JPH04212125A - Display device - Google Patents

Abstract

PURPOSE:To increase the contrast of a display by providing a selective transmittable layer. CONSTITUTION:This device has the display element 1 which makes display by selectively transmitting and scattering light according to input signals, the selective transmittable layer 2 which is disposed behind the display element 1 and a light absorptive layer 3 which is disposed behind the selective transmittable layer. Namely, the light exclusive of the incident angle of a prescribed range of the light past the display element 1 while scattered by the light scattering part of the display element 1 is reflected to the display element 1 side by the selective transmittable layer 2 and is supplied again to the display element 1. The quantity of the scattered light is increased in this way and the contrast is increased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for a TV or general office equipment, and more particularly to a display device using a lightweight and thin display element.

0002

2. Description of the Related Art As the above-mentioned lightweight and thin display elements, liquid crystal display elements formed by injecting a liquid crystal material between a pair of transparent electrode plates fixed at a spacing of several μm have been mainly used. In the liquid crystal display element having the above configuration, in order to express the alignment of the liquid crystal as an optical contrast, it is necessary to attach a polarizing plate whose polarization axes are perpendicular to each other to each of the pair of transparent electrode plates.

However, as is clear from the principle of general polarizing plates, the amount of light transmitted through a polarizing plate does not exceed 50%, so in order to achieve bright display, a powerful backlight that illuminates the element from behind is required. This has caused problems such as heat generation in the element and increased power consumption and manufacturing costs. Therefore, recently, a liquid crystal display element that does not require a polarizing plate has been developed, which displays by changing light scattering and transmission due to voltage application.

The above liquid crystal display element is constructed by sandwiching a liquid crystal film containing a matrix polymer and a low molecular weight liquid crystal between a pair of supports having a transparent conductive film. As a liquid crystal film, a polymer/liquid crystal composite film [Polymer Preprint
s, Japan Vol. 37, (8), 2450 (
1988)], and polymers using side-chain polymer liquid crystals as matrix polymers, in which side chains are attached to the polymer backbone chain with parts corresponding to liquid crystal compounds via flexible carbon skeletons, etc. Liquid crystal/low molecular liquid crystal mixed film [P
olymer Preprints, Japan Vo
l. 37, (8), 2453 (1988)].

The former polymer/liquid crystal composite film has a structure in which the pores of a matrix polymer with a sponge structure are filled with low molecular weight liquid crystal, and when no voltage is applied, the liquid crystal molecules in the pores are filled with matrix polymer. It lies along the interface with molecules and is in a macroscopically random state, so incident light is scattered and it becomes opaque. Then, when an electric field is applied by the pair of transparent conductive films, Δε>0 [where Δε is the dielectric constant anisotropy, and the formula:

[0006]

[Math 1]

[0007] (in addition,

[0008]

[Outside 1]

is the dielectric constant in the direction of the molecular axis,

0010

[Outside 2]

[0011] indicates a dielectric constant in the direction perpendicular to the molecular axis)], the liquid crystal molecules are oriented in the direction of the electric field due to electrostatic action, allowing incident light to pass through without being scattered. It exhibits an electro-optical effect in which the molecular/liquid crystal composite film transforms into a transparent state. On the other hand, in the latter polymer liquid crystal/low molecular liquid crystal mixed film, when a low frequency or direct current electric field is applied to a pair of transparent conductive films, turbulent flow occurs due to the movement of charges in the film along with the frequency. As a result, the incident light is strongly scattered, resulting in an opaque state. On the other hand, when a high-frequency electric field is applied, the liquid crystal molecules in the polymer liquid crystal/low molecular liquid crystal mixed film homeotropically align in the direction of the electric field, allowing incident light to pass through without being scattered, converting it to a transparent state. do. In addition, in this polymer liquid crystal/low molecular liquid crystal mixed film, when the electric field is removed in both of the above states, the light scattering state or non-scattering state is stably maintained due to the hysteresis characteristic of the applied frequency-optical response. It has memory properties.

