Thermal Interface Materials

Abstract

The thermally conductive curable composition includes a first part and a second part, the first part including a catalyst, a ceramic filler mixture, a low-volatility organic liquid, and water, and the second part including a silyl-modified reactive polymer, a low-volatility organic liquid, and a ceramic filler mixture, and the low-volatility organic liquid is present in the composition in an amount greater than about 50 wt % based on the total weight of the silyl-modified reactive polymer.

Description

[Background technology]

[0001] BACKGROUND OF THE INVENTION Thermal interface materials are widely used in the electronics industry to couple a heat source to a heat sink structure and aid in the dissipation of heat from the heat source. Typically, these thermal interface materials are used in conjunction with heat-generating electronic components. These thermal interface materials generally operate by transferring excess thermal energy generated by the heat source to the heat sink structure.

[0002] Similar to electronic devices, electric vehicles are typically equipped with a battery containing multiple battery cells that store the energy required to power the vehicle. The battery cells can be charged before use and recharged while the vehicle is in motion, either through regenerative braking or the internal combustion engine. Battery cells can heat up during use, necessitating the use of heat sink structures to prevent overheating. Heat is generated as a result of chemical reactions occurring within the battery during charging. Ideally, the battery temperature is maintained between 25 and 30°C. However, when performing normal or fast charging, the battery temperature far exceeds this desirable range. Furthermore, the ideal temperature of 25 to 30°C cannot be maintained if the outside temperature itself exceeds this range. This also applies when using cooling fans to exhaust air from within the battery tray during recharging. Therefore, overheating is a concern when recharging electric vehicle batteries.

[0003] When electric vehicle batteries overheat, they can deform and cause internal short circuits, which can cause vaporized battery gases to burn or explode, potentially causing the vehicle to catch fire. Thermal management of electric vehicle batteries is therefore necessary not only to achieve optimal efficiency and lifespan, but also to meet electric vehicle safety standards.

[0004] Thermal interface materials are typically used to maximize heat transfer from a heat source to a heat sink structure, providing intimate contact between the heat source and the heat sink structure. Thermal interface materials generally need to be able to bridge various gaps corresponding to differences in height between components. Therefore, thermal interface materials that have not only high thermal conductivity but also high flexibility are desirable. Thermal interface materials commonly used in electronic devices are small, often handheld. These thermal interface materials previously used in small electronic devices have not been able to be used with larger heat sources. Larger heat sources, such as the electric vehicle battery mentioned above, require different thermal interface materials with different properties. For example, the flow characteristics and viscosity of the thermal interface material must be modified when used with larger heat sources, such as electric vehicle batteries. Furthermore, the useful dispensing speed of a thermal interface material used with a large heat source will be different from that of a thermal interface material used with a small heat source. Summary of the Invention [Problem to be solved by the invention]

[0005] Thus, there remains a need for high thermal conductivity thermal interface materials that are silicone-free and have customizable dispensing rates to function on a larger scale, for example, in electric vehicle batteries. [Means for solving the problem]

[0006] (Brief summary of the invention)

[0007] Disclosed herein is a thermally conductive curable composition comprising a first part and a second part. The first part comprises a catalyst, a ceramic filler mixture, a low-volatility organic liquid, and water, and the second part comprises a silyl-modified reactive polymer, a low-volatility organic liquid, and a ceramic filler mixture. The low-volatility organic liquid is present in the composition in an amount greater than about 50 wt %, based on the total weight of the silyl-modified reactive polymer.

[0008] Another embodiment discloses a thermally conductive curable composition including a first part and a second part, wherein the first part includes a low-volatility organic liquid, water, a rheological additive, a pigment, a ceramic filler mixture, fumed silica, and an organotin catalyst, and the second part includes a low-volatility organic liquid, a rheological additive, a multifunctional polymer, a ceramic filler mixture, an antioxidant, and a water scavenger. The ceramic filler mixture includes 4 wt.% of a ceramic filler having a D50 of 0.3 μm, 36 wt.% of a ceramic filler having a D50 of 2.4 μm, and 60 wt.% of a ceramic filler having a D50 of 40 μm, based on the total weight of the filler mixture.

[0009] Another embodiment discloses a method of making a thermally conductive curable composition comprising mixing a first part comprising a catalyst, a ceramic filler mixture, and water with a second part comprising a reactive polymer, a ceramic filler mixture, and a water scavenger, wherein the mixture is solid after curing.

