JP2004269355A - Iron oxide particle, iron oxide powder containing iron oxide particle, and black pigment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an iron oxide particle having high blackness and excellent dispersibility and having a carbon-based component firmly and uniformly treated on the surface of the particle, iron oxide powder containing the iron oxide particle, and black pigment powder containing the iron oxide powder. <P>SOLUTION: The iron oxide particle has 0.05-1 μm average particle diameter, with the carbon-based component stuck on the surface of the particle in the quantity of 0.1-30 wt.% expressed in terms of carbon atom to total iron oxide particle and ≤15% desorption ratio of the carbon-based component in the case that water is used as a dispersion medium. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to iron oxide particles having high blackness, and more particularly to an iron oxide powder containing the iron oxide particles, and a black pigment using the iron oxide powder.

  Iron oxide particles formed by an aqueous solution reaction are widely used because of their magnetic properties and blackness.

  In particular, in recent years, many materials using iron oxide particles have been used as materials for magnetic toners of electrophotographic copying machines and printers.

  Various general developing characteristics are required for the magnetic toner, and in particular, a toner material corresponding to a high resolution of a digital copying machine or a printer is required.

  In other words, in addition to conventional characters, output of graphics, photographs, etc. is also required. In particular, some printers are required to have a capacity of 2400 dots or more per inch, and thin line reproducibility in development and Improvements in dot reproducibility and the like have been strongly demanded.

  In addition, the particle size of the toner has also been reduced, and a toner having a high blackness has been required.

  Further, as the low-temperature fixability for high-speed output has been improved, the demands on the resin side for forming the toner have been increasing, and the dispersibility of the black pigment component has been increasing in such various resins. Highness has also become an important required characteristic in development.

  As a material utilizing such iron oxide particles as an electrophotographic material, various improvements have been made to the particles, including Patent Document 1.

  On the other hand, carbon black as a powder for a black pigment has already been widely used as a pigment for a non-magnetic black toner even for a toner because of its high blackness.

  Attempts have also been made to compound iron oxide particles and carbon black particles. For example, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, etc. describe a magnetic material for toner.

  Patent Literature 2 discloses that carbon black is suspended in an aqueous solution of iron salt, and alkali is gradually added thereto to convert iron salt into triiron tetroxide. The resulting iron tetroxide and carbon black are coprecipitated. A method for producing a black pigment having magnetism, which comprises separating and collecting a precipitate, is described. According to this method, a pigment excellent in both blackness and magnetism can be obtained.

Patent Literature 3 is characterized in that magnetite is heat-treated with a reducing gas and then with a CO ₂ gas, and contains at least a magnetic substance coated with carbon black by a CO ₂ decomposition reaction and a binder resin. Magnetic toners are described. According to the publication, a magnetic substance having a surface coated with carbon black by a decomposition reaction of CO ₂ can be obtained.

Further, Patent Document 6 describes a carrier for developing an electrostatic charge image, wherein the surface of magnetite is coated with a resin in which carbon-deposited magnetite obtained by depositing and forming carbon is coated. According to this, carbon-deposited magnetite is subjected to heat treatment of magnetite with a reducing gas, followed by heat treatment in a CO ₂ gas atmosphere to cause a CO ₂ dispersion reaction, and to deposit a carbon component on the magnetite surface. It is described as being obtained by coating. In addition, by performing such a treatment, the carbon coating layer on the surface of the carbon-deposited magnetite has a specific resistance several orders of magnitude lower than that of magnetite, and therefore, the desired electric conductivity can be obtained by adding a relatively small amount to the carrier coat resin. It is described that the resulting toner has an effect of alleviating the accumulation of excessive charge of the toner, and that a uniform and stable charging property can be obtained.

Further, Patent Document 7 discloses a magnetic substance containing a magnetic iron oxide containing magnetic iron oxide, wherein the magnetic iron oxide has a volume resistivity of 5 × 10 ³ to 1 × 10 ⁸ Ωcm. According to the gazette, it is described that when the volume resistivity of iron oxide is high, the charge amount tends to be higher than necessary and the image density tends to decrease easily, especially when repeatedly used at low temperature and low humidity. Therefore, it is considered that the volume resistivity, that is, the electric resistance of iron oxide is preferably low to some extent.

  Patent Document 4 discloses a black toner characterized in that a toner having at least a binder resin and a colorant contains at least magnetic carbon black composite particles as the colorant. According to the publication, a fuel is burned to form a high-temperature combustion gas stream, and a hydrocarbon material is spray-injected into the high-temperature combustion gas stream to cause a pyrolysis reaction, thereby producing carbon black. In a method for producing carbon black, in which water is sprayed and cooled in a high-temperature gas stream, and carbon black is separated and collected, a magnetic transition metal compound is spray-injected from two positions of an upstream region and a downstream region of the high-temperature combustion gas. Then, it is said that magnetic carbon black composite particles can be obtained by subjecting the generated composite particles composed of carbon black and magnetic metal fine particles to heat treatment at a temperature of 400 to 900 ° C. in a non-oxidizing atmosphere.

