JP7229814B2 - Electrophotographic pigment and method for producing the same - Google Patents

Description

The present invention relates to a pigment obtained by coating the surface of a magnetic material containing triiron tetroxide as a main component 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 as an electrophotographic developer such as a magnetic one-component toner by a polymerization method. It relates to hydrophobic magnetic pigments suitable for use as materials.

In recent years, along with the functional improvement of equipment such as electrophotographic copiers, printers, facsimiles, and other multifunction machines (hereafter abbreviated as "printers"), the developer used (hereafter also referred to as toner) (synonymous with developer) is also required to be of high quality. There is a demand for a toner that can be printed accurately, quickly, in large quantities, and that is well-balanced with cost. Therefore, in order to improve image quality and reduce production costs, polymerized toner has been used in place of the conventional pulverized toner. Patent Document 1 discloses a method for producing a polymerized toner. When triiron tetroxide is used as a material for polymerized 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 many hydrophilic surfaces remain, the magnetic pigment containing triiron tetroxide is dispersed in the resin monomer and suspended in water in the process of manufacturing the polymerization toner. When the toner becomes cloudy, the pigment migrates to the aqueous phase, and the dispersibility of the pigment in the toner base particles deteriorates. In addition, a difference in pigment content occurs between the toner base particles, and in the worst case, there arises a problem that toner base particles containing no pigment at all are produced.

Patent Document 2 discloses a method of coating magnetic iron oxide particles such as triiron tetraoxide (magnetite) with n-decyltrimethoxysilane or the like. The hydrophobic magnetic iron oxide particles of Example 14 coated with n-hexadecyltrimethoxysilane, which has the highest degree of hydrophobicity among the examples of Patent Document 2, have a degree of hydrophobicity of 83 in a methanol wettability test. % (converted to 771 g/kg). Patent document 3 shows a manufacturing method of providing an alkylsilane compound layer on the surface of core particles of magnetite. 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 to 649 g/kg). These magnetic pigments with a high degree of hydrophobicity were suitable as materials for polymerized toners.

On the other hand, in recent years, due to the growing interest in health, the chemical substances generated during the use of printers have come to be viewed as a problem. As one of them, there is VOC generated by heating developer during printing, and suppression of the amount of generated VOC is a problem. For example, the German environmental label Blue Angel calls for a reduction in the environmental impact of products from manufacture to use and disposal, and for printers, a reduction in the amount of VOCs generated during printing.

Polymerized toners are also required to reduce the amount of VOCs generated during heating. As a result of investigating polymerized toners using magnetic pigments with high hydrophobicity obtained in Patent Documents 2 and 3, it was found that the amount of VOCs generated from the pigments during heating is large. In general, products containing alkyl groups with a large number of carbon atoms generate a large amount of VOCs when heated. In the case of the polymerized toner, when the number of carbon atoms in the alkyl group in the alkoxysilane used to coat 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 magnetic pigments containing alkoxysilanes, it is extremely effective to use alkoxysilanes whose alkyl groups have a small number of carbon atoms. However, when triiron tetroxide particles are coated with an alkoxysilane having an alkyl group with a small number of carbon atoms, there is a problem that it is difficult to obtain a magnetic pigment having a high degree of hydrophobicity. Patent Document 4 describes an example in which i-butyltrimethoxysilane, which is an alkoxysilane having an alkyl group with 4 carbon atoms, was used to coat the core particles of magnetite in Example 4, but a methanol wettability test was performed. Hydrophobicity is 60% (543 g / kg in terms of conversion), and Examples 1 to 3 and Examples 5 to 5 using alkoxysilanes with a large carbon number such as n-hexyl or n-octyl It is described that the hydrophobization degree became smaller than that of No. 8. The coated magnetite particles of Example 4 of Patent Document 4 have a lower degree of hydrophobicity than the pigments obtained in Patent Documents 2 and 3, and are unsuitable as a material for polymerized toner.

As an example of using a surface treatment agent other than alkoxysilane, Patent Document 5 discloses a manufacturing method of coating the surface of magnetic iron oxide particles with linear organopolysiloxane or silazane. The invention of Patent Document 5 succeeded in reducing the amount of VOCs generated, and the degree of hydrophobization was 66% (606 g/kg when converted) in Example 5, which was the largest. Although the coated magnetic iron oxide particles obtained in Patent Document 5 can be used for polymerized toner, 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 magnetic materials having various configurations that can achieve both a reduction in the amount of VOC generation and a high degree of hydrophobicity.

Japanese Patent Application Laid-Open No. 2003-131422 Japanese Patent Application Laid-Open No. 2005-263619 Japanese Unexamined Patent Application Publication No. 2014-148425 Japanese Patent Application Laid-Open No. 2013-193890 Japanese Patent Application Laid-Open No. 2016-210629

An object of the present invention is to provide a material for an electrophotographic developer by a polymerization method, which has a large degree of hydrophobicity necessary for maintaining a stable dispersed state in a resin monomer, and which is not harmful to the human body when the developer is actually used. To provide a magnetic pigment which generates a small amount of harmful VOCs and a method for producing the same.

