JP2023081751A - Method for producing water-resistant inorganic oxide hollow particles - Google Patents

Abstract

To provide a method for producing inorganic oxide hollow particles having excellent water resistance.SOLUTION: A method for producing water-resistant inorganic oxide hollow particles comprises: a first step of heating inorganic oxide hollow particles at a temperature within a range of -500°C±100°C relative to a melting point of the hollow particles; and a second step of slowly cooling the heated inorganic oxide hollow particles up to a temperature of 1/2±100°C of the heating temperature at an average cooling rate of 1°C/min or more and 28°C/min or less.SELECTED DRAWING: None

Description

The present invention relates to a method for producing water-resistant inorganic oxide hollow particles.

Inorganic oxide hollow particles have cavities inside the particles, so they are excellent in heat resistance and light weight, and are widely used as heat insulating materials, heat shielding materials, catalyst carriers, building materials, electronic materials, and the like.
Conventionally, for example, hollow fine mullite particles (Patent Document 1) containing Al ₂ O ₃ , SiO ₂ and mullite in a specific ratio and controlling the average circularity, average particle diameter and shell thickness within specific ranges, silica Inorganic oxide hollow particles of various compositions such as silica-containing hollow particles (Patent Document 2) having a shell (outer shell) containing metal and/or metal compound nanoparticles enclosed in the shell Proposed.

JP 2015-218071 A JP 2016-150880 A

In recent years, due to the remarkable progress of information network technology and the expansion of services utilizing information networks, further high-speed processing and transmission of information are desired, and the transmission signals of electronic devices are increasing in frequency. Higher frequencies increase the transmission loss of printed wiring boards in electronic equipment. Therefore, inorganic oxide hollow particles used in printed wiring boards are required to have excellent dielectric properties.
However, the inventors of the present invention have found that when a resin molding containing inorganic oxide hollow particles is immersed in water, there is a problem of deterioration in dielectric properties. In order to investigate the cause, the present inventors analyzed the immersed water, and confirmed an increase in electrical conductivity. It was presumed that the cause was that the inside of the cavity was flooded due to the occurrence of Therefore, in order to apply the inorganic oxide hollow particles to electronic materials, it is necessary to improve the water resistance of the inorganic oxide hollow particles and suppress the deterioration of the dielectric properties.
An object of the present invention is to provide a method for producing inorganic oxide hollow particles having excellent water resistance, a method for improving the water resistance of inorganic oxide hollow particles, and water-resistant inorganic oxide hollow particles.

The present inventors have found that by heating inorganic oxide hollow particles to a predetermined temperature and then slowly cooling them to a predetermined temperature at a constant average cooling rate, the particle surfaces become dense and stable. It was found that inorganic oxide hollow particles with excellent water resistance can be obtained because the elution of ion components from the particle surface is suppressed when immersed.

That is, the present invention provides the following [1] to [6].
[1] A first step of heating inorganic oxide hollow particles at a temperature within the range of −500° C.±150° C. with respect to the melting point of the hollow particles;
Water resistant, including a second step of slowly cooling the heated inorganic oxide hollow particles to a temperature of 1/2 ± 150 ° C. of the heating temperature at an average cooling rate of 1 ° C./min or more and 28 ° C./min or less a method for producing organic inorganic oxide hollow particles.
[2] The method for producing water-resistant inorganic oxide hollow particles according to [1] above, wherein the heating time in the first step is 15 minutes or more.
[3] Inorganic oxide hollow particles are periodic table group 1 elements, periodic table group 2 elements, periodic table group 4 elements, periodic table group 8 elements, periodic table group 9 elements, periodic table group 10 elements Inorganic oxidation containing one or more elements selected from elements, Group 11 elements of the periodic table, Group 12 elements of the periodic table, Group 13 elements of the periodic table, Group 14 elements of the periodic table and Group 15 elements of the periodic table The method for producing water-resistant inorganic oxide hollow particles according to the above [1] or [2], wherein the water-resistant inorganic oxide hollow particles are composed of a substance.
[4] a first step of heating the inorganic oxide hollow particles at a temperature within the range of −500° C.±150° C. with respect to the melting point of the hollow particles;
a second step of gradually cooling the heated inorganic oxide hollow particles to a temperature of 1/2 ± 150 ° C. of the heating temperature at an average cooling rate of 1 ° C./min or more and 28 ° C./min or less; A method for improving the water resistance of oxide hollow particles.
[5] Water-resistant inorganic oxide hollow particles having an electrical conductivity of 8.5 mS/m or less as measured by the following method.
(Measurement of electrical conductivity)
Inorganic oxide hollow particles and distilled water are mixed in a glass beaker at a liquid-solid ratio of 33:1 (wt %), and the mixture is boiled for 5 minutes. After cooling the mixture to 25° C., the electrical conductivity of the mixture is measured.
[6] The water-resistant inorganic oxide hollow particles according to [5] above, which have a hollowness of 70% or more.

