Emulsifier-Free Polyurethane-Polyurea Dispersion Adhesives
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Solution Overview
Problem
Aqueous polyurethane-polyurethane urea dispersion adhesives used in heat activation methods suffer from inadequate initial and final heat resistance, particularly in one-component adhesive bonding, and often require external emulsifiers that can affect hydrophilicity and adhesion.
Innovation Solution
The development of aqueous polyurethane-polyurethane urea dispersions prepared without emulsifiers, utilizing specific di- or higher-functional polyols, isocyanates, and a mixture of monoamino and diamino compounds with sulfonate and carboxylate groups, which enhances the dispersion's stability and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If external emulsifiers are used to prepare aqueous polyurethane-polyurethane urea dispersions, then the dispersion can be obtained, but the hydrophilicity and sensitivity to water increase adversely, and adhesion and bonding force are reduced due to migration effects
Solution Approach 1:
The invention extracts and eliminates the external emulsifier component from the dispersion formulation. By using polyols with built-in hydrophilic groups (carboxyl, hydroxyl, or sulfonate groups) as part of the polyurethane-polyurethane urea structure itself, the dispersion achieves stability without requiring separate emulsifying agents, thereby preventing migration effects that compromise adhesion.
Solution Approach 2:
The invention merges the emulsifying function with the polyol component by selecting polyols that contain both hydrophobic segments (for polyurethane structure) and hydrophilic groups (for dispersion stability). This combination integrates the emulsifier's function into the main polymer structure, eliminating the need for separate emulsifiers while maintaining bonding performance.
2Ease of operation
If heat activation is used to activate the adhesive film, then the adhesive becomes sticky, but high activation temperatures require high energy outlay and make manual joining difficult
Solution Approach 1:
The invention changes the chemical composition parameters of the polyurethane-polyurethane urea dispersion by incorporating polyols with specific hydrophilic groups and controlling the NCO:OH ratio. These compositional changes lower the activation temperature of the adhesive film to below 80°C, making manual joining feasible and reducing energy consumption during the activation process.
3Reliability
If aqueous polyurethane-polyurethane urea dispersions are used for adhesive bonding, then the adhesive can be applied, but the initial heat resistance and final heat resistance are inadequate
Solution Approach 1:
The invention creates a composite adhesive system by combining polyurethane and polyurethane urea segments within a single dispersion formulation. The polyurethane segments provide structural integrity and heat resistance, while the polyurethane urea segments contribute to adhesion and flexibility. This composite structure achieves both adequate initial heat resistance and final heat resistance while maintaining bonding performance.
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 adhesive films exhibit improved initial and high final heat resistance, with activation temperatures between 40° to 80°C, and excellent adhesion to various substrates, including wood, leather, and plastics, without the need for external emulsifiers.
Implementation Method 1
The equivalent ratio of NCO groups in the NCO prepolymer to the total amount of hydrogen atoms active towards isocyanates is from 0.5:1 to 0.98:1
Implementation Method 2
when the water has evaporated completely, the adhesive layer is activated by heating
Data Source
AI summary
The invention relates to aqueous dispersion adhesives based on aqueous polyurethane-polyurethane urea dispersions, to a process for their preparation and to the use of the dispersion adhesives in the production of adhesive composites.