Solvent-Borne Polyurethane Adhesive Composition for High Solids, Low Viscosity
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Solution Overview
Problem
Existing high molecular weight solvent-borne polyurethane adhesives and coatings rely heavily on toluene as a co-solvent, which is difficult to extract, limiting solid content and requiring high viscosity formulations, and there is a need for a toluene-free adhesive with lower viscosity and higher solid content suitable for brushing applications.
Innovation Solution
A composition comprising a polyurethane polymer, an aliphatic isocyanate cross-linker, a polar-aprotic solvent, and a co-solvent such as water or a primary alcohol, forming a homogeneous mixture without a second phase, with a hydroxyl group content of ≥ 1 weight-% and polyurethane content of ≥ 10 weight-%, allowing for a single continuous liquid phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If toluene is used as a co-solvent in high molecular weight polyurethane adhesives, then the polymer can be dissolved and applied, but the adhesive has high viscosity and low solid content (10-15 weight%)
Solution Approach 1:
The patent changes the chemical composition parameters of the solvent system by replacing toluene with a mixture of polar-aprotic solvent (acetone or MEK) and protic co-solvent (water, alcohol, or diol). This parameter change enables dissolution of high molecular weight polyurethane (Mw ≥ 50,000) at higher solid contents (≥10 weight%) while maintaining acceptable viscosity through the synergistic effect of the mixed solvent system.
Solution Approach 2:
The patent uses a composite solvent system combining two different types of solvents (polar-aprotic and protic) to achieve properties that neither solvent alone can provide. The polar-aprotic solvent dissolves the polyurethane polymer effectively, while the protic co-solvent modifies the viscosity and enables higher solid content, creating a synergistic effect that resolves the contradiction between solid content and viscosity.
2Strength
If toluene is used as a co-solvent, then the adhesive can be formulated with high molecular weight polyurethane, but toluene is difficult to extract entirely and requires special handling
Solution Approach 1:
The patent removes toluene from the solvent system entirely and replaces it with a toluene-free mixture of polar-aprotic solvent and protic co-solvent. This extraction of the harmful substance (toluene) eliminates the extraction difficulty and associated safety concerns while maintaining the ability to dissolve high molecular weight polyurethane and achieve the required mechanical properties through the alternative solvent composition.
Solution Approach 2:
The patent replaces expensive and hazardous toluene with cheaper, safer, and more environmentally friendly solvents (acetone, MEK, water, alcohols). These alternative solvents are easier to handle, require less special extraction equipment, and can be removed more easily, effectively substituting a problematic material with superior alternatives that achieve the same technical function.
3Quantity of substance
If solid content is increased in toluene-based formulations, then more polymer can be applied, but the viscosity becomes too high for brushing applications
Solution Approach 1:
The patent changes the physical parameters of the solvent system by introducing a protic co-solvent component that specifically targets viscosity reduction. The combination of polar-aprotic solvent and protic co-solvent creates a fluid system that can accommodate high solid content (≥10 weight%) while maintaining viscosity levels suitable for brushing applications, directly resolving the contradiction between quantity of polymer and ease of application.
Solution Approach 2:
The protic co-solvent acts as an intermediary substance that mediates between the polymer-solvent interaction and the desired viscosity characteristics. It facilitates the dissolution of high molecular weight polyurethane at high solid contents while simultaneously controlling the viscosity to remain brushable, serving as a bridge that enables both high polymer concentration and good applicability.
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 achieves a toluene-free, low viscosity adhesive with high solid content, suitable for brushing, maintaining good mechanical properties and initial bond strength, and enabling efficient application on various substrates.
Implementation Method 1
a solvent and a co-solvent which, when combined together, form a homogeneous mixture without the formation of a second phase
Data Source
AI summary
An adhesive composition comprising a polyurethane polymer, a solvent and a co-solvent, wherein: the polyurethane polymer is an internally and/or externally hydrophilized thermoplastic polyurethane having a mass average molecular weight Mw, as determined by gel permeation chromatography against polystyrene standards using N,N-dimethyl acetamide as the eluent, of ≥ 50000 g/mol, the solvent is a polar-aprotic solvent, the co-solvent is selected from water, a primary alcohol having ≤ 10 carbon atoms, a vicinal diol or a mixture of at least two of the aforementioned compounds, the solvent and the co-solvent are present in such amounts that they form a homogenous mixture without the formation of a second phase when combined together at 20 °C, the hydroxyl group content is ≥ 1 weight-%, based on the total weight of the composition, the polyurethane polymer content is ≥ 10 weight-%, based on the total weight of the composition and the composition forms a single continuous liquid phase. Examples for solvent/co-solvent combinations are methylethyl ketone (MEK) and water or MEK and ethanol.