By Cassandra Balentine
Part 1 of 4
Printing to glass involves many considerations, and in a majority of cases—a pretreatment. This is true for both flat and cylindrical glass and ceramics.
In part one of our four part series; we focus on printing to flat glass.
Factors to Consider
When printing to flat glass and ceramic products, considerations include the print process, type of glass, planned product use, and durability requirements.
It is important to remember that not all glass is created equally. “Glass is not just glass. Each manufacturer makes it slightly different, different recipe to get similar results,” says Adam Tourville, director of sales, North America, Direct Color Systems. For example, there is tin float glass, polished, soda lime, sand blasted, and etched—just to name a few.
Understanding the chemistry and post-manufacturing process helps set a print up for success, typically when it comes to adhesion.
“Glass is a complex material where adhesion and durability becomes a concern. Understanding the application is critical, as is selecting the proper inks to provide the correct adhesion,” offers Michael Hemmelgarn, territory sales manager, swissQprint America.
For flat items, Michael Perrelli, marketing director, Innovative Digital Systems, says the biggest nuance is defining the acceptable adhesion for the operator and/or customer. “When printing to flat glass objects, chances are it won’t be held to a dishwash standard, so the adhesion goal could be slightly different than the drinkware counterpart. Say for example, this product is a flat glass award. The printed product will be for display only, so print operators may be able to leverage wipe on or jettable primers to reach the required adhesion level.”
Sean Lanigan, president, Applied Surface Technologies, LLC, points out that generally, any process used to solve glass container adhesion can be used on flat glass, but flat glass does offer a few additional solutions. For example, one option for flat glass is that you can print on the surface and use a laminate material to adhere another piece of glass. Once sandwiched, the printed surface is perfectly protected.
Another solution for insulated glass windows is that you can print on a surface that will be on the inside of the insulated window—again, the surface is protected. “When you see large window murals, this is the most common method,” he adds.
There are a few ways to pretreat flat glass to ensure successful digital printing.
Bas Buser, consultant printing applications, Plasmatreat GmbH, lists possible pretreatment options as plasma, wet chemical (primer), and flame. “We at Plasmatreat recommend using plasma because of various advantages and benefits in contrast to wet chemical and flame,” he notes.
Wilson Lee, director of business development, Enercon Industries, finds the most common pretreatment methods are wet chemistries—including solvents and primers, as well as plasmas. “With ceramics, you can also use roughening methods like sanding to increase the overall surface area. For ink bonding, a clean surface with high surface energy and ample surface area to bond with is ideal for repeatable results.”
In general, Lee says both flat glass and ceramics treat very well with both plasma and flame plasma. However, this does not guarantee printing will always be successful. “There could be contamination on the surface that cannot be removed by the plasma, but outside of that possibility, both plasma and flame plasma are great pretreatment steps to printing.”
Perrelli suggests wipe-on primers are a good start, but flame and Pyrosil would yield the most durable results based on its testing.
“Wipe-on glass adhesion promoter is a bare minimum for any type of adhesion,” agrees Tourville. “If you need really rock solid adhesion I recommend Pyrosil and an approved wipe-on adhesion promoter.”
Tourville prefers tin float glass, which he says offers micro imperfections on the float side that can help with adhesion with a wipe-on primer or flame treatment. “Otherwise you will need to use a good, glass-specific wipe-on primer to get any decent adhesion. If you need bullet proof adhesion you should use a flame treatment like Pyrosil and an approved adhesion promoter to get the best adhesion possible with LED and UV inks. Pyrosil can also be used on ceramics and other hard-to-use substrates,” he explains.
If you are printing glass with standard UV LED inks, Hemmelgarn says swissQprint offers a jettable primer that can be jetted only where the image will be placed. There are also great hand primers on the market. In this case, the glass should be properly cleaned prior to any printing. You will need to eliminate the fingerprints, oils, or any other particles that may adhere to the glass.
When it comes to ink selection, UV inks are popular options when printing to glass.
“All types of printing inks can be used in this application, however, the most common would be digital inkjet and UV. Having said that, treating both ceramics and glass with plasma techniques generally gets the surface energy high enough that any print method should be successful,” offers Lee.
Hemmelgarn points out that swissQprint has been printing on glass for a while. “We recently introduced our latest GX1 UV LED, which is manufactured specifically for glass applications. swissQprint has created a glass UV LED ink that does not require a primer for adhesion. The GX1 increases efficiency and eliminates the primer step.”
Buser believes ink selection should depend on the use of the final product. He recommends ceramic inks for outdoor applications, UV curing inks for indoor use, or laminating the glass with a cover to help protect from outdoor conditions like UV light and weather including rain and snow.
Printing to flat glass presents many nuances, however it is possible to generate great results with a knowledgeable approach.
Stay tuned as part two of this series looks at printing to cylindrical glass and ceramics.
Feb2023, Industrial Print Magazine