“It’s a fiberglass-reinforced pultrusion that comes straight out of our die with a gloss, Class A finish,” says Rob Klawonn, company president. “We produce a very uniform, consistent surface finish for a low cost. We also add some UV inhibitors to the resin mix that gives it a long life as a composite outside; they can last 10 to 20 years in a rugged environment while maintaining a good surface finish without powdering or chalking.” A combination of processing techniques, resin chemistry and tool design enables the company to achieve this result, he says.
Putting on the Veil
Surface veils provide an extra layer of protection for composite parts. They are thin, lightweight materials weighing from 17 to 68 grams per square meter.
“With surface veils, we’re basically putting a fiber into a fabric manufacturing process to impart surface smoothness or to block the underlying reinforcements from blooming to the surface when exposed to UV or corrosive chemicals,” says Brandon Ratcliffe, market manager at Precision Fabrics Group. “The use of a veil creates a resin-rich surface layer that enhances the corrosion properties of the FRP composites. A lot of veils are used in FRP corrosion-resistant pipes and corrosion-resistant tanks that hold aggressive corrosive agents to improve durability and longevity.” The fiber choice and the means by which the veil is made into a nonwoven greatly affect processing and end use performance. Veils can also provide UV protection and fire resistance.
Veils fall into three major categories: glass, carbon and synthetic. Glass veils are common in everyday use because they process very easily and wet out well in compatible resin systems. They’re found in flooring and in corrosion-resistant products where the chemicals don’t attack the glass.
Composite manufacturers use carbon veils in niche applications, such as high-temperature caustic services or where the product needs electrical static dissipation. “FRP is highly insulative, which is great for electrical applications but can result in static charge build up in some pipe, tank or ducting applications. Conductive veil is often specified when there is a fire or explosive hazard, because it allows you to ground the equipment and prevent static build up and fires,” Ratcliffe says.
Both glass and carbon veils must be compatible with the resin they’re going to be used in. That’s not the case with synthetic veils. “They are resin agnostic, so you can use them in any resin system,” Ratcliffe says.
Synthetic veils provide better corrosion resistance with severe pH chemicals such as hydrofluoric acid, sodium hypochlorite and many others, he adds. They also work very well in any composite that is subjected to UV radiation.
Printed veil fabrics can provide graphic characteristics, such as a wood grain or camouflage look. Colored veils enable manufacturers to produce variations of their products without having to completely change over a line.
As with gel coats, a manufacturer’s decision on whether or not to use a veil often comes down to cost. “A lot of it is solving the problem for the right price,” Ratcliffe says. “Imparting improved UV protection is a complex problem to solve and often requires a solution that is more than just a basic veil fabric. You have to put a coating on the veil that incorporates different UV absorbers or antioxidants to improve UV protection. The same is true for improved flame and smoke mitigation.”
Customers are looking for better solutions that they can integrate into their manufacturing processes in one step, Ratcliffe adds. When deciding between veils, gel coats, in-mold coatings and post-paint processes, manufacturers typically consider total cost of the materials, processing cost and manufacturing scrap rates to determine the best way to proceed for their specific solution.
Measured Advances
Progress in surface materials comes incrementally – an improvement in a gel coat’s resin can enhance durability, a new type of fabric can offer better corrosion resistance. But those changes make a real difference over time. One of Ashland’s earliest marina gel coats had an expected lifetime of 1,000 hours; its latest generation of products can reach 4,000 to 4,500 hours.
While gel coat manufacturers are reluctant to give specifics about the new products their companies are working on, they will discuss the industry’s direction in general terms.
Gel coats designed for wind turbine blades provide added protection against abrasion, fatigue, heat, light and moisture. Photo credit: Polynt
“The main drivers of change related to the performance of composite surface finishes include the performance in the field (for example, weathering, water resistance, etc.), economics and environmental/safety issues,” Crump says. One environmental driver has been reduction of the amount of styrene used to make gel coats; manufacturers had to redesign their formulas to get the same properties they had previously offered in higher styrene-content formulas. Regulators are likely to continue the push toward lower styrene content and lower VOC materials in general.
Wilkins believes that ease of application and repair will continue to be a major focus at Ashland and other gel coat providers. “There is a lot of work being done around making gel coat products more forgiving when applied in changing environmental conditions,” he says.
Interplastic has implemented some new quality control rheological tools and techniques that measure how a gel coat is going to spray, level and sag. “Controlling the application characteristics of the coating from batch-to-batch is one way to reduce variation for our customers,” says Crump. “They can spray the same way every time, and it flows into the mold the same way every time.”
Customers and manufacturers are always looking for gel coats with new and different colors to help meet their design needs. Often times these gel coats are required for production on short notice. The use of gel coat quick tint systems, developed to meet this need, has grown over the last several years. Ashland’s Instint™ system, for example, operates similar to a paint mixer by rapidly tinting and mixing clear and white base gel coats to provide customers with just-in-time service.
While gel coat manufacturers work hard to meet the increased expectations of their largest customers, they are also looking for new opportunities. One potential market is construction. Diversified Structural Composite is already producing a garage door component with a class A satin finish.
Certain thinks the construction market could grow. “Gel coat is a pretty versatile material, and with some changes to its mechanical properties it might open up some opportunities,” he says. “Most of the gel coats out there today are designed to be very hard, high-gloss surfaces. But imagine that you had an in-mold coating that was more elastomeric. You could use it for other types of applications where you are not really looking for gloss or cosmetics, but for wearability.”
Gel coats could also play a role in 3-D printing technology. Polynt is working with a partner, TruDesign of Knoxville, Tenn., at the Oak Ridge National Laboratory, where they are producing molds for composite parts using a Big Area Additive Manufacturing (BAAM) printer from Cincinnati Inc. “With BAAM, they are putting down a very heavy bead of material,” says Pauer. “That leaves a very textured, corduroy surface on the mold.”
Researchers have been using a mill to grind off that rough surface, but Pauer thinks they could use specialized coatings and putties that bond well to the current thermoplastic printing materials. “You could under-print the part by ⅛ or ¼-inch thickness, then add a layer that bonds to the printed substrate with a material that is much easier to finish than carbon fiber-filled ABS. Then you can gel coat the mold to provide a durable and repairable mold surface,” says Pauer. “Some initial test results show that the concept works well for prototype and some limited production parts in both traditional open and closed molds, as well as in 350 degrees Fahrenheit autoclave molds.”
The gel coat layer would quickly provide the smooth, hard surface that the composite part makers require. That is, after all, what gel coats and other surface finishes do best.
