JP2001272664A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device having a wide visual field angle, bright display and excellent display characteristics. SOLUTION: The liquid crystal display device is provided with a pair of substrates 11 opposed to each other and having polarizing plates 13 whose polarization axes are orthogonal to each other and a liquid crystal layer 15 interposed between the substrates 11. The liquid crystal layer 15 holds liquid crystal molecules 17 in a region divided by a polymer wall 16 having a face parallel to the substrates 11 and the liquid crystal molecules 17 are aligned in a plane parallel to the substrates 11 in a light transmitting state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device is lightweight, thin, driven at a low voltage, and consumes low power, and is widely used as a display device for watches, calculators, notebook computers, personal computer monitors, and the like. The most widely used TN type liquid crystal display system at present has a display characteristic comparable to that of a CRT by incorporating an active switch element such as a TFT, and has been used in televisions and the like.

However, the TN type liquid crystal display device has a problem that the viewing angle is narrow, and various methods have been proposed to solve this problem. As methods for improving the viewing angle of the TN type liquid crystal display device, a method using a retardation film or a diffusion sheet, and a method for averaging the orientation direction of liquid crystal molecules in a liquid crystal cell are known. Regarding the former method, a viewing angle improving optical compensation film using a discotic liquid crystal has recently been developed. Regarding the latter method, an IPS method in which liquid crystal molecules are turned on and off in a plane parallel to the substrate, a VA method in which the voltage of a liquid crystal molecule is divided by applying a voltage to a vertical alignment cell using n-type liquid crystal, and the like have been proposed. ing.

As a method for improving the viewing angle, a method using a liquid crystal dispersed polymer (PDLC) cell has been proposed (Japanese Patent No. 2945143). PDLC
The cell is made by polymerizing the polymer after injecting the liquid crystal material and the polymer material into the cell, because the cell is made by randomly dispersing liquid crystal molecules in the region partitioned by the polymer. The size and shape of each region are different. Polarizing plates are attached to both sides of such a cell in a crossed Nicols state, and display is performed utilizing scattering caused by a difference in refractive index between the polymer and the liquid crystal. When the voltage is turned off, the light incident on the cell is scattered at the polymer / liquid crystal interface and passes through the polarizing plate, resulting in white display. When the voltage is turned on, the difference in the refractive index from the polymer interface is reduced due to the orientation of the liquid crystal molecules, so that scattering is reduced and black display is performed. Although this display method has improved viewing angle characteristics as compared with the TN method, there is a problem in that the use of scattering causes a large loss of light and darkens the display.

[0005]

As described above, it is important to improve the viewing angle of a liquid crystal display device in order to improve the display quality, but it is difficult to obtain a bright display by the conventional method. there were.

An object of the present invention is to provide a liquid crystal display having a wide viewing angle, a bright display, and excellent display characteristics.

[0007]

A liquid crystal display device according to the present invention comprises a pair of substrates having polarizing plates whose polarization axes are orthogonal to each other and facing each other, and a liquid crystal layer sandwiched between the substrates. The liquid crystal layer holds liquid crystal molecules in a region defined by a polymer wall having a plane parallel to the substrate, and the liquid crystal molecules are aligned in a plane parallel to the substrate in a light transmitting state. I do.

[0008] In the liquid crystal display device, it is preferable that a region defined by the polymer wall is formed of microcapsules.

In general, light that has passed through a polarizing plate changes its polarization state in a substance having optical anisotropy. Therefore, light is transmitted when the polarization axes of a pair of polarizing plates are orthogonal to each other (crossed Nicols state). I do. Conversely, since the polarization state is maintained in a substance having no optical anisotropy, no light is transmitted in the crossed Nicols state.

When a liquid crystal layer is sandwiched between polarizing plates in a crossed Nicols state, if liquid crystal molecules are oriented parallel to the polarizing plate, that is, parallel to the substrate surface, the liquid crystal will have optical anisotropy, and light will be generated. Will be transmitted. At this time, if the liquid crystal molecules are randomly oriented in a plane parallel to the substrate surface, the linearly polarized light incident on the liquid crystal layer can pass through the opposing polarizing plate because the polarization state changes variously, and Since the liquid crystal molecules are randomly aligned, a display having a wide viewing angle characteristic can be performed. On the other hand, when the liquid crystal molecules are oriented perpendicular to the polarizing plate, that is, perpendicular to the substrate surface, light is not transmitted because they are optically isotropic.

In the present invention, the liquid crystal layer is formed of a microcapsule (normally, the size of each microcapsule is almost the same, and the shape of each microcapsule is also almost the same).
By arranging the liquid crystal molecules randomly in a plane parallel to the substrate surface, and by arranging a pair of polarizing plates so that the polarization axes are orthogonal to each other, the above-described state can be achieved. ing. In such a structure, the viewing angle characteristics are not improved by scattering light as in the related art, but the optical anisotropy of the liquid crystal is used, so that light loss can be reduced, It is possible to realize a liquid crystal display device which is bright and has excellent display characteristics with a wide viewing angle.

