Light Diffusion Sheet Coating for High Transmittance Backlights
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Solution Overview
Problem
Conventional light diffusion sheets for liquid crystal display devices face challenges in achieving a balance between directional light diffusion, light transmissivity, and coating efficiency, often resulting in increased bead content leading to decreased transmittance and coating difficulties.
Innovation Solution
A light diffusion sheet utilizing monodisperse beads with a mean particle size of 1.5 μm to 5 μm, a weight ratio of beads to binder between 2.5 and 3, and a small amount of overlaid light diffusion layer (3-10 g/m²), combined with a gravure coating method and optional inorganic filler and antistatic agent, to enhance directional light diffusion and transmissivity while maintaining economic efficiency and thin film character.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the amount of incorporating beads and amount of the overlaid light diffusion layer are increased to improve light diffusibility, then light diffusion function is improved, but coating difficulty increases and light transmittance decreases
Solution Approach 1:
The patent changes the particle size parameter of beads from conventional large sizes (around 20 μm) to small sizes (1.5-5 μm), and adjusts the weight ratio parameter to 2.5-3 times. This parameter transformation enables achieving good light diffusion with smaller bead quantities, thereby improving coating facility while maintaining light diffusibility.
Solution Approach 2:
The patent uses a composite structure combining small monodisperse beads with specific resin binders. This composite material approach allows the light diffusion layer to achieve effective light diffusion with reduced material quantity, solving both the coating difficulty and transmittance issues associated with conventional high-bead-content formulations.
2Illumination intensity
If the amount of incorporating beads and amount of the overlaid light diffusion layer are increased to improve light diffusibility, then light diffusion function is improved, but light transmittance decreases
Solution Approach 1:
By transforming the bead size parameter to 1.5-5 μm and adjusting the weight ratio to 2.5-3 times, the patent achieves effective light diffusion with reduced bead content. This parameter optimization reduces light absorption and scattering losses, thereby improving light transmittance while maintaining diffusion performance.
3Ease of manufacture
If polydisperse beads with great mean particle size are used to maintain coating facility, then coating is easier, but directional light diffusion function is reduced
Solution Approach 1:
The patent transforms the particle size parameter to a specific small range (1.5-5 μm) and uses monodisperse beads with narrow size distribution. This parameter transformation enables the beads to provide strong directional light diffusion through uniform scattering patterns, while the small size maintains good coating facility.
Solution Approach 2:
The patent applies local quality by using monodisperse beads with uniform size distribution throughout the light diffusion layer. This uniformity creates consistent local scattering properties, enhancing directional light diffusion function compared to polydisperse beads that create variable scattering patterns.
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 provides improved directional light diffusion, light transmissivity, and economic efficiency, reducing thickness and cost while preventing defects and electrostatic issues, thereby enhancing the performance and reliability of backlight units in liquid crystal display devices.
Implementation Method 1
a light diffusion layer overlaid on the front face side of this substrate layer, wherein this light diffusion layer has resin beads and a resin binder; monodisperse beads having a mean particle size of 1.5 μm or greater and 5 μm or less are used as the beads
Data Source
AI summary
A light diffusion sheet usable, for example, in backlight units, includes a transparent substrate layer, and a light diffusion layer overlaid on a front face of the substrate layer. The light diffusion layer includes resin beads and a resin binder, the resin beads being provided as monodisperse beads having a mean particle size of 1.5 μm or greater and 5 μm or less. A weight ratio of the monodisperse beads to the binder is 2.5 or greater and 3 or less, and an amount of the overlaid light diffusion layer is 3 g/m2 or greater and 10 g/m2 or less. An acrylic resin may be used as the substrate polymer of the monodisperse beads and binder. A coefficient of variation of particle size distribution of the monodisperse beads is preferably equal to or less than 0.2. Advantageously, a gravure coating method is employed for forming the light diffusion layer.