Silyl Ester Stabilization of Polyisocyanate Flocculation
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Solution Overview
Problem
Polyisocyanates in solvents experience flocculation instability during storage, particularly in small containers exposed to atmospheric moisture, leading to premature degradation and reduced coating properties due to the high amounts of water scavengers required for stabilization, which also affect the NCO group content and solubility.
Innovation Solution
The use of silyl esters, specifically silyl phosphates and silyl phosphonates, in amounts ranging from 1 to 250 ppm, is introduced to reduce flocculation and precipitation in polyisocyanate mixtures, providing enhanced stability without significantly reducing the NCO group content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water scavengers (para-toluenesulfonyl isocyanate or triethyl orthoformate) are added stoichiometrically to prevent hydrolysis, then flocculation stability is improved, but NCO group content is reduced and coating properties deteriorate
Solution Approach 1:
The patent changes the chemical parameter by using a silyl ester with specific molecular structure and properties (low reactivity toward water, high solubility) compared to conventional water scavengers. This parameter change allows achieving the same water-scavenging effect with minimal impact on NCO group content, resolving the contradiction between flocculation stability and NCO group preservation
Solution Approach 2:
The patent employs a disposable silyl ester molecule that reacts with water to form volatile byproducts (alcohol and silanol), which can be easily removed. This approach allows using minimal amounts of additive (0.01-5% by weight) compared to conventional scavengers, thereby preserving NCO group content while maintaining flocculation stability
2Reliability
If high amounts of water scavengers (0.5-4.0% para-toluenesulfonyl isocyanate or 1-3% triethyl orthoformate) are used for stabilization, then hydrolysis prevention is improved, but the dilution effect reduces NCO groups and affects coating properties
Solution Approach 1:
The patent changes the concentration parameter by using silyl ester at very low levels (0.01-5% by weight based on polyisocyanate weight), compared to the 0.5-4.0% or 1-3% required for conventional scavengers. This parameter change minimizes dilution effects while maintaining effective hydrolysis prevention, thus preserving coating properties
Solution Approach 2:
The silyl ester acts as an intermediary substance that mediates between water and polyisocyanate. It preferentially reacts with water to form non-interfering byproducts, protecting the NCO groups from hydrolysis without requiring high concentrations that would dilute the active components and affect coating performance
3Quantity of substance
If para-toluenesulfonyl isocyanate is used as water scavenger, then water reaction capability is improved, but pressure build-up occurs and tosylamide crystallization causes bittiness
Solution Approach 1:
The patent uses a silyl ester that reacts with water to form volatile alcohol and silanol byproducts, which can be easily evaporated or removed. This contrasts with para-toluenesulfonyl isocyanate that forms non-volatile tosylamide crystals. The disposable nature of the silyl ester reaction products eliminates pressure build-up and bittiness problems
Solution Approach 2:
The patent converts the potential harm of water presence into a beneficial outcome by using silyl ester to scavenge water and form volatile byproducts. The reaction Cpd + H2O → Alcohol + Silanol transforms the harmful water into removable volatile substances, eliminating pressure build-up and crystallization issues while maintaining water-scavenging effectiveness
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
This approach significantly extends the storage stability of polyisocyanates by minimizing the amount of additives needed, maintaining the NCO group content and solubility, thus ensuring the retention of product properties for extended periods, even in high-humidity and high-temperature conditions.
Implementation Method 1
Water-scavenging reactive compounds react with water instead of the isocyanate groups and prevent the polyisocyanates from being hydrolyzed
Implementation Method 2
Flocculation in the sense of this patent refers comprehensively to formation of solids in such a way as to be visible to the naked eye
Data Source
AI summary
The present invention relates to a new process for preparing polyisocyanates containing isocyanurate groups and being flocculation-stable in solvents from (cyclo)aliphatic diisocyanates.