Optimizing Relief Height: First-Place 2018 FFTA Rossini Scholarship Recipient’s Research on FIRST Relief Guidance

Optical Analysis

An optical analysis of all collected print samples was conducted to determine the overall print quality from a consumer standpoint. In the first run, the quality of the print was more clear, compared to the second run. The second run contained more defects such as hickies, ink skipout and slight banding. It is believed these print issues were caused by excess static on the web, dirty plates and gear marking. An increase in the corona treatment at the start of the web decreased this effect a bit, but the ink skipout still occurred throughout the secondary run, specifically in the over-impressed samples.

Conclusions

Lower reliefs were found to have slightly greater shoulder angles in the highlight dot areas, compared to the highlight dot shoulder angles of plates with standard or greater reliefs. Optimized relief was found to provide less dot gain in the highlights and thus provide a more accurate linear dot output across multiple ink volumes without the presence of a compensation curve. The overall amount of dot gain was found to be similar between high linescreens across all reliefs. As expected, the 0.009-in. and 0.012-in. reliefs provided the least amount of dot gain in the highlight values. Therefore, as plate relief decreased, highlight dots from 1 percent to 10 percent held consistently at a linear output across all reliefs. However, decreased relief had no impact on supporting microtype.

Ultimately, it appears that the 0.016-in. relief had the widest resulting shoulder angle, creating the smallest resulting angle. However, this relief showed more dot gain than the 0.013-in. relief, as the 0.016-in. relief showed values more consistent with the greater reliefs. Though shoulder angle did effectively increase and the printing of traditional highlight dots across different linescreens was stable, accurate partial percentage dots were not able to consistently form or be supported under the tested conditions. The lower relief may affect how compressible the dot is, which would influence deformation at the print surface.

In order to optimize equipment for plates with decreased relief, the printer must take into account the current linescreen and anilox roll being used for the end product and make adjustments from there. For example, 133 linescreen is widely used in the industry due to its consistent stability. However, if a decreased relief plate is being considered, then perhaps an HD screening would be a better option, seeing as it performed similarly to the highlight 133 screening but suffered less loss in the shadows with the lowest volume anilox.

Plate relief optimization has proven to be a viable solution in combating dot gain, however more extensive research must be conducted to determine how to better support fine features. By slightly altering the plate making process, plates will be able to hold smaller dots. However, this may not be viable with a printer’s production times, due to increased exposure times. With the implementation of a compensation curve, these plates can be altered to be even more accurate. Though decreased plate relief helped decrease dot gain, more research into the support of microtype must occur before FIRST guidelines can be adjusted.

Limitations

The results of this study are relevant under the testing conditions, with a BOPP label stock and a single-color UV ink. More extensive testing would be warranted to determine the output under other variables, such as with water-based inks, a different substrate or different plate materials. Additionally, more testing with conventional exposure and an out-of-the-box flat top dot product could provide better support to these fine features.

Experimental practices were used to expose the plates outside of the recommended specifications, so looking at the impact of light intensity on plates must be conducted. A more consistent method of plate exposure for these irregular reliefs must be determined before the study can be expanded upon. Finding a consistent fail point for the relief depth should also be determined.

Acknowledgments

I’d like to first thank my professors at Clemson University, namely Dr. O’Hara, Dr. Ingram, Mrs. Fox and Mr. Cox for pushing me to pursue research. I’d also like to thank the FTA Scholarship Committee and Mr. and Mrs. Rossini for providing me with the means to complete my project; plus Kariahlyn Lindsey and all of the staff at the Sonoco Institute of Packaging Design and Graphics for letting me use their equipment and helping me troubleshoot. Also: Jason Cagle and the folks at MacDermid, and Matt Furr and Nathan Plavnik at Esko for providing me materials and giving me really great advice for this project. This definitely would not have been possible without them. I’d like to thank Lax and Rachel at the Electron Microscopy Lab at the Clemson Advanced Materials Research Lab for assisting with imaging my plates with their Scanning Electron Microscope. Finally, I’d like to thank my friends and family (specifically my dad) for their continuous support.