Sandwich structure and method for manufacturing the same

Abstract

An object of the present invention is to provide a sandwich structure having both excellent heat dissipation and excellent mechanical properties. To achieve this object, the sandwich structure of the present invention has the following configuration: a sandwich structure comprising a core material (I) and fiber-reinforced materials (II) disposed on both sides of the core material (I), wherein at least one of the fiber-reinforced materials (II) includes a sheet-like thermally conductive material (III) having an in-plane thermal conductivity of 300 W / m·K or greater.

Description

Technical Field

[0001] The present invention relates to a sandwich structure, a housing formed using the sandwich structure, and a method for producing the sandwich structure. Background Art

[0002] In recent years, market demand for improved heat dissipation in industrial products such as automobiles, aircraft, and electronic equipment has steadily increased. To meet these demands, molded products with high thermal conductivity have been widely used in various industrial applications. Sandwich structures containing thermally conductive materials with high thermal conductivity offer excellent mechanical properties in addition to excellent heat dissipation, and are therefore expected to be effectively utilized in various products. In particular, sandwich structures combining thermally conductive materials with high-strength materials have been extensively researched.

[0003] Patent Document 1 describes an invention of a sandwich structure in which a heat conducting material and a rigidity maintaining material are laminated. By laminating the heat conducting material and the rigidity maintaining material, a sandwich structure having both excellent heat conductivity and excellent rigidity can be obtained.

[0004] Patent Document 2 describes an invention of a sandwich structure comprising a graphite sheet with excellent thermal conductivity and a support sheet laminated on both sides of the graphite sheet, with a sealing spacer having a thickness approximately equal to the graphite sheet added to at least one end face of the graphite sheet. The sealing spacer, placed around the perimeter of the graphite sheet, achieves excellent thermal conductivity and mechanical strength, prevents graphite powder from detaching from the end faces, and provides excellent handleability without knife-like edges, thereby suppressing delamination.

[0005] Patent Document 3 describes an invention of a highly thermally conductive housing in which a stack of graphite sheets is coated with a resin layer. By coating the graphite sheets with resin up to the edges, peeling between the graphite films can be prevented.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2016 / 002457

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2007-44994

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2006-95935 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] The sandwich structure of Patent Document 1 has a problem of insufficient strength of the thermally conductive material because all ends of the thermally conductive material are exposed. In addition, if the bonding strength between the thermally conductive material and the rigidity retaining material is insufficient, there is a possibility of separation from the ends of the sandwich structure.

[0013] Although the sandwich structure disclosed in Patent Document 2 protects the ends of the graphite sheets with sealing spacers, adjusting the thickness and position of the sealing spacers is complex, resulting in low manufacturability. Furthermore, if the bonding strength between the sealing spacers and the support sheet is insufficient, there is a risk of the sealing spacers peeling off from the ends of the sandwich structure.

[0014] The high thermal conductive housing disclosed in Patent Document 3 protects the graphite sheet by covering the surface and ends of the graphite sheet with resin. However, the rigidity and strength are low due to the protection with resin.

[0015] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a sandwich structure having both excellent heat dissipation and excellent mechanical properties.

[0016] Means for solving problems

[0017] In order to solve the above-mentioned problems, the sandwich structure of the present invention has the following configuration.

[0018] A sandwich structure comprising a core material (I) and fiber-reinforced materials (II) arranged on both surfaces of the core material (I), wherein at least one of the fiber-reinforced materials (II) comprises a sheet-shaped thermally conductive material (III) having an in-plane thermal conductivity of 300 W / m·K or higher.

[0019] Effects of the Invention

[0020] According to the present invention, even when the strength of the thermal conductive material is insufficient or the bonding between the thermal conductive material and the material protecting the thermal conductive material is insufficient, a structure having both excellent heat dissipation and excellent mechanical properties can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram showing one embodiment of the sandwich structure of the present invention.

[0022] Figure 2 It is a schematic diagram showing another embodiment of the sandwich structure of the present invention.

[0023] Figure 3 This is a schematic diagram showing the status of heat dissipation evaluation.

[0024] Figure 4 Schematic cross-sectional view of the sandwich structure produced in Example 1.

[0025] Figure 5 Schematic cross-sectional view of the sandwich structure produced in Example 2.

[0026] Figure 6 Schematic cross-sectional view of the sandwich structure produced in Comparative Example 1.

[0027] Figure 7 Schematic cross-sectional view of the sandwich structure produced in Comparative Example 2.

[0028] Figure 8 Schematic cross-sectional view of the sandwich structure produced in Comparative Example 3. DETAILED DESCRIPTION

[0029] Hereinafter, the present invention will be described in detail.

[0030] Sandwich structure

[0031] The sandwich structure of the present invention has a core material (I) and a fiber-reinforced material (II) configured on both sides of the above-mentioned core material (I). The so-called sandwich structure in this specification is a structure in which a skin material having a high elastic modulus compared to the core material is configured on both sides of the core material. In the sandwich structure of the present invention, the skin material is a fiber-reinforced material (II), and at least one of the fiber-reinforced material (II) includes a sheet-like thermal conductive material (III). In addition, the so-called sheet-like refers to a shape with a thin thickness and a wide width. Specifically, it refers to a shape with a thickness of more than 0.01 μm and less than 10 mm, and a width-to-thickness ratio of width to thickness of more than 10.

[0032] At least one of the fiber-reinforced materials (II) of the sandwich structure of the present invention contains a sheet-like thermally conductive material (III) (hereinafter sometimes referred to simply as thermally conductive material (III)). "Containing" here means that the thermally conductive material (III) is present as part of a layer of the fiber-reinforced material (II) in the laminated structure of the sandwich structure.

[0033] For example, Figure 1 In this way, the fiber-reinforced material (II) 3 covers one surface of the heat-conducting material (III) 4 ( Figure 1 The upper surface of the middle) and one end surface ( Figure 1 The right side of the scheme, Figure 2 In such a scheme, the fiber-reinforced material (II) 3 covers both sides (two surfaces) and all end faces of the heat-conducting material (III) 4, that is, the fiber-reinforced material (II) contains the heat-conducting material (III). On the other hand, Figure 6The concept of "inclusion" is excluded in the case where the entire end surface of the thermally conductive material (III) (graphite sheet 9) is exposed, i.e., the thermally conductive material (III) is considered to form a separate layer. In this way, by including the thermally conductive material (III) within the fiber-reinforced material (II), the fiber-reinforced material (II) bears the stress applied to the sandwich structure, thereby suppressing the transfer of stress to the thermally conductive material (III) and preventing damage to the thermally conductive material (III).

