SILICONE ELASTOMERIC COATING

Abstract

A hydrosilylation curable silicone elastomeric coating composition, which generally has a low viscosity to be self-leveling and/or which is designed for coating transparent substrates (such as glass) is provided, as well as a coated article comprising a substrate coated with a silicone elastomeric coating and the preparation and use thereof. The composition comprises: (i) at least one polydiorganosiloxane polymer having a viscosity of from 0.10 to 1,000 Pa.s at 25° C. and having at least two alkenyl and/or alkynyl groups per molecule; (ii) reinforcing filler comprising an MQ resin and optionally silica; (iii) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule; (iv) a hydrosilylation catalyst; and (v) an adhesion promoter.

Claims

1. A hydrosilylation curable silicone elastomeric coating composition, comprising: (i) one or more polydiorganosiloxane polymer(s) having a viscosity of from 0.10 to 1,000 Pa.Math.s at 25° C. measured using a Brookfield LV CP-52 viscometer at 3 RPM, and having at least two alkenyl and/or alkynyl groups per molecule; (ii) a reinforcing filler comprising an MQ resin in an amount of from 5 to 37_wt. % of the composition, and optionally silica in an amount of 0 to 20 wt. % of the composition, wherein the total wt. % of reinforcing filler present is from 5 to 40 wt. %; (iii) an organohydrogenpolysiloxane, having at least 2, optionally at least 3 silicon-bonded hydrogen atoms per molecule in an amount such that the molar ratio of Si—H alkenyl is greater than or equal to 1:1; and optionally greater than or equal to 1.5:1; (iv) a hydrosilylation catalyst; and (v) an adhesion promoter; and optionally one or more additives selected from the group consisting of adhesion catalysts, pigments, particulate opacifiers, and hydrosilylation cure inhibitors; wherein the composition has a viscosity of from 1 to 100 Pa.Math.s, as measured at 10.0 s.sup.−1 using a parallel plate configuration on a TA Instruments AR2000 rheometer at a temperature of 25° C.

2. The hydrosilyiation curable silicone elastomeric coating composition in accordance with claim 1, wherein the silica of component (ii) is present and comprises fumed silica or precipitated silica.

3. The hydrosilyiation curable silicone elastomeric coating composition in accordance with claim 1, wherein component (ii) comprises the MQ resin and the silica.

4. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, wherein component (ii) comprises MQ resin in an amount of from 5 to 15wt. % of the composition.

5. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, further comprising an opacifier comprising calcium carbonate and/or titanium dioxide in an amount of from 5 to 25 wt. % of the composition.

6. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, wherein component (v) is one or more types selected from the group consisting of alkoxysilanes containing methacrylic groups or acrylic groups, and alkoxysilanes containing epoxy groups.

7. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, comprising one or more pigments and/or colorants in an amount of from 1.0 to 5.0 wt. % of the composition.

8. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, which is self-leveling.

9. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 8, wherein η is from 15 to 100 Pa.Math.s measured at 1.0s.sup.−1 and 25° C., Tan δ is >1.0 for at least 55 seconds, and the resulting coating has a lap shear peak stress of >1.25 MPa.

10. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 8, which is adapted to cure at a temperature of at least 100° C. in 10 minutes or less.

11. The hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, further comprising one or more near infrared reflective pigments.

12. A coated article comprising a substrate coated with a cured coating of the hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1.

13. The coated article in accordance with claim 12, wherein the substrate is glass, nylon, epoxy resin, polyurethane, polyester, or aluminum.

14. A coated article in accordance with claim 12, wherein the substrate is borosilicate glass, soda lime glass, silica glass, alkali barium glass, aluminosilicate glass, lead glass, phosphate glass, alkali borosilicate glass, xena glass, fluorosilicate glass, or a pre-treated glass.

15. A method of providing a substrate with a hydrosilylation cured elastomeric glass coating, the method comprising mixing the components of the hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, applying the composition onto a substrate, and curing the composition.

16. A method of providing a substrate with a hydrosilylation cured elastomeric coating, the method comprising applying the hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, to the substrate, wherein the composition is applied by spraying, brushing, rolling, flooding, squeegeeing, knife coating, or immersion in a bath.

17. (canceled)

18. The coated article in accordance with claim 12, wherein the substrate is optical glass, architectural glass, decorative glass, technical glass, construction glass, structural glass, float glass, shatterproof glass, laminated glass, extra clean glass, chromatic glass, tinted glass, toughened glass, glass bricks, frosted glass and/or bulletproof glass.

19. A coated article obtainable or obtained by coating a substrate with hydrosilylation curable silicone elastomeric coating composition in accordance with claim 1, and curing the composition.

Description

EXAMPLES

[0148] A series of hydrosilylation curable compositions were prepared in two parts. The compositions of the Parts A and B compositions are depicted in Tables 1a and 1b respectively below.

