Vertical Alignment Film Polymerization for LCD Drop Mark Suppression
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Solution Overview
Problem
Liquid crystal display devices face issues with drop marks and ghosting during production, which affect their performance and properties such as dielectric anisotropy, viscosity, and response speed, particularly in large-screen applications.
Innovation Solution
A liquid crystal display device is developed using a specific liquid crystal composition combined with a technique where a polymerizable compound with a polyimide skeleton and crosslinkable functional group is polymerized in a vertical alignment film by applying an active energy ray while applying a voltage between electrodes, controlling the pretilt angles of liquid crystal molecules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reactive monomer is added to a liquid crystal composition to create a PSA liquid crystal display device, then uniform pretilt angles and improved transmittance are achieved, but display failure such as ghosting occurs and high voltage holding capacity is compromised
Solution Approach 1:
The patent separates the reactive monomer from the liquid crystal composition and places it only in the alignment film layer. This segmentation allows the alignment film to provide uniform pretilt angles through polymerization while preventing the reactive monomer from causing ghosting and voltage holding issues in the liquid crystal composition.
Solution Approach 2:
The patent extracts the reactive monomer component from the liquid crystal composition and relocates it to the alignment film. This extraction eliminates the harmful effects of reactive monomers in the liquid crystal composition (ghosting, voltage holding capacity loss) while preserving the beneficial effects of polymerization for pretilt angle control.
2Adaptability or versatility
If projecting structures are formed on a substrate to divide a pixel in MVA liquid crystal display devices, then viewing angle characteristics are improved, but response speed deteriorates due to liquid crystal molecules remote from the projecting structure
Solution Approach 1:
The patent replaces the mechanical projecting structure system with a chemical field system. Instead of using physical protrusions to control liquid crystal alignment, the patent uses a polymer alignment film with chemical anisotropy to provide uniform pretilt angles across the entire pixel, eliminating the response speed issues caused by distant molecules while maintaining viewing angle characteristics.
3Manufacturing precision
If the alignment film material is designed to have a side chain reactive to ultraviolet light for polymerization, then pretilt angles can be controlled, but drop marks occur during the dropping process of liquid crystal composition
Solution Approach 1:
The patent applies a voltage between electrodes before and during the dropping process to preliminarily align the liquid crystal molecules. This preliminary action prevents the formation of drop marks by ensuring uniform distribution of liquid crystal material, while the polymerizable alignment film subsequently provides stable pretilt angle control after the liquid crystal is in place.
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 effectively suppresses drop marks and ghosting, maintaining high response speed and the necessary properties for liquid crystal display devices, making them suitable for large-screen applications like liquid crystal TVs and monitors.
Implementation Method 1
a polymerizable compound with a polyimide skeleton and crosslinkable functional group is polymerized in a vertical alignment film by applying an active energy ray while applying a voltage between electrodes
Data Source
AI summary
Provided are a liquid crystal display device that suppresses occurrence of drop marks during production without degrading various properties, such as dielectric anisotropy, viscosity, nematic phase upper limit temperature, rotational viscosity (γ1), and ghosting property, and a method for producing the liquid crystal display device.A liquid crystal display device 10 of the present invention includes a liquid crystal composition layer 13 sandwiched between a first substrate 11 and a second substrate 12 and vertical alignment films 16 and 17 that contain a polymer of a polymerizable compound having a polyimide skeleton as a main chain and a crosslinkable functional group as a side chain. The liquid crystal composition constituting the liquid crystal composition layer 13 contains compounds represented by general formulae (I) and (II).