JP3930177B2 - Liquid crystal display element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display element. More specifically, the present invention relates to a liquid crystal display element for multiplex driving in which the rising characteristics of liquid crystal are improved in order to improve the viewing angle of the liquid crystal display element.
[0002]
[Prior art]
In recent years, liquid crystal display elements have been widely used in various fields such as in-vehicle use, portable use, and desktop use such as a personal computer. As for the specification of the liquid crystal display element, there are a twisted nematic (TN) type in which the twist angle of liquid crystal molecules is about 90 ° and a super twisted nematic (STN) type in which the twist angle is 180 ° to 270 °. Are known.
[0003]
As required characteristics of an in-vehicle liquid crystal display element that is one application of a liquid crystal display element, high reliability and a wide viewing angle are desired. In particular, when viewing the liquid crystal display from the front, for example in the case of segment display, the difference between the background luminance due to no voltage and the luminance of the non-lighting voltage is large, and it may appear as an unnecessary display, reducing visibility. there were. For example, when a clock or car audio is displayed on the center console using a liquid crystal display element, it is necessary to be visually recognized from the driver's seat or passenger seat.
[0004]
Recently, in order to diversify and complicate the display, a multiplex drive that can simplify the circuit portion and the connection by connecting many segment electrodes in common is often employed. This multiplex drive can be applied to both STN type and TN type, but STN type liquid crystal display elements are less reliable than TN type liquid crystal display elements. Therefore, a TN type liquid crystal display element is often used as a vehicle-mounted liquid crystal display element in which reliability is particularly important.
[0005]
[Problems to be solved by the invention]
However, when the TN type liquid crystal display element is subjected to multiplex driving and the duty ratio is increased, the voltage margin is reduced and the contrast is lowered. In order to improve this, Japanese Patent Publication No. 60-2648 discloses that the twist angle of liquid crystal molecules is made larger than 90 ° to improve the sharpness and increase the voltage margin. However, the publication does not mention the expansion of the viewing angle, which is one of the objects of the present invention, and there is no specific description that leads to this.
[0006]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems, and nematic liquid crystal having positive dielectric anisotropy is sandwiched between two substrates each having a transparent electrode and an alignment film and provided substantially in parallel. In the multiplex driving liquid crystal display element having a liquid crystal panel and a pair of polarizing plates on the outside of the liquid crystal panel , the substrate is arranged so that the rise characteristic of the liquid crystal becomes steep in a range where the transmittance change is less than 10%. The pretilt angle, which is the angle between the director of the liquid crystal molecules at the interface and the substrate, is 0.5 ° to 1.5 °, the refractive index anisotropy of the liquid crystal is Δn, and the thickness of the liquid crystal layer is d. Provided is a liquid crystal display element for multiplex driving, characterized in that a product Δnd is 0.45 μm to 0.6 μm and a twist angle of liquid crystal molecules is 94 ° to 106 °. With such a configuration, the defective area is small, visibility is not impaired even at a low angle, and the viewing angle can be widened. Here, the rising characteristic of the liquid crystal means a transmittance-voltage curve in a range where the transmittance change is less than 10%.
[0007]
Also, an angle β ₁ (measured counterclockwise from the alignment direction of the liquid crystal molecules to the absorption axis direction of the polarizing plate) between the alignment direction of the liquid crystal molecules on one substrate side and the absorption axis of the polarizing plate is 0 ° to 15 °. The angle β ₂ (measured counterclockwise from the alignment direction of the liquid crystal molecules to the absorption axis direction of the polarizing plate) between the alignment direction of the liquid crystal molecules on the other substrate side and the absorption axis of the polarizing plate is −15 Provided is a liquid crystal display element for multiplex driving which is set to be in the range of 0 ° to 0 °.
With such a configuration, in a positive-type liquid crystal display element, the difference between the background luminance and the luminance of the non-lighting voltage is eliminated, and visibility can be improved.
[0008]
Further, the liquid crystal display for multiplex driving described above, wherein the angle β ₁ is 90 ° to 100 °, the angle β ₂ is 0 ° to 10 °, and the absorption axes of a pair of polarizing plates are substantially parallel. An element is provided.
By adopting such a configuration, it is possible to improve visibility and contrast in a negative-type liquid crystal display element.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, it demonstrates in detail according to drawing. FIG. 1 is a conceptual cross-sectional view of the liquid crystal display element of the present invention. As the substrates 2 and 3 used in the present invention, substrates such as glass and plastic used in ordinary liquid crystal display elements can be used. Transparent electrodes 4 and 5 such as ITO (In ₂ O ₃ —SnO ₂ ) and alignment films 6 and 7 are formed on the substrate.
