Industry Insights
The Basics of Fluid Coating November 7, 2013 | by Sarina Netzel, Mixing Product Engineer and Elliott Meckley, Mixing Process Engineer, Carestream Tollcoating

Precision fluid coating onto substrates involves many variables that can affect the final outcome of a quality product. This is why Carestream Contract Manufacturing places a large emphasis on the spot where it all begins – the fluid mixing room. Our professionals understand the intricacies involved in the mixing phase and help customers move complex coated web products from concept to full production. Carestream also has many years of experience scaling up a variety of products, which enables our professionals to quickly share ideas and suggestions for improving the cost efficiency of customer processes.

Customers come to us throughout various stages in their product development cycle. As discussed in our “Eliminating Guesswork in Mixing Solutions” blog, some customers bring solutions or their chemical components for mixing and solution delivery, while others are still working on ideas and requirements.

For each project, the mixing product engineers work closely with customers to determine needs, evaluate formulas and mix the optimal coating solution. Throughout the process, Carestream professionals ensure that the coaters are mixing enough solution, coatings are repeatable and there is an accurate method for tracking defects on the coater. This approach enables mixing engineers to troubleshoot potential issues, whether they are process oriented or require formulation change. Important factors during the mixing process include:

  • Temperature control
  • Mixing times
  • Dispersion
  • Pressure of the vessel
  • Shear level
  • Mixing speed
  • Pot life
  • Controlled additions

Once the mixing product engineer determines customer needs, mixing process engineers bring the mixing procedure to the next level by identifying the equipment needed. Some customers are looking to cut costs of existing products by mixing and coating at Carestream. In these cases where the mixing method has been established, mixing process engineers identify equipment required to imitate existing coating processes.

Other customers come to us with brand new products that have been mixed in a lab on a small scale. In these instances, mixing engineers devise the fluid coating and determine the appropriate way to scale up production.

The mixing department can create multiple solutions at a time, and can mix coating solutions of various viscosities and densities in quantities ranging from one quart to over 1,000 gallons. Carestream Contract Manufacturing also has mixing capabilities at the coater itself, and a wide range of mixing equipment with high shear, low shear, rotor-stator and temperature control capabilities.

Our mixing vessels have a wide variety of shapes and sizes with different capabilities, such as jackets, bottom outlets, etc. When batch sizes are determined, mixing vessels are chosen. Carestream’s large selection of different styles of mixers range in sizes from 60 hp motors for 1,800-gallon tanks to small air mixers built for five-gallon buckets. The mixers are selected based on the characteristics of the fluid and the adequate blade size and type required for each project.

Case Study

Below is a case study detailing the mixing process of a customer working with Carestream to scale up a coating for production.

Prior to turning to Carestream, the customer used a ball mill to mix the coating for their product. This ball milling process took 12 hours to complete and only produced one liter of solution, so the customer wanted to scale up to Carestream’s large coater. Since ball milling is a very slow process, our mixing engineers needed to determine how to duplicate the customer’s mixing metrics to decipher whether the existing mix was sufficient.

The mixing engineers designed a lab-scale mixing experiment testing different mixing methods, including low-shear marine prop blades, higher-shear Cowles blades, rotor-stator dispersion and homogenization. A number of lab-scale trials were completed using all methods – each measuring for factors such as particle size, surface tension, density, viscosity, percent solids, etc. Carestream mixing engineers wanted to determine which approach delivered the most repeatable, reliable coating solution. Furthermore, the mixing process needed to be scalable.

After the lab-scale testing, it was determined that the high-shear rotor-stator mixer produced the same results as the customer’s ball mill process so they moved to the pilot coater phase. During the pilot coater stage, the team calculated mix times and tip speeds necessary to transition from mixing one half liter of solution at a time to mixing 10 gallons of solution at a time. The high-shear rotor-stator mixer was used to wet out particles and then added the rest of the mix using a Cowles blade.

Next, a 55-gallon drum trial was conducted for the large coater. The necessary equipment was identified to mix 55 gallons to move the process to the next level.

Conclusion

The mixing stage is a critical step in the coating process, which is why Carestream Contract Manufacturing places a large emphasis on it. By understanding the factors required to produce a repeatable, reliable coating solution, Carestream helps customers move complex, multilayer-coated web products from concept to production.

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