Thermal conductive composition having electromagnetic interference suppression ability

Abstract

Provided is a thermally conductive composition which exhibits effective electromagnetic interference suppression capability even in a higher frequency band, and has high thermal conductivity, thereby enabling the stable industrial manufacture of members capable of solving both electromagnetic interference and heat dissipation in recent electronic devices which are highly advanced. A thermally conductive composition according to the present invention has an electromagnetic interference suppression capability and contains one or more types of powder, the thermally conductive composition being characterized in that: one of the powders is α-type silicon carbide powder; and in powder X-ray diffraction of the thermally conductive composition using Cu-Kα as a radiation source, a value I4H / I6H, obtained by dividing a peak intensity I4H derived from 4H-SiC appearing at 2θ=34.4-35° by a peak intensity I6H derived from 6H-SiC appearing at 2θ=35-36°, is 0.01 or more.

Description

[Technical Field]

[0001] The present invention relates to a heat conduction composition having electromagnetic interference suppression ability. [Background technology]

[0002] With the advancement of communications, electronic equipment circuits are becoming more integrated and denser. As a result, the amount of heat generated by devices on these circuits increases, making heat dissipation measures crucial. Thermal conductive materials are used to solve this problem. Thermal conductive materials consist of a highly thermally conductive filler supported in a soft resin, and are available in grease, putty, and sheet forms depending on the application. Thermal conductive materials fill the space gap between the device on the circuit and the heat sink, and their function is to transfer heat from the device to the heat sink. Therefore, the development of thermal conductive materials is becoming increasingly important as a heat dissipation measure for electronic equipment. Since thermal conductive materials make direct contact with the device on the circuit, materials with high electrical resistance are preferable.

[0003] As electronic circuits become more integrated and denser, electromagnetic interference problems are becoming a serious issue in addition to heat dissipation measures. For example, while previous mobile communications have used frequency bands ranging from several hundred MHz to around 3 GHz, fifth-generation mobile systems (5G) are considering using frequency bands up to 60 GHz, which is higher than those. In addition, as electronic devices become lighter, thinner, and smaller, the spatial margin in their internal structures is decreasing, making electromagnetic interference problems in electrical and electronic circuits even more serious. Noise suppression sheets are used to solve this electromagnetic interference problem. Noise suppression sheets consist of a resin on which fillers such as soft magnetic powder are supported, and they convert noise into heat through electromagnetic loss.

[0004] The noise suppression performance of a noise suppression sheet depends on the permeability of the soft magnetic powder contained in the sheet. Generally, permeability is expressed as complex permeability μ = μ' - jμ'' using the real permeability μ' and the imaginary permeability μ'', where μ' represents the measure of noise absorption and μ'' represents the measure of noise conversion into heat. When magnetic loss is utilized, as in noise suppression sheets, μ'' becomes important. That is, it is important that μ'' is distributed across the frequency band of the radio wave noise to be suppressed. On the other hand, when considering an electromagnetic interference suppression sheet for equipment that utilizes millimeter-wave radio waves, it may be more flexible in designing the electromagnetic interference suppression sheet to support a non-magnetic conductive material in a resin substrate to provide electrical loss, rather than using a magnetic filler, which is difficult to achieve high permeability in the millimeter-wave band, as a loss material.

[0005] In terms of solving the two problems of heat and electromagnetic interference in electronic devices, thermal conductive materials and noise suppression sheets are often used in close proximity inside electronic devices. Recently, as mentioned above, in addition to the shrinking space inside electrical equipment, there has been a growing need for hybrid materials of thermal conductive materials and noise suppression sheets from a cost perspective and from the standpoint of functional integration of materials, and thermal conductive materials with electromagnetic interference suppression capabilities exist. Among these, as mentioned above, as the frequency of electronic devices increases, there is a growing need for thermal conductive sheets with electromagnetic interference suppression capabilities in the millimeter-wave band. For example, Patent Document 1 (Japanese Patent No. 6737979) discloses a thermal conductive composition and sheet with electromagnetic interference suppression capabilities corresponding to frequencies of 18 to 26.5 GHz. Patent Document 1 states that by configuring the resin matrix to contain predetermined amounts of carbonyl iron powder and thermal conductive powder, the imaginary part of the magnetic permeability can be made 0.9 or more in at least a part of the 18 to 26.5 GHz band.

[0006] Patent Document 2 (JP 2022-052761) discloses a thermally conductive electromagnetic interference (EMI) absorber that has high thermal conductivity and efficiently absorbs microwaves. The thermally conductive electromagnetic interference (EMI) absorber is said to have a thermal conductivity of at least 6 watts per meter per kelvin (W / mK) and an attenuation of more than 15 decibels per centimeter (dB / cm) at frequencies of 10 gigahertz (GHz) or higher.

