JP6521254B2 - Black magnetic iron oxide particle powder and method for producing the same - Google Patents

Description

  The black magnetic iron oxide particle powder according to the present invention has an octahedral shape and is black, so it can be used as a black coloring pigment for paints, resins, printing inks and the like, and also black magnetic magnets for magnetic toners. When used as particles, a magnetic toner having a high degree of blackness can be obtained.

  Conventionally, as one of electrostatic latent image developing methods, a so-called "one-component magnetic toner" using composite particles obtained by mixing and dispersing magnetic particles such as magnetite particles in a resin without using a carrier as a developer "Development method by" is widely known and widely used.

  Recently, with the advancement of laser beam printers and digital copiers, there has been a demand for magnetic toners, which are developers, to have higher blackness.

  The degree of blackness of the magnetic toner is largely dependent on the degree of blackness of magnetite contained in the magnetic toner. Therefore, black magnetic particles having a high degree of blackness are strongly required.

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

  Various attempts have been made to obtain magnetite particles having a higher degree of blackness (Patent Documents 1 to 3).

JP-A-3-131866 JP, 2008-184338, A JP, 2011-213548, A

  In view of the above-mentioned problems, black magnetic iron oxide particle powder which is fine particles and excellent in blackness is the most demanded at present, but such black magnetic iron oxide particle powder is still provided. Absent.

  In the magnetite particles described in the above-mentioned Patent Document 1, the distribution of the silicon element is not constant, so it can not be said that the degree of blackness is sufficient.

  Moreover, in the magnetite particle powder described in the above-mentioned Patent Document 2, since the distribution of the silicon element is not constant, it can not be said that the degree of blackness is sufficient.

  Moreover, in the magnetite particles described in the above-mentioned Patent Document 3, since the distribution of the silicon element is not constant, it can not be said that the degree of blackness is sufficient.

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

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

That is, the present invention has an octahedral shape, and contains 0.19 to 1.90 atomic% silicon in terms of silicon element with respect to iron element, and the iron element dissolution rate (X%) is 20 <X _20. Solubility rate of silicon element (Y%) in each range of 40 _{to 40} ≦ 40%, 40 <X _{40 to 60} ≦ 60%, 60 <X _{60 to 80} ≦ 80%, iron element dissolution rate (X%) and iron element It is a black magnetic iron oxide particle powder characterized by satisfying the following formulas (1) and (2) consisting of the 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)

  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 It is a black magnetic iron oxide particle powder according to the present invention 1 which is 50% or more with respect to the total dissolved amount of sodium element (invention 2).

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

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

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

  Moreover, this invention is a black magnetic iron oxide particle powder in any one of this invention 1-5 which has a coating layer of Si and Al (this invention 6).

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

Further, according to the present invention, a ferrous salt aqueous solution, an aqueous solution of an alkali hydroxide of 0.90 to 1.00 equivalent to a ferrous salt in the ferrous salt aqueous solution, and a ferrous salt solution Adjust 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 to Fe to 8 to 9, 70 The first stage reaction which generates nuclear crystal magnetite particles by conducting an oxidation reaction until the oxidation reaction rate of iron is 7 to 12% by bubbling an oxygen-containing gas while heating to a temperature range of -100 ° C. An aqueous solution of alkali hydroxide is added so as to be 1.01 to 1.50 equivalents with respect to a ferrous salt reaction liquid containing nuclear crystal magnetite particles and ferrous hydroxide colloid after completion, and the temperature of 70 to 100 ° C. The oxidation reaction rate of iron reaches 40 to 60% by passing oxygen-containing gas while heating to the range. After the completion of the second stage reaction in which the second stage reaction is carried out, the pH is once adjusted to 5 to 9 and then the pH of the reaction solution is readjusted to 9.5 or more. a 20 to 200% relative to the water-soluble silicate added in stage reaction, added as elemental silicon to be added in the first stage reaction and the third stage reaction is 1.9 atomic% or less in total pressure The black magnetic iron oxide particles according to any one of the present inventions 1 to 7, characterized in that the oxidation reaction is carried out by passing an oxygen-containing gas while heating to a temperature range of 70 to 100 ° C (third step reaction). It is a method of producing a powder (Invention 8).

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

  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 particle powder according to the present invention is compositionally composed of magnetite ((FeO) x · Fe ₂ O ₃ , 0 <x ≦ 1).

