JP2007264168A - Two-layered liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-layered liquid crystal display device of a normally black display type that prevents a display section from forming a striped pattern. <P>SOLUTION: The liquid crystal display device has a liquid crystal display unit having a drive cell 11 which changes the twist orientation state of liquid crystal molecules by applying an electric field to liquid crystal 22 charged between a pair of glass substrates 20 and 21 having transparent electrodes 18 and 19; and a compensation cell 12 formed by charging liquid crystal 28 which is opposite in twist orientation from the liquid crystal 22 of the drive cell 11 and equal in twist angle between a pair of glass substrates 26 and 27. The drive cell 11 and compensation cell 12 are disposed between polarizing plates 13 and 14 in parallel continuously by spacers 31. Then a transparent TAC (cellulose triacetate) film 35 having no birefringence is fixed to an external surface of the glass substrate 21 as the front side of the drive cell 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device having a liquid crystal two-layer structure including a drive cell and a compensation cell.

A liquid crystal display device having a D-STN (double-super twisted nematic) structure is widely known as a liquid crystal display device having a liquid crystal two-layer structure.
FIG. 5 is a schematic configuration diagram of this type of liquid crystal display device. As shown in FIG. 5, a liquid crystal double layer in which a drive cell 11 and a compensation cell 12 are arranged in parallel between two polarizing plates 13 and 14. It has a configuration.

The drive cell 11, the compensation cell 12, and the polarizing plates 13 and 14 are covered with a resin cover 17 together with the backlight unit 15 and the drive circuit board 16, and are configured as a display unit of one display device. ing.
In the following description, the side where the backlight unit 15 is present is referred to as the back side, and the side where the polarizing plate 14 is present is referred to as the front side.

FIG. 6 is a cross-sectional view showing a specific configuration example of the display unit including the driving cell 11, the compensation cell 12, and the polarizing plates 13 and 14.
As shown in the figure, the drive cell 11 holds the liquid crystal 22 between a pair of glass substrates (transparent substrates) 20 and 21 on which transparent electrodes 18 and 19 are formed.

Further, the transparent electrodes 18 and 19 are provided with alignment films 23 and 24 on the surfaces facing each other.
The seal material 25 adheres the periphery of the transparent electrodes 18 and 19 and encloses the liquid crystal 22 between the glass substrates 20 and 21.

The compensation cell 12 has a configuration in which a liquid crystal 28 is sandwiched between a pair of glass substrates (transparent substrates) 26 and 27 whose periphery is bonded by a seal material 32.
The glass substrates 26 and 27 are provided with alignment films 29 and 30 on the surfaces facing each other.

  Further, the compensation cell 12 has a configuration in which the glass substrate 26 on the back side and the glass substrate 21 on the front side of the driving cell 11 described above are connected in parallel to the driving cell 11 by connecting them with a spacer 31. ing.

As described above, the drive cell 11 includes the transparent electrodes 18 and 19 for driving the display, but the compensation cell 12 does not include the transparent electrode because it does not drive the display.
Further, the liquid crystal 22 of the driving cell 11 and the liquid crystal 28 of the compensation cell 12 use the same liquid crystal material, and the cell thickness is also the same, so that the retardation of both cells is equal.

However, the twist direction of the liquid crystal is reversed between the driving cell 11 and the compensation cell 12.
For this purpose, a chiral material having a reverse twist direction is added to the liquid crystal 22 of the drive cell 11 and the liquid crystal 28 of the compensation cell 12. The twist angle (for example, 180 degrees) is the same.

  On the other hand, as shown in FIG. 7, the rubbing directions of the alignment films 23 and 24 of the drive cell 11 and the alignment films 29 and 30 of the compensation cell 12 are orthogonal to each other, and the polarization axis direction of the polarizing plate 13 And the polarization axis direction of the polarizing plate 14 are orthogonal Nicols.

  7A shows the polarization axis of the polarizing plate 13 disposed on the back side, and FIG. 7B shows the rubbing direction of the alignment film 23 of the driving cell 11 and the dotted line the rubbing direction of the alignment film 24. 7C, the solid line shows the rubbing direction of the alignment film 29 of the compensation cell 12, the dotted line shows the rubbing direction of the alignment film 30, and FIG. 7D shows the polarization axis of the polarizing plate 14 arranged on the front side. Each is shown.

