Thermally conductive silicone potting composition and cured product thereof

Abstract

[Problem] To provide a thermally conductive silicone potting composition that has low viscosity and high flowability in spite of containing a large amount of a thermally conductive filler, is capable of flowing into a minute space, and exhibits a desired thermal conductivity after being cured. [Solution] The thermally conductive silicone potting composition comprises: (A) 100 parts by mass of a linear organopolysiloxane having, on average, 0.5 to 1.8 alkenyl groups bonded to a silicon atom at a molecular chain terminal per molecule; (B) 500-2,000 parts by mass of a thermally conductive filler; (C) 0.1 to 100 parts by mass of an organohydrogensiloxane having at least two SiH groups in one molecule; and (D) a hydrosilylation reaction catalyst.

Description

Thermally conductive silicone potting composition and its cured product

[0001] The present invention relates to a thermally conductive silicone potting composition and a cured product thereof.

[0002] In response to growing awareness of global warming, the automotive industry is developing environmentally friendly vehicles, such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, with the aim of reducing greenhouse gas emissions. To improve their fuel efficiency, inverters installed in these vehicles are becoming more powerful and smaller. Accordingly, components such as ICs and reactors within the inverters are becoming smaller, resulting in increased heat generation. Conventionally, for such heat-generating components, the cooling efficiency of the components has been improved and the components protected by interposing a thermally conductive silicone composition, such as a thermally conductive silicone grease composition, a thermally conductive silicone gel composition, or a thermally conductive silicone potting composition, between the heat-generating component and the cooler.

[0003] For example, Patent Document 1 proposes a method of thermally connecting the heat-generating component and the cooler by assembling the cooler and the heat-generating component in advance and then pouring a highly fluid thermally conductive silicone potting composition therein. However, when the method of Patent Document 1 is used to maintain practical fluidity, the thermal conductivity is limited to about 1.0 W / m K, which is insufficient to deal with the further increase in heat generation that accompanies the recent trend toward miniaturization of devices and miniaturization of components.

[0004] As a technique for solving this problem, Patent Documents 2 to 5 propose silicone potting compositions that contain a large amount of thermally conductive filler to achieve high thermal conductivity while also maintaining high fluidity.

[0005] However, while these compositions have high fluidity, they also have high viscosity, and with the recent trend toward smaller devices and more miniaturized components, it can be difficult to pot every corner of the components, making it impossible to impart sufficient heat dissipation properties. For this reason, in order to improve the performance of inverters, there is a strong demand for thermally conductive silicone potting materials that not only have high thermal conductivity and high fluidity, but also have lower viscosity.

[0006] JP 2011-122000 A JP 2016-084378 A JP 2019-077843 A JP 2019-077845 A JP 2021-113290 A

[0007] The present invention has been made in view of the above circumstances, and its object is to provide a thermally conductive silicone potting composition that, despite containing a large amount of thermally conductive filler, has low viscosity and high flowability, is able to flow into minute spaces, and has a desired thermal conductivity after curing.

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors discovered that by using a base polymer with a specified amount of functional groups, it is possible to obtain a thermally conductive silicone potting composition that has low viscosity and high flowability, despite containing a large amount of thermally conductive filler, and this discovery led to the completion of the present invention.

[0009] That is, the present invention provides: 1. a thermally conductive silicone potting composition comprising: (A) 100 parts by mass of a linear organopolysiloxane having an average of 0.5 to 1.8 alkenyl groups bonded to silicon atoms at the molecular chain terminals per molecule; (B) 500 to 2,000 parts by mass of a thermally conductive filler; (C) 0.1 to 100 parts by mass of an organohydrogensiloxane having at least two SiH groups per molecule; and (D) a hydrosilylation reaction catalyst; 2. the thermally conductive silicone potting composition of 1, wherein the linear organopolysiloxane of component (A) has a viscosity of 10 to 500 mPa·s at 25°C as measured with a Brookfield type rotational viscometer; 3. (E) a thermally conductive silicone potting composition comprising a silane compound represented by the following general formula (1) and an organopolysiloxane represented by the following general formula (2) in an amount of 0.1 to 30 parts by mass per 100 parts by mass of component (A); (In the formula, R 1are each independently a monovalent hydrocarbon group, and n is an integer of 0 to 30. 4. A thermally conductive silicone potting composition according to claim 3, in which the thermally conductive filler (B) has been surface-treated with component (E); 5. A thermally conductive silicone potting composition according to claim 1, in which the viscosity at 25°C is 30 Pa·s or less; 6. A cured product obtained by curing any of the thermally conductive silicone potting compositions according to claims 1 to 5.

