Silane-Functional Prepolymers for Isocyanate-Free Adhesives
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Solution Overview
Problem
Conventional wood adhesives, such as polyvinyl acetate and isocyanate-crosslinking PU adhesives, face issues with slow curing speed, limited moisture resistance, and health hazards due to isocyanate sensitization, while silane-crosslinking adhesives have low tensile shear strength and cannot meet European standards like DIN EN 204, stress group D4.
Innovation Solution
Development of one-component silane-crosslinking compositions using prepolymers with short-chain polyols, urethane units, and specific silane termini, which improve mechanical properties, moisture resistance, and processability, eliminating the need for heavy metal catalysts and reducing viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isocyanate-crosslinking PU adhesives are used to achieve high mechanical strength and moisture resistance, then bond strength and durability are improved, but health hazards due to isocyanate sensitization and toxicity occur
Solution Approach 1:
The patent removes the harmful isocyanate component from the adhesive system while retaining the desired crosslinking functionality. This is achieved by extracting the toxic element (isocyanate) and replacing it with a safe alternative (silane crosslinking mechanism) that provides equivalent or superior performance without health hazards.
Solution Approach 2:
The patent changes the chemical mechanism from isocyanate-based crosslinking to silane-based crosslinking. This parameter change in the curing chemistry eliminates the toxic isocyanate groups while maintaining the crosslinking reaction that provides high bond strength and moisture resistance, thereby resolving the contradiction between performance and safety.
2Object-affected harmful factors
If conventional silane-crosslinking systems are used to eliminate isocyanates, then health safety is improved, but tensile shear strength is insufficient and DIN EN 204 D4 standards cannot be met
Solution Approach 1:
The patent creates a composite adhesive system combining silane-modified polyvinyl acetate with specific silane crosslinkers. This composite approach integrates the safety benefits of silane chemistry with enhanced mechanical properties through optimized formulation, achieving both non-toxicity and high tensile shear strength required for DIN EN 204 D4 compliance.
Solution Approach 2:
The patent optimizes parameters including silane content, molecular weight of polyvinyl acetate, and crosslinker selection to maximize tensile shear strength. By adjusting these parameters within specific ranges, the formulation achieves the required strength levels while maintaining the isocyanate-free safe chemistry.
3Ease of operation
If polyvinyl acetate dispersions are used for wood bonding, then ease of application is improved, but setting speed is very long and mechanical fixation is indispensable
Solution Approach 1:
The patent incorporates silane groups that are pre-positioned on the polyvinyl acetate chains. Upon contact with moisture, these pre-positioned silane groups immediately initiate crosslinking reactions, eliminating the need for separate catalyst addition or extended setting times. The preliminary placement of reactive groups enables rapid curing while maintaining easy application properties.
4Productivity
If isocyanate-crosslinking adhesives are used to achieve rapid curing through aggressive catalysis, then curing speed is improved, but storage stability deteriorates due to side reactions
Solution Approach 1:
The patent uses silane groups as intermediary reactive centers that mediate the crosslinking process. These silane intermediaries react with moisture to form stable crosslinks without requiring aggressive catalysts, thereby achieving rapid curing while preventing the formation of unstable side products and maintaining storage stability.
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 compositions achieve high tensile shear strength, rapid curing, and enhanced resistance to hot water, meeting DIN EN 204, stress group D4 standards, while being safer and more stable than conventional systems.
Implementation Method 1
alkoxysilane-functional prepolymers first hydrolyze upon contact with atmospheric moisture and then harden through a condensation reaction
Implementation Method 2
alkoxysilane-functional prepolymers first hydrolyze upon contact with atmospheric moisture and then harden through a condensation reaction
Data Source
AI summary
The invention relates to compounds (K) comprising A) 100 parts by weight of a pre-polymer (P) comprising units (E) in the backbone thereof that are selected from polyether and polyester units, wherein the pre-polymer (P) comprises at least one end group of the general formula (1) -L1-(CH2)y-SiR2 3-x(OR1)x (1), B) 1 to 100 parts by weight of silane (S) of the general formula (2) R4SiR2 3-Z(OR1)z (2), (G) 0 to 10 parts by weight of a curing catalyst (HK) that accelerates the curing of the compounds (K) in the presence of humidity, wherein L1 represents a divalent linking group selected from -O-, -S-, -(R3)N-, -O-CO-N(R3)-, -N(R3) -CO-O-, -N(R3)-CO-NH-, -NH-CO-N(R3)-, -N(R3)-CO-N(R3) and R1, R2, R3, x, y and z have the meanings cited in claim 1. R4 are hydrocarbon radicals having at least 7 hydrogen atoms. According to the invention, after hardening, the compounds (K) have high shear strength and are used as adhesives (K).