JP3248051B2 - Magnetic powder for external addition and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder and a method for producing the same, and the magnetic powder has an excellent filming preventing effect, and is particularly useful as a magnetic powder for external addition to an electrophotographic toner. It is expensive.

[0002]

2. Description of the Related Art In an electrophotographic developing method using toner, high image quality and high resolution are required, and in recent years, in addition to the above-mentioned high image quality and high resolution, copying has been performed. The demand for higher (fixing) speed is also increasing. Therefore, a toner that can be fixed at a low temperature is required, and a toner using a resin having a low softening point is being developed.

However, when the copying speed is increased in the electrophotographic developing method, the amount of toner remaining on the surface of the photoreceptor increases, and therefore, there is a problem that the occurrence rate of a toner film (filming) increases. Image quality formation (development, transfer,
As (fixing) is repeated, the amount of toner remaining on the photoreceptor surface increases, and the occurrence rate of filming also increases.
As a result, the electrical characteristics of the photoreceptor deteriorate, image quality becomes dirty, and the like. This phenomenon increases as the resin having a lower softening point is used. In order to solve such a problem, as a general method, a method of providing a cleaning device in an electrophotographic developing device and cleaning residual toner on a photoconductor has been performed. This method uses a fur brush cleaning method, a blade cleaning method, a magnetic brush cleaning method, or the like, in which the brush is rotated at a high speed to scrape off the residual toner on the photoconductor.

However, when the surface of the photoreceptor is cleaned by the above-described cleaning method, the surface of the photoreceptor is damaged if the abrasiveness of the brush or the like is strong, toner is embedded in the damaged portion, and a dot-like image is formed on the transferred image. This can cause stains.

[0005] Further, improvement of the cleaning property has been attempted by changing the charge amount and the specific resistance of the toner or by increasing the particle diameter of the toner to improve the fluidity. Has not been obtained.

That is, generally, toner is manufactured by a pulverization method.
A binder resin, a charge controlling agent, a colorant, and the like are mixed in a predetermined mixing ratio, melt-kneaded, and the resulting mass is dried, pulverized by a mechanical means such as a jet mill, and then classified to a predetermined particle size. In order to further improve the fluidity, the surface of the toner is treated with hydrophobic silica or the like. However, since the magnetic powder is exposed on the surface of the toner manufactured by the above-mentioned pulverization method, it is affected by the moisture in the air, which adversely affects the charge amount and causes a decrease in fluidity.

In order to solve the above-mentioned drawbacks, the toner produced by the pulverization method is further sprayed in a heated air stream to make the toner spherical, thereby improving the performance such as developability, transferability, transportability and fixability. Things have also been done. As a result, a stable toner such as particle size, particle size distribution, magnetic properties and surface physical properties can be obtained, and important factors such as developability, transferability, transportability and fixability are improved, but filming phenomenon is prevented. Is still insufficient.

It has also been proposed to add an octahedral magnetite produced by an ordinary method to a toner as an external additive. However, when the octahedral magnetite manufactured by the usual method is added to the toner, the dispersion state of the toner becomes worse, and the residual magnetic flux density increases, so that the toner powder aggregates and adheres to the surface of the photoreceptor, At present, it becomes a black spot at the time of transfer and fixing, and does not play a role as an agent for preventing the filming phenomenon.

Accordingly, an object of the present invention is to provide a magnetic powder for external addition of an electrophotographic toner which is useful for preventing a filming phenomenon caused by using a resin having a low softening point in the production of a toner, and its production. It is to provide a method.

[0010]

The present inventors have conducted intensive studies and have found that the average particle diameter, the geometric standard deviation of the particle diameter, and the FeO / F
It has been found that the magnetic powder for external addition of an electrophotographic toner composed of magnetite having a specific range of e ₃ O ₄ (weight ratio) can achieve the above object.

