Performance requirements of coating materials for wind turbine blades

Wind turbine blade coating needs to be exposed to the sun, high and low temperature changes in winter and summer day and night. In high-speed operation, it will be severely scoured by wind, sand, rain and snow. In addition, the adhesion of a large number of sand and water droplets will seriously affect its aerodynamic performance and reduce the output power of the generator set [5]. As the coating of wind turbine blades, the main performances required are: weather resistance, wear resistance, excellent adhesion, chemical resistance, etc. the specific technical indicators such as adhesion should be greater than 5MPa, natural surface drying time should be less than 8h, and the mass loss should be less than 20mg / 500g after 500 rpm wear resistance test.

At present, polyurethane is the main protective coating material for wind turbine blades in the world, mainly solvent based polyurethane primer with solvent based polyurethane topcoat, which has good performance and moderate price. In 2010, American PPG company launched high-performance film type hsp-7401 anti-corrosion and weather resistant polyurethane primer and aue-5000 polyurethane topcoat system, which further promoted the application of polyurethane in blade coatings. In order to make the coating have higher comprehensive performance, in recent years, the use of fluorinated polymer, acrylic resin and other supporting preparation of wind turbine blade coating.

Polyurethane material

Polyurethane resin has excellent oil resistance, abrasion resistance, chemical resistance and strong adhesion ability, so the coating made of polyurethane resin has been widely used in wind turbine blades. The weather resistance of wind turbine blade coating is very high. When polyurethane is used to prepare the coating, aliphatic or alicyclic polyisocyanates should be used instead of aromatic compounds which are prone to yellowing.

Northwest Yongxin Chemical Co., Ltd. has developed a high-performance wind power coating based on organic fluorosilicone modified elastic polyurethane urea resin, which mainly includes polyester and polytetrahydrofuran glycol as polyols, isophorone diisocyanate (IPDI) as diisocyanate, and then modified with hydroxyl containing siloxane and fluorosilicone. The coating performance is good after the component is evenly distributed with the auxiliary component, which has a certain promotion value.

Di Zhigang of CNOOC Changzhou paint Chemical Research Institute prepared a kind of high weather resistance and wear resistance elastic polyurethane curing agent. The curing agent was synthesized by reaction of weather resistant aliphatic copolyester and hydroxyl containing fluororesin with IPDI. The curing agent was distributed with high weather resistance hydroxyl group paint according to n (- NCO) ∶ n (- OH) = 1 ﹥ 2 ∶ 1, which can be applied to wind turbine blade coating.

Compared with traditional HDI Trimer and commercial polyurethane curing agent, this curing agent has advantages in weather resistance, wear resistance and adhesion to substrate. Li Huaming et al. Used silicone alcohol modified polyester resin with good weather resistance and certain elasticity as base material, Bayer polyurethane n-75 as curing agent and other additives to prepare protective coatings with excellent weather resistance and wind sand corrosion resistance.

COSCO Guanxi coatings Chemical Co., Ltd. developed a kind of waterborne polyurethane coating as the top coat of fan blade, which is used together with polyaspartic ester primer. The coating is made of pure c-hydroxy acrylic acid dispersion, the curing agent is mainly polyether modified HDI Trimer, and a part of polyester modified HDI Trimer is combined. Shen Jianping also used waterborne polyurethane as the wind turbine blade coating. Through experimental comparison, he found that the low viscosity HDI curing agent modified by sulfamate had the best comprehensive performance, and could mix with the water dispersions containing hydroxyl without dilution.

Abroad, kallesoee et al. Analyzed the selection of polyols and polyisocyanates for polyurethane. Polyols contain at least 70% of hydroxyl groups with 2-8 hydroxyl groups. Aliphatic polyester is recommended, and straight chain type is preferred. Polyester with branched chain or ring structure is not recommended; The curing agent is mainly polyisocyanate with polyester structure, urobutanedione group or urea formate structure. The use of more than 90% polyisocyanate with the above three structures is helpful to obtain better elasticity and service life of the coating.

Evonik Degussa company of Germany mixed high and low molecular weight polyols, combined with polyisocyanates and light stable aromatic amines to prepare polyurethane coating, and added pyrolytic silica modified by hexamethyldisilazane hydrophobic treatment and ball mill as filler. The coating shows good adhesion on epoxy resin. To some extent, the performance and performance of the coating on wind turbine blades are determined by the polyester and curing agent of polyurethane. It is very important to select one or several kinds of polyester or curing agent with strong weather resistance for improving the durability of polyurethane coating and improving its comprehensive performance.

In the current wind power market, solvent-based coatings occupy a dominant position, but the low volatile organic compounds (VOC) and environmental friendly high-performance waterborne polyurethane coatings are obviously more in line with the concept of "green energy" for wind power generation. Waterborne polyurethane coatings will become an important development direction and research hotspot of wind turbine blade coatings. With the continuous development of wind turbine blade coating technology and the continuous innovation of process technology, waterborne polyurethane coating is bound to occupy a place in wind turbine blade coating.