Thermally conductive sheet

Abstract

To provide a thermally conductive sheet that achieves excellent thermal conductivity and low specific gravity by being filled with two or more fibrous thermally conductive fillers having different average fiber diameters.SOLUTION: The present invention relates to a thermally conductive sheet containing two or more fibrous thermally conductive fillers (B) having different average fiber diameters in a polymer matrix (A), where the ratio of the maximum to the minimum of the average fiber diameters among the fibrous thermally conductive fillers is 2:1 to 45:1.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermally conductive sheet. [Background technology]

[0002] In recent years, automobiles have become increasingly electronic, and the number of electronic components installed has increased, leading to an increased demand for heat dissipation materials. Among these, sheet-type heat dissipation materials are preferred due to their ease of mounting. Furthermore, with autonomous driving as a backdrop, heat dissipation materials are required to have even higher thermal conductivity. Generally, in order to achieve high thermal conductivity, it is necessary to increase the filling rate of the filler dispersed within the polymer, which tends to result in a high specific gravity of over 2.0. However, this is a problem in promoting weight reduction to improve the fuel efficiency of gasoline-powered vehicles and the electricity consumption of electric vehicles.

[0003] For example, Patent Document 1 proposes a carbon fiber-containing sheet in which two types of carbon fibers having different fiber diameters are blended and oriented in one direction to increase the contact area of ​​the carbon fibers and improve thermal conductivity.

[0004] However, in Patent Document 1, the ratio of the fiber diameters of the first fiber elements and the second fiber elements is 50:1 to 100:1, and the first fiber diameter is extremely large or the second fiber diameter is extremely small. Therefore, when blended with a synthetic resin, the compound viscosity increases, making it impossible to form a uniform compound, and the filling ratio of the second fiber elements cannot be increased, leaving room for improvement in increasing the contact area.

[0005] In addition, by filling the material with multiple carbon fibers having different fiber diameters, the contact area could be increased further, thereby improving the thermal conductivity.

[0006] Furthermore, Patent Document 2 proposes a heat dissipation sheet in which carbon fibers having an average effective fiber length of 5 to 120 μm, an average fiber diameter of 200 to 900 nm, and an aspect ratio of 30 to 1,000 are oriented in the plane direction of a polymer.

[0007] However, heat dissipation sheets that generally transmit heat generated by a heat generating element to a heat sink are often required to conduct heat in the thickness direction rather than in the surface direction of the heat dissipation sheet, leaving room for improvement in the direction of heat conduction.

[0008] Furthermore, Patent Document 3 proposes a thermally conductive sheet having a volume fraction of 55 to 70% of thermally conductive filler including carbon fiber and inorganic filler, and a volume fraction of 30 to 45% of two-component addition reaction type silicone, and a thermal conductivity of 10 W / m K or more.

[0009] However, when the thermally conductive filler is contained in the volume ratio of Patent Document 3, the specific gravity becomes large, and there is room for improvement in terms of reducing the specific gravity. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2019-111728 A [Patent Document 2] Patent Publication No. 2021-008629 [Patent Document 3] JP 2022-127596 A Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made to solve the problems described above, and aims to provide a thermally conductive sheet that has excellent thermal conductivity and a low specific gravity by filling it with two or more types of fibrous thermally conductive fillers having different average fiber diameters. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a thermally conductive sheet comprising a polymer matrix (A) and two or more types of fibrous thermally conductive fillers (B) having different average fiber diameters, wherein the ratio of the maximum diameter to the minimum diameter of the average fiber diameters is 2:1 to 45:1.

[0013] In such a thermally conductive sheet, the ratio of fiber diameters is appropriate, which improves the packing efficiency of the fibrous thermally conductive filler and thereby improves thermal conductivity.

[0014] The thermally conductive sheet preferably has a thermal conductivity in the thickness direction of 25 W / m·K or more and a specific gravity of less than 1.4.

[0015] Such a thermal conductive sheet can improve the heat transfer efficiency by being placed between a heat generating body and a heat sink. In addition, the inclusion of fibrous thermal conductive filler shortens the heat transfer path in the thermal conductive sheet, and high thermal conductivity can be obtained with a small filling amount, making it ideal for reducing the specific gravity.

[0016] The aspect ratio of the fibrous thermally conductive filler (B) is preferably 2 or more and less than 30.

[0017] Such a fibrous thermally conductive filler does not entangle the filler particles, and can improve the filling property.

[0018] At least one of the fibrous thermally conductive fillers (B) is preferably a carbon fiber having an average fiber diameter of 8 μm or more.

[0019] Since such fibrous thermally conductive fillers have a high thermal conductivity in the long axis direction, the cross-sectional area can be increased to efficiently increase thermal conductivity. In addition, carbon has a lower specific gravity than general thermally conductive fillers such as alumina and aluminum nitride, making it suitable for reducing the specific gravity.

[0020] At least one of the fibrous thermally conductive fillers (B) is preferably a carbon fiber having an average fiber diameter of 1 μm or more and less than 8 μm, or an average fiber diameter of less than 1 μm.

[0021] Such fibrous thermally conductive filler is more likely to be disposed between fillers having an average fiber diameter of 8 μm or more, further enhancing thermal conductivity.

[0022] The content of the fibrous thermally conductive filler (B) in the thermally conductive sheet of the present invention is preferably 20 to 60% by mass.

[0023] Such a thermally conductive sheet is advantageous in achieving both high thermal conductivity and low specific gravity.

