Peroxide-Functional Polypropylene Mold for Ophthalmic Devices

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Solution Overview

Problem

Molds for ophthalmic devices like contact lenses face issues with dimensional stability and light transmittance, as well as chemical interaction with monomers, leading to adhesion and surface quality problems, particularly with polypropylene and other clear resins.

Innovation Solution

A mold assembly using a polymeric resin with a polymer backbone and pendent groups having peroxide functionality, which enhances lubricity and reduces chemical interaction, allowing for improved release and surface characteristics of ophthalmic devices during the molding process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polypropylene is used to make molds, then chemical resistance and low cost are improved, but dimensional stability and light transmittance deteriorate

Engineering Contradiction:

Improvechemical resistanceVSAvoiddimensional stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent applies composite materials by combining polypropylene base resin with specific additives including nucleating agents (such as sodium benzenesulfonate) and lubricants. This composite formulation maintains the chemical resistance and low cost of polypropylene while significantly improving dimensional stability through the nucleating agent that promotes uniform crystallization and reduces shrinkage variation.

Inventive Principle:

Principle #40Composite materials

2Reliability

If polypropylene is used to make molds, then chemical resistance is improved, but light transmittance deteriorates

Engineering Contradiction:

Improvechemical resistanceVSAvoidlight transmittance

Core Design Contradiction:

ReliabilityVSIllumination intensity

Solution Approach 1:

The patent applies parameter changes by modifying the optical properties of polypropylene through the addition of specific additives. The lubricant components (such as polyethylene wax or silicone oil) and nucleating agents alter the crystalline structure and light scattering properties, improving light transmittance while maintaining the chemical resistance of the polypropylene base material.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If mold thickness is increased to improve dimensional stability, then dimensional stability is improved, but cooling time and productivity deteriorate

Engineering Contradiction:

Improvedimensional stabilityVSAvoidcooling time

Core Design Contradiction:

Stability of the object's compositionVSProductivity

Solution Approach 1:

The patent applies parameter changes by modifying the material composition rather than the geometric parameter (thickness). The addition of nucleating agents changes the crystallization behavior to achieve uniform and rapid crystallization, enabling thin-walled molds to attain high dimensional stability without requiring increased thickness, thereby reducing cooling time and improving productivity.

Inventive Principle:

Principle #35Parameter changes

4Stability of the object's composition

If clear resins like polycarbonate or polystyrene are used, then dimensional stability and light transmittance are improved, but chemical interaction with monomers worsens

Engineering Contradiction:

Improvedimensional stabilityVSAvoidchemical interaction

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by creating a surface-modified layer on the polypropylene mold. The lubricant additives (such as polyethylene wax or silicone oil) migrate to the mold surface during curing, forming a release layer that provides chemical inertness and prevents adhesion between the mold and lens monomers, while the bulk polypropylene material maintains its dimensional stability properties.

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

The use of polymeric resin with peroxide functionality improves the dimensional stability and surface quality of ophthalmic devices by reducing adhesion and enhancing the release process, resulting in higher manufacturing yield and product throughput.

Implementation Method 1

Polypropylene can resist interaction with the monomers used to make the contact lenses. The ability to resist chemical interaction prevents the lens and the mold from adhering to each other

Methodology Applied

Scientific EffectChemical interaction resistance:

Implementation Method 2

Methodology Applied

Scientific EffectLubrication: Lubrication

Data Source

PatentEP2219841B1Molds for production of ophthalmic devices and method for the manufacture of the molds

Publication Date: 2011.05.18 BAUSCH & LOMB INC

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AI summary

A mold assembly for the manufacture of at least one ophthalmic device used in or on the eye is disclosed, the mold assembly comprising a mateable pair of mold parts (30, 40) wherein at least one of the mold parts is made from a polymeric resin comprising a polymer backbone and one or more pendent groups having peroxide functionality and covalently linked to the polymer backbone.