According to the present invention, inorganic oxide hollow particles having excellent water resistance can be produced by a simple operation. Moreover, the inorganic oxide hollow particles of the present invention not only have improved water resistance, but also have a sufficient hollowness and excellent dielectric properties, and are particularly useful as electronic materials.

[Method for producing water-resistant inorganic oxide hollow particles]
A method for producing water-resistant inorganic oxide hollow particles is characterized by including a first step and a second step. Each step will be described in detail below.

(Preparation process)
In this step, inorganic oxide hollow particles are prepared prior to the first step.
Here, the term “hollow particles” as used herein refers to particles having a hollow structure inside and having an outer shell portion that partitions the hollow portion. Unlike porous particles with Hollow particles can be distinguished from porous particles by a transmission electron microscope (TEM) image. Further, the term “inorganic oxide hollow particles” refers to hollow particles in which the outer shell portion defining the hollow portion is composed of an inorganic oxide.

The inorganic oxide is not particularly limited as long as it can form the outer shell. For example, periodic table group 1 element, periodic table group 2 element, periodic table group 4 element, periodic table group 8 element, periodic table group 9 element, periodic table group 10 element, periodic table group 11 element , an inorganic oxide containing one or more elements selected from Group 12 elements of the periodic table, Group 13 elements of the periodic table, Group 14 elements of the periodic table and Group 15 elements of the periodic table. One or more inorganic oxides can be contained.

Examples of Group 1 elements of the periodic table include lithium, sodium, potassium, and cesium. Examples of Group 2 elements of the periodic table include magnesium, calcium, strontium, and barium. Examples of Group 4 elements of the periodic table include titanium and zirconium. Examples of Group 8 elements of the periodic table include iron and ruthenium. Examples of Group 9 elements of the periodic table include cobalt, rhodium, and iridium. Examples of elements of Group 10 of the periodic table include nickel, palladium, and platinum. Examples of Group 11 elements of the periodic table include copper, silver, and gold. Examples of Group 12 elements of the periodic table include zinc and cadmium. Examples of Group 13 elements of the periodic table include boron, aluminum, gallium, indium, and thallium. Examples of Group 14 elements of the periodic table include silicon, germanium, tin, and lead. Examples of Group 15 elements of the periodic table include phosphorus, arsenic, antimony, and bismuth.

Among them, periodic table Group 1 elements, periodic table Group 2 elements, periodic table Group 4 elements, periodic table Group 8 elements, periodic table Group 11 elements, periodic table One or two or more inorganic oxides containing elements selected from Group 12 elements, Group 13 elements of the periodic table and Group 14 elements of the periodic table are preferable, Periodic table Group 1 elements, Periodic table Group 2 elements, periodic More preferably, one or more inorganic oxides containing elements selected from Group 8 elements of the periodic table, Group 12 elements of the periodic table, Group 13 elements of the periodic table and Group 14 elements of the periodic table, sodium, potassium, magnesium, More preferably, one or more inorganic oxides containing an element selected from calcium, iron, zinc, boron, aluminum and silicon, at least alkali metal oxides, group 2 element oxides, aluminum oxide, boron oxide and silicon oxide Even more preferred are those containing one or more selected from

Specific examples of inorganic compounds include sodium oxide, potassium oxide, magnesium oxide, barium oxide, calcium oxide, zinc oxide, copper oxide, aluminum oxide, iron oxide, silicon oxide, aluminosilicate, aluminoborosilicate, and barium borosilicate. can be mentioned. A composite oxide obtained by combining inorganic oxides may also be used.

