JP5400440B2 - Magnetite particles - Google Patents

Description

  The present invention relates to magnetite particles. The present invention also relates to a coated magnetite particle in which the surface of the magnetite particle is coated with a silane compound. The coated magnetite particles are particularly preferably used as a toner material for printers and electronic copying machines, for example.

  Conventionally, in the production of electrostatic copying magnetic toner, a so-called pulverization method in which magnetic powder, a binder or the like, which is a raw material of the toner, is mixed and melt-kneaded and then pulverized and classified has been the mainstream. However, the toner obtained by the pulverization method is approaching the limit in providing functions such as finer particle size and further low-temperature fixability. In particular, in order to achieve high image quality such as full color, a polymerization method that does not require a pulverization classification process or can significantly reduce the pulverization classification process has attracted attention.

  As a method for directly producing a toner by a polymerization method, a suspension polymerization method is known. When the toner is produced by the suspension polymerization method, the use of magnetic powder having a hydrophilic surface tends to lower the charging characteristics and image characteristics of the toner. This is because the surface of the magnetic powder is hydrophilic, and the magnetic powder cannot be sufficiently dispersed in the non-aqueous solvent. As a result, the dispersibility of the magnetic powder in the toner is reduced. This is because the magnetic powder is not sufficiently contained in the toner.

  Therefore, an attempt has been proposed to improve the dispersibility of the magnetic powder in a non-aqueous solvent by hydrophobizing the surface of the magnetic powder used as a raw material for the polymerization toner. For example, in Patent Document 1, magnetite particle powder and vaporized fluoroalkylsilane or alkoxysilane are contacted and reacted in a temperature range of 50 to 150 ° C., and then the obtained particle powder is heated to 160 to 250 ° C. Producing hydrophobized magnetite particle powder by heat treatment in a temperature range has been proposed.

  Patent Document 2 proposes hydrophobic magnetic iron oxide particles in which magnetic iron oxide is used as a base particle and the surface thereof is coated with a silane compound. In this document, the hydrophobicity of the magnetic iron oxide particles is reduced by setting the elution rate of the silane compound in the hydrophobic magnetic iron oxide particles to 30% or less, and the magnetic iron oxide particles are sufficiently hydrophobic. It is described that the particle size distribution becomes narrow. According to the document, the silane compound is preferably added to the slurry of magnetic iron oxide particles whose pH is set to 4 to 6, and the pH is preferably increased as the coating of the silane compound proceeds. .

  However, in the technique described in Patent Document 1, in order to increase the bond strength between the magnetite particle powder and fluoroalkylsilane or the like, an intermediate coating layer made of Si or Al hydroxide is introduced. The coating layer increases the specific surface area and water adsorption sites. This leads to the use of a large amount of fluoroalkylsilane and the like. Further, in the technique described in the same document, since the heat treatment is performed in a temperature range of 160 to 250 ° C., the particles are likely to aggregate and the dispersibility of the particles in the organic solvent tends to deteriorate due to the aggregation. It is in.

  In the technique described in Patent Document 2, although the bond strength between magnetic iron oxide and silane compound is high, it cannot be said that the degree of hydrophobicity of the surface is sufficiently high. Further, an alkali such as sodium hydroxide is used to adjust the pH during the treatment, and it remains on the surface of the particles, which may affect the hydrophobicity of the particles.

  Apart from the polymerization toner, the present applicant has previously proposed magnetite particles containing Ti and Si from the center to the surface of the particles (see Patent Documents 3 and 4). However, these magnetite particles have been proposed for the purpose of improving environmental resistance and fluidity, and are not optimized for polymerization toners.

JP 2000-327948 A JP 2005-263619 A JP 2002-154826 A JP 2000-272924 A

  The present invention provides magnetite particles that can eliminate the various drawbacks of the prior art described above.

The present invention comprises Ti or Si, these are present inside the particles, and composed of magnetite substantially free of Ti and Si on the outermost surface of the particles,
The present invention provides magnetite particles characterized in that the elution amounts of Ti and Si by a pure water boiling test are 50 ppm or less with respect to the whole particles.

  The present invention also provides coated magnetite particles wherein the surface of the magnetite particles is coated with a silane compound having an alkyl chain having 2 to 10 carbon atoms.

