JPH04214528A - liquid crystal device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device for displaying images, and more particularly to a ferroelectric liquid crystal display device.

0002

2. Description of the Related Art In recent years, ferroelectric liquid crystals have come to be used as large-screen, large-capacity liquid crystal display elements in place of nematic liquid crystals, which have been widely used in the past. Although ferroelectric liquid crystals have characteristics such as high-speed response and bistability, they also have the following problematic properties. That is, (1) the switching threshold of ferroelectric liquid crystals changes greatly with temperature, and the response speed becomes slower as the temperature decreases. (2) Ferroelectric liquid crystals have different structures depending on the temperature; they have a layered structure in a chiral smectic phase and have ferroelectric properties, but in a low temperature range they change from the chiral smectic phase to a crystalline state. Once crystallized, it does not return to the chiral smectic phase even at room temperature; it must be heated to a cholesteric phase or an isotropic liquid crystal phase and then slowly cooled. (This heat treatment is called reorientation.) (3) When a liquid crystal panel is subjected to an external mechanical force, the layer structure of the ferroelectric liquid crystal collapses, which tends to cause alignment defects such as sanded texture. If an image is displayed in this state, the regular switching of the ferroelectric liquid crystal will be impaired, making it impossible to obtain a good image. In this case as well, there is no self-healing property and reorientation treatment is required.

In order to solve the above-mentioned problems, a liquid crystal display device having a built-in heater as shown in FIG. 7 has been considered in the past, as described in Japanese Unexamined Patent Publication No. 1-237521. In the figure, 701 is a liquid crystal panel in which ferroelectric liquid crystal is sealed, and there are upper deflection plates 70 on both sides of the liquid crystal panel.
7. A lower polarizing plate 708 is adhesively fixed via an adhesive and supported on a support base 709. Further, 703 is a backlight for illuminating the liquid crystal panel 701, and a flat heating element 702 is closely attached to the surface of the backlight. The flat heating element 702 has a transparent electrode formed on one entire surface of a glass plate, and lead-out electrodes coated with conductive paint at both ends. A circuit board 704 includes a liquid crystal drive circuit and a heating element control circuit, and is connected to the liquid crystal panel 701 through leads 706 and to the flat heating element 702 through leads 710. The heating element control circuit on the circuit board 704 is connected to the temperature sensing element 7 attached to the liquid crystal panel 701.
The amount of heat generated by a flat heating element 702 (hereinafter referred to as a heater) is controlled by the temperature signal from 05.

0004

However, the liquid crystal display device using a heater like the conventional example described above has the following problems. That is, since the heater is in contact with other members such as the backlight, heat is absorbed by the backlight member, reducing heat generation efficiency and widening the temperature distribution of the heater. In particular, since the peripheral edges of the heater are exposed, the heat dissipation becomes even larger, and the temperature in the peripheral area decreases, increasing the temperature variation within the LCD panel surface. It was difficult to display a uniform image over the entire panel.

Further, when the temperature of the heater is further increased to realign the ferroelectric liquid crystal panel, the following problems occur. In order to perform reorientation, it is necessary to heat the ferroelectric liquid crystal to the temperature of the cholesteric phase or isotropic liquid phase, but these temperatures are generally as high as 70 to 90°C. On the other hand, the heat resistance temperature of polarizing plates is generally as low as 70 to 80 degrees Celsius.
The backlight is also sensitive to heat because it uses plastic parts. In the conventional example described above, the polarizing plate and backlight are in contact with or close to the heater, so during reorientation, the temperature of the polarizing plate and backlight member approaches or exceeds the heat-resistant temperature, which may cause deformation of these members. However, there was a problem that the polarizing plate peeled off or bubbles were generated. Additionally, at high temperatures, polarizing plates undergo thermal contraction in the direction of the polarization axis (the direction in which the polarizing film is stretched during manufacturing), but mechanical distortion occurs in the liquid crystal panel because the polarizing plate is directly attached to the liquid crystal panel. . Therefore, there are disadvantages in that orientation defects occur and switching threshold characteristics change, making it impossible to obtain a uniform image.

