Heat resistance and corrosion protection have been key drivers for the development of methyl/phenyl silicone resins, but current products are limited for high solids, low VOC formulation and longer life cycles. Oven curing silicone binders either use HAP's solvents or provide limited durability and ambient curing resins require complex combinations of catalyst.
This paper presents a new HAP's free silicone resin and a novel high solids NISO hardener as solutions for the high heat resistant coatings market where ambient curing and excellent corrosion protection are required. This new hardener is shown to be heat stable and offer improved weatherability and anti-corrosive properties when used together with the latest HAP's free methyl/phenyl silicone binder and other high solids silicone resins, compared against traditional oven curing systems. The combined performance properties along with the ease of handling and low VOC's offer the possibility to fulfill the evolving global regulations regarding environment.
For many years coatings based on methyl/phenyl silicone resins have proven to be one of the most effective and reliable products within the high heat and protective coatings segments. Their inorganic characters along with the methyl/phenyl modification provide outstanding long term thermal stability, attractive corrosion protection, weather resistance and good mechanical properties [3]. In general, silicone resins for high heat applications can be categorized into two sub-groups: i) oven curing and ii) ambient temperature curing systems.
In the case of typical oven cured silicone resins, the polysiloxanes have little-to-no alkoxy functionality [1]. This results in polymer structures of higher molecular weight and limits the resin solids content a formulation can support, compared to more highly functional ambient curing resins. The few remaining alkoxy functional groups crosslink at approximately 250°C and 30 minutes of curing time. Estimations based on typical applications for this type of high heat coating show that oven curing can consume 160 – 260 kJ per square feet of coated surface, depending on the oven efficiency and the ratio between the coated surface area and its mass.
