Guenther Keppler of Heidelberg India talks about special applications with Alok Singh of Indian Printer and Publisher

Alok Singh How do coatings help the offset printer?
Guenther Keppler — There are actually three major aspects. The first is purely process-oriented to support the printing principle in making the wet sheet dry or at least the surface. The varnish layer printed in line on top of the process colours seals the surface in order to convert the sheets in postpress immediately after printing.

That saves throughput time and hence improves productivity. The second purpose is to protect the printed and unprinted sheet surface against mechanical wear and tear. It is a product quality related precautionary measure [for] the print product. The third field of application is to make the product even more attractive and effective for its purpose. Thus, coating in its different forms supports the printing principle, it helps to improve product quality and it pushes print media to compete against other media and to be more effective for its final destination.

AS  How do coatings help end users in enhancing their products and/or in improving the impact of their products?
GK  The ability to print more than one colour in one pass was a great step and made the printed product more attractive than the pure black and white. Varnish opportunities are just further steps in print evolution in order to make the products more attractive. In five years coating and varnishing will be natural like today four colour printing.

AS   What do end users and designers need to know about coating?
GK  Learn the variety of available coating applications, the different types of varnishes and how to apply these for a designated purpose. Getting familiar with meaningful combinations and getting to know about effort and the cost behind these. Create expertise, in what cases which coating method should be applied and not.

A ticket for a cricket game does not need necessarily spot coating however a folding box with hair coloration should have at least a full coated surface to protect the package on the shelf. A pizza box might need a protective barrier inside the box but not necessarily a metallic effect highlighted text on the top. An advertisement brochure for a car can have a matte coated surface with a high gloss spot coating to emphasise the manufacturer’s logo and a mother of pearl effect inside to underline the elegancy of the car shape. For the wrapping of a candy stick the same effort probably will not pay off.

AS   How to specify coating for a print product? Or should this be left to the printer? Or should this be done in consultation with the printer?
GK  Whenever possible the print buyer should involve the “manufacturer” of the printed product right up front of the project. It will pay off for both sides if the printer feeds in his practical experiences already in the phase of product conception and design. This should not keep the print buyer away from creating knowledge about all the forms of application.

It is essential that he speak the language of the shop floor people. Of course not all printers are able to fulfil the requirement to jointly develop a print product; this is the challenge for a modern printer — putting more into the value-add basket than only or simply acting on orders.

Recently we analysed some printed products which airlines use in their in-flight service just to tide over the travel time. We found laminated menu cards for one-time use only and coated forms for frequent traveller application. Obviously there is a lot of potential in using coating and varnish appropriately.

AS  What about the costs? We know printers who want to use coating on every job but since the client does not want to pay for the coating, it comes out of the printer’s pocket. What do you think of this situation?
GK  Printing in colour is costlier than black and white only (with few exceptions). This insight did not stop the printing world from going into colour. Now there is more available than just this. Sure, any additional process step ads cost, however if these costs are out balanced by higher productivity (print a layer on top of the wet process ink to get a faster turnaround) it is worth thinking about the investment.

Another example that goes into the same direction is the lay down of a sealing layer in the press on top of the unprinted paper first before printing the process colours. This technique allows the use of less costly paper with the result of high quality image printing. The savings can be a lot since the cost of substrates is more than the half of the production cost of a printed product.

Every product has its price. We have to sell the media “print” to the print buyer. If he is not convinced that the added value will generate more benefit for him in his campaigns he will not pay for it. Without any doubt coating on its diverse variants is not an exception anymore.

Heidelberg spends a lot to demonstrate the wide range of coating and varnishing and produces samples that show how printed products can look if value-adding technologies are applied. This is promotion for print and the result is measurable: more than 60 per cent of all new sheet fed offset presses sold are equipped with the one or the other coating functionality.

AS   What are the different types of coatings?
GK  The title coating gathers a wide field of application. Coating is used for two major purposes: first as production tools (seal and protect the surface) and second for special effects (make the product more attractive, extend the range of usage). Sometimes there is a combination of both: coating seals, protects, and attracts at the same time.

For sealing a printed surface and for faster finishing, gloss normally does not play a major role. It is rather the instant dry effect that is requested. For simple product protection purposes an oil base varnish (pigment less ink) suffices. In this case no coating tower is required. However, for a more robust shielding an aqueous layer may be best suited and a specific coating unit mandatory.

If it comes to special effects the major purpose is to catch the final user’s attention even more. For such application often more gloss on certain areas of the surface is desired. Here, without dedicated coating functionalities nothing works. Water based coating reaches a gloss of about 85 points whereas a UV varnish goes up to a level of about 90 to 95 gloss points. A very economic combination is the recently developed and Heidelberg patented “drip-off” technique where the matt/gloss effect is achieved by an interaction between two different types of varnishes. For the spot effect, an ordinary offset plate is required.

The chart attached compares the different variants of coating, their requirements and resulting effects.

AS   What are the hardware requirement in terms of presses and applicators?
GK  It depends on which of the many possibilities the printer would like to apply. Aqueous coating is the most versatile tool in the printer’s toolbox and requires at least one coating tower, either with a roller transfer system or a screen roller chamber doctor blade combination. The latter is recommendable for fine spot coating and shaded effect. Printing with UV curable inks instead of the conventional process colours needs specific rollers in the inker and dedicated blankets. The plates must be baked to resist the aggressive ink substances. Special attention must be spent on the drying installations. A full UV press as well as a hybrid (conventional inks mixed with ultraviolet curable inks) configuration makes so-called “inter-deck” drying devices necessary.

Modern presses offer extended deliveries that take the sheet on a longer ride from the last lay down of varnish to the pile. These extended deliveries can be equipped with the respective drying systems like hot air for conventional inks, infrared for the aqueous coatings and ultra violet radiation for curing.

AS  What are the technology, knowledge and training requirements for printers to effectively use coatings? Where and how will this technology absorption and training come about?
GK  As in many other areas application know-how is key. UV printing and coating makes dedicated know-how mandatory because of the interlinked functions of drying intensity, printing speed and the photo inhibitors in the ink. Special attention is needed for the daily maintenance of the coating devices for both aqueous and ultra violet curing varnishes.

It is not enough to operate according to the instructions only. The successful application of coating variants regardless whether oil based, aqueous, ultraviolet or new recipes require a profound understanding of the different interacting materials, wherefore Heidelberg India is currently preparing a training course that talks about “material related printing problems” for operators and shop floor managers.