JP2008089772A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element capable of improving display quality by making a contrast of black display of black-and-white display excellent in a configuration such that only one optical retardation film is disposed. <P>SOLUTION: The liquid crystal display element of normally white mode which has a liquid crystal display cell 1 having a liquid crystal layer 6 containing nematic liquid crystal between a pair of transparent substrates 9A and 9B and also has the optical retardation film 10 disposed on at least one surface side between the top and reverse surfaces of the liquid crystal display cell 1, the ratio of retardation value of the optical retardation film 10 being 0.34 to 0.42 of the retardation value of the liquid crystal layer 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive type (normally white mode) STN type liquid crystal display element having an optical compensation function member, which can exhibit a good contrast for black display when realizing black and white display. About.

  When realizing black and white display in an STN (Super Twisted Nematic) type liquid crystal display element (hereinafter simply referred to as a liquid crystal display element), which is a kind of liquid crystal display element, optical compensation is used to compensate for the deviation of the polarization state due to the wavelength of light. A retardation film as a functional member is disposed on the surface of a liquid crystal display cell constituting the liquid crystal display element to improve the display quality.

  FIG. 7 is a schematic cross-sectional view showing a configuration of a positive (normally white mode) liquid crystal display element (hereinafter referred to as an FSTN liquid crystal display element) provided with the retardation film.

  The liquid crystal display cell 1 constituting the liquid crystal display element has two transparent substrates 2A and 2B made of a material such as glass and arranged in parallel with a distance therebetween, and both the transparent substrates 2A. , 2B is sealed with a peripheral sealing material 3. Among these, the transparent common electrode 4 is disposed so as to be in close contact with the lower surface of the one transparent substrate 2A located above, and the non-viewing region is covered below the transparent common electrode 4. A light-shielding film (not shown) is disposed on the surface.

  In addition, an alignment film (not shown) that controls the alignment of liquid crystal molecules according to the voltage applied between the electrodes is disposed below the light shielding film.

  On the other hand, a transparent segment electrode 5 is disposed on the upper surface of the transparent substrate 2B located below. An alignment film (not shown) is disposed above the transparent segment electrode 5 so as to be in close contact therewith. The transparent substrates 2A and 2B have the electrodes 4 and 5 facing each other, and the twist angle of the liquid crystal molecules enclosed in the sealed space surrounded by the transparent substrates 2A and 2B and the peripheral sealing material 3 is 180 °. The liquid crystal layer 6 made of STN type liquid crystal is sealed in the sealed space portion. Further, in order to keep the distance between the transparent substrates 2A and 2B accurately and constant, a plurality of spherical spacers 7 are interposed between the alignment films.

  An elliptically polarizing plate 8 constituting the liquid crystal display element is disposed on the upper surface of the transparent substrate 2A positioned above the liquid crystal display cell 1, and on the lower surface of the transparent substrate 2B positioned below. A polarizing plate 9B is provided.

  Here, the elliptically polarizing plate 8 is formed by laminating a polarizing plate 9A and a retardation film 10. The polarizing plates 9A and 9B serve to regulate the vibration direction of light. The retardation film 10 compensates for interference colors generated when passing through the liquid crystal layer 6. The basic characteristics required for the retardation film 10 are matched to the electro-optical characteristics of the liquid crystal display element. And having a phase difference value (Δn · d).

  The liquid crystal display element thus configured applies a voltage between the specific transparent common electrode 4 and the transparent segment electrode 5 so as to correspond to the image to be displayed, and is positioned between the electrodes 4 and 5. By controlling the orientation of the molecules of the liquid crystal by the alignment film, and passing only light of a specific wavelength from the backlight (not shown) to the transparent substrates 2A and 2B and the elliptically polarizing plate 8, a desired image display is performed. Can be visually observed.

Japanese Patent Laid-Open No. 11-153790

  As described above, in the FSTN liquid crystal display element, the retardation value of the retardation film 10 is usually optimized in order to achieve both monochrome display. However, conventionally, there has been a problem that the black color of the display color when an electric field is applied to a normally white mode liquid crystal display element is insufficient and the contrast is low.

  Although it is expected that this problem will be dealt with by increasing the number of disposed retardation films 10, it is more practical and versatile if the number of disposed retardation films 10 is smaller. desirable.

  Therefore, the present invention provides a liquid crystal display element capable of improving the display quality by improving the black display contrast in black and white display in a configuration in which only one retardation film is provided. It is intended.

  In order to achieve the above-described object, the liquid crystal display element of the present invention has a liquid crystal display cell in which a liquid crystal layer containing a nematic liquid crystal is formed between a pair of transparent substrates, and one of the front and back surfaces of the liquid crystal display cell. In the normally white mode liquid crystal display element in which a retardation film is arranged on one side, the ratio of the retardation value of the retardation film to the retardation value of the liquid crystal layer is 0.34 to 0.42. It is characterized by being.

  Further, the retardation film is laminated integrally with a polarizing plate to constitute an elliptical polarizing plate.

