Two-component low-density polyurethane potting formulation

Abstract

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

Description

[0001] UNITED STATES PROVISIONAL APPLICATION

[0002] TWO-COMPONENT LOW-DENSITY POLYURETHANE POTTING FORMULATION

[0003] BACKGROUND

[0004] 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 run-away 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 for meeting applicable flame retardance standards.

[0005] SUMMARY OF THE INVENTION

[0006] The present invention provides a two-component polyurethane-based potting formulation with good flame retardant properties and stabilized foam. The formulation comprises: a) an isocyanate component comprising an isocyanate; b) a polyol component comprising: i) at least one polyol; ii) 1 % to 20% of a low-density filler having a density of 1 g / cm3or less; iii) 0.1% to 20% of a rheology modifier; iv) at least one crosslinker; v) 0.5% to 5% of a foam stabilizer; vi) 0.1% to 5% of a nucleating agent; and vii) 0.01 % to 2% of a blowing agent;

[0007] All percentages above are weight percentages based on the total weight of the potting formulation.

[0008] DETAILED DESCRIPTION OF THE INVENTION

[0009] The potting formulation generally comprises an isocyanate component and a polyol component, typically in the form of a kit in which each component is kept separately prior to use. The ratio of the two components can vary within wide margins. In some embodiments, the potting formulation comprises 30%-80% of the polyol component by weight of the potting formulation.

[0010] I. Isocyanate Component

[0011] The isocyanate component of the two-component potting formulation is not limiting - any isocyanate chemicals may be used in the present invention. 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] The potting formulation of the present invention typically contains about 20-75%, preferably 25-70%, more preferably 30 to 65%, and most preferably 35 to 60%, of the isocyanate component based on the total weight of the potting formulation.

[0016] II. Polyol Component

[0017] A. Polyol

[0018] Suitable polyols for the polyol component can be any polyether polyol having a hydroxyl functionality of 2 to 7. In general, the polyol component can comprise 5-50 wt.%, preferably 8 to 30 wt.%, more preferably 8 to 20 wt.%, and most preferably 8 to 15 wt.% of one or more polyol compounds by weight of the polyol component. The polyol can be any glycerin initiated propoxylated or ethoxylated polyol or any propoxylated or ethoxylated polyol prepared from alternative tri-functional and bisfunctional starters. In some embodiments, the polyol can be a polyether polyol or mixture of polyether polyols. In a preferred embodiment, two different polyols are used in the polyol component to balance the viscosity and crosslinking density in order to improve the modulus of the potting formulation. In one particularly preferred embodiment, a first polyol with about 250 cps and low functionality of about 3 is used with a second polyol with a higher viscosity of about 55 cps and a higher functionality of about 4.3. 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 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.

[0019] 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.

[0020] B. Low-Density Filler

[0021] To maintain low weight of the potting formulation, embodiments of the formulation can comprise 1% to 20% by weight of the potting formulation of a low- density filler. The low-density filler can be present either or both components but preferably present in polyol component only. In some embodiments, the low-density filler is one that has a density of less than 1 g / cm3.

[0022] In some embodiments, the potting formulation comprises 1 % to 20%, preferably 2% to 15%, more preferably 3% to 10% and most preferably no less than 3.5% of the low-density filler based on the weight of the potting formulation. The presence of the low-density filler greatly improves the mechanical properties of the formulation and also makes the foam based formulation more stable. In a preferred embodiment, it was surprisingly discovered that when the amount of the low-density filler in the potting formulation is at or above 3.5%, based on the total weight of the potting formulation, the compression modulus of the formulation greatly improved to over 300 Mpa.

[0023] Various low-density fillers can be used. In some embodiments, the low-density filler comprises hollow microspheres or other syntactic fillers. The hollow microspheres can be hollow glass microspheres, hollow silica microspheres, silica aerogel, hollow phenolic resin microspheres or microballoons, or a combination thereof.

