Microstructured Mold Insert for Lens Defect Reduction
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Solution Overview
Problem
Injection molding of lenses with diverging geometry, such as −0.25 to −8.00 diopter lenses, often results in weld line and center distortion defects due to differential shrinkage and rapid cooling, which can lead to internal stress and defects like weld lines and center distortions.
Innovation Solution
A method for forming a microstructured mold insert with a low thermal conductivity using a glass or metal mold insert and a microstructured resin film, specifically SU-8 resin, which is imprinted with inverted microstructures to reduce thermal conductivity and enhance durability, allowing for reduced defects and improved lens fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If metal inserts are used for injection molding, then productivity is improved through rapid cooling, but weld line and center distortion defects increase due to excessive quenching
Solution Approach 1:
The patent applies local quality by creating microstructures (protrusions and recesses) on specific regions of the mold insert surface. These microstructures locally modify thermal conductivity, allowing certain areas to cool faster while others maintain temperature longer, thereby controlling the cooling process to prevent defects while maintaining productivity.
Solution Approach 2:
The patent changes the thermal conductivity parameter of the mold insert by incorporating materials with different thermal properties and creating microstructured surfaces. This modifies the cooling rate parameter locally, allowing optimization of both productivity and defect reduction by controlling heat transfer characteristics.
2Object-affected harmful factors
If low thermal conductivity materials are used to reduce defects, then weld line and center distortion defects are reduced, but productivity decreases due to prolonged cooling time
Solution Approach 1:
The microstructured surface creates regions of varying thermal conductivity on the mold insert. Some regions with higher thermal conductivity facilitate faster cooling for productivity, while regions with lower thermal conductivity prevent excessive quenching and reduce defects, achieving both goals simultaneously.
Solution Approach 2:
The mold insert surface is segmented into multiple microstructures (protrusions and recesses) that create distinct thermal zones. This segmentation allows different parts of the mold to perform different functions - some areas cool rapidly while others maintain temperature, optimizing both defect reduction and cooling efficiency.
3Object-affected harmful factors
If microstructured films are formed on mold inserts to reduce thermal conductivity, then defect reduction is achieved, but manufacturing complexity increases
Solution Approach 1:
The patent uses a master mold with predetermined microstructures to create replica molds. The microstructured pattern is copied from the master to the production molds, ensuring consistent defect reduction performance while simplifying the manufacturing process through replication rather than direct fabrication of complex microstructures.
Solution Approach 2:
The microstructured film is formed on the mold insert surface before the actual injection molding process. This preliminary preparation ensures that the thermal conductivity modification is already in place, allowing the molding process to proceed with optimized cooling characteristics without adding complexity during production.
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 method effectively reduces weld line and center distortion defects by slowing down the cooling process, allowing molecular chains to relax, thereby reducing internal stress and improving the quality of lenses with diverging geometries.
Implementation Method 1
using a material that has a very low thermal conductivity. This can prolong the initial cooling rates to hold the temperature of the polymer melt above the glass transition temperature (Tg) for a sufficient time
Implementation Method 2
pressing the stamp into a film or medium disposed on a surface of a first mold insert to form a microstructured film, the microstructured film including a plurality of microstructures formed on a surface of the microstructured film based on the plurality of inverted microstructures
Data Source
AI summary
A method for forming a mold insert includes forming a stamp, a surface of the stamp including a plurality of inverted microstructures formed thereon; and pressing the stamp into a medium disposed on a surface of a first mold insert to form a microstructured film, the microstructured film including a plurality of microstructures formed on a surface of the microstructured film based on the plurality of inverted microstructures, the plurality of microstructures being complementary to the plurality of inverted microstructures.