TWI871027B - Thermal interface materials with high temperature aging performance - Google Patents

Abstract

Thermally conductive compositions include an isocyanate component including a blocked isocyanate prepolymer having a mole percentage of 0.003 mole% or more, and one or more alkylalkoxysilanes including an alkyl chain of C12 or more; an isocyanate-reactive component comprising: one or more polyetheramines, and one or more catalysts selected from a group of carboxylate salts, tertiary amines, amidines, guanidines, and diazabicyclo compounds; and one or more glycol ether ester plasticizers present in one or more of the isocyanate component and the isocyanate-reactive component; and a thermally conductive filler.

Description

Thermal interface materials with high temperature aging performance

Embodiments relate to thermally conductive compositions and methods of using the same for use as thermal interface materials (such as gap fillers, sealants, spacers, or pastes) in applications requiring thermal management, such as electronic products and automotive applications.

Thermal interface materials such as gap fillers, adhesives, and gels are widely used for thermal management in electronic products and automotive applications. For example, electric vehicle (EV) battery packs are cooled by mounting one or more battery modules to a cooling plate that redirects the heat. For effective cooling, good thermal contact between the battery module and the cooling plate is required. Gap fillers fill this gap and provide thermal contact between the battery module and the cooling plate. Thermal gap pads and dispensable gap fillers are two of the basic gap filler technologies. Of the two, dispensable gap fillers have the advantage of providing more efficient heat transfer and less material waste compared to thermal pads that may require trimming and customization during installation. There is a need for a thermal interface material composition that has high thermal conductivity (> 0.5 W/m•K), is capable of forming a cured solid part without the application of heat, has low density and is easy to handle. In addition, the physical properties of the thermal interface material should remain stable at high temperatures and be resistant to thermal aging effects and degradation.

In one embodiment, the thermally conductive composition includes an isocyanate component containing a blocked isocyanate prepolymer at the thermally conductive composition, the thermally conductive composition including: an isocyanate component containing a blocked isocyanate at a molar percentage of 0.003 mol% or more, and one or more alkyl alkoxy silanes containing an alkyl chain of C12 or greater; an isocyanate reactive component including: one or more polyether amines, and one or more catalysts selected from the group consisting of carboxylates, tertiary amines, amidines, guanidines, and diaziridobicyclic compounds; and one or more glycol ether ester plasticizers present in one or more of the isocyanate component and the isocyanate reactive component; and a thermally conductive filler.

In another aspect, the thermally conductive gap filler can be prepared by combining an isocyanate component and an isocyanate-reactive component, and curing the resulting thermally conductive composition.

In another aspect, a method of using a thermally conductive composition includes combining an isocyanate component and an isocyanate-reactive component; and placing the thermally conductive composition between a heat source and a heat sink in an EV battery pack.

Embodiments disclosed herein relate to thermally conductive compositions for use in thermal management applications, including enhanced heat transfer in battery packs, electronic devices, automotive applications, and the like. The thermally conductive composition may include an isocyanate component and an isocyanate-reactive component that are combined and applied in situ to cure at room temperature and exhibit a durable Shore OO hardness when aged at elevated temperatures. The isocyanate component may include a blocked isocyanate prepolymer composition and an alkyl alkoxy silane having an alkyl chain of C12 or greater, and the isocyanate-reactive component may include one or more polyetheramines. The thermally conductive composition may further include a glycol ether ester plasticizer that reduces viscosity and improves heat aging performance.

The thermally conductive compositions disclosed herein can be formulated with plasticizers that increase processability while also being compatible with non-polar materials such as butyl rubber. For example, a plasticizer can be selected that has properties such as polarity, water solubility, and viscosity that minimize penetration of the plasticizer into surrounding non-polar materials used in conjunction with gap fillers and have low extrusion during installation.

During the battery assembly process, the gap filler composition is applied to a substrate and the battery module is assembled ("squeezed") onto the pre-applied gap filler. Once installed, the high temperatures encountered during the life of the vehicle can degrade known gap fillers. To meet these needs, gap fillers can be investigated using heat aging tests, which can involve heating the cured material to high temperatures for extended periods of time as a predictor of the long-term durability of the final product.

The thermally conductive compositions disclosed herein may include a combination of alkyl alkoxy silanes and plasticizers that reduce viscosity and reduce extrusion stress during preparation and application, while also producing a material that remains stable during high temperature aging. Reducing the viscosity and extrusion stress of the components of the thermally conductive composition can be beneficial, for example, by reducing the force required to assemble a gap filler between a heat source and a heat sink, such as in EV battery pack applications.

The numerical ranges disclosed herein include all values from lower values and higher values, and include the lower values and the higher values and all values therebetween. Unless stated to the contrary, implied from the context, or customary in the art, all parts and percentages are by weight, and all test methods are current methods as of the filing date of this disclosure.

As used herein, the term "average particle size" refers to the median particle size or diameter of a distribution of particles as determined, for example, by a Multisizer 3 Coulter Counter (Beckman Coulter, Inc., Fullerton, CA) according to the manufacturer's recommended procedure. The median particle size, _D50, is defined as the size at which 50 cumulative % of the particles in the distribution are smaller than the median particle size and 50 cumulative % of the particles in the distribution are larger than the median particle size. _D90 is defined as the size at which 90 cumulative % of the particles in the distribution are smaller than the stated value. _D10 is defined as the size at which 10 cumulative % of the particles in the distribution are smaller than the stated value. The average particle size can be estimated based on measuring the surface area according to 8-11 ASTM D4315 or by using sieves of various sieve hole sizes and calculating the average from the cumulative weight of each size fraction. These alternative methods give an estimate of the average particle size similar to that determined by laser diffraction methods. The span of the filler size distribution is defined as ( _D90 - _D10 )/ _D50 and indicates the width of the particle size distribution.

