Polythiol Composition Viscosity Control for Optical Lens Defect Prevention
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Solution Overview
Problem
The challenge is to control the viscosity and reaction rate of a polymerizable composition for polythiourethane-based plastic optical lenses to prevent the generation of striae and bubbles during polymerization, as excessive viscosity increase can lead to defects in the lens.
Innovation Solution
A polythiol composition is formulated with a first polythiol compound having at least four mercapto groups and a second polythiol compound with two or more mercapto groups and additional hydrogen-bondable functional groups like hydroxyl, amine, or carboxyl groups, which are used in specific proportions to manage viscosity and reaction rate effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a polythiol compound with multiple mercapto groups is used to increase viscosity at the initial stage of polymerization, then the generation of striae and bubbles is reduced, but the reaction rate decreases and excessive crosslinking occurs at low temperatures
Solution Approach 1:
The invention divides the polythiol compound into two distinct components: a first polythiol compound with multiple mercapto groups (Formula 1) that provides controlled viscosity increase, and a second polythiol compound with fewer mercapto groups (Formula 2) that maintains reaction rate. This segmentation allows each component to fulfill specific functions without the adverse effects of using a single compound with excessive crosslinking capability.
Solution Approach 2:
The invention changes the parameters of the polythiol system by specifying precise structural formulas and molecular weight ranges for the two polythiol compounds. The first polythiol compound has a weight average molecular weight of 200-500 g/mol with 3-8 mercapto groups, while the second has 1-3 mercapto groups. These parameter specifications enable controlled viscosity increase without excessive crosslinking, resolving the contradiction between manufacturing precision and productivity.
2Manufacturing precision
If the viscosity of the polymerizable composition is increased at the initial stage of polymerization to prevent convection, then striae and bubbles are reduced, but the composition becomes too thick for proper mixing and bubble removal
Solution Approach 1:
The invention applies preliminary action by controlling the viscosity increase to occur gradually during the polymerization process rather than immediately at the start. The first polythiol compound provides initial viscosity control to prevent severe convection, while the second polythiol compound ensures the composition remains processable. This staged approach allows proper mixing and bubble removal before the composition becomes too viscous.
Solution Approach 2:
The invention changes the viscosity parameter dynamically through the polymerization process by using two polythiol compounds with different molecular weights and functional group densities. The composition maintains an optimal viscosity range (50-200 Pa·s at 25°C) that balances convection prevention with processability, allowing adequate time for mixing and bubble removal while gradually increasing viscosity to prevent defects.
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
This approach stabilizes the viscosity and reaction rate during polymerization at low temperatures, preventing striae and bubbles, and results in high-quality plastic optical lenses with excellent appearance and optical characteristics.
Implementation Method 1
a polythiol compound having at least four mercapto groups only as a hydrogen-bondable functional group; and a second polythiol compound having at least two mercapto groups as a hydrogen-bondable functional group and at least one hydrogen-bondable functional group other than a mercapto group
Data Source
Figure 1
AI summary
Embodiments relate to a polythiol composition for a plastic optical lens and a polythiourethane-based plastic optical lens prepared therefrom. In the embodiments, a first polythiol compound having mercapto groups only as a hydrogen-bondable functional group and a second polythiol compound having mercapto groups as a hydrogen-bondable functional group and a hydrogen-bondable functional group other than a mercapto group are used in an appropriate amount. Thus, not only is it possible to control the viscosity of a polymerizable composition at the initial stage of polymerization at a low temperature of 5 to 15°C and to stabilize the rate of increase in the viscosity of the composition and the reaction rate thereof, but also the change in the viscosity at a low temperature is low, thereby preventing the generation of striae, bubbles, and the like. Further, various plastic lenses such as eyeglass lenses, camera lenses, and the like having excellent appearance characteristics (without striae and bubbles) and excellent optical characteristics can be obtained from the composition.