Thermally conductive electromagnetic wave shielding grease

Abstract

To provide a thermally conductive electromagnetic wave shielding grease excellent in thermal conductivity and electromagnetic wave shielding properties and exhibiting good fluidity.SOLUTION: The thermally conductive electromagnetic wave shielding grease contains a first inorganic powder, a base oil and a dispersant, wherein the first inorganic powder is copper powder, the content ratio of the first inorganic powder is ≥65 vol.% and ≤85 vol.%, and the content ratio of the dispersant is ≥0.5 vol.% and ≤3.0 vol.%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive, electromagnetic wave shielding grease. [Background technology]

[0002] Among the semiconductor components used in electronic devices, there are those that generate heat during operation, such as computer CPUs or power semiconductors for power supply control, such as inverters and converters. To protect these semiconductor components from heat and ensure their normal functioning, the generated heat is transferred to heat dissipation components such as heat sinks to dissipate it. In this process, thermally conductive grease is often used to efficiently promote heat conduction. Thermally conductive grease is applied between the semiconductor component and the heat dissipation component to ensure close contact between them. Thermally conductive grease has high thermal conductivity. As a result, it efficiently transfers heat from the semiconductor component to the heat dissipation component.

[0003] Incidentally, high-power semiconductor components such as power semiconductors generate magnetic fields around them due to the large currents that flow through them. These magnetic fields generate harmonic noise components in heat-dissipating components, which propagate along with the heat. As a result, the heat-dissipating components function as antennas, radiating electromagnetic waves to the outside, which can cause electromagnetic interference problems. Therefore, in recent high-performance electronic components, measures to combat electromagnetic noise are required in addition to heat dissipation measures.

[0004] Conventionally, heat dissipation and electromagnetic noise countermeasures have been implemented separately. That is, high thermal conductivity materials have been used for heat dissipation, and electromagnetic wave shielding materials have been used for electromagnetic noise countermeasures, and these have been applied separately to electronic components. However, in response to the trend toward miniaturization of electronic components, the use of materials that combine the functions of high thermal conductivity and electromagnetic wave shielding has been proposed.

[0005] Patent Document 1, which discloses such a material, discloses an electromagnetic wave suppressing, heat dissipating composition comprising a matrix made of a polymeric or low molecular weight material, and magnetic particles filled into the matrix by mixing magnetic powder having a relationship of {tap density / density} ≥ 0.58 with the matrix (Claim 1 of Patent Document 1). It also discloses that the electromagnetic wave suppressing, heat dissipating composition further comprises thermally conductive particles filled into the matrix for promoting heat dissipation (Claim 2 of Patent Document 1).

[0006] A material in which inorganic powder is dispersed in a silicone gel has also been proposed as a material that combines high thermal conductivity and electromagnetic wave shielding properties. Using a highly flexible silicone gel as a base material has the advantage of allowing compact storage in small or complex-shaped electronic components. For example, Patent Document 2 discloses a gel composition having a thermal conductivity of 0.8 W / mK or higher, which comprises a gel containing a polymer and an ionic liquid contained in the polymer network, and an electromagnetic wave suppressor dispersed in the gel (Claim 1 of Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-183033 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-165868 Summary of the Invention [Problem to be solved by the invention]

[0008] Although materials having both high thermal conductivity and electromagnetic wave shielding properties have been proposed, there is still room for improvement in conventional materials. In other words, many of the inorganic powders used in currently available electromagnetic wave shielding sheets and gels have an anisotropic shape, such as a flat or needle shape. This is because anisotropically shaped particles can more efficiently shield electromagnetic waves. However, although anisotropically shaped particles have excellent electromagnetic wave shielding performance, it is difficult to achieve high packing density. From the perspective of improving thermal conductivity, it is desirable to increase the packing density of inorganic powders, and anisotropically shaped particles, which are difficult to achieve high packing density, are disadvantageous in improving thermal conductivity.

