Coating applicator versatility
A coating can be defined as any decorative, protective or functional covering, applied to any surface, to improve its characteristics. Indeed, almost every surface that we come into contact with has a coating of some kind. Improvements to both the visual and functional aspects of coatings are continually sought in order to satisfy the demands of various industrial and commercial concerns. New coatings of course are not just conjured up; coating product development is about co-operation between the interested parties, whether chemists, marketing personnel, substrate producers and printer/converters, etc.
In order to develop new products or modify existing coating materials there must be systems in place that ensures that the product that the end user finally receives performs to expectation, that there are no nasty and costly surprises for the brand owner, marketer, converter and of course the intended customer. No one wants costly customer returns; rejects are not only costly in monetary terms but the knowledge that products have been returned harms reputation that may have been carefully built up over the years.
There are many issues to consider when undertaking product development, one of which is what coating applicator technology to employ. Sometimes the answer is clear-cut, often it is not and the converter or other processor is obliged to trial different applicator technologies to ensure that the coating finally settled upon meets various performance criteria
Tom Kerchiss of RK Print Coat Instruments says: “The increasingly complex process demands of modern day life has meant that it is essential to ensure that coating applicator technology, the coating material, the substrate and other performance related elements are optimised and compatible.”
Tom Kerchiss goes on to say: “Slot die coating is worthy of consideration and is ideal where very thin or optically clear coatings need to be laid; slot die is used to apply fluids or polymers such as adhesives, inks, electrolytes and magnetic slurries onto continuous web substrates employed in product areas such as window glazing, battery production, medical patches, liners, label stock, electronic displays and packaging.”
Unlike many coating technologies, which are open to the air, slot die offers a closed delivery path, which provides a more sterile atmosphere. Other benefits include minimal evaporation, minimal contamination and, if solvents are involved – reduced solvent discharge. The amount of coating material in a closed system such as slot die is pre-metred by means of a precision pump.
RK Print Coat Instruments offer a variety of applicator technologies for both the Rotary Koater and for the high-tech, bespoke VCM system. The RK slot die coating unit is designed for the application of non-heated aqueous or solvent-based coatings having low to medium viscosities and for a range of coating weights. The die is constructed from stainless steel and employs interchangeable shims to accurately set the slot gap and width. As standard, the coat hanger type die is positioned above a driven backing roller that supports the web. Depending on the substrate to be coated the roller supplied with the unit can be a precision ground stainless steel roller or the roller can be supplied with a rubber-covered face.
The gap between the die lips and web is accurately adjusted using micrometres but a manually operated quick release control can be used to immediately increase the gap for web threading, to allow splices to pass and to facilitate die cleaning. A second set of shims enables the centre line of the die to be set in various positions relative to the centre line of the backing roller. The standard unit supplied by RK Print Coat Instruments coats up to a width of 250mm but other widths or striped coating can be supplied.
Tom Kerchiss points out that every coating method has advantages and disadvantages. An applicator may be ideal for one application and totally unsuited to another. For this reason RK provide as many as fifteen different coating and print head technologies for systems such as the Rotary Koater.
RK Print Coat Instruments Ltd
Litlington, Royston, Hertfordshire