JP5826453B2 - Black magnetic iron oxide particle powder - Google Patents

Description

  Since the black magnetic iron oxide particles according to the present invention are black, they can be used as black coloring pigments for paints, resins, printing inks, etc., and are excellent in electrical properties, hygroscopicity, and dispersibility. Therefore, when used as black magnetic particles for magnetic toner, a toner having a high image density in a high temperature and high humidity environment can be constituted.

  Magnetite particle powder is a typical black pigment, and has been widely used as a colorant for paints, printing inks, cosmetics, rubber / resin compositions, etc. for a long time.

  In particular, the magnetite particle powder is frequently used in a one-component magnetic toner using, as a developing material, composite particles obtained by mixing and dispersing black magnetic iron oxide particles such as magnetite particles in a resin.

  Recently, along with the development of devices that can be used in various environments, in addition to increasing the speed and image quality of laser beam printers and digital copying machines, the characteristics of magnetic toner as a developer have been improved. There is a strong demand for toners that maintain good image density in a high temperature and high humidity environment.

  Therefore, further improvement in characteristics is strongly desired for the black magnetic iron oxide particle powder in order to satisfy the requirements for the magnetic toner.

  That is, in order to obtain a toner having excellent environmental stability, in particular, image density maintenance in a high-temperature and high-humidity environment, the electrical characteristics such as the black magnetic iron oxide particles having a sufficient resistance value are further improved. It is required to be excellent, have low hygroscopicity, excellent environmental stability, and excellent dispersibility.

This is because in the process of forming a toner image, when the toner particles are blown to the latent image on the photoreceptor, a mirror image force, which is the combined force of electrostatic attraction and magnetic restraint force, acts on the toner particles, and this strength is subtly This is due to the fact that the image density is controlled.
That is, when the resistance value of the toner particles is high, the charging performance is improved, and the image density is easily increased on the photosensitive member.

  In order to control the charging performance of the toner particles, the use of a charge control agent is usually raised, but as one of other means, the electric resistance value of the magnetic iron oxide particles which are pigment components exposed on the toner particle surface There is a way to control. That is, if the electric resistance value of the magnetic iron oxide particles exposed on the toner particle surface is high, the toner particles are easily charged, and conversely if the magnetic iron oxide particle has a low electric resistance value, it is charged by stirring in the toner hopper. As a result, the electrostatic charge on the surface of the toner particles escapes through the magnetic iron oxide particles exposed on the toner particle surface, and as a result, the charge amount of the toner particles decreases.

  These phenomena become remarkable in an environmental atmosphere to which the developing device is exposed, particularly in a high temperature and high humidity environment. That is, generally, the toner charging performance tends to be low in a high temperature and high humidity environment, and as a result, the image density tends to be low.

  Therefore, controlling the electrical properties and hygroscopicity of the black magnetic iron oxide particle powder is very important for obtaining a high image density image when the black magnetic iron oxide particle powder is used as the toner particle pigment. It has.

  The resistance value of black magnetic iron oxide particle powder is high or low resistance component (high resistance oxide / hydroxide / dielectric) on the surface of black magnetic iron oxide particles because magnetite generally has electrical characteristics of semiconductor. It is generally known that a powder having a high resistance value can be obtained by coating or adhering an organic or hydrophobic organic substance).

  Conventionally, attempts have been made to improve various characteristics by incorporating different elements other than iron into the black magnetic iron oxide particles and coating the surface of the black magnetic iron oxide particles with an inorganic substance or an organic substance.

For example, Patent Document 1 (Japanese Patent Laid-Open No. 2002-72545) discloses an iron oxide powder in which a composite iron oxide of aluminum and iron is present on the particle surface, and Patent Document 2 (Japanese Patent Laid-Open No. 2005-289673). Discloses a magnetite particle obtained by performing a dry mechanochemical treatment on a magnetite particle having a coating layer containing a compound of one or more elements other than iron.
Patent Document 3 (Japanese Patent Laid-Open No. 2007-314412) discloses black magnetic iron oxide in which the particle surface is covered with a surface layer made of a compound of at least one kind of alkaline earth metal and Al element. Has been.
Patent Document 4 (Japanese Patent Application Laid-Open No. 7-110598) discloses a magnetite particle powder in which a coprecipitate of silica and alumina is adhered to the particle surface.