[0007] However, Patent Document 1 does not mention the effect of suppressing electromagnetic interference in high-frequency bands such as 26.5 GHz or higher, nor does it describe a specific solution, so it cannot be expected to be effective in noise countermeasures for electronic equipment used in the millimeter-wave band. Furthermore, regarding thermal conductivity, while it states that a thermal conductivity of 2 W / mK or higher can be obtained in the sheet form, only examples with a thermal conductivity of less than 3 W / mK are disclosed. In today's electronic equipment, where heat generation is increasing, a thermal conductivity of 3 W / mK or higher is sometimes required, but Patent Document 1 does not have a configuration that can meet this requirement. Patent Document 2 adds 80 volume% or more of filler, which may result in low flexibility and make it impractical for use as a sheet or grease. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6737979 [Patent Document 2] Special Publication No. 2022-052761 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, in view of the above problems, the present invention aims to provide a thermal conductive composition having electromagnetic interference suppression ability that exhibits effective electromagnetic interference suppression ability even in higher frequency bands, while also having high thermal conductivity, thereby enabling the industrially stable production of components that can simultaneously solve the electromagnetic interference and heat dissipation problems of today's increasingly sophisticated electronic devices. [Means for solving the problem]

[0010] To solve the above problems, the inventors have diligently conducted research and obtained the following findings. Specifically, by using a powder mainly composed of α-type silicon carbide (SiC) as the dielectric loss material supported on the substrate, which provides lightness and high insulation, and by using α-type silicon carbide (SiC) whose X-ray diffraction data falls within predetermined conditions, it is possible to provide a thermal conductive composition that exhibits effective electromagnetic interference suppression even in higher frequency bands while simultaneously having high thermal conductivity.

[0011] Based on the above findings, the gist of the present invention is as follows. [1] A thermal conductive composition having electromagnetic interference suppression ability, comprising one or more types of powders, One of the aforementioned powders is α-type silicon carbide powder. In powder X-ray diffraction using Cu-Kα as a source in the aforementioned heat-conducting composition, the peak intensity I, which originates from 4H-SiC, appears at 2θ = 34.4~35°. 4H The peak intensity I, which appears at 2θ = 35~36°, originates from 6H-SiC. 6H The value I obtained by dividing by 4H / I 6H However, it is characterized by being 0.01 or greater. A heat-conducting composition having electromagnetic interference suppression capabilities.

[0012] [2] The average particle size of the α-type silicon carbide powder is 1 μm or more and 180 μm or less. The volume ratio of the entire powder to the entire heat-conducting composition is 45% or more and 80% or less. A thermal conductive composition having the electromagnetic interference suppression ability described in [1] above.

[0013] [3] The powder further includes one or more powders of metal magnetic powder and thermally conductive powder, The average particle size of the α-type silicon carbide powder is 30 μm or more and 180 μm or less, The volume ratio of the α-type silicon carbide powder to the entire thermally conductive composition is 10% or more and 75% or less, which is characterized by, The thermally conductive composition having electromagnetic interference suppression ability according to [1] above.

[0014] [4] The powder includes the metal magnetic powder, The particle size of the metal magnetic powder is 1 μm or more and 7 μm or less, The volume ratio of the metal magnetic powder to the entire thermally conductive composition is 5% or more and 65% or less, The ratio of the average particle size of the α-type silicon carbide powder to the average particle size of the metal magnetic powder is 4 or more, which is characterized by, The thermally conductive composition having electromagnetic interference suppression ability according to [3] above.

[0015] [5] The powder includes the thermally conductive powder, The average particle size of the thermally conductive powder is 0.1 μm or more and 1 μm or less, The volume ratio of the thermally conductive powder to the entire thermally conductive composition is 1% or more and 15% or less, which is characterized by, The thermally conductive composition having electromagnetic interference suppression ability according to [3] or [4] above.

[0016] [6] The thermal conductivity of the thermally conductive composition measured by the hot disk method is 1 W / mK or more, which is characterized by the thermally conductive composition having electromagnetic interference suppression ability according to any one of [1] to [5] above.

[0017] [7] The I 4H / I 6H is 0.1 or more, which is characterized by the thermally conductive composition having electromagnetic interference suppression ability according to any one of [1] to [6] above.

[0018] [8] A heat conductive composition having electromagnetic interference suppression ability according to any one of [1] to [7] above, characterized in that the heat conductive composition is in the form of a sheet, putty, or grease.

[0019] [9] A thermal conductive composition having electromagnetic interference suppression ability as described in any of [1] to [8] above, for use in near-field noise suppression applications.

[0020]

[10] A thermal conductive composition having electromagnetic interference suppression ability, comprising one or more types of powders, It is intended for near-field noise suppression applications. The radio wave attenuation at 40 GHz exceeds 1 dB / cm. The thermal conductivity of the aforementioned heat-conducting composition, as measured by the hot disk method, is 3 W / mK or higher. A heat-conducting composition having electromagnetic interference suppression capabilities. [Effects of the Invention]

[0021] The heat-conducting composition of the present invention exhibits effective electromagnetic interference suppression even in higher frequency bands, while simultaneously possessing high thermal conductivity. Therefore, it is possible to industrially and stably manufacture components that can simultaneously solve the electromagnetic interference and heat dissipation problems of today's increasingly sophisticated electronic devices. [Brief explanation of the drawing]

[0022] [Figure 1] An example of a scanning electron microscope image of a sheet prepared using the heat-conducting composition of the present invention is shown. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described below.

