Wetting & Dispersing Agents_Anuj Agrawal.pptx

A detailed study on different kinds of wetting and dispersing agents used in the paints and coatings industry

1. Wetting & Dispersing Additives Presented by: Anuj Agrawal BTech Oils & Surfactants Technology, UDCT Mumbai, India M.S. Polymer Science, University of Akron, USA Co-owner Texochem Industries

2. Topics to cover Why are wetting & d ispersing additives used? Understanding surface tension Influencing surface tension with surfactants What are wetting additives & how are they used? How do wetting additives affect static and dynamic surface tension? Selecting the right wetting additives Selecting the right wetting additives – Formulators choice Defects which can be solved using wetting additives Stages of pigment dispersion process Need for effective pigment dispersion How do dispersing additives work? Impact of dispersing additives on settling and syneresis Selecting the right dispersing additives – Formulators choice Determining optimum dispersant dosage Evaluation dispersing additive efficiency Defects which can be solved using dispersing additives

3. Why are Wetting and Dispersing Additives used? One of the most important steps in the production of pigmented coatings is the homogeneous distribution of solid pigments within the liquid binder solution. If this pigment grinding step is not optimized, then a wide variety of defects can occur.

4. Understanding Surface Tension General rules to remember: Higher the cohesion between molecules, higher is the surface tension (e.g., water molecules have high cohesion because of hydrogen bonding). Lower the polarity of the liquid, lower is the surface tension. Efficient wetting of substrate occurs when the surface tension of liquid is lower than the substrate. Liquid Surface tension (mN/m) Water 73 Epoxy Resin 45 – 60 Melamine Resin 42 – 58 Alkyd Resin 33 – 60 Acrylic Resin 32 – 40 Butyl Glycol 32 Xylene 29 – 30 Butyl acetate 25 Butanol 23 Hexane 18 Substrate Surface tension (mN/m) Glass 73 Phosphated Steel 43 – 46 Polyvinyl chloride 39 – 42 Tin plated steel 35 Aluminum 33 – 35 Polyethylene 32 – 39 Polypropylene 28 – 29 Untreated Steel 29 Polydimethyl siloxane 19 Polytetrafluoroethylene 19

5. Influencing Surface Tension using Surfactants (“surface active agents”) Surfactants (or surfactant-like molecules) are interfacially active. They have a strong tendency to migrate to accumulate at interfaces. There they lower the surface tension (or interfacial tension) between two phases. In that way surfactants may act as detergents, wetting agents, emulsifiers, foaming agents and dispersants.

6. What are Wetting Additives & How are they used? Wetting additives can be defined as substances which are designed to reduce the surface tension between pigment and resin solution and which, as a result speeds up the penetration of the liquid into the pigment agglomerate structure.

7. How do Wetting Additives affect the Static and Dynamic Surface Tension? If θ = 0⁰ then wetting takes place easily If 0⁰ < θ > 90⁰, partial wetting occurs If θ > 90⁰ then wetting is difficult Dynamic measurements more accurately reflect actual, in-process, surfactant, and coating performance. In effect, if you limit surfactant migration time (by using a faster coating process) you require more surfactant to perform the same job as in the slower process.

8. Selecting the right Wetting Additives Formulating a defect-free coating can be achieved by controlling the surface chemistry of the coating. More specifically, local surface tension differences are the actual cause of many surface defects . These local differences can be compensated using substrate wetting agents. After formation of new surfaces (stirring), surfactants need some time to migrate to the newly forme d interfaces and to lower the surface tension again. For fast processes it is recommended to use highly dynamic surfactants, which ensure low surface tension even if new surfaces are formed very quickly. Schematic representation of the dynamic behavior of surfactants.

9. Selecting the right Wetting Additive – Formulator’s Choice Surfactants that diffuse slowly may not lower surface tensions sufficiently, to acceptable levels and may be partially responsible for defects such as: Bénard cells, craters or pin holes, crawling or retraction, floating, orange peel, and picture framing (edge buildup). Surfactants that diffuse rapidly can mitigate surface defects by eliminating surface tension gradients. This occurs through rapid surfactant migration from high concentrations (low surface tension) to low concentrations (high surface tension). This type of surfactant can reduce surface tension with the extra benefit of reducing or preventing foam. Formulators will sometimes mistakenly increase surfactant concentration to reduce gradients, rather than use a better surfactant.   Formulators should try to use a suitable surfactant that ideally has both low equilibrium and low dynamic surface tension values – low enough so that the coating is applied to the surface at process speeds with a desirable velocity.

10. Selecting the right Substrate Wetting Agent The ability to lower the surface tension even under highly dynamic conditions (high bubble frequency) depends on the mobility of the surfactants. Sulfosuccinates and alkoxylated surfactants can cover newly formed interfaces rather quickly. Whereas the fluorinated polyacrylates and the silicone surfactants are slower due to their higher molecular weight and different aggregation behavior. Wetting Agents 0.5% in Demineralized Water Increasing speed and frequency

