JP2765046B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device having a high contrast ratio when viewed from an oblique direction.

[Related Art] Conventionally, a liquid crystal display device used for display of an instrument of a car, a clock, or the like includes a bright display on a dark display surface,
Negative type displays for displaying figures and the like are often used.

In a conventional negative-type liquid crystal display device, since no voltage is applied to the liquid crystal layer in a background portion other than the display portion, the liquid crystal molecules are twisted, and the light is twisted along the twisted light to advance the polarization of the pair of polarizing plates. By arranging the axes in parallel, light is prevented from transmitting through the background portion. However, in the background portion of the normal negative-type liquid crystal display device, when the light is twisted into the liquid crystal layer and the degree of polarization is reduced, light of a specific color is transmitted to some extent, resulting in insufficient contrast. There was a problem.

In order to solve this problem, a light-shielding film is formed on a background portion other than the display portion, and polarization is applied so that the liquid crystal is transmitted without applying a voltage, as in the case of a normal positive-type liquid crystal display device. A negative display device in which a plate is arranged has been proposed. That is, a voltage lower than a threshold voltage at which liquid crystal molecules rise is applied to a predetermined display pattern portion (hereinafter, referred to as a light-transmitting segment) of the display portion to transmit light, and a display portion other than the predetermined display pattern (hereinafter, referred to as a light-transmitting segment). A liquid crystal display device of a type in which a voltage higher than a threshold voltage is applied to block light to perform a negative type display has been proposed (JP-A-60-162227).

In this display device, since the light-shielding segment rises with respect to the substrate of the liquid crystal molecules, the direction perpendicular to the substrate is the optical axis direction of the liquid crystal molecules, and the liquid crystal molecules are birefringent from this direction. Is not shown. Therefore, the same degree of light shielding as that obtained when the polarizing axes of the polarizing plates are orthogonally bonded can be obtained, and a very high contrast ratio of 1000 or more can be obtained.

In order to prevent an image of the observer from being reflected on the surface of the substrate, a method of installing the liquid crystal cell substrate at an angle of 15 ° to 40 ° with respect to the observation direction is adopted. In this case, it is necessary to achieve a high contrast ratio mainly in the oblique direction of observation, but when the light-shielding segment is viewed obliquely, the liquid crystal layer shows birefringence, so that light leaks out and the contrast ratio decreases. And visibility deteriorates.

[Problems to be Solved by the Invention] In order to minimize the retardation, which is the product of the birefringence of the liquid crystal and the optical path length, it is effective to make the twist angle of the liquid crystal layer smaller than 90 °. (JP
01-63925). Further, when observed from an oblique direction, the polarization axis of the polarizing plate apparently rotates, and the intersection angle of the polarization axes shifts from orthogonal. In order to correct this deviation, the polarization axes are crossed at an angle of 1 ° to 10 ° from the orthogonal direction.
No. 90419), it is expected that a liquid crystal display device having a high contrast ratio in an oblique direction can be obtained by fully utilizing the light shielding performance of a polarizing plate.

However, even with such an improvement, a contrast ratio as high as expected in an oblique direction cannot be obtained, and further improvement has been desired.

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and has a nematic liquid crystal layer sandwiched between substrates provided with electrodes, and a polarizing axis of a polarizing plate on both sides thereof. In a liquid crystal display device in which a pair of polarizers are arranged so that light is transmitted in a portion where no voltage is applied, the retardation of the material layers excluding the liquid crystal layer among the material layers inside the polarizers of the polarizers on both sides. Is the sum of
8 nm or less in the direction inclined 30 ° from the vertical direction,
In addition, the sum of the retardations of all the material layers inside the polarizers of the polarizing plates on both sides including the liquid crystal layer in a voltage applied state is 3 nm or less in a direction inclined by 30 ° from the vertical direction. A liquid crystal display device, and a light-shielding film is provided on a portion other than the portion corresponding to the display pattern, and a voltage higher than the nematic liquid crystal is applied to electrodes of a display pattern portion other than a desired display pattern. Negative-type liquid crystal display devices, and that the twist angles of the liquid crystal layers thereof are set to 50 ° to 85 °, and that the polarizing axes of the pair of polarizing plates are arranged to form an intersection angle of 91 to 100 °. A feature of the present invention is to provide a liquid crystal display device.

