Crosslinked Hot Melt Adhesive Sheet for Wet Heat and Acid Resistance
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Solution Overview
Problem
Existing hot melt adhesive sheets lack sufficient wet heat resistance, acid resistance, and alcohol resistance, which are necessary for applications in harsh environments such as solid polymer fuel cells and redox flow cells.
Innovation Solution
A hot melt adhesive sheet comprising a crosslinked adhesive composition with a polyurethane resin, bisphenol A type epoxy resin, and an isocyanate-based crosslinking agent, where the polyurethane resin has a constituent unit derived from a polyol with 8 or more carbon atoms, and the epoxy resin has an epoxy equivalent of 450 g/eq to 3000 g/eq, enhancing the adhesive's resistance to hot water, acid, and alcohol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional hot melt adhesive sheet is used, then it provides basic adhesion functionality, but it lacks sufficient wet heat resistance, acid resistance, and alcohol resistance
Solution Approach 1:
The adhesive layer uses a composite material system combining polyurethane resin, epoxy resin, and isocyanate-based crosslinking agent. This composite formulation provides both the required chemical resistance (hot water, acid, alcohol) and adhesion functionality, resolving the contradiction by integrating multiple material properties into a single adhesive composition.
Solution Approach 2:
The patent specifies precise parameter ranges: 6-14 mass parts of isocyanate-based crosslinking agent per 100 mass parts of polyurethane resin, epoxy equivalent of 450-3000 g/eq for the epoxy resin, and polyol with 8+ carbon atoms. These controlled parameter changes optimize the crosslinking density and molecular structure to achieve superior chemical resistance while maintaining workability.
2Ease of operation
If the adhesive composition is simplified for easier handling, then workability improves, but long-term resistance to harsh environments deteriorates
Solution Approach 1:
The adhesive is prepared in advance as a pre-formed sheet with the adhesive layer already applied to the base material. This preliminary preparation eliminates the need for mixing components during application, maintaining ease of operation. The crosslinking reaction is designed to occur after application under controlled conditions, ensuring both workability and long-term reliability.
Solution Approach 2:
The molecular weight and structure of the polyol (8+ carbon atoms) and epoxy resin (specific epoxy equivalent range) are carefully selected to balance viscosity for easy application with crosslinking density for long-term durability. This parameter optimization allows simple handling while achieving the required 1000-hour resistance in harsh environments.
3Reliability
If crosslinking density is increased to improve chemical resistance, then wet heat resistance improves, but flexibility and workability may deteriorate
Solution Approach 1:
The isocyanate-based crosslinking agent content is precisely controlled at 6-14 mass parts per 100 mass parts of polyurethane resin. This optimized range achieves sufficient crosslinking for wet heat resistance while preventing excessive crosslinking that would reduce flexibility. The polyol with 8+ carbon atoms provides adequate chain length to maintain flexibility despite crosslinking.
Solution Approach 2:
The combination of polyurethane resin and epoxy resin creates a composite network where the polyurethane provides flexibility and the epoxy contributes to chemical resistance. This composite material system achieves both wet heat resistance and flexibility simultaneously, resolving the contradiction between crosslinking density and compositional 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 adhesive layer exhibits excellent long-term hot water resistance, acid resistance, and alcohol resistance, maintaining adhesiveness even after immersion in hot water, dilute sulfuric acid, or alcohol at high temperatures for 1000 hours, suitable for use in solid polymer fuel cells and redox flow cells.
Implementation Method 1
the hot melt adhesive includes a crosslinked product of an adhesive composition including a crosslinking agent... including 6 mass parts or more and 14 mass parts or less of an isocyanate-based crosslinking agent based on 100 mass parts of the polyurethane resin
Data Source
AI summary
A hot melt adhesive sheet according to the present invention is a hot melt adhesive sheet including a base material having at least one surface on which an adhesive layer made of a hot melt adhesive is disposed. The hot melt adhesive includes a crosslinked product of an adhesive composition including a crosslinking agent, and includes a polyurethane resin, an epoxy resin, and 6 mass parts or more and 14 mass parts or less of an isocyanate-based crosslinking agent based on 100 mass parts of the polyurethane resin. The polyurethane resin has a constituent unit derived from a polyol having a skeleton with 8 or more carbon atoms. The epoxy resin is a bisphenol A type epoxy resin having an epoxy equivalent of 450 g/eq or more and 3000 g/eq or less.