The majority of orders a screen print shop gets is for black or dark t-shirts. Often, the customers want a bold white or vibrant colors to really pop off the dark colored garment. As a printer, one easy way to get this vibrancy is to flash cure a white underbase. “Flash curing” is also referred to as “spot curing.” Flash curing uses a Flash Dryer to dry just the top of your white ink underbase before printing the desired color on top. You can also spot cure between printing different colored inks when screen printing a multi-color job and are worried about the colors muddling to much. The majority of shops use flash curing so knowing the “How To” is an important screen printing skill.
Flash curing when printing wet ink on top of wet ink allows the base layer of plastisol ink to dry to the touch before printing on top of it. You should be able to lightly touch the ink with no transfer onto your finger. Doing this keeps your second layer from smearing and improves the vibrancy of your color print. Primary, you will flash cure garments when:
- You are screen printing a dark t-shirt with a white underbase. To flash cure plastisol ink properly: Print your white underbase, flash the print, and then print the color on top.
- You are screen printing multiple colors. To flash properly: After printing your plastisol ink wet-on-wet, flash your print, then print your remaining color(s) on top.
The need to flash cure and at what time and temperature to flash vary depending on the ink and type of garment you are printing on. Different t-shirt inks need different times and temps. Not only do you have to take your plastisol ink choice into consideration, but different shirt material reacts differently to heat. For example, cotton and polyester blends are pretty durable when it comes to flash dryer heat. However, t-shirts made out of lycra or tri-blends could have limitations on how much heat they can handle without becoming distorted on-press. Nylon jackets and other wicking or dry-fit material often present the most flashing challenges.
Tips to ensure you are flash drying your t-shirts properly:
Mesh count for your underbase should allow you to print the thinnest layer possible.
Your white underbase is the most important layer to flash cure. It also should be your thinnest layer of ink, which can make it difficult to gel, but not cure.
Preheat your platen and ink. Your platen should be around 145 degrees and the ink should be around 90 degrees. If you properly pre-warm your platen and ink, you will only need to raise the temperature of the underbase another 40 degrees or so.
Time your flashes accordingly. Set your flash cure cycle to begin as soon as your press begins to index and reduce times until the peak of the flash happens right before the platen is under it. This will give you that 40 degree temperature bump needed, and drastically cut down on garment scorching, and over-flashing.
Knowing how to properly flash cure and understanding its advantages and weaknesses helps increase production speed, limit product damage, and give you a better print. Understanding how to flash dry, when to flash and why you are flashing will help improve your screen print quality. Better quality leads to happier customers and repeat business.