Furthermore, in the conventional example, since the liquid crystal panel is defenseless against external mechanical forces such as drop impact and vibration, alignment defects occur every time the liquid crystal panel is subjected to mechanical stress. Frequent reorientation will be required. Therefore, maintenance of the liquid crystal display device becomes complicated, and the number of times reorientation is performed increases, which further accelerates thermal deterioration of members such as polarizing plates, resulting in a shortened lifespan of the display device.

[0007]

[Means for Solving the Problems (and Effects)] In order to solve the above-mentioned problems, the present invention provides a means for reducing the temperature variation of the heater. It is characterized by no contact. Furthermore, it is characterized by a structure in which the liquid crystal display panel and the heater are suspended in a substantially sealed space provided inside the liquid crystal display device by an elastic member. Therefore, according to the present invention, when controlling the predetermined temperature of the liquid crystal panel using a heater, it is possible to obtain a uniform image because the temperature variation on the liquid crystal panel surface is reduced, and the liquid crystal display device It is possible to prevent a decrease in reliability.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 is a sectional view of a liquid crystal display device according to a first embodiment of the present invention. In FIG. 1, 100 is a liquid crystal panel in which a ferroelectric liquid crystal (not shown) is sandwiched between two opposing glass substrates 101 and 102 with a gap of about 1.4 μm. The phase of the ferroelectric liquid crystal used in this example changes from an isotropic liquid phase to a cholesteric phase to a smectic A phase to a chiral smectic C phase to a crystalline phase from the high temperature side, and among these, the chiral smectic C phase is ferroelectric. shows. The temperature range for the chiral smectic C phase is about -15°C to 55°C, and for the cholesteric phase about 75°C to 85°C. Next, 103 is an upper polarizing plate, 104 is an upper polarizing plate glass for bonding the upper polarizing plate 103, 105 is a lower polarizing plate, and 106 is a lower polarizing plate glass for bonding the lower polarizing plate 105. 107 is a backlight for illuminating the liquid crystal panel 100, and 108 is a diffusion plate for converting the light emitted from inside the backlight 107 into scattered and diffused light.The lamps, reflectors, etc. inside the backlight 107 are not shown. do not have.

Reference numeral 109 is a printed wiring film using, for example, a TAB film, which is electrically connected to the electrode portion of the liquid crystal panel 100, and 110 is a circuit board for driving the liquid crystal panel 100. 111 is a panel fixing board made of plastic, for example, for fixing the liquid crystal panel 100 and the circuit board 110; 112 is applied to the upper peripheral part of the liquid crystal panel 100, especially around the entire circumference near the sealing part of the liquid crystal, and fixes the liquid crystal panel 100 to the panel. It is a rubber-based adhesive for adhering to the substrate 111. Reference numeral 113 denotes a frame-shaped support member for supporting the opening panel fixing substrate 111, and an elastic member 11 made of, for example, a rubber-based silicone adhesive is placed between the opening and the peripheral edge of the panel fixing substrate 111.
4 is filled. Reference numeral 115 denotes a housing that supports the frame-shaped support member 113, and a lower polarizing plate glass 106 is installed in the opening of the housing.
is fixed with adhesive, for example, and the backlight 107 is fixed with screws or the like (not shown). At this time, the diffusion plate 108 at the top of the backlight is in surface contact with the lower polarizing plate 105, but in order to prevent interference fringes caused by contact, the diffusion plate 108
The surface of 08 has been subjected to anti-glare treatment such as graining. Reference numeral 116 indicates a screw (for example) attached to the frame-shaped support member 113.
This is a plastic cover for fixing the upper polarizing plate glass 104 using, for example, double-sided tape (not shown). 117 is the liquid crystal panel 100
The heater is fixed to the liquid crystal panel 100 by applying a rubber adhesive 118 all around its upper surface. As shown in FIG. 2, the heater 117 is provided with, for example, an IT
Transparent electrode 202 made of O(In2O3-SnO2) film
The extraction electrode 2 has a conductive paint applied to both ends.
03 is provided. Reference numeral 119 in FIG. 1 is a board having a heater control circuit, and the housing 115 is fixed with, for example, screws (not shown), and the amount of heat generated by the heater 117 is controlled by a temperature signal from a temperature detection element 120 attached to the liquid crystal panel 100. are doing. Reference numeral 121 indicates a liquid crystal panel 100, a heater 117, adhesives 112 and 118, and a panel fixing substrate 1.
11, a substantially sealed space surrounded by an elastic member 114, a support member 113, a housing 115, and a lower polarizing plate glass 106. Reference numeral 122 is a small hole through which a wiring cable is passed through for the purpose of supplying electric signals to the circuit board 110, through which the substantially sealed space communicates with the outside air. It also serves to pass the power supply line to the heater 117 and the lead wire (not shown) of the temperature detection element 120. The size, position, shape, number, etc. of the small holes 122 can be arbitrarily set within a range that satisfies the function of a substantially closed space, which will be described later. For example, a rectangular hole may be used. Although the support member 113 and the housing 115 are separate members in this embodiment, they may be integrated.

