Hollow particles and their manufacturing method

Abstract

Provided is a hollow particle having excellent dielectric properties.　This hollow particle of an embodiment includes a shell the inside of which is hollow. The shell is made of silica that includes aluminum. The abundance of aluminum is higher in a first region than in a second region. The first region is located in the shell, inward in the shell thickness direction. The second region is located in the shell, further outside than the first region in the shell thickness direction.

Description

[Technical Field]

[0001] The present invention relates to hollow particles having a hollow shell and a method for producing the same. [Background technology]

[0002] For example, in the field of information and communication devices, there is a demand for lower dielectric constants and lower dielectric loss tangents for electronic components (typically resin components) such as circuit boards to accommodate communications in high frequency bands. To achieve this, it has been proposed, for example, to incorporate air, which has a low relative dielectric constant, into the components. Specifically, as disclosed in Patent Documents 1 and 2, it has been proposed to introduce air using hollow particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 171858 [Patent Document 2] International Publication No. 2021 / 171859 Summary of the Invention [Problem to be solved by the invention]

[0004] Due to the recent trend toward higher speeds and larger capacities in information and communication devices, hollow particles are required to have further improved dielectric properties.

[0005] The present invention has been made to solve the above problems, and one of its objects is to provide hollow particles with further improved dielectric properties. [Means for solving the problem]

[0006] (1) The hollow particles of the present disclosure have a hollow shell. The shell is silica containing aluminum. The amount of aluminum present is greater in the first region than in the second region. The first region is located on the inner side of the shell in the thickness direction of the shell. The second region is located on the outer side of the first region in the thickness direction of the shell.

[0007] (2) The hollow particles of the present disclosure are the hollow particles described in (1) above, wherein the aluminum content is less than 1% of the components constituting the shell.

[0008] (3) In the hollow particles of the present disclosure described in (1) or (2) above, the amount of aluminum present decreases from the inside to the outside of the shell.

[0009] (4) The hollow particles of the present disclosure are the hollow particles according to any one of (1) to (3) above, wherein the epoxy resin oil absorption is 0.6 g / m 2 is less than.

[0010] (5) The present disclosure provides the hollow particles according to any one of (1) to (4) above, wherein the shell further contains sodium, and the sodium content of the shell is 3000 ppm or less.

[0011] (6) The hollow particles of the present disclosure are the hollow particles according to any one of (1) to (5) above, wherein the silica is amorphous silica.

[0012] (7) The hollow particles of the present disclosure are the hollow particles according to any one of (1) to (6) above, wherein the shell has a hollowness of 30% or more and 95% or less.

[0013] (8) The hollow particles of the present disclosure are the hollow particles according to any one of (1) to (7) above, wherein the thickness of the shell is 25 nm or more and 500 nm or less.

[0014] (9) The method for producing hollow particles according to the present disclosure is the method for producing hollow particles according to any one of (1) to (8) above, which includes coating core particles with a shell-forming material to obtain core-shell particles, removing the core particles from the core-shell particles to obtain hollow particle precursors, and coating the hollow particle precursors with the shell-forming material.

[0015] (10) The method for producing hollow particles according to the present disclosure is the method for producing hollow particles described in (9) above, wherein the core particles contain an alunite-type compound represented by the following general formula (I): M a [Al 1-x M' x ]3(SO4 2- ) y (OH) z mH2O (I) In formula (I), M is Na + , K. + , NH4 + and H3O + In formula (I), M' is at least one cation selected from the group consisting of Cu 2+ , Zn 2+ , Ni 2+ , Sn 4+ , Zr 4+ and Ti 4+ and at least one cation selected from the group consisting of: In formula (I), a satisfies 0.8≦a≦1.35. In formula (I), m satisfies 0≦m≦5. In formula (I), x satisfies 0≦x≦0.4. In formula (I), y satisfies 1.7≦y≦2.5. In formula (I), z satisfies 4≦z≦7. [Effects of the Invention]

[0016] According to embodiments of the present invention, excellent dielectric properties may be achieved. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic diagram illustrating a major axis and a minor axis. [Figure 2]FIG. 1 is a cross-sectional view schematically illustrating a hollow particle according to one embodiment of the present invention. [Figure 3A] 1 is a graph showing an outline of an example of a change in the amount of Al present in the thickness direction of the shell. [Figure 3B] 10 is a graph showing an outline of another example of the change in the amount of Al present in the thickness direction of the shell. [Figure 3C] 10 is a graph outlining yet another example of the change in the amount of Al present in the thickness direction of the shell. [Figure 4] 1 is a schematic cross-sectional view of a laminate according to one embodiment of the present invention. [Figure 5A] 1 is a TEM observation photograph of hollow particles of Example 1. [Figure 5B] 1 is a TEM observation photograph of hollow particles of Example 2. [Figure 5C] 1 is a TEM observation photograph of hollow particles of Example 3. [Figure 6] 1 is a SEM photograph of a cross section of a resin molded body of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0019] (Definition of terms) The definitions of terms used in this specification are as follows. 1. Major axis of particle The major axis of the particles is a value measured using a scanning electron microscope (SEM). The major axis of the particles is the average major axis of randomly selected primary particles, as shown by L in Figure 1. Note that primary particles are the smallest particles observed using SEM and are distinguished from agglomerated secondary particles. 2. Minor diameter of particle The minor diameter of the particles is a value measured by SEM observation, and is the average minor diameter of randomly selected primary particles, as shown by T in Figure 1, for example. 3. Aspect Ratio The aspect ratio is a value calculated by dividing the minor axis of the particle by the major axis of the particle.

[0020] A. Hollow particles In one embodiment of the present invention, the hollow particles have a hollow shell. In other words, the hollow particles have a shell and a space surrounded by the shell. The shell contains silica. The silica is typically amorphous silica. The silica content of the shell is, for example, 95% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more.

[0021] The shell of the hollow particles contains aluminum (Al). By including Al, hollow particles with excellent strength (breaking strength) can be obtained. The Al content is preferably 0.1% or more, more preferably 0.2% or more. On the other hand, the dielectric constant and dielectric loss tangent of hollow particles tend to be high when Al is included. Therefore, the Al content is preferably less than 1%, more preferably 0.9% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less. With such a content, the hollow particles can have extremely excellent dielectric properties. The Al content can be determined, for example, by composition analysis using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0022] The hollow particles are formed such that the amount of Al present is greater on the inner side of the shell in the thickness direction than on the outer side. This configuration allows for hollow particles with excellent strength (fracture strength), hollowness, and dielectric properties. Specifically, the Al-rich regions of the hollow particles are more likely to soften during firing. That is, hollow particles can be produced at a lower firing temperature during the manufacturing process. Furthermore, the Al-rich regions of the hollow particles can cause the hollow particle precursor forming the shell to shrink more on the inside than on the outside during firing. The Al-rich regions of the hollow particles can increase the fracture strength. Furthermore, hollow particles are thought to maintain particle diameter by suppressing softening and shrinkage on the outside of the shell, while expanding the internal space through softening and shrinkage on the inside, contributing to an improvement in the hollowness. In other words, the difference in the distribution of Al present on the outside and inside of the shell allows for improved shell strength and hollowness. The excellent strength and low dielectric properties of hollow particles can effectively prevent breakage of the hollow particles, for example, when preparing a resin composition containing resin and hollow particles. As a result, the hollow state of the particles is maintained, which can significantly contribute to improving the dielectric properties. Furthermore, if the shell thickness of hollow particles is thin, Al tends to be uniformly distributed. For example, if Al is uniformly distributed in hollow particles, the inside and outside of the shell tend to shrink equally, resulting in a smaller particle diameter.

