Silicone coating composition containing mica

Abstract

The present invention is a composition comprising a) mica and a TPh-poly(phenylmethylsiloxane) copolymer; and / or b) a mixture of mica, a TPh resin, and a poly(phenylmethylsiloxane). The composition is useful as a coating on a substrate, and the coating exhibits adhesion and crack resistance when exposed to high temperatures for hundreds of hours.

Description

[Technical Field]

[0001] The present invention relates to silicone coating compositions, more specifically compositions that are resistant to cracking and dielectric degradation at high temperatures, and methods for preparing the compositions. High-temperature protective coatings and insulating materials are used to protect various equipment and devices from extremely high temperatures. For example, heater elements for electric vehicles, exhaust systems for automobile engines, power plants, and stove top coatings all benefit from such protective coatings. In many applications, coating layers must withstand temperatures exceeding 300°C for several months without cracking or losing their dielectric and insulating properties, and must pass severe thermal shock tests over a wide temperature range.

[0002] Although the high-temperature resistance of silicones ostensibly makes them promising candidates for high-temperature protective coatings and sealants, silicone rubbers are nevertheless not resistant to cracking above 250°C for more than two weeks. Combining silicones with inorganic fillers such as SiO2, TiO2, and Al2O3 provides compositions with long-term high-temperature resistance. Coatings prepared from such compositions require aging at temperatures above 500°C to form ceramic-like coatings. At such extreme temperatures, the coatings are likely to crack and thermal shock fracture, and furthermore, electronic components beneath the coating's surface are susceptible to damage. Therefore, developing a composition that provides a coating resistant to cracking, delamination, and thermal shock fracture while maintaining acceptable dielectric properties for extended periods at temperatures above 300°C would be an advancement in the field of high-temperature protective coatings. Summary of the Invention

[0003] The present invention relates to a) mica and T Ph - poly(phenylmethylsiloxane) copolymer; and / or b) mica, T PhThe need in the art is addressed by providing a composition comprising a mixture of a resin and a silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane). The weight ratio of mica to copolymer or mica to T Ph The weight-to-weight ratio of the resin to the sum of the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) ranges from 10:90 to 90:10.The composition of the present invention is useful as a coating for a substrate, and the coating exhibits good adhesion and resistance to cracking when exposed to high temperatures for hundreds of hours. DETAILED DESCRIPTION OF THE INVENTION

[0004] The present invention relates to a) mica and T Ph - poly(phenylmethylsiloxane) copolymer; and / or b) mica, T Ph The composition includes a mixture of a resin and a silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane). The weight ratio of mica to copolymer or mica to T Ph The weight-to-weight ratio of the resin to the sum of the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) ranges from 10:90 to 90:10.

[0005] As used herein, the term "T Ph -Poly(phenylmethylsiloxane) copolymer" is T Ph It refers to a copolymer of resin and poly(phenylmethylsiloxane). Ph Resin" is Ph-SiO 3 / 2 , Ph-SiO 2 / 2 (OZ), and optionally, Ph—SiO 1 / 2 It refers to a kinetically stable three-dimensional polymer having repeating units of the formula (OZ)2, where Ph-SiO 3 / 2 The unit is represented by the following structure:

[0006] [ka] where Z is H, C1-C4-alkyl, or C(O)CH3, and Ph-SiO 1 / 2 The (OZ)2 unit is represented by the following structure:

[0007] [ka]

[0008] T Ph Each Z in the resin is preferably H. Ph The resin is DOWSIL™ RSN-0217 flake resin.

[0009] T Ph - Poly(phenylmethylsiloxane) copolymers contain repeating units of phenylmethylsiloxane groups, as shown below:

[0010] [ka] wherein n (or degree of polymerization) is preferably from 2 or 5 or 20 or 40 or 70 or 100 to 300 or 250 or 200. The silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) (PPhMS) in the blend is characterized as follows:

[0011] [ka] wherein X is H or C1-C4-alkyl; n (alternatively the degree of polymerization) is preferably from 2, or from 5, or from 20, or from 40, or from 70, or from 100, up to 300, or up to 250, or up to 200.

[0012] For copolymers, T Ph The weight to weight ratio of the repeating units to the PPhMS repeating units is preferably in the range of 20:80 or 30:70 to 80:20 or to 70:30.Ph The weight to weight ratio of resin to PPhMS is also preferably in the range of 20:80 or 30:70 to 80:20 or to 70:30.

