JP7335678B2 - Thermally conductive addition-curable silicone composition and its cured product - Google Patents

Description

The present invention relates to thermally conductive addition-curable silicone compositions. More particularly, the present invention relates to a thermally conductive addition-curable silicone composition that achieves high thermal conductivity by being highly filled with silver powder and has good addition curability.

Heat generation during operation and resulting deterioration in performance are widely known as problems common to electronic component packages and power modules, and various heat dissipation techniques are used as means for solving this problem. In particular, a technique of arranging a cooling member in the vicinity of the heat-generating part to bring them into close contact with each other and efficiently dissipating heat from the cooling member is generally used. At that time, if there is a gap between the heat-generating part and the cooling member, heat transfer is lowered due to the interposition of air with poor thermal conductivity, and the temperature of the heat-generating member cannot be lowered sufficiently. In order to prevent such intervening air and improve heat conduction, a heat-dissipating material with good thermal conductivity and conformability to the surface of the member, such as heat-dissipating grease and heat-dissipating sheet, is used (for example, Patent Document 1 ~9).

As a heat countermeasure for actual electronic component packages and power modules, thermal grease that can be compressed thinly and has excellent penetrability into the gap between the heat generating part and the cooling member is suitable from the viewpoint of heat radiation performance. Furthermore, by compressing it to a desired thickness and then heat-hardening it, it is difficult for the thermal grease to flow out (pumping out) due to expansion and contraction due to the thermal history of repeated heat generation and cooling in the heat-generating part, making it difficult for the heat-generating grease to flow out (pumping out). Addition-curing heat-dissipating greases are particularly useful because they can increase the reliability of power modules (eg, Patent Document 10).

In recent years, there has been an increasing demand for high thermal conductivity and high reliability in heat dissipation materials in order to respond to new applications such as high output and high performance electronic component packages and power modules, semiconductors for self-driving vehicles, and IoT. . Silver powder is an example of a thermally conductive filler that can satisfy such requirements. The thermal conductivity of silver itself is extremely high, and when the powder is partially sintered during heat hardening, it forms a heat transfer path efficiently. significantly improved.

On the other hand, addition-curable silicone compositions containing silver powder are known to show a decrease in curability. If it is mounted in an electronic component package or a power module in a state where it has not been sufficiently hardened, there is a risk that the reliability will be lowered. Patent Literature 11 discloses that the curability of an addition-curable silicone composition can be improved by blending silver powder surface-treated with a siloxane oligomer, an organopolysiloxane, and a silicone resin. However, the invention described in Patent Document 11 requires a step of surface-treating the silver powder with a siloxane oligomer, organopolysiloxane, and silicone resin, resulting in low productivity.

Japanese Patent Application Laid-Open No. 2002-327116 JP-A-2004-130646 JP 2009-234112 A Japanese Patent Application Laid-Open No. 2009-209230 JP 2010-095730 A JP 2008-031336 A Japanese Patent Application Laid-Open No. 2007-177001 Japanese Patent Application Laid-Open No. 2008-260798 JP 2009-209165 A JP 2016-053140 A JP-A-7-109501

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a thermally conductive addition-curable silicone composition containing silver powder that exhibits excellent curability.

The present inventors have conducted intensive studies to achieve the above objects, and as a result, found that aliphatic unsaturated hydrocarbon group-containing organopolysiloxane, silver powder, alkaline earth metal peroxide or alkali metal peroxide, organo The inventors have found that a thermally conductive, addition-curable silicone composition with excellent curability can be obtained by blending a specific amount of hydrogen polysiloxane and a platinum group metal catalyst, and have completed the present invention.

Accordingly, the present invention provides the thermally conductive addition-curable silicone composition described below.