 The present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a typical example of the twisted nematic liquid crystal display device of the present invention.

In FIG. 1, 1A is a substrate, 2A is an electrode formed thereon, and an alignment film 3A is further formed thereon. On the other hand, the other substrate 1B has electrodes 2B,
The light-shielding film 4 is formed in a portion other than the display pattern, and the alignment film 3B is formed thereon. The electrode surfaces of these two substrates are arranged so as to face each other, the periphery is sealed with a sealing material 5, and a nematic liquid crystal is injected into the inside to form a liquid crystal layer 6, thereby forming a liquid crystal cell. Further, on both sides of the liquid crystal cell, a pair of polarizing plates 7A and 7B are arranged so that the polarization axes thereof allow light to pass therethrough at a portion where no voltage is applied.

The product of the thickness d of the liquid crystal layer and the refractive index anisotropy n of the liquid crystal △
It is desirable that nd is determined to be between 0.3 and 1.0 μm for the purpose of reducing the angle dependence of the contrast and for increasing the transmittance of the light transmitting segment.

The alignment control direction of the alignment film is not particularly limited, but is mainly viewed from an oblique direction.
It is preferable that the upper and lower substrates intersect at a predetermined angle so as to form a twisted structure of ゜. This intersection angle is
According to the installation angle of the liquid crystal display device, it is selected so that a high contrast can be obtained mainly in the observation direction. In addition, the spread of the angle showing the maximum contrast and high contrast is
It depends on the torsion angle, drive voltage, and angle of attachment of the polarizing plate, and is selected according to the required performance. Generally, the lower the angle of observation, the smaller the torsion angle and the smaller the driving voltage. In particular, the torsion angle is
By setting the angle to ゜, the contrast in the direction inclined by about 15 ° to 40 ° from the vertical direction of the substrate is improved, which is preferable.

As described above, a pair of polarizing plates is provided on both sides of the liquid crystal cell.
7A and 7B are arranged. Usually, the polarization axes are arranged to be substantially orthogonal.

In the present invention, particularly, the background portion is entirely covered with a light-shielding film,
By applying a voltage higher than the excitation of the nematic liquid crystal to the electrodes of the display pattern portion other than the desired display pattern, apparently, the display becomes a negative type display, and a normal negative type liquid crystal display device in which the polarization axes are arranged in parallel. Driving at a much higher contrast ratio becomes possible.

In particular, in this case, in order to increase the contrast ratio in an oblique direction, it is preferable that the polarization axes are not orthogonal to each other but are arranged so as to form an intersection angle of 91 to 100 °.
In particular, when viewed from the principal viewing angle direction determined by the orientation direction of the liquid crystal, and when the liquid crystal molecules are twisted across the principal viewing angle direction, the polarization axes of the pair of polarizing plates are viewed from the principal viewing angle direction. Is preferably set to an intersection angle of 91 to 100 °. That is, it is preferable that the crossing angle is 91 to 100 ° when viewed from the liquid crystal molecule alignment direction at the center of the liquid crystal layer.

The polarizing plates 7A, 7B are usually provided with polarizers 71A, 71B, which actually exhibit polarization characteristics, respectively, from both sides of supports 72A, 73A, 72B, 73B.
It has a structure sandwiched by.

In the present invention, of the material layers inside the polarizers of the polarizing plates on both sides, the sum of the retardations of the material layers excluding the liquid crystal layer is:
8 nm or less in the direction inclined 30 ° from the vertical direction,
In addition, the sum of the retardations of all the material layers inside the polarizers of the polarizing plates on both sides including the liquid crystal layer in the voltage applied state is set to be 3 nm or less in a direction inclined by 30 ° from the vertical direction.

