Polyurethane composition with long pot-life and fast curing

Abstract

A polyol component for producing a polyurethane polymer comprising at least one polyol, a particulate filler, a tin catalyst for the formation of urethane bonds and a blocking agent for the catalyst. The blocking agent has the general formula HS-X- Si(R1)(R2)(R3) and the particulate filler has =O and / or -OH groups on its surface, wherein X is a linking group having at least one carbon atom and R1, R2 and R3 are, independent of each other, alkyl, aryl, alkoxy or aryloxy groups. At least one of R1, R2 and R3 is an alkoxy or aryloxy group. The particulate filler is present in an amount of 75 weight-% to 99 weight-%, based on the total weight of the polyol component. A reaction mixture of the polyol component and a polyisocyanate has a long pot- life, followed by a rapid increase in viscosity. The polymer can be used as a thermal interface material for electric and electronic devices.

Description

[0001] POLYURETHANE COMPOSITION WITH LONG POT-LIFE AND FAST CURING

[0002] The invention relates to a polyol component for producing a polyurethane polymer comprising at least one polyol, a particulate filler, a tin catalyst for the formation of urethane bonds and a blocking agent for the catalyst. The polymer can be used as a thermal interface material (TIM) for electric and electronic devices.

[0003] In order to improve the development of electronic products with multi-functionality, high-speed and high-power, a TIM plays a key role in thermal management design. How to increase thermal conductivity efficiency between elements and heat sinks, the characteristics of thermal conductivity and thermal resistance of the thermal interface material play an important role.

[0004] In battery powered vehicles, battery cells or modules are thermally connected to cooling units by thermal interface materials. Such TIM are typically formed of polymeric materials filled with thermally conductive fillers. To achieve a thermal conductivity of 2 W / m K or higher, fillers with thermal conductivity of 100 W / m K or higher, such as boron nitrides or aluminum powders, may be used. However, such fillers are expensive and abrasive. A cheaper and non-abrasive alternative is aluminum trihydroxide (ATH). Due to its lower thermal conductivity of about 10 W / m K, high loadings of ATH are needed. And for the ease of application, liquid based polymeric binders (e.g., polyols) are typically used.

[0005] For example, US 2022 / 209324 A1 discloses a thermal interface material composition and the use thereof in battery powered vehicles. The composition comprises a) a urethane based binder component, which comprises at least one non-reactive polyurethane prepolymer, and b) about 80-95 wt % of aluminum trihydroxide, with the total weight of the composition totaling to 100 wt %. The at least one non-reactive polyurethane prepolymer, i) is a reaction product of at least one polyisocyanate and at least one aliphatic monol, ii) is substantially free of residual isocyanate groups; and iii) has an average molecular weight of 2000-50000g / mol. If polyol based material is present in the composition, the content level of the polyol based material is less than the total content level of the urethane based binder component.

[0006] Two-component polyurethane compositions based on polyols and polyisocyanates have already been used for some time. Two-component polyurethane compositions have the advantage over one-component compositions that they cure rapidly after mixing and can therefore absorb and transmit higher forces after just a short time.

[0007] In order to achieve the desired mechanical properties and, especially, particularly rapid curing, it is advantageous if such compositions contain high proportions of isocyanates that are present in one of the two components in the form of free or polymer-bound polyisocyanates and that, after mixing with the other component, which contains polyols, cure to form a polymeric network. A high content of isocyanates does, however, lead to problems. Particularly with the use of crosslinking catalysts such two-component systems become almost uncontrollably fast and pot-lives much too short for use. In certain applications the pot life also needs to be long enough to allow the reaction mixture to flow into all cavities of a component to be covered. In other applications a long pot-life is desired for long and complex adhesive pattern dispensing to allow for enough time for parts to be joined, such as in battery modules.

[0008] US 4,788,083 discloses an activatable catalyst which is effective for the reaction of a hydroxyl compound and an isocyanate. Preferably, the catalyst is utilized in the cure of a coating composition of a polyol and a polyisocyanate. The activatable catalyst is activated in the presence of an amine activator or heat and comprises the reaction product of a metal catalyst selected from a tin catalyst, a bismuth catalyst, and mixtures thereof; and a molar excess of a blocking agent. The blocking agent is selected from a mercapto compound, a polyphenol characterized by being reactable with an isocyanate group in the presence of a tertiary amine activator, and mixtures thereof. A single polyol resin may bear both the complexing functionalityand the activatable catalyst. Advantageously, the polyol and polyisocyanate both are aliphatic.

[0009] EP 0454219 A1 relates to a catalyzed reaction mixture for producing a polyurethane, which catalyzed reaction mixture comprises (A) a polyol component, (B) a polyisocyanate component and (C) a complexed polyurethane catalyst from (C1) a tin and / or bismuth polyurethane catalyst and (C2) a molar excess of a blocking agent for the polyurethane catalyst, wherein the polyol component comprises an acid value of about 5 or less.