JP 2002-72545 A JP 2005-289673 A JP 2007-314412 A JP-A-7-110598

  Black magnetic iron oxide particles having high resistance in the high voltage region, low hygroscopicity, and excellent dispersibility are currently in most demand, but have not yet been obtained.

  That is, the conventional techniques described in the above-mentioned Patent Documents 1 and 2 are techniques that focus on the electric resistance value of the powder. However, the electric field applied to the toner particles inside the printer in which the toner is actually used varies depending on the apparatus, but is generally a high electric field, and the electric resistance in the high electric field is shown in a comparative example described later. As such, it is still not enough.

  The conventional technique described in Patent Document 3 is a technique that focuses on resistance in a high voltage region, but is still not sufficient as shown in a comparative example described later.

  The magnetite particle powder described in Patent Document 4 is intended to obtain a magnetite particle powder having excellent fluidity, small oil absorption, and excellent charging stability, and high electrical resistance in a high voltage range. It's hard to say.

  In terms of image density and image density maintainability, not only the electrical resistance value of the pigment used in the toner is high, but also the electrical resistance value at a high voltage is important. That is, even if a pigment with a high resistance value is obtained at a low voltage, if the resistance value is low in the electric field actually used, the static electricity on the toner surface escapes as a leak site from the pigment exposed on the toner surface. Since the charge amount of the toner is reduced, the image density is significantly reduced.

  Therefore, the black magnetic iron oxide particle powders disclosed in the aforementioned Patent Documents 1 to 4 do not satisfy the requirements from the viewpoint of increasing the electrical resistance value in the high voltage region that is currently most needed. .

  Accordingly, an object of the present invention is to provide a black magnetic iron oxide pigment capable of constituting a toner having a high image density in a high-temperature and high-humidity environment and improved image density maintenance.

  As a result of investigations in view of the above technical problems, the present inventors have been able to obtain black magnetic iron oxide particle powder having a high electric resistance value at a high voltage, leading to the present invention.

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

That is, in the present invention, the surface of black magnetic iron oxide particles is coated with a compound composed of one or more elements selected from Al, Mg, Mn, Zn, Ni, Cu, Ti, and Si. The abundance of the elements is 0.3 to 4.5% by weight, the average particle diameter of the black magnetic iron oxide particles is 0.05 μm to 2.0 μm, and 2.0 g of the sample powder is put in a measuring container to 14 MPa. a black magnetic iron oxide particles, wherein the electric resistance value of the applied voltage of 100V in a condition of a pressure of at 1 × 10 ⁸ Ω · cm or more (the present invention 1).

Further, the present invention is water adsorption amount _{Ma 0.9} is black magnetic iron oxide particles of the present invention 1, wherein not more than 15 mg / g (Invention 2).

Further, according to the present invention, the ratio of the electrical resistance value when the applied voltage is 10 V to the electrical resistance value when the applied voltage is 100 V (the electrical resistance value when the applied voltage is 100 V / the electrical resistance value when the applied voltage is 10 V) is The black magnetic iron oxide particle powder according to claim 1 or 2 which is 0.5 to 1.0 (Invention 3).

  The black magnetic iron oxide particle powder of the present invention, particularly when used as a pigment for toner, provides a high image density, a high electric resistance value at a high voltage, and a high image density particularly in a high temperature and high humidity environment. It is suitable as an application for obtaining

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

  The particle shape of the black magnetic iron oxide particle powder according to the present invention is not particularly limited, and may be hexahedron, octahedron, polyhedron shape, granular shape, spherical shape, or the like.

  The black magnetic iron oxide particles constituting the black magnetic iron oxide particle powder according to the present invention are composed of core particles and a surface layer existing on the particle surface of the core particles. The surface layer refers to a portion excluding a portion containing Fe from the central portion of the particle toward the surface. The core particle refers to the inside of the particle excluding the surface layer portion.

