US-20260125534-A1 - THERMALLY CONDUCTIVE SILICONE COMPOSITION AND CURED PRODUCT THEREOF

US20260125534A1US 20260125534 A1US20260125534 A1US 20260125534A1US-20260125534-A1

Abstract

A thermally conductive silicone composition that is liquid and curable, contains (A) a liquid silicone, (B) a hydrosilylation catalyst, and (C) a filler, where the filler includes at least (C-1) a thermally conductive filler having a true density greater than the density of the liquid silicone, and (C-2) a low-density filler having a true density equal to or less than the density of the liquid silicone, and the particle size distribution of the filler is controlled so that the filler is dispersed in a state close to the closest packing in a matrix including the liquid silicone.

Inventors

Takahiro Asami
Nono TODA

Assignees

FUKOKU CO., LTD.

Dates

Publication Date: 20260507
Application Date: 20221228

Claims (10)

1 . A thermally conductive silicone composition that is liquid and curable, comprising: (A) a liquid silicone, (B) a hydrosilylation catalyst, and (C) a filler, wherein the filler comprises at least (C-1) a thermally conductive filler having a true density greater than the density of the liquid silicone, and (C-2) a low-density filler having a true density equal to or less than the density of the liquid silicone, and wherein, when a number of particle sizes as calculation points for the cumulative frequency in the cumulative particle size distribution of the filler (C) on a volume basis is denoted as R, the particle sizes of the thermally conductive filler (C-1), as the minimum and maximum among the particle sizes as calculation points for the cumulative frequency, are denoted as P (μm) and Q (μm), respectively, the particle size of the filler (C) at the nth calculation point, determined to satisfy the following formulas (a1) and (a2), is denoted as x n (μm) (where n is an integer satisfying 1≤n≤R) and the volume-based cumulative frequency of the particle size of the thermally conductive filler (C-1) corresponding to the particle size x n in the cumulative particle size distribution is denoted as c n (%), with respect to the particle size distribution of the filler (C), the minimum value E min of the mean squared error E, expressed by the following formula (a3), and the value a 0 of the coefficient a in the following formula (a4), corresponding to the minimum value E min , satisfy the following formulas: 0 ≤ E min ≤ 40 ⁢ and 6. ≤ a 0 ≤ 13. . [ Math . 1 ]  x n = k n - 1 ⁢ P ( a1 ) x R = Q ( a2 ) E = 1 R ⁢ ∑ n = 1 R ( c n - y n ) 2 ( a3 ) where y n = { ax n 1 / 2 ( ax n 1 / 2 < 100 ) 100 ( ax n 1 / 2 ≧ 100 ) ( a4 )
2 . The thermally conductive silicone composition according to claim 1 , wherein the volume fraction of the filler (C) in the thermally conductive silicone composition is 70.0% by volume or more and 80.0% by volume or less, and the ratio of the volume of the thermally conductive filler to the volume of the low-density filler in the filler (C) is 1.67 or more and 22.0 or less.
3 . The thermally conductive silicone composition according to claim 1 , wherein the low-density filler comprises at least one or more of polyethylene solid particles, resin hollow particles, and glass hollow particles.
4 . The thermally conductive silicone composition according to claim 1 , wherein the thermally conductive filler comprises a filler made of aluminum hydroxide.
5 . The thermally conductive silicone composition according to claim 1 , wherein the liquid silicone comprises (A-1) an organopolysiloxane including an alkenyl group at each of both ends of the molecular chain, (A-2) an organopolysiloxane including an alkenyl group at one end of the molecular chain and no reactive functional group at the other end, (A-3) an organopolysiloxane including at least three or more alkenyl groups in the molecule, and (A-4) an organohydrogenpolysiloxane including a silicon atom-bound hydrogen atom at the ends of the molecular chain and no silicon atom-bound hydrogen atoms in the side chains of the molecular chain.
6 . The thermally conductive silicone composition according to claim 5 , wherein the liquid silicone comprises an organopolysiloxane represented by the following general formula (1):
7 . A cured product obtained by curing the thermally conductive silicone composition according to claim 1 via a hydrosilylation reaction.
8 . The thermally conductive silicone composition according to claim 2 , wherein the low-density filler comprises at least one or more of polyethylene solid particles, resin hollow particles, and glass hollow particles.
9 . The thermally conductive silicone composition according to claim 2 , wherein the thermally conductive filler comprises a filler made of aluminum hydroxide.
