Silicone coating composition

Abstract

The present invention relates to a composition comprising a TPh resin and a TPh-poly (phenylmethylsiloxane) copolymer. The composition can be used as a coating for a metal substrate, wherein the coating has excellent transparency, adhesion, crack resistance and retention of dielectric properties.

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 2 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] The present invention solves the need in the art by providing a composition comprising T Ph Resin, T Ph -poly(phenylmethylsiloxane) copolymers and substantially absent ZO-poly(phenylmethylsiloxane)-OZ, wherein each Z is independently H, C1-C4-alkyl or C(O)CH3, wherein T Ph Resin and T Ph The w / w ratio of the copolymer of the resin and poly(phenylmethylsiloxane) is in the range of 15:85 to 35:65, wherein the resin and the copolymer contain Si-OZ groups in a mol% concentration in the range of 7.5 mol% to 12.0 mol%. The composition of the present invention can be used as a coating for a metal substrate, wherein the coating exhibits transparency, adhesion and crack resistance when subjected to high temperatures for hundreds of hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 A series of three compositions of the invention and two comparative compositions 29 Si NMR spectrum. DETAILED DESCRIPTION

[0005] The present invention is a composition comprising T Ph Resin, T Ph -poly(phenylmethylsiloxane) copolymers and substantially absent ZO-poly(phenylmethylsiloxane)-OZ, wherein each Z is independently H, C1-C4-alkyl or C(O)CH3, wherein T Ph Resin and T Ph The w / w ratio of the copolymer of the resin and poly(phenylmethylsiloxane) is in the range of 15:85 to 35:65, wherein the resin and the copolymer contain Si-OZ groups in a mol % concentration in the range of 7.5 mol % to 12.0 mol %.

[0006] Terminology Ph Resin refers to a phenyl-SiO 3 / 2 , phenyl-SiO 2 / 2 (OZ) and optionally phenyl-SiO 1 / 2 (OZ)2 repeating units of cross-linked polymers, wherein phenyl-SiO 3 / 2 The unit is represented by the following structure:

[0007]

[0008] The dotted line indicates the point of attachment to another silicon atom; phenyl-SiO 2 / 2 The unit of (OZ) is represented by the following structure:

[0009]

[0010] wherein Z is H, C1-C4-alkyl or C(O)CH3; and phenyl-SiO 1 / 2 The unit of (OZ)2 is represented by the following structure:

[0011]

[0012] T Ph Each Z in the resin is preferably H. Commercially available T Ph Resins include DOWSIL TM RSN-0217 and 0220 flake resins (trademarks of The Dow Chemical Company or its affiliates).

[0013] T Ph Copolymer of resin and poly(phenylmethylsiloxane) (T Ph -PPhMS copolymer) contains repeating units of PPhMS:

[0014]

[0015] wherein Z is as previously defined and n is preferably from 20 or 40 or 70 or 100 to 300 or to 250 or to 200.

[0016] The composition can be prepared by first mixing the silanol terminated PPhMS and a crosslinking agent, preferably an acetoxylating agent or an alkoxylating agent, in a suitable solvent and under reaction conditions. 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 polar aprotic solvents such as ethyl acetate, propyl acetate and butyl acetate.

[0017] Then, the acetoxy- or alkoxy-terminated PPhMS is advantageously reacted with T at elevated temperature. Ph Resin contact to Ph The resin is partially converted into T Ph -PPhMS copolymers and completely or nearly completely consume acetoxy- or alkoxy-terminated PPhMS. Volatiles may be removed from the mixture to form copolymers and free T Ph The mixture was used without further purification.

[0018] The final composition comprises substantially no ZO-PPhMS-OZ. As used herein, "substantially no ZO-PPhMS-OZ" means that the composition comprises based on T Ph Resin, T Ph Based on the weight of the ZO-PPhMS copolymer and ZO-PPhMS-OZ, the content of ZO-PPhMS-OZ is less than 10 wt%, preferably less than 5 wt%, more preferably less than 1 wt%, and most preferably less than 0.5 wt%.

[0019] Or, T Ph Resin and T Ph The blend of T-PPHMS copolymer can be prepared as follows: Ph The resin is completely converted to T Ph -PPhMS copolymer, and then add enough T Ph , to form copolymers and free T Ph of the desired blend.

[0020] It has been surprisingly found that TPh Resin and T Ph The blend of the T-PPhMS copolymer is critical to achieving the combination of transparency, crack resistance and adhesion to the substrate of the film prepared from the composition. Ph Resin and T Ph - The w / w ratio of the PPhMS copolymer is in the range of 15:85 or 20:80 or 24:76 to 35:65 or to 30:70 to 28:72.

[0021] While not being bound by theory, it is believed that T Ph -PPhMS copolymers enable the original incompatible materials (T Ph and ZO-PPhMS-OZ) to produce transparent, haze-free coatings; in addition, the residual T Ph The presence of a critical concentration of unreacted Si-OH groups in the resin provides adhesion of the coating to the substrate through hydrogen bonding of the Si-OH groups, but T alone Ph -PPhMS copolymers lack sufficient properties.

