Communicating colour on fragile paper tissue/towelling
The flexo printing of paper towels, toilet rolls, tissues, wipes and napkins present unique challenges as customers expectations with regard to quality increases and as product design parameters become more demanding as Tom Kerchiss of RK Print Coat Instruments explains.
Notwithstanding the difficulties associated with printing colour designs at speed on highly fragile absorbent substrates, the converter has to make provision for higher levels of linting and dust than in other processes. Inks have to be closely matched to application requirement, they must print cleanly and at high speeds with a stable pH and at the appropriate viscosity.
Things to watch out for. Controlling process variables such as tension control and registration is a must. Dot gain can be noticeable, enhanced by substrate characteristics and by the level of print impression required. Careful fingerprinting, attention to graphic layout and to value-added enhancements is necessary. The tack of the ink has a tendency to increase the risk of web breaks when high speed is engaged. The absorbency of the substrate may also create problems when trying to obtain the high strength colours that designers and brand owners require.
The inks used must meet high wet rub resistant requirements and be formulated to withstand bleeding into for example, an aggressive household cleaner or an antiseptic hand wipe. Partnering with ink suppliers and other providers is a must. Consideration must be given to the fact that automatic web inspection system, closed loop or ultrasonic tension controllers and colour communication quality control equipment and systems helps to detect inconsistencies and help bring processing variants under control.
Flexo presses designed for printing on toilet tissue and kitchen rolls have to meet a number of unique requirements and it is worth reviewing how some, not all are configured. Not every company needs a new machine, many have worked well for years and for this reason the configuration outlined may differ at some converting plants.
To begin, drives are driven by bull gears in an oil bath so as to allow the use of steel gears. This arrangement reduces the amount of wear of the gears themselves and at the same time maintains the quality of the machine and also the integrity of the delicate product being produced.
The press itself has to be simple in construction with the plate rolls and anilox mounted on pivoting structures. The latter is under the control of a single pair of hydraulic cylinders. The diameter of the C.I cylinder also has to be engineered so that there will always be just the minimum amount of paper present between the first and last printing unit, reducing the risk of registration difficulties. Presses have to be equipped with an automatic plate roll cleaning system capable of keeping the plates in an optimum condition.
An essential requirement of the towelling and tissue sector is that the ink supplier is well acquainted with the customer’s press set up. Each operation is different and no two presses perform the same. This may also be the case with substrates, variation even between two rolls of substrate from the same batch can occur generating many a surprise when proofing and colour matching. On the subject of colour matching it is important to choose the correct colour matching and proofing method. This is necessary to match the speed and coat weight of the press involved so that colour control and density levels are within acceptable bounds. RK Print Coat Instruments range of colour communication proofing devices are used by ink formulators, pre-press and press room operatives and others with an investment or interest in processes such as flexo, gravure and coating.
The FlexiProof is an integrated stand-alone device that mirrors the performance of a production flexo press. Printing and proofing off machine, saves on press waste, time, labour costs, speeds press make ready and may improve production machine yields. The FlexiProof is a scaled down but component critically exact version of a production press it can be used for product development purposes, trialling; for the evaluation of different formulae and materials; to determine how substrates and ink react together over time as to assess areas associated with printability such as gloss, rub resistance, durability, chemical resistance, etc. Three variants of the FlexiProof are available, the FlexiProof 100 and FlexiProof UV and FlexiProof LED UV.
Both the FlexiProof UV and FlexiProof LED UV incorporate a miniaturised UV system enabling these devices to print and cure in a seamless operation in order that the generated proof is accurate and shows up pinholes and other blemishes, which traditional conveyor methods of UV proofing are unable to achieve as they cannot counter the effect of chemical changes that take place as the sample is taken to conveyor.
Until comparatively recent times one of the major problems facing brand owners and converters of paper wipes, toilet tissues and related items was that they were increasingly becoming viewed almost as a commodity item in a rapidly maturing market. Some say that this has changed. The pandemic, lock down – the (panic buying) temporary shortage of toilet rolls in supermarkets and the buying up of hand, household and anti-septic products has opened up new opportunities, not only for brand owners and marketers to take advantage of opportunities in a world very different from the one that we all new 18 months or so ago, but also for converters that will need to adapt processes and procedures to meet new demands.
Most toilet and many tissue products are processed roll to roll, many of the new fragile wipes now in demand are produced roll to sheet – requiring different converting techniques, equipment and a learning curve. Paper and tissue are not the only materials. Paper also has to compete with non-woven geotextile, spun woven fabrics and then there is the packaging.
Packaging is a subject in its own right and is the subject of a follow up article. In most instances, as much attention if not more has to go into the packaging as in the product itself. The interior of the pack must be kept moist until the peel back tab is removed for a sheet to be taken out and then re-sealed ready for the consumer to re-use the re-moistened wipe from the pack another time. An opportunity perhaps for RK Print Coat Instruments new VCML Lab/Pilot Coater which can be used for adhesive coating, to determine the integrity of seals and welds, and much more besides.