Study on the Roller Applied Wind Blade Coatings

Chen Mingjun (Xiangjiang Paint Technology Co., Ltd., Changsha 410299,China

Abstract:Based on polyester modified hydroxyacrylic resin,a primer-topcoat-in-one formulation for roller applied wind turbine blade coatings was developed,which met the need of roller applied wind turbine blade coatings. The results showed that the combination of fluoro-silicone defoamer and polyether modified silicone defoamer could eliminate the bubbles produced by the roller application. The combination of fluoro-silicone and fluoro-polyacrylate could achieve an excellent leveling effect. The combination of fumed silica and modified urea could eliminate the problems of“orange peel”and sagging on the vertical surface of a wind turbine blade. The type of matting agents and solvents in the formulation also contributed an effect to the surface finish.

According to statistics from China Wind Energy Association, in 2017, the nation ’s (except Hong Kong, Macao, and Taiwan regions) new installed capacity was 19.66 million kilowatts, and the cumulative installed capacity reached 188 million kilowatts, a year-on-year increase of 11.7%. According to the national “Thirteenth Five-Year Plan”, by 2020, we should strive to achieve an energy supply capacity of about 2 billion kW of installed power generation, and strive to make China’s wind power development not less than 150 million kWh, the proportion of wind power in primary energy is about 7. 5%. Based on the 150 million kWh of China’s wind power development in 2020, if the annual power generation is 2000 h, it can generate 300 billion kWh of electricity, about 100 million tons of standard coal. Therefore, the prospect of wind power in China is broad, and the corresponding blade coatings also have a large market demand.
At present, the domestic wind power blade coating market is dominated by several well-known foreign coating companies, and only one coating company abroad has a roll coating wind power blade coating supporting system. At present, domestic roll coating wind power blade coatings are still blank. Compared with spray coating, roller coating can reduce VOC by about 25 g / m2 and reduce coating usage by 15%. At the same time, it can improve the construction environment and reduce physical harm to painting personnel. Therefore, it is of great significance to consider the development of roller-coated wind power blade coatings from an economic and environmental perspective.
The orange peel phenomenon is the most and most difficult problem to be solved in the coating film of wind power blade rolls. In this study, by optimizing the design of the two-component polyurethane coating formula, the orange peel phenomenon of the wind power blade coating was basically eliminated.

1 Experimental part
1.1 Experimental materials and equipment
Polyester hydroxyacrylic resin (CY482): DSM; Isocyanate curing agent (N3390): Covestro; Dispersant (4010): AFCONA; Titanium dioxide (R902): DuPont; Antifoaming agent (2035, 2045): AFCONA; Leveling agent (3034, 3873): AFCONA; Ultraviolet absorber (400): BASF; Fumed silica (R972): Degussa; BYK-410, BYK Chemicals; Catalyst (T12): gas chemical industry; butyl acetate, cyclohexanone, propylene glycol methyl ether acetate: Shanghai Tecam Industrial Co., Ltd .; matting powder (ACEMATT82, OK500, OK520, TS100): Degussa. The above reagents are all industrial grade.

1.2 Roller Coating Type Bottom-in-one Wind Power Blade Coating Reference Formula
Table 1 is the reference formula of the bottom-in-one wind power blade coating.

Table 1 Formula of the one coat wind blade paint

1. 3 Preparation of the coating
According to Table 1A, the component formulation was weighed to 40% of the total film-forming resin, 0.4% of defoaming agent 1, 0.2% of defoaming agent 2, 0.5% of dispersant, 7 % Mixed solvent, 30% titanium dioxide, 0.4% R972, high-speed dispersion, grinding, filter out when fineness ≤ 25 μm, and then add the remaining 13.2% resin, 0.15% leveling agent 1, 0.4% leveling agent 2, 4% matting powder, 0.2% BYK410, 3% mixed solvent, 0.5% UV light absorber, 0.05% catalyst, and stir evenly at high speed to obtain wind power blade coating A Components. The curing agent and the solvent are formulated into a curing agent of a desired concentration at a ratio of 90:10 (mass ratio) to obtain a component B of a wind power blade coating.
The A and B components are mixed at a ratio of 5: 1 (mass ratio), and a self-made diluent is added to adjust the viscosity to 60-80 s (coated-4 # cup). The bottom surface can be roll coated with acrylic acrylic polyurethane. coating.

1. 4 Roller coating process of wind power blade coating

The coating process of roller coating type wind power blade coating is shown in Figure 1.

Fig.1 Coating process of the roller wind blade pain

According to the coating process in Figure 1, use the long hair roller for the first pass and the dry film thickness is not less than 70 μm. After the first pass, use polyurethane leveling roll for the second pass. The total film thickness is not less than 150 μm. Test performance after drying for 48 h.

