JPH0296115A - Phase compensation plate - Google Patents

Abstract

PURPOSE:To return intricate elliptically polarized light to complete linearly polarized light by laminating many thin inorg. films which are diagonally deposited by evaporation at every specified angle shifted in the intra-surface bearing of the substrate in the vapor deposition direction of the substrate by as much as the angle equal to the twist angle of a supertwisted nematic type liquid crystal element. CONSTITUTION:This phase compensation plate is formed by laminating the many thin inorg. films 8 which are diagonally deposited by evaporation at every specified angle shifted in the intra-surface bearing of the substrate in the vapor deposition direction of the substrate 2b by as much as the angle equal to the twist angle of the liquid crystal cell. Optical rotatory power can, therefore, be imparted in addition to double refractiveness to the compensation plate so that the plate has the optical properties equiv. to the optical properties of the supertwisted nematic (STN) type liquid crystal panel. The complete linearly polarized light is obtd. in this way from the transmitted light of the STN type liquid crystal panel. The complete phase compensation is thus possible and the coloration is entirely eliminated.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a phase compensation plate for an optical element, and in particular, it can completely eliminate coloring of a super rice 1-nematic type liquid crystal element and improve white/black display. The present invention relates to a phase compensation plate that is capable of high contrast, has excellent electro-optic properties, and is useful as a thin and lightweight liquid crystal color display device.

[Prior Art] Liquid crystal display devices utilize electro-optical effects, that is, changes in the optical properties of liquid crystal molecules that occur when an electric field is applied. Among these electro-optical effects, twisted nematic (T N ) effects are used. Twisted nematic (hereinafter referred to as TN) type liquid crystal display devices that utilize TN have been widely used. However, in a liquid crystal display device using this TN mode, it is difficult to display a large capacity due to the XY7 trix electrode structure.
Due to its unique relatively smooth electro-optical properties, high display contrast and sufficient visual range could not be obtained.

Then, the Super Twisted Nemadic (
Hereinafter referred to as STN. ) type liquid crystal display device.

In a TN type liquid crystal display device, the polarization direction of linearly polarized light incident perpendicularly to the substrate is rotated by 90 degrees along the twist of the liquid crystal molecules while passing through the cell, but in an STN type liquid crystal display device, is set to optically rotate in the range of 180° to 270°.As a result, steep electro-optical characteristics can be obtained, which can meet the demand for larger capacity display devices.

[Problems to be Solved by the Invention] However, since this STN type liquid crystal display device uses a color change effect due to an interference phenomenon using birefringence of liquid crystal for display, the display inevitably becomes colored. There is a problem. That is, -Finally, the STN type has two display colors, yellow mode and blue mode, depending on how the polarizing plate is attached, but it will appear colored no matter what angle the polarizing plate is attached.

Regarding the color tone of a display device, if white/black display is possible, the contrast will be better, and it can be applied to all kinds of display devices such as documents and charts, and furthermore, multicolor or full color display becomes possible. For this reason, various methods have been developed for converting white/black display into S T' N-type liquid crystal display devices, but the two-layer method is the most superior (Nikkei Microdevice, 198
(October 7, pp. 84-87). This method uses S as an optical compensation plate without an electrode structure to eliminate display coloration.
It consists of a two-layer panel structure with overlapping TN-type liquid crystal cells.

An STN type liquid crystal cell with an electrode structure (for driving) is overlaid with a compensating STN type liquid crystal cell having the same specifications except for the twisting direction of the liquid crystal molecules having an electrode structure (inactive), and the incident light side and A polarizing plate is placed on the transmitted light side. When the incident light passes through the polarized light T- (It?i light plate on the incident side), all colors become linearly polarized light. Next, when the light passes through the driving STN type liquid crystal cell, the linearly polarized light changes to elliptically polarized light due to birefringence. The elliptically polarized light then passes through a compensating STN type liquid crystal cell. At this point, the elliptically polarized light returns to its original linearly polarized light. Original linearly polarized light has the same vibration direction regardless of color, so if the analyzer (polarizing plate on the transmitted light side) and the polarizer are perpendicular to each other, no light will pass through it. In other words, a black display is obtained.

