Highly mica-filled polydimethylsiloxane

Abstract

The present invention relates to a composition comprising: a) a polyorganosiloxane functionalized with at least two Si-H groups; b) a polyorganosiloxane functionalized with at least two vinyl groups; c) micron-sized mica particles; and d) a hydrosilylation catalyst, wherein the concentration of the mica particles ranges from 90 to 200 parts by weight per 100 parts by weight of the polyorganosiloxane a) and b). The composition is useful as a coating material that can be applied to a battery pack casing or cover to protect against the consequences of thermal runaway.

Description

[Technical Field]

[0001] The present invention relates to compositions comprising polydimethylsiloxane and a relatively high concentration of mica, which are useful as coatings for metal or plastic composites in lithium ion battery packs.

[0002] Electric vehicles using lithium-ion batteries encased in aluminum or plastic composite housings are rapidly expanding their market share. A widespread problem associated with battery packs is thermal runaway, which can cause temperatures to rise above 1000°C, high enough to melt the aluminum or plastic, leading to the spread of fire and the release of molten particles. While steel can be used instead of aluminum, its high density negatively impacts the range and performance of electric vehicles. Therefore, it is desirable to find a coating material that can be applied to battery pack casings or covers to protect against the consequences of thermal runaway and to insulate vehicle occupants. Summary of the Invention

[0003] The present invention addresses a need in the art by providing, in one aspect, a composition comprising: a) a polysiloxane functionalized with at least two Si—H groups and having a degree of polymerization ranging from 2 to 400; b) a polyorganosiloxane functionalized with at least two vinyl groups and having a degree of polymerization up to 1000; c) micron-sized mica particles; and d) a hydrosilylation catalyst, wherein the concentration of the mica particles ranges from 90 to 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b), and the molar ratio of Si—H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) ranges from 0.8:1 to 5:1. The composition of the present invention is useful as a thermal insulating material for battery covers. DETAILED DESCRIPTION OF THE INVENTION

[0004] The present invention is a composition comprising: a) a polysiloxane functionalized with at least two Si—H groups and having a degree of polymerization ranging from 2 to 400; b) a polyorganosiloxane functionalized with at least two vinyl groups and having a degree of polymerization up to 1000; c) micron-sized mica particles; and d) a hydrosilylation catalyst, wherein the concentration of the mica particles ranges from 90 to 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b), and the molar to molar ratio of Si—H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) ranges from 0.8:1 to 5:1.

[0005] The polyorganosiloxane functionalized with at least two Si—H groups (polyorganosiloxane (a)) is preferably represented by formula I:

[0006] [ka] wherein the sum of m+n ranges from 2 or 3 to 400, or 200, or 100, or 50, and n is from 2 or 3 to preferably 100, or 50, or 20.

[0007] In one embodiment, the polyorganosiloxane functionalized with at least two vinyl groups (polyorganosiloxane (b)) is a Q-branched polyorganosiloxane as shown in Formula II:

[0008] [ka] wherein each R is represented by fragment IIa:

[0009] [ka] wherein each q ranges from 0 to 300 or 250, and each R 1 is independently C1-C6 alkyl, and each R 2is R 1 or a C1-C6 alkenyl group, provided that R 2 At least three of the groups are C1-C6 alkenyl groups. 1 is methyl and R 2 At least three of the groups are vinyl groups. Preferably, each R is represented by fragment IIb.

[0010] [ka]

[0011] An example of a Q-branched polyorganosiloxane is tetrakis(vinyldimethylsiloxy)silane (fragment IIb, where q=0), commercially available from Gelest Inc. Q-branched polysiloxanes with q>0 can be prepared by the acid-catalyzed equilibration reaction of tetrakis(vinyldimethylsiloxy)silane with octamethylcyclotetrasiloxane at elevated temperatures, followed by a neutralization step. The chain length (q) can be controlled by adjusting the relative amount of octamethylcyclotetrasiloxane.

