Sandwich structure and method for manufacturing the same

Abstract

The purpose of the present invention is to provide a sandwich structure that has both excellent heat dissipation properties and excellent mechanical properties.　In order to achieve this purpose, the sandwich structure of the present invention has the following structure. The sandwich structure includes a core member (I), and a fiber reinforced member (II) disposed on both sides of the core member (I), wherein the core member (I) includes a sheet-shaped heat conductive member (III) having an in-plane thermal conductivity of 300 W / m·K or more.

Description

Technical Field

[0001] The present invention relates to a sandwich structure and a method for manufacturing the same.

Background Art

[0002] In recent years, market requirements for heat dissipation in industrial products such as automobiles, aircraft, and electronic devices have been increasing year by year. In order to meet such requirements, molded products having a high thermal conductivity are widely used in various industrial applications. Among them, a sandwich structure including a heat conductive material having a high thermal conductivity is expected to be utilized in each product because it has excellent heat dissipation and excellent mechanical properties. In particular, a sandwich structure of a heat conductive material and a high-strength material has been widely studied.

[0003] Patent Document 1 describes an invention of a sandwich structure in which a heat conductive material and a rigidity retaining material are laminated. By laminating a heat conductive material and a rigidity retaining material, it is said that a sandwich structure having both excellent thermal conductivity and excellent rigidity can be obtained.

[0004] Patent Document 2 describes an invention of a sandwich structure in which a graphite sheet having excellent thermal conductivity and support sheets are laminated on both surfaces of the graphite sheet, and a sealing spacer having substantially the same thickness as the graphite sheet is attached to at least one end surface of the graphite sheet. By attaching a sealing spacer around the graphite sheet, it is said that it has excellent thermal conductivity and mechanical strength, prevents the detachment of graphite powder from the end face, has no knife-shaped edge and excellent handleability, and has an effect of suppressing peeling.

[0005] Patent Document 3 describes an invention of a high thermal conductivity housing in which a laminate of graphite sheets is covered with a resin layer. By covering the end portion of the graphite sheet with resin, it is said that it is possible to prevent peeling between the graphite films.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 International Publication No. 2016 / 002457 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2007-44994 Patent Document 3 Japanese Unexamined Patent Application Publication No. 2006-95935 Summary of the Invention Problems to be Solved by the Invention

[0007] In the sandwich structure in Patent Document 1, since all the ends of the heat conductive material are exposed, the strength of the heat conductive material is insufficient. Further, when the bonding strength between the heat conductive material and the rigidity retaining material is insufficient, there is a possibility of peeling from the end of the sandwich structure.

[0008] In the sandwich structure in Patent Document 2, although the end of the graphite sheet is protected by a sealing spacer, adjustment of the thickness of the sealing spacer and adjustment of the position of the sealing spacer are complicated, and the processability is low. Further, when the bonding strength between the sealing spacer and the support sheet is insufficient, there is a possibility of peeling from the end of the sandwich structure.

[0009] In the high heat conductivity housing in Patent Document 3, the surface and the ends of the graphite sheet are covered with resin to protect the graphite sheet, but due to the protection with resin, the rigidity and strength are low.

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a sandwich structure that achieves both excellent heat dissipation properties and excellent mechanical properties. Means for Solving the Problems

[0011] In order to solve the above problems, the sandwich structure of the present invention has the following configuration.

[0012] A sandwich structure having a core material (I) and fiber reinforcing materials (II) disposed on both sides of the core material (I), wherein the core material (I) includes a sheet-like heat conductive material (III) having an in-plane thermal conductivity of 300 W / m·K or more.

Advantages of the Invention

[0013] According to the present invention, even when the strength of the heat conductive material is insufficient or the bonding between the heat conductive material and the material for protecting the heat conductive material is insufficient, it is possible to obtain a sandwich structure that combines excellent heat dissipation performance and excellent mechanical properties.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0015] The present invention will be described in detail below.

[0016] <Sandwich Structure> As used herein, the sandwich structure refers to a structure in which skin materials having a higher elastic modulus than the core material are disposed on both sides of the core material. In the sandwich structure of the present invention, the core material is a core material (I) containing a sheet-like heat conductive material (III), and the skin material is a fiber reinforced material (II). Also, the term "sheet-like" refers to a material having a thin thickness and a wide width, having a thickness of 0.01 μm or more and 10 mm or less, and an aspect ratio of width to thickness of 10 or more.

[0017] The core material (I) contains a sheet-like heat conductive material (III) (hereinafter, may be simply referred to as the heat conductive material (III)). The term "contains" as used herein means that the heat conductive material (III) exists as a part of the layer of the core material (I) in the laminated structure of the sandwich structure.

[0018] For example, in the case of FIG. 1, an aspect in which the core material (I) 2 covers one end face (the right end face in FIG. 1) and one surface (the upper surface in FIG. 1) of the heat conductive material (III) 4, or in the case of FIG. 2, an aspect in which the core material (I) 2 covers both surfaces (both surfaces) and all end faces of the heat conductive material (III), that is, an aspect in which the core material (I) encloses the heat conductive material (III), can be said that the core material (I) contains the heat conductive material (III). On the other hand, an aspect in which all end faces of the heat conductive material (III) (graphite sheet 9) are exposed as in FIG. 6, that is, an aspect in which only the heat conductive material (III) forms an independent layer, is excluded from the above concept of "contains". Thus, by the heat conductive material (III) being contained in the core material (I), the core material (I) bears the stress applied to the sandwich structure, the transmission of stress to the heat conductive material (III) is suppressed, and the breakage of the heat conductive material (III) can be suppressed.

[0019] The core material (I) preferably covers at least two end faces of the heat conductive material (III), more preferably covers both surfaces of the heat conductive material (III), and even more preferably covers both surfaces and all end faces of the heat conductive material (III), that is, encloses the heat conductive material (III).

