JP2022156751A - Thermally conductive composition and thermally conductive sheet - Google Patents

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

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, with the advancement of high performance and diversification, in applications such as in-vehicle electrical components and communication equipment, heat dissipation countermeasure materials are used sandwiched between heating elements such as IC devices and radiators such as heat sinks, and have high thermal conductivity. , a thick-film heat-dissipating member is required. Heat-dissipating materials include heat-dissipating sheets, heat-dissipating gap fillers, heat-dissipating adhesives, heat-dissipating greases, etc. However, there is no particular need to control the amount of application and there is no fluidity, so it is sandwiched between the desired heat-generating body and heat-radiating body A thermally conductive sheet with excellent workability that can be used by itself is attracting attention.

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. ing. In addition, in order to improve productivity, in Patent Documents 2 and 3, a photopolymerizable composition containing a photopolymerization initiator is used, and a thermally conductive sheet is produced by photocuring with ultraviolet irradiation.

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

JP 2006-111644 A JP 2019-85441 A JP 2020-45386 A WO2020/067118

With the above background, while the demand for thermally conductive sheets is expected to increase, the method of producing a thick thermally conductive sheet by heat curing as in Patent Document 1 has a higher curing efficiency than curing by ultraviolet irradiation. Since it is low, polymerization takes a long time at high temperatures, and there is a limit to shortening the polymerization time even if the polymerization conditions are optimized.

On the other hand, as in Patent Documents 2 and 3, in the method of producing a thermally conductive sheet by photocuring, if the content of the thermally conductive filler is increased, even if the light such as ultraviolet rays is irradiated, the light transmittance decreases and the deep part Since it is difficult to reach the target, the film thickness is limited, resulting in a thin sheet. Therefore, in order to produce a thick thermally conductive sheet, there is a problem that the filler content 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 having both photopolymerization and thermal polymerization properties as a photopolymerization initiator. It has been unclear whether a cured product having good curability can be obtained from a composition in which a peroxide is highly filled with a filler having high thermal diffusivity, such as a thermally conductive filler.

Accordingly, an object of the present invention is to provide a thermally conductive composition from which a thermally conductive sheet having a high thermal conductivity and a thick film can be obtained with good productivity by light irradiation.

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

（一般式（１）中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、それぞれ独立してメチル基又はエチル基を表し、Ｒ^５は炭素数１～６のアルキル基又はフェニル基を表し、Ｒ^６は独立した置換基であって、炭素数１～４のアルキル基、炭素数１～４のアルコキシ基、又は塩素原子を表し、ｎは０～２の整数を表す。） The present invention is a thermally conductive composition comprising a binder component containing at least one of a radically polymerizable monomer and a partial polymer thereof and 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 is a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1): about things.

(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.)

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

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

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 irradiated with ultraviolet rays and photocured, the dialkyl peroxide having a thioxanthone skeleton is quickly activated, and the heat diffusivity of the highly filled thermally conductive filler is not easily affected. Therefore, a thermally conductive sheet having a high thermal conductivity and a thick film can be produced with good productivity.

<Radical polymerizable monomer>
A compound having an ethylenically unsaturated group can be preferably used as the radically polymerizable monomer. Examples of radically polymerizable monomers include (meth)acrylic acid esters, styrenes, maleic acid esters, fumaric acid esters, itaconic acid esters, cinnamic acid esters, crotonic acid esters, vinyl ethers, and 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 contain highly reactive (meth)acrylic acid esters. The radically polymerizable monomers may be used alone or in combination of two or more.

Monofunctional compounds and polyfunctional compounds can be used as the (meth)acrylic acid esters. Monofunctional compounds include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) Alkyl (meth)acrylates such as acrylates; 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 group-terminated polyethylene glycol mono ( Monomers having a hydroxyl group such as meth)acrylate, hydroxyl-terminated polypropylene glycol mono(meth)acrylate, etc.; methoxyethyl (meth)acrylate, methoxypolyethyleneglycol (meth)acrylate, phenoxypolyethyleneglycol (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, etc.; 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; 2-(meth) acryloyloxyethyl isocyanate monomers having an isocyanate group; glycidyl ( Epoxy group-containing monomers such as meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether; Phosphorus atom-containing monomers such as 2-((meth)acryloyloxy)ethyl phosphate; 3-(meth)acryloxypropyl Silicon atom-containing monomers such as trimethoxysilane; 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3,3-pentafluoropropyl (meth)acrylate, 2-(perfluorohexyl) Monomers having a fluorine atom such as ethyl (meth)acrylate; (meth)acrylic acid, monosuccinate (2-(meth)acryloyloxyethyl), monophthalate (2-(meth)acryloyloxyethyl), monomaleate monomers having a carboxyl group such as (2-(meth)acryloyloxyethyl), ω-carboxy-polycaprolactone mono(meth)acrylate, and the like;

Examples of the polyfunctional compound 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, neopentyl glycol hydroxypivalate di(meth)acrylate, glycerol propoxy tri(meth)acrylate tricyclodecane dimethanol di(meth)acrylate (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)acryl 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 the thermally conductive filler. In this case, the radically polymerizable monomer is preferably partially polymerized and thickened in advance to form a partial polymer of the radically polymerizable monomer. Although the viscosity of the partial polymer of the radically polymerizable monomer is not particularly limited, 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. 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.

