KR100805792B1 - Liquid crystal display using polymer dispersed liquid crystal - Google Patents

Abstract

The present invention relates to a polymer dispersed liquid crystal display device. The polymer dispersed liquid crystal display includes a pair of substrates, a polymer dispersed liquid crystal layer comprising a polymer and a liquid crystal between the substrates, a first electrode disposed on at least one of the substrates, and a substrate on which the first electrodes are disposed. And a second electrode disposed on the same substrate as the substrate, the second electrode disposed to face the first electrode, and a first polarizing plate disposed on a rear surface of one of the substrates. In the polymer dispersed liquid crystal display, an electric field is formed in parallel with the substrate by a voltage difference applied to the first electrode and the second electrode, and the long axis of the liquid crystal of the polymer dispersed liquid crystal layer is changed by the electric field. Are arranged parallel to In addition, the polarity of the first polarizing plate is parallel to the direction of the electric field formed by the first electrode and the second electrode.

In the polymer dispersed liquid crystal display according to the present invention, the driving voltage does not increase in proportion to the thickness of the polymer dispersed liquid crystal layer, and as a result, the thickness of the polymer dispersed liquid crystal layer can be increased even with the same driving voltage. The contrast ratio of the type liquid crystal display device can be improved.

Polymer dispersed liquid crystal, PDLC, PNLC

Description

Liquid crystal display using polymer dispersed liquid crystal

1 is a cross-sectional view schematically showing the configuration of a polymer dispersed liquid crystal display according to the related art.

2 is a cross-sectional view schematically illustrating a configuration of a polymer dispersed liquid crystal display according to a first embodiment of the present invention.

3 is a cross-sectional view schematically illustrating a configuration of a polymer dispersed liquid crystal display according to a second exemplary embodiment of the present invention.

4 is a cross-sectional view schematically illustrating a configuration of a polymer dispersed liquid crystal display according to a third exemplary embodiment of the present invention.

5 is a cross-sectional view schematically illustrating a configuration of a polymer dispersed liquid crystal display according to a fourth exemplary embodiment of the present invention.

6 is a cross-sectional view schematically illustrating a configuration of a polymer dispersed liquid crystal display according to a fifth exemplary embodiment of the present invention.

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

10, 30, 40, 50, 60, 70: polymer dispersed liquid crystal display

330, 430: polarizer

350, 352, 450, 452, 650, 652: substrate

320, 420, 520, 620, 720: polymer dispersed liquid crystal layer

340, 440, 540, 640, 740: first electrode

342, 442, 542, 642, 742: second electrode

630 and 730: first polarizing plate

632, 732: second polarizer

The present invention relates to a polymer dispersed liquid crystal display device using a polymer dispersed liquid crystal, and more particularly, to a polymer dispersed liquid crystal display device having improved operation efficiency by forming an electric field in a direction parallel to the substrate.

Currently, the mainstream liquid crystal display (TD) uses twisted nematic (TN) or super twisted nematic (STN) type liquid crystal materials, and since the liquid crystal display uses a polarizing plate, the light use efficiency is low and the contrast ratio is low. low. In addition, the above-described liquid crystal display device requires a surface alignment, and as the pixel density increases, not only the alignment processing around the TFT (Thin Film Transistor) element is difficult but also the viewing angle is about 20 °. In order to solve this problem, efforts have been made to apply a transmission and scattering mode of light to a display device without using a polarizing plate. As a result of this effort, PDLC (Polymer Dispersed Liquid Crystal) or PNLC (Polymer Network Liquid Crystal) in the light scattering mode in which the liquid crystal is dispersed in the transparent polymer resin has emerged.

U.S. Patent No. 4,435,047 discloses a liquid crystal material by uniformly dispersing a liquid crystal in gelatin, gum arabic or polyvinyl alcohol aqueous solution, and then on a substrate of a glass plate or polyester film coated with conductive material ITO (Indium Tin Oxide) The present invention discloses a PLDC device manufactured by uniformly coating a film having a thickness of 5 to 20 μm, evaporating water, and bonding a substrate of a glass plate or a polyester film coated with an ITO material thereon.

