New finishing techniques are the major topics at Drupa
By Johannes Kokot
Advertising overload is a growing issue. Today it is often the packaging alone that allows consumers to differentiate between products. The products themselves have become interchangeable. In other words, the decision to buy is normally made in a few seconds and is based on visual appeal. And it is exactly this reason that offers an appealing area of business for the printing machine manufacturer.

One of the central themes at Drupa 2004 — to be held May 6 – 19 in Dusseldorf, Germany will be finishing techniques. In particular, inline finishing for high-quality packaging printing will be a topic of great interest for job printers. This is because decreasing run sizes with special finishing and exceptional quality, with frequent changes of design, are now affordable and can be produced in very short turnaround times.

Across all processes, the supply industry offers new finishing solutions. On top of this are a variety of new plastics and films with many and varied surface characteristics and new effect colors and coating systems for finishing. However, not everything that looks good and has sensory appeal can be printed, finished and processed without problems. The more finishing components are used, the more delicate the overall process becomes. Before making the decision to invest in equipment, it is important to consider very carefully which process is best suited to which products and which new business areas and products it can be used to produce.

Flexo units for inline finishing
Most sheetfed offset machines in the packaging sector, and increasingly also in the jobbing sector, are equipped with flexo coating units. Offset printers are often unaware that they are utilizing flexo printing technology in such cases. Fitted with chamber doctor and screen roller, it is not only possible to coat but also to print with good register adherence. Flexo units downstream from the offset printing units are normally used for inline coating of the print products or for effect coatings. With upstream flexo units, the printing surface can be pre-treated, such as using opaque white coating on metallized paper or transparent plastic for subsequent brilliant offset color printing. However, the pre-printing of iriodines is an interesting finish to create opalescent effects in the printed image.

The advantages of offset printing are therefore high print quality and its favorable prepress and printing plate costs. In contrast, the advantages of flexo printing lie in the transmission of thick layers providing the option of embedding greater pigments, and in the simpler application technology. Flexo printing inks are very similar to thin gravure inks in terms of viscosity and in comparison to offset, form a thicker, even ink coating that can be varied using different screen rollers. The particle sizes of the metal pigments for offset are 3.5 millimeters, and for gravure and flexo printing, 8 to 9 millimeters. Typical areas of usage for these flexo units include opaque white coating, blister, opalescent or metallic coatings and the application of dispersion and Ultra Violet (UV) coatings.

A pure sheetfed flexo machine
The development of these sheetfed offset machines with flexo units into pure sheetfed flexo printing and coating machines was a logical progression. Sheetfed flexo machines are very common in corrugated cardboard printing as coating machines. However, the new sheetfed flexo machines for packaging printing and finishing have a gripper transport system to ensure precise transfer register from print unit to print unit. And the printed matter range extends from thin paper to cardboard up to 1.25 mm.

The sheetfed flexo machine which has the same design as a sheetfed offset machine, but which has two flexo units in the place of the offset print units, can also be used purely as a finishing machine for applying UV coating or effect coatings. Special coatings requiring a very thick coating, such as blister, scented, barrier coating, gumming, and heavily pigmented coating for iriodine and metallic effects can be applied in an accurately specified quantity. For frequent changes of coating, it is always advantageous to combine two coating units, one for dispersion coating, and the other for UV coating. Fully exchangeable coating circulation systems permit rapid conversion.

High quality packaging materials generally have a high degree of finishing which demands multiple runs through the coating unit/flexo printing unit. A printing machine that is only used for coating for multiple runs can very rapidly become a “bottleneck” in production if it might be blocking five or six print units in the process. The sheetfed flexo machine, used offline, can be a controllable introduction into the sector of high quality packaging finishing in terms of technology.

