Foaming Process & Types of Defoamers
Foaming Process & Types of Defoamers
Foam is a stable dispersion of a gas in a liquid medium that results when a surfactant layer forms around air bubbles and entrains them within it. Air can be incorporated into a coating by:
- Mixing during the polymer/pigment grinding and let-down steps,
- Pumping during package filling or
- Shear or spraying during application
In industrial coatings, defoamers are needed in waterborne (WB) as well as solvent-borne (SB) industrial paints.
- In the case of waterborne, defoamers play a major role during manufacturing as well as application.
- For solvent-borne, they are primarily used to avoid foaming during application as well as craters & foamy appearance in the dried film.
While, in architectural coatings, the use of defoamers is mainly needed in waterborne systems, only by exception in solvent-borne systems.
Dispersion paints, such as wall paints, are the largest segment. Defoamers are needed to avoid foam formation during manufacturing as well as application. Waterborne paints tend to stabilize foam, mainly due to the presence of surfactants and wetting agents.
To find an effective defoamer or anti-foaming agent for your system, you must understand what is leading to foam in your product. Revisit the basics of foam formation in coatings and understand the root cause of foam to support your search for a suitable product.
Foam-control agents are beneficial in preventing or reducing many common coating problems. The potential problems that can arise due to foaming are listed below.
- Viscosity increase and loss of mechanical shearing power during milling (resulting in smaller batch sizes and poor pigment/polymer dispersion).
- Volume increase during the letdown and mixing steps leading to overflowing.
- Slower package-filling rates due to inefficient pumping.
- Air incorporation during transport and handling.
- Slower printing-press speeds or lower pressures during spraying.
- Surface defects on coated substrates resulting in poor appearance, reduction in gloss or less substrate protection.
Stable foam occurs when surfactants are present, forming an interfacial layer around air bubbles that are entrained in the coating medium. Also, the dispersing and mixing stages during manufacture cause entrapment of air. If the physical and chemical conditions that cause foam cannot be altered, the addition of foam-preventing or foam-destroying agents is the best option available to the formulator.
What should you consider while selecting foam control agent(s)?
What should you consider while selecting foam control agent(s)?
Foam-control agents can be classified as antifoams or defoamers. Although the two terms are often used interchangeably, but strictly speaking, antifoams prevent the formation of stable foams, while defoamers act by destabilizing already existing foams. Foam-control agents function by a variety of mechanisms to prevent or rupture foam. Individual foam control efficiency is determined by three key factors:
- The insolubility of the foam control agent in the foaming medium,
- Low surface tension, so that it can be uniformly dispersed throughout the formulation, and
- Ability to penetrate the foam wall (or lamellae).
Anti-foaming agents or defoamers must be insoluble in the foaming medium. They function by being more surface active than the surfactant stabilizing the foam so that they are able to enter the surface layers of the potentially foaming liquid and displace it from the gas/liquid interface.
The mixed surfactant layers now prevent close association of molecules and exhibit low elasticity. The presence of random, highly surface-active, insoluble molecules in the surface film interrupts foam stabilization via the Marangoni effect, and thus foaming is prevented.
Here are some key considerations you should put attention to while selecting a defoamer of anti-foaming agent for your system.
| Defoamer |
Anti-foam Agent |
- Always check for defoamer with high surface activity, i.e., a stronger reduction of surface tension than the surfactant that causes the foam.
- Ensure compatibility with the binder so that it helps to prevent the formation of surface irregularities (crater defects).
- The selected defoamer must be able to enter into foam lamellae and spread effectively on the liquid/gas interface.
- Your selected chemistry should be effectively insoluble in the foaming medium.
|
- The surface tension of the anti-foaming agent must be lower than that of the foaming solutions.
- The solubility of the anti-foaming agent in the foaming solution must be low & must not react with the foaming solution.
- It should have a high spreading co-efficient.
- Always ensure there is no odor or residue left in the formulation that is detrimental to the end product
|
Additionally, defoamers must possess persistence, good storage stability for optimum handling and have coating system compatibility to prevent contributing to defects in the coating film. This compatibility is derived from compatibility with the resin, defoamer droplet size and surface and interfacial tension that the droplets make with the coating.
Even with the correctly chosen defoamer, performance may not be seen in laboratory test protocols. Identifying appropriate procedures is very important. Only with the proper test techniques that simulate end-user conditions, you can identify the suitable defoamer for use where the foam is a problem.