  According to the present invention, magnetite particles having high silane compound coverage and preventing magnetic aggregation are provided. In addition, according to the present invention, coated magnetite particles having high surface hydrophobicity and high dispersion stability in an organic solvent having a low dielectric constant are provided.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The magnetite particles of the present invention (the magnetite particles are also referred to as core magnetite particles in relation to the coated magnetite particles described later) contain Ti and / or Si. The core magnetite particles may contain only one of Ti and Si, or may contain both Ti and Si. Core magnetite particles are characterized by sites containing Ti and Si. Specifically, Ti and / or Si are present inside the core magnetite particles and are not substantially present on the outermost surface of the particles. Furthermore, it is preferable that the core magnetite particles are substantially free of other different elements in addition to Ti and Si on the outermost surface. The heterogeneous element here means an element other than Fe and O which are elements constituting magnetite. In other words, the different elements are all elements other than Fe and O.

  Since the core magnetite particles contain Ti and / or Si therein, the magnetic properties of the core magnetite particles are controlled and excessive magnetic aggregation is suppressed. As a result, the surface of the core magnetite particles can be uniformly coated with a silane compound described later. From the standpoint of preventing magnetic aggregation only, Ti or Si may be contained in any part of the core magnetite particle, but when Ti or Si is present on the outermost surface of the particle, conversely As a result of the examination by the present inventors, it was found that the coating with the silane compound is inhibited. It has also been found that the dissimilar elements other than Ti and Si also inhibit the coating with the silane compound when they are present on the outermost surface of the core magnetite particles. Therefore, in the present invention, Ti and Si are not substantially present on the outermost surface of the core magnetite particles, and preferably, other different elements are not substantially present.

  The “substantially non-existent” described above means that a different element is not intentionally present on the outermost surface of the core magnetite particle. Therefore, in the production process of the core magnetite particles and the coated magnetite particles using the same as a raw material, it is inevitably allowed that foreign elements are mixed into the outermost surface of the particles. Specifically, the elution amounts (element basis) of Ti and Si in the pure water boiling test performed by the following method are 50 ppm or less, preferably 20 ppm or less, more preferably 10 ppm or less, respectively, with respect to the entire core magnetite particles. In some cases, it can be said that these elements are not substantially present on the outermost surface of the core magnetite particles.

  As a result of the study by the present inventors, in addition to Ti and Si, among the different elements other than these, in particular, when Na is less on the outermost surface of the core magnetite particles, the coating state of the silane compound in the subsequent process is improved. It turns out that you can. Therefore, it is preferable that Na in addition to Ti and Si is not substantially present on the outermost surface of the core magnetite particles. Specifically, the elution amount (element basis) of Na in the pure water boiling test is preferably 50 ppm or less, preferably 20 ppm or less, more preferably 10 ppm or less, based on the entire core magnetite particles.

  If the amount of different elements including Ti and Si existing on the surface of the core magnetite particles is 50 ppm or less as described above, the smaller the amount, the better the coating state of the silane compound. However, it is extremely difficult to reduce the amount of different elements to the limit with the current core magnetite particle manufacturing technology known in the art. When the present inventors examined the lower limit of the abundance of different elements, it was found that satisfactory coverage could be obtained if the amount of each different element was reduced to 1 ppm.

  Measurement of the amount of elution by a pure water boiling test of different elements including Ti and Si is performed according to the following procedure. 25 g of core magnetite particles are accurately weighed and dispersed in 250 mL of pure water, then boiled for 5 minutes and cooled to room temperature. Add pure water corresponding to the amount of liquid reduced by evaporation to 250 mL again. Next, filtration is performed with 5 types C filter paper according to JIS P3801. Begin filtration and discard the first 50 mL and collect the remaining filtrate. About the extract | collected filtrate, the density | concentration of each element in a filtrate is measured using ICP. The measured concentration of each element is converted into the ratio of each element in the core magnetite particles.

  With respect to Ti and / or Si present in the core magnetite particles, the specific amounts of these elements are preferably as follows. Ti is preferably contained in the magnetite particles in the range of 500 to 5000 ppm, particularly 1000 to 4000 ppm, particularly 1500 to 3500 ppm. By setting the Ti content within this range, magnetic aggregation of the core magnetite particles can be effectively prevented without exposing Ti to the surface of the core magnetite particles. Si is also preferably contained in the magnetite particles in the range of 500 to 5000 ppm, particularly 1000 to 4000 ppm, particularly 1500 to 3500 ppm for the same reason as Ti.

  When both Ti and Si are present inside the core magnetite particles, the total amount of both is in the range of 1000 to 10000 ppm, particularly 3000 to 7000 ppm in the particles. From the viewpoint of improvement and further prevention of magnetic aggregation.

  The amount of Ti and Si contained in the core magnetite particles is measured using, for example, a scanning X-ray fluorescence analyzer ZSX Primus II manufactured by Rigaku Corporation.

