Two-component thermally conductive adhesive with low E-modulus

Abstract

The present invention relates to a two-component adhesive formulation comprising an isocyanate component and a polyol component, the isocyanate component comprising greater than 50 wt% of a thermally conductive filler wherein at least one of the isocyanate component and the polyol component further comprises a plasticizer, wherein at least one of the isocyanate component and the polyol component further comprises a mono-alcohol, and wherein the two-component adhesive has an E-modulus of less than 35 MPa.

Description

[0001] Over the past decade, the automotive industry has seen a trend towards reducing vehicle weight. This trend is driven by regulations aimed at reducing fleet CO2 emissions. In recent years, the increasing number of electric vehicles has further fueled lightweight construction strategies. To provide longer driving ranges, batteries with high energy density are required. All long-life battery cells require adequate thermal management. Thermal interface materials or thermally conductive adhesives are needed to thermally connect the battery cells or the modules housing them to cooling units.

[0002] Battery cells generate heat during charging and discharging. The cell should be maintained at an appropriate operating temperature (preferably 25°C–40°C) to avoid efficiency loss, overheating, and dangerous thermal runaway reactions. For this reason, active cooling is typically used. Effective active cooling methods involve pumping a cooling water-glycol mixture through channels to cool the metal bottom of a cooling plate on which the battery cell or module is mounted. The battery cell or cell housing can be directly bonded to the cooling plate using a thermally conductive adhesive. This provides good mechanical fixation and thermal bonding. The battery cell can be a pouch cell, a prismatic cell, or a cylindrical cell, all of which require cooling. The cooling unit can be bonded to the bottom of the battery cell using an adhesive or to the sides of the battery cell using a thermally conductive adhesive.

[0003] A key requirement for thermally conductive adhesives is a thermal conductivity of at least 1.5 W / mK. Additionally, an overlap shear strength > 1.5 MPa is required. Cooling units and battery cells / boxes are typically made of aluminum covered with a polyethylene terephthalate (PET) film or similar polymeric materials. Therefore, good adhesion between the thermally conductive adhesive and the PET film is necessary. For some battery applications, foam or potting compositions are applied to fill the battery box for better rigidity, preventing the PET film from rupturing from the battery cell in the event of a physical impact on the vehicle. In these applications, the modulus of the thermally conductive adhesive applied between the battery cell box and the cooling unit must be lower than that of the potting composition or foam, so that the energy of any physical impact will be transferred from the adhesive to the foam, thus maintaining the integrity of the PET film. Typically, the E-modulus of the thermally conductive adhesive should be as low as possible, and in most cases, it should remain below 35 MPa.

[0004] Various potential materials exist that can be used to formulate thermally conductive adhesives. Two-component polyurethane adhesives stand out among other candidates due to their good mechanical properties and elongation at break, as well as favorable curing kinetics. However, due to the high filler content typically used in these polyurethane adhesives, commonly available two-component polyurethane adhesives typically exhibit high E-modulus.

[0005] The desired outcome is a two-component polyurethane thermally conductive adhesive formulation that still exhibits low E-modulus even when the filler content in the adhesive formulation exceeds 70 wt.% of the total formulation. Summary of the Invention

[0006] This invention relates to a thermally conductive adhesive having an ultra-low e-modulus of less than 35 MPa, preferably less than 20 MPa, more preferably less than 10 MPa, and most preferably less than 7 MPa, while having a thermally conductive filler of greater than 50 wt.% based on the total weight of the adhesive formulation. This invention provides such a low e-modulus adhesive formulation by including a plasticizer and a monool in the formulation and carefully maintaining a critical mass ratio between the two. More specifically, this invention provides a two-component adhesive formulation comprising: an isocyanate component containing greater than 50 wt.% thermally conductive filler; and a polyol component; wherein at least one of the isocyanate component and the polyol component further comprises a plasticizer; wherein at least one of the isocyanate component and the polyol component further comprises a monool; and wherein the e-modulus of the two-component adhesive is less than 35 MPa. Detailed Implementation

[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% thermally conductive filler by weight. In one embodiment, each component of the adhesive formulation independently comprises 50% to 85% thermally conductive filler by weight. In another embodiment, each component of the adhesive formulation independently comprises 50% to 80% thermally conductive filler by weight. In a preferred embodiment, each component of the adhesive formulation independently comprises 50% to 75% thermally conductive filler by weight. In yet another preferred embodiment, each component of the adhesive formulation independently comprises 50% to 75% thermally conductive filler by weight.

