JP2000351629A - Iron oxide particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a particle having balanced tinting strength, opacifying power and hue and excellent kneadability with a resin by making the particle have a specific number-average particle diameter and, when accumulated numbers of primary particles from a small diameter side show plural specific percents of the number of whole particles, by making the accumulated numbers have specific relations. SOLUTION: This iron oxide particle has 0.1-1 μm number-average particle diameter. When particle diameters of accumulated numbers of primary particles from a small diameter side in 50%, 90% and 95% of the number of whole particles are D50, D90 and D95, respectively, the formula 5D50<=D90 and the formula 5D50<=D95 are satisfied. Preferably the iron oxide particle has <=40 L value and <=0 (a) value when the iron oxide particle is mixed with titanium oxide particle in the ratio of iron oxide particle : titanium oxide particle of 6:100. Preferably the iron oxide particle has <=28 ml/100 g oil absorption. The iron oxide particle has preferably >=18 wt.% FeO content, preferably >=50% coefficient of variation by a number-average particle diameter of particle size distribution. The shape of the iron oxide particle is preferably an octahedron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is suitable mainly as a coloring pigment for paints, inks, magnetic toners, magnetic carriers, rubbers and plastics, etc.
The present invention relates to iron oxide particles having a hiding power and a hue, and having excellent kneadability with a resin.

[0002]

2. Description of the Related Art Iron oxide particles are widely used in various fields, specifically for coloring pigments for paints, inks, magnetic toners, magnetic carriers, rubber and plastics, and the like. In particular, magnetic iron oxide particles are frequently used as material powder for magnetic toners in dry-type electronic copying machines, printers and the like.

[0003] In any of the above fields, there is no limit to the demand for higher performance and higher quality, and iron oxide particles must have a good balance of the coloring power, hiding power, and hue required of color pigments in a well-balanced manner. Required. A major factor satisfying such requirements is the particle size distribution of the iron oxide particles.

Generally, various inorganic powders are produced by setting a target particle size and adjusting production conditions. However, it is difficult to obtain a target particle size of 100%. By stabilizing the particle size distribution, the particle size distribution is adjusted.

[0005] The variation in the particle size distribution, that is, the variation in the particle size of the iron oxide particles greatly affects the coloring power when the iron oxide particles are kneaded with the resin. This fact is described, for example, in JP-A-6-310317, "If the granular magnetite particle powder can be colored in as small an amount as possible, it is advantageous not only in terms of workability such as handling but also in terms of resource saving and energy saving. Therefore, it is required that the coloring power be as high as possible. "

[0006] This coloring power is a kind of index in the evaluation of pigments, and it is known that the finer the particles, the higher the particle size when ideally dispersed in a vehicle.

[0007] The hiding power is a force that makes the base material invisible when a paint prepared by kneading a pigment with a coloring material is applied. According to “Powder Theory and Applications” (Maruzen), The coloring power and the hiding power increase as the pigment particles become smaller, but there is a statement that the hiding power becomes smaller as the particle diameter becomes smaller than the wavelength of light, and that the balance between the two means that this hiding is achieved. It is nothing less than selecting the vicinity of the maximum point of force.

On the other hand, iron oxide particles are disclosed in
JP-A-65406 describes that magnetite particles having a bluish tint with a powder having an average particle size of 0.2 μm are most suitable as a black pigment, and that the degree of blackness depends on the average particle size. Is also an important property.

This hue loses its bluish color as the particle size decreases, and tends to approach a red or brownish color. Therefore, it is difficult to balance the above coloring power and hiding power.

Another characteristic required of the iron oxide particles as a coloring pigment is kneadability with a resin. The fact that the kneadability and dispersibility of the pigment in the resin are important is described in Japanese Patent Publication No. Sho 62-14576, which states that the major cause of the color unevenness of the propylene-based colored resin is largely due to the uneven distribution of the black pigment component. It is clear from that.

