Epoxy-based compositions for thermal interface materials

Abstract

The two-part thermally conductive curable composition exhibits a high distribution rate and cures as a thermally conductive interface material having high thermal reliability, including high fracture toughness and elongation properties. The curable composition employs a combination of low viscosity polyfunctional and monofunctional liquid epoxy resins.

Description

Technical Field

[0001] The present invention relates generally to thermally conductive compositions and, more particularly, to two-part curable thermally conductive compositions for use in thermal interface materials that exhibit improved fracture toughness without reducing the dispensing rate of the curable composition. Background Art

[0002] Thermally conductive materials are widely used as interfaces between, for example, heat-generating electronic components and heat sinks to allow excess heat energy to be transferred from the electronic components to the heat sinks of the thermal coupling. Many designs and materials have been implemented for such thermal interfaces, wherein the highest performance is achieved when the gap between the thermal interface and the corresponding heat transfer surface is substantially avoided to promote conductive heat transfer from the electronic components to the heat sink. Therefore, the thermal interface material preferably mechanically fits the slightly uneven heat transfer surface of the corresponding component. Therefore, the important physical characteristics of high-performance thermal interface materials are flexibility and low modulus. In the case of dispensable materials, it is additionally important that the thermal interface is able to wet the heat transfer surface, and that it provides suitable bonding strength and cohesive strength to avoid delamination and maintain the form and function of the interface within the expected working life. Therefore, the dispensable thermal interface material can be designed to have a yield stress to avoid significant diffusion after dispensing, or to have no yield stress to maximize flow and penetration of the surface. The curing behavior of the material can also be designed to both avoid particle sedimentation and provide sufficient pre-curing time for rework and processing.

[0003] A particular application where there is an increasing need for thermally conductive materials is in automotive battery packs that utilize multiple different battery cells. Thermally conductive materials can adhesively connect adjacent cells in a pack and / or can secure one or more heat sinks to the battery pack or individual cells within a pack while simultaneously providing a thermally conductive path to dissipate excess heat energy from the operating cells. Thus, thermally conductive materials can perform both bonding and thermal management tasks.

[0004] Existing epoxy-based thermal interface materials are highly filled systems with relatively brittle mechanical and fracture behaviors and may perform poorly in vehicle crash evaluations of battery systems. Commonly used alternative thermal interface materials in battery systems include filled polyurethanes. However, most useful polyurethanes exhibit relatively high pre-cure viscosities, which slow down the dispensing rate. In addition, polyurethanes contain isocyanates, which pose health and safety challenges in manufacturing.

[0005] Two-part curable thermally conductive compositions have been widely used as thermal interface materials, potting compounds, adhesives and sealants in electronic devices, power and automotive applications. Both parts of the curable composition are stored in separate containers in a dispensable form and pumped through a hose and a mixing nozzle before applying them to a substrate or injecting them to fill a gap. The material solidifies during curing and at least partially serves to dissipate heat from a heat generating device to a cooling structure. For high throughput applications, the viscosity of the liquid phase in the curable composition is preferably low to facilitate high flow rates when pumped out of the container. However, conventional compositions generally require high particle filler loading to establish satisfactory thermal conductivity, and use a resin system that exacerbates low dispensing rates due to high viscosity. High particle filler loading causes further embrittlement of epoxy materials. Therefore, relatively low tensile elongation properties are observed in epoxy-based thermal interface materials.

[0006] Typically, the fracture toughness of epoxy resins is improved by the addition of polymer toughening agents. However, the incorporation of these high molecular weight (3,000 to 5,000+ g / mol) toughening agents based on carboxyl terminated butadiene-acrylonitrile (CTBN), blocked polyurethane prepolymers, and pre-dispersed core-shell rubber particle chemistries results in an undesirable increase in the viscosity of the pre-cured composition, which undesirably reduces the dispensing rate and correspondingly reduces the manufacturing rate.

[0007] Therefore, there is a need for a two-part curable thermally conductive epoxy composition that can be cured into a thermal interface material that exhibits improved material fracture toughness while maintaining a high pre-cure dispensing rate. The thermal interface material formed from such a curable composition should also exhibit good peel strength for bonding quality, increased tensile elongation for improved fracture toughness, and suitable lap shear strength and thermal reliability performance. Summary of the invention

[0008] By means of the present invention, the fracture toughness and other mechanical properties of highly thermally conductive adhesives / interface materials can be significantly improved without reducing the pre-cure dispensing rate. Thus, the epoxy resin system of the present invention maintains high throughput using standard two-part dispensing equipment while improving the reliability of the cured material.

[0009] In one embodiment, a two-part curable composition for forming a thermally conductive interface material comprises a first part having a first epoxy resin and a second epoxy resin different from the first epoxy resin. The second epoxy resin has an epoxy equivalent weight of at least 250, and the resin of the first part has a thermal conductivity of 0.0447 W / m at 25°C and 1 s -1The second part of the curable composition comprises an amine curing agent that is effective to cure the first epoxy resin and the second epoxy resin. The amine curing agent may have an amine equivalent weight of at least 80 g / equivalent and a viscosity of no more than 5000 cP at a shear rate of 1.5 s. -1 The curable composition further comprises a thermally conductive filler in at least one of the first part and the second part, wherein the cured thermally conductive interface material exhibits a thermal conductivity of at least 1.0 W / m*K.

[0010] The thermally conductive interface formed by the two-part curable composition exhibits at least 5 lb f / in t-peel strength, at least 5% tensile elongation at break, and at least 350 psi lap shear strength.

