Two-component thermally conductive adhesive with low e-modulus

Abstract

Two-component thermally conductive adhesive with improved E-Modulus characteristic and the made of making thereof.

Description

PATENT APPLICATIONTWO-COMPONENT THERMALLY CONDUCTIVE ADHESIVE WITH LOW E-MODULUS

[0001] There is a trend in the automotive industry to reduce the weight of the vehicles in the past decade. This trend has been driven by regulations to reduce CO2 emission of vehicle fleets. In recent years, lightweight construction strategies have been further fueled by the increasing number of electrically driven vehicles. To provide for longer driving range, batteries with a high energy density are needed. All long-range durable battery cells need adequate thermal management. To thermally connect battery cells or modules that house the battery cells to a cooling unit, thermal interface materials or thermally conductive adhesives are needed.

[0002] Battery cells produce heat during charge and discharge. The cells should be kept in the right operating temperature (preferably 25-40°C) to avoid efficiency losses, overheating, and dangerous runaway thermal reactions. For this reason, active cooling is commonly used. An efficient active cooling method involves pumping cooled water- glycol mixtures through channels that cool a metal bottom of a cooling plate on which the battery cells or modules are installed. Battery cells or box of cells can be bonded with thermal conductive adhesives directly to the cooling plate. This provides for good mechanical fixation and a thermal connection. Battery cells can be pouch cells, prismatic cells or cylindrical cells, all of them need cooling. The cooling unit can be bonded with the adhesive either to the bottom of the cells, or to the side of the cells with a thermal conductive adhesive.

[0003] A key requirement of the thermal conductive adhesives is a thermal conductivity of no less than 1 .5 W / mK. Further, a lap shear strength of > 2.5 MPa is required. The cooling unit and the battery cell / boxs are often made of aluminum covered with polyethylene terephthalate (PET) film or similar polymer materials. Therefore, a good adhesion between the thermal conductive adhesive and PET film is required. For some battery applications, a foam or a potting composition is applied to fill the battery box for better stiffness to avoid the rupture of the PET film from the battery cells in caseof a physical impact of the vehicles. In these applications, the modulus of the thermal conductive adhesives applied between the battery cell boxes and the cooling units must be lower than that of the potting composition or the foam so that any energy of physical impact will be transferred from the adhesives to the foam and thus maintaining the integrity of PET film. Typically, the E-modulus of the thermal conductive adhesives should be as low as possible and in most cases, they should stay below 35 MPa.

[0004] There is a variety of potential materials available that can be employed to formulate thermal conductive adhesives. Two-component polyurethane adhesives stand out among other candidates in that they have good mechanical properties and elongation at break and good curing kinetics. However, because of the high content of fillers typically used in these polyurethane adhesives, the commonly available two- component polyurethane adhesives typically exhibit high E-Modulus.

[0005] What is desired is a two-component polyurethane thermal conductive adhesive formulation with low E-Modulus even when the filler contents in the adhesive formulation exceeds 70 wt.% of the total formulation.SUMMARY OF THE INVENTION

[0006] The present invention relates to a thermal conductive adhesive with e- modulus at less than 35 MPa, preferably less than 15 MPa, while having a thermally conductive filler of more than 50 wt. %, based on the total weight of adhesive formulation. More specifically, the present invention relates to a two-component adhesive formulation comprising an isocyanate component comprising more than 50 wt.% of a thermally conductive filler; and a polyol component; wherein at least one of the isocyanate component and the polyol component further comprises a plasticizer; and wherein E-Modulus of the two-component adhesive is less than 35 MPa.DETAILED DESCRIPTION OF THE INVENTION

[0007] To achieve a thermal conductivity greater than 1 .5 W / mK, both components of a two-component adhesive formulation typically require at least 50 to 95% of a thermally conductive filler by weight of the component. In one embodiment, each component of the adhesive formulation independently comprises 50% to 85% of a thermally conductive filler by weight of the component. In another embodiment, each component of the adhesive formulation independently comprises 50% to 80% of a thermally conductive filler by weight of the component. In a preferred embodiment, each component of the adhesive formulation independently comprises 50% to 75% of a thermally conductive filler by weight of the component. In another preferred embodiment, each component of the adhesive formulation independently comprises 50% to 75% of a thermally conductive filler by weight of the component.

[0008] A variety of thermally conductive fillers can be used. Examples include aluminum hydroxide, also known as aluminum trihydroxide (ATH), aluminum oxide, such as spherical aluminum oxide, graphites, and any combination thereof. ATH can be monomodal ATH powders or ATH powders having a multi-modal particle size distribution (e.g., bi-modal, tri-modal, and the like). When monomodal ATH powders are used, the average particle size can be 5-100 pm. When multi-modal ATH powders are used, the average particle size of the smallest particles can be less than about 10 pm, while the average particle size of the largest particles can be greater than about 50 pm. Additionally, the ATH powders can be surface treated with silane, titanate, carboxylates, etc.

