Carbon Dual-Cure Patent Holds in Europe

The Carbon dual-cure patent stayed alive in Europe this week. On September 29, 2026, TCT reported that the EPO Board of Appeal kept European Patent No. 3158400 in amended form after a September 24 hearing. Carbon said the broadest claim held and that some dependent claims cut in 2025 came back. For shops, the point is narrow: that patent still covers a light-plus-heat route in Europe, not every dual-cure formula on the shelf.

What's Happening

Sam Davies at TCT Magazine laid out a long procedural path. European Patent No. 3158400 is titled “Methods of producing three-dimensional objects from materials having multiple mechanisms of hardening.” It was granted in 2022. TCT says the filing sits about ten years before that grant. Carbon’s Digital Light Synthesis process uses the idea in production: ultraviolet light sets geometry while the part is printing, and a later thermal reaction is meant to deliver strength, elasticity, durability, and temperature resistance. Carbon describes parts in automotive, healthcare, and consumer products as the use cases. Those property claims are Carbon’s.

After grant, Oxon IP B.V. filed an opposition in 2023 for an unnamed competitor. Third parties had already filed observations in 2019 and 2021. In 2025 the EPO Opposition Division kept the patent, but in amended form, and removed dependent claims. Two appeals followed, dated February 28, 2025, and March 3, 2025. The Board of Appeal examined both on September 24, 2026, and again maintained the patent in amended form. Carbon’s September 28 statement, as reported by TCT, says the broadest claim was upheld, the 2025 opposition result was affirmed, and additional dependent claims that had been removed were restored. TCT notes that pattern suggests at least one of the 2025 appeals was Carbon’s.

Philip DeSimone, Carbon’s CEO, said the decision confirms innovation that is foundational to Carbon’s platform, and that dual-cure chemistry enables end-use products that were difficult or impractical with other 3D printing technologies. That is a party statement, not the Board’s written reasons. TCT names the representatives, including Marks & Clerk. The news piece does not quote a claim chart.

Why the Carbon Dual-Cure Patent Matters for Shops

Single-cure resins are fast and detailed, and they are often brittle or heat-limited once the part leaves the printer. Dual-cure splits the job. One reaction, usually light, locks the shape so the part can be handled. A second reaction, usually heat, builds the network that carries load and temperature. Shops that specify Carbon DLS parts are buying that second step as much as the printer. A European patent that survives opposition tells suppliers the chemistry route is still contested property, not a settled commodity.

The limit is the claim set. An amended patent is not a blanket over every epoxy-acrylate or every desktop resin that happens to see a UV lamp and an oven. Procurement teams should ask which patent, which country, and which amended claims a vendor is pointing at. A U.S. jury fight over filament purge towers, already reported earlier this month, is a different docket. This European result does not decide that case, and it does not tell a desktop user which resin profile to load tonight.

What it does signal is that end-use polymer AM still runs through materials IP. If your part needs a published heat rating, a fatigue number, or a biocompatibility file, the vendor’s cure schedule and its license position both belong in the quote. Geometry files alone do not capture either one.

What the Carbon Dual-Cure Patent Does and Does Not Lock In

Question	What the September 2026 record shows	What it does not show
Which patent?	EP 3158400, methods using materials with more than one hardening mechanism	A new patent granted this week
Who challenged it?	Oxon IP B.V. in 2023, for an unnamed competitor	The competitor’s name or product list
What did the Board do?	Heard appeals on September 24, 2026, and maintained the patent in amended form	The full amended claim text in the news report
What did Carbon say?	On September 28, the broadest claim held and some dependent claims were restored	That every dual-cure resin infringes
Who is affected now?	Teams specifying Carbon-style end-use resin parts in Europe	Desktop FFF users choosing a filament profile

What the Research Says

Kopatz, Unangst, Cook, and Appelhans studied dual-cure epoxy/acrylate resins printed by direct ink writing, not by Carbon’s process (Kopatz et al., 2021). More acrylate lowered the glass transition temperature. After the thermal cure, room-temperature stiffness and strength stayed relatively independent of composition. Ultraviolet settings that produced the highest print quality were not, in most cases, the settings that maximized acrylate conversion. Green strength and final properties are tuned separately. Unconverted acrylate can leave residual monomer. A post-print flood cure fixed flat parts, and is harder inside a complex shape.

