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Scorching refers to the phenomenon where compounding agents in rubber products—such as sulfur, accelerators, antioxidants, plasticizers, zinc oxide, and others—exceed their solubility limit within the base rubber. Alternatively, these agents may migrate to the surface of the product over time due to mechanisms like migration or phase separation, gradually forming a white, frost-like deposit on the material's surface.

I. The main hazards include:
●Affecting appearance: White spots, bluish tints, color iridescence, or gray haze appearing on the product surface are considered quality defects.
●Performance Degradation: Bloom (Sulfur, Accelerators): This leads to inconsistent vulcanization levels between the surface and interior of the rubber compound, resulting in under-vulcanization or localized over-vulcanization, thereby reducing physical and mechanical properties such as tensile strength, elongation, and abrasion resistance.
● Blooming (antioxidant): After surface migration, the internal antioxidant concentration decreases, weakening the product's resistance to aging.
● Blooming (e.g., plasticizers): Affects surface adhesion performance, creating difficulties in subsequent processes such as coating, bonding, and printing.
●Increased risk of failure: For dynamically used components (such as tires and seals), blooming substances may become stress concentration points or sources of contamination, leading to premature failure.

II. Mechanism behind blooming:
The essence of frosting is the result of the combined effects of thermodynamic dissolution-precipitation equilibrium and kinetic migration rates. Its primary causes can be attributed to two key factors:
●Supersaturation in dissolution (formulation issue): In the formulation, the amount of a certain compounding agent exceeds its maximum solubility in the specific rubber matrix. As the temperature drops, solubility decreases, leading to supersaturation and subsequent precipitation.
●Migration and Exudation (Process/Storage Issues): Even with a properly formulated recipe, under conditions such as insufficient vulcanization, excessively high vulcanization temperature, prolonged curing time, or significant temperature fluctuations in the storage environment, compounding agents are more likely to migrate to the surface due to enhanced molecular thermal motion.

III. Formulation Design: How to Add Anti-Frosting Additives and Select Materials

This is the most fundamental and effective method to address the blooming issue. The core idea is: enhance the solubility of the compounding agent, slow down its migration rate, or opt for a more compatible alternative.

1. Use a dispersant:
●Mechanism of action: These additives can reduce the interfacial tension between the rubber phase and the compounding agent phase, promoting the uniform dispersion of compounding agents (especially fillers and powdered additives) within the rubber compound. This helps prevent localized areas of excessive concentration while also enhancing compatibility to a certain extent.
● Addition method: Typically added at the early stage of mixing, along with raw rubber and fillers, in an amount generally ranging from 1 to 3 phr.

2. Use high-molecular-weight or composite additives:
●Mechanism of action: Traditional small-molecule additives (such as accelerator M, DM, and antioxidant RD) have low molecular weights and migrate rapidly. Switching to high-molecular-weight or polymeric additives can significantly reduce their migratory behavior.
●Accelerator: Replace regular sulfur with insoluble sulfur (IS), which is less likely to migrate within the rubber compound. Additionally, use high-molecular-weight accelerators such as TBzTD instead of easily frosting formulations like TMTD.
●Antioxidants: Replace small-molecule antioxidants (such as Antioxidant A and D) with polymer-based antioxidants (like Antioxidant HP).
● Plasticizer: Choose a plasticizer with polarity similar to the main resin type and a higher molecular weight (e.g., use TP-95 instead of DOP).

3. Optimize the vulcanization system:
● Mechanism of action: Design a balanced and efficient vulcanization system that ensures the complete consumption of vulcanizing agents and accelerators during the reaction, thereby minimizing free residues.
Replace the traditional conventional vulcanization system (CV)—which uses a high amount of sulfur and is more prone to blooming—with either the "Semi-EV" or "EV" vulcanization systems, both of which offer improved performance.
● Primarily use post-curing accelerators (such as CBS) combined with a small amount of high-efficiency accelerators to ensure processing safety while minimizing blooming.
● Precisely calculate and control the ratio of sulfur to accelerator.

IV. Post-Processing: Methods for Defrosting and Frost-Inhibiting Treated Products That Have Been Sprayed with Frosting Agents
For products that have already experienced frosting, the common treatment methods are primarily physical removal and chemical inhibition—but these approaches often address only the symptoms rather than the root cause.

1. Physical Defrosting Method:
●Solvent wiping: Wipe the surface with solvents such as alcohol, acetone, or gasoline. Note: Always choose a solvent that will not cause swelling or damage to rubber products, and first test it on a small, inconspicuous area. While this method effectively removes surface deposits, it cannot prevent further frosting from occurring internally.

2. Chemical Anti-Frost/Post-Treatment Method:
●Isolation Coating: Apply a specialized isolating agent or protective varnish onto the thoroughly cleaned surface. This film physically blocks internal additives from migrating outward, while also preventing oxygen and ozone from the air from penetrating. For instance, tire surfaces are sometimes sprayed with a layer of protective wax.
● Heat Treatment (Re-refining/Baking): Place the products that have already exhibited frosting into an oven set at a temperature slightly below the vulcanization temperature (e.g., 60–80°C) for short-term baking. This method can sometimes help re-diffuse the surface frosting back into the rubber, but its effectiveness is limited and may even accelerate further aging—thus, it should be used with caution.
●Vulcanization Remediation: If the primary cause of blooming is identified as insufficient sulfur, the product can be returned to the vulcanization tank for a secondary curing process, allowing the remaining sulfur and accelerators to fully react. However, this may alter the product's physical properties.

V. Summary and Recommendations:
Addressing the rubber blooming issue is a systematic undertaking that should follow the principle of "prevention first, with treatment playing a supporting role."
The primary task is to conduct scientific formulation design, leveraging high-molecular-weight additives, uniformizers, and a balanced vulcanization system to fundamentally enhance the compatibility and stability of the system.
Secondly, strictly control the process conditions throughout the entire procedure—including mixing, vulcanization, and storage—to ensure uniform dispersion of compounding agents, thorough vulcanization, and stable environmental conditions.
For products that have experienced frosting, the composition of the frosting material and its root cause should first be analyzed. Then, depending on the situation, post-treatment methods such as physical cleaning or coating protection can be selectively applied, followed by an evaluation of their impact on the product's final performance.