The inventors of the present invention have extensively studied magnetic pigments that are used as materials for polymerized toner. By coating a substance in a specific amount range by a specific method, a magnetic pigment having a large degree of hydrophobicity suitable for the production of polymerized toner and generating a small amount of VOC when heated can be obtained. I found

The invention includes the following.
[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, which is composed of a hydrolyzate of i-butyltrimethoxysilane in an amount of 0 g/kg or less, and has a hydrophobicity 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 determined by image analysis using a transmission electron microscope is 0.20 μm or more and 0.35 μm or less.
[3] Magnetization at an external magnetic field of 79.6 kA/m is 64.0 Am ² /kg or more and 72.0 Am ² /kg or less, and residual magnetization after magnetization at an external magnetic field of 79.6 kA/m 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 material containing triiron tetraoxide as a main component is dispersed in water to produce a hydrolyzate of i-butyltrimethoxysilane, and this hydrolysis is performed. [1] to [3], including the step of depositing a substance on the surface of the magnetic substance, and the step of obtaining the magnetic substance coated with the hydrolyzate of i-butyltrimethoxysilane by solid-liquid separation and drying it. [5] (1) A magnetic substance containing triiron tetraoxide 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 temperature of the slurry is maintained within the temperature range described in (1) and stirred for 2 hours or more, thereby i- depositing a hydrolyzate of butyltrimethoxysilane;
(3) a step of solid-liquid separation of the cake containing the magnetic substance coated with the hydrolyzate from the slurry of (2); The production method according to [4], including the step of drying with.

According to the present invention, a magnetic material containing triiron tetroxide as a main component is coated with a hydrolyzate of i-butyltrimethoxysilane in a specific amount range using a specific method, so that the degree of hydrophobicity is increased. It is possible to provide a magnetic pigment that is large and that generates a small amount of VOC during actual use of an electrophotographic developer.

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

When the amount of hydrolyzate of i-butyltrimethoxysilane is less than 8.5 g/kg, the surface of the core is sufficiently covered considering the specific surface area of the core magnetic material mainly composed of triiron tetroxide. As a result, a hydrophilic surface remains and a highly hydrophobic pigment cannot be obtained. On the other hand, if the amount of hydrolyzate of i-butyltrimethoxysilane is more than 40.0 g/kg, the proportion of non-magnetic components in the pigment increases and the magnetization of the pigment decreases. In addition, since i-butyltrimethoxysilane is more expensive than iron oxide, i-butyltrimethoxysilane in the pigment can be used as long as the degree of hydrophobicity of the resulting pigment is within a range that does not interfere with the production of the polymerized toner. The smaller the amount of methoxysilane hydrolyzate, the better.

In the present invention, the amount of i-butyltrimethoxysilane hydrolyzate in the pigment is measured by the following method:
The carbon (C) content in the pigment is analyzed using a LECO model CS-230 carbon (C)/sulfur (S) analyzer. Assuming that the i-butyltrimethoxysilane is completely hydrolyzed, the i-butyltrimethoxysilane hydrolyzate content (g/kg) is calculated using the carbon (C) measurements by the following equation: ,calculate:
Hydrolyzate content (g/kg) = Carbon (C) measured value (wt%) x 2.773 x 10
The pigment of the present invention has a hydrophobicity of 575 g/kg or more. More preferably, it is 625 g/kg or more. If the degree of hydrophobicity is less than 575 g/kg, the pigment tends to migrate into the aqueous phase during production of the polymerized toner, resulting in poor dispersibility of the pigment in the toner base particles. In addition, a difference in the content of the pigment occurs between the toner base particles, and in the worst case, problems such as the formation of toner base 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 an opening of 1 mm is used as a measurement sample, and the measurement is performed within 5 minutes after passing through the sieve. Prepare a plurality of methanol aqueous solutions with different methanol contents by 25 g/kg (for example, 500 g/kg, 525 g/kg, 550 g/kg, 575 g/kg, 600 g/kg, 675 g/kg, 700 g/kg, 725 g/kg . A sample of 20 mg or more and 40 mg or less is gently put into each test tube, and the presence or absence of sedimentation is visually confirmed. When 5 seconds have passed since the sample was added, it is determined that the sample does not settle at all, and that it settles if even a part of the sample settles. In rare cases, even though the sample has passed through a sieve, small lumps may form, and a small amount of lumps may settle (up to 10% of the total, about 20 grains or less by eye measurement), but such an exception Judgment shall be made by excluding the sedimentation of typical lumps. The methanol content of the aqueous solution with the lowest methanol concentration in which the sample settles is defined as the degree of hydrophobicity (g/kg).

The pigment of the present invention preferably has a median diameter of primary particles of 0.20 μm or more and 0.35 μm or less as determined by image analysis using a transmission electron microscope. When the median diameter of the primary particles is larger than 0.35 μm, the coloring power of the pigment may be lowered, and the coloring power of the toner using the pigment may also be lowered. On the other hand, if the median diameter of the primary particles is less than 0.20 μm, the cohesive force of the pigment increases 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 image analysis of transmission electron microscope images. For example, it can be measured by the method described in Examples below.
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 at an external magnetic field of 79.6 kA/m, and after magnetization at an external magnetic field of 79.6 kA/m preferably has a residual magnetization of 2.8 Am ² /kg or more and 4.2 Am ² /kg or less. More preferably, the magnetization is 65.0 Am ² /kg or more when the external magnetic field is 79.6 kA/m. When the magnetization is less than 64.0 Am ² /kg or the residual magnetization is less than 2.8 Am ² /kg when the external magnetic field is 79.6 kA/m, the magnetization of the toner base particles after charging decreases, and the behavior of the toner deteriorates. It becomes difficult to control, and there is a risk that blurred images are likely to occur. When the magnetization is 72.0 Am ² /kg or more when the external magnetic field is 79.6 kA/m or the residual magnetization exceeds 4.2 Am ² /kg, the toner base particles tend to aggregate due to the magnetism, resulting in fogging and image deterioration. Bleeding may occur.