[1]
(A) Organopolysiloxane having at least two aliphatic unsaturated hydrocarbon groups in one molecule and a kinematic viscosity at 25° C. of 60 to 100,000 mm ² /s (B) Silver powder: Composition Medium, an amount that is 10 to 98% by mass,
(C) an alkaline earth metal peroxide or an alkali metal peroxide: an amount of 0.03 to 10% by mass in the composition;
(D) Organohydrogenpolysiloxane having two or more silicon-bonded hydrogen atoms in one molecule: an amount such that the total number of SiH groups is 0.5 to 5,
(E) a platinum group metal catalyst: a thermally conductive addition-curable silicone composition comprising an effective amount.

[2]
The thermally conductive addition-curable silicone composition according to [1], wherein component (B) has an average particle size of 0.01 to 300 μm.

[3]
The thermally conductive addition-curable silicone composition of [1] or [2], wherein component (C) is an alkaline earth metal peroxide.

[4]
The thermally conductive addition-curable silicone composition according to any one of [1] to [3], wherein component (C) is calcium peroxide.

[5]
Furthermore, as component (F), an effective amount of one or more addition curing reaction inhibitors selected from the group consisting of acetylene compounds, nitrogen compounds, organic phosphorus compounds, oxime compounds and organic chloro compounds [1] to The thermally conductive addition-curable silicone composition according to any one of [4].

[6]
A cured product of the thermally conductive addition-curable silicone composition according to any one of [1] to [5].

ADVANTAGE OF THE INVENTION The thermally conductive addition-curable silicone composition of the present invention achieves high thermal conductivity by incorporating silver powder into the composition and has excellent heat curing properties. As a result, it is possible to achieve both excellent heat dissipation performance and high reliability by mounting it on an electronic component package or power module.

The present invention will be described in detail below.

(A) component (A) component has at least 2, preferably 2 to 100, more preferably 2 to 50 aliphatic unsaturated hydrocarbon groups in one molecule, kinematic viscosity at 25 ° C. of 60 to 100,000 mm ² /s.

The aliphatic unsaturated hydrocarbon group is a monovalent hydrocarbon group preferably having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, having an aliphatic unsaturated bond. Examples of the aliphatic unsaturated hydrocarbon group include alkenyl groups such as vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl group, cyclohexenyl group, and octenyl group. Among these, a vinyl group is preferred. The aliphatic unsaturated hydrocarbon group may be bonded to either a silicon atom at the end of the molecular chain, a silicon atom in the middle of the molecular chain, or both.

The organic group other than the aliphatic unsaturated hydrocarbon group, which is bonded to the silicon atom of the component (A) organopolysiloxane, preferably has 1 to 18 carbon atoms, more preferably 1 to 10 carbon atoms, and further preferably has 1 to 10 carbon atoms. It is an unsubstituted or substituted monovalent hydrocarbon group of numbers 1 to 8. Examples of the monovalent hydrocarbon group include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group and nonyl. aryl groups such as phenyl group, tolyl group, xylyl group and naphthyl group; aralkyl groups such as benzyl group, phenylethyl group and phenylpropyl group; or part of the hydrogen atoms of these groups. Alternatively, all of them are substituted with halogen atoms such as fluorine, bromine and chlorine, cyano groups and the like, such as chloromethyl, chloropropyl, bromoethyl, trifluoropropyl and cyanoethyl groups. Among these, a methyl group is preferred.

The (A) component organopolysiloxane has a kinematic viscosity at 25° C. of 60 to 100,000 mm ² /s, preferably 100 to 30,000 mm ² /s. If the kinematic viscosity is less than 60 mm ² /s, the physical properties of the silicone composition may deteriorate, and if it exceeds 100,000 mm ² /s, the extensibility of the silicone composition may be poor.
In the present invention, kinematic viscosity is a value at 25° C. measured with an Ubbelohde Ostwald viscometer (the same shall apply hereinafter).

The molecular structure of the component (A) organopolysiloxane is not particularly limited as long as it has the properties described above. etc. In particular, those having a linear structure in which the main chain consists of repeating diorganosiloxane units and both ends of the molecular chain are blocked with triorganosiloxy groups are preferred. The organopolysiloxane having a linear structure may partially have a branched structure or a cyclic structure.

