What is a gelcoat? It is the top layer of composite materials, especially glass fiber reinforced plastics (GRP), and besides increasing the surface appearance quality, GRP is the material that provides the outdoor performance of the product. Generally, gelcoats are based on epoxy or unsaturated polyester resin.
Chemically, gelcoat is obtained from modified high performance polyester resins. Gelcoat CTP is applied to the mold surface in liquid form by brush, spraying or airless spray method during product production. It reaches from liquid form to solid form by curing thanks to the added MEK-P (Methyl Ethyl Ketone-Peroxide). Curing (hardening) occurs with the cross-links formed between polymers, reinforced with subsequent layers, and the classical composite matrix is formed. These reinforcement materials usually consist of polyester, epoxy and vinyl ester resins, and reinforcing fibers are glass fiber, carbon fiber or aramid (kevlar) fibers.
After the produced part hardens sufficiently, it is removed from the mold. The surface that appears when the product leaves the mold represents the gelcoat layer. Since the gelcoat surface usually contains pigment paste, it allows products in different colors to be obtained. The use of transparent color gelcoat without pigment added in the production of artificial marble gives the feeling of depth on the surface.
Today, many marine vessels (yachts, catamarans, etc.) are produced with composite materials due to their lightness and corrosion resistance. The outer layers (shells) of these tools are usually gelcoat between 0,5mm - 0,8mm thickness. When designing high performance gelcoats, they are designed considering chemical resistance, UV (UV) resistance and hydrolysis resistance. Gelcoats used in the molds of composite products are in a structure that can withstand the temperature and mechanical stresses that may occur during production.
Although their chemical structures (ISO, NPG, Acrylic, etc.) and modification types differ, in general, gelcoat types can be listed as follows.
- General purpose
- Post-dyeable gelcoats
- Performance ISO / NPG
- High performance gelcoats
- High performance marine gelcoats
- Flame retardant gelcoats
- Mold making gelcoats
- Chemical resistant gelcoat
- sandable gelcoats
Gelcoats are produced by combining eight basic chemical component groups. In addition to the selected resin, gelcoats also contain pigments, accelerators, thixotropic and plasticizing agents, fillers, inhibitors, monomers and various additives.
The type of resin chosen for a gelcoat formula depends on the intended use of the composite part. Isophthalic (iso) (CE 266 N12, CE 66 N4) and iso / neopentyl glycol (CE 67 HV 4) and orthophthalic (CE 92 N8, CE 188 N8, CE BV 8) resins are generally used in the composite industry. Flexible type, flame retardant type, mold type, chemical resistant type, vinyl ester and other special purpose resins are also used in gelcoat production.
Pigment selection Gelcoat production It is an important input. Choosing the right pigment is important in obtaining the optimum resistance to opacity, weather conditions and crumbling effect. Gelcoat manufacturers avoid the use of lead and chromium-based pigments in order to comply with official standards and be more environmentally friendly.
Thixotropic substances are low weight additives. (usually silica and organic clays) Thixotropic substances prevent the gelcoat from flowing during spraying and then sagging from the vertical surfaces of the mold during hardening.
Accelerators and Inhibitors
Inhibitors and accelerators affect the gelation and hardening time of gelcoats. Gelcoat manufacturer thus it has the opportunity to set the required working time foreseen for the hand lay-up process.
Monomer and Fillers
Styrene monomer is one of the primary ingredients in most gelcoat formulations to adjust the viscosity and make the system easy to work with. They are minerals that work with fillers, thixotropic agents and dispersing agents. It helps to control gelcoat viscosity and pigment ratio (suspension) in the formula, improve opacity, and increase hydraulic stability.
There are many other additives used in gelcoats to achieve specific performance properties. Wetting agents are used to increase the performance of the selected pigments. UV radiation gelcoat Ultra violet (UV) absorbers are used to delay the harmful effects on the layer. Other additives can be selected to overcome surface tension problems and to regulate air discharge as the gelcoat layer hardens. When self-colored products are demanded, gelcoat applied composite parts are preferred.
Marine, plumbing, casting industries are three examples of areas where gelcoat applied composite parts are widely used and accepted.