[0024] C. Rheology Modifier

[0025] One advantage of the described potting formulation is that the polyol component is thixotropic. The thixotropic nature of the polyol component 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.

[0026] In some embodiments, the potting formulation comprises 0.1-20%, preferably 0.5-15%, more preferably 0.5-10%, and most preferably 0.5-5% of a rheology modifier based on the weight of the potting formulation. In yet another embodiment, the potting formulation comprises 0.5-2%, preferably 0.5-1 .5% of a rheology modifier based on the weight of the potting formulation.

[0027] 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 a preferred embodiment, the rheology modifier is a modified urea.

[0028] D. Crosslinker

[0029] In some embodiments, the polyol component comprises one or more crosslinkers. 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 crosslinkers can be used, e.g., any short chain diol, triol, or tetrafunctional polyol or polyamine. Non-limiting examples include glycerol, triethanolamine, and pentaerythritol. The crosslinkers 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%. In a preferred embodiment, the potting formulation comprises, in its polyol component, two to three different crosslinkers in an amount about 8-10% based on the total weight of the potting formulation.

[0030] In one particularly preferred embodiment, three different crosslinkers are used in combination in order to provide a balanced crosslink density, viscosity and cure speed for the potting formulation of the present invention. In such an embodiment, triethanolamine is a trifunctional crosslinker with catalytic activity due to its tertiary amine group in the compound structure. Glycerol crosslinker is also used because of its trifunctionality. In additional, another crosslinker, a solid form of pentaerythritol is also used because it is a four functional crosslinker.

[0031] E. Foam Stabilizer

[0032] The polyol component of the present invention also comprises one or more foam stabilizers. Many different foam stabilizers may be used but in a preferred embodiment, the foam stabilizers may be one or more of silicone surfactant, or non-silicone non-ionic surfactant. These foam stabilizers can improve the stability of the foam and the low- density fillers. Typically, the potting formulation comprises 0.5 to 5%, preferably, 0.75 to 2.5%, more preferably 0.9-1 .5 %, and most preferably about 1 % of one or more foam stabilizers based on the total weight of the potting formulation.

[0033] F. Nucleating Agent

[0034] The polyol component of the present potting formulation also includes one or more nucleating agents. Many different nucleating agents may be used but in a preferred embodiment, the nucleating agents may be one or more of talc, silica, alumina trihydrate, zinc oxide, zinc stearate, calcium carbonate, titanium dioxide, graphite, microcrystalline, nanocellulose. The nucleating agents act as sites or nuclei for the formation of the gas bubbles that produce the foam. By introducing nucleating agents, the bubble formation process is accelerated and more uniform bubbles are formed throughout the foam. Typically, the potting formulation comprises 0.1 to 5%, preferably, 0.1 to 2.5%, more preferably 0.1-1 .5 %, and most preferably 0.1-1% of one or more nucleating agents based on the total weight of the potting formulation. G. Blowing Agent

[0035] The polyol component of the present potting formulation also includes a blowing agent. Many different blowing agents may be used but in a preferred embodiment, the blowing agents is DI water. The blowing agent, when included in the potting formulations, can generate gas that expands the mixture and creates the foam structure. For example, when water is used as a blowing agent, water can react with isocyanates to form CO2 which can result in a foam based potting formulation. Hydrocarbons such as pentane and cyclopentane and / or hydro-fluoro olefins (HFOs) may also be used as blowing agents in the present invention because they vaporize quickly during the foaming process and they contribute to the expansion of the foam. Typically, the potting formulation comprises 0.01 to 2%, preferably, 0.025 to 1.5%, more preferably 0.05-1%, and most preferably 0.05-0.5% of blowing agents based on the total weight of the potting formulation.

[0036] III. Additional Optional Additives

[0037] A. Catalyst

[0038] 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.

[0039] 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. 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.

[0040] 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.

[0041] 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.

