WO2015005452A1

WO2015005452A1 - Black magnetic iron oxide particle powder and method for producing same

Info

Publication number: WO2015005452A1
Application number: PCT/JP2014/068500
Authority: WO
Inventors: 亮岩井; 伸哉志茂; 内田　直樹
Original assignee: 戸田工業株式会社
Priority date: 2013-07-12
Filing date: 2014-07-10
Publication date: 2015-01-15
Also published as: JP6521254B2; JPWO2015005452A1

Abstract

The present invention pertains to a black magnetic iron oxide particle powder comprising a magnetite particle powder which is octahedral in shape, has silicon evenly distributed throughout the particle interior, and exhibits excellent blackness even when the applied coat thereof is thin. When producing a magnetic toner by using the black magnetic iron oxide particle powder in the present invention, it is possible to obtain a magnetic toner which exhibits excellent blackness. The black magnetic iron oxide particle powder is characterized by: being octahedral in shape; containing silicon in the amount of 0.19-1.90 at% calculated on a silicon element basis in relation to iron; and the silicon element solubility (Y), when the iron element solubility (X) is in the ranges of 20<X_20-40≤40%, 40<X_40-60≤60% and 60<X_60-80≤80%, satisfying a specific relational expression comprising the iron element solubility (X) and the silicon element solubility (a) when the iron element solubility is 10%.

Description

Black magnetic iron oxide particle powder and method for producing the same

Since the black magnetic iron oxide particles according to the present invention are octahedral and black, they can be used as black coloring pigments for paints, resins, printing inks, etc. When used as particles, a magnetic toner with high blackness can be obtained.

Conventionally, as one of the electrostatic latent image developing methods, a so-called “one-component magnetic toner” in which a composite particle in which magnetic particle powder such as magnetite particle powder is mixed and dispersed in a resin without using a carrier is used as a developer. Is widely known and widely used.

Recently, with the enhancement of the performance of laser beam printers and digital copying machines, magnetic toners with higher blackness are required.

The blackness of the magnetic toner greatly depends on the blackness of magnetite contained in the magnetic toner. Therefore, there is a strong demand for black magnetic particles with high blackness.

In particular, magnetite particles having an octahedral particle shape are known to have high blackness.

Various attempts have been made to obtain magnetite particles with higher blackness (Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 3-131866 JP 2008-184338 A JP 2011-213548 A

In view of the above-mentioned problems, black magnetic iron oxide particles having fine particles and excellent blackness are currently most demanded, but such black magnetic iron oxide particles are still provided. Absent.

The magnetite particles described in the above-mentioned Patent Document 1 cannot be said to have sufficient blackness because the distribution of silicon element is not constant.

Further, the magnetite particle powder described in the above-mentioned Patent Document 2 is not sufficiently black because the silicon element distribution is not constant.

In addition, the magnetite particles described in the above-mentioned Patent Document 3 are not sufficiently black because the distribution of silicon element is not constant.

Therefore, the present invention is an octahedral shape, in which silicon element is uniformly distributed inside the particle, and even when a thin coating film is formed, the black magnetic material suitably used for a magnetic toner having excellent blackness It is a technical subject to provide iron oxide particle powder.

The technical problem can be achieved by the present invention as follows.

That is, the present invention is octahedral, contains 0.19 to 1.90 atomic% of silicon in terms of silicon element, and has an iron element dissolution rate (X%) of 20 <X ₂₀ The silicon element dissolution rate (Y%) in each range of ≦ ₄₀ ≦ 40%, 40 <X _40-60 ≦ 60%, 60 <X _60-80 ≦ 80%, the iron element dissolution rate (X%) and the iron element A black magnetic iron oxide particle powder characterized by satisfying the following formulas (1) and (2) consisting of a silicon element dissolution rate (a%) when the dissolution rate is 10% (Invention 1).

{(100−a) X + 100 (a−10)} / 90−10 (1−a / 100) ≦ Y ≦ {(100−a) X + 100 (a−10)} / 90 + 10 (1−a / 100) (1)
10 ≦ a ≦ 80 (2)
(However, 10 ≦ X ≦ 100, 10 ≦ Y ≦ 100)

Further, in the present invention, the sodium content in the black magnetic iron oxide particles is 0.02 to 0.10% by weight, and the sodium element dissolution rate at an iron element dissolution rate of 50% with respect to the total iron element amount is This is the black magnetic iron oxide particle powder according to the first aspect of the present invention, which is 50% or more based on the total dissolved amount of sodium element (second aspect of the present invention).

Further, the present invention is the black magnetic iron oxide particle powder according to the present invention 1 or 2 having an average particle size of 0.05 to 0.30 μm (Invention 3).

Further, the present invention is the black magnetic iron oxide particle powder according to any one of the present inventions 1 to 3 having a change coefficient in particle size distribution of 30% or less (Invention 4).

Further, in the present invention, the b * value of the coating film when the film thickness prepared using black magnetic iron oxide particle powder is 23 to 26 μm is 2 or less,
a * (I): a * value when the coating film thickness is 4 to 6 μm a * (II): a * value when the coating film thickness is 23 to 26 μm α = a * (I) / a * (II) When
The black magnetic iron oxide particle powder according to any one of the present inventions 1 to 4, wherein 1.0 ≦ α ≦ 2.0 is satisfied (Invention 5).

Further, the present invention is the black magnetic iron oxide particle powder according to any one of the present inventions 1 to 5 having a coating layer of Si and Al (Invention 6).