[0024] (Thermal conductive composition) The thermal conductive composition of the present invention is a thermal conductive composition having electromagnetic interference suppressing ability and containing one or more kinds of powders, wherein one of the powders is α-type silicon carbide powder, and in the powder X-ray diffraction using Cu-Kα as a radiation source in the thermal conductive composition, the peak intensity I 4H derived from 4H-SiC appearing at 2θ = 34.4 to 35° is divided by the peak intensity I 6H derived from 6H-SiC appearing at 2θ = 35 to 36°, and the value I 4H / I 6H is 0.01 or more, which may be a thermal conductive composition having electromagnetic interference suppressing ability.

[0025] Also, the thermal conductive composition of the present invention has electromagnetic interference suppressing ability at 40 GHz, and preferably, the radio wave attenuation amount at 40 GHz exceeds 1 dB / cm. The thermal conductive composition of the present invention is a thermal conductive composition having electromagnetic interference suppressing ability and containing one or more kinds of powders, wherein the radio wave attenuation amount at 40 GHz exceeds 1 dB / cm, and the thermal conductivity measured by the hot disk method of the thermal conductive composition is 3 W / mK or more, which may be a thermal conductive composition having electromagnetic interference suppressing ability. In this case, the thermal conductive composition of the present invention can be suitably used for applications that suppress noise in the near field.

[0026] The thermal conductive composition of the present invention usually contains the one or more kinds of powders and a base resin, and the powders are supported in the base resin.

[0027] [Base resin] The base resin used in this invention is preferably a thermosetting resin, and silicone resins, acrylic resins, epoxy resins, urethane resins, etc., can be used. Among these, silicone resins or acrylic resins, which have excellent heat resistance, are particularly preferred as the base resin, given that the heat resistance temperature inside electronic devices often exceeds 100°C today. There are no particular restrictions on the form of the resin raw material; it can be used in either a granular or liquid form, but it should be selected according to the form of the final heat conductive composition. For example, if a grease-like heat conductive composition is to be obtained, a liquid form should be used. Here, as a representative example, an embodiment using liquid silicone resin as the resin base material will be described.

[0028] Liquid silicones can be commercially available general industrial-grade silicones. Silicones come in liquid form as one-component and two-component types (main component and curing agent), and in curing form as condensation reaction type and addition reaction type; however, either type can be applied in this invention. Condensation reaction type requires time to cure, but addition reaction type can be expected to cure in a relatively short time by including a heating step. Therefore, when obtaining sheet-like or putty-like heat-conducting compositions, it is preferable to use the addition reaction type from a productivity standpoint. On the other hand, when obtaining a grease-like heat-conducting composition, if the addition reaction type is used, the heating step is omitted, and the mixture with the powder filler is filled into a dispenser tube to form the final product. Liquid silicones with a viscosity of 1 to 10 Pa·s are preferable, as excessively low viscosity results in poor shape retention during sheet molding, while excessively high viscosity makes homogeneous dispersion of the powder filler difficult.

[0029] [Powder] The powder is usually supported in a base resin. The powder may contain α-type silicon carbide powder as described below. If the powder contains α-type silicon carbide powder, it may further contain other types of powders, such as metallic magnetic powder, thermally conductive powder, flame retardant, etc.

[0030] [Silicon carbide powder] When the heat-conducting composition of the present invention contains silicon carbide powder, the silicon carbide powder plays a role in controlling the thermal conductivity and electromagnetic interference suppression ability of the heat-conducting composition. Therefore, the present invention can be established simply by supporting a predetermined silicon carbide powder as a powder.

[0031] The average particle size of the silicon carbide powder is preferably 1 μm or more, more preferably 30 μm or more, and may also be 65 μm or more, 90 μm or more, or 105 μm or more. Furthermore, the average particle size of the silicon carbide powder is preferably 180 μm or less, and more preferably 120 μm or less. When supporting only silicon carbide powder as the powder, it is preferable to use multiple types of silicon carbide powder with different particle sizes so that the powder approaches a repacked structure. In addition, to obtain a thermal conductive composition with high thermal conductivity, it is necessary to use a predetermined amount of filler with high thermal conductivity and large particle size. In this invention, silicon carbide powder with an average particle size of preferably 1 μm or more, more preferably 30 μm or more, and preferably 180 μm or less is used. If the average particle size is less than 1 μm or less than 30 μm, the desired thermal conductivity cannot be obtained. Furthermore, because silicon carbide is a very hard material, if the average particle size exceeds 180 μm, it may cause damage to the device surface or other components in contact with the thermal conductive composition. Also, if the thermal conductive composition is in the form of a putty or sheet, it is prone to tearing of the substrate when bent. In general, large-particle silicon carbide powder used in this invention is specified by particle size rather than average particle size, and a particle size of #320 to #80 is preferred for the silicon carbide powder used in this invention.

