Composite materials and methods for manufacturing composite materials

Abstract

To provide a novel composite material with inorganic particles difficult to separate, while having a plurality of voids.SOLUTION: A composite material 1 includes: a skeleton part 30 containing a first resin; and a plurality of voids 40. The composite material 1 further includes a first layer 3 and a second layer 4 arranged along a circumference of each of the plurality of voids 40. The first layer 3 includes a plurality of inorganic particles 20. The second layer 4 includes at least one kind of resin selected from a group composed of the first resin and a second resin different from the first resin. Furthermore, the second layer 4 covers the first layer 3 from a side opposite to the skeleton part 30 while facing the voids 40.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention relates to a composite material and a method for manufacturing the composite material. 【Background Art】 【0002】 Conventionally, attempts have been made to enhance the thermal conductivity in materials having a plurality of voids such as foamed materials. 【0003】 For example, Patent Document 1 discloses a composite material including a flaky filler made of an inorganic material and a binding resin made of a thermosetting resin that binds the filler. This composite material is a foamed material formed such that a plurality of voids are dispersed, and the filler is accumulated on the inner wall of the void so that the flat surfaces of the fillers overlap each other (Claim 1 and FIG. 1). 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2018-109101 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 In the technique described in Patent Document 1, the filler is accumulated on the inner wall of the void. In this technique, for example, the filler is likely to be peeled off from the composite material against physical impacts such as vibration. Therefore, this technique has room for reconsideration from the viewpoint of providing a composite material having a plurality of voids and being difficult to peel off the filler. Thus, the present invention provides a novel composite material having a plurality of voids and being difficult to peel off inorganic particles. 【Means for Solving the Problems】 【0006】 The present invention is a composite material including a skeleton part containing a first resin and a plurality of voids, The system comprises a first layer and a second layer arranged along the periphery of each of the aforementioned plurality of voids, The first layer contains a plurality of inorganic particles, The second layer comprises at least one resin selected from the group consisting of the first resin and a second resin different from the first resin, and covers the first layer from the side opposite to the skeletal portion and faces the void. We provide composite materials. 【0007】 In another aspect, the present invention is A method for manufacturing a composite material comprising a skeletal part containing a first resin and a plurality of voids, Filling the voids in a particle aggregate containing multiple resin particles with a fluid containing the first resin or a precursor of the first resin, The invention comprises, in this order, heating and shrinking or removing the aforementioned plurality of resin particles to form a plurality of voids, A first layer and a second layer are present on the surface of the plurality of resin particles. The first layer and the second layer are arranged such that the second layer is interposed between the surface and the first layer, and the surface and the second layer are in contact with each other. The first layer contains a plurality of inorganic particles, The second layer comprises at least one resin selected from the group consisting of the first resin and a second resin different from the first resin. The present invention provides a method for manufacturing composite materials. [Effects of the Invention] 【0008】 According to the present invention, it is possible to provide a novel composite material that has multiple voids while being resistant to peeling of inorganic particles. [Brief explanation of the drawing] 【0009】 [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a composite material according to this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing another example of the composite material according to this embodiment. [Figure 3]Figure 3 illustrates the measurement locations in the composite material according to this embodiment, using energy-dispersive X-ray spectroscopy with an ultra-high-resolution field-emission scanning electron microscope. [Figure 4] Figure 4 shows the results of observing a cross-section of the composite material according to Example 1 using a scanning electron microscope. [Modes for carrying out the invention] 【0010】 Embodiments of the present invention will be described below with reference to the drawings. The following description is illustrative of the present invention and is not limited to the embodiments described below. 【0011】 As shown in Figure 1, the composite material 1 according to this embodiment includes a skeletal portion 30 and a plurality of voids 40. The skeletal portion 30 contains a first resin. The composite material 1 comprises a first layer 3 and a second layer 4. The first layer 3 and the second layer 4 are arranged along the respective peripheries of the plurality of voids 40. The first layer 3 contains a plurality of inorganic particles 20. The second layer 4 covers the first layer 3 from the side opposite to the skeletal portion 30 and faces the voids 40. The second layer 4 contains at least one resin selected from the group consisting of a first resin and a second resin different from the first resin. The second layer 4 may also contain a second resin. 【0012】 In the technology described in Patent Document 1, multiple inorganic particles are arranged facing the voids. In such a configuration, the inorganic particles are easily detached by physical shocks such as vibrations. As a result, the thermal conductivity of the composite material tends to decrease. In contrast, according to the configuration shown in Figure 1, the first layer 3 containing multiple inorganic particles 20 is covered by the second layer 4, so the inorganic particles 20 are less likely to detach from the composite material 1. As a result, the thermal conductivity of the composite material 1 does not tend to decrease. 【0013】 The detachment of the inorganic particles 20 from the composite material 1 can be confirmed, for example, by the following method. After the composite material 1 is shaken using a device such as a shaker, it is visually confirmed that the inorganic particles 20 have detached from the composite material 1. Alternatively, after the composite material 1 is shaken, the detachment of the inorganic particles 20 from the composite material 1 can also be confirmed by elemental analysis of the solid matter detached from the composite material 1. For elemental analysis, methods such as inductively coupled plasma (ICP) optical emission spectrometry, energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (ESCA), etc. are used. 【0014】 The detachment of the inorganic particles 20 from the composite material 1 can also be confirmed, for example, by examining the presence or absence of elution of the inorganic particles 20 from the composite material 1. The elution of the inorganic particles 20 from the composite material 1 can be confirmed, for example, by the following method. After the composite material 1 is immersed in a solvent such as toluene, the composite material 1 is taken out of the solvent, and the turbidity of the solvent is visually confirmed. Alternatively, the presence or absence of elution of the inorganic particles 20 from the composite material 1 can also be confirmed by elemental analysis of the solid content remaining after the solvent after the composite material 1 is immersed is volatilized. For elemental analysis, methods such as ICP, EDX, ESCA, etc. are used. 