Thermally conductive sheet

Abstract

The present invention is a thermally conductive sheet characterized by containing, in a polymer matrix (A), two or more types of fibrous thermally conductive fillers (B) having different average fiber diameters, the ratio of the maximum diameter to the minimum diameter of the average fiber diameters being 2: 1 to 45: 1. As a result, a thermally conductive sheet having excellent thermal conductivity and a low specific gravity is provided by filling two or more types of fibrous thermally conductive fillers having different average fiber diameters.

Description

Technical Field

[0001] This invention relates to a thermally conductive sheet. Background Technology

[0002] In recent years, the electrification of automobiles has increased significantly, with a rise in the number of electronic components, leading to a growing demand for heat dissipation components. Among these, sheet-type heat dissipation components are preferred due to ease of installation. Furthermore, with the advent of autonomous driving, heat dissipation components require even higher thermal conductivity. Generally, achieving high thermal conductivity necessitates increasing the filler content dispersed within the polymer, thus a trend towards higher proportions exceeding 2.0%. However, this has become a challenge in improving fuel efficiency in gasoline-powered vehicles, reducing electricity costs in EVs, and promoting lightweighting.

[0003] For example, in Patent Document 1, a sheet containing carbon fiber is proposed. By combining two types of carbon fibers with different diameters and oriented them in one direction, the contact area of ​​the carbon fibers is increased, thereby improving thermal conductivity.

[0004] However, in Patent Document 1, the ratio of the fiber diameters of the first fiber element and the second fiber element is 50:1 to 100:1, resulting in either an extremely large first fiber diameter or an extremely small second fiber diameter. Therefore, the viscosity of the compound increases when compounded in the synthetic resin, preventing the formation of a uniform compound. Furthermore, there is room for improvement in increasing the contact area, as it is difficult to increase the filling ratio of the second fiber element.

[0005] In addition, there is room to further increase the contact area and thus improve the thermal conductivity by filling multiple carbon fibers with different diameters.

[0006] In addition, Patent Document 2 proposes a heat sink material in which carbon fibers with an average actual 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 planar direction in a polymer.

[0007] However, generally speaking, heat sinks that transfer heat from the heat-generating element to the heat sink tend to conduct heat to the thickness direction rather than the surface direction of the heat sink, indicating that there is still room for improvement in the direction of heat conduction.

[0008] In addition, Patent Document 3 proposes a thermally conductive sheet containing a thermally conductive filler comprising 55-70% by volume of carbon fiber and inorganic filler, and a two-component addition reaction type silicone by volume of 30-45% with a content of 10 W / m·K or higher.

[0009] However, if the thermally conductive filler is included in the volume ratio of Patent Document 3, the specific gravity will increase, so there is still room for improvement in reducing the specific gravity. Existing technical documents Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2019-111728 Patent Document 2: Japanese Patent Application Publication No. 2021-008629 Patent Document 3: Japanese Patent Application Publication No. 2022-127596 Summary of the Invention The technical problem that the invention aims to solve

[0011] This invention was made to solve the above-mentioned problems, and its purpose is to provide a thermally conductive sheet with excellent thermal conductivity and low specific gravity by filling it with two or more fibrous thermally conductive fillers with different average fiber diameters. Technical means to solve the problem

[0012] To address the aforementioned problems, this invention provides a thermally conductive sheet containing two or more types of 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 is 2:1 to 45:1.

[0013] If the thermally conductive sheet is of this type, the fiber diameter ratio is appropriate, and the filling capacity of the fibrous thermally conductive filler is improved, which can improve the thermal conductivity.

[0014] Preferably, the thermal conductivity of the thermally conductive sheet in the thickness direction is 25 W / m·K or higher, and the specific gravity is less than 1.4.

[0015] If such a thermally conductive sheet is used, its thermal conductivity can be improved by placing it between the heat-generating element and the heat-dissipating element. Furthermore, by including fibrous thermally conductive fillers, the thermal conduction path within the sheet is shortened, allowing for high thermal conductivity with low filler content, making it ideal for applications requiring lower specific gravity.

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

[0017] If it is a fibrous thermally conductive filler, the fillers will not entangle with each other, which can improve the filling performance.

[0018] In addition, one or more of the fibrous thermally conductive fillers (B) are preferably carbon fibers with an average fiber diameter of 8 μm or more.

[0019] If it is a fibrous thermally conductive filler, the thermal conductivity can be effectively improved by increasing the cross-sectional area due to the high thermal conductivity along the long axis of the fibrous filler. In addition, carbon has a lower specific gravity than common thermally conductive fillers such as alumina and aluminum nitride, making it suitable for applications requiring low specific gravity.

[0020] In addition, preferably one or more of the fibrous thermally conductive fillers (B) are carbon fibers selected from those with 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] If it is a fibrous thermally conductive filler, the proportion of fillers with an average fiber diameter of 8μm or more is relatively large, which can further improve the thermal conductivity.

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

[0023] Such thermally conductive sheets are advantageous in balancing high thermal conductivity and low specific gravity.

[0024] Furthermore, the long axis direction of the fibrous thermally conductive filler (B) of the present invention is preferably oriented in the thickness direction of the thermally conductive sheet.

