JPS6323132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing transferable ferrite powder for electrophotographic magnetic toner. There are various developing methods in electrophotography, but toner is a powder made of a mixture of carbon and resin, and this is transferred onto an electrophotographic photoreceptor through a magnetic brush made of an iron powder carrier. , the so-called two-component method is currently mainstream. However, recently, research and development efforts have rapidly begun to develop a method known as the one-component method, in which magnetic powder is mixed into the toner instead of carbon to impart magnetism to the toner itself, without the use of a carrier. Some of them have even been commercialized. This is because in the one-component method, the developing operation is simple and therefore easy to eliminate adjustments, and since there is no need to replace the carrier, all that is needed is an additional supply of toner, and the developing unit is simple. This is because the labor required for maintenance can be significantly reduced, and the device can be simplified, making it possible to reduce the weight and cost of the device. Generally, the following properties are required of magnetic powder for magnetic toner in such a one-component system. (i) The magnetic flux density in a magnetic field of about 10 ³ Oe should be as high as possible. For example, in an external magnetic field of 1000 Oe, it is necessary to have a maximum magnetizing force σm of about 40 emu/g or more. This is to increase the height of the ears as magnetic brushes. (ii) At the same time as (i), the coercive force is high. for example
It is necessary to have a coercive force Hc of about 150 to 500 Oe in an external magnetic field of 1000 Oe. This is to obtain good characteristics in terms of toner transportability, fluidity, and cohesiveness. Therefore, the B-H product requires a value of about 0.6×10 ⁴ or more in terms of σm×H value. (iii) The electrical resistance must have an appropriate value. The appropriate electrical resistivity of the powder is 10 ² to ^{10 7} Ω·cm. (iv) Must be black enough for practical use. Although a coloring agent may be contained in the magnetic toner, it is preferable that the powder itself has a black color and no coloring agent is used. (v) High heat resistance. It is necessary that the color tone, especially the blackness, and the electromagnetic properties are sufficiently stable within the temperature range of about 0 to 150°C. (vi) Low hygroscopicity and good moisture resistance. This is because high hygroscopicity significantly changes the electrostatic properties of the toner. (vii) Good miscibility with resin. The particle size of toner is usually several tens of micrometers or less, and the degree of microscopic mixing in the toner is important for the characteristics of the toner. For this purpose, it is necessary to have a fine particle size of 1 μm or less, a sharp particle size distribution, and a stable particle size from production lot to production lot. (viii) Do not significantly deteriorate the electrostatic properties of the resin to be mixed, change the quality of the resin, or cause these to change over time. On the other hand, conventional magnetic powders for magnetic toner include magnetite, ferrite, alloys exhibiting ferromagnetism, Mn-Cu-Al, etc., which do not exhibit ferromagnetism, as disclosed in, for example, Japanese Unexamined Patent Publication No. 50-45639. It has been proposed to use alloys, chromium dioxide, etc. that become ferromagnetic when subjected to heat treatment. However, for use in magnetic toners, they must be made into fine powders, but the alloys are unstable and expensive to manufacture, while chromium dioxide is toxic, so both cannot be used practically.
The use of ferrite has been proposed in various patents, documents, etc., but these proposals are only suggestions, and there is no example of actually applying a specific ferrite having a specific component and composition to a magnetic toner.
Examples of magnetite include iron black, which is obtained as a precipitate from an aqueous solution reaction and is commonly used as a pigment (hereinafter referred to as magnetite produced by an aqueous solution method), which is applied to magnetic toner.
