Mica-containing silicone coating composition

Abstract

The present invention is a composition comprising a) mica and a TPH-poly (phenylmethylsiloxane) copolymer; and / or b) a mixture of mica, TPh resin and poly (phenylmethylsiloxane). The composition can be used as a coating for a substrate that exhibits adhesion and crack resistance when subjected to high temperatures for hundreds of hours.

Description

Background Art

[0001] The present invention relates to a silicone coating composition, more specifically a composition that resists cracking and dielectric degradation at high temperatures, and a method for preparing the composition. High-temperature protective coatings and insulation materials protect a variety of equipment and devices from extremely high temperatures. For example, heater elements for electric vehicles, exhaust systems for automotive engines, power plants, and top coatings for stoves all benefit from such protective coatings. In many applications, the coatings must withstand temperatures exceeding 300°C for months without cracking or losing dielectric and insulating properties, and must pass aggressive thermal shock tests over a wide temperature range.

[0002] The high-temperature resistance of silicones ostensibly makes them promising candidates as high-temperature protective coatings and sealants; however, silicone rubber is not resistant to cracking at temperatures above 250°C for more than two weeks. Combinations of silicones and 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 exceeding 500°C to form ceramic-like coatings. At such extreme temperatures, the coatings can crack and suffer thermal shock failure; in addition, electronic components beneath the coating surface are susceptible to damage. Therefore, it would be an advance in the field of high-temperature protective coatings to develop a composition that provides a coating that is resistant to cracking, delamination, and thermal shock failure while maintaining acceptable dielectric properties for long periods of time at temperatures exceeding 300°C. Summary of the Invention

[0003] The present invention addresses the need in the art by providing a composition comprising a) mica and T Ph - poly (phenyl methyl siloxane) copolymer; and / or b) mica, T Ph A mixture of a resin and a silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane); wherein mica and a copolymer or mica and T Ph The weight to weight ratio of the sum of the resin and the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) is in the range of 10:90 to 90:10. The composition of the present invention can be used as a coating for a substrate, wherein the coating exhibits good adhesion and resistance to cracking when subjected to high temperatures for hundreds of hours. DETAILED DESCRIPTION

[0004] The present invention is a composition comprising a) mica and T Ph - poly (phenyl methyl siloxane) copolymer; and / or b) mica, T Ph A mixture of a resin and a silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane); wherein mica and a copolymer or mica and T PhThe weight to weight ratio of the sum of the resin and the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) is in the range of 10:90 to 90:10.

[0005] As used herein, the term " Ph -poly(phenylmethylsiloxane) copolymer" refers to T Ph Copolymer of resin and poly(phenylmethylsiloxane). Ph Resin" refers to a resin with Ph-SiO 3 / 2 、Ph-SiO 2 / 2 (OZ) and optionally Ph-SiO 1 / 2 (OZ)2 repeating units, wherein Ph-SiO 3 / 2 The unit is represented by the following structure:

[0006]

[0007] Ph-SiO 2 / 2 (OZ);

[0008] wherein Z is H, C1-C4-alkyl or C(O)CH3; and Ph-SiO 1 / 2 The unit of (OZ)2 is represented by the following structure:

[0009]

[0010] Ph-SiO 1 / 2 (OZ)2

[0011] T Ph Each Z in is preferably H. Commercially available T Ph The resin is DOWSIL TM RSN-0217 flake resin.

[0012] T Ph - Poly(phenylmethylsiloxane) copolymers contain repeating units of phenylmethylsiloxane groups as shown below:

[0013]

[0014] Repeating units of phenylmethylsiloxane

[0015] wherein n (alternatively, the degree of polymerization) is preferably 2 or 5 or 20 or 40 or 70 or 100 to 300 or to 250 or to 200. The silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) (PPhMS) in the blend is characterized as follows:

[0016]

[0017] wherein X is H or C1-C4 alkyl; and n (alternatively, the degree of polymerization) is preferably from 2 or 5 or 20 or 40 or 70 or 100 to 300 or to 250 or to 200.

[0018] 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. Similarly, for the blends, T 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.

[0019] T Ph -PPhMS copolymers can be prepared by first mixing T in a suitable solution and under reaction conditions. Ph The crosslinking agent is preferably an acetoxylating agent or an alkoxylating agent. Examples of 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 TM OSF-1579 silane (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).

[0020] Then, the (R"MeSiO 2 / 2 ) n Acetoxy or alkoxy terminated PPhMS formed by the reaction of polymer and crosslinker reacts with T at high temperature. Ph The resin is contacted with an additional solvent to Ph The resin is partially or completely converted to T Ph -PPhMS copolymers, and completely or nearly completely consume the acetoxy or alkoxy terminated PPhMS. Volatiles can be removed from the mixture to form copolymers and free T Ph The blend of resins can be used without further purification.

