JP2004037831A - Retroreflector, polarizing plate with retroreflector, and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retroreflector as a transflector capable of obtaining bright display not only near a front surface but also in a wider range in the case of being used in a transreflective liquid crystal display device or a reflective liquid crystal display device. <P>SOLUTION: This retrorefelctor 1 is provided with a prism sheet 10 for which prisms are formed at every prescribed pitch on one surface. On the prism sheet 10, a metal deposition film 13 is formed on only one of the slopes of the respective prisms. Especially, in the case of applying the retroreflector 1 to the liquid crystal display device whose display screen is vertically placed, the metal deposition film 13 is formed to the slope 12 for which a normal line extended to the viewing side of the liquid crystal display device forms an elevation angle to a horizontal plane in the state of viewing the liquid crystal display device. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a retroreflective plate, a retroreflective polarizing plate with a retroreflective plate, and a retroreflective plate suitable for use in a transflective liquid crystal display device (also applicable to a reflective liquid crystal display device). The present invention relates to a liquid crystal display device used.
[0002]
[Prior art]
Conventionally, as a transflective plate used in a transflective liquid crystal display device, a material utilizing the translucency of a mica filler or a material utilizing the translucency of a metal-deposited thin film has been used. There were problems such as low reflectivity and coloring inherent to the thin film.
[0003]
As a transflective plate, there is also known a retroreflective plate formed of a prism sheet in which minute prisms having a triangular cross section are formed on one surface of the sheet at a predetermined pitch. Since such a retroreflective plate is based on the principle of using total reflection (critical reflection), the reflectivity is substantially close to 100% and the reflection spectrum is neutral. I can say. Further, since it has no light-impermeable surface, it has a high transmittance and has excellent characteristics as a transflective plate.
[0004]
However, in the case of a single retroreflective plate, light incident from a light source (external light) is totally reflected by the prism surface and only returns to the light source. Therefore, when the retroreflective plate alone is applied to the transflective liquid crystal display device or the reflective liquid crystal display device and it is intended to visually recognize the reflected light from the external light, only the viewer itself is reflected, and the light source ( External light) cannot be used efficiently, resulting in a problem that a bright display cannot be obtained.
[0005]
Therefore, it has also been attempted to improve the visibility by giving a diffusivity to the retroreflective plate to generate a scattered reflection characteristic, thereby giving a reflection ability in a direction slightly away from the retroreflection direction. I have.
[0006]
However, even if the diffusivity is given, the total reflection (critical reflection) itself occurs only for light incident within a narrow range of about ± several degrees from the front direction of the retroreflective plate. Light incident at a large angle deviates from the total reflection condition (critical condition), so that there is a problem that the light is lost without being retroreflected. For example, as shown in FIG. 3, in a retroreflective plate made of the prism sheet 10, the vertex angle α of the prism is 90 degrees, the inclination angle β of the slope 11 and the inclination angle γ of the slope 12 (the inclination angle of the prism sheet with respect to the front direction). Angle) is 45 degrees, and the refractive index of the prism is 1.5, the critical angle is about 42 degrees. In this case, only light incident within a range of about ± 5 degrees from the front direction of the prism sheet 10 satisfies the condition of total reflection. That is, as shown in FIG. 3, the light (L1 in FIG. 3) incident within the range is totally reflected by the slopes 11 and 12, and is retroreflected in the incident direction, while the light (outside the range) is incident outside the range. L2 and L3 in FIG. 3 reach the slope 12 after total reflection on the slope 11 (L2) or directly reach the slope 12 (L3), and the slope 12 does not satisfy the condition of total reflection. The light exits the prism sheet 10 without being reflected. Therefore, even if the diffusivity is given, the viewing direction and the light source are substantially in the same direction, and the light is viewed in a narrow range located near the front of the prism sheet 10 (the light source is also located in the narrow range). However, there is a problem that only a bright display can be obtained.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve the problems of the related art, and when used in a transflective liquid crystal display device or a reflective liquid crystal display device, it is bright not only in the vicinity of the front but also in a wider range. It is an object to provide a retroreflective plate as a transflective plate capable of obtaining a display, a polarizing plate with a retroreflective plate, and a liquid crystal display device using the same.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, the inventors of the present invention have conducted intensive studies and as a result, light having a large incident angle outside the vicinity of the front is totally reflected by any one of the slopes of the prism constituting the retroreflective plate. However, it has been found that if the problem that retroreflection cannot be performed because the remaining slope does not satisfy the total reflection condition can be solved, the reflectance of incident light can be improved, and the present invention has been completed.
