Two-component low-density polyurethane potting formulation

Abstract

Two-component polyurethane-based potting formulation with good flame retardant properties.

Description

UNITED STATES PROVISIONAL APPLICATIONTWO-COMPONENT LOW-DENSITY POLYURETHANE POTTING FORMULATIONBACKGROUND

[0001] As electric vehicle (EV) technology advances, demand is increasing for vehicles that are lighter and capable of traveling longer distances. This in turn creates a demand of each component manufacturer to minimize weight. At the same time, for certain applications such as battery potting materials, flame retardance is also an important requirement. The automotive EV battery pack typically includes multiple sections, or modules, with each module having several lithium-ion batteries assembled in a frame. A thermal runaway reaction can occur when damage occurs to a cell. A short circuit, for example, can cause heat and pressure to build up within a cell. The heat and pressure can trigger further exothermic reactions in adjacent cells. If the heat is not dissipated fast enough, a battery fire can result. To prevent this, a thermal barrier needs to surround each cell, which can isolate the heat generated in the damaged cell so that the adjacent cells are protected. A need in the art exists for new and alternative low density potting materials that provide for light weight and also meet applicable flame retardance standards.SUMMARY

[0002] Described herein is a two-component potting formulation, comprising: a) an isocyanate component comprising an isocyanate; and b) a polyol component comprising: i) a polyol having a viscosity of 5,000 cp or less at 25°C; ii) a low density filler having a density of 1 g / cm3or less; and iii) 0.1 % to 20% of a rheology modifier by weight of the potting formulation.

[0003] In general, the uncured potting formulation is in the form of a kit in which the first and second components are not mixed prior to use.

[0004] Also described is a process for curing the potting formulation, generally comprising mixing the isocyanate and polyol components of the potting formulation and allowing the mixture to cure.DETAILED DESCRIPTION

[0005] The potting formulation generally comprises an isocyanate component and a polyol components, typically in the form of a kit in which each component is kept separately prior to use. It is also contemplated that one or more individual components may be provided or sold individually, e.g., the polyol component may be provided without the isocyanate component and vice versa. The ratio of the two components can vary within wide margins. In some embodiments, the potting formulation comprises 50%-80% of the polyol component by weight of the potting formulation. In a further embodiment, the potting formulation comprises 20%-50% of the isocyanate component by weight of the potting formulation.I. Isocyanate Component

[0006] The isocyanate component of the two-component potting formulation is not limiting - any isocyanate component is contemplated. For example, the isocyanate can include any monomeric or polymeric isocyanate commonly used with polyurethane technology. In one embodiment, the isocyanate comprises an aromatic isocyanate, an aliphatic isocyanate, or a mixture thereof. In a further embodiment, the isocyanate comprises isophorone diisocyanate (IPDI), dicyclohexyl methane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), 4,4-diphenylmethane diisocyanate (MDI) or a polymeric variant thereof, 4,4’-methylenediphenyl diisocyanate, or a mixture thereof. In another embodiment, the isocyanate comprises polymeric 4,4-diphenylmethane diisocyanate (MDI), 4,4-diphenylmethane diisocyanate (MDI), tetramethylxylylene diisocyanate (TMXDI), or 4,4’- methylenediphenyl diisocyanate.

[0007] Other suitable isocyanates include 4, 4’-methylene-diphenyldiisocyanate; 2,2’-methylenediphenyldiisocyanate; 2,4-methylene-diphenyldiisocyanate; toluene diisocyanate (TDI); toluene-2,4-diisocyanate; toluene-2,6-diisocyanate; naphthyl- ene-1 , 5-diisocyanate; methoxyphenyl-2,4-diisocyanate; diphenyl-methane-4,4’- diisocyanate; diphenylmethane-2,4’-diisocyanate; 4,4’-bi-phenylene diisocyanate; 3,3’-dimethoxy-4,4’-biphenyl diisocyanate; 3,3’-dimethyl-4-4’-biphenyl diisocyanate; 3,3’-dimethyl-diphenyl methane-4, 4’-diisocyanate; 4,4’,4"-triphenyl methane triisocyanate; toluene-2, 4, 6-triisocyanate; 4,4,-dimethyl-di-phenylmethane-2,2,,5,5’- tetraisocyanate; and mixtures thereof.

