JP2008116487A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmissive liquid crystal display device having a backlight, the device hardly receiving such an influence that colors change depending on viewing angles, although the device selects a VA (vertically alignment) mode as an operation mode to obtain high contrast and further the device employs a passive matrix driving and an increased Δnd value to respond to a higher duty. <P>SOLUTION: The liquid crystal display device 10 of the present invention comprises a liquid crystal panel 11 that drives a vertically aligned liquid crystal layer by a passive matrix system and a backlight 12 disposed in an opposite side to the view side of the liquid crystal panel 11. The driving system is a 1/D duty driving (wherein D is an integer of 4 or more). The retardation value of the liquid crystal layer ranges from 500 nm to 1,500 nm. The backlight 12 has a monochromatic light source 121 having a peak of a single wavelength. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a transmissive liquid crystal display device having a backlight.

  Liquid crystal display devices are used in various electric appliances for home use, measuring instruments, automobile panels, word processors, electronic notebooks, printers, computers, televisions, etc., including watches and calculators. As a display form of the liquid crystal display device, there are a so-called transflective type and a transmissive type provided with a backlight, and a reflective type not provided with a backlight. Here, the types of the light source of the backlight include electroluminescence (Electro Luminescent: EL), light emitting diode (LED), and cold cathode fluorescent lamps (CCFL). The color of the light source includes a single wavelength having a narrow wavelength width and a white color having a luminance distribution in almost the entire wavelength range, but white is generally used in many cases.

  Next, liquid crystals are classified into three types, nematic, cholesteric, and smectic, depending on the molecular arrangement. When this liquid crystal is sandwiched between two alignment layers having fine grooves, liquid crystal molecules are aligned along the grooves of the alignment film. Typical operation modes of liquid crystal molecules include TN (Twisted Nematic) mode, STN (Super Twisted Nematic) mode, VA (Vertical Alignment) mode, and the like. Here, the TN mode is a mode in which liquid crystal molecules sandwiched between alignment films are twisted by 90 °. In STN mode, liquid crystal molecules sandwiched between alignment films are twisted by about 180 to 270 °. The VA mode is a vertical alignment mode in which, for example, a nematic liquid crystal having negative dielectric anisotropy is aligned so as to stand perpendicular to the substrate when no voltage is applied. In the case of the VA mode, the incident linearly polarized light reaches the output-side linear polarizing plate as it is without being affected by the birefringence of the liquid crystal molecules. Therefore, since it is interrupted by one polarizing plate, the liquid crystal display panel to which no voltage is applied hardly transmits light. The state in which light is blocked when no voltage is applied is referred to as a normally black mode. In the VA mode, almost no liquid crystal molecules are aligned vertically because no voltage is applied. The ratio is very small and high contrast can be obtained. In the VA mode, switching is performed by applying a voltage between the upper and lower substrates and forcibly arranging liquid crystal molecules in parallel with the substrates.

  As a driving method, there are a passive matrix method, and recently, an active matrix (AM) method driven by a TFT (thin film transistor), a TFD (thin film diode) or the like. Here, the passive matrix system is an arrangement in which X electrodes (Segment terminals) and Y electrodes (Common terminals) are arranged in a vertical and horizontal grid pattern, and has an advantage that the structure is simple and inexpensive. However, there is a demerit that the image quality deteriorates when the high duty drive is used. Next, the active matrix method is a structure in which a semiconductor (transistor) is sandwiched and switched between three terminals of each X electrode, Y electrode, and pixel electrode, and has high contrast and high image quality even when the number of pixels increases. It has the merit that. In recent years, a VA mode type display device driven by an active matrix system in particular is currently most expected in applications to televisions and the like that require a high speed and wide viewing angle. Such a technique is disclosed in Patent Document 1. However, the active matrix method has a disadvantage of high cost.

  Here, when the VA mode is selected in order to obtain high contrast and the driving by the passive matrix method having the merit that the structure is simple and inexpensive is selected, in order to eliminate the disadvantages in the high duty driving described above, This can be solved by increasing the retardation (Δnd) value, which is the product of the refractive index anisotropy (Δn) of the liquid crystal and the layer thickness (d) of the liquid crystal.

  FIG. 5 shows a cross-sectional view of a transmissive liquid crystal display device 100 including a conventional liquid crystal panel 11 and a backlight 12 having a white light source 121. In addition, the VA mode is selected as the operation mode of the liquid crystal molecules, and the liquid crystal layer 113 is aligned so that the liquid crystal molecules stand perpendicular to the glass substrate 112 between the two glass substrates 112 when no voltage is applied. To do. The liquid crystal panel 11 is formed by disposing the two glass substrates 112 and the liquid crystal layer 113 between the two polarizing plates 111. Here, the liquid crystal layer 113 shown in FIG. 5 shows a state where a voltage is applied. Further, the driving method employs a passive matrix method driving, and shows a cross-sectional view of the liquid crystal display device 100 having a 1 / D (D = 4) duty driving and a Δnd value of 1000 nm.

