JPH0243176B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a transferable electrophotographic magnetic toner and an image forming method using the same. 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 needs to have a value of σm×H of about 0.6×10 ⁴ or more. (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 that the particles have a fine particle size of 1 μm or less, have a sharp particle size distribution, and be stable between production lots. (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 widely used as a pigment (hereinafter referred to as magnetite produced by an aqueous solution method), which is applied to a 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 object of the present invention is to solve all of these drawbacks of conventional magnetic powders for electrophotographic magnetic toners, and to provide a magnetic toner containing high-performance magnetic powders that satisfies all of the required characteristics (i) to (viii) above. With the goal. The present inventors have conducted various studies regarding these objectives, and have discovered that an iron-rich spinel structure ferrite having a specific component and composition can provide a high-performance magnetic toner that achieves the above objectives. This has led to the present invention. First, the ferrite powder contained in the magnetic toner of the present invention will be explained. The ferrite powder 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,
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 (representing Ni, Co, Mg, Cu, Zn, or Cd) It is an iron-rich ferrite powder with a spinel-type structure consisting of. 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 0.002
~0.980, where M'O represents one to six types of MO in total of 1 mole], and there is almost no deviation from the stoichiometry. Note that the ferrite powder contained in the toner of the present invention contains impurities such as Al ₂ O ₃ , Ca ₂ O ₃ ,
It may contain Cr ₂ O ₃ , V ₂ O ₅ , CeO ₂ , SnO ₂ , TiO ₂ and the like 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. Ferrite particles having such a composition are given a spinel structure by firing by a so-called dry method, as described below. The average particle size of the ferrite powder contained in the toner of the present invention is approximately 1 μm or less, and is 0.2 to 1 μm.
It is preferably about 0.80 μm. Further, it is preferable that the particle size distribution is sharp. The ferrite powder contained in the toner of the present invention satisfies all of the properties required for magnetic toner powders (i) to (viii) above, and has a comprehensively higher quality than conventional powders. It's about performance. 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 heat resistance (v) above, the ferrite powder contained in the toner of 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. Suitable as magnetic powder for magnetic toner. The degree of deterioration of electrical and magnetic properties and color tone after heating below about 180℃ is significantly reduced to one to several tenths of that of magnetite produced using conventional aqueous solutions. There is. Generally, 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 if magnetite is produced using an aqueous solution method, the same level of heat resistance can be obtained if the average particle size is several times or more the particle size of the ferrite powder contained in the toner of the present invention. However, since the particle size becomes large in this case, the degree of mixing with the resin, affinity, and moisture resistance are significantly reduced, making it unusable. From this point of view, the heat resistance of the ferrite powder contained in the toner of the present invention is significantly improved compared to conventional ones, 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, it also has good miscibility with the resin (vii) above. 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 necessary that the resin and magnetic powder have a high affinity, but since the ferrite powder contained in the toner of the present invention has a stable surface state, it is necessary that the ferrite powder has a high affinity with the resin. , and is constant, and thus has the further advantage of not affecting the electrostatic properties of the resin in connection with (viii) above. Therefore, the use of a surface modifier, which is required with 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 contained in the toner of 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 be critically reduced, and when used alone, it cannot be used as a magnetic toner for practical use. As detailed above, the ferrite powder contained in the toner of the present invention has extremely high performance overall compared to conventional magnetic powder. Among the ferrite powders contained in the toner of the present invention, particularly preferred are the above-mentioned ferrite powders.
Examples of M'O 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 unicomponent system ZnO and CoO, MnO and
CoO, NiO and ZnO, NiO and CoO, MgO and ZnO,
Binary system of CoO and MgO or MnO and ZnO, CoO and
MnO and ZnO, NiO and CoO and ZnO, NiO and ZnO
CuO, MnO and ZnO and CuO or CoO and ZnO
A more favorable effect is achieved when it is composed of a ternary system of MgO, 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 (where 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 ferrite powder contained in the toner of the present invention detailed above is manufactured according to the following manufacturing method as the most preferred embodiment. The first step in the manufacturing method is the blending of starting materials. As starting materials, one or more of 99.9 to 51 mol% Fe ₂ O ₃ and a total of 0.1 to 49 mol % MO (M is the same as above) are usually used. In this case, instead of Fe ₂ O ₃ , 99.9 ~ 51 converted to Fe ₂ O ₃
One or more of Fe, FeO and Fe ₂ O ₃ can be used in an amount such that the mole %. Also, by using other oxides of M instead of MO or by heating
Compounds that can serve as MOs, 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 blending increases the degree of mixing of the raw materials, eliminates causes of performance deterioration such as compositional variations and uneven properties, and improves the quality and stability of the magnetic powder. After this, the slurry state proceeds to the next granulation step, but in some cases, the slurry may be dried in advance before the granulation step to keep the water content at 10% or less. Depending on the starting material used, the temperature may be lower than 1000°C, e.g. 800 to 1000°C.