The magnetization and remanent magnetization of the pigments of the present invention can be measured using a vibrating sample magnetometer at room temperature around 23°C. For example, it can be measured by the method described in Examples below.
The pigment of the present invention reduces the amount of VOC (volatile organic compounds) generated by coating magnetite (triiron tetroxide) particles using n-hexyltrimethoxysilane. It is preferably 30% or less of the VOC generation amount of the hydrophobic magnetic iron oxide particles obtained in Example 8 (hereinafter referred to as "n-hexyltrimethoxysilane-coated particles").

The amount of VOCs generated can be determined by, for example, using gas chromatography to determine the peak area detected between the peak of normal hexane and the peak of n-hexadecane, and the amount of the n-hexyltrimethoxysilane-coated particles as a control substance. It can be calculated by comparing the peak areas. More specifically, it can be measured by the method described in Examples below.

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

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

Examples of ferrous salt aqueous solutions include ferrous sulfate, ferrous chloride, and ferrous nitrate. Ferrous sulphate, which is produced with washing, is used. As alkali hydroxides, 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 salt aqueous solution and an alkali hydroxide are neutralized to form a ferrous hydroxide precipitate. 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 per 1 mol of iron ion, iron oxyhydroxide tends to be generated, which is not preferable. On the other hand, if the hydroxide ion exceeds 2.0 mol per 1.0 mol of iron ion, polyhedral particles such as cubes and octahedrons are formed, and the residual magnetization increases and the particles tend to aggregate, which is also not preferable. .

The temperature for oxidizing the ferrous hydroxide in the present invention is suitably 60° C. or higher and 100° C. or lower, more preferably 85° C. or higher and 90° C. or lower. If the temperature during oxidation is lower than 60° C., the magnetization and residual magnetization are reduced, and if the magnetization and residual magnetization of the toner base containing it are excessively reduced, it becomes difficult to control the behavior of the toner, resulting in blurred images. becomes more 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 suitably 68% or more and 74% or less, more preferably 70% or more and 71% or less. If the oxidation rate is small, the target magnetization and remanent magnetization may not be achieved, and if the oxidation rate is large, the resulting substrate will be dark red and may not be suitable for use as a toner. The oxidation rate of the substrate refers to the molar amount of iron ions (III) with respect to all iron ions in the production of a magnetic material containing triiron tetraoxide as a main component. The oxidation rate of a substrate can be measured by the following method:
Concentrated sulfuric acid is added to the substrate slurry and heated to dissolve the substrate. An aqueous solution of potassium permanganate is used to titrate iron (II) ions in the solution, and the titration amount at this time is referred to as "titration amount A". Next, mercury amalgam was used to reduce all the iron (III) ions in the solution to iron (II) ions, and then the potassium permanganate aqueous solution was used again to titrate the iron (II) ions in the solution. , the titration amount at this time is called "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 a main component, which is the base of the present invention, a component such as silica can be introduced into the 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 consisting only of triiron tetroxide, and particles containing triiron tetroxide as a main component but other than iron such as silicon or phosphorus. Particles to which trace amounts of other elements are added are included. Manganese does not need to be introduced into the magnetic material containing triiron tetraoxide as a main component. In the surface treatment step of the present invention, which will be described later, the alkylsilane compound layer can be thinly and uniformly coated regardless of the amount of manganese present on the surface of the magnetic material. The content of elements other than iron in the magnetic material containing triiron tetraoxide as a main component may be changed in accordance with the regulations regarding the amount of chemical substances contained in the toner. The magnetic material based on triiron tetroxide contains more than 950 g/kg of triiron tetroxide, more preferably more than 980 g/kg of triiron tetroxide, based on the weight of the magnetic material. The ratio of triiron tetraoxide in the magnetic substance can be obtained by measuring the amount of the compound containing elements other than iron added during the production of the magnetic substance (triiron tetraoxide) and subtracting the ratio. .

As the silicon compound, water glass, sodium silicate, potassium silicate, and other water-soluble silicon compounds are used. The amount added is 7 g/kg or more and 20 g/kg or less, more preferably 9 g/kg or more and 15 g/kg or less in terms of silica, relative to triiron tetraoxide. If the amount added is small, the particles tend to have a polyhedral shape, and residual magnetization increases, making them likely to agglomerate. On the other hand, if the addition amount is larger than 20 g/kg, silica precipitates on the surface of the triiron tetroxide, which hinders the adhesion of the alkoxysilane in the subsequent steps.

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

When silicon compounds and phosphorus compounds are added, they may be added to any of alkali hydroxides, ferrous salt aqueous solutions, and mixtures thereof. However, it must be added before crystallization of triiron tetraoxide begins.