  Next, FIG. 3 shows that in the liquid crystal display device 100 shown in FIG. 5, the angle (viewing angle) formed between the angle at which the liquid crystal panel 11 is viewed and the normal line from the top surface of the liquid crystal panel 11 is up to 80 °. It is a figure which shows the viewing angle dependence of the color in case of the voltage 2.5V. Here, the viewing angle dependency of the color is determined by measuring the color of the liquid crystal panel viewed from each direction and displaying the color. As described above, when the value of Δnd is a large value of 1000 nm, the viewing angle dependency is increased, and in the transmissive liquid crystal display device 100 including the white backlight, there is a problem that the color changes depending on the viewing angle. End up.

JP 2006-233182 A

  As described above, in a transmissive liquid crystal display device having a backlight, a VA mode liquid crystal display method is selected in order to obtain high contrast, and further, a passive matrix drive is adopted to cope with a high duty. , Δnd needs to be increased. As a result, there is a problem that the viewing angle dependency becomes high and the color changes depending on the viewing angle.

  The present invention has been made against the background of such circumstances, and the object of the present invention is to select an operation mode of the VA mode in order to obtain high contrast in a transmissive liquid crystal display device having a backlight, Further, it is to provide a liquid crystal display device that adopts a passive matrix drive and is less susceptible to changes in color depending on the viewing angle even though the value of Δnd is increased in order to cope with higher duty.

  A liquid crystal display device according to the present invention includes a liquid crystal panel that drives a vertically aligned liquid crystal layer by a passive matrix method, and a backlight disposed on the non-viewing side of the liquid crystal panel. The driving method is duty driving of 1 / D (D is an integer of 4 or more), the retardation value of the liquid crystal layer is in the range of 500 nm to 1500 nm, and the backlight has a single wavelength It is characterized by having a monochromatic light source consisting of the peaks.

  Such a liquid crystal display device achieves high contrast and high duty, and the backlight is a single color with a single wavelength with a narrow wavelength width, so that the color varies depending on the viewing angle despite the large Δnd value. Can be prevented from changing.

  Further, such a liquid crystal display device may be constituted by a backlight having a light source whose half-value width of the wavelength of the monochromatic light source is in the range of 15 nm to 45 nm. Here, in the present specification, the half-value width means a peak spread width at a height that is a half of the height at the peak of the wavelength.

  Such a liquid crystal display device can prevent the color from changing depending on the viewing angle even though the value of Δnd is large, by using a backlight having a half width of 15 nm to 45 nm and a narrow wavelength width. .

  Moreover, as such a liquid crystal display device, the backlight may be configured to have a light source including a light emitting diode capable of individually lighting three primary colors (R, G, and B).

  In the liquid crystal display device configured in this way, the three primary colors (R, G, and B) of light can be individually selected one by one in accordance with the retardation (Δnd) value of the liquid crystal layer, thereby suppressing the viewing angle dependency. be able to.

  According to the present invention, in a transmissive liquid crystal display device equipped with a backlight, the VA mode operation mode is selected to obtain a high contrast, the passive matrix drive is adopted, and the Δnd value is set to cope with a high duty. In spite of the increase in size, a liquid crystal display device can be provided which is not easily affected by the change in color depending on the viewing angle.

BEST MODE FOR CARRYING OUT THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view for explaining a liquid crystal display device 10 according to an embodiment of the present invention. FIG. 2 is a diagram showing the luminance and wavelength of a monochromatic light source used as a light source provided in the liquid crystal display device 10 according to the embodiment of the present invention and a commonly used white light source. FIG. 3 and FIG. 4 are diagrams showing the viewing angle dependency of measuring the color of the liquid crystal panel viewed from each direction and displaying the color. Here, FIG. 3 is a diagram showing the viewing angle dependency of the conventional liquid crystal display device 100. FIG. 4 is a diagram showing the viewing angle dependency of the liquid crystal display device 10 according to the embodiment of the present invention.

  The liquid crystal display device 10 according to the present embodiment is a transmissive liquid crystal display device including a liquid crystal panel 11 and a backlight 12. Specifically, in order to obtain high contrast, the VA mode is selected as the operation mode of the liquid crystal molecules, and the liquid crystal layer 113 is not applied with voltage, and the liquid crystal molecules are interposed between the two glass substrates 112. Orient to stand perpendicular to. The liquid crystal panel 11 is formed by disposing the two glass substrates 112 and the liquid crystal layer 113 between two polarizing plates 111. Here, the liquid crystal layer 113 shown in FIG. 1 shows a state where a voltage is applied. Further, the driving method employs passive matrix driving, and is 1 / D (D = 4) duty driving. The Δnd value of the liquid crystal layer is 1000 nm. Further, the liquid crystal display device 10 according to the present embodiment is characterized by including a backlight 12 having a single color 14 LED light source 122 having a single wavelength with a narrow wavelength width as shown in FIG. This is a transmissive liquid crystal display device 10.

