JP7611742B2 - Inorganic oxide micro hollow particles - Google Patents

Description

The present invention relates to inorganic oxide micro-hollow particles.

Since inorganic oxide hollow particles have cavities surrounded by an outer shell, they are lighter, have lower thermal conductivity, and have better thermal stability than non-hollow particles, and are widely used as heat insulating materials, heat shielding materials, catalyst carriers, building materials, electronic materials, etc. In recent years, electronic devices have rapidly become more compact and more powerful, and there is a high demand for thinner coatings, resin products, and film products used in electronic devices, and the inorganic oxide hollow particles used in these products are required to be small and have a uniform particle size.

Conventionally, hollow glass microspheres having an average particle size of 5 to 50 μm, with 80% or more of the total particles being 5 to 50 μm, have been known as small inorganic oxide hollow particles with a uniform particle size (Patent Document 1). In addition, there has been a report of hollow glass microspheres having an average particle size (volume basis ₎ of 15 μm or less, a maximum particle size of 45 μm or less, a particle density of 0.5 g/cm3 ^or less, a particle size gradient calculated by ( _d10 - _d90 )/ _d50 of 2.0 or less, and a _B2O3 content of 9.0 to 20.0 mass% in the glass (Patent Document 2).

Japanese Patent Application Publication No. 9-20526 International Publication No. 2001/2314

However, the inorganic oxide hollow particles of Patent Document 1 have a particle size of 5 to 50 μm in a ratio of about 80%, so there is room for improvement in terms of particle size uniformity. In addition, if the particle size uniformity is low, there is also a problem that the particles are easily peeled off from the substrate when mixed with a binder to form a coating film. On the other hand, the inorganic oxide hollow particles of Patent Document 2 have a large maximum particle size of 15 μm and a low yield of 30 to 45 mass%, even though only water-suspended matter is selected by classification in the manufacturing process. The causes of this are presumed to be that fine particles tend to aggregate during classification, causing clogging, and that the particles are broken when the aggregates are broken down due to their low strength. In this case, it is possible to increase the film thickness of the inorganic oxide hollow particles to improve the particle strength, but the occupancy rate of the air layer decreases as the hollowness decreases, so that a decrease in the insulation performance, dielectric properties, etc. is inevitable.
An object of the present invention is to provide inorganic oxide fine hollow particles which have a uniform particle size, excellent particle strength, and are unlikely to peel off when a coating film is formed.

As a result of investigations conducted in light of the above problems, the inventors have found that hollow particles with a small particle size that contain a specific inorganic oxide in a specific ratio, have a single-peaked particle size distribution, and have a small particle size gradient calculated based on the specific particle size, have excellent particle strength, and are less likely to peel off when a coating film is formed.

That is, the present invention provides the following [1] to [8].
[1] An inorganic oxide fine hollow particle having a shell that defines a hollow space,
The content of alkali metal oxide is 2 mass% or less,
The calcium oxide content is 5% by mass or less,
The total content of silicon oxide, boron oxide and aluminum oxide is 50 mass% or more,
The particle size distribution is monomodal and satisfies the following formula (1):
Particle size gradient = ( _D90 - _D10 ) / _D50 (1)
(In the formula, _D90 indicates a cumulative 90% particle size in the volume-based particle size distribution, _D10 indicates a cumulative 10% particle size in the volume-based particle size distribution, and _D50 indicates a cumulative 50% particle size in the volume-based particle size distribution.)
The particle size gradient calculated by is 2 or less.
Inorganic oxide micro hollow particles.
[2] The inorganic oxide fine hollow particles according to the above [1], having a _D100 of 15 μm or less.
[3] The inorganic oxide fine hollow particles according to the above [1] or [2], having a D ₅₀ of 0.5 to 5 μm.
[4] The inorganic oxide microhollow particles according to any one of [1] to [3] above, wherein the silicon oxide content is 20 to 70 mass %.
[5] The inorganic oxide fine hollow particles according to any one of [1] to [4] above, wherein the content of boron oxide is 15 to 35 mass %.
[6] The inorganic oxide microhollow particles according to any one of [1] to [5] above, wherein the aluminum oxide content is 5 to 20 mass %.
[7] The inorganic oxide microhollow particles according to any one of [1] to [6], wherein when a copper plate-attached test piece prepared by the following method is measured in accordance with JIS K 6854-1, the 90 degree peel adhesion strength of the resin layer from the copper plate exceeds 10 N/m.
[Preparation of test pieces with copper plates]
5 g of dried powder of inorganic oxide micro hollow particles is added to and mixed with an epoxy resin liquid containing 30 g of a mixture of liquid bisphenol A type epoxy resin and liquid bisphenol F type epoxy resin (average epoxy equivalent 165 g/mol), 20 g of liquid phenol novolac (hydroxyl equivalent 135 g/mol), and 1 g of triphenylphosphine. The resin mixture is applied to a flexible adherend bent at a right angle in a width of 25 mm, length of 150 mm, and thickness of 1 mm, and the adherend is attached to a horizontal copper plate, and a manual hydraulic press is used to apply pressure of 1 MPa for 10 minutes to bond the material. The material is then dried and cured in a dryer at 80°C for 12 hours to prepare a test piece.
[8] A resin composition comprising the inorganic oxide fine hollow particles according to any one of [1] to [7].