[0034] In the sandwich structure of the present invention, it is preferred that at least one of the fiber-reinforced materials (II) covers at least two end faces of the thermally conductive material (III), preferably further covers both sides of the thermally conductive material (III), and it is further preferred that at least one of the fiber-reinforced materials (II) covers both sides and all end faces of the thermally conductive material (III), i.e., it encloses the thermally conductive material (III).

[0035] It should be noted that, in the present invention, the fiber-reinforced material (II) may cover the thermally conductive material (III) via other components such as an adhesive, a buffer material, etc. In addition, a gap may exist between the fiber-reinforced material (II) and the thermally conductive material (III).

[0036] However, in the present invention, it is preferred that at least one end face of the heat-conducting material (III) is directly in contact with the fiber-reinforced material (II) without passing through other components. In addition, it is preferred that at least one surface of the heat-conducting material (III) is in contact with the fiber-reinforced material (II). By directly contacting the heat-conducting material (III) and the fiber-reinforced material (II), heat transferred from the surface of the sandwich structure can be quickly transferred from the fiber-reinforced material (II) to the heat-conducting material (III).

[0037] In addition, preferably in thickness direction, the surface of heat-conducting material (III) is configured to be more than 0.01mm and within 0.3mm from the surface of the fiber-reinforced material (II) comprising this heat-conducting material (III). More preferably, be more than 0.1mm and within 0.2mm. By configuring like this, so that the distance between heat source and heat-conducting material (III) shortens, the heat from heat source can be rapidly transferred to heat-conducting material (III) from the surface of sandwich structure. On the other hand, if the distance between the surface of heat-conducting material (III) and the surface of sandwich structure is too short, then sometimes mechanical properties reduce.

[0038] The bending stiffness per unit width of the sandwich structure of the present invention is preferably 0.5 N·m or more, more preferably 1.0 N·m or more, and further preferably 1.5 N·m or more. The higher the bending stiffness per unit width of the sandwich structure, the more preferred it is, so there is no particular restriction on the upper limit of the bending stiffness per unit width, which is usually around 1000 N·m. By making the bending stiffness per unit width within the above range, the sandwich structure becomes a rigid structure, which can be suitable for use in shells, etc. The bending stiffness per unit width can be determined by the elastic modulus E (Pa) and the moment of inertia I (m 4 ), the width b (m) of the sandwich structure is calculated by the following formula.

[0039] · Bending stiffness per unit width (N·m) = E (Pa) × I (m 4 ) / b(m)

[0040] In addition, when the cross section of the sandwich structure is a rectangular cross section, the cross-sectional moment of inertia I of the rectangular cross section is bh 3 / 12(m 4 ), so it can be calculated by the following formula.

[0041] Bending stiffness per unit width (N·m) = E (Pa) × h 3 (m 3 ) / 12

[0042] As a means for making the bending rigidity per unit width into the above range, for example, a method of using a fiber-reinforced material (II) as a skin material as in the sandwich structure of the present invention can be mentioned. In addition, for example, a method of making the thickness of the sandwich structure thicker can be mentioned.

[0043] The maximum thickness of the sandwich structure of the present invention is preferably 0.3 mm to 3.0 mm, more preferably 0.5 mm to 1.5 mm. Thinning the sandwich structure can achieve a lightweight effect, but sandwich structures thinner than 0.3 mm may sometimes lack rigidity.

[0044] [Thermal conductive material (III)]

[0045] In the present invention, the thermally conductive material (III) is in the form of a sheet. The in-plane thermal conductivity of the thermally conductive material (III) is 300W / m·K or more. The in-plane thermal conductivity of the thermally conductive material (III) is preferably 500W / m·K or more, and more preferably 1000W / m·K or more. The higher the in-plane thermal conductivity, the more preferred it is, so there is no particular limit to the upper limit of the in-plane thermal conductivity, but thermally conductive materials with an in-plane thermal conductivity of about 2000W / m·K are known. If the in-plane thermal conductivity of the thermally conductive material (III) is 300W / m·K or more, the diffusion of heat in the in-plane direction of the sandwich structure is excellent, and the heat dissipation of the sandwich structure is excellent. The thermal conductivity of the thermally conductive material (III) can be measured by placing a sample on a sample holder for in-plane measurement using a laser flash method so that the sample size is about 20 to 30 mm in diameter and the thickness is less than 1 mm. In addition, for materials that are not easy to absorb laser light, a blackened film is formed thinly and uniformly on the surface of the sample. For materials with low emissivity at the temperature measurement wavelength of the infrared detection element, the same treatment is performed on the back side of the sample.

[0046] The material of the thermally conductive material (III) is not particularly limited as long as the in-plane thermal conductivity is 300 W / m·K or higher. For example, ceramics, metals, graphite, and high thermal conductivity resins with improved thermal conductivity by adding high thermal conductivity fillers to the resin can be used.

[0047] In the sandwich structure of the present invention, the thermally conductive material (III) preferably comprises a thermally conductive sheet selected from graphite sheets, metal sheets, and ceramic sheets, and more preferably consists of a thermally conductive sheet selected from graphite sheets, metal sheets, and ceramic sheets. Examples of ceramic sheets include sheets of silicon dioxide, zirconium oxide, aluminum oxide, boron nitride, silicon carbide, silicon nitride, and the like. Examples of metal sheets include sheets formed from titanium, aluminum, magnesium, iron, silver, gold, platinum, copper, nickel, or alloys containing these elements as main components.

[0048] Metal sheets are relatively inexpensive, with copper sheets being particularly preferred due to their low cost and excellent thermal conductivity. Graphite sheets, due to their low specific gravity and excellent thermal conductivity, are particularly preferred in the present invention from the perspective of enhancing the lightweight and heat dissipation properties of the sandwich structure.

[0049] Examples of graphite sheets include sheets obtained by mixing graphite powder and a binder resin, sheets obtained by rolling expanded graphite, sheets obtained by laminating carbon atoms on a substrate using a hydrocarbon gas by CVD and then annealing, and sheets obtained by graphitizing a polymer compound film. Among these, sheets obtained by graphitizing a polymer compound film are preferred because they have very high thermal conductivity.