  Since the amount of Ti and Si contained in the core magnetite particles is very small as described above, it is extremely difficult to specify in what state Ti and Si are present in the particles with the current measurement technology. It is. Although it is speculated, the present inventors consider that Ti and Si are present in the state of their oxides or in the state of complex oxides with Fe.

  If Ti and / or Si is contained inside the core magnetite particle, it is effective in preventing magnetic aggregation of the particle regardless of the location of these elements. For example, Ti and / or Si may be present substantially uniformly in the radial direction inside the core magnetite particle, or may be distributed so as to have a peak of abundance at a specific position in the radial direction. For example, it may be unevenly distributed in the center of the core magnetite particles and in the vicinity thereof. Moreover, the site | part which has a peak may be the same in Ti and Si, or may differ. In particular, when core magnetite particles are dissolved from the outermost surface using a mineral acid such as sulfuric acid or hydrochloric acid, the amount of Ti or Si that elutes when the elution rate of Fe is 10 to 100% by weight When these elements are distributed in the particles so that the amount of Ti or Si contained in the whole particles is preferably 60 to 100% by weight, more preferably 70 to 100% by weight, the core magnetite particles Can be more effectively controlled to prevent the magnetic agglomeration more effectively. Moreover, exposure of Ti and Si on the outermost surface of the particles can be prevented more effectively.

  In addition to Ti and Si, other different elements may or may not be present in the core magnetite particles. When other different elements contribute to the improvement of the properties of the core magnetite particles, it is advantageous to positively contain such different elements. Examples of such elements include one or more of Al, Zr, Mn, Zn, Mg, and the like. These elements are preferably contained in the particles in the state of, for example, the oxide or a composite oxide with Fe. In the case of a dissimilar element that does not contribute to the improvement of the properties of the core magnetite particles, it is allowed to be contained in the core magnetite particles as long as its presence does not negatively affect the properties of the core magnetite particles. For example, the Na described above is allowed to be contained in the core magnetite in a range of 10 to 3000 ppm, particularly 20 to 2000 ppm. The amount of Na in the core magnetite particles can be determined by ICP analysis of a solution in which the particles are completely dissolved.

  As the core magnetite particles, those whose main peak coincides with the peak of magnetite when XRD measurement is used are used. In this case, only the magnetite peak may be observed, or a peak such as maghemite may be observed in addition to the main peak of magnetite.

  The core magnetite particles may be spherical, polyhedral (eg, hexahedral, octahedral), or the like. When the present inventors examined the shape of the particles, it was found that when the core magnetite particles are spherical, coating with a silane compound can be performed extremely well. Accordingly, spherical core magnetite particles are preferably used rather than polyhedral ones.

  The core magnetite particles have an average particle size of 0.1 to 0.3 μm, particularly 0.15 to 0.25 μm. When the coated magnetite particles described later are used as toner materials for printers and electronic copying machines, preferable. This is because if the average particle diameter of the core magnetite particles is within this range, the coloring power and color in the toner will be good. The average particle diameter of the core magnetite particles is measured by the following method.

[Measurement method of average particle diameter of core magnetite particles]
The core magnetite particles are measured from an image obtained by observing with a scanning electron microscope (SEM). Specifically, using a SEM photograph (magnification 40,000 times), the ferret diameter of 200 particles is measured, and the average value is taken as the average particle diameter.

The core magnetite particles preferably have a BET specific surface area of 4 to 12 m ² / g, particularly 4 to 10 m ² / g. The BET specific surface area of the core magnetite particles affects the hydrophobicity and dispersibility of the resulting coated magnetite particles. By setting the BET specific surface area in the above-mentioned range, the core magnetite particles can be successfully made with a silane compound. It is preferable because it can be well hydrophobized, and it is possible to achieve both suppression of the water vapor adsorption amount of the coated magnetite particles and dispersion stability in an organic solvent. In order to set the BET specific surface area within the above-described range, for example, the reaction rate and the reaction time when the core magnetite particles are synthesized may be appropriately controlled.

  Next, the coated magnetite particles containing the above-described core magnetite particles will be described. In the coated magnetite particles, the surface of the core magnetite particles is coated with a silane compound. By using the above-mentioned core magnetite particles, the silane compound uniformly covers the surface of the core magnetite particles, and the hydrophobicity of the coated magnetite particles becomes extremely high. As a result, the coated magnetite particles have a very small amount of water vapor adsorption and a very high dispersion stability in an organic solvent having a low dielectric constant. Examples of the organic solvent having a low dielectric constant include styrene, toluene, hexane, benzene, ethyl acetate, xylene and the like.

