CN118043390A

CN118043390A - Composite material and method for producing composite material

Info

Publication number: CN118043390A
Application number: CN202280065705.4A
Authority: CN
Inventors: 加藤智也; 伊藤孝彦; 大塚哲弥
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-09-30
Filing date: 2022-09-27
Publication date: 2024-05-14

Abstract

The present invention relates to a composite material (1 a) comprising a skeleton portion (10) containing a resin (11), inorganic particles (12), and a plurality of voids (20). At least a part of the inorganic particles (12) is disposed along the boundary between the void (20) and the skeleton (10). When the composite material (1 a) is viewed in cross-section, a first distribution D1 of the number-based dimensions Sz obtained by measuring the dimensions Sz of each of the plurality of voids (20) has 2 or more peaks.

Description

Composite material and method for producing composite material

Technical Field

The present invention relates to a composite material and a method for producing the composite material.

Background

Conventionally, attempts have been made to improve the thermal conductivity of materials such as foam materials having a plurality of voids.

For example, patent document 1 discloses a composite material including a scaly filler made of an inorganic material and a binder resin made of a thermosetting resin for binding the filler. The composite material is a foam material formed by dispersing a plurality of pores, and the filler is gathered together in such a manner that flat surfaces of the filler overlap each other on inner walls of the pores (see claim 1 and fig. 1). Patent document 1 describes the following: when the ratio of the average length of the flat surfaces of the filler to the thickness of the filler, that is, the aspect ratio is less than 50, the flat surfaces of the filler are not likely to overlap with each other.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2018-109101

Disclosure of Invention

Problems to be solved by the invention

In the technique described in patent document 1, the heat conductivity is improved by the accumulation of the filler by foaming. On the other hand, in patent document 1, no discussion is made regarding the relationship between the size distribution of the plurality of voids and the thermal conductivity. Based on this, the present invention provides a composite material in which a plurality of void sizes are distributed in a state advantageous from the viewpoint of thermal conductivity.

Means for solving the problems

The present invention provides a composite material comprising a resin-containing skeleton portion, inorganic particles, and a plurality of voids,

At least a part of the inorganic particles are arranged along the boundary between the voids and the skeleton portion,

When the composite material is viewed in cross-section, a first distribution of the dimensions based on a number obtained by measuring the dimensions of each of the plurality of voids has 2 or more peaks.

In addition, the present invention provides a method of manufacturing a composite material, the method comprising:

In a mixture comprising a plurality of composite particles each having a first resin and inorganic particles disposed around the first resin, and a resin composition having fluidity and filling gaps between the composite particles, the fluidity of the resin composition is reduced to form a solid portion containing a second resin; and

Forming a plurality of voids by shrinkage or removal of the first resin, and disposing at least a part of the inorganic particles along boundaries between the plurality of voids and the solid portion,

The plurality of composite particles includes a first composite particle and a second composite particle,

The size of the first resin of the first composite particles is included in a first range,

The size of the first resin of the second composite particles is included in a second range having an upper limit smaller than a lower limit of the first range.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the composite material described above, the sizes of the plurality of voids are distributed in a state advantageous from the standpoint of thermal conductivity.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of a composite material according to the present embodiment.

Fig. 2A is a graph showing an example of a first distribution of void sizes of the composite material according to the present embodiment with respect to the number references in cross section.

Fig. 2B is a graph showing an example of a second distribution of maximum diameters of annular cross sections of the composite material according to the present embodiment with reference to the number of cross sections.

Fig. 3 is a cross-sectional view schematically showing another example of the composite material of the present embodiment.

Fig. 4 is a photograph of a cross section of the composite of example 1.

Fig. 5 is a photograph of a cross section of the composite material of comparative example 1.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description is an example of the present invention, and the present invention is not limited to the following embodiments.

As shown in fig. 1, the composite material 1a includes a skeleton portion 10 including a resin 11, inorganic particles 12, and a plurality of voids 20. In the composite material 1a, a porous structure is formed by the skeleton portion 10, the inorganic particles 12, and the plurality of voids 20. At least a part of the inorganic particles 12 is disposed along the boundary between the void 20 and the skeleton portion 10.

In the composite material 1a, a layered structure having a predetermined thickness may be formed by stacking a plurality of inorganic particles 12 along the boundary between the void 20 and the skeleton portion 10.

Fig. 2A shows a first distribution D1 of the number-based dimensions Sz obtained by measuring the dimensions Sz of each of the plurality of voids 20 when the composite material 1a is viewed in cross section. As shown in fig. 2A, the first distribution D1 has 2 or more peaks.

By providing the first distribution D1 with 2 or more peaks, the volume of the boundary between the voids 20 and the skeleton portion 10 tends to be increased in the porous structure of the composite material 1 a. As described above, the inorganic particles 12 are arranged along the boundary between the voids 20 and the skeleton portion 10, and the inorganic particles 12 may have a thermal conductivity higher than that of the resin 11. Therefore, a large volume of the boundary between the void 20 and the skeleton portion 10 is advantageous for improving the thermal conductivity of the composite material 1 a. Therefore, the composite material 1a easily has a high thermal conductivity. In addition, by having 2 or more peaks in the first distribution D1, voids 20 are easily present at various portions of the porous structure. Therefore, the composite material 1a easily has flexibility.

In the composite material 1a, the cross section in which the dimension Sz is measured to obtain the first distribution D1 is not limited to a specific cross section. The composite material 1a has, for example, a flat outer surface. The cross section for measurement of the dimension Sz may be parallel or perpendicular or inclined with respect to its outer surface. The cross section in which the dimension Sz is measured to obtain the first distribution D1 may include a plurality of cross sections. In order to obtain the first distribution D1, the number of voids 20 in which the size Sz is measured is, for example, 200 or more. The observation of the cross section can be performed using a microscope such as an optical microscope, a metal microscope, or an electron microscope. The dimension Sz is, for example, the maximum diameter of the void 20 in cross section. The maximum diameter of the gap 20 is the maximum dimension of a line segment connecting two different points in the range of the gap 20.

As shown in fig. 2A, the first distribution D1 may be made into a histogram, for example. In this case, the amplitude of each section in the histogram is not limited to a specific value. The amplitude is, for example, 10 to 100. Mu.m. For example, when the peak of the first distribution D1 is located in a specific section of the histogram, the central value of the section may be regarded as the size Sz corresponding to the peak.

As shown in fig. 1, in the composite material 1a, the plurality of voids 20 has a plurality of first voids 21 and second voids 22. The second gaps 22 are disposed between the first gaps 21, for example. When the composite material 1a is viewed in cross-section, the dimension Sz of the first void 21 is included in the first range, and the dimension Sz of the second void 22 is included in the second range. The second range is a range having an upper limit smaller than the lower limit of the first range. According to such a configuration, the inorganic particles 12 can be disposed between the first voids 21 along the boundary between the second voids 22 and the skeleton portion 10. Thus, the composite material 1a is more likely to have a high thermal conductivity. In addition, the composite material 1a is more easily flexible.

