JP3473003B2 - Black magnetic iron oxide particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black pigment particle powder.
Powder or particle powder for magnetic toner, especially negatively chargeable magnetic toner
Heat and chemical resistance useful as magnetic particle powder for
And black magnetic iron oxide particles with strong negative charge
Is what you do. [0002] 2. Description of the Related Art In general, black pigments of inorganic pigments include:
Known carbon black powder and magnetite particle powder
ing. Of these, carbon black powder is carbon powder
Although it has excellent heat resistance, it is easy for dust to spread,
In addition, problems such as carcinogenicity have been pointed out,
It's not easy. On the other hand, magnetite particles powder
No problems such as toxicity compared with black powder
Is easy. [0003] As is well known, a resin coloring pigment is kneaded with a resin.
In order to soften and fluidize the resin,
Done in As a result, the pigments used can be colored even at high temperatures.
It is hoped that there will be no change. Magnetite grains used as black pigments
Child powder is ferrous iron²⁺And ferric iron³⁺Because it consists of
As the temperature becomes higher than room temperature, the contained ferrous Fe²⁺But
Slowly oxidizes in air, color changes from black to red as it oxidizes
It began to take on color, and eventually all ferrous iron
Fe²⁺Is ferric iron³⁺Turns into reddish-brown maghemite
Into powder particles. In addition, magnetite is
The temperature at which it transforms into ghemite depends on the shape of the magnetite particles.
It varies depending on the shape, size, surface condition, etc.
It is usually 300 ° C or less (50-300 ° C)
Are known. Therefore, magnetite particles for resin coloring
As powder, ferrous iron at high temperature²⁺Discoloration due to oxidation of
Less magnetite particle powder with excellent heat resistance is desired
ing. In general, magnetite particles for pigments
The powder easily dissolves in strong acids such as hydrochloric acid and mixed acids.
Problem of discoloration due to acid etc. after painting
have. This is based on Japanese Patent Publication No. 54-7292.
"... However, this iron oxide pigment is
Or contact with atmospheric sulfides such as hydrogen sulfide
The hue of the bear fades. This is the dissolution of iron in the composition,
Phenomena caused by oxidation, sulfide formation, or dehydration
This is a major drawback of iron oxide pigments. "Become
It is as described. Therefore, it is hard to be affected by acid etc.
Magnetite particle powder with excellent chemical resistance that has formed a film
Is desired. On the other hand, a toner for an electrophotographic developer
Magnetic particles such as netite particles and ferrite particles are used
ing. In particular, its shape, size, magnetic characteristics, etc.
Magnetite particles that are easy to control are often used. Magnetic
Neutral toners are exposed to high temperatures in developing equipment. others
The magnetite particles in the magnetic toner
Magnetic properties such as magnetization value and coercive force are greatly deteriorated, and
Will deteriorate. Therefore, for magnetic toner with excellent heat resistance
There is a need for magnetite particle powder. Further, the toner is used in a two-component developing system.
Between the toner and the carrier, the magnetic toner of the one-component system
Toner, between toner and toner, or between toner and
Positively or negatively charged by frictional charging between
In recent years, organic photoconductors are often used.
Electromagnetic toner is widely used, and is used for
Magnetite particles with strong negative charge
There is a need for powder. [0008] The chargeability of magnetic particles for magnetic toner
Japanese Patent Application Laid-Open No. 6-301245 discloses "... two-component
For the negatively charged developer of
In the short time before transport to the image area, an appropriate amount of negative charge
(Negative charge amount) is given to the toner, that is,
In other words, it is necessary to improve the charging rise characteristics.
You. ”, Magnetite particles with strong negative charge
There is a need for powder. The magnetization value of the magnetic particle powder for magnetic toner is described below.
In Japanese Patent Laid-Open No. 4-184354, "... magnetic force
By adding an appropriate amount of magnetic material that is appropriately small,
Improves reproducibility and develops images with high fidelity to latent images or signals.
Image quality is obtained. … ”
Demand for magnetite particle powder with low magnetization value
I have. Conventionally, various coating layers have been formed on iron oxide pigments.
To increase thermal stability.
Heat stability, especially by coating a silica layer
Attempts have been made to obtain pigments having a high water content. For example, iron oxide
At normal pressure to alkaline aqueous slurry of pigment particles
In the presence of fine silica sol, a continuous
Stable by depositing to form a fine silica coating
Method for obtaining iron oxide pigment (JP-B-54-7292)
Report), the pigment is dispersed in water or a weakly alkaline aqueous solution
And add silicic acid or silicate as a film constituent
And hydrothermally treated in an autoclave to remove the coating constituents once.
