Silicone Emulsion for Mold Release: Tire, Rubber, Foundry, and Fiberglass

Spraying neat release fluid on a high-volume rubber line gets expensive fast, and solvent-cut release brings flash-off fumes and a fire-watch mentality to a shop that mostly wants parts out of molds. That is the slot a water-based silicone emulsion fills. You buy concentrated silicone, dilute it into plain water at the plant, and spray, dip, or brush it onto tooling all day without a solvent in the building.

The short version: a silicone emulsion for mold release is polydimethylsiloxane (PDMS, CAS 63148-62-9) pre-dispersed in water as an oil-in-water concentrate, typically at a nominal 60% solids (RawSource’s silicone emulsion, RS-EM 350/60 and RS-EM 1000/60, runs a typical 63%). Diluted into cold water, it lays a thin PDMS film on the tool so tire, rubber, foundry, plastics, and fiberglass parts strip cleanly. It earns its place on high-volume tooling; its costs are a water flash-off step, freeze-sensitive storage, and the silicone-transfer caveat every PDMS release carries.

Why an emulsion instead of neat fluid?

The chemistry doing the releasing is identical: PDMS, the same low-surface-energy silicone covered in our silicone mold release selection guide. What the emulsion changes is the economics and the handling. One drum of 63%-solids concentrate becomes ten or twenty drums of working release once diluted, so cost per sprayed tool drops sharply on high-throughput lines. Water is the carrier. There is no solvent flash-off, no flammable-carrier storage, and rinse-downs are ordinary housekeeping.

The trade runs the other way on precision. A neat fluid gives tighter film control and skips the drying step, which is why low-volume, high-spec tooling often stays with neat Silicone Oil 350 cSt or Silicone Oil 1,000 cSt grades. If your line is compounding rubber around the clock, the emulsion usually wins; if you mold twenty critical parts a day, neat fluid may still be the better buy.

Matching the emulsion to the process

The TDS scope for the RS-EM grades reads like a tour of hot-tooling industries: foundries, rubber, and plastics, with fiberglass and glove manufacture alongside.

The single recommendation that holds across all six rows: qualify on your own tooling at your own temperatures before committing a grade, because film behavior at your cycle time is what decides release, transfer, and finish.

Dilution practice that keeps the emulsion stable

Dilution is where water-based release programs succeed or quietly fail. The RS-EM practice, straight from the technical data sheet, is short:

• Use cold water. Cold water is the best diluent for this emulsion; hot water works against stability.
• Pre-dilute under low shear. Add the concentrate to the dilution water with gentle stirring. High-shear mixing can damage the droplet structure you paid for.
• Check hardness. The non-ionic emulsifier system tolerates water up to roughly 200 ppm hardness. Harder supply than that, and you should be qualifying softened or deionized water instead.
• Agitate before use. Give standing dilutions a gentle stir before each shift.
• Apply thin (brush, dip, or spray). Excess release causes surface irregularities on the molded part, and over-application is the classic route to fouled tooling and a mechanical cleanout.

How far to dilute is process-dependent, so treat supplier ratios as starting points, not answers. As one grounded reference, polyurethane-foam tooling typically runs a release emulsion or solution at about 0.5 to 2% solids. The arithmetic for converting dilution ratios into delivered solids is in our companion piece, what a 60% silicone emulsion is and how to dilute one.

Storage, shelf life, and the freeze problem

An emulsion is a structure, and structures can be wrecked in the warehouse as easily as in the mix tank. The RS-EM grades store at 5–32 °C, should never sit above 38 °C, and must not be frozen — a hard freeze can break the emulsion irreversibly. Shelf life is 12 months from manufacture in the original container. If your release totes overwinter on an unheated dock, that, and not the chemistry, will be the failure mode. Plan storage before the first drum arrives, and rotate stock first-in, first-out against the 12-month clock.

The honest trade-offs

Two limits deserve equal billing with the benefits. First, silicone transfer: every PDMS release, emulsion or neat, leaves some silicone on the part, and trace PDMS fisheyes paint and kills adhesive bonds. Parts headed for painting, printing, plating, or structural bonding usually belong with a silicone-free release, and silicone should stay physically segregated from paint and bond lines. The full mechanism is in the selection guide.

Second, water must leave before molding. The sprayed film needs to flash dry, on hot tooling that is seconds, on cold tooling it is a real cycle-time line item. Where a molded part will contact food, release selection also becomes a regulatory question: FDA’s 21 CFR 175.300 recognizes dimethylpolysiloxane release agents at not less than 300 cSt in that context. The RS-EM grades are sold for industrial use, and no food-contact suitability is asserted here; confirm any regulated use against the regulation and your own qualification.

Buying silicone emulsion for release work

RawSource stocks silicone emulsion in two grades from US stock: RS-EM 350/60 on a 350 cSt base fluid, the general-purpose release workhorse, and RS-EM 1000/60 on a 1,000 cSt base for a heavier, longer-riding film, both non-ionic at a typical 63% solids, supplied in drums and totes with a batch Certificate of Analysis (CoA) and the full Safety Data Sheet (SDS) on request. For industrial manufacturing molders, tell us your process, tooling temperature, water hardness, and whether parts see downstream finishing, and request a sample to qualify release and transfer on your own tool.

Frequently asked questions

What is a silicone emulsion mold release?

It is polydimethylsiloxane (PDMS) supplied as a water-dilutable oil-in-water concentrate, typically in the 60% solids class. Diluted into cold water and applied by brush, dip, or spray, it deposits a thin low-surface-energy PDMS film on the mold so rubber, plastic, foundry, and fiberglass parts release cleanly.

How do I dilute a silicone emulsion for mold release?

Pre-dilute the concentrate into cold water under low shear, keep the dilution water below roughly 200 ppm hardness, and agitate before use. Start at high dilution and step the solids up only if parts begin to drag; excess film causes surface defects and mold fouling. End-use levels are process-dependent; polyurethane-foam tooling, for example, typically runs about 0.5 to 2% solids.

Which grade should I use: a 350 cSt or a 1,000 cSt base emulsion?

RS-EM 350/60 (350 cSt base fluid) spreads fast into a thin, even film and is the usual starting point for general rubber, plastics, and fiberglass release. RS-EM 1000/60 (1,000 cSt base) leaves a heavier film that survives more releases per application and holds better on hot or vertical surfaces. Qualify both on your own tooling if release count per coat is the deciding metric.

Can a silicone emulsion freeze?

Freezing is the main storage risk. The RS-EM grades store at 5–32 °C and must not be frozen; a hard freeze can break the emulsion irreversibly. Shelf life is 12 months from manufacture in the original container.

Will silicone emulsion release contaminate painted parts?

Yes: the same silicone-transfer caveat as every PDMS release. Trace silicone on a part causes fisheyes in paint and failed adhesive bonds. Use a silicone-free release for parts that will be painted, printed, or bonded, and keep silicone segregated from finishing areas.

Editorial note. This article is general technical guidance for molders, processors, and purchasing teams. Property values (solids content, hardness tolerance, storage range, shelf life) are typical values for the grades described, not guaranteed specifications; the Certificate of Analysis governs the lot you buy. Release performance, dilution level, transfer, and finishing compatibility depend on your compound, tool, temperature, and cycle, and must be validated on your own system. Products are sold for industrial and professional use only; the glove application discussed is a manufacturing-process release aid, and no medical or food-contact suitability is asserted or implied. Always consult the current Safety Data Sheet (SDS) before handling, and confirm regulatory status for your application and jurisdiction. RawSource makes no warranty, express or implied, and assumes no liability for use of this information.