[0011] The two-part curable composition may contain 50-95 wt% of a thermally conductive filler in each of the first part and the second part. The thermally conductive filler may be selected from boron nitride, aluminum nitride, aluminum oxide, aluminum oxide trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, and combinations thereof.

[0012] The first part of the two-part curable composition may include 2-15 wt % of the first epoxy resin, and 2-8 wt % of the second epoxy resin.

[0013] The first part of the two-part curable composition may include a monofunctional epoxy resin that is different from the first epoxy resin and the second epoxy resin. In some embodiments, the second epoxy resin includes a trifunctional epoxy resin.

[0014] In some embodiments, the amine curing agent may include an alkane chain having at least 20 carbon atoms. The alkane chain of the amine curing agent may include at least 30 carbon atoms.

[0015] The second epoxy resin may have an epoxy equivalent weight of at least 500.

[0016] In another embodiment, a two-part curable composition for forming a thermally conductive interface material comprises a first part having a first epoxy resin having an epoxy equivalent weight of at least 250 and a second monofunctional epoxy resin different from the first epoxy resin. The first part has a curable epoxy resin having an epoxy equivalent weight of at least 250 and a second monofunctional epoxy resin different from the first epoxy resin. -1 The second part of the two-part composition comprises an amine curing agent that is effective to cure at least the first epoxy resin and has a viscosity of no more than 5000 cP at a shear rate of 1.5 %. -1The two-part curable composition further comprises a thermally conductive filler in at least one of the first part and the second part, wherein the cured thermally conductive interface material exhibits a thermal conductivity of at least 1.0 W / m*K.

[0017] The first epoxy resin in the first part may be multifunctional, and the first part may include a third epoxy resin that is different from each of the first epoxy resin and the second epoxy resin and that is curable by an amine curing agent.

[0018] In some embodiments, the first part includes 1 wt % to 10 wt % of the first epoxy resin, 1 wt % to 10 wt % of the second epoxy resin, and 1 wt % to 30 wt % of the third epoxy resin.

[0019] At least one of the first part and the second part of the two-part curable composition may include 50 wt % to 95 wt % of the thermally conductive filler.

[0020] In some embodiments, the second monofunctional epoxy resin comprises an oxygen atom in the beta position.

[0021] In some embodiments, the amine curing agent does not contain ether groups.

[0022] The battery system includes: a battery cell; a heat sink; and a thermally conductive interface material disposed between the battery cell and the heat sink along a heat dissipation path. The thermally conductive interface material can be formed by curing a two-part curable composition, the two-part curable composition including a first part having a first epoxy resin with an epoxy equivalent weight of at least 250, and a second monofunctional epoxy resin different from the first epoxy resin. The two-part curable composition includes: a second part having an amine curing agent that effectively cures at least the first epoxy resin; and a thermally conductive filler in at least one of the first part and the second part, the amount of the thermally conductive filler being sufficient to allow the thermally conductive interface material to exhibit a thermal conductivity of at least 1.0 W / m*K along the heat dissipation path. The mixed two-part curable composition can exhibit a thermal conductivity of at least 1.0 W / m*K at 25°C and 1s -1 The viscosity does not exceed 500,000 cP at a shear rate of 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a battery system using a thermally conductive interface material according to the present invention. DETAILED DESCRIPTION

[0024] The above-listed objects and advantages, as well as other objects, features and developments described in the present invention are now described according to detailed embodiments. However, other embodiments and aspects of the present invention are considered to be understandable to those of ordinary skill in the art.

[0025] The thermally conductive interface material of the present invention can be formed as a coating on a surface, a gap filler arranged along a heat dissipation path, or a self-supporting body arranged along a heat dissipation path to typically remove excess heat from a heat generating electronic component or battery system. The thermally conductive interface material can exhibit adhesive properties, for example, to secure a battery cell within a battery pack. The thermally conductive interface material preferably exhibits a thermal conductivity of at least 1 W / m*K, and wettability sufficient to coat the corresponding surface before curing. The material also preferably exhibits flexibility and cohesive strength sufficient to provide a stable interface (including an interface suitable for withstanding a motor vehicle battery pack crash or other impact test with minimal or no failure).

[0026] The thermally conductive interface material is formed from a two-part curable composition that can be dispensed from at least two separate containers to separate a first curable component from a curing agent that promotes a curing reaction of the first curable component to form a matrix (e.g., a resin matrix). The first part or curable component includes a mixture of two or more different epoxy resins that are curable in the presence of a curing agent in the second part. A thermally conductive filler is included in at least one part to provide the desired thermal conductivity characteristics.

[0027] One or both parts of the two-part curable composition may additionally contain rheology modifiers, compatibilizers, plasticizers, pigments, water scavengers, antioxidants and other functional fillers.

[0028] Resin matrix material

[0029] The thermally conductive interface material of the present invention comprises a matrix formed by at least a curable resin component and a chemical curing agent. Preferably, in some cases, when there is an environmental curing reaction promoting factor (such as water, heat, pressure, electromagnetic radiation, etc.), the curing reaction is initiated by exposure between the curable resin component and the curing agent.

[0030] The curable resin component can include a combination of epoxy resins that are curable to exhibit unexpectedly enhanced fracture toughness, peel strength, tensile elongation, and lap shear strength compared to conventional epoxy resins and epoxy resin blends. Various epoxy-functional resins are contemplated for use in the curable compositions of the present invention. For example, liquid epoxy resins based on bisphenol A, liquid epoxy resins based on bisphenol F, multifunctional epoxy resins based on phenol novolac resins, dicyclopentadiene epoxy resins, naphthalene epoxy resins, etc. Examples of other epoxy-functional resins contemplated for use herein include cycloaliphatic alcohols, diepoxides of hydrogenated bisphenol A (commercially available as Epalloy 5000), difunctional cycloaliphatic glycidyl esters of hexahydrophthalic anhydride (commercially available as Epalloy 5200), Epiclon EXA-835LV, Epiclon HP-7200L, and the like, and mixtures of any two or more thereof.