Dissolve and apply silicic acid or silicate on the surface of pigment particles.
Coating method to deposit as a layer (Japanese Patent Publication No. 48-2)
No. 9528), sodium silicate is added to a suspension of yellow iron oxide pigment.
Add thorium aqueous solution and acetic acid aqueous solution at a constant rate
The yellow oxidation is performed so that the film formation rate is within the specified range.
SiO on iron pigment particle surface_TwoMethod for forming a film
No. 53-142399). [0011] Also, seeds of magnetic particles for electrophotographic developers are used as seeds.
Attempts have been made to improve various properties by forming various coating layers.
Came. For example, a one-component system that contains magnetic powder in toner
In the imaging agent, the magnetic powder is made of SiO._Two・ NH_TwoO chemistry
Electrophotography by bonding silica gel expressed by the formula
Developer (JP-A-2-73362), binder resin and
Magnetic toner having at least magnetic powder
The magnetic powder regulates the particle size distribution,
Magnetic toner which is magnetic iron oxide containing 0% by weight
No. 1-221754) have been attempted. [0012] Enhancing the negative chargeability of black magnetic iron oxide particles
One method is to use a silane-based cup on the surface of the magnetic particle powder.
Ring agent, titanium coupling agent or negatively chargeable
A method of performing a surface treatment consisting of a rimmer (Japanese Patent Publication No. 7-866)
No. 98) has been attempted. [0013] SUMMARY OF THE INVENTION Excellent heat resistance and chemical resistance
Black Magnetic Iron Oxide Particle Powder Having Positive and Strong Negative Charging Properties
Are currently the most demanding,
The black magnetic iron oxide particles described in the report have these properties.
Satisfaction is hard to say. The above-mentioned JP-B-54-7292 is disclosed.
Oxidation by forming a continuous fine silica coating on the particle surface
Iron pigment particles have a low silica content of 20% by weight or less.
And heat resistance is not sufficient. It is described in the above-mentioned JP-B-48-29528.
Pigment particles, the amount of silicate added is 10% or less.
Heat resistance is not sufficient. As described in the above-mentioned Japanese Patent Application Laid-Open No. 53-142399.
The method of forming a silica coating on the yellow iron oxide pigment described in
Add salt in advance and add acid gradually
For neutralization, the formed silica coating layer is low.
It seems to be a gel of particles with a degree of polymerization. [0017] Japanese Patent Application Laid-Open No. Hei 2-73362 discloses the above.
The magnetic powder used for the developer is SiO_Two・ NH_TwoConversion of O
Silica gel represented by the formula is attached and bonded
is there. As described in the above-mentioned Japanese Patent Application Laid-Open No. 1-2221754.
The magnetic iron oxide used in various magnetic toners contains silicon
Heat content as low as 10% by weight or less
Sex is not enough. As described in Japanese Patent Publication No. 7-86698,
The magnetic particle powder used in the negatively chargeable magnetic toner has a negative band.
High electrical conductivity, but insufficient heat resistance and chemical resistance
No. Accordingly, the present invention provides a method of coating a denser silica.
By forming a cover layer, it has excellent heat resistance, chemical resistance and
Black magnetic iron oxide particles with high negative chargeability
Is a technical task. [0021] Means for Solving the Problems The technical problems are as follows.
Can be achieved by the present invention. That is, according to the present invention, the magnetite particles ((F
eO) X · Fe_TwoO_Three, 0.3 ≦ x ≦ 1)
And silica ((SiO_Two)_n・ X H_TwoO) coating
And the average particle diameter of the layer is 0.02 to 0.5 μm
Black magnetic iron oxide particle powder consisting of granular particles of
When the coating amount x (parts by weight) of the silica is SiO_TwoAs before
More than 25 parts by weight and 400 parts by weight
Weight parts or less, and the shape of the core particles is spherical.
Specific surface area Sv of core particles calculated from area average diameter of core particles
Against 4.5 ≦ x / Sv ≦ 10.0 And the specific surface area Sv and the black magnetic oxide
BET specific surface area S of the whole iron particle powder_BETAnd the ratio 0.5 ≦ S_BET/Sv≦2.5 A black magnetic iron oxide particle powder characterized by being
You. The structure of the present invention will be described in more detail.
