JPH049006A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display device which has a wide field angle in the horizontal direction, has a high contrast ratio, and make a negative type display by arranging a liquid crystal layer and polarizing films so that the liquid crystal molecule orienting direction of the liquid crystal layer at the center part at the time of applying no electric field is nearly parallel to the polarization axis direction of some of the polarizing films. CONSTITUTION:The nematic liquid crystal layer 6 is sandwiched between substrates 1A and 1B provided with electrodes 2A and 2B which are oriented and a light shield film 4 is provided except at a part corresponding to a display pattern; and a couple of polarizing films 7A and 7B are arranged on both surfaces of a liquid crystal cell so that light is transmitted through a part which is not applied with an electric field, and a voltage higher than a voltage which excites the nematic liquid crystal 6 is applied to the electrode at a display pattern part other than a desired display pattern. Then the liquid crystal layer 6 and the polarizing films 7A and 7B are so arranged that the liquid crystal molecule orienting direction of the liquid crystal layer 6 at the center part at the time of applying no electric field is nearly parallel to the polarization axis direction of one of the polarizing films 7A and 7B. Consequently, the high contrast ratio can be obtained within a sufficiently wide range including a slanting direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device that performs negative type display and has a light shielding film formed thereon.

[Prior Art] Conventionally, liquid crystal display devices used for displaying automobile instruments or clocks, etc., are often negative-type displays that display bright characters, figures, etc. on a dark display surface. .

In negative type liquid crystal display devices, no voltage is applied to the liquid crystal layer in the background area other than the display area, so the liquid crystal molecules are twisted, and light travels along this twisted axis, changing the polarization axis of the pair of polarizing films. By arranging them in parallel, light does not pass through the background area. However, in the background area of a normal negative-type liquid crystal display device, as the light twists and travels through the liquid crystal layer, the degree of polarization decreases, so a certain amount of light of a certain color passes through, resulting in an undesirable contrast ratio. There was a problem that was enough.

In order to solve this problem, we formed a light-shielding film on the background area other than the display area, and also polarized the light so that it passes through without applying voltage to the liquid crystal, as in the case of normal positive type liquid crystal display devices. Negative display devices have been proposed in which a film is disposed. This display device applies a voltage below a threshold voltage at which liquid crystal molecules rise to a predetermined display pattern portion (hereinafter referred to as a light-transmitting segment) of the display portion to transmit light, and displays a display pattern other than the predetermined display pattern. This is a liquid crystal display device in which a voltage higher than a threshold voltage is applied to the light shielding segment (hereinafter referred to as a light shielding segment) to shield light and perform a negative type display.

(Japanese Unexamined Patent Publication No. 60-162227) In this display device, since the light-shielding segment portion stands up 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 when viewed from this direction. Insofar as liquid crystal molecules do not exhibit birefringence. Therefore, the same degree of light shielding as when the polarizing plates are laminated with their polarization axes perpendicular to each other can be obtained, and an extremely high contrast ratio of 1000 or more can be obtained.

However, when the light-shielding segment portion of this display device is viewed from an oblique direction, light leaks due to the birefringence of liquid crystal molecules, resulting in insufficient light-shielding of the light-shielding segment portion.

This light leakage increases as the angle becomes lower in a particular direction, and visibility deteriorates due to a decrease in contrast ratio. Further, the brightness of the background portion and the light-shielding segment portion is greatly different, and the difference in brightness between the light-shielding segment portion and the light-transmitting segment portion is small, so there is a problem that there is a risk of misunderstanding the displayed content.