[0010] Before curing, the thermally conductive silicone potting composition of the present invention has low viscosity and high flowability, allowing it to flow into minute spaces, and after curing, it achieves the desired thermal conductivity and is able to protect the heat-generating component without peeling off. For this reason, the composition of the present invention is effective for potting components with fine structures, such as transformers, that are fixed to coolers. In such components, after curing, the composition has high thermal conductivity, allowing heat from the component to be efficiently transferred to the cooler, making it highly reliable even when used in high-temperature environments.

[0011] The present invention will now be described in detail. The thermally conductive silicone potting composition of the present invention cures at room temperature or under heat and adheres to metals, organic resins, etc., and contains the following essential components (A) to (D): (A) an alkenyl group-containing organopolysiloxane, (B) a thermally conductive filler, (C) an organohydrogensiloxane, and (D) a hydrosilylation reaction catalyst.

[0012] [1] Component (A) Component (A) is a linear organopolysiloxane having an average of 0.5 to 1.8 alkenyl groups per molecule bonded to silicon atoms at the molecular chain terminals. The average number of alkenyl groups in component (A) is preferably 0.8 to 1.8, and more preferably 1.0 to 1.6, per molecule. If the number of alkenyl groups is less than 0.5, the strength of the cured product will be low or the composition will not cure, while if the number exceeds 1.8, the flowability of the composition will be reduced.

[0013] The viscosity of component (A) at 25°C is preferably 10 to 500 mPa·s, more preferably 10 to 200 mPa·s, and even more preferably 10 to 100 mPa·s. If the viscosity at 25°C is 10 mPa·s or higher, the composition will have excellent storage stability, and if it is 500 mPa·s or lower, the composition will have good flowability. The above viscosity is measured using a B-type rotational viscometer (the same applies hereinafter).

[0014] The alkenyl group bonded to the silicon atom is not particularly limited, but is preferably an alkenyl group having 2 to 10 carbon atoms, and more preferably an alkenyl group having 2 to 8 carbon atoms. Specific examples include vinyl, allyl, 1-butenyl, and 1-hexenyl groups, and among these, vinyl groups are preferred from the standpoints of ease of synthesis and cost.

[0015] The organic group bonded to the silicon atom other than the alkenyl group is not particularly limited, but is preferably a monovalent hydrocarbon group having 1 to 20 carbon atoms excluding aliphatic unsaturated bonds, and more preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms excluding aliphatic unsaturated bonds. Specific examples thereof include alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-hexyl, and n-dodecyl; aryl groups such as phenyl; and aralkyl groups such as 2-phenylethyl and 2-phenylpropyl. Some or all of the hydrogen atoms in these hydrocarbon groups may be substituted with halogen atoms such as chlorine, fluorine, and bromine. Specific examples thereof include halogen-substituted monovalent hydrocarbon groups such as fluoromethyl, 2-bromoethyl, chloromethyl, and 3,3,3-trifluoropropyl. Of these, the organic group bonded to the silicon atom other than the alkenyl group is preferably an alkyl group having 1 to 5 carbon atoms, and from the standpoint of ease of synthesis and cost, it is even more preferable that 90 mol % or more of these groups be methyl groups.

[0016] Component (A) preferably does not contain an organoxysilyl group, and examples of organoxy groups include alkoxy groups, alkoxyalkoxy groups, alkenyloxy groups, and acyloxy groups. Examples of alkoxy groups include those having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms, such as methoxy and ethoxy groups. Examples of alkoxyalkoxy groups include those having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, such as methoxyethoxy and methoxypropoxy groups. Examples of alkenyloxy groups include those having 2 to 6 carbon atoms, such as vinyloxy and allyloxy groups. Examples of acyloxy groups include those having 1 to 10 carbon atoms, such as acetyloxy and octanoyloxy groups.

