Crystalline Polyurethane Adhesive Pot Life and Crosslinking
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Solution Overview
Problem
Aqueous dispersion adhesives based on polyurethane polymers face challenges with short pot life due to rapid consumption of isocyanate groups, leading to inadequate heat resistance in adhesive bonds, and existing solutions like latent reactive dispersions are not applicable to systems with liquid aliphatic isocyanates.
Innovation Solution
An aqueous composition comprising crystalline or semicrystalline polyurethane polymers, liquid aliphatically bonded isocyanates, and compounds from sub-group 5 and 6 of the periodic table with an oxidation level of at least +4, which accelerates crosslinking reactions while maintaining a long pot life, allowing for strong adhesive bonds within 24 hours.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid aliphatic polyisocyanates are used in aqueous dispersion adhesives, then crosslinking reaction occurs, but isocyanate groups are consumed rapidly by water, resulting in short pot life
Solution Approach 1:
The patent introduces compounds of elements from sub-groups 5 and 6 (V, Nb, Ta, Cr, Mo, W) as intermediary catalysts that mediate between the polyisocyanate and water. These catalysts accelerate the desired crosslinking reaction while controlling the unwanted hydrolysis reaction, allowing the system to achieve both rapid crosslinking and extended pot life by regulating the reaction pathway through catalytic intervention
Solution Approach 2:
The patent changes the chemical parameter by selecting specific metal compounds with oxidation levels of at least +4 from sub-groups 5 and 6. These specific parametric choices (metal type, oxidation state) create optimal catalytic conditions that modify the reaction kinetics, enabling extended pot life while maintaining effective crosslinking capability
2Strength
If isocyanate reactivity is increased for rapid crosslinking, then adhesive strength is improved, but processing time is reduced
Solution Approach 1:
The metal compounds serve as intermediaries that decouple the relationship between reactivity and processing time. By introducing these catalytic intermediaries, the system achieves rapid crosslinking (improved strength) without the need for high isocyanate reactivity, thus preserving processing time. The catalyst mediates the reaction rate independently of the isocyanate's inherent reactivity
Solution Approach 2:
The patent applies preliminary action by adding the metal compound catalyst to the adhesive dispersion before application. This pre-added catalyst is dormant during storage and mixing but becomes active during the adhesive bonding process, preliminarily preparing the system for rapid crosslinking without affecting the pot life during storage and processing
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 enables a prolonged pot life and rapid crosslinking of adhesive bonds, achieving high strength within 24 hours without the need for thermal curing, thereby reducing production errors and costs.
Implementation Method 1
at least one or more compounds of elements of sub-group 5 and 6 of the periodic table in which the particular element has an oxidation level of at least +4
Data Source
AI summary
The present invention relates to aqueous compositions based on crystalline or semicrystalline polyurethane polymers, processes for the preparation thereof and adhesive systems comprising these aqueous compositions and the use thereof.