It is on the street. First, the black magnetic iron oxide particles according to the present invention
The end is described. The black magnetic iron oxide particles according to the present invention comprise:
Magnetite particles ((FeO) X · Fe_TwoO_Three, 0.3
≦ x ≦ 1) and silica ((SiO 2)_Two)_n
・ XH_TwoO) and a dense coating layer comprising
It is a powder composed of particles. With the granular particles in the present invention
Can be hexahedral, octahedral, spherical, granular and irregular
And the ratio between the longest diameter and the shortest diameter is 2.0 or less.
Things. The black magnetic iron oxide particles according to the present invention comprise:
The average particle size is 0.02 to 0.50 μm, preferably 0.1 to 0.5 μm.
03 to 0.30 μm. Constructs black magnetic iron oxide particles
Magnetite particles ((FeO) X · Fe_TwoO_Three,
The average particle diameter of the core particles composed of 0.3 ≦ x ≦ 1) is 0.0
15 to 0.30 μm, preferably 0.02 to 0.25 μm
m. The black magnetic iron oxide particles according to the present invention comprise:
BET specific surface area S_BETIs 3-150m^Two/ G, preferably
Is 5-125m^Two/ G. The black magnetic iron oxide particles according to the present invention comprise:
Specific gravity is 2.0 to 4.0, preferably 2.3 to 4.0
You. The black magnetic iron oxide particles according to the present invention comprise:
When the coating amount x (parts by weight) of silica is SiO_TwoAs the core grain
100 parts by weight, exceeding 25 parts by weight and 400 parts by weight
Or less, preferably 30 to 300 parts by weight.
You. When the amount is 25 parts by weight or less, the silica coating layer is thin.
Therefore, heat resistance and chemical resistance are not sufficient. 400
If the amount is more than 100 parts by weight, the silica coating layer becomes too thick.
This is not preferable because the magnetization value and the coloring power are lowered. What
Incidentally, in terms of the ratio to the total amount of the black magnetic iron oxide particles,
Calculated silica coating amount x (% by weight) exceeds 20% by weight.
80% by weight or less, preferably 23% by weight or more and 75% by weight
% Or less. The shape is spherical based on the area average diameter of the core particles.
The calculated specific surface area Sv is 2 to 60 m^Two/ G, preferably
4-50m^Two/ G. When the silica coating amount x (parts by weight) is S
iO_TwoThe shape is spherical based on the area average diameter of the core particles.
The ratio x / Sv to the specific surface area Sv calculated as
10.0, preferably 5.0 to 8.0. Ratio x / S
When v is less than 4.5, the silica coating layer becomes thin.
Therefore, heat resistance and chemical resistance are not sufficient. Ratio x / Sv
Exceeds 10.0, the silica coating layer becomes too thick.
It is not preferable because the magnetization value and
No. BET ratio table of the black magnetic iron oxide particles
Area S_BETAnd the shape from the area average diameter of the core particles as spherical
Ratio S to specific surface area Sv calculated_BET/ Sv is 0.5
-2.5, preferably 0.5-2.0. Ratio S_BET
When / Sv is less than 0.5, the silica coating layer is too thick.
Because it is too much, the magnetization value and coloring power will be low
Not preferred. Ratio S_BETWhen / Sv exceeds 2.5
Is, silica precipitation occurs other than the core particle surface,
Because the silica coating layer is not dense, heat resistance and
Insufficient chemical resistance. The black magnetic iron oxide particles according to the present invention comprise:
Saturation magnetization value is 10 to 70 emu / g, preferably 10 to 70 emu / g.
65 emu / g. If less than 10 emu / g
Are not preferred for magnetic toners. 70 emu / g
If it exceeds, dispersibility deteriorates due to magnetic aggregation and the like.
Therefore, when used for magnetic toner, high image quality, especially
Improvement in reproducibility of fine lines cannot be expected. The black magnetic iron oxide particles according to the present invention comprise:
L^*a^*b^*C in the color system represented by the system^*(=
(A^{* 2}+ B^{* 2})^1/2, Where a^*Is redness, b^*Is yellow
Represents chromaticity. ) In air, temperature 300 ℃, 1 hour
Δc indicating deterioration under different environment^*Is less than or equal to 5.0
Or 3.0 or less. The black magnetic iron oxide particles according to the present invention comprise:
The charge amount is -10 to -2 µC / m^Two, Preferably -8 to-
2.5 μC / m^TwoIt is. Next, as described above, the black magnet according to the present invention is used.
