Thermally conductive silicone compositions

Abstract

The composition comprises: (A) a curable silicone composition comprising: (a1) a vinyldimethylsiloxy terminated polydimethylpolysiloxane having a viscosity in the range of 30 to 400 mPascal*sec; (a2) a silicon hydride functional crosslinker; and (a3) ​​a hydrosilylation catalyst, wherein the molar ratio of silicon hydride functionality to vinyl functionality from the crosslinker is in the range of 0.5:1 to 1:1; (B) a filler treating agent comprising one or both of an alkyltrialkoxysilane and a mono-trialkoxysiloxy terminated dimethylpolysiloxane; and (C) a thermally conductive filler mixture comprising: (c1) 40 to 55 weight percent aluminum nitride filler; (c1-a) 100 to 200 weight percent aluminum nitride filler; (c1-b) an aluminum nitride filler containing a blend of 5-41 wt.% spherical aluminum nitride particles having a D50 particle size of 100 micrometers or more, and (c1-c) spherical or irregular shaped aluminum nitride particles having a D50 particle size of 20-80 micrometers; (c2) spherical aluminum oxide particles having a D50 particle size of 1-5 micrometers; and (c3) 10-20 wt.% irregular zinc oxide particles having a D50 particle size of 0.1-0.5 micrometers, the total amount of the thermally conductive filler mixture being 94-97 wt.%, and the weight percentages being based on the weight of the thermally conductive composition unless otherwise specified.

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive silicone composition containing an aluminum nitride filler.

[0002] Introduction As electronic devices become smaller and more powerful, the industry is increasingly demanding thermally conductive materials useful for dissipating heat generated by such devices. For example, the telecommunications industry is experiencing a shift to 5G networks, which require smaller, more integrated electrical devices and a doubling of power requirements (from 600 watts to 1200 watts). The heat generated by the high power in these smaller devices must be efficiently dissipated or the devices will be damaged. Thermally conductive interface materials are often used in electronic devices to thermally couple heat-generating and heat-dissipating components. To efficiently transfer heat between the coupled components, thermally conductive compositions desirably have a thermal conductivity of at least 9.0 watts per meter*Kelvin (W / m*K), as measured according to ASTM method D5470-06. At the same time, as electronic devices become smaller, it becomes more important to apply thermally conductive compositions accurately and precisely to the appropriate components during rapid manufacturing processes. In that regard, it is desirable for the thermally conductive material to have an extrusion rate (ER) of greater than 60 grams per minute (g / min) when measured at 0.62 megapascals (90 pounds per square inch) pressure using a standard 30 cubic centimeter EFD syringe package using the procedure described herein below.

[0003] It is difficult to simultaneously achieve such thermal conductivity and extrusion speed in a thermally conductive material. Increasing the amount of thermally conductive filler can increase thermal conductivity, but it also increases viscosity, hindering extrusion speed and impairing dispensability and usability. For example, conventional thermally conductive compositions containing aluminum nitride fillers with an ER greater than 60 g / min typically cannot achieve a thermal conductivity of 9.0 W / m*K. Further addition of the high thermal conductivity filler boron nitride at a concentration of 5 weight percent or more can increase the thermal conductivity to 9.0 W / m*K or more, but the resulting thermally conductive composition has too high a viscosity to achieve an ER greater than 60 g / min, or even becomes a powdery paste.

[0004] There remains a need to identify thermally conductive compositions that can simultaneously achieve an ER of greater than 60 g / min and a thermal conductivity of at least 9.0 W / m*K. Summary of the Invention

[0005] The present invention provides a thermally conductive composition that simultaneously achieves an extrusion rate of greater than 60 g / min and a thermal conductivity of at least 9.0 W / m*K. Furthermore, the thermally conductive composition is reactive and can be cured to a cured thermally conductive material. The present invention includes a novel combination of a curable organopolysiloxane, a filler treatment agent, and a specific thermally conductive filler mixture. The thermally conductive filler mixture includes an aluminum nitride filler having a specific particle size and / or shape, a specific blend of spherical aluminum oxide particles having a D50 particle size of 1 to 5 micrometers (μm), and irregularly shaped zinc oxide particles having a D50 particle size of 0.1 to 0.5 μm. The thermally conductive composition is useful, for example, as a thermally conductive interface material between components of electronic devices.

[0006] In a first aspect, the present invention provides a thermally conductive composition comprising: (A) a curable silicone composition, (a1) a vinyldimethylsiloxy-terminated polydimethylpolysiloxane having a viscosity in the range of 30 to 400 mPascal*seconds; (a2) a silicon hydride functional crosslinker; and (a3) a hydrosilylation catalyst; a curable silicone composition having a molar ratio of silicon hydride functionality to vinyl functionality from the crosslinker in the range of 0.5:1 to 1:1; (B) a filler treatment comprising one or both of an alkyltrialkoxysilane and a mono-trialkoxysiloxy-terminated dimethylpolysiloxane; and (C) a thermally conductive filler mixture, based on the weight of the thermally conductive composition, comprising: (c1) 40 weight percent to 55 weight percent aluminum nitride filler, (c1-a) 15 weight percent to 41 weight percent of spherical aluminum nitride particles having a D50 particle size of 100 micrometers or more; (c1-b) an aluminum nitride filler comprising a blend of spherical or irregularly shaped aluminum nitride particles having a D50 particle size of 20 to 80 micrometers; (c2) spherical aluminum oxide particles having a D50 particle size of 1 to 5 micrometers; (c3) 10 weight percent to 20 weight percent of irregularly shaped zinc oxide particles having a D50 particle size of 0.1 to 0.5 micrometers; and A thermally conductive composition, wherein the total amount of the thermally conductive filler mixture is 94 weight percent to 97 weight percent, based on the weight of the thermally conductive composition. Weight percent values ​​are relative to the weight of the thermally conductive composition, unless otherwise specified.

