Polysiloxane Mica Blend

Abstract

The present invention uses mica and T R -D R’R’ -(R''MeSiO 2 / 2 ) n and a copolymer (wherein R, R', R'', and n are defined herein). The composition is useful as a coating for a substrate, and the coating exhibits good adhesion and crack resistance when exposed to high temperatures for several weeks.

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 stovetop 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. [Background technology]

[0002] The high-temperature resistance of silicones ostensibly makes them promising candidates for high-temperature protective coatings and sealants. Nevertheless, silicone rubbers are not resistant to cracking above 250°C for more than two weeks. Combinations of silicones with inorganic fillers, such as SiO2, TiO2, and Al2O3, provide compositions with long-term high-temperature resistance. However, 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 suffer thermal shock failure, and 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 failure 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 uses mica and T R -D R’R’ -(R''MeSiO 2 / 2 ) nwherein each R, R', and R'' is independently methyl or phenyl; n is in the range of 2 to 800; and T R -D R’R’ -(R''MeSiO 2 / 2 ) n This invention addresses a need in the art by providing a composition having a weight to weight ratio of copolymer to mica ranging from 10:90 to 90:10.The composition of the invention is useful as a coating for a substrate, which coating exhibits good adhesion and crack resistance when exposed to high temperatures for several weeks. DETAILED DESCRIPTION OF THE INVENTION

[0004] The present invention uses mica and T R -D R’R’ -(R''MeSiO 2 / 2 ) n and a copolymer (wherein each R, R', and R'' is independently methyl or phenyl, and n is in the range of 2 to 800), comprising T R -D R’R’ -(R''MeSiO 2 / 2 ) n The composition has a weight to weight ratio of copolymer to mica ranging from 10:90 to 90:10.

[0005] The term “T R -D R’R’ -(R''MeSiO 2 / 2 ) n Copolymer" is T R -D R’R’ Resin and silanol- or C1-C4-alkoxy-terminated (R''MeSiO 2 / 2 ) n It refers to copolymers with polymers. R -D R’R’ The resin is R-SiO 3 / 2 , R-SiO 2 / 2 (OZ), and optionally R-SiO 1 / 2 (OZ)2(Together T R ), and R'2SiO 2 / 2 (D R’R’It is a kinetically stable three-dimensional polymer with repeating units of the formula:

[0006] R-SiO 3 / 2 The unit has the following structure:

[0007] [ka] where each R is methyl or phenyl.

[0008] R-SiO 2 / 2 (OZ) has the following structure:

[0009] [ka] wherein Z is H, C-C-alkyl, or C(O)CH; and RSiO 1 / 2 The (OZ)2 unit is represented by the following structure:

[0010] [ka]

[0011] Resin T R Each Z in the moiety is preferably methyl or H.

[0012] R'2SiO 2 / 2 The unit has the following structure:

[0013] [ka] wherein each R' is independently methyl or phenyl.

[0014] "Silanol- or C1-C4-alkoxylated (R"MeSiO 2 / 2 ) nThe term "polymer" refers to polyphenylmethylsiloxane (PPhMS) or polydimethylsiloxane (PDMS) containing the following repeating units:

[0015] [ka] wherein X is H or C1-C4-alkyl, and n (or degree of polymerization or DP) is preferably from 2, or from 5, or from 20, or from 40, or from 70, or from 100 to 800, or to 500, or to 300, or to 200. R -D R’R’ Resin unit (R''MeSiO 2 / 2 ) n The weight to weight ratio of the polymeric units preferably ranges from 20:80 or 30:70 to 80:20 or 70:30.

[0016] T R -D R’R’ -(R''MeSiO 2 / 2 ) n The copolymer is first prepared by reacting T R -D R’R’ Resins, silanol- or alkoxy-terminated (R''MeSiO 2 / 2 ) nThe polymer can be prepared by mixing a polymer and a crosslinking agent, preferably an acetoxylating agent or an alkoxylating agent. Suitable acetoxylating agents include alkyltriacetoxysilanes such as methyltriacetoxysilane and ethyltriacetoxysilane, and 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).

