Foaming Process Types of Defoamers

Foam Destabilization Mechanisms

Foam Control Agents Available Chemistries

Foam Control Agents Available Chemistries

Usually, defoamers or anti-foaming agents are based on materials with a low surface tension, such as silicone, mineral oils, fatty acids, etc. In order to increase the defoaming efficiency, more solid particles can be included in the composition. Further, carriers such as water or solvents are often used for easier addition & distribution of defoamers in the paints. Let's discuss some of the commonly employed defoamers chemistries in paints, coatings and inks.

Silicone-based Defoamers

Silicone-based liquid defoamers are composed of functional additives and non-ionic surfactants. These defoamers can either be aqueous, non-aqueous, or both cationic, which depends on the type of surfactant used, whether it is non-ionic, amphoteric or anionic. Silicone-based liquid defoamers are quite popular due to their surface tension-altering properties.

The most common silicone defoaming agents are based on polysiloxanes and modified polysiloxanes. The properties of silicones that make them suitable as aqueous foam-control agents are:

  • Very hydrophobic and, therefore, incompatible with water,
  • Highly surface-active, with liquid surface tension values of approximately 20 mN/m, and
  • Excellent chemical inertness & thermal stability

These properties ensure that silicones will migrate to the air/liquid interface of bubbles within a coating.

DyStar - FOAM BLAST® 4205 Polysiloxanes are used particularly frequently in modern waterborne coatings and printing inks where high demands are made on defoaming characteristics and surface finish. The main disadvantage is that PDMS is so insoluble that it is very difficult to disperse in waterborne systems and almost inevitably causes surface defects.

The incompatibility with the resin binder lead to dewetting of the coating as it dries and leaving defects in the dried films.

Hence, silicone defoamers are typically emulsified when added to aqueous coating systems using organic or silicone-based surfactants. They assist in delivering the foam-control agent and help with leveling/wetting of the applied coating. In addition, a hydrophobic particle may be incorporated into the fluid then used or emulsified to assist with antifoam entry and subsequent foam rupture. Blends of PDMS and silica are often referred to as silicone compounds.

Incorporating modified PDMS in the form of silicone-polyether copolymers into the foam-control formulations easily helps meet incompatibility challenges. The copolymers are synthesized from reactive siloxanes and polyethylene/polypropylene glycol ethers.

By varying the hydrophilic/hydrophobic nature of the silicone polyether, these materials can be used in conjunction with PDMS fluids and compounds such as emulsifiers and wetting agent components of an antifoam compound or emulsion.

Silicone polyethers have also been formulated with glycols to form easily incorporated dispersions for applications such as architectural paints, but they can also be designed to function as effective antifoams alone. Potential benefits for polymeric silicone polyether used as the sole antifoam in a coating or ink include:

  • 100% active to allow greater formulation flexibility and lower use levels,
  • Self-emulsifying for easier incorporation into aqueous or polar coatings,
  • No hydrophobic particles to separate or cause surface defects,
  • Balances effective foam control and good surface appearance, and
  • Stable polymer allows for incorporation under high shear, allowing for use during the pigment/polymer grind step and increases flexibility in addition point selection.

Silicone-based antifoams have progressed markedly since the first use of PDMS fluids in solvent-borne coatings and inks. Keeping pace with formulation changes and environmental drivers, silicone antifoams have evolved to comprise a variety of delivery systems and polymer types to meet the specific requirements of diverse formulations.

For waterborne coatings and inks, the product offerings have been expanded to include novel silicone polyether-based antifoams that offer effective foam control balance against ease of incorporation and good coated surface appearance in several coating and ink systems.

Silicone-Free or Non-silicone Defoamers

Silicone-free defoamers are effective in water based and solvent based systems. They are often polymers with low surface tension and they spread well over the surface.

These range of antifoaming agents are eco-friendly and therefore safe to use, which have balanced composition, precise pH value and long shelf life. These range of defoamers are widely bought due to their cost and work efficiency.

For polymer defoamers in water-based systems, hydrophobic particles are used to improve the defoaming action. Chemically, the particles are based on hydrophobic silicas, polyurea or polyamide. Non-polar and branched polymers are well suited to solvent-borne and solvent-free systems as active defoaming agents.

The advantage of non-silicone defoamers over silicone based defoamers become apparent when formulators require the utmost in defect free films, adhesion, and recoatability. Non-silicone defoamers range from high to low compatibility and therefore from moderate to powerful foam control. This offers the formulator considerable latitude with regard to foam control, surface defects, recoatability and defoamer longevity. Additionally, specific defoamers exhibit desirable handling characteristics such as ultra-stability and easy pumpability.

In many instances, non-silicone based defoamers are so efficient at low use levels, that they can be used within the coating's tolerance range and therefore do not cause film defects.

Oil-based Defoamers

Oil-based defoamers are quite popular. The oil-based products are either based on mineral oils, vegetable oils, white oils, etc. The most commonly used are paraffin and naphthenic oils.

  • Mineral oil-based defoamers deliver long-lasting defoaming effect at an optimum cost/performance ration
  • Vegetable oil-based defoamers add sustainability characteristic due to their origin

Oil-based defoamers may also contain wax or silica in order to boost the performance. However, there is one disadvantage associated with these defoamers which include gloss reduction in high gloss systems and odor associated with some chemistries.

Mineral oil defoamers consist of approximately 85–95 % mineral oil and 1–3 % hydrophobic particles. These defoamers are primarily intended for matt and semi-gloss emulsion paints and emulsion plasters.

Highly specific finely divided hydrophobic solids are added to mineral oil defoamers to provide an increased performance. The main role of these added solids is to decrease the entry barrier to the cell wall of foam and to provide fast defoaming action. The filler particle found inside the defoamer droplet acts as a needle or a pinto puncture the cell wall and burst the bubble. Defoamers formulated with hydrophobic particles can more easily puncture the pseudoemulsion film than those without. This results in more rapid defoamer oil droplet entry into the air-liquid interface. The actual mode of air bubble breakage could be various: spreading, bridging-stretching, bridging-dewetting, etc.

They are not suitable for high-quality aqueous industrial coatings as they may cause surface defects (oil separation, gloss reduction). Furthermore, they should not be used in solvent-borne systems as a result of their inadequate leveling properties.

Water-based or Emulsion-based defoamers

Defoamers in emulsion form are based on dispersions in water. These defoamers use oil, waxes, polymers, etc. in the solution that are dispersed into it. The types of oils are the same as oil-based and the wax is long chain alcohol, fatty acid soap and ester used to release entrained air.

This predispersed defoamer provides defoamer droplets at the correct size even before addition to a coating. Energy of incorporation is minimized since predispersion has already occurred. Since carrier fluid used here is plain water, VOCs are reduced to absolute minimum, making then suitable for used in eco-label formulations.

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Defoamers for Water-based and Solvent-based Systems

The defoamer chemistries discussed above are good for aqueous and non-aqueous systems.

For non-aqueous system, polysiloxanes, polyacrylates and or other organic polymers are often employed for air release than breaking down the surface foam. PDMS, however, might show some incompatibility associated with them depending on the system. Introducing perfluorinated organic modifications results in so-called fluorosilicone defoamers. These products are characterized by a very low surface tension and a high defoaming effect with a very low proportion of incompatible substances.

In order to achieve desired formulation latitude, you can choose defoamers ranging from mineral oil based to mineral oil free, to emulsions and to those fortified with several types of hydrophobic solids. The degree to which the defoamers are readily emulsified in the coating will indicate the relative ease of incorporation and can effect performance efficiency.

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