In addition, various manufacturing methods for polymer dispersed liquid crystal composites have been disclosed. US Pat. No. 4,688,900 and US Pat. No. 4,685,771 propose a method of phase separation using a difference in solubility between a polymer and a liquid crystal monomer. . PDLC produced by the method as described above, the polymer is a continuous phase and the liquid crystal forms a quadrature.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 1-198725, PNLC differs from PDLC in that the liquid crystal is a continuous phase, has a three-dimensional network structure in which the polymer is crosslinked, and the refractive index dependency of the liquid crystal and the polymer is not large. In general, the driving voltage is lower than PDLC.

Hereinafter, the operating principle of the polymer dispersed liquid crystal display having the PDLC layer will be described in detail with reference to FIGS. 1A and 1B. 1 (a) and (b) is a cross-sectional view conceptually showing the configuration of a polymer dispersed liquid crystal display using a TN liquid crystal, a polymer dispersed type of Normally White Mode operating in a white mode without an electric field applied thereto. It relates to a liquid crystal display device.

Referring to FIGS. 1A and 1B, the polymer dispersed liquid crystal display 10 may include a liquid crystal in which polymer dispersed liquid crystals are uniformly dispersed between an upper transparent electrode 100 and a lower transparent electrode 110. The layer 120 is formed, and the upper polarizing plate 130 is mounted on the upper transparent electrode, and the lower polarizing plate 140 is mounted on the lower transparent electrode.

Referring to FIG. 1A, an operation state of a white mode of a polymer dispersed liquid crystal display is as follows. The light output from the backlight in a state in which no electric field is applied from the outside is transmitted through the lower polarizer 140, and the light transmitted through the lower polarizer is scattered due to the difference in refractive index between the liquid crystal and the polymer interface of the liquid crystal layer 120. As scattered light passes through the upper polarizer 130, the polymer dispersed liquid crystal display operates in a white mode.

Referring to (b) of FIG. 1, the operating state of the black mode of the polymer dispersed liquid crystal display is as follows. When voltage is applied through the upper and lower transparent electrodes, the liquid crystals of the liquid crystal layer are arranged in a direction perpendicular to the lower polarizer due to the electric field formed by the applied voltage, and the polarized light passing through the lower polarizer causes the liquid crystal. It will not penetrate. As a result, the polymer dispersed liquid crystal display does not transmit light due to voltage application, and operates in a black mode.

Since the polymer dispersed liquid crystal display device operating as described above is operated by light scattering and transmissive properties, the use of light is higher than that of the conventional liquid crystal display device, resulting in improved luminance and wider viewing angles of up, down, left, and right. . However, in the above-described operation of the polymer dispersed liquid crystal display, light leakage in the black mode is proportional to the thickness of the liquid crystal layer 120. Therefore, when the thickness of the polymer dispersed liquid crystal is sufficiently small, light leakage can be minimized by placing the upper polarizing plate on the lower polarizing plate and the back surface of the panel.

However, in order for the polymer dispersed liquid crystal display device to fully exhibit the light scattering action, when the liquid crystal layer is manufactured to be at least 10 μm, a high driving voltage proportional to the thickness of the liquid crystal layer must be applied. There is a problem that is not suitable. On the other hand, if the thickness of the liquid crystal layer is reduced in order to eliminate such a problem, the driving voltage can be lowered, but the scattering effect of light is reduced, resulting in a problem that the contrast becomes worse.

In addition, when the amount of liquid crystal in the liquid crystal layer of the polymer dispersed liquid crystal display is mixed at 70% or more of the polymer, the driving voltage can be lowered even at a relatively high thickness, but the light scattering effect is reduced in the off state, resulting in a worse contrast ratio. There is a problem.

