JP2024029433A - Thermal conductive composition and thermally conductive sheet - Google Patents

Abstract

An object of the present invention is to provide a thermally conductive composition that can yield a thermally conductive sheet having high thermal conductivity and a thick film with good productivity by irradiation with light and has good storage stability. A thermally conductive composition containing at least one of a radically polymerizable monomer and a partial polymer thereof, a binder component containing a photopolymerization initiator, and a thermally conductive filler, the binder component being 100 parts by volume. , the thermally conductive filler is 100 parts by volume or more and 900 parts by volume or less, and the photopolymerization initiator is a dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) and a specific A thermally conductive composition which is a hydroperoxide (a-2) having a thioxanthone skeleton represented by the general formula (2). [Selection diagram] None

Description

The present invention relates to a thermally conductive composition and a thermally conductive sheet.

It is important to dissipate heat generated from various electronic and electrical devices. In recent years, high performance and diversification have progressed, and heat dissipation countermeasure components are used between a heat generating body such as an IC device and a heat dissipating body such as a heat sink for use in automotive electrical components and communication equipment. , there is a demand for thick film heat dissipation countermeasure members. Heat dissipation countermeasure materials include heat dissipation sheets, heat dissipation gap fillers, heat dissipation adhesives, heat dissipation greases, etc. However, there is no need to particularly control the amount of application and there is no fluidity, so they are sandwiched between the desired heat generating element and heat dissipation element. Thermal conductive sheets are attracting attention because of their excellent workability.

One method of increasing the thermal conductivity of a thermally conductive sheet is to increase the content of a thermally conductive filler, and Patent Document 1 discloses a method for producing a thermally conductive sheet with high thermal conductivity and a thick film by thermosetting. ing. Furthermore, in order to increase productivity, in Patent Documents 2 and 3, a thermally conductive sheet is produced by photocuring by ultraviolet irradiation using a photopolymerizable composition containing a photopolymerization initiator.

Further, in Patent Document 4, a dialkyl peroxide having a specific thioxanthone skeleton that has both photopolymerizability and thermal polymerizability is known as a photopolymerization initiator.

Japanese Patent Application Publication No. 2006-111644 JP2019-85441A JP2020-45386A International Publication No. 2020/067118

Against this background, demand for thermally conductive sheets is expected to increase, and the method of manufacturing thick thermally conductive sheets by thermosetting as in Patent Document 1 has a higher curing efficiency than curing by ultraviolet irradiation. Because of the low molecular weight, polymerization takes a long time at high temperatures, and even if the polymerization conditions are optimized, there is a limit to shortening the polymerization time.

On the other hand, in the method of producing a thermally conductive sheet by photocuring as in Patent Documents 2 and 3, if the content of the thermally conductive filler is increased, even when irradiated with light such as ultraviolet rays, the light transmittance decreases, causing deep penetration. Since it is difficult to reach the target area, the film thickness is limited, resulting in a thin sheet. Therefore, in order to produce a thick thermally conductive sheet, the content of filler is limited, resulting in a sheet with low thermal conductivity.

Further, Patent Document 4 describes that a cured product can be produced by using a dialkyl peroxide having a thioxanthone skeleton that is both photopolymerizable and thermally polymerizable as a photopolymerization initiator. It was unclear whether a cured product having good curability could be obtained even from a composition in which peroxide is highly filled with a filler having high thermal diffusivity such as a thermally conductive filler.

In addition, thermally conductive compositions are required to have stability during long-term storage, taking into account the environment inside shipping containers and work environments during sea transportation overseas and when staying at port facilities.

Therefore, an object of the present invention is to provide a thermally conductive composition that can be produced by light irradiation to obtain a thermally conductive sheet having high thermal conductivity and a thick film with good productivity and has good storage stability.

Another object of the present invention is to provide a thermally conductive sheet that is a cured product of the thermally conductive composition.

The present invention is a thermally conductive composition containing at least one of a radically polymerizable monomer and a partial polymer thereof, a binder component containing a photopolymerization initiator, and a thermally conductive filler, wherein 100 parts by volume of the binder component , the thermally conductive filler is 100 parts by volume or more and 900 parts by volume or less, and the photopolymerization initiator has the general formula (1):
(In general formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represent a methyl group or an ethyl group, R ⁵ represents an alkyl group having 1 to 6 carbon atoms or a phenyl group, R ⁶ is an independent substituent, and represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n represents an integer from 0 to 2.) Dialkyl peroxide (a-1) having a thioxanthone skeleton and general formula (2):
(In formula (2), R ¹ and R ² independently represent a methyl group or an ethyl group, and R ³ is an independent substituent, such as an alkyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 4 carbon atoms. represents an alkoxy group or a chlorine atom, and n represents an integer from 0 to 2.) is a polymerization initiator (A) containing a hydroperoxide (a-2) having a thioxanthone skeleton; The present invention relates to a thermally conductive composition in which the amount of the hydroperoxide (a-2) having a thioxanthone skeleton is 30 parts by mass or less in 100 parts by mass of the initiator (A).

The present invention also relates to a thermally conductive sheet that is a cured product of a thermally conductive composition.

The thermally conductive composition of the present invention has good storage stability, and even when it is highly filled with a filler having high thermal diffusivity such as a thermally conductive filler, it can be easily produced when photocured by irradiating ultraviolet rays. A thermally conductive sheet with high thermal conductivity and a thick film can be produced with ease.

The thermally conductive composition of the present invention contains at least one of a radically polymerizable monomer and a partial polymer thereof, a binder component containing a photopolymerization initiator, and a thermally conductive filler. When the thermally conductive composition is photocured by irradiation with ultraviolet rays, the dialkyl peroxide having a thioxanthone skeleton is quickly activated and is not easily affected by the thermal diffusivity of the highly filled thermally conductive filler. From this, a thermally conductive sheet having high thermal conductivity and a thick film can be produced with good productivity.

