Thermo-Reversible Hot-Melt Adhesive for Non-Polar Substrates
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Solution Overview
Problem
Conventional hot-melt adhesives, particularly those used in the automotive industry, face challenges with adhesion on non-polar substrates like polypropylene, polyethylene, and polystyrene, requiring primer treatments that increase costs, and exhibit decreased adhesion strength at elevated temperatures due to elastomeric network structures.
Innovation Solution
A thermally reversible crosslinked polymer network comprising acid anhydride functionalized polymers and crosslinking agents with multiple hydroxyl groups, combined with a non-functionalized thermoplastic polymer, which forms a chemically cured-like adhesive at room temperature but softens at elevated temperatures through transesterification, allowing for improved adhesion and re-solidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If moisture curing polyolefin hot-melt adhesives are used to bond non-polar substrates, then adhesion on non-polar substrates is improved without primer treatment, but adhesion strength decreases at elevated temperatures due to elastomeric network structure softening
Solution Approach 1:
The patent changes the chemical structure of the adhesive network from a permanent crosslinked elastomeric network to a thermally reversible crosslinked network. The crosslinks are formed through esterification reactions between acid anhydride functional groups and hydroxyl groups, which are reversible at elevated temperatures. This parameter change allows the adhesive to maintain strength at high temperatures while still providing good adhesion on non-polar substrates without primer treatment.
Solution Approach 2:
The patent creates a composite adhesive system combining thermoplastic polymer with acid anhydride functionalized polymer and crosslinking agent. This composite structure provides both the adhesion benefits of the thermoplastic matrix and the thermal stability of the reversible crosslinked network, resolving the contradiction between ease of bonding and high-temperature strength.
2Strength
If reactive hot-melt adhesives are used to achieve chemical curing and heat resistance, then adhesion at elevated temperatures is improved, but adhesion on non-polar substrates deteriorates requiring primer treatment
Solution Approach 1:
The patent modifies the reactivity parameters of the adhesive system. Instead of using highly reactive isocyanate or silane groups that permanently crosslink and damage non-polar substrates, the patent uses acid anhydride groups that form reversible crosslinks through esterification. This parameter change allows the adhesive to cure at room temperature for heat resistance while maintaining compatibility with non-polar substrates without primer treatment.
3Ease of operation
If conventional non-reactive hot-melt adhesives are used, then application simplicity is maintained, but adhesion strength at elevated temperatures deteriorates due to softening above glass transition temperature
Solution Approach 1:
The patent performs preliminary crosslinking action during the application process. The acid anhydride functional groups and hydroxyl groups form crosslinks as the adhesive cools after application, creating a heat-resistant network structure before the adhesive is subjected to elevated temperature service conditions. This preliminary action maintains application simplicity while preventing softening at elevated temperatures.
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 solution provides enhanced adhesion on non-polar substrates without primers and maintains strength at elevated temperatures, with adjustable gel point temperature through thermal treatment, enabling flexible application in various thermal conditions.
Implementation Method 1
a thermally reversible crosslinked polymer network comprising at least one acid anhydride functionalized polymer AP and at least one crosslinking agent CA having more than one hydroxyl group per molecule
Implementation Method 2
In case the hot-melt adhesive is heated to a temperature above the gel point temperature of the adhesive, thermally activated bond-exchange reactions take place within the crosslinked polymer network by transesterification, which results in significant decrease in viscosity of the hot-melt adhesive
Implementation Method 3
Hot-melt adhesives are solvent free adhesives, which are solid at room temperature and which are applied to the substrate to be bonded in form of a melt
Data Source
Figure 1~2
AI summary
The invention relates to a hot-melt adhesive composition comprising a thermally reversible crosslinked polymer network comprising at least one acid anhydride functionalized polymer and at least one crosslinking agent, and at least one at 25 °C solid non-functionalized thermoplastic polymer. The invention is also related to a method for producing the hot-melt adhesive composition, to the use of the adhesive composition as an assembly adhesive, laminating adhesive, or as adhesive for building of sandwich elements, to a method for bonding substrates to each other, and to a composite element produced by using the adhesive composition.