An object of the present invention for solving the above problems is to provide a polymer dispersed liquid crystal display device that can be operated at a relatively low driving voltage even if the thickness of the liquid crystal layer is thick.

Another object of the present invention is to provide a polymer dispersed liquid crystal display device having a good contrast ratio while being driven at a low driving voltage.

Features of the present invention for achieving the above technical problem relates to a polymer dispersed liquid crystal display device, the polymer dispersed liquid crystal display device

With a pair of substrates,

A polymer dispersed liquid crystal layer formed of a mixed phase of a polymer and a liquid crystal and formed between the substrates;

A first electrode disposed on at least one of the substrates;

A second electrode disposed on the same substrate as the substrate on which the first electrode is disposed and disposed to face the first electrode;

A first polarizing plate disposed on a rear surface of one of the substrates,

An electric field is formed in parallel with the substrate by a voltage difference applied to the first electrode and the second electrode, and the polymer dispersed liquid crystal is arranged in parallel with the substrate by the electric field.

The polarity of the first polarizing plate is parallel to the direction of the electric field formed by the first electrode and the second electrode.

Polymer dispersed liquid crystal display device according to another feature of the present invention,

With a pair of substrates,

A polymer dispersed liquid crystal layer formed between a mixed phase of a polymer and a liquid crystal and formed between the substrates;

A first electrode disposed on at least one of the substrates;

A second electrode disposed on the same substrate as the substrate on which the first electrode is disposed and disposed to face the first electrode;

A first polarizing plate disposed on a rear surface of a lower substrate among the substrates, and having a polarization direction parallel to a direction of an electric field formed by the first and second electrodes;

A second polarizing plate disposed on a rear surface of an upper substrate among the substrates, and having a second polarizing plate orthogonal to a polarizing direction of the first polarizing plate;

An electric field is formed in parallel with the substrate by a voltage difference applied to the first electrode and the second electrode, and the liquid crystal of the polymer dispersed liquid crystal layer is arranged in parallel with the substrate by the electric field.

First embodiment

Hereinafter, the structure and operation of the polymer dispersed liquid crystal display according to the first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 (a) and 2 (b) are cross-sectional views schematically showing a part of the internal configuration of the polymer dispersed liquid crystal display according to the first embodiment of the present invention, and FIGS. It is for explaining the operation of the white mode and the black mode, respectively.

First, referring to FIG. 2, in the polymer dispersed liquid crystal display device 30 according to the first embodiment of the present invention, a polymer dispersed liquid crystal layer 320 is formed between a pair of substrates 350 and 352. The polarizer 330 is disposed on the bottom of the lower substrate 352, and the first electrode 340 and the second electrode 342 are disposed at a predetermined position on the lower substrate.

The polymer dispersed liquid crystal layer 320 is formed of a mixed state of a liquid crystal and a polymer. In this embodiment, the liquid crystals are made of PDLC (Polymer Dispersed Liquid Crystal) in which liquid crystals are dispersed in a polymer matrix in the form of small particles. Meanwhile, another embodiment of the polymer dispersed liquid crystal layer 320 of the polymer dispersed liquid crystal display according to the present invention is not only PDLC, but also PNLC, Polymer Stabilized Liquid Crystal (PSLC), Liquid Crystal Stabilized Polymer (LCSP), and PSFLC ( Polymer Stabilized Ferroelectric Liquid Crystal) may be optionally used.

The first electrode 340 and the second electrode 342 are disposed at a predetermined position on the lower substrate 352, and are disposed to face each other at a predetermined distance from each other. In the present invention, another embodiment of the first electrode 340 and the second electrode 342 is disposed at a predetermined position of the upper substrate 350, but disposed to face each other at a predetermined distance. In addition, another embodiment of the first electrode 340 and the second electrode 342 is disposed on the upper substrate 350 and the lower substrate 352, respectively, the first electrode and the second electrode is a predetermined distance along the substrate direction Spaced apart from each other so that at least a portion of the first electrode and a portion of the second electrode overlap each other so that the first electrode disposed on the upper substrate and the second electrode disposed on the lower substrate Allow an electric field to form.

