Two-Layer Thermoplastic Optical Articles Preserving Microstructure Shape

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Solution Overview

Problem

Existing methods for manufacturing ophthalmic lenses with encapsulated microstructures face challenges in maintaining shape integrity and optical design due to deformation of microstructures during the injection overmolding process, and the selection of thermoplastic materials with specific refractive index and thermal resistance properties is not adequately addressed, leading to poor myopia control.

Innovation Solution

A method involving a two-layered lens structure where a low-index, low-thermal-resistance polymethyl methacrylate (PMMA) covering layer is injected over a high-index, high-thermal-resistance polycarbonate (PC) support layer with pre-heating to ensure strong bonding and preserve microstructure integrity, using a synchronized ejection mechanism to avoid damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If injection overmolding is used to encapsulate microstructures, then the microstructures are protected from external damage, but the microstructures deform under high heat and pressure causing loss of shape integrity

Engineering Contradiction:

Improveprotection of microstructuresVSAvoidshape integrity of microstructures

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The support layer is pre-heated to a temperature above its glass transition temperature before the covering layer is deposited. This preliminary heating action ensures the support layer remains in a rubbery state during overmolding, preventing microstructure deformation while still allowing the covering layer to bond effectively.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the thermal parameters of the system by heating the support layer to a specific temperature range (above Tg but below decomposition temperature) before deposition. This parameter change transforms the mechanical properties of the support layer, making it more compliant and less prone to deformation under overmolding pressure.

Inventive Principle:

Principle #35Parameter changes

2Length of stationary object

If a second optical thermoplastic material is injected over the micro-structured surface to form the lens body, then the lens achieves adequate thickness and structural integrity, but the interface between layers is difficult to define clearly affecting optical fidelity

Engineering Contradiction:

Improvethickness of lens bodyVSAvoidinterface definition and optical fidelity

Core Design Contradiction:

Length of stationary objectVSManufacturing precision

Solution Approach 1:

The patent applies different materials with specific local properties: the support layer uses a material with Tg above the deposition temperature to maintain structural integrity, while the covering layer uses a material that bonds effectively to the heated surface. This local differentiation of material properties ensures both adequate thickness and clear interface definition.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs a composite two-layer structure where each layer has specifically selected thermoplastic materials with complementary properties. The support layer material and covering layer material are chosen to ensure proper bonding at the interface while maintaining distinct layer boundaries for optical fidelity.

Inventive Principle:

Principle #40Composite materials

3Strength

If the support layer is pre-heated to a temperature above its glass transition temperature, then the bonding between layers is strengthened, but the microstructures may deform if the temperature is too high

Engineering Contradiction:

Improvebonding strength between layersVSAvoidshape integrity of microstructures

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent precisely controls the heating temperature parameter, maintaining it within a specific window: above the glass transition temperature for adequate bonding, but below the temperature that causes microstructure deformation. This controlled parameter change optimizes both bonding strength and shape integrity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The support layer is pre-heated to the optimal temperature range before the covering layer is deposited. This preliminary action ensures the surface is at the ideal temperature for bonding without exceeding the threshold that would cause microstructure deformation during the subsequent deposition process.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP4640417A1Method for manufacturing an optical article with encapsulated microstructures

Publication Date: 2025.10.29 ESSILOR INTERNATIONAL(COMPAGNIE GENERALE D OPTIQUE)

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AI summary

Method for manufacturing an optical article with encapsulated microstructures (64) comprising the steps of: - providing a support layer (56) having microstructures (58) on a front convex surface, the support layer (56) comprising a first optical thermoplastic material (52); - depositing, on said micro-structured surface, a second optical thermoplastic material (60) having a refractive index (RIWafer) and a glass transition temperature (TgWafer) lower than a respective refractive index (RILens) and glass transition temperature (TgLens) of the first optical thermoplastic material (52), thus obtaining a covering layer (62) which encapsulates the microstructures (58), the support layer (56) being thicker than the covering layer and forming, together with said covering layer (62), said optical article with encapsulated microstructures (64).