Heat conductor and method for manufacturing the same

Abstract

An object of the present invention is to provide a thermal conductor that combines excellent lightness with excellent rigidity and excellent heat dissipation. To achieve this object, the thermal conductor of the present invention has the following configuration: a thermal conductor comprising a sheet-like thermally conductive material (II) having an in-plane thermal conductivity of 300 W / m·K or greater, contained within a porous structure (I) composed of reinforcing fibers and a resin.

Description

Technical Field

[0001] The present invention relates to a heat conductor, a housing formed using the heat conductor, and a method for manufacturing the heat conductor. Background Art

[0002] In recent years, the market demand for lightweight properties in industrial products such as automobiles, aircraft, and electronic equipment has been increasing year by year. In addition, with the increasing performance of heat-generating modules such as engines, electric motors, and processors, the market demand for heat dissipation is also increasing year by year. In order to meet such requirements, molded products with excellent lightness and high thermal conductivity are widely used in various industrial applications. Among them, heat conductors that are a composite of a thermally conductive material with high thermal conductivity and a lightweight material with excellent lightness have excellent heat dissipation in addition to excellent lightness. Therefore, they are expected to be effectively used in various products and have been widely studied.

[0003] Patent Document 1 describes an invention of a thermal conductor comprising a laminate of a thermally conductive material and a rigidity-maintaining material formed of fiber-reinforced plastic. It is believed that by laminating the thermally conductive material and the rigidity-maintaining material formed of fiber-reinforced plastic, a thermal conductor having both excellent thermal conductivity and excellent lightness can be obtained.

[0004] Patent Document 2 describes an invention of a thermal conductor in which a stack of graphite sheets is coated with a resin layer. It is believed that forming a housing from graphite sheets and resin can achieve both excellent thermal conductivity and excellent lightness.

[0005] Patent Document 3 describes an invention of a thermal conductor in which a graphite sheet is sandwiched between two sponge layers. It is believed that excellent thermal conductivity can be obtained by sandwiching the graphite sheet between the two sponge layers.

[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. 2006-95935

[0010] Patent Document 3: International Publication No. 2018 / 198293 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] The heat conductor in Patent Document 1 is believed to have both excellent thermal conductivity and excellent lightness by laminating a heat conducting material and a rigidity retaining material. However, the rigidity retaining material is a dense fiber reinforced plastic, leaving room for improvement in lightness.

[0013] The thermal conductor disclosed in Patent Document 2 is believed to combine excellent thermal conductivity with excellent lightness by coating the surface and ends of a graphite sheet with resin. However, the resin coating the graphite sheet is dense, leaving room for improvement in lightness. Furthermore, the coating is made of a non-reinforced resin, which is believed to result in low rigidity of the thermal conductor.

[0014] The heat conductor in Patent Document 3 is believed to have excellent thermal conductivity by sandwiching a graphite sheet between two sponge layers. The sponge layer is a foamed resin and is excellent in lightness, but is believed to have very low rigidity.

[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 heat conductor having both excellent lightness and excellent rigidity and excellent heat dissipation properties.

[0016] Means for solving problems

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

[0018] A thermal conductor comprising a sheet-shaped thermally conductive material (II) having an in-plane thermal conductivity of 300 W / m·K or higher contained in a porous structure (I) composed of reinforcing fibers and a resin.

[0019] Effects of the Invention

[0020] According to the present invention, a heat conductor having both excellent lightness and excellent rigidity and excellent heat dissipation properties can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram showing one embodiment of the heat conductor of the present invention

[0022] Figure 2 Schematic diagram showing another embodiment of the heat conductor of the present invention

[0023] Figure 3 A schematic diagram showing an embodiment excluded from the embodiment of the heat conductor of the present invention

[0024] Figure 4 Schematic diagram showing the heat dissipation evaluation status DETAILED DESCRIPTION

[0025] The present invention will be described in detail below.

[0026] Thermal Conductor

[0027] The porous structure (I) constituting the thermal conductor of the present invention contains a sheet-like thermal conductive material (II) (hereinafter sometimes referred to simply as thermal conductive material (II)). The term "containing" here means that the thermal conductive material (II) is present as part of a layer of the porous structure (I).