[0012] In the liquid crystal display element having the above structure, flexibility can be imparted to the liquid crystal film by selecting a matrix polymer. When combined with a support made of a transparent film, there is an advantage that flexibility can be imparted to the liquid crystal display element. Incidentally, as a liquid crystal display element similar to this, "NCAP liquid crystal" manufactured by Taliq is commercially available.

[0013]

[Problems to be Solved by the Invention] The above-mentioned liquid crystal display elements that perform display by changing light scattering and transmission are of the light reflection type, in which only the light scattering portion scatters and reflects light, and the light transmission type, in which the light from the backlight is reflected only in the light transmission portion. Although it can be used for any light transmission type display device, it is mainly used for a light reflection type display device that can perform display with a simple structure that does not require a backlight. In this light reflection type display device, a light absorption layer that absorbs light that has passed through the light transmission portion is arranged behind the display element.

However, in the above display device, the light that is scattered by the light-scattering portion of the element and reflected toward the viewer is only 20 to 30% of the light that enters the light-scattering portion; Although it is scattered, it passes through the display element and is absorbed by the light absorption layer behind it, so there is a problem that the scattered area is not sufficiently clouded and sufficient contrast cannot be obtained.

[0015] Furthermore, when color display is performed using the conventional display element described above, a colored film is overlaid on the display element, but there is also the problem that clear color development cannot be obtained. The present invention has been made in view of the above circumstances, and aims to provide a display device with a high display contrast, and a display device with a high display contrast and a clear color display. .

[0016]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the display device of the present invention includes a display device that selectively transmits and scatters light according to an input signal to display a display device behind the display device. A selectively transmitting layer that transmits light with an incident angle within a predetermined range corresponding to the viewing direction of the element and reflects other light toward the display element is disposed, and a light absorbing layer is disposed behind this selectively transmitting layer. It is characterized by

According to another aspect of the present invention, there is provided a display element in which a color filter layer is provided on at least the display portion of the viewing side surface of the display element.

[0018]

[Operation] In the display device of the present invention having the above configuration, among the light that passes through the light transmitting portion of the display element, light having an incident angle within a predetermined range corresponding to the viewing direction of the display element is selectively transmitted. The light passes through the layer and is absorbed by the light absorbing layer. on the other hand,
Of the light that passes through the display element while being scattered by the light-scattering part of the display element, light with an incident angle outside the above-mentioned predetermined range is totally reflected in the selectively transmitting layer and reaches the display element again. Increase the amount of scattered light.

Furthermore, when a color filter layer is provided on at least the display portion of the viewing side surface of the display element,
Since the light colored by this color filter is incident on the selective transmission layer, the light scattering portion develops a vivid color.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A display device according to the present invention will be explained below with reference to drawings showing embodiments. As shown in FIG. 1, the display device of this embodiment includes a display element 1 that selectively transmits and scatters light according to an input signal to display a display;
a selectively permeable layer 2 disposed behind the selectively permissive layer 2;
The light absorbing layer 3 is arranged behind the light absorbing layer 3.

As the display element 1, as shown in FIG.
A liquid crystal display element is used in which a liquid crystal film 11 is held between a pair of supports 12 and 13 having transparent conductive films 12a and 13a corresponding to a predetermined display pattern. Further, as the liquid crystal film 11, the aforementioned polymer/liquid crystal composite film or polymer liquid crystal/low molecular liquid crystal mixed film is used. This liquid crystal film 11 is formed by the electro-optical effect when an electric field is applied by the transparent conductive films 12a and 13a.
It has a liquid crystal display function in which the optical characteristics of the liquid crystal in the portions corresponding to 2a and 13a change to perform a predetermined display.

Furthermore, since the liquid crystal film 11 contains a matrix polymer, it has a self-supporting property that maintains its own shape, which is not present in a layer consisting only of low molecular weight liquid crystals in conventional liquid crystal displays. There is. Therefore, the structure of the display element 1 can be simplified compared to a conventional liquid crystal display. In other words, in conventional liquid crystal displays, the layer made of low molecular weight liquid crystal does not have self-supporting properties, so a rod-shaped or spherical spacer made of plastic or glass is required to maintain the distance between the transparent conductive films. Met. On the other hand, since the liquid crystal film 11 has self-supporting properties, no spacer is required, and the structure can be simplified. Further, the liquid crystal film 11 is more resistant to impact than a low molecular weight liquid crystal layer that does not have self-supporting properties.