[0010] US 5,587,448 concerns a reaction system for producing a polyurethane having an isocyanate index value of at least 100, and a catalyzed reaction mixture thereof, having a gel time between 5 and 60 minutes. The reaction system, in one aspect, involves a mixture of first and second parts that are located in separate containers, respectively, which are effective to prevent contact between said first and second parts thereof until coating or sealing application is desired. This two-part reaction system includes:(a) a first part comprising a polyisocyanate component; b) a second part comprising: (i) a polyol component; (ii) a polyurethane catalyst comprising a bismuth / zinc polyurethane catalyst; and (iii) a molar excess of a blocking agent for the polyurethane catalyst, where the blocking agent is a mercaptan compound. This publication also concerns a method of forming a polyurethane sealant on a surface using the two-part reaction system and catalyzed reaction mixture.

[0011] JP H01213382 A is directed towards a two-pack type polyurethane based adhesive with low viscosity change for a prescribed time after mixing two liquids and rapidly causing gelation thereafter, by mixing a polyol containing an organotin compound and polyfunctional mercaptan compound with a prepolymer. This publication suggests to mix (A) a prepolymer having >=2 organic isocyanate groups at the terminals with (B) a polyfunctional polyol having >=2 hydroxyl groups. The component (B) contains an organotin compound and a polyfunctional mercaptan compound.WO 2019 / 002538 A1 relates to a polyurethane composition consisting of a first and a second component, wherein the first component is a polyol with an OH functionality in the range from 1.5 to 4 and a mean molecular weight in the range from 250 to 15,000 g / mol, a diol with two hydroxyl groups which are linked via a C2 to CO carbon chain, and a compound that comprises at least one thiol group. One of the two components also additionally contains at least one metal catalyst for the reaction of hydroxyl groups and isocyanate groups which can form thio complexes, and the second component contains enough polyisocyanate that at least 5 % by weight of isocyanate groups, in relation to the total polyurethane composition, are contained, and the molar ratio of all thiol groups of the mentioned compound to all metal atoms of the metal catalyst is between 1:1 and 250:1. A composition of this kind is reported to allow an arbitrary adjustment of the open time within certain limits and reported to make it possible to achieve long open times with subsequent very quick curing of the composition. The composition according to the publication is reported to be particularly suitable as a structural adhesive for the bonding of two substrates or as a matrix in composite materials.

[0012] WO 2020 / 127485 A1 discloses a polyurethane composition consisting of a first and a second component, the first component containing a polyol with an OH functionality in the range of 1.5 to 4 and a mean molecular weight in the range of 250 to 15,000 g / mol, a diol with two hydroxyl groups which are linked via a C2 to C9 carbon chain, and a compound which has at least one thiol group. One of the two components also contains at least one metal catalyst, for the reaction of hydroxyl groups and isocyanate groups which can form thio complexes, and the molar ratio of all the NCO groups of the polyisocyanates to all the OH groups of the polyols is 0.9 : 1 - 1.2 : 1, and the polyurethane composition is flowable, preferably self-levelling, directly after mixing of the components at 23 °C and has a viscosity of < 5000 Pa-s at a shear rate of 0.01 s-1 and < 500 Pa-s at a shear rate of 1 s-1 and < 50 Pa-s at a shear rate of 10 s-1. Furthermore, the molar ratio of all the thiol groups of the said compound to all the metal atoms of the metal catalyst is between 1:1 and 250:1. A composition of this type is reported to allow the open time to beset as desired within certain limits and reported to make it possible to achieve long open times with subsequent very quick curing of the composition. The composition according to the publication is reported to be particularly suitable as a casting compound, for example for repairing tracks.

[0013] US 2023 / 047357 A1 concerns a polyurethane composition which includes first and second components, wherein the first component contains between 30% and 99% by weight of a polyol mixture including 100 parts by weight of at least one hydrophobic polyol, 10 to 75 parts by weight of at least one hydrophilic polyol, 0 to 25 parts by weight of at least one diol having two hydroxyl groups linked via a C2 to C9 carbon chain; and also at least one compound having at least one thiol group; and the second component includes at least one polyisocyanate, wherein one of the two components additionally includes at least one metal catalyst for the reaction of hydroxyl groups and isocyanate groups that is able to form thio complexes and the molar ratio of all the thiol groups in the at least one compound to all metal atoms in the at least one metal catalyst is between 1:1 and 250:1.

[0014] US 2023 / 257506 A1 discloses a polyurethane composition which includes a first component wherein a polyol mixture containing at least one polyol P1 having an average molar mass of 800-30000 g / mol, the polyol being a polyhydroxy-functional fat and / or oil, or a chemical modification of natural fats and / or oils; preferably at least one polyol selected from the group of polyester polyols and polyether polyols; and a second component wherein at least one aliphatic polyisocyanate I, and at least one filler. The composition includes a tin catalyst for the reaction of hydroxyl and isocyanate groups, forming a thio complexes, and at least one compound including at least one thiol group, wherein the molar ratio of all thiol groups of all metal atoms of the at least one tin catalyst K (T / K) lies between 2.2:1 and 40:1, and the molar ratio of all NCO groups of the at least one tin catalyst K (NCO / K) lies between 50 and 1500.

