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Uzbekistan What are the No Foam for paints(1)

2023-05-04

Uzbekistan Selection of antifoaming agents for different applications:

Polyether polyester modified organosiloxane
An organic polysiloxane with a comb like structure. N+m is about 50-250, and the molecular weight is controlled between 1000-150000. Its compatibility is adjusted by polyethers and polyesters, and the longer the chain, the better the phase compatibility. Polyether modifications are the most common in this category, typically using ethylene oxide and propylene oxide. With the increase of the content of ethoxy groups, their compatibility with water also improves, so it is also possible to synthesize water-soluble siloxane type leveling agents. Ethylene oxide and propylene oxide can be used alone or mixed to control hydrophilicity and lipophilicity. If both ethoxy and propoxy groups are contained, a silicone based leveling agent for both water and oil use is prepared,

There is no unified understanding of the mechanism of defoaming agents. According to the mechanism of defoaming agents proposed by predecessors, there are generally the following types: [4]
General defoaming mechanism
Typical defoaming mechanisms with a broad overview are the Robinson defoaming mechanism and the Ross hypothesis. Among them, Robinson mechanism is the basis of Ross hypothesis, which mainly emphasizes the liquid drainage of defoamer destroying foam and Marangoni effect to realize defoaming; The Ross hypothesis is based on the fact that the defoamer particles are insoluble droplets, while some defoamers actually produce defoaming effects in a dissolved state, so the defoaming mechanism of the Ross hypothesis is not comprehensive

Stability factors of foam
The direct cause of foam is the presence of surfactant, which reduces the surface tension of the solution. Under the combined effect of this reason and the attenuation mechanism of foam, different foam systems show different stability properties, which are mainly related to the following factors: the surface tension of foaming solution, the surface viscosity of foam, the viscosity of solution, the self-healing effect of surface tension (i.e. Gibbs surface elasticity and Marangoni effect) "The surface double layer repulsion and entropy repulsion forces of liquid membranes, the hydrophobic end structure of surfactants, and the steric hindrance effect are not independent factors, and changes in one factor can cause other factors to also change.". The most important factors affecting the stability of foam are the elasticity of the liquid film and the liquid discharge rate. From this perspective, it can be seen that the main factors affecting the stability of foam are different in different foam systems, and sometimes several factors exist at the same time and work together.
In addition to the above factors, some other factors will also affect the stability of foam, such as the size of foam, the coordination of solute and solvent, temperature, pH value, the evaporation rate of solvent, the impact degree of foam and the adsorption rate of surfactant

Flat coating

agent

Features: Low viscosity, low defoaming pressure

Recommendation: Mineral oils or mineral oil modified polyethers

Elastic coating

dispersant

epoxy

Features: High viscosity, high No Foam pressure

Recommendation: Polyether modified silicone

Surface coating and film covering adhesive

Recommendation: Polyethers, which can effectively prevent surface defects and have a small impact on gloss

Water in Water Colorful

affect

Features: More surfactants, stable foam

Uzbekistan Recommendation: Use polyethers or mineral oil to modify polyethers

Precautions for use of paint No Foam:

Before use, stir thoroughly and mix evenly; Adding the paint while stirring; Before use, it is generally not diluted with water; The dosage should be appropriate. Excessive dosage can cause shrinkage, edge shrinkage, poor brushing performance, and other problems; Too little dosage leads to poor defoaming effect; Add it in two stages, namely, add it in the grinding stage and the paint mixing stage, generally accounting for half of the total amount each time. Use defoaming agents with good foam suppression effect in the grinding stage, and use defoaming agents with good foam breaking effect in the paint mixing stage