Thermal Conductive Composition and Thermal Conductive Sheet

Abstract

To provide a thermally conductive composition that can be irradiated with light to give a thermally conductive sheet having high thermal conductivity and thickness with high productivity.SOLUTION: A thermally conductive composition contains: a binder component containing a photopolymerization initiator and at least one of a radical polymerizable monomer and a partial polymer thereof; and a thermally conductive filler. Relative to the binder component 100 pts.vol., the thermally conductive filler is 100 pts.vol. or more and 900 pts.vol. or less. The photopolymerization initiator is a dialkyl peroxide having a thioxanthone skeleton represented by the general formula (1).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a thermally conductive composition and a thermally conductive sheet.

Background Art

[0002] It is important to dissipate heat generated from various electronic and electrical devices. In recent years, with the progress of higher performance and diversification, in in-vehicle electrical components applications and communication device applications, heat dissipation countermeasure members are used by sandwiching them between a heat generating body such as an IC device and a heat radiator such as a heat sink, and a heat dissipation countermeasure member with high thermal conductivity and a thick film is required. Examples of heat dissipation countermeasure members include heat dissipation sheets, heat dissipation gap fillers, heat dissipation adhesives, heat dissipation greases, etc. In particular, a thermally conductive sheet that does not require management of the coating amount and has no fluidity and has excellent workability that can be simply sandwiched between a desired heat generating body and a heat radiator has attracted attention.

[0003] As a method for increasing the thermal conductivity of a thermally conductive sheet, increasing the content of a thermally conductive filler can be mentioned. In Patent Document 1, a thermally conductive sheet with high thermal conductivity and a thick film is produced by thermosetting. Also, in order to improve productivity, in Patent Documents 2 and 3, a photocurable composition containing a photoinitiator is used to produce a thermally conductive sheet by photocuring with ultraviolet irradiation.

[0004] In addition, in Patent Document 4, as a photoinitiator, a dialkyl peroxide having a specific thioxanthone skeleton having both photopolymerizability and thermal polymerizability is known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] Based on the above background, while an increase in the demand for thermally conductive sheets is expected, in the method of producing a thick-film thermally conductive sheet by thermosetting as in Patent Document 1, since the curing efficiency is lower than that by ultraviolet irradiation, a long time is required for polymerization at high temperatures, and even if the polymerization conditions are optimized, there is a limit to shortening the polymerization time.

[0007] On the other hand, in the methods of producing a thermally conductive sheet by photocuring as in Patent Documents 2 and 3, when the content of the thermally conductive filler is increased, even if irradiated with light such as ultraviolet light, it becomes difficult to reach deep parts due to a decrease in light transmittance, so the film thickness is limited and a sheet with a thin film thickness is obtained. Therefore, in order to produce a thick-film thermally conductive sheet, there is a problem that the content of the filler is limited and a sheet with low thermal conductivity is obtained.

[0008] Further, in Patent Document 4, it is described that a cured product can be produced by using a dialkyl peroxide having a thioxanthone skeleton having both photopolymerizability and thermal polymerizability as a photopolymerization initiator, but it is unclear whether a cured product having good curability can be obtained even for a composition highly filled with a filler having a high thermal diffusivity such as a thermally conductive filler.

[0009] Therefore, an object of the present invention is to provide a thermally conductive composition capable of obtaining a thermally conductive sheet having a high thermal conductivity and a thick film with high productivity by light irradiation.

[0010] Another object of the present invention is to provide a thermally conductive sheet which is a cured product of the above thermally conductive composition.

Means for Solving the Problems

[0011] The present invention relates to a thermally conductive composition containing at least one of a radically polymerizable monomer and a partial polymer thereof, and a photoinitiator, as a binder component, and a thermally conductive filler, wherein the thermally conductive filler is 100 to 900 parts by volume with respect to 100 parts by volume of the binder component, and the photoinitiator is a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1). [Chemical formula] (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 of 0 to 2.)

