JP2020139101A - Pigment for electrophotography and method for producing the same - Google Patents

Abstract

To provide a pigment that can be used as materials for an electrophotographic developer by a polymerization method, has a high degree of hydrophobicity, and causes only a small amount of generation of VOCs (volatile organic compounds), which have adverse effect on human bodies, when a developer is used.SOLUTION: A pigment has an alkyl silane compound layer on the surface of a magnetic material having ferrosoferric oxide as the main component. The alkyl silane compound layer comprises a hydrolysate of i-butyl trimethoxysilane of 8.5 g/kg or more to 40.0 g/kg or less on the basis of the weight of coating particles. The pigment has a degree of hydrophobicity of 575 g/kg or more to 800 g/kg or less.SELECTED DRAWING: None

Description

The present invention relates to a pigment in which the surface of a magnetic material containing triiron tetroxide as a main component is coated with a hydrolyzate of i-butyltrimethoxysilane. More specifically, it is characterized by a large degree of hydrophobicity and a small amount of volatile organic compounds (hereinafter referred to as "VOC") generated, and is used in electrophotographic developing agents such as magnetic one-component toners produced by a polymerization method. The present invention relates to a hydrophobic magnetic pigment suitable for use as a material.

In recent years, with the improvement of the functions of devices such as copiers, printers, fax machines, and other multifunction devices (hereinafter, abbreviated as "printer" as a representative) by electrophotographic method, the developer used (hereinafter, also referred to as toner) High quality is also required for (synonymous with developer). There is a demand for toner that can be printed accurately, quickly, in large quantities, and that is well-balanced with cost. Therefore, for the purpose of improving image quality and reducing manufacturing cost, polymerization method toner has come to be used instead of the conventional pulverization method toner. Patent Document 1 shows a method for producing a polymerization method toner. When triiron tetroxide is used as a material for a polymerization method toner, it is important to modify the originally hydrophilic surface to be hydrophobic to increase the degree of hydrophobicity.

In other words, if the surface modification is not sufficient and a large number of hydrophilic surfaces remain, a magnetic pigment containing triiron tetroxide is dispersed in the resin monomer and suspended in water during the manufacturing process of the polymerization method toner. When it becomes turbid, the pigment shifts to the aqueous phase, and the dispersibility of the pigment in the toner matrix particles deteriorates. In addition, there is a difference in the pigment content between the toner matrix particles, and in the worst case, problems such as generation of toner matrix particles containing no pigment at all occur.

Patent Document 2 shows a production method in which magnetic iron oxide particles such as triiron tetroxide (magnetite) are coated with n-decyltrimethoxysilane or the like. The hydrophobic magnetic iron oxide particles of Example 14 coated with n-hexadecyltrimethoxysilane having the highest degree of hydrophobicity among the examples of Patent Document 2 have a degree of hydrophobicity of 83 in the methanol wettability test. It is stated that it was% (771 g / kg when converted). Patent Document 3 shows a manufacturing method in which an alkylsilane compound layer is provided on the surface of magnetite core particles. The coated magnetite particles of Example 3 coated with n-octyltrimethoxysilane, which has the highest degree of hydrophobicity among the examples of Patent Document 3, have a degree of hydrophobicity of 70% (converted) by a methanol wettability test. It is shown that it was 649 g / kg). These magnetic pigments having a high degree of hydrophobization were suitable as materials for polymerization method toners.

On the other hand, in recent years, due to growing interest in health, chemical substances generated when using printers have become a problem. One of them is VOC generated by heating the developer during printing, and suppressing the amount of VOC generated is an issue. For example, Blue Angel, which is an environmental label in Germany, requires reduction of the environmental load from manufacturing to use and disposal of products, and printers are required to reduce the amount of VOC generated during printing.

The polymerization method toner is also required to reduce the amount of VOC generated during heating. As a result of investigating the polymerization method toner using the magnetic pigment having a high degree of hydrophobicity obtained in Patent Document 2 and Patent Document 3, it was clarified that the amount of VOC generated from the pigment at the time of heating is large. In general, a product containing an alkyl group having a large number of carbon atoms generates a large amount of VOC during heating. In the case of the polymerization method toner, when the number of carbon atoms of the alkyl group in the alkoxysilane used for coating the core particles of the pigment is large, the amount of VOC generated during heating tends to be large.

In order to reduce the amount of VOC generated from the magnetic pigment containing alkoxysilane, it is extremely effective to use alkoxysilane having a small number of carbon atoms in the alkyl group. However, when the alkoxysilane having an alkyl group having a small number of carbon atoms is coated on the triiron tetroxide particles, there is a problem that it is difficult to obtain a magnetic pigment having a large degree of hydrophobicity. Patent Document 4 describes an example in which i-butyltrimethoxysilane, which is an alkoxysilane having an alkyl group having 4 carbon atoms, is used for coating the core particles of magnetite in Example 4, but a methanol wettability test is described. The degree of hydrophobicity according to the above is 60% (converted to 543 g / kg), and Examples 1 to 3 and Examples 5 to Examples using an alkoxysilane having a large carbon number such as n-hexyl or n-octyl. It is described that the degree of hydrophobicity was smaller than that of 8. The coated magnetite particles of Example 4 of Patent Document 4 have a smaller degree of hydrophobicity than the pigments obtained in Patent Documents 2 and 3, and are not suitable as a material for a polymerization method toner.

As an example of using a surface treatment agent other than alkoxysilane, Patent Document 5 discloses a production method of coating the surface of magnetic iron oxide particles with a linear organopolysiloxane or silazane. The invention of Patent Document 5 has succeeded in reducing the amount of VOC generated, and the degree of hydrophobicity was 66% (converted to 606 g / kg) in Example 5 having the largest degree of hydrophobicity. The coated magnetic iron oxide particles obtained in Patent Document 5 can be used for a polymerization method toner, but it is desirable to further increase the degree of hydrophobicity in order to stabilize the quality of the toner. Further, in order to meet the requirements of various toners, it is desirable to be able to provide a magnetic material having various configurations capable of achieving both a reduction in the amount of VOC generated and a high degree of hydrophobicity.

JP-A-2003-131422 JP-A-2005-236319 JP-A-2014-148425 Japanese Unexamined Patent Publication No. 2013-193890 JP-A-2016-210629

An object of the present invention is to have a large degree of hydrophobicity required to maintain a stable dispersed state in a resin monomer as a material for an electrophotographic developer by a polymerization method, and to the human body when the developer is actually used. An object of the present invention is to provide a magnetic pigment having a small amount of harmful VOC generated and a method for producing the same.

As a result of diligent studies on magnetic pigments used as materials for polymerization method toners, the present inventors have hydrolyzed i-butyltrimethoxysilane, which is an alkoxysilane, on the surface of a magnetic material containing triiron tetroxide as a main component. By coating the material in a specific amount range by a specific method, a magnetic pigment having a large degree of hydrophobicity suitable for producing a polymerization method toner and a small amount of VOC generated by heating can be obtained. I found it.