Thermal polymerization initiators used for partial polymerization include, for example, diacyl peroxides, peroxyketals, ketone peroxides, hydroperoxides, dialkyl peroxides, peroxyesters, peroxydicarbonates and the like. Organic peroxides; azo polymerization initiators and the like can be used. Specifically, lauroyl peroxide, benzoyl peroxide, cyclohexanone peroxide, 1,1-bis(t-butylperoxy) 3,3,5-trimethylcyclohexane, t-butyl hydroperoxide, 2,2'-azo bisbutyronitrile and the like.

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-based compounds, thioxanthone-based 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; 2-(o-chlorophenyl)-4,5-phenylimidazole dimer and other biimidazoles; 2-trichloromethyl-5-(p-methoxystyryl)-1,3,4-oxadiazole 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-phenyl ketone, 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-methyldiphenylsulfide, 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-benzoyloxyiminobutane-2-one, 3-acetoxyiminobutane-2- and the like. Among these, it is preferable to use a dialkyl peroxide having a thioxanthone skeleton represented by the following general formula (1) from the viewpoint of curability during sheet production. Alternatively, any combination of the thermal initiators or photoinitiators mentioned above can be used.

<Photoinitiator>
The photopolymerization initiator of the present invention contains a dialkyl peroxide having a thioxanthone skeleton represented by the following 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. 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 thermal conductive composition, R Both ³ and R ⁴ are preferably methyl groups.

In 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, 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 is selected from a methyl group, an ethyl group, and a propyl group. is more preferable. From the viewpoint of increasing the decomposition temperature of the dialkyl peroxide having a thioxanthone skeleton, improving the storage stability of the thermally conductive composition, and increasing the sensitivity to irradiation light, R ⁵ is a methyl group or an ethyl group. is more preferred.

In the general formula (1), the substitution position of the dialkyl peroxide with respect to the thioxanthone is not particularly limited, but from the viewpoint of increasing the sensitivity to irradiation light, it is substituted at the 2-, 3-, or 4-position of the thioxanthone skeleton. is preferred, and from the viewpoint of ease of synthesis, substitution at the 2- or 3-position of the thioxanthone skeleton is more preferred.

In 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. These substituents improve the light absorption characteristics of the dialkyl peroxide having a thioxanthone skeleton due to the push-pull effect of these substituents with respect to the emission wavelength of the lamp used, and efficiently absorb the irradiation light. can be done.

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 a thioxanthone skeleton, n is preferably an integer of 0 to 1, more preferably 0. .

In the general formula (1), when n is an integer of 1 to 2, the substitution position of R ⁶ is not particularly limited. It is preferably at the 7-position of the thioxanthone skeleton from the viewpoint of easily synthesizing the dialkyl peroxide having the thioxanthone skeleton.

Specific examples of R ⁶ include alkyl groups such as methyl group, ethyl group, isopropyl group and n-butyl group; methoxy group, ethoxy group, n-propyloxy group, sec-butyloxy group and tert-butyloxy group. alkoxy group such as; chlorine atom and the like. Among these, ^R6 is more preferably a methoxy group or an ethoxy group from the viewpoint of improving the sensitivity to irradiation light.

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

As the dialkyl peroxide having a thioxanthone skeleton, compounds 1 to 9 are preferred, and compounds 1, 2, 3, 7 and 8 are more preferred.

The content of the dialkyl peroxide having a thioxanthone skeleton is preferably 0.01 to 40 parts by mass, more preferably 0.05 to 20 parts by mass, with respect to 100 parts by mass of at least one of the radically polymerizable monomer and the partial polymer thereof. It is more preferably 0.1 to 10 parts by mass. If the content of the dialkyl peroxide having a thioxanthone skeleton is less than 0.01 parts by mass with respect to 100 parts by mass of at least one of the radically polymerizable monomer and the partial polymer thereof, the curing reaction does not proceed, which is not preferable. Further, when the content of the dialkyl peroxide having a 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 the partial polymer thereof, the radically polymerizable monomer and the partial polymer thereof When the solubility in at least one of reaches saturation, crystals of the photopolymerization initiator precipitate during the film formation of the thermally conductive composition, and roughening of the film surface becomes a problem, or the photopolymerization initiator itself absorbs light. , is not preferred because the light does not reach deep into the cured product. In addition, when the dialkyl peroxide having a thioxanthone skeleton contains the following other polymerization initiator, the ratio of the other polymerization initiator is 80% by mass or less in the total of the dialkyl peroxide having a thioxanthone skeleton and the other polymerization initiator. and more preferably 50% by mass or less.

