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Defoamers and leveling agents are mostly surface active substances that need to run towards the surface of the paint film to seize their position; One wants to reduce the surface tension difference and eliminate the gradient, while the other wants to locally lower the surface tension and puncture the bubble membrane. The logic of the two is naturally contradictory, so they often fight.

First of all, clarify that all surface additives essentially migrate to the gas-liquid interface for competitive adsorption.

1、 Mechanism disassembly, why conflicts occur

1. Objective of leveling agent

Leveling agent: evenly distributed on the entire surface of the paint film, it flattens the overall surface tension, reduces the surface tension gradient, suppresses the Bernard vortex, and eliminates orange peel, hair, shrinkage, and brush marks. Requirement: Spread evenly on the entire surface without local enrichment.

2. Objective of defoamers

Defoamer: It is a low surface tension component that must selectively migrate onto the liquid film of bubbles, rapidly reducing the surface tension locally on the bubble, causing the bubble to thin and rupture. Requirement: Local enrichment and significant reduction of surface tension locally.

Leveling agent: I hope the surface tension is the same everywhere;

Defoamer: It is necessary to create a local surface tension difference in order to break the foam. If the defoamer is spread too evenly, it will lose its defoaming ability; If the leveling agent is squeezed away by the defoamer and the surface tension fluctuates, it will directly produce shrinkage holes, fish eyes, and flowers.

2、 There are two types of additives with different conflicting behaviors

① Organic silicon leveling agent+organic silicon defoamer

Organic silicon leveling agent: weak polysiloxane, moderately reduces surface tension, evenly spreads. Organic silicon defoamer: higher activity, larger silicon chain segments, and stronger ability to reduce surface tension. Conflict phenomenon:

1. Defoamers compete for the interface, and leveling agents cannot adsorb evenly → leveling deteriorates, orange peel, and Benard vortex flowers appear;

2. Excessive/poor dispersion of defoamers → formation of extremely low surface tension zones locally → fish eyes, shrinkage cavities, pinholes;

3. In the later stage, it is also prone to re coating, loss of adhesion, poor adhesion, silicon migration, and oil stains.

Many people misunderstand that they are all made of silicon and should be compatible. On the contrary, the interface competition of silicon is the most intense.

② Acrylic leveling agent+organic silicon defoamer

Acrylic leveling agents do not significantly reduce surface tension, mainly relying on adjusting resin compatibility and improving flow. The conflict is relatively small, but it will still:

Defoamer spreading interferes with leveling;

When the defoamer is not well dispersed, point like shrinkage pores may appear; Advantages: Even if there is more silicon defoaming, the recoating performance is generally much better than silicon leveling.

Mineral oil defoamer: It has the best compatibility with acrylic acid leveling, but is prone to extinction, oil stains, poor water resistance, and oil return during baking.

3、 Other factors that amplify conflicts through superposition

1. Add defoamer first, then leveling agent: The defoamer has already occupied the interface, making it difficult for leveling agent to go up, resulting in poor leveling; First add leveling agent, then add defoamer: the leveling film has already formed, and the defoamer is difficult to migrate to the foam film, resulting in poor defoaming.   ✅  Practical operation: Add defoamer in the dispersion stage, and add leveling agent in the later stage of paint adjustment and before discharge, all of which need to be pre diluted.

2. The surface tension of the water-based system is inherently high, and the competition for additives is more intense, with conflicts far greater than those of solvent based paints; UV system and cationic UV are more sensitive: adding more silicone additives can also affect curing and adhesion.

3. The threshold for additive addition is that defoamers have an “effective window”:

Too little: unable to eliminate bubbles;

Suitable: selectively spread only at the bubble location;

Excess: Covering the entire surface, directly damaging leveling and causing shrinkage holes. Leveling agent also has an upper limit. Adding more will also stabilize the foam, but foam will be more.

1. Compatibility is the key. If the defoamer is too compatible with the resin, it will dissolve in the paint and refuse to run to the bubble interface, resulting in defoaming failure; Poor compatibility: prone to local precipitation, forming shrinkage cavities, oil spots, and damaging leveling. A good defoamer is “limited compatibility”: it is usually dispersed in the paint and only migrates to the foam film when encountering bubbles. Leveling agents require moderate compatibility and uniform distribution without precipitation. The requirements for compatibility between the two are inherently opposite.

Reason for the phenomenon

The foam cannot be eliminated, and the defoaming differential leveling agent is too strong to wrap the bubble film and inhibit the migration of defoamer; Leveling agent plays a stabilizing role in foam

Leveling agent, orange peel, and foaming defoamer occupy the interface, and leveling agent cannot spread evenly, resulting in the reappearance of surface tension gradient

Fish eye and dot shaped shrinkage defoamers locally aggregate, forming extremely low surface tension points, and the surrounding paint liquid pushes outwards

Oil stains and poorly coated silicone defoamers accumulate on the surface, forming an isolation layer

5、 Matching scheme for water-based industrial paint

1. Priority pairing strategy

Pursuing good leveling and balancing defoaming: Acrylic leveling agent+weakly active organic silicon defoamer/polyether defoamer, this is the most stable combination;

Try to avoid using high activity silicone leveling agents and silicone defoamers together unless absolutely necessary;

High gloss topcoat: Use less strong silicone defoamers, prioritize polyether defoamers, sacrifice some defoaming power for leveling and appearance;

Primer and thick anti-corrosion paint: Strong silicone defoamer can be used, with low leveling requirements and insensitivity to conflicts.

1. Graded addition of additives, do not pour in one pot

High speed dispersion stage: defoamer, which first eliminates the ground foam and the foam introduced into it;

Paint adjustment, film-forming aids, and pH adjustment;

Finally, add leveling agent while stirring at low speed to avoid excessive use of leveling agent by high shear and to prevent re foaming.

1. There are defoaming leveling two in one additives on the market that use “low conflict” composite additives, which essentially balance the interfacial activity of the two and are suitable for formula simplification. The disadvantage is that the upper limit of individual performance is not as good as that of individual additives.

2. Don’t rely on the unlimited addition of additives to solve the problem of foam, which is not only an additive problem in many cases: insufficient wetting, filler suction, such rheological powders as attapulgite/aerosilicon bring bubbles, and the lotion itself stabilizes the foam. First reduce the foam from the source, rather than the defoamer hard shoulder, to reduce the pressure of defoamer addition.