UV technology in sheet-fed offset
Sales levels in UV printing works have increased almost three times as quickly worldwide as those of their competitors in the conventional offset market. UV technology represents the highest level of quality, and when used in the inline process is efficient, consistent and equally as harmless as conventional offset in terms of user health when all the safety guidelines are observed. Of particular interest is finishing using UV coatings that provide high gloss values combined with good resistance to scratching. The UV ink and coating film is hardened in fractions of a second by the UV radiation in the printing machine, and the press sheet can be processed straight away. Naturally print dusting powder and solvent emissions are a thing of the past.

However, it is not possible to master the UV printing and finishing process simply in passing. UV printers need to accumulate comprehensive expertise, handle increased investment costs and material/energy costs, plan for change-over times for mixed conventional/UV operation, as well as adjust printing properties. And there is still room for improvement in terms of the smell of UV printed materials. However, the advantages far outweigh the disadvantages. The enormous range of non-absorbent printed materials is a real challenge for creatives in job, packaging and label printing.

Introducing mixed operation
UV printing machines need to be adjusted to the special requirements of the printer and his products. Even in small-format offset, powerful UV technology is available which is equal in every way to medium and large formats. For those new to UV, a mixed operation of UV and conventional is advisable to start with, assuming the finish coating is appropriate for UV press runs. In future, waterless UV sheetfed offset will also be able to manifest its finishing advantages in the field of non-absorbent printed materials in particular and even gain a boost with greater UV acceptance — not least because of the option to image both computer to plate (CTP) waterless and CTP plates for conventional offset in the same imagesetter without chemicals.

Plastic films are increasingly in demand. Previously the sole preserve of screen-printing, today offset printers can enter this high-sales marketplace thanks to UV technology. However, screen printing can now also use UV technology to make up ground on its strongest competitors. Problems in the dimension stability due to high temperatures on the UV beamer jeopardize the printing and finishing process that is register-accurate. This is why UV systems are available, which require considerably less beamer performance for the hardening process in an inerting chamber in a nitrogen atmosphere.

Inline coating in a double pack
As an alternative to a pure UV machine, double-coating machines are also available. This makes it possible for UV coatings to be applied inline on conventional inks, which are considerably cheaper. Tried and trusted special colors can also still be used. The prerequisite for this is a printing machine with two coating units, with a drying section in between the two.

Hybrid technology in finishing
Another interesting variant of inline finishing is hybrid technology. A special sheetfed offset ink allows the printer to use both conventional, mineral oil-based inks as well as hybrid inks, assuming the printing machine has been appropriately modified. Problems with coating adhesion and the resultant gloss inclusions are avoided, as the surface chemistry of the hybrid inks is virtually identical to the UV ink.

High-gloss and matt effects are possible in one machine run. An example: designs with hybrid colors are printed in the first print units. Then the ink is dried in the UV intermediate drying unit. Individual elements are then applied using conventional inks and conventional print coatings. Following the final UV coating and hardening, all the graphical elements printed using hybrid inks have a high-gloss surface. For all elements printed using conventional inks/coatings, the interaction of normal ink and UV coating forms a matt, shiny, structured surface which is similar to a plastic coating both visually and in terms of touch, representing an interesting design feature. The options for combining different effects from this point are many and varied.

It could be said that hybrid technology represents the route towards UV technology — yet remains a stand-alone option. In addition, those who are not able to make full use of a UV machine in job printing will find an appealing alternative in the shape of hybrid technology.

Avoiding exchangeability
Job offset printers in particular face problems today in offering their customers value-added printed materials at reasonable cost and to avoid becoming replaceable. The options outlined here for entering into UV technology are simplified by the modular construction of the printing machines. This is why Drupa 2004 is the ideal marketplace for comparing the various options and for gaining an overview of the printing ink and printing machines manufacturers. After all, the triumph of UV technology is surely set to move into commercial offset printing over the coming years.

About the author: Johannes Kokot writes about printing technology topics for Printing & Media, an industry trade magazine based Esslingen, Germany. Kokot also serves as a freelance editor in the packaging and label production department for publishing house Deutscher Drucker.