Multi-Layer Co-extrusion Film Structures (PA/PE, PET/AL/PE)
Material selection depends on product sensitivity and required shelf life:
PA/PE (Polyamide/Polyethylene): Typically structured as 7- to 9-layer co-extruded or laminated films (e.g., PA/Tie/PE). Polyamide provides puncture resistance and mechanical toughness during vacuum extraction and brick-forming mold compression. Polyethylene serves as the internal heat-seal layer. Ideal for grain processing, pet food, and standard agricultural exports.
PET/AL/PE (Polyethylene Terephthalate/Aluminum Foil/Polyethylene): Designed for stringent barrier protection. The continuous aluminum foil core yields an Oxygen Transmission Rate (OTR) approach <0.1 cm³/m²·24h·atm and Water Vapor Transmission Rate (WVTR) <0.1 g/m²·24h. Recommended for moisture-sensitive chemicals, hygroscopic additives, and long-haul overseas shipping.
Puncture Resistance and High-Barrier Property Requirements
During the compaction phase of brick vacuum packers, mechanical vacuum jaws compress granular material into rigid geometric blocks. Sharp-edged grains (such as long-grain milled rice or sharp mineral litter) exert localized point stresses exceeding 15–20 MPa against the bag walls.
To eliminate pinholing and corner stress cracking during mold formation, films must exhibit a ASTM D5748 puncture resistance rating of ≥25 N. High gas barriers (OTR <1.5 cm³/m²·24h·atm for PA/PE structures) prevent ambient oxygen ingress, suppressing lipid oxidation in pet foods and preventing aerobic microbial growth in stored grains.
Production Flexibility Advantages for Contract Manufacturers (OEM/ODM)
Matching film thickness to product density and particle sharpness directly reduces seal failure and vacuum loss:
| Product Category | Particle Geometry | Recommended Thickness | Primary Failure Mode Addressed |
| Smooth Grains (Rice, Pulses) | Rounded / Sub-angular | 100 µm – 120 µm (4.0–4.7 mil) | Corner abrasion during pallet stacking |
| Aggressive Granules (Cat Litter, Pellets) | Sharp / Irregular | 130 µm – 160 µm (5.1–6.3 mil) | Point puncture under mold compression |
| Heavy Industrial Chemicals / Minerals | Coarse / High-density | 160 µm – 200 µm (6.3–7.8 mil) | Flex-cracking and burst under drop test |
Thermal Sealing Window Optimization
A reliable brick shape vacuum packing machine demands a broad thermal sealing window (typically 140°C–180°C) to maintain seal strength (≥35 N/15mm per ASTM F88) without thermal degradation. Dust contamination from powdered products or fine grain dust within the seal area can cause channel leaks. Incorporating Linear Low-Density Polyethylene (LLDPE) or metallocene-PE (mPE) as the sealant layer ensures sealability through contamination and provides hot-tack strength capable of holding the brick structure immediately upon mold release.
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