The polarizer 330 is disposed on the rear surface of the lower substrate 352, and the direction of the polarity of the polarizer 330 is due to the electric field formed by the voltage difference applied to the first electrode and the second electrode. It is desirable to be parallel to the direction.

 In addition, by forming one of the substrates with a color filter (color filter), it is possible to manufacture a color display device.

In addition, by configuring the backlight disposed on the rear surface of the lower substrate with a red, green, blue light source, and sequentially scanning them, it is possible to implement a color display. In this case, when one frame is driven at 60 Hz to sequentially scan the red, green, and blue backlight light sources, the response speed of the liquid crystal is required to be 5 msec or less, which is the first structure in the polymer dispersed liquid crystal display according to the present invention. The gap between the electrode and the second electrode can be realized by making it sufficiently small to several micrometers.

Hereinafter, operations of the white mode and the black mode of the polymer dispersed liquid crystal display device 30 having the above-described configuration will be described.

First, a process in which the polymer dispersed liquid crystal display according to the first exemplary embodiment of the present invention operates in the white mode will be described with reference to FIG. 2A. In the state where no voltage is applied to the first electrode and the second electrode, light incident from the backlight passes through the polarizer 330 and is scattered by the liquid crystal and the polymer of the polymer dispersed liquid crystal layer 320, thereby dispersing the polymer. The type liquid crystal display device 30 operates in the white mode.

Referring to FIG. 2B, a process of operating the polymer dispersed liquid crystal display according to the first exemplary embodiment of the present invention in the black mode will be described. A predetermined voltage is applied to the first electrode and the second electrode to form an electric field between the first electrode and the second electrode due to the voltage difference generated between the first electrode and the second electrode. By the electric field formed between the first electrode and the second electrode, the long axes of the liquid crystals of the polymer dispersed liquid crystal layer disposed between the first electrode and the second electrode are arranged in a direction parallel to the direction of the electric field. At this time, the light incident from the backlight passes through the polarizing plate 330. Since the polarization direction of the polarizing plate is the same as the electric field direction, the light polarized by the polarizing plate is the same as the direction of the long axis of the arranged liquid crystal. Therefore, the light passing through the polarizing plate is blocked by the arranged polymer dispersed liquid crystal, and as a result, the polymer dispersed liquid crystal display 30 operates in the black mode.

Second embodiment

Hereinafter, the structure and operation of the polymer dispersed liquid crystal display 40 according to the second exemplary embodiment of the present invention will be described in detail with reference to FIG. 3.

3A and 3B are cross-sectional views schematically illustrating the operation of the polymer dispersed liquid crystal display 40 according to the second exemplary embodiment of the present invention, and FIG. 3B is a cross-sectional view for describing a black mode.

3, in the polymer dispersed liquid crystal display 40 according to the second embodiment, a polymer dispersed liquid crystal layer 420 is formed between a pair of substrates 450 and 452, and an upper substrate ( The polarizer 430 is disposed on the rear surface of the 452, and the first electrode 440 and the second electrode 442 are disposed at a predetermined position on the upper or lower substrate. Since the configurations of the first electrode 440 and the second electrode 442, the polymer dispersed liquid crystal layer 420, and the polarizing plate 430 are the same as those of the first embodiment described above, redundant descriptions thereof will be omitted.

Hereinafter, operations of the white mode and the black mode of the polymer dispersed liquid crystal display 40 according to the second embodiment having the above-described configuration will be described.

First, a process in which the polymer dispersed liquid crystal display according to the second exemplary embodiment of the present invention operates in the white mode will be described with reference to FIG. 3A. In the state where no voltage is applied to the first electrode and the second electrode, the light incident from the backlight is scattered by the liquid crystal, and the polymer dispersed liquid crystal display by the outgoing light passing through the polarizing plate 430 among the scattered light. The device 40 is operated in white mode.

