Marine paints and coatings are applied to ships’ hulls to protect them from corrosion when at sea.
The marine coating consists of a pigment diffused in a liquid called a vehicle. When this is spread thinly, the vehicle changes over time, turning it into a dry film with adhesive properties.
The drying phase undergoes one of these processes:
- When the vehicle has solid resinous material dissolved in a combustible solvent, it will evaporate to leave a dry film.
- If the vehicle includes linseed oil, the vehicle will create a film of dry paint through a chemical reaction with the air.
- A dry paint film is produced by a chemical reaction between the vehicle’s reactive ingredients after its application, either by mixing the separate reactive ingredients before application, the ingredients’ reaction to higher temperatures, or diluting the reactants with a solvent. In the latter process, the reaction happens while the paint is still in the can.
Vehicle types of paints that prevent corrosion
Marine coatings, such as the marine paint by Durabak, have different vehicle types.
- Pitch or bitumen.The solution is typically available in a solvent such as white spirit or naphtha. The pitch or the bitumen can be heat-blended with other materials to produce a vehicle.
- Oil-based.The materials may comprise vegetable drying oils like tung oil or linseed oil. Driers are added to accelerate the drying time by the natural reaction with oxygen.
- Alkyd resin.This type of vehicle improves the drying time and film-forming properties of the drying oil. The main ingredients are acids and alcohol. Alkyds may be made with oil-free acids or oil-fatty acids.
- Oleo-resinous. This vehicle mixes artificial or natural resins with drying oils. The reaction of the resins with the oil will hasten the drying time of the vehicle. Other resins need heat so that the resin can dissolve and the oil to form a body.
- Chemical-resistant.A chemical-resistant vehicle resists severe exposure conditions. This type includes epoxy resins, epoxy resin/coal tar, isomerized rubber, and chlorinated rubber, polyurethane resins, vinyl resins, and zinc-rich paints.
- Epoxy resinsare made from natural gas and petroleum and provide excellent chemical resistance and adhesion. The resins are tough and flexible. They are more expensive because they are filtered during their manufacturing to remove unwanted side products.
- Coal tar/epoxy resinis almost similar to epoxy resin, but the vehicle comes as a two-pack product. The resin and the coal tar pitch are blended before use.
- Isomerized rubber and chlorinated rubber. The isomerized rubber is chemically produced from natural rubber. The chlorinated rubber is plasticized, and both are made from natural rubber. When mixed with organic solvents, the vehicle has more solid content, so it is thicker, making it more resistant to alkalis and acids.
- Polyurethane resins.Urethane is produced by the reaction between compounds that contain hydroxyl and isocyanates. The paints have several properties, such as weather and chemical resistance, resistance to abrasions, high gloss, hardness, and toughness. However, polyurethane resins are not used underwater on steel ships. They are more applicable to yachts due to their high gloss.
- Vinyl resinsare produced through the polymerization of the vinyl group’s organic compounds. They produce very thin films when dry due to the mixture’s lack of solids, requiring the vehicle to be applied in several coats. The steel must be coated with a primer before applying the vinyl resin, but it is very effective as an underwater protector of steel hulls.
- Paints rich in zinccontain a sufficient quantity of metallic zinc to ensure that the electrical conductivity can cathodically protect the steel.
Knowing the characteristics and properties of marine paints will help you choose the right vehicle to use on a ship, yacht, or boat.