However, this two-layer STN type liquid crystal display device is thicker and heavier than a conventional STN type liquid crystal display device due to the thickness of the STN type liquid crystal cell for compensation, and in order to obtain perfect white color, it is necessary to The refedicon value (d△I], where d is the liquid crystal layer thickness and △!1 is the birefringence value of the liquid crystal) of the STN type liquid crystal cell and the STN type liquid crystal cell for compensation is set to a bold value. In order to make this adjustment, delicate control of the liquid crystal material used and the cell gap was required.

An unpublished prior art patent application No. 102 of 1983 was proposed to solve the drawbacks of the two-layer STN liquid crystal display device.
This is the invention of No. 988, in which an inorganic thin film for optical compensation is formed on a substrate on the transmitted light side forming an STN type liquid crystal cell.

However, the liquid crystal molecules of the STN type liquid crystal balloon are 18
The linearly polarized light that has passed through this has an orientation state twisted by 0° to 270°, and is not a simple elliptically polarized light as it is after passing through an axially stretched Oki film, but has two types of birefringence and optical rotation. It becomes elliptically polarized light with complex characteristics. Therefore, in the above-mentioned proposal of forming an inorganic thin film for optical compensation on the substrate and performing phase compensation as shown by Δ11d (Δ11.birefringence, d, thickness), the light passing through the STN liquid crystal parne is completely There was a drawback in that it was not possible to return the light to linearly polarized light, and a pure white/black display in which coloration was completely eliminated could not be obtained.

The present invention was made in view of the above-mentioned problems with the phase compensation plate of an STN type liquid crystal display element, and provides phase compensation that can return complex elliptically polarized light transmitted through an STN type liquid crystal display element to completely linearly polarized light. The purpose is to provide a board.

[Means for Solving the Problems] The phase compensation plate of the present invention is a phase compensation plate formed on a substrate on the transmitted light side of a super-twist nematic liquid crystal element, and the phase compensation plate is a phase compensation plate formed on a substrate on the transmitted light side of a super-twist nematic liquid crystal element. The gist is that a large number of inorganic thin films are laminated and deposited obliquely by a constant angle with respect to the in-plane direction of the substrate in the direction of vapor deposition of the substrate by an angle equal to the angle.

[Function] In the present invention, the phase compensation plate is formed by laminating multiple layers of inorganic thin films that are obliquely deposited at a fixed angle with respect to the in-plane direction of the substrate in the direction of deposition by an angle equal to the helix angle of the liquid crystal cell. It can provide optical rotation in addition to birefringence, and has optical properties equivalent to STN-type liquid crystal panels, so it is possible to obtain completely linearly polarized light from the transmitted light of an STN-type liquid crystal panel. can.

That is, the STN liquid crystal layer can be regarded as a cholesteric phase in which thin layers with homogeneous orientation parallel to the substrate are stacked one after another with their orientation vectors set at even a slight angle. Focusing on this, we recreated an equivalent structure with a phase compensation plate made by laminating many obliquely deposited films.However, optically, this phase compensation plate exhibits similar birefringence and optical rotation. .

While the unpublished prior art (Japanese Patent Application No. 63-102988) did not take into consideration the incident angle in the longitude direction of the obliquely deposited film on the substrate surface and the number of layers to be 1.1°, the present invention Specifications of the STN type liquid crystal panel used (Δ11 of the liquid crystal
, thickness d, twist angle and twist direction),
The obliquely deposited film that performs phase compensation is also characterized by laminating multiple layers with sequentially shifted incident angles in the longitude direction, creating a structure that eliminates the birefringence and optical rotation that occur in liquid crystal panels. It is.

The inorganic material to be deposited on the substrate is not particularly limited as long as it is transparent to visible light and exhibits birefringence when deposited obliquely. Examples of inorganic substances used for vapor deposition include oxides such as SiO□, WO3, and Ta205. A publicly known method is used for the oblique vapor deposition, such as an electronic vino vapor deposition method, a method of spuck vapor deposition from an oblique lateral direction, and the like. The obliquely deposited film may be formed directly on the outside or inside of the glass substrate of the liquid crystal cell, or it may be formed on the soil of another set of glass substrates and then combined.

[Example] A preferred embodiment of the present invention will be described below with reference to the drawings.

It should be noted that the present invention is not to be construed as being limited in any way by the description of the examples described below.

