Introduction
It’s important to maintain quality of products while reducing costs and remaining competitive in the inks, paints, and coatings market. To do so, manufacturers should take a deep look at their milling and mixing equipment to determine the best type of machinery for their process. Below, we take a look at a few common paint/coating processes and see what equipment stands up to the job.
Pigment dispersions
Pigment dispersions are typically prepared in a two-step process:
- powder wet-out in a batching tank
- one or more passes through a mill to achieve the desired fineness of grind
The costly and time-consuming milling step is often a production bottleneck. In the past, this has forced manufacturers to add more milling equipment to handle multiple passes or simply keep up with volume demands.
One of the most common applications of the Ross High Speed Disperser is the wetting out of pigments (pre-mix preparation). Turning at tip speeds up to around 5,000 fpm, the saw-tooth blade of the mixer produces a deep vortex on the liquid surface into which dry powder ingredients are added. At this stage, the High Speed Disperser generally disintegrates large and loose agglomerates. The resulting pre-mix is then fed to downstream milling equipment for the polishing step.
For pigment dispersions that demand very long milling times, manufacturers can improve overall production without costly modifications by upgrading the pre-mix step. One such solution is the patented Ross PreMax Ultra-High Shear Mixer, a batch rotor/stator device capable of wetting pigments while accomplishing some level of grinding and fine deagglomeration. The Delta generator of the PreMax produces a double vortex – it draws product components from above and below the rotor – enabling very fast powder incorporation and product turnover at ultra-high shear conditions.
Specialty inks
Specialty inks have become a staple in modern packaging, lending added appeal, security and functionality to products in ways that traditional inks could not achieve. From the thermochromic, glittery and metallic, to the fluorescent, color-shifting, and conductive kinds, specialty inks and coatings are typically customized for a specific brand or application and come in different colors, solid loadings, particle sizes, viscosities and print methods.
Ink formulations that undergo viscosity peaks as high as 2 million centipoise are more efficiently produced in a Ross PowerMix Planetary Disperser. This technology combines the thorough kneading action of a planetary mixer with the high speed mixing power of a disperser. Unlike conventional dispersers which turn from a fixed axis of rotation, the saw-tooth blades in a PowerMix moves around the vessel and contacts fresh product all the time. The planetary stirrer orbits the mixing zone as well, constantly turning over viscous batch material and dissipating heat created by the high speed blades. As a result of this robust agitation capability, the PowerMix is very effective in wetting out solids and creating a very fine dispersion virtually regardless of product rheology.
Mixer Selection Tips
- Different styles of mixers and blenders often have overlapping functions and applications. Determine:
- Working volume
- Friability / shear-sensitivity
- Viscosity
- Vacuum
- Shear level
- Heating/cooling
- Available footprint and space
- Cleanability
- Discharge requirements
- Economics
- Choose scalable mixing equipment.
- Run a mixing trial.
High viscosity coatings
Depending on their method of application and intended use, certain coatings are produced as high viscosity fluids. Controlling rheology is one way of achieving desired coating performance in terms of sag and spatter resistance, flow leveling, gloss, film formation and other attributes.
Ross Multi-Shaft Mixers are well-proven equipment in the manufacture of high viscosity coatings up to several hundred thousand centipoise. Equipped with two or more independently-driven agitators working in tandem, Multi-Shaft Mixers deliver a robust combination of high shear agitation and laminar bulk flow ideal for a wide range of non-Newtonian fluids. The agitators can be engaged in any combination and at any speed for any interval during the mixing cycle. Although this sounds complex, Multi-Shaft Mixers are actually engineered to be comparatively simple and cost-effective.
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