[0025] If the sheet is thermally conductive, the thermal conduction path in the thickness direction of the sheet will be shorter, which is therefore preferred.

[0026] The polymer matrix (A) is preferably a cured product of a curable polymer composition, which comprises one or more selected from the group consisting of organopolysiloxanes, polyurethanes, polyacrylates, perfluoropolyether elastomers, unsaturated polyester resins, polyamide resins, epoxy resins and phenolic resins.

[0027] If the polymer matrix (A) is this material, then the fibrous thermally conductive filler (B) has good filling properties. Invention Effects

[0028] As described above, by filling two or more fibrous thermally conductive fillers with different average fiber diameters in an appropriate fiber diameter ratio, a thermally conductive sheet with excellent thermal conductivity and low specific gravity can be obtained. Detailed Implementation

[0029] As mentioned above, there has been a continuous search for thermally conductive sheets with excellent thermal conductivity and low specific gravity.

[0030] In order to solve the above problems, the inventors conducted in-depth research and discovered that by filling the sheet with fibrous thermally conductive fillers of different average fiber diameters, it is possible to obtain a thermally conductive sheet with excellent thermal conductivity and low specific gravity, thus completing the present invention.

[0031] In other words, the present invention is a thermally conductive sheet containing two or more fibrous thermally conductive fillers (B) with different average fiber diameters in a polymer matrix (A), and the ratio of the maximum diameter to the minimum diameter of the average fiber is 2:1 to 45:1.

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

[0033] [Thermal Conductive Sheets] The thermally conductive sheet of the present invention is a thermally conductive sheet formed by molding a resin composition containing fillers in a polymer matrix (A) containing two or more fibrous thermally conductive fillers (B) with different average fiber diameters, wherein the ratio of the maximum diameter to the minimum diameter of the average fiber is 2:1 to 45:1. The details are described below.

[0034] [Resin compositions containing fillers] The resin composition containing filler is a resin composition containing a polymer matrix (A) and two or more fibrous thermally conductive fillers (B) with different average fiber diameters.

[0035] [Polymer Matrix (A)] The (A) component of the resin composition containing filler, i.e., the polymer matrix, is not particularly limited, but considering the filling properties of the (B) component, i.e., the fibrous thermally conductive filler, it is preferably a curable polymer composition selected from the group consisting of organopolysiloxanes, polyurethanes, polyacrylates, perfluoropolyether elastomers, unsaturated polyester resins, polyamide resins, epoxy resins, and phenolic resins. More preferably, it is an organopolysiloxane, perfluoropolyether elastomer, polyurethane, or polyacrylate with excellent flexibility. Even more preferably, it is an organopolysiloxane or perfluoropolyether elastomer with excellent heat resistance and cold resistance.

[0036] [Curing polymer composition] Therefore, component (A) is preferably a curable organopolysiloxane composition or a curable perfluoropolyether elastomer composition.

[0037] [Curing Organopolysiloxane Composition] The following is a detailed description of the curable organopolysiloxane composition.

[0038] Examples of curable organopolysiloxane compositions include thermosetting organopolysiloxane compositions, moisture-curing organopolysiloxane compositions, and electron beam-curing organosilicon resins. Examples of thermosetting organosilicon resins include addition-curing organopolysiloxane compositions and peroxide-curing organopolysiloxane compositions. Among these, addition-curing organopolysiloxane compositions are preferred, and addition-curing organopolysiloxane compositions containing the components (A-1) to (A-3) described below are more preferred. (A-1) Alkenyl-containing organopolysiloxanes, (A-2) Organohydrogen-containing polysiloxanes, (A-3) Platinum group metal-based curing catalysts.

[0039] [(A-1) Organopolysiloxanes containing alkenyl groups] (A-1) The component, namely the organopolysiloxane containing alkenyl groups, is an organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, and is the main agent in the resin composition containing filler of the present invention (to obtain a thermally conductive organosilicon cured product). Generally, the main chain portion is usually composed of repeating diorganosiloxane units, but it may contain branched structures or cyclic structures in some molecular structures. However, from the viewpoint of the mechanical strength and other physical properties of the cured product, linear diorganopolysiloxanes are preferred.

[0040] Examples of alkenyl groups include vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl alkenyl groups, which typically have 2 to 8 carbon atoms. Lower alkenyl groups such as vinyl and allyl are preferred, with vinyl being particularly preferred. It should be noted that while two or more alkenyl groups are preferably present in the molecule, to ensure good flexibility of the resulting cured product, they are preferably bonded only at the silicon atoms at the ends of the molecular chain.

[0041] The functional group other than the alkenyl group mentioned above is a monovalent hydrocarbon group, and examples 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 biphenyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Preferably, the functional group has 1 to 10 carbon atoms, particularly preferably 1 to 6 carbon atoms, and more preferably alkyl groups with 1 to 3 carbon atoms such as methyl, ethyl, propyl, and 3,3,3-trifluoropropyl, and phenyl groups. Furthermore, 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 typically preferred to be between 10 and 100,000 mm⁻¹. 2 The range of / s, particularly preferably, is 5,000 to 100,000 mm. 2 The range is / s. If the above viscosity is 10mm... 2 If the velocity is above a certain value (e.g., 1 / s), the resulting resin composition exhibits good storage stability. Additionally, if the velocity is above a certain value (e.g., 100,000 mm), the resin composition will have good storage stability. 2 If the ratio is below a certain value, the extensibility of the resulting resin composition will not deteriorate.