[0031] In some embodiments, the curable composition can include a combination of two or more different epoxy functionalized resins (including two or more different bisphenol-based epoxy resins). The bisphenol-based epoxy resin can be selected from bisphenol A epoxy resin, bisphenol F epoxy resin, or bisphenol S epoxy resin, and combinations thereof. In addition, two or more different bisphenol epoxy resins within the same resin type (such as A, F, or S) can also be used.

[0032] Commercially available examples of bisphenol epoxy resins contemplated for use herein include bisphenol F-type epoxy resins (such as RE-404-S available from Nippon Kayaku, Japan; and EPICLON 830 (RE1801), 830S (RE1815), 830A (RE1826), and 830W available from Dai Nippon Ink & Chemicals, Inc.; and RSL1738 and YL-983U available from Resolution) and bisphenol A-type epoxy resins (such as YL-979 and 980 available from Resolution). Additional examples of commercially available epoxy resins include Epon 828, Epon 826, Epon 862 (all from Hexion Co., Ltd.); DER331, DER 383, DER 332, DER 330-EL, DER 331-EL, DER 354, DER 321, DER 324, DER 29, DER353 (all from Dow Chemical Co.); JER YX8000, JER RXE21, JER YL 6753, JER YL6800, JERYL980, JER 825 and JER 630 (all from Japan Epoxy Resins Co.).

[0033] The bisphenol epoxy resins commercially available from Dai Nippon and mentioned above are advertised as liquid undiluted epichlorohydrin-bisphenol F epoxy resins (which have much lower viscosity than conventional bisphenol A epoxy resin-based epoxy resins) and have physical properties similar to liquid bisphenol A epoxy resins. Bisphenol F epoxy resins have lower viscosity than bisphenol A epoxy resins (everything else is the same between these two types of epoxy resins), which provides a lower viscosity and thus a fast flowing bottom fill encapsulant material. The epoxy equivalent weight (EEW) (which is the molecular weight divided by the number of epoxy groups) of these four bisphenol F epoxy resins ranges from 165 to 180. The viscosity at 25°C is 3000 to 4500 cps (except RE1801, which has an upper viscosity limit of 4000 cps). The hydrolyzable chloride content of RE1815 and 830W is reported to be 200 ppm, and the hydrolyzable chloride content of RE1826 is reported to be 100 ppm.

[0034] The bisphenol epoxy resins commercially available from Resolution and mentioned above are advertised as liquid epoxy resins containing low chlorides. The EEW (g / equiv) of bisphenol A epoxy resin is 180 to 195, and the viscosity at 25°C is 100 to 250 cP. The total chloride content of YL-979 is reported to be 500 to 700 ppm, and the total chloride content of YL-980 is reported to be 100 to 300 ppm. The EEW (g / equiv) of bisphenol F epoxy resin is 165 to 180, and the viscosity at 25°C is 30 to 60. The total chloride content of RSL-1738 is reported to be 500 to 700 ppm, and the total chloride content of YL-983U is reported to be 150 to 350 ppm.

[0035] In addition to bisphenol epoxy resins, other epoxy compounds are also considered to be used as epoxy resin components of the formulations of the present invention. For example, alicyclic epoxy resins such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexyl carbonate can be used. Monofunctional, difunctional or multifunctional reactive diluents can also be used to adjust the viscosity and / or reduce the glass transition temperature (Tg) of the resulting resin material. Exemplary reactive diluents include butyl glycidyl ether, toluene glycidyl ether, orthotoluene glycidyl ether, polyethylene glycol glycidyl ether, polypropylene glycol glycidyl ether, etc.

[0036] Other epoxy resins suitable for use herein include polyglycidyl derivatives of phenolic compounds, such as those commercially available under the trade name EPON, such as EPON 828, EPON 1001, EPON 1009, and EPON 1031 from Resolution; DER 331, DER 332, DER 334, and DER 542 from Dow Chemical Co.; and BREN-S from Nippon Kayaku. Other suitable epoxy resins include polyepoxides prepared from polyols and the like and polyglycidyl derivatives of phenol-formaldehyde novolacs, such as DEN 431, DEN 438, and DEN 439 from Dow Chemical. Cresol analogs are also commercially available under the trade name ARALDITE, such as ARALDITE ECN 1235, ARALDITE ECN 1273, and ARALDITE ECN 1299 from Ciba Specialty Chemicals Corporation. SU-8 is a bisphenol A type epoxy novolac available from Resolution. Polyglycidyl adducts of amines, amino alcohols and polycarboxylic acids can also be used in the present invention, and commercially available resins include GLYAMINE 135, GLYAMINE 125 and GLYAMINE 115 from FIC Corporation; ARALDITE MY-720, ARALDITE 0500 and ARALDITE 0510 from Ciba Specialty Chemicals and PGA-X and PGA-C from Sherwin-Williams Co.

[0037] The epoxy resin component of the curable composition may preferably be in liquid form and contained in one part of the two-part composition. The epoxy resin may exhibit a -1 The viscosity is no greater than 5000 cP at a shear rate of 1 s. -1 The viscosity is no greater than 2000 cP at a shear rate of 1 s. -1 The viscosity is no greater than 1000 cP at a shear rate of 1000 cP, and in some embodiments, at 25°C and 1 s -1 The curable composition has a viscosity of no more than 500 cP at a shear rate of 1.5 to 2.0 %. In some embodiments, the portion of the composition comprising the epoxy resin component exhibits the above viscosity parameters. Even when blended with thermally conductive particles, the curable composition exhibits a relatively low viscosity level that is conducive to high dispensing rates through conventional two-part curable resin dispensing systems.

