Hard Coat Layer Hardness via Irregular Silica
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Solution Overview
Problem
Conventional hard coat films for image display devices fail to achieve sufficient hardness and abrasion resistance, particularly when using ultraviolet-curable resins or spherical silica fine particles, and often result in substrate damage due to heat during polymerization.
Innovation Solution
An optical layered body with a hard coat layer formed on a triacetylcellulose substrate, containing reactive irregularly shaped silica fine particles bonded by an inorganic chemical bond, which provides a Martens hardness relationship of N2>N1>N3, achieving a pencil hardness of 4H or more and excellent abrasion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coat layer is formed using ultraviolet-curable resin, then the abrasion resistance is improved, but the hardness is insufficient to achieve 4H or more
Solution Approach 1:
The patent uses a composite material consisting of ultraviolet-curable resin combined with silica fine particles (containing reactive groups) to form the hard coat layer. This composite structure allows the resin to provide abrasion resistance while the silica particles contribute to hardness, achieving both 4H hardness and excellent abrasion resistance simultaneously
Solution Approach 2:
The patent changes the chemical parameters of the hard coat layer by incorporating silica fine particles with reactive groups that can form chemical bonds with the ultraviolet-curable resin. This parameter change in composition and bonding structure enables the hard coat layer to achieve both high hardness (4H or more) and high abrasion resistance
2Strength
If spherical silica fine particles are used in the hard coat layer, then the hardness is improved, but the abrasion resistance remains insufficient
Solution Approach 1:
The patent uses irregularly shaped silica fine particles instead of spherical particles. The irregular shape creates local quality variations in the hard coat layer, with protruding portions providing enhanced mechanical interlocking and abrasion resistance while maintaining hardness
Solution Approach 2:
The combination of irregularly shaped silica fine particles with ultraviolet-curable resin creates a composite material where the irregular particle morphology contributes to both hardness and abrasion resistance through mechanical interlocking and increased surface area for bonding
3Strength
If a large amount of light is irradiated during light curing to impart high hardness, then the hardness is improved, but the substrate suffers heat damage causing wrinkles
Solution Approach 1:
The silica fine particles act as a hardening agent that works efficiently with reduced light exposure. They enable the system to achieve high hardness with lower energy input, effectively replacing the need for high-intensity prolonged UV irradiation that causes substrate heat damage
Solution Approach 2:
The addition of silica fine particles changes the curing characteristics of the hard coat layer, allowing it to achieve high hardness at lower light irradiation levels. This parameter change in the curing process reduces the polymerization heat generated, preventing substrate heat damage and wrinkle formation
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 optical layered body exhibits enhanced hardness and abrasion resistance, suitable for image display devices like LCDs and PDPs, while maintaining transparency and preventing substrate damage during polymerization.
Implementation Method 1
containing reactive irregularly shaped silica fine particles bonded by an inorganic chemical bond
Implementation Method 2
it has been difficult to impart sufficient hardness to the hard coat layer... when a substrate such as a triacetylcellulose film that is susceptible to heat damage is used as a substrate for forming a hard coat layer, it unfortunately results in the formation of visually apparent wrinkles due to heat damage on the substrate caused by polymerization heat during polymerization of the materials for forming the hard coat layer
Data Source
AI summary
The present invention provides an optical layered body having excellent hardness, abrasion resistance, and flexibility.The present invention provides an optical layered body having a hard coat layer on one side of a triacetylcellulose substrate, wherein a Martens hardness (N1) of a surface of the hard coat layer, a Martens hardness (N2) of the center of the cross-section of the hard coat layer, and a Martens hardness (N3) of the center of the cross-section of the triacetylcellulose substrate have a relationship of N2>N1>N3 as determined by nanoindentation, and the hard coat layer has a pencil hardness of 4H or more as measured by a test in accordance with a pencil hardness test defined in JIS K5600-5-4 (1999) at a load of 4.9 N.