JPH03131864A - Magnetic toner for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To chip a photosensitive body uniformly to the required min. extent and to prevent the filming and fusing of the photosensitive body over a long period of time by specifying the average grain size and the coefft. of change in the grain size of a magnetic material, forming the magnetic material to a octahedral shape and incorporating the magnetic material and polyolefin based on the magnetic toner. CONSTITUTION:The average grain size of the magnetic material is 0.1 to 0.2mum and the coefft. of change expressed in % by dividing a standard deviation by the average diameter is <=40%. The magnetic material has the octahedral shape. The magnetic toner contains 35 to 60wt.% magnetic material and 0.5 to 4wt.% polyolefin by the weight of the magnetic toner. The grain size distribution and shape, of the magnetic material and the uniform fine dispersibility of the polyolefin to be incorporated are specified in such a manner, by which the photosensitive body is uniformly chipped to the min. required extent and the filming and fusing of the photosensitive body are prevented over a long period of time.

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
specification, Japanese Patent Publication No. 42-23910 (U.S. Patent No. 3,666.363) and Japanese Patent Publication No. 43-247
Publication No. 48 (U.S. Patent No. 4,071,361)
Although a number of methods are known, such as those described in J.D. The toner image is developed into a visible image, and if necessary, the toner image is transferred to a transfer material such as paper, and then fixed by heating, pressure, etc. to 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 these drawbacks, use only toner! Various development methods using component-based developers 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 and frictional charging tends to be insufficient, and the charged toner particles tend to aggregate on the sleeve due to the strong Coulomb force between them and the sleeve. This makes it difficult to implement in practice.

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 toner by applying a very thin layer of magnetic toner onto the sleeve, which enables sufficient frictional electrification, supports the toner by magnetic force, and moves the magnet and toner relative to each other. This prevents the toner particles from coagulating with each other by moving the toner particles (as well as creating sufficient friction with the sleeve), supporting the toner by magnetic force, and developing the toner by facing the electrostatic image without touching it. Excellent images can be obtained by preventing such problems.

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 both 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.

Today, there is a demand for smaller, lighter, faster speeds, especially higher image quality, higher durability, and longer lifespan.

In particular, photoreceptor drums are becoming smaller in diameter, and developing sleeves are also becoming smaller in diameter. If the space involved in electronic photography can be reduced in this way,
For example, in a machine such as an LBP, even if the volume of the storage device part and the part related to the laser is increased to make it multi-functional, the machine as a whole can be made quite small, light, and highly functional.

However, the smaller diameter of the drum requires the drum to rotate faster, which makes the photoreceptor more susceptible to abrasion and shortens its lifespan. In addition, as machines become smaller, the temperature inside the machine increases rapidly, causing problems such as filming and fusion on the photoreceptor.Furthermore, reducing the diameter of the sleeve also increases the rotation of the sleeve, causing toner This causes a charge-up phenomenon in which the charge on the photoreceptor increases more than necessary, causing problems such as a decrease in image density and background stains (hereinafter referred to as fog).

In addition, by increasing the speed of high-speed aircraft,
Particularly in the case of materials with extremely hard surfaces, such as amorphous silicon photoreceptors, toner adhesion to the photoreceptor becomes a problem. (Then, it becomes possible to handle high-speed machines, but in this case, not only filming and fusion (and scraping) become a problem.

In particular, as the speed increases, it becomes difficult not only to reduce the lifespan and durability of the photoreceptor but also to maintain stable high image quality over a long period of time. In particular, it is difficult to stabilize fog, sharpness, gradation, etc. over a long period of time and without environmental changes.

A toner containing a magnetic material, such as a one-component toner, has stronger abrasiveness than a toner that does not contain a magnetic material, and thus tends to severely abrade the photoreceptor.

For this reason, the life of the photoreceptor drum tends to be short, and the lifespan of the photoreceptor drum is particularly severe for small-diameter photoreceptor drums.

In order to improve this problem, reducing the amount of magnetic material can be considered, but the amount of charge on the toner increases more than necessary, and the magnetic binding force of the toner to the developing sleeve becomes weaker, making fogging more likely. Particularly in a low temperature, low humidity environment, charge-up may progress and the image density may decrease.

