JP2805392B2 - Insulating magnetic toner - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner used for electrophotography, electrostatic recording, and the like, and particularly to an insulating magnetic toner.

[Prior Art] Conventionally, as electrophotography, 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. 07
Many methods are known as described in US Pat. No. 1,361) and the like. Generally, a photoconductive substance is used to form an electric latent image on a photoreceptor by various means. The latent image is developed with a toner to form a visible image, and, if necessary, after transferring the toner image to a transfer material such as paper, heating,
It is fixed by 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 concerning 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 a drawback, various developing methods using a one-component developer composed of only a toner 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 unit, a conductive path is formed by the toner particles between the surface of the recording medium and the surface of the sleeve, and electric charges are guided to the toner particles from the sleeve via the conductive path. The toner particles adhere to the image area by the Coulomb force and are 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. However, since the toner is conductive, the developed image can be transferred from a recording medium to plain paper or the like. It has the disadvantage that it is difficult to transfer electrostatically to the final support member.

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.

The developing device used in such a developing method is characterized in that it can be made very small with a simple configuration.

Therefore, for example, in a high-speed machine, there is room around the photoreceptor, so several color developing units are arranged, color can be changed with one touch, or laser light and analog light can be used simultaneously. There is an advantage in that writing of characters can be performed simultaneously with copying, for example.

In particular, in the case of a small-sized machine, since the whole can be made light and small, it is becoming a necessary technique for personalizing the copying machine.

Also, in printers, such as small LBPs (laser beam printers), developing device space is extremely limited in order to achieve both quiet and high-speed conflicting performances that dot printers and thermal transfer printers do not have. It is very effective that it is small and simple and light.

However, since this developing method is characterized by a simple, light and small developing device, the toner used in this method is, on the contrary, superior in image quality, durability, and stability unless it has higher performance than the conventional toner. Includes the problem of not being able to obtain the sex. That is, the performance of the toner is often directly reflected in the performance of the system.

By the way, in particular, the copying machine itself has also been changed to a conventional analog type, and a digital latent image can be produced. Therefore, the latent image has been written more minutely than ever. Such toner that sufficiently follows 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, high durability and the like.

When such a developing method is used for a printer, there is a similar demand for high performance.However, in terms of high durability, since it is used as a computer output, the output frequency is high, and the durability performance is high for copiers. There are more severe things.

Also, images are becoming more than just black.

In the case of a copying machine, it is particularly required that a photograph be faithfully reproduced (that is, reproduction of halftone). In the digital latent image system, halftone is represented by a difference in line density.
If the thickness of the line is not always the same, the halftone cannot be expressed in the same way, causing a problem.

The reproduction of such gradation is highly demanded especially in digital latent image printers, and it is not enough with conventional toners to always output the same halftone stably at the beginning and end of durability. You can say that you haven't.

Furthermore, with respect to environmental stability, personalized copy machines or low-priced LBPs have been widely used in homes, and thus have been increasingly used in harsh environments that were not used before.

In particular, when used in a place where the environment is bad for many days at home, and occasionally several copies are used, the toner is required to have extremely high performance in terms of image stability and environment dependency.

In general, magnetic toner particles are produced by mixing a predetermined amount of raw materials such as a binder resin and a magnetic substance, melt-kneading, cooling, pulverizing, and classifying, but heat is applied in the melt-kneading step and the pulverizing step. Can be Especially coarse and medium grinding,
In a mechanical pulverizer used for fine pulverization or the like, heat is instantaneously applied.

The magnetic material of the magnetic toner is easily oxidized when heated, and the resistance increases when oxidized. Therefore, the magnetic toner is easily charged up.

In general, when the magnetic toner is charged up, it becomes difficult to separate from the toner carrier such as a developing sleeve, so that the image density may be reduced. In addition, the background may be fogged.