[0017] [2] Component (B) Component (B) is a thermally conductive filler that imparts thermal conductivity to the composition. Conventional thermally conductive fillers can be used, including aluminum powder, copper powder, silver powder, nickel powder, gold powder, alumina powder, zinc oxide powder, magnesium oxide powder, aluminum nitride powder, aluminum hydroxide powder, boron nitride powder, silicon nitride powder, diamond powder, carbon powder, indium, and gallium. These thermally conductive fillers may be used alone or in combination. To impart sufficient thermal conductivity to the composition, the thermally conductive filler preferably has a thermal conductivity of 10 W / m·K or higher. The average particle size of the thermally conductive filler is preferably 0.1 to 100 μm, more preferably 0.5 to 90 μm. This range suppresses aggregation of thermally conductive filler particles and provides excellent flowability. The average particle size in the present invention is the median diameter (D50) of the volume-based particle size distribution measured by laser diffraction. The thermally conductive filler may have any shape, such as an irregular shape or a spherical shape.

[0018] The blending amount of component (B) is 500 to 2,000 parts by mass, and preferably 800 to 1,500 parts by mass, per 100 parts by mass of component (A). If the blending amount is less than 500 parts by mass, sufficient thermal conductivity may not be obtained, and if the blending amount exceeds 2,000 parts by mass, the composition may become highly viscous or have reduced flowability.

[0019] [3] Component (C) Component (C) is an organohydrogensiloxane having at least two, preferably three or more, and more preferably 3 to 100 silicon-bonded hydrogen atoms (SiH groups) per molecule. The molecular structure of the organohydrogensiloxane of component (C) may be linear, branched, or network, and multiple organohydrogensiloxane chains may be linked by linking groups. The silicon-bonded hydrogen atoms may be present either at the molecular chain terminals (both terminals or one terminal) or non-terminal portions of the molecular chain, or may be present in both.

[0020] The organic groups other than hydrogen atoms bonded to silicon atoms in component (C) include monovalent hydrocarbon groups having 1 to 10 carbon atoms, excluding alkenyl groups. Specific examples include alkyl groups such as methyl, ethyl, propyl, and butyl; aryl groups such as phenyl and tolyl; aralkyl groups such as phenylethyl and phenylpropyl; and halogenated alkyl groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as chlorine, fluorine, and bromine, such as γ-chloropropyl and 3,3,3-trifluoropropyl. Among these, alkyl groups having 1 to 6 carbon atoms are preferred, and alkyl groups having 1 to 3 carbon atoms are more preferred. In particular, from the standpoints of ease of synthesis and cost, it is more preferred that 90 mol % or more of the organic groups other than hydrogen atoms be methyl groups.

[0021] The kinematic viscosity of component (C) at 25°C is not particularly limited, but is preferably 1 to 10,000 mm 2 / s is preferred, and 1 to 1,000 mm 2 The kinematic viscosity is a value measured at 25°C using a Cannon-Fenske viscometer (the same applies hereinafter). Several types of component (C) with different viscosities may be used in combination.

[0022] Component (C) may be a compound containing a cyclic organohydrogensiloxane represented by the following general formula (3-1) and / or a cyclic organohydrogensiloxane represented by the following general formula (3-2). These compounds have the roles of crosslinking with component (A) and imparting adhesiveness.

[0023]

[0024] In each of the above formulas, R 2 are each independently an alkyl group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and specific examples thereof include methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl groups. Among these, R 2 Preferably, 90 mol % or more of the groups are methyl groups.

[0025] R 3 are each independently an epoxy group or a trialkoxysilyl group bonded to a silicon atom via a carbon atom or via a carbon atom and an oxygen atom. Examples of epoxy groups bonded to a silicon atom via a carbon atom or via a carbon atom and an oxygen atom include 3-glycidoxypropyl, 3-glycidoxyethyl, and 3,4-epoxycyclohexylethyl groups. Examples of trialkoxysilyl groups bonded to a silicon atom via a carbon atom or via a carbon atom and an oxygen atom include trimethoxysilylpropyl, trimethoxysilylpropylmethyl, trimethoxysilylethyl, triethoxysilylpropyl, triethoxysilylpropylmethyl, and triethoxysilylethyl groups.

