THERMALLY CONDUCTIVE COMPOSITION

Abstract

Provided is a thermally conductive composition that is capable of effectively suppressing pump out. Specifically provided is a thermally conductive composition that contains a base oil composition and an inorganic powder filler, wherein: the base oil composition contains a base oil, a thermoplastic resin that has a softening point of 50-150° C., and a thixotropic agent; and when shaped into a thermally conductive sheet of the thermally conductive composition at a temperature not less than the softening point of the thermoplastic resin, the type-A hardness (in compliance with JIS K 6253-3) of the thermally conductive sheet as measured using a durometer is 30-80.

Claims

1. A thermally conductive composition comprising a base oil composition and an inorganic powder filler, the base oil composition comprising a base oil, a thermoplastic resin having a softening point of 50° C. or more and 150° C. or less, and a thixotropy adjusting agent, a thermally conductive sheet formed of the thermally conductive composition at a temperature being not lower than the softening point of the thermoplastic resin having a type A hardness of 30 or more and 80 or less as measured by a durometer (in accordance with JIS K 6253-3).

2. The thermally conductive composition according to claim 1, wherein the inorganic powder filler comprises a first inorganic powder filler having an average particle diameter in a range of 10 μm or more and 100 μm or less, a second inorganic powder filler having an average particle diameter being different from the average particle diameter of the first inorganic powder filler, and a third inorganic powder filler having an average particle diameter being different from the average particle diameter of the first inorganic powder filler and the average particle diameter of the second inorganic powder filler, and wherein the inorganic powder filler has average particle diameters satisfying the following formulae (1) and (2):
D.sub.2/D.sub.1<0.70  (1)
D.sub.3/D.sub.2<0.60  (2) wherein, in the formula, D.sub.1 represents an average particle diameter of the first inorganic powder filler, D.sub.2 represents an average particle diameter of the second inorganic powder filler, and D.sub.3 represents an average particle diameter of the third inorganic powder filler.

3. The thermally conductive composition according to claim 2, wherein the second inorganic powder filler has an average particle diameter in a range of 1 μm or more and 50 μm or less, and the third inorganic powder filler has an average particle diameter in a range of 0.1 μm or more and 5 μm or less.

4. The thermally conductive composition according to claim 2, comprising 40 parts by mass or more and 80 parts by mass or less of the first inorganic powder filler, 10 parts by mass or more and 50 parts by mass or less of the second inorganic powder filler, and 10 parts by mass or more and 40 parts by mass or less of the third inorganic powder filler, with respect to 100 parts by mass of the inorganic powder filler.

5. The thermally conductive composition according to claim 1, wherein the inorganic powder filler comprises at least one or more types selected from copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride, and silicon carbide.

6. The thermally conductive composition according to claim 1, wherein a total of the base oil and the thermoplastic resin is in a ratio of 5.3 parts by mass or more and 33.3 parts by mass or less with respect to 100 parts by mass of the inorganic powder filler.

7. The thermally conductive composition according to claim 1, comprising 50 parts by mass or more and 200 parts by mass or less of the thermoplastic resin with respect to 100 parts by mass of the base oil.

8. The thermally conductive composition according to claim 1, wherein the base oil contains at least one or more types selected from a mineral oil, a synthetic hydrocarbon oil, a diester, a polyol ester, and a phenyl ether.

9. The thermally conductive composition according to claim 1, wherein the thermoplastic resin includes at least one or more resins selected from an ester resin, an acrylic resin, a rosin resin, and a cellulose resin.

10. The thermally conductive composition according to claim 1, wherein the thixotropy adjusting agent contains at least one or more types selected from bentonite, mica, kaolin, sepiolite, saponite, and hectorite.

11. The thermally conductive composition according to claim 1, comprising 1 part by mass or more and 10 parts by mass or less of the thixotropy adjusting agent with respect to 100 parts by mass of the base oil.