  The particle shape of the black magnetic iron oxide particle powder according to the present invention is octahedral. In the present invention, the particle shape is octahedral to obtain a black magnetic iron oxide particle powder having a high degree of blackness.

  The black magnetic iron oxide particle powder according to the present invention contains silicon at 0.19 to 1.90 atomic percent in terms of silicon element based on iron element. When the content of silicon is less than 0.19 atomic%, the particle size distribution of the black magnetic iron oxide is deteriorated, and magnetic iron oxide particles excellent in blackness can not be obtained. When the content of silicon exceeds 1.90 atomic%, byproducts other than magnetite are generated, and magnetic iron oxide particles excellent in blackness can not be obtained. The preferred silicon content is 0.25 to 1.87 atomic percent, more preferably 0.30 to 1.85 atomic percent.

The black magnetic iron oxide particle powder according to the present invention has an iron element dissolution rate (X%) of 20 <X _{20 to 40} ≦ 40%, 40 <X _{40 to 60} ≦ 60%, 60 <X _{60 to 80} ≦ 80% The black magnetic iron oxide characterized in that the silicon element dissolution rate (Y%) in each range of the above satisfies the following formulas (1) and (2) consisting of the silicon element dissolution rate a% at an iron element dissolution rate of 10%. It is a particle powder.

{(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 black magnetic iron oxide particle powder according to the present invention is to obtain magnetic iron oxide particle powder excellent in blackness while being fine by satisfying the above-mentioned relational expression.
Here, the iron element dissolution rate (X) is the ratio of dissolved Fe to Fe in the whole particle, 0% being in the undissolved state and 100% in the dissolved state. Similarly, in the silicon element dissolution rate (Y), 0% is a state in which silicon is not dissolved, and 100% is a state in which all silicon present in the magnetic iron oxide particles is completely 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 among iron element dissolution rate (X), silicon element dissolution rate (a) and silicon element dissolution rate (Y) at black iron oxide dissolution rate of 10%, for black magnetic iron oxide particles. It shows the distribution of Si in the black magnetic iron oxide particles. That is, in the present invention, to satisfy 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 silicon element is dissolved at a similar ratio with the dissolution of the iron element, which means that the silicon element is uniformly present in the magnetic iron oxide. It is. In addition, iron element dissolution rate (X) in each range may select any dissolution rate within the range, and iron element dissolution rate (X%) is 20 <X _20-40 ≦ 40%, 40 In each range of <X _{40 to 60} ≦ 60%, 60 <X _{60 to 80} ≦ 80%, silicon measured at any point within the range of 20 to 40%, 40 to 60%, and 60 to 80%, respectively. The elemental dissolution rate (Y) may be evaluated. In addition, Formula (1) is satisfied in each range of iron element dissolution rate (X%) of 20 <X _20-40 ≦ 40%, 40 <X _40-60 ≦ 60%, 60 <X _60-80 ≦ 80%. There is a need to.

  In the formula (1), when Y is less than the lower limit value, a large amount of Si is present in the center of the particle, which is not preferable. In addition, 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, the ratio of silicon element dissolved up to the iron element dissolution range is the dissolution rate of iron element It is too low compared to the above, and there is still a large amount of silicon element not dissolved in the undissolved particles, and the silicon element is localized at the center of the particle and is uniformly present. It will not be. On the other hand, when the silicon element dissolution rate (Y) exceeds the upper limit value, the ratio of silicon element dissolved to the iron element dissolution range is too large compared to the dissolution rate of iron element, and the already dissolved portion In this case, the silicon element is contained in a large amount, and the silicon element is localized near the particle surface and is not uniformly present.

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

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

  In the black magnetic iron oxide particles according to the present invention, 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 (total sodium content). The proportion is preferably 50% or more. This indicates that the sodium element present in the black magnetic iron oxide particles is present in greater amounts in the vicinity of the surface than in the center of the particles. More preferably, it is preferable that the dissolution rate of sodium element when the dissolution rate of iron element is 50% with respect to the total amount of iron elements is 55% or more with respect to the total dissolution amount of sodium element (total sodium content).

