Moisture-Curable Polyurethane Adhesive for Structural Wood Bonding
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Solution Overview
Problem
Existing one-component moisture-curing polyurethane adhesive compositions struggle to balance a favorable assembly time to pressing time ratio (AT/PT) with good mechanical properties without the addition of fibers.
Innovation Solution
A one-component moisture-curable adhesive composition is formulated by reacting excess polyisocyanates with a specific polyol mixture, comprising a linear butylene oxide-based diol and a polyether triol, with a specific equivalent ratio and isocyanate group content ranging from 14 to 17 wt%, resulting in improved adhesion and AT/PT ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional polyol mixtures are used in one-component moisture-curing polyurethane adhesive compositions, then the adhesive can be manufactured with standard formulations, but the assembly time to pressing time ratio (AT/PT) is unfavorable and mechanical properties are compromised
Solution Approach 1:
The patent changes the chemical parameters of the polyol mixture by specifying precise equivalent weights (500-3000 for the first polyol, 300-1500 for the second polyol) and hydroxyl value ranges (70-150 mg KOH/g). This parameter optimization resolves the contradiction by achieving both manufacturability with standard polyurethane chemistry and improved mechanical properties through controlled molecular weight and hydroxyl content.
Solution Approach 2:
The patent uses a composite polyol mixture comprising two different polyols (a first polyol with equivalent weight 500-3000 and a second polyol with equivalent weight 300-1500) in specific proportions. This composite approach allows the adhesive to achieve favorable AT/PT ratio and good mechanical properties that cannot be obtained with a single polyol component.
2Reliability
If fibers are added to improve mechanical properties, then adhesion strength increases, but the adhesive composition becomes more complex and processing is more difficult
Solution Approach 1:
The patent optimizes the chemical parameters of the polyol mixture (equivalent weights, hydroxyl values, and polyol ratios) to achieve the desired mechanical properties without adding fibers. The specific parameter ranges ensure that the adhesive achieves sufficient bond strength through optimized polyurethane network formation, eliminating the need for fiber reinforcement and keeping the composition simple.
3Speed
If the isocyanate content is increased to improve curing speed, then pressing time is reduced, but assembly time is compromised and adhesion quality deteriorates
Solution Approach 1:
The patent optimizes the isocyanate content to a specific range (14-17 wt%) and controls the polyol equivalent weights and hydroxyl values to achieve the desired balance between curing speed and adhesion quality. This parameter optimization ensures that the adhesive cures at an appropriate rate while maintaining bond strength, resolving the contradiction between speed and quality.
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 composition achieves excellent adhesion properties and a favorable AT/PT ratio, suitable for bonding wood pieces into structural wood products without the need for fibers.
Implementation Method 1
One-component moisture-curing polyurethane adhesives are known for bonding pieces of wood to form structural wood products such as glued laminated wood products. Such adhesive compositions comprise an isocyanate-functional prepolymer that cures upon reacting with moisture. Isocyanate groups in the prepolymer react with water to form amine groups that react with further isocyanate group to form urea bonds.
Data Source
AI summary
A one-component moisture-curing polyurethane adhesive composition is provided, comprising an isocyanate-functional prepolymer obtainable by reacting (a) one or more polyisocyanates comprising methyl diphenyl diisocyanate; and (b) a polyol mixture comprising (b1) a linear butylene oxide-based diol with two primary hydroxyl groups; and (b2) a polyether triol with three secondary hydroxyl groups wherein 55 to 75% of the hydroxyl groups in polyol mixture (b) are hydroxyl groups from butylene oxide-based diol (b1), wherein the equivalent ratio between isocyanate groups in (a) and hydroxyl groups in (b) is in the range of from 3.5 to 7.0, and wherein the content of free isocyanate groups in the adhesive composition is in the range of from 14 to 17 wt %. A method of bonding a first piece of material to a second piece of material using such adhesive composition, and an object made using the method, are also provided.