[0024] In addition, it is preferable that the major axis direction of the fibrous thermally conductive filler (B) of the present invention is oriented in the thickness direction of the thermally conductive sheet.

[0025] Such a thermally conductive sheet is preferable because it further shortens the heat transfer path in the thickness direction of the sheet.

[0026] The polymer matrix (A) is preferably a cured product of a curable polymer composition containing one or more members selected from the group consisting of organopolysiloxane, polyurethane, polyacrylate, perfluoropolyether elastomer, unsaturated polyester resin, polyamide resin, epoxy resin, and phenol resin.

[0027] If the polymer matrix (A) has such a structure, the filling property of the fibrous thermally conductive filler (B) is good. Effect of the Invention

[0028] As described above, by filling two or more types of fibrous thermally conductive fillers having different average fiber diameters at an appropriate fiber diameter ratio, a thermally conductive sheet having excellent thermal conductivity and a low specific gravity can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] As described above, there has been a demand for a thermally conductive sheet that has excellent thermal conductivity and a low specific gravity.

[0030] As a result of intensive research to solve the above problems, the inventors discovered that by filling a sheet with fibrous thermally conductive fillers having different average fiber diameters, a thermally conductive sheet having excellent thermal conductivity and a low specific gravity can be obtained, and thus completed the present invention.

[0031] That is, the present invention is a thermally conductive sheet comprising a polymer matrix (A) and two or more types of fibrous thermally conductive fillers (B) having different average fiber diameters, and the ratio of the maximum diameter to the minimum diameter of the average fiber diameters is 2:1 to 45:1.

[0032] The present invention will be described in detail below, but the present invention is not limited thereto.

[0033] [Thermal conductive sheet] The thermally conductive sheet of the present invention is a thermally conductive sheet obtained by molding a filler-containing resin composition for a thermally conductive sheet, which contains two or more kinds of fibrous thermally conductive fillers (B) having different average fiber diameters in a polymer matrix (A) and has a ratio of the maximum diameter to the minimum diameter of the average fiber diameter of 2:1 to 45:1, by a method described below.

[0034] [Filler-containing resin composition] The filler-containing resin composition is a resin composition containing a polymer matrix (A) and two or more types of fibrous thermally conductive fillers (B) having different average fiber diameters.

[0035] [Polymer matrix (A)] The polymer matrix, which is component (A) of the filler-containing resin composition, is not particularly limited, but in terms of the filling ability of the fibrous thermally conductive filler, which is component (B), is preferably one or more curable polymer compositions selected from the group consisting of organopolysiloxane, polyurethane, polyacrylate, perfluoropolyether elastomer, unsaturated polyester resin, polyamide resin, epoxy resin, and phenol resin, more preferably an organopolysiloxane, perfluoropolyether elastomer, polyurethane, or polyacrylate, which have excellent flexibility, and even more preferably an organopolysiloxane or perfluoropolyether elastomer, which have excellent heat resistance and cold resistance.

[0036] [Curable polymer composition] Therefore, it is preferable that component (A) is a curable organopolysiloxane composition or a curable perfluoropolyether elastomer composition.

[0037] [Curable organopolysiloxane composition] The curable organopolysiloxane composition will now be described in detail.

[0038] Examples of the curable organopolysiloxane composition include a heat-curable organopolysiloxane composition, a moisture-curable organopolysiloxane composition, and an electron beam-curable silicone resin. Examples of the heat-curable silicone resin include an addition-curable organopolysiloxane composition and a peroxide-curable organopolysiloxane composition. Among these, an addition-curable organopolysiloxane composition is preferred, and an addition-curable organopolysiloxane composition containing the following components (A-1) to (A-3) is more preferred. (A-1) an alkenyl group-containing organopolysiloxane, (A-2) organohydrogenpolysiloxane, (A-3) Platinum group metal curing catalyst

[0039] [(A-1) Alkenyl-containing organopolysiloxane] The alkenyl-containing organopolysiloxane, which is the component (A-1), is an organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, and is the main component of the filler-containing resin composition of the present invention (which gives a thermally conductive silicone cured product). Usually, the main chain portion is generally basically composed of a repetition of diorganosiloxane units, but this may include a branched structure in part of the molecular structure, or may be a cyclic body, but from the viewpoint of physical properties such as the mechanical strength of the cured product, a straight-chain diorganopolysiloxane is preferred.

[0040] Examples of the alkenyl group include vinyl, aryl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups, each of which usually has about 2 to 8 carbon atoms, and among these, lower alkenyl groups such as vinyl and aryl groups are preferred, with vinyl being particularly preferred. Note that it is preferred that two or more alkenyl groups are present in the molecule, but in order to improve the flexibility of the resulting cured product, it is preferred that the alkenyl groups are present only bonded to silicon atoms at the molecular chain terminals.

[0041] The functional group other than the alkenyl group is a monovalent hydrocarbon group, for example, alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, etc., cycloalkyl groups such as cyclopentyl group, cyclohexyl group, cycloheptyl group, etc., aryl groups such as phenyl group, tolyl group, xylyl group, naphthyl group, biphenylyl group, etc., and aralkyl groups such as benzyl group, phenylethyl group, phenylpropyl group, methylbenzyl group, etc. Among them, those having 1 to 10 carbon atoms, particularly 1 to 6 carbon atoms, are preferred, and alkyl groups having 1 to 3 carbon atoms such as methyl group, ethyl group, propyl group, 3,3,3-trifluoropropyl group, etc., and phenyl group are more preferred. In addition, the functional groups other than the alkenyl group bonded to the silicon atom are not limited to being all the same.