The above-described liquid crystal two-layer display device has high contrast and high quality display characteristics that are not easily affected by temperature changes.
For this reason, although two liquid crystal cells are required and the cost is high, they are widely used for in-vehicle applications.

On the other hand, the drive cell 11 and the compensation cell 12 are attached by the spacer 31 so as to maintain a constant distance (about 0.05 mm to 0.5 mm).
This is because when the drive cell 11 and the compensation cell 12 are brought into close contact with each other, light interference occurs and the interference is observed as an interference fringe when the display device is viewed.

However, even in the conventional liquid crystal display device as described above in which a fixed interval is provided between the driving cell 11 and the compensation cell 12, the fringe pattern similar to the interference fringe as shown in FIG. Occurs with probability.
For this reason, in a D-STN type liquid crystal display device in which the base is black display (normally black display), the stripe pattern as described above deteriorates the display quality. Generated products are treated as defective products.

In addition, defective products are discovered for the first time in the state in which components such as drive circuits and backlights are incorporated, so the processing of defective products is discarded as products, which reduces manufacturing costs. It is an obstacle.
Moreover, since the waste is produced in units of products, there is a problem that the amount of waste is large and the environmental load is increased.
As a result, the production cost of the liquid crystal display device increases.

In addition, it is thought that the above-mentioned stripe pattern is not an interference fringe produced by a normal interference phenomenon.
Since the liquid crystal display device has a structure in which a medium having birefringence is sandwiched between two polarizing plates, it is complicated by reflection, refraction, phase shift, polarization axis shift, and wavelength dependency thereof. It is presumed that the phenomenon is superimposed in a complex manner and a fringe pattern different from the interference fringe is generated.

JP 2003-315826 A

  The problem to be solved is to prevent the occurrence of a striped pattern in the display section in a two-layer liquid crystal display device that performs normally-black display.

  In order to solve the above-described problems, in the present invention, as a first invention, a driving cell that changes the twisted alignment state of liquid crystal molecules by applying an electric field to liquid crystal sealed between a pair of transparent substrates having transparent electrodes. And a compensation cell in which a liquid crystal having the same twist angle and a twist orientation opposite to that of the liquid crystal of the driving cell is enclosed between a pair of transparent substrates, and two polarizing plates with their polarization axes orthogonal to each other, The drive cell and the compensation cell are arranged in parallel between the two polarizing plates, and at least one of the transparent substrates located on the opposite side of the drive cell and the compensation cell is substantially transparent without birefringence. A two-layer type liquid crystal display device characterized in that a film is fixed is proposed.

  As a second invention, a driving cell that changes the twisted alignment state of liquid crystal molecules by applying an electric field to liquid crystal sealed between a pair of transparent substrates having a transparent electrode, and the liquid crystal of the driving cell are opposite to each other. A compensation cell in which liquid crystals having a twisted orientation and an equal twist angle are sealed between a pair of transparent substrates, and two polarizing plates each having a polarization axis orthogonal to each other are provided, and the driving cell and the Compensation cells are arranged in parallel, and a resin film of a substantially transparent resin material having no birefringence is formed on at least one transparent substrate of these cells located on the opposite side of the drive cell and the compensation cell. A two-layer liquid crystal display device is proposed.

  According to a third aspect of the present invention, there is provided a driving cell that changes the twisted alignment state of liquid crystal molecules by applying an electric field to liquid crystal sealed between a pair of transparent substrates having transparent electrodes, and the liquid crystal of the driving cell is opposite to the driving cell. A compensation cell in which liquid crystals having a twisted orientation and an equal twist angle are sealed between a pair of transparent substrates, and two polarizing plates each having a polarization axis orthogonal to each other, the drive cell and the A two-layer structure in which a compensation cell and a compensation cell are arranged in parallel, and the space between the driving cell and the compensation cell is filled with a material having no birefringence and having a refractive index substantially equal to the glass refractive index. A liquid crystal display device is proposed.

