Defoaming / Deaerating - Bernd Schwegmann GmbH & Co. KG

Defoaming / Deaerating 

During production and application of paint systems, foam is an undesired side effect. Foam extends 

production time, causes inequality during filling of containers and surface defects at the hardened surface 

like pin holes, craters, loss in gloss, hazing etc. 

In pure liquids (i.e. water) foam is not stable. 

Foam is only stabilised by presence of surface active additives (tensides or surfactants). These 

substances in terms of dispersing additives, flow additives or similar, positively influence other important 

properties of a paint system but cause just mentioned side effects. 

These surface active additives migrate to the liquid/air interface surface and form so-called micelles. 

Something like a skin is built up at the boundary layer which makes an air bubble astonishing stable. The 

reason for this is that between the tenside layers – due to the created repelling forces – a layer of liquid is 

adhered which is protected at both sides. 

While then unstabilised air bubbles in a pure liquid rise to the surface (Stokes law), „dry“ there (due to a 

drainage effect) and brake down, tenside stabilised air bubbles remain stable on the surface. 

Reasons for the formation of foam are due to incorporation and distribution of air/gas: 

• During production (stirrer, dissolver) 

• During application 

• By chemical reactions (i.e. NCO, H2O) 

• During application on porous surfaces (wood) 

The above information is based on our current knowledge and experience. No binding assurance in respect of certain properties or 

suitability for certain applications must be read into our information. Patent rights and other proprietary rights must be observed if 

necessary. Further safety instructions please learn from our material safety data sheet. 04/2012 

Bernd Schwegmann GmbH & Co. KG · Wernher-von-Braun-Str. 14 · 53501 Grafschaft-Gelsdorf · Germany 

Tel.: +49 (0) 2225 9226-0 · Fax +49 (0) 2225 9226-33 · E-Mail: info@SchwegmannNet.de · www.SchwegmannNet.de

Kinds of foam 

Depending on the behaviour of the bubbles, foam is differed in macro and micro foam. 

• Macro foam rises to the surface and forms spherical or polyhedral foam. 

• Micro foam consists of bubbles to little to be able to rise to the surface 

but remain in the liquid phase. 

In order to avoid or destroy foam, defoamer and deaerating additives are used. Defoamers destroy foam 

at the surface while deaerating additives improve the rising velocity of the bubbles inside the paint layer. 

In practice it is often not possible to differ clearly whether an agent acts as a defoamer or as a deaerating 

agent. Mostly in both contexts all these additives are called defoamer. 

To be effective they need to have a low surface tension. They must not be dilutable in the system but 

should be dispersable and need a high level spreading power. If on the other hand the defoamer is too 

incompatible with the system it will also cause surface defects. This means only little changes in the 

system could lead to the ineffectiveness of a defoamer. 

Often used classes of active ingredients are: 

• Aromatic and aliphatic mineral oils 

• Silicone oils 

• Organically modified polysiloxanes 

• Derivatives of fatty acids 

• Special polymers 

• As well as combinations of these mentioned classes 

To improve the effectiveness often finely dispersed hydrophobic solids were used like: 

• Silicic acid 

• Waxes 

• Ureas 

• Metallic soaps 

The properties of the above mentioned classes of products can be abstract in the following table: 

Silicone oil Modified Mineral oil Special 

polysiloxanes 

silicone free 

Effectiveness very good very good good good 

Craters very poor good indifferent very good 

Haze poor indifferent poor good 

Recoatability poor good indifferent very good 






Defoamers have always been a matter of discussion, especially if they are intended for aqueous systems: 

they are supposed to be effective and compatible in as many different systems as possible. 

Many customers differ between those defoamers which are effective and hardly compatible and those 

which are compatible and hardly effective. The first statement refers to defoamers containing silicone, the 

second one refers to silicone free defoamers. Surely this is a prejudice and often this judgement is not 

correct. Nevertheless, the tendency of this statement is not completely wrong. 