[0012] The present invention also relates to a thermally conductive sheet which is a cured product of the thermally conductive composition. [Advantages of the Invention]

[0013] Even when the thermally conductive composition of the present invention is highly filled with a filler having high thermal diffusivity such as a thermally conductive filler, when irradiated with ultraviolet rays and photocured, a thermally conductive sheet having a high thermal conductivity and a thick film can be produced with high productivity. [Embodiments for Carrying Out the Invention]

[0014] The thermally conductive composition of the present invention contains a binder component containing at least one of a radically polymerizable monomer and its partial polymer, and a photoinitiator, and a thermally conductive filler. When the thermally conductive composition is irradiated with ultraviolet rays and photocured, a dialkyl peroxide having a thioxanthone skeleton is rapidly activated, and since it is hardly affected by the thermal diffusivity of the highly filled thermally conductive filler, a thermally conductive sheet having a high thermal conductivity and a thick film can be produced with high productivity.

[0015] <Radically polymerizable monomer> As the radically polymerizable monomer, a compound having an ethylenically unsaturated group can be preferably used. Examples of the radically polymerizable monomer include (meth)acrylic acid esters, styrenes, maleic acid esters, fumaric acid esters, itaconic acid esters, cinnamic acid esters, crotonic acid esters, vinyl ethers, vinyl esters, vinyl ketones, allyl ethers, allyl esters, N-substituted maleimides, N-vinyl compounds, unsaturated nitriles, olefins, and the like. Among these, it is preferable to include (meth)acrylic acid esters having high reactivity. The radically polymerizable monomer may be used alone or in combination of two or more.

[0016] As the (meth)acrylate esters, monofunctional compounds and polyfunctional compounds can be used. Examples of the monofunctional compounds include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; ester compounds of (meth)acrylic acid and alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; monomers having a hydroxy group such as 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(meth)acrylate, and hydroxyl-terminated polypropylene glycol mono(meth)acrylate; monomers having a chain or cyclic ether bond such as 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 (meth)acrylate, and cyclic trimethylolpropane formal (meth)acrylate; monomers having a nitrogen atom such as 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, and N-(meth)acryloyloxyethylhexahydrophthalimide;Monomers having an isocyanate group such as 2-(meth)acryloyloxyethyl isocyanate; monomers having an epoxy group such as glycidyl (meth)acrylate, glycidyl ether of 4-hydroxybutyl (meth)acrylate; monomers having a phosphorus atom such as 2-((meth)acryloyloxy)ethyl phosphate; monomers having a silicon atom such as 3-(meth)acryloxypropyltrimethoxysilane; monomers having a fluorine atom such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3,3-pentafluoropropyl (meth)acrylate, 2-(perfluorohexyl)ethyl (meth)acrylate; monomers having a carboxyl group such as (meth)acrylic acid, succinic acid mono(2-(meth)acryloyloxyethyl), phthalic acid mono(2-(meth)acryloyloxyethyl), maleic acid mono(2-(meth)acryloyloxyethyl), ω-carboxy-polycaprolactone mono(meth)acrylate, etc. are mentioned.;

[0017] Examples of the polyfunctional compound include ester compounds of polyhydric alcohols and (meth)acrylic acid such as 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, hydroxypivalic acid 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-(2-(meth)acryloyloxyethoxy)phenyl)fluorene, 9,9-bis(4-(2-(2-(meth)acryloyloxyethoxy)ethoxy)phenyl)fluorene; 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, etc.

[0018] <Partial polymer of radical polymerizable monomer> Since the radical polymerizable monomer generally has a low viscosity, the filler may settle when mixed with the thermal conductivity filler. In this case, it is preferable that the radical polymerizable monomer is partially polymerized in advance to increase the viscosity to form a partial polymer of the radical polymerizable monomer. The viscosity of the partial polymer of the radical polymerizable monomer is not particularly limited, but is preferably about 10 to 10,000 mPa·s.