Furthermore, Japanese Patent Application Laid-Open No. 56-16144 proposes that by incorporating an ethylene-based olefin polymer into a magnetic toner, adverse effects on the surface of the photoreceptor such as scratches on the photoreceptor and toner fusion can be eliminated. However, the photoreceptor referred to here mainly has an insulating layer made of polyester resin on the surface, and the magnetic powder is also mainly 0.2μ.
m or more, it is considered inappropriate for the OPC and amorphous silicon photoreceptors that are mainly used today, and the image density is also lower than 1.25, which is the high image density of today.
This is insufficient for strict requirements for high image quality. If you try to make this a high image density by mechanical adjustment, the characters will be crushed.
It is thought that the fog density will increase and become a problem. In particular, with today's higher-speed, smaller-diameter photosensitive drums, such toner tends to cause a charge-up phenomenon in low-temperature, low-humidity environments (a drop in image density and fogging). OPC, amorphous silicon, and Se, which are widely used today and do not have an insulating layer on their surfaces, are considered to be insufficient in terms of long life and maintenance-free performance.

Furthermore, in Japanese Patent Publication No. 61-39662, toner particles contain a lubricant and CeO2 is added as an abrasive to the toner as particles independent of the toner particles, thereby improving the slipperiness of the photoreceptor. It has been proposed to prevent the film formation phenomenon, but this is due to the presence of magnetic substances in the toner.
If it contains a material with high abrasive power, it will be too abrasive, causing a problem. Furthermore, the photoconductor described here mainly has an insulating layer on top of the photoconductor layer and is quite resistant to scratching, unlike today's OPC photoconductors and Se photoconductors. High durability and long life cannot be achieved with amorphous silicon photoconductor systems that are susceptible to abrasion or are hardly able to be abraded at all due to abrasion, filming, and fusion. In addition, especially in terms of maintaining high image quality stably over a long period of time,
If lubricant is simply added, dispersion in the toner will be poor;
CeO, which exists independently of toner, may be a problem.
□ may also be consumed arbitrarily during development, which is undesirable as it upsets the balance.

Therefore, US Pat. No. 4,051,077 proposes a method in which an abrasive as described above is added separately from the toner, thereby adding a lubricant separately to prevent excessive abrasion.

However, during development, toner is not always consumed at a fixed rate, so with long-term use, depending on the toner, more may remain in the developing device, or less may remain, resulting in polishing and slippage. The balance may be disrupted, excessive scraping, filming, fusion, or in some cases, image deterioration, such as fluctuations in image density, fogging, etc. may occur.

It is also known to add colloidal silica for the purpose of improving fluidity and homogenizing charging. Colloidal silica can be seen as an abrasive with little abrasiveness, but it can also become a core and cause filming and fusion, especially when using higher-speed machines or small-diameter photosensitive drums. This can be a problem in some cases.

It is possible to improve these problems by adding polyolefins, adjusting the amount of polyolefin, or adding some abrasives, but this is difficult when considering high durability and high image quality. Further, toners containing colloidal silica tend to charge up easily, especially in low temperature and low humidity environments, which may pose a problem.

Further, in order to improve image quality, it has been considered to reduce the particle size of toner. While the volume average diameter of conventionally put into practical use is 10 to 13μ, the diameter is set to 9μ or less. However, simply reducing the particle size increases the amount of charge and causes a charge-up phenomenon in high-speed machines and long-term durability, resulting in a decrease in image density and deterioration of image quality, such as fogging. Filming and fusion are likely to occur due to slight changes in the type and amount of the contained materials, and the practical tolerance range is narrow, posing a problem.

Furthermore, especially in laser beam printers (hereinafter referred to as LBPs), which are in high demand today, the machines themselves are very compact, so the fuser is placed very close to the developer, and the developer sleeve is heated to a higher temperature than expected. It has become. Moreover, since the LBP is usually used in a computer room, the room temperature is low and it tends to dry out.Furthermore, since the inside of the LBP machine is high temperature, the developing device has very low humidity. That is, the charge of the toner tends to increase more than necessary, and when images are continuously produced, a charge-up phenomenon easily occurs.

This is an even more difficult situation for high-speed LBPs, and today, improving performance at particularly severe low temperature and low humidity conditions is one of the important issues.

As mentioned above, it is smaller, lighter, faster, has a longer lifespan, and is more durable.
Toners that satisfy various demands such as high image quality and high stability have not yet been produced.

