Aqueous Polyurethane Primer Free Hydrazine Adhesion
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Solution Overview
Problem
Polyurethane compositions used as primers for plastic substrates often contain free hydrazine, which is toxic and detrimental to adhesive properties, especially when more than one equivalent of chain-extension agents containing hydrazine is used.
Innovation Solution
An aqueous polyurethane composition is developed using ammonia as a neutralization agent and hydrazine or its derivatives as chain-extension agents, with an equal or less than one stoichiometric equivalent of the chain-extension agent, resulting in a product without free hydrazine and providing good adhesion and high seal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If more than one equivalent of chain-extension agents containing hydrazine is used, then adhesion to plastic substrates is improved, but free hydrazine becomes present in the product which is toxic and detrimental to adhesive properties
Solution Approach 1:
The patent changes the stoichiometric parameter by using exactly one equivalent of chain-extension agent containing hydrazine, preventing excess free hydrazine while maintaining adhesion. It also changes the pH parameter by using ammonia to adjust pH to 7-9, which reduces free hydrazine presence while preserving adhesive properties.
Solution Approach 2:
The patent introduces ammonia as an intermediary substance to neutralize excess hydrazine and adjust the pH of the composition. This intermediary allows the system to maintain adhesion through hydrazine functionality while eliminating toxic free hydrazine through chemical neutralization.
2Manufacturing precision
If chain-terminators are used in polyurethane preparation, then molecular weight is controlled, but low molecular weight material is formed which is detrimental to adhesive properties
Solution Approach 1:
The patent removes chain-terminators from the formulation entirely, eliminating the source of low molecular weight material formation. Instead, it relies on precise stoichiometric control and ammonia treatment to achieve molecular weight management without compromising adhesive properties.
3Object-affected harmful factors
If ammonia is used as neutralization agent with sub-stoichiometric hydrazine, then free hydrazine is eliminated, but adhesion and seal strength must be maintained
Solution Approach 1:
The patent optimizes the pH parameter to 7-9 through ammonia neutralization, which eliminates free hydrazine while maintaining the functional hydrazine groups needed for adhesion. It also precisely controls the stoichiometric ratio of chain-extension agent to ensure sufficient bonding functionality remains.
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 composition achieves excellent adhesion to plastic substrates and maintains high initial and humid seal strength without the presence of free hydrazine, ensuring both safety and performance.
Implementation Method 1
the reaction product of: (A) an isocyanate-terminated prepolymer... and (B) at least one active-hydrogen chain-extending compound comprising at least 0.20 stoichiometric equivalents... of an active-hydrogen chain-extending compound selected from the group consisting of hydrazine, hydrazine derivatives
Implementation Method 2
wherein at least 0.2 stoichiometric equivalents of the anionic or potentially anionic water-dispersing groups are neutralised with ammonia
Data Source
AI summary
An aqueous polyurethane composition comprising a polyurethane which is the reaction product of: (A) an isocyanate-terminated prepolymer and (B) at least one active-hydrogen chain-extending compound comprising at least 0.20 stoichiometric equivalents with respect to the isocyanate content of the isocyanate-terminated prepolymer (A), of an active-hydrogen chain-extending compound selected from the group consisting of hydrazine, hydrazine derivatives and mixtures thereof; and wherein at least 0.2 stoichiometric equivalents of the anionic or potentially anionic water-dispersing groups are neutralised with ammonia.