How to successfully print dark polyester using DTG printing

Close up showing ink absorption into polyester fabric weave
Close up showing ink absorption into polyester fabric weave

Resolute DTG’s managing director, Colin Marsh, explains how you can successfully print onto dark polyester with the direct to garment printing process.

Printing polyester with DTG, especially dark colours requires a change in the normal print process to get the best results possible.

The ink used for the DTG process, no matter what brand or make of printer is used is pigmented. This means the colours are generated by physical particles not a liquid dye like sublimation. The benefits to this are being able to produce prints onto porous fabrics like cotton and mixed blends where the dye used in the fabric is stable and the pigments remain un-changed in the curing process. Unlike cotton, polyester fabric can release its original dye when re-heated which results in a process called dye migration. In a nutshell your prints are discoloured by the dye mixing with the ink making for a dull faded print. When using DTG to print polyester you can follow a modified process to reduce dye migration and get some pretty amazing results.

Pre-treating polyester

You should use a pre-treatment designed to dry the white ink as quickly as possible, some are specifically designed for this with polyester and in-line printing in mind.

Use approx 30gsm for a 40x50cm print area, curing should be done at low pressure on the shirt with silicone paper in between the shirt and the heat plate. Usually 30 to 40 seconds using 150⁰C should be enough time to dry the pre-treatment without creating a scorch mark.

Once dry you are ready to print.

Hover distance 5mm shown for polyester curing
Hover distance 5mm shown for polyester curing

Printing polyester

Everyone has their own opinion on what is the best method, after many tests on different machines I find the following to give the best results.

Before loading the shirt onto the printer place a sheet of silicone paper inside the shirt to stop any ink bleeding through onto the back. Create a print mode or print queue if using the CADlink RIP, based on printing a coloured (not black) shirt. Change it to have two white passes one based on 720×720 and the other on 1440×720 at 100% opacity.

The first pass will be quite dull but will dry before the second pass hits, this makes for a good receptor for the second pass of white ink. Now allow the CMYK to print on top and usually a single pass of 1440×720 will be sufficient. There are two important points to remember when using this print method:

  1. You are purposely reducing the amount of white ink in the first pass to allow for quick drying and a better surface for the second pass to adhere to which makes it brighter. The same amount of white ink in a single pass will not give comparable results.
  2. Once printed you must not cure the print, it must be left to air dry for at least a couple of hours, the longer the better. Curing can take place the following day if you have the time to leave it that long.

Curing polyester prints

This is one of the few occasions where a tunnel dryer has benefits over a heat press. Any pressure applied to a polyester print is almost guaranteed to reduce the quality of the final image. A heat press can successfully be used when following these guidelines.

Final polyester print after hover curing
Final polyester print after hover curing

Place the shirt on your heat press bed, an automatic hover press will make life much easier at this stage. With the temperature set to 150⁰C set to hover for three minutes. Once done remove and allow to cool, remove the silicone paper from inside the shirt. Now load onto the heat press again and hover for a further 60 seconds, you can gently rest the heat plate on the shirt but if it dulls revert to hovering only. Too much pressure at this stage and it will dull down quickly. Once done your print is ready and should look as bright as the pictures in this article.

As all DTG printers are slightly different you may need to tweak this process to suit your setup.

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