Sommer and colleagues printed (meth)acrylates on an LCD printer, then used heat on a bispropargyl ether that rearranges into chromene units (Sommer et al., 2022). After 18 hours at 170°C, 32% of the alkyne groups had converted, and about 74% of that ether had oligomerized or polymerized. They report crosslinking shrinkage below 1% for the prepolymer, and they report LCD printability. Neither paper maps the scope of EP 3158400. Both show why a second cure exists: light builds a shape, and heat is asked to finish properties light alone does not lock in.

Frequently Asked Questions

What is the Carbon dual-cure patent?

European Patent No. 3158400 is titled methods of producing three-dimensional objects from materials having multiple mechanisms of hardening. It was granted in 2022. In Carbon’s process, light sets the shape during printing and a later heat step sets engineering properties. The September 2026 result covers that European patent in amended form.

Did the EPO appeal kill Carbon’s dual-cure claims?

No. The EPO Board of Appeal heard the case on September 24, 2026, and kept the patent in amended form. Carbon said on September 28 that the broadest claim was upheld and that some dependent claims removed in the 2025 opposition were restored. That account is Carbon’s, as reported by TCT.

Does EP 3158400 cover every dual-cure resin?

No. The decision concerns European Patent No. 3158400 as maintained after appeal, not every light-plus-heat resin in the literature. Academic dual-cure systems, including epoxy-acrylate and chromene networks, are a research record. They are not a map of what this patent claim set reaches.

Fibricate's Place in This Story

Carbon’s route is an industrial resin platform: a light-defined shape, then a thermal cure. A desktop continuous-fiber printer solves a different problem. The FibreSeeker 3 continuous carbon fiber 3D printer co-extrudes continuous carbon or glass fiber in the bead on a 300×300×245 mm volume, with tensile strength listed up to 900 MPa in Hyper Strength Mode. Strength comes from the fiber path, not from a second oven cure of a photopolymer. A continuous carbon fiber spool is the feedstock for that path. Fibricate does not sell Carbon resins, DLS machines, or a license under EP 3158400. If the part is a specified dual-cure production resin, this European patent is part of the supplier conversation. If the part needs a fiber you can trace through the load, the desktop fiber printer is the relevant tool.

What to Watch Next

The next public document that matters is the Board’s written decision and the final amended claims, not another executive quote. Until that text is easy to read, “upheld” means the patent survived in amended form, which is what both the 2025 opposition and the 2026 appeal already said in outline. Watch whether Carbon or the unnamed opponent describes which dependent claims actually returned. Over the next year, dual-cure will keep showing up in end-use quotes for automotive clips, fixtures, and wearable lattices. Parallel patent fights in other chemistries will keep materials contracts longer than purchase orders. Desktop users can treat this as context. It does not change a filament profile, and it does not turn a hobby resin into an engineering datasheet.

References & Further Reading

1. Kopatz, J. W., Unangst, J., Cook, A. W., & Appelhans, L. N. (2021). Compositional effects on cure kinetics, mechanical properties and printability of dual-cure epoxy/acrylate resins for DIW additive manufacturing. Additive Manufacturing.
2. Sommer, K., Rieger, P., Müller, S. M., Schwarz, R., Trimmel, G., Feuchter, M., & Griesser, T. (2022). 3D Printing of Dual-Cure Networks Based on (Meth)acrylate/Bispropargyl Ether Building Blocks. Advanced Engineering Materials.
3. Foundational Carbon dual-cure patent survives challenge from competitor in Europe after appeal. TCT Magazine. Retrieved September 29, 2026.