[0043] It should be noted that, in this specification, the kinematic viscosity is the value at 25°C using a Cannonfinsko type viscometer as described in JIS Z 8803:2011.

[0044] The organopolysiloxane of component (A-1) can be used alone or in combination with two or more different viscosities.

[0045] [(A-2) Organohydrogen polysiloxane] The organohydrogen polysiloxane in component (A-2) is an organohydrogen polysiloxane having an average of 2 or more, preferably 2 to 100, hydrogen atoms (silyl groups) directly bonded to silicon atoms in one molecule, and functions as a crosslinking agent in component (A-1). That is, the silyl groups in component (A-2) and the alkenyl groups in component (A-1) undergo addition reactions via a hydrosilylation reaction promoted by the platinum group metal curing catalyst of component (A-3), described later, to obtain a three-dimensional network structure with a crosslinked structure. It should be noted that when the number of silyl groups is less than 2, curing will not occur.

[0046] As an organohydrogen polysiloxane, it can be represented by the following average structural formula (1), but is not limited thereto. [Chemical Formula 1] (In the formula, R is independently a hydrogen atom or a monovalent hydrocarbon group that does not contain aliphatic unsaturated bonds, but there are 2 or more, preferably 2 to 100, and more preferably 2 to 10 hydrogen atoms 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), the monovalent hydrocarbon group other than the hydrogen atom of R that does not contain an aliphatic unsaturated bond can be exemplified by 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 biphenyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Preferably, the group has 1 to 10 carbon atoms, particularly preferably 1 to 6 carbon atoms, and more preferably alkyl groups with 1 to 3 carbon atoms such as methyl, ethyl, propyl, and 3,3,3-trifluoropropyl, and phenyl groups. Furthermore, R is not limited to being all identical.

[0048] The amount of component (A-2) added is, for example, 0.1 to 5.0 moles of silanol from component (A-2) relative to 1 mole of alkenyl group from component (A-1), preferably 0.3 to 2.0 moles, and more preferably 0.5 to 1.5 moles. If the amount of silanol from component (A-2) is 0.1 moles or more relative to 1 mole of alkenyl group from component (A-1), sufficient curing will occur, and the strength of the cured product will be sufficient to maintain its shape as a molded body, thus preventing it from becoming unmanageable due to insufficient strength. Furthermore, if it is 5.0 moles or less, the cured product will have good flexibility and will not become brittle.

[0049] [(A-3) Platinum Group Metal Curing Catalyst] The platinum group metal solidification catalyst of component (A-3) is a catalyst used to promote the addition reaction of alkenyl groups from component (A-1) with silanyl groups from component (A-2). Known catalysts can be listed as catalysts for hydrosilylation reactions. Specific examples include, for instance, platinum group metals such as platinum (including platinum black), rhodium, and palladium; platinum chloride, chloroplatinic acid, and chloroplatinates such as H₂PtCl₄·nH₂O, H₂PtCl₆·nH₂O, NaHPtCl₆·nH₂O, KHPtCl₆·nH₂O, Na₂PtCl₆·nH₂O, K₂PtCl₄·nH₂O, PtCl₄·nH₂O, PtCl₂, and Na₂HPtCl₄·nH₂O (where n is an integer from 0 to 6, preferably 0 or 6); and alcohol-modified chloroplatinic acid (refer to US patents). Patent No. 3,220,972; complexes of chloroplatinic acid with alkenes (US Patent Nos. 3,159,601, 3,159,662, and 3,775,452); substances containing platinum group metals such as platinum black and palladium on supports such as alumina, silica, and carbon; rhodium-olefin complexes; rhodium tri(triphenylphosphine)chloride (Wilkinson catalyst); complexes of platinum chloride, chloroplatinic acid, or chloroplatinate with vinyl-containing siloxanes, particularly with vinyl-containing cyclic siloxanes, etc.

[0050] The amount of component (A-3) used need to be an effective amount, preferably 0.1 to 2,000 ppm, more preferably 50 to 1,000 ppm, based on the mass conversion of platinum group metal elements relative to component (A-1). If it is 0.1 ppm or more, sufficient catalyst activity can be obtained, and if it is 2,000 ppm or less, the effect of promoting the addition reaction is sufficient, and the cost can also be controlled.

[0051] [Cureable perfluoropolyether elastomer composition] In addition, another preferred form, namely a cured perfluoropolyether elastomer composition, will be described in detail.

[0052] Examples of curable perfluoropolyether elastomer compositions include thermosetting perfluoropolyether elastomer compositions, moisture-curing perfluoropolyether elastomer compositions, and electron beam-curing perfluoropolyether elastomers. Examples of thermosetting perfluoropolyether elastomer compositions include addition-curing perfluoropolyether elastomer compositions and peroxide-curing perfluoropolyether elastomer compositions. Among these, addition-curing perfluoropolyether elastomer compositions are preferred, and addition-curing perfluoropolyether elastomer compositions containing the components (A-4) to (A-6) described below are more preferred. (A-4) Perfluoropolyether compounds containing alkenyl groups, (A-5) Fluorinated organohydrogen polysiloxanes, (A-6) Platinum group metal curing catalysts.