A method for producing iron oxide particles will be described. The black magnetic iron oxide particles according to the present invention comprise:
Using the granular magnetite particles as the core particles,
Aqueous suspension of magnetite particles is heated to a temperature of 70 to 100 ° C.
The pH is adjusted to 9.0 to 9.7 with an aqueous silicate solution,
While maintaining the pH at 9.0 to 9.7, the SiO_TwoAs
0.05 to 0.3 parts by weight based on 100 parts by weight of core particles
/ Minute drop rate, the granular magnetite particles
After forming a coating layer made of silica on the particle surface of
H was adjusted to 6.5 to 7.0, and then filtered by a conventional method.
It is obtained by performing drying, washing and drying. The core particles in the present invention are made of magnetite.
((FeO) X · Fe_TwoO_Three, 0.3 ≦ x ≦ 1)
, Hexahedral, octahedral, spherical, granular and irregular
Either shape may be used, and the ratio of the longest diameter to the shortest diameter is
Is 2.0 or less. The granular magnet which is the core particle in the present invention
The average particle diameter of the powder particles is 0.015 to 0.30 μm.
m, preferably 0.02 to 0.25 μm. Granular magnet as core particles in the present invention
The particle particle powder is calculated as a spherical shape from the area average diameter.
Specific surface area Sv 'is 2 to 60 m^Two/ G, preferably 4
~ 50m^Two/ G. The granular magnet which is the core particle in the present invention
The iron particle powder has a ferrous iron content of Fe.²⁺As core particles
10 to 24% by weight, preferably 12 to 22% by weight
%. Granular magnet as core particle in the present invention
The solid concentration of the aqueous suspension of the particle particles is 10 to 200.
g / l, preferably 25 to 150 g / l. The granular magnet which is the core particle in the present invention
, A soluble salt contained in an aqueous suspension of
a, K, Ca and other alkali metals and alkaline earth metals
When the content is 50 g / l or less, preferably 30 g / l or less
is there. If it exceeds 50 g / l, the above-mentioned amount will be
Due to the effect of salt, the deposition rate of silica increases,
Is easily formed, which is not preferable. Granular Magnet as Core Particle in the Present Invention
The pH of the aqueous suspension of the particle particles is preferably 9.0 to 9.7,
Preferably, it is adjusted in the range of 9.1 to 9.5. The temperature of the silica coating treatment of the present invention is 70 to
The temperature is 100 ° C, preferably 75 to 95 ° C. Less than 70 ° C
In this case, sufficient dehydration reaction occurs during the polymerization of silica.
The coating layer contains hydroxyl groups (OH groups)
Is more likely to occur. If the temperature exceeds 100 ° C,
Requires special equipment such as toclave and is industrially preferred.
I don't. In the silica coating treatment of the present invention,
During the dropwise addition of the aqueous solution of the phosphate, the suspension of the granular magnetite particles was suspended.
The pH of the suspension is 9.0 to 9.7, preferably the pH is 9.1.
It is important to keep it in the range of ９9.5. pH
Is less than 9.0, the silicate ion is
The precipitation rate of the silica particles on the particle surface increases,
Polymerization of mosquito does not proceed sufficiently, and silica particles of low polymerization degree
Gelation is likely to occur. When the pH exceeds 9.7
In order to approach the ionization constant of silicic acid,
Elution of silicate ions from silicic acid precipitated at the same time
It is not preferable because it can come. Alkali hydroxide water used for the pH adjustment
Examples of the solution include sodium hydroxide and potassium hydroxide.
Aqueous solution of alkali metal hydroxide, magnesium hydroxide
Hydroxide of alkaline earth metals such as calcium hydroxide and calcium hydroxide
Aqueous solution of sodium carbonate, potassium carbonate, carbonic acid
Aqueous alkali carbonate solution such as ammonium and ammonia water
Etc. can be used. Industrially, sodium hydroxide
Of hydroxides of alkali metals such as potassium and potassium hydroxide
Solutions are preferred. The acid used for the pH adjustment is sulfuric acid.
Inorganic acids such as acid, hydrochloric acid and nitric acid, acetic acid, oxalic acid, formic acid, etc.