12. The thermally conductive composition according to claim 3, comprising 40 parts by mass or more and 80 parts by mass or less of the first inorganic powder filler, 10 parts by mass or more and 50 parts by mass or less of the second inorganic powder filler, and 10 parts by mass or more and 40 parts by mass or less of the third inorganic powder filler, with respect to 100 parts by mass of the inorganic powder filler.

13. The thermally conductive composition according to claim 2, wherein the inorganic powder filler comprises at least one or more types selected from copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride, and silicon carbide.

14. The thermally conductive composition according to claim 3, wherein the inorganic powder filler comprises at least one or more types selected from copper, aluminum, zinc oxide, magnesium oxide, aluminum oxide, aluminum nitride, and silicon carbide.

15. The thermally conductive composition according to claim 2, wherein a total of the base oil and the thermoplastic resin is in a ratio of 5.3 parts by mass or more and 33.3 parts by mass or less with respect to 100 parts by mass of the inorganic powder filler.

16. The thermally conductive composition according to claim 2, comprising 50 parts by mass or more and 200 parts by mass or less of the thermoplastic resin with respect to 100 parts by mass of the base oil.

17. The thermally conductive composition according to claim 2, wherein the base oil contains at least one or more types selected from a mineral oil, a synthetic hydrocarbon oil, a diester, a polyol ester, and a phenyl ether.

18. The thermally conductive composition according to claim 2, wherein the thermoplastic resin includes at least one or more resins selected from an ester resin, an acrylic resin, a rosin resin, and a cellulose resin.

19. The thermally conductive composition according to claim 2, wherein the thixotropy adjusting agent contains at least one or more types selected from bentonite, mica, kaolin, sepiolite, saponite, and hectorite.

20. The thermally conductive composition according to claim 2, comprising 1 part by mass or more and 10 parts by mass or less of the thixotropy adjusting agent with respect to 100 parts by mass of the base oil.

Description

EXAMPLES

[0071] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

1. Production of Thermally Conductive Composition

[0072] Materials shown in the following (A) to (E) were used to produce thermally conductive compositions having compositions shown in the following Tables 1 and 2.

[0073] [Configuration and Production Method of Thermally Conductive Composition]

(Constituting components)
(A) Inorganic powder filler
(A)-1: First inorganic powder filler
Alumina 1: Average particle diameter=40 μm
Alumina 2: Average particle diameter=30 μm
Alumina 3: Average particle diameter=50 μm
Alumina 4: Average particle diameter=70 μm
Alumina 5: Average particle diameter=110 μm
Alumina 6: Average particle diameter=5 μm

[0074] (A)-2: Second inorganic powder filler

Alumina 7: Average particle diameter=8 μm
Alumina 8: Average particle diameter=15 μm
Alumina 9: Average particle diameter=20 μm
Alumina 10: Average particle diameter=30 μm
Alumina 11: Average particle diameter=3.4 μm
Zinc oxide 1: Average particle diameter=10 μm

[0075] (A)-3: Third Inorganic Powder Filler

Alumina 12: Average particle diameter=0.53 μm
Alumina 13: Average particle diameter=0.83 μm
Alumina 14: Average particle diameter=0.18 μm
Alumina 15: Average particle diameter=5 μm
Zinc oxide 2: Average particle diameter=0.60 μm

[0076] Note here that the average particle diameter of each of the inorganic powder fillers was measured by using a particle size distribution measuring device (SALD-7000 manufactured by Shimadzu Corporation) by a laser diffraction and scattering method (in accordance with JIS R 1629: 1997).

[0077] (B) Base Oil

(B)-1: Dipentaerythritol isononanoate (ester-based oil)
(B)-2: Tri(2-ethylhexyl) trimellitate (ester-based oil)
(B)-3: Tri(3,5,5-trimethylhexyl) trimellitate (ester-based oil)

[0078] (C): Thermoplastic Resin

(C)-1: Mixture of ester wax and rosin derivative. A thermoplastic resin having a mixing ratio of 150 parts by mass of rosin derivative with respect to 100 parts by mass of ester wax was used. The softening point of this thermoplastic resin is 110° C.
(C)-2: Acrylic resin (softening point: 105° C.)
(C)-3: Cellulose resin (softening point: 135° C.)
(C)-4: Ester resin (softening point: 70° C.)

