JP3695780B2 - Liquid crystal display device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a liquid crystal display device having low viewing angle dependency.
[0002]
[Prior art]
Conventionally, in a display device using a liquid crystal cell (Japanese Patent Laid-Open No. 60-107020), a viewing angle (observation direction) at which a certain level of contrast and brightness are obtained is limited. In other words, even if the display is observed from the front, the display tends to be dark, and on a large screen, the display is observed from an oblique direction with respect to the peripheral portion of the display. It is said that viewing angle dependency is high because of such a large viewing angle limitation.
[0003]
The reason for the viewing angle dependency is that the liquid crystal molecules are twisted (such as the direction of the spiral or the spiral start position of the liquid crystal molecules determined by the rubbing direction), or the birefringence anisotropy of the liquid crystal (depending on the light passing direction). Due to differences in retardation, etc., due to the characteristics of the polarizing plate (such as the selectivity of the light vibration direction), or due to the directivity of the light source that irradiates the liquid crystal. Can be mentioned.
[0004]
In general, the liquid crystal display device is designed so that the position where the display is most easily seen is within the normal viewing range of the user in consideration of the viewing angle dependency, for example, the normal direction of the screen center or a slightly downward direction. It is designed to increase the contrast of the image compared to the surrounding area.
[0005]
[Problems to be solved by the invention]
The main object of the present invention is to improve the viewing angle dependency generated in the liquid crystal display device for the various reasons described above, and to realize improvement of the viewing angle dependency with a simple configuration.
[0008]
[Means for Solving the Problems]
The present invention relates to a liquid crystal cell having a predetermined liquid crystal layer, a light introducing means for guiding light that is condensed on the liquid crystal layer of the liquid crystal cell and having improved directivity, and a method among the light emitted from the liquid crystal cell. A light diffusing means for diffusing light incident in a predetermined angle range from the line, and the main direction of the light guided to the liquid crystal layer by the light introducing means is an angle for diffusing the light in the light diffusing means The light directivity of the light introducing means is set so as to be within the range of.
[0009]
The light diffusing means is preferably composed of a polymer film.
[0010]
[Action]
According to the present invention, since the light diffusing means for selectively diffusing the light in the predetermined direction emerging from the liquid crystal cell is provided, the twist of the liquid crystal molecules, the birefringence anisotropy of the liquid crystal, the characteristics of the polarizing plate, the orientation of the light source The light in the desired direction can be selected and diffused by the light diffusing means among the light emitted from the liquid crystal due to the influence of the property, etc., and the viewing angle dependency can be reduced.
[0011]
In addition, by setting the light directivity of the light introducing means so that the main direction of the light guided to the liquid crystal layer by the light introducing means and the incident direction of the light diffused by the light diffusing means are the same direction, the directivity is improved. The light in the desired direction out of the light emitted from the liquid crystal is more uniformly diffused by the light diffusing means, and the viewing angle dependency can be reduced by making the luminance and contrast uniform.
[0012]
【Example】
FIG. 1 is a cross-sectional view of a main part of a liquid crystal display device according to an embodiment of the present invention. 1 is a liquid crystal cell having a liquid crystal layer 10 having a predetermined thickness, and 2 is a direction substantially perpendicular to the liquid crystal layer 10 of the liquid crystal cell 1. A light introducing means 3 for guiding light is a light diffusing means for diffusing the light emitted from the liquid crystal cell 1.
[0013]
The liquid crystal cell 1 includes, for example, a so-called twisted nematic liquid crystal layer 10 in which liquid crystal molecules are arranged in a spiral shape of 90 to 270 degrees, and a substrate 11 provided with an electrode 12 for applying an electric field for each pixel orthogonal to the inner surface. I support. When the polarizing plate 13 is required for the liquid crystal cell 1, it is simple and preferable that the polarizing plate 13 is attached to the front and back sides of the substrate 11. In addition, an alignment film 14 for forming a predetermined alignment in liquid crystal molecules is formed on the substrate 11 with the liquid crystal layer 10 interposed therebetween. However, when the substrate 11 is directly rubbed and aligned, the alignment film 14 is omitted. You can also Here, alignment is performed such that a region where high contrast is obtained becomes a predetermined region of the liquid crystal cell 1, for example, a lower region (see the observation direction in FIG. 2).
[0014]
The light introducing means 2 is composed of, for example, a plastic lens sheet such as a polycarbonate in which fine prisms having apex angles of about 90 to 100 degrees are formed on the entire upper surface at a pitch of 10 to several hundreds μm. It has the function of condensing the light incident from and making it light with improved directivity. The light introducing means 2 may be configured by forming microlenses with transparent materials having different refractive indexes such as silicon, epoxy resin, silver chloride in a transparent flat plate such as acrylic resin or optical glass, You may comprise a flat convex lens array, the laminated body of a convex lens array and a concave lens array, or the laminated body of a some convex lens array and a concave lens array.
