In the coating system, primer is the key link between the substrate and the topcoat. Its adhesion directly affects the overall performance of the coating, and its durability under complex working conditions is even more related to the service life of the coating. Adhesion improvement technology aims to enhance the bonding between primer and substrate, while durability research focuses on the ability of primer to maintain stable performance under various harsh environments and mechanical stresses. The two complement each other and are of great significance to improving the quality of coatings.
Surface treatment is the basis and key technology for improving primer adhesion. For metal substrates, common treatment methods include sandblasting, phosphating, chemical etching, etc. Sandblasting uses high-speed sand particles to impact the surface of the substrate, increase the surface roughness, and form a microscopic anchor structure, so that the primer can penetrate and adhere better; phosphating treatment generates a layer of phosphate conversion film on the metal surface, which not only improves the surface roughness, but also reacts chemically with the active groups in the primer to form chemical bonds, significantly enhancing adhesion. For non-metallic substrates such as plastics and wood, flame treatment, corona treatment and other methods can change the chemical properties and surface energy of the substrate surface, making it easier to combine with primer. For example, flame treatment can instantly oxidize the plastic surface, introduce polar groups, and enhance the wetting and adhesion ability of the primer to the plastic surface.
The modification of primer materials is the core means to improve adhesion and durability. Performance optimization is achieved by adding functional additives and changing the resin system. In terms of the resin system, epoxy resin, polyurethane resin and other resins with good adhesion are used as primer base materials. The epoxy groups in the epoxy resin can react with the hydroxyl groups on the metal surface to form a strong chemical bond; at the same time, nanoparticles are introduced into the resin for modification, such as nano-silicon dioxide, nano-calcium carbonate, etc. The nanoparticles are evenly dispersed in the resin, which can fill the tiny pores on the surface of the substrate, enhance the mechanical bite, and improve the density and anti-permeability of the coating, thereby improving adhesion and durability. In addition, by adding additives such as coupling agents, one end of the coupling agent molecule can react with the active group on the surface of the substrate, and the other end can react with the primer resin, playing a "bridge" role, further strengthening adhesion.
Cross-linking curing technology has a significant effect on improving the adhesion and durability of primers. The resin molecules in the primer are cross-linked by heat curing, light curing, chemical cross-linking and other methods to form a three-dimensional network structure. During the heat curing process, the resin molecules react chemically at high temperature, the cross-linking density increases, and the intermolecular force is enhanced, which not only improves the hardness and wear resistance of the primer, but also reduces the mobility of the molecular chain, making the primer more firmly bonded to the substrate and not easy to fall off under complex working conditions. The light curing technology uses ultraviolet radiation to induce the photoinitiator in the resin to produce free radicals, which quickly triggers the cross-linking reaction. This method has a fast curing speed and can effectively avoid coating defects caused by factors such as solvent volatilization during the curing process, and improve the density and durability of the coating.
Under complex working conditions, the durability of the primer faces many challenges, such as high and low temperature cycles, acid and alkali corrosion, mechanical vibration, etc. To meet these challenges, it is necessary to start from two aspects: coating structure design and protective function enhancement. By designing a multi-layer composite coating structure, an intermediate transition layer is added on top of the primer. The intermediate layer can be made of materials with buffering and stress dispersion effects to alleviate the damage of the primer to the mechanical stress under complex working conditions; at the same time, the primer is given special protective functions, such as adding corrosion inhibitors to make anti-corrosion primers. The corrosion inhibitor forms a protective film on the metal surface to prevent the corrosive medium from contacting the metal and extend the corrosion resistance of the primer; adding anti-ultraviolet agents to prevent ultraviolet rays from degrading the primer resin and improve the aging resistance of the primer in outdoor environments.
The construction process has a direct impact on the adhesion and durability of the primer. It is crucial to reasonably control the construction temperature, humidity, spray thickness and other parameters of the primer. If the construction temperature is too low, the viscosity of the primer will increase, it will not be easy to level, and it will affect the adhesion; if the humidity is too high, it may cause defects such as bubbles and whitening on the surface of the primer, reducing durability. Accurately control the spray thickness to avoid being too thick or too thin. Too thick will cause incomplete drying of the coating and reduce the mechanical properties, while too thin will not form an effective protective layer. In addition, strictly follow the drying time and curing conditions of the primer to ensure that the primer is fully cured to achieve the best adhesion and durability.
With the continuous development of science and technology, intelligent monitoring technology provides a new direction for the durability research of primers under complex working conditions. By embedding sensors in the primer, real-time monitoring of the strain, temperature, humidity and other parameters of the coating, using big data analysis and artificial intelligence algorithms, predicting the performance changes and potential failure risks of the primer, taking maintenance measures in advance, and realizing intelligent management of the durability of the primer. At the same time, develop self-repairing primer materials. When the primer is slightly damaged, the repair agent in the material can automatically release and fill the damaged area, restore the integrity and protective performance of the coating, and further improve the durability of the primer under complex working conditions.
