Why does paint blister and peel off during recoating? In-depth analysis of the impact of additive balance on interlayer adhesion.

Introduction: Recoating Challenges and the Pain of Adhesion In automotive paint repair, industrial paint refurbishment, or the recoating of wood coatings, workers often encounter a tricky phenomenon: despite a clean substrate, large areas of blistering and peeling occur after recoating, sometimes even flake off with a gentle tear. Many people habitually attribute this to environmental humidity or thinner ratios, but laboratory analysis shows that the real “invisible killer” is often the overlooked paint additives. I. The Core Truth: How Do Additives Destroy Interlayer Adhesion? Although additives constitute a small proportion of paint formulations, they are the “stabilizing force” for regulating paint film performance. If chosen improperly or added in excess of a critical amount, they can transform from “performance catalysts” into “quality destroyers.” Excessive Leveling Agents (Overly Smooth Paint Film): Adding excessive amounts of silicone-based leveling agents in pursuit of a mirror-like finish results in extremely low surface tension and an overly smooth surface. This prevents new paint from wetting and spreading on the surface, failing to “grip” the primer, thus leading to delamination. Defoamer Abnormalities (Microscopic Defects): Strong defoamers, if incompatible or excessive, can easily leave tiny pinholes or depressions in the dry film. During recoating, the solvent seeps into the old paint layer through these pinholes, causing localized swelling and resulting in noticeable blistering. Dispersant Imbalance (Interface Weakness): An imbalance in dispersant dosage can lead to pigment agglomeration, which not only affects color richness but also weakens the cohesive force and interfacial bonding within the paint film, increasing the coating’s brittleness and making it prone to peeling. II. Why do recoating effects vary so drastically between different manufacturers? This reflects the depth of paint R&D. For the same can of paint, experienced manufacturers use “additive balancing technology” to ensure smooth application while reserving sufficient surface energy for recoating. The compatibility of the additive system determines the product’s tolerance under extreme application conditions. III. Professional Solutions: Three Steps to Say Goodbye to Bubbling and Peeling Strict Formula Control and Precise Addition: The production end must strictly control the additive ratio according to the experimentally determined formula, avoiding arbitrary addition on-site. Especially for high-performance industrial coatings, fine-tuning of additives requires verification through adhesion testing. Physical modification and mechanical sanding: Before recoating, the old paint film is deeply sanded. By increasing micro-roughness (anchoring points), physical adhesion is provided to the new paint, which is the most effective way to solve the problem of “excessive slippage of the paint film.” System compatibility is crucial; mixing is strictly prohibited: Choose additives from the same brand and system. Mixing additives from different brands can easily lead to chemical reactions or physical incompatibility, causing the paint film structure to collapse. In conclusion, whether it’s automotive paint pursuing ultimate craftsmanship or industrial anti-corrosion emphasizing weather resistance, the quality of coatings depends not only on pigments and resins but also on the art of balancing additives. Mastering additives means mastering the key to coating quality.