According to the present invention, it is possible to provide inorganic oxide hollow particles that not only have a small particle diameter and uniform particle size, but also have excellent particle strength and are difficult to peel off when a coating film is formed. Therefore, the inorganic oxide micro hollow particles of the present invention are useful for various applications such as electronic materials such as wiring circuit boards and semiconductor encapsulants, as well as heat insulating materials, heat shielding materials, catalyst carriers, and building materials.

FIG. 2 is a diagram showing the particle size distribution of the inorganic oxide hollow particles obtained in Example 4 and Comparative Example 1.

In this specification, "hollow particles" refers to particles that have a hollow structure inside and have an outer shell that defines the hollow space, and are different from porous particles that have multiple pores extending from the surface of the particle to the inside. Hollow particles can be clearly distinguished from porous particles by scanning electron microscope (SEM) images.

The inorganic oxide hollow particles of the present invention have an outer shell formed of inorganic oxides including alkali metal oxides, calcium oxide, silicon oxide, boron oxide and aluminum oxide. By forming the outer shell with such inorganic oxides, the hollow particles have a small particle diameter, a uniform particle size, excellent particle strength, and are difficult to peel off when a coating film is formed. From this viewpoint, it is preferable that the outer shell is non-porous. The fact that the particle surface is non-porous can be confirmed by scanning electron microscope (SEM) images or by floating on water.
In this specification, the content of each of the inorganic oxides constituting the hollow particles is a value obtained by measuring the amount of each of the inorganic oxides by fluorescent X-ray analysis in terms of oxide and calculating the chemical composition.

Examples of alkali metal oxides include Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O. Among them, from the viewpoints of miniaturization, uniformity of particle size, particle strength, and improvement of peel strength of the coating film, one or more selected from Li ₂ O, Na ₂ O, and K ₂ O are preferred, and Na ₂ O is more preferred.
As the calcium oxide, CaO is preferred from the viewpoints of miniaturization, uniformity of particle size, particle strength, and improvement of peel strength of the coating film.
As the silicon oxide, _SiO2 is preferred from the viewpoints of miniaturization, uniform particle size, and improvement of particle strength and peel strength of the coating film.
As the boron oxide, B ₂ O ₃ is preferred from the viewpoints of miniaturization, uniformity of particle size, and improvement of particle strength and peel strength of the coating film.
As the aluminum oxide, Al ₂ O ₃ is preferred from the viewpoints of miniaturization, uniformity of particle size, and improvement of particle strength and peel strength of the coating film.

The content of the alkali metal oxide is 2% by mass or less, but from the viewpoints of miniaturization, uniformity of particle size, and improvement of particle strength and peel strength of the coating film, it is preferably 1.8% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.3% by mass or less. The lower limit of the content of the alkali metal oxide may be 0% by mass, but from the viewpoint of lowering the firing temperature due to lowering the melting point of the inorganic oxide, it is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more.
The content of calcium oxide is preferably 5% by mass or less from the viewpoints of miniaturization, uniformity of particle size, and improvement of particle strength and peel strength of the coating film. The lower limit of the calcium oxide content may be 0% by mass, but from the viewpoint of lowering the firing temperature due to lowering of the melting point of the inorganic oxide, it is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more.

