Norbornene Optical Polymer Melt Viscosity Control
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Solution Overview
Problem
The challenge is to produce a thin optical element with a non-uniform thickness and a large optically effective area while minimizing optical defects such as birefringence and weld lines, which are common issues in injection molding processes for small and complex optical lenses.
Innovation Solution
A norbornene-based polymer with specific melt viscosity characteristics, measured at different shear rates, is used to control the formation process, ensuring a low shear rate dependence of melt viscosity, thereby reducing weld lines and birefringence, and incorporating α-olefins with 14 to 40 carbon atoms to enhance the optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If injection molding is used to produce small and thin optical lenses with non-uniform thickness, then production cost is reduced and mass production is enabled, but weld lines and birefringence occur reducing the optically effective area
Solution Approach 1:
The patent applies parameter changes by carefully controlling the melt viscosity of the polymer material and the injection molding process parameters (temperature, pressure, injection rate) to optimize the filling process. This ensures that the resin flows smoothly without forming weld lines or excessive birefringence, thereby maintaining high optical quality while enabling mass production through injection molding
Solution Approach 2:
The patent uses composite materials by incorporating specific additives and modifiers into the polymer matrix to adjust the melt viscosity and flow characteristics. This allows the material to exhibit optimal rheological properties during injection molding, preventing weld line formation and birefringence while maintaining the desired optical properties of the final lens product
2Area of stationary object
If the optically effective area is increased in small diameter lenses, then optical performance is improved, but weld lines and birefringence increase reducing the quality
Solution Approach 1:
The patent employs parameter changes by optimizing the melt viscosity and process conditions to enable filling of large optically effective areas without generating weld lines or birefringence. By adjusting temperature, pressure, and injection rate parameters, the resin flows uniformly across the entire optically effective area, maximizing its size while maintaining optical quality
Solution Approach 2:
The patent applies partial or excessive action by using a slightly higher injection pressure and longer dwelling time than conventional methods to ensure complete filling of the mold cavity. This excessive action compensates for the increased difficulty of filling large optically effective areas without defects, guaranteeing that the entire area is filled uniformly without weld line formation
3Shape
If high pressure is applied during the dwelling step to seal the gate, then the lens shape is maintained, but birefringence increases around the gate
Solution Approach 1:
The patent applies parameter changes by using a lower dwelling pressure combined with a longer dwelling time compared to conventional methods. This approach maintains the lens shape and compensates for shrinkage without applying excessive pressure that would cause molecular orientation and birefringence around the gate area
Solution Approach 2:
The patent employs periodic action by using a multi-stage injection process with varying pressure levels. The dwelling step is performed in a controlled manner with gradual pressure application and release, allowing the material to settle and fill shrinkage cavities without creating excessive molecular orientation and birefringence in the gate region
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 approach results in optical elements with a large optically effective area and reduced optical defects, making them suitable for applications like mobile phone camera lenses, with improved heat resistance and transparency.
Implementation Method 1
A norbornene-based polymer with specific melt viscosity characteristics, measured at different shear rates, is used to control the formation process, ensuring a low shear rate dependence of melt viscosity
Implementation Method 2
a polymer (norbornene-based ring-opening copolymer) obtained by subjecting a norbornene-based monomer to ring-opening polymerization in the presence of a linear α-olefin having 14 to 40 carbon atoms
Data Source
Figure 1~2
Figure 3
AI summary
An optical polymer satisfying an expression (1), where, ηA is the melt viscosity of the optical polymer measured at a temperature of 290°C and a shear rate of 200 (1/s), and ηB is the melt viscosity of the optical polymer measured at a temperature of 290°C and a shear rate of 2000 (1/s). ηA-ηB/ηB×100<60