Ming J. Chen

Silanes in High-Solids and Waterborne Coatings

Silanes have been used effectively in solvent-based or waterborne coatings to crosslink binder resins, increase pigment dispersion and improve end use properties, such as mar and solvent resistance and durability. A series of silylated styrene acrylic clearcoats have been prepared and studied in order to understand the chemical and physical parameters that influence the mar resistance and weathering properties of the cured coatings. It was found that the silane content affects the indentation hardness, coefficient of friction, modulus, and toughness of the cured coatings. A relationship between these coating characteristics and mar resistance is demonstrated. In water dispersed and emulsion polymer systems, silanes maximize properties, such as adhesion and solvent resistance. Silanes are incorporated into these systems via copolymerization or post addition. Recent advances in waterborne silane technologies are discussed, including methods of improving formulation stability.

Epoxy silanes in reactive polymer emulsions

Epoxy silanes are effective additives for the crosslinking of carboxy and amino latexes and polyurethane dispersions. A series of epoxy silane additives have been evaluated in both one-pack and two-pack systems. It is found that the structure and water solubility of the epoxysilane as well as the pH of the latex determine silane stability. New water insoluble epoxy silanes achieve long-term shelf stability in emulsions yet crosslink upon application of the coating. Formulating principles, performance improvements, and catalytic cure profiles are reported. Carboxyl-modified waterborne polymer dispersions with post-added epoxy silanes provide curable coatings, in which properties such as mar, chemical and solvent resistance, adhesion, and durability are dramatically improved. In many applications, this approach is a potential candidate for crosslinkable waterborne systems free of aziridines and formaldehyde.