Thermally conductive member

Abstract

Provided is a thermally conductive member that has flexibility and exhibits excellent electromagnetic wave shielding property and heat dissipation property.　A thermally conductive member 1 comprises an electrically conductive nonwoven fabric 2, a first thermally conductive resin layer 3 bonded to one surface of the electrically conductive nonwoven fabric 2, and a second thermally conductive resin layer 4 bonded to the other surface of the electrically conductive nonwoven fabric 2. The first thermally conductive resin layer 3 and the second thermally conductive resin layer 4 each include a binder resin 11, 11' and a thermally conductive filler 12, 12'. The thermally conductive filler 12 in the first thermally conductive resin layer 3 and the thermally conductive filler 12' in the second thermally conductive resin layer 4 are in contact with each other via an opening (H) in the electrically conductive nonwoven fabric 2.

Description

Thermally conductive material

[0001] This invention relates to a thermally conductive member.

[0002] As electronic devices become smaller and denser in their mounting, there is a need to use materials that provide both electromagnetic shielding to block electromagnetic waves generated by electronic components and heat dissipation to suppress failures of electronic devices due to heat generated by these components. As an example of a material that combines both electromagnetic shielding and heat dissipation, a thermal conductive material is known, as described in Patent Document 1, which comprises two thermally conductive resin layers and a conductive layer made of metal foil between them.

[0003] Japanese Patent Publication No. 2021-177561

[0004] However, the thermal conductive member described in Patent Document 1 uses metal foil to provide electromagnetic shielding, which blocks heat conduction between one thermal conductive resin layer and the other, resulting in insufficient heat dissipation. Furthermore, the metal foil lacks flexibility, making it difficult to process such as punching, and it cracks during molding, making it unsuitable for press processing.

[0005] Therefore, the object of the present invention is to provide a thermally conductive member that is excellent in electromagnetic wave shielding and heat dissipation and is flexible.

[0006] The present invention provides a thermal conductive member comprising a conductive nonwoven fabric, a first thermally conductive resin layer bonded to one side of the conductive nonwoven fabric, and a second thermally conductive resin layer bonded to the other side of the conductive nonwoven fabric, wherein the first thermally conductive resin layer and the second thermally conductive resin layer each contain a binder resin and a thermally conductive filler, and the thermally conductive filler in the first thermally conductive resin layer and the thermally conductive filler in the second thermally conductive resin layer are in contact with each other through an opening in the conductive nonwoven fabric.

[0007] The conductive nonwoven fabric preferably comprises a resin nonwoven fabric and a metal layer formed on the surface of the resin nonwoven fabric.

[0008] The above metal layer is preferably a metal plating layer.

[0009] The binder resin in the first thermally conductive resin layer and the second thermally conductive resin layer preferably contains a thermosetting resin.

[0010] Preferably, the thermal conductive filler in the first thermal conductive resin layer and the second thermal conductive resin layer contains a metal oxide and / or nitride.

[0011] The binder resin in the first thermally conductive resin layer and the second thermally conductive resin layer is preferably a silicone resin.

[0012] Preferably, the above-mentioned opening includes a hole that extends in a direction other than the thickness direction.

[0013] The thermally conductive member of the present invention has excellent electromagnetic shielding and heat dissipation properties, and is flexible. Therefore, when bonded to an object, it prevents electromagnetic waves generated within the object from being emitted to the outside or prevents electromagnetic waves from entering from the outside, and efficiently dissipates heat generated within the object. Furthermore, it is easy to punch out and is suitable for press working.

[0014] This is a cross-sectional view showing one embodiment of the thermal conductive member of the present invention. This is a partial cross-sectional view of the thermal conductive member near the conductive nonwoven fabric shown in Figure 1. This is a cross-sectional photograph of a thermal conductive member having a connecting hole in which a hole extending in the thickness direction and a hole extending in a direction other than the thickness direction are joined. This is a cross-sectional photograph of the thermal conductive member made in the example. This is a graph showing the evaluation results of the electric field wave shielding effect in the electromagnetic wave shielding properties of the thermal conductive member made in Example 1. This is a graph showing the evaluation results of the magnetic field wave shielding effect in the electromagnetic wave shielding properties of the thermal conductive member made in Example 1. This is a photograph showing any one of the plan view photographs of the conductive nonwoven fabric used in Example 1, taken from above at 200x magnification. This is a magnified photograph of the region containing the contour with the largest opening area among the images shown in Figure 7.

[0015] [Thermal Conductive Member] A thermal conductive member (heat dissipation member) according to one embodiment of the present invention comprises a conductive nonwoven fabric and thermal conductive resin layers bonded to both sides of the conductive nonwoven fabric. That is, the thermal conductive member comprises at least a conductive nonwoven fabric, a first thermal conductive resin layer bonded to one side of the conductive nonwoven fabric, and a second thermal conductive resin layer bonded to the other side of the conductive nonwoven fabric. Furthermore, the thermal conductive member may comprise other layers as long as they do not impair the objective of the present invention.

[0016] The first thermally conductive resin layer and the second thermally conductive resin layer each contain at least a binder resin and a thermally conductive filler. The first thermally conductive resin layer and the second thermally conductive resin layer may contain the same type of binder resin (e.g., silicone-based resin and silicone-based resin) or different types of binder resin. Furthermore, the first thermally conductive resin layer and the second thermally conductive resin layer may contain the same type of thermally conductive filler (e.g., alumina and alumina) or different types of thermally conductive filler. Therefore, the first thermally conductive resin layer and the second thermally conductive resin layer may have the same or different thicknesses, compositions (such as the type and proportion of binder resins and thermally conductive fillers), or physical properties.