[0020] In the present invention, the core material (I) may cover the heat conductive material (III) via other members such as an adhesive or a buffer material. Further, there may be a gap between the core material (I) and the heat conductive material (III).

[0021] However, in the present invention, it is preferable that at least one end face of the heat conductive material (III) is in direct contact with the core material (I) without any intervening member. Further, it is preferable that at least one surface of the heat conductive material (III) is in contact with the core material (I). By having the heat conductive material (III) in direct contact with the core material (I) in this way, the heat transmitted from the surface of the sandwich structure can be quickly transmitted from the core material (I) to the heat conductive material (III).

[0022] Furthermore, in the present invention, it is preferable that the heat conductive material (III) is not adhered to the core material (I). In order to adhere the heat conductive material (III) to the core material (I), generally, it is necessary to interpose an adhesive between them. However, the proportion of the heat conductive material (III) in the sandwich structure occupied by the adhesive decreases, and the heat dissipation property of the sandwich structure deteriorates. Further, since the heat conductive material (III) is not adhered to the core material (I), the proportion of the stress applied to the sandwich structure borne by the core material (I) increases. Therefore, the transmission of stress to the heat conductive material (III) is suppressed, and the breakage of the heat conductive material (III) can be suppressed.

[0023] The sandwich structure of the present invention preferably has a bending rigidity per unit width of 0.5 N·m or more, more preferably 1.0 N·m or more, and even more preferably 1.5 N·m or more. Since the higher the bending rigidity per unit width of the sandwich structure is, the more preferable it is, there is no particular limitation on the upper limit of the bending rigidity per unit width. Usually, it is about 1000 N·m. By setting the bending rigidity per unit width within the above range, the sandwich structure becomes a rigid structure and can be suitably used for a housing or the like. The bending rigidity per unit width can be calculated from the elastic modulus E (Pa) of the sandwich structure, the second moment of area I (m 4 ) of the cross section, and the width b (m) of the sandwich structure by the following formula. · Bending stiffness per unit width (N·m) = E (Pa) × I (m 4 ) / b (m) In addition, when the cross-section of the sandwich structure is a rectangular cross-section, the second moment of area I of the rectangular cross-section is bh 3 / 12 (m 4 ). Therefore, it can be calculated by the following formula. · Bending stiffness per unit width (N·m) = E (Pa) × h 3 (m 3 ) / 12 As a means for setting the bending stiffness per unit width within the above range, for example, a method of using the fiber-reinforced material (II) as the skin material, like the sandwich structure of the present invention, can be mentioned. Also, for example, a method of making the thickness of the sandwich structure thick can be mentioned.

[0024] In addition, the sandwich structure of the present invention preferably has a maximum thickness of 0.3 mm or more and 3.0 mm or less, and more preferably 0.5 mm or more and 1.5 mm or less. Making the thickness of the sandwich structure thin has the effect of weight reduction, but a sandwich structure thinner than 0.3 mm may lack rigidity.

[0025] [Thermal conductive material (III)] In the present invention, the heat conductive material (III) is in the form of a sheet, and its in-plane thermal conductivity is 300 W / m·K or more. The in-plane thermal conductivity of the heat conductive material (III) is preferably 500 W / m·K or more, and more preferably 1000 W / m·K or more. Since the higher the in-plane thermal conductivity, the more preferable it is, there is no particular limitation on the upper limit of the in-plane thermal conductivity. However, a heat conductive material having an in-plane thermal conductivity of about 2000 W / m·K is known. If the in-plane thermal conductivity of the heat conductive material (III) is 300 W / m·K or more, the heat diffusion in the in-plane direction of the sandwich structure is excellent, and the heat dissipation property of the sandwich structure is excellent. The in-plane thermal conductivity of the heat conductive material (III) can be measured by setting a sample in a sample holder for in-plane measurement by the laser flash method, and making the size of the sample about 20 to 30 mm in diameter and the thickness 1.0 mm or less. Further, for a material that is difficult to absorb laser light, a blackening film is thinly and uniformly formed on the sample surface. For a material having a low emissivity at the temperature measurement wavelength of the infrared detection element, the same treatment is performed on the back surface of the sample.

[0026] The material of the heat conductive material (III) is not particularly limited as long as the in-plane thermal conductivity is 300 W / m·K or more. For example, ceramics, metals, graphite, and a highly heat conductive resin obtained by adding a highly heat conductive filler to a resin can be used.

[0027] Furthermore, the heat conductive material (III) preferably includes a heat conductive sheet selected from the group consisting of a graphite sheet, a metal sheet, and a ceramics sheet, and more preferably consists of a heat conductive sheet selected from the group consisting of a graphite sheet, a metal sheet, and a ceramics sheet. Examples of the ceramics sheet include sheets of silica, zirconia, alumina, boron nitride, silicon carbide, silicon nitride, etc. Examples of the metal sheet include sheets made of titanium, aluminum, magnesium, iron, silver, gold, platinum, copper, nickel, or alloys mainly composed of these metals.

[0028] The metal sheet is relatively inexpensive, and among them, the copper sheet is inexpensive and has excellent thermal conductivity, so it is preferable from the viewpoint of raw material cost. The graphite sheet has a small specific gravity and excellent thermal conductivity, so it is particularly preferable in the present invention from the viewpoints of improving the light weight and heat dissipation of the sandwich structure.

[0029] Examples of the graphite sheet include a sheet obtained by mixing and molding graphite powder with a binder resin, a sheet obtained by rolling expanded graphite, a sheet obtained by depositing carbon atoms on a substrate by CVD method using a hydrocarbon-based gas and then annealing, and a sheet obtained by graphitizing a film of a polymer compound. Among them, a sheet obtained by graphitizing a film of a polymer compound is preferable because of its very high thermal conductivity.