[0015] US 2023 / 406993 A1 relates to a polyol composition consisting of a first component and a second component, wherein the first component contains a polyol having hadOH functionality in the range from 1.5 to 4 and an average molecular weight in the range from 250 to 15000 g / mol, a diol having at least two hydroxyl groups joined via a C2 to C9 carbon chain, and a compound having at least one thiol group. In addition, one of the two components additionally comprises at least one metal catalyst for the reaction of hydroxyl groups and isocyanate groups which is capable of forming thio complexes, and where the molar ratio of all NCO groups of the polyisocyanates I to all OH groups of the polyols=0.9:1-1.4:1, especially 1.05:1-1.3:1, and where the composition contains, in at least one of the two components, between 3% and 25% by weight, based on the overall composition, of at least one type of microscopic hollow beads, wherein the microscopic hollow beads have a compressive strength, measured to ASTM D3102-72, of at least 10 MPa and a density of at least 0.2 kg / L, and wherein the composition contains, in at least one of the two components, between 2.5% and 7.5% by weight, based on the overall composition, of at least one desiccant, wherein the desiccant is an aluminosilicate. Such a composition permits arbitrary adjustment of the open time within particular limits and enables achievement of long open times with subsequent very rapid curing of the composition. The composition of the publication is reported to have excellent strength and hardness, and to be grindable without difficulty. The composition of the invention is reported to be particularly suitable as filling compound, especially for wood.

[0016] WO 2023 / 031304 concerns a three-component polyurethane composition which is suitable as a laminating adhesive, consisting of a first, a second and a third component, the first component containing a polyol having an OH functionality in the range from 1.5 to 4 and an average molecular weight in the range from 250 to 15000 g / mol and a compound having at least one thiol group, the second component containing at least one metal catalyst for the reaction of hydroxyl groups and isocyanate groups, which can form thiol complexes and preferably has a drying agent, and the third component containing at least one polyisocyanate, the molar ratio of all thiol groups of said compound to all metal atoms of the metal catalyst being between 1:1 and 250:1. Such a composition allows the pot life and the opentime to be set as desired within certain limits and makes it possible to achieve long open times with subsequent very quick curing of the composition. The composition according to the publication is reported to be particularly suitable as a laminating adhesive for the production of composite materials and to have an extremely good storage stability and no sensitivity with respect to high relative air humidity during application.

[0017] WO 2023 / 126299 A1 discloses a polyurethane composition comprising a first component A and a second component B, wherein the first component A has a polyol mixture P, containing at least one polyol P1 having an average molecular weight of 800 to 30000 g / mol, and the second component B having at least one aromatic polyisocyanate. The polyurethane composition additionally contains at least one filler, and at least one tin catalyst or a bismuth catalyst for the reaction of hydroxyl groups and isocyanate groups, which can form thio complexes, and at least one compound which has at least one thiol group. The polyurethane compositions are reported to be suitable for the production of floor coatings and to have, independently of the curing conditions, both a long pot life and a short curing time, which both can be adjusted if required.

[0018] WO 2024 / 008717 A1 relates to a polyurethane composition comprising a first component A and a second component B. The first component A comprises a polyol mixture P containing - at least one polyol P1 having an average molecular weight of 800 to 30000 g / mol, the polyol P1 being a polyhydroxy-functional fat and / or a polyhydroxy-functional oil, or a polyol obtained by chemical modification of natural fats and / or natural oils; and - preferably at least one polyol P2 selected from the group consisting of polyester polyols and polyether polyols; and the second component B comprises at least one aliphatic polyisocyanate I. The polyurethane composition contains additionally fillers F, an acid SA with a pKa value of < 4.9, a tin catalyst K and a compound T that comprises at least one thiol group, the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one tin catalyst K (T / K) being between 2.75:1 and 10:1. The polyurethanecomposition is reported to be suitable for roof coatings and irrespective of the curing conditions to have a long pot life and short curing times.

[0019] The invention has the object of providing a polyurethane thermal interface material with improved processing properties. In particular the object is to provide a polyol component loaded with a thermally conductive filler which, after mixing with a polyisocyanate component, has a pot life suitable for efficient production processes and which displays a rapid curing after the open time has expired.

[0020] Accordingly a polyol component for producing a polyurethane polymer comprising at least one polyol, a particulate filler, a tin catalyst for the formation of urethane bonds and a blocking agent for the catalyst is provided wherein the blocking agent has the general formula HS-X-Si(R1)(R2)(R3) and the particulate filler has =0 and / or -OH groups on its surface and wherein X is a linking group having at least one carbon atom and R1, R2and R3are, independent of each other, alkyl, aryl, alkoxy or aryloxy groups and with the proviso that at least one of R1, R2and R3is an alkoxy or aryloxy group. The particulate filler is present in an amount of 75 weight-% to 99 weight-%, based on the total weight of the polyol component.

[0021] The polyol component may comprise a single polyol or two or more polyols. The exact composition of the polyol mixture may be tailored to the specific needs of the application, for example with respect to a low glass transition temperature for the polyurethane polymer. The total amount of polyols in the polyol component may be in a range of 5 weight-% to 20 weight-%, based on the total weight of the polyol component. Preferred are 7 weight-% to 15 weight-% and more preferred 8 weight-% to 13 weight-%.