As shown in fig. 2A, the first distribution D1 has, for example, a first peak P1 and a second peak P2. The size Sz of the void 20 corresponding to the second peak P2 is smaller than the size Sz of the void 20 corresponding to the first peak P1. The ratio N2/N1 of the number N2 of the voids 20 corresponding to the second peak to the number N1 of the voids 20 corresponding to the first peak P1 is not limited to a specific value. The ratio N2/N1 is, for example, 0.01 to 100. According to such a constitution, the composite material 1a is more likely to have a high thermal conductivity. In addition, the composite material 1a is more easily flexible. When the first distribution D1 is a histogram, the number of voids 20 corresponding to a specific peak is the number of voids 20 corresponding to the section to which the peak belongs in the histogram.

The ratio N2/N1 may be 0.05 or more, may be 0.1 or more, or may be 0.5 or more. The ratio N2/N1 may be 100 or less, 50 or less, or 20 or less. The first distribution D1 may have 3 or more peaks.

As shown in fig. 1, when the composite material 1a is viewed in cross-section, the inorganic particles 12 disposed along the boundary between the voids 20 and the skeleton portion 10 form, for example, a plurality of annular cross-sections 12c corresponding to the plurality of voids 20. Fig. 2B shows a second distribution D2 of the number references obtained by measuring the maximum diameter Tz of each of the plurality of annular cross sections 12c. As shown in fig. 2B, the second distribution D2 has, for example, a third peak P3 and a fourth peak P4. The maximum diameter Tz corresponding to the fourth peak P4 is smaller than the maximum diameter Tz corresponding to the third peak P3. Composite 1a satisfies, for example, the conditions of L1/L2. Gtoreq.1.25, { (L1 ²-d1²)h1}/{(L2²-d2²) h2 }. Gtoreq.0.8, and R.ltoreq.0.55. In these conditions, L1 is the maximum diameter Tz corresponding to the third peak P3, and L2 is the maximum diameter Tz corresponding to the fourth peak P4. d1 is the dimension Sz corresponding to the first peak P1, and d2 is the dimension Sz corresponding to the second peak P2. h1 is the number of voids 20 corresponding to the first peak P1, and h2 is the number of voids 20 corresponding to the second peak P2. R is the ratio of the cross-sectional area of the skeleton portion 10 of the composite material 1a in cross-section to the cross-sectional area of the composite material 1 a. As a result of intensive studies, the present inventors have found that, when the composite material 1a is adjusted so that L1, L2, d1, d2, h1, h2 and R satisfy the above-described conditions, the composite material 1a is more likely to have a high thermal conductivity. In addition, if the above conditions are satisfied, the plurality of voids 20 are easily present in a desired state, and the composite material 1a is more easily flexible.

In the composite material 1a, L1/L2 may be 1.26 or more, 1.27 or more, or 1.28 or more. L1/L2 is, for example, 15 or less, and may be 12 or less.

In the composite material 1a, { (L1 ²-d1²)h1}/{(L2²-d2²) h2} may be 0.9 or more, or may be 1 or more, or may be 1.5 or more, or may be 2 or more, or may be 2.5 or more. { (L1 ²-d1²)h1}/{(L2²-d2²) h2} is, for example, 7 or less, or may be 5 or less.

In the composite material 1a, the ratio R may be 0.54 or less, may be 0.53 or less, or may be 0.52 or less. The ratio R is, for example, 0.3 or more.

The second distribution D2 can be obtained, for example, by measuring the maximum diameter Tz of each of the plurality of annular cross sections 12c in the same cross section as that used to obtain the first distribution D1. The number of cross sections 12c in which the maximum diameter Tz is measured to obtain the second distribution D2 is, for example, 200 or more. For example, the maximum diameter Tz is measured for the annular cross section 12c corresponding to the void 20 for which the measurement of the dimension Sz for producing the first distribution D1 is performed. The maximum diameter Tz is, for example, a dimension at which a line segment connecting two different points in the range of the cross section 12c reaches the maximum. Section 12c does not necessarily form a complete ring. The cross section 12c is continuously present, for example, in a portion corresponding to 80% or more of the circumference of the complete ring.

As shown in fig. 2B, the second distribution D2 may be made into a bar graph, for example. In this case, the amplitude of each section in the histogram is not limited to a specific value. The amplitude is, for example, 10 to 100. Mu.m. For example, when the peak of the second distribution D2 is located in a specific section of the histogram, the central value of the section may be regarded as the maximum diameter Tz corresponding to the peak.

When the composite material 1a is viewed in cross-section, the arithmetic average S _AVG of the dimensions Sz of the voids 20 obtained by measuring the dimensions Sz of the respective voids 20 is not limited to a specific value. The arithmetic mean S _AVG is, for example, 50 to 1500. Mu.m. If the arithmetic mean S _AVG is 50 μm or more, the first distribution D1 tends to have 2 or more peaks, and the composite material 1a tends to have a high thermal conductivity more easily. In addition, the composite material 1a is more easily flexible. If the arithmetic average S _AVG is 1500 μm or less, the composite material 1a easily has a desired strength.

The arithmetic mean S _AVG may be 50 μm or more, or may be 100 μm or more, or may be 250 μm or more, or may be 350 μm or more, or may be 400 μm or more, or may be 450 μm or more, or may be 500 μm or more. The arithmetic mean S _AVG may be 550 μm or more, 600 μm or more, 650 μm or more, or 700 μm or more. The arithmetic mean S _AVG may be 1450 μm or less, 1400 μm or less, 1350 μm or less, or 1300 μm or less. The arithmetic mean S _AVG may be 1250 μm or less, or 1200 μm or less, or 1150 μm or less, or 1100 μm or less, or 1050 μm or less, or 1000 μm or less.

The relationship between the first peak P1 and the second peak P2 is not limited to a specific relationship as long as the first distribution D1 has 2 or more peaks. For example, the first peak P1 is present in the range of the dimension Sz of 500 to 1200 μm, and the second peak P2 is present in the range of the dimension Sz of 50 to 700 μm. According to such a constitution, the composite material 1a is more likely to have a high thermal conductivity. In addition, the composite material 1a is more easily flexible.

The shape of the void 20 is not limited to a specific shape. The outer shape of the space 20 may be, for example, spherical or substantially spherical. In the present specification, "substantially spherical" means that the ratio of the maximum diameter to the minimum diameter (maximum diameter/minimum diameter) is 1.0 to 1.5. The ratio of the maximum diameter to the minimum diameter of the substantially spherical void 20 may be 1.0 to 1.3. The shape of the space 20 may be a rod, a polyhedron, or an ellipse having a ratio of maximum diameter to minimum diameter of more than 1.5. In the composite material 1a, for example, 50% or more of the number of the plurality of voids 20 is spherical. More than 80% of the number of the plurality of voids 20 may be spherical. In the foaming technique, the shape of the void becomes irregular, and therefore, it is difficult to form the void in a shape that is uniform to this extent.

In the composite material 1a, the ratio of the volume of the plurality of voids 20 to the volume of the composite material 1a, that is, the void ratio is not limited to a specific value. The void ratio is, for example, 10 to 60% by volume, may be 15 to 50% by volume, or may be 20 to 45% by volume.

