JPH01124822A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To enable black and white display and thickness reduction by using light transparent plastic to form one of the substrates of the element consisting of a polarizer, a liquid crystal layer which is horizontal with the substrates and has specific twists in a thickness direction and a double refractive medium. CONSTITUTION:The liquid crystal layer 16 is formed between the 1st substrate on which transparent electrodes 13 are formed and which is subjected to an orientation treatment and the 2nd substrate 21 which is subjected to the similar treatment. The double refractive medium layer 26 is formed between the substrate 21 and the polarizer 27 on the opposite side of said substrate. The liquid crystal in the layer 16 is subjected to the orientation treatment approximately horizontally with the substrates and the liquid crystal molecules are preferentially oriented in this direction. The liquid crystal of the layer 16 has the structure twisted by >=120 deg. and <=360 deg. in the thickness direction. At least one of the substrates of this element is formed of the light transparent plastic. The black and white display is thereby enabled and the element having the smaller thickness and the higher quality is obtd.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a liquid crystal display element.

[Prior art]

The display mode of liquid crystals that has been mainly used in the past is called the twisted nematic (TN) type, in which the liquid crystal molecules are twisted approximately 90 degrees between a pair of upper and lower substrates, and the rotation of the plane of polarization by the liquid crystal is called the twisted nematic (TN) type. This method takes advantage of the fact that the effect disappears due to voltage. This display mode was sufficient for low time division driving of watches, calculators, etc., but when high time division driving was used to increase the display capacity, it had the drawbacks of reduced contrast and narrow viewing angles. there were. this is,
This is because when high time-division driving is used, the ratio of the voltage applied to one selected point and non-selected points approaches 1, resulting in high contrast.

In order to obtain a display element with a wide viewing angle, a voltage v1° at which the relative transmittance of the element changes by 10% and a voltage V at which the relative transmittance of the element changes by 50%.

It is necessary to minimize the steepness γ, which is expressed by the ratio (VS./V2°).

In the case of twisted nematic type, this γ value is 1.13
It is 8 degrees. In order to reduce this γ value.

A method has been proposed in which the twist angle of the liquid crystal molecules is increased to make the polarization axis deviate from the alignment direction, and these methods are called SBB mode or STN mode. According to such a system, the γ value can be reduced to 1.1 or less, and high time-division driving of about 1/400 duty is possible. However, since this type of method uses coloring due to birefringence and its change due to voltage, there are strict requirements for the accuracy of the liquid crystal layer thickness, for example, cells must be created within 0.12 m.
As a result, with the SBE and STN types, product production is extremely difficult, resulting in a low quality product rate and high costs. Further, since these devices utilize coloring due to birefringence and its change due to voltage, the display is displayed on a colored background, making it difficult to display in black and white. Furthermore, light leakage occurs depending on the wavelength, making it difficult to use as a light shutter for color display.

〔the purpose〕

The present invention overcomes the drawbacks seen in the prior art, has high time division drive characteristics, can display black on a white background or white on a black background, and can display colors with less color unevenness. The purpose is to provide a liquid crystal display element. Another object of the present invention is to provide a liquid crystal display element that is lightweight and free from double images and floating characters.

(Structure, - Effect) According to the present invention, it is sandwiched between a pair of polarizers, is oriented substantially horizontally with respect to the substrate, has a twisted structure of 120° or more and 360° or less between the upper and lower substrates, and has a positive dielectric In a liquid crystal display element composed of a liquid crystal layer having anisotropy and a birefringent medium provided between a substrate and a polarizer, at least one of the substrates is a plastic film having translucency. A liquid crystal display element is provided.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of the structure of a conventional STN type liquid crystal display element.

In this figure, a first substrate 11' having an alignment film 15' formed thereon and a transparent electrode 13' subjected to alignment treatment;
A similar second substrate 21' is arranged to be spaced apart and facing each other,
A liquid crystal 16' is sealed between them to form a liquid crystal cell. 23' is a transparent electrode, and 25' is an alignment film.

10' indicates a sealant. This liquid crystal cell is sandwiched between a first polarizer 17' and a second polarizer 27' to constitute a liquid crystal display element.

FIG. 2 is a sectional view showing an example of the structure of the liquid crystal display element of the present invention. The liquid crystal layer 16 is formed between a first substrate 11 on which a transparent electrode 13 is formed and subjected to an alignment process, and a second substrate 21 which is subjected to a similar process. On the opposite side of the substrate 21 from the liquid crystal layer, a birefringent medium layer 26 is formed between the substrate 21 and the polarizer 27 . In the liquid crystal layer 16, the liquid crystal is aligned so that it is aligned substantially horizontally with respect to the substrate, and the liquid crystal molecules are preferentially aligned along this alignment direction. in this case.

