JPS6237780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic powder for electrophotographic magnetic toner.

The development methods for electrophotography include a two-component method, in which a powder made of a mixture of resin and carbon is used as toner, and this is moved onto an electrophotographic photoreceptor using a magnetic brush made of carrier iron powder, and the other is a two-component method, in which the toner contains magnetite, There is a one-component method in which a magnetic powder such as ferrite, iron powder, or alloy powder is mixed in to give the toner itself magnetism and no carrier is used.

By the way, the two-component method is currently the mainstream. This is because the two-component method has better image characteristics, but each method has its advantages and disadvantages.

The main reason why the image characteristics of the one-component method are inferior to those of the two-component method is that the resin in two-component toner is usually 90wt.
% or more, one-component toner usually has 50 to 30 wt% resin and the rest is magnetic powder, so it has a larger heat capacity and melt viscosity than two-component toner, and this toner cannot be processed by heat or pressure. In addition, magnetic oxides such as magnetite and ferrite have poor moisture resistance, and toners made with these tend to leak electrically in humid conditions, reducing image characteristics. This is to do so. Iron powder and alloy powder have lower hygroscopicity than magnetic oxides such as magnetite, but iron powder and alloy powder The proposal to use it as a magnetic toner is only a suggestion;
There are no examples of it being actually applied.

On the other hand, with the two-component method, the toner concentration in the developer has a large effect on image quality, the developer deteriorates after long-term use, so the developer needs to be replaced, and the developer is circulated. For this reason, the developing mechanism is complicated and the device becomes large.

Under these current circumstances, the one-component method has a simple development mechanism and is easy to adjust, and there is no need to replace the developer just by supplying additional toner.
Moreover, since the developing unit is simple, maintenance can be greatly reduced, and the equipment can be simplified, making it possible to reduce the weight and cost of the equipment, which has led to the development of high-performance magnetic toner for single-component use. A dramatic development of the one-component method is expected.

By the way, it is preferable that the magnetic powder for one-component toner has a high magnetic velocity density in the magnetic field of about 1000 Oe of the magnetic roll of a copying machine. It's for a reason. Currently, magnetic powder for one-component toner is
Magnetic flux density (σs) 40 ~ in a magnetic field of about 1000 Oe
Magnetite of about 65 emu/g is generally used, but in this case, as mentioned above, it is necessary to mix 50 to 70% of magnetite into the magnetic toner.
It's not something I'm satisfied with.

An object of the present invention is to provide a high-performance magnetic powder for magnetic toner that solves all the drawbacks of the conventional magnetic powder for electrophotographic toner.

As a result of various studies, the present inventors found that the main component is iron nitride (Fe ₄ N), the nitrogen content is 3 to 10% by weight, the average particle size is 10μ or less, and
The present invention was completed based on the discovery that a magnetic powder for electrophotographic magnetic toner, which is characterized by a magnetic flux density of 60 to 140 emu/g at 1000 Oe, can achieve the above object.

Hereinafter, the magnetic powder for magnetic toner of the present invention will be explained in detail along with its various characteristics.

The high-performance magnetic powder for magnetic toner of the present invention is an iron powder containing nitrogen and having a high magnetic flux density.

The nitrogen content of the magnetic powder of the present invention is 3 to 10% by weight, and in this case, nitrogen is mainly contained as iron nitride (Fe ₄ N).

If the nitrogen content is within the above range, there will be almost no deterioration in magnetic properties even if it is left at 60°C and 90% relative humidity for two weeks, and the amount of moisture absorbed in this case is about 0.1 to 0.2%. Considering that the amount of moisture absorbed by magnetic oxides currently used for one-component systems such as magnetite and ferrite is 3 to 5%, this is extremely small. If the nitrogen content is 3% by weight or less, rust may occur during storage or toner production, resulting in a decrease in magnetic properties. Furthermore, when the nitrogen content is 10% by weight or more, nitrides such as Fe ₂ N and Fe ₃ N, which have low magnetic flux density, increase, resulting in a decrease in magnetic properties.

The average particle size of the magnetic powder of the present invention is about 10μ or less, and the particle size of magnetic toner is generally 7 to 40μ.
Considering that the thickness is about 5μ or less, it is particularly preferable. Further, it is preferable that the particle size distribution is sharp.

The nitrogen-containing iron powder for magnetic toner of the present invention is
The magnetic flux density (σs) in a magnetic field of 1000 Oe is 60 ~
It is 140emu/g.