If the thermally conductive composition of the present invention is photocured using a polymerization initiator containing a specific amount or more of hydroperoxide (a-2) having a thioxanthone skeleton, curing failure will occur. It is characterized in that the dialkyl peroxide (a-1) having a thioxanthone skeleton and the hydroperoxide (a-2) having a thioxanthone skeleton are contained in a specific ratio.

In addition, in the polymerization initiator (A) containing a dialkyl peroxide (a-1) having a thioxanthone skeleton and a hydroperoxide (a-2) having a thioxanthone skeleton in a specific ratio, some of the generated active radical species are While a hydroperoxide having a thioxanthone skeleton is inactivated by abstracting a hydrogen atom, a hydroperoxide having a thioxanthone skeleton is converted into a peroxy radical species by abstracting a hydrogen atom. On the other hand, active radical species that have not reacted with the hydroperoxide having a thioxanthone skeleton generate carbon radical species through an addition reaction to a radically polymerizable compound or a hydrogen abstraction reaction from a cured product, etc., but they do not combine with the peroxy radical species. By doing so, it becomes a thermally stable dialkyl peroxide compound, which is thought to suppress the increase in the molecular weight of the binder component. Therefore, the thermally conductive composition containing the polymerization initiator of the present invention has excellent storage stability while exhibiting good curability.

<Radical polymerizable monomer>
As the radically polymerizable monomer, a compound having an ethylenically unsaturated group can be preferably used. Examples of radically polymerizable monomers include (meth)acrylic esters, styrenes, maleic esters, fumaric esters, itaconic esters, cinnamic esters, crotonic esters, vinyl ethers, and vinyl esters. , vinyl ketones, allyl ethers, allyl esters, N-substituted maleimides, N-vinyl compounds, unsaturated nitriles, and olefins. Among these, it is preferable to include highly reactive (meth)acrylic esters. The radically polymerizable monomers may be used alone or in combination of two or more types.

As the (meth)acrylic esters, monofunctional compounds and polyfunctional compounds can be used. Monofunctional compounds include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. Alkyl (meth)acrylates such as acrylate; cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth) Ester compounds of (meth)acrylic acid and alicyclic alcohol such as acrylate and 2-ethyl-2-adamantyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate ; 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 3-hydroxy-1-adamantyl (meth)acrylate, hydroxyl-terminated polyethylene glycol mono( Monomers with hydroxy groups such as meth)acrylate, hydroxyl-terminated polypropylene glycol mono(meth)acrylate; methoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, 2-phenylphenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (3-ethyloxetan-3-yl)methyl ( Monomers having a chain or cyclic ether bond such as meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate; N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethyl(meth)acrylamide, N - Methylol (meth)acrylamide, N-isopropyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acryloylmorpholine, N-(meth)acryloyloxyethylhexahydrophthalimide Monomers having a nitrogen atom such as; monomers having an isocyanate group such as 2-(meth)acryloyloxyethyl isocyanate; monomers having an epoxy group such as glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether; Acid monomers having a phosphorus atom such as 2-((meth)acryloyloxy)ethyl; monomers having a silicon atom such as 3-(meth)acryloxypropyltrimethoxysilane; 2,2,2-trifluoroethyl (meth) Fluorine atom-containing monomers such as acrylate, 2,2,3,3,3-pentafluoropropyl (meth)acrylate, 2-(perfluorohexyl)ethyl (meth)acrylate; (meth)acrylic acid, succinic acid mono( 2-(meth)acryloyloxyethyl), mono(2-(meth)acryloyloxyethyl) phthalate, mono(2-(meth)acryloyloxyethyl) maleate, ω-carboxy-polycaprolactone mono(meth)acrylate, etc. Examples include monomers having a carboxyl group.

The polyfunctional compounds include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol di( meth)acrylate monostearate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, glycerin propoxytri(meth)acrylate tricyclodecane dimethanol di (meth)acrylate, 2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 9,9-bis(4- Polyhydric alcohols such as (2-(meth)acryloyloxyethoxy)phenyl)fluorene, 9,9-bis(4-(2-(2-(meth)acryloyloxyethoxy)ethoxy)phenyl)fluorene, and (meth)acrylic Ester compounds with acids; bis(4-(meth)acryloxyphenyl) sulfide, bis(4-(meth)acryloylthiophenyl) sulfide, tris(2-(meth)acryloyloxyethyl)isocyanurate, ethylene bis(meth) ) Acrylamide, zinc (meth)acrylate, zirconium (meth)acrylate, aliphatic urethane acrylate, aromatic urethane acrylate, epoxy acrylate, polyester acrylate, and the like.

<Partial polymer of radically polymerizable monomer>
Since the radically polymerizable monomer generally has a low viscosity, the filler may settle when mixed with a thermally conductive filler. In this case, it is preferable that the radically polymerizable monomer is partially polymerized in advance to thicken the radically polymerizable monomer to obtain a partial polymer of the radically polymerizable monomer. The viscosity of the partial polymer of the radically polymerizable monomer is not particularly limited, but it is preferably about 10 to 10,000 mPa·s.

Partial polymerization can be carried out by various methods, and known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization can be employed. During polymerization, a partial polymer can be obtained by using a polymerization initiator such as a thermal polymerization initiator or a photopolymerization initiator depending on the polymerization method.

Examples of thermal polymerization initiators used in partial polymerization include diacyl peroxides, peroxyketals, ketone peroxides, hydroperoxides, dialkyl peroxides, peroxyesters, and peroxydicarbonates. Organic peroxides; azo polymerization initiators, etc. can be used. Specifically, lauroyl peroxide, benzoyl peroxide, cyclohexanone peroxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, t-butylhydroperoxide, 2,2'-azo Examples include bisbutyronitrile.

