The differences in adhesion testing between water-based steel structure paint and solvent-based paint primarily manifest in three aspects: the test method selection, the performance characteristics of test results, and the impact of the test environment. These differences stem from fundamental differences in the film-forming materials, solvent properties, and application processes.
In terms of test method selection, water-based steel structure paint, due to the higher surface tension and poorer wettability of water, has weaker substrate penetration than solvent-based paint. Therefore, adhesion testing relies more heavily on the suitability of the substrate preparation process. For example, in the cross-cut test, water-based paint is more sensitive to substrate surface roughness. Uneven polishing or insufficient cleanliness of the substrate can easily lead to coating edge warping and increased tape peeling. Solvent-based paint, on the other hand, has a strong dissolving and penetrating effect on the substrate due to the organic solvent, which can partially compensate for any deficiencies in substrate preparation. Under the same testing conditions, its cross-cut test results are generally superior to those of water-based paint.
The differences in the performance characteristics of the test results are closely related to the film-forming mechanisms of the two types of paint. The film formation process of water-based steel structure paint relies on the evaporation of water and the fusion of emulsion particles. Its adhesion is more dependent on chemical bonding with polar groups on the substrate surface. Therefore, in pull-off testing, water-based paints are more likely to exhibit adhesion failure at the interface between the coating and the substrate. This means that when the tensile force reaches its peak, the coating completely peels off the substrate surface, resulting in a smooth fracture surface. In contrast, the film formation process of solvent-based paints involves the evaporation of the organic solvent and the cross-linking and curing of the resin molecules. Its adhesion relies on both mechanical intercalation and chemical bonding. In pull-off testing, solvent-based paints exhibit a more complex failure mode, potentially exhibiting both cohesive failure and interfacial adhesion failure. This means that when the tensile force reaches its peak, the coating breaks internally or partially remains on the substrate surface, resulting in a rough fracture surface.
The differences in the influencing mechanisms of the testing environment further exacerbate the divergence in the adhesion performance of the two types of paints. The application and testing of water-based steel structure paint are highly sensitive to ambient temperature and humidity. Low temperatures (below 5°C) or high humidity (relative humidity >85%) significantly slow water evaporation, resulting in poor coating leveling and uneven film formation, which in turn reduces the stability of adhesion testing. For example, in the circle scratch method, water-based paint is prone to coating buildup or cracking in the scratch path at low temperatures, affecting the accuracy of the rating. Solvent-based paint, on the other hand, offers more reproducible adhesion test results under the same testing conditions, as its organic solvent evaporates quickly and is less susceptible to temperature and humidity. This reduces the impact of environmental factors on test results.
Furthermore, the differences between the two types of paint in adhesion testing are also reflected in the flexibility of the test standards. Because the adhesion performance of water-based steel structure paint is more significantly affected by factors such as substrate preparation and construction technology, its testing standards often impose stricter requirements on aspects such as substrate pretreatment and coating thickness control. For example, in the ISO 12944 standard, when water-based paint is used for corrosion protection of steel structures, its adhesion test requires a comprehensive assessment based on parameters such as substrate surface roughness and cleanliness, while the testing standards for solvent-based paint focus more on the performance indicators of the coating itself.