The present invention includes:
[1] A pigment having an alkylsilane compound layer on the surface of a magnetic material containing triiron tetroxide as a main component, wherein the alkylsilane compound layer is 8.5 g / kg or more based on the weight of the pigment. The pigment comprising a hydrolyzate of i-butyltrimethoxysilane in an amount of 0 g / kg or less and having a degree of hydrophobicity of the pigment of 575 g / kg or more and 800 g / kg or less.
[2] The pigment according to [1], wherein the median diameter of the primary particles obtained from image analysis using a transmission electron microscope is 0.20 μm or more and 0.35 μm or less.
[3] When the external magnetic field is 79.6 kA / m, the magnetization is 64.0 Am ² / kg or more and 72.0 Am ² / kg or less, and the residual magnetization after magnetizing at the external magnetic field of 79.6 kA / m. The pigment according to [1] or [2], wherein is 2.8 Am ² / kg or more and 4.2 Am ² / kg or less.
[4] i-Butyltrimethoxysilane is added to a slurry in which a magnetic substance containing triiron tetroxide as a main component is dispersed in water to generate a hydrolyzate of i-butyltrimethoxysilane, and this hydrolysis is produced. [1] to [3] include a step of adhering the substance to the surface of the magnetic substance and a step of obtaining the magnetic substance adhered with the hydrolyzate of i-butyltrimethoxysilane by solid-liquid separation and drying it. ]. The method for producing a pigment according to any one of items up to [5] (1) A magnetic substance containing triiron tetroxide as a main component is contained in water in an amount of 0.18 kg / L or more and 0.60 kg / L or less. A step of preparing a slurry and adjusting the pH of the slurry to 7.0 or more and 11.5 or less and the temperature to 35 ° C. or more and 90 ° C. or less.
(2) i-Butyltrimethoxysilane is added to the slurry of (1), and the slurry is stirred for 2 hours or more while maintaining the temperature of the slurry in the temperature range described in (1), thereby causing i- on the surface of the magnetic material. Step of depositing a hydrolyzate of butyltrimethoxysilane,
(3) A step of solid-liquid separating the cake containing the magnetic substance adhered to the hydrolyzate from the slurry of (2), and a temperature of 60 ° C. or higher and 100 ° C. or lower in the air of the cake of (4) and (3). The production method according to [4], which comprises a step of drying with.

According to the present invention, a magnetic substance containing triiron tetroxide as a main component is coated with a hydrolyzate of i-butyltrimethoxysilane in a specific amount range by a specific method to increase the degree of hydrophobicity. It is possible to provide a magnetic pigment having a large amount and a small amount of VOC generated during actual use of the electrophotographic developer.

Hereinafter, the present invention will be described based on its preferred embodiment. The pigment of the present invention has an alkylsilane compound layer on the surface of a core which is a magnetic material containing triiron tetroxide as a main component, and the alkylsilane compound layer is 8.5 g based on the weight of the pigment. It consists of a hydrolyzate of i-butyltrimethoxysilane in an amount in the range of / kg or more and 40.0 g / kg or less. The above amount is more preferably 10.0 g / kg or more and 30.0 g / kg or less, and further preferably 12.0 g / kg or more and 25.0 g / kg or less.

When the amount of the hydrolyzate of i-butyltrimethoxysilane is less than 8.5 g / kg, the surface area of the core is sufficiently covered in consideration of the specific surface area of the magnetic material containing triiron tetroxide as the main component. Therefore, a hydrophilic surface remains and a pigment having a high degree of hydrophobicity cannot be obtained. On the other hand, when the amount of the hydrolyzate of i-butyltrimethoxysilane is larger than 40.0 g / kg, the proportion of the non-magnetic component in the pigment becomes large, and the magnetization of the pigment decreases. Further, since i-butyltrimethoxysilane is more expensive than iron oxide, i-butyltri in the pigment is contained as long as the degree of hydrophobicity of the obtained pigment does not interfere with the production of the polymerization method toner. It is preferable that the amount of the hydrolyzate of methoxysilane is small.

In the present invention, the amount of the hydrolyzate of i-butyltrimethoxysilane in the pigment is measured by the following method:
The carbon (C) content in the pigment is analyzed using a CS-230 type carbon (C) / sulfur (S) analyzer manufactured by LECO. Assuming that i-butyltrimethoxysilane is completely hydrolyzed, the hydrolyzate content (g / kg) of i-butyltrimethoxysilane is determined by the following formula using the carbon (C) measurement value. ,calculate:
Hydrolyzate content (g / kg) = carbon (C) measured value (wt%) x 2.773 x 10
The pigment of the present invention has a degree of hydrophobicity of 575 g / kg or more. More preferably, it is 625 g / kg or more. When the degree of hydrophobization is less than 575 g / kg, the pigment is likely to move to the aqueous phase during the production of the polymerization method toner, and the dispersibility of the pigment in the toner matrix particles is deteriorated. In addition, there may be a difference in the pigment content between the toner matrix particles, and in the worst case, problems such as generation of toner matrix particles containing no pigment at all may occur. The upper limit of the degree of hydrophobicity is not particularly limited, but in reality, it is considered to be about 800 g / kg or less, or about 750 g / kg or less.

In the present invention, the degree of hydrophobicity is measured by the following method:
A pigment that has passed through a sieve with a mesh opening of 1 mm is used as a measurement sample, and the measurement is performed within 5 minutes after passing through the sieve. A plurality of methanol aqueous solutions having different methanol contents of 25 g / kg are prepared (for example, ... 500 g / kg, 525 g / kg, 550 g / kg, 575 g / kg, 600 g / kg, 625 g / kg, 650 g / kg, 675 g / kg, 700 g / kg, 725 g / kg ...), about 2 mL each in separate test tubes. Gently put a sample of 20 mg or more and 40 mg or less into each test tube, and visually check for sedimentation. At 5 seconds after the sample is charged, if the charged sample does not settle at all, it is determined to be "not settled", and if even a part of the sample is settled, it is determined to "settle". In rare cases, the sample may form small lumps even though it has been sieved, and a small amount of lumps may settle (up to 10% of the total, or about 20 grains by eye measurement), but such an exception. It is decided to exclude the sedimentation of the sample. The methanol content of the aqueous solution having the lowest methanol concentration at which the sample precipitates is defined as the degree of hydrophobicity (g / kg).

In the pigment of the present invention, the median diameter of the primary particles determined by image analysis using a transmission electron microscope is preferably 0.20 μm or more and 0.35 μm or less. If the median diameter of the primary particles is larger than 0.35 μm, the coloring power of the pigment may decrease, and the coloring power of the toner using the pigment may also decrease. On the other hand, when the median diameter of the primary particles is smaller than 0.20 μm, the cohesive force of the pigment may increase and the dispersibility of the pigment in the toner may deteriorate.

The median diameter of the primary particles of the pigment of the present invention can be obtained from the image analysis of the transmission electron microscope image. For example, it can be measured by the method described in Examples described later.
The pigment of the present invention has a magnetization of 64.0 Am ² / kg or more and 72.0 Am ² / kg or less when the external magnetic field is 79.6 kA / m, and after magnetizing at an external magnetic field of 79.6 kA / m. The residual magnetization of is preferably 2.8 Am ² / kg or more and 4.2 Am ² / kg or less. More preferably, when the external magnetic field is 79.6 kA / m, the magnetization is 65.0 Am ² / kg or more. When the magnetization is less than 64.0Am ² / kg or residual magnetization when the external magnetic field is 79.6 kA / m is less than 2.8Am ² / kg, the magnetization decreases the toner base particles after charging, the behavior of the toner It becomes difficult to control, and there is a possibility that the image is easily blurred. When the magnetization is 72.0 Am ² / kg or more when the external magnetic field is 79.6 kA / m, or when the residual magnetization exceeds 4.2 Am ² / kg, the toner matrix particles tend to aggregate due to magnetism, resulting in fog and images. Bleeding may occur.