[0007] In a second aspect, the invention is an article comprising the thermally conductive composition of the first aspect on another material. DETAILED DESCRIPTION OF THE INVENTION

[0008] Test methods, unless a date is given with the test method number, refer to the test method most recent to the priority date of this document. References to test methods include both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International Methods, and ISO refers to the International Organization for Standardization.

[0009] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0010] "And / or" means "and, or alternatively." All ranges are inclusive of endpoints unless otherwise indicated. All weight percent (wt%) values ​​are by weight of the composition and all volume percent (vol%) values ​​are by volume of the composition unless otherwise specified.

[0011] "Viscosity" of polysiloxanes is determined according to ASTM D445-21 using a glass capillary Cannon-Fenske viscometer at 25 degrees Celsius (°C) unless otherwise specified.

[0012] standard 1 H, 13 C, and 29 The chemical structure of the polysiloxane is determined by Si nuclear magnetic resonance (NMR) analysis.

[0013] The average particle size of the filler particles is determined as the volume median particle size (D50) by using a laser diffraction particle size analyzer (CILAS920 particle size analyzer or Beckman Coulter LS 13 320 SW). "D" represents the diameter of the filler particles, and D50 is the size in micrometers (μm) that divides the volume distribution between half of the volume of the filler particles above this diameter and half of the volume of the filler particles below this diameter. For example, if D50=5 μm, it means that 50% of the volume of the particles is smaller than 5 μm.

[0014] Unless otherwise specified, all thermal conductivity values ​​are determined in accordance with ASTM D5470-06 using a LonGwin model LW9389TIM thermal resistance and conductivity measuring instrument (also designated "TC-LonGwin").

[0015] The thermally conductive composition of the present invention comprises a curable silicone composition comprising (a1) vinyldimethylsiloxy-terminated polydimethylpolysiloxane (PDMS), (a2) a silicon hydride (SiH)-functional crosslinker, and (a3) ​​a hydrosilylation catalyst. The relative concentrations of the vinyldimethylsiloxy-terminated PDMS and the SiH-functional crosslinker are such that the molar ratio of SiH functionality to vinyl functionality from the crosslinker is in the range of 0.5:1 to 1:1, and can be 0.5:1 or greater, 0.6:1 or greater, 0.7:1 or greater, 0.8:1 or greater, or even 0.9:1 or greater, while being 1:1 or less, 0.9:1 or less, 0.8:1 or less, 0.7:1 or less, or even 0.6:1 or less.

[0016] The vinyldimethylsiloxy-terminated PDMS (a1) useful in the present invention has a viscosity of 30 milliPascal*seconds (mPa*s) or more, 45 mPa*s or more, 60 mPa*s or more, 90 mPa*s or more, 100 mPa*s or more, 120 mPa*s or more, 140 mPa*s or more, 160 mPa*s or more, or even 180 mPa*s or more, and simultaneously has a viscosity of 400 mPa*s or less, 300 mPa*s or less, 200 mPa*s or less, 180 mPa*s or less, 160 mPa*s or less, 140 mPa*s or less, 120 mPa*s or less, 100 mPa*s or less, 80 mPa*s or less, or even 60 mPa*s or less. If the viscosity is too high, the thermally conductive composition will be too viscous to achieve the desired extrusion rate. If the viscosity is too low, the thermally conductive composition risks having silicone migration or bleeding problems, and will have poor mechanical properties after curing and be prone to crumbling.

[0017] The vinyldimethylsiloxy-terminated PDMS useful in the present invention can have the following chemical structure (I): [ka] where "Vi" refers to a vinyl group (-CH=CH2), and n refers to the average number of dimethylsiloxane units, which is the degree of polymerization (DP) of the vinyldimethylsiloxy-terminated PDMS. n is selected to achieve a desired viscosity of the vinyldimethylsiloxy-terminated PDMS. Typically, n is 25 or greater, and can be 30 or greater, 35 or greater, 40 or greater, 45 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, or even 90 or greater, while n is typically 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, 150 or less, 140 or less, 130 or less, 120 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, or even 50 or less.

[0018] Desirably, the vinyldimethylsiloxy-terminated PDMS contains 0.4 to 2.4 wt% vinyl functionality (i.e., vinyl groups), and can be 0.4 wt% or more, 0.5 wt% or more, 0.6 wt% or more, 0.7 wt% or more, 0.8 wt% or more, 0.9 wt% or more, 1.0 wt% or more, 1.1 wt% or more, 1.2 wt% or more, or even 1.25 wt% or more, while generally 2.4 wt% or less, 2.2 wt% or less, 2 wt% or less, 1.6 wt% or less, 1.55 wt% or less, 1.5 wt% or less, 1.4 wt% or less, or even 1.3 wt% or less. The concentration of vinyl functionality can be calculated by 27*2 / Mw, where Mw is the molecular weight of the vinyldimethylsiloxy-terminated PDMS. The Mw of the vinyldimethylsiloxy-terminated PDMS can be calculated using standard 1 H, 13 C, and 29 It can be determined by its chemical structure characterized by Si nuclear magnetic resonance (NMR) analysis.

[0019] Suitable divinyl PDMS materials can be made by ring-opening polymerization of cyclosiloxanes using terminating vinyl endblockers, as taught in U.S. Patent No. 5,883,215(A). Suitable commercially available divinyl PDMS include the polysiloxane available from Gelest under the designation DMS-V21.

