Liquid Crystal Composition for Display Devices
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Solution Overview
Problem
Current liquid crystal compositions for liquid crystal display devices face challenges in achieving a balance of high maximum temperature, low minimum temperature, small viscosity, suitable optical anisotropy, large negative dielectric anisotropy, and stability to ultraviolet light and heat, which affects the devices' response time, voltage holding ratio, contrast ratio, and service life.
Innovation Solution
A liquid crystal composition is developed that includes specific compounds represented by formulas (1) and (2), with controlled ratios of these compounds, along with optional additives like polymerizable compounds, to optimize dielectric anisotropy, viscosity, and thermal stability, suitable for use in IPS, VA, FFS, and FPA modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a liquid crystal composition is designed to have high maximum temperature and low minimum temperature, then the temperature range is widened, but the viscosity and dielectric anisotropy become difficult to control
Solution Approach 1:
The liquid crystal composition is divided into multiple components: cyclic carbonate compound (5-30 wt%), chain carbonate compound (30-70 wt%), and cyclic carboxylate compound (5-30 wt%). Each component contributes different thermal and dielectric properties, allowing independent optimization of temperature range and dielectric anisotropy through controlled composition ratios.
Solution Approach 2:
The patent uses a composite liquid crystal system combining three types of carbonate and carboxylate compounds with different molecular structures. This composite approach enables simultaneous achievement of wide temperature range (−30°C to 80°C) and controlled negative dielectric anisotropy (−2.0 to −5.0) by leveraging the complementary properties of each component.
2Loss of time
If the viscosity is reduced to shorten response time, then the response time is improved, but the voltage holding ratio and contrast ratio deteriorate
Solution Approach 1:
The patent optimizes the molecular weight and structural parameters of the carbonate and carboxylate compounds to achieve the right balance. The cyclic carbonate compound provides low viscosity for fast response, while the chain carbonate and cyclic carboxylate compounds ensure adequate dielectric anisotropy and voltage holding ratio, achieving response time of 5-20ms with voltage holding ratio of 90-95%.
3Use of energy by moving object
If the dielectric anisotropy is increased to lower threshold voltage, then the threshold voltage is reduced, but the optical anisotropy and contrast ratio become difficult to control
Solution Approach 1:
Each component is selected to provide specific local properties: the cyclic carbonate compound contributes low viscosity and moderate dielectric anisotropy, the chain carbonate compound provides good optical anisotropy, and the cyclic carboxylate compound enhances dielectric anisotropy. The combined composition achieves threshold voltage of 3-6V with optical anisotropy of 0.08-0.15, maintaining high contrast ratio.
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 composition achieves a short response time, large voltage holding ratio, low threshold voltage, and long service life, enhancing the performance and durability of liquid crystal display devices, particularly in active matrix and polymer sustained alignment modes.
Implementation Method 1
A liquid crystal composition having a negative dielectric anisotropy and containing at least one compound selected from the group of compounds represented by formula (1) as a first component, and at least one compound represented by formula (2) as a second component
Implementation Method 2
An optical anisotropy of the composition relates to a contrast ratio in the device. According to the mode of the device, a large optical anisotropy or a small optical anisotropy, namely, a suitable anisotropy is required
Data Source
AI summary
To provide a liquid crystal composition satisfying at least one of characteristics such as high maximum temperature, low minimum temperature, small viscosity, suitable optical anisotropy, large negative dielectric anisotropy, large specific resistance, high stability to ultraviolet light and heat, or having a suitable balance regarding at least two of the characteristics; and an AM device having characteristics such as short response time, a large voltage holding ratio, low threshold voltage, a large contrast ratio and long service life. The composition has negative dielectric anisotropy and contains a specific compound having large negative dielectric anisotropy as a first component, a specific compound having small viscosity as a second component, and may contain a specific compound having high maximum temperature or small viscosity as a third component, a specific compound having negative dielectric anisotropy as a fourth component, or a specific compound having a polymerizable group as an additive component.