The excessive use of fossil energy has led to the increasingly severe climate change and energy crisis in the world. This has caused more and more attention from governments, and the development of new energy sources is imminent.




    Wind energy is an inexhaustible resource in nature and a clean energy with great potential. In the past five years, the global wind power market has maintained rapid growth, and the cumulative annual growth rate of cumulative installed capacity has reached 16.9%. In 2014, the world's new installed capacity exceeded 50 GW for the first time, of which the newly installed capacity on land reached 48.8 GW, and the newly installed capacity on the sea was 2.3 GW. According to the forecast of the Global Wind Energy Council, the cumulative global installed capacity will increase at a compound annual growth rate of 12.9% in the next five years.




    With the rapid development of China's economy, increasingly serious environmental problems and energy waste have become a major problem facing the government. China has a vast territory and a long coastline. The special geographical location contains extremely rich wind energy resources. In the 11th Five-Year Plan of 2005, it was explicitly proposed to support the development of new energy sources such as wind power. Since then, China's wind power industry has ushered in rapid development. In 2010, the government issued a document requesting an increase in the level of wind power technology and equipment, and determined the strategic position of the wind power industry.




    In 2014, China's new installed capacity reached 23 GW, a year-on-year increase of 44.2%. After nearly 10 years of development, China has now become the world's largest wind power market.




    1 Protection of wind turbine blades




    The wind blade materials currently on the market are mainly fiber reinforced epoxy resins and unsaturated polyesters. Wind turbines are subject to many harsh environments, such as large temperature differences, strong light, sand abrasion, acid rain corrosion, and snow and ice. When the blades are running at high speed, the tip speed is generally over 100 m/s. Long-term exposure of the blade to the natural environment quickly wears, ages and pulverizes until it breaks. In addition, the lifting of large blades is time consuming and expensive, and it usually takes more than 10 years to perform maintenance. The simplest and most effective protection method is to use paint for protection. Different environments have different requirements for wind power blade protective coatings. There are two main types:




    1) Inland protective coatings. At present, more than 90% of wind turbines are working on land. The working environment is often strong, and the sand and temperature difference are large, such as the western part of China. This requires that the blade protective coating must have excellent weatherability, impact resistance, wear resistance and high and low temperature flexibility. In addition, these places tend to be cold in winter, with more rain and snow. Blade ice coating seriously affects power generation efficiency and greatly shortens the service life of the blades. Therefore, anti-icing performance is also an important indicator.




    2) Protective coatings for marine use. The ocean has huge wind resources, and European countries are at the forefront of offshore wind power. In 2011, a total of 1,247 offshore wind turbines from 49 wind farms in 9 countries including the United Kingdom, Denmark, the Netherlands and Belgium generated 3.294 GW. In 2014, the cumulative installed capacity at sea has reached 8.771 GW. It is estimated that by 2020, the total installed capacity of offshore wind power will reach 40~55 GW, accounting for 10% of the demand for electricity in Europe, and will increase to 17% by 2030. Future offshore wind power will be the fastest growing new energy technology. China's offshore wind power is in rapid development. For example, the Shanghai Donghai Bridge and the Lingang offshore wind farm under construction will lead the development of offshore wind power in China. Due to the influence of the marine environment, offshore wind power protective coatings require excellent corrosion resistance in addition to excellent weather resistance and high and low temperature flexibility. In addition, excellent icing resistance is also essential.




    Whether it is inland protective coatings or marine protective coatings, it is essential to have excellent adhesion to the substrate, chemical resistance and rain erosion resistance. The leading edge of the blade is the thinnest part of the blade, usually the curved surface, which is most vulnerable to wind and sand abrasion and rain erosion. The protection of the leading edge of the large blade is a very important task, which directly determines the service life and working efficiency of the blade. Traditionally, the method of filming on the leading edge of the blade is used to protect it, but air turbulence and many noises are generated during blade operation, and it is easily damaged by ultraviolet rays, and secondary maintenance of the film is also very difficult. Foreign protection of this part is very important, and currently it is protected by coatings. Therefore, the protective coating of wind power blades needs to have many excellent properties in order to prolong the service life of the blades and improve work efficiency. Resin is the most important factor affecting the coating of the blade. For the research of the resin, many work has been done at home and abroad. The resins currently applicable to the wind blade are mainly polyurethane resin, acrylic resin, fluorocarbon resin, silicone resin and epoxy resin. .


    2 Research on resin for wind power blade coating




    2.1 Polyurethane resin




    Polyurethane resin has excellent wear resistance and high and low temperature flexibility. Among them, aliphatic polyurethane has excellent weather resistance and is the most used resin in wind power blade coatings. At present, the more mature blade protective coatings are generally polyurethane systems, mainly composed of elastic polyurethane repair putty, polyurethane primer and polyurethane topcoat.




