Electromagnetic wave absorbing and heat dissipating sheet

Abstract

To provide an electromagnetic wave absorption heat dissipation sheet that includes a high heat transfer coefficient, and has excellent electromagnetic wave absorption characteristic, flexibility, and film forming property.SOLUTION: An electromagnetic wave absorption heat dissipation sheet 1 contains: a silicone resin 13; alumina powder 12; and mesocarbon microbeads as a black lead 11. A volume rate of the mesocarbon microbeads against a total of the alumina powder 12 and the mesocarbon microbeads as a black lead 11 is 61 to 79 volume%. The alumina powder 12 contains the alumina powder of which a median diameter is 1 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to an electromagnetic wave absorbing and heat dissipating sheet. [Background technology]

[0002] Printed circuit boards (PCBs) are widely used in electronic devices such as mobile phones, video cameras, and laptop computers to integrate circuits into their mechanisms. They are also used to connect movable parts, such as printer heads, to control units. Electromagnetic shielding is essential in these electronic devices, and shielded PCBs with electromagnetic shielding measures are used within these devices.

[0003] Shielded printed circuit boards utilize electromagnetic shielding films (hereinafter sometimes simply referred to as "shielding films") for the purpose of shielding against electromagnetic waves. For example, shielding films used by adhering them to printed circuit boards may consist of a shielding layer such as a metal layer, or a conductive adhesive sheet provided on the surface of the shielding layer, either alone or in combination.

[0004] The shielded printed circuit boards described above are used with electronic components mounted on them. In recent years, electronic components have become smaller and more functional, and the amount of heat generated by semiconductor elements has been increasing. When electronic components are exposed to high-temperature environments for extended periods, they may not be able to perform their intended function and their lifespan will be reduced. For this reason, highly heat-dissipating bonding materials are sometimes used in the shielding films applied to printed circuit boards to efficiently dissipate the heat generated by semiconductor elements.

[0005] Sheets with electromagnetic shielding and thermal conductivity (electromagnetic wave absorbing and heat dissipating sheets) are generally manufactured by filling an organic binder component with a high concentration of powder. Examples of such electromagnetic wave absorbing and heat dissipating sheets are disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-208316 [Patent Document 2] International Publication No. 2022 / 054478 [Overview of the project] [Problems that the invention aims to solve]

[0007] In recent years, electromagnetic wave absorbing and heat dissipating sheets are sometimes required to have not only high thermal conductivity and electromagnetic wave absorption properties, but also flexibility. Furthermore, during film formation, it is necessary that the sheet does not adhere to the substrate and is easy to peel off (film-forming properties). On the other hand, flexibility and film-forming properties are in a trade-off relationship, and sheets with excellent flexibility tend to have high adhesion to the substrate and poor film-forming properties. Patent documents 1 and 2 do not specifically disclose a sheet that possesses high thermal conductivity and combines electromagnetic wave absorption properties, flexibility, and film-forming properties, making it difficult to manufacture a sheet that has all of these properties.

[0008] Therefore, the object of this disclosure is to provide an electromagnetic wave absorbing and heat dissipating sheet that has high thermal conductivity and excellent electromagnetic wave absorption characteristics, flexibility, and film-forming properties. [Means for solving the problem]

[0009] The inventors of this disclosure have diligently studied to solve the above problems and have found that by using a silicone-based resin as a binder component, and containing specific alumina powder and specific graphite, and wherein the volume ratio of the specific graphite to the total of the specific alumina powder and specific graphite is within a specific range, an electromagnetic wave absorbing and heat dissipating sheet can be obtained that has high thermal conductivity and excellent electromagnetic wave absorption properties, flexibility, and film-forming properties. This disclosure relates to a product completed based on these findings.

[0010] This disclosure includes mesocarbon microbeads which are a silicone resin, alumina powder, and graphite. The volume ratio of the above-mentioned mesocarbon microbeads to the total of the above-mentioned alumina powder and the above-mentioned mesocarbon microbeads is 61 to 79% by volume, The above-mentioned alumina powder includes alumina powder with a median diameter of 1 μm or less, and provides an electromagnetic wave absorption and heat dissipation sheet.

[0011] It is preferable that the above-mentioned mesocarbon microbeads include those with an average particle diameter of 40 μm or less.

[0012] The filling rate of the above-mentioned mesocarbon microbeads is preferably 55 to 85% by volume based on the total amount of the powder contained in the above-mentioned electromagnetic wave absorption and heat dissipation sheet.

