Easily-Adhesive Polyester Film for Optical Laminates
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Solution Overview
Problem
PET films with a small in-plane phase difference suffer from irregular orientation in the thickness direction, leading to decreased pencil hardness and vulnerability to scratching. Additionally, biaxially stretched PET films with high pencil hardness exhibit poor adhesion to easily-adhesive layers, causing detachment issues in optical laminates.
Innovation Solution
An easily-adhesive layer-including polyester film with a pencil hardness of B or higher and an average δq/δa value of 1.60 or less on its surface. This film features a specific surface measurement using an atomic force microscope to ensure optimal adhesion of the optical laminate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the stretching ratio of PET film is decreased to reduce in-plane phase difference, then rainbow unevenness is suppressed, but pencil hardness decreases and scratch resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the stretching ratio and heat treatment conditions to achieve an optimal balance. Specifically, it sets the stretching ratio within a narrow range (MD direction: 1.05-1.30, TD direction: 1.05-1.30) and controls the in-plane phase difference to 0.015≤Δn×d<0.030, while maintaining pencil hardness through controlled crystallinity and surface morphology parameters.
Solution Approach 2:
The patent creates a composite structure by combining PET film with specific functional layers (easily-adhesive layer and functional layer) in a laminated configuration. This composite approach allows the PET film to provide mechanical strength and scratch resistance while the functional layers provide adhesion and optical functions, resolving the contradiction between hardness and adhesion.
2Strength
If biaxially stretched PET film is used to increase pencil hardness, then scratch resistance improves, but adhesion to easily-adhesive layer deteriorates causing detachment
Solution Approach 1:
The patent applies local quality by creating different surface characteristics in different regions of the PET film. The surface is designed to have specific roughness and chemical composition in the easily-adhesive layer interface to enhance adhesion, while maintaining high pencil hardness in the bulk material. The functional layers are also designed with specific local properties to facilitate bonding.
Solution Approach 2:
The patent introduces an easily-adhesive layer as an intermediary between the PET film and the functional layer. This intermediate layer has specific properties (controlled thickness, composition, and surface characteristics) that mediate the adhesion between the hard PET film and the functional layer, preventing detachment while maintaining scratch resistance.
3Object-affected harmful factors
If uniaxial stretching is used to increase in-plane phase difference to counter rainbow unevenness, then rainbow unevenness is suppressed, but the film tends to tear in the stretching direction
Solution Approach 1:
The patent inverts the conventional approach by using biaxial stretching instead of uniaxial stretching. Instead of stretching in one direction to increase in-plane phase difference, it stretches in two directions (MD and TD) with controlled ratios, which distributes the stress more evenly and prevents tearing while still achieving sufficient phase difference to suppress rainbow unevenness.
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 proposed solution achieves favorable adhesion of the optical laminate, suppressing defects due to poor adhesion and enhancing the scratch resistance of the optical laminate with a functional layer.
Implementation Method 1
a 10 μm×10 μm area of the surface of the easily-adhesive layer is measured using an atomic force microscope in a phase mode; a distribution of phase signal on the surface of the easily-adhesive layer is obtained from the measurement
Data Source
AI summary
Provided is an easily-adhesive layer-including polyester film such that an optical laminate including, in sequence, a polyester film with a high pencil hardness, an easily-adhesive layer, and a functional layer can achieve favorable adhesion. This easily-adhesive layer-including polyester film comprises an easily-adhesive layer on a polyester film, wherein the polyester film has a pencil hardness of B or higher, and an average value of δq/δa on a surface of the easily-adhesive layer is 1.60 or less, wherein δa is the arithmetic mean value of phase signals on a surface of the easily-adhesive layer and δq is the root-mean-square of the phase signals on the surface of the easily-adhesive layer.