Patent Application
20250122342
The present invention relates to curable thermally conductive compositions that contain thermally conductive fillers including diamond particles having a Dv50 particle size in a range of 60 to 150 micrometers.
An industry drive to smaller and more powerful electronic devices has increased demands on thermally conductive compositions useful for dissipating heat generated in such devices. For instance, the telecommunications industry is going through a generational shift to 5G networks, which demand highly integrated electrical devices with smaller sizes and that brings a requirement for double the power requirements (1200 Watts from 600 Watts). The heat generated by the high power in the smaller devices would damage the device if not efficiently dissipated. Thermally conductive interface materials are often used in electronics to thermally couple heat generating components and heat dissipating components.
A challenge with thermally conductive interface materials is to provide a combination of both high thermal conductivity properties while being easily extrudable so as to allow precise application of the thermally conductive material on small components. In particular, it is desirably to provide a thermally conductive interface material that has an extrusion rate of greater than 60 grams per minute as measured using the Extrusion Rate Test defined herein below and that cures to a material that has a thermal conductivity of at least 8 Watts per meter*Kelvin. Thermal conductivity can be increased by increasing the amount of thermally conductive filler, but that also reduces the extrusion rate for a composition. So meeting these two performance parameters is particularly challenging.
The present invention provides a thermally conductive interface material that has an extrusion rate of greater than 60 grams per minute (g/min) as measured using the Extrusion Rate Test defined herein below and that cures to a material that has a thermal conductivity of at least 8 Watts per meter*Kelvin (W/m*K).
Surprisingly, it has been determined such a composition can be prepared from a curable polysiloxane composition that contains 94 to 97 weight-percent (wt %) thermally conductive filler that includes 30 to 55 weight-percent (wt %) diamond particles having a Dv50 in a range of 60 to 150 micrometers, where wt % is relative to curable polysiloxane composition weight.
In a first aspect, the present invention is a curable thermally conductive composition comprising: (a) a vinyl-functional silicone polymer that is one or a combination of more than one vinyldimethyl terminated polydimethylsiloxane, the vinyl-functional silicone polymer having a viscosity in a range of 30 to 2000 millipascal*seconds as determined by ASTM D445-21 using a glass capillary Cannon-Fenske type viscometer at 25 degrees Celsius at a concentration in a range of one to 4.0 weight-percent; (b) at least one silyl-hydride functional polysiloxane crosslinker that contains at least two silyl-hydride groups per molecule and that is present at a concentration to provide a molar ratio of silyl-hydride groups to vinyl groups for the composition that is in a range of 0.5 to 1.0; (c) filler treating agents at a concentration in a range of 0.1 to 2.0 weight-percent, the filler treating agents comprising any one or any combination of more than one trialkoxysilyl compound; (d) thermally conductive filler at a concentration in a range of 94 to 97 weight-percent, where the thermally conductive filler comprises: (i) diamond particles having a Dv50 in a range of 60 to 150 micrometers at a concentration in a range of 30 to 55 weight-percent; (ii) thermally conductive fillers having a Dv50 in a range of greater than one to 10 micrometers at a concentration in a range of 25 to 35 weight-percent; (iii) thermally conductive fillers having a Dv50 in a range of 0.1 to one micrometers at a concentration in a range of 10 to 20 weight-percent; and (iv) optionally, thermally conductive filler having a Dv50 in a range of 20 to 60 micrometers at a concentration in a range of zero to 20 weight-percent; where weight-percentages are relative to curable thermally conductive composition weight.
In a second aspect, the present invention is a process for using the curable thermally conductive composition of the first aspect, the process comprising applying the curable thermally conductive composition between and in contact with two components and then heating the curable composition to cure the curable composition while in place between the components
In a third aspect, the present invention is an article comprising the curable thermally conductive composition of the first aspect between and in contact with two components of the article, wherein the curable thermally conductive composition is in either a cured or non-cured form.
The composition of the present invention is useful as a thermally conductive interface material to efficiently transfer heat between two components. The process of the present invention is useful to applying the composition of the present invention. The article of the present invention is useful as a device benefiting from efficient thermal conduction between components.
Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain 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; EN refers to European Norm; DIN refers to Deutsches Institut für Normung; ISO refers to International Organization for Standards; and UL refers to Underwriters Laboratory.
Products identified by their tradename refer to the compositions available under those tradenames on the priority date of this document.
“Multiple” means two or more. “And/or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated.
