Recyclable Polyester Film with Soluble Outer Layer
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Solution Overview
Problem
Biaxially oriented polyester films used in industrial processes become contaminated and are not directly recyclable due to adherent residues, preventing their reuse in high-value applications, and existing solutions compromise moisture resistance or solubility, making them unsuitable for efficient washing and recycling.
Innovation Solution
A multilayer, coextruded polyester film with an outer layer comprising at least 60 wt % of a copolyester derived from terephthalic acid, 5-sulfo-isophthalic acid, and ethylene glycol, which is soluble in aqueous alkali metal hydroxide solutions, allowing for selective detachment and recycling while maintaining mechanical and chemical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the polyester film surface is made insensitive to moisture for coating application, then coating anchoring is improved, but the film becomes resistant to washing and cannot be easily cleaned for recycling
Solution Approach 1:
The film is divided into two functional layers: a base layer (B) made of conventional moisture-insensitive polyester that provides structural integrity and coating anchoring, and an outer layer (A) made of water-soluble copolyester that enables easy washing. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the film have different properties: the base layer (B) has moisture insensitivity for coating application, while the outer layer (A) has water solubility for washing. This local differentiation of material properties resolves the contradiction between coating anchoring and washing ease.
2Ease of operation
If the polyester film is made soluble in water for easy washing and recycling, then cleaning efficiency is improved, but the film loses moisture resistance needed for coating application
Solution Approach 1:
The film structure separates the washing function (outer layer A with water-soluble copolyester) from the moisture resistance function (base layer B with conventional polyester), allowing the film to exhibit both properties at different locations.
Solution Approach 2:
The film combines two different polyester materials with complementary properties: conventional polyester for moisture resistance and water-soluble copolyester for washability. This composite structure enables the film to achieve both moisture resistance and washing ease simultaneously.
3Reliability
If process films are used for industrial applications with coatings and residues, then functional performance is improved, but direct recycling becomes impossible due to contamination
Solution Approach 1:
The outer layer (A) made of water-soluble copolyester is designed to be selectively removed during washing processes. This extraction of the outer layer eliminates adherent residues and contaminants, enabling direct recycling of the base layer without manual sorting or cleaning.
Solution Approach 2:
The outer layer is intentionally designed to be discarded during washing, while the base layer is recovered for recycling. This selective discarding and recovering process enables direct recycling of the functional base layer while removing all contamination from the outer layer.
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
Enables direct recycling of contaminated polyester films into high-quality biaxially oriented polyester, avoiding downcycling and maintaining film integrity and coating functionality, with the outer layer dissolving quickly in washing processes to separate from the base layer, ensuring complete cleaning and recyclability.
Implementation Method 1
the at least one outer layer (A) is soluble in aqueous alkali metal hydroxide solutions
Data Source
AI summary
The present invention relates to a multilayer, coextruded polyester film that includes at least one outer layer (A) and a base layer (B), in which the at least one outer layer (A) includes to an extent of at least 60 wt % of a copolyester that includes units derived from dicarboxylic acids and diols, in whichthe units derived from dicarboxylic acids include at least 65 mol % of units derived from terephthalic acidand at least 5 mol % of units derived from 5-sulfo-isophthalic acid andthe units derived from diols include at least 90 mol % of units derived from ethylene glycol.The present invention further relates to a process for producing the film according to the invention, to the use thereof and to a process for recycling the polyester film according to the invention.