[0026] In formula (3-1), i is an integer of 2 or greater, j is an integer of 1 or greater, and i+j is an integer of 4 to 12, preferably an integer of 4 to 8, more preferably an integer of 4 to 6, and even more preferably 4. The order of arrangement of the siloxane units in formula (3-1) may be arbitrary, and may be random, block, or alternating. In formula (3-2), X is a divalent hydrocarbon group which may contain an ether bond, and is preferably a group containing a bisphenol A residue represented by the following formula (4). Each k is independently an integer of 3 to 11, preferably an integer of 3 to 7, more preferably an integer of 3 to 5, and even more preferably 3.

[0027] (The dashed lines represent bonds to the silicon atom.)

[0028] Specific examples of component (C) include, but are not limited to, organohydrogensiloxanes represented by the following formula: Component (C) may be used alone or in combination of two or more types.

[0029]

[0030] The amount of component (C) blended is preferably 0.1 to 100 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of component (A) from the viewpoints of curability and mechanical properties of the cured product. If the amount is less than 0.1 part by mass, curing will be insufficient, and if it exceeds 100 parts by mass, the mechanical properties of the cured product may be reduced.

[0031] [4] Component (D) Component (D) is a hydrosilylation catalyst. Any hydrosilylation catalyst that promotes the addition reaction between the alkenyl group of component (A) and the Si—H group of component (C) can be used, and any conventionally known catalyst can be used. Specifically, platinum group metal catalysts are preferred, and among these, catalysts selected from platinum and platinum compounds are preferred.

[0032] Specific examples of the catalyst include platinum (including platinum black); platinum group metals such as rhodium and palladium; platinum chlorides such as HPtCl.nH.sub.2O, HPtCl.nH.sub.2O, NaHPtCl.nH.sub.2O, KHPtCl.nH.sub.2O, NaPtCl.nH.sub.2O, KPtCl.nH.sub.2O, PtCl.nH.sub.2O, PtCl.nH.sub.2O, NaHPtCl.nH.sub.2O (wherein n is an integer of 0 to 6, preferably 0 or 6); chloroplatinic acid; chloride Examples of such a catalyst include platinate salts; alcohol-modified chloroplatinic acid; complexes of chloroplatinic acid with olefins; platinum group metals such as platinum black or palladium supported on a support such as alumina, silica or carbon; rhodium-olefin complexes; chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst); and complexes of platinum chloride, chloroplatinic acid or chloroplatinate salts with vinyl group-containing siloxanes. These may be used singly or in combination of two or more.

[0033] The amount of component (D) to be blended is an effective amount as a catalyst, and may be any amount sufficient to promote the reaction between components (A) and (C), and may be adjusted appropriately depending on the desired curing rate. In particular, an amount equivalent to 0.1 to 7,000 ppm, and more preferably 1 to 6,000 ppm, of platinum group metal atoms relative to the mass of component (A) is preferred. When the amount of component (E) is within the above range, more efficient catalytic action can be expected.

[0034] [5] Component (E) The thermally conductive silicone potting composition of the present invention preferably contains, as component (E), a silane compound represented by the following general formula (1) and an organopolysiloxane represented by the following general formula (2). This component acts on the surface of the thermally conductive filler and has the role of improving fluidity.

[0035] (In the formula, R 1 each independently represents a monovalent hydrocarbon group, and n represents an integer of 0 to 30.

[0036] R 1The monovalent hydrocarbon group is not particularly limited, but is preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, more preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms, and even more preferably a monovalent hydrocarbon group having 1 to 3 carbon atoms. Specific examples of monovalent hydrocarbon groups include alkyl, alkenyl, aryl, and aralkyl groups, as well as halogenated monovalent hydrocarbon groups such as halogenated alkyl groups in which some or all of the hydrogen atoms of these monovalent hydrocarbon groups have been substituted with halogen atoms such as chlorine, fluorine, or bromine. The alkyl group may be linear, branched, or cyclic. Specific examples include linear alkyl groups such as methyl, ethyl, n-propyl, n-hexyl, and n-octyl; branched alkyl groups such as isopropyl, isobutyl, tert-butyl, and 2-ethylhexyl; and cyclic alkyl groups such as cyclopentyl and cyclohexyl. Specific examples of alkenyl groups include vinyl, allyl, 1-butenyl, and 1-hexenyl. Specific examples of aryl groups include phenyl and tolyl. Specific examples of the aralkyl group include 2-phenylethyl and 2-methyl-2-phenylethyl groups. Specific examples of the halogenated alkyl group include 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, and 2-(heptadecafluorooctyl)ethyl groups. Among these, R 1 As the alkyl group, a methyl group, a phenyl group, or a vinyl group is preferred, and a methyl group is more preferred.

