JP7610264B2 - Composition for thermally conductive material, thermally conductive material, and method for producing thermally conductive material - Google Patents

Description

The present invention relates to a composition for a thermally conductive material, a thermally conductive material, and a method for producing a thermally conductive material.

Thermally conductive materials made of acrylic resin filled with thermally conductive filler are known (for example, see Patent Document 1). This type of thermally conductive material is used by being placed in contact with a heat generating body such as an electronic component in order to promote heat dissipation from the heat generating body. Specifically, a sheet-shaped thermally conductive material is used by being interposed between the heat generating body (for example, a CPU) and a heat sink.

Patent No. 4009224

The thermal conductivity of conventional thermally conductive materials is about 3 W/m·K (e.g., Patent Document 1), leaving room for improvement.

The object of the present invention is to provide a thermally conductive material having high thermal conductivity.

The means for solving the above problems are as follows.
<1> A composition for a thermally conductive material, comprising an acrylic composition containing an acrylic polymer obtained by polymerizing one or more (meth)acrylates, and one or more (meth)acrylates, a polyfunctional monomer, a polymerization initiator, and a thermally conductive filler, wherein the blending amount of the polyfunctional monomer is 0.1 parts by mass or more and 0.5 parts by mass or less, the blending amount of the polymerization initiator is 0.1 parts by mass or more and 1.5 parts by mass or less, and the blending amount of the thermally conductive filler is 0.02 parts by mass or more and 0.03 ... a thermally conductive filler having a particle size of 50 μm or more and 150 μm or less and made of aluminum nitride, a medium-sized thermally conductive filler having a particle size of 7.5 μm or more and 20 μm or less, and a small-sized thermally conductive filler having a particle size of 3 μm or less, and the amount of the large-sized thermally conductive filler is 680 parts by mass or more and 750 parts by mass or less per 100 parts by mass of the acrylic composition.

<2> The composition for thermally conductive materials described in <1>, in which the amount of the medium-sized thermally conductive filler is 300 parts by mass or more per 100 parts by mass of the acrylic composition.

<3> The composition for thermally conductive materials according to <1> or <2>, in which the amount of the small-particle-sized thermally conductive filler per 100 parts by mass of the acrylic composition is greater than the amount of the medium-particle-sized thermally conductive filler per 100 parts by mass of the acrylic composition.

<4> A thermal conductive material comprising a cured product of the thermal conductive composition described in any one of <1> to <3> above, and having a thermal conductivity of 7.2 W/m·K or more.

<5> A method for producing a thermally conductive material using the composition for thermally conductive material described in any one of <1> to <3>, comprising: an application step of applying the composition for thermally conductive material to the surface of a first release film to form an application consisting of the composition for thermally conductive material; a coating step of covering the surface of the application with a second release film so that the application is sandwiched between the first release film and the second release film; and a heating and pressurizing step of hot-pressing the application sandwiched between the first release film and the second release film to harden the application, thereby obtaining a highly thermally conductive material consisting of the hardened product of the application.

The present invention can provide thermally conductive materials with high thermal conductivity.

A schematic diagram showing the cross-sectional structure of a thermally conductive material. An explanatory diagram showing an example of the use of thermal conductive materials A diagram (photo) showing a case where a very small amount of separated material was found to adhere to the release film when it was peeled off from the thermal conductive material. A diagram (photo) showing a case where separated material is found adhering to the release film when the release film is peeled off from the thermal conductive material.

[Heat Conductive Material Composition]
The composition for a thermally conductive material of the present invention is a composition for producing a thermally conductive material having high thermal conductivity, and is usually in a liquid state under room temperature (23° C.) conditions.

The thermally conductive material composition mainly contains an acrylic composition, a multifunctional monomer, a polymerization initiator, and a thermally conductive filler.

An acrylic composition is a composition that contains at least an acrylic polymer obtained by polymerizing one or more (meth)acrylates, and one or more (meth)acrylates. In this specification, "(meth)acrylate" means methacrylate and/or acrylate.