[0032] In this specification, the "average particle size" of various powders (e.g., silicon carbide powder, metal magnetic powder described later, thermal conductive powder) is determined by the following procedure. First, a backscattered electron image of the thermal conductive composition is taken using a scanning electron microscope. If the thermal conductive composition is in sheet or putty form, a cross-section of the thermal conductive composition polished by ion milling is taken. The magnification of the image should be set to 150x to 10000x according to the powder particle size to improve measurement accuracy. 10000x is good if the powder particles are mainly small, such as 1 μm, and 150x is good if the powder particles are mainly large, such as 180 μm. Next, in the captured image, the maximum diameter of each powder is taken as the particle size of that powder, and the average value of the particle sizes of all the various powders in the captured field of view is defined as the "average particle size" of the various powders contained in the thermal conductive composition. Powders that reach the edge of the captured image or powders with a particle size (maximum diameter) of less than 0.1 μm in the captured image are excluded from the measurement. Furthermore, if multiple types of powder exist, the separation is performed by identifying the type of each powder.

[0033] Industrially usable silicon carbide powders include those with an α-type structure for grinding and polishing applications, and those with a β-type structure for sintering applications. However, this invention uses α-type silicon carbide powder. α-type silicon carbide powder comes in a high-purity green type and a lower-purity black type. This invention can use either the green or black type of silicon carbide powder, and these powders are characterized by their crystal structure. Pure silicon carbide is an insulator, and the presence of impurities causes it to exhibit semiconductor properties. Semiconductor silicon carbide exhibits relatively large dielectric loss in the millimeter-wave band, making it suitable for application in electromagnetic interference suppressors used in the millimeter-wave band. Therefore, a desired thermal conductivity composition can be obtained by controlling the crystal structure, particle size, and amount of silicon carbide powder. The black type is characterized by a higher content of impurity elements such as Al and Fe compared to the green type. Generally, the black type contains 0.1-0.2 mass% Al and 0.1-0.3 mass% Fe, while the green type contains 0.01-0.1 mass% Al and 0.02-0.03 mass% Fe. In this invention, it is preferable to use a low-purity black type silicon carbide powder as a filler. It is also possible to identify the content of Al and Fe, which are impurity elements of silicon carbide. In this case, for example, the Al and Fe content can be detected by surface analysis of the silicon carbide powder by EPMA (WDS: wavelength-dispersive X-ray spectroscopy) on the polished surface (ion-milled surface, etc.) of the thermal conductive composition.

[0034] In this invention, silicon carbide powder with an α-type crystal structure may be used, and in powder X-ray diffraction using Cu-Kα as a source in the thermal conductive composition, the peak intensity I, which originates from 4H-SiC and appears at 2θ = 34.4~35°, is also observed. 4H The peak intensity I, which appears at 2θ = 35~36°, originates from 6H-SiC. 6H The value I obtained by dividing by 4H / I 6HThe value is preferably 0.01 or higher, more preferably 0.1 or higher, even more preferably 0.2 or higher, and even more preferably 0.3 or higher. Furthermore, there is no particular upper limit, but 0.5 or lower is preferred. The crystal structure of silicon carbide mainly consists of a tetrahedron as its minimum structure, and the stacking structure of these tetrahedra results in the existence of mainly 4H-type (4H-SiC) and 6H-type (6H-SiC) forms. High-purity green-type silicon carbide is predominantly 6H-structured, with a small proportion of 4H-type. On the other hand, low-purity black-type silicon carbide contains a mixture of 4H-type and 6H-type, with a larger proportion of 4H-type. 4H / I 6H A larger value indicates greater dielectric loss, and a superior electromagnetic interference suppression effect can be expected. The α-type silicon carbide powder contained in the heat-conducting composition of the present invention can be identified by X-ray diffraction using Cu-Kα as the source on the surface of the heat-conducting composition. The measurement conditions for X-ray diffraction in the present invention are as follows.