The above-mentioned supports 72A, 73A, 72B, 73B of the polarizing plate are usually made of a transparent film and made of a material having a relatively small birefringence, but the birefringence is not zero.

Further, if the substrate is a glass substrate, there is almost no birefringence, and since the thickness of the alignment film and the like is small, birefringence hardly causes a problem.

Therefore, between the pair of polarizers, except for the liquid crystal layer,
The problem of birefringence is the substrate when using the support of the polarizing plate and the substrate having birefringence. In particular, when a glass substrate is used as the substrate, only the support of the polarizing plate becomes a problem.

Therefore, substantially in the present invention, the total sum of the retardations of the supports 73A and 73B inside the polarizing plate having birefringence, which is the material layer inside the polarizer of both polarizing plates, is 30 ° from the vertical direction. The sum of the retardations of all the material layers inside the polarizers of the polarizing plates on both sides including the liquid crystal layer in the voltage applied state is 8 nm or less in the inclined direction,
What is necessary is just to make it 3 nm or less in the direction inclined 30 degrees from the vertical direction. Thereby, a high contrast ratio of 500: 1 or more can be obtained.

The voltage application state is an applied voltage in a state where the liquid crystal display device is driven and the liquid crystal molecules are almost up. The applied voltage may be set so as to obtain a high contrast ratio in a specific observation direction inclined from the vertical direction.

Further, it is preferable that the total retardation of the polarizers on both sides excluding the liquid crystal layer of the material layer inside the polarizer be 3 to 8 nm in a direction inclined by 30 ° from the vertical direction, because it is easy to adjust. Thereby, the total sum of the retardations of all the material layers inside the polarizers of the polarizers on both sides including the liquid crystal layer in a voltage applied state is set to 3 nm or less, particularly close to 0, in a direction inclined by 30 ° from the vertical direction. Becomes easier. That is, the adjustment of the applied voltage and the retardation makes it easier to select the optimum point.

The retardation as described above may be obtained by changing the thickness of the supports 73A and 73B inside the polarizing plate or eliminating one of them.

As for the sticking angle of the polarizing plate, the angle shown in FIG. 2 is taken. Reference numerals 301A and 301BB denote directions in which the orientation control directions of the substrates 1A and 1B are viewed from the substrate 1A side. As a method of controlling the orientation, a method of rubbing an organic polymer such as polyimide, polyamide, and polyvinyl alcohol is generally used.
1A and 301B indicate the rubbing directions. Alternatively, oblique deposition of SiO or the like may be performed. In this case, the installation direction of the deposition source is set to 301A or 301A.
B. FIG. 2 shows a case where the liquid crystal device has a helical structure in which the twist angle θ is a leftward helical structure. In Figure 2
The direction indicated by 801 is called the main viewing angle direction, and is a direction in which the threshold voltage of the liquid crystal display device decreases. Since a high contrast can be obtained in this direction, it is desirable to install the apparatus so that it can be observed mainly from the 801 direction.

Reference numerals 701A and 701B denote the directions of the polarization axes of the polarizers 71A and 71B of the polarizing plates 7A and 7B. In the present invention, the crossing angle is set to 91 to 100 °. This intersection angle is 91 to 100 ° when viewed from the viewing direction, and ψ = 91 to 10 when viewed from the main viewing angle direction.
It is set to 0 ゜. FIG. 2A shows an arrangement in which the polarization axis direction and the orientation control direction are arranged at an angle close to a right angle, and has a feature that a high contrast is obtained at an angle close to the front. FIG. 2B shows an arrangement in which the polarization axis direction and the orientation control direction are arranged so as to be nearly parallel to each other. The arrangement is such that a relatively high contrast can be obtained at a low angle over a wide range. For this reason, in the present invention, the arrangement of (b) is preferable,
It is particularly preferable from the viewpoint of display contrast that the crossing angle between the polarization axis direction and the liquid crystal molecule alignment direction on the adjacent substrate is 0 ° to 30 °. In particular, it is preferable that the crossing angle between the polarization axis direction and the liquid crystal molecule alignment direction on the adjacent substrate is substantially the same on both substrates. For example, θ
In the case of = 80 ° and ψ = 94 °, it may be 7 ° respectively.