The void fraction can be determined, for example, as follows: the cross section of the composite material 1a was observed, the ratio of the total area of the voids 20 to the total area of the observed cross section was calculated, and the average value of the ratio was taken for 10 images of different cross sections to determine. In addition, the void fraction may also be determined based on the results of the X-ray CT scan of the composite material 1 a. On the other hand, in the case where the manufacturing process of the composite material 1a is known, it can be found as follows. The mass of the inorganic particles 12 contained in the composite particles is calculated from the mass of the resin particles and the mass of the composite particles in which the inorganic particles 12 are disposed on the surfaces of the resin particles, which will be described later. On the other hand, the content [ mass% ] of the inorganic particles 12 in the composite material 1a is calculated based on the result of the inorganic element analysis of the composite material 1 a. The mass of the inorganic particles 12 in the composite material 1a is calculated from the content [ mass%) of the inorganic particles 12 in the composite material 1a and the mass of the composite material 1 a. The number of composite particles used in manufacturing the composite material 1a is calculated from the mass of the inorganic particles 12 in the composite material 1a and the mass of the inorganic particles 12 contained in the composite particles. The volume of the void 20 is calculated from the average diameter of the void 20. The total volume of the voids 20 in the composite 1a is determined from the product of the volume of the voids 20 and the number of composite particles. The void ratio was calculated by dividing this value by the volume of the composite material 1 a.

The plurality of voids 20 have, for example, mutually similar profiles. For example, in the composite material 1a, 80% or more of the plurality of voids 20 have mutually similar outer shapes on a number basis. The plurality of voids 20 are similar to each other in shape, such as a sphere. The profile may be substantially spherical. The voids formed by foaming may be connected to each other by expansion of each of the voids. In this case, however, in general, the internal pressure generated by foaming acts on the connecting portion of the void, so that the vicinity of the connecting portion is significantly deformed. Thus, in the foaming-based technique, a plurality of voids connected to each other and substantially similar in appearance cannot be formed in practice.

The porous structure of the composite material 1a may have through holes from one main face to the other main face of the composite material 1a. In the case where the composite material 1a has a pair of outer surfaces parallel to each other, the void 20 provided at one outer surface of the composite material 1a may communicate with a space facing the other outer surface of the composite material 1a. In addition, the void provided on one outer surface of the composite material 1a may communicate with a space connected at a side surface intersecting with the one outer surface of the composite material 1a. With such a configuration, the composite material 1a can achieve both thermal conductivity and air permeability.

As shown in fig. 1, the composite material 1a has, for example, a heat transfer path 5 formed of inorganic particles 12. With such a configuration, heat is easily transferred to the composite material 1a by heat conduction in the heat transfer path 5, and the composite material 1a easily has a high thermal conductivity.

The heat transfer path 5 is formed continuously by, for example, a plurality of inorganic particles 12 that are in contact or in proximity to each other. The heat transfer path 5 extends, for example, across a plurality of voids 20. The heat transfer path 5 does not pass through the interior of the skeleton portion 10, and extends along the boundary between the skeleton portion 10 and the plurality of voids 20, for example. The composite material 1a has, for example, a first outer surface 2a and a second outer surface 2b parallel to each other, and the heat transfer path 5 may extend from the first outer surface 2a to the second outer surface 2b. The inorganic particles 12 may be in direct contact with each other, and the inorganic particles 12 may be in close contact with each other in a state where a given resin is present between the inorganic particles 12.

In the composite material 1a, at least a part of the plurality of voids 20 may be arranged in a mutually connected manner. In this case, the pair of voids 20 connected to each other may be connected together by the connection portion 20j containing the inorganic particles 12. The pair of voids 20 connected to each other may be connected together by a connection portion 20k containing no inorganic particles 12. In this case, the pair of voids 20 forms 1 space communicating through the connection portion 20 k. The dimension of the connecting portion 20k is, for example, 25% or less of the dimension Sz of the space 20, and may be 20% or less, or may be 15% or less. In this case, the dimension Sz of each void 20 is determined as if a pair of voids 20 were partitioned by the connecting portion 20 k. The pair of voids 20 connected to each other may be connected together by the connection portion 20m containing only the resin and not the inorganic particles 12.

In the specific cross section as shown in fig. 1, not all the heat transfer paths 5 are necessarily present, and further, not all the portions of the specific heat transfer paths 5 are necessarily present. In a particular cross section, even a heat transfer path 5 that appears to be interrupted between the first outer surface 2a and the second outer surface 2b may extend to the first outer surface 2a, the second outer surface 2b, or both the first outer surface 2a and the second outer surface 2b by inorganic particles 12 that are not present in the cross section. Similarly, contact of all the voids 20 cannot be confirmed only in a specific cross section. For example, when viewing FIG. 1, the void 20i is isolated. However, the void 20i is in contact with another void 20 adjacent in the direction perpendicular to the cross section.

On the other hand, it is not required that all of the heat transfer paths 5 extend from the first outer surface 2a to the second outer surface 2b. Nor does it require that all of the voids 20 contained in the composite 1a be in contact with additional voids 20, either directly or via inorganic particles 12.

The material forming the inorganic particles 12 is not limited to a specific inorganic material. The material forming the inorganic particles 12 has, for example, a thermal conductivity higher than that of the resin 11. Examples of the material forming the inorganic particles 12 are hexagonal boron nitride (h-BN), aluminum oxide, crystalline silica, amorphous silica, aluminum nitride, magnesium oxide, carbon fiber, silver, copper, aluminum, silicon carbide, graphite, zinc oxide, silicon nitride, silicon carbide, cubic boron nitride (c-BN), beryllium oxide, diamond, carbon black, magnesium hydroxide, graphene, carbon nanotubes, carbon fiber, and aluminum hydroxide. The types of the inorganic particles 12 in the composite material 1a and the composite material 1b may be one, or two or more kinds of the inorganic particles 12 may be used in combination in the composite material 1a and the composite material 1 b.

The shape of the inorganic particles 12 is not limited to a specific shape. Examples of the shape of the inorganic particles 12 are spherical, rod-like, fibrous, and scaly. The inorganic particles 12 may be irregularly shaped.

The aspect ratio of the inorganic particles 12 is not limited to a specific value. The aspect ratio of the inorganic particles 12 is, for example, less than 50, and may be 40 or less, or 30 or less. The aspect ratio of the inorganic particles 12 may be 1,2 or more, or 3 or more. In the present specification, unless otherwise specified, the aspect ratio of particles is determined as a ratio of the second size of particles to the first size of particles (second size/first size). The second size of the particles corresponds to the largest size of the particles. The first size of the particle is the largest size of the particle in a direction perpendicular to the line segment that determines the largest size of the particle.

The average particle diameter of the inorganic particles 12 is not limited to a specific value. The average particle diameter of the inorganic particles 12 is, for example, 0.05 μm to 100. Mu.m, may be 0.1 μm to 50. Mu.m, may be 0.1 μm to 30. Mu.m, or may be 0.5 μm to 10. Mu.m. The "average particle diameter" can be determined by, for example, a laser diffraction scattering method. The average particle diameter is, for example, the median particle diameter in the volume-based particle size distribution. The volume-based particle size distribution of the inorganic particles 12 can be obtained, for example, using a MICROTRAC MT3300EXII manufactured by MICROTRAC BEL company.

