Heat dissipation sheet

Abstract

To provide a heat dissipation sheet that has low hardness and excellent heat resistance. [Solution] A heat dissipation sheet comprising polyurethane, a thermally conductive filler, and a carboxylic acid ester, wherein the content of polyurethane relative to the total mass of the heat dissipation sheet is greater than the content of carboxylic acid ester relative to the total mass of the heat dissipation sheet, and the content of thermally conductive filler is greater than 50% by volume relative to the total volume of the heat dissipation sheet.

Description

[Technical Field]

[0001] This disclosure relates to a heat dissipation sheet. [Background technology]

[0002] Heat dissipation sheets are useful as heat dissipation components for electronic devices where fans or heat sinks cannot be installed (e.g., smartphones, tablet devices, etc.) in order to achieve miniaturization and lightness, and for battery casings, etc.

[0003] For example, Patent Document 1 describes a polyurethane resin composition that can maintain heat dissipation and heat resistance over a long period of time, characterized by containing (A) a hydroxyl group-containing conjugated diene polymer, (B) at least one hydrogenated polyol selected from hydrogenated hydroxyl group-containing conjugated diene polymers and hydrogenated castor oil-based polyols, (C) a polyisocyanate, (D) an inorganic filler, (E) a phosphate ester represented by general formula (1), and (F) a plasticizer. Patent Document 2 describes a heat dissipation sheet formed from a flexible polyurethane elastomer, characterized by containing 1 to 50 parts by weight of a trimellitic acid ester-based plasticizer and a thermally conductive filler in 100 parts by weight of polyurethane obtained by reacting a castor oil-modified polyol with a polyisocyanate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-150475 [Patent Document 2] Japanese Patent Publication No. 2004-300300 [Overview of the project] [Problems that the invention aims to solve]

[0005] In heat dissipation sheets, there were cases where a balance between low hardness and heat resistance was required.

[0006] One embodiment of this disclosure aims to solve the problem of providing a heat dissipation sheet that has low hardness and excellent heat resistance. [Means for solving the problem]

[0007] This disclosure includes the following aspects: <1> A heat dissipation sheet comprising polyurethane, a thermally conductive filler, and a carboxylic acid ester, The polyurethane content relative to the total mass of the heat dissipation sheet is greater than the carboxylic acid ester content relative to the total mass of the heat dissipation sheet. A heat dissipation sheet in which the thermal conductive filler content exceeds 50% by volume relative to the total volume of the heat dissipation sheet. <2> Carboxylic acid esters include aliphatic carboxylic acid esters. <1> The heat dissipation sheet described above. <3> The thermally conductive filler consists of two or more types, Two or more thermally conductive fillers have different average particle sizes. <1> or <2> The heat dissipation sheet described above. <4> The thermally conductive filler includes thermally conductive fillers with an average particle size of 50 μm or more. <1> ~ <3> A heat dissipation sheet as described in one of the following items. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, a heat dissipation sheet is provided that has low hardness and excellent heat resistance. [Modes for carrying out the invention]

[0009] The contents of this disclosure will be described in detail below. The explanation of the constituent elements described below may be based on a typical embodiment of this disclosure, but this disclosure is not limited to such embodiments. In this disclosure, a numerical range indicated using "~" means a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0010] In this disclosure, the amount of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved.

[0011] [Heat dissipation sheet] The heat dissipation sheet of this disclosure is a heat dissipation sheet comprising polyurethane, a thermally conductive filler, and a carboxylic acid ester, wherein the content of polyurethane relative to the total mass of the heat dissipation sheet is greater than the content of the carboxylic acid ester relative to the total mass of the heat dissipation sheet, and the content of the thermally conductive filler is greater than 50% by volume relative to the total volume of the heat dissipation sheet.

