JP3385130B2 - Liquid crystal display device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a scattering type liquid crystal display element, and more particularly to a color liquid crystal display element utilizing depolarization by a scattering type liquid crystal cell and birefringence by a retardation plate.

[0002]

2. Description of the Related Art A phase transition type liquid crystal display device in which a liquid crystal composition obtained by adding cholesteric liquid crystal to a nematic liquid crystal is sandwiched between substrates, and a polymer dispersion type liquid crystal in which a fine dispersion structure composed of a liquid crystal and a polymer is sandwiched between substrates. A liquid crystal display device, such as a dynamic scattering mode (DSM) that uses a turbulence due to an electric current, uses a liquid crystal having a negative dielectric anisotropy. A display element that can switch states and utilizes this phenomenon has been proposed and developed. Attempts to perform direct-view color display by these methods are also known, and Kuroda et al. Have proposed a method in which a color filter is stacked on top of two polarizing plates in which a DSM cell is orthogonal. Television Society Image Display Study Group materials, 5-2 (1974)]. According to this method, in the state where no voltage is applied to the pixel, the polarized light transmitted through the liquid crystal cell is blocked by the other polarizing plate, so that a black display is obtained. When a voltage is applied to the pixel to bring the liquid crystal layer into a scattering state, the linearly polarized light that has entered the liquid crystal layer is depolarized by the liquid crystal layer and enters the other polarizing plate. At this time, since about half of the light passes through the polarizing plate, the color of the color filter is recognized, and thus color display can be performed. However, in this method, there is a problem in that light is largely absorbed by the color filter, so that bright display is difficult, or strong illumination is required to forcibly perform bright display, and power consumption increases.
In particular, since a micro color filter is used as a color filter and an additive color mixture using a color filter is used to obtain a white background, there is a problem that stronger illumination is required. Further, in this method, since the DSM method is used, there is a problem that the driving voltage is high and the reliability is low. Further, there is a problem that active matrix driving such as thin film transistor driving cannot be performed because the resistance of the liquid crystal layer is low.

[0003]

An object of the present invention is to provide a liquid crystal display device that solves the above problems in a color liquid crystal display device using a scattering type liquid crystal cell. That is, it is an object of the present invention to provide a liquid crystal display device that can obtain a bright white background even under weak illumination and can perform clear color display.

[0004]

A liquid crystal display device according to the present invention is characterized in that expression of birefringent color by a retardation plate can be controlled by using a change in depolarization function caused by a change in scattering property of a liquid crystal layer due to voltage application. It is a display element. That is, the liquid crystal display element of the present invention is provided between a pair of polarizing plates,
A retardation plate whose slow axis is arranged so as to exhibit coloration due to birefringence when no liquid crystal layer is present, and a retardation plate, which is provided between the retardation plate and the pair of polarizing substrates, and which scatters light by an applied voltage. The present invention relates to a liquid crystal display element including at least a liquid crystal light control layer having optical characteristics that change between a transparent state and a transparent state, and a transparent substrate that sandwiches the liquid crystal light control layer, as at least constituent elements. FIG. 1 shows an example of the configuration of a liquid crystal display element according to the present invention. A liquid crystal light control layer 13 is sandwiched between a pair of translucent substrates 11 and 12 such as glass, a resin plate, or a resin film to form a liquid crystal cell 10. Reference numerals 14 and 15 are pixel electrodes for applying a voltage to the liquid crystal light control layer. Polarizing plates 20 and 30 are arranged outside the liquid crystal cell 10, and a retardation plate 40 is arranged between the liquid crystal cell and at least one of the polarizing plates. However, in the figure, the liquid crystal cell 10 is provided between the polarizing plate 20 and the retardation plate 40.
A liquid crystal cell may be provided between 0 and the retardation plate 40. 50 is a cold cathode tube, a hot cathode tube, a dispersion type EL,
It is a lighting device such as a light emitting diode. Liquid crystal light control layer 13
Can be used as long as it is a system capable of switching between a scattering state and a transparent state by an external field. Among them, an electric field controlled dynamic scattering system (DSM), phase transition system (PC), polymer dispersion system (PDLC) Is typical. Of these, DSM
The method is a method in which a liquid crystal layer with a negative dielectric anisotropy added with an ionic dopant is used as a liquid crystal layer, and a scattering state is caused by turbulence due to an electric current.The phase transition method is a cholesteric method with a positive dielectric anisotropy. The liquid crystal is used as a liquid crystal layer, and the phase change from the focal conic structure of the cholesteric phase to the homeotropic alignment of the nematic phase by applying a voltage is utilized. PDLC has a structure in which liquid crystals are dispersed in a fine shape as an independent phase or a continuous phase in a porous film made of a polymer. The present invention can use any method in principle in the scattering mode, but it can be driven at a relatively low voltage, has a high response speed, and has a high retention rate when active driving is performed. Therefore, the polymer dispersion type liquid crystal display mode is particularly preferably used.