[0023] FIG. 2 is a cross-sectional view schematically illustrating a hollow particle according to one embodiment of the present invention. In FIG. 2, hatching is omitted from the cross section of the hollow particle for clarity. A hollow particle 2 has a shell 4 and a space (hollow portion) 6 surrounded by the shell 4. The amount of Al present in a first portion 4a located on the inner side of the shell 4 in the thickness direction is greater than the amount of Al present in a second portion 4b located on the outer side of the first portion 4a in the thickness direction. For example, as shown in FIG. 2 , when the first portion 4a is located on or near the inner surface of the shell 4 and the second portion 4b is located on or near the outer surface of the shell 4, the amount of Al present in the first portion 4a is preferably at least two times, and more preferably at least three times, the amount of Al present in the second portion 4b. The distribution of Al abundance can be determined, for example, by compositional analysis using energy dispersive X-ray spectroscopy (TEM-EDS) with a transmission electron microscope (TEM). In one embodiment, the amount of Al present can be evaluated by the molar ratio of Al to Si.

[0024] An example of the distribution of Al abundance in the thickness direction is one in which the Al abundance continuously decreases from the inside to the outside of the shell. In this case, the manner in which the Al abundance changes is not particularly limited. For example, the Al abundance may decrease linearly with distance from the inner surface of the shell, as shown in FIG. 3A. Alternatively, it may decrease exponentially with distance from the inner surface of the shell, as shown in FIG. 3B. Specifically, the Al abundance of hollow particles can be controlled by controlling the addition of the Al source material during the primary silica treatment of the core particles and the secondary silica treatment of the hollow particle precursor. Hollow particles with a linear decrease in Al abundance tend to have a higher hollow ratio than those with uniform Al distribution in the shell. Hollow particles with an exponential decrease in Al abundance tend to have a higher hollow ratio than those with a linear decrease.

[0025] Another example of the distribution of Al abundance in the thickness direction is one in which the Al abundance gradually decreases from the inside to the outside of the shell. In other words, the Al abundance of the hollow particles gradually decreases from the inside to the outside of the shell. For example, as shown in FIG. 3C , the hollow particles may have a first region 41 with a constant Al abundance from the inner surface of the shell to the outside, and a second region 42 with a lower Al abundance than the first region 41 outside the first region 41. Note that FIG. 3C illustrates the first region 41 and the second region 42 as a straight line for convenience, but a constant Al abundance means, for example, that the variation in the Al abundance is 20% or less. While FIG. 3C illustrates an example in which the Al abundance decreases in two stages, it may also have three or more stages. When the Al abundance of the hollow particles gradually decreases, the effect of improving the strength and hollowness can be enhanced.

[0026] The shell of the hollow particles may contain sodium (Na). If the Na content of the hollow particles is too high, it becomes difficult to increase the firing temperature in the hollow particle manufacturing process, and the particles tend to shrink. The Na content is preferably 3000 ppm or less, more preferably 2000 ppm or less, and even more preferably 1500 ppm or less. On the other hand, the Na content is preferably 100 ppm or more. The Na content can be determined, for example, by composition analysis using atomic absorption spectroscopy (AAS).

[0027] In hollow particles, the amount of Na present is preferably greater inside the shell in the thickness direction than outside the shell. It is thought that when some Si(4+) is replaced by Al(3+), Na easily enters the hollow particles to fill the electron vacancy. Therefore, it is thought that Na tends to be present in large amounts in regions of hollow particles where Al is abundant.

[0028] In one embodiment, the primary particles of the hollow particles are 1≦D SL It is preferable that the primary particles of the hollow particles satisfy the condition of 1≦D≦1.5. SLBy satisfying the condition of 1≦D≦1.5, it is possible to suppress the variation between particles and to achieve uniform dielectric properties. SL It is more preferable to satisfy 1≦D SL It is more preferable that D≦1.3 is satisfied. SL is D 75L / D 25L and D 25L and D 75L The values ​​respectively represent the 25th and 75th largest values ​​when the major axis of 100 randomly selected primary particles is measured and arranged in order of size from smallest to largest in observation with a scanning electron microscope.

[0029] The primary particle of the hollow particle is 1≦D ST It is preferable that the relationship 1≦D≦1.5 is satisfied, and more preferably 1≦D ST ≦1.4, and more preferably 1≦D ST ≦1.3, where D ST is D 75T / D 25T and D 25T and D 75T The minor axes of 100 randomly selected primary particles were measured using a scanning electron microscope, and the values ​​for the 25th and 75th smallest particles were arranged in order of size.

[0030] The aspect ratio of the hollow particles is preferably less than 2, more preferably 1.9 or less, while the aspect ratio of the hollow particles is 1 or more, preferably greater than 1, more preferably 1.1 or more.

[0031] The hollow particles may have any suitable shape. Examples of the shape of the hollow particles include ellipsoid, sphere, aggregate, scale, plate, film, cylinder, prism, flat, go stone, and rice grain. The shape of the hollow particles is preferably spherical or go stone. By adopting such a shape, for example, the above-mentioned D SL and D ST can be satisfactorily satisfied.

[0032] The major axis of the hollow particles is preferably 0.5 μm or more, more preferably 1 μm or more. This is because, for example, if the major axis of the hollow particles is 0.5 μm or more, the hollow ratio described below can be fully satisfied. On the other hand, the major axis of the hollow particles is preferably 10 μm or less, more preferably 5 μm or less. This is because, for example, if the major axis of the hollow particles is 10 μm or less, the hollow particles can greatly contribute to the miniaturization or thinning of the members in which they are used.

[0033] The minor axis of the hollow particles is preferably 0.25 μm or more, more preferably 0.5 μm or more. This is because, for example, if the minor axis of the hollow particles is 0.25 μm or more, the hollow ratio described below can be fully satisfied. On the other hand, the minor axis of the hollow particles is preferably 10 μm or less, more preferably 5 μm or less. This is because, for example, if the minor axis of the hollow particles is 10 μm or less, the hollow particles can greatly contribute to the miniaturization or thinning of the members in which they are used.

[0034] The shell thickness of the hollow particles is preferably 25 nm or more, more preferably 50 nm or more, and even more preferably 75 nm or more. Such a thickness can effectively prevent the hollow particles from breaking, for example, when preparing a resin composition. On the other hand, the shell thickness of the hollow particles is preferably 500 nm or less, more preferably 350 nm or less, and even more preferably 250 nm or less. Such a thickness can fully satisfy the hollow ratio described below, significantly contributing to improved dielectric properties and weight reduction. The shell thickness can be measured by TEM observation. For example, it can be determined by measuring the shell thickness of randomly selected hollow particles and calculating the average of the measured shell thicknesses. The shell thickness of the hollow particles may affect the distribution of Al abundance.

[0035] The hollow percentage of the hollow particles is preferably 30% or more, more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more. Such a hollow percentage can significantly contribute to, for example, improved dielectric properties and weight reduction. On the other hand, the hollow percentage of the hollow particles is preferably 95% or less, more preferably 90% or less, even more preferably 85% or less, and particularly preferably 80% or less. Such a hollow percentage can effectively prevent the hollow particles from breaking when, for example, preparing a resin composition. The hollow percentage can be calculated from the major and minor diameters and the shell thickness.

[0036] The BET specific surface area of ​​the hollow particles is preferably 30 m 2 / g or less, and more preferably 20m 2 / g or less, more preferably 10m 2 On the other hand, the BET specific surface area of ​​hollow particles is, for example, 0.5 m 2 / g or more, and 1m 2 / g or more.