In addition to the above dialkyl peroxide having a thioxanthone skeleton, the thermally conductive composition can be improved in surface curability, depth curability, etc. of the polymerizable composition by using other polymerization initiators. can. Other polymerization initiators are optional thermal polymerization initiators or photopolymerization initiators, and when selected, at least one of radically polymerizable monomers and partial polymers thereof, thermally conductive fillers, types of other additives, thermal conductivity The filling amount of the filler, the film thickness of the cured product, and the like are taken into consideration. Examples of the other polymerization initiator include the thermal polymerization initiator used for partial polymerization and the photopolymerization initiator used for partial polymerization (excluding dialkyl peroxide having a thioxanthone skeleton represented by general formula (1) ).

<Thermal conductive filler>
The thermally 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 and the like. In order to improve the strength of the sheet, a filler surface-treated with silane, titanate, or the like may be used. In addition, a filler having a surface coated with ceramics, polymer, etc., such as a waterproof coating, an insulating coating, or the like, 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, more preferably 10 or more. The thermally conductive fillers may be used alone or in combination of two or more.

The shape of the thermally conductive filler is regular or irregular, and examples thereof include polygonal, cubic, elliptical, spherical, needle-like, plate-like, flake-like, or combinations thereof. . Alternatively, particles in which a plurality of crystal particles are aggregated may be used. The shape of the filler is selected according to the viscosity of the radically polymerizable monomer or its partial polymer and the processability 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. It is preferable to use a large-diameter filler having a particle size of 25 μm or more and 100 μm or less.

The thermally conductive filler is 100 volume parts or more and 900 volume parts or less with respect to 100 volume parts of the binder component containing at least one of the radically polymerizable monomer and its partial polymer and the photopolymerization initiator. In conventional compositions that are photocured by ultraviolet light or the like, the content of the thermally conductive filler is limited in order to ensure the light transmittance necessary for curing, but the thermally conductive composition of the present invention has a thioxanthone skeleton. 100 parts by volume or more of the thermally conductive filler can be contained with respect to 100 parts by volume of the binder component. 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 with respect to 100 parts by volume of the binder component, It is more preferably 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.

<Other additives, etc.>
The thermally conductive composition may optionally contain a sensitizer (benzophenone derivatives such as 4,4′-bis(diethylamino)benzophenone; thioxanthone derivatives such as isopropylthioxanthone and diethylthioxanthone; anthracenes such as 9,10-dibutoxyanthracene). Derivatives; coumarin derivatives such as coumarin and ketocoumarin; acridine derivatives such as acridine orange and 9-phenylacridine; benzoates 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.), cross-linking agents, cross-linking accelerators, silane coupling agents, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.) ), anti-aging agents, fillers, colorants (pigments, dyes, etc.), UV absorbers, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, thickeners, flame retardants , inorganic compounds, inorganic fillers, electromagnetic wave-absorbing fillers, and the like can be used singly or in combination within a range that does not impair the characteristics of the present embodiment. Moreover, when forming the said heat conductive sheet, various general solvents can also be used.

The method of mixing each of the above constituent materials is not particularly limited, but manual mixing is possible for small amounts, but universal mixers, planetary mixers, hybrid mixers, Henschel mixers, kneaders, ball mills, and mixing. Common mixers such as rolls are used.

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

Examples of the method for processing the heat conductive sheet include conventionally known methods such as roll coating, spin coating, dip coating, brush coating, bar coating, knife coating, die coating, doctor blade, 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 irradiation with active energy rays such as electron beams, ultraviolet rays, visible rays, and radiation is preferable.

The active energy ray is preferably light with a wavelength of 250 to 450 nm, and more preferably light with a wavelength of 350 to 410 nm from the viewpoint of rapid curing, and light with a wavelength of 375 to 405 nm. It is further preferred to contain The amount of exposure to the active energy ray should be appropriately set according to the wavelength and intensity of the active energy ray and the composition of the thermally conductive composition. In addition, the intensity of the active energy ray is arbitrary, and when the intensity is high, curing can be performed in a short time, and when the intensity is low, curing can be performed by extending the time.

Light sources for the light irradiation include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high pressure mercury lamps, metal halide lamps, ultraviolet electrodeless lamps, light-emitting diodes (LEDs), xenon arc lamps, carbon arc lamps, sunlight, YAG lasers, and the like. A solid laser, a semiconductor laser, a gas laser such as an argon laser, or the like can be used. In the case of using light from visible light to infrared light, which absorbs little dialkyl peroxide having a thioxanthone skeleton, a sensitizer that absorbs the light is used as the additive for effective curing. be able to.