10 . The cured product according to claim 7 , wherein the volume fraction of the filler (C) in the thermally conductive silicone composition is 70.0% by volume or more and 80.0% by volume or less, and the ratio of the volume of the thermally conductive filler to the volume of the low-density filler in the filler (C) is 1.67 or more and 22.0 or less.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority under 35 U.S.C. § 371 to International Patent Application No. PCT/JP2022/048512, filed Dec. 28, 2022. The contents of this application are hereby incorporated by reference in their entireties. TECHNICAL FIELD The present invention relates to a thermally conductive silicone composition and a cured product thereof. BACKGROUND ART In recent years, electric and electronic components have become smaller and more integrated, and the amount of heat generated has increased accordingly. Similarly, the capacity and output of secondary batteries have increased, and the amount of heat generated has also increased. It is necessary to prevent the temperature of heat-generating elements, such as electric and electronic components and secondary batteries, from rising excessively, and therefore a structure is adopted in which the heat generated by the heat-generating elements is conducted away to a heat-dissipating element, such as a heat sink or exterior case. Thermally conductive compositions or their cured products are used to enhance the thermal bonding between the heat-generating element and the heat-dissipating element by interposing them between the heat-generating element and the heat-dissipating element, efficiently transferring heat from the heat-generating element to the heat-dissipating element. As the thermally conductive compositions, thermally conductive silicone compositions containing silicone as a matrix and various fillers added to the silicone matrix are widely used. The thermally conductive silicone compositions or their cured products are commercially available in various forms, such as heat-dissipating grease and heat-dissipating sheets. Among these, thermally conductive silicone compositions and their cured products which are called gap fillers are widely used because they are liquid when applied to heat-generating or heat-dissipating elements and exhibit excellent conformability to irregularities (i.e., gap filling properties), allowing for precise application, and as they harden over time, they prevent the occurrence of pumping out and dripping. In order to improve heat dissipation performance by interposing a thermally conductive silicone composition or its cured product between a heat-generating element and a heat-dissipating element, it is first important that the thermally conductive silicone composition or its cured product has high thermal conductivity, and in order to increase the thermally conductivity, a thermally conductive filler having high thermal conductivity is mixed into the thermally conductive silicone composition. In addition, it is also important to reduce the thermal resistance at the interface between the heat-generating element and the thermally conductive silicone composition or its cured product, and at the interface between the heat-dissipating element and the thermally conductive silicone composition or its cured product, in order to improve the heat-dissipation properties. However, when the mixing ratio of the thermally conductive filler is increased in order to obtain high thermal conductivity, the viscosity of the thermally conductive silicone composition increases, and as a result, the adhesion when the thermally conductive silicone composition or its cured product contacts the heat-generating element or the heat-dissipating element decreases, leading to higher heat resistance at the interface. In order to reduce the viscosity, a method of diluting the uncured thermally conductive silicone composition with an organic solvent may be used. However, if the thermally conductive silicone composition or its cured product contains volatile components due to the use of an organic solvent, air bubbles may form in the thermally conductive silicone composition or its cured product over time, or voids may form at the interface with the heat-dissipating element or heat-generating element, making it difficult to transfer heat. For the same reason, it is also undesirable for the thermally conductive silicone composition or its cured product to generate volatile components as a result of a chemical reaction. In addition, increasing the mixing ratio of the thermally conductive filler in the thermally conductive silicone composition results in an increase in the hardness of its cured product. As a result, the shock absorption capacity is reduced, and the ability to relax stress caused by expansion and contraction due to temperature changes in electric components, electronic components, secondary batteries, etc., is also diminished. Meanwhile, fillers made of inorganic materials with high thermal conductivity, that is, inorganic fillers, are generally used as thermally conductive fillers. However, the density of inorganic fillers is much higher than that of silicone. Therefore, when the mixing ratio of the thermally conductive filler in the thermally conductive silicone composition is increased, the density