The light-shielding film of the present invention is usually provided for a negative display, and may be provided on the inner surface or the outer surface of the liquid crystal cell, and has a light transmittance of about 0.02 to 1.0%. However, it is preferable to form a light-shielding film on the inner surface side of the liquid crystal cell, since a positional shift between the display pattern and the light-shielding film does not easily occur when viewed from an oblique direction.

This light-shielding film is formed on the background portion of the display, and usually only needs to be formed on one substrate. Of course, it may be formed separately on both substrates, but forming it on one substrate reduces the number of steps and improves productivity.

The light-shielding film is formed by depositing a metal light-shielding film of aluminum, nickel, chromium, or the like via a transparent electrode and an insulating film, by plating, or by forming a light-shielding ink such as a carbon paste by printing. It should just be formed.

The sealing material may be a normal sealing material such as an epoxy resin or a silicone resin.In general, an opening is formed in a part of the sealing material, and after the cell is formed, liquid crystal is injected from the opening, and the opening is formed. What is necessary is just to seal.

As the liquid crystal to be injected, a small amount of a chiral substance is usually added in order to prevent a spiral structure of reverse rotation, but in the present invention, a liquid crystal without a chiral substance can be used because the twist angle is smaller than 90 °. .

In addition, the color filter layer may be formed on the inner or outer surface of the substrate, the substrate may be a polarizing plate substrate, or a touch switch, an ultraviolet cut filter, and a non-reflection filter may be laminated on the outer surface of the substrate. Techniques applicable to ordinary liquid crystal display elements may be applied as long as the effect of (1) is not impaired.

The present invention provides a liquid crystal display device in which a nematic liquid crystal layer is sandwiched between substrates on which electrodes are provided, and a pair of polarizing plates is disposed on both sides of the nematic liquid crystal layer such that the polarization axis of the polarizing plate transmits light in a portion where no voltage is applied. If the display is a negative type display, the application of a voltage to the electrodes is similar to the positive type display. Therefore, it is preferable.

That is, in the display portion, a voltage lower than the threshold value at which the liquid crystal molecules rise is applied to a light-transmitting segment that transmits light, and a voltage higher than the threshold voltage is applied to the light-shielding segment.

In the present invention, as a method of applying a voltage, each segment may be individually driven, or multiplex driving in which a plurality of segments are driven by a common signal may be used.

As the driving voltage, a voltage that can obtain a high contrast mainly at the observed angle is selected. In general, the higher the driving voltage, the higher the contrast at a higher angle (perpendicular to the substrate). When driven at a low voltage, a high contrast can be obtained at a low angle, but when the voltage is too low, a sufficient contrast cannot be obtained. Generally, it is desirable to drive within a range of 1.5 to 6 times the vertical threshold voltage.

Normally, an illumination means is provided behind the polarizing plate on the back side and used, but a reflecting plate may be provided behind the polarizing plate and display may be performed using light from the front. In addition, the present invention can be applied to a device in which a lighting unit and a transflective plate are installed, and light from both the back and the front is used.

Further, the present invention is also suitable for an active matrix liquid crystal display device in which active elements such as TFTs and MIMs are provided in each pixel, and a liquid crystal display device in which each pixel is driven in a state of static driving or close to static driving, It is suitable for viewing the liquid crystal display device from a direction other than the front direction.

Further, by adding a negative or positive dichroic dye to the liquid crystal, higher contrast can be obtained at a wide viewing angle.

[Operation] FIG. 3 shows the result of measuring the retardation of the liquid crystal layer from an oblique direction inclined by 30 ° from the vertical direction while changing the applied voltage. The horizontal axis in FIG. 3 shows the applied voltage, and the vertical axis shows the retardation. This retardation value indicates the retardation value of the liquid crystal layer as positive for explanation.