Note that in order to make the display device flexible, in order to make the display element 1 flexible, a flexible matrix polymer is used to make the liquid crystal film 11 flexible, as described above. It is sufficient to impart flexibility. The liquid crystal film 11 is formed by dissolving a solution of a matrix polymer and a low molecular weight liquid crystal material in a solvent on one side of the pair of resin films 12 and 13 on which the transparent conductive film 12a (13a) is formed. It is formed by casting on the surface and drying it. Thereafter, another resin film 13 (12) is placed on top of this liquid crystal film 11 to complete the display element 1.

A pair of supports 12 that sandwich the liquid crystal film 11,
As the material 13, a glass plate, a plastic plate, etc. can be used, and in order to give the display element 1 flexibility, a flexible resin film can also be used. The above resin film is particularly made of polyethylene terephthalate (PE).
T), polyethylene naphthalate (PEN), polyethersulfone (PES), etc., are transparent resin films that have excellent mechanical, thermal, and optical properties, are thin, light, flexible, and do not have the risk of cracking. Preferably used. The thickness of the resin film is preferably within the range of 100 to 200 μm.

The transparent conductive films 12a and 13a formed on the surfaces of the supports 12 and 13 include thin films of ITO (indium tin oxide), SnO2, and the like. In order to form the transparent conductive films 12a and 13a into a shape corresponding to a predetermined display pattern, for example, a transparent conductive film is formed on the surfaces of the supports 12 and 13 by a vapor phase growth method such as vacuum evaporation or sputtering. After that, there is a method of etching away unnecessary portions, and a method of using a mask corresponding to a predetermined display pattern when forming a transparent conductive film by the above-mentioned vapor phase growth method.

In order for the display element 1 to display, for example, "A" shown by a two-dot chain line in FIG.
At least one of a and 13a may be formed into the shape of "A" described above. Further, the transparent conductive films 12a, 1
3a are a plurality of parallel plate electrodes, which are arranged perpendicularly to each other to form a simple dot matrix in which the intersections of the parallel plate electrodes are dots. Depending on the combination, the above-mentioned "A" can also be displayed on the display element 1.

Furthermore, an active matrix using thin film transistors, nonlinear resistance elements, etc. can also be used. The selective transmission layer 2 arranged behind the display element 1 has an incident angle (
In other words, it selectively transmits only light with a predetermined range of incident angles corresponding to the observation direction of the display element 1, and reflects light with other incident angles toward the display element 1, as shown in FIG. As such, a transparent plate is used in which the surface on the light absorption layer 3 side is a smooth surface 20 and the surface on the display element 1 side is an uneven surface 21. The uneven surface 21 is constructed by arranging a large number of inclined surfaces 21a, 21a, .

In the selective transmission layer 2, the inclined surface 21
The light refracted by a, 21a... hits the smooth surface 20 at an incident angle within the critical angle (θy in the figure) for refraction and reflection on the smooth surface 20.
0, it passes through the smooth surface 20 as shown by the dashed-dotted arrow K in the same figure, and when it reaches the smooth surface 20 at an incident angle exceeding the critical angle (θy), it passes through the smooth surface 20 as shown by the dashed-dotted arrow K in FIG. As shown, light is selectively transmitted and reflected by taking advantage of total internal reflection.

A more detailed function of the selectively permeable layer 2 will be explained below. As shown in FIG. 3, from the direction perpendicular to the permselective layer 2 (dashed double-dot line V in the figure),
The light K that reaches the selectively transmitting layer 2 at an incident angle θb (θb<θx) within the range that can be selectively transmitted through the selectively transmitting layer 2, indicated by the angles x and θx, is represented by the dashed line in the figure. As shown by the arrow, it is refracted by the inclined surface 21a, enters the smooth surface 20 at an incident angle θd within the critical angle θy (θd<θy), passes through this smooth surface 20, and reaches the light absorption layer 3. do.