The total content of silicon oxide, boron oxide and aluminum oxide is 50% by mass or more, but from the viewpoints of miniaturization, uniform particle size, and improved particle strength and peel strength of the coating film, it is preferably 55% by mass or more, more preferably 65% by mass or more, and even more preferably 70% by mass or more. The upper limit of this total content is preferably 93% by mass or less, from the viewpoint of lowering the firing temperature due to the lowering of the melting point of the inorganic oxide.

The silicon oxide, boron oxide and aluminum oxide may contain one or more of these three types, but it is preferable to contain all three types from the viewpoints of miniaturization, uniform particle size, particle strength and improved peel strength of the coating film.
The content of silicon oxide is preferably 20 to 70 mass%, more preferably 25 to 65 mass%, even more preferably 30 to 60 mass%, and particularly preferably 40 to 55 mass%, from the viewpoints of miniaturization, uniform particle size, and improvement of particle strength and peel strength of the coating film.
The content of boron oxide is preferably 15 to 35 mass%, more preferably 16 to 34 mass%, even more preferably 17 to 33 mass%, and particularly preferably 18 to 32 mass%, from the viewpoints of miniaturization, uniform particle size, and improvement of particle strength and peel strength of the coating film.
The content of aluminum oxide is preferably 5 to 20 mass %, more preferably 5 to 19 mass %, and even more preferably 5 to 18 mass %, from the viewpoints of miniaturization, uniform particle size, and improvement of particle strength and peel strength of the coating film.

In particular, controlling the calcium oxide content contributes most to miniaturization, uniform particle size, and improved particle strength and peel strength of the coating film.

The inorganic oxide hollow particles of the present invention may contain an inorganic oxide other than those mentioned above as the inorganic oxide constituting the outer shell, for example, an oxide of a Group 2 element other than calcium oxide, or an oxide of a Group 4 element.
Examples of Group 2 element oxides other than calcium oxide include MgO, SrO, BaO, and RaO.
Examples of Group 4 element oxides include TiO ₂ , ZrO ₂ , and HfO ₂ .
The content of these inorganic oxides can be appropriately selected within a range that does not impair the effects of the present invention, and the preferred embodiments are as follows.
The content of the Group 2 element oxide other than calcium oxide is preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less, from the viewpoint of improving the particle strength and the peel strength of the coating film.
The content of the Group 4 element oxide is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, from the viewpoint of improving the particle strength and the peel strength of the coating film.
The lower limit of the content of the Group 2 element oxide other than calcium oxide and the Group 4 element oxide may be 0 mass %.

The inorganic oxide hollow particles of the present invention are characterized by being minute. More specifically, the particle size distribution can have the following characteristics. Here, in this specification, "particle size distribution" refers to a volume-based particle size distribution measured in accordance with JIS R 1629 "Method for measuring particle size distribution of fine ceramic raw materials by laser diffraction/scattering method". The particle size distribution is represented by a distribution curve with the horizontal axis representing particle size (μm) and the vertical axis representing the volume-based frequency (%). In addition, for example, Microtrac (manufactured by Nikkiso Co., Ltd.) can be used as a particle size distribution measuring device using the laser diffraction/scattering method.
The cumulative 100% particle size ( _D100 ) in the volumetric particle size distribution is preferably 15 μm or less, more preferably 13 μm or less, from the viewpoints of miniaturization, particle strength, and improved peel strength of the coating film. The lower limit of _D100 is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 7 μm or more, from the viewpoints of improved heat insulating performance and dielectric properties.
The cumulative 10% particle size ( _D10 ) in the volumetric particle size distribution is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more, from the viewpoint of uniform particle size and improving the peel strength of the coating film. The upper limit of _D10 is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.5 μm or less, from the viewpoint of improving the particle strength.
The cumulative 50% particle size in the volume-based particle size distribution, i.e., the average particle size ( _D50 ), is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of miniaturization and uniform particle size. The upper limit of _D50 is 5 μm or less, more preferably 4.5 μm or less, and even more preferably 4.0 μm or less, from the viewpoint of improving particle strength.
The cumulative 90% particle size ( _D90 ) in the volume-based particle size distribution is preferably 3.0 μm or more, more preferably 3.5 μm or more, from the viewpoint of miniaturization and uniform particle size. The upper limit of _D90 is 10 μm or less, more preferably 9.5 μm or less, from the viewpoint of improving particle strength.