[0012] The heat dissipation sheet disclosed herein can achieve both low hardness and heat resistance. In particular, in the heat dissipation sheet of this disclosure, the polyurethane content relative to the total mass of the heat dissipation sheet is greater than the carboxylic acid ester content relative to the total mass of the heat dissipation sheet, and the thermal conductive filler content is more than 50% by volume relative to the total volume of the heat dissipation sheet, thus achieving both low hardness and heat resistance. On the other hand, in the polyurethane resin described in Patent Document 1, the polyurethane content is less than the carboxylic acid ester content. In addition, in the heat dissipation sheet described in Patent Document 2, the content of the heat conductive filler is 50% by volume or less.

[0013] <Polyurethane> The heat dissipation sheet of the present disclosure contains at least one kind of polyurethane. Polyurethane can be obtained, for example, by reacting a polyol and a polyisocyanate. Therefore, for example, by curing a composition containing a polyol, a polyisocyanate, a heat conductive filler, and a carboxylic acid ester and molding it into a sheet shape, the heat dissipation sheet of the present disclosure containing polyurethane, a heat conductive filler, and a carboxylic acid ester can be obtained.

[0014] Examples of the polyol include polyether polyol, polyester polyol, polyether ester polyol, polycarbonate diol, and polymer polyol.

[0015] Examples of the polyether polyol include polyether polyols obtained by adding an alkylene oxide such as ethylene oxide (EO) or propylene oxide (PO) to a polyhydric alcohol such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, glycerin, pentaerythritol, trimethylolpropane, sorbitol, or sucrose.

[0016] Examples of the polyester polyol include polyester polyols obtained by polycondensing an aliphatic carboxylic acid such as malonic acid, succinic acid, or adipic acid; an aromatic carboxylic acid such as phthalic acid; and an aliphatic glycol such as ethylene glycol, diethylene glycol, or propylene glycol.

[0017] Examples of the polyether ester polyol include compounds obtained by reacting the above polyether polyol with a polybasic acid for polyesterification.

[0018] Examples of polycarbonate diols include those obtained by polycondensation of a dihydric alcohol (e.g., 1,4-butanediol or 1,6-hexanediol, etc.) with a carbonate compound (e.g., dimethyl carbonate, diethyl carbonate, or diphenyl carbonate, etc.).

[0019] The polyisocyanate may be an aromatic polyisocyanate, an aliphatic polyisocyanate, or an alicyclic polyisocyanate.

[0020] Examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, xylylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, and 3,3'-dimethoxy-4,4'-biphenylene diisocyanate.

[0021] Examples of aliphatic polyisocyanates include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, nonamethylene diisocyanate, and 2,2'-dimethyl diisocyanate. Tylpentane diisocyanate, 2,2,4-trimethylhexane diisocyanate, decamethylene diisocyanate, butene diisocyanate, 1,3-butadiene-1,4-diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 1,6,11-undecamethylene diisocyanate, 1,3,6-hexamethylene diisocyanate, 1,8-diisocyanate-4-isocyanate methyl octane, 2,5,7-trimethyl-1,8-diisocyanate-5-isocyanate methyl octane, bis(isocyanate ethyl) carbonate, bis(isocyanate ethyl) ether, 1,4-butylene glycol dipropyl ether-ω,ω'-diisocyanate, lysine isocyanate Examples include methyl esters, lysine triisocyanate, 2-isocyanate ethyl-2,6-diisocyanate hexanoate, 2-isocyanate propyl-2,6-diisocyanate hexanoate, and bis(4-isocyanate-n-butylidene)pentaerythritol.

[0022] Examples of alicyclic polyisocyanates include isophorone diisocyanate, bis(isocyanate methyl)cyclohexane, dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, and 2,2'-dimethyl Diisocyanate dicyclohexylmethane diisocyanate, diisocyanate dima acid, 2,5-diisocyanate methyl-bicyclo[2.2.1]-heptane, 2,6-diisocyanate methyl-bicyclo[2.2.1]-heptane, 2-isocyanate methyl-2-(3-isocyanate propyl)-5-isocyanate methyl-bicyclo[2.2.1]-heptane, 2-isocyanate methyl-2-(3-isocyanate propyl)-6-isocyanate methyl-bicyclo[2.2.1]-heptane, 2-isocyanate methyl-3-(3-isocyanate propyl) Examples include natopropyl)-5-(2-isocyanatetoethyl)-bicyclo[2.2.1]-heptane, 2-isocyanatemethyl-3-(3-isocyanatetopropyl)-6-(2-isocyanatetoethyl)-bicyclo[2.2.1]-heptane, 2-isocyanatemethyl-2-(3-isocyanatetopropyl)-5-(2-isocyanatetoethyl)-bicyclo[2.2.1]-heptane, and 2-isocyanatemethyl-2-(3-isocyanatetopropyl)-6-(2-isocyanatetoethyl)-bicyclo[2.2.1]-heptane.

