The present disclosure is generally related to two-component siloxane-based coatings.
Polyurethane topcoats are the current technology used to provide protective camouflage, exterior color stability to UV/sunlight, chemical agent resistance, hydrocarbon and chemical resistance, flexibility, first line corrosion resistance, and a host of other properties for a variety of military assets. The majority of polyurethane topcoats utilized by the military are qualified to either MIL-DTL-53039E (Coating, Aliphatic Polyurethane, Single Component, Chemical Agent Resistant), MIL-DTL-64159B (Camouflage Coating, Water Dispersible Aliphatic Polyurethane, Chemical Agent Resistant), or MIL-PRF-85285E (Coating, Polyurethane, Aircraft and Support Equipment). Unfortunately, these polyurethane coatings contain toxic isocyanate-based materials that can cause serious health issues for both coating applicators and the environment, and the development of coating technologies that are both non-toxic and provide equivalent or greater performance (i.e., functional properties and exterior durability) than polyurethane coatings are highly desired by all branches of the military.
Most isocyanates are highly reactive molecules with a high vapor pressure, and airborne exposure to individuals can often result in severe irritation to the eyes, nose, throat, and skin. The spraying (aerosolized particles), brushing, or rolling of materials that contain isocyanates can induce symptoms of asthma, such as coughing, shortness of breath, wheezing, swelling of the arms and legs, and tightness of chest, in addition to hypersensitivity pneumonitis, which is a lung disease whose symptoms include fever, body aches, and cough with phlegm or sputum. The Department of Health Services of California estimates that about one in twenty people who work with isocyanates become "sensitized", meaning that an individual can experience a variety of adverse health conditions from subsequent exposures, even if the exposure is at extremely low levels. To reduce exposure, special personal protective equipment (PPE), such as Tyvek.RTM. suites, nitrile gloves, and forced air respirators must be worn by individuals when applying isocyanate-containing materials, such as the current polyurethane topcoats used by the military.
Advances in organosilicon chemistry have led to the large scale production of "hybrid" materials that contain both organic (e.g., carbon, hydrogen) and inorganic (silicon) segments. Coatings that contain silicon-oxygen bonds possess an inherent durability advantage over traditional organic-based materials. Organosilicon-based materials, such as polysiloxanes, are also relatively non-toxic to humans.
Two-component (2K) polysiloxane coatings, also referred to as "siloxanes", are commercially available by several manufacturers for use in the protective and marine coatings markets. These coatings offer good exterior durability, hardness, and chemical resistance. However, these coatings suffer from low flexibility due to their high crosslink density, which prohibits them from being used as topcoats for military aerospace and vehicle applications.
Disclosed herein is a coating composition comprising: an amine-functional compound, an alkoxysilane-terminated polyurea, and an epoxy- or acrylate-functional compound. The coating composition is a two-component system.