The material may be pre-fired for 1 to 3 hours, and then ground to a particle size of several tens of micrometers or less after firing. 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. This yields the ferrite powder of the present invention having an average particle size of 1 μm or less, usually 0.2 to 0.8 μm. 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 should be approximately 50% or less, and 10%
By milling for ~100 hours, a powder with an average particle size of 0.2-0.8 μm is obtained. This powder is dried at a temperature below 100°C to reduce the moisture content, preferably
After reducing the content to 0.7% or less, the ferrite powder of the present invention is obtained by crushing it into primary particles using an atomizer or the like. 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. The ferrite powder of the present invention will be explained in more detail below using synthesis examples and examples. Synthesis 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 elemental 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 dropped to room temperature, the fired body was taken out of 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 12.8.
m ² /g, and the particle size distribution was very sharp. Furthermore, when the magnetic properties were measured under an external magnetic field of 1000 Oe, σm was 45 emu/g and Hc was 415 Oe. Synthesis Example 2 A fired body was obtained by blending, granulating and firing in the same manner as in Example 1, except that Fe ₂ O ₃ was blended at 80 mol % and ZnO 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 0.45μm, 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. Synthesis 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. Synthesis 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 diameter of the powder was 0.46 μm, the specific surface area was 16.5 m ² /g, and the particle size distribution was very sharp. Also,
σm under 1000Oe external magnetic field is 62emu/g, Hc
was 220Oe. Synthesis 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. Synthesis Example 6 Blending and granulation were carried out in the same manner as in Example 1, except that 20 mol % of NiO and 80 mol % of Fe ₂ O ₃ were used as starting materials. 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 0.54 μm and a specific surface area of 11.9 m ² /g.
σm under 1000Oe external magnetic field is 50emu/g, Hc
was 220Oe. Synthesis 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, σm under an external magnetic field of 1000Oe
was 60emu/g, and Hc was 150Oe. Synthesis Example 8 Ferrite powder H was obtained under exactly the same conditions as in Example 7, except that 30 mol% MnO, 10 mol% ZnO, and 60 mol% Fe ₂ O ₃ were used as starting materials. The average particle size of the powder is 0.54 μm, the specific surface area is 12.3 m ² /g, and the particle size distribution is also very sharp, with a particle size of 1000 Oe.
σm under external magnetic field is 62emu/g, Hc is 148Oe
It was hot. Synthesis Example 9 Starting materials: 25 mol% MnO, 15 mol% ZnO,
Fe ₂ O ₃ 60 mol % was used, calcination was performed at 1350℃, 3
Ferrite powder I 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, the specific surface area was 16.2 m ² /g, and the particle size distribution was also very sharp.
Under an external magnetic field of 1000Oe, σm is 55emu/g, and Hc is
It was 136Oe. Synthesis example 10 Starting materials: 15 mol% NiO, 5 mol% ZnO,
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 the σm under an external magnetic field of 1000 Oe was 53 emu/g.
g and Hc were 200 Oe. Synthesis Example 11 Starting materials: 10 mol% NiO, 6 mol% CoO,
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, σm was 56 emu/g under an external magnetic field of 1000 Oe, and Hc was 300 Oe. Synthesis Example 12 10 mol% of NiO and 10 mol% of CoO were used as starting materials, the oxygen partial pressure during cooling after firing was kept constant at 0.05 mol% or less, and pulverization was performed for 24 hours using a wet attritor. Ferrite powder L was obtained under the same conditions as in Example 10 except for the above. The average particle size of the powder is 0.53 μm, and the specific surface area is 12.2 m ² /
g, the particle size distribution is also very sharp,
Under an external magnetic field of 1000Oe, σm is 44emu/g, and Hc is
It was 430Oe. The present inventors conducted various experiments to confirm the effects of the ferrite powder contained in the toner of 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
The particle size was 0.2 μm, the specific surface area was 28 m ² /g, and the particle size distribution was broader than that of the ferrites A to L.
Also, σm under an external magnetic field of 1000 Oe is 55 emu/g,
Hc was 80 Oe. 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 260 Oe. 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%, Fe ₂ O ₃ 49 mol%, average particle size 0.50 μm, specific surface area 18.4 m ² /g, σm
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, σm
at1000Oe=42emu/g, Hc=1750e These magnetites A to C, ferrites A to L of the present invention, and comparative ferrites H' and J' were used to measure their various properties. 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. Regarding 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 5000 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. In addition, after leaving each powder under 10 ^-3 torr for 2 hours, relative humidity 75
The water resistance was evaluated by exposing the sample to the atmosphere maintained at a certain temperature and observing the time change in the amount of moisture adsorbed. The water absorption values after 10 hours and 70 hours are also shown in Table 2. Further, add 100g of each powder to ion-exchanged water.