Organic acids and the like can be used. Industrially, sulfuric acid,
Acetic acid and the like are preferred. The aqueous silicate solution used in the present invention includes:
Sodium silicate aqueous solution, potassium silicate aqueous solution and
An aqueous solution of calcium formate or the like can be used. SiO in aqueous silicate solution_TwoAddition amount as
y (parts by weight) is granular magnetite used as core particles
More than 25 parts by weight and 400 parts by weight based on 100 parts by weight of particles
Parts by weight, preferably 30 parts by weight or more and 300 parts by weight or less
is there. Also, granular magnetite particles used as core particles
Specific surface area S calculated as a spherical shape from the area average diameter of
v 'and SiO_TwoSilicate addition amount y (parts by weight)
And the ratio y / Sv 'is 5.0 to 10.0, preferably 6.
0 to 10.0. The drop rate of the aqueous silicate solution of the present invention
100 weight of granular magnetite particles used as particles
Parts by weight of SiO_TwoAs 0.05-0.30 weight
Parts / minute, preferably 0.05 to 0.25 parts by weight / minute
is there. If less than 0.05 parts by weight / minute, silica coating
Layer formation is too slow, which is industrially undesirable. 0.
If it exceeds 30 parts by weight / min, silicic acid in water suspension
The ion concentration becomes too high and silica separates from the core particles.
Polymer that does not precipitate alone or cause sufficient dehydration reaction
Because a dense coating layer of silica is not formed
Not preferred. The water suspension after the silica coating treatment of the present invention
Adjust the pH to 6.5-7.0. Used for pH adjustment after the silica coating treatment.
Acids such as sulfuric acid, hydrochloric acid, and nitric acid; acetic acid;
Organic acids such as oxalic acid and formic acid can be used. Engineering
Industrially, sulfuric acid, acetic acid and the like are preferable. [0053] Conventionally, precipitation and growth of silica particles from silicates
The process is under study and silicate
Condition of silica particles depends on neutralization conditions
It is known. For example, silica during silicate neutralization
Depending on the acid concentration, temperature and pH, the silica monomer
In the process of merging, tertiary particles with a relatively low degree of polymerization
When gelling due to the original structure, or when silica monomer
May grow large as continuous and dense particles
(RK Iller, The Chemistry o
f Silica, John Wiley & Sons,
Inc. , New York, 1979). The surface of the iron oxide particles is coated with silica.
To improve various properties such as heat resistance
There have been many attempts to reduce the
Only a gel-like coating layer of silica particles is formed
And sufficient heat resistance was not obtained. Therefore, the present inventor has proposed that granular magnetite particles
Coating of silica particles with high polymerization degree silica
Aqueous suspension of granular magnetite particles powder to form a layer
Silica Amount on Particle Surface from Silicate Dropped in Liquid
As a result of intensive studies on the precipitation and growth processes of the
Rate of dripping of the phosphate, temperature of the aqueous suspension, pH, silicic acid
Regarding the adjusted pH etc. at the time of salt dripping and after the silicate dripping,
By selecting a specific range, granular magnetite particles
Continuous and dense coating layer of silica on the surface of particles
I found that I can do it. On the obtained particle surface, silica was continuously and
Granular magnetite particles with a dense coating layer are resistant to
Excellent heat and chemical resistance, and also shows strong negative chargeability
It is. [0057] DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.
It is as follows. Shape and particle size of black magnetic iron oxide particles
Are observed with a transmission electron microscope and observed with the electron microscope.
The Martin diameter in the projected diameter
Calculated from (length of line segment bisecting projected area in fixed direction)
It is represented by the number average diameter. The axial ratio is
From the photograph taken by the electron microscope, the longest diameter and the shortest diameter
And expressed as a ratio. Specific surface of core particles of black magnetic iron oxide particles
The product Sv cannot be measured directly due to the presence of the silica coating.
Although not possible, observation with a transmission electron microscope and the electron microscope
Microscopic photographs clearly distinguish silica coating layer from core particles
The Martin diameter (in the fixed direction) in the projected diameter of the core particle
The length of a line segment that divides the projected area into two equal parts)
Diameter d_ThreeIs calculated, and a ratio table when the shape of the core particles is spherical
It is obtained by substituting into the following expression representing the area. In addition,
The specific gravity ρ of the core particle is 5.2 g, which is the literature value of the specific gravity of magnetite.