The present invention has been made based on the above findings, and has an average particle diameter of 0.3 to 0.5 μm, a geometric standard deviation of the particle diameter of 1.5 or less, and FeO / Fe ₃ O.
₄ An object of the present invention is to provide a magnetic powder for external addition of an electrophotographic toner, which comprises magnetite having a weight ratio of 3/97 to 15/85.

The present invention also provides a preferable method for producing the externally added magnetic powder of the electrophotographic toner described above, wherein a reaction vessel purged with nitrogen gas has a concentration of 1.4 to 2.0 mol / l in a reaction tank. An alkali aqueous solution and a ferrous chloride aqueous solution having a concentration of 0.5 to 1.2 mol / l are mixed with a molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride). Is added to make a mixed solution, and then the mixed solution is replaced with an oxidizing gas (air) while the oxidizing gas (air) is blown into the reaction tank. While maintaining the temperature at 70-100 ° C.
After stirring and mixing for a period of time to generate magnetite, the mixed solution containing the generated magnetite is filtered, washed with water, dried and crushed to obtain magnetite, and then the magnetite is subjected to an oxide film forming treatment. And a method for producing a magnetic powder for external addition of an electrophotographic toner.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, the magnetic powder for external addition of the electrophotographic toner of the present invention will be described in detail. The magnetic powder for external addition of the electrophotographic toner of the present invention is made of magnetite having an average particle diameter, a geometric standard deviation of the particle diameter, and FeO / Fe ₃ O ₄ (weight ratio) in a specific range.

The above-mentioned specific average particle diameter of the magnetic powder for external addition of the electrophotographic toner of the present invention is 0.3 to 0.5 μm, preferably 0.35 to 0.45 μm. If the average particle size exceeds 0.5 μm, the polished effect of the octahedral projections is too strong, and the surface of the photoconductor is damaged. On the other hand, if the thickness is less than 0.3 μm, the polishing effect is weak, and the magnetic powder is agglomerated and adheres to the surface of the photoreceptor.

The geometric standard deviation of the specific particle diameter of the magnetic powder for external addition of the electrophotographic toner of the present invention is 1.5 or less, preferably 1.3 or less. That is, the magnetic powder for external addition of the electrophotographic toner of the present invention has a sharp particle size distribution. If the geometric standard deviation of the particle size exceeds 1.5, the polishing effect is weak, and the magnetic powder agglomerates and adheres to the surface of the photoreceptor, and does not play a role as an agent for preventing the filming phenomenon.

In addition, the specific FeO / Fe ₃ O ₄ (weight ratio) of the magnetic powder for external addition of the electrophotographic toner of the present invention is used.
Is 3/97 to 15/85, preferably 6/94 to 11 /
89. FeO / Fe ₃ O ₄ (weight ratio) is 3/97
If it is less than ₃ , the magnetite which is black powder is Fe ₂ O ₃
And the dispersibility is improved, but the reddish color is increased and causes poor image quality. On the other hand, when the ratio of FeO / Fe ₃ O ₄ (weight ratio) exceeds 15/85, the magnetic powder has a strong magnetism and a strong cohesive force, and the magnetic powder adheres to the surface of the photoconductor, thereby damaging the surface of the photoconductor.

The magnetic powder for external addition of the electrophotographic toner of the present invention contains an appropriate amount of a divalent metal ion such as Mn ²⁺ , Zn ²⁺ , Ni ²⁺ , Cr ²⁺ or Cu ^2+. You may. Examples of the divalent metal ion source include sulfates, chlorides, and nitrates thereof. When the divalent metal ion is contained in the magnetic powder for external addition of the electrophotographic toner of the present invention, its content is preferably 5 to 15 mol based on the total amount of FeO and Fe ₃ O _4. % (3.4 to 10.3% by weight).

It is preferable that the magnetic powder for external addition of the electrophotographic toner of the present invention has an oxide film formed on the surface. This is because by performing the oxide film forming treatment, the effect of preventing filming of the magnetic powder for external addition of the electrophotographic toner is further improved. Note that the oxide film forming process will be described in detail in the description of the “manufacturing method” described later.