[0037] The cumulative pore volume of the hollow particles having a diameter of 1 to 100 nm is preferably 0.1 cc / g or less, more preferably 0.08 cc / g or less, and even more preferably 0.06 cc / g or less. This pore volume effectively prevents, for example, resin from penetrating into the hollow particles in a resin composition, which can significantly contribute to improving dielectric properties. Meanwhile, the cumulative pore volume of the hollow particles having a diameter of 1 to 100 nm is, for example, 0.01 cc / g or more.

[0038] The cumulative pore volume of the hollow particles having a diameter of 1 to 10 nm is preferably 0.025 cc / g or less, more preferably 0.020 cc / g or less, and even more preferably 0.010 cc / g or less. This pore volume effectively prevents, for example, resin from penetrating into the hollow particles in a resin composition, which can significantly contribute to improving dielectric properties. Meanwhile, the cumulative pore volume of the hollow particles having a diameter of 1 to 10 nm is, for example, 0.001 cc / g or more.

[0039] The density of the hollow particles is preferably 0.90 g / cc or less, more preferably 0.80 g / cc or less. On the other hand, the density of the hollow particles is preferably 0.55 g / cc or more, more preferably 0.60 g / cc or more. With such a density, the hollow particles can maintain the strength of the shell and the hollow ratio.

[0040] The dielectric constant of the hollow particles at 25°C and 10 GHz is preferably 2.2 or less, more preferably 2.0 or less. Meanwhile, the dielectric constant of the hollow particles at 25°C and 10 GHz is, for example, 1.0 or more. The dielectric loss tangent of the hollow particles at 25°C and 10 GHz is preferably 0.005 or less, more preferably 0.002 or less. Meanwhile, the dielectric loss tangent of the hollow particles at 25°C and 10 GHz is, for example, 0.0001 or more.

[0041] The breaking strength of the hollow particles is preferably 10 MPa or more, more preferably 12 MPa or more, even more preferably 14 MPa or more, and particularly preferably 16 MPa or more. Such a breaking strength can effectively prevent the hollow particles from breaking, for example, when preparing a resin composition. As a result, the hollow state of the particles is maintained, which can greatly contribute to improving the dielectric properties. Meanwhile, the breaking strength of the hollow particles is, for example, 800 MPa or less.

[0042] The breaking strength of hollow particles can be measured, for example, using a microcompression tester ("MCT-510" manufactured by Shimadzu Corporation) with a length measurement kit and a side observation kit. Specifically, the breaking strength can be measured by scattering a very small amount of hollow particles on the lower pressure plate and performing a breaking test on each particle under the following measurement conditions. Test force: 0.980mN ·Load speed: 0.0223mN / sec ·Top pressure indenter: flat surface φ20μm

[0043] For example, 10 particles are measured, and the breaking strength Cs is calculated from the particle diameter d (mm) of each particle and the test force P (N) at the breaking point. The breaking strength Cs is calculated using the following formula from JIS R 1639-5, "Measurement methods for fine ceramic granule properties - Part 5: Single granule crushing strength." Cs=2.48P / πd 2 The breaking strength of the hollow particles can be determined by calculating the average value of the breaking strength Cs (MPa) of 10 particles.

[0044] The epoxy resin oil absorption per 1 g of hollow particles is preferably 2.3 g or less, more preferably 2.0 g or less. The epoxy resin oil absorption of hollow particles is 0.6 g / m 2 It is preferable that the density is less than 0.46 g / m 2 More preferably, it is 0.35 g / m or less. 2 The following is the result.

[0045] In one embodiment, the hollow particles are preferably surface-treated with any suitable surface treatment agent, such as at least one selected from the group consisting of higher fatty acids, anionic surfactants, cationic surfactants, phosphate esters, coupling agents, esters of polyhydric alcohols and fatty acids, acrylic polymers, and silicone treatment agents.

[0046] Any appropriate method can be used to produce the hollow particles. A method for producing hollow particles according to one embodiment of the present invention includes coating core particles with a shell-forming material to obtain core-shell particles, removing the core particles from the core-shell particles to obtain hollow particle precursors, and coating the hollow particle precursors with the shell-forming material. Coating the hollow particle precursors with the shell-forming material can form a strong shell while suppressing a decrease in hollow ratio, for example. Specifically, the hollow particle precursors obtained by removing the core particles can have pores and be brittle. Filling the pores of the hollow particle precursors with the shell-forming material can produce hollow particles with a strong shell without shrinking the hollow particle precursor. The shrinkage of the hollow particle precursors is, for example, softening shrinkage.

[0047] The core particles have a primary particle size of 1≦D SL It is preferable that the relationship 1≦D≦1.5 is satisfied, and more preferably 1≦D SL ≦1.4, more preferably 1≦D SL ≦1.3. The primary particles of the core particles are 1≦D ST It is preferable that the relationship 1≦D≦1.5 is satisfied, and more preferably 1≦D ST ≦1.4, more preferably 1≦D ST ≦1.3. SL and D ST As mentioned above,

[0048] The aspect ratio of the core particle is preferably less than 2, more preferably 1.9 or less. On the other hand, the aspect ratio of the core particle is 1 or more, preferably more than 1, more preferably 1.1 or more. Examples of the shape of the core particle include ellipsoid, sphere, agglomerate, scale, plate, film, cylinder, prism, flat, go stone, and rice grain. The core particle is preferably spherical or go stone-shaped.

[0049] The major axis of the core particle is preferably 0.5 μm or more, more preferably 1 μm or more. On the other hand, the major axis of the core particle is preferably 10 μm or less, more preferably 5 μm or less. On the other hand, the minor axis of the core particle is preferably 0.25 μm or more, more preferably 0.5 μm or more. On the other hand, the minor axis of the core particle is preferably 10 μm or less, more preferably 5 μm or less.

[0050] Any appropriate material can be used as the material for forming the core particle. For example, a material containing aluminum can be used to satisfy the above-mentioned distribution of Al abundance in the resulting hollow particle. In one embodiment, the core particle is preferably formed from an alunite-type compound represented by the following general formula (I): M a [Al 1-x M' x ]3(SO4 2- ) y (OH) z mH2O (I) In formula (I), M is Na + , K. + , NH4 + and H3O + In formula (I), M' is at least one cation selected from the group consisting of Cu 2+ , Zn 2+ , Ni 2+ , Sn 4+ , Zr 4+ and Ti 4+ and at least one cation selected from the group consisting of: In formula (I), a satisfies 0.8≦a≦1.35. In formula (I), m satisfies 0≦m≦5. In formula (I), x satisfies 0≦x≦0.4. In formula (I), y satisfies 1.7≦y≦2.5. In formula (I), z satisfies 4≦z≦7.

[0051] Examples of the shell-forming material include sodium silicate (Na2O·nSiO2) and alkoxysilanes, such as tetraethoxysilane (Si(OCH2CH3)4). In one embodiment, sodium silicate (water glass) is used. The presence of Na may facilitate softening during the firing process described below, making it easier to control the firing temperature. The shell-forming material may also contain Al. For example, when core particles are coated multiple times with shell-forming materials, the Al concentration in the shell-forming materials used in each process can be adjusted to achieve the desired distribution of Al content in the resulting hollow particles.

[0052] The amount of coating with the shell-forming material can be adjusted by any appropriate method. For example, the coating amount can be adjusted by controlling the pH value when coating with a shell-forming material containing sodium silicate. Specifically, sodium silicate can be stable in a high pH range. For example, sodium silicate can be stable at a pH of 11 or higher. Therefore, lowering the pH value can condense sodium silicate molecules, allowing silica to efficiently precipitate on the core particles. Here, when the core particles contain the alunite-type compound, the aqueous slurry of the alunite-type compound itself can exhibit acidity. The acidity of the aqueous slurry of the alunite-type compound itself is, for example, pH 3 to 5. Because the aqueous slurry of the alunite-type compound itself is acidic, silica can be efficiently precipitated on the core particles without using a pH adjuster to lower the pH, for example. When core particles containing an alunite-type compound are coated multiple times with a shell-forming material containing sodium silicate, a pH adjuster may be used in one or more of the multiple coating times. In this case, an acidic solution such as hydrochloric acid or sulfuric acid can be used as the pH adjuster. By using an acidic solution, hollow particles with a low Na content can be obtained.

