JPS6223292B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid crystal display device that uses a field effect mode of a nematic liquid crystal and uses a polarizing plate to detect electrically modulated portions as characters, numbers, etc. More specifically, in a transmission type liquid crystal display device, a pattern is created by changing the orientation of liquid crystal molecules using a polarizing plate installed in the optical path before and after the liquid crystal cell, and a mirror is installed in this optical path to change the optical path. This relates to a method of reading a reflected mirror image, and in these arrangements, it relates to the arrangement of a diffuser plate and a polarizing plate so that a background or bright field portion is obtained by a transparent diffuser plate provided outside the cell. It used to be said that the stronger the outside light, the brighter the surroundings, the easier it was to see the display on LCDs, but in reality, when the surroundings were too bright, it was difficult to identify them by reflection of outside light on the LCD screen or stray light. This has the disadvantage that annoying light enters the pattern, reducing the apparent contrast of the display surface and making it difficult to see.Also, when trying to obtain sufficient contrast, the display becomes dark and requires supplementary lighting means. However, when attempts are made to display the display in color in order to obtain a higher marketability, it has various drawbacks for practical display, such as the inability to obtain display brightness. The present invention is based on a detailed study of these conventional methods and the discovery of a method that eliminates these drawbacks and can realize an extremely high contrast, bright and easy-to-see display without losing the advantages of liquid crystal. That is, Table 1 shows the drawbacks of the conventional method.

【table】

[Table] A to H in Table 1 are methods that have been used or tried in the past, and will be briefly explained. A has the most well-known structure in the past, in which the liquid crystal undergoes an optical change due to the application of a voltage, causing a so-called dynamic scattering (DS) phenomenon, which has the effect of scattering light. The purpose is to identify a predetermined pattern based on the optical difference between the scattering part and the non-scattering part. In the technology up to now, the intensity of this scattering is not large enough, and therefore it is extremely difficult to see the scattered image formed between the transparent electrodes in front of a dark background. Alternatively, the scattering intensity is substantially increased by using the surface as a reflecting mirror and reciprocating the optical path with weak light diffusivity. However, in this configuration, the parts that do not undergo any optical changes are transparent, so the mirrored parts directly reflect the observer's face and background, making it difficult to distinguish them from the pattern being displayed, and at the same time making the bright background invisible. This results in a substantial reduction in contrast when distinguishing between the pattern and the pattern to be projected or displayed. In order to improve this drawback, in the case shown in example B, a hood can be placed to provide a background such as a black object to the specular reflection position of the observer, but this does not allow the observer to face the display surface. This prevents viewing when placed in front and limits the viewing angle. Example C, which is a transmission type and is used as it is, has low practicality due to the insufficient scattering intensity as described above, and as shown in Example D, this drawback can be compensated for by using a light source placed in an appropriate location. This results in the loss of one of the major characteristics of liquid crystals, which is low power consumption. Furthermore, in recent years, liquid crystal display cells using a field effect mode have been actively applied to liquid crystal display cells using a dynamic scattering mode, as they have the characteristics of being able to obtain high contrast with lower voltage and power consumption. The field effect mode here refers to a mode in which the orientation of liquid crystal molecules changes due to an electric field, and this change can be detected using two polarizing plates. These include parallel-aligned molecules arranged in a spiral in a direction perpendicular to the electrode surface. The external shape of the display using field effect mode and the display using dynamic scattering mode,
The structural difference is that, as shown in FIG. 1, a liquid crystal cell 1 has a liquid crystal sandwiched between transparent supports 2 and 2' having two transparent electrodes 5 and 5', and linear polarizing plates 6 and 6 on both outer sides thereof.
The point is that by arranging 6', it is possible to effectively identify a portion that has undergone an electrical change. These contrasts are due to the difference between the molecular orientation when the voltage is saturated and the molecular orientation when no voltage is applied. A value that corresponds to the ratio when placed orthogonally is easily obtained. Therefore, these can be obtained as a predetermined pattern by comparing bright field and dark field, and whether the polarization direction of the original polarizing plate is parallel or perpendicular,
In addition, the molecular orientation in our cell is either vertical to the electrode surface (using liquid crystal with negative dielectric anisotropy) or horizontally spirally aligned (using liquid crystal with positive dielectric anisotropy). Depending on the application of the electric field, either a change from bright field to dark field or from dark field to bright field may occur. This means that it is possible to create either a negative display or a positive display of the pattern to be identified. In addition, the molecular orientation at the point of non-saturation with respect to the voltage can be maintained in a state where the long axis of the molecules is inclined to the electrode surface. It also includes the ability to create color displays, similar to transmitting specific wavelengths. An example of a liquid crystal display device using such a field effect mode that has been put into practical use will be shown below. Example E is the most typical example using these devices, and has a structure that includes a polarizing plate, a field-effect liquid crystal cell, a polarizing plate, and a diffuse reflection plate. It is something. One major drawback of this display device is that it uses a linear polarizer.
