Time, Temperature and Pressure
We've already learned that dye sublimation is a marriage between art and science. In order to decorate a polyester-based product, the end user needs to introduce three elements to the printed sublimation transfer and the blank product. These three critical elements are
Based on the polyester coating, woven nature of the fabric or the other materials used in the manufacturing process, each sublimation substrate has a recommended dwell time when placing it under your heat press or within a convection oven. The harder a substrate's sublimation coating, the longer it will take to sublimate. Whereas you can decorate a t-shirt in 35 to 50 seconds, a large ceramic tile might take 12 minutes. Other factors contribute to dwell time, too. The condition of your heat press equipment, different paper types, the amount of ink saturation, and even altitude can affect the ideal transfer time. To determine the optimum results based on your conditions and equipment, you will often have to experiment with dwell times when you're starting out. Dealers usually sell test pieces of sublimation products, and you can always go to a fabric shop to purchase a quantity of 100% polyester fabric for testing purposes. Always check with your dealer or the manufacturer to determine the recommended dwell times, and use this as a starting place. If the image looks too light, try increasing the dwell time by five or ten seconds. If the image looks blurry, you might be leaving it under heat for too long.
The temperature at which you press your product is critical for the sublimation process to occur. Typically, the sublimation industry uses 400 degrees as a benchmark. That being said, it is not unusual for some product manufacturers to recommend a reduced temperature coupled with a longer dwell time based on their product. For example, while you can transfer an image to polyester fabric in 35 seconds at 400 degrees, Vapor Apparel recommends 390 degrees and 50 seconds for their apparel to reduce press and achieve optimum results. Some sublimation films and other thin, soft products might have you drop the temperature as low as 350 degrees based on a lower melting point of the product. Again, always check with your distributor and the manufacturer to determine recommended temperature settings.
How tightly you close the heat press on a product or ratchet a wrap around a ceramic mug determines pressure. For the most part, sublimation requires medium pressure for most products. While this might not sound as scientific as the other factors, it means exactly that: not too much, not too little.
So, how do you determine what equates to medium pressure? With a manual, flat heat press, an easy way to determine medium is to loosen the pressure on the press to where there is very little contact with the product after closing. Then, tighten the pressure as much as you can by hand. This usually works best from a cold state or using an extra substrate on hand.
With a pneumatic press, medium equates to about 30 - 40 psi (pounds per square inch). With some substrates, such as tiles, you might want to lighten the pressure a little bit to avoid breaking the product.
More than anything, determining the best dwell times, press temperature and pressure is a matter of practicing. Each heat press operates a little differently, so it's a matter of determining what works best for you. Order some substrate test pieces from your dealer or buy some polyester fabric, and keep practicing! Once you get time, temperature and pressure dialed in, it's a matter of consistently following the same rules down the line.