The acrylic polymer is made by polymerizing (meth)acrylates having linear or branched alkyl groups with 2 to 18 carbon atoms (hereinafter sometimes referred to as "alkyl (meth)acrylates") alone or in combination of two or more types. Examples of alkyl (meth)acrylates include ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-pentyl (meth)acrylate, i-pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-hexyl (meth)acrylate, octyl (meth)acrylate, i-octyl (meth)acrylate, nonyl (meth)acrylate, i-nonyl (meth)acrylate, i-decyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, i-myristyl (meth)acrylate, stearyl (meth)acrylate, and i-stearyl (meth)acrylate.

The acrylic composition contains a (meth)acrylate monomer together with an acrylic polymer. The (meth)acrylate monomer may be a single (meth)acrylate (i.e., an alkyl (meth)acrylate) exemplified as a material for the acrylic polymer, or a combination of two or more kinds thereof, or may be a (meth)acrylate other than an alkyl (meth)acrylate.

The acrylic composition may contain other copolymerizable monomers in addition to the acrylic polymer and the (meth)acrylate as a monomer. Examples of the other copolymerizable monomers include copolymerizable vinyl monomers having a vinyl group (e.g., acrylamide, acrylonitrile, methyl vinyl ether, ethyl vinyl ether, vinyl acetate, vinyl chloride, etc.), aromatic monomers (e.g., benzyl (meth)acrylate, phenoxyethyl (meth)acrylate), etc. These may be used alone or in combination of two or more.

The acrylic composition may further contain aromatic esters.

As the acrylic composition, commercially available products (such as the AcriCure (registered trademark) HD-A series manufactured by Nippon Shokubai Co., Ltd.) may be used.

(Polyfunctional Monomer)
The polyfunctional monomer is a monomer having two or more (meth)acryloyl groups in the molecule. In this specification, the term "(meth)acryloyl group" refers to an acryloyl group and/or a methacryloyl group.

Examples of bifunctional (meth)acrylate monomers having two (meth)acryloyl groups in the molecule include 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, 2-ethyl-2-butyl-propanediol ( meth)acrylate, neopentyl glycol modified trimethylolpropane di(meth)acrylate, stearic acid modified pentaerythritol diacrylate, polypropylene glycol di(meth)acrylate, 2,2-bis[4-(meth)acryloxydiethoxyphenyl]propane, 2,2-bis[4-(meth)acryloxypropoxyphenyl]propane, 2,2-bis[4-(meth)acryloxytetraethoxyphenyl]propane, etc.

Examples of trifunctional (meth)acrylate monomers include trimethylolpropane tri(meth)acrylate, tris[(meth)acryloxyethyl]isocyanurate, etc. Examples of tetrafunctional or higher (meth)acrylate monomers include dimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc.

The polyfunctional monomers may be used alone or in combination of two or more. Among these polyfunctional monomers, 1,6-hexanediol di(meth)acrylate and the like are preferred.

The amount of the polyfunctional monomer is 0.1 parts by mass or more, preferably 0.15 parts by mass or more, 0.5 parts by mass or less, preferably 0.4 parts by mass or less, and more preferably 0.3 parts by mass or less, per 100 parts by mass of the acrylic composition. When the amount of the polyfunctional monomer is within the above range in the thermal conductive material composition, a thermal conductive material (molded body) with high thermal conductivity and the like can be obtained, and the molded body (thermal conductive material) does not become too hard and maintains its shape.

(Polymerization initiator)
The polymerization initiator is made of a peroxide, and generates radicals when heated to a predetermined temperature or higher. Examples of the polymerization initiator include organic peroxides such as di-(4-t-butylcyclohexyl) peroxydicarbonate, lauroyl peroxide, t-amylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, and 4-(1,1-dimethylethyl)cyclohexanol. Among the polymerization initiators, di-(4-t-butylcyclohexyl) peroxydicarbonate is preferred. These polymerization initiators may be used alone or in combination of two or more.

The amount of the polymerization initiator is 0.1 parts by mass or more, preferably 0.4 parts by mass or more and 1.5 parts by mass or less, preferably 1.3 parts by mass or less, per 100 parts by mass of the acrylic composition. When the amount of the polymerization initiator in the thermal conductive composition is within the above range, a thermal conductive material (molded body) with high thermal conductivity and the like can be obtained, and the molded body (thermal conductive material) does not become too hard and maintains its shape.