[0013] The filling rate of the above-mentioned alumina powder is preferably 15 to 45% by volume based on the total amount of the powder contained in the above-mentioned electromagnetic wave absorption and heat dissipation sheet.

[0014] It is preferable that the above-mentioned alumina powder further includes alumina powder with a median diameter exceeding 1 μm.

[0015] The above-mentioned silicone-based resin is preferably a curable resin.

[0016] The filling rate of the powder in the above-mentioned electromagnetic wave absorption and heat dissipation sheet is preferably 73% by volume or more based on the total amount of the above-mentioned electromagnetic wave absorption and heat dissipation sheet.

Advantages of the Invention

[0017] The electromagnetic wave absorption and heat dissipation sheet of the present disclosure has high thermal conductivity and is excellent in electromagnetic wave absorption characteristics, flexibility, and film-forming properties.

Brief Description of the Drawings

[0018] [Figure 1] It is a partial cross-sectional view showing an embodiment of the electromagnetic wave absorption and heat dissipation sheet of the present disclosure.

Modes for Carrying Out the Invention

[0019] [Electromagnetic Wave Absorption and Heat Dissipation Sheet] The electromagnetic wave absorbing heat dissipation sheet of this disclosure comprises at least a silicone resin, alumina powder, and graphite.

[0020] The electromagnetic wave absorbing and heat dissipating sheet described above may be in a form without a base material (base layer), a so-called "base material-less" form, or it may be an electromagnetic wave absorbing and heat dissipating sheet provided on at least one side of a base material. Note that the "base material (base layer)" described above does not include the release sheet that is peeled off when the electromagnetic wave absorbing and heat dissipating sheet is used.

[0021] The electromagnetic wave absorbing and heat dissipating sheet may include a release sheet. The release sheet may be provided on only one side of the electromagnetic wave absorbing and heat dissipating sheet, or on both sides. Examples of the release sheet include a film formed from a low-tack resin, or a sheet comprising a substrate and a release treatment layer provided on at least one side of the substrate. The release sheet is peeled off and removed when the electromagnetic wave absorbing and heat dissipating sheet is used.

[0022] Figure 1 is a schematic cross-sectional view showing one embodiment of the electromagnetic wave absorbing heat dissipation sheet of the present disclosure. As shown in Figure 1, the electromagnetic wave absorbing heat dissipation sheet 1 includes a silicone resin 13 which is a matrix component, graphite 11 dispersed in the silicone resin 13, and alumina powder 13. Release sheets 2 and 3 are provided on both sides of the electromagnetic wave absorbing heat dissipation sheet 1, and the electromagnetic wave absorbing heat dissipation sheet 1 is sandwiched between the two release sheets 2 and 3.

[0023] (Silicone resin) The above-mentioned silicone resin is preferably a component (binder component) that forms the matrix of the electromagnetic wave absorbing heat dissipation sheet. Using a silicone resin as the binder component provides excellent thermal conductivity and heat resistance for the electromagnetic wave absorbing heat dissipation sheet. The above-mentioned silicone resin may be used by one type only, or by two or more types.

[0024] The above-mentioned silicone resin may be a thermoplastic resin or a curable resin such as a thermosetting resin. Examples of the thermosetting resin include both a thermosetting resin and a resin obtained by curing the thermosetting resin. As the above-mentioned silicone resin, a known or conventional silicone resin used in heat dissipation sheets can be used. From the viewpoint of being able to disperse the powder well without using a solvent, the above-mentioned silicone resin is preferably a two-component curable silicone resin.

[0025] The content of the above-mentioned silicone resin is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 7.0% by mass or more, based on the total amount (100% by mass) of the above-mentioned electromagnetic wave absorbing heat dissipation sheet. When the above-mentioned content is 3.0% by mass or more, the electromagnetic wave absorbing heat dissipation sheet is less likely to become brittle and the film-forming properties of the electromagnetic wave absorbing heat dissipation sheet are excellent. The above-mentioned content is preferably 20.0% by mass or less, and more preferably 15.0% by mass or less. When the above-mentioned content is 20.0% by mass or less, the thermal conductivity and electromagnetic wave absorption characteristics of the above-mentioned electromagnetic wave absorbing heat dissipation sheet are further improved.

[0026] (Alumina powder) The electromagnetic wave absorbing and heat dissipating sheet exhibits thermal conductivity due to the inclusion of the above-mentioned alumina powder. The above-mentioned alumina powder may be used alone or in combination of two or more types.