[0009] Furthermore, although Patent Document 1 uses magnetic powder to suppress electromagnetic waves, the magnetic powder has low thermal conductivity and cannot be said to have excellent heat dissipation properties. Increasing the amount of inorganic powder filled can be considered to increase thermal conductivity. However, in grease-type products, simply increasing the amount of inorganic powder filled can increase viscosity, making application difficult or making it impossible to maintain the grease state.

[0010] Furthermore, to improve the packing property of inorganic powders, it is effective to use a base material with high fluidity. This is because inorganic powders have a high degree of freedom of movement in a base material with high fluidity, enabling dense packing. In this regard, Patent Documents 1 and 2 use resins, rubbers, and polymers as base materials, which have limitations in improving the packing property of inorganic powders by increasing the fluidity of the materials.

[0011] Furthermore, as disclosed in Patent Document 2, materials that use silicone gel as a base material may generate siloxane gas when electronic components generate heat, which can cause malfunctions. For example, siloxane gas may accumulate on conductors, causing poor contact. Therefore, although a highly fluid material other than silicone gel is desired as a heat dissipation measure, especially for components that generate a large amount of heat, no effective material has been known.

[0012] The present inventors have conducted extensive research in light of these problems, and as a result have discovered that a grease containing copper powder as inorganic powder, a base oil, and a dispersant in predetermined proportions can have a high inorganic powder loading, and therefore has excellent thermal conductivity and electromagnetic wave shielding properties as well as good fluidity, making it suitable for use as a thermally conductive, electromagnetic wave shielding grease.

[0013] The present invention was completed based on these findings, and an object of the present invention is to provide a thermally conductive, electromagnetic wave shielding grease that is excellent in thermal conductivity and electromagnetic wave shielding properties and also exhibits good fluidity. [Means for solving the problem]

[0014] The present invention encompasses the following aspects (1) to (6). In this specification, the expression "to" includes the numerical values ​​at both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0015] (1) A composition comprising a first inorganic powder, a base oil, and a dispersant; the first inorganic powder is copper powder, A thermally conductive electromagnetic wave shielding grease, wherein the content of the first inorganic powder is 65% by volume or more and 85% by volume or less, and the content of the dispersant is 0.5% by volume or more and 3.0% by volume or less.

[0016] (2) further containing a second inorganic powder; the second inorganic powder is at least one powder selected from the group consisting of carbon, carbon nanotubes, graphene, aluminum, silicon, copper oxide, aluminum oxide, zinc oxide, titanium oxide, magnesium oxide, beryllium oxide, manganese oxide, tin oxide, silicon oxide, cerium oxide, germanium oxide, boron nitride, aluminum nitride, silicon carbide, silicon nitride, and diamond; The thermally conductive electromagnetic wave shielding grease of (1) above, wherein the content of the second inorganic powder is 0.01% by volume or more and 30% by volume or less.

[0017] (3) The thermally conductive, electromagnetic wave shielding grease according to (1) or (2) above, wherein the first inorganic powder has an average particle size of 0.01 μm or more and 50 μm or less.

[0018] (4) further containing an antioxidant; The thermally conductive electromagnetic wave shielding grease according to (1) or (2) above, wherein the content of the antioxidant is 0.001% by volume or more and 1.0% by volume or less.

[0019] (5) The thermally conductive electromagnetic wave shielding grease according to (1) or (2) above, wherein the first inorganic powder is composed of two or more types of powders having different average particle sizes.

[0020] (6) The thermally conductive electromagnetic wave shielding grease according to (1) or (2) above, wherein the base oil is at least one selected from the group consisting of mineral oil, synthetic hydrocarbon oil, diester, polyol ester, and phenyl ether. [Effects of the Invention]

[0021] According to the present invention, there is provided a thermally conductive, electromagnetic wave shielding grease that is excellent in thermal conductivity and electromagnetic wave shielding properties and also exhibits good fluidity. DETAILED DESCRIPTION OF THE INVENTION

[0022] A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention. Furthermore, in this specification, any combination of suitable aspects can be adopted as long as technical consistency can be achieved. For example, one of the suitable numerical ranges can be combined with the other.