【0015】 As shown in FIG. 1, the composite material 1 has, for example, a porous structure having a plurality of voids 40. The composite material 1 has, for example, heat transfer paths 5 and 6. The heat transfer paths 5 and 6 extend within the first layer 3. The heat transfer paths 5 and 6 extend, for example, across a plurality of voids 40. The heat transfer paths 5 and 6 are formed by a plurality of inorganic particles 20 that are arranged continuously, or in other words, in contact with or adjacent to each other. The heat transfer paths 5 and 6 extend, for example, without passing through the inside of the skeleton portion 30, and more specifically, along the ends of the skeleton portion 30. For example, some of the heat transfer paths 5 reach from the surface 1a of the composite material 1 to the surface 1b on the opposite side of this surface 1a. 【0016】 In the composite material 1, at least some of the plurality of voids 40 may be arranged to be in contact with each other. In the composite material 1, at least some of the plurality of voids 40 may be arranged such that the first layers 3 are connected to each other. For example, as shown in FIG. 1, in the composite material 1, at least some of the plurality of voids 40 are arranged such that, at the connection portion 41, the first layers 3 at the peripheries of the respective voids 40 are connected and the second layers 4 are not connected. 【0017】 It should be noted that not all heat transfer paths appear in a specific cross-section as shown in FIG. 1, and furthermore, not all parts of a specific heat transfer path appear. For example, the heat transfer path 6 does not seem to extend to the surface 1b as far as FIG. 1 is concerned. However, the heat transfer path 6 reaches the surface 1b through inorganic particles that do not appear in this cross-section. Similarly, the contact of all voids cannot be confirmed only in a specific cross-section. For example, the void 50 seems to be isolated as far as FIG. 1 is concerned. However, the void 50 is in contact with another void adjacent in the thickness direction of the paper surface. 【0018】 However, it is not necessary for all heat transfer paths to reach from the surface 1a to the surface 1b. Also, it is not necessary for all voids contained in the porous structure to be in contact with another void directly or through inorganic particles. 【0019】 For example, no inorganic particles 20 are present in the connection portion 41. In the connection portion 41, for example, the first layer 3 and the second layer 4 are formed. Therefore, the voids 40 that are directly in contact with each other in the connection portion 41 are not communicating. 【0020】 For example, inorganic particles 21 are present in the connection portion 43. The first layer 3 and the second layer 4 are also present in the connection portion 43. However, the voids 40 that seem to be adjacent to each other with the connection portions 41 and 43 interposed therebetween in FIG. 1 may be in direct contact and communicating in a cross-section different from FIG. 1. 【0021】 For example, the connection portion 45 includes areas where the inorganic particles 20, the first layer 3, and the second layer 4 are absent. The gaps 40 that are in contact with each other in the connection portion 45 form a single space that communicates through the connection portion 45. 【0022】 As shown in Figure 2, particles 60 may be present inside the void 40. The particles 60 are typically resin particles. The particles 60 may be resin particles that have shrunk due to heat treatment. The resin particles before shrinkage may have a shape corresponding to the void 40. The resin that occupied the void may be removed as shown in Figure 1, or it may remain deformed as shown in Figure 2. In the latter case, the particles 60 may be in contact with the second layer 4. Even in voids 50 where the presence of particles 60 cannot be confirmed in a particular cross-section, the presence of particles 60 may be confirmed when observing another cross-section. In the configuration shown in Figure 2, particles 60 smaller than the voids are present in at least a portion of the voids 40 and 50. 【0023】 The inorganic particles 20 are not limited to any particular material. For example, the inorganic particles 20 have a higher thermal conductivity than the resin 30. Examples of materials for the inorganic particles 20 include hexagonal boron nitride (h-BN), alumina, 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), beryllia, diamond, carbon black, graphene, carbon nanotubes, carbon fiber, and aluminum hydroxide. There may be only one type of inorganic particle 20 in the composite material 1, or two or more types of inorganic particles 20 may be used in combination in the composite material 1. The shape of the inorganic particles 20 is not limited to any particular shape. Examples of shapes include spherical, rod-shaped (including short fibrous), flaky, needle-shaped, and granular. Granular means, for example, a shape in which multiple inorganic particles 20 are aggregated using a binder, or a sintered body of multiple inorganic particles 20. 【0024】 The aspect ratio of the inorganic particle 20 is not limited to a specific value. The aspect ratio of the inorganic particle 20 may be less than 50, 40 or less, or even 30 or less. The aspect ratio of the inorganic particle 20 may be 1, or it may be a value greater than that, for example, 2 or more, or even 3 or more. Unless otherwise specified, the aspect ratio is determined by the ratio of the maximum diameter of the particle to the minimum diameter of the particle (maximum diameter / minimum diameter). In this specification, the minimum diameter is determined by the shortest line segment passing through the midpoint of the line segment that defines the maximum diameter. 【0025】 The average particle size of the inorganic particles 20 is not limited to a specific value. For example, the average particle size of the inorganic particles 20 may be 0.05 μm to 100 μm, or it may be 0.1 μm to 50 μm, 0.1 μm to 30 μm, or 0.5 to 10 μm. The "average particle size" can be determined, for example, by the laser diffraction scattering method. The average particle size is obtained, for example, from the particle size distribution curve in which the frequency is expressed as a fraction based on volume, using a particle size analyzer (Microtrac MT3300EXII) manufactured by Microtrac-Bell, and the 50% cumulative value (median diameter) d 50 That is the case. 【0026】 The shape of the inorganic particle 20 can be determined by observation using, for example, a scanning electron microscope (SEM). For example, if the aspect ratio (maximum diameter / minimum diameter) is 1.0 or more and less than 1.7, particularly 1.0 or more and 1.5 or less, and even 1.0 or more and 1.3 or less, and at least a part of the contour, particularly substantially all of it, is observed as a curve, then the inorganic particle 20 can be determined to be spherical. 【0027】 A flaky particle has a plate-like shape with a pair of main faces and side faces. The main face is the largest surface area of ​​the inorganic particle 20 and is usually a substantially flat surface. When the inorganic particle 20 is flaky, the aspect ratio is defined, instead of the above definition, as the ratio of the average dimension of the main face to the average thickness. The thickness of a flaky inorganic particle 20 means the distance between the pair of main faces. The average thickness can be determined by measuring the thickness of any 50 inorganic particles 20 using a SEM and calculating the average value. The average dimension of the main face is measured using the particle size analyzer described above. 50The values ​​of can be used. The aspect ratio of the flaky inorganic particles 20 may be 1.5 or greater, 1.7 or greater, or even 5 or greater. Rod-shaped refers to rod-like shapes such as rod-shaped, columnar, dendritic, needle-shaped, and conical. The aspect ratio of the rod-shaped inorganic particles 20 may be 1.5 or greater, 1.7 or greater, or even 5 or greater. Regardless of the shape of the inorganic particles 20, the examples of the upper limit of the aspect ratio are as described above. 