The inorganic oxide hollow particles may be commercially available or synthetically produced. The inorganic oxide hollow particles can be produced by a known method without any particular limitation. For example, a sol-gel method and a spray pyrolysis method can be mentioned. For the production of inorganic oxide hollow particles by the sol-gel method, for example, it is possible to refer to JP-A-2015-044987 and JP-A-2013-193950. For the production of particles, for example, JP-A-2003-019427 and JP-A-2013-220967 can be referred to.

(First step)
In this step, the inorganic oxide hollow particles are heated to a temperature within the range of −500° C.±150° C. relative to the melting point of the hollow particles. Thereby, sufficient heat is supplied to the particle surface, and the density can be increased. The melting point can be measured by differential thermal analysis using a thermogravimetric differential thermal analyzer (TG-DTA).
For example, when inorganic oxide hollow particles having a melting point of 1100° C. are used in this step, the heating temperature is set within the temperature range of 450 to 750° C. [(1100° C.-500° C.)±150° C.], and the inorganic oxidation Heat the hollow particles. If the set temperature is higher than the above upper limit, excessive heat accumulates on the surface of the particles, causing them to shrink and the hollowness to decrease. On the other hand, if the set temperature is lower than the above-described lower limit, sufficient heat is not supplied to the particle surface, making it difficult to densify the particles, so that the effect of improving the water resistance is not observed. From this point of view, the heating temperature is preferably within the range of −500° C.±100° C. with respect to the melting point of the inorganic oxide hollow particles.

A method for heating the inorganic oxide hollow particles is not particularly limited as long as the inorganic oxide hollow particles can be heated to a predetermined temperature. For example, the inorganic oxide hollow particles may be placed in a crucible and heated in a heating device maintained at a predetermined temperature.
The heating device is not particularly limited as long as it can withstand the heating temperature, and examples thereof include an electric furnace, a gas furnace, and an oil furnace.
Heating may be performed at normal pressure, and pressurization or vacuum is not required.
The atmosphere during heating may be an air atmosphere, an inert gas atmosphere, or an atmosphere of a mixed gas of these. Inert gases include, for example, nitrogen, helium, and argon.

If the heating time is too short, sufficient heat will not be supplied to the particle surface and densification will be difficult, so that the effect of improving the water resistance tends to be insufficient. Therefore, the heating time is preferably 15 minutes or longer, more preferably 20 minutes or longer, and even more preferably 25 minutes or longer. On the other hand, if the heating time is too long, excessive heat accumulates on the surface of the particles, shrinking the particles, and the hollowness tends to decrease. Therefore, the heating time is preferably 60 minutes or less, more preferably 50 minutes or less, and even more preferably 40 minutes or less.

(Second step)
In this step, the inorganic oxide hollow particles after heating are heated to a temperature of 1/2±150° C. of the heating temperature set in the first step, at an average cooling rate of 1° C./min or more and 28° C./min or less. Slowly cool. As a result, the state in which the particle surface is densified can be stably maintained. As a result, when the inorganic oxide hollow particles come into contact with water, elution of ion components from the particle surface is suppressed, and water resistance can be imparted to the inorganic oxide hollow particles.
For example, when the inorganic oxide hollow particles are heated at 500° C. in the first step, they are slowly cooled to a temperature of 100 to 400° C. [(500° C./2)±150° C.] in this step. If the target temperature after slow cooling is set to a temperature lower than 1/2 ± 150 ° C, the accumulated temperature (° C. min) becomes excessive, excessive heat accumulates on the particle surface and shrinks, resulting in a hollow rate. become smaller. On the other hand, if the target temperature after slow cooling is set to a temperature higher than 1/2 ± 150 ° C. of the heating temperature, the accumulated temperature (° C. min) is insufficient and sufficient heat is not supplied, making it difficult to densify. The effect of improving water resistance cannot be obtained. From this point of view, it is preferable to set the temperature of the second step within a range of 1/2±100° C. of the heating temperature.

In this step, the inorganic oxide hollow particles are slowly cooled at a predetermined average cooling rate. It can be calculated by the following formula based on the set temperature of the first step, the set temperature of the second step, and the time required for temperature decrease.

