Commercial products empowered by nanoparticle technology are showing high growth rates and are proliferating in new products. Nanoparticle manufacturing processes – from synthesis and stabilization to dispersion into coating formulations and integration into products – involve an interesting mixture of new and old technologies. High-precision, roll-to-roll nanoparticle solution coating is an efficient, cost-effective approach for incorporating nanoparticles into products.
Silver Nanowires and Carbon Nanotubes as Examples
Successful nanoparticle solution coating requires an understanding of the geometry and scale of nanoparticles, as well as how they behave in a coating environment. Silver nanowires or carbon nanotubes are the functional nanoparticle in many next-generation transparent conductive films, used as an ITO replacement with enhanced performance in touch screens. While the unique geometry and scale of nanoparticles enables exceptional performance characteristics, it poses a number of manufacturing challenges. For successful management of nanoparticles in solution coating, it is critical to maintain consistency in size and geometry of the particles, as well as particle dispersion throughout the roll-to-roll coating process.
The following factors are important in understanding the fundamentals of nanoparticle coating:
- Homogenous dispersion in coating solution: Agglomeration within a coating solution can lead to significant problems, so mixing expertise and advanced quality control systems are crucial to ensuring homogenous dispersion.
- Filtration schemes that allow passage of high aspect particles, yet trap unwanted material: The unique structure of nanoparticles makes filtration extremely difficult, so advanced filtration processes are required.
- Solution delivery systems that do not damage particles: The fragile nature of nanowires and other nanoparticles can limit options for pumping and metering solutions into the coating process.
- Coating methods that enable uniform deposition: Uniform deposition allows the desired distribution of nanoparticles and the stability required for high surface area materials.
- Functional properties potentially impacted by parts per million (PPM) of impurities: Since nanoparticles are extremely small, and often create their special properties at very low concentration, there is great potential for impurities to impact performance.
Solving Nanoparticle Coating Challenges
While nanotechnology is a new concept to many, Carestream has been dealing with nano-scale silver for over 100 years. Carestream grew out of 3M and Eastman Kodak Company, two pioneers that made precision, high-performance medical and photographic imaging films possible. The silver-based technology that works so well for imaging films provided Carestream with a natural starting point for creating high performance nanoparticle films for a wide variety of markets and applications.
High-demand nanoparticle applications require efficient scale-up from initial concept to full-scale production. A well-conceived rapid prototyping process can identify design and manufacturability issues early in the product development phase – saving time and money.
Rapid prototyping and scale-up for nanoparticle-coated products requires:
- Rheology of the solution — Newtonian, shear thinning/thickening, thixotropic, rheopectic
- Choice of binders, solvents, colloid dispersions, surfactants
- Interactions with film support, need for surface treatments and/or surface active materials, process aids
- Environmental interactions
- Homogenization, mixing, scale-up for lab to pilot to manufacturing
- Temperature, de-aeration, hold times
- Shelf life considerations
- Resolution and registration
- Waste vs. cost
- Choice of multi-head or tandem coating station methods
- Reduced cost through fewer machine passes
- Enhanced overall process efficiency
- Temperature, humidity and time
- Dry and/or UV curing process
- Nanoparticle orientations required
- Single pass vs. multiple pass — interleaves for protection, cleanliness and other metrics
- Cleanliness and electrostatic control
- Final product or intermediate step to final product
- Slitting and/or sheeting
- Sensitivity to dust, propensity to scratch and other quality considerations
- Package needs, such gas or water barrier and anti-static materials
- Hold times prior to next steps
- Storage and packaging condition
- Nanoparticle hazard evaluation
- Risk reduction through Process Hazard Analysis
- Exposure monitoring
- Waste stream compliance
Carestream Contract Manufacturing applies our proven process knowledge, experience and quality-driven practices to solve the unique challenges of nanoparticle coatings. Contact us to learn how our multi-layer coating expertise, combined with our exceptional rapid prototyping capabilities, help customers take their nanotechnology products from benchtop to pilot to production quickly and efficiently.