[0023] The polyisocyanate may be a modified isocyanate (for example, a urethane modified polyisocyanate, a carbodiimide modified polyisocyanate, a uretoimine modified polyisocyanate, a biuret modified polyisocyanate, an allophanate modified polyisocyanate, or an isocyanurate modified polyisocyanate). Furthermore, the polyisocyanate may be a prepolymer having terminal isocyanate groups, obtained by reacting a polyisocyanate compound in excess of an active hydrogen compound (for example, the polyol mentioned above) containing two or more active hydrogens.

[0024] In particular, polyurethane is preferably a material that contains a structure derived from aromatic polyisocyanate.

[0025] The polyurethane content is preferably 1% to 20% by mass, more preferably 2% to 15% by mass, and even more preferably 3% to 10% by mass, based on the total mass of the heat dissipation sheet.

[0026] <Thermal conductive filler> The heat dissipation sheet of this disclosure includes at least one thermally conductive filler. In this disclosure, a thermally conductive filler is a filler with a thermal conductivity of 1 W / (m·K) or higher. The thermal conductivity of a thermally conductive filler is a value measured by the laser flash method (JIS R1611:2010 (corresponding international standard: ISO 18755:2005)).

[0027] Examples of thermally conductive fillers include metal oxides or metal nitrides such as alumina, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, calcium oxide, magnesium oxide, zinc oxide, beryllia, aluminum oxide, aluminum nitride, and boron nitride; hydrated metal compounds; silica such as fused silica, crystalline silica, and amorphous silica; silicon carbide, silicon nitride, titanium carbide, and diamond. Furthermore, the thermally conductive filler may or may not be surface-treated.

[0028] In particular, the thermally conductive filler is preferably alumina, magnesium hydroxide, magnesium oxide, aluminum nitride, or boron nitride, and more preferably alumina.

[0029] The average particle size (average value of primary particles) of the thermally conductive filler is preferably 0.1 μm to 200 μm, and more preferably 1 μm to 100 μm.

[0030] The average particle size of a thermally conductive filler represents the particle size at which the cumulative volume calculated from the smallest diameter side accounts for 50% of the particle size distribution (volume-based) measured by laser diffraction. The average particle size of the thermally conductive filler is measured in accordance with JIS Z8825:2022.

[0031] The thermally conductive fillers consist of two or more types, and it is preferable that the average particle sizes of the two or more thermally conductive fillers differ from each other. The inclusion of thermally conductive fillers with a relatively small average particle size improves thermal conductivity. Conversely, the inclusion of thermally conductive fillers with a relatively large average particle size improves the moldability of the heat dissipation sheet. Therefore, by including two or more types of thermally conductive fillers with different average particle sizes in the heat dissipation sheet, the heat dissipation performance is dramatically improved.

[0032] From the viewpoint of moldability, it is preferable that the thermal conductive filler includes thermal conductive fillers with an average particle size of 50 μm or more.

[0033] When there are two or more types of thermally conductive fillers, it is preferable that the thermally conductive fillers include a thermally conductive filler with an average particle diameter of 50 μm or more and a thermally conductive filler with an average particle diameter of less than 50 μm. For thermally conductive fillers with an average particle diameter of 50 μm or more, the average particle diameter is preferably 50 μm to 200 μm, more preferably 55 μm to 180 μm, even more preferably 60 μm to 150 μm, and particularly preferably 65 μm to 120 μm. At the same time, for thermally conductive fillers with an average particle diameter of less than 50 μm, the average particle diameter is preferably 1 μm to 40 μm, more preferably 2 μm to 20 μm, and even more preferably 3 μm to 10 μm.