  According to the liquid crystal display device of the first aspect of the present invention, display is performed with a simple configuration in which a transparent film having no birefringence is provided on the transparent substrate of one of these cells located on the opposite side of the driving cell and the compensation cell or one of the transparent substrates. Occurrence of the striped pattern on the part can be prevented.

  The transparent film provided in this way is not particularly limited in material and thickness as long as a certain degree of transmittance can be secured, but a film having birefringence is suitable because it is disposed between the driving cell and the compensation cell. Absent.

  According to the liquid crystal display device of the second invention, by a simple configuration in which a resin film of a transparent resin material having no birefringence is formed on both or one of these cells located on the opposite side of the driving cell and the compensation cell. Occurrence of a stripe pattern on the display portion can be prevented.

In the present invention, the resin film can be formed by a spray method or a printing method.
The resin film may be of any material and film thickness as long as a certain degree of transmittance can be ensured as in the transparent film of the first invention, but a resin material having birefringence is not suitable.

According to the liquid crystal display device of the third invention, it is possible to prevent the occurrence of a stripe pattern in the display unit by a simple configuration in which a substance having a refractive index substantially equal to the glass refractive index is filled between the refractive power cell and the compensation cell. Can do.
A material having birefringence is not suitable for the filling material.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating a configuration example of a display unit including a drive cell 11, a compensation cell 12, and polarizing plates 13 and 14 according to the first embodiment.

The present embodiment is characterized in that a TAC (cellulosic triacetate) film 35 is adhered to the outer surface of a glass substrate (transparent substrate) 21 located on the front side of the drive cell 11 to prevent the occurrence of a striped pattern. Others are the same as the conventional example shown in FIG.
In this embodiment, a transparent TAC film 35 having a thickness of 30 μm is used.
The TAC film 35 does not have birefringence.

As described above, the display unit provided with the TAC film 35 was used as a D-STN-LCD, and an experiment of display operation was conducted.
As a result of this experiment, no stripe pattern as observed in the conventional example was observed.
In this experiment, the display was driven before and after the TAC film was pasted, and it was confirmed that a striped pattern was generated before the film was pasted, and no striped pattern was confirmed after the film was pasted. .

  Moreover, in the said embodiment, although the TAC film 35 was provided in the glass substrate 21 of the drive cell 11, even if it affixes the TAC film 35 on the outer surface of the glass substrate 26 of the compensation cell 12, it is acquired by experiment. confirmed.

FIG. 2 is a sectional view similar to FIG. 1 shown as the second embodiment.
In the present embodiment, in addition to attaching the TAC film 35 to the outer surface of the glass substrate 21 located on the front side of the driving cell 11, the TAC film 36 is attached to the outer surface of the glass substrate 26 located on the back side of the compensation cell 12. It is characterized by wearing and preventing the occurrence of stripes.

The display unit constructed as described above was assembled as a D-STN-LCD, and the display operation was tested in the same manner as described above.
As a result of this experiment, no stripe pattern was observed as in the first embodiment.

FIG. 3 is a sectional view similar to FIG. 1 shown as the third embodiment.
The present embodiment is characterized in that a resin film 37 is formed on the outer surface of the glass substrate 21 located on the front side of the drive cell 11 to prevent the generation of a stripe pattern.

The resin film 37 was formed by applying an acrylic resin-based transparent paint with a spray.
The display unit of this embodiment was assembled as a D-STN-LCD, and a display operation experiment was performed in the same manner as described above.
As a result of this experiment, a striped pattern as seen in the conventional example was not observed.

  In this embodiment, the resin film is provided on the glass substrate 21 located on the front side of the drive cell 11, but the resin film 37 may be formed on the outer surface of the glass substrate 26 located on the back side of the compensation cell 12. Experiments confirmed that similar effects were obtained.

FIG. 4 is a sectional view similar to FIG. 1 shown as the fourth embodiment.
This embodiment is characterized in that an optical adhesive 38 having a refractive index of 1.49 is poured between the driving cell 11 and the compensation cell 12 and cured to prevent the generation of a stripe pattern.
The optical adhesive 38 can be replaced with another material that has no birefringence and has a refractive index approximately equal to the glass refractive index.