[0008] Any polymer of a monomeric isocyanate can also be used to make an isocyanate prepolymer, which can in some embodiments be used in combination with monomeric isocyanates. Examples include any derivative or polymer of the above described isocyanates. Other examples include polyisocyanates that contain urethane, urea, biuret, carbodiimide, uretoneimine, allophonate or other groups formed by reaction of isocyanate groups. The isocyanate component can also include polymeric MDI (a mixture of MDI and polyMDI that is commonly referred to as “polymeric MDI”). Other examples include “liquid MDI" products that are mixtures of MDI and polyMDI derivatives that have biuret, carbodiimide, uretoneimine or allophonate linkages.

[0009] The isocyanate component can include an isocyanate prepared by reacting a monomeric or polymeric isocyanate with a polyol, or a lower molecular weight diol or triol. For example, any one of the polyols described below with reference to the polyol component; or for example any of the polyols described in W02016205252(A1), incorporated by reference, can be used.II. Polyol ComponentA. Polyol

[0010] Suitable first polyols for the polyol component can vary and can any polyether polyol having a hydroxyl functionality of 2 to 7. In general, the polyol component can comprise 20-80%, e.g., 25-65%, 25-50%, 25-40%, or 25-30% by weight of the polyol. The polyol can be any glycerin initiated propoxylated or ethoxylated polyol or any propoxylated or ethoxylated polyol prepared from alternative tri-functional and bis-functional starters. In some embodiments, the polyol can be a polyether polyol or mixture of polyether polyols. In other embodiments, the first 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 from 1 wt% to 30 wt% ethylene oxide. 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 secondaryhydroxyl groups. In another embodiment, 70% or more of the hydroxyl groups in the polyether polyol or mixture thereof can be primary hydroxyl groups.

[0011] In some embodiments, the polyol has a hydroxyl functionality ranging from 2 to 7. In a further embodiment, the polyol has a viscosity at room temperature (about 25°C) of 5,000 cp or less, e.g., 4,000 cp or less, 3,000 cp or less, 2,000 cp or less, or 1 ,500 cp or less.B. Low-Density Filler

[0012] To maintain low weight of the potting material, embodiments of the formulation can comprise 0.1 % to 50% by weight of the potting formulation of a low- density filler. The low-density filler can be present in the first component, the second components, or both components. In one embodiment, the low-density filler is present in the polyol component. In a further embodiment, the low-density filler is present in the polyol component but not the isocyanate component. In some embodiments, the low-density filler is one that has a density of less than 1 g / cm3.

[0013] In some embodiments, the potting formulation comprises 0.1 % to 20% by weight of the potting formulation of the low-density filler, which can be in either or both components, e.g., the polyol component. For example, in one embodiment, the formulation comprises 0.1% to 15% by weight of the potting formulation of the low- density filler, e.g., 0.1-10%. In a further embodiment, the formulation comprises 1 % to 10% by weight of potting formulation of the low-density filler, e.g., 1-8%, 2-6%, 2- 5%, or 3-5%.

[0014] Various low-density fillers can be used. In some embodiments, the low- density filler comprises hollow microspheres. The hollow microspheres can be hollow glass microspheres, hollow silica microspheres, silica aerogel, hollow phenolic resin microspheres or microballoons, or a combination thereof.C. Rheology Modifier

[0015] One advantage of the described potting formulation is that the polyol component is thixotropic. The thixotropic nature of the polyol side permits the low- density filler to stabilize under storage conditions. It is also desirable to obtain a formulation that flows easily under mixing or high-shear conditions. Such thixotropic properties can be achieved through the use of a rheology modifier.

[0016] In some embodiments, the potting formulation comprises 0.1-20% of a rheology modifier by weight of the potting formulation. In a further embodiment, the potting formulation comprises 0.5-15% of a rheology modifier by weight of the potting formulation. In a further embodiment, the potting formulation comprises 0.5-10% of a rheology modifier by weight of the potting formulation. In a further embodiment, the potting formulation comprises 0.5-5% of a rheology modifier by weight of the potting formulation. In a further embodiment, the potting formulation comprises 0.5-2% of a rheology modifier by weight of the potting formulation. In a further embodiment, the potting formulation comprises 0.5-1 .5% of a rheology modifier by weight of the potting formulation.