[0027] The above alumina powder may have one peak top in its particle size distribution, or it may have two or more peak tops.

[0028] The above alumina powder includes alumina powder with a median diameter of 1 μm or less. In this specification, alumina powder with a median diameter of 1 μm or less may be referred to as "alumina powder (A)". The alumina powder in the above electromagnetic wave absorbing heat dissipation sheet preferably has a peak top of 1 μm or less in its particle size distribution. By including alumina powder (A) with a median diameter of 1 μm or less, the packing density of the alumina powder in the above electromagnetic wave absorbing heat dissipation sheet can be increased, and the thermal conductivity of the above electromagnetic wave absorbing heat dissipation sheet can be increased. The median diameter of alumina powder (A) is preferably 0.7 μm or less, more preferably 0.5 μm or less. From the viewpoint of further increasing thermal conductivity, the median diameter is preferably 0.05 μm or more.

[0029] The above alumina powder preferably further includes alumina powder with a median diameter greater than 1 μm. In this specification, alumina powder with a median diameter greater than 1 μm may be referred to as "alumina powder (B)". The alumina powder in the above electromagnetic wave absorbing heat dissipation sheet preferably has peaks at 1 μm or less and greater than 1 μm in its particle size distribution. Including alumina powder (B) with a median diameter greater than 1 μm together with alumina powder (A) can further increase the packing density of alumina powder in the above electromagnetic wave absorbing heat dissipation sheet, thereby increasing the thermal conductivity of the above electromagnetic wave absorbing heat dissipation sheet. The median diameter of alumina powder (B) is preferably 1.2 μm or more, more preferably 1.5 μm or more. From the viewpoint of maintaining film-forming properties, the above median diameter is preferably 10 μm or less.

[0030] The shape of the alumina powder is not particularly limited, and examples include spherical (including perfect spheres and ellipsoids), flake-like (scale-like), dendritic, lumpy, flattened, needle-like, and irregular (polyhedral) shapes. Among these, a spherical shape is preferred from the viewpoint of achieving higher packing efficiency during electromagnetic wave absorption and heat dissipation, and superior thermal conductivity.

[0031] The alumina powder may or may not be surface-treated. A silane coupling agent can be used as a surface treatment agent. When the alumina powder is surface-treated with a silane coupling agent, it disperses well in the binder component (especially silicone resin) which is the matrix of the electromagnetic wave absorbing heat dissipation sheet, and has superior filling and film-forming properties. One type of silane coupling agent may be used, or two or more types may be used.

[0032] 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 not having 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 good wettability with alumina powder and improvement in bulk strength and flexibility of the electromagnetic wave absorbing heat dissipation sheet, more preferably silane coupling agents in which the terminal other than the alkoxy group is an alkyl group (terminal alkyl group-containing silane coupling agent), and particularly preferably n-octyltriethoxysilane.

[0033] The total amount of alumina powder in the electromagnetic wave absorbing and heat dissipating sheet is preferably 20 to 50% by mass, and more preferably 30 to 45% by mass, relative to the total amount (100% by mass) of the electromagnetic wave absorbing and heat dissipating sheet. When the total amount is 20% by mass or more, the packing density of alumina powder in the electromagnetic wave absorbing and heat dissipating sheet is high, resulting in superior thermal conductivity. When the total amount is 50% by mass or less, the electromagnetic wave absorbing and heat dissipating sheet is less likely to become brittle, and the film-forming properties when manufacturing the electromagnetic wave absorbing and heat dissipating sheet are excellent. Furthermore, it is preferable that the total ratio of alumina powder (A) and alumina powder (B) is within the above range.

[0034] The total proportion of alumina powder (A) and alumina powder (B) in the electromagnetic wave absorbing heat dissipation sheet described above is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total amount of alumina powder (100% by mass).

[0035] The volume ratio [former / latter] of alumina powder (A) and alumina powder (B) in the electromagnetic wave absorbing heat dissipation sheet is preferably 10 / 90 to 50 / 50, and more preferably 20 / 80 to 40 / 60. When the volume ratio is within the above range, the packing density of alumina powder in the electromagnetic wave absorbing heat dissipation sheet is high, resulting in superior thermal conductivity.

[0036] (graphite) By including the above-mentioned graphite, the dielectric properties of the electromagnetic wave absorbing heat dissipation sheet are increased, providing electromagnetic wave shielding capabilities. The above-mentioned graphite may be used by using only one type, or by using two or more types.

