Post-curing is not an optional upgrade. For a peroxide-cured system it’s the necessary step that drives residual decomposition products out of the network. For a platinum (hydrosilylation) system you can usually skip it. There is only one test — does this cure chemistry leave small-molecule byproducts behind.
The most common reading in an RFQ is “one extra pass for safety.” It is not a reinforcement step; it is the close-out of the first one. The first cure builds the network, the second drives out what should not stay in it. Confuse the two and you get the classic rework ticket: “we post-cured it and the smell is still there.”
First Cure vs Second Cure: Different Purposes Entirely
Post-curing is the step where, once the first cure finishes, you hold the part again at elevated temperature in an oven to drive out residual low-molecular species and let the network stabilize.
Different purpose, different equipment, and the cost they consume isn’t the same thing either. Settle the purpose before you argue about whether to run it.
| Dimension | First cure | Second cure (post-cure) |
|---|---|---|
| Purpose | Build the crosslink network and set the shape | Drive out residual low-molecular species and unconverted curative; stabilize the network |
| Where it happens | Inside the press (under pressure, constrained by the tool) | Inside an oven (atmospheric pressure, no tool constraint) |
| Temperature and time | Depends on compound and wall thickness | Reported typical conditions are near 200 °C with a ~2 h hold (Jiang & Yong, Polymers, 2024) |
| Cost shape | Press hours | Oven hours plus energy plus roughly two days of turnaround |
| If you skip it | No part at all | Residual byproducts stay in the network — odor, blooming, degradation in service |
What Post-Curing Actually Removes
It removes the waste the cure reaction left behind. It doesn’t reinforce anything. That is where the two cure chemistries part company: peroxide curing is free-radical crosslinking, and the curative decomposes into small-molecule byproducts; platinum curing is hydrosilylation, which generates no small-molecule leaving group. One needs a second cure, the other usually doesn’t, and that is the reason.
Harder evidence comes from Fan, Xian, Bian and co-authors, in “Effect of Curing Systems on the Thermal Aging Properties of Silicone Rubber”, Acta Materiae Compositae Sinica, 2024, 41(3): 1259–1269, DOI: 10.13801/j.cnki.fhclxb.20230814.004. They report that the byproducts generated by peroxide curing are strongly acidic, and that it is this residue that drives the performance loss after thermal aging — while the hydrosilylation (platinum) system came out ahead after aging in the same study.
Reported post-cure conditions cluster near 200 °C with roughly a two-hour hold. Jiang and Yong, in Polymers (2024, 16(16), 2304, DOI: 10.3390/polym16162304), ran exactly that schedule on a DBPMH-cured, silica-filled silicone rubber: 170 °C × (t90 + 2 min) for the first cure, then 200 °C × 2 h for the second.
You mostly need to drive out three things:
- Unconverted curative residue — the reaction is not one hundred percent complete when the first cure ends.
- Small-molecule byproducts from curative decomposition — strongly acidic in peroxide systems, and the main driver of high-temperature degradation.
- Low-molecular volatiles and moisture in the system — the main source of odor and blooming.
Platinum vs Peroxide: Which Parts Actually Need It
| Dimension | Platinum (hydrosilylation) | Peroxide |
|---|---|---|
| Is post-cure mandatory | Usually optional | Usually mandatory |
| Mechanistic basis | The reaction generates no small-molecule leaving group | Free-radical crosslinking; decomposition produces small-molecule byproducts (strongly acidic) |
| Post-cure conditions | If run, depends on compound and customer requirement | Near 200 °C with a ~2 h hold |
| If you skip it | Can usually ship directly | Odor, blooming, and performance loss at elevated service temperature |
| Cost | Oven hours and turnaround saved | Oven hours plus energy plus roughly two days of turnaround |
By part type: **any part with a defined odor or residue limit normally needs it — food-contact kitchenware (baking mats, ice trays) and baby articles that go in the mouth (teethers, feeding spoons) are the obvious cases. Purely industrial seals come down to the cure system.**
Skipping post-cure is a real advantage of platinum, but don’t stop at that one line. Platinum catalyst carries a far higher unit price than organic peroxide, and it’s extremely sensitive to contaminants such as sulfur, organotin compounds, and amines — contact can poison it, showing up as a tacky surface or as no cure at all. That’s why, when a platinum system is used, you normally keep mixing, storage, and tooling segregated from peroxide work. It’s one of the hidden costs. The full side-by-side, including the trade-offs, is in why platinum can skip the second cure.