[0022] Examples for polyols for the invention include polyether polyols, polyester polyols, poly(meth)acrylate polyols, polybutadiene polyols, polycarbonate polyols, and also mixtures of these polyols. All recited polyols may have a number average molecular weight from 250 to 15000 g / mol, preferably from 400 to 10000 g / mol, morepreferably from 1000 to 8000 g / mol and a mean OH functionality in the range of 1.5 to 4, preferably 1.7 to 3.

[0023] Suitable polyether polyols include polyoxyethylene polyols and polyoxypropylene polyols, in particular polyoxyethylene diols, polyoxypropylene diols, polyoxyethylene triols, and polyoxypropylene triols.

[0024] Likewise included among the suitable polyether polyols are so-called ethylene oxide-terminated (EO-endcapped / ethylene oxide-endcapped) polyoxypropylene polyols. The latter are special polyoxypropylene polyoxyethylene polyols that are obtained for example when pure polyoxypropylene polyols, in particular polyoxypropylene diols and triols, after completion of the polypropoxylation reaction, are further alkoxylated with ethylene oxide and thus have primary hydroxyl groups. Preferred in this case are polyoxypropylene polyoxyethylene diols and polyoxypropylene polyoxyethylene triols.

[0025] Also included among the suitable polyols are hydroxyl-terminated polybutadiene polyols, for example those produced by polymerization of 1,3-butadiene and allyl alcohol or by oxidation of polybutadiene and also the hydrogenation products thereof.

[0026] Suitable polyester polyols include in particular polyesters that bear, on average, between two and three hydroxyl groups and are produced by known processes, in particular polycondensation of hydroxycarboxylic acids or polycondensation of aliphatic and / or aromatic polycarboxylic acids with dihydric or polyhydric alcohols, suitable are polyester diols, in particular those produced from adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, dimer fatty acid, phthalic acid, isophthalic acid and terephthalic acid as the dicarboxylic acid or from lactones such as e-caprolactone and from ethylene glycol, diethylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, dimer fatty acid diol, and 1,4-cyclohexanedimethanol as the dihydric alcohol.Suitable polycarbonate polyols include in particular those obtainable by reaction for example of the abovementioned alcohols used to construct the polyester polyols with dialkyl carbonates such as dimethyl carbonate, diaryl carbonates such as diphenyl carbonate, or phosgene. Likewise suitable are polycarbonates obtainable from the copolymerization of CO2 with epoxides such as ethylene oxide and propylene oxide. Polycarbonate diols, in particular amorphous polycarbonate diols, are expressly included.

[0027] Also suitable are polyhydroxy-functional fats and oils, for example natural fats and oils, in particular castor oil, or so-called oleochemical polyols obtained by chemical modification of natural fats and oils, the epoxy polyesters or epoxy polyethers obtained for example by epoxidation of unsaturated oils and subsequent ring opening with carboxylic acids or alcohols respectively, or polyols obtained by hydroformylation and hydrogenation of unsaturated oils. Also suitable are polyols obtained from natural fats and oils by degradation processes such as alcoholysis or ozonolysis and subsequent chemical linking, for example by transesterification or dimerization, of the thus obtained degradation products or derivatives thereof. Suitable degradation products of natural fats and oils are in particular fatty acids and fatty alcohols and also fatty acid esters, in particular the methyl esters (FAME), which can be derivatized to hydroxy fatty acid esters, for example by hydroformylation and hydrogenation.

[0028] It is provided that the particulate filler has =0 and / or -OH groups on its surface. Examples for such materials include talcs, quartz powders, quartz sand, dolomites, wollastonites, kaolins, calcined kaolins, mica (potassium aluminum silicate), molecular sieves, aluminum oxides, aluminum hydroxides, magnesium hydroxide, silicas including finely divided silicas from pyrolysis processes, or hydrates of aluminum, preferably aluminum hydroxide. Preferred are metal oxides such as AI2O3, MgO, SiO2, TiO2 and ZnO, metal hydroxides such as aluminum trihydroxide “ATH” AI(OH)3, Mg(OH)2 and mixtures thereof.Suitable tin catalysts are those that may be used as a crosslinking catalyst in polyurethane chemistry and that can at the same time form thio complexes with thiols in the presence thereof. Examples include dibutyltin dilaurate, dimethyltin dineodecanoate, dibutyltin diacetate or a mixture of at least two of the aforementioned compounds. In one embodiment the polyol component is free from non-tin based catalysts for the formation of urethane bonds. In an alternative embodiment, the polyol component further comprises a bismuth catalyst for the formation of urethane bonds such as bismuth acetate, oleate, octoate or neodecanoate, bismuth nitrate, bismuth halides such as the bromide, chloride, or iodide, bismuth sulfide, basic bismuth carboxylates such as bismuthyl neodecanoate, bismuth subgallate or bismuth subsalicylate, bismuth(lll) carboxylates containing 1 to 3 molar equivalents of a 1,3-ketoamide ligand, bismuth(lll) carboxylates containing one molar equivalent of an 8-hydroxyquinoline ligand, and mixtures thereof.