[0012] In another embodiment, polyorganosiloxane (b) is a linear polyorganosiloxane having two terminal vinyl groups, as shown in Formula III:

[0013] [ka] wherein p ranges from 2, or 10, or 40, or 50 to 1000, or 500, or 250, or 150.

[0014] In yet another embodiment, polyorganosiloxane (b) is a combination of a polyorganosiloxane of Formula II and a polyorganosiloxane of Formula III, wherein the weight to weight ratio of the polyorganosiloxane of Formula II to the polyorganosiloxane of Formula III preferably ranges from 60:40 to 95:5.

[0015] Polyorganosiloxane (b) may further comprise a polyorganosiloxane resin functionalized with one or more ethylenically unsaturated groups, as shown in Formula IV and Formula V:

[0016] [ka] where R° is methyl, ethyl, or phenyl, and the dashed lines represent points of attachment to other groups.

[0017] The mole to mole ratio of Si—H groups of polyorganosiloxane (a) to vinyl groups of polyorganosiloxane (b) preferably ranges from 0.8:1 or 0.9:1 to 5:1, or 4:1, or 3:1, or 2:1, or 1.5:1.

[0018] Micron-sized mica particles are muscovite or phlogopite particles present in a concentration ranging from 90 or 100 to 200, or 180, or 160 pbw per 100 parts by weight (pbw) of polyorganosiloxane (a) and (b). As used herein, "micron-sized" refers to particles having a D in the range of 1 μm to 100 μm as measured by laser diffraction. 50 This refers to mica particles having particles. Surprisingly, curable polyorganosiloxane mixtures containing excessively high concentrations of mica particles form crack-free ceramicized coatings under pyrolysis conditions. Ceramization advantageously reduces the thermal conductivity of the coating, which is particularly useful in battery pack design to prevent burn-through of the battery pack substrate due to heat, fire, and molten particles that can be released with high energy during thermal runaway events. When batteries are used in electric vehicles, ceramicization can reduce the exposure of vehicle occupants to these hazards.

[0019] The compositions may exhibit even greater resistance to thermal degradation as measured by the 3-point break test (described below) by further including one or more auxiliary inorganic fillers or hydrates thereof, such as aluminum trihydroxide (i.e., aluminum trihydrate or ATH), hydromagnesite, aluminum oxide, epsomite, nesquehonite, boehmite, huntite, magnesium hydroxide, magnesium oxide, cesium oxide, iron oxide, titanium oxide, zinc oxide, calcium carbonate, boron nitride, boron oxide, kaolin clay, crushed quartz, and crushed glass frit.

[0020] Additionally, wollastonite fibers, potassium titanate fibers, and glass fibers can be used as auxiliary fillers to improve the mechanical strength of the ceramized coating, and hollow glass beads, hollow ceramics, and expanded perlite can be used to improve the thermal insulation performance of the ceramized coating. Without being bound by theory, it is believed that one or more auxiliary fillers promote the ceramization reaction, thereby improving the mechanical strength or thermal insulation properties of the composition after pyrolysis.

[0021] When used, the one or more auxiliary fillers are present in a concentration such that the total concentration of mica and auxiliary fillers does not exceed 200 pbw per 100 pbw of polyorganosiloxanes (a) and (b). Thus, in additional embodiments, the concentration of mica ranges from 100 to 180 pbw or 150 pbw, and the concentration of one or more auxiliary fillers ranges from 5 to 50 pbw, per 100 pbw of polyorganosiloxanes (a) and (b).

[0022] The hydrosilylation catalyst is preferably a platinum-based catalyst used in catalytic amounts, typically in the range of 0.5 ppm to 200 ppm Pt based on the weight of the composition. The catalyst may be unsupported or disposed on a solid support (e.g., carbon, silica, or alumina). The catalyst may be microencapsulated in a thermoplastic resin to enhance the storage stability of the curable composition. The microencapsulated catalyst, which may be prepared as described in U.S. Pat. No. 4,766,176 or U.S. Pat. No. 5,017,654, may be heated to near the melting or softening point of the resin in which the catalyst is microencapsulated, thereby exposing the hydrosilylation catalyst to the polyorganosiloxane components a) and b). Examples of suitable platinum-based catalysts include chloroplatinic acid and SYL-OFF™ 4000 catalyst, a commercially available organoplatinum complex dispersed in a polysiloxane.