[0037] n is preferably an integer of 0 to 20, and more preferably an integer of 1 to 10.

[0038] When component (E) is used, the blending amount is 0.1 to 30 parts by mass, and more preferably 0.1 to 20 parts by mass, per 100 parts by mass of component (A). Within this range, a composition with high fluidity is likely to be obtained. Component (E) may be used alone, or two or more types may be used in combination.

[0039] [7] Other Components In addition to the components (A) to (E) above, the thermally conductive silicone potting composition of the present invention may contain known additives, provided that the additives do not impair the objectives of the present invention. Examples of such additives include reaction inhibitors that inhibit the curing reaction of the composition at room temperature and thereby extend shelf life and pot life. Any reaction inhibitor capable of suppressing the catalytic activity of component (D) can be used, and conventional reaction inhibitors can be used. Specific examples include acetylene alcohol compounds such as 1-ethynyl-1-cyclohexanol and 3-butyn-1-ol; nitrogen-containing compounds such as triallyl isocyanurate; organic phosphorus compounds; oxime compounds; and organic chloro compounds. These compounds may be used alone or in combination of two or more. Among these, 1-ethynyl-1-cyclohexanol and triallyl isocyanurate are preferred.

[0040] When a reaction retarder is used, the amount added is preferably 0.01 to 5 parts by mass, and more preferably 0.05 to 1 part by mass, per 100 parts by mass of component (A), taking into consideration the shelf life and pot life of the composition and the curability of the composition. The reaction retarder may be diluted with an organic solvent such as toluene, xylene, or isopropyl alcohol to improve dispersibility in the composition.

[0041] Additionally, the thermally conductive silicone potting composition of the present invention may also contain added hindered phenol-based antioxidants, reinforcing or non-reinforcing fillers such as calcium carbonate, and colorants such as pigments and dyes.

[0042] The thermally conductive silicone potting composition of the present invention can be prepared by mixing the above-mentioned components (A) through (D), and, if necessary, component (E) and other components, using a known method such as a gate mixer, kneader, or planetary mixer.

[0043] The thermally conductive silicone potting composition of the present invention may be a two-part composition in which a first part consisting of components (A), (B), and (D) and, if necessary, component (E) and other components, and a second part consisting of components (A), (B), and (C) and, if necessary, component (E) and other components, are prepared separately, and the first and second parts are mixed together before use. It is also possible for some components to be shared by both the first and second parts. By forming the composition into such a two-part composition, further storage stability can be ensured.

[0044] The viscosity of the thermally conductive silicone potting composition of the present invention at 25°C is preferably 1 to 30 Pa·s, and more preferably 1 to 20 Pa·s, from the viewpoints of dispersibility of the thermally conductive filler and workability. The viscosity is measured using a Brookfield type rotational viscometer at 20 rpm (approximate shear rate of 4.2 s -1 ) is a value measured. Furthermore, the thixotropic index value of the thermally conductive silicone potting composition after mixing and before curing is preferably 1.3 or less. If the thixotropic index after mixing and before curing exceeds 1.3, the composition may have poor fluidity, making it difficult for the composition to flow into heat-generating components having a fine structure. Here, the thixotropic index is the value measured using a Brookfield viscometer at 10 rpm (approximate shear rate of 2.1 s -1 The viscosity was measured at 20 rpm (shear rate approx. 4.2 s -1 ) divided by the viscosity value measured.

[0045] The thermally conductive silicone potting composition of the present invention preferably has a flowability of 100 mm or more at 23°C, the measurement method of which will be described in detail in the Examples below. When the silicone potting composition is poured into a cooler where a component with a fine structure, such as a transformer, is attached, the flowability is preferably 120 mm or more. The higher the flowability, the better, but because the measurement limit depends on the length of the aluminum plate, the upper measurement limit here is 400 mm.

