Polythiourethane Pre-polymer Curing via Segmented Monomer Blending

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Solution Overview

Problem

Existing methods for manufacturing polythiourethane-based optical substrates, such as ophthalmic lenses, face challenges in achieving fast curing cycles without compromising thermomechanical properties or introducing optical defects like bubbles and striations, and are costly due to the need for large heating tanks in pre-polymer production.

Innovation Solution

A process involving the preparation of polythiourethane pre-polymers by initially blending a minor polythiol monomer with a part of the major polyisocyanate or polyisothiocyanate monomer, followed by thermal polymerization and subsequent dilution with the remaining monomer, to achieve a balanced molar ratio of isocyanate to thiol groups, which enhances the curing efficiency and thermomechanical properties of the final polymer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If monomers are directly polymerized in large heating tanks, then complete reaction can be achieved, but the process is time-consuming (20 hours) and energy-intensive

Engineering Contradiction:

Improvecuring speedVSAvoidenergy consumption

Core Design Contradiction:

ProductivityVSUse of energy by stationary object

Solution Approach 1:

The patent applies preliminary action by pre-polymerizing monomers outside the mold before casting. The monomers are partially reacted to form pre-polymers with reduced molecular weight and viscosity, which then cure faster in the mold. This preliminary reaction step enables the final curing to complete in 2-6 hours instead of 20 hours, dramatically improving productivity and reducing energy consumption.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If pre-polymers are used to reduce curing time, then curing speed improves, but the manufacturing cost increases due to large heating tanks required

Engineering Contradiction:

Improvecuring speedVSAvoidmanufacturing cost

Core Design Contradiction:

ProductivityVSEase of manufacture

Solution Approach 1:

The patent segments the polymerization process into two distinct stages: pre-polymerization in small reactors and final curing in the mold. This segmentation allows the pre-polymerization to be performed in small, inexpensive batches rather than requiring one large heating tank, thereby reducing capital equipment costs while maintaining fast curing speeds.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the pre-polymerization step from the final curing process. By separating these operations, the pre-polymer can be prepared in advance in small quantities using minimal equipment, and only the essential curing step requires the mold and heating apparatus. This extraction eliminates the need for large dedicated pre-polymerization tanks.

Inventive Principle:

Principle #2Taking out (Extraction)

3Productivity

If pre-polymers are used to shorten curing time, then productivity improves, but optical defects like bubbles and striations may form

Engineering Contradiction:

Improvecuring speedVSAvoidoptical quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent changes the molecular weight parameter of the polymer by using pre-polymers instead of full polymers. This parameter change reduces viscosity, allowing the material to flow more easily and escape from mold cavities during curing, thereby preventing bubble and striation formation while maintaining fast curing speeds.

Inventive Principle:

Principle #35Parameter changes

4Productivity

If monomers are pre-reacted to form pre-polymers, then curing time reduces, but local heat points may form during polymerization

Engineering Contradiction:

Improvecuring speedVSAvoidheat points

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by performing pre-polymerization in small reactors before mold casting. This preliminary reaction completes much of the exothermic polymerization outside the mold, so that when the pre-polymer is cast and cured in the mold, the remaining reaction generates minimal heat, avoiding local heat points and optical defects.

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 allows for a faster curing process with improved thermomechanical properties, reduced energy consumption, and minimal optical defects, while also reducing the equipment and energy requirements for polymerization, resulting in high-quality polythiourethane-based substrates with enhanced glass transition temperatures and clarity.

Implementation Method 1

followed by thermal polymerization

Methodology Applied

Scientific EffectThermal polymerization:

Implementation Method 2

polymerizing the monomer mixture

Methodology Applied

Scientific EffectPolymerization:

Implementation Method 3

Curing said mixture to obtain a transparent solid substrate

Methodology Applied

Scientific EffectCuring:

Data Source

PatentEP4442724A1Method of curing a polythiourethane-based substrate from a pre-polymer

Publication Date: 2024.10.09 ESSILOR INTERNATIONAL(COMPAGNIE GENERALE D OPTIQUE)

Figure 1

AI summary

The invention relates to a method of curing a polythiourethane-based transparent casted substrate, comprising the steps of providing a first component A comprising a polythiourethane pre-polymer having iso(thio)cyanate end groups, said pre-polymer having been prepared from at least one polythiol monomer and at least one polyiso(thio)cyanate monomer, used in amounts adapted so that the molar ratio R2 of NCX/SH groups ranges from 2 to 35, providing a second component B comprising at least one polythiol monomer, mixing together first and second components A and B and filling a molding cavity with the resulting polymerizable mixture, curing said polymerizable mixture to obtain a polythiourethane-based transparent substrate, wherein said pre-polymer has been prepared by mixing said at least one polyiso(thio)cyanate monomer and said at least one polythiol monomer in initial amounts such that the initial molar ratio R1 of NCX/SH groups for said monomers ranges from 0.3 R2 to 0.95 R2, polymerizing the mixture, and adding to the mixture an additional amount of at least one polyiso(thio)cyanate monomer such that the molar ratio of NCX/SH groups for all the monomers used in the preparation of said pre-polymer is equal to R2, X being O or S.