The environmental and health problems caused by inks containing volatile organic compounds (VOC) call for new solutions in printing ink chemistry and technology.
One of the approaches may be hot melt ink, which is ink solid at ambient temperature and liquid at the moment of printing.
Such ink contains no volatile solvent to be trapped in ink film or to produce VOC.
In this work, hot melt ink for rotogravure printing process based on ethylene vinyl acetate (EVA) chemistry was formulated, analyzed for rheological properties, and printed on publication and packaging substrates. The original inks based on ethylvinylacetate and polyethylene (PE) chemistry were too viscous for rotogravure.
The polymer matrix was mixed into the carnauba wax and then the rheology was tested again. Carnauba wax significantly decreased the viscosity of hot melt formulations.
Drawdowns were made on publication (supercalendered grade A and lightweight coated) and packaging (SBS board) substrates and then the printability data was collected. The EVA/carnauba wax inks showed slightly higher optical density than PE inks.
Print gloss, delta gloss and rub resistance properties were better on PE inks. Also, mottling was lower at PE inks. SBS board exhibited highest print and delta gloss and lowest mottle index.
Introduction
Rotogravure is an industrial printing process mainly used for the high-speed production of large print runs at constant and top quality, also known as “photographic quality image.” Many hundreds of millions of magazines each week are printed by the gravure process because advertisers want their products promoted in the best possible way. A large number of mail order catalogs are printed in gravure because the products must look attractive and must also demonstrate exactly what is on offer: therefore the catalogs must all look the same, which requires the constant print quality of the gravure process.[1]
Today, 15 percent to 20 percent of printing is achieved through the rotogravure technology. In Europe, Germany is far ahead in the number of gravure printing units with approximately 100 rotogravure printing machines, Italy with 40 printing machines, U.K., France and Holland with nearly 20 for each of them.[2]
According to Koenig & Bauer-Albert AG[3] and European Rotogravure Association,[4] the world demand for rotogravure publication presses, thus rotogravure printing, is increasing. Further growth of gravure printing is predicted to result from continued refinements of the process and gravure presses.[5]
Gravure is gaining the market share with various improvements in the technology, such as ultrasonic gravure cylinder plating, which is significantly faster than traditional copper plating. Publication presses are now as wide a four meters (142 inches). Development of gravure presses for packaging is directed toward short runs, which may help the gravure process to stay competitive. High printing speeds reduce dot gain and dot distortion, improving print quality. Electrostatic assist reduces the number of skipped dots and improves the uniformity of ink distribution within the dot.
In the history of rotogravure printing, water-based inks preceded solvent-based inks, but they were abandoned because of slow drying rates. Since the beginning of the 1960s, toluene has been used as a solvent in most rotogravure publication printing plants. However, toluene was the most likely cause of the lung cancer,[6] genotoxicity[7,8] and neurotoxicity.[9]
For all of these health-hazard problems, water-based inks are coming into use again. The use of water-based inks for packaging and product gravure grew from 26 percent in 1993 to 50 percent in 1997.[5]
There have been some technical problems related to the application of water-based inks to the high press speed, such as relatively low drying rates, issues such as printability on a variety of substrates and their cost/performance ratio.
Research is currently being done in attempt to create a new generation of inks: hot melt inks, which do not have any sort of dangerous effluent or carcinogenic properties.
However, aqueous formulations have also serious environmental disadvantages, as they cause greater water pollution and consume more energy.[10] UV gravure inks are not yet a reality.[11]