Next, the characteristics of the liquid crystal display device having the above structure will be described. In the liquid crystal display device described above, the heater 117 can be used to heat the liquid crystal panel 100 in order to maintain the high-speed response of the ferroelectric liquid crystal. The objective is to maintain the temperature constant at a predetermined temperature (referred to as Tc) within the temperature range that indicates the chiral smectic C phase, and to obtain uniform image quality by minimizing temperature variations within the surface of the liquid crystal panel. In this embodiment, the heater 117 does not come into contact with any other member except the liquid crystal panel 100, and is present in the substantially sealed space 121, so that the heat from the heater 117 is efficiently transferred to the liquid crystal panel. At the same time, heat radiation from the peripheral portion of the heater 117 is also reduced compared to the conventional example.

FIG. 3 schematically shows the characteristics of the conventional example (indicated by a broken line) and the present embodiment (indicated by a solid line) regarding the temperature distribution on the surface of the liquid crystal panel 100 when only the heater 117 is energized and heated. This is what is shown. In reality, it has a unique gentle distribution due to resistance value variations that occur during the heater fabrication process, but it is omitted here for the sake of clarity. Here, the horizontal axis represents the position of the liquid crystal panel, and corresponds to the position of the heater along line X-X' in FIG. The vertical axis indicates the temperature increase value due to heater heating, and represents the temperature distribution when the temperature increase value at the O point in the center of the liquid crystal panel is made equal for both the conventional example and the present example. Temperature rise value at center O point is 20deg, 40deg, 60deg
The temperature distributions at deg are A, B, and C, respectively. However, as mentioned above, since the heater of this embodiment has a higher thermal efficiency, it goes without saying that the actual power consumption of the heater required is less than that of the conventional example. In reality, the temperature distribution of the LCD panel is also affected by the backlight, drive IC, and the LCD panel's own heat generation, except during reorientation, but compared to these, the heater generates a large amount of heat, and it depends on the surrounding environment temperature. Since the effect is significant, here we will discuss the temperature distribution on the liquid crystal panel surface when only the heater is heated.

Now, A, B, and C in FIG. 3 correspond to the following situations. That is, when the control temperature Tc of the liquid crystal panel is 45°C, A shows the temperature distribution of the liquid crystal panel when the liquid crystal panel is heated and held at 45°C when the environmental temperature is 25°C, and similarly, B shows the temperature distribution of the liquid crystal panel when the environmental temperature is 25°C. This is the temperature distribution when the liquid crystal panel is held at 45°C when the temperature is as low as 5°C. C is the temperature distribution when the liquid crystal panel is heated to 85° C. for reorientation when the environmental temperature is 25° C. It can be seen from FIG. 3 that the larger the amount of heat generated by the heater, that is, the larger the temperature rise, the larger the temperature variation, and that the temperature drop in the peripheral area of the liquid crystal panel is smaller in this example than in the conventional example. Therefore, temperature variations within the surface of the liquid crystal panel are reduced, making it possible to display a uniform image over the entire surface of the panel.

Next, when the liquid crystal panel crystallizes in a low-temperature environment or suffers from mechanical stress and orientation defects such as sanded texture occur, the ferroelectric liquid crystal is converted into a cholesteric phase or an isotropic liquid. A reorientation process of heating to a phase and then slow cooling is required. For the ferroelectric liquid crystal used in this example, it is desirable to raise the temperature to an isotropic liquid phase in order to make the alignment state of the liquid crystal panel uniform. The lower limit temperature must be 85°C or higher. As shown in C in Figure 3, in the conventional example, there is a large temperature variation, so it is necessary to further increase the temperature in order to reach the periphery of the liquid crystal panel at 85°C or higher, and the temperature at point O in the center of the liquid crystal panel increases further. It gets hot. On the other hand, this embodiment has the advantage that the temperature variation is smaller than that of the conventional example, so the temperature of the liquid crystal panel surface is low, and the power consumption of the heater is small. Further, since the polarizing plate and the backlight member are installed apart from the heater, the temperature reached by these members during reorientation is lower than in the conventional example, and there is no problem of thermal deterioration of these members. In addition, since the polarizing plate is not directly attached to the liquid crystal panel, the reorientation process can be performed reliably without causing mechanical distortion to the liquid crystal panel.
It becomes possible to obtain a uniform alignment state.