The silane compound is a compound formed from, for example, an organic silane having an alkyl chain directly bonded to an Si atom. The “compound generated from organosilane” includes, for example, hydrolysis products and dehydration condensation products of organosilanes. The silane compound has an alkyl chain having 2 to 10 carbon atoms. Examples of the organic silane for generating such a silane compound include alkoxysilanes and compounds known as silane coupling agents. For example, organic silanes represented by R ¹ _x Si (OR ² ) _4-x can be used. In the formula, R ¹ represents the same or different alkyl group having 2 to 10 carbon atoms, and R ² represents a short-chain alkyl group. x preferably represents an integer of 1 to 3, more preferably 1 or 2, and still more preferably 1. When x is 2 or 3, R ¹ may be the same type of alkyl group or a different type of alkyl group, provided that the number of carbon atoms is in the above range.

  In the silane compound, the reason why the number of carbon atoms in the alkyl chain is limited to 10 or less is to uniformly coat the surface of the magnetite core particles to suppress the amount of water vapor adsorption. When the carbon chain exceeds 10, the molecular chain becomes large, and it becomes difficult to uniformly coat the surface of the core particle with the silane compound. On the other hand, the reason for limiting the number of carbon atoms to 2 or more is to increase the dispersion stability in the organic solvent. From these viewpoints, the number of carbon atoms in the alkyl chain in the silane compound is preferably 3-8, and more preferably 3-6.

  Specific examples of the organic silane that forms the silane compound include n-propyltrimethoxysilane, iso-propyltrimethoxysilane, n-butyltrimethoxysilane, iso-butyltrimethoxysilane, tert-butyltrimethoxysilane, n-hexyltrimethoxysilane, iso-hexyltrimethoxysilane, tert-hexyltrimethoxysilane, n-octyltrimethoxysilane, iso-octyltrimethoxysilane, tert-octyltrimethoxysilane, n-decyltrimethoxysilane, iso -Decyltrimethoxysilane, tert-decyltrimethoxysilane, n-propyltriethoxysilane, iso-propyltriethoxysilane, n-butyltriethoxysilane, iso-butyltriethoxysilane tert-butyltriethoxysilane, n-hexyltriethoxysilane, iso-hexyltriethoxysilane, tert-hexyltriethoxysilane, n-octyltriethoxysilane, iso-octyltriethoxysilane, tert-octyltriethoxysilane, n -Decyltriethoxysilane, iso-decyltriethoxysilane, tert-decyltriethoxysilane and the like. These organosilanes can be used alone or in combination of two or more.

  The coating amount of the silane compound is preferably 0.01 to 1.5% by weight, particularly 0.05 to 0.5% by weight, based on the weight of the coated magnetite particles, in terms of Si. When the ratio of the silane compound is within this range, there are advantageous effects that the water vapor adsorption amount is small and the aggregation of particles is suppressed. The coating amount of the silane compound is, for example, for coated magnetite particles, and the amount of Si measured using a scanning X-ray fluorescence analyzer ZSX Primus II manufactured by Rigaku Corporation and before being coated with the silane compound. It is obtained from the difference from the amount of Si measured using the same apparatus for the core magnetite particles.

  In the coated magnetite particles, the silane compound described above covers the surface of the core magnetite particles thinly. Therefore, the shape of the coated magnetite particles is the same as the shape of the core magnetite particles. As described above, since the core magnetite particles are preferably spherical, the coated magnetite particles are also preferably spherical. Further, due to the thin coating with the silane compound described above, the average particle size of the coated magnetite particles is not substantially different from the average particle size of the core magnetite particles. Therefore, the explanation detailed about the average particle diameter of a core magnetite particle | grain is applied suitably about the average particle diameter of a covering magnetite particle | grain. The same applies to the method for measuring the average particle diameter of the coated magnetite particles.

  The surface of the coated magnetite particles coated with the silane compound is hydrophobized by the action of the silane compound. It is necessary to examine the degree of hydrophobization from a microscopic viewpoint focusing on individual coated magnetite particles and a macroscopic viewpoint focusing on powder which is an aggregate of coated magnetite particles. It became clear as a result of examination. The degree of hydrophobization from a microscopic viewpoint can be expressed by using the water vapor adsorption amount of the coated magnetite particles as a scale. On the other hand, the degree of hydrophobization from a macro viewpoint can be expressed using the degree of methanol hydrophobization as a scale. In the present invention, the degree of hydrophobicity of the coated magnetite particles can be within a suitable range by successfully balancing the water vapor adsorption amount and the degree of methanol hydrophobization. These measuring methods are as follows.