[0037] The graphite mentioned above is preferably mesocarbon microbeads (MCMB). By using MCMB, dielectric properties are imparted to the electromagnetic wave absorbing heat dissipation sheet, while improving the release properties of the silicone resin from the substrate and providing superior film-forming capabilities. In particular, when the silicone resin is a curable resin, the release properties from the substrate are further improved because the silicone resin does not inhibit curing and the silicone resin hardens sufficiently.

[0038] The shape of the graphite is not particularly limited and can be spherical (including perfect spheres and ellipsoids), flake-like (scaly), dendritic, massive, flattened, needle-like, or irregular (polyhedron). Among these, the spherical shape is preferred. In this case, film-forming properties are superior. In particular, when the silicone resin is a curable resin, the graphite does not inhibit the curing of the silicone resin, and the silicone resin hardens sufficiently, further improving the peelability from the substrate.

[0039] The specific surface area of ​​the above graphite is 2.0 m². 2 Preferably less than / g, and more preferably 1.5m 2 / g or less, more preferably 1.0m 2The specific surface area is less than or equal to 2.0 m². 2 When the specific surface area is less than / g, film-forming properties are superior. In particular, when the silicone resin is a curing type resin, the specific surface area of ​​the graphite is not inhibited, and the silicone resin hardens sufficiently, resulting in improved peelability from the substrate. The specific surface area of ​​the above graphite is, for example, 0.1 m². 2 It is 1 / g or more.

[0040] The above-mentioned graphite preferably contains graphite with an average particle diameter of 50 μm or less (preferably 40 μm or less). Including graphite with an average particle diameter of 50 μm or less allows for a higher density of graphite in the electromagnetic wave absorbing heat dissipation sheet, thereby improving the dielectric properties of the electromagnetic wave absorbing heat dissipation sheet. The above-mentioned average particle diameter is, for example, 5 μm or more.

[0041] The graphite described above preferably includes graphite with an average particle size of 5 to 20 μm (sometimes referred to as "graphite (A)") and graphite with an average particle size of 25 to 50 μm (preferably 25 to 40 μm) (sometimes referred to as "graphite (B)"). In this case, the filling ratio of graphite in the electromagnetic wave absorbing heat dissipation sheet can be increased, and the dielectric properties of the electromagnetic wave absorbing heat dissipation sheet can be further improved.

[0042] The MCMB content in the above graphite is preferably 50% by volume or more, more preferably 80% by volume or more, even more preferably 90% by volume or more, and particularly preferably 95% by volume or more. When the above content is 50% by volume or more, the film-forming properties are superior. In particular, when the silicone resin is a curable resin, the MCMB does not inhibit the curing of the silicone resin, and the silicone resin hardens sufficiently, which further improves the peelability from the substrate. Furthermore, it is preferable that the content of graphite with an average particle size of 50 μm or less in the above graphite (preferably the total content of graphite (A) and graphite (B)) is within the above range.

[0043] The electromagnetic wave absorbing heat dissipation sheet described above may contain other components besides those listed above, to the extent that they do not impair the effects intended by this disclosure. Examples of these other components include those found in known or conventional heat dissipation sheets. Examples of these other components include curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, settling inhibitors, colorants, leveling agents, coupling agents, ultraviolet absorbers, tackifying resins, and blocking inhibitors. Only one of these other components may be used, or two or more may be used. The electromagnetic wave absorbing heat dissipation sheet may also contain fillers other than alumina powder and graphite, but the proportion of these fillers is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of the total of alumina powder and graphite.

[0044] (Electromagnetic wave absorbing and heat dissipating sheet) The volume ratio of MCMB to the total of alumina powder and MCMB is preferably 61 to 79 volume%, more preferably 63 to 75 volume%, and even more preferably 65 to 72 volume%. When the above volume ratio is within the above range, the flexibility of the electromagnetic wave absorbing heat dissipation sheet is excellent. Furthermore, when the above volume ratio is 75 volume% or less, the film-forming properties are excellent. Also, the volume ratio of graphite with an average particle size of 50 μm or less to the total of alumina powder and graphite with an average particle size of 50 μm or less, and the specific surface area of ​​alumina powder and graphite with an average particle size of 2.0 m² are also important. 2 The specific surface area relative to the total amount of graphite that is less than or equal to / g is 2.0m². 2 It is preferable that the volume ratio of graphite, which is less than or equal to / g, is within the above range.

