JPH03241319A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a uniform display over the entire surface of a liquid crystal display element by controlling the thicknesses of orientated films, thereby correcting a driving voltage distribution. CONSTITUTION:This device is provided with the liquid crystal display element 10 and a rear light source 20. The liquid crystal display element 10 is provided with substrates 1, electrodes 2, the orientated films 3, and liquid crystals 4. The back light source 20 irradiates the liquid crystal display element 10 from its back. In this case, irregularity in driving voltage caused by the rise of liquid crystal temperature due to the back light source is corrected by the thicknesses of the orientated films. That is, the thicknesses of the orientated films are thinner in a lower temperature area and thicker in a higher temperature area according to a liquid crystal temperature distribution caused by the back light source. Thus, a driving voltage to be applied is made optimum even when a temperature distribution occurs in the liquid crystals, and the irregularity in display can be prevented.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a liquid crystal display device, and aims to correct the unevenness of drive voltage caused by temperature rise of liquid crystal due to a backlight source by adjusting the film thickness of an alignment film. The liquid crystal display element has a substrate, an electrode, an alignment film, and a liquid crystal, the back light source illuminates the liquid crystal display element from the back, and the substrate is a transparent It is made of a glass plate, and the electrode is a transparent conductive thin film that is adhered to the substrate and is provided in a striped shape,
The alignment film is an insulating thin film that is adhered to the electrodes, and the liquid crystal is injected into a gap between two substrates facing each other and sealed together so that the electrodes intersect. The alignment film has a thickness that is thinner at low temperatures and thicker at high temperatures, corresponding to the temperature distribution of the liquid crystal caused by the backlight source. Configure it as follows.

[Industrial application field]

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which unevenness in drive voltage caused by temperature rise of liquid crystal caused by a backlight source is corrected by the thickness of an alignment film.

With the rapid progress in electronics in recent years, which has led to smaller and lighter equipment, there has been a growing demand for displays, which are one of the elemental devices of the human-machine interface, to be smaller and lighter.

The LCD, which uses a liquid crystal display element, is an alternative to the CRT display that has been widely used in the past.
(Liquid Crystal Display,
(liquid crystal display) is attracting attention.

LCDs were once considered slow operating speeds, low contrast, difficult to colorize, and complex drive circuits, making them unsuitable for displays with very large display capacities.However, with recent advances in new liquid crystal materials and drive methods, With innovative developments such as the development of CRT displays and the improvement of display elements, it has become possible to create a display that is as good as a CRT display.

However, in order to achieve uniform display quality throughout the large screen, there is still room for consideration in terms of manufacturing technology.

[Conventional technology]

Liquid crystal display elements move large molecules in a relatively viscous liquid and use optical effects such as polarization to obtain a display. Generally, the response is slow, so liquid crystal display elements It was said that the LCD used was not suitable for displaying fast-moving images such as moving images.

However, TN (Twist Nematic) liquid crystals and S T N (Super
A new liquid crystal material called TN) liquid crystal has been developed, and TF T (Thin Film Tran) has been developed.
With the development of a drive IC for the so-called active matrix drive system in which thin film transistors (sisters, thin film transistors) are arranged for each pixel, there is a prospect that a display comparable to a CRT will be realized.

Furthermore, in addition to conventional reflective displays that utilize incident incident light, transmissive displays that use a liquid crystal display element as a type of light valve and use a back light source, also called a bat light, have come into practical use. Displays can now be seen even in dark places, and LCDs using liquid crystal display elements are attracting attention not only for portable TVs but also as displays for small information devices such as personal computers.

FIG. 6 is a cross-sectional view of the structure of an example of a conventional transmissive liquid crystal display device, FIG. 7 is a diagram showing the relationship between temperature and driving voltage, and FIG. 8 is a diagram showing the relationship between driving voltage and transmittance.

In the figure, 1 is a substrate, 2 is an electrode, 3 is an alignment film, 4 is a liquid crystal, and 5
is a seal, 10 is a liquid crystal display element, 2o is a back light source, 30
is a liquid crystal display device.

In FIG. 6, the substrate 1 is a glass plate on which, for example, transparent IT○ (Indium Tin Oxid) is coated.
e) Two so-called transparent conductive glasses provided with electrodes 2 made of films are used.

Then, on each substrate 1, electrodes 2 are provided in a striped manner in the X direction and the Y direction by, for example, machining, chiming, etc.
When the two substrates 1 are stacked, the intersection of the electrodes 2 is, for example, 64
It has a so-called matrix electrode configuration that becomes a pixel of 0.times.400 dots.

