In the production and processing of rubber products, scorching is a widespread and significantly harmful technical challenge. “Scorching” refers to the premature partial cross-linking of rubber before the shaping process is complete. This leads to hardening, brittleness, and a decrease in plasticity. It not only severely hinders subsequent molding operations but also directly degrades the appearance and mechanical properties of the final product, drastically increasing scrap rates and production costs while lowering efficiency.
Anti-scorching Agent PVI (Chemical name: N-cyclohexylthiophthalimide, also known as CTP) is a high-performance rubber additive. Through its unique mechanism, it precisely delays the cross-linking process during the initial stages of vulcanization. This provides ample operation time for mixing, molding, and other processing steps, effectively suppressing the scorching phenomenon.
However, realizing the full potential of PVI is not as simple as just adding it to the mix. One must master scientific and standardized usage methods to fully leverage its anti-scorch capabilities, thereby helping enterprises improve product quality stability and production efficiency.
PVI offers strong compatibility and minimal impact on vulcanization characteristics. It is widely applicable to substrates such as Natural Rubber (NR), Styrene-Butadiene Rubber (SBR), and Nitrile Rubber (NBR), covering products ranging from tires and seals to hoses.
To use PVI effectively, strict control is required in the following four areas:
1. Precise Matching of the Rubber System & Preparation
The composition of the rubber system directly affects the efficacy of PVI. Therefore, system matching and preparation must be prioritized.
- System Compatibility: Different rubber varieties have different polarities and structures. For example, polar rubbers like NBR have complex molecular interactions with PVI, requiring adjustments to the addition ratio based on the actual formula.
- Accelerator Balance: In formulas containing fast-curing accelerators (like Accelerator M or DM), the risk of scorching is significantly higher. PVI should be prioritized in these cases to balance the reaction speed and prevent early cross-linking.
- Quality Assurance: Use high-purity products from reputable manufacturers. Inferior products with high impurity content must be avoided to prevent negative impacts on performance.
- Storage Conditions: PVI must be sealed and stored in a dry, ventilated, and cool environment, away from moisture, high temperatures, and direct sunlight. Clumping due to moisture must be avoided, as clumped PVI is difficult to disperse evenly, leading to localized failure of the anti-scorch effect.
2. Scientific Control of Dosage
The dosage of PVI is closely related to scorch safety, curing efficiency, and product performance. It must follow scientific ratio principles.
- Recommended Dosage: According to industry standards and practical experience, the recommended dosage is generally 0.1% to 0.5% of the rubber substrate weight. This should be adjusted based on the specific formula and processing conditions.
- Consequences of Imbalance:
- Insufficient Dosage: The molecules cannot fully cover the active sites of the rubber chains, failing to suppress early cross-linking.
- Excessive Dosage: This will overly delay the cure rate, extending the production cycle. It may also reduce cross-link density, compromising key mechanical properties such as tensile strength, hardness, and abrasion resistance.
- Verification: Before mass production, small-scale lab tests (using a rheometer) are essential to determine the optimal dosage that balances scorch safety with physical properties.
3. Optimal Timing of Addition & Dispersion
The timing of adding PVI determines its dispersion uniformity, which in turn affects the stability of the anti-scorch effect.
- Best Timing: The optimal time to add PVI is during the later stages of mixing.
- Process: First, mix the rubber substrate with reinforcing agents, fillers, softeners, and accelerators. Once these are well-dispersed, add PVI for a short, low-speed mix to ensure it blends quickly and evenly.
- Risks of Incorrect Timing:
- Too Early: PVI may interact prematurely with accelerators, losing its activity.
- Too Late: If added when the rubber viscosity is already high, diffusion becomes difficult, leading to agglomeration (local “hot spots” of poor scorching protection or over-retardation).
- Temperature Control: During mixing, keep the temperature below 100°C. Excessive heat can activate the rubber molecules and trigger vulcanization, rendering the PVI less effective.
4. Synergistic Optimization of Process Parameters
PVI does not work in isolation; it must function in synergy with the entire rubber processing workflow.
- Mixing: Control mixing time strictly. Excessive mixing generates friction heat, increasing scorch risk. Duration should be precise based on equipment power and formula complexity.
- Vulcanization: Strictly follow the design requirements for curing temperature.
- If the temperature is too high, the reaction rate will override PVI’s delaying effect.
- Curing pressure must be uniform; uneven pressure leads to inconsistent curing and potential defects.
- Molding: Adjust processing speeds to match the product structure. Avoid allowing the rubber to dwell in the mold for too long due to a fast-paced feeding rhythm, which can cause local scorching.
Conclusion
The effective use of Anti-scorching Agent PVI is a systematic technical task. It requires a holistic approach that balances rubber system matching, dosage control, timing of addition, and process parameter optimization.
By precisely managing these technical points, manufacturers can fully utilize PVI’s advantages to solve scorching issues. This not only enhances product quality and reduces waste but also optimizes production flows and lowers costs, ultimately strengthening market competitiveness.
Note: Production formulas and equipment vary by company. If you have questions regarding PVI selection, dosage, or application, it is recommended to consult with professional additive manufacturers for customized technical solutions.
Email:info@ctp-pvi-chem.com