The operation of the liquid crystal display device according to the present invention will be described with reference to FIG. In this example, as shown in FIG. 3, the transmission axes (20T, 30T) of the upper and lower polarizing plates are parallel, the retardation of the retardation plate is 550 nm, and the slow axis (40Z) of the retardation plate is the transmission of the polarizing plate. It was placed rotated 45 ° from the axis. The illumination light color was white. The randomly polarized light L1 emitted from the illuminating device 50 becomes linearly polarized light L2 by the polarizing plate 20 and enters the liquid crystal cell 10. When the liquid crystal layer is transparent,
The polarization state of the incident light does not change and the linearly polarized light is emitted from the liquid crystal cell (L3a) and enters the retardation plate 40. By passing through the retardation plate 40, light is emitted as elliptically polarized light determined by the retardation and wavelength of the retardation plate (L4a). When the light L4a passes through the polarizing plate 30, the light L4a is emitted with an intensity according to the polarization state for each wavelength.
Will be emitted. In the case of this example, a green birefringent color is observed. On the other hand, when the liquid crystal layer is in the scattering state, the linearly polarized light L2 is depolarized by the liquid crystal cell 10 and emitted as random polarized light (L3b). Random polarization L3b
Even after passing through the retardation plate 40, it reaches the polarizing plate 30 as random polarized light regardless of the wavelength. Therefore, the light after passing through the polarizing plate becomes white light. The retardation plate is generally an optical element having an in-plane refractive index anisotropy, and a normally stretched transparent polymer film is used. As the film,
Examples include stretched films of polycarbonate, triacetyl cellulose, polyester, polyvinyl alcohol and the like. The retardation of the retardation plate used in the present invention is preferably in the range of 150 to 1350 nm, and more preferably in the range of 200 to 1200 nm. Retardation of retardation plate is 150
If it is less than 1 nm, it becomes white or black and color display becomes impossible, and if it exceeds 1350 nm, it becomes white and color display becomes impossible. The slow axis of the retardation plate (Note: the slow axis is the direction in which the light velocity of the retardation plate is the slowest, in other words, the direction in which the refractive index is the largest) is the retardation plate when the liquid crystal cell is removed. It is necessary to arrange so as to cause coloring by birefringence, and in order to display a clear color, it is preferable that the transmission axis or the absorption axis of the polarizing plate and the slow axis of the retardation plate are three.
It is necessary to set in the range of 0 ° to 60 °, more preferably 35 ° to 55 °.

