JPH10123522A - Substrate for liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve transmittance and to obtain a bright liquid crystal display element by forming oriented films to film thicknesses of specific values and providing these oriented films with an antireflection effect. SOLUTION: The oriented film is formed by printing the surface of a glass substrate with a liquid crystal orienting agent which is a polyimide soln. and calcining the substrate. The film thickness D of the oriented film is controlled by adjusting the printing conditions of the orienting agent. The oriented film is provided with the antireflection effect by forming the oriented film in such a manner that its film thickness D holds the relation λ/4n×0.9<=D<=λ/4n×1.1 with respect to the wavelength λdesired to be prevented of refractive index and the refractive index (n) of the oriented film and attains <=1000 angstrom. More preferably, the relation is λ/4n×0.95<=D<=λ/4n×1.05 and the case D=λ/4 holds is most preferable. The prevention of the refection is no longer possible if the film thickness D of the oriented film is λ/4n×0.9>D or D>λ/4n×1.1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate used for a liquid crystal display device, and more particularly to a substrate for a liquid crystal display device capable of improving transmittance and obtaining a bright liquid crystal display device.

[0002]

2. Description of the Related Art At present, liquid crystal display devices have been widely used as thin displays. A commonly used liquid crystal display device is a twisted nematic (T
N) method and super twisted nematic (STN) method.When these liquid crystal display elements are manufactured, as shown in JP-B-62-38689, a liquid crystal sandwiched between substrates with transparent electrodes is used as a substrate. On the other hand, it is necessary to form an alignment film for orienting in a certain direction on the outermost surface of the substrate. Since the alignment film is formed inside the transparent electrode, it is said that it is preferable that the alignment film is thinner in consideration of the voltage applied to the liquid crystal. Is formed to an arbitrary thickness of about 400 to 1000 angstroms.

On the other hand, a liquid crystal display element is a display element for electrically controlling the case where light is transmitted and the case where light is not transmitted or scattered. Therefore, it is preferable that the transmittance in a state where light is transmitted is higher. In order to improve the transmittance of the entire liquid crystal display element, it is effective to improve the transmittance of each constituent material and to reduce reflection at the interface. At present, the transmittance of the constituent materials has been improved, the reflectance between the substrate and the polarizing plate has been reduced, and the reflectance of the outermost display element has been reduced. Cannot be formed, so that antireflection is not performed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and to provide a liquid crystal display element substrate capable of improving transmittance and obtaining a bright liquid crystal display element.

[0005]

According to the present invention, the film thickness D of the alignment film is such that the wavelength .lambda.
This is a substrate for a liquid crystal display device in which the relationship of the formula (1) is satisfied and the orientation film has an anti-reflection effect by being less than 1000 angstroms. λ / 4n × 0.9 ≦ D ≦ λ / 4n × 1.1 (1)

Making the alignment film have an antireflection effect is as follows.
This is possible by measuring the refractive index n of the alignment film and controlling the film thickness D of the alignment film so as to satisfy the relationship of equation (1) with respect to the wavelength λ of the light whose reflection is to be prevented. λ / 4n × 0.9 ≦ D ≦ λ / 4n × 1.1 (1) Further, preferably, λ / 4n × 0.95 ≦ D ≦ λ / 4n × 1.05 (2), and the relationship of the expression (3) may be satisfied. Most preferred. D = λ / 4n (3) If the film thickness D of the alignment film is λ / 4n × 0.9> D or D> λ / 4n × 1.1, reflection cannot be prevented. Also, if the thickness of the alignment film is too thick,
The film thickness is 1000
It is preferably equal to or less than Å.

[0007] Since a resin such as polyimide or polyamide is usually used for the alignment film, its refractive index is about 1.60 to 1.75 depending on the structure of the resin. The refractive index of the alignment film used can be measured by an ellipsometer.

As the wavelength λ for which reflection is desired to be prevented, it is usually preferable to use 500 nm which is a value substantially at the center of visible light. However, when the substrate material absorbs in a certain wavelength range and it is desired to make the entire transmittance uniform by reducing the reflection in the wavelength range of the substrate by the alignment film, D may be calculated using the wavelength.

[0009]

The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

(Example 1) A liquid crystal aligning agent, which is a polyimide solution, was printed and baked on a glass substrate to form an alignment film. When the refractive index was measured with an ellipsometer 1.
It was 65. If λ = 500 nm, D = 7 from equation (3).
Since the film thickness was 58 Å, the printing conditions of the alignment agent were adjusted so that the film thickness of the alignment film was the same, and the alignment film was formed on a glass substrate with ITO (thickness: 1.1 mm). Wavelength of this substrate 40
When the transmittance at 0, 500, and 600 nm was measured, it was 97, 97, respectively.
98,98%.

Example 2 An orientation film was formed by replacing a glass substrate with ITO with a polyethersulfone film substrate with ITO (thickness: 0.1 mm). Since the polyethersulfone film substrate used had absorption in a short wavelength region (400 nm or less), the film thickness of the alignment film D = 60
The printing was performed by adjusting the printing conditions of the alignment film so that the thickness became 6 Å. As in the first embodiment, the wavelength of the substrate is 400, 50
When the transmittance at 0,600 nm was measured, 96, 97,
97%.

(Comparative Example 1) The same procedure as in Example 1 was carried out except that the thickness of the alignment film was changed to 400 Å. When the transmittance of this substrate at wavelengths of 400, 500, and 600 nm was measured,
They were 94, 95 and 95%, respectively.

(Comparative Example 2) The same procedure as in Example 2 was performed except that the thickness of the alignment film was changed to 400 Å. When the transmittance of this substrate at wavelengths of 400, 500, and 600 nm was measured,
They were 92, 94 and 95%, respectively.

In each of Examples 1 and 2, a transmittance of 98% or more is shown in the state of the substrate with the alignment film.

In Comparative Example 1, the film thickness was smaller than that in Example 1.
It has been thinned to 400 angstroms, but its 3% transmittance is low.

In Comparative Example 2, the film thickness was smaller than that in Example 2.
It has been thinned to 400 angstroms, but has a low transmittance of 2-4%.

Since the liquid crystal display device substrate is used by forming a liquid crystal cell in pairs, the difference between the embodiment and the comparative example is magnified by the square, and the difference is further increased. Furthermore, since a general liquid crystal display element uses a polarizing plate, the transmitted light is
Since it is halved, the difference will spread here as well.
That is, the difference between the example and the comparative example indicates that the present invention is extremely effective.

The substrate for a liquid crystal display device of the present invention is a substrate for a liquid crystal display device capable of improving the transmittance and obtaining a bright liquid crystal display device.

Claims (1)

[Claims] 1. The relationship of the formula (1) with respect to the wavelength λ at which reflection is to be prevented and the refractive index n of the alignment film is satisfied, and the thickness D of the alignment film is 1000 Å or less. LCD substrate with anti-reflection effect. λ / 4n × 0.9 ≦ D ≦ λ / 4n × 1.1 (1)