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Leveling Agents for Coatings

Finding the right leveling agent is often a tedious process, considering all the parameters. It is important to check dosage and product variations to figure out the correct chemistry and fine tune the formulation. Make the selection of your leveling agents easy for your coating formulation by getting answers to most of your questions that arise during the selection process.

Leveling Agent: A Surface Tension Story!


It is admitted for many paints that a perfect appearance means also a perfect leveling.

Poor leveling (like orange peel or ghosting) may not influence significantly the paint parameters in time, as it is more aesthetic orientated. But the leveling agent itself may cause some severe issues.

Leveling Agents for Coatings

A correct leveling agent helps in reaching the wanted leveling. But a wrong choice may lead to surface defects such as craters, pinholes, loss of gloss or even inter-coat adhesion problems.

» View All Commercially Available Leveling Agents in Coatings Database 

This coatings database is available to all, free of charge. You can filter down your options by suitable resin, system or application (coatings, inks...), supplier and regional availability.

Role of Levelling Agent in Paint Appearance

Leveling is an important aesthetic parameter of the paint. To understand the leveling, it is important to understand the influence of the surface tension on the paint. Indeed, the paint has two interfacial areas:

  • One with its substrate
  • One with the surrounding atmosphere

General surfactants are active on these interfaces, and depending on their chemistry, can help with the substrate wetting or be active at the paint / air interface.

Continue Reading…


The substrate wetting of a liquid on a solid substrate is defined by the surface tension, function of the contact angle. The contact angle θ is the angle between the intersection of the liquid-solid interface and the liquid-air interface at the three phase contact line.

  • A good substrate wetting is important to reach a good paint surface leveling!

    contact angle
    Contact Angle

    Low Contact Angle vs High Contact Angle


    θ < 90° : low contact angle

    θ > 90° : high contact angle

    Favorable wetting - Positive influence on the leveling

    Unfavorable wetting - Negative influence on the leveling

    The paint will spread over the surface

    The paint will minimize its contact with the substrate

    Good wetting of the paint


     Good wetting of the paint

    Poor wetting of the paint


     Poor wetting of the paint

    Ideal theory, a perfect coating would have a contact angle θ = 0° regarding the substrate, which is not realistic. Nevertheless, we can consider reaching a good wetting when the contact angle θ < 90° , in other words, when the liquid has a lower surface energy than the substrate : γ (L) < γ(S)

    θ < 90° γ (Liquid) < γ (Substrate)

  • Decrease the surface tension of the liquid, improve the substrate wetting - positive influence on the leveling

  • Equalize the surface tension at the liquid / air interface - improve the leveling

  • Good flow means the avoidance of interfacial tension problems and surface texture issues & good leveling means the achievement of the lowest surface area possible

Using specific surfactants like leveling agents will improve the surface aspect of the paint! 

Other Factors Influencing Paint Leveling


Of course, besides the surface tension, many parameters are influencing the paint leveling:

  • Raw materials
  • Application method
  • Paint viscosity
  • Film thickness
  • Curing / drying conditions…

Above listed are some examples of the factors. But, the surface tension parameter plays also a critical role to avoid leveling defects such as the orange peel. In realistic conditions, it is not always possible to play with each parameter to reach the wanted leveling. But working on the surface tension parameters using solvents and additives will help in improving the paint surface quality.

Competing Forces in the liquid
Competing Forces within the Liquid


A paint drop is a combination of various materials, such as:


Each of them have their own surface tension, and the general tension is caused by the unbalanced forces of liquid molecules at the surface. During the paint drying, the solvent (or water) evaporation will further unbalanced this state, creating a surface tension gradient at the paint surface.

Role of Solvents in Leveling


The solvents used in the formulation are really important to reach the required leveling. Too fast evaporation will lead to poor leveling; too low evaporation may increase the risk of contamination, surface defects, and reduce the production speed. But this is also linked with the film thickness: higher film thickness, more solvent to evaporate, longer drying time.

Leveling agent working


During the paint drying / curing, the leveling agent will move to the liquid (paint) / air interface and orientates itself at the surface. The possible reactive modification will stay in the liquid part and react with the polymers during the drying / curing.

The leveling agent, as a surfactant, will:

  • Balance and harmonize this surface tension at the paint / air interface
  • Reduce the surface tension gradient
  • Improve the surface aspect

Finding a balance is critical:

  • Too low surface tension may be good for the substrate wetting, but may lead also to a wavy surface
  • Too high surface tension can cause adhesion and surface wetting issues

Unbalanced forces at the surface will create waves, (long waves and short waves) which may lead to surface aspect issues such as the orange peel, loss of gloss and poor DOI.