[0035] <Device> Manufacturer: Rigaku Equipment name: Fully automatic horizontal multipurpose powerful X-ray diffractometer SmartLab (9kW) Tube:Cu <Optical system conditions> CBO Select Slit: BB Incident parallel slit (Soller / PSC): 5.0deg Longitudinal limiting slit (IS longitudinal): 10.0 mm Photodetector (PSA): None Light-receiving parallel slit (Soller): 5.0 degrees <Measurement conditions> Scan axis: 2θ / θ, Mode: Continuous, Range specification: Absolute Speed ​​counting time: 3.0 degrees / min Scan: 20 degrees to 80 degrees Data acquisition interval: 0.01 degrees IS: 1 / 2 degree, Light-receiving slit RS1: 8.0 mm Light-receiving slit RS2: 13.0 mm Attenuator: Open

[0036] The procedure for analyzing the measurement data is as follows: Using Rigaku's integrated powder X-ray analysis software PDXL, the value yobs-bkg, obtained by subtracting bkg from the diffraction intensity data yobs, was used to exclude the background influence of the obtained data. In the range of 2θ = 34.4~35°, the value obtained by subtracting the minimum value from the maximum value of yobs-bkg was used to represent the peak intensity I originating from 4H-SiC. 4H Similarly, in the range of 2θ = 35~36°, the value obtained by subtracting the minimum value from the maximum value of yobs-bkg is the peak intensity I originating from 6H-SiC. 6H Let's assume that.

[0037] When the thermal conductive composition contains only α-type silicon carbide powder as a powder (filler), the volume ratio of silicon carbide powder to the total thermal conductive composition is preferably 45% or more, more preferably 50% or more, preferably 80% or less, and more preferably 75% or less. When the thermal conductive composition containing only α-type silicon carbide powder as a powder (filler) is used as a grease, the volume ratio of silicon carbide powder to the total thermal conductive composition can be 45% or more. When the thermal conductive composition containing only α-type silicon carbide powder as a powder (filler) is used as a sheet, the volume ratio of silicon carbide powder to the total thermal conductive composition can be 64% or more, preferably 70% or more. On the other hand, if the thermal conductive composition contains other powders (e.g., metallic magnetic powder, thermal conductive powder, etc.) in addition to α-type silicon carbide powder as a powder (filler), the volume ratio of silicon carbide powder to the total thermal conductive composition is preferably 10% or more, more preferably 30% or more, preferably 75% or less, and more preferably 40% or less.

[0038] In this specification, the "volume ratio" of various powders (e.g., silicon carbide powder, metal magnetic powder described later, thermal conductive powder) is determined by the following procedure. Using the backscattered electron images used to determine the "average particle size" of the various powders described above, the images of the various powders and the substrate are binarized to separate the various powders from the substrate. Once the separation is complete, the type of powder is identified, and the area ratio of each powder is determined according to the type of powder. This is defined as the "volume ratio (volume ratio to the entire thermal conductive composition)" of the various powders. When performing the binarization process, the settings can be adjusted as appropriate to ensure that the boundary between the various powders and the substrate is clear. Furthermore, if there are multiple types of powders, the types of powders can be identified and separated by multi-level processing, and the area ratio of each powder according to its particle size can be determined to obtain the "volume ratio" of each.

[0039] [Metal magnetic powder] In this invention, the metallic magnetic powder plays a role in controlling the thermal conductivity and electromagnetic interference suppression ability of the thermal conductive composition, but its role in controlling electromagnetic interference suppression ability is more significant. As the metallic magnetic powder, for example, carbonyl iron powder can be used, but any metallic magnetic powder that exhibits μ'' in the high-frequency band (e.g., frequencies of 26.5 GHz or higher) can be used, including FeSiAl alloy, FeSi alloy, FeSiCr alloy, FeSiB amorphous, and FeSiBNbCu nanocrystalline alloy. Among these, carbonyl iron powder is preferred from the viewpoint that (1) it has a high saturation magnetization due to its iron concentration of 95% or more, and a higher magnetic permeability than other materials can be expected in the high-frequency band, and (2) technology for industrially producing powder with an average particle size of 7 μm or less has been established. Magnetic materials with high saturation magnetization tend to have higher magnetic permeability at high frequencies.

[0040] To minimize the skin effect in the high-frequency range, the particle size of the metal magnetic powder is preferably 1 μm or larger, more preferably 3 μm or larger, preferably 7 μm or smaller, and more preferably 4 μm or smaller. If the average particle size is less than 1 μm, there is no established industrially inexpensive manufacturing method, and the thermal conductivity of the thermal conductive composition will also be low due to the smaller particle size.

[0041] The volume ratio of the metallic magnetic powder to the total thermal conductivity composition is preferably 5% or more, more preferably 30% or more, preferably 65% ​​or less, and more preferably 40% or less. Furthermore, the ratio of the average particle size of the α-type silicon carbide powder to the particle size of the metallic magnetic powder is preferably 4 or more, more preferably 9 or more, as this facilitates the formation of heat conduction pathways by the fillers distributed within the composition, thereby increasing thermal conductivity.

[0042] [Thermally conductive powder] In the present invention, the desired thermal conductivity composition can be obtained by using, for example, silicon carbide powder and metallic magnetic powder as fillers. However, if it is desired to further increase the thermal conductivity, a thermal conductive powder with a particle size smaller than that of the metallic magnetic powder can be added to fill the gaps between the metallic magnetic powder particles. From the viewpoint of increasing thermal conductivity, a thermal conductivity composition containing silicon carbide powder and thermal conductive powder, but without metallic magnetic powder, may also be used. As the thermal conductive powder, for example, aluminum oxide powder can be used, but other powders that perform the same function as aluminum oxide powder, such as those with high thermal conductivity, such as silicon carbide, aluminum nitride, boron nitride, magnesium oxide, and barium titanate, can also be used. Fine-particle aluminum oxide powder is widely used in known thermal conductivity compositions and is preferred from the viewpoint of being readily available.