【0028】 If the inorganic particles 20 are spherical, the average particle size is, for example, 0.1 μm to 50 μm, preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 5 μm. If the inorganic particles 20 are flaky, the average dimensions of the main surface of the inorganic particles 20 are, for example, 0.1 μm to 20 μm, and preferably 0.5 μm to 15 μm. The average thickness of the inorganic particles 20 is, for example, 0.05 μm to 1 μm, and preferably 0.08 μm to 0.5 μm. If the inorganic particles 20 are rod-shaped, the minimum diameter (usually the short axis length) of the inorganic particles 20 is, for example, 0.01 μm to 10 μm, and preferably 0.05 μm to 1 μm. The maximum diameter (usually the long axis length) of the inorganic particles 20 is, for example, 0.1 μm to 20 μm, and preferably 0.5 μm to 10 μm. If the size of the inorganic particles 20 is within this range, the inorganic particles 20 are easily arranged along the voids 40, so that a heat transfer path 5 extending across multiple voids 40 can be reliably formed. If the inorganic particles 20 are granular, the average particle size is, for example, 10 μm to 100 μm, preferably 20 μm to 60 μm. 【0029】 The content of inorganic particles 20 in composite material 1 is not limited to a specific value. For example, the content of inorganic particles 20 in composite material 1 is 10% to 80% by mass, preferably 10% to 70% by mass, and more preferably 10% to 55% by mass. Alternatively, the content of inorganic particles 20 in composite material 1 is 1% to 50% by volume, preferably 2% to 45% by volume, more preferably 5% to 40% by volume, and particularly preferably 5% to 30% by volume. By appropriately adjusting the content of inorganic particles 20, composite material 1 can exhibit higher thermal conductivity and have appropriate rigidity. 【0030】 The content [mass%] of inorganic particles 20 in composite material 1 can be determined by removing materials other than inorganic particles 20 from composite material 1 by burning or other means. For highly accurate measurement, the content [mass%] of inorganic particles may also be calculated using elemental analysis. Specifically, an acid is added to composite material 1, and microwaves are irradiated to decompose the composite material 1 under pressure. Examples of acids that can be used include hydrofluoric acid, concentrated sulfuric acid, concentrated hydrochloric acid, and aqua regia. The solution obtained by decomposition under pressure is analyzed for elements using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Based on the results, the content [mass%] of inorganic particles 20 can be determined. 【0031】 The inorganic particle content [volume %] in composite material 1 can be determined from the mass and density of the inorganic particles 20 contained in composite material 1, and from the volume and porosity of composite material 1. Specifically, the volume A of inorganic particles 20 in composite material 1 is calculated from the mass and density of the inorganic particles 20. Separately, the volume B of composite material 1, excluding the volume of voids 40, is calculated based on the porosity of composite material 1. The inorganic particle content [volume %] can be determined by (A / B) × 100. The method for calculating the porosity will be described later. 【0032】 The density of the inorganic particles 20 can be determined by burning off the organic material by heating the composite material 1 at a high temperature in an electric furnace, and then determining the remaining inorganic particles 20 in accordance with Japanese Industrial Standards (JIS) R 1628:1997 or JIS Z 2504:2012. 【0033】 At least a portion of the inorganic particles 20 are present in the portion between the skeletal structure 30 and the second layer 4 in the first layer 3. Other portions 21 and 22 of the inorganic particles 20 may be present in the connecting portions 43 of the voids 40 in the first layer 3. In these portions, portions 23 of the inorganic particles may be stacked with other inorganic particles in the thickness direction of the first layer 3. At least a portion of the inorganic particles 20 are in contact with or very close to adjacent inorganic particles and constitute part of the heat transfer paths 5 and 6. However, another portion 24 of the inorganic particles 20 may be present surrounded by the skeletal structure 30. In other words, the skeletal structure 30 may contain inorganic particles 24 that are not in contact with the voids 40. 【0034】 Substantially all of the inorganic particles 20 may be present within the first layer 3. In this specification, “substantially all” means 90% by mass or more, more precisely 93% by mass or more, and especially 95% by mass or more. This configuration increases the proportion of inorganic particles that contribute to improved thermal conductivity. The distribution of inorganic particles 20 inside the framework 30 can be measured, for example, using three-dimensional X-ray microscopy (X-ray CT). 【0035】 The first resin contained in the skeletal part 30 is, for example, a crosslinked polymer. The first resin may also be a thermosetting resin. Examples of thermosetting resins include phenolic resins, urea resins, melamine resins, diallyl phthalate resins, polyester resins, epoxy resins, aniline resins, silicone resins, furan resins, polyurethane resins, alkylbenzene resins, guanamine resins, xylene resins, and imide resins. The curing temperature of the resin is, for example, 25°C to 160°C. 【0036】 The first resin may be a thermoplastic resin. Examples of thermoplastic resins include (meth)acrylic resin, styrene resin, polyethylene terephthalate resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, acrylonitrile butadiene styrene resin, and acrylonitrile styrene resin. 【0037】 The skeleton part 30 does not contain, for example, the inorganic particles 20, or contains the inorganic particles 20 at a content lower than that of the first layer 3. According to such a configuration, the content of the inorganic particles 20 in the composite material 1 can be reduced. As a result, it is possible to obtain the composite material 1 having excellent thermal conductivity while reducing the usage amount of the inorganic particles 20. The comparison of the content of the inorganic particles 20 contained in the skeleton part 30 and the first layer 3 can be determined, for example, by using the method described later by scanning electron microscope / energy dispersive X-ray spectroscopy (SEM-EDX). Specifically, in the skeleton part 30, the ratio X of the ratio of the atoms derived from the inorganic particles 20 to the ratio of the atoms derived from the resin is calculated. Similarly, in the first layer 3, the ratio Y of the ratio of the atoms derived from the inorganic particles 20 to the ratio of the atoms derived from the resin is calculated. If the relationship between X and Y satisfies X < Y, it can be determined that the content of the inorganic particles 20 contained in the skeleton part 30 is lower than the content of the inorganic particles 20 contained in the first layer 3. 【0038】 The first layer 3 may contain the first resin and / or the second resin together with the inorganic particles 20. The second layer 4 contains the first resin and / or the second resin. The second resin may be a crosslinked polymer. The second resin is, for example, a thermosetting resin. Examples of the thermosetting resin are as described above. The flow temperature of the first resin may have a flow temperature higher than that of the resin particles used for forming the voids. The flow temperature of the second resin may also have a flow temperature higher than that of the resin particles. The resin particles used for forming the voids may not remain in the composite material 1, but may remain in the voids 40 as the shrunk particles 60. The flow temperature is, for example, the temperature at which the outflow of the resin starts. The flow temperature can be analyzed, for example, by an isothermal temperature rise test using a thermal flow evaluation device (flow tester) (manufactured by Shimadzu Corporation, CFT-500D (PC)). 【0039】 In the composite material 1, it is preferable that at least one resin selected from the group consisting of the first resin and the second resin contains a crosslinked polymer. 