The display unit of this embodiment was assembled as a D-STN-LCD, and a display operation experiment was performed in the same manner as described above.
As a result of this experiment, bubbles may be introduced when the optical adhesive 38 is poured, so that even if the generation of the stripe pattern can be prevented, the bubbles were visually recognized to some extent.
Therefore, it is necessary to minimize the generation of bubbles when the optical adhesive 38 is poured.

On the other hand, in the present invention, an experiment was conducted to confirm that the occurrence of the above-described stripe pattern is different from the normal interference phenomenon.
In this experiment, the display unit as shown in FIG. 6 was assembled and displayed as a D-STN-LCD module, and it was confirmed that this module generates a stripe pattern.

  After that, the module is disassembled to take out the drive cell and the compensation cell, and further, they are disassembled, and the substrate of the drive cell and the substrate of the compensation cell facing each other in the module state are modularized. When they are overlapped in the same state as in the state, pressed down by hand and brought into close contact with each other to generate normal interference fringes, the interference fringes observed in the module state are clearly different in shape. confirmed.

  It can be used for a liquid crystal display device having a liquid crystal double layer structure such as a D-STN-LCD.

It is sectional drawing of the display unit shown as 1st Embodiment. It is sectional drawing of the display unit similar to FIG. 1 shown as 2nd Embodiment. It is sectional drawing of the display unit similar to FIG. 1 shown as 3rd Embodiment. It is sectional drawing of the display unit similar to FIG. 1 shown as 4th Embodiment. It is a schematic block diagram of the liquid crystal display device shown as a prior art example. It is sectional drawing which shows the display unit of the conventional liquid crystal display device shown in FIG. It is a figure which shows the rubbing direction of the drive cell and compensation cell with which the conventional liquid crystal display device shown in FIG. 5 is provided, and the polarization axis direction of a polarizing plate. 6 is a photograph showing a stripe pattern seen in the conventional liquid crystal display device shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Drive cell 12 Compensation cell 13, 14 Polarizing plate 20, 21 Glass substrate 22 Liquid crystal 23, 24 Light distribution film 25 Seal material 26, 27 Glass substrate 28 Liquid crystal 29, 30 Alignment film 31 Spacer
32 Seal material 35, 36 TAC film 37 Resin film 38 Optical adhesive

Claims (3)

A drive cell that changes the twisted alignment state of liquid crystal molecules by applying an electric field to liquid crystal sealed between a pair of transparent substrates having transparent electrodes;
A compensation cell in which a liquid crystal having a twist orientation opposite to that of the liquid crystal of the drive cell and having the same twist angle is sealed between a pair of transparent substrates;
And two polarizing plates with their polarization axes orthogonal to each other,
The driving cell and the compensation cell are arranged in parallel between the two polarizing plates,
Further, a two-layer type liquid crystal display device characterized in that a substantially transparent film having no birefringence is fixed to at least one transparent substrate of the driving cell and the compensation cell located on the opposite side of the cell. A drive cell that changes the twisted alignment state of liquid crystal molecules by applying an electric field to liquid crystal sealed between a pair of transparent substrates having transparent electrodes;
A compensation cell in which a liquid crystal having a twist orientation opposite to that of the liquid crystal of the drive cell and having the same twist angle is sealed between a pair of transparent substrates;
And two polarizing plates with their polarization axes orthogonal to each other,
The driving cell and the compensation cell are arranged in parallel between the two polarizing plates,
Furthermore, a two-layer type liquid crystal display device characterized in that a resin film made of a substantially transparent resin material having no birefringence is formed on at least one transparent substrate of these cells located on the opposite side of the driving cell and the compensation cell. A drive cell that changes the twisted alignment state of liquid crystal molecules by applying an electric field to liquid crystal sealed between a pair of transparent substrates having transparent electrodes;
A compensation cell in which a liquid crystal having a twist orientation opposite to that of the liquid crystal of the drive cell and having the same twist angle is sealed between a pair of transparent substrates;
And two polarizing plates with their polarization axes orthogonal to each other,
The driving cell and the compensation cell are arranged in parallel between the two polarizing plates,
Furthermore, a space between the drive cell and the compensation cell is filled with a substance having no birefringence and having a refractive index substantially equal to the glass refractive index.

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