[0017] A variety of rheology modifiers can be used. In some embodiments, the rheology modifier is a urethane resin, such as an ethoxylated hydrophobic urethane resin (HEUR), a sulfonate such as a calcium sulfonate, a polyamide, or a modified urea such as an alkylated or polyether alkyl urea. In one embodiment, the rheology modifier is a modified urea.D. Crosslinker and Other Additives

[0018] In some embodiments, the polyol component comprises a crosslinker. A crosslinker can advantageously provide high hard segment content and high crosslink density, which can improve modulus after the potting formulation is fully cured. Any suitable crosslinker can be used, e.g., any short chain diol, triol, or tetrafunctional polyol or polyamine. Non-limiting examples include glycerol and triethanolamine. The crosslinker when present in the polyol component can be present in any suitable amount, e.g., 0.5% to 20% by weight of the polyol component, e.g., 0.5-15%, 0.5-10%, 1-10%, 2-10%, or 5-10%.

[0019] In a further embodiment, the polyol component can comprise a moisture scavenger. The potting formulation can comprise 0.1-10% by weight of the moisture scavenger by weight of the potting formulation, e.g., 0.1-5%, 0.1-3%, or 0.1-1.5%. A variety of moisture scavengers are suitable. Examples include molecular sieves, vinyl silanes, oxazolidine, monofunctional isocyanate (e.g., pTSI), triethyl orthoformate, among others.III. Additional Optional AdditivesA. Catalyst

[0020] Either component can include a catalyst for catalyzing the reaction of an isocyanate with an isocyanate reactive group, including for example a hydroxyl group of a polyol, amine group of a crosslinker, and the like. In one embodiment, the catalyst is present in the polyol component. In a further embodiment, the catalyst is present in the polyol component and not in the isocyanate component.

[0021] The catalyst can include, for example, one or more latent room temperature ( 25°C) organometallic catalysts. The latent room temperature organometallic catalysts can contain tin, zinc, bismuth, or a combination thereof. For example, the latent room temperature organometallic catalyst can include one or more catalysts such as zinc alkanoates, bismuth alkanoates, dialkyl tin alkanoates, dialkyl tin mercaptides, dialkyl tin bis(alkyl-mercaptoacetates), dialkyltin thioglycolates, or mixtures thereof. Specific examples include dioctyltinmercaptide, dibutylmercaptidem, dibutylmercaptide, dibutylmercaptide, bis(dodecylthio)dimethylstannane, dimethytin bis(2-ethylhexylmercaptoacetate), dioctylcarboxylates, dioctyltinneodecanoate, and mixtures thereof.

[0022] Another catalyst useful in the adhesive formulation is any catalyst that can be further heat activated (referred to as “thermosensitive catalysts”) or otherwise catalyze the reaction. In one embodiment, such catalysts can include for example amines-based solid amine catalysts such as a cyclic amidine catalyst compound, e.g., 1 ,8-diazabicyclo[5.4.0] undec-7-ene (DBU), 1 ,5-diazabicyclo[4.3.0]non-5-ene, 2,4,6-tris-(dimethylaminomethyl)-phenol, and mixtures thereof.

[0023] In a further embodiment, the adhesive formulation can include a combination of a latent tin-containing catalyst and a thermosensitive amine-based catalysts. Both the tin-containing organic catalyst and the amine-based catalyst can be readily formulated into the isocyanate component, the polyol component, or both the isocyanate component and the polyol component.

[0024] In a further embodiment, any non-tin-based metal-organic catalyst which exhibits similar curing kinetics or catalytic profile of the tin-based catalyst described above can be used as the catalyst ingredient in the adhesive formulation. For example, useful bismuth-based catalysts include bismuth(lll)-neodecanaote, and useful zinc-based catalysts include zinc-neodecanaote.

[0025] In yet another embodiment, non-tin-based catalysts or non-amine-based catalysts useful in the adhesive formulation include carboxylic acid blocked catalysts such as DBU carboxylic acid blocked catalysts. For example, a DBU carboxylic acid blocked catalyst can be TOYOCAT DB41 catalyst (a carboxylic DBU salt available from TOSOH), POLYCAT SA-102 / 10 (a carboxylic DBU salt available from Air Products), and mixtures thereof. Other useful catalysts include acid blocked amines including for example tertiary amines and organic acid-based catalysts such as TOYOCAT DB40, TOYOCAT DB60, and TOYOCAT DB70 available from TOSOH; 1 H-1 , 2, 4-triazole-based amine catalysts such as TOYOCAT DB30 available from TOSOH; and mixtures thereof. Any other known thermosensitive amine catalysts can also be used including TOYOCAT F22 available from TOSOH; triethylenediamine (TEDA); and mixtures thereof. In one embodiment, the catalyst useful can be selected from tin catalysts such as di-n-octyltin bis[isooctylmercaptoacetate]; and from amine catalysts such as POLYCAT SA 1 / 10, and TOYOCAT DB60; and mixtures thereof.

