JPH03131865A - Magnetic toner - Google Patents

Abstract

PURPOSE:To improve an image density and definition and to prevent the contamination of background by specifying the average grain size and the coefft. of a change in distribution of number of pieces of a magnetic material, the shape of the magnetic material and the volume average diameter of the magnetic toner. CONSTITUTION:This magnetic toner has 0.1 to 0.2mum average grain size of the magnetic material, <=40% (sigma/-X)X100 expressed in % by dividing the standard deviation sigma of the distribution of number of pieces thereof by the average grain size -X, a spherical shape, <=9mum volume average diameter D of the magnetic toner, and 25 to 35% (sigmaT/D)X100 when the standard deviation thereof is designated as sigmaT. Namely, the grain size distribution of the toner formed to the small grain size, the grain size of the magnetic material and the grain size distribution thereof are related with the stabilization of the electrostatic charge of the toner in development, the selectivity of the toner in development and others, such as splashing and fixing properties. The image density and definition are improved in this way and the contamination of the background is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a toner used in electrophotography, electrostatic recording, etc., and particularly relates to an insulating magnetic toner.

[Background technology]

As a conventional electrophotographic method, U.S. Patent No. 2,297,691
No. I'll, Japanese Patent Publication No. 42-23910 (U.S. Patent No. 3,666.363) and Japanese Patent Publication No. 43-2
Although many methods are known, such as those described in U.S. Pat. An electrical latent image is formed on the top, and then the latent image is developed with toner to become a visible image. If necessary, the toner image is transferred to a transfer material such as paper, and then fixed by heat, pressure, etc. and obtain a copy.

Various developing methods are also known in which an electrostatic latent image is visualized using toner. For example, the magnetic brush method described in U.S. Pat. No. 2,874,063, U.S. Pat.
A large number of development methods are known, such as the cascade development method described in No. 2,221,776, the powder cloud method, the fur brush development method, and the liquid development method. ing. Among these developing methods, the magnetic brush method, cascade method, liquid developing method, etc., which use a developer mainly consisting of toner and carrier, are in particular widely put into practical use. All of these methods are excellent methods in which good images can be obtained relatively stably, but on the other hand, they have common drawbacks associated with two-component developers, such as deterioration of the carrier and fluctuations in the mixing ratio of toner and carrier.

In order to avoid such drawbacks, various development methods using one-component developers made only of toner have been proposed, but among them, many methods using developers made of magnetic toner particles are superior. .

US Pat. No. 3,909,258 proposes a developing method using an electrically conductive magnetic toner. In this method, conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism inside, and is brought into contact with an electrostatic image to be developed. 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 sleeve, and charges are guided from the sleeve to the toner particles through this conductive path, thereby creating a connection between the image area of the electrostatic image and the image area of the electrostatic image. Toner particles adhere to the image area due to Coulomb force and are developed.

This developing method using conductive magnetic toner is an excellent method that avoids the problems associated with conventional two-component developing methods, but on the other hand, since the toner is conductive, the developed image
It has the disadvantage that it is difficult to electrostatically transfer it from a recording medium to a final support member such as plain paper.

As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, there is a developing method that utilizes dielectric polarization of toner particles. However, such a method inherently has drawbacks such as slow development speed and insufficient density of the developed image, and is difficult in practice.

Other developing methods using high-resistance magnetic toner include
A known method is to triboelectrically charge toner particles by friction between toner particles or friction between toner particles and a sleeve or the like, and then develop the toner particles by bringing them into contact with an electrostatic image holding member. However, these methods have drawbacks such as the number of times the toner particles come into contact with the friction member is small (frictional charging tends to be insufficient), and the Coulomb force between the charged toner particles and the sleeve increases and they tend to aggregate on the sleeve. This makes it difficult to put it into practical use.

However, in JP-A-55-18656, etc.,
A new development method has been proposed which eliminates the above-mentioned drawbacks. This involves applying a very thin layer of magnetic toner onto the sleeve, triboelectrically charging it, and then developing it in close proximity to the electrostatic image. This method increases the chances of contact between the sleeve and the toner by applying an extremely thin layer of magnetic toner onto the sleeve, enabling sufficient frictional charging, supporting the toner with magnetic force, and moving the magnet and toner relative to each other. By moving the toner particles together, the toner particles are prevented from agglomerating each other, and at the same time, the toner particles are sufficiently rubbed against the sleeve.
Excellent images can be obtained by developing the images facing each other to prevent blurring.

