Heat Shield for Cookware

Hybrid coatings based on organic polymers and silicones protect pans, exhaust pipes and wood-burning stoves equally well, and silicone resins add a special degree of heat resistance to such coatings.

Coated aluminum pans are part of the basic equipment of every kitchen: they are lightweight, inexpensive to produce and accommodate the demands of modern, health-conscious consumers – because aluminum pans require less oil than their expensive cast-iron or stainless-steel counterparts, they make it possible to prepare fish, omelets and pancakes with much less fat. Resistance to heat, however, had long been the Achilles heel of aluminum pans, which is why ambitious chefs prefer other metals for techniques such as frying steaks at high temperatures. Aluminum pans have improved in that regard too, however, as they are usually coated on the inside with polytetrafluoroethylene – known by the brand name Teflon – and on the outside with a finish based on silicone polyester resins.

“Organosilicone resins allow us to adjust the properties of coatings to match the needs of a given application quite closely.”

Philipp Haas, Marketing Manager at WACKER

Since coated aluminum pans need less oil than their cast-iron or stainless-steel counterparts, they are in line with the trend for healthy, low-fat diets.

“Aluminum pans coated on the outside with silicone polyester resins can remain stable at temperatures of up to 250 °C for relatively long periods of time – even up to 300 °C for short periods,” says Walter Göblmeier, a technical service engineer in the WACKER SILICONES Plastics & Coatings business team in Burghausen. He added that, in contrast, heat resistance is limited in conventional surface coating resins based on purely organic polymers, but improves markedly when silicones and polyester resins are bound chemically.

Crosslinking takes place during baking, where the applied coating layer, once it has evaporated, is heated to between 250 °C and 280 °C for around 10 to 15 minutes. Used as a binder, the organosilicone resin envelops the solid particles in the coating – pigments and fillers – and binds them together and to the substrate. This forms a strong coating, which protects the treated object against external influences.

A look inside Benasedo’s production facilities: headquartered in the Milan metropolitan area, the Benasedo company has been producing alkyd-based and polyester-based specialty resins for coatings and printing inks since 1959. Benasedo uses intermediates from WACKER SILICONES for modifying its organic resins.

Even greater heat resistance can be achieved in silicone resin coatings formulated with no organic component: if made with pigment fillers, these coatings can even withstand temperatures of over 650 °C for brief periods of time. This works best with silicone resins that have not been organically modified, such as those used in coatings for engine components. Because cookware and other household items are not subjected to the kind of punishment that pure silicone resin binders can take, these qualities – which also come at a higher price – are not absolutely necessary and wouldn’t be the first choice for the application either. “While maintaining excellent adhesion to a substrate, organosilicone resins allow us to adjust the properties of coatings to match the needs of a given application quite closely – and we can do that at competitive prices,” says Philipp Haas, WACKER’s marketing manager responsible for silicone resin intermediates.

“Water-based paints are increasingly in demand in markets where sensitivity to environmental issues is high.”

Dr. Tania Trombetta, Technical Manager at Benasedo

Improved Properties

With a 75-strong workforce and an annual capacity of 25,000 metric tons, the Italian company numbers among the major players in its niche on the European market. Benasedo supplies well-known manufacturers of paints and coatings.

The Milan-based Benasedo company, one of Europe’s leading silicone resin producers, likes to use WACKER silicone resins for its modifiers – silicone polyesters that the Italian firm produces on the basis of organic resins. “Benasedo uses our intermediates to modify its organic polymers as a way of improving their properties,” says Göblmeier. These organically modified silicone resins are then sold to major European paints and coatings manufacturers, who use them as binders in their products.

The Italian resin producer has been working with WACKER for over ten years. “Our market is fairly demanding,” explains Dr. Tania Trombetta, technical manager at Benasedo. “The standards of quality are high, products need to be available quickly, and additional quantities sometimes have to be produced on short notice. WACKER has been providing us with reliable support for years. The silicone resin intermediates we produce,” Trombetta goes on to say, “are primarily used in coatings for cookware.” Other applications, of course, such as stoves, ovens and fire pits, benefit from WACKER products as well.

Products coated with silicone polyester resins include exhaust systems and other molded parts. Crosslinking takes place during baking, where the coating layer is heated to between 250 °C and 280 °C for around 10 to 15 minutes.

WACKER provides the Milan company with more than just silicone resins, however – applications expertise is also part of its portfolio. “We support our customers with recommendations for basic formulations,” Haas explains. “In other words, we provide information for a specific formulation, and they can use that information for developing their own formulations.” This support can shorten development times – in some cases by more than half – and saves money. “We bring our many years of experience to bear to help our customers develop innovations,” Göblmeier adds.

Over the past year, Benasedo has been working with WACKER to launch a number of innovations – in part to strengthen its competitive position on the market. “We have no doubt that better quality is what will prevail on the market,” says Trombetta, which is why Benasedo is increasing its investments in the development process. “We want to keep improving the heat resistance of some of our resins – and we want to develop new ones,” the chemist explains. “Our focus also covers water-based coatings, because demand for these is growing on markets where sensitivity to environmental issues is high. So, we’re building on the support from WACKER and its wide range of intermediates and silicone resin emulsions.”

As Walter Pisoni, a sales manager for WACKER in Italy, goes on to observe, “Of course, sustainability is also becoming increasingly important in the paints and coatings industry.” To make coatings in household appliances, for instance, Benasedo needed a product that would not exceed allowable limits for methanol and VOCs (volatile organic compounds). WACKER experts helped their colleagues in Milan develop a low-VOC resin: “Collaboration on the project was very close and straightforward – we were on the phone with each other every day,” recalls Luciano Pau, Benasedo’s sales manager. “Their technical staff gave us good advice, and often came to help us right on site.” Thanks to this spirit of open collaboration, the two companies managed to develop a product meeting all EU environmental standards within just one year.

SILRES® MPF 52 E: Heat-Resistant and Low-Solvent

Alkoxy-functional phenyl methyl silicone resins have been used as binders in heat-resistant coatings for quite some time. SILRES® MPF 52 E is among those binders which contain a silicone resin of this type – one in liquid form. In the new binder, however, the resin is finely dispersed as tiny droplets in an aqueous medium.

This type of formulation has only become possible over the past few years: it used to be the case that an aqueous emulsion of an alkoxy-functional – and consequently reactive – silicone resin could not be stabilized without additional solvent. By using a suitable nonionic emulsifier and skillfully selecting the silicone product, WACKER scientists found a way of formulating a workable, low-solvent emulsion.

Despite its high solids content of 55 to 65 percent, SILRES® MPF 52 E has a low viscosity and can thus be easily processed into coatings by conventional means. Here, it must only be observed that the shear forces on the binder are not too high. Applications tests carried out at WACKER show that SILRES® MPF 52 E is highly suitable as the sole binder for the manufacture of heat-stable coatings. Aqueous formulations of the new binder are tack-free after only 15 minutes.

After baking, sample formulations that contain small aluminum flakes as pigments can resist temperatures as high as 500 °C. The thermal stability of black-paint sample formulations was slightly lower at around 400 °C. The baked coatings adhere well to metal surfaces, exhibiting good chemical and abrasion resistance, losing hardly any gloss after thermal stressing and remaining hard, even in the heat.

The binder can also be used to formulate water-based coatings that, when fully cured, meet the food regulatory requirements of the German Federal Institute for Risk Assessment (BfR) and the US Food and Drug Administration (FDA).

The use of heat-stable coatings based on SILRES® MPF 52 E is thus not restricted to technical objects; they are also suitable for coating cooking utensils, kitchen appliances, barbecue grills and raclette sets.