Thermally conductive sheet

Abstract

A thermally conductive sheet containing a silicone resin, a thermally conductive filler, and a compound (A) and / or a compound (B) which each have a specific structure, wherein the melting point of the compound (B) is 35°C or higher, and the compound (B) is a graft copolymer.

Description

Thermal conductive sheet

[0001] This invention relates to a thermal conductive sheet.

[0002] In recent years, with the miniaturization and increased performance of electronic devices, there has been a growing demand for material technologies that efficiently dissipate the heat generated during operation. Heat from heat sources such as IC chips is dissipated through a heat sink, but to ensure efficient heat conduction between the heat source and the heat sink, a resin composition called TIM (Thermal Interface Material) is often sandwiched between the heat source and the heat sink.

[0003] TIM is a resin composition that combines resin and a thermally conductive filler, and is often used in the form of a sheet with a thickness corresponding to the gap between the heat source and the heat sink. In recent years, there has been a demand for highly compressible sheets to broaden the tolerance range of TIM for assembly tolerances of the gap. Also, because high compression can cause chip breakage when high load is applied, the sheet needs to be flexible. On the other hand, adding flexibility to the sheet tends to worsen its handling properties. As a means of resolving this trade-off between compressibility and handling properties, a resin composition containing a matrix such as silicone resin, a phase change material (PCM), and a thermally conductive filler has been proposed.

[0004] For example, Patent Document 1 discloses an invention relating to a thermally conductive sheet having excellent compressibility, comprising a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B), and a thermally conductive filler (C) dispersed in the binder component and oriented in the thickness direction of the thermally conductive sheet, and having a thickness within a certain range.

[0005] Patent Document 2 discloses an invention relating to a thermally conductive sheet that has excellent thermal conductivity and suppresses expansion at high temperatures, comprising a binder component which is a mixture of a silicone matrix and an alkyl silicone compound, and a thermally conductive filler dispersed in the binder component, wherein the alkyl silicone compound is contained in a predetermined amount.

[0006] Patent No. 7089322 Patent No. 7424714

[0007] Incidentally, sheets made of TIM are also required to have reworkability in order to improve the yield during mounting. To improve reworkability, for example, it is conceivable to improve the toughness of the TIM to prevent tearing or parts of the sheet from remaining on the adherend when peeling the sheet from the adherend, but there is still room for improvement in terms of reworkability. Furthermore, while phase change materials (PCMs) disclosed as prior art can improve the compressibility at high temperatures and the handlingability at room temperature of resin compositions containing them, the phase change materials (PCMs) may bleed to the surface at high temperatures, so there is room for improvement in terms of reliability as well.

[0008] Therefore, the object of the present invention is to provide a highly reliable thermal conductive sheet that can achieve both ease of handling at room temperature, high-temperature compressibility, and reworkability, while suppressing bleeding to the surface of the phase change material.

[0009] The inventors have found that the above problems can be solved by incorporating a silicone resin, a thermally conductive filler, and at least one of compound (A) and compound (B), each having a specific structure, into a thermally conductive sheet. That is, the present invention provides the following [1] to

[13] .

[0010] [1] A thermal conductive sheet comprising a silicone resin, a thermal conductive filler, and a compound (Z) selected from the group consisting of a compound (A) having a structure represented by the following formula (1) and a compound (B) having a structure represented by the following formula (2), wherein the melting point of compound (B) is 35°C or higher. (In formula (1), X １ ~X ３ Each of these is an independent trivalent organic group, Y １ ~Y ３ Each of these is an independent divalent organic group, Z １ is a monovalent organic group, Z ２is a hydrogen atom or a monovalent organic group, each R is independently a monovalent organic group, W is a divalent organic group containing one or more carbon-carbon double bonds or triple bonds, k is a number from 16 to 33 inclusive, n, m, o, r, s are each a number of 1 or more, and p and q are each a number of 0 or more) (In formula (2), X1 and X2 are each independently a trivalent organic group, Y1 and Y2 are each independently a divalent organic group, Z is a monovalent organic group, each R is independently a monovalent organic group, c is a number from 16 to 33 inclusive, a, f, g are each a number of 1 or more, b is a number of 0.5 or more, and d and e are each a number of 0 or more) [2] The heat conductive sheet according to [1], wherein in the compound (A), W contains one or more vinylidene groups or vinylene groups. [3] The heat conductive sheet according to [1] or [2], wherein in the compound (A), X １ to X ３ is a hydrocarbon group having 2 to 3 carbon atoms. [4] In the compound (A), Y １ to Y ３A thermal conductive sheet according to any one of [1] to [3], wherein the compound (A) contains an ester group or an amide group. [5] A thermal conductive sheet according to any one of [1] to [4], wherein the m, n, and o satisfy the following relationship (α): m / (n+m+o)≧0.025 Formula (α) [6] A thermal conductive sheet according to any one of [1] to [5], wherein the m, n, o, and r satisfy the following relationship (β): o*r / (n+m+o)≧1.00 Formula (β) [7] A thermal conductive sheet according to any one of [1] to [6], wherein the compound (B) is such that X1 and X2 are each independently trivalent saturated hydrocarbon groups having 2 to 6 carbon atoms, and Y1 and Y2 are each independently divalent organic groups containing an ester group or an amide group. [8] The thermal conductive sheet according to any one of [1] to [7], wherein the content of compound (Z) is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the silicone resin. [9] The thermal conductive sheet according to any one of [1] to [8], wherein in compound (B), b, f, and a satisfy the following relationship: b * f / (b + a) ≥ 0.3 Formula (γ)

[10] The thermal conductive sheet according to any one of [1] to [9], wherein the thermal conductive filler is at least one selected from the group consisting of metal, inorganic hydroxide, inorganic oxide, inorganic nitride, carbon fiber, graphite, and diamond.

[11] The thermal conductive sheet according to any one of [1] to

[10] , wherein the thermal conductive filler includes an anisotropic filler.

[12] The thermal conductive sheet according to

[11] , wherein the thermal conductive filler includes an anisotropic filler, and the volume ratio of the anisotropic filler content to the anisotropic filler content (anisotropic filler content / anisotropic filler content) is 0.30 or more and 3.0 or less.

[13] The thermal conductive sheet according to

[11] or

[12] , wherein the anisotropic filler is oriented in the thickness direction of the thermal conductive sheet.

[0011] According to the present invention, it is possible to provide a highly reliable thermal conductive sheet that achieves both ease of handling at room temperature, high-temperature compressibility, and reworkability, while suppressing bleeding to the surface of the phase change material.

[0012] [Thermal Conductive Sheet] The thermal conductive sheet of the present invention comprises a silicone resin, a thermally conductive filler, and a compound (Z) selected from the group consisting of a compound having a structure represented by formula (1) described later (hereinafter also simply referred to as "compound (A)") and a compound having a structure represented by formula (2) described later (hereinafter also simply referred to as "compound (B)"). The thermal conductive sheet of the present invention may contain only compound (A) or compound (B), or it may contain both compound (A) and compound (B). The components contained in the thermal conductive sheet will be described in detail below.

[0013] (Compound (A)) Compound (A) is the compound represented by the following formula (1). (In formula (1), X １ ~X ３ Each of these is an independent trivalent organic group, Y １ ~Y ３ Each of these is an independent divalent organic group, Z １ is a monovalent organic group, Z ２ (where is a hydrogen atom or a monovalent organic group, R is independently a monovalent organic group, W is a divalent organic group containing one or more carbon-carbon double or triple bonds, k is a number between 16 and 33, n, m, o, r, s are each a number of 1 or more, and p, q are each a number of 0 or more)

[0014] The thermal conductive sheet of the present invention contains compound (A), which functions as a phase change material, making it possible to improve the handling properties of the thermal conductive sheet at room temperature (25°C) while increasing its compressibility at high temperatures (e.g., 60°C). Furthermore, compound (A) has a specific structure represented by formula (1), which improves the reworkability of the thermal conductive sheet, preventing the sheet from tearing when peeling it from an adherend, for example. In addition, it can reduce the amount of bleed and increase reliability.

[0015] Compound (A) is X １ ~X ３The main chain is composed of a portion having a long-chain alkyl group as a branched chain, a portion having a carbon-carbon double or triple bond (hereinafter also referred to as an "unsaturated carbon bond"), and a portion having a silicone chain. Compound (A) is a compound having a unit represented by the following formula (3), a unit represented by formula (4), and a unit represented by formula (5) in a molar ratio n:m:0. In this specification, the unit represented by formula (3) is also called a long-chain alkyl group-containing unit, the unit represented by formula (4) is also called an unsaturated carbon bond-containing unit, and the unit represented by formula (5) is also called a silicone chain-containing unit. Compound (A) is a graft copolymer having a polyorganosiloxane structure as a side chain. (In equations (3) to (5), X １ ~X ３ , Y １ ~Y ３ Z １ Z ２ (R, k, p, q, r, and s are equivalent to those in equation (1))

[0016] Compound (A) has a long-chain alkyl group-containing unit, which is crystalline and therefore has a melting point above a certain level. As a result, it remains unmelted at room temperature and melts at high temperatures. Consequently, a thermal conductive sheet containing compound (A) is considered to have good handling properties at room temperature and high compressibility at high temperatures. Furthermore, because compound (A) has an unsaturated carbon bond-containing unit, the unsaturated carbon bond in this unit functions as a crosslinking group and reacts with the silicone resin described later to form a crosslinked body. This makes it compatible with silicone resin, improving the toughness of the thermal conductive sheet and resulting in good reworkability. Moreover, because compound (A) has a silicone chain-containing unit, it is compatible with silicone resin and its cured products, improving dispersibility. In addition, the presence of silicone chains as side chains is thought to reduce bleed and further increase compressibility at high temperatures.

[0017] X in compound (A) １ ~X ３ These are each independently trivalent organic groups. １ ~X ３X may have heteroatoms such as oxygen atoms, nitrogen atoms, and sulfur atoms, but it is preferable that it does not have heteroatoms. That is, X １ ~X ３ Each of these is preferably an independent hydrocarbon group. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, but it is more preferably an aliphatic hydrocarbon group. １ ~X ３ Preferably, each is independently a trivalent hydrocarbon group having 2 to 6 carbon atoms, and more preferably a hydrocarbon group having 2 to 3 carbon atoms. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but it is preferably a saturated hydrocarbon group. １ ~X ３ It is even more preferable that each of these is independently a group represented by the following formula (6) or (7): X １ The base represented by equation (6), X ２ and X ３ It is particularly preferable that the group is represented by formula (7). (In formulas (6) and (7), *1 is a bond that connects to an atom constituting the main chain of compound (A), and *2 and *3 are Y １ , Y ２ or Y ３ (It is a coupling that connects with)

[0018] Y １ ~Y ３ These are each independently divalent organic groups. １ ~Y ３ Each of these is preferably an organic group having 1 to 10 carbon atoms, and preferably an organic group having 1 to 6 carbon atoms. １ ~Y ３ It may have heteroatoms such as oxygen atoms, nitrogen atoms, and sulfur atoms, and it is preferable that it has oxygen atoms or nitrogen atoms, and more preferably that it has oxygen atoms. More specifically, Y １ ~Y ３ Each of these is preferably a divalent organic group containing an ester group or an amide group, and more preferably an organic group containing an ester group. Among these, Y１ ~Y ３ It is even more preferable that each of these is independently a group represented by the following formula (8) or (9): Y １ Y is a base represented by equation (8). ２ and Y ３ It is particularly preferable that the base is represented by formula (9). In formulas (8) and (9), *4 is a bond that connects to an atom constituting the main chain of compound (A), and *5 is a bond that connects to an atom constituting the side chain of compound (A). In formula (9), Ra is an alkylene group having 1 to 10 carbon atoms, preferably an alkylene group having 1 to 4 carbon atoms.