The shape of the inorganic particles 12 can be determined by observation using a Scanning Electron Microscope (SEM) or the like, for example. For example, in a case where the inorganic particles 12 have an aspect ratio of 1.0 or more and less than 1.7, and at least a part of the outline of the inorganic particles 12 is observed in the form of an arc, the inorganic particles 12 may be spherical. When the inorganic particles 12 are spherical, the inorganic particles 12 may have an aspect ratio of 1.0 to 1.5, in particular, an aspect ratio of 1.0 to 1.3.

The scale shape is a plate shape having a pair of main surfaces and side surfaces. The main surface is the surface where the area of the inorganic particles 12 is largest. The main surface may be a flat surface or a surface having irregularities. In the case where the inorganic particles 12 are scaly, the aspect ratio is defined as the ratio of the average size of the main surface of the inorganic particles 12 to the average thickness, instead of the definition described above. The thickness of the scale-like inorganic particles 12 refers to the distance between the pair of main surfaces. The average thickness can be obtained by measuring the thickness of any 50 inorganic particles 12 by SEM and calculating the average value thereof. The average size of the main surface may be a value of the median diameter d ₅₀ measured by the particle size distribution analyzer described above. The aspect ratio of the scale-like inorganic particles 12 is, for example, 1.5 or more, and may be 1.7 or more, or may be 5 or more. The rod shape may include a rod shape, a columnar shape, a truncated cone shape, and the like. The aspect ratio of the rod-shaped inorganic particles 12 is, for example, 1.5 or more, and may be 1.7 or more, or may be 5 or more.

When the inorganic particles 12 are spherical, the average particle diameter may be, for example, 0.1 μm to 50. Mu.m, 0.1 μm to 10. Mu.m, or 0.5 μm to 5. Mu.m. When the inorganic particles 12 are in the form of scales, the average size of the main surface of the inorganic particles 12 may be, for example, 0.1 μm to 20 μm or 0.5 μm to 15 μm. The average thickness of the inorganic particles 12 may be, for example, 0.05 μm to 1 μm, or 0.08 μm to 0.5 μm. When the inorganic particles 12 are rod-shaped, the minimum diameter (usually the minor axis length) of the inorganic particles 12 is, for example, 0.01 μm to 10 μm, and may be 0.05 μm to 1 μm. The maximum diameter (usually the length of the long axis) of the inorganic particles 12 is, for example, 0.1 μm to 20. Mu.m, and may be 0.5 μm to 10. Mu.m. If the size of the inorganic particles 12 is in such a range, the inorganic particles 12 are easily arranged along the boundary between the voids 20 and the skeleton portion 10, and the heat transfer paths 5 extending across the plurality of voids 20 are easily formed. When the inorganic particles 12 are irregular masses, the average particle diameter of the inorganic particles 12 may be, for example, 10 μm to 100 μm or 20 μm to 60 μm.

The content of the inorganic particles 12 in the composite material 1a is not limited to a specific value. The content of the inorganic particles 12 in the composite material 1a is, for example, 10 to 80% by mass, 10 to 70% by mass, or 10 to 55% by mass. The content of the inorganic particles 12 in the composite material 1a is, for example, 1 to 50% by volume, may be 2 to 45% by volume, may be 5 to 40% by volume, or may be 5 to 30% by volume. By properly adjusting the content of the inorganic particles 12, the composite material 1a easily has a high thermal conductivity and easily has a desired flexibility.

The content [ mass% ] of the inorganic particles 12 in the composite material 1a can be determined by removing materials other than the inorganic particles 12 from the composite material 1a by burning/decomposing or the like. The content [ mass%) of the inorganic particles 12 can be determined by elemental analysis. Specifically, an acid is added to the composite material 1a, and the composite material 1a is decomposed by irradiation with microwaves under pressure. Examples of the acid include hydrofluoric acid, concentrated sulfuric acid, concentrated hydrochloric acid, and aqua regia. The solution obtained by the pressurized acid decomposition was analyzed for elements by inductively coupled plasma atomic emission spectrometry (ICP-AES). Based on the result, the content [ mass% ] of the inorganic particles 12 can be determined.

The density of the inorganic particles 12 can be determined as follows: the composite material 1a was heated by an electric furnace at a high temperature to burn out the organic material, and the residual inorganic particles 12 were obtained based on Japanese Industrial Standard (JIS) R1628:1997 or JIS Z2504:2012.

The resin 11 contained in the skeleton portion 10 is not limited to a specific resin. The resin 11 contains, for example, a crosslinked polymer. The resin 11 may be a thermosetting resin. Examples of the thermosetting resin are phenol resin, urea resin, melamine resin, diallyl phthalate resin, polyester resin, epoxy resin, aniline resin, silicone resin, furan resin, polyurethane resin, alkylbenzene resin, guanamine resin, xylene resin, and imide resin. The curing temperature of the resin 11 is, for example, 25℃to 160 ℃.

The resin 11 may be a thermoplastic resin. Examples of the thermoplastic resin are (meth) acrylic resin, styrene resin, polyethylene terephthalate resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, acrylonitrile-butadiene-styrene resin, and acrylonitrile-styrene resin.

The composite material 1a is, for example, a non-foam. The conventional foam described in patent document 1 cannot have a characteristic structure as shown in fig. 1, that is, a structure in which the arrangement of the inorganic particles 12 is finely and accurately controlled.

An example of a method for producing the composite material 1a will be described. The composite material 1a is produced, for example, by a method including the following steps (I) and (II). The gaps between the composite particles are filled with a resin composition having fluidity. The plurality of composite particles each include a first resin and inorganic particles disposed around the first resin.

(I) In a mixture comprising a plurality of composite particles and a resin composition having fluidity, the fluidity of the resin composition is reduced to form a solid portion comprising a second resin.

(II) forming a plurality of voids by shrinkage or removal of the first resin, and disposing at least a part of the inorganic particles along boundaries between the plurality of voids and the solid portion.

In the mixture used in the step (I), the plurality of composite particles include a first composite particle and a second composite particle. The size of the first resin in the first composite particles is included in the first range. The size of the first resin in the second composite particles is contained in a second range having an upper limit smaller than a lower limit of the first range. Thus, in the composite material 1a, the first distribution D1 has 2 or more peaks. The size of the first resin is, for example, the largest diameter of the first resin.

In the step (I), for example, at least a part of the second composite particles are placed between the first composite particles. In this case, in the composite material 1a, voids 20 having a relatively small size are easily formed between voids 20 having a relatively large size.

The composite particles can be produced, for example, as follows. A premix of resin particles formed from the first resin and an additive is prepared. The additive contains, for example, a given resin. The resin contains, for example, a crosslinkable polymer or a thermosetting resin. Next, the inorganic particles 12 are added to the premix and mixed, whereby composite particles in which the inorganic particles 12 are disposed on the surfaces of the plurality of resin particles are obtained. The step of adding the additive to the resin particles to obtain a premix and the step of adding the inorganic particles 12 to the premix may be repeated a plurality of times. The method of mixing is not limited to a specific method. Examples of the method of mixing include mixing using a ball mill, a bead mill, a planetary mixer, an ultrasonic mixer, a homogenizer, a rotation/revolution mixer, a flow mixer, a henschel mixer, a container rotation type mixer, a belt mixer, and a conical screw mixer.