[0034] From the viewpoint of further improving moldability and heat dissipation, it is preferable that the content of thermally conductive fillers with an average particle diameter of 50 μm or more is greater than the content of thermally conductive fillers with an average particle diameter of less than 50 μm. The mass ratio of the content of thermal conductive fillers with an average particle diameter of 50 μm or more to the content of thermal conductive fillers with an average particle diameter of less than 50 μm is preferably greater than 1.0 and less than or equal to 3.0, more preferably between 1.05 and 2, and even more preferably between 1.1 and 1.5.

[0035] The thermally conductive filler content is more than 50% by volume relative to the total volume of the heat dissipation sheet. By having a thermally conductive filler content of more than 50% by volume, it is possible to mold the material into a heat dissipation sheet with good thermal conductivity.

[0036] From the above viewpoint, the content of the thermally conductive filler is preferably 50% to 75% by volume, more preferably 55% to 70% by volume, and even more preferably 60% to 65% by volume.

[0037] <Carboxylic acid esters> The heat dissipation sheet of this disclosure contains at least one carboxylic acid ester.

[0038] Examples of carboxylic acid esters include monocarboxylic acid esters, dicarboxylic acid esters, tricarboxylic acid esters, and tetracarboxylic acid esters.

[0039] Examples of monocarboxylic acid esters include aliphatic carboxylic acid esters such as butyl stearate (BS), methoxyethyl oleate (MEO), methyl acetylricinoleate (MAR), ethyl acetylricinoleate (EAR), methoxyethyl acetylricinoleate (MEAR), and glycerol triheptanoate; Aromatic carboxylic acid esters such as butyl benzoate, octyl benzoate, butyl phenylacetate, and hexyl phenylacetate; Examples of alicyclic carboxylic acid esters include methyl cyclopropanecarboxylate, butyl cyclopropanecarboxylate, methoxyethyl cyclobutanecarboxylate, ethyl cyclopentanecarboxylate, butyl cyclopentanecarboxylate, methyl cyclohexanecarboxylate, methoxyethyl cyclohexanecarboxylate, and octyl cyclohexanecarboxylate.

[0040] Examples of dicarboxylic acid esters include aliphatic dicarboxylic acid esters of adipic acid esters (e.g., di-2-ethylhexyl adipic acid (DOA), diisodecyl adipic acid (DIDA), di(methylcyclohexyl) adipic acid, etc.), azelaic acid esters (e.g., di-n-hexyl azelaic acid (DNHZ), di-2-ethylhexyl azelaic acid (DOZ), etc.), and sebacate acid esters (e.g., dibutyl sebacate (DBS), di-2-ethylhexyl sebacate (DOS), etc.); Examples include aromatic dicarboxylic acid esters of phthalate esters (e.g., dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), heptyl nonyl phthalate (HNP), di-2-ethylhexyl phthalate (DOP), di-n-octyl phthalate (DNOP), di-i-octyl phthalate (DIOP), di-s-octyl phthalate (DCapP), di(79-alkyl) phthalate (D79P), i-decyl phthalate (DIDP), ditridecyl phthalate (DTDP), dicyclohexyl phthalate (DCHP), butyl benzyl phthalate (BBP), ethyl phthalyl ethyl glycolate (EPEG), butyl phthalyl butyl glycolate (BPBG), etc.).

[0041] Examples of tricarboxylic acid esters include citrate esters [e.g., aliphatic tricarboxylic acid esters such as triethyl citrate (TEC), tributyl citrate (TBC), triethyl acetyl citrate (ATEC), tributyl acetyl citrate (ATBC), tricyclohexyl acetyl citrate, trioctyl citrate, tri(octyldecyl) citrate, etc.]. Examples include aromatic tricarboxylic acid esters such as triethyl trimellitate and trioctyl trimellitate.