[0023] <<1. Thermally conductive electromagnetic wave shielding grease>> The thermally conductive electromagnetic wave shielding grease (hereinafter sometimes simply referred to as "grease") of this embodiment contains a first inorganic powder, a base oil, and a dispersant. The first inorganic powder is copper powder. The content of the first inorganic powder in the grease is 65% by volume or more and 85% by volume or less, and the content of the dispersant is 0.5% by volume or more and 3.0% by volume or less. Each component that makes up the grease will be described below.

[0024] (1) First inorganic powder The first inorganic powder is copper powder. Copper has an especially high thermal conductivity among metals. Specifically, the thermal conductivity of copper (386-402 W / mK) is higher than that of aluminum (226-237 W / mK) and iron (72-80.4 W / mK). The use of copper powder can impart excellent heat dissipation properties to the grease.

[0025] Furthermore, the use of copper powder can impart electromagnetic wave shielding properties to the grease. The copper powder is dispersed in a matrix component, such as a base oil, contained in the grease. In other words, the particles that make up the copper powder are separated by the matrix component. Because the matrix component has electrical insulation properties, electrostatic capacitance occurs in the matrix component interposed between the particles. It is believed that the matrix exhibits a dielectric relaxation phenomenon, or that the capacitance component (C component) of the matrix interacts with the resistance component (R component) and / or inductance component (L component) of the copper powder to exhibit a resonance phenomenon, increasing dielectric loss at a specific frequency, thereby exhibiting electromagnetic wave shielding properties.

[0026] The content of the first inorganic powder (copper powder) in the grease is 65% by volume or more and 85% by volume or less. Increasing the content of copper powder can improve the heat dissipation and electromagnetic wave shielding properties of the grease. That is, in the grease, copper powder with high thermal conductivity forms a heat conduction path, while matrix components such as base oil with low thermal conductivity act as thermal resistance components. Increasing the content of copper powder suppresses the influence of the thermal resistance components, thereby improving the heat dissipation properties of the grease.

[0027] Furthermore, the higher the copper powder content, the smaller the average spacing between the particles constituting the copper powder, i.e., the smaller the thickness of the matrix component interposed between the particles. As a result of the increased capacitance, the effective dielectric constant of the material as a whole increases, thereby improving the electromagnetic wave shielding properties. From the viewpoint of obtaining excellent heat dissipation properties and electromagnetic wave shielding properties, a high copper powder content is desirable. The content is preferably 70% by volume or more, more preferably 75% by volume or more, and even more preferably 80% by volume or more.

[0028] On the other hand, if the copper powder content is too high, the fluidity of the grease will deteriorate, making it difficult to apply to semiconductor components and heat dissipation components.To maintain fluidity, the copper powder content was limited to 85% by volume or less.

[0029] Preferably, the average particle size of the first inorganic powder (copper powder) is 0.01 μm or more and 50 μm or less. Fine copper powder is expensive, which increases production costs and makes handling difficult. Furthermore, because of its high specific surface area, a large amount of base oil is required to wet the surface, which makes it difficult to increase the copper powder content. By making the average particle size of the copper powder 0.01 μm or more, the consistency of the grease can be adjusted within an appropriate range and oil separation can be prevented. The average particle size is more preferably 1.0 μm or more, and even more preferably 5.0 μm or more. On the other hand, copper powder with an excessively large particle size is difficult to achieve high filling. Another problem is that the coating film obtained by applying the grease becomes too thick. The average particle size is more preferably 40.0 μm or less, and even more preferably 30.0 μm or less.

[0030] Preferably, the average aspect ratio of the first inorganic powder (copper powder) is 5.0 or less. The average aspect ratio is the average value of the aspect ratios of the particles constituting the copper powder. The aspect ratio is also the ratio of the major axis diameter to the minor axis diameter of each particle (major axis diameter / minor axis diameter). By using powder with a small average aspect ratio, the packing property of the powder can be improved, and as a result, the heat dissipation properties and electromagnetic wave shielding properties of the grease can be further improved. From the viewpoint of achieving high packing, a small average aspect ratio is preferable. The average aspect ratio may be 4.0 or less, 3.0 or less, or 2.0 or less.

