Vacuum aluminized film is a key product in the field of vapor-deposited composite films. It is produced by melting and evaporating aluminum wire under high vacuum conditions using high temperatures, allowing the aluminum vapor to condense on the surface of a plastic film, forming a barrier layer approximately 35–40 nm thick. The plastic substrate can be PE, PP, PET, PA, PVC, or similar materials. This type of film offers excellent barrier properties, making it an ideal choice for non-transparent packaging. Aluminized films also exhibit good aroma retention, metallic luster, and aesthetic appeal. However, due to the ductility of metal and limitations in aluminizing technology, the aluminized layer may develop pinholes or cracks when subjected to mechanical stress such as folding or bending, which can compromise its oxygen and moisture barrier performance.
ASTM F392 is a standardized method used to evaluate the resistance of flexible packaging materials to tamping and koji (a process involving mechanical stress). This test simulates real-world conditions during production, processing, and transportation. By measuring changes in the number of pinholes or barrier properties before and after the test, it provides a quantitative basis for assessing the anti-caries performance of packaging materials, supporting practical applications in packaging design and material selection.
**1. Introduction to ASTM F392 Test Method**
The test begins with preparing a sufficient number of samples that meet the standard's requirements. Initial measurements are taken for pinhole count, barrier properties, or other relevant parameters. The samples are then pre-treated according to the standard’s specifications, and the test is conducted under controlled environmental conditions (typically 23°C and 50% RH) using one of five available modes (A, B, C, D, E).
To evaluate the anti-caries performance, two main methods are employed: first, detecting the number of pinholes formed using dyed turpentine; second, comparing the permeability or moisture permeability of the sample before and after the test. Pinholes formed during the test can only be measured using the dyeing method. However, if only one layer of a multi-layer composite is damaged or if certain plastic films are difficult to form pinholes, specialized barrier testing equipment may be required to assess the material’s resistance to cracking. Multiple test modes are available to ensure that the number of pinholes or changes in barrier properties remain within a reasonable range. When evaluating the material’s resistance, the average of multiple samples should be considered to minimize the impact of accidental factors during testing.
**2. Detection Application**
Recently, Labthink Languang Lab (Jinan Languang Electromechanical Technology Co., Ltd.) conducted a comparison test on the anti-caries performance of vacuum-aluminized PET (VMPET, 12μm), PET (20μm), and PE/EVOH/PE (76μm) according to ASTM F392. The B, C, and D test modes were applied, and the results were evaluated based on moisture permeability without physical hole formation. The following data was obtained:
**Rubbing Test Data Sheet**
| Material | Before Test (WVTR) | After D Mode (WVTR) | After C Mode (WVTR) | After B Mode (WVTR) |
|------------------|--------------------|----------------------|----------------------|----------------------|
| VMPET | 1.248 | 18.352 | 22.112 | 30.363 |
| PET | 15.64 | 16.654 | 16.321 | 26.012 |
| PE/EVOH/PE | 5.09 | 5.523 | 5.556 | 5.083 |
*Note: 1. WVTR unit: g/m²·24h. 2. Test average.*
The moisture permeability of vacuum-aluminized PET (VMPET, 12μm), PET (20μm), and PE/EVOH/PE (76μm) falls within the medium to high barrier range. However, their anti-caries performance varies significantly. Among them, the PE/EVOH/PE (76μm) exhibited the best anti-cracking properties, maintaining consistent moisture permeability throughout the test. PET (20μm) showed stable initial moisture permeability but experienced a significant increase after 900 cycles. In contrast, the high-barrier VMPET (12μm) demonstrated poor anti-cracking performance, with moisture permeability increasing by more than ten times even after just a few cycles.
**3. Conclusion**
The anti-caries properties of a material directly influence the stability of its barrier performance throughout the entire supply chain. If the barrier layer degrades due to poor resistance to deformation or tampering, it could lead to product spoilage, resulting in significant losses for both packaging manufacturers and product producers. While aluminum-plastic composite packaging offers strong mechanical and barrier properties, it still faces challenges in terms of resistance to tampering and warping. Although vacuum-aluminized materials have shown improvements in flexibility and toughness, they still exhibit varying levels of anti-caries performance compared to other polymer-based materials. Therefore, testing the resistance to tampering remains an essential step to ensure the safety and quality of packaged products.
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