  The average particle diameter 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 size is less than 0.05 μm, the number of particles in a unit volume increases excessively and the number of contact points between particles increases, so the adhesion between powder layers increases, and when it is used as a magnetic toner, in the resin Dispersion to When the average particle size exceeds 0.30 μm, the number of black magnetic iron oxide particles contained in one toner particle decreases, and the distribution of black magnetic iron oxide particles in each toner particle is uneven, and the result is as a result. And the uniformity of charging of the toner is impaired. A more preferable average particle size is in the range of 0.07 to 0.28 μm.

  The variation coefficient in the particle size distribution of the black magnetic iron oxide particle powder 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.

  It is preferable that the b * value of the coating film with a film thickness of 23 to 26 μm (typically 24 μm) prepared using the black magnetic iron oxide particle powder according to the present invention is 2 or less. When the b * value is 2.0 or less, the blackness is excellent. More preferable b * value is 0 to 1.8.

Moreover, it is preferable that a * which changed and measured the film thickness of the coating film created using the black magnetic iron oxide particle powder which concerns on this invention variously satisfy | fills the following relational expression.
a * (I): a * value at a coating film thickness of 4 to 6 μm (typically 5 μm) a * (II): a * value at a coating film thickness of 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, the blackness is excellent. The 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 size exceeds 0.50 μm, and as described above, when it is used as toner particles, the charging uniformity of the toner is impaired and the coloring power is reduced. I can not get high resolution toner. When the BET specific surface area exceeds 30 m ² / g, the adhesion between the powder layers becomes large, and in the case of using a magnetic toner, the dispersibility in the resin becomes worse. A more preferred BET specific surface area is 4 to ²⁰ m ² / g.

Saturation magnetization of preferably 85.0~92.0Am ² / kg in the external magnetic field 796 kA / m of the black magnetic iron oxide particles according to the present invention (10 kOe), more preferably be 86.0~90.0Am ² / kg In particular, it is suitable when used as a toner for high speed copying machines.

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

The molded product density of the black magnetic iron oxide particles according to the present invention is preferably 2.7 × 10 ⁵ Ωcm or less, more preferably 8 × 10 ⁵ at a DC voltage of 15 g of a molded product of 2.7 g / cm ^{3. It is 4} Ωcm or less.

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

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

  A black magnetic iron oxide particle powder according to the present invention comprises a ferrous salt aqueous solution, an aqueous alkali hydroxide solution of 0.90 to 1.00 equivalents with respect to a 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 a water-soluble silicate in terms of Si to Fe in a monoiron salt solution Adjust to 9 and pass oxygen containing gas while heating to a temperature range of 70 to 100 ° C to perform oxidation reaction to 7 to 12% of iron oxidation reaction rate to generate nuclear crystal magnetite particles An aqueous alkali hydroxide solution is added in an amount of 1.01 to 1.50 equivalents with respect to the ferrous salt reaction solution containing the nucleated magnetite particles and ferrous hydroxide colloid after completion of the first stage reaction; Oxidation of iron by passing oxygen-containing gas while heating to a temperature range of 70 to 100 ° C. The second step reaction of oxidation reaction to 40 to 60% of the reaction rate, the pH is once adjusted to 5 to 9 after completion of the second step reaction, and then the pH is readjusted to 9.5 or more, and then the water-soluble silicic acid 20 to 200% (total of 1.9 at% or less of silicon element added in the first reaction and the third reaction) to the water-soluble silicate added in the first reaction The oxidation reaction can be carried out by passing oxygen-containing gas while heating to 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 can be used.

  The aqueous alkali hydroxide solution in the present invention includes 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, Aqueous alkali carbonate solutions such as sodium carbonate, potassium carbonate, ammonium carbonate and the like, aqueous ammonia and the like can be used.

The amount of the aqueous alkali hydroxide solution added in the first stage reaction is 0.90 to 1.0 equivalent with respect to Fe ²⁺ in the ferrous salt aqueous solution. Preferably, it is in the range of 0.92 to 0.99 equivalents. If it is less than 0.90 equivalent, needle-like goethite particles are mixed. When it exceeds 1.0 equivalent, the silicon element is easily taken in, and magnetic iron oxide particles excellent in blackness can not be obtained.

  The amount of water-soluble silicate added in the first stage reaction is 0.05 to 1.00 atomic% in terms of Si based on Fe in the ferrous salt solution. When the addition amount of the water-soluble silicate is out of the above range, the distribution of the silicon element is not constant, and magnetic iron oxide particles excellent in blackness can not be obtained. The more preferable addition amount of water-soluble silicate is 0.07 to 0.95 atomic%.

