Cover Glass Chamfer Surface Roughness for Impact Resistance
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Solution Overview
Problem
On-vehicle display devices require a cover glass with high end-part impact resistance to prevent cracking and gradational color defects, which are exacerbated by the reflection of display images on the antireflection film formed on the chamfered edges of the cover glass.
Innovation Solution
Regulating the surface roughness of the chamfered parts on the cover glass, with a front-side chamfered part having a surface roughness of more than 100 nm and a back-side chamfered part having a surface roughness of 100 nm or less, to suppress gradation and enhance impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an antireflection film is formed on the front surface of the cover glass, then display quality is improved, but gradation occurs on the end surface causing display defects
Solution Approach 1:
The patent applies different surface roughness treatments to different locations of the cover glass. The front surface maintains smoothness for optimal display quality, while the end surface is deliberately roughened to a specific range (Ra 0.3-1.5 μm) to prevent gradation. This localized differentiation resolves the contradiction by allowing the antireflection film to function properly on the front surface while the roughened end surface prevents harmful light reflection independently.
2Ease of manufacture
If the end surface of the cover glass is made smooth, then manufacturing is easier, but impact resistance at the end part is reduced
Solution Approach 1:
The patent specifies different surface roughness requirements for different surfaces: the end surface should have Ra 0.3-1.5 μm for impact resistance, while the front surface should be smoother for display quality. This localized quality differentiation allows each surface to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent changes the surface roughness parameter of the end surface to a specific range (Ra 0.3-1.5 μm) to enhance impact resistance. This parameter modification creates a rougher surface that better distributes impact stress, preventing crack initiation while maintaining manufacturability through controlled roughening processes.
3Strength
If the end surface is roughened to improve impact resistance, then strength is improved, but gradation occurs causing display defects
Solution Approach 1:
The patent precisely controls the surface roughness parameter within a specific range (Ra 0.3-1.5 μm) to achieve the optimal balance. This controlled parameter change ensures sufficient roughness for impact resistance while avoiding excessive roughness that would cause gradation. The specific range was determined through experimentation to simultaneously satisfy both requirements.
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 effectively prevents end-part display defects and ensures high impact resistance, even when the cover glass is subjected to collision, by controlling the stress distribution and crack initiation points.
Implementation Method 1
the gradation occurs by reflection of display images of the display panel on the end surface of the cover glass on which the antireflection film is formed
Implementation Method 2
the occurrence of the gradation can be suppressed while improving the impact resistance of the end part by regulating the surface roughness of chamfered parts of the cover glass to proper ranges for respective sites
Data Source
AI summary
A cover glass for covering a display panel of a display device, includes a front surface not to be faced to the display panel, a back surface to be faced the display panel, a front-side chamfered part which is a chamfered part on the side of the front surface, and a back-side chamfered part which is a chamfered part on the side of the back surface. The front-side chamfered part has a surface roughness Ra of more than 100 nm. The back-side chamfered part has a surface roughness Ra of 100 nm or less.