It has been described in various patents, documents, etc., and has also been put into practical use. This kind of magnetite is
The electrical and magnetic properties required in (i) to (iii) above are satisfactory enough to withstand use, and the color tone in (iv) is satisfactory; )〜(iii)
It is difficult to control the magnetic and electrical properties of There are problems with various requirements such as miscibility with resins, no adverse effects on resins, etc., and there is also a drawback that these properties may vary depending on the production. This is due to the fact that it is essentially difficult to satisfy the required properties with magnetite produced using an aqueous solution method, and there are many variables in the manufacturing conditions for each manufacturing lot. This is because properties, particle size, particle size distribution, contained impurities, etc. can vary greatly. Therefore, due to these drawbacks, when magnetite is applied to toner, various limitations arise in the use of the toner, and troubles occur during copying. In addition,
Magnetite manufactured using an aqueous solution method uses a large amount of alkali, making it difficult to clean, and also requires labor to treat wastewater after cleaning, which increases the cost of powder production. . Research is also being conducted on maghemite produced by the same method as the above-mentioned magnetite, or on maghemite produced by adding cobalt to change its magnetic properties. However, these also have the same drawbacks as the above-mentioned magnetite. The present invention solves all of these drawbacks of conventional magnetic powders for electrophotographic magnetic toners, and efficiently and stably produces magnetic powders for high-performance magnetic toners that satisfy all of the required characteristics (i) to (viii) above. The purpose is to provide a manufacturing method that can The present inventors have conducted various studies regarding these objectives, and have found that iron-rich spinel structure ferrite having a specific component and composition is a magnetic powder for high-performance magnetic toner that achieves the above objectives. This led to the invention of the title. The first step in the production method of the present invention is the blending of starting materials. As a starting material, typically 99.9
~51 mol% _Fe2O3 and a total of _0.1-49 mol% MO
One or more of (M is the same as above) is used. In this case, instead of Fe ₂ O ₃ , one or more of Fe, FeO and Fe ₂ O ₃ may be used in an amount of 99.9 to 51 mol % in terms of Fe ₂ O ₃ . In addition, instead of MO, other oxides of M or compounds that can become MO by heating, such as carbonates,
Oxalates, chlorides, etc. can also be used. These starting materials with appropriate component ratios are blended. As for the blending method, wet blending is preferred, and a normal method may be used for wet blending. Generally, the mixture is mixed using a wet ball mill for several hours, for example, about 5 hours. This wet formulation allows
The degree of mixing of the raw materials increases, eliminating causes of performance deterioration such as compositional variations and uneven properties, and improving the quality and stability of the magnetic powder. After this, the slurry goes to the next granulation process, but in some cases, it is pre-dried before the granulation process to reduce the moisture content to 10%.
The following may be used. Depending on the starting material used, the temperature may be lower than 1000°C, for example 800°C.
Temporarily baked at ~1000℃ for 1 to 3 hours, and after baking several 10μ
It may be ground to a particle size of about m or less. The second step is granulation. This granulation transforms the formulation into granules of 20 to 30 mesh sizes. Granulation may be carried out by passing the dried blend through a sieve, or by using a spray dryer to form a slurry after wet blending. The third step is calcination of the granules. Heating during sintering is performed at an appropriate temperature of 1000°C or higher. In this case, since the ferrite powder of the present invention is an iron-rich ferrite, it is sintered by appropriately lowering the oxygen partial pressure of the firing atmosphere (usually to an oxygen content of 5% by volume or less), and is cooled after sintering is completed. It is better to cool rapidly, but when cooling relatively slowly, maintain the oxygen partial pressure during sintering until the temperature drops to around room temperature.
More preferably, cooling is performed by lowering the oxygen partial pressure, thereby obtaining the above-mentioned stoichiometric composition. Preferred firing conditions include the following. First, start heating in air. The temperature increase rate is preferably about 2 to 300°C/hr. 800
When the furnace temperature rises to ~900°C, the oxygen content in the atmosphere is reduced to 5% by volume or less, more preferably 3% by volume or less. Sintering is carried out in such an atmosphere at a maximum temperature of 1450°C, usually 1300-1400°C, for 3-5 hours. Next, stop heating, e.g. 300℃/hr.
Cool at the cooling rate above. It is preferable that the oxygen partial pressure be 0.5% by volume or less at the start of cooling. Cooling may proceed at this partial pressure, but when the furnace temperature reaches about 1100° C., preferable results can be obtained by lowering the oxygen content in the atmosphere to, for example, 0.1% by weight or less. When the temperature falls below 100°C, the fired body is taken out of the furnace and firing is completed. The fourth step is mechanical crushing of the fired body. As a result, the ferrite powder of the present invention having an average particle size of 1 μm or less, usually 0.2 to 0.8 μm is obtained. Various methods are possible for mechanical pulverization, but the most preferred method is the following procedure. First, it is medium-ground to an average particle size of 150 mesh or less. A vibration mill or an atomizer may be used for this medium grinding. Further, prior to this medium pulverization, it is efficient to coarsely pulverize the fired body to the above-mentioned granule size of 20 mesh under or less using a die crusher or stamp mill.
