Blocked Polyisocyanate Composition for Low-Temperature 1K PU Baking
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Solution Overview
Problem
Existing polyisocyanates containing isocyanurate groups blocked with secondary amines, such as diisopropylamine, have a high tendency to crystallize and are not storage-stable in paint solvents, limiting their use in one-component polyurethane (1K-PU) coating materials, particularly for automotive OEM finishing and coil coating applications.
Innovation Solution
A blocked polyisocyanate component is produced by reacting polyisocyanates with isocyanurate and/or iminooxadiazinedione structures, branched aliphatic diols, and secondary amines like diisopropylamine, ensuring at least 95 mol% of isocyanate groups are blocked, to create a stable crosslinker suitable for 1K PU baking enamels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polyisocyanates containing isocyanurate groups are blocked with secondary amines like diisopropylamine, then low baking temperatures are achieved, but the solutions show high tendency to crystallize and are not storage-stable
Solution Approach 1:
The patent applies parameter changes by modifying the molecular structure of the polyisocyanate through partial urethanization with branched aliphatic diols. This structural modification changes the physical properties of the blocked polyisocyanate, specifically reducing its crystallization tendency while maintaining the low deblocking temperature characteristic of secondary amine blocking. The branched diol components introduce steric hindrance and disrupt crystal lattice formation, thereby improving storage stability without sacrificing the low baking temperature advantage.
Solution Approach 2:
The invention creates a composite blocked polyisocyanate system by combining multiple components: isocyanurate group-containing polyisocyanates, branched aliphatic diols (such as 2-methyl-1,3-propanediol), and secondary amines (such as diisopropylamine). This composite structure integrates the low-temperature deblocking property from the secondary amine blocking with the crystallization-inhibiting effect from the branched diol modification, achieving both low baking temperature and storage stability simultaneously.
2Strength
If polyisocyanates are blocked with secondary amines to enable low baking temperatures, then coating flexibility is improved, but crystallization stability is reduced
Solution Approach 1:
The patent modifies the molecular parameters of the polyisocyanate by introducing branched aliphatic diol structures. This structural change affects the packing efficiency and intermolecular forces, reducing crystallization stability while preserving the secondary amine blocking characteristics that provide coating flexibility. The branched structures create steric hindrance that prevents tight molecular packing, thereby inhibiting crystallization.
Solution Approach 2:
The branched aliphatic diol acts as an intermediary structure that mediates between the conflicting requirements of flexibility and stability. It modifies the polyisocyanate backbone to reduce crystallization tendency while allowing the secondary amine blocking to maintain its flexibility-providing function. The diol structure serves as a molecular spacer that disrupts crystal formation without interfering with the deblocking reaction.
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 provides a crystallization- and storage-stable blocked polyisocyanate that can be formulated into 1K PU baking enamels, suitable for coil coating applications, with improved flexibility and stability at low baking temperatures.
Implementation Method 1
They show a very high tendency to solidify, e.g. by crystallization of the blocked polyisocyanate present
Implementation Method 2
At higher temperatures, the blocking agent is cleaved off again and releases the isocyanate group for crosslinking with the polyol component
Data Source
AI summary
The invention relates to a one-component burn-in system comprising A) a blocked polyisocyanate component containing at least one reaction product of a) at least one polyisocyanate component, which has at least isocyanurate and/or iminooxadiazinedione structures, b) at least one branched aliphatic diole, and c) at least one secondary amine with aliphatic, cycloaliphatic, and/or araliphatic substituents, wherein the component b) is used in a quantity of more than 2 wt. % based on the total quantity of the components a) and b), and the component c) is used in a quantity which corresponds to at least 95 mol. % of the isocyanate groups mathematically still present after the reaction of the components a) and b), B) at least one binder which is reactive to isocyanate groups and comprises at least two isocyanate-reactive groups per molecule on statistical average, C) optionally catalysts, and D) optionally solvents and/or optionally auxiliary agents and additives.