[0079] (D): Thixotropy Adjusting Agent

(D)-1: Organically treated bentonite
(D)-2: Organically treated sepiolite

[0080] (E) Dispersing Agent

(E)-1: Acid-based hydrocarbon polymer
(E)-2: Higher fatty acid ester

[0081] The materials (A) to (E) having the compositions shown in following Tables 1 and 2 were mixed in a planetary mixer, the obtained mixture was placed in a tank of a universal mixing stirrer which had been heated at 150° C., subjected to kneading and vacuum-defoaming for 30 minutes, cooled, and then, taken out of the tank to obtain a thermally conductive composition.

TABLE-US-00001 TABLE 1 Inorganic powder filler Content of each component with respect Ratio of to 100 parts by mass average of inorganic powder particle Type filler(Parts by mass) diameters First Second Third First Second Third D.sub.2/D.sub.1 D.sub.3/D.sub.2 Example 1 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 2 Alumina 1 Alumina 7 Alumina 12 70.0 17.5 12.5 0.20 0.07 Example 3 Alumina 1 Alumina 7 Alumina 12 80.0 10.0 10.0 0.20 0.07 Example 4 Alumina 1 Alumina 7 Alumina 12 52.0 28.0 20.0 0.20 0.07 Example 5 Alumina 1 Alumina 7 Alumina 12 41.0 29.5 29.5 0.20 0.07 Example 6 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 7 Alumina 2 Alumina 7 Alumina 12 62.0 24.0 14.0 0.27 0.07 Example 8 Alumina 3 Alumina 7 Alumina 12 62.0 24.0 14.0 0.16 0.07 Example 9 Alumina 4 Alumina 7 Alumina 12 62.0 24.0 14.0 0.11 0.07 Example 10 Alumina 1 Alumina 8 Alumina 12 62.0 24.0 14.0 0.38 0.04 Example 11 Alumina 1 Alumina 9 Alumina 13 62.0 24.0 14.0 0.40 0.04 Example 12 Alumina 1 Alumina 7 Alumina 13 62.0 24.0 14.0 0.20 0.10 Example 13 Alumina 1 Alumina 7 Alumina 14 62.0 24.0 14.0 0.20 0.02 Example 14 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 15 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 16 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 17 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 18 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 19 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 20 Alumina 1 Zinc oxide 1 Alumina 12 62.0 24.0 14.0 0.25 0.05 Total content of base oil and Thixotropy thermo- Content adjusting agent plastic of Content of Dispersing agent resin with thermo- thixotropy Content of respect to plastic adjusting dispersing 100 parts resin with agent with agent with by mass of respect to respect to respect to inorganic 100 parts 100 parts 100 parts Thermo- powder by mass by mass by mass Base plastic filler of base of base of base oil resin (Parts oil(Parts oil(Parts oil(Parts Type Type by mass) by mass) Type by mass) Type by mass) Example 1 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 2 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 3 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 4 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 5 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 6 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 7 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 8 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 9 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 10 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 11 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 12 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 13 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 14 (B)-1 (C)-1 19.5 100 (D)-1 5.6 (E)-1 0.5 Example 15 (B)-1 (C)-1 19.1 100 (D)-1 9.9 (E)-1 0.5 Example 16 (B)-1 (C)-1 19.9 100 (D)-1 1.5 (E)-1 0.5 Example 17 (B)-1 (C)-1 19.9 100 (D)-1 1.2 (E)-1 0.5 Example 18 (B)-1 (C)-1 19.8 60 (D)-1 2.5 (E)-1 5.5 Example 19 (B)-1 (C)-1 19.8 190 (D)-1 2.5 (E)-1 5.5 Example 20 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5