The developing device used in this type of developing method is characterized by its simple construction and the fact that it can be made very small.

For this reason, for example, in high-speed machines, there is more space around the photoreceptor, so several developing devices of other colors are placed.
Advantages include the ability to change colors with a single touch, use laser light at the same time as analog light, and make it easier to write on pages and text at the same time as copying.

Particularly in small machines, the overall size can be made lighter and smaller, so this technology has become necessary for the personalization of copying machines.

In addition, in printers such as small LBPs (laser beam printers), the developer space is extremely small in order to achieve the contradictory performance of being quiet and high speed, which dot printers and thermal transfer printers do not have. Moreover, the fact that it is simple and lightweight makes it extremely effective.

However, because this developing method is characterized by a simple, lightweight, and small developing device, the toner used in this method has better overall image quality, durability, and stability than conventional toners, unless it has higher performance. This includes the problem of not being able to have sex. In other words, the performance of such toner is often directly reflected in the performance of the system.

By the way, in particular, copying machines themselves have changed from the conventional analog type to ones that use digital latent images, and as a result, latent images can be written more minutely than ever before. A toner that can sufficiently follow such a fine latent image must have a high-resolution developing ability. Furthermore, as copying machines are moving toward higher speeds, toners must meet high standards such as high resolution, high speed development, and high durability.

When such a developing method is used in a printer, there is a similar high performance requirement, but in terms of high durability, since it is used as output for a computer, the output frequency is high (and the durability is There are things that are more severe than machines.

Furthermore, it has become insufficient for images to simply be black. In the case of copying machines, in particular, it is required to faithfully reproduce photographs (that is, reproduce halftones), and in the digital latent image method, halftones are expressed by differences in line density.
If the line thicknesses are not always the same, the midtones cannot be expressed in the same way, which poses a problem.

Reproduction of such gradation is also highly required, especially for digital latent image printers, and it is not possible with conventional toner to consistently output the same halftones at the beginning and end of life. It's safe to say that I haven't.

Furthermore, with regard to environmental stability, as copiers have become more personalized and LBPs have become more popular in households due to lower prices, they are now often used in harsh environments where they could not be used in the past.

Especially when toner is used at home, where it is left in a harsh environment for many days and several copies are made from time to time, toner requires extremely high performance in terms of image stability and environmental dependence.

In order to satisfy these performances, it has been considered to reduce the particle size of toner. This is typically 10-14μ
The particle size of the toner, which is the volume average diameter of m, is 9 μm or less. It is true that fine line reproducibility, halftone reproducibility, gradation reproducibility, etc. are significantly improved. However, if the conventional toner is simply made smaller, the amount of charge per gram increases too much, resulting in a decrease in image density and deterioration in image quality. This is particularly noticeable in small and high-speed machines that use small-diameter sleeves, and in low-temperature, low-humidity environments. Therefore, various methods of adjusting the amount of charge have been studied. However, if the amount of charge is simply lowered, image density and image quality will be lowered in a normal temperature and humidity environment, particularly in a high temperature and high humidity environment, or when left for a long period of time.

In addition, toner with small particle size tends to scatter easily.
This tends to cause the interior of the aircraft to become dirty and the background of the image to become dirty, resulting in fogging.

In order to meet these strict demands, research and development of toner is being carried out diligently.

Among the materials used in magnetic toner, the magnetic material in particular accounts for 20 to 70% by weight of the entire toner, and therefore greatly influences the performance of the toner. Proposals have been made regarding the particle size and particle size distribution of the magnetic material.

In JP-A-58-169153, the 50% number average diameter is 0.3 to 1.0 μm, and the 50% weight average diameter is 0.4.
~1.3 μm, and magnetic powder having a particle size distribution of 0.4 to 1.3 μm, which gives the maximum value in the number particle size distribution, improves the fidelity and stability of image quality, as well as the phenomenon of soil blurring. It has been proposed for its removal, high resolution, high concentration, and other good environmental characteristics.

It is true that conventional analog machines have sufficient performance for practical purposes, but today's high-speed machines that can process more than 50 sheets per minute require high-speed development, high durability, high gradation, and digital latency. The high resolution of images and fine line reproducibility cannot be said to be sufficient.

In particular, it is no longer sufficient to produce halftones stably over a long period of time. In particular, it is completely insufficient for toner with small particle size.

