Flame-Retardant Polyurethane Adhesive for Structural Wood Bonding

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Solution Overview

Problem

Polyurethane adhesives used in wood constructions lack heat and fire resistance, leading to structural failure during fires, and existing flame retardants either compromise bonding strength or pose environmental concerns due to toxic gases or sedimentation issues.

Innovation Solution

A flame-retardant reactive polyurethane prepolymer with divalent phosphonic or phosphoric ester groups, containing at least one isocyanate end group and a phosphorus content between 0.3 wt % and 2.0 wt %, which enhances fire resistance without affecting adhesion or storage stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If liquid flame retardants are incorporated into polyurethane adhesives, then fire resistance is improved, but bonding strength is lowered

Engineering Contradiction:

Improvefire resistanceVSAvoidbonding strength

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The invention changes the molecular weight parameter of the flame retardant from low (liquid) to high (polymeric), transforming it from a small molecule additive to a macromolecular component that becomes part of the adhesive matrix, thereby maintaining bonding strength while achieving fire resistance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention creates a composite adhesive system by integrating polymeric flame retardant molecules into the polyurethane adhesive matrix, forming a homogeneous composite material that simultaneously provides both adhesive properties and fire resistance

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If halogenated flame retardants are used, then fire resistance is improved, but toxic gases are generated during fire

Engineering Contradiction:

Improvefire resistanceVSAvoidtoxic gases

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The invention replaces harmful halogenated flame retardants with beneficial polymeric phosphorus-containing compounds that provide fire resistance through a different mechanism (intumescent or char-forming) that does not generate toxic gases, thus converting the harmful approach into a beneficial one

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Object-affected harmful factors

If solid flame retardants are incorporated into adhesive, then fire resistance is improved, but storage stability is compromised due to sedimentation

Engineering Contradiction:

Improvefire resistanceVSAvoidstorage stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The invention changes the physical state parameter of the flame retardant from solid particles to polymeric (liquid or soluble) form, allowing homogeneous mixing into the adhesive without sedimentation while maintaining fire resistance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention achieves homogeneous distribution of the flame retardant throughout the adhesive by using polymeric compounds that are miscible with the adhesive matrix, eliminating the heterogeneity and sedimentation issues associated with solid particulate flame retardants

Inventive Principle:

Principle #33Homogeneity

4Strength

If polyurethane adhesives are used for wood bonding, then adhesion properties are superior, but heat and fire resistance are lacking

Engineering Contradiction:

Improveadhesion propertiesVSAvoidheat and fire resistance

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The invention creates a composite polyurethane adhesive system that integrates flame retardant functionality into the polymer matrix, resulting in a material that exhibits both superior adhesion properties and improved heat/fire resistance

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention makes the polyurethane adhesive multi-functional by incorporating flame retardant properties into the adhesive formulation, allowing it to simultaneously provide bonding strength and fire resistance that it previously lacked

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 improved fire resistance, durability, and heat resistance while maintaining strong adhesion and storage stability, as demonstrated by passing UL 94 fire tests and maintaining tensile lap shear strength, even at elevated temperatures.

Implementation Method 1

Such polyurethane adhesives when bonding wood substrates cure when exposed to moisture at room temperature and create a duroplastic adhesive joint

Methodology Applied

Scientific EffectMoisture curing: Hydrolysis

Implementation Method 2

a flame-retardant reactive polyurethane prepolymer having divalent phosphonic or phosphoric ester groups

Methodology Applied

Scientific EffectFlame retardancy:

Data Source

PatentUS20240150616A1Flame-Retardant Adhesive Composition for Structural Wood Bonding

Publication Date: 2024.05.09 HENKEL KGAA

AI summary

The present invention relates to a flame-retardant adhesive composition comprising a reactive polyurethane prepolymer, in particular a one-component flame-retardant adhesive composition, and to the use of the adhesive composition for the structural bonding of wood substrates.