Heat conductive sheet and method for producing same
An object is to provide a heat conductive sheet having good handleability when mounting between the heating element and the heat dissipator, and softness that enables the distortion of the heating element, the heat dissipator, and the like to be suppressed in use. The heat conductive sheet contains: a matrix comprising a cured product of organopolysiloxane; and heat conductive fillers comprising anisotropic fillers with their major axes oriented in the thickness direction, and has a load property P represented b formula (1) below of 0.1 to 0.7: Load property P =( F 30 −F 20 )/ F 10 (1) wherein F 10 is a load of the heat conductive sheet at 10% compression, F 20 is a load of the heat conductive sheet at 20% compression, and F 30 is a load of the heat conductive sheet at 30% compression.
1. A heat conductive sheet comprising: a matrix comprising in an entirety of the matrix a cured product of organopolysiloxane; and heat conductive fillers comprising anisotropic fillers and non-anisotropic fillers,
wherein a major axes of the anisotropic fillers is oriented in a thickness direction,
wherein the anisotropic fillers have an aspect ratio over 2,
wherein a volume filling rate of the anisotropic fillers based on a total amount of the heat conductive sheet is 2 to 40 vol %,
wherein the non-anisotropic fillers comprise aluminum and aluminum oxide, wherein the non-anisotropic fillers comprise 10 to 70 vol % of the aluminum and 10 vol % or less of the aluminum oxide, the total amount of the non-anisotropic fillers being 10 to 70 vol % of the heat conductive sheet,
wherein the non-anisotropic fillers have an aspect ratio of 2 or less,
wherein an average particle size of the non-anisotropic fillers is 0.1 to 70 μm,
wherein the heat conductive fillers are dispersed in and throughout the matrix, and
wherein the heat conductive sheet has a load property P represented by formula (1) below of 0.1 to 0.7:
Load property P =( F 30 −F 20 )/ F 10 (1)
wherein F 10 is a load of the heat conductive sheet at 10% compression, F 20 is a load of the heat conductive sheet at 20% compression, and F 30 is a load of the heat conductive sheet at 30% compression.
2. The heat conductive sheet according to claim 1 , wherein the load F 30 at 30% compression is 5 to 18 N/144 mm 2 .
3. The heat conductive sheet according to claim 1 , wherein the load F 10 at 10% compression is 3.5 to 10 N/144 mm 2 .
4. The heat conductive sheet according to claim 1 , wherein the heat conductive sheet is formed from a heat conductive composition comprising a silicone compound comprising the organopolysiloxane; the heat conductive fillers comprising the anisotropic fillers and the non-anisotropic fillers; and a volatile compound.
5. The heat conductive sheet according to claim 4 , wherein the volatile compound is a volatile silane compound.
6. The heat conductive sheet according to claim 5 , wherein a volume of the volatile silane compound with respect to a total volume of the silicone compound and the volatile silane compound in the heat conductive composition is 15 to 50 vol %.
7. The heat conductive sheet according to claim 1 , wherein an aspect ratio of the anisotropic fillers is 5 or more.
8. The heat conductive sheet according to claim 1 , wherein the non-anisotropic fillers further comprise aluminum hydroxide.
9. The heat conductive sheet according to claim 1 , wherein the heat conductive sheet has voids.
10. The heat conductive sheet according to claim 1 , wherein the non-anisotropic fillers comprise 40 to 42 vol % of the aluminum and 10 vol % or less of the aluminum oxide.
11. A method for producing the heat conductive sheet according to claim 1 , the method comprising:
preparation step 1 of preparing a heat conductive composition comprising a silicone compound comprising the organopolysiloxane, the heat conductive fillers comprising the anisotropic fillers, and a volatile compound;
curing step 2 of heating the heat conductive composition to cure the organopolysiloxane, thereby forming a primary cured product retaining the volatile compound;
sheet-forming step 3 of slicing the primary cured product to obtain a sheet having a surface with the heat conductive fillers exposed, and
volatilization step 4 of volatilizing the volatile compound contained in the sheet obtained by the sheet-forming step 3.
12. The method for producing the heat conductive sheet according to claim 11 , wherein the volatile compound is a volatile silane compound, and when a temperature at 90% weight loss when heated at 2° C./minute in a thermogravimetric analysis of the volatile silane compound is referred to as T 1 , the heating temperature in the curing step 2 is T 1 −50° C. or lower.
13. A heat conductive sheet comprising: a matrix comprising in an entirety of the matrix a cured product of organopolysiloxane; and heat conductive fillers comprising anisotropic fillers and non-anisotropic fillers,
wherein a major axes of the anisotropic fillers is oriented in a thickness direction,
wherein a number of the anisotropic fillers with their major axis direction being less than 20° with respect to the thickness direction accounts for over 60% of a total number of the anisotropic fillers,
wherein an aspect ratio of the anisotropic fillers, which are fiber materials or flat materials, is over 2 and less than 100,
wherein when the anisotropic fillers are fiber materials, an average fiber length of the fiber materials is 5 to 600 μm,
wherein when the anisotropic fillers are flat materials, an average major axis length of the flat materials is 5 to 300 μm,
wherein a volume filling rate of the anisotropic fillers based on a total amount of the heat conductive sheet is 2 to 40 vol %,
wherein the non-anisotropic fillers comprise aluminum and aluminum oxide, wherein the non-anisotropic fillers comprise 10 to 70 vol % of the aluminum and 10 vol % or less of the aluminum oxide, the total amount of the non-anisotropic fillers being 10 to 70 vol % of the heat conductive sheet,
wherein the non-anisotropic fillers have an aspect ratio of 2 or less,
wherein an average particle size of the non-anisotropic fillers is 0.1 to 70 μm,
wherein the heat conductive fillers are dispersed in and throughout the matrix, and
wherein the heat conductive sheet has a load property P represented by formula (1) below of 0.1 to 0.7:
Load property P =( F 30 −F 20 )/ F 10 (1)
wherein F 10 is a load of the heat conductive sheet at 10% compression, F 20 is a load of the heat conductive sheet at 20% compression, and F 30 is a load of the heat conductive sheet at 30% compression.
14. The heat conductive sheet according to claim 13 , wherein the non-anisotropic fillers further comprise aluminum hydroxide.
15. The heat conductive sheet according to claim 13 , wherein the heat conductive sheet has voids.
16. The heat conductive sheet according to claim 13 , wherein the non-anisotropic fillers comprise 40 to 42 vol % of the aluminum and 10 vol % or less of the aluminum oxide.