The working principle of defoamers in coatings

1, the production of bubbles in the coating and the principle of stability:
in the production process of the coating, will be involved in the air and the formation of bubbles, some raw materials in the coating such as: surfactants, dispersants, etc. will make the bubble stable.
can also produce bubbles during the construction of the coating, depending on the way the coating is constructed. For example: curtain coating can be continuously involved in the paint air, airless spray is also easy to get involved in the air, in relatively low humidity conditions or under high temperature conditions spraying construction is easy to produce bubbles

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Stabilized bubble principle: Marangueni effect
(liquid reflow caused by surfactants, offsetting gravity)
stration effect
:the static rejection of surfactants thickens the liquid film of the bubble, thus stabilizing the bubble.
2, the bubbly agent's principle of operation
defrosting agent is in the foam thin layer formation stage or after the effect:
dispersed even defrosting agent penetrates into the foam elastic film and distributed in the membrane, and through the reduction of surface pressure leads to the thin layer burst.
evenly dispersed defrosting agent penetrates into the foam thin layer and forms a single molecule film, making it less adhesive and prone to thin layer rupture.
a third mechanism for de-foaming agents containing hydrophobic particles. These hydrophobic particles reach the surface of the thin layer and absorb surfactants at the top of the thin layer. The thin layer breaks due to the absence of surfactants.
3, defrost selection and evaluation method:
defrost must be able to spread quickly on the foam surface and can penetrate quickly, so that the foam burst quickly. The types commonly used in desosters are silicones and polyacrylates.
silicone defoiling agents are usually polysilicone types.
such as polydymethylsiloxane containing acrylic energy groups and polydymethylsiloxane, etc. Silicone class has high temperature resistance, low temperature resistance, physical stability, chemical inertness, very low surface pressure, is commonly used desiccant.
such as polypropyleneic acid deblisters by altering the polarity and molecular weight of the polymer leading to selective incompatible deblistering, the use of such desolants needs to be used to assess the effect on gloss.
to choose the right defrost in the future, we must take into account the process of foam generation in the system, the compatibility and concentration of the system, temperature and viscosity. Each of these factors has a direct effect on the choice of desiccant.
evaluation foam control agent mainly consider several aspects:
spread rate, compatible with the system, deblistering stability and cost-effective. However, the above factors are often contradictory in a formula, for example, the de-foaming agent with the best system compatibility is often the worst de-foaming stability;
the diversity of coating raw materials and construction methods, defoulants need to be evaluated on a case-by-case basis.
1, according to a certain proportion of the need to compare the defoaming agent added to the varnish, put in the glass bottle, in the shock instrument vibration for 5 minutes, while taking out observation, according to the number of foams to determine the initial defoaming ability of the defoaming agent; After 10 minutes /30 minutes, observe the height of the foam again, compare the defrosting speed,
2, scraping paint liquid with scraper fineness to determine the compatible between defrosting agent and the system (with or without shrink holes);
3, after the system foam is eliminated, observe the clarity of the system, whether there is turbidity, layering, oil sequestration and other phenomena;
4, storage stability: after half a month, repeat 1, 2, 3 steps of experiments, and determine the long-term
of desiccant;
is reproduced from the Polymer Learning