[0010]
Further, if necessary, a color filter may be formed on at least one of the substrates. At this time, the transparent electrode may be formed either above or below the color filter, but it is preferable to provide the transparent electrode above the color filter because it is not necessary to increase the applied voltage.
[0011]
The transparent electrodes 4 and 5 and the alignment films 6 and 7 formed on the substrates 2 and 3 are opposed to each other and surrounded by a peripheral sealing material 8, and a liquid crystal 9 is injected and sealed therein to seal the liquid crystal cell 1. Is done. Although not shown, conductive spacers are mixed in the peripheral sealing material 8 to conduct conductive connection between the substrates. As this conductive connection means, conductive spacers are mixed in the peripheral sealing material to have conductivity throughout the peripheral seal, and the sealing material mixed with conductive spacers only in the conductive connection part between the substrates is printed in a dot shape. Other peripheral sealing materials include peripheral seals that are mixed with non-conductive spacers.
[0012]
The manufacturing method of the liquid crystal cell 1 will be described in more detail. After the alignment film is formed, the alignment film is rubbed with a cloth called a rubbing cloth made of nylon or rayon, and a treatment for aligning liquid crystal molecules in one direction is performed. The two substrates subjected to this treatment face each other and enclose the liquid crystal, so that the liquid crystal molecules are gradually twisted from the substrate interface and reach the other substrate. In the present invention, the twist angle is 94 ° to 106 °. If the twist angle is small, the sharpness is deteriorated and it becomes difficult to perform multiplex driving. If it is too large, the drive voltage will rise.
[0013]
The angle between the director of the liquid crystal molecules at the substrate interface and the substrate is called the pretilt angle. The pretilt angle is governed by the alignment film and the alignment treatment. In the present invention, the pretilt angle is set to 0.5 ° to 1.5 °. If this is small, it becomes difficult to control the alignment of the liquid crystal molecules, and domains are likely to be generated. Conversely, if it is too large, the rise characteristic of the liquid crystal is deteriorated.
[0014]
Furthermore, when the refractive index anisotropy of the liquid crystal is represented by Δn and the thickness of the liquid crystal layer is represented by d, Δnd is set to 0.45 μm to 0.6 μm. This makes it easy to improve the rise characteristics of the liquid crystal and widen the viewing angle. If it is out of this range, the behavior at the time of rising of the liquid crystal is different and the effect as in the present invention cannot be obtained. For example, in a positive specification liquid crystal display element, the luminance of the non-lighting voltage becomes higher than the background luminance when Δnd of the liquid crystal panel is set to 1.0 μm to 1.3 μm and voltage is applied. This is presumed to be due to the fact that the viewing angle does not widen.
[0015]
Polarizers 10 and 11 are disposed outside the liquid crystal cell 1, respectively. FIG. 2 shows and explains the relationship between the alignment direction of the liquid crystal molecules and the absorption axis of the polarizing plate. The alignment direction of the upper liquid crystal molecules of the substrate 2 and D _1, the alignment direction of liquid crystal molecules of the lower substrate 3 and D _2, the angle ω i.e. twist angle of the liquid crystal molecules of D ₁ and D ₂ 94 It is set to -106 degrees. Further, if the absorption axis of the upper polarizing plate 10 is P ₁ and the absorption axis of the lower polarizing plate 11 is P ₂ , the angle β ₁ formed by D ₁ and P _{1 in} the positive specification is 0 ° to is a 15 °, the angle beta ₂ between D ₂ and P ₂ are as -15 ° ~0 °. Here, the angles β ₁ and β ₂ are angles with the counterclockwise direction being positive from the alignment directions D ₁ and D ₂ of the liquid crystal molecules on each substrate side to the absorption axes P ₁ and P ₂ of the polarizing plate. If it deviates from this, the contrast decreases due to the occurrence of light leakage.
[0016]
Further, in the case of a negative specification, the angle beta ₁ of D ₁ and P ₁ is a 90 ° to 100 °, the angle beta ₂ between D ₂ and P ₂ are the 0 ° to 10 °, and P ₁ And P ₂ are substantially parallel. If it deviates from this, light leakage occurs and the contrast is lowered.
