JPH11304434A - Measuring method for liquid crystal layer thickness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the liquid crystal layer thickness of a liquid crystal cell. SOLUTION: A pair of light deflecting plates are arranged in both side of a liquid crystal cell in the predetermined condition and the spectral distribution of the transmitted light is measured in the condition of no voltage applied between electrodes of the liquid crystal cell, and chromaticity of the transmitted light is displayed on a CIE chromaticity graph, and the liquid crystal layer thickness is obtained on the basis of the angle θ of inclination against the x-axis of a straight line L passing through an achromatic color point WP on the chromaticity graph and a point CP for expressing the chromaticity of the transmitted light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal layer thickness measuring method.

[0002]

2. Description of the Related Art Conventionally, the measurement of the thickness of the liquid crystal layer of a liquid crystal cell in which a liquid crystal layer in which liquid crystal molecules are aligned in a predetermined alignment state is provided between a pair of substrates having electrodes formed on opposing surfaces, respectively. This is performed by one of the following methods (1) and (2).

(1) Light is incident on a liquid crystal cell from one surface thereof, and the interference light intensity of light reflected at two interfaces between the inner surfaces of the pair of substrates and the liquid crystal layer is measured to reduce the thickness of the liquid crystal layer. How to calculate.

(2) A pair of polarizers are arranged under a predetermined condition with a liquid crystal cell interposed therebetween, and the transmitted light is measured without applying a voltage between the electrodes of the liquid crystal cell. A method of detecting the wavelength and calculating the liquid crystal layer thickness from that wavelength using Gooch and Tarry's theoretical formula.

[0005]

However, each of the above methods (1) and (2) has a problem that it is difficult to accurately measure the thickness of the liquid crystal layer. That is, in the method (1), the light reflected at the interface between the liquid crystal layer and the front substrate of the pair of substrates of the liquid crystal cell when viewed from the incident direction of the light, and the inner surface of the rear substrate and the liquid crystal layer. The liquid crystal layer thickness is calculated based on interference caused by a difference in optical path length with light reflected at the interface with the liquid crystal layer. This difference in optical path length depends on the refractive index and length of the liquid crystal layer, but it is difficult to accurately determine the refractive index of the liquid crystal layer enclosed between the substrates, and in particular, the light transmitted through the twisted liquid crystal layer. It is extremely difficult to determine the optical path length of Further, actually, light is reflected not only at the interface between the alignment film surface on the inner surface of the substrate and the liquid crystal layer, but also at the interface between the electrode formed on the substrate surface and the substrate, or between the electrode and the alignment film. It is difficult to accurately measure the thickness of the liquid crystal layer.

In the method (2), the thickness of the liquid crystal layer can be measured with high accuracy in theory. However, in practice, the gap material portion (in which the liquid crystal exists) sandwiched between the substrates of the liquid crystal cell in a dispersed state. This is important for detecting wavelengths where the transmittance is minimal due to the influence of noise light transmitted through portions having a different refractive index from the original refractive index of the liquid crystal layer, such as portions where the alignment of liquid crystal molecules is disturbed. Since an error occurs, it is difficult to accurately measure the thickness of the liquid crystal layer. SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal layer thickness measuring method capable of measuring a liquid crystal layer thickness of a liquid crystal cell with high accuracy.

[0007]

According to the present invention, a spectral distribution of transmitted light in a state where a polarizing plate is arranged on at least one surface of a liquid crystal cell under predetermined conditions and no voltage is applied between electrodes of the liquid crystal cell. And the point representing the chromaticity of the transmitted light is referred to as CI
The liquid crystal of the liquid crystal cell is obtained from the inclination angle of a straight line passing through an achromatic point on the chromaticity diagram and a point representing the chromaticity of the transmitted light on the chromaticity diagram with respect to either the x or y axis. It is characterized in that a layer thickness is obtained.

That is, the present invention obtains the liquid crystal layer thickness of the liquid crystal cell based on the liquid crystal layer thickness dependence of the spectral distribution of light transmitted through the liquid crystal cell and a polarizing plate arranged under predetermined conditions. Since the spectral distribution of the transmitted light of the liquid crystal cell corresponds to the thickness of the liquid crystal layer, the thickness of the liquid crystal layer can be obtained from the spectral distribution of the transmitted light.