[Purpose of the invention]

An object of the present invention is to provide a magnetic toner for developing electrostatic images that solves these problems.

A further object of the present invention is to provide a magnetic toner for developing electrostatic images that is environmentally stable, particularly at low temperatures and low humidity, and is free from charge-up.

A further object of the present invention is to provide a magnetic toner for developing electrostatic images that is highly durable, does not cause charge-up or charge-down, and has excellent stability even in high-speed machines.

A further object of the present invention is to provide an electrostatic image developing toner that does not scrape the photoreceptor drum more than necessary and has a longer lifespan.

A further object of the present invention is to provide a toner for developing electrostatic images that does not cause filming or fusion on a photoreceptor drum.

A further object of the present invention is to provide a magnetic toner for developing electrostatic images that has good durability, good gradation, good fogging, and good sharpness.

A further object of the present invention is to provide a magnetic toner for developing electrostatic images suitable for toner having a volume average diameter of 9 μm or less.

[Summary of the invention]

The present invention provides a magnetic toner for developing electrostatic images containing at least a magnetic material, in which the average particle size of the magnetic material is 0.1 to 0.0.
2 μm, the coefficient of change expressed in % by dividing the standard deviation by the average diameter is 40% or less, the magnetic material has an octahedral shape, and the magnetic material is 35 to 60 wt% based on the magnetic toner.
The present invention relates to a magnetic toner for developing electrostatic images characterized by containing 0.5 to 4 wt % of polyole and finka.

[Detailed description of the invention]

In the present invention, the average particle size of the magnetic material is determined by taking a transmission electron microscope (TEM) photograph taken at a magnification of 10,000 times, magnifying it by a factor of 4, and then randomly selecting 250 magnetic materials and determining their diameter. This method calculates the number distribution and number average diameter from the measured diameter. From the number distribution, σ (standard deviation)
The spread of the distribution is used as a change coefficient, and it is expressed as a percentage from (σ/number average diameter) xlOO. The average particle size is more preferably 0.14 to 0.19 μm, even more preferably 0.15 to 0.19 μm. Further, the variation coefficient is preferably 30% or less, more preferably 25% or less, further preferably 20% or less, and even more preferably 18% or less. If the variation coefficient is too large, the dispersibility of the magnetic material tends to be poor.

If the content of the magnetic material is less than 35 wt%, the abrasiveness of the photoreceptor will be poor and it will not be effective (furthermore, fogging and charge-up will occur in low temperature and low humidity environments.
If it is larger than 0 wt%, the photoconductor may be scraped more than necessary, and the image density tends to be low (especially in long-term durability, it may cause a decrease in image density and deterioration of image quality, such as sharpness). It becomes a problem.

Furthermore, if the average particle size of the magnetic material is less than 0.1 μm, dispersibility in the binder resin becomes a problem, and image density is also difficult to achieve. If it is larger than 0.2 μm, the dispersibility of the polyolefin may become a problem, and the photoreceptor may be scraped.

Furthermore, although the magnetic material is mostly octahedral, it may contain a slight hexahedral or spherical shape.

The bulk density of this nail-shaped magnetic material is 0.35 g/crt
? The above is preferable, more preferably 0.40 g/crrf or more, further 0.5 g/crrr or more, and even 0.6 g
/crrf or more, and even 0.7g/ctr? The above is preferable. The measurement of umbrella density is based on the Shuhoku method.

Further, the particle size of the toner is preferably 9 μm or less in volume average diameter (based on Coulter Counter TA-II type) and 37% or less in variation coefficient, more preferably 34% or less, and even more preferably 32% or less.

Without being bound to any theory, we have found that there is a relationship between the particle size and distribution of the magnetic material and the uniformity and fine dispersibility of the polyolefin contained therein. In particular, we were able to find specific conditions under which the photoreceptor could be scraped uniformly and only to the minimum extent necessary, and filming and fusion of the photoreceptor could be prevented for a long period of time.

This is due to the extremely uniform scraping of the photoreceptor, which is made of a magnetic material with a narrow particle size distribution of 0.1 to 0.2 μm, and the even lubricity of the polyolefin, which is finely and uniformly dispersed in the toner. This is thought to be due to the fact that

Furthermore, magnetic materials with a diameter of 0.1 to 0.2 μm have a much larger number of magnetic materials per important point than magnetic materials larger than 0.2 μm, which have been put into practical use in the past, so toner particles are particularly difficult to use in low-temperature, low-humidity environments. It has the ability to charge and stabilize electricity without charging up even when used continuously on high-speed machines. Furthermore, since the polyolefin has good dispersibility, the polyolefin does not exist loosely or unevenly in the toner, so there is no fogging or deterioration of image quality.