The shape of the magnetic powder for external addition of the toner for electrophotography of the present invention is not particularly limited, but the particle size distribution is sharp and constant in size from the viewpoint of polishing the toner or toner film remaining on the surface of the photoreceptor. It is preferable to have.

The magnetic powder for external addition of the electrophotographic toner of the present invention can be used as a magnetic powder for external addition of an electrophotographic toner, a toner charge controlling agent and a magnetic material for a one-component toner. It has an excellent anti-minging effect, so it is added to toners such as the two-component developing method, non-magnetic one-component developing method, and one-component developing method used in the electrophotographic developing method, and is mixed and adhered to the toner surface to form an electrophotographic toner. It can be used as a magnetic powder for external addition. The mixing means is not particularly limited, and for example, a Henschel mixer or the like can be used. When the magnetic powder for external addition of the electrophotographic toner of the present invention is used by being mixed and adhered to the surface of the toner, the amount used is preferably 0.05 to 5.0% by weight based on the total amount of the toner. .

Next, a method for producing the magnetic powder for external addition of the toner for electrophotography of the present invention, which is a preferred method for producing the magnetic powder for external addition of the toner for electrophotography of the present invention, will be described.
According to the method for producing an externally added magnetic powder of an electrophotographic toner of the present invention, a concentration of 1.4 to 2.times.
0 mol / l alkali hydroxide aqueous solution and concentration 0.5 to
A 1.2 mol / l aqueous solution of ferrous chloride is mixed with a molar ratio of alkali hydroxide and ferrous chloride (moles of alkali hydroxide /
(Moles of ferrous chloride) to be 2 to 3 to form a mixed solution. Then, the inside of the reaction tank is replaced with an oxidizing gas (air), and the oxidizing gas (air ), While stirring and mixing the mixed solution for 7 to 10 hours while maintaining the temperature at 70 to 100 ° C. to generate magnetite. Further, the mixed solution containing the generated magnetite is filtered, washed with water, and dried. Crushing to obtain magnetite, and then subjecting the magnetite to an oxide film forming treatment.

The method for producing the magnetic powder for external addition of the electrophotographic toner according to the present invention is as follows. First, an aqueous solution of an alkali hydroxide having a concentration of 1.4 to 2.0 mol / l is placed in a reaction vessel purged with nitrogen gas. An aqueous solution of ferrous chloride having a concentration of 0.5 to 1.2 mol / l has a molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride) of 2 to 2. 3 to obtain a mixed solution.

As the reaction tank, a wet reaction tank is preferably used, and among them, a stirring reaction tank, a circulation reaction tank and a bubble column are particularly preferably used. The concentration of the aqueous alkali hydroxide solution added to the mixed solution is 1.4 to 2.0.
Mol / l, preferably 1.6 to 2.0 mol / l. When the concentration of the aqueous alkali hydroxide solution is less than 1.4 mol / l, the particle size of the generated magnetite becomes small,
The particle size distribution becomes wider. On the other hand, if it exceeds 2.0 mol / l, the particle size of the produced magnetite increases, but the particle size distribution increases. Examples of the alkali hydroxide include, for example, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide and hydroxides of alkaline earth metals such as magnesium hydroxide and calcium hydroxide. In the present invention, these alkali hydroxides can be used alone or in combination of two or more.

The concentration of the aqueous ferrous chloride solution added to the above mixed solution is 0.5 to 1.2 mol / l, preferably 0.7 to 1.1 mol / l. When the concentration of the aqueous ferrous chloride solution is less than 0.5 mol / l, the productivity of magnetite is inferior, and when it exceeds 1.2 mol / l, the viscosity of the reaction slurry increases, and the particle size distribution of the produced magnetite is wide. Become. Further, Mn ²⁺ , Zn
^A divalent metal ion such as ²⁺ , Ni ²⁺ , Cr ²⁺ or Cu ²⁺ may be contained. Examples of the divalent metal ion source include sulfates, chlorides, and nitrates thereof.
When the divalent metal ion is contained in the ferrous chloride aqueous solution, the content is based on the total amount of ferrous chloride.
Preferably 5 to 15 mol% [3.4 to 10.3 wt%
(In terms of sulfate, chloride and nitrate concentrations)].

The molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride) in the above mixed solution is 2 to 3, preferably 2 to 2.5. It is. If the molar ratio of the alkali hydroxide and ferrous chloride exceeds 3, the particle size of the produced magnetite will increase, but the viscosity of the reaction slurry will increase and the particle size distribution of the produced magnetite will widen. On the other hand, when the molar ratio is less than 2, the viscosity of the reaction slurry decreases, and the particle size of the generated magnetite decreases.

Next, the inside of the reaction tank containing the mixed solution is replaced with an oxidizing gas (air), and while the oxidizing gas (air) is being blown into the reaction tank, the mixed solution is reduced to 70 to 100%.
Stirring and mixing for 7 to 10 hours while maintaining the temperature at 100 ° C.,
Generates magnetite.

As the oxidizing gas, air is preferably used, but oxygen can also be used.

The blowing rate of the oxidizing gas into the reaction tank varies depending on the reaction tank, the amount of the reaction solution, the concentration of the reaction solution, and the like. For example, in a 450-liter reaction tank, the concentration of the alkali hydroxide is 480 mol / l. When the concentration of ferrous chloride is 180 l, the linear velocity is preferably in the range of 45 to 55 cm / min. If the blowing speed of the oxidizing gas does not reach the above range, the particle size of the generated magnetite increases,
The particle size distribution becomes too large to achieve the object of the present invention. Also, when the blowing speed of the oxidizing gas exceeds the above range, the particle size of the generated magnetite becomes small. The particle size of the generated magnetite can also be changed by appropriately changing the blowing speed.

The reaction temperature of the mixed solution contained in the reaction tank is 70 to 100 ° C., preferably 85 to 95 ° C. If the reaction temperature is lower than 70 ° C., goethite is mixed into the product, and if it exceeds 100 ° C., it is industrially undesirable.

The above reaction time is 7 to 10 hours, preferably 7 to 8 hours. If the reaction time is less than 7 hours, the reaction speed is high, the particle size of the generated magnetite is smaller than the target particle size, and if the reaction time is longer than 10 hours, the reaction speed is slow, so that the particle size of the generated magnetite is smaller than the target particle size. growing.

The mixed solution containing magnetite thus obtained is filtered, washed with water, dried and crushed to obtain magnetite. The magnetite thus obtained has an effect of preventing filming, but the effect of preventing filming is further improved by subjecting the magnetite to “an oxide film forming treatment” described later. When magnetite is used as an external additive for electrophotographic toner,
It is necessary to uniformly adhere the toner particles to individual surfaces, and for that purpose, the dispersibility of magnetite becomes a problem. The magnetite obtained as described above is made of FeO
, Which is about 22 to 32% and has strong magnetism, has a strong cohesive force, and may cause damage to the photoreceptor surface.

The method of forming an oxide film on magnetite is not particularly limited, and it can be performed by a conventionally known method. For example, there is a method of firing magnetite in an electric firing furnace in an air atmosphere. For firing, for example,
The magnetite obtained as described above is heated at 55 to 75 ° C / h.
A method of baking at a temperature of 170 to 230 ° C. for 8 to 15 hours at a heating rate of r may be used. The magnetite fired in this manner is cooled and crushed again to obtain the magnetic powder for external addition of the electrophotographic toner of the present invention.
Thus outside the electrophotographic toner obtained添用magnetic powder FeO / Fe ₃ O ₄ (weight ratio) 3 / 97-15
Since the ratio is / 85, the dispersibility is improved, and the effect of preventing filming is further improved.

[0033]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples.