Since the light transmitted through the liquid crystal cell includes noise light transmitted through the gap material portion and the portion where the alignment of the liquid crystal molecules is disturbed, the actual spectral distribution of the transmitted light includes noise light.

However, even if the transmitted light actually measured contains noise light, the shape of the spectral distribution curve of the transmitted light, that is, the ratio of the transmittance for each wavelength light in the visible light band hardly changes. Since the spectral distribution curve only translates upward on the spectral distribution diagram, the change in chromaticity due to the influence of noise light on the CIE chromaticity diagram is caused by the achromatic point when the liquid crystal layer thickness is the same. And a substantially linear change along a straight line passing through the point representing the theoretical chromaticity of the transmitted light.

That is, if the thickness of the liquid crystal layer of the liquid crystal cell is the same, the inclination angle of the straight line passing through the achromatic point and the point representing the chromaticity of the transmitted light with respect to either the x or y axis becomes the noise light. It is almost constant with or without influence.

Therefore, in the present invention, the liquid crystal layer thickness is determined from the inclination angle of a straight line passing through the achromatic point on the CIE chromaticity diagram and a point representing the chromaticity of transmitted light. The relationship between the tilt angle and the liquid crystal layer thickness can be obtained in advance, and the tilt angle of the straight line is almost constant regardless of the influence of noise light. The chromaticity of the transmitted light is represented on the CIE chromaticity diagram, and the inclination angle of a straight line passing through the achromatic point on the chromaticity diagram and the point representing the chromaticity of the transmitted light is determined. Measurement can be performed with high accuracy with almost no error due to the influence of noise light.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION
As described above, a polarizing plate is arranged on at least one surface of the liquid crystal cell under a predetermined condition, and a spectral distribution of transmitted light in a state where no voltage is applied between the electrodes of the liquid crystal cell is measured. A point representing the chromaticity is obtained on the CIE chromaticity diagram, and a straight line passing through the achromatic point on the chromaticity diagram and the point representing the chromaticity of the transmitted light is calculated from the inclination angle with respect to either the x or y axis. The thickness of the liquid crystal layer is measured with high accuracy by determining the thickness of the liquid crystal layer.

The present invention can be applied to the measurement of the thickness of a liquid crystal layer of a liquid crystal cell for displaying black and white and the thickness of a liquid crystal cell for displaying a color image provided with a plurality of color filters. When measuring the thickness of the liquid crystal layer of a liquid crystal cell having a color filter, the measured spectral distribution of transmitted light is determined based on the spectral distribution of light transmitted through only the color filters of the plurality of colors, which has been measured in advance. In this case, the spectral distribution of only the liquid crystal cell may be corrected by using the CIE chromaticity diagram, and the chromaticity corresponding to the corrected spectral distribution may be displayed on the CIE chromaticity diagram.

In the present invention, the measurement of the spectral distribution of the transmitted light is performed by arranging the polarizing plate under the condition that the light transmittance is minimized when no voltage is applied between the electrodes of the liquid crystal cell. It is preferable that the spectral distribution depends on the thickness of the liquid crystal layer. The smaller the transmittance of light, the larger it looks. Therefore, if the polarizing plate is arranged under such conditions and the spectral distribution of the transmitted light is measured, the transmitted light can be measured. Is more accurately represented on the chromaticity diagram, and the thickness of the liquid crystal layer can be measured more accurately.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. First, a liquid crystal cell whose thickness is to be measured will be described. FIGS. 6 and 7 are cross-sectional views of the liquid crystal cell.

The liquid crystal cell 1 shown in FIG. 6 performs a black-and-white display. Transparent electrodes 13 and 14 are formed on opposing surfaces, and alignment films 15 and 16 are formed on the electrode forming surfaces. The pair of transparent substrates 11 and 12 are joined via a frame-shaped sealing material 16, and liquid crystal molecules are aligned in a predetermined alignment state in a region surrounded by the sealing material 16 between the substrates 11 and 12. A liquid crystal layer 18 is provided.

Although not shown in the drawing, the gap between the pair of substrates 11 and 12 is regulated by a plurality of gap members made of glass particles and the like sandwiched between the substrates 11 and 12 in a dispersed state. .

The liquid crystal cell 1 is of an active matrix type. One of its substrates, for example, an electrode 13 formed on the inner surface of a rear substrate 11 is composed of a plurality of pixel electrodes arranged in a matrix and the other substrate. For example, the electrode 14 formed on the inner surface of the front substrate 12 is a single-film counter electrode that forms a pixel region by a portion facing the plurality of pixel electrodes 13.