The shape of the magnetic material containing triiron tetraoxide as a main component is preferably spherical. When the shape of the core magnetic material is substantially spherical, it is easy to adjust the residual magnetization to an appropriate range, and problems such as particle agglomeration 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, i-butyltrimethoxysilane is used to coat the surface of the magnetic material with an alkylsilane compound layer. The method of adhesion includes a wet method and a dry method, but it is preferable to use the wet method from the viewpoint that unevenness of adhesion is less likely to occur and the degree of hydrophobicity can be easily increased. When performing the adhesion by the wet method, first, the magnetic material (substrate) that will be the core is dispersed in water to form a slurry. A suitable concentration of the magnetic material in the slurry is 0.18 kg/L or more and 0.60 kg/L or less. When the concentration of the magnetic material is less than 0.18 kg/L, the contact frequency between i-butyltrimethoxysilane and triiron tetroxide decreases, resulting in a decrease in the adhered amount. As a result, the resulting pigment having an alkylsilane compound layer tends to be less hydrophobic. On the other hand, when the concentration of the magnetic substance is more than 0.60 kg/L, uniform stirring is difficult due to the high viscosity of the slurry, which may result in non-uniform adhesion between the triiron tetroxide particles.

The temperature of the slurry during the deposition is suitably 35°C or higher and 90°C or lower, more preferably 50°C or higher and 90°C or lower. If the slurry temperature is lower than 35° C., the adhesion rate of the i-butyltrimethoxysilane hydrolyzate to the surface of triiron tetroxide tends to be low, and the hydrophobicity of the resulting pigment tends to be low. On the other hand, when the slurry temperature is higher than 90° C., the deposition progresses rapidly, so there is a possibility that uneven deposition may occur between the triiron tetroxide particles.

The slurry pH at the time of deposition is suitably 7.0 or more and 11.5 or less, more preferably 9.5 or more and 11.0 or less. If the pH of the slurry is lower than 7.0, the i-butyltrimethoxysilane hydrolyzate adheres at a lower rate, and the resulting pigment tends to have a lower degree of hydrophobicity. When the pH of the slurry is higher than 11.5, the condensation reaction between i-butyltrimethoxysilanes is likely to proceed, and the amount adhered to the substrate is reduced. be. Alkaline hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide and the like can be used to adjust the pH, but are not limited to these.

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

If alkali hydroxide remains in the pigment having an alkylsilane compound layer and causes problems in the process of producing the polymerized toner, neutralize the alkali component after the addition of i-butyltrimethoxysilane. Therefore, the slurry pH may be readjusted to 7.0 to 9.0. Acids such as sulfuric acid and hydrochloric acid can be used to adjust the pH, although not limited thereto.

It is desirable that all of the methoxy groups in the i-butyltrimethoxysilane molecule adhered to the surface of the triiron tetroxide are hydrolyzed at the stage of completion of the adherence. When a methoxy group remains in the molecule of i-butyltrimethoxysilane, it is difficult to cover the surface of triiron tetroxide without gaps, and the surface of hydrophobic triiron tetroxide remains, resulting in a pigment. may be less hydrophobic.

The coated slurry is subjected to solid-liquid separation to obtain a cake containing the magnetic material coated with the alkylsilane compound layer. After thoroughly washing the cake, 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. Heating to a temperature higher than 100° C. in the presence of moisture promotes condensation of the hydrolyzate of i-butyltrimethoxysilane in the pigment, generating aggregates and possibly deteriorating the dispersibility of the pigment. If the drying temperature is lower than 60° C., water may remain and the hydrophobicity of the resulting pigment may be reduced. Drying is suitably carried out for one hour or longer. It is not necessary to rotate the pigment during drying, but the pigment may be loosened or moved during drying in order to speed up drying.

After drying the cake, a heat treatment may be carried out to make the pigment more hydrophobic. If the heat treatment is carried out in the air, the oxidation of the core magnetic material may progress and the pigment may become dark red. Furthermore, since the alkylsilane compound layer may be partially decomposed and the degree of hydrophobicity may be reduced, it is preferable to perform the heat treatment in an inert atmosphere using an inert gas typified by nitrogen gas. The heat treatment is preferably performed 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, the heat spreads to the inside of the pigment, and the degree of hydrophobicity tends to increase. When the heat treatment temperature is 250° C. or lower, the decomposition of the alkylsilane compound layer is suppressed, and a decrease in hydrophobicity can be prevented.

The pigment of the present invention is characterized by a small amount of VOC generation when heated and a high degree of hydrophobicity, and is particularly suitable as a material for electrophotographic developers such as polymerized toners.

EXAMPLES The following examples illustrate aspects of the present invention, which are provided for illustrative purposes only and are not intended to limit the scope of the invention. In addition, "L" shows a liter below.

[Measurement method]
[Measurement and calculation of median diameter]
It was measured using a JEOL transmission electron microscope JEM-1400plus. The observation magnification was 30,000 times (observation magnification of 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 circular diameters of about 300 particles in the observation field to the reference circular diameter (4 mm to 10 mm) of Carl Zeiss Particle Size Analyzer TGZ-3. Taking the diameter of the circle as the particle size, a cumulative curve of the cube of the particle size was created, and the particle size corresponding to 50% thereof was taken as the median size (μm).

[Measurement of Alkoxysilane Hydrolyzate Content]
The carbon (C) content of the sample was analyzed using a LECO model CS-230 carbon (C)/sulfur (S) analyzer. The amount of alkoxysilane hydrolyzate (g/kg) was calculated from the carbon (C) measurements, assuming complete hydrolysis of the alkoxysilane.

