Latent Two-Part Polyurethane Adhesives Cured With Infrared
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Solution Overview
Problem
Two-part polyurethane adhesives with amine compounds have a short open time and poor storage stability, making it difficult to achieve both prolonged flowability and rapid curing, especially when infrared heating is used for curing.
Innovation Solution
A two-component polyurethane adhesive composition without primary and secondary amino groups, featuring a polyol component with specific hydroxyl equivalent weights and functionalities, and an isocyanate component with a balanced isocyanate index, utilizing acid-blocked cyclic amidine and latent room temperature organometallic catalysts for room temperature curing and enhanced infrared activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If amine compounds are added to accelerate curing, then curing speed is improved, but open time is shortened and storage stability deteriorates
Solution Approach 1:
The patent removes amine compounds from the adhesive formulation entirely, extracting the problematic accelerating agent that caused short open time and poor storage stability. Instead, the invention uses a moisture-curing polyurethane system that achieves acceptable curing speed without amine catalysts, thereby resolving the contradiction between curing speed and open time.
Solution Approach 2:
The patent changes the chemical parameters of the adhesive system by using specific polyol molecular weights (3000-20000) and hydroxyl functionalities (2-4), along with controlled isocyanate index (1.05-1.30), to achieve optimal balance between open time and curing speed without requiring amine compounds.
2Speed
If amine compounds are added to accelerate curing, then curing speed is improved, but storage stability deteriorates
Solution Approach 1:
The patent removes amine compounds from the adhesive formulation entirely, extracting the problematic accelerating agent that caused poor storage stability. The moisture-curing mechanism replaces the amine-catalyzed system, eliminating the stability issues while maintaining curing functionality.
Solution Approach 2:
The patent uses a simple moisture-curing mechanism that relies on ambient moisture rather than stable catalysts, effectively using a 'disposable' curing approach where the curing agent (moisture from air) is naturally available and does not require long-term stable storage in the adhesive formulation.
3Reliability
If conventional oven heating is used for curing, then complete cure is achieved, but production time increases and cost increases
Solution Approach 1:
The patent replaces the mechanical/thermal convection heating system (conventional ovens) with a chemical moisture-curing mechanism that operates at ambient conditions. This substitution eliminates the need for energy-intensive heating equipment and reduces production time while achieving adequate cure through reaction with environmental moisture.
4Productivity
If infrared heating is used for partial curing, then production speed is improved and energy consumption is reduced, but complete bond strength development is limited
Solution Approach 1:
The patent replaces thermal infrared heating with a chemical moisture-curing mechanism that naturally progresses to complete cure without external energy input. The moisture-curing system ensures complete bond strength development through chemical reaction with ambient moisture, eliminating the trade-off between production speed and strength development.
Solution Approach 2:
The adhesive system is self-curing through reaction with moisture from the environment, requiring no external heating or catalysts. The curing process serves itself by utilizing naturally available moisture, ensuring complete bond strength development while maintaining production efficiency.
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 adhesive exhibits prolonged open time at room temperature while allowing rapid curing upon infrared heating, maintaining strong bond strength without the need for elevated temperatures, thus optimizing production processes and energy efficiency.
Implementation Method 1
The polyol component or the polyisocyanate component includes an acid-blocked cyclic amidine catalyst... the polyol component includes from 0.05 to 0.15 parts by weight, per 100 parts by weight of component a), of the one or more latent room temperature organometallic catalysts
Implementation Method 2
Latent two-part polyurethane adhesives that rapidly develop adhesive strength when cured by application of infrared radiation... Infrared heating methods have been developed. These methods permit the substrate/adhesive assembly to be brought more rapidly to the curing temperature
Implementation Method 3
When the two components mixed, the polyisocyanates and polyols react to form a cured polyurethane adhesive... the isocyanate equivalent weight of the polyisocyanate component and the hydroxyl equivalent weight of the polyol component are such that when the polyisocyanate component and the polyol component are mixed at a 1:1 ratio by volume the isocyanate index is 1.1 to 1.8
Data Source
AI summary
Two-component polyurethane adhesives include a polyol component and a polyisocyanate component. The polyol component includes a polyether polyol and an aliphatic diol chain extender, but is devoid of primary and second amine compounds. The polyisocyanate component includes one or more polyisocyanate compounds. The adhesive contains a mixture of a dialkyltinthioglycolate catalyst and an acid-blocked cyclic amidine catalyst. The tin catalyst is formulated into the polyol component, whereas the cyclic amidine catalyst can be formulated into either the polyol or the polyisocyanate components.