[0045] The filling ratio (content) of the powder in the electromagnetic wave absorbing heat dissipation sheet is preferably 88% by mass or more, and more preferably 90% by mass or more, relative to the total amount (100% by mass) of the electromagnetic wave absorbing heat dissipation sheet. The powder contains alumina powder and graphite. When the filling ratio is 88% by mass or more, the dielectric properties and thermal conductivity are superior. Furthermore, the electromagnetic wave absorbing heat dissipation sheet can have a higher filling ratio by using specific alumina powder and specific graphite. From the viewpoint of superior flexibility, the filling ratio is preferably 99% by mass or less, and more preferably 94% by mass or less.

[0046] The filling ratio (content) of the powder in the electromagnetic wave absorbing heat dissipation sheet is preferably 73% by volume or more, more preferably 75% by volume or more, and even more preferably 78% by volume or more, based on the total amount (100% by volume) of the electromagnetic wave absorbing heat dissipation sheet. The powder contains alumina powder and graphite. When the filling ratio is 73% by volume or more, the dielectric properties and thermal conductivity are superior. Furthermore, the electromagnetic wave absorbing heat dissipation sheet can have a higher filling ratio by using specific alumina powder and specific graphite. From the viewpoint of superior flexibility, the filling ratio is preferably 90% by volume or less, and more preferably 85% by volume or less.

[0047] The graphite filling rate (content ratio) in the electromagnetic wave absorbing heat dissipation sheet is preferably 55 to 85 volume%, more preferably 60 to 80 volume%, and even more preferably 63 to 78 volume%, relative to the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet (100 volume%). When the above filling rate is 55 volume% or more, the dielectric properties are superior. When the above filling rate is 85 volume% or less, the flexibility is superior.

[0048] The filling rate (content ratio) of graphite (A) in the electromagnetic wave absorbing heat dissipation sheet is preferably 40% by volume or less, and more preferably 30% by volume or less, relative to the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet (100% by volume). In one embodiment, the filling rate of graphite (A) is preferably 10 to 40% by volume, and more preferably 20 to 30% by volume. In another embodiment, the filling rate of graphite (A) may be 5% by volume or less (0 to 5% by volume).

[0049] In the electromagnetic wave absorbing heat dissipation sheet, the filling rate (content ratio) of graphite (B) is preferably greater than that of graphite (A), and is preferably 25 to 80 volume% and more preferably 30 to 70 volume% based on the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet (100 volume%). In one embodiment, the filling rate of graphite (B) is preferably 35 to 60 volume%, and more preferably 40 to 50 volume%. In another embodiment, the filling rate of graphite (B) is preferably 50 to 80 volume%, and more preferably 60 to 70 volume%.

[0050] The packing ratio (content percentage) of alumina powder in the electromagnetic wave absorbing heat dissipation sheet is preferably 15 to 45 volume%, more preferably 20 to 40 volume%, and even more preferably 22 to 37 volume%, relative to the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet (100 volume%). When the packing ratio is 15 volume% or more, the thermal conductivity is superior. When the packing ratio is 45 volume% or less, the flexibility is superior.

[0051] The packing ratio (content) of alumina powder (A) in the electromagnetic wave absorbing heat dissipation sheet is preferably 1 to 20 volume% and more preferably 5 to 15 volume% relative to the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet (100 volume%). The packing ratio (content) of alumina powder (B) in the electromagnetic wave absorbing heat dissipation sheet is preferably greater than that of alumina powder (A), and is preferably 10 to 40 volume% and more preferably 15 to 30 volume% relative to the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet (100 volume%). When the above packing ratios are within the above ranges, the packing ratio of alumina powder is further improved, resulting in superior thermal conductivity.

[0052] The thickness of the electromagnetic wave absorbing heat dissipation sheet is, for example, 0.1 to 10 mm, preferably 0.3 to 5 mm. Furthermore, the electromagnetic wave absorbing heat dissipation sheet can be manufactured with good film-forming properties even when thin, making it suitable for use in small portable electronic devices. Therefore, its thickness is preferably 3.0 mm or less, more preferably 2.5 mm or less, even more preferably 2.0 mm or less, even more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less.

[0053] The electromagnetic wave absorbing and heat dissipating sheet described above preferably has a hardness of 65 or less, more preferably 63 or less, and even more preferably 60 or less. A hardness of 65 or less provides superior flexibility. The hardness is, for example, 50 or more. The hardness described above is measured using an Asker rubber hardness tester type C.

