Polydimethylsiloxane with high mica loading

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 mica particles is in the range of from 90 parts by weight to 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b). The composition according to the invention can be used as a coating material that can be applied to a battery pack housing or cover to prevent the consequences of thermal runaway.

Description

Background Art

[0001] The present invention relates to a composition comprising polydimethylsiloxane and a relatively high concentration of mica. The composition of the present invention is useful as a coating for metal or plastic composite materials in lithium ion batteries.

[0002] The market share of electric vehicles using lithium-ion batteries enclosed in aluminum or plastic composite housings is rapidly growing. A common problem associated with battery packs is thermal runaway, which causes temperatures to rise to over 1000°C—high enough to melt the aluminum or plastic, with the accompanying spread of fire and release of molten particles. While steel can be used instead of aluminum, its higher density adversely affects the range and performance of electric vehicles. Therefore, it is desirable to develop a coating material that can be applied to the battery pack housing or cover to prevent the consequences of thermal runaway and protect the vehicle's occupants. Summary of the Invention

[0003] The present invention addresses this need in the art by, in one aspect, providing a composition comprising a) a polyorganosiloxane 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 of 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 wherein the mole:mole 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 can be used as an insulator for battery covers. DETAILED DESCRIPTION

[0004] The present invention is a composition comprising a) a polyorganosiloxane 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 of up to 1000; c) micron-sized mica particles; and d) a hydrosilylation catalyst; wherein the concentration of the mica particles is in the range of 90 to 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b); and wherein the mole:mole ratio of Si-H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) is in the range of 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]

[0007] wherein the sum of m+n is in the range of 2 or 3 to 400 or to 200 or to 100 or to 50, and wherein n is 2 or 3 to preferably 100 or to 50 or to 20.

[0008] In one embodiment, the polyorganosiloxane functionalized with at least two vinyl groups (polyorganosiloxane (b)) is a Q-branched polyorganosiloxane, as shown in Formula II:

[0009]

[0010] where each R is represented by fragment IIa:

[0011]

[0012] Wherein each q is in the range of 0 to 300 or to 250; each R 1 are independently C1-C6 alkyl; and each R 2 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 a methyl group, and R 2 At least three of the groups are vinyl groups. Preferably, each R is represented by fragment IIb:

[0013]

[0014] 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 an acid-catalyzed equilibrium reaction of tetrakis(vinyldimethylsiloxy)silane with octamethylcyclotetrasiloxane at elevated temperature, followed by a neutralization step. The chain length (q) can be controlled by adjusting the relative amount of octamethylcyclotetrasiloxane.

[0015] In another embodiment, the polyorganosiloxane (b) is a linear polyorganosiloxane having two terminal vinyl groups, as shown in Formula III:

[0016]

[0017] wherein p is in the range of 2 or 10 or 40 or 50 to 1000 or to 500 or to 250 or to 150.

[0018] In yet another embodiment, polyorganosiloxane (b) is a combination of polyorganosiloxanes of formula II and III, wherein the weight / weight ratio of polyorganosiloxane of formula II to polyorganosiloxane of formula III is preferably in the range of 60:40 to 95:5.

[0019] The polyorganosiloxane (b) may also comprise a polyorganosiloxane resin functionalized with one or more ethylenically unsaturated groups, such as those shown in Formulas IV and V:

[0020]

[0021] wherein R° is methyl, ethyl, or phenyl, and the dashed lines indicate the points of attachment to other groups.

[0022] The mole:mole ratio of Si—H groups of polyorganosiloxane (a) to vinyl groups of polyorganosiloxane (b) is preferably in the range of 0.8:1 or 0.9:1 to 5:1 or to 4:1 or to 3:1 or to 2:1 or to 1.5:1.

[0023] The micron-sized mica particles are muscovite or phlogopite particles, which are present in a concentration ranging from 90 parts by weight (pbw) or 100 pbw to 200 pbw or to 180 pbw or to 160 pbw per 100 pbw of polyorganosiloxane (a) and (b). As used herein, "micron-sized" refers to D as measured by laser diffraction. 50 Mica particles ranging in size from 1 μm to 100 μm. Surprisingly, curable polyorganosiloxane mixtures containing very high concentrations of mica particles form crack-free, ceramicized coatings under pyrolysis conditions. Ceramics advantageously reduce the thermal conductivity of the coating, which is particularly useful in battery pack designs to protect the battery pack substrate from burn-through by heat, flames, and molten particles, which can be released with high energy during thermal runaway events. When the batteries are used in electric vehicles, ceramicization can reduce these hazardous exposures to vehicle occupants.

