Water-Based Anti-Abrasion Coating for Ophthalmic Lenses
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Solution Overview
Problem
Current liquid hard coating compositions for optical plastics rely heavily on organic solvents, which pose health and environmental concerns, and struggle with achieving effective primerless adhesion over time, especially on thermosetting polythiourethane resins, while maintaining mechanical and optical properties.
Innovation Solution
A liquid hard coating composition primarily using water as the solvent, with limited organic solvents, comprising the product of epoxyalkoxysilane hydrolysis, cationic silica particles, an inorganic Lewis acid, and a surfactant to form a reticulated network providing scratch and abrasion resistance, and incorporating cationic particles for improved adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If organic solvents are used in liquid hard coating compositions, then the coating achieves good mechanical and optical properties, but health and environmental concerns arise
Solution Approach 1:
The patent changes the fundamental parameter of the solvent system from organic-based to water-based. This involves modifying the chemical composition parameters of the coating formulation, replacing organic solvents with water as the primary solvent, while adjusting other formulation parameters (resin types, catalysts, additives) to compensate for the different solvent properties and achieve comparable coating performance.
Solution Approach 2:
The patent substitutes the chemical system based on organic solvents with an alternative chemical system based on water. This replacement fundamentally changes the solvent chemistry, requiring adaptations in resin selection, crosslinking mechanisms, and curing processes to achieve equivalent coating properties without organic solvent emissions.
2Object-affected harmful factors
If water is used as the main solvent instead of organic solvents, then health and environmental issues are reduced, but achieving stable and uniform hard coatings becomes difficult
Solution Approach 1:
The patent introduces surfactants as intermediary substances that mediate between the water-based solvent system and the coating ingredients. These surfactants modify surface tension, improve wetting characteristics, and ensure uniform distribution of coating components, thereby achieving stable and uniform coatings despite using water as the primary solvent instead of organic alternatives.
Solution Approach 2:
The patent adjusts multiple formulation parameters to optimize water-based coating stability, including selecting specific resin types compatible with water, controlling pH levels, adjusting solid content percentages, and incorporating stabilizing additives. These parameter modifications enable the water-based system to achieve composition stability comparable to organic solvent systems.
3Object-affected harmful factors
If water-based coating composition is used, then organic solvent usage is minimized, but adhesion over time on thermosetting polythiourethane resins deteriorates
Solution Approach 1:
The patent modifies formulation parameters specifically to enhance adhesion performance in water-based systems on thermosetting polythiourethane substrates. This includes selecting resins with appropriate functional groups for substrate bonding, optimizing crosslinking density, and adjusting curing conditions to achieve strong, durable adhesion without relying on organic solvents.
Solution Approach 2:
The patent substitutes organic solvent-based adhesion mechanisms with water-based adhesion mechanisms, relying on hydrogen bonding, polar interactions, and covalent crosslinking to achieve strong substrate bonding. This requires careful selection of water-compatible resin chemistry and curing protocols to replicate the adhesion performance previously achieved with organic solvents.
4Ease of manufacture
If water is used as solvent, then the deposition process becomes simpler, but maintaining transparency and preventing light diffusion through aggregates or cracks becomes challenging
Solution Approach 1:
The patent employs surfactants and dispersing agents as intermediary substances that prevent aggregation of coating ingredients in the water-based system. These intermediaries ensure uniform distribution of particles and molecules, prevent crack formation during drying, and maintain optical clarity by eliminating light-scattering defects that would otherwise compromise transparency.
Solution Approach 2:
The patent optimizes formulation parameters to control the physical chemistry of the water-based coating, including adjusting pH to prevent premature polymerization, controlling solid content to ensure proper flow and leveling, and selecting resin molecular weights that balance processability with optical properties. These parameter controls prevent aggregate formation and maintain transparency.
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 composition achieves stable, uniform hard coatings with enhanced mechanical and optical properties, including improved primerless adhesion over time on thermosetting polythiourethane resins, while minimizing organic solvent usage and maintaining transparency.
Implementation Method 1
the product of hydrolysis of an epoxyalkoxysilane of formula (I): SiXY3; wherein the X group represents a monovalent organic groups linked to the silicon atom through a carbon atom and containing at least one epoxy function and the Y groups are identical or different and represent alkoxy groups linked to the silicon atom
Implementation Method 2
cationic particles with an average diameter comprised between 5 nm and 100 nm, wherein a sol of said cationic particles dispersed in water is stable at acidic pH
Data Source
AI summary
The invention relates to a water based composition to be used for the preparation of anti-abrasion coatings on ophthalmic lenses. The composition comprises: the product of hydrolysis of an epoxyalkoxysilane SiXY3, wherein X represents a monovalent organic group linked to the silicon atom through a carbon atom and containing at least one epoxy function and Y represents an alkoxy group; cationic nanoparticles comprising silica, wherein a water sol of said cationic particles is stable at acidic pH; an inorganic non-hydrogen Lewis acid; a surfactant such that a water solution of 15 wt % of said surfactant exhibits a static surface tension below 25 mN/m at 20° C.; less than 0.5 wt % of a water miscible organic solvent less volatile than water. Moreover, the composition comprises no organic solvents other than said water miscible organic solvent less volatile than water and other than organic solvents that are a product of hydrolysis of the epoxyalkoxysilane.