[0043] From the viewpoint of filling the gaps between the metal magnetic powders, the average particle size of the aluminum oxide powder is preferably 0.1 μm or more, more preferably 0.3 μm or more, preferably 1 μm or less, and more preferably 0.9 μm or less.

[0044] The volume ratio of the thermally conductive powder to the total thermal conductive composition is preferably 1% or more, more preferably 5% or more, preferably 15% or less, and more preferably 10% or less. If the volume ratio of the thermally conductive powder becomes too large, the volume ratio of silicon carbide powder to carbonyl iron powder decreases, and the thermal conductivity of the thermal conductive composition decreases. The ratio of the average particle size of the metallic magnetic powder to the average particle size of the thermally conductive powder is preferably greater than 1, more preferably greater than 4, as this facilitates the formation of heat conduction pathways by the fillers distributed within the composition, thereby increasing thermal conductivity.

[0045] [Other additives] In addition to silicon carbide powder, metal magnetic powder, and thermally conductive powder, other additives such as flame retardants, fillers, plasticizers, dispersants, and antioxidants may be added to the base resin as needed, provided that they do not reduce thermal conductivity or electromagnetic interference suppression effects. For example, flame retardants that do not pose an environmental burden are preferred, and examples include hydroxyl compounds such as aluminum hydroxide and magnesium hydroxide, and nitrogen compounds such as melamine cyanurate. Furthermore, red phosphorus, a flame retardant aid, can also be added if necessary.

[0046] [Other characteristics of the heat conductive composition] The volume ratio of the total powder to the total heat conductive composition is preferably 45% or more, more preferably 50% or more, preferably 80% or less, and more preferably 75% or less. When the heat conductive composition is used as grease, the volume ratio of the total powder to the total heat conductive composition can be 45% or more. When the heat conductive composition is used as a sheet, the volume ratio of the total powder to the total heat conductive composition can be 64% or more, preferably 70% or more.

[0047] The thermal conductivity of the thermal conductive composition of the present invention is preferably 1 W / mK or higher, more preferably 3 W / mK or higher, and even more preferably 4 W / mK or higher. The thermal conductivity is measured by the hot disk method. The measurement of thermal conductivity by the hot disk method conforms to ISO 22007-2. As the apparatus and measuring sensor used in the hot disk method, for example, those described in the examples can be used.

[0048] The thermal conduction composition of the present invention exhibits effective electromagnetic interference suppression even in high frequency bands. As an indicator of electromagnetic interference suppression in high frequency bands, the thermal conduction composition of the present invention preferably exhibits a large value of radio wave attenuation at 40 GHz, specifically, preferably exceeding 1 dB / cm, more preferably exceeding 11 dB / cm, and even more preferably exceeding 20 dB / cm. The radio wave attenuation at 40 GHz can be measured, for example, in accordance with the method described in the examples.

[0049] (Manufacturing method for heat-conducting compositions) The heat-conducting composition of the present invention can be obtained by mixing one or more of the above-mentioned powders with a base resin, for example, by kneading. The kneading process of mixing the base resin and the above-mentioned powders will be described below. Kneading can be achieved by any of the following methods: planetary agitator, kneader, three-roll mixer, Banbarrier mixer, twin-screw mixer, etc. In this case, if hardening progresses due to the heat generated by the material during kneading, it is necessary to knead under cooling. In addition, in order to obtain a final product free of air bubbles, it is preferable to perform degassing by reducing the pressure at any timing during the kneading process. If the heat-conducting composition obtained after kneading is to become a grease product, it is filled into a tube for a dispenser. On the other hand, if it is to become a putty or sheet, the process proceeds to the molding process described below.

[0050] The resulting mixture can be molded into a putty-like or sheet-like form by any of the following methods: compression molding, extrusion molding, or rolling molding. As an example, in the case of compression molding, the mixture is placed into a mold with grooves formed so that the molded putty-like or sheet-like heat-conducting composition has a predetermined thickness (generally 25 to 5000 μm), and compression molding is performed under conditions that allow the silicone to vulcanize (temperature 80 to 200°C, time 5 to 60 minutes). In this case, in order to improve the release properties between the molded product and the mold, a release agent (fluorine-based is preferable if it is silicone) may be applied to the mold in advance, or the mixture can be sandwiched between PET films coated with a release agent and molded in the mold.