[0042] The kinematic viscosity of this organopolysiloxane at 25°C is usually preferably 10 to 100,000 mm 2 / s, and particularly preferably 5,000 to 100,000 mm 2 / s. The above viscosity is in the range of 10mm 2 / s or more, the resulting resin composition has good storage stability, and 2 If the viscosity is 1 / s or less, the extensibility of the resulting resin composition will not deteriorate.

[0043] In this specification, the kinematic viscosity is a value at 25°C when using a Cannon-Fenske viscometer described in JIS Z 8803:2011.

[0044] The organopolysiloxane of the component (A-1) may be used either alone or in combination of two or more different types having different viscosities.

[0045] [(A-2) Organohydrogenpolysiloxane] The organohydrogenpolysiloxane of component (A-2) is an organohydrogenpolysiloxane having an average of 2 or more, preferably 2 to 100, hydrogen atoms (hydrosilyl groups) directly bonded to silicon atoms in one molecule, and acts as a crosslinking agent for component (A-1). That is, the hydrosilyl groups in component (A-2) and the alkenyl groups in component (A-1) are added by a hydrosilylation reaction promoted by the platinum group metal curing catalyst of component (A-3) described later, to give a three-dimensional network structure having a crosslinked structure. If the number of hydrosilyl groups is less than 2, the product will not cure.

[0046] The organohydrogenpolysiloxane used is one represented by the following average structural formula (1), but is not limited thereto. [ka] (In the formula, R is independently a hydrogen atom or a monovalent hydrocarbon group not containing an aliphatic unsaturated bond, and 2 or more, preferably 2 to 100, and more preferably 2 to 10, hydrogen atoms are present in one molecule, and e is an integer of 1 or more, preferably an integer of 10 to 200.)

[0047] In the above general formula (1), examples of the monovalent hydrocarbon group of R that does not contain an aliphatic unsaturated bond other than a hydrogen atom include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Among these, those having 1 to 10 carbon atoms, particularly 1 to 6 carbon atoms, are preferred, and more preferred are alkyl groups having 1 to 3 carbon atoms such as methyl, ethyl, propyl, and 3,3,3-trifluoropropyl, and phenyl. In addition, R is not limited to being all the same.

[0048] The amount of the (A-2) component added is, for example, 0.1 to 5.0 mol of hydrosilyl groups derived from the (A-2) component per mol of alkenyl groups derived from the (A-1) component, preferably 0.3 to 2.0 mol, more preferably 0.5 to 1.5 mol. If the amount of hydrosilyl groups derived from the (A-2) component is 0.1 mol or more per mol of alkenyl groups derived from the (A-1) component, the curing is sufficient, and the strength of the cured product is sufficient to maintain the shape as a molded product, so that the strength is not insufficient to make it difficult to handle. If it is 5.0 mol or less, the flexibility of the cured product is good, and the cured product does not become brittle.

[0049] [(A-3) Platinum group metal curing catalyst] The platinum group metal curing catalyst of component (A-3) is a catalyst for promoting the addition reaction between the alkenyl group derived from component (A-1) and the hydrosilyl group derived from component (A-2), and examples of such catalysts include those well known as catalysts used in hydrosilylation reactions. Specific examples thereof include platinum group metals such as platinum (including platinum black), rhodium, and palladium, platinum chlorides such as H2PtCl4·nH2O, H2PtCl6·nH2O, NaHPtCl6·nH2O, KHPtCl6·nH2O, Na2PtCl6·nH2O, K2PtCl4·nH2O, PtCl4·nH2O, PtCl2, and Na2HPtCl4·nH2O (wherein n is an integer of 0 to 6, preferably 0 or 6), chloroplatinic acid and chloroplatinic acid salts, and alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972, specification). and the like), complexes of chloroplatinic acid and olefins (see U.S. Pat. Nos. 3,159,601, 3,159,662, and 3,775,452), platinum black, platinum group metals such as palladium supported on supports such as alumina, silica, and carbon, rhodium-olefin complexes, chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst), complexes of platinum chloride, chloroplatinic acid, or chloroplatinate with vinyl group-containing siloxanes, particularly vinyl group-containing cyclic siloxanes.

[0050] The amount of component (A-3) used may be an effective amount, preferably 0.1 to 2,000 ppm, more preferably 50 to 1,000 ppm, calculated as the mass of the platinum group metal element relative to component (A-1). If it is 0.1 ppm or more, sufficient catalytic activity is obtained, and if it is 2,000 ppm or less, the effect of promoting the addition reaction is sufficient and costs can be suppressed.

[0051] [Curable perfluoropolyether elastomer composition] Also, a curable perfluoropolyether elastomer composition, which is another preferred embodiment, will be specifically described.