[0017] The thermal conductive filler in the first thermal conductive resin layer and the thermal conductive filler in the second thermal conductive resin layer are in contact through the opening in the conductive nonwoven fabric. The thermal conductive fillers in the first thermal conductive resin layer and the thermal conductive filler in the second thermal conductive resin layer may both penetrate the opening and be in contact within the opening, or the thermal conductive filler in one thermal conductive resin layer may penetrate and pass through the opening and be in contact with the thermal conductive filler in the other thermal conductive resin layer outside the opening. In other words, it is sufficient that the thermal conductive resin layers are in communication within the opening to form a path for the thermal conductive filler.

[0018] The above-mentioned heat-conducting member may be provided with a release film. The release film may be provided on only one side of the heat-conducting member or on both sides. Examples of the release film include a film formed from a low-tack resin or a sheet comprising a release treatment layer provided on the surface of the film. The release film is peeled off and removed when the heat-conducting member is used.

[0019] The thermally conductive member of the present invention comprises a conductive nonwoven fabric as a base material. Because the conductive nonwoven fabric is a nonwoven fabric, it has lower hardness and flexibility than metal layers such as metal foil or metal wire. Furthermore, since the conductive nonwoven fabric has openings, thermally conductive fillers in the thermally conductive resin layer can enter these openings, and as a result the thermally conductive fillers in the thermally conductive resin layers located on both sides come into contact with each other, creating a pathway for thermally conductive fillers within the openings. Therefore, the thermal conductivity between the two thermally conductive resin layer surfaces is excellent, and the thermally conductive member of the present invention has excellent heat dissipation properties. In addition, since the openings in the conductive nonwoven fabric are smaller than those in woven fabrics such as glass cloth, electromagnetic waves can be sufficiently blocked. Therefore, using a conductive nonwoven fabric as a base material also provides excellent electromagnetic shielding properties.

[0020] Figure 1 is a schematic cross-sectional view showing one embodiment of the thermal conductive member of the present invention. As shown in Figure 1, the thermal conductive member 1 comprises a conductive nonwoven fabric 2, a first thermal conductive resin layer 3 bonded to one side of the conductive nonwoven fabric 2, and a second thermal conductive resin layer 4 bonded to the other side of the conductive nonwoven fabric 2. That is, the first thermal conductive resin layer 3 and the second thermal conductive resin layer 4 are directly laminated so as to be in contact with the conductive nonwoven fabric 2. The first thermal conductive resin layer 3 includes a binder resin 11 which is a matrix component and a thermal conductive filler 12 dispersed in the binder resin 11. The second thermal conductive resin layer 4 includes a binder resin 11' which is a matrix component and a thermal conductive filler 12' dispersed in the binder resin 11'. Release films 5 and 6 are provided on both sides of the thermal conductive member 1, and the thermal conductive member 1 is sandwiched between the two release films 5 and 6.

[0021] Figure 2 shows one embodiment of a partial cross-sectional view of the conductive nonwoven fabric 2 of the thermal conductive member 1 shown in Figure 1. Figure 2 is a cross-sectional view of the thermal conductive member 1 shown in Figure 1, obtained by cutting the conductive nonwoven fabric 2 in the thickness direction. Since the conductive nonwoven fabric 2 has a shape in which circular cross-section fibers overlap in random directions, in Figure 2, the fibers located perpendicular to the cross-section are cut in the width direction (radial direction), and openings H are formed in the parts of the cross-section where there are no fibers. The first thermal conductive resin layer 3 and the second thermal conductive resin layer 4 penetrate into the openings H of the conductive nonwoven fabric 2 and communicate with each other to form a path for the thermal conductive filler. The thermal conductive filler 12 and the thermal conductive filler 12' are in contact and electrically conductive.

[0022] The above-mentioned opening has one opening surface on one surface of the conductive nonwoven fabric and the other opening surface on the other surface of the conductive nonwoven fabric. The above-mentioned opening may include a hole extending in the thickness direction, or a hole extending in a direction other than the thickness direction. The above-mentioned opening may be a hole that penetrates in the thickness direction, or a hole that penetrates in a direction other than the thickness direction (for example, the surface direction), or it may be a connecting hole formed by the joining of a hole extending in the thickness direction and a hole extending in a direction other than the thickness direction. Figure 3 shows a cross-sectional photograph (SEM, 500x magnification) of a thermally conductive member having a connecting hole formed by the joining of a hole extending in the thickness direction and a hole extending in a direction other than the thickness direction. As shown in Figure 3, the opening H is formed by the joining of at least a hole extending in the thickness direction, a hole extending in the surface direction, and a hole extending in the thickness direction in this order. In the opening H, the fibers of the conductive nonwoven fabric 2 extend in the surface direction, and the opening H is formed along these fibers. Thus, since there are no through-holes penetrating the conductive nonwoven fabric in the thickness direction at opening H, the electromagnetic shielding performance is even better, and because opening H forms paths for the thermally conductive filler on both sides of the conductive nonwoven fabric, the thermal conductivity in the thickness direction is also excellent.

[0023] <Conductive Nonwoven Fabric> Examples of the above conductive nonwoven fabric include one in which a metal layer is formed on the surface of a resin nonwoven fabric (conductive nonwoven fabric A), and one in which the fibers constituting the nonwoven fabric include conductive threads (conductive nonwoven fabric B). Among these, conductive nonwoven fabric A is preferred because the size of the openings is appropriate, making it easy for paths of the thermal conductive filler in the thermal conductive resin layer to be formed, resulting in excellent heat dissipation, excellent electromagnetic wave shielding, and high flexibility of the thermal conductive member.