    Research on coatings for wind turbine blades has already been carried out abroad. In recent years, there have been many studies on coatings for leading edges of blades. The blade front edge repair topcoat has high requirements for sand abrasion resistance and rain erosion resistance. Due to the different climate environments at home and abroad, foreign countries have carried out a lot of work on the rain erosion resistance of blade coatings. Polyurethane topcoats are often used. Kuehneweg et al. prepared a two-component polyurethane-based protective coating that can be applied to wind turbine blades. It was found that the hydroxyl component has a great influence on the mechanical properties of the paint film, and the high molecular weight and low molecular weight polyether polyols are mixed. The paint film has better tensile strength and elongation at break. After 3 h of rain-resistant corrosion test, the paint film has no change. After 9 h, there is only a slight corrosion damage, which can effectively protect the leading edge of the blade. Connel et al. prepared a multi-layer coating system for wind turbine blade protection, consisting of epoxy primer and polyurethane topcoat. The topcoat with the increase of NCO:OH ratio, the rain-resistant performance increased, and the contrast was different. After the effect of the resin topcoat on the rain-resistant performance of the leading edge of the blade, it was found that the rain-resistant performance of the polyurethane resin topcoat was better than that of the fluorine-modified acrylic resin and the polyurea resin topcoat, up to 3.5 h. Kallesoee et al. believe that the elasticity and wear resistance of wind power blade leading edge protective coatings are equally important. They prepared a series of two-component polyurethane topcoats composed of polyols and isocyanates of different functionalities and relative molecular masses. It was found that the polyol component contained at least 50% of the polyester polyol, and the relative molecular mass was 200~. Between 3000g/mol, the isocyanate component functionality is between 2 and 3, and the relative molecular mass is between 250 and 2000. The obtained polyurethane topcoat has no change after 4 h of rain erosion test and can effectively be applied to the wind turbine blade. Edge protection.




    Limited by the rain-resistant detection conditions, the domestic research on the application of polyurethane coatings on wind turbine blades mainly focuses on elasticity and wear resistance. The sand in the inland area is the main way to damage the blades. Polyurethane can be used to obtain coatings with excellent elasticity and wear resistance by selecting different types of polyols. Zhonghao North Coatings Industry Research and Design Institute Co., Ltd. prepared a corrosion-resistant and impact-resistant polyurethane coating using elastic hydroxyl resin. The elastic hydroxy resin is prepared from caprolactone polyol, polycarbonate and isophorone isocyanate, and the result of the falling sand of the top coat is 32 L/μm, and the result of the falling sand after 4 d of water resistance is 29 L/μm. It is applied to high-humidity environments with high requirements for impact and corrosion resistance, such as offshore wind farms.




    Jiangsu Haiyan Coating Co., Ltd. discloses a coating for wind turbine blade, which is made of a high hydroxyl value polyester polyol and polyether polyol. The stone impact resistance can reach 7A and the adhesion can reach 9 MPa. Used in wind turbines. Zhang Ruizhu and others sprayed an elastic polyurethane protective coating on the turbine blades. The coating has excellent comprehensive mechanical properties, and the physical bonding force with the turbine blades is 12.6 MPa, and the wear value is maintained at 2~3 mg/min. Solve the problem of impeller abrasion in water conservancy and hydropower projects and irrigation and drainage projects.




    At present, the wind power blade coating market is basically a polyurethane system. For example, PPG's HSP7401 polyurethane primer, AUE5000 polyurethane topcoat system and Selemix DTM series of bottom-bonded polyurethane coatings have been applied to the market; 3M's W4600 polyurethane topcoat has a rain-resistant test up to 10 h, sand-resistant Corrosion test >30 g/cm3, wear resistance <30 mg (CS-10, 1000g/1000 r), also put on the market, mainly used for sand erosion and rain erosion protection of the leading edge of the blade; WU200 of Mecca The polyurethane gel coat can pass the 9 h rain-tolerant test, and the rain-tolerant time is basically unchanged after artificial accelerated aging for 4000 h, which can protect the leading edge of the blade well.




    Today, with the increasing emphasis on environmental protection, high solids and waterborne polyurethanes are used in wind power blade coatings. Polyaspartic acid ester is a kind of high solid and low viscosity amino resin, which has good thick coating property. The coating prepared by reacting with aliphatic isocyanate has excellent wear resistance and weather resistance, and can be considered for wind power blade coating. Layer, but it is expensive and has poor flexibility. It is generally necessary to use an elastic curing agent to obtain an elastic coating, but it can play an important role in places where wear resistance and weather resistance are high. The application of waterborne polyurethane coatings on wind turbine blades has also been reported, but it is still at a disadvantage in terms of process and price compared with solvent-based polyurethanes. However, with the development of waterborne polyurethane technology, it is expected to play an important role in wind turbine blade coatings. The role.




    2.2 Acrylic resin




    The hydroxy acrylic resin has excellent weather resistance and gloss and color retention. The two-component acrylic polyurethane coating made of aliphatic isocyanate as a curing agent is widely used in the automotive and aerospace industries, and is an excellent outdoor coating. In the past 20 years, China has also done a lot of work on acrylic polyurethane coatings, and has begun to use it for wind power blade protective coatings [27-28].