[0030] In the present invention, the heat conductive material (III) preferably includes a laminated structure of a plurality of heat conductive sheets, and more preferably is a laminated structure of a plurality of heat conductive sheets. In particular, for the graphite sheet, the orientation of the graphene structure in the sheet affects the thermal conductivity, and generally, a thinner graphite sheet has a higher thermal conductivity. Therefore, when a graphite sheet is used as the heat conductive sheet, the heat dissipation of the sandwich structure can be improved by using a laminated structure of a plurality of sheets as the heat conductive material (III). In this case, it is preferable that the plurality of heat conductive sheets constituting the heat conductive material (III) are in direct contact with each other without an adhesive or the like. When the heat conductive sheets are in direct contact with each other, the proportion of the heat conductive material (III) in the sandwich structure can be increased, and the heat dissipation of the sandwich structure is improved. In addition, when the heat conductive sheets are in direct contact with each other, it is also excellent in heat diffusion in the out-of-plane direction. The number of laminated heat conductive sheets is preferably 2 or more and 10 or less, and more preferably 3 or more and 5 or less. When 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 too much, the processability will be low.

[0031] The average thickness of the heat 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 even more preferably 15 μm or more and 0.5 mm or less. If the average thickness of the heat conductive material (III) is too small, the heat dissipation property of the sandwich structure will decrease. If the average thickness of the heat conductive material (III) is too large, the weight of the sandwich structure will increase. The measurement method of the average thickness of the heat conductive material (III) is to measure the thickness of 9 points of the heat conductive material (III) to one decimal place using a micrometer, and take the average value as the average thickness. Regarding the measurement points, the measurement is performed at a total of 9 points, 3 points each in the vertical and horizontal directions, so that the intervals between each measurement point and the adjacent point or the sample end are equal in both the vertical and horizontal directions.

[0032] [Core material (I)] In the present invention, it is preferable that the core material (I) contains a porous body, and it is more preferable that the core material (I) is a porous body. When the core material (I) contains a porous body, it is advantageous from the viewpoint of the light weight of the sandwich structure. Further, when the heat conductive material (III) is included in the core material (I), the porous core material (I) can include the heat conductive material (III) without displacement of the heat conductive material (III) due to crushing or swelling in the out-of-plane direction. When the core material (I) is a porous body, the volume content ratio of voids in the core material (I) is preferably 10% or more and 85% or less, more preferably 20% or more and 85% or less, and even more preferably 50% or more and 80% or less from the viewpoint of achieving both light weight and mechanical properties.

[0033] The material of the core material (I) is not particularly limited. For example, a fiber-reinforced resin reinforced with continuous fibers or discontinuous fibers is preferably used. Here, the continuous reinforcing fibers shall mean reinforcing fibers that are continuous over a length of at least 15 mm, preferably 100 mm or more, in at least one direction. As the fiber-reinforced resin reinforced with continuous fibers, a unidirectional fiber-reinforced resin or a woven fiber-reinforced resin can be used. As the fiber-reinforced resin reinforced with discontinuous fibers, either a short fiber-reinforced resin or a long fiber-reinforced resin can be used. Further, as the non-fiber-reinforced resin, a resin sheet, a resin foam, etc. can also be used.

[0034] Whether it is a fiber-reinforced resin or a non-fiber-reinforced resin, when the core material (I) contains a resin, the resin is not particularly limited and may be a thermosetting resin or a thermoplastic resin. Examples of the thermoplastic resin include "polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and liquid crystal polyester, polyolefins such as polyethylene (PE), polypropylene (PP), and polybutylene, polyarylene sulfides such as polyoxymethylene (POM), polyamide (PA), and polyphenylene sulfide (PPS), polyketone (PK), polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether nitrile (PEN), and fluorine-based resins such as polytetrafluoroethylene", crystalline resins, "in addition to styrene-based resins, polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyether sulfone, and polyarylate (PAR)", amorphous resins, and other thermoplastic resins selected from phenolic resins, phenoxy resins, and furthermore, thermoplastic elastomers such as polystyrene-based, polyolefin-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based, polyisoprene-based, fluorine-based resins, and acrylonitrile-based resins, as well as copolymers and modified products thereof. Among them, polyolefins are preferred from the viewpoint of the light weight of the obtained sandwich structure. In particular, when the core material (I) contains a porous body, polyolefins are preferred in order to synergistically enhance the light weight effect. Also, polyamides are preferred from the viewpoint of strength. In particular, when the core material (I) is made of a fiber-reinforced resin, polyamides are preferred from the viewpoint of the interfacial bonding strength between the reinforcing fibers and the resin. Examples of the thermosetting resin include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic (resole) resins, urea resins, melamine resins, polyimide resins, maleimide resins, benzoxazine resins, and resins obtained by blending two or more of these thermosetting resins.Among them, particularly when the core material (I) is made of a fiber-reinforced resin, an epoxy resin is preferably used from the viewpoint of the interfacial bonding strength between the reinforcing fiber and the resin.

[0035] Furthermore, fillers such as mica, talc, kaolin, hydrotalcite, sericite, bentonite, zonotrite, sepiolite, smectite, montmorillonite, wollastonite, silica, calcium carbonate, glass beads, glass flakes, glass microballoons, 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, conductivity-imparting materials such as metal-based, metal oxide-based, carbon black, and graphite powders, halogen-based flame retardants such as brominated resins, antimony-based flame retardants such as antimony trioxide and antimony pentoxide, phosphorus-based flame retardants such as ammonium polyphosphate, aromatic phosphates, and red phosphorus, organic acid metal salt-based flame retardants such as metal borates, metal carboxylates, and metal aromatic sulfonimides, inorganic-based flame retardants such as zinc borate, zinc, zinc oxide, and zirconium compounds, nitrogen-based flame retardants such as cyanuric acid, isocyanuric acid, melamine, melamine cyanurate, melamine phosphate, and nitrided guanidine, 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 aids 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, mold release agents, compatibilizers, dispersants, crystal nucleating agents such as mica, talc, and kaolin, plasticizers such as phosphate esters, heat stabilizers, antioxidants, anti-coloring agents, ultraviolet absorbers, fluidity modifiers, foaming agents, antibacterial agents, vibration damping agents, deodorants, sliding property modifiers, and antistatic agents such as polyether ester amide may be added. In particular, when the application is for electrical and electronic equipment, automobiles, aircraft, etc., flame retardancy may be required, and phosphorus-based flame retardants, nitrogen-based flame retardants, and inorganic-based flame retardants are preferably added. In order to maintain a good balance of properties such as the mechanical properties of the resin to be used and the resin fluidity during molding while exhibiting the flame retardant effect, it is preferable that the flame retardant is 1 to 20 parts by mass with respect to 100 parts by mass of the resin. More preferably, it is 1 to 15 parts by mass.

