Low Haze ETFE Film Biaxial Stretching Process
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Solution Overview
Problem
Existing fluoropolymer films, such as ETFE, face challenges in achieving low haze values necessary for architectural applications while maintaining mechanical strength, as thicker films tend to have high haze due to crystallinity and scattering issues.
Innovation Solution
A stretching process using a tenter-frame machine to biaxially stretch ETFE films from an initial thickness of 400 μm or more, resulting in a final thickness of 150 μm or more with haze values of 2% or less, which modifies the molecular structure and reduces scattering centers, enhancing transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ETFE film thickness is increased to provide sufficient mechanical strength for architectural applications, then mechanical strength is improved, but haze value increases reducing transparency
Solution Approach 1:
The patent applies biaxial stretching to change the physical and structural parameters of the ETFE film. This process reorganizes the molecular structure, reduces crystallinity, and decreases scattering centers, thereby reducing haze values to 2% or less while maintaining film thickness of 150 μm or more, achieving both mechanical strength and transparency
Solution Approach 2:
The patent creates a composite structure within the ETFE film through biaxial stretching, producing a unique molecular arrangement with reduced crystallinity and fewer scattering centers. This composite microstructure enables the film to simultaneously achieve high mechanical strength and exceptional transparency (haze < 2%)
2Strength
If ETFE film is extruded with standard crystallinity (35-60%), then mechanical properties are maintained, but haze values range from 2.5% to 9% or higher
Solution Approach 1:
The patent changes the crystallinity parameter through biaxial stretching, reducing it from the standard 35-60% range to below 35%. This parameter change, combined with molecular reorganization, reduces light scattering and achieves haze values of 2% or less while preserving mechanical properties
Solution Approach 2:
The patent introduces dynamic mechanical stretching processes (biaxial stretching) to transform the static extruded film into a dynamically reorganized structure. The stretching process creates a more uniform molecular arrangement with fewer defects, reducing haze while maintaining mechanical integrity
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 process achieves ETFE films with low haze values, appearing glass-like, while retaining mechanical properties suitable for architectural applications, by reorganizing molecular structure and reducing scattering centers, thus improving optical clarity.
Implementation Method 1
The crystallinity typically ranges from 35 to 60%... stretching the film to have an Ax > 1.6... reorganizing molecular structure and reducing scattering centers
Data Source
AI summary
An ETFE film that has a haze value of 2% or less, and preferably 1% or less, which advantageously may have a thickness greater than 150 pm, and preferably In the range of 200 pm to 300 pm, A film of ETFE, as received from the manufacturer, is stretched under special processing conditions to produce a processed (or final) film having an area stretch factor (Ax) greater than about 1.6. Ax —Initial film thickness/film thickness after stretching. However, it is important that the initial film thickness has a starting thickness of at least 400 pm, and preferably at least 500 pm. Processing conditions Include, in some embodiments, pre-beating and heating during stretching, and post-stretching annealing If the film is stretched in a 2.5×1 or a 4×1 ratio, at a processing temperature in THV range of 130° C. to 150° C., the haze of the resulting film can be reliably brought down to less than 2%. We have also found that this low haze value is not dependent on whether the larger stretch {e.g., 2,5× or 4×) is in the machine direction (MD) or the transverse direction (TD) of the extruded film. Annealing the stretched film decreases the film shrinkage to almost 0%.