Adhesion testing on glass is an important quality assurance measure in the glass printing and decorating industries. Glass is smooth and has a low surface energy, which poses UV ink adhesion challenges. With UV printing technology gaining popularity, the ability to print durable prints on glass is very important. However, the durability of the UV printed images depends on the UV ink’s ability to stick to the glass. As a result, the use of UV adhesion promoters and adhesion testing becomes a critical step in evaluating the prints’ ability to resist peeling, scratching, or fading over time.

Why test

Today, there are very many industries using glass for a wide range of applications. Glass finds applications in various industries such as interior design, architecture, promotional products, and product branding. By subjecting UV-printed glass to rigorous testing, it guarantees the manufacturers that their products will last a long time. Additionally, rigorous testing of UV-printed glass products provides a reliable benchmark for meeting the diverse expectations of end-users in terms of both aesthetics and durability.

Adhesion testing standard

The ASTM international standards set the adhesion requirements for UV digital printing on glass. Additionally, the ASTM not only sets the standard for adhesion testing on glass but also the specific requirements for other materials. While there are several testing processes, not all of them are required for every UV-printed product. It is important to understand the intended use of the product before proceeding with adhesion testing. Lastly, if you are not sure how to proceed with adhesion testing, please reach out. At Boston Industrial Solutions, Inc., we provide free adhesion testing on glass and many other materials.

Boston Industrial Solutions process

To test a product, we ask our customers to send us 6–12 samples for testing. Once these parts are received, we follow up with a question-check list to determine the customer requirements. This check list enables us to understand the current printing process, if any, and what pre-treatment and post-treatment are needed.

For glass printing, once we have established the intended glass use, all the glass substrates are cleaned and wiped with a lint-free towel to remove any finger oils and debris. Next, we wet a lint-free towel with Natron® G1 Glass primer and apply a very small amount of it evenly to the glass. After two minutes, we digitally print the glass.

After 24 hours, we conduct adhesion testing.  We write a comprehensive adhesion testing report after adhesion testing. This report describes the adhesion tests performed and the overall resistance. The samples are then photographed for documentation purposes and sent back to the customer for evaluation.

Tape adhesion test.

Tape adhesion testing on glass is simple. Additionally, this testing process is mild. Its purpose is to determine if the UV ink has adequate adhesion to glass. A piece of pressure-sensitive clear tape is applied to the print or graphic. Pressure is then applied to the tape. Then, the tape is vigorously peeled off at a 90–180-degree angle. If the ink delaminates, then the test has failed, and the adhesion is not good.

Scratch test.

This test uses a sclerometer tool, which measures the scratch hardness of the material. To use the sclerometer tool, loosen the screw and move the scale to 8N of force.To begin, loosen the screw on the collar and move the scale to 8 Newtons of force. Hold the sclerometer at right angles to the object that you are testing. Then drag the tool on one side of the glass right through the print. If no ink comes off, then the bond between the ink and the glass is strong—the ink has passed this test.

Cross hatch adhesion test (A & B Test)

Crosshatch A uses a razor to mark an X on the printed material. Then pressure-sensitive tape is applied to the cross-hatched print and pulled off quickly. If the ink comes off, then the object has failed adhesion testing on glass.

The other crosshatch test is the B. Crosshatch B testing uses a multi-tooth adhesion cutter. The operator drags this tool across the decorated surface in one direction. Then you repeat the same process at 90 degrees—intersecting the first cut and forming a lattice pattern. Then tape is applied to the crosshatch and pulled off quickly. If the UV inkjet ink does not delaminate, then the adhesion testing is a success.

Lastly, it is important to note that ASTM international guidelines are for establishing if the adhesion of a coating to a material is adequate in general. These testing methods and guidelines do not establish the level of adhesion. The level of adhesion is determined by sophisticated methods and equipment.

In addition to our in-house ink adhesion testing services, we also offer custom color matching services for screen and pad printing inks, technical support, and customer pad printing training services. Contact us today, visit our support hub, and follow us on YouTube for the latest printing and silicone technology updates.

Learn more about our printing ink for silicone rubber.