Although not shown in FIG.
The pixel electrodes 1 are formed on the inner surface of the substrate 11 on which the pixel electrodes 3 are formed.
3 are provided, and a plurality of active elements are connected to each other, and signal supply lines for supplying signals to these active elements are provided. The active element is, for example, a TFT (thin film transistor), in which case,
A gate signal supply line for supplying a gate signal to the TFT and a data signal supply line for supplying a data signal to the TFT are provided on the inner surface of the substrate 11.

This liquid crystal cell is used for a TN (twisted nematic) type liquid crystal display element, and has a liquid crystal layer 18 provided between a pair of substrates 11 and 12.
The orientation direction of the liquid crystal molecules in the vicinity of the respective substrates 11 and 12 is regulated by the alignment films 15 and 16, and the liquid crystal molecules are twist-aligned between the substrates 11 and 12 at a twist angle of approximately 90 °.

The liquid crystal cell 2 shown in FIG. 7 displays a multicolor image such as a full-color image. In this liquid crystal cell 2, any one of the substrates, for example, the front substrate 1
2, color filters of a plurality of colors having different transmission wavelength bands, for example, color filters 17R, 17G, and 17B of three colors of red, green, and blue are provided in correspondence with the respective pixel regions. A transparent electrode 14 is provided.

The liquid crystal cell 2 is provided with color filters 17R, 17G and 17B, but the other structure is the same as that of the liquid crystal cell 1 shown in FIG. The same reference numerals are given and omitted.

Next, the method of measuring the thickness of the liquid crystal layer will be described by taking the measurement of the thickness of the liquid crystal layer of the liquid crystal cell 1 shown in FIG. 6 as an example.
Is measured.

First, as shown in FIG. 6, a pair of polarizing plates 21 and 22 are opposed to both surfaces of the liquid crystal cell 1, respectively.
Are arranged under predetermined conditions, and the electrodes 13 and 1 of the liquid crystal cell 1 are arranged.
In the state where no voltage is applied between the four, white light is made incident from one surface as shown by an arrow in the figure, and is transmitted through one polarizing plate 21, the liquid crystal cell 1 and the other polarizing plate 22, and The spectral distribution of the transmitted light emitted to the surface is measured by a measuring device (not shown).

In the measurement of the spectral distribution of the transmitted light, the pair of polarizing plates 21 and 22 are measured under the condition that the light transmittance is minimized when no voltage is applied between the electrodes 13 and 14 of the liquid crystal cell 1, that is, Are arranged under the condition of displaying normally black.

That is, when the twist angle of the liquid crystal molecules of the liquid crystal layer 18 of the liquid crystal cell 1 is approximately 90 ° as described above, the pair of polarizing plates 21 and 22 are connected to the respective optical axes (for example, transmission axes). Are almost parallel to each other,
The alignment direction of the liquid crystal molecules in the vicinity of each of the substrates 11 and 12 of the liquid crystal cell 1 and the optical axes of the polarizing plates 21 and 22 adjacent to the substrates 11 and 12 are arranged so as to be substantially parallel or substantially orthogonal to each other. And measuring the spectral distribution of the transmitted light.

Next, based on the measured spectral distribution of the transmitted light,
The chromaticity coordinates (x, y values) are calculated, and the chromaticity of the transmitted light is represented on the CIE chromaticity diagram. In FIG. 1, CP is a point representing the chromaticity of the transmitted light (hereinafter referred to as a chromaticity point), and WP is an achromatic point (x = 0.317, y = 0.341).
Point).

In this embodiment, as described above, the measurement of the spectral distribution of the transmitted light is performed by using a pair of polarizing plates 21 and 22.
Are arranged under the condition that the light transmittance is minimized in a state where no voltage is applied between the electrodes 13 and 14 of the liquid crystal cell 1. The dependency of the spectral distribution of the transmitted light on the thickness of the liquid crystal layer is determined by Since the smaller the ratio, the clearer the observation, the chromaticity of the transmitted light can be represented more accurately on the chromaticity diagram.

Next, the inclination angle θ of the straight line L passing through the achromatic color point WP on the chromaticity diagram and the chromaticity point CP of the transmitted light with respect to the x-axis was measured, and the inclination angle θ shown in FIG. The liquid crystal layer thickness d of the liquid crystal cell 1 is obtained based on the relationship between the liquid crystal layer thickness d.