[0031] Preferably, the first inorganic powder (copper powder) is composed of two or more types of powder with different average particle sizes. This allows for even higher packing density of the copper powder. For example, when the copper powder contains coarse particles and fine particles, the fine particles fill the gaps between the coarse particles. This allows for dense packing of the copper powder while maintaining the fluidity of the grease, thereby further improving the heat dissipation properties and electromagnetic wave shielding properties. The first inorganic powder may be composed of three or four types of powder with different average particle sizes.

[0032] When the first inorganic powder (copper powder) is composed of four types of powder, it may be composed of a large powder having an average particle size of 5 μm to 50 μm, a medium powder having an average particle size of 1 μm to less than 5 μm, a small powder having an average particle size of 0.3 μm to less than 1 μm, and a fine powder having an average particle size of 0.01 μm to less than 0.3 μm. In this case, the blending ratio of each powder is not particularly limited. However, it is preferable that the ratio of the large powder is 40% to 90% by volume, the ratio of the medium powder is 10% to 40% by volume, the ratio of the small powder is 10% to 30% by volume, and the ratio of the fine powder is 1% to 15% by volume, relative to the total amount of the first inorganic powder. Furthermore, it is preferable to decrease the ratio of the medium powder to the fine powder as the particle size decreases. By blending in such ratios, the powders can be filled in a balanced manner, preventing oil separation and imparting the required consistency to the grease.

[0033] (2) Second inorganic powder The grease may further contain a second inorganic powder, which is at least one powder selected from the group consisting of carbon, carbon nanotubes, graphene, aluminum, silicon, copper oxide, aluminum oxide, zinc oxide, titanium oxide, magnesium oxide, beryllium oxide, manganese oxide, tin oxide, silicon oxide, cerium oxide, germanium oxide, boron nitride, aluminum nitride, silicon carbide, silicon nitride, and diamond.

[0034] The addition of the second inorganic powder can further increase the thermal conductivity of the grease. The addition of the second inorganic powder can also change the frequency characteristics of the electromagnetic wave shielding properties, specifically the peak frequency of the transmission attenuation rate. Therefore, by controlling the material and amount of the second inorganic powder, it is possible to improve the electromagnetic wave shielding properties and heat dissipation properties in the desired frequency range.

[0035] The content of the second inorganic powder in the grease is preferably 0.01% by volume or more and 30% by volume or less. By increasing the content to 0.01% by volume or more, the effects of the second inorganic powder can be efficiently exerted. The content may be 0.05% by volume or more, or even 0.1% by volume or more. On the other hand, if the content of the second inorganic powder exceeds 30% by volume, the heat dissipation properties and electromagnetic wave shielding properties based on the first inorganic powder (copper powder) may be impaired. The content may be 25.0% by volume or less, or even 20.0% by volume or less.

[0036] The total content of the first inorganic powder and the second inorganic powder in the grease is preferably 85% by volume or less. If the total amount of inorganic powders (first inorganic powder, second inorganic powder) is excessively large, the amount of base oil will be relatively small, which may result in reduced fluidity. By keeping the total amount of inorganic powders at 85% by volume or less, the necessary fluidity can be imparted to the grease.

[0037] The particle size of the second inorganic powder is preferably appropriately small. This allows the particles of the second inorganic powder to fill the gaps between the particles that make up the first inorganic powder (copper powder). For example, if the first inorganic powder is composed of four types of powder: large, medium, small, and fine powder, the average particle size of the second inorganic powder is preferably similar to or smaller than the medium powder contained in the first inorganic powder. If the average particle size of the second inorganic powder is similar to or larger than the large powder, the second inorganic powder will be exposed on the surface of the coating film obtained by applying the grease, making it difficult to fully obtain the effects of the second inorganic powder.