[0052] Examples of the curable perfluoropolyether elastomer composition include a heat-curable perfluoropolyether elastomer composition, a moisture-curable perfluoropolyether elastomer composition, and an electron beam-curable perfluoropolyether elastomer. Examples of the heat-curable perfluoropolyether elastomer include an addition-curable perfluoropolyether elastomer composition and a peroxide-curable perfluoropolyether elastomer composition. Among these, an addition-curable perfluoropolyether elastomer composition is preferred, and an addition-curable perfluoropolyether elastomer composition containing the following components (A-4) to (A-6) is more preferred. (A-4) alkenyl group-containing perfluoropolyether compound, (A-5) fluorine-containing organohydrogenpolysiloxane, (A-6) Platinum group metal curing catalyst

[0053] [(A-4) Alkenyl group-containing perfluoropolyether compound] The alkenyl-containing perfluoropolyether compound, which is the component (A-4), is a perfluoropolyether compound having two or more alkenyl groups in one molecule, and serves as the main component of the filler-containing resin composition of the present invention (which produces a thermally conductive perfluoropolyether cured product). In general, the main chain portion is basically composed of a repetition of perfluoropolyether units (perfluorooxyalkylene units).

[0054] Among them, the following general formula (2) CH2=CH-(X) z -Rf 1 -(X') z -CH=CH2(2) [wherein X is a group represented by the formula: -CH2-, -CH2O-, -CH2OCH2- or -Y-NR 1 -CO- (wherein Y is a group of the formula: -CH2- or [ka] R is a divalent group represented by 1is a hydrogen atom or a monovalent hydrocarbon group; X' is a group represented by the formula: -CH2-, -CH2O-, -CH2OCH2- or -CO-NR 1 -Y'- (wherein Y' is a group represented by the formula: -CH2- or the formula: [ka] R is a divalent group represented by 1 is the same as above.) is a divalent group represented by Rf 1 is represented by the following general formula (i): -C t F 2t [OCF2CF(CF3)] p OCF2(CF2) r CF2O[CF(CF3)CF2O] q C t’ F 2t’ -(i) (In the formula, p and q are integers of 1 to 150, and the average of the sum of p and q is 2 to 200. wherein r is an integer of 0 to 6, and t and t' are 2 or 3; or a compound represented by the following general formula (ii): -C t F 2t [OCF2CF(CF3)] u (OCF2) v O.C. t’ F 2t’ -(ii) (In the formula, u is an integer of 1 to 200, v is an integer of 1 to 50, and t and t' are the same as above.) be.) and z is independently 0 or 1.

[0055] Rf 1 The lower limit of the degree of polymerization (p+q) or (u+v) of the divalent perfluoropolyether group represented by the formula (1) is not particularly limited as long as it is an integer of 2 or more, but it is preferable that the degree of polymerization is low and that the degree of polymerization is low. Therefore, it is preferably 30 or more, and particularly preferably 80 or more.

[0056] R1 When is a monovalent hydrocarbon group, examples of the monovalent hydrocarbon group include monovalent hydrocarbon groups having 1 to 20 carbon atoms, and specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, cyclohexyl, octyl, and decyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl, tolyl, and naphthyl; and aralkyl groups such as benzyl and phenylethyl.

[0057] [(A-5) Fluorine-containing organohydrogenpolysiloxane] The fluorine-containing organohydrogenpolysiloxane, which is the component (A-5), acts as a crosslinking agent or chain extender for the above component (A-4). For this purpose, the above fluorine-containing organohydrogenpolysiloxane has two or more, preferably three or more, hydrogen atoms bonded to silicon atoms (i.e., hydrosilyl groups) in one molecule. The component (A-5) can be used alone or in combination of two or more.

[0058] From the viewpoints of compatibility with component (A-4), dispersibility, etc., the fluorine-containing organohydrogenpolysiloxane preferably has in one molecule one or more groups selected from perfluoroalkyl groups, perfluoroalkylene groups, perfluorooxyalkyl groups, and perfluorooxyalkylene groups. Examples of these perfluoro groups include those represented by the following general formula: Perfluoroalkyl groups: C g F 2g+1 - (In the formula, g is an integer of 1 to 20, preferably 2 to 10.) Perfluoroalkylene groups: -C g F 2g - (In the formula, g is the same as above.) Perfluorooxyalkyl groups: [ka] (In the formula, f is an integer of 2 to 200, preferably 2 to 100, and h is an integer of 1 to 3. .) Perfluorooxyalkylene groups: [ka] In the formula, i and j are integers of 1 or more, and the average of i+j is 2 to 200, preferably 2 to 100. be.) -(CF2CF2O) k (CF2O) L CF2- (In the formula, k and L are each an integer of 1 or more, and the average of k+L is 2 to 200, preferably is between 2 and 100.)

[0059] In addition, a divalent linkage connecting these perfluoroalkyl groups, perfluorooxyalkyl groups, perfluoroalkylene groups, or perfluorooxyalkylene groups to a silicon atom The group may be an alkylene group, an arylene group, or a combination thereof, or these groups may have an ether group. The alkyl group may be one in which a aryl bond, an amide bond, a carbonyl bond, or the like is interposed, for example, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2OCH2-, -CH2CH2CH2-NH-CO-, -CH2CH2CH2-N(Ph)-CO-, -CH2CH2CH2-N(CH3)-CO-, -CH2CH2CH2-O-CO-, -Ph'-N(CH3)-CO- (Ph represents a phenyl group, and Ph' represents a phenylene group) and the like having 2 to 12 carbon atoms.

