Repositionable Hot Melt Adhesive for Timepiece Assembly
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Solution Overview
Problem
Existing adhesives used in clock-making and jewelry making lack the ability to allow for repositioning of timepiece parts during assembly, maintenance, or repair while also providing resistance to chemical cleaning operations, as they either lack heat reworkability or have poor solvent resistance.
Innovation Solution
A repositionable hot melt adhesive formulation comprising polymer chains with pendant diene units and coupling molecules that undergo Diels-Alder and retro-Diels-Alder reactions at specific temperature ranges, allowing for the assembly and repositioning of timepiece parts by changing between a three-dimensional network and a mixture form in response to temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If shellac is used as adhesive, then repositionability by heating is achieved, but resistance to chemical cleaning operations deteriorates
Solution Approach 1:
The adhesive's physical and chemical properties are changed by controlling the polymerization degree of polyene units. By adjusting this parameter, the adhesive achieves a balance between repositionability (through reversible Diels-Alder reactions) and chemical resistance (through adequate polymerization), resolving the contradiction between ease of repair and reliability
Solution Approach 2:
The adhesive is formulated as a composite system containing polyene-functional polymer chains, dienophile-functional crosslinking agents, and optional fillers. This composite structure enables both repositionability through reversible bonding and sufficient chemical resistance through the network architecture, addressing the contradiction between ease of repair and reliability
2Reliability
If thermosetting glue is used, then resistance to chemical cleaning operations is improved, but repositionability by heating deteriorates
Solution Approach 1:
The key parameter change is the use of reversible Diels-Alder chemistry instead of irreversible thermosetting reactions. By controlling the reaction conditions and polymerization degree, the adhesive maintains chemical resistance while enabling repositionability through temperature-controlled reversible bonding, resolving the contradiction between reliability and ease of repair
Solution Approach 2:
The adhesive system transitions from a static, irreversible bond to a dynamic, reversible bond. The Diels-Alder reaction allows the adhesive to dynamically respond to temperature changes, enabling repositionability while maintaining chemical resistance during normal use, thus resolving the contradiction between reliability and ease of repair
3Reliability
If adhesive polymerization degree is increased, then resistance to chemical cleaning operations is improved, but repositionability by heating deteriorates
Solution Approach 1:
The polymerization degree is precisely controlled within a specific range to achieve optimal balance. By adjusting this parameter, the adhesive forms enough crosslinks for chemical resistance while maintaining sufficient reversibility for repositionability, resolving the contradiction between reliability and ease of operation
Solution Approach 2:
Instead of complete polymerization, the adhesive uses partial polymerization with controlled crosslinking density. This partial action approach maintains enough reversibility for repositionability while providing sufficient chemical resistance, resolving the contradiction between reliability and ease of operation
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
Enables the assembly of timepiece parts to be repositioned and separated while maintaining resistance to chemical cleaning operations, as the adhesive transforms between a three-dimensional network at ambient temperatures and a reworkable state at higher temperatures, ensuring both repositionability and durability.
Implementation Method 1
bond together by means of the Diels-Alder reaction at a temperature TDA
Implementation Method 2
regenerate by means of the retro-Diels-Alder reaction at a temperature TRDA
Implementation Method 3
the adhesive transforms between a three-dimensional network at ambient temperatures and a reworkable state at higher temperatures
Data Source
AI summary
An assembly of timepiece parts assembled together with an adhesive at a temperature TA and to be repositioned when the adhesive is at a temperature TC. The adhesive includes a formulation, which at TC includes a mixture of polymer chains with pendant diene units X and coupling molecules including two dienophile end groups Y, wherein the X units and the Y groups are arranged to react with one another and to bond together with the Diels-Alder reaction at a temperature TDA and to regenerate with the retro-Diels-Alder reaction at a temperature TRDA, at TA forms a three-dimensional network, in which the polymer chains are linked to one another by the coupling molecules with the Diels-Alder reaction, where TA<TRDA≤TC, where temperature TDA ranges between 0° C. and 100° C. and temperature TRDA ranges between 50° C. and 200° C., and TDA is strictly lower than TRDA. A process for assembling and repositioning two timepiece parts with a repositionable hot melt adhesive to enable the timepiece parts to be repositioned when the adhesive is heated.