The thermally conductive filler includes large particle size thermally conductive filler, medium particle size thermally conductive filler, and small particle size thermally conductive filler.

The large-particle-size thermally conductive filler is a thermally conductive filler having a larger particle size than the medium-particle-size thermally conductive filler and the small-particle-size thermally conductive filler. The particle size of the large-particle-size thermally conductive filler is 50 μm or more, preferably 55 μm or more, more preferably 60 μm or more, and 150 μm or less, preferably 130 μm or less, more preferably 110 μm or less.

Aluminum nitride (AlN) powder (particulate aluminum nitride) is used as the large particle size thermally conductive filler.

The medium-sized thermally conductive filler is a thermally conductive filler that has a smaller particle size than the large-sized thermally conductive filler and a larger particle size than the small-sized thermally conductive filler. The particle size of the medium-sized thermally conductive filler is 7.5 μm or more, preferably 8.5 μm or more, more preferably 9.0 μm or more, and 20 μm or less, preferably 16 μm or less, more preferably 13 μm or less.

The medium-sized thermally conductive filler used is, for example, a powder of silicon carbide (SiC).

The small-particle-size thermally conductive filler is a thermally conductive filler having a smaller particle size than the large-particle-size thermally conductive filler and the medium-particle-size thermally conductive filler. The particle size of the small-particle-size thermally conductive filler is 3 μm or less, preferably 2 μm or less, and more preferably 1.5 μm or less. The lower limit of the particle size of the small-particle-size thermally conductive filler is not particularly limited as long as it does not impair the object of the present invention, but is preferably 0.01 μm or more, more preferably 0.1 μm or more, and even more preferably 0.5 μm or more.

The small particle diameter thermally conductive filler may be, for example, a powder of aluminum oxide (Al ₂ O ₃ ).

The amount of thermally conductive filler (large particle size thermally conductive filler, medium particle size thermally conductive filler, and small particle size thermally conductive filler) is 1550 parts by mass or more and 1600 parts by mass or less per 100 parts by mass of the acrylic composition. When the amount of thermally conductive filler (large particle size thermally conductive filler, medium particle size thermally conductive filler, and small particle size thermally conductive filler) in the thermally conductive material composition is within the above range, a thermally conductive material (molded body) with high thermal conductivity and the like can be obtained, and the viscosity of the thermally conductive composition and the hardness of the molded body (thermal conductive material) can be prevented from becoming too high.

The amount of the large-particle-sized thermally conductive filler is 680 parts by mass or more and 750 parts by mass or less per 100 parts by mass of the acrylic composition. When the amount of the large-particle-sized thermally conductive filler in the thermally conductive material composition is within the above range, a thermally conductive material (molded body) with high thermal conductivity and the like is obtained, the spacing between the large-particle-sized thermally conductive fillers formed in the thermally conductive material is appropriately maintained, and the formation of cracks and irregularities on the surface of the thermally conductive material (molded body) is suppressed.

The amount of the medium-sized thermally conductive filler is preferably 300 parts by mass or more, more preferably 350 parts by mass or more, relative to 100 parts by mass of the acrylic composition. The upper limit of the amount of the medium-sized thermally conductive filler is not particularly limited as long as it does not impair the object of the present invention, but is preferably 450 parts by mass or less, more preferably 400 parts by mass or less, relative to 100 parts by mass of the acrylic composition. When the amount of the medium-sized thermally conductive filler is within the above range, it is easy to obtain a thermally conductive material (molded body) with high thermal conductivity, and it is easy to prevent the viscosity of the thermally conductive composition and the hardness of the molded body (thermal conductive material) from becoming too high. The medium-sized thermally conductive filler is arranged so as to fill the gaps (intervals) formed between the large-sized thermally conductive fillers in the thermally conductive material.

In addition, in the thermally conductive material composition, it is preferable that the amount of small-particle-sized thermally conductive filler per 100 parts by mass of the acrylic composition is greater than the amount of medium-particle-sized thermally conductive filler per 100 parts by mass of the acrylic composition.

