Turn up the Heat

Silicone-based paints and coatings withstand temperatures of up to 600 °C. WACKER now presents two new binders for heatresistant coatings: SILRES^® M 51 E and SILRES^® IC 900. Manufacturers can use these to expand their portfolios to include water-based coatings, as well as both high-solids and high-build formulations.

When Germans want to say that something is less valuable or attractive than it used to be, they say “the paint’s come off.” And for commercial goods, a flawless surface with a high-quality coating is indeed a sign that the product works as it should and has high value. But for this to be the case, a coating has to be fine-tuned to the surface on which it is applied and to the environmental conditions – heat, for example – to which it will be exposed when the product is used. Specialized, heat-resistant coatings lend themselves well here. After all, unsuitable coatings would flake off from the substrate or be destroyed by oxidation after a short time.

Heat-resistant coatings are needed in automotive engineering and the process industry, as well as in private households. In many vehicles, for example, heat-stable coatings are applied to the exhaust system and to various parts mounted close to the engine. Piping, furnaces, flues, smokestacks and heat exchangers in industrial processing plants need to be protected from high temperatures and, in most cases, from the elements. And in households, heat-resistant paints ensure that stoves, stove pipes, chimneys, water heaters, stove tops, barbecue grills and raclette sets still work well and look good after years of service.

For applications like these, WACKER will be presenting two innovative silicone resin binders to a broad industry audience at the 2023 European Coatings Show: SILRES^® M 51 E, which is suitable for formulating waterbased coatings, and SILRES^® IC 900, which is processed by conventional methods – using organic solvents – and can be used in high-build and high-solids coatings alike.

Many of the solvents still commonly used in the paints and coatings industry are volatile organic compounds (VOCs). “The use of organic solvents has come under increasing scrutiny, however, and is subject to government regulation as well,” says Philipp Haas, marketing manager for Performance Solutions at WACKER SILICONES. “This is putting the paints and coatings industry under intense pressure to reduce the use of solvents in their products.”

For companies working to comply with more stringent government regulations, water-based coatings represent an excellent alternative to conventional solvent-based products. This also applies to heat-stable liquid coatings. Among coating systems designed for high-temperature applications, liquid coatings hold a market share of over 80 percent. “But only a relatively small portion of heat-stable liquid coatings are currently water-based,” Haas explains. “Part of the reason is because there weren’t any suitable binders for those kinds of coatings.”

When WACKER comes to ECS 2023, it will unveil SILRES^® M 51 E, a new aqueous, emulsion-based silicone resin binder promising relief. “Silicone resins like these, which are used as binders in heat-resistant coatings, generally crosslink at elevated temperatures to form a tough film that can withstand high temperatures,” explains Christian Putz, who heads up an applications laboratory for the Performance Solutions business unit of WACKER SILICONES. “That’s why as binders, they play the key role in curing the coating.”

SILRES^® M 51 E cures over a period of 30 minutes at 220 °C to 260 °C. The silicone resin envelops the solid particles present in the coating – pigments and fillers – and binds them, both to each other and to the substrate. “That produces a strong coating,” says Putz, “which protects the treated object against external influences.”

After crosslinking, cured silicone resins are characterized by their extended, close-meshed silicon-oxygen backbone, i.e., by their silicone- resin network. Organic components – generally methyl and/ or phenyl groups – bond to this inorganic foundation, which exhibits extraordinary chemical stability. The organic groups’ key influence is on the coating’s properties before baking.

Pure methyl resins are also notable for their exceptional hardness, excellent mechanical resistance and very good resistance to chemicals and the elements. Thanks to their high concentration of inorganic components, products like these also develop far less smoke the first time they are heated than is the case for binders containing large quantities of organic components.

Methyl silicone resins have been used as binders in conventional heat-resistant, solvent-based coatings for a long time. The new SILRES^® M 51 E coating binder likewise contains this type of silicone resin, which is finely dispersed in the form of tiny droplets within an aqueous medium.

When a coating has to be highly resilient and processing conditions are difficult, for example, protecting chemical plants with complex geometries against corrosion, so-called high-build coatings are used. “High-build coatings do an especially effective job of protecting the metal substrate and are easier to use than conventional coatings, which have to be applied in relatively thin layers that can’t vary in thickness,” Haas explains. High-build coatings, in other words, make jobs such as maintenance work easier to carry out, especially in places that are difficult to access. For applications like these involving solvent-based, heat-resistant coatings, WACKER has developed SILRES^® IC 900 – a pure, undiluted active ingredient that, depending on the application and the coating formulation, will crosslink at temperatures between 100 °C and 280 °C.