[Measurement method of water vapor adsorption amount]
Using a water vapor adsorption amount measuring apparatus BELSORP18 (manufactured by Nippon Bell Co., Ltd.), the water vapor adsorption amount per 1 g of the coated magnetite particles at 25 ° C. and a relative pressure of 0.9 was measured.

[Method of measuring the degree of hydrophobicity of methanol]
Using a powder wettability tester (WET101P manufactured by Reska Co., Ltd.), 50 mg of the coated magnetite particles are added to 60 mL of a methanol aqueous solution having a volume concentration of 40% (temperature: 25 ° C.), and stirred with a stirring blade. Under this condition, methanol is dropped, and along with this, an aqueous methanol solution is irradiated with laser light having a wavelength of 780 nm, and the transmittance is measured. The volume concentration of the aqueous methanol solution where the coated magnetite particles get wet, settle and suspend and the transmittance is 80% is defined as the degree of methanol hydrophobization.

  The water vapor adsorption amount tends to increase the degree of hydrophobicity as the value decreases. From this viewpoint, the preferable range of the water vapor adsorption amount of the coated magnetite particles is 0.01 to 1.0 mg / g, and the more preferable range is 0.05 to 0.8 mg / g.

  The degree of methanol hydrophobization takes a value of 0 to 100%, and the higher the hydrophobicity, the higher the value. Therefore, from the viewpoint of hydrophobicity, a higher value of methanol hydrophobization degree is preferable. However, even if the hydrophobicity is not actually high, the degree of methanol hydrophobization tends to be high due to the progress of particle aggregation. Therefore, a high value of the degree of hydrophobicity of methanol may not be synonymous with the high hydrophobicity of the coated magnetite particles.

  Similarly, the value of the degree of methanol hydrophobization is also high when a silane compound that is not actually highly hydrophobic (for example, a magnetite core particle is coated with a long-chain alkyl group (for example, a silane compound having more than 10 carbon atoms)). Tend to be. This is because the particles tend to aggregate due to the entanglement between the long-chain alkyl groups. In this case, the presence of the long chain alkyl group reduces the surface tension and increases the degree of hydrophobicity of methanol, but such coated magnetite particles have low compatibility with the resin, and the degree of hydrophobicity is high. I can not say. Also, the presence of air entrained between the particles due to the aggregation of the particles tends to reduce the compatibility with the resin. Therefore, also in this case, a high value of the degree of methanol hydrophobization may not be synonymous with the high hydrophobicity of the coated magnetite particles.

  Taking the above into consideration, it is preferable that the methanol hydrophobicity has a higher value, but it is better not to be excessively high. From this viewpoint, the coated magnetite particles preferably have a methanol hydrophobization degree of 50 to 70%, more preferably 53 to 68%, and still more preferably 58 to 64%. When the degree of methanol hydrophobization is within this range, the coated magnetite particles have good dispersibility not only in organic solvents but also in various resins including polyester resins. In the coated magnetite particles, it is preferable that the surface of the core magnetite particles is coated with an amount of a silane compound sufficient for the methanol hydrophobization degree to be in the above range.

  Next, a preferred method for producing coated magnetite particles will be described. This production method is roughly divided into two processes: (1) a process for producing core magnetite particles, and (2) a process for coating the surface of core magnetite particles with a silane compound. Hereinafter, each process will be described.

  First, in the manufacturing process of core magnetite particles (1), two-stage wet oxidation is performed. Specifically, the first wet oxidation is performed, for example, by blowing an oxidizing gas into a ferrous hydroxide colloid solution generated by a neutralization reaction of a ferrous salt. In this case, one or more of a water-soluble Ti salt (for example, titanyl sulfate) and / or a water-soluble Si compound (for example, sodium silicate) is added to the reaction solution (before reaction, start of reaction) Either during or during the reaction). Furthermore, if necessary, a water-soluble compound containing one or more metals such as Al, Zr, Mn, Zn, Mg, etc. other than Ti and / or Si may be added to the reaction solution. (Either before the reaction, at the start of the reaction, or during the reaction).

  In the first wet oxidation, it is preferable to appropriately adjust the pH of the liquid when performing the wet oxidation method. For example, while maintaining the pH of the liquid at preferably 7 or less, more preferably 5.5 to 7.0, and even more preferably 5.5 to 6.0, an oxidizing gas such as air is blown into the liquid to perform wet oxidation. Do. By adjusting the pH, the obtained core magnetite particles can be easily made spherical. On the other hand, when wet oxidation is performed with the pH of the liquid set to the alkali side, for example, preferably pH 9 or higher, polyhedral core particles are generated instead of spherical.

