**Addressing Smoke and Buildup in High-Temperature Continuous Molding: Should You Increase Viscosity or Switch to a Low-Carbon-Residue Silicone Oil? A Selection Guide for IOTA-28027 and IOTA-255A**


In high-temperature continuous molding, the recurring appearance of smoke and buildup on mold surfaces often leads operators to assume that the silicone oil’s viscosity is too low or that switching to a phenyl-modified silicone oil will solve the problem. However, technical documentation from Anhui IOTA Silicone Oil Co., Ltd. indicates that neither assumption should be treated as a universal rule. While increasing viscosity might reduce the volatilization of low-molecular-weight components, it can also hinder the oil’s ability to spread evenly, potentially causing it to accumulate on the mold surface over successive cycles. Similarly, simply opting for a "phenyl-modified" silicone oil is insufficient; one must distinguish between standard methyl-phenyl silicone oils and specialized alkyl-aralkyl-modified systems designed specifically for low-carbon-residue applications. Without first identifying the root cause of the smoke and buildup, changing the viscosity or the base oil type may merely shift the problem from one stage of the process to another.


**Why Do Smoke and Buildup Occur in High-Temperature Molding?**


Under continuous molding conditions, the actual temperature of the mold surface is often higher than the nominal temperature used during material selection. Low-molecular-weight components or diluent carriers within the silicone oil can volatilize at high temperatures, creating a white mist immediately after application. Prolonged exposure to heat in the presence of air leads to the thermal oxidation of the silicone oil, which manifests as a yellowish-brown residue after continuous operation. Furthermore, if the amount of lubricant applied is excessive, the excess material—which does not participate in the mold-release process—can accumulate on the surface, forming a transparent, oily film. Additionally, substances migrating from the molded material itself—such as plasticizers, oligomers, internal release agents, or filler-treatment agents—can accumulate on the mold. Incompatibilities between existing release-agent layers, residual cleaning agents, and the new molding material can also create deposits that "look like" silicone oil buildup. Because the color of a residue is not a reliable indicator of its chemical origin, it is often necessary to collect and compare samples of the fresh lubricant, the mold residue, and any substances exuded from the molded material. **Can Increasing Viscosity Reduce Smoke?**


While increasing the viscosity of silicone oil may reduce the volatility of certain low-molecular-weight components, it is not a universal solution for continuous high-temperature molding processes. Higher viscosity does not necessarily equate to greater stability under specific high-temperature conditions. Furthermore, high-viscosity silicone oils are more difficult to apply as a uniform, thin layer; excessive local application can actually increase the risk of oil film buildup. If the material does not transfer easily from the mold surface, high viscosity will exacerbate the accumulation of residues over successive cycles. Moreover, if the smoke originates primarily from diluents, spray carriers, or outgassing from the molded material itself, increasing the viscosity of the base oil will have a very limited effect. According to IOTA’s technical documentation, the volatile content of IOTA-28027 (an alkyl-aralkyl polysiloxane) is less than 10% (measured at 150°C for 3 hours). It is specifically designed for high-temperature lubrication, mold release, and low-carbon-residue die-casting applications—data points that are far more meaningful than simply comparing viscosity values.


**Selecting Specific Grades for Low-Carbon-Residue Applications**


IOTA-28027 is an alkyl-aralkyl polysiloxane, distinguished from conventional dimethyl silicone oil by its dual-modified structure featuring long-chain alkyl groups and phenyl groups. The phenyl groups enhance high-temperature resistance and oxidation stability, resulting in minimal carbon residue or sludge formation during high-temperature processing. The long-chain alkyl groups improve adhesion to metal mold surfaces and enhance the load-bearing capacity of the oil film, ensuring that the silicone oil is not entirely stripped away by high-pressure jets or repeated mold-release cycles, while also preventing excessive buildup. IOTA positions this product as a "high-temperature lubricating mold-release silicone oil" and a "specialized low-carbon-residue silicone oil for die-casting." It is available in a range of viscosities (from 600 to 4500 cSt), and parts treated with it can be printed or painted directly, as the product minimizes issues related to silicone oil transfer that could otherwise interfere with downstream coatings. For processes involving yellowish-brown oxidative residues or localized carbon buildup during continuous molding, IOTA-28027 is a prime candidate for evaluation—far more so than a simple, generic switch to a higher-viscosity dimethyl silicone oil. If operating temperatures rise further, or if there is increased exposure to air or more frequent thermal cycling, IOTA-255A—a modified phenyl silicone oil with a high phenyl content—serves as an alternative candidate. According to its published specifications, IOTA-255A features a viscosity of 50–1000 cSt, an open-cup flash point of ≥320°C, and a pour point of ≤-70°C. Its thermal stability is characterized by an ability to remain chemically stable and resistant to oxidative degradation during prolonged exposure to high temperatures. The distinction between IOTA-255A and IOTA-28027 lies in their primary functions: IOTA-28027 is designed for a combination of low carbon residue, effective mold release, and compatibility with organic phases, whereas IOTA-255A focuses on medium stability and low volatility at higher temperature ranges. The choice between them should not be based solely on the presence of phenyl groups; rather, it should be determined through empirical validation, taking into account the actual mold temperature, the extent of air exposure, and the required mold-cleaning cycle.


**Key Operating Parameters for Selection**


Before specifying a viscosity grade or product type, it is essential to determine the following: the actual surface temperature of the mold (including localized peak temperatures); the cumulative duration of heat exposure (whether in continuous or intermittent production); the mold’s exposure to air (e.g., open heating versus localized exhaust); the nature of the molding material and any potential precipitates; and the specific type of mold-release agent used—whether it is a pure silicone oil, an emulsion, or a solvent-based spray. Other critical factors include the application rate, dilution ratio, nozzle distance, and the frequency of re-application. It is also important to distinguish between different types of failure: a white haze appearing immediately after application typically points to volatile components or excessive spray volume; a yellowish-brown residue accumulating during continuous operation suggests thermal oxidation or the buildup of precipitates; and localized black carbonized deposits often indicate the presence of "hot spots" or the repeated thermal degradation of old residue. Furthermore, any subsequent processes—such as painting, printing, or bonding—will dictate the allowable tolerance for the transfer of the mold-release agent onto the molded part. **Design Principles for Comparative Testing**


A practical approach involves maintaining consistent conditions—including the mold, batch of molding material, temperature, and cycle time—while establishing three test groups: the material currently in use, the IOTA-28027 candidate, and the IOTA-255A candidate. Standardize the application amount, spraying distance, and re-application frequency for each run. Record the number of consecutive molding cycles completed before the first appearance of smoke, oil film, or noticeable residue buildup; then, evaluate the ease of demolding, the appearance of the finished parts, and the total number of consecutive cycles achieved before mold cleaning becomes necessary. For products requiring downstream processing, also verify their compatibility with subsequent operations such as painting, printing, or bonding. While public documentation for IOTA-28027 highlights its compatibility with mineral oils and synthetic resins—as well as its suitability for direct printing or painting after demolding—these claims serve only as general product positioning. The final selection should always be based on the results of comparative tests conducted under your facility’s specific operating conditions, including mold temperature, exposure to ambient air, and established mold-cleaning intervals.