[0024] The conductive nonwoven fabric A comprises a resin nonwoven fabric and a metal layer formed on the surface of the resin nonwoven fabric. The metal layer may be formed on at least one surface of the resin nonwoven fabric, or on both surfaces. If metal layers are formed on both surfaces, the thickness, composition, and formation method of the metal layers on both surfaces may be the same or different. Furthermore, the metal layer on one surface may be a single layer or a multi-layered layer.

[0025] From the viewpoint of providing greater flexibility for the thermally conductive member, the above metal layer is preferably a metal plating layer formed by electrolysis, vapor deposition (e.g., vacuum deposition), sputtering, chemical vapor deposition (CVD), metal-organic growth (MO), plating, etc.

[0026] The metals constituting the above metal layer are not particularly limited, but examples include aluminum, copper, tungsten, iron, molybdenum, nickel, titanium, silver, gold, and alloys thereof.

[0027] The fibers that make up the above-mentioned resin nonwoven fabric include natural fibers such as cotton, hemp, natural pulp, and linter pulp; regenerated fibers such as cupro and rayon; carbon fibers such as polyacrylonitrile (PAN) carbon fibers and pitch carbon fibers; nylon; polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PET), and polytrimethylene terephthalate (PTT); and chemical fibers such as acrylic fibers, aramid fibers, and phenolic fibers.

[0028] The conductive nonwoven fabric B may contain conductive yarn as its constituent fibers, and may also contain nonconductive yarn. The conductive yarn is not particularly limited, but it is preferable to include nonconductive yarn and a metal layer covering at least a portion of the surface of the nonconductive yarn. Examples of the nonconductive yarn include those described and illustrated as the fibers constituting the resin nonwoven fabric above. Examples of the metal layer include those described and illustrated as the metal layer in the conductive nonwoven fabric A above.

[0029] The basis weight of the above conductive nonwoven fabric is 30 to 50 g / m². ２ Preferably, and more preferably, 35 to 45 g / m² ２ The above weight is 30 g / m². ２ The above specifications result in superior electromagnetic shielding properties. ２ The following conditions result in an appropriate amount of openings, facilitate the formation of paths for the thermally conductive filler, and improve thermal conductivity in the thickness direction.

[0030] The conductive nonwoven fabric described above is constructed by randomly overlapping fibers rather than weaving them regularly, resulting in varying aperture ratios depending on the location. Areas with large apertures (where thermally conductive fillers can be connected in the thickness direction) and areas with small apertures (areas with high electromagnetic shielding properties) coexist. Conventional conductive meshes and other materials with regularly woven fibers have a uniform aperture size. Large apertures reduce electromagnetic shielding, while small apertures prevent the formation of paths between thermally conductive fillers in the thickness direction, reducing thermal conductivity. Therefore, it is difficult to achieve both shielding effect and thermal conductivity simultaneously.

[0031] The aperture ratio of the conductive nonwoven fabric described above is preferably 30% or less, more preferably 25% or less, and even more preferably 15% or less, from the viewpoint of superior electromagnetic wave shielding performance. When there are no through holes penetrating the conductive nonwoven fabric in the thickness direction in a plan view, the aperture ratio becomes smaller, resulting in superior electromagnetic wave shielding performance. Furthermore, even when the aperture ratio is small, if holes extending in the thickness direction, holes extending in the surface direction, and holes extending in the thickness direction are formed in this order in connection, as described above, and paths for thermally conductive fillers are formed, then thermal conductivity is also excellent. In addition, from the viewpoint of facilitating better contact between thermally conductive fillers, the aperture ratio is preferably 3% or more.

[0032] The aperture ratio of the conductive nonwoven fabric described above is measured by the following method. Using a digital microscope, ten arbitrary regions within a field of view (1770 μm × 1325 μm) are selected from the surface of the conductive nonwoven fabric in a plan view, and each is photographed at a magnification of 200x. In the captured images, the black areas represent the fibers of the conductive nonwoven fabric. Using the area measurement function of the digital microscope, the ratio of the area excluding the black areas to the total area of ​​the captured image of each region is determined, and the average value of these ratios is taken as the aperture ratio of the conductive nonwoven fabric. Specifically, it can be calculated by the method described in the examples.

[0033] From the viewpoint of reducing contact resistance between thermally conductive fillers and improving thermal conductivity, the length of the opening in the conductive nonwoven fabric described above is preferably equal to or greater than the median diameter of the thermally conductive filler (B) described below. Specifically, the length of the opening is preferably 5 μm or more, and more preferably 15 μm or more. This makes it easier to form paths for the thermally conductive filler (B) and further reduces contact resistance between the thermally conductive fillers. Furthermore, in order to further improve thermal conductivity, the length of the opening is preferably equal to or greater than the median diameter of the thermally conductive filler (A). Specifically, the length of the opening is preferably 50 μm or more, and more preferably 70 μm or more. This makes it easier to form paths for the thermally conductive filler (A) and reduces contact resistance between the thermally conductive fillers. The length of the opening is, for example, 120 μm or less.