[Problems to be Solved by the Invention] In order to minimize the birefringence exhibited by this liquid crystal layer when voltage is applied in an oblique direction, the twist angle of the liquid crystal layer is set to 9.
The present inventors have also proposed shifting the angle from 0° to 50 to 80°. (Unexamined Japanese Patent Publication No. 62-2203
No. 80) When observed from an oblique direction, the polarization axis of the polarizing film appears to rotate upward, and the crossing angle of the polarization axes deviates from orthogonality. By arranging the crossing angle of the polarization axes 1-10 degrees from orthogonal to correct this deviation, the light-shielding properties of the polarizing film can be fully utilized, and the LCD display has a high contrast ratio in diagonal directions. A device is obtained. (Unexamined Japanese Patent Publication No. 6
2=245862) However, even with these improvements, there were problems in that a high contrast ratio could not be obtained over a sufficiently wide range, and that the contrast ratio in the front direction decreased.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. A nematic liquid crystal layer is sandwiched between substrates provided with aligned electrodes, and a layer corresponding to a display pattern is formed. A light shielding film is provided in areas other than the desired display pattern area, and a pair of polarizing films are placed on both sides of the liquid crystal cell so that the polarization axis of the polarizer film passes through the area where no voltage is applied. In a negative-type liquid crystal display device in which a voltage higher than the excitation of the nematic liquid crystal is applied to the electrode, the orientation direction of liquid crystal molecules in the central part of the liquid crystal layer when no electric field is applied, and the polarization axis direction of one of the polarizing films. A nematic liquid crystal layer is provided between substrates provided with electrodes which are aligned so that the twist angle of the liquid crystal molecules is 60 to 120 degrees. A light-shielding film is provided on the areas other than those corresponding to the display pattern, and the polarizing films are placed on both sides of the liquid crystal cell so that the angle of intersection of the polarization axes of the respective polarizing films is approximately 90°. In a negative-type liquid crystal display device in which two voltages are applied to the electrodes of the portions to excite the nematic liquid crystal, the polarization of the polarization film is approximately bisector of the intersection angle of the alignment processing force direction and the polarization of either polarizing film is applied. To provide a liquid crystal display device characterized in that the liquid crystal display device is arranged so that the axial direction is substantially parallel to it, and a liquid crystal display device with a light source characterized in that a light source is arranged on the back side of the liquid crystal display device. It is.

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

FIG. 1 shows a sectional view of a basic example of a twisted nematic liquid crystal display device with a negative tone display according to the present invention.

In FIG. 1, IA is a substrate, 2A is an electrode formed on its second side, and an alignment film 3A is further formed on it. On the other hand, the other substrate 1B has an electrode 2B on it, a light shielding film 4 on the part other than the display pattern, and a first
An alignment film 3B is formed thereon. These two substrates are arranged so that their electrode surfaces face each other, their peripheries are sealed with a sealing material 5, and nematic liquid crystal is injected inside to form a liquid crystal layer 6 to form a liquid crystal cell.

A pair of polarizing films 7A and 7B are arranged on both sides of this liquid crystal cell, and the polarizing axis is set so that light is blocked at the part to which a voltage is applied, as in the case of a normal positive type liquid crystal display element. is being used.

Thickness of liquid crystal layer (d) and refractive index anisotropy of liquid crystal (80)
It is preferable that the product Δnd be between 0.3 and 1.0 μm for the purpose of reducing the angular dependence of contrast and increasing the transmittance of the light-transmitting segment portion. .

Furthermore, in order to reduce the coloring of the transparent segment part, △
It is preferable that nd is determined to be between 0.3 and 0.54 zm.

The intersection angle of the orientation processing direction of the alignment film is usually set to 90°, but if necessary, it may be twisted by about 606 to 120', and the intersection angle of the alignment processing direction is 90°.
However, the twist of liquid crystal molecules is not 90° but 270°.
The crossing angle of the polarization axes of the polarizing film may be set to 90° to ensure that the light is blocked when a voltage is applied, that is, when the liquid crystal molecules are standing up. In order to improve visibility from a specific oblique direction, the upper polarization axes may be arranged so that they are apparently perpendicular to each other by shifting them by about 1 to 5 degrees, if necessary.

In the present invention, the polarization axis of this polarizing film is not arranged so as to be substantially parallel or substantially perpendicular to the orientation treatment Jj direction, but
The liquid crystal molecules are arranged so that the orientation direction of liquid crystal molecules in the central part of the liquid crystal layer when no electric field is applied is substantially parallel to the direction of the polarization axis of one of the polarizing films. Normally, it is sufficient to arrange the polarizing film so that the direction of the bisector of the intersection angle of the orientation processing direction is substantially parallel to the direction of the polarization axis of one of the polarizing films.

FIGS. 2(a) and 2(b) are explanatory diagrams showing the direction of the alignment process and the direction of the polarization axis.

In the figure, 13A and 23A are the alignment processing directions of the front substrate IA, 13B and 23B are the alignment processing directions which are the two-pink directions of the back substrate IB, 17A and 27A are the polarization axes of the front polarizing film 7A, 17B and 27B indicates the polarization axis of the polarizing film 7B on the back side, and 18.28 indicates the main viewing angle direction.

This example shows a case where the twist of the liquid crystal takes a leftward spiral structure when viewed from the front side, and by changing the alignment direction of the front substrate from the lower left side to the upper right side,
The main viewing angle direction is at the bottom of the figure. This main viewing angle direction is
This is the direction in which the threshold voltage of the liquid crystal display device is low. When viewed from this direction, the birefringence exhibited by the liquid crystal layer is small when voltage is applied, and a high contrast ratio is obtained. It is preferable to install it so that it can be observed from this direction.