Average slow cooling rate (°C/min) = (AB)/C
[In the formula, A indicates the set temperature (° C.) for the first step, B indicates the set temperature (° C.) for the second step, and C indicates the set temperature (° C.) for the first step. The time (minutes) required to reach the set temperature (°C) of the second step is shown. ]

For example, when the inorganic oxide hollow particles are heated at 500° C. in the first step and slowly cooled to 350° C. over 30 minutes in this step, the average slow cooling rate is 5° C./min. [(500° C.-350° C.)/30 minutes].

If the average cooling rate is too fast, the accumulated temperature (° C.·min) is insufficient and sufficient heat is not supplied, making it difficult to densify, resulting in an insufficient improvement in water resistance. Therefore, the average cooling rate is preferably 1° C./min or more and 25° C./min or less, more preferably 1° C./min or more and 20° C./min or less, and even more preferably 1° C./min or more and 15° C./min or less.

The slow cooling method of the inorganic oxide hollow particles is not particularly limited. , the temperature of the heating device and the cooling time may be set so that the set temperature of the first step reaches the set temperature of the second step.
Then, when the set temperature of the second step is reached, the inorganic oxide hollow particles are taken out from the heating device and allowed to cool to room temperature. For example, the taken-out inorganic oxide hollow particles can be stored in a desiccator until the temperature of the inorganic oxide hollow particles reaches room temperature.

The water-resistant inorganic oxide hollow particles obtained by the production method of the present invention can have the properties described below for the water-resistant inorganic oxide hollow particles.

[Water-resistant inorganic oxide hollow particles]
The water-resistant inorganic oxide hollow particles of the present invention have the property that ion components are less likely to elute from the particle surface even when immersed in water.
Pure water has a very low electrical conductivity because it hardly conducts electricity. However, when the inorganic oxide hollow particles are immersed in water, ionic components are eluted from the particle surfaces, the amount of ions contained in water increases, and the electrical conductivity increases. Thus, since the ion elution amount is correlated with the electrical conductivity, it can be judged that the water resistance is excellent if the increase in the electrical conductivity is suppressed when the inorganic oxide hollow particles are immersed in water.
Specifically, when the electrical conductivity is measured by the following method, it can be suppressed to 8.5 mS/m or less. From the viewpoint of improving water resistance, the electrical conductivity is preferably 8.0 mS/m or less, more preferably 7.5 mS/m or less, and even more preferably 7.0 mS/m or less. The electrical conductivity can be measured using an electrical conductivity meter.

(Measurement of electrical conductivity)
Inorganic oxide hollow particles and distilled water are mixed in a glass beaker at a liquid-solid ratio of 33:1 (wt %), and the mixture is boiled for 5 minutes. After cooling the mixture to 25° C., the electrical conductivity of the mixture is measured.

Moreover, the water-resistant inorganic oxide hollow particles of the present invention have a sufficient hollowness. The hollowness of the water-resistant inorganic oxide hollow particles of the present invention is usually 70% or more, preferably 75% or more. The hollowness can be calculated from the apparent density and the true density by the following formula.

Hollow ratio = (true density - apparent density) x 100/true density

The water-resistant inorganic oxide hollow particles of the present invention generally have an average particle size of 0.5 to 50 μm, preferably 0.5 to 20 μm, more preferably 1 to 10 μm. Here, the "average particle size" as used herein means the particle size (d50) corresponding to ₅₀ % of the cumulative distribution curve when the particle size distribution of the sample is created on a volume basis in accordance with JIS R 1629. means. As a particle size distribution measuring device, for example, Microtrac (manufactured by Nikkiso Co., Ltd.) can be used.

The thickness of the outer shell portion of the surface-coated inorganic oxide hollow particles of the present invention is usually 50 nm to 1 μm, preferably 50 to 500 nm. By setting the thickness of the outer shell portion in such a manner, the hollow portion is sufficiently secured, so that excellent heat insulating properties, heat shielding properties, and dielectric properties can be exhibited. The thickness of the outer shell can be measured from a transmission electron microscope (TEM) image.