[0015]
A surface illumination means 4 can be provided on the back side of the light introduction means 2 as required. The surface illumination means 4 is provided on the light guide plate 41 as necessary, for example, a light guide plate 41 such as an acrylic resin flat plate, a linear light source 42 formed of a cold cathode tube provided on the side surface of the light guide plate 41, and the like. Further, it can be constituted by the front surface light diffusion sheet 43, the back surface reflection sheet 44, or a cylindrical reflection sheet (not shown) that covers the linear light source. Here, the surface light diffusion sheet 43 can also be used as the light introducing means 2.
[0016]
As shown in FIG. 2, the light diffusing means 3 has the same rectangular planar shape as the liquid crystal cell 1 and extends from a predetermined range, for example, a normal (φ = 0 degrees) to a range of about 30 degrees in a predetermined direction. A polymer thin film having a special structure set to scatter incident light. When the light diffusing unit 3 observes an object through the light diffusing unit 3 as shown in FIG. 2, for example, a range of 0 to 30 degrees from the viewpoint in one direction of the front surface is in an opaque state, and the other ranges appear to be transparent. Thus, it has a function of selectively diffusing incident light. In the opaque state, the light diffusing means 3 has the same light transmittance as that in the transparent state, and diffuses most of the transmitted light to form a ground glass-like appearance.
[0017]
The polymer thin film constituting the light diffusing means 3 can be an acrylic resin molded product having a blind phase structure, for example. When observed with an optical microscope, the internal structure of this molded product is formed into a phase of a certain length although it is cut into a tatami-like shape in surface observation, and a depth of about 50 μm from the film surface in longitudinal section observation. As a result, a phase structure with shades is formed in a blind shape. The interval of such a phase structure is about 2 μm at the top of the film and 3 to 4 μm at a depth of about 300 μm from the irradiation surface, and the interval gradually increases along the depth direction. May be set according to the light diffusion direction and the light diffusion degree. In addition, if the direction of the phase structure is changed to change the inclination of the phase structure with respect to the light irradiation surface, the manifestation angle of the opaque state can be freely set, so the incident angle range of the light to diffuse is required. It can be set accordingly. Furthermore, there is a large composition distribution difference between the phase structures, for example, the refractive index is 1.55 for one phase, 1.51 for the other phase, and the refractive index difference between the phases is as large as 0.4. Could be set to. These values can be molded so as to show the same value at any position in the depth direction of the film. The above-described viewing angle-dependent light scattering that occurs in the polymer thin film can be controlled largely due to the difference in refractive index between the phase structure and the phase structure. If a polymer thin film constituting such a light diffusing means 3 is to be obtained as a commercial product, it is optical for the series of visibility control films (product name “Lumsty”) manufactured by Sumitomo Chemical Co., Ltd. It is preferable to specify and use characteristics.
[0018]
The light diffusing means 3 is affixed to the surface of the liquid crystal cell 1 using an adhesive. At that time, the positioning of the light diffusing means 3 is adjusted so that the viewing angle of the liquid crystal cell 1 is improved. Done. In the present embodiment, for example, the case of improving the viewing angle when viewing the upper side from the lower side of the liquid crystal cell 1 is illustrated, and when observing through the light diffusing means 3 with the line of sight fixed as shown in FIG. The range of the line of sight in which the object appears opaque is a range of 0 to 30 degrees upward from the normal direction (when the viewpoint is changed and one point of the light diffusing means 3 is viewed, the range of the viewpoint that appears opaque is the normal direction. The light diffusing means 3 is positioned and attached to the liquid crystal cell 1 so as to be in the range of 0 to 30 degrees downward. That is, the light diffusing means 3 is positioned so that light traveling from the liquid crystal cell 1 toward the viewing angle direction to be improved is diffused by the light diffusing means 3 (entering an incident angle range in which the light diffusing means 3 diffuses light). The liquid crystal cell 1 is attached. Here, since the light diffusing means 3 is composed of a thin film, the display device can be thinned and can be easily attached to the liquid crystal cell 1 using an adhesive or the like. Simplification can be achieved.
[0019]
As a result of attaching the light diffusing means 3 to the liquid crystal cell 1 in this way, data as shown in FIGS. 3 to 5 was obtained in the vertical direction of the liquid crystal cell 1. In this data measurement, the back side of the light introduction means 2 is illuminated by the surface illumination means 4 having a predetermined luminance, and the light introduction means 2 has a main direction of light guided to the liquid crystal cell 1 with respect to the liquid crystal cell 1. It is assumed that the directivity is substantially vertical.
