Moisture curable polyorganosiloxane composition with nepheline syenite

Abstract

The present invention is a composition comprising a) a hydrolyzable polyorganosiloxane; b) an organosilane crosslinking agent; c) nepheline syenite particles; and d) a condensation cure catalyst; wherein the weight-to-weight ratio of the nepheline syenite to the hydrolyzable polyorganosiloxane is in the range of from 1:5 to 4:1. The composition of the present invention is useful as a coating for electric battery pack housings such as housings made of metal and polymer composites to provide ceramic strength and reduce backside temperature arising from thermal runaway.

Description

[0001] Moisture Curable Polyorganosiloxane Composition with Nepheline Syenite

[0002] Background of the Invention

[0003] The present invention relates to a composition comprising a moisture curable composition with nepheline syenite filler. The composition of the present invention is useful as a coating for metal or plastic composites in lithium-ion battery packs.

[0004] Electric vehicles using lithium-ion batteries encased in aluminum or plastic composite housings are rapidly growing in market share. A pervasive problem associated with battery packs is thermal runaway, which causes the temperature to rise above 1000 °C, which is sufficiently high to melt the aluminum or plastic with concomitant proliferation of fire and the release of molten particles. Although steel may be used in place of aluminum, the higher density of steel adversely impacts the range and performance of the electric vehicle. It would therefore be desirable to discover a coating material that can be applied to a battery pack casing or cover to protect against the consequences of thermal runaway and shield the occupants of the vehicle.

[0005] Summary of the Invention

[0006] The present invention addresses a need in the art by providing a composition comprising a) a hydrolyzable polyorganosiloxane; b) an organosilane crosslinking agent; c) nepheline syenite particles; and d) a condensation cure catalyst; wherein the weight-to-weight ratio of the nepheline syenite to the hydrolyzable polyorganosiloxane is in the range of from 1:5 to 4:1. The composition of the present invention is useful as a coating for electric battery pack housings such as housings made of metal and polymer composites to provide ceramic strength and reduce backside temperature arising from thermal runaway.

[0007] Detailed Description of the Invention

[0008] The present invention is a composition comprising a) a hydrolyzable polyorganosiloxane; b) an organosilane crosslinking agent; c) nepheline syenite particles; and d) a condensation cure catalyst; wherein the weight-to-weight ratio of the nepheline syenite to the hydrolyzable polyorganosiloxane is in the range of from 1:5 to 4: 1. As used herein, the term “hydrolyzable polyorganosiloxane” refers to a linear or branched polyorganosiloxane functionalized with groups that react with water to form a crosslinking network of Si-O-Si linkages. The hydrolyzable polyorganosiloxane is preferably represented by one or more compounds of Formula 1 : Formula 1: where R is either of Fragment 1 or Fragment 2: each R1is independently Ci-G,-alkyl or phenyl; each R2is independently C(O)CHs, Ci-Ce- alkyl, or N=C(R3)2, where each R3is independently Ci-C4-alkyl; R4is Ci-Ce-alkyl, phenyl, OR2, or -(R5)y-vinyl, where Rsis a divalent Ci-Ci2-linear or branched hydrocarbyl group, and y is 0 or 1 ; and n is from 50 to 1000. The compound of Formula 1 functionalized with Fragment 1 (R1and R2= Me in each case) can be prepared in accordance with Scheme 1: where the catalyst is preferably a platinum catalyst.

[0009] The compound of Formula 1 functionalized with Fragment 2 (R1, R2, and R4= Me in each case) can be synthesized in accordance with Scheme 2: Scheme 2: where the catalyst is preferably a titanate or tin catalyst.

[0010] In one aspect, the hydrolyzable polyorganosiloxane is a mixture of hydrolyzable polyorganosiloxanes of different degrees of polymerization.

[0011] As used herein, an organosilane crosslinking agent refers to an organosilicon compound containing hydrolyzable groups such as Si-Ci-C4-alkoxy, Si-OC(O)CH3, and Si-O-N=C(R3)2 groups. Preferably, the organosilane crosslinking agent one or more compounds of Formula 2:

[0012] Formula 2 where R6is -OR2or -(R5)y-vinyk and R7is R6, Ci-C4-alkyl, or phenyl. More preferably, R6is -OR2, and R7is -OR2or -(R5)y-vinyl or a combination thereof. Thus, in another aspect, the organosilane crosslinking agent preferably comprises either or both of the following compounds:

[0013] Examples of preferred organosilane crosslinking agents include methyltrimethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, 6-hexenyltrimethoxysilane, methyltris(methylethylketoimino)silane, and vinyltris(methylethylketoimino)silane.