Photopolymerization initiators used for partial polymerization include aromatic ketones, benzoin ethers, halomethyloxadiazole compounds, α-aminoketones, α-aminoacetophenone compounds, acylphosphine compounds, biimidazoles, N,N-dimethylamino Examples include benzophenone, triazine compounds, thioxanthone compounds, and oxime compounds. Specific examples of the photopolymerization initiator include aromatic ketones such as benzophenone, 4,4'-bisdiethylaminobenzophenone, and 4-methoxy-4'-dimethylaminobenzophenone; benzoin ethers such as benzoin methyl ether; ethylbenzoin. benzoin such as; biimidazole such as 2-(o-chlorophenyl)-4,5-phenylimidazole dimer; 2-trichloromethyl-5-(p-methoxystyryl)-1,3,4-oxadiazole Halomethyloxadiazole compounds such as 2-(4-butoxy-naphth-1-yl)-4,6-bis-trichloromethyl-S-triazine, having a thioxanthone skeleton represented by the following general formula (1) Dialkyl peroxide, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone, 1,2-benzyl-2-dimethyl Amino-1-(4-morpholinophenyl)-butanone-1,1-hydroxy-cyclohexyl-phenylketone, benzyl, benzoylbenzoic acid, methyl benzoylbenzoate, 4-benzoyl-4'-methyldiphenyl sulfide, benzyl methyl ketal , dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, 2-n-butoxyethyl-4-dimethylaminobenzoate, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 4- Benzoyl-methyldiphenyl sulfide, 1-hydroxy-cyclohexyl-phenyl ketone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-(dimethylamino)- 2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, α-dimethoxy-α-phenylacetophenone, phenylbis(2,4,6-trimethylbenzoyl) Phosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, 3-benzoyloxyiminobutan-2-one, 3-acetoxyiminobutan-2- Ong et al. Among these, from the viewpoint of curability during sheet production, it is preferable to use at least a dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the following general formula (1). Alternatively, any combination of the thermal polymerization initiators or photopolymerization initiators described above can also be used.

<Photopolymerization initiator (A)>
The polymerization initiator (A) of the present invention comprises a dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the following general formula (1) and a hydroperoxide having a thioxanthone skeleton represented by the following general formula (2). Contains (a-2).

<Dialkyl peroxide having a thioxanthone skeleton (a-1)>
The dialkyl peroxide (a-1) having a thioxanthone skeleton of the present invention can be represented by the following general formula (1).
(In formula (1), R ¹ , R ² , R ³ and R ⁴ independently represent a methyl group or an ethyl group, R ⁵ represents an alkyl group having 1 to 6 carbon atoms or a phenyl group, and R ⁶ is an independent substituent and represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n represents an integer from 0 to 2.)

In the general formula (1), R ¹ , R ² , R ³ and R ⁴ independently represent a methyl group or an ethyl group. R ¹ , R ² , R ³ and R ⁴ are preferably methyl groups from the viewpoint of increasing the storage stability of the polymerizable composition since the decomposition temperature of the dialkyl peroxide having a thioxanthone skeleton is high.

In the general formula (1), R ⁵ is an alkyl group having 1 to 6 carbon atoms or a phenyl group. The alkyl group may be linear or branched. Specific examples of R ⁵ include methyl group, ethyl group, propyl group, 2,2-dimethylpropyl group, and phenyl group. Among these, methyl group, ethyl group, and propyl group are preferable from the viewpoint of easy synthesis of the dialkyl peroxide having the thioxanthone skeleton. Since the decomposition temperature of the dialkyl peroxide having a thioxanthone skeleton is high, the storage stability of the polymerizable composition is high, and the sensitivity to lamp light is high, so methyl, ethyl, and propyl groups are preferred. preferable.

In the general formula (1), the substitution position of the dialkyl peroxide on the thioxanthone is not particularly limited, but from the viewpoint of high sensitivity to lamp light, it is substituted at the 2-position, 3-position, or 4-position of the thioxanthone skeleton. is preferable, and from the viewpoint of easy synthesis, substitution at the 2- or 3-position of the thioxanthone skeleton is more preferable.

In the general formula (1), R ⁶ is an independent substituent and represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom. Due to the push-pull effect on these substituents, the light absorption characteristics of the dialkyl peroxide having a thioxanthone skeleton can be adjusted with respect to the emission wavelength of the lamp used, and the light from the lamp can be efficiently absorbed. can.

In the general formula (1), n represents an integer from 0 to 2. From the viewpoint of easy synthesis of the dialkyl peroxide having the thioxanthone skeleton, n is preferably an integer from 0 to 1, and more preferably 0.

In the general formula (1), when n is an integer from 1 to 2, the substitution position of R ⁶ is not particularly limited, but from the viewpoint of high sensitivity to lamp light, it is substituted at the 6th or 7th position of the thioxanthone skeleton. Substitution is preferable, and from the viewpoint of easy synthesis of the dialkyl peroxide having a thioxanthone skeleton, substitution is more preferable at the 7-position of the thioxanthone skeleton.

Specific examples of R ⁶ include alkyl groups such as methyl group, ethyl group, isopropyl group, n-butyl group; methoxy group, ethoxy group, n-propyloxy group, sec-butyloxy group, tert-butyloxy group. Examples include alkoxy groups such as; chlorine atoms, etc. From the viewpoint of high sensitivity to lamp light, methoxy and ethoxy groups are more preferred.

Specific examples of the dialkyl peroxide (a-1) having a thioxanthone skeleton of the present invention are shown below, but the present invention is not limited thereto.

The dialkyl peroxide (a-1) having a thioxanthone skeleton preferably includes Compounds 1 to 9, more preferably Compound 1, Compound 2, Compound 3, Compound 7, and Compound 8.