11. Selecting the right Substrate Wetting Additive – Formulator’s Choice Additive Reduction in static surface tension Reduction in dynamic surface tension Foaming tendency Price Sulfosuccinate Medium – good Very Good Strong Low Alcohol alkoxylate Low Good Low Medium Polyether modified siloxane Good Medium Medium Medium – high Fluorosurfactant Very good Low Very Strong High Acetylenediol and derivatives Medium – good Very good Low High Note: Stronger the reduction in static surface tension, higher is the tendency to stabilize foam To control foaming, most effective wetting agent will be the one with more hydrophobic “tail” and less hydrophilic “head” . In general, surfactants with a smaller (lighter) molecule mass (short hydrophobic tail) diffuse more rapidly to the interface. Nonionic surfactants with ethylene oxide groups usually diffuse very rapidly to the surface while fluorinated surfactants are slower and more effective at equilibrium

12. Defects which can be solved using Wetting Agents Cissing Fish Eyes

13. Stages of Pigment Dispersion Process During the grinding process the particle surface needs to be wetted by the surrounding liquid . During the grinding step the agglomerated particles are mechanically broken down to smaller particles using grinding equipment such as dissolvers or bead mills. This newly formed surface area has to be stabilized to avoid re-agglomeration – typically done using Dispersing Additives.

14. Need for efficient pigment dispersion Desired Property Preferred Particle Size Low Viscosity Large Low Dispersant demand Large Increased photostability Large Higher Opacity Medium High Tinting Strength Low

15. Need for efficient pigment dispersion

16. How do Dispersing Additives work? Dispersing additives absorb onto the pigment surface and therefore maintain proper pigment spacing through electrostatic repulsion and/or steric hindrance , thus reducing the tendency towards uncontrolled flocculation. These are typically polyelectrolytes – higher molecular weight products, which do not have any wetting properties. These are composed of pigment affinic groups and resin-compatible chains, which exhibit surface-active properties. (i.e. they behave both as dispersing and wetting additives)

17. Impact of Dispersing Additives on Settling & Syneresis? Settling takes place when the pigment has a higher density than the liquid media (most cases). The pigments can also rise and agglomerate at the surface when the pigment has a lower density than the media. Syneresis is like settling but it is a stratification of liquids in a coating. In extreme cases in a water-based paint, enough water will separate out the latex resins which undergo coalescence. An optimized surfactant package will: Stabilize the pigments from re-agglomerating or re-aggregating, as the larger agglomerates or aggregates will settle out faster. Cause any settling to be soft and easily re-incorporated. Act as a humectant, keeping water within the resin matrix to prevent syneresis.

18. Selecting the right Dispersing Additive-Formulators Choice Conventional Dispersing Agents These are mainly low molecular weight and are based on polyesters, polyamides, polyglycols and fatty acid chemistry (FAME). General Characteristics: • Mol wt. = 500 – 2000 g/mol • Good compatibility with the media • Provide mainly electrostatic stabilization. Polymeric Dispersing Agents These are mainly polyacrylates, polyester, polyether, or polyurethane-based systems. General Characteristics: Mol wt. = 5000 – 50,000 g/mol Very effective for long term stabilization Provide mainly steric stabilization. Provide multiple pigment anchoring groups. Ionic and Non-Ionic Dispersing Agents These are mainly alkyl phenol ethoxylate and more precisely nonyl phenol ethoxylate General Characteristics: Mol wt. = 300 – 1,000 g/mol Good wetting property Provide mainly electrostatic stabilization.

19. Selecting the right Dispersing Additive-Formulators Choice The most important selection criteria is the type of pigment being dispersed and what properties you are looking for. Ionic dispersants work best with inorganic primary pigments (titanium dioxide, iron oxides, etc.) and extender pigments. Non-ionic or polymeric dispersants are generally classified by their molecular weight. Low-molecular-weight dispersants are economical solutions for inorganic primary and extender pigments. Medium- molecular-weight dispersants give the broadest compatibility with pigments and resins, leading to a more universal system. High-molecular-weight dispersants are used when you require the lowest viscosities, highest color strength and highest gloss. High-molecular-weight dispersants are generally best for expensive organic pigments, as they maximize color development. The higher the molecular weight of the dispersant, the more you will need, as you get fewer molecules per unit weight . If the molecular mass is too high, incompatibility, flocculation and viscosity rise may occur. You have to balance out the increased cost of higher-molecular-weight dispersants versus the cost of the increased performance of the pigments.

20. Determining optimum Dispersant level The key is not to formulate on a pinhead. We see that the red curve has the lowest viscosity and is the preferred dispersant, but its curve has a narrower plateau than the green or purple curves. At dispersant concentration 1, the red dispersant is the obvious choice. It uses less dispersant and has the lowest viscosity. But what if the concentration change between 1 and 3 is so small your production process cannot consistently weigh out the dispersant accurately within the range of the curve? Then the purple curve would be better. While the purple curve is the flattest of the three curves, in almost all areas the green curve has a lower viscosity and is preferred over the purple curve if the red dispersant cannot be used.

21. Evaluating Efficiency of Dispersing Additives 1. Compatibility Check 2. Pigment Shock 3. Drawdown 4. Rub out

22. Defects which can be solved using Dispersing Additives Streaking/silking

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25. Product Overview Styrene Acrylic Emulsions Pure Acrylic Emulsions Dampproof Emulsions DTM Emulsions Waterproofing Coatings Polymer Seal Coats Acrylic Thickeners HASE Thickeners Ammonia Polyacrylate Thickeners Dispersing Agents Wetting & Dispersing Agents

26. THANK YOU Contact Details: Anuj Agrawal Mob: [phone] Email: [email protected]