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】

[Table] From the results in Tables 1 and 2, the ferrite powders A to F, H, and J according to the present invention have significantly superior performance in each characteristic compared to conventional magnetites A to C. Therefore, it can be seen that the overall performance is extremely high. In addition, the above ferrite G, I
Regarding ~L, its properties are ferrite A~
It was almost equivalent to F, H, and J. Furthermore, in a comparison between ferrites H and J according to the present invention and comparative ferrites H' and J', an iron oxide content of less than 51 mol% in terms of Fe ₂ O ₃ leads to poor electromagnetic properties, especially blackness. It can be seen that the value is 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 ferrite powder and the method for producing the same according to the present invention have been described in detail above. Next, the case where the above-mentioned ferrite powder is applied to a magnetic toner will be described. The magnetic toner of the present invention is made by mixing ferrite powder and a resin component. Various thermoplastic resins can be used as the resin component. Examples of thermoplastic resins include homopolymers such as styrenes, vinylnaphthalene, vinyl esters, esters of α-methylene aliphatic monocarboxylic acids, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers, vinyl ketones, and N-vinyl compounds. , a copolymer combining two or more of these, or a mixture thereof, which are known as resin components for magnetic toners, can be effectively used.
Those having a weight average molecular weight of about 10 ³ to ^{10 5} are preferred.

[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, ferrite powder and a resin component are mixed in a ball mill or the like, kneaded using heated rolls, cooled, and pulverized according to a known method. Then, it may be classified as necessary. In this way, the magnetic toner of the present invention 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 the magnetic toner of the present invention using known methods and devices. EXAMPLES Next, the present invention will be explained in more detail by giving examples of the present invention. Using the above-mentioned ferrite powders A to L, 2.3 parts by weight of a styrene resin commercially available as Picolastic D-100 from Etsuso Petrochemical Co., Ltd. and Betsukasite 1110 from Nippon Reichhold Co., Ltd. per 1 part by weight of ferrite. Mix it with 1 part by weight of a commercially available modified maleic acid resin, apply it to a ball mill, cool it, grind it, dry it, and classify it to determine the average particle size.
Twelve types of 15 μm toner were created. 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. Homopolymers of styrenes, vinylnaphthalene, vinyl esters, esters of α-methylene aliphatic monocarboxylic acids, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers, vinyl ketones, and N-vinyl compounds. , or a copolymer made by combining two or more of these monomers, or a vinyl thermoplastic resin component formed from a mixture thereof, iron oxide of 99.9 to 51 mol% in terms of Fe ₂ O ₃ , and MO (M teeth
represents Mn, Ni, Co, Mg, Cu, Zn or Cd)
It has 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, and has an average particle size of 1 μm or less. A transferable electrophotographic magnetic toner comprising ferrite particles. 2. An electrophotographic magnetic toner containing 0.2 to 0.7 parts by weight of ferrite particles per 1 part by weight of the thermoplastic resin component. 3 The thermoplastic resin component is a styrene resin,
Claim 1 containing a charge control agent
The electrophotographic magnetic toner according to item 1 or 2. 4 Ferrite particles contain 55 to 99 mol% iron oxide in terms of Fe ₂ O ₃ and 45 to 1 mol % in terms of MO of manganese oxide, nickel oxide, cobalt oxide, magnesium oxide, copper oxide, zinc oxide, or The electrophotographic magnetic toner according to claim 1, which is formed with at least one kind of cadmium oxide. 5 Thermoplastic resin component and in terms of Fe ₂ O ₃
99.9 to 51 mol% iron oxide and MO (M is Mn, Ni,
0.1 to 49 mol% manganese oxide, nickel oxide,
It has a spinel structure consisting of at least one of cobalt oxide, magnesium oxide, copper oxide, zinc oxide, or cadmium oxide, and has an average particle size of 1 μm.
An electronic image forming method comprising: developing an electrostatic image on a photoreceptor using a magnetic toner containing ferrite particles as described below, and then transferring and fixing the toner image onto a carrier. 6. The image forming method according to claim 5, wherein the electrostatic image is developed with a magnetic brush formed of magnetic toner. 7 The thermoplastic resin component is a homopolymer of styrenes, vinylnaphthalene, vinyl esters, esters of α-methylene aliphatic monocarboxylic acids, acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers, vinyl ketones, N-vinyl compounds , or a copolymer obtained by combining two or more of these monomers, or a mixture thereof. 8. The image forming method according to claim 5, wherein the ferrite particles are contained in an amount of 0.2 to 0.7 parts by weight per 1 part by weight of the thermoplastic resin component. 9 The thermoplastic resin component is a styrene resin,
The image forming method according to claim 5 or 8, characterized in that the image forming method contains a charge control agent. 10 Ferrite particles are 55 to 99 in terms of Fe ₂ O ₃
mol% of iron oxide and 45 to 1 mol% as MO.
manganese oxide, nickel oxide, cobalt oxide,
The image forming method according to claim 5, wherein the image forming method is formed with at least one of magnesium oxide, copper oxide, zinc oxide, and cadmium oxide.