Synthetic papers, most often based on polypropylene, sit somewhere between paper and film. They look and handle like a heavy paper, but they resist tearing and are not weakened by water. That makes them popular for roll-up banners, short-term outdoor posters, menus, tags and educational materials that get handled a lot.
Many customers coat synthetic prints because the substrate is water-resistant but the ink on it may not be, particularly with aqueous inks. A coating can extend that resistance to the printed surface, and add protection against scuffing and fading.
The substrate question
Polypropylene is a plastic, and some plastics can be affected by solvents. Most synthetic papers are also surface-treated or coated to accept ink, and that top layer is what a coating touches first. Possible problems include:
- curl or waviness as the coating dries, especially on thinner grades;
- a change in the surface feel or a slight tackiness;
- poor adhesion of the coating to unprinted areas;
- changes to the ink, such as softening or a shift in colour.
None of this is certain to happen, and many synthetic papers coat perfectly well, but results do vary between brands and between grades from the same maker.
Matching ink and media
Synthetic papers are sold for particular ink types: some for pigment and dye aqueous printers, others for eco-solvent, latex or UV. Use the grade made for your printer. A print on the wrong grade may look acceptable but have weak ink adhesion, which a coating will expose rather than fix. Our pages on pigment inks and eco-solvent inks cover ink-side points.
How we would test it
- Print a strip with heavy colour and some bare media, and let it dry fully.
- Coat it with the method you would use in production.
- Leave it flat, then check for curl, tack and adhesion once dry.
- Roll and unroll it a few times if it is destined for a roll-up stand, and fold a corner to check for cracking.
- Wipe it with water and a mild cleaner to confirm the protection you are offering.
For posters and short-term outdoor use, our page on moisture protection explains what a coating can and cannot do against rain and condensation.
If you are switching synthetic paper suppliers or starting a new type of job, we would happily discuss your test results. Call 01252 624 411 or use the contact form.