JPH10206639A - Hologram reflecting plate and reflection type liquid crystal display using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hologram reflecting plate by which a bright display of a full color image can be realized without using a color filter by arranging a reflecting layer on a back face of a hologram, and forming the reflecting layer on a lens sheet having a unit lens group on one surface. SOLUTION: A transparent lenticular sheet 12 having a convex cylindrical lens group on one surface is used as a lens sheet, and a metallic reflecting layer 13 is formed on a cylindrical surface. A hologram reflecting plate 10 is composed of a volume phase transmission type hologram 11 and the lenticular sheet 12 having the metallic reflecting layer 13. When the external light is made incident on a liquid crystal display, it is modulated according to a display pattern by a liquid crystal panel 20, and is spectrally diffracted by the hologram 11. The diffracted light which is spectrally diffracted and has respective band widths of R, G and B, is regularly reflected by the metallic reflecting layer 13 of the lenticular sheet 12, and is condensed toward a liquid crystal cell (a picture element) of the liquid crystal panel 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device which does not require a backlight and allows a display pattern to be viewed by reflection of external light (such as illumination). Also, the present invention relates to a reflection type liquid crystal display device suitable for color display and a hologram reflection plate used for the same.

[0002]

2. Description of the Related Art A reflection type liquid crystal display device having a reflection layer on the back surface of a liquid crystal panel is known. FIG. 1 is a cross-sectional view schematically showing the display device. External light is reflected by a metal reflective layer disposed on the back side of a liquid crystal panel (hereinafter, the side of the liquid crystal panel not facing the viewer is referred to as the "back side"). Then, the viewer is made to visually recognize the display pattern on the liquid crystal panel. Since the metal reflection layer specularly reflects the incident light, it is difficult to increase the amount of reflected light reaching the observer in FIG. When observed from the direction of regular reflection, glare caused by reflection on the surface of the display device (the liquid crystal panel in the figure) is visually recognized.

In recent years, it has been attempted to use a reflection hologram as a reflection layer in the above-mentioned display device instead of an existing metal reflection layer. By using the reflection hologram, the viewing area and the reflection direction can be specified, and a brighter display in a specific direction can be achieved as compared with the metal reflection layer.

However, when the reflection hologram to be used is a surface relief hologram, it is difficult to increase the diffraction efficiency, and when the hologram is a volume phase reflection hologram, the wavelength to be reflected and diffracted by its wavelength selectivity. Since the width is narrow, the reflected light is colored in a specific color, and there is a problem that it is difficult to realize a bright display over a visible wavelength range. Furthermore, there is also a problem that, due to the chromatic dispersion, the displayed color changes depending on the viewing direction and is visually recognized due to the characteristics of the hologram itself.

When a color display is performed on a liquid crystal display device, a color filter such as a pigment dispersion type, which is well known, is used in combination with a liquid crystal panel. In the display device, the brightness of the display is reduced due to absorption by the color filter or the like, and the problem of cost increase due to the use of the color filter also occurs.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a reflection type liquid crystal display device which uses a hologram as a reflection layer instead of a metal reflection layer, and realizes bright display of a full-color image without using a color filter. It is an object of the present invention to provide a simple hologram reflector and a reflection type liquid crystal display device using the same.

[0007]

According to the present invention, a volume phase transmission type hologram is employed as a hologram constituting a hologram reflector and a reflection hologram designed so that reflected light is incident on a liquid crystal cell of a desired color. The layer is arranged on the back of the hologram.

According to a first aspect of the present invention, there is provided a hologram reflector having a reflection layer disposed on the back surface of a volume phase transmission hologram, wherein the reflection layer is formed on a lens sheet having a unit lens group on one side. It is characterized by having a configuration.

According to a second aspect of the present invention, there is provided a lenticular sheet having a cylindrical lens group on one side, wherein a reflecting layer is formed on a cylindrical surface.

A third aspect of the present invention is characterized in that one pitch of the cylindrical lens corresponds to one set of liquid crystal cells including R, G, and B of the liquid crystal display device.

According to a fourth aspect of the present invention, there is provided a reflection type liquid crystal display device comprising the hologram reflection plate according to any one of the above arrangements such that the hologram faces the back side of the liquid crystal panel.

<Operation> By employing a volume phase transmission type hologram, the diffraction efficiency is high, the wavelength width of diffraction is wide, and a bright display over the visible wavelength range is possible. It is suitable for.