[0014] The concentration of the organosilane crosslinking agent is typically present at a concentration in the range of from 0.1 or from 0.3, or from 0.7 weight percent, to 10 or to 5 or to 3 weight percent, based on the weight of the composition. The nepheline syenite particles are micron-sized, i.e., the particles have a D50 particle size in the range of from 1 pm to 100 pm, as measured by laser diffraction. The weight-to-weight concentration of the nepheline syenite to the Ci-C4-alkoxysilyl functionalized polyorganosiloxane is in the range of from 1:5 or from 1:3 or from 1:2 or from 2:3 or from 1.6:2, to 4: 1 or to 2: 1 or to 3:2 to 2: 1.6.

[0015] The composition further comprises a condensation cure catalyst, which is preferably a titanate catalyst such as titanium diisopropoxy bis(ethylacetoacetate) or tetra-n-butyl titanate.

[0016] The composition may further comprise an adhesion promoter such as a compound of the general Formula 2: where X is a glycidyl ether group, a thiol group, or an aminoethyl amine group: glycidyl ether group aminoethyl amine group thiol group

[0017] The composition may further comprise one or more ancillary inorganic fillers or their hydrates such as aluminum trihydroxide (i.e., alumina trihydrate or ATH), mica, hydromagnesite, aluminum oxides, epsomite, nesquihonite, boehmite, huntite, magnesium hydroxides, magnesium oxides, cerium oxide, iron oxides, titanium oxide, zinc oxide, calcium carbonate, boron nitride, boron oxides, kaolin clays, ground quartz, ground glass frits, glass 1'ibers, fumed silica, hollow glass beads, hollow ceramics, expanded perlite, wollastonite fibers, and potassium titanate fibers.

[0018] When used, the one or more ancillary fillers are present at such a concentration so that the weight-to-weight ratio of the sum of the mica and ancillary fillers to the hydrolyzable polyorganosiloxane is not greater than 2:1. Accordingly, in an additional aspect of the invention, the ratio of the nepheline syenite to the hydrolyzable polyorganosiloxane is in the range of 1:4 or from 1:3 or from 1:2 or from 2:3 to 7:3 or to 3:2, and the ratio of the one or more ancillary fillers to the hydrolyzable polyorganosiloxane is in the range of from 1:50 or from 1:20 or from 1:10 or from 1:5 or from 1:4 to 2:3 or to 1:3. A preferred combination of fillers comprises nepheline syenite at a concentration in the range of from 20 to 40 weight percent, mica at a concentration in the range of from 20 to 40 weight percent, and ATH at a concentration in the range of from about 2 to 10 weight percent, based on the weight of the hydrolyzable polyorganosiloxane, nepheline syenite, mica, and ATH.

[0019] The composition of the present may be applied with or without a primer to a suitable substrate such as steel, epoxy-coated steel (E-coated steel), aluminum, and polymer composites, and then allowed to moisture cure under standard conditions (typically at 20 °C to 25 °C, at 50% relative humidity). Application of the composition may be carried out by manual or automated means including spray-coating, and draw-down coating. Accordingly, in another aspect, the present invention is a method comprising the steps of coating an aluminum, steel, E-coated steel or polymer composite substrate with the composition of the present invention, and allowing the composition to cure. In yet another aspect, the present invention is an article comprising a battery pack or a module having a housing shell coated with a composition of the present invention. Preferably, the housing shell is made from aluminum, steel, E-coated steel, or a polymer composite, and the composition is cured.

[0020] Surprisingly, a moisture-curable polyorganosiloxane mixture containing an unusually high concentration of nepheline syenite particles and optionally one or more ancillary fillers forms a crack-free ceramified coating at temperatures above 1000 °C. Ceramification causes an advantageous reduction in the thermal conductivity of the coating, which is particularly useful in a battery pack design to prevent burn-through of the battery pack substrates from heat, flame, and molten particles that can be released at high energy during a thermal runaway event. When the battery is used in an electric vehicle, ceramification can attenuate the exposure of these hazards to the vehicle occupants.