TABLE-US-00002 TABLE 2 Inorganic powder filler Content of each component with respect Ratio of to 100 parts by mass average of inorganic powder particle Type filler(Parts by mass) diameters First Second Third First Second Third D.sub.2/D.sub.1 D.sub.3/D.sub.2 Example 21 Alumina 1 Alumina 7 Zinc oxide 2 62.0 24.0 14.0 0.20 0.08 Example 22 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 23 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 24 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 25 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 26 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 27 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 28 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 29 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 30 Alumina 2 100.0 — — Example 31 Alumina 7 Zinc oxide 2 70.0 30.0 — 0.08 Example 32 Alumina 2 Alumina 13 65.0 35.0 — — Example 33 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 34 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Example 35 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Comparative Example 1 Alumina 1 Alumina 10 Alumina 12 62.0 24.0 14.0 0.75 0.02 Comparative Example 2 Alumina 1 Alumina 7 Alumina 15 62.0 24.0 14.0 0.20 0.63 Comparative Example 3 Alumina 5 Alumina 9 Alumina 12 62.0 24.0 14.0 0.18 0.03 Comparative Example 4 Alumina 6 Alumina 11 Alumina 12 62.0 24.0 14.0 0.68 0.16 Comparative Example 5 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Comparative Example 6 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Comparative Example 7 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Comparative Example 8 Alumina 1 Alumina 7 Alumina 12 62.0 24.0 14.0 0.20 0.07 Total content of base oil and Thixotropy thermo- Content adjusting agent plastic of Content of Dispersing agent resin with thermo- thixotropy Content of respect to plastic adjusting dispersing 100 parts resin with agent with agent with by mass of respect to respect to respect to inorganic 100 parts 100 parts 100 parts Thermo- powder by mass by mass by mass Base plastic filler of base of base of base oil resin (Parts oil(Parts oil(Parts oil(Parts Type Type by mass) by mass) Type by mass) Type by mass) Example 21 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 22 (B)-2 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 23 (B)-3 (C)-1 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 24 (B)-1 (C)-1 19.8 100 (D)-2 2.5 (E)-1 5.5 Example 25 (B)-1 (C)-1 19.8 100 (D)-2 2.5 (E)-2 5.5 Example 26 (B)-1 (C)-1 19.8 75 (D)-1 2.5 (E)-1 5.5 Example 27 (B)-1 (C)-1 19.8 55 (D)-1 2.5 (E)-1 5.5 Example 28 (B)-1 (C)-1 19.8 150 (D)-1 2.5 (E)-1 5.5 Example 29 (B)-1 (C)-1 19.8 195 (D)-1 2.5 (E)-1 5.5 Example 30 (B)-1 (C)-1 32.3 100 (D)-1 2.5 (E)-1 5.5 Example 31 (B)-1 (C)-1 24.3 100 (D)-1 2.5 (E)-1 5.5 Example 32 (B)-1 (C)-1 24.3 100 (D)-1 2.5 (E)-1 5.5 Example 33 (B)-1 (C)-2 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 34 (B)-1 (C)-3 19.8 100 (D)-1 2.5 (E)-1 5.5 Example 35 (B)-1 (C)-4 19.8 100 (D)-1 2.5 (E)-1 5.5 Comparative Example 1 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 0.5 Comparative Example 2 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 0.5 Comparative Example 3 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 0.5 Comparative Example 4 (B)-1 (C)-1 19.8 100 (D)-1 2.5 (E)-1 0.5 Comparative Example 5 (B)-1 (C)-1 18.6 100 (D)-1 14.7 (E)-1 0.5 Comparative Example 6 (B)-1 (C)-1 19.9 100 (D)-1 0.61 (E)-1 0.5 Comparative Example 7 (B)-1 (C)-1 19.8 20 (D)-1 2.5 (E)-1 5.5 Comparative Example 8 (B)-1 (C)-1 19.8 250 (D)-1 2.5 (E)-1 5.5