Selecting the Right Leveling Agent


Which Leveling Agent for which Coating? Leveling agent may be based on several chemistries. Continue reading OR Click on the links below to know more about the most common types of leveling agents:


Characteristics of Silicone-based Leveling Agents


  1. Strong surface tension reduction, controlled tensions at all the interfaces: improve the paint wetting properties, recommended to reduce the surface long waves (> 1.2mm)
  2. Reduce the turbulences and rheological currents during the solvent evaporation
  3. Excellent to improve the slip
  4. May have a negative influence on the inter-coat adhesion and may provoke unwanted negative side effects (contamination / craters, migration in the upper layer in case of multi layers systems)
  5. Polyether modifications with various Ethylene Oxide (polar) / Propylene Oxide (unipolar) units will improve the compatibility
  6. Thermal stability can be also enhanced (like with a polyester modification for instance)
  7. To lower the possible negative influence on the inter-coat adhesion, it is possible to use some reactive silicone based leveling agents, which will have a lower migration tendency

» Select Right Silicone-based Leveling Agent for your Development 

Summary of Silicone based Leveling Agent Specificities

Modified

PDMS

EO dominant

PO dominant

Short Modification

Long Modification

Long Backbone

Anti-Crater

Leveling

Slip

Substrate Wetting

Risk of inter layer defects / contamination

low

low

low

medium

high



Silicone based Leveling Agents

Improve the leveling by reducing the surface tension
Recommended for Long Waves reduction
Advantage
Disadvantage
Give good flow, reduce orange peel  Incompatibility
Increase the surface slip, improve scratch and mar resistance  May provoke intercoat adhesion issue
Avoid air draft sensitivity  May provoke contamination
Avoid silking

Characteristics of Acrylate-based Leveling Agents


  1. Have a relatively high surface tension: avoid intercoat adhesion issues
  2. They improve the localized harmonization of surface tension by reducing the gradient surface tension, and as a consequence improve the leveling. excellent to reduce the surface short waves (< 1.2mm)
  3. Limited in the surface tension reduction. But as surface tension agents, they can also have an influence on the air entrapment, especially high molecular weight versions
  4. Due to their low influence on the surface tension, polyacrylates are also recommended in primers!

» View All Acrylate-based Leveling Agents Available in the Market 

Summary of Acrylate-based Leveling Agent Specificities

Polyacrylates

Low Molecular weight

Medium Molecular Weight

High Molecular Weight

Modified

Compatibility

Gloss

Haze

Degassing

Hardness

Leveling






Acrylate-based Leveling Agents

Improve the leveling by reducing the surface tension gradient
Recommended for Short Waves reduction
Advantage
Disadvantage
Reduce orange peel, improve the DOI
Do not improve the slip effect

Efficient against ghosting and clouding

Incompatibility may cause loss of gloss, loss of DOI, and may increase the haze
Efficient against craters and pinholes
Can decrease surface hardness for low molecular weight
Temperature resistance


Characteristics of Fluorocarbon-based Leveling Agents


  • Pure fluorocarbons are too strong and provoke many defects. That is why this chemistry is often modified
  • Strong surface tension reduction, even more than silicone based agents
  • May resist at higher temperature than standard silicon based agents (over 150°C)
  • Usually more expensive than acrylates and silicones modified products
  • Fluorocarbon chemistry is often acrylate modified. These products can offer a polyvalent action, reducing the orange peel acting both on long waves and short waves, and improve the gloss and DOI

» See All Fluorosurfactants Leveling Agent Grades! 

Fluorocarbon based agents (Modified Fluorocarbons)
Polyvalent agent

Benefits
Limitations
Reduce orange peel
Strong surface tension reduction

Improve DOI

Can decrease surface hardness for low molecular weight
Efficient against craters and pinholes
May provoke intercoat adhesion issue
Relatively polyvalent


Leveling Agents and their Effects in the Coating System


Nowadays, you can easily find leveling agent chemistries for solvent-borne and waterborne coatings. In case of powder coatings, acrylic based leveling agents are preferable due to their low contamination tendency.

Surface tension reduction


Leveling Agents and their Effects in the Coating System


This summary table compares the global tendency of each leveling agent’s chemistry.

Type of Leveling agent

Modified Acrylates

Modified Silicones

Modified Fluorocarbon

Anti-benard Cell effect

0

Anti crater effect

Flow

Leveling / Orange Peel 

Slip

0

Substrate wetting effect



Surface tension reduction     
 
Risk of inter layer defects / contamination  No   High Low 
High temperature resistance   
 


The formulator has a large choice in the selection the leveling agent. In the most exigent end-uses, the best solution is often achieved by a combination of technologies, such as modified acrylates with modified silicones.

The best leveling agent for a formulation will, of course, improve the leveling,
without any influence on the other parameters and will not provoke any unwanted negative side-effect!


Some recommendation:

  • Always check the all parameters when using a leveling agent, and not only the leveling and surface aspect. As surface active material, it can have an influence on the substrate wetting, the haze, the intercoat adhesion, or foam stabilization (especially in waterborne).
  • Do not hesitate in testing variation of a product: not only in the dosage, but also try different molecular weight, and product modifications (such as EO/PO for PDMS for instance). Some variations may better fit your system and improve the leveling agent compatibility, reducing the loss of gloss and haze negative effects.

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