Some developers have been proposed for the purpose of improving image quality. JP-A-51-32
No. 44 proposes a non-magnetic toner intended to improve the image quality by regulating the particle size distribution. The toner is mainly composed of a toner having a particle size of 8 to 12 μm, and is relatively coarse. According to the study of the present inventors, it is difficult for the toner to have a dense “glue” to a latent image, Further, from the characteristic that 5 μm or less is 30 number% or less and 20 μm or more is 5 number% or less, there is a tendency that the particle size distribution is broad and the uniformity is also lowered. In order to form a clear image using such a coarse toner particle and a toner having a broad particle size distribution, it is necessary to fill the gap between the toner particles by thickly overlapping the toner particles. There is also a problem that it is necessary to increase the image density, and the amount of toner consumption required to obtain a predetermined image density increases.

Further, Japanese Patent Application Laid-Open No. 54-72054 proposes a non-magnetic toner having a sharper distribution than the former,
The size of particles having an intermediate weight is as coarse as 8.5 to 11.0 μm, and there is still room for improvement as a high-resolution toner.

In Japanese Patent Application Laid-Open No. 58-1229437, the average particle size is 6 to 10 μm.
Non-magnetic toners having the largest number of particles of 5 to 8 μm have been proposed, but the number of particles of 5 μm or less is as small as 15% by number or less, and an image lacking sharpness tends to be formed.

According to the study of the present inventors, it has been found that toner particles having a size of 5 μm or less clearly reproduce the outline of the latent image and have a main function of dense toner adhesion to the entire latent image. In particular, in the electrostatic latent image on the photoreceptor, due to the concentration of lines of electric force, the contour edge portion has a higher electrolytic strength than the inside, and the sharpness of the image quality is determined by the quality of the toner particles collected in this portion. According to the study of the present inventors, it has been found that the amount of particles of 5 μm or less is effective in solving the problem of sharpness of image quality.

However, a magnetic substance having a fine particle diameter is preferably used for a toner having a small particle diameter, but the surface is easily oxidized due to an increase in specific surface area. In addition, in order to reduce the particle size, the residence time in the pulverization process in production becomes longer,
It tends to be susceptible to heat and oxidized.

[Problems to be Solved by the Invention] An object of the present invention is to provide a magnetic toner which has solved the above problems.

That is, an object of the present invention is to provide a magnetic toner having a high-resolution developing ability.

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

Still another object of the present invention is to provide a magnetic toner having excellent durability.

Still another object of the present invention is to provide a magnetic toner having excellent gradation reproducibility.

Another object of the present invention is to provide a magnetic toner which can provide halftone and fine line reproducibility stably over a long period of time.

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

Another object of the present invention is to provide a magnetic toner which always provides a stable image for a long period of time even when the frequency of use is low.

Another object of the present invention is to provide a high-density, high-resolution, high-gradation reproducibility-free stain on the background, and a magnetic field capable of stably producing a good image for a long period of time even in a low-temperature and low-humidity environment. This is to provide a toner.

[Means and Actions for Solving the Problems] Each component constituting the magnetic toner of the present invention will be described below.

The present invention relates to an insulating magnetic toner containing at least a binder resin and a magnetic substance, wherein the magnetic substance is a spherical magnetic substance having an aluminum atom on its surface, and a peak of heat generation by differential thermal analysis is 250 ° C. or more. And a hardened apparent density of 1.2 to 2.5 g / cm ³ .

The peak of heat generation by differential thermal analysis of the magnetic material according to the present invention is 250 ° C. or higher, preferably 265 ° C. or higher.

More preferably, the onset temperature of exotherm is 220 ° C. or higher, more preferably 240 ° C. or higher.

In the present invention, the peak temperature of the heat generated by the differential thermal analysis is determined by a high sensitivity differential scanning calorimeter manufactured by Seiko Instruments Inc.
This refers to the temperature at the top of the peak showing heat generation when about 10 mg of a sample is measured in an air atmosphere at a heating rate of 10 ° C./min using SSC5000.