[0008] A variety of thermally conductive fillers can be used. Examples include aluminum hydroxide (also known as aluminum trihydride (ATH)), alumina (such as spherical alumina), graphite, and any combination thereof. ATH can be a unimodal ATH powder or an ATH powder with a multimodal particle size distribution (e.g., bimodal, trimodal, etc.). When using unimodal ATH powder, the average particle size can be 5-100 µm. When using multimodal ATH powder, the average particle size of the smallest particles can be less than about 10 µm, while the average particle size of the largest particles can be greater than about 50 µm. Additionally, ATH powder can be surface-treated with silanes, titanates, carboxylates, etc.

[0009] In one embodiment, a combination of ATH and alumina, such as spherical alumina, can be used in the isocyanate component, polyol component, or both. When using such a combination, the ratio of ATH to alumina can vary and, for example, can range 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 is preferably 60:40 to 40:60. In another embodiment, the thermally conductive filler is ATH combined with graphite based on about 10% of the total weight of the filler. The graphite used in such filler combinations can be of the same shape or different shapes, with different shapes being a preferred component.

[0010] The two-component adhesive formulation of the present invention contains at least one plasticizer in one or both of the isocyanate component and the polyol component, preferably in both components. When the plasticizer is present in the component, the component typically contains 0.1% to 40%, preferably 1% to 30%, 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 the isocyanate component and the polyol component, the mass ratio between the plasticizer in the isocyanate component and the polyol component is about 5:1. It should be understood that other mass ratios may also work in other embodiments.

[0011] Many different plasticizers can be used in this invention. Those skilled in the art are capable of selecting a suitable plasticizer based on parameters such as compatibility and the desired properties of the final composition (e.g., viscosity). Generally, suitable plasticizers include ester derivatives of acids and anhydrides such as adipic acid, azelaic acid, benzoic acid, citric acid, dimer acid, fumaric acid, isobutyric acid, isophthalic acid, lauric acid, linoleic acid, maleic acid, maleic anhydride, beeswax acid, myristic acid, oleic acid, palmitic acid, phosphoric acid, phthalic acid, castor oil, sebacic acid, stearic acid, succinic acid, 1,2-phthalic acid, and mixtures thereof. Also suitable are epoxidized oils, glycerol derivatives, paraffin derivatives, sulfonic acid derivatives, mixtures thereof, and mixtures thereof with the aforementioned derivatives. Specific examples of such plasticizers include diethylhexyl adipate, heptyl nonyl adipate, diisodecyl adipate, polyester adipate, dioctyl adipate, dimethyl azelaate, 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) phthaloyl ethyl glycolate, and citric acid ester. Triethyl phthalate, dibutyl fumarate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, methyl laurylate, methyl linoleate, di-n-butyl maleate, trioctyl trimellitate, heptyl nonyl trimellitate, triisodecyl trimellitate, triisononyl trimellitate, isopropyl myristate, butyl oleate, methyl palmitate, tricresyl phosphate, trioctyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, phthalic acid... bis-2-ethylhexyl formate, octyldecyl phthalate, diisodecyl phthalate, heptylnonyl phthalate, diundecyl phthalate, ditridecyl phthalate, dicyclohexyl phthalate, diphenyl phthalate, butyl benzyl phthalate (such as n-butyl benzyl phthalate), isodecyl benzyl phthalate, alkyl (C7 / C9) benzyl phthalate, dimethoxyethyl phthalate, 7-(2, 6,6,8-Tetramethyl-4-oxa-3-oxo-nonyl)benzyl ester, di-2-ethylhexyl sebacate, butyl castor oil, dimethyl sebacate, methyl stearate, diethyl succinate, butylphenyl methyl ester of 1,2-phthalic acid, epoxidized linseed oil, glyceryl triacetate, chlorinated paraffin having about 40% to about 70% Cl, o-, p-toluenesulfonamide, N-ethyl-p-toluenesulfonamide, N-cyclohexyl-p-toluenesulfonamide, sulfonamide-formaldehyde resins and mixtures thereof.Other suitable plasticizers known to those skilled in the art include castor oil, aromatic petroleum concentrates, partially hydrogenated terphenyl, silicone plasticizers (such as polydimethylsiloxane copolyesters, polydimethylsiloxane alcohol esters, silicone carboxylic esters), Guerbet esters, alone or in mixtures with other plasticizers.

