Why is there foam in the paint and coating? What we should do to eliminate foam?

Why is there foam in the paint and coating? What we should do to eliminate foam?

           
check below details:

•          Surface tension

The surface tension of the coating has a great influence on the defoaming agent. 

The surface tension of the defoaming agent must be lower than the surface tension of the coating. Otherwise, there is no defoaming and foam suppression. The surface tension of the coating is a variable factor, so a constant surface tension is required when using the defoamer, and then the surface tension variation factor is taken into account.

• The influence of other additives

Surfactants used in coatings are mostly functionally incompatible with defoamers. In particular, emulsifiers, wetting and dispersing agents, leveling agents, thickeners, etc., have an effect on the effect of the antifoaming agent. Therefore, we must pay attention to the relationship between different additives when mixing various additives, and choose the best balance point.

• Baking temperature

The paint enters the high temperature baking at normal temperature, and the viscosity begins to drop back at the beginning. The bubbles can be moved to the surface. However, due to the evaporation of the solvent, the curing of the coating, and the increase of the surface viscosity, the foam tends to be more stable, trapped on the surface, and shrinks. Holes and pinholes, so the baking temperature, the fixed speed, and the solvent evaporation rate also have an effect on the defoaming agent.

• Solid content, viscosity, elasticity of the coating

High solids thick coating film, high viscosity, high elasticity coatings are very difficult to defoam. In these coatings, the defoaming agent is difficult to diffuse, the microbubbles become slow, the foam migration to the surface is reduced, and the foam viscoelasticity is large. There are many unfavorable defoaming factors. The foam in these coatings is quite difficult to eliminate, and it is best to use an antifoaming agent in combination with a defoaming agent.

•     Painting method and construction temperature

There are many coating construction methods, such as brush coating, roller coating, shower coating, blade coating, spray coating, screen printing and the like. The coating method used differs in the degree of foaming of the different coatings. Brushing and roller coating are more than spraying and scraping. When the temperature is higher than the temperature, the foam is more, but when the temperature is high, the foam is eliminated.

How to choose defoamer for different paints?

There are many types of defoamers and different characteristics, so the defoamers selected in different formulations are also different.

Flat coating

Formulation features: low viscosity, low defoaming pressure

Recommendation: mineral oil or mineral oil modified polyether

Elastic coating

Formulation features: high viscosity, large defoaming pressure

Formulation suggestion: polyether modified silicone

Topcoat and film adhesive

Formulation recommendations: Polyethers, which can effectively prevent surface defects and have less effect on gloss

Water in water colorful

Formula features: more surfactants, stable foam

Formulation recommendations: polyether or mineral oil modified polyether

Defoamer use precautions

Must be thoroughly stirred and mixed well before use;

Adding while the paint is stirring;

Before use, it is generally diluted without water;

The dosage should be appropriate, and the dosage should be too much, which will cause problems such as shrinkage, shrinkage, and poor brushing; if the dosage is too small, the defoaming effect is poor;

It is best to add it in two parts, that is, it is added in the grinding stage and the paint adjustment stage, generally half of the total amount, and the defoaming agent with good antifoaming effect in the grinding stage is used, and the foam breaking effect is good in the paint adjustment stage. .