The present invention also relates to black magnetic iron oxide particles having octahedral shape and containing 0.19 to 1.90 atomic% of silicon in terms of silicon element with respect to iron element. The b * value of the coating film when the film thickness prepared using the particle powder is 23 to 26 μm is 2 or less,
a * (I): a * value when the film thickness is 4 to 6 μm a * (II): a * value when the film thickness is 23 to 26 μm α = a * (I) / a * (II) When
It is a black magnetic iron oxide particle powder characterized by satisfying 1.0 ≦ α ≦ 2.0 (Invention 7).

The present invention also provides an aqueous ferrous salt solution, an aqueous alkali hydroxide solution of 0.90 to 1.00 equivalent to the ferrous salt in the aqueous ferrous salt solution, The pH of the reaction solution containing ferrous hydroxide colloid obtained by reacting Fe with 0.05 to 1.00 atomic% of water-soluble silicate in terms of Si was adjusted to 8 to 9; A first-stage reaction in which oxygen-containing gas is aerated while heating in a temperature range of ˜100 ° C., and the oxidation reaction rate of iron is reduced to 7 to 12% to generate nucleated magnetite particles, the first-stage reaction An aqueous alkali hydroxide solution is added to the ferrous salt reaction liquid containing the nucleated magnetite particles and the ferrous hydroxide colloid after completion so as to be 1.01 to 1.50 equivalent, and the temperature is 70 to 100 ° C. The oxygen oxidation reaction rate is 40-60% by aeration of oxygen-containing gas while heating in the range After the completion of the second stage reaction, the pH is temporarily adjusted to 5 to 9, and then the pH of the reaction solution is readjusted to 9.5 or higher, and then the water-soluble silicate is added. Add 20 to 200% to the water-soluble silicate added in the first stage reaction (total of 1.9 atomic% or less of silicon elements added in the first stage reaction and the third stage reaction) and add 70 to 100 ° C. 8. The method for producing black magnetic iron oxide particle powder according to any one of the present inventions 1 to 7, wherein an oxidation reaction is performed by aeration of an oxygen-containing gas while heating to a temperature range (third stage reaction). (Invention 8).

The black magnetic iron oxide particle powder according to the present invention has an octahedral shape, and by making the distribution of silicon element contained inside the particle constant, the crystallinity of the black magnetic iron oxide particle becomes uniform, and the average particle diameter is Even fine particles of 0.05 to 0.30 μm are excellent in blackness, and therefore can be suitably used as magnetic particle powders for electrophotographic magnetic toners.

The configuration of the present invention will be described in more detail as follows.

First, the black magnetic iron oxide particle powder according to the present invention will be described.

The black magnetic iron oxide particles according to the present invention are composed of magnetite ((FeO) x · Fe ₂ O ₃ , 0 <x ≦ 1) in terms of composition.

The particle shape of the black magnetic iron oxide particle powder according to the present invention is an octahedron. In this invention, it is set as the black magnetic iron oxide particle powder with a high blackness because a particle shape is an octahedron.

The black magnetic iron oxide particle powder according to the present invention contains 0.19 to 1.90 atomic% of silicon in terms of silicon element with respect to iron element. When the silicon content is less than 0.19 atomic%, the magnetic particle size distribution of black magnetic iron oxide is deteriorated and magnetic iron oxide particles having excellent blackness cannot be obtained. When the silicon content exceeds 1.90 atomic%, by-products other than magnetite are generated, and magnetic iron oxide particles having excellent blackness cannot be obtained. The silicon content is preferably 0.25 to 1.87 atomic%, more preferably 0.30 to 1.85 atomic%.

The black magnetic iron oxide particle powder according to the present invention has an iron element dissolution rate (X%) of 20 <X _20-40 ≦ 40%, 40 <X _40-60 ≦ 60%, 60 <X _60-80 ≦ 80%. The black magnetic iron oxide characterized by satisfying the following formulas (1) and (2) in which the silicon element dissolution rate (Y%) in each range of the above consists of the silicon element dissolution rate a% at an iron element dissolution rate of 10% Particle powder.

The black magnetic iron oxide particle powder according to the present invention obtains a magnetic iron oxide particle powder excellent in blackness while being fine by satisfying the relational expression.
Here, the iron element dissolution rate (X) is the ratio of the dissolved Fe to the Fe of the entire particle, where 0% is not dissolved and 100% is all dissolved. Similarly, the silicon element dissolution rate (Y) is 0% in a state where silicon is not dissolved, and 100% is a state in which all silicon existing in the magnetic iron oxide particles is dissolved. In particular, the silicon element dissolution rate when the iron element dissolution rate is 10% (X = 10%) is defined as (a).

Formula (1) shows the relationship between the iron element dissolution rate (X), the silicon element dissolution rate (a), and the silicon element dissolution rate (Y) at an iron element dissolution rate of 10% for black magnetic iron oxide particles. Yes, it shows the distribution state of Si in the black magnetic iron oxide particles. That is, in the present invention, satisfying the formula (1) means that the iron element dissolution rate (X) and the silicon element dissolution rate (Y) in each range are shown in a specific narrow range (formula (1)). Range)), that is, the dissolution of the iron element and the dissolution of the silicon element at a close ratio, which means that the silicon element is uniformly present in the magnetic iron oxide It is. Incidentally, the iron element dissolution rate in the range (X) may select one of the dissolution rate within that range, the iron element dissolution ratio (X%) is _{20 <X 20 ~ 40 ≦ 40} %, 40 <X _40-60 ≦ 60%, 60 <X _60-80 ≦ 80%, in each range of 20-40%, 40-60%, 60-80%. The element dissolution rate (Y) may be evaluated. Formula (1) is satisfied when the iron element dissolution rate (X%) is 20 <X _{20 to 40} ≦ 40%, 40 <X _{40 to 60} ≦ 60%, and 60 <X _{60 to 80} ≦ 80%. There is a need to.