[0060] In the fluorine-containing organohydrogenpolysiloxane of component (A-5), examples of the monovalent fluorine-containing substituent bonded to a silicon atom other than an organic group containing a perfluoroalkyl group or a perfluorooxyalkyl group include unsubstituted hydrocarbon groups such as hydrocarbon groups having 1 to 20 carbon atoms, for example, alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group, cyclohexyl group, octyl group, and decyl group; alkenyl groups such as vinyl group and allyl group; aryl groups such as phenyl group, tolyl group, and naphthyl group; and aralkyl groups such as benzyl group and phenylethyl group, as well as substituted hydrocarbon groups in which at least a portion of the hydrogen atoms of these hydrocarbon groups are substituted with chlorine atoms or the like, such as chloromethyl group, chloropropyl group, and cyanoethyl group.

[0061] The fluorine-containing organohydrogenpolysiloxane of the component (A-5) may be cyclic, linear, three-dimensional network, or a combination thereof. The number of silicon atoms in this fluorine-containing organohydrogenpolysiloxane is not particularly limited, but is usually about 3 to 60, and preferably about 4 to 30.

[0062] The molecular weight of the fluorine-containing organohydrogenpolysiloxane of the component (A-5) is preferably in the range of 750 to 3,000, and more preferably 800 to 2,400.

[0063] The amount of the (A-5) component is an effective amount required to cure the (A-4) component and obtain a cured product having the required rubber elasticity. In particular, the amount of hydrosilyl groups of the (A-5) component is 0.5 to 5.0 moles, preferably 1.0 to 2.0 moles, per mole of the total alkenyl groups of the (A-4) component in the present composition. If the amount is sufficient, the degree of crosslinking is sufficient, and if it is not too much, the chain length extension is not prioritized, so that curing is sufficient, foaming does not occur during curing, and the heat resistance of the obtained cured film is not reduced.

[0064] [(A-6) Platinum group metal curing catalyst] The platinum group metal curing catalyst of component (A-6) is a catalyst for promoting the addition reaction between the alkenyl group derived from component (A-4) and the hydrosilyl group derived from component (A-5), and examples of such catalysts include those well known as catalysts used in hydrosilylation reactions.Specific examples of such catalysts include the same curing catalysts as those exemplified for component (A-3) above.

[0065] The amount of component (A-6) used may be an effective amount as a catalyst, for example, 0.1 to 500 ppm (by mass) calculated as platinum group metal relative to the amount of component (A-4).

[0066] [Fibrous thermally conductive filler (B)] The component (B) of the filler-containing resin composition of the present invention is two or more types of fibrous thermally conductive fillers having different average fiber diameters.

[0067] The shape of the fibrous thermally conductive filler is not particularly limited as long as it is fibrous, and examples thereof include fibers, needles, whiskers, and the like.

[0068] The size of the above-mentioned fibrous thermally conductive filler may be appropriately selected as needed, and is not particularly limited, but it is preferable that the aspect ratio (average major axis length / average minor axis length) be a filler of 2 or more and less than 30, and more preferably 5 or more and less than 30.

[0069] If such a material is used, the fibrous thermally conductive filler particles will not become entangled with each other, improving the packing properties and the thermal conductivity.

[0070] The average major axis length and the average minor axis length of the fibrous thermally conductive filler can be measured by a scanning electron microscope (SEM), and the aspect ratio can be calculated from the measured values. For example, the aspect ratio of carbon fibers is the value of "average fiber length / average fiber diameter" of the carbon fibers.

[0071] The average fiber diameter of the fibrous thermally conductive filler is not particularly limited, but is preferably 0.1 to 20 μm, more preferably 0.3 to 15 μm. It is preferable that one of the fibrous thermally conductive fillers is a carbon fiber having an average fiber diameter of 8 μm or more.

[0072] Such a fibrous thermally conductive filler has a high thermal conductivity in the major axis direction of the fibrous thermally conductive filler, and therefore the cross-sectional area in the horizontal axis direction becomes large, thereby efficiently increasing the thermal conductivity.

[0073] In addition, carbon has a lower specific gravity than common thermally conductive fillers such as alumina and aluminum nitride, and is therefore preferable for reducing the specific gravity.

[0074] At least one of the fibrous thermally conductive fillers is preferably a carbon fiber having an average fiber diameter of 1 μm or more and less than 8 μm, or an average fiber diameter of less than 1 μm.

[0075] Such fibrous thermally conductive filler is more likely to be disposed between fillers having an average fiber diameter of 8 μm or more, further enhancing thermal conductivity.

[0076] The present invention is also characterized by containing two or more kinds of fibrous thermally conductive fillers with different average fiber diameters. The ratio of the maximum diameter to the minimum diameter of the average fiber diameters is 2:1 to 45:1, and preferably 3:1 to 40:1. If the ratio is less than 2:1, the interference between the fibers is not sufficiently reduced, which is undesirable, and if it exceeds 45:1, the compound viscosity increases, making it difficult to increase the filling ratio of the minimum fiber diameter, which is undesirable.

[0077] The content of the fibrous thermally conductive filler (B) in the thermally conductive sheet of the present invention is preferably 20 to 60 mass %, more preferably 30 to 52 mass %, in which case the balance between high thermal conductivity and low specific gravity is good, and this range is preferable.

[0078] It is also preferred that the major axis direction of the fibrous thermally conductive filler, component (B), is oriented in the thickness direction of the thermally conductive sheet obtained by curing the composition.

[0079] Such a thermally conductive sheet is preferable because it further shortens the heat transfer path in the thickness direction of the sheet.

[0080] [Other ingredients] If necessary, the above-mentioned filler-containing resin composition may further contain components such as a solvent, a thixotropic agent, a dispersant, a curing agent, a curing accelerator, a retarder, a slight tackifier, a plasticizer, a flame retardant, an antioxidant, a stabilizer, and a colorant.

