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Screen Printing: Production
Proper Use of a Screen-Printing Flash Unit for Apparel Decoration
A properly functioning flash unit is vital to successful screen-printing on T-shirts and other apparel. Photo courtesy of Lawson Screen & Digital Products Inc.
One of the most necessary pieces of screen-printing equipment for any apparel decorator is a good flash cure unit. A flash, also called a spot cure, helps every printing company achieve better screen-printed T-shirts. This is especially true when printing on a dark colored shirt and/or where a white underbase is needed. Since black is the most popular T-shirt color, a flash unit is a necessity for better prints. This screen-printing article will cover the basics of how to properly use your screen-printing flash and spot cure dryer.
First, it is good to know some basic facts about the different types of flash cure units. Flash and spot cure units are designed for use with either manual or automatic printing presses. Most manual flashes produce heat through infrared panels. Flash units optimized for use with an automatic screen-printing press typically use quartz bulbs that produce the heat. The major difference is cost and speed. Infrared spot cure units are typically less expensive but take a little longer to cure.
Here are some how-to tips for getting the most out of your flash unit, whether you are using a manual flash, or one designed for an automatic press.
Vibrant Screen Printing
The best time to incorporate a flash into your print is when screen printing onto a black, or dark colored garment. When screen printing on a dark T-shirt you will need to do an extra step to create a bright and vibrant looking design. The easiest way to achieve vibrant colors on a black shirt is by printing a white underbase and then printing your colors on top, or by doing a print-flash-print technique.
Flashing your white underbase, or first print stoke, helps create a better-looking screen print by “gelling” the plastisol ink. This gelled ink serves as a base for which to print the next color or the same screen again. This second print will deposit the ink on top of the first one and be more vibrant. It is very important not to totally cure your ink when flash curing.
Gel Your Plastisol Ink, Don’t Fully Cure
When you use a flash cure unit to spot cure your T-shirt or garment, it is vital that you just gel the ink. You do not want to fully dry it as you would when running it through a conveyor dryer. If it is fully dry, the next colors you screen print will have a hard time adhering to the underbase layer.
You can judge whether the ink is properly gelled under the flash dryer by touching the print. After the print is under your flash dryer, it should feel a bit tacky, but touching it should not smudge your print. If it feels like this, your print has been properly flashed. You can also measure the surface temperature with a heat gun. Each ink is different, but generally speaking a temperature gun would read somewhere between 240°F – 250°F.
Getting your garment flashed properly is a combination of perfect timing and temperature. The temperature on a flash is often controlled by a temperature knob. If your flash unit does not have one (not all do), raising and lowering the flash unit itself is a way to regulate the amount of heat your garment absorbs. The closer to the screen-printing platen, the higher the temperature and faster you can flash. For manual printing, if you load and print slow, it might be a better idea to set your flash unit a bit higher above your pallets. Be mindful of the type of garment you are printing on. A 100% cotton shirt can handle a hotter flash than a 50/50 or 100% polyester shirt.
Watch Your Screen-Printing Platens
As you get further into a production run, your manual and automatic screen-printing press platens will heat up. The more heat your pallet absorbs, the quicker your flash time will need to be. Some screen printers will preheat their pallets so they can start out with a faster flash.
Wood platens can burn and warp after excessive use, or if you accidently leave your flash over the platen too long. Aluminum or steel pallets absorb heat and can be hot the touch. Adding platen rubber to either wood or aluminum platens helps evenly distribute the heat and helps prevent pallet scorching.
Since flashing causes your platens to heat up, make sure you use the right adhesive for holding down your shirt. Regular T-shirt pallet adhesive can break down when exposed to excessive heat. You want to use a specially designed flash spray adhesive.
Monitor Print Shop Conditions
A strong wind or breeze can affect the temperature of your flash and the amount of heat that goes to the shirt. Many screen-printing shops are not air conditioned and use fans in the summer to stay cool. Having a fan blow across your screen-printing press could reduce the flash temperature that is spot drying your T-shirt. Make sure to adjust as necessary.
Keeping these four screen-printing tips in mind will be a big help to every screen printer who uses a flash curing unit. As with anything, it is best to test a new screen-printing method out before putting it to practice on a big order in your shop.
Taylor Landesman is vice president of Lawson Screen & Digital Products Inc., St. Louis, Mo., a family-owned and operated company. For more information, visit lawsonsp.com, email email@example.com or call (314) 382-9300.
Article updated Nov 7, 2023
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