[0038] In some embodiments, the epoxy resin component includes an epoxy resin having an EEW of at least 100. In some embodiments, the epoxy resin component includes an epoxy resin having an EEW of at least 250. In some embodiments, the epoxy resin component includes an epoxy resin having an EEW of at least 500. In some embodiments, the epoxy resin having an EEW of at least 100, at least 250, or at least 500 may be a difunctional, trifunctional, or other multifunctional epoxy resin. In one embodiment, the epoxy resin component includes a trifunctional epoxy resin having an EEW of at least 500. An example of such a polyepoxide resin is 9-octadecenoic acid, 12-(2-oxiranylmethoxy)-1,2,3-propanetriyl ester homopolymer. Preferably, epoxy resins having an EEW of at least 100, at least 250, or at least 500 exhibit relatively low pre-cure viscosities to facilitate low viscosity epoxy resin components.

[0039] The epoxy resin component of curable composition can also comprise monofunctional epoxy resin.It has been unexpectedly found that such monoepoxide resin causes the maintenance of cured material property changing over time to be improved, and this may be due to reacting with originally unreacted 2' amine and even 3' amine to limit the further change of crosslinking density and / or network property after gelation starts.Monoepoxide resin can also react with-OH group existing on epoxy resin main chain.In addition, by adding monoepoxide resin at least in specific loading concentration relative to other epoxy resins, the improvement of thermal reliability is unexpectedly observed.

[0040] Examples of the monoepoxide resin include monoglycidyl ethers such as phenyl glycidyl ether, alkyl phenol monoglycidyl ether, aliphatic monoglycidyl ether, alkyphenol mono glycidyl ether, alkylphenol monoglycidyl ether, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane and o-toluene glycidyl ether.

[0041] In some embodiments, the monofunctional epoxy resin may have an epoxy group with an alkyl group having from about 6 to about 28 carbon atoms, examples of which include C 6-28 Alkyl glycidyl ether, C 6-28 Fatty acid glycidyl ether, C 6-28Alkylphenol glycidyl ether, etc. In some embodiments, the monofunctional epoxy resin may have an oxygen atom at the β position.

[0042] The matrix formed by the curable component of the present invention and the curing agent accounts for about 0.01% to about 50% by weight of the total composition, preferably about 0.1% to about 50% by weight of the total composition, preferably about 0.5% to about 50% by weight of the total composition, preferably about 1% to about 50% by weight of the total composition. In some embodiments, the matrix formed by the curable component of the present invention and the curing agent accounts for 5% to about 50% by weight of the total composition, more preferably 10% to about 50% by weight of the total composition.

[0043] Curable component is preferably an epoxy resin component comprising one or more epoxy resins. In some embodiments, the epoxy resin component comprises two or more epoxy resins different from each other. In some embodiments, the epoxy resin component is the first part in the two-part curable composition, or is a part for the first part in the two-part curable composition. The first part can include the composition except the epoxy resin. The epoxy resin in the first part can be cured by being exposed to the curing agent in the second part of the two-part curable composition.

[0044] In some embodiments, the epoxy resin in the first part may account for 1% to 50% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 5% to 50% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 10% to 50% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 12% to 50% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 1% to 40% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 5% to 40% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 10% to 40% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 12% to 40% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 1% to 30% by weight of the first part. In some embodiments, the epoxy resin in the first part may account for 5% to 30% by weight of the first part. In some embodiments, the epoxy resin in the first part may comprise 10 wt % to 30 wt % of the first part. In some embodiments, the epoxy resin in the first part may comprise 12 wt % to 30 wt % of the first part.

[0045] The one or more multifunctional epoxy resins in the first part may account for 1% to 40% by weight of the first part. In some embodiments, the one or more multifunctional epoxy resins in the first part may account for 2% to 35% by weight of the first part. In some embodiments, the one or more multifunctional epoxy resins in the first part may account for 5% to 30% by weight of the first part. The first multifunctional epoxy resin may account for 2% to 15% by weight of the first part, and in some embodiments, 2% to 8% by weight of the first part. The second multifunctional epoxy resin may account for 2% to 15% by weight of the first part, and in some embodiments, 2% to 8% by weight of the first part. The third multifunctional epoxy resin may account for 2% to 15% by weight of the first part, and in some embodiments, 2% to 8% by weight of the first part. At least one of the multifunctional epoxy resins may be a trifunctional epoxy resin.

[0046] In some embodiments, the one or more monofunctional epoxy resins in the first part may account for 1 wt % to 10 wt % of the first part. In some embodiments, the one or more monofunctional epoxy resins in the first part may account for 2 wt % to 8 wt % of the first part. In some embodiments, the one or more monofunctional epoxy resins in the first part may account for 2 wt % to 5 wt % of the first part.

[0047] Amine curing agent

[0048] The second part of the two-part curable composition of the present invention comprises an amine curing component having one or more amine curing agents, at least one of which is preferably effective to cure the epoxy resin in the first part of the curable composition. In some embodiments, the amine curing agent is effective to cure each epoxy resin in the first part of the curable composition. For this purpose, the term "curing" is intended to mean a cross-linking reaction that forms a three-dimensional polymer network. In some embodiments, the amount of amine curing agent provided is sufficient to solidify the liquid portion of the two-part curable composition at least to a gel state or solidify through a gel state.