When the twist angle of the liquid crystal is 90°, the orientation treatment direction is inclined by 45° to the left and right with respect to the main viewing angle direction. In this case, the orientation direction of liquid crystal molecules at the center of the liquid crystal layer when no electric field is applied coincides with this principal viewing angle direction.

In the present invention, one of the polarizing films is arranged so that its polarization axis direction is substantially parallel to the orientation direction of liquid crystal molecules in the central portion of the liquid crystal layer when no electric field is applied.

Figure 2 (a) shows the polarization axis direction 17A of the polarizing film on the front side arranged so that it is almost parallel to this direction, and (b) shows the polarization axis direction 17A of the polarizing film on the back side being arranged in this direction. The arrangement is shown so that the direction 27B is substantially parallel to each other.

The difference between these two examples is that the angular dependence of the left and right contrast ratios is reversed, and they can be selectively used depending on the purpose. For example, in the example of FIG. 2(a), there is a tendency for the contrast ratio on the left side to be higher than on the right side when viewed from the main viewing angle direction, and in FIG. 2(b), the contrast ratio is opposite.

When a driver uses polarized sunglasses, such as an on-vehicle liquid crystal display device, it is preferable to arrange the polarizing film on the front side so that the polarization axis is substantially horizontal as shown in (b).

In addition, the twist angle of the liquid crystal may be shifted from 906, and in this case, the direction of the approximately bisector of the intersection angle of the alignment treatment direction is set as the liquid crystal molecule alignment direction in the center of the liquid crystal layer when no electric field is applied. What is necessary is just to arrange|position so that this direction and the polarization axis direction of one of the polarizing films may be substantially parallel.

In addition, the example in Figure 2 shows a case where the liquid crystal twists in a leftward helical structure when viewed from the front side, but if it takes a rightward helical structure, the directions are replaced with A and B, respectively. Bye.

The orientation control method used in the present invention includes films of organic polymers such as polyimide, polyamide, polyvinyl alcohol, etc. 5102. A method of rubbing an inorganic film such as TlO2 or A1201, or an oblique evaporation method of SiO or the like may be used.

The light shielding film of the present invention may be provided on the inner surface of the liquid crystal cell, or
It may be provided on the outer surface, and its light transmittance is 0.02 to 1.0.
It is said to be about %. However, it is preferable to form a light-shielding film on the inner surface of the liquid crystal cell because it is less likely to cause misalignment between the display pattern and the light-shielding film 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 on one substrate requires fewer steps and is more productive.

This light-shielding film is formed by depositing or plating a metallic light-shielding film such as aluminum, nickel, or chromium through a transparent electrode and an insulating film, or by printing a light-shielding ink such as carbon paste. It is sufficient if it is formed.

The sealing material may be an ordinary sealing material such as epoxy resin or silicone resin. Usually, an opening is formed in a part of the sealing material, and after forming a cell, liquid crystal is injected through the opening. Just seal it.

The liquid crystal to be injected may be a normal nematic liquid crystal, but it is usually preferable to add a small amount of chiral substance to prevent the formation of a counter-rotating helical structure.

In addition, a color filter layer may be formed on the inner or outer surface of the substrate, a polarizing film substrate may be used as the substrate, a touch switch, an ultraviolet cut filter, or a non-reflection filter may be laminated on the outer surface of the substrate. The technique applied to ordinary liquid crystal display elements may be applied within a range that does not impair the effects of the invention.

Although the present invention is a negative type display as a whole, voltage is applied to the electrodes in the same way as a positive type display.

That is, in the light-transmitting segment of the display portion that transmits light, a voltage lower than the threshold voltage at which liquid crystal molecules rise is applied, and in the light-blocking segment, a voltage higher than the threshold voltage is applied. As for the voltage application method, each segment may be driven individually, or multiplex driving may be used in which a plurality of segments are driven with a common signal.

As a result, the background part is shielded from light by the light-shielding film, the light-shielding segment is shielded from light by a pair of polarizing films, and the light-transmitting segment is transmitted through the light-transmitting segment because the light is twisted according to the twisting of the liquid crystal molecules. A bright display can be obtained.

In this case, the driving voltage may be selected so as to obtain a high contrast ratio in the direction in which the image is mainly observed. Generally, the higher the driving voltage, the higher the contrast ratio obtained at a higher angle (direction perpendicular to the substrate). On the other hand, if the liquid crystal molecules are driven at a relatively low voltage within the range where they rise,
High contrast ratio can be obtained at low angles. in particular,
It is preferable to drive within a range of about 1.5 to 6 times the threshold voltage in the vertical direction.

