"Durable Thin-Film DLC on Wafer Surfaces of Gravure Cylinders for Roll-to-Roll Printing of 1-Bit Electrodes and Microtext in Flexible Electronics and Graphic Security"

Summary of “Durable Thin-Film DLC on Wafer Surfaces of Gravure Cylinders for Roll-to-Roll Printing of 1-Bit Electrodes and Microtext in Flexible Electronics and Graphic Security” by Chandramohan Seetharamiah Srinivasaraju et al., published in Advanced Materials, Volume 37, Issue 6, February 12, 2025. https://doi.org/10.1002/adma.202413551

Introduction

The increasing demand for flexible electronics, including sensors, antennas, and batteries, necessitates reliable printing techniques. Gravure printing has long been used for high-quality fine-line graphics and microtext, especially in security applications such as banknotes and tax stamps. Traditional gravure cylinders are coated with chromium due to its durability, but environmental concerns have led to the search for alternatives. Diamond-like carbon (DLC) is a promising substitute, offering superior ink transfer, increased durability, and lower electrical resistance compared to chrome.

Gravure Cylinder Fabrication and Engraving Process

Gravure cylinders are constructed with multiple metal layers (nickel, copper, and zinc) on a steel base, onto which fine-line electrode patterns and security features are engraved. A durable thin-film coating, traditionally chrome, is then applied to protect the cylinder. The hardness of chrome (900-1100 HV) makes it wear-resistant, but its use is being phased out due to toxicity concerns. DLC, a highly durable and chemically inert material, presents an eco-friendly alternative, demonstrating superior ink transfer capabilities.

Experimental Setup and Printing Process

Two gravure cylinders were fabricated—one coated with chrome and the other with DLC. Both were laser-engraved with micro-scale patterns, including electrode grids, fine lines, and microtext. The goal was to evaluate the ink transfer behavior of DLC in comparison to chrome.

Ink and Substrate: A conductive carbon ink (LOCTITE ECI 7007 E&C) was printed onto a PET substrate (Melinex ST506) using a roll-to-roll gravure printing process.
Printing Conditions: The printing was carried out using a gravure proofing press, and the printed samples were analyzed for line width, electrical resistance, transparency, and adhesion.

Key Findings

1. Ink Transfer and Line Width

DLC-coated surfaces demonstrated higher ink transfer efficiency, resulting in increased line widths compared to chrome.
Isometric grid patterns with 15, 20, and 30 µm lines exhibited more uniform conformity with DLC, leading to better ink distribution.

2. Electrical Resistance and Transparency

Prints from DLC-coated cylinders had lower electrical resistance, indicating higher conductivity, which is crucial for functional electronics.
Transparency measurements showed darker and denser lines from DLC prints, confirming increased ink deposition.

3. Performance of Electrode Patterns

Solid electrodes printed using DLC surfaces had an average electrical resistance of 8.0 kΩ, significantly lower than chrome prints (12.8 kΩ).
The adhesion of DLC-printed electrodes was excellent, withstanding standard cross-hatch tape tests.

4. Security Printing and Microtext

DLC performed exceptionally well in printing security features such as guilloche patterns and microtext.

• Microtext with sizes as small as 50 µm was legible with DLC, whereas chrome prints exhibited missing or unreadable text.

5. Statistical Analysis and Repeatability

Line width and electrical resistance measurements confirmed statistically significant improvements with DLC.
Variability in ink spreading was lower with DLC, making it more consistent and repeatable in high-volume production.

Conclusion

The study confirms that DLC-coated gravure cylinders outperform chrome in printing conductive fine-line electrodes and microtext patterns. The higher ink transfer efficiency, lower electrical resistance, and better print reproducibility make DLC an excellent alternative for flexible electronics and security printing. As environmental regulations push industries away from toxic chrome coatings, DLC presents a sustainable, high-performance solution for roll-to-roll printing applications. For more details on the complete experiment, results and conclusions, see the article published in Advanced Materials, 37(6), 2413551 and its access link is given in the reference section below.

Reference:

[1] Seetharamiahsrinivasaraju, C., Shetty, R., Saxena, S., Sharma, P., Cohen, D., Springstead, J., & Oldenzijl, R. (2025). Durable Thin‐Film DLC on Wafer Surfaces of Gravure Cylinders for Roll‐to‐Roll Printing of 1‐Bit Electrodes and Microtext in Flexible Electronics and Graphic Security. Advanced Materials, 37(6), 2413551. https://doi.org/10.1002/adma.202413551

Dr. Chandramohan Seetharamiah Srinivasaraju is an expert in the printing, packaging and paper industries. His research has been published in leading scientific journals, and his work on developing new technology cylinders with environmentally friendly, durable surfaces for graphic printing earned him GAA Technical Paper award and the prestigious Technical Association of Graphic Arts (TAGA) Individual Award. Dr. Chandramohan holds a Master’s degree in Print Media Technology and a PhD in Paper & Printing Science. With over 15 years of experience in the printing industry, he has worked extensively in areas such as software development, color management, printed electronics, inkjet and conventional printing, as well as the manufacturing and qualification of printing methods and substrates. Currently, Dr. Chandramohan Seetharamiah Srinivasaraju is pursuing advanced research focused on sustainable materials for use in printing and packaging. He can be reached at [email protected].