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Blog Post By Inky Fingers

Colour communication in corrugated supply chain


“No one should be in any doubt, the flexographic printing of corrugated /boxboard material is not without its challenges. In order to create high quality process print using water-based flexographic inks it is necessary to print very small, very sharp dots of ink. It is possible to achieve this if the ink thickness deposited on the material is minimal. However, when reducing ink film thickness, ink colour strength is also reduced. For this reason, printers producing quality graphics demand high pigmented inks and then print them at very low film weights,” says Tom Kerchiss of colour communication technology specialist RK Print Coat Instruments Ltd.

There are several problems with using low film weight inks to achieve low dot gains. To begin with if the paper of the corrugated board is rough, then there could be insufficient ink coverage when using low weight inks. This means that a compromise must be reached between dot gain and paper quality. Second, if the ink formulator raises the pigmentation level of the ink too much, then there will be insufficient resin in the ink to bind the pigment to the paper surface, resulting in a dramatic reduction in rub resistance.

The amount of ink printed onto the material is also dependent on the viscosity of the ink. The viscosity is normally determined through consultation and experimentation via ink supplier, press manufacturer, etc. Once the viscosity question has been addressed the printer must strive to maintain the determined viscosity level, as variations in this area will result in changes in colour strength and print quality. Maintaining the desired viscosity level can be easier said than done: factors influencing viscosity include the heat and shearing action of the pumps. The latter may reduce viscosity by breaking down the small amount of thixotropy that exists in pigmented water-based flexo inks.

No one should be in any doubt, the flexographic printing of corrugated /boxboard material is not without its challenges. In order to create high quality process print using water-based flexographic inks it is necessary to print very small, very sharp dots of ink


Ink manufacturers also faces challenges in terms of producing faster drying inks for today’s faster runs, without compromising on re-solubility and wash-up. Other issues to contend with include surface properties and rub and slip resistance. As the surface of the box is covered with more and more graphics the co-efficient of friction, or slip of the ink becomes more important.

Ink producers typically add waxes in order to enhance scratch and scuff and rub resistance. This however alters the co-efficient of friction and may result in problems during stacking and shipping, which in turn means that there must be a degree of compromise and consultation between printer/converter and ink supplier. Colour communication systems and other devices are playing an important role in standardising print processes and making print less of an art and more of a scientific documentable process.

As with many instances of printing and converting, various workarounds and innovative product development tools have provided printers/converters of corrugated and boxboard material with potentially ways of working smarter rather than harder.

Much of corrugated board is printed flexo, either directly onto the finished board, pre-printing on the outer layer or liner, or by laminating. Defects that can occur during the corrugating process may impact on flexo print quality and on production rates. These defects are associated with flute integrity, calliper, wash-boarding and warped board. Ink formulation, photopolymer plate selection, and anilox and inking system, etc, all of which make major contribution to the final print quality, must be chosen or formulated with care if print quality and workflow consistency is to be achieved.

Other factors that impact on print quality include achieving the optimum printing pressure; the pressure that will affect good ink transfer to the linerboard and viscosity profile during the print run, colour matching and ink drying speed, etc.

To begin with let us consider the inherent difficulties that the earlier printers and converters of corrugated faced. Applying high quality print directly to corrugated has and always will be difficult because of the construction of board. The flutes cause an uneven pressure, which in turn, gives an unequal pressure, which in turn gives an uneven quality of print.

Applying high quality print directly to corrugated has and always will be difficult because of the construction of board



In addition, manufacturers would rather not squeeze the material between printing rollers and risk deformation of the fluting and subsequent reduction of strength. So methods have been developed to pre-print the outermost layer prior to gluing to the fluting in the board machine.

The technique of pre-printed liner has revolutionised decorative possibilities. A downside is that manufacturing corrugated board with pre-printed liner is expensive; to make it economical pre-printed liner is favoured for long runs where possible.

Another option is to laminate a pre-printed liner. This gives the best results since the printing can be undertaken on the highest grade of paper. Again an expensive option but recommended when exclusive high quality, high value consumer and/or industrial goods are being sold.

Everyone these days is striving for the ultimate in brand presentation. Looks are everything. Poor printability and thus poor presentation affects sales. The consumable producer: ink maker, substrate producer, press component producer; the anilox and plate producer must cooperate to a greater degree than they perhaps did in the past with the printer in order that rejects and costly reworking are avoided.

Everyone these days is striving for the ultimate in brand presentation. Looks are everything. Poor printability and thus poor presentation affects sales


Colour communication devices such as the FlexiProof 100 and variants FlexiProof UV and FlexiProof UV/LED for users and producers of flexo inks enable ink manufacturers, chemists, resin and additive producers to trial various formulations under conditions that replicate on press conditions. Sited on an appropriate bench top these devices can determine how the ink interacts with the substrate over time; printability issues such as scuff resistance, rub resistance, durability and gloss can also be evaluated.

The FlexiProof can also be used by press component providers to ensure that devices such as anilox rollers, etc., are optimised for the application and of course by the printer/converter for colour matching; for the production of customer presentation samples and to determine commercial and process viability.

To conclude, Tom Kerchiss says that an advantage for ink producers and indeed for many other suppliers is that it is generally quicker and less costly in terms of make ready, material waste, labour and energy to resolve issues surrounding the use of inks and other coatings off press using the FlexiProof or one of the other colour communication devices designed and developed by RK Print Coat Instruments Ltd.

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