Water-Based Polyurethane Urea Coating for Expanded TPU Adhesion
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Solution Overview
Problem
Expanded thermoplastic polyurethane (TPU) substrates face challenges with adhesion of coatings due to the presence of lubricants, which lead to poor processability and reproducibility, and existing solutions either require washing steps with harsh substances or result in coatings that crack and peel when the substrate is flexed.
Innovation Solution
A water-based polyurethane urea solution with polycarbonate structural units is used to coat expanded TPU substrates, which adheres effectively even in the presence of lubricants and maintains adhesion when the substrate is bent, without the need for washing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If lubricants are added to expanded TPU particles to prevent adhesion during transport, then the processability and flowability improve, but the adhesion of subsequent coatings deteriorates
Solution Approach 1:
A silane coupling agent is introduced as an intermediary substance between the lubricant-coated TPU substrate and the aqueous coating. The silane coupling agent contains both organofunctional groups that interact with the lubricant and inorganic functional groups that promote coating adhesion, effectively mediating the interface between the substrate and coating while preventing direct negative interaction between lubricant and coating
Solution Approach 2:
The surface properties of the TPU substrate are modified by applying a silane coupling agent that changes the chemical parameters of the surface. This treatment alters the surface energy and chemical composition without removing the bulk lubricant, creating a new surface layer that is compatible with both the lubricant and the aqueous coating
2Reliability
If acrylic coatings are applied to improve resistance properties, then chemical resistance and water resistance improve, but the coating cracks and peels when the substrate is flexed
Solution Approach 1:
The coating formulation is changed from rigid acrylic to flexible polyurethane dispersion, fundamentally altering the mechanical parameters of the coating. The new coating has lower modulus and higher elongation at break, allowing it to accommodate substrate flexing without cracking while maintaining protective properties
Solution Approach 2:
The solution uses a composite approach by combining polyurethane dispersion with specific additives and using it in conjunction with the silane coupling agent. This creates a multi-layer composite system where the silane layer provides chemical bonding and the polyurethane layer provides flexible mechanical protection
3Reliability
If washing steps with harsh substances are used to remove lubricants, then coating adhesion improves, but the manufacturing complexity and environmental impact worsen
Solution Approach 1:
Instead of removing the lubricant (which would require complex washing steps), the invention converts the harmful effect of the lubricant into a beneficial one by using the silane coupling agent to create a compatible interface. The lubricant that was previously an obstacle becomes part of the system that the silane coupling agent mediates, eliminating the need for washing steps
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 coating provides improved water resistance, chemical resistance, scratch resistance, and durability, while maintaining the mechanical properties of the TPU substrate, and can be applied without altering its bulk properties or requiring additional cleaning steps.
Implementation Method 1
A water-based polyurethane urea solution with polycarbonate structural units is used to coat expanded TPU substrates, which adheres effectively even in the presence of lubricants
Implementation Method 2
The coating provides improved water resistance, chemical resistance, scratch resistance, and durability
Data Source
AI summary
The present invention relates to an article comprising expanded thermoplastic polyurethane as a substrate and a specific polyurethane urea coating on said substrate, as well as footwear, a process for producing the article and a use of a polyurethane urea dispersion/solution. It has been found that a polurethane urea coating comprising polycarbonate structural units strongly binds to expanded TPU substrates and maintains the intrinsic properties of the expanded TPU.