/ Cm^ThreeCalculated as Sv = 6 / (ρ × d_Three) In addition, granular magnetite particles which are core particles before silica coating
The specific surface area Sv 'of the child was also calculated in the same manner as above. BET specific surface area of black magnetic iron oxide particles
S_BETIs "Mono SorbMS-11" (Ayu Yuasa)
(Manufactured by Ionics Corporation). The specific gravity of the black magnetic iron oxide particles is
Tibolium Densitometer Model 1305 "(manufactured by Shimadzu Corporation)
Helium gas pressure 1.6 kgf / cm^ThreeCondition
Measured below. The magnetic properties of the black magnetic iron oxide particles are as follows:
"Vibration sample magnetometer VSM-3S-15" (Toei Kogyo
(Manufactured by K.K.) under an external magnetic field of 10 kOe. SiO of black magnetic iron oxide particles_TwoThe quantity is
"X-ray fluorescence spectrometer Model 3063M" (Rigaku Denki)
(Manufactured by Kogyo Co., Ltd.). Black Magnetic Iron Oxide Particle Powder and Magnetite
Fe of particle powder²⁺Measurement before mixed acid (phosphoric acid-sulfuric acid)
After dissolving the particle powder, diphenyl
Add a few drops of amine and titrate with potassium bichromate aqueous solution
I asked. The degree of blackness of the black magnetic iron oxide particles, and
The change in blackness can be measured by using the multi-source spectrophotometer MS
C-IS-2D ”(manufactured by Suga Test Instruments Co., Ltd.)^*a
^*b^*Lightness L in color system^*, Redness a^*, Yellowness b
^*, And saturation c^*(= (A^{* 2}+ B^{* 2})^1/2) Measure
Was. Here, as the blackness, the saturation c^*Evaluated by
Changes in blackness are heat resistant in air at 300 ° C for 1 hour
Saturation c after test^*'And Δc^*As
You. The colorimetric sample piece was made of black magnetic iron oxide particles.
0.5 g of powdered powder and 0.5 cc of castor oil
Kneaded with a roller to form a paste, and then clear the paste
4.5 g of lacquer was added, kneaded and made into a paint, and cast
Coated on paper with a 6 mil applicator
Was. The charge amount of the black magnetic iron oxide particles
Low-off charge measurement device TB-200 ”(Toshiba Chemical
TFV-200 / 300 (PA)
Powdered black magnetic iron oxide particles
The concentration was 5% and the mixing time was 30 minutes. Chemical resistance test of black magnetic iron oxide particles
Is mixed with 0.5 g of black magnetic iron oxide particles and mixed acid (
Method: Add about 1 liter of water to a 2 liter beaker and add concentrated phosphoric acid
ml using a 500 ml graduated cylinder.
Stir well with a stick. Cool the beaker with water
Add 300 ml of concentrated sulfuric acid to 500 ml while stirring.
Add slowly using a cylinder. After water cooling, 2l scale
Add water and mix well to adjust. ) About 25ml
In a 500 ml Erlenmeyer flask for 15 minutes at room temperature
After performing the nitrogen substitution, heat the black magnetic iron oxide particles
The solubility of the powder in the mixed acid was evaluated by the dissolution time.
Was used as an index for the chemical resistance test. A hexahedral magnetite having an average particle size of 0.17 μm
Particle powder (Fe²⁺17.8% by weight, saturation magnetization 86.1
emu / g, charge amount-1.2 μC / m^Two, Area average diameter
5.6m specific surface area calculated from^Two/ G) 10 kg to 200
18.0N aqueous sodium hydroxide solution.
After adding 0.5 l of the liquid, Micro Agiter (manufactured by Shimazaki Co., Ltd.)
Aqueous suspension of the magnetite particles (solid
(The concentration of the form was about 50 g / l). An aqueous suspension of the magnetite particle powder was added to 8
The temperature was raised to 0 ° C., and p was added with 22.4 mol / l of industrial sulfuric acid.
Adjusted to H9.5. Salt contained in the aqueous suspension after adjustment
The concentration is adjusted so that the total amount of sodium hydroxide added
Assuming that it was neutralized by more sulfuric acid added,
Sodium Na_TwoSO_FourIs 3.2 g / l.
Separately, sodium silicate (SiO_Two28.6% by weight in conversion
Silicic acid diluted 17.5 kg with 5 l of water
A drop rate of about 0.10 parts by weight / minute (S
iO_TwoIn the aqueous suspension of the magnetite particle powder as
Solid content, that is, 100 weights of hexahedral magnetite particle powder
In 500 parts for 500 minutes.