[0046] The curing conditions for the thermally conductive silicone potting composition of the present invention are not particularly limited and can be the same as those for conventionally known silicone gels. After pouring, the thermally conductive silicone potting composition can be cured by heat from a heat-generating component, or by active heating. Heat curing conditions are preferably 60 to 180°C, more preferably 80 to 150°C, and are preferably 0.1 to 3 hours, more preferably 0.5 to 2 hours.

[0047] The thermal conductivity of the cured product of the thermally conductive silicone potting composition of the present invention at an ambient temperature of 25°C is preferably 1.5 W / m K or more, and more preferably 2.0 W / m K or more. There is no particular upper limit, but it is usually 10.0 W / m K or less. The hardness of the cured product, as measured with a Type A durometer, is preferably 10 or more, and there is no particular upper limit, but it is usually 80 or less.

[0048] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, the weight average molecular weight is a polystyrene equivalent value measured by gel permeation chromatography (GPC). The components used in the examples and comparative examples are shown below.

[0049] Component (A) A-1: ​​A dimethylpolysiloxane in which 80% of the terminals are blocked with dimethylvinylsilyl groups and 20% are blocked with trimethylsilyl groups, and which has a viscosity of 50 mPa·s at 25°C. A-2: A dimethylpolysiloxane in which both terminals are blocked with dimethylvinylsilyl groups, and which has a viscosity of 60 mPa·s at 25°C.

[0050] Component (B) B-1: Alumina powder with an average particle size of 1.0 μm B-2: Alumina powder with an average particle size of 10 μm B-3: Alumina powder with an average particle size of 40 μm B-4: Alumina powder with an average particle size of 80 μm

[0051] Component (C) C-1: Organohydrogensiloxane represented by the following formula:

[0052] C-2: Organohydrogensiloxane having an average structure represented by the following formula: (In the formula, the order of the siloxane units in parentheses is not specified.)

[0053] C-3: Cyclic organohydrogensiloxane represented by the following formula:

[0054] C-4: Cyclic organohydrogensiloxane derivative represented by the following formula:

[0055] Component (D) D-1: Dimethylpolysiloxane solution of platinum-divinyltetramethyldisiloxane complex (both ends of which are capped with dimethylvinylsilyl groups, dissolved in dimethylpolysiloxane having a viscosity of 0.6 Pa·s at 25°C; platinum concentration: 1% by mass)

[0056] Component (E) E-1: Trimethylsilanol

[0057] E-2: Organopolysiloxane represented by the following formula

[0058] (F) Other components F-1: 1-ethynyl-1-cyclohexanol F-2: triallyl isocyanurate

[0059] Examples 1-3, Comparative Examples 1-3 Components (A)-(E) and other components were mixed as follows to obtain a silicone potting composition. Components (A), (B), and (E) were added to a 5L gate mixer (manufactured by Inoue Seisakusho Co., Ltd., product name: 5L Planetary Mixer) in the amounts shown in Table 1, and mixed at 25°C for 1 hour. Then, the mixture was vacuum-mixed at 150°C for 2 hours to obtain a mixture (for Example 2, component (B) was surface-treated with component (E)). After cooling the mixture, component (D) was added and the mixture was mixed at 25°C for 30 minutes. Next, reaction inhibitors (F-1) and (F-2) were added and the mixture was mixed at 25°C for 30 minutes. Finally, component (C) was added and the mixture was mixed at room temperature for 30 minutes.