Example 1 250 l of a 1.87 mol / l sodium hydroxide aqueous solution was added to a stirred reaction vessel having a gas injection pipe while nitrogen gas was passed at a linear velocity of 25.5 cm / min. Next, the temperature of the solution was raised to 90 ° C. while stirring the solution in the reaction tank. next,
200 l of an aqueous solution of ferrous chloride having a concentration of 0.9 mol / l was added to the reaction vessel to obtain a mixed solution. At this time, the concentration of hydroxylated hydroxide in the reaction vessel was 480 mol / l, the concentration of ferrous chloride was 180 mol / l, and the molar ratio of alkali hydroxide to ferrous chloride (the alkali hydroxide (Moles / moles of ferrous chloride) is 2.60.

The mixed solution thus obtained in the reaction tank was stirred and mixed for 30 minutes, and ferrous chloride was replaced with Fe (OH) ₂
And Next, while maintaining the temperature of the mixed solution in the reaction tank at 90 ° C. and stirring the mixture for 8 hours while blowing air at a linear velocity of 50 cm / min, magnetite was produced. The mixed solution containing magnetite thus generated was filtered, washed with water, and crushed by a conventional method to obtain magnetite. The magnetite particles thus obtained were octahedral. Next, the magnetite particles obtained as described above were treated with an electric firing furnace in an air atmosphere at a heating rate of 60 ° C./hr for 18 minutes.
Baking was performed at a temperature of 0 ° C. for 10 hours to perform an oxide film forming process. Next, the magnetite particles on which the oxide film was formed were cooled and crushed again to obtain a magnetic powder for external addition of the electrophotographic toner of the present invention.

The obtained magnetic powder for external addition of the electrophotographic toner was evaluated according to the following [Evaluation criteria for magnetic powder for external addition of electrophotographic toner]. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used for the reaction and the total amount of each in the mixed solution, the number of moles of the alkali hydroxide /
Table 1 shows the molar number of ferrous chloride, the average particle diameter and the geometric standard deviation of the magnetic powder for external addition of the obtained electrophotographic toner, and the magnetic powder for external addition of the obtained electrophotographic toner. Fe
The values of O / Fe ₃ O ₄ (weight ratio) and the results of the cleaning effect test are shown in [Table 2].

[Evaluation Criteria for Externally Added Magnetic Powder of Electrophotographic Toner] (1) Average Particle Size Photographs of the externally added magnetic powder of the electrophotographic toner were taken with a scanning electron microscope (magnification: 15, 15. After magnifying the photograph with a copier, a parallel line of a predetermined width was drawn, and the particle size of 150 particles on the line was visually measured.
The particle size was divided by the magnification to obtain a particle size value, and the average value was determined. (2) Geometric standard deviation From the particle diameters of 150 magnetic powders measured to determine the average particle diameter, it was determined using the following equation.

[0038]

(Equation 1)

(3) FeO / Fe ₃ O ₄ (weight ratio) Determined by a method for determining ferric oxide in iron ore (M-8213). (4) Cleaning Effect 1.0 part by weight of the magnetic powder for external addition of the toner for electrophotography is mixed with 100 parts by weight of the toner using a Henschel mixer and attached to the toner surface.
After copying 30,000 sheets, the surface of the photoconductor immediately after being cleaned is visually observed, and the presence or absence of fouling on the surface of the photoconductor and the cleaning effect are visually observed. Done. Existence of attachments, scratches ○: good. Δ: Somewhat good. ×: Bad. Cleaning effect A: Especially effective. ○: Effective. △: Some effect. ×: no effect.

Example 2 As an aqueous solution of ferrous chloride, a concentration of 0.09 mol / l was further added.
Example 1 except that an aqueous solution containing manganese chloride was used.
In the same manner as in the above, a magnetic powder for external addition of the electrophotographic toner of the present invention was obtained. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used for the reaction and the respective concentrations in the mixed solution,
Table 1 shows the number of moles of alkali hydroxide / the number of moles of ferrous chloride, the average particle size and the geometric standard deviation of the magnetic powder for external addition of the obtained electrophotographic toner. FeO / Fe ₃ O ₄ (weight ratio) of magnetic powder for external addition of toner
The values and the results of the cleaning effect test are shown in [Table 2].