  Further, in Patent Document 5, an organosilane compound generated from alkoxysilane is coated on the particle surface of a magnetic iron oxide powder having an average particle size of 0.055 to 0.95 nm. A black magnetic composite powder to which 0.002 to 0.05 μm carbon black fine powder is attached, wherein the amount of the carbon black fine powder attached is 1 to 25 parts by weight based on 100 parts by weight of the magnetic iron oxide powder. A black magnetic powder for a black magnetic toner is described. According to the publication, carbon black particles can be sufficiently adhered to the extent that blackness and fluidity can be improved by performing an organosilane treatment.

  When such a black composite magnetic material is used for toner, it is important to increase the degree of blackness, but at the same time, it is required that the environmental system and the transfer system can also solve the problems of image density and fog. ing.

  That is, there is a need for high fluidity and optimization of electrical properties such as electrical resistance and chargeability of the toner, which are required for a magnetic toner, and high dispersibility of a composite magnetic material in a thermoplastic resin during toner production.

  This is because, when a large amount of carbon black is used on the surface of a magnetic material to determine the degree of blackness, a decrease in electric resistance, a deterioration in dispersibility, and the like occur, and as a result, the uniformity of the toner is impaired, resulting in insufficient image density and fog. The problem such as high occurs.

  In addition, there is a high market demand for inexpensive products as electrophotographic materials, and there is a demand for regulations on the use of environmentally hazardous substances. There is a demand for a method capable of stably producing a large amount.

  Iron oxide particles having a high blackness as described above, having excellent dispersibility as a toner, and being compatible with the environment and cost, and a method for producing the same have not yet been obtained.

JP-A-53-94932 JP-A-54-163927 JP-A-5-66609 JP-A-11-194532 JP-A-11-305480 JP-A-5-61258 JP-A-7-72654

  That is, when carbon black is suspended in an aqueous solution of an iron salt and an alkali is gradually added thereto to convert the iron salt to triiron tetroxide, rapid precipitation of ferrous hydroxide is required. At the same time, the carbon black is fixed, and it is impossible to uniformly and stably adhere the fine carbon black particles to the optically effective surface of the iron oxide particles, and obtain sufficient hiding power and coloring power as a pigment. It is hard to be.

Further, in the method described in Patent Document 3 mentioned above, that is, in a method of coating carbon black on the particle surface by a dry method using CO ₂ gas, uniform attachment of the carbon black component to the particle surface is possible, If the heat treatment time and temperature are not adjusted, the magnetite will be reduced, and the electrical resistance of the magnetic material will be reduced more than necessary, and the dry heat treatment method has a large energy cost compared to the wet treatment etc. .

  Patent Literature 6 describes a function of adjusting the chargeability of carbon-deposited magnetite formed by depositing a carbon component. However, since the iron oxide particles are treated in a dry manner, the cost is high, and the oxidation is further increased. It is not clear whether the carbon component on the iron particle surface has sufficient adhesion strength.

  Further, in the method described in Patent Document 4, that is, in the method of generating a magnetic material simultaneously with the generation of carbon black in a high-temperature region, the characteristics of the composite particles may be significantly changed by conditions such as spraying conditions and temperature control. Due to the high temperature reaction such as the combustion method, the cost is high and the method is not industrially easy to implement.

  Further, in the method of Patent Document 5, that is, in the method of adhering carbon black fine particles by mixing and stirring after organosilane treatment, since only a dry mixing operation, the carbon black particles are advantageously reduced in cost from iron oxide particles. Although it can be attached to the surface, carbon black particles, which are fine particles, have a high cohesive force, and it is difficult to attach uniformly and firmly to the surface of the iron oxide particles. In addition, there is a problem of environmental load due to the use of organosilane and the like, and it cannot be said that the product sufficiently meets the demands of the market.

  Therefore, an object of the present invention is to provide iron oxide particles having high blackness, excellent dispersibility, and a carbon-based component more strongly and uniformly treated on the particle surface, and a method for producing the same. And a toner, a carrier, and a black pigment powder containing the iron oxide powder.

  As a result of the study, the present inventors have found a method for more firmly and uniformly attaching a carbon-based component to the surface of iron oxide particles, and have found that the above object can be achieved.

  That is, the present invention has been made based on the above findings, and has an average particle diameter of 0.05 to 1 μm and a carbon-based component on the particle surface in an amount of 0.1% based on the total amount of iron oxide particles in terms of carbon atoms. The present invention provides iron oxide particles characterized by having a carbon-based component detachment rate of 15% or less when water is used as a dispersion medium and which is attached to the dispersion medium in an amount of about 30% by weight.

  Since the iron oxide particles of the present invention can be more firmly and uniformly attached in a wet manner by a carbon-based component whose surface has been activated in advance, the blackness can be increased and the dispersibility can be improved. It is suitable for applications such as black pigment powder, material powder for electrostatic copying magnetic toner, and material powder for carrier for developing an electrostatic latent image.