【0040】 The second layer 4 contains inorganic particles 20, for example, at a content lower than that of the first layer 3. According to such a configuration, the content of the inorganic particles 20 in the composite material 1 can be reduced. As a result, it is possible to obtain the composite material 1 that can have excellent thermal conductivity performance while reducing the usage amount of the inorganic particles 20. The comparison of the content of the inorganic particles 20 contained in the second layer 4 and the first layer 3 can be determined, for example, by using the method described later with SEM-EDX. Specifically, the second layer 4 is analyzed by SEM-EDX to calculate the ratio P [atomic%] of atoms derived from the inorganic particles 20. Similarly, the first layer 3 is analyzed to calculate the ratio Q [atomic%] of atoms derived from the inorganic particles 20. If P and Q satisfy the relationship of P < Q, it can be determined that the content of the inorganic particles 20 contained in the second layer 4 is lower than the content of the inorganic particles 20 contained in the first layer 3. In the composite material 1, P and Q may satisfy the relationship of P / Q ≤ 0.3. 【0041】 The second layer 4 has an average thickness of, for example, 0.01 μm to 100 μm. The average thickness of the second layer 4 may be 0.05 μm to 50 μm, or may be 0.1 μm to 20 μm. The average thickness of the second layer 4 may be smaller than the average thickness of the first layer. 【0042】 The average thickness of the second layer 4 can be determined, for example, by observing the cross-section of the composite material 1 using SEM or the like. Specifically, using SEM, the arithmetic mean of the thicknesses of the second layer 4 at 10 randomly selected locations, and in some cases 30 locations, can be taken as the average thickness of the second layer 4. The average thickness of the first layer 3 can be determined in the same manner. The boundaries between the first layer 3 and the skeleton part 30 and between the second layer 4 can be determined continuously, that is, by regarding the layer regions where inorganic particles are present as the first layer 3 when they are in contact with or close to each other. 【0043】 The external shapes of the voids 40 and 50 may be spherical or substantially spherical. In this 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, particularly 1.0 to 1.3. However, the external shapes of the voids 40 and 50 are not limited to a specific shape. Their external shapes may be rod-shaped, polyhedral, or elliptical, where the above ratio is too large to be called spherical. More than 50%, and even more than 80%, of the voids 40 and 50 may be spherical. In foaming technology, it is difficult to form voids with such uniform shapes because the shape of the voids tends to be irregular. 【0044】 The average diameter of the voids 40 is not limited to a specific value. For example, it is between 50 μm and 5000 μm, preferably between 100 μm and 2000 μm, and more preferably between 300 μm and 1500 μm. In this specification, the "average diameter" of the voids 40 refers to the average value of the diameters obtained by observing the cross-section of the composite material 1 with an SEM. Specifically, for any 100 voids 40 whose entirety can be observed, their maximum and minimum diameters are measured, and the average value of these is taken as the diameter of each void. The average value of the diameters of the 15 voids with the largest values ​​is defined as the "average diameter". 【0045】 In composite material 1, the ratio of the volume of voids 40 to the volume of composite material 1, i.e., the porosity, is not limited to a specific value. The porosity is, for example, 10% to 60% by volume, preferably 15% to 50% by volume, and more preferably 20% to 45% by volume. 【0046】 The porosity can be determined by observing a cross-section of the composite material 1 using a scanning electron microscope (SEM), calculating the ratio of the total area of ​​voids 40 to the total area observed, and taking the average of the ratios for 10 different cross-sectional images. However, if the manufacturing process is known, it may be determined as follows: The mass of inorganic particles 20 contained in the composite particles is calculated from the mass of the resin particles and the mass of the composite particles on which inorganic particles 20 are arranged on the surface of the resin particles, as described later. Separately, the content [mass %] of inorganic particles 20 in the composite material 1 is calculated by inorganic elemental analysis. The mass of inorganic particles 20 in the composite material 1 is calculated from the content [mass %] of inorganic particles 20 and the mass of the composite material 1. The number of composite particles used to manufacture the composite material 1 is calculated from the mass of inorganic particles 20 in the composite material 1 and the mass of inorganic particles 20 contained in the composite particles. The volume of voids 40 is calculated from the average diameter of voids 40. The total volume of voids 40 in the composite material 1 is determined by the product of the volume of voids 40 and the number of composite particles. The porosity is calculated by dividing this value by the volume of composite material 1. 【0047】 Multiple voids 40 may have substantially similar external shapes. In this specification, "substantially similar" means that, based on the number, 80% or more, and especially 90% or more, of the voids 40 have the same geometric shape, for example, a spherical shape and a regular polyhedron shape. The external shape of multiple substantially similar voids 40 is preferably spherical. This external shape may be substantially spherical. Multiple voids formed by foaming may also come into contact with each other as they expand individually. However, in this case, the internal pressure generated by foaming usually acts on the connection between the voids, causing significant deformation near the connection. For this reason, foaming techniques cannot, in fact, form multiple voids that are in contact with each other and have substantially similar external shapes. 【0048】 The porous structure may have through holes extending from one main surface of the composite material 1 to the other main surface. If the composite material 1 is in the form of a plate, the voids provided on one main surface of the composite material 1 may communicate with the space facing the other main surface of the composite material 1. Also, the voids provided on one main surface of the composite material 1 may communicate with the space adjacent to the side surface that intersects with the one main surface of the composite material 1. With such a configuration, the composite material 1 can achieve both thermal conductivity and breathability. The main surface refers to the surface of the composite material 1 that has the largest surface area. 【0049】 Multiple voids 40 may be in local contact. This prevents a decrease in the strength of the composite material 1 even when the porosity is increased. The diameter of the connecting portion of the voids at the connection portion 45 may be 25% or less, 20% or less, or even 15% or less of the average diameter of the voids 40. The diameter of the connecting portion can be measured by SEM or X-ray CT, similar to the average diameter. Since the connection portions 41 and 43 of the voids 40 are demarcated by the first layer 3, there are no connecting portions. 【0050】 As is clear from the above explanation, the composite material 1 may be a non-foamed material. Conventional foams, such as those described in Patent Document 1, cannot have the characteristic structure shown in Figures 1 and 2, that is, a structure in which the arrangement of inorganic particles 20 is finely and precisely controlled. In addition, conventional foams cannot have a structure in which a second layer is formed so as to cover a first layer containing inorganic particles. 