[0036] From the viewpoint of the light weight of the sandwich structure, the specific gravity of the core material (I) is preferably 0.01 to 1.5. More preferably, it is 0.1 to 1.3, and still more preferably, it is 0.3 to 1.1. The specific gravity can be measured by cutting out the core material (I) and measuring it in accordance with ISO1183 (1987) or ISO0845 (1988).

[0037] When the core material (I) is a fiber-reinforced material, the type of reinforcing fiber contained is not particularly limited. 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, and these may be used alone or in combination of two or more. Among them, from the viewpoint of high specific strength and specific rigidity and the weight reduction effect, carbon fibers such as PAN-based, pitch-based, and rayon-based are preferably used. Also, from the viewpoint of enhancing the economy of the obtained sandwich structure, glass fiber can be preferably used, and in particular, it is preferable to use carbon fiber and glass fiber in combination from the balance of mechanical properties and economy. Furthermore, from the viewpoint of enhancing the impact absorbency and formability of the obtained sandwich structure, aramid fiber can be preferably used, and in particular, it is preferable to use carbon fiber and aramid fiber in combination from the balance of mechanical properties and impact absorbency. Also, from the viewpoint of enhancing the conductivity of the obtained sandwich structure, it is also possible to use reinforcing fibers coated with metals such as nickel, copper, and ytterbium or pitch-based carbon fibers.

[0038] It is preferable from the viewpoint of improving mechanical properties that the reinforcing fibers are surface-treated with a sizing agent. Examples of the sizing agent include polyfunctional epoxy resins, acrylic acid-based polymers, polyhydric alcohols, polyethyleneimine, etc. Specifically, polyglycidyl ethers of aliphatic polyhydric alcohols such as glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, arabitol polyglycidyl ether, trimethylolpropane triglycidyl ether, 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 of these, polyvinyl alcohol, glycerol, diglycerol, polyglycerol, sorbitol, arabitol, trimethylolpropane, pentaerythritol, polyethyleneimine containing more amino groups in one molecule, etc. Among these, glycerol triglycidyl ether, diglycerol polyglycidyl ether, and polyglycerol polyglycidyl ether are preferably used because they contain many highly reactive epoxy groups in one molecule, have high water solubility, and are easy to apply.

[0039] When the core material (I) in the present invention contains a porous body, it is particularly preferable that the porous body is made of a fiber-reinforced resin. The reinforcing fibers of the fiber-reinforced resin may be continuous fibers or discontinuous fibers, but discontinuous fibers are preferable. It is more preferable that the discontinuous fibers form a three-dimensional network and have a structure in which the intersections of the discontinuous fibers are bonded by a resin. By bonding the discontinuous fibers to each other with a resin, the shear modulus of the core material (I) increases, and the rigidity of the sandwich structure increases. Hereinafter, this aspect will be described.

[0040] In the fiber-reinforced resin, the discontinuous fibers preferably exist as less than 500 fine-strand fibers, more preferably, they are preferably dispersed in the form of single fibers. The fiber length of the discontinuous fibers is preferably 1 to 50 mm, more preferably 3 to 30 mm. When it is 1 mm or more, the reinforcing effect by the discontinuous fibers can be efficiently exerted. Also, when it is 50 mm or less, the dispersion of the discontinuous fibers can be kept good.

[0041] The ratio of the number of bonding portions where the single fibers of the discontinuous fibers are bonded by the resin is 50% or more, more preferably 70% or more, still more preferably 90% or more, based on the number of all crossing portions where the discontinuous fibers cross each other.

[0042] From the viewpoint of achieving both mechanical properties and moldability, the mass ratio of the discontinuous fibers is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, still more preferably 15 to 40% by mass, based on the whole of the core material (I).

[0043] In the fiber-reinforced resin, it is preferable that 30% or more, more preferably 50% or more, still more preferably 80% or more of the surface of the discontinuous fibers is coated with the resin. By setting such a coating rate, the rigidity of the core material (I) can be increased. The coating rate is measured by observing the cross section of the core material (I) with a scanning electron microscope (SEM) and distinguishing the reinforcing fibers from the resin.

[0044] [Fiber Reinforcement Material (II)] In the present invention, the fiber reinforcement material (II) is a member containing reinforcing fibers, which constitutes the skin material of the sandwich structure and has a higher elastic modulus than the core material (I).

[0045] The material of the fiber reinforcement (II) is not particularly limited as long as it has a modulus of elasticity greater than that of the core material (I), and it may be a fiber-reinforced resin reinforced with continuous fibers or a fiber-reinforced resin reinforced with discontinuous fibers. As the fiber-reinforced resin reinforced with continuous fibers, a unidirectional fiber-reinforced resin or a woven fiber-reinforced resin can be used. As the fiber-reinforced resin reinforced with discontinuous fibers, either a short fiber-reinforced resin or a long fiber-reinforced resin can be used. From the viewpoint of the mechanical properties of the sandwich structure, it is preferable to use a continuous fiber reinforcement, and among them, it is more preferable to use a unidirectional fiber reinforcement. On the other hand, from the viewpoint of the formability of the sandwich structure, a discontinuous fiber reinforcement material can be preferably used. Also, the matrix resin of the fiber-reinforced resin is not particularly limited, and any of a thermosetting resin and a thermoplastic resin can be used, and the same resins as those exemplified in the description of the above-mentioned core material (I) can be used. Further, additives may be contained in the matrix resin, and examples of the additives include the additives exemplified in the description of the above-mentioned core material (I).