[0053] [(A-4) Perfluoropolyether compounds containing alkenyl groups] Component (A-4), namely the perfluoropolyether compound containing alkenyl groups, is a perfluoropolyether compound having two or more alkenyl groups in one molecule, and is the main agent in the resin composition containing filler of the present invention (to obtain a thermally conductive perfluoropolyether cured product). Generally, the main chain portion is usually composed of repeating perfluoropolyether units (perfluorooxyalkylene units).

[0054] Wherein, is the following general formula (2). [In the formula, X is -CH2-, -CH2O-, -CH2OCH2-, or -Y-NR] 1 -CO- (where Y is a divalent group represented by formula -CH2- or the following chemical formula 2, R 1 A divalent group (represented by a hydrogen atom or a monovalent hydrocarbon group), where X' is of the formula -CH2-, -CH2O-, -CH2OCH2-, or -CO-NR. 1 -Y'- (where Y' is a divalent group represented by formula -CH2- or the following chemical formula 3, R 1 (Same as above) representing divalent groups, [Chemical Formula 2] [Chemical Formula 3] Rf 1 The divalent perfluoropolyether group is represented by the following general formula (i) or the following general formula (ii), where z is independently 0 or 1. (In equation (i), p and q are integers from 1 to 150, and the average of the sum of p and q is 2 to 200, r is an integer from 0 to 6, and t and t' are 2 or 3.) (In equation (ii), u is an integer from 1 to 200, v is an integer from 1 to 50, and t and t' are the same as above.)

[0055] Rf 1 The lower limit of the degree of polymerization (p+q) or (u+v) of the divalent perfluoropolyether group is not particularly limited as long as it is an integer greater than or equal to 2. However, in order to achieve low pollution and low residue, it is preferred to be 30 or higher, and particularly preferred to be 80 or higher.

[0056] When R1 When it is a monovalent hydrocarbon group, examples can be listed of monovalent hydrocarbon groups with 1 to 20 carbon atoms, specifically 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 phenethyl.

[0057] [(A-5) Fluorinated organohydrogen polysiloxane] Component (A-5), namely the fluorinated organohydrogen polysiloxane, acts as a crosslinking agent or chain length extender for component (A-4). Therefore, each molecule of the aforementioned fluorinated organohydrogen polysiloxane has two or more, preferably three or more, hydrogen atoms bonded to silicon atoms (i.e., silane groups). It should be noted that component (A-5) can be used alone or in combination with two or more components.

[0058] From the viewpoint of compatibility and dispersibility with component (A-4), the fluorinated organohydrogen polysiloxane preferably has one or more groups selected from perfluoroalkyl, perfluoroalkylene, perfluorooxyalkyl, and perfluorooxyalkylene groups in one molecule. Examples of these perfluoro groups include, in particular, substances represented by the following general formula. Perfluoroalkyl: (In the formula, g is an integer from 1 to 20, preferably from 2 to 10.) Perfluoroalkylene: (In the formula, g is the same as above.) Perfluoroalkyl: [Chemical Formula 4] (In the formula, f is an integer from 2 to 200, preferably from 2 to 100, and h is an integer from 1 to 3.) Perfluoroalkylene: [Chemical Formula 5] (In the formula, i and j are integers greater than or equal to 1, and the average of i + j is 2 to 200, preferably 2 to 100.) (In the formula, k and L are integers greater than or equal to 1, and the average of k + L is 2 to 200, preferably 2 to 100.)

[0059] In addition, the divalent linking group that connects these perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene, or perfluorooxyalkylene groups to silicon atoms can be alkylene, arylene, or a combination thereof, or it can be a group formed by intervening ether bonds, amide bonds, carbonyl bonds, etc. in these groups. Examples of such groups with 2 to 12 carbon atoms are listed below. (Ph represents phenyl, Ph' represents phenylene.)

[0060] In the fluorinated organohydrogen polysiloxane of component (A-5), the monovalent substituents that are bonded to silicon atoms, other than organic groups containing perfluoroalkyl or perfluorooxyalkyl groups, can be listed as hydrocarbon groups with 1 to 20 carbon atoms, such as 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 unsubstituted hydrocarbon groups such as benzyl and phenethyl. In addition, at least some of the hydrogen atoms of these hydrocarbon groups can be replaced by chlorine atoms, such as substituted hydrocarbon groups such as chloromethyl, chloropropyl, and cyanoethyl.

[0061] The fluorinated organohydrogen polysiloxane as component (A-5) can be any of the following: cyclic, chain, three-dimensional network, or combinations thereof. The number of silicon atoms in the fluorinated organohydrogen polysiloxane is not particularly limited, but is typically 3 to 60, preferably around 4 to 30.

[0062] In addition, the molecular weight of the fluorinated organohydrogen polysiloxane of component (A-5) is preferably in the range of 750 to 3,000, and more preferably 800 to 2,400.