[0019] Z １ Each of these is an independently monovalent organic group. The organic group preferably has 1 to 10 carbon atoms, and more preferably 1 to 4 carbon atoms. １ It may have heteroatoms such as oxygen atoms, nitrogen atoms, and sulfur atoms, but it is preferable that it does not have heteroatoms. That is, Z １ It is preferable that it be a hydrocarbon group. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, but an aliphatic hydrocarbon group is preferred. Z １ Preferably, each is independently a hydrocarbon group having 1 to 10 carbon atoms, and more preferably a hydrocarbon group having 1 to 4 carbon atoms. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but it is preferable that it be a saturated hydrocarbon group. Among them, Z １ Each of these is independently preferably an alkyl group, and more preferably an alkyl group having 1 to 4 carbon atoms. The alkyl group may be linear or have a branched structure. Also, Z １ It is even more preferable that it be a methyl group.

[0020] Z ２ This is a hydrogen atom or a monovalent organic group. ２ It is preferable that it is a monovalent organic group. ２ If it is a monovalent organic group, Z ２ is, Z １It may be the same organic group as Z １ It may be a different organic group, but Z １ It is preferable that it is the same organic group as Z. ２ Regarding the monovalent organic group in the above Z １ As explained in the description, a detailed explanation will be omitted.

[0021] In formula (1), k is a methylene group (-CH ２ The number of -) is between 16 and 33. By setting k to this range, compound (A) will have a melting point above a certain level, which improves the handling properties of the thermal conductive sheet at room temperature, increases its compressibility at high temperatures, and further improves its reworkability. k is preferably between 16 and 30, and more preferably between 17 and 25. Note that in formula (1), Y １ The portion that forms a long-chain alkyl group that is bonded, i.e., "-(CH ２ The part ")k-" can exist in multiple forms depending on the number of n. k is one of multiple "-(CH ２ This is the average value of k-.

[0022] Y in equation (1) ２ The W bonded to is a divalent organic group having one or more unsaturated carbon bonds. The organic group preferably has 1 to 10 carbon atoms, and more preferably 1 to 4 carbon atoms. W may have heteroatoms such as oxygen, nitrogen, or sulfur atoms, but it is preferable that it does not have heteroatoms. In other words, it is preferable that W is an unsaturated hydrocarbon group. The unsaturated hydrocarbon group may be an unsaturated aliphatic hydrocarbon group. W is preferably an unsaturated hydrocarbon group having 1 to 10 carbon atoms, and more preferably an unsaturated hydrocarbon group having 1 to 4 carbon atoms. The unsaturated carbon bonds may be reactive double bonds or reactive triple bonds, but it is preferable that they are reactive double bonds. In particular, it is even more preferable that W contains one or more vinylidene groups or vinylene groups, even more preferable that it contains one or more vinylidene groups, even more preferable that it contains one vinylidene group, and especially preferable that it is a vinylidene group.

[0023] Y in formula (1) ３ bonded to -(SiO ４／２ ) p -(SiRO ３／２ ) q -(SiR ２ O ２／２ ) r -(SiR ３ O １／２ ) s - moiety is a silicone chain. Generally, as shown below, the SiR ３ O １／２ moiety is referred to as an M unit, the SiR ２ O ２／２ moiety is referred to as a D unit, the SiRO ３／２ moiety is referred to as a T unit, and the SiO ４／２ moiety is referred to as a Q unit. The silicone chain in formula (1) comprises SiR ３ O １／２ (M unit) and SiR ２ O ２／２ (D unit), and may optionally comprise either one or both of SiRO ３／２ (T unit) and SiO ４／２ (Q unit). The arrangement of SiR ３ O １／２ (M unit), SiR ２ O ２／２ (D unit), SiRO ３／２ (T unit), and SiO ４／２ (Q unit) in the silicone chain is not particularly limited. p, q, r, and s in formula (1) respectively represent the number of SiO ４／２ (Q unit), SiRO ３／２ (T unit), SiR ２ O ２／２ (D unit), and SiR ３ O １／２ (M unit). Note that SiR ３ O １／２ (M unit) is monovalent and is a terminal moiety of the silicone chain. SiR ２ O ２／２ (D unit) is divalent and is a linear moiety of the silicone chain. SiRO ３／２The (T unit) is trivalent, and each of the three oxygen atoms bonds with one of the units to form a branched structure. SiO ４／２ The (Q unit) is tetravalent, and each of the four oxygen atoms bonds with one of the units to form a branched structure.

[0024] Y in equation (1) ３ In the silicone chain bonded to the molecule, R is a monovalent organic group. The organic group preferably has 1 to 10 carbon atoms, and more preferably has 1 to 4 carbon atoms. R may have heteroatoms such as oxygen, nitrogen, or sulfur atoms, but it is preferable that it does not have heteroatoms. In other words, R is preferably a hydrocarbon group. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, but an aliphatic hydrocarbon group is preferred. R is preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, and more preferably a hydrocarbon group having 1 to 4 carbon atoms. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but it is preferable that it is a saturated hydrocarbon group. R is preferably an alkyl group having 1 to 4 carbon atoms, and among these, at least one selected from a methyl group and a butyl group is preferred. Furthermore, of the multiple R groups in one molecule, it is preferable that 50% or more are methyl groups, more preferably 80% or more are methyl groups, and more preferably 90% or more are methyl groups.

[0025] In formula (1), it is preferable that m, n, and o satisfy the following relationship in formula (α): m / (n+m+o) ≥ 0.01 Formula (α) As described above, when m / (n+m+o) is 0.01 or higher, the reworkability of the resin composition is easily improved. Note that m / (n+m+o) is an indicator of the content ratio of unsaturated carbon bond-containing units in compound (A) of formula (1), and having this value above a certain level is effective for the reworkability improvement effect of the present invention. From this viewpoint, m / (n+m+o) is more preferably 0.015 or higher, even more preferably 0.025 or higher, even more preferably 0.04 or higher, and preferably 0.1 or lower, and more preferably 0.08 or lower.

[0026] In compound (A) of formula (1), r is a number of 1 or more. Preferably, r is 5 to 200, more preferably 10 to 150, and even more preferably 30 to 100. When r is within the above range, the compressibility of the resin composition tends to improve. Also, when r is within the above range, the amount of bleed tends to be reduced.

[0027] Furthermore, it is preferable that m, n, o, and r in formula (1) satisfy the following relationship in formula (β): o*r / (n+m+o) ≥ 1.00 Formula (β) As described above, when o*r / (n+m+o) is 1.00 or higher, the compressibility of the thermal conductive sheet tends to increase. Note that o*r / (n+m+o) is an indicator of the content ratio of the linear portion (unit D) of the silicone chain in compound (A) of formula (1), and it is effective for the compressibility effect of the present invention to be above a certain value. From this viewpoint, o*r / (n+m+o) is more preferably 1.02 or higher, even more preferably 1.05 or higher, and preferably 10.0 or lower, and more preferably 7.0 or lower.

[0028] In compound (A) of formula (1), s is a number of 1 or more. Preferably, s is 1 or more and 10 or less, more preferably 1 or more and 5 or less, and even more preferably 1. In compound (A) of formula (1), p is a number of 0 or more, preferably 0 or more and 5 or less, more preferably 0 or more and 1 or less, and even more preferably 0. In compound (A) of formula (1), q is a number of 0 or more, preferably 0 or more and 5 or less, more preferably 0 or more and 1 or less, and even more preferably 0. Note that in formula (1), Y ３ Multiple silicone chains can be bonded to the oxygen atom, depending on the number of oxygen atoms. The values ​​of p, q, r, and s in equation (1) are obtained as the average values ​​across multiple silicone chains.

[0029] In formula (1), n, m, and o correspond to the number of long-chain alkyl group-containing units, unsaturated carbon bond-containing units, and silicone chain-containing units, respectively. From the viewpoint of improving the compressibility of the thermal conductive sheet at high temperatures while also improving reworkability, these numbers are preferably as follows: n is a number of 1 or more, for example, 5 to 1000, preferably 10 to 500, more preferably 50 to 300, and even more preferably 100 to 250. m is a number of 1 or more, preferably 2 to 70, more preferably 3 to 50, and even more preferably 5 to 40. o is a number of 1 or more, preferably 3 to 70, more preferably 5 to 50, and even more preferably 8 to 40.

[0030] In equation (1), n, m, o, k, p, q, r, and s are: １ H-NMR, ２９ This can be determined by methods such as Si-NMR and size exclusion chromatography, and further details are described in the examples.

[0031] The melting point of compound (A) is preferably 30°C to 100°C, more preferably 35°C to 80°C, and even more preferably 40°C to 60°C. A melting point above a certain level of compound (A) ensures good handling at room temperature and compressibility at high temperatures. Furthermore, a melting point below a certain level of compound (A) can further enhance compressibility at high temperatures. The melting point of compound (A) is measured by differential scanning calorimeter, and details are described in the examples.

[0032] The method for producing compound (A) is not particularly limited, but examples include polymerizing a monomer for forming a long-chain alkyl group-containing unit represented by formula (3), a monomer for forming an unsaturated carbon bond-containing unit represented by formula (4), and a monomer for forming a silicone chain-containing unit represented by formula (5). In the following description, the monomer for forming the long-chain alkyl group-containing unit represented by formula (3) will be referred to as a crystalline monomer, the monomer for forming the unsaturated carbon bond-containing unit represented by formula (4) will be referred to as a crosslinkable monomer, and the monomer for forming the silicone chain-containing unit represented by formula (5) will be referred to as a silicone monomer. Examples of the crystalline monomer include alkyl (meth)acrylates. Examples of the crosslinkable monomer include unsaturated carbon bond-containing (meth)acrylates represented by the following formula (X), which are represented by isoprenyl group-containing (meth)acrylates.

[0033] (In formula (X), R is a hydrogen atom or a methyl group, and Z ２ (And W is synonymous with equation (1), and Ra is synonymous with equation (9))

[0034] Furthermore, examples of the above-mentioned silicone monomers include one-end (meth)acrylic acid-modified silicones, in which one end of the silicone chain is modified with (meth)acrylic acid. Note that (meth)acrylic is a concept that includes both acrylic and methacrylic.