[0054] The electromagnetic wave absorbing and heat dissipating sheet described above preferably has a thermal conductivity in the thickness direction of 6.5 W / mK or higher when compressed by 20% in the thickness direction, and more preferably 7.0 W / mK or higher. A thermal conductivity of 6.5 W / mK or higher provides superior thermal conductivity and heat dissipation.

[0055] The electromagnetic wave absorbing and heat dissipating sheet described above preferably has a relative permittivity of 40 or higher at 23°C and 1 GHz, more preferably 65 or higher, and even more preferably 80 or higher. When the relative permittivity is 40 or higher, it exhibits excellent dielectric properties and superior electromagnetic wave absorption performance.

[0056] The electromagnetic wave absorbing and heat dissipating sheet described above preferably has a dielectric loss tangent of 0.1 or higher, and more preferably 0.5 or higher. A dielectric loss tangent of 0.1 or higher results in superior electromagnetic wave absorption performance.

[0057] The electromagnetic wave absorbing heat dissipation sheet described above preferably has a waveguide shielding characteristic of 10 dB or more, more preferably 11 dB or more, and even more preferably 12 dB or more, under at least one of the following conditions: 20 GHz, 30 GHz, and 40 GHz. A waveguide shielding characteristic of 10 dB or more provides superior electromagnetic wave absorption performance. It is particularly preferable that the waveguide shielding characteristic is within the above range under all conditions: 20 GHz, 30 GHz, and 40 GHz.

[0058] The method for forming the electromagnetic wave absorbing heat dissipation sheet described above is not particularly limited, and known or conventional methods for forming films or molded articles can be employed.

[0059] The electromagnetic wave absorbing and heat dissipating sheet described above can be manufactured, for example, by coating a composition containing the various components described above onto the release surface of a substrate or release sheet to form a coating layer, and then drying and curing it by heating to form a film. Heating may also be performed with the release surface of a release sheet further attached to the coating layer.

[0060] The above composition comprises a silicone resin, alumina powder, and graphite. The alumina powder and graphite may be mixed beforehand and then mixed with the silicone resin, or the alumina powder and graphite may be mixed with the silicone resin at the same time. The above composition is preferably in the form of a paste that does not contain organic solvents.

[0061] The method for producing the above composition sheets is not particularly limited, and known coating methods such as the sandwich method, in which the material is placed between release sheets coated with a release agent and laminated with a roll laminator, a hot press molding machine, or an extruder can be employed.

[0062] The electromagnetic wave absorbing heat dissipation sheet of this disclosure has high thermal conductivity and excellent electromagnetic wave absorption characteristics, flexibility, and film-forming properties. [Examples]

[0063] The embodiments of this disclosure will be described in more detail below based on the examples, but the invention of this disclosure is not limited to these examples. Unless otherwise specified, the content of each component listed in the table is expressed in "parts by mass".

[0064] Example 1 Particle composition 1 was prepared by mixing 68.89g of product name "PL-40" (manufactured by Eitan Co., Ltd.) and 34.44g of product name "PS" (manufactured by Eitan Co., Ltd.) as MCMB, and 56.37g of product name "DAW-01" (manufactured by Denka Co., Ltd.) and 22.53g of product name "ASFP-20" (manufactured by Denka Co., Ltd.) as alumina powder, and then adding 1.82g of silane coupling agent (product name "BS1601", n-octyltriethoxysilane, manufactured by Asahi Kasei Wacker Silicone Co., Ltd.). The particles were then surface-treated with the silane coupling agent using a dry method. The above particle composition 1 was mixed with a mixture of 7.4 g of component 1 and 7.4 g of component 2 of silicone resin (product name "CENUSIL GEL 100", manufactured by Asahi Kasei Wacker Silicone Co., Ltd.) and 0.0044 g of Pt catalyst to prepare a resin paste. Next, the resin paste was placed between the release treatment surfaces of two release sheets and laminated using a roll laminator to prepare a laminate of [release sheet / resin paste layer / release sheet]. At this time, three different film thicknesses were prepared using three types of spacers (0.8 mm, 1.5 mm, and 2.0 mm). Then, the resin paste layer of the laminate was heat-cured by heating the laminate at 70°C for 30 minutes to prepare the heat dissipation sheet of Example 1 as a laminate of [release sheet / heat dissipation sheet / release sheet].