[0063] The amount of component (A-5) is the effective amount required to cure component (A-4) and obtain a cured product with the desired rubber elasticity. Specifically, for every 1 mole of the total alkenyl groups present in component (A-4) of this composition, 0.5 to 5.0 moles, preferably 1.0 to 2.0 moles, of the silanol groups in component (A-5) are supplied. If the above-mentioned amount is sufficient, the degree of crosslinking will be sufficient; if it is not excessive, chain length elongation will not preferentially occur, thus curing will be sufficient, and bubbling will not occur during curing, and the heat resistance, etc., of the resulting cured film will not decrease.

[0064] [(A-6) Platinum Group Metal Curing Catalyst] The platinum group metal curing catalyst of composition (A-6) is a catalyst used to promote the addition reaction between the alkenyl group from composition (A-4) and the silane group from composition (A-5). Known catalysts can be listed as catalysts for hydrosilylation reactions. Specifically, curing catalysts identical to those exemplified in composition (A-3) above can be shown.

[0065] The amount of component (A-6) used should be the effective amount as a catalyst. For example, it is preferred to use a formulation of 0.1 to 500 ppm (mass basis) relative to component (A-4) in platinum group metals.

[0066] [Fibrous thermally conductive filler (B)] The (B) component of the filler-containing resin composition of the present invention comprises two or more fibrous thermally conductive fillers with different average fiber diameters. There is no particular limit to the number of different average fiber diameters in the (B) component, but it can be, for example, four or fewer.

[0067] The shape of the aforementioned fibrous thermally conductive filler is not particularly limited as long as it is fibrous; examples include fibrous, needle-like, and whisker-like forms.

[0068] The size of the aforementioned fibrous thermally conductive filler can be selected appropriately as needed, without any particular limitation. Preferably, the filler has an aspect ratio (average major axis length / average minor axis length) of 2 or more and less than 30, and more preferably 5 or more and less than 30.

[0069] If it is a fibrous thermally conductive filler, the fibrous thermally conductive fillers will not entangle with each other, which can improve the filling performance and increase the thermal conductivity.

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

[0071] The average fiber diameter of the above-mentioned fibrous thermally conductive filler is not particularly limited, but is preferably 0.1 to 20 μm, more preferably 0.3 to 15 μm. It should be noted that one of the above-mentioned fibrous thermally conductive fillers is preferably carbon fiber with an average fiber diameter of 8 μm or more.

[0072] If it is a fibrous thermally conductive filler, the thermal conductivity is high in the long axis direction, so the cross-sectional area in the transverse direction becomes larger, which can effectively improve the thermal conductivity.

[0073] In addition, carbon has a lower specific gravity than common thermally conductive fillers such as alumina and aluminum nitride, making it suitable for applications requiring low specific gravity.

[0074] In addition, preferably one or more of the fibrous thermally conductive fillers are carbon fibers selected from those with 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] If it is a fibrous thermally conductive filler, the proportion of fillers with an average fiber diameter of 8μm or more is relatively large, which can further improve the thermal conductivity.

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

[0077] The proportion of component (B), i.e., the fibrous thermally conductive filler, in the thermally conductive sheet of the present invention is preferably 20 to 60% by mass, more preferably 30 to 52% by mass. Within this range, a good balance is achieved between high thermal conductivity and low specific gravity, which is therefore preferred.

[0078] In addition, the long axis direction of component (B), i.e., the fibrous thermally conductive filler, is preferably oriented in the thickness direction of the thermally conductive sheet formed by curing the composition.

[0079] If the sheet is thermally conductive, the thermal conduction path in the thickness direction of the sheet will be shorter, which is therefore preferred.

[0080] [Other ingredients] In the above-mentioned resin composition containing fillers, components such as solvents, thixotropic agents, dispersants, curing agents, curing accelerators, retardants, micro-adhesion agents, plasticizers, flame retardants, antioxidants, stabilizers, and colorants can be further added as needed.

[0081] In addition, filler materials other than component (B) may be incorporated into the above-mentioned resin composition containing filler. Specifically, examples include silica and titanium dioxide. There are no particular limitations on the amount of the above-mentioned filler material, but it is preferably 0 to 60 parts by weight, more preferably 0 to 40 parts by weight, relative to 100 parts by weight of component (A).

[0082] [Method for manufacturing resin compositions containing fillers] The above-mentioned resin composition containing filler can be manufactured by mixing the above-mentioned polymer matrix and the above-mentioned fibrous thermally conductive filler using a mixer or the like, and further mixing the above-mentioned other components as needed.

[0083] [Manufacturing method of thermally conductive sheet] The method for manufacturing the thermally conductive sheet of the present invention includes a step of molding the above-mentioned resin composition containing filler and a step of curing. Examples of such methods are as follows.

[0084] A method for obtaining a thermally conductive sheet with excellent thermal conductivity in the thickness direction and low specific gravity through the following process: Preparation step (I-1): Prepare a resin composition containing the above-mentioned polymer matrix (A) and the above-mentioned thermally conductive filler (B); In the filling process (I-2), the above-mentioned resin composition containing filler is filled into the mold; In the molding process (I-3), the filler-containing composition filled into the mold is solidified by heating or the like to obtain a molded body containing filler. The slicing process (I-4) involves slicing the above-mentioned filler-containing molded body to obtain a thermally conductive sheet.