  As water-soluble silicates 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 aqueous ferrous salt solution, the aqueous alkali hydroxide solution and the water-soluble silicate is adjusted to 8-9. By adjusting the pH of the reaction solution to the above range, it is possible to suppress the Si distribution at the center of the particle.

  After adjusting the pH of the reaction solution, the oxygen-containing gas is bubbled while heating to a temperature range of 70 to 100 ° C. When the temperature is less than 70 ° C., needle-like goethite particles are mixed. When the temperature exceeds 100 ° C., magnetite particles are formed, but this is not industrially easy because an apparatus such as an autoclave is required. A more preferable 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 to carry out the oxidation reaction to an iron oxidation reaction rate of 7 to 12%, thereby forming a first-stage reaction that produces nuclear crystal magnetite particles. 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 excellent in blackness can not be obtained. If 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%, the Fe ²⁺ content in the reaction solution is measured over time by the method shown in the examples described later to obtain the oxidation reaction rate (%), When the oxidation reaction rate in the above range is reached, the first stage reaction is terminated.

  An aqueous alkali hydroxide solution is added so as to be 1.01 to 1.50 equivalents with respect to the ferrous salt reaction solution containing the nucleated magnetite particles and ferrous hydroxide colloid after completion of the first stage reaction. When the addition amount of the aqueous alkali hydroxide solution is less than 1.01 equivalent, hexahedrons, polyhedrons and spherical particles other than octahedrons are mixed. When the addition amount of the aqueous alkali hydroxide solution exceeds 1.5 equivalents, the particle size distribution becomes large, and a uniform particle size can not be obtained. The addition amount of the aqueous alkali hydroxide solution is more preferably 1.02 to 1.48.

  While heating to a temperature range of 70 to 100 ° C., an oxygen-containing gas is passed to perform a second step reaction in which the oxidation reaction rate of iron is oxidized to 40 to 60%. When the temperature is less than 70 ° C., needle-like goethite particles are mixed. When the temperature exceeds 100 ° C., magnetite particles are formed, but this 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 to an iron oxidation reaction rate of 40 to 60%. If the oxidation reaction rate is less than 40%, the oxidation reaction in the latter stage becomes long, the particle size distribution becomes large, and a uniform particle size can not be obtained. If it exceeds 60%, the oxidation reaction in the third step reaction becomes short, the particle size distribution becomes large, and a uniform particle size can not be obtained. As a method of adjusting the oxidation reaction rate of iron to 40 to 60%, the Fe ²⁺ content in the reaction solution is measured over time by the method shown in the examples described later to obtain the oxidation reaction rate (%), When the oxidation reaction rate in the above range is reached, the second stage reaction is terminated.

  After completion of the second stage reaction, the pH of the reaction solution is temporarily adjusted to 5 to 9 (relay conditions). If the pH is not adjusted, the viscosity of the aqueous ferrous reaction solution containing ferrous hydroxide colloid becomes high, the uniformity of the reaction temperature and the uniformity of the reaction rate are impaired, and as a result, the crystals of the particles are formed. The growth rate is nonuniform, the crystallinity is poor, and particles having a uniform particle size can not be obtained.

Thereafter, the pH of the reaction solution is readjusted to 9.5 or more. The amount of the aqueous alkali hydroxide solution used is at least 1.00 equivalent to the remaining Fe ²⁺ . If it is less than 1.00 equivalent, the total amount of remaining Fe ²⁺ may not be precipitated. For practical use, an amount of 1.00 equivalent or more in consideration of industrial efficiency is preferable.

  The water soluble silicate is again added 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 to the water-soluble silicate added in the first stage reaction, and the first stage reaction and the third stage reaction The total amount of silicon elements to be added is preferably 1.9 atomic% or less.

  Then, while the reaction solution is heated to a temperature range of 70 to 100 ° C., an oxidation reaction is carried out by bubbling an oxygen-containing gas. A more preferred temperature range is 72-98 ° C.

  Also, when forming a compound consisting of Al or Al and Si on the particle surface of the black magnetic iron oxide particles, the water-soluble aluminum in the suspension containing the black magnetic iron oxide particles after completion of the second stage reaction After adding salts or water-soluble aluminum salts and water-soluble salt silicates so that the amount of Al is 0.02 to 1.0% by weight and the amount of Si is 0.02 to 1.0% by weight, the pH is 5 It can be obtained by depositing Si and Al on the surface of the black magnetic iron oxide particles by adjusting to a range of ̃9.