Regarding the orientation of liquid crystal molecules, "substantially horizontal" means that the tilt angle of the liquid crystal molecules with respect to the substrate is in the range of approximately 0 to 30". Also, in the liquid crystal layer 16, the liquid crystal has an orientation of 120" to 360" in the thickness direction. It has a twisted structure.

FIG. 3 shows the definition of angles related to the present invention. The above twist angle ω is the orientation processing direction D1 of the first substrate.
．． It is determined by the orientation processing direction D2 of the second substrate. This orientation treatment can be performed by conventionally known oblique vapor deposition or by forming an inorganic or organic film and then rubbing it with a cotton cloth or the like.

In the present invention, a liquid crystal obtained by adding cholesteric liquid crystal or chiral nematic liquid crystal to a nematic liquid crystal having positive dielectric anisotropy is preferably used.

In this case, if W is too small, the steepness will worsen and the time-division drive characteristics will deteriorate, and if W is too large, scattering structure will occur when an electric field is applied, resulting in a decrease in display quality, which is undesirable. Therefore, it is preferable to define this angle in the range of 120° to 360″.

In FIG. 3, the twist direction is counterclockwise from the first substrate to the second substrate.

Clockwise rotation can also be achieved depending on the direction of alignment treatment and selection of cholesteric liquid crystal or chiral nematic liquid crystal.

In the present invention, a birefringent medium layer 26 is formed between the substrate 21 and the polarizer 27.

As such a birefringent medium, any material having in-plane refractive index anisotropy may be used, specifically.

Examples include stretched films of polymers such as triacetylcellulose, polyester, polyvinyl alcohol, polyethylene, and cellophane, and thin slices of crystals such as mica, calcite, and quartz cut in a plane parallel to the optical axis. As shown in FIG. 3, the optical axis Ω of the birefringent medium is arranged at an angle of δ with the alignment direction of the liquid crystal layer on the adjacent substrate.

In the present invention, liquid crystal can also be used as the birefringent medium. The configuration in this case is shown in FIG. 4. In FIG. 4, a second liquid crystal layer 46 is formed between the second substrate 21 and the third substrate 41. 35.45 is distribution,
It's out of pocket. For the alignment treatment, the same method as in the case of the first liquid crystal layer can be used. Examples of liquid crystals to be used include smectic liquid crystals, nematic liquid crystals, and nematic liquid crystals to which cholesteric liquid crystals are added.

Similarly to the first liquid crystal layer l, the second liquid crystal layer 46 can also have a twisted structure between the upper and lower substrates.

In this case, δ in FIG.
This is the angle formed by the alignment direction of the liquid crystal layer and the alignment direction of the second liquid crystal layer.

As shown in FIG. 3, the polarizers 17.27 arranged to sandwich the cell have their polarization axes P1. P is arranged so as to form an angle of β1°β2 with the liquid crystal alignment direction 01 or the optical axis Q of the birefringent medium.

In the liquid crystal display element of the present invention, the product of the refractive index anisotropy Δn of the first liquid crystal and the liquid crystal layer thickness d is Δnd, the refractive index anisotropy Δn' of the birefringent medium or the second liquid crystal layer, If the product of the thicknesses d' is Δn'd', the color tone when no voltage is applied can be changed to white (transparent) or It can be black, and can be black or white, respectively, when a voltage is applied.

The first feature of the present invention is that in the liquid crystal display element having such a structure, at least one of the substrates is made of a light-transmitting plastic. By doing so, the thickness of the substrate can be reduced from 1 to 0.51 to about 100 μι.

By making all the substrates plastic, the thickness of the cell can be reduced from about 3 .mu.m to 0.4 .mu.m or less.

Although it is possible in principle to achieve the above object using thin glass, the glass is easily broken, which poses major problems in manufacturing and use, and is virtually impossible.

Examples of the plastic film include polymer films such as polyvinyl alcohol, polyester, polyether sulfone, polysulfone, polyether ether ketone, and triacetyl cellulose. An alignment film and, if necessary, a transparent electrode are formed on the side of these films in contact with the liquid crystal. Note that it is not necessarily necessary to form a transparent electrode in the second liquid crystal layer.

By forming and activating electrodes, the color of the cell can also be adjusted.