[0038] (3) Base oil The base oil is a component that imparts fluidity to the grease. The base oil is not particularly limited as long as it is one that can be used in grease. Examples include hydrocarbon-based base oils such as mineral oil and synthetic hydrocarbon oil, ester-based base oil, ether-based base oil, phosphate ester, silicone oil, and / or fluorine oil, and among these, hydrocarbon-based base oil, ester-based base oil, and / or ether-based base oil are preferred. Silicone oil and fluorine oil have low surface tension and may cause oil separation. The base oil may be used alone or in combination of two or more.

[0039] Mineral oils are obtained by refining mineral oil-based lubricating oil fractions. Refining can be carried out by appropriately combining techniques such as solvent extraction, solvent dewaxing, hydrorefining, hydrocracking, and wax isomerization. Specific examples of mineral oils include 150 neutral oil, 500 neutral oil, bright stock, and high viscosity index base oils, with highly hydrogenated high viscosity index base oils being particularly preferred.

[0040] Preferably, the base oil content in the grease is 13% by volume or more and 35% by volume or less. Increasing the content to 13% by volume or more can impart sufficient fluidity to the grease. From the viewpoint of improving the fluidity of the grease, the base oil content is preferably 15.0% by volume or more, and more preferably 20.0% by volume or more. On the other hand, by keeping the content to 35% by volume or less, it becomes possible to fully exhibit the heat dissipation properties and electromagnetic wave shielding properties based on the inorganic powders (first inorganic powder, second inorganic powder). From the viewpoint of improving the heat dissipation properties and electromagnetic wave shielding properties, the base oil content is preferably 30.0% by volume or less, and more preferably 25.0% by volume or less.

[0041] (4) Dispersant The dispersant is a component that functions as a surface modifier. That is, it adsorbs to the surface of the inorganic powders (first inorganic powder, second inorganic powder) and improves the affinity with the base oil. Adding the dispersant improves the dispersibility of the inorganic powders. The dispersant is not particularly limited as long as it has the effect of improving dispersibility. However, acid-based dispersants, basic-based dispersants, or dispersants having both properties are preferred because they are more likely to achieve the desired effect.

[0042] The content of the dispersant in the grease is 0.5% by volume or more and 3.0% by volume or less. A content of less than 0.5% by volume is insufficient to make the surface of the inorganic powder lipophilic. The inorganic powder tends to aggregate and harden the grease, making it difficult to increase the filling rate of the inorganic powder. On the other hand, if the content exceeds 3.0% by volume, the viscosity of the grease may become excessively high. A grease with high filling ability can be obtained with a content within the above range. The content of the dispersant is preferably 0.5% by volume or more and 2.5% by volume or less, and more preferably 1.0% by volume or more and 2.0% by volume or less.

[0043] (5) Other additives The grease may contain other additives such as antioxidants, base oil diffusion inhibitors, thickeners, etc., as long as the additives do not impair the desired properties.

[0044] Antioxidants are used to prevent oxidation of base oils, but also function to prevent oxidation of copper powder. Examples of antioxidants include known compounds used in greases, specifically hindered amine-based, hindered phenol-based, sulfur-based, phosphorus-based, benzotriazole-based, triazine-based, benzophenone-based, benzoate-based, and HALS-based compounds. Among these, hindered amine-based compounds are particularly preferred due to their excellent effects. As the antioxidant, one type of compound may be used alone, or multiple types of compounds may be used in combination.

[0045] The content of the antioxidant in the grease is not particularly limited. However, a small amount is preferable, specifically, 0.001% by volume or more and 1% by volume or less. By making the content 0.001% by volume or more, the antioxidant's effect can be fully exerted, and oxidation of the base oil and copper powder can be prevented. On the other hand, by keeping the content 1% by volume or less, a decrease in hardening performance and thermal durability due to an increase in the viscosity of the grease can be suppressed.