[0028] For example, Figure 1 The porous structure (I) 2 covers one end surface of the thermal conductive material (II) 3 ( Figure 1 The right end face in the figure) and a surface ( Figure 1 the upper surface of the Figure 2 In such a scheme, the porous structure (I) 2 covers both sides (two surfaces) and all end faces of the thermal conductive material (II) 3, that is, the porous structure (I) contains the thermal conductive material (II). On the other hand, Figure 3 The concept of "containing" is excluded if the entire end surface of the thermal conductive material (II) 3 is exposed, i.e., the thermal conductive material (II) is considered to be a separate layer. In this way, by containing the thermal conductive material (II) within the porous structure (I), the porous structure (I) bears the stress applied to the thermal conductive material, thereby suppressing the transmission of stress to the thermal conductive material (II) and preventing damage to the thermal conductive material (II).

[0029] The porous structure (I) preferably covers at least two end surfaces of the thermal conductive material (II), preferably further covers both surfaces of the thermal conductive material (II), and further preferably covers both surfaces and all end surfaces of the thermal conductive material (II), i.e., encloses the thermal conductive material (II).

[0030] It should be noted that in the present invention, the porous structure (I) may cover the thermal conductive material (II) via other components such as an adhesive, a buffer material, etc. In addition, a gap may exist between the porous structure (I) and the thermal conductive material (II).

[0031] However, in the present invention, it is preferred that at least one end surface of the thermally conductive material (II) is in direct contact with the porous structure (I) without intervening any other member. Furthermore, it is preferred that at least one surface of the thermally conductive material (II) is in contact with the porous structure (I). By directly contacting the thermally conductive material (II) with the porous structure (I), heat transferred from the surface of the thermally conductive material can be rapidly transferred from the porous structure (I) to the thermally conductive material (II).

[0032] Furthermore, in the present invention, the thermally conductive material (II) is preferably not bonded to the porous structure (I). In order to bond the thermally conductive material (II) to the porous structure (I), generally, an adhesive needs to be interposed between them. However, the proportion of the thermally conductive material (II) in the thermal conductor decreases correspondingly with the adhesive, and the heat dissipation of the thermal conductor decreases. In addition, by not bonding the thermally conductive material (II) to the porous structure (I), the proportion of the stress applied to the thermal conductor borne by the porous structure (I) increases, thereby suppressing the transmission of stress to the thermally conductive material (II) and suppressing the destruction of the thermally conductive material (II).

[0033] The bending modulus of the heat conductor of the present invention is preferably 3 GPa or more, more preferably 5 GPa or more. There is no particular limit to the upper limit of the bending modulus of the heat conductor, but it is generally around 20 GPa. By having a bending modulus of 3 GPa or more, the heat conductor becomes a rigid structure, which can be suitable for use in housings, etc. As a means for making the bending modulus be within such a range, for example, a method of using a porous structure made of a fiber-reinforced resin as the porous structure (I) can be cited.

[0034] The bending stiffness per unit width of the heat conductor of the present invention is preferably 0.3 N·m or more, more preferably 0.5 N·m or more, and even more preferably 1.5 N·m or more. The higher the bending stiffness per unit width of the heat conductor, the more preferred. Therefore, there is no particular upper limit on the bending stiffness per unit width, but it is generally around 45 N·m. The bending stiffness per unit width is determined by the elastic modulus E (Pa) and the moment of inertia I (m 4 ), the width b (m) of the heat conductor is calculated by the following formula.

[0035] · Bending stiffness per unit width (N·m) = E (Pa) × I (m 4 ) / b(m)

[0036] In addition, when the cross section of the heat conductor 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.

[0037] Bending stiffness per unit width (N·m) = E (Pa) × h 3 (m 3 ) / 12

[0038] As a means for achieving the bending rigidity per unit width within the above range, for example, a method of using a porous structure made of a fiber-reinforced resin as the porous structure (I) is mentioned. In addition, for example, a method of increasing the thickness of the thermal conductor is mentioned.

[0039] The maximum thickness of the heat conductor of the present invention is preferably 0.3 mm to 3.0 mm, more preferably 0.5 mm to 1.5 mm. While thinning the heat conductor can reduce weight, heat conductors thinner than 0.3 mm may lack rigidity.