[0053] The coating with the shell-forming material can also be promoted by heating when coating with the shell-forming material. Specifically, the precipitation of the shell can be promoted, thereby increasing the shell formation rate. The heating temperature when coating with the shell-forming material is, for example, 80°C to 90°C. The coating amount can also be adjusted by controlling the concentration, amount of the shell-forming material when coating. When core particles are coated with a shell-forming material containing sodium silicate, the concentration of sodium silicate in the shell-forming material is, for example, 0.1 mol / L to 2 mol / L.

[0054] The removal of the core particles is typically carried out by dissolving the core particles in an acidic solution. Examples of the acidic solution include hydrochloric acid, sulfuric acid, and nitric acid. The dissolution temperature is, for example, 30°C to 90°C, and preferably 50°C to 80°C. At such a temperature, the core particles can be efficiently dissolved while preventing problems such as the shell becoming easily broken. In one embodiment, sulfuric acid is used as the acidic solution, for example, from the viewpoint of reusing the substance obtained by reaction with the core particles. Examples of the substance obtained by reaction with the core particles include salts. The concentration of sulfuric acid is, for example, 0.1 mol / L to 3.5 mol / L, and preferably 0.5 mol / L or more. When dissolving core particles containing an alunite-type compound, the Al content can be satisfactorily achieved by adjusting, for example, the acidic solution, the dissolution temperature, and the dissolution time.

[0055] The method for producing hollow particles may include calcining the core-shell particles before removing the core particles. When the core particles contain the alunite-type compound, calcination is preferably performed before removing the core particles. Calcination is preferably performed, for example, in an air atmosphere. This is because the alunite-type compound can be acid-resistant, and calcination changes the alunite-type compound, making the calcined core particles more soluble in acidic solutions. Specifically, for core particles containing an alunite-type compound, portions with low agglomeration density are more soluble in acidic solutions, while portions with high agglomeration density are less soluble in acidic solutions, resulting in a dissolution amount in acidic solutions of, for example, approximately 30% by weight. Calcination produces aluminum oxide (Al2O3) from the alunite-type compound, which is more soluble in acidic solutions, thereby improving the solubility of the core particles in acidic solutions.

[0056] The firing temperature for the core-shell particles is, for example, 300°C to 900°C, and preferably 300°C to 650°C. At such a firing temperature, crystallization of the shell can be suppressed, allowing the aluminum oxide to be produced. The firing time is, for example, 0.5 hours to 20 hours. The firing may be carried out continuously or in multiple stages at different temperatures. When firing is carried out in multiple stages, the firing time is the total of the firing times for each stage. In one embodiment, the firing temperature for the core-shell particles may be adjusted to satisfy the distribution of the amount of Al present in the resulting hollow particles.

[0057] The shell-forming material used to coat the hollow particle precursor is preferably selected corresponding to the shell-forming material used to coat the core particle. Specifically, when sodium silicate is used as the shell-forming material used to coat the core particle, sodium silicate is preferably used as the shell-forming material used to coat the hollow particle precursor.

[0058] When coating hollow particle precursors with a shell-forming material containing sodium silicate, it is preferable to adjust the coating amount by controlling the pH value. Specifically, sodium silicate can be stable in a high pH range. A high pH range is, for example, pH 11 or higher. For sodium silicate, it is preferable to use, for example, a pH adjuster to lower the pH value, thereby condensing the sodium silicate molecules and efficiently precipitating silica on the hollow particle precursors. As the pH adjuster, for example, an acidic solution such as hydrochloric acid or sulfuric acid is used.

[0059] The method for producing hollow particles may include calcining a hollow particle precursor coated with a shell-forming material. Specifically, the calcination of the hollow particle precursor may be performed after the hollow particle precursor is coated with the shell-forming material. Calcining the hollow particle precursor can produce hollow particles that significantly contribute to improving dielectric properties. Specifically, the hydrophobicity of the hollow particle precursor surface can be improved. More specifically, silanol groups on the hollow particle precursor surface can be converted to siloxanes. Furthermore, hollow particles that are easy to incorporate or disperse into resins when preparing resin compositions can be obtained. Specifically, appropriate shrinkage by calcination can prevent fusion between particles while filling the pores on the hollow particle precursor surface, resulting in hollow particles with a smooth surface. Obtaining hollow particles with a smooth surface can, for example, favorably achieve the BET specific surface area and pore volume. In one embodiment, the calcination temperature of the hollow particle precursor may be adjusted to satisfy the Al abundance distribution in the resulting hollow particles.

[0060] The calcination temperature of the hollow particle precursor is, for example, 300°C to 1300°C, preferably 700°C to 1300°C, and more preferably 900°C to 1300°C. Such a calcination temperature can effectively achieve the hydrophobicity. Furthermore, even when calcined at such a temperature, a high hollowness can be achieved. Specifically, calcining the hollow particle precursor in a state in which the pores are filled with a coating of a shell-forming material can effectively achieve hydrophobicity while suppressing shrinkage of the hollow particle precursor. The calcination time of the hollow particle precursor is, for example, 0.1 hours to 10 hours. Calcination may be performed continuously or in multiple stages at different temperatures. For example, calcination may be performed at a temperature T1 below 950°C, followed by calcination at a temperature T2 of 950°C or higher. In this case, the difference between temperatures T1 and T2 (T2 - T1) is preferably 150°C or higher, more preferably 250°C or higher. When firing is performed in multiple stages, the firing time is the total of the firing times for each stage.

[0061] The method for producing hollow particles may include subjecting the hollow particle precursor to an acid treatment before calcining the hollow particle precursor. The acid treatment is preferably carried out using an acidic solution, typically hydrochloric acid, sulfuric acid, or the like. When sodium silicate is used as the shell-forming material, the hollow particle precursor may contain Na. By removing Na through the acid treatment, the calcination temperature of the hollow particle precursor can be set high, resulting in hollow particles that can significantly improve the dielectric properties.

[0062] In the method for producing hollow particles, the step of obtaining the core-shell particles preferably includes a drying treatment. Specifically, when the core particles are coated with the shell-forming material multiple times, the core particles coated with the shell-forming material are preferably dried and then coated again with the shell-forming material. The drying temperature in the step of obtaining the core-shell particles is, for example, 90°C to 120°C. The drying time in the step of obtaining the core-shell particles is, for example, 3 hours to 24 hours. By including such a drying treatment, the above oil absorption can be satisfactorily achieved, for example, regardless of whether a pH adjuster is used when coating with the shell-forming material.

[0063] In one embodiment of the present invention, the hollow particles are used as a function-imparting agent for a resin material. A resin composition containing the hollow particles will be described below.

[0064] B. Resin composition A resin composition according to one embodiment of the present invention includes a resin and the hollow particles. In the resin composition, the hollow particles can be well maintained in their hollow state. Furthermore, in a resin molded product formed using the resin composition, the hollow particles can be well maintained in their hollow state.

[0065] Any appropriate resin can be selected as the resin, depending on, for example, the intended use of the resulting resin composition. For example, the resin may be a thermoplastic resin or a thermosetting resin. Specific examples of the resin include epoxy resins, polyimide resins, polyamide resins, polyamideimide resins, polyether ether ketone resins, polyester resins, polyhydroxy polyether resins, polyolefin resins, fluororesins, liquid crystal polymers, and modified polyimides. These may be used alone or in combination of two or more.