[0085] The following is a detailed explanation of each of the above-mentioned processes.

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

[0087] Filling process (I-2) Using a dispenser, the prepared resin composition containing filler is filled into a mold with an X-axis (width) length of 40mm, a Y-axis (length) length of 40mm, and a Z-axis (height) length of 80mm. (Filling method) (i) The ejection direction is arranged neatly and ejected in a manner that is parallel to the X-axis direction of the mold, and then piled up and filled in the Z-axis direction. (ii) The ejection direction is arranged neatly and ejected in a manner that is parallel to the Y-axis direction of the mold, and then piled up and filled in the Z-axis direction. If this is done, oriented molded articles such as fibrous thermally conductive fillers can be obtained more preferably and efficiently. The stacking process in the Z-axis direction is preferably performed at least twice, and more preferably at least 20 times.

[0088] Molding method (I-3) The molding process can obtain a filled molded body by heating the resin composition containing filler that has been filled into the mold. The curing conditions for the above-mentioned resin composition containing filler are optimized according to the type of resin in the resin composition containing filler. For example, the curing conditions for the molded article containing filler obtained from the resin composition containing filler using silicone resin are preferably as follows. The curing temperature is preferably 0–200°C, more preferably 10–150°C. Furthermore, the curing time is preferably 1 minute–24 hours, more preferably 5 minutes–1 hour.

[0089] Slicing process (I-4) The slicing process is a process of obtaining a thermally conductive sheet of desired thickness by slicing the molded body containing filler obtained in the above-mentioned molding process. Specifically, it involves the following steps (i) or (ii). (i) The molded body containing filler is neatly arranged and ejected in such a way that the ejection direction is parallel to the X-axis direction of the mold, and is stacked and filled in the Z-axis direction. The molded body is sliced ​​to the desired thickness with respect to the YZ plane. (ii) The molded body containing filler is neatly arranged and ejected in such a way that the ejection direction is parallel to the Y-axis direction of the mold, and is stacked and filled in the Z-axis direction. The molded body is sliced ​​to the desired thickness with respect to the XZ plane. This allows the production of thermally conductive sheets in which the long axis of the fibrous thermally conductive filler is oriented in the thickness direction. Example

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

[0091] It should be noted that the kinematic viscosity is the value at 25°C using a Cannonfinsko type viscometer as described in JIS Z 8803:2011. The average fiber length, average fiber diameter, and aspect ratio were determined by SEM (scanning electron microscope). The average particle size is the cumulative average particle size (median diameter) on a volume basis, measured using a Microtrac MT3300EXII particle size analyzer manufactured by MicrotracBEL.

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

[0093] (A-1)Ingredients The following formula represents an organopolysiloxane: 97.1% by mass [Chemical Formula 6] In the above formula, n is the kinematic viscosity at 25°C, which is set to 30,000 mm³. 2 The number of seconds.

[0094] (A-2)Ingredients The following formula represents an organohydrogen polysiloxane: 2.2% by mass [Chemical Formula 7] In the above formula, o=27 and p=3, which are the average degree of polymerization, respectively.

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

[0096] The filler-containing resin composition of the present invention was manufactured in the following manner.

[0097] <Organopolysiloxane composition A containing fillers> An addition-reactive organopolysiloxane composition (specific gravity 1.0) of 55.0% by mass was mixed with carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2) of 30.4% by mass, carbon fiber B (average fiber length 40 μm, average fiber diameter 3 μm, aspect ratio 13, specific gravity 2.2) of 3.6% by mass, and carbon fiber C (average fiber length 10 μm, average fiber diameter 0.5 μm, aspect ratio 20, specific gravity 2.2) of 11.0% by mass to obtain a filler-containing organopolysiloxane composition A (specific gravity 1.32).

[0098] <Organopolysiloxane composition B containing fillers> An addition-reactive organopolysiloxane composition (specific gravity 1.0) of 55.0% by mass was mixed with carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2) of 34.0% by mass and carbon fiber B (average fiber length 40 μm, average fiber diameter 3 μm, aspect ratio 13, specific gravity 2.2) of 11.0% by mass to obtain an organopolysiloxane composition B containing filler (specific gravity 1.32).

[0099] <Organopolysiloxane composition C containing fillers> An addition-reactive organopolysiloxane composition (specific gravity 1.0) of 55.0% by mass was mixed with carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2) of 34.0% by mass and carbon fiber C (average fiber length 10 μm, average fiber diameter 0.5 μm, aspect ratio 20, specific gravity 2.2) of 11.0% by mass to obtain an organopolysiloxane composition C (specific gravity 1.32) containing filler.

[0100] <Organopolysiloxane composition D containing fillers> 55.0% by mass of an addition-reactive organopolysiloxane composition (specific gravity 1.0) was mixed with 45.0% by mass of carbon fiber D (average fiber length 300 μm, average fiber diameter 10 μm, aspect ratio 30, specific gravity 2.2) to obtain an organopolysiloxane composition D containing filler (specific gravity 1.32).