[0009] In one embodiment, a combination of ATH and aluminum oxide such as spherical aluminum oxide can be used in the isocyanate component, the polyol component, or both. When this combination is used, the ratio of ATH to aluminum oxide can vary and can range for example from 0.1 :99.9 to 99.9:0.1. In one embodiment, the ratio of ATH to aluminum hydroxide ranges from 80:20 to 20:80, and preferably, 60:40 to 40:60. In another embodiment, the thermally conductive fillers are ATH in combination with about 10 % of graphites, based on the total weight of the fillers.Graphites used in such filler combinations can be the same shapes or different shapes with different shape being a preferred ingredient. In a preferred embodiment, a mixture of Timrex™ graphites, such as Timrex C-thermo11 (Graphite with aspect ratio > 2, D90: 90 pm: BET 25 m2 / g ) and Timrex KS44 (Spherical graphite with D50 of 15.8 pm; D90: 45 pm, BET 9 m2 / g) may be used in the present invention. Timrex is brand name for various graphites commercially available from Imerys.

[0010] The present two-component adhesive formulation contains at least one plasticizer in either or both isocyanate and polyol components, preferably in both components. When the plasticizer is present in a component, the component typically contains 0.1% to 40%, preferably 1% to 30%, and more preferably 2% to 20%, and most preferably 5% to 10% of the plasticizer, based on the total weight of the component. In one embodiment when the plasticizer is present in both isocyanate and polyol component, the mass ratio between plasticizer in isocyanate component and polyol component is about 5:1. It is understood that other mass ratio might also work in other embodiments.

[0011] Many different plasticizers may be used in the present invention. It is within the ability of those skilled in the art to select suitable plasticizers according to parameters such as compatibility and desired properties of the final composition (e.g., viscosity). In general, suitable plasticizers include ester derivatives of such acids and anhydrides as adipic acid, azelaic acid, benzoic acid, citric acid, dimer acids, fumaric acid, isobutyric acid, isophthalic acid, lauric acid, linoleic acid, maleic acid, maleic anyhydride, melissic acid, myristic acid, oleic acid, palmitic acid, phosphoric acid, phthalic acid, ricinoleic acid, sebacic acid, stearic acid, succinic acid, 1 ,2- benzenedicarboxylic acid, and the like, and mixtures thereof. Also suitable are epoxidized oils, glycerol derivatives, paraffin derivatives, sulfonic acid derivatives, and the like, and mixtures thereof and with the aforesaid derivatives. Specific examples of such plasticizers include diethylhexyl adipate, heptyl nonyl adipate, diisodecyl adipate, the adipic acid polyesters, dicapryl adipate, dimethyl azelate, diethylene glycol dibenzoate and dipropylene glycol dibenzoate, polyethylene glycol dibenzoate, 2,2,4- trimethyl-1 ,3-pentanediol monoisobutyrate benzoate, 2,2,4-trimethyl-1 ,3-pentanediol diisobutyrate, methyl (or ethyl, or butyl) phthalyl ethyl glycolate, triethyl citrate, dibutylfumarate, 2,2,4-trimethyl-1 ,3-pentanediol diisobutyrate, methyl laurate, methyl linoleate, di-n-butyl maleate, tricapryl trimellitate, heptyl nonyl trimellitate, triisodecyl trimellitate, triisononyl trimellitate, isopropyl myristate, butyl oleate, methyl palmitate, tricresyl phosphate, tri-octyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, di-2-ethylhexyl phthalate, octyl decyl phthalate, diisodecyl phthalate, heptyl nonyl phthalate, diundecyl phthalate, ditridecyl phthalate, dicyclohexyl phthalate, diphenyl phthalate, butyl benzyl phthalates such as the n-butylbenzyl ester of o-phthalic acid, isodecyl benzyl phthalate, alkyl (C7 / C9) benzyl phthalate, di methoxyethyl phthalate, 7-(2,6,6,8-tetramethyl-4-oxa-3-oxo-nonyl) benzyl phthalate, di-2-ethylhexyl sebacate, butyl ricinoleate, dimethyl sebacate, methyl stearate, diethyl succinate, the butyl phenylmethyl ester of 1 ,2-benzenedicarboxylic acid, epoxidized linseed oil, glycerol triacetate, chloroparaffins having about 40% to about 70% Cl, o,p- toluenesulfonamide, N-ethyl p-toluene sulfonamide, N-cyclohexyl p-toluene sulfonamide, sulfonamide-formaldehyde resin, and mixtures thereof. Other suitable plasticizers known to those skilled in the art include castor oil, aromatic petroleum condensate, partially hydrogenated terphenyls, silicone plasticizers such as dimethicone copolyol esters, dimethiconol esters, silicone carboxylates, guerbet esters, and the like, alone or as mixtures with other plasticizers.