[0026] In general, the amount of the catalyst in the adhesive formulation can be in the range of from 0.005 wt % to 2.0 wt %; from 0.01 wt % to 1 .0 wt %; and from 0.015 wt. % to 0.07 wt %, based on either i) the total weight of the formulation or ii) the total weight of the first or second component of the formulation (i.e. , the polyol or isocyanate component). In one illustrative embodiment, for example when a tin catalyst such as di-n-octyltin bis[isooctylmercaptoacetate] is used in the adhesive formulation, the concentration of such catalyst in the formulation or in either component can be from 0.005 wt % to 1.0 wt %; from 0.02 wt % to 0.08 wt %; and from 0.03 wt. % to 0.05 wt based on the total weight of the formulation as a whole or either component thereof.

[0027] In another illustrative embodiment, when a thermosensitive amine catalyst such as POLYCAT SA 1 / 10 is used in the adhesive formulation, the concentration of such catalyst in the formulation can be from 0.01 wt % to 2.0 wt %; from 0.01 wt % to 1.0 wt %; and from 0.015 wt. % to 0.025 wt % based on the weight of the formulation as a whole or either component of the formulation.

[0028] In still another illustrative embodiment, when a catalyst such as TOYOCAT DB60 is used in the adhesive formulation, the concentration of such catalyst in the formulation can be from 0.01 wt % to 2.0 wt %; from 0.01 wt % to 1 .0 wt %; and from0.045 wt. % to 0.065 wt %, based on the weight of the formulation as a whole or either component of the formulation.

[0029] If the concentration of the catalyst is lower than 0.005 wt % by weight of the formulation as a whole, the catalyst used may not be effectively active in the formulation and the storage stability of the resulting formulation may be “poor,” that is, any residual water present in the formulation can deactivate the small amounts of catalyst. If the concentration of the catalyst is more than 2.0 wt %, the reaction of the components present in the formulation may be too quick resulting in a short open time, that is, an open time of for example less than 3 minutes may occur. In addition, a high catalyst level (e.g., greater than 2.0 wt %) in the formulation may lead to an increase in handling and formulation costs for the resulting formulation.B. Flame Retardant

[0030] Either component or both components can comprise a flame retardant. In some embodiments, the polyol component comprises a flame retardant. Any suitable flame retardant can be used, such as a halogenated phosphate, non-halogenated flame retardants, reactive flame retardants, or any combination thereof. Suitable halogenated phosphates include for instance chlorinated or brominated organophosphates. Non-limiting examples include Tris(1 ,3-dichloro-2- propyl)phosphate (TDCPP), Tris(1-chloro-2-propyl)phosphate (TCPP), Tris(2,3- dichloro-1-propyl)phosphate, and Tris(2-chloroethyl) phosphate (TCEP). In one embodiment, the first halogenated phosphate is TCPP. Any suitable halogen-free phosphate can be used in combination with the halogenated organophosphate.C. Plasticizer

[0031] Either component and in some embodiments the polyol component can comprise a plasticizer. In one embodiment, the plasticizer can have a weight average molecular weight of 2,000 g / mol or less, e.g., 1 ,000 g / mol or less, 800 g / mol or less, or 600 g / mol or less. The plasticizer will generally be a liquid at a temperature of about 100°C. The plasticizer can be present in any suitable amount, e.g., 1-20% by weight of either component, or alternatively by weight of the formulation.

[0032] Suitable plasticizers include any ester based plasticizers such as adipates, azelates, citrates, benzoates, butyrates, orthophtalates, terephthalates, sebacates,and trimellitates. Examples include ester derivatives of acids and anhydrides such 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.

[0033] 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, dibutyl fumarate, 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, tris(2-ethylhexyl)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, dimethoxyethyl 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.