[0082] 2. Production of Thermally Conductive Sheet

[0083] The thermally conductive composition of each of Examples and Comparative Examples was heated on one-side fluorine-treated PET film having a thickness of 0.05 mm and width of 100 mm in a heating furnace set at 100° C. to make the thermally conductive composition into a melted state, and then the one-side fluorine-treated PET film of the same type was placed on the fluorine-treated surface so as to bring the fluorine-treated surfaces into contact with each other so as to be sandwiched by the thermally conductive compositions, which was allowed to pass between heating rolls set at 100° C. After cooling, the obtained product was cut into 100 mm in length, and the PET film was peeled off to obtain a thermally conductive sheet having film thicknesses of 0.1 mm and 0.5 mm.

[0084] 3. Evaluation

[Evaluation of Thermal Conductivity]

[0085] The thermal conductivity of the thermally conductive sheets of the thermally conductive compositions of Examples and Comparative Examples produced above was measured. Specifically, the thermal conductivity of the thermally conductive sheets was measured using a transient heat measuring device (in accordance with ASTMD5470) at room temperature. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “thermal conductivity”).

[Evaluation of Malleability]

[0086] The thermally conductive sheets of the thermally conductive compositions of Examples and Comparative Examples produced above were evaluated for malleability. Specifically, a film thickness of the thermally conductive sheet when the thermally conductive sheet having a film thickness of 0.5 mm was pressed and crushed with a pressure of 0.1 MPa applied under environment at 80° C. was measured. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “malleability”).

[Evaluation of Hardness]

[0087] Evaluation of hardness was carried out for the thermally conductive sheets of the thermally conductive compositions of the Examples and the Comparative Examples produced above. Specifically, the hardness was measured using a durometer according to JIS K 6253-3. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “hardness”).

[Evaluation of Initial Flexibility of Thermally Conductive Sheet]

[0088] The thermally conductive sheets of the thermally conductive compositions of Examples and Comparative Examples produced above were observed for flexibility in the initial state. Specifically, when a thermally conductive sheet having a film thickness of 0.1 mm was folded, the thermally conductive sheet having no crack and having excellent flexibility was evaluated as “0 (good)” for the initial flexibility. On the other hand, when a thermally conductive sheet was folded, the thermally conductive sheet having a crack and having poor flexibility was evaluated as “X (poor)” for the initial flexibility. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “initial state” in “flexibility”).

[Evaluation of Flexibility of Thermally Conductive Sheet after Heating]

[0089] The thermally conductive sheets of the thermally conductive compositions of the Examples and the Comparative Examples produced above were evaluated for flexibility after heating. Specifically, a PET film was cut into 100 mm in length after the rolling treatment with the heating roll, and at this time, a thermally conductive sheet having a film thickness of 0.1 mm, in which only one side of the PET film was peeled off and the other side was attached to the PET film, was used as a test sample. This test sample was placed in an electric furnace that has been heated to 250° C. in such a manner that a surface to which the PET film was attached faced lower side, and held for four hours. Thereafter, the test sample was taken out and cooled, and the thermally conductive sheet was bent at about 150° ten times, the flexibility of the sheet was determined based on two criteria of “0 (good)” (no crack occurred), “X (poor)” (crack occurred at less than 10 times), and presence or absence of flexibility after heating was determined. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “after heating” in “flexibility”).

[Evaluation of Sagging Resistance]

[0090] The thermally conductive sheets of the thermally conductive compositions of Examples and Comparative Examples produced above were evaluated for sagging resistance. Specifically, a thermally conductive sheet having a film thickness of 0.5 mm was placed on a glass substrate and heated in a heating furnace set at 80° C. for 10 minutes, and the thermally conductive sheet and the glass substrate were allowed to adhere to each other to obtain a test sample. Next, the test sample was then placed in a vertical orientation in an electric furnace that had been heated to 150° C. and held for 4 hours. The test sample was taken out and cooled, and then the thermally conductive sheet was visually observed. The presence or absence of sagging was determined based on two criteria, that is, sagging was evaluated as “0 (good)” (no sagging was observed) and “X (poor)” (sagging was observed) immediately after the test sample was placed in a vertical orientation in the electric furnace (initial state) and when the test sample was placed in a vertical orientation in the electric furnace and held for four hours. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “initial state” and “after heating” in “sagging resistance”).