[0023] The viscosity of the formulation is preferably less than 300,000 cP, more preferably less than 200,000 cP, more preferably less than 100,000 cP, and most preferably less than 50,000 cP. The composition may optionally contain silicone polyether and silane filler treating agents to further reduce the viscosity of the composition, as needed, and hydrosilylation inhibitors to adjust pot life. The composition may also optionally contain an adhesion promoter.

[0024] The compositions can be prepared in one- or two-part formulations. In two-part formulations, the components can be mixed in a static or dynamic mixer before coating. Coating processes include spray coating (e.g., flat-stream nozzle spray), extrusion, or drawdown processes. After application of the coating, samples can be cured for times generally ranging from 10 minutes to 8 hours, typically at temperatures ranging from 20°C to 175°C. One-part formulations typically use a microencapsulated catalyst that is exposed to the reactants upon heating. The compositions can also be molded into desired shapes and cured to adhere to substrates, including metal and plastic composites. The thickness of the composition coating generally ranges from 0.5 mm to 10 mm.

[0025] In another aspect, the invention is an article comprising a battery encased in a metal or plastic composite housing coated with the composition of the invention. [Example]

[0026] In the following examples, all ingredients were mixed using a FlackTek Speed ​​Mixer. Q-branched polymers A, B, and C are represented by formula II, where each R group is, on average, represented by fragment IIb:

[0027] [ka]

[0028] For Q-branched polymer A, n=124 (1.1 wt% vinyl groups), for Q-branched polymer B, n=0 (23.3 wt% vinyl groups), and for Q-branched polymer C, n=220 (0.6 wt% vinyl groups). Inhibitor A is a blend of ethynylcyclohexanol (0.1 pbw) and polyorganosiloxane (b) of formula III (99.9 pbw) in which p=158.

[0029] Viscosity measurements were performed on inventive example formulations prepared separately without catalyst or inhibitor by mixing all other ingredients together at 3000 rpm for 30 seconds. Viscosity versus shear rate sweeps were performed using an Anton-Paar MCR 301 rheometer using a 25 mm parallel plate cell. -1 The viscosity at this point was recorded.

[0030] Comparative Example 1 - Preparation of a two-part composition containing mica filler The first component (Part A) was prepared by adding Q-branched Polymer A (49.67 pbw) and SYL-OFF™ 4000 catalyst (0.33 pbw) to a mixer and mixing at 2000 rpm for 30 seconds. Imersy WG-325 mica (20 pbw) was then added to the mixture and mixing continued at 3000 rpm for an additional 30 seconds.

[0031] Q-branched polymer A (41.12 pbw), formula MD 3.2 D H 5.8 The second component (Part B) was prepared by adding M polyorganosiloxane (a) (6.44 pbw) and Inhibitor A (2.44 pbw) to a mixer and mixing for 30 seconds at 2000 rpm. Imersy WG-325 mica (20 pbw) was then added to the mixer and mixing continued for an additional 30 seconds at 3000 rpm.

