Thermoplastic Polyurethane Lenses Urethane Content

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Solution Overview

Problem

Existing materials for optical lenses, such as commercially available thermoplastic polyurethanes, lack a balance of mechanical and optical properties, particularly exhibiting low glass transition temperatures, high yellowness, and poor refractive index and Abbe number combinations, making them unsuitable for ophthalmic lenses.

Innovation Solution

A method of forming thermoplastic polyurethanes with a weight percentage of urethane repeating units (—NHCOO—) above 23%, combined with additives like antioxidants and ultra-violet light absorbers, to create lenses with enhanced stress resistance, improved optical clarity, and reduced yellowness, suitable for rimless spectacles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If commercially available thermoplastic polyurethanes are used for optical lenses, then ease of manufacture is improved, but optical properties (refractive index, Abbe number) and mechanical properties (hardness, stress resistance) deteriorate

Engineering Contradiction:

Improveease of manufactureVSAvoidoptical and mechanical properties

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the chemical composition parameters of the TPU by specifying a urethane repeating unit content of at least 23% by weight and incorporating specific additives (antioxidants, UV absorbers, hydrogen bonding agents). This parameter adjustment resolves the contradiction by achieving both manufacturability and improved optical-mechanical property balance suitable for ophthalmic lenses

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite material system by combining TPU base polymer with multiple functional additives including antioxidants, ultra-violet light absorbers, and hydrogen bonding agents. This composite approach enables simultaneous achievement of ease of manufacture, improved stress resistance, reduced yellowness, and enhanced optical properties

Inventive Principle:

Principle #40Composite materials

2Strength

If TPU with high urethane repeating unit content is used, then stress resistance and resistance to cracking improve, but manufacturing complexity increases

Engineering Contradiction:

Improveresistance to stress induced cracking and crazingVSAvoidmanufacturing complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent optimizes the urethane repeating unit content to a minimum threshold of 23% by weight, which provides sufficient stress resistance and resistance to cracking and crazing while avoiding excessive manufacturing complexity. This parameter optimization resolves the contradiction between strength improvement and manufacturing simplicity

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If TPU is used for optical lenses, then ease of manufacture and processing are improved, but optical clarity and yellowness resistance deteriorate

Engineering Contradiction:

Improveease of manufactureVSAvoidyellowness and optical clarity

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent introduces ultra-violet light absorbers and antioxidants as intermediary substances that protect the TPU from UV-induced degradation and oxidation. These additives act as mediators between the TPU and harmful environmental factors, preventing yellowness and maintaining optical clarity while preserving ease of manufacture

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Inventive Principle:

Principle #40Composite materials

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 resulting lenses exhibit increased resistance to stress-induced cracking and crazing, improved optical properties, and stability against thermo-oxidative degradation, meeting mechanical and optical requirements for ophthalmic lenses.

Implementation Method 1

the stated weight percentage of urethane repeating units (—NHCOO—) renders an optical surface formed from a final lens shaping operation having greater resistance to stress induced cracking and crazing

Methodology Applied

Scientific EffectHydrogen bonding: Chemical Bonding

Implementation Method 2

additives like antioxidants and ultra-violet light absorbers, to create lenses with enhanced stress resistance, improved optical clarity, and reduced yellowness

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Implementation Method 3

additives like antioxidants and ultra-violet light absorbers, to create lenses with enhanced stress resistance, improved optical clarity, and reduced yellowness

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS8270089B2Thermoplastic polyurethane lenses with a specified weight percentage of urethane repeating units

Publication Date: 2012.09.18 ESSILOR INTERNATIONAL(COMPAGNIE GENERALE D OPTIQUE)

AI summary

A method of forming thermoplastic polyurethane (TPU) into an optical lens. Suitable TPUs contain urethane (—NHCOO—) repeating units that are present in at least 23% by weight. This range of urethane weights is an indicator of a flexural modulus above 1,400 MPa. The TPUs have refractive indices above 1.54 and Abbe numbers above 27. They have glass transition temperatures above about 100 degrees C. The selected TPU can be injection molded to form ophthalmic lenses, that are well suited for use in rimless spectacles. The lenses are highly solvent resistant, while at the same time being readily tintable. The lenses made according the invention meet FDA 21 CFR 801.41 Impact Requirement, and ANSI Z87.1 high velocity impact (HVI) standard.