[0034] The length of the opening in the conductive nonwoven fabric is measured by the following method: Using a digital microscope, an arbitrary area within the field of view (1770 μm × 1325 μm) of the surface of the conductive nonwoven fabric in a plan view is selected and photographed at a magnification of 200x. In the captured image, the black areas represent the fibers of the conductive nonwoven fabric. From the contours of the areas other than the black areas, the 10 largest areas are selected, the diameters of the circles inscribed in these contours are determined, and the average value of these is taken as the length of the opening in the conductive nonwoven fabric. Specifically, it can be calculated by the method described in the examples.

[0035] <Thermal Conductive Resin Layer> In this specification, the first thermal conductive resin layer and the second thermal conductive resin layer may be collectively referred to simply as the "thermal conductive resin layer." The thermal conductive resin layer comprises at least a binder resin and a thermal conductive filler.

[0036] (Binder Resin) The binder resin contained in the first thermal conductive resin layer and the second thermal conductive resin layer is a component that forms the matrix of the thermal conductive resin layer. The thermal conductive resin layer exhibits adhesion to the adherend, which is a heat source, by containing the binder resin. Examples of the binder resin include thermoplastic resins, thermosetting resins, active energy ray curing resins, etc. Only one type of binder resin may be used, or two or more types may be used.

[0037] Examples of the thermoplastic resins mentioned above include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (e.g., polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, and acrylic resins. Only one type of thermoplastic resin may be used, or two or more types may be used.

[0038] The above thermosetting resin includes both resins having thermosetting properties (thermosetting resins) and resins obtained by curing the above thermosetting resins. Examples of the above thermosetting resin include silicone resins, phenolic resins, epoxy resins, urethane resins, urethane urea resins, melamine resins, alkyd resins, polyimide resins, and acrylic resins. Only one type of the above thermosetting resin may be used, or two or more types may be used.

[0039] The above active energy ray-curable resin includes both resins curable by irradiation with active energy rays (active energy ray-curable resins) and resins obtained by curing the above active energy ray-curable resins. The above active energy ray-curable resin is not particularly limited, and for example, a polymer of a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule can be used. Only one type of the above active energy ray-curable resin may be used, or two or more types may be used.

[0040] Among the above binder resins, thermosetting resins are particularly preferable. Further, as the above binder resin, a silicone resin is preferable from the viewpoint of excellent thermal conductivity, heat resistance, and insulation properties. As the above silicone resin, silicone resins used in known or conventional thermally conductive resin layers can be used. The above silicone resin is preferably a two-part curable silicone resin from the viewpoint that a thermally conductive filler can be favorably dispersed without using a solvent. Only one type of the above silicone resin may be used, or two or more types may be used.

[0041] The content of the above binder resin is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and still more preferably 5 to 14% by mass, relative to 100% by mass of the total amount of the above thermally conductive resin layer. When the content is 1% by mass or more, the thermally conductive resin layer is less likely to become brittle, and the moldability of the thermally conductive resin layer is excellent. When the content is 20% by mass or less, the thermal conductivity of the above thermally conductive member becomes more favorable. In particular, it is preferable that the content of the silicone resin falls within the above range.

[0042] (Thermally conductive filler) The thermally conductive filler is a filler (particle) that has thermal conductivity and is a component that exhibits thermal conductivity in the thermally conductive resin layer. Examples of the thermally conductive filler include inorganic fillers such as ceramic fillers and carbon fillers. Only one type of thermally conductive filler may be used, or two or more types may be used.

[0043] Examples of materials for the ceramic fillers mentioned above include metal oxides such as alumina (aluminum oxide), titania (titanium oxide), magnesia (magnesium oxide), zirconia (zirconium oxide), and zinc oxide; nitrides such as aluminum nitride, titanium nitride, and boron nitride; metal hydroxides such as aluminum hydroxide; carbides such as silicon carbide; silicon compounds such as glass, silica, silicon carbide, silicon nitride, and silicon; and minerals such as steatite, forsterite, sialon, perlite, mullite, and zeolite.

[0044] Examples of the carbon fillers mentioned above include carbon fibers, carbon nanotubes, and carbon material-containing particles such as diamond.

[0045] The above-mentioned thermally conductive filler plays a role in mediating between the heat source and a cooling element such as a heat sink, and from the viewpoint of ensuring insulation, it is preferable that the material includes a ceramic filler. As the ceramic filler, metal oxides and nitrides are preferred, and from the viewpoint of superior thermal conductivity, it is even more preferable to include both. In particular, titanium oxide and alumina are preferred as the metal oxides, and titanium nitride, aluminum nitride, and boron nitride are preferred as the nitrides. When both metal oxides and nitrides are included, the ratio of metal oxides to the total of metal oxides and nitrides is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. When the above ratio is within the above range, the thermal conductivity of the thermally conductive resin layer is further improved.

[0046] The above-mentioned thermal conductive filler preferably includes at least a thermal conductive filler with a diameter that can penetrate the above-mentioned opening. Examples of the above-mentioned thermal conductive filler include thermal conductive filler (B) and thermal conductive filler (C) described later.

[0047] The above-mentioned thermal conductive filler preferably includes a thermal conductive filler (sometimes referred to as "thermal conductive filler (A)") having a median diameter (D50) of 30 to 65 μm, from the viewpoint of providing excellent thermal conductivity and easy to achieve appropriate hardness in the thermal conductive resin layer. Thermal conductive filler (A) is a group of particles. The median diameter of thermal conductive filler (A) is preferably 35 to 60 μm, more preferably 40 to 55 μm. Only one type of thermal conductive filler (A) may be used, or two or more types (i.e., two or more groups of particles with different median diameters) may be used.