In Formula (1), when Y is less than the lower limit, a large amount of Si is present in the center of the particle, which is not preferable. Further, when Y exceeds the upper limit value, a large amount of Si is present near the particle surface, which is not preferable. That is, in the iron element dissolution rate (X) in a certain range, the silicon element dissolution rate (Y) is less than the lower limit value, which means that the ratio of the silicon element dissolved up to the iron element dissolution range is the iron element dissolution rate. This means that there is still a large amount of undissolved silicon element in the particles that are not yet dissolved, and the silicon element is unevenly distributed in the center of the particle and exists uniformly. It will not be. On the other hand, when the silicon element dissolution rate (Y) exceeds the upper limit value, it means that the ratio of silicon element dissolved up to the iron element dissolution range is too much compared with the dissolution ratio of iron element, and the already dissolved part This means that the silicon element contains a large amount of silicon element, and the silicon element is unevenly distributed in the vicinity of the particle surface and is not present uniformly.

In Formula (2), when a is less than the lower limit, a large amount of Si is present in the center of the particle, which is not preferable. Moreover, when a exceeds the upper limit, an excessive Si component is present on the particle surface, which is not preferable. More preferably, 10.5 ≦ a ≦ 75, and still more preferably 11.0 ≦ a ≦ 70.

The sodium content in the black magnetic iron oxide particles according to the present invention is preferably 0.02 to 0.10% by weight. A more preferable sodium content is 0.03 to 0.9% by weight. It is preferable in that the hygroscopicity does not increase by controlling the sodium content within the above range.

Further, the sodium element of the black magnetic iron oxide particles according to the present invention has a sodium element dissolution rate when the iron element dissolution rate is 50% with respect to the total iron element amount, and the total sodium element dissolution amount (total sodium content). On the other hand, it is preferably 50% or more. This indicates that the sodium element present in the black magnetic iron oxide particles is present in a larger amount near the surface than in the center of the particles. More preferably, the sodium element dissolution rate when the iron element dissolution rate is 50% with respect to the total iron element amount is preferably 55% or more with respect to the total sodium element dissolution amount (total sodium content).

The average particle size of the black magnetic iron oxide particle powder according to the present invention is preferably 0.05 to 0.30 μm. When the average particle diameter is less than 0.05 μm, the number of particles in a unit volume increases so that the number of contacts between the particles increases, so that the adhesion between the powder layers increases, and in the case of using a magnetic toner, The dispersibility to become worse. When the average particle diameter exceeds 0.30 μm, the number of black magnetic iron oxide particles contained in one toner particle is reduced, and the distribution of black magnetic iron oxide particles is uneven for each toner particle. In addition, the uniformity of charging of the toner is impaired. A more preferable average particle diameter is in the range of 0.07 to 0.28 μm.

The change coefficient in the particle size distribution of the black magnetic iron oxide particles according to the present invention is preferably 30% or less. When the change coefficient of the particle size distribution is 30% or less, the influence of the fine particle component is reduced and the blackness is improved. A more preferable change coefficient is 29% or less.

The b * value of a coating film having a film thickness of 23 to 26 μm (typically 24 μm) prepared using the black magnetic iron oxide particles according to the present invention is preferably 2 or less. When the b * value is 2.0 or less, it has excellent blackness. A more preferred b * value is 0 to 1.8.

Moreover, it is preferable that a * measured by changing the film thickness of the coating film prepared using the black magnetic iron oxide particle powder according to the present invention satisfies the following relational expression.
a * (I): a * value when the film thickness is 4 to 6 μm (typically 5 μm) a * (II): a * value when the film thickness is 23 to 26 μm (typically 24 μm) When α = a * (I) / a * (II), 1.0 ≦ α ≦ 2.0 is satisfied. When the α is 1.0 to 2.0, it has excellent blackness. A more preferable α value is 1.1 to 1.9.

The black magnetic iron oxide particles according to the present invention preferably have a BET specific surface area of 3 to 30 m ² / g. More preferably, it is 4 to 20 m ² / g. When the BET specific surface area is less than 3 m ² / g, the average particle diameter exceeds 0.50 μm. As described above, when toner particles are used, the uniformity of charging of the toner is impaired and the coloring power is reduced. High-resolution toner cannot be obtained. When the BET specific surface area exceeds 30 m ² / g, the adhesion between the powder layers is increased, and when the magnetic toner is used, the dispersibility in the resin is deteriorated. A more preferable BET specific surface area is 4 to 20 m ² / g.

The saturation magnetization of the black magnetic iron oxide particles according to the present invention in an external magnetic field of 796 kA / m (10 kOe) is preferably 85.0 to 92.0 Am ² / kg, more preferably 86.0 to 90.0 Am ² / kg. Particularly, it is suitable when used as a toner for a high-speed copying machine.