[0034] 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.IV. Process for Curing the Potting Formulation

[0035] Also disclosed is a cured potting formulation made by mixing the components of the described potting formulation and allowing the mixture to cure, for example after application onto a desired substrates such as a battery module. Similarly, this disclosure encompasses a process for curing the potting formulation, comprising mixing the isocyanate and polyol components of the potting formulation and allowing the mixture to cure. In some embodiments, the first and second components of the potting formulation are mixed at a ratio ranging from 4:1-1 :4, e.g, 2: 1 to 1 :2 (by weight). In a further embodiment, the first and second components of the potting formulation are mixed at a ratio of 1 :1.

[0036] In one specific embodiment, the lightweight filler can optionally be dried for instance at above 100°C, e.g., 110°C, to achieve a desired maximum moisture content. The isocyanate component and polyol component can be prepared, respectively, by mixing for 30 min-1 hr under a maximum pressure, e.g., 80 mbar, under an inert atmosphere such as nitrogen. To pot the two components, the first and second components can be mixed at the desired mass ratio under vacuum for an adequate amount of time. For test methods, density of each component can be measured using a density cup. Flame retardant performance can be evaluated by the UL94 standard.EXAMPLES

[0037] The following examples further illustrate this disclosure. The scope of the disclosure and claims is not limited by the scope of the following examples.Materials

[0038] The raw materials described in Table 1 were used in the examples.Table 1.Optional: Water can be added to the polyol side as a blowing agent. Water can react with isocyanates to form CO2 which can result in a foam based potting compound.

[0039] Contemplated substitutes for the specific materials listed in Table 1 are listed in Table 2 below. Table 2.II. Inventive and Comparative Examples

[0040] The composition of inventive and comparative examples are shown below in Table 3. Amounts listed are weight percentages of each material. Table 3.III. Methods and Testing

[0041] Polyols and ANTIFLAME TCPP were first dried under 3A molecular sieves for 3 days prior to using in the formulation. The Part B of the formulation (polyol blend) was prepared by adding all liquid components in a Max 300 cup (Flackteck Inc.). The contents were mixed in a Flackteck Speedmixer operating at 2000 rpm for 2 min under 50 mBar vacuum. The solid contents were then added to the cup and the contents were mixed at 1200 rpm for 2 min without vacuum. The contents were then mixed again at 1200 rpm under 50 mBar vacuum for 2 min. The blended Part B was stored under nitrogen blanket prior to mixing with Part A. For Example 2, the Expancel 920 DE 40 d30 was first blended with TCPP to form a slurry, which was then added to the final blend.

[0042] To prepare cured potting compound, Part A and B were mixed in a Max 100 cup at the given ratio given in Table 2. The contents were mixed in a Flackteck Speedmixer operating at 1200 rpm for 2 min under 50 mBar vacuum. After mixing, the contents were immediately poured in a mold and allowed to cure at room temperature for 3 days.

[0043] Rheology. Rheology measurements were conducted on Discovery HR1 (TA Instruments) Rheometer using 25 mm aluminum parallel plate setup. Part B viscosity was measured at 25°C with shear flow ramp from 0.01 / s to 100 / s in 120 s. The viscosity at 0.01 and 100 / s shear rates are reported in Table 4. For mixed viscosity, the two parts were mixed using a Speedmixer and a small sample was transferred to a 25 mm parallel plate and the viscosity was measured at 25 / s shear rate at 25°C. To measure working time, the viscosity measurement was continued until the viscosity reached 5000 cps.

[0044] Flammability: Flammability test was performed using the UL94 standard for safety of flammability of plastic materials for parts in devices and appliances testing.Five specimens, 127mm long, 13mm wide, and 3 mm thick were prepared for this test. Each specimen was cured for 3 days prior to performing the UL 94 test. The sample was rated V-0 if: (1) None of the five samples had flaming combustion for more than 10 seconds after each of two 10 second flame applications; (2) the total flaming combustion time for the ten 10 second flame applications (5 samples, 2 applications each) of more than 50 seconds; (3) none of the five samples burned with flaming or glowing combustion up to the holding clamp; (4) none of the five samples dripped flaming particles which ignite dry absorbent cotton located 305mm below the sample; (5) none of the five samples had glowing combustion which persisted for more than 30 seconds after the second removal of the flame.

[0045] A V1 rating was given to the sample if burning stopped within 60 seconds after two applications of ten seconds each of a flame to a test bar.