  According to the present invention, even in a liquid crystal display element having a configuration in which only one retardation film is provided, black display during black and white display is set to the target color black, contrast is improved, and display quality is improved. It becomes possible to make it.

  In addition, by forming the retardation film integrally with the polarizing plate to make an elliptical polarizing plate, the vibration direction of light can be regulated by the function of the polarizing plate, and extremely good display quality can be obtained. It becomes.

  The liquid crystal display element of the present embodiment is an FSTN type liquid crystal display element adjusted to a normally white mode. Like the conventional liquid crystal display element of FIG. The liquid crystal display cell 1 has a liquid crystal layer 6 made of a nematic liquid crystal containing an optical rotatory material between a pair of transparent substrates 2A and 2B. An elliptically polarizing plate 8 is disposed on the front side of the liquid crystal display cell 1, and a polarizing plate 9B is disposed on the back side.

  The elliptically polarizing plate 8 is formed by integrally laminating a retardation film 10 on a polarizing plate 9A. In this embodiment, the ratio between the retardation value of the retardation film and the retardation value of the liquid crystal layer. Is set to 0.34 to 0.42.

  Here, Table 1 shows a liquid crystal display element having the configuration shown in FIG. 7, and each liquid crystal display in the case of using 11 types of retardation films 10 having different retardation values within a range of 250 to 585 nm. It is a table | surface which shows the measurement result of the transmittance | permeability T of an element (sample 1-sample 11).

  FIG. 1 shows the ratio of the retardation value of the retardation film to the retardation value of the liquid crystal layer of the liquid crystal display cell (Δn · d (Film) / Δn · d (LC It is a graph which shows the relationship between)) and the transmittance | permeability T. FIG.

  The purpose of the measurement is to specify a retardation range in which the transmittance T is lower than that of a conventional liquid crystal display element, and a liquid crystal using the retardation film 10 having a retardation value of the sample 11 of 585 nm. The display element is a conventional liquid crystal display element having the problem of poor contrast in the black display described above.

  FIG. 2 is an explanatory diagram showing an axial arrangement of the polarizing axes of the polarizing plates 9A and 9B and the retardation axis of the retardation film 10 with respect to the viewing-side alignment axis of the liquid crystal display cell 1 in the liquid crystal display element. In the liquid crystal display element used for the measurement, the phase difference value of the liquid crystal layer 6 of the liquid crystal display cell 1 is 850 nm, the polarization axis angle of the polarizing plate 9A constituting the elliptically polarizing plate 8 (θ1 in FIG. Is the same as the orientation axis on the viewing side of the liquid crystal display cell 1 135 ° clockwise (40 ° in the sample 11), the retardation axis angle of the retardation film (θ2 in FIG. ) Is 90 ° clockwise with respect to the alignment axis, and the polarization axis angle of the polarizing plate disposed on the back surface side of the liquid crystal display cell (θ3 in FIG. 2 (d), the same applies hereinafter). The angle is 162 ° clockwise with respect to the orientation axis. In Sample 11, the polarization axis angle θ1 of the polarizing plate 9A constituting the elliptically polarizing plate 8 is arranged to be different from that of other liquid crystal display elements by about 90 ° when the retardation is about ½. This is to eliminate the phase shift of about ½ that occurs in FIG.

  As a result of this measurement, as shown in Table 1 and FIG. 1, the phase difference values are 290 nm (fourth sample), 300 nm (fifth sample), 330 nm (sixth sample), 350 nm (seventh sample), 360 nm (first sample). In the liquid crystal display element provided with each of the five types of retardation films 10 (8 samples), it is better than the conventional liquid crystal display element provided with the retardation film 10 having a retardation value of 585 nm (11th sample). It turned out that the transmittance | permeability which can obtain the contrast of a black display is shown.

  Therefore, in this embodiment, liquid crystal is used by using the retardation film 10 in which the retardation value of the retardation film 10 is 0.34 to 0.42 (ratio) with respect to the retardation value of the liquid crystal layer 6. If the display element is configured, a good black display contrast in the normally white mode can be obtained.

[Example 1 (Sample 5)]
In the liquid crystal display element having the configuration shown in FIG. 7, the retardation value of the liquid crystal layer 6 of the liquid crystal display cell 1 is 850 nm, the retardation value of the retardation film 10 is 300 nm (ratio with the retardation value of the liquid crystal layer 6: 0.35).

  The axis angle θ1 of the polarizing plate 9A constituting the elliptically polarizing plate 8 of the liquid crystal display element is 135 ° clockwise with respect to the alignment axis on the viewing side of the liquid crystal display cell 8, and the phase difference axis angle θ2 of the retardation film 10. Was 90 ° clockwise relative to the alignment axis, and the polarization axis angle θ3 of the polarizing plate 9B disposed on the back side of the liquid crystal display cell 1 was 162 ° clockwise relative to the alignment axis.

  The chromaticity coordinates of the display color of the ON segment measured by applying an optimum voltage from the direction perpendicular to the surface of the liquid crystal display element in Example 1 are x = 0.326 and y = 0.317. As shown in the graph, it was possible to obtain values close to x = 0.310 and y = 0.316 of the chromaticity coordinates of the target color (black).