[0050] In the present invention, the thermally conductive material (III) preferably comprises a laminated structure of multiple thermally conductive sheets, more preferably a laminated structure of multiple thermally conductive sheets. In particular, the orientation of the graphene structure within the sheet of the graphite sheet affects thermal conductivity. Generally speaking, the thermal conductivity of a thin graphite sheet is higher. Therefore, when a graphite sheet is used as a thermally conductive sheet, by making the laminated structure of multiple sheets a thermally conductive material (III), the heat dissipation of the sandwich structure can be improved. In this case, it is preferred that the multiple thermally conductive sheets constituting the thermally conductive material (III) are in direct contact with each other without an adhesive or the like. By directly contacting each other with the thermally conductive sheets, the proportion of the thermally conductive material (III) in the sandwich structure can be increased, and the heat dissipation of the sandwich structure is improved. In addition, by directly contacting each other with the thermally conductive sheets, the diffusion of heat in the out-of-plane direction is also excellent. The number of laminated sheets of the thermally conductive sheet is preferably more than 2 and less than 10, more preferably more than 3 and less than 5. If the number of laminated sheets is increased, the heat dissipation of the sandwich structure is improved. On the other hand, if the number of laminated sheets is increased excessively, the processability will be reduced.

[0051] The average thickness of the thermally conductive material (III) is preferably 0.01 μm or more and 2.0 mm or less, more preferably 5 μm or more and 1.0 mm or less, and further preferably 15 μm or more and 0.5 mm or less. If the average thickness of the thermally conductive material (III) is too small, the heat dissipation of the sandwich structure is reduced, and if the average thickness of the thermally conductive material (III) is too large, the weight of the sandwich structure becomes heavier. The average thickness of the thermally conductive material (III) is determined by measuring the thickness of 9 points of the thermally conductive material (III) using a micrometer to 1 decimal place, and setting the average value as the average thickness. About the points to be measured, each measuring point is measured at an equal interval in the longitudinal and transverse directions, for a total of 9 points, 3 points each in the longitudinal and transverse directions.

[0052] [Core material (I)]

[0053] In the present invention, it is preferred that core material (I) includes a porous body, and more preferably core material (I) is a porous body. Porous body is included by core material (I), thereby being advantageous from the viewpoint of the lightness of sandwich structure. In addition, when fiber-reinforced material (II) is made to include thermally conductive material (III), the core material (I) as a porous body collapses or expands along the out-of-plane direction, thereby fiber-reinforced material (II) can include thermally conductive material (III) without causing the positional offset of thermally conductive material (III).

[0054] When the core material (I) is a porous body, the volume content of the voids in the core material (I) is preferably greater than 10% and less than 85% relative to the apparent volume of the core material (I), more preferably greater than 20% and less than 85%, and further preferably greater than 50% and less than 80% from the viewpoint of combining lightness and mechanical properties.

[0055] When the core material (I) is a porous body, it is preferred that the porous body is made of a fiber-reinforced resin. The fiber-reinforced resin referred to herein is a resin reinforced by continuous fibers or discontinuous fibers. It should be noted that the so-called continuous reinforcing fibers refer to reinforcing fibers that are continuous in at least one direction with a length of more than 15 mm, preferably more than 100 mm. As fiber-reinforced resins reinforced by continuous fibers, unidirectional fiber-reinforced resins, fabric fiber-reinforced resins, etc. can be used. As fiber-reinforced resins reinforced by discontinuous fibers, either short fiber-reinforced resins or long fiber-reinforced resins can be used. In addition, as non-fiber-reinforced resins, resin sheets, resin foams, etc. can also be used.

[0056] Whether it is a fiber reinforced resin or a non-fiber reinforced resin, when the core material (I) contains a resin, there is no particular limitation on the resin, and it can be a thermosetting resin or a thermoplastic resin. Thermoplastic resins include, for example, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyethylene naphthalate (PEN), liquid crystal polyesters, polyolefins such as polyethylene (PE), polypropylene (PP), polybutene, polyoxymethylene (POM), polyamide (PA), polyarylene sulfide such as polyphenylene sulfide (PPS), polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyethernitrile (PEN), fluorine-based resins such as polytetrafluoroethylene, etc. Thermoplastic resins such as esters, "styrene resins, and amorphous resins such as polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyimide (PI), polyamide-imide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone, and polyarylate (PAR)", as well as phenolic resins, phenoxy resins, and further thermoplastic elastomers such as polystyrene, polyolefin, polyurethane, polyester, polyamide, polybutadiene, polyisoprene, fluorine resin, and acrylonitrile, and their copolymers and modified bodies. Among them, polyolefins are preferred from the viewpoint of the lightness of the resulting sandwich structure. In particular, when the core material (I) is a porous body, polyolefins are preferred in consideration of the synergistic light-weight effect. In addition, polyamides are preferred from the viewpoint of strength. In particular, when the core material (I) is a porous body and the porous body is made of a fiber-reinforced resin, polyamide is preferred from the viewpoint of the interfacial bonding strength between the reinforcing fiber and the resin. In addition, thermosetting resins include, for example, unsaturated polyester resins, vinyl ester resins, epoxy resins, phenol (cresol) resins, urea resins, melamine resins, polyimide resins, maleimide resins, benzophenone resins, and the like. Among them, in particular, when the core material (I) is a porous body and the porous body is made of a fiber-reinforced resin, epoxy resin is preferably used from the viewpoint of enhancing the interfacial bonding strength between the fiber and the resin.

[0057] Furthermore, fillers such as mica, talc, kaolin, hydrotalcite, sericite, bentonite, xonotlite, sepiolite, smectite, montmorillonite, wollastonite, silicon dioxide, calcium carbonate, glass beads, glass flakes, glass microspheres, clay, molybdenum disulfide, titanium oxide, zinc oxide, antimony oxide, calcium polyphosphate, graphite, barium sulfate, magnesium sulfate, zinc borate, calcium borate, aluminum borate whiskers, potassium titanate whiskers, and polymer compounds, conductive materials such as metals, metal oxides, carbon black, and graphite powder, halogen flame retardants such as brominated resins, antimony flame retardants such as antimony trioxide and antimony pentoxide, phosphorus flame retardants such as ammonium polyphosphate, aromatic phosphates, and red phosphorus, organic acid metal salt flame retardants such as borate metal salts, carboxylic acid metal salts, and aromatic sulfonimide metal salts, zinc borate, zinc oxide, and the like can be added to the resin depending on its application. Inorganic flame retardants such as zinc and zirconium compounds, nitrogen-based flame retardants such as cyanuric acid, isocyanuric acid, melamine, melamine cyanurate, melamine phosphate and guanidine nitride, fluorine-based flame retardants such as PTFE, silicone-based flame retardants such as polyorganosiloxane, metal hydroxide-based flame retardants such as aluminum hydroxide and magnesium hydroxide, and other flame retardants, flame retardant additives such as cadmium oxide, zinc oxide, cuprous oxide, cupric oxide, ferrous oxide, ferric oxide, cobalt oxide, manganese oxide, molybdenum oxide, tin oxide and titanium oxide, pigments, dyes, lubricants, release agents, compatibilizers, dispersants, crystallization nucleating agents such as mica, talc and kaolin, plasticizers such as phosphate esters, heat stabilizers, antioxidants, anti-coloring agents, UV absorbers, flow modifiers, foaming agents, antibacterial agents, vibration dampeners, deodorants, sliding modifiers, and antistatic agents such as polyetheresteramide. In particular, when the application is electric / electronic equipment, automobiles, aircraft, etc., flame retardancy may be required, and it is preferable to add a phosphorus-based flame retardant, a nitrogen-based flame retardant, or an inorganic flame retardant.