Next, the composite particles are accommodated in the mold so as to be connected to each other. A resin composition having fluidity, which is prepared separately, is added to the mold, and gaps between the composite particles are filled with the resin composition, thereby obtaining the mixture in the step (I). Alternatively, the composite particles and the resin composition may be mixed in advance to prepare a premix, and the premix may be flowed into a mold and then treated so as to interconnect the composite particles, thereby obtaining the mixture in the step (I).

Bubbles may be removed from the mixture as desired. The method of removing bubbles from the mixture is not limited to a specific method. An example of such a process is degassing under reduced pressure. The degassing under reduced pressure is carried out, for example, at 25℃to 200℃for 1 to 10 seconds.

In the step (I), for example, the fluidity of the resin composition is reduced by heating the mixture. The resin composition is heated, for example, to effect a curing reaction of the thermosetting resin, and the fluidity of the resin composition is lowered.

In the step (II), the method of shrinking or removing the first resin of the composite particles is not limited to a specific method. Examples of the method are a method of heating the precursor of the composite material 1a and a method of immersing the precursor of the composite material 1a in a specific solvent. These methods may also be used in combination. Thereby forming a plurality of voids 20.

The temperature at which the precursor of the composite material 1a is heated is not limited to a specific temperature as long as it is a temperature at which the first resin can be softened. The temperature is, for example, 95℃to 130℃and may be 120℃to 160 ℃.

In the case where the precursor of the composite material 1a is immersed in a specific solvent to shrink or remove the first resin, the solvent is not limited to the specific solvent as long as the second resin is not dissolved and the first resin can be dissolved. Examples of solvents are toluene, ethyl acetate, methyl ethyl ketone, and acetone.

The resin particles formed of the first resin may also have a hollow structure. The hollow portion in the hollow structure may be a single hollow portion or may be constituted by a plurality of hollow portions. In the case where the composite particles include resin particles having a hollow structure, the resin constituting the resin particles is softened by the heat treatment to cause the hollow portions to disappear or shrink, so that a plurality of voids 20 can be formed in accordance therewith. The resin particles formed of the first resin may be solid particles.

In the step (II), when the precursor of the composite material 1a is immersed in a specific solvent, the first resin is more easily dissolved in the solvent than the second resin contained in the solid portion, for example. Therefore, the void 20 having a desired shape is easily formed. Examples of the first resin are: polystyrene (PS), polymethyl methacrylate (PMMA), ethylene vinyl acetate copolymer (EVA), polyvinyl chloride (PVC), polypropylene (PP), acrylonitrile butadiene styrene copolymer (ABS), ethylene propylene diene rubber (EPDM), thermoplastic elastomer (TPE), and polyvinyl alcohol (PVA).

According to the above-described manufacturing method, the plurality of voids 20 can be formed without going through the foaming step.

The composite material 1a may be modified from various points of view. For example, the composite material 1a may be modified to be the composite material 1b shown in fig. 3. The composite material 1b is configured in the same manner as the composite material 1a except for the portions specifically described. The same or corresponding constituent elements of composite material 1b as those of composite material 1a are denoted by the same reference numerals, and detailed description thereof will be omitted. The description of the composite material 1a may also be applied to the composite material 1b as long as there is no technical contradiction.

As shown in fig. 3, particles 30 are disposed in the composite material 1b in the voids 20. The particles 30 are typically resin particles. The particles 30 may be resin particles that have been shrunk by heat treatment. The resin particles before shrinkage may have a shape corresponding to the voids 20. In the composite material 1a, the resin occupying the space corresponding to the void 20 is removed. On the other hand, as shown in fig. 3, in the composite material 1b, the resin occupying the space corresponding to the void 20 is deformed and remains. Even if the presence of the particles 30 cannot be confirmed in a specific cross section, the presence of the particles 30 may be confirmed when another cross section is observed.

Examples

The invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

Example 1 >

100 Parts by weight of pure water, 0.2 part by weight of tricalcium phosphate, and 0.01 part by weight of sodium dodecylbenzenesulfonate were added to an autoclave equipped with a stirrer. To the autoclave were added 0.15 parts by weight of benzoyl peroxide and 0.25 parts by weight of 1, 1-bis (t-butylperoxy) cyclohexane as an initiator, thereby preparing a mixed solution. While stirring the mixture at 350 rpm, 100 parts by weight of styrene monomer was added. Then, polymerization was carried out by heating the solution to 98 ℃. When the polymerization reaction was about 80% completed, it took 30 minutes to heat the reaction solution to 120 ℃. Then, the reaction solution was incubated at 120℃for 1 hour to prepare a solution containing styrene resin particles. After cooling the solution containing styrene resin particles to 95 ℃,2 parts by weight of cyclohexane and 7 parts by weight of butane as a foaming agent were pressed into an autoclave. Then, the solution was warmed again to 120 ℃. Then, the solution was kept at 120℃for 1 hour and then cooled to room temperature, whereby a polymerization syrup was obtained. The polymer slurry is dehydrated, washed and dried to obtain expandable styrene resin particles. The expandable styrene resin particles were sieved to obtain expandable styrene resin particles having a particle diameter of 0.2mm to 0.3 mm. Spherical expanded polystyrene beads α having an average particle diameter of 650 μm to 1200 μm were obtained from the expandable styrene resin particles using a pressurized foaming machine (BHP) manufactured by large-scale industrial Co., ltd. The expanded polystyrene beads α were subjected to sieving with a JIS test sieve having a nominal mesh (JIS Z8801-1:2019) of 1.18mm and 1 mm. At this time, expanded polystyrene beads A which passed through a sieve having a nominal mesh of 1.18mm and failed to pass through a sieve having a nominal mesh of 1mm were used for sample production. The average particle diameter of the expanded polystyrene beads A was 1050. Mu.m, and the bulk density of the expanded polystyrene beads A was 0.025 g/milliliter (mL).

Spherical expanded polystyrene beads β were produced in the same manner as expanded polystyrene beads α except that the foaming conditions in BHP were adjusted so as to have an average diameter of 400 μm to 600 μm. The expanded polystyrene beads β were sieved using sieves of 500 μm and 600 μm nominal mesh. At this time, expanded polystyrene beads B that passed through a sieve of 600 μm nominal mesh and failed to pass through a sieve of 500 μm nominal mesh were used for sample production. The average particle diameter of the expanded polystyrene beads B was 550. Mu.m, and the bulk density of the expanded polystyrene beads B was 0.088g/mL.

The additive was prepared by mixing silicone resin KE-106F manufactured by Xinyue chemical Co., ltd, curing agent CAT-106F manufactured by Xinyue chemical Co., ltd, and silicone oil KF-96-10CS manufactured by Xinyue chemical Co., ltd. In the additive, the relation of the mass of the silicone resin to the mass of the curing agent to the mass of the silicone oil=10:1:10 is satisfied. For 1 part by mass of expanded polystyrene beads a, 7 parts by mass of an additive was prepared. Further, 14 parts by mass of scaly boron nitride was prepared for 1 part by mass of expanded polystyrene beads a. The average thickness of boron nitride was 0.4 μm and the aspect ratio of boron nitride was 20.