As disclosed herein, "room temperature" means a temperature range of 18°C to 35°C.

As disclosed herein, "molecular weight" means the number average molecular weight.

As disclosed herein, "thermally conductive filler" means a thermal conductivity value greater than 1 W/m·K as measured using a hot plate according to ISO 22007-2 or according to ASTM D-5470.

As disclosed herein, a "thermally conductive composition" (which includes cured and uncured compositions) means a composition having a thermal conductivity value greater than 1.0 W/m·K as measured using a hot plate according to ISO 22007-2 or according to ASTM D-5470.

As disclosed herein, "squeeze force" refers to the resistance of a thermally conductive composition or component to compression, measured in Newtons. Squeeze force is measured using a TA.XTplus texture analyzer equipped with a 50 kg load cell. After dispensing each sample onto a flat aluminum substrate, an acrylic probe with a 40 mm diameter is lowered to clamp the test material onto the flat substrate to achieve a standard 5.0 mm gap thickness. Any excess overflow material is trimmed with a flat-edge spatula. After trimming, the test begins and the probe is moved at a rate of 1.0 mm/second to a final thickness of 0.3 mm while recording the force. The specific force value recorded at a gap of 0.5 mm is recorded as the "squeeze force."

Viscosity can be measured using methods generally known in the art using a TA Instruments ARES-G2, AR2000 Rheometer, or Anton Paar MCR Rheometer using parallel plates or cone and plate fixtures.

Thermally conductive compositions for use in thermal management applications include enhanced heat transfer in electronic devices, battery packs, automotive applications, and the like. The described compositions can be used as thermally conductive gap fillers or pre-cured thermal pads for use in applications requiring thermal management, such as electric vehicle battery packs.

The thermally conductive compositions disclosed herein generally include the product obtained from the combination of a two-component curable composition: an isocyanate component ("A-side") and an isocyanate-reactive component ("B-side"). During application, the A-side and the B-side are mixed, a curing reaction is initiated at room temperature, and a thermally conductive composition is formed. The thermally conductive composition may also include one or more thermally conductive fillers in the A-side and/or the B-side to enhance heat transfer properties. A.) Isocyanate Component

The isocyanate component (or A-side) may contain one or more blocked isocyanate prepolymers, one or more alkyl alkoxy silanes, and other additives such as glycol ether ester plasticizers and thermally conductive fillers. Blocked isocyanate prepolymers

The thermally conductive composition disclosed herein may include a blocked isocyanate prepolymer in a weight percentage (wt%) of the isocyanate component greater than 5 wt%, which improves the durability and thermal stability of the composition when cured. The isocyanate component may include a blocked isocyanate prepolymer product produced by reacting the isocyanate-terminated prepolymer (including any residual monomeric diisocyanate) with one or more blocking agents. Reacting with the blocking agent can limit the presence of free isocyanate (e.g., a concentration below 0.1 wt%) and minimize premature gelation and crosslinking of the prepolymer. In some cases, reacting the isocyanate groups with the blocking agent reduces the free isocyanate content in the prepolymer to less than 0.1 wt%, less than 0.01 wt%, less than 0.001 wt%, or zero wt%.

The isocyanate-terminated prepolymer may be any prepolymer prepared by reacting one or more polyols with a stoichiometric excess of one or more polyisocyanates containing two or more isocyanate groups. The polyisocyanate may be an aromatic, aliphatic, araliphatic, or cycloaliphatic polyisocyanate, or a mixture thereof. Suitable polyisocyanates include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tetramethylene-1,4-diisocyanate, cyclohexane-1,4-diisocyanate, hexahydrotolylene diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, 4,4'-diphenyl diisocyanate, 3,3'-dimethoxy-4,4'-diphenyl diisocyanate, and 3,3'-dimethyldiphenylpropane-4,4'-diisocyanate; isomers thereof, or mixtures thereof. Suitable polyisocyanates may have an average isocyanate functionality of 1.9 or greater, 2.0 or greater, 2.1 or greater, or 2.2 or greater, and at the same time 3.5 or less, 3.2 or less, 3.0 or less, or 2.8 or less. The isocyanate-terminated prepolymer may have an isocyanate (NCO) content of 1% or more, 2.7% or more, or 5% or more by weight, and at the same time 30% or less, 25% or less, or 20% or less, according to ASTM D5155-19.

The isocyanate used to prepare the isocyanate-terminated prepolymer may include the above-mentioned monomeric polyisocyanates, isomers thereof, polymeric derivatives thereof, or mixtures thereof. In some cases, the isocyanate may include toluene diisocyanate (TDI), polymeric derivatives thereof, or mixtures thereof. The TDI used to prepare the isocyanate-terminated prepolymer may be 2,4-isomers and 2,6-isomers of toluene diisocyanate, etc. Prepolymers based on toluene diisocyanate may result in lower deblocking temperatures and high conversion and reaction rates. Mixtures of two or more polyisocyanates may also be used.

The polyols and polyol mixtures used to prepare the isocyanate-terminated prepolymers may include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, bis(hydroxy-methyl)cyclohexane (such as 1,4-bis(hydroxymethyl)cyclohexane), 2-methylpropane-1,3-diol, methylpentanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, polyether polyols, and the like. The isocyanate-terminated prepolymers may be prepared by the procedures described in U.S. Patent Nos. 4,294,951; 4,555,562; and 4,182,825; and International Publication No. WO 2004/074343. A catalyst may be used in some embodiments to form the isocyanate prepolymer and/or the blocked isocyanate prepolymer, which may include an amine-based catalyst and/or a tin-based catalyst.