[0040] The specific gravity of the heat conductor of the present invention is preferably 1.00 or less, more preferably 0.80 or less, and even more preferably 0.50 or less. A lower specific gravity of the heat conductor improves lightness, but a specific gravity of 0.10 or less may result in insufficient rigidity.

[0041] Part or all of the surface of the heat conductor may be coated with resin. Coating the heat conductor with resin can prevent short circuits caused by exposure of the reinforcing fibers. This is also preferred from the perspectives of design and mechanical properties.

[0042] [Thermal Conductive Materials (II)]

[0043] In the present invention, the thermal conductive material (II) is in the form of a sheet, and its in-plane thermal conductivity is 300W / m·K or more. The in-plane thermal conductivity of the thermal conductive material (II) 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 thermal conductive materials with an in-plane thermal conductivity of about 2000W / m·K are known. If the in-plane thermal conductivity of the thermal conductive material (II) is 300W / m·K or more, the thermal diffusion of heat in the in-plane direction of the thermal conductor is excellent, and the heat dissipation of the thermal conductor is excellent. The thermal conductivity of the thermal conductive material (II) 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 evenly on the surface of the sample. For materials with low emissivity at the temperature measurement wavelength of the infrared detection element, the back of the sample is treated in the same way. In the present invention, the sheet-like shape refers to a thin and wide shape, and refers to a shape 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.

[0044] The material of the thermally conductive material (II) 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.

[0045] Furthermore, the thermally conductive material (II) 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 composed of titanium, aluminum, magnesium, iron, silver, gold, platinum, copper, nickel, or alloys containing these elements as main components.

[0046] 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 for improving the lightness and heat dissipation of the heat conductor.

[0047] 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.

[0048] In the present invention, the thermally conductive material (II) 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 (II), the heat dissipation of the thermal conductor can be improved. In this case, it is preferred that the multiple thermally conductive sheets constituting the thermally conductive material (II) are in direct contact with each other without an adhesive or the like. By directly contacting each other through the thermally conductive sheets, the proportion of the thermally conductive material (II) in the thermal conductor can be increased, and the heat dissipation of the thermal conductor can be improved. In addition, by directly contacting each other through the thermally conductive sheets, the diffusion of heat in the outward 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 thermal conductor is improved. On the other hand, if the number of laminated sheets is increased excessively, the processability will be reduced.

[0049] The average thickness of thermally conductive material (II) is preferably more than 0.01 μm and less than 2.0 mm, more preferably more than 5 μm and less than 1.0 mm, further preferably more than 15 μm and less than 0.5 mm. If the average thickness of thermally conductive material (II) is too small, the heat dissipation of the thermal conductor is reduced, and if the average thickness of thermally conductive material (II) is too large, the weight of the thermal conductor becomes heavy. The average thickness of thermally conductive material (II) is determined by measuring the thickness of 9 points of thermally conductive material (II) using a micrometer until 1 decimal place, and setting its average value as the average thickness. About the points measured, each measuring point is measured in a manner that the interval between the adjacent points or the sample end is evenly spaced in the longitudinal and transverse directions, and 9 points in total are measured for each of 3 points in the longitudinal and transverse directions.

[0050] [Porous structure (I)]

[0051] As long as the material of the porous structure (I) is a fiber reinforced resin made of reinforcing fibers and resin, there is no particular limitation. For example, a material obtained by impregnating a resin containing a foaming agent in continuous fibers and foaming them, a material obtained by impregnating a resin containing a foaming agent in discontinuous fibers and foaming them, or a material obtained by impregnating a resin in discontinuous fibers and expanding them by the rebound of the discontinuous fibers, etc. It should be noted that the so-called continuous reinforcing fibers refer to reinforcing fibers that are continuous with a length of more than 15 mm, preferably more than 100 mm, in at least one direction. By being a fiber reinforced resin, it is advantageous from the perspective of the lightness and rigidity of the heat conductor. In addition, when the porous structure (I) is made to include a thermal conductive material (II), the porous structure (I) is collapsed or expanded in an out-of-plane direction, so that the porous structure (I) can include a thermal conductive material (II) without the positional offset of the thermal conductive material (II) occurring.

[0052] The volume content of voids in the porous structure (I) is preferably 10% or more and 85% or less relative to the apparent volume of the porous structure (I), more preferably 20% or more and 85% or less, and further preferably 50% or more and 80% or less from the viewpoint of combining lightness and mechanical properties.

