JP2007322946A - Ocb mode liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OCB mode liquid crystal display device with which heightening of contrast and widening of a viewing angle are materialized by optimizing a construction of a PDM compensation film and a condition of bend alignment of a liquid crystal without depending on trial-and-error methods, in an OCB-LCD using the PDM compensation film. <P>SOLUTION: The OCB mode liquid crystal display device using the PDM compensation film is constructed in such a way that a polarization state of light after passing through a biaxial substrate 2 turns into elliptically polarized light having an elliptical longitudinal direction of about 45° or about -45° with respect to an incident plane (a biaxial substrate 8 similarly functions) in an orientation plane of a bend aligned liquid crystal 5 or in a plane vertical thereto without being influenced by an incident angle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an OCB mode liquid crystal display device, and more particularly to an OCB mode liquid crystal display device in which a retardation film (same as an optical compensation film) and a liquid crystal cell are optimized to realize a wide viewing angle and a high contrast.

  An OCB (Optically Compensated Bend) mode liquid crystal display device (hereinafter also referred to as an OCB mode LCD) is attracting attention as a next-generation liquid crystal display because it can display a wide viewing angle and high-speed moving images. The OCB mode LCD is composed of a bend alignment liquid crystal, an optical compensation film, and a polarizer. In recent years, Mori et al. Proposed using a polymerized discotic material as the optical compensation film, and reported that the OCB mode LCD can achieve a wide viewing angle (but a viewing angle of 160 °) (non-patented). References 1, 2).

A film using a polymerized discotic material is scientifically called a PDM film (Polymerized Discotic Material film), and a product name is called an OCBWV film (OCB Wide View-film). This PDM film As shown in FIG. 2, the PDM layer 20 is provided on a biaxial substrate (substrate having biaxial optical anisotropy) 10. The PDM layer 20 is formed by applying a hybrid aligned discotic liquid crystal material on the biaxial substrate 10 and polymerizing it.
H.Mori and Philip J.Bos: Jpn.Appl.Phys., Vol.38 pp.2838 (1999) Y. Ito, R. Matsubara, R. Nakamura, M. Nagai, S. Nakamura, H. Mori and K. Mihayashi: SID Symp Digest Tech. Papers, p. 986 (2005)

  In order to design an OCB mode LCD using a PDM film as an optical compensation film, it is necessary to match the configuration of the PDM film and the bend alignment conditions of the liquid crystal well. However, this analysis is very difficult, and in the past, it often relied on trial and error. Therefore, in the OCB mode, there is still room for improvement in terms of contrast ratio and viewing angle characteristics as compared with the IPS (in-plane-switching) mode and the VA (vertical alignment) mode.

  Incidentally, FIG. 1 is an isocontrast diagram (where the contrast ratio is a calculated value) showing an example of the display performance of a conventional OCB mode LCD (PDM film is used as the optical compensation film). The isocontrast diagram is a line of isocontrast ratio on a concentric coordinate system representing a visual field (a coordinate system in which the center of the concentric circle is a polar angle of 0 °, a polar angle in the radial direction and an azimuth angle in the circumferential direction). (The same shall apply hereinafter.) In this example, it is hard to say that local non-uniformity appears in the contrast ratio, and high contrast and wide viewing angle (a state in which both the contrast characteristics and viewing angle characteristics are improved) are realized.

  The present invention solves the above-mentioned problems, and in an OCB mode LCD using a PDM compensation film (meaning a PDM film as an optical compensation film), the configuration of the PDM compensation film and the bend alignment conditions of the liquid crystal without trial and error. An object of the present invention is to provide an OCB mode liquid crystal display device that can realize high contrast and wide viewing angle.

  In order to achieve the above object, the inventors analyzed the optical characteristics of an OCB mode LCD (using PMD compensation film) and found that high contrast and a wide viewing angle can be realized if the following condition 1 is satisfied. I found it.

  Condition 1: The polarization state after passing through the biaxial substrate is an elliptical major axis orientation of 45 ° or −45 ° with respect to the incident surface regardless of the incident angle in the bend alignment plane or a plane perpendicular thereto. It is an elliptically polarized light having (or a state close to this).

  Furthermore, in addition to the condition 1, when one or more of the following conditions 1-2, 2 and 3 are satisfied, the greater the number of conditions to be satisfied, the greater the contrast characteristics and / or the viewing angle characteristics. I found it to improve.

  Condition 1-2: The ellipticity of the elliptically polarized light is as small as possible.

  Condition 2: Light that has passed through the PDM layer next to the biaxial substrate is incident on the bend alignment liquid crystal, and the polarization state is 45 ° or −45 ° linear with respect to the incident plane when the light reaches the middle point of the bend alignment. It must be linearly polarized light with orientation (or a state close to this).