Determine particle size (which is used interchangeable with “average particle size” and “Dv50”) as the volume-weighted median value of particle diameter distribution (Dv50) using a Mastersizer™ (trademark of Malvern Instruments Limited) 3000 laser diffraction particle size analyzer from Malvern Instruments.
Determine viscosity, unless otherwise stated, according to ASTM D445-21 using a glass capillary Cannon-Fenske type viscometer at 25 degrees Celsius.
Measure thermal conductivity for cured composition samples using a Hot Disk TPS 2500 S instrument that meets ISO 22007-2 with cured samples. The sensor is model 5465 (3.189 millimeter Kapton sensor). Prepare cured samples for thermal conductivity evaluation by curing samples having dimensions of 25 millimeters by 25 millimeters square by 8 millimeters thick at 120 degrees Celsius (° C.) for 60 minutes.
Measure extrusion rate (ER) for a composition using the following Extrusion Rate Test using Nordson EFD dispensing equipment. Package a sample composition into a 30 milliliter syringe with a 2.54 millimeter opening (EFD syringe from Nordson Company). Dispense the sample through the opening by applying a pressure of 0.62 MegaPascals to the syringe plunger. Record the mass of the sample in grams that is expelled through the 2.54 millimeter opening during the course of one minute to obtain an extrusion rate value in grams per minute (g/min).
The present invention, in one aspect, is a curable thermally conductive composition. In that regard, it is a “curable composition”. A curable composition can undergo a crosslinking reaction (“curing”). In the present composition, the crosslinking reaction is a hydrosilylation reaction between vinyl-functional silicone polymer components and silyl-hydride (Si—H) functional polysiloxane crosslinker.
The vinyl-functional silicone polymer comprises, or consists of, one or any combination of more than one vinyldimethyl terminated polydimethylsiloxane provided the vinyl-functional silicone polymer has a viscosity in a range of 30 to 2000 millipascal*seconds (mPa*s). When the vinyl-functional silicone polymer is a combination of more than one vinyldimethyl terminated polydimethylsiloxane then the viscosity is the combined viscosity of vinyldimethyl terminated polydimethylsiloxanes. The viscosity of the vinyl-functional silicone polymer is 30 mPa*s or more, and can be 40 mPa*s or more, 50 mPa*s or more, 60 mPa*s or more, 70 mPa*s or more, 75 mPa*s or more, 78 mPa*s or more, 80 mPa*s or more, 100 mPa*s or more, 125 mPa*s or more, 150 mPa*s or more, 175 mPa*s or more, even 200 mPa*s or more, while at the same time is 2000 mPa*s or less, 1500 mPa*s or less, 1000 mPa*s or less, 500 mPa*s or less, and desirably is 400 mPa*s or less, 300 mPa*s or less, 200 mPa*s or less, 150 mPa*s or less, 100 mPa*s or less, 90 mPa*s or less, even 80 mPa*s or less.
Each vinyldimethyl terminated polydimethylsiloxane can have an average chemical structure (I):
Vi(CH3)2SiO—((CH3)2SiO)d—Si(CH3)2Vi (I)
where subscript d is the average number of ((CH3)2SiO) groups per molecule and has a value of 25 or more, 30 or more, 40 or more, 50 or more, 60 or more 70 or more, 80 or more, 90 or more, 100 or more, 120 or more, 140 or more, 160 or more, 180 or more, 200 or more, 220 or more, 240 or more, 260 or more, 280 or more, 300 or more, 320 or more, even 340 or more, and at the same time 350 or less, 340 or less, 320 or less, 300 or less, 280 or less, 260 or less, 240 or less, 240 or less, 220 or less, 200 or less, 180 or less, 160 or less, 140 or less, 120 or less, 100 or less, 80 or less, 60 or less, even 40 or less. For example, the vinyl-functional silicone polymer can be a vinyldimethyl terminated polydimethylsiloxane having a viscosity of 78 mPa*s and containing 1.25 weight-percent (wt %) vinyl groups relative to molecular weight such as that available from Gelest under the name SMS-V21.
The concentration of vinyl-functional silicone polymer is one wt % or more and can be 2.0 wt % or more, 2.5 wt % or more, 2.7 wt % or more, even 3.0 wt % or more while at the same time is 4.0 wt % or less and can be 3.5 wt % or less, even 3.3 wt % or less relative to curable thermally conductive composition weight.
The curable thermally conductive composition further comprises at least one silyl-hydride (SiH) functional polysiloxane crosslinker. The SiH functional crosslinker contains at least two SiH groups per molecule. The SiH groups can be pendant, terminal or a combination of both pendant and terminal. “Terminal” groups are on end siloxane groups of a molecule. “End” siloxane groups are attached to only one other siloxane group. “Pendant” groups are on interior siloxane group—siloxane groups bound to at least two other siloxane groups—of the molecule. “Siloxane group” is a group containing SiO that is bound to another Si through the oxygen of the SiO.