The black magnetic iron oxide particles according to the present invention preferably have an Si compound, an Al compound, an Si compound and an Al compound on the particle surface, contain 0.02 to 1.0% by weight of Si, and have an Al content of 0.1. The content of 02 to 1.0% by weight is preferable for forming a heat-resistant layer on the black magnetic iron oxide particles. When the amount of Al or Si exceeds 1.0% by weight, the amount of adsorbed water may increase. When toner is used, the environmental stability of the toner may be affected. When the amount of Al and the amount of Si are less than 0.02% by weight, it is insufficient as a heat-resistant layer.

The electric resistance value of the black magnetic iron oxide particle powder according to the present invention when the molded body density is 2.7 g / cm ^{3 and} a DC voltage of 15 V is applied is preferably 1 × 10 ⁵ Ωcm or less, more preferably 8 × 10. ⁴ Ωcm or less.

The black magnetic iron oxide particle powder of the present invention has an octahedral shape and contains 0.19 to 1.90 atomic% of silicon in terms of silicon element with respect to the iron element. The b * value of the coating film is 2 or less when the film thickness prepared using is 23 to 26 μm,
a * (I): a * value when the film thickness is 4 to 6 μm a * (II): a * value when the film thickness is 23 to 26 μm α = a * (I) / a * (II) When
It is black magnetic iron oxide particle powder characterized by satisfying 1.0 ≦ α ≦ 2.0. The black magnetic iron oxide particle powder preferably satisfies the above-described formulas (1) and (2) of the present invention 1, and preferably satisfies the definitions of the present inventions 2 to 6 and the above description.

Next, a method for producing black magnetic iron oxide particles according to the present invention will be described.

The black magnetic iron oxide particle powder according to the present invention comprises an aqueous ferrous salt solution, an alkaline hydroxide aqueous solution of 0.90 to 1.00 equivalent to the ferrous salt in the ferrous salt aqueous solution, The pH of the reaction solution containing ferrous hydroxide colloid obtained by reacting 0.05 to 1.00 atomic% of water-soluble silicate in terms of Si with respect to Fe in the ferrous salt solution is 8 to The first-stage reaction that produces nucleated magnetite particles by adjusting the temperature to 9 and conducting an oxygen-containing gas while heating in a temperature range of 70 to 100 ° C. to conduct an oxidation reaction of iron to a rate of 7 to 12%. Then, an alkali hydroxide aqueous solution is added so as to be 1.01 to 1.50 equivalent to the ferrous salt reaction solution containing the nucleated magnetite particles and the ferrous hydroxide colloid after the completion of the first stage reaction, While heating in the temperature range of 70-100 ° C, oxygen-containing gas is vented to iron acid The second stage reaction in which the reaction rate is 40 to 60%, the pH is once adjusted to 5 to 9 after the completion of the second stage reaction, and then the pH is readjusted to 9.5 or more. 20 to 200% (total of 1.9 atomic% or less of silicon elements added in the first stage reaction and third stage reaction) is added to the water-soluble silicate added in the first stage reaction. It can be obtained by conducting an oxidation reaction by passing an oxygen-containing gas while heating in a temperature range of 100 ° C. (third stage reaction).

As the ferrous salt aqueous solution in the present invention, ferrous sulfate aqueous solution, ferrous sulfate and ferrous chloride aqueous solution or the like can be used.

Examples of the alkali hydroxide aqueous solution in the present invention include an aqueous solution of an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, an aqueous solution of an alkaline earth metal hydroxide such as magnesium hydroxide and calcium hydroxide, An aqueous alkali carbonate such as sodium carbonate, potassium carbonate or ammonium carbonate, aqueous ammonia, or the like can be used.

In the first stage reaction, the addition amount of the alkali hydroxide aqueous solution is 0.90 to 1.0 equivalent with respect to Fe ²⁺ in the ferrous salt aqueous solution. The range is preferably 0.92 to 0.99 equivalent. When the amount is less than 0.90 equivalent, acicular goethite particles are mixed. When exceeding 1.0 equivalent, a silicon element becomes easy to be taken in and the magnetic iron oxide particle which is excellent in blackness cannot be obtained.

In the first stage reaction, the amount of water-soluble silicate added is 0.05 to 1.00 atomic% in terms of Si with respect to Fe in the ferrous salt solution. When the addition amount of the water-soluble silicate is outside the above range, the distribution of silicon element is not constant, and magnetic iron oxide particles having excellent blackness cannot be obtained. A more preferred amount of water-soluble silicate is 0.07 to 0.95 atomic%.

As the water-soluble silicate used in the present invention, sodium silicate, potassium silicate and the like can be used.

The pH of the reaction solution obtained by reacting the ferrous salt aqueous solution, the alkali hydroxide aqueous solution and the water-soluble silicate is adjusted to 8-9. By adjusting the pH of the reaction solution within the above range, the Si distribution at the center of the particles can be suppressed.

After adjusting the pH of the reaction solution, an oxygen-containing gas is aerated while heating in the temperature range of 70 to 100 ° C. When the temperature is lower than 70 ° C., acicular goethite particles are mixed. Magnetite particles are produced even when the temperature exceeds 100 ° C., but it is not industrially easy because an apparatus such as an autoclave is required. A more preferred temperature range is 75 to 98 ° C.

The oxidation means is performed by venting an oxygen-containing gas (for example, air) into the liquid.