Next, the medium-ground powder is finely ground. Fine pulverization is preferably carried out by a wet method, for example, using a wet attritor or the like. In this case, the slurry concentration is about 50% or less, and by grinding for 10 to 100 hours, a powder with an average particle size of 0.2 to 0.8 μm can be obtained. This powder is dried at a temperature of 100° C. or lower to reduce the moisture content to preferably 0.7% or lower, and then crushed into primary particles using an atomizer or the like to obtain the ferrite powder of the present invention. All of the ferrite powders obtained in this way were confirmed to have a spinel structure as a result of X-ray diffraction, and as a result of chemical analysis, a part of Fe was present as divalent, and the stoichiometric composition was It has been confirmed that the deviation is also very small. Moreover, it has characteristics as an extremely high-performance magnetic powder for magnetic toner. Next, the ferrite powder for magnetic toner produced according to the present invention will be explained. The ferrite powder for magnetic toner produced according to the present invention contains iron oxide of 99.9 to 51 mol% in terms of Fe ₂ O ₃ and MO (M is Mn, Ni, Co, Mg, Cu, Zn).
Iron having a spinel structure consisting of 0.1 to 49 mol% of at least one of manganese oxide, nickel oxide, cobalt oxide, magnesium oxide, copper oxide, zinc oxide, or cadmium oxide (calculated as Cd) It is an excess type ferrite powder. The composition of ferrite with a spinel structure defined in this way is (M′O) _x (FeO) _1-x Fe ₂ O ₃ [where x is 0.02 to
0.980, M'O represents one to six types of MO in total of 1 mole], and there is almost no deviation from the stoichiometry. The ferrite powder of the present invention contains impurities such as Al ₂ O ₃ , Ca ₂ O ₃ , Cr ₂ O ₃ , V ₂ O ₅ , CeO ₂ ,
It may contain SnO ₂ , TiO _{2 ,} etc. in an amount of 1.0% by weight or less. Further, the powder may contain a surface modifier or the like which is added as desired during the manufacturing process. As mentioned above, the ferrite particles having such a composition are given a spinel structure by firing by the so-called dry method. The average particle size of the ferrite powder produced by the present invention is about 1 μm or less, and is 0.2 to 0.80 μm.
It is preferable that the degree of Further, it is preferable that the particle size distribution is sharp. The ferrite powder produced according to the present invention satisfies all of the properties required for magnetic toner powders (i) to (viii) above, and has overall higher performance than conventional powders. It is something. That is, it has a high maximum magnetic force σm and coercive force Hc that can be used as a magnetic toner, has a large B-H product value, and has a satisfactory electrical resistivity of 10 ⁵ to ^{10 7} Ω·cm, Furthermore, these electrical and magnetic properties do not vary from production to production, unlike the above-mentioned aqueous solution method magnetite, and the property values can be controlled with strict precision during production. Furthermore, the color tone is low, that is, the reflectance is low, and there is little difference in reflectance with respect to the spectrum, and the color itself is black or a color close to it, so if it is applied as a toner, is there no need to use a colorant? Only a small amount is required, and as a result, the properties (i) to (iv) above are satisfied. In addition to these, the ferrite powder of the present invention has the great feature of exhibiting much higher performance than conventional magnetic powders in the properties (v) to (viii) above. First, regarding the heat resistance (v) above, the ferrite powder produced by the present invention shows almost no change in electrical or magnetic properties or color tone even after being heated to about 180°C or less, and is suitable for magnetic toner. Suitable as magnetic powder for use. Electrical after heating below about 180℃,
The degree of deterioration of magnetic properties and color tone is a fraction of that of conventional aqueous solution method magnetite.