Defoamers are based on different chemistries and are fine tuned. A successful selection is one that has evolved based on time proven techniques of synthesis, formulation and testing.
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.
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.
Architectural Coatings - Defoamer Selection Based on Application
Architectural Coatings - Defoamer Selection Based on Application
There are several types of defoamers currently used in architectural coatings. Let's check out their benefits and risks in the table below:
| Defoamer Families |
Benefits |
Risks |
| Oil-based, Non-dispersible |
- High defoaming efficacy
- Lowest cost
|
- Needing good incorporation, intercoat adhesion
|
| Oil-based, Si dope, Non dispersible |
|
- Some risk for (intercoat) adhesion
- Breaking flow curtain
- Needing good incorporation, intercoat adhesion
|
| Oil- & Si-based, Easy dispersible |
- Easy incorporation
- Good film properties
|
- Low risk for intercoat adhesion failure
|
| Si-based, Easy dispersible |
- Easy incorporation
- Good film properties
- Meeting oil-free regulation
|
- Low risk for intercoat adhesion failure
- Low risk for haziness
|
| High Si content, Oil-free |
- Excellent binder compatibility, for best film appearance
|
|
| Oil- & Si-free, Non-dispersible |
|
- Risk for poor film appearance
- Risk for loosing efficacy during storage
|
| Wax-, Si- & Oil-free, Dispersible |
- Best adhesion
- Film appearance
- Modest defoaming efficiency
|
- Risk for loosing efficacy during storage
|
One of the main aspects of selecting the right defoaming agent for architectural coating applications is based on application mode for a typical class of coating (See below).
Defoamers for Flat or Matt wall paints
In most of the cases, paints used for flat / matt wall applications are high PVC dispersion paints (PVC ~60 to 85), with the risk of foam formation leading to opacity issues. In flat / matt wall paints, the choice of the right defoamer is cost sensitive.
| Type of Flat/Matt Wall Paint |
Millbase |
Let-down |
Brush and Roller Application |
Spraying |
Dipping |
Flow Coat |
Industrial |
| Oil-based, Non-dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
| Oil-based, Si dope, Non dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐ |
⭐ |
⭐⭐ |
| Oil- & Si-based, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
| Si-based, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
| High Si content, Oil-free |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
| Oil- & Si-free, Non-dispersible |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
| Wax-, Si- & Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
Defoamers for Satin or Eggshell Paints
Medium to high PVC dispersion paints are commonly used for satin/eggshell architectural coatings (PVC ~ 45 to 60). In satin/eggshell paints, foam formation decreases the appearance, including the degree of satin. Brush and Roller is the main procedure of application for satin/eggshell paints. Notably with rolling, there is a high risk of air inclusion making the choice of the right defoamer a critical step.
| Type of Satin Paint |
Millbase |
Let-down |
Brush and Roller Application |
Spraying |
Dipping |
Flow Coat |
Industrial |
Baked |
2-pack |
| Oil-based, Non-dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
| Oil-based, Si-dope, non-dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐ |
⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
| Oil- & Si-based, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
| Si-based, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐⭐
⭐⭐ |
| Oil- & Si-free, Non-dispersible |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
| Wax-, Si- & Oil-free, Dispersible |
⭐⭐ |
⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
Defoamers for Semi Gloss Dispersion Paints
Main paints used for semi-gloss applications are exhibiting low to medium PVC (~ 30 to 45). In semi-gloss paint applications, formation of foam affects film appearance, but also gloss level.
| Type of Semi Gloss Paint |
Millbase |
Let-down |
Brush and Roller Application |
Spraying |
Dipping |
Flow Coat |
Industrial |
Baked |
2-pack |
| Oil-based, Non-dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐ |
⭐⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
| Oil-based, Si dope, Non dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐ |
⭐ |
⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
| Oil- & Si-based, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
| Oil- & Si-free, Non-dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
| Wax-, Si- & Oil-free, Dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
Defoamers for High Gloss Paints
Typical paints used for high-gloss architectural applications are low PVC dispersions. In high gloss paints, surface disturbances resulting of foam formation are easy visible. This is thus critical to select the right defoamer in order to maintain constant gloss level.
| Type of High Gloss Paint |
Millbase |
Let-down |
Brush and Roller Application |
Spraying |
Dipping |
Flow Coat |
Industrial |
Baked |
2-pack |
| Oil-based, Non-dispersible |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
| Oil-based, Si-dope, non-dispersible |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐ |
⭐ |
⭐ |
⭐ |
⭐⭐ |
⭐⭐ |
⭐⭐ |
| Oil- & Si-based, Easy dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
| High Si-content, oil-free |
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐ ⭐⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
| Oil-free, Si-free, non-dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
| Wax-, Si-, and Oil-free, dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
Defoamers in Clear Varnishes
In unpigmented clear varnishes architectural applications, main binders used may be dispersion or clear solution. Foam formation can affect transparency in the liquid varnish as well as in the dry film, hence the need for careful monitoring.