The organopolysiloxane can be used singly or in combination of two or more.
The component (A) content in the composition of the present invention is preferably 1.5 to 90% by mass, more preferably 2 to 20% by mass.

(B) Component (B) Component is silver powder. The method for producing the silver powder is not particularly limited, and examples thereof include an electrolysis method, a pulverization method, a heat treatment method, an atomization method, a reduction method and the like. Moreover, the shape is not particularly limited and may be flake-like, spherical, granular, amorphous, dendritic, needle-like, or the like.
If the average particle size of the component (B) is less than 0.01 µm, the viscosity of the resulting composition may become too high, resulting in poor spreadability. The range of 0.01 to 300 μm is preferable, the range of 0.1 to 100 μm is more preferable, and the range of 1 to 50 μm is particularly preferable, because there is a possibility of uniformity. The average particle diameter is a value determined as a volume-based average value (or median diameter) in particle size distribution measurement by a laser beam diffraction method.

In addition, component (B) can be used singly or in combination of two or more, and the ratio is not particularly limited and is arbitrary.
The amount of component (B) is 10 to 98% by mass, preferably 70 to 97% by mass, more preferably 80 to 95% by mass, in the composition of the present invention. If the amount is more than 98% by mass, the viscosity of the composition may be significantly increased and workability may be lowered. If the amount is less than 10% by mass, the thermal conductivity may be poor.

Component (C) Component (C) is an alkaline earth metal peroxide or an alkali metal peroxide, and acts as a co-catalyst for improving the curability of the composition of the present invention.

From the viewpoint of safety and chemical stability, it is preferable to use alkaline earth metal peroxides, and calcium peroxide is particularly preferable.

The amount of component (C) is 0.03 to 10% by mass, preferably 0.05 to 5% by mass, in the composition of the present invention. If the amount is less than 0.03% by mass, the effect of improving the curability of the composition of the present invention is poor, and even if it exceeds 10% by mass, the promoter effect does not significantly increase, which is uneconomical There is a possibility that the composition of the present invention may be significantly thickened.

Component (D) Component (D) is an organohydrogenpolysiloxane having 2 or more, preferably 2 to 100, and more preferably 2 to 50 silicon-bonded hydrogen atoms (SiH groups) per molecule. is. In the organohydrogenpolysiloxane, the SiH groups in the molecule undergo an addition reaction with the aliphatic unsaturated hydrocarbon groups of component (A) described above in the presence of a platinum group metal catalyst (component (E)) described later. , as long as it can form a crosslinked structure.

The molecular structure of the organohydrogenpolysiloxane is not particularly limited as long as it has the properties described above, and has a linear structure, a branched chain structure, a cyclic structure, a partially branched structure, or a partially cyclic structure. Linear structure etc. are mentioned. Among these, linear structures and cyclic structures are preferred.
The organohydrogenpolysiloxane has a kinematic viscosity at 25° C. of preferably 1 to 1,000 mm ² /s, more preferably 10 to 300 mm ² /s. If the kinematic viscosity is 1 mm ^{2 /} s or more, the physical properties of the silicone composition may not deteriorate. There is no

Examples of the organic group bonded to the silicon atom of the organohydrogenpolysiloxane include unsubstituted or substituted monovalent hydrocarbon groups other than aliphatic unsaturated hydrocarbon groups, particularly preferably having 1 to 12 carbon atoms. is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms. Examples of the monovalent hydrocarbon group include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group and dodecyl group, aryl groups such as phenyl group, 2-phenylethyl group and 2-phenylpropyl group. aralkyl groups such as groups, those in which some or all of these hydrogen atoms are substituted with halogen atoms such as fluorine, bromine, chlorine, etc., cyano groups, epoxy ring-containing organic groups (glycidyl groups or glycidyloxy group-substituted alkyl groups), etc. , for example, chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, cyanoethyl group, 2-glycidoxyethyl group, 3-glycidoxypropyl group, and 4-glycidoxybutyl group. . Among these, a methyl group and a 3-glycidoxypropyl group are preferred.