Referring to FIG. 3B, a process of operating the polymer dispersed liquid crystal display according to the second exemplary embodiment of the present invention in the black mode will be described. A predetermined voltage is applied to the first electrode and the second electrode to form an electric field between the first electrode and the second electrode due to the voltage difference generated between the first electrode and the second electrode. By the electric field formed between the first electrode and the second electrode, the long axes of the liquid crystals of the polymer dispersed liquid crystal layer 420 disposed between the first electrode and the second electrode are arranged in a direction parallel to the direction of the electric field. At this time, the same direction as that of the liquid crystal long axis among the light incident from the backlight is blocked by the arranged liquid crystals. In addition, the light passing through the polymer dispersed liquid crystal is blocked by the polarizing plate 430, there is no emitted light. As a result, the polymer dispersed liquid crystal display 40 operates in a black mode.

Third embodiment

Hereinafter, the configuration and operation of the polymer dispersed liquid crystal display device 50 according to the third embodiment of the present invention will be described in detail. As shown in FIG. 4, the polymer dispersed liquid crystal layer 520 of the polymer dispersed liquid crystal display 50 according to the third embodiment has a polymer network liquid crystal (PNLC) in which liquid crystal is continuously contained in a 3D polymer network structure. ) In this case, since the structure and operation of the polymer dispersed liquid crystal display device having the polymer dispersed liquid crystal layer made of PNLC are the same as those of the above-described preferred embodiment, redundant description thereof will be omitted.

Fourth embodiment

Hereinafter, the configuration and operation of the polymer dispersed liquid crystal display 60 according to the fourth embodiment of the present invention will be described.

 5A and 5B are cross-sectional views schematically illustrating a part of an internal configuration of a polymer dispersed liquid crystal display 60 according to a fourth exemplary embodiment of the present invention. b) is for explaining the operation of the white mode and the black mode, respectively.

First, referring to FIG. 5, in the polymer dispersed liquid crystal display 60 according to the fourth embodiment, a polymer dispersed liquid crystal layer 620 is filled between a pair of substrates 650 and 652. The first polarizing plate 630 and the second polarizing plate 632 are disposed on the back surfaces of the substrates 650 and 652, respectively, and the first electrode 640 and the second electrode 642 are disposed at predetermined positions on the lower substrate. Is placed. Since the first electrode 640 and the second electrode 642 are the same as those of the first embodiment described above, overlapping description thereof will be omitted.

The first polarizer 630 is disposed on the rear surface of the lower substrate 652, and the direction of the polarity of the first polarizer 630 is due to the voltage difference applied to the first electrode and the second electrode. It is preferable to be parallel to the direction of the electric field to be formed.

The second polarizer 632 is disposed on the rear surface of the upper substrate 650, and the direction of the polarity of the second polarizer 632 is orthogonal to the polarity of the first polarizer.

Hereinafter, operations of the white mode and the black mode of the polymer dispersed liquid crystal display 60 according to the fourth embodiment having the above-described configuration will be described.

First, a process of operating the polymer dispersed liquid crystal display according to the fourth embodiment in the white mode will be described with reference to FIG. 5A. When no voltage is applied to the first electrode and the second electrode, light incident from the backlight passes through the first polarizer 630 and is scattered by the liquid crystal, and the scattered light passes through the second polarizer 632. Accordingly, the polymer dispersed liquid crystal display 60 is operated in the white mode.