[0022] In T Ph Resin and T Ph The mole % concentration of Si-OZ groups in the blend of the poly(vinylpyrrolidone)-PPHMS copolymer is in the range of 7.5 mole % or 9.0 mole % or 10.5 mole % or 11.0 mole % to 12 mole % or to 11.5 mole %. As used herein, the term mole % concentration of Si-OZ groups refers to the area measured for the resonance associated with the Si-OZ groups and the area of ​​the composition sample. 29 Ratio of the total area of ​​the resonance in the Si spectrum.

[0023] Preferably, based on T Ph Resin, T Ph -weight of PPhMS copolymer and ZO-PPhMS-OZ, T Ph Resin and T Ph -PPhMS copolymers make up at least 90 or at least 95 or at least 99 wt. % or at least 99.5 wt. % of the composition, as described by 29 SiNMR spectroscopy. Alternatively, the composition comprises less than 5, or less than 1, or less than 0.5 wt% OZ-PPhMS-OZ.

[0024] In another aspect, the present invention is a method comprising the steps of: coupling terminally alkoxylated or acetylated PPhMS with T Ph The resin is in contact for a sufficient time to absorb the initial T Ph In comparison, T PhThe total mole % of Si-OZ groups, preferably Si-OH groups, in the resin is reduced by 10 mole % or 15 mole % to 30 mole % or to 25 mole %, such as by 29 The method is measured by the decrease in the area under the resonance between -65 ppm and -75 ppm of the Si NMR spectrum. More specifically, the method comprises the following steps: Ph The resin is contacted with ZO-PPhMS-OZ in the presence of a polar aprotic solvent at a temperature ranging from 77°C or 100°C to 200°C or to 150°C for a time ranging from 15 minutes or 30 minutes to 10 hours or to 5 hours or to 2 hours; and preferably accompanied by distillation and removal of the solvent. The method provides a simple and effective way to prepare a coating composition.

[0025] Example

[0026] Nuclear Magnetic Resonance Spectroscopy (NMR) Measurements

[0027] Nuclear magnetic resonance (NMR) spectra were obtained on a Varian EX-400 5 MHz Mercury spectrometer using C6D6 or CDCl3 solvent. 29 Chemical shifts of Si-NMR spectra are referenced to internal solvent resonances and are reported relative to tetramethylsilane.

[0028] Comparative Example 1-T Ph Preparation of blends of resin and hydroxyl-terminated PPhMS

[0029] Preparation of hydroxyl-terminated PPhMS (65 g) with a degree of polymerization of 139 and DOWSIL TM RSN-0217 flake resin (T Ph The mole % of Si-OH groups is determined by 29 Si NMR spectrum measured 12.7 mol % as determined by dividing the area under the resonances in the range of -65 ppm to -75 ppm by the area of ​​all resonances appearing in the spectrum ( Figure 1 a).

[0030] Example 1 - Preparation of partially coupled T Ph Resin and T Ph -PPhMS copolymer

[0031] 65 g of hydroxyl-terminated PPhMS (DP 139), XIAMETER TM OSF-1579 silane (5 g) and butyl acetate (50 g) were added to a 500-mL 3-neck dry flask equipped with a Dean-Stark trap. The mixture was stirred at 50°C under N2 for 30 minutes, after which DOWSIL TM RSN-0217 Flake Resin ((T PhResin, 35 g) and butyl acetate (60 g) were added to the reaction mixture. The mixture was heated to reflux for 1 hour, during which time volatiles (60 g) were gradually removed and collected in a Dean-Stark trap. The contents of the flask were cooled to room temperature and used as a coating composition without filtering or further purification. Gel permeation chromatography of the product showed T Ph Incomplete conversion of the resin and an upward shift in the molecular weight of the peak associated with PPhMS. 29 Si NMR spectroscopy ( Figure 1 b) Demonstrating the complete (or nearly complete) absence of resonances associated with the acetoxylated PPhMS group at -25 ppm ( Figure 1 a), which gives the complete conversion of acetylated PPhMS to T Ph -PPhMS copolymers. The mole % of Si-OZ groups is determined by 29 Si NMR spectroscopy measured 11.3 mol %. Residual T Ph The weight % of resin was found to be 26.5% by gel permeation chromatography.

[0032] Comparative Example 2 - Preparation of Extensively Coupled T Ph Resin and T Ph -PPhMS

[0033] The steps of Example 1 were repeated except that T Ph After the resin was added, the contents of the vessel were heated to reflux for 36 hours. After removal of volatiles, the composition had a solid content of about 67 wt%. The reaction solution was cooled and used directly as a coating composition without filtration and further purification. The mole % of Si-OZ groups was determined by 29 SiNMR spectroscopy measured 6.6 mol% ( Figure 1 c).

[0034] Gel Permeation Chromatography (GPC) Method

[0035] Gel permeation chromatography (GPC) analysis was performed using an Agilent 1260 Infinity II chromatograph equipped with a triple detector consisting of a differential refractometer, an online differential viscometer, low angle light scattering (LALS: detection angles 15° and 90°) and a column (2PL Gel Mix C, Varian). Toluene (HPLC grade, Biosolve) was used as the mobile phase at a flow rate of 1 ml / min.