In some embodiments, the blocked isocyanate prepolymer can be formed by mixing and reacting one or more of the isocyanate functional groups on the isocyanate prepolymer with one or more blocking agents. The blocking agent reacted with the isocyanate-terminated prepolymer can include a monophenol; an alkylphenol, such as nonylphenol; or an alkenylphenol, such as cardanol or a mixture, such as cashew nut shell liquid, and its analogs, and derivatives and any mixtures thereof. The blocking agent can be used in an amount such that the equivalents of the functional groups of the blocking agent correspond to the amount of isocyanate groups to be blocked, in moles or in excess of equivalents. In some embodiments, a blocked isocyanate prepolymer is made from TDI using a number average equivalent weight of 500 to 2500 Da and a PO polyol with a functionality of 1.9 to 3.1 and 2% to 15% NCO, followed by blocking with a blocking agent such as cardanol.

The isocyanate component may include a blocked isocyanate prepolymer in a weight percent (wt%) of 5 wt% or more, such as 5 wt% to 10 wt%, 5.5 wt% to 10 wt%, or 6 wt% to 10 wt%. The isocyanate component may include a blocked isocyanate prepolymer in a molar percentage (mol%) of 0.0032 mol% or more, such as 0.003% to 0.006 mol%, 0.0035 mol% to 0.0065 mol%, or 0.004 mol% to 0.0065 mol%.

The blocked isocyanate prepolymer composition may include a thermally conductive filler present in an amount of 50 wt% to 95 wt%, 75 wt% to 94 wt%, or 80 wt% to 92 wt%. Alkyl alkoxy silane

The thermally conductive compositions disclosed herein may include alkyl alkoxysilanes, which, without being bound by theory, when combined with an isocyanate component, can provide significant improvements in the high temperature aging performance of the cured article. In some cases, the isocyanate component may include one or more alkyl alkoxysilanes having a chemical structure of Si(OR) _n (R') _4-n , wherein n is an integer from 1 to 3, R is independently a C1 to C3 alkyl group, and R' is independently a C12 or greater alkyl group, such as a C12 to C25, or a C12 to C20 alkyl group. Suitable alkyl alkoxysilanes include dodecyltrimethoxysilane, tridecyltrimethoxysilane, tetradecyltrimethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, and the like. In one embodiment, the alkylalkoxysilane is hexadecyltrimethoxysilane. The alkylalkoxysilane may have a boiling point greater than 200°C, 250°C, or 300°C and less than 1000°C.

The alkylalkoxysilane disclosed herein may be added in an amount of 1.5 wt% or more, 1.5 wt% to 10 wt%, 1.5 wt% to 8 wt%, or 1.5 wt% to 5 wt% of the isocyanate component. B.) Isocyanate-Reactive Component

The isocyanate-reactive component (or B-side) may contain one or more polyetheramines, and one or more additives, such as glycol ether ester plasticizers and thermally conductive fillers. Polyetheramines

The isocyanate reactive component may include one or more polyetheramines. The polyetheramines may include monoamines, diamines, and higher amines (e.g., triamines, tetramines, etc.). In some cases, the isocyanate reactive component may include high molecular weight and low molecular weight polyetheramines, such as one or more polyetheramines with a molecular weight of 3000 or more (high MW) and one or more polyetheramines with a molecular weight of 3000 or less (low MW). The high MW polyetheramine and the low MW polyetheramine may be independently selected from polyetheramines with an amine functionality in the range of 1.5 to 4, 2 to 4, or 2.5 to 3.5. The molar ratio of high MW polyetheramine: low MW polyetheramine may be in the range of 10:1 to 1:10, 5:1 to 1:5, or 3:1 to 1:3.

Suitable polyetheramines include resins made from appropriate initiators to which lower alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, or mixtures thereof are added, followed by amination of the resulting hydroxyl-terminated polyols. When two or more oxides are used, they may be present as a random mixture or as blocks of one or the other polyether. In the amination step, the terminal hydroxyl groups in the polyol may be primary or secondary hydroxyl groups. Reductive amination processes are known and are described in U.S. Patent No. 3,654,370. The polyetheramines may include commercially available amines such as the primary aliphatic JEFFAMINE ^™ series of polyetheramines available from Huntsman Corporation, including JEFFAMINE ^™ T-403, JEFFAMINE ^™ T-3000, and JEFFAMINE ^™ T-5000, or available from BASF, including Baxxodur ^™ EC 3003 and Baxxodur ^™ EC 311.

In some embodiments, the isocyanate-reactive component may include at least one polyetheramine present in a weight percent (wt%) of the isocyanate-reactive component of 0.2 wt% to 40 wt%, 0.5 wt% to 30 wt%, or 1 wt% to 15 wt%. In formulations containing a mixture of high MW and low MW polyetheramines, the wt% ranges may apply to each type of polyetheramine individually or as a combined total. The isocyanate-reactive component may include one or more thermally conductive fillers present in a weight percent (wt%) of 50 wt% to 95 wt%, 75 wt% to 94 wt%, or 80 wt% to 92 wt%. Glycol Ether Ester Plasticizer

The thermally conductive composition may include a glycol ether ester plasticizer that increases storage stability, rubber compatibility, and heat aging characteristics. The glycol ether ester plasticizer may be mixed into at least one of the isocyanate component or the isocyanate reactive component in an amount ranging from 1 wt % to 20 wt %, 2 wt % to 16 wt %, or 4 wt % to 15 wt % of the respective composition (wt %).

Plasticizers disclosed herein include various types of glycol ether esters, including mixtures of one or more types. Suitable glycol ether esters include monoesters, such as the monoester described by formula (I): (I) wherein _R1 is a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, _R2 is hydrogen or methyl, _R3 is a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, and n is an integer of 1 to 4.