[0058] The flame retardant is preferably present in an amount of 1 to 20 parts by mass, more preferably 1 to 15 parts by mass, per 100 parts by mass of the resin in order to achieve a flame retardant effect while maintaining a good balance with the mechanical properties of the resin used and the resin fluidity during molding.

[0059] From the perspective of lightweight sandwich structures, the specific gravity of the core material (I) is preferably 0.01 to 1.5. It is more preferably 0.1 to 1.3, and even more preferably 0.3 to 1.1. The specific gravity can be measured by cutting out the core material (I) and measuring it according to ISO 1183 (1987) or ISO 0845 (1988).

[0060] When the core material (I) is a porous body and the porous body is made of a fiber-reinforced resin, there is no particular limitation on the type of reinforcing fiber included. For example, carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, natural fiber, mineral fiber, etc. can be used. They can be used as one or in combination of two or more. Among them, from the perspective of high specific strength and specific rigidity, and lightweight effect, it is preferred to use carbon fibers such as PAN, asphalt, and rayon. In addition, from the perspective of improving the economy of the sandwich structure obtained, glass fiber can be preferably used, and in particular, carbon fiber and glass fiber are preferably used in combination from the perspective of balancing mechanical properties and economy. Further, from the perspective of improving the impact absorbability and shapeability of the sandwich structure obtained, aramid fiber can be preferably used, and in particular, carbon fiber and aramid fiber are preferably used in combination from the perspective of balancing mechanical properties and impact absorbency. In addition, from the perspective of improving the conductivity of the sandwich structure obtained, reinforcing fibers coated with metals such as nickel, copper, and ytterbium, and carbon fibers of asphalt can also be used.

[0061] It is preferable that the reinforcing fibers are surface-treated with a sizing agent from the viewpoint of improving mechanical properties. Examples of the sizing agent include polyfunctional epoxy resins, acrylic polymers, polyols, and polyethyleneimines. Specific examples include polyglycidyl ethers of aliphatic polyols such as glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, arabitol polyglycidyl ether, trimethylolpropane triglycidyl ether, and pentaerythritol polyglycidyl ether; polyacrylic acid; copolymers of acrylic acid and methacrylic acid; copolymers of acrylic acid and maleic acid; or mixtures of two or more thereof; polyvinyl alcohol, glycerol, diglycerol, polyglycerol, sorbitol, arabitol, trimethylolpropane, pentaerythritol; and polyethyleneimines containing a larger number of amino groups per molecule. Among these, glycerol triglycidyl ether, diglycerol polyglycidyl ether, and polyglycerol polyglycidyl ether are preferably used because they contain a large number of highly reactive epoxy groups per molecule, have high water solubility, and are easy to coat.

[0062] The core material (I) in the present invention is particularly preferably a porous body made of a fiber-reinforced resin having a structure in which discontinuous reinforcing fibers form a three-dimensional network, and the intersections of the discontinuous fibers are bonded by the resin. The bonding of the discontinuous fibers by the resin increases the shear modulus of the core material (I), thereby increasing the rigidity of the sandwich structure. This embodiment is described below.

[0063] In such fiber-reinforced resins, the discontinuous fibers are preferably present as fine-denier tows of less than 500 fibers, and more preferably dispersed into single fibers. The discontinuous fibers preferably have a fiber length of 1 to 50 mm, more preferably 3 to 30 mm. A fiber length of 1 mm or greater allows for efficient reinforcement by the discontinuous fibers. Furthermore, a fiber length of 50 mm or less allows for good dispersion of the discontinuous fibers.

[0064] The ratio of the number of bonded portions where the discontinuous fibers are bonded to each other via the resin to the total number of intersecting portions where the discontinuous fibers intersect each other is 50% or more, more preferably 70% or more, and even more preferably 90% or more.

[0065] From the viewpoint of achieving both mechanical properties and moldability, the mass proportion of the discontinuous fibers in the core material (I) is preferably 5 to 60 mass%, more preferably 10 to 50 mass%, and even more preferably 15 to 40 mass%.

[0066] In a porous body made of a fiber-reinforced resin, the discontinuous fibers are preferably coated with resin over 30% or more, more preferably 50% or more, and even more preferably 80% or more of their surface. Such a coating ratio can enhance the rigidity of the core material (I). The coating ratio is measured by observing a cross section of the core material (I) using a scanning electron microscope (SEM) to distinguish between the reinforcing fibers and the resin.

[0067] [Fiber-reinforced materials (II)]

[0068] In the present invention, the fiber-reinforced material (II) is a member that constitutes a skin material of a sandwich structure and has a higher elastic modulus than the core material (I) and contains reinforcing fibers.

[0069] The material of the fiber-reinforced material (II) is not particularly limited as long as it has a larger elastic modulus than that of the core material (I). It can be a fiber-reinforced resin reinforced by continuous fibers, or it can be a fiber-reinforced resin reinforced by discontinuous fibers. As the fiber-reinforced resin reinforced by continuous fibers, unidirectional fiber-reinforced resins or fabric fiber-reinforced resins can be used. As the fiber-reinforced resin reinforced by discontinuous fibers, any of short fiber-reinforced resins or long fiber-reinforced resins can be used. However, from the perspective of the mechanical properties of the sandwich structure, it is preferred to use a continuous fiber-reinforced resin, among which unidirectional fiber-reinforced resins can be more suitable. On the other hand, from the perspective of the shapeability of the sandwich structure, discontinuous fiber-reinforced resins can be suitable. In addition, the matrix resin of the fiber-reinforced resin is not particularly limited. Any of thermosetting resins and thermoplastic resins can be used, and the same resin as the resin exemplified in the description of the core material (I) can be used. Furthermore, the matrix resin can contain additives, and as additives, the additives exemplified in the description of the core material (I) can be cited.

[0070] The type of reinforcing fibers contained in the fiber-reinforced material (II) is not particularly limited, and the same reinforcing fibers as those exemplified in the description of the core material (I) can be used.