[0042] 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. In a preferred embodiment, a tertiary amine based catalyst, e.g. NIAX-A575 commercially available from Momentive Performance Materials Inc. is used due to its delayed action function. Such latent catalysts are designed to remain inactive under normal storage conditions but to become highly active when exposed to heat due to the exotherm of the polyurethane reaction. Use of such delayed action catalysts allow for a longer working time where viscosity of the potting formulation is low. It also provides a faster gel time to finish the cure / foam rise during application of the potting formulations.

[0043] In general, the amount of the catalyst in the potting formulation can be in the range of from 0.005 % to 4.0 %; from 0.01 % to 2.5 %; and from 0.015 % to 2.0 %, based on the total weight of the formulation.

[0044] If the concentration of the catalyst is lower than 0.005 % by weight of the potting 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 %, 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 %) in the potting formulation may lead to an increase in handling and formulation costs for the resulting formulation.

[0045] B. Flame Retardant

[0046] Either component or both components may comprise a flame retardant. Any suitable flame retardant can be used, such as a halogenated phosphate, nonhalogenated 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 a preferred embodiment, the halogenated phosphate is TCPP. Any suitable halogen-free phosphate can also be used in combination with the halogenated organophosphate.

[0047] In general, the amount of flame retardant in the potting formulation can be in the range of from 5% to 30 %; preferably from 8% to 25%; more preferably from 10% to 23%, and most preferably from 15% to 20%, all based on the total weight of the potting formulation.

[0048] IV. Process for Curing the Potting Formulation

[0049] The present invention also provides 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, the present invention 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 isocyanate and the polyol components are mixed at a ratio ranging from 4:1-1 :4, preferably from 2:1 to 1 :2; and most preferably about 1 :1 (by weight).

[0050] In one specific embodiment, the low-density filler can optionally be dried for instance at above 100°C, to achieve a desired maximum moisture content. The isocyanate component and polyol component can be prepared, respectively, by mixing for 30 min-1hr under a maximum pressure, e.g., 80 mbar, under an inert atmosphere such as nitrogen. To make the final potting formulation, the isocyanate and the polyol components can be mixed at the desired mass ratio under vacuum for an adequate amount of time.

[0051] EXAMPLES

[0052] The following examples further illustrate the present invention. The scope of the present invention and claims is not limited by the scope of the following examples.

[0053] Materials

[0054] The raw materials described in Table 1 were used in the examples.

[0055] Table 1.

[0056] Inventive Example

[0057] The formulation inventive example is shown below in Table 2. Amounts listed are weight percentages of each material.

[0058] Table 2.

[0059] II. Methods and Testing

[0060] Formulation preparation’. Polyols, crosslinkers and flame retardant were first dried under 3A molecular sieves for 3 days prior to using in the formulation. The Part B of the formulation 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. To prepare cured potting formulation, 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.

[0061] 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 Is to 100 Is in 120 s. The viscosity at 0.01 and 100 / s shear rates are reported below in Table 3. 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 Is shear rate at 25°C. The time to reach 5000 cps viscosity was reported as the working time. Gel time was measured by applying oscillatory stress at 1 Hz frequency and 0.12% strain. The time to reach G7G” crossover was reported as the gel time. Flammability. Flammability test was performed using the LIL94 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.

[0062] 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.

[0063] 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.

[0064] 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 [c / ] 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.

[0065] 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.

[0066] 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.

[0067] Lap Shear Test. For lap shear test, 1 -inch x 3-inch sized e-coated steel coupons were used. The liquid potting formulation was applied in an area of 12 mm x 25 mm. After applying the liquid potting formulation, a lap shear joint was prepared using another e-coated steel coupon placed at 2.5 mm gap. After expansion, the gap between the two coupons was filled by the potting formulation. The potting formulation was allowed to cure for 3 days and the joint was pulled at the rate of 1 inch / min on an INSTRON 5969.

[0068] 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.

[0069] 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.

[0070] III. Results

[0071] Measured properties of the inventive example are shown in Table 3. Table 3.

