Modified Polyisocyanate Composition for Low-Viscosity Membrane Sealing
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Solution Overview
Problem
Existing MDI-based polyisocyanate compositions used for membrane sealing materials face challenges in achieving low viscosity while minimizing the elution of low molecular weight reaction products and maintaining high crosslink density, leading to issues like phase separation and poor appearance in polyurethane resins.
Innovation Solution
A polyisocyanate composition comprising diphenylmethane diisocyanate, isocyanate-terminated prepolymer, and modified isocyanate, such as carbodiimide- or uretonimine-modified diphenylmethane diisocyanate, with specific mass content ratios, is used in conjunction with a polyol to form a polyurethane resin with controlled crosslink density and low viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the amount of MDI monomer in the polyisocyanate is decreased to reduce low molecular weight reaction products eluted, then the amount of polyol introduced increases, but the viscosity of the polyisocyanate becomes too high
Solution Approach 1:
The patent applies parameter changes by modifying the chemical structure of MDI through carbodiimide or uretonimine modification. This chemical modification changes the molecular weight and reactivity parameters of the isocyanate, allowing reduction of MDI content while maintaining appropriate viscosity levels. The modified isocyanate reacts differently with polyol, reducing low molecular weight eluates while keeping the composition workable.
Solution Approach 2:
The patent creates a composite polyisocyanate system combining multiple components: unmodified MDI, carbodiimide-modified MDI, and uretonimine-modified MDI in specific ratios. This composite approach allows balancing the contradictory requirements by having unmodified MDI contribute to reactivity while modified MDI components reduce eluate formation and control viscosity through their different molecular characteristics.
2Stability of the object's composition
If partially dehydrated castor oil is used in the polyurethane resin forming composition, then the crosslink density decreases, but shaping defects are generated
Solution Approach 1:
The patent modifies the chemical parameters of the castor oil component by using partially dehydrated castor oil with controlled water content and chemical structure. This parameter modification maintains sufficient crosslinking capability while improving the material's flow and shaping characteristics, thereby reducing shaping defects while preserving crosslink density.
3Stability of the object's composition
If partially dehydrated castor oil with high hydrophobicity is used in the polyurethane resin forming composition, then phase separation occurs inside the polyurethane resin, but the appearance of the shaped product deteriorates
Solution Approach 1:
The patent controls the hydrophobicity parameter of the castor oil component through partial dehydration and selects specific polyol molecular weights and structures. This parameter control reduces excessive hydrophobicity that causes phase separation, thereby maintaining compositional stability while improving appearance quality by preventing internal phase separation defects.
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 results in a membrane sealing material with reduced low molecular weight eluates, high hardness, and excellent appearance, suitable for membrane modules with improved mechanical properties.
Implementation Method 1
a polyisocyanate (A), in which the polyisocyanate (A) contains: a diphenylmethane diisocyanate (a1); an isocyanate-terminated prepolymer (a2); and a modified isocyanate (a3)... and a polyol (B)
Implementation Method 2
the crosslink density of the polyurethane resin decreases and shaping defects are generated
Implementation Method 3
a modified isocyanate (a3), in which the modified isocyanate (a3) is a modified product of a diphenylmethane diisocyanate... the isocyanate-terminated prepolymer (a2) is a reaction product of a polyisocyanate (a2-1) and a polyol (a2-2)
Data Source
AI summary
A polyisocyanate composition containing:a diphenylmethane diisocyanate (a1); an isocyanate-terminated prepolymer (a2) that is a reaction product of a polyisocyanate (a2-1) and a polyol (a2-2); and a modified isocyanate (a3), in whichthe polyisocyanate (a2-1) contains a diphenylmethane diisocyanate (a2-1-1) and a modified isocyanate (a2-1-2), in whichthe modified isocyanate (a2-1-2) is at least one selected from the group consisting of a carbodiimide-modified diphenylmethane diisocyanate and a uretonimine-modified diphenylmethane diisocyanate, andthe modified isocyanate (a3) is a modified product of a diphenylmethane diisocyanate, andthe content of the modified isocyanate (a2-1-2) in the polyisocyanate (a2-1) is 4.5% to 15% by mass.