KR20030077820A - Holographic polymer dispersed liquid crystal display - Google Patents

Abstract

PURPOSE: A holography polymer injection type LCD is provided to avoid the use of polarization plates and color filters which absorb light and deteriorate light efficiency, thereby realizing relatively high light efficiency and the rapid response time characteristics. CONSTITUTION: A holography polymer injection type LCD includes transparent electrodes(110,210) formed on facing surfaces of upper and lower substrates, vertical orientation films(120,220) formed on the transparent electrodes, liquid crystal layers(310,320) aligned between the orientation films. A liquid crystal polymer(350) is interposed between the liquid crystal layers. The liquid crystal layers are driven and the orientation films align the liquid crystal layers, as electric fields are applied to the transparent electrodes. The liquid crystal layers and the liquid crystal polymer layer are adjacent and inclined by an inclination angle of 25-45° with respect to a horizontal surface. As a voltage is applied, the polymers of the liquid crystal polymer layer do not move while the liquid crystal of the liquid crystal layers become laid, generating a difference of refractive index among the liquid crystal layers and the liquid crystal polymer layer. A diffraction state is generated and the light advances toward viewers outside HPDLCD cells.

Description

Holographic polymer injection type liquid crystal display device {HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a holographic polymer injection type liquid crystal display device, and more particularly, to a holographic polymer injection type liquid crystal display device capable of improving contrast ratio.

In the holographic polymer injection type liquid crystal display device, as shown in FIG. 1, the upper substrate 10 including the color filter and the lower substrate 20 including the pixel electrode are disposed to face each other with a predetermined interval, and the upper substrate 10 Transparent electrodes 11 and 21 are formed on inner surfaces of the lower substrate 20, respectively. Alignment films 12 and 22 are formed on the transparent electrodes 11 and 21, respectively, and a holographic polymer jet liquid crystal (hereinafter referred to as HPDLC) 30 is interposed between the alignment films 12 and 22.

The HPDLCD configured as described above allows the light emitted from a light source such as an LED 40 to be totally reflected inside the upper substrate 10 and the lower substrate 20 having the HPDLC 30 embedded therein. To maintain the transparent stage (dotted line). However, since the liquid crystals of the inclined liquid crystal layer adjacent to the polymer layer of the HPDLC 30 are twisted by a field depending on whether a voltage is applied or not, diffraction of light is caused by a difference in refractive index between the polymer layer and the liquid crystal layer. This causes light to proceed toward the observer 50 (solid line).

2 is a view showing the structure of HPDLC using a conventional isotropic polymer.

As shown in FIG. 2, transparent electrodes 11 and 21 are formed on inner surfaces of the upper substrate 10 and the lower substrate 20, respectively, and horizontal alignment layers 12 are formed on the transparent electrodes 11 and 21, respectively. After the 22 is formed, the unaligned liquid crystal layers 31 and 32 are respectively inserted between the horizontal alignment layers 12 and 22, and the isotropic polymer 35 is disposed between the unaligned liquid crystal layers 31 and 32. Through).

On the other hand, when the light is irradiated to the HPDLCD in an oblique direction, the liquid crystal layers 30a and 30b in the homogeneous state and the isotropic state polymer layers 35 are oriented in the diagonal direction. do.

At this time, when no voltage is applied, the light emitted by the light source such as the LED (not shown) on the side surface of the refractive index between the polymer layer 35 and the liquid crystal layers 31 and 32 in the isotropic state Due to the difference, the light is diffracted (diffraction state), as shown in the solid line of FIG. In other words, light travels toward the observer.

However, when a voltage is applied, the liquid crystals 31 and 32 are aligned in a specific direction, and the light passing through the isotropic polymer layer 35 passes through the liquid crystal layers 31 and 32 as it is. Since it is totally reflected from the 10 and the lower substrate 20, the state of light passing through (10), that is, as shown in the dotted line of FIG. On the other hand, after the voltage is applied, the liquid crystals 31 and 32 must be completely set up by the field to obtain a transparent state. However, in reality, the anchoring energy of the liquid crystal is caused by the horizontal alignment layer. And the liquid crystal layers 31 and 32 do not stand in the same vertical direction due to various factors.

Therefore, the light is totally reflected from the upper substrate 10 and the lower substrate 20 surface and should not go out of the cell, but diffraction leakage occurs, which eventually lowers the color contrast.

In order to solve this problem, FIG. 3 is a view showing the HPDLCD structure using a conventional liquid crystal polymer.

