Transparent Resin Substrate Hard Coating Crack Resistance
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Solution Overview
Problem
The existing methods for forming a hard coating on a transparent thermoplastic resin substrate often result in uneven thickness, leading to striped patterns and increased susceptibility to cracking, especially when the substrate has complex shapes or when an antireflection film is applied, as the hard coating is harder than the underlying material and cannot flexibly comply with it during processes like insert forming or falling ball tests.
Innovation Solution
A transparent resin substrate with a hard coating composed of urethane acrylate, silica sol, and a metal chelate compound, combined with a low refractive index layer of hollow silica sol, which enhances adhesion and flexibility, preventing cracking during insert forming and falling ball tests, and allows for the formation of an antireflection film without compromising the substrate's integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coating is formed on a transparent thermoplastic resin sheet to provide scratch resistance, then the surface hardness is improved, but the hard coating cracks during insert forming due to its inability to comply with the flexible underlying sheet
Solution Approach 1:
The hard coating is formulated as a composite material containing inorganic particles (silica, alumina, or zirconia) dispersed in a polymer matrix. This composite structure combines the hardness provided by the inorganic particles with the flexibility of the polymer binder, allowing the coating to resist scratching while accommodating the deformation of the underlying thermoplastic resin sheet during insert forming without cracking.
2Ease of manufacture
If a hard coating is formed by dip coating followed by curing, then the coating process is simple, but the coating thickness becomes uneven on formed bodies with dents and protuberances, causing striped patterns
Solution Approach 1:
The invention changes the rheological parameters of the coating solution by carefully selecting the polymer binder type and adjusting the solvent composition and ratio. This optimization ensures the coating solution has appropriate viscosity and flow characteristics that allow it to uniformly coat complex three-dimensional surfaces with dents and protuberances during dip coating, preventing uneven thickness and striped patterns while maintaining process simplicity.
3Illumination intensity
If an antireflection film is formed on the hard coating to improve optical properties, then light reflection is reduced, but both the hard coating and antireflection film crack during forming due to their high hardness relative to the thermoplastic resin sheet
Solution Approach 1:
Both the hard coating and the antireflection film are formulated as composite materials containing inorganic particles in a polymer matrix. This composite structure provides the necessary optical properties (hardness for the hard coating, low refractive index for the antireflection film) while the polymer binder ensures flexibility and adhesion, allowing both layers to withstand the deformation stresses during insert forming and falling ball tests without cracking.
Solution Approach 2:
The invention optimizes the polymer binder parameters including glass transition temperature, molecular weight, and chemical composition to ensure that both the hard coating and antireflection film have appropriate flexibility and adhesion. This allows the multi-layer structure to accommodate the deformation of the underlying thermoplastic resin sheet during forming processes while maintaining the integrity and optical properties of each layer.
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 substrate effectively prevents cracking of the hard coating and antireflection film during insert forming and falling ball tests, maintaining the substrate's integrity and ensuring high productivity by sharing components that provide excellent adhesion and flexibility, thus addressing the issues of uneven thickness and hardness differences.
Implementation Method 1
a low refractive index layer which comprises a low refractive index hollow silica sol (a) having a grain size of 10 to 150 nm and a refractive index of not more than 1.44
Implementation Method 2
a hard coating formed on one surface of the underlying sheet, wherein the hard coating comprises: 100 parts by weight of a resin component (A) obtained by curing an urethane acrylate
Data Source
AI summary
The transparent resin substrate has a light-transmitting thermoplastic resin underlying sheet 1 and a hard coating formed on one surface of the underlying sheet, wherein the hard coating includes a resin component obtained by curing an urethane acrylate that contains a tri-functional or less functional urethane acrylate and a tetra-functional or more functional urethane acrylate; a silane coupling agent or a hydrolyzed product thereof, a silica sol having a grain size of 5 to 500 nm and a refractive index in a range of 1.44 to 1.5; and a metal chelate compound. A low refractive index layer is formed on the hard coating, the low refractive index layer includes a low refractive index hollow silica sol having a grain size of 10 to 150 nm and a refractive index of not more than 1.44, the silane coupling agent or the hydrolyzed product thereof, and a metal chelate compound.