Micro layered films have reached a new level of sophistication. Advanced microlayer feedblock technology, used to put multiple alternating layers into specialty films is being used to make stretch films with alternating synergistic pairs of materials in microlayers to give higher strength, as per ptonline.com. Until now, microlayer feedblocks have been used to make specialty films like 76-layer gas bladders with built-in nitrogen barrier for inflatable shoe soles, or brightness-enhancing computer-display films with up to 900 layers. AEP Flexible Packaging BV (AFP) makes the most complex structure so far. It has 27 layers in a split sandwich that puts 11 microlayers on either side of a core, together with intermediate and skin layers. AFP's film is called Katanex after a traditional Japanese method of making stronger samurai swords using layers of steel. Cloeren Inc built the feedblock and die. Quasi-conventional film can be made on the same feedblock and die by putting the same material in all the extruders. The result is slightly higher throughput because of the two additional extruders and slightly higher properties because of the ‘plywood effect' of all the layers. AFP's 27-layer structure made with one LLDPE resin in all the layers achieves the same high ultimate tensile strength of 9000 psi as the Katanex film with special microlayer resins, vs. about 6000 psi for typical machine stretch wrap, with extraordinary holding strength and TD tear strength. AFP had been looking to offer film with higher strength than its existing 3- and 5-layer films and was considering investing in a new 7- or 9-layer cast film line; to make sturdier pallet wrap with higher holding strength to contain two-liter PET soda bottles. Cloeren had an 11-microlayer feedblock which produced 11-microlayer film with properties substantially higher than those of the conventional 7- or 9-layer coex film that AFP was considering. The only hitch was that the film that AFP wanted to make was unproven; to put the microlayers on either side of an LLDPE core layer, with the microlayers as close to the surface as possible to add strength. Cloeren had built many microlayer feedblocks with up to 600 layers, but had always put the microlayers in the middle of the film, surrounded and protected by thicker layers providing stiffness and strength. One concern was that shear forces in the die might disrupt the microlayers if they were near the surface. Cloeren's NanoLayer feedblock forms each microlayer individually with a forming plate that's thinner than forming plates in conventional feedblocks. Cloeren typically creates a packet of 11 or 17 alternating microlayers, then splits and realigns the packet to multiply the layers. The number of layers in the packet determines the height of the feedblock, which is much taller than normal. Microlayer feedblocks are provided with a spacer that can be removed later to make room for more layers in the packet. An equally long selector plug with a hole for each microlayer connects the extruders to the feedblock. AFP's feedblock forms an 11-layer packet, then slits it in two and feeding one half to either side of the core, followed by intermediate and skin layers, instead of aligning the split packets side by side. The LLDPE core is about 40% of the whole film structure, intermediate layers are each about 10%, skin layers each 10% and the two microlayer sections are each 10%. So each individual microlayer is about 1% of total film thickness. Layer-multiplier technology applied by Extrusion Dies Industries (EDI) has yielded micro-layer film that stretches up to 45% more than conventional three-layer products, opening the possibility that users of stretch wrap will need fewer pounds of film to unitize a given number of pallet loads. Micro-layer film has an order-of-magnitude greater number of layers than a conventional coextruded film but a similar overall thickness. EDI builds tooling for producing such film as a licensee of a patented "layer multiplier" system developed by Dow Chemical Company. In tests by EDI comparing 48-layer micro-layer film with conventional three-layer film produced from the same resins, the micro-layer product stretched up to 34% more in the machine direction before failure in the case of an LLDPE/LDPE/LLDPE structure, and 45% more for an all-LLDPE structure. Like the conventional coextrusion, the micro-layer film had started out as a three-layer structure, but in the innovative tooling built by EDI these were subsequently multiplied into twelve, then into 48. Increasing the number of layers-even if all are produced from the same resin-enhances properties like stretchability, tear-resistance, and puncture-resistance. The greater the number of layers, the less the likelihood of breakage caused by gels, pinholes and other defects. This is because the large number of layer-to-layer interfaces increases the chances for defects to be encapsulated and rendered harmless. By preventing web breaks, the encapsulation of defects in micro-layer structures has advantages in many other applications besides stretch film, benefits of particular importance in food packaging. In packaging film produced with barrier resin, the sheer increase in the number of barrier layers creates a 'torturous path' for gas and moisture molecules between ambient air and the food contents inside a package. Hence, layer-multiplier technology is expected to achieve widespread use in barrier packaging. In a typical layer-multiplier production line, three or more extruders feed melt streams into a streamlined feedblock, which produces a uniform multi-layer "sandwich"; this in turn is fed into a layer-multiplier device, which multiplies the layers in stages. The finished micro-layer structure is then distributed in a coextrusion manifold to the target product width.