In the present invention, an oxygen-containing gas is bubbled through the reaction solution, and the oxidation reaction is performed to an iron oxidation reaction rate of 7 to 12%, thereby forming the first stage reaction in which nucleated magnetite particles are generated. When the oxidation reaction rate is less than 7%, the particle size distribution of the black magnetic iron oxide is deteriorated and magnetic iron oxide particles having excellent blackness cannot be obtained. When it exceeds 12%, hexahedrons other than octahedrons, polyhedrons, and spherical particles are mixed. A more preferable oxidation reaction rate is 8-11. As a method of adjusting the oxidation reaction rate of iron to 7 to 12%, while measuring the Fe ²⁺ content in the reaction solution with time by the method shown in the examples described later to obtain the oxidation reaction rate (%), When the oxidation reaction rate falls within the above range, the first stage reaction is terminated.

An aqueous alkali hydroxide solution is added so as to be 1.01 to 1.50 equivalent to the ferrous salt reaction solution containing the nucleated magnetite particles and the ferrous hydroxide colloid after the completion of the first stage reaction. When the addition amount of the alkali hydroxide aqueous solution is less than 1.01 equivalent, hexahedral, polyhedral and spherical particles other than octahedron are mixed. When the addition amount of the alkali hydroxide aqueous solution exceeds 1.5 equivalents, the particle size distribution becomes large and a uniform particle size cannot be obtained. A more preferable addition amount of the aqueous alkali hydroxide solution is 1.02 to 1.48.

A second-stage reaction is performed in which an oxygen-containing gas is vented while heating in a temperature range of 70 to 100 ° C. to perform an oxidation reaction until the iron oxidation reaction rate reaches 40 to 60%. When the temperature is lower than 70 ° C., acicular goethite particles are mixed. Magnetite particles are produced even when the temperature exceeds 100 ° C., but it is not industrially easy because an apparatus such as an autoclave is required.

In the second stage reaction of the present invention, an oxygen-containing gas is passed through the reaction solution to carry out the oxidation reaction until the iron oxidation reaction rate is 40 to 60%. If the oxidation reaction rate is less than 40%, the subsequent oxidation reaction becomes long and the particle size distribution becomes large, and it is impossible to obtain a product having a uniform particle size. If it exceeds 60%, the oxidation reaction in the third stage reaction becomes short, the particle size distribution becomes large, and a uniform particle size cannot be obtained. As a method for adjusting the oxidation reaction rate of iron to 40 to 60%, while measuring the Fe ²⁺ content in the reaction solution over time by the method shown in the examples described later to obtain the oxidation reaction rate (%), When the oxidation reaction rate falls within the above range, the second stage reaction is terminated.

After completion of the second stage reaction, the pH of the reaction solution is once adjusted to 5 to 9 (relay condition). If the pH is not adjusted, the viscosity of the ferrous reaction aqueous solution containing ferrous hydroxide colloid is increased, and the uniformity of the reaction temperature and the uniformity of the reaction rate are impaired. The growth rate is not uniform, the crystallinity is poor, and a uniform particle size cannot be obtained.

Thereafter, the pH of the reaction solution is readjusted to 9.5 or higher. The amount of the aqueous alkali hydroxide used is 1.00 equivalent or more with respect to the remaining Fe ²⁺ . If the amount is less than 1.00 equivalent, the remaining Fe ²⁺ may not precipitate in its entirety. Practically, the amount is preferably 1.00 equivalent or more and considering industrial properties.

The water-soluble silicate is added again to the reaction solution subjected to the second stage reaction. In the third stage reaction, the water-soluble silicate to be added is 20 to 200% in molar ratio with respect to the water-soluble silicate added in the first stage reaction. It is preferable that silicon elements to be added are 1.9 atomic% or less in total.

Next, an oxygen-containing gas is passed through the reaction solution while heating the reaction solution to a temperature range of 70 to 100 ° C. to perform an oxidation reaction. A more preferred temperature range is 72 to 98 ° C.

Further, when forming a compound comprising Al or Al and Si on the surface of the black magnetic iron oxide particles, water-soluble aluminum is contained in the suspension containing the black magnetic iron oxide particles after the second stage reaction. After adding a salt, or a water-soluble aluminum salt and a water-soluble salt silicate so that the Al amount is 0.02 to 1.0 wt% and the Si amount is 0.02 to 1.0 wt%, the pH is 5 It can be obtained by precipitating and depositing Si and Al on the surface of the black magnetic iron oxide particles while adjusting to a range of ˜9.

<Action>
The black magnetic iron oxide particle powder according to the present invention has an octahedral shape, and by making the distribution of silicon element contained inside the particle constant, the value of a * is small even when the coating film thickness is thin. It has excellent blackness, and even when used as a magnetic toner, it has excellent blackness.

The black magnetic iron oxide particle powder according to the present invention has an octahedral shape and the distribution of silicon element contained in the particle can be made constant, so that magnetite particles having excellent blackness can be obtained. It is a thing.

A typical embodiment of the present invention is as follows.

Shape, average particle size, coefficient of change:
The particle shape and average particle diameter of the black magnetic iron oxide particles were observed by “Scanning Electron Microscope S-4800” (manufactured by Hitachi High-Technologies Corporation), and indicated by average values measured from electron micrographs.

The change coefficient in the particle size distribution was expressed as% by dividing the standard deviation σ of the number distribution by the average particle diameter and multiplying by 100.

Specific surface area:
The specific surface area was represented by a value measured by BET method using “Mono Sorb MS-II” (manufactured by Yuasa Ionics Co., Ltd.).