[Cycle Test Evaluation]

[0091] The thermally conductive sheets of the thermally conductive compositions of Examples and Comparative Examples produced above were subjected to a cycle test. Specifically, a thermally conductive sheet having a film thickness of 0.5 mm which had been punched to a diameter of 10 mm was placed on an aluminum plate, and was heated in a heating furnace set at 80° C. for 10 minutes to allow the thermally conductive sheet to adhere to the aluminum plate. Thereafter, 0.5 mm-spacer was provided and a slide glass was put thereon, and the thermally conductive sheet was sandwiched to obtain a test sample. The test sample was placed vertically from the ground in a heat cycle tester set to alternate between 0° C. and 100° C. (30 minutes each) and tested for 1000 cycles. After 1000 cycles, a migration length (mm) by which the thermally conductive sheet moved from its original location was measured. Evaluation results are shown in Tables 3 and 4 (in Tables, described as “cycle test”).

TABLE-US-00003 TABLE 3 Evaluation results Thermal Flexibility Sagging resistance Cycle test conductivity Malleability Initial After Initial After After 1000 (W/(m .Math. K)) (um) Hardness state heating state heating cycles Example 1 2.27 46 48 ∘ ∘ ∘ ∘ 0.5 Example 2 2.31 62 59 ∘ ∘ ∘ ∘ 0.6 Example 3 2.40 78 65 ∘ ∘ ∘ ∘ 0.7 Example 4 2.36 83 75 ∘ ∘ ∘ ∘ 0.5 Example 5 2.40 92 76 ∘ ∘ ∘ ∘ 0.6 Example 6 2.18 42 49 ∘ ∘ ∘ ∘ 0.5 Example 7 2.17 43 45 ∘ ∘ ∘ ∘ 0.5 Example 8 2.44 72 71 ∘ ∘ ∘ ∘ 0.5 Example 9 2.53 85 74 ∘ ∘ ∘ ∘ 0.9 Example 10 2.31 53 57 ∘ ∘ ∘ ∘ 0.5 Example 11 2.36 68 65 ∘ ∘ ∘ ∘ 0.5 Example 12 2.40 55 58 ∘ ∘ ∘ ∘ 0.5 Example 13 2.23 72 65 ∘ ∘ ∘ ∘ 0.5 Example 14 2.44 48 52 ∘ ∘ ∘ ∘ 0.4 Example 15 2.53 51 49 ∘ ∘ ∘ ∘ 0.4 Example 16 2.14 45 42 ∘ ∘ ∘ ∘ 0.6 Example 17 2.10 44 43 ∘ ∘ ∘ ∘ 0.7 Example 18 2.34 51 42 ∘ ∘ ∘ ∘ 0.7 Example 19 2.45 65 70 ∘ ∘ ∘ ∘ 0.6 Example 20 2.43 45 47 ∘ ∘ ∘ ∘ 0.7