[0066] The content of the hollow particles in the resin composition is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and is preferably 90% by weight or less, more preferably 85% by weight or less.

[0067] The resin composition preferably contains 0.5 parts by weight or more, more preferably 1 part by weight or more, of hollow particles per 100 parts by weight of resin, while the resin composition preferably contains 300 parts by weight or less, more preferably 200 parts by weight or less, of hollow particles per 100 parts by weight of resin.

[0068] The volume ratio of hollow particles in the resin composition is preferably 0.1% or more, more preferably 0.5% or more. On the other hand, the volume ratio of hollow particles in the resin composition is preferably 70% or less, more preferably 60% or less. This is because, for example, the processability when producing the resin composition can be excellent.

[0069] The hollow ratio of the hollow particles in the resin composition is preferably 30% or more, more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more.

[0070] The resin composition may contain optional components. Examples of optional components include a curing agent, a stress reducing agent, a coloring agent, an adhesion improver, a release agent, a flow control agent, a defoaming agent, a solvent, and a filler. These may be used alone or in combination of two or more. In one embodiment, the resin composition contains a curing agent. The content of the curing agent is, for example, 1 part by weight to 150 parts by weight per 100 parts by weight of the resin.

[0071] Any suitable method can be used to prepare the resin composition. Specifically, the hollow particles are dispersed in the resin by any suitable dispersion method to obtain the resin composition. Examples of dispersion methods include dispersion using various agitators such as a homomixer, a disperser, or a ball mill, dispersion using a planetary mixer, dispersion using shear force using a three-roll mill, and dispersion using ultrasonic treatment.

[0072] The resin composition is typically formed into a resin molded article having a desired shape. For example, the resin molded article is formed into a desired shape using a mold. When forming the resin molded article, the resin composition may be subjected to any appropriate treatment. For example, the resin composition may be subjected to a curing treatment.

[0073] In one embodiment of the present invention, the resin composition is used as a resin layer included in a laminate. A laminate having a resin layer formed from the resin composition will be described below.

[0074] C. Laminate FIG. 4 is a schematic cross-sectional view of a laminate according to one embodiment of the present invention. The laminate 10 includes a resin layer 11 and a metal foil 12. The resin layer 11 is formed from the resin composition. Specifically, the resin layer 11 includes the resin and the hollow particles. Although not shown, the laminate 10 may include other layers. Examples of such layers include a substrate. The substrate may be laminated on one side of the resin layer 11. Specifically, the substrate may be disposed on the side of the resin layer 11 where the metal foil 12 is not disposed. A resin film is typically used as the substrate. Unlike the illustrated example, the laminate 10 may have a configuration in which the metal foil 12 is disposed on the surface of a laminate structure including multiple resin layers 11. The laminate 10 may also have a configuration in which the metal foil 12 is disposed on each side of a laminate structure including multiple resin layers 11. The laminate 10 may also have a configuration in which multiple combinations of resin layers 11 and metal foils 12 are stacked. The laminate 10 is typically used as a wiring circuit board. The metal foil 12 is formed into a predetermined shape so as to form, for example, a predetermined circuit wiring.

[0075] The thickness of the resin layer is, for example, 5 μm or more, preferably 10 μm or more. On the other hand, the thickness of the resin layer is, for example, 100 μm or less, preferably 50 μm or less, more preferably 25 μm or less. Such a thickness can, for example, fully accommodate the recent trend toward miniaturization of electronic components.

[0076] Any appropriate metal can be used as the metal for forming the metal foil. Examples include copper, aluminum, nickel, chromium, and gold. These can be used alone or in combination of two or more. The thickness of the metal foil is, for example, 2 μm to 35 μm.

[0077] Any appropriate method can be adopted as a method for producing the laminate. For example, the resin composition is applied to the substrate to form a coating layer, and the metal foil is laminated on this coating layer to obtain a laminate. In another specific example, the resin composition is applied to the metal foil to form a coating layer to obtain a laminate. Typically, the coating layer is subjected to an energy imparting treatment such as heating or light irradiation at any appropriate timing to cure the coating layer. When coating, the resin composition may be dissolved in any appropriate solvent and used. [Example]

[0078] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The measurement methods for each property are as follows unless otherwise specified. Furthermore, "%" and "ppm" are based on weight unless otherwise specified. 1. Major axis of particle The particle length was calculated by FE-SEM observation. Specifically, the length of 100 primary particles randomly selected from the SEM photograph was measured, and the arithmetic mean (average length) of the measured values ​​was calculated. The magnification for SEM observation was 10,000x. 2. Minor diameter of particle The minor diameter of the particles was calculated by FE-SEM observation. Specifically, the minor diameter of 100 primary particles randomly selected from the SEM photograph of the particles was measured, and the arithmetic mean (average minor diameter) of the obtained measurements was calculated. The magnification of the SEM observation was 10,000x. 3.D SL and D ST FE-SEM observation revealed that SL and D ST Specifically, the major axis of each of 100 primary particles randomly selected from the SEM photograph of the particles was measured, and the 75th value (D 75L ) to the 25th value (D 25L ) and divide by D SL The minor axis of each of 100 primary particles randomly selected from the SEM photograph of the particles was measured, and the 75th value (D 75T ) to the 25th value (D 25T) and divide by D ST was calculated. 4. Aspect Ratio The aspect ratio was calculated by FE-SEM observation, specifically by dividing the average major axis of the particles by the average minor axis of the particles.

[0079] [Example 1] (Preparation of hollow silica particles) Elliptical alunite particle powder (NaAl3(SO4)2(OH)6, major axis: 1.98 μm, D SL :1.13, Short diameter: 1.35μm, D ST 800 g of the granular material (wt.: 1.18, aspect ratio: 1.47) was suspended in 5 L of ion-exchanged water to obtain a slurry of alunite particles.

[0080] The resulting alunite particle slurry was then heated to 90°C while stirring, and 816 ml of 0.55 mol / L No. 3 water glass (Na2O·2.97SiO2, Fujifilm Wako Pure Chemical Industries, Ltd.) was added over 4 hours. The resulting slurry was aged for 1 hour, then dehydrated and washed with water to obtain a cake of the first core-shell particle precursor. The cake of the first core-shell particle precursor was then dried at 105°C for 1 day to obtain a powder of core-shell particles.

[0081] Next, the powder of the first core-shell particle precursor was suspended in 5 L of ion-exchanged water and heated to 90°C while stirring. 136 ml of 0.55 mol / L No. 3 water glass was then added over 10 minutes. Subsequently, 680 ml of 0.55 mol / L No. 3 water glass and 757 ml of 0.50 mol / L sulfuric acid were added simultaneously. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a cake of the second core-shell particle precursor.

[0082] The resulting cake of second core-shell particle precursor was suspended in 5 L of ion-exchanged water and heated to 90°C with stirring. 136 ml of 0.55 mol / L No. 3 water glass was then added over 10 minutes. Then, 680 ml of 0.55 mol / L No. 3 water glass and 757 ml of 0.50 mol / L sulfuric acid were added simultaneously. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water, and then dried at 105°C for one day to obtain a powder of core-shell particles.

[0083] The obtained powder of core-shell particles was then fired at 500° C. for 3 hours and then at 550° C. for 1 hour. It is believed that the firing caused the alunite particles to change as follows: NaAl3(SO4)2(OH)6→NaAl(SO4)2+Al2O3+3H2O

[0084] Next, 737 g of the calcined core-shell particles were added to 6 L of ion-exchanged water and resuspended under stirring at room temperature. 3.95 L of 2 mol / L sulfuric acid was added to this, heated to 90°C, and reacted for 5 hours to dissolve the core particles, yielding a slurry of the first hollow silica precursor. The first hollow silica precursor is also a hollow particle precursor. The resulting slurry of the first hollow silica precursor was dehydrated and washed with water to yield a cake of the first hollow silica precursor.

