“The mold surface turned black, and the parts started sticking!”
An industrial rubber manufacturer encountered severe demolding failure while producing vulcanized products above 180°C. After investigation, the root cause was traced to the release agent base oil: standard methyl silicone oil lacked sufficient thermal stability. Under high temperature, it oxidized, degraded, and even carbonized — forming stubborn residues instead of a clean release layer.
This is not an isolated case.
In high-temperature compression molding applications such as automotive seals, railway vibration pads, and industrial rubber rollers, many users still formulate release agents with low-cost methyl silicone oil, overlooking its thermal decomposition threshold — typically around 200°C.
When mold temperatures continuously exceed 180°C, the silicone molecular chains begin to break down, generating low-molecular-weight volatiles and carbonaceous residues. The result: mold contamination, surface defects on molded parts, and difficulties in secondary processing.
By contrast, phenyl-modified silicone oils or high-phenyl-content silicone resins benefit from the conjugation stability of phenyl groups. Their thermal decomposition temperature can increase to 250–300°C. Even under prolonged high heat, they maintain a dense, smooth release film — enabling truly clean, residue-free demolding.
Test comparison (simulated 200°C × 4h thermal aging):
Standard methyl silicone oil: noticeable black carbonized layer on mold surface; adhesive residue remained even after wiping.
Phenyl-modified silicone oil: transparent, intact film layer; mold surface remained smooth after release; no transfer or contamination on molded parts.
“Not every silicone oil qualifies as a ‘high-temperature release agent,’” an application engineer emphasized. “The key lies in whether the polymer backbone incorporates thermally stable groups such as phenyl or vinyl — and whether it has been validated through high-temperature film-forming tests.”
We recommend upgrading the release agent base oil under the following conditions:
Vulcanization temperature ≥ 180°C
Precision steel or mirror-finish molds
Products requiring secondary processing such as painting, printing, or bonding
As a professional silicone oil supplier, we offer a range of high-temperature release-grade silicone oils and provide thermogravimetric analysis (TGA), high-temperature film evaluation, and on-site trial support to help eliminate carbonization risks at the source.
Demolding is not just about applying a layer of oil —
Choosing the right base oil ensures every high-temperature release is clean and efficient.