[0021] Mica is a hydrated aluminum silicate mineral, including muscovite, biotite, chrome mica, phlogopite, pearl mica, glauconite and lepidolite, among which muscovite and phlogopite are the main ones.Ph -PPhMS copolymer or mica and 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 to 20:80 or to 30:70 or to 35:65. The composition may comprise the copolymer or blend and mica, or the copolymer and blend and mica.

[0022] In another aspect of the invention, the composition comprises T Ph -PPhMS copolymer and / or blends of: T Ph 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, such as 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 tin octoate or tin butyrate, or titanium-based catalysts such as tetraisopropyl titanate, tetra-n-butyl titanate and tetra-tert-butoxy titanate.

[0023] 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 to 10,000 cP or to 5,000 cP or to 1200 cP; alternatively, the concentration of the aprotic solvent is typically in the range of 5 wt % or 10 wt % or 20 wt % to 90 wt % or to 75 wt % or to 60 wt % based on the weight of the composition.

[0024] In yet another aspect, the present invention is a method for preparing a cured coating on a substrate. The present invention is also an article comprising a substrate coated with the cured composition. The thickness of the coating is generally in the range of 20 μm to 300 μm.

[0025] The composition of the present invention provides a coating for substrates such as metal, metal oxide, ceramic or plastic substrates that is tack-free in less than 30 minutes at ambient temperature and thermally stable to cracking for hundreds or even thousands of hours.

[0026] Example

[0027] In the following examples, pbw means parts by weight.

[0028] Comparative Example 1-T Ph Preparation of -PPhMS copolymer

[0029] Silanol-terminated PPhMS (65 pbw, n=170), XIAMETER TM 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. The temperature was raised to 50°C and the mixture was stirred for 30 minutes. TM RSN-0217 flake resin (217 flakes, 35 pbw) and butyl acetate (60 pbw) were added to the reaction mixture, which was then heated to reflux for 1 hour, during which time a mixture of acetic acid and H2O (approximately 1.5 pbw) collected at the bottom of the Dean-Stark trap. A portion of the solvent (approximately 60 pbw) was then gradually removed to a solids content of approximately 68 wt%. The reaction solution was cooled and used directly in the coating composition without filtration or further purification.

[0030] Comparative Example 2 and Comparative Example 3-T Ph Preparation of blends of resin and silanol-terminated PPhMS

[0031] 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 N2 to form a blend with a solids content of 67%. The mixture was stirred for 30 minutes.

[0032] Example 1 and Example 2 - Preparation of blends containing mica

[0033] MRX muscovite (median particle size 11.4 μm) was dried at 120°C in vacuum for 10 hours and then cooled to room temperature under N2. The dried mica (66.7 pbw or 100 pbw) was added to a container containing tin(II) 2-ethylhexanoate (1 pbw), silanol-terminated PPhMS (65 pbw), 217 flakes (35 pbw), and butyl acetate (30 pbw).

[0034] Examples 3 and 4 - Preparation of Copolymers Containing Mica

[0035] The examples were prepared by the following general procedure: C-4000 muscovite (K2Al4(Al2Si6O 20 )(OH)4) (median particle size 10.8 μm, obtained from IMERYS) or MRX muscovite (median particle size 11.4 μm) was dried at 120°C in vacuum for 10 hours and then cooled to room temperature under N2. The dried mica (100 pbw) was added to a mixture containing tin(II) 2-ethylhexanoate (1 pbw), T Ph-PPhMS copolymer (100 pbw) and butyl acetate (30 pbw) were added to a container. The contents of the container were mixed by mechanical stirring under N2. The mixture was then poured into a bottle and sealed for further use.

[0036] Coating preparation

[0037] Aluminum panels (Type A from Gardco, 3" x 6") were washed with toluene and acetone and dried by air flow before use. A portion of the prepared formulation (2 g) was coated on 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 at 70°C under air flow for 30 minutes to remove the solvent. The dried film was cured at room temperature or 200°C for 10 to 60 minutes and then heat aged at 300°C.

[0038] Measurement of cracking time

[0039] The cured coatings were aged in an oven at 300° C. For the first 14 days (d), the samples were checked for cracking every other day for each sample and then weekly. When some cracking was observed in the coating, the time to cracking was recorded.

[0040] Thermal Cycling Test

[0041] 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. The samples were then subjected to 100 temperature cycles of 10 minutes each between -50°C and 150°C using a Tenney hot chamber at a temperature ramp rate of 20°C / min. If no cracking or delamination was observed after the test was completed, the coated sample was considered to have passed the thermal cycling test.

[0042] Table 1 shows the cracking time results for samples with and without mica. TCT refers to thermal cycling test. Mica / wt% refers to the weight percent of mica based on the weight of the blend and mica or copolymer and mica. PPhMS / n refers to the degree of polymerization of the PPhMS. MRX refers to MRX muscovite, and C-4000 refers to C-4000 muscovite.