To a high-speed flow mixer SMP-2 manufactured by KAWATA Co., ltd, 1 part by mass of expanded polystyrene beads A was added. Next, 0.7 parts by mass of the above-mentioned additive was added to prepare a mixture. The mixture was stirred in a high-speed flow mixer at 1000 revolutions per minute for 1 minute. Next, 1.4 parts by mass of boron nitride was added to the high-speed flow mixer, and the resultant mixture was stirred at 1000 rpm for 1 minute in the high-speed flow mixer. Thus, the operation of attaching boron nitride to the expanded polystyrene beads a via the additive was repeated 10 times, to obtain expanded polystyrene beads M coated with boron nitride. The polystyrene beads M were heated in a constant temperature bath at 60 ℃ for 2 hours, and the silicone resin of the additive was cured to obtain composite particles a as the polystyrene beads coated with boron nitride.

2 Parts by mass of the above additive was prepared for 1 part by mass of expanded polystyrene beads B. Further, 4 parts by mass of scale-like nitriding was prepared with respect to 1 part by mass of expanded polystyrene beads B. The average thickness of boron nitride was 0.4 μm and the aspect ratio of boron nitride was 20.

To a high-speed flow mixer SMP-2 manufactured by AWATA Co., ltd, 1 part by mass of expanded polystyrene beads B was added. Next, 0.2 parts by mass of the above-mentioned additive was added to prepare a mixture. The mixture was stirred in a high-speed flow mixer at 1000 revolutions per minute for 1 minute. Next, 0.4 parts by mass of boron nitride was added to the high-speed flow mixer, and the resultant mixture was stirred at 1000 rpm for 1 minute in the high-speed flow mixer. Thus, the operation of attaching boron nitride to the expanded polystyrene beads B via the additive was repeated 10 times, to obtain expanded polystyrene beads N coated with boron nitride. The polystyrene beads N were heated in a constant temperature bath at 60 ℃ for 2 hours, and the silicone resin of the additive was cured to obtain composite particles B as the polystyrene beads coated with boron nitride.

The resin precursor was prepared by mixing the agent A and the agent B of the thermosetting silicone resin DOWSIL SE 1817CV M manufactured by Dow Toray Co., ltd in a mass ratio of 1:1. Composite particles a and composite particles B were thoroughly mixed. In this mixing, the relationship of the bulk volume of composite particles a to the bulk volume of composite particles b=90:10 is satisfied. Next, the mixture of composite particles a and composite particles B was filled to a height of 20mm inside a rectangular parallelepiped plastic box having internal dimensions of 95mm, 95mm and 24 mm. A plain metal mesh made of stainless steel manufactured by Ji Tianlong co was laid on the mixture of composite particles a and composite particles B inside the box, and punched metal made of stainless steel was laid on the plain metal mesh. The diameter of the openings in the plain weave metal mesh was 0.18mm and the mesh number of the plain weave metal mesh was 50. In the punched metal, the diameter of the openings was 5mm, and the distance between adjacent openings was 8mm. The thickness of the punched metal was 1mm. The plain metal mesh and the punched metal are fixed with clamps.

The resin precursor is added to the inside of the box, and vacuum deaeration is performed on the resin precursor. The gauge pressure in the vacuum degassing was adjusted to-0.08 MPa to-0.09 MPa. The operations including the addition of the resin precursor and the vacuum degassing were repeated 3 times to impregnate the resin precursor between the composite particles. Next, the resin precursor was heated so as to be kept in an environment where the resin precursor was placed at 80 ℃ for 2 hours, thereby curing the silicone resin contained in the resin precursor, and a resin molded article in which the composite particles were embedded was obtained. The resin molded article was cut into a predetermined size, and the cut resin molded article was immersed in acetone for 30 minutes. Thus, the polystyrene contained in the composite particles was dissolved in acetone, and eluted from the resin molded article. Then, the resin molded article was heated at 90℃to volatilize acetone, thereby obtaining a composite material of example 1.

Example 2 >

A composite material of example 2 was produced in the same manner as in example 1, except that the conditions for mixing the composite particles a and the composite particles B were changed so as to satisfy the relationship of the bulk volume of the composite particles a to the bulk volume of the composite particles b=80:20.

Example 3 >

A composite material of example 3 was produced in the same manner as in example 1, except that boron nitride having an aspect ratio of 50 and an average thickness of 0.8 μm was used instead of the boron nitride used in example 1 in the production of composite particles.

Example 4 >

A composite material of example 4 was produced in the same manner as in example 1, except that, in the production of composite particles, scaly graphite having an aspect ratio of 12 and an average thickness of 1.8 μm was used instead of the boron nitride used in example 1.

Example 5 >

A composite material of example 5 was produced in the same manner as in example 1, except for the following points. As the resin precursor, a mixture of polyurethane SU-3001A and SU-3001B manufactured by Sanyu Rec company was used instead of the silicone resin. In this mixture, the components of SU-3001A and SU-3001B were adjusted in such a way that the relationship of SU-3001A mass: SU-3001B mass=34:100 was satisfied. The polyurethane contained in the resin precursor was cured by heating in such a manner that the environment in which the resin precursor was placed was maintained at 80 ℃ for 2 hours.

Example 6 >

A composite material of example 6 was produced in the same manner as in example 1, except for the following points. In the production of the composite particle a, the amount of the additive was changed to 3.5 parts by mass and the amount of the boron nitride was changed to 7 parts by mass. In the production of the composite particle B, the amount of the additive was changed to 3 parts by mass and the amount of the boron nitride was changed to 6 parts by mass.

Example 7 >

A composite material of example 7 was produced in the same manner as in example 2, except for the following points. In the production of the composite particle a, the amount of the additive was changed to 3.5 parts by mass, and the amount of the boron nitride was changed to 7 parts by mass. In the production of the composite particle B, the amount of the additive was changed to 3 parts by mass and the amount of the boron nitride was changed to 6 parts by mass.

Example 8 >

As an additive, DOWSIL SE and 1896FR A/B agents manufactured by Dow Corp. Were mixed at a weight ratio of 1:1 to prepare a silicone resin precursor. 10 parts by weight of the silicone resin precursor was prepared for 1 part by weight of plastic microspheres (Matsumoto Microsphere F-80 DE) manufactured by Song oil pharmaceutical Co., ltd. On the other hand, 25 parts by weight of scaly boron nitride was prepared with respect to 1 part by weight of F-80 DE. The aspect ratio of boron nitride was 20 and the average thickness of boron nitride was 0.4 μm.

To a high-speed flow mixer SMP-2 manufactured by KAWATA Co., ltd, 1 part by weight of F-80DE was added. Next, it took 30 minutes to simultaneously add the silicone resin precursor and the boron nitride, and the silicone resin precursor and the boron nitride were respectively equalized in amounts, and the mixture was stirred at 1000 rpm using the mixer. By this operation, plastic microspheres coated with boron nitride were obtained using a silicone resin precursor. The plastic microspheres were heated in a constant temperature bath at 80 ℃ for 2 hours to cure the silicone resin, resulting in composite particles C coated with boron nitride.