The magnetization and remanent magnetization of the pigment of the present invention can be measured using a vibrating sample magnetometer at room temperature of around 23 ° C. For example, it can be measured by the method described in Examples described later.
The pigment of the present invention has a VOC (volatile organic compound) generation amount of which magnetite (triiron tetroxide) particles are coated with n-hexyltrimethoxysilane (Japanese Patent Laid-Open No. 2005-263619). It is preferable that the amount of VOC generated by the hydrophobic magnetic iron oxide particles (hereinafter referred to as “n-hexyltrimethoxysilane-coated particles”) obtained in Example 8 of the above is 30% or less.

For the amount of VOC generated, for example, gas chromatography was used to determine the peak area detected between the peak of normal hexane and the peak of n-hexadecane, and the above-mentioned n-hexyltrimethoxysilane-coated particles as a control substance were obtained. It can be calculated by comparing with the peak area. More specifically, it can be measured by the method described in Examples described later.

The pigment of the present invention is typically produced by the following method. First, a method for producing a magnetic material containing triiron tetroxide as a main body as a substrate (core) will be described by taking the wet method for producing triiron tetroxide as an example.

In the wet method, triiron tetroxide produces ferrous hydroxide precipitate by neutralization reaction of ferrous salt aqueous solution and alkali hydroxide, and if necessary, silicon, phosphorus, etc. are added before, during, or after production. It is obtained by adding and oxidizing by blowing air while controlling the pH and temperature. The composition and particle size can be controlled by controlling the pH and the time of air oxidation.

Examples of the ferrous salt aqueous solution include ferrous sulfate, ferrous chloride, ferrous nitrate, etc., but in general, ferrous sulfate, which is a by-product of the sulfuric acid method titanium oxide production, and scrap iron Use ferrous sulfate produced during washing. As the alkali hydroxide, alkali metals such as sodium hydroxide, potassium hydroxide and calcium hydroxide, hydroxides of alkaline earth metals, ammonium hydroxide and ammonia gas can be used.

First, a ferrous hydroxide precipitate is formed by neutralizing the ferrous salt aqueous solution with an alkali hydroxide, and at that time, the iron ions (II) in the ferrous salt aqueous solution are reduced to 1.0 mol. On the other hand, the hydroxide ion (OH ⁻ ) is preferably 1.8 mol or more and 2.0 mol or less. If the amount of hydroxide ion is less than 1.8 mol with respect to 1 mol of iron ion, iron oxyhydroxide is likely to be produced, which is not preferable. Further, if the hydroxide ion exceeds 2.0 mol with respect to 1.0 mol of iron ion, polyhedral particles such as cuboctahedron and octahedron are generated, the residual magnetization becomes large, and the particles tend to aggregate, which is also not preferable. ..

The temperature for oxidizing ferrous hydroxide in the present invention is preferably 60 ° C. or higher and 100 ° C. or lower, and more preferably 85 ° C. or higher and 90 ° C. or lower. If the temperature at the time of oxidation is lower than 60 ° C., the magnetization and residual magnetization become small, and if the magnetization and residual magnetization of the toner matrix containing it become excessively small, it becomes difficult to control the behavior of the toner and the image is blurred. Is likely to occur. On the other hand, it is industrially difficult to oxidize while heating to a temperature higher than 100 ° C.

The oxidation rate of the substrate is preferably 68% or more and 74% or less, and more preferably 70% or more and 71% or less. If the oxidation rate is small, the magnetization and remanent magnetization may not reach the target, and if the oxidation rate is large, the obtained substrate becomes dark red, which may not be suitable for use as a toner. The oxidation rate of the substrate refers to the mol amount of iron ions (III) with respect to all iron ions in the production of a magnetic material containing triiron tetroxide as a main component. The oxidation rate of the substrate can be measured by the following methods:
Concentrated sulfuric acid is added to the substrate slurry and heated to dissolve the substrate. The iron (II) ion in the solution is titrated using an aqueous solution of potassium permanganate, and the titration amount at this time is referred to as "titration amount A". Next, all the iron (III) ions in the solution were reduced to iron (II) ions using mercury amalgam, and then the iron (II) ions in the solution were titrated again using an aqueous potassium permanganate solution. The titration amount at this time is referred to as "titration amount B". Calculate the oxidation rate using the following formula:
Oxidation rate (mol%) = 100 × (titration B-titration A) / titration B
In the magnetic material containing triiron tetroxide as the main component, which is the substrate of the present invention, a component such as silica can be introduced into triiron tetroxide by adding a compound of silicon or phosphorus. In the present invention, the magnetic material containing triiron tetroxide as a main component includes particles substantially composed of triiron tetroxide only, and triiron tetroxide as a main component but other than iron such as silicon or phosphorus. It contains particles to which a small amount of other elements are added. It is not necessary to introduce manganese into the magnetic material containing triiron tetroxide as the main component. In the surface treatment step of the present invention described later, the alkylsilane compound layer can be thinly and uniformly coated regardless of the abundance of manganese on the surface of the magnetic material. The content of elements other than iron in the magnetic material containing triiron tetroxide as the main component may be changed according to the regulation regarding the amount of chemical substances contained in the toner. The magnetic material containing triiron tetroxide as a main component contains more than 950 g / kg of triiron tetroxide, and more preferably more than 980 g / kg of triiron tetroxide, based on the weight of the magnetic material. The ratio of triiron tetroxide in the magnetic material can be determined by measuring the amount of a compound containing an element other than iron added during the production of the magnetic material (triiron tetroxide) and reducing the ratio. ..

As the silicon compound, water-soluble silicon compounds such as water glass, sodium silicate, and potassium silicate are used. The amount added is 7 g / kg or more and 20 g / kg or less in terms of silica with respect to triiron tetroxide, and more preferably 9 g / kg or more and 15 g / kg or less. When the amount added is small, the particle shape tends to be polyhedral, and the residual magnetization becomes large, which may cause aggregation. On the other hand, if the addition amount is larger than 20 g / kg, silica is precipitated on the surface of triiron tetroxide, and the adhesion of alkoxysilane is inhibited in a later step.

The silicon (Si) or silica (SiO ₂ ) content in the pigment can be measured, for example, by the method described in Examples described later.
As the phosphorus compound, a water-soluble phosphorus compound such as sodium hexametaphosphate is used. The amount added is preferably 5.0 g / kg or less in terms of diphosphorus pentoxide with respect to triiron tetroxide. By adding a phosphorus compound, the residual magnetization of triiron tetroxide can be lowered. The residual magnetization does not change significantly even if the addition amount is increased above 5.0 g / kg, and if the addition amount is further large, the crystal growth of triiron tetroxide may be inhibited. If the residual magnetization of triiron tetroxide is within the target range without adding the phosphorus compound, it may not be added.

When a silicon compound and a phosphorus compound are added, they may be added to an alkali hydroxide, an aqueous ferrous salt solution, or a mixture thereof. However, it must be added before crystallization of triiron tetroxide begins.

The shape of the magnetic material containing triiron tetroxide as the main component is preferably spherical. When the shape of the magnetic material as the core is substantially spherical, the residual magnetization can be easily adjusted within an appropriate range, and problems such as particle aggregation are less likely to occur. Further, it is not necessary that a specific element other than triiron tetroxide is unevenly distributed on the surface of the magnetic material.