[0042] Examples of tetracarboxylic acid esters include tetramethyl pyromelliate, tetraethyl pyromelliate, tetrapropyl pyromelliate, tetraisopropyl pyromelliate, tetrabutyl pyromelliate, tetrahexyl pyromelliate, and tetradecyl pyromelliate.

[0043] In particular, from the viewpoint of further reducing hardness, the carboxylic acid ester preferably contains an aliphatic carboxylic acid ester, and more preferably contains an aliphatic dicarboxylic acid ester.

[0044] Furthermore, from the viewpoint of improving compatibility with polyols and obtaining a heat dissipation sheet with excellent moldability, the solubility parameter (SP value) of the carboxylic acid ester is set to 7.0 (cal / cm³). 3 ) 1 / 2 ~9.0 (cal / cm 3 ) 1 / 2 Preferably, it is 8.0 (cal / cm³). 3 ) 1 / 2 ~9.0 (cal / cm 3 ) 1 / 2 It is preferable that it be so.

[0045] In this disclosure, the SP value refers to the Hansen solubility parameter. The Hansen solubility parameter is a representation in three dimensions of the solubility parameter introduced by Hildebrand, divided into three components: the dispersion term δd, the polarity term δp, and the hydrogen bonding term δh.

[0046] The heat dissipation sheet of this disclosure has a polyurethane content greater than the carboxylic acid ester content relative to the total mass of the heat dissipation sheet. A higher polyurethane content than carboxylic acid ester content allows for both low hardness and heat resistance. The ratio of polyurethane content to carboxylic acid ester content is preferably greater than 1, more preferably 1.5 to 6.0, and even more preferably 2.0 to 3.0.

[0047] The heat dissipation sheet of this disclosure may contain other components besides polyurethane, a thermally conductive filler, and a carboxylic acid ester. Examples of other components include flame retardants, plasticizers, catalysts, water absorbers (bubble inhibitors), antioxidants, pigments, stabilizers, dispersants, colorants, antibacterial agents, and ultraviolet absorbers.

[0048] <Physical properties> The heat dissipation sheet of this disclosure preferably has a thermal conductivity of 1.0 W / m·K or higher, more preferably 1.2 W / m·K or higher, and even more preferably 1.5 W / m·K or higher. The upper limit of the thermal conductivity is not particularly limited, and is, for example, 30 W / m·K. In this disclosure, thermal conductivity is measured using a thermal conductivity meter in the following manner. Cut a sample measuring 100mm wide x 50mm long x 2.0mm high from the heat dissipation sheet. Measure the thermal conductivity at 23°C using a "Rapid Thermal Conductivity Meter QTM-710" manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0049] The heat dissipation sheet of this disclosure preferably has a hardness of 35 or less, more preferably 33 or less, and even more preferably 30 or less. The lower limit of the hardness is not particularly limited, and is, for example, 10. In this disclosure, hardness refers to Asker C hardness. Asker C hardness is measured in accordance with JIS K7312:1996.

[0050] Furthermore, the heat dissipation sheet of this disclosure exhibits a small change in hardness (rate of change in hardness) before and after heat treatment. The heat treatment is performed at 130°C for 500 hours. In this disclosure, "excellent heat resistance" means that the rate of change in hardness is small. Specifically, the rate of change in hardness is preferably 60% or less, more preferably 50% or less, even more preferably 30% or less, particularly preferably 20% or less, and extremely preferably 10% or less. The lower limit of the rate of change in hardness is, for example, 0%. The rate of change in hardness is calculated using the following formula. Percentage change in hardness (%) = {(absolute value of "hardness after heat treatment - hardness before heat treatment") / (hardness before heat treatment)} × 100

[0051] The thickness of the heat dissipation sheet of this disclosure is not particularly limited, but is preferably 0.1 mm to 10 mm, more preferably 0.5 mm to 5.0 mm, and even more preferably 1.0 mm to 2.5 mm.