Hereinafter, embodiments of the present invention will be described.
The iron oxide particles referred to in the present invention are preferably composed mainly of magnetite, and include those containing various effective elements such as silicon, aluminum, and titanium, or those coated with these effective elements. . As for the shape of the iron oxide particles, various shapes such as a spherical shape, a polyhedron such as a hexahedron and an octahedron, and a needle shape are known, and in the present invention, any shape can be used. Here, the iron oxide powder or the magnetite powder means an aggregate of iron oxide particles or magnetite particles.

  The iron oxide particles of the present invention have an average particle diameter of 0.05 to 1 μm, and have a carbon-based component adhered to the particle surface in an amount of 0.1 to 30% by weight based on the total amount of iron oxide particles in terms of carbon atoms. Things. Here, the term “adhesion” means that the carbon-based component is hardly detached from the iron oxide particles due to mechanical and / or chemical external factors. Therefore, these particles were simply physically mixed. Different from the ones.

  The average particle size of the iron oxide particles in the present invention is 0.05 to 1 μm, preferably 0.08 to 0.5 μm, and more preferably 0.1 to 0.3 μm as described above. The size of the iron oxide particles is important in evaluating the blackness, which is also a factor for evaluating the optimal absorption / scattering effect with respect to the wavelength of visible light. Therefore, it is important to define the size of the primary particles, and it is desirable that the particle size distribution of the primary particles is excellent and that the particles do not aggregate. That is, it is needless to say that monodisperse particles are preferable. If the average particle size of the iron oxide particles is less than 0.05 μm, it is difficult to obtain a sufficient monodispersion, and optical transparency is caused, so that the blackness is inferior. If the average particle size of the iron oxide particles exceeds 1 μm, reflection becomes dominant over optical absorption, and blackness is reduced under white light.

  The carbon-based component adhering to the particle surface is preferably one that allows the surface of the carbon-based component to be chemically exposed, as will be described later. Those which have a large effect are preferable. More specifically, it is preferable that the size of the carbon component is as small as 1/5 or less of the iron oxide particles, the dispersibility is high, and the surface activity is high. Typical examples of such substances are coke and artificial graphite obtained by liquid-phase carbonization, activated carbon and carbon fiber obtained by solid-phase carbonization, carbon black obtained by gas-phase carbonization, and pyrolysis. Carbon, highly oriented graphite, vapor growth type carbon fiber and the like. In addition, so-called activated carbon can be used for such a carbon-based component. In the present invention, it is preferable to select and use a particle size that satisfies the optical characteristics of such a carbon-based component. It is also a desirable method to select and use fine particles such as carbon black.

  It is important that the iron oxide particles of the present invention have a carbon-based component desorption rate of 15% or less when water is used as a dispersion medium. The desorption rate of the carbon-based component is determined based on the amount of the carbon-based component adhered, the iron oxide particles dispersed in water, and how much carbon-based component is depleted against mechanical external factors such as ultrasonic waves. The evaluation is based on whether the components have adhesiveness. Therefore, in this evaluation, the desorption rate is preferably as low as 15% or less, more preferably 10% or less.

  The important point here is that the iron oxide particles of the present invention are more hydrophilic because both the iron oxide particles and the carbon-based component whose surface is chemically activated as described later are hydrophilic. , The desorption rate is reduced. Therefore, as described in JP-A-11-305480, this is different from the method of increasing the adhesive force using an organosilane compound generated from alkoxysilane in order to firmly adhere the carbon black particles.

  When carbon black particles are selected as the carbon-based component, the particle size of the carbon black is preferably 1 to 100 nm, more preferably 5 to 50 nm. Thereby, the blackness of the iron oxide particles can be further increased, and at the same time, the adhesion between the iron oxide particles can be reduced, and the dispersibility of the iron oxide particles can be improved.

  As such carbon black particles, commercially available particles may be used. For example, in carbon black manufactured by Mitsubishi Chemical Corporation, # 52, # 50, # 47, # 45, # 45L, # 44, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, CF9, # 95, # 260, # 1000, # 990, # 980, # 970, # 960, # 950, # 900, # 850, MCF88, MA600, # 750B, # 650B, # 2700B, # 2650, # 2600, # 2450B, # 2400B, # 2350, # 2300, # 2200B, and the like. In Cabot Special Black, MONARCH 1400; 1300 1100; 1000: 900, VULCAN, XC72R, MOGL-L, REGAL 400R, REGA L660R, ELFTEX-8, BLACK PEARLS 1400; 1300; 1100; 1000; 900, VULCAN XC72, BLACK PEARLS-L, REGAL 400, REGAL 660 and the like. In the present invention, a combination of such carbon black particles and adjusted to desired pigment properties can also be used.