[0049] Amine curing agents for curing epoxy resins are well known. However, it has been found that certain amine curing agents can provide improved T-peel strength and tensile elongation properties of the cured material. In particular, the amine curing agent may contain a branched or unbranched alkane chain having at least 20 carbon atoms, preferably at least 30 carbon atoms. In addition, the amine curing agent may not contain an ether group. In some embodiments, the amine curing agent may be hydrophobic. The amine curing agent may have an amine hydrogen equivalent weight ("AHEW") of at least 50 g / equivalent, at least 80 g / equivalent, and at least 100 g / equivalent in some embodiments. Examples of amine curing agents can be prepared by polymerization of dimer fatty acids with polyamines, wherein the dimer acid has 4-60 carbon atoms, preferably at least 20 carbon atoms, preferably at least 30 carbon atoms, and in some embodiments 36 carbon atoms. 36 Dimeric diamines are examples of amine curing agents useful in the curable compositions of the present invention.

[0050] In some embodiments, the amine curing agent may be present in the second part of the two-part curable composition in a range of 1% to 30% by weight of the second part. In some embodiments, the amine curing agent may be present in the second part in a range of 5% to 25% by weight of the second part. In some embodiments, the amine curing agent may be present in the second part in a range of 10% to 20% by weight of the second part. In some embodiments, the amine curing agent may be present in the second part in a range of 10% to 15% by weight of the second part.

[0051] In addition to the thermally conductive particles, the second part of the curable composition may preferably be in a liquid state, which exhibits a thermal conductivity of 1 s at 25°C. -1 The viscosity is no greater than 5000 cP at a shear rate of 1 s. -1 The viscosity is no greater than 2000 cP at a shear rate of 1 s. -1 The viscosity is no greater than 1000 cP at a shear rate of 1000 cP, and in some embodiments, at 25°C and 1 s -1 The curable composition has a viscosity of no more than 500 cP at a shear rate of 1.5 to 2.0 %. In some embodiments, the portion of the curable composition containing the amine curing agent and the composition exhibit the above viscosity parameters. Even when blended with thermally conductive particles, the curable composition exhibits a relatively low viscosity level that is conducive to high dispensing rates through conventional two-part curable resin dispensing systems.

[0052] In some embodiments, the ratio of the amine equivalents in the second part to the epoxy equivalents in the first part, or more generally the ratio of the amine equivalents to the epoxy equivalents in the curable composition of the present invention, can be 0.7 to 1.2 to achieve the desired physical properties of the cured material. In some embodiments, the ratio of the amine equivalents to the epoxy equivalents in the curable composition of the present invention can be 0.8 to 1.2. In some embodiments, the first and second parts of the curable composition are blended in a weight ratio (first part: second part) of 0.8 to 1.2 to perform the curing reaction.

[0053] Thermally conductive fillers

[0054] The curable composition of the present invention comprises at least one thermally conductive filler in at least one of the first part and the second part in order to provide suitable thermal conductivity to the cured material.

[0055] Conductive fillers contemplated for use herein include, for example, boron nitride, aluminum nitride, aluminum oxide, aluminum oxide trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, gold, silver, copper, platinum, palladium, nickel, aluminum, indium, nickel alloys (e.g., Alloy 42), zinc alloys, iron alloys, indium alloys, silver-plated copper, silver-plated aluminum, bismuth, tin, bismuth-tin alloys, silver-plated fibers, silver-plated graphite, silver-plated silicon carbide, silver-plated boron nitride, silver-plated diamond, silver-plated aluminum oxide, silver-plated Alloy 42, graphene, silver-plated graphene, graphene nanosheets, single-walled carbon nanotubes and multi-walled carbon nanotubes, silver-plated polymers, cadmium and cadmium alloys, lead and lead alloys, antimony and antimony alloys, and the like, and mixtures of any two or more thereof. In some embodiments, the thermally conductive filler may be selected to be electrically conductive or electrically insulating. In some embodiments, the thermally conductive filler may be in the form of particles having a particle size ranging from about 1 nm to about 200 μm; in some embodiments, the conductive filler has a particle size ranging from about 10 nm to about 20 μm.

[0056] In some embodiments, the particulate thermally conductive filler can be substantially spherical, flaky, rod-shaped, or a combination thereof. The thermally conductive filler can be present in a range of 50% to 95% by weight of the total composition. In some embodiments, the thermally conductive filler can be present in a range of 60% to 95% by weight of the total composition. In some embodiments, the thermally conductive filler can be present in a range of 70% to 90% by weight of the total composition.

[0057] The thermally conductive filler may be distributed to one or more parts of the curable composition so that the cured thermally conductive interface material exhibits a thermal conductivity of at least 1.0 W / m*K, more preferably at least 2.0 W / m*K. The two mixed parts of the curable composition containing the thermally conductive filler may exhibit a thermal conductivity of at least 1.0 W / m*K at 25°C and 1 s. -1The viscosity is less than 500000 cP at a shear rate of 1 s, in some embodiments, at 25 ° C and 1 s -1 The viscosity is less than 300000 cP at a shear rate of 1 s, in some embodiments, at 25 ° C and 1 s -1 The viscosity is less than 200000 cP at a shear rate of 1000 ℃ and 1000 ℃, in some embodiments, at 25 ℃ and 1s -1 The viscosity is less than 100000 cP at a shear rate of 100000 cP, in some embodiments, at 25 ° C and 1s -1 The viscosity is less than 50000 cP at a shear rate of 1 s, in some embodiments, at 25 ° C and 1 s -1 The viscosity is less than 10000cP at a shear rate.

