JPH01147433A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the title element which enables black and white display, has good display quality and decreases unequal colors by specifying the difference between the product of the liquid crystal double refractive index and liquid crystal layer thickness of a 2nd liquid crystal cell and the product of the liquid crystal double refractive index and liquid crystal layer thickness of a 1st liquid crystal cell. CONSTITUTION:The 1st liquid crystal layer 23 is formed between a 1st glass substrate 21, subjected to an orientation treatment and a 2nd substrate 21' subjected to the similar treatment. The 2nd liquid crystal layer 13 is formed between 3rd and 4th substrates 11 and 11' consisting of light transparent plastic films on the side of the substrate 21 opposite to the 1st liquid crystal layer 23. The difference (DELTAn1d1-DELTAn2d2) between the product DELTAn1d1 of the refractive index anisotropy DELTAn1 of the 1st liquid crystal layer 23 and the thickness d1 of the liquid crystal layer and the product DELTAn2d2 of the refractive index index anisotropy DELTAn2 of the 2nd liquid crystal layer 13 and the thickness d2 of the liquid crystal layer is specified in a -0.6-0.6mum range. The display element which is capable of making black and white display and has an excellent time sharing driving characteristic and excellent display quality is thereby obtd.

Description

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

[Prior art]

TN (twisted nematic) has traditionally been the mainstream
A type liquid crystal display element is composed of a liquid crystal cell having a liquid crystal layer having a 90 degree spiral structure between two electrode substrates, and a pair of polarizers sandwiching the cell.

However, the number of time divisions has increased with the recent increase in the size of dot matrix type liquid crystal display elements, but the time division characteristics of conventional TN type liquid crystal display elements are no longer able to cope with the increase in size. When time-division driving is performed over one time or more, the contrast and viewing angle deteriorate.

On the other hand, the super twisted nematic type (STN type) or 5BE (Super Twisted Birefring type), in which the liquid crystal molecules are twisted 270 degrees between the substrates,
IngenceEffect) type liquid crystal display elements have been proposed, and it has been reported that wide viewing angles and high contrast can be obtained [Cheffer et al.
, SID Digec+t, 120 (1985)].

However, in this case, since a large pretilt angle of about 30 degrees is required, there is a problem in that orientation treatment must be performed by oblique vapor deposition, which is poor in productivity. Orientation treatment by rubbing produces a scattering structure, making it impossible to obtain the desired characteristics.

On the other hand, thinness, weight reduction, strength and workability.

Liquid crystal display elements using plastic films are attracting attention from the viewpoint of cost reduction.

〔the purpose〕

It is an object of the present invention to provide a liquid crystal display element that overcomes the above-mentioned drawbacks found in conventional STN type liquid crystal display elements, enables alignment treatment by rubbing, and is lightweight, thin, and cost-reduced. .

〔composition〕

According to the present invention, the display electrode has a display electrode, is sandwiched between two substrates, at least one of which is a glass substrate, is oriented substantially horizontally to the substrates, and is twisted by 120° or more and 360° or less in the thickness direction. a first liquid crystal cell having a first liquid crystal layer having a positive dielectric anisotropy, and a first liquid crystal cell sandwiched between two transparent plastic film substrates and oriented substantially horizontally with respect to the substrates. It has a structure in which a laminate including a second liquid crystal cell having two liquid crystal layers is sandwiched between two polarizing plates, and the product Δn, d of the liquid crystal birefringence Δn2 of the second liquid crystal cell and the liquid crystal layer thickness d2
2, the liquid crystal birefringence Δn□ of the first liquid crystal cell, and the liquid crystal layer thickness d1
Provided is a liquid crystal display element characterized in that the difference between the product Δn0d1 and Δn0d1 is in the range of −0.6 to 0.6 μm.

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 l having transparent electrodes 3 on which alignment films 5, 5' have been formed and which has been subjected to an alignment process, and a similar second substrate 1' are arranged facing each other and separated from each other. .

A liquid crystal 33' is sealed between them to form a liquid crystal cell. 3 and 3' are transparent electrodes, 5 and 5' are alignment films, and 14 is a sealant. This liquid crystal cell is sandwiched between a first polarizer 7 and a second polarizer 7' 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 first liquid crystal layer 23 is formed between a first glass substrate 21 on which transparent electrodes 27 are formed and which has been subjected to alignment treatment, and a second substrate 21' which has been subjected to the same treatment. On the opposite side of the substrate 21 from the first liquid crystal layer, there are third and fourth substrates 11. made of translucent plastic films.
A second liquid crystal layer 13 is formed between the liquid crystal layer 11' and the liquid crystal layer 11'. In the first liquid crystal layer 23, the liquid crystal is aligned so as to be aligned substantially horizontally with respect to the substrate, and the liquid crystal molecules are preferentially aligned along the alignment direction. In this case, "substantially horizontal" with respect to the orientation of liquid crystal molecules means that the tilt angle of the liquid crystal molecules with respect to the substrate is approximately in the range of 0 to 30 degrees.