<Function>
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 in the inside of the particles constant, the value of a * is small even if the coating film thickness becomes thin. It is excellent in blackness and is excellent in blackness even when used as a magnetic toner.

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

  Representative examples of the present invention are as follows.

Shape, average particle size, change coefficient:
The particle shape and the average particle diameter of the black magnetic iron oxide particles were observed by "Scanning Electron Microscope S-4800" (manufactured by Hitachi High-Technologies Corp.), and were shown by the average value of the values measured from the electron micrograph.

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

Specific surface area:
The specific surface area was shown by the value measured by BET method using "Mono Sorb MS-II" (made by Yuasa Ionix Co., Ltd.).

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

Si and Al elemental amounts:
The amount of Si and the amount of Al of the black magnetic iron oxide particle powder were measured by "Fluorescent X-ray analyzer RIX-2100" (manufactured by Rigaku Denki Kogyo Co., Ltd.), and determined in terms of element with respect to the black magnetic iron oxide particle powder. It is a value.

Surface Si content:
The amount of Si on the particle surface of the black magnetic iron oxide particle powder is obtained by mixing the black magnetic iron oxide particle powder and ion-exchanged water, and then dispersing it to form a suspension and mixing it with an aqueous alkali hydroxide solution for 30 minutes or more After stirring, the suspension was filtered and dried, the amount of Si of the black magnetic iron oxide particle powder obtained was measured, and the difference with the total amount of Si before the treatment with the alkali was taken as the amount of Si on the particle surface.

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

Elemental iron dissolution rate (%) = elemental iron concentration in the sample (mg / l) / elemental iron concentration when completely dissolved (mg / l) × 100
Elemental silicon dissolution rate (%) = elemental silicon concentration in sample (mg / l) / elemental silicon concentration when completely dissolved (mg / l) x 100
Sodium element dissolution rate (%) = elemental sodium concentration in the sample (mg / l) / elemental sodium concentration when completely dissolved (mg / l) × 100

Coating color characteristics:
The a * value and the b * value of the coating film using the black magnetic iron oxide particle powder were measured as follows.
8 g of 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 with a paint conditioner for 4 hours to obtain a dispersion. This dispersion is applied on cast coated paper using a bar with a wet film thickness of 12 μm, 40 μm, and 100 μm. After drying, the color is measured using a spectrometric densitometer X-rite 939.

  First, the thickness (A) of cast coated paper is measured using a digital electronic micrometer K351C (manufactured by Adachi Electric Co., Ltd.). Next, the cast coated paper and the thickness (B) of the coating film formed on the cast coated paper (the sum of the thickness of the cast coated paper and the thickness of the coated film) are measured in the same manner. The film thickness of the coating film was (B)-(A), and measurement was performed 30 times, and the average value was made into the film thickness of the coating film.

Electrical resistance:
The electrical resistance value of the black magnetic iron oxide particle powder was obtained by weighing 0.5 g of the particle powder to be measured, and using a KBr tablet molding machine (manufactured by Shimadzu Corporation), the gauge reading of a hand press (SSP-10 manufactured by Shimadzu Corporation) The pressure molding is performed for 10 seconds at a pressure of 14 MPa in this value (under this condition, a molded body with a density of about 2.7 g / cm ³ can be obtained, but when using another molding machine, the density is appropriately 2 The condition should be set to about 7 g / cm ^3. If the density greatly exceeds 2.5 to 2.8 g / cm ³ , the electrical resistance value changes, making it difficult to compare the measured values. Become.). Next, the pressure-molded sample is set between the stainless steel electrodes. At this time, the electrodes are completely isolated from the outside with a fluoroplastic holder. The resistance value is measured by applying a voltage of 15 V to the set sample with a Wheaton Bridge (Type 2768 type manufactured by Yokogawa Electric Corporation). The measured value R (Ω) at that time and the electrode area A (cm ² ) and thickness t (cm) of the sample are measured, and the volume specific resistance value X (Ω cm) is calculated by the following equation.
X = R / (A / t)