[0046] There is no particular limitation on the type of reinforcing fiber contained in the fiber reinforcement (II), and the same reinforcing fibers as those exemplified in the description of the above-mentioned core material (I) can be used.

[0047] From the viewpoint of achieving both mechanical properties and moldability, the mass ratio of the reinforcing fiber in the fiber reinforcement (II) is preferably 30 to 90% by mass, more preferably 40 to 80% by mass, and still more preferably 50 to 70% by mass with respect to 100% by mass of the fiber reinforcement (II). Any combination of the above upper and lower limits may be used.

[0048] In the sandwich structure of the present invention, the fiber reinforcing material (II) preferably contains a carbon fiber reinforced resin, and more preferably consists of a carbon fiber reinforced resin. The carbon fiber reinforced resin is composed of carbon fibers and a matrix resin. By consisting of a carbon fiber reinforced resin, it becomes easier to obtain a sandwich structure excellent in light weight, rigidity, and strength. Among carbon fibers, pitch-based carbon fibers having a high elastic modulus and high thermal conductivity are more preferable. By using pitch-based carbon fibers, an improvement in the rigidity and heat dissipation of the sandwich structure can be expected.

[0049] Note that the fiber reinforcing material (II) may have a laminated structure in which a plurality of the above-described members are laminated.

[0050] <Manufacturing method of sandwich structure> The sandwich structure of the present invention can be preferably manufactured by any one of the following methods [1] to [3].

[0051] Method [1]: A method for manufacturing the sandwich structure of the present invention, including, in this order, a step of arranging a precursor of the core material (I) on at least one surface and at least one end face of the heat conductive material (III) and performing hot pressing, and a step of bonding the fiber reinforcing material (II) to both surfaces of the core material (I). A method for manufacturing a sandwich structure.

[0052] Method [2]: A method for manufacturing the sandwich structure of the present invention, including, in this order, a step of arranging a precursor of the core material (I) on at least one surface and at least one end face of the heat conductive material (III), a step of arranging precursors of the fiber reinforcing material (II) on both surfaces of the precursor of the core material (I), and a step of performing hot pressing. A method for manufacturing a sandwich structure.

[0053] Method [3]: A method for manufacturing the sandwich structure of the present invention, including, in this order, a step of arranging a precursor of the core material (I) on at least one surface and at least one end face of the heat conductive material (III) and performing hot pressing, a step of arranging precursors of the fiber reinforcing material (II) on both surfaces of the core material (I), and a step of performing hot pressing. A method for manufacturing a sandwich structure.

[0054] In Methods [1] to [3], "disposing the precursor of the core material (I) on at least one surface and at least one end face of the heat conductive material (III)" means disposing the precursor of the core material (I) so as to cover at least one surface and at least one end face of the heat conductive material (III).

[0055] In Methods [1] to [3], it is preferable that the precursors of the core material (I) are disposed on both surfaces of the heat conductive material (III). Further, in Methods [1] to [3], it is more preferable that the precursors of the core material (I) are disposed on at least two end faces of the heat conductive material (III), still more preferably disposed on both surfaces of the heat conductive material (III), and particularly preferably disposed on both surfaces and all end faces of the heat conductive material (III), that is, surrounding the heat conductive material (III).

[0056] The precursor of the core material (I) is, for example, a prepreg containing reinforcing fibers and a resin when the core material (I) is a fiber-reinforced resin. Further, when the core material (I) is a non-fiber-reinforced resin, examples include a resin sheet containing a foaming agent and a laminate of resin sheets.

[0057] When the core material (I) contains a porous body and the porous body is made of a fiber-reinforced resin, which is one of the preferred embodiments of the present invention, the precursor of the core material (I) can be produced, for example, by impregnating a discontinuous reinforced fiber mat with a thermoplastic resin film or non-woven fabric while compressing it. The discontinuous reinforced fiber mat is produced, for example, by previously dispersing discontinuous reinforcing fibers in a strand shape, preferably in a substantially single fiber shape, more preferably in a single fiber shape. More specifically, dry processes such as the airlaid method of dispersing discontinuous reinforcing fibers in an air stream to form a sheet, the carding method of mechanically carding discontinuous reinforcing fibers to form them on a sheet, and wet processes such as the wet laid method of stirring discontinuous reinforcing fibers in water and papermaking can be mentioned.

[0058] As a means of bringing discontinuous reinforcing fibers closer to a single-fiber state, in a dry process, means such as providing a fiber-opening bar, vibrating the fiber-opening bar, making the carding teeth finer, and adjusting the rotational speed of the card can be exemplified. In a wet process, means such as adjusting the stirring conditions of discontinuous reinforcing fibers, diluting the reinforcing fiber concentration of the dispersion, adjusting the viscosity of the dispersion, and suppressing vortex when transferring the dispersion can be exemplified. In particular, the discontinuous reinforced fiber mat is preferably manufactured by a wet method, and by increasing the concentration of the input fibers, adjusting the flow rate (flow volume) of the dispersion and the speed of the mesh conveyor, the ratio of the reinforcing fibers in the discontinuous reinforced fiber mat can be easily adjusted. For example, by reducing the speed of the mesh conveyor relative to the flow rate of the dispersion, the orientation of the fibers in the obtained discontinuous reinforced fiber mat becomes less likely to be in the take-up direction, and a bulky discontinuous reinforced fiber mat can be manufactured. The discontinuous reinforced fiber mat may be composed of discontinuous reinforcing fibers alone, or the discontinuous reinforcing fibers may be mixed with a matrix resin component in powder or fiber form, or the discontinuous reinforcing fibers may be mixed with an organic compound or an inorganic compound, or the discontinuous reinforcing fibers may be held together with a resin component.