The heat generation start temperature refers to the temperature at the intersection of the extension line of the maximum slope of the rising peak of heat generation and the extension line of the baseline.

Here, a magnetic substance having a peak of heat generation by differential thermal analysis of less than 250 ° C. is susceptible to oxidation due to heat when it is formed into a toner (particularly when a toner is manufactured using a mechanical pulverizer with heat generation), The resistance of the toner increases, and the toner is easily charged up. Further, the specific surface area increases as the diameter of the toner decreases, and these phenomena tend to occur.

The magnetic particles having aluminum atoms (preferably aluminum oxide) on the surface used in the magnetic toner according to the present invention have good heat resistance and can be obtained by treatment with an aluminum compound.

Examples of the treatment with the aluminum compound include a treatment with aluminum sulfate or polyalumina. For example, magnetic particles are dispersed in an aqueous solution of aluminum sulfate, and a potassium hydroxide solution is added to the dispersion to obtain a surface of the magnetic particles. Aluminum hydroxide is precipitated and is oxidized by heating, then washed with water and dried.

The magnetic substance whose exothermic peak is 250 ° C. or higher by differential thermal analysis is, for example, that the main body of the magnetic substance is ferrite containing manganese, or lauric acid, palmitic acid, stearic acid, or oleic acid in the crushing process. It is obtained by treating the surface with a fatty acid such as but not limited to the above.

The magnetic material having a spherical shape used in the present invention is such that the magnetic material particles having a curved magnetic particle surface have a number of 50% or more (preferably 70% or more, more preferably 80% or more).
% Or more).

Furthermore, the spherical magnetic material preferably has an average particle size of 0.1 to
Those having 0.3 μm are used.

In the present invention, the average particle size of the spherical magnetic material is taken in an enlarged photograph of a sample with a scanning electron microscope, and randomly selected from 100 to 2 particles.
It is determined by measuring the major axis of 00 particles and calculating the average value.

Here, if the particle diameter of the magnetic material is less than 0.1 μm, the cohesive force is large and it is difficult to loosen, so the dispersibility becomes poor, and the durability,
Problems such as image stability arise.

On the other hand, if the thickness is larger than 0.3 μm, the magnetic substance does not uniformly enter the toner particles, and the non-uniformity increases particularly in the case of toner having a fine particle diameter, and the image quality, especially the half tone and the fine line reproducibility under a low temperature and low humidity environment is improved. It is difficult to maintain stability for a long time.

The spherical magnetic material according to the present invention has a compact apparent density of 1.2 to 2.5 g / cm ³ , preferably 1.5 to 2.0.

In the present invention, the solid apparent density of the magnetic material is a value measured using a powder tester manufactured by Hosokawa Micron Co., Ltd. and a container attached to the powder tester according to the procedure in the instruction manual for the powder tester. Say.

The value of the solid apparent density is so large that ordinary untreated cubic magnetic material and untreated spherical magnetic material cannot be satisfied. The specific spherical magnetic material preferably used in the present invention can be prepared by crushing a spherical magnetic material having a compact apparent density of 0.7 g / cm ³ or more and less than 1.0 g / cm ³ . As a means used for crushing the spherical magnetic material, a mechanical crusher equipped with a high-speed rotor for crushing powder, and a load for dispersing or crushing powder A pressure disperser having rollers is exemplified.

When using a mechanical pulverizer to crush the aggregates of magnetic particles, the impact force of the rotor is likely to be excessively applied to the primary particles of the magnetic particles, and the primary particles themselves are destroyed. Fine powder of magnetic particles is easily generated. Therefore, when a magnetic material that has been crushed by a mechanical crusher is used as a raw material for the toner, the wear charging characteristics of the toner deteriorate due to the presence of fine magnetic particles. Therefore, a decrease in the toner image density due to a decrease in the triboelectric charge amount of the toner is likely to occur.

