JP2003106817A - Method for evaluating liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an evaluation method for calculating the cell gap in a reflection type liquid crystal display element. SOLUTION: A polarizer 1 is arranged between the liquid crystal element 2 and a light source 3. Light is applied from the light source 3 to the liquid crystal display element 2. A peak value in the spectral reflection characteristics in the liquid crystal display element 2 is measured by an optical detector. The peak value in the minimum value out of the measured peak values is obtained. The distance between both the substrates in the liquid crystal display element 2 is calculated from the peak value in the extreme value, thus evaluating the liquid crystal display element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a liquid crystal display device, and more particularly to a method for evaluating a cell gap of a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been developed for large capacity, high speed response and mass production. The cell gap of a liquid crystal display element shows the optical phase difference distance by taking the product of the birefringence of liquid crystal, and is widely used as an index showing the characteristics of the liquid crystal display element.

In a homogeneously aligned liquid crystal display device, the long axis direction of liquid crystal molecules is 45 between orthogonal polarizers in the polarization direction.
When arranged so that the birefringence of the liquid crystal is Δn,
When the incident light intensity is I0 and the incident light wavelength is λ, the emitted light intensity I is represented by the correlation of (Equation 3). (For example, Shoichi Matsumoto and Ichino Tsunoda: Basics and Applications of Liquid Crystals, page 46.
Industrial Research Institute Co., Ltd.).

[0004]

[Equation 3]

However, in the STN type field effect birefringence mode using a liquid crystal having a positive or negative dielectric anisotropy, the optical rotation effect due to the twist in the direction perpendicular to the substrate is added, and The relationship of Expression 3 does not hold. Therefore, Japanese Patent Laid-Open No. 09-113865 has been disclosed as a method for evaluating a liquid crystal display device by transmission spectral evaluation. This is a method for evaluating an STN type liquid crystal display device which teaches a liquid crystal having a dielectric anisotropy between a pair of substrates. The STN type liquid crystal display device has an incident side of the liquid crystal display device between the liquid crystal display device and a light source. At a 45 ° angle to the alignment axis with respect to the substrate
Is disposed between the liquid crystal display element and the photodetector, and the alignment axis direction is 45 ° with respect to the substrate on the emission side of the liquid crystal display element.
The second polarizer is arranged at an angle of 1 to measure the peak value on the spectral transmission characteristic, and from the peak value of the minimum value among the peak values obtained by the measurement, the peak value between the both substrates of the liquid crystal display device is measured. The distance is calculated and the liquid crystal display device is evaluated. However, this is applied to the reflective liquid crystal display element in the method described in the publication because incident light that enters is passed through the liquid crystal layer twice in the measurement of the reflective liquid crystal display element having the reflective layer. I couldn't.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for evaluating a reflection type liquid crystal display device capable of performing optical measurement simply and with good reproducibility. To do.

[0006]

A method for evaluating a liquid crystal display device according to the present invention comprises: an incident side substrate on which visible light is incident from a light source; and a reflection side substrate having a reflection layer for reflecting the visible light. , STN sandwiching liquid crystal having dielectric anisotropy
In the method for evaluating a liquid crystal display element, a polarizing plate is arranged between the liquid crystal display element and the light source so that the absorption axis angle forms an angle of 45 ° with the alignment axis direction of the incident side substrate, The liquid crystal display element is irradiated with light from a light source, the light reflected by the reflection side substrate of the liquid crystal display element is detected by a photodetector, and the peak value on the spectral reflection characteristic of the liquid crystal display element is measured. The distance between the substrates of the liquid crystal display element is calculated from the minimum peak value among the peak values obtained by the measurement, and the liquid crystal display element is evaluated.

Thus, the cell gap of the reflection type liquid crystal display element can be evaluated optically easily and with good reproducibility.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The embodiment shown here is merely an example, and the present invention is not necessarily limited to this embodiment.

(Embodiment 1) A method for evaluating a liquid crystal display element according to Embodiment 1 of the present invention will be described below with reference to FIGS. 1, 2 and 3. FIG. 1 is a configuration diagram of an evaluation method for a liquid crystal display element according to the first embodiment.

In FIG. 1, reference numeral 1 is a polarizer, and for example, NPF-G1225DU (manufactured by Nitto Denko Corporation) is used. 1a is the absorption axis angle of the polarizer. Reference numeral 2 denotes a liquid crystal display element, which is a liquid crystal having a positive or negative dielectric anisotropy between an incident side substrate 21 on which visible light is incident from the light source 3 and a reflective side substrate having a reflective layer for reflecting the visible light. , ZLI-2293 (manufactured by Merck Japan Co., Ltd.), for example. 2a is the incident side substrate 21
2b shows the orientation axis angle of the reflection side substrate 23. The absorption axis angle 1a of the polarizer 1 and the orientation axis direction of the incident side substrate 21 form an angle of 45 °. Three
Is a light source and emits visible light. Reference numeral 4 denotes a photodetector, which detects the intensity of the light from the light source 3, which is transmitted through the liquid crystal display element 2 and reflected by the reflection layer of the reflection plate substrate 22.

Next, a method of evaluating the liquid crystal display element will be described. Visible light is made incident from the light source 3, and the photodetector 4 measures the spectral characteristics that pass through the evaluation system shown in FIG. As a result of the measurement, the photodetector 4 showed the optical spectral characteristic as shown in FIG. In this example, the twist angle ω = 250 °,
A sample 3D having a liquid crystal birefringence Δn = 0.171 and an actual cell gap d ₀ = 4.9930 μm was used. The actual cell gap here is a value measured by the evaluation method disclosed in Japanese Patent Laid-Open No. 09-113865. In FIG. 2, some peak values showing valleys in the visible light region are shown, but the peak value with the strongest visibility, that is, the second valley peak value is used here. Also, the abscissa of the extremum is λ _rb ,
In this example, a value of "492 nm" is shown.