This has significantly decreased to one-tenth. Furthermore, in general,
If the average particle size of the powder is increased and its specific surface area is decreased, its activity will decrease and its heat resistance will also improve. Even with aqueous solution method magnetite, if the average particle size is several times or more the particle size of ferrite produced by the present invention, the same level of heat resistance may be obtained. When the particle size becomes large, the degree of mixing and affinity with the resin as well as moisture resistance are significantly reduced, making it unusable. From this point of view, the heat resistance of the ferrite powder produced by the present invention is significantly improved compared to conventional powders, and there is little variation in heat resistance from production to production. Next, regarding the moisture resistance (vi) above, the amount and rate of moisture adsorption are smaller than conventional ones, especially magnetite, and it is suitable for use in toners. Also, regarding this water absorption property, there is less variation in the value for each production compared to conventional products. Furthermore, the above
The miscibility with the resin (vii) is also good. This is because the ferrite powder of the present invention has a stable particle size at an average particle size of 1 μm or less, and can be controlled reliably and easily. In addition, in magnetic toner, it is also necessary that the affinity between the resin and the magnetic powder is high, but since the ferrite powder produced by the present invention has a stable surface condition,
It has a large and constant affinity with the resin, and therefore has the further advantage of not affecting the electrostatic properties of the resin in relation to (viii) above. Therefore, the use of a surface modifier, which is required for conventional magnetic powders, is not necessary or only needs to be used in a small amount. Finally, regarding the adverse effect on the resin (viii) above, there is no problem because the ferrite powder produced by the present invention exhibits very stable neutrality. Therefore, like magnetite manufactured using a conventional aqueous solution method, it inevitably contains alkali during its manufacture, which has a negative effect on the resin, requires labor to clean the alkali, and increases the manufacturing cost. There is no disadvantage that the alkali content varies from time to time, resulting in variations in the electrostatic properties of the toner. Note that when the amount of iron oxide exceeds 99.9 mol% in terms of Fe ₂ O ₃ value, the same drawbacks as the above-mentioned magnetite occur. If the amount is less than 51 mol %, the blackness will decrease critically, and when used alone, it cannot be used as a magnetic toner for practical use. As detailed above, the ferrite powder produced according to the present invention has extremely high performance overall compared to conventional magnetic powder. Among the ferrite powders produced according to the present invention, particularly preferred are the above M'O
Examples include those having a composition containing at least one of CoO, MnO, ZnO, and NiO as an essential component, and further including one to three of CuO, MgO, and CdO depending on the case. Further, iron oxide contains 55 to 99 mol%, more preferably 60 to 90 mol%, in terms of Fe ₂ O ₃ , and the remaining 45 to 1 mol%, more preferably 40 to 10 mol%, is M′O. Preferably, it consists of: In this case, M′O in the above stoichiometric composition is ZnO, CoO, NiO, MgO or MnO, a one-component system of ZnO and CoO, MnO and CoO,
NiO and ZnO, NiO and CoO, MgO and ZnO, CoO and
Binary system of MgO or MnO and ZnO, CoO and MnO
ZnO, NiO and CoO and ZnO, NiO and ZnO and CuO,
A more favorable effect is achieved when it is composed of a ternary system of MnO, ZnO, and CuO or CoO, ZnO, and MgO, or a quaternary system of CoO, MnO, ZnO, and NiO, etc. In such a ferrite powder, the magnetic characteristic values of maximum magnetizing force σm, coercive force Hc, and B-H product value are higher, the reflection spectrum of the powder is flatter, and the colorant is usually contained in the toner. This is because there is no need to mix them. Among these, the most preferable ones include those shown below. The following compositions are expressed as the molar ratio of iron oxide converted to Fe ₂ O ₃ and M oxide converted to MO. (M ⁽¹⁾ O) _a (Fe ₂ O ₃ ) _1-a (where M ⁽¹⁾ represents Mn, Zn, Ni, Co or Mg; Mn, Zn, Ni or Co, especially Mn, Zn or Ni is more preferable.Also, a is
It is 0.01-0.4, more preferably 0.1-0.3. ) (M ⁽²⁾ O) _b (ZnO) _c (Fe ₂ O ₃ ) _1-bc (Here, M ⁽²⁾ represents Mn, Ni, Co or Mg, and when Mn, Ni or Co More preferably, b+c is 0.01 to 0.45, more preferably 0.1 to 0.45.