[0048] The content of the thermally conductive filler (A) is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and even more preferably 45 to 60% by mass, based on 100% by mass of the total amount of the thermally conductive resin layer. When the content is within the above range, it is easier to achieve high thermal conductivity of the thermally conductive resin layer while ensuring appropriate hardness.

[0049] The content of the thermally conductive filler (A) is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and even more preferably 45 to 60% by mass, based on 100% by mass of the total amount of thermally conductive filler in the thermally conductive resin layer. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermally conductive resin layer while ensuring appropriate hardness.

[0050] The above-mentioned thermal conductive filler preferably includes a thermal conductive filler (sometimes referred to as "thermal conductive filler (B)") having a median diameter of 1 to 20 μm, from the viewpoint of easily achieving particularly high thermal conductivity of the thermal conductive resin layer. Thermal conductive filler (B) is a group of particles. The median diameter of thermal conductive filler (B) is preferably 1 to 15 μm, more preferably 2 to 10 μm. Only one type of thermal conductive filler (B) may be used, or two or more types (i.e., two or more groups of particles with different median diameters) may be used.

[0051] The content of the thermally conductive filler (B) is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and even more preferably 20 to 40% by mass, based on 100% by mass of the total amount of the thermally conductive resin layer. When the content is within the above range, it is easier to achieve high thermal conductivity of the thermally conductive resin layer while ensuring appropriate hardness.

[0052] The content of the thermally conductive filler (B) is preferably 20 to 60% by mass, more preferably 25 to 55% by mass, and even more preferably 30 to 50% by mass, based on 100% by mass of the total amount of thermally conductive filler in the thermally conductive resin layer. When the content is within the above range, it is easier to achieve high thermal conductivity in the thermally conductive resin layer while ensuring appropriate hardness.

[0053] The above-mentioned thermal conductive filler preferably includes a thermal conductive filler (sometimes referred to as "thermal conductive filler (C)") having a median diameter of 0.01 μm or more and less than 1 μm. Using thermal conductive filler (C) allows for close-packed thermal conductive filler in the thermal conductive resin layer, and facilitates connection between the thermal conductive fillers. Thermal conductive filler (C) is a group of particles. The median diameter of thermal conductive filler (C) is preferably 0.05 to 0.8 μm, more preferably 0.1 to 0.6 μm. Only one type of thermal conductive filler (C) may be used, or two or more types (i.e., two or more groups of particles with different median diameters) may be used.

[0054] The content of the thermal conductive filler (C) is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 8% by mass, based on 100% by mass of the total amount of the thermal conductive resin layer. When the content is within the above range, the thermal conductive filler in the thermal conductive resin layer can be closely packed, and the thermal conductive fillers can be easily connected to each other.

[0055] The content of the thermal conductive filler (C) is preferably 1 to 10% by mass, more preferably 2 to 9% by mass, and even more preferably 3 to 8% by mass, based on 100% by mass of the total amount of thermal conductive filler in the thermal conductive resin layer. When the content is within the above range, the thermal conductive filler in the thermal conductive resin layer can be closely packed, and the thermal conductive fillers can be easily connected to each other.

[0056] When titanium oxide is used as the metal oxide and titanium nitride as the nitride, the median diameter of titanium oxide and titanium nitride is preferably 10 to 100 nm, more preferably 15 to 90 nm, and even more preferably 20 to 85 nm. When the median diameter is 15 nm or greater, the dielectric constant tends to be lower. The median diameter refers to the median diameter in the particle size distribution of the mixture of titanium oxide and titanium nitride.

[0057] Furthermore, metal oxides other than titanium oxide (especially alumina) preferably have two or more peak tops in their particle size distribution, and more preferably two. One of these two or more peak tops is preferably in the range of 2 to 30 μm, and the other is preferably in the range of 35 to 100 μm. In this case, the packing of the metal oxide in the thermally conductive resin layer becomes higher, resulting in superior thermal conductivity.

[0058] In this specification, the median diameter of a thermally conductive filler is measured by laser diffraction and scattering. The median diameter (μm) of a thermally conductive filler can be measured, for example, by the following method. First, the particle size distribution of the particle group is measured using a laser diffraction particle size distribution analyzer, and a volume-based cumulative particle size distribution curve is obtained. In the obtained cumulative particle size distribution curve, the particle size value at the point of 50% accumulation from the fine particle side is D50. As a laser diffraction particle size distribution analyzer, for example, a particle size distribution analyzer such as the product name "MT3300EXII" (manufactured by Microtrac Co., Ltd.) can be used.

[0059] The shape of the thermally conductive filler is not particularly limited and can be spherical (including perfect spheres and ellipsoids), flake-like (scaly), dendritic, massive, flattened, needle-like, polyhedral, fibrous, or irregular. Among these, a spherical shape is preferred from the viewpoint of achieving higher filling properties in the thermally conductive resin layer and superior thermal conductivity.

[0060] The above-mentioned thermally conductive filler may or may not be surface-treated. Examples of surface treatment agents include silane coupling agents. When the surface is treated with a silane coupling agent, the thermally conductive filler disperses well in the binder resin (especially silicone resin) which is the matrix of the thermally conductive resin layer, resulting in superior filling and moldability. One type of silane coupling agent may be used, or two or more types may be used.

[0061] Examples of the silane coupling agents mentioned above include silane coupling agents having functional groups other than alkoxy groups, such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane (functional group-containing silane coupling agents); and silane coupling agents without functional groups other than alkoxy groups, such as n-octyltriethoxysilane and n-decyltrimethoxysilane (functional group-free silane coupling agents). Among these, functional group-free silane coupling agents are preferred from the viewpoint of having good wettability with metal oxides and being expected to improve the bulk strength and flexibility of the thermally conductive resin layer, more preferably silane coupling agents in which the terminal other than the alkoxy group is an alkyl group (terminal alkyl group-containing silane coupling agents), and particularly preferably n-octyltriethoxysilane.