[0009]
That is, the present invention is a retroreflective plate having a prism sheet in which prisms are formed on one surface at predetermined pitches as described in claim 1, wherein one of the plurality of inclined surfaces forming each of the prisms is provided. It is an object of the present invention to provide a retroreflective plate characterized in that a metal deposition film is formed on the portion.
[0010]
According to the invention according to claim 1, of the light having a large incident angle outside the vicinity of the front of the retroreflective plate, the slope on which the metal deposition film is formed after being totally reflected on the slope on which the metal deposition film is not formed , Or light that directly reaches the slope on which the metal deposition film is formed can be retroreflected on the slope on which the metal deposition film is formed. Therefore, when the retroreflective plate according to claim 1 is used in a transflective liquid crystal display device or a reflective liquid crystal display device, it is possible to obtain a bright display not only near the front but also in a wider range. In addition, since the inclined surface on which the metal deposition film is not formed has light transmittance, the function as a semi-transmissive reflection plate is maintained, and application to a transflective liquid crystal display device is possible. Further, the shape of each prism is not particularly limited as long as it functions as a retroreflective plate (the prism is not limited to two, and may be composed of three or more inclined surfaces). Is an example in which a metal vapor-deposited film is formed on a part of a slope constituting each prism, such as a form in which a metal vapor-deposited film is formed on two surfaces of each prism (triangular pyramid prism) composed of three inclined surfaces. Form is included.
[0011]
Preferably, the metal deposition film is formed of a metal having a reflectance of 50% or more, such as aluminum, silver, gold, chromium, nickel, platinum, and palladium. The reflectance means a reflectance corrected for visibility, and the metal deposition film is preferably formed of a metal having a reflectance of 60% or more, more preferably 70% or more.
[0012]
In the case where the retroreflective plate includes a supporting base material, recent liquid crystal display devices often include a reflective polarizer, and from the viewpoint of not impairing the polarization characteristics of the reflective polarizer, preferably, the claims. As described in 3, the in-plane retardation value of the supporting substrate is set to 50 nm or less, more preferably, 20 nm or less, and further preferably, 10 nm or less.
[0013]
According to a fourth aspect of the present invention, there is provided the retroreflector according to any one of the first to third aspects, and the other surface of the retroreflector (the surface opposite to the prism forming surface). And a polarizing plate stuck on the side).
[0014]
Preferably, as described in claim 5, the polarizing plate with a retroreflective plate is a surface of the polarizing plate opposite to a surface facing the retroreflective plate, or the retroreflective plate and the polarizing plate. And a light diffusing unit that does not substantially eliminate the polarization state.
[0015]
According to the invention according to claim 5, since the light diffusing means is provided, the reflection ability in a direction away from the retroreflection direction is improved, and thus the polarizing plate with the retroreflection plate is used as a transflective liquid crystal display device. There is an advantage that the visibility when used for, for example, is improved.
[0016]
Preferably, as described in claim 6, the light diffusing means is formed of an adhesive and isotropic spherical particles dispersed in the adhesive and having a refractive index different from that of the adhesive. Adhesive.
[0017]
Further, according to the present invention, the liquid crystal cell and the liquid crystal may be arranged such that the other surface (the surface opposite to the prism forming surface) of the retroreflective plate faces the liquid crystal cell. A liquid crystal display device comprising the retroreflective plate according to any one of claims 1 to 3 or a polarizing plate with a retroreflective plate according to any one of claims 4 to 6, which is attached to a cell. Also provided as.
