## 1 Introduction  
Compared with traditional organic coatings, waterborne coatings on wood surfaces have the advantages of safety, innocuity, wear resistance and good chemical resistance [1, 2, 3, 4], but it is necessary to improve the physical and mechanical properties [5, 6, 7]. Recent studies have shown that it has a broad research prospect on regulating the characteristics of coatings on a wood surface and inhibiting their defects by adding microcapsules [8, 9, 10]. [PERSON] et al. [11] fabricated the poly urea-formaldehyde coated epoxy microcapsules via in-situ polymerization, and the coating with microcapsules had good self-healing performance and good corrosion resistance. [PERSON] et al. [12] prepared poly(urea-formaldehyde-melamine) microcapsules containing epoxy resin via in-situ polymerization. It was shown that the coatings containing microcapsules achieved significant self-repairing protection effect after damage caused by artificial and mechanical stress. By in-situ polymerization, [PERSON] et al. [13] successfully prepared a kind of self-healing coating which contained microcapsules embedded with linseed oil in the shell structure composed of poly urea-formaldehyde. Compared with the artificial epoxy resin coating, this coating showedexcellent self-healing performance on artificial cracks. [PERSON] et al. [14] used oil-in-water emulsion polymerization to achieve the encapsulation of epoxy resins by encapsulating poly melamine-formaldehyde and poly urea-formaldehyde shells around emulsion epoxy droplets separately. The microcapsules also exhibited excellent self-healing properties after being added into waterborne coatings. These studies show that microcapsules can significantly improve the abilities of the coating on anti-corrosion and self-healing performance, while there are still some deficiencies on improving the mechanical properties of waterborne coatings on wooden substrates, which are problems that must be overcome in the use of waterborne coatings. In order to obtain better mechanical properties and prolong the service life of the coating, the elasticity of the coating can be enhanced by improving the polymer elasticity in the microcapsule wall. At the same time, the types and properties of adhesives in microcapsules are also very important for the self-repairing effect of microcracks [15; 16; 17]. With low price, excellent mechanical properties and thermal stability, the melamine resin is often used as wall material of microcapsules [18; 19; 20]. The rice husk powder, as a natural material, which is rich in plant fibers, has excellent toughness [21]. It can make melamine resin denser and firmer by being mixed with rice husk powder to obtain the microcapsules which have higher toughness and impermeability. It also can improve the mechanical properties of the coating on wooden substrate by extending the threshold of resistance to force and prolonging the self-healing time as a result of the good toughness of rice husk powder [22; 23; 24], as the core material, the shellac, a natural material, is green and environmentally friendly. The shellac has some excellent characteristics, such as moisture resistance, antirust, embalming, oil protection, acid resistance, and strong binding [25; 26; 27], and has been widely applied to the surface remediation of wooden crafts and precious musical instruments [28; 29; 30]. Therefore, the application of shellac microcapsule coated with melamine/rice husk powder has positive exploration significance and practical value on modification waterborne coatings on wood surface. In addition, the comprehensive properties of waterborne coating on wood surface are also affected by coating processes. Improper coating process leads to the decline of mechanical properties of the coating and initiates undesirable consequences like cracks. In this paper, the microcapsules containing rice husk powder with a mass fraction of 5.5% were added to primer and finish, respectively.