[0010] Another embodiment discloses a battery that includes a heat source, a cooling mechanism, and the thermally conductive curable composition disclosed herein disposed therebetween. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Detailed Description of the Invention> Disclosed herein are two-part thermally conductive curable compositions that can be used as thermal interface materials after curing. The thermally conductive curable compositions disclosed herein are useful for applications in large, i.e., 1500 mm, batteries, for example, in electric and hybrid vehicle batteries. 2 These thermally conductive curable compositions can be useful as thermal interface materials for surfaces of 1000 to 15000 mm thick, 1000 to 2000 mm thick, and 1000 to 2000 mm thick. These thermally conductive curable compositions can cure at room temperature independent of environmental moisture. They also have fast dispensing speeds, post-dispensing stability, and low compressive stress during application.

[0012] The thermally conductive curable compositions disclosed herein are formulated at low viscosity for use in commercial automatic dispensers and are intended to reduce induced compressive stresses during assembly of equipment, particularly in automotive manufacturing, which require the delivery of significant amounts of material and assembly of automotive equipment in a timely manner.

[0013] The thermally conductive curable compositions disclosed herein comprise two parts, part 1 and part 2. The terms part 1 and part 2 are used throughout to refer to two separate parts and do not limit the parts in terms of order of application or otherwise.

[0014] The first part contains a catalyst, and the second part contains a reactive polymer. The catalyst and reactive polymer are contained in separate parts, regardless of the other components of the first and second parts. Preferably, the first part contains a catalyst, a ceramic filler mixture, a low-volatility organic liquid, and water, and the second part contains a silyl-modified reactive polymer, a low-volatility organic liquid, and a ceramic filler mixture. When the first and second parts are mixed, the mixture cures to a solid at room temperature through silyl hydrolysis and condensation.

[0015] reactive polymers Reactive polymer can be any reactive polymer that can participate in silyl hydrolysis reaction.For example, reactive polymer can be selected from a wide range of polymers as a polymer system with reactive silyl group, for example, silyl-modified reactive polymer.When used in electronic device, silyl-modified reactive polymer can have non-silicone backbone to limit silicone release.Preferably, silyl-modified reactive polymer has non-silicone backbone, more preferably, this silyl-modified reactive polymer has polyether backbone.

[0016] The silyl-modified reactive polymer can be obtained by reacting a polyether with at least one ethylenically unsaturated silane in the presence of a radical starter, where the ethylenically unsaturated silane has at least one hydrolyzable group on the silicon atom. For example, the silyl-modified reactive polymer can be a dimethoxysilane-modified polymer, a trimethoxysilane-modified polymer, or a triethoxysilane-modified polymer. For example, the silyl-modified reactive polymer can be a silane-modified polyether.

[0017] The ethylenically unsaturated silane is particularly preferably selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyldimethoxymethylsilane, vinyldiethoxymethylsilane, trans-β-methylacrylic acid trimethoxysilylmethyl ester, and trans-β-methylacrylic acid trimethoxysilylpropyl ester.

[0018] The silyl-modified reactive material preferably comprises silyl groups having at least one hydrolyzable group on the silicon atom in a statistical distribution.

[0019] For example, the silyl-modified reactive polymer can be a silane-modified polymer of the general formula (Ia): [ka] where R is a monovalent to tetravalent polymer radical, and R 1 , R 2 , R 3 are independently an alkyl or alkoxy group having 1 to 8 C atoms, A represents a carboxy, carbamate, amide, carbonate, ureido, urethane or sulfonate group or an oxygen atom, x=1 to 8 and n=1 to 4.

[0020] Silyl-modified reactive polymers can also be obtained by reacting polyethers with hydroxy groups and alkoxysilanes with isocyanate groups. For example, the silyl-modified reactive polymer can be a dimethoxysilane-modified polyurethane polymer, a trimethoxysilane-modified polyurethane polymer, or a triethoxysilane-modified polyurethane polymer.

[0021] Additionally, the silyl-modified reactive polymer can be an α-ethoxysilane-modified polymer of the average general formula (Ib): [ka] In the formula, R is a monovalent to tetravalent polymer residue, and the polymer-containing residue R of formula (Ib) 1 , R 2 and R 3 at most one-third of the radicals R are independently alkyl radicals having 1 to 4 carbon atoms, and the polymer-containing residue R of formula (Ib) 1 , R 2 and R 3 At least one-quarter of the groups R are independently ethoxy residues, and the remaining groups R 1 , R 2 and R 3 are each independently a methoxy group, and n=1 to 4.