【0051】 Referring to Figure 3, the method for determining measurement locations to determine the composition of each element in the first layer 3, the second layer 4, and the framework 30 of the composite material 1 is illustrated below. First, the voids 40 of the composite material 1 are observed by SEM. The longest diameter of the voids 40 observed by SEM is measured, and a line segment A having a length L of this longest diameter is determined. Next, a line segment B is determined that passes through the midpoint of line segment A, is perpendicular to line segment A, and has a length L' from one end of the void 40 to the other. Furthermore, a rectangle C is determined with the midpoint of line segment A as its centroid, and two adjacent sides are parallel to line segments A and B, respectively, and have a length twice that of the parallel line segments A or B (2L in the direction parallel to line segment A, and 2L' in the direction parallel to line segment B). The area of ​​this rectangle C excluding the void portion is defined as the measurement area. This measurement area is divided into multiple areas D defined by 50 μm squares. In each of the multiple regions D, the proportion of atoms contained in region D is analyzed. For example, energy-dispersive X-ray spectroscopy using an ultra-high-resolution field-emission scanning electron microscope is used for the analysis. 【0052】 Based on the analysis results in multiple regions D, the region where the proportion of atoms (e.g., B) contained in the inorganic particles [atomic %] is maximized is defined as the measurement position for the composition of the first layer 3. Based on the analysis results in multiple regions D, the region where the proportion of atoms (e.g., B) contained in the inorganic particles [atomic %] is minimized is defined as the measurement position for the composition of the skeleton 30. On the other hand, the region defined by a 50 μm square with the centroid at the intersection of line segments A and B is defined as region E. This region E is defined as the measurement position in the second layer 4. Note that the atoms to be analyzed may be the elements of the positive ions of the compound if the inorganic particles are composed of a compound, or the elements constituting the element if the inorganic particles are composed of an element. For example, if the inorganic particles are boron nitride (BN), the atom to be analyzed is boron (B). If the inorganic particles are alumina (Al2O3), the atom to be analyzed is aluminum (Al). If the inorganic particles are graphite, the atom to be analyzed is carbon (C). 【0053】 <Method for manufacturing composite materials> An example of a method for manufacturing the composite material 1 according to this embodiment is described below. The composite material 1 includes a skeleton portion 30 containing a first resin and a plurality of voids 40. The method for manufacturing the composite material 1 comprises, in this order, a step of filling the voids of a particle aggregate containing a plurality of resin particles with a fluid containing a first resin or a precursor of the first resin, and a step of forming a plurality of voids 40 by heating and shrinking or removing the plurality of resin particles. Here, a first layer 3 and a second layer 4 are present on the surface of the plurality of resin particles. The first layer 3 and the second layer 4 are arranged such that the second layer 4 is interposed between the surface of the resin particles and the first layer 3, and the surface of the resin particles and the second layer 4 are in contact. The first layer 3 also contains a plurality of inorganic particles. The second layer 4 contains at least one resin selected from the group consisting of a first resin and a second resin different from the first resin. The at least one resin selected from the group consisting of a first resin and a second resin may include a crosslinked polymer. The flow temperature of the first resin, and the flow temperature of the second resin if the second layer 4 contains the second resin, may be higher than the flow temperature of the resin constituting the resin particles. 【0054】 First, to obtain composite particles, a mixture of resin particles and an impregnator is prepared. The impregnator includes, for example, a first resin and / or a second resin. The impregnator may also include precursors of the first resin and / or the second resin. 【0055】 Next, inorganic particles 20 are added to this mixture and mixed to obtain composite particles in which inorganic particles 20 are arranged on the surface of multiple resin particles. The step of adding an impregnator to the resin particles to obtain a mixture and the step of adding inorganic particles 20 to this mixture may be repeated multiple times. Alternatively, composite particles may be obtained by simultaneously adding the impregnator and inorganic particles 20 to a mixture of resin particles and an impregnator and mixing. The mixing method is not limited to any particular method. Examples of mixing methods include mixing using a ball mill, bead mill, planetary mixer, ultrasonic mixer, homogenizer, rotational mixer, fluid mixer, Henschel mixer, container-rotating blender, ribbon blender, and conical screw blender. 【0056】 Next, the composite particles are placed inside a mold so that they are in contact with each other and form a particle aggregate. A separately prepared fluid is then added to this mold to prepare a mixture. The fluid contains a first resin. The fluid may also contain a precursor of the first resin. The fluid fills the voids in the particle aggregate containing the multiple resin particles. The fluid is present at least on the surface of the composite particles and in the contact areas between the composite particles. In this way, an aggregate of composite particles is formed in which at least some of the multiple composite particles are in contact with each other, such that a heat transfer path formed by the inorganic particles 20 in contact with each other extends through the surfaces of the multiple composite particles. 【0057】 Next, bubbles are removed from the mixture. The method for removing bubbles from the mixture is not limited to any particular method. One example of such a method is degassing under reduced pressure. Degassing under reduced pressure is carried out, for example, at 25°C to 200°C for 1 to 10 seconds. 【0058】 Subsequently, the fluidity of the mixture is reduced by heating. When the fluid is heated, a reaction proceeds, for example, in which the first resin is produced from the precursor of the first resin, or the first resin hardens, and its fluidity decreases. In this way, a skeletal part 30 containing the first resin is produced. This yields a precursor for the composite material. 【0059】 Next, the composite material 1 is prepared by shrinking or removing resin particles from the composite material precursor. The method for shrinking or removing resin particles from the composite material precursor is not limited to a specific method. Examples of methods include heating the composite material precursor and immersing the composite material precursor in a specific solvent. These methods may be used in combination. This creates voids 40. Thus, a composite material 1 comprising a framework 30, a first layer 3, and a second layer 4 can be obtained. 【0060】 Alternatively, composite material 1 may be manufactured as follows. First, composite particles are manufactured in which an impregnator and inorganic particles 20 are arranged on the surface of a plurality of resin particles. The method for manufacturing the composite particles is as described above. Next, the manufactured composite particles are heated to reduce the fluidity of the impregnator arranged on the surface of the composite particles. When the impregnator is heated, a reaction proceeds in which, for example, the first resin and / or second resin is produced from the precursors of the first resin and / or second resin, or the hardening of the first resin and / or second resin proceeds, and its fluidity is reduced. In this way, a composite particle material is produced that includes the first layer and the second layer on the surface of the resin particles and also includes inorganic particles 20. 【0061】 Voids are formed within a composite particle material by shrinking or removing resin particles. The method for shrinking or removing resin particles is as described above. 【0062】 Next, the composite particle material with voids formed is placed inside the mold. A separately prepared fluid is then added to this mold to prepare a mixture. The method for preparing the mixture is as described above. 