Heat-Shrinkable Polyester Film for Stable Aging and Low Shrink Stress
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Solution Overview
Problem
Existing heat-shrinkable polyester-based films face issues with high shrinkage ratios in the main direction, low shrinkage ratios after aging, high shrinkage stress, and thickness irregularities, which affect their performance and appearance.
Innovation Solution
A heat-shrinkable polyester-based film using an amorphous copolymerized polyester resin with a specific composition, including 7-15 mol% diethylene glycol, 50-95 mol% ethylene terephthalate, and controlled intrinsic viscosity, is produced through controlled stretching and relaxation processes to achieve high shrinkage ratios with low stress and thickness uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a high shrinkage ratio is achieved in the main direction, then the film can adapt to various containers, but the natural shrinkage ratio and hot-water shrinkage ratio at 70°C become high after aging treatment
Solution Approach 1:
The invention changes the chemical composition parameters of the polyester resin by incorporating specific amounts of neopentyl glycol (5-20 mol%) and cyclohexanedimethanol (10-40 mol%) units into the polymer structure. This compositional modification alters the molecular characteristics to achieve both high initial shrinkage ratio and stable shrinkage performance after aging at 70°C
Solution Approach 2:
The invention creates a composite polyester resin system combining multiple monomer units (terephthalic acid, neopentyl glycol, cyclohexanedimethanol) to achieve synergistic effects. The combination of these specific units provides both the required shrinkage properties and aging stability that cannot be achieved with single-component polymers
2Force
If high-temperature stretching is used to suppress necking force, then the necking force is reduced, but the molecular orientation in the stretching direction is reduced and thickness irregularity increases
Solution Approach 1:
The invention modifies the thermal and mechanical parameters during stretching by conducting the process at temperatures of 80-120°C for 1-24 hours. This controlled thermal treatment parameter change allows sufficient molecular relaxation to reduce necking force while maintaining adequate molecular orientation and thickness uniformity through the extended treatment time
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 film maintains consistent shrinkage properties before and after aging, reduces shrinkage stress, and minimizes thickness irregularities, enabling stable and aesthetically pleasing packaging solutions.
Implementation Method 1
a heat-shrinkable polyester-based film which shrinks greatly in the width direction
Implementation Method 2
a shrinkage ratio in the longitudinal direction, which is a non-shrinking direction, is made to be below zero (so-called extend due to heating)
Data Source
AI summary
[Problem] The present invention aims to provide a heat-shrinkable polyester-based film having a high heat-shrinkage ratio in the main shrinkage direction, a low heat-shrinkage ratio in the non-shrinking direction and a small change in the shrinkage ratio before and after the aging treatment. Further, he present invention also aims to provide a raw material to produce the heat-shrinkable polyester-based film. [Solution] An amorphous copolymerized polyester raw material for a film, wherein the polyester raw material satisfies the following requirements (1) to (4): (1) the copolymerized polyester raw material contains ethylene terephthalate as a main constituent component, and comprises neopentyl glycol by 15 mol% or more and 30 mol% or less when a total amount of glycol component in a total polyester resin component is taken as 100 mol%, (2) the copolymerized polyester raw material comprises a constituent unit derived from diethylene glycol by 7 mol% or more and 15 mol% or less in the total amount of glycol component 100 mol% in the total polyester resin component, (3) the copolymerized polyester raw material has an intrinsic viscosity of 0.60 dl/g or more and less than 0.70 dl/g, and (4) the copolymerized polyester raw material has a glass transition temperature of 60°C or higher and 70°C or lower.