Further, by making the cross-sectional shape of the microcapsules in a direction perpendicular to the substrate surface substantially rectangular, it is possible to further facilitate the random alignment of the liquid crystal molecules in a plane parallel to the substrate surface. Also, the refractive index anisotropy Δ of the liquid crystal molecules
By reducing n to 0.1 or less, scattering of light in the liquid crystal layer can be reduced, and a brighter display can be realized. Further, the difference between the refractive index of the polymer and the refractive index of the liquid crystal molecules in the minor axis direction is set to 0.01 or less, and the difference in the refractive index between the polymer and the liquid crystal during light-blocking display (black display) is reduced. And the light leakage at the time of black display can be significantly suppressed, and the display contrast can be improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a liquid crystal display device according to the present invention, schematically showing a state during white display (during light transmission display).

A pair of opposing glass substrates (transparent substrates) 1
A transparent electrode 12 is formed on the opposing surface of the first substrate 1, and a pair of polarizing plates 13 are arranged on the outer surface of each glass substrate 11 so that their polarization axes are orthogonal to each other. A liquid crystal layer 15 having a plurality of liquid crystal microcapsules 14 arranged in layers is sandwiched between the opposing glass substrates 11.
In the liquid crystal microcapsules 14, liquid crystal molecules 17 are held in a region surrounded by a polymer wall 16, and the size and shape of each microcapsule 14 are substantially uniform, and the cross-sectional shape is substantially square. I have.

FIG. 2 is a plan view of the liquid crystal layer 15 shown in FIG. The direction of the long axis of each liquid crystal molecule 17 held in the liquid crystal microcapsule 14
1 is a direction parallel to the opposing surface, that is, a direction parallel to the surface of the polarizing plate 13, and is a random direction in a plane parallel to the opposing surface of the glass substrate 11.

Although FIG. 2 shows only two directions of orientation of the liquid crystal molecules 17, they are actually oriented in countless random directions. Further, in the figure, the alignment directions of the liquid crystal molecules 17 are aligned in each liquid crystal microcapsule 14, but as described above, the liquid crystal molecules 17
And the alignment direction of the liquid crystal molecules 17 between the liquid crystal microcapsules 14 may be random,
The orientation direction of the liquid crystal molecules 17 in each liquid crystal microcapsule 14 may be random.

FIG. 3 is a cross-sectional view schematically showing a state of the liquid crystal display device shown in FIG. 1 at the time of black display (at the time of light blocking display). As shown in the figure, each liquid crystal molecule 17 has a direction perpendicular to the facing surface of the glass substrate 11, that is, the polarizing plate 13.
Are oriented in a direction perpendicular to the plane.

Hereinafter, an example of a manufacturing method for manufacturing the liquid crystal display device shown in FIGS. 1 to 3 will be described.

First, an ITO film having a thickness of 100 nm was deposited as a transparent conductive film on a transparent glass substrate having a thickness of 0.7 mm, and the ITO film was patterned to produce a glass substrate with a transparent electrode.

The liquid crystal microcapsules have a polymer wall composed mainly of diisobutyl fumarate (DIBF) and a P-type nematic liquid crystal (Δn =
0.0601). The polymer wall material is DIBF
However, general acrylic polymers such as methyl methacrylate (MMA) and isobutyl methacrylate (PIBM) can be used.

The liquid crystal material may be a nematic liquid crystal, and may be P-type or N-type. When using N type,
It is necessary that the polymer be provided with vertical orientation and be vertically oriented when no voltage is applied. In this case, the display is normally black, and when a voltage is applied, the liquid crystal is aligned in parallel with the substrate, and the display becomes white.

If the difference between the refractive index n _{p of the} polymer and the refractive index n ₁ of the liquid crystal material during black display (corresponding to the refractive index of the liquid crystal molecules in the short axis direction) is large, light leakage occurs due to scattering. The black level decreases, and the contrast characteristics deteriorate. FIG.
Shows the relationship between the refractive index difference | n _p −n ₁ | and the contrast. As can be seen from the relationship shown in this figure,
When the refractive index difference | n _p −n ₁ | is 0.01 or less, a contrast of 100 or more can be obtained, but the refractive index difference | n _p −n ₁ |
If it exceeds 01, the contrast will be lower than 100. Therefore, it is preferable to set the refractive index difference | n _p −n ₁ | to 0.01 or less.

Further, even when the birefringence (refractive index anisotropy) Δn of the liquid crystal material is large, scattering at the polymer interface increases, and the display characteristics deteriorate. When Δn was 0.08, a contrast of about 100 to 150 was obtained. Measurement of more liquid crystal materials revealed that Δn was about 0.1 or less and the contrast was 100 or more. Therefore, the birefringence Δn of the liquid crystal material is preferably 0.1
Or less, more preferably 0.08 or less.

The liquid crystal microcapsules were synthesized by a film emulsion polymerization method. In the present embodiment, the ratio (volume ratio) of the liquid crystal material in the liquid crystal microcapsules made of the liquid crystal material and the polymer is 90%, but the ratio of the liquid crystal material is 80% to 9%.
It is possible to arbitrarily select between 8%. The higher the ratio of the liquid crystal material, the greater the ratio of the substantial display portion. In particular, by setting the ratio of the liquid crystal material to 90% or more, favorable display can be obtained.