A composite material of example 8 was produced in the same manner as in example 1, except that the composite particles C described above were used instead of the composite particles B used in example 1.

Example 9 >

A composite material of example 9 was produced in the same manner as in example 1, except that composite particles B were used instead of composite particles a used in example 1, and composite particles C were used instead of composite particles B.

Comparative example 1 >

A composite material of comparative example 1 was produced in the same manner as in example 1, except that only composite particles a were used as composite particles filled in a cassette.

Comparative example 2 >

A composite material of comparative example 2 was produced in the same manner as in example 4, except that only composite particles a were used as composite particles filled in a cassette.

Comparative example 3 >

A composite material of comparative example 3 was produced in the same manner as in example 5, except that only composite particles a were used as composite particles filled in a cassette.

Comparative example 4 >

Boron nitride having an aspect ratio of 20 and an average thickness of 0.4 μm, agents A and B of silicone resin DOWSIL SE 1817CV M manufactured by Dow Toray Co., ltd, and ethanol were mixed to prepare a slurry-like mixture. In this mixture, the relationship of the mass of boron nitride to the mass of agent a to the mass of agent B to the mass of ethanol=23:38:38:1 is satisfied. The mixture was added to a mold having a bottomed cylinder shape with a diameter of 50mm and a height of 7 mm. Next, the mixture in the mold was heated at 150 ℃ for 1 hour, thereby allowing ethanol to function as a foaming agent, foaming the silicone resin, and curing the foamed silicone resin. Thus, a composite material of comparative example 4 was produced.

Comparative example 5 >

A composite material of comparative example 5 was produced in the same manner as in comparative example 4, except that boron nitride having an aspect ratio of 50 and an average thickness of 0.4 μm was used instead of the boron nitride used in comparative example 4 in the production of composite particles.

(Microscopic observation)

The cross sections of the composite materials of each example and each comparative example were observed using a microscope Digital Microscope VHX-7000 manufactured by Keyence corporation. In this observation, a plurality of cross sections of the observation target were selected so that 200 or more voids could be confirmed. In this observation, the maximum diameter of each void was measured. Based on the measurement results, the distribution of the maximum diameters (sizes) of voids based on the number of the composites was obtained. The distribution was made into a histogram, and the amplitude of each section in the histogram was 50 μm. The central value of the interval corresponding to the peak in the distribution is regarded as the size of the void corresponding to the peak. In the case where the distribution has a plurality of peaks, the size of the void corresponding to the peak (first peak) having the largest void size among the plurality of peaks is determined as d1. Further, the size of the void corresponding to the peak (second peak) having the second largest void size among the plurality of peaks is determined as d2. The amplitude of each section of the histogram for determining d2 in examples 8 and 9 was 20 μm. The frequency (number) of the section including d1 of the histogram is determined as h1, and the frequency (number) of the section including d2 of the histogram is determined as h2. The arithmetic average of the maximum diameters of the voids was obtained based on the measurement results. The results are shown in tables 1 and 2. Fig. 4 and 5 show photographs of the cross section of the composite material of example 1 and the cross section of the composite material of comparative example 1, respectively.

In the cross section of the composite material, boron nitride or graphite is aggregated, and 200 annular cross sections are formed corresponding to each of 200 or more voids in which the maximum diameter is measured. The maximum diameter of each of the 200 annular cross sections was measured. Based on the measurement results, the distribution of the maximum diameters of the annular cross sections of the respective composite materials was obtained. The distribution was made into a histogram, and the amplitude of each section in the histogram was 50 μm. The central value of the section corresponding to the peak in the distribution is regarded as the maximum diameter of the annular cross section corresponding to the peak. When the distribution has a plurality of peaks, the maximum diameter of the annular cross section corresponding to the peak (third peak) having the largest maximum diameter of the annular cross section among the plurality of peaks is determined as L1. The maximum diameter of the annular cross section corresponding to the peak (fourth peak) having the second largest maximum diameter of the annular cross section among the plurality of peaks is defined as L2. The amplitude of each section for determining the histogram of L2 in examples 8 and 9 was 20 μm. The results are shown in Table 1.

The ratio R of the cross-sectional area of the skeleton portion of the observation object to the cross-sectional area of the entire cross-section was obtained. The cross-sectional area of the skeleton portion is determined by subtracting the sum of the area of the void in the cross-section and the area of the annular cross-section in which the boron nitride or graphite is aggregated from the cross-sectional area of the entire cross-section of the observation object. The results are shown in Table 1.

(Calculation of inorganic particle content [ mass% ])

The content of inorganic particles [ mass% ] was determined as follows. First, about 10mg of the composite material was weighed and added to a container made of a fluororesin. Hydrofluoric acid was added to a container made of fluororesin and the container was tightly covered. The vessel made of fluororesin was irradiated with microwaves, and the vessel was subjected to acid decomposition under pressure at a maximum temperature of 220 ℃. Ultrapure water was added to the obtained solution to a volume of 50mL. The boron atom (B) was quantitatively analyzed by ICP-AES SPS-3520UV manufactured by HITACHI HIGH-TECH SCIENCE, and the content of boron nitride [ mass%) was calculated from the detected content of boron atom. In the case where the inorganic particles are graphite, the solution obtained by decomposing the composite material under pressure with hydrofluoric acid is filtered, and the weight of the residue is measured, whereby the content [ mass% ] of the inorganic particles is calculated. The results are shown in Table 2.

(Measurement of thermal conductivity)

The thermal conductivity of the composite materials of each example and each comparative example was measured by a thermal flow meter method using a 1-piece test body and a symmetrical structure using a thermal conductivity measuring device TCM1001 manufactured by RHESCA Co., ltd.) according to American society for testing and materials standard (ASTM) D5470-01 (unidirectional thermal flow steady state method). Each composite material having a thickness t was cut into a square shape having a length of 20mm on 1 side in plan view, and test pieces were obtained. A silicon grease SCH-20 manufactured by Sunhayato Co., ltd was applied to both surfaces of the main surface of the test piece, and the thickness of the silicon grease layer was set to 100. Mu.m. The thermal conductivity of the silicon grease was 0.84W/(mK). As standard bars, an upper bar with a heating block adjusted to 110 ℃ and a lower bar with a cooling block adjusted to 20 ℃ were used. As the test pieces, oxygen-free copper pieces were used. The test piece was sandwiched between oxygen-free copper blocks with a silicon grease layer interposed therebetween, and a measurement sample was prepared. The measurement sample was sandwiched between an upper rod and a lower rod, and heat was allowed to flow in the thickness direction of the test piece.

The temperature difference Δt _S between the upper and lower surfaces of the test piece was determined according to the following formulas (1) and (2). In the formulas (1) and (2), Δt _C is the temperature difference between the upper surface and the lower surface of the block (test block) made of oxygen-free copper. Q ₁ is a heat flux (W/m ²],q₂) determined from a temperature gradient calculated based on a temperature difference between a plurality of temperature measurement points of the upper rod, and k _b is a heat conductivity coefficient of an oxygen-free copper block, wherein W/m ²].t_b is a sum of thicknesses of oxygen-free copper blocks.