On this electrode 2, for example, a polyurethane film ξ with a film thickness of several tens of nanometers is placed.
An alignment film 3 made of polyvinyl alcohol or polyvinyl alcohol is provided, but since it is necessary to form the alignment film 3 very thinly, it is provided by, for example, a transfer printing method. And 1. The surface of the alignment film 3 is subjected to alignment treatment by mechanical rubbing called rubbing.

The liquid crystal 4 includes a TN type liquid crystal display element 10 shown here.
In this case, a liquid crystal material called nematic type is used.

By the way, the substrate 1 on which the electrode 2 and the alignment film 3 are attached is 2
The respective electrodes 2 of the two substrates 1 are stacked so as to cross each other, and the periphery is sealed with a seal 5 made of, for example, a thermosetting adhesive with a minute gap of, for example, 7 μm. Then, the liquid crystal 4 is injected, for example, under vacuum, into this minute gap through an injection port that is partially unsealed 5, and then sealed liquid-tightly.

In this way, the liquid crystal display element 10 is completed, and when the back light source 20 is disposed on the back side of this liquid crystal display element 10, a liquid crystal display device 30 is obtained.

Molecules of the injected liquid crystal 4 are exposed to the upper and lower alignment films 3 sandwiched between them.
They are twisted and oriented in a spiral manner according to the orientation direction of each shift.

Then, when a voltage is applied to the electrode 2, this orientation is released and the electrodes are aligned in the direction of the electric field, that is, in the thickness direction of the gap. Differences in the state in which the molecules of the liquid crystal 4 are twisted and oriented or aligned in the direction of the electric field can be used for display, and this allows the liquid crystal display element 10 to be of a twisted nematic (TN) type. That is why it is called.

Which state, the oriented state in which no voltage is applied to the electrode 2 or the state in which the orientation is released by applying a voltage, should be a bright state through which light is transmitted or a dark state through which light is not transmitted is determined by
It can be arbitrarily determined by the arrangement of polarizing plates (not shown).

In this diagram, the alignment state where no voltage is applied to the electrodes 2 is defined as a bright state, and the state where voltage is applied and the alignment is released is defined as a dark state, and the voltage required to release the alignment state of the liquid crystal 4 is defined as the drive voltage. It is called.

On the other hand, it is preferable that the back light source 20 is disposed on the back side of the liquid crystal display element 10 and irradiates every corner of the substrate 1 uniformly. For this purpose, thin EL (electroluminescent element) light sources and light sources that combine a cold cathode discharge tube and a diffuser plate are also used. The heat generated by the backlight source 20 causes a temperature distribution between the center and the periphery of the liquid crystal display element 10.

Incidentally, the liquid crystal display element 10 controls the movement of large viscous liquid crystal molecules using an electric field. Therefore, it is essentially unavoidable that the movement of molecules is influenced by the viscosity of the material of the liquid crystal 4 itself. Moreover,
The viscosity of the liquid crystal 4 depends on the temperature, which is also essentially unavoidable. In other words, when the temperature is low, the viscosity decreases, making it difficult for molecules to move, and when the temperature is high, the viscosity decreases, making it easier for liquid crystal molecules to move.

Such temperature-dependent behavior of the liquid crystal 4 appears as a difference in the driving voltages applied to the electrodes 2, as shown in FIG. In other words, if the temperature is low, the liquid crystal molecules are difficult to move, so a higher driving voltage is required. If the temperature is high, the liquid crystal molecules are easier to move, so the orientation of the liquid crystal 4 can be released with a lower driving voltage.

However, since the drive voltage applied to the electrode 2 is generally constant within the range of variation determined by the circuit constants of the drive circuit,
When there is temperature unevenness in the liquid crystal display element 10, the temperature unevenness causes unevenness in the alignment state of the liquid crystal molecules.

In FIG. 8, the applied driving voltage is ■. At this time, in the central part (high temperature part) of the liquid crystal display element 10 indicated by the broken line,
Since the temperature is relatively high, the liquid crystal molecules are in a state where they are easy to move, and the orientation is completely released and the state becomes dark. On the other hand, in the peripheral area (low-temperature area) of the liquid crystal display element 10 shown by the solid line, the temperature is relatively low and the liquid crystal molecules do not easily move, so the alignment is not yet solved and the area is in a bright state.

In this way, due to the influence of heat from the back light source 20, it sometimes happens that the liquid crystal display element 10 cannot display a uniform image over the entire surface.

[Problem to be solved by the invention]

In this way, when a backlight source that generates heat is used, temperature unevenness occurs between the center and the periphery of the liquid crystal display element, and when a predetermined driving voltage is applied, the temperature may vary due to unevenness in the molecular orientation of the liquid crystal. Unevenness appears in the light transmittance. Therefore, there is a problem that this unevenness in transmittance appears as display unevenness in the liquid crystal display element.