<Production method of dialkyl peroxide (a-1) having a thioxanthone skeleton>
The method for producing the dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) is not particularly limited, and for example, WO 2020/067118 may be referred to.

<Hydroperoxide having a thioxanthone skeleton (a-2)>
The hydroperoxide (a-2) having a thioxanthone skeleton of the present invention can be represented by the following general formula (2).
(In formula (2), R ¹ and R ² independently represent a methyl group or an ethyl group, and R ³ is an independent substituent, such as an alkyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 4 carbon atoms. represents an alkoxy group or a chlorine atom, and n represents an integer from 0 to 2.)

In the general formula (2), R ¹ and R ² independently represent a methyl group or an ethyl group. R ¹ and R ² are preferably methyl groups from the viewpoint of increasing the storage stability of the polymerizable composition since the hydroperoxide having the thioxanthone skeleton has a high decomposition temperature.

In the general formula (2), R ³ is an independent substituent and represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom. Due to the push-pull effect of these substituents, the light absorption characteristics of the hydroperoxide having a thioxanthone skeleton can be adjusted according to the emission wavelength of the lamp used, and the light from the lamp can be efficiently absorbed. can.

In the general formula (2), n represents an integer from 0 to 2. From the viewpoint of easy synthesis of the hydroperoxide having a thioxanthone skeleton, n is preferably an integer from 0 to 1, and more preferably 0.

In the general formula (2), when n is an integer from 1 to 2, the substitution position of ^R3 is not particularly limited, but from the viewpoint of high sensitivity to lamp light, it is substituted at the 6th or 7th position of the thioxanthone skeleton. Substitution is preferable, and from the viewpoint of easy synthesis of the hydroperoxide having the thioxanthone skeleton, substitution is more preferable at the 7-position of the thioxanthone skeleton.

Specific examples of R ³ include alkyl groups such as methyl group, ethyl group, isopropyl group, n-butyl group; methoxy group, ethoxy group, n-propyloxy group, sec-butyloxy group, tert-butyloxy group. Examples include alkoxy groups such as; chlorine atoms, etc. From the viewpoint of high sensitivity to lamp light, methoxy and ethoxy groups are more preferred.

Specific examples of the hydroperoxide (a-2) having a thioxanthone skeleton of the present invention are shown below, but the present invention is not limited thereto.

The hydroperoxide (a-2) having a thioxanthone skeleton preferably includes compounds 10 to 18, more preferably compounds 10 and 11.

<Production method of hydroperoxide (a-2) having a thioxanthone skeleton>
The method for producing the hydroperoxide (a-2) having a thioxanthone skeleton represented by the general formula (2) is, for example, as shown in the reaction formula below, in which an isoalkyl group-substituted thioxanthone derivative is reacted with a hydroperoxide in the presence of a metal complex. Examples include a method including a step of reacting (hereinafter also referred to as step (A)). Note that, after the reaction, a step of distilling off (removing) excess raw materials and the like under reduced pressure, and a purification step may be included.
(In the above reaction formula, R ¹ , R ² , R ³ and n are the same as in the above general formula (2), R ⁴ and R ⁵ independently represent a methyl group or an ethyl group, and R ⁶ is the number of carbon atoms Represents an alkyl group of 1 to 6 or a phenyl group.)

In the step (A), a commercially available product can be used as the isoalkyl group-substituted thioxanthone derivative. In addition, if there is no commercially available product, for example, J. Chem. Soc. 99,645 (1911), it can be synthesized by reacting 2,2'-dithiodibenzoic acid with an aromatic compound in sulfuric acid.

In the step (A), it is preferable that 0.8 mol or more of the hydroperoxide be reacted with 1.0 mol of the isoalkyl group-substituted thioxanthone derivative, and 1.0 mol or more, from the viewpoint of increasing the yield of the target product. It is more preferable to react at least 10.0 mol or less, and more preferably to react at 6.0 mol or less. The hydroperoxide can be commercially available, and if there is no commercially available product, it can be synthesized according to the known synthesis method described in JP-A-58-72557 and the like.

In the step (A), a metal complex of a metal selected from the fourth and fifth period transition metals can be used as the metal complex. Examples of metals in metal complexes include copper, cobalt, manganese, iron, chromium, and zinc, and examples of ligands include halogens such as bromine and chlorine, and minerals such as sulfuric acid, phosphoric acid, nitric acid, and carbonic acid. Examples include organic acids such as acids, formic acid, acetic acid, naphthenic acid, octenoic acid, and gluconic acid, cyanide, acetylacetonate, and the like. From the viewpoint of increasing the yield of the target product, the metal complex is preferably used in an amount of 0.0001 mol or more, more preferably 0.001 mol or more, and, It is preferable to use 1.0 mol or less, more preferably 0.1 mol or less.

In the step (A), the reaction temperature is preferably 0°C or higher, more preferably 20°C or higher, and preferably 100°C or lower, from the viewpoint of increasing the yield of the target product. The temperature is preferably 80°C or lower, and more preferably 80°C or lower. Although the reaction time cannot be determined unconditionally since it varies depending on the raw materials, reaction temperature, etc., from the viewpoint of increasing the yield of the target product, 1 hour to 60 hours is usually preferable.

In the step (A), water is preferably used as a medium, and water and an organic solvent may be used in combination. As the organic solvent, for example, benzene, toluene, chlorobenzene, o-dichlorobenzene, nitrobenzene, etc. can be used. The amount of the organic solvent and water used is usually about 50 to 1000 parts by weight based on 100 parts by weight of the total amount of raw materials. The hydroperoxide having a thioxanthone skeleton may be taken out by distilling off or separating the organic solvent and water after step (A).

The step (A) can be carried out under normal pressure, increased pressure, or reduced pressure, but it is preferably carried out in an inert gas atmosphere such as nitrogen or in the atmosphere, and more preferably in the atmosphere. preferable.