[0017] Then, silanol- or alkoxy-terminated (R″MeSiO 2 / 2 ) n Acetoxy or alkoxy terminated (R''MeSiO) polymers formed from the reaction of the polymer with a crosslinker 2 / 2 ) n The polymer is advantageously R -D R’R’ Resin and additional solvent are contacted at elevated temperatures to form T R -D R’R’ Resin R -D R’R’ -(R''MeSiO 2 / 2 ) n The copolymers were partially or completely converted to acetoxy or alkoxy-terminated (R"MeSiO 2 / 2 ) n The polymer is completely or nearly completely consumed. Volatiles are removed from the mixture to leave the copolymer and free T R -D R’R’ Blends with resins can be formed and used without further purification.

[0018] Micas are hydrated aluminum silicate minerals such as muscovite, biotite, fuchsite, phlogopite, margarite, glauconite, and lepidolite micas, of which muscovite and phlogopite are the major ones. R -D R’R’ -(R''MeSiO 2 / 2 ) n Copolymer and free T R -D R’R’ The w / w ratio of resin to total ranges from 90:10, or from 80:20, or from 70:30, or from 65:35 to 10:90, or to 20:80, or to 30:70, or to 35:65.

[0019] In another aspect of the invention, the composition comprises T R -D R’R’ -(R''MeSiO 2 / 2 ) n copolymer, mica, and R 2 Si(OR 3 )3(wherein, R 2 is C1~C 12 - alkyl or aryl, R 3 is C1-C4-alkyl), for example, methyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, and ethyltrimethoxysilane; an aprotic solvent such as propylene glycol methyl ether acetate, ethyl acetate, propyl acetate, butyl acetate, or propyl propionate; and a moisture curing catalyst, for example, a tin-based catalyst such as stannous octoate or stannous butanoate, or a titanium-based catalyst such as tetraisopropyl titanate, tetra-n-butyl titanate, and tetra-t-butoxy titanate.

[0020] The amount of aprotic solvent is sufficient to achieve a Brookfield viscosity at 25°C ranging from 20 cP, or from 50 cP, or from 100 cP to 20,000 cP, or from 10,000 cP, or from 5,000 cP, or from 1,200 cP; alternatively, the concentration of the aprotic solvent ranges from 5, 10, or 20 weight percent to 90, 75, or 60 weight percent, based on the weight of the composition. In yet another aspect, the present invention is a process for preparing a cured coating on a substrate. The present invention also is an article comprising a substrate coated with the cured composition. The thickness of the coating generally ranges from 20 μm to 300 μm.

[0021] 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]

[0022] Intermediate Example 1 - Resin 1 (D MeMe 0.15 D PhPh 0.05 T 0.10 T Ph 0.70 Preparation of To a vessel containing a mixture of MeSiCl (0.15 mol), PhSiCl (0.05 mol), MeSiCl (0.10 mol), and PhSiCl (0.70 mol) in toluene, water (2.5 mol) was added slowly at room temperature. The mixture was heated at 60 °C for 4 hours to obtain T R D R’R’ A solution containing the resin was obtained. The solution was washed with water to remove the acid and then stripped under vacuum and heat to produce a solid resin, which was then converted to resin flakes by grinding.

[0023] Intermediate Example 2 - Resin 2 (D MeMe 0.15 T Me 0.40 T Ph0.45 Preparation of To a vessel containing a mixture of MeSiCl (0.15 mol), PhSiCl (0.45 mol), and MeSiCl (0.40 mol) in toluene, water (2.5 mol) was added slowly at room temperature. The mixture was heated at 60 °C for 4 hours to obtain T R D R’R’ A solution containing the resin was obtained. The solution was washed with water to remove the acid and then stripped under vacuum and heat to produce a solid resin, which was then converted to resin flakes by grinding.

[0024] Intermediate Example 3 - Preparation of Resin 1 / PPhMS Copolymer Silanol-terminated PPhMS (50 g, DP=140), XIAMETER™ OSF-1579 silane (OSF-1579, 5 g), and butyl acetate (5 g) were added to a 500 mL, three-necked, dry flask equipped with a Dean-Stark apparatus under N2 with stirring. The mixture was stirred at room temperature for 1 hour, after which Resin 1 (50 g) and butyl acetate (120 g) were added to the reaction mixture. The mixture was heated to reflux (approximately 126 °C) for 3 hours, during which time approximately 1.8 g of water and 105 g of organic solvent were removed. The mixture was cooled to room temperature and poured into a glass bottle as the final product (70 wt% solids).

[0025] Intermediate Example 4 - Preparation of Resin 2 / PPhMS Copolymer The procedure of Intermediate Example 3 was repeated except that Resin 2 (45 g) was used. The solids content of the final product was 68 wt %.

