Aqueous Polyurethane Adhesive with Surface Passivated Polyisocyanate
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Solution Overview
Problem
Existing adhesives based on aqueous polyurethane dispersions face challenges with short operating times and poor hydrolysis resistance, especially in high-temperature and high-humidity environments, limiting their industrial applicability and storage stability.
Innovation Solution
Aqueous polyurethane dispersion-based adhesive comprising surface passivated polyisocyanate, polycarbodiimide, and optionally carbodiimide with specific molecular weights and functionalities, applied to substrates, heated, dried, and irradiated to form a bonded product with enhanced hydrolysis resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the crosslinking of the adhesive is increased to improve hydrolysis resistance, then the hydrolysis resistance is improved, but the operating time becomes short
Solution Approach 1:
The adhesive composition is prepared in advance with all necessary components (aqueous polyurethane dispersion, surface passivated polyisocyanate, polycarbodiimide, and carbodiimide) that will enable crosslinking only after application. The surface passivated polyisocyanate is pre-prepared with protected isocyanate groups that remain dormant until the adhesive is applied and heated, at which point the passivation is removed and crosslinking begins. This preliminary preparation allows the adhesive to maintain stability during storage and application while ensuring crosslinking occurs at the desired time to achieve hydrolysis resistance.
Solution Approach 2:
The patent utilizes temperature-dependent parameter changes to control the crosslinking process. The surface passivated polyisocyanate remains stable at room temperature but undergoes decomposition of the passivation layer when heated to 60-80°C, triggering the crosslinking reaction. This parameter change (temperature) allows the adhesive to transition from a stable, non-crosslinked state during application to an active crosslinking state during curing, thereby resolving the contradiction between operating time and hydrolysis resistance.
2Reliability
If high temperature heating is applied to activate the adhesive and improve crosslinking, then the hydrolysis resistance is improved, but substrates resistant to high temperature are required
Solution Approach 1:
The patent employs a two-stage temperature parameter change strategy. First, the adhesive and substrate are heated to a moderate temperature of 60-80°C to remove water and activate the surface passivated polyisocyanate. This lower temperature is sufficient to trigger the crosslinking reaction due to the specific design of the passivation layer, which decomposes at this temperature range. Second, the bonded product undergoes post-curing at elevated temperatures (100-200°C) to complete the crosslinking and achieve full hydrolysis resistance. This staged temperature approach allows bonding of heat-sensitive substrates while still achieving the required crosslinking density for hydrolysis resistance.
3Ease of operation
If the adhesive is designed for long operating time, then ease of operation is improved, but hydrolysis resistance deteriorates
Solution Approach 1:
The patent introduces surface passivated polyisocyanate as an intermediary component that mediates between the aqueous polyurethane dispersion and the crosslinking agents (polycarbodiimide and carbodiimide). The surface passivation layer protects the isocyanate groups from premature reaction with water and other components, allowing the adhesive to remain stable and operational for extended periods. When heated, the passivation layer decomposes, releasing the active isocyanate groups that then react with the carbodiimide and polycarbodiimide to form the crosslinked network. This intermediary mechanism enables long operating time while ensuring hydrolysis resistance is achieved through controlled crosslinking.
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 formulation significantly improves hydrolysis resistance, extending the operating time and ensuring stability in adverse environmental conditions, as demonstrated by increased degumming time under high-temperature and high-humidity testing.
Implementation Method 1
heated to remove water from the dispersion through evaporation
Implementation Method 2
crosslinked with carbodiimide to increase the heat resistance
Data Source
AI summary
The present invention relates to an adhesive and application thereof, and a bonded product obtained by using the adhesive. The adhesive comprises: a. at least one aqueous polyurethane dispersion; b. at least one surface passivated polyisocyanate; c. at least one polycarbodiimide having a weight-average molecular weight of 500 to 100,000; and d. optionally a carbodiimide having a carbodiimide group functionality of 1. The coating formed by the adhesive provided according to the present invention has good hydrolysis resistance.