[0022] Silyl-modified reactive polymers are available, for example, as dimethoxysilane-modified MS polymers from Kaneka, trimethoxysilane-modified ST polymers from Evonik, triethoxysilane-modified Tegopac polymers from Evonik, silane-modified Desmoseal polymers from Covestro, or silane-modified SMP polymers from Henkel. Preferably, the silyl-modified reactive polymer is a dimethoxysilane-terminated MS polymer.

[0023] The silyl-modified reactive polymer is present in the part of the composition that does not contain the catalyst.

[0024] The silyl-modified reactive polymer can be present in the composition in an amount of about 20% to about 90% by weight, for example, about 30% to about 70% by weight, based on the total weight of the part of the composition that includes the silyl-modified reactive polymer.

[0025] Ceramic Filler Mixture The ceramic filler mixture preferably includes alumina and is preferably added in equal amounts to each of the first and second parts to enhance thermal conductivity. The ceramic filler mixture is preferably present in each of the first and second parts in an amount of about 80% to about 95% by weight, for example, about 90 to 92% by weight, based on the total weight of each of the first and second parts.

[0026] In a particularly useful embodiment, the ceramic filler mixture includes a 2.4 μm ceramic filler, a 40 μm ceramic filler, and a 0.3 μm ceramic filler. Preferably, the 2.4 μm ceramic filler is present in the composition in an amount of about 4 wt. % based on the total weight of the ceramic filler mixture, the 40 μm ceramic filler is present in an amount of about 36 wt. % based on the total weight of the ceramic filler mixture, and the 0.3 μm ceramic filler is present in an amount of about 60 wt. % based on the total weight of the ceramic filler mixture.

[0027] catalyst The catalyst is included in the first part of the composition. Specifically, the catalyst can be an organometallic catalyst for silyl hydrolysis and condensation, such as an organotin catalyst. The catalyst should not be included in the second part of the composition containing the polymer. Preferably, the catalyst is an organotin catalyst or an organobismuth catalyst.

[0028] Low-Volatile Organic Liquids A low volatility organic liquid is included in the composition to reduce the viscosity of the first and second parts under high shear rates. The low volatility organic liquid can be included in the first part and / or the second part.

[0029] The viscosity of the low-volatility organic liquid is about 10 to 1000 cPs, for example, about 10 to 100 cPs.

[0030] The low-volatility organic liquid is present in both the first and second parts in an amount greater than about 50% by weight, based on the total weight of the polymer. If the composition contains too much low-volatility organic liquid, the composition will not cure to a solid at room temperature and will instead become a highly viscous liquid. If the composition contains too little low-volatility organic liquid, the composition will cure too hard and the viscosity of the second part will be too high.

[0031] Preferably, the low-volatility organic liquid is miscible with the resin and compatible with the filler matrix, e.g., the low-volatility organic liquid may be a plasticizer. Even more preferably, the low-volatility organic liquid is selected from phthalates, cyclohexanedicarboxylic acid diisononyl esters, trimellitates, terephthalates, adipates, sebacates, maleates, alkyl citrates, epoxidized vegetable oils, alkylsulfonic acid phenyl esters, sulfonamides, organic phosphates, glycols and polyethers, and polymeric plasticizers. Even more preferably, the low-volatility organic liquid is selected from ethylhexyl adipate, isononyl adipate, and combinations thereof, more preferably isononyl adipate.

[0032] water Water may also be present in the composition. While water can be present due to the inclusion of ceramic fillers and other components of the formulation, the first part of the composition preferably cures within 72 hours, preferably within 24 hours, without the aid of external moisture, with the addition of water to enhance hydrolysis. In a preferred embodiment, water is present in the first part in an amount of 500 ppm to 5000 ppm based on the total weight of the first part.

[0033] Water Scavenger The second part of the composition preferably contains a water scavenger to extend pot life. Examples of water scavengers include alkyltrimethoxysilane, oxazolidine, zeolite powder, p-toluenesulfonyl isocyanate, and ethyl orthoformate. The water scavenger is preferably vinyltrimethoxysilane. Too much water scavenger in the composition slows down curing. The amount is greater than about 1 PHR and less than about 5 PHR, for example, about 2 PHR.

[0034] Optional ingredients In another embodiment, the composition can optionally include a rheological additive. These rheological additives can be included in the first part, the second part, or both the first and second parts. The rheological additive can be further included in the composition to prevent sagging of the polymer. The rheological additive can be included in an amount of less than about 1 wt %, for example, less than about 0.5 wt %, based on the total weight of the composition.

