Preparation of Thermochromic UV Coating with Urea–Formaldehyde-Coated Ternary System on Bleached Poplar Wood Surface

In this study, poplar boards were bleached and treated with two types of urea–formaldehyde-coated ternary system thermochromic microcapsules (UF@TS), which were mixed with UV primer. The bleached poplar boards were manually painted with two layers of primer and topcoat. Coating samples with varying microcapsule contents were prepared and evaluated based on factors such as glossiness, reflectivity, and other surface properties. The experimental results showed that bleaching treatment significantly increased the whiteness of poplar wood, with an improvement rate of up to 17%. Among the two microcapsule types, the coating containing #2 microcapsules exhibited superior surface quality compared to #1 microcapsules. As the microcapsule content increased, the coating glossiness showed an overall decreasing trend and a certain degree of fluctuation, and the #2 microcapsule showed lower reflectivity values. The addition of UF@TS microcapsules negatively affected the coating adhesion but had little effect on hardness. The #2 microcapsule enhanced the impact resistance of the coating to a certain extent and increased surface roughness. Regarding thermochromic performance, the #1 microcapsule exhibited higher color-changing temperature and larger color difference, while the #2 microcapsule showed color-changing temperature closer to room temperature. Despite a decline in thermochromic performance and glossiness during aging, the 1# microcapsule showed slightly better stability. The coating containing 10% #2 microcapsules demonstrated the best comprehensive performance on bleached poplar wood, with glossiness of 2.1 GU, reflectivity of 67.95%, adhesion grade of 1, hardness of 6 H, impact resistance grade of 4, and surface roughness of 0.681 μm. The ΔE in the range of −20 °C to 50 °C was 7.434. After aging, ΔE was 5.846, and the light loss rate was 9%, with excellent comprehensive performance.