Oxidation reaction rate:
The oxidation reaction rate of the ferrous salt in the first stage reaction and the second stage reaction was calculated by the following formula by measuring the Fe ²⁺ content in the reaction solution.
(AB) ÷ A × 100 = Oxidation reaction rate (%)
However, A is the content of Fe ^{2+ in} the reaction solution immediately after mixing the aqueous ferrous salt solution and the aqueous alkaline solution, and B is the ferrous salt reaction solution containing a mixture of ferrous hydroxide and magnetite particles. Fe ²⁺ content.

Si and Al element amounts:
The amount of Si and the amount of Al in the black magnetic iron oxide particle powder were measured with a “fluorescence X-ray analyzer RIX-2100” (manufactured by Rigaku Denki Kogyo Co., Ltd.), and found in terms of elements with respect to the black magnetic iron oxide particle powder Value.

Surface Si amount:
The amount of Si on the surface of the black magnetic iron oxide particle powder is 30 minutes or more by mixing the black magnetic iron oxide particle powder and ion-exchanged water and then dispersing and mixing it with an aqueous alkali hydroxide solution. After stirring, the amount of Si in the black magnetic iron oxide particle powder obtained by filtering and drying the suspension was measured, and the difference from the total amount of Si before treatment with the alkali was defined as the amount of Si on the particle surface.

Dissolution rate of silicon element and sodium element:
The dissolution rates of silicon element and sodium element relative to the dissolution rate of iron element can be determined by the following method.
30 g of black magnetic iron oxide particle powder is suspended in 3 L of 3 mol / l hydrochloric acid solution. Next, the black magnetic iron oxide particle suspension hydrochloric acid solution is kept at 50 ° C., and sampling is performed at regular intervals until all the black magnetic iron oxide particles are dissolved, and this is filtered through a membrane filter to obtain a filtrate. The filtrate is subjected to quantitative determination of iron element and silicon element with an induction plasma atomic emission spectrophotometer. The iron element dissolution rate and the silicon element dissolution rate are calculated by the following equations.

Iron element dissolution rate (%) = iron element concentration in sample (mg / l) / iron element concentration when completely dissolved (mg / l) × 100
Dissolution rate of silicon element (%) = concentration of silicon element in sample (mg / l) / concentration of silicon element when completely dissolved (mg / l) × 100
Sodium element dissolution rate (%) = concentration of sodium element in sample (mg / l) / concentration of sodium element when completely dissolved (mg / l) × 100

Film color characteristics:
The a * value and b * value of the coating film using the black magnetic iron oxide particle powder were measured as follows.
8 g of the polyester resin is dissolved in 20 g of toluene. 8 g of black magnetic iron oxide particle powder and 50 g of 1.5 mmφ glass beads are added to a solution in which a polyester resin is dissolved in toluene, and dispersed by a paint conditioner for 4 hours to obtain a dispersion. This dispersion is applied onto a cast-coated paper using a bar coater using a bar having a wet film thickness of 12 μm, 40 μm, or 100 μm. After drying, colorimetry is performed using a spectrocolorimetric densitometer X-rite 939.

First, the thickness (A) of the cast coated paper is measured using a digital electronic micrometer K351C (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the cast coated paper and the coating film formed on the cast coated paper (total of the thickness of the cast coated paper and the coating film) is measured in the same manner. The film thickness of the coating film was (B)-(A), 30 measurements were taken, and the average value was taken as the film thickness of the coating film.

Electrical resistance:
The electrical resistance value of the black magnetic iron oxide particle powder was measured by measuring 0.5 g of the particle powder to be measured and using a KBr tablet molding machine (manufactured by Shimadzu Corporation) with a hand reading (SSP-10 model manufactured by Shimadzu Corporation) The pressure molding is performed at a pressure of 14 MPa for 10 seconds (under this condition, a molded body having a density of about 2.7 g / cm ³ is obtained. However, when other molding machines are used, the density is suitably 2 It is sufficient to set a condition of about 0.7 g / cm ^3, and if the density greatly exceeds 2.5 to 2.8 g / cm ³ , the electric resistance value changes and it is difficult to compare the measured values. Become.). Next, the pressure-formed sample is set between stainless steel electrodes. At that time, the electrodes are completely separated from the outside by a fluororesin holder. A voltage of 15 V is applied to the set sample with a Wheatstone bridge (TYPE 2768 manufactured by Yokogawa Electric Corporation), and the resistance value is measured. The measured value R (Ω) at that time, the electrode area A (cm ² ) and the thickness t (cm) of the sample are measured, and the volume resistivity X (Ωcm) is calculated by the following equation.
X = R / (A / t)

Example 1:
Fe ²⁺ : mixed with 16 l of ferrous sulfate aqueous solution containing 1.5 mol / l (Fe ²⁺ : 24 mol) and 15.2 l of 3.0N sodium hydroxide solution (corresponding to 0.95 equivalent to Fe ²⁺ ). Then, the pH was adjusted to 8.2 to produce a ferrous salt suspension. At this time, 13.3 g of No. 3 water glass (SiO ₂ : 28.8 wt%) as a silicon component (corresponding to 0.25 atomic% in terms of Si with respect to Fe) was diluted in 0.5 l of ion-exchanged water. This was previously added to sodium hydroxide. The ferrous salt suspension was aerated at 70 ° C. per minute at a temperature of 90 ° C. to carry out the oxidation reaction until the ferrous salt oxidation reaction rate reached 10%. A ferrous salt suspension was obtained (first stage reaction).

