JPH0769534B2 - Twisted nematic liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a twist nematic liquid crystal display device used for displaying an automobile or a watch, and a negative display type liquid crystal display device in which a bright display pattern appears on a dark background. It is about.

[Prior Art] A twist nematic liquid crystal display device is roughly classified into a negative display type and a positive display type according to its appearance. The negative display type is a format in which bright characters and figures are displayed on a dark display surface and is already widely used for automobile instruments, watches and the like.

FIG. 2 is a perspective view schematically showing an example of a conventional negative type twist-lenematic liquid crystal display device.

Generally, it is composed of a backside illumination means 1, polarizing plates 3 and 5, and a twist-lenematic cell (TN cell) 4, and a color filter 2 may be used together depending on the application.

The TN cell is equipped with electrodes of a desired shape facing two transparent supports such as glass and plastic, and between the transparent supports,
The nematic liquid crystal molecules are aligned substantially parallel to the surface of the transparent support, and the orientation is controlled so as to form a 90 ° helical structure. Further, the polarization axes of the polarizing plates 3 and 5 are set so as to be parallel or orthogonal to the alignment direction of the liquid crystal molecules on the surfaces of the adjacent substrates, and the polarization axes are parallel to each other. With such a configuration, the light from the light source 1 is linearly polarized by the polarizing plate 3 and is incident on the TN cell 4 in a portion to which no voltage is applied. In the TN cell 4, the plane of polarization of the linearly polarized light is rotated by approximately 90 °, and is blocked by the polarizing plate 5. On the other hand, since the plane of polarization does not rotate in the portion of the TN cell to which an excitation voltage higher than the threshold voltage is applied, the plane of polarization that has passed through the TN cell 4 coincides with the polarization axis of the polarizing plate 5 and forms a bright pattern. Occurs.
Further, if the color filter 2 is provided, the transmitted light can be colored, and a display device in which the display color is partially changed can also be configured.

[Problems to be Solved by the Invention] This method, which has been conventionally used, has been theoretically analyzed. (CH Gooch et al., J. Phys., D, 8 , 1975, P.157.
5) The transmittance (Toff) of the background part is when using a theoretical polarizing plate. u = 2dΔn / λ (2) d: gap of TN cell Δn: refractive index anisotropy of nematic liquid crystal λ: wavelength of light The transmittance (Ton) of the display part (voltage application part) can be approximated by the transmittance when two polarizing plates are installed so that their polarization axes are parallel to each other.
≒ 0.5 Therefore, the contrast ratio (CR) can be approximated by CR = Ton / Toff≈0.5 / Toff (3), and it has cell gap (d), liquid crystal refractive index anisotropy (Δn) and wavelength dependence. There is.

On the other hand, it is difficult to control the liquid crystal cell gap (d) to be strictly constant, and there is variation with respect to the set value, and Δn has both temperature dependence and wavelength dependence. In other words, there is a restriction condition such that the light may be displayed, that is, light of different wavelengths may be used.

As a result, the conventional device has the following problems.

(1) The contrast ratio is small.

(2) The background is not sufficiently dark, and the background looks bright to some extent. In other words, Toff is large.

(3) The temperature dependence of Toff is large, and the darkness of the background changes depending on the temperature.

Both problems are due to the fact that Toff is not an ideal optical shutter because it follows the equation (1).

In order to avoid this by using a negative type display, it has been considered that a positive type cell is used and an electrode is provided in the background portion so that a voltage is always applied, but a two-layer cell or a two-layer electrode is used. It must be done, and we do not like it because of its ease of pattern design, readability, productivity, and cost. It was also considered to make the orientation parallel to a portion, but it is not so difficult if only a fixed display portion is provided, but it is extremely difficult to change only the orientation direction of all the portions other than the display pattern. Therefore, it cannot be applied to complicated displays.

[Means for Solving Problems] The present invention has been made in order to solve the problems of the conventional device, and has a light amount equivalent to that in the case where the polarization axes of two polarizing plates are made to intersect at Toff. The present invention provides a negative twisted nematic liquid crystal display device having a high contrast.

The present invention provides a lighting means, a nematic liquid crystal layer having a helical structure of about 90 °, a plurality of transparent supports sandwiching the nematic liquid crystal layer and having electrodes, and light transmission to a position corresponding to a display pattern. In a twist-lenematic liquid crystal display device including a light-shielding mask having a portion formed therein, a pair of polarizing plates provided outside a transparent support, and means for applying a voltage to electrodes, the light provided on the light-shielding mask The transparent part
In addition to being provided so as to include a portion outside the display segment pattern defined by the opposing electrodes,
Arranged so that the polarization axes of the respective polarizing plates are orthogonal to each other,
Further, the present invention provides a twist-lenematic liquid crystal display device characterized in that an excitation voltage is applied between electrodes other than between electrodes corresponding to a desired display pattern.