First, the values of λ _rb and ω are substituted into the following (Equation 1), and further, the value of λ _tb obtained in the calculation of (Equation 1), the value of Δn, and the result of (Equation 1) By substituting and into (Equation 2), a value of d = 4.9936 μm can be obtained. This is the cell gap required for evaluation. This cell gap d is the actual cell gap d ₀ = 4.9.
Since the value is close to 930 μm, it can be seen that the cell gap can be evaluated by this evaluation method.

[0013]

[Equation 4]

[Equation 5] Here, in (Equation 1) and (Equation 2), Re (Retardati
on) is the optical distance, λ ₁ and λ ₂ are constants for correcting the optical activity due to the twist of the measurement sample, λ _tb is the peak minimum value in the transmission measurement, λ _rb is the peak minimum value in the reflection measurement, Δn
_1, Δn ₂ is a value obtained by correcting the wavelength dispersion from the birefringence Δn, and A ₁ and A ₂ are constants for calculating the optical distance from the birefringence parameter.

A similar evaluation is shown in FIG.
As shown here, the value d according to the evaluation method of the liquid crystal display element of the present invention shows a value that is very close to the actual cell gap d ₀ and is very useful. In addition, the parameters are also consistent, and as shown in FIG. 3, consistent evaluations have been obtained in various samples, which can be said to be useful in this respect as well.

In the present embodiment, Δn is 0.
138-0.171, TWIST is 240 ° -250
The range of ° and Δnd ₀ was evaluated from 0.8538 to 1.0432, but it goes without saying that the present invention can be applied to any optical measurement having a birefringence.

In the liquid crystal display element evaluation method according to the first embodiment, between the incident-side substrate 21 on which visible light is incident from the light source 3 and the reflective-side substrate 23 having a reflective layer for reflecting the visible light. When evaluating a liquid crystal display element 2 formed by sandwiching a liquid crystal having dielectric anisotropy, the absorption axis angle 1a
The polarizer 1 is arranged between the liquid crystal display element 2 and the light source 3 so that an angle of 45 ° is formed with the alignment axis direction 2a of the incident side substrate 21, and the peak value on the spectral reflection characteristic of the liquid crystal display element is Since the distance between the two substrates of the liquid crystal display element 2 was calculated from the peak value of the minimum value of the measured peak values measured by the photodetector 4, the liquid crystal display element was evaluated. The cell gap can be measured by dividing the optical distance of the element into the birefringence, the optical rotation effect due to twisting, and the deviation effect due to reflection spectroscopy. The cell gap of a reflective liquid crystal display device can be evaluated.

[0017]

As described above, according to the method for evaluating a liquid crystal display element of the present invention, an incident side substrate on which visible light is incident from a light source, and a reflective side substrate having a reflective layer for reflecting the visible light are provided. S which is formed by sandwiching a liquid crystal having dielectric anisotropy between
In the method for evaluating a TN type liquid crystal display device, a polarizing plate is arranged between the liquid crystal display device and the light source so that the absorption axis angle forms an angle of 45 ° with the alignment axis direction of the incident side substrate, The liquid crystal display element is irradiated with light from the light source, the light reflected by the reflection side substrate of the liquid crystal display element is detected by a photodetector, and the peak value on the spectral reflection characteristic of the liquid crystal display element is measured. Then, from the peak value of the minimum value among the peak values obtained by the above measurement, the distance between the two substrates of the liquid crystal display element was calculated, and the liquid crystal display element was evaluated. The cell gap of the reflective liquid crystal display device can be evaluated optically with good performance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a method for evaluating a liquid crystal display element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing optical spectral characteristics according to the evaluation method of the present invention.

FIG. 3 is a diagram showing evaluation values according to the evaluation method of the present invention.

[Explanation of symbols]

1 Polarizer 1a Absorption axis angle of polarizer 2 Liquid crystal display element 2a Orientation axis angle of incident side substrate 2b Reflection side substrate orientation axis angle 3 light sources 4 Photodetector 21 incident side substrate 22 Reflection side substrate

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F065 AA21 BB22 CC21 GG23 GG24                       LL33 LL67 QQ25 QQ29 UU07                 2G086 EE10                 2H088 FA11 FA20 HA21                 2H089 QA14 RA10 SA01 TA17                 2H091 FA14Z FD11 GA08 KA04                       LA12 LA18

Claims (2)

[Claims] 1. An STN in which a liquid crystal having dielectric anisotropy is sandwiched between an incident side substrate on which visible light is incident from a light source and a reflective side substrate having a reflective layer for reflecting the visible light.
In the method for evaluating a liquid crystal display element, the absorption axis angle is 45 ° with the alignment axis direction of the incident side substrate.
A polarizing plate is arranged between the liquid crystal display element and the light source so that the light source irradiates the liquid crystal display element with light, and the light is reflected by the reflection side substrate of the liquid crystal display element. The light is detected by a photodetector, the peak value on the spectral reflection characteristic of the liquid crystal display element is measured, and the minimum value of the peak values obtained by the above measurement is used to determine the minimum value of the peak values, and the both substrates of the liquid crystal display element A method for evaluating a liquid crystal display device, comprising: calculating a distance between the liquid crystal display devices and evaluating the liquid crystal display device. 2. The liquid crystal display element evaluation method according to claim 1, wherein the obtained peak value of the minimum value is substituted into the following equation (1), and the result is substituted into the equation (2). Then, the substrate-to-substrate distance of the liquid crystal display device is obtained, and a method for evaluating a liquid crystal display device is provided. [Equation 1] [Equation 2]