[0012] In preferred embodiments, both components of the present adhesive formulation contain a trialkyl phosphate as a plasticizer. The alkyl is preferably a C8 alkyl group. In one embodiment, the alkyl group is linear and one example of this plasticizer is trioctyl phosphate. In another embodiment, the alkyl group is branched and one example of this plasticizer is tris(2-ethylhexyl)phosphate.I. Isocyanate Component (also referred to as the first component of the two- component polyurethane adhesive formulation)A. Polyurethane Prepolymer

[0013] The isocyanate component of the two-component polyurethane adhesive formulation comprises a polyurethane prepolymer made insitu by a reaction between a polyol and an isocyanate.

[0014] The isocyanate used to make the prepolymer may be aliphatic, aromatic, or a mixture, with aromatic polyisocyanates being preferred. Examples of aromatic isocyanate groups include methylene diphenyl diisocyanate (MDI), polycarbodiimide- modified MDI, toluene diisocyanate (TDI), p-phenylene diisocyanate (PPDI), and naphthalene diisocyanate (NDI). MDI is particularly preferred. In one embodiment, a modified MDI, ISONATE M143, commercially available from Dow Chemical, is used and it is a low viscosity, modified diphenylmethane diisocyanate containing a high percentage of pure diphenylmethane diisocyanate, and a lesser amount of polycarbodiimide adducts and it has an isocyanate functionality of about 2.2, and a molecular weight of 315 Da. In some other embodiments, a mixture of MDI and polycarbodiimide-modified MDI is used. For example, Voranate M220, a polymeric MDI with a low viscosity polymethylene polyphenylisocyanate of high reactivity and with a total isocyanate content of about 31% and an average functionality of 2.7, can be mixed with other MDI materials. Voranate is commercially available from Dow Chemical.Examples of aliphatic isocyanate group include hexamethylene-1 ,6-diisocyanate (“HDI”), isophorone diisocyanate(“IPDI”), or other similar isocyanate compounds. Aliphatic isocyanate can also be a homo-polymers having aliphatic diisocyanate groups such as HDI dimer, HDI trimer (e.g. biuret, isocyanurate) or a mixture thereof. In a preferred embodiment, the prepolymer is made from the reaction between the aliphatic isocyanate and a polyol which is based on polyether or polyester. The resulting prepolymer is the polyol capped with aliphatic isocyanate.

[0015] Any polyol typically used in making polyurethane prepolymers may be used. Preferred polyols include all those used in the polyol component of the present invention.

[0016] In one embodiment, the isocyanate component comprises 1 % to 50 % of the polyurethane prepolymers by weight of the component. In another embodiment, the isocyanate component comprises 5% to 40% of the polyurethane prepolymers by weight of the component. In a preferred embodiment, the isocyanate component comprises 10% to 30% of the polyurethane prepolymers by weight of the component. In a more preferred embodiment, the isocyanate component comprises 15% to 25% of the polyurethane prepolymers by weight of the component. In another more preferredembodiment, the isocyanate component comprises 21 % to 23% of the polyurethane prepolymers by weight of the component.B. Organofunctional Silane

[0017] The isocyanate component can also optionally comprise at least a first and / or a second organofunctional silane. The isocyanate component can comprise 0.1 % to 5% of the organofunctional silane by weight of the component. The first organofunctional silane can be the same or different from the second organofunctional silane. In one embodiment, both silanes are the same. The organofunctional silane can function as a surface modifier for the thermally conductive filler. For example, the organofunctional silane can partially or completely cover the surface of the conductive filler particle. The conductive filler can include surface M-OH groups, where M is a metal atom, and the organofunctional silane can include a functional group that reacts with the M-OH group to form a direct or indirect bond between the surface modifier and M.

[0018] The surface of the conductive filler can be hydrophobized with the organofunctional silane. It will be appreciated that the organofunctional silane can be added to the filler before or after mixing the conductive filler with the matrix phase material. For example, the conductive filler can be coated or reacted with organofunctional silane prior to mixing the conductive filler and the matrix phase material. As another example, the organofunctional silane can be mixed with the matrix phase material to form a premix which is then combined with the conductive filler. As another example, the conductive filler and the matrix phase material can be mixed and then organofunctional silane can be added to the mixture.

[0019] In one embodiment, the isocyanate component comprises 0.1% to 5% of the organofunctional silane by weight of the component. In a further embodiment, the isocyanate component comprises 0.5% to 3% of the organofunctional silane by weight of the component. In a further embodiment, the isocyanate component comprises 1% to 2% of the organofunctional silane by weight of the component.