Next, an alkylsilane compound layer is adhered to the surface of the magnetic material using i-butyltrimethoxysilane. There are a wet method and a dry method as the method of adhesion, but it is preferable to use the wet method from the viewpoint that adhesion spots are less likely to occur and the degree of hydrophobicity is easily increased. When performing adhesion by the wet method, first, the magnetic material (base) to be the core is dispersed in water to form a slurry. The concentration of the magnetic substance in the slurry is preferably 0.18 kg / L or more and 0.60 kg / L or less. When the concentration of the magnetic substance is smaller than 0.18 kg / L, the contact frequency between i-butyltrimethoxysilane and triiron tetroxide decreases, so that the amount of adhesion decreases. As a result, the degree of hydrophobicity of the obtained pigment having the alkylsilane compound layer tends to decrease. On the other hand, when the concentration of the magnetic substance is larger than 0.60 kg / L, uniform stirring is difficult due to the high viscosity of the slurry, and adhesion amount unevenness may occur between the triiron tetroxide particles.

The slurry temperature at the time of adhering is preferably 35 ° C. or higher and 90 ° C. or lower, and more preferably 50 ° C. or higher and 90 ° C. or lower. When the slurry temperature is lower than 35 ° C., the adhesion rate of the i-butyltrimethoxysilane hydrolyzate on the surface of triiron tetroxide tends to decrease, and the degree of hydrophobicity of the obtained pigment tends to decrease. On the other hand, when the slurry temperature is higher than 90 ° C., the adhesion progresses rapidly, so that the adhesion amount unevenness may occur between the triiron tetroxide particles.

The slurry pH at the time of adhering is preferably 7.0 or more and 11.5 or less, and more preferably 9.5 or more and 11.0 or less. When the slurry pH is smaller than 7.0, the adhesion rate of the i-butyltrimethoxysilane hydrolyzate tends to decrease, and the degree of hydrophobicity of the obtained pigment tends to decrease. When the slurry pH is higher than 11.5, the condensation reaction between i-butyltrimethoxysilanes tends to proceed and the amount of adhesion to the substrate becomes small, so that the degree of hydrophobicity of the obtained pigment also tends to be small. is there. Alkali hydroxides such as sodium hydroxide, potassium hydroxide and calcium hydroxide can be used for adjusting the pH without being limited to these.

The retention time at the above temperature and pH after the addition of i-butyltrimethoxysilane is preferably 2 hours or more, more preferably 4 hours or more. If the holding time is shorter than 2 hours, the degree of hydrophobicity may not be stable because the adhesion may not be completed. At the time of holding, it is preferable to stir the slurry in order to promote uniform adhesion.

If the alkali hydroxide remains in the pigment having the alkylsilane compound layer, which interferes with the process of producing the polymerization method toner, the alkali component is neutralized after the retention after the addition of i-butyltrimethoxysilane is completed. Therefore, the slurry pH may be readjusted to 7.0 to 9.0. The pH can be adjusted with, but not limited to, an acid such as sulfuric acid or hydrochloric acid.

It is desirable that all the methoxy groups in the i-butyltrimethoxysilane molecule adhered to the surface of triiron tetroxide are hydrolyzed at the stage when the adhesion is completed. If a methoxy group remains in the molecule of i-butyltrimethoxysilane, it is difficult to coat the surface of triiron tetroxide without gaps, so the surface of hydrophobic triiron tetroxide remains, and the obtained pigment. The degree of hydrophobization may be reduced.

The slurry that has been adhered is solid-liquid separated to obtain a cake containing a magnetic material to which the alkylsilane compound layer is adhered. After the cake is thoroughly washed, it is dried to obtain the pigment of the present invention. Drying is preferably carried out at a temperature of 60 ° C. or higher and 100 ° C. or lower. When heated to a temperature higher than 100 ° C. in the presence of water, condensation of the hydrolyzate of i-butyltrimethoxysilane in the pigment proceeds, aggregates are generated, and the dispersibility of the pigment may be deteriorated. If the drying temperature is lower than 60 ° C., water may remain and the degree of hydrophobicity of the obtained pigment may be reduced. It is suitable to carry out drying for 1 hour or more. It is not necessary to rotate the pigment during drying, but the pigment may be loosened or the position of the pigment may be moved during drying to accelerate the drying.

After the cake has dried, heat treatment may be performed to increase the degree of hydrophobicity of the pigment. When the heat treatment is performed in air, the core magnetic material may be oxidized and the pigment may turn dark red. Further, since the alkylsilane compound layer may be partially decomposed and the degree of hydrophobicity may be reduced, it is preferable to carry out the heat treatment in an inert atmosphere using an inert gas typified by nitrogen gas. The heat treatment is preferably carried out at 150 ° C. or higher and 250 ° C. or lower, more preferably 180 ° C. or higher and 225 ° C. or lower. When the heat treatment temperature is 150 ° C. or higher, heat is distributed to the inside of the pigment, and the degree of hydrophobicity tends to increase. When the heat treatment temperature is 250 ° C. or lower, decomposition of the alkylsilane compound layer is suppressed, and a decrease in the degree of hydrophobicity can be prevented.

The pigment of the present invention has the characteristics that the amount of VOC generated during heating is small and the degree of hydrophobicity is large, and is particularly suitable as a material for an electrophotographic developer such as a polymerization method toner.

Hereinafter, examples showing aspects of the present invention will be described, but the following examples are shown merely for illustration purposes, and the scope of the invention is not limited thereto. In the following, "L" indicates liter.

[Measurement method]
[Measurement and calculation of median diameter]
The measurement was performed using a transmission electron microscope JEM-1400plus manufactured by JEOL Ltd. The observation magnification was 30,000 times (observation magnification of a transmission electron microscope 10,000 times x printing 3 times). The area equivalent to the area of the primary particle image that can be obtained by matching the circle diameter of about 300 particles in the observation field with the reference circle diameter (4 mm to 10 mm) of the Particle Size Analyzer TGZ-3 manufactured by Carl Zeiss. The diameter of the circle was defined as the particle diameter, a cumulative curve of the cube of the particle diameter was created, and the particle diameter corresponding to 50% of the cumulative curve was defined as the median diameter (μm).

[Measurement of Hydrolyzate Content of Alkoxysilane]
The carbon (C) content of the sample was analyzed using a CS-230 type carbon (C) / sulfur (S) analyzer manufactured by LECO. Assuming that the alkoxysilane was completely hydrolyzed, the amount of hydrolyzate (g / kg) of the alkoxysilane was calculated from the carbon (C) measurement value.

