Two-Component Polyurethane Adhesive Bonding Fiber-Reinforced Substrates
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Solution Overview
Problem
Existing two-component polyurethane adhesives face challenges in maintaining high mechanical stability and resistance to environmental factors like temperature and humidity fluctuations, especially in subtropical and tropical regions, while also requiring a long open time and stable adhesion on uneven surfaces.
Innovation Solution
A two-component polyurethane adhesive comprising a polyol component with oleochemical polyols, ethoxylated and/or propoxylated polyphenols, glass fibers, and a catalyst, combined with an isocyanate component having an NCO/OH ratio of 0.9:1 to 1.5:1, which crosslinks to achieve a glass transition temperature of at least 65°C, allowing for stable bonding of fiber-reinforced substrates without the need for surface pretreatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high crosslinking density is achieved by increasing functional group concentration and using higher-functional polyols or polyisocyanates, then high strength is achieved, but embrittlement of the adhesive joint occurs at excessively high crosslinking densities
Solution Approach 1:
The patent applies parameter changes by carefully controlling the NCO/OH ratio within a specific range (0.8:1 to 1.2:1) and limiting the content of polyols with functionality greater than 2 to 5-30% by weight. This optimization of chemical parameters achieves high adhesive strength while preventing embrittlement that would occur at excessively high crosslinking densities.
Solution Approach 2:
The patent introduces local quality by incorporating glass fibers (10-40% by weight) as a reinforcing phase within the polyurethane adhesive matrix. This creates a composite structure where the glass fibers provide localized reinforcement and crack propagation resistance, allowing the adhesive to achieve high strength without requiring excessive crosslinking density that would cause embrittlement.
2Loss of time
If long open time is required for adhesively bonding large surfaces, then sufficient bonding time is available, but curing time increases and mechanical stability may be compromised
Solution Approach 1:
The patent applies parameter changes by selecting specific catalysts and controlling their content (0.1-5% by weight), along with optimizing the NCO/OH ratio and polyol composition. This enables the adhesive to maintain a long open time (at least 30 minutes) while still achieving adequate curing and mechanical stability, resolving the contradiction between extended bonding time and curing performance.
3Strength
If high adhesive strength is achieved through high crosslinking density, then load-bearing capacity increases, but processing time decreases due to faster curing
Solution Approach 1:
The patent resolves this contradiction by optimizing multiple parameters simultaneously: controlling the NCO/OH ratio (0.8:1 to 1.2:1), limiting polyol functionality (5-30% of polyols with functionality >2), and adding specific catalysts. This combination achieves high tensile shear strength (at least 12 MPa) while maintaining a sufficient open time (at least 30 minutes) for processing large surfaces.
Solution Approach 2:
The patent introduces catalysts as intermediary substances that mediate between the polyol and polyisocyanate components. The catalysts (0.1-5% by weight) accelerate the curing reaction to achieve high strength, while the controlled catalyst content and specific catalyst selection prevent the reaction from proceeding too rapidly, thus maintaining adequate open time for processing.
4Strength
If sufficient strength is achieved with epoxy adhesives, then mechanical requirements are met, but high curing temperatures and special surface preparation are required
Solution Approach 1:
The patent replaces expensive epoxy adhesives that require complex surface preparation and high curing temperatures with a polyurethane-based adhesive system that cures at ambient temperatures and requires minimal surface preparation. The polyol component with specific composition (oleochemical polyols, polyphenols, glass fibers) provides sufficient mechanical strength without the manufacturing complexity of epoxy systems.
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 adhesive exhibits high tensile shear strength, modulus of elasticity, and resistance to aging, maintaining mechanical properties under varying environmental conditions, with a sufficiently long open time and curing at moderate temperatures, suitable for bonding fiber-reinforced components in applications like wind turbine rotor blades.
Implementation Method 1
Two-component PU adhesive can advantageously cure even at room temperature ('cold curing') after the components have been mixed
Implementation Method 2
the crosslinked adhesive has a glass transition temperature (Tg) of at least 65°C
Implementation Method 3
The adhesive comprises: I) a polyol component containing at least one catalyst
Implementation Method 4
These components must have a high mechanical stability. It is therefore desirable for the corresponding adhesives to also be able to absorb corresponding forces
Implementation Method 5
5 to 35% by weight at least one polyol that is different from (a) and has 3 to 14 hydroxy groups; (c) 5 to 35% by weight at least one polyol that is different from (a) and (b) selected from ethoxylated and/or propoxylated polyphenols; (d) 1 to 65% by weight glass fibers
Data Source
AI summary
The invention relates to a two-component polyurethane adhesive containing i) a polyol component including a mixture of three different polyols to ensure crosslinking for a mechanically stable adhesive bonding, and also to achieve hydrophobia to ensure that the crosslinked adhesive layer is impervious to moisture, and glass fibers, and ii) an isocyanate component containing polyisocyanates in an NCO/OH ratio of 0.9:1 to 1.5:1. The polyol component further includes a metal catalyst. The two-component adhesive has a high adhesive strength, a high glass temperature, a low curing time and a sufficiently long processing time, which can adhesively bond also substrates having uneven surfaces. The invention further relates to an article comprising the two-component polyurethane adhesive.