[0036] Cracking time measurement

[0037] The cured coatings were aged at 300° C. Cracking was checked every other day for the first 14 days and then weekly. When cracking was observed in the coating, the time to cracking was recorded.

[0038] Dielectric resistance measurement

[0039] The aged coating was kept in a room with 85% humidity for 24 hours and then placed between electrodes to measure the current resistance with a multimeter. If the measured resistance was found to be less than 1000 ohms, the aged coating was considered to have failed in dielectric resistance.

[0040] Thermal Cycle Test :

[0041] Each formulation was coated into a 100-μm film, then cured at ambient temperature or 150°C, and then aged at 300°C for 10 days, after which each aged sample was subjected to a 100-cycle thermal cycle test (between -50°C and 150°C) by using a Tenney Thermal Chamber. The aged sample was placed in the chamber and then tested between -50°C and 150°C (heating rate 20°C / min, 10 min per cycle). If no cracking and delamination were observed on the film during 100 test cycles, the coating sample was considered to have passed the thermal cycle test.

[0042] Thermal stability test

[0043] The thermal stability of the test composition. Each sample (70 parts by weight) was dissolved in butyl acetate (30 parts by weight) and a 50-μm film was coated on an alumina plate for cracking and adhesion testing. The film cracking time (synonymous with dielectric failure) of each sample was recorded during 300°C aging. According to ASTM method D3359, % adhesion was measured after aging 240h at 300°C using a Gardco PA-2000 adhesion test kit. In Table 1, % adhesion refers to the percentage of adhesion retained after thermal aging. The higher the percentage, the stronger the adhesion of the material to the substrate. The coating transparency, cracking time and adhesion of each coating were recorded.

[0044] Table 1 - Thermal stability test results

[0045] Example Coating transparency Cracking time % Adhesion Example 1 transparent 888h 100 Comparison 1 turbid 480h 100 Comparison 2 transparent 408h 60

[0046] The data show that the blends of epoxy resin and OZ-terminated PPhMS or the more extensively coupled T Ph Resin and T Ph -PPhMS copolymer, the compositions of the present invention exhibited superior transparency, crack time, and adhesion. The example compositions also had a measured resistance of >1000 ohms, confirming that dielectric properties were maintained.

Claims

1. A composition comprising T Ph Resin, T Ph -poly(phenylmethylsiloxane) copolymer and substantially absent ZO-poly(phenylmethylsiloxane)-OZ, wherein each Z is independently H, C1-C4-alkyl or C(O)CH3, wherein said T Ph Resin and the T Ph The w / w ratio of the resin and the copolymer of the poly(phenylmethylsiloxane) is in the range of 15:85 to 35:65, wherein the resin and the copolymer contain Si-OZ groups in a mol% concentration in the range of 7.5 mol% to 12.0 mol%.

2. The composition according to claim 1, wherein the Ph Resin and the T Ph -poly(phenylmethylsiloxane) copolymer in a w / w ratio ranging from 20:80 to 30:70; wherein the composition comprises less than 5 wt% ZO-poly(phenylmethylsiloxane)-OZ; wherein the resin and the copolymer comprise Si-OZ groups in a mol% concentration ranging from 9.0 mol% to 12.0 mol%; and wherein the degree of polymerization of the poly(phenylmethylsiloxane) is in the range of 20 to 300.

3. The composition according to claim 1, wherein the Ph Resin and the T Ph -poly(phenylmethylsiloxane) copolymer in a w / w ratio ranging from 24:76 to 30:70; wherein the composition comprises less than 1 wt% ZO-poly(phenylmethylsiloxane)-OZ; wherein the resin and the copolymer comprise Si-OZ groups in a mol% concentration ranging from 10.5 mol% to 11.5 mol%; wherein Z is H or C(O)CH3; and wherein the degree of polymerization of the poly(phenylmethylsiloxane) is in the range of 40 to 250.

4. The composition of any one of claims 1 to 3, wherein the degree of polymerization of the poly(phenylmethylsiloxane) is in the range of 100 to 200.

5. A method comprising the following steps: Under coupling conditions, ZO-poly(phenylmethylsiloxane)-OZ and T Ph The resin is in contact for a sufficient time to convert the T Ph The total mole % of Si-OZ groups in the resin is reduced by 10 mole % to 30 mole %; wherein each Z is independently H, C1-C4-alkyl or C(O)CH3.

6. The method according to claim 5, wherein the ZO-poly(phenylmethylsiloxane)-OZ is mixed with the T Ph The resin is contacted in the presence of a polar protic solvent at a temperature in the range of 77°C to 150°C for a reaction time in the range of 15 minutes to 10 hours.

7. The method according to claim 6, wherein the solvent is ethyl acetate, propyl acetate or butyl acetate, and the reaction time is in the range of 30 minutes to 2 hours; wherein the method further comprises the step of distilling and removing the solvent.

8. The method of claim 7, wherein the solvent is butyl acetate.

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