[0024] The compositions can exhibit even greater resistance to pyrolysis, as measured by the 3-point fracture test (described below), wherein further comprise one or more auxiliary inorganic fillers or hydrates thereof, such as aluminum trihydroxide (i.e., aluminum trihydrate or ATH), hydromagnesite, aluminum oxides, epsomite, nesquehonite, boehmite, calcium magnesium carbonate, magnesium hydroxide, magnesium oxide, cerium oxide, iron oxide, titanium oxide, zinc oxide, calcium carbonate, boron nitride, boron oxide, kaolin, ground quartz, and ground glass frit.

[0025] Additionally, wollastonite fibers, potassium titanate fibers, and glass fibers can be used as auxiliary fillers to enhance the mechanical strength of the ceramic coating. Furthermore, hollow glass beads, hollow ceramics, and expanded perlite can be used to improve the thermal insulation properties of the ceramic coating. While not wishing to be bound by theory, it is believed that one or more auxiliary fillers accelerate the ceramicization reaction, thereby enhancing the mechanical strength or thermal insulation properties of the pyrolyzed composition.

[0026] 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 another embodiment, the concentration of mica is in the range of 100 pbw to 180 pbw or to 150 pbw per 100 pbw of polyorganosiloxanes (a) and (b) and the concentration of the one or more auxiliary fillers is in the range of 5 pbw to 50 pbw per 100 pbw of polyorganosiloxanes (a) and (b).

[0027] The hydrosilylation catalyst is preferably a platinum-based catalyst used in a catalytic amount, typically in the range of 0.5 ppm to 200 ppm of 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 increase the stability of the curable composition during storage. 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 about the melting point or softening point of the resin encapsulating the catalyst, thereby exposing the hydrosilylation catalyst to the components polyorganosiloxanes a) and b). Examples of suitable platinum-based catalysts include chloroplatinic acid and SYL-OFF TM 4000 catalyst, which is a commercially available organoplatinum complex dispersed in polysiloxane.

[0028] 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. If desired, the composition may optionally contain a silicone polyether and a silane filler treatment agent to further reduce the viscosity of the composition, as well as a hydrosilylation inhibitor to adjust the pot life. The composition may optionally contain an adhesion promoter.

[0029] The composition can be prepared as a one-part or two-part formulation. For a two-part formulation, the parts can be mixed in a static or dynamic mixer before coating. Coating processes include spraying (e.g., flat flow nozzle spraying), extrusion, or blade coating. After the coating is applied, the sample can be cured at a temperature typically in the range of 20°C to 175°C for a period typically in the range of 10 minutes to 8 hours. One-part compositions typically use microencapsulated catalysts that are exposed to reactants when heated. The composition can also be molded and cured into a desired shape and adhered to a substrate, including metal and plastic composites. The composition coating thickness is typically in the range of 0.5mm to 10mm.

[0030] In another aspect, the invention is an article comprising a battery enclosed in a metal or plastic composite casing, the casing being coated with the composition of the invention.

[0031] Example

[0032] In the following examples, all components were mixed using a FlackTek speed mixer. Q branched polymers A, B, and C are represented by Formula II, wherein each R group is represented by an average of fragment IIb:

[0033]

[0034] 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 a polyorganosiloxane (b) of Formula III, where p=158 (99.9 pbw).

[0035] Viscosity measurements were performed on formulations of the present invention that were prepared separately without catalyst or inhibitor by mixing all other components 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. 10 s was recorded. -1 The viscosity of the

[0036] Comparative Example 1 - Preparation of a 2-Part Composition Containing Mica Filler

[0037] By Q branched polymer A (49.67 pbw) and SYL-OFF TMThe first component (Part A) was prepared by adding 4000 catalyst (0.33 pbw) to the 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 another 30 seconds.

[0038] By Q branched polymer A (41.12 pbw), formula MD 3.2 D H 5.8 The second component (Part B) was prepared by adding polyorganosiloxane (a) (6.44 pbw) of M and Inhibitor A (2.44 pbw) to the mixer and mixing at 2000 rpm for 30 seconds. Imersy WG-325 mica (20 pbw) was then added to the mixer and mixing continued at 3000 rpm for another 30 seconds.

