Introduction
Vinyl ester (VE) barrier coats are gel coats specially formulated to improve performance of composite laminates. They are used when enhanced blister resistance and help improve cosmetics. One will most commonly find them being used in the marine industry. Under some conditions, their use can also decrease production cycle times.
Materials
Barrier coats and gel coats are made from the same type of materials, however, vinyl ester polymers are typically used in barrier coats. Another difference lies in their usage. Barrier coats are not made to be an exterior coating. When used in this manner, barrier coats quickly chalk and fade.
Application
Barrier coats are applied behind the gel coat before the structural laminate. Vinyl ester barrier coats and gel coats are applied similarly. VE barrier coats should be mixed first. This gives homogeneity to the material and breaks down viscosity for spraying. Barrier coats that are MACT compliant are higher in viscosity and should be no cooler than 75°F when sprayed. If conditions are colder, in-line heaters may be needed to increase the temperature of the barrier coat. In addition, bigger angle tips and hoses may be necessary.
Conventional and low-emission spray equipment can be used with VE barrier coats. Conventional or air-atomized spray, air-assisted airless, or airless applications methods are preferred. Use your product data sheet for specific information.
Correct application of the vinyl ester barrier coat is a must for the performance benefits of VE barrier coats. The thickness of the coat is especially important. A thin coat will result tin undercure, which causes poor cosmetics and blister resistance. A thick coast can cause more cracking.
Performance
When comparing composite parts made with a barrier coat to those made without one, greatly reduced blistering is apparent. A decrease in osmotic blistering is achieved by two properties. First, the vinyl ester polymers in the barrier coat have low water-absorption. Additionally, a VE barrier coat helps move air bubbles away from the surface gel coat, making for a better finish. Blistering and cosmetic defects are a result of laminate porosity where the gel coat and laminate meet.
Vinyl ester barrier coats better laminate cosmetics as well. VE barrier coats decrease fiber print-through and distortion. When a barrier coat is used, the distance of the laminate’s reinforcing fibers, balsa, and other structural parts from the gel-coated surface is increased. This reduces the effect of these features on laminate cosmetics.
Vinyl ester barrier coats also decrease dimensional changes, or shrinkage, of the laminating resin during post-demold curing. VE barrier coats are two to three times stronger than the typical pigmented gel coat. Because of this, the added thickness can be applied with no increased risk of cracking, which is seen with thick gel application.
Not only are there performance benefits, but there are production cycle benefits to VE barrier coats as well. Fabricators have found that their use speeds up production cycles in comparison to laminates made using a conventional skin coat. In order for the cosmetic benefits of a skin coat to be achieved, it must be left to cure completely before laminate application. In contrast, a vinyl ester barrier coats needs only to be tack-free before laminate application. A tack-free condition in a vinyl ester barrier coat is achieved much more quickly than a conventional skin takes to completely cure.