The most commonly used linear polarizing plate that can be put to practical use is one in which a stretched plastic film containing dichroic molecules is bonded to a substrate film. One is that, in principle, the light transmittance cannot be made sufficiently large in terms of practical cost. The limit is that it can only pass about 50% of linearly polarized light compared to unpolarized light. As the transmittance approaches the limit value, the polarizing ability decreases, and this essentially limits the brightness of the display. When trying to make the display as bright as possible, with the structure shown in the example of E, in order to obtain a sufficiently bright background and a dark pattern, the observer can directly detect the area changed by the electric field by using two polarized lights. The combination of looking through the board and simultaneously looking at the shaded area of the area that has undergone this change due to external light allows you to see the area that has apparently undergone the change with twice the density. can. From a practical standpoint, there is a limit to the thickness of the substrate glass used for the cell, which results in a misalignment between the directly observed area and the shadowed area, resulting in the formation of a double image. This is particularly good for display patterns that are combinations of large areas, but it is very troublesome for combinations of thin lines or dotted patterns, and especially when viewed from an angle, it becomes a problem. It is also possible to make this shadow part as thin as possible so that it cannot be discerned by the observer.This can be done by thickening the back side of the substrate glass used or increasing the diffusivity of the reflector. When it decreases, it results in a problem of decreased optical density. Also, if the diffusivity of the reflector is made too large, the amount of bright field light reaching the observer will be reduced and the background will become substantially darker. Although positive displays with a reflective structure have these drawbacks, they have sufficient contrast when observed from the front and can be used for practical purposes, but they do not meet the requirements of many optical elements. As mentioned above, liquid crystal displays are also more versatile, and can satisfy the requirements for use in dark rooms, that is, to be able to see the same level of visibility even in the darkness that is equivalent to the limit that normal printed matter can be read. It's not a thing. On the other hand F
As shown in the example above, negative display is possible in principle as described above, but this is because the display pattern is made up of thin lines and small dots. When forming a pattern as a set of relatively small areas, two polarizing plates placed at a distance from each other will receive this small optical modulation, which is exactly the opposite effect mentioned in example E. It has a slit-like effect in which only the top and bottom of the part are open, making it difficult for light from the surroundings to reach the reflecting plate. This drawback that it is difficult for light other than light that is relatively close to normal incidence to reach the bright field area results in the bright field of the pattern not being able to obtain a sufficient amount of light. Therefore, the actual value is lower than that of the former reflective type positive display. A transmission type cell using field effect mode uses a cell similar to a reflection type, but uses a diffuse transmission plate behind the cell instead of a diffuse reflection plate.
Outside light passes through from the direction of the diffuser-transmitting plate behind this and forms the background of the bright field. This method is an example shown in G and H, but it has similar drawbacks to the DS display mentioned above, and in G, it has extremely good contrast and brightness, especially when there is a bright window or skylight behind it. However, if you place it on a table or a regular stand and try to view it at an angle that looks down on the display, it is not possible to display the diffused transmitted light under such bright external light, and the use of a light source is not as described above. Similarly, the power consumption is high, so the application is limited. The method according to the present invention is based on a detailed study of these conventional methods, and it takes into account a layout that makes maximum use of windows and ceiling light as external light behind the device, and allows the display to be placed on a tabletop or stand. Based on the above, these images do not show the reflected image of the background, the viewing angle can be selected arbitrarily, and the images can be viewed with sufficient brightness and high contrast. Furthermore, there is no double image, and extremely good results can be obtained even in negative display.
