Guidelines for Selection of Defoamers for Epoxy Coatings Ink
Core premise for selection: Epoxy systems are divided into three categories: water-based two-component epoxy, solvent based epoxy, and solvent-free/high solid epoxy; The epoxy amine curing system is highly sensitive to defoamers, and the selected defoamer must not interfere with the amine curing reaction. At the same time, it is necessary to take into account the efficiency of breaking bubbles and removing microbubbles, and strictly control common drawbacks such as shrinkage, fisheye, and re coating adhesion.
I. Selection Based on the System
1. Water-based Two-component Epoxy (Water-based epoxy anti-corrosion coatings, water-based epoxy inks; amine-cured)
Key Control Points: Water-based epoxy systems are highly sensitive to silicone-based additives, which easily trigger defects such as fish-eyes (craters); therefore, prioritize the selection of low-silicone or silicone-free additive systems.
- Grinding stage (foam suppression): Non-silicone polymer-type defoamers (RK-3062G, RK-3062E, RK-3062H)
- Paint mixing stage (micro-foam removal and pinhole prevention): Low-silicone polyether-modified silicone emulsion defoamers (RK-8405, specifically for water-based epoxy systems)
- When selecting defoamers for water-based two-component epoxy systems, avoid two high-risk categories: Exercise caution with mineral oil-based defoamers, as they can impair the cured film's water and salt spray resistance and cause a loss of gloss; high-solid-content silicone emulsion defoamers are prone to causing cratering defects and poor inter-coat adhesion.
2. Solvent-based Epoxy Coatings/Inks (Anti-corrosion primers, epoxy anti-rust primers, solvent-based screen-printing epoxy inks)
- For solvent-based epoxy colored paint (primer) systems, select silicone-based defoamers loaded with hydrophobic particles (RK-3108, RK-3109). These offer excellent defoaming efficiency, completely eliminating air bubbles entrapped during mixing and spraying processes. The recommended dosage range is 0.1%–0.3%; the additive should be diluted with solvent before incorporation. - For solvent-based epoxy clear coats and high-gloss topcoat systems, preference should be given to low-silicon modified polysiloxane or non-silicone polymer defoamers (e.g., RK-3041, RK-3067, RK-3162). These achieve a balance between defoaming efficiency and system compatibility, effectively reducing the likelihood of surface defects such as fish-eyes and loss of gloss.
3. Solvent-free / High-solids epoxy (flooring, epoxy screen printing inks, potting compounds; characterized by high viscosity and the difficulty of releasing entrapped micro-bubbles)
- For solvent-free or high-solids epoxy systems, modified silicone polymer-type deaerators (e.g., RK-3108RR, RK-3109RR, RK-3268) are the preferred choice. These additives focus primarily on deaeration, facilitating the migration and release of entrapped micro-bubbles; they are suitable for thick-film and self-leveling epoxy applications. The recommended dosage range is 0.2%–0.8%; the additive must be pre-dispersed into the resin phase and must not be added during the final stage of paint formulation.
- An alternative option for solvent-free or high-solids epoxy systems is the non-silicone polymer defoamer (e.g., RK-3178), which features a polymer structure free of silicon. Its key advantages include the elimination of risks associated with silicone migration and contamination, no negative impact on inter-coat adhesion, and a very low probability of causing cratering defects. However, its defoaming efficiency is relatively lower, making it better suited for applications requiring high surface clarity, such as high-gloss clear coats and transparent epoxy inks.
- When selecting epoxy defoamers, avoid standard pure dimethylsiloxane additives; these substances are highly prone to causing cratering defects and can impair inter-coat adhesion.
II. Additional Special Requirements for Epoxy Inks
Screen-printing epoxy inks are high-solids, thick-film systems; entrapped air bubbles can easily lead to surface defects such as pinholes and pitting:
1. Dual functionality—addressing both bubble breaking and air release—must be achieved simultaneously; reliance solely on surface-level bubble suppression mechanisms is insufficient.
2. For epoxy ink systems requiring high light transmission after curing, the use of high-silicon-content defoamers must be strictly avoided, as such additives readily cause haziness or loss of transparency in the cured ink layer.
3. For screen-printing epoxy ink systems involving subsequent overprinting or multi-layer printing processes, non-silicone defoamers should be prioritized to fundamentally prevent issues such as inter-layer adhesion failure and coating delamination caused by silicone migration.
III. Key Points for General Selection and Validation of Additives in Epoxy Systems (Mandatory for Laboratory-Scale Trials)
1. Dosage Gradient Test: Conduct validation using dosage gradients of 0.1%, 0.2%, and 0.3%. Epoxy systems have a critical saturation threshold; exceeding this limit will directly trigger cratering defects.
2. Addition Sequence: Incorporate the majority of the foam-suppressing components during the grinding stage and add a small amount of defoaming components during the final paint-blending stage; strictly avoid adding a large dose all at once at the end of the process.
3. Four Validation Indicators:
① Bubble-breaking and micro-bubble removal performance after mixing and spraying processes;
② Surface appearance of the cured coating (pinholes, fish-eyes, craters, gloss);
③ Interlayer adhesion performance of the cured epoxy coating;
④ Thermal storage stability test for the epoxy system (constant temperature of 50°C for 7 days; observe for phase separation, precipitation, or degradation of defoaming efficacy).
4. Curing Interference Validation Test: Confirm that the defoamer does not react with the epoxy resin or amine curing agent and does not affect the system's surface-dry or hard-dry times.
IV. Reference List of Common Commercial Grades (Source: Official Technical Documentation)
1. RK-3062G: Water-based epoxy; non-silicone polymer defoamer
2. RK-8405: Developed specifically for two-component water-based epoxy systems; addresses pinholes and micro-bubbles
3. RK-3108: Polyether-modified silicone; for solvent-free epoxy and screen-printing epoxy inks
4. RK-3109: For solvent-based epoxy colored coatings; highly efficient defoaming and de-aeration
5. RK-3268: For solvent-based/solvent-free epoxy; silicone polymer de-aerator; suitable for micro-bubble removal in thick-film epoxy coatings and epoxy inks
