The global shift toward a circular economy has put the flexible packaging industry in a difficult spot. For years, the durability and barrier performance of food and medical packaging have relied on complex, multi-material laminates. By combining layers of PET for strength, aluminum foil for gas barriers, and polyethylene for sealing, manufacturers created high-performance materials that were nearly impossible to recycle. Because these different polymers and metals cannot be easily separated in standard recycling streams, most flexible packaging ends up in landfills.
The most effective solution is a “mono-material” structure-a multilayer body where every functional layer comes from the same resin family. However, moving to a 100% polyethylene (PE) structure has historically involved trade-offs. While PE is highly recyclable, it often lacks the heat resistance, piercing strength, and drop-impact durability required for industrial use. A recent development by TOPPAN Holdings, detailed in US12565028B2, offers a practical engineering solution. By combining stretched and unstretched polyethylene films in a specific sequence, the invention achieves a polyethylene content of 90% or more by mass while exceeding the durability of previous mono-material designs.
Balancing Rigidity and Impact Absorption in PE Films
The main innovation in this patent is the finding that different types of polyethylene layers must work together. In typical packaging, the “base layer” is the outer skin, providing the stiffness and heat resistance needed for printing and bag-making. The “intermediate layer” provides extra bulk or barrier support, and the “heat seal layer” allows the package to be fused shut.
The inventors found a specific failure point in existing all-PE designs: when both the base and intermediate layers are made of stretched (oriented) PE films, the material becomes brittle. Under the stress of a drop test, the tightly packed molecular chains in stretched films cannot absorb enough energy, causing the package to burst. Conversely, if all layers are unstretched, the material is too weak and looks cloudy. As shown in Figure 1, this system solves the issue by pairing a stretched polyethylene film with an unstretched polyethylene film.
The mechanical logic is based on polymer physics. The stretched film provides high tensile strength and clarity for the exterior. Meanwhile, the unstretched layer acts as a buffer. Within an unstretched PE film, the molecular structure consists of spherical crystals, called spherulites, connected by “tie molecules”. When a package is dropped, these folded molecular chains can uncoil and stretch, absorbing the force of the impact. This hybrid approach makes the package tough enough to resist punctures while remaining flexible enough to survive a fall.
Technical Structure and Gas Barrier Specifications
The multilayer body follows a five-layer hierarchy. At the top is the base layer (10), usually a biaxially stretched film of medium-density or high-density polyethylene (MDPE or HDPE). This layer is treated with a corona or plasma process to ensure high-quality printing. A first adhesive layer (40) joins this base to the intermediate layer (20).
The intermediate layer (20) is where the unstretched PE is located. To make the material more useful for food storage, this layer can be equipped with a gas barrier (21). This barrier often consists of a vacuum-deposited layer of silicon oxide (SiO2) or aluminum oxide (Al2O3). Because these inorganic layers are extremely thin-between 5 nm and 50 nm-they provide excellent oxygen and water vapor resistance without interfering with the recycling process.
The final component is the heat seal layer (30), typically made of low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). This allows the material to be turned into various formats, such as standing pouches or flat bags. For standing pouches, the heat seal layer thickness can be increased up to 200um to support heavy contents.
Test Results and Impact Resistance
The claims in the patent are backed by testing that compared this hybrid structure to other mono-material attempts. The evaluation looked at three main areas: recyclability, piercing strength, and impact resistance.
In “Comparative Example 1,” where both the base and intermediate layers were unstretched, the material failed on two fronts: it had low piercing strength (only 5.0 N) and the image visibility was poor. In “Comparative Example 2,” where both layers were stretched, the impact resistance was the problem, with 8 out of 10 bags breaking during the drop test.
The patented examples performed much better. By using a stretched base layer with an unstretched intermediate layer, the system reached a piercing strength of 8.7 N and had zero failures in the 50-drop impact test. Because the PE proportion stayed between 92% and 94%, the material is considered highly recyclable.
The data also showed the benefit of using specific adhesives. By using epoxy-based adhesives that have their own gas barrier properties, the inventors protected the thin SiO2 or Al2O3 layers. This prevents small cracks from forming in the barrier during physical stress, keeping the Oxygen Transmission Rate (OTR) low.
Practical Solutions for Global Packaging Standards
This technology is a direct response to new environmental standards, such as the EU’s Packaging and Packaging Waste Regulation (PPWR). The regulation requires all packaging to be recyclable by 2030, which pushes manufacturers toward mono-materials.
The patent also considers the total environmental footprint. It notes that the structure works with biomass-derived polyethylene-plastic made from plants-and biomass-derived inks. This makes the packaging more sustainable from the start of its life, not just at the end.
For engineers and packaging professionals, the “028” architecture shows a new way to design films. By changing the physical state of the same plastic across different layers, it is possible to match the performance of heavy-duty multi-resin systems. As global rules on plastic waste get stricter, these high-strength, 90%+ polyethylene structures provide a clear path forward for sustainable containers.
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