## 2 Materials and Methods
### Testing and Characterization  
The experimental instruments used to test the performance of coating film are shown in Table 4. The color aberration of coating film was tested by 3 NH portable color aberration meter. Two chromaticity values on the coating film were tested, and the L, a and b values were recorded respectively. L\({}_{1}\) and L\({}_{2}\) represent the brightness value of two points on the coating film, a\({}_{1}\) and a\({}_{2}\) represent the red-green value of two points on the coating film, and b\({}_{1}\) and b\({}_{2}\) represent the yellow-blue value of two points on the coating film. The color aberration (\(\Delta\)E) of the coating film was calculated according to the formula (1) [26]:  
\[\Delta\text{E}=[(\text{L}_{1}-\text{L}_{2})^{2}+(\text{a}_{1}-\text{a}_{2})^{2 }+(\text{b}_{1}-\text{b}_{2})^{2}]^{1/2} \tag{1}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample Number**} & **Primer (Number** & **Topoat (Number** & **Ways of Adding** \\  & **of Depositions)** & **of Depositions)** & **Microcapsules** \\ \hline
1 & 2 & 2 & primer \\
3 & 3 & 2 & primer \\
4 & 3 & 3 & primer \\
5 & 2 & 2 & topcoat \\
6 & 2 & 3 & topcoat \\
7 & 3 & 2 & topcoat \\
8 & 3 & 3 & topcoat \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental schedule of coating technology. Figure 1: Diagram of Nippon water-based coatings added with water-based emulsion microcapsules. The morphology and chemical constituents of microcapsules were observed by Quanta 200 electron microscope and VERTEX 80V infrared spectrometer. The glossiness of coating film was measured at 20\({}^{\circ}\), 60\({}^{\circ}\) and 85\({}^{\circ}\) with gloss meter [27]. Pencil hardness tester was used to examine the hardness of coating film. Pencils with hardness of 6H-6B were prepared, and the wooden part of the pencil was cut off to expose the pencil lead of about 3.0 mm, which was polished with sandpaper until the end face was flat and the edge was sharp. The pencil formed an angle of 45\({}^{\circ}\) with the linden and was pushed on the coating film at a speed of about 1.0 cm/s. The hardness of two or more pencils that broke the coating film was recorded, the hardness one grade lower than the hardness of this pencil was the hardness of coating film [28]. Adhesion of coating film was analyzed by HGQ film scratch tester. The coating film was cut into rectangular grid with a cutter, and the scratches reached the substrate through the coating film. Then the adhesive tape was attached to the grid and torn off, and the adhesion grade was evaluated by the coating detachment area [29]. The QCJ impactor tester was used to test the shock resistance. The weight fell freely at a certain height to impact the sample, and the maximum height at which the coating film did not break was the impact strength [30]. The fracture elongation was tested by ZCW-WL precision universal mechanical testing machine. The two ends of the coating film were clamped by clampers, and the machine stretched the coating film at a uniform speed until it broke, and the fracture elongation was calculated [31]. Anti-aging experiments were carried out in the oven and ultraviolet weathering test box according to GB/T 23987-2009 [32], and the surface damage of the coating film containing microcapsules and the coating film without microcapsules after aging were compared. The oven temperature was set at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C and the color aberration and glossiness of the coating film were examined every 8 h for 40 h. The color aberration and glossiness of the coating film were tested every 40 h in the UV weathering test box, and the aging time was 200 h.  
The self-healing properties were assessed by a scratch experiment. Scratch experiments were performed on the coating film with a blade, and photographs were compared with an optical microscope for self-repairing. The repairing time was 7 d, and the repairing environment was room temperature.