[0032] Parts A and B were combined in a 1:1 w / w ratio and mixed at 2000 rpm for 30 seconds. The blend was then placed into a 2 mm thick Teflon-coated mold and cured at 125°C for 1 hour. Disks or ½" x 4" rectangles were punched from the cured molded samples, and the samples were pyrolyzed at 1000°C using a Fisher Scientific Isotemp programmable 750 series furnace as follows: With the fan on, the temperature was increased at a rate of 5°C / min to 450°C and held for 19 hours, then increased at a rate of 5°C / min to 500°C and held for 2 hours. The fan was then turned off, and the temperature was increased at a rate of 1°C / min to 1050°C and held for 2 hours. The fan and heat were then turned off, and the samples were cooled to 25°C. Samples that showed cracks or did not develop a solid structure were excluded from post-pyrolysis thermal conductivity or 3-point break testing. Thermal conductivity (TC) was measured before and after pyrolysis using a HotDisk Thermal Constants Analyzer with a 50 mW pulse for 10 seconds. Three-point break tests after pyrolysis were performed using a TA Instruments RSA-G2 Solids Analyzer (Linear Rheometer) equipped with a 25 mm gap stage and a 13 mm single-contact wedge attachment. A 1 / 2" x 4" sample was placed on the stage, and the wedge was lowered at 0.1 mm / s while the force was measured. The force and cross-sectional area at break were used to calculate the three-point break strength in MPa.

[0033] Comparative Examples 2 and 3 and Examples 1-4 were prepared essentially as described in Example 1, except for the different filler concentrations and filler types as shown in Table 1. Mica pbw refers to the pbw of Imersy WG-325 mica per 100 pbw of polyorganosiloxanes (a) and (b), and clay pbw refers to the pbw of Glomax LL calcined kaolin clay per 100 pbw of polyorganosiloxanes (a) and (b). SiH:Vi refers to the mole-to-mole ratio of SiH groups from polyorganosiloxane (a) to vinyl groups in polyorganosiloxane (b). Viscosity is in centipoise (cP), with a viscosity of less than 300,000 cP considered acceptable. TC o refers to the thermal conductivity of the sample before pyrolysis, and TC f refers to the thermal conductivity of the sample after pyrolysis.

[0034] [Table 1] a These samples disintegrated during pyrolysis and could not be accurately tested for three-point break.

[0035] The data show that high concentrations of mica were effective in achieving samples that did not crack under rigorous pyrolysis conditions, and that acceptable viscosities and thermal conductivities were achieved in the samples of the present invention. Additionally, the cured compositions of the present invention exhibit a surprising and advantageous reduction in thermal conductivity, which further promotes desired thermal insulation.

[0036] Table 2 shows the effect of different vinyl-functionalized polymers on viscosity, thermal conductivity, and crack resistance after sample pyrolysis. The samples were prepared in the same manner as in Example 2, except for the different vinyl-functionalized polymers (vinyl polymers). QB refers to Q-branched polymer B, QC refers to Q-branched polymer C, and linear refers to the linear polyorganosiloxane of Formula III. Vinyl polymer DP refers to the degree of polymerization of the vinyl polymer (n in Formula IIb and p in Formula III).

[0037] [Table 2]

[0038] The data show that all samples passed the thermal degradation test, and that the samples prepared using the Q-branched vinyl-functionalized polymer exhibited particularly desirable viscosity and TC. Example 5 showed a significant increase in the 3-point break test, indicating higher mechanical strength of the ceramized material and greater protection against thermal runaway.

[0039] The effect of using mica and auxiliary fillers on viscosity, thermal conductivity, and crack resistance after sample pyrolysis is shown in Table 3. The experiment was performed as described in Comparative Example 1, except that auxiliary fillers were added in addition to mica in the amounts shown in Table 3. ATHpbw refers to parts by weight of Micral 855 aluminum trihydrate per 100 parts of polyorganosiloxanes (a) and (b), HCMpbw refers to parts by weight of Extendospheres HA hollow ceramic microspheres per 100 parts of polyorganosiloxanes (a) and (b), and wollastonitepbw refers to parts by weight of Nyad G wollastonite per 100 parts of polyorganosiloxanes (a) and (b).

[0040] [Table 3]

[0041] The data show that the use of auxiliary fillers has somewhat lower viscosity and similar or lower thermal conductivity compared to samples containing only mica. Example 10 in particular exhibited significant mechanical strength.

