Milling and Blending Paints and Coatings: 3 Top Challenges and Solutions

Justin Klinger, Apr 15, 2021 9:02:08 AM

technician painting a car

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

The dispersion process in paints, inks, and coatings can be incredibly complex. Each component adds its own variables to the mix, and their potential interaction demands scientific know-how.

Particle sizes can affect attributes ranging from color, hiding power, and level of gloss in paints to the coefficient of friction in industrial coatings. So tight control over milling and dispersion processes is an absolute must for consistent quality. 

Grinding and blending processes need to address characteristics that range from abrasiveness to viscosity to temperature sensitivity and more.

In addition to achieving target particle sizes, grinding is indispensable for blending and dispersion. This is true whether the product is a liquid dispersion (such as solvent- or water-based paint) or a powdered solid (as in heat-cured coatings used in metal finishing).

The path to optimal particle sizes, homogenous dispersions, and high-performance paints, inks, and coatings can involve multiple technologies and a wide range of variable adjustments. Particle surface treatments like coating and encapsulation can be game-changers, but it takes an expert team to know how to make them work for your formulation.

When it comes to selecting a toll processing partner for grinding and blending for paints, inks, and coating solutions, it’s critical to keep these three things in mind: 

  1. Particle size determines many critical characteristics of inks, pigments, paints, and coatings.
  2. Homogenous dispersions can be challenging to achieve.
  3. Demonstrated mastery in processes including surface treatments is a must for your toll manufacturer to reliably achieve your product goals. 

Read on to learn more about the particle size reduction, uniform blending, surface treatments, and milling methods your toll processor may use to ensure consistent outcomes that are vital to success in pigments, inks, paints, and coating formulations.

1. PARTICLE SIZE DETERMINES MANY CRITICAL CHARACTERISTICS OF PAINTS AND COATINGS.

Most ink, paint and coating formulations 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. 

PAINTS

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 or settling
  • 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.

INKS

Dispersing solid pigments in inks requires advanced technical know-how to prevent unstable formulations that can lead to settling — which can cause serious performance problems that can even damage printing equipment.

As with paints and powder coatings, printing inks are often formulated to perform on a specific set of equipment and substrate. A deep technical understanding of all the specifics can help you ensure proper flow, adhesion, curing, and final print quality.

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 it’s not enough to know your tolling partner has the right particle dispersion equipment. 

Process knowledge is key in selecting the right additives and 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.

Wet and dry dispersion processes in paints, inks, and coatings can also call for specialty in-process dispersion additives or particle surface treatments to achieve precise characteristics such as surface tension or other particle behavior.

Powder coatings can require multiple milling and grinding methods in a specific, prescribed series to achieve uniform dispersion and predictable, consistent quality. First, ingredients may be individually milled to their various required particle sizes. Next, they may be melted and blended using an extrusion method such as a twin screw extruder. The resulting blended product requires another milling step before it can be used.

3. MULTIPLE MILLING METHODS AND PROCESSES MAY BE NEEDED TO ACHIEVE YOUR GOAL.

In the cases of paints, inks, pigments, 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. Specialty dispersion blenders can be equipped to address issues such as temperature sensitivity, high viscosity, pigment reagglomeration, and more.

After powder coating ingredients are milled and blended, often in a twin screw extruder, they need to be 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 necessary final particle size (typically 15 to 60 microns) and shape.

Process adjustments and specialty services such as cryo-milling or particle surface conditioning may be needed. This can involve special coatings and treatments to apply a thin film at the particle level on pigment surfaces to achieve specific final product qualities.

FINDING THE RIGHT TOLL PROCESSOR FOR PIGMENTS, PAINTS, INKS, AND COATINGS

So many types of milling, blending, and dispersion equipment — along with so many possible process steps, technologies, and fine adjustments — add up to almost infinite combinations of capabilities in the hands of an expert toll processor. That’s why it’s so important to choose a toll processing partner that brings more than just advanced equipment to the job. 

Having the capacity to meet your toll milling, blending, and dispersion challenges demands a scientific approach to problem-solving, years of experience, and the technical expertise of a trusted team. Material scientists, engineers, and equipment operators with years of experience in pigments, inks, paints, and coatings will approach your project with a deep understanding of your challenges and goals, and a solid foundation in processing formulations like yours.

If you’re looking for more information about milling technologies and how they apply to different types of projects, 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

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