Latent Borate-Ammonium Catalysts for Polythiourethane Curing
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Solution Overview
Problem
Existing methods for manufacturing polythiourethane-based substrates, such as ophthalmic lenses, face challenges with short pot life of the polymerizable mixture due to high reactivity, leading to premature gelling and difficulty in processing, especially in batch production, and the presence of optical defects like bubbles and striations.
Innovation Solution
The use of latent thermal catalysts composed of tertiary ammonium or iminium cations and borate anions, which are inactive until activated by heat, allowing controlled polymerization and extended pot life, reducing premature gelling and enhancing processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional catalysts are used to accelerate polymerization, then curing speed is improved, but the mixture gels too quickly causing short pot life and processing difficulty
Solution Approach 1:
The catalyst is pre-blocked with an protecting group before use, rendering it inactive during mixing and filling operations. The catalyst is then activated in situ during the curing cycle, providing controlled acceleration of polymerization only when needed. This preliminary deactivation allows extended pot life while maintaining fast cure capability.
Solution Approach 2:
The catalyst's chemical state is changed from active to blocked form, and then back to active form during curing. This parameter change (activation state) allows the system to have both long mixing time (when blocked) and fast polymerization (when activated), resolving the contradiction between processing time and curing speed.
2Productivity
If high reactivity species are used to achieve fast curing, then productivity is improved, but the mixture becomes difficult to handle and mix due to rapid viscosity increase
Solution Approach 1:
The high reactivity catalyst is pre-blocked before mixing, preventing premature polymerization. This allows the mixture to remain low-viscosity and easy to handle during manufacturing operations. The catalyst is then activated during the controlled curing cycle to achieve fast curing and high productivity.
Solution Approach 2:
The blocking group acts as an intermediary that temporarily deactivates the high reactivity catalyst, allowing the system to maintain both high potential reactivity (for productivity) and low actual reactivity (for ease of manufacture) at different stages of the process.
3Loss of energy
If the polymerization reaction is initiated quickly, then energy consumption during curing is reduced, but optical defects like bubbles and striations occur
Solution Approach 1:
The catalyst is activated in a controlled manner during the curing cycle rather than immediately upon mixing. This controlled activation allows the polymerization to proceed uniformly, avoiding rapid gas evolution and striation formation. The blocking group ensures activation occurs only when the mixture is properly positioned and ready for curing.
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 latent catalysts provide a stable polymerizable mixture with improved shelf life and reduced risk of clogging, enabling efficient filling and curing without optical defects, achieving similar mechanical and thermal properties to conventional catalysts.
Implementation Method 1
at least one heat-activatable latent catalyst composed of a tertiary ammonium or tertiary iminium cation and a borate anion... which are inactive until activated by heat
Data Source
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AI summary
The present invention relates to a method of fast curing a polythiourethane based transparent substrate, comprising in one of its embodiments providing a first component A comprising a polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups, providing a second component B comprising a polythiourethane pre-polymer B1 having thiol end groups, mixing together first and second components A and B to form a polymerizable mixture, curing said mixture to obtain a transparent substrate, wherein at least one heat-activatable latent catalyst composed of a tertiary ammonium or tertiary iminium cation and a borate anion is added in the process prior to the curing step, and said latent catalyst is subsequently activated to accelerate the polymerization reaction forming the polythiourethane-based transparent substrate.