[0053] From the perspective of lightweight thermal conductors, the specific gravity of the porous structure (I) is preferably 0.01 to 1.5. More preferably, it is 0.1 to 1.3, and even more preferably, it is 0.3 to 1.1. The specific gravity is measured by cutting out the porous structure (I) and measuring it in accordance with ISO 0845 (1988).

[0054] There is no particular restriction on the type of reinforcing fiber contained in the porous structure (I), and 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 they can be used alone 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 resulting heat conductor, it is preferred to use glass fiber, and in particular, it is preferred to use carbon fiber and glass fiber in combination from the perspective of balancing mechanical properties and economy. Further, from the perspective of improving the impact absorbability and shapeability of the resulting heat conductor, it is preferred to use aramid fiber, and in particular, it is preferred to use carbon fiber and aramid fiber in combination from the perspective of balancing mechanical properties and impact absorbency. In addition, from the perspective of improving the electrical conductivity of the resulting heat conductor, it is also possible to use reinforcing fibers coated with metals such as nickel, copper, and ytterbium, and carbon fibers of asphalt systems.

[0055] It is preferable to surface-treat the reinforcing fibers 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.

[0056] The resin contained in the porous structure (I) is not particularly limited and can be a thermosetting resin or a thermoplastic resin. The thermoplastic resin can be, for example, selected from "polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), liquid crystal polyester and other polyesters, polyethylene (PE), polypropylene (PP), polybutylene and other polyolefins, polyoxymethylene (POM), polyamide (PA), polyphenylene sulfide (PPS) and other polyarylene sulfides, polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyethernitrile (PEN), polytetrafluoroethylene and other fluorine-based resins" and other crystalline resins. Thermoplastic resins such as esters, "styrene resins, and polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyimide (PI), polyamide-imide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone, polyarylate (PAR)" and phenolic resins, phenoxy resins, and further thermoplastic elastomers such as polystyrene, polyolefin, polyurethane, polyester, polyamide, polybutadiene, polyisoprene, fluorine resins, and acrylonitrile, their copolymers and modified bodies. Among them, polyolefins are preferred from the viewpoint of the lightness of the obtained thermal conductor. In addition, polyamides are preferred from the viewpoint of strength. In particular, when the porous structure (I) is made of fiber-reinforced resin, polyamides are preferred from the viewpoint of reinforcing the interface bonding strength between the 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, Among them, in particular, when the porous structure (I) 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] In the thermal conductor of the present invention, the porous structure (I) is particularly preferably made of a discontinuous fiber-reinforced resin. Discontinuous fiber-reinforced resin has a structure in which discontinuous 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 porous structure (I), thereby increasing the rigidity of the thermal conductor. This aspect is described below.

[0060] In discontinuous fiber-reinforced resins, the discontinuous fibers are preferably present in the form of fine 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.

[0061] 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.

[0062] From the viewpoint of achieving both mechanical properties and moldability, the mass proportion of the discontinuous fibers in the porous structure (I) is preferably 5 to 60 mass%, more preferably 10 to 50 mass%, and even more preferably 15 to 40 mass%.

[0063] In the porous discontinuous 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 coverage ratio can enhance the rigidity of the porous structure (I). The coverage ratio is measured by observing a cross-section of the porous structure (I) using a scanning electron microscope (SEM) to distinguish between the reinforcing fibers and the resin.

[0064] The voids of the porous discontinuous fiber reinforced resin are preferably measured by mercury intrusion method and have an average pore diameter of 200 μm or less. Such an average pore diameter is preferably 10 μm or more and 150 μm or less, more preferably 30 μm or more and 100 μm or less. If it is less than such a range, the lightweight curing is sometimes insufficient, and if it is greater than such a range, the mechanical properties are sometimes reduced. The so-called mercury intrusion method is a method for measuring the pore diameter using a mercury intrusion porosimeter, in which mercury is injected into the sample at high pressure, and the pore diameter can be obtained from the applied pressure and the amount of injected mercury. The average pore diameter can be calculated by the following formula.