[0035] (Compound (B)) Compound (B) has the structure shown in the following formula (2). Compound (B) functions as a phase change material, similar to compound (A) described above, and can improve the handling of the thermal conductive sheet at room temperature (25°C) while increasing its compressibility at high temperatures (e.g., 60°C). Furthermore, because compound (B) has the specific structure represented by formula (2), it can reduce the amount of surface bleed in the thermal conductive sheet, thereby improving the reliability of the product. In addition, because compound (B) has a silicone chain-containing unit, it blends well with silicone resin and its cured products, improving dispersibility. As a result, stress does not concentrate on the phase change material inside the thermal conductive sheet, making it less prone to breakage and improving reworkability. In addition, it is thought that the presence of silicone chains as side chains further reduces the amount of bleed and increases compressibility at high temperatures.

[0036] The melting point of compound (B) is 35°C or higher. If the melting point of compound (B) is below 35°C, the handling properties of the thermal conductive sheet at room temperature and its compressibility at high temperatures will be poor. The melting point of compound (B) is preferably 40°C or higher, and more preferably 42°C or higher. Furthermore, from the viewpoint of further improving compressibility at high temperatures, the melting point of compound (B) is preferably 60°C or lower, and more preferably 58°C or lower. The melting point of compound (B) is measured by differential scanning calorimeter, and the details are as described in the examples.

[0037] Compound (B) has a structure represented by the following formula (2). (In formula (2), X1 and X2 are each independently trivalent organic groups, Y1 and Y2 are each independently divalent organic groups, Z is a monovalent organic group, R is each independently monovalent organic group, c is a number between 16 and 33, a, f, and g are each a number of 1 or more, b is a number of 0.5 or more, and d and e are each a number of 0 or more.)

[0038] Compound (B) is a graft copolymer in which the main chain is composed of X1 and X2, and which comprises a molar portion having a long-chain alkyl group and a molar portion having a silicone chain as branched chains. Compound (B) is a compound having a unit represented by the following formula (10) and a unit represented by formula (11) in a molar ratio a:b. In this specification, the unit represented by formula (10) is also referred to as the long-chain alkyl group-containing unit, and the unit represented by formula (11) is also referred to as the silicone chain-containing unit. (In equations (10) and (11), X1, X2, Y1, Y2, Z, R, c, d, e, f, and g are equivalent to those in equation (2).)

[0039] Compound (B), like compound (A) described above, has a long-chain alkyl group-containing unit, which is crystalline and therefore has a melting point above a certain level. As a result, it remains unmelted at room temperature and melts at high temperatures. Consequently, a thermal conductive sheet containing compound (B) is expected to have good handling properties at room temperature and high compressibility at high temperatures. Furthermore, because compound (B) has a silicone chain-containing unit, it is compatible with silicone resins and their cured products, improving dispersibility. In addition, the presence of silicone chains as side chains is expected to reduce bleed and further increase compressibility at high temperatures.

[0040] X1 and X2 are X in the above-mentioned compound (A). １ ~X ３ Similarly, each is an independent trivalent organic group, and for details, see X １ ~X ３ As explained in the description above, a detailed explanation will be omitted. In compound (B), it is particularly preferable that X1 is the group represented by formula (6) and X2 is the group represented by formula (7). In formulas (6) and (7) that constitute compound (B), *1 is a bond that connects to an atom constituting the main chain of compound (B), and *2 and *3 are bonds that connect to Y1 or Y2.

[0041] Y1 and Y2 are Y in the above compound (A) １ ~Y ３Similarly, each is an independently divalent organic group, and for details, see Y １ ~Y ３ As explained in the description above, a detailed explanation will be omitted. In compound (B), it is particularly preferable that Y1 is the group represented by formula (8) and Y2 is the group represented by formula (9). In formulas (8) and (9) that constitute compound (B), *4 is a bond that connects to an atom constituting the main chain of compound (B), and *5 is a bond that connects to an atom constituting the side chain of compound (B).

[0042] Z is the Z in compound (A) described above. １ Similarly, it is a monovalent organic group, and for details, see Z １ As explained in the previous section, a detailed explanation will be omitted.

[0043] In formula (2), c is a methylene group (-CH), similar to k in formula (1) described above. ２ The number of -) is between 16 and 33, preferably between 16 and 30, and more preferably between 17 and 25. By setting c to a certain range, compound (B) will have a melting point above a certain level, thereby improving the handling properties of the thermal conductive sheet at room temperature while increasing its compressibility at high temperatures. Note that in formula (2), the portion that forms the long-chain alkyl group bonded to Y1 is, i.e., "-(CH ２ The part ")c-" can exist in multiple forms depending on the number of a. c is a multiple "-(CH ２ This is the average value of )c-".

[0044] -(SiO2) bonded to Y2 in equation (2) ４／２ ) ｄ - (SiRO ３／２ ) ｅ - (SiR ２ O ２／２ ) ｆ - (SiR ３ O １／２ ) ｇ Regarding the - part, Y in equation (1) ３ Bonded, -(SiO ４／２ ) p - (SiRO ３／２ )q - (SiR ２ O ２／２ ) r - (SiR ３ O １／２ ) s As explained in the section marked with a dash, a detailed explanation will be omitted.

[0045] For R in the silicone chain bonded to Y2 in formula (2), the same applies to Y in formula (1). ３ As explained in the description of R in the silicone chain bonded to (1), a detailed explanation is omitted. Also, as explained in the description of r in equation (1), a detailed explanation of f in equation (2) is omitted.

[0046] Furthermore, it is preferable that b, f, and a in formula (2) satisfy the following relationship in formula (γ): b*f / (b+a) ≥ 0.3 Formula (γ) As described above, when b*f / (b+a) is 0.3 or more, the compressibility of the thermal conductive sheet is increased, and the amount of bleed is further reduced. Note that b*f / (b+a) is an indicator of the content ratio of the linear portion (D unit) of the silicone chain in the compound of formula (2), and having this value above a certain level is effective for the compressibility and bleed reduction effects of the present invention. From this viewpoint, b*f / (b+a) is preferably 0.5 or more, more preferably 0.8 or more, even more preferably 1.2 or more, and preferably 3.0 or less, and more preferably 2.5 or less.

[0047] In the compound of formula (2), g is a number of 1 or more. g is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1. In the compound of formula (2), d is a number of 0 or more, preferably 0 to 5, more preferably 0 to 1, and even more preferably 0. In the compound of formula (2), e is a number of 0 or more, preferably 0 to 5, more preferably 0 to 1, and even more preferably 0. In formula (2), there are multiple silicone chains bonded to Y2, depending on the number of b. The values ​​of d, e, f, and g in formula (2) are determined as the average values ​​of multiple silicone chains.

[0048] In formula (2), a and b correspond to the number of long-chain alkyl group-containing units and silicone chain-containing units, respectively. From the viewpoint of improving the compressibility of the thermal conductive sheet at high temperatures while reducing the amount of bleed, these numbers are preferably as follows: a is a number of 1 or more, preferably 10 to 500, more preferably 50 to 300, and even more preferably 100 to 250. b is a number of 0.5 or more, preferably 0.5 to 50, more preferably 1 to 50, even more preferably 1 to 30, and even more preferably 2 to 10.

[0049] In equation (2), a, b, c, d, e, f, and g are the same as n, m, k, p, q, r, and s in equation (1) above. １ H-NMR, ２９ This can be determined by methods such as Si-NMR and size exclusion chromatography.

[0050] The method for producing compound (B) is not particularly limited, but for example, one method involves preparing a monomer (crystalline monomer) for forming a long-chain alkyl group-containing unit represented by formula (10) and a monomer (silicone monomer) for forming a silicone chain-containing unit represented by formula (11), and polymerizing these monomers. Specific examples of the crystalline monomer and silicone monomer are as described above in the description of the method for producing compound (A).

[0051] The content of compound (Z) in the thermal conductive sheet is not particularly limited, but is preferably 5 to 70 parts by mass, more preferably 7 to 60 parts by mass, and even more preferably 10 to 50 parts by mass, per 100 parts by mass of silicone resin. Including a certain amount of compound (Z) makes it easier to improve the handling, compressibility, and reworkability of the thermal conductive sheet. Furthermore, keeping the content of compound (Z) below a certain level makes it easier to reduce the amount of bleed in the thermal conductive sheet.

[0052] (Silicone Resin) The thermal conductive sheet of the present invention contains a silicone resin. The silicone resin is a matrix component of the thermal conductive sheet, and the thermal conductive filler described later is dispersed in the silicone resin. The silicone resin is not particularly limited as long as it is not compound (A) and compound (B) described above, and may be a non-curing type silicone resin or a curing type silicone resin, but a curing type silicone resin is preferred. The curing type silicone resin may be either a condensation-curing type silicone resin or an addition-reaction-curing type silicone resin, but an addition-reaction-curing type silicone resin is preferred. The silicone resin may also be silicone rubber. The addition-reaction-curing type silicone resin preferably consists of a silicone compound that serves as the main component (silicone main component) and a curing agent that cures the main component (silicone curing agent). The silicone compound used as the main component is preferably an organopolysiloxane having an alkenyl group, and more preferably an organopolysiloxane having a vinyl group. The number of alkenyl groups in one molecule of the organopolysiloxane is preferably two or more, and it is more preferable that alkenyl groups are contained at both ends. Examples of organopolysiloxanes having vinyl groups include vinyl-terminated polydimethylsiloxanes, vinyl-terminated polyphenylmethylsiloxanes, vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymers, vinyl-terminated dimethylsiloxane-phenylmethylsiloxane copolymers, and vinyl-terminated dimethylsiloxane-diethylsiloxane copolymers.

[0053] The curing agent used in addition-curing type silicone resins is not particularly limited as long as it can cure the silicone compound, which is the main component described above, but it is preferable that it contains an organopolysiloxane (organohydrogenpolysiloxane) having at least one hydrosilyl group (SiH) in one molecule. The number of SiHs in one molecule of organopolysiloxane may be one or two or more, but it is more preferable that the curing agent contains an organopolysiloxane having two or more SiHs in one molecule in order to form a crosslinked structure on the thermal conductive sheet. The organopolysiloxane having two or more SiHs in one molecule may be used alone or in combination with an organopolysiloxane having one SiH.

[0054] Examples of organohydrogenpolysiloxanes include methylhydrosiloxane-dimethylsiloxane copolymer, polymethylhydrosiloxane, polyethylhydrosiloxane, and methylhydrosiloxane-phenylmethylsiloxane copolymer. These may or may not contain hydrosilyl groups at their terminal ends.

[0055] The viscosity of the silicone resin at 25°C is preferably 5 mPa·s to 1000 mPa·s, more preferably 30 mPa·s to 700 mPa·s, and even more preferably 50 mPa·s to 600 mPa·s. The viscosity of the silicone resin is preferably measured using a viscometer (BROOKFIELD rotational viscometer DV-E) with a rotor of spindle No. 14, at a rotation speed of 5 rpm and a measurement temperature of 25°C. As described above, if the silicone resin has a main component and a curing agent, the viscosity of the mixture of the main component and curing agent at 25°C should be within the above range, but the viscosity of the main component and curing agent at 25°C may be within the above range individually.