The SiH functional polysiloxane crosslinker can have an average chemical structure (II):
R(3-h)HhSiO—(HRSiO)a—(R2SiO)b-SiHh′R(3-h′) (II)
where:
The SiH functional polysiloxane crosslinker can be one or a combination of both polymers selected from a group consisting of: (i) trimethyl terminated dimethyl-co-hydrogen methyl polysiloxane with a viscosity of 14 millipascals*seconds and containing 0.36 weight-percent hydrogen in silylhydride groups; and (ii) hydride terminated polydimethylsiloxane having a viscosity in a range of 7-10 millipascals*seconds and containing 0.16 weight-percent hydrogen in silylhydride groups.
The concentration of SiH functional polysiloxane crosslinker is sufficient to provide a molar ratio of SiH groups to vinyl groups (SiH/Vi ratio) that is 0.5 or higher, and can be 0.6 or higher, 0.7 or higher, 0.8 or higher, even 0.9 or higher while at the same time is 1.0 or less and can be 0.9 or less, 0.8 or less, 0.7 or less, or even 0.6 or less. The SiH/Vi ratio determines the extent of crosslinking that occurs when the curable thermally conductive composition cures. If the SiH/vinyl ratio is too low, then the composition does not cure enough to provide sufficient vertical stability. If the SiH/vinyl ratio is too high then the composition cures so much it becomes brittle and tends to suffer from surface cracking.
The curable thermally conductive composition comprises filler treating agents. Filler treating agents are trialkoxysilyl compounds, which are compounds that contain a —Si(OR)3 group, where each R is independently in each occurrence as described for R herein above.
The filler treating agent is desirably one or any combination of more than one component selected from a group consisting of alkyl trialkoxysilanes and mono-trialkoxysiloxy terminated diorganopolysiloxanes.
Suitable alkyl trialkoxysilanes include those having the chemical formula Ra(RbO)3Si where each of Ra and Rb is independently in each occurrence an alkyl having 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more even 11 or more carbon atoms while at the same time typically contains 20 or fewer, 18 or fewer, 16 or fewer, 14 or fewer, 12 or fewer, and can contain 10 or fewer carbon atoms. Rb is desirably methyl so as to form methoxyl groups attached to the silicon atom. A particularly desirably alkyltrialkoxysilane is n-decyltrimethoxysilane.
Suitable monotrialkoxysiloxy-terminated diorganopolysiloxanes include those having the average chemical formula Rc3SiO[Rd2SiO]gSi(ORc)3 where each Rc, Rd and Rc is independently in each occurrence selected from hydrocarbyls having one or more, and can have 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, even 8 or more carbon atoms while at the same time typically contain 10 or fewer, 8 or fewer, 6 or fewer, 4 or fewer, even 2 or fewer carbon atoms and subscript g typically has a value of 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, even 110 or more while at the same time typically has a value of 200 of less, 150 or less, 125 or less, 120 or less, or even 110 or less. A particularly desirable monotrialkoxysiloxy-terminated diorganopolysiloxane has the average chemical formula
(CH3)3SiO[(CH3)2SiO]3OSi(OCH3)3.
The concentration of filler treating agent is 0.1 wt % or more, 0.2 wt % of more, 0.3 wt % or more, 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, 1.2 or more, 1.3 wt % or more, even 1.4 or more while at the same time is typically 2.0 wt % or less, 1.8 wt % or less, 1.6 wt % or less, 1.4 wt % or less, 1.3 or less, or even 1.2 or less, with wt % relative to curable composition weight.
For example, the curable composition can comprise any one or any combination of n-decyltrimethoxysilane and (CH3)3SiO[(CH3)2SiO]3OSi(OCH3)3. Preferably, the curable composition can comprise of 0.2 weight-percent n-decyltrimethoxy silane and 0.10-0.12 weight-percent of monotrimethoxysiloxy and trimethylsiloxy terminated polydimethylsiloxane having an average chemical structure
(CH3)3SiO[(CH3)2SiO]3OSi(OCH3)3.
The curable thermally conductive composition further comprises thermally conductive filler. The concentration of thermally conductive filler is 94 wt % or more, and can be 94.5 wt % or more, 95 wt % or more, even 95.5 wt % or more while at the same time is typically 97 wt % or less, and can be 96 wt % or less, 95.5 wt % or less, even 95 wt % or less with wt % relative to curable composition weight.