The glycol ether esters disclosed herein may also include glycol ether esters described by formula (II): (II) wherein _R1 and _R4 are independently a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, _R2 is hydrogen or methyl, _R3 is a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, and n is an integer from 1 to 4. Suitable glycol ether ester plasticizers include bis(2-(2-butoxyethoxy)ethyl)adipate, bis-dipropylene glycol n-butyl ether adipate, bis-diethylene glycol n-butyl ether malonate, bis-diethylene glycol n-butyl ether glutarate, bis-dipropylene glycol methyl ether maleate, tetraethylene glycol di-2-ethylhexanoate, and the like.

The glycol ether esters disclosed herein can also be described by the glycol ether esters of formula (III): (III) wherein _R1 and _R3 are independently a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, _R2 is hydrogen or methyl, and n is an integer from 1 to 4.

Suitable plasticizers also include glycol ether esters prepared by esterification of glycol ethers with one or more carboxylic acid equivalents. Glycol ethers may include 1 to 4 repeats of one or more glycol units, including ethylene glycol, propylene glycol, and the like. Carboxylic acids may include C2 to C12 carboxylic acids, such as acetic acid, propionic acid, isobutyric acid, adipic acid, 2-ethylhexanoic acid, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and the like. Carboxylic acids may include monocarboxylic acids and dicarboxylic acids.

Examples of suitable plasticizers include ethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, bis-dipropylene glycol n-butyl ether adipate, bis-dipropylene glycol n-butyl ether maleate, triethylene glycol-di-2-ethylhexanoate, bis(2-(2-butoxyethoxy)ethyl)adipate, bis-diethylene glycol n-butyl ether malonate, bis-diethylene glycol n-butyl ether glutarate, bis-dipropylene glycol methyl ether maleate tetraethylene glycol di-2-ethylhexanoate, propylene glycol methyl ether acetate, and the like.

In one embodiment, the one or more plasticizers are selected from the group consisting of bis-dipropylene glycol n-butyl ether adipate, triethylene glycol-di-2-ethylhexanoate, bis(2-(2-butoxyethoxy)ethyl) adipate, and tetraethylene glycol di-2-ethylhexanoate or a combination thereof.

While not being limited by theory, the polarity of the plasticizer can be selected to control the extrusion pressure of the formulation during application (where high polarity results in thickening and increased extrusion pressure), while also controlling the permeation rate to surrounding non-polar materials such as sealants. For example, the polarity of the plasticizer can be controlled to disadvantage the permeation and softening of non-polar materials (such as butyl rubber), where the increase in extrusion pressure of the A-side and B-side components is minimized. Other relevant factors that affect permeation rate may include water solubility, viscosity, and boiling point. In some embodiments, the thermally conductive compositions disclosed herein are compatible with butyl rubber, as indicated by no change in the Shore OO hardness of butyl rubber after contact with the thermally conductive composition for 28 days at 60° C., greater than 10%, greater than 20%, or greater than 30%. In some embodiments, the thermally conductive compositions disclosed herein are compatible with butyl rubber, as indicated by no change in the integrity of butyl rubber after contact with the thermally conductive composition for 28 days at 60° C. Loss of integrity can be visually observed as a change in the firmness or texture of the butyl rubber.

The plasticizer disclosed herein may be relatively polar, with a water solubility in the range of 5 mg/L to 10,000 mg/L, 10 mg/L to 5000 mg/L, 20 mg/L to 3000 mg/L. The water solubility of the plasticizer may be measured by methods generally known in the art, such as ASTM E1148-02. The plasticizer may be present in an amount sufficient to disperse or reduce the viscosity of at least one of the blocked isocyanate prepolymer composition or the amine composition. In some embodiments, the plasticizer may have a viscosity of less than 25 cps, less than 30 cps, or less than 35 cps. The plasticizer may have a viscosity in the range of 1 cps to 35 cps, 1 cps to 30 cps, or 5 cps to 30 cps. The plasticizer may also have a boiling point greater than 300°C at 1 atmosphere (760 mm Hg) to minimize or eliminate loss of the plasticizer by evaporation during testing and use. The plasticizer may have a boiling point in the range of 300°C to 1000°C, 290°C to 1000°C, or 290°C to 950°C at 1 atmosphere (760 mm Hg). The above ranges may be combined in any order to define a class of plasticizers. For example, the plasticizer disclosed herein may have a water solubility in the range of 5 mg/L to 10,000 mg/L, a viscosity less than 30 cps, and a boiling point in the range of 290°C to 1000°C at 1 atmosphere (760 mm Hg). Mixtures of different plasticizers may be used. Thermally conductive filler

The thermally conductive composition may also include one or more thermally conductive fillers in the A side and/or the B side. The fillers disclosed herein may have a thermal conductivity of at least 1 W/m•K, at least 5 W/m•K, or at least 20 W/m•K, and may have a thermal conductivity of less than 1000 W/m•K, or less than 100 W/m•K. The fillers disclosed herein may be low density and low hardness to reduce the overall weight of the composition and reduce the weight of the automobile, EV, and reduce the abrasiveness of the composition. In one embodiment, the filler density is < 6 gm/cc, < 4 gm /cc, or < 2.5 gm/cc.

The thermally conductive fillers disclosed herein may include one or more of metal oxides, metal nitrides, metal carbides, metal hydroxides, metal carbonates, metal sulfates, natural and synthetic minerals (primarily silicates and aluminum silicates). Suitable fillers include aluminum trihydrate (ATH), natural or synthetic alumina, quartz, silicon dioxide, and the like. The thermally conductive composition may include one or more fillers, which are added to the formulation in their final state or formed in situ.

The thermally conductive filler disclosed herein may be modified with a treating agent prior to incorporation into the A-side and/or B-side of the thermally conductive composition, the treating agent altering the hydrophobicity/hydrophilicity of the surface of the thermally conductive filler, thereby altering the filler and polymer interaction, viscosity, and/or extrusion pressure of the resulting thermally conductive composition. The treating agent may include a fatty acid, a silane treating agent, a titanium salt, a zirconate, an aluminum salt, or a silazane compound.