[0020] A variety of organofunctional silanes can be used. In one embodiment, the organofunctional silane is an alkyl silane. In another embodiment, the organofunctionalsilane is an epoxysilane. In a further embodiment, the organofunctional silane has the following structure:wherein n is an integer ranging from 0 to 24 and R3-R7are independently hydrogen or optionally substituted C1-C4 alkyl. In a further embodiment, R3-R7are independently hydrogen or unsubstituted C1-C4 alkyl. In a further embodiment, n is an integer ranging from 1 to 15, e.g., 2-14, 5-14, 8-14, or 10-14. Specific non-limiting examples include trimethoxy(methyl)silane, ethyltrimethoxysilane, trimethoxy(propyl)silane, butyltrimethoxysilane, trimethoxy(pentyl)silane, hexyltrimethoxysilane, heptyltrimethoxysilane, trimethoxy(octyl)silane, trimethoxy(nonyl)silane, decyltrimethoxysilane, trimethoxy(undecyl)silane, dodecyltrimethoxysilane, trimethoxy(tridecyl)silane, trimethoxy(tetradecyl)silane, trimethoxy(pentadecyl)silane, hexadecyltrimethoxysilane, or a combination thereof.

[0021] While the organofunctional silane is preferably present in the isocyanate component, it is understood that it can also be present in the polyol component or in both. The weight percentage of such organofunctional silane should be adjusted accordingly so that the total weight percentage present will be less than 5 wt. % based on the total weight of the adhesive. A typical range of such organofunctional silane should be 0.1 to 5 wt.%, preferably 0.2 to 3 wt.%, more preferably 0.3 to 2 wt.% and most preferably 0.5 to 1.5 wt.% based on the total weight of the adhesive formulation.C. Stabilizer

[0022] The isocyanate component may also optionally contain a stabilizer in order to lower the risk of degradation of the adhesive and to improve the shelf-life of the adhesive component. Any stabilizers known to those skilled in the art may be used here but in preferred embodiment, the present isocyanate component contains typically0.01 % to 0.1 %, preferably 0.01 % to 0.05%, and more preferably 0.01 % to 0.03% of trisnonylphenyl phosphite, all based on the total weight of the isocyanate component.II. Polyol Component (also referred to as the second component of the two- component polyurethane adhesive formulation)

[0023] The second component is the polyol component and in general comprises i) a polyol, the polyol having a molecular weight of at least 400 g / mol; ii) a diol, used as chain extender, the diol having a molecular weight of 200 g / mol or less; and iii) a catalyst capable of promoting the reaction between the polyol and the polyurethane prepolymer of the isocyanate component; and iv) a rheology filler / additiveA. Polyol

[0024] In some embodiments, the polyol component comprises 1% to 50% of the polyol by weight of the component. In other embodiments, the polyol component comprises 5% to 40% of the polyol by weight of the component. In a preferred embodiment, the polyol component comprises 10% to 30% of the polyol by weight of the component. In a further preferred embodiment, the polyol component comprises 15% to 25% of the polyol by weight of the component.

[0025] The molecular weight of the polyol can vary. In general, the polyol has a molecular weight of 100 g / mol to 5000 g / mol with some preferred embodiments having a narrower range of such polyol molecular weight ranges. In some more preferred embodiments of the present invention, the polyol has a molecular weight between 400 g / mol to 5000 g / mol. In some even more preferred embodiments of the present invention, the polyol has a molecular weight between 400 g / mol to 3000 g / mol.

[0026] In general, the polyol can be any polyol used with polyurethane technology. For example, the polyol can be any glycerin initiated propoxylated or ethoxylated polyol or any propoxylated or ethoxylated polyol prepared from alternative tri-fu notional and bis-functional starters. In some embodiments, the polyol can be a polyether polyol or mixture of polyether polyols. In other embodiments, the polyol can be a homopolymer or copolymer of propylene oxide, or a copolymer of propylene oxide with 70 wt.% to 99wt.% propylene oxide and from 1 wt.% to 30 w.t% ethylene oxide. Such a copolymer of propylene oxide and ethylene oxide can be preferred if a single polyether polyol is present. If two or more polyether polyols are present, it can be preferred that at least one of the polyols is such a copolymer of propylene oxide and ethylene oxide. In the case of a copolymer, the propylene oxide and ethylene oxide can be randomly copolymerized, block copolymerized, or both. In some embodiments, 50 % or more of the hydroxyl groups of the polyether polyol or mixture of polyether polyols are primary hydroxyl, with the remainder of the hydroxyl groups being secondary hydroxyl groups. In another embodiment, 70% or more of the hydroxyl groups in the polyether polyol or mixture thereof can be primary hydroxyl groups.