In the purification step, in order to remove surplus raw materials and by-products, for example, organic solvents, ion exchange water, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, sulfuric acid are used. Examples include a step of purifying the target product by washing with a basic aqueous solution such as a sodium or sodium sulfite aqueous solution, or an acidic aqueous solution such as hydrochloric acid or sulfuric acid. As the organic solvent, for example, benzene, toluene, heptane, methanol, chlorobenzene, o-dichlorobenzene, nitrobenzene, etc. can be used. Among these, washing with an organic solvent is preferable, and washing with heptane or methanol is more preferable. The organic solvents may be used alone or in combination of two or more. The amount of the organic solvent used is usually about 50 to 1000 parts by weight based on 100 parts by weight of the total amount of raw materials.

<Polymerization initiator (A)>
The polymerization initiator (A) of the present invention comprises a dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the above general formula (1) and a hydroperoxide having a thioxanthone skeleton represented by the above general formula (2). Contains (a-2). The polymerization initiator (A) is decomposed by active energy rays or heat, and the generated radicals have the function of initiating polymerization (curing) of the radically polymerizable compound (B). In 100 parts by mass of the polymerization initiator (A), the amount of the hydroperoxide (a-2) having a thioxanthone skeleton is 30 parts by mass or less from the viewpoint of suppressing the increase in the molecular weight of the radically polymerizable compound, and 15 parts by mass or less is Preferably, from the viewpoint of storage stability, the amount is preferably 0.1 part by mass or more, and more preferably 0.5 part by mass or more. Further, in 100 parts by mass of the polymerization initiator (A), the dialkyl peroxide (a-1) having a thioxanthone skeleton is preferably 30 parts by mass or more, and preferably 50 parts by mass or more, from the viewpoint of curability. From the viewpoint of storage stability, the amount is preferably 98 parts by mass or less, and preferably 95 parts by mass or less.

The total content of the dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) and the hydroperoxide (a-2) having a thioxanthone skeleton represented by the general formula (2) is , preferably 0.01 to 40 parts by mass, more preferably 0.05 to 20 parts by mass, and 0.01 to 40 parts by mass, more preferably 0.05 to 20 parts by mass, per 100 parts by mass of at least one of the radical polymerizable monomer and its partial polymer. More preferably, it is 1 to 10 parts by mass. The total content of the dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) and the hydroperoxide (a-2) having a thioxanthone skeleton represented by the general formula (2) is If the amount is less than 0.01 parts by mass based on 100 parts by mass of at least one of the radically polymerizable monomer and its partial polymer, the curing reaction will not proceed, which is not preferable. Further, the total content of the dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) and the hydroperoxide (a-2) having a thioxanthone skeleton represented by the general formula (2) When the amount is more than 40 parts by mass based on 100 parts by mass of at least one of the radically polymerizable monomer and its partial polymer, the solubility in at least one of the radically polymerizable monomer and its partial polymer reaches saturation. When forming a film of a thermally conductive composition, crystals of the photopolymerization initiator may precipitate, resulting in a rough surface of the film, or the photopolymerization initiator itself absorbs light, preventing light from reaching the deep part of the cured product. Therefore, it is not desirable. In addition, to the dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) and the hydroperoxide (a-2) having a thioxanthone skeleton represented by the general formula (2), the following others may be added. When containing a polymerization initiator, the ratio of other polymerization initiators is the dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1) and the dialkyl peroxide (a-1) represented by the general formula (2). The amount of the hydroperoxide having a thioxanthone skeleton (a-2) and other polymerization initiators is preferably 80% by mass or less, more preferably 50% by mass or less.

The thermally conductive composition also includes a dialkyl peroxide (a-1) having a thioxanthone skeleton represented by the general formula (1), and a hydroperoxide (a-1) having a thioxanthone skeleton represented by the general formula (2). In addition to a-2), by using other polymerization initiators, the surface curability, deep curability, etc. of the polymerizable composition can be improved. The other polymerization initiator is optional, such as a thermal polymerization initiator or a photopolymerization initiator. When selecting the other polymerization initiator, select at least one of a radically polymerizable monomer and its partial polymer, a thermally conductive filler, the type of other additives, and the thermal conductivity. The amount of filler filled, the film thickness of the cured product, etc. are taken into consideration. Examples of the other polymerization initiators include the thermal polymerization initiator used in the above partial polymerization and the photopolymerization initiator used in the partial polymerization (however, dialkyl peroxide (a) having a thioxanthone skeleton represented by the general formula (1) -1) and the hydroperoxide (a-2) having a thioxanthone skeleton represented by the above general formula (2).

<Thermal conductive filler>
The thermally conductive filler is not particularly limited, and includes, for example, aluminum oxide, silicon oxide, magnesium oxide, zinc oxide, titanium oxide, zirconium oxide, iron oxide, silicon carbide, boron nitride, aluminum nitride, titanium nitride, silicon nitride, Examples include titanium boride, carbon black, carbon fiber, carbon nanotubes, diamond, nickel, copper, aluminum, titanium, gold, and silver. In order to improve the strength of the sheet, fillers surface-treated with silane, titanate, etc. may be used. Alternatively, a filler whose surface is coated with a waterproof coat, an insulating coat, etc. using ceramics, polymers, etc. may also be used. Among these, those having high thermal conductivity at room temperature are preferred, and the thermal conductivity (W/m·k) at 20° C. is 1 or more, preferably 5 or more, and more preferably 10 or more. The thermally conductive filler may be used alone or in combination of two or more types.

The shape of the thermally conductive filler is regular or irregular, and examples include polygonal, cubic, elliptical, spherical, acicular, flat plate, flake, or a combination thereof. . Further, the particles may be aggregates of a plurality of crystal particles. The shape of the filler is selected depending on the viscosity of the radically polymerizable monomer or its partial polymer and the ease of processing of the final thermally conductive composition after polymerization.