The thermally conductive fillers disclosed herein may have a wide range of particle size distributions and/or have a bimodal particle size distribution. The average D ₅₀ particle size of the fillers disclosed herein may be in the range of 0.05 μm to 500 μm, 0.1 μm to 300 μm, 0.5 μm to 100 μm, or 0.5 μm to 50 μm. The average D ₉₀ particle size of the fillers disclosed herein may be in the range of 0.05 μm to 500 μm, 1 μm to 300 μm, 5 μm to 200 μm, or 10 μm to 150 μm. The average D ₁₀ particle size of the fillers disclosed herein may be in the range of 0.05 μm to 30 μm, 0.08 μm to 10 μm, 0.1 μm to 10 μm.

The span may be controlled in some cases to reduce the extrusion stress of the resulting thermally conductive composition. The thermally conductive fillers disclosed herein may have a wide particle size characterized by a span greater than 2, greater than 3, or greater than 4, or less than 50. In some cases, the thermally conductive filler may have a bimodal particle size distribution produced by blending two fillers with one filler having a _D50 in the range of 0.1 to 20 μm and another filler having a _D50 in the range of 10 to 200 μm.

The thermally conductive fillers disclosed herein may be present in a weight percent (wt%) of 50 wt% to 95 wt%, 75 wt% to 94 wt%, or 80 wt% to 92 wt% of the total weight of the thermally conductive composition. The fillers may be loaded in equal or different amounts in the A side and/or the B side, when combined, to produce a thermally conductive composition having a filler concentration in any of the above ranges. It should be noted that different filler sizes/types may be blended to obtain the desired filler loading and viscosity of the formulation.

In some cases, the thermally conductive filler can be aluminum trihydrate. The thermally conductive filler can have a span of >4, a _D10 in the range of 0.1 to 10 microns, a _D50 in the range of 5 to 50 microns, and a _D90 in the range of 50 to 200 microns. The thermally conductive filler can also be pre-treated with a C5-C20 silane treatment agent to modify the hydrophobicity and compatibility with the isocyanate component and/or the isocyanate-reactive component. Catalyst

The thermally conductive composition may include one or more catalysts mixed into at least one of the isocyanate component or the isocyanate-reactive component to promote the reaction of the blocked isocyanate functional group with the polyetheramine. The catalyst may be selected from any one of carboxylates, tertiary amines, amidines, guanidines, and diaziridobicyclic compounds or any combination/mixture of more than one. Suitable catalysts include bismuth octanoate, bismuth neodecanoate, potassium acetate, potassium 2-ethylhexanoate, or mixtures thereof. The catalyst may include a hindered tertiary amine; a long chain tertiary amine (i.e., an amine substituent with at least 6 hydrocarbons); or a cyclic tertiary amine. Suitable tertiary amines include di-N- dimorpholinodialkyl ether, di((dialkyl N- phthaloyl)alkyl) ethers, such as (di-(2-(3,5-dimethyl-N- 1-Methyl-1-piperidinium chloride, ... Morpholine, N-methyl Phosphine, N-ethyl In some embodiments, the amidine or guanidine is an N-alkyl substituted amidine or guanidine; in another embodiment, the amidine or guanidine is a cyclic amidine or cyclic guanidine. Suitable amidines or guanidines include 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene, diazabicyclo[5.4.0]undec-7-ene, and N-methyl-1,5,7-triazabicyclododecene. The catalyst may be present in the isocyanate-reactive component in a weight percent (wt %) ranging from 0.001 wt % to 5.0 wt %, 0.01 wt % to 2.0 wt %, or 0.02 wt % to 0.5 wt %.

The thermally conductive composition may include one or more additives, which may include moisture scavengers (e.g., zeolites, molecular sieves, toluenesulfonyl isocyanate), adhesion promoters, modifiers, colorants (e.g., dyes or pigments), antioxidants, wetting agents (e.g., surfactants), filler dispersants, thickeners, compatibilizers, anti-settling agents, anti-syneresis agents, flame retardants, and/or filler treatment agents. C. Preparation Methods

Prior to combining to form the thermally conductive composition, the isocyanate component and/or the isocyanate-reactive component may have an extrusion pressure of 180 N or less, 150 N or less, or 100 N or less. The isocyanate component and/or the isocyanate-reactive component may have an extrusion pressure in the range of 35 N to 250 N, 35 N to 150 N, or 35 N to 100 N. In some embodiments, the isocyanate component and the isocyanate-reactive component exhibit an extrusion pressure variation of less than 50% within 3 days, or an extrusion pressure variation of less than 20% after heating at 60° C. for 7 days, indicating excellent storage stability.

The preparation of the thermally conductive composition disclosed herein can be achieved by mixing the individual components of the isocyanate component and the isocyanate-reactive component in any order, and combining the components to prepare the final mixture. Suitable mixing techniques include the use of Ross PD mixers (Charles Ross), Myers mixers, FlackTek Speedmixers, butterfly mixers, and the like. Continuous methods such as twin-screw extrusion can also be used to mix the various components of the composition. The various streams can be fed separately to the extruder or pre-mixed in various combinations to form the blocked isocyanate composition and the isocyanate-reactive component. Such methods can be applicable to large-scale production.

The isocyanate-reactive component and the isocyanate component can be combined so that the molar ratio of the blocked isocyanate groups to the amine-reactive groups is in the range of 0.90:1.1 to 1.1:0.9, such as 0.90:1.1, 0.95:1.05, 0.97:1.03, or 1:1. At the same time, the volume ratio of the isocyanate-reactive component to the isocyanate component in the curable composition can be controlled in the range of 0.90:1.1, 0.95:1.05, 0.97:1.03, or a ratio of 1:1.