The inorganic oxide hollow particles of the present invention are also characterized in that they have a unimodal particle size distribution and a sharp shape.
An example of the particle size distribution of the inorganic oxide hollow particles of the present invention is shown in Figure 1. In the particle size distribution of the inorganic oxide hollow particles, the distribution is generally broad with a large particle size gradient as shown in Comparative Example 1 in Figure 1. In contrast, the inorganic oxide hollow particles of the present invention have a particle size distribution in which particles with large diameters are excluded and a single peak with a sharp shape is composed of particles with small diameters as shown in Example 4 in Figure 1. As described above, the inorganic oxide hollow particles of the present invention are composed of fine particles and have a uniform particle size, so that the particle strength is improved, and when a coating film is formed using a binder, the particles are uniformly dispersed in the binder and the binder is sufficiently filled between the particles, resulting in improved adhesion of the coating film and less peeling.

Furthermore, as described above, the inorganic oxide hollow particles of the present invention are characterized in that they have a sharp particle size distribution and a particle size gradient calculated by the following formula (1) of 2 or less.

Particle size gradient = ( _D90 - _D10 ) / _D50 (1)

(In the formula, _D90 indicates a cumulative 90% particle size in the volume-based particle size distribution, _D10 indicates a cumulative 10% particle size in the volume-based particle size distribution, and _D50 indicates a cumulative 50% particle size in the volume-based particle size distribution.)

From the viewpoint of uniform particle size and further improving the peel strength of the coating film, the particle size gradient is preferably 1.8 or less, more preferably 1.7 or less, and even more preferably 1.6 or less. The lower limit of the particle size gradient is preferably 1.0 or more, more preferably 1.1 or more, and even more preferably 1.2 or more, from the viewpoint of improving the filling property during resin kneading.

The thickness of the outer shell of the inorganic oxide hollow particles of the present invention is preferably 50 nm or more, more preferably 100 nm or more, and preferably 1 μm or less, more preferably 500 nm or less. By setting the thickness of the outer shell within the above range, the hollow portion can be sufficiently secured without impairing the particle strength, and therefore the heat insulating performance, dielectric properties, etc. can be improved. The thickness of the outer shell can be measured from a scanning electron microscope (SEM) image.

The hollow ratio of the inorganic oxide hollow particles of the present invention is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more, from the viewpoint of improving the heat insulating performance and dielectric properties. The upper limit of the hollow ratio is preferably 95% or less, and even more preferably 90% or less, from the viewpoint of ensuring sufficient particle strength. Here, in this specification, the "hollow ratio" is calculated from the apparent density and true density measured by a density meter using the following formula. In addition, the "true density" is measured by a density meter after heating at or above the melting point in a box-type electric furnace for 6 hours and cooling in order to remove the voids. In addition, as the density meter, for example, a dry automatic density meter Accupic (Shimadzu Corporation) can be used.

Hollow ratio = (1 - apparent density ÷ true density) x 100

The shape of the inorganic oxide hollow particles of the present invention may be any of a perfect sphere, an oblate ellipsoid, an oblate ellipsoid, and an approximately spherical shape such as a sphere. From the viewpoint of improving the dielectric properties, the average circularity is preferably 0.85 or more, and more preferably 0.90 or more. Here, the "circularity" is expressed as A/B, where the projected area (A) and the perimeter (PM) of a particle are measured from a scanning electron microscope photograph, and the area of a perfect circle relative to the perimeter (PM) is (B). Therefore, the perimeter and area of a perfect circle having the same perimeter as the perimeter (PM) of the sample particle are PM=2πr and B= ^πr2 , respectively, so that B=π×(PM/2π) ² , and the circularity of this particle is calculated as circularity=A/B=A×4π/(PM) ² . The circularity of 100 particles is measured, and the average value is taken as the average circularity.