[0071] From the viewpoint of achieving both mechanical properties and moldability, the content of the reinforcing fibers in the fiber-reinforced material (II) is preferably 30 to 90% by mass, more preferably 40 to 80% by mass, and even more preferably 50 to 70% by mass, based on 100% by mass of the fiber-reinforced material (II). The content may be a range combining any of the above upper and lower limits.

[0072] In the sandwich structure of the present invention, the fiber-reinforced material (II) is preferably made of a carbon fiber-reinforced resin. By making it from a carbon fiber-reinforced resin, it is easy to obtain a sandwich structure with better lightness, rigidity, and strength. Among carbon fibers, pitch-based carbon fibers with high elastic modulus and thermal conductivity are more preferred. By using pitch-based carbon fibers, it is expected that the rigidity and heat dissipation properties of the sandwich structure will be improved.

[0073] In the present invention, the fiber-reinforced material (II) can form a laminated structure obtained by laminating multiple sheets of the above-mentioned components. Regarding the sandwich structure of the present invention, it is preferred that the fiber-reinforced material (II) is made of a unidirectional fiber-reinforced resin and is laminated in a manner such that the fibers of the fiber-reinforced material (II) between the surface of the fiber-reinforced material (II) containing the thermal conductive material (III) and the thermal conductive material (III) are oriented in multiple directions. By laminating the fiber-reinforced sheets between the surface of the sandwich structure and the thermal conductive material (III) in a manner such that the fibers are oriented in multiple directions, excellent mechanical properties can be exhibited against stress from all directions.

[0074] <Method for manufacturing a sandwich structure>

[0075] The sandwich structure of the present invention can be preferably produced by the methods [1] to [3] shown below.

[0076] Method [1]: A method for manufacturing a sandwich structure is a method for manufacturing the sandwich structure of the present invention, which comprises the following steps in sequence: a step of disposing a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of the above-mentioned thermal conductive material (III); a step of performing hot pressing; and a step of joining the above-mentioned fiber-reinforced material (II) to both sides of the above-mentioned core material (I).

[0077] Method [2]: A method for manufacturing a sandwich structure is a method for manufacturing the sandwich structure of the present invention, which comprises the following steps in sequence: a step of arranging a thermally conductive material (III) having a precursor of a fiber-reinforced material (II) arranged on at least one surface and at least one end face in the order of a precursor of a core material (I) and a precursor of a fiber-reinforced material (II); and a step of performing hot pressing.

[0078] Method [3]: A method for manufacturing a sandwich structure is a method for manufacturing the sandwich structure of the present invention, which comprises the following steps in sequence: a step of arranging a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of the above-mentioned thermal conductive material (III); a step of performing hot pressing; a step of arranging the above-mentioned fiber-reinforced material (II) on both sides of the precursor of the core material (I); and a step of performing hot pressing.

[0079] In methods [1] to [3], the phrases “arranging a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of a thermally conductive material (III)” and “arranging a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of a thermally conductive material (III)” mean that the precursor of the fiber-reinforced material (II) is arranged so as to cover at least one surface and at least one end face of the thermally conductive material (III).

[0080] In methods [1] to [3], it is preferred that the precursor of the fiber-reinforced material (II) is arranged on both sides of the heat-conducting material (III). That is, in method [2], "the step of arranging in the order of heat-conducting material (III) with the precursor of the fiber-reinforced material (II) arranged on at least one surface and at least one end face / precursor of the core material (I) / precursor of the fiber-reinforced material (II)" is preferably "the step of arranging in the order of precursor of the fiber-reinforced material (II) / heat-conducting material (III) / precursor of the fiber-reinforced material (II) / precursor of the core material (I) / precursor of the fiber-reinforced material (II)". In addition, in methods [1] to [3], the precursor of the fiber-reinforced material (II) is more preferably arranged on at least two end faces of the heat-conducting material (III), further preferably on both sides of the heat-conducting material (III), and particularly preferably on both sides and all end faces of the heat-conducting material (III), i.e., enclosing the heat-conducting material (III).

[0081] The precursor of the core material (I) is, for example, a prepreg comprising reinforcing fibers and a resin when the core material (I) is a fiber-reinforced resin. Furthermore, when the core material (I) is a non-fiber-reinforced resin, examples thereof include a resin sheet containing a foaming agent and a laminate of resin sheets.

[0082] In the case of forming the core material (I) with a porous body made of a fiber-reinforced resin, which is a preferred embodiment of the present invention, the precursor of the core material (I) can be produced by compressing a thermoplastic resin film or nonwoven fabric while impregnating it with a discontinuous reinforcing fiber mat. The discontinuous reinforcing fiber mat is produced, for example, by pre-dispersing discontinuous reinforcing fibers into a fiber (strand) shape, preferably a roughly monofilament shape, and more preferably a monofilament shape. More specifically, dry processes such as an air-laid method in which discontinuous reinforcing fibers are dispersed and formed into sheets using an air flow, a carding method in which discontinuous reinforcing fibers are mechanically combed and formed into sheets, and a wet process based on the Radright method in which discontinuous reinforcing fibers are stirred in water and papered can be cited as known techniques.

[0083] As means for making the discontinuous reinforcing fibers closer to a single fiber shape, in a dry process, examples include means for setting a fiber opening rod, means for vibrating the fiber opening rod, means for making the teeth of the carding machine fine, means for adjusting the rotation speed of the carding machine, etc., and in a wet process, examples include means for adjusting the stirring conditions of the discontinuous reinforcing fibers, means for diluting the reinforcing fiber concentration of the dispersion, means for adjusting the viscosity of the dispersion, means for suppressing eddy currents when transferring the dispersion, etc. In particular, the discontinuous reinforcing fiber mat is preferably manufactured by a wet method, and the proportion of reinforcing fibers in the discontinuous reinforcing fiber mat can be easily adjusted by increasing the concentration of the input fibers or adjusting the flow rate (flow rate) of the dispersion and the speed of the mesh conveyor. For example, by slowing the speed of the mesh conveyor relative to the flow rate of the dispersion, the orientation of the fibers in the resulting discontinuous reinforcing fiber mat is difficult to face the pulling direction, and a bulky discontinuous reinforcing fiber mat can be manufactured. The discontinuous reinforcing fiber mat may be composed of discontinuous reinforcing fibers alone, or the discontinuous reinforcing fibers may be mixed with a powdery or fibrous matrix resin component, or the discontinuous reinforcing fibers may be mixed with an organic or inorganic compound, or the discontinuous reinforcing fibers may be filled with a resin component.