[0012] In a preferred embodiment, both components of the adhesive formulation of the present invention contain a trialkyl phosphate as a plasticizer. The alkyl group is preferably C8 alkyl. In one embodiment, the alkyl group is straight-chain, and an example of such a plasticizer is trioctyl phosphate. In another embodiment, the alkyl group is branched, and an example of such a plasticizer is tri(2-ethylhexyl) phosphate.

[0013] I. Isocyanate component (also known as the first component of a two-component polyurethane adhesive formulation)

[0014] A. Polyurethane prepolymer

[0015] The isocyanate component of the two-component polyurethane adhesive formulation contains a polyurethane prepolymer manufactured in situ through a reaction between a polyol and an isocyanate.

[0016] The isocyanate used to manufacture the prepolymer can be aliphatic, aromatic, or a mixture thereof, 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. This modified MDI is a low-viscosity modified diphenylmethane diisocyanate containing a high percentage of pure diphenylmethane diisocyanate and a small amount of polycarbodiimide adduct, and 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 highly reactive, low-viscosity polymethylene polyphenyl isocyanate and a total isocyanate content of about 31% and an average functionality of 2.7) can be blended with other MDI materials. Voranate is commercially available from Dow Chemical Company. Examples of aliphatic isocyanate groups include hexamethylene-1,6-diisocyanate (“HDI”), isophorone diisocyanate (“IPDI”), or other similar isocyanate compounds. Aliphatic isocyanates can also be homopolymers having aliphatic diisocyanate groups, such as HDI dimers, HDI trimers (e.g., biuret, isocyanurate), or mixtures thereof. In a preferred embodiment, the prepolymer is prepared by reacting an aliphatic isocyanate with a polyol based on a polyether or polyester. The resulting prepolymer is a polyol terminated with an aliphatic isocyanate.

[0017] Any polyol typically used in the manufacture of polyurethane prepolymers can be used. Preferred polyols include all of those used in the polyol components of this invention.

[0018] In one embodiment, the isocyanate component comprises 1% to 50% polyurethane prepolymer by weight of the component. In another embodiment, the isocyanate component comprises 5% to 40% polyurethane prepolymer by weight of the component. In a preferred embodiment, the isocyanate component comprises 10% to 30% polyurethane prepolymer by weight of the component. In a more preferred embodiment, the isocyanate component comprises 15% to 25% polyurethane prepolymer by weight of the component. In another more preferred embodiment, the isocyanate component comprises 21% to 23% polyurethane prepolymer by weight of the component.

[0019] B. Organofunctional silanes

[0020] The isocyanate component may optionally contain at least a first and / or a second organofunctional silane. The isocyanate component may contain 0.1% to 5% organofunctional silane by weight of the component. The first organofunctional silane may be the same as or different from the second organofunctional silane. In one embodiment, the two silanes are the same. The organofunctional silane may act as a surface modifier for the thermally conductive filler. For example, the organofunctional silane may partially or completely cover the surface of the conductive filler particles. The conductive filler may contain surface M-OH groups, where M is a metal atom, and the organofunctional silane may contain functional groups that react with the M-OH groups to form a direct or indirect bond between the surface modifier and M.

[0021] The surface of the conductive filler can be hydrophobized with organofunctional silanes. It should be understood that organofunctional silanes 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 with or reacted with an organofunctional silane before mixing it with the matrix phase material. As another example, the organofunctional silane can be mixed with the matrix phase material to form a premix, and then the premix can be combined with the conductive filler. As yet another example, the conductive filler can be mixed with the matrix phase material, and then an organofunctional silane can be added to the mixture.

[0022] In one embodiment, the isocyanate component comprises 0.1% to 5% by weight of an organofunctional silane. In another embodiment, the isocyanate component comprises 0.5% to 3% by weight of an organofunctional silane. In yet another embodiment, the isocyanate component comprises 1% to 2% by weight of an organofunctional silane.

[0023] A variety of organofunctional silanes can be used. In one embodiment, the organofunctional silane is an alkylsilane. In another embodiment, the organofunctional silane is an epoxysilane. In yet another embodiment, the organofunctional silane has the following structure:

[0024] ,

[0025] Where n is an integer in the range of 0 to 24, and R 3 -R 7 Independently, it is hydrogen or optionally substituted C1-C4 alkyl. In another embodiment, R 3 -R 7Independently, it is hydrogen or an unsubstituted C1-C4 alkyl group. In other embodiments, n is an integer ranging from 1 to 15, for example, 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(pentadecanyl)silane, hexadecyltrimethoxysilane, or combinations thereof.

