Alan Harris of RK Print Coat Instruments gives us the lowdown on water-based flexo ink development and the role of quality monitoring devices

Aqueous or water based inks are based on a combination of acidic resins held in solution with amine and water-based resin dispersions – collectively termed emulsions. Solution resins aid print quality while the emulsion provides resistance properties in the dried ink.

Tom Kerchiss of colour communication technologist specialists RK Print Coat Instruments Ltd says: “Water based flexographic inks have been around for some time now. Printing on paper and paperboard substrates with water-based inks is largely trouble-free due to the absorbent nature and structure of paper fibres. The inks and solvents  (water included) are partially absorbed into the substrate and are partially vaporised into the surrounding air”.

The first large scale testing of water-based flexographic inks on filmic materials and on foil took place in the late 1970s in plants on both sides of the Atlantic and continued on into 1980. The imposition of the Clean Air Act and legislation restricting the use of harmful solvents provided the impetus for research and development.


 Amongst the drawback to using water based inks on films in those early days was that the slip agent and/or EVA component, added to introduce specific performance properties into the film at manufacture tended to rise to the surface and proved problematic with regard to ink adhesion. Other problems, which were far from being insignificant, centred on poor wet run properties, low gloss and generally low press speeds.
 
Tom Kerchiss says: “The printing of flexible packaging could be tricky in that the finished product could be subject to challenging conditions such as water vapours, exposure to chemicals in packing departments (relevant at the time under discussion); for instance ammonia fumes, and in some cases (relevant as much as today as then) extremes of temperature. The inks developed therefore had to be resistant to these influences. Overcoming these barriers posed major problems for the ink maker and for the printer or converter that elected to use water-based inks. However, that was then. Today things are different.”

As each year passes newer and more capable water ink technology becomes available. The introduction of a new class of water dispersible polyester resins has proved suitable for use in water-borne flexographic inks and overprint lacquers.  Unlike earlier aqueous systems that relied on relatively high acid resins for water dispersibility, newer polyesters need no neutralising agents such as amines or ammonia to maintain water dispersibility.  The need to balance ink pH on the press is unnecessary, and the odour, formerly associated with volatile amines are avoided.
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Water based ink technology has advanced considerably, in some segments its in the mainstream of printing. The colours produced are more vibrant and crisp than their oil-based counterparts. That is not to say that further improvements cannot be made.

Some filmic materials need further development to tailor them for the wetting out and adhesion of water based inks. Inking and drying systems need modification to achieve more effective transfer and drying. In addition there is a need for cleaning systems that will extend the life of anilox rolls and doctor blade systems.

To maintain its position as a leading print medium flexography must strive to meet quality demands. Continued growth can only occur through an expansion of the market or through the capture of market share from other print processes. To maintain and grow the market flexo will need to improve the ability to print process colours and consistently make a good impression from the beginning of every run right through to the last print. The on-going advances in water based technology has resulted in improvements in resolubility, a search for new surfactants and the use of cleaner slow solvents for film laminations.

Water based inks have obvious advantages in the area of VOC compliance, environmental safety, and in cost savings associated with shipping and storage and in insurance as inks and inked products are generally non-flammable.
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The need to achieve better control over process variables in the shortest possible time has become almost a mantra for the producer of water based inks and for the printer using them .The ink producer focuses on meeting the quality focussed demands of the printer for batch to batch consistency.  

Thorough and on-going tests have to be carried out to ensure that the inks interact in a positive manner with the differing and constantly changing substrates coming onto the market. This testing has to be undertaken in an as accurate manner as possible to meet the tolerances required, and to accommodate variations in colour strength, rheology, tack and working properties.

Manufacturers of inks and substrates each have their own methods for testing and quality control procedures. Often an old flexographic press has been used for tests, while for the printer who generally up until recently has not been able to afford the luxury of a dedicated machine for testing, had to tie up existing production resources in order to undertake quality control and other product monitoring test procedures. Another drawback was that test results could vary very much from machine to machine.

The FlexiProof 100 is a well rounded production tool that has been developed to enable users and producers of water based flexo and solvent based inks to produce reproducible quality proofs for customer approval, for colour matching purpose; for trialling new materials; for determining printability issues and much more.

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Used by packaging printers, label converters, ink producers, paper, film and foil suppliers, component producers and many others, the FlexiProof developed by RK Print Coat Instruments is functionally identical in every way to a full sized production flexo press, yet weighs just 45kg and occupies a bench top space of just 55cm x 45cm. Whether sited in a laboratory, in a dedicated pre-press environment, next to a press or anywhere else, the FlexiProof 100 and two newer variants, the FlexiProof UV and FlexiProof LED/UV saves on press waste by enabling functions such as colour matching, pilot runs, research and development, and much else to be undertaken off-press.

Concluding Tom Kerchiss remarks that an important advantage of the FlexiProof is that every supply chain provider can utilise a FlexiProof in their product development or production workflow. The ink maker can determine how ink interacts with a particular substrate; conversely a substrate producer can do the same. Results are reproducible, everyone is in synch with everyone else and consequently issues are identified much quicker and rectified more speedily.