[0062] The content ratio (filling rate) of the thermal conductive filler in the thermal conductive resin layer is preferably 70 to 98% by mass, more preferably 75 to 96% by mass, even more preferably 85 to 95% by mass, and particularly preferably 90 to 94% by mass, based on 100% by mass of the total amount of the thermal conductive resin layer. When the content ratio is 70% by mass or more, the filling rate of the thermal conductive filler in the thermal conductive resin layer is high, making it easier to achieve high thermal conductivity. When the content ratio is 98% by mass or less, the thermal conductive resin layer is less likely to become brittle, and the moldability when manufacturing the thermal conductive resin layer is excellent.

[0063] The above-mentioned thermally conductive resin layer may contain other components in addition to the various components described above. Examples of these other components include thixotropy imparters, dispersants, curing agents, curing accelerators, curing retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, and colorants other than titanium dioxide and titanium nitride. Only one of these other components may be used, or two or more may be used.

[0064] The above-mentioned thermally conductive resin layer preferably does not contain other colorants such as black colorants other than titanium oxide and titanium nitride, from the viewpoint of having insulating properties and excellent low dielectric constant, and from the viewpoint of suppressing inhibition of the hardening of the binder resin. However, it is also possible to include the above-mentioned other colorants as long as it does not impair the effects of the present invention. Examples of the above-mentioned other colorants include conductive colorants such as carbon black and carbon nanotubes. Furthermore, it is preferable not to include colorants containing sulfur, as they inhibit the hardening of the binder resin. The content ratio of the above-mentioned other colorants is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 1 part by mass or less, per 100 parts by mass of the total thermally conductive filler.

[0065] The thickness of the above-mentioned thermally conductive resin layer is, for example, 10 to 5000 μm, preferably 100 to 4000 μm. When the thickness is within this range, it can be manufactured with good moldability and the film thickness can be made sufficiently thin, making it suitable for use in small electronic devices.

[0066] Preferably, the thermally conductive resin layer has a thermal conductivity in the thickness direction at 5% compression of 3.0 W / mK or more, more preferably 4.0 W / mK or more, and still more preferably 5.0 W / mK or more. When the thermal conductivity is 3.0 W / mK or more, the thermally conductive resin layer is excellent in thermal conductivity in the thickness direction and heat dissipation. A specific method for measuring the thermal conductivity is, for example, as described in the Examples below.

[0067] Preferably, the Asker C hardness of the thermally conductive resin layer is 40 or more, and more preferably 45 or more. When the hardness is 40 or more, the thermally conductive resin layer has appropriate hardness and is excellent in handleability. From the viewpoint of excellent conformability to an adherend that is a heat generation source, the Asker C hardness of the thermally conductive resin layer is preferably 70 or less. The hardness can be measured, for example, with an Asker C hardness tester.

[0068] <Thermally Conductive Member> Preferably, the thickness of the thermally conductive member of the present invention is 0.05 to 10 mm, more preferably 0.1 to 5 mm, and still more preferably 0.2 to 3 mm. When the thickness falls within the above range, the thermally conductive member can exhibit flexibility while being suppressed in thickness, and being excellent in thermal conductivity and electromagnetic shielding properties. Note that the thickness of the thermally conductive member is the thickness from the surface of the first thermally conductive resin layer to the surface of the second thermally conductive resin layer, and does not include the thickness of the release film.

[0069] The thermal diffusivity of the thermally conductive member of the present invention is 0.95×10 －６ m ２ / s or more, more preferably 0.97×10 －６ m ２ / s or more, and still more preferably 1.00×10 －６ m ２ / s or more. A higher thermal diffusivity leads to better heat dissipation. The upper limit is, for example, 1.50×10 －６ m ２ / s or less. The thermal diffusivity is measured based on JIS R7240, and an average value of n=5 or more measured values may be employed.

[0070] The thermally conductive member of the present invention preferably has an electric field wave shielding effect of 30 dB or more at frequencies of 10 MHz to 1000 MHz as measured by the KEC method, more preferably 40 dB or more, and even more preferably 50 dB or more. When the electric field wave shielding effect is 30 dB or more, the electromagnetic wave shielding performance is superior.

[0071] The thermally conductive member of the present invention preferably has a magnetic field wave shielding effect of 5 dB or more at frequencies of 10 MHz to 1000 MHz as measured by the KEC method, more preferably 10 dB or more, and even more preferably 15 dB or more. When the magnetic field wave shielding effect is 5 dB or more, the electromagnetic wave shielding performance is superior.

[0072] The thermally conductive member of the present invention can be manufactured, for example, by the following method. First, a resin paste layer for forming the thermally conductive resin layer is prepared. The resin paste layer can be manufactured, for example, by placing a composition containing the various components described above between the release surfaces of two release films having flat release surfaces. From the viewpoint of continuous molding and excellent productivity, it is preferable to manufacture the resin paste layer in a roll-to-sheet manner.

[0073] The above composition includes, for example, the binder resin and the thermally conductive filler. If multiple types of thermally conductive fillers are used, they may be mixed beforehand and then mixed with the binder resin, or multiple types of thermally conductive fillers and the binder resin may be mixed simultaneously. The above composition is preferably in the form of a paste that does not contain organic solvents.