  In the surface layer of black magnetic iron oxide particles in the present invention, a compound composed of one or more elements selected from Al, Mg, Zn, Ni, Cu, Ti, and Si forms a uniform layer on the particle surface. doing.

  In the black magnetic iron oxide particle powder according to the present invention, the content of one or more elements selected from Al, Mg, Zn, Ni, Cu, Ti, Si present in the surface layer of the black magnetic iron oxide particles Is 0.3 wt% or more and 4.5 wt% or less with respect to the whole black magnetic iron oxide particles. When the content of the element is less than 0.3% by weight, the electric resistance value is low. When it exceeds 4.5% by weight, the hygroscopicity is increased, which is not preferable. Preferably it is 0.5-4.0 weight%, More preferably, it is 0.6-3.5 weight%, More preferably, it is 0.7-3.0 weight%.

The black magnetic iron oxide particles according to the present invention have an electric resistance value of 1.0 × 10 ⁸ Ω · cm or more when a 100 V DC voltage is applied. When the electric resistance value when a 100 V DC voltage is applied is less than 1.0 × 10 ⁸ Ω · cm, the electric resistance in a high electric field is insufficient. A preferable electric resistance value when applying a 100 V DC voltage is 3.0 × 10 ^{8 to} 1.0 × 10 ¹⁷ Ω · cm, and more preferably 3.0 × 10 ^{8 to} 1.0 × 10 ¹⁵ Ω · cm. is there.

In addition, as for the electrical resistance value at the time of 10V DC voltage application of the black magnetic iron oxide particle powder which concerns on this invention, 1.0 * 10 < ⁸ > -1.0 * 10 < ¹⁷ > ohm * cm is preferable, More preferably, it is 3.0 * 10. ^{8 to} 1.0 × 10 ¹⁵ Ω · cm.

  The ratio of the electrical resistance value of the black magnetic iron oxide particles according to the present invention when the applied voltage is 10V to the electrical resistance value when the applied voltage is 100V (the electrical resistance value when the applied voltage is 100V / the applied voltage is 10V. The electrical resistance value) is preferably 0.5 to 1.0, more preferably 0.6 to 0.95.

  The average particle diameter of the black magnetic iron oxide particle powder according to the present invention is 0.05 to 2.0 μm. When the average particle size is smaller than 0.05 μm, it is difficult to disperse the pigment in the toner particles when used as toner particles, which is not preferable. When the average particle diameter is larger than 2.0 μm, the number of magnetic particles in the toner particles is decreased, so that the coloring power is lowered, which is not preferable. A preferable average particle diameter is 0.07 to 0.50 μm, and a more preferable average particle diameter is 0.09 to 0.40 μm.

The water adsorption amount Ma _0.9 of the black magnetic iron oxide particle powder according to the present invention is preferably 15 mg / g or less. When it is larger than 15 mg / g, the hygroscopicity is high and the environmental stability is deteriorated. A more preferable moisture adsorption amount Ma _0.9 is 3.0 to 12.0 mg / g.

The BET specific surface area of the black magnetic iron oxide particles according to the present invention is preferably 3.0 to ²⁰ m ² / g.

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

  The black magnetic iron oxide particles according to the present invention produce magnetite core particles according to a conventional method, and then hold the slurry containing the core particles in a temperature range of 70 to 95 ° C. Is controlled to the pH of the slurry in the range of 8.0 to 9.0, and the aluminum salt is added at 0.015 wt% / min or less with respect to the core particles, then ripened for 30 minutes or more, After adjusting the pH, it can be obtained by washing and drying according to a conventional method. Mg, Mn, Zn, Ni, Cu, Ti, and Si elements have the pH of the slurry containing the core particles, 9.5 to 10.5 for Mg element, and 8.0 to 9.0 for Mn element. In the case of Zn element, 8.0 to 9.0, in the case of Ni element 7.5 to 8.5, in the case of Cu element 6.5 to 7.5, in the case of Ti element 8.0 to 9 0.0, in the case of Si element, the metal salt is controlled within the range of 6.5 to 7.5, and each metal salt is added at 0.015 wt% / min or less with respect to the core particles, and then ripened for 30 minutes or more. Then, after adjusting the pH, it can be obtained by washing with water and drying according to a conventional method.