1.5 Coating performance test
Number of bubbles: use 100 mm × 100 mm tinplate sheet, visually check the number of bubbles, calculate the number of bubbles per square meter;
shrinkage: use 100 mm × 100 mm tinplate sheet, visually check The number of shrinkage holes is less than 2;
leveling: use a 100 mm × 100 mm tinplate sheet, visual inspection, the paint film is smooth and smooth; test items and test methods for coating film performance are shown in Table 2.

Table 2 Performance of the film and test methods

1. 6 main experimental equipment
BGD 750/1 Sanding-dispersion-stirring multi-purpose machine, paint film divider (100 grid knife), electronic balance UW6200H, BGD880 salt spray corrosion test box, BGD886 xenon lamp aging test box: Guangzhou Biaogeda Experimental Instrument Supplies Co., Ltd. ; MG-268 gloss meter: KonicaMinolta (Konica Minolta).

2 Results and discussions
2.1 The influence of the main components of the paint on the appearance of the paint film
2.1. 1 The resin
epoxy resin blades are easily powdered directly under the sunlight, and may even break in high-speed rotation when reaching a certain level; Rotating blades are subject to large forces and deformations; most of China’s wind farms are located in environments with severe wind erosion, so wind power blade coatings are required to have high weather resistance, excellent flexibility and wear resistance. In addition, the wind power blade coating uses a roller coating construction process. The roller coating surface is a vertical surface. The coating is required to have excellent flow and leveling properties, so the relative molecular mass of the main resin cannot be too large, which requires the main resin to have a high solid content and low Viscosity. Polyester modified hydroxyacrylic resin was selected in this experiment, with a solid content of about 73% and a viscosity of about 6.0 Pa · s (23 ° C). The resin has good mechanical properties, corrosion resistance, weather resistance, abrasion resistance, etc. performance. The main paint and HDI trimer (N3390) formulated with this resin have good facade leveling.

2. 1. 2 Antifoaming agent

When roller coating is applied, it is easy to cause bubbles on the surface of the paint film. This is because air is easily introduced into the paint film when roller coating is applied, thereby forming air bubbles. Therefore, the antifoaming agent is required to have strong defoaming, defoaming and antifoaming effects. The defoamer with too strong defoaming ability is too poorly compatible with the system, which will cause orange peel and shrinkage in the paint film. Therefore, the defoamer used in the coating of the roller coating system must have strong defoaming Ability and certain compatibility with the system will not cause shrinkage and orange peel of the paint film. The amount of other raw materials is shown in Table 1. The effects of the two defoamers and their combined use were experimentally studied. The results are shown in Table 3.

Tabe 3 Effect comparison of different defoamers

Note: The added amount of defoaming agent is based on the total mass of the formula, the same below.
As can be seen from Table 3, when the amount of defoaming agent 1 is 0.5% and the amount of defoaming agent 2 is 0.3%, it has a strong defoaming ability and is compatible with the system. Properties will not cause shrinkage of the paint film and orange peel, thus achieving the effect of leveling the paint film. This is because the defoamer 1 is a fluorine-modified silicone defoamer, which is less polar and has certain compatibility with the system. It can make adjacent small bubbles in the coating aggregate and merge into large bubbles. Accelerate the migration of air bubbles to the surface of the paint film. Defoamer 2 is a polyether modified silicone defoamer, which can enhance the compatibility with the system, so they can quickly migrate to the surface of the paint film and enter the bubble wall, spread quickly, and form a very thin double film layer. Further diffusion, penetration and laminar invasion, thereby replacing the thin walls of the original bubble film. This way, the low surface tension antifoam molecules continue to diffuse and penetrate between the gas-liquid interface, causing the film wall to quickly thin, and the foam is simultaneously affected by the surrounding surface The film layer with high tension is pulled by force, and the stress around the foam is unbalanced, which causes it to “break”.

2. 1. 3 Leveling agent

The roller coating construction is easy to cause orange marks on the paint film. The leveling agent plays a crucial role in the leveling performance of the coating facade. The effects of two types of leveling agents and their mixed use on the leveling of coatings were experimentally studied. The appearance of paint film leveling is shown in Figure 2.