  FIG. 4 shows isocontrast curves of the liquid crystal display element of Example 1.

[Example 2 (Sample 6)]
In the liquid crystal display element having the configuration shown in FIG. 7, the retardation value of the liquid crystal layer 6 of the liquid crystal display cell 1 is 850 nm, the retardation value of the retardation film 10 is 330 nm (ratio with the retardation value of the liquid crystal layer 6: 0.39).

  The axial angle θ1 of the polarizing plate 9A constituting the elliptically polarizing plate 8 of the liquid crystal display element is 135 ° clockwise with respect to the alignment axis on the viewing side of the liquid crystal display cell 1, and the retardation axis of the retardation film 10 The angle θ2 was 90 ° clockwise with respect to the alignment axis, and the polarization axis angle θ3 of the polarizing plate 9B disposed on the back surface side of the liquid crystal display cell 1 was 162 ° clockwise with respect to the alignment axis.

  The chromaticity coordinates of the display color of the ON segment measured by applying the optimum voltage from the direction perpendicular to the display surface of the liquid crystal display element in Example 2 are x = 0.313 and y = 0.326. As shown in FIG. 3, the values close to x = 0.310 and y = 0.316 of the chromaticity coordinates of the target color (black) could be obtained.

  In addition, in FIG. 5, the isocontrast curve of the liquid crystal display element of Example 2 is shown.

[Comparative Example (Conventional Example: Sample 11)]
In the liquid crystal display element having the configuration shown in FIG. 7, the retardation value of the liquid crystal layer 6 of the liquid crystal display cell 1 is 850 nm, the retardation value of the retardation film 10 is 585 nm (ratio with the retardation value of the liquid crystal layer 6: 0.69).

  The axial angle θ1 of the polarizing plate 9A constituting the elliptically polarizing plate 8 of the liquid crystal display element is 40 ° clockwise with respect to the alignment axis on the viewing side of the liquid crystal display cell 1, and the retardation of the retardation film 10 The axis angle θ2 is 90 ° clockwise with respect to the alignment axis, and the polarization axis angle θ3 of the polarizing plate 9B disposed on the back side of the liquid crystal display cell 1 is 162 ° clockwise with respect to the alignment axis. .

  The chromaticity coordinates of the display color of the ON segment measured by applying an optimum voltage from the direction perpendicular to the display surface of the liquid crystal display element in this comparative example are x = 0.307 and y = 0.192. As shown in FIG. 5, values significantly different from the chromaticity coordinates x = 0.310 and y = 0.316 of the target color were obtained.

  In addition, in FIG. 6, the isocontrast curve of the liquid crystal display element of a comparative example is shown.

[result]
From the liquid crystal display elements in Example 1, Example 2, and Comparative Example, as in the liquid crystal display element of the above-described embodiment, the phase difference value is 0.34-0. By providing the retardation film 10 of 42, it was proved that a black color substantially equivalent to the target color can be obtained at the time of monochrome display, and a good contrast can be obtained. Further, in that case, as shown in FIGS. 4 to 6, it was also found that the viewing angle characteristics were almost the same as those of the conventional liquid crystal display element, and no problems were caused.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible as needed. For example, the retardation film may be disposed on the back side (anti-viewing side) of the liquid crystal display cell.

The graph which shows the relationship between the ratio of the retardation value of retardation film with respect to the retardation value of the liquid crystal layer of a liquid crystal display cell, and the transmittance | permeability T Explanatory drawing which shows axial arrangement | positioning with respect to the visual recognition side orientation axis | shaft of a liquid crystal display cell of the polarizing axis of the polarizing plate in the liquid crystal display element of embodiment of this invention, and the retardation axis of retardation film. Chromaticity coordinates of ON segments in the liquid crystal display elements of Example 1, Example 2 and Comparative Example (conventional example) of the embodiment of the present invention Isocontrast curve diagram of the liquid crystal display element of Example 1 of the embodiment of the present invention Isocontrast curve diagram of the liquid crystal display element of Example 2 of the embodiment of the present invention Isocontrast curve diagram of the liquid crystal display element of the comparative example (conventional example) A longitudinal sectional view showing the structure of a conventional general FSTN liquid crystal display element

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display cell 2A, 2B Transparent substrate 3 Sealing material 4 Transparent common electrode 5 Transparent segment electrode 6 Liquid crystal layer 7 Spacer 8 Ellipse polarizing plate 9A, 9B Polarizing plate 10 Phase difference film

Claims (2)

A normally white mode liquid crystal having a liquid crystal display cell in which a liquid crystal layer containing a nematic liquid crystal is formed between a pair of transparent substrates, and having a retardation film disposed on one of the front and back surfaces of the liquid crystal display cell. In the display element, the ratio of the retardation value of the retardation film to the retardation value of the liquid crystal layer is 0.34 to 0.42. The liquid crystal display element according to claim 1, wherein the retardation film is laminated integrally with a polarizing plate to constitute an elliptically polarizing plate.

Images