Optical Polyester Film Brightness and Static Control

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Solution Overview

Problem

Optical films used in display devices face issues with mechanical strength, surface hardness, and polarization unevenness, which affect brightness and transmittance, particularly in large-sized liquid crystal displays and thin displays where thickness is a concern.

Innovation Solution

A uniaxially or biaxially stretched polyester film with specific tensile strengths, moduli, and in-plane retardation values, along with a prism sheet and polarizing reflective sheet configurations, to enhance mechanical strength and brightness while minimizing polarization unevenness and thickness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If a brightness enhancement film is used to enhance brightness and contrast, then luminous efficiency is improved, but surface resistance increases causing static electricity generation and foreign substance attachment

Engineering Contradiction:

ImprovebrightnessVSAvoidstatic electricity generation

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

An intermediate layer comprising a copolymer of terephthalic acid and 1,4-cyclohexanedimethanol units is introduced between the polyester film and the brightness enhancement film. This intermediate layer acts as a mediator that reduces static electricity generation at the interface, preventing foreign substance attachment while maintaining the brightness enhancement function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If a hard coating layer is laminated on the film surface to improve mechanical properties, then surface hardness and scratch resistance are improved, but film thickness increases which is problematic for thin displays

Engineering Contradiction:

Improvesurface hardnessVSAvoidfilm thickness

Core Design Contradiction:

StrengthVSLength of stationary object

Solution Approach 1:

The invention merges the protective function with the base polyester film by creating a crosslinked structure within the film itself through the copolymer units. This eliminates the need for a separate hard coating layer, as the film acquires enhanced scratch resistance and surface hardness intrinsically while maintaining thin profile.

Inventive Principle:

Principle #5Merging (Combining)

3Loss of energy

If a protective layer with low refractive index is applied to improve transmittance, then light transmission is improved, but brightness improvement is limited due to refractive index mismatch with prism pattern layer

Engineering Contradiction:

Improvelight transmittanceVSAvoidbrightness

Core Design Contradiction:

Loss of energyVSIllumination intensity

Solution Approach 1:

The invention changes the refractive index parameter of the protective layer by using a copolymer with specific chemical composition (terephthalic acid and 1,4-cyclohexanedimethanol units). This copolymer provides a refractive index that is optimized to reduce the mismatch with the prism pattern layer, thereby simultaneously improving both light transmittance and brightness extraction.

Inventive Principle:

Principle #35Parameter changes

4Stability of the object's composition

If the film is stretched to achieve optical isotropy, then optical uniformity is improved, but mechanical strength anisotropy increases with different tensile strengths in longitudinal and transverse directions

Engineering Contradiction:

Improveoptical isotropyVSAvoidmechanical strength anisotropy

Core Design Contradiction:

Stability of the object's compositionVSStrength

Solution Approach 1:

The invention uses a composite polymer structure comprising polyester units and copolymer units of terephthalic acid and 1,4-cyclohexanedimethanol. This composite material structure allows the film to achieve optical isotropy through controlled stretching while the copolymer components provide mechanical reinforcement that reduces strength anisotropy, creating a more balanced mechanical profile.

Inventive Principle:

Principle #40Composite materials

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 improves mechanical strength and brightness of optical films, reduces polarization unevenness, and simplifies manufacturing by maintaining a single-layer structure, making them suitable for small and thin display devices.

Implementation Method 1

a uniaxially or biaxially stretched polyester film

Methodology Applied

Scientific EffectMechanical stretching: Deformation

Implementation Method 2

an in-plane retardation of 3,000 nm to 30,000 nm

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS11668863B2Optical polyester film, and prism sheet or polarized reflection sheet comprising same

Publication Date: 2023.06.06 MICROWORKS CO LTD

AI summary

An embodiment relates to an optical polyester film. The optical polyester film according to one embodiment can minimize the difference between the orientation angle at the center and the orientation angle at the end of the film while producing a difference between the tensile strengths in the lengthwise/widthwise directions of the film, thereby increasing mechanical strength and brightness and suppressing the occurrence of polarization Mura defects. Further, the optical polyester film employs a single layer film, and thus is more easily processed and has a slimmer thickness. Therefore, the optical polyester film can be usefully applied to small-sized thin film display devices and, specifically, can be favorably used as a substrate material of a prism sheet or a polarized reflection sheet.