[0013] T Ph The T-PPhMS copolymer was first prepared in a suitable solvent and under suitable reaction conditions. Ph It can be prepared by mixing a resin, a silanol-terminated PPhMS, and a crosslinking agent, preferably an acetoxylating agent or an alkoxylating agent. Suitable acetoxylating agents include alkyltriacetoxysilanes such as methyltriacetoxysilane and ethyltriacetoxysilane. Suitable alkoxylating agents include phenyltrimethoxysilane, phenyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, and ethyltriethoxysilane. A commercial example of an acetoxylating agent is XIAMETER™ OSF-1579 Silane (a trademark of The Dow Chemical Company and its affiliates), which is a 50:50 w / w blend of methyltriacetoxysilane and ethyltriacetoxysilane. Suitable solvents include aprotic solvents such as ethyl acetate, propyl acetate, propyl propionate, butyl acetate, and propylene glycol methyl ether acetate (PGMEA).

[0014] Then, silanol-terminated or alkoxy-terminated (R"MeSiO 2 / 2 ) n The acetoxy- or alkoxy-terminated PPhMS formed from the reaction of the polymer with the crosslinker is advantageously Ph Resin and additional solvent are contacted at elevated temperatures to form T Ph Resin Ph The acetoxy- or alkoxy-terminated PPhMS is partially or completely converted to the copolymer, and the acetoxy- or alkoxy-terminated PPhMS is completely or nearly completely consumed. Volatiles are removed from the mixture to obtain the copolymer and free T Ph Blends with resins can be formed and used without further purification.

[0015] Micas are hydrated aluminum silicate minerals that include muscovite, biotite, chromite, phlogopite, nacre, glauconite, and lepidolite, of which muscovite and phlogopite are predominant. Ph -PPhMS copolymer or mica vs. T Ph The w / w ratio of the blend of resin and PPhMS ranges from 90:10 or 80:20 or 70:30 or 65:35 to 10:90 or 20:80 or 30:70 or 35:65. The composition may comprise a copolymer or blend with mica, or a copolymer and blend with mica.

[0016] In another embodiment of the present invention, the composition comprises T Ph -PPhMS copolymer and / or T Ph A blend of resin and silanol-terminated or C1-C4-alkoxy-terminated PPhMS, mica, RSi(OR')3, where R is C1-C 12 -alkyl or aryl, and R' is C1-C4-alkyl, for example, methyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, and ethyltrimethoxysilane; aprotic solvents such as propylene glycol methyl ether acetate, ethyl acetate, propyl acetate, butyl acetate, or propyl propionate, and moisture curing catalysts, for example, tin-based catalysts such as stannous octoate or stannous butanoate, or titanium-based catalysts such as tetraisopropyl titanate, tetra-n-butyl titanate, and tetra-t-butoxy titanate.

[0017] The amount of aprotic solvent is sufficient to achieve a viscosity in the range of 20 cP, or 50 cP, or 100 cP to 20,000 cP, or 10,000 cP, or 5,000 cP, or 1,200 cP, or alternatively, the concentration of the aprotic solvent is in the range of 5, or 10, or 20 weight percent to 90, or 75, or 60 weight percent based on the weight of the composition.

[0018] In yet another aspect, the present invention is a process for preparing a cured coating on a substrate. The present invention is also an article comprising a substrate coated with the cured composition. The coating thickness generally ranges from 20 μm to 300 μm.

[0019] The compositions of the present invention provide coatings for substrates, such as metal, metal oxide, ceramic, or plastic substrates, that are non-tacky in less than 30 minutes at ambient temperature and thermally stable against cracking for hundreds or thousands of hours. [Example]

[0020] In the following examples, pbw refers to parts by weight.

[0021] Comparative Example 1-T Ph Preparation of -PPhMS copolymer Silanol-terminated PPhMS (65 pbw, n=170), XIAMETER™ OSF-1579 silane (OSF-1579, 5 pbw), and butyl acetate (50 pbw) were added to a 500 mL three-necked dry flask equipped with a Dean-Stark apparatus under nitrogen. The temperature was increased to 50°C, and the mixture was stirred for 30 minutes. DOWSIL™ RSN-0217 Flake Resin (217 flake resin, 35 pbw) and butyl acetate (60 pbw) were added to the reaction mixture, which was then heated to reflux for 1 hour, during which a mixture of acetic acid and HO (approximately 1.5 pbw) was collected at the bottom of the Dean-Stark trap. A portion of the solvent (approximately 60 pbw) was then slowly removed to obtain a solids content of approximately 68 wt%. The reaction solution was cooled and used directly in a coating composition without filtration or further purification.