[0019] The 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 the polymerization, a partial polymer can be obtained by using a polymerization initiator such as a thermal polymerization initiator or a photoinitiator according to the polymerization method.

[0020] Examples of the thermal polymerization initiator used for the partial polymerization include organic peroxides such as diacyl peroxides, peroxyketals, ketone peroxides, hydroperoxides, dialkyl peroxides, peroxy esters, and peroxydicarbonates; and azo-based polymerization initiators. Specifically, lauroyl peroxide, benzoyl peroxide, cyclohexanone peroxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, t-butyl hydroperoxide, 2,2'-azobisbutyronitrile, etc. can be mentioned.

[0021] Examples of the photoinitiator used for partial overlap include aromatic ketones, benzoin ethers, halomethyl oxadiazole compounds, α-amino ketones, α-aminoacetophenone compounds, acylphosphine compounds, biimidazoles, N,N-dimethylaminobenzophenone, triazine compounds, thioxanthone compounds, oxime compounds, and the like.Specific examples of the photopolymerization initiator include aromatic ketones such as benzophenone, 4,4'-bis(diethylamino)benzophenone, 4-methoxy-4'-dimethylaminobenzophenone; benzoin ethers such as benzoin methyl ether; benzoins such as ethyl benzoin; biimidazoles such as 2-(o-chlorophenyl)-4,5-phenylimidazole dimer; halomethyl oxadiazole compounds such as 2-trichloromethyl-5-(p-methoxystyryl)-1,3,4-oxadiazole; 2-(4-butoxy-naphthalen-1-yl)-4,6-bis-trichloromethyl-s-triazine, dialkyl peroxides having a thioxanthone skeleton represented by the following general formula (1), 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone, 1,2-benzyl-2-dimethylamino-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-methyl-diphenyl sulfide, 1-hydroxy-cyclohexyl-phenylketone, 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-one, etc.Among these, from the viewpoint of curability during sheet production, it is preferable to use a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1). Alternatively, any combination of the above-described thermal polymerization initiator or photoinitiator can also be used.

[0022] <Photoinitiator> The photoinitiator of the present invention contains a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1).

Chemical formula

[0023] In the general formula (1), R 1 , R 2 , R 3 and R 4 each independently represents a methyl group or an ethyl group. In the present invention, from the viewpoint of increasing the decomposition temperature of the dialkyl peroxide having a thioxanthone skeleton represented by the general formula (1) and improving the storage stability of the thermally conductive composition, R 1 , R 2 , R 3 and R 4 are all preferably methyl groups.

[0024] 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 a methyl group, an ethyl group, a propyl group, a 2,2-dimethylpropyl group, and a phenyl group. Among these, from the viewpoint of ease of synthesis of the dialkyl peroxide having a thioxanthone skeleton, R 5 is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably one selected from a methyl group, an ethyl group, and a propyl group. From the viewpoints of increasing the decomposition temperature of the dialkyl peroxide having a thioxanthone skeleton and improving the storage stability of the thermally conductive composition, and increasing the sensitivity to irradiated light, R 5is more preferably a methyl group or an ethyl group.

[0025] In the general formula (1), the substitution position of the dialkyl peroxide with respect to thioxanthone is not particularly limited. However, from the viewpoint of enhancing the sensitivity to irradiation light, it is preferably substituted at the 2-position, 3-position, or 4-position of the thioxanthone skeleton. From the viewpoint of ease of synthesis, it is more preferably substituted at the 2-position or 3-position of the thioxanthone skeleton.

[0026] In the general formula (1), R 6 represents 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. These substituents can improve the light absorption characteristics of the dialkyl peroxide having the thioxanthone skeleton over the push-pull effect exerted on these substituents with respect to the emission wavelength of the lamp used, and can efficiently absorb the irradiation light.