  As described above, the core particles for obtaining the black magnetic iron oxide particle powder of the present invention can be selected in various shapes and particle sizes from the viewpoint of magnetic properties and dispersibility required as a black magnetic pigment. There are various production methods, but in order to achieve the object of the present invention more effectively, from the viewpoint of performing the surface treatment described later more uniformly, the core particle slurry contains an inhibitor of the surface treatment. It is preferable that there is no mixing of substances that tend to become, for example, unreacted iron hydroxide fine particles.

As described above, there are various methods for obtaining the slurry containing the core particles. For example, by controlling the pH during the oxidation reaction of the Fe ²⁺ aqueous solution to a predetermined value, the octahedron, polyhedron, hexahedron・ Spherical and irregular shapes can be obtained. Moreover, the core particle of a desired particle diameter can be obtained by controlling the growth conditions of the particles during the oxidation reaction. The surface smoothness of the core particles controls the growth conditions at the end of the oxidation reaction, and, as is generally known, the components such as silica, aluminum and calcium, and the spinel ferrite crystal structure such as zinc and manganese. It can also be controlled by adding components that are easy to form.

As the Fe ²⁺ aqueous solution, for example, a general iron compound such as ferrous sulfate or ferrous chloride can be used. In order to obtain iron hydroxide or an alkaline solution as a pH adjuster, an aqueous solution such as sodium hydroxide or sodium carbonate can be used. Each raw material may be selected in consideration of economy and reaction efficiency.

  The pH of the slurry during the Al surface treatment is preferably 8.0 to 9.0, and more preferably 8.2 to 8.8. When the pH of the slurry is less than 8.0, the Al component is not coated on the surface of the core particles and is precipitated by the Al compound alone, resulting in a low electrical resistance value, a high BET specific surface area value, and hygroscopicity. It becomes high and is not preferable. Even when the pH of the slurry exceeds 9.0, the Al component is not coated on the surface of the core particles and is precipitated by the Al compound alone, resulting in a low electrical resistance value, and a high BET specific surface area value. Is undesirably high. The pH of the slurry during Mg surface treatment is 9.5 to 10.5, the pH of the slurry during Mn surface treatment is 8.0 to 9.0, and the pH of the slurry during Zn surface treatment is 8.0 to 9.0. The pH during Ni surface treatment is 7.5 to 8.5, the pH during Cu surface treatment is 6.5 to 7.5, the pH during Ti surface treatment is 8.0 to 9.0, and during Si surface treatment The pH of is preferably 6.5 to 7.5. When the pH is out of the above range, the electric resistance value is low, and the hygroscopicity is high, which is not preferable.

  The temperature range of the slurry for surface-treating Al, Mg, Mn, Zn, Ni, Cu, Ti, and Si components is preferably 70 to 95 ° C. When the temperature of the slurry is less than 70 ° C., the BET specific surface area value is high, which is not preferable from the viewpoint of hygroscopicity. Although the condition value is not particularly limited, it is an aqueous slurry, and therefore the upper limit is about 95 ° C. in consideration of productivity and cost.

  The addition rate of the metal compound to the slurry containing the core particles is preferably 0.015 wt% / min or less with respect to the core particles. More preferably, the metal element is added at 0.01% by weight / min or less with respect to the core particles. When the metal element is added at a rate of more than 0.015% by weight / min, the metal compound is not coated on the surface of the core particles and precipitates alone, resulting in a low electrical resistance value and a high BET specific surface area value. Will be expensive. The lower limit is not particularly limited, but considering productivity, the lower limit is 0.002% by weight / min.

  After adding the metal compound, aging is preferably performed for 30 minutes or more in order to uniformly treat the metal compound on the surface of the core particles. The upper limit is not particularly limited, but considering productivity, the upper limit is about 240 minutes. The slurry is preferably well stirred.