[0020] The SiH-functional crosslinker (a2) useful in the present invention can be a polysiloxane containing SiH functionality. Desirably, the SiH-functional crosslinker contains two or more, or even three or more, SiH functionalities per molecule. Preferably, the SiH-functional crosslinker has a concentration of hydrogen atoms (H) as SiH (i.e., the concentration of silicon-bonded hydrogen atoms) of at least 0.1 wt.%, at least 0.2 wt.%, at least 0.3 wt.%, at least 0.4 wt.%, or at least 0.5 wt.%, based on the weight of the SiH-functional crosslinker. It can be at least 0.6 wt.%, at least 0.7 wt.%, at least 0.8 wt.%, or even at least 0.9 wt.%, while generally at most 1.0 wt.%, at most 0.9 wt.%, at most 0.8 wt.%, at most 0.7 wt.%, at most 0.6 wt.%, at most 0.5 wt.%, at most 0.4 wt.%, or even at most 0.3 wt.%. The content of silicon-bonded hydrogen atoms can be determined by NMR analysis.

[0021] The SiH functional crosslinker may desirably comprise one or more polysiloxanes having a chemical structure selected from (II), (III), or a combination thereof: [ka] [ka] wherein the subscript x has a value ranging from 10 to 100, and can be 10 or more, 15 or more, 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, or even 80 or more, while generally being 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, or even 20 or less; The subscript y has a value in the range of 3 to 30 and can be 3 or more, 4 or more, 5 or more, 10 or more, 15 or more, 20 or more, or even 25 or more, while generally 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, or even 4 or less; the subscript z has a value in the range of 3 to 100 and can be 3 or more, 5 or more, 10 or more, 15 or more, 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, or even 80 or more, while generally 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, 20 or less, 10 or less, 5 or less, or even 4 or less.

[0022] Suitable commercially available SiH functional crosslinkers include those available under the designations HMS-071, HMS-301 and DMS-H11, all available from Gelest.

[0023] The hydrosilylation catalyst (a3) ​​useful in the present invention can be any hydrosilylation catalyst. The hydrosilylation catalyst can include a platinum-based catalyst such as Speier's catalyst (HPtCl) and / or Karstedt's catalyst (an organoplatinum compound derived from a divinyl-containing disiloxane and also identified as a platinum-divinyltetramethyldisiloxane complex or a 1,3-diethenyl-1,1,3,3 tetramethyldisiloxane platinum complex). The hydrosilylation catalyst can be encapsulated (typically in a phenyl resin) or non-encapsulated. Exemplary hydrosilylation reaction catalysts are described in U.S. Pat. Nos. 3,159,601 and 3,220,972. The hydrosilylation catalyst is typically present at a concentration of 0.01 wt. % or more, 0.02 wt. % or more, 0.03 wt. % or more, 0.04 wt. % or more, or even 0.05 wt. % or more, based on the weight of the thermally conductive composition, while generally 0.10 wt. % or less, 0.09 wt. % or less, 0.08 wt. % or less, 0.07 wt. % or less, or even 0.06 wt. % or less.

[0024] The thermally conductive compositions of the present invention also include one or more filler treating agents, which include alkyltrialkoxysilanes (B1), mono-trialkoxysiloxy-terminated dimethylpolysiloxanes (B2), or mixtures of (B1) and (B2).

[0025] The alkyltrialkoxysilane can be an alkyltrimethoxysilane. The alkyltrialkoxysilane can be a 6 to 20 carbon (C6 to C8) alkyltrimethoxysilane. 20 ) alkyltrimethoxysilane, C6 to C 12 It may be an alkyltrimethoxysilane, preferably C8-C 12 It may be an alkyltrimethoxysilane, which may be n-decyltrimethoxysilane. Suitable alkyltrialkoxysilanes include n-decyltrimethoxysilane, available from Dow, Inc. as DOWSIL™ Z-6210 silane (DOWSIL is a trademark of The Dow Chemical Company) or from Gelest under the name SID2670.0.

[0026] An example of a suitable mono-trialkoxysiloxy-terminated dimethylpolysiloxane has the chemical structure (IV): [ka] wherein the subscript a has a value in the range of 20 to 150, and can be 20 or more, 30 or more, 40 or more, 50 or more, 60 or more than 30, 70 or more, 80 or more, or even 90 or more, while typically being 150 or less, 140 or less, 130 or less, 120 or less, 110 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, or even 30 or less. R' is an alkyl group, preferably containing 1 to 12 carbon atoms (C1 to C 12 ), most preferably methyl. Desirably, the mono-trialkoxysiloxy-terminated dimethylpolysiloxane is a mono-trimethoxy-terminated dimethylpolysiloxane.

[0027] Suitable mono-trialkoxysiloxy-terminated dimethylpolysiloxanes can be synthesized according to the teachings of US Patent Application Publication No. 2006 / 0100336. Desirably, the mono-trialkoxysiloxy terminated dimethylpolysiloxane is typically present at a concentration of 0.5 wt.% or more, 0.6 wt.% or more, 0.7 wt.% or more, 0.8 wt.% or more, 0.9 wt.% or more, 1.0 wt.% or more, 1.1 wt.% or more, 1.2 wt.% or more, 1.3 wt.% or more, 1.4 wt.% or more, 1.5 wt.% or more, or even 1.6 wt.% or more, based on the weight of the thermally conductive composition, while typically present at a concentration of 3.0 wt.% or less, 2.9 wt.% or less, 2.8 wt.% or less, 2.7 wt.% or less, 2.6 wt.% or less, 2.5 wt.% or less, 2.4 wt.% or less, 2.3 wt.% or less, 2.2 wt.% or less, 2.1 wt.% or less, 2.0 wt.% or less, 1.9 wt.% or less, 1.8 wt.% or less, or even 1.7 wt.% or less. Simultaneously, or alternatively, the alkyltrialkoxysilane can be present in a concentration of 0.05 wt. % or more, 0.1 wt. % or more, 0.2 wt. % or more, 0.3 wt. % or more, or even 0.4 wt. % or more, based on the weight of the thermally conductive composition, while typically being present in a concentration of 0.5 wt. % or less, 0.4 wt. % or less, 0.3 wt. % or less, or even 0.2 wt. % or less.