The thermally conductive filler comprises, and can consist of, a combination of at least three, optionally four, different thermally conductive fillers.
The first thermally conductive filler is diamond particles having a Dv50 of 60 micrometers or more, and can have a Dv50 of 70 micrometers or more, 80 micrometers or more, 90 micrometers or more, 100 micrometers or more, 110 micrometers or more, 120 micrometers or more, 130 micrometers or more, even 140 micrometers or more while at the same time have a Dv50 of 150 micrometers or less, and can have a Dv50 of 140 micrometers or less, 130 micrometers or less, 120 micrometers or less, 110 micrometers or less, 100 micrometers or less, 90 micrometers or less, 80 micrometers or less, or even 70 micrometers or less. The concentration of the first thermally conductive filler is 30 wt % or more, 34 wt % or more, and can be 35 wt % or more, 40 wt % or more, even 50 wt % or more while at the same time is 55 wt % or less, and can be 50 wt % or less, 45 wt % or less, 40 wt % or less, or even 35 wt % or less with wt % relative to curable thermally conductive composition weight.
The second thermally conductive filler has a Dv50 of one micrometer or more and can have a Dv50 of 2 micrometers or more, 3 micrometers or more, 4 micrometers or more, even 5 micrometers or more while at the same time have a Dv50 of 10 micrometers or less, and can have a Dv50 of 9 micrometers or less, 8 micrometers or less, 7 micrometers or less, 6 micrometers or less, or even 5 micrometers or less. The concentration of the second thermally conductive filler is 25 wt % or more and can be 26 wt % or more, 28 wt % or more, 30 wt % or more, 32 wt % or more, even 34 wt % or more while at the same time is 35 wt % or less, and can be 33 wt % or less, 31 wt % or less, 29 wt % or less, even 27 wt % or less, with wt % relative to curable thermally conductive composition weight.
The third thermally conductive filler has a Dv50 of 0.1 or more and can have a Dv50 of 0.3 or more, 0.5 or more, 0.7 or more, even 0.9 or more while at the same time has a Dv50 of one or less, and can have a Dv50 of 0.8 or less, 0.6 or less, 0.4 or less, or even 0.2 or less. The concentration of the third thermally conductive filler is 10 wt % or more, and can be 12 wt % or more, 14 wt % or more, 16 wt % or more, even 18 wt % or more while at the same time is 20 wt % or less, and can be 19 wt % or less, 17 wt % or less, 15 wt % or less, 13 wt % or less, or even 11 wt % or less, with wt % relative to curable thermally conductive composition weight.
The fourth thermally conductive filler has a Dv50 of 20 micrometer or more, and can have a Dv50 of 25 micrometers or more, 30 micrometers or more, 35 micrometers or more, 40 micrometers or more, 45 micrometers or more, even 50 micrometers or more while at the same time has a Dv50 of 60 micrometers or less, and can have a Dv50 of 55 micrometers or less, 50 micrometers or less, or even 45 micrometers or less. The concentration of the fourth thermally conductive filler is zero wt % or more, and can be 2 wt % or more, 4 wt % or more, 6 wt % or more, 8 wt % or more, 10 wt % or more, 12 wt % or more, 14 wt % or more, 16 wt % or more, even 18 wt % or more while at the same time is 20 wt % or less, and can be 19 wt % or less, 17 wt % or less, 15 wt % or less, 13 wt % or less, or even 11 wt % or less, with wt % relative to curable thermally conductive composition weight.
The thermally conductive filler can comprise fillers in addition to these four thermally conductive fillers or be free of thermally conductive fillers other than these four.
The particles can have any shape such as spherical, irregular, crushed or platelet. Desirably, the second thermally conductive filler is one or both of spherical aluminum oxide and irregular aluminum nitride. Desirably, the third thermally conductive filler is crushed zinc oxide. Desirably, the fourth thermally conductive filler is spherical aluminum nitride.
Desirably, each thermally conductive filler is independently selected from a group consisting of diamond particles, aluminum nitride particles, aluminum oxide particles, zinc oxide particles, and boron nitride particles. Preferably, the first thermally conductive filler is selected from 34 weight-percent diamond particles having a Dv50 of 120 micrometers; or 30.5 weight-percent diamond particles having a Dv50 of 120 micrometers and 20 weight-percent diamond particles having a Dv50 of 20 micrometers; or 50.4 to 50.8 weight-percent diamond particles having a Dv50 of 60 micrometers.