[0059] When impregnating a discontinuous reinforced fiber mat with a film or nonwoven fabric of a thermoplastic resin, the pressure is preferably 0.5 MPa or more and 30 MPa or less, more preferably 1 MPa or more and 5 MPa or less. If the pressure is less than 0.5 MPa, the thermoplastic resin may not impregnate the discontinuous reinforced fiber mat, and if it is more than 30 MPa, it becomes difficult to adjust the thickness of the precursor of the core material. The temperature when impregnating the film or nonwoven fabric of the thermoplastic resin is preferably a temperature equal to or higher than the melting point or glass transition point of the thermoplastic resin, more preferably a temperature equal to or higher than the melting point or glass transition point plus 10 °C, and even more preferably a temperature equal to or higher than the melting point or glass transition point plus 20 °C. Note that if the temperature when impregnating the film or nonwoven fabric of the thermoplastic resin is too high compared to the melting point or glass transition point of the thermoplastic resin, decomposition or deterioration of the thermoplastic resin may occur, so it is preferably a temperature equal to or lower than the melting point or glass transition point plus 150 °C.

[0060] As equipment for realizing a method of impregnating a discontinuous reinforced fiber mat with a film or nonwoven fabric of a thermoplastic resin, a compression molding machine or a double belt press machine can be preferably used. The compression molding machine is of a batch type, and productivity can be improved by using two or more machines for heating and cooling in parallel as an intermittent press system. The double belt press machine is of a continuous type and is excellent in continuous productivity because continuous processing can be easily performed.

[0061] The precursor of the fiber reinforcing material (II) is usually a prepreg containing reinforcing fibers and a resin. For example, a unidirectional fiber prepreg or a woven fiber prepreg reinforced with continuous fibers, or a laminate in which a reinforcing fiber sheet and a resin sheet are laminated can be mentioned.

[0062] All of the methods [1] to [3] have a hot pressing step. In this step, a precursor of the core material (I) is placed on at least one surface and at least one end face of the heat conductive material (III), and hot pressing is performed at the expansion temperature of the precursor of the core material (I) or the temperature required for bonding, whereby the heat conductive material can be incorporated into the core material. As equipment for hot pressing, a compression molding machine can be preferably used. The compression molding machine is of a batch type, and productivity can be improved by using an intermittent pressing system in which two or more machines for heating and cooling are arranged in parallel.

[0063] Method [1] is a method in which, in the process of forming the core material (I), after incorporating the heat conductive material (III) into the core material (I), a fiber reinforcing material (II) is bonded to both surfaces of the formed core material (I). The means for bonding the core material (I) and the fiber reinforcing material (II) is not particularly limited. For example, there are methods of bonding the core material (I) and the fiber reinforcing 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 reinforcing material (II) are greatly different.

[0064] Method [2] is a method of simultaneously performing the molding and bonding of the core material (I) and the fiber reinforcing 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 reinforcing material (II) are close. Since the molding and bonding of the core material (I) and the fiber reinforcing material (II) can be performed simultaneously, it is preferable from the viewpoint of productivity.

[0065] Method [3] is a method in which, in the process of forming the core material (I), after incorporating the heat conductive material (III) into the core material (I), precursors of the fiber reinforcing material (II) are placed on both surfaces of the formed core material (I) and hot pressing is performed. Since the bonding of the core material (I) and the fiber reinforcing material (II) and the molding of the fiber reinforcing material (II) can be performed simultaneously, it is preferable from the viewpoint of productivity.

[0066] <Housing> The housing of the present invention is made using the sandwich structure of the present invention. By utilizing the sandwich structure of the present invention, a housing with excellent mechanical properties and light weight can be obtained. Also, from the viewpoint of mass productivity, it is preferable because it can be formed by high-cycle forming such as press forming.

[0067] The housing of the present invention can be obtained, for example, by producing a sandwich structure having the shape of a desired housing according to the above-described method for manufacturing a sandwich structure.

Example

[0068] Hereinafter, the present invention will be described in more detail with reference to examples.

[0069] (1) Measurement of flexural strength and flexural modulus of sandwich structure The flexural test pieces of the produced sandwich structure were measured for flexural properties according to the ISO178 method (1993). With the fiber direction of the outermost surface of the flexural test piece as the flexural direction, the number of measurements n = 5, and the average value was taken as the flexural strength and flexural modulus. As the measuring device, an Instron 5565 type universal material testing machine manufactured by Instron Japan Co., Ltd. was used.

[0070] (2) Evaluation of heat dissipation of sandwich structure As shown in FIG. 3, rubber spacers 6 with a thickness of 3 mm and a size of 10 mm × 10 mm were attached to the four corners of the back surface of the produced sandwich structure 1 and installed on the experimental table. A micro ceramic heater 5 (manufactured by Sakaguchi Denki Co., Ltd., micro ceramic heater MS-2 (product name)) with a size of 50 mm × 25 mm was installed at one corner of the surface of the installed sandwich structure, and the heater was heated at 10 W under a constant current and constant voltage. The heat dissipation was evaluated according to the following criteria based on the heater temperature when the heater temperature became constant 15 minutes after the start of heater heating. A: Heater temperature less than 100°C (very high heat dissipation) B: Heater temperature 100°C or more and less than 120°C (high heat dissipation) C: Heater temperature 120°C or more (low heat dissipation) (Reference Example 1) Production of carbon fiber bundle A polymer mainly composed of polyacrylonitrile was spun and subjected to a baking treatment to obtain a continuous carbon fiber bundle with a total of 12,000 filaments. A sizing agent was applied to the continuous carbon fiber bundle by an immersion method and dried in hot air at a temperature of 120°C to obtain a carbon fiber bundle. The properties of this carbon fiber bundle were as follows.

