Heat-shrinkable Polyester Film Thickness Control
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Solution Overview
Problem
Conventional heat-shrinkable polyester-based films either have low heat-resistant properties, high irregularity in thickness, or inadequate shrinkage ratios in specific directions, making them unsuitable for applications requiring high heat-shrinkage ratios and uniform thickness.
Innovation Solution
A heat-shrinkable polyester-based film is developed with a composition of 90 mol% ethylene terephthalate units, processed through a transverse stretching method where preheating is done at (Tg+40° C.) to (Tg+70° C.), followed by transverse stretching at (Tg+5° C.) to (Tg+40° C.), and further stretching at (Tg−10° C.) to (Tg+15° C.), achieving high heat-shrinkage ratios and reduced thickness irregularity in both width and longitudinal directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If amorphous polyester raw material is used to increase shrinkage ratio, then the shrinkage ratio increases, but heat resistant property deteriorates and thickness irregularity increases
Solution Approach 1:
The patent changes the chemical composition parameters of the polyester resin by limiting amorphous components to 5 mol% or less and setting ethylene terephthalate content to 90-100 mol%, thereby achieving both high heat resistance and controlled shrinkage properties through precise compositional control
Solution Approach 2:
The patent applies different stretching ratios in different directions (higher transverse stretching ratio of 3.0-5.0 times versus longitudinal stretching ratio of 1.0-2.0 times) to create directional shrinkage characteristics while maintaining overall thermal stability
2Shape
If amorphous polyester raw material is used to increase shrinkage ratio, then the shrinkage ratio increases, but thickness uniformity deteriorates
Solution Approach 1:
The patent modifies the resin composition parameters by using predominantly crystalline polyester (ethylene terephthalate 90-100 mol%) with minimal amorphous content, which provides more uniform molecular structure and predictable shrinkage behavior, thereby improving thickness uniformity
Solution Approach 2:
The patent applies differential stretching ratios where transverse stretching (3.0-5.0 times) is greater than longitudinal stretching (1.0-2.0 times), creating controlled anisotropic shrinkage that maintains uniform thickness distribution across the film
3Shape
If transverse stretching is performed at high temperature to achieve high shrinkage ratio, then shrinkage ratio increases, but thickness irregularity increases
Solution Approach 1:
The patent optimizes the temperature parameter within a controlled range (Tg+40°C to Tg+70°C for preheating, Tg+5°C to Tg+40°C for stretching) to balance molecular mobility for shrinkage expression while preventing excessive thermal expansion that would cause thickness irregularity
Solution Approach 2:
The patent performs preheating at higher temperature (Tg+40°C to Tg+70°C) before the actual stretching operation, which gradually activates the polymer chains and prepares the material for controlled shrinkage, preventing sudden deformation and thickness variation
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 a heat-shrinkage ratio of 50% to 75% in the width direction, -6% to 14% in the longitudinal direction, and maximum heat shrinkage stress of 4 MPa to 13 MPa, with a crystallinity degree of 1% to 15%, ensuring effective shrinkage and stability for label applications.
Implementation Method 1
the heat-shrinkage ratio in a width direction measured by shrinking the film for 10 seconds in 90° C. hot water is 50% or more and 75% or less
Implementation Method 2
the heat-shrinkage ratio in a longitudinal direction measured by shrinking the film for 10 seconds in 90° C. hot water is −6% or more and 14% or less
Data Source
AI summary
The invention provides a heat-shrinkable polyester-based film, where the heat-shrinkage ratio in the width direction is high and the irregularity of thickness is small. The heat-shrinkable polyester-based film of the present invention contains 90 mol % or more of ethylene terephthalate unit based on 100 mol % of whole ester unit, wherein, the heat-shrinkable polyester-based film satisfies the requirements: (1) heat-shrinkage ratio in a width direction measured by shrinking the film for 10 seconds in 90° C. hot water is 50%-75%, (2) heat-shrinkage ratio in a longitudinal direction measured by shrinking the film for 10 seconds in 90° C. hot water is −6% or more and 14% or less, (3) heat-shrinkage ratio in the longitudinal direction measured by shrinking the film for 10 seconds in 70° C. hot water is −6% or more and 6% or less, and (4) irregularity of thickness in the width direction is 1%-20%.