[0027] In the general formula (1), n represents an integer of 0 to 2. Among them, from the viewpoint of easily synthesizing the dialkyl peroxide having the thioxanthone skeleton, n is preferably an integer of 0 to 1, and more preferably 0.

[0028] In the general formula (1), when n is an integer of 1 to 2, the substitution position of the R 6 is not particularly limited. However, from the viewpoint of enhancing the sensitivity to irradiation light, it is preferably at the 6-position or 7-position of the thioxanthone skeleton. From the viewpoint of easily synthesizing the dialkyl peroxide having the thioxanthone skeleton, it is more preferably at the 7-position of the thioxanthone skeleton.

[0029] Specific examples of the R 6 include, for example, alkyl groups such as methyl group, ethyl group, isopropyl group, and n-butyl group; alkoxy groups such as methoxy group, ethoxy group, n-propyloxy group, sec-butyloxy group, and tert-butyloxy group; and chlorine atom. Among these, from the viewpoint of enhancing the sensitivity to irradiation light, R 6 is more preferably a methoxy group or an ethoxy group.

[0030] Specific examples of the dialkyl peroxide having the thioxanthone skeleton are shown below, but are not limited thereto.

Chemical formula

[0031] Examples of the dialkyl peroxide having the thioxanthone skeleton preferably include Compounds 1 to 9, and more preferably include Compounds 1, 2, 3, 7, and 8.

[0032] The content of the dialkyl peroxide having the thioxanthone skeleton is preferably 0.01 to 40 parts by mass, more preferably 0.05 to 20 parts by mass, and even more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of at least one of the radically polymerizable monomer and its partial polymer. If the content of the dialkyl peroxide having the thioxanthone skeleton is less than 0.01 part by mass with respect to 100 parts by mass of at least one of the radically polymerizable monomer and its partial polymer, the curing reaction does not proceed, which is not preferable. Further, when the content of the dialkyl peroxide having the thioxanthone skeleton is more than 40 parts by mass with respect to 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, crystals of the photoinitiator precipitate during film formation of the thermally conductive composition, and roughness of the film surface becomes a problem, or light does not reach the deep part of the cured product due to light absorption by the photoinitiator itself, which is not preferable. In addition, when the following other polymerization initiators are included in the dialkyl peroxide having the thioxanthone skeleton, the ratio of the other polymerization initiator is preferably 80% by mass or less, and more preferably 50% by mass or less in the total of the dialkyl peroxide having the thioxanthone skeleton and the other polymerization initiator.

[0033] In addition to the dialkyl peroxide having the thioxanthone skeleton described above, the thermal conductive composition can improve the surface curability, deep curability, etc. of the polymerizable composition by using other polymerization initiators. The other polymerization initiator can be arbitrarily selected from a thermal polymerization initiator or a photopolymerization initiator. In the selection, at least one of a radically polymerizable monomer and its partial polymer, the type of the thermal conductive filler, other additives, the filling amount of the thermal conductive filler, the film thickness of the cured product, etc. are considered. Examples of the other polymerization initiator include a thermal polymerization initiator used for the above partial polymerization and a photopolymerization initiator used for the partial polymerization (however, the dialkyl peroxide having the thioxanthone skeleton represented by the general formula (1) is excluded).

[0034] <Thermal conductive filler> The thermal conductive filler is not particularly limited, and examples thereof include aluminum oxide, silicon oxide, magnesium oxide, zinc oxide, titanium oxide, zirconium oxide, iron oxide, silicon carbide, boron nitride, aluminum nitride, titanium nitride, silicon nitride, titanium boride, carbon black, carbon fiber, carbon nanotube, diamond, nickel, copper, aluminum, titanium, gold, silver, etc. In order to improve the strength of the sheet, a filler surface-treated with silane, titanate, etc. may be used. Further, a filler having a coating such as a water-resistant coating or an insulating coating with ceramics, a polymer, etc. on the filler surface may be used. Among these, those having high thermal conductivity at room temperature are preferable, 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 thermal conductive filler may be used alone or in combination of two or more kinds.

