Drawing for Package Material Elongation
Material elongation in packaging films requires precise control of molecular orientation and crystallization behavior. Modern packaging substrates must achieve 150-300% elongation while maintaining barrier properties, with gel counts below 10 per square meter and uniform thickness variation within ±5%. These requirements become particularly challenging when incorporating recycled content or designing for sterilization resistance.
The fundamental challenge lies in balancing molecular orientation during stretching with the final mechanical properties, especially when working with multi-layer structures or materials with different crystallization behaviors.
This page brings together solutions from recent research—including controlled spherulite formation in medical packaging, powered pre-stretcher mechanisms for agricultural films, and coextrusion techniques for polyolefin-based barrier substrates. These and other approaches focus on achieving consistent elongation while maintaining critical package performance requirements like gas barrier properties and layer adhesion.
1. Biaxial Stretching Method for Thermoplastic Films with Localized Pre-Stretch Heating Control
TOHCELLO CO LTD, 2009
Stretching a film of a thermoplastic resin like polypropylene to obtain a stretched film with high thickness and thinness accuracy. The technique involves controlling the starting point of stretching during biaxial stretching to improve thickness uniformity. The key is to create localized high temperature spots on the film before stretching. This can be done by sequentially heating specific areas, using infrared lasers, or pulsed heating. By heating these spots before stretching, it forces the stretching to start from those areas instead of random spots. This allows more controlled and uniform stretching.
2. Method for Manufacturing and Storing Uniform Thickness Stretched Plastic Sheets with Trimmed Edges
INTEGRATED PACKAGING AUSTRALIA PTY LTD, 2005
A method to manufacture and store stretched plastic sheets that allows for improved packaging and dispensing of the sheets. The method involves stretching the plastic sheet beyond its elastic limit, then trimming the thickened edge areas to create a sheet with uniform thickness. This prevents issues like soft center, clogging, and tearing when winding and unrolling the stretched sheet. The stretched sheet is stored with some elasticity retained, allowing it to better conform to loads and avoid tearing when packaged or dispensed.
3. Two-Step Stretching Method for Plastic Film with Sequential High and Low Stretch Ratios
ITW MIMA FILMS LLC, 2003
A method to manufacture stretched plastic film with improved stretch ratio and reduced breakage compared to existing techniques. The method involves a two-step stretching process with higher stretch in the first step followed by relaxation. The first stretch ratio is higher than the second stretch ratio. This allows the film to be stretched more without breaking during the first step, followed by relaxation to release elastic deformation. The total stretch ratio can be adjusted by the two-step stretches.
4. Polypropylene Film with Bidirectional Stretching Utilizing Differential Ratio Profiles
MINNESOTA MINING & MANU PACKAGING CAMPANY, 2001
Stretching films like polypropylene to improve properties like thickness uniformity and strength by using specific stretching profiles. The profiles involve stretching simultaneously in both directions, but with lower ratios in one direction compared to natural stretch ratios. This prevents necking and maintains uniformity. The method involves first stretching at high ratios in both directions, then reducing only the first direction ratio. This allows uniform stretching even at lower ratios. The films have improved properties like thickness uniformity, tensile strength, and elongation at break compared to conventionally stretched films.
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