[0060] The resulting composition was measured for the following physical properties. The results are shown in Table 2. [1] Viscosity The viscosity of the thermally conductive silicone potting composition at 25°C was measured using a Brookfield viscometer (TVB-10H, manufactured by Toki Sangyo Co., Ltd.) with a No. 7 rotor at 20 rpm (approximate shear rate of 4.2 s -1) was measured. [2] Flowability 0.60 mL of the thermally conductive silicone potting composition was weighed out and dropped onto an aluminum plate (JIS H 4000:2022, width 25 mm x length 400 mm x thickness 0.5 mm). After dropping, the aluminum plate was immediately tilted at 28° and left to stand for 1 hour in an atmosphere of 23°C (±2°C). After leaving, the length of the thermally conductive silicone potting composition was measured from one end to the other of the flow. [3] Thixotropic Index The viscosity of the thermally conductive silicone potting composition at 25°C was measured using a Brookfield viscometer (TVB-10H, manufactured by Toki Sangyo Co., Ltd.) with a rotor No. 7 at 10 rpm (approximate shear rate of 2.1 s -1 The viscosity was measured at 20 rpm (shear rate approx. 4.2 s -1) and calculated by dividing the viscosity by the viscosity measured by the JIS K 6251:2017 standard. [4] Thermal Conductivity: The thermally conductive silicone potting composition was press-cured at 120°C for 10 minutes at a thickness of 2.0 mm, and then heated in an oven at 120°C for 50 minutes. The thermal conductivity of the resulting cured product was measured in accordance with ISO 22007-2 using a hot disc method thermal property measurement device TPA-501 (Kyoto Electronics Manufacturing Co., Ltd.) at an ambient temperature of 25°C. [5] Density: The thermally conductive silicone potting composition was press-cured at 120°C for 10 minutes at a thickness of 2.0 mm, and then heated in an oven at 120°C for 50 minutes. The density of the resulting silicone sheet was measured in accordance with JIS K 6251:2017. [6] Elongation at Break, Tensile Strength: The thermally conductive silicone potting composition was press-cured at 120°C for 10 minutes at a thickness of 2.0 mm, and then heated in an oven at 120°C for 50 minutes. The elongation at break and tensile strength of the obtained silicone sheet were measured according to JIS K 6251:2017. [7] Tensile shear adhesive strength: A thermally conductive silicone potting composition was sandwiched between 1.0 mm thick aluminum plates (JIS H 4000:2022) to a thickness of 2.0 mm and an adhesive area of ​​25 mm x 10 mm. The composition was then heated at 120°C for 1 hour to cure the silicone potting composition, producing an adhesive test specimen. The tensile shear adhesive strength of the obtained test specimen was measured according to JIS K 6850:1999. [8] Hardness: The thermally conductive silicone potting composition was press-cured at 120°C for 10 minutes to a thickness of 2.0 mm, and then heated in an oven at 120°C for 50 minutes. Three of the obtained silicone sheets were stacked, and the hardness was measured using a Type A durometer as specified in JIS K 6253:2012.

[0061]

[0062]

[0063] As shown in Table 2, the thermally conductive silicone potting compositions of Examples 1 and 2 exhibit low viscosity and high flowability, and are found to have excellent thermal conductivity after curing. On the other hand, the thermally conductive silicone potting compositions of Comparative Examples 1 and 2, in which component (A) was changed to a linear organopolysiloxane terminated at both ends with dimethylvinylsilyl groups, were found to have high viscosity and poor flowability.

Claims

1. A thermally conductive silicone potting composition comprising: (A) 100 parts by mass of a linear organopolysiloxane having an average of 0.5 to 1.8 alkenyl groups bonded to silicon atoms at the molecular chain terminals per molecule; (B) 500 to 2,000 parts by mass of a thermally conductive filler; (C) 0.1 to 100 parts by mass of an organohydrogensiloxane having at least two SiH groups per molecule; and (D) a hydrosilylation reaction catalyst.

2. The thermally conductive silicone potting composition according to claim 1, wherein the viscosity of the linear organopolysiloxane of component (A) at 25°C is 10 to 500 mPa·s as measured with a B-type rotational viscometer.

3. The thermally conductive silicone potting composition according to claim 1, which contains (E) a silane compound represented by the following general formula (1) and an organopolysiloxane represented by the following general formula (2) in an amount of 0.1 to 30 parts by mass per 100 parts by mass of component (A). (In the formula, R 1 each independently represents a monovalent hydrocarbon group, and n represents an integer of 0 to 30.

4. The thermally conductive silicone potting composition according to claim 3, wherein said thermally conductive filler (B) is surface treated with said component (E).

5. The thermally conductive silicone potting composition of claim 1, which has a viscosity at 25°C of 30 Pa·s or less.

6. A cured product obtained by curing the thermally conductive silicone potting composition according to any one of claims 1 to 5.

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