Furthermore, this embodiment is characterized by a structure having a substantially closed space, which was previously proposed by the present inventors for the purpose of improving shock resistance and vibration resistance. Therefore, in the liquid crystal display device of this embodiment, alignment defects do not occur unless a very severe impact is applied, and there is no need to perform realignment as frequently as in the conventional example. Therefore, it is easy to use as a liquid crystal display device, easy to maintain, and there is no thermal deterioration of members such as deflection plates, which improves the reliability of the liquid crystal display device. (Other Embodiments) FIG. 4 shows a second embodiment of the present invention. In the figure, members with the same reference numerals as in FIG. 1 are the same members as in FIG. In this embodiment, the heater 4 is used to further reduce the temperature variation of the liquid crystal panel 100 compared to the first embodiment.
01 is larger than the size of the liquid crystal panel 100. That is, by making the heat generating area of the heater relatively larger than the area of the display section of the liquid crystal panel, it is possible to further reduce the temperature drop in the peripheral area of the liquid crystal panel 100. Also, with this configuration, many of the same effects as in the first embodiment can be obtained.

FIG. 5 is a plan view of a heater 500 used in a third embodiment of the present invention. The structure of the liquid crystal display device of the third embodiment is the same as that of the first embodiment shown in the figure except for the heater 500. (not shown) Heater 5
00, a plurality of band-shaped transparent electrodes serving as a heat generation source are formed in a striped manner in parallel on a glass substrate 501. These band-shaped transparent electrodes consist of wide electrodes 502 (referred to as correction electrodes) formed at the left and right ends, and multiple narrow electrodes 503 (referred to as main electrodes) formed inside. ing. Although the main electrodes 503 are formed on the entire interior surface at regular intervals, only a portion is shown in the figure and the rest is omitted. At both ends of the correction electrode 502 and the main electrode 503, a low-resistance extraction electrode 504 for applying a voltage is provided. Figure 6 is Figure 5
To explain the details of the electrode shape of the heater 500,
This is a schematic enlarged view of a part of the electrode. Figure 5
The individual main electrodes 503 have a symmetrical shape in the vertical and horizontal directions, and have different electrode widths at the ends and inside, and have a tapered shape between them. a is the electrode width at the end of the main electrode, c is its length, b is the width of the wide electrode part, e is its length, d
is the distance from the end of the wide electrode section, and P is the pitch between the main electrodes. Further, f indicates the width of the correction electrode, and g indicates the distance from the main electrode. In this example, the dimensions are 300 x 300 mm.
, the specific resistance ρ was measured by sputtering on a glass substrate with a thickness of 1.1 mm.
After forming an ITO film of 1000 Å with a thickness of 3×10 −4 Ωcm, transparent electrodes were formed in the pattern shown in FIG. 6 using photolithography. At this time, a=100μ
m, b = 140 μm, c = 10 mm, d = 50 mm, e
=200mm, p=g=250μm, f=10mm. In addition, as the voltage application electrode 504, Al3000
A heater 500 was formed by forming .ANG. on both ends of the transparent heating electrode.

The liquid crystal display device of this embodiment having the heater configured as described above has the following features. That is, at the ends of the main electrode, the electrode width is small, so the current density increases and the amount of heat generated increases compared to the center, and at the left and right ends of the heater, the width of the correction electrodes is wide, so the amount of heat generated increases. Therefore, there is almost no temperature drop on the four sides around the heater, and it is possible to further reduce temperature variations in the liquid crystal display panel compared to the first embodiment. Further, in FIG. 6, the main electrode and the correction electrode made of ITO are formed independently, but they may be connected at the upper and lower ends (positions directly below the Al extraction electrode). The extraction electrode is not limited to Al either, and may be formed by, for example, Ag paste printing, ultrasonic solder, copper foil tape, or a combination of these. Also in this embodiment, the same effects as described in the first embodiment can be obtained.