  Condition 3: The wavelength dispersion of birefringence between the liquid crystal material and the PDM layer is equal (or close to this).

  This invention is made | formed based on the above-mentioned new knowledge, The summary structure is as follows.

  1. An OCB mode liquid crystal display device using a PDM compensation film, in which the polarization state after passing through the biaxial substrate is not relative to the incident plane in the alignment plane of the bend alignment liquid crystal or in a plane perpendicular thereto. An OCB mode liquid crystal display device characterized by being elliptically polarized light having an elliptical major axis orientation of approximately 45 ° or approximately −45 °.

  Here, “approximately Θ (Θ = 45 ° or −45 °)” means that the major axis direction of the ellipse is within the range of Θ ± 10 °.

  2. 2. The OCB mode liquid crystal display device according to item 1, wherein the ellipticity of the elliptically polarized light is 0.5 or less.

  Here, the ellipticity (ratio of the minor axis length to the major axis length of the ellipse) is preferably 0.25 or less, more preferably 0.1 or less. In addition, elliptically polarized light (that is, linearly polarized light) having an ellipticity of 0 is most preferable.

  3. After passing through the PMD compensation film on the incident side, it enters the bend-aligned liquid crystal, and the polarization state when it reaches the intermediate point of the liquid crystal becomes approximately 45 ° or almost −45 ° with respect to the incident surface. 3. The OCB mode liquid crystal display device as described in 1 or 2 above.

  Here, “approximately Θ (Θ = 45 ° or −45 °)” means that the major axis direction of the ellipse is within the range of Θ ± 10 °. Further, “substantially linearly polarized light” means elliptically polarized light having an ellipticity in the range of 0 to 0.2.

  4). 4. The OCB mode liquid crystal display device according to any one of items 1 to 3, wherein the liquid crystal material and the PDM layer have substantially the same birefringence wavelength dispersion.

  Here, “the wavelength dispersion of the birefringence between the liquid crystal material and the PDM layer is substantially equal” means that the equation represented by [Equation 1] with ε = 0.05 is satisfied over all wavelengths λ of visible light. . Preferably, ε = 0.025, more preferably ε = 0.01.

  According to the present invention, it is possible to realize an OCB mode LCD having a high contrast and a wide viewing angle characteristic far superior to those of the prior art.

  FIG. 3 is a schematic diagram showing the configuration of an OCB mode LCD using a PDM compensation film. Here, it is assumed that light passes from the bottom to the top of the figure (the lower part of the LCD is the incident side and the upper part is the outgoing side).

  In the best mode of the present invention, the OCB mode LCD has a vertically symmetrical structure with respect to the alignment center plane of the bend alignment liquid crystal 5. Therefore, the retardation Γ relationship and the slow axis orientation relationship between the upper part and the lower part of the OCB mode are expressed by the following equations.

Γ _LC1 = Γ _LC2 , Φ _LC1 = −Φ _{LC2
Γ PDM1 = Γ PDM2, Φ PDM1} = -Φ PDM2
Γ _Biax1 = Γ _Biax2 , Φ _Biax1 = −Φ _Biax2
Here, the subscripts LC1, PDM1, and Biax1 represent the upper part and upper (outgoing side) PMD layer 7 and biaxial substrate 6 of the liquid crystal 5, respectively, and the subscripts LC2, PDM2, and Biax2 represent the liquid crystal, respectively. 5 represents the PMD layer 3 and the biaxial substrate 2 in the lower part, the lower part (incident side).

  In this case, in order to achieve a high contrast ratio within a wide viewing angle, the best conditions (ideal conditions) that the biaxial substrate and the OCB mode liquid crystal cell should satisfy are the following (a) to (c).

  (A) The orientation of the polarization state after passing through the biaxial substrate 2 (the major axis orientation of elliptically polarized light) is 45 ° or −45 ° with respect to the incident surface (the same applies to the biaxial substrate 8).

  (B) The polarization state at the center (between the upper and lower portions) of the bend-aligned liquid crystal 5 is 45 ° or −45 ° linearly polarized light.

  (C) The birefringence wavelength dispersion of the liquid crystal 5 is the same as that of the PDM layer.

  FIG. 4 is a diagram showing a polarization state corresponding to an ideal condition of an OCB mode LCD for obtaining a high contrast ratio during oblique observation. In this figure, each point on the Poincare sphere corresponds to each polarization state on a one-to-one basis, and a great circle having S1 of 0 corresponds to a polarization state of 45 ° or −45 °.