The mixture of the isocyanate component and the isocyanate-reactive component can be cured at a temperature of 0°C to 60°C, 10°C to 50°C, 15°C to 45°C, or 18°C to 35°C (e.g., RT). Curing can be indicated by an increase in viscosity after mixing the A side and the B side, ultimately forming a cured thermally conductive solid with a measurable hardness. The cured thermally conductive composition can have a hardness range of 40 to 90 Shore OO, 50 to 85 Shore OO, or 60 to 80 Shore OO as determined by ASTM D-2240-15. In some embodiments, the thermally conductive composition has a cured hardness determined by ASTM D-2240-15 of 50 to 85 Shore OO.

The thermally conductive compositions disclosed herein can be cured in less than 14 days, less than 10 days, or less than 7 days, and typically the time scale is greater than 30 minutes. The cured thermally conductive compositions can have a thermal conductivity of > 0.5 W/m•K, or > 1 W/m•K, or optimally > 1.5 W/m•K, or < 50 W/m•K. The cured thermally conductive compositions disclosed herein can have a density of 1 gm/cc to 4 gm/cc, 1.5 to 3.5 gm/cc, or 1.8 to 3.1 gm/cc. In addition, the viscosity of the A side and the B side allows the material to be easily processed.

In some embodiments, the thermally conductive compositions disclosed herein are compatible with butyl rubber, as indicated by no change in the integrity of the butyl rubber after contact with the thermally conductive composition for 28 days at 60° C. Loss of integrity can be visually observed as a change in the firmness or texture of the butyl rubber.

The cured thermally conductive composition may have a thermal conductivity of >1.0 W/m•K, or >1.5 W/m•K, or >1.9 W/m•K, or <50 W/m•K. In some embodiments, the cured thermally conductive composition may have a density of 1 gm/cc to 4 gm/cc, 1.5 to 3.5 gm/cc, or 1.8 to 3.1 gm/cc. The cured thermal composition may have an initial Shore OO hardness of 60 or greater, 65 or greater, or 70 or greater, such as in the range of 60 to 85. In some embodiments, when combined and formed into a cured article, the thermally conductive composition may exhibit a change in Shore OO hardness of less than 30%, less than 25%, or less than 20% after aging at 100°C for 10 days. In some embodiments, when combined and formed into a cured article, the thermally conductive composition can exhibit a change in Shaw OO hardness of less than 30%, less than 25%, or less than 20% after aging at 90°C for 21 days.

The thermally conductive compositions disclosed herein can be used as gap fillers in thermal management of energy storage devices and electronic vehicle battery packs. In some cases, the composition can include gap fillers and pastes applied between a heat source and a heat sink to provide a thermally conductive interface, such as between a battery module and a cooling plate. Manual or automated dispensing tools can be used to apply the thermally conductive composition directly to a target surface to minimize waste. In one embodiment, the thermally conductive composition can be prepared by combining an isocyanate component and an isocyanate-reactive component and applying an automated mix-meter-dispense system to a cooling plate or heat sink, followed by mounting a battery cell, module, or package, or other heat source.

Additionally, the thermally conductive composition can be used to form pre-cured articles, such as thermal interface gap pads. In one example, the pre-cured article can be formed by curing the thermally conductive composition at a desired thickness, cutting the article into the desired shape, and then compressing as needed to secure it in place. In some cases, the cured article can also help reduce vibration stresses to dampen shock. Example

The following examples are provided to illustrate embodiments of the present invention and are not intended to limit the scope thereof. Unless otherwise indicated, all parts and percentages are by weight. Table 1 lists the materials used in the following examples: Table 1: Chemical components used in the examples Components describe Blocked isocyanate prepolymer TDI-based blocked isocyanate prepolymers prepared from polypropylene oxide (approximately 3 kDa) had 2.7% NCO prior to blocking with cardanol, a viscosity of 15,000 to 30,000 Pa•s and an equivalent weight NCO of 1555 Amine-1 A triamine based on a polypropylene glycol backbone with a molecular weight of 5000 Da. Amine-2 A triamine based on a polypropylene glycol backbone with a molecular weight of 440 Da. Filler-1 Hydrophobic surface treated aluminum trihydrate (ATH) with a D10 of 0.5 microns, a D50 of 8 microns, and a D90 of 80 microns Filler-2 Hydrophobic surface treated aluminum trihydrate (ATH) with a D10 of 1 micron, a D50 of 12 microns, and a D90 of 85 microns Plasticizer-1 Bis(2-(2-butoxyethoxy)ethyl) adipate, viscosity 18 cps to 23 cps, boiling point 417°C, and water solubility 570 mg/L Plasticizer-2 Methyl ester derivative of soybean oil, C16-C18 methyl ester Plasticizer-3 Bis-dipropylene glycol n-butyl ether adipate, viscosity 19 cps, boiling point 485℃, water solubility 31.1 mg/L Catalyst-1 Diazabicyclo[5.4.0]undec-7-ene Silane-1 Hexadecyltrimethoxysilane, boiling point 350℃ Comparison with Silane-1 Octyltriethoxysilane, boiling point 225°C. Comparison with Silane-2 Decyltrimethoxysilane, boiling point 213℃ Antioxidants Irgonox-1010 Phenolic Primary Antioxidant Butyl rubber Butyl rubber beads with a cross section of 4 mm x 4 mm and a hardness of 55 OO

Sample formulations were prepared by mixing the individual components in a high speed mixer. Part A and Part B of each formulation were prepared separately. To cure the two part system, Part A and Part B were mixed in a 1:1 weight ratio and mixed using a high speed mixer. Samples were prepared in a speed mixer cup, 20 gm total, formed into a disk of approximately 3.5 cm diameter and approximately 1 cm height.