That is, in this liquid crystal layer thickness measuring method, a liquid crystal cell 1 and a pair of polarizing plates 21 and 22 arranged under predetermined conditions are used.
The liquid crystal layer thickness d of the liquid crystal cell 1 is obtained based on the dependence of the spectral distribution of light transmitted through the liquid crystal layer thickness on the liquid crystal layer 1. The liquid crystal layer thickness d can be obtained from the spectral distribution of the transmitted light without considering the transmitted noise light.

The principle of the above measuring method will be described below. The dependence of the spectral distribution of the transmitted light of the liquid crystal cell on the thickness of the liquid crystal layer is
If the refractive index anisotropy Δn of the liquid crystal, the alignment state of the liquid crystal molecules, the wavelength of transmitted light, and the cell gap are known, Gooch and
It can be calculated by Tarry's theoretical formula.

That is, the twist angle of the liquid crystal molecules is 90 °
90 ° twisted TN liquid crystal display device (TN-LC
The transmitted light intensity T in the normally black state of D) is
It is expressed by the following equation (1) based on Goochand Tarry's theoretical equation.

[0034]

(Equation 1)

According to the above equation (1), the liquid crystal layer thickness d is 4.5 μm.
m, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm
m, 5.0 μm, 5.1 μm, and 5.2 μm, the spectral distribution of transmitted light in the normally black state of the TN-LCD is calculated by calculating the transmittance of each wavelength in the visible light band. You can ask.

When the Y value (brightness of transmitted light) for the liquid crystal layer thickness d and the chromaticity coordinates (x and y coordinate values) on the CIE chromaticity diagram are calculated from the obtained spectral distribution at each liquid crystal layer thickness, The result is shown in the following [Table 1].

[0037]

[Table 1]

Based on the Y values shown in Table 1 and the x and y coordinates indicating the chromaticity coordinates on the CIE chromaticity diagram, the chromaticity points corresponding to the respective liquid crystal layer thicknesses are described in the CIE chromaticity diagram. Expressed above, it is as shown in FIG. As shown in FIG. 3, a point CP ₀ representing the chromaticity of the transmitted light is represented by a liquid crystal layer thickness d.
Depends on Therefore, from the spectral distribution of the transmitted light, that is, the chromaticity point of the transmitted light on the CIE chromaticity diagram, the liquid crystal layer thickness d
Can be requested.

Since the actually measured transmitted light includes the noise light, the actual spectral distribution of the transmitted light is different from the spectral distribution of the transmitted light calculated as described above.
That is, FIG. 4 shows the TN having a liquid crystal layer thickness d of 4.6 μm.
-The liquid crystal layer thickness d is the same as the spectral distribution (calculated value) of transmitted light obtained by the above equation (1) for the LCD (d = 4.6 μm).
For the plurality of TN-LCDs with different amounts of noise in m), the polarizer shows the spectral distribution (measured value) of the transmitted light actually measured in the case of the above-described normally black arrangement.

The noise light is emitted from a portion having a refractive index different from the original refractive index of the liquid crystal layer, such as a gap material portion (a portion where no liquid crystal exists) of the liquid crystal cell 1 or a portion where the alignment of liquid crystal molecules is disturbed. Is the light leakage.

As shown in FIG. 4, the actual spectral distribution of the transmitted light is different from the spectral distribution of the transmitted light obtained by calculation without considering the noise light. Although the light transmittance increases, the shape of the spectral distribution curve (the ratio of the transmittance of all wavelength light in the visible light band) is almost the same as the spectral distribution of the transmitted light on the spectral distribution curve obtained by the above calculation. In other words, the spectral distribution curve shows a characteristic shifted in the direction of higher transmittance.

Based on the spectral distribution of the transmitted light including the noise light shown in FIG. 4, when there is no noise light (Y value = 7.
34) and x and y coordinates on the respective CIE chromaticity diagrams when the transmitted light intensity Y value differs depending on the noise light intensity are shown in [Table 2].

[0043]

[Table 2]

FIG. 5 shows the chromaticity points CP on the CIE chromaticity diagram based on the chromaticity coordinates in Table 2. As can be seen from FIG. 5, when the liquid crystal layer thickness d is the same, the change in the Y value due to the influence of noise light is caused by the achromatic point WP
And the calculated chromaticity point CP ₀ (when there is no noise light)
This is a substantially linear change along a straight line passing through.