As shown in this figure, shifts in the position of the point P ₁ polarization state T _in of the incident light by biaxial substrate 2, and if the polarization state at the center of the bend-aligned liquid crystal 5 is a point P _0, the liquid crystal The polarization state after passing through the cell 15 is a point P ₂ , and this polarization rotates to the absorption axis direction A _{out of the} biaxial substrate 8. As a result, a dark state can be obtained within a wide viewing angle range.

  An OCB mode LCD was designed according to the conditions (a) to (c). FIG. 5 shows the conversion of the polarization state by the biaxial substrate 2 during oblique observation of this LCD. As shown in the figure, it was confirmed that the polarization state after passing through the biaxial substrate 2 was 45 ° elliptical polarization within a wide viewing angle range. FIG. 5 shows an example in which the ellipticity of the elliptically polarized light is more than 0.5.

  FIG. 5A shows an example (a) in which the ellipticity of the elliptically polarized light is 0.5 or less and more than 0.1, and an example (b) in which the ellipticity is 0.1 or less. It was also confirmed that the contrast ratio improved as the ellipticity decreased.

  FIG. 6 shows isocontrast lines (calculated values) for the designed OCB mode liquid crystal cell. Comparing FIG. 6 with the conventional IPS mode isocontrast diagram (see FIG. 7), it can be seen that the present invention achieves a high contrast ratio in a wide viewing angle range.

  Designed to meet the ideal conditions, and in accordance with this design, a normal manufacturing process (the manufacturing error in this process is so large that the product deviates from the scope of the present invention, that is, the “substantially” described in the preceding items 1 to 4. A 15-inch CFS (Color-field sequential refreshing) -LCD was prototyped by combining a scanning LED backlight with the OCB mode liquid crystal cell manufactured in (1). Table 1 shows the specifications of this LCD. The appearance of this LCD prototype is shown in FIG.

  This LCD showed a high contrast ratio of 1350: 1, a wide viewing angle over 170 ° (contrast ratio> 10: 1) and no grayscale inversion over a wide viewing angle range. . Further, an additional feature of the LCD is applicability to overdrive for suppressing color-shift.

  Thus, according to the present invention, there is provided a high-quality CFS-LCD that exhibits an extremely high contrast ratio and high brightness within a wide viewing angle range, and also has a high-quality moving image display characteristic without color break-up. It was confirmed that this was realized.

It is an iso-contrast diagram which shows an example of the display performance of the conventional OCB mode LCD (PDM film is used for the optical compensation film). It is a schematic diagram which shows the structure of a PDM film. It is a schematic diagram which shows the structure of OCB mode LCD using a PDM compensation film. It is a figure which shows the polarization state corresponding to the ideal condition of OCB mode LCD for obtaining a high contrast ratio at the time of diagonal observation. It is a figure which shows conversion of the polarization state by the biaxial board | substrate of an incident side (example in which the ellipticity of elliptically polarized light is more than 0.5). The figure which shows conversion of the polarization state by the incident side biaxial substrate ((a) is an example in which the ellipticity of elliptically polarized light is 0.5 or less and more than 0.1, (b) is an example in which the ellipticity of elliptically polarized light is 0.1 or less) It is. FIG. 5 is an isocontrast diagram showing an example of display performance of the OCB mode LCD of the present invention. It is an isocontrast diagram which shows an example of the display performance of the conventional IPS mode LCD. 2 is a monochrome photocopy of a color photograph showing the appearance of a color field sequential OCB mode LCD prototype according to the present invention. FIG.

Explanation of symbols

1 Polarizer (incident side)
2 Biaxial substrate (incident side)
3 PDM layer (incident side)
4 Transparent substrate (incident side)
5 Liquid crystal (bend alignment liquid crystal)
6 Transparent substrate (outgoing side)
7 PDM layer (outgoing side)
8 Biaxial substrate (outgoing side)
9 Polarizer (outgoing side)
15 LCD cell
10 Biaxial substrate
20 PDM layer

Claims (4)

  An OCB mode liquid crystal display device using a PDM compensation film, in which the polarization state after passing through the biaxial substrate is not relative to the incident plane in the alignment plane of the bend alignment liquid crystal or in a plane perpendicular thereto. An OCB mode liquid crystal display device characterized by being elliptically polarized light having an elliptical major axis orientation of approximately 45 ° or approximately −45 °.   2. The OCB mode liquid crystal display device according to claim 1, wherein an ellipticity of the elliptically polarized light is 0.5 or less.   After passing through the PMD compensation film on the incident side, it enters the bend-aligned liquid crystal, and the polarization state when it reaches the intermediate point of the liquid crystal becomes approximately 45 ° or almost −45 ° with respect to the incident surface. The OCB mode liquid crystal display device according to claim 1 or 2, characterized in that   4. The OCB mode liquid crystal display device according to claim 1, wherein the liquid crystal material and the PDM layer have substantially the same birefringence wavelength dispersion.