[0084] The pressure applied when impregnating the discontinuous reinforcing fiber mat produced as described above with a thermoplastic resin film or nonwoven fabric is preferably 0.5 MPa to 30 MPa, more preferably 1 MPa to 5 MPa. If the pressure is less than 0.5 MPa, the discontinuous reinforcing fiber mat may not be impregnated with the thermoplastic resin. If the pressure is greater than 30 MPa, adjusting the thickness of the core material precursor becomes difficult. The temperature applied when impregnating the thermoplastic resin film or nonwoven fabric is preferably at least the melting point or glass transition temperature of the thermoplastic resin, more preferably at least 10°C above the melting point or glass transition temperature, and even more preferably at least 20°C above the melting point or glass transition temperature. It should be noted that if the temperature applied when impregnating the thermoplastic resin film or nonwoven fabric is too high compared to the melting point or glass transition temperature of the thermoplastic resin, decomposition and degradation of the thermoplastic resin may occur. Therefore, the temperature applied is preferably at or below the melting point or glass transition temperature of the thermoplastic resin plus 150°C.

[0085] As equipment for achieving the method of impregnating a discontinuous reinforcing fiber mat with a thermoplastic resin film or nonwoven fabric under the above conditions, compression molding machines and double-belt presses are suitable. Compression molding machines are intermittent, and their use of an intermittent pressing system with two or more machines for heating and cooling in parallel improves productivity. Double-belt presses are continuous, facilitating continuous processing and thus offering excellent continuous productivity.

[0086] The precursor of the fiber-reinforced material (II) is generally a prepreg comprising reinforcing fibers and a resin, and examples thereof include unidirectional fiber prepregs or woven fiber prepregs reinforced with continuous fibers, and laminates comprising reinforcing fiber sheets and resin sheets.

[0087] Methods [1] to [3] all include a hot pressing step. In this step, by arranging a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of a heat-conducting material (III), and hot pressing at a temperature required for solidification or melting of the resin of the precursor of the fiber-reinforced material (II), the heat-conducting material can be included in the fiber-reinforced material. Method [3] includes a secondary hot pressing step. In the second hot pressing step, the fiber-reinforced material (II) containing the heat-conducting material is laminated with the core material and hot pressed. By the second hot pressing, the fiber-reinforced material and the core material can be bonded and the sandwich structure can be formed at the same time. As a hot pressing device, a compression molding machine can be suitably used. The compression molding machine is an intermittent type, and productivity can be improved by using an intermittent pressing system with two or more machines for heating and cooling in parallel.

[0088] Method [1] is a method for joining the formed fiber-reinforced material (II) on both sides of the core material (I) after the heat-conducting material (III) is included in the fiber-reinforced material (II) during the molding process of the fiber-reinforced material (II). As a means for joining the core material (I) and the fiber-reinforced material (II), there is no particular limitation. For example, there is a method for joining the core material (I) and the fiber-reinforced material (II) by hot plate welding, vibration welding, ultrasonic welding, laser welding, resistance welding, induction heating welding, or an adhesive. It can be preferably used when the molding conditions such as the molding temperature and molding pressure of the core material (I) and the fiber-reinforced material (II) are greatly different.

[0089] Method [2] is a method for simultaneously forming / joining the core material (I) and the fiber-reinforced material (II). It can be preferably used when the molding conditions such as the molding temperature and molding pressure of the core material (I) and the fiber-reinforced material (II) are close. Since the molding / joining of the core material (I) and the fiber-reinforced material (II) can be carried out simultaneously, it is preferred from the perspective of productivity.

[0090] Method [3] is a method in which, during the molding process of the fiber-reinforced material (II), the heat-conductive material (III) is incorporated into the fiber-reinforced material (II), and then the molded fiber-reinforced material (II) is placed on both sides of the precursor of the core material (I) and hot-pressed. This method is preferred from the perspective of productivity because the core material (I) and the fiber-reinforced material (II) can be joined simultaneously with the molding of the core material (I).

[0091] <Housing>

[0092] The housing of the present invention utilizes the sandwich structure of the present invention. By utilizing the sandwich structure of the present invention, a housing having both excellent mechanical properties and lightness can be obtained. Furthermore, from the perspective of mass production, high-cycle molding such as press molding is also possible, which is therefore preferred.

[0093] The housing of the present invention can be obtained, for example, by manufacturing a sandwich structure having a desired housing shape using the above-mentioned method for manufacturing a sandwich structure.

[0094] Example

[0095] Hereinafter, the present invention will be described in further detail with reference to examples.

[0096] (1) Determination of flexural strength and flexural modulus of sandwich structures

[0097] The bending properties of the prepared sandwich structure were measured using the ISO 178 method (1993). The bending direction was defined as the fiber direction at the outermost surface of the bending test piece and the direction perpendicular to it. The number of measurements, n = 5, was used, and the average values ​​were used as the flexural strength and flexural modulus. The measuring apparatus used was the "Instron" (registered trademark) 5565 universal testing machine manufactured by Instron Japan Co., Ltd.

[0098] (2) Evaluation of heat dissipation properties of sandwich structures

[0099] like Figure 3 As shown, 10 mm x 10 mm, 3 mm thick rubber spacers 6 were attached to the four corners of the back surface of the fabricated sandwich structure 1 and placed on a laboratory bench. A 50 mm x 25 mm micro-ceramic heater 5 (Micro-ceramic Heater MS-2 (trade name), manufactured by Sakaguchi Denka Co., Ltd.) was placed at one corner of the front surface of the sandwich structure. The heater was heated at 10 W under constant current and constant voltage conditions. Heat dissipation was evaluated using the following criteria based on the heater temperature at which it became constant 15 minutes after the start of heating.

[0100] A: Heater temperature is less than 120℃ (high heat dissipation)

[0101] B: Heater temperature is 120° C. or higher (low heat dissipation).

[0102] (Reference Example 1) Preparation of Carbon Fiber Bundles

[0103] A continuous carbon fiber bundle containing 12,000 filaments was obtained by spinning and calcining a polymer primarily composed of polyacrylonitrile. A sizing agent was applied to the continuous carbon fiber bundle by an impregnation method and then dried in heated air at 120°C. The properties of this carbon fiber bundle are described below.

[0104] Single fiber diameter: 7μm

[0105] Mass per unit length: 0.8g / m

[0106] Density: 1.8g / cm 3

[0107] Tensile strength: 4.2GPa

[0108] Tensile elastic modulus: 230GPa

[0109] Sizing type: polyoxyethylene oleyl ether

[0110] Sizing adhesion: 1.5% by mass

[0111] (Reference Example 2) Preparation of carbon fiber felt

[0112] The carbon fiber bundle of Reference Example 1 was cut into 6 mm fiber lengths using a drum cutter to obtain chopped carbon fiber bundles. A 0.1% by mass aqueous dispersion of a surfactant (polyoxyethylene lauryl ether (trade name) manufactured by Nakalai Technologies Co., Ltd.) was prepared and this dispersion and the chopped carbon fiber bundles were fed into a papermaking machine to produce a carbon fiber mat.