[0081] The filler-containing resin composition may contain a filler other than the component (B). Specific examples include silica, titanium oxide, etc. The amount of the filler is not particularly limited, but is preferably 0 to 60 parts by mass, more preferably 0 to 40 parts by mass, per 100 parts by mass of the component (A).

[0082] [Method for producing filler-containing resin composition] The filler-containing resin composition can be produced by mixing the polymer matrix, the fibrous thermally conductive filler, and, if necessary, the other components using a mixer or the like.

[0083] [Method of manufacturing thermally conductive sheets] The method for producing the thermally conductive sheet of the present invention includes a step of molding the above-mentioned filler-containing resin composition and a step of curing the same, and examples of the method include the following methods.

[0084] (I-1) a preparation step of preparing a filler-containing resin composition containing the polymer matrix (A) and the thermally conductive filler (B); (I-2) a filling step of filling the filler-containing resin composition into a mold; (I-3) a molding step of curing the filler-containing composition filled in the mold by heating or the like to obtain a filler-containing molded body; (I-4) There is a method for obtaining a thermally conductive sheet having excellent thermal conductivity in the thickness direction and a low specific gravity by a slicing step of slicing the above-mentioned filler-containing molded body to obtain a thermally conductive sheet.

[0085] Each of the above steps will now be described in detail.

[0086] Preparation process (I-1) In this step, a filler-containing resin composition containing the polymer matrix (A) and the fibrous thermally conductive filler (B) is prepared according to the method for producing the filler-containing resin composition.

[0087] Filling process (I-2) The prepared filler-containing resin composition is filled into a mold measuring 40 mm in the X-axis direction (width direction) × 40 mm in the Y-axis direction (length direction) × 80 mm in the Z-axis direction (height direction) using a dispenser. (Filling method) (i) The material is discharged so that the discharge direction is parallel to the X-axis direction of the mold, and then piled up and filled in the Z-axis direction. (ii) The material is discharged in a direction parallel to the Y-axis of the mold, and then stacked and filled in the Z-axis direction. In this way, a molded body in which the fibrous thermally conductive filler or the like is oriented can be obtained more preferably and efficiently. The number of times of stacking in the Z-axis direction is preferably 2 or more, and more preferably 20 or more.

[0088] Molding method (I-3) In the molding step, the filler-containing resin composition filled in the mold is heated to obtain a filler-containing molded body. The curing conditions of the filler-containing resin composition are optimized depending on the type of resin in the filler-containing resin composition, etc. For example, the curing conditions of the filler-containing molded body obtained from the filler-containing resin composition using a silicone resin are preferably as follows. The curing temperature is preferably from 0 to 200° C., more preferably from 10 to 150° C. The curing time is preferably from 1 minute to 24 hours, more preferably from 5 minutes to 1 hour.

[0089] Slicing process (I-4) The slicing step is a step of obtaining a thermally conductive sheet of a desired thickness by slicing the filler-containing molded body obtained in the molding step. Specifically, the slicing step is carried out through the following steps (i) or (ii). (i) The material is discharged into the mold so that the discharge direction is parallel to the X-axis direction, and then stacked in the Z-axis direction. The filled molded body is parallel to the YZ plane. (ii) The filler-containing molded body is discharged into the mold so that the discharge direction is parallel to the Y-axis direction, and then stacked in the Z-axis direction. The filled filler-containing molded body is parallel to the XZ plane. The molded product is sliced ​​to a desired thickness to obtain a thermally conductive sheet in which the major axis direction of the fibrous thermally conductive filler is oriented in the thickness direction. EXAMPLES

[0090] The present invention will be described in detail below, but the present invention is not limited thereto.

[0091] The kinetic viscosity is a value measured at 25°C using a Cannon-Fenske viscometer as described in JIS Z 8803:2011. The average fiber length, average fiber diameter, and aspect ratio were determined by SEM measurement. The average particle size is a cumulative average particle size (median diameter) on a volume basis measured using a Microtrac MT3300EXII particle size analyzer manufactured by Microtrac Bell.

[0092] <Addition reaction type organopolysiloxane composition> The components of the addition reaction type organopolysiloxane composition are the following (A-1) to (A-3).

[0093] Ingredient (A-1) Organopolysiloxane represented by the following formula: 97.1% by mass [ka] In the above formula, n is the kinematic viscosity at 25°C in units of 30,000 mm 2 / s.

[0094] Ingredient (A-2) Organohydrogenpolysiloxane represented by the following formula: 2.2% by mass [ka] In the above formula, o=27 and p=3, each of which is the average degree of polymerization.

[0095] Ingredient (A-3) 5% chloroplatinic acid in 2-ethylhexanol: 0.7% by mass

[0096] A filler-containing resin composition of the present invention was produced as follows.

[0097] <Filler-containing organopolysiloxane composition A> A filler-containing organopolysiloxane composition A (specific gravity 1.32) was obtained by mixing 55.0 mass% of an addition reaction type organopolysiloxane composition (specific gravity 1.0), 30.4 mass% of carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2), 3.6 mass% of carbon fiber B (average fiber length 40 μm, average fiber diameter 3 μm, aspect ratio 13, specific gravity 2.2), and 11.0 mass% of carbon fiber C (average fiber length 10 μm, average fiber diameter 0.5 μm, aspect ratio 20, specific gravity 2.2).