The incident light (or the reflected light from the reflection layer) undergoes transmission diffraction by the hologram,
As a result, the reflected light is emitted in a direction different from the specular reflection direction of the incident light, and it is not necessary to be conscious of the image of the light source of the incident light due to reflection on the hologram surface, and the visual field and the reflection direction are specified. Can be.

A reflection layer disposed on the back of the volume phase transmission type hologram is formed on the cylindrical surface of the lenticular sheet, and one pitch of the cylindrical lens corresponds to one set of liquid crystal cells composed of R, G, and B. , The RGB divided by the hologram
Are reflected so as to be accurately incident on the liquid crystal cell of the corresponding color.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> FIG. 2 is a cross-sectional view schematically showing one embodiment of a reflection type liquid crystal display device using a hologram reflector of the present invention. In the figure, a transparent lenticular sheet having a convex cylindrical lens group on one side is used as a lens sheet, and a metal reflection layer is formed on the cylindrical surface. The hologram reflection plate 10 is arranged on the back surface of the liquid crystal panel 20, and includes a volume phase transmission hologram 11 and a lenticular sheet 12 having a metal reflection layer 13.

FIG. 3 shows the optical path in the display device as 1
It is an explanatory view showing one cylindrical lens,
This will be described below with reference to FIG. One pitch of the cylindrical lens is equivalent to three liquid crystal pixel cells (RGB) of the liquid crystal panel 20.

When external light enters the liquid crystal display device, it is first modulated by the liquid crystal panel 20 according to the display pattern, and then reaches the hologram reflector 10.

The liquid crystal panel side of the hologram reflecting plate 10 is a volume phase transmission type hologram 11, and the incident light incident at an angle α is spectrally diffracted by the hologram 11, and the spectrally diffracted R
The diffracted lights having the respective bandwidths of G and B are incident from the flat surface of the lenticular sheet 12. (Fig. 3 (a))

The diffracted lights having the respective bandwidths of R, G, and B are specularly reflected by the metal reflecting layer 13 on the cylindrical surface.
The light is condensed toward the R, G, and B liquid crystal cells (pixels) of the liquid crystal panel 20 according to the shape of the refraction and reflection surface of the lens. (Fig. 3 (b))

The diffracted reflected light that has passed through the liquid crystal panel 20 reaches the observer as pattern display light.

<Embodiment 2> FIG. 4 is a sectional view schematically showing another embodiment of the reflection type liquid crystal display device. In the figure, as a lens sheet, a transparent lenticular sheet 12 having a convex cylindrical lens group on one side is used, and the cylindrical surface faces the liquid crystal panel 20 side.
Volume phase transmission hologram 11 and metal reflection layer 13 on the flat surface side
Is provided. (Fig. 4 (a))

FIGS. 4B to 4C are explanatory views showing the optical path in the above display device for one cylindrical lens.

External light (not shown) modulated according to the display pattern on the liquid crystal panel 20 is applied to a hologram reflector at an angle α.
It is incident on 10.

The incident light is condensed and incident on the hologram 11 according to the characteristics of the cylindrical lens. Then, the light is spectrally diffracted when passing through the hologram 11, and the spectrally diffracted R
The diffracted lights having the respective bandwidths of G and B are incident on the metal reflection layer 13 which is in close contact. (Fig. 4 (b))

The diffracted light of each of the R, G, and B bandwidths is specularly reflected by the metal reflection layer 13, and is reflected by the R, G, and B of the liquid crystal panel 20 according to the refraction of the lens and the shape of the reflection surface. Light is condensed toward the liquid crystal cell (pixel). (Fig. 4 (c))

In the above case, R, G,
The reflected light of each color is emitted in a mirror-symmetric direction to the emission direction of the diffracted light of B, and the R of the liquid crystal panel 20 is changed according to the refraction by the lens.
・ To condense light toward the liquid crystal cell (pixel) of GB
The optical path shown in FIG.

In each of the above embodiments,
The incident external light is transmitted and diffracted before passing through the hologram 11 and reaching the metal reflection layer 13, and the light reflected by the metal reflection layer 13 is not transmitted and diffracted when transmitted through the hologram 11. This is due to the angle selectivity of the volume phase transmission type hologram (the property of transmitting and diffracting only incident light at a specific angle), and the property is determined by the hologram imaging conditions.