[0056] When an addition-curing type silicone resin is used as the silicone resin, a curing catalyst is usually added to the thermal conductive resin composition (also referred to as the "mixed composition" in the following description) for manufacturing the thermal conductive sheet. Examples of curing catalysts include platinum catalysts, palladium-based catalysts, and rhodium-based catalysts, with platinum catalysts being preferred. The curing catalyst is a catalyst for curing the silicone compound, which is the raw material for the silicone resin, and the curing agent. The amount of curing catalyst added is usually 0.1 ppm to 200 ppm, preferably 0.5 ppm to 100 ppm, relative to the total mass of the silicone resin.

[0057] When an addition-curing type silicone resin is used as the silicone resin, a curing retarder may be added to the thermally conductive resin composition. Known curing retarders can be used, but examples include acetylene compounds such as 1-ethynyl-1-cyclohexanol and 3,5-dimethyl-1-hexyne-3-ol, various nitrogen compounds such as tributylamine and tetramethylethylenediamine, organophosphorus compounds such as triphenylphosphine, oxime compounds, and organochloro compounds. By including a curing retarder and suppressing the catalytic activity of the curing catalyst, the shelf life and pot life of the thermally conductive resin composition can be extended. The content of the curing retarder in the thermally conductive resin composition is preferably 0.01 parts by mass or more and 2 parts by mass or less, more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of silicone resin.

[0058] (Thermally conductive filler) The thermally conductive sheet of the present invention includes a thermally conductive filler. The inclusion of a thermally conductive filler improves the thermal conductivity of the thermally conductive sheet and enhances heat dissipation. Examples of thermally conductive fillers include metals, inorganic hydroxides, inorganic oxides, inorganic nitrides, carbon fibers, graphite, and diamond. Examples of metals include aluminum, copper, and nickel. Examples of inorganic hydroxides include metal hydroxides such as aluminum hydroxide, calcium hydroxide, and magnesium hydroxide. Examples of inorganic oxides include iron oxide, zinc oxide, silicon oxide (silica), alumina, magnesium oxide, titanium oxide, cerium oxide, and zirconium oxide. Examples of inorganic nitrides include silicon nitride, aluminum nitride, gallium nitride, chromium nitride, tungsten nitride, magnesium nitride, molybdenum nitride, lithium nitride, and boron nitride.

[0059] Examples of the carbon fibers mentioned above include pitch-based carbon fibers, PAN-based carbon fibers, carbonized resin fibers, and graphitized resin fibers. The graphite may be natural graphite or artificial graphite. The diamond may be as-grown particles, crushed diamond particles obtained by crushing as-grown particles, or other types of diamond particles, and two or more of these may be used in combination. Generally, as-grown particles are crystalline diamond particles that maintain their shape from the time of synthesis without being crushed, and have a polyhedral shape. Crushed diamond particles are obtained by crushing crystalline diamond particles, and generally have an angular shape due to the crushing. These thermally conductive fillers may be used individually or in combination of two or more types.

[0060] It is preferable to include an anisotropic filler as the thermally conductive filler. Including an anisotropic filler makes it easier to improve thermal conductivity. When anisotropic filler is included, it may be oriented in the thickness direction of the thermal conductive sheet, for example, as described later. When oriented in the thickness direction, its long axis does not need to be strictly parallel to the thickness direction; it is acceptable for the long axis to be slightly tilted relative to the thickness direction to still be oriented in the thickness direction. Specifically, anisotropic fillers whose long axis is tilted by less than 20° are considered to be oriented in the thickness direction, and such anisotropic fillers should be oriented in the thickness direction if they constitute the majority of the thermal conductive sheet (for example, more than 60%, preferably more than 80%, of the total number of anisotropic fillers).

[0061] The volumetric filling rate of the thermal conductive filler is preferably 45% to 85% by volume, more preferably 50% to 80% by volume, and even more preferably 55% to 75% by volume, based on the total volume of the thermal conductive sheet. When the volumetric filling rate of the thermal conductive filler is above a certain level, a certain level of heat conduction can be imparted to the thermal conductive sheet. Furthermore, when the volumetric filling rate of the thermal conductive filler is below a certain level, the thermal conductive filler can be appropriately dispersed in the silicone resin. In addition, it is possible to prevent the viscosity of the mixed composition, which will be described later, from becoming unnecessarily high.

[0062] The content of the thermally conductive filler is preferably 150 parts by mass or more and 3000 parts by mass or less, more preferably 200 parts by mass or more and 2000 parts by mass or less, and even more preferably 300 parts by mass or more and 1000 parts by mass or less, per 100 parts by mass of silicone resin.

[0063] <Anisotropic Fillers> Anisotropic fillers are fillers that have anisotropy in shape and are oriented. Examples of anisotropic fillers include fibrous materials and flake-like materials. Anisotropic fillers have a high aspect ratio, specifically an aspect ratio greater than 2, and preferably an aspect ratio of 5 or higher. By making the aspect ratio greater than 2, it becomes easier to orient the anisotropic filler in one direction, such as the thickness direction, and it is easier to improve the thermal conductivity in one direction, such as the thickness direction of the thermal conductive sheet. Furthermore, there is no particular upper limit to the aspect ratio, but practically it is 100. Note that the aspect ratio is the ratio of the length in the long axis direction to the length in the short axis direction of the anisotropic filler, and in the case of fibrous materials, it means fiber length / fiber diameter, and in the case of flake-like materials, it means the length in the long axis direction of the flake-like material / thickness.

[0064] The volumetric filling rate of the anisotropic filler is preferably 15% to 60% by volume, more preferably 20% to 50% by volume, and even more preferably 25% to 40% by volume, based on the total volume of the thermal conductive sheet. When the volumetric filling rate of the anisotropic filler is above a certain level, it becomes easier to improve thermal conductivity. Furthermore, a certain level of thermal conductivity can be imparted to the thermal conductive sheet. Moreover, when the volumetric filling rate of the anisotropic filler is below a certain level, the viscosity of the mixed composition described later tends to become appropriate, and the orientation of the anisotropic filler becomes good. Furthermore, the dispersibility of the anisotropic filler in the silicone resin also becomes good.

[0065] The anisotropic filler content in the thermal conductive sheet is preferably 10 parts by mass or more and 500 parts by mass or less per 100 parts by mass of silicone resin, more preferably 30 parts by mass or more and 300 parts by mass or less, and even more preferably 50 parts by mass or more and 250 parts by mass or less.

[0066] When the anisotropic filler is a fibrous material, its average fiber length is preferably 10 μm to 500 μm, more preferably 20 μm to 350 μm, and even more preferably 50 μm to 300 μm. If the average fiber length is 10 μm or more, the anisotropic fillers will be in proper contact with each other within the thermal conductive sheet, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive sheet. On the other hand, if the average fiber length is 500 μm or less, the bulk of the anisotropic filler will be reduced, allowing for higher filling in the silicone resin. Furthermore, it is preferable that the average fiber length of the fibrous material is shorter than the thickness of the thermal conductive sheet. A shorter average fiber length prevents the fibrous material from protruding excessively from the surface of the thermal conductive sheet. The average fiber length can be calculated by observing the anisotropic filler under a microscope. More specifically, for example, the fiber lengths of 50 arbitrary anisotropic fillers can be measured using an electron microscope or optical microscope, and the average value (arithmetic mean) can be used as the average fiber length.

[0067] Furthermore, when the anisotropic filler is a flake-like material, its average particle size is preferably 10 μm to 400 μm, more preferably 15 μm to 300 μm, and even more preferably 20 μm to 200 μm. By setting the average particle size to 10 μm or more, the anisotropic fillers can easily come into contact with each other in the thermal conductive sheet, ensuring a heat transfer path and improving the thermal conductivity of the thermal conductive sheet. On the other hand, if the average particle size is 400 μm or less, the bulk of the thermal conductive sheet is reduced, making it possible to fill the silicone resin with a high density of anisotropic filler. The average particle size of the flake-like material can be calculated by observing the anisotropic filler under a microscope and taking its longest axis as the diameter. More specifically, for example, by measuring the longest axis of 50 arbitrary anisotropic fillers using an electron microscope or optical microscope, the average value (arithmetic mean) can be taken as the average particle size.

[0068] Anisotropic fillers can be made from known materials with thermal conductivity, but if they are oriented by magnetic field orientation as described later, it is preferable that they possess diamagnetism. On the other hand, if they are oriented by flow orientation or if the anisotropic filler is not oriented, diamagnetism is not required. Specific examples of anisotropic fillers include graphite represented by carbon fibers or flake-shaped graphite powder, metal materials represented by metal fibers, metal oxides, inorganic nitrides such as boron nitride and metal nitrides, and metal hydroxides. Among these, graphite is preferred because it has a low specific gravity and good dispersibility in the binder component, and graphitized carbon material with high thermal conductivity is more preferred. Graphitized carbon material possesses diamagnetism when the graphite planes are aligned in a predetermined direction. Boron nitride is also preferred as an anisotropic filler. Boron nitride is not particularly limited, but it is preferable to use it as a flake-shaped material. The flake-shaped boron nitride may or may not be aggregated, but it is preferable that some or all of it is not aggregated. Furthermore, materials such as boron nitride also exhibit diamagnetism when their crystal planes are aligned in a predetermined direction.

[0069] Furthermore, while the anisotropic filler is not particularly limited, its thermal conductivity along the anisotropic direction (i.e., the long axis direction) is generally 30 W / m·K or higher, preferably 60 W / m·K or higher, more preferably 100 W / m·K or higher, and even more preferably 200 W / m·K or higher. The upper limit of the thermal conductivity of the anisotropic filler is not particularly limited, but for example, it is 2000 W / m·K or lower. The thermal conductivity can be measured by methods such as the laser flash method.

[0070] Anisotropic fillers may be used individually or in combination of two or more types. For example, at least two anisotropic fillers having different average particle sizes or average fiber lengths may be used. It is believed that using anisotropic fillers of different sizes allows smaller anisotropic fillers to fill in between relatively larger ones, thereby enabling high-density filling of the anisotropic fillers in the silicone resin and improving thermal conductivity.

[0071] Graphite carbon fibers are preferred as the carbon fibers used as the anisotropic filler. Flake-shaped graphite powder is preferred as the flake-shaped carbon powder. It is also preferable to use both graphite carbon fibers and flake-shaped graphite powder as the anisotropic filler. Graphite carbon fibers have graphite crystal planes aligned along the fiber axis, resulting in high thermal conductivity in that direction. Therefore, by aligning the fiber axis in a predetermined direction, the thermal conductivity in a specific direction can be increased. Similarly, flake-shaped graphite powder has graphite crystal planes aligned in the in-plane direction of the flake surface, resulting in high thermal conductivity in that in-plane direction. Therefore, by aligning the flake surfaces in a predetermined direction, the thermal conductivity in a specific direction can be increased. Graphite carbon fibers and flake-shaped graphite powder with a high degree of graphitization are preferred.