[0058] Optional additives

[0059] The second part of the two-part curable composition containing the curing agent may contain a curing accelerator to accelerate the curing of the epoxy resin. The curing accelerator may be selected from tertiary amines, imidazole derivatives, and combinations thereof.

[0060] Examples of tertiary amines include trimethylamine, triethylamine, tetraethylmethylenediamine, tetramethylpropane-1,3-diamine, tetramethylhexane-1,6-diamine, pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl)ether, ethylene glycol (3-dimethyl)aminopropyl ether, dimethylaminoethanol, dimethylaminoethoxyethanol, triethylenediamine, and hexamethylenetriamine. In some embodiments, the curing accelerator may be present in an amount of 0% to 1% by weight of the second part, preferably 0.1% to 0.6% by weight of the second part.

[0061] The two-part curable composition may also include a thixotropic agent in one or both of the first and second parts. Suitable thixotropic agents include talc, fumed silica, surface-treated calcium carbonate, fine-grained alumina, flaky alumina, montmorillonite, aluminum borate whiskers, and the like. The thixotropic agent may be present in an amount of 0% to 3% by weight, preferably 0.2% to 2% by weight, based on the total weight of the corresponding first or second part.

[0062] The composition may also include inorganic pigments or organic pigments (including iron oxide, brick dust, carbon black, titanium oxide, and combinations thereof) in one or both of the first part and the second part.

[0063] The composition may also include one or more flow additives, adhesion promoters, rheology modifiers, toughening agents, fluxing agents, film flexibilizers, phenol-novac hardeners, and mixtures of any two or more thereof.

[0064] As used herein, the term "flow aid" refers to compounds that modify the viscosity of the formulation into which they are introduced. Exemplary compounds that impart this property include silicone polymers, ethyl acrylate / 2-ethylhexyl acrylate copolymers, alkanolammonium salts of phosphate esters of ketoximes, and the like, and combinations of any two or more thereof.

[0065] As used herein, the term "tackifier" refers to compounds that enhance the adhesive properties of formulations into which they are introduced.

[0066] As used herein, the term "rheology modifier" refers to additives that alter one or more physical properties of a formulation into which they are introduced.

[0067] As used herein, the term "toughening agents" refers to additives that enhance the impact resistance of the formulations into which they are introduced.

[0068] As used herein, the term "flux" refers to a reducing agent that prevents oxides from forming on the surface of a molten metal.

[0069] As used herein, the term "film toughening agent" refers to an agent that imparts flexibility to a film prepared from a formulation containing it.

[0070] As used herein, the term "novolac hardener" refers to a material that participates in further interactions of reactive groups to increase their crosslinking, thereby enhancing their rigidity.

[0071] Another aspect of the present invention relates to a method for preparing a thermally conductive interface material that adheres to a substrate of an assembly. A two-part curable composition as described above is prepared, and the first part and the second part are mixed to form a reaction mixture. In some embodiments, the first part and the second part are mixed at less than 100° C., in some embodiments at less than 70° C., in some embodiments at less than 60° C., and in some embodiments at about 25° C. The reaction mixture is then applied to at least one surface of the substrate.

[0072] The first and second parts of the two-part curable composition are kept separate from each other and mixed immediately before use, and then the mixture is applied to the part to cure the mixture. In some embodiments, the mixture is cured at an elevated temperature (such as 60° C. to 100° C.) for 30 to 240 minutes. In some embodiments, the mixture is cured at an elevated temperature of 80° C. to 90° C. for 30 to 90 minutes.

[0073] The reaction mixture may be applied to the substrates by any convenient technique. Typically, the composition is applied to one surface of a pair of substrates, and the substrates are then aligned to be bonded by the thermally conductive interface material.

[0074] One aspect of the present invention is that the cured thermally conductive interface material exhibits improved mechanical properties including an adhesive strength of greater than 10 MPa on an aluminum substrate and a 100% cohesive failure mode. The cured thermally conductive interface material also exhibits a mechanical strength of at least 2 lb as measured by ASTM D1876. f / in, preferably at least 5lb f / in, in some embodiments at least 6 lb f The cured thermally conductive interface material may also exhibit a tensile elongation at break of at least 2%, preferably at least 5%, and in some embodiments at least 7%, as measured by ASTM D638. The cured thermally conductive interface material may also exhibit a lap shear strength of at least 350 psi, preferably at least 500 psi, and in some embodiments at least 600 psi, as measured by ASTM D1002.

[0075] It has been discovered that the curable compositions of the present invention form thermally conductive interface materials that unexpectedly exhibit significantly higher fracture toughness than conventional thermally conductive epoxy adhesive systems while maintaining high dispense rates and high thermal conductivity.

[0076] Another aspect of the present invention relates to the use of the two-part curable composition for bonding battery modules of an electronic automotive battery system. Figure 1 A battery system 10 is shown including a battery cell 12 having a housing 14, and a first terminal 16 and a second terminal 18. The battery cell 12 may be any of a variety of battery types, where the need for a thermally conductive interface 20 is determined. Particular embodiments of the battery system 10 may employ lithium-ion type battery cells 12, which may be assembled into a battery module 22 of a plurality of battery cells 12, or may be assembled in a battery pack (not shown), and between corresponding portions of a container for a plurality of battery modules 22. The thermally conductive interface 20 is preferably applied along a heat dissipation path between the battery cell 12, the battery module 22, and one or more heat dissipation elements.

[0077] Example

[0078] The following examples are intended to help those skilled in the art better understand and practice the present invention. The scope of the present invention is not limited by the examples, but is defined in the appended claims. Unless otherwise indicated, all parts and percentages are based on weight.