[0028] The thermally conductive composition of the present invention further comprises a thermally conductive filler mixture (C). The thermally conductive filler mixture (C) contains all of the thermally conductive fillers in the thermally conductive composition. The thermally conductive filler refers to fine particles that promote heat conduction through the thermally conductive composition.

[0029] A thermally conductive filler mixture useful in the present invention comprises an aluminum nitride filler (c1) that comprises a blend of two different aluminum nitride fillers (c1-a) and (c1-b).

[0030] (c1-a) The aluminum nitride filler is a spherical aluminum nitride particle having a D50 particle size of 100 μm or greater. A "spherical" particle is one having an aspect ratio of 1.0 + / - 0.2. Scanning electron microscope (SEM) imaging is used to determine the particle aspect ratio by taking the average ratio of the longest dimension (major axis) to the shortest dimension (minor axis) of at least 10 particles.

[0031] The spherical aluminum nitride particles (c1-a) have a D50 particle size of 100 μm or more, and may be greater than 100 μm, 105 μm or more, 110 μm or more, 115 μm or more, or even 120 μm or more. The spherical aluminum nitride filler (c1-a) may have a D50 particle size of 200 μm or less, 190 μm or less, 180 μm or less, 175 μm or less, 170 μm or less, 160 μm or less, 150 μm or less, 140 μm or less, 130 μm or less, or even 120 μm or less. The spherical aluminum nitride particles (c1-a) may be present in a concentration of 15% to 41% by weight, based on the weight of the thermally conductive composition, and may be 15% by weight or more, 16% by weight or more, 17% by weight or more, 18% by weight or more, 19% by weight or more, 20% by weight or more, 21% by weight or more, 22% by weight or more, 24% by weight or more, 25% by weight or more, 28% by weight or more, 30% by weight or more, or even 32% by weight or more, while typically present in an amount of 41% by weight or less, 40% by weight or less, 39% by weight or less, 38% by weight or less, 37% by weight or less, 36.5% by weight or less, or even 36% by weight or less, preferably 30% to 38% by weight.

[0032] (c1-b) Aluminum nitride filler is a spherical or irregularly shaped aluminum nitride particle having a D50 particle size of 20 to 80 μm. "Irregular" shaped particles have an aspect ratio other than 1.0 + / - 0.2 and have at least three faces evident by SEM imaging (distinguishing them from two-sided "plate" particles). Spherical or irregularly shaped aluminum nitride particles (c1-b) have a D50 particle size of 20 μm or more, 22 μm or more, 25 μm or more, 28 μm or more, 30 μm or more, 32 μm or more, 35 μm or more, 38 μm or more, or even 40 μm or more, while also having a D50 particle size of 80 μm or less, 75 μm or less, 70 μm or less, 65 μm or less, 60 μm or less, 55 μm or less, 50 μm or less, or even 45 μm or less. Desirably, the spherical or irregularly shaped aluminum nitride particles (c1-b) have a D50 particle size of 50 μm to 80 μm. The aluminum nitride particles (c1-b) can be spherical aluminum nitride particles, irregularly shaped aluminum nitride particles, or a mixture thereof. The spherical or irregularly shaped aluminum nitride particles (c1-b) may be present in a concentration of 10 wt.% to 39 wt.%, and may be 10 wt.% or more, 10.5 wt.% or more, 11 wt.% or more, 11.5 wt.% or more, 12 wt.% or more, 12.5 wt.% or more, 13 wt.% or more, 13.5 wt.% or more, 14 wt.% or more, or even 14.5 wt.% or more, while typically being present in a concentration of 39 wt.% or less, 38 wt.% or less, 37 wt.% or less, 36 wt.% or less, 35 wt.% or less, 32 wt.% or less, 30 wt.% or less, 29 wt.% or less, 28 wt.% or less, 25 wt.% or less, 22 wt.% or less, 20 wt.% or less, or even 19 wt.% or less, based on the weight of the thermally conductive composition. Desirably, the spherical or irregularly shaped aluminum nitride particles (c1-b) are present in a concentration of 14% to 20% by weight, based on the weight of the thermally conductive composition.

[0033] Preferably, the blend of aluminum nitride particles is a mixture of 30% to 38% spherical aluminum nitride particles (c1-a) having a D50 size of 100 μm or more and 14% to 20% spherical or irregularly shaped aluminum nitride particles (c1-b) having a D50 size of 50 μm to 80 μm. Alternatively, the blend of aluminum nitride particles can be a mixture of 30% to 38% spherical aluminum nitride particles (c1-a) having a D50 size of 100 μm or more and 14% to 20% spherical or irregularly shaped aluminum nitride particles (c1-b) having a D50 size of 20 μm to 40 μm.

[0034] The concentration of aluminum nitride filler (c1) from this blend, desirably as the sum of (c1-a) and (c1-b), more desirably as the sum of any and all aluminum nitride fillers in the thermally conductive composition, is 40% to 55% by weight, based on the weight of the thermally conductive composition, and can be 40% by weight or more, 41% by weight or more, 42% by weight or more, 43% by weight or more, 44% by weight or more, 45% by weight or more, 46% by weight or more, 47% by weight or more, 48% by weight or more, 49% by weight or more, or even 50% by weight or more, while generally is 55% by weight or less, 54% by weight or less, 53% by weight or less, 52% by weight or less, or even 51% by weight or less, and can be 45% by weight to 55% by weight.