A process of operating the polymer dispersed liquid crystal display according to the fourth exemplary embodiment of the present invention in the black mode will be described with reference to FIG. 5B. A predetermined voltage is applied to the first electrode and the second electrode to form an electric field between the first electrode and the second electrode due to the voltage difference generated between the first electrode and the second electrode. By the electric field formed between the first electrode and the second electrode, the long axes of the polymer dispersed liquid crystals disposed between the first electrode and the second electrode are arranged in a direction parallel to the direction of the electric field. At this time, the light incident from the backlight passes through the first polarizing plate 630. Since the polarization direction of the first polarizing plate is the same as the electric field direction, the light polarized by the first polarizing plate is the same as the direction of the arranged long axis of the liquid crystal. Therefore, the light passing through the first polarizing plate is not only blocked by the arranged polymer dispersed liquid crystal, but also light that is not completely blocked by the second polarizing plate 632 is completely blocked. As a result, the polymer dispersed liquid crystal display 60 operates in a black mode.

Fifth Embodiment

Hereinafter, the structure and operation of the polymer dispersed liquid crystal display 70 according to the fifth embodiment of the present invention will be described in detail. As shown in FIG. 6, the polymer dispersed liquid crystal layer 720 of the polymer dispersed liquid crystal display 70 according to the fifth embodiment is made of PNLC. Since the structure and operation of the polymer dispersed liquid crystal display device having the polymer dispersed liquid crystal layer made of PNLC according to the present embodiment are the same as those of the above-described fourth embodiment, redundant description thereof will be omitted.

Although the present invention has been described above with reference to preferred embodiments thereof, this is merely an example and is not intended to limit the present invention, and those skilled in the art do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications which are not illustrated above in the scope are possible. And differences relating to such modifications and applications should be construed as being included in the scope of the invention defined in the appended claims.

According to the present invention, the liquid crystal long axis of the liquid crystal layer is arranged parallel to the substrate by arranging the first electrode and the second electrode to face each other on one substrate so that an electric field is formed in a direction parallel to the substrate. As a result, even if the thickness of the liquid crystal layer is increased to improve the performance of the polymer dispersed liquid crystal display device, it is possible to operate with a small driving voltage.

In addition, the polymer dispersed liquid crystal display according to the present invention may increase contrast as the thickness of the liquid crystal layer is increased.

In addition, the polymer dispersed liquid crystal display according to the present invention can improve the contrast ratio by attaching both the upper and lower polarizers according to the required purpose even when the thickness of the liquid crystal layer is thin.

Claims (9)

A substrate comprising a pair of an upper substrate and a lower substrate; A polymer dispersed liquid crystal layer formed of a mixed phase of a polymer and a liquid crystal and formed between the substrates; A first electrode disposed on one of the substrates; A second electrode disposed to be spaced apart from the first electrode by a predetermined distance along the substrate direction, and disposed to face the first electrode; A first polarizer disposed on a rear surface of the lower substrate placed in front of the light source; A second polarizer disposed on a rear surface of the upper substrate; And a horizontal electric field parallel to the substrate by a voltage difference applied to the first electrode and the second electrode, and the liquid crystal of the polymer dispersed liquid crystal layer is parallel to the substrate by the electric field. Characterized in that arranged,  The polarity of the first polarizing plate is disposed to be the same direction as the direction of the electric field formed by the first electrode and the second electrode, the polarity of the second polarizing plate is arranged to be perpendicular to each other and the polarity of the first polarizing plate. A polymer dispersed liquid crystal display device. delete delete delete delete The liquid crystal display of claim 1, wherein the polymer dispersed liquid crystal display operates in a white mode in a state in which no voltage is applied to the first electrode and the second electrode, and a predetermined voltage is applied to the first electrode and the second electrode. The polymer dispersed liquid crystal display device, which operates in a black mode. The polymer dispersed liquid crystal display of claim 1, wherein any one of the substrates is a color filter. The polymer dispersed liquid crystal display of claim 1, wherein the polymer dispersed liquid crystal display further comprises a backlight including red, green, and blue light sources. 2. The substrate of claim 1, wherein the first electrode and the second electrode are disposed on different substrates, and at least a portion of the first electrode and the second electrode overlap each other. A polymer dispersed liquid crystal display, characterized in that a horizontal electric field is formed with respect.

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