[0026] While the organofunctional silane is preferably present in the isocyanate component, it should be understood that it may also be present in the polyol component or both. The weight percentage of this organofunctional silane should be adjusted accordingly so that the total weight percentage present is less than 5 wt.% based on the total weight of the adhesive. A typical range for this 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.

[0027] C. Stabilizer

[0028] The isocyanate component may also optionally contain a stabilizer to reduce the risk of adhesive degradation and improve the shelf life of the adhesive component. Any stabilizer known to those skilled in the art can be used here, but in preferred embodiments, the isocyanate component of the present invention typically contains 0.01% to 0.1%, preferably 0.01% to 0.05%, and more preferably 0.01% to 0.03% of trinonylphenyl phosphite, all based on the total weight of the isocyanate component.

[0029] II. Polyol component (also known as the second component of two-component polyurethane adhesive formulations)

[0030] The second component is a polyol component and typically includes i) a polyol having a molecular weight of at least 400 g / mol; ii) a diol used as a chain extender having a molecular weight of 200 g / mol or less; iii) a catalyst capable of promoting the reaction between the polyol and the isocyanate component of the polyurethane prepolymer; iv) a rheology filler / additive; and v) a monool.

[0031] A. Polyols

[0032] In some embodiments, the polyol component comprises 1% to 50% polyol by weight of the component. In other embodiments, the polyol component comprises 5% to 40% polyol by weight of the component. In a preferred embodiment, the polyol component comprises 10% to 30% polyol by weight of the component. In a further preferred embodiment, the polyol component comprises 15% to 25% polyol by weight of the component.

[0033] The molecular weight of polyols can vary. Typically, polyols have a molecular weight ranging from 100 g / mol to 5000 g / mol, with some preferred embodiments having a narrower range of such molecular weights. In some more preferred embodiments of the invention, the polyols have a molecular weight between 400 g / mol and 5000 g / mol. In some even more preferred embodiments of the invention, the polyols have a molecular weight between 400 g / mol and 3000 g / mol.

[0034] Typically, the polyol can be any polyol used with polyurethane technology. For example, the polyol can be any glycerol-initiated propoxylated or ethoxylated polyol or any propoxylated or ethoxylated polyol prepared from alternative trifunctional and bifunctional starting materials. In some embodiments, the polyol can be a polyether polyol or a 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 99 wt.% propylene oxide and 1 wt.% to 30 wt.% ethylene oxide. If a single polyether polyol is present, such a copolymer of propylene oxide and ethylene oxide is preferred. If two or more polyether polyols are present, it is preferred that at least one of the polyols is such a copolymer of propylene oxide and ethylene oxide. In the case of copolymers, propylene oxide and ethylene oxide can be random copolymers, block copolymers, or both. In some embodiments, 50% or more of the hydroxyl groups in the polyether polyol or mixture thereof are primary hydroxyl groups, and the remainder of the hydroxyl groups are secondary hydroxyl groups. In another embodiment, 70% or more of the hydroxyl groups in the polyether polyol or mixture thereof may be primary hydroxyl groups.

[0035] In another embodiment, the polyol may be a polyether polyol or a polyester polyol. Other suitable polyols that can be used as a polypropylene-based diol may include VORANOL 1010L with a molecular weight of 500 g / mol, VORANOL 2000L with a molecular weight of 1,000 g / mol, VORANOL CP4610, a glycerol-initiated ethylene oxide-based propoxylated triol with an average molecular weight of 4,700 g / mol, and mixtures thereof. All of these are commercially available from Dow Chemical Company.

[0036] In some specific embodiments, the polyol may be a glycerol-initiated ethylene oxide-based propoxylated triol having a molecular weight of 1,500 g / mol to 1,700 g / mol, which may be present in amounts of 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.

[0037] B. Low molecular weight diols

[0038] Diols with a molecular weight of 200 g / mol or less act as chain extenders. The polyol component may contain 0.1% to 10% diol by weight of the component. In some embodiments, the polyol component may contain 0.1% to 5% diol by weight of the component. In other embodiments, the polyol component may contain 0.5% to 4% diol by weight of the component.

[0039] Typically, a diol may have at least two carbon atoms, may be branched, linear, or functionalized, and may have at least two hydroxyl groups / molecules. In some embodiments, the diol may be a linear or branched aliphatic diol having 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).