[0035] The shape of the thermal conductive filler is a regular shape or an irregular shape, and examples thereof include a polygonal shape, a cubic shape, an elliptical shape, a spherical shape, a needle shape, a flat plate shape, a flake shape, or a combination thereof. Further, it may be particles in which a plurality of crystal particles are aggregated. The shape of the filler is selected based on the viscosity of the radically polymerizable monomer or its partial polymer and the ease of processing of the final thermal conductive composition after polymerization.

[0036] Also, the average particle size of the thermal conductivity filler is preferably 0.5 μm or more and 100 μm or less. In particular, from the viewpoints of dispersibility and thermal conductivity, it is preferable to use in combination a filler with a small diameter having an average particle size of 1 μm or more and 20 μm or less and a filler with a large diameter having an average particle size of 25 μm or more and 100 μm or less.

[0037] The thermal conductivity filler is in an amount of 100 parts by volume or more and 900 parts by volume or less with respect to 100 parts by volume of a binder component containing at least one of a radically polymerizable monomer and its partial polymer and a photoinitiator. In the conventional composition cured by photocuring with ultraviolet rays or the like, there was a limit to the content of the thermal conductivity filler in order to ensure the light transmittance necessary for curing. However, since the thermal conductivity composition of the present invention contains a dialkyl peroxide having a thioxanthone skeleton, the thermal conductivity filler can be contained in an amount of 100 parts by volume or more with respect to 100 parts by volume of the binder component. The thermal conductivity 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, more preferably 600 parts by volume or less with respect to 100 parts by volume of the binder component. If the amount of the thermal conductivity 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 thermal conductivity sheet becomes weak.

[0038] <Other additives, etc.> In the heat conductive composition, sensitizers (benzophenone derivatives such as 4,4'-bis(diethylamino)benzophenone; thioxanthone derivatives such as isopropyl thioxanthone and diethyl thioxanthone; anthracene derivatives such as 9,10-dibutoxyanthracene; coumarin derivatives such as coumarin and ketocoumarin; acridine derivatives such as acridine orange and 9-phenylacridine; benzoic acid ester derivatives such as ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, and (2-dimethylamino)ethyl benzoate; 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, inorganic compounds, inorganic fillers, electromagnetic wave absorbing fillers, and other known additives can be used alone or in combination within a range that does not impair the characteristics of this embodiment. Also, when forming the heat conductive sheet, various common solvents can be used.

[0039] The mixing method of each of the above constituent materials is not particularly limited. In the case of a small amount, hand mixing is possible, but general mixers such as universal mixers, planetary mixers, hybrid mixers, Henschel mixers, kneaders, ball mills, and mixing rolls are used.

[0040] <Heat Conductive Sheet> The heat conductive sheet of the present invention is a cured product of the heat conductive composition.

[0041] As a processing method for the heat conductive sheet, conventionally known methods can be used, such as various molding methods like roll coating method, spin coating method, dip coating method, brush coating method, bar coating method, knife coating method, die coating method, doctor blade method, extrusion molding method, injection molding method, and press molding method.

[0042] 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 rays, and radiation rays.

[0043] The active energy rays are preferably light with a wavelength of the active energy rays of 250 to 450 nm, more preferably light with a wavelength of 350 to 410 nm from the viewpoint of being able to cure rapidly, and still more preferably include light with a wavelength of 375 to 405 nm. The exposure amount of the active energy rays should be appropriately set according to 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. At high intensity, curing can be carried out in a short time, and at low intensity, curing can be carried out by extending the time.

[0044] As the light source for the light irradiation, 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 solid laser such as a YAG laser, a semiconductor laser, a gas laser such as an argon laser, etc. can be used. Note that when using light from visible light to infrared light with little absorption of a dialkyl peroxide having a thioxanthone skeleton, the curing can be carried out effectively by using a sensitizer that absorbs the light as the additive.