The particle strength of the inorganic oxide hollow particles of the present invention is preferably 18 MPa or more, more preferably 20 MPa or more, and even more preferably 23 MPa or more, from the viewpoint of ensuring sufficient strength. Here, in this specification, "particle strength" refers to the particle strength when the inorganic oxide phosphor hollow particle residual rate is 50% when pressure is applied to the hollow particles with a pressure molding press. Specifically, it can be measured by the method described in the examples below.

The inorganic oxide hollow particles of the present invention can also provide a 90 degree peel adhesion strength of the resin layer from the copper plate, preferably exceeding 10 N/m, when measured in accordance with JIS K 6854-1 for a substrate with a copper plate prepared using the inorganic oxide hollow particles of the present invention. As described above, the inorganic oxide micro hollow particles of the present invention are small and have a uniform particle size, so that when the particles are dispersed in a binder, the binder is sufficiently filled between the particles, enhancing the adhesion of the coating film and making it difficult to peel off. The method for preparing the substrate with a copper plate follows the method described in the examples below.

The inorganic oxide hollow particles of the present invention can be applied to heat insulating materials, heat shielding materials, catalyst carriers, building materials, electronic materials, etc. In particular, the inorganic oxide hollow particles of the present invention are fine particles with uniform particle size and excellent particle strength and coating peel strength, so they are useful for electronic materials, particularly wiring circuit boards, semiconductor encapsulants, etc.

In addition, the inorganic oxide hollow particles of the present invention are very small particles and therefore have excellent dispersibility in a medium.
The medium is not particularly limited, but examples thereof include resin, paint, rubber, and solvent, which are likely to provide the effects of the present invention.
When a resin is used as the medium, it can be used as a resin composition for forming electronic materials, such as wiring circuit boards and semiconductor encapsulants. The resin is not particularly limited as long as it is generally used in the fields of wiring circuits and semiconductor encapsulants.

The content of inorganic oxide hollow particles in the resin composition can be appropriately selected depending on the application, but is usually 1 to 97% by mass, preferably 5 to 60% by mass, and more preferably 15 to 40% by mass.

The resin composition may be in the form of a varnish in which it is dissolved or dispersed in an organic solvent, and the varnish may be impregnated into a substrate to form a prepreg.
The solids (non-volatile content) concentration in the varnish can be appropriately selected depending on the application, but is usually 5 to 80% by mass, and preferably 10 to 70% by mass.
The substrate to be impregnated with the varnish is not particularly limited, and examples thereof include inorganic fibers, organic fibers, carbon fibers, etc. The impregnation can be carried out by immersion (dipping) or coating.

Furthermore, for example, a wiring circuit board can be manufactured by applying the above-mentioned varnish to a metal foil substrate, heating and curing the varnish to form a resin layer on the metal substrate, and then removing the metal by etching to form a conductor pattern. When applying the varnish to the substrate, any suitable application method can be used, such as spraying, roll coating, rotary coating (spin coating), slit die coating (slit coating), or bar coating.

The method for mixing the medium and the inorganic oxide hollow particles is not particularly limited, but for example, each component may be thoroughly and uniformly stirred and mixed using a mixer or the like, and then kneaded using a mixing roll, extruder, kneader, roll, extruder, or the like. The mixing conditions can be appropriately set depending on the mixing method.

The method for producing the inorganic oxide hollow particles of the present invention is not particularly limited as long as it can produce inorganic oxide hollow particles having the above-mentioned configuration. For example, a method can be mentioned in which a liquid to be sprayed containing a raw material compound is sprayed from a spray device installed in a spray pyrolysis device, and the sprayed droplets (mist) are pyrolyzed.

Examples of raw material compounds include compounds containing one or more elements selected from alkali metals, calcium, silicon, boron, and aluminum as elements that constitute oxides. Such compounds are not particularly limited as long as they are compounds that dissolve in water, and examples include inorganic salts, organic salts, and alkoxides, which may contain one or more elements. Examples of inorganic salts include nitrates, sulfates, carbonates, hydroxides, and halides. Examples of organic salts include formates, acetates, propionates, oxalates, and citrates.

