3 Keys to Mechanical & Jet Milling in the Paints & Coatings Industry

Justin Klinger, Oct 1, 2020 6:45:00 AM

toll milling paints and coatings

Consistency, uniformity, and performance are critical challenges for paint and coating manufacturers, and milling processes are vital to achieving these goals. 

Particle sizes can affect characteristics ranging from color, hiding power, and level of gloss in paints to the coefficient of friction in industrial coatings. Grinding is also indispensable for blending or dispersing particles. This is true whether the dispersion is liquid (such as solvent or water-based paint) or powdered solid (as in heat-cured coatings used in metal finishing).

The path to optimal particle sizes, homogenous dispersions, and paints and coatings that perform as intended can be complex, involving multiple technologies and an almost limitless range of variable adjustments.

When it comes to selecting a toll processing partner for grinding and blending in the paints and coatings industry, it’s absolutely critical to keep these three things in mind: 

  1. Particle size determines critical characteristics of paints and coatings.
  2. Homogenous dispersions can be challenging to achieve.
  3. Multiple processes and/or complex variable adjustments may be needed to achieve your goal.

Read on to learn more about the importance of particle size reduction and uniform blending in paint and coating formulations, and some of the milling methods your toll processor may use to ensure the consistent outcomes that are vital to your success.

1. Particle Size Determines Critical Characteristics of Paints and Coatings.

Most paints and coatings are composed of ingredients that may include pigments, fillers, resins, solvents, catalysts, and/or additives. Particle sizes and distributions in the formulation can affect the final product’s functionality, durability, and appearance. 


Particle size can affect many characteristics of paint, primer, lacquer, or other liquid-applied coating, including:

  • Hue/tint strength
  • Hiding power
  • Color uniformity
  • Gloss vs. flatting
  • Viscosity
  • Stability
  • Strength on aging
  • Water resistance

Powder Coatings

In industrial coatings, the use of waxes, polyethylenes, and polymers achieve smoothness, scuff resistance, and reduced metal marking. These additives rise to the surface as the finish cures, so particle size is vital. Larger particles can cause problems during heat curing. Very tiny particles agglomerate easily, and can also result in an unintended flat finish.

Particle size can affect a coating’s behavior during application and curing, including:

  • Movement in a fluidized bed chamber
  • Electrostatic charging
  • Spray trajectories
  • Layer build-up
  • Adhesion

Just as in a paint formulation, particle size can also affect coating properties including color, matting, texture, and weather-resistance or durability.

2. Homogenous Dispersions can be Challenging to Achieve.

When blending paint ingredients, particle size can make it easier or harder to disperse pigments in solvent. The smaller the particle size, the more surface area, and the more pigment particles will tend to agglomerate — so process knowledge is key in selecting effective agents for wetting, dispersing, and stabilizing, in addition to choosing the right blending technology. 

Milling and blending technologies not only help ensure homogenous dispersion throughout the batch of liquid slurry; they also help create a more stable mixture that resists settling and sedimentation.

Powder coatings can also require multiple milling and grinding methods to achieve uniform dispersion. Often, constituent ingredients are first individually milled to the required particle size; next, they are melted and blended using an extrusion method such as a twin screw extruder. The resulting blended product requires further milling before it can be used.

3. Multiple Milling Methods and Processes May be Needed to Achieve Your Goal.

In the cases of paints, inks, and powder coatings, depending on the raw material and desired particle size, mechanical milling, wet media milling, or jet milling may be required at various steps in the process.

Powder coatings, after initial ingredient milling steps followed by screw extrusion blending, are milled to a fine powder or micronized, sometimes using several mill types in succession — such as a roller mill followed by a hammer mill or a jet mill and classifier — to achieve the desired final particle size (typically 15 to 60 microns) and shape.

Depending on the characteristics of the ingredients, process adjustments and specialty services such as cryo-milling or surface conditioning may be called for.

Finding the Right Toll Processor for Paints, Inks, and Coatings

It’s easy to see that there are numerous types of milling equipment, and multiple process steps, technologies, and fine adjustments, that a toll processor can use to mill and blend paint and coating ingredients for results that achieve your product vision. The combinations of mill types and potential process adjustments make milling and blending possibilities almost infinite.

That’s why it’s so important to choose a toll processing partner that brings more than just the necessary equipment to the job. Having the capacity to meet your toll milling and blending challenges demands a scientific approach to problem-solving, years of experience, and the technical expertise of a trusted team.

If you’re looking for more information about milling, our Milling Methods Comparison Guide is a great place to start. Just click below to download. And if you have questions or want to reach out, it’s easy to contact us.

Learn about the finder points of particle size reduction when you download the milling methods comparison guide