[0027] In additional embodiments, the polyol can be a polyether polyol or a polyester polyol. Other suitable polyols useful in the polyol component can include polypropylene based diols such as VORANOL 1010L with a molecular weight of 500 g / mol, VORANOL 2000L with a molecular weight of 1 ,000 g / mol, glycerin-initiated ethylene oxide based propoxylated triol VORANOL CP4610 with an average molecular weight of 4700 g / mol; and mixtures thereof. All these are commercially available from the Dow Chemical Company.

[0028] In certain specific embodiments, the polyol can be a glycerin-initiated ethylene oxide based propoxylated triol having a molecular weight of 1 ,500 g / mol to 1 ,700 g / mol, which can be present at 15% to 75%, 20% to 70%, 25% to 65%, 30% to 60%, 35% to 55%, 40% to 50%, or 45% to 50% by weight of the component.B. Low Molecular Weight Diol

[0029] The diol having a molecular weight of 200 g / mol or less functions as a chain extender. The polyol component can comprise 0.1% to 10% of the diol by weight the component. In some embodiments, the polyol component can comprise 0.1 % to 5% of the diol by weight the component. In other embodiments, the polyol component can comprise 0.5% to 4% of the diol by weight the component.

[0030] In general, the diol can have at least two carbon atoms, can be branched, linear, or functionalized, and can have at least two hydroxyl groups per molecule. Insome embodiments, the diol can be a linear or branched aliphatic diol having from 2-20 carbons, e.g., 2-18 carbons, 2-16 carbons, 2-14 carbons, 2-12 carbons, 2-10 carbons, 2-8 carbons, or 2-6 carbons. In various embodiments, the diol has a molecular weight of 20-200 g / mol, e.g., 20-150 g / mol, 40-150 g / mol, 50-130 g / mol, or 60-120 g / mol.

[0031] In some embodiments, the diol has the formula CxHyOz, where x is an integer ranging from 2 to 20, y is an integer equal to x + m (m being an integer ranging from 4 to 12), and z is an integer equal to x-n (n ranging from 0 to 6). Non-limiting examples include monoethylene glycol (MEG), diethylene glycol, triethylene glycol, 1 ,2-propane diol, 1 ,3-propane diol, 2,3-dimethyl-1 ,3-propane diol, dipropylene glycol, tripropylene glycol, 1 ,4-butane diol, or 1 ,6-hexane diol. In one embodiment, the diol can be monoethylene glycol, 1 ,4-butanediol, or a mixture thereof.C. Catalyst

[0032] The polyol component can include a catalyst capable of catalyzing the reaction of a hydroxyl group with an isocyanate group. Catalyst can be present in the isocyanate component, the polyol component, or both. In some preferred examples, the catalyst is present in the polyol component. The polyol component can comprise 0.001% to 5% of the catalyst by weight the component. In some embodiments, the polyol component can comprise 0.01% to 1% of the catalyst by weight the component. In other embodiments, the polyol component can comprise 0.01 % to 0.1 % of the catalyst by weight the component.

[0033] Examples of such catalysts include tertiary amine catalysts, organometallic catalysts, such as bismuth catalysts, alkyl tin carboxylates, oxides and tin mercaptides.

[0034] Specific examples of tertiary amine catalysts include N-methyl morpholine, N- methyl imidazole, triethylenediamine, bis-(2-dimethylaminoethyl)-ether, 1 ,4- diazabicyclo[2.2.2]octane (DABCO), dimethylcyclohexylamine, dimethylethanolamine,2.2-dimorpholinyl-diethylether (DMDEE), N,N,N-dimethylaminopropyl hexahydrotriazine, dimethyltetrahydropyrimidine, tetramethylethylenediamine, dimethylcyclohexylamine,2.2-N,N benzyldimethylamine, dimethylethanol amine, dimethylaminopropyl amine, Penta-dimethyl diethylene triamine, N,N,N',N'-tetramethyl-1 ,6-hexanediamine, N,N',N'- trimethylaminoethylpiperazine, 1 ,1'-[[3-(dimethylamino)propyl]imino]bispropan-2-ol,1 ,3,5-tris[3-(dimethylamino)propyl]hexahydro-1 ,3,5-triazine, N-N-dimethyldipropylene triamine, N,N,N'-trimethylaminoethylethanolamine, with DMDEE being particularly preferred.