Usually, an illumination means is provided behind the polarizing film on the back surface, but a reflective plate may be provided behind the polarizing film and display may be performed using light from the front.

The present invention can also be applied to a device that uses light from both the back and the front by installing an illumination means and a semi-transparent and semi-reflecting plate.

Furthermore, by adding a negative or positive dichroic dye to the liquid crystal, an even higher contrast ratio can be obtained over a wider viewing angle. Additionally, this dichroic dye may be used to compensate for the color temperature of the illumination means.

[Operation] In order to obtain a high degree of light shielding, it is necessary to satisfy two points: the liquid crystal layer exhibits almost no birefringence, and the polarizing film maintains a sufficient degree of polarization.

In a conventional twisted nematic liquid crystal display device with a 90" twist, the main viewing angle direction and the polarization axis direction are approximately 45"'
has an intersection angle of When these liquid crystal display devices are used at an angle, it is possible to increase the contrast ratio in a specific direction, but when the angle is tilted to the left or right,
A decrease in the degree of polarization of the polarizing film is unavoidable. This is observed from an angle of 45'' with respect to the polarization axis, and this is the angle at which the rotation effect of the polarization axis and the minute birefringence of the support film that makes up the polarizing film are most effective. This is because.

Therefore, the contrast ratio is high only in the main viewing angle direction, but
The left and right angle dependence is poor, and a liquid crystal display device with a wide viewing angle cannot be obtained.

On the other hand, in the present invention, the main viewing angle direction and the polarization axis direction are almost the same, and even when the angle is changed left and right, the angle makes a small angle with the polarization axis, as described in 5 above. This effect is less likely to appear, and therefore the degree of polarization decreases less. Therefore, a liquid crystal display device having good left and right angular dependence and a wide viewing angle can be obtained.

[Example] 1L comparative example With the configuration shown in Figure 1, the twist angle of the liquid crystal layer was 70°1, the cell gap was 6.011 m, and the liquid crystal was R manufactured by Merck & Co.
ZLJ-2978-000J (△n=0.087
), rG-1220DuJ manufactured by Nitto Denko Corporation was used as a polarizing film.
was used.

The polarizing axes of the polarizing films form an angle of 11.8° with the liquid crystal molecule alignment treatment direction on the adjacent substrates, and the intersection angle of the polarizing axes of the two polarizing films when viewed from the main viewing angle direction is 93.6°. ”.

A light shielding film was formed on the inner surface of the cell by printing with carbon ink, and had a light transmittance of about 0.2%.

This liquid crystal display device is arranged at an angle of 30 degrees, and
By changing the angle in the direction (orthogonal to the main viewing angle direction 18 in the figure),
Its visibility was evaluated.

The drive signal was a square wave of 6.9 V and 100 t (z). The angular change in contrast ratio of this device is shown by the dotted line in Figure 3. The viewing angle of this liquid crystal display device is approximately symmetrical left and right. The angle at which the contrast ratio was 100 or more was 22° from the center in the viewing angle direction.

Example 1 The same liquid crystal cell as the comparative example was used, with the same configuration as the comparative example, except that the twist angle of the liquid crystal layer was 90°.

As shown in FIG. 2(a), this liquid crystal cell was arranged so that its alignment treatment direction was 45° to the left and right, respectively, from the main viewing angle direction. In this case, the orientation direction of liquid crystal molecules in the central part of the liquid crystal layer when no electric field is applied coincides with the principal viewing angle direction, which is approximately the bisector of the intersection angle of the orientation treatment direction.

The polarizing film was arranged so that the polarizing axis of the front polarizing film coincided with the main viewing angle direction, and the polarizing axis of the back polarizing film was arranged so as to be perpendicular thereto. A cold cathode discharge tube light source was placed on the back side.

Similar to the comparative example, this liquid crystal display device is arranged at an angle of 30°, and the horizontal direction (direction perpendicular to the principal viewing angle direction 18 in FIG. 2)
The visibility was evaluated by changing the angle.

Note that the drive signal was a 6.3 V, 100 Hz square wave. The angular change in contrast ratio of this element is shown by a solid line in FIG. Regarding the viewing angle of this liquid crystal display device, the angle dependence on the right side was about 10° worse than that of the comparative example, but the left side showed very good angle dependence with a contrast ratio of 300 or more even in a direction tilted by 40°.