On the other hand, a pressure disperser having a load roller such as a fred mill is preferred in terms of the efficiency of the crushing treatment of the aggregates of the spherical magnetic particles and the suppression of the generation of the fine magnetic particles.

It can be understood that the solid apparent density of the magnetic material indirectly indicates the shape of the magnetic particles, the surface state of the magnetic material, and the amount of agglomerates of the magnetic particles. When packed bulk density of the magnetic material is less than 1.2 g / cm ^3, either magnetic particles in the form of cubic in the magnetic body is abundant or in agglomerates of magnetic particles are present many This indicates that the disintegration of the magnetic material is substantially insufficient. Therefore, when a magnetic material having a hardened apparent density of less than 1.2 g / cm ³ is used, it is difficult for the magnetic material to be uniformly dispersed in the binder resin. And the surface of the photoreceptor is easily damaged by toner particles.

If the apparent density of the magnetic material exceeds 2.5 g / cm ³ , the aggregates of the magnetic particles are disintegrated transiently, causing the magnetic particles to adhere to each other due to the pressure and forming magnetic material pellets. As a result, non-uniform magnetic toner particles tend to form.

The spherical magnetic material according to the present invention is contained in an amount of 50 to 120 parts by weight (preferably 70 to 110 parts by weight) based on 100 parts by weight of the binder resin. If the amount is less than 50 parts by weight, the transportability of the magnetic toner on a developer carrier such as a sleeve is insufficient. If the amount exceeds 120 parts by weight, the insulating property and the heat fixing property of the magnetic toner decrease.

As the binder resin used in the magnetic toner according to the present invention, when a heating and pressing roller fixing device having an oil application device is used, the following binder resins for toner can be used.

For example, polystyrene, poly-p-chlorostyrene,
Styrenes such as polyvinyltoluene and their substituted homopolymers; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate 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 Styrene-based copolymers such as copolymers, styrene-butadiene copolymers, styrene-isopropylene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally modified phenolic resins, modified with natural resins Maleic resin, a Lil resin, methacrylic resin, polyvinyl acetate, silicone resins, polyester resins, polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resin, coumarone-indene resins, and petroleum resins.

In the heat and pressure roller fixing method in which little oil is applied, when a part of the toner image on the toner image support member is transferred to the roller, so-called offset phenomenon, and the adhesion of the toner to the toner image support member are important problems. is there.
A toner that fixes with less heat energy usually has a property of easily blocking or caking during storage or in a developing machine. Therefore, these problems must be considered at the same time. In these developments, the physical properties of the binder resin in the toner are most important. However, according to the study of the present inventors, when the content of the magnetic material in the toner is reduced, the toner image supporting member is not fixed during fixing. Although the adhesiveness of the toner to the toner is improved, offset tends to occur, and blocking or caking tends to occur. Therefore, in the present invention, when using the heating / pressing roller fixing method in which almost no oil is applied, the selection of the binder resin is more important.
Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylic. Acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, a monocarboxylic acid having a double bond such as acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like and their substituted products; for example, vinyl chloride, vinyl acetate,
Vinyl esters such as vinyl benzoate; ethylene olefins such as ethylene, propylene, butylene; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl methyl ether, vinyl ethyl ether; Vinyl monomers such as vinyl isobutyl ether and the like; alone or two or more vinyl monomers are used.

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, for example, an aromatic divinyl compound such as divinylbenzene, divinylnaphthalene and the like; for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate Double bonds such as 1,3-butanediol dimethacrylate, etc.
Carboxylic acid esters having two or more compounds; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone; and compounds having three or more vinyl groups are used alone or as a mixture.

When used in a pressure fixing system, a binder resin for a pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Coalescent, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin and the like.