[0085] Next, the resulting first hollow silica precursor cake (88 g of powder) was suspended in 4 L of ion-exchanged water and heated to 90°C while stirring. 40 ml of 0.55 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 200 ml of 0.55 mol / L No. 3 water glass and 210 ml of 0.5 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a second hollow silica precursor cake. The resulting second hollow silica precursor cake was then suspended in 4 L of ion-exchanged water and heated to 90°C with stirring. 40 ml of 0.55 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 200 ml of 0.55 mol / L No. 3 water glass and 210 ml of 0.50 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid was added over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a third hollow silica precursor cake. The resulting third hollow silica precursor cake was then suspended in 4 L of ion-exchanged water and heated to 90°C with stirring. 40 ml of 0.55 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 200 ml of 0.55 mol / L No. 3 water glass and 210 ml of 0.50 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid was added over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a cake of the fourth hollow silica precursor.

[0086] Next, 2 L of ion-exchanged water and 1,083 ml of 2 mol / L sulfuric acid were added to the resulting cake of the fourth hollow silica precursor (282 g of powder), and the mixture was left at 90°C for 1.5 hours to obtain a slurry of the fifth hollow silica precursor. The cake was then dehydrated and washed with water, and dried at 105°C for 1 day to obtain a powder of the fifth hollow silica precursor.

[0087] The resulting powder of the fifth hollow silica precursor was then calcined in an electric furnace at 800°C for 1 hour and then at 1100°C for 1 hour to obtain hollow silica particles. Specifically, the powder of the fifth hollow silica precursor was calcined in the air to obtain hollow particles.

[0088] (Preparation of Resin Composition) 95.2 phr of bisphenol F epoxy resin ("JER806" manufactured by Mitsubishi Chemical Corporation) and 40 phr of the obtained hollow silica particles were mixed for 3 minutes under atmospheric pressure at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm using a planetary centrifugal mixer ("ARV-310P" manufactured by Thinky Corporation) to obtain a mixture. Hereinafter, the hollow silica particles may be referred to as a filler. The resulting mixture and 4.8 phr of an imidazole-based epoxy resin curing agent ("2E4MZ" manufactured by Shikoku Kasei Co., Ltd.) were mixed for 3 minutes using a planetary centrifugal mixer under conditions of a rotation of 1000 rpm, a revolution of 2000 rpm, and 0.7 kPa to obtain a resin composition.

[0089] (Production of resin molded body) The obtained resin composition was poured into a 1.0 mm thick Teflon (registered trademark) mold and press-molded at 80°C for 1 hour. After cooling, the molded product was removed from the mold and placed in a dryer at 150°C for 4 hours for further heat curing. The molded product was then cooled to obtain an evaluation sample.

[0090] [Example 2] (Preparation of hollow silica particles) Elliptical alunite particle powder (NaAl3(SO4)2(OH)6, major axis: 1.98 μm, D SL :1.13, minor axis: 1.35μm, D ST 200 g of the granular material (aspect ratio: 1.18, aspect ratio: 1.47) was suspended in 1.4 L of ion-exchanged water to obtain a slurry of alunite particles.

[0091] The resulting alunite particle slurry was then heated to 90°C while stirring, and 202 ml of 0.56 mol / L No. 3 water glass (Na2O·2.97SiO2, Fujifilm Wako Pure Chemical Industries, Ltd.) was added over 4 hours. The resulting slurry was aged for 1 hour, then dehydrated and washed with water to obtain a cake of the first core-shell particle precursor. The cake of the first core-shell particle precursor was then dried at 105°C for 1 day to obtain a powder of core-shell particles.

[0092] Next, the powder of the first core-shell particle precursor was suspended in 1.4 L of ion-exchanged water and heated to 90°C while stirring. 34 ml of 0.56 mol / L No. 3 water glass was then added over 10 minutes. Subsequently, 168 ml of 0.56 mol / L No. 3 water glass and 188 ml of 0.51 mol / L sulfuric acid were added simultaneously. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a cake of the second core-shell particle precursor.

[0093] The resulting cake of second core-shell particle precursor was suspended in 1.4 L of ion-exchanged water and heated to 90°C with stirring. 34 ml of 0.56 mol / L No. 3 water glass was then added over 10 minutes. Subsequently, 168 ml of 0.56 mol / L No. 3 water glass and 188 ml of 0.51 mol / L sulfuric acid were added simultaneously. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water, and then dried at 105°C for one day to obtain a powder of core-shell particles.

[0094] The obtained powder of core-shell particles was then fired at 500° C. for 3 hours and then at 550° C. for 1 hour. It is believed that the firing caused the alunite particles to change as follows: NaAl3(SO4)2(OH)6→NaAl(SO4)2+Al2O3+3H2O

[0095] Next, 1305 ml of ion-exchanged water was added to 177 g of the calcined core-shell particles and resuspended under stirring at room temperature. 555 ml of 3.35 mol / L sulfuric acid was added to this, and the mixture was heated to 90°C and reacted for 5 hours to dissolve the core particles, yielding a slurry of the first hollow silica precursor. The obtained slurry of the first hollow silica precursor was dehydrated and washed with water to obtain a cake of the first hollow silica precursor.

[0096] Next, the resulting first hollow silica precursor cake (18.8 g of powder) was suspended in 1.36 L of ion-exchanged water and heated to 90°C while stirring. 20 ml of 0.56 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 100 ml of 0.56 mol / L No. 3 water glass and 105 ml of 0.51 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a second hollow silica precursor cake. The resulting second hollow silica precursor cake was then suspended in 1.36 L of ion-exchanged water and heated to 90°C with stirring. 20 ml of 0.56 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 100 ml of 0.56 mol / L No. 3 water glass and 105 ml of 0.51 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid was added over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a third hollow silica precursor cake. The resulting third hollow silica precursor cake was then suspended in 1.36 L of ion-exchanged water and heated to 90°C with stirring. 20 ml of 0.56 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 100 ml of 0.56 mol / L No. 3 water glass and 105 ml of 0.51 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid was added over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a cake of the fourth hollow silica precursor.

[0097] Next, 1.36 L of ion-exchanged water and 146 ml of 3.35 mol / L sulfuric acid were added to the resulting cake of the fourth hollow silica precursor (52.8 g of powder), and the mixture was left at 90°C for 1.5 hours to obtain a slurry of the fifth hollow silica precursor. The cake was then dehydrated and washed with water, and dried at 105°C for 1 day to obtain a powder of the fifth hollow silica precursor.

[0098] Next, the obtained powder of the fifth hollow silica precursor was fired in an electric furnace (in the air atmosphere) at 800°C for 1 hour and at 1100°C for 1 hour to obtain hollow silica particles.

[0099] (Production of resin molded body) A molded body (evaluation sample) was obtained in the same manner as in Example 1, except that the hollow silica particles were used.

[0100] [Example 3] (Preparation of hollow silica particles) Elliptical alunite particle powder (NaAl3(SO4)2(OH)6, major axis: 1.98 μm, D SL :1.13, Short diameter: 1.35μm, D ST 1500 g of the granular material (wt.: 1.18, aspect ratio: 1.47) was suspended in 7.5 L of ion-exchanged water to obtain a slurry of alunite particles.