[0051] (Applications of thermal conductive materials) The thermal conductive composition of the present invention is suitably used for applications that suppress near-field noise. In particular, it is suitably used as a thermally conductive near-field noise suppression sheet, near-field noise suppression putty, near-field noise suppression grease, etc. It should be noted that the thermal conductive composition of the present invention is specialized for thermal conductivity applications, and applications other than thermal conductivity, such as radio wave absorption applications (e.g., radio wave absorption sheets), are excluded from the present invention. Furthermore, by adjusting the particle size and amount of additives in the material composition of the present invention, it can also be used as a radio wave absorber for far-field applications, so it can be applied when both thermal conductivity and far-field radio wave absorption are required. [Examples]

[0052] The present invention will be described below with reference to examples of sheet-like and grease-like heat-conducting compositions, but the present invention is not limited to these.

[0053] <Characteristic Evaluation> "Average particle size" The measurement conditions and analysis procedures were as described in the embodiments. When multiple types of silicon carbide powder with different average particle sizes were used (Tables 1 and 4 below), the average particle size values ​​of the various silicon carbide powders as raw materials before mixing are shown.

[0054] "Volume % (Volume ratio to the total heat-conducting composition)" The measurement conditions and analysis procedures were as described in the embodiments. When multiple types of silicon carbide powder with different average particle sizes were used (Tables 1 and 4 below), the volume ratios of the various silicon carbide powders as raw materials before mixing are shown.

[0055] I calculated from X-ray diffraction measurements 4H / I 6H 』 The measurement conditions and analysis procedures were as described in the embodiment, and the results are shown in Tables 1 to 5.

[0056] Thermal conductivity The measurement of thermal conductivity using the hot disk method conforms to ISO 22007-2. The measurement results for thermal conductivity were categorized as follows: C for 1.0 W / mK or higher and less than 2.5 W / mK, B for 2.5 W / mK or higher and less than 4.0 W / mK, and A for 4.0 W / mK or higher. [Device] Manufacturer: Hot Disk AB Device name: TPS2500 [Measurement Sensor] Manufacturer: Hot Disk AB Sensor name: RTK sensor φ7

[0057] "Amount of radio wave attenuation" [Device] Manufacturer: KEYSIGHT TECHNOLOGY Device name: Vector Network Analyzer P5008A [Waveguide] Manufacturer: EM Lab Device name: R-band waveguide sample holder fixture WSF-R [Measurement conditions] Frequency: 40GHz [Measurement method] A rectangular sample measuring 7.112 × 3.556 mm was cut from the prepared sheet, and the sample was inserted into an R-band waveguide sample holder fixture. S11 and S21 were measured, and the resulting absorption amount of the sample was divided by the sample thickness to determine the radio wave attenuation (dB / cm). The measurement results of the radio wave attenuation were classified as follows: × for 1 dB / cm or less, C for greater than 1 dB / cm and 11 dB / cm or less, B for greater than 11 dB / cm and 20 dB / cm or less, and A for greater than 20 dB / cm.

[0058] (Examples 1-12, Comparative Examples 1-2) Alpha-type silicon carbide powders of different particle sizes were added to liquid silicone resin. The mixture, kneaded in a planetary stirrer, was poured into a mold with grooves formed to ensure the resulting sheet would be of a predetermined thickness. Compression molding was performed at a mold temperature of 160°C for 20 minutes to produce a sheet with a thickness of 1000 μm. Ten of these sheets were stacked, and their thermal conductivity was measured using the hot disk method. A rectangular sample measuring 7.112 × 3.556 mm was cut from one of the sheets, and the radio wave attenuation (dB / cm) at 40 GHz was determined using a waveguide. Examples 1-4, Examples 8-12, and Comparative Examples 1-2 use green type silicon carbide powder, while Examples 5-7 and Example 11 use black type silicon carbide powder. For example, Examples 5-7 are different from Examples 1-4. 4H / I 6H The value was large, and the radio wave attenuation was also large. From this, I 4H / I 6H A tendency was observed where the higher the value of [the variable], the greater the radio wave attenuation. When the total amount of silicon carbide powder fell below 70%, the thermal conductivity became relatively low. • Comparative Examples 1 and 2 are I 4H / I 6H The value was below 0.01, and the radio wave attenuation was also small.

[0059] [Table 1]

[0060] (Examples 13-23) Alpha-type silicon carbide powder, carbonyl iron powder, and aluminum oxide powder of different particle sizes were added to liquid silicone resin. Except for Example 22, the amount of each powder added was 35% silicon carbide powder, 35% carbonyl iron powder, and 5% aluminum oxide powder by volume relative to the total volume of the sheet substrate. The mixture, kneaded in a planetary stirrer, was poured into a mold with grooves formed so that the molded sheet would be of a predetermined thickness, and compression molding was performed at a mold temperature of 160°C for 20 minutes to produce a sheet with a thickness of 1000 μm. Ten of the produced sheets were stacked and the thermal conductivity was measured using the hot disk method. In addition, a rectangular sample of 7.112 × 3.556 mm was cut from one of the produced sheets, and the radio wave attenuation (dB / cm) at 40 GHz was determined using a waveguide.