[0101] <Organopolysiloxane composition E containing fillers> An addition-reactive organopolysiloxane composition (specific gravity 1.0) of 55.0% by mass was mixed with carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2) of 34.0% by mass and carbon fiber E (average fiber length 50 μm, average fiber diameter 10 μm, aspect ratio 5, specific gravity 2.2) of 11.0% by mass to obtain an organopolysiloxane composition E containing filler (specific gravity 1.32).

[0102] <Organopolysiloxane composition containing filler F> An addition-reactive organopolysiloxane composition (specific gravity 1.0) of 45.6% by mass was mixed with carbon fiber A (average fiber length 250 μm, average fiber diameter 10 μm, aspect ratio 25, specific gravity 2.2) of 34.0% by mass and carbon fiber E (average fiber length 50 μm, average fiber diameter 10 μm, aspect ratio 5, specific gravity 2.2) of 20.4% by mass to obtain a filler-containing organopolysiloxane composition F (specific gravity 1.42).

[0103] <Organopolysiloxane composition G containing fillers> 55.0% by mass of an addition-reactive organopolysiloxane composition (specific gravity 1.0) was mixed with 45.0% by mass of carbon fiber B (average fiber length 40 μm, average fiber diameter 3 μm, aspect ratio 13, specific gravity 2.2) to obtain an organopolysiloxane composition G (specific gravity 1.3) containing filler.

[0104] <Organopolysiloxane composition H containing fillers> 55.0% by mass of an addition-reactive organopolysiloxane composition (specific gravity 1.0) and 45.0% by mass of carbon fiber C (average fiber length 10 μm, average fiber diameter 0.5 μm, aspect ratio 20, specific gravity 2.2) were mixed to obtain an organopolysiloxane composition H (specific gravity 1.3) containing filler.

[0105] Using the above-mentioned organopolysiloxane compositions A to H containing fillers, thermally conductive sheets are manufactured as follows.

[0106] <Example 1> Using a dispenser (MOHNO MASTER V2) manufactured by MUSASHI ENGINEERING and a nozzle with an inner diameter of 1.64 mm, the above-mentioned organopolysiloxane composition A containing filler was filled into the container in a manner that arranged 24 columns in the X-axis direction and 24 segments in the Z-axis direction along the Y-axis. The mixture was then heated at 80°C for 20 minutes to obtain a filled molded body 1. The filled molded body, i.e., the cured product, was then sliced ​​parallel to the XZ plane using a cutting blade to obtain a thermally conductive sheet 1 with a thickness of 2 mm.

[0107] <Example 2> The above-mentioned organopolysiloxane composition containing fillers was changed to the above-mentioned organopolysiloxane composition B containing fillers, and the thermally conductive sheet 2 was obtained by the same manufacturing method as in Example 1.

[0108] <Example 3> The above-mentioned organopolysiloxane composition containing fillers was changed to the above-mentioned organopolysiloxane composition C containing fillers, and the thermally conductive sheet 3 was obtained by the same manufacturing method as in Example 1.

[0109] <Comparative Example 1> The above-mentioned organopolysiloxane composition containing filler was changed to the above-mentioned organopolysiloxane composition D containing filler, and the thermally conductive sheet was attempted to be produced using the same manufacturing method as in Example 1, but it could not be ejected from the nozzle and the thermally conductive sheet could not be obtained.

[0110] <Comparative Example 2> The above-mentioned organopolysiloxane composition containing fillers was changed to the above-mentioned organopolysiloxane composition E containing fillers, and the thermally conductive sheet 4 was obtained by the same manufacturing method as in Example 1.

[0111] <Comparative Example 3> The above-mentioned organopolysiloxane composition containing fillers was changed to the above-mentioned organopolysiloxane composition F containing fillers, and thermally conductive sheet 5 was obtained by the same manufacturing method as in Example 1.

[0112] <Comparative Example 4> The above-mentioned organopolysiloxane composition containing fillers was changed to the above-mentioned organopolysiloxane composition G containing fillers, and the thermally conductive sheet 6 was obtained by the same manufacturing method as in Example 1.

[0113] <Comparative Example 5> The above-mentioned organopolysiloxane composition containing fillers was changed to the above-mentioned organopolysiloxane composition H containing fillers, and the thermally conductive sheet 7 was obtained by the same manufacturing method as in Example 1.

[0114] <Assessment Items> The thermal conductivity and specific gravity of each thermally conductive sheet obtained in Examples 1 to 3 and Comparative Examples 2 to 5 were measured in the following manner.

[0115] Thermal conductivity The thermally conductive sheets obtained in Examples 1-3 and Comparative Examples 2-5 were stamped into circles with a diameter of 12.7 mm and used as test pieces. The thermal conductivity was measured using the laser flash method (LFA 447 Nanoflash, manufactured by Netzsch) according to JIS R 1611:2010 standard. The results are shown in Table 1 below.

[0116] Specific gravity The specific gravity of each thermally conductive sheet obtained in Examples 1-3 and Comparative Examples 2-5 was measured at 25°C according to JIS K 6249:2003. The results are shown in Table 1 below.

