Application analysis of defoaming agents in water-based coatings
As countries have successively formulated limit standards and regulations for volatile organic compounds (VOC), water-based coatings have developed rapidly in various countries due to their green, environmentally friendly, energy-saving, safe, and easy-to-use characteristics.
Water-based coatings, especially water-based industrial coatings based on various emulsions, need to add a variety of coatings during the formula design process due to the characteristics of the base material itself and the high requirements on the surface condition of the coating film and the high requirements on workability. Additives, among which the choice of defoaming agent is crucial.
If there are too many bubbles in the coating, it will limit production capacity, affect product quality, cause waste, pollute the environment, and may cause safety issues.
The main causes of foam in water-based coatings are:
- Bubbles are generated during stirring during the coating production process;
- Bubbles are generated during the paint canning process;
- Bubbles are generated during the construction process, such as roller coating or airless spraying;
- Paint produces gas during the curing process;
- Work on porous substrates such as stone, wood or cement boards creates air bubbles.
The stabilizing factor of bubbles is generally the role of surfactants. In the coating application process, surfactants may be the resin base material itself, emulsifiers, substrate wetting agents, wetting and dispersing agents, etc.
Adding defoaming agents to water-based coatings is the main method to reduce foam generated during the entire production and application process. The main functions of defoaming agents include defoaming and foam suppression.
There are many types of defoaming agents currently used, and there are three main categories of defoaming agents for water-based coatings: mineral oil type, with a market share of 80%; silicone type, with a market share of 17%; and polyether type, with a market share of 3%. Among them, mineral oil defoaming agents are the most cost-effective and commonly used. They can be used in most flat and semi-gloss latex paints, but their foam breaking and defoaming effects are not as good as those of silicone and polyether defoaming agents. Silicone defoaming agents have extremely low surface tension, excellent defoaming and foam suppression capabilities, and have little impact on the gloss of the coating film. However, when used improperly, they can cause poor recoatability and shrinkage in the coating film. Polyether defoaming agents are mainly used in systems that require high compatibility, but have weak defoaming capabilities and a small market share. The compatibility and anti-foaming and anti-foaming performance of the above-mentioned defoaming agents can be improved through technical means such as compounding and modification.
Defoaming agents can be evaluated from aspects such as foam suppression, defoaming, compatibility, degassing and brushability.
Commonly used methods to evaluate the anti-foaming and anti-foaming performance include: high-speed dispersion method, shake flask method, air blowing method, vibration method and cyclic bubbling method, etc. These methods all use changes in foam volume to evaluate the performance of defoaming agents.
There is no fixed standard for the evaluation of defoaming agents. The defoaming performance is judged by mutual comparison. The test method, test conditions, defoaming agent concentration, stirring time and intensity, etc. all have an impact on the test results. Which method to choose? The evaluation depends on the actual application.