The highest risk in clear varnishes formulation is micro-foaming: in such cases, defoamer with de-aeration features and easily dispersible will be the best solution.
| Type of Clear Varnish |
Let-down |
Brush and Roller Application |
Spraying |
Dipping |
Flow Coat |
Industrial |
Baked |
2-pack |
| Oil-based, Non-dispersible |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
| Oil-based, Si dope, non dispersible |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
⭐ |
| Oil- & Si-based, Easy dispersible |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐ |
| High Si- content, oil-free |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐⭐ |
| Oil-free, Si-free, non-dispersible |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐ |
| Wax-, Si-, and Oil-free, dispersible |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐⭐ |
Defoamers for Pigment Dispersions
Typical binders used for pigmented architectural applications are concentrated dispersions of pigments/ extenders in binder-free liquid. The key to formulate successfully is to avoid effect of pigment dispersion in aqueous medium, usually binder free. When selecting a defoamer for pigment dispersion applications, there is a high risk of loosing defoaming action due to adsorption of defoamer onto pigment, hence the criticity of the choice.
| Type of Pigment Dispersion |
Millbase |
Let-down |
| Oil-based, non dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐ |
| Oil-based, Si dope, non dispersible |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐ |
| Easy dispersible, oil, Si based |
⭐⭐⭐
⭐ |
⭐⭐⭐
⭐⭐ |
| High Si content, oil free |
⭐⭐⭐
⭐⭐ |
⭐⭐⭐
⭐ |
| Oil-free, Non-silicone defoamer, non dispersible |
⭐⭐⭐ |
⭐⭐ |
| Wax-, Si-, and oil free, dispersible |
⭐⭐⭐ |
⭐⭐⭐
⭐ |
Industrial Coatings - Defoamer Selection Tips
Industrial Coatings - Defoamer Selection Tips
Let’s have a quick overview on various types of defoamers used in industrial coatings, highlighting their risks and benefits:
| Defoamer Families |
Key Benefits |
Risks |
| Oil-based, Non-dispersible |
|
- Needing good incorporation
- Some risk for intercoat adhesion
- Breaking flow curtain
|
| Si-based, Oil-free, Easy dispersible |
- Easy incorporation
- Good film properties
- Meeting oil-free regulation
|
- Low risk for intercoat adhesion failure
- Low risk for haziness
|
| High Si content, Oil-free |
- Excellent binder compatibility for best film appearance
|
|
| Wax- & Si-based, Oil-free, Dispersible |
- Best adhesion
- Film appearance
- Modest defoaming efficiency
|
- Risk for loosing efficacy during storage
|
| Polyolefins Compound |
- Excellent film surface characteristics
- Recoatability
|
- Limited efficacy against micro foaming
|
| Polysiloxane |
- Excellent de-aeration, also usually also vs microfoam
- Best balance between compatibility and incompatibility (=defoaming activity)
|
- May give some risk of adhesion failure and/ or recoatibility
|
| Compounded Defoamers |
- Often compounds of polyacrylates, with siloxanes, and/ or fluor-derivatives for lowest surface tension
|
|
Explore key factors to select defoamers/anti-foaming agents for industrial coatings applications according to:
- Coatings function -- Primers, protective, repair, topcoats.
- Coatings system -- 2 component, bake finishes, UV curable.
- Substrate on which you are applying your coatings -- Wood, floor, OEM, can and coil coatings.