[0101] The resulting alunite particle slurry was then heated to 90°C with stirring, and 1507 ml of 0.54 mol / L No. 3 water glass (Na2O 3.14SiO2, Fujifilm Wako Pure Chemical Industries, Ltd.) was added over 4 hours. The resulting slurry was aged for 1 hour, then dehydrated and washed with water to obtain a cake of first core-shell particle precursors.

[0102] The resulting first core-shell particle precursor cake was then suspended in 7.5 L of ion-exchanged water and heated to 90°C with stirring. 1507 ml of 0.54 mol / L No. 3 water glass was added over 2 hours. The resulting slurry was aged for 1 hour, left to stand with stirring for 15 hours, then dehydrated and washed with water to obtain a second core-shell particle precursor cake. The resulting second core-shell particle precursor cake was then suspended in 7.5 L of ion-exchanged water and heated to 90°C with stirring. 1507 ml of 0.54 mol / L No. 3 water glass was added over 2 hours. The resulting slurry was aged for 1 hour, left to stand with stirring for 15 hours, then dehydrated and washed with water, and then dried at 100°C for 1 day to obtain a core-shell particle powder.

[0103] The obtained powder of core-shell particles was then fired at 500° C. for 3 hours and then at 550° C. for 1 hour. It is believed that the firing caused the alunite particles to change as follows: NaAl3(SO4)2(OH)6→NaAl(SO4)2+Al2O3+3H2O

[0104] Next, 6 L of ion-exchanged water was added to 864 g of the calcined core-shell particles and resuspended under stirring at room temperature. 7.8 L of 1 mol / L sulfuric acid was added to this, and the mixture was heated to 90°C and reacted for 5 hours to dissolve the core particles, yielding a slurry of the first hollow silica precursor. The obtained slurry of the first hollow silica precursor was dehydrated and washed with water to obtain a cake of the first hollow silica precursor.

[0105] Next, the resulting first hollow silica precursor cake (130 g of powder) was suspended in 860 ml of ion-exchanged water and heated to 90°C while stirring. 33 ml of 0.54 mol / L No. 3 water glass was added over 10 minutes, followed by the simultaneous addition of 163 ml of 0.54 mol / L No. 3 water glass and 186 ml of 0.50 mol / L sulfuric acid. The No. 3 water glass was added over 50 minutes, and the sulfuric acid over 60 minutes. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain a hollow silica precursor cake. This same procedure was repeated twice more to obtain a second hollow silica precursor cake.

[0106] Next, 2 L of ion-exchanged water and 400 ml of 2.87 mol / L sulfuric acid were added to the resulting cake of the second hollow silica precursor (284 g of powder), and the mixture was left at 90°C for 1.5 hours to obtain a slurry of the third hollow silica precursor. The cake was then dehydrated and washed with water, and dried at 100°C for 1 day to obtain a powder of the third hollow silica precursor.

[0107] Next, the obtained powder of the third hollow silica precursor was fired in an electric furnace (in the air atmosphere) at 800°C for 1 hour and at 1100°C for 1 hour to obtain hollow silica particles.

[0108] (Production of resin molded body) A molded body (evaluation sample) was obtained in the same manner as in Example 1, except that the above hollow silica particles were used and the blending amount of the hollow silica particles was 25 phr. Although an attempt was made to blend the hollow silica particles so as to have the same blending amount as in Example 1, it was not possible to blend them any further.

[0109] [Comparative Example 1] A molded body (evaluation sample) was obtained in the same manner as in Example 1, except that no hollow silica particles were blended.

[0110] [XRD Measurement] When the hollow silica particles of Example 1, 2 and 3 were analyzed by X-ray diffraction (''EMPYRIAN'' manufactured by PANalytical), they were amorphous silica.

[0111] [TEM-EDS Measurement] Regarding the hollow silica particles of Example 1, 2 and 3, an image was captured under the conditions of an acceleration voltage of 200 kV and a magnification of 200,000 times using a transmission electron microscope (''JEM-2100PLUS'' manufactured by JEOL Ltd.) and an energy dispersive X-ray analyzer (JED2300 series manufactured by JEOL Ltd.) attached thereto, and compositional analysis was performed on three points in the thickness direction in the point analysis mode. The observation results of the hollow silica particles of Example 1 are shown in Fig. 5A, the observation results of the hollow silica particles of Example 2 are shown in Fig. 5B, and the observation results of the hollow silica particles of Example 3 are shown in Fig. 5C. Also shown are the atomic ratios of oxygen (O), aluminum (Al) and silicon (Si) determined from the obtained peak intensities. In each case, a tendency for the amount of Al to decrease from the inside to the outside of the shell was confirmed.

[0112] The following evaluations were also performed on the hollow silica particles of Example 1, 2 and 3. The evaluation results are summarized in Table 1. 1. Content of Al The Al content was measured by pretreating hollow silica particles to prepare an Al content measurement sample and analyzing it using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Specifically, 250 mg of hollow silica particles were weighed into a PMP resin beaker. The hollow silica particles were then soaked in ultrapure water, followed by the addition of 3 mL of nitric acid and 5 mL of hydrofluoric acid, followed by heating and dissolution. The solution was then concentrated to 5 mL, and a 1% boric acid solution was added to mask the remaining hydrofluoric acid. The solution was then inactivated without damaging the analytical equipment and heated for 10 minutes. After cooling, the solution was diluted to 50 mL with ultrapure water to prepare an Al content measurement sample for analysis. From the obtained results, the Al content was calculated. 2.Na content The sodium content was measured by atomic absorption spectrometry (AAS) after preparing a sample for sodium content measurement from hollow silica particles through pretreatment. Specifically, 250 mg of hollow silica particles were weighed into a PMP resin beaker. The hollow silica particles were then soaked in ultrapure water, followed by the addition of 3 ml of nitric acid and 5 ml of hydrofluoric acid, followed by heating and dissolution. The solution was then concentrated to 5 ml, after which a 1% boric acid solution was added to mask the remaining hydrofluoric acid, inactivating it without damaging the analytical equipment, and heated for 10 minutes. After cooling, the solution was diluted to 50 ml with ultrapure water to prepare a sample for sodium content measurement, which was then subjected to analysis. From the results obtained, the Na content was calculated. 3. Shell thickness of hollow particles The shell thickness of the particles was calculated by TEM observation. Specifically, the shell thickness of 10 primary particles randomly selected from the TEM photograph of the particles was measured, and the arithmetic mean (average thickness) of the obtained measurements was calculated. The magnifications for TEM observation were 10,000x and 100,000x. 4.Hollow rate The hollow ratio was calculated from the major and minor diameters and the shell thickness. Specifically, the primary particle diameter (major and minor diameters) and the shell thickness were used to approximate the particle shape with the volume of a cylinder, and the hollow ratio was calculated using the following formula. Hollowness = hollow volume of hollow particle ÷ volume of hollow particle × 100 Volume of hollow particle = π x radius 2 × height = π × (major axis ÷ 2)2 × Short diameter Hollow volume of hollow particle = π × ((long diameter - shell thickness × 2) ÷ 2) 2 ×(minor diameter - shell thickness × 2) 5.BET specific surface area The specific surface area was measured using a "BELsorp-mini" manufactured by Microtrac BEL Co., Ltd. Specifically, it was measured using a constant volume gas adsorption method using nitrogen gas, and the specific surface area was calculated by analysis using the BET multipoint method. 6. Pore volume The pore volume was measured using a "BELsorp-max" manufactured by Microtrac-Bell Co., Ltd. Specifically, measurements were performed using a constant volume gas adsorption method using nitrogen gas, and the pore volume (cumulative pore volume of pores with diameters of 1 nm to 100 nm and cumulative pore volume of pores with diameters of 1 nm to 10 nm) was calculated by analysis using the BJH method. 7. Density The density was determined by a nitrogen gas substitution method. Specifically, a gas substitution density measurement device (Micromeritics, dry automatic density meter Accupic II 1340) was used, and 0.15 to 0.2 g of sample was measured at 1 cm 3 The measurement was repeated five or more times and the average value was calculated. 8. Dielectric constant and dielectric loss tangent The dielectric constant and dielectric loss tangent were measured by a cavity resonance method using a powder dielectric constant measuring device. The measurements were performed at 10 GHz under conditions of a temperature of 25°C and a humidity of 44% RH. The density required for calculating the dielectric properties was determined by the nitrogen gas substitution method. 9.Oil absorption amount Epoxy resin ("JER819" manufactured by Mitsubishi Chemical Corporation) was added dropwise to 1 g of hollow silica particles to be measured and mixed, and the amount of oil absorption was calculated using the following conversion formula from the amount of epoxy resin added when the particles turned into a paste. Specifically, epoxy resin was repeatedly added dropwise to the hollow silica particles and mixed, and the end point was the point when the hollow silica particles turned into a paste. Near the end point, the epoxy resin was added drop by drop while being blended in. After that, the amount of epoxy resin per 1 g of the measurement object was calculated using the formula below, and the obtained oil absorption per 1 g was divided by the specific surface area of ​​the measurement object to obtain the unit area of ​​the surface area (m 2 The oil absorption per 100g of the powder was calculated. Oil absorption per 1g = epoxy resin titration amount (g) / mass of powder to be measured (g) Unit area of ​​surface area (m 2 ) = oil absorption per 1g (g / g) / specific surface area of ​​powder to be measured (m 2 / g)

