Polyester Film Tensile Strength Ratio for Envelope Cuttability
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Solution Overview
Problem
Existing polyester films used for mail envelopes with windows lack sufficient strength and ease of cutting, particularly in the transverse direction, which affects their durability and manufacturing efficiency.
Innovation Solution
A polyester film with specific tensile strength ratios in the machine and transverse directions, high light transmittance, and optimized stretching and heat setting processes to enhance cuttability and tensile strength, primarily composed of polyethylene terephthalate with a high diol component and dicarboxylic acid content, is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the polyester film is stretched more in the transverse direction to improve cuttability, then the tensile strength in the transverse direction increases, but the tensile strength in the machine direction decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the stretch ratios in machine direction (1.8-3.5 times) and transverse direction (2-6 times), along with controlling the ratio A of tensile strengths to fall within 0.5-6. This optimization of physical parameters enables the film to be easily cut in the machine direction while maintaining sufficient strength, resolving the contradiction between cuttability and strength.
2Illumination intensity
If the polyester film thickness is reduced to improve envelope aesthetics and light transmittance, then the light transmittance increases, but the tensile strength decreases
Solution Approach 1:
The patent resolves this contradiction by changing the material parameters through optimized stretching ratios and controlling the tensile strength ratio A between machine and transverse directions. This allows thin films (5-50 μm) to achieve high light transmittance (85% or more) while maintaining sufficient tensile strength through the optimized molecular orientation achieved by the specific stretching process.
3Strength
If the polyester film is stretched more in the machine direction to improve strength, then the tensile strength in the machine direction increases, but the cuttability worsens
Solution Approach 1:
The patent optimizes the stretch ratio in the machine direction to a specific range (1.8-3.5 times) rather than maximizing it, and controls the tensile strength ratio A to fall within 0.5-6. This balanced parameter optimization ensures sufficient strength while maintaining good cuttability, as excessive machine direction stretching would make the film difficult to cut.
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 achieves improved cutting performance and stability, allowing for easy cutting in the transverse direction while maintaining sufficient strength for envelope windows, with enhanced manufacturing process efficiency and reduced thickness deviations.
Implementation Method 1
The polyester film has been stretched about 1.8-3.5 times in the MD and about 2-6 times in the TD
Implementation Method 2
a polyester film with specific tensile strength ratios in the machine and transverse directions, high light transmittance, and optimized stretching and heat setting processes
Data Source
AI summary
The embodiments relate to a polyester film, which has a high tensile strength in the transverse direction and a low tensile strength in the longitudinal direction, while satisfying the condition of 0.5<A<6, A being calculated by Equation 1. A polyester film according to the embodiments can easily be cut in the transverse direction.