In the present invention, the two polarizing plates are arranged so that their polarization axes are orthogonal to each other, and normally the polarizing axes may be arranged so as to be orthogonal or parallel to the alignment direction of liquid crystal molecules adjacent to each other. .

In the present invention, by adopting such a configuration, that is,
By displaying a negative type with a positive type cell configuration, the background part is shielded from light by a light-shielding mask and the To
ff shows the same amount of light as when the polarization axes of the two polarizing plates are made orthogonal because the liquid crystal molecules are no longer twisted when a voltage is applied, so it can be sufficiently dark and the same dark state regardless of temperature and color. Can be As a result, even when a color filter or a different-color light source is partially provided, it is not recognized, and the contrast can be increased.

Further, in the present invention, the light-transmitting portion provided on the light-shielding mask is provided so as to include a portion outside the display segment pattern defined by the opposing electrodes, that is, provided on the light-shielding mask rather than the display segment pattern. Since the light transmitting portion is made large, the display segment pattern has a portion through which light is always transmitted.

As a result, regardless of whether the display pattern is displayed or not,
The contour can be visually recognized, and a display having a unique design can be obtained.

Also, even if nothing is displayed for this application,
You can determine what is displayed. For example, in the case of such a configuration, if "" is displayed in the dark, it is not known how many objects are displayed, but in the configuration of the present invention, "○" is slightly identified by its outline. It is possible to easily identify how many objects are displayed by displaying five items so that they can be displayed or by displaying five items so that "-" can be slightly identified by the outline.

Further, even if the alignment accuracy is lowered and the position is deviated, the width through which light is emitted is not uniform, the display quality is not significantly lowered, and the alignment tolerance is high. improves.

The TN cell used in the present invention may have the same configuration as a conventional positive type TN cell, and the polarizing plate may be arranged in a positive type display.
Apply a voltage between the electrodes corresponding to the segment electrodes that correspond to the display pattern, and use the light-shielding mask that configures the light-transmitting portion for the pattern that you want to display. Without doing so, a negative type display is performed by applying a voltage between the electrodes corresponding to the segment electrodes which are not desired to be lighted (want to be brightened) in the positive type display.

The light-shielding mask is printed with a conventionally known pigment-containing ink,
Anything that shields light, such as metal vapor deposition or plating, may be used,
It may be formed outside the cell or inside the cell. The light blocking degree may be appropriately set depending on how much the light leakage through the background portion is set, but normally, the light leakage may be approximately equal to that in the dark segment portion.

Further, in the present invention, the light-transmitting portion provided on the light-shielding mask is made larger than the display segment pattern, but the distance between them is, for example, about 0.1 to 10 mm, and the width of the display pattern, the alignment accuracy, etc. It may be set appropriately.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1, 3, and 4.

Embodiment 1 FIG. 1 shows a perspective view of a basic configuration example of the present invention. The portion different from the conventional example is provided with a light-shielding mask 7, the shape of the display pattern is almost the same as the shape of the light-shielding mask, and the light-transmitting portion provided on the light-shielding mask is more than the display segment pattern defined by the opposing electrodes. The polarizing axes of the polarizing plates 3 and 5 are substantially orthogonal to each other, and are substantially orthogonal to or parallel to the alignment direction of the adjacent liquid crystal molecules, and the voltage is applied to the TN cell 4. The means for applying 6 is TN only in the non-display segment.
This is to carry out a driving operation opposite to the conventional one in which a cell operating voltage is applied (hereinafter referred to as an R-TN cell).

FIG. 3 is an enlarged plan view showing the light-shielding mask 7 and the TN cell 4, and FIG. 4 is a plan view showing the relationship between the light-shielding mask and the display segment pattern by the electrodes.

In FIG. 3, the plurality of display segment patterns 11 to 18 of the TN cell 4 are installed so as to be substantially aligned with the light transmitting portion 8 of the light shielding mask 7. At this time, in the present invention, the light transmitting portion provided on the light shielding mask is provided so as to include a portion outside the display segment pattern defined by the opposing electrodes. The outline of this display pattern is determined by the shape of the light transmitting portion 8 of the light shielding mask,
The portion where the display changes is only the display segment pattern portion which is determined by the electrodes facing each other, and the portion between the two always emits light so that the outline of the display pattern is displayed.