0.45, b is 0.005-0.445, c is 0.05
-0.35, more preferably 0.1-0.3. ) (M ⁽³⁾ O) _d (CoO) _e (Fe ₂ O ₃ ) _1-de (where M ⁽³⁾ represents Mn, Ni or Mg,
More preferably, it is Mn or Ni. d+e
is 0.01 to 0.45, more preferably 0.1 to 0.45,
d is 0.005 to 0.445, and e is 0.005 to 0.2. ) (M ⁽⁴⁾ O) _f (CoO) _g (ZnO) _h (Fe ₂ O ₃ ) _1-fgh (here, M ⁽⁴⁾ represents Mn, Ni or Mg,
More preferably Mn or Ni, especially Ni. f+g+h is 0.01 to 0.45, more preferably 0.1
~0.45, f is 0.003~0.443, and g is
h is 0.003 to 0.25, and h is 0.004 to 0.4, more preferably 0.05 to 0.3. ) The present invention will be explained in more detail with reference to Examples below. Example 1 27.5 mol% of Mn ₃ O ₄ converted to MnO, CoO
12.5 mol % and 60 mol % of Fe ₂ O ₃ were blended using a wet ball mill for 5 hours. This blended slurry was made into granules using a spray dryer. The granules obtained were less than 20 mesh. The granules were then placed in a furnace and fired. The heating rate is 200
°C/hr, sintering temperature is 1350 °C for 3 hours, cooling rate
The temperature was set at 300°C/hr. In addition, the oxygen partial pressure in the atmosphere is
21% by volume at elevated temperatures up to 900℃, 900-1350
5% by volume when increasing temperature at ℃, 1.5% by volume when stable at 1350℃,
0.3% by volume when cooling from 1350 to 1100℃, 1100 to 150℃
The amount was adjusted to 0.01% by volume. After the temperature reached room temperature, the fired body was taken out from the furnace.
This fired body was coarsely pulverized for 0.5 hours using a stamp mill to reduce the particle size to 20 meshes or less, and then to an average particle size of 150 meshes or less using an atomizer. Then, using a wet attritor, the slurry concentration was 40%.
The mixture was ground for 40 hours. The powder obtained from this slurry was dried at 90° C. for 24 hours and then crushed using an atomizer to obtain ferrite powder A. The average particle size of the obtained powder was 0.55 μm, and the specific surface area was
The particle size distribution was 12.8 m ² /g, and the particle size distribution was very sharp. In addition, when the magnetic properties were measured under an external magnetic field of 1000 Oe, σm was 45 emu/g, and Hc was
It was 415Oe. Example 2 A fired body was obtained by blending, granulating, and firing in exactly the same manner as in Example 1, except that Fe ₂ O ₃ was blended at 80 mol % and ZnO was blended at 20 mol %. This fired body was medium-pulverized using an atomizer to a particle size of 10 μm or less, and then pulverized for 48 hours using a wet attritor at a slurry concentration of 50%. This slurry was dehydrated, dried at 90°C for 48 hours, and then crushed using an atomizer to obtain ferrite powder B. The average particle size of the obtained powder was 0.45 μm, and the specific surface area was
The particle size distribution was 17.2 m ² /g, and the particle size distribution was very sharp. Also, σm under an external magnetic field of 1000Oe is
65emu/g, Hc was 1850e. Example 3 Ferrite powder C was obtained under the same conditions as in Example 2, except that 6 mol% of CoO, 14 mol% of ZnO, and 80 mol% of Fe ₂ O ₃ were used as starting materials. The average particle diameter of the obtained powder was 0.45 μm, the specific surface area was 17.8 m ² /g, and the particle size distribution was very sharp. Also,
σm under 1000Oe external magnetic field is 62emu/g, Hc
was 310Oe. Example 4 Ferrite powder D was obtained under the same conditions as in Example 2, except that 3 mol% of CoO, 17 mol% of ZnO, and 80 mol% of Fe ₂ O ₃ were used as starting materials. The average particle size of the powder is 0.46 μm, the specific surface area is 16.5 m ² /g,
The particle size distribution was very sharp. Also,
σm under 1000Oe external magnetic field is 62emu/g, Hc
was 220Oe. Example 5 Ferrite powder E was obtained under the same conditions as in Example 2, except that 10 mol% of CoO, 10 mol% of ZnO, and 80 mol% of Fe ₂ O ₃ were used as starting materials. The average particle diameter of the powder was 0.43 μm, the specific surface area was 18.8 m ² /g, and the particle size distribution was very sharp. Also,
σm under 1000Oe external magnetic field is 50emu/g, Hc
was 360Oe. Example 6 Blending and granulation were carried out in the same manner as in Example 1, except that 20 mol% NiO and 80 mol% Fe ₂ O ₃ were used as starting materials, and then the mixture was heated and granulated during both heating and cooling. The firing was carried out under the same conditions as in Example 1, except that the oxygen partial pressure was kept constant at 0.1% by volume or less. It was mechanically crushed under the same procedure and conditions as in Example 1 to obtain ferrite powder F. The powder had an average particle size of 0.44 μm and a specific surface area of 11.9 m ² /g.
