Song Zhenwei1, Wang Xiao2, Liu Lizhen2, Pan Jie2, Hou Peimin2, Xu Yuanhao2
(1. Military Representative Office of Naval Station 426 in Dalian, Dalian 116000, Liaoning; 2. Marine Chemical Research Institute Co., Ltd., Qingdao 266071, China)
Abstract: The development history, research status and development prospects of antifouling coatings are discussed.
Key words: environmentally friendly non-toxic antifouling coating; development history; research status; development prospects
CLC number: TQ630.7 Document code: A Article ID: 1009-1696(2015)03-0021-05
1. Development history of antifouling coatings
Antifouling paint refers to a protective coating applied to prevent sea creatures from being stained on ships, marine facilities, pipes, etc., thereby accelerating corrosion, affecting their service life and efficiency. The antifouling paint can keep the water-immersed part of the protected object smooth and free from dirt, and is mainly used in anti-fouling projects such as ships, marine facilities and pipelines in seawater and fresh water.
When the bottom of a ship navigating in the sea is attached by sea creatures, it will increase the navigational resistance of the ship, reduce the speed of navigation, increase fuel consumption, and increase the wear of mechanical equipment parts. The attachment of marine organisms also destroys the protective paint film and accelerates the corrosion of the hull steel plate, which not only increases the maintenance cost of the ship, but also reduces the sailing rate of the ship. The application of antifouling coatings is the most economical and effective measure to prevent the attachment of marine organisms.
More than two thousand years ago, people used a thin lead plate to cover the hull of a wooden shell ship to protect the bottom of the ship. In the 5th century BC, a mixture of arsenic, sulfur and oil was applied to the bottom of the ship to prevent sea otters. Attachment; in the 17th century, people began to use copper plates as antifouling materials for wooden ships; in the 18th century, the British Navy began to use copper extensively to solve the problem of sea creatures' fouling on wooden ships [1]; in the 19th century, with the appearance of steel hulls The accelerated corrosion of copper on steel hulls eventually abolished the antifouling technology of coated copper plates. However, people have realized the killing effect of copper ions on sea creatures, and thus began the history of making antifouling coatings for ship bottom with copper ions as poisonous materials [2].
In 1906, the Navfolk Naval Shipyard in the United States successfully produced an antifouling coating using a thermoplastic resin as a film-forming material. In 1926, the US Navy successfully used rosin in marine antifouling coatings, while using copper and mercury oxides as poisons, increasing the antifouling period of marine antifouling coatings from 9 months to 18 months. The use of organotin as a poison in marine antifouling coatings began in the mid-1950s [3]. Tributyltin (TBT) has been found to have a broad spectrum of high toxicity, and marine antifouling coatings containing TBT poisons have been successfully developed and quickly commercialized [4]. In the 1970s, a long-lasting organotin self-polishing marine antifouling coating (TBT-SPC) was developed [5], mainly based on hydrolyzed tributyltin methacrylate copolymer as a film-forming material, and cuprous oxide. The poison is prepared by adding pigments such as zinc oxide [6-9].
At present, Asia is one of the most polluted areas of organic tin on the earth. Among them, oysters in some ports in Japan and Taiwan have found 100% female phenomenon [10-15]. According to the survey, organotin compounds have been the most toxic substances introduced into the marine environment to date, and TBT pollution has also been found in many waters in China's land [16]. In order to prevent environmental pollution caused by anti-fouling coatings containing organic tin poisons, since the late 1980s, the United States, Britain, France, Japan and some European countries have imposed restrictions on the coating of organotin antifouling coatings. Measures [17-19]: In 1985, the United Kingdom enacted regulations for the control of antifouling coatings; in 1988, the US Congress passed a bill to control the use of organotin antifouling coatings; in 1989, Japan prohibited the use of triphenyl in antifouling coatings. Tin Chloride; In 1995, China issued the 21st Century Ocean Development Declaration, which clearly stated the necessity and urgency of developing pollution-free marine anti-corrosion and anti-fouling technologies. The International Maritime Organization's IMO (International Marine Organization) issued a regulation in October 2000: the final life of the tin-containing antifouling coating is January 1, 2003, and the deadline for the operation of ships coated with such coatings is 2008. January 1. That is, after 2008, any ship coated with tin-coated paint will no longer be allowed to operate at sea [20-21]. This opened the curtain for the development of non-toxic antifouling coatings.