[0046] Compression’. Compression testing was conducted in accordance with ASTM D1621. Material was mixed within a 300mL-Max speed mixer cup, filled to a height of approximately 20mm. The material was allowed to cure within the speed mixer cup into a solid “puck” approximately 150mm in diameter. The top and bottom surfaces of the “puck” were sanded to ensure the surfaces were parallel to one another. Individual test specimens were extracted from the “puck” using a 1-1 / 8” hole-bit.

[0047] Each individual specimen was measured to record both geometrical dimensions and mass. Specimens were compressed using an INSTRON 5967, equipped with a 30kN load cell and parallel compression platens. The testing was conducted at a rate of 1 / 1 OX the measured height of each specimen, until a maximum compressive strain of 16% was reached. Transient Force [F ] and deflection [d ] data was recorded during each test at an acquisition rate of 2.5Hz. Using the dimensions of the samples recorded prior to testing, the compressive engineering stress [s ] and engineering strain [e ] data were calculated using equations known in the art.

[0048] Tensile Test: Tensile testing was conducted in accordance with ASTM D638, utilizing specimens with dimensions of an ISO 8256 Type-3 bar. Material was mixed within a Max speed mixer cup and poured into a rectangular mold to a height of approximately 2.5-3mm. The material was allowed to fully cure before being trimmed and machined into the ISO 8256 geometry using a router fixture.

[0049] Each individual specimen was measured to record both geometrical dimensions and mass. Specimens were tested in tension using an INSTRON 5969, equipped with a 10kN load cell, mechanical grips, and a non-contact extensometer. The testing was conducted at a rate of 25mm / min, until failure. Transient force [F] and local deflection [d] data was recorded during each test at an acquisition rate of 50Hz. Using the dimensions of the samples recorded prior to testing, the engineering stress [s] and engineering strain [e] data were calculated using equations known in the art.

[0050] Density. The density of the cured material was determined using Archimedes principle under room temperature. The weight of the cured material was weighed in air and when submerged in water and the difference was used to obtain the volume of water displaced (density of water = 1 g / cc). The density was then calculated by dividing the mass of the cured sample by the volume.

[0051] Thermal conductivity. Thermal conductivity was measured on a ThermTest Hot Disk TPS 2500 S using ISO 22007-2:2022 Plastics — Determination of thermal conductivity and thermal diffusivity — Part 2: Transient plane heat source (hot disc) method. Kapton 4922 (Radius of 14.61 mm) sensor was used. The instrument can measure thermal diffusivity of the material. The thermal conductivity was calculated by multiplying the thermal diffusivity value obtained on the instrument by the heat capacity and density, which were independently determined. Each sample were measured in triplicate and the average thermal conductivity value was reported.IV. Results

[0052] Measured properties of the inventive and comparative examples are shown in Table 4.Table 4.

[0053] The Part B (polyol blend) viscosity was measured over a range of shear rates. The low shear rate viscosity (1 / s) for the potting compound of Inventive Example 1 was 4,280 cps and at high shear rate viscosity (100 / s) was measured at 850 cps. Similarly, the low shear rate viscosity (1 / s) for potting compound of Inventive Example 2 was 6,500 cps and at high shear rate viscosity (100 / s) was measured at 1100 cps. In both cases, a high degree of thixotropy or “shear thinning” was observed. The high viscosity at low shear rate is due to the formation of hydrogen bonding network of the modified urea-based stabilizer used in the formulation. The high viscosity at low or no shear allows the low-density fillers to stabilize during storage. The hydrogen bonding breaks down at a high shear rate, resulting in low viscosity and high flowability. When the two parts A and B were mixed, the resulting initial viscosity was measured at 1 ,040 and 1 , 100 cps for Inventive Examples 1 and 2, respectively. The working time defined as the time to reach 5,000 cps viscosity after mixing was determined to be 11 and 12 minutes for Inventive Examples 1 and 2, respectively. The low mix viscosity in combination with long working time makes this material suitable to pour in a battery pack and to fill the small gaps between two cells.

[0054] Both inventive potting compounds show high flame resistance in the UL94 test (V0 rating). In addition, they both have very high thermal resistivity as indicated by the low thermal conductivity values. The low thermal conductivity in combination with high flame resistance makes these materials suitable as thermal barriers to prevent propagation of thermal runaway reactions in lithium-ion battery packs.

[0055] The addition of low-density fillers allows the inventive compositions to have a lower density compared to the comparative example which has a significantly higher density (1 .2 g / cc).