σm under 1000Oe external magnetic field is 50emu/g, Hc
was 220Oe. Example 7 Ferrite powder G was obtained in substantially the same manner as in Example 1, except that 20 mol% of MnO and 80 mol% of Fe ₂ O ₃ were used as starting materials. However, in the firing process
Sintered at 1320℃ for 3 hours with an oxygen partial pressure of 3% by volume or less, and an oxygen partial pressure of 0.1% by volume during cooling after sintering.
This differs from Example 1 in that the following values were kept constant and that fine pulverization was carried out using a wet attritor for 24 hours. The obtained powder had an average particle diameter of 0.53 μm, a specific surface area of 13.2 m ² /g, and a very sharp particle size distribution. Also, σ under an external magnetic field of 1000Oe
m was 60emu/g, and Hc was 150Oe. Example 8 Starting materials: 30 mol% MnO, 10 mol% ZnO,
Ferrite powder H was obtained under exactly the same conditions as in Example 7 except that 60 mol % of Fe ₂ O ₃ was used. The average particle diameter of the powder was 0.54 μm, the specific surface area was 12.3 m ² /g, and the particle size distribution was also very sharp. Under an external magnetic field of 1000 Oe, σm was 62 emu/g and Hc was 148 Oe. Example 9 Starting materials: 25 mol% MnO, 15 mol% ZnO,
Using 60 mol% of Fe ₂ O ₃ , sintering at 1350℃, 3
Ferrite powder was obtained under exactly the same conditions as in Example 7, except that the grinding was carried out for 40 hours and the pulverization was carried out using a wet attritor for 40 hours. The average particle size of the obtained powder was 0.47 μm, and the specific surface area was 16.2 m ² /g.
The particle size distribution is also very sharp.
σm under an external magnetic field of 1000Oe is 55eum/g, Hc is
It was 136 Oe. Example 10 NiO 15 mol%, ZnO 5 mol%, as starting materials
Ferrite powder J was obtained under exactly the same conditions as in Example 9, except that 80 mol % of Fe ₂ O ₃ was used and the powder was pulverized using a wet attritor for 48 hours. The average particle diameter of the obtained powder was 0.42 μm, the specific surface area was 19.9 m ² /g, the particle size distribution was also very sharp, and σm under an external magnetic field of 1000 Oe was
It was 53emu/g and Hc was 200Oe. Example 11 NiO 10 mol%, CoO 6 mol%, as starting materials
Ferrite powder was prepared under exactly the same conditions as Example 10, except that 4 mol% ZnO and 80 mol% Fe ₂ O ₃ were used, and the oxygen partial pressure during cooling after sintering was kept constant at 0.5% or less. I got K. The average particle size of the powder is
The particle size was 0.44 μm, the specific surface area was 18.3 m ² /g, the particle size distribution was very sharp, the σm under an external magnetic field of 1000 Oe was 56 emu/g, and the Hc was 300 Oe. Example 12 10 mol% of NiO and 10 mol% of CoO were used as starting materials, the oxygen partial pressure during cooling after sintering was kept constant at 0.05 mol% or less, and pulverization was carried out using a wet attritor for 24 hours. Ferrite powder L was obtained under exactly the same conditions as in Example 10 except for the above. Average particle size of powder is 0.53μm, specific surface area is 12.2
m ² /g, the particle size distribution is also very sharp, and σm under an external magnetic field of 1000 Oe is 44 emu / g.