In addition, Japanese Patent Application Laid-open No. 187951/1983 also states that the particle size distribution of the magnetic material has a volume-based 50% diameter of 1.5 to 1.
4.5μm1Similarly, the volume-based 20% diameter is 1.0-4
．． It has been proposed that particles having a particle size distribution with a 0 μm 175% diameter of 2.5 to 6.0 μm are suitable, but this is for color toners and is not suitable for black images. That is, the blackness is insufficient and undesirable.

Furthermore, Japanese Patent Publication No. 62-51208 proposes to provide a toner with improved dispersibility and excellent image density by using a spherical magnetic material.

It is true that spherical magnetic bodies have such advantages, but they tend to have high electrical resistance. Therefore, as mentioned above, especially under conditions where toner is likely to be charged up in high-speed machines, small machines, etc., the problem becomes even more severe when the particle size of the toner becomes smaller. Generally, when the toner is charged up, it becomes difficult to separate from the toner carrier such as the developing sleeve, which may lower the image density, and may also cause a fogging phenomenon in which the background is smeared.

For example, if you simply try to achieve high resolution and high fine line reproducibility using toner with such a small particle size, the amount of toner applied will be reduced, the line will become thinner, and the excess toner will flow around the line. One idea is to prevent it from scattering. However, this method is not preferable because the solid black image density decreases.

Merely increasing the image density tends to cause background stains, and in particular, if the toner is left in a low temperature, low humidity environment for a long time, background stains may become noticeable. That is, it is not easy to improve image density, high resolution, and background stains to a high degree.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a magnetic toner that solves these problems.

That is, an object of the present invention is to provide a magnetic toner having a particularly high resolution phenomenon capability.

Another object of the present invention is to provide a magnetic toner that provides stable images even during high-speed development.

A further object of the present invention is to provide a magnetic toner with excellent durability.

A further object of the present invention is to provide a magnetic toner that has particularly excellent gradation reproducibility.

Another object of the present invention is to provide a magnetic toner that stably provides halftones, fine line reproducibility, and sharpness over a long period of time.

Another object of the present invention is to provide a magnetic toner with excellent environmental stability.

Another object of the present invention is to provide a magnetic toner that always provides stable images over a long period of time even when used infrequently.

In addition, the object of the present invention is to provide images with high image density, particularly high resolution, and high gradation reproducibility, without background stains, with little scattering, and which are stable even in low-temperature, low-humidity environments. The purpose of this invention is to provide a magnetic toner that can produce long-term results.

[Summary of the invention]

Specifically, in the present invention, in a magnetic toner containing at least a magnetic material, the average particle diameter of the magnetic material is 0.1 to 0.2.
μm, the standard deviation σ of the number distribution is divided by the average particle diameter X, and (σ/X) is 9
If the standard deviation is στ below μm, then (σT/D)
The present invention relates to a magnetic toner characterized in that X100 is 25 to 350 stones.

[Detailed description of the invention]

In the present invention, the average particle size and coefficient of change (%) of a magnetic material are defined as a photograph of a magnetic material obtained by a transmission electron microscope magnified 10,000 times, magnified 4 times, , 250 magnetic bodies are selected at random, their diameters are actually measured, and the number distribution is determined from the diameter and number of magnetic bodies.

The coefficient of change is calculated by finding the standard deviation σ of the distribution and dividing it into the mean value
It is divided by 100 and expressed as a percentage.

Further, the volume average diameter of the toner was determined from the distribution using a Coulter Counter particle size distribution analyzer (TA-It type) using a 100 μm aperture.

Conventionally, the particle size of magnetic materials, particularly their particle size distribution, has not received much attention. The biggest reason for this is that the magnetic material was considered primarily for toner transportability, and other materials were considered only from the standpoint of improving dispersibility with the binder resin. However, due to today's strict requirements for copying machines and printers, such as increased speed, miniaturization, and digitization, as well as the smaller particle size of toner related to higher image quality, we have improved the precision of how to capture magnetic materials and have conducted extensive research. This led to the present invention.

Although not bound by any theory, the particle size distribution of the toner having a reduced particle size, the particle size of the magnetic material, and its particle size distribution are important for stabilizing the charging of the toner during development, selectivity of the toner during development, etc. It was found that this is related to scattering properties, fixing properties, etc.