  In the present invention, it is desirable to use a carbon-based component whose surface is chemically activated. In general, carbon-based materials such as carbon black and graphite are constituted by carbon-carbon bonds, but active points such as carbon-oxygen, carbon-hydroxyl groups, and carbon-carboxylic acid groups as terminal groups on the material surface. It is known that there is. Therefore, the present inventors presumed that by increasing the number of such active points, a hydroxyl group or the like existing on the surface of the iron oxide particles could be chemically bonded to the carbon-based material. Further, by increasing the number of active sites, the hydrophilicity of the carbon-based component is increased as described above, so that the carbon-based component is more strongly and uniformly adhered to the iron oxide particles manufactured by a wet method in a dispersed state using water as a medium. It was presumed that it could be processed.

  In addition, the present inventors have found that the use of an alkali and / or an oxidizing agent as a method for chemically activating the surface of a carbon-based component improves the adhesion to iron oxide particles. . This is a method of treating a carbon-based component with an alkali such as an alkali hydroxide or ammonia, or a method using an oxidizing agent such as dichromate, permanganate, hydrogen peroxide or benzoyl peroxide, and a combination thereof. It has been found that the method improves the adhesion between the iron oxide and the carbon-based component. It is not clear why the carbon-based component subjected to such a surface treatment can be attached to the surface of the iron oxide particles. Oxidized by oxygen, an active site such as a carbon-hydroxyl group or a carbon-carboxylic acid group is generated, and a hydrogen atom of the above-mentioned hydroxyl group or carboxylic acid group is removed by alkali treatment, and an alkoxide ion or a carboxylic acid anion is formed. Was added to the iron oxide slurry, and the carbon-based component adhered to the surface of the iron oxide particles via these anions and was neutralized, thereby stabilizing the surface of the iron oxide particles. It was presumed that binding could occur. By making such an improvement, a sufficient adhesion strength can be imparted to the carbon-based component without performing a treatment of an organosilane or the like having a problem of environmental load as disclosed in JP-A-11-305480. Can be granted.

  Further, the iron oxide particles of the present invention preferably have an L value of 12 or less as measured by a color difference meter by a method according to the pigment dispersion method described in JIS K 5101-1991. Further, as the evaluation of blackness, in the evaluation method based on the L value, the lower the L value is, the higher the blackness is, the lower blackness is preferably 12 or less. .

Further, the iron oxide particles of the present invention, 3~30m ² / g is preferable as a specific surface area, more preferably from 5~25m ² / g. The magnetic properties are 70 Am ² / kg or more, more preferably 75 Am ² / kg or more when the external magnetic field is 796 kA / m. Further, the pH of the powder is preferably 5 to 10. Further, the electric resistance value is preferably about the same as or lower than ordinary iron oxide particles, more specifically, 1 × 10 ⁵ Ωcm or less, preferably 1 × 10 ⁴ Ωcm or less, more preferably 5 × 10 5 Ωcm or less. ³ Ωcm or less. As a result, when the iron oxide particles of the present invention are used as a toner or a carrier, an adverse effect on an image due to excessive charging can be prevented. The oil absorption is also preferably low for dispersibility with the resin, more specifically, 30 ml / 100 g or less, preferably 28 ml / 100 g or less, more preferably 25 ml / 100 g or less for octahedral magnetic materials. It is. In the case of a spherical magnetic material, the volume is 20 ml / 100 g or less, preferably 18 ml / 100 g or less, and more preferably 16 ml / 100 g or less. Thereby, high dispersibility at the time of kneading to the resin can be ensured.

Further, the present invention is an iron oxide powder containing the iron oxide particles in an amount of 1% by weight or more. The iron oxide particles may be appropriately mixed with iron oxide particles to which no carbon-based component is adhered, and may be used by adjusting the mixing ratio so as to have appropriate characteristics for various uses. The iron oxide powder obtained by the blending has a magnetic property of 70 Am ² / kg or more, more preferably 75 Am ² / kg or more when the external magnetization is 796 kA / m at a saturation magnetization value. Further, the FeO content is at least 18% by weight, more preferably at least 20% by weight, based on the weight of iron oxide.

  Further, the iron oxide powder whose composition ratio has been adjusted is suitable for use as a toner for electrostatic copying, a carrier for developing an electrostatic latent image, and a black pigment. For example, as the toner for electrostatic copying, an iron oxide powder containing iron oxide particles to which the carbon-based component of the present invention is attached, a thermoplastic binder resin, a charge control agent, additives such as wax, a fluidity imparting agent In addition to the iron oxide powder containing iron oxide particles to which the carbon-based component is adhered, known materials and processing methods can be arbitrarily selected and used. As an example thereof, JP-A-11-194532 and the like can be mentioned.

