Discover how common coatings on metals can affect print results and why you need to select inks carefully before producing jobs on these materials.
By Frank Blanco Jr., Laura Maybaum
Among the characteristics that have made screen printing a popular decorating method, one of the most important is the durability of screen-printed inks. Both solvent and UV-curable screen inks have a reputation for delivering prints with vibrant colors that resist handling, abrasion, fading, and a host of other environmental factors. Combine these attributes with highly durable substrates, and the results are printed products that perform their functions for years.
Some of the ultimate examples of high-performance screen-printed products are those that feature prints on metal substrates, such as steel and aluminum (examples of graphics printed on metal are pictured throughout this article). Metal signs, nameplates, appliance fascias and trim, containers, and many other products often rely on screen-printed inks to provide functionality in the form of graphics or markings. But producing such prints can be more than a little challenging for screen shops that are inexperienced at working with metal substrates.
When it comes to printing on metallic materials, doing your homework is a must. Knowing the nature of coatings typically found on metal substrates, the manufacturing tolerances of these materials, and the best ink/substrate combinations can mean the difference between success and failure. This article will review the main attributes of metal substrates that must be explored before a shop can work with these materials effectively. Additionally, the discussion will consider the ink formulations that are best suited for different types of metals and the performance parameters of images printed on metal.
Understanding metal substrates
In most cases, when we talk about printing on metal, the substrate is not raw metal. Rather, most metal screen-printing applications involve printing onto a coated or treated metal material. The coatings on metals tend to fall into two categories: thermoplastic or thermoset.
A thermoplastic coating does not chemically react when the substrate un-dergoes drying after the coating process. The drying of thermoplastic coatings is accomplished by evaporation or by applying heat to fuse the material to the metal. The key thing to remember about metals with thermoplastic coatings is that the coatings typically are not resistant to high heat or aggressive solvents. In other words, the coating on the metal can re-melt with exposure to heat or strong solvents from the screen-printing process.
Did you enjoy this article? Click here to subscribe to the magazine.