The coating adhesion of the color coated coil is the core factor that determines its anti-peeling performance during bending. This adhesion is reflected in the bonding strength between the coating and the substrate, as well as the cohesion between the layers inside the coating. The two work together to affect whether the coating can remain intact during the bending process without peeling or cracking.
When the coating adhesion is strong, the coating and the substrate are tightly bound as if by an invisible force. During the bending process, the deformation of the substrate will drive the coating to extend or shrink synchronously. The intermolecular force inside the color coated coil coating can also be adjusted with this deformation, and will not separate from the substrate due to uneven force. On the inner side of the bend, the coating is squeezed, and the strong adhesion allows the coating to fit tightly with the substrate to avoid wrinkles and peeling due to squeezing; on the outer side of the bend, the coating is stretched, and the adhesion can resist this stretching force to prevent the coating from being torn or lifted from the surface of the substrate. In this state, even after multiple bends or large-angle bends, the coating can still maintain integrity with the substrate, and the anti-peeling performance is stable.
If the coating adhesion is insufficient, a gap is likely to appear between the coating and the substrate during the bending process, resulting in a significant increase in the risk of peeling. When the substrate is bent, the coating with weak adhesion cannot move synchronously with the deformation of the substrate, and a relative displacement will occur between the coating and the substrate. This displacement will destroy the local bonding force, and firstly, a small peeling will appear at the stress concentration point of the bending. As the degree of bending increases, these small peelings will gradually expand, and eventually cause the coating to warp and peel off from the substrate, especially in the parts with small bending angles or repeated bending. This peeling will be more obvious. In addition, insufficient adhesion may also cause separation between the layers inside the coating, forming a stratification phenomenon, further weakening the overall anti-stripping ability.
The bonding state of the coating and the substrate surface directly affects the effect of adhesion on the anti-stripping performance of bending. If the substrate surface is well pretreated, such as through phosphating, passivation and other processes to form a rough and active surface, the color coated coil coating can penetrate deeper into the tiny pits on the substrate surface to form a structure similar to "mechanical bite", which can significantly enhance adhesion. During bending, this "bite" effect can effectively resist the relative sliding between the coating and the substrate, allowing the coating to adhere more firmly to the substrate and reduce the possibility of peeling. On the contrary, if there are impurities such as oil, oxide layer, etc. on the surface of the substrate, it will hinder the close combination of the coating and the substrate. Even if the coating itself has good texture, it will peel off in a large area during bending due to insufficient adhesion.
The coordination of the coating's own flexibility and adhesion will also affect the anti-peeling performance during bending. A coating with strong adhesion and good flexibility can better adapt to the deformation of the substrate during bending, and will not produce excessive internal stress inside the coating, thereby reducing cracking and peeling caused by internal stress concentration. If the coating has poor flexibility, even if the adhesion is strong, the coating may crack itself during bending due to the inability to withstand deformation. The cracked coating will lose its integrity, and it is difficult to avoid peeling no matter how strong the adhesion is. Therefore, the adhesion needs to cooperate with the flexibility of the coating to achieve the best anti-peeling effect during bending.
Environmental factors also have an indirect impact on the relationship between adhesion and anti-peeling performance. In a humid or high temperature environment, the bonding strength between the coating and the substrate may be weakened to a certain extent. At this time, if the coating originally has insufficient adhesion, the risk of peeling during bending will be further increased. A humid environment may cause micro-corrosion between the coating and the substrate, destroying the bonding surface; high temperature may reduce the viscosity of the coating and affect the stability of adhesion.
A coating with strong adhesion can resist the erosion of these environmental factors to a certain extent, maintain the bonding strength with the substrate, and even if the bending process is performed in an unfavorable environment, the anti-peeling performance can still be well guaranteed.
The thickness of the coating is equally important to match the adhesion. When a coating that is too thick is bent, its own weight and internal stress will increase. If the adhesion cannot support this additional stress, the coating is prone to peeling at the bending part. The color coated coil coating with moderate thickness and strong adhesion can be evenly stressed during bending, and the stress distribution inside the coating is reasonable. With strong adhesion, it can effectively resist peeling. In addition, the uniform coating thickness can make the adhesion uniformly distributed on the coating surface, avoiding the adhesion difference caused by excessively thick or thin local coatings, thereby maintaining the overall anti-peeling performance balance during bending.
The chemical bond formed during the curing process of the coating is the chemical basis of adhesion and also affects the anti-stripping performance during bending. If a stable chemical bond is formed between the coating and the substrate, this bond can provide continuous bonding force during bending and resist the separation trend caused by deformation. However, the adhesion formed by physical adsorption alone is easily destroyed by external force during bending, resulting in coating peeling. Therefore, by optimizing the curing process to enhance the chemical bond between the coating and the substrate, the adhesion can be significantly improved, thereby enhancing the anti-stripping performance during bending.
In short, the coating adhesion of the coated steel color coated coil directly determines the anti-stripping performance during bending by affecting the bonding strength between the coating and the substrate, the integrity of the coating, and the resistance to environmental factors. The stronger the adhesion, the firmer the bonding between the color coated coil coating and the substrate, the more it can adapt to the deformation during bending, and the better the anti-stripping performance; on the contrary, insufficient adhesion will make the coating easily separate from the substrate during bending, resulting in peeling.
