Slot nozzle coating

The slot nozzle coating (slot die or wide slot nozzle ) is a coating technique to apply thin layers of liquid to web-shaped substrates (paper, foil, fabrics, etc.) or piece goods (glass, metal plates, etc.). For some substrates in the coating industry, especially for those with functional layers ( photovoltaics , medical products, wafers , lithium-ion batteries , fuel cellsetc.), but it is precisely the accuracy of the layer thicknesses to be applied that is of essential importance. Uncontrollable layer thickness variations, caused by changes in production conditions or changes in fluid properties, are not justifiable for a large number of coatings.

However, flawless coatings on substrates not only require processes and application tools that work reliably and are easy to use, such as slot nozzles , but also make special demands on the solvents used, e.g. B. freedom from bubbles. In addition, controlled stirring processes are required in order to ensure the special properties of the applied coating fluids for defect-free layers on substrates. In addition, the fluid supply to the coating tools used must be pulsation-free in order to produce defect-free films on substrates. It is therefore the reproducible, controlled interaction of all products and peripheral processes of a coating process that must be mastered in order to achieve high-quality film layers on substrates.

The self-metering coating process

The self-metering processes ( roller , knife or dip coating ) are characterized by the fact that the wet film thickness achieved is determined by the coating process and cannot be determined by determining the mass flow rate when the coating tool is in operation. The layer thickness on the substrate is relatively uncontrolled and is heavily dependent on the fluid properties, the selected coating process and its freely selectable parameters and the coating speed. For some substrates in the coating industry, especially for those with functional layers, the accuracy of the layer thicknesses to be applied is of essential importance. Uncontrollable layer thickness variations, caused by changes in production conditions or changes in fluid properties, are not justifiable for a large number of coatings.

The pre-metering slot nozzle coating process

In contrast to the selbstdosierenden coating method in vordosierenden slot die coating, the desired wet film thickness by the measured mass flow and the known substrate velocity ( , velocity web be determined) . The special feature of the pre-metered slot nozzle coating is that film thickness variations can only be achieved by slightly controlling the pump mass flow and the process speed. By specifying a constant mass flow over the entire nozzle width , the layer thickness is clearly determined at a given density , at a web speed and web width . This simple control option is unique among all known coating processes and guarantees reproducible and extremely homogeneous coatings of the highest quality. ${\ displaystyle U _ {\ text {w}}}$ ${\ displaystyle m = \ varrho U _ {\ text {w}} hB}$ ${\ displaystyle m}$ ${\ displaystyle h}$ ${\ displaystyle \ varrho}$ ${\ displaystyle U}$ ${\ displaystyle B}$

The slot nozzle operated in different modes (curtain coating mode, bead coating mode, web tensioned coating mode, extrusion coating mode) is used in particular in industrial coating processes when one or more layers of liquid are applied to a wide variety of substrates very precisely, very reproducibly and very economically should. Depending on the different modes as well as the fluid rheology , the wet film thickness to be applied and the distance between the nozzle and the substrate, coating speeds of 0.1 to >> 2000 m / min can be achieved. With the slot nozzle coating, typical wet film thicknesses are in the range from 0.5 to 500 µm. The exact machine setting for the production of this flawless wet film thickness can either be determined empirically or carried out quickly and purposefully on the basis of analytical calculations of so-called coating windows.

Typical areas of application

Paper industry, cardboard industry
Film production (film painting, adhesive tape production, silicone films, film extrusion)
technical textiles, nonwovens (for impregnation, finishing, coating etc.)
Renewable energies (printed electronics, Li-ION production, OLED etc.)
Medical products ( plasters , latex bandages, indicators)
Construction industry (coating of concrete slabs , timber, etc.)
Etc.

Typical coating media

Water-based and solvent-based fluids
Abrasive pigments ( corundum , titanium dioxide etc.)
Hot melt coatings
Film extrusion

Typical manufacturers of slot nozzles

Slot nozzles are used all over the world for industrial productions as well as in research and development. There were numerous suppliers of coating nozzles on the international market, although these differ mainly in terms of their design and the physical functionality it defines:

Almost all coating nozzles (e.g. with a “coat hanger” distribution chamber etc.) produce the uniform distribution of the coating fluid across the width of the substrate web by combining the distribution chamber geometry, the coating fluid rheology , the coating quantity, the coating speed and the internal pressure distribution of the slot nozzle. For this reason, these pressure-dependent slot nozzles do not work for a wide variety of fluids and different layer thicknesses without having to suffer quality losses in terms of transverse distribution accuracy.

The so-called viscosity- and mass-flow-independent coating nozzles take a different approach , these new slot nozzles work almost without pressure. The uniform distribution of the coating fluid, independent of the mass flow and viscosity, is guaranteed by a patented diffuser integrated into the distribution chamber. With the mass flow and viscosity-independent slot nozzles, users can process a wide variety of coating liquids and a wide variety of flow rates, always with the same transverse distribution accuracy of the resulting wet film thickness.

References

Novel coating tools for mass flow and viscosity-dependent transverse distributions of applied wet film thicknesses, Coating-Magazin (2009)

Nano-Coatings with FMP slot dies, Coating Magazin (2010)

Production of functional, nanoparticulate coatings in the sub-micrometer range using the slot nozzle process, cfi ceramic forum international (2013)

Refinement: New, resource-saving application system, Contextile magazine (2014)

Novel forced application systems for web-shaped textiles, Textilplus magazine (2014)

All-in-one: coating nozzle for unlimited applications, avr magazine (2014)

Patent EP2323775 : Coating tool for applying a liquid film to a substrate. ‌

Franz Durst, Hans Raszillier (Ed.): Advances in Coating and Drying of Thin Films - 3rd European Coating Symposium 1999 . Shaker Verlag, Aachen 1999, ISBN 3-8265-6636-X .

F. Durst, HG Wagner: Slot coating . In: Stephan F. Kistler (Ed.): Liquid Film Coating: Scientific Principles and Their Technological Implications . Chapman and Hall, 1997, ISBN 0-412-06481-2 .

Ulrich Lange: Fluid mechanics optimization of components of a curtain coating system . 1995, OCLC 231656546 (dissertation, Technical Faculty of the University of Erlangen, 1995).

Gerhard Sünderhauf: Flow investigation of the curtain coating of paper . 2001 (Dissertation, Technical Faculty of the University of Erlangen-Nuremberg, 2001).

Slot nozzle coating . In: PackMittel. Specialist magazine for development, production and finishing . No. 1 , 2010, ISSN 0048-2897 , p. 42 .

Efficient process analysis and simulation - precisely design painting processes . In: Journal for surface technology . No. 8 , 2011, p. 36 ff .

Keeping an eye on the bottom line . In: C2 Coating & Converting Europe . (May / June), 2011, p. 48-52 .

N. Alleborn, F. Durst, H. Lienart: Application of the curtain coating for the surface finishing of construction elements made of concrete . In: Chemical Engineer Technology . tape 77 , no. 1–2 , February 3, 2005, pp. 84-89 , doi : 10.1002 / cite.200407060 .