Coloring by the phase difference plate arranged in parallel is shown in FIG.
It can be adjusted by the retardation of the retardation plate as shown in the chromaticity diagram. Further, when the two polarizing plates are arranged so that their transmission axes are orthogonal to each other, complementary colors in the case of parallel arrangement can be obtained as shown in the chromaticity diagram of FIG. As can be seen from both figures, the retardation is preferably in the range of 150 nm to 1350 nm. Below this range, it becomes white, and when it is smaller, it becomes very dark. Further, if it is more than this range, the color purity is lowered, and if it is further larger, it becomes white. As is clear from the above description, since the liquid crystal display element according to the present invention performs color display without using a color filter, there is no light loss due to the filter as in the conventional color filter method, and it is extremely bright. It becomes possible to display. In the above example, a single type of retardation plate is used to display between white and one type of colored state. However, as shown in FIG. 6, a plurality of retardation plates having different retardations correspond to pixels. By arranging them in parallel in the device, a plurality of colors can be displayed in one device. For example, when the retardation plate 41 having a retardation of 350 nm and the retardation plate 42 having a retardation of 600 nm are used, it is possible to display two colors of blue and yellowish green. In addition, a plurality of phase difference plates are miniaturized and arranged in parallel, whereby multi-color display can be performed by additive color mixture of each color. In the above example, the retardation plate is provided on the viewer side, but the positional relationship between the retardation plate and the liquid crystal cell may be reversed. Also, as the retardation plate, as in the above example,
One sheet may be used or a plurality of sheets may be used. Use multiple sheets,
When the slow axis is arranged offset, the spectrum width at the time of coloring can be widened, and the birefringent color on the long wavelength side and the birefringent color on the short wavelength side can be avoided when the retardation is large. There are advantages. For the same reason, it is also preferable to use a retardation plate which is not substantially uniaxially oriented but has a twist orientation in which the orientation direction is continuously changed in the thickness direction. In the above description, the case where the illumination is provided has been described, but it is also possible to provide a light reflecting plate instead of the illumination and use it as a reflection type. However, it is preferable to provide an illumination means in order to express bright white.

[0007]

【Example】

Example 1 A pair of vertically aligned glass substrates having transparent electrodes were superposed on each other with a spacer of 8 μm so that the surfaces to be aligned faced each other, and a nematic liquid crystal B manufactured by Merck & Co., Inc. was placed in the gap.
A liquid crystal mixture of L002 and chiral nematic liquid crystal S811 (S811 concentration: 4.4% by weight) is provided between the glass plate polarizers, and when there is no liquid crystal layer, birefringent color injection is performed to produce a phase transition type liquid crystal cell. did. Using this cell, a polarizing plate, a retardation plate, a liquid crystal cell, a polarizing plate, and a diffuse reflection plate were stacked in this order from the observation side. The absorption axes of the upper and lower polarizing plates are parallel or orthogonal, and the slow axis of the retardation plate is arranged so as to form an angle of 45 ° with the absorption axis of the polarizing plate.
A stretched film of polycarbonate was used for the retardation plate. This liquid crystal display element becomes a grayish white when a voltage of 4 V is applied, and the birefringent color of the retardation plate is shown in Table 1 when a voltage of 15 V is applied.
Was displayed. Color purity of 150 nm to 13
The 50 nm range was excellent.

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━     Polarizer arrangement Retardation color of retardation plate                         nm ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━         Parallel 150 dark yellow                         200 yellow                         350 blue                         550 green                         850 blue                         950 blue green                       1300 purple                       1400 light purple ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━         Direct 150 light blue                         400 yellow                         470 orange                         550 purple                         620 blue                         800 green                       1000 orange                       1200 blue purple                       1400 pale yellow ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Example 2 A pair of glass substrates having transparent electrodes were superposed with a 7 μm spacer so that the orientation-treated surfaces faced each other, and 2-ethylhexyl carbitol acrylate, tripropylene glycol diacrylate, benzoin propyl ether were placed in the voids. A mixed composition of liquid crystal BL046 (12/12/1/75 in weight ratio) manufactured by Merck & Co., Inc. was injected, and ultraviolet irradiation was carried out to produce a polymer dispersion type liquid crystal display device. Using this liquid crystal cell, a liquid crystal display element was produced in the same manner as in Example 1. This element was off-white when no voltage was applied, and exhibited the same color as in Table 1 when a voltage was applied. However, in the case of this example, the voltage for performing color display was as low as 5 V, and the hysteresis characteristic observed in Example 1 was not observed. The response speed was 40 msec, which was also superior to Example 1 (100 msec) in this respect.