The particle size of the iron oxide particles is also important for the kneadability with the resin, and it can be said that the larger the particle size, the better. However, there is a limit in considering the balance between coloring power and hiding power.

However, fine particles are inferior in hue in practical use and remarkably agglomerated, and are liable to cause poor kneading with resin, deterioration in various environments, and the like.

As described above, iron oxide particles having a good balance of tinting power, hiding power, hue, and kneading ability with resin could not be obtained with iron oxide particles having a sharp distribution with a uniform particle size.

Accordingly, it is an object of the present invention to provide iron oxide particles having a good balance of coloring power, hiding power and hue, and excellent in kneading with a resin.

[0015]

As described above, the hiding power and the coloring power are simply improved by reducing the particle diameter of the iron oxide particles, or the hue and the kneadability with the resin are improved by increasing the particle diameter. Since the present inventors have a limit, the present inventors simply specify the particle size, without being limited to the means for uniforming the particle size distribution, the specific particle size by the cumulative number of primary particles from the small particle size side It has been found that the above object can be achieved by the related iron oxide particles.

The present invention has been made based on the above findings, and has a number average particle diameter of 0.1 to 1 μm, and the cumulative number of primary particles from the small particle side is 50%, 90% and An object of the present invention is to provide iron oxide particles characterized by satisfying the following formulas (1) and (2) when the particle diameters at 95% are D ₅₀ , D ₉₀ and D ₉₅ , respectively. 1.5D ₅₀ ≦ D ₉₀ … (1) 2.5D ₅₀ ≦ D ₉₅ … (2)

[0017]

Embodiments of the present invention will be described below. The iron oxide particles of the present invention have a number average particle diameter of 0.1.
A ~1μm, 50% of the cumulative number is the total number of particles from the smaller particle size side of primary particles, the particle diameter at 90% and 95% is taken as D _50, D _90, D _95, respectively, the following formulas ( Satisfies 1) and (2). 1.5D ₅₀ ≦ D ₉₀ … (1) 2.5D ₅₀ ≦ D ₉₅ … (2)

Further, it is preferable that the following expressions (3) and (4) are satisfied, and it is more preferable that the following expressions (5) and (6) are satisfied. _{1.8D 50 ≦ D 90 ... ... (} 3) 2.8D 50 ≦ D 95 ... ... (4) 2D 50 ≦ D 90 ... ... (5) 3D 50 ≦ D 95 ... ... (6)

The iron oxide particles of the present invention, since the relative D ₅₀ in gap greater tendency of the D ₉₀ and D _95, the particle size distribution has intentionally wide. In such particles, not only the balance effect of various characteristics by simply mixing the size of the particle size, but also the filling property to the resin by filling the voids between the large particle size with the small particle size, Can also be expected to have a synergistic effect such as an improvement in dispersibility due to the small-sized particles being rolled during dispersion.

Region not satisfying the above equations (1) and (2)
Iron oxide particles, ie, D ₅₀Against D₉₀as well as/
Or D₉₅Iron oxide particles tend to have a small difference with
The particle size distribution is narrow and coloring power and hiding power, or between hue and resin
Although it has excellent kneading properties,
Lance is not enough.

The iron oxide particles of the present invention preferably have an L value of 40 or less and an a value of 0 or less when mixed at a weight ratio of iron oxide particles: titanium oxide particles of 6: 100, More preferably, the L value is 35 or less and the a value is -0.1 or less. If this L value exceeds 40,
If the coloring power is insufficient and the value a exceeds 0, redness becomes strong and hue becomes poor.

The iron oxide particles of the present invention have an oil absorption of 28 ml.
/ 100 g or less, preferably 25 ml / 10
It is more preferable that the weight be 0 g or less. This oil absorption is 28m
If it exceeds 1/100 g, the dispersibility is poor and the kneadability with the resin is poor due to the poor mixability with the resin.