In addition, the average particle size of the thermally conductive filler is preferably 0.5 μm or more and 100 μm or less, and in particular, from the viewpoint of dispersibility and thermal conductivity, small fillers with an average particle size of 1 μm or more and 20 μm or less, and It is preferable to use a large filler with a particle size of 25 μm or more and 100 μm or less.

The amount of the thermally conductive filler is 100 parts by volume or more and 900 parts by volume or less with respect to 100 parts by volume of the binder component containing at least one of a radically polymerizable monomer and a partial polymer thereof, and a photopolymerization initiator. In conventional compositions that are photocured using ultraviolet rays, etc., there is a limit to the content of the thermally conductive filler in order to ensure the light transparency necessary for curing, but the thermally conductive composition of the present invention has a thioxanthone skeleton. The thermally conductive filler can be contained in an amount of 100 parts by volume or more based on 100 parts by volume of the binder component. The amount of the thermally conductive filler is preferably 200 parts by volume or more, more preferably 300 parts by volume or more, and preferably 700 parts by volume or less, based on 100 parts by volume of the binder component. More preferably, it is 600 parts by volume or less. If the amount of the thermally conductive filler is less than 100 parts by volume with respect to 100 parts by volume of the binder component, sufficient thermal conductivity cannot be imparted, and if it exceeds 900 parts by volume, the strength of the thermally conductive sheet will be weakened.

<Other additives, etc.>
The thermally conductive composition may contain a sensitizer (benzophenone derivatives such as 4,4'-bis(diethylamino)benzophenone; thioxanthone derivatives such as isopropylthioxanthone and diethylthioxanthone; and anthracene such as 9,10-dibutoxyanthracene). Derivatives: Coumarin derivatives such as coumarin and ketocoumarin; Acridine derivatives such as acridine orange and 9-phenylacridine; Benzoic acid such as ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, and (2-dimethylamino)ethyl benzoate. Acid ester derivatives; alkylamine derivatives such as triethanolamine and methyldiethanolamine; camphorquinone, etc.), crosslinking agents, crosslinking accelerators, silane coupling agents, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.) ), anti-aging agents, fillers, colorants (pigments, dyes, etc.), ultraviolet absorbers, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, thickeners, flame retardants , an inorganic compound, an inorganic filler, an electromagnetic wave absorbing filler, and other known additives can be used alone or in combination within a range that does not impair the characteristics of this embodiment. Moreover, various common solvents can also be used when forming the thermally conductive sheet.

The method of mixing the above constituent materials is not particularly limited, but in the case of small quantities, manual mixing is also possible, but it is possible to mix by hand using a universal mixer, planetary mixer, hybrid mixer, Henschel mixer, kneader, ball mill, or mixing method. A common mixer such as a roll is used.

<Thermal conductive sheet>
The thermally conductive sheet of the present invention is a cured product of the thermally conductive composition.

As a method for processing the thermally conductive sheet, conventionally known methods such as a roll coating method, a spin coating method, a dip coating method, a brush coating method, a bar coating method, a knife coating method, a die coating method, a doctor blade method, Various molding methods such as extrusion molding, injection molding, and press molding can be used.

The method for curing the thermally conductive composition is not particularly limited, and it is preferably carried out by irradiation with active energy rays such as electron beams, ultraviolet rays, visible light, and radiation.

The active energy ray is preferably light with a wavelength of 250 to 450 nm, more preferably light with a wavelength of 350 to 410 nm, and more preferably light with a wavelength of 375 to 405 nm, from the viewpoint of rapid curing. It is even more preferable to include. The exposure amount of the active energy rays should be appropriately set depending on the wavelength and intensity of the active energy rays and the composition of the thermally conductive composition. Note that the intensity of the active energy rays is arbitrary; with high intensity, curing can be performed in a short time, and with low intensity, curing can be performed by increasing time.

Examples of the light source for the light irradiation include a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, an ultraviolet electrodeless lamp, a light emitting diode (LED), a xenon arc lamp, a carbon arc lamp, sunlight, a YAG laser, etc. A solid laser, a semiconductor laser, a gas laser such as an argon laser, etc. can be used. In addition, when using visible light to infrared light, which is poorly absorbed by dialkyl peroxides having a thioxanthone skeleton, effective curing can be achieved by using a sensitizer that absorbs the light as the additive. be able to.

In addition, as a manufacturing method of said hardened|cured material, a dual cure process may be applied and the process of heating may be performed before and after the process of irradiating with active energy rays. In the step of heating the thermally conductive composition, examples of heating methods include heating, ventilation heating, and the like. The heating method is not particularly limited, and examples thereof include an oven, a hot plate, infrared irradiation, electromagnetic wave irradiation, and the like. Further, examples of the ventilation heating method include a ventilation drying oven.

The thickness of the thermally conductive sheet is preferably 0.3 mm or more and 5 mm or less. In conventional compositions that are photocured using ultraviolet rays, etc., there is a limit to the film thickness in order to ensure the light transparency necessary for curing, but the thermally conductive composition of the present invention has a composition expressed by the general formula (1) above. The dialkyl peroxide (a-1) having a thioxanthone skeleton represented by Can be cured depending on the film thickness. The thermally conductive sheet can be produced in a wide range of film thicknesses (for example, film thicknesses of 0.5 mm or more, 0.8 mm or more are examples), and therefore can be applied to various uses. The thermally conductive sheet is usually used as a single layer, but it can also be used as a multilayer of two or more layers, if necessary. Further, the thermal conductivity of the thermally conductive sheet is preferably 1.5 (W/m・K) or more at room temperature (23° C.) in a general environment, and 2.0 (W/m・K). ) or more is more preferable.