[0113] <Evaluation of resin molded products> The resin molded bodies (evaluation samples) of the examples and comparative examples were subjected to density measurement, cross-sectional observation, and dielectric property measurement. The porosity of the resin molded body, the filler density in the resin molded body, and the filler hollowness in the resin molded body were also calculated. The evaluation results are summarized in Table 1. The results of observing the resin molded body of Example 1 at 2000x magnification are shown in Figure 6.

[0114] (density measurement) The density of the resin molded body was measured using an electronic density meter ("SD120L" manufactured by Alpha Mirage Co., Ltd.) Specifically, the obtained resin molded body was cut into a size of 5 cm x 6 cm using an ultrasonic cutter, and the molded body sample obtained by cutting was subjected to measurement.

[0115] 1.Porosity of resin molded body From the results of the density measurements, the porosity (volume ratio of air in the resin molded body) Va % of the resin molded body was calculated. 2. Filler density in resin molded body The filler density in the resin molded body was calculated using the following formula. The filler density in the resin molded body was calculated by subtracting the volume of the resin component from the volume of the filler-containing resin molded body to calculate the filler volume, and then dividing the amount of filler added by the calculated filler volume. The volume of the filler-containing resin molded body was measured using an electronic density meter ("SD120L" manufactured by Alpha Mirage Co., Ltd.). The volume of the resin component was calculated from the weight and density of a blank resin molded body separately prepared without adding filler. Filler density in resin molded body = wf / (Vc-mr / ρr) = wf / (Vc-100 / ρr) wf: weight part of particles (filler) when the weight of resin is 100 parts by weight (phr) Vc: Volume of resin molded body mr: resin weight (g) ρr: Density of resin (g / ml) 3. Hollow filler ratio in resin molded body The filler hollow fraction Va / (Va+Vs) in the resin molded body was calculated from the value of the void fraction Va% of the resin molded body, where Vs can be calculated using the following formula.

number

[0116] (Cross-section observation of resin molded body) The obtained molded body sample was cut using a cross-section polisher ("IB-09010CP" manufactured by JEOL Ltd.), and the cross section was observed using an FE-SEM ("JSM-7600F" manufactured by JEOL Ltd., magnification: 2000x, 5000x, or 10000x).

[0117] (Measurement of dielectric constant and dielectric loss tangent) The dielectric constant and dielectric loss tangent of the obtained molded sample were measured under the following conditions. Measurement method: Complies with IEC 62810 (cavity resonator perturbation method) Sample shape: Length 55mm or more, width 1.6-2.4mm, height 0.7-1.0mm Test conditions: Frequency 10GHz Number of measurements: 2 Conditioning: 23°C ± 1°C, 50% RH ± 5% RH, 24 hours Testing room environment: 23°C ± 1°C, 50% ± 5% RH Measurement equipment: PNA network analyzer N5222B (Keysight Technologies, Inc.) Cavity resonator: CP531 for 10 GHz (manufactured by Kanto Electronics Application Development Co., Ltd.)

[0118] [Table 1]

[0119] In each example, cross-sectional observation of the resin molded body showed that no resin had penetrated into the hollow region, and destruction of the hollow particles was suppressed, as shown in Figure 6. In Examples 1 and 2, which had low oil absorption, it was possible to blend a larger amount of filler into the resin, and it was found that the dielectric properties of the resin composition (resin molded body) were superior. [Industrial Applicability]

[0120] The hollow particles of the present invention can be suitably used, typically, in electronic materials, but can also be used, for example, in heat insulating materials, sound insulating materials, shock absorbing materials, stress absorbing materials, optical materials, and lightweight materials. [Explanation of symbols]

[0121] L major axis T Short diameter 2 hollow particles 4 Shell 6 Space (hollow part) 10 Laminate 11 Resin layer 12 Metal foil

Claims

1. A hollow particle having an internal hollow shell, The shell is silica containing aluminum, the aluminum content is less than 1% of the components constituting the shell, and the amount of aluminum present in a first portion of the shell located on the inner side in the thickness direction of the shell is at least twice as much as that present in a second portion of the shell located near the surface on the outer side in the thickness direction of the shell than in the first portion.

2. A hollow particle as described in claim 1, wherein the amount of aluminum present decreases from the inside to the outside of the shell.

3. A hollow particle as described in claim 2, wherein the amount of aluminum present decreases continuously from the inside to the outside of the shell, or the amount of aluminum present decreases stepwise from the inside to the outside of the shell.

4. Epoxy resin oil absorption: 0.6 g / m ２ The hollow particle of claim 1 , wherein the diameter is less than 1 / 2 mm.

5. 2. The hollow particle according to claim 1, wherein the shell further contains sodium, and the sodium content of the shell is 3000 ppm or less.

6. The hollow particle according to claim 1 , wherein the silica is amorphous silica.

7. The hollow particle according to claim 1 , wherein the shell has a hollowness of 30% or more and 95% or less.

8. The hollow particle according to claim 1 , wherein the shell has a thickness of 25 nm or more and 500 nm or less.

9. coating the core particles with a shell-forming material to obtain core-shell particles; removing the core particles from the core-shell particles to obtain hollow particle precursors; and coating the hollow particle precursor with a shell-forming material; The method for producing hollow particles according to any one of claims 1 to 8, comprising:

10. The method according to claim 9, wherein the core particles contain an alunite-type compound represented by the following general formula (I): M ａ [Al １－ｘ M’ ｘ ] ３ (SO ４ ２－ ) ｙ (OH) ｚ ・mH ２ O・・・(I) In formula (I), M is Na ＋ , K. ＋ , N.H. ４ ＋ and H ３ O ＋ and M' is at least one cation selected from the group consisting of Cu ２＋ , Zn ２＋ , Ni ２＋ , Sn ４＋ , Zr ４＋ and Ti ４＋ wherein a satisfies 0.8≦a≦1.35, m satisfies 0≦m≦5, x satisfies 0≦x≦0.4, y satisfies 1.7≦y≦2.5, and z satisfies 4≦z≦7.

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