Printed Dot Quality in Response to Doctor Blade Angle in Gravure Printing

Doctor blade is one of the critical machine part of the gravure printing press that controls the amount of ink transfer on the substrate. The angle of the blade can be varied; however, an improper angle may cause major problems. In this study, the doctor blade angle was positioned at three different level to address its effect on the printed dot quality. Print trials were made on a web-fed gravure press at the speed of 650 ft./min. A high-resolution overhead camera was used to analyze the key dot attributes. The results showed that measuring only the density of printed dot –a traditional quality control method– is insufficient. Incorporating the camera was assisted capturing missing dots, as well as quantifying dot area, perimeter and circularity. Print trials showed that the image quality was undesirable, when the blade angle exceeded or fell behind the optimum position

Controlling unequal surface energy results caused by test liquids: the case of UV/O3 Treated PET

Ultraviolet/ozone (UV/O3) treatment has been reported to be an effective method to modify properties such as wettability, adhesion or adsorption of plastic surfaces. The change in the surface is measured by contact angle analysis, which employs liquids and their surface tensions (ST) to estimate the surface energy (SE). We found two different practices in the scientific community: (1) the majority of researchers adopted the ST value of liquids from the literature, while (2) other researchers conducted real-time measurements in the lab under ambient conditions prior to SE estimation. To the best of our knowledge, there is no study that compares the difference between the two practices. One study was found to show different SE methods generating unequal SE values for the same substrate. However, there was no definitive conclusion backed by general thermodynamics rules. In this study, we presented (1) a statistical significance test that showed the literature and experimental ST values are significantly different, and studied (2) the effect of different liquid pairs on the SE estimation for UV/O3 treated poly(ethylene terephthalate) (PET) substrate. Modification techniques such as atmospheric pressure plasma or chemical modification were studied previously to examine PET’s wettability and the SE. The UV/O3 treatment was studied to improve adhesion and to modify its chemical properties for adsorption. In contrast, we studied (3) the effect of UV/O3 on wettability at different timeframes and addressed (4) how to control unequal SE based on a method that was refined on a rigorous thermodynamic three-phase system. It must be noted that this method can be generalized to other types of solid surfaces to estimate thermodynamically self-consistent SE values. This work also provides (5) a web-based calculator that complements computational findings available to the readership in the data availability section

The Study of Missing Dots of Electromechanical and Laser Engraved Cylinders

According to the previous study, the printability of electromechanical engraved cylinder and laser engraved cylinder were different in terms of density, tone reproduction and mottle. In this study, the missing dots of two different engraved cell types were investigated. It showed that different cell structures had strong effect to ink transferring and the characteristics of missing dots. Lasers engraved cells were less affected by ESA (electrostatic assist). When there was no ESA applied, the laser engraved cells showed less missing dot area, which indicated better ink release from spherical shaped cells. ESA had more effects to coated substrates than supercalendered substrates

Gravure Printability From Laser and Electromechanically Engraved Cylinder

Gravure printability comparison of laser engraved and electromechanically engraved cylinders was done on five different substrates. Ink transfer was less reduced on laser print than electromechnaical when printed without electrostatic assist. Print mottle was significantly lower and yellow, magenta and black laser engraved images, while cyan print from laser engraved cylinder had higher mottle on some substrates (SCB, SCA and freesheet). Overall, the print quality than that from the electromechanically engraved one