## 1 Introduction  
Waterborne wood coating is a kind of green and environmentally friendly coating with water as the main solvent. Compared with the traditional solvent-based wood coatings, it has the advantages of non-toxic and environmental protection, no smell, little volatile matter, non-combustion and explosion, no yellowing and large painting area, which is more and more welcomed by the market [1, 2, 3]. However, due to the low molecular weight and a large number of hydrophilic groups, the mechanical properties of waterborne wood coatings decrease to some extent [4, 5]. In addition, due to the change in environmental factors (temperature, humidity, light), insufficient toughness of the coatings, and poor self-adaptation, microcracks will occur inside the paint film, and even damage the overall structure of the paint film, thus affecting the service life of the paint film and woodwork [6, 7, 8]. Therefore, it is an urgent problem to improve the mechanical properties of the paint film and inhibit the generation of microcracks. Microcapsule is a kind of \"core-shell structure\". The shell materials are deposited on the surface of the healing agent, which successfully covers the healing agent and forms microcapsules after certain drying treatment [9]. When the matrix with microcapsules is affected by various external forces, the embedded microcapsules are destroyed, and the repairing agent flows to the cracks to repair the cracks [10]. Microcapsule technology has been widely used in construction, shipping, dyeing and coatings [11]. [PERSON] et al. [12] studied the encapsulation of linseed oil in graphene oxide shells and prepared the self-healing composite coatings on the steel surfaces. The results showed that the waterborne polyurethane composite coatings containing 10% microcapsules autonomously healed a scratch with 20 um in width. [PERSON] et al. [13] improved the corrosion and water resistance of waterborne polyacrylate coating through introducing benzotriazole @ zinc oxide microcapsules. [PERSON] et al. [14] used in situ interfacial polymerization method to prepare the lubricating oil-encapsulated urea-formaldehyde microcapsules, and found that electrodeposited Ni coating containing oil-encapsulated microcapsules exhibited improved tribological properties compared to plain nickel coating. [PERSON] et al. [15] prepared tung oil-loaded microcapsules with the protection of poly(urea-formaldehyde) shells by in situ polymerization method. The epoxy coatings have an excellent corrosion resistance performance and self-lubricating performance by incorporating tung oil-loaded microcapsules into epoxy. [PERSON] et al. [16] synthesized urea formaldehyde (UF) microcapsules loaded with linseed oil and mercaptobenzothiazzole as core materials by in situ emulsion polymerization. The UF microcapsules incorporated epoxy coating on mild steel was found to offer better corrosion protection and self-healing ability than the microcapsules-free epoxy coating. [PERSON] et al. [17] synthesized two differently sized poly(urea-formaldehyde)-shelled microcapsules with the suspension of carbon nanoparticles as the core via in situ polymerization. The results demonstrated that the smaller microcapsules in Ag paste exhibited better restoration efficiency than the larger one from the tensile test, whereas an opposite result was obtained from the scratching test. These above results showed that the application of microcapsule technology can prolong the service life of coatings and even improve the performance of coatings. UF resin has the advantages of good compactness and toughness, good wear resistance and surface hardness [18; 19]. Waterborne acrylic resin is environmentally friendly, non-toxic, good at film-forming, has excellent color retention, and can be cured at room temperature. The waterborne acrylic resin, as the core material of the microcapsules, was added into waterborne acrylic coatings, which is equivalent to using a part of the coatings as a repair agent for secondary curing at room temperature.