Slot die pre metered coating process for organic coating of architectural steels

The project will examine the feasibility of using slot die coating as a means of coating paint to steel which is used for exterior facades on steel buildings. . The project aims to develop the understanding of the slot die and curtain coating processes to allow it to deposit a high viscosity solvent based coating for the steel industry. The processes potentially offer a more repeatable and controlled means of depositing the paint, while also allowing smoother surfaces, shorter changeover times between colours, multi-layer wet on wet coating and reduced operator exposure to VOCs. It will use a combination of modelling and experimental techniques to investigate the operational envelope of the process when substrate - die contacted must be mitigated by an increased substrate / die surface. Through understanding of the underlying physical mechanisms associated with rheology, substrate wetting, free and surface flows, the deposition process will be understood.

WP1 - Coating rheological characterization
As with all liquid coating processes, there is an interaction between the liquid coating rheology and its deposition characteristics. WP1 will utilize controlled stress and oscillatory rheometry to investigate the physical flow characteristics of liquid coatings. This will examine current paint formulations, generic model coatings and bespoke formations WP1 will also look to examine the wetting characteristics of the coating on the galvanized steel substrate. The primary output from WP1 is an understanding of the material envelope limitations under which the slot die coating must operate and the understanding of how the formulation can be refined in order to improve the deposition quality

WP 2 - Die coating characterization
WP2 will address the practical aspects of slot die coating of galvanized steel substrates. This will predominantly be carried out using a laboratory sheet slot die coater at SPECIFIC fitted with a die / shims which have been selected according to the rheological characterization in WP1 and that experience which has already been gathered in other TATA R&D activities. Parametric studies will be to understand primary control strategies and develop the operating window for the process. This will also examine the impact of the transition from "kiss" to curtain coating mode. In kiss mode, substrate - die distances are small requiring tighter tolerances on substrate thickness, flatness while curtain mode is tolerant to changes in substrate dimensions but can be less stable at speed. Coated steel samples will be characterized using a variety of techniques including SEM and WLI. The primary outputs from WP2 are a defined operational envelope, validation for WP3 and a means of consistent manufacture of samples through slot die at laboratory scale.

WP 3 - Modelling
This WP will focus on developing process models which can be used to determine operational limits and formulation boundaries for the liquid coating. Predictive models exist either strategy for simple liquids, but the quality of these predictions reduces once non-Newtonian particulate laden materials are considered as many fundamental assumptions are incorrect. A review will be undertaken at a prescribed point in the WP to examine which methodology provides the most promising insight into the relationship between material properties, operational parameters and coating uniformity.


WP4 - Coating performance evaluation
The performance characteristics of the steel samples created in WP2 will undergo standard laboratory testing to evaluate whether the change in deposition process has any beneficial or detrimental impact on product function

WP5 - System specification
WP5 will bring together the learnings from the experimental and modelling work packages to develop the material and operational specification of a slot / slide die coil coating system.