The most commonly used materials in the marine construction industry and in the manufacture of composites are polyester resins. There are several types of polyester resins and they are designed to be used in different areas of industry according to their individual properties. All of these resins use styrene as a cross linker and methyl ethyl ketone peroxide as a catalyst. In recent years polyester resins have become very popular in the powder coating industry, so much so that they have replaced conventional paint in many applications.
Orthophthalic Polyester Resins
Orthophthalic polyester resin is the standard resin that is widely used in the manufacture of composites. This type of resin can be used with a wide variety of base materials such as Kevlar, carbon fibre and fibreglass. In some divisions of the industry it is also used to coat urethane foam and other materials used as a core. These resins harden to a rigid base and can be quite brittle, depending on the base material.
Isophthalic Polyester Resins
Isophthalic polyester resins are used where strength is of paramount importance. These resins shrink and distort far less than orthophthalic resins and are far more resistant to water. It is for this reason that they are used extensively in the marine construction industry, especially in the construction of boat hulls by means of fibreglass moulds. Most yachts and dinghies built of fibreglass use isophthalic polyester resins.
Carboxyl Polyester Resins
Carboxyl polyesters are used primarily for powder coatings and show an extremely high outdoor toughness, being resistant to sunlight and weathering. They can be produced for a variety of finishes from matt to a high gloss. A number of different physical properties can be incorporated into their design, such as chemical resistance, a metallic look and even a leathery touch. They can be used for exterior light fitting, for the automotive industry and for metal and machinery coatings.
Hydroxyl polyester resins
Hydroxyl polyester resins are also widely used in powder coatings but are less robust than their carboxyl counterparts, being less resistant to sunlight and weathering. These resins are more suited to indoor use in such items as appliances, machinery and equipment.