In addition, as the method for producing the cured product, a dual curing step may be applied, and a step of heating may be performed before and after the step of irradiating with active energy rays. In the step of heating the thermally conductive composition, the method of heating includes, for example, 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. Moreover, as a ventilation heating method, for example, a ventilation drying oven or the like can be used.

The film thickness of the thermally conductive sheet is preferably 0.3 mm or more and 5 mm or less. Conventional compositions that are photo-cured with ultraviolet light or the like have limitations on film thickness in order to ensure the light transmittance necessary for curing, but the thermally conductive composition of the present invention contains a dialkyl peroxide having a thioxanthone skeleton. Therefore, it can be cured with a film thickness of 0.3 mm or more and 5 mm or less. The thermally conductive sheet can be produced in a wide range of film thicknesses (for example, film thicknesses of 0.5 mm or more and 0.8 mm or more can be exemplified), so that it can be applied to various uses. The thermally conductive sheet is usually used as a single layer, but may be used as a multilayer of two or more layers, if necessary. In addition, the thermally conductive sheet preferably has a thermal conductivity of 1.5 (W/mK) or more at room temperature (23°C) under a general environment, and preferably 2.0 (W/mK). ) or more is more preferable.

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

<Example 1>
<Preparation of partial polymer>
0.5 parts by mass of compound 1 as a photopolymerization initiator is mixed with 100 parts by mass of 2-ethylhexyl acrylate (2-EHA) and irradiated with ultraviolet rays to polymerize 10 to 20% of the total amount of monomers. to obtain a thickened partial polymer.

<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 0.1 part of 1,6-hexanediol diacrylate (HDDA) were added. Thermal conductive filler 1 (alumina: average particle size 50 μm, thermal conductivity at 20 ° C. 25 W / m · k) and 80 volume parts of thermally conductive filler 2 (alumina: average particle size 2 μm, thermal conductivity at 20 ° C. 25 W / m · k) were mixed, and a rotation and revolution mixer (THINKY A thermally conductive composition was obtained by stirring for 2 minutes with Awatori Mixer ARV-310).

<Production of thermally conductive sheet>
The heat 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 on one side, using a spacer. Thereafter, one side of each of the two release films was irradiated with ultraviolet rays (illuminance: 2000 mW/cm ² ) for 10 seconds using a 385 nm LED light source to cure the thermally conductive composition, thereby producing 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. manufactured.

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

<Example 4>
Heat was applied in the same manner as in Example 1, except that the mixed amount of the thermally conductive filler 1 was changed to 150 parts by volume and the mixed amount of the 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 produced.

<Example 5>
Heating was performed in the same manner as in Example 1, except that the mixed amount of the thermally conductive filler 1 was changed to 400 parts by volume and the mixed 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. A conductive sheet was produced.

<Comparative Example 1>
Using compound R1 (2,4,6-trimethylbenzoyldiphenylphosphine oxide: manufactured by IGM) as a photopolymerization initiator in place of compound 25 in the preparation of the partial polymer and the preparation of the thermally conductive composition, and A thermally conductive sheet was produced 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 production of the partial polymer.

<Comparative Example 2>
Heat conduction was performed in the same manner as in Example 1 except that the mixed amount of the thermally conductive filler 1 was changed to 30 parts by volume and the mixed 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. A sex sheet was produced.

<Comparative Example 3>
Heat conduction was performed in the same manner as in Example 1 except that the mixed amount of the thermally conductive filler 1 was changed to 800 parts by volume and the mixed 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. A sex sheet was produced.

<Comparative Examples 4 and 5>
In the preparation of the thermally conductive composition, compound R2 (lauroyl peroxide "Perroyl L" manufactured by NOF), which is a thermal polymerization initiator, was used instead of compound R1 as a polymerization initiator, and instead of irradiating ultraviolet rays Second, 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.

<Curability>
When peeling off the release film of the thermally conductive sheet 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.
x: 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>
The 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.).

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

Comparative Example 1 had poor curability because a photopolymerization initiator other than a dialkyl peroxide having a thioxanthone skeleton was used. Comparative Example 2 had poor thermal conductivity because the content of the thermally conductive filler was small. Comparative Example 3 had poor curability because the content of the thermally conductive filler was too large. In Comparative Examples 4 and 5, since the thermal polymerization initiator (compound R2) was used, curing was not possible even in 600 seconds, and it took 900 seconds to cure.

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 thermally conductive filler is 100 volume parts or more and 900 volume parts or less with respect to 100 volume parts of the binder component,
A thermally conductive composition, wherein the photopolymerization initiator is a dialkyl peroxide having a thioxanthone skeleton represented by the following 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 of 0 to 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, having a thickness of 0.3 mm or more and 5 mm or less.