1. Harm of attached organisms to ships and marine facilities
Antifouling paint is a special paint applied to the underwater part of marine ships. Its main function is to prevent marine organisms from attaching and fouling, and to keep the surface of ships and other marine facilities immersed in water clean.
Vessels in seawater are all deeply attacked by marine organisms, especially in the southeast and southern oceans. Wooden ships are rapidly corroded by shipworms, and steel ships are attached by marine organisms, resulting in reduced speed, increased fuel consumption, and accelerated corrosion. In addition to causing economic losses, they pose a greater threat to safety.
Tests have proved that Qingdao Zhonggang can attach more than 20kg of organisms per square meter in a peak growth season; the cooling water pipeline (φ2000mm) of the power plant loses an effective diameter of 50~100mm every year. Statistics show that if the bottom of an ocean-going ship with a capacity of more than 10,000 tons is polluted by 5%, the fuel consumption will increase by 10%, and the annual economic loss will exceed 1 million US dollars. The speed of a warship is the basis of its maneuverability and combat effectiveness. The fouling of the bottom of the ship, the fouling of the sonar cover, the biological blockage of the seabed door and the seawater pipeline will all affect the combat effectiveness. Docking maintenance has caused huge economic losses. Cage culture also causes fish kills due to biofouling clogging the mesh.
According to reports, the annual increase in oil consumption by 10-15% in the United States due to marine biofouling is about 50 million U.S. dollars, and that of the British Navy is about 4 million pounds.
Preventing biofouling is one of the focal issues of the marine industry.
Marine fouling organisms are divided into two categories: plants and animals. Among them, there are 600 species of plants attached to ship hulls and structures in the sea, about 1,300 species of animals, and 50 species are common. The larvae or spores of these fouling organisms can swim or float, and after growing to a certain stage, they go to the bottom of ships and underwater structures to settle down.
Among the fouling organisms, the most threatening attached plants are seaweeds: diatoms, enteromorpha; attached animals include barnacles: red barnacles, triangular barnacles, etc.; molluscs: oysters, sea squirts, shellfish; bryozoans : lime worm, etc.; sponges: lime sponge, etc. The coastal fouling organisms in my country are mainly barnacles, oysters, bryozoans, hydra, and sea squirts.
Second, the role of antifouling coatings
Essentially, antifouling coatings are meant to provide a coated surface that is free of biofouling for a specified period of validity. It can adopt different antifouling principles, but the most practical one is to use antifouling agent to effectively control the concentration of poisonous materials and inhibit biological adhesion. This requires that the antifouling coating can meet the requirement of controlled and slow release of antifouling agent, that is, there is a stable and effective antifouling agent exudation rate—the exudation amount of antifouling agent per square centimeter per day. Its antifouling effect is mainly determined by the exudation amount (exudation rate) of antifouling agent in the paint film. After the poison dissolves, it oozes into the seawater and forms a thin layer of toxic solution on the surface of the paint film to resist or kill the spores or larvae of marine organisms that try to stay on the paint film. The minimum exudation rate of the poison material required to prevent marine organisms from attaching is the critical exudation rate. If the exudation rate is too high, it will cause food costs and shorten the life of the coating. If the exudation rate is low, it will not be enough to play an antifouling role.
Anti-fouling coatings also require: good adhesion with the anti-rust paint film on the lower layer, and no mutual solubility between layers; the paint film has good seawater impact resistance and long-term immersion resistance.