Example 3 As an aqueous solution of sodium hydroxide, a concentration of 1.44 mol / l
And the molar ratio of alkali hydroxide and ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride) was set to 2.00, using the same aqueous solution as in Example 1. A magnetic powder for external addition of the electrophotographic toner of the invention was obtained. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner Average particle size and geometric standard deviation of magnetic powders for use [Table 1]
And the magnetic powder for external addition of the obtained electrophotographic toner
The values of FeO / Fe ₃ O ₄ (weight ratio) and the results of the cleaning effect test are shown in Table 2.

Example 4 As an aqueous sodium hydroxide solution, the concentration was 1.72 mol / l.
And the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride) was set to 2.41. A magnetic powder for external addition of the electrophotographic toner of the invention was obtained. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner Average particle size and geometric standard deviation of magnetic powders for use [Table 1]
And the magnetic powder for external addition of the obtained electrophotographic toner
The values of FeO / Fe ₃ O ₄ (weight ratio) and the results of the cleaning effect test are shown in Table 2.

Comparative Example 1 An aqueous solution of sodium hydroxide was used at a concentration of 1.37 mol / l.
And the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride) was set to 1.91, using the aqueous solution of A magnetic powder for external addition of the electrophotographic toner of the invention was obtained. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner Average particle size and geometric standard deviation of magnetic powders for use [Table 1]
And the magnetic powder for external addition of the obtained electrophotographic toner
The values of FeO / Fe ₃ O ₄ (weight ratio) and the results of the cleaning effect test are shown in Table 2.

Comparative Example 2 An aqueous solution of sodium hydroxide was used at a concentration of 1.44 mol / l.
Is used as an aqueous ferrous chloride solution having a concentration of 1.0 mol / l, and the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride)
The magnetic powder for external addition of the electrophotographic toner of the present invention was obtained in the same manner as in Example 1 except that 1. was changed to 1.80. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner The average particle size and geometric standard deviation of the magnetic powder for use are shown in Table 1, and the value of FeO / Fe ₃ O ₄ (weight ratio) and the cleaning of the magnetic powder for external addition of the obtained electrophotographic toner were evaluated. The results of the test are shown in [Table 2].

Comparative Example 3 An aqueous solution of sodium hydroxide having a concentration of 1.44 mol / l
Is used as an aqueous ferrous chloride solution having a concentration of 1.1 mol / l, and the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride)
Was changed to 1.64, and a magnetic powder for external addition of the electrophotographic toner of the present invention was obtained in the same manner as in Example 1. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner The average particle size and geometric standard deviation of the magnetic powder for use are shown in Table 1, and the value of FeO / Fe ₃ O ₄ (weight ratio) and the cleaning of the magnetic powder for external addition of the obtained electrophotographic toner were evaluated. The results of the test are shown in [Table 2].

Comparative Example 4 As an aqueous ferrous chloride solution, an aqueous solution having a concentration of 0.7 mol / l was used, and the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / ferrous chloride A magnetic powder for external addition of the electrophotographic toner of the present invention was obtained in the same manner as in Example 1 except that the molar number) was changed to 3.34. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner Table 1 shows the average particle size and geometric standard deviation of the magnetic powder for electrophotography, and FeO / F of the magnetic powder for external addition of the obtained electrophotographic toner.
The values of e ₃ O ₄ (weight ratio) and the results of the cleaning effect test are shown in [Table 2].