The organohydrogenpolysiloxane may be used alone or in combination of two or more.
The amount of component (D) organohydrogenpolysiloxane to be blended is such that the total number of SiH groups in component (D) relative to the total number of aliphatic unsaturated hydrocarbon groups in component (A) is 0.5 to 5, preferably 0.7 to 4.5, more preferably 1 to 4. If the amount of component (D) is less than the above lower limit, the addition reaction will not proceed sufficiently, resulting in insufficient cross-linking. On the other hand, when the above upper limit is exceeded, the crosslinked structure may become non-uniform, and the storage stability of the composition may be significantly deteriorated.

Component (E) Component (E) is a platinum group metal catalyst and acts to promote the addition reaction between the components (A) and (D) described above. As the platinum group metal catalyst, conventionally known ones used for addition reactions can be used. Examples of the platinum group metal catalyst include platinum-based, palladium-based, and rhodium-based catalysts, among which platinum or platinum compounds, which are relatively easily available, are preferable. Examples of platinum or platinum compounds include simple platinum, platinum black, chloroplatinic acid, platinum-olefin complexes, platinum-alcohol complexes, and platinum coordination compounds.
The platinum group metal catalysts may be used singly or in combination of two or more.

Component (E) may be added in an effective amount as a catalyst, that is, in an effective amount necessary to accelerate the addition reaction and cure the thermally conductive addition-curable silicone composition of the present invention. The effective amount is preferably from 0.1 to 500 ppm, more preferably from 1 to 200 ppm, and even more preferably from 10 to 100 ppm, based on the mass in terms of platinum group metal atoms in the composition. If the amount of the catalyst is less than the above lower limit, the effect as a catalyst may not be obtained. Even if the above upper limit is exceeded, the catalytic effect does not increase, which is uneconomical.

In addition to the components described above, the thermally conductive addition-curable silicone composition of the present invention may optionally contain the following optional components.

Component (F) Component (F) is a reaction control agent that suppresses the progress of the hydrosilylation reaction at room temperature, and is added to prolong shelf life and pot life. As the reaction control agent, conventionally known reaction control agents used for addition curing silicone compositions can be used. Examples of the reaction control agent include acetylene compounds such as acetylene alcohols (e.g., ethynylmethyldecylcarbinol, 1-ethynyl-1-cyclohexanol, 3,5-dimethyl-1-hexyn-3-ol); Various nitrogen compounds such as butylamine, tetramethylethylenediamine, and benzotriazole, organic phosphorus compounds such as triphenylphosphine, oxime compounds, organic chloro compounds, and the like can be mentioned.

When component (F) is blended, the blending amount is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, per 100 parts by mass of component (A). If the amount of the reaction inhibitor is less than 0.05 parts by mass, the desired shelf life and pot life may not be obtained. may decrease.

In order to improve the dispersibility in the silicone composition, the reaction control agent may be diluted with conventionally known organo(poly)siloxane, toluene, or the like.

Other Components The thermally conductive addition-curable silicone composition of the present invention may contain a non-reactive organo(poly)siloxane such as methylpolysiloxane in order to adjust the strength and viscosity of the composition. .
Furthermore, one or more conventionally known thermally conductive fillers other than silver may be used in combination.
Furthermore, hydrolyzable organopolysiloxanes, various modified silicones, and hydrolyzable organosilanes may be blended for the purpose of improving the filling properties of the thermally conductive filler or imparting adhesiveness to the composition.
Furthermore, a solvent may be added to adjust the viscosity of the composition.
Furthermore, in order to prevent deterioration of the silicone composition, conventionally known antioxidants such as 2,6-di-tert-butyl-4-methylphenol may be contained as necessary.
Furthermore, dyes, pigments, flame retardants, anti-settling agents, thixotropy improvers, etc. can be blended as needed.