Hc was 430 Oe. The present inventors conducted various experiments to confirm the effects of the ferrite powder produced according to the present invention.
An example is shown below. Experimental Example Magnetite A was produced by an aqueous solution method belonging to the prior art as follows. First, ferrous sulfate 7
Water salt was dissolved in 1 kg of pure water and placed in an airtight constant temperature reaction tank. At this time, the air in the upper margin was replaced with N ₂ gas to prevent oxidation. The water temperature was raised to 60°C, and a 6N aqueous solution of sodium hydroxide was added to cause a neutralization reaction, and when the water was neutralized, the addition of the sodium hydroxide solution was stopped. After obtaining iron hydroxide through a neutralization reaction, air was passed through it at a rate of 10% per minute to form spinel over 24 hours, and then heated at 80°C.
Magnetite powder A was obtained by drying for 48 hours. The average particle size of magnetite A obtained in this way is 0.2μ
m, the specific surface area was 28 m ² /g, and the particle size distribution was broader than the above ferrites A to L. Also, σm under an external magnetic field of 1000 Oe is 55 emu/g,
Hc was 80Oe. In addition, EPT manufactured by Toda Kogyo Co., Ltd., which is commercially available as magnetite powder using an aqueous solution method, is also available.
-1000 (average particle size 0.7 μm, specific surface area 4.5 m ² /g) and MTA-650 manufactured by Toda Kogyo Co., Ltd. (average particle size 0.5 μm,
(specific surface area: 19.9 m ² /g) were prepared and designated as magnetite B and magnetite C, respectively. In addition, magnetite B
and σm and Hc under an external magnetic field of 1000 Oe of C
are 65emu/g, 90Oe and 58emu/g, respectively.
It was 260Oe. Furthermore, for comparison, iron oxide-deficient ferrite H' and ferrite J' were similarly produced in correspondence to the above-mentioned ferrite H and ferrite J. Ferrite H′ MnO 30 mol%, ZnO 21 mol%, FeO ₂ O ₃ 49 mol%, average particle size 0.50 μm, specific surface area 18.4 m ² /g, σ
m at1000Oe=40emu/g, Hc=150Oe Ferrite J' NiO30 mol%, ZnO21 mol%, Fe ₂ O ₃ 49 mol%, average particle size 0.50 μm, specific surface area 17.8 m ² /g, σ
m at1000 Oe = 42 emu/g, Hc = 175 Oe Using these magnetites A to C, ferrites A to L of the present invention, and comparative ferrites H' and J', various properties thereof were measured. First, we measured the electrical and magnetic properties and color tone of ferrite A to F, H', J' and magnetite A.
-C are shown in Table 1 in comparison. Separately, heat resistance was measured. As for heat resistance, deterioration of magnetic properties and color tone due to heat was observed. Regarding the magnetic properties, Table 2 shows the deterioration of the maximum magnetizing force σm in an external magnetic field of 50000 Oe after being placed in an atmosphere of 80° C. and 120° C. for 1 hour, respectively, expressed as a percentage. Regarding the deterioration of color tone, the deterioration of the difference between the reflectance at 630 nm and the reflectance at 450 nm after being placed in an atmosphere at 150° C. for 1 hour is expressed as a percentage and is also shown in Table 2. Also,
After each powder was left under 10 ^-3 torr for 2 hours, it was exposed to the atmosphere at a relative humidity of 75%, and the water resistance was evaluated by observing the time change in the amount of water adsorption. The water absorption values after 10 hours and 70 hours are also shown in Table 2. Furthermore, each powder was placed in ion-exchanged water for 100g/
After stirring, the pH of the supernatant liquid was measured to evaluate the amount of residual alkali, that is, the adverse effect on the resin. The results are also shown in Table 2.

