Application analysis of defoamer in water-based coatings
Application analysis of defoamer in water-based coatings
Aug 19, 2024
Waterborne coatings have been rapidly developed in various countries by virtue of their green, energy-saving and peace of mind, and ease of use.
Waterborne coatings, especially waterborne industrial coatings based on various types of emulsions, need to add a variety of additives in the formulation design process due to the characteristics of the base material itself and the high demand for the surface state of the coating film and the high demand for constructability, in which the choice of defoamer is crucial. If there are more bubbles in the coating it will limit production capacity, affect product quality, cause waste, pollute the environment, and may bring about protection problems.
The main reasons for foam generation in water-based coatings are 1, The paint production process mixing bubbles; 2, Paint canning process produces air bubbles. 3, In the construction process to produce air bubbles, such as roller coating or airless spraying, etc.;. 4, The paint in the curing process produces gas; 5, In the construction of porous substrates produce bubbles, such as stone, wood or cement board.
The stabilizing factor of air bubbles is generally the role of surfactants. In the process of coating application, surfactants may be the resin base itself, emulsifiers, substrate wetting agents, wetting and dispersing agents and so on.
Adding defoamer to water-based coatings is the main method to reduce the foam generated throughout the production and application process, and the main functions of defoamers include defoaming and foam inhibition.
There are many varieties of defoamers in use at present, and the defoamers for water-based coatings mainly include mineral oils, organosilicones and polyethers. Mineral oil defoamers are cost-effective, more commonly used, can be used in the vast majority of flat and semi-gloss latex paint, but the effect of breaking the bubble and defoaming is not as good as organosilicon defoamers. Organosilicon defoamer has low surface tension, excellent defoaming and foam inhibition ability, and has little effect on the gloss of the coating film, but when used improperly, it will produce poor recoatability, film shrinkage and other drawbacks. Polyether defoamers are mainly used in systems with higher compatibility requirements, weaker defoaming ability and smaller market share. Through compounding, modification and other technical means can improve the compatibility and anti-foaming performance of the above defoamers.
The evaluation of defoamers can be assessed in terms of foam inhibition, defoaming, compatibility, degassing and brushability.
The commonly used methods for evaluating the antifoaming performance include: high-speed dispersion method, shaking bottle method, puffing method, shaking method and cyclic puffing method, etc. All of these methods utilize the change of foam volume to assess the performance of antifoaming agents. However, there is no fixed standard for the evaluation of defoamers, and the advantages and disadvantages of defoaming performance are judged by comparing with each other. The test method, test conditions, defoamer concentration, mixing time and intensity, etc., all have an impact on the test results, and the choice of which method is used for the evaluation depends on the actual application situation.
