If you’re looking into doing multi-color silkscreened heat transfers, it is important to first understand how a one color transfer works. Follow this link to our blog to get more information: http://www.ryonetblog.com/screen-printing-plastisol-heat-tranfers/
Doing heat transfers can be tricky by themselves, because you have two curing points- the gel cure and the final press. When you throw in multiple colors, it can become more difficult, depending on the type of image you’re doing.
Best case scenario is that you’re printing multiple colors that do not touch. This means no underbasing and none of the colors touching side by side. This is best case because you can print the colors wet on wet without adding an additional flash, then add the adhesion powder and gel cure. This would be the exact same process as the single color, heat transfers.
Your second option is to flash in between colors. This is not ideal because this is going to require some testing on your part. There are 2 different multi-color transfers you can do- those that require and underbase, and those that are side by side (which may include an underbase).
Underbasing is tricky. White ink has a tendency to spread when you print it directly onto a garment, so what’s going to happen if you heat press it? It’s going to spread even more. Consider this- you would print your top coat color, then your white (reverse from direct print) and when you go to heat press, you are literally squishing the white down between the garment and the paper. This will cause the underbase to flatten out and spread even further. What does this mean for your artwork? It means you will have to play with either choking or spreading until you really have it down so the white doesn’t poke out around the edges of the design. An alternative would be to have the white come out around the design as an intentional outline of the graphic. This will take testing on your part to figure out the appropriate choke or spread, or whether it would be best to just keep the outline. When flashing the first color, prior to adding the underbase, you want to flash at the lowest temp possible to allow the ink to be dry to the touch- you do not want to flash like you would on a garment.
Top Coat Colors:
Printing more than one color and having them touch, introduces an additional curing step, which can cause more issues. If you were to over cure prior to the final press, the adhesive will not work properly. Additionally, if you were to under cure to avoid over curing, then you would run into the same issue. How do you avoid this? It depends on who you ask. Some printers may recommend making each color of ink thicker than others so that it would require longer curing, which would avoid over curing. So say you had a red and blue print. If red is your first color, you would print that thicker than the blue so that it could go through 2 flashes without fully curing. If you added green after the blue, then you would print red thicker than blue and blue thicker than green. Again, you want to do the lowest flash temp possible.
Other printers may recommend that you trap the colors in black, printing wet on wet, that way if there is any smearing, the black trap will cover it up.
Silkscreened heat transfers are an art to be mastered. They take a lot of practice, trial and error to really dial in your process and to get correct, consistent results. Transfers are a challenge. Printers who take the time to really hone their skills in this area, have created a niche for themselves- not very many printers want to hassle with this and will often outsource their transfers.