How to use a wetting agent that does not affect recoating
How to use a wetting agent that does not affect recoating
In applications such as coatings, inks, and adhesives, the selection and use of wetting agents that do not affect recoating must follow scientific principles to avoid adhesion loss or shrinkage problems caused by migration, residue, or system incompatibility. The following is a detailed usage strategy:
1. Selection principle: avoid "minefields" and match the system
Core logic:
The wetting agent must be compatible with the base resin (such as acrylates, epoxies, and polyurethanes) and the upper coating material (such as topcoats and inks) to avoid performance conflicts due to differences in chemical properties.
Counterexample: Silicone wetting agents (such as polydimethylsiloxane) easily migrate to the surface to form low surface energy areas, resulting in shrinkage or poor adhesion of subsequent coatings.
Positive example: Polyether, fluorocarbon, and polyacrylate wetting agents are compatible with most resin systems and have no migration risk.
Specific scenario matching:
Water-based system: Water-soluble polyether wetting agents are preferred to avoid reactions with water-based resins.
UV curing system: Use fluorocarbon wetting agents to prevent side reactions with photoinitiators.
High solid coatings: Use low-volatility polyacrylate wetting agents to avoid residual solvents that affect recoating after evaporation.
2. Usage: Precise control, synergistic effect
Addition amount control:
Principle: Excessive wetting agent will lead to low surface tension, causing shrinkage or poor leveling; insufficient wetting will result in insufficient wettability.
Data reference:
Water-based coatings: 0.1%-1.0% (based on solid content).
UV curing coatings: 0.2%-0.5%.
Experimental verification: Determine the optimal addition amount through gradient experiments, such as testing adhesion and shrinkage rate in the range of 0.2%-0.8%.
Addition time:
Addition in the dispersion stage: Add the wetting agent before pigment grinding or in the dispersion stage to ensure uniform adsorption on the pigment surface and improve wetting efficiency.
Avoid late addition: Addition after grinding may cause the wetting agent to be unable to fully penetrate the pigment particles, affecting the dispersion effect.
With defoamer:
Synergy principle: Wetting agent and defoamer need to be used in combination to avoid performance imbalance caused by using them alone.
Example:
Water-based coatings: Polyether wetting agent is used with mineral oil defoamer to balance wetting and defoaming.
UV-curing coatings: Fluorocarbon wetting agent is used with non-silicone defoamer to prevent silicone migration.
3. Testing and verification: Ensure recoatability
Laboratory testing:
Adhesion test: Test the adhesion between coatings under simulated recoating conditions (such as different drying time and temperature) to ensure no peeling or shrinkage.
Surface tension test: Use a contact angle meter to evaluate the wetting effect of the wetting agent on the substrate to ensure that the surface tension is within a reasonable range (such as 25-35 mN/m).
Practical application verification:
On-site recoating test: Carry out multiple recoating experiments on the production line to observe the changes in the appearance and performance of the coating.
Customer feedback collection: Adjust the type or amount of wetting agent based on customer feedback.
4. Common Problems and Solutions
Problem 1: Shrinkage after recoating
Cause: Silicone migrates to the surface to form low surface energy areas.
Solution: Use non-silicon wetting agents (such as polyethers) and ensure that the upper coating is compatible with the wetting agent.
Problem 2: Poor interlayer adhesion
Cause: The wetting agent is incompatible with the resin of the upper coating.
Solution: Select a wetting agent that matches the upper resin, or add an adhesion promoter to the upper coating.
Problem 3: Surface fogging or gloss reduction
Cause: Excessive wetting agent or reaction with photoinitiator.
Solution: Reduce the amount added, or change to a wetting agent type that is compatible with the photoinitiator.
5. Recommended wetting agent types and cases
Polyether wetting agents
Applicable scenarios: water-based coatings, inks, architectural coatings.
Advantages: Compatible with a variety of resins, balanced wetting and defoaming.
Fluorocarbon wetting agents
Applicable scenarios: UV-curing coatings, high weather-resistant coatings.
Advantages: low surface tension, chemical resistance, no effect on recoatability.
Polyacrylate wetting agent
Applicable scenarios: high solids coatings, industrial coatings.
Advantages: low volatility, long-term stability, improved recoating adhesion.
Summary
Selecting and using a wetting agent that does not affect recoating should follow the principle of "matching system, precise control, and synergistic enhancement". Through laboratory testing and actual application verification, it can be ensured that the wetting agent does not damage the recoatability while improving the wetting performance. It is recommended to select polyether, fluorocarbon or polyacrylate wetting agents according to the specific application scenario, and match them with appropriate defoaming agents to achieve the best effect.