[0065] Average pore diameter (m) = 4 × pore volume (m 3 / g) / specific surface area (m 2 / g)

[0066] <Method for manufacturing thermal conductor>

[0067] The method for manufacturing a thermal conductor of the present invention is a method for manufacturing the thermal conductor of the present invention, comprising the following steps in sequence: a step of disposing a precursor of a porous structure (I) on at least one surface and at least one end face of the thermal conductive material (II); and a step of performing hot pressing. By using this method, the molding and bonding of the porous structure (I) can be performed simultaneously, thereby achieving excellent productivity. In the method for manufacturing a thermal conductor of the present invention, the phrase "disposing a precursor of the porous structure (I) on at least one surface and at least one end face of the thermal conductive material (II)" means that the precursor of the porous structure (I) is disposed so as to cover at least one surface and at least one end face of the thermal conductive material (II).

[0068] In the method for producing a thermal conductor of the present invention, the precursor of the porous structure (I) is preferably disposed on both surfaces of the thermal conductive material (II). Furthermore, in the method for producing a thermal conductor of the present invention, the precursor of the porous structure (I) is more preferably disposed on at least both end surfaces of the thermal conductive material (II), further preferably disposed on both surfaces of the thermal conductive material (II), and particularly preferably disposed on both surfaces and all end surfaces of the thermal conductive material (II), i.e., enclosing the thermal conductive material (II).

[0069] When the porous structure (I) is made of a discontinuous fiber-reinforced resin, the precursor of the porous structure (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 substantially monofilament shape, more preferably a monofilament shape. More specifically, dry processes such as the air-laid method in which discontinuous reinforcing fibers are dispersed by air flow to form sheets, the carding method in which discontinuous reinforcing fibers are mechanically combed and formed into sheets, and wet processes based on the Radright method in which discontinuous reinforcing fibers are stirred in water and made into paper are exemplified as known techniques.

[0070] 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.

[0071] The pressure applied when impregnating the discontinuous reinforcing fiber mat 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 porous structure 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.

[0072] Compression molding machines and double-belt presses are suitable equipment for impregnating discontinuous reinforcing fiber mats with thermoplastic resin films and nonwoven fabrics. 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 offering excellent continuous productivity.

[0073] The manufacturing method of the heat conductor of the present invention has a process of hot pressing. In this process, the precursor of the porous structure (I) is arranged on at least one surface and at least one end face of the heat conductive material (II), and hot pressing is performed at the expansion temperature of the precursor of the porous structure (I) or the temperature required for bonding, so that the heat conductive material can be contained in the core material. At this time, when a discontinuous reinforced fiber mat is used, the resin impregnated in the discontinuous reinforced fiber mat melts or softens to release the compressed state, thereby causing rebound. Through this rebound, fine gaps are formed to form a porous discontinuous fiber reinforced resin. As a hot pressing device, a compression molding machine can be used appropriately. The compression molding machine is intermittent, and productivity can be improved by using an intermittent pressing system with two or more machines for heating and cooling in parallel.

[0074] <Housing>

[0075] The housing of the present invention utilizes the heat conductor of the present invention. By utilizing the heat conductor 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.

[0076] The housing of the present invention can be obtained, for example, by manufacturing a heat conductor having a desired housing shape using the above-mentioned method for manufacturing a heat conductor.

[0077] Example

[0078] Hereinafter, the present invention will be described in further detail with reference to examples.

[0079] (1) Measurement of the bending elastic modulus of the thermal conductor

[0080] The bending properties of the prepared thermal conductor flexural test specimens were measured according to ISO 178 (1993). The number of measurements, n, was set to 5, and the average value was defined as the flexural modulus. The measurement apparatus used was the Instron 5565 (registered trademark) universal testing machine manufactured by Instron Japan Co., Ltd.

[0081] (2) Evaluation of heat dissipation properties of thermal conductors

[0082] like Figure 4 As shown, 10 mm x 10 mm, 3 mm thick rubber spacers 5 were attached to the four corners of the back surface of the fabricated heat conductor 1, which was then placed on a laboratory bench. A 50 mm x 25 mm micro-ceramic heater 4 (Micro-ceramic Heater MS-2 (trade name), manufactured by Sakaguchi Electric Heater Co., Ltd.) was placed at one corner of the surface of the heat conductor. 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.

[0083] A: Heater temperature is less than 130°C (high heat dissipation)

[0084] B: Heater temperature 130°C or above (low heat dissipation)

[0085] (Reference Example 1) Preparation of Carbon Fiber Bundles

[0086] 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 impregnation and then dried in air at 120°C. The properties of this carbon fiber bundle are described below.