[0029] The blocking agent for the metal catalyst coordinates to the tin catalyst via its thiol group, thereby initially deactivating the catalyst and inhibiting the formation of urethane bonds between the polyol(s) and the polyisocyanate(s) that are added for polyurethane synthesis. As the thiol groups are also reactive towards isocyanate groups they will be slowly consumed until a sufficient amount of catalyst is available to noticeably initiate the urethane formation. The time-dependent viscosity curve of such a reaction has occasionally been referred to as a “hockey stick”.

[0030] In the blocking agent R1, R2and R3are, independent of each other, alkyl, aryl, alkoxy or aryloxy groups. The linking group X can also be an alkyl, aryl, alkoxy or aryloxy group as well. The alkyl radicals can in each case be straight-chain or branched. They have preferably up to five carbon atoms. Cycloalkyl radicals and radicals derived therefrom such as cycloalkyloxy have preferably 3 to 7 carbon atoms. Aryl radicals have preferably 6 to 12 carbon atoms; preferred radicals are phenyl, naphthyl and biphenyl, in particular phenyl. The same applies analogously to radicals derived therefrom such as aryloxy, arylmercapto, aroyl, aralkyl, aralkyloxy and aralkylmercapto. Aralkyl is preferably benzyl.With the at least one alkoxy or aryloxy group bound to the silicon atom the blocking agent is able to undergo further reactions. Without wishing to be bound by theory it is believed that an at least partial reaction with oxygen or hydroxyl groups on the surface of the filler can take place. The inventors have observed that the desired “hockey stick” reactivity profile is far less apparent or even missing if a thiol-based blocking agent without an organooxygroup bound to a silicon atom is used instead.

[0031] The pot-life, defined as the time elapsed between mixing of the polyol and isocyanate components and a doubling of the initial viscosity of the mixture, can be adjusted and, for example, be in a range of 5 to 60 minutes or 5 to 30 minutes.

[0032] The invention has the advantage that a system that cures and hardens with extraordinary rapidity is provided, while at the same time having an adequately long pot life that allows it to be processed in a user-friendly manner. This means, for example, that structural bonding may be carried out on relatively large substrates too, which can be subjected to mechanical stress just a very short time after application of the adhesive. This results, for example, in a significant shortening of throughput times in industrial production. A further advantage the possibility of being able to adjust the pot-life by varying the amount of catalyst and the ratio of catalyst to blocking agent. This is very advantageous particularly in automated applications and can, for example, allow further optimization of throughput times in industrial production, since the pot life can be tailored to the desired use.

[0033] Suitable ranges of molar ratios of thiol groups in the blocking agent to catalyst molecules include 1.5:1 to 100:1, preferably 2:1 to 55:1 and more preferred 2.5:1 to 50:1.

[0034] The polyol component may further comprise additives such as dispersants, defoamers, antioxidants, rheology modifiers, colorants, moisture scavengers and other customary ingredients known in the art.In one embodiment in the general formula for the blocking agent X is -(CH2)n- with n being 1, 2, 3, 4 or 5 and R1, R2and R3are, independent of each other, methoxy or ethoxy groups. Preferred blocking agents are 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane and mixtures thereof.

[0035] In another embodiment the particulate filler is alumina, aluminum hydroxide (ATH) or a mixture of the aforementioned compounds. Besides fire retardancy, ATH has also the advantage of a lower specific weight than standard metal powders, bringing less weight to the battery modules in or other devices in which the polymers according to the invention are used.

[0036] In another embodiment the particulate filler is present in an amount of 80 weight-% to 98 weight-%, based on the total weight of the polyol component. Preferred is an amount of 83 weight-% to 90 weight-%.

[0037] Based on the total weight of the polyol component preferred compositions are, with the proviso that amounts of polyols, fillers and additives add up 100 weight-% or less: polyols 5 weight-% to 20 weight-% (preferably 7 weight-% to 15 weight-%, more preferred 8 weight-% to 13 weight-%), fillers 75 weight-% to 99 weight-% (preferred 80 weight-%to 98 weight-%, more preferred 83 weight-%to 90 weight-%) and additives 1 weight-% to 10 weight-% (preferred 2 weight-% to 7 weight-%, more preferred 2.5 weight-% to 5 weight-%).

[0038] In another embodiment the particulate filler has a median particle size (D50) of 5 pm to 100 (preferred 10 pm to 80 and more preferred 15 pm to 50 pm). The median particle size or diameter of a distribution of particles may be determined, for example, by a Multisizer 3 Coulter Counter (Beckman Coulter, Inc., Fullerton, CA) according to the procedure recommended by the manufacturer. The median particle size D50 is defined as the size wherein 50 cumulative-% of the distribution is smaller than the stated value. This definition also applies overall to a filler which is a mixture of several fillers having different particle size distribution.The overall particle size distribution of the filler may be monomodal, bimodal or polymodal. Polymodal filler compositions may include one or more filler types and having three or more modes characterized by local maxima. Bimodal filler compositions may include a first thermally conductive filler, for example ATH or alumina, having a D50 particle size in the range of 15 pm to 50 pm and a second thermally conductive filler, for example ATH or alumina, having a D50 in the range of 1 pm to 5 pm, wherein the first thermally conductive filler and the second thermally conductive filler are present at a percent by weight of the bimodal filler composition (wt%) in a range of 90 weight-% to 99 weight-% and 1 weight-% to 10 weight-%, respectively. The weight percentages of first and second filler in the overall filler composition add up to 100 weight-%.