[0046] The base oil diffusion inhibitor functions to prevent the diffusion of the base oil. After the grease is applied, the base oil in the grease may diffuse (bleed) from the coating film over time. The use of the base oil diffusion inhibitor can suppress the bleed of the base oil. As the base oil diffusion inhibitor, a perfluoroalkyl group-containing compound is preferred, and a perfluoroalkyl group-containing compound having the structure represented by the following (A) is particularly preferred.

[0047] [ka]

[0048] Rf shown in (A) above 1 , Rf 2 and Rf 3are the same or different perfluoroalkyl groups having 1 to 6 carbon atoms, and may be linear or branched. X is CO or SO, and Y is any one of various solvent-solubilizing groups selected from the group consisting of anionic, amphoteric, nonionic, and oligomeric groups.

[0049] As the thickener, polybutene, polymethacrylate, fatty acid salt, urea compound, petroleum wax, polyethylene wax, organically treated bentonite, and / or silica, etc., can be used.

[0050] (6) Grease characteristics The grease of this embodiment has excellent thermal conductivity and electromagnetic wave shielding properties. Specifically, the thermal conductivity is 1.0 W / mK or more, 2.0 W / mK or more, 3.0 W / mK or more, 4.0 W / mK or more, or 5.0 W / mK or more. The transmission attenuation rate in the frequency range of 1.0 GHz to 6.0 GHz is 10 dB or more, 15 dB or more, 20 dB or more, or 25 dB or more.

[0051] When evaluating electromagnetic wave shielding performance (transmission attenuation rate), it is desirable to mold the grease into a sheet to suppress its fluidity. The grease of this embodiment has excellent fluidity. Therefore, if the grease is measured as is, there is a risk of contaminating the equipment during measurement. Forming the grease into a sheet prevents equipment contamination. The sheet can be produced by the following procedure. First, a resin to suppress fluidity is added to the grease, and the resin is melted and stirred in a heating furnace. Next, an appropriate amount of grease with added resin is applied to a PET film, and another PET film is placed on top, and the two PET films are sandwiched between the two PET films. The grease sandwiched between the PET films is heated to a temperature above the softening point and below the melting point of the resin and rolled out in a rolling mill to form a sheet. There is no specific requirement for the resin to be used; a resin with a melting point that matches the heating temperature of the heating furnace or rolling mill can be selected.

[0052] Furthermore, the grease of this embodiment has an appropriate viscosity and exhibits good fluidity. The shear viscosity at a shear rate of 6 (1 / sec) is typically 10.0 Pa·s or more and 200.0 Pa·s or less.

[0053] <<2. Manufacturing method of thermally conductive electromagnetic wave shielding grease>> The method for producing the grease of this embodiment is not limited to any particular method as long as it can uniformly mix the components, and examples include a method in which the components are mixed and kneaded using a device such as a mortar, a planetary mill, or a twin-screw extruder to form a grease-like mixture, and then further kneaded uniformly using a triple-roll mill. [Example]

[0054] The present invention will be described in more detail using the following examples, but the present invention is not limited to the following examples.

[0055] (1) Preparation of grease The following raw materials were used to prepare the greases of the Examples and Comparative Examples.

[0056] - First inorganic powder: 15 types of copper powder with different average particle sizes - Second inorganic powder: magnesium oxide powder with an average particle size of 0.05 μm (Example 6), aluminum nitride powder with an average particle size of 0.05 μm (Example 7), copper oxide powder with an average particle size of 0.05 μm (Example 8), titanium oxide powder with an average particle size of 0.05 μm (Comparative Example 5) - Base oil: Ester base oil (NOF Corporation, H-281R) - Dispersant: Acid-based higher fatty acid polyester (Lubrizol Japan, HPA-N107) - Antioxidant: n-phenyl-1-naphthylamine (Tokyo Chemical Industry Co., Ltd.) - Diffusion inhibitor: Megafac F554 (DIC Corporation)

[0057] [Examples 1 to 5 and Comparative Examples 1 to 4] A first inorganic powder (copper powder), a base oil (ester-based base oil), and a dispersant (acid-based higher fatty acid polyester) were prepared as raw materials and kneaded in a three-roll mill (manufactured by Inoue Seisakusho Co., Ltd.) to produce grease. The copper powder shown in Table 1 below was used as the first inorganic powder. Specifically, in Example 1, copper powder with an average particle size of 10 μm was used alone, while in Examples 2 to 5 and Comparative Examples 1 to 4, two or more types of copper powder with different average particle sizes were used in combination. The blending amounts of copper powder (first inorganic powder), base oil, and dispersant were adjusted to the values ​​shown in Table 2 below.