[0035] If an organometallic catalyst is used, it is any organometallic catalyst capable of catalyzing the reaction of isocyanate with a functional group having at least one reactive hydrogen. Examples include bismuth catalysts, metal carboxylates such as tin carboxylate and zinc carboxylate. Metal alkanoates include stannous octoate, bismuth octoate or bismuth neodecanoate. Preferably the at least one organometallic catalyst is a bismuth catalyst or an organotin catalyst. Examples include dibutyltin dilaurate, dimethyl tin dineodecanoate, dimethyltin mercaptide, dimethyltin carboxylate, dimethyltin dioleate, dimethyltin dithioglycolate, dibutyltin mercaptide, dibutyltin bis(2- ethylhexyl thioglycolate), dibutyltin sulfide, dioctyltin dithioglycolate, dioctyltin mercaptide, dioctyltin dioctoate, dioctyltin dineodecanoate, dioctyltin dilaurate. In a particularly preferred embodiment, it is a tin catalyst, particularly preferably dioctyltin mercaptide.D. Rheology Filler / Additive

[0036] The polyol component may also contain rheology additive or filler to prevent sedimentation. Optionally, such additive may also be present in the isocyanate component. The rheology filler can be a particulate filler. The particulate filler can be a solid material at room temperature, and is not soluble in the other ingredients of the polyol component or the isocyanate component. The filler can be a material that does not melt, volatilize, or degrade under the conditions of the curing reaction between the polyol and isocyanate components. The filler can be, for example, an inorganic filler such as glass, silica (e.g., fumed silica), boron oxide, boron nitride, titanium oxide, titanium nitride, fly ash, calcium carbonate, and various alumina-silicates including clays such as wollastonite and kaolin, and the like; metal particles such as iron, titanium, aluminum, copper, brass, bronze and the like; thermoset polymer particles such as polyurethane, cured particles of an epoxy, phenol-formaldehyde, or cresolformaldehyde resin, crosslinked polystyrene, and the like; thermoplastics such as polystyrene, styrene acrylonitrile copolymers, polyimide, polyamide-imide, polyetherketone, polyether-ether ketone, polyethyleneimine, poly(p-phenylene sulfide), polyoxymethylene, polycarbonate and the like; and various types of carbon such as activated carbon, graphite, molecular sieve, carbon black and the like; and mixtures thereof.

[0037] The particulate filler can be in the form of particles having a size of from 50 nanometers (nm) to 100 micrometers (pm) in one embodiment. In other embodiments, the fillers may have a particle size (d50) of 250 nm or greater in one embodiment, 500 nm or greater in another embodiment and 1 pm or greater in still another embodiment. In other embodiments, the fillers can have a particle size (d50) of 50 pm or less, 25 pm or less, or 10 pm or less. Particles sizes are conveniently measured using dynamic light scattering methods, or laser diffraction methods for particles having a size below 100 nm.

[0038] In some embodiments, particulate filler particles can have an aspect ratio of up to 5, an aspect ratio of up to 2, or an aspect ratio of up to 1 .5. In other embodiments, a portion or all of the filler particles can be grafted onto one or more of the polyether polyol(s) of the polyol component.

[0039] In general, when a rheology filler is present in the polyol component, the polyol component can comprise 0.1% to 10% of the rheology filler by weight the component. In some embodiments, the polyol component can comprise 0.1 % to 5% of the rheology filler by weight the component. In other embodiments, the polyol component can comprise 0.5% to 1.5% of the rheology filler by weight the component.

[0040] In some embodiments, rheology filler can also be present in the isocyanate component, or in both the isocyanate and the polyol component.

[0041] Additional optional ingredients may also be used to adjust certain properties of the polyol component. For instance, Monomix™ G, a fine high-brightness talc commercially available from Imerys, may be added to help with the failure mode and molecular sieves may be added to address excess moisture concerns. The amounts of these optional ingredients can be adjusted with the typical knowledge of one skilled in the art.III. Methods and Applications

[0042] In one embodiment, the process for preparing the thermal conductive adhesive formulation of the present invention includes providing the isocyanate and the polyol components. When provided as a kit, the two components can be co-packaged or packaged separately. When the adhesive formulation is ready to be used, the components can be mixed, admixed, or blended together which results in a reaction product when the combination of components are cured. One or more additional optional components, such as additional anti-settling aid such as precipitated calcium carbonate, and additional rheology additives such as waxy polyester polyols or urea based rheology additives can be added to the formulation as desired.

[0043] While the amount of the components useful in making the reaction product constituting the adhesive formulation can vary, once the isocyanate component and the polyol component are formulated (separately and individually) and the two components are ready for combining to form the reaction product adhesive formulation, the isocyanate component and the polyol component can be mixed at a volume ratio ranging from 2:1 to 1 :2. In one preferred embodiment, such volume ratio between the isocyanate component and the polyol component is about 1 :1.

[0044] In making the components separately and individually, the ingredient raw materials can be mixed together in the desired concentrations discussed above at a temperature of from 5°C to 80° C, e.g., 15°C to 50°C, or room temperature for example. In one embodiment, the mixing of the ingredients can be carried out under vacuum and or with a planetary mixer or on a dual asymmetric centrifuge. The order of mixing is not critical and two or more compounds can be mixed together followed by addition of the remaining ingredients.