  In the method for producing the iron oxide particles of the present invention, it is an important requirement that the treatment is first performed by a wet method. According to this method, the carbon-based component can be uniformly attached to the fine iron oxide particles. As in the prior art, when adhered by a dry method, particularly small carbon-based component particles have a strong cohesive force and enhance the dispersibility of these particles even with a strong disperser or pulverizer. It is difficult. Therefore, by dispersing by the wet method, it becomes possible to loosen the agglomerated particles, and further, since the carbon-based component can be adhered in a state where the iron oxide particles are sufficiently dispersed, uniform treatment is performed for the first time. The present inventors have found that this is possible. According to the present invention, such manufacturing steps as uniform dispersion and adhesion by the wet method can be performed consistently, and continuous production is also possible. In the case of dispersing such particles, not only water but also a liquid at room temperature such as alcohol can be used. More preferably, a method using water capable of pH adjustment as a dispersion medium as described later is used for uniformity and cost reduction. Is preferred.

  When the carbon-based component is attached, it is preferable that the surface of the carbon-based component is subjected to an alkali treatment and / or an oxidation treatment in advance to increase the chemical activity in view of the uniform treatment and the adhesion strength of the particles. It is not clear why such a pretreatment is effective, but this treatment increases the number of chemically active sites such as carboxyl groups and hydroxyl groups exposed on the surface of the carbonaceous component. It is presumed that the adsorption force on the surface of the iron oxide particles can be further increased.

As a treatment to increase the activity of the surface of the carbon-based component, the oxidation treatment includes a gas oxidizing agent such as oxygen and ozone, and an inorganic oxidizing agent such as nitric acid, hydrogen peroxide, an aqueous solution of permanganate, and an aqueous solution of dichromate. And an organic oxidizing agent such as benzoyl peroxide. When the carbon-based component is treated with such an oxidizing agent, it is preferable to adjust the treatment time, the treatment temperature, the concentration of the treatment liquid, and the like. For example, when nitric acid is used as the oxidizing agent, a nitric acid aqueous solution concentration of 0.1 mol / dm ³ or more, a processing temperature of 20 ° C. to 100 ° C., and a processing time of about 5 minutes to 12 hours are appropriately selected. Preferably, a treatment is performed.

In the case of performing the alkali treatment, it is more preferable to perform the treatment on the carbon-based component that has been subjected to such an oxidation treatment. In the case of performing the alkali treatment, preferably, a gas such as ammonia, an aqueous solution of an alkali hydroxide, an aqueous solution of an alkaline earth metal hydroxide, an aqueous solution of an alkali metal carbonate, an aqueous solution of an alkaline earth metal carbonate, or the like can be optionally used. As a preferred treatment method, it is preferable to appropriately select an alkali concentration, a treatment temperature, a treatment time, and the like. For example, when treating with an aqueous sodium hydroxide solution, the concentration is 0.001 mol / dm ³ or more, and the treatment temperature is It is preferable to perform the treatment by appropriately selecting 20 to 100 ° C. and a treatment time of about 5 minutes to 12 hours.

  The carbon-based component subjected to such treatment is added to the suspension of the iron oxide particles, and the pH is adjusted with an acid or an alkali, whereby the carbon-based component can be attached to the surface of the iron oxide particles. The pH is adjusted in a range of preferably pH 5 to 12, more preferably 6 to 9, and as a pH change rate, preferably at a slow rate of preferably 5 minutes / pH, more preferably 10 minutes or more / pH. The retention time at the target final pH is preferably 5 minutes or more. According to this method, the carbon-based component can be uniformly attached to the surface of the iron oxide particles, the chemically active sites exposed on the surface of the carbon-based component can be stabilized, and the adhesion to the surface of the iron oxide particles can be further improved. Can be higher.

  Furthermore, the outermost surface of the iron oxide particles of the present invention may be treated with a fatty acid, a titanate-based and / or a silane-based coupling agent, if necessary.

  Hereinafter, the present invention will be specifically described based on examples and the like, but the present invention is not limited to these examples.

[Production example of magnetite slurry]
And an aqueous solution of ferrous 50 dm ³ sulfuric acid containing Fe ²⁺ 2.0mol / dm ^3, were mixed and stirred aqueous sodium hydroxide solution 50 dm ³ of 4.0 mol / dm ^3. The ferrous hydroxide slurry thus obtained was maintained at a temperature of 80 ° C. and a pH of the slurry of 6 to 9, and air was ventilated with continuous stirring to obtain a spherical particle having a specific surface area of 5 to 5 according to the BET method. Observation with a scanning electron microscope of 0.5 m ² / g gave magnetite slurry (A) having an average Feret diameter of 100 particles of 0.23 μm.

An aqueous solution of ferrous and aqueous sodium hydroxide sulfate was mixed and stirred 50 dm ³ and 51Dm ³ respectively as well. The temperature of the ferrous hydroxide slurry thus obtained was maintained at 80 ° C. and the pH of the slurry was maintained at 10, the air was passed while stirring, the particle shape was hexahedral, and the specific surface area by the BET method was 6. Observation with a scanning electron microscope at 0.0 m ² / g gave magnetite slurry (B) having an average Feret diameter of 100 particles of 0.25 μm.