The present invention is not limited to the above embodiment, and the incident external light is not transmitted and diffracted when first transmitted through the hologram 11, but is transmitted and diffracted when the reflected light from the metal reflection layer 13 is transmitted through the hologram 11. Such an embodiment does not depart from the gist of the present invention. (In this case, the hologram 11 should be turned upside down.)

<Embodiment 3> FIG. 5B is a sectional view schematically showing another embodiment of the reflection type liquid crystal display device. In the figure, as the lens sheet, a transparent fly-eye lens sheet 12 in which convex lens groups are arranged in an array on one side is used, and the flat surface of the lens sheet 12 faces the volume phase transmission hologram 11, The structure has a metal reflection layer 13 on the lens surface.

The R, G, and B diffracted lights incident on the liquid crystal panel (not shown) from the hologram reflector 10 are condensed in a matrix as shown in the figure according to the arrangement of the lens array (and the liquid crystal cell). As a result, the external light utilization efficiency is further improved as compared with the case where the light is condensed linearly as shown in FIG. 5A (corresponding to the first and second embodiments).

<Other Embodiments> In each of the above embodiments, a transparent lens sheet having a convex lens group was used. However, the present invention is not limited to this, and is an embodiment exemplified below. Is also good.

(1) A configuration in which a reflecting layer is formed on a cylindrical surface of a lenticular sheet having a concave cylindrical lens group on one side, and the reflecting layer faces the hologram.

(2) A configuration in which a reflection layer is formed on a lens surface of a lens sheet having a concave lens group arranged in an array, and the reflection layer faces the hologram.

(3) A configuration in which the lens sheet is not a convex lens group but a prism lens group (linear or arrayed).

In any case of the lens sheet, the pitch of the lens array must be fine enough to correspond to the pitch of the liquid crystal cells of the liquid crystal display device. At present, lenticular sheets are obtained by pressing a transparent thermoplastic resin (acrylic etc.) sheet or by performing double-sided molding simultaneously with melt extrusion. In the molding method, it is very difficult to make the above fine pitch. The reason for this is that the temperature is non-uniform at the time of cooling after thermoforming, and the molded product is warped or the heat shrinkage is non-uniform.

As a production method suitable for molding a fine pitch lens sheet, a known molding method using an ultraviolet curable resin or an electron beam curable resin (collectively referred to as photosensitive resin) is preferable. is there.

As the structure of the lens sheet, it is preferable that a lens portion made of a cured product of a photosensitive resin is molded on a transparent support. As the transparent support, a transparent resin film having ultraviolet (or electron beam) transmittance is preferable, and it is more preferable that the side on which the lens portion is to be formed is subjected to a process of easily adhering to a photosensitive resin. As the material, polyethylene terephthalate (PET), polycarbonate (PC), polyvinyl chloride (PVC), or the like is used.

The apparatus for applying the ultraviolet-curable resin is not particularly limited, but an applicator such as a doctor blade or a die coat is preferable. The thickness of the ultraviolet curable resin applied to one side of the transparent support varies depending on the shape of the lenticular lens to be formed, but is suitably 0.1 mm to 0.2 mm.

There are various photosensitive resins.
In general, it has an acryloyl group in the molecule, and has oligomers and polymers such as epoxy acrylates, urethane acrylates, polyester acrylates, and polyol acrylates, and monofunctional, bifunctional, and polyfunctional groups ( A (meth) acrylic monomer; for example, a mixture of a polymer and an oligomer such as tetrahydrofurfuryl acrylate, polyethylene glycol diacrylate, and trimethylolpropane triacrylate is used.

FIG. 6 is a graph 32 showing the reflection light amount distribution of a reflection type liquid crystal display device using an existing metal reflection layer, and a graph 33 showing the reflection light amount distribution when using the hologram reflection plate of the present invention. It is. As shown in the figure, in the metal reflection layer (graph 32), the intensity of the reflected light in the specular reflection direction is the strongest, and weakens in a normal distribution toward the periphery. On the other hand, in the hologram reflector of the present invention (graph 33), since the viewing area can be controlled by the manufacturing method, the light amount distribution becomes as shown in the drawing, and uniform brightness can be maintained within a predetermined viewing area range. In addition, since the image can be observed at a position deviated from the specular reflection direction, a bright display can be easily viewed without being conscious of the specular reflected light from the light source.