The present invention will be explained in more detail with reference to Examples below. The present invention is not limited to these examples.

[Synthesis of dialkyl peroxide having thioxanthone skeleton]
[Synthesis Example 1: Synthesis of Compound 1]
30 mL of benzene, 6.10 g (24.0 mmol) of 2-isopropylthioxanthone, and 0.0238 g (0.24 mmol) of copper(I) chloride were placed in a 200 mL four-necked flask and stirred at room temperature. 15.7 g (0.12 mol) of a 69% by mass aqueous solution of tert-butyl hydroperoxide was gradually added. The mixture was heated to 65° C. under a nitrogen stream and reacted for 60 hours. After cooling the reaction solution and adding 20 mL of ethyl acetate, the aqueous phase was separated. The oil phase was washed with 5% by mass hydrochloric acid, 5% by mass aqueous sodium hydroxide solution, and ion-exchanged water, and dried over anhydrous magnesium sulfate. After filtration, the oil phase was concentrated under reduced pressure to obtain a crude product. The crude product was purified by silica gel column chromatography (n-hexane/ethyl acetate = 5/1) to obtain 2.55 g (yield 31%) of Compound 1. Table 1 shows the analysis results of Compound 1 obtained by EI-MS and ¹ H-NMR.

[Synthesis Example 2: Synthesis of Compound 2]
Compound 2 of the present invention was synthesized according to the method described in Synthesis Example 1, except that the 69% by mass aqueous tert-butyl hydroperoxide solution described in Synthesis Example 1 was changed to 85% by mass tert-amyl hydroperoxide. . Table 1 shows the analysis results of Compound 2 obtained by EI-MS and ¹ H-NMR.

[Synthesis of dialkyl hydroperoxide having thioxanthone skeleton]
[Synthesis Example 3: Synthesis of Compound 10]
In a 2L four-neck flask, add 300.8 mL of water, 100.3 g (0.39 mol) of 2-isopropylthioxanthone, 1.0 g of Rapizol A-80 (manufactured by NOF Corporation), and 0.79 g (0.7 mol) of copper acetate dihydrate. 004 mol) and 154.4 g (1.18 mol) of a 69% by mass aqueous tert-butyl hydroperoxide solution were added thereto, and the mixture was stirred at 70°C for 9 hours. After adding 444.9 g of n-heptane, 444.9 g of methanol, and 222.5 g of a 10% by mass aqueous sodium hydroxide solution to the reaction solution, the oil phase and the water phase were separated. The aqueous phase and 444.9 g of heptane were mixed, and the extracted oil phase was concentrated under reduced pressure to obtain a crude product. The crude product was purified by silica gel column chromatography (n-hexane/ethyl acetate = 5/1) to obtain 11.5 g (yield 5.4%) of Compound 10. Table 1 shows the analysis results of the obtained compound 10 by EI-MS and ¹ H-NMR.

[Synthesis Example 4: Synthesis of Compound 11]
Compound 11 of the present invention was synthesized according to the method described in Synthesis Example 1, except that 2-isopropylthioxanthone described in Synthesis Example 3 was changed to 2-methoxy-7-isopropylthioxanthone. Table 1 shows the analysis results of the obtained compound 11 by EI-MS and ¹ H-NMR.

<Example 1>
<Preparation of partial polymer>
0.45 parts by mass of Compound 1 and 0.05 parts by mass of Compound 10 as photopolymerization initiators were mixed with 100 parts by mass of 2-ethylhexyl acrylate (2-EHA), and the mixture was irradiated with ultraviolet rays to dissolve the entire monomer. 10 to 20% of the amount was polymerized to obtain a partial polymer with increased viscosity.

<Preparation of thermally conductive composition>
85 parts by mass of the partial polymer of 2-ethylhexyl acrylate (2-EHA) obtained above, 15 parts by mass of isobornyl acrylate (IBXA), and 0.0 parts of 1,6-hexanediol diacrylate (HDDA). Thermal conductive filler 1 (alumina: average particle 220 parts by volume of thermal conductive filler 2 (alumina: average particle size 2 μm, thermal conductivity 25 W/m·k at 20°C) and 80 parts by volume of were mixed and stirred for 2 minutes using a rotation-revolution mixer (Awatori Rentaro ARV-310, manufactured by THINKY) to obtain a thermally conductive composition.

<Manufacture of thermally conductive sheet>
The thermally conductive composition obtained above was sandwiched between the release-treated surfaces of two polyethylene terephthalate films, each of which had been subjected to a release treatment, using a spacer. Thereafter, ultraviolet irradiation (illuminance 2000 mW/cm ² ) was performed for 10 seconds from one side of the two release films using a 385 nm LED light source to cure the thermally conductive composition and produce a thermally conductive sheet.

<Example 2>
A thermally conductive sheet was prepared in the same manner as in Example 1, except that a monomer of 2-ethylhexyl acrylate (2-EHA) was used instead of the partial polymer of 2-ethylhexyl acrylate (2-EHA) as the radically polymerizable compound. was manufactured.

<Example 3>
A thermally conductive sheet was produced in the same manner as in Example 1, except that the film thickness after curing of the thermally conductive sheet was changed to the film thickness listed in Table 1, and ultraviolet irradiation was performed for 60 seconds.

<Example 4>
In the production of the partial polymer and the preparation of the thermally conductive composition, the same procedure as in Example 1 was carried out, except that 0.4 parts by mass of Compound 2 and 0.1 parts by mass of Compound 11 were used as photopolymerization initiators. A thermally conductive sheet was manufactured.

<Example 5>
Heat was applied in the same manner as in Example 4, except that the amount of thermally conductive filler 1 was changed to 150 parts by volume and the amount of thermally conductive filler 2 was changed to 50 parts by volume with respect to 100 parts by volume of the binder component. A conductive sheet was manufactured.

