Preparation Of Melamine Resin-coated Shellac Water-based Coating Microcapsules And Its Effect On The Performance Of Wood Coatings

As a heterogeneous composite material of natural polymer,wood has the characteristics of shrinking and swelling.The coating on the wood can protect and beautify the surface of the wood,close the wood pipe hole,and improve the stability of the wood.However,in the long-term use of wood,the cracks will occur due to environmental changes and paint film performance degradation,which will affect the service life.The self-healing technology,as an effective method to automatically repair microcracks,has become a research hotspot in many fields.This paper selects shellac and water-based paint mixed solution as the research focus,applies it to the surface of wood coatings,uses shellac and water-based paint mixed solution as the core material,and melamine formaldehyde resin as the wall material to prepare self-healing microcapsules.The influence of capsule concentration and coating process on the optics,mechanics,liquid resistance,aging and repair performance of wood coating film.The research conclusion are as follows:（1）The five-factor four-level orthogonal test method was used to study the W _core:W _wall,W emulsifier:W core,rotation rate,W shellac:W water,W emulsifier solution:the influence of W core on the yield and coating rate of microcapsules.Microcapsules with the best morphology and structure are analyzed by microscope,SEM,and infrared spectroscopy.The results showed that the factor that has a greater impact on the preparation process is the rotation rate.Through the paint film repair effect,SEM and infrared spectroscopy analysis,it is concluded that the best preparation process for preparing microcapsules is W _core:W _wall is 0.8:1,W _emulsifier:W _core is 3:100,rotation rate is 600rpm,W shellac:W water is 1:1,W emulsifier solution:W core is 9:1.（2）When the microcapsule stirring speed is 600rpm and the optimal concentration is 5.0%,the overall performance of the basswood water-based primer film is the best.The basswood primer film and topcoat film with 5.0%microcapsules have rounded cracks during aging,but the diameter of the cracks is smaller than that without microcapsules.Different aging environments are for those without and with 5.0%microcapsules.The primer film and topcoat composition have no effect.（3）The best construction process for the water-based coating of basswood is two-pass primer,three-pass topcoat,and microcapsules were added to the topcoat.At this time,the hardness of the basswood paint film with 5.0%microcapsules is 5H,the adhesion grade is 1,the impact resistance is 7.0（kg·cm）,and the elongation at break is 16.28%.Na Cl,ethanol and detergent have a liquid resistance level of the basswood paint film,and red ink has a liquid resistance level of 2.Two-pass primer,three-pass topcoat,and the microcapsules were added to the topcoat have better liquid resistance.The basswood paint film with 5.0%microcapsules had a better microscopic appearance.Ultraviolet light aging has a great influence on the color of shellac.In the scratch repair experiment,the repair effect of the basswood paint film with microcapsules is obvious,and the repair effect reaches the best effect within the first 7 days.（4）From the range and variance analysis of the film roughness in the three factors and two levels orthogonal experiment,it is concluded that the polishing method between primers has a great influence on the film roughness.The grinding mesh was fixed between the base/surface and the topcoat,and change the grinding mesh between the primers to conduct independent experiments,and it is concluded that 240 grit sandpaper is better for the grinding between the primers.After 240 hours of UV aging,the color difference of the paint film polished with 600grit sandpaper is the smallest,and the paint film polished with 1000 grit sandpaper is the largest.In general,the aging resistance gloss of the paint film with 240 grit sandpaper between the primers is relatively stable.The paint films of different polished meshes all have cracks after aging.The cracks of the paint film polished with 240-mesh sandpaper are smaller and regular.The repair effect of the paint film without sanding between the primers is better than that of240-mesh.