How heat transfer film is screen printed: layer order from release film to adhesive
A screen-printed heat transfer is built upside down. The design is printed in reverse on a release-coated carrier, colour by colour, and finished with the adhesive that will face the fabric. The layer order, drying and curing decide whether the transfer releases cleanly and lasts on the garment.
The carrier: release-coated film
A release liner is a paper or plastic film coated with a release agent, such as crosslinkable silicone or another low-surface-energy coating, so that the layer on top does not bond to it permanently. Biaxially oriented PET film is used as a liner because it is tough and resists high temperatures.
For heat transfers this matters twice: the film has to stay stable through the dryers between colours, and the printed layers have to let go of it when the transfer is pressed. Agree the film and its release behaviour together with the ink system before sampling.
Printing in reverse, one colour per screen
An iron-on transfer carries its image in reverse, so it reads correctly once it is turned over onto the fabric. The first layer printed on the film therefore becomes the visible top surface on the garment.
In screen printing one colour is printed at a time through its own screen, so a multi-colour design needs several screens in register. Plastisol-type inks, one of the two main types of iron-on transfer ink, give a flexible image with a rubber-like feel.
Backing layer and adhesive come last
Plastisol is particularly useful for opaque graphics on dark fabrics, and screen printers use under-basing on dark garments. On a transfer, a white or blocking layer, when the design needs one, is printed after the colours so that it ends up between the colours and the fabric.
The adhesive is the last layer because it must face the fabric: it melts under the press and bonds the print. It can be a printed adhesive layer or hot-melt powder on wet ink; the separate guide compares the two.
Curing and what to record
Plastisol inks do not dry; they must be cured with heat, in a flash dryer or an oven. Reference figures differ: about 150 °C for many inks and about 180 °C for full curing of most plastisols. Follow the ink supplier's data and confirm it with tests.
Layers printed later must not disturb earlier ones, so decide where each colour is dried before the next is printed. For every approved sample record the film, ink and adhesive system, the mesh for each layer, the dryer settings and the web speed, so repeat orders print the same stack.
Related process and equipment
- Choose a release-coated film that suits the dryer heat and the ink system.
- Print the artwork mirrored; the first layer becomes the top surface.
- Plan colours, backing layer and adhesive as one stack, one screen each.
- Cure to the ink supplier's data and record the settings of each approved lot.
PET heat transfer film printing and adhesive layers · Screen printed plastisol heat transfers · Hot-melt powder or printed adhesive layer: choosing the glue for heat transfers · Multi-colour heat transfer film registration: PET shrinkage, mesh and CCD · LC-6080SYJ-C roll-to-roll CCD screen printer
Frequently asked questions
Why is a heat transfer printed as a mirror image?
Because it is turned over onto the fabric. The image on the carrier is in reverse so that it reads correctly after pressing, and the first layer printed becomes the top surface.
At what temperature is plastisol transfer ink cured?
It depends on the ink. Reference sources give about 150 °C for many plastisol inks and about 180 °C for full curing of most plastisols; use the supplier's data sheet and verify with peel and wash tests.
Technical references
Related process and equipment
Silicone heat transfer labels: layer build-up, cure and adhesion ↗
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Hot peel vs cold peel plastisol transfers: paper, ink and peel timing ↗