The phenomenon of oil shrinkage (also known as cratering or fisheyes) in industrial paint coatings is mainly caused by uneven surface tension or substrate contamination. Below is a comprehensive solution:
I. Substrate Treatment
1. Thorough Cleaning: Ensure the substrate is free from oil, rust, or residual surfactants. Strengthen pre-degreasing and water-washing processes.
2. Surface Sanding: Lightly sanding the substrate helps improve adhesion. Smooth substrates are more prone to oil shrinkage.
II. Paint Formula Optimization
1. Adjust Surface Tension:
• Use low-surface-tension wetting agents (such as HY Wetting and Leveling Agent 2042) to improve paint spreading performance.
• Avoid excessive use of silicone-based defoamers. Add them early in the process and disperse at high speed.
2. Enhance Leveling:
• Add de-flocculating dispersants to stabilize pigments and reduce floating and mottling.
• Choose non-mineral-oil defoamers.
• Increase the use of hydrophobic alkali-swellable thickeners (such as HY Thickener 680) and reduce polyurethane thickener dosage to resist cratering.
III. Application Control
Environmental Management:
1. Control temperature and humidity to avoid construction under high heat or humidity.
2. Ensure compressed air is dry to prevent moisture from entering the coating system.
Process Adjustment:
• Optimize coating viscosity, film thickness, and drying conditions to prevent sagging or bubbling.
• Regularly clean spraying equipment to avoid powder contamination.
IV. Dynamic Problem Handling
• Surface Tension Imbalance: During high-shear coating processes, use surfactants with rapid directional orientation properties.
• Bubble Control: Use defoamers to eliminate pinholes; adding cyclohexanone can improve polyurethane shrinkage resistance.
V. Special Situation Handling
• Re-coating Issues: Avoid excessive silicone additives; balance crater resistance with recoatability.
• Solvent Selection: Adjust solvent evaporation rate (e.g., using butanol) to reduce film shrinkage.
By applying the above measures systematically and combining them according to specific situations, oil shrinkage issues in industrial paint coatings can be effectively resolved.
