What is a dye migration phenomenon?
This phenomenon is widely known, particularly with synthetic fabrics like polyester and fabrics that have been heavily saturated with dye. Because the fibres in synthetic fabric tend to be affected by the heat more than the natural fibres, when the heat is applied to transfer the design (DTF transfer) onto the fabric, the dye in the fabric rises (reactivates) and 'bleeds' into the ink (from the design/DTF transfer).
Troubleshooting for this
1- increase white ink percentage, incrementally, towards 100%. Sometimes 75% is good, or you'll find that 90% is better. Just find a good white proportion by iteration.
2- apply lower heat press temperature but longer press time. For synthetic fabrics we would recommend 120°C - 130°C, and for natural fabric (cotton, linen) around 160°C. And press for between 30-60 seconds longer than usual.
Try different combinations of transfer temperature and time if our recommendation doesn't give you the desired result, as this combination depends on your fabric type and the type of dye and its ink saturation level. When you try lower press temperature and longer time, most of the time the result will look good and there will be no issues with dye migration. But you will need to check the wash fastness, because if you don't transfer it for long enough, there will be insufficient time for your transfer to adhere to the fabric.
3- use DTF black adhesive power as it has built in dye migration blocking agent. Use this powder especially for synthetic fabrics and fabrics you know (from experience) has has had these issues.