[0043] Table 1 - Coating cracking time and thermal cycle test results

[0044] Example resin PPhMS / n type Mica / weight% Cracking time TCT 1 <![CDATA[T Ph ]]> 8 blends MRX / 40% 60 days qualified 2 <![CDATA[T Ph ]]> 140 blends MRX / 50% 88 days qualified 3 <![CDATA[T Ph ]]> 170 Copolymer MRX / 50% <![CDATA[>100 days a ]]> qualified 4 <![CDATA[T Ph ]]> 170 Copolymer C-4000 / 50％ <![CDATA[>100 days a ]]> qualified C1 <![CDATA[T Ph ]]> 170 Copolymer No mica 11 days qualified C2 <![CDATA[T Ph ]]> 8 blends No mica 3 days Unqualified C3 <![CDATA[T Ph ]]> 140 blends No mica 10 days Unqualified

[0045] a The test was stopped at 100 days.

[0046] The results showed that the blends and copolymers containing mica showed significant differences in cracking time and thermal cycling test results compared to the samples without mica. Ph -PPhMS copolymer combination gave robust cracking time results, but surprisingly found that for only the blending T Ph The samples prepared by copolymer, silanol-terminated PPhMS and mica can also achieve excellent cracking time.

[0047] Discover T Ph The combination of resin and mica alone failed the crack test within 2 days, while the combination of PPhMS copolymer and mica alone readily delaminated from the substrate at 300° C. Furthermore, among the fillers tested (silicon dioxide, calcium carbonate, aluminum silicate, calcium silicate, aluminum oxide, iron oxide, and mica), mica was found to be the only type of filler that exhibited a cracking time exceeding 120 hours.

Claims

1. A composition comprising a) mica and T Ph - poly (phenyl methyl siloxane) copolymer; and / or b) mica, T Ph A mixture of a resin and a silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane); wherein the mica and the copolymer or the mica and the T Ph The weight to weight ratio of the sum of the resin and the silanol-terminated or C1-C4 alkoxy-terminated poly(phenylmethylsiloxane) is in the range of 10:90 to 90:

10.

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

3. The composition according to claim 2, wherein the mica and the T Ph -poly(phenylmethylsiloxane) copolymer or the mica and the T Ph The weight to weight ratio of the sum of the resin and the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) is in the range of 80:20 to 20:80, wherein the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) has a degree of polymerization in the range of 2 to 300; and wherein the concentration of the aprotic solvent is sufficient to achieve a viscosity in the range of 50 cP to 5,000 cP.

4. The composition according to claim 3, comprising the mica and T Ph - poly(phenylmethylsiloxane) copolymer, wherein the T Ph The weight to weight ratio of the poly(phenylmethylsiloxane) portion of the copolymer to the poly(phenylmethylsiloxane) portion is in the range of 30:70 to 70:30; and wherein the mica is muscovite, biotite, chrome mica, phlogopite, nacre, glauconite, or lepidolite; and wherein the concentration of the aprotic solvent is sufficient to achieve a viscosity in the range of 100 cP to 1,200 cP.

5. The composition according to claim 3, comprising mica, the T Ph A mixture of a resin and said silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane), wherein said mica and said T Ph The invention relates to a method for preparing an aqueous solution of the present invention wherein the weight to weight ratio of the sum of the resin and the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) is within the range of 30:70 to 70:30; wherein the silanol-terminated or C1-C4-alkoxy-terminated poly(phenylmethylsiloxane) is a silanol-terminated poly(phenylmethylsiloxane); and wherein the mica is muscovite, biotite, chrome mica, phlogopite, nacre, glauconite, or lepidolite; and wherein the concentration of the aprotic solvent is sufficient to achieve a viscosity within the range of 100 cP to 1200 cP.

6. The composition of claim 4, wherein the poly(phenylmethylsiloxane) portion of the copolymer has a degree of polymerization in the range of 5 to 250; the mica is muscovite or phlogopite; and the mica is in a crystalline form with the T-type silicate. Ph - The weight to weight ratio of the poly(phenylmethylsiloxane) copolymer is in the range of 65:35 to 35:

65.

7. The composition of claim 5, wherein the silanol-terminated poly(phenylmethylsiloxane) has a degree of polymerization in the range of 5 to 250; the mica is muscovite or phlogopite; and the mica is in a crystalline form with the T-type silicate. Ph A weight to weight ratio of the sum of the resin and the poly(phenylmethylsiloxane) is in the range of 65:35 to 35:

65.

8. The composition according to any one of claims 1 to 7, further comprising RSi(OR')3, wherein R is C1-C 12 -alkyl or aryl, and R' is C1-C4-alkyl; and Moisture cure catalyst.

9. The composition of claim 8, wherein 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 curing catalyst is a tin-based or titanium-based catalyst.

10. A method comprising the steps of coating a substrate with the composition according to claim 8 and then curing the coating. 11 . An article comprising a substrate and a coating disposed on the substrate having a thickness in a range of 20 μm to 300 μm, wherein the coating comprises the cured composition according to claim 8 .

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