That is, if the liquid crystal layer thickness d of the liquid crystal cell 1 is the same, the inclination angle θ of the straight line passing through the achromatic point WP on the CIE chromaticity diagram and the point representing the chromaticity of the transmitted light with respect to the x-axis. Is
It is almost constant regardless of the influence of noise light.

Then, as shown in FIG.
Since the liquid crystal layer has different chromaticity points CP ₀ corresponding to each liquid crystal layer thickness on the E chromaticity diagram, the chromaticity points CP on the CIE chromaticity diagram of the transmitted light including the noise light at each liquid crystal layer thickness. Is on a straight line connecting the chromaticity point CP ₀ corresponding to the liquid crystal layer thickness and the achromatic color point WP.

Accordingly, the inclination angle of the straight line L connecting the chromaticity point CP ₀ and the achromatic point WP, which are shown on the CIE chromaticity diagram, with the transmitted light of the TN-LCD in which the polarizing plate is arranged in normally black, with respect to the x-axis. θ corresponds to the thickness of the liquid crystal layer.

The relationship between the inclination angle θ of the straight line L with respect to the x-axis and the liquid crystal layer thickness d is represented by the chromaticity coordinates of the chromaticity point CP ₀ corresponding to each liquid crystal layer thickness d shown in Table 1; It can be obtained from the chromaticity coordinates of the achromatic color point WP. In this way,
FIG. 2 shows the relationship between the obtained inclination angle θ of the straight line L with respect to the x-axis and the liquid crystal layer thickness d.

As described above, the inclination angle θ of the straight line L
Is almost constant irrespective of the presence or absence of the noise light, the spectral distribution of the transmitted light of the TN-LCD is measured, and the chromaticity point of the transmitted light is represented on the CIE chromaticity diagram. Achromatic point WP and a point CP representing the chromaticity of the transmitted light
And the liquid crystal layer thickness d is determined based on FIG. 2 showing the relationship between the tilt angle θ and the liquid crystal layer thickness d, thereby causing almost all errors due to the influence of noise light. It can be measured with high accuracy without any problems.

In the above embodiment, the measurement of the spectral distribution of the transmitted light is performed under the condition that the light transmittance of the pair of polarizing plates 21 and 22 is minimized in a state where no voltage is applied between the electrodes of the liquid crystal cell. Since the dependence of the spectral distribution of the transmitted light on the thickness of the liquid crystal layer can be clearly measured when the light transmittance is smaller, the polarizing plates 21 and 22 are disposed under such conditions to disperse the transmitted light. By measuring the spectral distribution, the chromaticity of the transmitted light can be more accurately represented on a chromaticity diagram, and the thickness of the liquid crystal layer can be measured more accurately.

As described above, when the polarizers 21 and 22 are arranged under the condition that the light transmittance is minimized in the state where no voltage is applied between the electrodes of the liquid crystal cell, and the spectral distribution of the transmitted light is measured, The measurement error of the thickness d is in a range of ± 0.01 μm, and the liquid crystal layer thickness d can be measured with high accuracy.

The liquid crystal layer thickness measuring method can be applied to the measurement of the liquid crystal layer thickness d of the liquid crystal cell 2 provided with the color filters 17R, 17G, 17B shown in FIG. As shown in FIG. 7, the liquid crystal cell 2 is sandwiched between a pair of polarizing plates 21 and 22 to measure the spectral distribution of the transmitted light, and from the measured spectral distribution, the color filters of the plurality of colors that have been measured in advance. 17R, 17G, 17B
A spectral distribution without a color filter is obtained by subtracting a spectral distribution component of light transmitted through only the chromaticity corresponding to the spectral distribution on a CIE chromaticity diagram. The tilt angle θ of the straight line passing through the point representing the chromaticity of the transmitted light with respect to the x-axis is calculated, and the liquid crystal of the liquid crystal cell 1 is determined based on the relationship between the tilt angle θ and the liquid crystal layer thickness d shown in FIG. What is necessary is just to obtain the layer thickness d.

In the above embodiment, the liquid crystal layer thickness d is determined from the inclination angle θ of the straight line L passing through the achromatic point WP and the point CP representing the chromaticity of transmitted light on the CIE chromaticity diagram with respect to the x-axis. However, the liquid crystal layer thickness d may be determined from the inclination angle of the straight line L with respect to the y-axis.