【0063】 Subsequently, the fluidity of the mixture is reduced by heating it. The method for reducing the fluidity of the mixture is as described above. In this way, a composite material 1 comprising a skeletal structure 30, a first layer 3, and a second layer 4 can be obtained. 【0064】 In the example of the manufacturing method described above, the second layer 4 is formed from the resin or its precursor interposed between the surface of the resin particles and the inorganic particles 20. The resin may be the first resin, i.e., the resin contained in the skeleton 30, or it may be the second resin, i.e., a different resin. A crosslinked polymer that undergoes crosslinking is suitable as the resin or its precursor. In this example of manufacturing method, it was confirmed that the second layer 4 is not formed when polyethylene glycol, a non-crosslinked polymer, is used. However, depending on the manufacturing method of the composite material 1, it is possible to relax the material restrictions and form the second layer 4. An example of such a method is to first form only the second layer 4 containing the resin or its precursor on the entire surface of the resin particles, and then form the first layer 3 thereafter. 【0065】 The temperature at which the composite material precursor is heated is not limited to a specific temperature, as long as it is a temperature that can soften the resin particles. For example, the temperature may be 95°C to 130°C or 120°C to 160°C. As mentioned above, the flow temperature of the impurity agent is higher than, for example, the flow temperature of the resin particles. Therefore, even if the composite material precursor is heated to soften the resin particles, the impurity agent does not flow easily. As a result, the second layer 4 is more likely to form, covering the first layer 3 containing the inorganic particles 20. 【0066】 When immersing a composite material precursor in a specific solvent, the solvent is not limited to a specific solvent as long as it can dissolve the resin particles without dissolving the first or second resin. Examples of solvents include toluene, ethyl acetate, methyl ethyl ketone, and acetone. 【0067】 The resin particles may have a hollow structure. The hollow portion in the hollow structure may be a single hollow portion, or it may be composed of multiple hollow portions, such as foamed resin beads. When resin particles with a hollow structure are used, the resin constituting the resin particles softens upon heat treatment, causing the hollow portion to disappear or shrink, and a plurality of voids 40 are formed accordingly. However, the hollow structure of the resin particles is not essential. When immersing the composite material precursor in a specific solvent, it is preferable that the resin particles dissolve more easily in the solvent than, for example, the first resin or the second resin. According to such a method, voids 40 having the desired shape are easily formed. Examples of resin particles include polystyrene (PS), polyethylene (PE), polymethyl methacrylate (PMMA), ethylene vinyl acetate copolymer (EVA), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), acrylonitrile-butadiene-styrene copolymer (ABS), ethylene-propylene-diene rubber (EPDM), thermoplastic elastomer (TPE), and polyvinyl alcohol (PVA). The first resin is, for example, the resin contained in the skeletal part 30. 【0068】 The resin particles are not limited to a specific size. If the resin particles are spherical, their average diameter is, for example, 50 μm to 5000 μm, preferably 300 μm to 2000 μm, and particularly 500 μm to 1500 μm. By appropriately adjusting the size of the resin particles, the composite material 1 can have an appropriate porosity. In addition, the composite material 1 can have an appropriate void size. The resin particles may be made of multiple sizes of resin selected from these sizes. That is, the resin particles may have substantially similar shapes to each other. This allows the composite material 1 to have a shape in which multiple voids 40 are substantially similar to each other. 【0069】 According to the manufacturing method of the composite material 1 of this embodiment, a second layer 4 can be formed that covers the first layer 3 containing inorganic particles 20 from the opposite side of the skeletal portion 30 and faces the voids 40. In addition, heat transfer paths extending across the multiple voids 40 can be formed by the inorganic particles 20. 【0070】 According to the manufacturing method of the composite material 1 of this embodiment, voids 40 are formed inside the first resin without going through a foaming process. In other words, the voids 40 are not formed by foaming. [Examples] 【0071】 The present invention will be described in more detail by reference to examples. However, the present invention is not limited to the following examples. 【0072】 (Making polystyrene beads) 100 parts by weight of pure water, 0.2 parts by weight of tricalcium phosphate, and 0.01 parts by weight of sodium dodecylbenzenesulfonate were added to an autoclave equipped with a stirrer. To this autoclave, 0.15 parts by weight of benzoyl peroxide and 0.25 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane were added as initiators to prepare a mixture. While stirring the mixture at 350 rpm, 100 parts by weight of styrene monomer were added. The polymerization reaction was then carried out by raising the temperature of this solution to 98°C. When the polymerization reaction was approximately 80% complete, the reaction solution was raised to 120°C over 30 minutes. The reaction solution was then kept at 120°C for 1 hour to prepare a styrene resin particle-containing solution. After cooling the styrene resin particle-containing solution to 95°C, 2 parts by weight of cyclohexane and 7 parts by weight of butane were injected into the autoclave under pressure as blowing agents. The solution was then raised to 120°C again. Subsequently, the solution was kept warm at 120°C for 1 hour, and then cooled to room temperature to obtain a polymerization slurry. This polymerization slurry was dehydrated, washed, and dried to obtain expandable styrene resin particles. These expandable styrene resin particles were sieved to obtain expandable styrene resin particles with a particle size of 0.2 mm to 0.3 mm. These expandable styrene resin particles were used with a pressurized foaming machine (BHP) manufactured by Daikai Kogyo Co., Ltd. to obtain spherical expanded polystyrene beads with an average diameter of 650 μm to 1200 μm. These expanded polystyrene beads were passed through JIS test sieves with nominal mesh sizes (JIS Z 8801-1:2019) of 1.18 mm and 1 mm. At this time, expanded polystyrene beads that passed through the 1.18 mm sieve but did not pass through the 1 mm sieve were used in subsequent tests. The bulk density of these expanded polystyrene beads was 0.025 g / cm³. 3 That was the case. 【0073】 (Example 1) As an additive, a silicone resin precursor was prepared by weighing and mixing Shin-Etsu Chemical Co., Ltd.'s silicone resin (KE-106F), Shin-Etsu Chemical Co., Ltd.'s curing agent (CAT-106F), and Shin-Etsu Chemical Co., Ltd.'s silicone oil (KF-96-10CS) in a weight ratio of 10:1:10. Ten parts by weight of this silicone resin precursor were prepared for every one part by weight of expanded polystyrene beads. Separately, fifteen parts by weight of flaky boron nitride (aspect ratio 20) were prepared for every one part by weight of expanded polystyrene beads. 【0074】 One part by weight of the aforementioned spherical expanded polystyrene beads was added to a high-speed fluid mixer (SMP-2) manufactured by Kawata Corporation. Next, one part by weight of the above-mentioned silicone resin precursor was added to prepare a mixture. This mixture was stirred for 1 minute at 1000 revolutions per minute using the above-mentioned mixer. Then, 1.5 parts by weight of the above-mentioned boron nitride was added to prepare a mixture. This mixture was stirred for 1 minute at 1000 revolutions per minute using the above-mentioned mixer. This process of coating expanded polystyrene beads with boron nitride via the silicone resin precursor was repeated 10 times to obtain expanded polystyrene beads coated with boron nitride. These polystyrene beads were heated in a constant temperature bath at 60°C for 2 hours to cure the silicone resin, thereby obtaining polystyrene beads (composite particles) coated with boron nitride. 