  Note that the conditions for blowing an oxidizing gas such as air in wet oxidation are not particularly critical in the present production method, and appropriate conditions may be adopted.

  After the completion of the first wet oxidation (at this time, all Ti and Si in the liquid are taken into the core particles), the second wet oxidation is performed. In the second wet oxidation, an aqueous solution of ferrous salt not containing Ti and Si is added to the reaction system, and wet oxidation is performed while adjusting the pH of the reaction system using an alkali or the like as necessary. By this wet oxidation, core magnetite particles substantially free of Ti and Si on the outermost surface can be successfully obtained.

  The operation for reducing the amount of different elements other than Ti and Si present on the outermost surface of the core magnetite particles includes the following operations. For example, when the amount of an alkali metal element such as Na is reduced, the core magnetite obtained in the step (1) is performed after the completion of the step (1) and before the step (2) described later. The particles may be washed with water using a medialess disperser. By using a medialess type disperser for washing with water, there is an advantageous effect that the aggregate can be loosened and Na can be efficiently removed. From this point of view, for example, a homogenizer can be used as the medialess disperser. As the homogenizer, there are types such as a high-speed stirring type, an ultrasonic type and a high-pressure type, and any type of homogenizer can be used in the present invention. Among these methods, it is preferable to use a high-speed stirring type homogenizer from the viewpoint of more efficient removal of Na. Examples of the high-speed stirring type homogenizer include a Harel homogenizer manufactured by Kokusan Seiko Co., Ltd. and a pipeline homomixer manufactured by Primix Co., Ltd. The operating conditions of the medialess type disperser are not critical in the present production method, and the operating conditions may be appropriately adjusted so that the amount of Na present on the surface of the core magnetite particles is reduced to the above range. For example, the amount of Na can be adjusted by measuring the conductivity of the liquid when the core magnetite particles are washed with water. In addition, the amount of Na which exists in a core magnetite particle | grain is hardly changed by this water washing.

  In the step (2), the surface of the core particles thus obtained is then coated with a silane compound having an alkyl chain having 2 to 10 carbon atoms. For this coating, in this step, the above-mentioned organosilane is used, and the silane compound is generated from the organosilane.

  Specifically, the above-mentioned organosilane is hydrolyzed on the surface of the core magnetite particles to produce the silane compound comprising the hydrolyzate or dehydrated condensate, thereby covering the surface of the core magnetite particles. . Alternatively, the organic silane may be hydrolyzed in advance, and the generated silane compound may be coated on the surface of the core magnetite particles. There are a wet method and a dry method for coating the surface of the core magnetite particles with a silane compound formed by hydrolyzing an organic silane. In the wet method, the surface of the core magnetite particles is coated by adding organic silane or a silane compound to a slurry containing water as a medium, including core magnetite particles, and having a pH set in a predetermined range. In the dry method, core magnetite particles and organic silane or a silane compound are mixed in the substantial absence of a liquid medium to coat the surfaces of the particles. In this production method, the dry method is adopted because the surface of the core magnetite particles can be successfully coated with the silane compound among these two methods.

  In the dry method, a known mixing and stirring device can be used for mixing the core particles and the organic silane. For example, a Henschel mixer, a high speed mixer, an edge runner, a ribbon blender, or the like can be used. As operating conditions of these apparatuses, it is preferable to set the temperature at the time of mixing and stirring to 10 to 50 ° C, particularly 20 to 40 ° C. As a result, the organic silane is unintentionally hydrolyzed before the two are sufficiently mixed, and the organic silane and the silane compound are volatilized before being sufficiently mixed with the core magnetite particles. Can be prevented. The blending ratio of the core particles and the organic silane is such that the organic silane is 0.1 to 10 parts by weight, particularly 0.3 to 3 parts by weight, with respect to 100 parts by weight of the core magnetite particles. The amount of the silane compound contained in the particles is appropriate, which is preferable from the viewpoint that the hydrophobicity of the coated magnetite particles becomes sufficiently high.

  When dry mixing is completed, the mixture is heated to a temperature at which dehydration condensation of the organic silane or silane compound occurs, thereby causing dehydration condensation of the organic silane or the silane compound. Although depending on the type of organic silane or silane compound, the heating temperature is preferably 100 to 160 ° C, particularly 110 to 150 ° C. By performing heating in this temperature range, dehydration condensation of the organic silane or the silane compound can be performed while preventing excessive aggregation of the core particles. There is no restriction | limiting in particular in the atmosphere at the time of a heating. In general, heating may be performed in the atmosphere.