[0040] In some embodiments, the diol has the formula C x H y O z Where x is an integer ranging from 2 to 20, y is an integer equal to x + m (where m is an integer ranging from 4 to 12), and z is an integer equal to xn (where n ranges from 0 to 6). Non-limiting examples include monoethylene glycol (MEG), diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,3-dimethyl-1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,4-butanediol, or 1,6-hexanediol. In one embodiment, the diol may be monoethylene glycol, 1,4-butanediol, or a mixture thereof.

[0041] C. Catalyst

[0042] The polyol component may contain a catalyst capable of catalyzing the reaction of hydroxyl groups with isocyanate groups. The catalyst may be present in the isocyanate component, the polyol component, or both. In some preferred embodiments, the catalyst is present in the polyol component. The polyol component may contain 0.001% to 5% catalyst by weight of the component. In some embodiments, the polyol component may contain 0.01% to 1% catalyst by weight of the component. In other embodiments, the polyol component may contain 0.01% to 0.1% catalyst by weight of the component.

[0043] Examples of such catalysts include tertiary amine catalysts, organometallic catalysts such as bismuth catalysts, alkyltin carboxylates, alkyltin oxides, and tin thiols.

[0044] Specific examples of tertiary amine catalysts include N-methylmorpholine, N-methylimidazolium, triethylenediamine, bis-(2-dimethylaminoethyl)-ether, 1,4-diazabicyclo[2.2.2]octane (DABCO), dimethylcyclohexylamine, dimethylethanolamine, 2,2-dimorpholino-diethyl ether (DMDEE), N,N,N-dimethylaminopropylhexahydrotriazine, dimethyltetrahydropyrimidine, tetramethylethylenediamine, dimethylcyclohexylamine, 2,2-N,N-benzyldimethylamine, and dimethylethanolamine. Dimethylaminopropylamine, penta-dimethyldiethylenetriamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, N,N',N'-trimethylaminoethylpiperazine, 1,1'-[[3-(dimethylamino)propyl]imino]bisprop-2-ol, 1,3,5-tris[3-(dimethylamino)propyl]hexahydro-1,3,5-triazine, NN-dimethyldipropylenetriamine, N,N,N'-trimethylaminoethylethanolamine, of which DMDEE is particularly preferred.

[0045] If an organometallic catalyst is used, it is any organometallic catalyst capable of catalyzing the reaction of isocyanates 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, dimethyltin dinedecanoate, dimethyltin thiol, dimethyltin carboxylate, dimethyltin dioleate, dimethyltin dithioglycolate, dibutyltin thiol, bis(2-ethylhexyl thioglycolate) dibutyltin, dibutyltin sulfide, dioctyltin dithioglycolate, dioctyltin thiol, dioctyltin dioctanoate, dioctyltin dinedecanoate, and dioctyltin dilaurate. In a particularly preferred embodiment, it is a tin catalyst, particularly preferably dioctyltin thiol.

[0046] D. Rheological fillers / additives

[0047] The polyol component may also contain rheology modifiers or fillers to prevent sedimentation. Optionally, such modifiers may also be present in the isocyanate component. The rheology filler may be a particulate filler. The particulate filler may be a solid material at room temperature and is insoluble in the polyol component or other components of the isocyanate component. The filler may be a material that does not melt, volatilize, or degrade under the conditions of the curing reaction between the polyol and the isocyanate component. The fillers can be, for example, inorganic fillers such as glass, silica (e.g., fumed silica), boron oxide, boron nitride, titanium oxide, titanium nitride, fly ash, calcium carbonate, and various aluminosilicates (including clays such as wollastonite and kaolin); metal particles such as iron, titanium, aluminum, copper, brass, bronze, etc.; thermosetting polymer particles such as polyurethane, epoxy resin, cured particles of phenol-formaldehyde or cresol-formaldehyde resin, cross-linked polystyrene, etc.; thermoplastic plastics such as polystyrene, styrene-acrylonitrile copolymer, polyimide, polyamide-imide, polyetherketone, polyetheretherketone, polyethyleneimine, poly(p-phenylene sulfide), polyoxymethylene, polycarbonate, etc.; and various types of carbon such as activated carbon, graphite, molecular sieves, carbon black, etc.; and mixtures thereof.

