## 3 Results and Discussion
### Effect of Coating Process on Aging Resistance Properties  
The paint films with microcapsules and without microcapsules prepared by the process of \"3 layers of primer, 2 layers of topcoat\" were put into a 120 \({}^{\circ}\)C oven, 160 \({}^{\circ}\)C oven and ultraviolet weather resistance test chamber for aging test. In the 120 \({}^{\circ}\)C oven (Figure 6), when the aging time of the paint film without microcapsules increased from 8 to 40 h, the color difference increased from 1.8 to 4.2, and the color difference of the paint film with microcapsules added in primer increased from 1.4 to 3.7. In the 160 \({}^{\circ}\)C oven (Figure 7), when the aging time of the paint film without microcapsules increased from 8 to 40 h, the color difference increased from 4.0 to 24.2, and the color difference in the paint film with microcapsules in primer increased from 2.0 to 22.1. When, in the UV weather resistance test chamber (Figure 8), the aging time of the paint film without microcapsules increased from 40 to 200 h, the color difference increased from 3.1 to 6.7, and the color difference in the paint film with microcapsules increased from 0.5 to 3.1. The results showed that the color difference in the paint film gradually increased with the increase in aging time. Moreover, in the same environment, after the same aging time, the color difference of the paint film without microcapsules increased more obviously than that of the paint film with microcapsules. This may be because the paint film with microcapsules will crack after aging, the core material emulsion (waterborne emulsion) repairs the microcracks and reduces the degree of discoloration [33]. The aging gloss of the paint film was observed at an incident angle of 60\({}^{\circ}\). After the paint film was aged in 120 \({}^{\circ}\)C oven (Figure 9), the gloss of the paint film without microcapsules decreased from 61.2 to 55.8, while the gloss of the paint film with microcapsules in the primer slightly decreased from 30.9 to 29.2. After the paint film was aged in 160 \({}^{\circ}\)C oven (Figure 10), the gloss of the paint film without microcapsules decreased from 50.8 to 43.7, and that with microcapsules in primer decreased from 15.8 to 13.6. After the paint film was aged in the UV weather resistance test chamber (Figure 11), the gloss of the paint film without microcapsules decreased from 46.6 to 42.7, and the gloss of the paint film with microcapsules in primer decreased from 25.9 to 25.1. The results showed that the gloss of the paint film decreased with the increase in aging time and the gloss of the paint film without microcapsules decreased more obviously than that with microcapsules. This is because after aging for a certain period of time, the paint film would produce microcracks under the influence of the environment, so that the microcapsules rupture, and the healing agent outflows. Therefore, the healing agent can repair the microcracks and slow down the gloss [34]. Figure 6: Effect of aging time on color difference of the paint film in the 120 \({}^{\circ}\)C oven. Figure 8: Effect of aging time on color difference in the paint film in the ultraviolet weather resistance test. Figure 7: Effect of aging time on color difference of the paint film in the 160 \({}^{\circ}\)C oven. Figure 9: Effect of aging time on gloss of paint film in the 120 \({}^{\circ}\)C oven. The SEM images of the paint films without microcapsules and with microcapsules before and after aging tested in the 120 \({}^{\circ}\)C oven, 160 \({}^{\circ}\)C oven and ultraviolet weather resistance are shown in Figures 12-14. The surface of the paint films without microcapsules is smooth in Figures 12A, 13A and 14A. Figures 12B, 13B and 14B show the paint film containing microcapsules in primer, with obvious particles on the surface. Figures 12C, 13C and 14C show the SEM pictures of the paint film without microcapsules after aging test. It can be seen that the paint film had obvious damage. The bubble cracks of a large size can be observed.