    Coatings made of hydroxy acrylic resin tend to have excellent weatherability and hardness, but are not ideal in terms of flexibility, impact resistance and abrasion resistance [29]. Currently, polyester resins are generally used for modification. Zhou Shujun used E-10 (glycidyl glyceryl carbonate) synthetic polyester prepolymer modified acrylic resin and pure acrylic resin, and prepared into a topcoat respectively. The performance comparison results showed that the surface made of polyester modified acrylic resin The flexibility and impact resistance of the paint are significantly increased, and the hardness of the paint film can be well balanced. Li Rujian et al. used a combination of acrylic resin and polyester to prepare a coating that can be applied to wind turbine blades and compared it with an imported brand sample. It is found that with the increase of the amount of acrylic resin, the weather resistance of the coating film becomes better; and when the amount of polyester polyol is increased, the impact resistance, adhesion and abrasion resistance of the product are improved. The wear resistance and adhesion of the developed products are better than that of an imported product, and the weather resistance is equivalent to that of an imported product.




    The polyester modified acrylic polyurethane system can significantly improve the flexibility, impact resistance and wear resistance of the paint film, but it will reduce the weather resistance and low temperature elongation of the paint film. Sun Wei et al. compared the stone-resistance performance of topcoats made of acrylic polyurethane, polyester modified acrylic polyurethane, polyester polyol polyurethane and polycarbonate polyurethane, and found the abrasion resistance of polyester modified acrylic polyurethane topcoat. Preferably, acrylic polyurethane topcoats have the worst abrasion resistance, but their stone-resisting properties are poor, while the abrasion resistance of polycarbonate polyurethane topcoats and polyester polyol polyurethane topcoats is better than polyester modification. Acrylic polyurethane topcoats are a bit worse, but these two topcoats have the best stone resistance.




    The polyester modified acrylic polyurethane topcoat is simple in preparation, convenient in construction, and has excellent comprehensive performance of the paint film. It is widely used in the field of domestic wind power blades, but it has better performance than the polyurethane of the polyester polyol system. Abrasion resistance, but poor stone resistance, not suitable for the leading edge protection of the blade, so the polyester modified acrylic polyurethane system is used as the blade topcoat, and the polyurethane with the polyester polyol system is used as the blade leading edge repairing surface. Paint can bring better protection to wind turbine blades.




    At present, the acrylic polyurethane coatings used in China are mainly solvent-based, and the future is bound to be replaced by water-based coatings. The two-component waterborne acrylic polyurethane coating not only has good adhesion, low temperature flexibility, weather resistance and wear resistance, but also has extremely low VOC. With the development of waterborne polyurethane coating, this will be the future of wind power blade protective coating. An important development direction.


    2.3 fluororesin




    The fluororesin currently used is mainly a copolymer in which fluoroolefin units and alkyl vinyl ethers (or alkyl vinyl esters) are alternately arranged, and isocyanate or amino resin can be cured at room temperature. The most excellent performance of fluororesin is super weather resistance. Li Yunde once used the fluororesin and acrylic urethane resin for the all-weather outdoor exposure test in different regions and different climatic conditions in China. The results showed that:




    After 2 years, all the acrylic polyurethane samples showed more than 2 grades of powdering, and the loss rate reached 40%. The fluororesin samples were not powdered and only slightly lost light; after 4 years, all the acrylic polyurethane samples were obviously powdered. There was severe loss of light, and the fluororesin samples were not powdered, and only a slight loss of light occurred. Zeng Fanhui and others compared the weather resistance of PTFE, trifluoro-type fluororesin and acrylic resin. It was found that after 30 months of outdoor exposure, the fluorination rate of PTFE fluororesin can reach 90% with only slight loss of light. The light retention rate of the trifluoro-type fluororesin drops to about 82%, and the gloss retention of the acrylic resin is below 60%.




    In addition to excellent weather resistance, fluororesins tend to have low surface energy due to their high electronegativity, so fluororesins can be used to obtain coatings with excellent icing resistance.




    In winter, the leaves are prone to snow and ice, especially in northern Europe, North America and northwestern China. If the ice on the leaves is not removed in time, it will bring a series of serious problems. There are currently two types of ice-clearing technologies - active ice-clearing techniques using heat, electricity, machinery and ultrasound, and passive ice-clearing techniques using anti-icing coatings. Active ice-clearing technology is widely used, and the effect is very good. However, when using energy-saving, the use of anti-icing coating is simple and convenient, and environmentally friendly. Therefore, in the long run, anti-icing coating will replace the traditional active ice-clearing technology. It can protect the normal operation of wind turbine blades more effectively.




    Peng et al. prepared a super-hydrophobic PVDF coating on wind turbine blades with water contact angles and sliding angles of 156° and 2°, respectively, which have excellent ice resistance compared to blade surfaces without PVDF coating protection.