[0039] Part A and Part B are combined in a 1:1 w / w ratio and mixed at 2000 rpm for 30 seconds. The blend is then placed in a 2-mm thick Teflon-coated mold and cured at 125°C for 1 hour. Discs or 1 / 2 "× 4" rectangles are punched out from the cured molded samples as follows, and the samples are pyrolyzed at 1000°C using a Fisher Scientific isotemp programmable 750 series furnace. With the fan turned on, the temperature is raised to 450°C at a rate of 5°C / min, staying for 19 hours, and then raised to 500°C at a rate of 5°C / min, with a residence time of 2 hours. The fan is then turned off, and the temperature is raised to 1050°C at a rate of 1°C / min, staying for 2 hours. The fan and heating are then turned off, and the sample is cooled to 25°C. Samples that show cracking or do not produce a solid structure are excluded from thermal conductivity or 3-point fracture tests after pyrolysis. Thermal conductivity (TC) before and after pyrolysis was measured using a HotDisk thermal constant analyzer with a 50-mW pulse duration of 10 seconds. Three-point fracture testing after pyrolysis was performed using a TA Instruments RSA-G2 solid analyzer (linear rheometer) 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 and the force measured. The fracture force and cross-sectional area were used to calculate the 3-point fracture strength in MPa.

[0040] Comparative Examples 2 and 3 and Examples 1-4 were prepared essentially as described in Example 1, except for differences in filler concentration and filler type as shown in Table 1. Mica pbw refers to the pbw of Imersy WG-325 mica per 100 pbw of the sum of polyorganosiloxanes (a) and (b); clay pbw refers to the pbw of Glomax LL calcined kaolin per 100 pbw of the sum of polyorganosiloxanes (a) and (b); SiH:Vi refers to the mole / mole ratio of SiH groups from polyorganosiloxane (a) to vinyl groups in polyorganosiloxane (b); viscosity is in centipoise (cP), where a viscosity of less than 300,000 cP is considered acceptable; TC o refers to the thermal conductivity of the sample before pyrolysis; and TC f It refers to the thermal conductivity of the sample after pyrolysis.

[0041] Table 1 - Properties of Polyorganosiloxane Samples with Mica or Clay

[0042]

[0043] aThese samples fell apart during pyrolysis and could not be accurately tested for 3-point fracture.

[0044] The data show that high concentrations of mica are effective in obtaining samples that do not crack under severe pyrolysis conditions, and that acceptable viscosities and thermal conductivities are achieved with the samples of the present invention. In addition, the cured compositions of the present invention exhibit a surprising and advantageous decrease in thermal conductivity, which further contributes to the desired thermal insulation.

[0045] Table 2 illustrates the effect of different vinyl functionalized polymers on the viscosity, thermal conductivity, and crack resistance of the samples after pyrolysis. The samples were prepared as in Example 2, except for the differences in the 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).

[0046] Table 2 - Effect of vinyl polymer on sample properties

[0047] Example 5 Example 6 Example 7 Mica pbw 127 127 127 vinyl polymers QB QC Linear Vinyl polymer DP 0 220 52 SiH:Vi 1.3 1.3 1.3 Viscosity (cP) 8,000 45,000 70,000 <![CDATA[TC o (W / m·K)]]> 0.60 0.58 0.47 <![CDATA[TC f (W / m·K)]]> 0.19 0.13 0.24 3-point fracture (MPa) 15.6 5.9 6.3

[0048] The data shows that all samples passed the pyrolysis test, and the samples prepared using the Q-branched vinyl functionalized polymer showed particularly desirable viscosities and TC. Example 5 showed a significant increase in the 3-point fracture test, indicating greater mechanical strength of the ceramized material and better protection against thermal runaway.

[0049] The effects of using mica and auxiliary fillers on the viscosity, thermal conductivity, and crack resistance of the samples after pyrolysis are shown in Table 3. The experiment was conducted as described in Comparative Example 1, except that the auxiliary fillers and mica were added in the amounts shown in Table 3. ATH pbw refers to the parts by weight of Micral 855 aluminum trihydrate per 100 parts of polyorganosiloxanes (a) and (b); HCM pbw refers to the parts by weight of Extendospheres HA hollow ceramic microspheres per 100 parts of polyorganosiloxanes (a) and (b); and wollastonite pbw refers to the parts by weight of Nyad G wollastonite per 100 parts of polyorganosiloxanes (a) and (b).

