Silicone Bonding via Partial-Cure and Re-Cure
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Solution Overview
Problem
Achieving strong and reliable bonding between silicone structures is challenging due to the chemical inertness of polydimethylsiloxane, leading to issues like stress concentrations, variable bond strength, and difficulties in maintaining mechanical properties during lamination processes in silicone-based soft machines.
Innovation Solution
A polymer composition comprising a blended resin with a first siloxane polymer containing hydride-functional groups and a second siloxane polymer with vinyl-functional groups, along with a hydroperoxide inhibitor that temporarily inhibits some crosslinking reactions, allowing for partial curing and subsequent full curing without adhesives or surface treatments, maintaining mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesives are used to bond silicone structures, then bonding is achieved, but stress concentrations occur at the interface leading to debonding and delamination
Solution Approach 1:
The patent uses the silicone material itself for bonding through partial-cure and re-cure processes, eliminating the heterogeneity introduced by adhesives. The bonded interface consists of the same silicone polymer chains continuing across the junction, creating a homogeneous structure without foreign adhesive layers that would create stress concentrations.
Solution Approach 2:
The patent removes the adhesive layer from the bonding system entirely. By using partial-cure silicone that can be re-cured after lamination, the bonding function is integrated directly into the silicone material itself, extracting the problematic adhesive component that causes stress concentrations and reliability issues.
2Ease of manufacture
If O2 plasma treatment and silane primers are used to create bonding sites, then bonding capability is improved, but bond strength becomes highly variable depending on processing conditions
Solution Approach 1:
The silicone material performs its own bonding function through the partial-cure and re-cure process. The unreacted vinyl and hydride groups that remain after partial curing naturally serve as bonding sites when the material is re-cured after lamination, eliminating the need for external plasma treatment and silane primer applications.
Solution Approach 2:
The patent controls the bonding process through temperature and time parameters of the re-cure step rather than through complex surface treatment parameters. By heating the laminated structure to complete the curing reaction, the bonding strength is consistently achieved through well-controlled thermal processing rather than variable plasma or primer application conditions.
3Strength
If glues are added to bond silicone structures, then bonding is achieved, but local mechanical properties change and material channels may be filled
Solution Approach 1:
The bonding process uses the same silicone material throughout, maintaining homogeneous mechanical properties across the entire structure. The partial-cure and re-cure process creates continuous silicone polymer chains at the bond interface, ensuring that the mechanical properties (such as elasticity, tensile strength, and softness) remain consistent throughout the bonded structure without local variations introduced by adhesives.
4Ease of operation
If silicone structures are fully cured before lamination, then mechanical properties are optimized, but bonding becomes difficult due to chemical inertness
Solution Approach 1:
The silicone structures are partially cured in advance to achieve sufficient mechanical strength for handling and lamination, while deliberately leaving unreacted functional groups available for subsequent bonding. This preliminary partial-cure action creates an intermediate state that balances both mechanical property development and bonding capability.
Solution Approach 2:
The curing process is divided into periodic stages: first a partial-cure stage to develop mechanical properties for lamination, then a re-cure stage after lamination to complete the bonding. This periodic action allows the material to transition between different functional states at appropriate times in the manufacturing process.
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 enables robust bonding between silicone substrates with tensile strength equal to individual substrates, maintaining mechanical properties and allowing for complex geometries without compromising material integrity, while avoiding the use of adhesives or surface treatments.
Implementation Method 1
the catalyzed reaction of silicon hydride with vinyl groups between different polymeric precursors (e.g., SiH+C═C)
Implementation Method 2
temporary inhibition of silicone reactions is achieved either through the addition of a chemical agent (i.e., an inhibitor) to the multi-part mixture that can increase the lifespan of C═C and SiH functional groups during curing
Implementation Method 3
after removal (usually at elevated temperatures) of the chemical agent blended with the multi-part mixtures of an addition-cured silicone, the resulting material reaches its final mechanical properties
Data Source
AI summary
A polymer article is provided that includes a first silicone component formed from (i) a first siloxane polymer comprising a first plurality of hydride-functional groups and (ii) a second siloxane polymer comprising a first plurality of vinyl-functional groups. The polymer article also includes a second silicone component formed from (i) a third siloxane polymer comprising a second plurality of hydride-functional groups and (ii) a fourth siloxane polymer comprising a second plurality of vinyl-functional groups. Lastly, the polymer includes a contact interface, between the first and second silicone components, comprising chemical crosslinks between the first siloxane polymer and the fourth siloxane polymer. Notably, a tensile strength of the polymer article across the contact interface is substantially equal to a tensile strength of the first silicone component or the second silicone component alone.