A second feature of the present invention is that an optically isotropic film is used as the substrate in the STN liquid crystal display element having the above structure. Here, optically isotropic means that the retardation is 0.05 μm or less. In this case, examples of preferable isotropic films include polyether sulfone, polysulfone, diacetyl cellulose, triacetyl Examples include polymer films such as cellulose. This optically isotropic film is
The use of an isotropic film, which can be used for any of the substrates 11, 21, and 41, or can be made entirely of this isotropic film, allows the device to maintain the same high display quality as a glass substrate. Not only can the thickness be reduced, but also a dramatic weight reduction is possible. In particular, it is particularly preferable to use an isotropic film substrate as the substrate 21 separating the first liquid crystal layer and the birefringent medium or the second liquid crystal layer. may not be white or black, or the contrast may be significantly reduced.

Another feature of the invention relates to the use of a uniaxially stretched plastic film in the substrate of a two-layer STN type liquid crystal display element. Here, uniaxially stretched plastic film means that the retardation is 2 or more. Among uniaxially stretched films, polyethylene terethalate has excellent heat resistance, mechanical strength, gas barrier properties, and dimensional stability. However, due to its optical properties, even if a two-layer liquid crystal display element is constructed, the contrast will be significantly reduced or black and white display will not be possible. 6 The present inventor has proposed a method for solving this problem.

It has been found that these drawbacks can be overcome by the method described below, and both excellent display quality and substrate characteristics can be achieved.

(1) In the first method, when a uniaxially stretched film is used as a substrate adjacent to a polarizer, the optical axis of the film and the absorption axis or transmission axis of the adjacent polarizer are approximately parallel to each other. Parallel as used herein means that the angle between the two is within 5 degrees, preferably within 3''. If this angle exceeds this range, the contrast will drop significantly.

In the above configuration, Δnd, Δn′d′, β
The values of β2, δ, etc. are preferably within the above-mentioned suitable ranges.

(2) In the second method, when a uniaxially stretched film is used as a substrate that partitions two liquid crystal layers, the alignment direction of the liquid crystal on the substrate adjacent to the polarizer and the transmission axis or absorption axis of the polarizer are and the orientation direction of the liquid crystal on the uniaxially stretched film substrate that partitions the liquid crystal layer from another liquid crystal layer or a birefringent medium.

The angle formed by the optical axis of the substrate is in the range of 25 to 65 degrees, preferably in the range of 30 to 60''.

If the angle is outside the above range, the background color may not be white or black; for example, in the case of white.

When the brightness is black, darkness decreases and contrast decreases.

This method made it possible for the first time to use a uniaxially stretched film with optical anisotropy as a substrate that partitions two liquid crystal layers. Further, by combining the method with the first method, the entire substrate can be made of a uniaxially stretched film, and in this case, the cell can be made extremely thin.

In the above explanation, the liquid crystal layer and the birefringent medium are separated by a single substrate, but as shown in FIG. In addition, when the film is a uniaxially stretched film, it is preferable that the optical axes of the plurality of films are parallel.

Thus, in the liquid crystal display element of the present invention, the background color of the cell can be set to white or black by satisfying the above conditions. Further, when a voltage is applied, the display becomes black or white, respectively, and black and white display is possible.

Note that the steepness of the liquid crystal display element of the present invention is higher than that of the conventional STN.
It is 1.05 or less, similar to the type liquid crystal display element, and has excellent time-division drive characteristics.

〔effect〕

Since the liquid crystal display element of the present invention has little color change due to changes in cell thickness, two-color unevenness is less likely to occur. Furthermore, since it has excellent steepness, it can be used as a liquid crystal display element with a large display capacity. Furthermore, it can display black and white, which was previously impossible, and has little light leakage due to wavelength, so it can be used as a light shutter for color displays. In addition, as a substrate,
Since a plastic film is used, the device can be made thinner, and since the substrate is thin, images do not appear double, and the display quality is extremely high.

〔Example〕

Next, the present invention will be explained in further detail with reference to Examples.

Example 1 Polyimide was applied to a polyether sulfone film having a transparent electrode (with a film thickness of 100 μm), and after drying, rubbing was performed to perform orientation treatment (first substrate).

Next, a polyether sulfone film (second substrate) which had been subjected to the same treatment was produced, and this substrate was attached to the first substrate at a distance such that the twist angle was 200°. In this case, the distance between the upper and lower substrates was set to 7 μm using spacers. Δn= between the upper and lower boards
A liquid crystal composition in which chiral nematic liquid crystal 5811, which induces counterclockwise twisting, was added to a nematic liquid crystal having a molecular weight of 0.10 was filled.

Δn'd
' = 0.7μ cellulose film (thickness 20
A pair of neutral gray plates are glued together (δ=90＠) so that their tip axes (direction with the highest refractive index) make a 90° angle with the liquid crystal orientation direction on the upper substrate. It was sandwiched between two polarizing plates to form a liquid crystal display element.