In FIG. 3, the retardation value of the liquid crystal layer rapidly decreases as the applied voltage increases, and then increases again. At the voltage at which the value of the retardation becomes the minimum, it indicates that the optical axis of the liquid crystal molecule is substantially oriented in the observation direction.

FIG. 4 shows a change in the sum of all the retardations including the liquid crystal layer caused by the applied voltage when a conventional ordinary polarizing plate is used.

The retardation of the support of the conventional ordinary polarizing plate is relatively large, and its direction is opposite to the direction of the retardation of the liquid crystal. For this reason, the sum of the retardations between the two polarizers becomes small in such a manner as to cancel the retardation of the liquid crystal. That is, in FIG. 4, the graph of the retardation of the liquid crystal layer in FIG. 3 is translated downward as it is. The broken line at the bottom of FIG. 4 shows the retardation value of the support of the polarizing plate.

As a result, a portion where the total retardation becomes 0 appears, and the range where the sum of the retardation becomes 3 nm or less is widened. However, the voltage V ₂ on the side where the liquid crystal molecules are almost rising, the optical axis of the liquid crystal molecules is almost in the observation direction. , The voltage becomes considerably higher than that of the voltage, and it becomes difficult to obtain a high contrast ratio. Incidentally, not risen sufficiently liquid crystal molecules in the applied voltage reverse V _1, since the loss of the helical structure is not sufficient, result in poor contrast ratio.

On the other hand, FIG. 5 is a view showing an example of the liquid crystal display device of the present invention. The liquid crystal in the case where the retardation value of the support of the polarizing plate is reduced to 8 nm or less as compared with FIG. The change with the applied voltage of the total of all the retardations including the layer is shown.

According to this example of the present invention, the retardation of the support of the polarizing plate is relatively small as compared with the conventional example, and the direction thereof is opposite to the direction of the retardation of the liquid crystal. Therefore, the sum of the retardations between the two polarizers becomes small in such a manner as to cancel the retardation of the liquid crystal, and the voltage V ₃ on the side where the liquid crystal molecules almost rise is
The optic axis of the liquid crystal molecules is close to the voltage that is oriented substantially in the observation direction. As a result, a high contrast ratio can be obtained with a low driving voltage.

Example Comparative Example In the configuration shown in FIG. 1, the twist angle of the liquid crystal layer was set to 70 °, the interval between the two glass substrates was set to 6 μm, and Δn was set as the liquid crystal.
A cyclohexane liquid crystal composition of 0.078 was used, and KH-18240T manufactured by Arisawa Seisakusho was used as a polarizing plate. As shown in FIG. 2, the polarizing plate is arranged at an angle of 11.8 ° with respect to the polarization axis so that the liquid crystal alignment direction on the adjacent substrates is 2 °.
The polarizing plates were arranged such that the crossing angle of the polarizing axes of the polarizing plates was 93.6 °.

Of the supports of the polarizing plate in this case, the retardation value of only the support closer to the glass substrate is individually measured, and the total is 13 nm.The direction is the retardation indicated by the liquid crystal layer. The opposite is true. This cell was installed at an inclination of 30 °, and the measurement result of the contrast ratio was measured. As a result, the contrast ratio at 6.0 V was 800: 1.

Example 1 As shown in FIG. 4, one of the polarizing plates was replaced with a type having the same configuration as that of the comparative example except that the support near the substrate was removed. As a result, the retardation of the support of the polarizing plate was 6.5 μm, which is half that of the comparative example.

When this cell was installed at an inclination of 30 ° and the contrast ratio was measured, the cell exhibited a contrast ratio of 800: 1 at 4.8 V, indicating that the cell could be driven at a lower voltage than the comparative example.