Method for Producing Silicone Composition A method for producing the silicone composition of the present invention will be described. The method for producing the silicone composition of the present invention is not particularly limited, and conventionally known production methods can be used.
The above components (A) to (D), and if necessary, component (E) and other components, for example, Trimix, Twinmix, and Planetary Mixer (both registered trademarks of Mixer manufactured by Inoue Seisakusho Co., Ltd.), Using a mixer such as Ultra Mixer (registered trademark of mixer manufactured by Mizuho Kogyo Co., Ltd.), Hibismix (registered trademark of mixer manufactured by Primix Co., Ltd.), etc., at 25 ° C. for usually 3 minutes to 24 hours, preferably A method of mixing for 5 minutes to 12 hours, particularly preferably 10 minutes to 6 hours, can be used. Further, degassing may be performed during mixing, and mixing may be performed while heating in the range of 40 to 170°C.

In the production of the composition of the present invention, the components (A) and (B) are preliminarily mixed at 25°C, and then (C) and (D) are mixed at 25°C. It is preferable from the viewpoint that the cured product exhibits good thermal conductivity and curability. When blending optional components (E) and/or (F), components (A) and (B) are mixed in advance, and then components (E) and/or (F) are mixed. , and then mixing components (C) and (D).

The thermally conductive addition-curable silicone composition of the present invention has a viscosity measured at 25° C. of preferably 10 to 1,000 Pa·s, more preferably 20 to 700 Pa·s, still more preferably 40 to 600 Pa·s. is s. If the viscosity is less than 10 Pa·s, workability may be deteriorated, such as difficulty in shape retention and sedimentation of the silver powder. Also, if the viscosity exceeds 1,000 Pa·s, there is a possibility that workability will be deteriorated, such as difficulty in discharge or application. The said viscosity can be obtained by adjusting the compounding quantity of each component mentioned above.

A cured product of the thermally conductive addition-curable silicone composition of the present invention has a thermal conductivity of 0.5 to 20 W/m·K.

Curing conditions for heat-curing the thermally conductive addition-curable silicone composition of the present invention are not particularly limited, but are preferably 80 to 200°C, more preferably 100 to 180°C, and preferably 15 minutes. ~4 hours, more preferably 30 minutes to 2 hours.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The kinematic viscosity indicates the value at 25° C. measured by an Ubbelohde-type Ostwald viscometer.

[Examples 1 to 10, Comparative Examples 1 to 6]
Preparation of Thermally Conductive Addition-Cure Silicone Composition The following components (A) to (F) are blended in the amounts shown in Tables 1 to 3 below according to the method shown below to prepare a thermally conductive addition-curable silicone composition. was prepared.
That is, components (A) and (B) were added to 0.3 liter of Hibismix (manufactured by Primix Co., Ltd.) and mixed at 25° C. for 1 hour. Next, components (F), (E), (D) and (C) were added and mixed uniformly to prepare each silicone composition.
For each silicone composition obtained, the viscosity and thermal conductivity were measured according to the following methods, and the state of the cured product was confirmed. The results are shown in Tables 1-3.
In Tables 1 to 3 below, the mass of component (E) is the mass of a solution of a platinum-divinyltetramethyldisiloxane complex dissolved in dimethylpolysiloxane (platinum atom content: 1% by mass). SiH/SiVi is the ratio of the total number of SiH groups in component (D) to the total number of alkenyl groups in component (A).

(A) Component A-1: Dimethylpolysiloxane having both ends capped with dimethylvinylsilyl groups and having a kinematic viscosity at 25°C of 600 mm ² /s A-2: Both ends capped with dimethylvinylsilyl groups and having a kinematic viscosity of 600 mm 2 /s Dimethylpolysiloxane having a kinematic viscosity of 30,000 mm ² /s at

(B) Component B-1: Silver flake powder with an average particle size of 4 μm B-2: Silver flake powder with an average particle size of 3 μm B-3: Silver flake powder with an average particle size of 15 μm B-4: Average particle size 3 μm spherical silver powder

(C) Component C-1: Calcium peroxide (manufactured by Sigma-Aldrich, purity 75%)

(D) Component D-1: Methylhydrogendimethylpolysiloxane represented by the following formula (1) (kinematic viscosity at 25° C.=100 mm ² /s)

(E) Component E-1: A solution of a platinum-divinyltetramethyldisiloxane complex dissolved in the same dimethylpolysiloxane as A-1 above (platinum atom content: 1% by mass)

(F) Component F-1: 1-ethynyl-1-cyclohexanol represented by the following formula (2)

[viscosity]
The absolute viscosity of each silicone composition was measured at 25° C. using a Malcolm viscometer (type PC-1T) (rotor A, 10 rpm, shear rate 6 [1/s]).

