The primary function of water-based wetting agents is to reduce interfacial surface tension, ensuring effective wetting of various substrates—such as plastic, paper, and metal—as well as thorough wetting of pigment powders. Selection requires a comprehensive evaluation across four dimensions: preventing cratering, maintaining foam stability and recoatability, and ensuring compatibility with printheads in digital inkjet applications.
I. Benchmarking and Selection Guide for Mainstream Wetting Agents
1. Non-ionic fatty alcohol polyoxyethylene ether additives
✅ Good system compatibility; drawbacks include high foaming and insufficient dynamic wetting performance; rarely used in the ink industry nowadays.
2. Sulfonate-based anionic substrate wetting agents
✅ Key advantages include good powder wetting performance and assistance in efficient pigment dispersion; offers good overall cost-performance;
❌ Performance limitations include a tendency to foam and sensitivity to system pH fluctuations; can compromise storage stability under certain conditions;
Suitable for the pigment grinding stage; applicable to water-based color pastes and standard water-based inks.
3. Acetylenic diol wetting agents (Industry-preferred choice; suitable for all coating and ink systems)
✅ Advantages include low-foaming characteristics, excellent dynamic surface tension performance, no adverse effects on recoating, and minimal interference with pigment systems; the top choice for digital inkjet inks;
❌ Less effective at lowering surface tension compared to silicone-based products; spreading performance on hard-to-wet substrates is insufficient;
Widely used in water-based inks, water-based digital inkjet systems, and water-based topcoats, balancing excellent wetting with low foaming;
Recommended grades: RK-8030, RK-8014XD.
4. Polyether-modified polysiloxane wetting agents
✅ Performance advantages include excellent surface tension reduction and superior spreading/wetting on hard-to-wet plastic substrates;
❌ Application risks include potential defects such as craters, pinholes, recoating failure, and poor adhesion if overdosed; some grades may stabilize foam;
Suitable for low-adhesion substrates like PP and PET; strictly avoid use in digital inkjet systems, as they can easily cause printhead clogging. Recommended models: RK-8026, RK-8065.
II. First, define the two core application dimensions: pigment powder wetting and substrate interface wetting.
1. Pigment powder wetting: Add during the grinding and dispersion stage.
Prioritize the use of low-foaming anionic or non-ionic wetting and dispersing additives. These displace air adsorbed on the pigment surface, shorten sand-milling times, and reduce the risk of system flocculation.
- Suitable for wet-grinding processes involving water-based pigment concentrates, water-based inks, and water-based coatings.
- Strictly avoid high-foaming additives to prevent the entrapment of large amounts of micro-bubbles during grinding, which could otherwise cause pinhole defects in the final coating.
2. Substrate interface wetting: Add during the paint or ink blending stage.
For hard-to-wet substrates such as PE, PP, PET, and laminated paper, select silicone-based or acetylenic diol-based additives to simultaneously lower the system's static and dynamic surface tension.
Dynamic surface tension is a critical parameter: in high-speed spraying or high-speed digital inkjet printing, wetting agents with poor dynamic surface tension performance can easily lead to surface defects such as misting/cobwebbing, edge retraction, and dry spray.
III. Selection guide based on application scenarios
1. Water-based industrial coatings (water-based paints for metal and plastic): For hard-to-wet substrates, select low-migration polyether-modified silicones; for standard substrates, use acetylenic diol wetting agents. Recommended grades: RK-8030, RK-8014XD.
2. Standard water-based inks (flexo and gravure printing): Prioritize acetylenic diol wetting agents; for challenging substrates, small amounts of silicone-based products may be used in combination. Recommended grades: RK-8026, RK-8065.
3. Water-based digital inkjet inks: Prioritize the use of acetylenic diol wetting agents; strictly prohibit high-migration silicone components to avoid issues such as printhead clogging and ink misting. Recommended models: RK-8030, RK-8014XD.
IV. Key Evaluation Indicators for Formulation Selection (Mandatory Small-Scale Trial Required)
1. Standard dosage range: 0.1%–1.0%. For silicone-based products, the lower end of the dosage range is preferred; excessive use significantly increases system risks.
2. Surface tension evaluation: Prioritize dynamic surface tension (to match high-speed coating or inkjet applications); static surface tension is used to assess substrate wetting performance.
3. System compatibility: No precipitation or oil separation; otherwise, coating defects such as craters (fish-eyes) may occur.
4. Foam characteristics: Low-foaming grades are preferred for ink and inkjet systems to prevent coating defects such as pinholes and fish-eyes.
5. Side-effect performance evaluation: Includes recoatability, inter-layer adhesion, water resistance, and heat storage stability. For digital inkjet applications, additional testing for printhead corrosion risk and continuous jetting stability is required.
V. Practical Risk Mitigation Guidelines
- Do not blindly pursue extremely low surface tension; excessive use of silicone-based additives is a primary cause of cratering defects.
- Powder wetting and substrate wetting represent distinct functional requirements; in most formulations, they need to be addressed through a synergistic combination of additives.
- Mandatory tests during the small-scale trial phase: heat storage stability, appearance of the formed coating film, and verification of inter-layer recoatability.
