Defoaming agents for paint square measure employed in waterborne coatings systems to cut back foam formation throughout production, transportation, storage and application. many take a look at strategies square measureused for determinative the potency of defoaming agents for paint. reckoning on the reason behind the froth formation, the most effective corresponding laboratory take a look at methodology is chosen.
Waterborne coatings systems
This article describes a brand new generation of radical stable defoaming agents for paint. reckoning on the particularcriteria for compatibility and usage, a range of correct defoaming agents for paint may be created.
Excessive foam formation is one drawback that may surface throughout the formulation of waterborne paint systems. Foam will develop, and may be a major concern, throughout all stages of a waterborne paint: production, filling, transportation and application.
Foam formation ought to be avoided by all means that. throughout the assembly and filling stages, foam results inunskillfulness, overflow in tanks, instability and different issues. Foam formation throughout paint application willcause properties like cratering, loss of opacity and protection.
To fight foam formation, defoaming agents for paint square measure used. virtually each waterborne paint system contains associate anti-foaming agent, generally within the concentration vary of zero.05-0.5% by weight.
There square measure several defoaming agents for paint on the market. choosing the correct kind for a preciseapplication is kind of a task. The potency of defoaming agents for paint powerfully depends upon the particular paint system and method used. this text presents some take a look at procedures and properties of a brand newgeneration of defoaming agents for paint.
Foam may be a stable dispersion of a gas during a liquid or solid phase; for functions of this text, it's shaped from air distributed within the water section of the paint formulation. The air is stable by the surface active parts within the paint, like emulsifiers, wetting agents and thickeners.
Air is another throughout many stages, like throughout mix, dispersing, filling, transportation and application. Besides the incorporation of air, different gases will develop as a results of chemical reactions within the paint. for instance, in two-component systems like those supported isocyanates, greenhouse gas may be shaped once the salt teams react with water.
Pure liquids do not kind foam. The entrapped air are going to be free impromptu as a results of variations in relative density (Stokes Law). within the presence of surface active agents, air dispersions are going to be stable.
Optimizing the paint formulation and also the production and application method will cut back the defense of air. However, air defense can't be avoided utterly. Defoaming agents for paint square measure required in virtually eachwaterborne system.
The potency of defoaming agents for paint depends on their ability to unfold themselves throughout the media and also the ability to penetrate into the froth.
The following parameters may be delineated as follows1,2:
Penetration constant E:
E = sf - South Dakota + sint. (1)
Spreading constant S:
S = sf - South Dakota - sint. (2)
sf = physical phenomenon of liquid to be defoamed
South Dakota = physical phenomenon of anti-foaming agent
sint. = surface tension between defoamer and also the liquid to be defoamed.
A defoamer will penetrate a foam containing medium if E >0 and a defoamer may also unfold itself impromptu at intervals the medium if S>0.
A positive worth for S is of nice importance for a defoamer since E-S=2sint. (see Figure 1).
The potency of defoaming agents for paint is magnified if surface tensions and/or surface tensions square measuredecreased; defoaming agents for paint, therefore, contain surface active parts.
Also, the defoamer's body and compatibility with the medium to defoam can play a vital role in its potency. an occasional body contributes to economical penetration and spreading. Incompatibility ensures a defoamer concentration build-up at the interface liquid/air; that's, if the particular gravity of the defoamer is below the liquid to defoam.
The composition of defoamers is very numerous. However, characteristic parts of defoamers embody the subsequent.
One or additional hydrophobic compounds. The hydrophobic part destabilizes the froth dispersion as a result of it displaces the stabilizer. Hydrophobic parts square measure thought-about among the foremost active ingredients in defoamers.
Also, hydrophobic parts stop the formation of stable surface surfaces between air/liquid. Consequently, the bubblewill penetrate the interface and unleash itself or it will kind a much bigger, less stable, bubble by coalescing with another bubble. Typical hydrophobic parts square measure principally solids, like silicas, polyamides and waxes.
Mineral oil. The oil acts because the carrier for the hydrophobic parts.
Surface active dispersing agents/emulsifiers. The dispersing agent ensures associate optimum distribution of the hydrophobic part within the oil whereas the surfactant eases the spreading of the defoamer throughout the medium to defoam. the sort and amount of surfactant to be used rely on the applying of the defoamer and will be selected rigorously. The minimum doable amount of surfactant ought to be used since emulsifiers themselves willcontribute to foam formation. Also, the terribly fine distribution and stability of the defoamer hinders its potencysince the operating mechanism is predicated on a surface activity, partially caused by a precise incompatibility and robust activity on the interface air-water.