Next, 3.2 l of a 3.0N sodium hydroxide solution was added to the ferrous salt suspension containing the magnetite nuclei particles (corresponding to 1.15 equivalents with respect to Fe ²⁺ ). 70 l of air was ventilated to carry out the oxidation reaction until the ferrous salt oxidation reaction rate reached 50% (second stage reaction).

Next, an appropriate amount of 16.1 N sulfuric acid was added to the ferrous salt suspension containing the magnetite nuclei particles and adjusted to pH 8 (relay conditions).

Then, an appropriate amount of 3.0N sodium hydroxide solution was added to adjust the pH to 10.5. At this time, 21.3 g of No. 3 water glass (SiO ₂ 28.8 wt%) as a silicon component (corresponding to 0.40 atomic% in terms of Si with respect to Fe. Water-soluble silicate added in the first stage reaction) The total amount of silicon elements added in the first stage reaction and the third stage reaction is 0.65 atomic%) diluted in 0.5 l of ion-exchanged water. The mixture was added to the ferrous salt suspension containing the particles, and 70 l of air was aerated at a temperature of 90 ° C. to generate magnetite particles (third stage reaction).

The generated particles were washed with water, filtered, dried and pulverized by a conventional method. The obtained magnetite particles were octahedral, the average particle size was 0.14 μm, the coefficient of change in particle size distribution was 26%, and the Si content was 0.65 atomic%.

Further, the silicon element dissolution rate (a) at an iron element dissolution rate of 10% is 10.8%, the iron element dissolution rate is 20 <X _20-40 ≦ 40%, 40 <X _40-60 ≦ 60%, 60 <X The silicon element dissolution rate (Y) in each range of _{60 to 80} ≦ 80% is 31.6% for the iron element dissolution rate of X _{20 to 40} , 32.5% for the silicon element dissolution rate, and the iron element of X _{40 to 60} The dissolution rate is 53.6%, the silicon element dissolution rate is 53.9%, the iron element dissolution rate of X _60-80 is 72.8%, the silicon element dissolution rate is 71.2%, and the iron element dissolution rate is 50%. %, The dissolution rate of sodium element was 63%.

This black magnetic particle powder has a b * value of 0.3 at a coating film thickness of 24 μm, an a * value (a * (II)) of 0.4, and an a * value at a coating film thickness of 5 μm ( a * (I)) is 0.5, and the ratio α (a * (I) / a * (II)) of the a * value at a coating film thickness of 5 μm to the a * value at a coating film thickness of 24 μm is 1. .3.

The electric resistance of the black magnetic particle powder was 5 × 10 ⁴ Ωcm. This black magnetic powder had a uniform distribution of silicon elements contained in the particles and was excellent in blackness.

Examples 2-12, Comparative Examples 5-9:
Equivalent ratio in first stage reaction, silicon element amount, oxidation reaction rate up to 10% pH, equivalent ratio in second stage reaction, oxidation reaction rate, pH of relay conditions, pH in third stage reaction, silicon element amount A black magnetic powder was obtained in the same manner as in Example 1 except that the changes were made as shown in FIG.
The coating layer of Si and Al was adjusted to pH 7 by adding appropriate amounts as shown in the table using No. 3 water glass as the silicon component and 1.9 mol / l aluminum sulfate solution 1 as the aluminum component in the suspension containing magnetite particles. Then, a coating layer was formed.

Comparative Example 1:
Fe ²⁺ 1.5 mol / l containing ferrous solution ^16l sulfate (Fe 2+ 24 mol) and sodium hydroxide 3.0N solution 16.8l ^{(Fe 2+} to 1.05 corresponds to eq.) Were mixed, A ferrous salt suspension was produced. At this time, 75.7 g of No. 3 water glass (SiO ₂ 28.8 wt%) as a silicon component (corresponding to 1.42 atomic% in terms of Si with respect to Fe) was diluted in 0.5 l of ion-exchanged water. Was added to sodium hydroxide. The ferrous salt suspension was oxidized at a temperature of 90 ° C. by passing 70 l of air per minute to generate magnetite particles.

Comparative Example 2:
1 in terms of Si with respect to ferrous sulfate aqueous solution ^16l (Fe 2+ ^24mol) No. 3 water glass _(SiO 2 _28.8wt%) as the silicon component 80.0 g (Fe containing Fe ²⁺ 1.5mol / l. It corresponds to 50 atomic%.) Diluted in 0.5 l of ion exchange water and added. This aqueous solution was mixed with 16.3 l of a 3.0N sodium hydroxide solution (corresponding to 1.02 equivalent to Fe ²⁺ ) to obtain a ferrous salt suspension. The pH of this ferrous salt suspension was adjusted to 12 using sodium hydroxide solution. The ferrous salt suspension was oxidized at a temperature of 90 ° C. by aeration of 30 l of air per minute, and when the oxidation reaction rate exceeded 50%, the aeration rate was reduced to 20 l per minute. Further, when the oxidation reaction rate exceeded 75%, the aeration rate was reduced to 10 l per minute. When the oxidation reaction rate exceeded 90%, the aeration rate was reduced to 5 liters per minute and oxidation was performed until Fe ²⁺ ions disappeared to generate magnetite particles.

