Mica-containing protective silicone coating composition

Abstract

The present invention is a composition comprising a TR-(RMeSiO2 / 2) n copolymer and mica, wherein each R is independently phenyl or methyl. The compositions of the invention are useful as coatings for metal substrates wherein the coatings exhibit adhesion, uniformity and crack resistance when subjected to hundreds of or even thousands of hours of high temperature.

Description

Background Art

[0001] The present invention relates to a silicone coating composition, more specifically a composition that is resistant to cracking and dielectric degradation at high temperatures, and a method for preparing the composition. High temperature protective coatings and insulating materials protect various 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 in excess of 300°C for months without cracking or loss of 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 rubbers are not resistant to cracking at temperatures above 250°C for more than 3 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 in excess of 500°C to form ceramic-like coatings. At such extreme temperatures, the coatings may 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 in excess of 300°C. Summary of the invention

[0003] In one aspect, the present invention provides a method comprising: R -(RMeSiO 2 / 2 ) n The copolymer and mica compositions address the need in the art, wherein each R is independently methyl or phenyl, and wherein T R -Poly(RMeSiO 2 / 2 ) n The weight-to-weight ratio of copolymer to mica is in the range of 10:90 to 90:10, wherein n is in the range of 20 to 800. The composition of the present invention can be used as a coating for metal, ceramic or plastic substrates, 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 comprises T R -(RMeSiO 2 / 2 ) n A composition of a copolymer and mica, wherein R is methyl or phenyl, and wherein T R -(RMeSiO 2 / 2 ) nThe weight-to-weight ratio of copolymer to mica is in the range of 10:90 to 90:10, wherein n is in the range of 20 to 800.

[0005] As used herein, the term “ R -(RMeSiO 2 / 2 ) n "Copolymer" refers to a copolymer comprising T R Resin unit and (RmeSiO 2 / 2 ) n units, wherein each R is independently methyl or phenyl. R Resin refers to R-SiO 3 / 2 、R-SiO 2 / 2 (OZ) and optionally phenyl R-SiO 1 / 2 (OZ)2 repeating units, where R-SiO 3 / 2 The unit is represented by the following structure:

[0006]

[0007] The dotted line indicates the point of attachment to another silicon atom; R-SiO 2 / 2 The unit of (OZ) is represented by the following structure:

[0008]

[0009] wherein Z is H, C1-C4-alkyl or C(O)CH3; and R-SiO 1 / 2 The unit of (OZ)2 is represented by the following structure:

[0010]

[0011] T R Each Z in the resin is preferably H. Commercially available T Ph Resin is DOWSIL TM RSN-0217 flake resin, and commercially available T Me Resin is DOWSIL TM RSN-2403 and DOWSIL TM RSN-2405 flake resin (a trademark of The Dow Chemical Company or its affiliates).

[0012] T R -(RMeSiO 2 / 2 ) n The copolymer contains units of poly(dimethylsiloxane) (PDMS) or poly(phenylmethylsiloxane) (PPhMS):

[0013]

[0014] wherein n is preferably from 20 or 40 or 70 or 100 to 800 or to 500 or to 300 or to 200. R Group and (RMeSiO 2 / 2 ) n The ratio of the groups is preferably in the range of 30:70 to 70:30.

[0015] T R -(RMeSiO 2 / 2 ) n The copolymer can be prepared by first mixing T in a suitable solution and under reaction conditions. R Resin, silanol terminated (RMeSiO 2 / 2 ) n- and a crosslinking agent, wherein the crosslinking agent is preferably an acetoxylating agent or an alkoxylating agent. Examples of suitable acetoxylating agents include alkyl triacetoxysilanes, such as methyl triacetoxysilane and ethyl triacetoxysilane; suitable alkoxylating agents include phenyl trimethoxysilane, phenyl triethoxysilane, methyl trimethoxysilane, ethyl trimethoxysilane, methyl triethoxysilane and ethyl triethoxysilane. 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 very aprotic solvents such as ethyl acetate, propyl acetate, propyl propionate, and butyl acetate.

[0016] Acetoxy or alkoxy terminated (RMeSiO 2 / 2 ) n Then advantageously with T R The resin and another solvent are contacted at high temperature to R The resin is partially or completely converted to T R -(RMeSiO 2 / 2 ) n copolymers, and completely or nearly completely depleted of acetoxy or alkoxy terminated (RMeSiO 2 / 2 ) n The volatiles can be removed from the mixture to form a copolymer and free T R The mixture can be used without further purification.