[0117] [Table 1]

[0118] The carbon fiber content (total) of Examples 1, 2, and 3 was all 45.0%, and they contained two or more types of carbon fibers with different average fiber diameters: one with an average fiber diameter of 8 μm or more, and the other with an average fiber diameter of 1 μm or more but less than 8 μm or less than 1 μm. Furthermore, the ratio of the maximum to the minimum average fiber diameter was in the 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 Examples 2 (carbon fibers A and E with an average fiber diameter of 10 μm), 4 (carbon fiber B with an average fiber diameter of 3 μm), and 5 (carbon fiber C with an average fiber diameter of 0.5 μm) all had a total carbon fiber content of 45.0%, but all contained only one type of average fiber diameter. 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. These thermal conductivityes were lower than those of Examples 1-3. This result indicates that even with the same amount of fibrous thermally conductive filler, thermal conductivity can be improved by using fibrous thermally conductive fillers containing two or more types with different average fiber diameters.

[0120] Although Comparative Example 1 had a total carbon fiber content of 45.0%, its average fiber diameter was of one type (carbon fiber D with an average fiber diameter of 10 μm and an aspect ratio of 30). This meant that it could not be dispensed using a distributor during the manufacturing process of the thermally conductive sheet, making sheet forming impossible. This result indicates that if the average fiber diameter is 8 μm or more and the aspect ratio is 30 or more, the viscosity of the composite increases, making high-filling quantification difficult.

[0121] The carbon fiber content (total) of Comparative Example 3 was 54.4% by mass, which was higher than that of Examples 1-3 (carbon fibers A and E with an average fiber diameter of 10 μm). The carbon fiber with an average fiber diameter of 10 μm had a thermal conductivity of 20.6 W / m·K and a specific gravity of 1.40, which was lower than that of Examples 1-3. This result indicates that even with a low filling amount of fibrous thermally conductive filler, thermal conductivity can be improved by using fibrous thermally conductive fillers containing two or more fibers with different average fiber diameters and a ratio of the maximum to minimum average fiber diameter ranging from 2:1 to 45:1.

[0122] As described above, the present invention provides a thermally conductive sheet with excellent thermal conductivity and low specific gravity by filling it with two or more fibrous thermally conductive fillers of different average fiber diameters and with the ratio of the maximum diameter to the minimum diameter of the average fiber diameter ranging from 2:1 to 45:1.

[0123] This instruction manual includes the following methods. [1] A thermally conductive sheet, characterized in that it contains 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 is 2:1 to 45:1. [2] According to the thermally conductive sheet described in [1], the thermal conductivity in the thickness direction of the thermally conductive sheet is 25 W / m·K or more, and the specific gravity is less than 1.4. [3] The thermally conductive sheet according to [1] or [2] is characterized in that the aspect ratio of the fibrous thermally conductive filler (B) is 2 or more and less than 30. [4] The thermally conductive sheet according to any one of [1] to [3] is characterized in that, in the fibrous thermally conductive filler (B), one or more are carbon fibers with an average fiber diameter of 8 μm or more. [5] The thermally conductive sheet according to any one of [1] to [4] is characterized in that, of the fibrous thermally conductive filler (B), one or more are carbon fibers with an average fiber diameter of 1 μm or more and less than 8 μm or an average fiber diameter of less than 1 μm. [6] The thermally conductive sheet according to any one of [1] to [5] is characterized in that the proportion of the fibrous thermally conductive filler (B) contained in the thermally conductive sheet is 20 to 60% by mass. [7] The thermally conductive sheet according to any one of [1] to [6] is characterized in that the long axis of the fibrous thermally conductive filler (B) is oriented in the thickness direction of the thermally conductive sheet. [8] The thermally conductive sheet according to any one of [1] to [7] is characterized in that the polymer matrix (A) is a cured product of a curable polymer composition comprising one or more selected from the group consisting of organopolysiloxanes, polyurethanes, polyacrylates, perfluoropolyether elastomers, unsaturated polyester resins, polyamide resins, epoxy resins and phenolic resins.

[0124] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are merely illustrative, and any structure that has the same essential technical concept as that described in the claims of the present invention and produces the same effect is included within the technical scope of the present invention.

Claims

1. A thermally conductive sheet, characterized in that, The polymer matrix contains two or more types of fibrous thermally conductive fillers with different average fiber diameters, wherein the ratio of the maximum diameter to the minimum diameter of the average fiber is 2:1 to 45:

1.

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

4.

3. The thermally conductive sheet according to claim 1, characterized in that, The aspect ratio of the fibrous thermally conductive filler is greater than 2 and less than 30.

4. The thermally conductive sheet according to claim 1, characterized in that, Of the fibrous thermally conductive filler, one or more are carbon fibers with an average fiber diameter of 8 μm or more.

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

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

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

8. The thermally conductive sheet according to claim 1, characterized in that, The polymer matrix is ​​a cured product of a curable polymer composition, which comprises one or more selected from the group consisting of organopolysiloxanes, polyurethanes, polyacrylates, perfluoropolyether elastomers, unsaturated polyester resins, polyamide resins, epoxy resins and phenolic resins.

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