Preventing Cratering: Selecting Defoamers for Single-Component Water-Based Adhesives

In single-component water-based adhesives, defoamer selection directly impacts coating quality and bond strength. Surfactants (e.g., emulsifiers, wetting agents) generate stable foam, while incompatible defoamers may cause cratering due to localized surface tension differences. Chemi Tech’s dynamic compatibility technology provides the following solutions:

1. Cratering Mechanism & Defoamer Selection

Root Cause: Hydrophobic components migrate to the air-liquid interface, creating surface tension gradients that trigger adhesive flow away from defect points.

Defoamer Comparison:

Case Alert: An automotive adhesive plant using silicone defoamer (0.05%) encountered microbubbles during coating. Increasing dosage to 0.1% caused 12% cratering and 15% adhesion loss.

2. Key Anti-Cratering Technologies

Staged Addition:

Grinding Phase: Add high-activity defoamers (e.g., modified silicone KM-231) for pre-dispersing macrofoam.

Adjustment Phase: Use polyether-modified defoamers (e.g., KM-237) for post-addition compatibility.

Molecular Design:

PEG Segments: Enhance hydrophilicity to reduce polarity mismatch with acrylic resins.

Controlled Particle Size (D50≤2μm): Minimize high-energy agglomeration sites.

Synergistic Wetting:

Combine alkynediol-based wetter (KMP-120) to lower dynamic surface tension below 25mN/m, eliminating substrate tension differences.

3. Chemi Tech Solutions & Case Data

KM-3050 (Polyether-Silicone Hybrid):

Scenario: PVC laminating adhesive (60% solids).

Performance:

0.4% dosage reduces initial foam height from 42mm to 15mm;

Crater-free coating on PE film with ≥98% peel strength retention.

KM-2080 (Block-Polyether Type):

Case: High-speed dispensing for electronics encapsulation.

0.3% addition improves bubble escape speed 3×, achieving Ra≤0.2μm surface smoothness.

Breakthrough: For high-solids acrylic adhesives (≥65%), pre-emulsified nanocapsules enable slow release of active components, reducing cratering by 90% while boosting defoaming efficiency 40%.