[0020]
As is apparent from the data shown in FIG. 3, the luminance (cd / m ² ) in the vertical direction when the liquid crystal cell 1 is lit is about 10 degrees downward from the normal compared to the case where the light diffusing means 3 is not provided. Although there was a drop, the range of luminance of 30 or more in the downward direction expanded from 20 degrees to around 35 degrees. Further, as shown in FIG. 5, the contrast changed in the same manner as the luminance, and the range of contrast 5 or more was expanded from 20 degrees to 35 degrees. Incidentally, the brightness and contrast in the upward direction from the normal line are hardly changed. In this way, while maintaining the upper state as it is, the range of brightness and contrast in the lower direction can be expanded beyond the predetermined value, so the viewing angle when looking from the desired lower side to the upper side can be improved. I was able to do it positively. Furthermore, the range in which the contrast in the downward direction is inverted expanded from around 25 degrees to around 45 degrees.
[0021]
In the above embodiment, the case of improving the viewing angle in the downward direction is taken as an example, but in order to improve the viewing angle in the upward direction (when viewing the display surface from the upper side to the lower side of the normal line) For this, the light diffusing means 3 may be attached to the liquid crystal cell 1 by turning it upside down. However, in order to improve the viewing angle in the right direction or the left direction, the light diffusing means 3 can be attached to the liquid crystal cell 1 by rotating it 90 degrees left and right, but the good viewing direction is set to the lower side. In this example, the viewing angle could not be improved as much as the vertical direction.
[0022]
Next, in the above-described embodiment for improving the viewing angle in the downward direction, as shown in FIGS. 3 and 5, the luminance and the contrast drop in the vicinity of 10 degrees in the downward direction. You can increase the brightness. Therefore, as another embodiment, for example, the directivity of the light introducing means 2 that had directivity in the direction perpendicular to the liquid crystal cell 1 is changed according to the characteristics or arrangement of the light diffusing means 3. Is desirable. For example, in order to increase the luminance around 10 degrees in the downward direction where the brightness is decreasing, the main direction of the light guided to the liquid crystal cell 1 by the light introducing means 2 is directed to around 10 degrees in the downward direction where the brightness is decreasing. It is desirable to set the directivity of the light introducing means 2. That is, the light diffusing means 3 has a special structure that scatters incident light in a range of about 0 degree to 30 degrees downward with respect to the normal line (φ = 0 degree). The main direction of light introduced into the liquid crystal cell 1 by the light introducing means 2 is about 0 degree to about 30 degrees downward with respect to the normal line (φ = 0 degree). It is desirable to set the directivity of the light introducing means 2 so that the range is preferably about 15 degrees downward with respect to the normal line (φ = 0 degree) which is the middle of the range.
[0023]
【The invention's effect】
According to the present invention, since the light diffusing means for selectively diffusing the light in the predetermined direction emerging from the liquid crystal cell is provided, the twist of the liquid crystal molecules, the birefringence anisotropy of the liquid crystal, the characteristics of the polarizing plate, the orientation of the light source Viewing angle by selectively diffusing the light in the desired direction by the light diffusing means out of the light that has been influenced by one or a combination of the two, etc. The dependency can be reduced.
[0024]
In addition, by setting the light directivity of the light introducing means so that the main direction of the light guided to the liquid crystal layer by the light introducing means and the incident direction of the light diffused by the light diffusing means are the same direction, the directivity is improved. The light in the desired direction out of the light emitted from the liquid crystal is more uniformly diffused by the light diffusing means, and the viewing angle dependency can be reduced by making the luminance and contrast uniform.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a perspective view showing an arrangement of a liquid crystal cell and light diffusing means according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram of luminance change when the liquid crystal is ON according to an embodiment of the present invention.
FIG. 4 is a luminance change characteristic diagram when the liquid crystal is OFF according to the embodiment of the present invention.
FIG. 5 is a contrast characteristic diagram according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Liquid crystal cell 2 Light introducing means 3 Light diffusing means 4 Surface illumination means

Claims (2)

A liquid crystal cell having a predetermined liquid crystal layer, and a light introducing means for guiding the light with enhanced directivity by condensing on the liquid crystal layer of the liquid crystal cell;
A light diffusing means for diffusing the light incident from a normal line within a predetermined angle range among the light emitted from the liquid crystal cell;
The light directivity of the light introducing means is set so that a main direction of light guided to the liquid crystal layer by the light introducing means is within an angle range in which light is diffused in the light diffusing means. Liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the light diffusing means is formed of a polymer film.

Images