[0026] Intermediate Example 5 - Preparation of Resin 1 / PDMS Copolymer Silanol-terminated PDMS (50 g, DP=80), (OSF-1579, 5 g), and butyl acetate (5 g) were added to a 500 mL, three-necked, dry flask equipped with a Dean-Stark apparatus under N2 with stirring. Resin 2 (50 g) and butyl acetate (120 g) were added to the reaction mixture, which was then heated to reflux for 3 h, during which time approximately 1.8 g of water and 105 g of organic solvent were removed. The reaction was cooled to room temperature and poured into a glass bottle as the final product (67 wt% solids).

[0027] Comparative Examples 1 to 3-T R D R’R’ Preparation of resin-copolymer blends Each comparative example was prepared as follows: Intermediate 3, 4, or 5 copolymer (100 pbw) was added to a flask under N2 along with methyltrimethoxysilane (5 pbw) and n-butyl acetate (30 pbw), followed by tetraisopropyl titanate (1 pbw). The contents of the flask were stirred for 1 hour, then poured into a glass bottle and sealed under N2.

[0028] Examples 1 to 3-T R D R’ -(RMeSiO 2 / 2 ) 120 Preparation of copolymer and mica blends Each example was prepared as follows: 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 hours and then cooled to room temperature under N2. The dried mica (100 pbw) was added to a vessel containing the contents of the comparative example and additional n-butyl acetate (30 pbw). The contents of the vessel were mixed with a mechanical stirrer under N2. The mixture was then poured into a bottle and sealed for further use.

[0029] 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.

[0030] Cracking time measurement The cured coatings were oven aged 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 crack formation was observed in the coating.

[0031] 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.

[0032] Table 1 shows the crack time results for samples with and without mica. In each example, the weight to weight ratio of resin to PPhMS or PDMS polymer was 45:55. TCT refers to thermal cycle test. Mica / wt% refers to the weight percent of mica based on the weight of copolymer and mica. MRX refers to MRX muscovite, and C-4000 refers to C-4000 muscovite.

[0033] [Table 1]

[0034] The results show that the cracking time and thermal cycling test results of the blends containing mica are dramatically different from the samples without mica. The cracking time test was stopped at 100 days.

[0035] The combination of PPhMS or PDMS with mica alone easily 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 cracking time greater than 120 hours.

Claims

1. Mica and T Ｒ -D Ｒ’Ｒ’ -(R''MeSiO ２／２ ) ｎ wherein each R, R', and R'' is independently methyl or phenyl, and n is in the range of 2 to 800; Ｒ -D Ｒ’Ｒ’ -(R''MeSiO ２／２ ) ｎ A composition wherein the weight to weight ratio of copolymer to said mica 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 Brookfield viscosity of the composition at 25°C in the range of 20 cP to 10,000 cP.

3. The T of the mica Ｒ -D Ｒ’Ｒ’ -(R''MeSiO ２／２ ) ｎ 3. The composition of claim 2, wherein the weight to weight ratio of the aprotic solvent to the copolymer ranges from 20:80 to 80:20, and the concentration of the aprotic solvent is sufficient to achieve a Brookfield viscosity at 25° C. in the range of 50 cP to 5,000 cP.

4. The T of the mica Ｒ -D Ｒ’Ｒ’ -(R''MeSiO ２／２ ) ｎ 4. The composition of claim 3, wherein the weight to weight ratio of the aprotic solvent to the copolymer ranges from 30:70 to 70:30, the mica is muscovite, biotite, fuchsite, phlogopite, margarite, glauconite, or lepidolite mica, and the concentration of the aprotic solvent is sufficient to achieve a Brookfield viscosity at 25° C. in the range of 100 cP to 1200 cP.

5. n is in the range of 5 to 300, the mica is muscovite or phlogopite, and the T Ｒ -D Ｒ’Ｒ’ -(R''MeSiO ２／２ ) ｎ The composition of claim 4, wherein the weight to weight ratio of copolymer to mica ranges from 65:35 to 35:

65.

6. The composition of claim 5 wherein the mica is muscovite.

7. R ２ Si(OR ３ ) ３ wherein R ２ is C １ -C １２ - alkyl or aryl, R ３ is C １ ~C ４ - R is alkyl ２ Si(OR ３ ) ３ and a moisture cure catalyst.

8. R ２ Si(OR ３ ) 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.

9. A process comprising the steps of coating a substrate with the composition of claim 7 and then curing the coating.

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 7.

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