- Main application -- Dipping bath, curtain coatings, powder coatings
Select Defoamers According to Coatings Function
Primers
Adhesion onto substrate is the key factor to be considered in order to avoid foam formation when formulating primers for waterborne, solvent borne or solvent-free coatings. Especially, microfoam formation can occur in case of corrosion protection.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Protective Coatings
Like for primers, the selection of the most appropriate defoamer for protective coatings applications will mainly depend on how the defoamer affects adhesion onto substrate and how it can help overcome microfoaming formation.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Repair Coatings
In repair finishes coatings, various binder systems can be used. They are mainly applied by spray application leading to air inclusion risks and microfoaming formation. Hence, the need for persistant defoamer is critical.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Topcoats
Topcoat applications is one of the largest group in industrial coatings, with wide options for resin selection. Critical factors for defoamers selection are include their effect on:
- Film properties
- Cratering
- Pinholes
- Levelling
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Select Defoamers According to Your Coatings System
2 Component Coatings
In case of two component industrial coatings applications (2K) presence of reactive groups, such as OH could reduce mechanical film properties. The main procedure of application for this segment is brush / roller, notably with rolling high risk of air inclusion. The choice of the right defoamer must take these challenges into consideration.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Baking Finishes Industrial Coatings
For these coatings, temperature stability is key criterium. Polyethersiloxanes are more critical for this than polyestersiloxanes. The most recommended defoamers are Wax-, Si-, and oil free, dispersible for low risk of adhesion failure.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
UV Curable Coatings
In UV curable coatings, the main binders used are based on Acrylates and PE. One of the characteristics of CV Curable paints and coatings is that they contain low or no solvents. Selecting the right defoamer for UV cured coatings will be mainly a question of:
- Compatibility with the binder system
- Overcoming the risk linked to de-aeration effect
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐ |
⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Select Defoamers According to Your Substrate
Wood Coatings
Wood coatings refer to a large variation in term of binders systems. The risk of foam formation is mainly linked to inclusion of (micro) bubbles due to slow substrate wetting. Critical factors for selection would be to avoid microfoaming formation.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐ |
⭐⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐ |
⭐⭐⭐⭐⭐ |
Select Right Defoamer for Wood & Furniture Coatings »
Floor Finishes
Main examples of flooring coatings are epoxy (EP) and polyurethane (PUR) floorings, which can be solvent borne, waterborne or solvent-free.
Roller application being the main procedure of application, there is a strong risk of air inclusion, affecting appearance of final flooring coating. Another risk is microfoam formation issue due to film thickness.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐⭐ |
⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
OEM Coatings
They can be base coat or clear coat, with a high risk of microfoaming, whatever the binder system is (various binders systems can be used in OEM Coatings applications). Selecting the right defoamer system will avoid unwanted side effects.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐ |
⭐⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐⭐ |
⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Can Coatings
In can coatings, EP and PE systems are the most used binders. In case of direct food contact, the required approval defoamer must be selected.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐ |
⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
Coil Coatings
Coil coatings are generally cured at high temperature. Critical criteria of defoamer selection are:
- Effect on MEK resistance
- Effect on adhesion
- Temperature stability
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐ |
⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
View Several Defoamers for Coil Coatings »
Select Defoamers According to Your Application
Dipping Bath Coatings
A wide variation of binder systems can be used in dipping bath industrial coatings. Though they are systems that commonly exhibit low viscosity, leading to risks for creaming and separation. As a result, there is a continuous air incorporation issue: choosing the right defoamer is a key factor of success overcome these issues.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐⭐ |
⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐⭐ |
⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Curtain Coatings
Various binders systems are used in curtain coatings applications. Curtain break is the main concern why using defoamers in this application.
| Defoamer Families |
Millbase |
Let-down |
| Oil-based, Non-dispersible |
⭐⭐⭐⭐⭐ |
⭐ |
| Si-based, Oil-free, Easy dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐ |
| High Si content, Oil-free |
⭐⭐⭐ |
⭐⭐⭐ |
| Wax- & Si-based, Oil-free, Dispersible |
⭐⭐⭐⭐ |
⭐⭐⭐⭐⭐ |
| Polyolefins Compound |
⭐ |
⭐⭐⭐⭐ |
| Polysiloxane |
⭐⭐⭐⭐ |
⭐⭐⭐⭐ |
| Compounded Defoamers |
⭐⭐ |
⭐⭐⭐⭐⭐ |
Powder Coatings
In powder coatings, there is a vast choice for binder systems. The highest risk of foam formation is linked to air entrapment in the liquid film via powder during melting and / or polymerization stage. Criteria for defoamers selection are mainly:
- Good temperature stability
- Compatibility with the binder
- Ease of incorporation
Check Out Various Defoamers Suitable for Powder Coatings »
| Defoamer Families |
Millbase |
Let-down |
| Compounded Defoamers |
⭐ |
⭐⭐⭐⭐⭐ |
When should you add defoamer
When should you add defoamer
It is also important to note that the necessary dosage or effectiveness of a defoamer depends on the formulation. The type and stabilization of the binder, the level of pigmentation, as well as the composition and properties of the surface-active substances used for pigment and substrate wetting have a particularly strong effect.
