Many mills still treat microfibrillated and nanofibrillated cellulose (MFC/NFC) as useful but difficult to run consistently.
Low solids, complex rheology, drying load, and cross‑direction (CD) variability—especially on wider machines—remain common challenges. However, with the right application approach and equipment setup, mills are increasingly achieving stable, repeatable performance at production scale. The following five strategies reflect practices that have proven effective across a range of applications.
1) Match the Application Method to MFC/NFC Rheology—and Use Air to Your Advantage
Conventional coating methods struggle with low‑solids, high‑viscosity suspensions. Single‑layer application often can’t reach target coat weights, and viscosities in the 14,000–20,000 cP range at ~2% solids limit many wet‑end and dry‑end options. Air‑assisted spray techniques‑Air‑assisted spray techniques provide a more workable path by allowing the gel‑like material to be sheared and distributed more evenly.
With independently controlled liquid flow, fan air, and atomizing air, operators can adjust for sheet speed, CD coverage, and droplet size without relying on guessing if their adjustment is accurate.
Figure 1: Spraying Systems Co. VX70 Air Atomizing Nozzle
Practical tip: Begin with low liquid pressure (~5 psi), moderate fan air (~5 psi), and higher atomizing air (~10 psi) to establish a stable pattern before adjusting for coat weight. This approach has supported uniform coverage at 2% solids and has been used successfully up to ~ 3 5% solids in trials.
2) Engineer CD Uniformity—Don’t Leave It to Chance
CD variation is one of the quickest ways to create waste and downtime. Using adjustable air caps, multiple nozzle/air‑cap combinations, and defined fan angles allows operators to set overlap and spacing that match basis‑weight targets at actual line speeds. Features such as cleanout needles and anti‑bearding‑anti‑bearding caps help maintain pattern stability by reducing buildup and clogging during long runs.
Figure 2: SprayScan VOA software calculating spraying 3% MFC with 70% fines
Practical tip: Treat CD setup as a defined process:
- Fix spray height and standoff first.
- Select fan angle and overlap based on the required coverage at width.
- Use a coating‑weight calculator (speed, solids, overlap, nozzle count, angle, height) to preset the header before trials.
3) Use Liquid Pressure to Control Coat Weight—Reserve Air for Pattern Quality
Increasing atomizing air to chase higher coat weights often leads to misting, spray drift, or added maintenance. A more stable approach is to use liquid pressure as the primary control for coat weight, while keeping low air flows dedicated to atomization quality, fan shape and width. Systems with independent metering make this separation straightforward and help maintain consistent application conditions.
Figure 3: Air Atomizing Spray Pattern
Figure 4: AutoJet 1750+ Spray Controller with Liquid, Atomizing Air, and Fan Air controls
4) Verify Spray Quality with Laser Imaging Before Committing to Production
Relying on visual judgment alone can be costly at scale. Laser‑sheet imaging tools such as SpraySCAN mPT allow operators to capture pattern size, shape, and distribution in real time. This creates a repeatable link between lab settings and mill performance, reducing trial time and improving grade‑change readiness.
Figure 5: SprayScan mPT Mobile Patternator for verifying uniformity and coverage
Practical tip: Maintain a reference library of “acceptable” and “unacceptable” spray images and pair them with corresponding setpoints. Incorporate these into run‑readiness checks for each of your MFC/NFC formulations.
5) Prioritize Maintainability—Fast Changes, Recirculation, and Predictable Operation
MFC/NFC will eventually challenge any system that isn’t designed for easy maintenance. Quick‑release mounts‑Quick‑release mounts allow rapid nozzle changes, while recirculation ports help keep material moving and reduce sedimentation or plugging. Tight manufacturing tolerances and anti‑bearding features support longer run times and fewer interruptions. These incremental design choices collectively improve reliability and reduce coating‑related defects.
Figure 6: VX-Series Air Atomizing Nozzle Cutaway
About the Authors
Bernard Pyzdrowski and Brian Moran are the project engineers for Pulp & Paper Industries at Spraying Systems Co.
About Spraying Systems
Spraying Systems Co. is the world’s leading manufacturer of spray nozzles. Every day, our local spray technology experts help customers optimize operations and create more sustainable manufacturing practices. With tens of thousands of standard products, we have the right nozzle for your application – and we ship most standard products in one day. If you need a special product or material, contact us! We develop hundreds of custom nozzles, injectors and headers every year. Our engineering and manufacturing resources can help solve your toughest spray technology challenges.
