Blocked Polyisocyanate Crosslinking for Stable Plastics
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Solution Overview
Problem
Existing methods for producing plastics using isocyanates face challenges with storage stability and catalyst-induced premature crosslinking, and unsuitable blocking agents can decrease the hardness of coatings, particularly when using pyrazoles and dibutyltin dilaurate as catalysts.
Innovation Solution
A process involving a polyisocyanate composition with blocked isocyanates using phenols, oximes, or lactams as blocking agents and a specific catalyst to predominantly form isocyanurate structures, ensuring that at least 80% of isocyanate groups remain blocked until curing, resulting in dimensionally stable plastics with high glass transition temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If free isocyanate groups are used with crosslinking catalyst, then crosslinking reaction occurs, but storage stability deteriorates due to premature crosslinking at low temperatures
Solution Approach 1:
The isocyanate groups are preliminarily blocked with blocking agents (oximes, lactams, or phenols) before the crosslinking reaction. This preliminary blocking action prevents premature crosslinking during storage, while the blocked groups can be subsequently unblocked by heating to enable the desired crosslinking reaction when needed
Solution Approach 2:
The reactivity of isocyanate groups is temporarily reduced by blocking them, changing the physical-chemical state from highly reactive to storage-stable. The blocking agents modify the isocyanate groups' parameters (reactivity, stability) to enable storage, and subsequent heating reverses this modification to restore reactivity for crosslinking
2Reliability
If pyrazoles are used as blocking agents, then isocyanate groups can be blocked, but coating hardness decreases due to catalyst interaction
Solution Approach 1:
The patent replaces pyrazole blocking agents with alternative blocking agents (oximes, lactams, phenols) that do not have the harmful interaction with crosslinking catalysts. These alternative blocking agents serve their temporary purpose of stabilizing the isocyanate groups during storage and application, then are eliminated upon heating to allow proper crosslinking and hardness development
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 process produces plastics that are dimensionally stable at room temperature with high glass transition temperatures, avoiding the issues of premature crosslinking and hardness reduction, and allows for the use of storage-stable, non-toxic reaction mixtures.
Implementation Method 1
the catalyst mediates a crosslinking reaction even at low temperatures
Implementation Method 2
the blocking is removed by heating of the mixture and the reactive isocyanate groups are available for a crosslinking reaction
Data Source
Figure 1
AI summary
The present invention relates to the production of plastics by crosslinking of blocked polyisocyanates. The plastics obtainable are characterized in that they are substantially free of urethane groups and the crosslinking of the monomers is predominantly effected by isocyanurate groups.