[0039] Polymodal filler compositions may include a first thermally conductive filler, for example ATH or alumina, having a D50 particle size in the range of 15 pm to 50 pm, a second thermally conductive filler, for example ATH or alumina, having a D50 in the range of 3 pm to 5 pm and a third thermally conductive filler, for example ATH or alumina, having a D50 in the range of 1.5 pm to 2.5 pm, wherein the first thermally conductive filler, the second thermally conductive filler and the third thermally conductive filler are present at a percent by weight of the bimodal filler composition (wt%) in a range of 60 weight-% to 80 weight-%, 10 weight-% to 30 weight-% and 5 weight-% to 15 weight-%, respectively. The weight percentages of first, second and third filler in the overall filler composition add up to 100 weight-%.

[0040] In another embodiment the polyol component comprises polyol component comprises a polybutadiene polyol, a first polyester polyol, a second polyester polyol, a first polyether polyol, a second polyether polyol, a third polyether polyol or a mixture of at least two of the aforementioned polyols. Examples for these polyols include an OH-terminated polybutadiene polymer having an average functionality between 2 and 3 and an OH number of 30 to 60 mg KOH / g, a polyester polyol having an average functionality between 2 and 3 and an OH number of 70 to 90 mg KOH / g, a difunctional polyester polyol having an OH number of 210 to 240 mg KOH / g, a difunctional PO-polyether polyol having an OH number of 100 to 120 mgKOH / g, a difunctional PO-polyether polyol having an OH number of 250 to 270 mg KOH / g and a difunctional PO-polyether polyol having an OH number of 390 to 410 mg KOH / g, respectively.

[0041] The invention also relates to method of manufacturing a polyurethane polymer comprising the reaction of a polyol component according to the invention with an isocyanate component, the isocyanate component comprising a polyisocyanate.

[0042] Suitable polyisocyanates are in particular monomeric di- or triisocyanates and also oligomers, polymers, and derivatives of monomeric di- or triisocyanates, and any mixtures thereof. Suitable aromatic monomeric di- or triisocyanates are in particular tolylene 2,4- and 2,6-diisocyanate and any mixtures of these isomers (TDI), diphenylmethane 4,4’-, 2,4’-, and 2,2’-diisocyanate and any mixtures of these isomers (MDI), mixtures of MDI and MDI homologs (polymeric MDI or PMDI), 1,3-and 1,4-phenylene diisocyanate, 2,3,5,6-tetramethyl-1,4-diisocyanatobenzene, naphthalene 1,5-diisocyanate (NDI), 3,3’-dimethyl-4,4’-diisocyanatodiphenyl (TODI), dianisidine diisocyanate (DADI), 1,3,5-tris(isocyanatomethyl)benzene, tris(4-isocyanatophenyl)methane, and tris(4-isocyanatophenyl) thiophosphate.

[0043] Suitable aliphatic monomeric di- or triisocyanates are in particular tetramethylene 1 ,4-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene 1 ,6-diisocyanate (HDI), 2,2,4- and 2,4,4-trimethylhexamethylene 1,6-diisocyanate (TMDI), decamethylene 1,10-diisocyanate, dodecamethylene 1,12-diisocyanate, lysine diisocyanate and lysine ester diisocyanate, cyclohexane 1,3- and 1,4-diisocyanate, 1-methyl-2,4- and -2,6-diisocyanatocyclohexane and any mixtures of these isomers (HTDI or H6 TDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (=isophorone diisocyanate or I PDI), perhydrodiphenylmethane 2,4’- and 4,4’-diisocyanate (HMDI or H12 MDI), 1,4-diisocyanato-2,2,6-trimethylcyclohexane (TMCDI), 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, m- and p-xylylene diisocyanate (m- and p-XDI), m- and p-tetramethylxylylene 1,3- and 1,4-diisocyanate (m- and p-TMXDI) and bis(1-isocyanato-1-methylethyl)naphthalene, dimer and trimer fatty acidisocyanates such as 3,6-bis(9-isocyanatononyl)-4,5-di-(1-heptenyl)cyclohexene (dimeryl diisocyanate). Preference among these is given to MDI, TDI, HDI, and IPDI.