The amount of the small-particle-sized thermally conductive filler is not particularly limited as long as it does not impair the object of the present invention, but may be, for example, preferably 400 parts by mass or more, more preferably 450 parts by mass or more, preferably 550 parts by mass or less, and more preferably 500 parts by mass or less, relative to 100 parts by mass of the acrylic composition. When the amount of the small-particle-sized thermally conductive filler is in the above range, a thermally conductive material (molded body) having a high thermal conductivity is easily obtained, and the viscosity of the thermally conductive composition and the hardness of the molded body (thermal conductive material) are easily prevented from becoming too high. In addition, the small-particle-sized thermally conductive filler is arranged so as to fill the gaps (spacing) formed between the large-particle-sized thermally conductive fillers, the gaps formed between the medium-particle-sized thermally conductive fillers, and the gaps (spacing) formed between the large-particle-sized thermally conductive fillers and the medium-particle-sized thermally conductive fillers in the thermally conductive material.

In this specification, the particle size (μm) of various fillers such as thermally conductive fillers (large particle size thermally conductive fillers, medium particle size thermally conductive fillers, small particle size thermally conductive fillers) is the volumetric particle size (D50) measured by the laser diffraction method. The particle size (D50) can be measured using a laser diffraction type particle size distribution measuring device.

The thermal conductive material composition may further contain an antioxidant, a plasticizer, and a dispersant.

(Antioxidants)
Examples of the antioxidant include phenol-based antioxidants, phosphorus-based processing heat stabilizers, lactone-based processing heat stabilizers, sulfur-based heat stabilizers, and phenol-phosphorus-based antioxidants. Phenol-based antioxidants are preferred, and hindered phenol-based antioxidants are particularly preferred. The amount of the antioxidant is not particularly limited as long as it does not impair the object of the present invention, but may be, for example, in the range of 2 parts by mass or less (0 to 2 parts by mass) relative to 100 parts by mass of the acrylic composition. Note that the antioxidant is not an essential component in the thermal conductive material composition, so it may not be included. The antioxidant may be used appropriately for the purpose of long-term stability of the thermal conductive material obtained from the thermal conductive material composition, hardness adjustment of the thermal conductive material (adjustment of the polymerization reaction of the acrylic resin during production), etc.

An example of a commercially available antioxidant is Adeka STAB (registered trademark) AO-60 (manufactured by ADEKA Corporation).

As the plasticizer, for example, trimellitic acid ester-based plasticizers are preferable. Examples of trimellitic acid ester-based plasticizers include trioctyl trimellitate, triisononyl trimellitate, triisodecyl trimellitate, and 2-ethylhexyl trimellitate. These may be used alone or in combination of two or more. As a commercially available trimellitic acid ester-based plasticizer, the product name "Adeka Cizer (registered trademark) C-880" (manufactured by ADEKA Corporation) can be used.

The amount of plasticizer is preferably 4 parts by mass or more, more preferably 6 parts by mass or more, and preferably 15 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the acrylic composition. When the amount of plasticizer is in this range, it is easy to adjust the thermal conductive material to the desired hardness (Asker C hardness). When the amount of plasticizer is in the above range, it is easy to obtain a thermal conductive material (molded body) with high thermal conductivity, etc., and it is easy to prevent the viscosity of the thermal conductive composition and the hardness of the molded body (thermal conductive material) from becoming too high.

As a dispersant, for example, polyester phosphate is preferred.

The amount of dispersant is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and preferably 14 parts by mass or less, and more preferably 9 parts by mass or less, based on 100 parts by mass of the acrylic composition. When the amount of dispersant is within this range, crosslinking inhibition is unlikely to occur, making it easier to adjust the viscosity of the thermal conductive material composition to an appropriate range, and, for example, when producing a thermal conductive material, it becomes easier to form an application made of the thermal conductive material composition on a release film (i.e., it becomes easier to obtain a molded product of a predetermined shape (e.g., a sheet)).

The thermal conductive composition may further contain other components as long as they do not impair the objective of the present invention. Examples of other components include colorants (pigments, dyes, etc.), UV absorbers, flame retardants, preservatives, solvents, mildew inhibitors, anti-aging agents, antistatic agents, tackifiers, etc.

