Sticky Uncured Silicone: Mold Inhibition | RUUIPON

If the face that touched the master is still tacky after the posted cure window, and the back of the jacket is a firm rubber, you do not have "silicone that needs another day." You have platinum-cure inhibition. Sulfur clay, latex gloves, some SLA/DLP resins, tin-cure leftovers, and certain amines poison the addition-cure catalyst at the contact face. Washing will not finish it. For a food-contact cavity the skin is scrap. We remake from a sealed, post-cured, or different master.

RUUIPON pours platinum (and, for some craft jobs, tin) RTV tools in Bao'an since 2018: master, box, A/B, vacuum, keys, jacket. LSR or HCR *parts* from steel: wydsilicone.com — heated cavity, often a cold-runner, never a "LIM hot tool" story here.

Does not apply when the *entire* mass is still wet (ratio or expired B side), when you poured tin-cure and expected platinum odor, or when the tack is chocolate fat or resin amine on a fully cured face. Those wipe. Inhibition does not.

Face tacky, jacket cured — that split is the tell

Cavity face gummy; sprue and jacket snap-dry. Cause: the master contaminated the platinum at contact. Classic sources: sulfur-bearing modeling clay, latex gloves used to handle the master, uncured or unsealed SLA, a master that previously sat in a tin-cure mold, condensation-cure residue, and some 3D-print washes that leave an amine film. Confirm: glove up and press a clean tongue depressor on the face vs the back. Face strings; back snaps. A raking light shows a dull, under-crosslinked skin only on the detail. Fix: do not bake "a little longer" and ship it as food. Remake. Tell us what the master was printed or modeled in. We seal or post-cure SLA, or we cut a CNC master when the print chemistry will not quiet down.

Whole pouring is still soft, including the back. Cause: off-ratio mix, B side too old, or the cup sat so long the platinum started and then you poured a dead mix. That is not inhibition. Confirm: durometer on a leftover puck from the same cup. If the puck is also soft, the cup failed. Fix: remake the pour with weighed 1:1 or 10:1. Check shelf life of B. We would not "save" an off-ratio batch with extra catalyst from a different kit.

Face was fine at demold, then went tacky after the first resin pour. Cause: often the *resin* (amine epoxy, some UV oligomers) attacking the surface, not a failed RTV cure. Confirm: a cavity you never poured into is still dry. The used cavity smears. Fix: that is a chemical-compatibility limit. Barrier coat or a different resin, or a recast in a grade we will actually spec for that pour. Don't call it inhibition of the original cure.

Edges of a split mold cure; the core face against a 3D-printed plug stays wet. Cause: the plug is the poison. Keys and jacket saw clean wood or resin; the plug saw SLA. Confirm: swap in a sealed or painted plug on a test cup. Fix: seal the plug (and post-cure the print) before the next RTV. Structure Decision still applies: if the plug is load-bearing, seal it; don't switch to a one-piece glove to dodge the print.

Tin-cure leftover on a platinum recast. Cause: tin salts inhibit platinum. Mixing families on a recast is a shop error we refuse. Confirm: which rubber was the previous skin. Fix: new platinum on a cleaned, sealed master. We would not spec tin for a food cavity to "avoid inhibition."

Typical shop values

Caption: Typical shop values.

The photo that would prove inhibition: cavity face and jacket back in one frame, a stick lifting strings only on the face, master noted on a card.

Worked example (anonymized)

A customer DLP mascot, still smelling of wash, boxed for a platinum 20A gummy skin. Face stayed wet at 24 h; jacket was a clean 20A. They asked us to post-cure the tray. We refused to food-path it. We sealed the master, poured a witness slug, then the production skin. Face cured. CAD already locked, so no $50 3D. MOQ 20 after the clean witness.

One procurement mix-up

"Platinum food grade" on the PO does not mean "pour against whatever STL we mailed." If you supply the master, you also supply its chemistry. A print that inhibits is not a warranty against our rubber. Write who owns the master after the job — tooling charge is not unrestricted ownership.

We would not recommend

We would not recommend putting an inhibited food cavity into service after a soap-and-hope wash.

We would not recommend handling a platinum master with latex gloves.

We would not recommend using sulfur clay "just for the logo" on a food tool.

We would not skip the sealed-master step to hit a date. CAD lock includes a chemically quiet master, not only pretty mm.

flowchart TD
  A[RTV still tacky after cure window] --> B{Jacket / sprue firm?}
  B -->|No, whole mass soft| C[Off-ratio or expired B — remake the mix]
  B -->|Yes, only face strings| D[Inhibition at the master]
  D --> E{Master family?}
  E --> F[Sulfur clay]
  E --> G[Latex glove film]
  E --> H[Unsealed SLA / DLP]
  E --> I[Tin-cure leftover]
  E --> J[Amine wash / some resins]
  F --> K[Rebuild master, no sulfur]
  G --> K2[Nitrile only; solvent wipe]
  H --> L[Post-cure + seal, or CNC master]
  I --> M[New platinum on a cleaned master — do not recast mixed families]
  J --> L
  D --> N{Food-contact face?}
  N -->|Yes| O[Scrap the skin — remake, do not wash-and-ship]
  N -->|Craft only| P[Still remake the face; barrier is a maybe, not a food path]

What to ask when you're buying

• What is the master: CNC, sealed SLA, customer sample, sulfur clay?
• Will the shop refuse latex in the mold room for platinum jobs?
• If a print inhibited a sample, is the skin remake quoted separately from a new master?
• Food vs craft — an inhibited food tool is scrap. Who keeps the master? 21 CFR 177.2600 / LFGB are article tests,.

RFQ copy-pack

[email protected] · +86 135 3006 2969

RUUIPON inhibition / tacky-face RFQ Photo: face + jacket back in one frame Master: CNC / SLA resin name / clay / customer sample Sealed + post-cured? yes / no / unknown Latex used on master? yes / no Previous rubber on that master: none / platinum / tin Food-contact? yes / craft only Market docs: 177.2600 / LFGB / none Qty: remake sample / MOQ 20 CAD: locked / need $50 3D

Matched next step: send the face-and-back photo and the master notes. Remake from a quiet master. We will not post-cure an inhibited food face and call it done. Prototype 3–7 business days after CAD lock, which here includes "master will not poison platinum." MOQ 20 per design.

Related: custom silicone resin molds, custom silicone gummy molds, mold from photos, contact.

FAQ

Can I oven-post-cure a tacky platinum face until it dries? If the jacket is already cured and only the face strings, heat will not finish a poisoned network. Scrap a food skin. Remake.

Do all 3D-printed masters inhibit platinum? No. Plenty of prints are fine after wash, post-cure, and a seal coat. Unsealed, still-smelling DLP is the usual failure. Send the resin name.

Is sticky resin on a used mold the same as inhibition? Usually not. Check a cavity you never poured. If that one is dry, your resin is attacking the surface. Different fix.

Why not switch the food job to tin-cure so inhibition goes away? We would not spec tin for a food-contact cavity. Odor, shrink-in-storage, and the document path all get worse. Seal the master instead.

Does a remake restart MOQ? The failed food sample is not production. After a clean witness, production is still MOQ 20 pieces per design. $50 3D only if we still need CAD scope — a poisonous print sometimes needs a remodel, sometimes only a seal.