In the magnetic toner of the present invention, it is preferable that a charge control agent is blended (internally added) to the toner particles or mixed (externally added) with the toner particles for use. The charge control agent makes it possible to control the optimal charge amount according to the development system. In particular, in the present invention, it is possible to further stabilize the balance between the particle size distribution and the charge, and by using the charge control agent It is possible to further clarify the function separation and the complementarity for higher image quality for each particle size range as described above.

As the negative charge controlling agent that can be used in the present invention, for example, metal complexes or salts of monoazo dyes; metal complexes or salts of salicylic acid, alkylsalicylic acid, dialkylsalicylic acid or naphthoic acid are preferably used.

The above-mentioned charge control agent (having no action as a binder resin) is preferably used in the form of fine particles. In this case, the number average particle size of the charge control agent is specifically preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the toner, such a charge control agent is used in an amount of 0.1 to 10 parts by weight (more preferably 0.1 to 5 parts by weight) based on 100 parts by weight of the binder resin.
Parts by weight).

The magnetic toner of the present invention may optionally contain additives. Dyes conventionally known as colorants,
Pigments can be used, and usually 0.5 to 20 parts by weight per 100 parts by weight of the binder resin may be used. Further, in the magnetic toner of the present invention, if necessary, as an external additive, for example, a lubricant such as zinc stearate, or cerium oxide,
It is also a preferable embodiment of the present invention to add an abrasive such as silicon carbide, a fluidity-imparting agent such as silica fine powder or aluminum oxide, an anti-caking agent, or a conductivity-imparting agent such as carbon black or tin oxide. It is.

Further, in order to improve the releasability at the time of hot roll fixing, a wax-like substance such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, paraffin wax, etc.
Addition of 55 wt% is also a preferred embodiment of the present invention.

To prepare the magnetic toner according to the present invention, a magnetic powder and a vinyl-based or non-vinyl-based thermoplastic resin, if necessary, a pigment or dye as a colorant, a charge control agent, other additives, etc. After thoroughly mixing with a mixer, using a hot kneader such as a heating roll, kneader, or extruder, disperse or disperse the pigment or dye in the resin mixed with each other by melting, kneading, and kneading. Then, after cooling and solidification, pulverization and strict classification are performed to obtain the insulating magnetic toner according to the present invention.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 The above mixture was melt-kneaded in a twin-screw kneading extruder heated to 140 ° C., and the cooled kneaded material was coarsely pulverized with a hammer mill, and the coarsely pulverized material was medium-pulverized to 20 μm with a Hosokawa Micron ACM pulperizer, and jet milled. The resulting finely pulverized material was classified and removed by a multi-segmentation classifier to obtain a magnetic toner having a volume average particle diameter of 6.5 μm.

This is a Canon Laser Beam Printer LBP-8II
Was placed in a printer modified from 8 sheets / min to 16 sheets / min to evaluate the image.

As a result, the image density, fine line reproducibility and tone reproducibility were stable and very good under the normal environment from the beginning to the end of toner, and the image density was particularly high at 1.40 to 1.45.

Further, even in a continuous image output test under low temperature and low humidity, there was no charge-up phenomenon, no background fouling (hereinafter referred to as fogging), image density and image quality were good and stable.

Example 2 As a magnetic substance, stearic acid was added at 0.5 w
Exothermic peak by differential thermal analysis at 268 ° C. (exothermic onset temperature 250 ° C.), average particle size 0.14
A magnetic toner was obtained in the same manner as in Example 1, except that spherical magnetite particles having aluminum atoms having a surface density of 1.73 g / cm ³ and a solidified apparent density of 1.73 g / cm ³ were used.

 This was evaluated in the same manner as in Example 1.

As a result, in a test under a normal environment and under low temperature and low humidity, a good image was obtained as in Example 1.

Example 3 As a magnetic substance, manganese was contained at 10 mol%, the peak of heat generation by differential thermal analysis was 288 ° C. (heat generation starting temperature: 226 ° C.), the average particle size was 0.17 μm, and the apparent bulk density was 1.69 g / cm.
^A magnetic toner was obtained in the same manner as in Example 1 except that spherical ferrite particles having aluminum atoms on the surface of No. ³ were used.