It is preferable that the first liquid crystal cell consisting of the first liquid crystal layer and the second liquid crystal cell consisting of the second liquid crystal layer are separately brought into close contact with each other with a bonding agent 16. The laminate of the first liquid crystal cell and the second liquid crystal cell is held between two polarizing plates 15°25.

FIG. 3 shows the preferential alignment direction of liquid crystal, and shows the preferential alignment direction D1 and the second preferential alignment direction of liquid crystal molecules on the first glass substrate 21.
The liquid crystal molecules have a twisted structure by ω1 with respect to the preferential alignment direction D2 on the substrate 21'. In this way, ω□ is the twist angle determined by the orientation treatment, and this orientation control can be performed by conventionally known oblique vapor deposition or by rubbing with cotton cloth after forming an inorganic or organic film. In addition.

In the present invention, the liquid crystal preferably used is a nematic liquid crystal having positive dielectric anisotropy to which cholesteric liquid crystal or chiral nematic liquid crystal is added and adjusted to an appropriate pitch. In this case, if ω1 is small, the steepness will worsen and the time-division folding characteristics will deteriorate. Furthermore, if ω1 is too large, a scattering structure is generated when an electric field is applied, which deteriorates display quality, which is not preferable. From these things, ω1 is 12
It must be between 0' and 3606.

In Fig. 3, the twist direction is configured to be counterclockwise from the first substrate to the second substrate, but it may also be twisted clockwise depending on the orientation treatment direction and selection of cholesteric liquid crystal or chiral nematic liquid crystal. can.

In FIG. 2, a second liquid crystal layer 13 is formed between a third plastic film substrate 11 and a fourth plastic film substrate 11 on the opposite side of the first liquid crystal layer from the polarizer 25. In FIG. The sides of both panels that come into contact with the liquid crystal are subjected to an alignment treatment that preferentially orients the liquid crystal molecules approximately horizontally. For the alignment treatment, a method similar to that for aligning the first liquid crystal layer can be used, but it is not necessary to use the same method. As the liquid crystal, smectic liquid crystal, nematic liquid crystal, or nematic liquid crystal to which cholesteric liquid crystal or chiral nematic liquid crystal is added can be advantageously used. As shown in FIG. 3, the preferential alignment direction D3 of liquid crystal molecules on the third substrate 11.

The liquid crystal has a twisted structure by ω2 with respect to the preferential alignment direction D4 on the fourth substrate 11'.

In such a configuration, when passing through the first liquid crystal layer,
Light becomes elliptically polarized light with different ellipticities and elliptical azimuthal angles depending on its wavelength.The principle of the present invention is that the second liquid crystal layer converts this light back into linearly polarized light or elliptically polarized light close to linearly polarized light. By passing the light through a polarizer arranged parallel to or at right angles to, a background color of white or black when no voltage is applied is obtained, respectively. Express this principle.

In order to obtain a display element that is capable of black-and-white display, has excellent display quality, and has little color unevenness, the refractive index anisotropy Δn of the first liquid crystal layer is
The product Δn of 0 and the thickness d□ of the liquid crystal layer, the product Δn, d of d□, the refractive index anisotropy Δn2 of the second liquid crystal layer, and the thickness d2 of the liquid crystal layer,
The difference (Δn1d, -Δn, d,) from -0,6-0,
It is preferable to set it as the range of 6 micrometers. Δn work d knee Δn
, d□ is above this range, the color is colored in the order of blue, green, and orange, and the same applies when below this range. This relationship is shown in Table-1.

Table 1 In the present invention, it is preferable that the angle δ between the alignment directions of the first liquid crystal layer and the second liquid crystal layer is 60° or more and 120° or less. Although the direction of twist of the first liquid crystal layer is shown as positive, the angle formed by the orientation direction of the liquid crystal is -120° or more -6
0° or less is also included in the above range. Further, the second liquid crystal layer may or may not be twisted like the first liquid crystal layer, and the direction of twist may be the same or opposite to that of the first liquid crystal layer. It's okay. The twist angle of the second liquid crystal layer is preferably 0" or more and 720 degrees or less, more preferably 120 degrees or more and 360 degrees or less. Also, the twist direction is opposite to that of the first liquid crystal layer. It is more preferable.

In addition, in Table 1, the angle between the polarizing plate transmission axis and the liquid crystal alignment direction in the first substrate is β, and the angle between the polarizing plate transmission axis and the liquid crystal alignment direction in the third substrate is β2, β, = β2 = 4
In the case of 5°, the twist angle ω0. ω2 is 180° each
In the case shown above, when one polarizing plate is rotated by 90 degrees, the colors become complementary colors.

