Polyisocyanate Composition for Water-Based Coatings
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Solution Overview
Problem
Conventional polyisocyanate compositions used in water-based coating systems face issues with reduced isocyanate functional group numbers, leading to unsatisfactory curability, drying properties, hardness, and water resistance due to hydrophilicity and increased viscosity when combined with active hydrogen group-containing agents.
Innovation Solution
A polyisocyanate composition derived from aliphatic or alicyclic diisocyanates with a high mole fraction of isocyanurate groups, optimized molecular weight distribution, and modified with hydrophilic compounds to maintain viscosity stability and enhance pot life, drying properties, gloss, hardness, and water resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyisocyanate is dispersed in water by introducing ethylene oxide units, then water dispersibility is improved, but isocyanate functional group number is reduced
Solution Approach 1:
The patent changes the molecular weight parameters of the polyisocyanate components, specifically using a mixture where 5-20% by mass has number average molecular weight of 1,000 or more, while controlling the ratio (B)/(A) of medium to low molecular weight components to be 1-150. This parameter optimization maintains high isocyanate functional group numbers while achieving water dispersibility without requiring ethylene oxide modification.
2Ease of operation
If polyisocyanate with low viscosity is used as curing agent, then compatibility with water-based main agent is improved, but isocyanate functional group number per molecule is reduced
Solution Approach 1:
The patent creates a composite polyisocyanate system combining multiple components with different molecular weights (low: 200-400, medium: 400-700, and high: ≥1,000). This composite structure provides both the low viscosity needed for compatibility and the high functional group number from the high molecular weight component, achieving both requirements simultaneously.
3Ease of operation
If polyisocyanate mixture with hydrophilic groups is used, then water dispersibility is improved, but viscosity increase when combined with active hydrogen group-containing main agent is marked
Solution Approach 1:
The patent applies local quality by having only a portion (5-20% by mass) of the polyisocyanate mixture consist of high molecular weight components, while the majority (80-95%) consists of low and medium molecular weight components. This localized distribution maintains low overall viscosity while providing sufficient water dispersibility through the high molecular weight fraction.
Data Source
AI summary
The invention provides a polyisocyanate composition that exhibits favorable viscosity change, good pot life when used in a water-based coating composition, and excellent drying properties, gloss, hardness, water resistance and salt water spray resistance when used in a coating film. The polyisocyanate composition contains a polyisocyanate derived from at least one diisocyanate selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, wherein among the bonded groups derived from isocyanate groups within the polyisocyanate, the mole fraction of isocyanurate groups is the highest, the ratio of the mass fraction (B) of polyisocyanate for which the number average molecular weight is at least 400 but not more than 700, relative to the mass fraction (A) of polyisocyanate for which the number average molecular weight is at least 200 but less than 400, is within a range from 1 to 150, and the mass fraction of polyisocyanate for which the number average molecular weight is 1,000 or greater, relative to the total mass of the polyisocyanate composition, is within a range from 5 to 20% by mass.