In particular, it is possible to control the amount of charge so that it does not increase more than necessary, even in a situation where the toner is strongly charged by friction with the developing sleeve, which is a charge imparting member. This is because by using a magnetic material with a smaller particle size and a uniform particle size distribution than what has been conventionally put into practical use, more magnetic particles are present near the surface of the toner than in conventional toners. Even if the surface is viewed microscopically,
This is because it becomes more uniform. In other words, when the toner is frictionally charged with the developing sleeve, in the case of conventional toner, if the part of the toner surface that comes into contact with the sleeve is a place where there is no magnetic material on the toner surface, the charge on the toner surface becomes higher by that area.
The toner will be non-uniformly charged. If an attempt is made to obtain the same effect by increasing the content of magnetic material, the magnetic force of each toner will also increase, making it difficult for the toner to separate from the developing sleeve, resulting in a decrease in image density and deterioration of fixing properties, which is undesirable. .

In particular, if the particle size distribution is not uniform as the particle size is reduced, various problems will occur. If there are too many fine particles, the fine particles have a strong cohesive property and cannot be sufficiently dispersed in the toner using ordinary toner manufacturing equipment, and are also unfavorable for fixing properties.

Furthermore, if rough particles are present, a toner containing rough magnetic material will be selected during development, making it difficult to maintain a stable high-quality image over a long period of time.

At this time, if the particle size distribution of the toner is too wide than 35%, problems such as a decrease in image density and scattering will occur, and if it is smaller than 25%, it will be unfavorable in terms of production efficiency.

Here, if the particle size of the magnetic material is less than 0.1 μm, the color of the magnetic material becomes obvious reddish, which is not preferred in practice.
In addition, the cohesive force is large and the dispersibility is poor (because it is difficult to unravel).
Therefore, problems such as durability and image stability arise.

In addition, if it is larger than 0.2 μm, the magnetic material will not be uniformly contained in the toner, and unevenness will increase, especially in toner with a fine particle size, resulting in poor image quality, especially midtone and fine line reproducibility, especially in a low temperature and low humidity environment. It is difficult to maintain the image stably over a long period of time, and scattering and fogging are likely to occur.In particular, it is difficult to obtain a stable image over a long period of time with high-speed development. Preferably 0.14-0.
19 μm1, more preferably 0.15 to 0.19 μm.

Furthermore, if the change coefficient is greater than 40%, fixing performance may deteriorate, resulting in fluctuations in image quality and problems with fine line reproducibility during long-term durability.Also, image density may decrease during durability in low-temperature, low-humidity environments. We believe that this is a problem related to the dispersion of the magnetic material.

The coefficient of change is preferably 35% or less, more preferably 30% or less, even more preferably 2506 or less, even more preferably 20% or less.

Further, the bulk density of the magnetic material is preferably 0.60 g/cc or more, more preferably 0.70 g/cc, furthermore 0.80 g/cc, and even more preferably 0.90 g/cc.
It is cc. In particular, the particle size of the magnetic material is 0.2 μm or less,
Further, when the particle diameter is 0.18 μm or less, the magnetic material tends to contain air between particles, so a higher bulk density is preferable for dispersion.

As the binder resin for the toner, homopolymers of styrene and its substituted products, such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, and styrene-vinyltoluene copolymer, and copolymers thereof are used. Coalescence: Copolymers of styrene and acrylic esters such as styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-n-butyl acrylate copolymer; Styrene-methyl methacrylate copolymer Copolymers of styrene and methacrylic acid esters such as styrene-ethyl methacrylate copolymer, styrene-n-butyl methacrylate copolymer; multi-component copolymers of styrene and acrylic esters and methacrylic acid esters ;
Others: styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-butadiene copolymer, styrene-vinyl methyl ketone copolymer,
Styrenic copolymers of styrene and other vinyl monomers such as styrene-acrylonitrile-indene copolymers and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyesters, polyamides, Epoxy resins, polyvinyl butyral, polyacrylic acid, phenolic resins, aliphatic or alicyclic hydrocarbon resins, petroleum resins, chlorinated paraffins, etc. can be used alone or in combination.

In particular, binder resins for toners used in pressure fixing systems include low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymers, ethylene-acrylic acid ester copolymers, higher fatty acids, polyamide resins, polyester resins, etc. can be used alone or in combination.

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

In addition to the magnetic material, any suitable pigment or dye may be used in the magnetic 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, alloys and compounds of iron, cobalt, nickel, and manganese such as magnetite, magnetite, and ferrite, and other ferromagnetic alloys.