TABLE-US-00004 TABLE 4 Evaluation results Thermal Flexibility Sagging resistance Cycle test conductivity Malleability Initial After Initial After After 1000 (W/(m .Math. K)) (um) Hardness state heating state heating cycles Example 21 2.35 48 50 ∘ ∘ ∘ ∘ 0.7 Example 22 2.25 48 45 ∘ ∘ ∘ ∘ 0.6 Example 23 2.28 47 49 ∘ ∘ ∘ ∘ 0.6 Example 24 2.24 45 52 ∘ ∘ ∘ ∘ 0.5 Example 25 2.24 45 46 ∘ ∘ ∘ ∘ 0.5 Example 26 2.18 45 42 ∘ ∘ ∘ ∘ 0.8 Example 27 2.16 41 43 ∘ ∘ ∘ ∘ 1.1 Example 28 2.35 55 62 ∘ ∘ ∘ ∘ 0.7 Example 29 2.42 68 70 ∘ ∘ ∘ ∘ 0.6 Example 30 1.52 85 77 ∘ ∘ ∘ ∘ 0.9 Example 31 1.85 43 65 ∘ ∘ ∘ ∘ 0.6 Example 32 1.97 47 52 ∘ ∘ ∘ ∘ 0.8 Example 33 2.25 48 57 ∘ ∘ ∘ ∘ 0.7 Example 34 2.28 53 51 ∘ ∘ ∘ ∘ 0.6 Example 35 2.26 43 72 ∘ ∘ ∘ ∘ 1 Comparative Example 1 x Comparative Example 2 x Comparative Example 3 2.40 243 90 Comparative Example 4 2.12 274 90 Comparative Example 5 x Comparative Example 6 2.10 47 32 ∘ ∘ ∘ x 26 Comparative Example 7 2.25 43 7 ∘ ∘ ∘ x 15 Comparative Example 8 x

[0092] As is apparent from Tables 3 and 4, the thermally conductive compositions of Examples 1 to 35 in which a formed thermally conductive sheet had type A hardness measured by a durometer of 30 or more and 80 or less showed good flexibility and sagging resistance after heating, and showed a small migration length from the original place in the cycle evaluation test. This shows that in a thermally conductive composition in which type A hardness of the formed thermally conductive sheet measured by a durometer was made to be 30 or more and 80 or less by controlling the content of each component could effectively suppress occurrence of pump-out.

[0093] In particular, the thermally conductive compositions of Examples 1 to 29 containing the first, second, and third inorganic powder fillers having a predetermined relation of the average particle diameters (D.sub.2/D.sub.1<0.70, and D.sub.3/D.sub.2<0.60) showed higher thermal conductivity as compared with Examples 30 to 32. It can be understood that this is because the thermally conductive compositions of Examples 1 to 29 could spread uniformly in a state in which the content of the inorganic powder filler was increased. On the other hand, the thermally conductive compositions of Examples 30 to 32 could be formed into a thermally conductive sheet, and could effectively suppress occurrence of pump-out, but the content of the inorganic powder filler was smaller as compared with the thermally conductive compositions of Examples 1 to 29. Thus, it is considered that the thermal conductivity was relatively deteriorated.

[0094] Note here that similarly, in Examples 33 to 35 in which the type of “thermoplastic resin having a softening point of 50° C. or more and 150° C. or less” was changed, it is shown that the occurrence of pump-out could be effectively suppressed.

[0095] On the other hand, in Comparative Examples 3 and 4 in which the formed thermally conductive sheet had type A hardness measured by a durometer of more than 80, malleability was poor at the time of heating at 80° C. and pressurizing at 0.1 MPa, and it was not possible to form the thermally conductive composition into a thermally conductive thin film (forming a sheet). Furthermore, in Comparative Example 7 in which the type A hardness measured by a durometer was below 30, since a migration length from the original place after the cycle test was large, showing that the pump-out resistance was bad. Furthermore, in Comparative Examples 1, 2, 5, and 8, crack occurred after the thermally conductive sheet was folded, and the thermally conductive sheet was not able to be formed in the first place. Note here that since the thermally conductive compositions of Comparative Examples 1, 2, 5, and 8 were not able to be formed into a thermally conductive sheet, thermal conductivity, malleability, flexibility after heating, sagging resistance, and cycle test were not carried out. Furthermore, in Comparative Examples 3 and 4 in which a film thickness of the thermally conductive sheet when the thermally conductive sheet was pressed and crushed was large in the evaluation of malleability, the thermal conductivity, flexibility after heating, sagging resistance, and cycle tests were not carried out.