  In this way, the desired coated magnetite particles are obtained. Since the surface of this particle is coated with the above silane compound, the hydrophobicity is extremely high. The obtained coated magnetite particles are particularly useful as a raw material for the polymerization toner. For example, when the suspension polymerization method is performed, the coated magnetite particles of the present invention are mixed with the monomer component of the binder and the charge control agent, then water is added, and the suspension stabilizer is added and suspended. A toner is obtained by subjecting the liquid to a monomer polymerization step for polymerization. According to this method, a toner having a uniform particle diameter can be obtained in one stage. Further, the coated magnetite particles of the present invention may be used as a raw material for the pulverized toner.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “% by weight”.

[Example 1 (Production of core magnetite particles)]
40 liters of ferrous sulfate aqueous solution containing 1.8 mol / L of Fe ²⁺ , 100 g of titanyl sulfate having a Ti grade of 20.0%, and 5.8 kg of sodium hydroxide were mixed, and water was further added. The total amount was 140 liters, and an aqueous ferrous salt solution containing ferrous hydroxide colloid was obtained. While maintaining the temperature of this liquid at 90 ° C., air was aerated at 15 L / min to conduct wet oxidation of ferrous hydroxide to obtain magnetite particles containing Ti. During this time, the pH of the solution was maintained at 6 by adding an aqueous sodium hydroxide solution.

Next, 10 liters of ferrous sulfate aqueous solution containing 1.8 mol / L of Fe ²⁺ was added to the reaction system, and wet oxidation was again performed at 90 ° C. while maintaining the pH at 6 by adding sodium hydroxide. Thereafter, the decantation was performed three times to wash the particles with water, followed by drying and pulverization according to a conventional method. In this way, spherical core magnetite particles containing Ti were obtained. When the core magnetite particles were dissolved using 1N sulfuric acid and the amount of eluted Ti was analyzed over time by ICP, the amount of Ti eluted while the elution rate of Fe was 10 to 100% was It was 70% of the amount of Ti contained in. The properties of the obtained core magnetite particles are shown in Table 1 below. The BET specific surface area was measured using a 2200 type BET meter made by Shimadzu-Micromeritics.

[Example 2 (Production of core magnetite particles)]
In Example 1, the core magnetite particles were washed with water using a Hallel homogenizer, and then dried and pulverized according to a conventional method. Thus, spherical core magnetite particles containing Ti and having a reduced amount of Na were obtained. The properties of the obtained core particles are shown in Table 1 below.

[Example 3 (Production of core magnetite particles)]
40 liters of ferrous sulfate aqueous solution containing Fe ²⁺ 1.8 mol / L, 100 g of titanyl sulfate having a Ti grade of 20.0%, and 180 g of sodium silicate aqueous solution (concentration 0.9 mol / L in terms of Si) And 5.8 kg of sodium hydroxide were added, and water was further added to make the total volume 140 liters to obtain a ferrous salt aqueous solution containing ferrous hydroxide colloid. While maintaining the temperature of this liquid at 90 ° C., air was aerated at 15 L / min to conduct wet oxidation of ferrous hydroxide to obtain magnetite core particles containing Ti and Si. During this time, the pH of the solution was maintained at 6 by adding an aqueous sodium hydroxide solution.

Next, 10 liters of ferrous sulfate aqueous solution containing 1.8 mol / L of Fe ²⁺ was added to the reaction system, and wet oxidation was again performed at 90 ° C. while maintaining the pH at 6 by adding sodium hydroxide. Thereafter, the particles were washed with water using a Hallel homogenizer, followed by drying and pulverization according to a conventional method. In this way, spherical core magnetite particles containing Ti and Si and having a reduced amount of Na were obtained. The properties of the obtained core magnetite particles are shown in Table 1 below.

[Example 4 (Production of core magnetite particles)]
In Example 1, spherical core magnetite particles containing Ti were obtained in the same manner as in Example 1 except that the amount of titanyl sulfate used was increased from 100 g to 180 g. The properties of the obtained core magnetite particles are shown in Table 1 below.

[Comparative Example 1 (Production of core magnetite particles)]
50 liters of ferrous sulfate aqueous solution containing 1.8 mol / L of Fe ²⁺ and 5.8 kg of sodium hydroxide are mixed, and water is further added to make a total amount of 140 liters, including ferrous hydroxide colloid A ferrous salt aqueous solution was obtained. While maintaining the temperature of this liquid at 90 ° C., air was aerated at 15 L / min to conduct wet oxidation of ferrous hydroxide to obtain magnetite core particles. During this time, the pH of the solution was maintained at 6 by adding an aqueous sodium hydroxide solution. Thereafter, the decantation was performed three times to wash the core particles with water, followed by drying and pulverization according to a conventional method. In this way, spherical core magnetite particles (not containing Ti) were obtained. The properties of the obtained core magnetite particles are shown in Table 1 below.