TABLE-US-00001 TABLE 1a Part A Compositions Ex. 1 Ex. 2 Ex. 3 Comp. 1 Comp. 2 (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) Dimethylvinyl terminated 65.46 65.46 65.46 65.46 70.82 polydimethylsiloxane having a viscosity of 2 Pa .Math. s at 25° C. Fumed silica 6.29 6.29 6.29 6.29 12.4 Trimethyl and dimethylvinyl silylated MQ 10.68 10.68 10.68 10.68 — resin Tetra-isopropoxy titanate (TIPT) 1.07 1.07 1.07 1.07 0.6 Calcium Carbonate (stearate treated) 15.5 15.5 15.5 15.5 15.18 chloroplatinic acid divinyltetramethyl- 1.00 1.00 1.00 1.00 1.00 disiloxane complex (effectively 20 ppm catalytic Pt) polydimethylsiloxane having a viscosity of 0.45 Pa .Math. s at 25° C.

TABLE-US-00002 TABLE 1b Part B Compositions Ex. 1 Ex. 2 Ex. 3 Comp. 1 Comp. 2 (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) Dimethylvinyl terminated 48.54 49.05 49.28 49.75 53.56 polydimethylsiloxane having a viscosity of 2 Pa .Math. s at 25° C. Trimethyl silyl treated fumed silica 6.09 6.15 6.18 6.24 12.4 Trimethyl and dimethylvinyl end-capped 11.35 11.46 11.51 11.63 — MQ resin Calcium Carbonate (stearate treated) 14.9 15.04 15.11 15.26 14.9 trimethylsilyl terminated poly(dimethyl, 16.35 16.51 16.59 16.75 16.36 methylhydrogen) siloxane, viscosity 0.03 Pa .Math. s at 25° C. Glycidoxypropyltrimethoxysilane 1.42 1.43 1.42 Methacryloxypropyltrimethoxysilane 0.96 — 0.97 0.96 bis dimethylhydroxy terminated, 0.36 0.36 0.36 0.37 0.36 dimethymethylvinyl siloxane, viscosity about 0.01 Pa .Math. s at 25° C. 1-ethynyl-1-cyclohexanol (ETCH) 0.03 0.04

[0149] For each example the respective Parts A and B were prepared using a centrifugal mixer and were stored at room temperature for a period of 24 hours.

[0150] Parts A and B were then mixed together using the Example 1 composition and 2 mm thick test sheets were prepared by curing the samples at 120° C. for a period of 10 minutes. The elastomeric physical properties of samples were determined and average results are depicted in Table 2 below.

TABLE-US-00003 TABLE 2 Physical properties of Ex. 1 Property Test Method Average Result Elongation at break (%) ASTM D412 Die C 250 Tensile strength (MPa) ASTM D412 Die C 2.5 Shore A hardness ASTM D2240 33.0

[0151] Respective Parts A and B were then mixed together for each example and the resulting mixture was applied by a standard draw down blade technique to produce a 150 μm coating on borosilicate glass substrates and the coated substrates were then placed in an oven and cured for 2 minutes at 150° C. Commercially, a roll coating process would efficiently transfer material from a trough across the roller and onto a glass substrate. It is desirable to have a lower viscosity, self-levelling composition to allow for high speed coating combined with rapid self-levelling followed by quick cure with instantaneous adhesion.

Rheology Characterization

[0152] The rheology characterization of the inventive and comparative materials was generated using a parallel plate configuration on a TA Instruments AR2000 rheometer. The instrument was configured with the base being a Pelletier stage and the upper platen was a 40 mm diameter stainless steel plate. All characterizations were performed at 25° C.

[0153] Information was obtained using a 3-step sequence:

[0154] Step 1: a 5-minute shear break down of the coating: ω=6.28 rad/s (1 Hz), γ=50%;

[0155] Step 2, (which immediately starts at the completion of step 1) was the viscoelastic recovery: ω=6.28 rad/s (1 Hz), γ=0.5% strain and was measured for 30 minutes, used to measure the Tan δvalues.

[0156] These first two steps are representative of the deformation that a coating material is subjected followed by the dwell before being cured.

[0157] Step 3: Measures the continuous flow viscosity, using a controlled shear rate sweep ranging from 100 s.sup.−1 down to 0.1s.sup.−1 rates, in which:

[0158] η=shear stress/shear rate=σ/γ;

[0159] Tan δΔ=G″/G′;

[0160] η*=G*/ω; and

[0161] G*=[(G′).sup.2+(G″).sup.2].sup.1/2 as previously discussed.