[Measurement of silica content]
10 g of the sample was weighed into a heat-resistant crucible, heated in air at 600° C. for 1 hour using an electric furnace SUPER-C SO-2035D manufactured by Motoyama Co., Ltd., and calcined. After the sample was completely cooled, an aluminum ring with an inner diameter of 40 mm and a height of 5 mm was filled with 8.0 g of the sample and compression molded at 150 kg/cm ² using a BRIQUETTING MACHINE MP-35 manufactured by Shimadzu Mectem. The silicon content of the molded sample was measured using Rigaku Simultix10. The silicon content of the substrate (core) was similarly measured. 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 carbon/silicon molar ratio in the i-butyltrimethoxysilane hydrolyzate was calculated from the carbon (C) content measured using a LECO CS-230 type carbon (C)/sulfur (S) analyzer. . Furthermore, the state in which all three methoxy groups in the i-butyltrimethoxysilane molecule are hydrolyzed, that is, the state in which the molar ratio of carbon/silicon is 4.00 is defined as the state in which hydrolysis has progressed 100%, and the hydrolysis rate is (mmol/mol) was calculated by the following formula:
Hydrolysis rate (mmol/mol) = 1000 x {1-(carbon (C) content/silicon (Si) content-4.00)/3.00}
[Measurement of VOC Emission Amount]
A 2.0 g sample was placed in a 30 mL screw vial with a rubber stopper and heated at 120° C. for 1 hour. Immediately after heating, a syringe was inserted into the screw vial to collect 5 mL of the internal gas, which was then injected into a Yanaco gas chromatograph G3800 equipped with a packed column (3 m) SE-30 manufactured by J-Science West Japan. 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 a rate of 5°C/min. Also, 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 n-hexane peak and the n-hexadecane peak was determined. The corresponding peak area of the sample with respect to the corresponding peak area of the n-hexyltrimethoxysilane-coated particles was calculated and used as the VOC generation amount (%) of the sample relative to the conventional product.

[Measurement of hydrophobicity]
A measurement sample passed through a sieve with an opening of 1 mm was used, and the measurement was performed within 5 minutes after passing through the sieve. A plurality of methanol aqueous solutions with different methanol contents of 25 g/kg were prepared, and about 2 mL of 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 the charged sample did not settle at all after 5 seconds from the charging of the sample, it was determined as "not settling", and when even a part of the sample was settling, it was determined as "settling". The methanol content of the aqueous solution with the lowest methanol concentration in which the sample settled was defined as the degree of hydrophobicity (g/kg).

[Measurement of magnetic properties]
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 Industry Co., Ltd. . Details of the operation are shown below. In this measurement, "-" of the external magnetic field value indicates that the direction of the magnetic field is opposite to the case of "+". Moreover, 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 was adjusted to 5 EMU when +398 kA/m was applied. A cylindrical cell having a base area of 38.47 mm ² , a height of 7 mm, and an internal capacity of 0.05655 cm ³ was filled with the sample powder so that the packing density was in the range of 2.20 g/cm ³ or more and 2.40 g/cm ³ or less. filled to 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 rate was lowered from around +63.7 kA/m, and at +78 kA/m or more, the application rate was set to the lowest 20 min/Full-scale, and applied so as not to exceed +79.6 kA/m. It was confirmed that the output value of the GAUSS METER was +1.000 V when +79.6 kA/m was applied. The output value (V) of the MAIN AMPLIFIER was read as the magnetization (+σs) with +79.6 kA/m applied. Since the magnetization gradually changes with the passage of time, the reading of the output value was performed immediately after confirming the application of +79.6 kA/m. After reading the +σs value, it was demagnetized. After confirming that the external magnetic field was 0 A/m, the +σr value of residual magnetization was obtained, and the magnetic field was reversed to apply charging in the opposite direction to -79.6 kA/m. The application speed was increased to -79.6 kA/m, and the output value of the MAIN AMPLIFIER was read as magnetization (-σs) in the state of applying -79.6 kA/m. As in the reading operation of +σs, the application speed is reduced at -63.4 kA/m or more negative charge, and the application speed at -78.0 kA/m or more negative charge is set to the lowest 20 min / full scale, and -79.6 kA. /m was prevented from applying a negative charge. -79.6 kA/m is confirmed with the output value of GAUSS METER, and -σs is the same as +σs in that the output value of MAIN AMPLIFIER is quickly read. After reading the -σs value, it was demagnetized. An external magnetic field of 0 A/m was confirmed, and the -σr value of residual magnetization was obtained. The magnetic field was reversed and applied to +79.6 kA/m. These magnetization transitions accompanying changes in the external magnetic field were also visually read. Also, the application speed was set to 7 min/Fullscale.

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

[Production of Substrate (Magnetic Material Containing Triiron Tetroxide as Main Component)]
[Production example A of substrate]
170 L of an aqueous solution containing 22 kg of sodium hydroxide was placed in a reaction vessel, and after adding 800 mL of an aqueous sodium silicate solution of 0.40 kg/L in terms of silica, the temperature was raised to 40°C. While blowing nitrogen at 80 L per minute into the aqueous solution, add an aqueous ferrous sulfate solution of 0.10 kg / L in terms of Fe until the pH of the aqueous solution reaches 8.1 to generate ferrous hydroxide. and a slurry containing this was obtained. After adding water to adjust the Fe concentration in the slurry to 0.04 kg/L, a 1 mol/L sodium hydroxide aqueous solution was added to adjust the pH of the slurry to 8.5. The slurry was oxidized by blowing air at 70 L/min for 40 minutes. After raising the temperature of this slurry to 90° C., air was blown in at 70 L/min to oxidize the slurry until the oxidation rate reached 70% or more and 71% or less to obtain a magnetic material containing triiron tetraoxide as a main component. The resulting magnetic material (substrate) was filtered, washed with water and repulped in a conventional manner to obtain a substrate 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.

