Self-aligning Liquid-Crystalline Medium for VA Displays
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Solution Overview
Problem
Current liquid-crystalline mixtures for electro-optical displays, particularly those using the ECB effect, face challenges in achieving high performance with regards to response times, reliability, and stability, especially in terms of image sticking and the need for polyimide layers, which increase costs and reduce electric resistance.
Innovation Solution
A liquid-crystalline medium is developed that includes self-aligning additives, specifically compounds of a certain formula, which enable homeotropic orientation without a polyimide layer, improving light and temperature stability, and allowing for multidomain switching with reactive mesogens to enhance switching times and contrast ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide layers are used for homeotropic orientation, then alignment is achieved, but costs increase and electric resistance decreases
Solution Approach 1:
The patent extracts and eliminates the polyimide alignment layer from the display structure by incorporating self-aligning additives directly into the liquid-crystalline composition. These additives (compounds of formula I with specific molecular structures containing rigid core groups and flexible alkyl chains) autonomously induce homeotropic orientation at the liquid crystal-substrate interface, replacing the function previously performed by the polyimide layer and thereby reducing both structural complexity and electrical resistance.
Solution Approach 2:
The liquid-crystalline composition performs self-alignment through the inherent properties of the added compounds of formula I. These compounds spontaneously organize at the interface and induce vertical orientation of the liquid crystal molecules without requiring external polyimide layers or complex alignment processes, enabling the system to self-organize and achieve homeotropic alignment autonomously.
2Productivity
If conventional liquid-crystalline mixtures are used, then basic display function is achieved, but response times are slow and image sticking occurs
Solution Approach 1:
The patent modifies the physical and chemical parameters of the liquid-crystalline mixture by incorporating compounds of formula I with specific molecular characteristics. These compounds alter the rotational viscosity and elastic constants of the mixture, enabling faster response times and reduced image sticking. The specific parameter changes include optimizing the balance between K33 (bend elastic constant) and γ1 (rotational viscosity) to achieve video-compatible response times while maintaining stability.
Solution Approach 2:
The invention creates a composite liquid-crystalline system by combining conventional liquid crystal compounds with specially designed self-aligning additives of formula I. This composite composition integrates the functional properties of both components: the base liquid crystal provides the electro-optical effect, while the additive compounds provide improved response characteristics and stability, achieving synergistic performance that neither component could achieve alone.
3Reliability
If high K3/K1 ratio is achieved for ECB effect, then vertical alignment is improved, but manufacturing complexity increases
Solution Approach 1:
The patent achieves the required high K3/K1 ratio parameter through the molecular design of compounds of formula I. The specific molecular structure (containing rigid aromatic cores with particular substitution patterns and flexible alkyl chains of controlled length) inherently provides the necessary elastic constant ratios for effective ECB operation and vertical alignment, while the formulation process remains relatively simple by using well-established liquid crystal host mixtures.
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 medium achieves improved rotational viscosity, elastic constants, and low-temperature stability, along with reduced image sticking, enabling high-performance displays with short response times and extended operational reliability without the need for polyimide layers.
Implementation Method 1
Self-aligning additives for vertical alignment of liquid crystalline mixtures have been disclosed in prior publications... The compounds in these publications don't have any polymerizable groups attached as the present compounds of formula I
Implementation Method 2
The principle of electrically controlled birefringence, the ECB effect or also DAP (deformation of aligned phases) effect, was described for the first time in 1971... Media of this type can be used, in particular, for electro-optical displays having active-matrix addressing based on the ECB effect
Implementation Method 3
J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) showed that liquid-crystalline phases must have high values for the ratio of the elastic constants K 3 /K 1 , high values for the optical anisotropy Δn
Implementation Method 4
J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) showed that liquid-crystalline phases must have high values for the ratio of the elastic constants K 3 /K 1 , high values for the optical anisotropy Δn and values for the dielectric anisotropy of Δε ≤ -0.5
Data Source
AI summary
The invention relates to the compounds of the formula I and to a liquid-crystalline medium based on a mixture of polar compounds which contains at least one compound of the formula I (I) in which in which R1, R2, ring A1, Z1, Z2, Sp, P, L1, L2, r1, r2, r3, m, n, p1 and p2 have the meanings indicated in Claim 1 and to the use of the LC mixtures in electro-optical displays, especially for the self-aligning VA, PSA, PS-VA, PVA, MVA, PM-VA, HT-VA or VA-IPS mode.