[0021] Examples

[0022] Table 1 illustrates coating formulations using methyltrimethoxysilane as the sole organosilane crosslinking agent. Fimso refers to a compound of Formula 1 functionalized with fragment 1, n = 780; Fmiso refers to the compound of Formula 1 with fragment 1, n = 180; R1and R2of Formula 1 are methyl in each instance. NephSy refers to HiFill N300 Nephiline Syenite; Mica refers to Imerys WG 325 Mica; ATH refers to Hymod M855 SP alumina trihydrate; TDIDE refers to titanium diisopropoxy bis(ethylacetoacetate); TnBT refers to tetra-n-butyl titanate; and MTMS refers to methyltrimethoxysilane. The values are all in terms of wt%.

[0023] Table 1 - Coating Formulations with Methyltrimethoxysilane Crosslinking Agent

[0024] Table 2 illustrates coating formulations using MTMS vinyltrimethoxysilane the organosilane crosslinking agents. VTMS refers to vinyltrimethoxysilane.

[0025] Table 2 - Coating Formulations with Methyltrimethoxysilane and Vinyltrimethoxysilane

[0026] Crosslinking Agents

[0027] Torch Test Procedure

[0028] Test samples were drawn down over 1.5 -mm thick steel or aluminum panes and cured for 7 d at 23 °C and 50% relative humidity. A torch test was conducted using 5.8-kW flame using an oxygen / propane torch. The torch was calibrated before each series using both a thermocouple and high-temp infrared camera until the backside temperature on a blank steel plate measured 1200°C + / - 50° C after 5 min of flame impingement on the front side. The torch was placed 3” from the coating and the test was conducted for 5 min by sliding the sample on a test jig in front of the flame and simultaneously beginning an IR video recording of the temperature profile on the backside of the steel test plate.

[0029] Procedure for Testing Ceramic Strength

[0030] The post torch ceramic strength was ranked via a fingernail test. Two operators pressed on the ceramic and rated the strength relative to each other. The ceramics were rated from 1 to 5, with 5 being the strongest ceramic. The reported values are the average from the two operators’ rankings. Table 2 illustrates the ceramic strength (CS) and steel backside temperature (T) of the samples. The ratings are described as follows: Rating 1: Ceramic lacks mechanical integrity and / or ceramic breaks during test; Rating 2) Brittle. Ceramic easily crushed from application of pressure; Rating 3) Ceramic tears after pressure application with some resistance to the pressure; 4) Little penetration by nail pressure to the ceramic. No tear of ceramic. 5) Strong ceramic. No penetration by nail pressure. Ceramic maintains complete integrity. Table 2 - Ceramic Strength and Steel Backside Temperature of Sample

[0031] Ceramic became burnt and fell off the substrate before testing could be completed.

[0032] The data show that backside temperatures of less than 600 °C and good ceramic strength can be achieved with moisture cured PDMS compositions and relatively high amounts of nepheline syenite. The coating prepared from Example 6 with 25 wt% nepheline syenite, 25 wt% mica, and 5 wt% ATH (55 wt% total filler 45 wt% compounds of Formula 1) showed exceptional ceramic strength and backside temperature. Moreover, the coating prepared from Examples 7 and 8, which further included organosilane crosslinking agents with terminal double bonds, showed the best combination of ceramic strength and low backside temperature.

Claims

Claims:

1. A composition comprising a) a hydrolyzable polyorganosiloxane; b) an organosilane crosslinking agent; c) nepheline syenite particles; and d) a condensation cure catalyst; wherein the weight-to- weight ratio of the nepheline syenite to the hydrolyzable polyorganosiloxane is in the range of from 1 :5 to 4: 1.

2. The composition of Claim 1 wherein the hydrolyzable polyorganosiloxane is one or more compounds of Formula 1 :Formula 1 where R is Fragment 1 or Fragment 2:each R1is independently Ci-G>-alkyl or phenyl; each R2is independently Ci-C6-alkyl, C(O)CHr, or N=C(R3)2, each R3is independently Ci-C4-alkyl; R4is Ci-Ce-alkyl, phenyl, OR2, or -(R5)y-vinyl, R5is a divalent Ci-Cn-linear or branched hydrocarbyl group; y is 0 or 1; and n is from 50 to 1000; wherein the hydrolyzable crosslinking agent is represented by one or more compounds of Formula 2:Formula 2 where R6is -OR2or -(R5)y-vinyl; and R7is R6, Ci-C4-alkyl, or phenyl.