The specimens were allowed to cure at ambient conditions for 7 to 14 days to measure hardness before aging.

The samples were aged in an oven in air and periodically removed, placed on a bench and allowed to cool to room temperature. The hardness was then measured after aging.

Thermal conductivity was measured using a Hot Disk Thermal Constants Analyzer (TPS 2500S, Thermtest Instruments, Canada) according to ISO 22007-2. All measurements were performed with a hot probe using double-sided measurement with a 2 to 6 mm cup at 150 W heating power and 5 s measurement time.

Extrusion pressure is measured using a texture tester equipped with a 50 kg load cell. After dispensing the gap filler onto the aluminum substrate, an acrylic probe with a 40 mm diameter is lowered to clamp the test material onto the substrate to achieve a standard 5.0 mm gap thickness. Any excess material is trimmed off with a flat blade scraper. After trimming, the test is started and the probe is moved at a rate of 1.0 mm/second to a final thickness of 0.3 mm while recording the force. "Extrusion pressure" is defined as the specific force value recorded at a gap of 0.5 mm.

Hardness was measured using a Schroder OO durometer according to ASTM D2240.

To test compatibility with butyl rubber, 150 to 175 gm each of the A and B sides of the respective compositions were mixed in a 1:1 weight ratio and applied to a 6 inch by 12 inch aluminum plate using a spatula. A 6 mm aluminum shim was placed on both sides of the aluminum plate to control the thickness of the sample. A polytetrafluoroethylene (PTFE) sheet was placed on top of the gap filler and a 6 inch by 12 inch top aluminum plate was applied and the assembly was compressed by applying a paper clip on the four corners of the aluminum plate. The sample was cured at room temperature for 3 to 4 days after which the top plate and PTFE were removed and excess sample was removed from the sides. A butyl rubber bead (4 mm square) approximately 4 to 6 inches long is applied to the middle of the test sample and tapped gently to provide good contact. The sample is then placed in an oven at 60°C. To monitor any degradation of the butyl rubber, the sample is periodically removed, cooled, and the hardness of the butyl rubber is measured using a Shaw OO durometer. A qualitative analysis of the toughness of the butyl rubber is performed using a wooden tongue depressor, by touching the sample and stretching it to determine if the rubber has softened or lost integrity due to the migration of the plasticizer. The initial hardness of the butyl rubber is approximately 55 Shaw OO.

The results are summarized in Tables 2 to 5, where samples labeled "C" indicate comparative samples and "I" indicates inventive samples according to the present disclosure. Table 2: Composition and characteristics of the comparison samples C1 C2 C3 C4 A side B side A side B side A side B side A side B side Blocked isocyanate prepolymer 9 - 15 0 9 - 15 0 Amine-1 - 10.5 0 10 - 10.5 0 10 Amine-2 - - - 0.65 - - - 0.65 Blue Dye 0.5 - 0.5 0 0.5 - 0.5 0 Catalyst-1 - 0.035 0 0.025 - 0.035 0 0.025 Plasticizer-1 29.5 27.46 24.5 28.04 24.5 27.46 21.5 28.04 Filler-1 211 212 210 211.3 211 212 210 211.3 Silane-1 - - - - 5 - 3 - Total 250 250 250 250 250 250 250 250 Extrusion pressure [N] 82 83 117 63 53 83 94 63 Thermal conductivity [W/m•K] 2.18 2.18 2.04 2.07 1.92 2.17 1.93 2.07 Characteristics of the components of the combination Hardness before aging (OO) 68 75 68 75 Hardness after aging for 8 to 10 days at 100°C (OO) 0 0 52 55 Table 3: Composition and characteristics of the comparison samples C5 C6 C7 C8 A side B side A side B side A side B side A side B side End-capped prepolymer 12 0 15 - 15 - 15 - Amine-1 0 8.1 - 10 - 10.5 - 10.5 Amine-2 0.5 - 0.65 - - - - Blue colorant 0.5 0 0.5 0.5 - 0.5 - Catalyst-1 0 0.025 - 0.0125 - 0.035 - 0.035 Plasticizer-1 22.5 29.84 - - 17.5 27.46 17.5 27.46 Plasticizer-2 - - 15.5 25.34 - - - - Filler-1 210 211.29 214 214 212 212 212 212 Silane-1 5 - 5 - - - - - Comparison with Silane-1 - - - - 5 - - - Comparison with Silane-2 - - - - - - 5 - Antioxidants - 0.25 - - - - - - Total 250 250 250 250 250 250 250 250 Extrusion pressure [N] 56 58 69 35 93 83 91 83 Thermal conductivity [W/mK] 1.80 2.05 2.00 1.98 2.03 2.17 1.94 2.17 Characteristics of the components of the combination Hardness before aging (OO) 70 77 77 78 Hardness after aging for 8 to 10 days at 100°C (OO) 45 40 0 0 Table 4: Composition and properties of the samples of the present invention I1 I2 I3 A side B side A side B side A side B side End-capped prepolymer 15 0 13.5 - 14.5 - Amine-1 0 10 - 10 - 10 Amine-2 0.65 - 0.5 - 0.6 Blue Dye 0.5 0 0.5 - 0.5 - Catalyst-1 0 0.028 - 0.025 - 0.035 Plasticizer-1 17.5 28.0 twenty one 27.9 17.5 28.08 Filler-1 212 211.29 210 211.3 212.5 211.3 Silane-1 5 - 5 - 5 - Antioxidants - - - 0.25 - - Total 250 250 250 250 250 250 Extrusion pressure [N] 105 70 63 61 107 59 Extrusion pressure [N] -60℃-7 days 117 56 - - - - Thermal conductivity [W/mK] 2.13 2.08 1.82 2.08 1.96 2.11 Characteristics of the components of the combination Hardness before aging (OO) 75 70 75 Hardness after aging for 8 to 10 days at 100°C (OO) 70 62 65 Hardness after aging at 90℃ for 21 days (Short OO) 72 - - Thermal conductivity after aging at 90℃ for 21 days (School OO) [W/mK] 2.16 - - Butyl rubber hardness after 28 days 60℃-Short OO 55 (no change) - - Table 5: Composition and properties of the samples of the present invention I4 I5 A side B side A side B side End-capped prepolymer 15 0 15 0 Amine-1 0 10 0 10 Amine-2 - 0.65 - 0.65 Blue Dye 0.5 0 0.5 0 Catalyst-1 0 0.028 0 0.010 Plasticizer-1 18.5 28.0 - - Plasticizer-3 - - 14.5 24.34 Filler-1 212 211.3 - - Filler-2 - - 215 215 Silane-1 4 - 5 - Total 250 250 250 250 Extrusion pressure [N] 113 60 133 75 Thermal conductivity [W/mK] 2.01 2.03 1.94 2.02 Characteristics of the components of the combination Hardness before aging (OO) 75 75 Hardness after aging for 8 to 10 days at 100°C (OO) 60 71 Hardness after aging at 90℃ for 21 days (Short OO) - 76 Butyl rubber hardness after 28 days at 60℃ - OO 55 (no change) 55 (no change)