[0056] During each test, the modulus was calculated at two distinct ranges within the stress-strain curves: 1 ) initial slope (the linear portion within the first 1 % strain), and 2) secondary slope (the linear portion within approximately 10%-15% strain). The compressive strength was also recorded at distinct compressive strain values, 5%, 10%, and 15%. A tabulated summary of the compression results can be seen inTable 5.Table 5.Table 5 Continued.

[0057] During each test, the modulus was calculated within the initial linear portion of the stress-strain curve from approximately 0.5-1.0% strain. The maximum tensile strength and elongation at break was also recorded for each test. A tabulated summary of the compression results can be seen in Table 6.Table 6.Table 6 Continued.

[0058] Features and advantages of this disclosure are apparent from the detailed specification, and the claims cover all such features and advantages. Numerousvariations will occur to those skilled in the art, and any variations equivalent to those described in this disclosure fall within the scope of this disclosure. Those skilled in the art will appreciate that the conception upon which this disclosure is based may be used as a basis for designing other compositions and methods for carrying out the several purposes of this disclosure. As a result, the claims should not be considered as limited by the description or examples.

Claims

CLAIMSWhat is claimed is:

1. A two-component potting formulation, comprising: a) an isocyanate component comprising an isocyanate; b) a polyol component comprising: i) a polyol having a viscosity of 5,000 cp or less at 25°C; ii) a low-density filler having a density of 1 g / cm3or less; iii) 0.1 % to 20% of a rheology modifier by weight of the potting formulation; wherein the uncured potting formulation is in the form of a kit in which the first and second components are not mixed prior to use.

2. The potting formulation of claim 1 , wherein the polyol is a polyether polyol having a hydroxyl functionality ranging from 2 to 7.

3. The potting formulation of claim 1 , wherein the low-density filler comprises hollow glass microspheres, hollow silica microspheres, silica aerogel, hollow phenolic resin microspheres or microballoons, or a combination thereof.

4. The potting formulation of claim 1 , which comprises 0.1 % to 50% of the low- density filler by weight of the potting formulation.

5. The potting formulation of claim 1 , which comprises 0.1 % to 20% of the low- density filler by weight of the potting formulation.

6. The potting formulation of claim 1 , which comprises 0.1 % to 15% of the low- density filler by weight of the potting formulation.

7. The potting formulation of claim 1 , which comprises 0.1 % to 10% of the low- density filler by weight of the potting formulation.

8. The potting formulation of claim 1 , which comprises 1 % to 10% of the low- density filler by weight of the potting formulation.

9. The potting formulation of claim 1 , which comprises 1 % to 8% of the low- density filler by weight of the potting formulation.

10. The potting formulation of claim 1 , which comprises 2% to 6% of the low- density filler by weight of the potting formulation.11 . The potting formulation of claim 1 , which comprises 2% to 5% of the low- density filler by weight of the potting formulation.

12. The potting formulation of claim 1 which comprises 3% to 5% of the low- density filler by weight of the potting formulation.

13. The potting formulation of claim 1 , which comprises 0.5% to 15% of the rheology modifier by weight of the potting formulation.

14. The potting formulation of claim 1 , which comprises 0.5% to 10% of the rheology modifier by weight of the potting formulation.

15. The potting formulation of claim 1 , which comprises 0.5% to 5% of the rheology modifier by weight of the potting formulation.

16. The potting formulation of claim 1 , which comprises 0.5% to 2% of the rheology modifier by weight of the potting formulation.

17. The potting formulation of claim 1 , which comprises 0.5% to 1.5% of the rheology modifier by weight of the potting formulation.

18. The potting formulation of claim 1 , wherein the rheology modifier is a urethane resin, a sulfonate, a polyamide, or a modified urea.

19. The potting formulation of claim 1 , wherein the polyol component further comprises a crosslinker having at least two hydroxyl or amino functional groups which are reactive with the isocyanate.

20. The potting formulation of claim 1 , wherein the polyol component further comprises a moisture scavenger.21 . The potting formulation of claim 1 , further comprising a catalyst capable of catalyzing the reaction of the isocyanate with an isocyanate-reactive group.

22. The potting formulation of claim 1 , further comprising a plasticizer.

23. A process for curing the potting formulation of claim 1 , comprising mixing the isocyanate and polyol components of the potting formulation and allowing the mixture to cure.

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