Furthermore, charge-up can be suppressed even when colloidal silica is included.

The polyolefin that can be used in the present invention is preferably low molecular weight polyethylene, low molecular weight polypropylene,
It is a low molecular weight propylene-ethylene copolymer, especially one having a melting point of 100 to 200°C. It is also possible to use a mixed system of these low molecular weight polyethylene, low molecular weight polypropylene, low molecular weight propylene-ethylene copolymer and a waxy substance such as microcrystalline wax, carnauba wax, Sasol wax, or a fatty acid metal salt. .

Further, as the octahedral magnetic substance, a substance that is magnetized when placed in a magnetic field is used, and magnetite and magnetite are preferable. In particular, the method of making a magnetic material into an octahedron is
Any known method may be used; for example, it is known that when magnetite is manufactured by a wet method, if the pH of the oxidation step is kept near alkaline, octahedral formation occurs.

Among these magnetic materials, magnetite will be described.

Magnetite is produced by mixing a ferrous salt solution and an alkaline aqueous solution to produce a suspension containing ferrous hydroxide at a temperature of 70 to 100°C and a pH of 10 or more, and then introducing an oxygen-containing gas into the suspension. Obtained by aeration. The shape of magnetite particles exhibits an octahedral particle size depending on the generation conditions.

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 2.0% by weight calculated as SiO2 based on the generated magnetite particles) is present in a suspension containing ferrous hydroxide, This is preferable because the distribution of the generated magnetite can be further improved.

When an oxygen-containing gas is passed through a suspension containing ferrous hydroxide obtained by mixing an alkaline aqueous solution and a ferrous salt aqueous solution at a temperature of 70 to 100°C and a pH of 10 or higher while heating,
Magnetite particles with fine particle size and sharp particle size distribution, that is, with a small coefficient of variation, can be obtained.

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 50 f was used as a reactor. Fe” 1.75mol/j!
Ferrous sulfate aqueous solution containing 20I! , 4N aqueous sodium hydroxide solution 181, water 4I! and sodium silicate (No. 3)
(SiO228, 55wt%) 18.9g (corresponding to 0.23wt% in terms of Si02 with respect to the generated magnetite) was used at a temperature of 88°C and a pH of 13.
A suspension containing 21 Fe(OH)2 was prepared.

Air was passed through the suspension containing Fe (OH) 2 at a temperature of 90° C. for 120 minutes at a rate of 100 f/min to form a black precipitate. The produced particles were washed with water, filtered, dried, and pulverized using a conventional method. The obtained magnetite particles were observed under an electron microscope and were found to be octahedral particles with an average particle size of 0.16 μm and a variation coefficient of 19%. This is called magnetite A. Among the above reaction conditions, Fe"+ concentration, temperature, and pH when producing a suspension containing ferrous hydroxide.
, magnetite B under the same conditions as Experimental Example-1 except that the amount of sodium silicate added and the temperature and air amount of the oxidation conditions were changed.
, C..., L were obtained. Table 1 summarizes the reaction conditions, the average particle diameter of the produced magnetite, and the coefficient of change.

As a method for increasing the bulk density of the magnetic material, it is possible to crush it under pressure using, for example, a fret mill.

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. Coalescing: 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 esters such as styrene-ethyl methacrylate copolymer, styrene-n-butyl methacrylate copolymer; multi-component copolymers of styrene and acrylic esters and methacrylic 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, phenol resins, aliphatic or alicyclic hydrocarbon resins, petroleum resins, chlorinated paraffins, and the like 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, ultramarine blue, quinacridone, and benzidine yellow.

Additives may be mixed with the toner as necessary. Examples of such additives include organic compounds such as Teflon, vinylidene borate, and zinc stearate, or inorganic compounds such as (1:eo 2.5rTiO3).
Metal oxides such as tin oxide are also used as fluidity imparting agents, anti-caking agents, and conductivity imparting agents.