Furthermore, it was mixed and stirred so as to become an aqueous solution of ferrous and aqueous sodium hydroxide sulfate respectively 50 dm ³ and 52dm ^3. The temperature of the ferrous hydroxide slurry thus obtained was maintained at 80 ° C. and the pH of the slurry at 11.5, and air was ventilated while stirring was continued. A magnetite slurry (C) having a surface area of 6.8 m ² / g and an average Feret diameter of 100 particles of 0.21 μm was obtained by observation with a scanning electron microscope.

[Example of carbon black treatment]
Mitsubishi Chemical Corporation carbon black # 44 (hydrophilicity, particle diameter 24 nm, specific surface area 110 m ² / g, pH 8.0) was maintained in a 10 mol / dm ³ aqueous sodium hydroxide solution at 50 ° C. for 30 minutes, The carbon component was subjected to a surface treatment to obtain a carbon black slurry (a).

Further, this carbon black # 44 manufactured by Mitsubishi Chemical Corporation was dispersed in a nitric acid aqueous solution (concentration: 3 mol / dm ³ ), kept at 50 ° C. for 30 minutes, and then repeatedly decanted with pure water to remove nitric acid. A carbon black slurry (b) was obtained.

Further, the carbon black slurry (b) was maintained in a 10 mol / dm ³ aqueous sodium hydroxide solution at 50 ° C. for 30 minutes to perform a surface treatment of the carbon-based component to obtain a carbon black slurry (c).

[Example 1]
As shown in Table 1, a carbon black slurry (a) was added to the magnetite slurry (A) so as to be 3.2% by weight of carbon based on the total amount of magnetite particles. The temperature of the mixed slurry was adjusted to 50 ° C., the pH was adjusted to 6.5 with sulfuric acid while stirring, and this state was maintained for 30 minutes. The obtained mixed slurry was subjected to ordinary filtration, washing, drying and pulverization to obtain a magnetite powder subjected to carbon black treatment. The obtained magnetite powder was evaluated by the following method. Table 2 shows the obtained results. FIG. 1 shows an SEM photograph (× 40000) of this magnetite powder.

<Evaluation method>
(1) Specific surface area The specific surface area due to nitrogen gas was measured using a 2200 type BET meter manufactured by Shimadzu-Micro Meritech.
(2) Magnetic Properties Using a vibration type magnetometer VSM-P7 manufactured by Toei Kogyo, saturation magnetization (σs), remanence magnetization (σr) and coercive force (Hc) in an external magnetic field of 796 kA / m and 79.6 kA / m. ) Was measured.
(3) pH
It was measured according to the method described in JIS K 5101-1991 26 (3.1).
(4) Oil absorption The oil absorption was measured according to the method described in JIS K 5101-199121.
(5) Electric Resistance 10 g of a sample was put in a holder, and after applying a pressure of 60 MP to form a tablet having a diameter of 25 mm, an electrode was attached and measurement was performed under a pressure of 15 MP. The electrical resistance was determined from the thickness and cross-sectional area of the sample used for the measurement and the resistance.
(6) Paint colorimetry The color was measured by a method based on JIS K5101-1991.
First, 10 g of magnetite powder and 60 g of a resin solution prepared by adjusting styrene-acrylic resin (TB-1000F, manufactured by Sanyo Kasei Co., Ltd.): Toluene = 1: 2 to a glass bottle having an inner volume of 120 ml, and 90 g of glass beads having a diameter of 1 mm were further added. The mixture was dispersed in a paint shaker, applied to a mirror-coated paper using a 4 mil applicator, dried, and then subjected to color measurement with the above color difference meter.
(7) Desorption rate of carbon-based components 5 g of a sample was put in 100 ml of pure water, and dispersed in an ultrasonic cleaning tank (Silent Sonic UC-602 type) manufactured by Sharp Corporation for 5 minutes. The resulting dispersion was allowed to stand for 3 minutes, the supernatant was immediately discarded, and the precipitated magnetite particles were collected by filtration and dried to obtain a sample after ultrasonic dispersion treatment. The carbon-based component content in the sample before and after the ultrasonic dispersion treatment was measured using a carbon-in-metal analyzer (EMIA-110) manufactured by Horiba, with a combustion temperature of 1250 ° C. Measurement was performed by a method in accordance with 6.10, and the carbon-based component desorption rate before and after ultrasonic dispersion was evaluated by the following equation.
Carbon-based component desorption rate (%) = 100− [Carbon content (% by weight) of sample after ultrasonic treatment / carbon content (% by weight) of sample before ultrasonic treatment × 100]
When the carbon black slurries (a) to (c) were dispersed by the present evaluation method, the carbon black particles did not precipitate even after standing for 3 minutes. As a result, the carbon black particles desorbed by the ultrasonic dispersion do not precipitate, and thus, by collecting the precipitated magnetite, only the carbon-based components remaining attached to the surface of the magnetite particles can be evaluated.