[0071] Single fiber diameter: 7 μm Mass per unit length: 0.8 g / m Density: 1.8 g / cm 3 Tensile strength: 4.2 GPa Tensile modulus: 230 GPa Sizing type: Polyoxyethylene oleyl ether Sizing adhesion amount: 1.5 mass% (Reference Example 2) Preparation of carbon fiber mat The carbon fiber bundle of Reference Example 1 was cut into 6 mm fiber lengths using a cartridge cutter to obtain a chopped carbon fiber bundle. An aqueous dispersion of 0.1 mass% of a surfactant (manufactured by Nacalai Tesque, Inc., polyoxyethylene lauryl ether (trade name)) was prepared, and this dispersion and the chopped carbon fiber bundle were put into a papermaking machine to prepare a carbon fiber mat.

[0072] The papermaking machine is equipped with a dispersion tank, a papermaking tank, and a transport section connecting the dispersion tank and the papermaking tank. The dispersion tank is attached with a stirrer and can disperse the input dispersion and chopped carbon fiber bundle. The papermaking tank is equipped with a mesh conveyor having a papermaking surface at the bottom, and a conveyor capable of transporting the papermade carbon fiber mat is connected to the mesh conveyor. Papermaking was performed with the fiber concentration in the dispersion being 0.05 mass%. The papermade carbon fiber mat was dried in a drying furnace at 200°C. Subsequently, a 3 mass% aqueous dispersion of a binder (manufactured by Nippon Shokubai Co., Ltd., "Poliment" (registered trademark) SK-1000) was sprayed as a binder on the upper surface of the carbon mat transported by the conveyor. The excess binder was sucked off and dried in a drying furnace at 200°C to obtain a carbon fiber mat. The basis weight of the obtained carbon fiber mat was 50 g / m 2 It was.

[0073] (Reference Example 3) Preparation of Polypropylene Resin Film 90% by mass of non-modified polypropylene resin (manufactured by Prime Polymer Co., Ltd., "Prime Polypro" (registered trademark) J105G) and 10% by mass of acid-modified polypropylene resin (manufactured by Mitsui Chemicals, Inc., "Admer" (registered trademark) QE510) were blended. After melting and kneading this blend in an extruder, it was extruded from a T-die. Then, it was taken up by a chill roll at 60°C and the resin was cooled and solidified to obtain a polypropylene resin film.

[0074] (Reference Example 4) Preparation of Epoxy Resin Film An epoxy resin (base resin: dicyandiamide / dichlorophenylmethylurea-cured epoxy resin) was applied onto release paper using a coater to obtain an epoxy resin film.

[0075] (Reference Example 5) Preparation of Unidirectional Prepreg The carbon fiber bundles of Reference Example 1 were arranged in a sheet shape in one direction, and two sheets of the epoxy resin film of Reference Example 4 were overlaid from both sides of the carbon fiber bundles, and the resin was impregnated by heating and pressurization, and a unidirectional prepreg having a carbon fiber areal density of 110 g / m 2 , a thickness of 0.1 mm, and a mass fraction of the matrix resin of 30% by mass was obtained.

[0076] (Example 1) Using the carbon fiber mat 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 Corporation, "PGS" (registered trademark) EYGS182307, in-plane thermal conductivity 1000 W / m·K), a sandwich structure was fabricated. The carbon fiber mat, the polypropylene resin film, and the 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, [unidirectional prepreg 0° / unidirectional prepreg 90° / polypropylene resin film / carbon fiber mat / graphite sheet / carbon fiber mat / polypropylene resin film / unidirectional prepreg 90° / unidirectional prepreg 0°] were laminated in this order 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. This laminate was sandwiched between a release film and further sandwiched between tool plates. They were put into a press molding machine with a platen temperature of 180°C and heated and pressed at 3 MPa for 10 minutes to cure the prepreg and impregnate the carbon fiber mat with the polypropylene resin. Next, a spacer with a thickness of 1 mm was inserted between the tool plates, and it was put into a press molding machine with a platen temperature of 40°C and cooled and pressed at a surface pressure of 3 MPa until the laminate cooled down to obtain a sandwich structure in which a core material was arranged around the heat conductive material. When the thickness of the sample was measured with a micrometer, the thickness was 1.0 mm. By inserting a spacer with a thickness of 1.0 mm between the tool plates, the carbon fiber mat impregnated with the polypropylene resin spring back, and the core material became a porous body. Since the sample in this example is a flat plate, the thickness is constant. Therefore, the thickness measured at any point of the sample is the maximum thickness. The same applies to other examples and comparative examples.

[0077] In addition, the bending test piece was prepared in the same manner except that the carbon fiber mat, the polypropylene resin film, and the unidirectional prepreg were adjusted to a size of 50 mm × 40 mm, and the graphite sheet was adjusted to a size of 40 mm × 30 mm. Then, a preform was made, press molding was performed, and a bending test piece of a sandwich structure in which a core material was arranged around a heat conductive material was obtained. A cross-sectional view of the obtained sandwich structure is shown in FIG. 4. In the obtained sandwich structure, as shown in FIG. 4, fiber reinforced material layers composed of a unidirectional fiber reinforced material 0° 7 and a unidirectional fiber reinforced material 90° 8 are provided on both sides of the core material 2. Further, the graphite sheet 9 has a structure in which both sides and all end faces are covered by the core material, and is protected by the core material. Therefore, the mechanical properties of the obtained sandwich structure are excellent, and there is no peeling of the graphite sheet or scattering of graphite sheet fragments. Also, since it contains a graphite sheet, the heat dissipation property was excellent.

