Foaming Process Types of Defoamers

Foam Destabilization Mechanisms

Foam Control Agents Available Chemistries

Architectural Coatings

Select Defoamers for Industrial Coatings

When should you add defoamer

How to Evaluate the Efficiency of a Defoamer

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.

Testing 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.

Defoamer Exhaustion

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.

  • Adequately determine the time frame for defoamer performance. In some cases one day is sufficient and in other cases years may be required.
  • 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?

DyStar - FOAM BLAST® 4205 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:

  • How is the current defoamer failing?
  • What is the resin type?
  • What is the coating's PVC?
  • Where is the foam generated and under what conditions?
  • What is the coating VOC?
  • 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.

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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
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 »

Solving Coatings Film Defect_SG_Prop

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