The water-resistant inorganic oxide hollow particles of the present invention can be applied, for example, to heat-insulating materials, heat-shielding materials, catalyst carriers, building materials, and electronic materials. Application to electronic materials is particularly preferred.

The water-resistant inorganic oxide hollow particles of the present invention can be produced by an appropriate method as long as they have the properties described above. can be manufactured.

[Method for improving water resistance of inorganic oxide hollow particles]
The method for improving the water resistance of inorganic oxide hollow particles of the present invention is characterized by including a first step and a second step, like the method for producing water-resistant inorganic oxide hollow particles of the present invention. Further, the method for improving water resistance of the present invention may include a preparatory step like the manufacturing method described above. The specific configurations of the preparation process, the first process, and the second process are as described above.

EXAMPLES The embodiments of the present invention will now be described more specifically with reference to Examples. However, the present invention is not limited to the following examples.

1. Measurement of Hollowness Ratio Acupic (manufactured by Shimadzu Corporation) was used as a dry automatic densitometer to measure the apparent density and true density of the inorganic oxide hollow particles, which were calculated according to the following formula. The true density was measured by a dry automatic densitometer after heating at the melting point or above for 6 hours in a box-shaped electric furnace to remove voids, followed by cooling.

Hollow ratio (%) = (true density - apparent density) x 100/true density

2. Measurement of Melting Point Differential thermal analysis of the inorganic oxide hollow particles was performed using a thermogravimetric differential thermal analyzer (TG-DTA), and the melting point was determined from the endothermic peak in the obtained DTA curve.

3. Measurement of Electrical Conductivity Inorganic oxide hollow particles and distilled water were mixed in a glass beaker at a liquid-solid ratio of 33:1 (wt %), and the mixture was heated with a heater and boiled for 5 minutes. After that, the mixed liquid was cooled to 25° C., and the electric conductivity of the mixed liquid was measured using an electric conductivity meter (manufactured by HORIBA).

Production example 1
The raw material inorganic compound-containing aqueous solution was put into the reaction vessel, and the raw material inorganic compound-containing aqueous solution was stirred for 3 hours. At this time, the liquid temperature of the aqueous solution was adjusted to 5°C using a chiller. The raw material inorganic compound-containing aqueous solution contained 0.045 mol/L of calcium nitrate (manufactured by Osaki Kogyo), 0.091 mol/L of aluminum nitrate (manufactured by Hikoh Kagaku Kogyo), and 0.04 mol/L of tetraethyl orthosilicate (manufactured by Tama Kagaku Kogyo). 215 mol/L and boric acid (Yoneyama Chemical Co., Ltd.) were dissolved in tap water so as to have a concentration of 0.270 mol/L. Subsequently, the raw material inorganic compound-containing aqueous solution was fed to a three-fluid nozzle, and the raw material inorganic compound-containing aqueous solution was sprayed from the nozzle into the spray pyrolysis furnace and fired at 1150° C. to recover inorganic oxide hollow particles. The obtained inorganic oxide hollow particles had a melting point of 1100°C.

Comparative example 1
The hollowness and electrical conductivity of the inorganic oxide hollow particles obtained in Production Example 1 were measured. Table 1 shows the results.

Example 1
3 g of the inorganic oxide hollow particles obtained in Production Example 1 were placed in a 30 mL alumina crucible and heated at 500° C. for 30 minutes in a desktop high-speed heating electric furnace. Next, the inorganic oxide hollow particles after heating were gradually cooled to 350° C. at an average cooling rate of 1° C./min in the electric furnace. Then, when it reached 350°C, it was taken out from the electric furnace and allowed to cool to room temperature in a desiccator. The average cooling rate was controlled by setting the temperature of the electric furnace and the cooling time so that the temperature of the heating device reached 500° C. to 350° C. in 150 minutes. Then, the hollowness and electrical conductivity of the cooled inorganic oxide hollow particles were measured. Table 1 shows the results.

Examples 2-17 and Comparative Examples 2-11
The inorganic oxide hollow particles were heated at the temperature and time shown in Table 1, and the inorganic oxide hollow particles after heating were gradually cooled to the temperature shown in Table 1 at the average cooling rate shown in Table 1. The same procedure as in Example 1 was carried out. Then, the hollowness and electrical conductivity of the cooled inorganic oxide hollow particles were measured. Table 1 shows the results.