Currently, magnetite, which is widely used for magnetic toner, has a magnetic flux density (σs) of about 55 emu/g in a magnetic field of about 1000 Oe, and if the amount of magnetic powder in the magnetic toner is 50% (weight), the magnetic toner is The magnetic flux density (σs) of is about 27.5emu/g. On the other hand, if the magnetic powder of the present invention, for example, one with a magnetic flux density (σs) of 120 emu/g, is used, only 22.9% (weight) is required to produce a magnetic toner with a magnetic flux density (σs) of 27.5 emu/g. Since the heat capacity and melt viscosity of the resin are significantly reduced, the fixing properties are further improved.

The nitrogen-containing iron powder for high-performance magnetic toner of the present invention can be produced by the following method.

Iron oxide is reduced to the iron stage using a reducing gas such as H ₂ , CO, or CH ₄ in a temperature range of 400 to 900°C, and then nitrided with a nitrogen-containing gas such as NH ₃ .
After cooling, the powder is taken out of the reduction nitriding furnace, pulverized using a ball mill, vibration mill, attritor, sand mill, etc. as necessary, and classified to obtain magnetic powder of a predetermined particle size.

Although it is convenient and industrially preferable to carry out the nitriding reaction with NH ₃ , it is also possible to use nitrogen or nitrogen compounds such as tyrene amines and hydrazines. Nitrogen has a slow nitriding rate, and organic nitrogen compounds such as ethyleneamines are expensive compared to NH ₃ , which is an industrial difficulty, but the nitriding reaction is possible, and these nitriding agents are also widely used. It can be used to produce the magnetic powder of the invention.

Furthermore, in the above manufacturing method, direct reduction-nitridation can be performed using NH ₃ without using a reducing gas such as H ₂ , CO, or CH ₄ .

Furthermore, instead of iron oxide, reduced iron powder, electrolytic iron powder,
Various iron powders such as atomized iron powder and carbonyl iron powder can be nitrided at 400 to 900°C in an NH ₃ atmosphere, and then, if necessary, crushed using a ball mill, etc., and classified to obtain particles within a specified particle size range. . In this case, depending on the raw materials and reductive nitriding conditions, the nitriding reaction may proceed too much and produce substances with low magnetic flux density such as Fe ₂ N and Fe ₃ N. Therefore, denitrification treatment may be performed as necessary to reduce the magnetic flux. The object of the present invention can also be achieved by converting into Fe ₄ N or the like having a high density, followed by pulverization and classification.

The nitrogen-containing fine iron powder of the present invention is used after its surface is oxidized, if necessary. This oxidation treatment
This is carried out by heating nitrogen-containing fine iron powder in an inert gas containing water vapor or in air.

The present invention will be explained below with reference to Examples showing the magnetic powder for electrophotographic magnetic toner of the present invention along with its manufacturing method.

Example 1 Pigment iron oxide (NSR-300 manufactured by Morishita Bengara) was charged into a reduction furnace, and when the temperature was raised to 500°C in an N ₂ atmosphere, N ₂ was switched to H ₂ . After this, the temperature was increased at a rate of 100℃/hr, maintained at a temperature of 700℃ for 3 hours, and then
H ₂ was switched to NH ₃ and held for 1 hr, then cooled. After cooling to 500°C, NH ₃ was replaced with N ₂ , the mixture was further cooled to room temperature, and the nitrogen-containing iron powder was taken out.

This was placed in a ball mill and pulverized for about 32 hours, and when the pulverized product was taken out and classified, the amount of particles with a particle size of 10μ or less was 35% (by weight).

Note that if the crushed material is taken out into the air as it is, since it is a fine iron powder, an oxidation reaction will occur rapidly and it will burn. To prevent this, pulverization was carried out while controlling the oxygen concentration in the ball mill. In other words, when the ball mill starts operating, the pressure inside the ball mill decreases, but this is thought to be due to the reaction between the fine iron powder and oxygen in the air. It was possible to prevent oxidation reactions.

When we investigated the magnetic properties of iron powder with a particle size of 10 μ or less, we found that in an external magnetic field of 1000 Oe, Hc70Oe, σ
It was s105emu/g.

Also, from X-ray diffraction, its composition is Fe ₄ N 90%,
The Fe content was 10%, and the nitrogen content was 5.4% (by weight).

Example 2 Iron oxide (S-2000 manufactured by Anshiron Kogyo Co., Ltd.) was placed in a reduction furnace, and when the temperature was raised to 500°C in an N ₂ atmosphere, the N ₂
was switched to _NH3 . Thereafter, the temperature was increased at a rate of 100°C/hr, and the temperature was maintained at 700°C for 4 hours to carry out a reductive nitriding reaction. It was cooled in an NH ₃ atmosphere, and when the temperature reached 500° C., the NH ₃ was replaced with N ₂ , and it was further cooled to room temperature and taken out.