Why the Ramp Has to Be Staged (Especially on Thick Parts)
Post-curing isn’t a matter of dropping parts into a 200 °C oven. The ramp has to be staged, with dwell time between steps. Jump straight to temperature and the skin reaches post-cure temperature while the core has not, so residual volatiles expand with nowhere to go and the part blisters instead. For why thick sections are bound by this more tightly, and for the staged-ramp windows reported for the molding stage, see Why Thick-Section Silicone Parts Are Hard to Make: Wall Thickness, Thermal Gradient, and Cure Synchrony. You still have to settle the oven-stage condition per compound and part geometry.
Four Problems Post-Curing Cannot Fix
Post-curing solves none of the four below. Pinning your hopes on it only buys you two extra days of turnaround.
- Bubbles caused by mold venting design → the first cure seals the gas into the network; post-cure only lets it expand. Causes and countermeasures are in the three bubble types and their countermeasures.
- Entrapped gas and cure asynchrony from abrupt wall-thickness changes → that is a design problem, and changing the drawing works far better than adding a second cure.
- Incoming compound whose volatile content is out of spec to begin with → post-curing is an end-of-line measure; it cannot replace incoming material control.
- Aging and embrittlement from too high a temperature or too long a hold → post-curing is itself a thermal process, and overdoing it degrades the part in the other direction.
We don’t commit to a specific VOC number, and we don’t promise “odorless.” Residual level depends on compound, part geometry, wall thickness, and the limit your target market sets — you have to establish it by third-party testing against that market. For reference, the silicone raw material we use is covered by SGS testing across 12 regulations, with results of compliant or not detected; the reports are issued by a third-party laboratory and commissioned by the raw-material supplier. You can have finished parts tested separately on request.
Three Questions Buyers Ask Most
What temperature and time does post-curing usually use?
Reported typical conditions cluster near 200 °C with roughly a two-hour hold (Jiang & Yong, Polymers, 2024). But those numbers come from one specific compound and part geometry in one study. Change the compound or the wall and you have to confirm them again. Treat them as the start of a negotiation, not as an entry for the process card.
Does a platinum-cured part still need post-curing?
You can usually skip it, for a mechanistic reason: hydrosilylation generates no small-molecule byproducts. If you have an explicit limit on odor or residuals, you can still specify it.
Can post-curing remove silicone odor?
It can reduce it substantially, but it cannot guarantee zero. Odor comes mainly from residual low-molecular volatiles, and post-curing drives them out of the network; if incoming volatile content is out of spec, or the mold venting is wrong, post-curing will not rescue the part.
How to Specify Post-Curing in Your RFQ
This is the item most often left out of an inquiry and most often argued about once production starts. Put these on the drawing or the RFQ form directly:
- Whether post-curing is required (don’t write “handle as usual”)
- The condition: temperature × hold time (state it if you have one; if not, note that the supplier should recommend one for the compound)
- Whether a cure system is specified (platinum or peroxide) — this decides whether post-curing is optional or mandatory
- How odor and residuals will be accepted (is there a target-market limit, is a third-party test report required)
With those four written down, quotes are comparable. Without them, two quotes can look close while one includes a second cure and the other does not.
The whole decision comes down to one question: are there small-molecule byproducts that need to be driven out. If yes, post-curing is a mandatory close-out. If not, it is two days of turnaround and a block of oven hours you don’t have to buy.
See our sampling and trial-molding workflow. Post-curing is not a judgement call made by feel — service temperature and the regulations of your target market narrow it to one answer. Send those two along with the drawing: within 24 hours you get the answers — whether this part needs it, at what temperature and for how long, and which regulatory requirement carries the risk if you skip it.
Shenzhen Lixinyuan Technology Co., Ltd. | Custom silicone OEM/ODM | MOQ 50 pcs | Sampling in 5–7 days | Contact us
References
Process parameters cited here are typical conditions reported in the public literature below, not measurements from our own production; actual runs are validated per your drawing and compound.
Frequently Asked Questions
What is post-curing, and is it mandatory?+
Post-curing means holding the moulded part at temperature in an oven after forming, to drive off peroxide decomposition residues and relieve internal stress. Peroxide systems usually need it; platinum systems mostly do not. Whether to run it depends on material grade and end use, not a blanket rule.
Does post-curing remove silicone odour?+
It reduces odour substantially. Most odour comes from peroxide decomposition products, and post-curing drives those small molecules out. It cannot remove odour inherent to the raw material, nor compensate for a poor formulation or under-cure — in those cases the cycle is wasted effort.
What can post-curing not fix?+
Four things: it cannot improve dimensional accuracy (it relieves stress, it does not reshape), cannot repair under-cure, cannot raise the material performance ceiling, and cannot substitute for regulatory compliance testing of the raw material. Treating it as a cure-all is a common misconception.