Branched-Diol Modified Blocked Polyisocyanates for Storage Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing blocked polyisocyanates based on linear aliphatic diisocyanates with isocyanurate groups and secondary amines suffer from poor storage stability due to high crystallization tendencies, limiting their use in applications like coil coating.
Innovation Solution
A process involving the reaction of polyisocyanates containing isocyanurate and/or iminooxadiazinedione structures with branched aliphatic diols and secondary amines, where the diol is used in excess of 2% by weight and the amine reacts with at least 95 mol% of remaining isocyanate groups, producing stable blocked polyisocyanates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polyisocyanates with isocyanurate groups based on linear aliphatic diisocyanates are blocked with secondary amines, then low baking temperatures are achieved, but storage stability deteriorates due to high crystallization tendency
Solution Approach 1:
The patent changes the chemical structure parameters of the polyisocyanate by introducing specific cyclic structures (isocyanurate and iminooxadiazinedione groups) and controlling the NCO content within 15-30% by weight range. This parameter modification prevents crystallization while maintaining low deblocking temperature characteristics of secondary amine blocking
Solution Approach 2:
The patent creates a composite molecular structure combining multiple functional groups (isocyanurate, iminooxadiazinedione, and urethane linkages) within the polyisocyanate chain. This composite structure disrupts molecular packing and prevents crystallization, while the secondary amine blocking agent maintains its low-temperature deblocking capability
2Productivity
If secondary amines are used as blocking agents for isocyanurate polyisocyanates, then reactivity is improved, but storage stability worsens due to crystallization
Solution Approach 1:
The patent optimizes the NCO content parameter to 15-30% by weight and controls the molecular weight and structure of the polyisocyanate component. These parameter changes prevent crystallization of the amine-blocked product while preserving the high reactivity characteristics of secondary amine blocking agents
Solution Approach 2:
The patent introduces specific cyclic structures (isocyanurate and iminooxadiazinedione groups) as intermediary structural elements that mediate between the conflicting requirements of reactivity and storage stability. These structures prevent molecular packing that leads to crystallization while maintaining the chemical reactivity of the blocked isocyanate groups
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 resulting polyisocyanates exhibit improved storage stability without crystallization, making them suitable for low-temperature crosslinking in applications such as coil coating.
Implementation Method 1
Blocked polyisocyanates, of the kind which may be obtained by reacting isocyanate groups with so-called blocking agents
Implementation Method 2
A process involving the reaction of polyisocyanates containing isocyanurate and/or iminooxadiazinedione structures with branched aliphatic diols
Implementation Method 3
At higher temperatures, the blocking agent is cleaved again and releases the isocyanate group for crosslinking with the polyol component
Data Source
AI summary
The invention relates to a method for producing a blocked polyisocyanate, having the steps of reacting A) at least one polyisocyanate component, which has at least isocyanurate and/or iminooxadiazindione structures, with B) at least one branched aliphatic diol and C) at least one secondary amine with aliphatic, cycloaliphatic, and/or araliphatic substituents. The invention is characterized in that the component B) is used in a quantity of more than 2 wt. % based on the total quantity of the components A) and B), 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), and as the polyisocyanate component A), polyisocyanates are used which are produced by modifying simple linear aliphatic, cycloaliphatic, araliphatic, and/or aromatic diisocyanates and which have at least isocyanurate and/or iminooxadiazindione structures, wherein >70 equiv. %, based on the NCO content, is used for the modification process. The invention also relates to said blocked polyisocyanates.