The reduced iron nitride and toluene were placed in a batch-type vibration mill and ground for 15 hours. Toluene was added to prevent the iron powder from being burned due to rapid oxidation reaction during removal. Note that the ratio of iron to toluene was 1:1 (by weight).

After grinding, the slurry of fine iron powder was taken out and the toluene was removed by air drying, and the magnetic properties were examined. In an external magnetic field of 1000 Oe, Hc82Oe,
It was σs90emu/g.

The composition was investigated using X-ray diffraction method.
Fe ₄ N was 80% and Fe 20%. In addition, 87% (by weight) had a particle size of 10μ or less.

Example 3 The reduced iron nitride powder obtained in Example 1 and methyl alcohol were charged into an attritor and pulverized for 10 hours.

After taking out the crushed material and blowing off the methyl alcohol by air-drying it, we examined its magnetic properties.
Hc110Oe, σs85emu/g.

In addition, 98% (by weight) had a particle size of 10μ or less.

Example 4 A mixture of 70% (by weight) epoxy resin, 4% (by weight) carbon black, and 26% (by weight) nitrogen-containing iron powder obtained in Example 1 was thoroughly kneaded using a heating kneader, and the mixture was heated to room temperature. After cooling, it was ground to a particle size of about 35μ or less using a jog mill. This was classified to obtain magnetic toner of 10 to 35μ. The magnetic properties of this magnetic toner are
Hc85Oe, σs27emu/g.

Next, an electrostatic image was formed on a selenium photosensitive drum, developed using this toner by a magnetic brush method according to a conventional method, and then transferred onto plain paper and fixed. A good image was obtained. did it. Furthermore, even when the selenium photosensitive plate was replaced with a zinc oxide photosensitive plate, similarly good images were obtained.

Comparative Example A magnetic toner was produced in the same manner as in Example 4 using a mixture of 50% (by weight) epoxy resin, 4% (by weight) carbon black, and 46% (by weight) cubic magnetite. The magnetic properties of this magnetic toner are
Hc90Oe, σ in an external magnetic field of 1000Oe
It was s28emu/g. When the image characteristics of this were examined under the same conditions as in Example 4, edge effects and fogging phenomena were observed and the results were not satisfactory.
In particular, the high-humidity characteristics were poor, and almost no images were produced at high humidity.

As described above, the magnetic toner using the magnetic powder of the present invention had further improved image characteristics in both heat and pressure fixing methods.

Example 5 Electrolytic iron powder (Mylon manufactured by Toho Zinc) was charged into a nitriding furnace and heated to 400°C in _an N ₂ atmosphere.
was switched to _NH3 . Thereafter, the temperature was raised to 600°C and maintained at this temperature for 4 hours to perform nitriding.
Cooled in NH ₃ atmosphere and reached 400℃.
NH ₃ was replaced with N ₂ , cooled to room temperature, and taken out.

This was pulverized under the same conditions as in Example 2.

When we investigated the magnetic properties of this material, we found that it
At 1000Oe, Hc65Oe and σs85emu/g.

Furthermore, when we investigated its composition using X-ray diffraction, we found that
Only the Fe ₄ N peak was detected.

Example 6 Reduced iron was nitrided to produce iron nitride. The nitriding temperature was 700°C, but the other conditions were the same as in Example 5.

The magnetic properties of this material were Hc98Oe and σs77emu/g in an external magnetic field of 1000Oe.

Further, when its composition was examined by X-ray diffraction, it was found to be approximately 25% Fe ₃ N, 15% Fe ₂ N, and 60% Fe ₄ N.

It should be noted that the magnetic toner using the magnetic powder of the present invention can also be used for electrophotography using magnetic latent imaging, which is currently attracting attention due to its magnetic properties.

Claims (1)

[Scope of Claims] 1 The main component is iron nitride (Fe ₄ N), the nitrogen content is 3 to 10% by weight, the average particle size is 10 μ or less, and the magnetic flux density is 60 to 60 in an external magnetic field of 1000 Oe.
A magnetic powder for electrophotographic magnetic toner, characterized by having a concentration of 140 emu/g. 2. Magnetic powder for electrophotographic magnetic toner according to claim 1, which contains other iron nitrides (Fe ₂ N, Fe ₃ N) as components other than iron nitride (Fe ₄ N). .