Wrinkling, shrinkage, and the formation of wrinkles in the paint film are common surface defects during the coating process. These issues are often related to the paint formulation, application conditions, or improper substrate preparation. Below are the specific causes and corresponding solutions:

1. Primary Cause Analysis

1.1 Excessive Coating Thickness

● Applying too thick a coat in a single application causes the surface to dry much faster than the underlying layer. As the surface cures and contracts, the uncured bottom layer wrinkles.

● Common in high-solids or high-viscosity paints.

1.2 Mismatched Solvent Evaporation Rates

● Excessively fast solvent evaporation (e.g., in high-temperature environments or with fast-evaporating solvents) causes the surface to harden rapidly, trapping solvents beneath.

● Too much slow-evaporating solvent residue can also lead to localized shrinkage.

1.3 Unsuitable Ambient Temperature

● High temperatures (>35°C) accelerate surface curing, while low temperatures (<5°C) slow down the entire curing process, both potentially causing uneven shrinkage and wrinkling.

1.4 Improper Substrate Preparation

● Substrate contamination (oil, grease, dust), inadequate cleaning of old coatings, or applying a topcoat before the primer is fully dry can lead to poor adhesion and subsequent shrinkage.

1.5 Paint Formulation Issues

● Incompatibility between the resin and solvent system, or excessive use of driers (e.g., excess cobalt driers in alkyd paints).

1.6 Application Tools or Technique

● Uneven pressure during brushing or rolling creates significant thickness variations. Poor atomization during spraying leads to localized paint buildup.

2. Solutions and Preventive Measures

2.1 Adjust Paint and Application Parameters

● Control Coating Thickness: Follow the “multiple thin coats” principle, ensuring each layer’s dry film thickness does not exceed the paint’s recommended value (e.g., 80-120 µm).

● Adjust Solvent Evaporation Rate: Add slow-evaporating solvents (e.g., xylene, butyl acetate) in high temperatures; use faster solvents in low temperatures.

● Check Paint Compatibility: Ensure primers, intermediate coats, and topcoats are compatible from the same system; avoid mixing different paint systems.

2.2 Optimize the Application Environment

● Temperature Control: Maintain ambient temperature between 15-30°C and humidity below 80%. Avoid direct sunlight in heat; use heating equipment in cold conditions.

● Ventilation Management: Ensure adequate ventilation (avoid strong drafts directly on the coating surface) to allow uniform solvent evaporation.

2.3 Substrate Preparation and Application Operation

● Thorough Substrate Cleaning: Wipe with solvent to remove oils; sand old coatings and remove dust (recommended cleanliness: ISO 8501 Sa 2.5).

● Ensure Underlying Coat is Dry: Allow primer or previous coats to dry completely (per product instructions) before applying the next coat.

● Optimize Application Tools: Adjust spray gun pressure (e.g., 0.4-0.6 MPa), fluid flow, and atomization for spraying; avoid over-brushing during manual application.

2.4 Paint Formulation Adjustments (For Manufacturers)

● Add leveling agents (e.g., silicone or acrylic additives, dosage 0.1%-0.5%) to improve surface tension.

● Adjust the resin-to-solvent ratio to prevent excessive retention of high-boiling-point solvents.

● For baking paints (e.g., electrophoretic paints), use a stepped temperature curing program (e.g., 80°C → 120°C → 150°C).

2.5 Problem Remediation Methods

● Slight Wrinkling: Sand smooth and reapply a thin topcoat.

● Severe Wrinkling: Completely remove the defective coating, re-prepare the substrate, and reapply according to specifications.

3. Typical Case References

● Alkyd Paint Wrinkling: Often caused by excess cobalt driers; can be balanced by adding zinc/calcium driers.

● Epoxy Floor Coating Shrinkage: Often caused by unsealed substrate pores; recommended to apply a penetrating primer first.

● Automotive Topcoat Orange Peel: Adjust spray gun distance (15-20 cm) and add leveling agents (e.g., BYK-358).

4. Preventive Measures Checklist

1. Conduct a small test area before full application to verify suitability for conditions.

2. Use a viscosity cup (e.g., Ford Cup #4) to control paint viscosity (recommended 18-25 seconds).

3. For multi-component paints, mix strictly according to the ratio and allow induction time (e.g., 10-15 minutes for epoxy paints).

By systematically analyzing the causes of coating wrinkling and making targeted adjustments, such defects can be effectively avoided, enhancing the overall quality of the coating work.