Example 1:
Fe ²⁺ : A mixture of 16 l of an aqueous ferrous sulfate solution containing 1.5 mol / l (Fe ²⁺ : 24 mol) and 15.2 l of a 3.0 N sodium hydroxide solution (corresponding to 0.95 equivalents to Fe ²⁺ ) is mixed. And adjusted to pH 8.2 to produce a ferrous salt suspension. At this time, 13.3 g of a No. 3 water glass (SiO ₂ : 28.8 wt%) (corresponding to 0.25 atomic% in terms of Si based on Fe) as a silicon component is diluted in 0.5 l of ion-exchanged water Were added to sodium hydroxide in advance. The above ferrous salt suspension is aerated at 70.degree. C. at a temperature of 90.degree. C. to carry out an oxidation reaction until the oxidation reaction rate of the ferrous salt reaches 10%. A monoiron salt suspension was obtained (first stage reaction).

Then, 3.2 l of 3.0 N sodium hydroxide solution is added to the ferrous salt suspension containing the magnetite nuclear crystal particles (corresponding to 1.15 equivalents with respect to Fe ²⁺ ), and at a temperature of 90 ° C. A portion of 70 l of air was bubbled to carry out the oxidation reaction until the oxidation reaction rate of the ferrous salt became 50% (second stage reaction).

  Then, an appropriate amount of 16.1 N sulfuric acid was added to the ferrous salt suspension containing the magnetite nucleated crystal particles to adjust to pH 8 (relay condition).

Then, an appropriate amount of 3.0 N 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%) (corresponding to 0.40 atomic% in terms of Si based on Fe) as a silicon component. Water-soluble silicate added in the first step reaction And the total of silicon elements added in the first step reaction and the third step reaction is 0.65 atomic%) diluted in 0.5 l of ion-exchanged water to the above magnetite nucleus crystals. It was added to the ferrous salt suspension containing the particles and air was blown at 70 l / min at a temperature of 90 ° C. to produce magnetite particles (third stage reaction).

  The produced particles were washed with water, separated by filtration, dried and crushed by a conventional method. The obtained magnetite particles were octahedron, and had an average particle diameter of 0.14 μm, a variation coefficient in particle size distribution of 26%, and an Si content of 0.65 atomic%.

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

  Further, 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 ( The a * (I) is 0.5, and the ratio α (a * (I) / a * (II)) of the a * value of the coating film thickness 5 μm to the a * value at the coating film thickness 24 μm is 1 It was .3.

Moreover, the electrical resistance of this black magnetic particle powder was 5 × 10 ⁴ Ωcm. The black magnetic powder had a uniform distribution of silicon element contained in the inside of the particles and was excellent in blackness.

Examples 2 to 12 and Comparative Examples 5 to 9:
The equivalent ratio in the first stage reaction, the amount of silicon element, the pH up to 10% oxidation reaction ratio, the equivalent ratio in the second stage reaction, the oxidation reaction ratio, the pH of relay condition, the pH in the third stage reaction, the amount of silicon element A black magnetic powder was obtained in the same manner as in Example 1 except that it was changed as shown in Table 1.
In addition, the coating layer of Si and Al is adjusted to pH 7 by adding a suitable amount of suspension containing magnetite particles to the No. 3 water glass as silicon component and aluminum sulfate solution 1 of 1.9 mol / l as aluminum component as shown in the table. And formed a covering layer.

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. Under the present circumstances, 75.7g (it corresponds to 1.42 atomic% in conversion of Si with respect to Fe) is diluted to 0.5 liter ion-exchange water as No. 3 water glass (SiO ₂ 28.8wt%) as a silicon component. Was added to sodium hydroxide. The above ferrous salt suspension was subjected to an oxidation reaction at a temperature of 90 ° C. by passing air at 70 l / min to produce 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. (Equivalent to 50 atomic%)) diluted with 0.5 l of ion exchange water and added. This aqueous solution was mixed with 16.3 l of a 3.0 N sodium hydroxide solution (corresponding to 1.02 equivalents 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 above ferrous salt suspension was subjected to an oxidation reaction at a temperature of 90 ° C. by passing air at a rate of 30 l / min, and when the oxidation conversion exceeded 50%, the aeration amount was reduced to 20 l / min. Furthermore, the air flow rate was reduced to 10 l / min when the oxidation conversion exceeded 75%. Then, when the oxidation conversion rate exceeded 90%, the aeration amount was reduced to 5 l / min, 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 above ferrous salt suspension is aerated at 70.degree. C. at a temperature of 90.degree. C. to carry out an oxidation reaction until the oxidation conversion of the ferrous salt reaches 50%. A monoiron salt suspension was obtained (first stage reaction).