[0035] The spherical aluminum nitride particles in this blend are typically present in a concentration of greater than 60 wt. %, e.g., 61 wt. % or more, 62 wt. % or more, 64 wt. % or more, 65 wt. % or more, 66 wt. % or more, 68 wt. % or more, 70 wt. % or more, 71 wt. % or more, 73 wt. % or more, 75 wt. % or more, 76 wt. % or more, 78 wt. % or more, or even 80 wt. % or more, based on the total weight of the blend (i.e., the total weight of aluminum nitride particles (c1-a) and (c1-b)), and can also be present in a concentration of 100 wt. % or less, e.g., 98 wt. % or less, 95 wt. % or less, 92 wt. % or less, 90 wt. % or less, 88 wt. % or less, 85 wt. % or less, or even 82 wt. % or less. Desirably, the spherical aluminum nitride particles having a D50 particle size of 20 μm or greater are present in the same concentration as described herein, based on the total weight of aluminum nitride fillers having a D50 particle size of 20 μm or greater in the thermally conductive composition. Concurrently, or alternatively, the spherical aluminum nitride particles having a D50 particle size of 30 μm or greater are at the same concentration as described herein, based on the total weight of the aluminum nitride fillers having a D50 particle size of 30 μm or greater in the thermally conductive composition.

[0036] The thermally conductive composition of the present invention may have additional aluminum nitride particles (c1-c) in addition to this particular blend of aluminum nitride particles (c1-a) and (c1-b) described above, or the thermally conductive composition may not contain additional aluminum nitride particles (c1-c) in addition to this particular blend of aluminum nitride particles (c1-a) and (c1-b) described above.

[0037] The thermally conductive filler mixture useful in the present invention further comprises spherical aluminum oxide particles (c2). The spherical aluminum oxide particles (c2) have a D50 particle size of 1 μm or more, and can be 1.2 μm or more, 1.5 μm or more, 1.8 μm or more, or even 2 μm or more, while typically having a D50 particle size of 5 μm or less, 4.8 μm or less, 4.5 μm or less, 4.2 μm or less, 4 μm or less, 3.8 μm or less, 3.5 μm or less, 3.2 μm or less, 3 μm or less, 2.8 μm or less, or even 2.5 μm or less. The spherical aluminum oxide particles (c2) may be present in an amount of 27% by weight or more, 28% by weight or more, 29% by weight or more, or even 30% by weight or more, based on the weight of the thermally conductive composition, while generally being present in a concentration of 41% by weight or less, 40% by weight or less, 39% by weight or less, 38% by weight or less, 37% by weight or less, 36% by weight or less, 35% by weight or less, 33% by weight or less, 32% by weight or less, or even 31% by weight or less.

[0038] The thermally conductive filler mixture useful in the present invention further comprises irregularly shaped zinc oxide particles (c3). The irregularly shaped zinc oxide particles have a D50 particle size of 0.1 μm to 0.5 μm, and can be 0.1 μm or more, 0.11 μm or more, or even 0.12 μm or more, while typically having a D50 particle size of 0.5 μm or less, 0.45 μm or less, 0.4 μm or less, 0.35 μm or less, 0.3 μm or less, 0.25 μm or less, 0.2 μm or less, or even 0.15 μm or less. The irregularly shaped zinc oxide particles (c3) may be present in a concentration of 10% to 20% by weight, and may be 11% by weight or more, 12% by weight or more, 13% by weight or more, or even 14% by weight or more, based on the weight of the thermally conductive composition, while typically being present in a concentration of 20% by weight or less, 19% by weight or less, 18% by weight or less, 17% by weight or less, 16% by weight or less, 15% by weight or less, or even 14.5% by weight or less.

[0039] The thermally conductive filler mixture may include one or more additional thermally conductive fillers (c4) in addition to those mentioned, or may include no additional thermally conductive fillers other than those mentioned (e.g., (c1-a), (c1-b), (c2), and (c3)). The additional thermally conductive fillers may include metal nitrides and metal oxides other than the above (c1-a), (c1-b), (c2), and (c3), such as additional aluminum nitride particles (c1-c), boron nitride, magnesium oxide, or mixtures thereof.

[0040] The additional aluminum nitride particles (c1-c) useful in the present invention may have a D50 particle size of less than 20 μm, for example, 18 μm or less, 15 μm or less, 12 μm or less, 10 μm or less, 8 μm or less, or even 5 μm or less, while having a D50 particle size of 1 μm or more, 1.5 μm or more, 2 μm or more, 3 μm or more, or even 4 μm or more. The concentration of the additional aluminum nitride particles (c1-c) may be zero to 10 wt.%, for example, 8 wt.% or less, 7 wt.% or less, 5 wt.% or less, 4 wt.% or less, 3 wt.% or less, or even 2 wt.% or less, based on the weight of the thermally conductive composition, while typically being 0.5 wt.% or more, 1 wt.% or less, or even 1.5 wt.% or more.

[0041] Boron nitride fillers useful in the present invention typically have a D50 particle size of greater than 20 μm, for example, 30 μm or more, 40 μm or more, 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, 100 μm or more, or even 110 μm or more, while having a D50 particle size of 200 μm or less, 175 μm or less, 160 μm or less, 150 μm or less, 140 μm or less, 130 μm or less, or even 125 μm or less. The boron nitride filler may be present in an amount of zero to 5 wt.%, for example, 4.5 wt.% or less, 4 wt.% or less, 3.5 wt.% or less, 3 wt.% or less, less than 2.1 wt.%, less than 2.0 wt.%, less than 1.6 wt.%, less than 1.5 wt.%, less than 1.2 wt.%, less than 1 wt.%, less than 0.9 wt.%, less than 0.8 wt.%, less than 0.7 wt.%, less than 0.6 wt.%, less than 0.5 wt.%, less than 0.4 wt.%, less than 0.3 wt.%, less than 0.2 wt.%, less than 0.1 wt.%, or even zero, based on the weight of the thermally conductive composition, and may be zero to less than 1 wt.%.

