TECHNOLOGICAL CAPABILITY
Antifoulings: antifouling mechanisms
Silicone-based antifouling coatings are available in both biocide-free fouling-release systems and formulations containing biocides, and both types continue to be used in the market depending on vessel operation profiles and customer requirements. Biocide-free systems are selected where fouling-release performance is prioritised, while biocide-containing systems are applied to enhance antifouling performance under wider operating conditions.
Recent developments focus on improving overall efficiency by combining silicone-based low surface energy technologies with optimised coating design to reduce hull fouling and maintain performance over extended service intervals.
Hydrolysis antifoulings
Hydrolysis antifoulings react with seawater, gradually dissolving the coating surface and exposing fresh coating underneath. Therefore, this mechanism continuously maintains a smooth coating film surface and sustained antifouling performance. Another advantage is the ability to control the effective duration of the antifouling effect by changing the coating film thickness. This is currently the most popular type of antifouling.
The antifouling coating film contains a hydrolysis polymer (high-molecular-weight polymer) and biocides.
In seawater, the coating constituents change from hydrophobic to hydrophilic, gradually dissolving the coating film surface layer and releasing biocide components while exposing a fresh coating surface.
As the coating surface is renewed uniformly, long-lasting antifouling performance can be maintained.
Hydrolysis antifouling mechanism
The crosslinking zinc (acrylate) polymer used in SEAFLO NEO CF PREMIUM undergoes a controlled hydrolysis reaction characteristic of self-polishing antifouling systems. As a result, the hydrolysis proceeds in a stable and continuous manner, providing excellent long-term and uniform coating performance.
When the hydrolysis reaction does not progress smoothly, a hydrolyzed layer that prevents the release of biocides forms on the coating surface.
CMP’s newly developed crosslinking zinc (acrylate) polymer forms an extremely thin hydrolyzed layer on the coating surface, which allows the optimal release of biocides.
Hydration antifoulings
Hydration antifoulings use polymers that have an affinity for seawater and are slightly soluble.
Biocides in the coating film are slowly released into seawater through a hydrated layer formed by seawater penetrating the coating film, while this hydrated layer is gradually renewed by the shearing action of water during vessel operation.
Compared to hydrolysis antifoulings, hydration antifoulings have slightly lower antifouling performance, but are suitable for pleasure craft moored for long periods and use in areas of fresh or brackish water. More recently, a hybrid-type antifouling that combines the features of hydrolysis and hydration antifoulings has been developed.
Although hydration antifoulings typically use polymers with an affinity for water, unlike hydrolysis antifoulings, the polymer matrix itself does not undergo a chemical reaction in seawater.
Water penetrates the coating film, forming a hydrated surface layer, and biocides are gradually released into the water through this hydrated layer.
The hydrated layer is dissolved and renewed by the shearing action of water during vessel operation. As biocide release is dependent on the coating’s affinity for water, this hydration mechanism is effective in both seawater and fresh water.
Silicone-based antifoulings
Silicone-based antifoulings are mainly composed of silicone rubber, do not contain biocides, and create a low-adherence barrier that prevents the adhesion of marine organisms based on the elasticity, water-repellent properties, and smoothness of the coating film. Silicone-based antifoulings create surface properties that make the adhesion itself unstable and encourage the detachment of marine organisms.
In recent years, silicone-based antifoulings have emerged that are formulated with small amounts of biocides to improve their antifouling effect.
Adhesion of contamination and marine organisms is reduced by a highly water-repellent coating surface with low surface free energy.
The surface of silicone-based coating is smooth enough that marine organisms have difficulty gaining a foothold, while a degree of elasticity in the coating creates a so-called trampoline effect that prevents stable adhesion.
Adhered contamination and marine organisms are removed relatively easily by the shearing action of water during vessel operation.