[0045] In addition, as the method for manufacturing the above-mentioned cured product, a dual-cure process may be applied, and a heating process may be carried out before and after the process of irradiating with active energy rays. In the process of heating the thermally conductive composition, examples of the heating method include heating and ventilation heating. The heating method is not particularly limited, and examples include an oven, a hot plate, infrared irradiation, and electromagnetic wave irradiation. In addition, examples of the ventilation heating method include a forced-air drying oven.

[0046] The film thickness of the heat conductive sheet is preferably 0.3 mm or more and 5 mm or less. In the conventional compositions cured by photocuring with ultraviolet rays or the like, there was a limitation on the film thickness in order to ensure the light transmittance necessary for curing. However, since the heat conductive composition of the present invention contains a dialkyl peroxide having a thioxanthone skeleton, it can be cured with a film thickness of 0.3 mm or more and 5 mm or less. Since the heat conductive sheet has a wide range of film thicknesses that can be produced (for example, a film thickness of 0.5 mm or more, 0.8 mm or more can be exemplified), it can be applied to various uses. The heat conductive sheet is usually used as a single layer, but can also be used in two or more layers as needed. Further, the heat conductive sheet preferably has a thermal conductivity of 1.5 (W / m·K) or more at room temperature (23°C) in a general environment, and more preferably 2.0 (W / m·K) or more.

Examples

[0047] The present invention will be described in more detail with reference to the following examples. The present invention is not limited to these examples.

[0048] <Example 1> <Production of partial polymer> To 100 parts by mass of 2-ethylhexyl acrylate (2-EHA), 0.5 part by mass of Compound 1 was mixed as a photopolymerization initiator, and irradiated with ultraviolet rays to obtain a partially polymerized product in which 10 to 20% of the total amount of the monomers was polymerized and thickened.

[0049] <Preparation of heat 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 0.1 part by mass of 1,6-hexanediol diacrylate (HDDA), and 0.5 part by mass of Compound 1 as a photopolymerization initiator were mixed. To 100 parts by volume of the resulting binder component, 220 parts by volume of a thermal conductivity filler 1 (alumina: average particle diameter 50 μm, thermal conductivity at 20 °C 25 W / m·k) and 80 parts by volume of a thermal conductivity filler 2 (alumina: average particle diameter 2 μm, thermal conductivity at 20 °C 25 W / m·k) were mixed, and the mixture was stirred for 2 minutes with a planetary mixer (manufactured by THINKY, Awatori Renkotoraro ARV-310) to obtain a thermal conductivity composition.

[0050] <Manufacture of Thermal Conductivity Sheet> Using spacers, the thermal conductivity composition obtained above was sandwiched and molded between the release-treated surfaces of two polyethylene terephthalate films having a release treatment on one side. Then, ultraviolet irradiation (irradiance 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 thermal conductivity composition and manufacture a thermal conductivity sheet.

[0051] <Example 2> A thermal conductivity sheet was manufactured 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.

[0052] <Example 3> A thermal conductivity sheet was manufactured in the same manner as in Example 1, except that the film thickness after curing of the thermal conductivity sheet was changed to the film thickness described in Table 1 and ultraviolet irradiation was performed for 60 seconds.

[0053] <Example 4> A thermal conductivity sheet was manufactured in the same manner as in Example 1, except that the mixing amount of the thermal conductivity filler 1 was changed to 150 parts by volume and the mixing amount of the thermal conductivity filler 2 was changed to 50 parts by volume with respect to 100 parts by volume of the binder component.

[0054] <Example 5> A thermally conductive sheet was produced in the same manner as in Example 1, except that the mixing amount of the thermally conductive filler 1 was changed to 400 parts by volume and the mixing amount of the thermally conductive filler 2 was changed to 150 parts by volume with respect to 100 parts by volume of the binder component.