[Measurement of silica content]
10 g of the sample was weighed in a heat-resistant crucible, heated in air at 600 ° C. for 1 hour using a Motoyama electric furnace SUPER-C SO-2035D, and fired. After the sample was completely cooled, 8.0 g of the sample was filled in an aluminum ring having an inner diameter of 40 mm and a height of 5 mm, and compression molding was performed at 150 kg / cm ² using BRIQUETTING MACHINE MP-35 manufactured by Shimadzu Mectem. The silicon content of the molded sample was measured using Simultix 10 manufactured by Rigaku. The silicon content of the substrate (core) was measured in the same manner. The silica (SiO ₂ ) content of the sample was calculated from the silicon (Si) content of the sample. The silicon content in the i-butyltrimethoxysilane hydrolyzate was calculated by subtracting the silicon content of the substrate from the silicon content of the pigment (after coating). The mol ratio of carbon / silicon in the i-butyltrimethoxysilane hydrolyzate was calculated from the carbon (C) content measured using a LECO CS-230 type carbon (C) / sulfur (S) analyzer. .. Further, the state in which all three methoxy groups in the i-butyltrimethoxysilane molecule are hydrolyzed, that is, the state in which the mol ratio of carbon / silicon is 4.00 is defined as the state in which the hydrolysis has proceeded 100%, and the hydrolysis rate (Mmol / mol) was calculated by the following formula:
Hydrolysis rate (mmol / mol) = 1000 × {1- (carbon (C) content / silicon (Si) content-4.00) /3.00}
[Measurement of VOC generation amount]
2.0 g of the sample was placed in a screw tube bottle with a rubber stopper and a volume of 30 mL, and heated at 120 ° C. for 1 hour. Immediately after heating, a syringe was inserted into a screw tube bottle to collect 5 mL of the gas inside, and the gas was injected into a Yanaco gas chromatograph G3800 equipped with a J-Science West Japan packed column (3 m) SE-30. Helium was used as the carrier gas, and the flow rate was 30 mL / min. The column temperature was raised from 80 ° C. to 200 ° C. at 5 ° C./min. As a control substance, n-hexyltrimethoxysilane-coated particles produced according to Example 8 of Patent Document 2 were measured by the same procedure. For the sample and the n-hexyltrimethoxysilane-coated particles, the peak area detected between the peak of normal hexane and the peak of n-hexadecane was determined, respectively. The corresponding peak area of the sample was calculated with respect to the corresponding peak area of the n-hexyltrimethoxysilane coated particles, and used as the VOC generation amount (%) of the sample with respect to the conventional product.

[Measurement of hydrophobicity]
As the measurement sample, a sample passed through a sieve having an opening of 1 mm was used, and the measurement was carried out within 5 minutes after passing through the sieve. A plurality of aqueous methanol solutions having different methanol contents of 25 g / kg were prepared, and about 2 mL each was placed in a test tube. A sample of 20 mg or more and 40 mg or less was gently put into each test tube, and the presence or absence of sedimentation was visually confirmed. When 5 seconds have passed since the sample was charged, it was determined that the sample did not settle at all, that it did not settle, and that even a part of the sample settled, it settled. The methanol content of the aqueous solution having the lowest methanol concentration at which the sample settled was defined as the degree of hydrophobicity (g / kg).

[Measurement of magnetic characteristics]
Magnetization: σs (Am ² / kg) and residual magnetization: σr (Am ² / kg) at an external magnetic field of 79.6 kA / m were measured using a vibrating sample magnetometer VSM-3 manufactured by Toei Kogyo. .. The details of the operation are shown below. In this measurement, the external magnetic field value "-" indicates that the direction of the magnetic field is opposite to that of "+". The operation was carried out in a room where the room temperature was maintained at 23.0 ° C.

First, using a standard sample, the magnetization of the vibrating sample magnetometer when +398 kA / m was applied was adjusted to 5 EMU. Bottom area 38.47mm ^2, height 7 mm, a cylindrical cell having an inner volume is 0.05655cm ^3, so as to be 2.20 g / cm ³ or more 2.40 g / cm ³ or less in the range of sample powder as packing density Filled with. The columnar cell was set in the apparatus so that the height direction was vertical, the external magnetic field was set to +79.6 kA / m, and the external magnetic field was applied to the sample from 0 A / m. The application speed was lowered from around +63.7 kA / m, and at +78 kA / m or higher, the application speed was set to the minimum of 20 min / Full-scale, and the application was applied so as not to exceed +79.6 kA / m. It was confirmed that the output value of GAUSS METER was + 1.000V when +79.6 kA / m was applied. The output value (V) of MAIN AMPLIFIER was read as the magnetization (+ σs) in the state where + 79.6 kA / m was applied. Since the magnetization changes slowly with the passage of time, the output value was read promptly when the application of +79.6 kA / m was confirmed. After reading the + σs value, it was demagnetized. After confirming that the external magnetic field was 0 A / m, the + σr value of the residual magnetization was obtained, the magnetic field was inverted, and charging was applied in the reverse direction to −79.6 kA / m. The application speed was increased to -79.6 kA / m, and the output value of MAIN AMPLIFIER was read as the magnetization (-σs) in the state where -79.6 kA / m was applied. Similar to the + σs reading operation, the application speed is reduced for negative charges of -63.4 kA / m or more, and the application speed for negative charges of -78.0 kA / m or more is set to the minimum of 20 min / Fullscale, which is -79.6 kA. Negative charging was not applied beyond / m. It is the same as + σs in that the confirmation of -79.6 kA / m is performed by the output value of GAUSS METER and the output value of MAIN AMPLIIER is read promptly as -σs. After reading the −σs value, it was demagnetized. The external magnetic field of 0 A / m was confirmed, and the −σr value of the residual magnetization was determined. The magnetic field was inverted and applied up to +79.6 kA / m. These also visually read the transition of magnetization due to changes in the external magnetic field. The application speed was set to 7 min / Full scale.

The average value of the absolute values of the magnetization σs and the residual magnetization σr at the two positive and negative external magnetic fields 79.6 kA / m read by the above operation was taken as the magnetization σs and the residual magnetization σr of the external magnetic field 79.6 kA / m.

[Manufacturing of substrate (magnetic material containing triiron tetroxide as the main component)]
[Material Production Example A]
170 L of an aqueous solution containing 22 kg of sodium hydroxide was placed in a reaction vessel, 800 mL of a 0.40 kg / L sodium silicate aqueous solution in terms of silica was added, and then the temperature was raised to 40 ° C. While blowing 80 L of nitrogen per minute into the aqueous solution, a ferrous sulfate aqueous solution of 0.10 kg / L in terms of Fe is added until the pH of the aqueous solution reaches 8.1 to produce ferrous hydroxide. A slurry containing this was obtained. Water was added to adjust the Fe concentration in the slurry to 0.04 kg / L, and then a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH of the slurry to 8.5. Air was blown into this slurry at 70 L / min for 40 minutes to oxidize it. After raising the temperature of this slurry to 90 ° C., air was blown at 70 L / min and oxidized until the oxidation rate became 70% or more and 71% or less to obtain a magnetic material containing triiron tetroxide as a main component. The obtained magnetic material (base) was filtered, washed with water, and repulped by a conventional method to obtain a base slurry. The obtained substrate had a silica content of 11.1 g / kg, a BET specific surface area of 8.4 m ² / g, and a median diameter of primary particles of 0.24 μm.

[Material Production Example B]
A substrate slurry was prepared in the same manner as in Production Example A, except that the time for blowing air at 70 L / min into the slurry after adjusting the pH to 8.5 was 38 minutes. The obtained substrate had a silica content of 10.5 g / kg, a BET specific surface area of 7.6 m ² / g, and a median diameter of 0.28 μm.

[Material Production Example C]
The substrate slurry of Production Example A and the substrate slurry of Production Example B were mixed in equal amounts and stirred well. The obtained substrate had a silica content of 10.8 g / kg, a BET specific surface area of 8.0 m ² / g, and a median diameter of 0.26 μm.

