Polyurethane-Polyurea Dispersion Adhesives for Flexible Foam Bonding
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Solution Overview
Problem
Existing adhesives for bonding foam substrates, such as polychloroprene dispersion adhesives, are not suitable for spray-application methods due to lack of rapid coagulation, insufficient initial strengths, and long open times, and polyurethane dispersions result in stiff bond seams unsuitable for flexible foams, while chlorine-free and bisphenol A-free alternatives are needed to meet environmental standards.
Innovation Solution
An aqueous dispersion comprising a polyurethane-polyurea polymer formed from difunctional polyester polyol, difunctional polyol, diisocyanate, and optional ionic chain extenders, with specific molecular weights and glass transition and melting temperatures, applied to substrates and bonded under controlled pressure and temperature to achieve high initial strengths and long open times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat-activation method is used with polyurethane dispersions, then bonding strength is improved, but substrates undergo irreversible deformation and bond seam becomes stiff
Solution Approach 1:
The invention changes the fundamental bonding parameter from thermal activation to moisture-based activation. The adhesive composition is formulated to undergo polyurea formation reaction with ambient moisture, eliminating the need for heat activation. This allows bonding to occur at temperatures below the foam's deformation point while maintaining high bonding strength through the chemical reaction between isocyanate groups and water.
Solution Approach 2:
The invention replaces the thermal field (heat activation) with a chemical field (moisture-based polyurea formation). Instead of using infrared radiators or heating elements to activate the adhesive, the system utilizes ambient moisture to trigger the bonding reaction, thereby avoiding thermal damage to temperature-sensitive foam substrates.
2Duration of action of moving object
If wet-bonding method is used, then open time is extended, but adhesive diffuses into foam pores and initial strength is reduced
Solution Approach 1:
The invention changes the activation mechanism from moisture-dependent to chemistry-controlled. By formulating the adhesive with specific isocyanate index and molecular weight parameters, the polyurea formation reaction proceeds rapidly upon contact with moisture, providing immediate initial strength while maintaining extended open time for positioning.
Solution Approach 2:
The adhesive is pre-formulated with optimal composition parameters (isocyanate index 1.05-2.00, specific molecular weight range) that enable rapid polyurea formation upon moisture contact. This preliminary preparation ensures that when the adhesive contacts the foam substrate, it quickly forms strong bonds without excessive diffusion into pores, balancing initial strength and open time.
3Strength
If polychloroprene dispersion adhesive is used, then initial strength and heat resistance are improved, but environmental compliance is compromised
Solution Approach 1:
The invention changes the chemical composition parameters of the adhesive by replacing polychloroprene with polyurethane-polyurea polymers. The new composition uses difunctional polyester polyols with specific molecular weights and isocyanate indices that enable high-performance bonding without chlorine-containing compounds, achieving both environmental compliance and superior bonding properties.
Solution Approach 2:
The invention creates a composite adhesive system combining polyurethane and polyurea polymer components in specific ratios. This composite structure leverages the advantages of both polymer types: polyurethane provides adhesion and flexibility, while polyurea contributes rapid curing and high strength, resulting in an environmentally friendly adhesive that matches or exceeds the performance of polychloroprene.
4Productivity
If spray-application method is used, then productivity is improved, but adhesive coagulation and initial strength are compromised
Solution Approach 1:
The invention changes the rheological and chemical parameters of the adhesive to be spray-compatible. The viscosity, solids content, and molecular weight are optimized for aerosolization and rapid coagulation upon spraying. The polyurea formation reaction occurs quickly after spray application, providing immediate initial strength even in the spray-application format.
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 provides a chlorine- and bisphenol A-free adhesive with high initial strengths and extended open time, suitable for spray-application, forming a soft and efficient bond without requiring heat activation, suitable for bonding foam substrates.
Implementation Method 1
the polyurethane-polyurea polymer formed from (a) at least one difunctional polyester polyol... for the bonding of at least two substrates
Implementation Method 2
drying the dispersion present on the at least one substrate
Data Source
AI summary
The invention relates to the use of an aqueous dispersion containing at least one polyurethane-polyurea polymer formed from (a) at least one difunctional polyester polyol having a number-average molecular weight of 400 to 5000 g/mol, (b) at least one difunctional polyol component having a number-average molecular weight of 762 to 399 g/mol, c) at least one diisocyanate and (d) at least one chain extender optionally having at least one ionic group, for the bonding of at least two substrates by application of the aqueous dispersion to at least one of the substrates to be bonded, subsequent drying of the dispersion present on the at least one substrate in order to obtain at least one adhesive layer, and contacting of the at least one adhesive layer with a further substrate or with an adhesive layer present on a further substrate at a pressure of from 0.1 to 5 bar(a) and a temperature of less than 40° C., wherein the polyurethane-polyurea polymer after the drying has a glass transition temperature Tg of from −65 to 10° C. and a melting point of from 40 to 80° C., to a corresponding process for joining at least two substrates, and to an adhesive composite obtained in this way and comprising at least two substrates and an adhesive layer present between every two substrates.