[0072] Table 3: Uncured Potting Formulation Properties

[0073] 5 Properties of the uncured potting formulation of the inventive example are shown in 3. The polyol component’s viscosity was measured over a range of shear rates. The low shear rate viscosity (1 / s) for potting formulation of the inventive example was 8900 cps and at high shear rate viscosity (100 / s) was measured at 3600 cps. A high degree of thixotropy or “shear thinning” can be observed from these values. The high viscosity w 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 high shear rate, resulting in low viscosity and high flowability. When the two components were mixed, the working time, defined as the time to reach 5000 cps

[0074] 15 viscosity after mixing, was determined to be 2 minutes for the inventive example. The working time allows the liquid formulation to remain flowable and self-leveling to form a void-free potting. 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. In addition, the potting formulation gels around 5 min after mixing the two parts. The quick gel time renders the battery pack adaptable to post-processing techniques.

[0075] Table 4: Cured Potting Formulation Properties

[0076] 5

[0077] Properties of the cured potting formulation is shown in Table 4. The cured potting formulation shows a high flame resistance in the UL94 test (VO rating). In addition, it has w a very high thermal resistivity as indicated by the low thermal conductivity value. The low thermal conductivity in combination with high flame resistance makes these material suitable as thermal barrier to prevent propagation of thermal runway reactions in lithium- ion battery pack. The low density (0.39 g / cc) helps significant weight saving for the battery pack. In addition, the high compression modulus (410 Mpa) and tensile modulus (432 Mpa) enables the potting formulation to be a structural component of the battery pack and serves to mechanically stabilize the battery pack from shock and vibration.

Claims

CLAIMSWhat is claimed is:

1. A two-component potting formulation, comprising: a) an isocyanate component comprising an isocyanate; b) a polyol component comprising: b1 ) at least one polyol; b2) 1 % to 20% of a low-density filler having a density of 1 g / cm3or less; b3) 0.1 % to 20% of a rheology modifier; b4) at least one crosslinker; b5) 0.5% to 5% of a foam stabilizer; b6) 0.1 % to 5% of a nucleating agent; and b7) 0.01 % to 2% of a blowing agent; wherein all % are weight percentages based on the total weight of the potting formulation.

2. The potting formulation of claim 1 , wherein the polyol component further comprises: b8) 0.005% to 4% of a catalyst; and b9) 5% to 30% of a flame retardant; wherein all % are weight percentages based on the total weight of the potting formulation.

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 , wherein the foam stabilizer is a modified urea- based stabilizer.

5. The potting formulation of claim 3 comprising no less than 3.5%, based on the total weight of the potting formulation, of the low-density fillers.

6. The potting formulation of claim 4 comprising no less than 1 %, based on the total weight of the potting formulation, of the foam stabilizer.

7. The potting formulation according to any one of the preceding claims wherein the polyol component comprises two different polyols.

8. The potting formulation according to any one of the preceding claims wherein the polyol component comprises three different cross-linkers.

9. The potting formulation according to any one of the preceding claims wherein the polyol component comprises triethanolamine, glycerol and pentaerythritol as a combination of cross-linkers.

10. The potting formulation according to any one of the preceding claims wherein the nucleating agent is one or more selected from talc, silica, alumina trihydrate, zinc oxide, zinc stearate, calcium carbonate, titanium dioxide, graphite, microcrystalline, and nanocellulose.11 . The potting formulation according to Claim 2 wherein the catalyst is a tertiary amine based delayed action catalyst.

12. A two-component potting formulation, comprising: a. an isocyanate component comprising an isocyanate; b. a polyol component consisting of: i. a polyol; ii. no less than 3.5% of a low-density filler having a density of 1 g / cm3or less; iii. 0.5% to 5% of a rheology modifier; iv. at least one crosslinker; v. no less than 1 % of a foam stabilizer; vi. 0.1 % to 1 % of a nucleating agent; andvii. 0.01 % to 2% of a blowing agent; viii. 0.005% to 4% of a catalyst; and ix) 15% to 20% of a flame retardant; wherein all % are weight percentages based on the total weight of the potting formulation.

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