Injection Molded Contact Lens Surface Defect Management

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Solution Overview

Problem

Direct injection molding of ophthalmic lenses often results in irregular areas such as gate witnesses or recesses on the lens surface, which require additional processing steps to smooth, leading to increased production costs and potential lens defects.

Innovation Solution

A method involving a mold insert with a raised non-uniform region forming a depression in the lens cavity, allowing the lens forming composition to cure and create a negative image of the irregular area, which is then hidden beneath the lens surface, eliminating the need for post-molding smoothing and reducing production costs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If direct injection molding is used to manufacture ophthalmic lenses, then production efficiency is improved, but irregular areas such as gate witnesses or recesses appear on the lens surface

Engineering Contradiction:

Improveproduction efficiencyVSAvoidlens surface quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The mold insert is pre-configured with a raised non-uniform region that will form a depression in the lens cavity. This preliminary structural preparation ensures that when the lens forming composition is injected and cured, any irregular areas such as gate witnesses will be formed within the depression rather than on the lens surface, thereby preventing surface defects before they occur

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention converts the harmful effect of irregular areas (gate witnesses) by designing the mold insert to create a depression that captures these irregularities. The raised non-uniform region on the mold insert forms a corresponding depression in the lens cavity, transforming the potential surface defect into a contained feature that does not affect lens performance or appearance

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Manufacturing precision

If additional processing steps are added to smooth irregular areas on the lens surface, then lens surface quality is improved, but production costs increase

Engineering Contradiction:

Improvelens surface qualityVSAvoidproduction cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The mold insert with the raised non-uniform region performs the function of both molding the lens and preventing surface defects simultaneously. The depression formed in the lens cavity self-containing any irregular areas, eliminating the need for separate post-processing steps to smooth or remove gate witnesses, thereby reducing production costs while maintaining lens surface quality

Inventive Principle:

Principle #25Self-service

3Manufacturing precision

If additional processing steps are added to smooth irregular areas, then lens surface quality is improved, but potential lens defects increase

Engineering Contradiction:

Improvelens surface qualityVSAvoidlens defect rate

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

By pre-configuring the mold insert with the raised non-uniform region, the invention prevents irregular areas from occurring on the lens surface in the first place. This preliminary structural design ensures that gate witnesses and other irregularities are contained within the depression, eliminating the need for post-processing that could potentially introduce defects and thereby improving lens reliability

Inventive Principle:

Principle #10Preliminary action

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 minimizes or eliminates irregular areas on the lens surface, enhancing ophthalmic acceptability and reducing the need for secondary operations, thereby improving the efficiency and quality of ophthalmic lens production.

Implementation Method 1

the lens forming composition may be injected into the mold cavity and then exposed to thermal radiation; actinic light, including UV and visible light: or other forms of radiation effective to polymerize the composition

Methodology Applied

Scientific EffectPolymerization: Photopolymerisation

Implementation Method 2

the polymer composition is first heated in the injection unit of the molding machine to allow the polymer material to flow or be injected into the mold cavity

Methodology Applied

Scientific EffectThermal heating: Heating

Data Source

PatentEP2585285B1Methods, devices, and systems for injection molding contact lenses

Publication Date: 2021.10.06 COOPERVISION INT LTD

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AI summary

Methods, devices, and systems for manufacturing ophthalmic lenses using direct injection molding are described. The present methods, devices, and systems include a mold block having a first mold insert and a second mold insert defining a lens-shaped cavity between them. A raised non-uniform region that projects into the lens-shaped cavity is incorporated in a peripheral zone of the molding surface of at least one of the mold inserts. When an ophthalmic lens is formed using the described mold block, at least one depression is produced in the lens. A gate placed at the non-uniform region allows the depression to hide any gate witness that may form when the mold is closed or separated.