3. The composition of Claim 2 where R is represented by Fragment 1, and each R1is independently methyl or phenyl.

4. The composition of Claim 3 where each R2is methyl.

5. The composition of Claim 2 which further comprises one or more ancillary inorganic fillers or their hydrates selected from the group consisting of aluminum trihydroxide, mica, hydromagnesite, aluminum oxides, epsomite, nesquihonite, boehmite, huntite, magnesium hydroxides, magnesium oxides, cerium oxide, iron oxides, titanium oxide, zinc oxide, calcium carbonate, boron nitride, boron oxides, kaolin clays, ground quartz, ground glass frits, glass fibers, hollow glass beads, fumed silica, hollow ceramics, expanded perlite, wollastonite fibers, and potassium titanate fibers; wherein the ratio of the one or more ancillary fillers to the hydrolyzable polyorganosiloxane is in the range of from 1:20 to 1:2; wherein the weight-to- weight ratio of the sum of the mica and ancillary fillers to the hydrolyzable polyorganosiloxane is not greater than 2: 1.

6. The composition of Claim 5 wherein the ancillary fillers are mica or aluminum trihydroxide or a combination thereof; where R is represented by Fragment 1, and each R1is independently methyl or phenyl.

7. The composition of Claim 2 wherein the organosilane crosslinking agent comprises either or both of the following compounds:

8. The composition of any of Claims 1 to 7 wherein the organosilane crosslinking agent is one or more compounds selected from the group consisting of methyltrimethoxysilane, methyltris(methylethylketoimino)silane, vinyltrimethoxysilane, allyltrimethoxysilane, 6-hexenyltrimethoxysilane, methyltris(methylethylketoimino)silane, and vinyltris(methylethylketoimino)silane.

9. The composition of Claim 8 wherein the organosilane crosslinking agent is methyltrimethoxysilane and one or more additional organosilane crosslinking agents selected from the group consisting of vinyltrimethoxysilane, allyltrimethoxysilane, and6-hexenyltrimethoxysilane; wherein the ancillary fillers comprise mica and aluminum trihydroxide, wherein based on the weight of the hydrolyzable polyorganosiloxane, the nepheline syenite, the mica, and the aluminum trihydroxide, the concentration of the nepheline syenite is in the range of from 20 to 40 weight percent; the concentration of the mica is in the range of from 20 to 40 weight percent; and the concentration of the ATH is in the range of from about 2 to 10 weight percent.

10. The composition of Claim 9 wherein the organosilane crosslinking agent is a combination of methyltrimethoxysilane and vinyltrimethoxysilane.

11. The composition of Claim 2 where R is represented by Fragment 2; and each R1is independently methyl or phenyl; and each R4is methyl.

12. The composition of Claim 12 which further comprises one or more ancillary inorganic fillers or their hydrates selected from the group consisting of aluminum trihydroxide, mica, hydromagnesite, aluminum oxides, epsomite, nesquihonite, boehmite, huntite, magnesium hydroxides, magnesium oxides, cerium oxide, iron oxides, titanium oxide, zinc oxide, calcium carbonate, boron nitride, boron oxides, kaolin clays, ground quartz, ground glass frits, glass fibers, hollow glass beads, fumed silica, hollow ceramics, expanded perlite, wollastonite fibers, and potassium titanate fibers; wherein the ratio of the one or more ancillary fillers to the hydrolyzable polyorganosiloxane is in the range of from 1:20 to 1:2; wherein the weight-to- weight ratio of the sum of the mica and ancillary fillers to the hydrolyzable polyorganosiloxane is not greater than 2: 1.

13. The composition of Claim 12 wherein the ancillary fillers comprise mica and aluminum trihydroxide, and wherein the organosilane crosslinking agent comprises either or both of the following compounds:

14. A method comprising the steps of a) coating an aluminum, steel, E-coated steel or polymer composite substrate with the composition of Claim 1 , and b) allowing the composition to cure.

15. An article comprising a battery pack or a module having a housing shell coated with the composition of Claim 1.

16. The article of Claim 15 where the housing shell is made from aluminum, steel, E-coated steel, or a polymer composite, wherein the composition is cured.

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