[Table] From the results in Tables 1 and 2, the ferrite powders A to F, H, and J produced according to the present invention have significantly superior performance in each characteristic compared to conventional magnetite A to C. Therefore, it can be seen that the overall performance is extremely high. The properties of the ferrites G, IL to L were almost the same as those of the ferrites A to F, H and J. Also,
In a comparison between ferrites H and J produced according to the present invention and comparative ferrites H' and J', Fe ₂ O ₃
It can be seen that when the amount of iron oxide is less than 51 mol%, the electromagnetic properties become low, and in particular, the degree of blackness becomes extremely low. In this case, it has been confirmed that ferrites H' and J' have color tones that are completely unsuitable for practical use as magnetic toners without colorants. The method for producing ferrite powder according to the present invention has been described above in detail. Next, the case where the ferrite powder produced according to the present invention is applied to magnetic toner will be described. The magnetic toner is made by mixing ferrite powder produced according to the present invention with a resin component. Various thermoplastic resins can be used as the resin component. Examples of thermoplastic resins include styrenes, vinylnaphthalene, vinyl esters, α-methylene aliphatic monocarboxylic acid esters, acrylonitrile, methacrylonitrile, acrylamide,
Any known resin component for magnetic toners can be effectively used, such as homopolymers such as vinyl ethers, vinyl ketones, and N-vinyl compounds, copolymers combining two or more of these, or mixtures thereof. It is preferable to have a glass transition point of about 10° C. and a weight average molecular weight of about 10 ³ to ^{10 5} .

【table】

[Table] The magnetic toner preferably contains 0.2 to 0.7 parts by weight of the ferrite powder per 1 part by weight of the resin component. To produce a magnetic toner, according to a known method, ferrite powder and a resin component are mixed in a ball mill or the like, then kneaded using heated rolls, cooled, and pulverized. Then, it may be classified as necessary. In this way, a magnetic toner having an average particle size of about 5 to 40 μm is produced. Note that a colorant such as a pigment or dye, a charge control agent, or the like may be added to the magnetic toner, if necessary. Images can be formed using such magnetic toner using known methods and devices. The present inventor created a magnetic toner using the ferrite powder produced according to the present invention, and conducted various experiments to determine the superiority of the toner. One example is listed below as a reference example. Reference example Ferrite powder A to L produced according to the present invention
Etsuso Petrochemical per 1 part by weight of ferrite
2.3 parts by weight of a styrene resin commercially available as Picolastic D-100 from Nippon Reichhold Co., Ltd. and 1 part by weight of a modified maleic acid resin commercially available as Betsukasite 1110 from Nippon Reichhold Co., Ltd. were mixed, and the mixture was ball milled. After cooling the minced meat, crushing and drying,
It was classified to create 12 types of toners with an average particle size of 15 μm. Next, an electrostatic image was formed on a selenium photosensitive plate drum, developed using the above toner by a magnetic brush method according to a conventional method, and then transferred onto plain paper and fixed, and a good image was obtained with each toner. I was able to get it. Further, when development and transfer were repeated, good images were always reproduced. Furthermore, even when the selenium plate was replaced with a zinc oxide photosensitive plate, similarly good images were obtained.

Claims (1)

[Claims] 1 Iron and/or iron oxide in an amount calculated to be 99.9 to 51 mol% when converted to Fe ₂ O ₃ , and MO (M represents Mn, Ni, Co, Mg, Cu, Zn or Cd). manganese, nickel, in an amount calculated to be 0.1 to 49 mol% when converted to
At least one of oxides of cobalt, magnesium, copper, zinc, or cadmium or compounds that become oxides upon heating are blended; then granulated; and then fired in an atmosphere with controlled oxygen partial pressure. ; followed by mechanical grinding:
99.9 to 51 mol% iron oxide calculated as Fe ₂ O ₃ ,
0.1 to 49 mol% converted to MO (M is the same as above)
manganese oxide, nickel oxide, cobalt oxide,
Consists of at least one of magnesium oxide, copper oxide, zinc oxide or cadmium oxide,
A method for producing transferable ferrite powder for electrophotographic magnetic toner, which is composed of ferrite particles imparted with a spinel-type structure by firing and has an average particle size of 1 μm or less.