Interesting Times - The Role Drying & Energy Curable Technology Will Play
By Tom Kerchiss, RK Print Coat Instruments
It could be said with some justification that label and package printers and converters as well as the provider of consumables and materials live ‘in interesting’ times. The need to tackle environmental concerns, make better use of the planet’s resources and develop sustainable products and process alternatives challenges us all.
While many of the processing issues and problems that print/converting and other segments of industry are likely to come up against in the next few years may be taxing: difficulties are not insurmountable. Especially if we consider how far we have come. Take drying and curing as an example. Today drying and curing technology provides converters with more options than at any previous time, and that’s a good thing.
As with the selection of the most appropriate method of coating, choosing a suitable drying/curing technology is not necessarily as clear-cut as it was in the past.
The need to differentiate an item from other competitive items is far from easy, especially with so many new products being launched all the time. The ‘brown box’ days are gone as bill- boarding opportunities abound; premium quality items may incorporate neck wrap around labels, decorative foils; marketers may specify a no-label look, conceivably they may opt for embossing or another value added option.
Not only are those engaged in product packaging manufacture and conversion tasked with adding value, they are faced with developing and producing new materials and techniques for industrial sectors such as electronics, electrical, security, medical devices, etc., all of which require different approaches to printing, coating, laminating – and of course drying.
The Rotary Koater and its high tech bespoke counterpart the VCM offer users a choice of hot air, infrared and UV curing in order that products can be developed, trialled and performance monitored. Designed and developed by RK Print Coat Instruments Ltd these pilot coat/print, laminate and drying/curing systems also allow for different coating and print technologies to be tried in order that formulations, substrates and other associated product elements prove viable and that they have a minimal effect on the environment. Small-scale production can be undertaken with the Rotary Koater and with the customer configurable VCM.
In the early days of converting a typical dryer oven was relatively unsophisticated and bore more than just a passing similarity to a bakers oven. Typically they had a small fan and relied almost solely on heat, there was little in the way of air velocity and no finesse of control.
The impetus to redefine and improve drying techniques was due in part to the move away from solvent to water based coatings and adhesive systems
The increasing complexities of the production process and the need to process a more broad and varied range of substrates also spurred on the development of other methods of drying (heating) such as infrared (IR) and energy curable systems, UV and EB. For the moment lets stay with hot air drying.
When drying a coating it is critical that the drying technology is optimised for the substrate and associated consumable elements. For instance some coatings do not react well when hit with a lot of heat. This is unlikely to happen now but certainly in the past if a product contained high levels of solvents there would be a tendency for the solvents to become trapped or skim. If a substrate was a lightweight gauge substrate the coating when hit by heat when being dried could pucker or dimple.
Converters have witnessed a number of changes with regard to hot air drying over the years. Impingement systems generate controlled turbulence in the dryer. Air hits the substrate and breaks through the laminar zone of the boundary layer of air and efficiently heat dries an appropriate substrate. In physics this is known as the Bertolli fluid dynamic effect.
Infrared (IR) unlike conductive and convective heat transfer methods is regarded as a surface energy technology. Energy is transferred not heat. The material converts the radiated energy to heat by adsorption. It has some similarities with conductive and convection heating but provides very much more in the way of ‘through’ heating. As with virtually every aspect of modern day technology, improvements and refinements are on going.
IR technology is used extensively in a wide range of industries. Infrared and combination drying systems, IR air dryers have been used on coating lines to enhance drying and curing capabilities. Systems have been used for curing PVC coatings on non-woven and woven fabrics and for the treatment of specific films for laminates and embossing, etc.
IR provides for a calculated and defined depth of drying, which is critical for translucent plastics, some grades of paper and for textiles. Infrared is often selected for spot drying application where coatings and adhesives are applied selectively to precise and masked areas.
IR units integrated in with the Rotary Koater and VCM are compact in design and are quick to start up quick to stop. In general and due to the space saving IR configuration most IR systems can be fitted in with existing process line in order that they can be used in conjunction with or as a replacement to other drying methods.
There are advantages and disadvantages with most processing systems and drying/radiation curable processes are no exception. Since IR is a surface drying process it is harder to dry very heavy coatings and it can be difficult to use with fragile temperature sensitive materials. Higher temperature can cause some coating materials to form a skin and to blister.
Ultraviolet of UV curing is often thought of as a new technology but in actual fact has been around for almost 70 years. In contrast to convection type ovens, which are used to drive off solvents or water by applying heat to dry the coating, UV energy cures by polymerisation rather than evaporation, therefore VOCs and HAP emissions are virtually limited.
A drawback with mercury arc lamps that are used for many UV applications is that they peak at around 365 nm but there are extraneous spikes in the visible and infrared bands, which in turn is responsible for the heat that these lamps generate and which can distort sensitive substrates.
Though not suited to every application LED lamp technology and other methods of heat management minimises many of the difficulties associated with curing heat sensitive materials, broadening the range of products that can be subject to UV curing.
Early commercial applications for LED UV were for small area adhesive bonding application of medical devices, thermal ink jet coding and marking and for the curing of heat sensitive fibreglass composites. LED UV has found its way into niches areas associated with electronic production, wood coating flooring and digital printing, etc.
LED UV is also gaining traction in labelling and packaging conversion. One of the drawbacks in the past was the lack of suitable inks formulated to react to the output from the LED UV light source but this has changed.
LED UV lamps are ozone-free when in use and operate within a relatively narrow part of the UV spectrum. RK Print Coat Instruments FlexiProof colour communication devices for those users and producers of LED UV optimised flexo inks incorporates the Phoseon Firejet UV Systems range of products. Typically the lamps offer a tailored output either at the important 385 or 395 nm wavelength.
LED UV lamps do not require a warm up time and are fully operational at the flick of a switch. They also only need a small power unit and the energy/heat output is significantly lower than with mercury arc lamps.
LED UV is amongst a range of technology being utilised by ink and coating manufacturers and others in the development of low migratory products that will be used for printing a safe product, one that will not pose a health and environmental problem.
Prepress colour communication devices including the FlexiProof family of devices such as the FlexiProof UV and FlexiProof LED UV have a role to play as well in that they can be used for determining how an ink/coating and substrate perform over time. They can be used for trialling, determining printability issues and for colour matching, etc.
RK Print Coat Instruments Ltd
Litlington, Royston, Hertfordshire SG8 0QZ
www.rkprint.com sales@rkprint.com
Source: RK Print Coat Instruments Ltd