[0044] Suitable oligomers, polymers, and derivatives of the recited monomeric di- and triisocyanates are in particular those derived from MDI, TDI, HDI, and IPDI. Particularly suitable among these are commercially available types, in particular HDI biurets such as Desmodur® N 100 and N 3200 (from Covestro), Tolonate® HDB and HDB-LV (from Vencorex), and Duranate® 24A-100 (from Asahi Kasei); HDI isocyanurates such as Desmodur® N 3300, N 3600, and N 3790 BA (all from Covestro), Tolonate® HDT, HDT-LV, and HDT-LV2 (from Vencorex), Duranate® TPA-100 and THA-100 (from Asahi Kasei), and Coronate® HX (from Nippon Polyurethane); HDI uretdiones such as Desmodur® N 3400 (from Covestro); HDI iminooxadiazinediones such as Desmodur® XP 2410 (from Covestro); HDI allophanates such as Desmodur® VP LS2102 (from Covestro); IPDI isocyanurates, for example in solution as Desmodur® Z 4470 (from Covestro) or in solid form as Vestanat® T1890 / 100 (from Evonik); TDI oligomers such as Desmodur® IL (from Covestro); and also mixed isocyanurates based on TDI / HDI, for example as Desmodur® HL (from Covestro). Also particularly suitable are MDI forms that are liquid at room temperature (so-called “modified MDI”), which are mixtures of MDI with MDI derivatives such as, in particular, MDI carbodiimides or MDI uretonimines or MDI urethanes, known by trade names such as Desmodur® CD, Desmodur® PF, Desmodur® PC (all from Covestro) or Isonate® M 143 (from Dow), and mixtures of MDI and MDI homologs (polymeric MDI or PMDI), available under trade names such as Desmodur® VL, Desmodur® VL50, Desmodur® VL R10, Desmodur® VL R20, Desmodur® VH 20 N, and Desmodur® VKS 20F (all from Covestro), Isonate® M 309, Voranate® M 229 and Voranate® M 580 (all from Dow) or Lupranat® M 10 R (from BASF). The abovementioned oligomeric polyisocyanates are in practice typically mixtures of substances having different degrees of oligomerization and / or chemical structures. They preferably have a mean NCO functionality of 2.1 to 4.0.The polyisocyanate preferably contains isocyanurate, iminooxadiazinedione, uretdione, biuret, allophanate, carbodiimide, uretonimine or oxadiazinetrione groups.

[0045] With respect to the NCO index this parameter, including the thiol groups of the blocking agent, is preferably 95 to 115 or 98 to 107. The isocyanate component may further comprise a particulate filler. The filler may be of the same type as in the polyol component or of a different type.

[0046] In one embodiment the polyisocyanate is a biuret, uretdione or isocyanurate of an aliphatic diisocyanate ora mixture of at least two of the aforementioned compounds. PDI (pentamethylene diisocyanate), HDI, IPDI and H12-MDI are preferred diisocyanates in this respect.

[0047] Another aspect of the invention is a kit-of-parts for manufacturing a polyurethane polymer comprising a polyol component according to the invention as a first part and an isocyanate component as the second part, the isocyanate component comprising a polyisocyanate.

[0048] Another aspect of the invention is a polyurethane polymer obtainable by a method according to the invention. Properties of the cured polyurethane polymer may include at least one of: a tensile strength (25 °C, ISO 527-2) of 1.5 MPa to 4 MPa, an elongation at break (25 °C, ISO 527-2) of 10% to 25%, an elastic modulus (25 °C, ISO 527-2) of 40 MPa to 60 MPa, an elongation at break (25 °C, ISO 527-2) of 5% to 15%, a lap shear strength (25 °C after curing for 24 hours at 25 °C, ISO 4587) of 3 MPa or more (preferably 3 MPa to 4 MPa) and a shore A hardness (25 °C, ISO 868) of 80 to 90.

[0049] In one embodiment the polyurethane polymer has a thermal conductivity of 2 W / m.K or more as determined according to ASTM D7984. Preferably the thermal conductivity is 2 W / m.K to 4 W / m.K and more preferred 2.2 W / m.K to 3.5 W / m.K.In another embodiment the polyurethane polymer has a glass transition temperature of -30 °C or lower as determined by thermomechanical analysis at a heating rate of 5 °C / min. Preferred are glass transition temperatures from -65 °C to -30 °C and more preferred from -60 °C to -35 °C. A TMA measurement protocol including the erasing of the thermal history of the sample (nitrogen flow, 0.05 N of applied force) is: 1) from -120 °C to 110 °C at 5 °C / min; 2) from 110 °C to -120 °C at -10 °C / min; 3) isothermal for 10 minutes at -120 °C; 4) from -120 °C to 110 °C at 5 °C / min.

[0050] In another embodiment the polyurethane polymer has a lap shear strength at 25 °C after curing for 30 minutes at 25 °C of 3 MPa or more as determined according to ISO 4587. Preferably the lap shear strength is 3 MPa to 4 MPa or 3.2 MPa to 3.8 MPa and more preferred 3.3 MPa to 3.7 MPa.

[0051] The invention is also directed towards the use of a polyurethane polymer according to the invention as a thermal interface material in contact with an electrical or electronic device. The device may be a battery cell. One or more battery cells may be connected to a cooling unit via the thermal interface material, thereby forming a battery module.

[0052] Another aspect of the invention is a method of modifying an electrical or electronic device comprising contacting the device with a mixture comprising a polyol component according to the invention and an isocyanate component, the isocyanate component comprising a polyisocyanate. Details regarding the isocyanate component have been described above and will not be repeated for the sake of brevity. The device may be a battery cell as described above. The outcome of the method may be an assembly of the device, a heat sink or cooling unit and the polyurethane polymer according to the invention at least partially adhesively joining the device and heat sink / cooling unit.EXAMPLES

[0053] The invention will be described in greater detail by the following examples without wishing to be limited by them. Comparative examples are marked with an asterisk (“*”). Unless otherwise specified, room temperature (“RT”) means 25 °C.