[0074] Next, a first thermally conductive resin layer and a second thermally conductive resin layer are formed on both sides of the conductive nonwoven fabric. Specifically, one release film is peeled off from the resin paste layer, and the resin paste layer is stretched, for example, in the planar direction and bonded to one side of the conductive nonwoven fabric. Similarly, the other resin paste layer is bonded to the other side of the conductive nonwoven fabric to produce a laminate. The resulting laminate is then inserted into a known molding apparatus such as a roll laminator, roll press, hot press molding machine, or sheet laminating machine and molded. Heating and pressurization may be performed during molding. If a thermosetting resin is used as the binder resin, it can be thermoset by the above molding process. In this way, the thermally conductive member of the present invention can be manufactured.

[0075] The thermally conductive member of the present invention has excellent electromagnetic shielding and heat dissipation properties and is flexible. Therefore, when bonded to an object, it prevents electromagnetic waves generated within the object from being emitted to the outside or prevents electromagnetic waves from entering from the outside, and efficiently dissipates heat generated within the object. Furthermore, it is easy to punch out and suitable for press working. For this reason, the thermally conductive member of the present invention can be preferably used in small electronic components and the like.

[0076] Embodiments of the present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0077] Example 1 As a thermally conductive filler, particle composition 1 was prepared by mixing 100 parts by mass of alumina (a mixture of 55% by mass of alumina with a median diameter of 46.1 μm, 40% by mass of alumina with a median diameter of 6.4 μm, and 5% by mass of alumina with a median diameter of 0.3 μm) with 0.75 parts by mass of a mixture of titanium oxide and titanium nitride (mass ratio 40:60, median diameter: 20 nm). The thermally conductive filler was previously surface-treated with a silane coupling agent by stirring and mixing 0.15 parts by mass of a silane coupling agent (product name "Z-6210", manufactured by Dow-Toray Industries, Ltd., n-decyltrimethoxysilane) with 100 parts by mass of the thermally conductive filler in a solvent. The above particle composition 1 was mixed with the above silicone resin (product name "TSE-3062", manufactured by Momentive) in such a ratio of alumina to 1425.6 parts by mass per 100 parts by mass of the mixture of the first and second components of the silicone resin to prepare a resin paste. Subsequently, the above resin paste was placed between the release surfaces of two release-treated polyethylene terephthalate films (release films), and laminated using a roll laminator to prepare a laminate of [release film / resin paste layer / release film].

[0078] Two of the above laminates are prepared, and one release film is peeled off from each laminate. The resin paste layer is stretched in the planar direction, and a conductive nonwoven fabric (a resin nonwoven fabric with a metal plating treatment on its surface, with a basis weight of 39.65 g / m²) is used. ２ The layers were bonded to both sides of the material and pressed at a temperature of 170°C, a pressure of 2 MPa, and for 3 minutes. Afterwards, the resin paste layer was heat-cured at 150°C for 1 hour. In this way, a thermally conductive resin layer (thickness of the thermally conductive resin layer: approximately 0.5 mm) having a laminated structure of [release film / thermally conductive resin layer / conductive nonwoven fabric / thermally conductive resin layer / release film] was fabricated.

[0079] Comparative Example 1 The laminate prepared in Example 1 was placed in a heating furnace and heated at 70°C for 30 minutes to heat-cur it, forming a sheet-like thermal conductive resin layer. In this way, a thermal conductive resin layer (thickness of the thermal conductive resin layer: approximately 0.5 mm) having a laminated structure of [release film / thermal conductive resin layer / release film] was prepared. Two of the above thermal conductive resin layers were prepared, and one release film was peeled off from each thermal conductive resin layer. At room temperature, using a roll press, the two layers were bonded to both sides of the conductive nonwoven fabric used in Example 1, respectively, to produce a thermal conductive member (thickness of the thermal conductive resin layer: approximately 0.5 mm) having a laminated structure of [release film / thermal conductive resin layer / conductive nonwoven fabric / thermal conductive resin layer / release film].

[0080] <Evaluation> In the examples and comparative examples, each thermally conductive filler, conductive nonwoven fabric, and the resulting thermally conductive resin layer and each thermally conductive component were evaluated as follows.

[0081] (1) Cross-sectional observation The thermal conductive members obtained in Example 1 and Comparative Example 1 were cut in the thickness direction so as to cut the fibers in the conductive nonwoven fabric in the width direction. The exposed cross-sections were then observed using a scanning electron microscope (SEM). Cross-sectional photographs are shown in Figure 4.

[0082] (2) Thermal diffusivity The release film was peeled off the thermal conductive material, and the thermal diffusivity was measured in accordance with JIS R7240 using a thermophysical property measuring device (product name "Thermowave Analyzer TA35", manufactured by Bethel Co., Ltd.). The evaluation results are shown in Table 1.

[0083] (3) Both sides of the thermally conductive member obtained in the electromagnetic wave shielding example were heated and pressurized using a press machine at a temperature of 170°C, a time of 30 minutes, and a pressure of 3 MPa to cure it. After removing the release film, it was cut into 15 cm squares, the thermally conductive resin layer was cured, and the electric field wave shielding effect and magnetic field wave shielding effect up to 1 GHz were measured by the KEC method. The results of the electric field wave shielding effect are shown in Figure 5, and the results of the magnetic field wave shielding effect are shown in Figure 6.

