Do I need an adhesive additive for polyester garments?

The answer is NO. Plastisol ink will adhere to polyester substrates without the aid of catalysts or additives. Introduction of catalysts or additives will reduce the bleed resistance of the ink. Polyester garments will bleed unless printed with pure bleed resistant inks. Be sure to check the label on the garment before you proceed with the print. Many substrates look similar, but they require different print parameters, so test the garment for dye sublimation.