[0042] Magnesium oxide fillers useful in the present invention typically have a D50 particle size of 50 μm or more, 60 μm or more, 70 μm or more, 90 μm or more, or even 120 μm or more, and may simultaneously have a D50 particle size of 150 μm or less, 140 μm or less, or even 130 μm or less. The magnesium oxide filler may be present in an amount of zero to 20 wt. %, for example, 20 wt. % or less, 18 wt. % or less, 16 wt. % or less, 14 wt. % or less, 12 wt. % or less, or even 10 wt. % or less, based on the weight of the thermally conductive composition.

[0043] The total concentration of the additional thermally conductive filler (c4) comprising or consisting of additional aluminum nitride particles (c1-c), boron nitride, magnesium oxide, or mixtures thereof, can be zero to 20 wt. %, for example, 20 wt. %, 18 wt. % or less, 15 wt. % or less, 12 wt. % or less, or even 11 wt. % or less, based on the weight of the thermally conductive composition.

[0044] The thermally conductive filler mixture in the thermally conductive composition desirably consists of aluminum nitride fillers (c1-a) and (c1-b), spherical aluminum oxide particles (c2), and irregularly shaped zinc oxide (c3). The thermally conductive filler mixture (and the thermally conductive composition as a whole) may be free of magnesium oxide fillers, boron nitride fillers, additional aluminum nitride particles (c1-c), or any combination thereof.

[0045] The concentration of the thermally conductive filler mixture in the thermally conductive composition is generally 97 wt.% or less, 96.9 wt.% or less, 96.8 wt.% or less, 96.7 wt.% or less, 96.6 wt.% or less, 96.5 wt.% or less, 96.4 wt.% or less, 96.3 wt.% or less, 96.2 wt.% or less, 96.1 wt.% or less, or even 96 wt.% or less, based on the weight of the thermally conductive composition.

[0046] The thermally conductive compositions of the present invention may or may not contain one or more inhibitors (hydrosilylation reaction inhibitors) useful for modifying the reaction rate between silicon-bonded hydrogen atoms in the composition and vinyl groups, compared to the reaction rate of the same composition without the inhibitor. Examples of suitable inhibitors include acetylenic compounds such as 2-methyl-3-butyn-2-ol, 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, 3-phenyl-1-butyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,1-dimethyl-2-propynyl)oxy)trimethylsilane, and methyl(tris(1,1-dimethyl-2-propynyloxy))silane; 3-methyl-3-penten-1-yne, and 3,5-dimethyl The reaction may be subjected to one or more further steps including one or more ene-yne ​​compounds such as benzotriazole, triazoles such as benzotriazole, hydrazine-based compounds, phosphine-based compounds, mercaptan-based compounds, cycloalkenylsiloxanes including methylvinylcyclosiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane, or combinations thereof. The inhibitor may be present in an amount of zero to 0.3 wt.%, and may be 0.0001 wt.% or more, 0.001 wt.% or more, 0.002 wt.% or more, 0.005 wt.% or more, or even 0.01 wt.% or more, while generally being 0.3 wt.% or less, 0.2 wt.% or less, 0.1 wt.% or less, 0.05 wt.% or less, or even 0.03 wt.% or less, based on the weight of the thermally conductive composition.

[0047] The thermally conductive composition of the present invention may further comprise any one, or any combination of two or more of the following additional components: a thermal stabilizer and / or pigment (such as copper phthalocyanine powder), a thixotropic agent, fumed silica (preferably surface-treated), and a spacer additive (such as glass beads). The total concentration of these additional components may range from zero to 2% by weight, and may be zero or more, 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, or even 0.5% or more, while typically being 2% or less by weight, 1.9% or less, 1.8% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.2% or less, 1% or less, 0.8% or less, or even 0.6% or less.

[0048] The thermally conductive compositions of the present invention achieve extrusion rates of greater than 60 g / min. Herein, extrusion rates are determined using a standard 30 cubic centimeter EFD syringe package at 0.62 megapascals (90 pounds per square inch) pressure (further details are provided below in Extrusion Rate Characterization). Thermally conducive compositions can have extrusion rates of 65 g / min or greater, 68 g / min or greater, 70 g / min or greater, 72 g / min or greater, 75 g / min or greater, 78 g / min or greater, or even 80 g / min or greater. ER is a useful property as a measure of extrudability, viscosity, dispensability, and usability, allowing the thermally conductive composition to be easily dispensed for application onto another material, such as an electronic component or heat sink. At the same time, the thermally conductive compositions of the present invention provide a thermal conductivity of at least 9.0 W / m*K, as measured according to ASTM D5470-06 using a LonGwin Model LW 9389 TIM Thermal Resistance and Conductivity Measuring Instrument. Such high thermal conductivity and ease of disposability make the thermally conductive composition particularly useful as a thermal interface material (TIM). A TIM is used to thermally couple two items or components of a device. For example, TIMs are useful, particularly in electronic devices, for thermally coupling a heat-generating device to a heat sink, cooling plate, metal cover, or other heat-dissipating component. In such applications, the thermally conductive composition is present between and in thermal contact with at least two components, typically a heat-generating device and at least one of a heat sink, cooling plate, metal cover, or other heat-dissipating component. [Example]

[0049] Some embodiments of the present invention will now be described in the following examples, where all weight percentages are by weight of the thermally conductive composition and all particle sizes of fillers are D50 particle sizes unless otherwise specified. Table 1 shows materials for use in the sample thermally conductive compositions described herein below. Note: "Vi" refers to a vinyl group. "Me" refers to a methyl group. SYL-OFF and DOWSIL are trademarks of The Dow Chemical Company. [Table 1] *The viscosity of polysiloxane was measured by ASTM D445-21. "TC filler" refers to thermally conductive filler. "Fractured" particles are particles having one or more sharp, angular fracture surfaces; in this specification, fractured particles also refers to irregularly shaped particles.