  After aging, it is preferable to control the pH of the slurry in the range of 4.0 to 10.0. More preferably, the pH of the slurry is controlled in the range of 6.0 to 8.0. When the pH is less than 4.0, it is difficult to uniformly form the metal compound layer on the surface of the core particles. Even when the pH exceeds 10.0, it is difficult to uniformly form the metal compound layer on the core particle surface. In controlling, the slurry is preferably well stirred.

  After the reaction, it may be washed with water and dried according to a conventional method.

<Action>
The electric resistance when a high voltage is applied can be increased by uniformly covering the outer side (surface layer) of the core particle of the black magnetic iron oxide particles according to the present invention with an Al compound. In fact, particle powders (JP-A 2007-314412) obtained by surface treatment by adding an Al component and an alkaline earth metal component after synthesis of magnetite particles previously filed by the present inventors, and composite oxidation on the surface In the particle powder having an iron layer (Japanese Patent Laid-Open Nos. 2005-289673 and 2002-72545), the electric resistance when a high voltage such as 100 V is applied is insufficient. The present inventors presume that this is because an insulating layer as a film-like hydroxide phase or a hydrated oxide phase can be formed uniformly without gaps on the surface of the core particles.

  Representative examples of the present invention are as follows.

<Measurement method>
The average particle diameter of the black magnetic iron oxide particles was shown as an average value measured from an electron micrograph.

  The particle shape of the black magnetic iron oxide particle powder was judged from a photograph observed with a transmission electron microscope and “scanning electron microscope S-4800” (manufactured by Hitachi High-Technologies Corporation).

The water adsorption amount Ma _0.9 of the black magnetic iron oxide particle powder was measured at the time of adsorption at 25 ° C. and a relative pressure of 0.9 using a “high accuracy vapor adsorption amount measuring apparatus BELSORP-aqua 3” (Nippon Bell Co., Ltd.). It was expressed as a value of the amount of adsorbed moisture.

  The BET specific surface area value was determined by the BET method using “Mono Sorb MS-II” (manufactured by Yuasa Ionics Co., Ltd.).

  The amount of Al and the amount of metal element contained in the black magnetic iron oxide particle powder are measured with a “fluorescence X-ray analyzer RIX-2100” (manufactured by Rigaku Denki Kogyo Co., Ltd.). It is a value obtained by conversion.

  The electrical resistance value of the black magnetic iron oxide particle powder was determined by weighing 2.0 g of the sample powder to be measured, putting it in a measurement container, and applying a constant voltage of 100 V or 10 V while applying a pressure of 14 MPa, “HIGH REISTANCE METER 4339B ”(Manufactured by Hewlett-Packard Co., Ltd.), and the volume specific resistance value was determined from the resistance value at that time and the electrode area and thickness of the sample.

  According to JIS K 5101, the black magnetic iron oxide particle powder has a crushing value of 0.5 g of castor oil added to 0.5 g of the sample and repeated 50 rotations with a Hoover Muller. Measure.

Example 1
<Method of producing iron oxide particles>
After 100 L of a slurry containing 90 g / l of Fe ₃ O ₄ iron oxide core particles A having a spherical shape and an average particle diameter of 0.24 μm was adjusted to pH 8.5 by adding a sodium hydroxide solution at a temperature of 90 ° C., 1.9 mol / l 1 L of an aqueous aluminum sulfate solution and an aqueous sodium hydroxide solution were added over 190 minutes while simultaneously adjusting the pH to 8.5 ± 0.2. Next, after aging for 60 minutes, diluted sulfuric acid was added to adjust to pH 7.0, followed by filtration, washing with water and drying to obtain iron oxide particles surface-treated with Al.

The obtained iron oxide particles have a BET specific surface area of 7.4 m ² / g, an Al amount of 1.68%, an electric resistance value of 7.1 × 10 ⁹ Ω · cm at an applied voltage of 100 V, and a saturation magnetization of 83.8 Am ² / kg and the amount of adsorbed water Ma _0.9 were 7.2 mg / g.

Example 5
A black magnetic iron oxide particle powder was obtained in the same manner as in Example 1 except that an aluminum sulfate aqueous solution and a magnesium sulfate aqueous solution were mixed and added.