On the other hand, the light k that reaches the selectively transmitting layer 2 at an incident angle θc (θc>θx) outside the range where it can be selectively transmitted, as shown by the dashed-dotted line in FIG. As shown by the arrow, it is refracted by the inclined surface 21a, enters the smooth surface 20 at an incident angle θe exceeding the critical angle θy (θe>θy), is totally reflected by this smooth surface 20, and is reflected again into the display element. 1 side.

In the selectively transmitting layer 2, as is clear from the principle of geometric optics, the range of incident angles of light that can be selectively transmitted depends on the refractive index of the transparent plate constituting the selectively transmitting layer 2; It is determined by the inclination angle θa of the inclined surfaces 21a, 21a... For example, the selective transmission layer 2 has a refractive index of 1.49.
is formed of acrylic resin, and the inclination angle θa of the inclined surfaces 21a, 21a... is set to 45 degrees, the said θx is 34 degrees.
When the selective transmission layer 2 is formed of a silicone resin with a refractive index of 1.41 and the inclination angle θa of the inclined surfaces 21a, 21a, . . . is also set to 45°, θx becomes 45°.

Further, in the case of transparent plates having the same refractive index, the smaller the above-mentioned inclination angle θa, the larger θx becomes, and the observation direction in the display element 1 is expanded, but the light is reflected from the selective transmission layer 2 to the display element 1. As a result, the amount of light that is transmitted decreases, and the effect of increasing scattered light becomes less effective. On the other hand, if the inclination angle θa is increased, the amount of light reflected from the selective transmission layer 2 to the display element 1 will increase, and the contrast will be strengthened, but the viewing direction in the display element 1 will be narrowed.

[0033] Therefore, the above-mentioned inclination angle θa and the refractive index of the transparent plate vary depending on the conditions in which the display device is used.
Just set it to an appropriate value. As the selective transmission layer 2, a hard transparent plate such as a glass plate or an acrylic plate can be used, and in order to make the display device flexible, a flexible and highly transparent resin such as polycarbonate can be used. A board can also be used. As such a highly flexible selectively permeable layer, SOLF (Scotch O) manufactured by 3M Company is available.
optical Lighting Film, refractive index 1.
62, θa=45°, unevenness pitch 0.3 mm, made of polycarbonate) is commercially available.

The light absorption layer 3 disposed behind the selective transmission layer 2 can be the same as the conventional one. for example,
In order to make the display device flexible, it is preferable to use something that is thin, flexible, light, and can efficiently absorb incident light.
A resin film colored in a deep color such as black or red, or a resin film laminated with paper colored in the above color is preferably used.

In the display device of this embodiment, which is composed of the above-mentioned parts, out of the light that has passed through the light-transmitting portion of the display element 1, the light having an incident angle within a predetermined range corresponding to the observation direction of the display element 1 is , passes through the selective transmission layer 2 and is absorbed by the light absorption layer 3. On the other hand, among the light that passes through the display element 1 even though it is scattered by the light scattering portion of the display element 1, light having an incident angle outside the above-mentioned predetermined range is totally reflected in the selective transmission layer 2 and re-reflected as described above. It reaches the display element 1. The reflected light that reaches the light scattering portion of the display element 1 increases the amount of scattered light at this light scattering portion, and as a result, the contrast of the display element 1 increases.

For example, as the selectively permeable layer 2, the above-mentioned 3
When SOLF manufactured by Company M is used, the ratio of the light scattering intensity of the light scattering part and the light transmitting part is 15:1, and the contrast is lower than the ratio of 10:1 when the selective transmission layer 2 is not used. I was able to improve. Next, another embodiment shown in FIG. 5 will be described.

The display device of the illustrated embodiment includes a display element 1 that selectively transmits and scatters light according to an input signal to display a display.
A selective transmission layer 2 and a light absorption layer 3 are arranged behind the display element 1, and a color filter layer 4 is provided in front of the display element 1. The display element 1 displays "AB" as shown by the two-dot chain line in FIG. 6 by forming at least one of the transparent conductive films 12a and 13a shown in FIG. 2 in the shape of "AB". It is. The configuration of the other parts of the display element 1 is similar to the display element 1 in the embodiment shown in FIG. 1 above. Furthermore, the same selective transmission layer 2 and light absorption layer 3 as in the embodiment shown in FIG. 1 are used.