The iron oxide particles of the present invention have an FeO content of 1
It is preferably at least 8% by weight. If the FeO content is less than 18% by weight, the blackness is poor, which is not preferable.

The iron oxide particles of the present invention have a coefficient of variation depending on the number average particle diameter on the particle size distribution.

[0025]

(Equation 1)

Is preferably 50% or more. If the variation coefficient is less than 50%, the particle size distribution of the iron oxide particles is too narrow, and the coloring power, hiding power, hue, and kneading properties with the resin cannot be balanced.

The shape of the iron oxide particles of the present invention is granular (spherical, spherical).
The shape is not particularly limited as long as the shape is a hexahedron, an octahedron, or the like, but is preferably an octahedron. The reason for this is that octahedral particles are more bluish in hue than spherical particles and the like, and tend to have high saturation magnetization in terms of magnetic properties, which is advantageous in fields such as magnetic toners and magnetic carriers. Points.

The form of the iron oxide particles of the present invention includes magnetite (Fe ₃ O ₄ ) and maghemite (γ-F
e ₂ O ₃ ) and a belt-ride compound (Fe
Ox.Fe ₂ O ₃ , 0 <x <1), and Si, Al, Mn, Ni, Z other than Fe
n, Cu, Mg, Ti, Co, Zr, W, Mo, may be selected depending on the properties required spinel ferrite particles containing at least one kind of P, etc., etc., particularly high Fe ²⁺ content blackness Higher amounts of magnetite are more preferred.

Further, the iron oxide particles of the present invention may be subjected to a surface treatment with Si, Al, an organic treating agent or the like in order to improve dispersibility.

Next, an example of a specific method for producing the iron oxide particles of the present invention will be described. Iron oxide particles of the present invention,
Iron oxide particles by passing an oxygen-containing gas through a ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by neutralizing a ferrous salt aqueous solution containing Fe ²⁺ with an alkaline aqueous solution and oxidizing the same; In producing, the reaction temperature during the oxidation reaction,
Change the type and amount of oxygen-containing gas during the reaction,
It can be produced by adjusting the oxidation reaction speed.

An oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by neutralizing an aqueous ferrous salt solution containing Fe ²⁺ with an aqueous alkaline solution to oxidize the ferrous salt aqueous solution. The method for producing iron oxide particles is very common as a method for producing iron oxide particles.However, usually, in order to stably impart desired properties to iron oxide particles or narrow the particle size distribution, In many cases, the conditions for the above-mentioned oxidation reaction are performed without changing as much as possible.

The present inventors have developed a method for producing iron oxide particles satisfying a specific relationship with the particle size based on the cumulative number of primary particles from the small particle size side without being bound by such a sharp particle size distribution. As a result of examining the conditions, they have found that the iron oxide particles of the present invention can be produced by controlling the conditions at the time of the oxidation reaction.

In the method for producing iron oxide particles, it is known that control factors such as reaction temperature, oxidation rate, seed amount, oxidizing gas used, excess alkali component amount and the like are controlled as the control factors affecting the particle size. However, an important condition in the present invention is that the iron oxide particles of the present invention can be produced by appropriately changing these control factors of the particle size during the oxidation reaction.

First, it is preferable to carry out the reaction at a temperature of 75 to 90 ° C. using air as the oxygen-containing gas at the start of the reaction.
85-90 degreeC is more preferable. When oxygen is used as the oxygen-containing gas from the start of the reaction, the oxidation reaction proceeds excessively, the number of particles serving as nuclei increases, and the particle size distribution may be extremely widened.
If the reaction temperature is lower than 75 ° C., the reaction speed is slow and there is a concern that goethite may be generated. If it exceeds 90 ° C., it is uneconomical in energy cost.