Example 3 In Example 2, an illuminating device having a light diffusing plate on the top and a hot cathode tube as a light source was used in place of the diffuse reflection plate, and the element was used as a transmissive type. In this case, the color was more vivid and white was pure white, and a very vivid display was obtained.

Example 4 In Example 3, the electrodes of the liquid crystal cell were divided into three, and the positions corresponding to the pixels were 400 nm, 550 nm and 620 nm.
A seed retarder was placed. This element was white when no voltage was applied, and blue, green, and red could be displayed depending on the pixel to which the voltage was applied.

[0011]

The liquid crystal display device of the present invention utilizes depolarization by the scattering type liquid crystal cell and birefringence by the retardation plate, and does not require a color filter unlike the conventional color liquid crystal display device. Therefore, extremely bright display can be performed. Further, by optimizing the retardation of the retardation plate, color display with high color purity becomes possible. Further, by arranging retardation plates having different retardations in parallel in the device, it is possible to display a plurality of colors, and various displays are possible. Furthermore, when a polymer-dispersed liquid crystal light control layer is used as the liquid crystal light control layer, a display element that can be operated at a low voltage and has a quick response can be obtained. In addition, when active driving is performed using the light control layer, a large capacity display is possible in addition to a variety of display colors, which has a wide application as an information display device.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of an example of a liquid crystal display element of the present invention.

FIG. 2 is a diagram illustrating the operation of the liquid crystal display element shown in FIG.

FIG. 3 is a diagram showing an arrangement relationship between a transmission axis of a polarizing plate and a slow axis of a retardation plate of the liquid crystal display element shown in FIGS. 1 and 2.

FIG. 4 is a chromaticity diagram showing that the coloring by the retardation plate can be adjusted by the retardation of the retardation plate.

FIG. 5 is a chromaticity diagram when the retardation plates are arranged in parallel.

FIG. 6 is a liquid crystal display device in which a plurality of retardation plates having different retardations are arranged in parallel in the device so as to correspond to pixels.

[Explanation of symbols]

10 liquid crystal cell 11 translucent substrate 12 translucent substrate 13 liquid crystal dimming layer 14 pixel electrode 15 pixel electrode 20 polarizing plate 30 polarizing plate 40 retardation plate 41 retardation plate (with retardation of 350 nm) 42 retardation plate (With retardation of 600 nm) 50 illuminator x xy in xy chromaticity diagram of ClE y in xy chromaticity diagram of ClE

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-4-134322 (JP, A) JP-A-4-212928 (JP, A) JP-A-4-225322 (JP, A) JP-A-3- 280015 (JP, A) Actual development Sho 52-51659 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/13363 G02F 1/1335 G02F 1/1334 G02F 1/137

Claims (6)

(57) [Claims] 1. A retardation plate which is provided between a pair of polarizing plates and whose slow axis is arranged so as to exhibit coloring by birefringence when no liquid crystal layer is present, and the retardation plate and the pair. A liquid crystal dimming layer provided between the polarizing substrates, the optical characteristics of which change between a light scattering state and a transparent state depending on an applied voltage,
A liquid crystal display device comprising, as at least a constituent element, a transparent substrate sandwiching the liquid crystal light control layer. 2. The liquid crystal according to claim 1, wherein the retardation plate is set such that the transmission axis or the absorption axis of the polarizing plate and the slow axis of the retardation plate are in the range of 30 ° to 60 °. Display element. 3. The retardation of the retardation plate is 150 n
The range of m-1350 nm is the range of 1 or 2.
The liquid crystal display element described. 4. The liquid crystal display device according to claim 1, wherein a plurality of retardation plates having different retardations are arranged in parallel as the retardation plate. 5. The liquid crystal display element according to claim 4, wherein the plurality of retardation plates have mutually different slow axes. 6. The liquid crystal display device according to claim 1, wherein the liquid crystal light control layer is a fine dispersion structure formed of a liquid crystal and a polymer.