Silylated Polyurethane Adhesives with Low Residual Tack
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Solution Overview
Problem
There is a need for isocyanate-free compositions that offer good elasticity, strength, and a low modulus of elasticity, with a user-friendly curing time, and without residual stickiness, particularly for 1-component or 2-component adhesives and sealants.
Innovation Solution
A process involving reacting a polyol compound with a diisocyanate in stoichiometric excess to form an isocyanate-terminated polyurethane prepolymer, which is then reacted with OH-terminated silanes to produce silylated polyurethanes with alkoxysilyl groups, incorporating monofunctional compounds like monoalcohols or monoamines to achieve the desired properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If isocyanate-terminated polyurethane prepolymers are reacted with amino-functional silanes to form silane-terminated prepolymers, then the compositions become free from isocyanate groups, but the mechanical properties particularly elongation and tear resistance become unsatisfactory
Solution Approach 1:
The patent changes the chemical parameters by using hydroxy-functional silane compounds instead of amino-functional silanes, and employs sub-stoichiometric amounts of silane relative to isocyanate groups. This parameter change achieves both isocyanate-free compositions and satisfactory mechanical properties through optimized stoichiometry
Solution Approach 2:
The patent creates a composite system combining polyurethane prepolymers with hydroxy-functional silane compounds, where the silane groups provide crosslinking functionality while the polyurethane matrix maintains mechanical integrity. The composite structure achieves both isocyanate elimination and preserved mechanical properties
2Strength
If high crosslinking density is achieved through silane condensation, then the strength and rigidity of the material improve, but the elasticity and elongation decrease
Solution Approach 1:
The patent applies partial action by using sub-stoichiometric amounts of silane compounds (less than equivalent to isocyanate groups), creating a controlled crosslinking density that provides strength while preserving elasticity. The partial crosslinking avoids excessive network formation that would reduce elongation
Solution Approach 2:
The patent creates local quality differences in the polymer network by distributing crosslinks non-uniformly through controlled silane condensation. The crosslinked regions provide strength while uncrosslinked polyurethane segments maintain elasticity, achieving a heterogeneous structure with both properties
3Ease of operation
If monofunctional compounds are added to the polyol mixture, then the viscosity and processing characteristics improve, but the crosslinking density and final strength may be reduced
Solution Approach 1:
The patent changes the functional distribution parameter by incorporating monofunctional compounds with the polyols, creating a mixture with average functionality less than 2. This parameter change reduces viscosity for easier processing while the subsequent silane crosslinking compensates for the reduced crosslinking density
Solution Approach 2:
The monofunctional compounds act as intermediaries that modify the polyol mixture properties, reducing viscosity and improving processability. Although they reduce average crosslinking density, the hydroxy-functional silanes serve as additional crosslinking agents that compensate for this reduction and maintain final strength
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 silylated polyurethane compositions exhibit high elasticity, low modulus of elasticity, and a balanced curing time, with improved viscoelastic properties and reduced residual tack, making them suitable for various applications.
Implementation Method 1
In the presence of atmospheric moisture, these alkoxysilane-terminated polymers are able to condense with one another at room temperature, eliminating the alkoxy groups
Implementation Method 2
In the presence of atmospheric moisture, these alkoxysilane-terminated polymers are able to condense with one another at room temperature, eliminating the alkoxy groups
Implementation Method 3
reacting a polyol compound with a diisocyanate in stoichiometric excess to form an isocyanate-terminated polyurethane prepolymer, which is then reacted with OH-terminated silanes to produce silylated polyurethanes with alkoxysilyl groups
Data Source
AI summary
Silylated polyurethanes can be obtained by reacting at least one polyol compound having a molecular weight of 4000 to 20000 Daltons with a diisocyanate at a stoichiometric excess of the diisocyanate compound in relation to the polyol compound or the polyol compounds, thereby producing a polyurethane prepolymer which has isocyanate terminal groups; and then reacting the polyurethane prepolymer with one or more OH-terminated silanes of formula (1) to give a polyurethane having mainly terminal alkoxysilyl groups. In the formula (1), m = 0, 1 or 2, R1 represents an alkyl group with 1 to 4 carbon atoms, R2 represents an alkyl group with 1 to 4 carbon atoms, R3 represents a divalent organic group with 1 to 12 atoms selected from C, N and/or O in the chain, preferably however carbon atoms only, R4 represents a hydrogen atom or an alkyl group with 1 to 10 carbon atoms and R represents a difunctional organic group, preferably a linear or branched alkyl group with 1 to 6 C atoms. The silylated polyurethanes are suitable for use in a preparation as adhesive, sealing or coating agent.