[0113] The papermaking machine includes a dispersion tank, a papermaking tank, and a conveying section connecting the dispersion tank and the papermaking tank. The dispersion tank is equipped with a stirrer that can disperse the dispersion liquid and chopped carbon fiber bundles put in. The papermaking tank is equipped with a mesh conveyor having a papermaking surface at the bottom, and a conveyor that can convey the carbon fiber felt obtained by papermaking is connected to the mesh conveyor. Papermaking is carried out by making the fiber concentration in the dispersion liquid 0.05% by mass. The carbon fiber felt obtained by papermaking is dried in a drying furnace at 200°C. Then, a 3% by mass aqueous dispersion of a binder ("Polyment" (registered trademark) SK-1000 manufactured by Nippon Shokubai Co., Ltd.) is spread on the upper portion of the carbon felt conveyed by the conveyor as a binder. The remaining binder is sucked out and dried in a drying furnace at 200°C to obtain a carbon fiber felt. The obtained carbon fiber felt has a basis weight of 50 g / m 2 .

[0114] (Reference Example 3) Preparation of polypropylene resin film

[0115] 90% by mass of an unmodified polypropylene resin ("Plain Polypropylene Pro" (registered trademark) J105G, manufactured by Premier Polymer Co., Ltd.) and 10% by mass of an acid-modified polypropylene resin ("Admar" (registered trademark) QE510, manufactured by Mitsui Chemicals, Inc.) were blended. This blend was melt-kneaded in an extruder and extruded through a T-die. The resin was then cooled and solidified by drawing it through a cooling roll at 60°C, thereby producing a polypropylene resin film.

[0116] (Reference Example 4) Preparation of epoxy resin film

[0117] An epoxy resin (base resin: dicyandiamide / dichlorophenylmethylurea curing epoxy resin) was applied onto release paper using a coater to obtain an epoxy resin film.

[0118] (Reference Example 5) Preparation of unidirectional prepreg

[0119] The carbon fiber bundle of Reference Example 1 was arranged in one direction into a sheet, and two sheets of epoxy resin film of Reference Example 4 were overlapped from both sides of the carbon fiber bundle. The epoxy resin film was impregnated with the resin by heating and pressing to obtain a carbon fiber with a basis weight of 110 g / m 2 , thickness 0.1mm, unidirectional prepreg with a matrix resin mass fraction of 30% by mass.

[0120] (Example 1)

[0121] A sandwich structure was produced using the carbon fiber felt of Reference Example 2, the polypropylene resin film of Reference Example 3, the unidirectional prepreg of Reference Example 5, and a graphite sheet (manufactured by Panasonic Co., Ltd., "PGS" (registered trademark) EYGS182307, in-plane thermal conductivity 1000 W / m·K). The carbon fiber felt, polypropylene resin film, and unidirectional prepreg were adjusted to a size of 50 mm × 150 mm, and the graphite sheet was adjusted to a size of 40 mm × 140 mm. Then, the layers were stacked in the order of [unidirectional prepreg 0° / graphite sheet / unidirectional prepreg 90° / polypropylene resin film / carbon fiber felt / carbon fiber felt / polypropylene resin film / unidirectional prepreg 90° / unidirectional prepreg 0°] so that the fiber direction of the unidirectional prepreg on the surface was in the longitudinal direction of the sample. At this time, the graphite sheet was placed in the center of the laminate. The laminate was sandwiched between release films and further between tool plates. They were put into a press molding machine with a disk surface temperature of 180°C and hot pressed at 3MPa for 10 minutes to cure the prepreg and impregnate the carbon fiber felt with polypropylene resin. Next, a spacer with a thickness of 1mm was inserted between the tool plates, and the laminate was put into a press molding machine with a disk surface temperature of 40°C and cold pressed at a surface pressure of 3MPa until the laminate cooled, thereby obtaining a sandwich structure in which fiber reinforcement material was arranged around the thermal conductive material. The thickness of the sample was measured with a micrometer and the result was 1.0mm. By inserting a spacer with a thickness of 1.0mm between the tool plates, the carbon fiber felt impregnated with polypropylene resin rebounded and the core material became a porous body. It should be noted that the sample in this embodiment is a flat plate, so the thickness is constant. Therefore, the thickness measured at any point of the sample becomes the maximum thickness. The same applies to other embodiments and comparative examples.

[0122] In addition, the bending test piece was preformed and press-molded in the same manner except that the carbon fiber felt, polypropylene resin film, and unidirectional prepreg were adjusted to 50 mm × 40 mm in size, and the graphite sheet was adjusted to 40 mm × 30 mm in size. A bending test piece of a sandwich structure with fiber reinforcement material arranged around the thermal conductive material was obtained. A cross-sectional view of the obtained sandwich structure is shown in FIG. Figure 4 For the sandwich structure obtained, Figure 4 In this way, fiber-reinforced material layers formed from unidirectional fiber-reinforced material 0° 7 and unidirectional fiber-reinforced material 90° 8 are provided on both sides of core material 2. Furthermore, graphite sheet 9 is covered on both sides and all end faces by the fiber-reinforced material, providing protection from the fiber-reinforced material. Consequently, the resulting sandwich structure exhibits excellent mechanical properties, preventing the graphite sheet from peeling off or scattering of graphite sheet fragments. Furthermore, the inclusion of the graphite sheet provides excellent heat dissipation.

[0123] (Example 2)

[0124] The number of unidirectional prepreg layers was changed to [unidirectional prepreg 0° / unidirectional prepreg 90° / graphite sheet / unidirectional prepreg 90° / unidirectional prepreg 0° / polypropylene resin film / carbon fiber felt / carbon fiber felt / polypropylene resin film / unidirectional prepreg 0° / unidirectional prepreg 90° / unidirectional prepreg 90° / unidirectional prepreg 0° / ], and preforming and press molding were performed in the same manner as in Example 1 to obtain a sandwich structure having a fiber reinforcement material disposed around the thermal conductive material, and a bending test piece of the sandwich structure. A cross-sectional view of the obtained sandwich structure is shown in FIG. Figure 5 Because the ends of the graphite sheet are protected by the fiber reinforcement, the resulting sandwich structure has excellent mechanical properties. Furthermore, because the unidirectional prepreg is laminated on the surface of the graphite sheet in multiple directions, the mechanical properties in the direction perpendicular to the surface fibers are also excellent.