Therefore, an object of the present invention is to provide a liquid crystal display device in which the temperature unevenness of the liquid crystal caused by the back light source is corrected by the driving voltage effectively applied to the liquid crystal by the thickness of the alignment film. .

[Means to solve the problem]

The above-mentioned problem includes: a liquid crystal display element and a backlight source; the liquid crystal display element includes a substrate, an electrode, an alignment film, and a liquid crystal; and the backlight source includes a liquid crystal display element. The irradiation is from the back side, the substrate is made of a transparent glass plate, and the electrode is a transparent conductor! The alignment film is a thin film that is adhered to the substrate and is provided in a striped pattern, and the alignment film is an insulating thin film that is adhered to the electrode. The liquid crystal is injected into a gap between two substrates that are sealed facing each other so that the electrodes intersect, and the thickness of the alignment film corresponds to the temperature distribution of the liquid crystal caused by the back light source. This problem is solved by a liquid crystal display device configured to be thinner at low temperatures and thicker at high temperatures.

[For production]

As mentioned above, in a liquid crystal display device with a backlight source, a temperature distribution occurs in the liquid crystal due to the heat generated by the backlight source, and this temperature distribution causes a distribution in the optimal driving voltage for the liquid crystal, which in turn causes the display In contrast, in the present invention, even if temperature distribution occurs in the liquid crystal, the applied drive voltage is optimized to prevent unevenness from appearing in the display.

A liquid crystal display element is considered to constitute one circuit in which a resistance (R) and a capacitance (C) are connected. In other words, both the alignment film and the liquid crystal each have an impedance in which both the R and C components are connected in parallel. The alignment film to liquid crystal alignment film are connected in series between the upper and lower electrodes.

Therefore, the driving voltage applied to the upper and lower electrodes is distributed according to the impedance ratio between the two alignment films and the liquid crystal.

FIG. 5 is a diagram showing the relationship between the thickness of the alignment film and the drive voltage.

From the figure, the driving voltage of the liquid crystal display element has a good proportional relationship with the thickness of the alignment film, and as the thickness of the alignment film increases,
It can be seen that the driving voltage increases linearly.

Therefore, in the present invention, first, we first investigate in advance what kind of temperature distribution occurs in the liquid crystal of the liquid crystal display element due to the backlight source, and from the results, we can determine the distribution of the driving voltage of the liquid crystal display element. This can be understood from Figure 7.

Next, in order to make the distribution of drive voltage uniform,
How the thickness of the alignment film should be distributed can be understood from FIG. 6.

In this way, in a liquid crystal display device in which a backlight source is disposed on a liquid crystal display element under predetermined conditions, a certain shape (
(pattern) causes a drive voltage distribution in the liquid crystal of the liquid crystal display element due to temperature distribution, so if the thickness of the alignment film is controlled to correct this distribution, it is possible to obtain a liquid crystal display device with no display unevenness. can.

〔Example〕

FIG. 1 is a sectional view explaining the present invention in detail, FIG. 2 is a temperature distribution diagram, FIG. 3 is a film thickness distribution diagram of an alignment film, and FIG. 4 is a driving voltage distribution diagram.

In the figure, l is the substrate, 2 is the electrode, 3 is the alignment film, 4 is the liquid crystal, and 5
is a seal, 0 is a liquid crystal display element, 20 is a back light source, 30
is a liquid crystal display device.

In FIG. 1, transparent and smooth glass plates are often used for circuit board work except for special purposes. In this case, 200X3
00 mm uses a glass plate of %'A4 size.

The electrode 2 is, for example, an ITO film with a film thickness of several tens of nanometers, and is
is installed on top of the

This ITO film is etched in a stripe shape with a pinch of 0.33 mm and a pattern width of 0.3 mm in the X direction or Y direction, and when two substrates 1 are stacked facing each other,
It has a so-called matrix electrode configuration in which the intersections of the electrodes 2 form pixels of, for example, 640 x 400 dots.

On this electrode 2, an alignment film 3 made of polyimide or polyvinyl alcohol with a thickness of 50 nm, for example, is provided, and alignment treatment is performed by rubbing.

There are various film forming methods for depositing the alignment film 3, but it is necessary to have a thin film thickness and a film thickness distribution.
Since it is necessary to expose the electrode 2 in the peripheral area of , a transfer printing method using the alignment film material as ink is used.

As the liquid crystal 4 is a TN type liquid crystal display element 10, a liquid crystal material called a nematic type is used.