[Method of manufacturing thermally conductive material]
The method for producing a thermally conductive material of the present invention is a method for producing a thermally conductive material by using the above-mentioned composition for a thermally conductive material. The method for producing a thermally conductive material includes an applying step, a coating step, and a heating and pressurizing step.

The application process is a process in which the thermally conductive composition is applied to the surface of the first release film to form an application consisting of the thermally conductive composition.

The coating process is a process in which the surface of the object to be coated with a second release film so that the object to be coated is sandwiched between the first release film and the second release film.

The heating and pressurizing process is a process in which the applied material sandwiched between the first release film and the second release film is hot-pressed to harden the applied material, thereby obtaining a highly thermally conductive material consisting of the hardened applied material. The hot-pressing conditions may be, for example, a heating temperature of 100°C to 110°C, a pressing time of 5 to 10 minutes, and a pressure of 20 MPa to 40 MPa.

[Thermal Conductive Material]
The thermal conductive material is manufactured using the thermal conductive material composition and has excellent thermal conductivity. Specifically, the thermal conductive material has a thermal conductivity of 7.2 W/m·K or more (preferably 7.5 W/m·K or more, more preferably 8.0 W/m·K or more). The method for measuring the thermal conductivity will be described later. In addition, the thermal conductive material has excellent peelability, as described later. That is, when the release film is peeled off from the surface of the thermal conductive material, a part of the thermal conductive material (separated material) is prevented from adhering to the release film and moving, so that the formation of unevenness on the surface of the thermal conductive material is prevented (that is, the smoothness of the surface of the thermal conductive material is maintained). Therefore, air (air bubbles) is prevented from accumulating between the thermal conductive material and the object to which it is attached, and the high thermal conductivity of the thermal conductive material is maintained. In addition, the thermal conductive material has adhesiveness on its surface. Therefore, the thermal conductive material can be attached to the object by utilizing the adhesiveness (adhesive force) of the surface, and can be positioned relative to the object or fixed to the object.

The hardness of the thermally conductive material is not particularly limited as long as it does not impair the object of the present invention, and may be set appropriately. The hardness (Asker C hardness) of the thermally conductive material may be, for example, 10 or more and 75 or less.

Figure 1 is an explanatory diagram showing a schematic cross-sectional structure of a thermally conductive material 1. The thermally conductive material 1 is a sheet having a predetermined thickness, and includes an acrylic resin layer 2 and a thermally conductive filler 3 contained in the acrylic resin layer 2. The thermally conductive filler 3 is composed of a large particle size thermally conductive filler 31, a medium particle size thermally conductive filler 32, and a small particle size thermally conductive filler 33. Release films 4 and 5 are attached to the front and back surfaces of the thermally conductive material 11, respectively. Release film 5 corresponds to the "first release film", and release film 4 corresponds to the "second release film".

The release films 4 and 5 are made of PET films having a predetermined thickness. A release agent made of silicone resin or the like may be applied to the portions of the release films 4 and 5 that come into direct contact with the thermally conductive material 11. As the release films 4 and 5, films made of other resins (polyolefin resins, etc.) other than PET films may also be used.

Figure 2 is an explanatory diagram showing an example of the use of the thermally conductive material 1. The thermally conductive material 1 is used, for example, when attaching a heat dissipation member 20 to an electronic component (CPU) 10 mounted on a printed circuit board 11. Specifically, a sheet-shaped heat dissipation member 1 with the release films 4, 5 (see Figure 1) peeled off is attached to the upper surface of the electronic component 10, and then a plate-shaped bottom 21 of the heat dissipation member 20 is attached to the heat dissipation member 1. A plurality of heat dissipation fins 22 are erected on the bottom 21. The heat dissipation member 1 is made of a metal material (e.g., aluminum) with excellent thermal conductivity. Heat generated from the electronic component 10 moves to the heat dissipation member 1 while passing through a conductive path made of heat conductive fillers 3 (31, 32, 33) present in the heat dissipation member 1. Then, the heat is dissipated by the heat dissipation member 1.