The amount of surfactant another can rely upon the ultimate application of the anti-foaming agent: for applications within which the defoamer is another with high shear forces or for applications of defoamers in media with high emulsifying properties, the number of surfactant within the defoamer ought to be restricted.
Together with the dispersant - and in several formulations conjointly the oil - the surfactant determines to an excellent extent the interface activity of the defoamer. conjointly conducive to the present square measuresilicones. Silicones, however, will cause negative facet effects like crater building and adhesion issues.
Traditionally, hydrophobic elements ar spread within the oil or blended within the soften stage. the topmerchandise ar meta-stable. Most typical defoaming agents for paint can struggle with phase-separation in time and, therefore, they have to be homogenized before use.
When not homogenized, there's a risk that solely the highest layer of the defoamer is employed whereas most of the active ingredients stay within the bottom layer. This leads to non-efficient defoaming and surface issueswithin the paint film. typically|this can be} a development seen only too often in follow.
By employing a new procedure - during this study stated as radical dispersion method (UDP) - the hydrophobic element are often spread into the carrier, leading to very stable defoaming agents for paint. Above all, the mixturedispersing agent/emulsifier is optimized. Defoamers created by the UDP method show spreading potency and stability of the hydrophobic element (see Table 1).
In this check series, we tend to by design selected a variety of defoamers with totally different emulsifying properties in water. SERDAS 7010 and 7015 ar created following the UDP method, leading to a very fine dispersion of the hydrophobic element within the oil. SERDAS 7540 and 7580 ar composed of only 1 element: the hydrophobic element is with chemicals anchored among the organic compound component. the normal, factory-made in step with the traditional technique, relies on a silica-mineral oil system and is employed as a reference.
The potency of the defoaming agents for paint is incontestable by victimisation the subsequent laboratory checkprocedures.
Shelf Life Stability check
The defoaming agents for paint ar keep for 3 months at temperature in a very 100-mL glass bottle. Afterwards, separation are going to be judged.
Paint with anti-foaming agent is agitated on a barbiturate shaker 3|for 3} minutes (or multiple three minute time periods): dose is a hundred and fifty grams of paint in a very 300-mL bottle. straight off when shaking, the particular gravity is decided with a 50-mL pycnometer. the proportion of froth are often expressed as:
A de-aired paint is obtained by centrifuging a paint sample till a continuing relative density is obtained. This shake check has well-tried to administer a decent indication regarding the defoamer potency in follow, specifically for dispersion paints, and is employed for systems with a consistency between 750-3,000 mPa.s. This check are oftenrecurrent when a precise shelf time, betting on the appliance.
High-Speed Mixer check
This check technique is very helpful for defoamer evaluations in low-viscosity systems (50-750 mPa.s) also as for pigment pastes. the proportion of froth is decided straight off when stirring a hundred and fifty grams of checkmedium for 3 minutes in a very one,000-mL plastic beaker. the froth breakdown is noted, for instance, one minute when stirring.
For this check, a typical application technique is used: roller, brush or spray application. for example, in evaluating a wall paint, a roller with coarse pores is employed. the froth development is evaluated in each the wet stage and dry stage of the paint and noted as: ten = excellent; no foam or different defects; one = poor; foam and differentdefects like craters and coagulates. The defects are going to be represented in every case.
Also, changes in properties like consistency, pH, color and adhesion are going to be determined. All checkprocedures for defoaming agents for paint ought to mirror the 'real-life situation' as shut as doable.
For this study, the potency of the defoamers mentioned in Table one are going to be incontestable within thefollowing systems.
System 1: Interior/exterior acrylic dispersion paint, PVC 55%
System 2: High loaded styrene-acrylic dispersion paint, PVC 73%
System 3: Acrylic dispersion gloss paint, PVC 16%
System 4: Water primarily based alkyd resin paint, PVC approx. 18%
System 5: Pigment paste, supported TiO2, associative HEUR material, acrylic primarily based dispersing agent and water
System 6: furnishings coating, acrylic copolymer-based
The dose of defoaming agents for paint all told systems is unbroken to a minimum of zero.2% by weight, supported total formulation, so variations in defoamer potency will best be highlighted.
Results and Discussion
Many oil-based defoamers can show some kind of section separation upon storage. Shelf-life stability tests of the product listed in Table one indicate that so the standard defoamer showed section separation as seen in Figure two.