Further, as colloidal silica, those caught on a boat can be used, but from the viewpoint of hygroscopicity, those that have been hydrophobically treated are preferable, such as those that have been treated with a silane coupling agent or silicone oil.

As a method for manufacturing the toner, a conventionally known general method is used. For example, the materials are powder-mixed using a mixer such as a Henschel mixer, then heat-kneaded for 5 to 30 minutes using a kneader such as a roll mill, and the resulting kneaded product is cooled and then coarsely or finely pulverized, e.g. jet mill) to obtain toner of the required particle size, and if necessary, use Alpine's zigzag classifier to cut fine powder and coarse powder to use as a developer. Furthermore, if necessary, a fluidity imparting agent such as colloidal silica may be mixed in powder to prepare a magnetic toner to which colloidal silica is externally added.

Example 1 The above materials were mixed into powder using a Henschel mixer, and this was mixed into 1
Heat kneading is carried out for 15 minutes in a roll mill set at 50°C. The obtained kneaded material was coarsely pulverized with a cutter mill and finely pulverized with a jet mill to obtain a pulverized product having a volume average diameter (Coulter Counter TA-n; using 100 .mu.m aperture) of 7.5 .mu.m. This was classified using a zigzag classifier manufactured by Alpine, to obtain a magnetic toner having a volume average diameter of 8.1 μm and a variation coefficient of 31%. A colloidal silica externally added magnetic toner was prepared by powder-mixing 0.6 parts by weight of positively charged hydrophobic colloidal silica treated with amino-modified silicone oil per 100 parts by weight of the magnetic toner.

Colloidal silica externally added magnetic toner was applied to a modified Canon high-speed digital copier NP-9030 (30 sheets/min to 45 sheets/minute).
(modified to 1 sheet per minute).

A durability test of 60,000 sheets was conducted under normal conditions, and there was no problem with the photoreceptor being scratched, and no filming or fusion occurred.

Furthermore, there is no fluctuation in image density (reflection density is 1.0 from the initial stage).
37, there was no fluctuation, and the fog and gradation were also good (and stable).

Furthermore, we conducted durability tests on 20,000 sheets under low temperature and low humidity environments, but there was no charge-up phenomenon (no image density, fogging,
The gradation was good and stable, and there were no other problems.

Comparative Example 1 A magnetic toner was prepared in the same manner as in Example 1, except that instead of magnetite A, octahedral magnetite B having an average particle size of 0.22 μm1 and a variation coefficient of 42% and a bulk density of 0.20 g1crd was used. did. The volume average diameter of the magnetic toner was 8.4 μm1 and the coefficient of change was 39%.

Evaluation was carried out in the same manner as in Example 1, but in the durability test under normal environment, the image density decreased from the initial 1.4 to 1.0 after 50,000 sheets.
It dropped to 5. In addition, the fogging was a little bad, and the gradation was worse than the initial one after 50,000 copies.

Furthermore, in a low-temperature, low-humidity environment, after 10,000 prints, fog due to the charge-up phenomenon became a problem.

Example 2 A magnetic toner was prepared in the same manner as in Example 1 using the above materials. 0.7 parts by weight of negatively charged hydrophobic colloidal silica treated with hexamethyldisilazane was added to 100 parts by weight of this magnetic toner to prepare a magnetic toner to which colloidal silica was externally added. The volume average particle size of the toner is 8
．． 4μm1 change coefficient was 29%.

The evaluation was based on Canon's NP-8580, a high-speed copying machine.
An 80 sheets/minute machine was used. This copier uses an amorphous silicon photoreceptor.

We conducted a durability test of 300,000 sheets in a normal environment, and there were no problems with photoreceptor scraping, filming, or fusion, and the image was stable, with an image density of 1.35 to 1.40, and no fogging. , gradation, and sharpness were good and stable.

Furthermore, we conducted an 80,000-sheet durability test in a low-temperature, low-humidity environment.
There was no charge-up phenomenon, and there were no problems at all.

Comparative Example 2 Instead of magnetite C, octahedral magnetite D having an average particle size of 0.23 μ, a variation coefficient of 23%, and a bulk density of 0.25 g/crrf was used, and low molecular weight polypropylene (T
m 150°C), except that 8 parts by weight of
A magnetic toner was prepared in the same manner as in Example 2. The volume average particle diameter of the magnetic toner is 8.2 μm, and the variation coefficient is 39%.
Met.