Fig. 2 Effect comparison of different leveling agents

It can be seen from FIG. 2 that when the two leveling agents are used in combination, the coating film has excellent vertical leveling effect. This is because the leveling agent 1 is a fluorine-modified silicone-based leveling additive, which is very effective in promoting the leveling of the facade, it is effective in eliminating short-wave orange streaks on the paint film, and it can form a thin layer on the surface of the paint film. A layer of surface tension molecules to provide uniform surface tension, ie, low surface tension drives leveling. The leveling agent 2 is a fluorine-modified polyacrylate leveling additive, which is very effective in eliminating the long-wave orange streaks of the paint film, reduces the surface tension between the coating and the substrate, and makes the coating and the substrate have optimal wetting. It reduces the tension gradient caused by solvent volatility, that is, the difference in surface tension drives the leveling. Therefore, the compounding of two kinds of leveling agents can achieve very excellent vertical leveling effect.

2. 1. 4 Anti-sagging additives
Wind power blade coatings use two rollers in the construction process. The wet film thickness of each coating must be more than 100 μm. The coating roller is applied on the surface of the facade. The wet film will flow downward due to the influence of gravity. Sagging phenomenon, then the paint film will inevitably produce orange peel phenomenon, a slight orange peel is inevitable and must be accepted. Therefore, an anti-sagging additive with good performance should be selected. With appropriate dosage, the coating and the wet film on the vertical surface can reach the balance between leveling and sagging. That is, under the application conditions, the viscosity of the coating is reduced, and the The viscosity hysteresis recovery period is maintained at a low viscosity, showing good coating film leveling; once it has been leveled, the viscosity gradually recovers, which plays a role in preventing sagging [4]. This article uses fumed silica together with BYK-410 modified urea solution to make the coating have good rheology and anti-precipitation. When the amount of fumed silica and BYK-410 is different and the other ingredients are the same, the anti-sagging and leveling properties of the coating are tested. The results are shown in Table 4. As can be seen from Table 4, when the amount of fumed silica is 0.3% and the amount of BYK-410 is 0.2%, the prepared coating has both suitable sag resistance and excellent leveling.

Table 4 Effect of the gas-phase SiO2 and BYJ-410's dosage to Vertical Leveling, Tabe 5 Effect of different flatting agents to the coating's properties

2. 1. 5 Matting powder

The coating of wind power blades is required to be matt. Matting powder has a great influence on the gloss, thixotropy and abrasion resistance of the coating. In the experiment, four representative matting powders were selected, and the other components remained unchanged. At the same temperature and the same viscosity of the two components, the effects of different types of matting powders and their dosages on the gloss and leveling of the coatings were investigated. The test results are shown in Table 5.
It can be seen from Table 5 that when TS100 matting powder is used and the amount is 4%, the gloss of the prepared coating can be reduced to 15 °, and the abrasion resistance and leveling of the coating can meet the requirements.

2. 1. 6 Influence of Solvent on Facade Leveling
For roll coating construction, the surface drying time of the paint film should be 30-50 minutes. During the roll coating construction, if a solvent with a low boiling point and a fast volatilization speed is used, the wet film viscosity will increase sharply and the wet film will not have a leveling force. It causes the orange peel to affect the appearance quality. When using a thinner with a high boiling point and a slow volatilization speed, the wet film has good leveling after roller coating, but the wet film is more than 100 μm in one roll coating, which may cause sagging. Combining the above analysis and actual construction, the experiment uses a mixed solvent of m (butyl acetate): m (cyclohexanone): m (propylene glycol ether methyl ether acetate) = 5: 3: 2, and is matched with three kinds of medium boiling point solvents Use to make the diluent have a suitable volatilization speed to meet the construction needs of large-area roll coating.

2.2Coating performance

Test results of coating performance are shown in Table 6.

Table 6 Performance of the coatings

By using two-component hydroxyacrylic polyurethane bottom paint, and two roller coatings, the technical requirements of wind power blade coatings can be achieved.

3 Conclusion
At present, domestic wind power blade coatings are mainly imported from Germany, the United States and Italy. Domestic paint manufacturers are still in the research stage of wind power coatings. The roll coating type wind power blade coating products developed in this paper can meet the requirements of wind power blade coatings through optimized formulation design. skills requirement.
(1) Polyester-modified acrylic resin can provide the mechanical properties and durability required for wind power coatings;
(2) 0.4% fluorine-modified silicone defoamer and 0.2% polyether-modified silicone defoamer Compounding can effectively eliminate air bubbles during coating production and roll coating;
(3) 0.15% fluorine modified silicone leveling agent and 0.4% fluorine modified polyacrylate leveling agent can provide excellent paint film the facade leveling;
(4) 0.3% fumed silica with 0. 2% BYK-410 can both coatings suitable excellent sag resistance and leveling;
(5) using 4 % TS100 matting powder can meet the requirements of matting, wear resistance and leveling. Using a mixed solvent of butyl acetate, cyclochirone and propylene glycol methyl ether acetate, the coating has a good volatilization speed, which can meet the construction requirements of large-area roll coating.

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