Heat-Shrinkable Polyester Film Humidity Stability
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Solution Overview
Problem
Heat-shrinkable polyester films used as labels for PET bottles experience physical property changes, such as tensile strength and breakage resistance deterioration, in high-humidity environments, leading to storage instability and breakage during transportation and storage.
Innovation Solution
A heat-shrinkable polyester film with specific tensile strength differences (C2−C1) within a predetermined range, combined with controlled heat shrinkage rates and resin composition, to maintain stability and resistance in high-humidity conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heat-shrinkable polyester film is used as a label for PET bottles, then the label provides shrinkage characteristics and initial strength, but the tensile strength and breakage resistance deteriorate over time in high-humidity environments
Solution Approach 1:
The patent applies parameter changes by precisely controlling the limiting viscosity average molecular weight (Mv) to 180 ml/g or more and the diol component ratio to 30 mol% or more. These parameter adjustments modify the molecular structure and intermolecular forces of the polyester resin, enhancing its resistance to hydrolysis in high-humidity environments. The controlled parameters ensure that the film maintains its tensile strength and breakage resistance characteristics over time, directly resolving the contradiction between storage stability and strength retention.
2Strength
If the film is exposed to high-humidity environment for extended periods, then storage stability is compromised, but the label breaks during transportation and storage
Solution Approach 1:
The patent implements preliminary action by pre-establishing optimal molecular weight (Mv ≥ 180 ml/g) and compositional parameters (diol ≥ 30 mol%) during the film manufacturing process. These preliminary structural configurations create inherent resistance to humidity-induced degradation before the film is actually used as a label. The pre-optimized molecular structure ensures that even during extended storage and transportation periods, the film maintains sufficient breakage resistance, preventing label failure without requiring additional protective measures during storage.
3Stability of the object's composition
If the tensile strength changes significantly after aging treatment, then physical property stability is poor, but the label cannot maintain its functional characteristics
Solution Approach 1:
The patent resolves this contradiction through parameter changes by establishing specific thresholds for limiting viscosity average molecular weight (Mv ≥ 180 ml/g) and diol component content (≥ 30 mol%). These parameter specifications directly control the film's physical property stability by reducing the rate of molecular chain scission and hydrolysis during aging. The optimized parameters ensure that tensile strength retention remains above 80% after aging treatment, thereby maintaining both physical property stability and functional characteristics simultaneously.
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 exhibits reduced physical property changes and enhanced storage stability and breakage resistance, preventing label breakage during transportation and storage, even in high-humidity environments.
Implementation Method 1
a heat shrinkage rate in the TD direction in a case where the heat-shrinkable polyester film is caused to shrink under the conditions of 10 seconds in hot water at 90° C. is 60% or more
Data Source
AI summary
Provided is a heat-shrinkable polyester film which undergoes less change in the physical properties even in a high-humidity environment, has excellent storage stability, and effectively suppresses a breakage phenomenon of the film after heat shrinkage.Disclosed is a heat-shrinkable polyester film derived from a polyester resin, in which when tensile strengths in a main shrinkage direction obtained before and after immersion in water at 23° C. for 168 hours in a tensile test as measured according to JIS K 7127 are designated as C1 (MPa) and C2 (MPa), the following Relational Expression (1) is satisfied:−5.3<(C2−C1)<4.2 (1)