Furthermore, it maintains the low power consumption that is the original characteristic of LCD,
In addition, the display can be observed from the front, and the effect of enlarging or reducing the display can be used as desired. Another effect is that it provides a structure most suitable for realizing color field-effect displays. It also has various features, such as literally the brighter the surroundings, the easier it is to see the display, and on the other hand, the display can be read within the same range as characters printed on normal white paper in a dark room. The invention is based on the discovery of an optical arrangement which provides a bright display which does not present any practical problems in addition to the basic structure which makes it possible to realize these features. The basic structure of the present invention is shown in FIGS. 2 and 3. 9 is a liquid crystal cell equipped with a predetermined first polarizing plate and a light transmitting diffuser plate; 10 is a reflecting mirror; 11 is the main body of the device that requires display; An effect type liquid crystal cell, a second polarizing plate (not shown), and a reflecting mirror are provided in this order from the light incident side in front of the second polarizing plate and after the field effect type liquid crystal cell. 8 is external light and 7 is an observer. 1
2 is an image of the display directly seen by the observer. These liquid crystal cells are connected to a predetermined drive circuit, but are not shown in the figure. Fig. 4 shows the structures shown in Figs. 2 and 3, in which the 10 reflecting mirrors are used as concave mirrors in a for enlarged display, and in b the 10 are used as convex mirrors for reduced display. be. Furthermore, a cylindrical mirror with convex and concave reflecting mirrors can also be used. In addition to these basic structures, the present invention is characterized in that the diffuser-transmitting plate is arranged so that there are more horizontal parts than vertical parts. As shown in FIG. 5, there is a horizontal component h and a vertical component v with respect to the external light incident surface of the diffuser plate. The present invention is based on the discovery that by increasing the horizontal component h in this way, outside light can be brought in effectively in most cases. That is, as a result of testing various situations in which these devices were used, it was found that reading was performed using more than 70% of external light coming from above. In other words, whether it is from a ceiling light or from outside light coming through a window during the day, when used outdoors, as long as the device using these devices is placed in a position that looks down on it, there is a lot of light coming from above. The effect is achieved in exactly the same way for the act of reading under the influence of bright ambient light, which is customary in the United States. That is, when reading in a dark place, the object is placed facing the bright direction, and when the observer's back is to the bright direction, this arrangement provides sufficient readability. As a means for effectively supplementing such an arrangement, it is preferable to arrange the reflection angle of the mirror surface used so that the optical path is sent to the observer in the direction of specular reflection for these vertically incident components from above. These devices are equipped with a diffuser transmitting plate 13 arranged such that the horizontal component h is larger than the vertical component v, as shown in FIG.
diffuses a lot of external light 8' coming from above, becomes linearly polarized by the first linear polarizing plate 6, passes through the field effect liquid crystal cell 14, and although these are omitted in the figure, it produces a desired pattern of electricity. A part of it passes through the target modulation part,
The other light passes through according to the characteristics of this cell, and a desired pattern is revealed by the other second polarizing plate (not shown). These are extremely good conditions for daylighting, and can be identified as a clear pattern when viewed from below. However, since such conditions cannot be created with commonly used equipment, the observer 7 can see the mirror image 12 using the reflector 10. The display can be observed as FIG. 6 shows an example of a structure in which the arrangement according to the invention can be further put to practical use. Reference numeral 13 denotes a diffuser-transmitting plate, which is arranged according to the present invention. 15 is a transmission type field effect cell using a first polarizing plate on the light incident side of the cell,
The observer 7 can identify the pattern using the reflecting mirror 10 and the display window 16 in which the second polarizing plate is arranged. These displays using the method according to the present invention have the various features described above, and are particularly suitable for providing bright and easy-to-read displays under various usage conditions.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one configuration of a liquid crystal display device, and FIGS. 2 to 6 are explanatory diagrams of configuration examples of the present invention. 1...Liquid crystal cell, 2,2...Substrate, 3,3'...
...Spacer, 4...Liquid crystal, 5,5'...Electrode,
6, 6'... Polarizing plate, 7... Observer, 8... Incident light, 8'... External light, 9... Liquid crystal cell with built-in polarizing plate and diffuse transmission plate, 10... Reflecting mirror, 11 ……
Main body of display device, 12... Display image, 13... Diffuse transmission plate, 14... Field effect liquid crystal cell, 15...
Field-effect liquid crystal cell with built-in polarizing plate, 16...
Display window, 17...keys, 18...desk calculator.

Claims (1)

[Claims] 1 Diffuse transmission plate, first polarizing plate, field effect liquid crystal cell, second polarizing plate, and in front of the second polarizing plate and after the field effect liquid crystal cell, place a reflective mirror from the light incident side in this order. A liquid crystal display device characterized in that the horizontal component of the arrangement of the diffuser-transmitting plate is equal to or greater than the vertical component.