[0045] The two-component polyurethane adhesive formulation may also be premixed before using. In doing so, all adhesive formulation ingredients that make up the components can be mixed together by any known mixing process and equipment. In mixing various raw material ingredient, it is preferred that the liquid phases are mixed first before the addition of solid ingredients. The entire mixture should be mixed forapproximately 30 to 45 minutes to form the final formulation before being packed into cartridges, pails, drums or other commonly known packages.

[0046] The adhesive formulation of the present invention can be used in a variety of applications. Various articles comprising the adhesive are contemplated. In one embodiment, the article comprises a battery module that is formed of at least one battery cell and a cooling plate, wherein the battery module is affixed to the cooling plate via the cured thermal conductive adhesive of the present invention. In a further embodiment, the battery module is part of an electrically driven vehicle.EXAMPLE

[0047] The following examples further illustrate the present invention. The scope of the invention and claims is not limited by the scope of the following examples.Raw Material Ingredients and Inventive Example

[0048] The following tables list an Inventive Example of the present invention and two Comparative Examples. All weight percent is based on the total weight of the respective components.Table 1 . Ingredients for the Isocyanate ComponentTable 2. Ingredients for the Polyol Component

[0049] Organofunctional silane used in the example contains epoxysilane. Thermal conductive fillers used in the example is a bimodally distributed aluminum trihydroxide (ATH).

[0050] The polyol used in the present example is an ethyleneoxide capped polypropyleneoxide polyether polyol commercially available under the trade name Voranal™ from Dow Chemical Company.1 ,4-Butanediol is commercially available from ARCO Chemical.

[0051] The rheology additive used in the present example is hydrophobic fumed silica commercially available from Evonik.

[0052] Graphite used in the present examples are Timrex mixture commercially available from Imerys.

[0053] Catalyst used in the present examples is Fomrez UL29, a dioctyltin mercaptide catalyst commercially available from Momentive.MethodsA. Sample preparation

[0054] In each of the Comparative Example and the Inventive Examples, all ingredients as listed in Table 1 and Table 2 (first liquid components, then solid components) were added in a planetary mixer or dual asymmetric centrifuge, mixed for about 30 minutes under vacuum then transferred into cartridges, pails or drums for storage. The mixture of the isocyanate-component is mixed for 60 min at 80 °C under vacuum to form the prepolymer and then cooled down to room temperature and transferred to the packaging.B. Tests

[0055] The test methods described herein include both of those used in the examples shown and for those values included in the detailed description of the present invention.

[0056] Press-in Force: The press-in force is measured with a tensiometer (Zwick). The gap filler material is placed on a metal surface. An aluminum piston with 40 mm diameter is placed on top and the material is compressed to 5 mm (initial position). The material is then compressed to 0.3 mm with 1 mm / s velocity and force deflection curve is recorded. The force (N) at 0.5 mm thickness is then reported in the data table and considered as the press-in force.

[0057] Thermal Conductivity: Thermal conductivity is measured according to ASTM 5470-12, using a thermal interface material tester from ZFW Stuttgart. The tests are performed with 2 mm thick adhesive plates cured for 7 days at room temperature. The thermal conductivity tests are performed at 1-5 bar pressure and the effective thermal conductivity is reported at 5 bar pressure. The upper contact is heated to approximately 40°C and the lower contact is heated to approximately 10°C, resulting an overall sample temperature of about 25°C.

[0058] Gel Permeation Chromatography (GPC): Molecular weight data of the polyurethane prepolymers were measured by gel permeation chromatography (GPC)with a Malvern Viscothek GPC max equipment. Emsure - THF (ACS, Reag. Ph EUR for analysis) was used as an eluent, PL GEL MIXED-D (Agilent, 300 x 7.5 mm, 5 m) was used as a column, and MALVERN Viscotek TDA was used as a detector.

[0059] Lap Shear tests: e-coated steel substrates with a cathoguard 800 coating were used. Size of the samples are 100 mm x 25 mm with a thickness of 1 .2 mm. The substrates were cleaned with isopropanol before use. The adhesive is applied on one substrate, before the second substrate is joined in less than 3 minutes. The thickness is adjusted to 1 .0 mm, the overlap area is 25 mm x 15 mm. The now joined substrates unit is cured and rested for 7 days at 23 °C, 50 % relative humidity before the lap shear tests were performed. The sample units were then mounted in a tensiometer and the lap shear tests were performed using a pull speed of 10 mm / min. The force deflection curve is monitored and the strength at break is reported as lap shear strength.

[0060] Viscosity: Rheology measurements were performed on an Anton Paar MC 302 rheometer with a parallel plate geometry 25 mm diameter plates were used, the gap was fixed at 0.5 mm. The thermal interface material is brought between the two plates and then a shear rate test was performed from 0.001 to 20 1 / s and the viscosity at 10 1 / s was reported.