[0048] In one embodiment, the particulate filler may be in the form of particles having a size of 50 nanometers (nm) to 100 micrometers (µm). In other embodiments, the filler may have a particle size (d50) of 250 nm or larger in one embodiment, 500 nm or larger in another embodiment, and 1 µm or larger in yet another embodiment. In one embodiment, the filler may have a particle size (d50) of 50 µm or smaller, 25 µm or smaller, or 10 µm or smaller. The particle size of particles having a size less than 100 nm can be conveniently measured using dynamic light scattering or laser diffraction.

[0049] In some embodiments, the particulate filler particles may have an aspect ratio of up to 5, up to 2, or up to 1.5. In other embodiments, some or all of the filler particles may be grafted onto one or more polyether polyols of the polyol component.

[0050] Typically, when rheology fillers are present in a polyol component, the polyol component may contain 0.1% to 10% rheology fillers by weight of the component. In some embodiments, the polyol component may contain 0.1% to 5% rheology fillers by weight of the component. In other embodiments, the polyol component may contain 0.5% to 1.5% rheology fillers by weight of the component.

[0051] In some embodiments, the rheology filler may also be present in the isocyanate component, or in both the isocyanate and polyol components.

[0052] E. monool

[0053] The polyol component of the present invention further comprises one or more monools having a molecular weight of 100 to 3000. A “monool” is a compound having exactly one hydroxyl group and is an alkoxylated alcohol. The monool may have a molecular weight of at least 100, at least 200, at least 300, or at least 500. The molecular weight of the monool may be up to 3000, up to 2000, up to 1500, or up to 1000. The monool used in the present invention is preferably linear. “Linear” means that the monool does not have side chains with more than four, especially more than two, carbon atoms. The monool may contain a hydrocarbon chain with four or more carbon atoms, especially at least ten carbon atoms. The hydrocarbon chain may contain up to 50, up to 30, or up to 20 carbon atoms. The hydrocarbon chain is preferably aliphatic.

[0054] The monool may contain polyether chains. The polyether chains may be polymers of one or more of, for example, ethylene oxide, propylene oxide, 1,2-epoxybutane, 2,3-epoxybutane, or tetrahydrofuran. The polymerized ethylene oxide (if present) preferably constitutes no more than 50% of the total weight of the monool.

[0055] The monool can be a monool represented by the structure AB-OH, where A represents a hydrocarbon group and B represents a polyether chain, wherein the lengths of A and B are such that the monool has the molecular weight as described above. A can represent, for example, a saturated or unsaturated aliphatic group having 2 to 50 carbon atoms. Group A preferably has 4 to 30, 4 to 30, or 4 or 20 carbon atoms. In some embodiments, A is a C4-20 straight-chain aliphatic hydrocarbon group, which can be saturated or unsaturated, but is preferably saturated. "Hydrocarbon group" indicates a molecule or group containing only carbon and hydrogen atoms (as the case may be). Group B can be a polymer of one or more of, for example, ethylene oxide, propylene oxide, 1,2-epoxybutane, 2,3-epoxybutane, or tetrahydrofuran. The polymerized ethylene oxide (if present) preferably accounts for no more than 50% of the total weight of group B. Group B can have a weight of, for example, 100 to 1900 atomic mass units. In certain embodiments, it has a weight of at least 300 or at least 500, up to 1500, up to 1200 or up to 1000. Monools having the structure AB-OH can be prepared by alkoxylating a monohydric alcohol having the form A-OH, wherein A is as described above.

[0056] In a preferred embodiment, the monool is a fatty acid alcohol alkoxylated with polypropylene oxide, polyethylene oxide, or a mixture thereof. In another preferred embodiment, the monool is a fatty acid-initiated polypropylene oxide polyether, commonly known as PAG-15, which is commercially available from Dow Chemical Company.

[0057] The polyol component may contain 0.1% to 20%, preferably 1% to 10%, and more preferably 1% to 5% monools based on the total weight of the components. While monools are preferably used in the polyol component, they may also be used in the isocyanate component or both components.

[0058] Other optional ingredients can also be used to adjust certain properties of the polyol components. For example, Monomix can be added. TM G (a commercially available fine, high-brightness talc from Erythrope) aids in failure modes, and molecular sieves can be added to address excess moisture. The amounts of these optional components can be adjusted using typical knowledge of those skilled in the art.

[0059] III. Methods and Applications

[0060] In one embodiment, a method for preparing the thermally conductive adhesive formulation of the present invention includes providing an isocyanate component and a polyol component. When provided as a kit, the two components may be co-packaged or packaged separately. When the adhesive formulation is ready for use, the components may be mixed, blended, or co-blended together, and a reaction product is generated when the combination of components cures. One or more additional optional components (such as additional anti-settling agents such as precipitated calcium carbonate) and additional rheology modifiers (such as waxy polyester polyols or urea-based rheology modifiers) may be added to the formulation as needed.