FIG. 7 is an explanatory diagram showing a comparison between the spectral diffraction efficiency of the volume phase reflection hologram (graph 34) and the spectral diffraction efficiency of the volume phase transmission hologram (graph 35).
The diffraction efficiency and the diffraction wavelength width of the volume phase hologram are
It mainly depends on the film thickness of the photosensitive material on which the hologram is recorded, the spatial frequency of the interference fringes recorded and the degree of refractive index modulation. When the parameters of the photosensitive material described above are the same, as shown in the drawing, the diffraction wavelength width of the transmission hologram 35 is clearly wider than that of the reflection hologram 34. It becomes a reflector that is several times brighter than the hologram.

In order to obtain a wide diffraction wavelength width similar to that of a volume phase transmission hologram with a volume phase reflection hologram, the refractive index modulation degree must be several times that required for a transmission type hologram. The required performance becomes severe and is not realistic. It is a known matter in the art that the diffraction wavelength width of the volume phase transmission hologram is wider than that of the volume phase reflection hologram, and detailed description is omitted in this specification.
E BELL SYSTEM TECHNICAL JOURNAL, November 1969,
Volume 48, Number 9 ".

The volume phase transmission type hologram employed in the present invention can be recorded by a usual two-beam hologram photographing optical system using a volume phase type hologram photosensitive material. As the photosensitive material, gelatin dichromate, silver salt photosensitive material, photopolymer and the like can be used. In order to realize the object of the present invention, the thickness of the photosensitive material is preferably about 1 to 100 μm.

[0045]

In a reflection type liquid crystal display device using a hologram as a reflection layer instead of a metal reflection layer, a hologram reflection plate capable of realizing a bright display of a full-color image without using a color filter and a reflection plate using the hologram reflection plate. A liquid crystal display device is provided. In the configuration of the present invention, since there is no element for attenuating incident light, the utilization efficiency of external light is improved, and a bright display is possible.

[0046]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a conventional reflection type liquid crystal display device having a metal reflection layer on the back surface of a liquid crystal panel.

FIG. 2 is a cross-sectional view schematically showing one embodiment of a reflection type liquid crystal display device using the hologram reflection plate of the present invention.

FIGS. 3A and 3B are explanatory diagrams showing an optical path in the display device and one cylindrical lens, wherein FIG. 3A shows an incident optical path and FIG.

FIG. 4A is a cross-sectional view schematically showing another embodiment of the reflection type liquid crystal display device using the hologram reflection plate of the present invention, and FIGS. 4B and 4C show one lens array. FIG. 3 is an explanatory diagram showing an incident optical path and a reflected optical path.

FIG. 5 (a) shows a lenticular sheet;
(B) shows a case where each lens sheet is used as a hologram reflector for a fly-eye lens sheet;
FIG. 4 is an explanatory diagram showing a difference in light focusing characteristics of light that is spectrally diffracted.

FIG. 6 shows a comparison between a reflection light amount distribution of a reflection type liquid crystal display device using an existing metal reflection layer (graph 32) and a reflection light amount distribution using a hologram reflector of the present invention (graph 33). Graph.

FIG. 7 is an explanatory diagram showing a comparison between the spectral diffraction efficiency of a volume phase reflection hologram (graph 34) and the spectral diffraction efficiency of a volume phase transmission hologram (graph 35).

[Explanation of symbols]

10 Hologram Reflector 11 Volume Phase Transmission Hologram 12 Lens Sheet 13 Metal Reflective Layer 20 Liquid Crystal Panel 32 Graph Showing Reflected Light Distribution of Liquid Crystal Display Using Metal Reflective Layer 33 Hologram Reflector Graph showing the distribution of the amount of reflected light of the liquid crystal display device 34 ... Spectral diffraction efficiency of volume phase reflection hologram 35 ... Spectral diffraction efficiency of volume phase transmission hologram

Claims (4)

[Claims] 1. A hologram reflector comprising a reflection layer disposed on the back of a volume phase transmission hologram, wherein the reflection layer is formed on a lens sheet having a unit lens group on one side. A hologram reflector that features. 2. The hologram reflector according to claim 1, wherein a lenticular sheet having a group of cylindrical lenses on one side thereof has a structure in which a reflection layer is formed on a cylindrical surface. 3. The hologram reflector according to claim 2, wherein one pitch of the cylindrical lens corresponds to one set of R, G, and B liquid crystal cells of the liquid crystal display device. 4. A reflection type liquid crystal display device comprising the hologram reflection plate according to claim 1 arranged so that the hologram faces the back side of the liquid crystal panel.