[0055] <Comparative Example 1> In the preparation of the partial polymer and the preparation of the thermally conductive composition, compound R1 (2,4,6-trimethylbenzoyldiphenylphosphine oxide: manufactured by IGM) was used instead of compound 25 as the photoinitiator, and in the preparation of the partial polymer, 4 parts by mass of compound R1 was mixed with respect to 100 parts by mass of 2-ethylhexyl acrylate (2-EHA). A thermally conductive sheet was produced in the same manner as in Example 1, except for this.

[0056] <Comparative Example 2> A thermally conductive sheet was produced in the same manner as in Example 1, except that the mixing amount of the thermally conductive filler 1 was changed to 30 parts by volume and the mixing amount of the thermally conductive filler 2 was changed to 15 parts by volume with respect to 100 parts by volume of the binder component.

[0057] <Comparative Example 3> A thermally conductive sheet was produced in the same manner as in Example 1, except that the mixing amount of the thermally conductive filler 1 was changed to 800 parts by volume and the mixing amount of the thermally conductive filler 2 was changed to 300 parts by volume with respect to 100 parts by volume of the binder component.

[0058] <Comparative Examples 4 and 5> In the preparation of the thermally conductive composition, compound R2 (lauroyl peroxide "Peroyl L": manufactured by NOF Corporation), which is a thermal polymerization initiator, was used instead of compound R1 as the polymerization initiator, and a thermally conductive sheet was produced in the same manner as in Comparative Example 1, except that heating was performed at 150°C for 600 seconds or 900 seconds instead of irradiating with ultraviolet rays.

[0059] <Curability> When peeling the release film of the thermally conductive sheets obtained in the examples and comparative examples, the interface between the thermally conductive sheet and the release film was visually observed. 〇: The release film can be smoothly peeled off, and the thermally conductive sheet has no damage. ×: The release film cannot be peeled off, or the thermally conductive sheet is damaged.

[0060] <Film thickness> For the thermally conductive sheets obtained in the examples and comparative examples, the film thickness was measured using a digital micrometer.

[0061] <Thermal conductivity> For the thermally conductive sheets obtained in the examples and comparative examples, the thermal conductivity was measured using a thermal conductivity measuring instrument (QTM-710: manufactured by Kyoto Electronics Industry Co., Ltd.).

[0062]

Table 1

[0063] In Examples 1 to 5, thermally conductive sheets having high thermal conductivity and thick films were obtained.

[0064] In Comparative Example 1, a photopolymerization initiator that is not a dialkyl peroxide having a thioxanthone skeleton was used, resulting in poor curability. In Comparative Example 2, the thermal conductivity was poor because the content of the thermally conductive filler was low. In Comparative Example 3, the curability was poor because the content of the thermally conductive filler was too high. In Comparative Examples 4 and 5, since a thermal polymerization initiator (Compound R2) was used, curing could not be achieved even after 600 seconds, and it took 900 seconds to cure.

Claims

1. A binder component containing at least one of a radically polymerizable monomer and its partial polymer, and a photoinitiator, A thermally conductive composition containing a thermally conductive filler, The thermally conductive filler is one or more selected from the group consisting of magnesium oxide, aluminum oxide, boron nitride, aluminum nitride, and carbon black, and has a thermal conductivity (W / m·k) at 20 °C of 10 or more, With respect to 100 parts by volume of the binder component, the thermally conductive filler is 300 parts by volume or more and 900 parts by volume or less, The thermally conductive composition is characterized in that the photoinitiator is a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1). 【Chemical Formula 1】 (In the 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 of 0 to 2.)

2. A thermally conductive sheet, which is a cured product of the thermally conductive composition according to Claim 1.

3. The thermally conductive sheet according to Claim 2, characterized in that the thickness is 0.3 mm or more and 5 mm or less.

Images