As shown in FIG. 3, transparent electrodes 11 and 21 are formed on inner surfaces of the upper substrate 10 and the lower substrate 20, respectively, and horizontal alignment layers 12 are formed on the transparent electrodes 11 and 21, respectively. (22), the horizontal alignment layers 12 and 22 are anti-parallel in opposite directions, and the alignment liquid crystal layers 33 and 22 are respectively interposed between the horizontal alignment layers 12 and 22. Insert 34). The liquid crystal polymer 37 is interposed between the alignment liquid crystal layers 33 and 34.

Accordingly, the liquid crystals are uniformly arranged in a predetermined direction by rubbing in the opposite direction and the horizontal alignment layers 12 and 22, and thus the liquid crystal polymers 37 are arranged in the same direction.

That is, in the structure as described above, the optical switching characteristics exhibit the characteristics opposite to those of FIG. 1.

When no initial voltage is applied, the arrangement of liquid crystals and polymers in the cell is uniformly arranged in a specific direction, and diffraction does not occur so that light from the light source at the side of the cell is not diffracted with the upper substrate 10. Total reflection occurs in the lower substrate 20, and light does not come out of the cell. Thus, light enters the state.

On the other hand, when the voltage is driven, the liquid crystals are twisted in the vertical direction to stand and the difference in refractive index with the polymer layer 37 around the liquid crystal layers 33 and 34 is caused to be in a diffraction state. As a result, light leaks to the observer outside the cell.

Therefore, the color contrast ratio is improved compared to HPLCD using an isotropic polymer. In addition, since it can realize a wide viewing angle, and has a responsive characteristic that is not unreasonable in the video implementation, it has excellent electro-optic characteristics.

However, the above-mentioned conventional HPDLC has the following problems.

When a liquid crystal polymer is used for the horizontally aligned HPDLC, an additional process is performed compared to the HPDLC using an isotropic polymer. That is, a rubbing process should be performed while forming a horizontal alignment film.

Meanwhile, the rubbing process is a process of rubbing in a specific direction by using a physical force of rubbing cloth on the surface of the alignment layer. In the rubbing process, cells are broken or defects are generated due to various static electricity, and are vulnerable to particles.

An object of the present invention is to provide an HPDLCD having light switching characteristics, light efficiency, fast response time, and high color contrast ratio without using a polarizing plate and a color filter.

1 is a cross-sectional view showing a general holographic polymer injection type liquid crystal display device

Figure 2 is a perspective view showing the structure of a conventional holographic polymer injection type liquid crystal display using an isotropic polymer

3 is a perspective view showing the structure of a holographic polymer injection type liquid crystal display device using a conventional liquid crystal polymer

4 is a perspective view showing the structure of a holographic polymer injection type liquid crystal display device according to an embodiment of the present invention;

5 is a cross-sectional view for installing a light source on the side of FIG.

<Explanation of symbols for the main parts of the drawings>

100: upper substrate 200: lower substrate

110, 210: transparent electrode 120, 220: vertical alignment layer

300: HPDLC 310, 320: alignment liquid crystal layer

350: liquid crystal polymer layer 400: light source

500: HPDLC Cell

HPLCD of the present invention for achieving the above object is formed on the inner surface of the upper substrate and the lower substrate, respectively, is formed on the transparent electrode for driving the liquid crystal of the liquid crystal layer by applying an electric field, respectively on the transparent electrode In the HPDLCD having an alignment film for aligning the liquid crystal and a liquid crystal layer and a polymer layer inclined adjacent to each of the alignment films, respectively, and having a light source at the side of the cell, the alignment film is a vertical alignment film. The liquid crystal layer is initially vertically aligned using a polymer as a liquid crystal polymer, and the polymer is vertically aligned with the initial liquid crystal layer.

In addition, as the light source, any one of an LED and a fluorescent lamp is used, and the angle of incidence is preferably 40 to 90 ° so that the emission angle is 90 to 140 ° when the light source is installed.

In addition, the inclination angle of the liquid crystal layer and the polymer layer is preferably 25 to 40 ° based on the horizontal plane.

The cell gap of the HPDLCD is 2 to 20 µm, and the refractive index anisotropy value of the liquid crystal is 0.05 to 0.2.

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

4 is a diagram showing an HPLCD structure according to an embodiment of the present invention.

