Optical Hard Coating Durability via Silane-Plasticizer Ratio
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing abrasion and/or scratch-resistant coatings for optical articles suffer from durability issues, including fracturing, especially under varying humidity and temperature conditions, and often require non-REACH compliant solvents in their primer coatings, posing manufacturing and safety challenges.
Innovation Solution
A coating composition comprising an epoxy compound with hydrolysable silicon atoms, a silane hydrolysate, colloidal silica, and a plasticizer, where the weight ratio of silane to plasticizer is higher than 0.4, and the plasticizer content is less than 10wt%, providing improved durability and REACH compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a primer layer comprising polyurethane and particulate silica is used in combination with an abrasion and/or scratch-resistant coating, then the risk of fracturing throughout wear is lowered, but the primer coating becomes non-REACH compliant due to use of non-REACH compliant solvents such as 1-methyl-2-pyrrolidone
Solution Approach 1:
The invention changes the chemical composition parameters of the primer coating by replacing non-REACH compliant solvents with REACH compliant alternatives. Specifically, it uses a primer coating comprising polyurethane and colloidal silica without non-REACH compliant solvents, thereby maintaining durability while achieving REACH compliance.
Solution Approach 2:
The invention employs a composite primer coating formulation combining polyurethane with colloidal silica particles. This composite structure provides both the mechanical properties needed for crack-resistance and the chemical compliance required by REACH regulations, eliminating the need for harmful solvents.
2Ease of manufacture
If classical hard coating stacks are used to provide mechanical properties to optical articles, then the coating structure is simple and easy to manufacture, but durability problems and fracturing occur throughout wear under varying humidity and temperature conditions
Solution Approach 1:
The invention uses a composite abrasion and/or scratch-resistant coating comprising an inorganic matrix (silica, glass beads) embedded in an organic binder (polyurethane). This composite structure provides enhanced durability and resistance to fracturing under varying environmental conditions while maintaining ease of manufacture through conventional coating processes.
Solution Approach 2:
The invention introduces local quality variations within the coating by incorporating particulate materials (silica, glass beads) at specific concentrations and sizes within the polyurethane matrix. This creates regions of enhanced mechanical properties throughout the coating, improving overall durability without complicating the manufacturing process.
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 solution significantly reduces the risk of fracturing and cracking of the coating, ensuring high mechanical resistance and safety while maintaining low diffusion levels, even when used with REACH compliant primer coatings.
Implementation Method 1
a silane hydrolysate having formula (I): wherein T1 and T2 are groups which will each react to give a OH group on hydrolysis of the silane of formula (I)
Data Source
AI summary
The present invention relates to an optical article comprising a substrate having at least one main surface coated with a coating comprising at least one layer of an abrasion and/or scratch-resistant coating, wherein the abrasion and/or scratch-resistant coating is formed from a composition comprising at least one epoxy compound bearing at least one silicon atom having at least one hydrolysable group directly linked to the silicon atom and at least one group comprising an epoxy function linked to the silicon atom through a carbon atom, and/or a hydrolysate thereof, at least one plasticizer, a silane hydrolysate and colloidal silica, wherein the total amount of plasticizer in the composition is lower than 10wt% of the dry extract of the total composition, and wherein the weight ratio of silane of formula (I) to plasticizer is higher than 0.4 in the dry exact of the composition. The invention further relates to a process for the manufacture of such an abrasion and/or scratch-resistant coating on a substrate.