Table 1 shows the following.
In the first step, when the inorganic oxide hollow particles are heated at a temperature of 400° C., which is lower than −500° C.±150° C. relative to the melting point (1100° C.) of the hollow particles, sufficient heat is supplied to the particle surfaces. Since it was hard to densify because it was hard to densify, the effect of improving water resistance was not observed (Comparative Examples 2 to 5).
On the other hand, when the particles were heated at a temperature of 800° C., which is higher than −500° C.±150° C. with respect to the melting point, excessive heat was accumulated on the particle surfaces and the hollowness decreased (Comparative Example 6).
In the second step, when slowly cooling the inorganic oxide hollow particles after heating, if the target temperature after slow cooling is set to a temperature higher than 1/2 ± 150 ° C. of the heating temperature, the integrated temperature (° C.・min) was insufficient, and sufficient heat was not supplied to the particle surface, making it difficult to densify the particles, so no improvement in water resistance was observed (Comparative Example 7).
On the other hand, if the target temperature after slow cooling is lower than 1/2 ± 150 ° C., the accumulated temperature (° C. min) becomes excessive, excessive heat accumulates on the particle surface, and the hollowness decreases. (Comparative Example 8).
Furthermore, in the second step, if the inorganic oxide hollow particles after heating are quenched at an average cooling rate of 30° C./min, the accumulated temperature (° C. min) is insufficient and sufficient heat is not supplied to the particle surface. Since it was difficult to densify, no improvement in water resistance was observed (Comparative Examples 9 to 11).
On the other hand, the inorganic oxide hollow particles are heated at a temperature within the range of −500° C.±150° C. with respect to the melting point (1100° C.) of the hollow particles, and then the inorganic oxide hollow particles after heating are heated. Slow cooling at an average cooling rate of 1°C/min or more and 28°C/min or less to a temperature of 1/2 ± 150°C of the temperature makes the particle surface densified and stable, and the ion component is removed from the particle surface. Elution was suppressed and water resistance was improved (Examples 1 to 17).

Claims (6)

a first step of heating the inorganic oxide hollow particles at a temperature within the range of −500° C.±150° C. with respect to the melting point of the hollow particles;
Water resistant, including a second step of slowly cooling the heated inorganic oxide hollow particles to a temperature of 1/2 ± 150 ° C. of the heating temperature at an average cooling rate of 1 ° C./min or more and 28 ° C./min or less a method for producing organic inorganic oxide hollow particles. 2. The method for producing water-resistant inorganic oxide hollow particles according to claim 1, wherein the heating time in the first step is 15 minutes or longer. Inorganic oxide hollow particles are periodic table group 1 elements, periodic table group 2 elements, periodic table group 4 elements, periodic table group 8 elements, periodic table group 9 elements, periodic table group 10 elements, period Consists of an inorganic oxide containing one or more elements selected from Group 11 elements of the periodic table, Group 12 elements of the periodic table, Group 13 elements of the periodic table, Group 14 elements of the periodic table and Group 15 elements of the periodic table The method for producing water-resistant inorganic oxide hollow particles according to claim 1 or 2, wherein the water-resistant inorganic oxide hollow particles are a first step of heating the inorganic oxide hollow particles at a temperature within the range of −500° C.±150° C. with respect to the melting point of the hollow particles;
a second step of gradually cooling the heated inorganic oxide hollow particles to a temperature of 1/2 ± 150 ° C. of the heating temperature at an average cooling rate of 1 ° C./min or more and 28 ° C./min or less; A method for improving the water resistance of oxide hollow particles. Water-resistant inorganic oxide hollow particles having an electrical conductivity of 8.5 mS/m or less as measured by the following method.
(Measurement of electrical conductivity)
Inorganic oxide hollow particles and distilled water are mixed in a glass beaker at a liquid-solid ratio of 33:1 (wt %), and the mixture is boiled for 5 minutes. After cooling the mixture to 25° C., the electrical conductivity of the mixture is measured. 6. The water-resistant inorganic oxide hollow particles according to claim 5, having a hollowness of 70% or more.