[0084] (3) Opening Ratio The surface of the conductive nonwoven fabric was observed from above using a digital microscope (product name "VHX-5000") with a field of view of 200x magnification (approximately 1770 μm × approximately 1325 μm) while illuminating the underside of the conductive nonwoven fabric. Ten arbitrary regions were each photographed at a magnification of 200x. From the acquired images, the area measurement function of the digital microscope was used to measure the area of ​​the fiber portion (black portion in the image). Based on the measured total area ratio, the opening ratio was calculated using the following formula, and the average value of the conductive nonwoven fabric was taken as the opening ratio. One of the acquired images is shown in Figure 7. In the image in Figure 7, the black portion is the fiber, and the white portion is the opening. As a result, the opening ratio of the conductive nonwoven fabric used in the examples and comparative examples was 11.8%. Area ratio of openings (opening ratio) = 100% - Total area ratio of fiber portion [%]

[0085] (4) Length of the opening For any one of the images obtained in the evaluation of the opening ratio above, the 10 contours of the parts other than the black area were selected in order of largest area, the diameter of the circle inscribed in these contours was determined, and the average value of these was taken as the length of the opening of the conductive nonwoven fabric. As a result, the length of the opening of the conductive nonwoven fabric used in the example and comparative example was 40.2 μm. Figure 8 shows an enlarged image of the region containing the contour with the largest area from the image shown in Figure 7. In Figure 8, the four contours selected in order of largest area are indicated by circles.

[0086]

[0087] As shown in Figure 4, in a cross-sectional photograph taken in the thickness direction of the conductive nonwoven fabric of the thermal conductive member of Example 1, it was confirmed that the thermal conductive filler of the thermal conductive resin layers on both sides filled and contacted the openings of the conductive nonwoven fabric, and that the thermal conductive resin layers on both sides of the conductive nonwoven fabric communicated to form paths for the thermal conductive filler. As a result, as shown in Table 1, the thermal conductive member of Example 1 was evaluated to have a higher thermal diffusivity and superior heat dissipation compared to the comparative example. Furthermore, as shown in Figures 5 and 6, it was confirmed that the thermal conductive member of Example 1 had high electromagnetic wave shielding effect and magnetic field wave shielding effect, resulting in excellent electromagnetic wave shielding performance. In addition, since the thermal conductive member of Example 1 uses a conductive nonwoven fabric as the base material, it has higher flexibility compared to the case where metal foil is used.

[0088] The following describes variations of the invention according to the present invention. [Note 1] A thermal conductive member comprising a conductive nonwoven fabric, a first thermally conductive resin layer bonded to one side of the conductive nonwoven fabric, and a second thermally conductive resin layer bonded to the other side of the conductive nonwoven fabric, wherein the first thermally conductive resin layer and the second thermally conductive resin layer each contain a binder resin and a thermally conductive filler, and the thermally conductive filler in the first thermally conductive resin layer and the thermally conductive filler in the second thermally conductive resin layer are in contact through an opening in the conductive nonwoven fabric. [Note 2] The thermal conductive member according to Note 1, wherein the conductive nonwoven fabric comprises a resin nonwoven fabric and a metal layer formed on the surface of the resin nonwoven fabric. [Note 3] The thermal conductive member according to Note 2, wherein the metal layer is a metal plating layer. [Note 4] The thermal conductive member according to any one of Notes 1 to 3, wherein the binder resin in the first thermal conductive resin layer and the second thermal conductive resin layer includes a thermosetting resin. [Note 5] The thermal conductive member according to any one of Notes 1 to 4, wherein the thermal conductive filler in the first thermal conductive resin layer and the second thermal conductive resin layer includes a metal oxide and / or nitride. [Note 6] The thermal conductive member according to any one of Notes 1 to 5, wherein the binder resin in the first thermal conductive resin layer and the second thermal conductive resin layer is a silicone resin. [Note 7] The thermal conductive member according to any one of Notes 1 to 6, wherein the opening includes a hole extending in a direction other than the thickness direction.

[0089] 1 Thermally conductive member 2 Conductive nonwoven fabric 3 First thermally conductive resin layer 4 Second thermally conductive resin layer 5, 6 Release film 11, 11' Binder resin 12, 12' Thermally conductive filler H Opening

Claims

1. A thermal conductive member comprising a conductive nonwoven fabric, a first thermally conductive resin layer bonded to one side of the conductive nonwoven fabric, and a second thermally conductive resin layer bonded to the other side of the conductive nonwoven fabric, wherein the first thermally conductive resin layer and the second thermally conductive resin layer each contain a binder resin and a thermally conductive filler, and the thermally conductive filler in the first thermally conductive resin layer and the thermally conductive filler in the second thermally conductive resin layer are in contact with each other through an opening in the conductive nonwoven fabric.

2. The thermal conductive member according to claim 1, wherein the conductive nonwoven fabric comprises a resin nonwoven fabric and a metal layer formed on the surface of the resin nonwoven fabric.

3. The thermal conductive member according to claim 2, wherein the metal layer is a metal plating layer.

4. The thermal conductive member according to any one of claims 1 to 3, wherein the binder resin in the first thermal conductive resin layer and the second thermal conductive resin layer includes a thermosetting resin.

5. The thermal conductive member according to any one of claims 1 to 3, wherein the thermal conductive filler in the first thermal conductive resin layer and the second thermal conductive resin layer comprises a metal oxide and / or nitride.

6. The thermal conductive member according to any one of claims 1 to 3, wherein the binder resin in the first thermal conductive resin layer and the second thermal conductive resin layer is a silicone resin.

7. The thermal conductive member according to any one of claims 1 to 3, wherein the opening includes a hole extending in a direction other than the thickness direction.

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