The oxidation reaction rate at the time of reaction switching is 15
-70% is preferable, and 30-60% is more preferable.
If the oxidation reaction rate is less than 15%, the number of core particles is too small,
When the frequency of the target particle diameter becomes small and the oxidation reaction rate exceeds 70%, the above formulas (1) and (2), that is, 1.5D ₅₀ ≦ D ₉₀ and 2.5D ₅₀ ≦
It is difficult to satisfy the D _95.

The reaction conditions after switching the reaction conditions are as follows:
It is preferable to increase the reaction speed by increasing the oxidizing atmosphere in the reaction tank before switching. By this operation, it is possible to suppress the phenomenon that individual particles grow slowly and the particle size distribution narrows. Therefore, it suffices to perform operations such as using oxygen as the oxygen-containing gas or increasing the air ventilation amount by 1.5 to 5 times. When adjusting the air ventilation amount, it is more preferable to adjust the air ventilation amount by 2 to 4 times. preferable.

When the iron oxide particles of the present invention are produced, the iron oxide particles which have already been produced are used as starting materials, and an aqueous solution of a ferrous salt containing Fe ²⁺ is added to a slurry in which the particles are dispersed in water. An alkaline aqueous solution may be charged, and an additional oxidation reaction may be appropriately performed according to the particle size distribution of the iron oxide particles as the starting material.

[0038]

The present invention will be described below in detail with reference to examples.

Example 1 As shown in Table 1, Fe 1
50 liters of an aqueous solution of ferrous sulfate containing 2.0 mol / l of ²⁺ and 55 liters of sodium hydroxide of 4.0 mol / l were mixed and stirred to obtain an aqueous solution of ferrous salt containing a ferrous hydroxide colloid. Was. While maintaining the temperature of the reaction aqueous solution at 90 ° C., air was blown at 20 liters / min, and when the oxidation reaction rate of Fe ²⁺ in the reaction aqueous solution reached 60%, the ventilation was temporarily stopped. The temperature of the reaction aqueous solution was lowered to 75 ° C., and while maintaining this temperature, oxygen was reduced to 20 l / mi.
The mixture was vented with n to terminate the oxidation reaction. The obtained magnetite slurry was processed by usual filtration, washing, drying and pulverization steps to obtain octahedral magnetite particles.

The properties of the magnetite particles thus obtained (specific surface area, particle size, coloring power and hue when titanium oxide is mixed, kneading with resin, coloring power after molding, hue, color unevenness, oil absorption) ) Was evaluated. Table 2 shows the results.

The characteristics were measured by the following methods. (1) Specific surface area Measured with a Shimadzu-Micromeritex Model 2200 BET meter. (2) Particle Size A photograph of 10,000 times was taken with a scanning electron microscope, and the Feret diameter of 200 particles was measured. Based on this data, the number average diameter of the sample and the cumulative number particle diameter D integrated from the small particle side
₅₀ , D ₉₀ and D ₉₅ were determined. (3) Coloring power and hue at the time of mixing titanium oxide 1.2 g of sample, titanium oxide particles (A manufactured by Ishihara Sangyo Co., Ltd.)
-100) 20 g, steel ball (6 mmφ) 100
g into a glass pot and shaker
Mix for 5 minutes at 0 rpm. The obtained powder is formed into a pellet, and a color difference meter (manufactured by Tokyo Denshoku Co., Ltd., Color Analyzer T)
L, a, and b values were measured using a C-1800 model. (4) Kneading with resin, tinting strength, hue, and color unevenness after molding <Preparation of molded plate using sample and resin> 0.4 part by weight of sample, ethylene content of 8% by weight, ethylene / propylene of MFR 1.8 After 100 parts by weight of the block copolymer was mixed using a V-type blender for 20 minutes, the mixture was granulated with a single screw extruder to produce colored pellets. 350 mm × 100 using an injection molding machine (manufactured by Taiki Seisakusho) using the pellets.
A molded plate of mm × 2 mm was prepared. <Preparation of Molded Plate Using Sample Mixed with Titanium Oxide and Resin> The above sample was prepared except that 7.6 parts by weight of the titanium oxide mixed powder containing the magnetite particles obtained in (3) was used instead of the above sample. A molded plate was prepared in the same manner as the method of preparing a molded plate using the resin. The molded plate created by the above method is used as a color difference meter (Tokyo Denshoku Co., Ltd.
L using a color analyzer TC-1800)
The a and b values were measured. In addition, the molded plate was observed for color unevenness. A sample in which no color unevenness was observed was evaluated as ○, a case in which color unevenness was slightly observed was evaluated as △, and a case in which color unevenness was clearly observed was evaluated as ×. (5) Oil Absorption Amount was measured using linseed oil according to the method described in JIS K 5101 (1978).