[0058] [Examples 6 to 8 and Comparative Example 5] Grease was prepared by mixing a first inorganic powder (copper powder), a base oil (ester-based base oil), a dispersant (acid-based higher fatty acid polyester), a second inorganic powder, an antioxidant, and a diffusion inhibitor. The copper powder shown in Table 1 below was used as the first inorganic powder. The magnesium oxide powder (Example 6), aluminum nitride powder (Example 7), copper oxide powder (Example 8), and titanium oxide powder (Comparative Example 5) were used as the second inorganic powder. The amounts of the copper powder (first inorganic powder), base oil, dispersant, antioxidant, and diffusion inhibitor were adjusted to the values ​​shown in Table 2 below.

[0059] (2) Evaluation The greases obtained in Examples 1 to 8 and Comparative Examples 1 to 5 were evaluated for various properties as follows.

[0060] <Heat dissipation characteristics (thermal conductivity)> The thermal conductivity of the grease was measured at room temperature using a thermal conductivity measuring device (Mentor Graphics, DynTimS). The higher the thermal conductivity, the better the radiation performance of the grease.

[0061] <Electromagnetic wave shielding characteristics (transmission attenuation rate)> To evaluate the electromagnetic wave shielding performance (transmission attenuation rate), the grease was molded into a sheet. The sheet was produced using the following procedure. First, a resin was added to the grease, and the resin was melted and stirred in a heating furnace. The resins used were a wax-based resin with a melting point of 80°C and rosin with a melting point of 90°C for the purpose of releasing the film. Next, an appropriate amount of the grease with the added resin was applied to a PET film, and another PET film was placed on top, sandwiching the two PET films together. The grease sandwiched between the PET films was heated and rolled out in a rolling mill to form a sheet. The rolling mill temperature was set to 70°C, and a sheet measuring 100 mm long, 60 mm deep, and 1 mm high was produced.

[0062] Next, the electromagnetic wave shielding properties of the grease sheet were evaluated using the microstrip line method. Specifically, a vector network analyzer and a measuring jig (Keycom Corporation, TF-6C) were used to measure the reflection coefficient (S 11 ) and permeability coefficient (S 21 ) was measured. 11 and S 21 Using the above, the transmission attenuation rate R is calculated according to the following equation (1). tp asked for.

[0063]

number

[0064] (3) Evaluation results The evaluation results of the obtained samples are shown in Table 2. The sample containing one type of copper powder (Example 1) had a thermal conductivity of 1.7 W / mK. The transmission attenuation rate in the 5 GHz band was 15.0 dB.

[0065] Comparing a sample containing one type of copper powder (Example 1) with a sample containing four types of copper powder (Example 2), although the copper powder content was almost the same, Example 2 had a higher thermal conductivity and transmission attenuation rate. By using multiple types of copper powder with different particle sizes, fine powder filled the gaps between the coarse powder, which is thought to have improved the heat dissipation properties and electromagnetic wave shielding properties.

[0066] Furthermore, by using three or four types of copper powder with different average particle sizes, the blending ratio of the copper powder could be adjusted (Examples 2 to 5). Furthermore, the higher the blending ratio of copper powder, the higher the thermal conductivity and transmission attenuation rate. In particular, Example 5 had a high blending ratio of copper powder, at 85% by volume. Therefore, both the thermal conductivity (5.6 W / mK) and transmission attenuation rate (26.0 dB) were high.