Examples of alkali metal-containing compounds include lithium-containing compounds, sodium-containing compounds, potassium-containing compounds, rubidium-containing compounds, and cesium-containing compounds. Among them, from the viewpoints of miniaturization, uniform particle size, and improvement of particle strength and peel strength of the coating film, one or more selected from lithium-containing compounds, sodium-containing compounds, and potassium-containing compounds are preferred, and sodium-containing compounds are even more preferred. Specific examples of sodium-containing compounds include sodium salts such as sodium nitrate, sodium chloride, sodium hydroxide, sodium sulfate, and sodium borate. Specific examples of alkali metal-containing compounds other than sodium-containing compounds include salts similar to those of sodium-containing compounds.

Examples of calcium-containing compounds include calcium salts, such as calcium nitrate, calcium chloride, calcium hydroxide, calcium formate, calcium acetate, and calcium propionate.
Examples of boron-containing compounds include borates and boric acid. Examples of borates include metaborates such as sodium borate and potassium borate, tetraborates such as sodium tetraborate and potassium tetraborate, and pentaborates such as sodium pentaborate and potassium pentaborate.

Examples of silicon-containing compounds include silicate alkoxides, such as tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetrapropyl orthosilicate (TPOS), and tetrabutoxysilane.
Examples of aluminum-containing compounds include aluminum salts and aluminum alkoxides. Examples of aluminum salts include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum hydroxide, aluminum acetate, and aluminum oxalate. Examples of aluminum alkoxides include aluminum methoxide, aluminum ethoxide, and aluminum isopropoxide.
Examples of silicon and aluminum-containing compounds include aluminosilicates, such as sodium aluminosilicate, potassium aluminosilicate, and calcium aluminosilicate.
Furthermore, a solution in which aluminum oxide or silicon oxide is dispersed in a solvent, or a sol solution of aluminum oxide or silicon oxide can also be used as the raw compound solution.

In the present invention, the raw material compounds may further contain compounds containing elements other than alkali metals, calcium, silicon, boron and aluminum.
Such compounds are not particularly limited as long as they are water-soluble metal compounds, and include, for example, Group 2 element-containing compounds other than calcium-containing compounds, and Group 4 element-containing compounds. Examples of Group 2 element-containing compounds other than calcium-containing compounds include magnesium salts, strontium salts, barium salts, and radium salts. Examples of Group 4 element-containing compounds include titanium salts, zirconium salts, and hafnium salts. Other examples include zinc salts and yttrium salts. These compounds can be used alone or in combination. Examples of salts of these metals include inorganic salts, organic salts, and alkoxides, and specific examples thereof are as described above.

Among these raw material compounds, it is preferable to use one or more selected from alkali metal salts, calcium salts, silicate alkoxides, aluminum alkoxides, aluminosilicates, borates, and boron, and, if necessary, one or more selected from magnesium salts, strontium salts, barium salts, titanium salts, and zirconium salts, in order to easily obtain the effects of the present invention.

The liquid to be sprayed can be prepared by mixing the raw material compounds with water or an organic solvent such as ethanol. The mixing ratio of the raw material compounds can be adjusted appropriately according to the type of raw material compounds so as to obtain inorganic oxide micro-hollow particles of the above-mentioned composition.

The concentration of the raw material compounds in the liquid to be sprayed is preferably 0.01 mol/L to 2.0 mol/L, and more preferably 0.1 mol/L to 1.0 mol/L, as the total amount of each element.

The spray pyrolysis device preferably has a pyrolysis furnace with a vertical cylindrical shape, and the size of the pyrolysis furnace can be appropriately selected depending on the production scale.

Examples of spray devices include fluid nozzles such as two-fluid nozzles, three-fluid nozzles, and four-fluid nozzles. Fluid nozzles can be either an internal mixing method in which the gas and raw material solution are mixed inside the nozzle, or an external mixing method in which the gas and raw material solution are mixed outside the nozzle, and either method can be used. Gases that can be supplied to the nozzle include, for example, air, and inert gases such as nitrogen and argon. Among these, air is preferred from the viewpoint of economy. One or more spray devices can be installed.

The flow rate of the liquid to be sprayed is usually 1 to 100 L/h, preferably 3 to 80 L/h, and more preferably 5 to 60 L/h.

The droplets sprayed from the spray device are heated by a heater in the pyrolysis furnace to form a film containing an inorganic compound, and the film acts as a starting point for the formation of hollow inorganic oxide particles.
The droplet ejection speed is usually 1 to 50 m/s, preferably 5 to 35 m/s, and more preferably 10 to 20 m/s.