The color filter layer 4 is entirely made of a transparent film with low light scattering,
The parts indicated by the two-dot chain lines in FIGS. 5 and 6, which correspond to "B" and
” is colored blue. The portions of the color filter layer 4 other than “A” and “B” are different from the light absorption layer 3 because the corresponding portions of the display element 1 are always in a light scattering state. It is preferable to color them in the same color, for example, black.

As described above, in order to pattern the coloring of the color filter layer 4, a multicolor printing technique such as offset printing or screen printing, a photolithography technique, a photographic technique using a color photographic film, or a thermal transfer technique can be used. Technology such as color copying may be used. In addition, when the display element 1 performs display by combining a plurality of dots in a dot matrix, the color filter layer 4 is formed in a dot matrix shape corresponding to the above-mentioned dots, thereby creating a visual color mixing effect. It is also possible to perform multicolor display.

[0040] The reason why a transparent film with low light scattering is used as the color filter layer 4 is that due to light scattering, light may go around to the part that should be displayed in black by the light absorbing layer 3 on the back side, and the contrast of the display will deteriorate. This is to prevent this from happening. Furthermore, if an air layer exists between the display element 1 and the color filter layer 4, contrast will be reduced due to reflection loss at the interface between the display element 1 and the air layer and at the interface between the color filter layer 4 and the air layer. There is a risk that it will decrease. For this reason, the display element 1 and the color filter layer 4 should be brought into close contact with each other without any gaps, or a substance with a refractive index similar to that of the two, such as high viscosity silicone oil or a solvent-free adhesive, should be placed in the gap between the two. It is desirable to fill it.

In the two embodiments described above,
A liquid crystal display element was used as the display element 1, but the display element can selectively transmit light depending on the input signal.
Various display elements that provide scattering display can be used. In addition, within the scope of not changing the gist of the present invention,
Various design changes can be made.

[0042]

Effects of the Invention The display device of the present invention is constructed as described above, and among the light that passes through the display element even though it is scattered by the light scattering portion of the display element, a predetermined amount of light that corresponds to the viewing direction of the display element is Since light outside the range of incident angles can be reflected to the display element side by the selective transmission layer and supplied to the display element again, the amount of scattered light in the light scattering portion can be increased and the contrast of the display element can be enhanced.

Furthermore, when a color filter layer is provided on at least the display portion of the observation side surface of the display element,
Since the light colored by this color filter is incident on the selective transmission layer, the light scattering portion can be vividly colored.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view showing one embodiment of a display device of the present invention.

2 is a cross-sectional view showing the layer structure of a liquid crystal display element as a display element used in the display device of FIG. 1. FIG.

FIG. 3 is an enlarged cross-sectional view of a permselective layer as a main part of the embodiment of FIG. 1;

FIG. 4 is an enlarged cross-sectional view of a permselective layer as a main part of the embodiment of FIG. 1;

FIG. 5 is a partially cutaway perspective view showing another embodiment of the display device of the present invention.

FIG. 6 is an exploded perspective view of the embodiment of FIG. 5;

[Explanation of symbols]

1 Display element 2 Selective transmission layer 3 Light absorption layer 4 Color filter layer

Claims (3)

[Claims] Claim 1: A display device that transmits light at a predetermined angle of incidence corresponding to the viewing direction of the display element behind a display element that selectively transmits and scatters light according to an input signal to display a display; 1. A display device comprising: a selectively transmitting layer that reflects other light toward a display element; and a light absorbing layer disposed behind the selectively transmitting layer. 2. A transparent plate in which the selective transmission layer has a smooth surface on the light-absorbing layer side and an uneven surface consisting of a large number of inclined surfaces inclined at a predetermined angle with respect to the smooth surface. 2. The display device according to claim 1, comprising: 3. The display device according to claim 1, further comprising a color filter layer provided on at least the display portion of the viewing side surface of the display element.