[0052] The heat dissipation sheet of this disclosure can be used, for example, in electronic devices such as smartphones, tablet devices, mobile phones, telephones, personal computers, digital cameras, e-books, electronic dictionaries, music players, radios, game consoles, hearing aids, pacemakers, power tools, electric shavers, AV equipment, and OA equipment; as casing material for lithium batteries; as control boards; as heat dissipation components for medical robots, industrial robots, etc.; as lighting fixtures and backlight fixtures using light-emitting diodes (LEDs), electroluminescent devices, etc.; as batteries such as solar cells and lithium-ion batteries; as computer components such as ICs and CPUs; as power control devices such as modules; and as power supply circuits such as inverters.

[0053] The heat dissipation sheet of this disclosure can be manufactured, for example, by the following method.

[0054] First, the liquid containing the polyol and the carboxylic acid ester is stirred using a mixer or similar device. Next, add the heat-conductive filler and mix with a mixer or similar device. Furthermore, polyisocyanate is added and stirred with a mixer or the like to obtain a heat dissipation sheet composition.

[0055] The heat dissipation sheet composition is poured onto a release film. It is then cured in a constant temperature bath at 60°C to 100°C for, for example, 1 to 3 hours. The curing time can be appropriately adjusted depending on the molding method and the presence or absence of a catalyst in the heat dissipation sheet composition. Next, peel the heat dissipation sheet from the release film. [Examples]

[0056] The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited in any way by these examples.

[0057] [Preparation of compositions for heat dissipation sheets] A composition for a heat dissipation sheet was prepared by mixing the components shown in Table 1. Specifically, a solution containing a polyol and a carboxylic acid ester was stirred for 1 minute at 1800 rpm (revolutions per minute) using a planetary mixer. Next, a thermally conductive filler was added, and the mixture was stirred using a planetary mixer at 1800 rpm for 3 minutes. Furthermore, polyisocyanate was added and the mixture was stirred at 1800 rpm for 3 minutes using a planetary mixer to obtain a heat dissipation sheet composition.

[0058] Details of each component are as follows:

[0059] (Polyol) Product name: "SU-3001B", manufactured by Sanyurec Co., Ltd., aliphatic polyester polyol

[0060] (Polyisocyanate) • Product name "SU-3001A", manufactured by Sanyurec Co., Ltd., a prepolymer of diphenylmethane diisocyanate.

[0061] (Carboxylic acid ester) • Carboxylic acid ester 1: Di-2-ethylhexyl sebacate (product name "Sensor DOS", manufactured by Shin Nippon Rika Co., Ltd.) • Carboxylic acid ester 2: Pyromellitic acid mixed long-chain alkyl ester (product name "UL-100", manufactured by ADEKA Corporation) • Carboxylic acid ester 3: Trioctyl trimellitic acid (product name "TOTM", manufactured by DIC Corporation) • Carboxylic acid ester 4: Di-2-ethylhexyl azelaate (product name "Sensor DOZ", manufactured by Shin Nippon Rika Co., Ltd.)

[0062] (Thermal conductive filler) • Thermally conductive filler 1: Alumina (product name "WA F220", manufactured by Resonaq, average particle size 75 μm) • Thermally conductive filler 2: Alumina (product name "AL-45-H", manufactured by Resonaq Corporation, average particle size 5 μm)

[0063] (others) • Tributyl phosphate: Product name "TBP", manufactured by Daihachi Chemical Industry Co., Ltd. • Cresyl diphenyl phosphate: Product name "TCP", manufactured by Daihachi Chemical Industry Co., Ltd.

[0064] [Fabrication of heat dissipation sheets] A heat dissipation sheet composition was poured onto a release PET (polyethylene terephthalate) film (product name "SP3000", manufactured by Toyo Cross Co., Ltd.). It was cured in a constant temperature bath at 80°C for 2 hours. The heat dissipation sheet was peeled off the release PET film at room temperature (25°C).

[0065] The following evaluations were performed using the obtained heat dissipation sheets.

[0066] <Hardness before heat treatment> The hardness was measured using an Asker C hardness tester.