Desirably, the second thermally conductive filler is one or a combination of both of aluminum nitride and aluminum oxide. Preferably, the second thermally conductive filler is selected from 30 weight-percent spherical aluminum oxide particles having a Dv50 in a range of 2 to 5 micrometers; or 19 weight-percent spherical aluminum oxide particles having a Dv50 of 2 micrometers in combination with 10 weight-percent irregular aluminum nitride particles having a Dv50 of 1.5 micrometers.
Desirably, the third thermally conductive filler is zinc oxide. Preferably, the third thermally conductive filler is 15 weight-percent irregular zinc oxide particles having a Dv50 of 0.2 micrometers.
Desirably, the fourth thermally conductive filler is aluminum nitride. Preferably, the fourth thermally conductive filler, when present, is 16.50 weight-percent of spherical aluminum nitride particles having a Dv50 in a range of 30 to 50 micrometers.
Typically, the curable thermally conductive composition further comprises a platinum-based hydrosilylation catalyst. Platinum-based hydrosilylation catalysts include compounds and complexes such as platinum (0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt's catalyst), H2PtCl6, di-μ.-carbonyl di-.π.-cyclopentadienyldinickel, platinum-carbonyl complexes, platinum-divinyltetramethyldisiloxane complexes, platinum cyclovinylmethylsiloxane complexes, platinum acetylacetonate (acac), platinum black, platinum compounds such as chloroplatinic acid, chloroplatinic acid hexahydrate, a reaction product of chloroplatinic acid and a monohydric alcohol, platinum bis(ethylacetoacetate), platinum bis(acetylacetonate), platinum dichloride, and complexes of the platinum compounds with olefins or low molecular weight organopolysiloxanes or platinum compounds microencapsulated in a matrix or core-shell type structure. The hydrosilylation catalyst can be part of a solution that includes complexes of platinum with low molecular weight organopolysiloxanes that include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. These complexes may be microencapsulated in a resin matrix. The catalyst can be 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum. Typically, the platinum-based hydrosilylation catalyst is present at a concentration sufficient to provide a platinum concentration of 0.03 wt % or more, 0.04 wt % or more, 0.05 wt % or more, even 0.06 wt % or more while at the same time is typically 0.4 wt % or less, or 0.3 wt % or less, 0.2 wt % or less, 0.1 wt % or less, 0.09 wt % or less, 0.08 wt % or less, 0.07 wt % or less, 0.06 wt % or less, 0.05 wt % or less, or even 0.04 wt % or less with wt % relative to curable thermally conductive composition weight.
The curable thermally conductive composition can further comprise a cure inhibitor. Cure inhibitors can serve to stabilize the curable thermally conductive composition from premature curing and provide storage stability to the composition. Examples of suitable cure inhibitors include any one or any combination of more than one of acetylene-type 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; ene-yne compounds such as 3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne; triazols such as benzotriazole; hydrazine-based compounds; phosphines-based compounds; mercaptane-based compounds; cycloalkenylsiloxanes including methylvinylcyclosiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenyl cyclotetrasiloxane.
The concentration of cure inhibitor is zero wt % or more, and can be 0.001 wt % or more, 0.002 wt % or more, even 0.003 wt % or more while at the same time is typically 0.5 wt % or less, or even 0.3 wt % or less, 0.1 wt % or less, 0.05 wt % or less, 0.01 wt % or less, or even 0.005 wt % or less, 0.004 wt % or less, or even 0.003 wt % or less with wt % relative to curable thermally conductive composition weight.
The present invention also includes a process for using the curable thermally conductive composition, the process comprising applying the curable thermally conductive composition between and in contact with two components and then heating the curable composition to cure the curable composition while in place between the components.
The present invention further includes an article comprising the curable thermally conductive composition and at least two components where the curable thermally conductive composition is between and in contact with the two components. The curable thermally conductive composition can be in either a cured or non-cured form.
Table 1 lists the materials for use in the following Examples (Exs) and Comparative Examples (Comp Exs).
Characterize each sample for extrusion rate using the Extrusion Rate Test and thermal conductivity using the method described herein, above. The objective is to obtain an extrusion rate of greater than 60 g/min and a thermal conductivity of at least 8 W/m*K. Table 2 contains characterization results for each sample composition.
Samples that do not have diamond filler with a Dv50 in a range of 60-150 micrometers fail to achieve both an ER greater than 60 g/min and a thermal conductivity (TC) of at least 8 W/m*K even when the samples include diamond filler, just diamond filler that is smaller than 60-150 micrometers.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/132300 | 11/23/2021 | WO |