[Comparative Example 2 (Production of core magnetite particles)]
50 liters of ferrous sulfate aqueous solution containing 1.8 mol / L of Fe ²⁺ , 100 g of titanyl sulfate having a Ti grade of 20.0%, and 7.2 kg of sodium hydroxide were mixed, and water was further added. The total amount was 140 liters, and an aqueous ferrous salt solution containing ferrous hydroxide colloid was obtained. While maintaining the temperature of this liquid at 90 ° C., air was aerated at 15 L / min to conduct wet oxidation of ferrous hydroxide to obtain magnetite core particles containing Ti. During this time, the pH of the solution was maintained at 6 by adding an aqueous sodium hydroxide solution. Thereafter, the decantation was performed three times to wash the core particles with water, followed by drying and pulverization according to a conventional method. In this way, spherical core particles containing Ti were obtained. The properties of the obtained core particles are shown in Table 1 below.

[Examples 5 to 8 and Comparative Examples 3 and 4 (Production of coated magnetite particles)]
Using 100 parts by weight of the core magnetite particles obtained in Examples 1 to 4 and Comparative Examples 1 and 2, and 2 parts by weight of n-hexyltrimethoxysilane which is an organic silane, these were mixed in a dry manner. A Henschel mixer was used for dry mixing. The mixing temperature was 35 ° C. The obtained mixture was heated to 110 ° C. and heat-treated for 1 hour. The organic silane was hydrolyzed by this treatment, and the surface of the core magnetite particles was coated with the silane compound produced thereby to obtain coated magnetite particles. The amount of the silane compound contained in the thus obtained coated magnetite particles (in terms of Si) was measured by the method described above. The results are shown in Table 2 below. Moreover, the water vapor adsorption amount and methanol hydrophobization degree of the coated magnetite particles were measured by the above-described methods. These results are also shown in Table 2.

  As is clear from the results shown in Table 2, core magnetite particles containing Ti and / or Si inside the particles and substantially free of Ti and Si on the outermost surface are substituted with alkyl chains having 2 to 10 carbon atoms. It can be seen that the coated magnetite particles of the examples (product of the present invention) which were dry-coated with the silane compound having a low water vapor adsorption amount and a methanol hydrophobization degree within a specific range. In contrast, when core magnetite particles containing neither Ti nor Si and core magnetite particles having Ti on the outermost surface of the particles are used (Comparative Examples 3 and 4), the alkyl chain of the silane compound Even when the number of carbon atoms in the range was 2 to 10, the water vapor adsorption amount was increased.

Claims (10)

Containing Ti or Si, these are present in the interior of the particle, and consists of magnetite substantially free of Ti and Si on the outermost surface of the particle,
Magnetite particles, wherein the elution amounts of Ti and Si by a pure water boiling test are 50 ppm or less, respectively, with respect to the whole particles. The magnetite particle according to claim 1 , wherein an elution amount of Na by a pure water boiling test is 50 ppm or less based on the whole particle. The magnetite particles according to claim 2 , wherein the elution amounts of different elements other than Fe and O in the pure water boiling test are each 50 ppm or less with respect to the whole particles.   When the particles are dissolved from the outermost surface, the amount of Ti or Si eluted while the elution rate of Fe is 10 to 100% by weight is 60 to 60% of the amount of Ti or Si contained in the entire particles. The magnetite particle according to any one of claims 1 to 3, which is 100% by weight.   The magnetite particles according to any one of claims 1 to 4, wherein the Ti content is 500 to 5000 ppm, and the Si content is 500 to 5000 ppm.   The coated magnetite particles according to any one of claims 1 to 5, wherein the total amount of Ti and Si is in the range of 1000 to 10,000 ppm.   The magnetite particles according to any one of claims 1 to 6, which are used as a raw material for a polymerized toner.   The coated magnetite particle | grain characterized by the surface of the magnetite particle | grain in any one of Claim 1 thru | or 7 being coat | covered with the silane compound which has a C2-C10 alkyl chain.   The coated magnetite particles according to claim 8, wherein the coating amount of the silane compound is 0.01 to 1.5% by weight in terms of Si.   A method for producing coated magnetite particles according to claim 8 or 9, wherein the magnetite particles according to any one of claims 1 to 6 and a silane compound having an alkyl chain having 2 to 10 carbon atoms are mixed in a dry manner. A method for producing coated magnetite particles, wherein the silane compound is bonded to the surface of the magnetite particles.