[0079] raw material :

[0080] EPON-862 is a liquid diglycidyl ether of bisphenol F with an epoxy equivalent weight (EEW) of 165-173.

[0081] EPON-826 is a liquid diglycidyl ether of bisphenol A with an epoxy equivalent weight (EEW) of 178-186.

[0082] Heloxy 62 is a liquid monofunctional o-cresol glycidyl ether with an epoxy equivalent weight (EEW) of 175-195.

[0083] Heloxy 505 is a liquid trifunctional epoxy resin of 9-octadecenoic acid, 12-(2-oxiranylmethoxy)-1,2,3-propane triyl ester homopolymer with an epoxy equivalent weight (EEW) of 500-650.

[0084] Cardolite NC-513 is a liquid glycidyl ether derived from cashew nut shells.

[0085] UTWFA240 is fused alumina.

[0086] TM2250 is surface treated aluminum oxide.

[0087] Lansco CB is a carbon black pigment.

[0088] R974 is a hydrophobic fumed silica treated with dimethyldichlorosilane.

[0089] TLT 100LV is the reaction product of bisphenol A diglycidyl ether and polyetheramine, used as a toughening agent.

[0090] Epikure 3251 is an amine curing agent for alkylphenols, aliphatic amines, alkyletheramines, 4-nonylphenol, alkylamines.

[0091] Priamine 1074 is a hydrogenated 36 -Amine curing agent of dimerized fatty acid diamine.

[0092] The following table shows embodiments 1-9, wherein comparative example 1 represents the formulation of prior art. The embodiment composition is mixed with the 1:1 ratio of part A and part B. The composition shown in embodiment 2-9 has improved tensile elongation, T-peel strength and failure mode on aluminum adherend and thermal conductivity of 2.0W / m*K. In addition, compared with comparative example 1, embodiment 9 demonstrates that thermal reliability performance (thermal resistance (resistance) between transistor and heat sink) is significantly improved. It should be noted that conventional adhesive systems based on polyurethane resins show a distribution rate in the range of about 45g / min under 90psi usually.

[0093] The data shown in Table 1 show that by using C 36The improvement of the B-side of Comparative Example 1 by directly replacing the Mannich base type curing agent with a dimerized fatty acid diamine resulted in a 114.3% improvement in T-peel strength on 6061 aluminum (Al). This improvement may be due to improved surface wetting of the adhesive on the aluminum surface and increased flexibility of the resulting cured epoxy network.

[0094] Table 1

[0095]

[0096] Further improvements to Part A were investigated. Tougheners with high epoxy equivalent weight (EEW) and low viscosity, and self-assembled PEO-PBO block copolymer toughening agents for epoxy resins were investigated to ensure that the dispensing rate was maintained. Toughening agents with molecular weight (MW) of about 3,000 to 5,000 g / mol or higher were excluded from the study due to their deleterious effects on viscosity (resistance to flow) and the resulting reduction in dispensing rate. The data show that when compared with C 36 When used in combination with a dimer fatty acid diamine curing agent, Heloxy 505 or castor oil polyglycidyl ether toughening agent provided a 707.1% improvement in T-peel strength. This improvement is greater than that provided by the PEO-PBO diblock copolymer toughening agent, which can significantly improve the fracture toughness of neat epoxy resin at low loading levels (5 phr or about 5 wt% in a filler-free system). This may be due to the effects of high Al2O3 concentration on the self-assembly and phase separation of the block copolymer before and during curing, respectively.

[0097] Table 2 describes a study on incorporating commercial PEO-PBO block copolymers, trifunctional epoxy tougheners, and GLYMO to improve the T-peel strength properties of thermally conductive interface materials on 6061 aluminum substrates.

[0098] Table 2

[0099]

[0100] Further investigation of the toughening agent in the A-side is shown in Table 3. These results show that the incorporation of both PEO-PBO diblock copolymer and castor oil polyglycidyl ether toughening agent into the A-side composition, together with the improvements to the B-side as shown in Example 2, resulted in a further improvement in T-peel strength (+742.9%). However, the improvement was less than 'additive', so no synergy between the toughening agent and the self-assembling block copolymer was observed. Unexpectedly, the incorporation of the monofunctional epoxy diluent resulted in an improvement in the consistency of the lap shear strength with respect to time after gelation, which may be due to the reaction of the monofunctional diluent with any unreacted secondary (2') and tertiary (3') amines to form the corresponding 3' amines and even quaternary amines, as well as reaction with -OH groups on the epoxy backbone.

[0101] Table 3

[0102]

[0103] The mode I fracture toughness or strain energy release rate GIc of Comparative Example 1 and Example 9 was measured by a tapered double cantilever beam (TDCB) test based on ISO / FDIS25217. The GIc of Comparative Example 1 was 179.6 J / m 2 , while the GIc of Example 9 is 536.6 J / m 2 , corresponding to a 198.8% increase in fracture toughness or resistance to crack propagation. Therefore, conventional carboxyl-terminated butadiene-acrylonitrile copolymers and polyurethane prepolymer toughening agents are not required to significantly improve the Mode I fracture properties of epoxy-based, highly filled thermal interface material compositions. The Mode I fracture toughness of conventional polyurethane-based thermal interface materials was measured to be 778.2 J / m 2 . Although polyurethane-based thermal interface materials generally show better fracture toughness than epoxy thermal interface materials, the composition of Example 9 shows a 79.8% higher tensile modulus than conventional polyurethane-based thermal interface materials. Therefore, the composition described in Example 9 provides good shear modulus, tensile elongation (>8%), thermal conductivity and fracture toughness close to conventional polyurethane-based thermal interface materials, as well as an 80.9% improvement in dispensing rate. At 25°C and 1s -1 The viscosity of the two-part composition of Example 9 was 290 Pa*s for Part A and 167 Pa*s for Part B at a shear rate of 1.38 %.