[0072] As the graphitized carbon materials such as the graphitized carbon fibers and flaky graphite powder mentioned above, the following raw materials can be graphitized. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, PAN (polyacrylonitrile), and condensed heterocyclic compounds such as pitch can be used, but it is particularly preferable to use graphitized mesophase pitch, polyimide, or polybenzazole, which have a high degree of graphitization. For example, by using mesophase pitch, in the spinning process described later, the pitch is oriented in the direction of the fiber axis due to its anisotropy, and graphitized carbon fibers with excellent thermal conductivity in the direction of the fiber axis can be obtained. The manner in which mesophase pitch is used in graphitized carbon fibers is not particularly limited as long as it is spinnable, and mesophase pitch may be used alone or in combination with other raw materials. However, using mesophase pitch alone, that is, graphitized carbon fibers with a mesophase pitch content of 100%, is most preferable in terms of high thermal conductivity, spinnability, and quality stability.

[0073] Graphitized carbon fibers can be obtained by sequentially performing spinning, infusibility, and carbonization processes, followed by pulverization or cutting to a predetermined particle size and then graphitization, or by pulverization or cutting after carbonization and then graphitization. When pulverization or cutting is performed before graphitization, the condensation polymerization and cyclization reactions proceed more easily during the graphitization treatment on the newly exposed surface after pulverization, thereby increasing the degree of graphitization and obtaining graphitized carbon fibers with even greater thermal conductivity. On the other hand, when pulverizing spun carbon fibers after graphitization, the carbon fibers after graphitization are rigid and easy to pulverize, allowing for the acquisition of carbon fiber powder with a relatively narrow fiber length distribution in a short pulverization time.

[0074] As described above, the average fiber length of the graphitized carbon fiber is preferably 10 μm to 500 μm, more preferably 20 μm to 350 μm, and even more preferably 50 μm to 300 μm. The aspect ratio of the graphitized carbon fiber is greater than 2, and preferably 5 or more, as described above. The thermal conductivity of the graphitized carbon fiber is not particularly limited, but the thermal conductivity in the fiber axis direction is preferably 400 W / m·K or more, and more preferably 800 W / m·K or more.

[0075] When a thermal conductive sheet contains an anisotropic filler, the anisotropic filler may or may not be exposed on the sheet surface, but exposure is preferable. The sheet surface of the thermal conductive sheet can be made non-adhesive by exposing the anisotropic filler. The thermal conductive sheet is the main surface of the sheet, and the anisotropic filler may be exposed on only one of the two surfaces of the sheet, or on both surfaces. Because the sheet surface of the thermal conductive sheet is non-adhesive, it can be slid when assembled into electronic equipment, improving assembly ease.

[0076] <Non-anisotropic filler> The thermally conductive filler in the present invention may contain a non-anisotropic filler, and the anisotropic filler and the non-anisotropic filler may be used in combination. The non-anisotropic filler, in particular, when used in combination with anisotropic filler oriented in one direction, interposes in the gaps between the oriented anisotropic fillers, thereby further increasing thermal conductivity. The non-anisotropic filler is a filler that does not substantially have anisotropy in shape, and even in environments where anisotropic fillers are oriented in a predetermined direction, such as under magnetic field line generation or shear force action as described later, it is a filler that does not align in that predetermined direction.

[0077] The non-anisotropic filler has an aspect ratio of 2 or less, preferably 1.5 or less. When used in combination with anisotropic fillers, non-anisotropic fillers with a low aspect ratio are more easily positioned in the gaps of the anisotropic fillers, thus improving thermal conductivity. Furthermore, by setting the aspect ratio to 2 or less, it becomes possible to prevent an increase in the viscosity of the mixed composition described later, thereby enabling high-filling.

[0078] Specific examples of non-anisotropic fillers include metals, inorganic oxides, inorganic nitrides, inorganic hydroxides, graphite, and diamond. Details of these are as described above, but among them, aluminum oxide, aluminum, and aluminum hydroxide are preferred due to their high thermal conductivity and the availability of spherical forms. Aluminum oxide and aluminum are more preferred, with aluminum oxide being even more preferred. The shape of the non-anisotropic filler can be spherical, amorphous powder, etc. The non-anisotropic filler may be used individually or in combination of two or more types.

[0079] The average particle size of the non-anisotropic filler is, for example, 0.1 μm to 200 μm. For example, when used in combination with an anisotropic filler, the average particle size of the non-anisotropic filler is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 35 μm, and even more preferably 1 μm to 15 μm. By setting the average particle size to 50 μm or less, problems such as disrupting the orientation of the anisotropic filler are less likely to occur when used in combination with anisotropic filler. Furthermore, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become unnecessarily large, the viscosity of the mixed composition does not increase easily even when a large amount is added, and it becomes easier to fill the non-anisotropic filler to a high degree. As for the non-anisotropic filler, for example, at least two non-anisotropic fillers having different average particle sizes may be used.

[0080] Furthermore, the average particle size of the anisotropic filler is preferably 0.1 μm or more and 200 μm or less, more preferably 0.5 μm or more and 100 μm or less, and even more preferably 1 μm or more and 70 μm or less. The average particle size of the anisotropic filler can be observed and measured using an electron microscope or the like. More specifically, for example, the particle sizes of 50 arbitrary anisotropic fillers can be measured using an electron microscope or optical microscope, and the average value (arithmetic mean) can be taken as the average particle size.

[0081] The volumetric filling rate of the non-anisotropic filler is preferably 20% to 55% by volume, more preferably 24% to 50% by volume, and even more preferably 28% to 45% by volume, based on the total volume of the thermal conductive sheet. If the volumetric filling rate of the non-anisotropic filler is above a certain level, the thermal conductivity of the thermal conductive sheet can be improved. Furthermore, if the volumetric filling rate of the non-anisotropic filler is below a certain level, the non-anisotropic filler can be appropriately dispersed in the silicone resin, and the effect of improving thermal conductivity according to the content can be obtained. In addition, it is possible to prevent the viscosity of the mixed composition from increasing more than necessary.

[0082] The content of the non-anisotropic filler is preferably 50 parts by mass or more and 2,500 parts by mass or less per 100 parts by mass of silicone resin, more preferably 100 parts by mass or more and 1,500 parts by mass or less, and even more preferably 200 parts by mass or more and 750 parts by mass or less.

[0083] The volume ratio of the anisotropic filler content to the anisotropic filler content (anisotropic filler content / anisotropic filler content) is preferably 0.30 to 3.0, more preferably 0.40 to 2.5, and even more preferably 0.50 to 2.0. By setting the volume ratio above a certain level, a certain degree of heat transfer pathways can be secured by the anisotropic filler, making it easier to improve thermal conductivity. Furthermore, by setting the volume ratio below a certain level, the viscosity of the mixed composition does not become excessively high, making it easier to handle the composition during the manufacture of the thermal conductive sheet.

[0084] (Additives) In a thermal conductive sheet, various additives may be added to the matrix component, to the extent that they do not impair the function of the thermal conductive sheet. Examples of additives include at least one selected from dispersants, coupling agents, adhesives, flame retardants, antioxidants, colorants, and anti-settlement agents. Furthermore, as will be described later, compatible substances may be added to the mixed composition. Compatible substances do not need to remain in the thermal conductive sheet after volatilization during the manufacturing process, but at least a portion of the added compatible substances may remain.

[0085] (Thickness) The thickness of the thermal conductive sheet is not particularly limited and may be set appropriately depending on the shape and application of the electronic device on which the thermal conductive sheet is mounted, but it is preferable that it be in the range of 0.1 mm to 5 mm. Furthermore, from the viewpoint of ease of use in small electronic devices, the thickness of the thermal conductive sheet is preferably 0.1 mm to 3 mm, and more preferably 0.1 mm to 1 mm.

[0086] (E Hardness) The thermal conductive sheet of the present invention preferably has a Type E hardness (hereinafter also referred to as "E hardness") as defined in JIS K6253, which is 70 or less, more preferably 65 or less, and even more preferably 60 or less. Having an E hardness below a certain level results in excellent flexibility of the thermal conductive sheet. Furthermore, from the viewpoint of the handlingability of the thermal conductive sheet, the E hardness is, for example, 20 or more, preferably 30 or more, and more preferably 35 or more. Note that the E hardness referred to here is the initial hardness, and specifically, is obtained by measurement in a 25°C environment.

[0087] The heat-conducting sheet of the present invention preferably has an E-hardness (hereinafter also referred to as "post-heating E-hardness") of 80 or less after heating the sheet at 150°C for 250 hours, more preferably 75 or less, and even more preferably 70 or less. By keeping the E-hardness below a certain level, the flexibility of the heat-conducting sheet is well maintained even when exposed to a high-temperature environment. Furthermore, from the viewpoint of ensuring a certain degree of shape retention during actual use of the heat-conducting sheet, the E-hardness is preferably 30 or more, preferably 40 or more, and more preferably 45 or more.

[0088] [Method for Manufacturing a Thermal Conductive Sheet] The thermal conductive sheet of the present invention can be manufactured, for example, by a manufacturing method comprising the following steps X and Y. Step X: A step of mixing a curable silicone composition, a compound (Z), and a thermal conductive filler to obtain a mixed composition. Step Y: A step of curing the mixed composition obtained in step X by heating. Each step will be described in detail below.

[0089] (Step X) In Step X, a mixed composition is preferably obtained by mixing at least a curable silicone composition, compound (Z), and a thermally conductive filler, but it is preferable to further mix a volatile substance into the mixed composition. In addition, other components such as additives may be added to the mixed composition as needed.

[0090] In step X, the mixing method and mixing order are not particularly limited, as long as the above components can be mixed to obtain a mixed composition. The curable silicone composition, compound (Z), thermally conductive filler, volatile substances added as needed, and other components added as needed may be mixed in any order to obtain the mixed composition. As described above, the curable silicone composition consists of, for example, a main component and a curing agent. In such a case, the main component, curing agent, compound (Z), thermally conductive filler, volatile substances added as needed, and other components may be mixed in any order to obtain the mixed composition. The form of the mixed composition may be a one-component type or a two-component type consisting of a first component and a second component. In the two-component type, the first component and the second component are mixed at the time of use to obtain the mixed composition.

[0091] (Volatile Substances) The volatile substances used in this invention may be any components that volatilize in step Y described later. By volatilizing due to heating during curing, the proportion of thermal conductive filler in the thermal conductive sheet can be increased. In addition, the viscosity of the mixed composition decreases due to the inclusion of volatile substances. Therefore, it becomes easier to increase the amount of thermal conductive filler, and furthermore, it becomes easier to orient the anisotropic filler in a predetermined direction, for example, by magnetic field orientation described later.