Although the ferroelectric liquid crystal has been explained above,
It goes without saying that the liquid crystal panel and Harter support structure of the present invention are also useful for neck liquid crystals from the viewpoint of improving impact resistance and image quality. Furthermore, the present invention is not limited to transmissive liquid crystal display devices, but is also effective for reflective liquid crystal display devices. In this case, the backlight member shown in FIG. 1 does not have an illumination function but becomes a support member that has a reflection function. Furthermore, although the shape of the main electrode in FIG. 6 is vertically and horizontally symmetrical, the values of the pattern shape parameters a to g and p can be appropriately selected depending on the actual temperature distribution of the liquid crystal panel. It is also possible to combine the shapes of the heaters in the second and third embodiments.

[0018]

[Effects of the Invention] As explained above, according to the present invention, the heater does not come into contact with any other components except the liquid crystal panel and exists in a substantially closed space, so that heat radiation from the surrounding area of the heater is reduced. It is characterized by small temperature variations on the liquid crystal panel surface, and the following effects can be obtained. (1) In a liquid crystal display device whose high temperature is controlled using a heater, a uniform image can be displayed on the entire liquid crystal display surface regardless of the ambient temperature. (2) Since the heating efficiency of the liquid crystal panel by the heater is high, the power consumption of the heater can be reduced. (3) There is no thermal deterioration of heat-sensitive members such as polarizing plates and backlights, and the reliability of the liquid crystal display device can be greatly improved. (4) Due to the air damper effect of the nearly sealed space, it is possible to prevent the alignment of the liquid crystal panel from deteriorating due to external mechanical forces, drop shocks, and vibrations that occur during transportation or use of the liquid crystal display device. There is no need to perform alignment treatment frequently, and the practicality (ease of use) and maintainability of the liquid crystal display device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a perspective view of the heater used in FIG. 1.

FIG. 3 is a characteristic diagram showing temperature distribution of a liquid crystal panel.

FIG. 4 is a sectional view of a liquid crystal display device showing a second embodiment of the present invention.

FIG. 5 is a plan view of a heater used in a third embodiment of the present invention.

FIG. 6 is an enlarged view of the pattern of the heater in FIG. 5;

FIG. 7 is a cross-sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

100 LCD panel 103 Upper polarizing plate 105 Lower polarizing plate 107 Backlight 110 Circuit board 111 Panel fixing board 113 Support member 114 Elastic member 115 Housing 117 Heater 120 Temperature sensing element 121 Almost closed space 122 Small hole 501 Glass substrate 502 Correction electrode 503 Main electrode 504 Extraction electrode

Claims (9)

[Claims] [Claim 1] a. A liquid crystal panel having a pair of substrates provided with electrodes and a liquid crystal disposed between the substrates b. A panel fixing substrate for fixing the liquid crystal panel c. A support member that supports the panel fixing board d. an elastic member that suspends and fixes the panel fixing substrate to the support member; and e. A flat heating element is fixed to the panel, and a space surrounded by the liquid crystal panel, the panel fixing substrate, the supporting member, the elastic member, and the flat heating element is a substantially sealed space. Characteristic liquid crystal device. 2. The liquid crystal device according to claim 1, wherein the area of the heat generating portion of the flat heating element is larger than the area of the display portion of the liquid crystal panel. 3. The liquid crystal device according to claim 1, wherein the flat heating element has a transparent electrode formed on a transparent substrate. 4. The liquid crystal device according to claim 1, wherein the transparent electrode is composed of a plurality of strip-shaped electrodes, and the heat generation density at the peripheral portion of the flat heating element is greater than the heat generation density at the center portion. . 5. Claim 1, wherein the support member has a puck light that illuminates the liquid crystal panel.
The liquid crystal device described in Section 1. 6. The liquid crystal device according to claim 1, wherein the elastic member is a rubber adhesive. 7. The liquid crystal device according to claim 1, wherein the flat heating element is fixed to the liquid crystal panel via an adhesive and does not come into contact with other members. 8. The liquid crystal device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal. 9. The liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal.