any of these treatment methods may be used.

The amount to be treated is slightly different depending on the kind, but is 0.1 to 5% by weight based on the magnetic material.

Additives may be added to the toner as needed. Such additives include, for example, lubricating agents such as Teflon and zinc stearate, or fixing aids (eg, low molecular weight polyethylene, etc.), fluidity-imparting agents, and anti-caking agents (eg, colloidal silica).

To prepare the magnetic toner according to the present invention, a resin composition and a charge control agent, the magnetic substance according to the present invention, if necessary, a pigment or a dye, additives and the like are sufficiently mixed by a ball mill or other mixer, and then heated roll. , Kneading and kneading using a hot kneading machine such as a kneader, extruder, etc. to disperse the magnetic material in which the resins are mutually compatible, solidify by cooling, pulverize and classify to obtain an average particle size of 4 It is possible to obtain a magnetic toner for developing an electrostatic image of up to 20 μm.

Alternatively, a method in which the material is dispersed in a binder resin solution and then obtained by spray drying, or a method in which a predetermined material is mixed with a monomer to constitute the binder resin to emulsify and form a suspension, followed by polymerization. A method of forming a toner by polymerization to obtain a toner or a method of forming a capsule toner comprising a core and a shell can be applied.

Hereinafter, the present invention will be described specifically with reference to Examples. All parts in the following formulations are parts by weight.

(Reference Example 1) ・ Styrene-butyl acrylate copolymer 100 parts ・ Negative charge control agent 0.5 parts ・ Release agent 3 parts ・ Polyammonium A is a polycarboxylate ammonium salt.
60 parts of magnetic material treated with 40% Powder mixed using a Hensiel mixer
This was heat-kneaded at 140 ° C. with an extruder. After cooling the obtained kneaded material, coarse pulverization, fine pulverization,
Further, using an Alpine classifier, classification was performed to obtain a magnetic toner.

The resulting magnetic toner is a Coulter Counter TA-II
The volume average diameter measured by the mold was 12.4 μm. At this time, the cumulative number% of 6.35 μm or less was 15 number%.

This magnetic toner was mixed with 0.5 wt% of hydrophobic colloidal silica to prepare a magnetic toner to which hydrophobic colloidal silica was externally added.

The prepared magnetic toner was evaluated by modifying a Canon copier NP-8580 at a rate of 100 sheets / min.

As a result, in the endurance image output test from the initial stage to 30,000 sheets, the image density was stable at a high density of 1.4 ± 0.05, the fine line reproducibility was good, the photographic image reproduction was good, and the halftone was stable and did not change. .

Also, even in a low-temperature and low-humidity environment, the back ground did not become dirty and did not deteriorate at all even when left for a long time. In particular, white stripes on a solid black image due to contamination of the charged wire due to toner scattering did not occur.

Reference Example 2 A toner was prepared in the same manner as in Reference Example 1, except that magnetite A was used without surface treatment in place of the magnetic substance of Reference Example 1. The volume average particle size of toner is 6.35μ at 12.6μm
In the case of m or less, it was 14 number%.

In the same evaluation as in Reference Example 1, the image quality was practically good, and there was no problem even under low temperature and low humidity. However, 20,000 solid black-and-white streaks occurred, and the wires were cleaned and repaired.

(Reference Example 3) ・ Styrene-butyl acrylate copolymer 100 parts ・ Negative charge control agent 0.5 parts ・ Release agent 3 parts ・ Magnetite C is replaced with a cationic surfactant (C ₁₂ H ₂₅ NH)
₂ ) 60 parts of a magnetic material treated with 0.5% by weight Powder mixed with the above material using a Hensiel mixer,
This was heat-kneaded at 140 ° C. with an extruder. After cooling the obtained kneaded material, coarse pulverization, fine pulverization,
Further, using an Alpine classifier, classification was performed to obtain a magnetic toner.

The resulting magnetic toner is a Coulter Counter TA-II
The volume average particle size measured by a mold was 12.2 μm. At this time, the cumulative number% of 6.35 μm or less was 18 number%.

0.5% by weight of this magnetic toner and hydrophobic colloidal silica
Was mixed to prepare a magnetic toner to which hydrophobic colloidal silica was externally added.

The prepared magnetic toner was evaluated by modifying a Canon copier NP-8580 at a rate of 100 sheets / min.

As a result, in an endurance image output test from the initial stage to 30,000 sheets, the image density was 1.38 ± 0.05, which was stable at high density, the fine line reproducibility was good, the photographic image reproduction was good, and the halftone was stable and did not change. .

Also, even in a low-temperature and low-humidity environment, the back ground did not become dirty and did not deteriorate at all even when left for a long time. In particular, no white streaks on the solid black image due to the contamination of the charged wire due to toner scattering were observed.

(Reference Example 4) In the same manner as in Reference Example 3, except that a magnetic substance obtained by treating magnetite B with 0.5% by weight of a cationic surfactant (C ₁₂ H ₂₅ NH ₂ ) instead of the magnetic substance of Reference Example 3 was used. A magnetic toner was prepared. The volume average diameter of the magnetic toner is 12.3 μm, and 6.
When the diameter was 35 μm or less, the number was 16% by number.

In the same evaluation as in Reference Example 3, the image quality was practically good, but worse than in Reference Example 3, particularly under a low temperature and low humidity, there was a slight background stain. However, there were no solid black and white stripes.

(Example 1) 100 parts of styrene-2-ethylhexyl acrylate copolymer 2 parts of positive charge control agent 3 parts of mold release agent Magnetite D was used as a surfactant (C ₁₂ H ₂₅ OC ₄ H ₈ CO
₂ H) 3 using wt% of a magnetic material 80 parts The material treated in the same manner as in Reference Example 1 to obtain a magnetic toner.

The volume average particle diameter of the obtained magnetic toner was 12.2 μm, and 16% by number was 6.35 μm or less.

This magnetic toner and hydrophobic positively chargeable colloidal silica
0.4 wt% to prepare a magnetic toner to which hydrophobic positively chargeable colloidal silica was externally added.

The prepared magnetic toner is transferred to Canon Digital Copier NP-
The 9030 was modified, and the speed was increased to 40 sheets / min. The sleeve diameter was further reduced by 10%.

As a result, the image density was 1.35 ± 0 from the initial stage to 20,000 sheets.
05 was good, and particularly, fine line reproducibility, gradation reproducibility, and halftone stability were good, and it was stable even in a low-temperature and low-humidity environment, and no background dirt was generated.

In particular, fine lines from digital latent images were also reproduced. In particular, no solid black and white streaks were generated.

Comparative Example 1 A magnetic toner was produced in the same manner as in Example 1, except that magnetite D was used without surface treatment. The volume average particle size of the magnetic toner is 12.1 μm, and 6.35 μm or less
18% by number.

When the evaluation was performed in the same manner as in Example 1, white streaks were generated on solid black in about 12,000 sheets especially in a low-temperature and low-humidity environment. However, when the primary charging wire was cleaned, white streaks applied to the solid black portions were eliminated.

(Example 2) 100 parts of styrene-butyl acrylate copolymer 0.5 parts of negative charge control agent 4 parts of mold release agent 60 parts of magnetic material obtained by treating magnetite E with 0.3% by weight of C ₁₂ H ₂₅ OSO ₃ Na A magnetic toner was produced in the same manner as in Reference Example 1 using the above materials.

The volume average particle diameter of the produced magnetic toner was 11.8 μm, and the number accumulation of 6.35 μm or less was 17 number%.

This magnetic toner was mixed with 0.4% by weight of hydrophobic colloidal silica to prepare a magnetic toner to which hydrophobic colloidal silica was externally added.

Prepare the magnetic toner with a Canon printer LBP-8 I
I was placed in a machine that was converted from 400 dpi to 600 dpi, and 6 to 12 and evaluated. As a result, the digital latent image was faithfully reproduced, the resolution was good, the gradation was excellent, the halftone and the image density were high, and the image was stable until the toner ran out.

In particular, the above-mentioned performance was stable even when the output of the computer was used until the toner was almost exhausted for connection.

Further, even in a low-temperature and low-humidity environment, the background was not stained, and the toner was good until the toner ran out, and there was no problem that white streaks appeared on solid black.

Further, the test was performed for one year in a mode in which the images are output twice or less per week, and a good image was obtained stably.

Comparative Example 2 A toner was prepared and evaluated in the same manner as in Example 2, except that magnetite E was used without surface treatment in place of the magnetic substance used in Example 2.

The performance was almost the same, but black streaks were generated at about 4/6 of the toner exhaustion, especially in image output in a low temperature and low humidity environment. The generation of black streaks was eliminated by cleaning the primary charging wire.

Claims (2)

(57) [Claims] 1. A magnetic toner for developing an electrostatic latent image used for developing a digital latent image, wherein the magnetic toner contains a binder resin and a magnetic material,
The magnetic material has an average particle size of 0.05 to 0.2 μm, and
A magnetic toner for developing an electrostatic latent image, wherein a coefficient of change of a particle diameter is 25% or less, and a surface of the magnetic material is surface-treated with a surfactant. 2. The magnetic toner for developing an electrostatic latent image according to claim 1, wherein said magnetic material has an average particle size of 0.10 to 0.18 μm.