TABLE-US-00004 TABLE 3a Rheology Performance Rheology Property Ex. 1 Ex. 2 Ex. 3 Comp. 1 Comp. 2 η at 0.1 s.sup.−1 (Pa .Math. s) 153 142.1 136.6 44.2 497.4 η at 1.0 s.sup.−1 (Pa .Math. s) 20.4 19.9 19.4 10.8 68 Tan δ at 55 s 1.39 1.7 1.79 5.64 0.54 Structuring level low low low low high

[0162] Given the composition when mixed has an apparent viscosity (η) of from 1 to 100 Pa.S as measured at 1.0 s.sup.−1 using a parallel plate configuration on a TA Instruments AR2000 rheometer at a temperature of 25° C., the composition, pre-cure, is of a low enough viscosity to be considered self-levelling as hereinbefore described, with the coating composition being easily spread on a substrate surface such as a glass substrate surface. It was found that for the present composition η (i.e. shear stress/shear rate or σ/γ) was from 15 to 100 Pa.S measured at a shear rate of 1.0s.sup.−1 and 25° C. Compositions made using our composition were also found to advantageously have Tan δ (i.e. viscous modulus/elastic modulus (G″/G′)) at a value of >1.0 for at least 55 seconds indicating a viscous-dominant (i.e. liquid-like) behaviour and as such is then better for flow as it will spread faster and further, hence having self-levelling properties. The coating exhibits a low viscosity and tan 6>1 whilst providing a high Peak Stress of >1.25 MPa measured via a Lap Shear test as described herein. The time for maintaining self levelling behavior is critical in the coating application such that the coating can wet out the substrate effectively prior to curing and being fixed in position. In this regard a tan 6>1 for at least 55 seconds allows the mixed system to adequately flow in the allotted time available during a mass production scenario.

[0163] Comparative example 1 has a low viscosity and high tan 6 making it suitable for making a self-levelling coating, yet without the use of adhesion promoters it suffers from adhesive failure at low stress levels. A composition such as comparative 2 that contains an adhesion package, yet relies purely on fumed silica for reinforcement, does not exhibit a self-levelling character and exhibits a tan 6<1 instantaneous after high shear has ceased. The removal of the MQ resin mean you require more silica to achieve reinforcement, and this alters the rheology making it not as good for a self-levelling coating. In contrast in Comparative 1 there is provided an example of the lack of an adhesion package allows for a good low viscosity self-levelling coating, yet it does not produce sufficient adhesion as demonstrated by the lower force, and combined adhesive/cohesive failure at the glass interface. This is because as indicated above, the shorter the time period a materials has a tan 6>1, the less the material will flow before the elastomeric component minimizes flow. So, comparative 2 actually drops below 1 prior to a data point being obtained. Essentially, the very first data point after thinning the material out by applying a high shear is a tan 6 of about 0.89 @ 18.5 s. So, the larger tan 6, and the longer it is greater than 1 for such a structuring material, the easier it is for the material to self-level and make a good coating from the aspect of being smooth.

[0164] The examples and comparative examples were then assessed with respect to their respective scratch and adhesive performance and the results are provided in Table 3b below.

Scratch Off Failure

[0165] The scratch off failure results were achieved after applying a 0.0039″ (0.99 cm) thick coating layer to 0.25″ (0.635 cm) thick borosilicate glass slides purchased from McMaster-Carr. The layer was then cured and the scratch off force was measured<3 hours after application on to the slides. Excepting the fact that the process was done by hand ASTM D7027 was followed for these tests.

Lap Shear Preparation

[0166] Lap shear testing was performed as a measure of the quality of the adhesion of the inventive coating to the targeted substrate. The protocol used as a variant of ASTM D1002. The variant was that rather than accessing the strength of an adhesive (or glue) to bond two similar substrates, this test was to quantify the strength of the inventive compositions to the targeted substrate of interest, which is the substrate that the coating was applied, per step 1 below.

[0167] The substrate of interest was borosilicate glass (101.8 mm×25.4 mm×3.2 mm) slide was placed in a jig for forming lap shear specimens. A 1.5g portion of adhesive (DOWSIL™ RBL-9694-45M from Dow Silicones Corporation) was applied on top of the coating, and a rectangular aluminum panel (101.8 mm×25.4 mm×1.6 mm) that was primed with DOWSIL™ 92-023 Primer (from Dow Silicones Corporation) was placed into the second half of the jig to form a lap shear joint. DOWSIL™ RBL-9694-45M is a cure in place gasket (CIPG) product that has high bonding strength. The assembly was place in 150° C. oven for 10 minutes and allowed to cool for 5 minutes prior removal of the test specimens. Bond lines of the adhesive were 1.4 mm+/−0.15 mm.

[0168] Step 1. Apply 150 μm coating to the substrate of interest (glass, nylon, aluminum, etc.) and cure.

[0169] Step 2. After 120 minutes and before 180 minutes, seat the coated specimen from step one into the lower portion of a lap shear jig.