[0018]
In a case where the display screen of the liquid crystal display device is of a vertical type, preferably, in a state where the liquid crystal display device is viewed, a normal extending to a viewing side of the liquid crystal display device is in a state where the liquid crystal display device is viewed. The metal deposition film is formed on a slope that forms an elevation angle with respect to a horizontal plane.
[0019]
Most of the light incident on a transflective liquid crystal display device or the like in which the display screen is vertically arranged is incident light from above (in a direction at an elevation angle with respect to a horizontal plane), and such light is incident on the viewing side of the liquid crystal display device. After the normal extending to the horizontal plane is totally reflected by the inclined plane at the angle of depression with respect to the horizontal plane, the normal reaches the inclined plane at the elevation angle, or directly reaches the inclined plane at the elevation angle. Therefore, when a metal vapor-deposited film is formed on an inclined surface that forms an elevation angle in a state where the liquid crystal display device is visually recognized (a state in which the display screen is placed vertically), the reflection of the liquid crystal display device can be improved. The rate can be greatly improved.
[0020]
Preferably, as described in claim 9, the liquid crystal display device includes a backlight disposed on the one surface (prism forming surface) side of the retroreflective plate, the retroreflective plate and the backlight. And a reflective polarizer disposed between them.
[0021]
According to the ninth aspect of the present invention, a transflective liquid crystal display device is configured to include a backlight, and the use efficiency of backlight light can be increased because a reflective polarizer is included.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0023]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a retroreflective plate according to an embodiment of the present invention. FIG. 2 is a perspective view of a transflective liquid crystal display device using the retroreflective plate shown in FIG. It is a longitudinal section showing an example schematically.
[0024]
As shown in FIG. 2, the transflective liquid crystal display device 100 according to the present embodiment includes a retroreflective plate 1, a backlight 2, polarizing plates 3 and 4, a liquid crystal cell 5, and a diffusing plate 6. , A reflective polarizer 7.
[0025]
As shown in FIGS. 1 and 2, the retroreflective plate 1 according to the present embodiment has a prism sheet 10 on one surface of which a prism having a triangular cross section is formed at a predetermined pitch at every predetermined pitch. Here, each prism of the prism sheet 10 can be formed by various known methods such as shape transfer or cutting by hot pressing or UV polymerization.
[0026]
In the prism sheet 10 according to the present embodiment, the metal deposition film 13 is formed only on one of the inclined surfaces 11 and 12 (in the present embodiment, the inclined surface 12) of each prism formed at a predetermined pitch. In particular, in the present embodiment, it is assumed that the retroreflective plate 1 is applied to a liquid crystal display device having a vertical display screen, and therefore, as shown in FIG. A metal vapor-deposited film 13 is formed on a slope 12 whose normal line extending in the right direction forms an elevation angle with respect to a horizontal plane. Here, most of the light (external light) incident on the liquid crystal display device whose display screen is vertically arranged is incident light (L2, L3 in FIG. 1) from above (in a direction forming an elevation angle with respect to the horizontal plane). The light reaches the slope 12 after the normal extending to the viewing side of the liquid crystal display device is totally reflected by the slope 11 forming a depression angle with respect to the horizontal plane (L2), or directly reaches the slope 12 (L3). Will be. The light (both L2 and L3) that reaches the slope 12 is reflected by the metal deposition film 13 formed on the slope 12, so that it is possible to retroreflect incident light from above. Light incident from the vicinity of the front of the retroreflective plate 1 is totally reflected by the slope 11 and reflected by the slope 12, or by being reflected by the slope 12 and totally reflected by the slope 11, similarly. Retroreflection is possible. Therefore, when the retroreflective plate 1 according to the present embodiment is used in a transflective liquid crystal display device (FIG. 2) or a reflective liquid crystal display device, bright display is obtained not only in the vicinity of the front but also in a wider range. It is possible. Since the slope 11 on which the metal deposition film 13 is not formed has light transmittance, in other words, the light-transmissive surface (the slope 12 on which the metal deposition film 13 is formed) is substantially only ２ in area. ), The function as a semi-transmissive reflector is maintained, and as shown in FIG. 2, the backlight 2 is arranged on the prism forming surface side (leftward in FIG. 2) of the retroreflector 1. Thereby, the transflective liquid crystal display device 100 can be configured.