[0022] Comparative Examples 2 and 3-T Ph Preparation of blends of resin with silanol-terminated PPhMS A mixture of 217 flakes (35 pbw), silanol-terminated PPhMS (65 pbw, n=8 or 140), methyltrimethoxysilane (5 pbw), tin(II) 2-ethylhexanoate (1 pbw), and butyl acetate (45 pbw) was added to a dry flask under N to form a blend with 67% solids. The mixture was stirred for 30 minutes.

[0023] Examples 1 and 2 - Preparation of Blends with Mica MRX muscovite mica (median particle size 11.4 μm) was dried in vacuum at 120 °C for 10 h and then cooled to room temperature under N. The dried mica (66.7 pbw or 100 pbw) was added to a vessel containing tin(II) 2-ethylhexanoate (1 pbw), silanol-terminated PPhMS (65 pbw), 217 flakes (35 pbw), and butyl acetate (30 pbw).

[0024] Examples 3 and 4 - Preparation of copolymers containing mica The examples were prepared by the following general procedure: C-4000 muscovite (KAl(AlSiO 20 )(OH)4 (median particle size 10.8 μm, obtained from IMERYS) or MRX muscovite (median particle size 11.4 μm) was dried in vacuum at 120 °C for 10 h and then cooled to room temperature under N2. Dried mica (100 pbw) was dissolved in tin(II) 2-ethylhexanoate (1 pbw), T Ph The resulting mixture was added to a vessel containing PPhMS copolymer (100 pbw) and butyl acetate (30 pbw). The contents of the vessel were mixed under N2 with a mechanical stirrer. The mixture was then poured into a bottle and sealed for further use.

[0025] Preparation of coatings Aluminum panels (Gardco Type A, 3" x 6") were cleaned with toluene and acetone and dried under airflow before use. A portion (2 g) of the prepared formulation was coated onto the panel using a 4 mil drawdown bar to form a film with a thickness ranging from 50 μm to 100 μm. The coated film was dried under airflow at 70°C for 30 minutes to remove the solvent. The dried film was cured at room temperature or at 200°C for 10 to 60 minutes, followed by heat aging at 300°C.

[0026] Cracking time measurement The cured coatings were aged in an oven at 300°C. Each sample was checked for cracking every other day for the first 14 days (d), then once a week. The time to cracking was recorded when cracking was observed in the coating.

[0027] Thermal cycling test: Each formulation was coated as a 100 μm thick film, subsequently cured at room temperature or 150°C, and then aged at 300°C for 10 days. Using a Tenney Thermal Chamber, the samples were then subjected to 100 cycles of temperature cycling from -50°C to 150°C at a temperature ramp rate of 20°C / min, 10 minutes per cycle. If no cracking or delamination was observed after the test was completed, the coated sample was considered to have passed the thermal cycling test.

[0028] Table 1 shows the time-to-cracking results for samples with and without mica. TCT refers to thermal cycling test. Mica / wt% refers to the weight % of mica based on the weight of the blend and mica or copolymer and mica. PPhMS / n refers to the degree of polymerization of PPhMS. MRX refers to MRX muscovite and C-4000 refers to C-4000 muscovite.

[0029] [Table 1] aThe trial was stopped on the 100th day.

[0030] The results show dramatic differences in cracking times and thermal cycling test results between the blends and copolymers containing mica and the samples without mica. Ph The combination of PPhMS copolymer gave strong cracking time results, but surprisingly, T Ph It was discovered that excellent crack times could also be achieved for samples prepared by simply blending resin, silanol-terminated PPhMS, and mica.

[0031] T Ph The resin and mica combination was found to fail the crack test within two days, while the PPhMS copolymer and mica combination readily delaminated from the substrate at 300° C. Furthermore, of the fillers tested - silica, calcium carbonate, aluminum silicate, calcium silicate, alumina, ferric oxide, and mica - mica was found to be the only class of filler that exhibited a crack time greater than 120 hours.