[0067] <Hardness after heat treatment> The heat dissipation sheet was placed in a constant temperature bath and subjected to heat treatment at 130°C for 500 hours. After removing the heat dissipation sheet from the constant temperature bath and leaving it at room temperature (25°C) for 1 hour, its hardness was measured using an Asker C hardness tester.

[0068] <Thermal conductivity> A sample measuring 100mm wide x 50mm long x 2.0mm high was cut from a heat dissipation sheet. The thermal conductivity was measured at 23°C using a "Rapid Thermal Conductivity Meter QTM-710" manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0069] <compatibility> The compatibility of the heat dissipation sheet composition was evaluated. In Examples 1 to 4, 10 mL of a polyol and 10 mL of a carboxylic acid ester were placed in a 100 mL polycup to obtain a mixed solution. In Comparative Example 1, 10 mL of a polyol and 10 mL of tributyl phosphate were placed in a 100 mL polycup to obtain a mixed solution. In Comparative Example 2, 10 mL of a polyol and 10 mL of cresyl diphenyl phosphate were placed in a 100 mL polycup to obtain a mixed solution. Each mixed solution was stirred for 1 minute at 1800 rpm (revolutions per minute) using a planetary mixer. The mixed solutions were transferred to 20 mL vials and cured at room temperature (25 °C) for 12 hours. Then, the state of the mixed solutions was visually confirmed to evaluate the compatibility. The evaluation criteria are as follows. A: No interface was confirmed in the mixed solution. B: The mixed solution was turbid. C: The mixed solution separated into two phases and an interface was confirmed.

[0070] <Moldability> The moldability was evaluated based on the peelability when peeling the heat dissipation sheet from the release PET film. The evaluation criteria are as follows. A: It could be peeled from the release PET film without problems. B: It could not be peeled from the release PET film, or although it could be peeled, cracks were formed on the surface of the heat dissipation sheet due to peeling.

[0071] The evaluation results are shown in Table 1. In Table 1, "content of the thermal conductivity filler" means the content of the thermal conductivity filler with respect to the total volume of the heat dissipation sheet. The unit of the SP value is (cal / cm 3 ) 1 / 2 is.

[0072]

Table 1

[0073] As shown in Table 1, Examples 1 to 4 contained polyurethane, a thermally conductive filler, and a carboxylic acid ester. The polyurethane content was greater than the carboxylic acid ester content, and the thermally conductive filler content exceeded 50% by volume relative to the total volume of the heat dissipation sheet. As a result, it was found that the hardness was low and the heat resistance was excellent. Furthermore, it was found that good compatibility leads to excellent moldability of the heat dissipation sheet. On the other hand, Comparative Example 1 did not contain carboxylic acid esters, and although its hardness was low, it was found to have poor heat resistance. In Comparative Example 2, the material did not contain carboxylic acid esters, and its moldability was poor, making it impossible to measure its hardness. Comparative Example 3 did not contain carboxylic acid esters and was found to have high hardness. Comparative Example 4 lacks both a carboxylic acid ester and a thermally conductive filler, resulting in low thermal conductivity, making it unsuitable as a heat dissipation sheet.

Claims

1. A heat dissipation sheet comprising polyurethane, a thermally conductive filler, and a carboxylic acid ester, The amount of polyurethane relative to the total mass of the heat dissipation sheet is greater than the amount of carboxylic acid ester relative to the total mass of the heat dissipation sheet. A heat dissipation sheet in which the content of the thermally conductive filler is greater than 50 volume percent of the total volume of the heat dissipation sheet.

2. The heat dissipation sheet according to claim 1, wherein the carboxylic acid ester includes an aliphatic carboxylic acid ester.

3. The aforementioned thermally conductive filler consists of two or more types, The heat dissipation sheet according to claim 1 or claim 2, wherein the two or more thermally conductive fillers have different average particle sizes.

4. The heat dissipation sheet according to claim 1 or claim 2, wherein the heat conductive filler comprises a heat conductive filler with an average particle diameter of 50 μm or more.

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