[0027]
The metal deposition film 13 is preferably formed of a high-reflectivity metal such as aluminum, silver, gold, chromium, nickel, platinum, and palladium. In addition, the vapor deposition pattern of the metal vapor deposition film 13 (that is, the pattern in which the metal vapor deposition film 13 is formed only on one slope 12) can be formed by a resist process, an etching process, or the like, and can be obliquely vapor-deposited on the retroreflective plate 1. By forming a metal thin film only on the slope facing the evaporation source.
[0028]
In the case of the retroreflective plate 1 alone, the light reflection distribution is sharp, the range of angles that can be displayed brightly is narrow (the reflection ability in a direction away from the retroreflection direction is poor), and as a result, the viewing angle characteristics are narrowed. However, this problem can be solved by arranging the diffusion plate 6 as the light diffusion means as shown in FIG. More specifically, more practical viewing angle characteristics can be obtained by disposing a diffusion plate 6 that does not substantially cancel the polarization state between the retroreflective plate 1 and the polarizing plate 3. The arrangement of the diffusion plate 6 is not limited to that shown in FIG. 3. For example, the polarizing plate 3 is attached to the surface of the retroreflective plate 1 on the side opposite to the prism forming surface without the diffusion plate 6 interposed therebetween. It is also possible to adopt a configuration in which a polarizing plate with a retroreflective plate is formed by attaching the polarizer, and a diffusing plate 6 is arranged on the polarizer side of the polarizer with the retroreflective plate (to the right of the polarizer 3 shown in FIG. 3). It is possible.
[0029]
The diffusion plate 6 is preferably a light-diffusing adhesive formed of an adhesive and isotropic spherical particles dispersed in the adhesive and having a refractive index different from that of the adhesive. More specifically, for example, an acrylic pressure-sensitive adhesive (refractive index: 1.48) is used as the pressure-sensitive adhesive, and melamine-based resin beads (φ6 μm, refractive index: 1.57) and styrene-based resin are used as the isotropic spherical particles. Beads (φ6 μm, refractive index 1.59), silica beads (φ4 μm, refractive index 1.44) and the like are preferably used.
[0030]
It is obvious that members such as the prism sheet 10 constituting the retroreflective plate 1 need to be formed from a transparent material. When the retroreflective plate 1 has a supporting substrate (not shown), it is desirable to use a supporting substrate having a small in-plane retardation. In particular, as shown in FIG. 3, in the case where a reflective polarizer 7 applied to many liquid crystal display devices in recent years is provided in order to increase the use efficiency of light emitted from the backlight 2, the polarization characteristics of the reflective polarizer are provided. From the viewpoint of not impairing the above, the in-plane retardation is preferably 50 nm or less, more preferably 20 nm or less, and still more preferably 10 nm or less.
[0031]
【Example】
Hereinafter, the characteristics of the present invention will be further clarified by showing Examples and Comparative Examples.
[0032]
(Example)
On the slope of the retroreflective plate made of an acrylic prism sheet having a prism pitch of 50 μm, metal evaporation was performed in the same manner as in the pattern shown in FIG. 1 (a metal evaporation film was formed only on the slope 12). More specifically, aluminum was obliquely deposited, and a metal deposition film could be formed only on the substantially inclined surface 12.
[0033]
The reflectance of the metal-deposited film of this example was about 80%, and the reflectance of the non-deposited surface (slope 11) was 10% or less. In addition, the reflectance of light incident within a range of ± 5 degrees from the front direction of the retroreflector was as high as about 80%. In addition, the diffuse reflectance after disposing the diffuser was 70%, and the diffuse transmittance was 25%, which proved to be excellent numerical values. Further, when the retroreflective plate of this embodiment is applied to a liquid crystal display device and observed at a position 20 degrees or more away from the front direction in the reflection mode, it is possible to obtain a brightness such that the display can be visually recognized. I understood.