  Then, an appropriate amount of 16.1 N sulfuric acid was added to the ferrous salt suspension containing the magnetite nucleated crystal particles to adjust to pH 8 (relay condition).

Then, 9.2 l of 3.0 N sodium hydroxide solution is added to the ferrous salt suspension containing the magnetite nuclear crystal particles (corresponding to 1.15 equivalents with respect to the remaining Fe ²⁺ ), in which case 20.8 g (corresponding to 0.39 atomic% in terms of Si based on Fe) of No. 3 water glass (SiO ₂ 28.8 wt%) diluted with 0.5 l of ion-exchanged water as a silicon component Added to sodium hydroxide. At a temperature of 90 ° C., 70 l / min of air was blown to generate magnetite particles (second stage reaction).

  The production conditions at this time are shown in Table 1, and the various properties of the resulting 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 particle powder.

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

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

Claims (8)

The octahedral shape contains 0.19 to 1.90 atomic% silicon in terms of silicon element with respect to iron element, and iron element dissolution rate (X) is 20 <X _{20 to 40} ≦ 40%, 40 Silicon element dissolution rate (Y) in each range of <X _{40 to 60} ≦ 60%, 60 <X _{60 to 80} ≦ 80% 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 the 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 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 the total sodium element dissolution amount 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, which has an average particle size of 0.05 to 0.30 μm.   The black magnetic iron oxide particle powder according to any one of claims 1 to 3, wherein the variation coefficient in the particle size distribution is 30% or less. B * value of the coating film is 2 or less when the film thickness is 23 to 26 μm, which is prepared using the black magnetic iron oxide particle powder,
a * (I): a * value at a coating film thickness of 4 to 6 μm a * (II): a * value at a coating film thickness of 23 to 26 μm α = a * (I) / a * (II) When you
The black magnetic iron oxide particle powder according to any one of claims 1 to 4, wherein 1.0 1.0 α 2.0 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 which is octahedral in shape and contains 0.19 to 1.90 atomic% silicon in terms of silicon element with respect to iron element, and is prepared using black magnetic iron oxide particle powder B * value of the coating film when the film thickness is 23 to 26 μm is 2 or less,
a * (I): a * value at a coating film thickness of 4 to 6 μm a * (II): a * value at a coating film thickness of 23 to 26 μm α = a * (I) / a * (II) When you
Black magnetic iron oxide particle powder characterized by satisfying 1.0 ≦ α ≦ 2.0. An aqueous solution of an aqueous solution of ferrous salt, an aqueous solution of an alkali hydroxide of 0.90 to 1.00 equivalents with respect to a ferrous salt in the aqueous solution of ferrous salt, and a ratio of Si to Fe in a solution of ferrous salt The pH of the reaction solution containing ferrous hydroxide colloid obtained by reacting with 0.05 to 1.00 atomic% water-soluble silicate is adjusted to 8 to 9, and the temperature range of 70 to 100 ° C. The first reaction, which causes the oxidation reaction rate of iron to generate 7-12% of oxidation reaction rate by passing oxygen-containing gas while heating to generate nuclear magnetite particles, nuclear magnetite after completion of the first reaction An aqueous solution of alkali hydroxide is added so as to be 1.01 to 1.50 equivalents to a ferrous salt reaction solution containing particles and ferrous hydroxide colloid, and oxygen is heated to a temperature range of 70 to 100 ° C. Aeration of contained gas to perform oxidation reaction to 40 to 60% of iron oxidation reaction rate After completion of the two-stage reaction and the second-stage reaction, the pH was once adjusted to 5 to 9, and then the pH of the reaction solution was readjusted to 9.5 or more, and then water-soluble silicate was added in the first-stage reaction a 20 to 200% relative to the water-soluble silicate, added pressure tooth 70 to 100 ° C. as the silicon element is 1.9 atomic% or less in total to be added in the first stage reaction and the third step reaction The method for producing a black magnetic iron oxide particle powder according to any one of claims 1 to 7, wherein the oxidation reaction is carried out by passing oxygen-containing gas while heating to a temperature range of (3).