Comparative Example 3:
Fe ²⁺ 1.5 mol / l containing ferrous solution ^16l sulfate (Fe 2+ 24 mol) and sodium hydroxide 3.0N solution 18.4l ^{(Fe 2+} to 1.15 corresponds to eq.) Were mixed, A ferrous salt suspension was produced. The ferrous salt suspension was aerated at 70 ° C. per minute at a temperature of 90 ° C. to carry out an oxidation reaction until the oxidation reaction rate of the ferrous salt reached 50%. A ferrous salt suspension was obtained (first stage reaction).

Next, 9.2 l of a 3.0N sodium hydroxide solution was added to the ferrous salt suspension containing the magnetite nuclei particles (corresponding to 1.15 equivalents of the remaining Fe ²⁺ ). What diluted 20.8 g (corresponding to 0.39 atomic% in terms of Si with respect to Fe) of No. 3 water glass (SiO ₂ 28.8 wt%) as a silicon component in 0.5 l of ion-exchanged water Added to sodium hydroxide. Magnetite particles were generated by aeration of 70 l of air per minute at a temperature of 90 ° C. (second stage reaction).

The production conditions at this time are shown in Table 1, and the characteristics of the produced magnetite particle powder are shown in Table 2.

Comparative Example 4:
Based on Comparative Example 3, various conditions were changed to obtain black magnetic iron oxide particles.

Since the black magnetic iron oxide particles according to the present invention are excellent in environmental stability, they can be suitably used as magnetic powder for magnetic toner for electrophotography.

Claims

It has an octahedral shape, contains 0.19 to 1.90 atomic% of silicon in terms of silicon element, and has an iron element solubility (X) of 20 <X 20 to 40 ≦ 40%, 40 <X 40-60 ≦ 60%, 60 <X 60-80 ≦ 80% Silicon element dissolution rate (Y) is silicon when iron element dissolution rate (X) and iron element dissolution rate are 10% A black magnetic iron oxide particle powder characterized by satisfying the following formulas (1) and (2) consisting of an element dissolution rate (a).
{(100−a) X + 100 (a−10)} / 90−10 (1−a / 100) ≦ Y ≦ {(100−a) X + 100 (a−10)} / 90 + 10 (1−a / 100) (1)
10 ≦ a ≦ 80 (2)
(However, 10 ≦ X ≦ 100, 10 ≦ Y ≦ 100)
The sodium content in the black magnetic iron oxide particles is 0.02 to 0.10% by weight, and the sodium element dissolution rate when the iron element dissolution rate is 50% with respect to the total iron element amount is the total sodium element dissolution amount. 2. The black magnetic iron oxide particle powder according to claim 1, which is 50% or more.
The black magnetic iron oxide particle powder according to claim 1 or 2, having an average particle diameter of 0.05 to 0.30 µm.
The black magnetic iron oxide particle powder according to any one of claims 1 to 3, wherein a change coefficient in particle size distribution is 30% or less.
The b * value of the coating film when using a black magnetic iron oxide particle powder with a film thickness of 23 to 26 μm is 2 or less,
a * (I): a * value when the film thickness is 4 to 6 μm a * (II): a * value when the film thickness is 23 to 26 μm α = a * (I) / a * (II) When
The black magnetic iron oxide particle powder according to claim 1, wherein 1.0 ≦ α ≦ 2.0 is satisfied.
The black magnetic iron oxide particle powder according to any one of claims 1 to 5, which has a coating layer of Si and Al.
A black magnetic iron oxide particle powder having an octahedral shape and containing 0.19 to 1.90 atomic% of silicon in terms of silicon element with respect to iron element, and made using black magnetic iron oxide particle powder The b * value of the coating film when the film thickness is 23 to 26 μm is 2 or less,
a * (I): a * value when the film thickness is 4 to 6 μm a * (II): a * value when the film thickness is 23 to 26 μm α = a * (I) / a * (II) When
Black magnetic iron oxide particle powder characterized by satisfying 1.0 ≦ α ≦ 2.0.
Ferrous salt aqueous solution, 0.90 to 1.00 equivalent of an alkali hydroxide aqueous solution with respect to the ferrous salt in the ferrous salt aqueous solution, and Fe in the ferrous salt solution in terms of Si The pH of the reaction solution containing ferrous hydroxide colloid obtained by reacting with 0.05 to 1.00 atomic% of water-soluble silicate was adjusted to 8 to 9, and the temperature range was 70 to 100 ° C. A first stage reaction in which an oxygen-containing gas is ventilated while heating to a temperature to cause an oxidation reaction rate of iron to 7 to 12% to produce nucleated magnetite particles, and the nucleated magnetite after completion of the first stage reaction An aqueous alkali hydroxide solution was added to the ferrous salt reaction liquid containing particles and ferrous hydroxide colloid so as to be 1.01 to 1.50 equivalents, and oxygen was added while heating to a temperature range of 70 to 100 ° C. Oxidation reaction is performed up to 40-60% of iron oxidation reaction rate by venting the contained gas After the completion of the second stage reaction, the pH is temporarily adjusted to 5-9 after the completion of the second stage reaction, and then the pH of the reaction solution is readjusted to 9.5 or higher, and then water-soluble silicate is added in the first stage reaction. 20 to 200% of the water-soluble silicate added (total of 1.9 atomic percent or less of silicon elements added in the first stage reaction and third stage reaction) is added and heated to a temperature range of 70 to 100 ° C. The method for producing black magnetic iron oxide particle powder according to any one of claims 1 to 7, wherein the oxidation reaction is carried out by aeration of an oxygen-containing gas (third stage reaction).