Along with these factors, time of addition, the duration and incorporation method (shear forces) also define selection of a foam control agent. All of these parameters have an impact on the distribution and therefore on the droplet size of the defoamer in the coating formulation.
Grind Stage
High shear grinding, milling and mixing are required to disperse pigments and extenders. This high shear draws air into the batch that must be rapidly released, or processing times will be long. In extreme cases, the required grind will never be attained due to high air content.
In this high intensity stage, a defoamer may be added all at once or used on an as-is-needed basis. Frequently the most powerful defoamers are required and must be used sparingly. Overuse may result in film defects in the applied final coating. In the grind, strong defoamers are incorporated under such high shear that the necessary compatibilization is achieved.
Grind stage defoamers must act quickly in order to be effective. Here, foam is being generated so quickly that the defoamer, to be effective, must allow entrained air bubbles to have effective collisions, i.e., collisions that result in bubble coalescence to form large and therefore very buoyant bubbles. These bubbles will successfully make the trip up to the air-liquid interface and break. Spreading may or may not be a part of the defoamer mode of action during high speed mixing.
The choice of defoamer and its optimized level in the grind will frequently influence the type and use of defoamers required for mixing and filling operations and for paint application.
Correlation Between Defoamer Incompatibility and Defoaming Efficiency
Source: Defoamer.info
Mixing & Filling Operations
In mixing and filling operations, the defoamers previously employed for grind and application may be sufficient.
If additional foam control agent is required, compatibility must be considered. If required, very low use levels of the more powerful defoamers may be used. These defoamers have hydrophobic solids and are effective during milling and filling. In some cases, foam in either the grind or in the application does not pose a problem, and specific defoamers for only mixing and filling operations are needed.
Application
The standard methods of applying coatings by roller, brush, pad, dip, curtain coat and spray are sufficiently vigorous to cause foam problems.
Roller, brush and pad all confer their topography to the applied film. As a result there is much air entrainment. The successful defoamer will act rapidly and allow for these macro bubbles to very quickly coalesce and result in large bubbles that rise rapidly and break. Successful defoamers typically provide for a very specific type of adsorbed layer at the air bubble-liquid interface. This adsorbed layer provides little drag to the rising air bubble and little cohesive strength in the foam lamella, so the bubble can break when it reaches the surface.
Spray application generates entrained air due to the high shear forces during atomization. This entrained air can be very difficult to eliminate. The recommended defoamers are particularly successful in spray generated foam. Here the defoamer must again allow for rapid rate of rise of air bubbles.
Meeting VOC requirements
It is well known that glycols and other solvents used in water-based coatings, being low in surface tension, contributed to defoaming. However, their use has been eliminated because of the drive towards low odor, zero VOC compliant coatings. The elimination of these solvents has resulted in much more difficult foaming issues to overcome both during the paint manufacturing process and during application.
Choosing the correct defoamer is therefore a kind of “balancing act” between compatibility and incompatibility. The optimum level is found when good defoaming is achieved without defects (turbidity, cratering).
There is no "universal" foam-control agent has been developed to date, therefore, before selecting any foam-control agent it should be evaluated in a particular formulation for suitability.
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How to Evaluate the Efficiency of a Defoamer?
How to Evaluate the Efficiency of a Defoamer?
There exist several test methods to help the paint formulator to choose the best possible defoamer and know the exact amount needed for formulation. With proper test protocol & techniques, a desired form control agent can be identified for use where the foam is a problem. The selection of a test method to determine the performance of defoamers depends on:
- Area/surface of use (porous, non-porous...)
- Application method (brushing, rolling, spraying, printing...)
In many test methods, the foam generation procedure has been developed as a simulation of practical application and both manual and automated methods are used to do this.
Some of the common test methods employed to determine defoamers performance include:
Stirring Test/Density Test - The complete formulation (with/without defoamer) is stirred with a dissolver under defined parameters (time, rotation speed …). After the stirring step, measure directly the density with a density bottle. Best efficiency is the product with the highest density.
