VEC Shield Eliminates Gel Coat And Post-mold Painting
Thermoformed outer shell for molded fiberglass cuts emissions and provides a stronger, more durable, nearly Class A finish.
By Berry Berenberg, Web Editor/Technical Writer | October 2003
The Virtual Engineered Composites (VEC) closed molding process, developed by VEC Technology (Greenville, Pa., U.S.A.) in the late 1990s, has been an unqualified success for parent company Genmar Holdings Inc. (Minneapolis, Minn., U.S.A.). The computer-controlled resin injection process features a manufacturing cell that comprises two matched composite molds situated between two fluid-filled pressure vessels. Each mold floats on a fluid (usually water) and forms a tight seal over the vessels. Adapted for use on select models from Genmar's Four Winns, Glastron, Larson, Seaswirl and Wellcraft boat lines, VEC improves part quality, cuts layup time by a factor of four, and reduces styrene emissions by more than 90 percent, compared to open molding — garnering environmental awards from the U.S. Environmental Protection Agency (EPA) and the state of Minnesota along the way. Recently, Genmar premiered VEC Shield, the next generation of VEC, which introduces to boatbuilding and fiberglass molding a new surface finishing technology that not only reduces process emissions even further, but is both tougher and more aesthetically pleasing than traditional gel coat, as well.
SAYING GOODBYE TO GEL COAT
Until recently, Genmar's VEC process used a conventional gel coat to achieve a good cosmetic finish. The lower, female mold is gel coated via sprayup, dry reinforcements are arranged on the cured gel coat surface, the two vessels are clamped together, then resin is injected. The water is used to heat the part to cure temperature while the fluid pressure supports the molds. In all, the VEC computer system controls over 500 processing variables. After cure, the mold automatically opens, the upper mold and vessel are lifted off the lower section, and the part is removed. (For a review of the VEC process in greater detail, see CT November/ December 2000, p. 34).
Although gel coats are a standard in the marine industry, they do have some limitations. Application of mold release and gel coat increases layup time. The gel coat must be applied when the mold is open, which allows volatile organic compounds (VOCs) to be emitted. Finally, gel coats are susceptible to cracking, crazing, blistering and other types of environmental damage. VEC Shield overcomes these problems by eliminating the gel coat altogether. In its place, a thin, thermoformed plastic shell is bonded to the fiberglass laminate during the VEC molding process.
BUILDING ON BORROWED TECHNOLOGY
Much of the press surrounding VEC Shield has focused on its marine applications, but a bathtub-and-shower manufacturer drove initial development. Better Bath (Waxahachie, Tex., U.S.A.) manufactures thermoformed sanitary products for the manufactured housing, do-it-yourself (DIY) and export markets. The manufactured housing sanitary market is divided roughly evenly between plastic and fiberglass products. Better Bath has an 80 to 85 percent market share in plastics, according to Better Bath's Rich Clark. Five years ago, the company began looking for a product to compete against fiberglass. The company tried several approaches, such as spraying foam on the back of thermoformed skins, but nothing worked.
Source: Genmar
VEC Shield offers several advantages over conventional gel coats, including a near Class A finish, 10 to 20 percent higher gloss, and (as demonstrated above) an obvious improvement in depth of image.
Then, about three years ago, Better Bath came up with the idea of marrying the VEC process to thermoformed plastics. Sam Hughes, vice president of technology for Genmar and president of VEC Technology, was aware of other efforts to reinforce thermoformed shells with fiberglass, usually by spraying chopped glass onto the shell. These attempts had failed, due primarily to warping problems and the exotherm of the resin during cure. The VEC process, though, could overcome these problems. Maintaining fluid pressure during cure would keep the part from warping, and the flowing water would draw the excess heat away from the part.
Finding the right thermoplastic sheet material, and figuring out how to bond the plastic to the fiberglass, would be key to the success of the program. The two companies brought in GE Plastics (Pittsfield, Mass., U.S.A.) and Spartech Corporation (St. Louis, Mo., U.S.A.) to help with the materials development. Bill Phillips, vice president of sales for Spartech, explains that they started with a GE Plastics WeatherPro-G sheet previously used on the Ford THINK neighbor and the DaimlerChrysler Global Electric Motorcar (GEM). Because the material was developed for vehicles, it already had great chemical and scratch resistance, impact strength, depth of image, and gloss — all properties that would also be important for bath and boat applications. The material is also easily repaired, using the same techniques developed for gel coats and painted surfaces.
Source: Genmar
VEC Shield has passed Genmar's 200+ hour on-water-testing program.
VEC Shield uses a multilayer extruded sheet. A clear, outer acrylic layer provides chemical and scratch resistance, gloss, and depth of image. Just below the acrylic, a second layer composed of Geloy ASA (GE Plastics), available in solid or metallic colors, adds color and provides UV resistance. Phillips says that Spartech will switch to a new Geloy resin, to be introduced in late 2003, that offers better pigment dispersion and more color dimensions. The next layer, Cycolac high-impact ABS (GE Plastics), provides strength sufficient to maintain structural integrity until the shell can be bonded to the VEC composite. The development team further customized the sheet to provide superior adhesion to the VEC composite.
The sheets are produced on extrusion lines with custom dies and machines developed by Spartech. Although thin gauge packaging sheets may have up to seven layers, it is very unusual for heavy gauge sheets to have more than one or two layers. Microscopes are used to check the gauge of the individual layers during extrusion. Surface finish is extremely important, so only virgin materials are used, and the finish is checked continually during the process. The finished sheets are protected with a thin film before shipping on a flatbed trailer. Company wide, Spartech has over 110 extrusion lines. Spartech is increasing the number of lines that can manufacture the specialized WeatherPro-G product, in response to increasing demand for large VEC parts. Current production is handled by the company's U.S. facilites in Cape Girardeau, Mo. and La Mirada, Calif.