Note that the above use example of thermally conductive material 1 is just one example, and thermally conductive material 1 may be used for other purposes.

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

[Heat Conductive Material Composition]
Example 1
A polyfunctional monomer, a polymerization initiator, an antioxidant, a plasticizer, a dispersant, and thermally conductive fillers (large particle size thermally conductive filler, medium particle size thermally conductive filler, and small particle size thermally conductive filler) were added to 100 parts by mass of the acrylic composition in the amounts (parts by mass) shown in Table 1, and mixed to obtain a composition for thermally conductive materials of Example 1. Details of each component are as follows.

"Acrylic composition": Product name "Acrycure (registered trademark) HD-A218" (manufactured by Nippon Shokubai Co., Ltd., a composition containing (meth)acrylic acid ester polymer (an example of an acrylic polymer), 2-ethylhexyl acrylate (an example of a (meth)acrylate), and aromatic esters)

"Multifunctional monomer": Product name "Light Acrylate (registered trademark) 1.6HX-A" (Kyoeisha Chemical Co., Ltd., 1,6-hexanediol diacrylate)

"Polymerization initiator": Trade name "Perkadox (registered trademark) 16" (manufactured by Kayaku Akzo Co., Ltd., di-(4-tert-butylcyclohexyl) peroxydicarbonate, 4-(1,1-dimethylethyl)cyclohexanol)

"Plasticizer": Product name "Adeka Cizer (registered trademark) C-880" (manufactured by ADEKA Corporation, trimellitic acid ester plasticizer, viscosity: 100 mPa·s (25°C))

"Dispersant": Product name "BYK-W 9010" (BYK Corporation, polyester phosphate)

"Antioxidant": Product name "Adekastab (registered trademark) AO-60" (manufactured by ADEKA Corporation, tetrakis [methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane)

"Aluminum nitride (large particle size thermal conductive filler)": Product name "HF-100" (manufactured by Combustion Synthesis Co., Ltd., particle size 100 μm)

"Silicon carbide (large particle size thermally conductive filler)": Product name "NGF180" (manufactured by Pacific Random Co., Ltd., particle size 63 μm)

"Silicon carbide (medium-grain thermal conductive filler)": Product name "GC#1200" (manufactured by Pacific Random Co., Ltd., grain size 10 μm)

"Aluminum oxide (small particle size thermal conductive filler)": Product name "AX1M" (manufactured by Nippon Steel Chemical & Material Co., Ltd., particle size 1 μm)

(Comparative Examples 1 to 3)
Compositions of Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the blending amount (parts by mass) of each component was changed to that shown in Table 1.

[Preparation of thermally conductive material]
Example 1
Using the composition for thermal conductive material of Example 1, a sheet (an example of a thermal conductive material, thickness: 1.5 mm) was produced in the following procedure. First, a first release film (PET film, product name "Purex A50", manufactured by Toyobo Film Solutions Co., Ltd., thickness: 50 μm) was laid on a predetermined mounting table, and a frame-shaped spacer (inner frame size: 120 mm x 130 mm, thickness: 5 mm) was placed on the first release film. Then, a liquid composition for thermal conductive material was poured inside (inside the inner frame) of the frame-shaped spacer to form an application made of the composition for thermal conductive material on the surface of the first release film (application process). Next, the surface of the application was covered with a second release film so that the application in the spacer was sandwiched between the first release film (covering process). Then, the applied material sandwiched between the first release film and the second release film (a laminated film formed by laminating a PET film having a thickness of 5 μm and a PET film having a thickness of 50 μm) was hot-pressed in the spacer to harden the applied material, thereby obtaining a highly thermally conductive material made of the hardened material of the applied material (heating and pressing step). The obtained highly thermally conductive material was sandwiched between the first release film and the second release film. The hot pressing conditions were a heating temperature of 100° C. to 110° C., a pressing time of 5 minutes to 10 minutes, and a pressure of 20 MPa to 40 MPa.

(Comparative Examples 1 to 3)
Using the compositions of Comparative Examples 1 to 3, attempts were made to produce sheets in the same manner as in Example 1. The compositions of Comparative Examples 1 and 3 gave the sheets of Comparative Examples 1 and 3, respectively. Note that the composition of Comparative Example 2 had too high a viscosity to be molded into a sheet.