Further, in the above embodiment, the measurement of the spectral distribution of the transmitted light was performed under the condition that the light transmittance of the polarizing plate was minimized when no voltage was applied between the electrodes 13 and 14 of the liquid crystal cell 1 (No. The display was measured under the condition that the light transmittance was maximized in a state where the light transmittance of the polarizing plate was maximized when no voltage was applied between the electrodes of the liquid crystal cell. (Conditions for displaying normally white).

The present invention is not limited to a liquid crystal cell in which liquid crystal molecules are twist-aligned, but can be applied to a liquid crystal layer thickness measurement in a so-called parallel alignment liquid crystal cell in which liquid crystal molecules are aligned substantially in parallel. Also, a pair of polarizing plates are arranged under predetermined conditions with the liquid crystal cell interposed therebetween, and the spectral distribution of transmitted light in a state where no voltage is applied between the electrodes of the liquid crystal cell is measured, and the chromaticity of the transmitted light is measured. The liquid crystal of the liquid crystal cell is determined from the inclination angle of a straight line passing through an achromatic point on the chromaticity diagram and a point representing the chromaticity of the transmitted light on the CIE chromaticity diagram with respect to either the x or y axis. What is necessary is just to obtain the layer thickness.

In the measurement of the thickness of the liquid crystal layer of the parallel alignment liquid crystal cell, the measurement of the spectral distribution of transmitted light was performed under the condition that the light transmittance of the polarizing plate was minimized in a state where no voltage was applied between the electrodes of the liquid crystal cell. In this case, the light transmission intensity T ₀ of the parallel alignment liquid crystal cell is expressed by the following equation (2), where Δn is the refractive index anisotropy of the liquid crystal and d is the thickness of the liquid crystal layer.

[0057]

(Equation 2)

Therefore, similarly to the first embodiment described above, the transmittance of each wavelength in the visible light band is calculated for each of a plurality of different liquid crystal layer thicknesses d using the above equation (2), and the spectral distribution of the transmitted light is calculated. Is calculated, and chromaticity coordinates (x and y coordinate values) on the CIE chromaticity diagram with respect to the liquid crystal layer thickness d are calculated from the spectral distribution to obtain a chromaticity point, and the chromaticity point and the achromatic color point are calculated. The inclination angle of the connecting line with respect to the x-axis is obtained. And
The liquid crystal layer thickness can be determined based on the relationship between each of the liquid crystal layer thicknesses and the tilt angle, which has been previously calculated from the chromaticity coordinates for each liquid crystal layer thickness and the chromaticity coordinates of the achromatic color point. .

Further, in the above embodiment, a pair of polarizing plates 21 and 22 are arranged with the liquid crystal cell 1 interposed therebetween, and the light is transmitted through one polarizing plate 21, the liquid crystal cell 1 and the other polarizing plate 22 and emitted. Although the spectral distribution of the transmitted light is measured, a polarizing plate is arranged on one surface of the liquid crystal cell under predetermined conditions, and a reflecting plate is arranged on the other surface of the liquid crystal cell. Is measured, the spectral distribution of transmitted light that is transmitted through the liquid crystal cell and the polarizing plate, is reflected by the reflection plate, and is transmitted and emitted, and the chromaticity of the transmitted light is represented on a CIE chromaticity diagram. The liquid crystal layer thickness of the liquid crystal cell may be obtained from the inclination angle of a straight line passing through the achromatic point on the chromaticity diagram and the point representing the chromaticity of the transmitted light with respect to either the x or y axis.

[0060]

According to the method for measuring the thickness of a liquid crystal layer of the present invention, a polarizing plate is disposed on at least one surface of a liquid crystal cell under a predetermined condition, and transmitted light in a state where no voltage is applied between electrodes of the liquid crystal cell. The spectral distribution is measured, the chromaticity of the transmitted light is represented on a CIE chromaticity diagram, and x and y of a straight line passing through an achromatic point on the chromaticity diagram and a point representing the chromaticity of the transmitted light. Since the thickness of the liquid crystal layer is determined from the inclination angle with respect to any of the axes, the thickness of the liquid crystal layer can be measured with high accuracy.

