3D printing offers unparalleled accuracy and complexity for creating master models, making it the ideal rapid prototyping tool for mold making. However, for those using UV-cured resins in stereolithography (SLA), digital light processing (DLP) or masked stereolithography (MSLA or LCD-type) printers, there is a major chemical hurdle: platinum cure silicone inhibition.
This issue is notorious for turning an otherwise perfect master model into a disaster zone, resulting in a sticky, gooey mess rather than a fully cured silicone mold. In this article we explain what causes this problem and offer a solution to make platinum silicone moulds with the use of 3D-printed master models.
Image: platinum cured silicone part without inhibition despite the use of a resin 3D-printed master model.
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The Technical Problem: Why Platinum Silicone Won’t Cure
The mold-making material of choice for many professionals is addition-cured (platinum-catalyzed) silicone due to its low shrinkage, dimensional stability, and long mold life. Unfortunately, this type of silicone is extremely sensitive to contaminants, which are found in common 3D-prints resins. If you want to find the solution, scroll down! First more information about the process and problem!
The curing process of platinum cured silicones relies on a chemical reaction where a platinum catalyst facilitates cross-linking between two components (Part A and Part B). Any chemical that bonds with or disturbs this platinum catalyst effectively shuts down the curing process.
The Source of Platinum Cure Inhibition Contaminants
The primary culprits leaching from the 3D-printed part are:
- Leftover Photoinitiators: The most common source of contamination. These compounds, used to kick-start the resin’s polymerization under UV light, can remain unreacted within the surface layers of the print. They are highly reactive with the platinum catalyst.
- Uncured Monomers or oligomers: Any residual liquid resin on the surface is a guaranteed cure inhibitor.
- Sulfur Compounds: Some resins contain sulfur-based accelerators or residuals that are potent platinum poisons.
- Leftover cleaning liquid: After washing a print in cleaning liquid (IPA, ethanol, resin cleaner), any leftover cleaning agent can inhibit platinum cured silicones.
- Dust: This is an easy one to fix, so work in a clean environment!
The result is that any area of the silicone that touches the contaminated surface will remain permanently uncured, making the mold useless.
Solutions: The workflow to a Perfect Platinum cured Silicone Mold with resin 3D-printed master model
When using a 3D-printed master, mold makers must choose between two strategies: changing the silicone to a more forgiving one (Tin-cure silicone with lower properties) or follow the exact preparation workflow of the 3D-printed resin master model as described below.
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The Alternative: Switch to Tin-Cure Silicone
The simplest and most reliable solution to bypass inhibition is to use tin-cured (condensation-cured) silicone. This type of silicone uses a tin catalyst, which is not poisoned by the chemicals in 3D-print resins.
- Pro: Cures reliably every time with minimal prep.
- Con: Tin-cure silicones generally have a shorter shelf life and are less dimensionally stable over time compared to platinum-cure types.
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Preparing the Master: The Platinum Cure Workflow
If the superior properties of platinum silicone are required, the master must be rigorously prepared to reduce the amount of contaminants to a level that it does not inhibit platinum silicone cure. This process involves a four stages:
Choose the right resin
You can follow all the steps below, but if you start with a resin that has too many mono-functional monomers, wrong initiator or other vague additives, it is likely to fail. So the first thing is to start with a good quality resin with low amount of leachables and silicone inhibition elements. From our tests the best one was Liqcreate Rigid Pro.
Aggressive Cleaning
The goal is to remove every trace of surface residue.
- – IPA Wash: Use multiple baths of >90% Isopropyl Alcohol (IPA) to dissolve uncured resin. Make sure to wash the last time in fresh IPA or ethanol to remove as much liquid resin as possible. Then let the part sit on your desk for an hour so the solvent can evaporate. Alternatively use multiple washing cycles with Liqcreate Resin Cleaner.
Image: resin 3D-printed master model made with Liqcreate Rigid Pro. After proper post-processing it can be used with Platinum cured silicones.
Extreme Post-Curing
Another critical step is ensuring the resin is fully polymerized, driving out the last bit of the photoinitiators and making sure that all the oligomers are cured and can’t interfere with the platinum silicone curing.
- – Extended UV Exposure: UV-Cure the print for a 10 minutes immersed in a jar of water. By immersing the part in water, oxygen is (mostly) eliminated at the surface and your surface will be more inert. Then take the p0art out and UV-cure it for 60 minutes at 60°C in a heated UV-curing unit like the Formlabs formcure.
Waiting or heating?
Now you have chosen the right material, post-processed it as good as possible and it can still inhibit platinum silicone curing. The reason is that this platinum silicones are so extremely sensitive. One last step is required to get it to work and that contains waiting. Let the part sit on your desk for 3 days. Then all the remaining washing solvent can get out. If you do not have that time, just place it in an oven for 2 hours at 80°C and it works too!
Good luck with your project! And please do share your projects involving resin 3D-printed master models and platinum cured silicone molds!
Liqcreate Rigid Pro
Liqcreate Rigid Pro is a rigid black photopolymer resin and can be processed on most open DLP, MSLA and laser based 3D-printers operating at a wavelength of 385-405nm. 3D-printed parts from this material exhibit high strength and rigidity. Liqcreate Rigid Pro only requires UV post-curing with heat to reach its optimal strength. This material has excellent features like: high stiffness, durability, high strength and good temperature resistance which makes it ideal for molding, and industrial applications like pulleys, automotive connectors, covers, brackets, housings and demanding engineering parts.
Key benefits |
3D-Printer compatibility |
| · High strength | · Asiga & Nexa3D series |
| · Dimensional stability | · Elegoo & Anycubic series |
| · Good chemical stability | · Phrozen & Creality series |
| · Good temperature resistance | · And many more |
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Rigid Pro
Price range: €103,95 through €592,52 ex. VAT