[0125] (Comparative Example 1)

[0126] The same procedures as in Example 1 were followed except that the graphite sheet was adjusted to 50 × 150 mm in size, and pre-molding and press molding were performed to obtain a sandwich structure with all ends of the thermal conductive material exposed. Furthermore, when preparing the bending test piece, the same procedures as in Example 1 were followed except that the graphite sheet was adjusted to 50 mm × 40 mm in size, and pre-molding and press molding were performed to obtain a sandwich structure with all ends of the thermal conductive material exposed. A cross-sectional view of the obtained sandwich structure is shown in FIG. Figure 6 In the obtained sandwich structure, all the ends of the graphite sheets were exposed, so peeling occurred between the layers of the graphite sheets.

[0127] (Comparative Example 2)

[0128] The graphite sheet was adjusted to 50 × 150 mm in size. Pre-molding and press molding were performed in the same manner as in Example 2, and a sandwich structure with all ends of the thermal conductive material exposed was obtained. Furthermore, when preparing the bending test piece, the graphite sheet was adjusted to 50 mm × 40 mm in size. Pre-molding and press molding were performed in the same manner as in Example 2, and a sandwich structure with all ends of the thermal conductive material exposed was obtained. A cross-sectional view of the obtained sandwich structure is shown in FIG. Figure 7 In the obtained sandwich structure, all the end faces of the graphite sheets were exposed, so peeling occurred between the layers of the graphite sheets.

[0129] (Comparative Example 3)

[0130] The same procedures as in Example 1 were followed except that the graphite sheet was not laminated, and preforming and press molding were performed to obtain a sandwich structure containing no thermal conductive material. Furthermore, in the preparation of the bending test piece, the same procedures as in Example 1 were followed except that the graphite sheet was not laminated, and preforming and press molding were performed to obtain a bending test piece of a sandwich structure containing no thermal conductive material. A cross-sectional view of the obtained sandwich structure is shown in FIG. Figure 8 The resulting sandwich structure does not contain a thermally conductive material and therefore has low heat dissipation.

[0131] [Table 1]

[0132]

[0133] Industrial availability

[0134] The sandwich structure of the present invention combines excellent heat dissipation with excellent mechanical properties. Therefore, it can be used in a wide range of industrial fields, such as as structural components for electrical / electronic equipment, remote-controlled devices (robots), two-wheeled vehicles, automobiles, and aircraft. In particular, it is preferably used in housings for electronic devices requiring high heat dissipation.

[0135] Explanation of symbols

[0136] 1. Sandwich structure

[0137] 2. Core material (I)

[0138] 3. Fiber-reinforced materials (II)

[0139] 4. Thermally conductive materials (III)

[0140] 5. Heater

[0141] 6. Rubber spacers

[0142] 7.Unidirectional fiber reinforced resin 0°

[0143] 8.Unidirectional fiber reinforced resin 90°

[0144] 9. Graphite sheet.

Claims

1. A sandwich structure comprising a core material (I) and fiber-reinforced materials (II) arranged on both surfaces of the core material (I), at least one of the fiber-reinforced materials (II) comprising a sheet-like thermally conductive material (III) having an in-plane thermal conductivity of 300 W / m·K or higher, the core material (I) comprising a porous body, and the volume content of voids in the core material (I) being 10% or higher and 85% or lower relative to the apparent volume of the core material (I). At least one of the fiber-reinforced materials (II) covers both sides and all end faces of the thermally conductive material (III), The fiber reinforcement material (II) is made of unidirectional fiber reinforced resin and is laminated so that the fiber directions of the fiber reinforcement material between the surface of the fiber reinforcement material (II) including the thermal conductive material (III) and the thermal conductive material (III) are in multiple directions. 2 . The sandwich structure according to claim 1 , wherein the heat-conducting material (III) comprises a heat-conducting sheet selected from the group consisting of a graphite sheet, a metal sheet, and a ceramic sheet. 3 . The sandwich structure according to claim 2 , wherein the thermally conductive material (III) comprises a stacked structure of a plurality of thermally conductive sheets.

4. The sandwich structure according to claim 1, wherein the surface of the heat conductive material (III) is arranged at a distance of 0.01 mm or more and 0.3 mm or less from the surface of the fiber-reinforced material (II) containing the heat conductive material (III). The sandwich structure according to claim 1 , wherein the porous body is made of fiber-reinforced resin.

6. The sandwich structure according to claim 5, wherein the fiber-reinforced resin is a resin reinforced with discontinuous reinforcing fibers, and has a structure in which the discontinuous reinforcing fibers form a three-dimensional network and the intersections of the discontinuous reinforcing fibers are bonded by the resin. 7 . The sandwich structure according to claim 5 , wherein the fiber-reinforced resin is a resin reinforced with discontinuous reinforcing fibers, and 30% or more of the surface of the discontinuous reinforcing fibers is coated with the resin.

8. The sandwich structure according to claim 1, wherein the fiber-reinforced material (II) is made of carbon fiber-reinforced resin. 9 . The sandwich structure according to claim 1 , wherein the sandwich structure has a bending rigidity per unit width of 0.5 N·m or more. 10 . The sandwich structure according to claim 1 , wherein the maximum thickness is 0.3 mm to 3.0 mm.

11. A housing formed by using the sandwich structure according to any one of claims 1 to 10.

12. A method for manufacturing a sandwich structure, which is a method for manufacturing a sandwich structure according to any one of claims 1 to 10, comprising the following steps in sequence: a step of disposing a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of the heat-conductive material (III); a step of performing hot pressing; and a step of joining the fiber-reinforced material (II) to both surfaces of the core material (I).

13. A method for manufacturing a sandwich structure, which is a method for manufacturing the sandwich structure according to any one of claims 1 to 10, which comprises the following steps in sequence: a step of arranging a thermally conductive material (III) having a precursor of a fiber-reinforced material (II) arranged on at least one surface and at least one end face / a precursor of a core material (I) / a precursor of a fiber-reinforced material (II) in the order; and a step of performing hot pressing.

14. A method for manufacturing a sandwich structure, which is a method for manufacturing a sandwich structure according to any one of claims 1 to 10, comprising the following steps in sequence: a step of arranging a precursor of a fiber-reinforced material (II) on at least one surface and at least one end face of the thermally conductive material (III); a step of performing hot pressing; a step of arranging the fiber-reinforced material (II) on both sides of a precursor of a core material (I); and a step of performing hot pressing.

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