Effect of Shellac–Rosin Microcapsules on the Self-Healing Properties of Waterborne Primer on Wood Surfaces

Microcapsules with self-healing properties were synthesized via emulsion polymerization, with melamine formaldehyde resin serving as the microcapsule wall and a mixture of shellac and rosin solutions encapsulated as the core. The core–wall ratio was tested as a variable, and two ratios of 0.59:1 and 0.68:1 were selected for the preparations. Microcapsules were added to the waterborne paint films at concentrations of 0%, 5.0%, 10.0%, 15.0%, 20.0%, and 25.0%, respectively, to obtain self-healing waterborne paint films with different microcapsule contents. The effects of microcapsules with different core–wall ratios and concentrations in the paint films on the optical, mechanical, and self-healing properties of the paint film were investigated. The results showed that an increase in microcapsule content led to a corresponding rise in the paint film ∆E. The coating-film glossiness exhibited a decreasing tendency with an increase in microcapsule concentration. When the content of microcapsules was below 15.0%, the coating maintained a high level of adhesion and hardness. However, once the concentration surpassed 20.0%, coating adhesion began to decline. The addition of microcapsules effectively enhanced the thermal-aging resistance of the paint film. At the core–wall ratio of 0.68:1 and a microcapsule content of 20.0%, the paint film exhibited the best aging resistance, and the repair rate reached 16.1%, indicating good self-healing performance.