[0065] Example 2 and Comparative Examples 1-5 Except for using the types and proportions of silicone resin, graphite, and alumina powder shown in Table 1, the heat dissipation sheets for Example 2 and Comparative Examples 1-5 were prepared in the same manner as in Example 1.

[0066] The graphite and alumina powders shown in the table are as follows. The specific gravity of the silicone resin is 0.97 g / cm³. 3, the specific gravity of the silane coupling agent is 0.88 g / cm 3 is as follows. <Graphite> Artificial spherical graphite: Spherical graphite produced by the cold isostatic pressing method (CIP method), median diameter 50 μm, specific surface area 4.90 m 2 / g, specific gravity 2.2 g / cm 3 CGB50: Product name "CGB50", natural graphite, median diameter 50 μm, specific surface area 2.33 m 2 / g, specific gravity 2.2 g / cm 3 , manufactured by Nippon Graphite Industry Co., Ltd. PL-40: Product name "PL-40", MCMB, median diameter 35 μm, specific surface area 0.26 m 2 / g, specific gravity 2.2 g / cm 3 , manufactured by Eiraku Carbon Co., Ltd. PS: Product name "PS", MCMB, median diameter 11 μm, specific surface area 1.22 m 2 / g, specific gravity 2.2 g / cm 3 , manufactured by Eiraku Carbon Co., Ltd. <Alumina powder> DAW-01: Product name "DAW-01", median diameter 1.9 μm, specific gravity 3.6 g / cm 3 , manufactured by Denka Co., Ltd. ASFP-20: Product name "ASFP-20", median diameter 0.3 μm, specific gravity 3.6 g / cm 3 , manufactured by Denka Co., Ltd.

[0067] (Evaluation) Each heat dissipation sheet obtained in the examples and comparative examples was evaluated as follows. The evaluation results are shown in the table.

[0068] (1) Powder packing property The surface state of the resin paste obtained at the stage of manufacturing the heat dissipation sheet was observed visually and by touch, and the powder packing was evaluated according to the following evaluation criteria. [Evaluation criteria] ○: The silicone resin and the powder are integrated and in a state like clay ×: The silicone resin and the powder are not completely integrated, and the powder remains on the surface of the paste

[0069] (2)Hardness The hardness of the heat dissipation sheet was measured using an Asker rubber hardness tester Type C (manufactured by Polymer Instruments Co., Ltd.). The measurement was performed by stacking four heat dissipation sheets, each made with 2.0 mm spacers to ensure a total film thickness of 6.0 mm or more.

[0070] (3) Film formability For each of the three heat dissipation sheets with different film thicknesses, the film-forming properties were evaluated according to the following evaluation criteria based on the condition of the peeled release sheet and the degree of hardening of the heat dissipation sheet after peeling one of the release sheets from the heat dissipation sheet. [Evaluation Criteria] ○: No powder was found to be attached to the release sheet. △: A small amount of powder was observed adhering to the release sheet. ×1: Numerous instances of powder adhesion were observed on the release sheet. ×2: The heat dissipation sheet was not sufficiently cured.

[0071] (4) Thermal conductivity Using a thermophysical property measuring device (product name "DynTIM," manufactured by Siemens K.K.), the thermal resistance of heat dissipation sheets fabricated with three types of spacers was measured when compressed by 20% in the thickness direction. Next, the thermal conductivity was calculated from the slope of the extrapolation line of the thermal resistance values ​​obtained for each thickness of heat dissipation sheet.

[0072] (5) Relative permittivity and dielectric loss tangent For heat dissipation sheets fabricated using 1.5 mm spacers, the relative permittivity (ε) and dielectric loss tangent (tanδ) were measured using the parallel plate method (conditions: 23°C, 1 GHz) with an impedance analyzer "E4991B" (manufactured by KEYSIGHT). If resonance occurred due to the influence of electrical conductivity and the measurement could not be performed correctly, it was marked as "measurement impossible."

[0073] (6) Waveguide Shielding Characteristics Using a coaxial waveguide adapter manufactured by KEYSIGHT, the attenuation of electromagnetic waves in the 18-40 GHz range was measured by the heat dissipation sheets (fabricated using 1.5 mm spacers) obtained in each example and comparative example.