[Substrate Production Example B]
A substrate slurry was prepared in the same manner as in Production Example A, except that air was blown into the slurry after adjusting the pH to 8.5 at 70 L/min for 38 minutes. The resulting 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.

[Substrate Production Example C]
The base slurry of Production Example A and the base slurry of Production Example B were mixed in equal amounts and well stirred. The resulting 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.

[Substrate Production Example D]
A substrate slurry was prepared in the same manner as in Production Example A, except that air was blown into the slurry after adjusting the pH to 8.5 at 70 L/min for 49 minutes. The resulting 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.

[Substrate Production Example E]
A substrate slurry was prepared in the same manner as in Production Example A, except that air was blown into the slurry after adjusting the pH to 8.5 at 70 L/min for 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.

[Substrate Production Example F]
Equal amounts of the base slurry of Production Example D and the base slurry of Production Example E were mixed and thoroughly stirred. The resulting 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.

[Substrate Production Example G]
After adjusting the Fe concentration to 0.10 kg / L by adding water to the slurry containing ferrous hydroxide, adjusting the pH to 9.6, and blowing air into the slurry at 70 L per minute for 2 hours A substrate slurry was prepared in the same manner as in Production Example A, except that the time was set to 1 minute. 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.

[Substrate Production Example H]
22.5 m ³ of an aqueous solution containing 2,700 kg of sodium hydroxide was placed in a reaction vessel, and after adding 100 L of an aqueous sodium silicate solution of 0.40 kg/L in terms of silica, the temperature was raised to 40°C. While blowing 700 L of nitrogen per minute into the aqueous solution, add an aqueous ferrous sulfate solution of 0.10 kg / L in terms of Fe until the pH of the aqueous solution reaches 8.0 to generate ferrous hydroxide. and a slurry containing this was obtained. After adding water to adjust the iron (Fe) concentration to 0.04 kg/L, a 1 mol/L sodium hydroxide aqueous solution was added to adjust the pH of the slurry to 8.5. The slurry was oxidized by blowing air at 8.0 m ³ per minute for 39 minutes. After heating this slurry to 90° C., air is blown in at 6.6 m ³ /min to oxidize until the oxidation rate reaches 70% or more and 71% or less to obtain a magnetic material containing triiron tetraoxide as a main component. rice field. The resulting magnetic material (substrate) was filtered, washed with water and repulped in a conventional manner to obtain a substrate slurry. The resulting 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.

[Substrate Production Example I]
A substrate slurry was prepared in the same manner as in Production Example A, except that air was blown into the slurry after adjusting the pH to 8.5 at 70 L/min for 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.

[Production Example J of Substrate]
A substrate slurry was made in the same manner as in Preparation I, but in a separate lot. The resulting 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.

[Production example K of substrate]
A substrate slurry was prepared in the same manner as in Production Example A, except that air was blown into the slurry after adjusting the pH to 8.5 at 70 L/min for 30 minutes. The resulting 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.

[Substrate Production Example L]
A substrate slurry was prepared in the same manner as in Production Example H, except that air was blown into the slurry after adjusting the pH to 8.5 at 8.0 m ³ /min for 30 minutes. The resulting 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.

[Production example M of substrate]
22.5 m ³ of an aqueous solution containing 2,700 kg of sodium hydroxide was placed in a reactor, and 100 L of an aqueous sodium silicate solution with a silica conversion of 0.40 kg/L and 13.0 kg of sodium hexametaphosphate were added, and then the temperature was raised to 40°C. While blowing nitrogen at 700 L per minute into the aqueous solution, add an aqueous ferrous sulfate solution of 0.10 kg / L in terms of Fe until the pH of the aqueous solution reaches 8.2 to generate ferrous hydroxide. and a slurry containing this was obtained. After adding water to adjust the iron (Fe) concentration to 0.04 kg/L, a 1 mol/L sodium hydroxide aqueous solution was added to adjust the pH of the slurry to 8.5. The slurry was oxidized by blowing air at 8.0 m ³ per minute for 45 minutes. After heating this slurry to 90° C., air is blown in at 6.6 m ³ /min to oxidize until the oxidation rate reaches 70% or more and 71% or less to obtain a magnetic material containing triiron tetraoxide as a main component. rice field. The resulting magnetic material (substrate) was filtered, washed with water and repulped in a conventional manner to obtain a substrate slurry.

[Substrate Production Example N]
A substrate slurry was prepared in the same manner as in Production Example M, except that the time for blowing air into the slurry after adjusting the pH to 8.5 at 8.0 m ³ /min was changed to 42 minutes.

[Production example O of substrate]
Equal amounts of the base slurry of Production Example M and the base slurry of Production Example N were mixed and thoroughly stirred. The resulting 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.