[0061] Although the amounts of the components that can be used to form 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 to be combined to form the reaction product adhesive formulation, the isocyanate component and the polyol component can be mixed in a volume ratio ranging from 2:1 to 1:2. In a preferred embodiment, this volume ratio between the isocyanate component and the polyol component is about 1:1.

[0062] When the components are manufactured separately and individually, the raw materials can be mixed together at the desired concentrations discussed above at temperatures, for example, 5°C to 80°C (e.g., 15°C to 50°C) or at room temperature. In one embodiment, the mixing of the components can be carried out under vacuum and / or using a planetary mixer or on a double asymmetric centrifuge. The order of mixing is not critical, and two or more compounds can be mixed together, followed by the addition of the remaining components.

[0063] Two-component polyurethane adhesive formulations can also be premixed before use. When doing so, all the components of the adhesive formulation can be mixed together using any known mixing method and equipment. When mixing the various raw material components, it is preferable to mix the liquid phase first, before adding the solid components. The entire mixture should be mixed for approximately 30 to 45 minutes to form the final formulation, and then packaged into tubes, drums, cylinders, or other commonly known packaging.

[0064] 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 formed of at least one battery cell and a cooling plate, wherein the battery module is fixed to the cooling plate by a cured thermally conductive adhesive of the present invention. In another embodiment, the battery module is part of an electric vehicle. Example

[0065] The following examples further illustrate the invention. The scope of the invention and the claims is not limited to the scope of the following examples.

[0066] I. Raw material composition and invention examples

[0067] The table below lists examples of the invention and two comparative examples. All weight percentages are based on the total weight of the respective components.

[0068] Table 1. Composition of isocyanate components

[0069]

[0070] Table 2. Composition of polyol components

[0071]

[0072] The organofunctional silanes used in the examples contain epoxy silanes. The thermally conductive filler used in the examples is bimodal aluminum hydroxide (ATH).

[0073] The polyol used in this example is the trade name Voranal. TM Ethylene oxide-terminated polypropylene oxide polyether polyols are commercially available from Dow Chemical Company.

[0074] 1,4-Butanediol is commercially available from ARCO Chemical.

[0075] The rheology modifier used in this example is hydrophobic fumed silica, which is commercially available from Evonik.

[0076] The graphite used in this example is a Timrex blend commercially available from Erythrope.

[0077] The catalyst used in this example is Fomorez UL29 (dioctyltin thiol catalyst), which is commercially available from Momentive.

[0078] The monool used in this example is PAG-15.

[0079] II. method

[0080] A. Sample Preparation

[0081] In each of the comparative and inventive examples, all components listed in Tables 1 and 2 (first the liquid components, then the solid components) are added to a planetary mixer or a double asymmetric centrifuge and mixed under vacuum for approximately 30 minutes, then transferred to a cylinder, barrel, or drum for storage. The mixture of isocyanate components is mixed under vacuum at 80°C for 60 minutes to form a prepolymer, and then cooled to room temperature and transferred to packaging.

[0082] B. Test

[0083] The test methods described herein include both those used in the illustrated examples and those values ​​included in the detailed description of the invention.

[0084] Indentation force: The indentation force was measured using a tension meter (Zwick). The gap filler material was placed on a metal surface. An aluminum piston with a diameter of 40 mm was placed on top, and the material was compressed to 5 mm (initial position). The material was then compressed to 0.3 mm at a speed of 1 mm / s, and the force-deflection curve was recorded. The force (N) at a thickness of 0.5 mm was then reported in the datasheet and considered as the indentation force.

[0085] Thermal conductivity: Thermal conductivity was measured according to ASTM 5470-12 using a thermal interface material tester from ZFW, Stuttgart. Tests were performed on 2 mm thick adhesive boards cured at room temperature for 7 days. Thermal conductivity tests were conducted at pressures of 1–5 bar, and the effective thermal conductivity was reported at 5 bar. The upper contact was heated to approximately 40°C. o C, and heat the lower contact to approximately 10 o C, yielding approximately 25 o C represents the overall sample temperature.