 This was evaluated in the same manner as in Example 1.

As a result, in a test under a normal environment and under low temperature and low humidity, a good image was obtained as in Example 1.

Comparative Example 1 As a magnetic substance, the average particle size was 0.12 μm, the apparent bulk density was 1.33 g / cm ³ , and the peak of heat generation by differential thermal analysis was 231.
A magnetic toner was obtained in the same manner as in Example 1 except that untreated spherical magnetite particles at a temperature of 201 ° C. (exothermic onset temperature: 201 ° C.) were used.

 This was evaluated in the same manner as in Example 1.

As a result, in the test under the normal environment, the resolution and the halftone slightly decreased near the toner exhaustion.
It was stable to almost no problem.

However, in a test under a low temperature and a low humidity, the image density was slightly lowered with the durability. Also, the background fog is getting a little worse.

Comparative Example 2 As a magnetic material, the average particle size was 0.14 μm, the apparent bulk density was 0.73 g / cm ³ , and the peak of heat generation by differential thermal analysis was 245.
A magnetic toner was obtained in the same manner as in Example 1, except that untreated cubic magnetite particles at a temperature of 203 ° C (exothermic onset temperature: 203 ° C) were used.

 This was evaluated in the same manner as in Example 1.

As a result, in the test under the normal environment, the resolution and the halftone were lower and the image density was lower than those in Examples 1 and 2.

Further, in the test under low temperature and low humidity, the fog of the background became worse as well as the durability.

Example 4 The same magnetite particles 70 as in Example 1 were used as the magnetic material.
Except for using parts by weight, the same raw material mixture as in Example 1 was melt-kneaded with a twin-screw kneading extruder heated to 140 ° C.
The cooled kneaded material is roughly pulverized with a hammer mill, the coarsely pulverized material is medium-pulverized to a size of 20 μm with an ACM pulperizer manufactured by Hosokawa Micron Co., Ltd., and finely pulverized with a turbo mill which is a mechanical pulverizer. The ultrafine powder and the coarse powder were classified and removed by a machine to obtain a magnetic toner having a volume average particle diameter of 8.0 μm.

 This was evaluated using a Canon copier NP-6650.

As a result, stable images such as image density and gradation reproducibility were obtained even in a 100,000-sheet durability test under a normal environment.

Further, even in a continuous image output test under low temperature and low humidity, there was no charge-up phenomenon, no fogging occurred, and the image density and image quality were good and stable.

Comparative Example 3 A magnetic toner was obtained in the same manner as in Example 4, except that 70 parts by weight of untreated magnetite particles were used as the magnetic substance.

 This was evaluated in the same manner as in Example 4.

As a result, even in a test under a normal environment, a charge-up phenomenon occurred, and a little fog occurred.

Further, in the test under low temperature and low humidity, the charge-up phenomenon was severe and fog occurred on the entire surface, and halftone shading unevenness was conspicuous.

The results of the above Examples and Comparative Examples are summarized in Table 1 below.

[Effects of the Invention] According to the present invention, a spherical magnetic body having aluminum atoms on its surface has a specific heat generation peak, and the compact apparent density is set to 1.2 to 2.5 g / cm ³ , so that it is not affected by the environment. A high-quality image with high image density can be obtained for a long period of time.

Continued on the front page (72) Inventor Kiyoko Tsuchiya 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroshi Yuza 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-63-17222 (JP, A) JP-A-58-91463 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/083

Claims (1)

(57) [Claims] 1. An insulating magnetic toner containing at least a binder resin and a magnetic substance, wherein the magnetic substance is a spherical magnetic substance having an aluminum atom on its surface, and the peak of heat generation by differential thermal analysis is 250 ° C. or less. And an insulating magnetic toner having a hardened apparent density of 1.2 to 2.5 g / cm ³ .