Reinforced-plastic gel coat

Gel coat In RP processing a gel coat on the outer surface can be used to ensure a smooth surface appearance and a tough surface. It could contain a thin synthetic fiber veil to improve performance of the gel coat and/or a surfacing mat. It is a quick setting plastic and gelled prior to reinforcement layup. The gel coat becomes an integral part of the finished RP product. 

Storage May develop pressure vent bottle periodically Uses Polymerization initiator/catalyst/crosslinking agent for cure of unsaturated polyester resins in gel coats to eliminate or reduce porosity mfg. of acrylic resins hardener for fiberglass-reinforced plastics catalyst in food-contact crosslinked polyesters Regulatory FDA 21 CFR 177.2420... 

Other polyester products include flag poles, doors, waste bins, ski rack enclosures, ski poles, fish hatchery basins, water slides and storage vessels. Many reinforced plastic products are protected by an outer gel coat layer which can be built in during composite construction most easily in hand and spray lay-up processing. 

Embedment decorating n. A technique fur decorating reinforced-plastics articles in which a mat or web of fibrous material printed with a design is embedded in the surface of the article and covered with a transparent gel coat. The technique can be adapted for use in hand lay-up, continuous laminating, pultrusion, and matched-die molding. 

Fiber show (fiber prominence). In reinforced plastics, a condition in which ends of reinforcement strands, rovings, or bundle unwetted by resin appear on or above the surface. It is beUeved to be caused by a deficiency in the glass, and may not appear until the part is fully cured. Remedies include measures to improve wet-out, use of resins of optimum viscosity, and reducing exotherm rates, which cause stresses within the laminate, and gel coating after the main body of the part has partly cured. Harper CA (ed) (2002) Handbook of plastics, elastomers and composites, 4th edn. McGraw-Hill, New York. 

Wet layup In the reinforced plastics molding, the process of forming an article by first applying a liquid resin (sometimes a special gel coat) to the mold surface, then applying a reinforcing backing layer with more resin. 

The process consists of a thin, unreinforced outer coat called a gel coat. The reinforcement (normally glass fibers) mixed with resin (usually polyester) is then applied by hand (lay-up) or via a spray gun (spray-up). When the desired amount of resin and reinforcement is in the mold, the air bubbles are pressed out with a roller. The part is then left to set up which, depending on the size of the part and the amount of resin, can take more than an hour. Consequently, many molds are used when higher production volumes are required. The molds themselves are made of plastic cast from a pattern. As such, they have a very short life and must be replaced frequently. Fortunately, they are inexpensive imfortunately, they are not capable of producing fine detail or close tolerances. Since the mold has only one side, only that side of the part has a finished surface the other side is very rough. The... 

Uses. Two-component polyesters are well known as gel coats for glass-reinforced plastic bathtubs, lavatories, boats, and automobiles. Figure 10.2 shows tub and shower imits using a polyester gel coat. 

Figure 10.2 Polyester gel coats are used to give a decorative and protective surface to tub shower units which are made out of glass fiber-reinforced plastics. (Courtesy of Owens-Coming Fiberglas Corporation.)...

Resin injection moulding is a cold moulding process applied at medium pressures (approximately 450 kPa), where mould surfaces are enriched with release agents and gel coat before GF reinforcement is placed on the bottom of the mould, allowing the plastic to extend beyond the sides of the mould. Then the upper mould is placed in its place and it is clamped to stop followed hy injection of activated resin under pressure into the mould cavity (Figure 9.11). By using this technique, it is possible to obtain a fibre/matrix ratio of 65 wt%. 

Basically a polymer composite contains a polymer and a nonpolymer. While polymer composites include such compositions as foams and some types of gels, this chapter will be restricted to compositions of one or more polymers and one or more nonpolymers in the bulk state. There are a few points of overlap between blends and composites polymer-impregnated wood (where wood itself is a natural polymer blend), and organic fiber (e.g., polyester) reinforced plastics constitute examples. Compositions of special interest to this chapter include glass fiber reinforced plastics, carbon black reinforced rubber, and mineral-pigmented coatings. 

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