The defoamers, made per the UDP method, area unit stable and no separation is determined when 3 months. This clearly is that the case for the clear defoamers SERDAS 7540 and 7580 similarly (see Table 2).
For System one, the simplest results area unit obtained with SERDAS 7010 (see Table 3). The defoaming potencysimilarly because the film look is ideal. outstanding is that the potency when six months of paint storage and therefore the virtually nonexistent relation of froth development and 'dispersing energy.' Typical for SERDAS 7010 is that the weak emulsification rate. However, the paint itself shows sufficient emulsifying properties, permittingthe defoamer to distribute itself homogeneously within the system.
Although SERDAS 7580, a robust emulsifying grade, provides wonderful defoaming properties, the wet paint film contains foam leading to craters within the dry paint. it's assumed that the compatibility of this defoamer with this paint system is simply too sensible, going away a too-low concentration of the SERDAS 7580 at the interface liquid/air. higher|the next} dose of the defoamer within the paint formulation may lead to better application take a look at results.
For System two, a dispersion paint, best results area unit obtained with SERDAS 7010: sensible potency and sensible time period storage properties (see Table 4).
The other defoamers, all with higher emulsifying properties, show the next loss in potency upon storage. this maypresumably be explained by the actual fact that most likely the full surface surface defoamer/medium in these fine dispersions is larger/more intense, leading to associate inflated modification of physical or chemical interactions, like sorption or absorption onto the pigment.
System 3, the gloss dispersion paint shown in Table five, shows that best results area unit obtained with SERDAS 7580, the sort with the simplest water-emulsifying properties. Besides economical anti-foaming properties the potency is maintained upon storage. A paint film while not surface defects is obtained, as hostile the system with SERDAS 7010.
Hard-to-emulsify defoamers, like SERDAS 7010, show poor spreading during this system, leading to concentrates of the defoamer on the surface of the paint film. This leads to surface defects and during a loss of gloss.
Table vi shows that for a waterborne synthetic resin, SERDAS 7540 may be a sensible defoamer. This product shows sensible potency and no surface defects. conjointly SERDAS 7580 performs well. The paint with SERDAS 7015 shows surface defects, presumptively caused by the silicones gift within the defoamer.
In the system shown in Table seven, SERDAS 7540 shows the simplest results. 7540 is one among the higheremulsifying defoamer varieties. Remarkably, the defoamers with weak emulsifying properties and silicones area unit less economical during this system. there's no sensible rationalization for these results, and this shows all over again that choosing the optimum defoamer for a selected system needs testing of a spread of defoamers.
In associate acrylic copolymer-based end, sensible results area unit obtained with SERDAS 7015 (see Table 8). This wood end is developed with associate acrylic dispersion with sensible emulsifying properties. Again, we have a tendency to see that the silicone-free defoamers, showing sensible emulsifying properties naturally, don't offerthe simplest results. will this development be explained by the actual fact that these product area unit 'silicone free' or 'good emulsifiers'? each area unit assumed. The silicone-based product yield an occasional surface tension. This relates to a positive impact for the penetration and spreading coefficients. sufficient emulsifying properties of the medium to be defoamed can guarantee a robust surface activity and, therefore, an occasional surface tensionbetween liquid/air. Yielding higher surface tension, the silicone-free product cannot concentrate themselves within the interface liquid/air in favor of the foam-stabilizing elements, and might so not act as economical defoaming agents for paint.
SERDAS 7540 and 7580, with sensible emulsifying properties, area unit well distributed throughout the fullmedium. At the low concentrations else to the present medium during this study, possibly associate inadequatedefoamer concentration winds up within the interface space liquid/air. In another similar wood finishing system, SERDAS 7580 seems to be the foremost economical defoamer: the rosin during this system shows poor emulsifying properties.
A new production technique, the radical dispersion method, permits production of defoaming agents for paint with glorious period stability. the potency of defoaming agents is very system dependent. However, by employing aelite series of defoaming agents for paint with totally different properties, it's doable to pick the foremost economicaldefoamer for every individual paint system. the choice of defoamers is chosen supported emulsifying properties and silicone-based or silicone-free varieties.
Also, the sensitivity of the paint film to come up with surface defects is vital once selecting the correct defoamer. In extremely pigmented systems, a silicone-based and weak emulsifying defoamer, created per the radical dispersion method, tends to be the most effective selection.