[0087] Single fiber diameter: 7μm

[0088] Mass per unit length: 0.8g / m

[0089] Density: 1.8g / cm 3

[0090] Tensile strength: 4.2GPa

[0091] Tensile elastic modulus: 230GPa

[0092] Sizing type: polyoxyethylene oleyl ether

[0093] Sizing adhesion: 1.5% by mass

[0094] (Reference Example 2) Preparation of carbon fiber felt

[0095] 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.

[0096] 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 / m2 .

[0097] (Reference Example 3) Preparation of polypropylene resin film

[0098] 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.

[0099] (Example 1)

[0100] A thermal conductor was produced using the carbon fiber felt of Reference Example 2, the polypropylene resin film of Reference Example 3, and a graphite sheet (manufactured by Panasonic Co., Ltd., "PGS" (registered trademark) EYGS182307, in-plane thermal conductivity 1000 W / m·K). After adjusting the carbon fiber felt and the polypropylene resin film to a size of 50 mm × 150 mm and the graphite sheet to a size of 40 mm × 140 mm, the layers were stacked in the order of [polypropylene resin film / carbon fiber felt / polypropylene resin film / carbon fiber felt / graphite sheet / carbon fiber felt / polypropylene resin film / carbon fiber felt / polypropylene resin film]. At this time, the graphite sheet was arranged in the center of the laminate. The laminate was sandwiched between a release film and further between a tool plate. They were placed in a press molding machine with a plate surface temperature of 180°C and hot-pressed at 3 MPa for 10 minutes to impregnate the carbon fiber felt with polypropylene resin. Next, a spacer with a thickness of 1 mm was inserted between the tool plates, and the laminate was placed in a press molding machine with a plate surface temperature of 40°C and cold pressed at a surface pressure of 3 MPa until the laminate was cooled, thereby obtaining a thermal conductor with a porous structure arranged around the thermal conductive material. The thickness of the sample was measured with a micrometer, and the result was a thickness of 1.0 mm. By inserting a spacer with a thickness of 1 mm between the tool plates, the carbon fiber felt impregnated with polypropylene resin rebounded and became a porous structure. 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. In addition, with respect to the bending test piece, the carbon fiber felt and the polypropylene resin film were adjusted to a size of 50 mm × 40 mm, and the graphite sheet was adjusted to a size of 40 mm × 30 mm. In addition, the same operation was performed, and pre-molding and press molding were performed to obtain a bending test piece of a thermal conductor with a porous structure arranged around the thermal conductive material. The obtained thermal conductor exhibits excellent rigidity, lightness, and heat dissipation properties because the graphite sheet is protected by the porous structure containing reinforcing fibers.

[0101] (Example 2)

[0102] Preforming and press molding were performed in the same manner as in Example 1, except that the number of polypropylene resin films and carbon fiber felt sheets was changed, with the sheets stacked in the order of [polypropylene resin film / carbon fiber felt / graphite sheet / carbon fiber felt / polypropylene resin film / carbon fiber felt / polypropylene resin film]. A thermal conductor having a porous structure disposed around the thermal conductive material and a bending test piece of the thermal conductor were obtained. The resulting thermal conductor exhibited superior lightweight properties due to its increased porosity while maintaining excellent rigidity and heat dissipation.

[0103] (Comparative Example 1)

[0104] Preforming and press molding were performed in the same manner as in Example 1, except that the carbon fiber mat was not laminated. The number of polypropylene resin films was adjusted to achieve a laminate thickness of 1.0 mm, and the polypropylene resin films and graphite sheets were laminated in the order of [polypropylene resin film / graphite sheet / polypropylene resin film]. A thermal conductor having polypropylene resin disposed around the thermal conductive material and a bending test piece of the thermal conductor were obtained. The resulting thermal conductor had poor lightweight properties because the graphite sheets were protected by a dense resin with no voids. Furthermore, due to the lack of reinforcing fibers, the rigidity was also low.