Comparative Example 1
<Method of producing iron oxide particles>
100 l of a slurry containing 90 g / l of Fe ₃ O ₄ iron oxide core particles A having a spherical shape and an average particle diameter of 0.24 μm was adjusted to pH 11 by adding a sodium hydroxide solution at a temperature of 90 ° C., and then 1.9 mol / l. After adding 3.5 l of an aluminum sulfate aqueous solution and stirring, 0.3 l of a 1.1 mol / l magnesium sulfate solution was added and mixed for 20 minutes, then the pH was adjusted to 9.0 and mixed for 5 minutes. Then, diluted sulfuric acid was added to adjust the pH to 7.0, followed by filtration, washing with water, and drying to obtain black magnetic iron oxide particles surface-treated with Al and Mg.

Comparative Example 7
80 L of a slurry containing 70 g / l of Fe ₃ O ₄ iron oxide core particles A having a spherical shape and an average particle diameter of 0.24 μm is 6.9 L of an aluminum sulfate aqueous solution of 0.5 mol / l at a temperature of 80 ° C. and 1.5 mol / l. After adding 4.6 liters of ferrous sulfate aqueous solution and sodium hydroxide solution to adjust to pH 9.0, 80 liters of air was passed through every minute to terminate the oxidation reaction, followed by filtration, washing with water and drying. Black magnetic iron oxide particles having an iron oxide layer formed thereon were obtained.

Comparative Example 8
To 100 L of slurry containing 70 g / l Fe ₃ O ₄ iron oxide core particles C having a hexahedral shape and an average particle size of 0.23 μm, 4.1 l of 0.5 mol / l aluminum sulfate aqueous solution was added at 80 ° C. to adjust the pH. The mixture was adjusted to 8 and stirred and mixed for 3 hours, followed by filtration, washing with water and drying. 2 kg of this black magnetic iron oxide particle powder surface-treated with Al was put into a Simpson MixMuller “Sandmill MPUV-2” (manufactured by Matsumoto Foundry) and treated at a line load of 160 kg / cm for 30 minutes. When the temperature of the powder was measured after the treatment was completed, it was 105 ° C.

Examples 2-4, 6, 7, Comparative Examples 2-6
A black magnetic iron oxide particle powder was obtained in the same manner as in Example 1 except that the production conditions of the black magnetic particle powder were variously changed.

  Various characteristics of the iron oxide core particles are shown in Table 1, and the production conditions of the iron oxide particles are shown in Table 2. Table 3 shows various properties of the obtained black magnetic iron oxide particle powder.

  As shown in Table 3, the black magnetic iron oxide particle powders of Comparative Examples 1, 3, 5 and 6 could not be measured because the electric resistance value at an applied voltage of 100 V was low.

The black magnetic iron oxide particle powder having a high electric resistance value in the high voltage region obtained by the present invention, a low hygroscopic property, and an excellent dispersibility is suitable as a pigment used in various fields. When used for toner, a high image density is obtained in a high temperature and high humidity environment, which is particularly preferable.

Claims (3)

The surface of the black magnetic iron oxide particles is coated with a compound composed of one or more elements selected from Al, Mg, Mn, Zn, Ni, Cu, Ti, Si, and the abundance of the elements Is 0.3 to 4.5% by weight, the average particle diameter of the black magnetic iron oxide particles is 0.05 μm to 2.0 μm, and 2.0 g of the sample powder is put in a measuring container and a pressure of 14 MPa is applied. the black magnetic iron oxide particles, wherein the electric resistance value of the applied voltage 100V is 1 × 10 ⁸ Ω · cm or more at. Black magnetic iron oxide particles according to claim 1 Symbol placement water adsorption amount _{Ma 0.9} is not more than 15 mg / g. The ratio of the electrical resistance value when the applied voltage is 10 V to the electrical resistance value when the applied voltage is 100 V (the electrical resistance value when the applied voltage is 100 V / the electrical resistance value when the applied voltage is 10 V) is 0.5 to 1. The black magnetic iron oxide particle powder according to claim 1 or 2, which is 0.