[0078] (Example 2) The number of laminated graphite sheets was changed to 4, and preforming and press molding were performed in the same manner as in Example 1 except that [unidirectional prepreg 0° / unidirectional prepreg 90° / polypropylene resin film / carbon fiber mat / graphite sheet / graphite sheet / graphite sheet / graphite sheet / carbon fiber mat / polypropylene resin film / unidirectional prepreg 90° / unidirectional prepreg 0°] were laminated in this order. A sandwich structure and a bending test piece of the sandwich structure in which a core material was arranged around a heat conductive material were obtained. A cross-sectional view of the obtained sandwich structure is shown in FIG. 5. Since the graphite sheet was protected by the core material, the mechanical properties of the obtained sandwich structure were excellent. Also, since it contains a plurality of graphite sheets, the heat dissipation property was very excellent.

[0079] (Comparative Example 1) The preform and press forming were carried out in the same manner as in Example 1, except that the size of the graphite sheet was adjusted to 50×150 mm, and a sandwich structure in which all ends of the heat conductive material were exposed was obtained. Also, when preparing the bending test piece, the preform and press forming were carried out in the same manner as in Example 1, except that the size of the graphite sheet was adjusted to 50 mm×40 mm, and a bending test piece of the sandwich structure in which all ends of the heat conductive material were exposed was obtained. The cross-sectional view of the obtained sandwich structure is shown in FIG. 6. Since all ends of the graphite sheet were exposed in the obtained sandwich structure, delamination occurred between the layers of the graphite sheet.

[0080] (Comparative Example 2) The preform and press forming were carried out in the same manner as in Example 2, except that the size of the graphite sheet was adjusted to 50×150 mm, and a sandwich structure in which all ends of the heat conductive material were exposed was obtained. Also, when preparing the bending test piece, the preform and press forming were carried out in the same manner as in Example 2, except that the size of the graphite sheet was adjusted to 50 mm×40 mm, and a bending test piece of the sandwich structure in which all ends of the heat conductive material were exposed was obtained. The cross-sectional view of the obtained sandwich structure is shown in FIG. 7. The strength of the obtained sandwich structure was very low, and delamination occurred between the graphite sheets after press forming, so the bending test and heat dissipation evaluation could not be carried out.

[0081] (Comparative Example 3) The preform and press forming were carried out in the same manner as in Example 1, except that the graphite sheets were not laminated, and a sandwich structure without a heat conductive material was obtained. Also, when preparing the bending test piece, the preform and press forming were carried out in the same manner as in Example 1, except that the graphite sheets were not laminated, and a bending test piece of the sandwich structure without a heat conductive material was obtained. The cross-sectional view of the obtained sandwich structure is shown in FIG. 8. Since the obtained sandwich structure did not contain a heat conductive material, its heat dissipation performance was low.

[0082]

Table 1

Industrial Applicability

[0083] The sandwich structure of the present invention can achieve both excellent heat dissipation and excellent mechanical properties. Therefore, it can be applied to a wide range of industrial fields such as structural members of electric and electronic devices, robots, motorcycles, automobiles, and aircraft. In particular, it can be preferably applied to the casings of electronic devices and the like that require high heat dissipation.

Explanation of Reference Numerals

[0084] 1. Sandwich structure 2. Core material (I) 3. Fiber reinforcement (II) 4. Heat conductive material (III) 5. Heater 6. Rubber spacer 7. Unidirectional fiber reinforcement 0° 8. Unidirectional fiber reinforcement 90° 9. Graphite sheet

Claims

1. A sandwich structure having a core material (I) and fiber reinforcement materials (II) disposed on both sides of the core material (I), wherein the core material (I) includes a porous body and a sheet-like heat conductive material (III) having an in-plane thermal conductivity of 300 W / m·K or more.

2. The sandwich structure according to claim 1, wherein the core material (I) covers at least one surface and at least one end surface of the heat conductive material (III).

3. The sandwich structure according to claim 2, wherein the core material (I) covers both surfaces and all end surfaces of the heat conductive material (III).

4. The sandwich structure according to any one of claims 1 to 3, wherein the heat conductive material (III) includes a heat conductive sheet selected from the group consisting of a graphite sheet, a metal sheet, and a ceramic sheet.

5. The sandwich structure according to claim 4, wherein the heat conductive material (III) includes a laminated structure of a plurality of the heat conductive sheets.

6. The sandwich structure according to any one of claims 1 to 5, wherein the heat conductive material (III) is not adhered to the core material (I).

7. The sandwich structure according to any one of claims 1 to 6, wherein the porous body is made of a fiber-reinforced resin.

8. The sandwich structure according to any one of claims 1 to 7, wherein the fiber reinforcement material (II) includes a carbon fiber-reinforced resin.

9. The sandwich structure according to any one of claims 1 to 8, having a bending rigidity per unit width of 0.5 N·m or more.

10. The sandwich structure according to any one of claims 1 to 9, having a maximum thickness of 0.3 mm or more and 3.0 mm or less.

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

12. A method for manufacturing the sandwich structure according to any one of claims 1 to 10, including, in this order, a step of disposing a precursor of the core material (I) on at least one surface and at least one end surface of the heat conductive material (III) and performing hot pressing, and a step of joining the fiber reinforcement materials (II) to both surfaces of the core material (I).

13. A method for manufacturing a sandwich structure according to any one of claims 1 to 10, comprising the steps of arranging a precursor of the core material (I) on at least one surface and at least one end face of the heat conductive material (III), arranging precursors of the fiber reinforcement material (II) on both surfaces of the precursor of the core material (I), and hot pressing in this order. A method for manufacturing a sandwich structure.

14. A method for manufacturing a sandwich structure according to any one of claims 1 to 10, comprising the steps of arranging a precursor of the core material (I) on at least one surface and at least one end face of the heat conductive material (III) and hot pressing, arranging precursors of the fiber reinforcement material (II) on both surfaces of the core material (I), and hot pressing in this order. A method for manufacturing a sandwich structure.

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