[0017] Commercially available T Ph An example of a PDMS copolymer is DOWSIL TM1-2577 Conformal Coating (a trademark of The Dow Chemical Company and its affiliates) having a PDMS degree of polymerization (DP) of 40.

[0018] 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. R -(RMeSiO 2 / 2 ) n The w / w ratio of polymer to mica is in the range of 10:90 or 20:80 or 30:70 or 40:60 to 90:10 or to 80:20 or to 70:30 or to 65:35.

[0019] In another aspect of the invention, the composition comprises T R -(RMeSiO 2 / 2 ) n copolymer, mica and one or more of the following components: a) T R b) 5 to 15 wt% of C1-C 12 -alkyl-tri-C1-C4-alkoxysilane; c) aprotic solvents such as ethyl acetate, propyl acetate, butyl acetate, propyl propionate and propylene glycol methyl ether acetate; d) moisture curing catalysts such as 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.

[0020] 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.

[0021] In another aspect of the present invention, the composition comprises T R -(RMeSiO 2 / 2 ) n Copolymer, Mica, C1-C 12 -alkyl-tri-C1-C4-alkoxysilane, an aprotic solvent and a moisture curing catalyst. The composition of the present invention provides a coating for metal, ceramic or plastic substrates that is tack-free and thermally stable to cracking for hundreds or even thousands of hours.

[0022] Example

[0023] Using DOWSILTM 1-2577 conformal coating as intermediate Example 1.

[0024] Intermediate Example 2 - T with DP = 50 Me Preparation of -PPhMS copolymer

[0025] Silanol-terminated PPhMS (65 g, n=50), XIAMETER TM OSF-1579 silane (OSF-1579, 5 g) and butyl acetate (50 g) 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-2403 flake resin (2403 resin, 35 g) and butyl acetate (60 g) were added to the reaction mixture, which was then heated to reflux for 1 hour, during which a mixture of acetic acid and H2O (about 1.5 g) was collected at the bottom of the Dean-Stark trap. Then, a portion of the solvent (about 60 g) was gradually removed to obtain a solid content of about 68 wt%. The reaction solution was cooled and used directly in the coating composition without filtration or further purification.

[0026] Intermediate Example 3 - T with DP = 60 Me Preparation of -PDMS copolymers

[0027] Silanol-terminated PDMS (65 g, n=60), XIAMETER TM OSF-1579 silane (OSF-1579, 5 g) and butyl acetate (50 g) 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-2403 flake resin (2403 resin, 35 g) and butyl acetate (60 g) were added to the reaction mixture, which was then heated to reflux for 1 hour, during which a mixture of acetic acid and H2O (about 1.5 g) was collected at the bottom of the Dean-Stark trap. Then, a portion of the solvent (about 60 g) was gradually removed to obtain a solid content of about 68 wt%. The reaction solution was cooled and used directly in the coating composition without filtration or further purification.

[0028] Comparative Example 1 was prepared by mixing Intermediate 1 with tetraisopropyl titanate (1 pbw).

[0029] Example 1-5-T Ph -Preparation of a mixture of PDMS and mica

[0030] 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) or HRX phlogopite (K2(Mg,Fe)6(Al2Si6O 20 ) (OH, F) 4, median particle size 10.6 μm, obtained from Arctic Minerals) was dried at 120°C in vacuum for 10 hours and cooled to room temperature under N2. The dried mica was added to a mixture containing T Ph A mixture of PDMS (DP=40, see Table 1), tetraisopropyl titanate (1 pbw) and butyl acetate was placed in a container and the contents were mixed using a mechanical stirrer. The mixture was then stored under N2.

[0031] Comparative Example 2 was prepared by mixing Intermediate 2 with tetraisopropyl titanate (1 pbw).

[0032] Example 6-T Me -Preparation of a mixture of PPhMS and mica

[0033] Dried mica (100 pbw) was added to a mixture containing (100 pbw), tetraisopropyl titanate (1 pbw), T Me -PPhMS copolymer (100 pbw, Intermediate 2) and butyl acetate (60 pbw) were placed in 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.

