How to Choose a Water-Based Silicone Defoamer That Won't Cause Pinholes?
I. The Principle of Pinholes Caused by Water-Based Silicone Defoamers
1. Silicone defoamers with large particle sizes, excessive local weight, and uneven surface tension. Their defoaming
mechanism involves reducing surface tension to break down the bubble film. However, if the amount added is too
large, the dispersion is uneven, or the compatibility with the water-based resin system is poor, excess silicone that
doesn't participate in defoaming will remain in the paint film as microdroplets.
2. During the coating film-forming process, these silicone microdroplets migrate to the paint film surface, forming
"low surface tension islands." This causes the surrounding high surface tension paint to flow towards these islands,
ultimately resulting in pinholes, fisheyes, and oil shrinkage.
II. Criteria for Selecting Non-Pockmarking Waterborne Silicone Defoamers
1. Polyether-modified silicone is required. Pure dimethyloxane emulsions have poor compatibility, strong migration,
and are prone to pinhole formation. Polyether-modified silicone has good water compatibility, is less prone to migration,
and reduces the risk of pinhole formation. A mixture of polyether-modified silicone and hydrophobic silica has strong
defoaming performance, is less prone to migration, and has better compatibility.
2. The silicone particle size should be fine (20-200nm) and narrowly distributed to ensure system stability and prevent
precipitation and pinhole formation.
3. Low silicone content is required, with 5%-15% effective silicone. Nonionic or anionic composite emulsifiers should
be used in the emulsion system to prevent stratification and oil floating.
4. Do not add excessive amounts to the resin system: Exceeding the required effective amount (generally recommended
between 0.05% and 0.5%, optimally about 0.1%) can easily induce pinhole formation. 5. Compatibility with resin systems:
For waterborne acrylic systems, choose polyether-modified silicone defoamers with microemulsification and moderate
defoaming power (RK-8413 recommended); For waterborne epoxy polyurethane systems: Silicone is highly sensitive
and easily causes pinholes, requiring low silicone content and high compatibility. Generally, non-silicone defoamers
or polyether-siloxane copolymer defoamers are chosen (RK-8409 recommended); For transparent varnish systems:
Defoamers with low silicone content and good compatibility are required (RK-8405 recommended).
