Aliphatic Polyurea Coating UV Weatherability and Mechanical Strength
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Solution Overview
Problem
Conventional polyurethane (polyurea) waterproofing coatings have poor weatherability and mechanical properties, limiting their use on outdoor structures like high-speed railway bridges, especially due to issues such as yellowing, chalking, and inadequate elongation and tensile strength after UV aging tests.
Innovation Solution
An aliphatic polyurea coating comprising NCO-terminated polycarbonate diol modified or polyether polyol modified isophorone diisocyanate prepolymer, hexamethylene diisocyanate oligomers, and sterically hindered secondary aliphatic diamines, which provides improved elongation, tensile strength, and weatherability, allowing for manual application at room temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aromatic polyisocyanate compound (MDI, TDI) is used as coating binder, then the coating can be applied and cured, but the weatherability is poor with yellowing and chalking after outdoor exposure
Solution Approach 1:
The patent changes the chemical structure parameter of the polyisocyanate from aromatic (MDI, TDI) to aliphatic (HDI oligomers), which fundamentally alters the UV resistance properties and eliminates yellowing and chalking issues while maintaining curing functionality
Solution Approach 2:
The patent creates a composite coating system combining aliphatic polyisocyanate (HDI oligomers) with polyol and catalyst, forming a new material composition that achieves both durability and aesthetic stability without the harmful effects of aromatic compounds
2Strength
If conventional polyurethane coating is used, then the coating can be applied manually, but the mechanical properties are insufficient with elongation <200% and tensile strength <4 MPa
Solution Approach 1:
The patent modifies the chemical composition parameters by using HDI oligomers with specific NCO content (15-23.7%) and molecular weight (200-500), which enables the coating to achieve elongation ≥200% and tensile strength ≥4 MPa while remaining applicable by manual methods
Solution Approach 2:
The patent replicates the successful application properties of conventional coatings while improving mechanical performance by copying the two-component system approach (polyisocyanate + polyol) and optimizing the formulation ratios to achieve both ease of application and superior mechanical properties
3Reliability
If powder coating based on IPDI and HDI is used, then the weatherability is improved, but the curing temperature is 150-220°C which is not suitable for room temperature operation
Solution Approach 1:
The patent changes the curing temperature parameter from high temperature (150-220°C) to room temperature by introducing a catalyst (dibutyltin dilaurate or similar) that enables low-temperature curing of the aliphatic polyisocyanate system while maintaining weatherability
Solution Approach 2:
The patent introduces a catalyst as an intermediary substance that mediates the reaction between HDI oligomers and polyol at room temperature, enabling the curing process to proceed without high temperature while preserving the weatherable properties of the aliphatic structure
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 aliphatic polyurea coating exhibits enhanced mechanical strength, flexibility, abrasion resistance, and weatherability, meeting the requirements for high-speed railway bridges with elongation ≥200% and tensile strength ≥4 MPa, and maintaining performance after 1500h artificial accelerated UV aging tests.
Implementation Method 1
An aliphatic polyurea coating comprising NCO-terminated polycarbonate diol modified or polyether polyol modified isophorone diisocyanate prepolymer, hexamethylene diisocyanate oligomers, and sterically hindered secondary aliphatic diamines
Data Source
AI summary
The present invention pertains to an aliphatic polyurea coating, comprising a product mixed by the components including NCO-terminated polycarbonate diol modified and/or polyether polyol modified isophorone diisocyanate (IPDI) prepolymer; hexamethylene diisocyanate (HDI) oligomers; and amino resin comprising sterically hindered secondary aliphatic diamines. The aliphatic polyurea coating layer prepared by the aliphatic polyurea coating presented in this invention possesses good elongation and tensile strength, good flexibility in low temperature, good abrasion resistance, good adhesion property, good weatherability and good chemical resistance.