Polyethylene homopolymers, copolymers in VOC-compliant coating systems.

This paper was presented at the Western Coatings Societies' 22nd Biennial Symposium & Show Feb. 20-22, 1995, in San Francisco. Donald Loar and Ann Tiefenthaler are with AlliedSignal Inc. Performance Additives, P.O. Box 1039, 101 Columbia Road, Morristown, N.J. 07962-1039. Phone: (201) 455-2145. FAX: (201) 455-2551.

Introduction

Traditionally, solvent-borne coatings based on alkyd, vinyl, or nitrocellulose resins have had solids in the range of 10-40 percent. Today's higher solids coatings are typically epoxy or urethane solvent-borne systems, powder coatings, or water-borne acrylics or urethanes. These newer coating technologies need modified additives to achieve performance comparable to their lower solids predecessors. This paper outlines AlliedSignal's efforts to respond to the greater demands of compliant coating systems.

In a typical coating formulation, polyethylene additives will migrate to the surface of the coating, forming a thin layer with reduced coefficient of friction, decreased surface tension, and a non-uniform index of refraction compared to a coating with-out polyethylene. The reduced coefficient of friction creates a surface with improved resistance to rubbing and marring from other objects. Decreased surface tension allows the coating to flow and level, creating a smoother, more uniform surface. This is a benefit for high solids systems, which have higher viscosity and surface tension. In addition, a non-uniform index of refraction scatters light destructively and reduces the gloss of the coating. The benefits provided by polyethylene additives offer solutions to problems commonly encountered when formulating compliant coatings.

High solids coatings

High solids coatings (70-100 percent solids) present formulating challenges due to their higher viscosity and increased need for additives to enhance flow, leveling, and other surface properties. Traditional polyethylene dispersions used to improve surface properties are formulated at 10-20 percent solids, in standard coating solvents. If these dispersions were used in high solids coatings they would significantly impact the VOC of the finished formulation. Therefore, it is necessary to use a polyethylene with particle size and dispersion characteristics that allow easy incorporation into high solids coatings. The preferred solution is to use a micronized polyethylene powder with a particle size finer than 25 [micro]m (6 Hegman). These fine particles can usually be dispersed directly into the finished product with normal high shear dispersion equipment. AlliedSignal's ACUMIST(R) …