Examples of the heating device include a combustion burner, a hot air heater, an electric heater, etc. One or more heating devices can be installed. Any of the combustion burners, hot air heaters, and electric heaters that are generally available on the market can be used.
The temperature of the heating device is preferably 400 to 1800° C., more preferably 600 to 1500° C., even more preferably 700 to 1400° C., and even more preferably 800 to 1200° C. At such a temperature, pyrolysis is sufficient, and the particles are less likely to aggregate when discharged outside the pyrolysis furnace.

The inorganic oxide hollow particles produced by the pyrolysis reaction are collected downstream of the pyrolysis furnace. The inorganic oxide hollow particles can be collected using a powder collection device that uses a high-performance cyclone powder collection machine or a bag filter.

The following examples are provided to further explain the embodiments of the present invention. However, the present invention is not limited to the following examples.

1. Analysis of Chemical Composition The inorganic oxide hollow particles were molded using a press to prepare briquettes, and the chemical components of the briquettes were measured in terms of oxides using an X-ray fluorescence analyzer (ZSX primus II, manufactured by Rigaku Corporation) to calculate the chemical components.

2. Measurement of particle size distribution and calculation of particle size gradient Using a particle size distribution measuring device (MT3000II, manufactured by Microtrackbell Co., Ltd.), a volume-based particle size distribution was prepared in accordance with JIS R 1629, and _D100 , _D90 , _D50 , and _D10 were obtained, and the particle size gradient was calculated by the following formula (1).

Particle size gradient = ( _D90 - _D10 ) / _D50 (1)

(In the formula, _D90 indicates a cumulative 90% particle size in the volume-based particle size distribution, _D10 indicates a cumulative 10% particle size in the volume-based particle size distribution, and _D50 indicates a cumulative 50% particle size in the volume-based particle size distribution.)

3. Measurement of Particle Strength Particle strength was measured by the following powder pressing method.
(1) Hollow particles and ethanol were mixed in a mass ratio of 4:1 to prepare a sample.
(2) The sample was placed in a pressure molding machine, and a predetermined pressure (10 MPa, 20 MPa, 30 MPa) was applied using a hydraulic press.
(3) The sample was left to stand for one minute while a predetermined pressure was applied.
(4) The sample was removed from the pressure molder and dried at 80° C. for 2 hours.
(5) The density of the hollow particles after compression was measured using a microcompression tester (MCT-510, manufactured by Shimadzu Corporation).

Then, the remaining rate for each given pressure was calculated from the density of the hollow particles before and after pressure application using the following formula, and the pressure at which 50% remained was read from a graph of the remaining rate and applied pressure. The density was measured using the density measuring device described above, and the true density of the hollow shell was measured after heating above the melting point for 6 hours in a box-type electric furnace and then cooling in order to remove voids.

Survival rate P [%] = (1-ρ/y)/ρ×(1/x-1/y)×100

[In the formula, ρ represents the density after compression, y represents the true density of the hollow shell, and x represents the density before compression.]

4. Test for 90 degree peel adhesive strength Test pieces prepared by the method described below were set in a 90 degree peel tester (P90-200N, manufactured by Imada Co., Ltd.), and the 90 degree peel adhesive strength of the resin layer from the copper plate was measured at a tensile speed of 50 mm/min in accordance with JIS K 6854-1:1999, and evaluated according to the following criteria.

[Preparation of test pieces with copper plates]
5 g of dried powder of inorganic oxide micro hollow particles was added and mixed with an epoxy resin liquid containing 30 g of a mixture of liquid bisphenol A type epoxy resin and liquid bisphenol F type epoxy resin (average epoxy equivalent 165 g/mol), 20 g of liquid phenol novolac (hydroxyl equivalent 135 g/mol), and 1 g of triphenylphosphine. The resin mixture was applied to a flexible adherend bent at a right angle with a width of 25 mm, a length of 150 mm, and a thickness of 1 mm, and the adherend was attached to a horizontal copper plate and bonded by applying a pressure of 1 MPa for 10 minutes using a manual hydraulic press. The mixture was then dried and cured in a dryer at 80°C for 12 hours to prepare a test specimen.

