The curing process of tinplate coating one-sided gold paint is the core factor determining its final performance. Temperature control, time management, curing method, and environmental conditions all directly alter the physicochemical properties of the coating, thus affecting key indicators such as corrosion resistance, adhesion, abrasion resistance, and machinability.
Curing temperature is the primary factor affecting the performance of tinplate coating one-sided gold paint. If the temperature is too low, the resin molecular chains cannot fully cross-link, making it difficult for the coating to form a dense structure, leading to decreased adhesion and even back-side smudging or reverse printing. If the temperature is too high, the molecular chains may break, causing the coating to become brittle and prone to peeling during machining or high-temperature cooking. For example, when epoxy resin-based gold plating paint is cured at low temperatures, its polar groups fail to react completely, significantly reducing water resistance; while alkyd resins may yellow due to excessive oxidation at high temperatures, affecting the hygiene standards of food packaging.
Curing time is equally crucial. Insufficient curing time leads to incomplete solvent evaporation, leaving residual bubbles or pinholes within the coating and reducing corrosion resistance; excessive curing time can cause over-curing, making the coating brittle and reducing abrasion resistance. For example, acrylic resin-based gold plating paints require cross-linking with amino resins to form a flexible structure in the early stages of curing. Improper time control, resulting in insufficient or excessive cross-linking, will affect its impact resistance, especially in high-speed bottling production lines where coating peeling is likely.
The choice of curing method directly affects coating uniformity. Traditional baking curing is prone to uneven temperature distribution, leading to localized performance differences in the coating. While infrared or ultraviolet curing can improve efficiency, insufficient penetration may cause internal solvent retention. For example, during rapid drying of water-based amino baking coatings, the surface resin concentration increases sharply, and the internal moisture does not completely evaporate before forming a dense structure. Subsequent moisture escape can cause blistering or pinholes on the coating surface, severely weakening its protective ability.
Environmental humidity and cleanliness also have a significant impact on the curing process. In high-humidity environments, water molecules may penetrate the coating, interfering with the resin cross-linking reaction and leading to decreased adhesion. Dust or oil contamination can create defects on the coating surface, becoming channels for corrosive media to penetrate. For example, if the surface oil film on tinplate is not thoroughly removed before printing, the cured coating is prone to peeling due to poor compatibility between the oil film and the resin, especially in sulfur-containing food cans, where sulfides accelerate coating failure.
The cooling process after curing is equally important. Sudden cooling can cause stress concentration within the coating, leading to cracking or deformation; slow cooling helps release stress and improves coating stability. For example, if epoxy phenolic gold plating paint is not sufficiently cooled after high-temperature curing, its free phenolic and aldehyde components may evaporate faster due to residual stress, resulting in a whitening of the coating, which does not meet hygiene standards.
The curing process is also closely related to the characteristics of the tinplate substrate. Electroplated tinplate surfaces typically undergo chemical passivation to form a stable oxide film. However, if the passivation layer is too thick, it may hinder the chemical bonding between the resin and the metal surface, reducing adhesion. Hot-dip tinplate, on the other hand, does not undergo passivation, resulting in higher surface activity, but the curing temperature must be strictly controlled to prevent excessive oxide film growth. Furthermore, pretreatment parameters such as substrate smoothness and oil film thickness can indirectly alter the curing effect by affecting resin wettability.
The curing process for tinplate coating with one-sided gold paint requires a balance between temperature, time, method, environment, and substrate characteristics. By optimizing process parameters, the coating's corrosion resistance, adhesion, and machinability can be significantly improved, thus meeting the stringent requirements of food packaging, chemical containers, and other fields.
