Biaxially Stretched Polyester Light Diffusion Film for LCD Backlight
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Solution Overview
Problem
Existing light diffusion films for liquid crystal displays face challenges in achieving high heat resistance, mechanical strength, and thickness accuracy while maintaining excellent light transmittance and diffusibility, particularly in large direct-type back light units, where curling issues arise due to differences in linear expansion coefficients of resin layers.
Innovation Solution
A biaxially stretched laminate film with a crystalline polyester supporting layer and a light diffusion layer containing 60-98% crystalline polyester and 2-40% incompatible light diffusion additive, co-extruded to achieve a planar orientation degree of 0.080-0.160, total light transmittance of 85% or more, and haze of 30% or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light diffusion film is used in a direct-type back light unit, then high luminance is achieved, but luminance variation occurs between positions over light sources and positions not over light sources
Solution Approach 1:
The patent applies local quality by using light diffusion films with different thicknesses in different regions. Specifically, the film thickness is increased in regions directly over light sources compared to regions between light sources, creating localized optical properties that compensate for the concentrated light emission and achieve uniform overall luminance distribution.
2Adaptability or versatility
If multiple resin layers with different linear expansion coefficients are laminated, then light diffusion functionality is achieved, but curling occurs due to differential thermal expansion
Solution Approach 1:
The patent applies homogeneity by using the same resin material (polycarbonate) for both the supporting layer and the light diffusion layer. This ensures identical thermal expansion coefficients and compatible physical properties between layers, eliminating curling issues while maintaining light diffusion functionality through controlled internal void structures.
Solution Approach 2:
The patent uses composite materials by combining polycarbonate resin with inorganic fine particles (such as titanium oxide, silicon oxide, or zirconium oxide) in the light diffusion layer. This composite structure provides both the mechanical properties of the polymer and the light scattering properties of the inorganic particles, achieving effective light diffusion without layer delamination or curling.
3Ease of manufacture
If inorganic fine particles are mixed into the resin, then light diffusibility is improved, but heat resistance and mechanical strength may be compromised
Solution Approach 1:
The patent applies local quality by concentrating inorganic fine particles specifically in the light diffusion layer while keeping the supporting layer as pure polycarbonate resin. This localized particle distribution provides light diffusion functionality where needed while preserving the high heat resistance and mechanical strength of the polycarbonate in the supporting structure.
Solution Approach 2:
The patent uses composite materials by combining polycarbonate resin with inorganic fine particles (such as titanium oxide, silicon oxide, or zirconium oxide) in the light diffusion layer. This composite structure provides both the mechanical properties of the polymer and the light scattering properties of the inorganic particles, achieving effective light diffusion without layer delamination or curling.
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 a light diffusion film with enhanced heat resistance, mechanical strength, and thickness accuracy, while ensuring uniform luminance and reducing curling, thus addressing the limitations of previous films in large direct-type back light units.
Implementation Method 1
a light diffusion film having excellent heat resistance, mechanical strength and thickness accuracy intrinsic to a biaxially stretched film, and having excellent light transmittance and light diffusibility
Implementation Method 2
a light diffusion film consisting of a biaxially stretched laminate film having a supporting layer (A) consisting of a crystalline polyester, and a light diffusion layer (B) laminated on at least one side of the supporting layer
Implementation Method 3
co-extruded to achieve a planar orientation degree of 0.080-0.160
Data Source
AI summary
A light diffusion film which has excellent light transmittance and light diffusibility while maintaining excellent heat resistance, mechanical strength and thickness accuracy intrinsic to a biaxially stretched film, and is suppressed in generation of curling after heat treatment, wherein the film comprises a biaxially stretched laminated film having a supporting layer consisting of a crystalline polyester, and a light diffusion layer laminated on at least one side of the supporting layer by a co-extrusion method, wherein the light diffusion layer comprises 60 to 98 parts by mass of the crystalline polyester and 2 to 40 parts by mass of a light diffusion additive incompatible with the polyester, and the light diffusion film has a planar orientation degree (ΔP) of 0.080 to 0.160, a total light transmittance of 85% or more, and a haze of 30% or more.