[Evaluation of toner conversion]
Using the magnetite powder subjected to the carbon black treatment obtained in Example 1, an electrophotographic toner was manufactured according to the following formulation.
-100 parts by weight of the magnetite powder of Example 1-100 parts by weight of a styrene-acrylic thermoplastic resin (TB-1000F, manufactured by Sanyo Chemical Co., Ltd.)
・ Wax 1 part by weight (Viscol 550P manufactured by Sanyo Chemical Co., Ltd.)
-2 parts by weight of charge control agent (Orient Chemical Co., Ltd., Bontron S-34)

  After mixing the above sample with a Henschel mixer, melt kneading at 180 ° C. was performed with a biaxial kneader. The obtained kneaded material was cooled to room temperature, coarsely pulverized with a bantam mill, finely pulverized with a jet mill, and averaged with a wind classifier (Nissin Engineering Co., Ltd., Turbo Classifier TC-15M). A 7 μm powder was obtained. To this powder was added 2% by weight of silica fine particles (R-972, manufactured by Nippon Aerosil Co., Ltd.) as a fluidizing agent to prepare a developing toner. Using an LBP printer (manufactured by Canon Co., Ltd., LBP-320), the obtained toner was changed to low-temperature and low-humidity (10 ° C., 20% RH), normal temperature and normal humidity (23 ° C., 55% RH), and high temperature. The measurement was performed at a high humidity (35 ° C., 85% RH), and the initial image density of the solid black portion and the image density after 1k printing were measured with a Macbeth densitometer (RD918). Table 3 shows the obtained results.

[Career evaluation]
Using the magnetite powder subjected to the carbon black treatment obtained in Example 1, the carrier for developing an electrostatic latent image was evaluated according to the following formulation.
-100 parts by weight of the magnetite powder of Example 1-400 parts by weight of a styrene-acrylic thermoplastic resin (TB-1000F, manufactured by Sanyo Chemical Co., Ltd.)

  After mixing the above materials with a Henschel mixer, melt kneading at 200 ° C. was performed with a biaxial kneader. The obtained kneaded material was cooled to room temperature, coarsely pulverized by a bantam mill, then finely pulverized by a jet mill, and averaged to 30 μm by an air classifier (Turbo Classifier TC-15M manufactured by Nisshin Engineering Co., Ltd.). Was obtained. This powder was mixed with 10% by weight of the toner produced in the above-mentioned evaluation of toner formation to obtain a developer. 30 g of this developer was put in a poly bottle, and mixing was continued at a rotation of 120 rpm by a ball mill rotating device under an environment of 23 ° C. and 55% RH. Samples at the mixing time of 5 minutes and 4 hours were collected from the polybin, and the charge amount was measured by a blow-off method using a charge amount measuring device (TB-200, manufactured by Toshiba Chemical Corporation). In each of the samples, when the charge amount was 3 μC / g or less, the stability was judged to be excellent. When the charge stability was evaluated as ○, when the charge amount exceeded 3 μC / g, the charge stability was evaluated. Judgment was not made, and the evaluation of charging stability was evaluated as x. Table 3 shows the obtained results.

(Pigment evaluation)
Using the magnetite powder subjected to the carbon black treatment obtained in Example 1, the black pigment was evaluated according to the following formulation.
20 g of titanium oxide powder for white pigment (R-820, manufactured by Ishihara Sangyo Co., Ltd.), 0.8 g of magnetite powder, and 100 g of steel balls (6 mmφ) were placed in a glass pot, and mixed for 5 minutes with a shaker (500 rpm). After the mixed powder was formed into a pellet, the color was measured with a color difference meter (manufactured by Tokyo Denshoku Co., Ltd., color analyzer TC-1800). Table 3 shows the obtained results.

[Examples 2 to 8]
As shown in Table 1, magnetite powders subjected to various carbon black treatments were obtained by changing the type of magnetite, the type and treatment amount of the treated carbon black, and adjusting the final pH as a treatment condition. This magnetite powder was evaluated in accordance with Example 1, and the obtained results are shown in Tables 2 and 3. 2 and 3 show SEM photographs (× 40000) of the magnetite powders of Examples 2 and 3.

[Comparative Examples 1-2]
As shown in Table 1, the magnetite slurries (A) and (C) were subjected to ordinary filtration, washing, drying, and pulverization, and the obtained magnetite powders A and C were evaluated in accordance with Example 1 to obtain The results obtained are shown in Tables 2 and 3.

[Comparative Examples 3 and 4]
# 44 was dispersed in pure water as a carbon black powder, and added to the magnetite slurry (A) or (B) to adjust the pH of the mixed slurry to 8.5, followed by filtration and washing according to Example 1. , Drying and grinding. The obtained magnetic material was evaluated according to Example 1, and the obtained results are shown in Tables 2 and 3.

[Comparative Example 5]
As shown in Table 1, a magnetite powder subjected to carbon black treatment was obtained in the same manner as in Example 4, except that the final pH at the time of carbon black treatment was set to 3. This magnetite powder was evaluated according to Example 1, and the obtained results are shown in Tables 2 and 3.

