Hydroxy Functional Waterborne Resins for Leather Urethane Crosslinking
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Solution Overview
Problem
Current leather finishing technologies using waterborne coating systems face challenges with low crosslinking density, leading to a trade-off between cohesive properties and flexibility due to the self-condensation of isocyanate crosslinkers, resulting in an inter-penetrating network rather than urethane formation.
Innovation Solution
A coating composition comprising a polyol resin with hydroxyl groups and a polyurethane crosslinker, along with water, which allows for increased urethane crosslink density while maintaining flexibility, by using a polyurethane crosslinker that effectively crosslinks the hydroxyl groups in the polyol resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If isocyanate crosslinkers are used to increase crosslinking density, then cohesive properties are improved, but flexibility deteriorates due to formation of inter-penetrating network instead of urethane crosslinks
Solution Approach 1:
The invention changes the chemical parameter of the crosslinking mechanism from self-condensation of isocyanates forming urea linkages to reaction between hydroxyl groups and isocyanates forming urethane crosslinks. This parameter change in the chemical reaction pathway resolves the contradiction by achieving both high crosslink density and maintained flexibility through the specific urethane bonding mechanism.
Solution Approach 2:
The invention extracts and eliminates the problematic self-condensation pathway of isocyanate crosslinkers that creates inter-penetrating networks. By removing this unwanted reaction mechanism and replacing it with hydroxyl group-based crosslinking, the system achieves improved cohesive properties without the detrimental loss of flexibility associated with IPN formation.
2Reliability
If high molecular weight resins are used to achieve performance through coalescence, then coating performance is improved, but crosslinking density remains low
Solution Approach 1:
The invention creates a composite coating system combining high molecular weight waterborne resins with hydroxyl-functional polyol resins and isocyanate crosslinkers. This composite approach allows the high molecular weight resins to provide coating performance through coalescence while the polyol crosslinking system simultaneously provides high crosslinking density, resolving the contradiction between these two requirements.
Solution Approach 2:
The invention merges two previously separate functional systems into one unified coating composition: the high molecular weight waterborne resin system responsible for film formation and coalescence, and the hydroxyl-functional polyol crosslinking system responsible for high crosslinking density. This merging allows both functions to operate simultaneously without compromise.
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 solution enhances the crosslinking density of the leather finishing system, improving performance while maintaining flexibility, thereby overcoming the limitations of existing technologies.
Implementation Method 1
a polyurethane crosslinker that crosslinks the hydroxyl groups when cured
Data Source
AI summary
A coating composition includes at least one, low Tg, polyol resin having hydroxyl groups available for crosslinking, a polyurethane crosslinker that crosslinks the hydroxyl groups when cured, and water in an amount from about 4 to 20 wt. % of the total weight of the coating composition. Characteristically, solvents other than water are present in an amount less than half the amount of water. The coating composition is advantageously used to finish leather.