Claims

1. 1. A composition comprising: a) a polysiloxane functionalized with at least two Si—H groups and having a degree of polymerization ranging from 2 to 400; b) a polyorganosiloxane functionalized with at least two vinyl groups and having a degree of polymerization up to 1000; c) micron-sized mica particles; and d) a hydrosilylation catalyst, wherein the concentration of the mica particles ranges from 90 to 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b), and the molar to molar ratio of Si—H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) ranges from 0.8:1 to 5:

1.

2. The polysiloxane functionalized with at least two Si—H groups is a polyorganosiloxane of Formula I: 【Chemistry 1】 wherein the sum of m+n ranges from 2 to 400, and n is from 2 to 100; The polyorganosiloxane functionalized with at least two vinyl groups is a polyorganosiloxane of Formula II: 【Chemistry 2】 wherein each R is represented by fragment IIa: 【Transformation 3】 wherein each q ranges from 0 to 300, and each R １ is independently C １ ~C ６ alkyl, and each R ２ is R １ or C １ ~C ６ alkenyl group, provided that R ２ At least three of the groups are C １ ~C ６ is an alkenyl group, The composition of claim 1 , wherein the hydrosilylation catalyst is a platinum-based catalyst.

3. Each R is represented by fragment IIb: 【Chemistry 4】 3. The composition of claim 2, wherein the sum of m+n ranges from 3 to 200, n ranges from 3 to 100, and the molar to molar ratio of Si—H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) ranges from 0.9:1 to 3:

1.

4. The polysiloxane functionalized with at least two Si—H groups is a polyorganosiloxane of Formula I: 【Transformation 5】 wherein the sum of m+n ranges from 2 to 400, and n is from 2 to 100. The polyorganosiloxane functionalized with at least two vinyl groups is a linear polyorganosiloxane of Formula III: 【Transformation 6】 wherein p ranges from 2 to 1000. The composition of claim 1 , wherein the hydrosilylation catalyst is a platinum-based catalyst.

5. The polysiloxane functionalized with at least two Si—H groups is a polyorganosiloxane of Formula I: 【Transformation 7】 wherein the sum of m+n ranges from 2 to 400, and n is from 2 to 100, said polyorganosiloxane functionalized with at least two vinyl groups is a polyorganosiloxane of Formula II: 【Transformation 8】 wherein each R is represented by fragment IIb: 【Chemistry 9】 In combination with a linear polyorganosiloxane of formula III: 【Chemistry 10】 wherein p ranges from 2 to 1000. The composition of claim 1 , wherein the hydrosilylation catalyst is a platinum-based catalyst.

6. 6. The composition of claim 5, wherein the weight to weight ratio of the polyorganosiloxane of Formula II to the polyorganosiloxane of Formula III ranges from 60:40 to 95:5, and the molar to molar ratio of Si—H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) ranges from 0.9:1 to 2:

1.

7. 10. The composition of claim 1, further comprising one or more auxiliary inorganic fillers, wherein the total concentration of mica and said one or more auxiliary fillers does not exceed 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b), and said hydrosilylation catalyst is a platinum-based catalyst.

8. and one or more auxiliary inorganic fillers selected from the group consisting of aluminum trihydrate, hydromagnesite, aluminum oxide, magnesium oxide, cerium oxide, iron oxide, titanium oxide, zinc oxide, calcium carbonate, boron nitride, boron oxide, kaolin clay, ground quartz, ground glass frit, wollastonite, potassium titanate fiber, glass fiber, hollow glass beads, hollow ceramic, and expanded perlite, wherein the concentration of the mica particles is 4. The composition of claim 3, wherein the total concentration of mica and the one or more auxiliary fillers is in the range of 5 to 50 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b), with the proviso that the total concentration of mica and the one or more auxiliary fillers does not exceed 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b), and the molar to molar ratio of Si—H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) is in the range of 0.9:1 to 2:

1.

9. 9. The composition of claim 8, wherein the one or more auxiliary inorganic fillers are selected from the group consisting of aluminum trihydrate, hollow ceramic microspheres, and wollastonite.

10. An article comprising a battery encased in a metal or plastic composite material coated with the composition of any one of claims 1 to 9.

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