[0104] The results in Table 4 below show that the thermal reliability properties of Example 9 are significantly improved compared to Comparative Example 1. This may be due to the improvement in permanent adhesion due to the improvement in wettability of the uncured adhesive, and the increase in strain-to-failure to improve interfacial adhesion.

[0105] Table 4

[0106]

Claims

1. A two-part curable composition for forming a thermally conductive interface material, the composition comprising: The first part comprises an epoxy resin component, wherein the epoxy resin component comprises a first epoxy resin and a second epoxy resin different from the first epoxy resin, wherein the second epoxy resin has an epoxy equivalent weight of at least 100, and the epoxy resin component has an epoxy equivalent weight of at least 100 at 25° C. and 1 s -1 The viscosity does not exceed 5000 cP at a shear rate of The second part comprises an amine component having an amine curing agent effective to cure the first epoxy resin and the second epoxy resin, wherein the amine curing agent has an amine hydrogen equivalent weight of at least 80 g / equivalent, and the amine component has a relative humidity of 10% to 20% at 25° C. and 1 s -1 The viscosity does not exceed 5000 cP at a shear rate of as well as A thermally conductive filler in at least one of the first portion and the second portion, wherein the cured thermally conductive interface material exhibits a thermal conductivity of at least 1.0 W / m*K.

2. The two-part curable composition of claim 1, wherein the thermally conductive interface exhibits at least 5 lb f / in t-peel strength, at least 5% tensile elongation at break, and at least 350 psi lap shear strength.

3. The two-part curable composition of claim 1, comprising 50-95 wt% of the thermally conductive filler in each of the first part and the second part of the two-part composition.

4. The two-part curable composition of claim 2, wherein the epoxy resin component comprises 2-15 wt% of the first epoxy resin, and 2-8 wt% of the second epoxy resin.

5. The two-part curable composition of claim 1, wherein the epoxy resin component comprises a monofunctional epoxy resin different from the first epoxy resin and the second epoxy resin.

6. The two-part curable composition of claim 4, wherein the second epoxy resin comprises a trifunctional epoxy resin.

7. The two-part curable composition of claim 1, wherein the thermally conductive filler is selected from the group consisting of boron nitride, aluminum nitride, aluminum oxide, aluminum oxide trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, and combinations thereof.

8. The two-part curable composition of claim 4, wherein the thermally conductive filler comprises aluminum oxide.

9. The two-part curable composition of claim 1, wherein the curing agent comprises a branched or unbranched alkane chain having at least 20 carbon atoms.

10. The two-part curable composition of claim 8, wherein the alkane chain of the curing agent comprises at least 30 carbon atoms.

11. The two-part curable composition of claim 1 , wherein the second epoxy resin has an epoxy equivalent weight of at least 250.

12. A two-part curable composition for forming a thermally conductive interface material, the composition comprising: The first part comprises an epoxy resin component, wherein the epoxy resin component comprises a first epoxy resin and a second monofunctional epoxy resin different from the first epoxy resin, wherein the epoxy resin component has a temperature between 25° C. and 1 s -1 The viscosity does not exceed 5000 cP at a shear rate of The second part comprises an amine component having an amine curing agent effective to cure at least the first epoxy resin, the amine component having a temperature between 25° C. and 1 s -1 The viscosity does not exceed 5000 cP at a shear rate of as well as A thermally conductive filler in at least one of the first portion and the second portion, wherein the cured thermally conductive interface material exhibits a thermal conductivity of at least 1.0 W / m*K.

13. The two-part curable composition of claim 11, wherein the first epoxy resin is multifunctional.

14. The two-part curable composition of claim 11, comprising a third epoxy resin different from each of the first epoxy resin and the second epoxy resin, wherein the third epoxy resin is curable by the amine curing agent.

15. The two-part curable composition of claim 13, wherein the epoxy resin component comprises 1 wt% to 10 wt% of the first epoxy resin, 1 wt% to 10 wt% of the second epoxy resin, and 1 wt% to 30 wt% of the third epoxy resin.

16. The two-part curable composition of claim 11, wherein at least one of the first part and the second part comprises 50 wt% to 95 wt% of the thermally conductive filler.

17. The two-part curable composition of claim 15, wherein the thermally conductive filler is selected from particles of boron nitride, aluminum nitride, aluminum oxide, aluminum oxide trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, and combinations thereof.

18. The two-part curable composition of claim 11, wherein the second monofunctional epoxy resin comprises an oxygen atom in the beta position.

19. The two-part curable composition of claim 11, wherein the amine curing agent does not contain an ether group.

20. A battery system, comprising: Battery cells; heat sink; as well as A thermally conductive interface material, the thermally conductive interface material is disposed between the battery cell and the heat sink along a heat dissipation path, the thermally conductive interface material is formed by curing a two-part curable composition, the two-part curable composition comprising: (i) a first part having a first epoxy resin having an epoxy equivalent weight of at least 250 and a second monofunctional epoxy resin different from the first epoxy resin; (ii) a second part having an amine curing agent effective to cure at least the first epoxy resin; as well as (iii) a thermally conductive filler in at least one of the first portion and the second portion, the thermally conductive filler being present in an amount sufficient to enable the thermally conductive interface material to exhibit a thermal conductivity of at least 1.0 W / m*K along the heat dissipation path.

21. The battery system of claim 19, wherein the mixed two-part curable composition exhibits a -1 The viscosity does not exceed 500,000 cP at a shear rate of 1.

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