DeltaT _S＝ΔT_C－(q_S×t_b)/k_b (1)

Q _S＝(q₁+q₂)/2 (2)

The thermal conductivity [ lambda ] [ W/(m.K) ] of the test piece in the thickness direction was determined according to the following formula (3). The results are shown in Table 2. The thickness t of the test piece was measured by using a camera. Further, the thermal resistance value R _T was obtained from the relation of expression (4). The results are shown in Table 2.

Lambda=q _S×t/ΔT_S (3)

R _T =t/lambda type (4)

(Compression test)

Test pieces for compression test having a thickness of 3mm were prepared from the composite materials of each example and each comparative example. The test piece was subjected to compression test at a compression rate of 0.5 mm/min using a tester EZ-test manufactured by Shimadzu corporation so as to generate a compression strain of 30%. The stress corresponding to 30% compressive strain was measured. The results are shown in Table 2.

As can be understood from the comparison of examples 1 to 3 with comparative examples 1, 4 and 5, the distribution of the size of voids passing through the composite material has 2 peaks, whereby the thermal conductivity of the composite material easily becomes high. Further, it is understood that the distribution of the size of the voids passing through the composite material has 2 peaks, whereby the compressive stress of the composite material is easily lowered and the flexibility of the composite material is improved. The same will be understood from the comparison of example 4 with comparative example 2 and the comparison of example 5 with comparative example 3.

As shown in Table 1, in examples 1 to 9, the conditions of L1/L2.gtoreq.1.25, { (L1 ²-d1²)h1}/{(L2²-d2²) h2 }. Gtoreq.0.8, and R.ltoreq.0.55 were satisfied. Examples 1 to 7 show that the thermal conductivity of the composite material is easily increased by satisfying such conditions.

In accordance with the 1 st aspect of the present invention, there is provided a composite material comprising a skeleton portion containing a resin, inorganic particles, and a plurality of voids,

In accordance with aspect 2 of the present invention, there is provided the composite material of aspect 1, wherein,

The plurality of voids has a plurality of first voids and second voids disposed between the first voids,

The size of the first void is included in a first range and the size of the second void is included in a second range having an upper limit smaller than a lower limit of the first range when the composite material is viewed in cross section.

In accordance with aspect 3 of the present invention, there is provided the composite material of aspect 1 or 2, wherein,

The first distribution has a first peak and a second peak,

The size corresponding to the second peak is smaller than the size corresponding to the first peak,

When the composite material is viewed in cross section, the inorganic particles disposed along the boundary form a plurality of annular cross sections corresponding to the plurality of voids,

The second distribution of the number reference obtained by measuring the maximum diameter of each of the plurality of annular cross sections has a third peak and a fourth peak,

The maximum diameter corresponding to the fourth peak is smaller than the maximum diameter corresponding to the third peak,

The composite material meets the conditions that L1/L2 is more than or equal to 1.25, L1 ²-d1²)h1}/{(L2²-d2²) h2 is more than or equal to 0.8 and R is less than or equal to 0.55,

In the above condition, L1 is the maximum diameter corresponding to the third peak, L2 is the maximum diameter corresponding to the fourth peak, d1 is the size corresponding to the first peak, d2 is the size corresponding to the second peak, h1 is the number corresponding to the first peak, h2 is the number corresponding to the second peak, and R is the ratio of the cross-sectional area of the skeleton portion of the composite material in cross section to the cross-sectional area of the composite material.

In accordance with aspect 4 of the present invention, there is provided the composite material of aspect 1 or 2, wherein,

The first distribution has a first peak and a second peak,

The ratio of the number of the voids corresponding to the second peak to the number of the voids corresponding to the first peak is 0.01 to 100.

The 5 th aspect of the present invention provides the composite material according to any one of the 1 st to 4 th aspects, wherein,

The arithmetic average of the dimensions obtained by measuring the dimensions of each of the plurality of voids when the composite material is viewed from the cross-section is 50 to 1500 μm.

The 6 th aspect of the present invention provides the composite material according to any one of the 1 st to 5 th aspects, wherein,

The first distribution has a first peak and a second peak,

The first peak is present in the size range of 500 to 1200 μm, and the second peak is present in the size range of 50 to 700 μm.

The 7 th aspect of the present application provides the composite material according to any one of the 1 st to 6 th aspects, which has a heat transfer path formed of the above-mentioned inorganic particles.

In accordance with the 8 th aspect of the present application, there is provided the composite material of the 7 th aspect, wherein,

The composite material has a first major face and a second major face parallel to each other,

At least one of the heat transfer paths extends from the first major surface to the second major surface.

In accordance with the 9 th aspect of the present application, there is provided the composite material according to any one of the 1 st to 8 th aspects, wherein,

The plurality of voids have mutually similar profiles.

A 10 th aspect of the present application provides the composite material according to any one of the 1 st to 9 th aspects, wherein,

The composite material is a non-foam body.

In accordance with an 11 th aspect of the present application, there is provided a method of manufacturing a composite material, the method comprising:

The 12 th aspect of the present application provides the method for producing a composite material according to the 11 th aspect, wherein,

At least a portion of the second composite particles are disposed between the first composite particles.

The 13 th aspect of the present application provides the method for producing a composite material according to the 11 th or 12 th aspect, wherein,

The plurality of voids are formed without a foaming step.

Claims

1. A composite material, comprising:

A skeleton portion containing a resin,

Inorganic particles, and

A plurality of the air gaps are arranged on the inner wall of the hollow body,

At least a part of the inorganic particles are arranged along the boundary between the void and the skeleton portion,

2. The composite material of claim 1, wherein,

The dimensions of the first void are included in a first range and the dimensions of the second void are included in a second range when the composite is sectioned, the second range having an upper limit that is less than a lower limit of the first range.

3. The composite material of claim 1, wherein,

The first distribution has a first peak and a second peak,

The composite material meets the conditions that L1/L2 is more than or equal to 1.25, { (L1 ²-d1²)h1}/{(L2²-d2²) h2} -is more than or equal to 0.8 and R is less than or equal to 0.55,

4. The composite material of claim 1, wherein,

The first distribution has a first peak and a second peak,

5. The composite material of claim 1, wherein,

6. The composite material of claim 1, wherein,

The first distribution has a first peak and a second peak,

The first peak is present in the size range of 500 to 1200 μm and the second peak is present in the size range of 50 to 700 μm.

7. The composite of claim 1 having a heat transfer path formed by the inorganic particles.

8. The composite material of claim 7, wherein,

At least one of the heat transfer paths extends from the first major face to the second major face.

9. The composite material of claim 1, wherein,

The plurality of voids have mutually similar profiles.

10. The composite material of claim 1, wherein,

The composite material is a non-foam.

11. A method of manufacturing a composite material, the method comprising:

In a mixture including a plurality of composite particles each having a first resin and inorganic particles disposed around the first resin, and a resin composition having fluidity and filling gaps between the composite particles, the fluidity of the resin composition is reduced to form a solid portion including a second resin; and

The plurality of composite particles comprises a first composite particle and a second composite particle,

12. The method for producing a composite material according to claim 11, wherein,

13. The method for producing a composite material according to claim 11, wherein,

The plurality of voids are formed without going through a foaming process.