[0050] Table 3 - Effect of auxiliary fillers on sample properties

[0051] Example 2 Example 8 Example 9 Example 10 Mica pbw 127 112 112 127 ATH pbw - 44 12 14 HCM pbw - - 34 - Wollastonite pbw - - - 14 SiH:Vi 1.3 1.3 1.3 1.3 Viscosity (cP) 35,000 22,000 18,000 38,000 <![CDATA[TC o (W / m·K)]]> 0.55 0.71 0.51 0.53 <![CDATA[TC f (W / m·K)]]> 0.20 0.23 0.15 0.22 3-point fracture (MPa) 7.0 11.8 13.2 20.4

[0052] The data show that the use of the auxiliary filler has slightly lower viscosity and comparable or lower thermal conductivity than the sample containing only mica. In particular, Example 10 shows significant mechanical strength.

Claims

1. A composition comprising: a) a polyorganosiloxane 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 of up to 1000; c) micron-sized mica particles; and d) a hydrosilylation catalyst; wherein the concentration of the mica particles is in the range of 90 to 200 parts by weight per 100 parts by weight of polyorganosiloxanes a) and b); and wherein the mole:mole ratio of Si-H groups in polyorganosiloxane a) to Si-vinyl groups in polyorganosiloxane b) is in the range of 0.8:1 to 5:

1.

2. The composition according to claim 1 , wherein the polyorganosiloxane functionalized with at least two Si—H groups is a polyorganosiloxane of formula I: wherein the sum of m+n is in the range of 2 to 400, and wherein n is 2 to 100; and wherein the polyorganosiloxane functionalized with at least two vinyl groups is a polyorganosiloxane of formula II: where each R is represented by fragment IIa: Each q is in the range of 0 to 300; each R 1 are independently C1-C6 alkyl; and each R 2 R 1 or a C1-C6 alkenyl group; provided that R 2 At least three of the groups are C1-C6 alkenyl groups; The hydrosilylation catalyst is a platinum-based catalyst.

3. The composition of claim 2, wherein each R is represented by fragment IIb: The sum of m+n is in the range of 3 to 200; and n is in the range of 3 to 100; wherein the mole:mole ratio of Si-H groups in the polyorganosiloxane a) to Si-vinyl groups in the polyorganosiloxane b) is in the range of 0.9:1 to 3:

1.

4. The composition according to claim 1 , wherein the polyorganosiloxane functionalized with at least two Si—H groups is a polyorganosiloxane of formula I: wherein the sum of m+n is in the range of 2 to 400, and wherein n is 2 to 100; and wherein the polyorganosiloxane functionalized with at least two vinyl groups is a linear polyorganosiloxane of formula III: Where p is in the range of 2 to 1000; The hydrosilylation catalyst is a platinum-based catalyst.

5. The composition according to claim 1 , wherein the polyorganosiloxane functionalized with at least two Si—H groups is a polyorganosiloxane of formula I: wherein the sum of m+n is in the range of 2 to 400, and wherein n is 2 to 100; and wherein the polyorganosiloxane functionalized with at least two vinyl groups is a combination of: a polyorganosiloxane of formula II: where each R is represented by fragment IIb: Linear polyorganosiloxane of formula III: Where p is in the range of 2 to 1000; The hydrosilylation catalyst is a platinum-based catalyst.

6. The composition of claim 5, wherein the weight / weight ratio of the polyorganosiloxane of formula II to the polyorganosiloxane of formula III is in the range of 60:40 to 95:5; The mole:mole ratio of Si-H groups in the polyorganosiloxane a) to Si-vinyl groups in the polyorganosiloxane b) is in the range of 0.9:1 to 2:

1.

7. The composition of claim 1 , further comprising one or more auxiliary inorganic fillers, wherein 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); wherein the hydrosilylation catalyst is a platinum-based catalyst.

8. The composition according to claim 3, further comprising 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, ground quartz, ground glass frit, wollastonite, potassium titanate fiber, glass fiber, hollow glass beads, hollow ceramics, and expanded perlite; wherein the concentration of the mica particles is in the range of 100 to 160 parts by weight per 100 parts by weight of the polyorganosiloxanes a) and b), and the total concentration of the one or more auxiliary fillers is in the range of 5 to 50 parts by weight per 100 parts by weight of the polyorganosiloxane. a) and b), provided 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 polyorganosiloxane a) and b); wherein the polyorganosiloxane The mole:mole ratio of Si-H groups in a) to Si-vinyl groups in the polyorganosiloxane b) is in the range of 0.9:1 to 2:

1.

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 enclosed in a metal or plastic composite casing, the casing being coated with the composition of any one of claims 1 to 9.

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