[0098] <Filler-containing organopolysiloxane composition B> A filler-containing organopolysiloxane composition B (specific gravity 1.32) was obtained by mixing 55.0 mass% of an addition reaction type organopolysiloxane composition (specific gravity 1.0), 34.0 mass% of carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2), and 11.0 mass% of carbon fiber B (average fiber length 40 μm, average fiber diameter 3 μm, aspect ratio 13, specific gravity 2.2).

[0099] <Filler-containing organopolysiloxane composition C> A filler-containing organopolysiloxane composition C (specific gravity 1.32) was obtained by mixing 55.0 mass% of an addition reaction type organopolysiloxane composition (specific gravity 1.0), 34.0 mass% of carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2), and 11.0 mass% of carbon fiber C (average fiber length 10 μm, average fiber diameter 0.5 μm, aspect ratio 20, specific gravity 2.2).

[0100] <Filler-containing organopolysiloxane composition D> Filler-containing organopolysiloxane composition D (specific gravity 1.32) was obtained by mixing 55.0 mass% of addition reaction type organopolysiloxane composition (specific gravity 1.0) and 45.0 mass% of carbon fiber D (average fiber length 300 μm, average fiber diameter 10 μm, aspect ratio 30, specific gravity 2.2).

[0101] <Filler-containing organopolysiloxane composition E> A filler-containing organopolysiloxane composition E (specific gravity 1.32) was obtained by mixing 55.0 mass% of an addition reaction type organopolysiloxane composition (specific gravity 1.0), 34.0 mass% of carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2), and 11.0 mass% of carbon fiber E (average fiber length 50 μm, average fiber diameter 10 μm, aspect ratio 5, specific gravity 2.2).

[0102] <Filler-containing organopolysiloxane composition F> A filler-containing organopolysiloxane composition F (specific gravity 1.42) was obtained by mixing 45.6 mass% of an addition reaction type organopolysiloxane composition (specific gravity 1.0), 34.0 mass% of carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2), and 20.4 mass% of carbon fiber E (average fiber length 50 μm, average fiber diameter 10 μm, aspect ratio 5, specific gravity 2.2).

[0103] <Filler-containing organopolysiloxane composition G> Filler-containing organopolysiloxane composition G (specific gravity 1.3) was obtained by mixing 55.0 mass% of addition reaction type organopolysiloxane composition (specific gravity 1.0) and 45.0 mass% of carbon fiber B (average fiber length 40 μm, average fiber diameter 3 μm, aspect ratio 13, specific gravity 2.2).

[0104] <Filler-containing organopolysiloxane composition H> Filler-containing organopolysiloxane composition F (specific gravity 1.3) was obtained by mixing 55.0 mass% of addition reaction type organopolysiloxane composition (specific gravity 1.0) and 45.0 mass% of carbon fiber C (average fiber length 10 μm, average fiber diameter 0.5 μm, aspect ratio 20, specific gravity 2.2).

[0105] Using the above filler-containing organopolysiloxane compositions A to H, thermally conductive sheets were produced as follows.

[0106] <Example 1> The above filler-containing organopolysiloxane composition A was dispensed using a dispenser (MOHNO MASTER V2) manufactured by Musashi Engineering Co., Ltd., with a nozzle having an inner diameter of 1.64 mm. The container was filled with the resin arranged in the Y-axis direction to form 24 rows in the X-axis direction and 24 columns in the Z-axis direction, and then heated at 80°C for 20 minutes to obtain a filler-containing molded body 1. The cured product, which was the filler-containing molded body, was sliced ​​parallel to the XZ plane with a cutter knife to obtain a thermally conductive sheet 1 having a thickness of 2 mm.

[0107] <Example 2> A thermally conductive sheet 2 was obtained by the same production method as in Example 1, except that the above filler-containing organopolysiloxane composition was changed to the above filler-containing organopolysiloxane composition B.

[0108] <Example 3> A thermally conductive sheet 3 was obtained by the same production method as in Example 1, except that the above filler-containing organopolysiloxane composition was changed to the above filler-containing organopolysiloxane composition C.

[0109] <Comparative Example 1> An attempt was made to produce a thermally conductive sheet using the same manufacturing method as in Example 1, except that the filler-containing organopolysiloxane composition was changed to the filler-containing organopolysiloxane composition D. However, the composition could not be ejected from the nozzle, and a thermally conductive sheet could not be obtained.

[0110] <Comparative Example 2> A thermally conductive sheet 4 was obtained by the same production method as in Example 1, except that the above filler-containing organopolysiloxane composition was changed to the above filler-containing organopolysiloxane composition E.

[0111] <Comparative Example 3> A thermally conductive sheet 5 was obtained by the same production method as in Example 1, except that the filler-containing organopolysiloxane composition was changed to the filler-containing organopolysiloxane composition F.

[0112] <Comparative Example 4> A thermally conductive sheet 6 was obtained by the same production method as in Example 1, except that the filler-containing organopolysiloxane composition was changed to the filler-containing organopolysiloxane composition G.

[0113] <Comparative Example 5> A thermally conductive sheet 7 was obtained by the same production method as in Example 1, except that the filler-containing organopolysiloxane composition was changed to the filler-containing organopolysiloxane composition H.

[0114] <Evaluation items> For each of the thermally conductive sheets obtained in Examples 1 to 3 and Comparative Examples 2 to 5, the thermal conductivity and specific gravity were measured as follows.

