The market for screen printing on metal provides ample opportunities for screen printing businesses. To succeed in that market, screen printers have to understand the technical aspects of screen printing on metal substrates.

Not all metal substrates are created equal, and not all inks will adhere to all metals. Laying down a great print means understanding your metal substrate, knowing which inks will print well on that substrate and meeting the demands that will be placed on the printed product.

Know Your Metal Substrate

The metal substrates sent out for printing typically aren’t raw metal; they feature coatings and treatments that affect how the metal will react with certain inks and how well inks printed on the metal will resist scratching and fading. There are two types of metal coatings:

• Thermoplastic. Thermoplastic coatings are air dried, so they don’t form a permanent bond with the underlying metal. Thermoplastic coatings are softer, so they do accept ink deposits fairly readily. However, because they are not bonded to the metal, thermoplastic coatings will scratch or rub away more easily, taking with them any ink that has been printed on top. Thermoplastic coatings also don’t hold up to harsh solvents or high temperatures, which can cause problems during screen printing.
• Thermoset. Thermoset coatings, by contrast, are cured on the metal by a long baking process. That process causes polymerization to occur, meaning the coating forms a firm bond with the metal below. That makes thermoset more durable, but it also can cause problems with ink adhesion during screen printing.

Successful screen printing on metal substrates begins with understanding your metal substrate. You have to know whether your metal features a thermoplastic or a thermoset coating. You should also ask whether the metal has been treated with any additional chemicals that may interfere with ink adhesion; if they do, your supplier generally can recommend what you can use to clean off any surface chemicals before printing.

Deciding Which Screen Printing Ink to Use on Your Metal Substrate

Metal substrates call for different inks, and the ink you choose will depend on what type of coating your metal substrate has and the durability and flexibility required in the final product. The types of inks used for printing on metal substrates include:

• Air-dried solvent inks. Air-dried solvent inks are inks that don’t require heat curing, and they commonly include vinyl, acrylic and lacquer formulas. These inks don’t go through a chemical bonding process as they dry. As a result, they are more susceptible to scratching and scuffing, and won’t withstand exposure to solvents. They are, however, useful for applications that require the metal to remain flexible, and they do fair decently well to the outside elements.
• Heat-cured solvent inks. Heat-cured solvent inks require a baking process that allows the ink to form a secure bond. This category of inks includes epoxies, enamels, polyesters and modified acrylics. Because of the chemical reactions they undergo, heat-cured inks are much more resistant to scuffing and solvents, but the cured ink will be much less flexible on the finished product than air-dried solvent inks.
• UV inks. UV inks are less popular for screen printing on metal, but they do have a growing fan base. UV inks do undergo a chemical bonding process and, thus, tend to be resistant to wear and solvents. The primary problem faced by printing with UV inks on metal substrates is that many UV prints will shrink on the metal surface as they cure, which interferes with adhesion and can result in the print popping off of the substrate.

When choosing which ink to use with metal substrates — air-dried solvent ink, heat-cured solvent ink or UV ink — there is no one right or wrong choice. Your ink choice ultimately will depend on the metal substrate you’ve chosen for the job.

Meeting with Demands of Your Product Requirements

Successfully screen printing on metal substrates depends on knowing what requirements your product will have to meet, so you know which type of metal and which type of ink you should be using for the job. You need to know if it has to be hard and durable, or softer and more flexible, as well as whether it needs to be scratch and solvent resistant. While thermoset-coated metals are more commonly used in screen printing, a job that requires a less durable application might allow you to choose easier-to-print-on thermoplastic coated metals. The type of metal, along with the flexibility and durability requirements, will help you to select the right ink for the job.

In the end, most screen printers who work with metal substrates end up using a range of metal materials and a range of ink to meet their clients’ needs. Succeeding in making metal substrates a part of your screen printing business means understanding the different types metals, and the different types of inks to use on those metals, so you can choose the right materials for a successful screen printing job.