[0034]
(Comparative example)
The same evaluation test was performed using the same prism sheet as in Example 1 (however, no metal vapor-deposited film was formed).
[0035]
The reflectance of light incident within a range of ± 5 degrees from the front direction of the retroreflector was as high as about 90%. In addition, the diffuse reflectance after disposing the diffuser was 50% and the diffuse transmittance was 50%, showing excellent numerical values. However, the reflectance decreases as the distance from the front direction increases, and a sufficient reflectance cannot be obtained in a direction away from the front direction by 20 degrees or more. When observed at a position 20 degrees or more away from the front direction, it was difficult to visually recognize the display.
[0036]
【The invention's effect】
As described above, according to the retroreflective plate according to the present invention, of the light having a large incident angle outside the vicinity of the front of the retroreflective plate, the light was totally reflected on the slope where the metal deposition film is not formed. Light that later reaches the slope on which the metal deposition film is formed or light that directly reaches the slope on which the metal deposition film is formed can be retroreflected on the slope on which the metal deposition film is formed. Therefore, when the retroreflective plate according to the present invention is used in a transflective liquid crystal display device or a reflective liquid crystal display device, it is possible to obtain a bright display not only near the front but also in a wider range. In addition, since the inclined surface on which the metal deposition film is not formed has light transmittance, the function as a semi-transmissive reflection plate is maintained, and application to a transflective liquid crystal display device is possible.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a retroreflective plate according to an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view schematically showing an example of a transflective liquid crystal display device using the retroreflective plate shown in FIG.
FIG. 3 is a longitudinal sectional view showing a schematic configuration of a conventional retroreflective plate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Retroreflector 2 ... Backlight 3,4 ... Polarizer 5 ... Liquid crystal cell 6 ... Diffusion plate 7 ... Reflective polarizer 11,12 ... Slope 13 ... Metal deposition film 100 ... Transflective liquid crystal display

Claims (9)

A retroreflective plate having a prism sheet in which a prism is formed at a predetermined pitch on one surface,
A retroreflective plate, wherein a metal vapor-deposited film is formed on a part of a plurality of slopes constituting each of the prisms. The retroreflective plate according to claim 1, wherein the metal deposition film is formed of a metal having a reflectance of 50% or more, such as aluminum, silver, gold, chromium, nickel, platinum, and palladium. The retroreflective plate according to claim 1, wherein the retroreflective plate includes a support base material, and the in-plane retardation value of the support base material is 50 nm or less. 4. A polarizing plate with a retroreflective plate, comprising: the retroreflective plate according to claim 1; and a polarizing plate attached to the other surface of the retroreflective plate. A light diffusing unit that is disposed on the surface of the polarizing plate opposite to the surface facing the retroreflective plate, or disposed between the retroreflective plate and the polarizing plate and does not substantially eliminate the polarization state. The polarizing plate with a retroreflective plate according to claim 4, wherein the polarizing plate is provided. The light diffusing means is a light diffusing adhesive formed of an adhesive and isotropic spherical particles dispersed in the adhesive and having a different refractive index from the adhesive. 6. The polarizing plate with a retroreflective plate according to 5. 4. The retroreflective plate or the retroreflective plate according to claim 1, wherein the liquid crystal cell and the retroreflective plate are attached to the liquid crystal cell such that the other surface side of the retroreflective plate faces the liquid crystal cell. 7. A liquid crystal display device comprising the polarizing plate with a retroreflective plate according to any one of items 1 to 6. In the liquid crystal display device, the display screen is a vertical type, and in a state where the liquid crystal display device is visually recognized, a normal extending to the viewing side of the liquid crystal display device forms an elevation with respect to a horizontal plane with respect to an inclined surface. The liquid crystal display device according to claim 7, wherein the metal deposition film is formed. 8. The image display device according to claim 7, further comprising: a backlight disposed on the one surface side of the retroreflective plate; and a reflective polarizer disposed between the retroreflective plate and the backlight. Or the liquid crystal display device according to 8.

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