[0050] IE1-11 and CE1-16 samples The sample formulations are shown in Tables 2 and 3, with the amount of each component reported in grams (g).

[0051] The samples were prepared by mixing the components together using a SpeedMixer™ DAC 400 FVZ mixer from FlackTek Inc. (South Carolina, USA). The Vi polymer, crosslinker, treating agent, and C2 and C3 TC fillers were added to the SpeedMixer cup. Mixing was continued at 1000 revolutions per minute (RPM) for 20 seconds, then at 1500 RPM for 20 seconds. Half of the C1 TC filler was then added and mixed at 1000 revolutions per minute (RPM) for 20 seconds, then at 1500 RPM for 20 seconds. The remaining C1 TC filler was added, followed by the C4-1 TC filler, if present, and mixed in the same manner. The resulting composition in the cup was scraped to ensure mixing, and then the inhibitor E-1, pigment F-1, and catalyst D-1 were added and mixed in the same manner to obtain the thermally conductive composition sample. The resulting thermally conductive composition samples were evaluated for extrusion speed and thermal conductivity according to the following test methods.

[0052] Extrusion speed characterization The extrusion rate ("ER") of the sample is measured using a Nordson EFD dispensing device. The sample material is packaged in a 30 cubic centimeter syringe (EFD syringe from Nordson Company) with a 2.54 millimeter (mm) opening. The sample is dispensed through the opening by applying a pressure of 0.62 MPa to the syringe. The mass (grams) of sample extruded after 1 minute corresponds to the extrusion rate (grams / minute). The objective of the present invention is to achieve an extrusion rate of greater than 60 g / minute, preferably 65 g / minute or greater, more preferably 70 g / minute or greater, and even more preferably 75 g / minute or greater.

[0053] In particular, some samples were reported to have an ER of 0 (thermal conductivity was not measured) because they were powdered pastes that could not be extruded.

[0054] Thermal conductivity characterization A LonGwin Model LW 9389 TIM Thermal Resistance and Conductivity Measuring Instrument from LonGwin Science and Technology Corporation, Taiwan, is used to determine thermal conductivity ("TC") in accordance with ASTM D5470-06. The objective of the present invention is to achieve a thermal conductivity (also designated "TC-LonGwin") of at least 9.0 Watts / meter*Kelvin (W / m*K).

[0055] Thermally conductive composition samples (uncured samples) were applied between a guarded central hot plate and a cold plate when operated at 80°C for 12 minutes. A pressure of 275.8 kilopascals (40 pounds per square inch) was applied to keep the sample in contact with the plates. Thermal impedance was measured at different bond-line thicknesses (BLT) (0.5 mm, 1.0 mm, and 2.0 mm). By fitting a linear equation to the thermal impedance versus BLT, bulk thermal conductivity (denoted as "K") was calculated by K = 10 / slope and reported as "TC-LonGwin" in Tables 2 and 3.

[0056] As shown in Table 2, all of the samples in Examples 1-11 achieved both the requirements of an ER of more than 60 g / min and a TC of more than 9.0 W / m*K. In particular, Examples 1-10 exhibited even higher ER of 75 g / min or more.

[0057] In contrast, the samples shown in Table 3 failed to achieve at least one of the TC and ER requirements.

[0058] The CE1 sample, which used a combination of AlN particles (D50=80 μm) and spherical MgO (D50=60 μm) instead of a combination of at least two types of AlN particles with specific particle sizes, provided a TC of less than 9.0 W / m*K.

[0059] The CE2 sample, which used a combination of AlN particles (D50 = 80 μm), irregular AlN particles (D50 = 60 μm), irregularly shaped Al2O3 particles (D50 = 2 μm), and spherical Al2O3 particles (D50 = 10 μm) as the TC filler, was a powdery paste that could not be extruded.

[0060] The CE3 sample using AlN particles (D50 = 80 μm) and spherical Al2O3 particles of different sizes (2 μm and 0.3 μm, respectively) gave a TC of less than 9.0 W / m*K.

[0061] The CE4 sample containing spherical AlN particles (D50=80 μm) with irregular AlN particles (D50=70 μm) instead of spherical AlN particles with D50 of 100 μm or more provided both a low ER and a lower TC.

[0062] The CE5 samples containing spherical AlN particles (D50 = 80 μm), spherical MgO particles (D50 = 120), and spherical Al2O3 particles with different particle sizes (D50 = 2 μm and 0.3 μm, respectively) as TC fillers provided both low ER and low TC.

[0063] Compared to Example 2, replacing spherical Al2O3 particles with irregularly shaped Al2O3 particles having a D50 of 2 μm (CE6 sample), replacing irregular ZnO particles (D50=0.2 μm) with spherical or irregularly shaped Al2O3 (CE7 and CE8 samples), or replacing spherical AlN with a D50 of 120 μm with irregularly shaped AlN with a D50 of 100 μm (CE9) all resulted in lower ER.

[0064] CE10, which contains only one type of AlN particles with a D50 of 80 μm, still could not meet the TC requirement of TC above 9.0 W / m*K even with the addition of 2.1% BN particles.