Note that Δn and d□ are preferably selected from a range of 0.4 to 1.3 μm; if they are outside this range, the contrast decreases.

In this manner, the liquid crystal display element of the present invention can have the cell background color 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 voltage pass rate characteristic of the liquid crystal display element of the present invention is 1.05 or less, similar to the conventional STN type liquid crystal display element, and has excellent time-division drive characteristics.

Although the conditions for the cell configuration have been exemplified above, the feature of the present invention is that the display is uniform and there is no floating appearance of characters.

In order to realize a thin display element, a plastic film is further used as the substrate of the second liquid crystal cell. A plastic film liquid crystal cell can be made as thin as about 200 μm, and the above characteristics can be achieved by using such a thin cell.

Preferred conditions for producing a plastic film cell, which is the second liquid crystal cell, are as follows: As the plastic film, an isotropic film or a film stretched in the -axial direction can be used. - In the case of an axially stretched film, the film is optically anisotropic and has an optic axis in the direction of stretching and in the direction perpendicular to it. Therefore, it is necessary to make the angles formed by the stretching axes of adjacent substrates and the transmission or absorption axes of the polarizing plates substantially parallel. From the viewpoint of display contrast, it is preferable that this angle be within ±3 degrees. If it exceeds ±3 degrees, the display will become dark and this is not practical. Furthermore, -
The extinction angle distribution of the axially stretched film is ±5 degrees or more,
Preferably, it is required to be within ±2.5 degrees.

On the other hand, regardless of whether isotropic or -axially stretched film substrates are used, it is necessary to accurately maintain the distance between the two substrates. For this purpose, spacers are distributed between the two substrates.

At this time, it is necessary to control the diameter distribution of the spacer used to have a standard deviation of 0.27 μl or less. If more than this is used, uneven coloring will occur and display quality will deteriorate.

Furthermore, better display quality can be maintained if the first liquid crystal cell using a glass substrate and the second liquid crystal cell using a plastic film are brought closer to each other. For this purpose, the first liquid crystal cell and the second liquid crystal cell are brought into close contact with each other using a binder 16. The bonding agent for this purpose needs to absorb the difference in thermal expansion and contraction rate between the first liquid crystal cell and the second liquid crystal cell, and be able to withstand the heat history. It is preferable to have an excellent refractive index close to that of the substrate. For these reasons, a flexible polymeric material having a refractive index of 1.2 to 1.7 and having elasticity is used as the bonding agent. As a practical material, a commonly used adhesive for liquid crystal cells such as acrylic resin or a polymer adhesive is used. As the polymer adhesive, silicone resin, acrylic resin, epoxy resin, liquid rubber, etc. are used, and silicone resin can be used easily in terms of handling.

It is essentially not necessary to form a transparent electrode inside the plastic film cell, which is the second liquid crystal cell, but in order to prevent malfunction of the liquid crystal due to static electricity, a transparent electrode may be formed or the transparent electrode may be grounded. Alternatively, it can also be operated by a drive circuit.

〔effect〕

The liquid crystal display element of the present invention constructed in this manner is very easy to manufacture, unlike the conventional STN type, and is capable of black and white display. The steepness is 1, same as the conventional STN type liquid crystal display element.
．． 05 or less, and has excellent time division drive characteristics.

〔Example〕

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

Example 1 Polyimide was applied and rubbed onto a glass substrate having a transparent electrode, and the upper and lower substrates were bonded together so that the twist angle was 180°. The distance between the upper and lower boards is 8 with spacers.
．． It was configured to have an output of 25 μI.

A nematic liquid crystal with Δn=0.115 to which chiral nematic liquid crystal S-811, which induces counterclockwise twisting, was added was filled between the upper and lower substrates to form a first liquid crystal cell. Δn□d1=0.95 μrn.

A film substrate mainly made of translucent polyether sulfonate film was used, treated in the same way, and a granular polymer spacer with a standard deviation of particle size distribution of 0.25 μm was used between the upper and lower substrates. The second liquid crystal cell (Δn2d, =0
, 95 μm). The first liquid crystal cell and the second liquid crystal cell were stacked so that the rubbing directions on the overlapping substrate surfaces were substantially orthogonal, and the cells were further sandwiched between neutral gray polarizing plates to form a liquid crystal display element. The polarization axis of the polarizing plate was arranged to form an angle of 45° with the rubbing direction of the polarizing plate on the adjacent substrate.

The liquid crystal display element obtained in this way has a white background color,
Black display was possible by applying voltage to the first cell. Moreover, no color unevenness was observed even when the cell thickness varied by about 0.3 μm. The steepness of the voltage-transmittance characteristic is 1.03
Sufficient contrast was observed even in time-sharing motion with a duty of 1/200.