Among these magnetic materials, magnetite will be described.

Magnetite consisting of particles exhibiting a spherical shape is prepared by mixing an aqueous ferrous salt solution and an alkaline aqueous solution of less than 1.0 equivalent to Fe''+ in the aqueous ferrous salt solution at a temperature of 70 to 100 ml.
to produce a suspension containing ferrous hydroxide at a temperature of 7°C.
The first stage generates magnetite particles by passing oxygen-containing gas while heating in the range of 0 to 100°C, and after the second stage reaction, 1.0 equivalent or more of an alkaline aqueous solution is added to the residual Fe''+. It is obtained by a two-step reaction consisting of the first step and the second step of heating and oxidizing under the same conditions.The magnetite made of spherical particles obtained in this way has a particle size of It is fine and has a sharp particle size distribution, that is, the coefficient of change is small.

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

When a water-soluble silicate such as sodium silicate or potassium silicate (0.1 to 5.0 at% in terms of Si based on p e 24-) is present in a suspension containing ferrous hydroxide, This is preferable because the spherical diameter, particle size distribution, and temperature stability of the produced magnetite particles can be further improved.

Next, the synthesis of magnetite used in the present invention will be explained in detail using experimental examples.

Experimental Example 1 A bubble oxidation type reaction tower with a diameter of 35 cm and an internal volume of 501 cm was used as a reactor. Ferrous sulfate aqueous solution containing 1.6 mol/l of Fe"20!!, 3.07N sodium hydroxide aqueous solution 201! (corresponds to 0.96 equivalent to Fe"+), and sodium silicate ( No. 3) (SiO22
A suspension containing Fe(OH) 2 was heated at a temperature of 82 g using 20.2 g (0.3 at % of Fe) of 55 wt%
Produced at ℃.

After the suspension containing Fe (OH) 2 was heated to 85° C., 100 l/min of air was passed through the suspension for 240 minutes to generate magnetite particles. Then 1.34N NaO
H aqueous solution 2j7 was added (corresponding to 1.05 equivalents to the residual Fe"+), and air was aerated at a rate of 1001/min for an additional 30 minutes at a temperature of 85°C. The generated particles were washed with water and filtered by the usual method. Separately, it was dried and pulverized.The obtained magnetite particles were observed with an electron microscope and were found to be spherical particles with an average particle diameter of 0.18 μm and a variation coefficient of 18%.This is referred to as magnetite A. Among the reaction conditions, when producing a suspension containing ferrous hydroxide,
“Experimental example-1 except that the concentration, temperature, alkali equivalent ratio, amount of sodium silicate added, and temperature and air amount of oxidation conditions were changed.
Magnetite B, C..., K were obtained under the same conditions as above. Table 1 shows the relationship between the reaction conditions and the average particle diameter and variation coefficient of the produced magnetite.

・', \ (Hereinafter, blank) In the present invention, the magnetic material is preferably used in an amount of 20 to 150 parts by weight, preferably 120 parts by weight of 3ON, based on 100 parts by weight of the binder resin.

Additives may be mixed with the toner as necessary. Examples of such additives include lubricants such as Teflon and zinc stearate, and metal oxides such as tin oxide as conductivity imparting agents.

Example 1 The above materials were mixed into powders, heat-kneaded for about 15 minutes in a roll mill set at 150°C, and after cooling, coarsely pulverized and finely pulverized (jet mill). Furthermore, fine powder and coarse powder were set using a zigzag classifier manufactured by Albine, and as measured by TA-II manufactured by Coulter Counter, the volume average diameter was 8.2 μm and (σr/D)X100 was 30%. Got toner.

0.5 parts by weight of hydrophobic colloidal silica was externally added to 100 parts by weight of the obtained magnetic toner, and this was transferred to a Canon copier N.
Evaluation was made using P-8580.

As a result, image density, fine line reproducibility, and gradation reproducibility are stable and very good even in a 15% sheet durability test under normal conditions.In particular, fine line reproduction is stable at 6 lines/mm or more, and there is no fogging. (, scattering was not a problem either.

Furthermore, even in continuous image output tests under low temperature and low humidity environments, there was no charge-up phenomenon, no fogging occurred, and both image density and quality were stable and good.

Comparative Example 1 A magnetic toner was prepared in the same manner as in Example 1, except that magnetic substance B was used instead of magnetic substance A in Example 1. The volume average diameter of the magnetic toner is 8.1 μm, and (σa/D
)X100 was 31%.