【0075】 Silicone resin (KE-106F) and silicone oil (KF-96-10CS) manufactured by Shin-Etsu Chemical Co., Ltd. were added in a weight ratio of 10:5. To this mixture, a curing agent (CAT-106F) manufactured by Shin-Etsu Chemical Co., Ltd. was further added so that the weight ratio of silicone resin to curing agent was 10:0.85, thereby producing a thermosetting resin. 【0076】 The aforementioned boron nitride-coated polystyrene beads were filled into a plastic case with an inner diameter of 95mm x 95mm x 24mm. A plain weave wire mesh (diameter: 0.18mm, 50 mesh) manufactured by Yoshida Takashi Stainless Steel was placed inside the plastic case, and then a stainless steel perforated metal (diameter: 5mm, thickness: 1mm, pitch: 8mm) was placed on top of that and secured with clamps. 【0077】 The aforementioned thermosetting resin was added to this plastic case and degassed under reduced pressure. The pressure at this time was -0.08 MPa to -0.09 MPa in gauge pressure. This operation was repeated three times to impregnate the polystyrene beads with the thermosetting resin. Next, the silicone resin was cured by heating at 80°C for 2 hours to obtain a resin molded product containing polystyrene beads. This resin molded product was cut to the specified dimensions. It was then immersed in acetone for 30 minutes to dissolve the polystyrene beads and allow them to flow out of the resin molded product. After that, the resin molded product was heated at 90°C to evaporate the acetone, thereby producing the composite material according to Example 1. 【0078】 (Example 2) The composite material according to Example 2 was obtained in the same manner as in Example 1, except that the boron nitride listed in Table 1 was used and the mixture was prepared in the quantities listed in Table 1. 【0079】 (Example 3) The composite material according to Example 3 was obtained in the same manner as in Example 1, except that the boron nitride listed in Table 1 was used, polyurethane (UF820A / B) manufactured by Sunyurec Co., Ltd. was used instead of silicone resin in the preparation of the composite particles and composite material, and the mixture was prepared in the quantities listed in Table 1. 【0080】 (Example 4) The composite material according to Example 4 was obtained in the same manner as in Example 1, except that graphite (CPB) manufactured by Nippon Graphite Co., Ltd. was used instead of boron nitride, and the mixture was prepared in the quantities listed in Table 1. 【0081】 (Example 5) The composite material according to Example 5 was obtained in the same manner as in Example 1, except that alumina particles (AL-30) manufactured by Showa Denko Corporation were used instead of boron nitride, and the mixture was prepared in the quantities listed in Table 1. 【0082】 (Example 6) As an impregnating agent, a silicone resin precursor was prepared by mixing components A and B of DOWSIL SE 1896 FR A / B manufactured by Dow Corporation in a 1:1 weight ratio. 7.5 parts by weight of this silicone resin precursor were prepared per 1 part by weight of expanded polystyrene beads. Separately, a filler mixture was prepared by mixing 13.3 parts by weight of flaky boron nitride (aspect ratio 20) and 1.3 parts by weight of graphite (aspect ratio 12) per 1 part by weight of expanded polystyrene beads. 【0083】 One part by weight of the aforementioned spherical expanded polystyrene beads was added to a high-speed fluid mixer (SMP-2) manufactured by Kawata Corporation. Next, 0.3 parts by weight of the above-mentioned silicone resin precursor was added, and the mixture was stirred at 1000 rpm for 1 minute. The remaining silicone resin precursor and the above-mentioned filler mixture were added to this mixture simultaneously, and the silicone resin precursor and filler mixture were added in equal amounts over 30 minutes, while stirring at 1000 rpm using the above-mentioned mixer. Through this operation, expanded polystyrene beads coated with boron nitride and graphite via the silicone resin precursor were obtained. These polystyrene beads were heated in a constant temperature bath at 80°C for 2 hours to cure the silicone resin, thereby obtaining polystyrene beads (composite particles) coated with boron nitride and graphite. 【0084】 As the thermosetting resin, we used DOWSIL SE 1817 CV M (composed of components A and B) from Dow Corporation, along with silicone oil (KF-96-300CS). The thermosetting resin was prepared by mixing components A, B, and silicone oil in a weight ratio of 37.5:37.5:25. 【0085】 A composite material according to Example 6 was obtained in the same manner as in Example 1, except that the composite particles and thermosetting resin described above were used. 【0086】 (Example 7) Except for using Sanyurec's urethane resin SU-4500A / B (mixed in a weight ratio of A:B = 5:100) as an additive for producing composite particles, and using Sanyurec's urethane resin SU-3001A / B (mixed in a weight ratio of A:B = 34:100) as a thermosetting resin for producing the composite material, a composite material according to Example 7 was obtained in the same manner as in Example 6. 【0087】 (Comparative Example 1) In the preparation of the composite particles, polystyrene beads coated with boron nitride (composite particles) according to Comparative Example 1 were prepared in the same manner as in Example 1, except that polyethylene glycol (average molecular weight 400) was used as an additive instead of a silicone resin precursor. A composite material according to Comparative Example 1 was obtained in the same manner as in Example 1, except that these composite particles according to Comparative Example 1 were used. 【0088】 (Comparative Example 2) A slurry mixture was prepared by weighing and adding flaky boron nitride (aspect ratio 50), silicone resin (KE-106F) manufactured by Shin-Etsu Chemical Co., Ltd., silicone oil (KF-96-10CS) manufactured by Shin-Etsu Chemical Co., Ltd., curing agent (CAT-106F) manufactured by Shin-Etsu Chemical Co., Ltd., and ethanol in a weight ratio of 60:25:13:2:1 and mixing them together. Next, the mixture was added to a bottomed cylindrical mold with a diameter of 50 mm and a height of 7 mm. Then, the mixture in the mold was heated at 150°C for 1 hour, causing the silicone resin to foam with ethanol and curing the foamed silicone resin to obtain the composite material according to Comparative Example 2. 【0089】 (Comparative Example 3) A composite material according to Comparative Example 3 was obtained in the same manner as in Comparative Example 2, except that an unsaturated polyester resin (WP2820) manufactured by Hitachi Chemical Co., Ltd. was used instead of silicone resin. 【0090】 (Confirmation of elution of inorganic particles) The composite materials according to Examples 1-7 and Comparative Examples 1-3 were immersed in toluene for 1 hour. Afterward, the composite materials were removed from the toluene, and the turbidity of the toluene, originating from inorganic particles, was visually inspected. If no turbidity was detected, it was evaluated as "absent." If turbidity was detected, it was evaluated as "present." The results are shown in Tables 1 and 2. 【0091】 (Confirmation of detachment of inorganic particles) The composite materials of Examples 1-7 and Comparative Examples 1-3 were vibrated at vibration level 6 using a desktop vibrator (Angel Vibrator Digital) manufactured by Daiei Dental Industry Co., Ltd. After vibrating the composite materials, it was visually confirmed whether or not inorganic particles had detached from the composite materials. If no detachment of inorganic particles was confirmed from the composite material, it was evaluated as "None". If detachment of inorganic particles was confirmed from the composite material, it was evaluated as "Present". The results are shown in Tables 1 and 2. 