The particle size of the capsule is 3 μm, 10 μm, 20
Three types of liquid crystal microcapsules of μm were produced. After preparing the prepared liquid crystal microcapsules for ink for printing, the liquid crystal microcapsules were applied to a glass substrate with a transparent electrode by screen printing so that the film thickness was about 5 to 10 μm. Further, the applied film was dried at about 100 ° C. At this time, when the alignment state of the liquid crystal molecules was observed, it was confirmed that the liquid crystal molecules were randomly aligned in the plane.

Thereafter, the other glass substrate is stacked so as to face the glass substrate on which the liquid crystal microcapsule film is formed as described above, and is heated under a load in an oven at 100 ° C. for several hours. The liquid crystal cell was fabricated by pressing the substrate and bonding the periphery. Further, a polarizing plate was stuck on both glass substrates such that their polarization axes were orthogonal to each other, to obtain a liquid crystal display device.

When a voltage was applied to the obtained liquid crystal display device and the transmission contrast was measured, the microcapsules having a particle size of 3 μm were 100: 1, those having a 10 μm particle size were 120: 1, and those having a 20 μm particle size were 90: 1, and a good display could be obtained. At this time, the brightness of the panel was reduced to about 65% when the particle size of the microcapsules was 3 μm as compared with the case where the particle size was 10 μm, and the brightness was insufficient. This is presumably because when the size of the liquid crystal domain is small, scattering increases and light transmittance decreases. The microcapsules have a particle size of 20μ.
Observation of the pixel with a microscope using a microscope revealed that coloring of the liquid crystal due to retardation was observed in a part of the display portion. Therefore, the size of the liquid crystal domain is about 5 μm to 20 μm.
It is considered that about μm is preferable.

When the number of liquid crystal domains (corresponding to liquid crystal microcapsules) of the liquid crystal layer is large, and when the thickness of the liquid crystal layer is large, it is necessary to increase the driving voltage. When the number of layers is four or more, and when the film thickness is 10 μm or more,
The threshold voltage exceeded 10 V, which proved to be impractical. Therefore, it is desirable that the number of laminated liquid crystal microcapsules is 3 or less, and the thickness of the liquid crystal layer is 10 μm or less. From the viewpoint of increasing the effect of random orientation, the number of layers is preferably two or more.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

For example, a film other than glass can be used for the substrate. The transparent conductive film is made of IT
It is also possible to print the O particle dispersion liquid in a pixel shape and sinter it. As for the driving method, either a simple matrix or an active matrix can be used, but active matrix driving is preferable in consideration of display quality. Further, in order to improve the display contrast, a retardation plate may be appropriately attached.

In addition, the present invention can be variously modified and implemented without departing from the spirit thereof.

[0033]

According to the present invention, it is possible to obtain a liquid crystal display device having excellent display characteristics by improving the viewing angle characteristics and obtaining a bright display with little light loss.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a state of a liquid crystal display device according to the present invention during white display.

FIG. 2 is a plan view schematically showing a state of a main part of the liquid crystal display device shown in FIG.

FIG. 3 is a sectional view schematically showing a state of the liquid crystal display device shown in FIG. 1 at the time of black display.

FIG. 4 is a diagram showing a relationship between a refractive index difference | n _p −n ₁ | between a refractive index n _{p of a} polymer and a refractive index n ₁ of a liquid crystal material during black display, and display contrast.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Glass substrate 12 ... Transparent electrode 13 ... Polarizer 14 ... Liquid crystal microcapsule 15 ... Liquid crystal layer 16 ... Polymer wall 17 ... Liquid crystal molecule

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masao Tanaka 1-term, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term in the Toshiba R & D Center (reference) 2H089 HA06 QA16 RA05 SA01 TA01 TA09 TA15 2H091 FA08X FA08Z GA01 GA13 HA05 HA07 LA17 5C094 AA12 AA60 BA43 EA05 EB02 ED14 HA08

Claims (5)

[Claims] 1. A substrate comprising a pair of substrates having polarizing plates whose polarization axes are orthogonal to each other and facing each other, and a liquid crystal layer sandwiched between the substrates, wherein the liquid crystal layer has a surface parallel to the substrate. A liquid crystal display device, wherein liquid crystal molecules are held in a region defined by a polymer wall, and the liquid crystal molecules are aligned in a plane parallel to the substrate in a light transmitting state. 2. The liquid crystal display device according to claim 1, wherein the area defined by the polymer wall is made of a microcapsule. 3. The liquid crystal display device according to claim 2, wherein a cross-sectional shape of the microcapsules in a direction perpendicular to the facing surfaces of the pair of substrates is substantially rectangular. 4. The liquid crystal molecule has a refractive index anisotropy Δn of 0.1.
The liquid crystal display device according to claim 2, wherein: 5. The liquid crystal display device according to claim 2, wherein the difference between the refractive index of the polymer wall and the refractive index of the liquid crystal molecules in the minor axis direction is 0.01 or less.