[0061] [Table 2]

[0062] (Examples 24-35) The sheet preparation and evaluation methods were the same as those used in Examples 13 to 23. When the amount of aluminum oxide added exceeded 15%, the thermal conductivity became relatively low.

[0063] [Table 3]

[0064] (Examples 36-38) Alpha-type silicon carbide powders with different particle sizes were added to a liquid silicone resin (grease base material). The amount of each powder added was 50% by volume relative to the total volume of the grease base material. The mixture, kneaded using a planetary agitator, was filled into a dispenser container. The kneaded grease was then filled from the dispenser container into a liquid sample measuring jig for a hot disk, and its thermal conductivity was measured. In addition, the kneaded grease was filled into a 7.112 × 3.556 mm rectangular sample, and the radio wave attenuation (dB / cm) at 40 GHz was determined using a waveguide. Examples 36-38 all exhibited thermal conductivity exceeding 1 W / mK and radio wave attenuation exceeding 5 dB / cm, demonstrating that they were thermal conductive greases with practical electromagnetic interference suppression capabilities.

[0065] [Table 4]

[0066] (Examples 39-41) Alpha-type silicon carbide powder, carbonyl iron powder, and aluminum oxide powder of different particle sizes were added to liquid silicone resin. The amount of each powder added was 30% silicon carbide powder, 15% carbonyl iron powder, and 5% aluminum oxide powder by volume relative to the total volume of the sheet substrate. The mixture was mixed in a planetary stirrer and filled into a dispenser container. The mixed grease was then filled into a hot disk liquid sample measuring jig from the dispenser container, and its thermal conductivity was measured. In addition, the mixed grease was filled into a 7.112 × 3.556 mm rectangular sample, and the radio wave attenuation (dB / cm) at 40 GHz was determined using a waveguide. Examples 39 to 41 all exhibited thermal conductivity exceeding 1 W / mK and radio wave attenuation exceeding 5 dB / cm, demonstrating that they were thermal conductive greases with practical electromagnetic interference suppression capabilities.

[0067] [Table 5] [Industrial applicability]

[0068] The heat-conducting composition of the present invention is industrially useful because, when installed in electronic devices and the like, it exhibits effective electromagnetic interference suppression even in higher frequency bands, while simultaneously possessing high thermal conductivity. This allows for the industrially stable production of components that can simultaneously solve the electromagnetic interference and heat dissipation problems of today's increasingly sophisticated electronic devices.

Claims

1. A heat conduction composition having electromagnetic interference suppression ability, comprising one or more types of powders, One of the aforementioned powders is α-type silicon carbide powder. In powder X-ray diffraction using Cu-Kα as a source in the aforementioned heat conductive composition, the peak intensity I, which originates from 4H-SiC, appears at 2θ = 34.4 to 35°. ４Ｈ The peak intensity I, which appears at 2θ = 35-36°, originates from 6H-SiC. ６Ｈ The value I obtained by dividing by ４Ｈ / I ６Ｈ However, it is characterized by being 0.01 or greater. A heat-conducting composition having electromagnetic interference suppression capabilities.

2. The average particle size of the α-type silicon carbide powder is 1 μm or more and 180 μm or less. The volume ratio of the entire powder to the entire heat-conducting composition is 45% or more and 80% or less. A heat conduction composition having electromagnetic interference suppression ability as described in claim 1.

3. The powder further comprises one or more powders that are either metallic magnetic powder or thermally conductive powder. The average particle size of the α-type silicon carbide powder is 30 μm or more and 180 μm or less. The volume ratio of the α-type silicon carbide powder to the total heat-conducting composition is 10% or more and 75% or less. A heat conduction composition having electromagnetic interference suppression ability as described in claim 1.

4. The powder includes the metal magnetic powder, The particle size of the aforementioned metal magnetic powder is 1 μm or more and 7 μm or less. The volume ratio of the metal magnetic powder to the total heat conductive composition is 5% or more and 65% or less. The ratio of the average particle size of the α-type silicon carbide powder to the average particle size of the metal magnetic powder is 4 or more. A heat conduction composition having electromagnetic interference suppression ability as described in claim 3.

5. The powder includes the thermally conductive powder, The average particle size of the thermally conductive powder is 0.1 μm or more and 1 μm or less. The thermally conductive powder is characterized in that its volume ratio to the entire thermally conductive composition is 1% or more and 15% or less. A heat conduction composition having electromagnetic interference suppression ability according to claim 3 or 4.

6. A heat-conducting composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, characterized in that the thermal conductivity of the heat-conducting composition measured by the hot disk method is 1 W / mK or more.

7. The above I ４Ｈ / I ６Ｈ A heat conduction composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, characterized in that the value is 0.1 or greater.

8. A heat conduction composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, characterized in that the heat conduction composition is in the form of a sheet, putty, or grease.

9. A thermal conductive composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, for use in near-field noise suppression applications.

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