[0035] The rheological additive should be added to the composition in an amount of about 0.01 to 1 wt. %, for example, about 0.1 to 0.2 wt. %, based on the total weight of the reactive polymer in the composition. The rheological additive can be, for example, fumed silica, organoclay, and branched polymers, thixotropic agents, and dispersants for ceramic fillers.

[0036] composition

[0037] The composition can be useful as a thermal interface material, for example, for use in electric vehicles. The composition is made by mixing the first and second parts, preferably in a 1:1 ratio. The composition cures to a solid at room temperature through hydrolysis and condensation of the silane. After mixing the first and second parts, the composition cures at room temperature and any external humidity.

[0038] The first and second parts have similar viscosities before mixing. For example, the first part has a viscosity greater than about 300 Pas, e.g., about 200-1500 Pas at 1 / s, and less than about 200 Pas at 3000 / s, e.g., about 300-500 Pas at 1 / s, and less than about 50 Pas at 3000 / s. The second part has a viscosity of about 200-1500 Pas at 1 / s and less than about 200 Pas at 3000 / s, e.g., about 300-500 Pas at 1 / s, and less than about 50 Pas at 3000 / s.

[0039] After curing, the composition has a thermal conductivity of about 2.0 to about 5.0 W / mK, for example, about 2.5 to 3.5 W / mK.

[0040] In an alternative embodiment, disclosed herein is a battery that includes a heat source, a cooling mechanism, and a composition disclosed herein disposed therebetween.

[0041] For the purposes of this invention, "polyether" is understood to mean a polymer whose repeating units are held together by C-O-C ether functional groups. Thus, polymers with lateral ether groups, such as cellulose ethers, starch ethers, vinyl ether polymers, as well as polyacetals, are excluded from this definition.

[0042] "Ethylenically unsaturated silane" is understood as a non-polymeric silicon compound in which at least one silicon atom is linked by a chemical bond to at least one organic residue containing a carbon-carbon double bond (C=C).

[0043] "Hydrolyzable group" is understood in the context of the present invention as a substituent that can be converted into a hydroxy group (OH) by reacting with water. Hydrolyzable groups are to be understood in particular as alkoxy groups (also called alkyloxy groups) and acyloxy groups. [Example]

[0044] Example A is a two-component thermally conductive material comprising a first part and a second part. The first part comprises less than 10 wt.% of a low-volatility organic liquid having a viscosity of less than 100 cps, less than 0.5 wt.% of a rheological additive (fumed silica, organoclay, or liquid rheological additive), less than 0.2 wt.% of an organotin catalyst, less than 0.5 wt.% of a pigment, more than 90 wt.% of alumina powder, and optionally less than 0.5 wt.% of DI water. The second part comprises less than 10 wt.% of a low-volatility organic liquid having a viscosity of less than 100 cps, less than 10 wt.% of an alkoxysilane-modified polyether, less than 0.5 wt.% of a rheological additive (fumed silica, organoclay, or liquid rheological additive), less than 0.5 wt.% of an antioxidant, less than 0.5 wt.% of a water scavenger, and more than 90 wt.% of alumina powder. Curing of the composition was achieved by mixing the first and second parts in an approximately 1:1 volume ratio, and the composition became solid within approximately 24 hours. The hardness of a cured 250 mm pack is about 50 to about 80 as measured by a Shore 00 durometer.

[0045] Example B Part 1 was prepared by adding 98g of plasticizer, 3.5g of rheology additive, 63g of alumina filler having an average size of 0.3 microns, 357g of alumina filler having an average size of 3 microns, 630g of alumina filler having an average size of 40 microns, 1g of dibutyltin catalyst, and 1g of deionized water to a 0.6 gallon mixing bucket and mixing for two minutes at 800 rpm in a Flacktec DAC-5000 high speed mixer. The second part was prepared by adding 46 g of plasticizer, 50 g of methoxysilane terminated polyether, 4 g of rheology additive, 2 g of hindered phenol antioxidant, 21 g of alumina filler having an average size of 0.3 microns, 399 g of alumina filler having an average size of 3 microns, 630 g of alumina filler having an average size of 40 microns, and 2 g of water scavenger to a 0.6 gallon mixing bucket and mixing twice for 2 minutes at 800 rpm using a Flacktec DAC-5000 high speed mixer.

