Miscible Cellulose-Polysiloxane Blends for LCD Optical Films
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Solution Overview
Problem
Current cellulose ether films used in polarizing plates for LCDs face challenges with high moisture permeability, excessive out-of-plane retardation, and poor adhesion to hydrophilic PVA-based polarizers, which affect their performance and stability under varying environmental conditions.
Innovation Solution
A highly miscible blend of cellulose derivatives and polysiloxanes is developed, allowing for the creation of optical films with reduced and adjustable out-of-plane retardation, improved moisture barrier properties, and hydrophilic surface properties without compromising mechanical properties, using a composition that includes specific polysiloxane structures and a manufacturing process involving solution casting and optional stretching and plasma treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cellulose ether films are used as optical films in polarizing plates, then they provide good transparency and mechanical properties, but they exhibit high moisture permeability which is not acceptable for LCD applications
Solution Approach 1:
The patent applies composite materials by blending cellulose ether with TAC (triacetyl cellulose) to create a composite film structure. This combination leverages the transparency and mechanical properties of cellulose ether while incorporating the low moisture permeability characteristics of TAC, achieving a material that satisfies both optical performance and moisture barrier requirements for LCD applications
Solution Approach 2:
The patent utilizes parameter changes by controlling the degree of substitution (DS) of the cellulose ether and the thickness ratio of TAC layers to optimize film properties. By adjusting these parameters, the film achieves appropriate transparency, mechanical strength, and moisture barrier performance without requiring additional protective layers
2Length of moving object
If the thickness of optical films is reduced to enable thinner polarizing plates, then the overall device becomes more compact, but the mechanical strength and barrier properties of the films deteriorate
Solution Approach 1:
The patent employs composite materials with a multilayer structure consisting of cellulose ether layers and TAC layers. This composite design allows each layer to contribute its strengths: cellulose ether provides transparency and basic mechanical support, while TAC layers enhance moisture barrier properties and surface hardness, enabling thin films to maintain adequate mechanical strength and barrier function
Solution Approach 2:
The patent applies local quality by assigning different functional characteristics to different layers of the optical film. The TAC layers are positioned to provide specific local functions such as moisture barrier protection and surface hardness, while the cellulose ether layers maintain transparency and flexibility, allowing the thin film to achieve uniform performance across its structure
3Reliability
If conventional plasticizers are added to reduce moisture permeability of cellulose acylate films, then moisture barrier properties improve, but the plasticizers tend to bleed out which degrades optical and mechanical film properties on the long term
Solution Approach 1:
The patent replaces conventional small-molecule plasticizers with TAC polymer material that provides moisture barrier function without bleeding. Although TAC requires a thicker layer to achieve the same moisture barrier performance as plasticizers, it offers long-term compositional stability and maintains optical properties by eliminating the bleeding issue inherent in small-molecule additives
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 resulting films exhibit low haze, high transparency, and reduced moisture permeability, meeting the requirements for polarizing plates, with the polysiloxane additive enabling effective reduction of out-of-plane retardation and enhancement of hydrophilic surface properties, thus improving the films' suitability for LCD applications.
Implementation Method 1
If such optical film has significant birefringence, it may alter the polarization state of a light wave traveling through it, thus being referred to as a retardation film
Implementation Method 2
cellulose acylate and in particular triacetyl cellulose (TAC) films are most frequently used as protection or retardation films since they provide comparatively low water vapor permeation rates
Data Source
AI summary
Compositions comprise a highly miscible polymer blend of at least one cellulose derivative and at least one polysiloxane additive of formula [R1R2R3SiO0.5]a[R4R5SiO]b[R6SiO1.5]c[SiO2]d, wherein the substituents R1, R2, R3, R4, R5 and R6 each independently represents a hydrocarbon group or a functional group selected from a hydroxyl group, an acyloxy group or an alkoxy group, and may be the same or different from each other with respect to each individual silicon atom, and 0≦a≦0.4, 0.01≦b≦0.99, 0.01≦c≦0.99, 0≦d≦0.3, under the proviso that at least one hydrocarbon group and at least one functional group are present and a+b+c+d=1. Articles such as optical films comprising such a composition exhibit improved moisture barrier properties, reduced and adjustable out of plane retardation, adjustable glass transition temperature and provide for a facile generation of hydrophilic surface properties without considerable difference of the mechanical properties compared to corresponding articles of the pure cellulose derivative. A method to prepare such optical films, which can be particularly useful as retardation or protection films for polarizing plates in liquid crystal display devices, is also provided.