As shown in the examples, the comparative samples exhibited a change in Shore hardness after aging at 100°C. Samples C1 and C2 show that excluding silanes produces a material with a Shore hardness of 0 after aging. Samples C3 and C5 have low prepolymer concentrations (<5wt% prepolymer, or <0.003 mol% on the A side) and silanes, and show a significant decrease in hardness after aging. Similarly, C4, which has an increased prepolymer concentration and a low silane concentration, exhibits a significant decrease in hardness after aging. C6 is a formulation containing soy methyl ester plasticizer and silane on the A side, which also exhibits a decrease in hardness, indicating that the combination of glycol ether esters and silanes produces stable aging performance. Samples C7 and C8 used silanes with carbon numbers of 8 and 10, respectively, and both exhibited a decrease in hardness over time. Silanes with alkyl groups less than 12 have correspondingly lower boiling points, which can cause the silane to evaporate during aging and change the material properties of the gap filler.

Samples I1 to I4 of the present invention have relatively high concentrations of prepolymer (>5 wt% on the A side) and alkyl alkoxy silane and glycol ether ester plasticizers, and all samples exhibit acceptable hardness changes under aging. I5 shows similar effects with different glycol ether ester plasticizers. I1 and I5 also show retention of hardness after aging for 21 days at 90°C. I1 also shows retention of thermal conductivity after aging for 21 days at 90°C. I1 also shows that the paste has good storage stability, which is indicated by minimal change in extrusion pressure after aging for 1 week at 60°C. I1, I4, and I5 also show that the composition is compatible with butyl rubber, as indicated by no change in the hardness of butyl rubber after contact with the curing composition at 60°C for 28 days or more.

While the foregoing is directed to exemplary embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope of the same is to be determined by the following claims.

without

without

Claims (10)

A thermally conductive composition comprising: an isocyanate component comprising a blocked isocyanate prepolymer in a molar percentage of 0.003 mol% or more, and one or more alkyl alkoxy silanes comprising an alkyl chain of C12 or greater; an isocyanate reactive component comprising: one or more polyether amines, and one or more catalysts selected from the group consisting of carboxylates, tertiary amines, amidines, guanidines, and diaziridobicyclic compounds; and one or more glycol ether ester plasticizers present in one or more of the isocyanate component and the isocyanate reactive component; and a thermally conductive filler. The composition of claim 1, wherein the one or more glycol ether ester plasticizers are one or more selected from the group of glycol ether esters of formula (I): (I) wherein R ₁ is a saturated, unsaturated, and/or substituted carbon chain of 2 to 12 carbon atoms, R ₂ is hydrogen or methyl, R ₃ is a saturated, unsaturated, and/or substituted carbon chain of 2 to 12 carbon atoms, and n is an integer of 1 to 4; Formula (II): (II) wherein _R1 and _R4 are independently a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, _R2 is hydrogen or methyl, _R3 is a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, and n is an integer from 1 to 4; or formula (III): (III) wherein _R1 and _R3 are independently a saturated, unsaturated, and/or substituted carbon chain comprising 2 to 12 carbon atoms, _R2 is hydrogen or methyl, and n is an integer from 1 to 4. The composition of claim 1, wherein the alkylalkoxysilane is present in an amount of 1.5 wt % or more of the isocyanate component. The composition of claim 1, wherein the alkylalkoxysilanes may have a chemical structure of Si(OR) _n (R') _4-n , wherein n is an integer from 1 to 3, R is independently a C1 to C3 alkyl group, and R' is independently an alkyl group having 12 to 20 carbon atoms. The composition of claim 1, wherein the thermally conductive filler is aluminum trihydrate (ATH) with a hydrophobic surface modification. The composition of claim 1, wherein the cured article exhibits a change in Shore 00 hardness of less than 20% after aging at 100°C for 10 days. The composition of claim 1, wherein the isocyanate component exhibits a change in extrusion pressure of <20% after heating at 60°C for 7 days. The composition of claim 1, wherein the thermally conductive composition is compatible with butyl rubber, as indicated by a change in hardness of butyl rubber of no more than 20% after contact with the thermally conductive composition at 60°C for 28 days. A thermally conductive gap filler is prepared by combining an isocyanate component and an isocyanate-reactive component and curing the thermally conductive composition obtained as described in any one of claims 1 to 7. A method of using the thermally conductive composition of any one of claims 1 to 7, the method comprising combining the isocyanate component and the isocyanate-reactive component; and placing the thermally conductive composition between a heat source and a heat sink in an EV battery pack.