Custom Processing Services Blog

Why Wet Milling & Ultrafine Particle Sizes Matter to Manufacturers

Justin Klinger, Apr 14, 2022 9:55:00 AM


Particle size is a key consideration when it comes to virtually any product that’s formulated and manufactured, no matter the industry or application. 

Inks, cosmetics, paints, construction materials, plastics, industrial chemicals, ceramics, powder coatings, food, and pharmaceuticals can all contain ingredients that require wet milling services to achieve ultrafine particle sizes.

Wet media milling is a grinding method that’s capable of producing ultrafine solid particles in a liquid slurry — achieving particle sizes that mechanical and jet milling methods often can’t.

Particles that range in sizes measured from the submicron- to micron-scale can be vital to achieving specific product characteristics or capabilities.

In this article, we’ll take a look at some of the different ways these very small particles play important roles in applications across multiple industries.

Which Materials are Good Candidates for Wet Media Milling?

Wet milling can be an effective technique for achieving extremely fine particle size ranges for materials used in a wide variety of industries and applications. Pigments and fillers including talc, silica, calcium carbonate, kaolin, micas and barytes are often wet-milled. So are metallic ores, glass, ceramics, and polymers. Active pharmaceutical ingredients (APIs) are often candidates for wet milling, as well.

Whatever your industry, material, and particle specifications, working with an experienced wet milling services provider is key. That’s because the wet milling process can become quite complex, requiring multiple steps and important variables to achieve the target particle size with optimal process efficiency:

  • Choosing compatible milling media
  • Identifying the best liquid for the milling slurry
  • Adding dispersants and/or surfactants if necessary
  • Adjusting pressure, circulation speed, and time on the mill

Are there materials that aren’t good candidates for wet milling? Certainly. Issues such as solubility in liquid, exposure to liquid, or characteristics that wouldn’t perform well in a recirculating mill process may exclude some materials from wet milling — but before writing off the possibility, be sure to talk to an expert toll processor. You may be surprised to learn what’s possible.

How Particle Size Can Affect Pigment Properties

Pigments are often wet milled to achieve mechanical properties, rather than color. Many ink applications such as inkjet and offset printing require very fine particle sizes to prevent clogging of printer nozzles, and wet milling is a go-to method for achieving these specifications.

In some cases, particle size can also affect the actual perceived color of the material. Color strength, hiding power, and gloss or sheen are other properties that can be enhanced with the smaller particle sizes wet milling can deliver. Agglomeration can sometimes be a problem with micronized or nanonized powders, and wet milling is an effective technique for deagglomeration, removing entrapped air, and dispersing those ultrafine particles in suspension.

Smaller Particles Pack More Punch

The key to getting more power from the particle — stability, durability, and even API efficacy — lies in the increased surface area that’s created when a particle’s size is reduced.

Along with improved color and finish properties in pigments, smaller particles can result in improved scratch and crack resistance, better coverage, and even increased UV resistance of final products. These qualities are particularly important when it comes to automotive and aerospace coatings, industrial powder coatings, and construction materials.

In applications like cosmetics, pharmaceuticals, and industrial chemicals, emulsions and suspensions that incorporate finer particles tend to have better stability than those with larger particles. Finer particles can also be better absorbed through the skin or mucous membranes, in the case of personal care products and pharmaceuticals.

Special Light and Optical Effects

Special light and optical effects like pearlescence and angle-dependent color have as broad a range of applications as wet milling itself—among them are automotive and industrial finishes, cosmetics, specialty inks, and more. 

Birefringence, or birefractivity, is an important quality for polarization-maintaining optical fibers, liquid crystal displays, and other technical and industrial applications. Raw materials used for birefringence include tourmaline, calcite, and quartz.

Sheen, Smoothness, and Mouthfeel

Products like personal care, cosmetics, beverages, and pharmaceutical preparations benefit from smaller particles to achieve improved palatability, mouthfeel, and flavor. In personal care and cosmetic products, finer particle sizes can result in higher-end formulations that command premium prices using the same key ingredients as similar products at lower price-points.

Experience is a Key Ingredient, Too

When it comes to particle size reduction, working with a team of experts helps ensure you’re taking the most efficient and cost-effective route to achieve the desired material characteristics and specifications. When you collaborate with an experienced toll processor, you get more than access to the milling equipment you need; you also get a team of material scientists, engineers and equipment operators who work hard to understand and solve even your toughest challenges.

Learn more about wet media milling and a range of other particle size reduction technologies when you download our free Milling Methods Comparison Guide. Click below to claim your copy today.

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Posted in:Grinding/Milling