FIG. 4 is a plan view showing the shapes of the light-shielding mask pattern and the display segment pattern, where the light-shielding mask pattern (solid line) is provided slightly outside the display segment pattern (broken line) determined by the opposing electrode patterns. Is shown.

As a result, it is possible to obtain a display having a unique display design in which the outline of the display segment pattern is always displayed, and the segment electrode portion to be displayed appears to be in a bright state as in the case of a normal negative display.

Further, since the pattern of the light-transmitting portion of the light-shielding mask is made larger than the display segment pattern, even if the positions of the electrodes and the light-shielding mask are deviated, the contours will look slightly uneven within the range of this interval. However, there is an advantage that a situation such as misidentification is unlikely to occur, and the tolerance for the deviation of the pattern increases.

FIG. 3 shows an example of a pattern for displaying numbers 0 to 9 in 7 segments. If no voltage is applied to the display segments 11-18, all segments are in the bright state.
Next, when a required voltage higher than the threshold voltage of the liquid crystal is applied to one segment, the liquid crystal molecules rise in that part, the display segment pattern becomes dark, and the outline of the display segment pattern in that dark state and the voltage are applied. The display pattern of the non-application segment is recognized as the display pattern.
As an example, when a voltage is applied only between the electrodes corresponding to the segments 47 and 45, the display is 3, but the outlines of the dark segments 47 and 45 are also displayed. In this case, the background portion 10 of the cell is in the same bright state as that of the portion to which no voltage is applied, but is shielded by the light shielding mask 7 and is visually recognized as a dark state.

Therefore, the contrast of the R-TN cell of the present invention is analyzed in the same manner as in the above-mentioned conventional example, as follows. When an ideal polarizing plate is used and a sufficient applied voltage is applied, Toff≈O (4) Therefore, the contrast ratio (Ton / Toff) is close to infinity. Actually, only a finite contrast ratio can be obtained due to the characteristics of the polarizing plate or the limit of the applied voltage, but it is possible to make a dramatic improvement as compared with the conventional method. Table 1 shows the measurement results of the contrast ratio. The liquid crystal used is ZL made by Merck
I-1565, the polarizing plate is Q-12 manufactured by Nitto Denko Corporation, and the cell gap is 9.3 μm. The applied voltage was 10 V, the transmitted light intensity was measured in the direction perpendicular to the cell surface, and the values of Ton and Toff were represented by the output voltage of Photomul.

Further, the viewing angle is also important for practical use as a display device. As a result of various studies by the present inventors, the product Δnd of the refractive index anisotropy (Δn) of the liquid crystal and the cell gap (d) is 1.0 to
It has been found that a practical viewing angle can be obtained by setting 0.3 μm, more preferably 0.8 to 0.3 μm.

FIG. 5 is a graph showing the angle dependence of the contrast ratio together with a comparative example. FIG. 5A is a graph showing the relationship between the contrast ratio and the viewing angle.

In the R-TN cell which is the embodiment of the present invention, the cell gap is set to 5 μm, and in the conventional example, the cell gap is set to 9.3 μm and 5 μm. The conditions for the liquid crystal and the polarizing plate are the same as in Table 1. Further, FIG. 5 (b) is a perspective view showing the measurement angle condition, and the main visual field direction (θ> 0 °) and anti-visual field direction (θ <0 °) of the TN cell.
The angle dependence was measured.

As shown in FIG. 5, in the conventional cell, the viewing angle is widened by simply reducing Δnd, but the contrast ratio is small, while the viewing angle is increased by increasing the contrast in the vertical direction (θ = 0 °). While having the contradiction that the angle becomes narrow, the present invention was able to utilize the excellent characteristics of both.

Further, in the present invention, if a polarizing plate having a high degree of polarization is used, the value of Toff can be further reduced, and Ton / To
It is also possible to set the contrast ratio of ff to 1000 or more, and it is possible to obtain a negative liquid crystal display device having a high contrast ratio that could not be obtained by the conventional negative liquid crystal display device.

Example 2 A negative liquid crystal display device similar to that of Example 1 was manufactured except that the light-shielding mask of Example 1 was provided on the inner surface of the cell.

This liquid crystal display device has the advantage that the contrast ratio is the same as that of the first embodiment and that the displacement of the electrodes and the light shielding mask when viewed from an oblique direction is unlikely to occur.