〔evaluation〕
(Processability)
For each composition such as Example 1, the processability was evaluated based on whether or not the composition could be molded into a sheet. The results are shown in Table 1. In Table 1, the case where the sheet could be molded is indicated by "◯", and the case where the sheet could not be molded is indicated by "×".

(hardness)
Seven pieces of 50 mm x 100 mm size were cut out from the molded product of Example 1 etc. (a sheet with a thickness of 1.5 mm (excluding the thicknesses of the first release sheet and the second release sheet)), and these seven pieces were stacked together (thickness: 10.5 mm) to prepare a test piece for hardness measurement. In addition, a constant pressure loader for rubber hardness meter (manufactured by Elastron Co., Ltd.) and an Asker C hardness meter were prepared. The needle of the hardness meter was brought into contact with the test piece, and the value of the hardness meter was read 30 seconds after the full load was applied, and this was recorded as the hardness (Asker C). The results are shown in Table 1.

(Thermal Conductivity)
A test piece (thickness: 7.5 mm) was prepared by stacking five pieces cut into a size of 30 mm x 30 mm from the molded product (sheet with a thickness of 1.5 mm (excluding the thicknesses of the first release sheet and the second release sheet)) of Example 1, etc. A set of such test pieces was prepared. A polyimide sensor was sandwiched between the set of test pieces, and the thermal conductivity (W/m·K) was measured by the hot disk method. For the measurement, a hot disk thermal property measuring device (product name "TPS500", manufactured by Hot Disk Co., Ltd.) was used. The results are shown in Table 1.

(Adhesiveness)
From a sheet having a thickness of 1.5 mm (excluding the thicknesses of the first release sheet and the second release sheet) of the molded article in Example 1, a number of strips having a width of 50 mm were cut out, and these were joined together to form a measurement object having a length of 1000 mm and a width of 50 mm. A rolling ball tackiness test was performed on the measurement object in accordance with JIS Z 0237, and the rolling distance (cm) of the ball was measured. The results are shown in Table 1. If the rolling distance of the ball was less than 80 cm, it was judged to be "adhesive", and if the rolling distance of the ball was 80 cm or more, it was judged to be "not adhesive". If the rolling distance of the ball was less than 80 cm, when the test piece was placed vertically, the ball placed on the test piece was maintained in a state of adhering to the test piece without falling. On the other hand, if the rolling distance of the ball was 80 cm or more, when the test piece was placed vertically, the ball placed on the test piece was separated from the test piece and fell.

(Removability)
When the first release film (PET film, thickness: 50 μm) attached to the surface of the molded body such as Example 1 was peeled off from the molded body, whether or not the separated matter such as filler separated from the molded body was transferred to the release film side was visually confirmed based on the following evaluation criteria. In addition, a release layer made of a silicone release agent was formed on the surface of the PET film used as the first release film. The results are shown in Table 1.

<Evaluation criteria>
・If no separated matter or only a very small amount of separated matter is found on the release film, it is judged as "○".
・If any separated matter is found on the release film, it is marked as "X".

(Thermal conductivity)
As shown in Table 1, the thermal conductive material of Example 1 was confirmed to have excellent thermal conductivity, with a thermal conductivity of 9.59 W/m·K.

Comparative Example 1 does not contain aluminum nitride as a large-diameter thermally conductive filler, but contains silicon carbide (particle size: 63 μm) as a large-diameter thermally conductive filler. In this comparative example 1, the thermal conductivity was 6.10 W/m·K, and the thermal conductivity was insufficient. In addition, as described below, there was also a problem with peelability.

Comparative Example 2 is a case where the amount of thermally conductive filler blended is too high (particularly, the amount of large-particle-sized thermally conductive filler blended is too high). In this comparative example 2, as described above, the viscosity of the thermally conductive material composition became too high, and a sheet could not be formed.

Comparative Example 3 does not contain aluminum nitride as a large-diameter thermally conductive filler, but contains silicon carbide (particle size: 63 μm) as a large-diameter thermally conductive filler. In the case of Comparative Example 3, the thermal conductivity is excellent, but there is a problem with peelability, as described below.