Comparative Example 5 As an aqueous sodium hydroxide solution, the concentration was 1.72 mol / l.
Is used as an aqueous ferrous chloride solution having a concentration of 1.1 mol / l, and the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride)
The magnetic powder for external addition of the toner for electrophotography of the present invention was obtained in the same manner as in Example 1, except that was changed to 1.95. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner The average particle size and geometric standard deviation of the magnetic powder for use are shown in Table 1, and the value of FeO / Fe ₃ O ₄ (weight ratio) and the cleaning of the magnetic powder for external addition of the obtained electrophotographic toner were evaluated. The results of the test are shown in [Table 2].

Comparative Example 6 As an aqueous sodium hydroxide solution, the concentration was 1.72 mol / l.
Is used as an aqueous ferrous chloride solution having a concentration of 0.6 mol / l, and the molar ratio of alkali hydroxide to ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride)
The magnetic powder for external addition of the toner for electrophotography of the present invention was obtained in the same manner as in Example 1, except that was changed to 1.95. The concentrations of the aqueous ferrous chloride solution and the aqueous alkali hydroxide solution used in the reaction and the respective concentrations in the mixed solution, the number of moles of alkali hydroxide / the number of moles of ferrous chloride, and the external addition of the obtained electrophotographic toner The average particle size and geometric standard deviation of the magnetic powder for use are shown in Table 1, and the value of FeO / Fe ₃ O ₄ (weight ratio) and the cleaning of the magnetic powder for external addition of the obtained electrophotographic toner were evaluated. The results of the test are shown in [Table 2].

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

The magnetic powder for external addition of the electrophotographic toner according to the present invention is excellent in the effect of preventing the filming phenomenon and the cleaning effect.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Shuichi Miya 425 Kanai, Shibukawa-shi, Gunma Recording Materials Research Laboratory, Kanto Denka Kogyo Co., Ltd. (56) References JP-A-8-286421 (JP, A) JP-A Sho JP-A-61-151551 (JP, A) JP-A-5-100474 (JP, A) JP-A-7-201542 (JP, A) JP-A-7-183111 (JP, A) A) JP-A-58-189646 (JP, A) JP-A-2-45570 (JP, A) JP-A-3-155562 (JP, A) JP-A-3-122658 (JP, A) JP-A-4 JP-A-86672 (JP, A) JP-A-55-105253 (JP, A) JP-A-3-63660 (JP, A) JP-A-7-152197 (JP, A) JP-A-7-69643 (JP, A) JP-A-50-51498 (JP, A) JP-A-6-144840 (JP, A) JP-A-5-345616 JP, A) JP Akira 61-163120 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) G03G 9/08

Claims (3)

(57) [Claims] An average particle diameter is 0.3 to 0.5 μm, a geometric standard deviation of the particle diameter is 1.5 or less, and FeO / Fe
_A magnetic powder for external addition of an electrophotographic toner, comprising magnetite having ₃ O ₄ (weight ratio) of 3/97 to 15/85. 2. An aqueous solution of alkali hydroxide having a concentration of 1.4 to 2.0 mol / l and an aqueous solution of ferrous chloride having a concentration of 0.5 to 1.2 mol / l are placed in a reaction vessel purged with nitrogen gas. , The molar ratio of alkali hydroxide and ferrous chloride (moles of alkali hydroxide / moles of ferrous chloride) is adjusted to 2 to 3 to form a mixed solution. With an oxidizing gas (air)
While blowing the oxidizing gas (air) into the reaction tank,
While maintaining the mixed solution at a temperature of 70 to 100 ° C.,
After stirring and mixing for 10 hours to generate magnetite, the mixed solution containing the generated magnetite is filtered, washed with water, dried, and crushed to obtain magnetite. Then, the magnetite is subjected to an oxide film forming treatment. 2. A method for producing a magnetic powder for external addition to an electrophotographic toner according to claim 1 . 3. The process for forming an oxide film according to claim 2, wherein the magnetite is fired in an air atmosphere at a temperature of 170 to 230 ° C. for 8 to 15 hours.
A method for producing a magnetic powder for external addition to the electrophotographic toner according to the above.