As shown in FIG. 4, transparent electrodes 110 and 210 are formed on inner surfaces of the upper substrate 100 and the lower substrate 200, respectively, and vertical alignment layers 120 are formed on the transparent electrodes 110 and 210, respectively. After forming the 220, the alignment liquid crystal layers 310 and 320 are inserted between the vertical alignment layers 110 and 220, respectively. The liquid crystal polymer 350 is interposed between the alignment liquid crystal layers 310 and 320.

In this case, the transparent electrodes 110 and 210 apply an electric field to drive the liquid crystals of the liquid crystal layers 310 and 320, and the vertical alignment layers 120 and 220 align the liquid crystals of the liquid crystal layers 310 and 320. The liquid crystal layers 310 and 320 and the liquid crystal polymer layer 350 are inclined adjacent to each other. In this case, the inclination angles of the liquid crystal layers 310 and 320 and the liquid crystal polymer layer 350 are 25 to 45 ° based on the horizontal plane.

On the other hand, a light source (not shown) is provided on the side of the HPDLCD cell 500 configured as described above.

Here, the role of the optical switching element of HPLCD comprised as mentioned above is as follows.

Before the voltage is applied to the HPDLCD cell 500, the liquid crystal and liquid crystal polymer 350 of the liquid crystal layers 310 and 320 are vertically arranged. In this case, since the difference in refractive index does not occur between the liquid crystal layers 310 and 320 and the polymer layer 350, the light from the light source on the side of the cell 500 is moved straight to the upper substrate 100 and the lower substrate 200. ), Total reflection of light is achieved. That is, perfect light that does not go out of the cell 500 is transmitted.

Subsequently, when the voltage is applied, the polymers of the liquid crystal polymer layer 350 are intact, but the liquid crystals of the liquid crystal layers 310 and 320 are laid down by the field, so the difference in refractive index between the liquid crystal layers 310 and 320 and the polymer layer 350 is different. Is generated and becomes a diffraction state. Therefore, the light propagates toward the observer outside the cell 500 due to the diffraction of the light.

6 is a side view for installing a light source on the side of FIG. 5.

As shown in FIG. 6 by Snell's Law for the installation of the light source 400 of the HPDLC cell 500 with the HPLC 300 interposed between the upper substrate 100 and the lower substrate 200.

The formula n1 × sin (Θ1) = n2 × sin (Θ2). (N1: refractive index of the substrate, n2: refractive index of the air, Θ1: incident angle, Θ2: exit angle.)

Here, the exit angle Θ2 should be 90 to 140 °, so if you substitute sin90 ° = 1,

Θ1 = sin (n2 / n1), if the refractive index n1 of the substrate is 1.5 and the refractive index of air is 1, Θ1 becomes 41.8 °. Therefore, in this case, the light source 400 should be disposed on the side surface so that Θ1 may be greater than 41.8 ° to allow total internal reflection into the upper substrate 100 and the lower substrate 200. On the other hand, the incident angle Θ1 is preferably 40 to 90 degrees.

As described above, the HPDLCD of the present invention does not use a polarizing plate and a color filter, which absorbs light and reduces light efficiency, and thus has a relatively high light efficiency and a fast response time of about 3 ms. It can be effective.

In addition, compared to the conventional HPDLCD, it may have a high color contrast ratio characteristic and does not need rubbing, thereby reducing defects such as correcting particles and particles due to rubbing, thereby simplifying the process.

Claims (4)

A transparent electrode formed on each of the upper and lower substrate inner surfaces to apply an electric field to drive the liquid crystal of the liquid crystal layer, an alignment film formed on each of the transparent electrodes to align the liquid crystal, and the respective alignments In the holographic polymer injection type liquid crystal display device having a liquid crystal layer and a polymer layer obliquely adjacent to each other on the film, and having a light source at the side of the cell, The alignment layer is a vertical alignment layer, the polymer layer is a liquid crystal polymer using the liquid crystal layer is initially arranged vertically, the polymer layer is holographic polymer, characterized in that the same as the initial liquid crystal layer Jet liquid crystal display device. The method of claim 1, The light source may be any one of an LED and a fluorescent lamp. The light source has an incidence angle of 40 to 90 ° and an emission angle of 90 to 140 °. The method of claim 1, And an inclination angle of the liquid crystal layer and the polymer layer is 25 to 40 degrees with respect to the horizontal plane. The method of claim 1, The cell gap of said HPDLCD is 2-20 micrometers, and the refractive index anisotropy value of the said liquid crystal is 0.05-0.2, The holographic polymer injection type liquid crystal display device.