[Evaluation Criteria]
Good: 90 degree peel adhesive strength is more than 10 N/m Bad: 90 degree peel adhesive strength is 10 N/m or less

Examples 1 to 6 and Comparative Examples 1 and 2
The raw material compounds (colloidal silica, tetraethyl orthosilicate, aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, calcium nitrate tetrahydrate, boric acid, sodium tetraborate decahydrate) were dissolved in 30 L of distilled water to the molar concentrations shown in Table 1, and the aqueous solution of the raw material compounds was charged into a solution tank. Next, the charged aqueous solution of the raw material compounds was sent to a two-fluid nozzle by a liquid sending pump and sprayed in the form of mist, and heated in a furnace (1000°C). The operating conditions of the two-fluid nozzle were a nozzle air volume of 100 L/min and a liquid sending volume of 67 mL/min. Then, the mixture was quenched by a cooling mechanism installed at the outlet of the reaction zone of the furnace, and then the inorganic oxide hollow particles were collected using a bag filter.

The chemical composition and particle size of the obtained inorganic oxide hollow particles were analyzed, and the particle strength and 90-degree peel adhesion strength were evaluated. The results are shown in Table 2. The particle size distribution of the inorganic oxide hollow particles obtained in Example 4 and Comparative Example 1 is shown in Figure 1.

From Table 2, it can be seen that the inorganic oxide hollow particles of this example not only have a small particle diameter and uniform particle size, but also have excellent particle strength and are not easily peeled off when a resin composition is formed as a coating film.

Claims (5)

An inorganic oxide hollow microparticle having a shell defining a hollow chamber,
The shell is composed of inorganic oxides including alkali metal oxides, magnesium oxide, calcium oxide, silicon oxide, boron oxide, and aluminum oxide;
The content of alkali metal oxide is 0.1% by mass or more and 2% by mass or less,
The magnesium oxide content is 1.2% by mass or more and 9.5% by mass or less,
The calcium oxide content is 0.5% by mass or more and 5% by mass or less,
The silicon oxide content is 20% by mass or more and 70% by mass or less,
The content of boron oxide is 15% by mass or more and 35% by mass or less,
The content of aluminum oxide is 5% by mass or more and 20% by mass or less,
The total content of silicon oxide, boron oxide and aluminum oxide is 70 mass% or more,
The particle size distribution is monomodal and satisfies the following formula (1):
Particle size gradient = ( _D90 - _D10 ) / _D50 (1)
(In the formula, _D90 indicates a cumulative 90% particle size in the volume-based particle size distribution, _D10 indicates a cumulative 10% particle size in the volume-based particle size distribution, and _D50 indicates a cumulative 50% particle size in the volume-based particle size distribution.)
The particle size gradient calculated by is 2 or less.
Non-oxide micro hollow particles. 2. The inorganic oxide hollow fine particles according to claim 1, having a _D100 of 15 μm or less. 3. The inorganic oxide hollow microparticles according to claim 1 or 2, wherein D ₅₀ is from 0.5 to 5 μm. The inorganic oxide microhollow particles according to any one of claims 1 to 3, wherein a 90 degree peel adhesive strength of the resin layer from the copper plate exceeds 10 N/m when a copper plate-attached test piece prepared by the following method is measured in accordance with JIS K 6854-1.
[Preparation of test pieces with copper plates]
5 g of dried powder of inorganic oxide micro hollow particles is added to and mixed with an epoxy resin liquid containing 30 g of a mixture of liquid bisphenol A type epoxy resin and liquid bisphenol F type epoxy resin (average epoxy equivalent 165 g/mol), 20 g of liquid phenol novolac (hydroxyl equivalent 135 g/mol), and 1 g of triphenylphosphine. The resin mixture is applied to a flexible adherend bent at a right angle in a width of 25 mm, length of 150 mm, and thickness of 1 mm, and the adherend is attached to a horizontal copper plate, and a manual hydraulic press is used to apply pressure of 1 MPa for 10 minutes to bond the material. The material is then dried and cured in a dryer at 80°C for 12 hours to prepare a test piece. A resin composition comprising the inorganic oxide hollow particles according to any one of claims 1 to 4 .