  Here, the liquid crystal panel 11 is a portion that displays an image. The polarizing plate 111 is a part that plays a role of allowing light in the polarization direction to pass and blocking light other than the polarization direction.

  As shown in FIG. 5, the conventional liquid crystal display device 100 is a liquid crystal display device 100 having the same specifications as the liquid crystal display device 10 according to the present embodiment, and has a luminance in almost the entire wavelength region as shown in FIG. A backlight 12 having a white 13 LED light source 121 having a distribution is used. Here, FIG. 3 shows that the angle (viewing angle) formed between the viewing angle of the liquid crystal panel 11 in the conventional liquid crystal display device 100 and the normal line from the top surface of the liquid crystal panel 11 is up to 80 °, and the voltage is 2.5V. In this case, the viewing angle dependency of the color is shown. As shown in FIG. 3, if the Δnd value is as high as 1000 nm, the viewing angle dependency becomes high, the color difference depending on the viewing angle is severe, and the color changes depending on the viewing angle.

  However, since the liquid crystal display device 10 according to the present embodiment is composed of the backlight 12 having the LED light source 122 of a single color 14 having a single wavelength with a narrow wavelength width, as shown in FIG. The property is displayed by the brightness difference of a single color. Therefore, the liquid crystal display device 10 according to the present embodiment solves the problem that there is no color difference depending on the viewing angle, and the color is changed depending on the viewing angle.

  Here, in the transmissive liquid crystal display device 100 including the backlight 12 having the white LED light source 121, the operation mode of the VA mode and the passive matrix system driving are adopted, and the D is increased to 4 or higher. It has been confirmed that the viewing angle problem that occurs when the response is made and the color changes depending on the viewing angle occurs at least in the range of the Δnd value of 500 nm to 1500 nm. However, it has been confirmed that the use of the backlight 12 having a single-color LED light source having a single wavelength with a narrow wavelength width can solve the viewing angle problem that occurs when the Δnd value is in the range of 500 nm to 1500 nm. Furthermore, if the Δnd value is higher than 1500 nm, even if the LED light source 122 of the single color 14 is used, the brightness difference of the single color becomes severe, and it has been confirmed that it cannot be used as a liquid crystal display device.

  Further, it is preferable to use a backlight having a light source whose half-value width is in the range of 15 nm to 45 nm. If the half-value width is 15 nm or less, it is a special monochromatic backlight light source, which causes a problem of cost increase. If the half-value width is 45 nm or more, the color changes depending on the viewing angle. Because it starts. Furthermore, if a backlight using LEDs capable of individually lighting the three primary colors (R, G, and B) as a light source is used, it can be displayed in an arbitrary color, and a preferable display color can be selected based on the Δnd value. Furthermore, a pair of retardation films may be disposed between the polarizing plate 111 and the glass substrate 112, respectively. Coloration in the voltage application state can be compensated for by the retardation film.

It is sectional drawing which shows the liquid crystal display device 10 which concerns on embodiment of this invention. It is a figure which shows the light source which concerns on embodiment of this invention. It is the figure which measured the viewing angle dependence of the conventional liquid crystal display device. It is the figure which measured the viewing angle dependence of the liquid crystal display device 10 which concerns on embodiment of this invention. It is sectional drawing which shows the conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Liquid crystal panel 12 Backlight 13 White 14 Monochromatic 15 Half width 111 Polarizing plate 112 Glass substrate 113 Liquid crystal layer 121 White light source 122 Monochromatic light source

Claims (3)

A liquid crystal panel for driving a vertically aligned liquid crystal layer by a passive matrix method;
A backlight arranged on the non-viewing side of the liquid crystal panel, and a transmissive liquid crystal display device comprising:
The driving method is 1 / D (D is an integer of 4 or more) duty driving, and the retardation value of the liquid crystal layer is in a range of 500 nm to 1500 nm,
The backlight is a liquid crystal display device having a monochromatic light source having a single wavelength peak.   2. The liquid crystal display device according to claim 1, wherein a half-value width of the wavelength of the monochromatic light source is in a range of 15 nm to 45 nm.   3. The liquid crystal display device according to claim 1, wherein the backlight includes a light source composed of a light emitting diode capable of individually lighting three primary colors (R, G, and B). 4.