For the seal 5, for example, an epoxy-based thermosetting adhesive is used, and the two substrates 1 are placed facing each other with a gap of, for example, about 10 μm, and the seal 5 is made by going around the substrate 1 with a width of 1 mm, for example, leaving an injection port for the liquid crystal 4. It is applied as follows.

Then, when the liquid crystal 4 is injected under vacuum, the injection port is liquid-tightly sealed, and the liquid crystal display element 10 is completed.

The back light source 20 is a 20W incandescent light bulb, and is arranged at the back of the center part of the liquid crystal display element 10 with an interval of 70 mm,
It is covered with a cover 6 to constitute a liquid crystal display device 3o.

By the way, the liquid crystal 4 injected into the liquid crystal display element 10 is affected by the heat generated by the back light source 20, and a temperature distribution as shown in FIG. 2 occurs in the center and peripheral parts.

This temperature distribution is similar to that of the simulated liquid crystal display element 10.
The measurements were taken by applying thermopaint, which changes color depending on the temperature, to the inside of stacked glass plates at multiple measurement points.

Based on this result and the relationship between the thickness of the alignment film and the drive voltage shown in FIG. 5, the alignment film 3 is given a thickness distribution so that the drive voltage is corrected and becomes uniform regardless of the temperature distribution. .

That is, when depositing the alignment film 3, the size of the opening of the concave portion of the intaglio is distributed, so that the thickness of the alignment film 3 is 50 nm at the periphery and 70 nm at the center, as shown in FIG.
Make it so.

As shown in FIG. 4, the driving voltage of the liquid crystal display device 30 assembled with the substrate 1 having the alignment film 3 with a film thickness distribution is as shown in FIG. Despite having the temperature distribution shown in , the display quality is uniform in both the center and the periphery, and the temperature distribution is effectively corrected by the thickness of the alignment film 3 according to the present invention. was confirmed.

The shape of the temperature distribution and the absolute value of the thickness of the alignment film that corrects it,
The absolute value of the driving voltage depends on the backlight source, the physical properties of the liquid crystal material and alignment film material, the gap between the substrates, the constants of the driving circuit, etc., and various modifications are possible.

In addition, in order to give the alignment film a film thickness distribution, a transfer printing method is used, and in order to supply the ink of the alignment film material to the transfer roll, the size of the opening of the concave part of the intaglio plate with fine irregularities is adjusted. The film was distributed so that the film thickness was thicker in the center.

However, it is also possible to distribute the arrangement density of the recesses or the depth of the recesses, and various modifications are possible.

〔Effect of the invention〕

Compared to conventional liquid crystal display devices, where a temperature distribution occurs in the liquid crystal display element due to the heat generated by the backlight source, which causes a distribution in the driving voltage of the liquid crystal, making it impossible to obtain a uniform display over the entire surface of the liquid crystal display element. In the present invention, the distribution of driving voltage is corrected by controlling the thickness of the alignment film.

As a result, according to the present invention, there is more room for selection of backlight sources, which greatly contributes to expanding the applications of liquid crystal display devices.

[Brief explanation of drawings]

Fig. 1 is a sectional view explaining the present invention in detail, Fig. 2 is a temperature distribution chart, Fig. 3 is a film thickness distribution chart of the alignment film, Fig. 4 is a drive voltage distribution diagram, and Fig. 5 is a diagram of the alignment film. Figure 6 is a diagram showing the relationship between film thickness and drive voltage. Figure 6 is a cross-sectional view of the structure of an example of a conventional transmission type liquid crystal display. Figure 7 is a diagram showing the relationship between temperature and drive voltage. Figure 8 is drive voltage and transmittance. This is a diagram of the relationship between In the figure, 1 is a substrate, 3 is an alignment film, 10 is a liquid crystal display element, and 30 is a liquid crystal display device. 2 is an electrode, 4 is a liquid crystal, 20 is a back light source,

Claims (1)

[Claims] It has a liquid crystal display element (10) and a back light source (20), and the liquid crystal display element (10) has a substrate (1) and an electrode (2).
, an alignment film (3), and a liquid crystal (4), the back light source (20) irradiating the liquid crystal display element (10) from the back side, and the substrate (1) comprising: It is made of a transparent glass plate, and the electrode (2) is a transparent conductive thin film that is adhered to the substrate (1) and is provided in a striped pattern. The alignment film (3) is an insulating thin film that is attached to the electrode (2), and the liquid crystal (4) is attached to the substrate ( 1)-2
The alignment film (3) has a film thickness that corresponds to the temperature distribution of the liquid crystal (4) caused by the back light source (20). A liquid crystal display device characterized in that it is thinner in areas where the temperature is low and thicker in areas where the temperature is high.