By Cassandra Balentine
Part one of three
Surface’s energy is an important part of the adhesion equation when digitally printed inks on glass.
Ken Tyler, national sales manger, Engineered Printing Solutions, admits there is no single number that applies to every application. The level required depends on the ink chemistry, the durability requirements, the geometry of the part, and the overall print process. In practice, we start by measuring the surface condition using methods such as dyne testing or a goniometer. “We then test pretreatment options, remeasure the surface, and evaluate how the print performs. So, while there are target ranges we look for, the real answer comes from testing the actual combination of substrate, pretreatment, and ink to provide the final direct to object (DTO) printing solution for glass.”
A general rule is to maintain a surface energy difference of ~10 to15 millinewton per meter (mN/m), where the substrate has higher surface energy than the ink. “Most inks have a surface energy from around 26 to 28 mN/m which means that we aim on a surface energy of the object from around 45 to 55 mN/m,” shares Bas Buser, global segment manager printing applications, Plasmatreat GmbH.
These numbers are given and determent by the ink and has to be present on the surface to get a good wetting and bonding of the ink, adds Buser.
Surface energy—measured by a substrate’s dyne level—impacts the way ink wets out on a substrate. To have a controlled ink dot with ideal wet out, typically requires a dyne level above 50 says Sandi Baginski, creative director, Innovative Digital Systems (IDS). “Obtaining this dyne level does not guarantee adhesion, just more optimal dot gain.”
Dr. Arnd Schimanski, managing director, SURA Instruments GmbH, feels that it isn’t surface tension is not the major factor for digital ink adhesion. “Mostly the suitable active groups for ink adhesion are needed. SURALink contains the suitable chemical groups for good ink adhesion. By combination with Pyrosil process a chemical bonding between glass surface and ink is achieved.”
Evaluating Surface Energy
There are two common methods used to evaluate surface energy on materials—contact angle measurement and dyne level testing.
Erik Kiel, president/owner, 3DT LLC, explains that contact angle measurement analyzes the angle formed by a droplet of liquid placed on a surface using a digital surface analyzer. “This method provides a clear visual indication of how surface treatment has affected wettability and surface energy.”
Untreated glass typically exhibits contact angles above 60 degrees, indicating limited wetting. After plasma or corona treatment, contact angles commonly drop below 30 degrees, demonstrating significantly improved surface energy and ink wetting. In some cases, Kiel says plasma treatment can achieve contact angles in the single-digit to low-teen range, indicating highly activated surfaces.
For untreated glass, Kiel says the surface condition for untreated glass is ~55–70° and results in droplet beads, limited wetting; Plasma or corona treated glass ~15–30° for droplet spreads, strong wetting, and 3DT plasma or corona treated glass offers ~3–18° and very strong wetting.
Kiel notes that the graphic produced from actual surface analyzer data, surface treatment testing shows the contact angle of a water droplet changing from approximately 89 degrees on untreated glass (hydrophobic) to about 13 degrees after plasma treatment (hydrophilic). This reduction indicates that the glass surface has been effectively cleaned and activated, making it more receptive to inks, paint, coatings, adhesives, and other media.
Surface contamination can strongly influence these measurements. Materials such as release agents, organic residues, handling oils, and dust can act as a barrier on the surface, increasing the contact angle and preventing proper wetting. Surface analyzers provide a fast, quantitative method for evaluating surface energy by measuring how well a liquid spreads across the substrate, explains Keil.
Alternatively, surface activation can be evaluated using dyne level testing. Keil says reliable digital ink adhesion typically requires glass surface energy levels of approximately 50 to 60 dynes/cm or higher. For proper wetting to occur, the surface energy of the substrate should exceed the surface tension of the ink. When this condition is met, ink spreads more uniformly and bonds more effectively to the surface.
This range works well because most UV-curable digital inks have surface tensions in the 30 to 45 dynes/cm range; for good wetting.
Also, the substrate surface energy should exceed the ink surface tension by about 10 dynes/cm or more; and when this condition is met, the ink spreads uniformly rather than forming droplets.
Both corona and atmospheric plasma treatments can raise surface energy into this range. However, atmospheric plasma often provides more thorough surface cleaning and more uniform activation, which can help ensure consistent wetting and adhesion in demanding digital printing applications.
Jun2026, Industrial Print Magazine
