Defoamers for high-PVC formulations

Defoamers for high-PVC formulations

Wednesday, 13 September, 2017

In water-borne systems, foam build-up is a constant issue. In high-PVC paints, this problem combines with other characteristics, such as the use of dissolvers in production, the high viscosity of paint, homogenisation prior to application and use of the roller, giving rise to situations that are not simple to solve. To add further complications to the matter, the updating of eco-labels and the CLP regulations have limited – and even banned – the use of some surfactants. For this reason, eco-sensitive markets have been compelled to make changes to their formulae and even develop new paints that meet current demands.

In order to produce and apply these types of coatings free of foam, the guidelines that are already known should be followed:

Avoid the components that stabilise the foam or introduce them during completion (surfactants, emulsions, etc.).
Adjust the production amounts and the viscosity to prevent the dissolver from taking in air.
Choose the right defoamer and add it at the right moment.

When it comes to the choice of defoamer, BYK offers the following products:

Nevertheless, in order to help effectively produce formulations and yield the utmost efficiency, not only are suitable products required; the pertinent technical information to adjust and optimise their use is also needed.

Mineral oils such as BYK-037 and BYK LPD 23470 are rapid defoamers and it is desirable for them to be used to remove the foam created during production. BYK LP-D 23470 (with polyamide hydrophobic particles) is a highly effective defoamer and its dose should be optimised – even halved – compared to other mineral oil-based defoamers. Once in the paint container, mineral oil loses efficiency over time. After roughly one month in storage, the defoamer could lose half of its effect. Accordingly, we add a small amount of silicone to the defoamer to guarantee its effectiveness as time passes by. Mineral oil defoamers have other limitations that may lead the formulator to choose other options

The pick-up of surfactants can impair the uptake of colorants (pigment concentrates)
The price depends on oil price variations.
Due to their low molecular weight, they have a tendency to pick up dirt.
They can pose problems owing to their emissions (SVOC) and their potential content of polycyclic aromatic traces, thus limiting specific uses, such as food contact applications.

Silicone defoamers:
their chemistry is highly versatile and makes it possible to synthesise defoamers that are closely aligned to the needs of each circumstance. In general, they are fairly long dimethylsiloxane chains, modified with polyether chains. Polyether chains may also be of variable length and we use varying proportions of propylene or ethylene oxide to make these products. The most common structures are in the shape of a comb, but linear structures are also employed. We can thus synthesise additives that we may add to a bead mill without losing effectiveness owing to their high shear or other products that may easily be added so they may be incorporated ex-factory using very tiny shearing forces. For high-PVC, roller-applied paints, the best – and indeed a very efficient– option is to use highly incompatible silicones. Defoamers are almost always offered in emulsion so that the doses will be between 0.1 and 0.5% and they can be easily added.

As with all of the company’s silicone defoamers, BYK-1617 stays effective throughout the shelf life of the paint, although as it is generally not as effective as mineral oils, it is largely recommended when the best production practices prevent initial foam formation, and the main problem lies in application. The foremost limitation is the fact that in diluted applications on non-porous surfaces, these defoamers are more prone to crater formation (due to their major incompatibility).

Polymeric defoamers:
also constitute a major product variety as there is a huge range of chemistries and structures. BYK-1640 has a new hyperbranched structure and is the most effective defoamer in this family of additives, affording the following features:

Its chemistry is resistant to extreme pH conditions, temperatures and oxidising surroundings. It may be used in a range of applications from resin production in emulsion, through silicate and cationics to traditional high-PVC paints for walls.
The product is suitable for paints in contact with food, meets eco-labelling requirements and has no emissions, making it suitable for indoor paints.
As it is oil-free, it does not impair colour acceptance and its effectiveness remains stable during storage.

The three families of defoamers provide innovative solutions for high-PVC formulations based on an integrated chemistry, formulation and experience in the final application. The choice of a suitable defoamer will depend on environmental variables, the paint manufacturing process and the final formulation.

For further information, please contact:
Jaume.Figueras@altana.com
Pilar.casas@altana.com
Technical advisors for BYK-Chemie GmbH

For further information about these products, please contact our Technical Sales Advisers.

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Defoamers for high-PVC formulations

Defoamers for high-PVC formulations

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