[0086] Gel permeation chromatography (GPC): Molecular weight data of the polyurethane prepolymer were measured by gel permeation chromatography (GPC) using a Malvern Viscothek GPC max instrument. Emsure-THF (ACS, Reag. Ph EUR for analysis) was used as the eluent, PL GEL MIXED-D (Agilent Technologies, 300 x 7.5 mm, 5 µm) was used as the column, and MALVERN Viscotek TDA was used as the detector.

[0087] Overlap Shear Test: E-coated steel substrates with Cathoguard 800 coating were used. Sample dimensions were 100 mm x 25 mm with a thickness of 1.2 mm. The substrates were cleaned with isopropyl alcohol before use. Adhesive was applied to one substrate, and then the second substrate was joined within less than 3 minutes. The thickness was adjusted to 1.0 mm, with an overlap of 25 mm x 15 mm. The joined substrate units were cured at 23°C and 50% relative humidity and allowed to stand for 7 days prior to the overlap shear test. The sample units were then mounted in a tension meter, and the overlap shear test was performed using a pulling speed of 10 mm / min. The force-deflection curve was monitored, and the breaking strength was reported as the overlap shear strength.

[0088] Viscosity: Rheological measurements were performed on an Anton Paar MC 302 rheometer with a parallel plate geometry, using plates with a diameter of 25 mm and a fixed gap of 0.5 mm. The thermal interface material was placed between the two plates, and shear rate tests were then performed from 0.001 to 20 1 / s, with the viscosity reported at 10 1 / s.

[0089] Tensile testing: Tensile strength, E-modulus, and elongation at break were determined according to DIN 527-2. A dog bone-shaped sample with a thickness of 2.0 mm was used. The tensile test was performed at 10 mm / min.

[0090] The test results are summarized in Tables 3 and 4.

[0091] Table 3. Viscosity (Pa.s) at 23°C and 10 1 / s

[0092]

[0093] Table 4. Other test data for two-component polyurethane adhesive formulations (1:1 v / v combination of isocyanate and polyol components).

[0094]

[0095] C. Discussion of Results

[0096] As shown in the table above, the comparative examples do not contain any monools. The E-modulus of the comparative examples is 12 MPa, which greatly contributes to the presence of plasticizers in both the isocyanate and polyol components.

[0097] Example 1 of the invention contains 2 wt.% of a monool based on the total weight of the polyol component. The modulus is significantly reduced to 9 MPa. As shown in Example II of the invention, this phenomenon is further demonstrated by increasing the monool content to approximately 4 wt.%. Here, the E-modulus is further reduced to 6.6 MPa. In all examples, the viscosity and indentation force values ​​are not significantly affected by the addition of the monool.

[0098] All other test values ​​between the comparative example and the two inventive examples are comparable, with the inventive examples showing a slight improvement.

Claims

1. A two-component adhesive formulation, the two-component adhesive formulation comprising: The isocyanate component contains greater than 50 wt.% thermally conductive filler; and Polyol components; At least one of the isocyanate component and the polyol component further comprises a plasticizer; At least one of the isocyanate component and the polyol component further comprises a monool; and The E-modulus of the two-component adhesive is less than 35 MPa.

2. The two-component adhesive formulation according to claim 1, wherein, Both the isocyanate component and the polyol component contain plasticizers.

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. A two-component adhesive formulation according to any one of the preceding claims, wherein, The polyol component includes monools.

6. The two-component adhesive formulation according to claim 5, wherein, The polyol component comprises 0.1% to 20% monools based on the total weight of the polyol component.

7. The two-component adhesive formulation according to any one of the preceding claims, wherein, The monool is a fatty acid alcohol alkoxylated with polypropylene oxide, polyethylene oxide, or a mixture thereof.

8. A two-component adhesive formulation according to any one of the preceding claims, wherein, The monool is a fatty acid alcohol-initiated polypropylene oxide polyether.

9. A two-component adhesive formulation according to any one of the preceding claims, wherein, The polyol component has a mass ratio between the plasticizer and the monool between 1:1 and 1:

2.

10. A two-component adhesive formulation according to any one of the preceding claims, wherein, The E-modulus of the two-component adhesive is less than 20 MPa.

11. A two-component adhesive formulation according to any one of the preceding claims, wherein, The E-modulus of the two-component adhesive is less than 10 MPa.

12. The two-component adhesive formulation according to claim 2, wherein, The mass ratio of the plasticizer present in the isocyanate component to the plasticizer present in the polyol component is approximately 5:

1.

13. The two-component adhesive formulation according to claim 3, wherein, The plasticizer contains branched C8 alkyl groups.

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

2.

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

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