High-temperature cross-linking dispersion
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Solution Overview
Problem
Existing aqueous polyurethane dispersions and paint formulations contain solvents like N-methylpyrrolidone and butylglycol, which are difficult to remove, leading to stability issues and limited mechanical strength, and conventional solvent-based paints are not fully replaced by aqueous systems due to viscosity and storage stability challenges.
Innovation Solution
A process involving reacting polyisocyanate with primary monofunctional alcohols to partly block it, followed by nonionic hydrophilization and further blocking to create a blocked polyisocyanate, which can be converted to unblocked form at high temperatures, forming stable aqueous dispersions without solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solvents are used in polyurethane dispersions to achieve proper viscosity and film formation, then the coating quality and storage stability are improved, but the environmental compliance and solvent emission control deteriorate
Solution Approach 1:
The patent extracts and removes solvents from the polyurethane dispersion system entirely, creating a solvent-free aqueous dispersion. This is achieved through a multi-step process involving partial blocking of isocyanate groups, hydrophilization, and controlled dispersion formation, eliminating the need for solvents like NMP while maintaining product performance and storage stability
Solution Approach 2:
The patent changes the chemical state of isocyanate groups by applying partial blocking (converting some NCO groups to blocked forms) and controlled hydrophilization. This parameter change allows the system to function without solvents by modifying the molecular interactions and dispersion characteristics of the polyurethane prepolymer in aqueous media
2Object-generated harmful factors
If solvents are removed from polyurethane dispersions to reduce emissions, then environmental compliance is improved, but film formation capability and storage stability deteriorate
Solution Approach 1:
The patent applies preliminary blocking of isocyanate groups before dispersion formation. By pre-blocking a portion of NCO groups with compounds like cyclohexane carbonate or phenyl carbonate, the system prevents unwanted crosslinking and maintains stability during storage. This preliminary action ensures the dispersion remains stable without solvents while retaining reactivity for crosslinking during application
Solution Approach 2:
The patent introduces hydrophilizing agents as intermediaries to enable aqueous dispersion of polyurethane prepolymers without solvents. These agents facilitate the interaction between the hydrophobic polyurethane chains and water, creating stable aqueous dispersions that maintain film formation capability without requiring organic cosolvents
3Reliability
If blocking agents are used to stabilize polyisocyanate dispersions, then storage stability is improved, but the crosslinking reactivity at application temperature deteriorates
Solution Approach 1:
The patent applies partial blocking, where only a portion (typically 20-50%) of the isocyanate groups are blocked rather than all of them. This partial action maintains sufficient unblocked NCO groups for crosslinking reactivity while providing enough blocked groups to stabilize the dispersion during storage. The balance is optimized to achieve both storage stability and crosslinking performance
Solution Approach 2:
The patent employs thermally reversible blocking agents that dynamically transition between blocked and unblocked states based on temperature. At storage temperatures, the blocking is predominant, providing stability. At application temperatures (above 100°C), the blocking reverses, releasing the NCO groups for crosslinking. This dynamic behavior allows the same system to exhibit different properties under different thermal conditions
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 results in a storage-stable aqueous dispersion with high versatility, enabling the use in various formulations and achieving mechanical strength comparable to solvent-based paints.
Implementation Method 1
reacting at least one polyisocyanate with at least one thermally eliminatable blocking agent... in order to obtain at least one blocked polyisocyanate... which can be converted to unblocked form at high temperatures
Data Source
AI summary
The present invention relates to a process for preparing at least one blocked polyisocyanate, comprising the following steps: (A) reacting at least one polyisocyanate with at least one thermally cleavable blocking agent selected from the group consisting of primary, monofunctional alcohols and mixtures thereof to obtain at least one partially blocked polyisocyanate, (B) reacting the at least one partially blocked polyisocyanate from step (A) with at least one non-ionic hydrophilizing agent to obtain an intermediate product, and (C) reacting the intermediate product obtained in step (C) with at least one thermally cleavable blocking agent selected from the group consisting of primary, monofunctional alcohols and mixtures thereof, to obtain the at least one blocked polyisocyanate. The invention further relates to a correspondingly obtained blocked polyisocyanate, to the use of the blocked polyisocyanate for producing coating agents, adhesives, sealants or elastomers, to corresponding coating agents, adhesives, sealants or elastomers, and to substrates that are provided with coatings obtained using the at least one blocked polyisocyanate according to the invention.