[0067] In contrast, the sample with too low an inorganic powder content (Comparative Example 1) had too much base oil and therefore low viscosity. It was unable to maintain its shape after application and spread wetly. Grease evaluation was not performed because an appropriate evaluation was not possible. Conversely, the sample with too high an inorganic powder content (Comparative Example 2) had too little base oil and did not become grease-like after kneading. Therefore, evaluation was not possible. The sample with too little dispersant (Comparative Example 3) had inorganic powder agglomerate during kneading and did not become a smooth grease-like material. Therefore, an appropriate grease evaluation was not possible. The sample with too much dispersant (Comparative Example 4) hardened after kneading, making an appropriate grease evaluation impossible. It is believed that the excess dispersant became entangled and hardened.

[0068] Examples 6 to 8 and Comparative Example 5 are samples containing a second inorganic powder. Comparing Example 7 with Example 3, which has approximately the same copper powder content, it can be seen that adding the second inorganic powder improves only the thermal conductivity, while the transmission attenuation rate does not change significantly. Furthermore, comparing Examples 7 and 8, it can be seen that the rate of improvement in thermal conductivity can be changed by changing the type and content of the second inorganic powder. On the other hand, the sample (Comparative Example 5), which contains a higher content of the second inorganic powder, had a lower thermal conductivity and transmission attenuation rate, even though the total amount of inorganic powder (first inorganic powder, second inorganic powder) was the same as in Example 5. Because the second inorganic powder has a lower thermal conductivity than copper powder, it is thought that this resulted in poorer thermal conductivity even when the total amount of inorganic powder was the same, and poorer electromagnetic wave shielding properties due to the small amount of copper powder.

[0069] In all samples, the average aspect ratio of the first inorganic powder (copper powder) was 2.0 or less.

[0070] As described above, in the grease of this embodiment, the peak frequency of the transmission attenuation rate can be controlled by adjusting the content of the first inorganic powder (copper powder), thereby achieving the desired electromagnetic wave shielding characteristics. Furthermore, the thermal conductivity value can be controlled by adjusting the type and amount of the second inorganic powder. Therefore, the grease of this embodiment is suitable for use in miniaturized electronic components where electromagnetic waves and heat generation are significant.

[0071] [Table 1]

[0072] [Table 2]

Claims

1. Contains a first inorganic powder, a base oil, and a dispersant; the first inorganic powder is copper powder; A thermally conductive electromagnetic wave shielding grease, wherein the content of the first inorganic powder is 65% by volume or more and 85% by volume or less, and the content of the dispersant is 0.5% by volume or more and 3.0% by volume or less.

2. Further containing a second inorganic powder, the second inorganic powder is at least one powder selected from the group consisting of carbon, carbon nanotubes, graphene, aluminum, silicon, copper oxide, aluminum oxide, zinc oxide, titanium oxide, magnesium oxide, beryllium oxide, manganese oxide, tin oxide, silicon oxide, cerium oxide, germanium oxide, boron nitride, aluminum nitride, silicon carbide, silicon nitride, and diamond; 2. The thermally conductive, electromagnetic wave shielding grease according to claim 1, wherein the content of the second inorganic powder is 0.01% by volume or more and 30% by volume or less.

3. 3. The thermally conductive, electromagnetic wave shielding grease according to claim 1, wherein the first inorganic powder has an average particle size of 0.01 μm or more and 50 μm or less.

4. Further containing an antioxidant, 3. The thermally conductive electromagnetic wave shielding grease according to claim 1, wherein a content of the antioxidant is 0.001% by volume or more and 1.0% by volume or less.

5. 3. The thermally conductive electromagnetic wave shielding grease according to claim 1, wherein the first inorganic powder is composed of two or more types of powders having different average particle sizes.

6. 3. The thermally conductive electromagnetic wave shielding grease according to claim 1, wherein the base oil is at least one selected from the group consisting of mineral oil, synthetic hydrocarbon oil, diester, polyol ester, and phenyl ether.

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