Incrementally Stretched Thermoplastic Films with Ribbed Patterns
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Solution Overview
Problem
Conventional methods of stretching thermoplastic films in the machine direction to increase tensile strength often result in a reduction of machine direction tear resistance and puncture resistance, which is undesirable for applications like trash bags and food storage bags that require high tear resistance.
Innovation Solution
Implementing incremental stretching in both machine and transverse directions using cold ring rolling processes, which maintains or increases tear resistance while reducing the film's gauge, thereby enhancing its physical properties without compromising its strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermoplastic films are stretched in the machine direction to increase tensile strength, then tensile strength is improved, but machine direction tear resistance deteriorates
Solution Approach 1:
The stretching process is divided into multiple incremental stages rather than a single large stretch. The film passes through multiple pairs of rollers with progressively increasing speed ratios, applying small increments of stretch (e.g., 1.05 to 1.20) in sequence. This segmented approach allows molecular chains to reorganize gradually, maintaining tear resistance while achieving the desired tensile strength enhancement.
Solution Approach 2:
The film undergoes periodic stretching cycles through multiple roller pairs, with each pair applying a small incremental stretch. The periodic nature of this process allows the material to relax and reorganize between stretches, preventing the catastrophic failure of tear resistance that would occur with a single continuous stretch.
2Strength
If thermoplastic films are stretched to increase tensile strength, then tensile strength is improved, but puncture resistance deteriorates
Solution Approach 1:
The stretching is segmented into multiple small increments applied sequentially through different roller pairs. This prevents the formation of weak points that would compromise puncture resistance, while still achieving the overall tensile strength improvement needed for the application.
3Reliability
If incremental stretching is applied to maintain tear resistance, then tear resistance is maintained, but film gauge is reduced
Solution Approach 1:
The process changes the physical parameters of the film by applying controlled incremental stretches that reorganize molecular chains and reduce gauge thickness. By carefully controlling the stretch ratios and number of roller pairs, the film achieves reduced gauge (material efficiency) while maintaining tear resistance through the incremental stretching mechanism.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves maintained or increased tear resistance and puncture resistance in thermoplastic films, allowing for reduced material usage and cost savings while maintaining consumer perception of film strength through visible ribbed patterns.
Implementation Method 1
incremental stretching in both machine and transverse directions using cold ring rolling processes
Implementation Method 2
cold ring rolling processes
Implementation Method 3
visible ribbed patterns
Data Source
AI summary
Methods of enhancing one or more physical properties of a thermoplastic film include incrementally stretching thermoplastic films in the machine direction and/or transverse direction. In one or more implementations, methods of incrementally stretching thermoplastic films include reducing the gauge of the films without reducing the films' machine-direction tear resistance. The methods can involve cold stretching the films and imparting rib patterns into the film. The linear ribs can have alternating thick and thin gauges. Incrementally stretched thermoplastic films can have a machine-direction tear resistance that is approximately equal to or greater than the machine-direction tear resistance of the film prior to stretching.