The present invention can be applied to the measurement of the thickness of a liquid crystal layer of a liquid crystal cell for displaying black and white and the thickness of a liquid crystal cell for displaying a color image having a plurality of color filters. Even in the case of a liquid crystal cell having a color filter, the spectral distribution of light transmitted through only the color filters of the plurality of colors, which has been measured in advance, is subtracted from the measured spectral distribution of transmitted light. By obtaining the distribution and expressing the chromaticity corresponding to the spectral distribution on the CIE chromaticity diagram, the above-described measurement of the liquid crystal layer thickness can be performed.

In the present invention, the measurement of the spectral distribution of the transmitted light is performed by arranging the polarizing plate under the condition that the light transmittance is minimized between the electrodes of the liquid crystal cell when no voltage is applied. It is preferable that the spectral distribution depends on the thickness of the liquid crystal layer. The smaller the transmittance of light, the larger it looks. Therefore, if the polarizing plate is arranged under such conditions and the spectral distribution of the transmitted light is measured, the transmitted light can be measured. Is more accurately represented on the chromaticity diagram, and the thickness of the liquid crystal layer can be measured more accurately.

[Brief description of the drawings]

FIG. 1 is a CIE chromaticity diagram showing an example of the inclination angle of a straight line passing through an achromatic color point and a point representing the chromaticity of transmitted light.

FIG. 2 is a diagram showing the relationship between the inclination angle of the straight line and the thickness of a liquid crystal layer.

FIG. 3 is a CIE chromaticity diagram showing a relationship between a liquid crystal layer thickness and a chromaticity point of transmitted light, calculated from a spectral distribution of transmitted light obtained for liquid crystal display elements having different liquid crystal layer thicknesses.

FIG. 4 shows the spectral distribution of transmitted light in the absence of noise light obtained for a liquid crystal display element having a liquid crystal layer thickness of 4.6 μm, and the noise light intensity differs for the same liquid crystal layer thickness d (d = 4.6 μm). FIG. 9 is a diagram showing spectral distributions of transmitted light actually measured for a plurality of liquid crystal display elements.

FIG. 5 is the same as the chromaticity point of transmitted light obtained for a liquid crystal display element having a liquid crystal layer thickness of 4.6 μm and the liquid crystal layer thickness d (d = 4.
FIG. 6 is a CIE chromaticity diagram showing chromaticity points of transmitted light actually measured for a plurality of liquid crystal display elements having different amounts of noise at 6 μm).

FIG. 6 is a cross-sectional view of a liquid crystal cell that performs black and white display.

FIG. 7 is a cross-sectional view of a liquid crystal cell which performs color display.

[Explanation of symbols]

WP: achromatic point CP: point representing chromaticity of transmitted light L: straight line passing through the achromatic point and a point representing chromaticity of transmitted light θ: inclination angle of the straight line with respect to x-axis

[Procedure amendment]

[Submission date] July 9, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

[0034]

(Equation 1)

Claims (3)

[Claims] 1. A method for measuring the thickness of a liquid crystal layer of a liquid crystal cell comprising a liquid crystal layer in which liquid crystal molecules are aligned in a predetermined alignment state between a pair of substrates having electrodes formed on opposing surfaces. A polarizing plate is arranged on at least one surface of the liquid crystal cell under a predetermined condition, and a spectral distribution of transmitted light in a state where no voltage is applied between electrodes of the liquid crystal cell is measured, and a color of the transmitted light is measured. A point representing the chromaticity is obtained on the CIE chromaticity diagram, and a line passing through the achromatic point on the chromaticity diagram and the point representing the chromaticity of the transmitted light is obtained from the inclination angle with respect to either the x or y axis. A method for measuring the thickness of a liquid crystal layer, comprising determining the thickness of a liquid crystal layer of a liquid crystal cell. 2. The liquid crystal cell includes a color filter of a plurality of colors on one of the opposing inner surfaces of the pair of substrates, and the spectral distribution of the transmitted light is determined by measuring the transmitted light of the liquid crystal cell. 2. The spectral distribution of the liquid crystal cell is corrected based on the spectral distribution of light transmitted through only the color filters of the plurality of colors which has been measured in advance. The liquid crystal layer thickness measurement method described in the above. 3. The measurement of the spectral distribution of the transmitted light is performed by arranging the polarizing plate under the condition that the light transmittance is minimized when no voltage is applied between the electrodes of the liquid crystal cell. The method for measuring the thickness of a liquid crystal layer according to claim 1.