[0017]
In addition, a known material and a known technique used in a normal liquid crystal display element can be applied as long as the effects of the present invention are not impaired.
[0018]
【Example】
Example 1 (Example)
A transparent electrode made of ITO was formed on a glass substrate, and a substrate on which an alignment film LQ-5900 made by Hitachi Chemical was formed was created. The substrate is rubbed, the surfaces are opposed to each other, and a portion other than the opening for injecting the liquid crystal is surrounded by a peripheral sealing material. The refractive index anisotropy Δn is 0.094 from the opening and the dielectric constant is different. A nematic liquid crystal having a positive isotropic property was injected, and the opening was sealed to prepare a liquid crystal cell. The thickness of the liquid crystal layer of this liquid crystal cell is 6 μm, and Δnd is about 0.56 μm. Further, the twist angle of the liquid crystal molecules of the prepared liquid crystal cell was 100 °, and the pretilt angle was 1 °.
[0019]
Thereafter, a polarizing plate NPF-EG1425DU made by Nitto Denko was attached to the outside of the glass substrate to obtain a liquid crystal display element. The angle β ₁ formed by the absorption axis of this polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell was 10 °, and β ₂ was −10 °. Note that this example is a positive-type liquid crystal display element.
[0020]
When the obtained liquid crystal display element was lit and displayed by multiplex driving with 1/4 duty and 1/3 bias, the front contrast was 1/20. The effect will be further described with reference to FIG. 3. FIG. 3 is a diagram showing the light transmittance of the liquid crystal display element when a voltage is applied. In the figure, the solid line indicates the liquid crystal display element of Example 1, and the broken line indicates the liquid crystal display element of Example 2.
[0021]
The applied voltage at a transmittance of 90% in this figure the V _90, the applied voltage at a transmittance of 10% and a V _10, as the voltage difference (V ₁₀ -V ₉₀₎ is small sharpness of liquid crystal It is said to be steep. Further, when the transmittance is 10%, the lighting voltage V _ON is set, and when the non-lighting voltage at which the transmittance is 90% is V _OFF , the drive voltage V is defined by (V _ON + V _OFF ) / 2. . In general, (V _OFF −V _ON ) is called a voltage margin.
[0022]
In particular, in this example, one of the features is that the transmittance change with a transmittance of less than 10% is steep. That is, the rising characteristics of the liquid crystal are excellent. In the drive voltage V, the transmittance of the OFF waveform is b%, it can be seen that the difference between the transmittance of the background portion of the liquid crystal display device (non-application portion) is small.
[0023]
This is shown by another numerical value as shown in FIG. FIG. 4 shows the luminance ratio between the background luminance and the OFF luminance. 4 (a) shows the liquid crystal display element of Example 1 confirmed in an environment of 25 ° C. and 4 (b) shows an environment of 80 ° C. It is. 4 (c) and 4 (d) show the liquid crystal display element of Example 2 confirmed in an environment of 25 ° C. and 80 ° C., respectively, and FIG. 5 shows the definition of the angle. As a way of viewing 4 (a) to 4 (d), when there is no difference between the background luminance and the OFF luminance, the display is not misidentified and the visibility is good. Assuming that the luminance ratio is deteriorated in an area where the luminance ratio is 95% or less (hatched portion), the present invention has a small defective area, the visibility is not impaired even at a low angle (large θ), and the viewing angle is widened.
[0024]
Example 2 (comparative example)
The transparent electrode by ITO was formed in the glass substrate, and the board | substrate which formed the Hitachi Chemical orientation film LX-5800 on it was created. The substrate is rubbed, the surfaces are opposed to each other, and a portion other than the opening for injecting the liquid crystal is surrounded by a peripheral sealing material. The refractive index anisotropy Δn is 0.094 from the opening and the dielectric constant is different. A nematic liquid crystal having a positive isotropic property was injected, and the opening was sealed to prepare a liquid crystal cell. The thickness of the liquid crystal layer of this liquid crystal cell is 6 μm, and Δnd is about 0.56 μm. Further, the twist angle of the liquid crystal molecules of the prepared liquid crystal cell was 100 °, and the pretilt angle was 2.5 °.
[0025]
Thereafter, a polarizing plate NPF-EG1425DU made by Nitto Denko was attached to the outside of the glass substrate to obtain a liquid crystal display element. The angle β ₁ formed by the absorption axis of this polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell was 10 °, and β ₂ was −10 °. This liquid crystal display element became a positive specification.