[Material Production Example D]
A substrate slurry was prepared in the same manner as in Production Example A, except that the time for blowing air at 70 L / min into the slurry after adjusting the pH to 8.5 was 49 minutes. The obtained substrate had a silica content of 10.9 g / kg, a BET specific surface area of 8.9 m ² / g, and a median diameter of 0.24 μm.

[Material Production Example E]
A substrate slurry was prepared in the same manner as in Production Example A, except that the time for blowing air at 70 L / min into the slurry after adjusting the pH to 8.5 was 47 minutes. The obtained substrate had a silica content of 10.5 g / kg, a BET specific surface area of 8.1 m ² / g, and a median diameter of 0.25 μm.

[Material Production Example F]
The substrate slurry of Production Example D and the substrate slurry of Production Example E were mixed in equal amounts and stirred well. The obtained substrate had a silica content of 10.7 g / kg, a BET specific surface area of 8.5 m ² / g, and a median diameter of 0.24 μm.

[Material Production Example G]
Water was added to the slurry containing ferrous hydroxide to adjust the Fe concentration to 0.10 kg / L, then the pH was adjusted to 9.6, and the time for blowing air into the slurry at 70 L / min was 2 A substrate slurry was prepared in the same manner as in Production Example A, except that the minutes were taken. The obtained substrate had a silica content of 11.7 g / kg, a BET specific surface area of 6.8 m ² / g, and a median diameter of 0.29 μm.

[Material Production Example H]
22.5 m ³ of an aqueous solution containing 2700 kg of sodium hydroxide was placed in a reaction vessel, 100 L of an aqueous sodium silicate solution of 0.40 kg / L in terms of silica was added, and then the temperature was raised to 40 ° C. While blowing 700 L of nitrogen per minute into the aqueous solution, 0.10 kg / L ferrous sulfate aqueous solution in terms of Fe is added until the pH of the aqueous solution reaches 8.0 to produce ferrous hydroxide. A slurry containing this was obtained. Water was added to adjust the iron (Fe) concentration to 0.04 kg / L, and then a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH of the slurry to 8.5. Blowing 39 minutes air per minute 8.0 m ³ to the slurry, it was oxidized. After heating the slurry to 90 ° C., blowing air per minute 6.6 m ^3, is oxidized to the oxidation rate falls below 71% 70%, to obtain a magnetic material mainly composed of triiron tetraoxide It was. The obtained magnetic material (base) was filtered, washed with water, and repulped by a conventional method to obtain a base slurry. The obtained substrate had a silica content of 12.0 g / kg, a BET specific surface area of 8.0 m ² / g, and a median diameter of 0.23 μm.

[Material Production Example I]
A substrate slurry was prepared in the same manner as in Production Example A, except that the time for blowing air at 70 L / min into the slurry after adjusting the pH to 8.5 was 42 minutes. The obtained substrate had a silica content of 10.8 g / kg, a BET specific surface area of 8.3 m ² / g, and a median diameter of 0.25 μm.

[Material Production Example J]
The same method as in Production Example I was used, but a substrate slurry was prepared in a different lot. The obtained substrate had a silica content of 10.7 g / kg, a BET specific surface area of 8.0 m ² / g, and a median diameter of 0.26 μm.

[Material Production Example K]
A substrate slurry was prepared in the same manner as in Production Example A, except that the time for blowing air at 70 L / min into the slurry after adjusting the pH to 8.5 was set to 30 minutes. The obtained substrate had a silica content of 9.7 g / kg, a BET specific surface area of 7.0 m ² / g, and a median diameter of 0.34 μm.

[Material Production Example L]
pH is performed except that the time for blowing air for 30 minutes at min 8.0 m ³ of the slurry was adjusted to 8.5 to prepare a substrate slurry in Preparation H the same way. The obtained substrate had a silica content of 10.8 g / kg, a BET specific surface area of 8.4 m ² / g, and a median diameter of 0.27 μm.

[Material Production Example M]
22.5 m ³ of an aqueous solution containing 2700 kg of sodium hydroxide was placed in a reaction vessel, 100 L of an aqueous sodium silicate solution of 0.40 kg / L in terms of silica and 13.0 kg of sodium hexametaphosphate were added, and then the temperature was raised to 40 ° C. While blowing 700 L of nitrogen per minute into the aqueous solution, a ferrous sulfate aqueous solution of 0.10 kg / L in terms of Fe is added until the pH of the aqueous solution reaches 8.2 to produce ferrous hydroxide. A slurry containing this was obtained. Water was added to adjust the iron (Fe) concentration to 0.04 kg / L, and then a 1 mol / L sodium hydroxide aqueous solution was added to adjust the pH of the slurry to 8.5. Blowing 45 minutes air per minute 8.0 m ³ to the slurry, it was oxidized. After heating the slurry to 90 ° C., blowing air per minute 6.6 m ^3, is oxidized to the oxidation rate falls below 71% 70%, to obtain a magnetic material mainly composed of triiron tetraoxide It was. The obtained magnetic material (base) was filtered, washed with water, and repulped by a conventional method to obtain a base slurry.

[Material Production Example N]
except that it has changed to the time of blowing air for 42 minutes at min 8.0 m ³ to the slurry after the pH was adjusted to 8.5 to prepare a substrate slurry in Preparation M and the same method.

[Material Production Example O]
The substrate slurry of Production Example M and the substrate slurry of Production Example N were mixed in equal amounts and stirred well. The obtained substrate had a silica content of 11.9 g / kg, a BET specific surface area of 8.0 m ² / g, and a median diameter of 0.25 μm.

[Material Production Example P]
It was produced according to the method described in Production Example D of the substrate particles of Patent Document 2 (Japanese Unexamined Patent Publication No. 2005-263619). After adjusting to 40 ° C. Put aqueous 180L containing sodium hydroxide 18.5kg tank, with respect to sodium hexametaphosphate 86.4g _(Fe 3 _{O 4,} corresponding to 0.32 wt% in terms _of P 2 _{O 5} ) and to 413.5g / L sodium silicate solution 681.7mL _(Fe 3 _{O 4} as SiO _2, corresponding to 1.50 wt% in terms of SiO ₂₎ was added, pH of the aqueous ferrous sulfate solution Was added until a value of 8.5 was reached. Then, after adjusting the pH to 9.0 with 1 mol / L NaOH, the iron concentration was 34 g / L and the liquid volume was 400 L, and the mixture was maintained for 30 minutes. Air was blown at 100 L / min and oxidized until the oxidation rate (Fe ³⁺ / t-Fe weight ratio) reached 8%. After adjusting this slurry to 90 ° C., it was oxidized to an oxidation rate of 68% while blowing air at 50 L / min. Then, the reaction was completed by stirring and holding for 3 hours while blowing 80 L of nitrogen gas per minute. The produced particles were filtered, washed with water, and repulped by a conventional method to prepare a substrate slurry. The obtained substrate particles had a silica content of 12.4 g / kg, a BET specific surface area of 7.5 m ² / g, and a median diameter of 0.23 μm.

Table 1 shows the silica content, BET specific surface area, and median diameter of the substrates used in Examples and Comparative Examples.

