KR19980031931A - LCD - Google Patents

Abstract

A liquid crystal display device having a novel structure capable of improving a wide viewing angle is disclosed. The liquid crystal display device includes a rear substrate having pixels arranged on its surface, an alignment film formed on the rear substrate, an optical fiber plate spaced apart from the rear substrate by a predetermined distance, and two positioned on the front of the plate and the rear of the rear substrate. Two polarizing plates, a common electrode formed on the front surface of the polarizing plate attached to the front surface of the plate, and a liquid crystal encapsulated in a space between the polarizing plate and the rear substrate. Accordingly, the optical viewing angle can be improved by using an optical fiber plate that causes multiple reflections instead of the conventional front glass substrate.

Description

Liquid crystal display

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a novel structure capable of improving a wide viewing angle.

In response to the demand for personalization of display devices and space saving in the information and information era, a large cathode ray tube (CRT), which has been the dominant display device, has been replaced. Accordingly, various flat panel display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an electroluminescence (EL) have been developed.

Among them, LCD is a display device that combines liquid crystal technology and semiconductor technology that uses the optical properties of liquid crystals whose molecules are changed by an electric field.

The configuration of such an LCD is schematically shown in FIG.

Referring to FIG. 1, first, a pixel composed of a thin film transistor 12 switched by a signal line and a scan line and a pixel electrode 14 for driving a liquid crystal is formed on a rear glass substrate 10. Is arranged. The common electrode 24 corresponding to the pixel electrode 14 and a color filter layer 22 corresponding to each pixel electrode are formed on the front glass substrate 20. Between the rear glass substrate 10 and the front glass substrate 20, a liquid crystal in which the arrangement of molecules is changed by an electric field is injected, and the back of the pair of glass substrates 10 and 20 polarizes the incident light. The polarizing plate 30 which has a function is provided, respectively.

When a predetermined voltage is applied to the LCD configured as described above, the liquid crystal molecules are aligned according to the rubbing direction of the alignment film surface. The liquid crystal molecules contained between a pair of glass substrates are twisted in a spiral with a constant pitch, and in order to form such a pitch, 0.01 to 8.0 weight of chiral dopant in the liquid crystal is formed. Can be added at a concentration of%.

On the other hand, twisted nematic liquid crystal display (TN-LCD) devices, which have recently been widely applied in the field of flat panel displays, are generally known to have a narrow and non-uniform viewing angle. The viewing angle of the LCD is mainly determined by the orientation of the liquid crystal molecules located in the middle of the cell. The liquid crystal molecules are formed in a long and thin rod shape, and the long axis and the short axis act differently on the incident polarized light. do. When the LCD is applied at various angles, the long axis of the liquid crystal molecules is changed, resulting in gray inversion and reduction in viewing angle.

To solve this problem, pixel split rubbing method, optical compensation method using retardation film, TN method LCD using non-rubbing method and light using photo-polymerization Orientation and the like have been reported, but there are many problems such as an increase in cost and a decrease in yield due to the addition of additional processes and materials.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a liquid crystal display device having a new structure having an improved optical viewing angle.

1 is a three-dimensional view showing an example of a general liquid crystal display device in three dimensions.

2 is a three-dimensional view of a liquid crystal display device according to an exemplary embodiment of the present invention in three dimensions.

3 is a cross-sectional view illustrating a cross section of the liquid crystal display of the present invention shown in FIG. 2.

4 is a diagram illustrating a light transmission path of an optical fiber's plate.

5A and 5B are views for explaining the operation of the liquid crystal display device according to the present invention.

According to an aspect of the present invention, there is provided a liquid crystal display device comprising: a back substrate having pixels arranged on a surface thereof; An alignment film formed on the rear substrate; An optical fiber plate spaced apart from the rear substrate by a predetermined distance; Two polarizing plates positioned on the front surface of the plate and the rear surface of the rear substrate; A common electrode formed on the front surface of the polarizer plate attached to the front surface of the plate; And liquid crystal encapsulated in a space between the polarizing plate and the back substrate.

According to one embodiment of the present invention, the alignment layer is made of a rubbed polyimide layer, and the liquid crystal is preferably a nematic liquid crystal having a dielectric anisotropy positive.

According to another embodiment of the present invention, the alignment layer is made of an unrubbed polyimide layer, the liquid crystal is doped with a photopolymerized dopant, and the dielectric anisotropy is positive. It is preferable that it is a liquid crystal. Here, the photopolymerized dopant is any one selected from the group consisting of cinnamate, acrylate and coumarin derivatives, and the concentration is preferably 0.01 to 5% by weight.