[0026]
When the obtained liquid crystal display element was lit and lit with 1/4 duty and 1/3 bias, the front contrast was 1/18 and the viewing angle was narrow as shown in FIG. .
[0027]
Example 3 (Example)
In order to achieve negative specifications, the angle β ₁ between the absorption axis of the polarizing plate and the alignment direction of the liquid crystal molecules of the liquid crystal cell is 95 °, β ₂ is 5 °, and the absorption axes of the two polarizing plates are parallel. A liquid crystal display element was produced in the same manner as in Example 1 except that.
When this was evaluated as in Example 1, the front contrast showed a high value of 1/50 and the viewing angle was wide as in Example 1.
[0028]
Example 4 (comparative example)
An alignment film LX-5800 manufactured by Hitachi Chemical Co., Ltd. was used as the alignment film, and the configuration was the same as in Example 3 except that the pretilt angle was 2.5 °.
The obtained liquid crystal display had a front contrast of 1/30 and a narrow viewing angle.
[0029]
【The invention's effect】
With the configuration of the present invention, the rising characteristics of the liquid crystal can be made steep. Further, in the positive type liquid crystal display element, the difference between the background luminance and the luminance of the non-lighting voltage is eliminated, the visibility is improved, and the viewing angle can be expanded. Further, in the negative liquid crystal display element, the viewing angle can be increased and the contrast can be improved. Furthermore, since the characteristics hardly deteriorate even in a high temperature environment, it can be applied to an in-vehicle liquid crystal display element, and the application range as a display can be expanded.
[Brief description of the drawings]
FIG. 1 is a conceptual cross-sectional view of the present invention.
FIG. 2 is a graph showing the relationship between the alignment direction of liquid crystal molecules and the absorption axis of a polarizing plate in an example of the present invention.
FIG. 3 is a diagram illustrating light transmittance of a liquid crystal display element when a voltage is applied in an embodiment of the present invention.
FIG. 4 is a diagram illustrating a luminance ratio of OFF luminance to background luminance in an embodiment of the present invention.
FIG. 5 is a diagram illustrating the definition of the angle in FIG. 4;
[Explanation of symbols]
1: liquid crystal cell 2, 3: substrate 4, 5: transparent electrode 6, 7: alignment film 8: peripheral sealing material 9: liquid crystal 10, 11: polarizing plate

Claims (3)

A liquid crystal panel in which a nematic liquid crystal having a positive dielectric anisotropy is sandwiched between two substrates each having a transparent electrode and an alignment film and provided substantially in parallel; a pair of polarizing plates on the outside of the liquid crystal panel; In a multiplex drive liquid crystal display element having
The pretilt angle, which is the angle between the director of the liquid crystal molecules at the substrate interface and the substrate, is 0.5 ° to 1.5 ° so that the rising characteristics of the liquid crystal in the range where the transmittance change is less than 10% become steep . When the refractive index anisotropy of the liquid crystal is Δn and the thickness of the liquid crystal layer is d, the product Δnd is 0.45 μm to 0.6 μm, and the twist angle of the liquid crystal molecules is 94 ° to 106 °. A liquid crystal display element for multiplex driving characterized by comprising: The angle β ₁ (measured counterclockwise from the alignment direction of the liquid crystal molecules to the absorption axis direction of the polarizing plate) between the alignment direction of the liquid crystal molecules on one substrate side and the absorption axis of the polarizing plate is 0 ° to 15 °. The angle β ₂ (measured counterclockwise from the alignment direction of the liquid crystal molecules to the absorption axis direction of the polarizing plate) between the alignment direction of the liquid crystal molecules on the other substrate side and the absorption axis of the polarizing plate is −15 ° to The multiplex driving liquid crystal display element according to claim 1, wherein the liquid crystal display element is set to 0 °. The angle β ₁ (measured counterclockwise from the alignment direction of the liquid crystal molecules to the absorption axis direction of the polarizing plate) between the alignment direction of the liquid crystal molecules on one substrate side and the absorption axis of the polarizing plate is 90 ° to 100 ° The angle β ₂ (measured counterclockwise from the alignment direction of the liquid crystal molecules to the absorption axis direction of the polarizing plate) between the alignment direction of the liquid crystal molecules on the other substrate side and the absorption axis of the polarizing plate is 0 ° to 10 °. The multiplex driving liquid crystal display element according to claim 1, wherein the absorption axes of the pair of polarizing plates are substantially parallel to each other.

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