[Manufacturing of pigments]
[Example 1]
The substrate slurry obtained in Production Example C was used. The slurry containing 1.92 kg of the substrate was adjusted to a slurry concentration of 0.48 kg / L, and dispersed at 9000 rpm for 20 minutes using ROBOMICS fMODEL (hereinafter abbreviated as “TK Robomix”) manufactured by a special instrument. The temperature of the slurry was raised to 70 ° C. while stirring at 550 rpm, the pH of the slurry was adjusted to 10.0 using a 0.05 kg / L aqueous sodium hydroxide solution, and the mixture was held for 1 hour, and then 32. An amount equivalent to 0 g / kg of i-butyltrimethoxysilane was added, and the mixture was kept at the same pH for 5.0 hours. Next, the slurry pH was adjusted to 9.0 with dilute sulfuric acid (hereinafter referred to as "1/10 dilute sulfuric acid") obtained by diluting 98% concentrated sulfuric acid with deionized water 10 times by volume, and the slurry was held for 0.5 hours. The slurry that had been retained was filtered using a filter press and washed with tap water until the electrical conductivity of the filtrate became 200 μS / cm or less. The washing cake was dried at 90 ° C. for 3 hours. The dried product was pulverized using a TASM-1 type sample mill manufactured by Tokyo Atomizer (hereinafter abbreviated as "sample mill") to obtain a hydrophobic black magnetic pigment. The hydrolyzate content of i-butyltrimethoxysilane in the obtained pigment was 22.5 g / kg, the degree of hydrophobicity was 625 g / kg, the median diameter of the primary particles was 0.26 μm, and the external magnetic field was 79.6 kA / m. The magnetization σs was 64.9 Am ² / kg, the residual magnetization σr was 2.9 Am ² / kg, and the amount of VOC generated was less than 0.1% with respect to the n-hexyltrimethoxysilane-coated particles.

[Example 2]
The dried product obtained in Example 1 was heat-treated at 180 ° C. for 1 hour in a nitrogen atmosphere. The heat-treated product was pulverized using a sample mill to obtain a hydrophobic black magnetic pigment. The hydrolyzate content of i-butyltrimethoxysilane in the obtained pigment was 23.1 g / kg, the degree of hydrophobicity was 675 g / kg, the median diameter was 0.26 μm, and the magnetization σs under an external magnetic field of 79.6 kA / m. Was 68.2 Am ² / kg, the residual magnetization σr was 4.0 Am ² / kg, and the amount of VOC generated was less than 0.1% with respect to the n-hexyltrimethoxysilane-coated particles.

[Example 3]
The substrate slurry obtained in Production Example F was used. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 2 except that the slurry pH adjusted by using an aqueous sodium hydroxide solution was changed to 11.2.

[Example 4]
The substrate slurry obtained in Production Example G was used. The slurry containing 7.74 kg of the substrate was adjusted to a slurry concentration of 0.48 kg / L and dispersed at a current value of 4.0 A for 20 minutes using a TK HOMOMIXER MARKII40 (hereinafter abbreviated as “TK homomixer”) manufactured by a special instrument. .. The temperature of the slurry was raised to 70 ° C. while stirring at 550 rpm, the pH of the slurry was adjusted to 9.5 using a 0.05 kg / L aqueous solution of sodium hydroxide, and the mixture was held for 1 hour. An amount equivalent to 6 g / kg of i-butyltrimethoxysilane was added, and the mixture was kept at the same pH for 6.0 hours. Next, the slurry pH was adjusted to 9.0 with 1/10 dilute sulfuric acid and held for 0.5 hours. The slurry that had been retained was filtered using a filter press and washed with tap water until the electrical conductivity of the filtrate became 200 μS / cm or less. The washed cake was dried at 90 ° C. for 3 hours and heat treated in a nitrogen atmosphere at 225 ° C. for 1 hour. The heat-treated product was pulverized using a sample mill to obtain a hydrophobic black magnetic pigment. The mol ratio of carbon / silicon in the i-butyltrimethoxysilane hydrolyzate of the obtained pigment was 4.07. From this, it was found that the hydrolysis rate was 977 (mmol / mol), and most of the methoxy groups in i-butyltrimethoxysilane were hydrolyzed.

[Example 5]
The substrate slurry obtained in Production Example F was used. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 3 except that the slurry pH adjusted by using an aqueous sodium hydroxide solution was changed to 11.0.

[Example 6]
The substrate slurry obtained in Production Example H was used. First, using a slurry containing 1.44 kg of the substrate, the amount of i-butyltrimethoxysilane added was changed to 14.0 g / kg based on the weight of the substrate, and then the pH was kept at 10.0 for 4.3 hours, and 1 /. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 2 except that the slurry pH was adjusted to 7.0 with 10 dilute sulfuric acid and the temperature at which the dried washing cake was heat-treated in a nitrogen atmosphere was changed to 150 ° C. ..

[Example 7]
The substrate slurry obtained in Production Example I was used. The temperature at which the slurry is heated after dispersion is changed to 50 ° C., the amount of i-butyltrimethoxysilane added is changed to 24.0 g / kg with respect to the weight of the substrate, and the temperature at which the dried washing cake is heat-treated in a nitrogen atmosphere is set to 150. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 2 except that the temperature was changed to ° C.

[Example 8]
The substrate slurry obtained in Production Example J was used. Hydrophobic black by the same operation as in Example 7 except that the temperature for heating the slurry after dispersion was changed to 90 ° C. and the amount of i-butyltrimethoxysilane added was changed to 20.6 g / kg with respect to the substrate weight. A magnetic pigment was obtained.

[Example 9]
The substrate slurry obtained in Production Example H was used. Hydrophobic black magnetism was carried out in the same manner as in Example 8 except that the initial slurry concentration was adjusted to 0.60 kg / L, the pH was maintained at pH 10.0 for 5.0 hours, and then the adjusted pH was changed to 7.0. Obtained a pigment.

[Example 10]
The substrate slurry obtained in Production Example J was used. The slurry containing 2.70 kg of the substrate was adjusted to a slurry concentration of 0.18 kg / L, the pH of the slurry was adjusted to 10.0 using an aqueous sodium hydroxide solution, and the pH was 10.0 after adding i-butyltrimethoxysilane. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 4 except that the temperature at which the dried washed cake was heat-treated in a nitrogen atmosphere was changed to 150 ° C.

[Example 11]
The substrate slurry obtained in Production Example K was used. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 4 except that a slurry containing 7.66 kg of the substrate was used first.

[Example 12]
The substrate slurry obtained in Production Example L was used. The pH of the slurry adjusted with an aqueous sodium hydroxide solution is 9.5, the amount of i-butyltrimethoxysilane added is 19.0 g / kg based on the weight of the substrate, and the pH is maintained after the addition of i-butyltrimethoxysilane. A hydrophobic black magnetic pigment was obtained by the same operation as in Example 3 except that the pH was changed to 6.0 hours and the temperature at which the dried washed cake was heat-treated in a nitrogen atmosphere was changed to 225 ° C.

[Example 13]
The substrate slurry obtained in Production Example I was used. Hydrophobic black by the same operation as in Example 7 except that the temperature for heating the slurry after dispersion was changed to 35 ° C. and the amount of i-butyltrimethoxysilane added was changed to 27.0 g / kg with respect to the substrate weight. A magnetic pigment was obtained.