Example 2 A cell was formed using a TAC film that had been subjected to a special heat treatment as a support for a polarizing plate. The birefringence is reduced by the heat treatment. In this case, the retardation value of a polarizing plate support that is close to the glass substrate is individually measured, and the total is 4 nm. The direction is opposite to the retardation indicated by the liquid crystal layer. This cell was installed at an inclination of 30 °, and the measurement result of the contrast ratio was measured. As a result, it was found that the cell exhibited a contrast ratio of 600: 1 at 4.4 V, and could be driven at a lower voltage than the comparative example.

[Effects of the Invention] The present invention has an effect of inclining a viewing angle direction having a high contrast ratio from a direction perpendicular to the cell substrate, and has an effect of preventing a decrease in visibility due to an image of an observer being reflected on the substrate surface.

In addition, compared to conventional liquid crystal display devices, the drive voltage can be reduced, driving can be performed with a high contrast ratio even at a drive voltage of 5 V or less, and it can be driven with the same power supply as logic circuits and CPUs and other ICs There are also benefits.

In addition, when the retardation of the support of the polarizing plate is small, the amount of change of the retardation when the polarizing plate is stuck in a high temperature state after sticking the polarizing plate to the glass substrate with an adhesive is reduced, and the secular change is reduced, Increases reliability. This means that the optimum driving voltage is hard to change even after being left at a high temperature, and that the contrast ratio does not significantly decrease when driven at the same driving voltage.

In particular, the present invention relates to a liquid crystal display device of a type in which a light-shielding film is provided in a portion other than a portion corresponding to a display pattern, and a voltage higher than the excitation of the nematic liquid crystal is applied to an electrode in a display pattern portion other than a desired display pattern. A liquid crystal display device which is suitable and exhibits a high contrast ratio in an oblique direction can be easily obtained.

Further, the present invention can be applied to an active matrix liquid crystal display device in which a TFT or the like is formed in a substrate, and has an effect that the drive voltage is reduced, so that the TFT design is facilitated or the drive life is improved.

The present invention is also applicable to various applications within a range that does not impair the effects of the present invention, and is a liquid crystal display device viewed from an oblique direction, and can be used for various applications.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal cell of the present invention. FIG. 2 is a plan view showing the relationship between the liquid crystal alignment direction of the liquid crystal cell of the present invention and the polarization axis of the polarizing plate. FIG. 3 is a view showing the results of measurement from oblique directions while changing the voltage for applying the retardation of the liquid crystal layer. 4 and 5 are diagrams showing the results of obliquely measuring the retardation of the sum of the materials between the polarizers of the conventional liquid crystal display device and the liquid crystal display device of the present invention while changing the applied voltage. Substrate: 1A, 1B Electrode: 2A, 2B Alignment film: 3A, 3B Light shielding film: 4 Sealing material: 5 Liquid crystal layer: 6 Polarizing plate: 7A, 7B

Claims (3)

(57) [Claims] 1. A liquid crystal display in which a nematic liquid crystal layer is sandwiched between substrates on which electrodes are provided, and a pair of polarizing plates is disposed on both sides of the nematic liquid crystal layer so that light is transmitted through a polarizing axis of the polarizing plate where no voltage is applied. In the device, the sum of the retardations of the material layers excluding the liquid crystal layer among the material layers inside the polarizers of the polarizers on both sides is 8 nm or less in a direction inclined by 30 ° from the vertical direction, and the voltage is applied. The sum of the retardations of all the material layers inside the polarizers of the polarizing plates on both sides including the liquid crystal layer at 3 nm in the direction inclined 30 ° from the vertical direction
A liquid crystal display device characterized by the following. 2. The liquid crystal display device according to claim 1, wherein a light-shielding film is provided in a portion other than a portion corresponding to the display pattern, and the nematic liquid crystal is excited at an electrode in a display pattern portion other than a desired display pattern. A negative-type liquid crystal display device, characterized by applying a negative voltage. 3. The liquid crystal display device according to claim 1, wherein the twist angle of the liquid crystal layer is 50 ° to 85 °, and the polarization axes of the pair of polarizing plates are an intersection angle of 91 ° to 100 °. A liquid crystal display device, wherein the liquid crystal display device is arranged so as to form a liquid crystal display.