[0092] Furthermore, the volatile substance is preferably a compatible substance that is compatible with or dissolves in the curable silicone composition. When the volatile substance is compatible, the curable silicone composition and the volatile substance can be mixed uniformly, making it easier to reduce viscosity or increase the amount of thermally conductive filler. Moreover, the bubbles formed by the volatilization of the volatile substance can be made fine and uniform.

[0093] The volatile substance is preferably a substance that is liquid at room temperature (25°C) and 1 atmosphere. Examples of volatile substances include alkoxysilane compounds, hydrocarbon solvents, and alkoxysiloxane compounds. These compounds can increase the solubility or compatibility with the curable silicone composition, making it easier to reduce the viscosity of the mixed composition or to increase the amount of thermally conductive filler. In addition, it makes it easier to create fine and uniform bubbles formed by the volatilization of the volatile substance. The volatile substance may be used alone or in combination of two or more types.

[0094] It is preferable to use an alkoxysilane compound as the volatile substance. By using an alkoxysilane compound, the surface of the heat-conductive sheet obtained by curing is free from roughness and other defects, resulting in a good appearance. The alkoxysilane compound used as the volatile substance is a compound having a structure in which one to three of the four bonds of the silicon atom (Si) are bonded to an alkoxy group, and the remaining bonds are bonded to an organic substituent. By having an alkoxy group and an organic substituent, the alkoxysilane compound can improve the compatibility of compound (A) and compound (B) with the curable silicone composition. Examples of alkoxy groups in the alkoxysilane compound include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, and a hexatoxy group. The alkoxysilane compound may be contained in the curable silicone composition as a dimer.

[0095] Among alkoxysilane compounds, those having at least one of a methoxy group and an ethoxy group are preferred from the viewpoint of availability. The number of alkoxy groups in the alkoxysilane compound is preferably 2 or 3, and more preferably 3, from the viewpoint of compatibility and solubility with the curable silicone composition, compound (A), and compound (B). Specifically, the alkoxysilane compound is preferably at least one selected from trimethoxysilane compounds, triethoxysilane compounds, dimethoxysilane compounds, and diethoxysilane compounds.

[0096] Examples of functional groups included in the organic substituents of alkoxysilane compounds include acryloyl groups, alkyl groups, carboxyl groups, vinyl groups, methacrylic groups, aromatic groups, amino groups, isocyanate groups, isocyanurate groups, epoxy groups, hydroxyl groups, and mercapto groups. When using a platinum catalyst as a curing catalyst for a curable silicone composition, it is preferable to select and use an alkoxysilane compound that does not easily affect the curing reaction of the organopolysiloxane. Specifically, when using an addition reaction type organopolysiloxane utilizing a platinum catalyst, it is preferable that the organic substituent of the alkoxysilane compound does not contain amino groups, isocyanate groups, isocyanurate groups, hydroxyl groups, or mercapto groups.

[0097] From the viewpoint of the dispersibility of compound (A) and compound (B) in the curable silicone composition, the alkoxysilane compound preferably includes alkylalkoxysilane compounds having an alkyl group bonded to a silicon atom, that is, alkoxysilane compounds having an alkyl group as an organic substituent. Therefore, dialkyldialkoxysilane compounds and alkyltrialkoxysilane compounds are preferred, and alkyltrialkoxysilane compounds are preferred among them. The number of carbon atoms of the alkyl group bonded to the silicon atom is preferably 1 to 16. Furthermore, in trialkoxysilane compounds such as trimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms of the alkyl group is preferably 6 or more, more preferably 8 or more, preferably 12 or less, and more preferably 10 or less. On the other hand, in dialkoxysilane compounds such as dimethoxysilane compounds and diethoxysilane compounds, the number of carbon atoms of the alkyl group may be 1 or more, preferably 10 or less, more preferably 6 or less, and more preferably 4 or less.

[0098] Examples of alkyl group-containing alkoxysilane compounds include methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, and n-decyltriethoxysilane. Among alkyl group-containing alkoxysilane compounds, n-decyltrimethoxysilane and n-octyltriethoxysilane are even more preferred from the viewpoint of compatibility with curable silicone compositions.

[0099] Alkoxysiloxane compounds used as volatile substances have two or more siloxane bonds and a structure in which an alkoxy group is bonded to at least one silicon atom. Alkoxysiloxane compounds have a structure in which an organic substituent is bonded to at least one silicon atom among the silicon atoms constituting the siloxane bond. By having an alkoxy group and an organic substituent, alkoxysiloxane compounds can improve the dispersibility of compound (A) and compound (B) in a curable silicone composition. Examples of alkoxy groups and organic substituents of alkoxysiloxane compounds are those exemplified in the description of alkoxysilane compounds above, and from the viewpoint of improving the dispersibility of compound (A) and compound (B), it is preferable that they have at least an alkyl group.

[0100] Examples of alkoxysiloxane compounds include methyl methoxysiloxane oligomers, methylphenyl methoxysiloxane oligomers, methyl epoxy methoxysiloxane oligomers, methyl mercaptomethoxysiloxane oligomers, and methyl acryloyl methoxysiloxane oligomers. One or more alkoxysiloxane compounds can be used.

[0101] Aromatic hydrocarbon solvents are used as volatile substances. Among these, aromatic hydrocarbon solvents are preferred from the viewpoint of compatibility with curable silicone compositions. Examples of aromatic hydrocarbon solvents include those having 6 to 10 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, propylbenzene, butylbenzene, and t-butylbenzene, with toluene and xylene being preferred.

[0102] In the mixed composition, the content of volatile substances per 100 parts by mass of the curable silicone composition is preferably 6 parts by mass or more and 60 parts by mass or less. A content of 6 parts by mass or more makes it easier to exert the effects of the volatile substances, for example, allowing for the formation of an appropriate amount of fine bubbles in the silicone resin. Furthermore, a content of 60 parts by mass or less allows for obtaining effects commensurate with the amount of volatile substances used. From these viewpoints, the above content of volatile substances is more preferably 8 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 35 parts by mass or less. It is preferable that some or all of the volatile substances volatilize upon heating in step Y. Therefore, volatile substances do not necessarily have to be contained in the heat conductive sheet, but they may be contained in the heat conductive sheet in an amount less than that contained in the mixed composition.

[0103] Further details regarding the components of the mixed composition other than volatile substances (i.e., the curable silicone composition, compound (A), compound (B), thermally conductive filler, and other additives) are as described above. The content of the thermally conductive filler in the mixed composition is also as described above. However, while the amounts of each component shown above are based on 100 parts by mass of silicone resin, in the case of the mixed composition, the amounts are based on 100 parts by mass of the curable silicone composition.

[0104] (Step Y) Step Y is a step in which the mixed composition is cured by heating. The temperature at which the mixed composition is heated is not particularly limited as long as the curable silicone composition can be cured by heating, and it is sufficient to be higher than room temperature (23°C), but it is preferable to heat it at a temperature of 50°C or higher. The heating temperature is not particularly limited, but it is sufficient to be a temperature at which the heat conductive sheet and the mixed composition do not deteriorate due to heat, for example, 180°C or lower, preferably 150°C or lower. The heating of the mixed composition may be carried out in one stage or in two or more stages. If it is carried out in two or more stages, it is sufficient that the heating temperature is within the above range in at least one stage, but it is preferable that the heating temperature is within the above range in all stages, and it is also preferable that at least the first stage of heating is carried out at a temperature lower than the boiling point of the volatile substance. The total heating time is, for example, about 10 minutes to 24 hours. If it is carried out in two or more stages, for example, the mixed composition may be partially cured in the first stage (primary curing), and the mixed composition may be fully cured by heating in the second stage and subsequent stages (secondary curing). Furthermore, the curing process may involve complete curing during the first stage, with subsequent heating stages not resulting in further curing.

[0105] In step Y, the mixed composition may be molded into a predetermined shape such as a block or a sheet, and then heated to cure it. In step Y, if the mixed composition contains an anisotropic filler as a thermally conductive filler, the anisotropic filler may be oriented in one direction and then heated to cure it. The anisotropic filler can be oriented by the magnetic field orientation method or the flow orientation method, but it is preferable to align it by the magnetic field orientation method.

[0106] In the magnetic field orientation method, the mixed composition is injected into a mold or the like and then placed in a magnetic field to orient the anisotropic filler along the magnetic field. The oriented molded body is then obtained by curing the curable silicone composition. The curing of the mixed composition is carried out under the heating conditions described above. The oriented molded body is preferably in block form, but it may also be in sheet form. If it is in sheet form, the oriented molded body can be used as a heat conductive sheet without slicing. On the other hand, if it is in block form, the orientation of the anisotropic filler can be improved.

[0107] In the magnetic field orientation method, a release film may be placed in the part of the mold that comes into contact with the mixed composition. For example, the release film can be a resin film with good release properties or a resin film on one side that has been treated with a release agent. Using a release film makes it easier to remove the oriented molded product from the mold.

[0108] In the magnetic field orientation method, the viscosity of the mixed composition used is preferably between 10 Pa·s and 300 Pa·s in order to enable magnetic field orientation. A viscosity of 10 Pa·s or higher prevents the thermally conductive filler from settling. A viscosity of 300 Pa·s or lower ensures good fluidity, allowing the anisotropic filler to be properly oriented by the magnetic field without causing problems such as excessive orientation time. Viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at 25°C and a rotational speed of 10 rpm. However, when using a thermally conductive filler that is less prone to settling, or when combining it with additives such as settling inhibitors, the viscosity of the mixed composition may be less than 10 Pa·s.

[0109] In the magnetic field orientation method, examples of magnetic field source for applying magnetic field lines include superconducting magnets, permanent magnets, and electromagnets, but superconducting magnets are preferred because they can generate a magnetic field with a high magnetic flux density. The magnetic flux density of the magnetic field generated from these magnetic field source sources is preferably 1 Tesla or more and 30 Tesla or less. Setting the magnetic flux density to 1 Tesla or more makes it possible to easily orient the anisotropic filler material made of carbon material or the like. Setting it to 30 Tesla or less makes practical manufacturing possible.

[0110] In the flow orientation method, a shear force is applied to the mixed composition to produce a primary sheet in which the anisotropic filler is oriented along the planar direction. More specifically, in the flow orientation method, first, the mixed composition prepared in step X is flattened and stretched while applying a shear force to form a sheet (primary sheet). By applying a shear force, the anisotropic filler can be oriented in the shear direction. As a means of forming the sheet, for example, the mixed composition may be coated onto a base film using an applicator such as a bar coater or doctor blade, or by extrusion molding or discharge from a nozzle, and then dried, semi-cured, or fully cured as needed. The thickness of the primary sheet is preferably 50 μm to 5000 μm. In the primary sheet, the anisotropic filler is oriented in one direction along the planar direction of the sheet. The mixed composition used in the flow orientation method has a relatively high viscosity so that a shear force is applied when stretching it into a sheet. The viscosity of the mixed composition is preferably 3 Pa·s or more and 500 Pa·s or less.