[0034] Comparative Example 3 was prepared by mixing Intermediate 3 with tetraisopropyl titanate (1 pbw).

[0035] Example 7-T Me -Preparation of a mixture of PDMS and mica

[0036] Dried mica (100 pbw) was added to a mixture containing (100 pbw), tetraisopropyl titanate (1 pbw), T Me -PDMS copolymer (100 pbw, Intermediate 3) and butyl acetate (630 pbw) were placed in 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.

[0037] Long-term high temperature resistance test

[0038] Each sample was coated onto an aluminum panel at a coating thickness of 100 μm and then heat cured and aged in an oven at 300° C. The time to film cracking (in days) was recorded as the first instance of visible cracks in the coating.

[0039] Table 1 shows the thermal stability of the coatings as measured by the cracking time. A cracking time of at least 10 days is considered a pass. The weight % loading of mica is reported as 100 weight % minus T Ph -PDMS or 100 wt% minus T Me -PDMS or 100 wt% minus T Me -PPhMS.

[0040] Table 1 - Thermal stability of coatings

[0041]

[0042] The data show a significant difference in crack resistance for the coating containing mica. The coating also exhibited acceptable uniformity and adhesion throughout the test period. Ph or T Me The combination of resin and mica failed the crack test within 2 days, while the combination of PDMS or PPhMS alone and mica easily delaminated from the substrate at 300° C. In addition, 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 of more than 120 hours.

[0043] Example 8 - Preparation of Room Temperature Non-Tack Coating

[0044] Methyltrimethoxysilane (10 parts by weight) and titanium tetra-tert-butoxide (0.5 parts by weight) were added to the composition of Example 1. A sample of the composition was applied to an aluminum plate at a coating thickness of 100 μm. At room temperature and 50% humidity, the coating became non-stick within 10 minutes. The coating was then subjected to a heat aging test at 300°C and found to be crack-free for >100 days.

Claims

1. A method comprising T R -(RMeSiO 2 / 2 ) n A composition of a copolymer and mica, wherein each R is independently methyl or phenyl, and wherein the T R -(RMeSiO 2 / 2 ) n The weight-to-weight ratio of the copolymer to the mica is in the range of 10:90 to 90:10, wherein n is in the range of 20 to 800.

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 T R Unit and (RMeSiO 2 / 2 ) n The weight-to-weight ratio of the units is in the range of 30:70 to 70:30; and wherein the mica is muscovite or phlogopite; 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, wherein the T R -(RMeSiO 2 / 2 ) n A weight-to-weight ratio of copolymer to said mica is in a range of 20:80 to 80:20; wherein the concentration of said aprotic solvent is sufficient to achieve a viscosity in a range of 100 cP to 1200 cP.

5. The composition according to claim 4, wherein the T R -(RMeSiO 2 / 2 ) n The weight-to-weight ratio of the copolymer to the mica is in the range of 30:70 to 70:

30.

6. The composition according to claim 5, wherein the T R -(RMeSiO 2 / 2 ) n The weight-to-weight ratio of the copolymer to the mica is in the range of 40:60 to 60:

40.

7. The composition according to any one of claims 1 to 6, wherein the mica is muscovite; and R -(RMeSiO 2 / 2 ) n It is T Ph -(DimethylSiO 2 / 2 ) n or T Me -(DimethylSiO 2 / 2 ) n or T Me -(phenylmethylSiO 2 / 2 ) n .

8. A composition comprising T based on the weight of the composition R -(RMeSiO 2 / 2 ) n Copolymer, Mica, C1-C 12 -alkyl-tri-C1-C4-alkoxysilane, an aprotic solvent, and a moisture curing catalyst; wherein each R is independently methyl or phenyl; and wherein the T R - a weight-to-weight ratio of PDMS copolymer to said mica is in the range of 20:80 to 80:20; and wherein the concentration of said aprotic solvent is sufficient to achieve a viscosity in the range of 50 cP to 5,000 cP.

9. The composition according to claim 8, wherein T R -(RMeSiO 2 / 2 ) n It is T Ph -(DimethylSiO 2 / 2 ) n or T Me -(DimethylSiO 2 / 2 ) n or T Me -(phenylmethylSiO 2 / 2 ) n , and the mica is muscovite.

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