[Comparative Example 1]
The substrate slurry obtained in Production Example O was used. The slurry containing 2.16 kg of the substrate was adjusted to a slurry concentration of 0.12 kg / L and dispersed at a current value of 4.0 A for 20 minutes using a TK homomixer. Raise the slurry temperature to 40 ° C. while stirring at 500 rpm, adjust the slurry pH to 9.0 using a 0.05 kg / L aqueous sodium hydroxide solution, hold for 1 hour, and then 20 based on the substrate weight. An amount equivalent to .6 g / kg of i-butyltrimethoxysilane was added, and the mixture was kept at the same pH for 50.0 hours. Next, the slurry pH was adjusted to 7.0 with 1/10 dilute sulfuric acid and held for 1.0 hour. The retained slurry was filtered using a filter press and washed with tap water until the electrical conductivity of the filtrate became 200 μS / cm or less. The washed cake was dried at 90 ° C. for 3 hours and then heat-treated at 150 ° C. for 1 hour in a nitrogen atmosphere. The heat-treated product was pulverized using a sample mill to obtain a black magnetic pigment. The hydrolyzate content of i-butyltrimethoxysilane in the obtained pigment was 8.2 g / kg, the degree of hydrophobicity was 425 g / kg, the median diameter of the primary particles was 0.25 μm, and the external magnetic field was 79.6 kA / m. The magnetization σs was 72.1 Am ² / kg, the residual magnetization σr was 4.2 Am ² / kg, and the amount of VOC generated was 1.0% with respect to the n-hexyltrimethoxysilane-coated particles.

[Comparative Example 2]
Using the substrate slurry using Production Example P, it was produced according to Example 8 of Patent Document 2. The pH of the substrate slurry was adjusted to 5.0 and dispersed with a TK homomixer (6,000 rpm) for 30 minutes. The average particle size of the dispersed slurry was 0.72 μm. After adjusting the temperature of the dispersed slurry to 40 ° C. and the substrate concentration to 100 g / L, the slurry pH was adjusted to 5.0 with dilute hydrochloric acid of hydrochloric acid: water = 1: 9 (volume ratio), and the slurry was held for 30 minutes. After readjusting the slurry pH to 5.0, an amount of n-hexyltrimethoxysilane stock solution corresponding to 1.64% based on the weight of the substrate magnetite was added, and the mixture was kept stirred at the same pH for 20 hours. A TK homomixer was used as the stirrer. Next, a 100 g / L sodium hydroxide aqueous solution was continuously added for 2 hours using a roller pump to adjust the pH to 8.0 and held for 1 hour. The temperature of the slurry was maintained at 40 ° C. from the start to the end of the treatment. The treated slurry was filtered using a filter press and washed with pure water until the electrical conductivity of the filtrate became 200 μS / cm or less. The washed cake was dried at 90 ° C. for 2 hours and then heat-treated at 130 ° C. for 1 hour. The heat-treated product was pulverized using a TASM-1 type sample mill.

Table 2 shows the adhesion conditions of the alkoxysilanes of Examples 1 to 13 and Comparative Examples 1 and 2. Table 3 shows various characteristics of the pigments obtained in Examples 1 to 13 and Comparative Examples 1 and 2.

As can be seen from Table 3, in Examples 1 to 13, the degree of hydrophobization is 575 g / kg or more, and the amount of VOC generated is less than 30% of the amount of n-hexyltrimethoxysilane-coated particles of Comparative Example 2. A hydrophobic black magnetic pigment was obtained. On the other hand, in Comparative Example 1, although i-butyltrimethoxysilane was used, the adherence was carried out using a low-concentration substrate slurry, so that the amount of i-butyltrimethoxysilane hydrolyzate adhered was reduced, and the result was obtained. The degree of hydrophobicity of the pigment became smaller. In the present invention, in order to obtain a sufficient degree of hydrophobicity of the pigment, as described above, the concentration of the substrate slurry is set high in order to increase the contact frequency between the i-butyltrimethoxysilane and the substrate, and the substrate slurry is applied. It can be said that it is desirable to set the temperature and pH high in order to increase the landing speed and to take a sufficient holding time at the above temperature and pH. It is considered that these can be adjusted to each other to some extent. For example, when the temperature is low, the i-butyltri is obtained by increasing the concentration of the substrate slurry or setting the pH higher and taking a longer holding time. It is considered that the adhesion amount of methoxysilane can be increased to increase the degree of hydrophobicity. However, it is considered that there is a limit to these adjustments. For example, in Comparative Example 1, the concentration of the substrate slurry was very low at 0.12 kg / L, so that the holding time was set to a long time of 50.0 hours. Nevertheless, it is considered that the result was that the adherence amount (hydrolyzate content) and the degree of hydrophobicity were small. Considering these points, it can be said that the concentration of the substrate slurry at the time of adhesion is preferably 0.18 kg / L or more as described above. In Comparative Example 2, as a result of changing the type of alkoxysilane, the degree of hydrophobicity was increased, but the amount of VOC generated was also very large.

As described above, in the present invention, i-butyltrimethoxysilane is used on the surface of a magnetic material (core) containing triiron tetroxide as a main component to form an alkylsilane compound layer in a specific amount range of i-butyltri. By coating with a magnetic material slurry having a high concentration preferably at a high temperature and a high pH so as to have an amount of methoxysilane hydrolyzate, a pigment having a small amount of VOC generated can be obtained. The obtained pigment is suitable as a material for an electrophotographic developer such as a polymerization method toner.

Claims (5)

A pigment having an alkylsilane compound layer on the surface of a magnetic material containing triiron tetroxide as a main component, wherein the alkylsilane compound layer is 8.5 g / kg or more and 40.0 g / kg based on the weight of the pigment. The pigment comprising the following amount of a hydrolyzate of i-butyltrimethoxysilane and having a degree of hydrophobicity of the pigment of 575 g / kg or more and 800 g / kg or less. The pigment according to claim 1, wherein the median diameter of the primary particles obtained from image analysis using a transmission electron microscope is 0.20 μm or more and 0.35 μm or less. When the external magnetic field is 79.6 kA / m, the magnetization is 64.0 Am ² / kg or more and 72.0 Am ² / kg or less, and the residual magnetization after magnetizing at 79.6 kA / m is 2. The pigment according to claim 1 or 2, which is 8 Am ² / kg or more and 4.2 Am ² / kg or less. I-Butyltrimethoxysilane is added to a slurry in which a magnetic substance containing triiron tetroxide as a main component is dispersed in water to generate a hydrolyzate of i-butyltrimethoxysilane, and this hydrolyzate is used as described above. Claims 1 to 3 include a step of adhering to the surface of the magnetic material and a step of obtaining the magnetic material adhered with the hydrolyzate of i-butyltrimethoxysilane by solid-liquid separation and drying it. The method for producing a pigment according to any one item. (1) Prepare a slurry containing a magnetic substance containing triiron tetroxide as a main component in water in an amount of 0.18 kg / L or more and 0.60 kg / L or less, and adjust the pH of the slurry to 7.0 or more and 11.5. Below, and the step of adjusting the temperature to 35 ° C or higher and 90 ° C or lower,
(2) i-Butyltrimethoxysilane is added to the slurry of (1), and the slurry is stirred for 2 hours or more while maintaining the temperature of the slurry in the temperature range described in (1), thereby causing i- on the surface of the magnetic material. Step of depositing a hydrolyzate of butyltrimethoxysilane,
(3) A step of solid-liquid separation of the cake containing the magnetic substance adhered to the hydrolyzate from the slurry of (2), and a temperature of 60 ° C. or higher and 100 ° C. or lower in the air of the cake of (4) and (3). The production method according to claim 4, which comprises a step of drying with.