[Production example P of substrate]
It was produced according to the method described in Production Example D of Substrate Particles in Patent Document 2 (Japanese Patent Application Laid-Open No. 2005-263619). After putting 180 L of an aqueous solution containing 18.5 kg of sodium hydroxide in a tank and adjusting the temperature to 40 ° C., 86.4 g of sodium hexametaphosphate (corresponding to 0.32% by weight in terms of P ₂ O ₅ with respect to Fe ₃ O ₄ ) and 681.7 mL of a sodium silicate solution of 413.5 g/L as SiO ₂ (corresponding to 1.50% by weight in terms of SiO ₂ with respect to Fe ₃ O ₄ ) were added, and the ferrous sulfate aqueous solution was adjusted to pH was added until the OD reached 8.5. Then, after adjusting the pH to 9.0 with 1 mol/L NaOH, the iron concentration was adjusted to 34 g/L, the liquid volume was adjusted to 400 L, and the solution was held for 30 minutes. Air was blown in at 100 L/min to oxidize until the oxidation rate (Fe ³⁺ /t-Fe weight ratio) reached 8%. After the slurry was adjusted to 90° C., it was oxidized to an oxidation rate of 68% while blowing air at 50 L/min. Thereafter, the reaction was terminated by stirring and holding for 3 hours while blowing nitrogen gas at 80 L/min. The produced particles were filtered, washed with water, and repulped by a conventional method to obtain a substrate slurry. The resulting 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 pigment]
[Example 1]
The substrate slurry obtained in Production Example C was used. A 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 ROBOMICS") manufactured by special equipment. The temperature of the slurry was raised to 70° C. while stirring at 550 rpm, and the pH of the slurry was adjusted to 10.0 using a 0.05 kg/L sodium hydroxide aqueous solution. An amount equivalent to 0 g/kg of i-butyltrimethoxysilane was added, and the same pH was maintained for 5.0 hours. Next, the pH of the slurry was adjusted to 9.0 with dilute sulfuric acid obtained by diluting 98% concentrated sulfuric acid with deionized water to ten times its volume (hereinafter referred to as "1/10 dilute sulfuric acid") and held for 0.5 hours. The retained slurry was filtered using a filter press and washed with tap water until the electric conductivity of the filtrate became 200 μS/cm or less. The washed cake was dried at 90°C for 3 hours. The dried product was pulverized using a TASM-1 model sample mill manufactured by Tokyo Atomizer Manufacturing Co., Ltd. (hereinafter abbreviated as "sample mill") to obtain a hydrophobic black magnetic pigment. The resulting pigment had a hydrolyzate content of i-butyltrimethoxysilane of 22.5 g/kg, a hydrophobicity of 625 g/kg, a median diameter of primary particles of 0.26 μm, and an external magnetic field of 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 VOC generation amount 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 resulting pigment had a hydrolyzate content of i-butyltrimethoxysilane of 23.1 g/kg, a hydrophobicity of 675 g/kg, a median diameter of 0.26 μm, and a 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 VOC generation amount 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 in the same manner as in Example 2, except that the pH of the slurry adjusted with an aqueous sodium hydroxide solution was changed to 11.2.

[Example 4]
The substrate slurry obtained in Production Example G was used. A slurry containing 7.74 kg of the substrate was adjusted to a slurry concentration of 0.48 kg/L, and dispersed for 20 minutes at a current value of 4.0 A using a special equipment TK HOMOMIXER MARKII40 (hereinafter abbreviated as "TK homomixer"). . The temperature of the slurry was raised to 70° C. while stirring at 550 rpm, and the pH of the slurry was adjusted to 9.5 using a 0.05 kg/L sodium hydroxide aqueous solution. Equivalent to 6 g/kg of i-butyltrimethoxysilane was added and maintained at the same pH for 6.0 hours. Next, the slurry pH was adjusted to 9.0 with 1/10 diluted sulfuric acid and held for 0.5 hours. The retained slurry was filtered using a filter press and washed with tap water until the electric conductivity of the filtrate became 200 μS/cm or less. The washed cake was dried at 90°C for 3 hours and heat-treated at 225°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 molar 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 in the same manner as in Example 3, except that the pH of the slurry, which was adjusted using an aqueous sodium hydroxide solution, was changed to 11.0.

[Example 6]
The substrate slurry obtained in Production Example H was used. First, a slurry containing 1.44 kg of the substrate was used, and the amount of i-butyltrimethoxysilane added was changed to 14.0 g/kg of the substrate weight. A hydrophobic black magnetic pigment was obtained in the same manner as in Example 2, except that the pH of the slurry was adjusted to 7.0 with 10-diluted sulfuric acid, and the temperature for heat-treating the dried washed cake in a nitrogen atmosphere was changed to 150°C. .

[Example 7]
The substrate slurry obtained in Production Example I was used. The temperature for heating the slurry after dispersion was changed to 50° C., the amount of i-butyltrimethoxysilane added was changed to 24.0 g/kg based on the weight of the substrate, and the temperature for heat-treating the dried washed cake in a nitrogen atmosphere was changed to 150° C. A hydrophobic black magnetic pigment was obtained in the same manner 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 color was obtained in the same manner 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 weight of the substrate. A magnetic pigment was obtained.

[Example 9]
The substrate slurry obtained in Production Example H was used. Hydrophobic black magnetic powder was prepared in the same manner as in Example 8, except that the initial slurry concentration was adjusted to 0.60 kg / L, held at pH 10.0 for 5.0 hours, and then the adjusted pH was changed to 7.0. A pigment was obtained.

[Example 10]
The substrate slurry obtained in Production Example J was used. A slurry containing 2.70 kg of substrate was adjusted to a slurry concentration of 0.18 kg/L, the slurry pH was adjusted to 10.0 using sodium hydroxide aqueous solution, and pH 10.0 after adding i-butyltrimethoxysilane. A hydrophobic black magnetic pigment was obtained in the same manner as in Example 4, except that the temperature for heat-treating the dried washed cake 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 in the same manner 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 was adjusted to 9.5, the amount of i-butyltrimethoxysilane added was adjusted to 19.0 g/kg relative to the weight of the substrate, and the pH was maintained after the addition of i-butyltrimethoxysilane. A hydrophobic black magnetic pigment was obtained in the same manner as in Example 3, except that the heating time was changed to 6.0 hours and the temperature for heat-treating the dried washed cake in a nitrogen atmosphere was changed to 225°C.