Compatibility Test - In compatibilities of defoamer in any given coating system can result in the formation of film defects, such as orange peels, fisheyes, crater, etc. In this test, the paint (with defoamer) is applied with a doctor blade on the glass. After the drying of the paint, a visual comparison with blank sample (without defoamer) is done to measure the influence of the defoamer on gloss, haze and leveling.
Sponge Roller Test - The paint (defined amount, with defoamer) is applied with a sponge roller to a substrate to simulate the paint application on the wall. Micro- and macrofoam can be evaluated on the dried paint film to evaluate the efficiency of defoamer.
A Shake Flask Method - The shake flask test method involves the addition of a certain amount of foaming liquid in the cylinder with plug-in, each time under the same number of shake flask, static observation of foam height and defoaming time.
Other Test Methods - Further depending on the coating systems and end-application requirements, other tests like gloss measurement, volume test, circulation foam tests, etc. can be employed to evaluate the defoaming efficiency.
ASTM D1173 - Standard Test Method for Foaming Properties of Surface-Active Agents [original Ross-Miles method]
This test method covers the determination of the foaming properties of surface-active agents as defined in Terminology D 459. This test method is applicable under limited and controlled conditions but does not necessarily yield information correlating with specific end uses. The Ross-Miles method is used for measuring the foamability of surfactant solutions and the stability of the foam produced, which is based on height measurement.
Source: KRÜSS
This test method covers the determination of the foaming properties of surface-active agents.
Note: There exist several other methods to determine foaming behavior, but they all are not discussed here There are several in-house testing methods being used by material suppliers to obtain qualitative and quantitative results of foam reducing agents.
The results obtained from above mentioned test methods along with surface tension analysis will also help the paint formulator to choose the best possible defoamer and know the exact amount needed for formulation.
What can be done when your defoamer is not performing
What can be done when your defoamer is not performing
Here we present you some case studies to easily troubleshoot the issues you might face when incorporating defoamer in your system.
What can you do to improve scale-up from lab to plant?
The commercial consequence of foam in paints and coatings is a serious matter and all formulators pay particular attention to controlling it. Paint companies all have their own and sometimes unique test methods for evaluating foam in a particular coating. This is commendable as long as the test techniques correlate with the foam problems experienced in manufacture and application of the paint.
Too frequently, the foam problems observed in the actual application of paint bear little resemblance to those studied in the laboratory. It is critical that the laboratory defoamer tests performed and the experimental results which are guidelines for the correct defoamer recommendations and dosage are suitable for controlling foam problems in the real-world use of paint.
Laboratory test methods must duplicate or simulate the real-world foam problem. It is here the defoamer supplier can provide much assistance.
Classification of the most probable level of shear (high, medium, low) associated with and responsible for the real-world foam problem can help in deciding on a suitable laboratory test method. For instance, if the problem is in spray or milling it is judged as a high shear environment. Suitable laboratory methods best approximating this would be the use of a high speed mixer or spray itself.
Although high speed mixers require little paint for testing compared to, for example, airless spray one needs to correlate results between these types of tests. If correlation exists, then the more simple and quick test protocols are acceptable. Possible medium shear test techniques such as paint can shake tests, recirculatory tests and roll coating all have their place so long as correlation has been demonstrated. Air sparging is an example of low shear and provides useful information on the ability of a coating to release entrained air.
In summary, whenever possible, use the same foam generating laboratory technique that is present in field or plant. If in the field, spray or roll coat generates foam, use this as a test technique. If high speed mixing is the cause of foam, choose a high speed mixer as the laboratory instrument of choice. When shortcuts are desirable due to large number of tests that need to be made, make sure correlation exists between the shortcut and the real-world.
What can you do to ensure long lasting performance?
Effective foam control requires not only the efficient performance of a defoamer at the time of manufacture, but also continued performance on application after extended storage. The fact that this is often not the case implies that there exists a process of defoamer exhaustion. Frequently referred to as defoamer longevity, deactivation and performance loss over time, this phenomenon must be controlled. A paint or coating with no foam at the time of manufacture is not adequate, if foam is a problem when later applied.
Defoamer exhaustion is difficult for defoamer producers to control, but not impossible. Those who intensively study defoamers have discovered there are several reasons why defoamers fail with time. Frequently, the defoamer droplet size changes with time and is either reduced or enlarged (with 5 - 30µm being the ideal) due to either over-emulsification or coalescence. Another cause for performance loss over time can be due to loss of the spread defoamer film in the foam cell wall. This is caused by over-emulsification of the defoamer and can occur if the coating system is subjected to continuous high shear agitation.