Example 2 A first liquid crystal cell was fabricated in the same manner as in Example 1 using a glass substrate so that the twist angle was 180° and the Δand force was less than 0.7 μm. On the other hand, the second liquid crystal cell uses a uniaxially stretched polyester film instead of the polyether sulfone film. N, Δ1. d2=0.7μ
It was produced in the same manner so that it became m. A first liquid crystal cell and a second liquid crystal cell were stacked so that the liquid crystal orientation directions on the assembled substrates were substantially perpendicular to each other and sandwiched between polarizing plates to form a liquid crystal display element. The transmission axis of the polarizing plate was made parallel to the optical axis of the substrate adjacent to the polarizing plate. The background color of this device was almost white, and dark blue display scum was produced by applying a voltage to the first liquid crystal layer.

Example 3 A first liquid crystal cell and a second liquid crystal cell were manufactured in the same manner as in Example 1, and the two cells were stacked so that the orientation directions of the liquid crystals on the molded substrates were almost perpendicular to each other to form a first liquid crystal cell. The cell and the second liquid crystal cell were closely bonded through a bonding layer of low temperature curing silicone resin with a thickness of about 1 μm, and then sandwiched between two polarizing plates to form a liquid crystal display element.

The background color of this element was almost white, and a dark blue display was produced by applying a voltage to the first liquid crystal cell. Furthermore, since the silicone resin used as the bonding agent was transparent and had almost the same refractive index as the substrate (n-point 1.4), there was no damage to the display performance. Rather, the display became brighter because there was no air layer between the first liquid crystal cell and the second liquid crystal cell. Further, even when this display element was exposed to 5001 (rs) at 60° C. and 90%, no defects in display quality appeared.

The same results were also obtained when a synthetic resin adhesive was used instead of silicone resin.

Example 4 Polyimide was applied and rubbed onto a glass substrate having a transparent electrode, and the upper and lower substrates were bonded together so that the twist angle was 180°. The distance between the upper and lower boards is 8 with spacers.
．． It was configured to have a diameter of 25 μm.

A nematic liquid crystal with Δn=0.115 to which a chiral nematic liquid crystal that induces counterclockwise twisting was added was filled between the upper and lower substrates to produce a first liquid crystal cell with Δn1d1=0.95 μm. As in Example 1, a second film was prepared using a translucent polyether sulfone film (100 μm).
A liquid crystal cell was fabricated (Δn, d, = 0.95 μm).

The first liquid crystal cell and the second liquid crystal cell were stacked so that the rubbing directions on the overlapping substrate surfaces were perpendicular to each other, and the cells were further sandwiched between neutral gray polarizing plates to form a liquid crystal display element. The polarization axis of the polarizing plate is the rubbing direction of the polarizing plate on the adjacent substrate and β, = 45°, β, = -45'
They were placed so as to form an angle of . This liquid crystal display element had a white background and was capable of displaying black by applying a voltage to the first cell.

Example 5 Same as Example 1, twist angle is 180°, Δn1
d, = 0.95, Δn1d, -Δn, d, = -0,45
Or +0.45 liquid crystal display element was produced. This was a white display on a black background, and black and white were reversed by rotating one polarizing plate by 90 degrees. It also showed excellent time-division drive characteristics.

Example 6 A liquid crystal display element was produced in the same manner as in Example 1 except that the second liquid crystal cell was added with chiral nematic liquid crystal CB15 that induces clockwise twist.

In this case as well, black and white display was possible and excellent time-division drive characteristics were observed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of the structure of a conventional liquid crystal display element, FIG. 2 is a cross-sectional view showing an example of the structure of a liquid crystal display element of the present invention, and FIG. 3 is an explanation of the angular relationship of the liquid crystal display element of the present invention. It is a diagram. 1.1', 11.11', 21.21'...Substrate, 1
1.11'...transparent plastic film substrate, 2
1.21'...Glass substrate, 5.5', 12.12
', 22.22'... alignment film, 3.3', 22,
22'... Electrode, 7, 7', 15, 25... Polarizing plate.

Claims (1)

[Claims] (1) It has a display electrode, is sandwiched between two substrates, at least one of which is a glass substrate, is oriented substantially horizontally to the substrates, and has a twisted structure of 120° or more and 360° or less in the thickness direction. a first liquid crystal cell having a first liquid crystal layer exhibiting positive dielectric anisotropy; and a second liquid crystal layer sandwiched between two transparent plastic film substrates and oriented substantially horizontally to the substrates. It has a structure in which a laminate with a second liquid crystal cell having Liquid crystal birefringence Δn_1 and liquid crystal layer thickness d_1
A liquid crystal display element characterized in that the difference between the product Δn_1d_1 and the product Δn_1d_1 is in the range of −0.6 to 0.6 μm.