Rubber products may sometimes turn white on the surface after being stored for a period of time, which is commonly known as frosting. Why is that?
I. Blooming Phenomenon Definition
| Item | Description |
|---|---|
| Essence | Migration and precipitation of liquid/solid compounding ingredients from rubber interior to surface |
| Appearance | Whitening on rubber product surface, often accompanied by aging performance degradation |
| Impact | • Compromises product aesthetics • Reduces product cleanliness • May deteriorate mechanical properties |
II. Five Major Causes of Blooming & Typical Cases
1. Improper Formula Design (Intrinsic Material Factors)
| Bloom Type | Mechanism | Common Ingredients |
|---|---|---|
| Saturation bloom | Dosage exceeds solubility limit | Sulfur, accelerators, ZnO |
| Migration-induced bloom | High molecular mobility | Processing oils, migratory antioxidants |
| Reaction-induced bloom | Insoluble byproducts from additive reactions | Accelerator reaction products |
| Stress-induced bloom | Poor filler-rubber compatibility | CaCO₃, clay |
| Reaction residue bloom | Low-MW residues in peroxide systems | DCP decomposition byproducts |
2. Process Operation Errors (Procedural Failures)
| Stage | Specific Error | Consequence |
|---|---|---|
| Mixing | Poor dispersion / Excessive temperature | Local concentration超标 |
| Weighing | Over/under/mis-weighing | Formula imbalance |
| Curing | Temperature too low or time insufficient | Under-cure → Unreacted ingredients |
| Post-processing | Excessive mold release agent spraying | Surface white spots |
III. Systematic Preventive Measures
(1) Formula Design Optimization
| Strategy | Implementation | Effect |
|---|---|---|
| Additive blending | Antioxidant RD+4020 (total ↓30%) | Suppresses single-component oversaturation |
| Migration inhibition | Add 5-10 phr factice/recycled rubber | Adsorbs easily precipitated molecules |
| Solubility control | Sulfur ≤1.8phr, Accelerators total <1.2phr | Ensures safe solubility range |
(2) Precision Process Control
IV. Blooming Diagnosis Flow
Suggest using Fourier transform infrared spectroscopy (FTIR) to identify the composition of the spray material and develop targeted solutions.