Claims

1. a) Mica and T Ｐｈ - poly(phenylmethylsiloxane) copolymer; and / or b) mica, T Ｐｈ Resin, and silanol terminal or C １ -C ４ -alkoxy-terminated poly(phenylmethylsiloxane), wherein the weight to weight ratio of the mica to the copolymer or the T Ｐｈ Resin and the silanol terminal or C １ -C ４ a composition wherein the weight to weight ratio of said mica to the total alkoxy-terminated poly(phenylmethylsiloxane) ranges from 10:90 to 90:

10.

2. 10. The composition of claim 1, further comprising an aprotic solvent in a concentration sufficient to achieve a composition viscosity in the range of 20 cP to 10,000 cP.

3. The mica and the T Ｐｈ - the weight to weight ratio of the mica to the poly(phenylmethylsiloxane) copolymer, or the Ｐｈ Resin and the silanol terminal or C １ -C ４ -alkoxy-terminated poly(phenylmethylsiloxane) in a weight to weight ratio ranging from 80:20 to 20:80, １ -C ４ 3. The composition of claim 2, wherein the alkoxy-terminated poly(phenylmethylsiloxane) has a degree of polymerization in the range of 2 to 300, and the concentration of the aprotic solvent is sufficient to achieve a viscosity in the range of 50 cP to 5,000 cP.

4. The mica and T Ｐｈ -poly(phenylmethylsiloxane) copolymer, wherein the T Ｐｈ 4. The composition of claim 3, wherein the weight to weight ratio of the poly(phenylmethylsiloxane) portion of the copolymer to the poly(phenylmethylsiloxane) portion of the copolymer ranges from 30:70 to 70:30, the mica is muscovite, biotite, chromite, phlogopite, nacre, glauconite, or lepidolite, and the concentration of the aprotic solvent is sufficient to achieve a viscosity in the range of 100 cP to 1200 cP.

5. Mica, T Ｐｈ Resin, and the silanol terminal or C １ -C ４ -alkoxy-terminated poly(phenylmethylsiloxane), Ｐｈ Resin and the silanol terminal or C １ -C ４ - the weight to weight ratio of the silanol-terminated or C alkoxy-terminated poly(phenylmethylsiloxane) to the total of the silanol-terminated or C alkoxy-terminated poly(phenylmethylsiloxane) is in the range of 30:70 to 70:30, １ -C ４ 4. The composition of claim 3, wherein the alkoxy-terminated poly(phenylmethylsiloxane) is a silanol-terminated poly(phenylmethylsiloxane); the mica is muscovite, biotite, chromite, phlogopite, nacreous mica, glauconite, or lepidolite, and the concentration of the aprotic solvent is sufficient to achieve a viscosity in the range of 100 cP to 1200 cP.

6. The poly(phenylmethylsiloxane) portion of the copolymer has a degree of polymerization ranging from 5 to 250, the mica is muscovite or phlogopite, and the mica and the T Ｐｈ The composition of claim 4, wherein the weight to weight ratio of the poly(phenylmethylsiloxane) copolymer ranges from 65:35 to 35:

65.

7. the silanol-terminated poly(phenylmethylsiloxane) has a degree of polymerization ranging from 5 to 250, the mica is muscovite or phlogopite, and the T Ｐｈ 6. The composition of claim 5, wherein the weight to weight ratio of said mica to the sum of resin and said poly(phenylmethylsiloxane) ranges from 65:35 to 35:

65.

8. RSi(OR') ３ wherein R is C １ -C １２ - alkyl or aryl, R' is C １ -C ４ The composition of any one of claims 1 to 7, wherein the alkyl group is -alkyl and the composition comprises a moisture cure catalyst.

9. RSi(OR') ３ is methyltrimethoxysilane or phenyltrimethoxysilane, the aprotic solvent is propylene glycol methyl ether acetate, ethyl acetate, propyl acetate, butyl acetate, or propyl propionate, and the moisture cure catalyst is a tin-based or titanium-based catalyst.

10. 10. A process comprising the steps of coating a substrate with the composition of claim 8 and then curing the coating.

11. 10. An article comprising a substrate and a coating disposed thereon having a thickness in the range of 20 μm to 300 μm, said coating comprising the cured composition of claim 8.

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