The magnetic toner was evaluated in the same manner as in Example 1. As a result, in durability tests under normal environments, although it is at a good level for practical use, there is a slight tendency for fogging and scattering, and fine line reproducibility, gradation reproducibility, etc. It has declined slightly. Additionally, in tests conducted under low temperature and low humidity environments, a slight charge-up phenomenon occurred, resulting in fogging. Moreover, the gradation reproducibility also decreased as the durability progressed.

In addition, the fixing properties were slightly worse.

Example 2 A magnetic toner was prepared in the same manner as in Example 1 using the above materials. The volume average diameter of the magnetic toner is 7.51 t m
(Standard deviation cr 7 /D) X 100 was 27%. 0.5 parts by weight of hydrophobic colloidal silica was externally added to 100 parts by weight of magnetic toner, and this was placed in a Canon laser beam printer LBP-8II for evaluation. As a result, the digital latent image was faithfully reproduced from the initial stage until the toner ran out, and the resolution and halftones in particular were extremely stable. In addition, the image density is high at 1.4 to 1.45,
It was stable with no fogging or scattering.

In particular, durability tests under low temperature and low humidity environments showed similar stability and no background fog.

Furthermore, the cartridge was left in a low temperature and low humidity environment for about 3 months.
I tried to print the image, but there were no problems at all (it was stable with good image quality and density.

Comparative Example 2 A magnetic toner was prepared in the same manner as in Example 2, except that a magnetic material was used instead of the magnetic material C in Example 2.

The volume average diameter of the magnetic toner is 7.9 μm (σT /
D) X100 was 28%.

This was evaluated in the same manner as in Example 2. As a result, resolution and halftones deteriorated slightly near the toner exhaustion.

However, in a durability test under a low temperature and low humidity environment, the image density slightly decreased with durability. This is because the fine lines have gradually become thinner than they were at the beginning. Also, the background fog has gotten a little worse.Furthermore, the fixability has gotten worse.

Example 3 A magnetic toner was produced in the same manner as in Example 1 using the above materials. The volume average particle size of the magnetic toner is 8.9 μm.
and (a T/D) X 100 was 26%. 0.5 parts by weight of hydrophobic colloidal silica was externally added to 100 parts by weight of magnetic toner, and this was evaluated using a digital copier NP-9030 manufactured by Canon.

As a result, in a durability test under normal conditions, the image density was high (1.4 or higher) from the initial stage up to 50,000 copies, and the image density was particularly good and stable in terms of resolution, halftone fog, and scattering.

In particular, resolution and midtones were excellent.

In addition, durability tests under low temperature and low humidity environments also showed good performance and stability. The resolution of fine lines in the digital latent image was particularly good (and there was no fogging).

Comparative Example 3 Example 3 except that magnetic material F was used as magnetic material E in Example 3.
Magnetic toner was prepared in the same manner as above. The volume average particle size of the magnetic toner is 8.8 μm, and (cr/D)xlo
o was 27%.

This was evaluated in the same manner as in Example 3. As a result, in a durability test under a normal environment, there was no problem in practical use, but the durability was unfavorable, as resolution, halftones, etc. were slightly degraded, and scattering occurred.

In addition, in continuous durability tests under low temperature and low humidity environments, some fogging occurred and the image density decreased slightly as well as durability. In particular, the thin wires have become a little thinner as they become more durable. Also,
Fixability also deteriorated.

Examples 4 to 6 and Comparative Examples 4 to 5 Magnetic substance G-K was used instead of magnetic substance C in Example 2, respectively.
A magnetic toner was prepared in the same manner as in Example 2 except that
evaluated. Each toner has a volume average diameter of 9. czm or less, (cr, /D)×100 was in the range of 25-35%. The results are summarized in Table-2.

Claims (1)

[Claims] (1) In a magnetic toner containing at least a magnetic substance, the average particle size of the magnetic substance is 0.1 to 0.2 μm, and the standard deviation σ of the number distribution is divided by the average particle size @X @, and it is expressed as %. The expressed (σ/@X@)×100 is 40% or less,
The magnetic body has a spherical shape, and the volume average diameter D of the magnetic toner is 9.
μm or less, and its standard deviation is σ_r (σ_r/
D) A magnetic toner characterized in that x100 is 25 to 35%.