FIG. 3 is a sectional view of the phase compensation plate of the present invention applied to an STN type liquid crystal display device, and FIG. 4 is a three-dimensional view schematically showing the STN type liquid crystal display device of FIG. 3. Polarizing plates 14 and 16 are arranged on the incident light side and the transmitted light side of the STN type liquid crystal cell 10, and the polarizing plate (referred to as a polarizer) 14 on the incident light side and the polarizing plate (referred to as an analyzer) on the transmitted light side. )16 polarization directions are orthogonal.

Next, the structure of the STN liquid crystal cell 10 will be explained. A pair of glass substrates 2uJ3 and 2b are made of thin soda lime glass sheets and are arranged to face each other, and transparent electrode layers 4a and 4b made of IT"O1 indium oxide or the like are formed on the opposing surfaces, respectively. Alignment films 3a and 3b are formed thereon.The alignment film 3 is made by applying a solution of an alignment agent such as polyimide to the substrate surface and subjecting it to a heating dry soot paper alignment treatment. The alignment direction of the alignment film 3a on the incident light side is parallel to the polarization direction of the polarizer 14, and the alignment film 31 on the transmitted light side is parallel to the alignment film 3 on the incident light side.
The orientation direction of a is set in the range of 180 to 270 degrees in a counterclockwise direction or in a direction twisted around the platform.

The two glass substrates 2a and 2b are held by a not-shown scrubber so as to form a desired cell gap, and their peripheral edges are sealed with a sealing material 5 such as epoxy resin. In the space formed by the glass substrates 2a and 2b, ZLI-1694, ZLI-1565, ZLI
A liquid crystal material 7 such as -3201 is filled to form an STN liquid crystal cell 10.

Further, a phase compensation plate 6 is formed on the outer surface of the glass substrate 21 on the transmitted light side, and this phase compensation plate 6 is formed by laminating a large number of inorganic thin films 8. is transparent to visible light and exhibits no birefringence due to oblique deposition and is made of oxides of WO3 and S02.

Next, a method for forming the phase compensation plate 6 will be explained based on FIG. 1 and FIGS. 2(A) and 2(B). Figure 2 (A)
2 is a three-dimensional view showing the direction in which the inorganic thin film 8 is deposited on the substrate 21), and FIG. 2(B) is a plan view showing the direction in which the inorganic thin film 11!8 is deposited on the substrate 2b.

Here, the molecular alignment structure of the STN type liquid crystal cell 10 is 240°.
Field 6, which has a twisted structure, will be explained. This is inorganic i'! In order to reproduce this 240° twist by diagonally depositing and stacking a large number of fV8 layers, as shown in FIG. After the incident angle ψ of the vapor deposited particles of the thin film 8 in the longitude direction of the substrate surface matches the longitude direction of the substrate, the incident angle ψ of the substrate longitude direction of the second and subsequent layers is shifted by 30' and stacked up to the 91st layer. FIG. 1 shows a perspective view of a phase compensation plate 6 formed by laminating an inorganic thin film 8 on a substrate 21).

At this time, the incident angle θ measured from the normal to the substrate surface is usually around 70°, although it varies depending on the material.

Further, the thickness of each layer of the inorganic thin film 8 is designed as follows.

Note that the twisting direction is opposite to that of the STN liquid crystal cell 10.

d, -((ΔfloHdo) X 1.2-1.3)/
Δ11.・N here, Δ! 1o; Birefringence of the liquid crystal used, Δ11. : birefringence of the inorganic thin film, do: thickness of the STN liquid crystal cell, dl: thickness of one layer of the inorganic thin film, N: number of layers of the inorganic thin film. Moreover, the coefficients 12 to 1.3 in the formula are accurately determined by experiments, or are corrections for the loss of the birefringence effect of the inorganic thin film due to twisting.

Next, regarding the operation of the STN type liquid crystal display device of this example,
This will be explained according to the schematic diagram in FIG. The incident light is polarizer 1
4, any color of light becomes linearly polarized light. In the STN type liquid crystal cell 10, all liquid crystal molecules are aligned parallel to the substrate surface 2, but the alignment axis 3A on the incident light side is parallel to the polarization axis 14A of the polarizer, whereas the transmitted light (W
Since the alignment axis 3B of 1 is shifted clockwise or counterclockwise within a range of 180 to 270 degrees, the alignment direction of liquid crystal molecules changes continuously between the side substrates, and at the cell interface on the emission side
Twisted in the range of 80-270°. Therefore, when the incident light passes through the STN liquid crystal cell 10, it undergoes optical rotation and birefringence within the range of angles (T, linear leakage light changes into elliptically polarized light, but the orientation and eccentricity of the long axis of the ellipse differ depending on the wavelength. .