[0115] <Thermal conductivity> Each of the thermally conductive sheets obtained in Examples 1 to 3 and Comparative Examples 2 to 5 was punched out to have a circle with a diameter of 12.7 mm, and the thermal conductivity of the test pieces was measured using a laser flash method (LFA 447 Nanoflash, manufactured by Netzsch) in accordance with JIS R 1611: 2010. The results are shown in Table 1 below.

[0116] <Specific gravity> The specific gravity at 25° C. was measured for each of the thermally conductive sheets obtained in Examples 1 to 3 and Comparative Examples 2 to 5 in accordance with JIS K 6249:2003. The results are shown in Table 1 below.

[0117] [Table 1]

[0118] Examples 1, 2, and 3 all had a carbon fiber content (total) of 45.0%, and contained two or more types of carbon fibers with different average fiber diameters, with an average fiber width of 8 μm or more and 1 μm or more but less than 8 μm or less than 1 μm. The ratio of the maximum diameter to the minimum diameter of the average fiber diameters was within a range of 2:1 to 45:1. Example 1 had a thermal conductivity of 32.1 W / m K and a specific gravity of 1.30, Example 2 had a thermal conductivity of 26.0 W / m K and a specific gravity of 1.31, and Example 3 had a thermal conductivity of 28.1 W / m K and a specific gravity of 1.31.

[0119] Comparative Example 2 (carbon fibers A and E with an average fiber diameter of 10 μm), Comparative Example 4 (carbon fiber B with an average fiber diameter of 3 μm), and Comparative Example 5 (carbon fiber C with an average fiber diameter of 0.5 μm) have a carbon fiber content (total) of 45.0%, but all of them have one average fiber length of carbon fiber. Comparative Example 2 had a thermal conductivity of 17.1 W / m·K and a specific gravity of 1.31, Comparative Example 4 had a thermal conductivity of 8.9 W / m·K and a specific gravity of 1.30, and Comparative Example 5 had a thermal conductivity of 4.7 W / m·K and a specific gravity of 1.31, which were lower than those of Examples 1 to 3. This result means that even if the filling amount of the fibrous thermally conductive filler is the same, the thermal conductivity is increased by containing two or more types of fibrous thermally conductive fillers with different average fiber diameters.

[0120] In Comparative Example 1, in which the carbon fiber content (total) was 45.0% but the average fiber diameter was one type (carbon fiber D with an average fiber diameter of 10 μm and an aspect ratio of 30), the dispenser could not be discharged in the manufacturing process of the thermal conductive sheet, and the sheet was not molded. This result means that if the average fiber diameter is 8 μm or more and the aspect ratio is 30 or more, the compound viscosity increases, making it difficult to increase the filling amount.

[0121] Comparative Example 3 (carbon fibers A and E with an average fiber diameter of 10 μm) had a carbon fiber content (total) of 54.4 mass%, which was higher than that of Examples 1 to 3. The carbon fiber content was 54.4 mass%, but the carbon fiber had one type with an average fiber diameter of 10 μm, and had a thermal conductivity of 20.6 W / m K and a specific gravity of 1.40, which were lower than those of Examples 1 to 3. This result means that even if the filling amount of the fibrous thermally conductive filler is low, the thermal conductivity is increased by containing two or more types of fibrous thermally conductive fillers with different average fiber diameters and with a maximum / minimum average fiber diameter ratio in the range of 2:1 to 45:1.

[0122] In this way, the present invention can provide a thermally conductive sheet that has excellent thermal conductivity and a low specific gravity by filling with two or more types of fibrous conductive fillers having different average fiber diameters and a ratio of maximum to minimum average fiber diameters in the range of 2:1 to 45:1.

[0123] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A thermally conductive sheet characterized by containing two or more fibrous thermally conductive fillers (B) with different average fiber diameters in a polymer matrix (A), wherein the ratio of the maximum diameter to the minimum diameter of the average fiber diameter is 2:1 to 45:

1.

2. The thermal conductive sheet according to claim 1, characterized in that the thermal conductivity in the thickness direction of the thermal conductive sheet is 25 W / m·K or more, and the specific gravity is less than 1.

4.

3. The thermal conductive sheet according to claim 1, characterized in that the aspect ratio of the fibrous thermal conductive filler (B) is 2 or more and less than 30.

4. The thermal conductive sheet according to claim 1, characterized in that one or more of the fibrous thermal conductive fillers (B) are carbon fibers with an average fiber diameter of 8 μm or more.

5. The thermal conductive sheet according to claim 1, characterized in that one or more of the fibrous thermal conductive fillers (B) are carbon fibers with an average fiber diameter of 1 μm or more and less than 8 μm, or with an average fiber diameter of less than 1 μm.

6. The thermal conductive sheet according to claim 1, characterized in that the proportion of the fibrous thermal conductive filler (B) contained in the thermal conductive sheet is 20 to 60% by mass.

7. The thermal conductive sheet according to claim 1, characterized in that the long axis direction of the fibrous thermal conductive filler (B) is oriented in the thickness direction of the thermal conductive sheet.

8. The thermally conductive sheet according to claim 1, characterized in that the polymer matrix (A) is a cured product of a curable polymer composition containing one or more selected from the group consisting of organopolysiloxane, polyurethane, polyacrylate, perfluoropolyether elastomer, unsaturated polyester resin, polyamide resin, epoxy resin, and phenolic resin.

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