Here, the directions of the polarizing plates were adjusted so that β1 = 45° and β3 = 45°.

This element is white (colorless) when no voltage is applied.

Black display was possible by applying voltage. Furthermore, the steepness was 1.04, indicating extremely excellent time-division drive characteristics.

Furthermore, when one polarizer was rotated by 90 degrees, an inverted display of white on a black background was obtained. In addition, the thickness of the element is determined by the polarizing plate (thickness 1
It was approximately 0.5■ including 20μugly).

When patterns were formed on the electrodes and characters were displayed,
No double image was observed at all, and even with cell thickness variations of 0.5 μm, almost no background color unevenness was observed.

Example 2 A device was produced in the same manner as in Example 1, except that instead of the cellulose film layer, a liquid crystal cell layer using polyether sulfone as a substrate was used (second liquid crystal cell). The second liquid crystal cell has a twist angle of 180°
, Δn'd' was 0.7μ■. δ,
β1 and β2 were the same as in Example 1. This device also showed excellent characteristics similar to Example 1.

Example 3 Polyester film with transparent electrode (film thickness 100μ
m, Δnd=lO) after applying polyimide and drying.

I rubbed it and processed it as a travelogue. The rubbing direction was 45'' with respect to the stretching direction of the polyester.A polyester film that had been subjected to the same treatment and the above substrate were attached to each other with a gap such that the twist angle was 2001.Upper and lower substrates The interval between is 7 μm.Δn
A liquid crystal composition of =0.13 was filled between the substrates to form a liquid crystal cell. Δn' was prepared in the same manner on the top of the liquid crystal cell.
A liquid crystal cell with d'=0.9μ and a twist angle of 200"
(second cell) were bonded together so that the liquid crystal orientations of the overlapping substrates were parallel.

With this configuration, δ=O@, and both cells are partitioned.

In the two substrates, the optical axis (stretching axis) of the substrate and the liquid crystal alignment force/direction formed an angle of 45°, and the whole was sandwiched between a pair of neutral gray polarizing plates to form a liquid crystal display element. The transmission axis of the polarizing plate was parallel to the optical axis of the adjacent substrates, that is, the top and bottom substrates. This element was almost white when no voltage was applied, and showed sufficient contrast, no double images, and excellent steepness.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the structure of a conventional liquid crystal display element, FIG. 2 is a sectional view showing an example of the structure of a liquid crystal display element of the present invention, and FIG. It is an explanatory diagram. FIGS. 4 and 5 are cross-sectional views showing other configuration examples of the present invention. 11', 21', 11, 21, 31.41... Substrate, 15', 25', 15, 25° 35.45...
・Alignment film, 13', 23', 13, 23, 33, 43
...electrode, 17', 27', 17.27...
・Polarizer. Patent applicant Rico Co., Ltd. - Figure 2

Claims (6)

[Claims] (1) A liquid crystal layer sandwiched between a pair of polarizers, oriented substantially horizontally to the substrates, having a twisted structure of 120° or more and 360° or less between the upper and lower substrates, and having positive dielectric anisotropy; A liquid crystal display element comprising a birefringent medium provided between a substrate and a polarizer, characterized in that at least one of the substrates is a translucent plastic film. element. (2) The liquid crystal display element according to claim 1, wherein the plastic film is optically isotropic. (3) A patent claim characterized in that the substrate adjacent to the polarizer is a uniaxially stretched plastic film, and the optical axis of the film is substantially parallel to the absorption axis or transmission axis of the adjacent polarizer. A liquid crystal display element according to scope 1. (4) The substrate adjacent to the birefringent medium is a uniaxially stretched plastic film, and the angle between the alignment direction of liquid crystal on the substrate adjacent to the polarizer and the transmission axis or absorption axis of the polarizer, birefringence. the angle between the optical axis of the substrate adjacent to the birefringent medium and the alignment direction of the liquid crystal on the substrate, the angle between the optical axis of the substrate and the optical axis of the birefringent medium adjacent to the substrate, and the polarizer. Claims characterized in that the angles formed by the optical axis of the adjacent birefringent medium and the absorption axis or transmission axis of the polarizer adjacent to the birefringent medium are both in the range of 20° to 70°. A liquid crystal display element according to any one of the ranges 1 to 3. (5) A liquid crystal display element according to any one of claims 1 to 4, wherein the birefringent medium is a liquid crystal layer formed between substrates. (6) The liquid crystal display element according to claim 5, wherein the film sandwiching the liquid crystal layer is a plastic film.