[Comparative Example 6]
Using # 44 as it is as the carbon black particles, the carbon black particles were physically adhered by mixing and compacting in a dry process. Specifically, the magnetite slurry (A) is subjected to ordinary filtration, washing, drying, and pulverization, and the obtained magnetite powder and carbon black powder are weighed, and a Henschel mixer (manufactured by Mitsui Miike Kakoki Co., Ltd.) is used. After mixing for 30 minutes, using a sand mill (manufactured by Yodo Casting Co., Ltd., MPUV-2 type), processing was performed at a processing amount of 10 kg / batch, a linear pressure of 80 kg / cm, and a rotation speed of 8.5 rpm for 60 minutes. Was. The obtained magnetite powder was evaluated according to Example 1, and the obtained results are shown in Tables 2 and 3. FIG. 4 shows an SEM photograph (× 1000) of the magnetite powder.

  As is clear from Table 2, it can be seen that the Example has a lower desorption rate of the carbon-based component and a higher adhesion strength between the carbon black particles and the magnetite particles than the Comparative Example. Further, even when the same amount of carbon black particles were adhered, in the case of Examples 2 and 6 in which the carbon black particles were subjected to oxidation treatment and alkali treatment, in Examples 1 and 4 in which only the alkali treatment was performed. It can be seen that the desorption rate of this carbon-based component is lower than in such a case. In addition, the magnetite particles subjected to such treatment showed a tendency to decrease in oil absorption and electric resistance, which is presumed to be because carbon black particles were uniformly contained in the gaps between the magnetite particles. did. On the other hand, in Comparative Examples 3 to 6, the desorption rate of the carbon-based component was high, and it was found that sufficient adhesion strength of the carbon-based component could not be obtained by the dry physical treatment alone. In the dry physical treatment, the magnetite particles were subjected to surface oxidation, and it was not possible to perform a uniform surface treatment with carbon black particles having a low electric resistance. Further, in Comparative Examples 3 and 4, carbon black particles whose surfaces were not chemically treated were used, so that sufficient adhesion to the iron oxide particle surfaces could not be obtained, and thus the desorption rate was somewhat high. Met.

  Further, as is clear from Table 3, the examples have higher image density stability in toner evaluation and a sufficient blackness as compared with the comparative examples. It is presumed that the uniformity of the charging property and the electric resistance was sufficiently achieved because the carbon black particles were uniformly attached to the magnetite particle surfaces. On the other hand, in the comparative example, it was difficult to obtain a sufficient image density with the carbon black untreated product, and the decrease in image density particularly under high temperature and high humidity was conspicuous.

  In addition, the carrier stability in the evaluation of carrier conversion was high in the examples, but the carrier particles having high stability were obtained. However, in Comparative Examples 3 to 6, especially in Comparative Example 6 in which the adhesion strength of the carbon black particles was low, the charge stability was low. It was low.

  Regarding these evaluation results, the present inventors have found that when carbon black particles are subjected to hot melt kneading with a binder component such as a resin, the carbon black particles are separated from the surface of the magnetite particles, or the carbon black particles It is presumed to be a phenomenon that occurred due to lack of uniformity as a powder.

  In the pigment evaluation, it is found that the blackness is further improved by subjecting the carbon black particles to an oxidation treatment and an alkali treatment in advance. This is presumably because the uniform treatment of carbon black particles has been improved by this chemical pretreatment. On the other hand, in the case of Comparative Example 6 in which the physical treatment was particularly performed, the dispersibility of the consolidation treatment was not sufficient, and the carbon black treatment could not be further uniformly performed. , A high blackness as a pigment could not be obtained.

  When observed with a SEM at a magnification of 40,000, carbon black particles did not adhere to the surface of most of the magnetite particles. At a magnification of 1,000, undispersed carbon black particles were scattered in an island shape as shown in FIG. I found out.

FIG. 1 is an SEM photograph (× 40000) of the magnetite powder obtained in Example 1. FIG. 2 is an SEM photograph (× 40000) of the magnetite powder obtained in Example 2. FIG. 3 is an SEM photograph (× 40000) of the magnetite powder obtained in Example 3. FIG. 4 is an SEM photograph (× 1000) of the magnetite powder obtained in Comparative Example 6.

Claims (5)

  The average particle diameter is 0.05 to 1 μm, the carbon-based component is attached to the particle surface in an amount of 0.1 to 30% by weight in terms of carbon atoms based on the total amount of iron oxide particles, and water is used as a dispersion medium. The iron oxide particles, wherein the carbon-based component desorption rate in the case of performing is 15% or less.   The iron oxide particles according to claim 1, wherein the carbon-based component is surface-activated carbon black particles having an average particle size of 1 to 100 nm.   The iron oxide particles according to claim 1 or 2, wherein the L value measured by a color difference meter based on the coloring power measurement method described in JIS K 5101-1991 is 12 or less.   An iron oxide powder comprising the iron oxide particles according to claim 1 or more in an amount of 1% by weight or more. A black pigment containing the iron oxide powder according to claim 4.