When this magnetic toner was evaluated in the same manner as in Example 2, it was found that fusion occurred on the photoconductor after 150,000 sheets were printed in a normal environment.
It also appeared as a black dot on the image. In addition, fogging is somewhat bad, and there is some variation in image density, with an initial reflection density of 1.4.
2 decreased to 1.15.

Furthermore, a durability test of 50,000 sheets was conducted in a low-temperature, low-humidity environment, but a charge-up phenomenon occurred and fogging became slightly worse.

Example 3 A magnetic toner was prepared in the same manner as in Example 1 using the above materials. The volume average particle diameter of the magnetic toner was 7.8 μm1 and the coefficient of change was 30%. To 100 parts by weight of magnetic toner, 0.6 parts by weight of positively charged hydrophobic colloidal silica was added to 100 parts by weight of a Canon copier NP with a small diameter photoreceptor drum.
We evaluated a modified machine that increased the speed of the -1215 machine from 15 sheets/min to 20 sheets/min.

A durability test of 40,000 sheets was conducted in a normal environment, and there were no problems with photoreceptor scraping, filming, or fusion, and the image density was high (and stable) at 1.37 to 1.40 from the beginning. There is also no fog, and the sharpness and gradation are very good.
It was stable.

Furthermore, we conducted a 40,000-sheet durability test in a low-temperature, low-humidity environment.
There was no charge-up phenomenon, and the performance was stable and good.

Comparative Example 3 Instead of magnetite E, average particle size 0.23 μm 1 variation coefficient 23%, bulk density 0.20 g/crr? A magnetic toner was prepared in the same manner as in Example 3 except that octahedral magnetite D was used and zinc stearate was used instead of low molecular weight polypropylene.

This was evaluated in the same manner as in the examples. In a durability test under normal conditions, uneven image density occurred after 30,000 copies due to uneven scratching of the photoreceptor. Furthermore, in a durability test in a low-temperature, low-humidity environment, slight fogging and a decrease in image density occurred due to charge-up phenomenon after 20,000 sheets were printed.

Example 4 A magnetic toner was prepared in the same manner as in Example 2 using the above materials. The volume average particle diameter of the magnetic toner was 11.8 μm, and the variation coefficient was 30%. 100 parts by weight of magnetic toner and 0.4 parts by weight of hydrophobic colloidal silica were added to a modified Canon laser beam printer LBP-3X with a small diameter OPC photoreceptor drum to print 6 sheets per minute to 12 sheets. The evaluation was performed using a modified machine with a speed of 1/min.

A durability test of 6,000 sheets was conducted under normal conditions, and there were no problems such as scraping, filming, or fusion of the photoreceptor. In addition, there was no charge-up, the image density was stable at 1.40 from the beginning, and fogging was also very good.

Furthermore, even in a low temperature, low humidity environment, a 6,000 sheet durability test was conducted, and the results were very good, with no charge-up phenomenon.

Comparative Example 4 Instead of octahedral magnetite F, average grain size 0.22
μm, variation coefficient 42%, bulk density 0.21g/crrr
A magnetic toner was prepared in the same manner as in Example 4, except that Magnetite B was used.

In the same evaluation as in Example 4, there was some fogging, especially under low temperature and low humidity conditions, and filming occurred on the photoreceptor after 4,500 sheets in the durability test, which was a problem.

Comparative Example 5 A toner was prepared in the same manner as in Example 4, except that 5 parts of fatty acid amide was used in the low molecular weight polypropylene.

In the same evaluation as in Example 4, in the durability test after 4,200 sheets, density unevenness occurred on the image due to excessive abrasion of the photoreceptor drum, and filming and fusion also occurred around 4,600 sheets.

Claims (2)

[Claims] (1) In a magnetic toner for developing an electrostatic image containing at least a magnetic substance, the average particle size of the magnetic substance is 0.1 to 0.2μ.
m, the coefficient of change expressed in % by dividing the standard deviation by the average diameter is 40% or less, and the magnetic body has an octahedral shape,
A magnetic toner for developing electrostatic images, characterized in that it contains 35 to 60 wt% of a magnetic material and 0.5 to 4 wt% of a polyolefin, based on the magnetic toner. (2) The magnetic toner for developing electrostatic images according to claim 1, wherein colloidal silica is externally added.