Development of suitable laboratory test methods for improved communication between printers and paper and ink suppliers

The focus area of this project application is the printing industry and in particular the sheetfed offset printing process. The offset printing process is a rotative reproduction process using unilevel printing forms and creating images via the differences of wetting properties during a competition of aqueous (fountain solution for non-image areas) and oily liquids (inks for image areas) simultaneously fed to the printing form.

The transfer of the image from the printing form to the substrate is of indirect nature using a transfer cylinder carrying an elastomeric rubber blanket (and therefore to offset the image). This process is bringing together a very complex combination of materials which can be made to match only under very strict conditions. Under pressure of ever increasing demands on speed, quality and diversity of printing materials the tolerances in all parts of the production chain have been reduced and production of the different materials has to conform to very strict specifications.

Due to the smaller allowed tolerances in the final product there is a requirement for a better specification of the different materials down the chain. To reach this, test and evaluation methods for the different materials need to be developed, starting with the highest cost section: the substrate, to be able to specify according to the specific needs of the printer for the specific purpose of the job.

All aspects of the image reproduction on the substrate (this research will deal with paper substrates only) are captured under the term printability.

The purpose is to develop reproducible methods to test the relevant paper properties for printability and image reproduction in the printing process. The properties covered in this research are mottling, striking-in/setting and pick.

• Mottling is a cloudy visual appearance of printed areas intended to appear homogeneous. The cause of mottling is inhomogeniety in the penetration speed of either fountain solution or ink and consecutive differences in ink repelling/wetting or ink splitting in subsequent printing units.
• Striking in/setting is the velocity of ink penetration into the substrate combined with a solidification of ink.
• Picking is the occurence of localized paper surface damage caused by strong cohesion within the ink and strong adhesion forces of ink on both the rubber blanket and the paper surface during the splitting process at the end of the printing nip. It causes visible damage in the image, it contaminates the blanket and plate  and therefore limits print quality and causes additional press cleaning.

This research will be limited to papers used in sheetfed offset printing:

• Develop standardized test and measuring methods
• Determine the influence of the parameters which are known or expected to have influence on the result of the tests
• Determine achievable tolerances through round-robin tests
• Check material variability over time between different batches
• Benchmark the materials most common in the market to determine the material tolerances practically achievable in the market
• Investigate which test equipment and which methods are actually used in the market by paper, ink and printing companies 

An essential component of this project is the effort devoted to dissemination and implementation of the results: This project has been initiated by CEPI (Confederation of European Paper Industries) and is supported by Intergraf (International Confederation for Printing and Allied Industries), who represent the whole value chain of printed communication across Europe. These two confederations will widely disseminate the results of the projects through the networks of their members.

A particular aim of the project is to establish the fundamentals for an improved information exchange between the printing industry and its paper and ink suppliers.