Examples 2 to 5, Comparative Examples 1 to 4 As shown in Table 1, magnetite particles were produced in the same manner as in Example 1 except that the production conditions were changed.

Example 1 of the magnetite particles
Table 2 shows the results of evaluating the respective characteristics in the same manner as in the above. FIG. 1 shows a scanning micrograph (× 10,000) showing the particle size and particle shape of the magnetite particles of Example 2.

[0044]

[Table 1]

[0045]

[Table 2]

As is clear from the results in Table 2, Examples 1 to
5 magnetite particles are 1.5D ₅₀≤D₉₀And 2.
5D₅₀≤D₉₅Is satisfied when mixing titanium oxide or resin
When the coloring power and hue of the molded product
In addition, no color unevenness was observed in the molded product.

On the other hand, the magnetite particles of Comparative Examples 1 to 4 did not satisfy 1.5D ₅₀ ≦ D ₉₀ and 2.5D ₅₀ ≦ D ₉₅ . Since the magnetite particles of Comparative Example 1 had a high oil absorption, they had poor mixing properties with the resin, and the color of the molded article with the resin was poor. Since the magnetite particles of Comparative Example 2 had poor color when mixed with titanium oxide, the color of the molded article with the resin was even worse. In addition, the color unevenness of the molded article with the resin was also poor. Since the magnetite particles of Comparative Example 3 were inferior in coloring power when mixed with titanium oxide, the coloring power of the molded article with the resin was further inferior. In addition, the color unevenness of the molded article with the resin was also poor. The magnetite particles of Comparative Example 4 were inferior in tinting strength and tint of the molded article with the resin.

[0048]

The iron oxide particles according to the present invention are characterized by the particle size according to the cumulative number from the smaller particle size side with respect to the particle size distribution, and the coloring power, hiding power and hue are balanced.
In addition, since it has excellent kneading properties with resins, it is suitable for applications such as coloring pigments for paints, inks, magnetic toners, magnetic carriers, and rubber and plastics.

[Brief description of the drawings]

FIG. 1 is a scanning micrograph (× 10,0) showing the particle size and particle shape of magnetite particles of Example 2.
00).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 11/02 G03G 9/10 (72) Inventor Hiroyuki Watanabe 6-1-1 Hibi, Tamano-shi, Okayama Mitsui F-term (reference) in Metal Mining Co., Ltd.

Claims (4)

[Claims] 1. The number average particle diameter is 0.1 to 1 μm, and the cumulative number of primary particles from the small particle side is 50% of the total number of particles.
%, 90% and 95%, respectively, as D ₅₀ ,
Iron oxide particles satisfying the following formulas (1) and (2) when D ₉₀ and D ₉₅ are satisfied. 1.5D ₅₀ ≦ D ₉₀ … (1) 2.5D ₅₀ ≦ D ₉₅ … (2) 2. The iron oxide particles according to claim 1, wherein the L value is 40 or less and the a value is 0 or less when the weight ratio of the iron oxide particles: titanium oxide is 6: 100. 3. The iron oxide particles according to claim 1, wherein the oil absorption is 28 ml / 100 g or less. 4. The method according to claim 1, wherein the shape is octahedron.
The iron oxide particles according to the above.