Next, the elliptically polarized light passes through the phase compensation plate 6;
has optically equivalent birefringence and optical rotation to the STN liquid crystal panel 10. As a result, the transmitted light has the same size as the STN liquid crystal cell, and the special image exhibits opposite birefringence, so that regardless of the wavelength, the elliptically polarized light completely returns to its original linear aperture, and aligns with the polarization axis 16A of the analyzer. Since they are perpendicular to each other, no light passes through them, resulting in a black display.

When a signal voltage is applied, the twist angle of the STN liquid crystal panel 10 is canceled and the liquid crystals are aligned in the normal direction of the panel surface, thereby losing optical anisotropy with respect to incident light and becoming a mere isotropic medium. Therefore, the straight line (optical rotation) that passes through the polarizing plate 14 becomes elliptically polarized light depending on the wavelength at the phase compensation plate 6, of which only the polarized light component of the blanking plate 16 is transmitted.At this time,
Approximately white display can be obtained by appropriately adjusting the liquid crystal cell thickness and phase compensation plate thickness.

In this embodiment, the phase compensation plate 6 is formed on the outer surface of the glass substrate 2b, but it may also be formed on the inside of the STN liquid crystal cell 10, or it may be formed on a separate set of glass substrates and then combined. It's okay.

[Effects of the Invention] As explained above, the phase compensation plate of the present invention can eliminate coloring of an optical element such as an STN liquid crystal display device by adjusting the longitude of the substrate by an angle equal to the helix angle of the optical element. No. 11, which was deposited by shifting it by a certain angle with respect to the direction! It is characterized by being formed by laminating a large number of thin films, and can eliminate coloration without using a separate optical compensation element such as an STN type liquid crystal cell for compensation. This makes it possible to reduce the thickness and weight of the device. Moreover, depending on the birefringence and optical rotation of the optical element, the phase compensator is given optical rotation in addition to birefringence, and is set to be optically equivalent to that of the optical element.
Complex elliptically polarized light received when passing through an optical element can be made into completely linearly polarized light. Therefore, complete phase compensation is possible, coloration is completely eliminated, and black/white display of STN type liquid crystal display devices with high display contrast and steep electro-optic characteristics is possible, which enables large capacity display devices. It can be applied to all kinds of display devices such as documents and charts. Furthermore, since color display is possible by using a color filter or the like, it is possible to manufacture a thin, lightweight, and high-quality liquid crystal color display device.

Further, the present invention is applicable not only to STN type liquid crystal panels but also to any optical element whose optical properties such as birefringence and optical rotation need to be controlled. Furthermore, in the present invention, since an inorganic thin film as a retardation compensation plate is directly formed on the liquid crystal cell,
The structure is extremely simplified and manufacturing costs are reduced. Moreover, since the phase compensation plate itself is an inorganic thin film, thermal
It is resistant to premature staining and can be used even under harsh environmental conditions. In terms of manufacturing technology, it is suitable for mass production as it uses a dry process called evaporation and a large vacuum layer allows many processes to be carried out at once.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG.
B) is a plan view showing the direction of evaporation of the inorganic thin film onto the substrate;
FIG. 3 is a sectional view of the phase compensation plate of the present invention applied to an STN type liquid crystal display device, and FIG. 4 is a three-dimensional view schematically showing the STN type liquid crystal display device of FIG. 3. 2Q, 2b... Crow substrates 3a, 3b - Alignment films 4a, 4b... Transparent electrodes 6... 10... None 8! Thin film liquid crystal inorganic WJ model STN type liquid crystal cell polarizer analyzer patent

Claims (1)

[Claims] (1) A phase compensation plate formed on a substrate on the transmitted light side of a super-twist nematic liquid crystal element, the plate being oriented in the substrate plane in the evaporation direction of the substrate by an angle equal to the twist angle of the super-twist nematic liquid crystal element. A phase compensation plate characterized by being formed by laminating a large number of inorganic thin films obliquely deposited at a constant angle relative to each other.