[0074] [Table 1]

[0075] As can be seen from Table 1, the heat dissipation sheets of the examples had low hardness, excellent flexibility, excellent film-forming properties, high thermal conductivity, good reliability of dielectric constant and dielectric loss tangent, and good electromagnetic wave absorption properties. On the other hand, both when the proportion of specific graphite to the total with alumina powder was high and low, the hardness was high and the flexibility was poor (Comparative Examples 1 and 2). In addition, the dielectric properties were low and the electromagnetic wave absorption properties and film-forming properties were poor in some cases. When alumina powder of 1 μm or less was not used, the thermal conductivity was low and the thermal conductivity was poor (Comparative Example 3). When artificial graphite or natural graphite was used as the graphite, the dielectric properties were low and the electromagnetic wave absorption properties were poor, as was the film-forming properties (Comparative Examples 4 and 5).

[0076] The following describes variations of the invention relating to this disclosure. [Note 1] Contains silicone resin, alumina powder, and mesocarbon microbeads which are graphite. The volume ratio of the mesocarbon microbeads to the total amount of the alumina powder and the mesocarbon microbeads is 61-79% by volume. The aforementioned alumina powder is an electromagnetic wave absorbing and heat dissipating sheet containing alumina powder with a median diameter of 1 μm or less. [Note 2] The electromagnetic wave absorbing and heat dissipating sheet described in Note 1, wherein the mesocarbon microbeads include those with an average particle size of 40 μm or less. [Note 3] The electromagnetic wave absorbing and heat dissipating sheet according to Note 1 or 2, wherein the filling rate of the mesocarbon microbeads is 55 to 85 volume% of the total amount of powder contained in the electromagnetic wave absorbing and heat dissipating sheet. [Note 4] The electromagnetic wave absorbing heat dissipation sheet according to any one of Notes 1 to 3, wherein the filling rate of the alumina powder is 15 to 45 volume percent relative to the total amount of powder contained in the electromagnetic wave absorbing heat dissipation sheet. [Note 5] The alumina powder further includes alumina powder with a median diameter of 1 μm or more, and is an electromagnetic wave absorbing and heat dissipating sheet according to any one of Notes 1 to 4. [Note 6] The electromagnetic wave absorbing and heat dissipating sheet described in any one of Notes 1 to 5, wherein the silicone resin is a curing type resin. [Note 7] The electromagnetic wave absorbing heat dissipation sheet according to any one of Notes 1 to 6, wherein the filling rate of the powder in the electromagnetic wave absorbing heat dissipation sheet is 73% by volume or more relative to the total amount of the electromagnetic wave absorbing heat dissipation sheet. [Explanation of Symbols]

[0077] 2.1' Electromagnetic wave absorbing and heat dissipating sheet 2,3 Release sheets 11 Graphite 12 Alumina powder 13 Silicone resins 4a, 4b Nickel-gold plated copper foil 5. Polyimide film

Claims

1. It comprises a silicone resin, alumina powder, and graphite, wherein the graphite contains mesocarbon microbeads. The volume ratio of the mesocarbon microbeads to the total of the alumina powder and the mesocarbon microbeads is 61 to 79 volume%, The aforementioned alumina powder is an electromagnetic wave absorbing and heat dissipating sheet containing alumina powder with a median diameter of 1 μm or less.

2. The electromagnetic wave absorbing and heat dissipating sheet according to claim 1, wherein the mesocarbon microbeads include those with an average particle diameter of 40 μm or less.

3. The electromagnetic wave absorbing and heat dissipating sheet according to claim 1 or 2, wherein the filling rate of the mesocarbon microbeads is 55 to 85 volume percent relative to the total amount of powder contained in the electromagnetic wave absorbing and heat dissipating sheet.

4. The electromagnetic wave absorbing and heat dissipating sheet according to claim 1 or 2, wherein the filling rate of the alumina powder is 15 to 45 volume percent relative to the total amount of powder contained in the electromagnetic wave absorbing and heat dissipating sheet.

5. The electromagnetic wave absorbing and heat dissipating sheet according to claim 1 or 2, wherein the alumina powder further comprises alumina powder having a median diameter of more than 1 μm.

6. The electromagnetic wave absorbing and heat dissipating sheet according to claim 1 or 2, wherein the silicone resin is a curable resin.

7. The electromagnetic wave absorbing and heat dissipating sheet according to claim 1 or 2, wherein the filling rate of the powder in the electromagnetic wave absorbing and heat dissipating sheet is 73 volume% or more of the total amount of the electromagnetic wave absorbing and heat dissipating sheet.

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