【0092】 (Average thickness of the second layer) The thickness of the second layer of the composite materials in Examples 1-7 and Comparative Examples 1-3 was measured using a scanning electron microscope (SEM). The voids were observed using the SEM, and the thickness of the second layer was measured at 10 randomly selected locations. The average value of these measurements was taken as the average thickness of the second layer. For Comparative Examples 1-3, the presence of a second layer could not be confirmed, nor could the layered structure of the second layer / first layer / skeleton be confirmed. The results are shown in Tables 1 and 2. 【0093】 (Elemental analysis and inorganic particle content) Elemental analysis of the composite material was performed using the method described above, and the proportion of atoms derived from inorganic particles was calculated. Note that for each comparative example, at least a second layer was absent, but the results of elemental analysis performed at the measurement locations described above are shown. In Table 1, "-" indicates that atoms derived from inorganic particles were not detected. 【0094】 In Example 4, the proportion of atoms derived from inorganic particles in the second layer was higher than in Examples 1-3 and 5. In Example 4, graphite was used as the inorganic particle. In addition, silicone resin was used as an impregnator for forming the second layer and as the resin constituting the framework in the composite material of Example 4. Therefore, it is thought that in Example 4, carbon atoms derived from silicone resin were detected in addition to carbon atoms derived from graphite. As a result, the proportion of atoms derived from inorganic particles in the second layer of Example 4 was higher than the proportion of atoms derived from inorganic particles in the second layer of the other examples. However, even in the composite material of Example 4, the proportion of carbon atoms in the second layer was smaller than the proportion of carbon atoms in the first layer. In other words, even in the composite material of Example 4, the second layer contained inorganic particles at a lower content than the first layer. 【0095】 In Examples 6 and 7, boron nitride and graphite were used as inorganic particles. In the composite material according to Example 6, silicone resin was used as an impregnator for forming the second layer and as a resin constituting the framework. In the composite material according to Example 7, polyurethane was used as an impregnator for forming the second layer and as a resin constituting the framework. As a result, it is thought that in the elemental analysis of the composite materials according to Examples 6 and 7, carbon atoms derived from silicone resin and polyurethane were detected in addition to carbon atoms derived from graphite. Therefore, in Examples 6 and 7, the proportion of atoms derived from inorganic particles in the second layer shows results for boron atoms derived from boron nitride only. In Examples 6 and 7, the proportion of boron atoms in the second layer was smaller than the proportion of boron atoms in the first layer. In addition, as described above, in the composite material according to Example 4, which used graphite as inorganic particles, the proportion of carbon atoms in the second layer was smaller than the proportion of carbon atoms in the first layer. That is, even when graphite is used as inorganic particles, it can be understood that the second layer contains inorganic particles at a lower content than the first layer. These results suggest that, in the composite materials of Examples 6 and 7, the second layer also contains graphite at a lower content than the first layer. 【0096】 [Table 1] 【0097】 [Table 2] 【0098】 Figure 4 shows the results of observing a cross-section of the composite material according to Example 1 using a scanning electron microscope. As illustrated in Figure 4, in the composite material according to each example, a void 40 is formed within the framework 30, and a first layer 3 containing inorganic particles and a second layer 4 covering the first layer 3 from the void 40 side are arranged along the periphery of the void 40. In each example, a single resin material was used, but it is also possible to use different resins for the additive and the framework, and to configure the framework and the second layer to contain different resins. [Explanation of symbols] 【0099】 1, 2 Composite materials 1a, 1b Surface of composite material 3 1st layer 4 2nd layer 5, 6 Heat transfer path 20, 21, 22, 23, 24 Inorganic particles 30 Skeletal parts 40, 50 voids 41, 43, 45 Connection parts 60 Shrunken resin particles

Claims

[Claim 1] A composite material comprising a skeletal part containing a first resin and a plurality of voids, The system comprises a first layer and a second layer arranged along the periphery of each of the aforementioned plurality of voids, The first layer contains a plurality of inorganic particles, The second layer comprises at least one resin selected from the group consisting of the first resin and a second resin different from the first resin, and covers the first layer from the side opposite to the skeletal portion and faces the void. The second layer contains the inorganic particles in a lower concentration than the first layer. Composite material. [Claim 2] The composite material according to claim 1, wherein at least one resin selected from the group consisting of the first resin and the second resin comprises a crosslinked polymer. [Claim 3] The composite material according to claim 1 or 2, wherein the second layer contains the inorganic particles in a lower content than the first layer. [Claim 4] The composite material according to any one of claims 1 to 3, wherein the second layer comprises the second resin. [Claim 5] The composite material according to any one of claims 1 to 4, wherein the skeletal portion does not contain the inorganic particles, or contains the inorganic particles in a lower content than the first layer. [Claim 6] The composite material according to any one of claims 1 to 5, wherein the second layer has an average thickness of 0.01 μm to 100 μm. [Claim 7] The composite material according to any one of claims 1 to 6, wherein at least a portion of the plurality of voids are arranged such that the first layer is connected to one another. [Claim 8] The composite material according to any one of claims 1 to 7, wherein a heat transfer path is formed by the plurality of inorganic particles. [Claim 9] The composite material according to any one of claims 1 to 8, wherein the plurality of voids have similar external shapes to one another. [Claim 10] A method for manufacturing a composite material comprising a skeletal part containing a first resin and a plurality of voids, Filling the voids in a particle aggregate containing multiple resin particles with a fluid containing the first resin or a precursor of the first resin, The invention comprises, in this order, heating and shrinking or removing the aforementioned plurality of resin particles to form a plurality of voids, The surfaces of the plurality of resin particles have a first layer and a second layer. The first layer and the second layer are arranged such that the second layer is interposed between the surface and the first layer, and the surface and the second layer are in contact with each other. The first layer contains a plurality of inorganic particles, The second layer comprises at least one resin selected from the group consisting of the first resin and a second resin different from the first resin. In the second layer, at least one resin selected from the group consisting of the first resin and the second resin includes a crosslinked polymer. The second layer contains the inorganic particles in a lower concentration than the first layer. A method for manufacturing composite materials. [Claim 11] A method for producing a composite material according to claim 10, wherein at least one resin selected from the group consisting of the first resin and the second resin includes a crosslinked polymer. [Claim 12] A method for producing a composite material according to claim 10 or 11, wherein the flow temperature of the first resin, and the flow temperature of the second resin if the second layer includes the second resin, are higher than the flow temperature of the resin constituting the resin particles.

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