[0061] Tensile tests: Tensile tests for values in tensile strength, E-Modulus, and elongation at break were performed according to DIN 527-2. Dog-bone samples with 2.0 mm thickness were used. Tensile tests are at performed 10 mm / min.Tests results are summarized in Tables 3 and 4.Table 3. Viscosity at 10 1 / s at 23 °C (Pa.s)Table 4. Other Testing Data of the Two Component Polyurethane Adhesive Formulation (with 1 :1 v / v combination of the Isocyanate and the Polyol Components)C. Discussion of the Results

[0062] As shown in Table 1 , the Comparative Example contains about the same kinds and amounts of thermal conductive fillers and graphite as the Inventive Examples but it does not comprise tris(2-ethylhexyl)phosphateor other plasticizers. The viscosity of the isocyanate component is about 1190 Pa.s at 10 1 / s which is very high. Also, the press-in force value of the initially mixed components is about 2120 N, which is also very high. When the press-in force value is tested after 5 min from the initial mixing of the two components at room temperature (RT), the value is about 9500 N, still very high. The thermal conductivity of the comparative example is 1 .5 W / mK, similar to that of the two inventive examples. The E-modulus is 80 MPa, too high for many applications intended for the two component polyurethane adhesives.

[0063] Inventive Example I used essentially the same ingredients as the comparative example. The difference is that it further comprises 5 wt.% of a plasticizer in the isocyanate component and 1 wt. % of the same plasticizer in the polyol component, withthe wt.% based on the total weight of the respective components. In the isocyanate component, it is observed as shown in Table 3, that the viscosity of the isocyanate component is significantly reduced to 376 Pa.s. Also, the press-in force value, as shown in Table 4, is reduced to 959 N right after the initial mixing of the two components, and the press-in force value rises to 4043 N five minutes later. The E- modulus value is at 33 MPa.

[0064] In inventive example II, the plasticizer level is increased to 10 wt.% in the isocyanate component, and to 2 wt. % in the polyol component, with the wt.% based on the total weight of the respective components. It is observed, as shown in Tables 3 and 4, that the viscosity of the isocyanate component is further reduced to 151 Pa.s. The press-in force value of the mixed components is significantly lower with 508 N right after the initial mixing of the two components, and it rises only to 2494 N five minutes later. The E-modulus of inventive example II is at 12 MPa, very low and desired for many applications.

[0065] All other tests values between the comparative example and the two inventive examples are comparable to each other with slight improvement shown with the inventive examples.

Claims

CLAIMSWhat is claimed is:1 . A two-component adhesive formulation comprising: an isocyanate component comprising more than 50 wt.% of a thermally conductive filler; and a polyol component; wherein at least one of the isocyanate component and the polyol component further comprises a plasticizer; and wherein E-Modulus of the two-component adhesive is less than 35 MPa.

2. The two-component adhesive formulation according to Claim 1 wherein both isocyanate component and the polyol component comprise a plasticizer.

3. The two-component adhesive formulation according to any one of the preceding claims wherein the plasticizer is a trialkyl phosphate.

4. The two-component adhesive formulation according to any one of the preceding claims wherein the plasticizer containing component comprises 0.1 % to 40% of the plasticizer, based on the weight of the component.

5. The two-component adhesive formulation according to any one of the preceding claims where in the E-Modulus of the two-component adhesive is less than 15 MPa.

6. The two-component adhesive formulation according to claim 2 wherein the mass ratio between plasticizer present in the isocyanate component and plasticizer present in the polyol component is about 5: 1 .

7. The two-component adhesive formulation according to any one of the preceding claims where both of the isocyanate component and the polyol component further comprise an organofunctional silane.

8. The two-component adhesive formulation according to Claim 7 wherein the organofunctional silane is an epoxysilane.

9. The two-component adhesive formulation according to any one of the preceding claims having a thermal conductivity of no less than 1 .5 W / mK.

10. The two-component adhesive formulation according to Claim 3, wherein the trialkyl phosphate comprises branched C8 alkyl group.11 . The two-component adhesive formulation according to Claim 3, wherein the trialkyl phosphate comprises linear C8 alkyl group.

12. The two-component adhesive formulation according to Claim 10, wherein the plasticizer is tris(2-ethylhexyl)phosphate.

13. The two-component adhesive formulation according to any one of the preceding claims wherein the polyol component further comprises a rheology filler and a talc.

14. The two-component adhesive formulation according to any one of the preceding claims wherein the volume ratio between the isocyanate component and the polyol component ranges from 2:1 to 1 :2.

15. The two-component adhesive formulation according to any one of the preceding claims wherein the volume ratio between the isocyanate component and the polyol component is about 1 :1.

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