According to another embodiment of the present invention, the alignment layer is made of a rubbed polyimide layer, the liquid crystal is doped with an asymmetric dopant (chiral dopant), the dielectric anisotropy is preferably a nematic liquid crystal (negative) . It is preferable that ratio (d / p) of the thickness of the said liquid crystal cell and liquid crystal pitch is in the range of 0.25-0.50, and the density | concentration of the said asymmetric dopant is 0.25-0.50 weight /%.

According to the present invention, the optical viewing angle can be improved by using an optical fiber plate causing multiple reflections instead of the conventional front glass substrate.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

Example 1

2 is a cross-sectional view showing a liquid crystal display device according to a first embodiment of the present invention, and FIG. 3 is a cross-sectional view of the liquid crystal display device.

2 and 3, on the rear glass substrate 40, pixels composed of a thin film transistor 42 which is switched by a signal line and a scanning line and a pixel electrode 44 for driving a liquid crystal are arranged in a matrix form. . A rubbed polyimide layer is coated on the rear glass substrate 40 as an alignment layer.

On the other hand, there is a transparent plate 50 made of an optical fiber instead of the conventional front glass substrate (reference numeral 20 of FIG. 1), and the pixel electrode 14 of the rear glass substrate on the optical fiber's plate. The common electrode 52 corresponding to the above is formed, and although not shown, the color filter layer is formed to correspond to each pixel electrode.

In addition, between the rear glass substrate 40 and the optical fiber plate 50, the arrangement of molecules is changed by an electric field, and a nematic liquid crystal having positive dielectric anisotropy is injected, and the rear surface of the rear glass substrate 40 and the optical fiber are injected. The front surface of the plate 50 is provided with polarizing plates 60 for polarizing incident light.

A feature of the liquid crystal display device of the present invention lies in the optical fiber plate 50 attached to the upper polarizer 60. The method for preparing the optical fiber plate is a known method, Chemical processing of synthetic fibers and blends, Jhon Wiley Sons, Inc., Newyork, 1984, author; K. V. Datye or Sol-gel technology for thin films, fibers, performs, electronics, and especially shapes, Noeys Publications, New Jersey, 1988, author; It is well shown in L. C. Klein.

The optical fiber plate 50 improves the optical viewing angle by allowing the incident light to be multi-reflected therein so that the incident light in a single direction is emitted at all azimuth angles.

4 schematically shows the path of light passing through the fiber optic plate.

The incident angle of light incident on the optical fiber plate satisfies Equation 1 below.

[Equation 1]

Where n is the refractive index of the external medium of the optical fiber plate, ψ is the angle of incidence of light incident on the optical fiber plate, and NUMA is the numerical aperture of the optical fiber.

Light incident on the optical fiber plate is transmitted to the core to make multiple reflections at the interface between the core and the cladding and then exit the optical fiber plate at all possible azimuths. Accordingly, the light incident in a single direction is emitted in a hollow cone shape having the same apex angle as the incident angle. This phenomenon makes the light uniform at all azimuth angles, thereby improving the viewing angle.

Example 2

The liquid crystal display device according to the second embodiment of the present invention has the same three-dimensional structure and cross section as the first embodiment.

That is, the pixels composed of the thin film transistor 42 and the pixel electrode 44 are arranged in a matrix form on a single glass substrate 40, and an alignment film is formed thereon. Instead of the conventional front glass substrate (reference numeral 20 of FIG. 1), there is a transparent plate 50 made of an optical fiber, and a common electrode 52 and a color filter layer (not shown) are provided on each pixel electrode on the optical fiber plate. It is formed to correspond.

In addition, between the rear glass substrate 40 and the optical fiber plate 50, a liquid crystal in which the arrangement of molecules is changed by an electric field is injected. The rear surface of the front glass substrate 40 and the front surface of the optical fiber plate 50 are injected. Are each provided with the polarizing plates 60 which polarize the incident light.

In particular, an unrubbed polyimide film is used as the alignment layer, and the nematic liquid crystal injected between the rear glass substrate and the optical fiber plate has a positive dielectric anisotropy and is doped with a photopolymerized dopant.

A feature of the liquid crystal display device according to the second embodiment of the present invention resides in a mixture of an optical fiber plate attached to the upper polarizing plate and a nematic liquid crystal and a photopolymerized dopant. It is well known that the method for providing a high density optical fiber plate is well known in the literature as a known technique.

The process of preparing a mixture of the nematic liquid crystal and the photopolymerized dopant and encapsulating it in a cell is as follows.

