Compression Molding of Thermoplastic Optical Lenses
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Solution Overview
Problem
Current lens molding processes, such as injection molding and cast molding, are inefficient and wasteful, particularly when working with crosslinked bioplastic polymers, which do not exhibit flowable properties, leading to high material waste and costly equipment maintenance in producing prescription eyeglasses.
Innovation Solution
A method involving compression molding of thermoplastic materials, including crosslinked polymers, using stainless steel molds and glass molds to shape thermoplastic materials into semi-finished and finished lens blanks with reduced waste, employing heating, pressure, and vacuum techniques to form lenses with precise radii and curvatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If injection molding or cast molding is used to produce prescription eyeglasses from thermoplastic materials, then lenses can be formed with precise optical properties, but material waste increases to 80-90% and equipment maintenance costs increase
Solution Approach 1:
The patent applies preliminary action by pre-forming lens blanks with the exact final dimensions and optical curvatures required for specific prescriptions. The compression molding process directly forms the finished lens shape without requiring subsequent lathe cutting or material removal, thereby eliminating 80-90% material waste while maintaining optical precision through precise mold design
Solution Approach 2:
The patent utilizes parameter changes by controlling temperature, pressure, and time parameters during compression molding to achieve precise optical properties. By heating the thermoplastic material to its melting point and applying controlled compression forces, the process forms lenses with exact radii and curvatures required for different prescriptions, maintaining manufacturing precision while minimizing waste
2Productivity
If injection molding is used to form thermoplastic lenses, then lenses can be produced efficiently, but birefringence occurs and equipment maintenance costs increase
Solution Approach 1:
The patent replaces the high-pressure injection molding mechanical system with a compression molding system that applies uniform compressive forces from all directions. This substitution eliminates the shear stresses and directional forces inherent in injection molding that cause birefringence, while maintaining production efficiency through direct formation of finished lenses without subsequent machining
Solution Approach 2:
The patent changes the molding parameters by using controlled compression heating and gradual pressure application rather than high-velocity injection. By controlling the temperature profile and applying pressure uniformly during the molding process, the patent prevents stress-induced birefringence while maintaining lens formation efficiency
3Manufacturing precision
If lathe cutting is used to process lens blanks into prescription lenses, then precise prescriptions can be achieved, but production time increases and equipment maintenance costs increase
Solution Approach 1:
The patent applies preliminary action by pre-forming lens blanks with the exact final dimensions, curvatures, and optical properties required for specific prescriptions. The compression molding process directly creates the finished lens shape without requiring subsequent lathe cutting or material removal, thereby eliminating production time delays and maintenance requirements while maintaining prescription precision through precise mold design
Solution Approach 2:
The patent extracts the unnecessary intermediate processing steps (lathe cutting, grinding, polishing) from the lens manufacturing process. By using compression molding to directly form finished lenses with precise prescriptions, the patent removes the time-consuming and maintenance-intensive machining operations while preserving the ability to achieve accurate optical specifications
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 significantly reduces material waste to 10-20% and lowers production costs by using less expensive glass molds, while maintaining optical quality and precision in lens production.
Implementation Method 1
heating the assembly to a predetermined heating temperature for a predetermined heating time
Implementation Method 2
The thermoplastic material can be in the form of a slab or a disc having a substantially cylindrical shape... The thermoplastic material is heated to its melting point
Implementation Method 3
compressing the assembly at a predetermined compression pressure for a predetermined compression time
Implementation Method 4
cooling the assembly to room temperature, thereby forming one or more thermoplastic optical elements
Data Source
AI summary
Provided herein are methods of molding thermoplastic polymers into optical elements. The optical elements in the form of cylindrical discs, semi-finished lens blanks or finished lenses are compression molded at high temperature typically above thermoplastic polymers softening temperature and under high pressure. The semi-finished lens blanks and finished lenses are molded using front and back glass molds inside a mold assembly which reshapes the cylindrical discs that are either previously molded or cut out from thick slab. Also provided are methods for producing single vision and progressive addition lens prescriptions.