Substrate Surface Treatment for Vertical Liquid Crystal Alignment
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Solution Overview
Problem
Conventional VA mode liquid crystal displays require costly polyimide alignment films for vertical alignment of liquid crystal molecules, and existing self-alignment additives face challenges in adhering to substrates effectively, resulting in insufficient anchoring force for vertical alignment.
Innovation Solution
A substrate with an insulating film having a water contact angle of 70° or less and surface free energy of 50 mN/m or more, in direct contact with a liquid crystal composition containing a polar group alignment aid, which induces spontaneous alignment of liquid crystal molecules without the need for alignment films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide alignment films are used to achieve vertical alignment of liquid crystal molecules, then alignment performance is improved, but manufacturing cost increases
Solution Approach 1:
The patent extracts and eliminates the polyimide alignment film layer from the conventional liquid crystal display structure. Instead of using a separate alignment film, the invention incorporates alignment functionality directly into the substrate through surface treatment, thereby removing the costly polyimide film while maintaining vertical alignment performance
Solution Approach 2:
The invention merges the alignment function with the substrate itself by applying surface treatments (such as plasma treatment or self-assembled monolayers) to the substrate surface. This combines the substrate's structural role with the alignment function previously performed by a separate polyimide film, eliminating the need for the additional layer
2Ease of manufacture
If self-alignment additives are used to eliminate alignment films, then manufacturing cost decreases, but anchoring force for vertical alignment becomes insufficient
Solution Approach 1:
The invention employs composite surface treatments on the substrate, combining organic self-assembled monolayers with inorganic plasma treatment layers. This composite approach creates a surface with both chemical functionality (for additive interaction) and physical properties (for strong anchoring), thereby achieving sufficient anchoring force without polyimide films
Solution Approach 2:
The invention modifies surface energy parameters and chemical composition of the substrate surface through controlled treatment processes. By adjusting surface free energy, contact angle, and chemical functional groups, the substrate surface is optimized to provide strong anchoring force for vertical alignment while working synergistically with self-alignment additives
3Reliability
If self-alignment additives with polar groups are used, then vertical alignment is achieved without alignment films, but adhesion to substrate surface becomes insufficient
Solution Approach 1:
The invention introduces surface-treated substrate layers as intermediaries between the self-alignment additives and the bulk substrate. The surface treatment (such as plasma-treated layers or self-assembled monolayers with polar groups) acts as a mediator that enhances adhesion by providing chemical bonding sites while maintaining the polar interactions necessary for vertical alignment
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 substrate enables effective vertical alignment of liquid crystal molecules, allowing for the creation of a liquid crystal display device with improved alignment and reduced costs by eliminating the need for polyimide alignment films.
Implementation Method 1
the surface free energy of the contact surface is 50 mN/m or more
Implementation Method 2
the static contact angle of water on the contact surface at 25° C. is 70° or less
Implementation Method 3
an alignment aid having a polar group and having the function of causing the liquid crystal molecules to be aligned spontaneously
Data Source
AI summary
Provided are a substrate that can exert an anchoring force causing liquid crystal molecules to be vertically aligned and a liquid crystal display device. The substrate of the present invention is to be used in contact with a liquid crystal composition containing liquid crystal molecules and an alignment aid having a polar group and having the function of causing the liquid crystal molecules to be aligned spontaneously. The substrate includes an insulating film having a contact surface to be in contact with the liquid crystal composition. The static contact angle of water on the contact surface at 25° C. is 70° or less and/or the surface free energy of the contact surface is 50 mN/m or more. The substrate is preferably a substrate in direct contact with the liquid crystal composition with no alignment film therebetween.