TPO-Free Inks and Their Impact on Print Substrates: What You Need to Know

As regulations tighten and sustainability climbs higher on customer priority lists, more ink manufacturers are reformulating to eliminate tripropylene glycol diacrylate (TPO) from UV-curable inks.

For printers, this shift brings benefits — but also questions. And one of the biggest? How do TPO-free inks affect print substrates? Let’s unpack what’s happening, why it matters, and how substrate compatibility plays a critical role in getting the most from TPO-free printing.

What Are TPO-Free Inks — and Why Are They Important?

TPO (tripropylene glycol diacrylate) is a photoinitiator commonly used in UV-curable inks. It helps the ink harden (or cure) quickly when exposed to UV light. However, TPO is being scrutinized for its potential environmental and health risks, especially around skin sensitivity and the presence of substances of very high concern (SVHCs) under EU REACH regulations.

As a result, many print service providers — particularly those working in packaging, interior décor, and healthcare — are demanding TPO-free ink formulations that are safer for people and the planet.

Leading ink manufacturers are responding with new UV-LED ink sets that exclude TPO, offering better compliance with REACH, Swiss Ordinance, and other evolving frameworks.

What This Means for Print Substrates

Switching to TPO-free inks isn’t just a change in chemistry — it’s a change in how inks behave on substrates. And that has real implications for print performance, material compatibility, and final output.

Here’s what printers and material suppliers need to be aware of:

1. Ink Adhesion Can Vary

TPO plays a key role in the curing speed and cross-linking of UV inks. Without it, ink adhesion can behave differently, especially on challenging surfaces like plastics, films, or coated media. Some substrates may require longer curing times or pre-treatment to achieve the same durability.

2. Surface Energy Becomes More Critical

Materials with low surface energy (like certain polypropylenes or polyethylenes) are already tricky to print on. With TPO-free inks, achieving proper wetting and bonding becomes even more dependent on the substrate’s surface characteristics and coatings.

3. Gloss and Texture May Shift

Because curing chemistry changes, print gloss and surface finish may also shift slightly when moving to TPO-free formulations. Some users report more matte results or subtle differences in tactile feel.

4. Material Compatibility Needs Testing

Not all substrates that worked with traditional UV inks will behave identically with TPO-free versions. It’s important to validate key substrates — especially for mission-critical jobs like floor graphics, signage, or rigid panels — before going full scale.

For Substrate Manufacturers: Time to Get Proactive

As more printers adopt TPO-free inks, substrate manufacturers have a crucial role to play. Now is the time to:

• Test and certify materials with TPO-free ink sets

• Update product data sheets to reflect compatibility with evolving ink formulations

• Support printers with guidance on curing settings, surface treatment, and recommended applications

• Collaborate with platforms like Substrate Bank to make this information searchable, transparent, and accessible

Substrates that are proven compatible with TPO-free inks will become more attractive — especially in high-regulation sectors like packaging, healthcare, and décor.

For Printers: Test Early, Print Confidently

If you're planning to switch to TPO-free inks — or if your clients are pushing for more sustainable solutions — be sure to:

• Test your go-to substrates under real production conditions

• Work closely with your material suppliers to confirm compatibility

• Adjust curing settings and ink laydown as needed to optimize results

• Use material libraries like Substrate Bank to find certified, tested alternatives

Conclusion: Safer Inks Require Smarter Substrate Choices

TPO-free inks represent an important step forward for health, safety, and sustainability in digital print. But as with any change in chemistry, the substrate matters more than ever.

Success with TPO-free printing will come from informed testing, open collaboration between printers and suppliers, and access to data that helps everyone make better material choices.

Because at the end of the day, a more sustainable print isn’t just about what’s in the ink — it’s about how it works with the surface beneath it.