[Example 13]
The substrate slurry obtained in Production Example I was used. Hydrophobic black color was obtained in the same manner 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 weight of the substrate. A magnetic pigment was obtained.

[Comparative Example 1]
The substrate slurry obtained in Production Example O was used. A slurry containing 2.16 kg of the substrate was adjusted to a slurry concentration of 0.12 kg/L and dispersed using a TK homomixer at a current value of 4.0 A for 20 minutes. The slurry temperature was raised to 40° C. while stirring at 500 rpm, and the slurry pH was adjusted to 9.0 using a 0.05 kg/L sodium hydroxide aqueous solution. 0.6 g/kg equivalent of i-butyltrimethoxysilane was added and maintained at the same pH for 50.0 hours. Next, the slurry pH was adjusted to 7.0 with 1/10 diluted sulfuric acid and held for 1.0 hour. The retained slurry was filtered using a filter press and washed with tap water until the electric conductivity of the filtrate became 200 μS/cm or less. After drying the washed cake at 90° C. for 3 hours, it was 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 resulting pigment had a hydrolyzate content of i-butyltrimethoxysilane of 8.2 g/kg, a hydrophobicity of 425 g/kg, a median diameter of primary particles of 0.25 μm, and an external magnetic field of 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 VOC generation amount was 1.0% with respect to the n-hexyltrimethoxysilane-coated particles.

[Comparative Example 2]
Using the substrate slurry using Production Example P, production was carried out 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 pH of the slurry was adjusted to 5.0 with dilute hydrochloric acid (hydrochloric acid:water=1:9 (volume ratio)) and held for 30 minutes. After readjusting the pH of the slurry to 5.0, n-hexyltrimethoxysilane stock solution was added in an amount corresponding to 1.64% of the base magnetite weight, and the mixture was stirred and maintained at the same pH for 20 hours. A TK homomixer was used as a stirrer. Next, a 100 g/L sodium hydroxide aqueous solution was added continuously for 2 hours using a roller pump to adjust the pH to 8.0, and the mixture was held for 1 hour. The slurry temperature 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 electric 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 model sample mill.

Table 2 shows the deposition 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 hydrophobicity is 575 g/kg or more, and the VOC generation amount is less than 30% of the generation amount of the 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 deposition was carried out using a low-concentration base slurry. The degree of hydrophobicity of the pigment decreased. 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 frequency of contact between the i-butyltrimethoxysilane and the substrate. It can be said that it is desirable to set the temperature and pH to a high value in order to increase the deposition speed, and to take a sufficient holding time at the above temperature and pH. It is believed that these can be adjusted to each other to some extent. It is considered that the degree of hydrophobicity can be increased by increasing the amount of methoxysilane adhered. However, it is considered that there is a limit to these adjustments. Nevertheless, it is considered that the amount of deposition (hydrolyzate content) and degree of hydrophobization were small. Considering these points, it can be said that the concentration of the substrate slurry during deposition is desirably 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 increased, but the VOC generation amount also increased significantly.

As described above, in the present invention, i-butyltrimethoxysilane is used to form an alkylsilane compound layer on the surface of a magnetic material (core) containing triiron tetroxide as a main component. A pigment with a small amount of VOC generation can be obtained by coating at a high temperature and a high pH using preferably a high-concentration magnetic slurry so as to obtain the amount of methoxysilane hydrolyzate. The resulting pigment is suitable as a material for electrophotographic developers such as polymerized toners.

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 above pigment, which is composed of a hydrolyzate of i-butyltrimethoxysilane in the following amount and has a hydrophobicity of 575 g/kg or more and 800 g/kg or less. 2. The pigment according to claim 1, wherein the median diameter of the primary particles determined by image analysis using a transmission electron microscope is 0.20 [mu]m or more and 0.35 [mu]m or less. The magnetization at an external magnetic field of 79.6 kA/m is 64.0 Am ² /kg or more and 72.0 Am ² /kg or less, and the residual magnetization after magnetization at an external magnetic field of 79.6 kA/m is 2. 3. The pigment according to claim 1 or 2, which is 8 ^Am2 /kg or more and 4.2 ^Am2 /kg or less. A hydrolyzate of i-butyltrimethoxysilane is produced by adding i-butyltrimethoxysilane to a slurry in which a magnetic material containing triiron tetraoxide as a main component is dispersed in water, and this hydrolyzate is used as the hydrolyzate as described above. Claims 1 to 3, comprising a step of coating the surface of the magnetic substance, and a step of obtaining the magnetic substance coated with the i-butyltrimethoxysilane hydrolyzate by solid-liquid separation and drying it. A method for producing the pigment according to any one of (1) Prepare a slurry containing a magnetic substance containing triiron tetraoxide as a main component in an amount of 0.18 kg/L or more and 0.60 kg/L or less in water, and adjust the pH of the slurry to 7.0 or more and 11.5. and 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 temperature of the slurry is maintained within the temperature range described in (1) and stirred for 2 hours or more, thereby i- depositing a hydrolyzate of butyltrimethoxysilane;
(3) a step of solid-liquid separation of the cake containing the magnetic substance coated with the hydrolyzate from the slurry of (2); 5. The manufacturing method according to claim 4, comprising the step of drying with.