[0065] Both samples CE11 and CE14, which contain a mixture of AlN particles with two different particle sizes but with AlN particles having a D50 particle size of 100 μm or larger at concentrations of 45 wt % and 10 wt %, respectively, failed to meet at least one of the ER and TC requirements.

[0066] The CE12 and CE13 samples demonstrate that a total concentration of AlN filler less than 40% provided undesirably low TC, while a total content of AlN filler >55 wt % resulted in low ER.

[0067] The CE15 sample, which contained only one type of AlN filler, i.e., irregularly shaped AlN particles with a D50 of 20 μm, was a powdery paste that could not be extruded. The CE16 sample, which contained only spherical AlN particles with a D50 of 100 μm as the AlN filler, provided an ER of less than 60 g / min. [Table 2] Note: In this Table 2 and Table 3 below: "SiH / Vi ratio" refers to the molar ratio of SiH functionality to vinyl functionality from the crosslinker. "Spherical large AlN wt%" refers to the weight percent of spherical AlN fillers with a D50 ≥ 100 μm relative to the total weight of all components in the sample. "Small AlN wt%" refers to the weight percent of AlN fillers with a D50 between 20 and 80 μm relative to the total weight of all components in the sample. "ER" and "TC-LonGwin" (also "TC") were measured according to the test methods described above. "TC-Hot Disk" refers to thermal conductivity measured by using a hot disk in accordance with ISO 22007-2. The thermal conductivity of the cured samples was measured by a hot disk TPS 2500 S instrument equipped with a 3.189 mm Kapton sensor (Model 5465). The cured samples were prepared by curing thermally conductive composition samples having dimensions of 25 mm x 25 mm x 8 mm at 120°C for 60 minutes. [Table 3]

Claims

1. A thermally conductive composition comprising: (A) a curable silicone composition, (a1) a vinyldimethylsiloxy-terminated polydimethylpolysiloxane having a viscosity in the range of 30 to 400 mPascal*seconds; (a2) a silicon hydride functional crosslinker; and (a3) a hydrosilylation catalyst; a curable silicone composition having a molar ratio of silicon hydride functionality to vinyl functionality from said crosslinker in the range of 0.5:1 to 1:1; (B) a filler treating agent comprising one or both of an alkyltrialkoxysilane and a mono-trialkoxysiloxy-terminated dimethylpolysiloxane; and (C) a thermally conductive filler mixture, based on the weight of the thermally conductive composition, (c1) 40 weight percent to 55 weight percent aluminum nitride filler; (c1-a) 15 weight percent to 41 weight percent spherical aluminum nitride particles having a D50 particle size of 100 micrometers or greater; (c1-b) an aluminum nitride filler comprising a blend of 10 weight percent to 39 weight percent of spherical or irregularly shaped aluminum nitride particles having a D50 particle size of 20 to 80 micrometers; (c2) 27 weight percent to 41 weight percent spherical aluminum oxide particles having a D50 particle size of 1 to 5 micrometers; (c3) 10 weight percent to 20 weight percent of irregular zinc oxide particles having a D50 particle size of 0.1 to 0.5 micrometers; and A thermally conductive composition, wherein the total amount of the thermally conductive filler mixture is 94 weight percent to 97 weight percent based on the weight of the thermally conductive composition.

2. 10. The thermally conductive composition of claim 1, wherein the spherical or irregularly shaped aluminum nitride particles (c1-b) having a D50 particle size of 20 to 80 micrometers are present in a concentration of 10 weight percent to 38 weight percent, based on the weight of the thermally conductive composition.

3. 3. The thermally conductive composition of claim 1, wherein the spherical aluminum nitride particles in the blend are in a total concentration of greater than 60 weight percent to 100 weight percent, based on the total weight of the blend of the aluminum nitride particles (c1-a) and (c1-b).

4. 4. The thermally conductive composition of claim 1, wherein the thermally conductive filler mixture (C) comprises zero to less than 1 weight percent boron nitride filler, based on the weight of the thermally conductive composition.

5. The thermally conductive composition according to any one of claims 1 to 4, wherein the spherical aluminum nitride particles (c1-a) have a D50 particle size of 120 micrometers or more.

6. 6. The thermally conductive composition of claim 1, wherein the spherical aluminum nitride particles (c1-a) having a D50 particle size of 100 micrometers or greater are present in a concentration of 30 weight percent to 38 weight percent, based on the weight of the thermally conductive composition.

7. 7. The thermally conductive composition of claim 1, wherein the aluminum nitride filler (c1) is present in a concentration of 45 weight percent to 55 weight percent, based on the weight of the thermally conductive composition.

8. the silicon hydride functional crosslinker comprises one or more polysiloxanes having a chemical structure selected from (II), (III), or a combination thereof; 【Chemistry 1】 【Chemistry 2】 8. The thermally conductive composition of claim 1, wherein subscript x has a value in the range of 10 to 100, subscript y has a value in the range of 3 to 30, and subscript z has a value in the range of 3 to 100.

9. The alkyltrialkoxysilane is C ６ ~C １２ alkyltrimethoxysilanes, wherein the mono-trialkoxysiloxy-terminated dimethylpolysiloxane has the average chemical structure (IV): 【Transformation 3】 wherein the subscript a has a value ranging from 20 to 150 and R′ is C １ ~C １２ The thermally conductive composition according to any one of claims 1 to 8, wherein the group is an alkyl group.

10. An article comprising the thermally conductive composition of any one of claims 1 to 9 on another material.

11. 11. The article of claim 10, wherein the thermally conductive composition is between and in thermal contact with a heat-generating component of an electronic device and one or more of a heat sink, a cooling plate, and a metal cover of the electronic device.

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