Join "CAT" for a tour of the IOTA Silicone booth | High-temperature continuous molding: When mold smoke and buildup occur, should you increase silicone oil viscosity or switch to methyl-phenyl silicone oil?


Reported by Xiao Mao (Exhibition Correspondent): At the CHINACOAT 2026 Guangzhou exhibition, Xiao Mao visited the IOTA Silicone booth. Technical engineers at the booth addressed a common issue in high-temperature continuous molding—"When mold smoke and buildup occur, should one increase the silicone oil viscosity or switch to methyl-phenyl silicone oil?"—and showcased product options such as IOTA 201, IOTA 250, and IOTA 255 silicone oils.


I. The first question at the booth: It cannot simply be attributed to low viscosity


IOTA technical engineers explained that the appearance of smoke and buildup on high-temperature molds cannot be immediately attributed to the silicone oil viscosity being too low. One must first determine whether the smoke and residue originate from silicone oil volatilization, thermal oxidation, the spray carrier, excessive application, or exudation from the molding material itself. Increasing viscosity might reduce some volatility but could also increase mold residue; while methyl-phenyl silicone oil is a candidate for higher-temperature operations, final validation must consider temperature, air exposure, demolding cycles, and subsequent processing steps.


II. Why do smoke and buildup occur on high-temperature molds?


The actual surface temperature of the mold exceeds the nominal temperature used during material selection.


Low-molecular-weight components, diluent carriers, or atomizing agents volatilize at high temperatures.


Silicone oil undergoes continuous heating in the presence of air, causing gradual changes in its properties.


Excessive material is applied in a single pass, leading to the accumulation of unused material on the mold surface.


Plasticizers, oligomers, filler treatment agents, or other components within the molding material migrate to the mold surface.


Residual cleaning agents, oil stains, or old release layers on the mold are incompatible with the new material.


Instability in the nozzle, spray distance, or atomization pressure causes localized over-application.


III. How can smoke, oily residue, and carbonized deposits be distinguished? Phenomenon | Potential Source | Priority Areas for Inspection
White mist or smoke immediately after spraying | Low-boiling-point carriers, low-molecular-weight components, or overspraying | Volatile composition, mold temperature, spray quantity
Transparent oil film forming on mold surface | Excessive application, insufficient transfer, or accumulation of high-viscosity material | Dosage per application, spray uniformity, demolding cycle
Yellowish-brown residue after continuous operation | Prolonged heat exposure, oxidation, or precipitation of molding material | Air exposure, temperature, source of residue
Localized black charred deposits | Hot spots, repeated heating of old residue, or material decomposition | Mold temperature differentials, mold cleanliness, molding material
Oily surface or contamination on the molded part | Transfer of release agent to the part | Dosage, viscosity, requirements for subsequent coating or bonding
IV. Can increasing silicone oil viscosity reduce smoke?


Increasing viscosity may reduce the volatilization of some low-molecular-weight components, but it is not a universal solution.


Higher viscosity does not necessarily equate to greater stability under all high-temperature conditions.


High-viscosity silicone oil may be more difficult to apply in a uniform, thin layer, increasing the risk of localized overspraying.


If the material does not transfer easily from the mold surface, it may accumulate over successive cycles, forming an oil film or buildup.


If the smoke originates primarily from diluents, spray carriers, or the molding material itself, increasing the base oil viscosity may not be effective.


Regarding the IOTA product range: for dimethyl silicone oils, consider IOTA 201-100, IOTA 201-350, and IOTA 201-1000; for high-temperature release applications, consider IOTA 255 and IOTA 255H. However, the final grade selection should be verified based on actual operating conditions.


V. How should dimethyl silicone oil and methyl phenyl silicone oil be compared? Comparison Criteria | Dimethyl Silicone Oil | Methyl Phenyl Silicone Oil
Basis for Selection | Wide viscosity range; proven track record in spreading and mold release applications | Suitable for operating conditions requiring further evaluation of high-temperature stability
Example Grades | IOTA 201-100, IOTA 201-350, IOTA 201-1000 | IOTA 250-100, IOTA 250-350, IOTA 250-1000
Key Evaluation Points | Viscosity, volatility, spray uniformity, residue | Phenyl content, viscosity, volatility, thermal oxidation, and compatibility
Potential Risks | Volatility and oxidation must be monitored during continuous high-temperature use | Mold release and buildup performance cannot be judged solely by the presence of phenyl groups
Validation Focus | Mold cleaning cycle, product transfer, continuous operation stability | Comparison with the current system regarding release performance, residue, and downstream processing
Public technical data indicates that methyl phenyl silicone oil can offer superior high-temperature stability compared to conventional dimethyl silicone oil; however, the actual usable temperature range depends on specific materials and operating conditions. IOTA field engineers suggest that if the issue is confirmed to stem from the thermal oxidation or high-temperature volatility of the base silicone oil—and the dimethyl silicone oil is nearing its temperature limit—one should prioritize comparing IOTA 250-350 and IOTA 250-1000 against the currently used IOTA 201-350 and IOTA 201-1000. Conversely, if the smoke originates from the diluent carrier or excessive spraying, application conditions should be adjusted first rather than blindly switching the oil type.


VI. What operating conditions need to be confirmed before selecting a product? **Operating Conditions** | **Information to Confirm**
**Mold Temperature** | Actual measured surface temperature, peak local temperature, and temperature fluctuations
**Production Method** | Intermittent vs. continuous production; duration of single-cycle heat exposure vs. cumulative run time
**Air Exposure** | Open heating, local exhaust ventilation, or relatively enclosed environment
**Molding Material** | Rubber, plastic, composite, or other systems and their exudates/by-products
**Release Method** | Pure silicone oil, emulsion, solvent-based, spray, or compounded release agent
**Application Conditions** | Spray quantity, dilution ratio, nozzle type, spray distance, and re-application frequency
**Failure Symptoms** | Smoke, transparent oil film, yellowish-brown residue, charring, or difficult demolding
**Post-processing** | Painting, printing, bonding, electroplating, or direct assembly
**Evaluation Metrics** | Number of release cycles, mold cleaning interval, product appearance, and surface contamination
**VII. How to Design a Comparative Test?**


Keep the mold, molding material batch, production temperature, and molding cycle consistent.


Include the current material, a high-viscosity candidate material, and a methyl-phenyl silicone oil candidate material.


Standardize the application amount per cycle, spray distance, nozzle type, and re-application frequency.


Record the cycle number at which smoke, oil film, and significant buildup first appear.


Compare demolding force (or release quality), product appearance, and mold residue.


Record the number of continuous production cycles achieved before the mold cleaning threshold is reached.


Conduct post-processing verification for products requiring painting, printing, or bonding.


Analyze residues if necessary to distinguish between silicone oil, spray carriers, and molding material exudates.


**Summary Conclusion:** In continuous high-temperature compression molding, mold smoke and buildup issues cannot be solved simply by choosing between "increasing viscosity" or "switching to methyl-phenyl silicone oil." First, diagnose the source of the problem, then conduct comparative verification using grades such as IOTA 201-350/1000, IOTA 250-350/1000, or IOTA 255/255H. Viscosity, phenyl content, spraying method, and mold cleaning intervals must be compared under identical production conditions. CHINACOAT
China International Coatings Show
November 11–13, 2026 | Guangzhou
Visit our booth
Hall 6.1
Booth 6.1D59