[0054] The amounts of the components in the experiments are given as parts by weight unless stated otherwise. For the examples the polyol mixtures were combined with the catalyst and the blocking agent. This polyol component was then combined with the polyisocyanate to produce a polyurethane polymer.

[0055] Polyol mixture 1 (catalyst- and blocking agent-free):

[0056]

[0057] Polyol mixture 2 (catalyst- and blocking agent-free):

[0058]

[0059] Polyol mixture 3 (catalyst- and blocking agent-free):

[0060]

[0061] Further components:

[0062]

[0063] Examples 1 to 3 investigate the effect of different amounts of the blocking agent in the compositions. FIG. 1 shows the time-dependent viscosity behaviors.

[0064]

[0065] Examples 4 to 7 investigate the aging behavior of polyol components as a function of different blocking agents. FIGs. 2 to 7 show the time-dependent viscosity behaviors.

[0066]

[0067] Polymers made with the same formulation as Ex. 4 were analyzed with respect to their thermal and mechanical properties. The thermal conductivity (ASTM D7984)was 2.4 W / m.K, the glass transition temperature (TMA) ca. -55 °C, the lap shear (ISO 4587) at 25 °C after curing for 30 minutes at 25 °C was 3.4 MPa and after 24 hours at 25 °C was 4.4 MPa.

[0068] Examples 8 to 10 investigate the aging behavior of polyol components as a function of different blocking agents. FIGs. 8 to 13 show the time-dependent viscosity behaviors.

[0069]

[0070] Examples 11 and 12 are contrasted to show the effect of a blocking agent according to the invention. FIG. 14 shows the time-dependent viscosity behaviors.

[0071]

[0072] Polymers made with the same formulation as Ex. 12 were analyzed with respect to their thermal properties. The thermal conductivity (ASTM D7984) was 3.0 W / m.K and the glass transition temperature (TMA) ca. -35 °C.

Claims

Claims1. A polyol component for producing a polyurethane polymer comprising at least one polyol, a particulate filler, a tin catalyst for the formation of urethane bonds and a blocking agent for the catalyst, characterized in that the blocking agent has the general formula HS-X-Si(R1)(R2)(R3) and the particulate filler has =0 and / or -OH groups on its surface, wherein X is a linking group having at least one carbon atom and R1, R2and R3are, independent of each other, alkyl, aryl, alkoxy or aryloxy groups and with the proviso that at least one of R1, R2and R3is an alkoxy or aryloxy group, wherein the particulate filler is present in an amount of 75 weight-% to 99 weight-%, based on the total weight of the polyol component.

2. The polyol component according to claim 1 , wherein in the general formula for the blocking agent X is -(CH2)n- with n being 1, 2, 3, 4 or 5 and R1, R2and R3are, independent of each other, methoxy or ethoxy groups.

3. The polyol component according to claim 1 or 2, wherein the particulate filler is alumina, aluminum hydroxide or a mixture of the aforementioned compounds.

4. The polyol component according to any one of the preceding claims, wherein the particulate filler is present in an amount of 80 weight-% to 98 weight-%, based on the total weight of the polyol component.

5. The polyol component according to any one of the preceding claims, wherein the particulate filler has a median particle size (D50) of 5 pm to 100 pm.

6. The polyol component according to any one of the preceding claims, wherein the polyol component comprises a polybutadiene polyol, a first polyester polyol, a second polyester polyol, a first polyether polyol, a second polyether polyol, a third polyether polyol or a mixture of at least two of the aforementioned polyols.

7. A method of manufacturing a polyurethane polymer comprising the reaction of a polyol component according to any one of claims 1 to 6 with an isocyanate component, the isocyanate component comprising a polyisocyanate.

8. The method according to claim 7, wherein the polyisocyanate is a biuret, uretdione or isocyanurate of an aliphatic diisocyanate or a mixture of at least two of the aforementioned compounds.

9. A kit-of-parts for manufacturing a polyurethane polymer comprising a polyol component according to any one of claims 1 to 6 as a first part and an isocyanate component as the second part, the isocyanate component comprising a polyisocyanate.

10. A polyurethane polymer obtainable by a method according to claim 7 or 8.

11. The polyurethane polymer according to claim 10, having a thermal conductivity of 2 W / m.K or more as determined according to ASTM D7984.

12. The polyurethane polymer according to claim 10 or 11, having a glass transition temperature of -30 °C or lower as determined by thermomechanical analysis at a heating rate of 5 °C / min.

13. The polyurethane polymer according to any one of claims 10 to 12, having a lap shear strength at 25 °C after curing for 30 minutes at 25 °C of 3 MPa or more as determined according to ISO 4587.

14. Use of a polyurethane polymer according to any one of claims 10 to 13 as a thermal interface material in contact with an electrical or electronic device.

15. A method of modifying an electrical or electronic device comprising contacting the device with a mixture comprising a polyol component according to any one of claims 1 to 6 and an isocyanate component, the isocyanate component comprising a polyisocyanate.

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