[0170] Step 3. Apply a sufficient quantity of adhesive to overlap zone (25.4 mm×12.75 mm×1.62 mm).

[0171] Step 4. Apply a second substrate known to have excellent bonding to said adhesive and press to form bond line.

[0172] Step 5. Cure assembly.

[0173] Step 6. Lap shear force was measured at a crosshead speed of 50.8 mm/min using an MTS Alliance RF/100 Tensile Frame with MTS 2.5 kN load Cell.

TABLE-US-00005 TABLE 3b Coating Adhesion Performance Ex. 1 Ex. 2 Ex. 3 Comp. 1 Comp. 2 Scratch off Failure (N) 4.0 3.5 4.0 2.5 3.0 Lap Shear Peak Stress 1.492 1.684 2.257 0.922 1.558 (MPa) Lap Shear Failure Mode Adhesive Adhesive Adhesive Adhesive/ Adhesive/ cohesive cohesive

Description of Adhesive and Cohesive Failure

[0174] Adhesive—clean separation between two layers [0175] Cohesive—failure within one of the elastomeric materials of interest [0176] Adhesive/Cohesive—mixed failure that exhibit zones of clean adhesive failure along with cohesive failure in the elastomeric material [0177] Adhesive failure Coating/CIPG=the failure occurs as a clean separation between the inventive or comparative coating and the applied adhesive. Hence, the coating to the glass remains intact, and the CIPG remains bonded with the aluminum panel. [0178] Adhesive—Cohesive between coating and glass=specifically, the comparative coating adhesively delaminates from the glass slide and additionally cohesively tears within the bulk of the coating.

[0179] It can be seen from the results observed in Table 3b that a quality coating that has both good scratch resistance and adhesion strength is achievable when the inventive composition is used. Inventive samples 1-3 show how the combination of components create a flowable low viscosity formulation based on a combination of MQ resin, methacryloxypropyl silane, and/or glycidoxypropyltrimethoxysilane silane. These solutions provide sufficient resistance to incidental scratching force (<3N) and when necessary allow for attachments to be applied that would be estimated require high stresses (>1300 kPa) to adhesively remove the coating from the glass.

Introduction of Near Infrared (NIR) Reflective Pigments

[0180] The function of a commercial NIR reflective pigment, Chrome Iron Brown Hematite (PBR29), available from Ferro Corporation, was assessed with respect to the composition of Ex.1 as identified in Tables 1a and 1b above.

[0181] The pigment used, PBR29, a dimethylvinyl terminated polydimethylsiloxane having a viscosity of about 450 mPa.Math.s at 25° C. (hereafter referred to as “Polymer F”). The different compositions are identified in Table 4a below. were prepared as shown in Table 4a below together with a comparative using carbon black.

TABLE-US-00006 TABLE 4a Composition of PBR29 pigment mixtures (wt. %) Composition PBR29 Carbon Black Polymer 1 PBR29 Mix 1 70 30 PBR29 Mix 2 70 30 PBR29 Mix 3 50 50 Comp Mix 20 80

[0182] The compositions of the part A formulation and the part B formulation were prepared as described above and the three components were mixed together in the combinations identified in Table 4b below.

TABLE-US-00007 TABLE 4b compositions of com. 4 and Ex. 4-9 (wt. %) PBR29 PBR29 PBR29 Comp Part A Part B Mix 1 Mix 2 Mix 3 Mix (of Ex. 1) (of Ex. 1) Comp. 3 9 45.5 45.5 Ex. 4 9 45.5 45.5 Ex. 5 16.6 41.7 41.7 Ex. 6 9 45.5 45.5 Ex. 7 16.6 41.7 41.7 Ex. 8 9 45.5 45.5 Ex. 9 16.6 41.7 41.7

[0183] The composition of each example was prepared by mixing the respective components. The resulting compositions were then applied onto sample glass substrates using a draw down bar to obtain a coating thickness on the glass substrate of approximately 150 microns. The coated glass was then cured in an oven at 150° C. for a period of 2 minutes. The % Reflectance of the coating was then taken and recorded at 1500 nm, using a Perkin Elmer Lambda 950 spectrophotometer with integrating sphere. % reflectance was measured from 300-2500 nm, in 2 nm step size, resulting in a spectrum being obtained in about a 4 minute period. The value at 1500 nm was taken and recorded for comparison as shown in Table 4c below. Coated samples are measured with the coated face measured first.

TABLE-US-00008 TABLE 4c Reflectance results % Reflectance of coating, value taken at 1500 nm Comp. 3 1.5 Ex. 4 70.8 Ex. 5 70.5 Ex. 6 65.1 Ex. 7 71.8 Ex. 8 59.3 Ex. 9 58.8

[0184] It will be seen that the introduction of the PBR29 pigment into the formulations had a significant effect on the reflectance of the coatings, especially when compared with com. 3 using carbon black.