Thin Plastic Lens Injection-Compression Molding

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Solution Overview

Problem

The production of thin plastic lenses for electronic devices and other applications faces challenges in managing stress induced during fabrication, leading to issues like birefringence due to uneven molecular orientation and internal stresses, which can result in optical distortions and unwanted rainbow effects.

Innovation Solution

The use of an injection-compression molding process eliminates the conventional runner system, incorporating a mold with an integral runner and center sprue, allowing for laminar flow and reduced stress, and includes features like holograms and metallization, with in-mold de-gating and separation processes to minimize stress and enhance optical clarity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional injection molding with runner system is used, then production efficiency is improved, but stress and birefringence increase causing optical distortion

Engineering Contradiction:

Improveproduction efficiencyVSAvoidoptical clarity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent removes the conventional runner system from the injection molding process. By extracting the runner component, the process eliminates the sources of stress concentration and molecular orientation defects that cause birefringence, thereby improving optical clarity while maintaining production efficiency through direct cavity injection.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of using a conventional runner system that distributes material through channels, the patent inverts the approach by using a direct sprue system that injects material directly into the cavity. This reversal of the material flow path eliminates the harmful effects of runner-induced stress and molecular alignment defects.

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of manufacture

If conventional injection molding process is used, then manufacturing simplicity is maintained, but internal stress and molecular orientation defects occur

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidmolecular orientation uniformity

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The patent modifies the injection molding parameters by eliminating the runner system and using a direct sprue injection method. This parameter change in the process design alters the flow dynamics, reducing shear rates and preventing uneven molecular orientation while maintaining manufacturing simplicity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent incorporates a sprue directly in the mold design that guides material flow from the beginning of injection. This preliminary structural action ensures uniform material distribution and reduces stress accumulation before the molding process even begins, preventing molecular orientation defects.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If runner system is eliminated, then stress and birefringence are reduced, but process complexity increases

Engineering Contradiction:

Improveoptical clarityVSAvoidmold design complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent merges the sprue and cavity interface into a unified direct injection design. By combining these elements into a simple direct-path system without separate runner channels, the mold design achieves reduced stress and birefringence without significantly increasing complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent applies local quality optimization at the critical sprue-cavity interface by designing a direct injection path. This localized design focus addresses the specific problem area of stress concentration without requiring complex modifications throughout the entire mold system.

Inventive Principle:

Principle #3Local quality

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 stress and birefringence, enabling the production of high-strength, optically clear light transmission devices with reduced cycle time and improved optical characteristics, addressing the challenges of stress management and optical distortion.

Implementation Method 1

incorporating a mold with an integral runner and center sprue, allowing for laminar flow and reduced stress

Methodology Applied

Scientific EffectLaminar flow: Laminar Flow

Implementation Method 2

injection-compression molding process

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentUS7807226B2System, device, and method for producing thin plastic lenses

Publication Date: 2010.10.05 NIPRO INC

AI summary

Light transmission devices, such as lenses and windows for portable electronic devices, are produced using an injection/compression molding technique in which a light transmission device mold includes an integral runner in substantially the same plane and with substantially the same wall thickness as the light transmission device to be produced. The finished light transmission devices are mechanically separated from the molded product. Molding equipment and processes traditionally used to produce information discs can be leveraged to produce light transmission devices. Various processes can be performed to add metallization, coatings, and printing to the light transmission devices.