The structure of the present invention is not limited to the example shown in the embodiment of FIG. 1, but can be applied to TN cells, and can be applied to liquid crystal materials including the use of color filters, color polarizing plates and various light guide plates. The addition of the dichroic dye, the active element may be provided on the substrate.

The light-shielding mask of the present invention may be arranged on the back side of the cell, or may be arranged on the front side of the cell or the inner surface of the cell.

However, in applications requiring a wide viewing angle or applications requiring a fine display pattern, a display defect may occur if there is a parallax between the shape of the light-shielding mask and the display segments 11-18. Therefore, in such a case, it is preferable to provide a light shielding mask on the inner surface of the TN cell 4.

Further, in the present invention, since the background portion is darkened by the light-shielding mask, light is not necessary for that portion, and by concentrating the light of the light source on the display pattern portion, a brighter display is possible. It is possible to provide a reflection plate that reflects light on the back surface of the back side or the back side of the back side polarizing plate excluding the display pattern portion, or to use a light guide plate that radiates light only to the display pattern portion.

In addition, Δn of the nematic liquid crystal used has a preferable region in consideration of a practical cell gap of 6 to 10 μm, and is 0.03
≦ Δn ≦ 0.17, and more preferably 0.03 ≦ Δn ≦ 0.13
Is. As a liquid crystal material with a small Δn, Compounds having a trans-cyclohexane ring such as

[Effect of the Invention] As described above, according to the present invention, not only the lack of contrast of the conventional negative type TN cell is eliminated, but also the viewing angle is improved.

Further, in the present invention, the pattern of the light-transmitting portion of the light-shielding mask is provided so as to include a portion outside the display segment pattern defined by the opposing electrode pattern, and the pattern of the light-transmitting portion of the light-shielding mask is the display segment pattern. Since it is larger than the above, a unique display design in which the contour of the display segment pattern is always displayed is generated.

Further, even if the positions of the electrodes and the light-shielding mask are displaced due to misalignment in the manufacturing process, the width of the contour will be slightly uneven within the range of this interval, and the visibility will be remarkably reduced or misidentified. This also has the advantage of being less likely to occur and having a high degree of tolerance for pattern shifts.

In particular, by forming the light-shielding mask on the inner surface of the cell, the electrodes and the light-shielding mask are less likely to be displaced even when viewed from an oblique direction, and the appearance is good.

Further, there is a secondary effect that the response speed is improved because the cell gap can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. 2 is a perspective view showing a configuration example of a conventional negative display type TN liquid crystal display device. FIG. 3 is a partially enlarged view of FIG. FIG. 4 is a plan view showing an example of a display segment pattern (broken line) and a light-shielding mask pattern (solid line) according to the present invention. FIG. 5A is a graph showing the angle dependence of the contrast ratio, and FIG. 5B is a perspective view showing the measurement angle condition. 1 ... Illumination light source, 2 ... Color filter, 3 ... Polarizing plate,
4 ... TN cell, 5 ... polarizing plate, 6 ... voltage applying means, 7
…… Shading mask, 8 …… Light transmitting part, 11 to 18 …… Display segment

Claims (4)

[Claims] 1. A lighting means, a nematic liquid crystal layer having a helical structure of about 90 °, a plurality of transparent supports sandwiching the nematic liquid crystal layer and having electrodes, and light at a position corresponding to a display pattern. A light-shielding mask with a transparent portion formed,
In a twist-lenematic liquid crystal display device including a pair of polarizing plates provided on the outer side of a transparent support and a means for applying a voltage to electrodes, a light-transmitting portion provided on a light-shielding mask is defined by opposing electrodes. It is provided so as to include a portion outside the display segment pattern, and the polarization axes of the respective polarizing plates are arranged so as to be orthogonal to each other, and the excitation voltage is applied between the electrodes other than the electrodes corresponding to the desired display pattern. A twist-lenematic liquid crystal display device characterized by applying a voltage. 2. The twisted nematic liquid crystal display device according to claim 1, wherein the product Δnd of the refractive index anisotropy (Δn) of the liquid crystal and the thickness (d) of the liquid crystal layer is 0.3 to 1.0 μm. 3. The twist-lenematic liquid crystal display device according to claim 1, wherein the polarizing axis of the polarizing plate is parallel or orthogonal to the alignment direction of the liquid crystal molecules adjacent to each other. 4. The twist-lenematic liquid crystal display device according to claim 1, wherein a light-shielding mask is formed on the inner surface of the cell.