The defoamer droplet spreads across the foam surface. Foam stabilizing surfactant is displaced and the foam cell wall is thinned, all contributing to foam destruction.
In the case of mixed defoamers containing oils and hydrophobic solids, the separation of these two components into solids-enriched oil droplets and solids-depleted oil droplets can lead to this performance drop. Almost all defoamer oil droplets have the correct solids dispersed in them.
Solids enriched/depleted defoamer droplets lead to poor foam control. These observations and insights have helped defoamer producers develop long lasting defoamers.
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Adequately determine the time frame for defoamer performance. In some cases one day is sufficient and in other cases years may be required.
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Determine an acceptable and realistic level of foam over the extended lifetime of the system in question.
Your current defoamer is not working. What can you do?
Formulation changes to waterborne coatings, raw material substitutions and new coatings development may all interfere with foam control. All too often, the formulator's favorite defoamer does not work.
Unfortunately, this occurs frequently due to the high selectivity of defoamers for the coatings they work best in. Just thinking about the complexity of defoamers and how they work makes one realize that "universality" of defoamer performance in many types of coatings systems, is certainly the "holy grail". Surface and interfacial tension, defoamer emulsification into droplets, and defoamer mechanics all have to be in compliance for the defoamer to function.
Defoamers that have a positive Entering and Spreading Coefficient (S and E) derived from surface and interfacial tension, usually exhibit the best foam control. Likewise, defoamers that emulsify into a controlled droplet size will perform best. The image captures the effect of formulation on droplet size. From left, the emulsion is coarsest and on the right, a microemulsion.
Formulation change, even seemingly simple change can destroy the performance of the system's "standard" defoamer.
Familiarization with resin type, pigment volume concentration and surfactant used in particular coatings with previously used defoamers, can guide the formulator toward the right defoamer. More specifically, the history of use of specific defoamers in particular coatings lines can provide guidance.
To best minimize the number of defoamer recommendations additional information should be provided to the supplier such as:
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How is the current defoamer failing?
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What is the resin type?
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What is the coating's PVC?
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Where is the foam generated and under what conditions?
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What is the coating VOC?
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What are the FDA requirements of the defoamer?
- What are the defoamer longevity requirements?
The defoamer producer can choose a defoamer with an appropriate emulsifier level that should have the required longevity. Or, a limited number of defoamers can be recommended. For the most difficult problems, the defoamer supplier can screen products before making suggestions.
What can you do to avoid secondary defects?
There are many reasons for the appearance of an applied paint or coating to be less than optimal. One contributing factor can be the defoamer! Since defoamers work by virtue of their incompatibility in paint, this incompatibility could lead to defects such as fisheyes, craters, pinholes, and orange peel. In a very general sense, this incompatibility is responsible for the inability of the liquid coating to completely wet the incompatible component.
Defects in paint caused by defoamers incompatibility: Craters
Two strategies can be employed to solve the defect problem. One involves keeping the existing defoamer and trying to solve the problem and the other requires a new defoamer.
For a defoamer that causes defects but is otherwise acceptable, reducing the use level and/or introducing it into the grind may be the remedy. The grind will apply significant shear and can assist in compatibilization. Allowing the defoamer to "sweat in" for 24 hours may help also.
Another approach is to increase the surfactant(s) employed in the coating formulation so as to achieve the same result. The surfactant approach works by reducing the interfacial tension between the defoamer droplet and the water so smaller droplets are formed. This approach may also cause a reduction in the interfacial tension between the droplet and the resin resulting in better compatibility.
In some instances, defoamers at low use levels may contribute low levels of defects. These can be formulated out with an Interfacial Tension Modifier that works by reducing the interfacial tension between the defoamer droplet and the coating. This interfacial tension reduction allows for smaller droplets and improved compatibility, resulting in defect free films.
One additional benefit gained by using low use levels of high performance defoamers is that recoatability is rarely an issue and treatment cost is minimal.
Alternatively, choose another defoamer that has been formulated properly with the correct emulsifier/surfactant package so that the defoamer droplets formed when introduced into the coating are small enough to go undetected but of sufficient size to still control foam. Here working closely with a defoamer supplier can be beneficial.
Either approach, when properly executed, can turn a nasty looking coating into a well behaved coating. In case non of this approach works, go deeper to understand the root causes behind your coating film defects & get assistance to solve them with practical examples »
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