(About adhesiveness)
It was confirmed that the surface of the thermally conductive material in Example 1 was sticky, while that in Comparative Example 1 and Comparative Example 3 was not sticky.

(Regarding peelability)
In Example 1, a trace amount of separated matter (such as thermally conductive filler) was found to adhere to the first release film. For reference, FIG. 3 shows a case where a trace amount of separated matter was found to adhere to the release film. FIG. 3 is a diagram (photograph) showing a case where a trace amount of separated matter was found to adhere to the release film when the release film was peeled off from the thermally conductive material. Within the circular frame shown in FIG. 3, a state in which a trace amount of separated matter consisting of thermally conductive filler or the like separated from the thermally conductive material adheres to the first release film is shown. Note that even if a trace amount of separated matter adheres to the release film when the thermally conductive material is used, contamination by the separated matter can be minimized by quickly removing the release film, etc.

In the cases of Comparative Examples 1 and 3, adhesion of separated matter was observed on the first release film. For reference, FIG. 4 shows a case where adhesion of separated matter was observed on the release film. FIG. 4 is a diagram (photograph) showing a case where adhesion of separated matter was observed on the release film when the release film was peeled off from the thermally conductive material. Within the circular frame shown in FIG. 4, granular (lumpy) separated matter consisting of thermally conductive filler etc. that separated from the thermally conductive material is shown adhering to the release film. If such granular separated matter adheres to the release film, there is a risk that the separated matter will peel off from the release film and pollute the surrounding environment.

1...Thermal conductive material, 2...Acrylic resin layer, 3...Thermal conductive filler, 31...Large particle size thermal conductive filler, 32...Medium particle size thermal conductive filler, 33...Small particle size thermal conductive filler, 4, 5...Release film

Claims (5)

an acrylic composition including an acrylic polymer obtained by polymerizing one or more (meth)acrylates, and one or more (meth)acrylates;
A multifunctional monomer,
A polymerization initiator;
A thermally conductive material composition comprising a thermally conductive filler,
the blending amount of the polyfunctional monomer is 0.1 parts by mass or more and 0.5 parts by mass or less, the blending amount of the polymerization initiator is 0.1 parts by mass or more and 1.5 parts by mass or less, and the blending amount of the thermally conductive filler is 1550 parts by mass or more and 1600 parts by mass or less, relative to 100 parts by mass of the acrylic composition,
The thermally conductive filler includes a large-particle-size thermally conductive filler having a particle size of 50 μm or more and 150 μm or less and made of aluminum nitride, a medium-particle-size thermally conductive filler having a particle size of 7.5 μm or more and 20 μm or less and made of silicon carbide, and a small-particle-size thermally conductive filler having a particle size of 0.5 μm or more and 3 μm or less and made of aluminum oxide , and the amount of the large-particle-size thermally conductive filler is 680 parts by mass or more and 750 parts by mass or less per 100 parts by mass of the acrylic composition. The thermal conductive material composition according to claim 1, wherein the amount of the medium-sized thermal conductive filler is 300 parts by mass or more per 100 parts by mass of the acrylic composition. The composition for thermally conductive materials according to claim 1 or 2, wherein the amount of the small-particle-sized thermally conductive filler per 100 parts by mass of the acrylic composition is greater than the amount of the medium-particle-sized thermally conductive filler per 100 parts by mass of the acrylic composition. A cured product of the thermal conductive material composition according to any one of claims 1 to 3,
A thermally conductive material having a thermal conductivity of 7.2 W/m·K or more and 9.59 W/m·K or less . A method for producing a thermally conductive material by using the composition for thermally conductive material according to any one of claims 1 to 3, comprising the steps of:
a step of applying the thermal conductive material composition to a surface of a first release film to form an application comprising the thermal conductive material composition;
a covering step of covering a surface of the object with a second release film so that the object is sandwiched between the first release film and the second release film;
and a heating and pressurizing step of hot-pressing the additive sandwiched between the first release film and the second release film to harden the additive, thereby obtaining a highly thermally conductive material consisting of the hardened product of the additive.

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