[0046] Examples B and C have different resin compositions in the second part, and Example D has a higher filler loading compared to Example B. Each of Examples A-D is otherwise prepared in the same manner as Example B above. A comparison of the sample compositions is shown in Table 1 below.

[0047] [Table 1]

[0048] The viscosity of the thermally conductive compositions described in Examples A, B, C, and D was measured by a parallel plate rheometer at a shear rate of 1 / s and by a capillary rheometer at a shear rate of 3000 / s. The hardness of the compositions was measured by using a 1:1 mixture of Part 1 and Part 2 and curing at room temperature for approximately 72 hours. A comparison of the composition properties is shown in Table 2 below.

[0049] [Table 2]

Claims

1. A thermally conductive curable composition for a thermal interface material comprising a first part and a second part, the first part comprising a catalyst, a ceramic filler mixture, a low volatility organic liquid, and water; a second part comprising a silane-modified polyether, a low-volatility organic liquid, and a ceramic filler mixture; the ceramic filler mixture is present in each of the first part and the second part in an amount of 80 wt. % to 92 wt. % based on the total weight of each of the first part and the second part; the ceramic filler mixture comprising a ceramic filler having an average particle size (D50) of 0.3 μm in an amount of 4 wt % based on the total weight of the ceramic filler mixture, a ceramic filler having an average particle size (D50) of 2.4 μm in an amount of 36 wt % based on the total weight of the ceramic filler mixture, and a ceramic filler having an average particle size (D50) of 40 μm in an amount of 60 wt % based on the total weight of the ceramic filler mixture; A thermally conductive curable composition wherein the low volatility organic liquid is present in each of the first part and the second part in an amount greater than 50 weight percent based on the total weight of the silane-modified polyether.

2. A thermally conductive curable composition comprising a first part and a second part, the first part comprising a catalyst, a ceramic filler mixture, a low volatility organic liquid, and water; a second part comprising a silane-modified polyether, a low-volatility organic liquid, and a ceramic filler mixture; the ceramic filler mixture is present in each of the first part and the second part in an amount of 80 wt. % to 92 wt. % based on the total weight of each of the first part and the second part; the ceramic filler mixture is comprised of alumina having an average particle size (D50) of 0.3 μm in an amount of 4 wt. % based on the total weight of the ceramic filler mixture, alumina having an average particle size (D50) of 2.4 μm in an amount of 36 wt. % based on the total weight of the ceramic filler mixture, and alumina having an average particle size (D50) of 40 μm in an amount of 60 wt. % based on the total weight of the ceramic filler mixture; the low volatility organic liquid is present in each of the first part and the second part in an amount greater than 50 wt % based on the total weight of the silane-modified polyether; A thermally conductive curable composition wherein the silane-modified polyether is present at 1.7% to 6.5% by weight based on the total weight of the second part.

3. 3. The thermally conductive curable composition of claim 1 or 2, wherein the silane-modified polyether is a dimethoxysilane-modified polyether, a trimethoxysilane-modified polyether, a triethoxysilane-modified polyether, or a combination thereof.

4. 3. The thermally conductive curable composition of claim 1 or 2, wherein water is present in the first part in an amount of 500 ppm to 5000 ppm based on the total weight of the first part.

5. 3. The thermally conductive curable composition of claim 1 or 2, wherein the second part further comprises a water scavenger.

6. 3. The thermally conductive curable composition of claim 1 or 2, wherein the first part and / or the second part further comprises a rheological additive.

7. 3. The thermally conductive curable composition of claim 1 or 2, wherein the catalyst is an organotin catalyst, an organobismuth catalyst, or a combination thereof.

8. 3. The thermally conductive curable composition of claim 1 or 2, wherein the first part and the second part have a viscosity higher than 300 Pas as measured by a parallel plate rheometer at a shear rate of 1 / s and a viscosity lower than 50 Pas as measured by a capillary rheometer at a shear rate of 3000 / s.

9. the first part further comprises a pigment and fumed silica; The thermally conductive curable composition of claim 1 or 2, wherein the second part further comprises an antioxidant.

10. 10. A method of making the thermally conductive curable composition of any one of claims 1 to 9, comprising mixing a first part with a second part, A method in which the mixture is solid after hardening.

11. The method of claim 10, wherein the mixture is cured at room temperature.

12. 11. The method of claim 10, wherein the first part and the second part are mixed in a 1:1 ratio.

13. A battery comprising a heat source, a cooling mechanism, and the composition of any one of claims 1 to 9 disposed therebetween.

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