Читать книгу Additives for Water-borne Coatings - Wernfried Heilen - Страница 90

In many applications the use of defoamers cannot be avoided. To achieve optimum defoaming a few points must be considered.

 It is important to ensure that the defoamer is sufficiently mixed in. Defoamers must have a limited compatibility with the system to be defoamed. Inadequate mixing can result in surface defects such as craters.

 Defoamer concentrates need to be incorporated with high shear forces. Preferably they should be added to the mill base.

 Foam formation is also related to application conditions. When testing defoamers, efficiency and compatibility should be checked under conditions close to those of the application.

 The addition of a defoamer to the mill base increases the former’s compatibility with the system.

 Slight defoamer incompatibility can be improved by the addition of, for example, a substrate wetting additive or a flow and glide additive.

 In many cases optimum defoaming can be achieved with a combination of defoamers. Splitting the defoamer between the mill base and the let down often gives the best results.