2. Research status of environmentally friendly non-toxic antifouling coatings
At present, the new environmentally friendly non-toxic antifouling coatings mainly include tin-free self-polishing antifouling coatings, low surface energy antifouling coatings, electrolytic antifouling coatings and bionic non-toxic antifouling coatings.
2.1 Wuxi self-polishing antifouling coating
Wuxi self-polishing antifouling coating (TF-SPC) is one of the most advanced research and development in non-toxic antifouling coatings, and it is also one of the main varieties to replace traditional organotin self-polishing antifouling coatings. The main body of this type of antifouling coating is a hydrolyzable polymer with self-polishing properties [22]. Its antifouling mechanism is similar to that of organotin self-polishing antifouling coating, but with other non-tin metals, such as Copper, zinc and silicon replace the organotin in the copolymer. Since the hydrolysis of the polymer itself does not achieve sufficient antifouling ability, it is necessary to use cuprous oxide as an antifouling agent in the antifouling coating, and at the same time, it has to be approved by various national environmental protection departments for use in antifouling coatings. Organic adjuvant biocides [23]. The organic antifouling agent can be quickly degraded and released from the film after being released from the film, so it is less harmful to the marine environment [24]. The copolymers commonly used in Wuxi self-polishing antifouling coatings are mainly copper, zinc, silicon and some low molecular polymers combined with the carboxyl groups of the acrylic copolymer.
Copper antifouling agents have strong antifouling activity on barnacles, pipeworms and most algae, but they are not effective against several algae such as canola, water cloud and curved algae. Algae is the most abundant species of marine attachment organisms. Therefore, the copper antifouling agent must be used in combination with other organic antifouling auxiliaries to enable the antifouling coating to have a broad spectrum of poisoning effects on marine organisms.
2.2 Low surface energy antifouling coating
Antifouling mechanism of low surface energy antifouling coating: The coating has a very low surface energy, and sea creatures are difficult to adhere to the surface of the coating film, even if the adhesion is not strong, and it is easy to fall off under the action of water flow or other external force. Since the low surface energy antifouling coating is based on the physical action of the surface of the coating for antifouling, there is no problem of release of toxic substances, which fundamentally solves the pollution problem of the antifouling coating to the marine environment, and thus becomes the current antifouling coating for ships. One of the research hotspots [25-27]. It is generally believed that when the surface energy of the coating is less than 25 mJ/m2 or the contact angle of the coating with the liquid is greater than 98°, the coating can have excellent antifouling and desorption cleaning effects [28].
2.3 Conductive antifouling coating
Conductive antifouling paint is a coating that passes a weak current on the surface of the paint film to electrolyze seawater to produce hypochlorite ions to achieve antifouling effect. It uses a conductive coating as the anode and a cathode on the bottom of the ship that is in contact with seawater. When a small current passes, it produces hypochlorite ions. Because the concentration of hypochlorite ions produced in seawater is lower than that in tap water, conductive antifouling coatings do not pollute the environment [29]. In the 1990s, Mitsubishi Heavy Industries Co., Ltd. of Japan developed this conductive antifouling coating [30]. Another conductive antifouling coating is an antifouling effect by using a conductive polymer material as an active ingredient in the absence of current. In 1992, China began to develop coatings with conductive polyaniline as the main antifouling agent [31], which was directly coated on bare carbon steel plates and tested for 9 months without marine organisms. Compared with other conjugated conductive polymer materials, polyaniline is inexpensive, has a simple synthesis process, and has good stability. It not only prevents the attachment of marine fouling organisms such as barnacles, but also removes the marine organisms adhered to the previous stage. Jinguang Yang et al. [32] made a series of pollution-free antifouling coatings and coating systems for seawater electrolysis type vinylidene chloride-vinyl chloride copolymer resin. The electrolytic antifouling method is combined with the hull electrochemical protection method. Although the economy is long-lasting, the technical difficulty is great, and because it requires an applied current or a conductive coating, it cannot be used in a large area of ​​the hull, but in a small range. Success has been achieved in small areas, such as power plant drains [33].
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