Example 2 The same liquid crystal cell as in Example 1 was used, and the polarizing film on the front side was rotated 2 degrees clockwise compared to Example 1 and installed. That is, the orientation treatment direction of the front substrate is tilted by 47 degrees from the main viewing angle direction,
The orientation treatment direction of the back side substrate was tilted at 45° from the main viewing angle direction as in Example 1. As a result, the crossing angle of the polarization axes of the polarizing film was 88°.

Note that the drive signal is 6. OV was a 100 Hz square wave. This result is shown in FIG. 3 by a dashed line. As a result, the angle dependence on the right side was improved, and the difference became about 2 degrees. On the other hand, on the left side, although the recontrast ratio was lower than in Example 1, even in the 406 tilted direction, the contrast ratio was 300 or more, showing very good angle dependence.

Example 3 The orientation treatment direction of Example 1 was reversed between the upper and lower substrates, and the polarization axis of the polarizing film was left unchanged. The twist of the liquid crystal layer becomes a rightward spiral structure, contrary to the first embodiment.

This liquid crystal display device exhibited an angular dependence of contrast that was almost horizontally inverted from that of Example 1.

In a 30° tilted arrangement, there are 4 on the right side in the horizontal direction.
Even in a direction tilted by 0°, the contrast ratio was 300 or more, showing very good angle dependence.

[Effects of the Invention] In the present invention, a nematic liquid crystal layer is sandwiched between substrates provided with aligned electrodes, a light shielding film is provided in areas other than those corresponding to the display pattern, and the polarization axis of the polarizing film is formed on both sides of the liquid crystal cell. A pair of polarizing films are arranged so that light is transmitted through the areas where no voltage is applied, and a voltage higher than that which excites the nematic liquid crystal is applied to the electrodes of display pattern areas other than the desired display pattern. In a liquid crystal display device, by arranging the orientation direction of liquid crystal molecules in the center of the liquid crystal layer when no electric field is applied and the direction of the polarization axis of one of the polarizing films to be almost parallel, the viewing angle direction can be adjusted. It is possible to easily obtain a negative type liquid crystal display device with a high contrast ratio and a wide viewing angle in the left and right directions.

In addition, various other applications are possible within a range that does not impair the effects of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a basic example of the present invention. FIGS. 2(a) and 2(b) are explanatory diagrams illustrating the direction and polarization axis of the polarizing film. Substrate Electrode Alignment Film Light Shielding Film Sealing Material Liquid Crystal Layer Polarizing Film Alignment Processing Direction Polarization Axis Main Viewing Angle Direction The relationship between the alignment processing power and main viewing angle direction of the present invention is explained: IA, IB: 2A, 2B: 3A, 3B = 4: 5 : 6 : 7A, 7B : 13A, 13B, 23A, : 17A, 17B, 27A, : 18, 28 3B 7B ri 1 Figure (a) (b) Procedural amendment (method) % formula % 1, Display of the case 1990 Patent Application No. 27196 2, Name of the invention Liquid crystal display device 3, Person making the amendment Relationship to the case Patent applicant Address 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name
(004) Asahi Glass Co., Ltd. August 27, 1991 (Shipping) 6. Column 7 for a brief explanation of drawings in the specification subject to amendment 7. Contents of amendment

Claims (1)

[Claims] (1) A nematic liquid crystal layer is sandwiched between substrates provided with aligned electrodes, a light-shielding film is provided in areas other than those corresponding to the display pattern, and the polarization axis of the polarizing film is provided on both sides of the liquid crystal cell. A pair of polarizing films are arranged so that light is transmitted through the areas where no voltage is applied, and a voltage higher than that which excites the nematic liquid crystal is applied to the electrodes of display pattern areas other than the desired display pattern. 1. A liquid crystal display device, characterized in that the liquid crystal molecules are arranged so that the orientation direction of liquid crystal molecules in the center of the liquid crystal layer when no electric field is applied is substantially parallel to the polarization axis direction of one of the polarizing films. (2) A nematic liquid crystal layer is sandwiched between substrates provided with electrodes that are aligned so that the twist angle of the liquid crystal molecules is 60 to 120 degrees, and a light-shielding film is provided in areas other than those corresponding to the display pattern. A negative type in which polarizing films are arranged on both sides of the cell so that the angle of intersection of the polarization axes is approximately 90°, and a voltage higher than that which excites the nematic liquid crystal is applied to the electrodes of display pattern parts other than the desired display pattern. 1. A liquid crystal display device for display, characterized in that the direction of the bisector of the intersection angle of the alignment processing direction is arranged so that the direction of the polarization axis of one of the polarizing films is substantially parallel to each other. (3) On the back side of the liquid crystal display device according to claim 1 or 2,
A liquid crystal display device with a light source, characterized in that a light source is arranged.