[0105] (Comparative Example 2)

[0106] Graphite sheets and foamed polypropylene sheets (manufactured by Furukawa Electric Industries, Ltd., "EFSEL" (registered trademark) RC2008W, density 0.46 g / cm 3 ), the foamed polypropylene sheet was adjusted to a thickness of 0.5 mm and laminated in the order of [foamed polypropylene sheet / graphite sheet / foamed polypropylene sheet]. Preforming and press molding were performed in the same manner as in Example 1 to obtain a thermal conductor having foamed polypropylene disposed around the thermal conductive material. The resulting thermal conductor exhibited excellent lightness due to protection by the foamed resin, but had significantly low rigidity.

[0107] (Comparative Example 3)

[0108] Preform and press molding were performed in the same manner as in Example 1, except that the graphite sheet was not laminated, to obtain a thermal conductor containing no thermal conductive material. Furthermore, a bending test piece was similarly prepared, except that the graphite sheet was not laminated, and preform and press molding were performed in the same manner as in Example 1, to obtain a bending test piece containing no thermal conductive material. The resulting thermal conductor had low heat dissipation properties due to the absence of a thermal conductive material.

[0109] (Comparative Example 4)

[0110] Preform and press molding were performed in the same manner as in Example 1, except that the graphite sheet was adjusted to 50 × 150 mm. This resulted in a thermal conductor with all ends of the thermal conductive material exposed. Furthermore, for the preparation of the bending test piece, preform and press molding were performed in the same manner as in Example 1, except that the graphite sheet was adjusted to 50 mm × 40 mm. This resulted in a thermal conductor with all ends of the thermal conductive material exposed. The resulting thermal conductor, with all ends of the graphite sheet exposed, exhibited delamination between the graphite sheets, resulting in reduced rigidity.

[0111] [Table 1]

[0112]

[0113] Industrial availability

[0114] The thermal conductor of the present invention combines excellent lightness with excellent rigidity. Therefore, it can be used in a wide range of industrial fields, such as as a structural member for electrical / electronic equipment, remote-controlled devices (robots), two-wheeled vehicles, automobiles, and aircraft. In particular, it is preferably used in the housings of portable electronic devices, which require high lightness.

[0115] Explanation of symbols

[0116] 1. Thermal conductor

[0117] 2. Porous structure (I)

[0118] 3. Thermally conductive materials (II)

[0119] 4. Heater

[0120] 5. Rubber spacer.

Claims

1. A thermal conductor comprising a sheet-shaped thermally conductive material (II) having an in-plane thermal conductivity of 300 W / m·K or greater, contained in a porous structure (I) made of reinforcing fibers and a resin, wherein the porous structure (I) covers both surfaces and all end surfaces of the thermally conductive material (II); The porous structure (I) is made of discontinuous fiber reinforced resin; The porous structure (I) is made of a material obtained by impregnating discontinuous fibers with a resin containing a foaming agent and foaming the fibers, or a material obtained by impregnating discontinuous fibers with a resin and expanding the fibers by the rebound of the discontinuous fibers. More than 30% of the surface of the discontinuous fibers is coated with resin; The volume content of voids in the porous structure (I) is 10% or more and 85% or less relative to the apparent volume of the porous structure (I); The thermal conductor has a bending rigidity per unit width of 0.3 N·m or more. 2 . The heat conductor according to claim 1 , wherein the heat conductive material (II) comprises a heat conductive sheet selected from graphite sheets, metal sheets and ceramic sheets. The heat conductor according to claim 1 or 2, wherein the heat conductive material is not bonded to the porous structure. The heat conductor according to claim 1 or 2, wherein the heat conductive material (II) comprises a stacked structure of a plurality of heat conductive sheets. The heat conductor according to claim 1 or 2, wherein the discontinuous fiber reinforced resin has a structure in which discontinuous fibers form a three-dimensional network, and intersections of the discontinuous fibers are bonded by the resin. The heat conductor according to claim 1 or 2, which has a bending modulus of elasticity of 3 GPa or more. The heat conductor according to claim 1 or 2, wherein the maximum thickness is not less than 0.3 mm and not more than 3.0 mm. The heat conductor according to claim 1 or 2, which has a specific gravity of 1.00 or less. 9 . A housing formed by using the heat conductor according to claim 1 .

10. A method for producing a heat conductor according to any one of claims 1 to 8, comprising the following steps in sequence: a step of arranging a precursor of the porous structure (I) on both surfaces and all end faces of the heat conductive material (II); and a step of hot pressing.

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