[0111] The primary sheet may be used as a heat conductive sheet without forming a block, as described later. Alternatively, multiple primary sheets may be stacked so that their orientation is the same, and then bonded together by heat pressing or the like while curing by heating as needed to form a laminated block (a block-shaped oriented molded body). When forming a laminated block, at least one of the overlapping surfaces of the primary sheets may be irradiated with vacuum ultraviolet light before stacking the primary sheets. When the primary sheets are stacked with the surface irradiated with vacuum ultraviolet light in between, the primary sheets can be strongly bonded to each other. When irradiating with vacuum ultraviolet light, the mixed composition may be fully cured when the primary sheets are made, and there is no need to cure it by heating or the like when stacking the primary sheets to form a laminated block. In the flow orientation method as well, the curing of the mixed composition should be carried out under the heating conditions described above.

[0112] As described above, when forming a block-shaped oriented molded body, it is preferable to cut the obtained oriented molded body perpendicular to the direction in which the anisotropic filler is oriented, for example, by slicing, to obtain a sheet-like molded body. Slicing can be done with a shear blade or laser, for example. When the sheet-like molded body is cut by slicing, a portion of the fibrous filler will be exposed from the matrix at each surface, which is the cut surface. The sheet-like molded body obtained by cutting can be used as a thermal conductive sheet as is, but it may also be subjected to further processing. For example, each surface, which is the cut surface, may be polished. Surface polishing can be done using sandpaper, for example.

[0113] [Method of Using the Thermal Conductive Sheet] The thermal conductive sheet of the present invention is used, for example, inside electronic equipment. Specifically, the thermal conductive sheet is interposed between two components to conduct heat from one component to the other. More specifically, the thermal conductive sheet is interposed between a heat-generating element and a heat-sinking element, and the heat generated by the heat-generating element is conducted to the heat-sinking element, which then dissipates the heat. Here, examples of heat-generating elements include various electronic components used inside electronic equipment, such as CPUs, power semiconductors, and power supplies. Examples of heat-sinking elements include heat sinks, heat pumps, and metal casings of electronic equipment. The thermal conductive sheet is preferably used with both surfaces in close contact with the heat-generating element and the heat-sinking element, respectively, and compressed.

[0114] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0115] [Compound (A)] The following materials were used as raw materials for synthesizing compound (A).

[0116] (Silicone monomer) - One-terminated methacrylic modified silicone. Viscosity at 25°C is 60 cSt. This compound has a structure represented by the following formula (12).

[0117] (Crystalline monomer) Stearyl acrylate (Crosslinkable monomer) Isoprenyl methacrylate (IPEMA)

[0118] (Initiator) 5 wt% azo initiator solution in toluene (Solvent) toluene

[0119] <Synthesis of Compound (A): PCM(E1) to PCM(E6)> Silicone monomer, crystalline monomer, and crosslinkable monomer are mixed with toluene and N ２ Bubbling was performed for more than 20 minutes. Heating was started, and after the temperature had risen to 62°C, a 5 wt% toluene solution of the azo initiator was added. After heating and stirring at 62°C for 17 hours, the mixture was allowed to cool, the solvent was removed by distillation, and then the mixture was heated under vacuum at 150°C for 2 hours to synthesize PCM(E1) to PCM(E6) as compound (A). The amount of each starting material added is shown in Table 1.

[0120] PCM(E1) to PCM(E6) are compounds having the structure of formula (1) described above, and more specifically, they have the structure represented by formula (13) below. Tables 2 and 3 show the detailed structures of PCM(E1) to PCM(E6).

[0121]

[0122]

[0123]

[0124] [Compound (B)] The following materials were used as raw materials for synthesizing compound (B): (Silicone monomers) ・Methacrylic-modified silicone 1 This is the same as the silicone monomer used to synthesize compound (A). ・Methacrylic-modified silicone 2 Viscosity at 25°C is 27 cSt This compound has the structure represented by the following formula (14).

[0125] (Crystalline monomers) Stearyl acrylate, docosyl acrylate

[0126] (Initiator, Solvent) Both are the same as those used to synthesize compound (A).

[0127] <Synthesis of compound (B): PCM(N1) to PCM(N6)> Silicone monomer and crystalline monomer are mixed with toluene and N ２ Bubbling was performed for more than 20 minutes. Heating was started, and after the temperature had risen to 62°C, a 5 wt% toluene solution of the azo initiator was added. After heating and stirring at 62°C for 17 hours, it was allowed to cool, the solvent was removed by distillation, and then the mixture was heated under vacuum at 150°C for 2 hours to synthesize PCM(N1) to PCM(N6) as graft copolymer compound (B). The amount of each raw material added is shown in Table 4.

[0128]

[0129] PCM(N1) to PCM(N6) are compounds having the structure of formula (2) described above, and more specifically, the structure shown in formula (15) below. Table 5 shows the detailed structure of the synthetic compounds.

[0130]

[0131] <Compounds other than Compound (A) and Compound (B)> The following compounds (PCM(C1), PCM(C2)) were used as compounds other than Compound (A) and Compound (B): • PCM(C1) MM, manufactured by Nikko Chemicals Co., Ltd., ester compound • PCM(C2) HS-Crysta 4100P, manufactured by Toyokuni Oil Co., Ltd., poly-α-olefin, melting point 35°C

[0132] <Weight-Average Molecular Weight> The weight-average molecular weight (Mw) of the synthetic products (PCM(E1) to PCM(E6), PCM(N1) to PCM(N6)) was measured by size exclusion chromatography using THF as the solvent. Note that the weight-average molecular weight (Mw) is the value equivalent to standard polystyrene.

[0133] <Melting Point> The melting points of the synthetic products (PCM(E1) to PCM(E6), PCM(N1) to PCM(N6)) were determined by differential scanning calorimeter (DSC) measurement. The temperature was changed at a rate of 10°C / min from -20°C to 100°C to -20°C to 100°C. The peak temperature of the largest peak in the chart obtained during the cooling process from 100°C to -20°C (temperature 1) and the peak temperature of the largest peak in the chart obtained during the second heating process from -20°C to 100°C (temperature 2) were obtained, and the average value of temperature 1 and temperature 2 was taken as the melting point.

[0134] <Calculation of each structural parameter in equation (1)> (Calculation of p, q, r, s) For each synthesized PCM (PCM(E1) to PCM(E6)) ２９ Si NMR spectra were measured in a 0.1% tetramethylsilane-containing deuterated chloroform solution. With the tetramethylsilane peak set to 0 ppm, peaks around 6.5–9.0, 20–24, -55–-65, and -105–-115 ppm were assigned to (SiO1 / 2), (SiO2 / 2), (SiO3 / 2), and (SiO4 / 2), respectively, and p, q, r, and s were determined from the following formula. However, if R is not a methyl group and the peak position differs, the following formula should be applied based on the appropriate peak assignment.

[0135] When <SiO₄ / ₂>≠0, p = 1, q = <SiO₃ / ₂> / <SiO₄ / ₂>, r = s * <SiO₂ / ₂> / <SiO₁ / ₂>, s = p * 3 * q * 2

[0136] When <SiO₄ / ₂> = 0 and <SiO₃ / ₂> ≠ 0, then p = 0, q = 1, r = s * <SiO₂ / ₂> / <SiO₁ / ₂>, s = 2 * q

[0137] When <SiO4 / 2> = 0 and <SiO3 / 2> = 0, p = 0, q = 0, r = s * <SiO2 / 2> / <SiO1 / 2>, s = 1, where <SiOx / 2> represents the integral value of the peak attributed to SiOx / 2.

[0138] (Calculation of k) Each of the synthesized PCMs (PCM(E1) to PCM(E6)) １ The 1H NMR spectrum was measured in a deuterated chloroform solution and determined based on appropriate peak assignment. The case for PCM(E1) is shown below. k = (<4.0> / <0.9> + <1.6> / <0.9> + <1.3> / <0.9>) * 3 / 2, where <x.x> represents the integral value of the peak with its peak top around x.x ppm.

[0139] (Calculation of o*r / (n+m+o)) Each of the synthesized PCMs (PCM(E1) to PCM(E6)) １ The 1H NMR spectrum was measured in a deuterated chloroform solution and determined based on appropriate peak assignment. The case for PCM(E1) is shown below. o*r / (n+m+o) = (<0.1> / 6) / (<4.0> / 2) m / (n+m+o) = <4.81> / <4.0> where <x.x> represents the integral value of the peak with its peak top around x.x ppm.

[0140] (Calculation of m, n, o, m+n+o) As described above, the weight-average molecular weight Mw of each PCM was calculated by performing size exclusion chromatography in THF solvent. Using Mw, m, n, and o were calculated from the following formulas. After defining P = m+n+o, [m] = m / P, and [o] = o / P, m, n, and o were calculated using the following formulas (A) to (C), respectively. m = [m] * P ... Formula (A) n = (1 - [m] - [o]) * P ... Formula (B) o = [o] * P ... Formula (C)

[0141] Here, [m] and [o] are the respective PCMs (PCM(E1) to PCM(E6)). １ From the measured values ​​of the 1H NMR spectrum, the following values ​​could be calculated: [m] = (<4.81> + <4.76>) / 2 and [o] = <0.53> / 2. Using these measured values, P was calculated using the following formula (D): P = Mw / ([m] * Mlink + [o] * Msil + (1 - [m] - [o]) * Mcryst) ... formula (D) where, Mlink: formula weight of repeating units derived from crosslinkable monomer Mcryst: formula weight of repeating units derived from crystalline monomer Msil: formula weight of repeating units derived from silicone monomer. These values ​​are shown in the table in this example, but can be determined by combining appropriate one-dimensional, two-dimensional, and multinuclear NMR spectroscopy methods.

[0142] <Calculation of each structural parameter in equation (2)> (Calculation of d, e, f, g) Each synthesized PCM (PCM(N1) to PCM(N6)) ２９ Si NMR spectra were measured in a 0.1% tetramethylsilane-containing deuterated chloroform solution. With the tetramethylsilane peak set to 0 ppm, peaks around 6.5–9.0, 20–24, -55–-65, and -105–-115 ppm were assigned to (SiO1 / 2), (SiO2 / 2), (SiO3 / 2), and (SiO4 / 2), respectively, and d, e, f, and g were determined from the following formula. However, if R is not a methyl group and the peak position differs, the following formula should be applied based on the appropriate peak assignment.

[0143] When <SiO₄ / ₂>≠0, d = 1 e = <SiO₃ / ₂> / <SiO₄ / ₂> f = g * <SiO₂ / ₂> / <SiO₁ / ₂> g = d * 3 * e * 2

[0144] When <SiO₄ / ₂>=0 and <SiO₃ / ₂>≠0, d=0 e=1 f=g * <SiO₂ / ₂> / <SiO₁ / ₂> g=2 * e

[0145] When <SiO4 / 2> = 0 and <SiO3 / 2> = 0, d = 0 e = 0 f = g * <SiO2 / 2> / <SiO1 / 2> g = 1 where <SiOx / 2> represents the integral value of the peak attributed to SiOx / 2.