<Example 6>
Heat was applied in the same manner as in Example 4, except that the amount of thermally conductive filler 1 was changed to 400 parts by volume and the amount of thermally conductive filler 2 was changed to 150 parts by volume with respect to 100 parts by volume of the binder component. A conductive sheet was manufactured.

<Comparative example 1>
In the production of the partial polymer and the preparation of the thermally conductive composition, the same procedure as in Example 1 was carried out, except that 0.25 parts by mass of Compound 2 and 0.25 parts by mass of Compound 10 were used as photopolymerization initiators. A thermally conductive sheet was manufactured.

<Comparative example 2>
In the production of the partial polymer and the preparation of the thermally conductive composition, Compound R1 (2,4,6-trimethylbenzoyldiphenylphosphine oxide: IGM RESINS B.V.) was used instead of Compound 1 and Compound 10 as a photopolymerization initiator. Thermal conductivity was determined in the same manner as in Example 1, except that 4 parts by mass of compound R1 was mixed with 100 parts by mass of 2-ethylhexyl acrylate (2-EHA) in the preparation of the partial polymer. The sheet was manufactured.

<Comparative example 3>
Thermal conduction was carried out in the same manner as in Example 1, except that the mixed amount of thermally conductive filler 1 was changed to 30 parts by volume and the mixed amount of thermally conductive filler 2 was changed to 15 parts by volume with respect to 100 parts by volume of the binder component. A plastic sheet was manufactured.

<Comparative example 4>
With respect to 100 parts by volume of the binder component, the mixed amount of thermally conductive filler 1 was changed to 800 parts by volume, and the mixed amount of thermally conductive filler 2 was changed to 300 parts by volume, and ultraviolet irradiation was performed for 900 seconds. A thermally conductive sheet was produced in the same manner as in Example 4.

<Comparative example 5>
A thermally conductive sheet was produced in the same manner as in Example 1, except that only 0.5 parts by mass of Compound 2 was used as a photopolymerization initiator in the preparation of the partial polymer and the thermally conductive composition. did.

<Comparative Examples 6 and 7>
In the preparation of the thermally conductive composition, a thermal polymerization initiator, compound R2 (lauroyl peroxide "Perloyl L" manufactured by NOF Corporation) was used instead of compound R1 as a polymerization initiator, and instead of irradiating ultraviolet rays. A thermally conductive sheet was produced in the same manner as in Comparative Example 2 except that the sheet was heated at 150° C. for 600 seconds or 900 seconds.

<Curability>
When peeling off the release film of the thermally conductive sheets obtained in Examples and Comparative Examples, the interface between the thermally conductive sheet and the release film was visually observed.
○: The release film can be peeled off smoothly, and the thermally conductive sheet is not damaged.
×: The release film cannot be peeled off, or the thermally conductive sheet is damaged.

<Film thickness>
The film thickness of the thermally conductive sheets obtained in Examples and Comparative Examples was measured using a digital micrometer.

<Thermal conductivity>
Thermal conductivity of the thermally conductive sheets obtained in Examples and Comparative Examples was measured using a thermal conductivity meter (QTM-710: manufactured by Kyoto Electronics Industry Co., Ltd.).

<Storage stability>
The thermally conductive compositions prepared in Examples and Comparative Examples were placed in a brown glass bottle, shielded from light with aluminum foil, and then left to stand in a constant temperature constant temperature machine at 60° C. for transportation and storage. A case where hardening was not visually confirmed after 3 months of storage was marked as "○", and a case where curing was visually confirmed after 3 months of storage was marked as "x". The results are shown in Table 1.

In Examples 1 to 6, thermally conductive sheets having high thermal conductivity and a thick film were obtained.

Comparative Example 1 had poor curability due to the high content of hydroperoxide having a thioxanthone skeleton. Comparative Example 2 had poor curability because it used a photopolymerization initiator that was not a dialkyl peroxide having a thioxanthone skeleton. Comparative Example 3 had poor thermal conductivity due to the low content of thermally conductive filler. Comparative Example 4 had poor curability because the content of the thermally conductive filler was too large. Comparative Example 5 had poor storage stability because it did not contain a hydroperoxide having a thioxanthone skeleton. Comparative Examples 6 and 7 used a thermal polymerization initiator (compound R2), so they could not be cured even for 600 seconds, took 900 seconds to cure, and had poor storage stability.

Claims (3)

a binder component containing at least one of a radically polymerizable monomer and a partial polymer thereof, and a photopolymerization initiator;
A thermally conductive composition containing a thermally conductive filler,
The amount of the thermally conductive filler is 100 parts by volume or more and 900 parts by volume or less with respect to 100 parts by volume of the binder component,
The photopolymerization initiator has general formula (1):
(In general formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represent a methyl group or an ethyl group, R ⁵ represents an alkyl group having 1 to 6 carbon atoms or a phenyl group, R ⁶ is an independent substituent, and represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a chlorine atom, and n represents an integer from 0 to 2.) A dialkyl peroxide (a-1) having a thioxanthone skeleton,
General formula (2):
(In formula (2), R ¹ and R ² independently represent a methyl group or an ethyl group, and R ³ is an independent substituent, such as an alkyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 4 carbon atoms. represents an alkoxy group or a chlorine atom, n represents an integer from 0 to 2.) is a polymerization initiator (A) containing a hydroperoxide (a-2) having a thioxanthone skeleton,
A thermally conductive composition, wherein the amount of the hydroperoxide (a-2) having a thioxanthone skeleton is 30 parts by mass or less in 100 parts by mass of the polymerization initiator (A). A thermally conductive sheet comprising a cured product of the thermally conductive composition according to claim 1. The thermally conductive sheet according to claim 2, having a thickness of 0.3 mm or more and 5 mm or less.