(1) Before injecting the liquid crystal into the cell, for example, 2% of photocurable vinyl4-methoxy-cinnamate as a dopant is doped into the nematic liquid crystal. The dopant may be any one of cinnamate, acrylate and coumarin derivatives, and the doping concentration is preferably about 0.01 to 5% by weight.

② The doped liquid crystal is encapsulated in the cell, but the liquid crystal should be encapsulated at a temperature higher than the clearing temperature of the nematic liquid crystal.

(3) After the liquid crystal encapsulation, the cell is irradiated with ultraviolet rays at about 5 J / cm 2 for about 10 minutes. At this time, the ultraviolet light can be obtained by using a high-pressure mercury lamp having a light intensity of 10 ㎷ / ㎠, linearly polarized, having a wavelength of 320nm. And voltage is applied at 5-20 volts (V), and it irradiates at the temperature more than the clearing temperature of the said nematic liquid crystal.

The transmission path of light in the optical fiber plate is the same as described in the first embodiment.

Example 3

Since the liquid crystal display device according to the third embodiment of the present invention has the same three-dimensional and cross-sectional structure as those of the first and second embodiments, description thereof will be omitted.

In the third embodiment of the present invention, in particular, as the alignment film 65, a rubbed polyimide film is used so that the liquid crystal can be aligned in the same direction. The nematic liquid crystal injected between the glass substrate 40 and the optical fiber plate 50 is negative in dielectric anisotropy and doped with asymmetrical dopants. At this time, it is preferable that ratio (d / p) of the pitch which a cell thickness and a liquid crystal make exists in the range of 0.25-0.50, and the density | concentration of the chiral dopant which satisfy | fills the said range is about 0.25-0.50.

In the liquid crystal display device according to the third embodiment of the present invention, the transmission path of the light in the optical fiber plate and the effect of the invention are the same as those of the first and second embodiments, and thus description thereof will be omitted.

5A and 5B are diagrams for describing an operation of a liquid crystal display device according to an exemplary embodiment of the present invention.

5A illustrates a state in which no voltage is applied, reference A denotes an axes of polarizer of the upper polarizer, and P denotes a polarization axis of the lower polarizer attached to the rear substrate.

As shown, when no voltage is applied in a state in which the directors of the liquid crystal molecules are arranged in a direction perpendicular to the substrate, since the upper and lower polarizers are orthogonal to each other, the light is not beneficiated by the liquid crystal molecules. You will not pass this.

5B illustrates a state in which a voltage is applied, the liquid crystal molecules are arranged in a spiral by 90 °, and the polarizing plane of incident light is rotated by 90 ° by a polarizing plate arranged in accordance with the arrangement of the liquid crystal molecules so that light is transmitted. do.

While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and many modifications are possible by those skilled in the art within the technical idea to which the present invention pertains.

According to the liquid crystal display device according to the present invention described above, the optical viewing angle can be improved by using an optical fiber plate causing multiple reflections instead of the conventional front glass substrate, and using an alignment film and a liquid crystal suitable for this.

Claims (8)

A back substrate having pixels arranged on its surface; An alignment film formed on the rear substrate; An optical fiber plate spaced apart from the rear substrate by a predetermined distance; Two polarizing plates positioned on the front surface of the plate and the rear surface of the rear substrate; A common electrode formed on the front surface of the polarizer plate attached to the front surface of the plate; And And a liquid crystal encapsulated in a space between the polarizing plate and the back substrate. The method of claim 1, wherein the alignment layer is made of a rubbed polyimide layer, And said liquid crystal is a nematic liquid crystal having a dielectric anisotropy positive. The method of claim 1, wherein the alignment layer is made of an unrubbed polyimide film, And the liquid crystal is doped with a photopolymerized dopant and is a positive nematic liquid crystal having a dielectric anisotropy. The method of claim 3, wherein the photopolymerized dopant, Liquid crystal display device, characterized in that any one selected from the group consisting of cinnamate (acrylate), acrylate (acrylate) and coumarin (coumarin) derivative. 4. The liquid crystal display device according to claim 3, wherein the concentration of the photopolymerized dopant is 0.01 to 5% by weight. The method of claim 1, wherein the alignment layer is made of a rubbed polyimide film, The liquid crystal is doped with asymmetric dopant (chiral dopant), the liquid crystal display device characterized in that the dielectric anisotropy is a negative nematic liquid crystal (negative). 7. The liquid crystal display device according to claim 6, wherein a ratio (d / p) of the thickness of the liquid crystal cell and the pitch of the liquid crystal is in a range of 0.25 to 0.50. The method of claim 7, wherein the concentration of the asymmetric dopant, It is 0.25-0.50 weight /%, The liquid crystal display element characterized by the above-mentioned.