Whereas silicone or siloxane containing defoamers destroy foam in a very short time, they cause 

incompatibilities in many cases which result in e.g. surface defects or similar deficiencies, which is also 

shown in the previous table. 

Silicone free defoamers need more time to produce an effect, but they are as reliable as these containing 

silicones and often provide better long term stability. 

Due to easy application and the universal scope of use, most of the defoamers which we offer, are 

silicone free. Furthermore, we of course take valid and planned EU regulations in account, when 

developing our additives. 

With the new VOC free/poor defoamers are in line with this strategy, but also with new EU regulations 

such as the VOC regulation. It was very important to develop products which destroy foam fast and are 

compatible to a great variety of systems. The active matters of defoamers are aliphatic hydrocarbons, 

copolymers and various low molecular tensides and their mixtures, which have the desired properties. 

The VOC free/poor defoamers are SCHWEGO ® foam 6303, 6354, 6356, 6377 and 6388. They are 

counters to the reliable BLISTER FREE grades. In comparison to them they are not only VOC free/poor 

but also their effectiveness has been even improved. 

Additionally, we offer the new crosslinking defoamers SCHWEGO ® foam 6360 and 6361 for UV curing 

coatings. 

The attached graphs show that the effectiveness of our new products incorporated in a choice of binders, 

which shall serve as examples, is the same or even better than the effectiveness of the marketable 

defoamers. 

Test methods for judgement of defoamers: 

Measurement of density: in a paint system air is dispersed at defined conditions. Immediately after that 

the density of the system is measured for example with a pycnometer. The lower the value is, the better 

the effectiveness of the defoamer. 

Test of compatibility: the above treated test specimen is poured on a film fixed on an inclined plane. The 

dried film then is tested for defects. Also deaerating effectiveness is tested in the same way. 

Volume test: air is supplied in the defoaming system by stirring or shaking under defined conditions. Thus 

the resulting total volume is determined. Furthermore the time-dependent foam reduction is observed. 

With the help of this test it is possible to quantify the polyhedral foam, also called macro-foam. In addition 

to this a declaration of the defoaming behaviour in final coating formulations can be given. 






Air content [%] 

Air content [%] 

35 

30 

25 

20 

15 

10 

40 

35 

30 

25 

20 

15 

10 

5 

0 

5 

0 

Blind test 

Blind test 

BLISTER FREE 3 


SCHWEGO ® foam 6303 








green: VOC-free 






Defoamer comparison: 

Alkydal F681 (long oil alkyd); 

Dosage: 0.5% 

green: VOC-free 









Tel.: +49 (0) 2225 9226-0 · Fax +49 (0) 2225 9226-33 · E-Mail: info@SchwegmannNet.de · www.SchwegmannNet.de 





Defoamer comparison: 

Setal 1151 X51 (Polyisocyanat / Acrylate); 

Dosage: 0.5% 










MITTEL S 

MITTEL S 

Competition 1 

















Competition 9

Our defoamers in summary: 

Defoamer 

Deaerating 

additives 

Silicone 

free 

For 

water-based 

systems 

For 

solvent borne 

systems 

For 

solvent free 

systems 

Blister Free 3 X X X X X X 

Blister Free 45 X X X 

Blister Free 54 X X X X 


Blister Free 56 X X X X X X 

Blister Free 66 X X 

Blister Free 75 X X X X 


Blister Free 88 X X 

SCHWEGO ® foam 6303 X X X X X X X 

SCHWEGO ® foam 6325 X X X X 

SCHWEGO ® foam 6343 X (X) X 

SCHWEGO ® foam 6351 X X X X X X 

SCHWEGO ® foam 6354 X X X X X 





SCHWEGO ® foam 6377 X X X 

SCHWEGO ® foam 6388 X X 





MITTEL S X (X) X 

For 

UVcoatings

Defoaming / Deaerating - Bernd Schwegmann GmbH & Co. KG

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