[Thermal conductivity]
Each silicone composition was sandwiched between two aluminum plates with a diameter of 12.7 mm and was cured by heating at 150°C for 1 hour under a pressure of 0.14 MPa to prepare a test piece for thermal resistance measurement. was measured. Furthermore, the thickness of the test piece was measured with a microgauge, and the thickness of the silicone composition was calculated from the difference from the previously measured thickness of the aluminum plate. After that, the thermal conductivity of the silicone composition was derived from the following formula.

(thickness of silicone composition [μm]) ÷ (thermal resistance value of silicone composition [mm ² K/W])

Nanoflash (LFA447 manufactured by Nitschei) was used for the thermal resistance measurement.

[State of cured product]
Each uncured silicone composition was applied to a thickness of 2 mm between two parallel plates with a diameter of 2.5 cm. After the coated plate was heated from 25° C. to 150° C. at 5° C./min, it was held at 150° C. for 1 hour and then cooled to 25° C. to determine whether it cured to a rubbery state or remained liquid in an uncured state. was judged by finger touch. A viscoelasticity measuring device (ARES-G2: manufactured by TA Instruments Japan Co., Ltd.) was used to prepare the cured product.

From the results in Tables 1 to 3, it was found that the thermally conductive addition-curable silicone compositions of Examples 1 to 10, which satisfied the requirements of the present invention, gave rubber-like cured products after heat curing. That is, the composition of the present invention can obtain high reliability when electronic component packages and power modules are mounted.

On the other hand, the thermally conductive addition-curable silicone compositions of Comparative Examples 1 to 5 did not form a rubber-like cured product after heat curing, and remained liquid. That is, the compositions of Comparative Examples 1 to 5 may deteriorate in reliability when mounted on electronic component packages or power modules. Also, in Comparative Example 6, a pasty thermally conductive addition-curable silicone composition could not be obtained.

Accordingly, the cured product of the thermally conductive addition-curable silicone composition of the present invention achieves high thermal conductivity and good heat curability by incorporating a large amount of silver powder into the composition. Due to such properties, it can be particularly suitably used as a heat dissipation grease for use in electronic component packages and power modules that require high reliability.

Claims (5)

(A) Organopolysiloxane having at least two aliphatic unsaturated hydrocarbon groups in one molecule and a kinematic viscosity at 25° C. of 60 to 100,000 mm ² /s (B) Silver powder: Composition Medium, an amount that is 10 to 98% by mass,
(C) alkaline earth metal peroxide : an amount of 0.03 to 10% by mass in the composition;
(D) Organohydrogenpolysiloxane having two or more silicon-bonded hydrogen atoms in one molecule: an amount such that the total number of SiH groups is 0.5 to 5,
(E) a platinum group metal catalyst: a thermally conductive addition-curable silicone composition comprising an effective amount. 2. The thermally conductive addition-curable silicone composition according to claim 1, wherein component (B) has an average particle size of 0.01 to 300 μm. 3. The thermally conductive addition-curable silicone composition according to claim 1 , wherein component (C) is calcium peroxide. Claims 1 to 3, further comprising, as component (F), an effective amount of one or more addition curing reaction inhibitors selected from the group consisting of acetylene compounds, nitrogen compounds, organic phosphorus compounds, oxime compounds and organic chloro compounds. 4. The thermally conductive addition-curable silicone composition according to any one of 3 . A cured product of the thermally conductive addition-curable silicone composition according to any one of claims 1 to 4 .