The Role of Defoamers in Industrial Applications

Apr 8, 2021

In many inks and coatings processing production process, the need to use surface-active substances to achieve special effects. For example, in the production of water-based paint, water-insoluble base material production, water-insoluble base material is required to deal with the use of emulsifiers. At the same time, we have to improve substrate wetting and coating pigment dispersion by using additives.

Surfactant most important characteristic is that they have a tendency to build in the interface, such as air / water interface. Arrangement of surfactant at the interface depending on their solubility and chemical structure. It will reduce the interfacial surface tension, which allows the system to stabilize. However, surfactants can also bring people want to see side effects - stable coatings in the production and construction process into the air, forming a stable foam, which is particularly common in aqueous coating systems.

Foam definitions and concepts
It can be defined as the foam of air bubbles in a liquid medium in a stable dispersion. If the general air into the liquid, the bubble generated can assume a spherical shape. Since the air is less dense than the liquid, and thus it will migrate to the surface, when the gas reaches the surface of the liquid without surfactant, the bubble will burst, the air inside the bubble dissipates, the liquid surrounding the bubble in the previous and together. Thus, the pure liquid (liquid containing no surfactant) there is no bubble.
In a liquid containing a surface active agent, a spherical bubble rising, into a stable macro bubble (big bubble). While these bubbles rise to the air interface, but which is encircled by a layer of surfactant molecules. On the air interface also has a layer of surfactant molecules of the surface film, and therefore, when the bubbles rise to the surface to form a double layer. Double layer thickness of up to several microns, these small surface of the foam is very stable and difficult to eliminate. Bubbles rise to the surface to form a foam crown increased. As the liquid is discharged from the double layer, the microbubbles will be transformed into a stable macro dynamics bubble, foam and foam crowns double layers were thin, the foam easily burst.
Foam stability is affected by several factors. One factor which is stable thin sandwich, sandwich the liquid inside can’t be discharged or discharged slowly. Also electrostatic repulsion occupy the mezzanine between ionic surfactants also prevents the bubble burst. Another factor prompting the foam stabilizer is Gibbs elasticity. By stretching a film having a surface-active substance, such an elastic effect will be shown. In this case, the surface of the double layer is expanded, resulting in local concentration of the surfactant reduces the surface tension rises. The film is stretched like an elastic layer of the skin, like poly interference, Shidao surface tension as low as possible.
Water-based coatings and inks in the manufacturing or construction process will produce foam. Manufacturing process of mixing, dispersing, or filter, so that the foam is formed and rises crown, it will extend the production time and reduce the effective volume of the system. Construction, build stable foam on the air interface in the film after drying will have a common surface defects. During printing ink foam damage mobility, even under the most adverse conditions caused by the overflow of the ink from the work tank.
Defoamers need role

Current theories about the formation of anti-foaming and foam degassing is different. Defoamers the role of the air trapped in the interface. Defoaming agent role in the process and the coated film after coating is completed, so that the coating film dispersed in the tiny air (microbubbles), rapid rise to the surface. But the practical application is often not clearly make this distinction. Defoamers also can eliminate microbubbles to some extent. Defoamers defoaming mechanism discussed below in waterborne coatings and inks.

Defoamers To show the effect, and must meet certain requirements. One of them is that they must be able to break the foam stabilization mechanism described above. To this end, defoamers in the system have a certain incompatibility, it can migrate to the air interface. Of course, it can not appear similar to the shrinkage as serious side effects caused by the use of defoamers. In order to defoaming, in coatings emulsified microdroplets defoamer and surfactant must be stable foam layer to bind and penetrate the bilayer film in the foam. Subsequently, defoamers must quickly spread through the surfactant layer cracked. At this film compared to previous surfactant stable interlayer film, an elastic been significantly reduced. Finally, the instability of this bimolecular film rupture, so as to achieve the effect of defoaming. Therefore, no compatibility, high spread ability and low surface tension properties of each is an important anti-foaming agent must possess.

Adding defoamers fine hydrophobic particles, such as: silica, its anti-foaming ability will be effectively strengthened. Their mechanism of action is interpreted as an anti-wetting process. Stable bimolecular layer of surfactant does not readily wet the solid particles hydrophobic, surface tension causes unstable local region, so that bimolecular film rupture.