At the time of dropping of aqueous solution of sodium silicate 22.4m
ol / l industrial sulfuric acid, pH range of 9.1 to 9.4
Maintained. After completion of the dropping of the aqueous solution of sodium silicate, p
After stirring and mixing with H9.5 for 30 minutes,
Adjusted to pH 6.7 with acid, filtered, washed with water and dried,
Density of silica on the surface of magnetite particles as core particles
A black magnetic iron oxide particle powder having a suitable coating layer was obtained. Saturation magnetism of the obtained black magnetic iron oxide particles
Conversion value is 55.3 emu / g and specific gravity is 3.5 g / m
1, the charge amount is -7.1 μC / m^Two, BET specific surface area S
_BET9.6m^Two/ G, SiO_TwoWith a content of 30.1% by weight
there were. As the evaluation of heat resistance, the black magnetic iron oxide particles
After placing 10 g of powder in air at 300 ° C for 1 hour.
The change amount Δσs of the sum magnetization value and the change rate Δc of the saturation^*Measure
did. When the variation Δσs of the saturation magnetization is 0.6 emu / g
Yes, saturation change Δc^*Was 0.4. As a result,
The black magnetic iron oxide particles are almost acid-free even at 300 ° C.
No deterioration and discoloration due to aging, and extremely high heat resistance
I was able to confirm that. The black magnetic iron oxide particles are mixed with a mixed acid
Acid-sulfuric acid) and heated at around the boiling point for 1 hour
Does not completely dissolve even in the test, so chemical resistance
It was confirmed that it was excellent. [0074] Next, examples and comparative examples will be described. Examples 1 to 7, Comparative Examples 1 to 6; Examples 1 to 7, Comparative Examples 1 to 6 The type of magnetite particle powder used as the core particles,
Solid concentration, salt concentration of aqueous suspension of magnetite particle powder
Degree, temperature, pH, silicate type, dropping rate, dropping amount,
Except for changing the adjusted pH after silicate dripping,
Black magnetic iron oxide particles powder in the same manner as in the embodiment of the invention
I got Table 1 shows the main production conditions at this time, and the obtained black
Table 2 shows properties of the magnetic iron oxide particles. [0075] [Table 1][0076] [Table 2][0077] The black magnetic iron oxide particles according to the present invention
Has a dense silica coating layer for excellent resistance
Black with thermal, chemical and strong negative charge
Particle powder for color pigment or particle powder for magnetic toner, especially negative band
It is most suitable as a magnetic particle powder for an electric magnetic toner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a transmission electron micrograph (×) showing a particle structure of a black magnetic iron oxide particle powder obtained in an embodiment of the present invention.
FIG. 2 is a transmission electron micrograph (× 5000) showing the particle structure of the black magnetic iron oxide particles obtained in Comparative Example 1.
0)

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigenori Miyazaki 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Inside Toda Industries Co., Ltd. Creative Center (72) Minoru Yoshizawa Funairi, Naka-ku, Hiroshima-shi, Hiroshima 4-1-2 Minami Toda Kogyo Co., Ltd. Creative Center (72) Inventor Naoki Uchida 4-1-2 Funairi Minami, Naka-ku, Hiroshima City, Hiroshima Prefecture Toda Kogyo Co., Ltd. Creative Center (56) References 60-81012 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 49/08 C09C 1/24 C09C 3/06 G03G 9/083 H01F 1/00

Claims (1)

(57) [Claims] [Claim 1] Magnetite particles (( FeO ) x.Fe
_{2 O 3, 0.3 ≦ x ≦} 1) core particles composed of a silica having an average particle diameter of which is composed of a _{((SiO 2) n · x} H 2 O) consisting of the coating layer is 0.02~0.5μm Black magnetic iron oxide particles composed of granular particles having a silica coating amount x (parts by weight) of SiO ₂ as the core particles 1
More than 25 parts by weight and not more than 400 parts by weight with respect to 00 parts by weight, and the specific surface area Sv of the core particle calculated from the area average diameter of the core particle by making the shape of the core particle spherical is 4.5 ≦. x / Sv ≦ 10.0, and the ratio of the specific surface area Sv to the BET specific surface area S _BET of the whole black magnetic iron oxide particles is 0.5 ≦ S _BET /Sv≦2.5. A black magnetic iron oxide particle powder characterized by the following.