[0146] (Calculation of c) Each of the synthesized PCMs (PCM(N1) to PCM(N6)) １ The 1H NMR spectrum was measured in a deuterated chloroform solution, and c was determined using the same method as when k in equation (1) was determined.

[0147] (Calculation of b*f / (a+b)) Each of the synthesized PCMs (PCM(N1) to PCM(N6)) １ The 1H NMR spectrum was measured in a deuterated chloroform solution and determined based on appropriate peak assignment. The case for PCM(N1) is shown below. b*f / (a+b) = (<0.1> / 6) / (<4.0> / 2) where <x.x> represents the integral value of the peak with its peak top around x.x ppm.

[0148] (Calculation of a and b) As described above, the weight-average molecular weight Mw of each PCM (PCM(N1) to PCM(N6)) was calculated by performing size exclusion chromatography in THF solvent. Using Mw and b*f / (a+b), a and b were calculated from the following equations: a = b*((f-b*f / (a+b)) / (b*f / (a+b))) b = Mw / (Mcryst*(f-b*f / (a+b)) / (b*f / (a+b))+Msil) where, Mcryst: formula weight of repeating units derived from crystalline monomer Msil: formula weight of repeating units derived from silicone monomer. These values ​​are shown in the table in this example, but can be determined by combining appropriate one-dimensional, two-dimensional, and multinuclear NMR spectroscopy methods.

[0149] [Change in Elastic Modulus] A 2 mm thick thermal conductive sheet was cut to create two rectangular parallelepiped test pieces measuring 6 mm in length, 6 mm in width, and 2 mm in thickness. The elastic modulus was then measured in the range of -10°C to 70°C using a viscoelasticity measuring device (DVA200, manufactured by IT Measurement Control Co., Ltd.) and a shear measurement jig. The change in elastic modulus was then calculated using the following formula, where log is the common logarithm: Change in elastic modulus = log(measured value at 10°C) - log(measured value at 70°C) The measurement conditions for the elastic modulus were as follows: Temperature range: -10 to 70°C Heating rate: 10°C / min Frequency: 10 Hz Strain: 0.01% The elastic modulus was then evaluated according to the following evaluation criteria: AA: 0.75 or higher A: 0.50 or higher and less than 0.75 B: 0.30 or higher and less than 0.50 C: Less than 0.30

[0150] [Elongation] A 2 mm thick thermal conductive sheet was processed into a test specimen using a test specimen punching die (Tensile No. 7 dumbbell shape, Polymer Instruments Co., Ltd.). Then, a tensile test was performed at 25°C using a Tensilon universal material tester (RTI1310, AND Co., Ltd.), and the elongation was calculated using the following formula: Elongation (%) = ((Gauge length at fracture) - (Gauge length before tensile test)) / (Gauge length before tensile test) The elongation was then evaluated according to the following evaluation criteria: AA: 110% or more A: 106% or more and less than 110% B: 103% or more and less than 106% C: Less than 103%

[0151] [Bleed Amount] A 3.5 mm thick thermal conductive sheet was cut into 20 mm x 1 mm squares to prepare test specimens T, and their weight was measured (Weight 1). Each test specimen T was compressed to a thickness of 2 mm by sandwiching it between metal plates and then heated at 150°C for 64 hours. After heating, the test specimens were removed and their weight was measured (Weight 2), and the bleed amount was calculated using the following formula: Bleed amount = (Weight 1 - Weight 2) / (Weight 1) The bleed amount was then evaluated according to the following evaluation criteria: AA: Bleed amount less than 0.25 A: Bleed amount 0.25 or more and less than 0.35 B: Bleed amount 0.35 or more and less than 0.45 C: Bleed amount 0.45 or more

[0152] [Hardness Change] A 3.5 mm thick thermal conductive sheet was used as the test specimen. Three of these specimens were stacked, and the Type E hardness was measured using a durometer in a 25°C environment. This measured value was taken as the initial hardness. In addition, a hot plate was prepared near the durometer, and the test specimen was heated at 150°C for 250 hours. After heating, the Type E hardness was measured using a durometer, and this measured value was taken as the hardness after heating.

[0153] [Precipitation] A 2.0 mm thick thermal conductive sheet was used as a test specimen and left to stand for 100 days in an environment of 25°C. Then, the presence or absence of precipitation was evaluated according to the evaluation criteria below. A: No white precipitates were observed on the sheet surface. B: White precipitates were observed on the sheet surface.

[0154] [Example 1] PCM(E1) as compound (A) and a silane coupling agent (n-decyltrimethoxysilane) as a volatile substance were mixed at 60°C according to the proportions shown in Table 6 to obtain a mixture in which PCM(E1) was dissolved in the silane coupling agent. The obtained mixture, a curable silicone composition, and a platinum catalyst were uniformly mixed, and then a thermally conductive filler was mixed according to the proportions shown in Table 6 to obtain a mixed composition. Here, the curable silicone composition contained an organopolysiloxane having a vinyl group as the main component and an organohydrogenpolysiloxane as the curing agent.

[0155] As thermally conductive fillers, the following anisotropic fillers were used: graphitized carbon fiber (average fiber length 85 μm, aspect ratio 8.5, thermal conductivity 900 W / m·K), flaky graphite powder (average particle size 15 μm, aspect ratio 10, thermal conductivity 550 W / m·K), and boron nitride (average particle size 40 μm, aspect ratio 4-8, thermal conductivity 100 W / m·K). In addition, the following non-anisotropic fillers were used: aluminum oxide 1 (spherical, average particle size 3 μm, aspect ratio 1.0), aluminum oxide 2 (polyhedral shape, average particle size 0.5 μm, aspect ratio 1.0), and aluminum oxide 3 (irregular shape, average particle size 3.5 μm, aspect ratio 0.95).

[0156] Next, the block-shaped oriented molded body was sliced ​​into a sheet using a shearing blade to obtain a sheet-like molded body in which the anisotropic filler was exposed. This sheet-like molded body was then heated at 150°C for 2 hours to obtain a heat-conducting sheet. The obtained heat-conducting sheet was evaluated in various ways. The results are shown in Table 6.

[0157] [Examples 2-6] Thermal conductive sheets were obtained in the same manner as in Example 1, except that the type of compound (A) was changed as shown in Table 6, and each evaluation was performed. The results are shown in Table 6.

[0158] [Examples 7-12] Thermal conductive sheets were obtained in the same manner as in Example 1, except that compound (A) was replaced with compound (B) listed in Table 6, and each evaluation was performed. The results are shown in Table 6.

[0159] [Examples 13-25, Comparative Examples 1-7] Thermal conductive sheets were obtained in the same manner as in Example 1, except that the formulation of the mixed composition was changed as shown in Tables 6 and 7, and each evaluation was performed. The results are shown in Tables 6 and 7.

[0160]

[0161]

[0162] As is clear from the above results, the thermal conductive sheets prepared in the examples contained compounds (A) and (B) as PCMs, resulting in a large change in elastic modulus, which indicated excellent handling and high-temperature compressibility. Furthermore, their high elongation demonstrated excellent reworkability. They also exhibited low bleed and high reliability. Additionally, the sheets showed low hardness and excellent flexibility before and after heating. In contrast, the thermal conductive sheets prepared in Comparative Examples 1-3, 5, and 6 contained compounds other than compounds (A) and (B) as PCMs, resulting in high bleed and low reliability, or low elongation, preventing them from exhibiting excellent reworkability. Furthermore, the sheets showed higher hardness and insufficient flexibility before and after heating. Finally, the thermal conductive sheets prepared in Comparative Examples 4 and 7, which contained no PCMs, showed small changes in elastic modulus, resulting in insufficient handling and high-temperature compressibility.

Claims

1. A thermal conductive sheet comprising a silicone resin, a thermally conductive filler, and a compound (Z) selected from the group consisting of a compound (A) having a structure represented by the following formula (1) and a compound (B) having a structure represented by the following formula (2), wherein the melting point of compound (B) is 35°C or higher. (In formula (1), X １ ~X ３ Each of these is an independent trivalent organic group, Y １ ~Y ３ Each of these is an independent divalent organic group, Z １ is a monovalent organic group, Z ２ (where is a hydrogen atom or a monovalent organic group, R is independently a monovalent organic group, W is a divalent organic group containing one or more carbon-carbon double or triple bonds, k is a number between 16 and 33, n, m, o, r, s are each a number of 1 or more, and p, q are each a number of 0 or more) (In formula (2), X1 and X2 are each independently trivalent organic groups, Y1 and Y2 are each independently divalent organic groups, Z is a monovalent organic group, R is each independently monovalent organic group, c is a number between 16 and 33, a, f, and g are each a number of 1 or more, b is a number of 0.5 or more, and d and e are each a number of 0 or more.) 2. The thermal conductive sheet according to claim 1, wherein in compound (A), W comprises one or more vinylidene groups or vinylene groups.

3. In the compound (A), the X １ ~X ３ The thermal conductive sheet according to claim 1 or 2, wherein the hydrocarbon group has 2 or more carbon atoms and 3 or fewer carbon atoms.

4. In the aforementioned compound (A), the aforementioned Y １ to Y ３ comprises an ester group or an amide group, the heat conductive sheet according to claim 1 or 2.

5. The thermal conductive sheet according to claim 1 or 2, wherein in compound (A), m, n, and o satisfy the following relationship (α): m / (n + m + o) ≥ 0.025 (α) 6. The thermal conductive sheet according to claim 1 or 2, wherein in compound (A), m, n, o, and r satisfy the following relationship (β): o*r / (n+m+o)≧1.00 (β) 7. The thermal conductive sheet according to claim 1 or 2, wherein in compound (B), X1 and X2 are each independently trivalent saturated hydrocarbon groups having 2 to 6 carbon atoms, and Y1 and Y2 are each independently divalent organic groups containing an ester group or an amide group.

8. The thermal conductive sheet according to claim 1 or 2, wherein the content of the compound (Z) is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the silicone resin.

9. The thermal conductive sheet according to claim 1 or 2, wherein in compound (B), b, f, and a satisfy the following relationship (γ): b * f / (b + a) ≥ 0.3 (γ) 10. The thermal conductive sheet according to claim 1 or 2, wherein the thermal conductive filler is at least one selected from the group consisting of metals, inorganic hydroxides, inorganic oxides, inorganic nitrides, carbon fibers, graphite, and diamond.

11. The thermal conductive sheet according to claim 1 or 2, wherein the thermal conductive filler includes an anisotropic filler.

12. The thermal conductive sheet according to claim 11, wherein the thermal conductive filler includes an anisotropic filler, and the volume ratio of the anisotropic filler content to the anisotropic filler content (anisotropic filler content / anisotropic filler content) is 0.30 or more and 3.0 or less.

13. The thermal conductive sheet according to claim 11, wherein the anisotropic filler is oriented in the thickness direction of the thermal conductive sheet.

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