JPH09152598A - Reflection type light scattering liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the liquid crystal display device which makes a display of high quality by preventing a decrease in lightness and unevenness of lightness and eliminating the defect that a display is seen double as to a light scattering liquid crystal display element using a selective light reflecting layer. SOLUTION: This device has a light scattering liquid crystal layer 7 held between two substrates 6 and 7 provided with electrodes for liquid crystal driving and is provided with the selective light reflecting layer 9 outside the liquid crystal layer 7 and with a light absorbing layer 10 on the opposite surface side of the light reflecting layer 9 from the liquid crystal layer 7, thereby imposing optical modulation by controlling the extent of light scattering by the liquid crystal layer 7 with an electric field applied to the electrodes for liquid crystal driving. The selective light reflecting layer 9 has the angles selectivity that light having an angle of incidence within a specific range is transmitted and light having an angle of incidence exceeding the range is reflected. Further, a gap is formed between the selective light reflecting layer 9 and light absorbing layer 10 and the thickness of this gap becomes constant in a display surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-scattering display device using selective light transmission (reflection) means.

[0002]

2. Description of the Related Art Conventionally, the most common liquid crystal mode is TN (t
Wisted nematic mode and STN (su
Although it is a per twisted nematic mode, in these modes, the display becomes dark due to insufficient steepness in electro-optical characteristics and the necessity of using two polarizers. When a dichroic dye is added to the liquid crystal to form a guest-host (GH) type, it becomes possible to display even one sheet of the polarizer, which makes it somewhat brighter, but in this case, the contrast is remarkably lowered. Resulting in. When performing color display, it is impossible to adopt the TN type or the STN mode GH type because a large contrast is required.
E using DAP type (or VAN type), horizontal alignment cell
In order to construct a color liquid crystal display device using these birefringence modes including the CB type, it is necessary to make the backlight extremely bright for the above-mentioned reason. Although the liquid crystal display element itself consumes less power than other display elements, the provision of a bright illuminating means significantly impairs its remarkable features. Further, although the liquid crystal display element is originally of a thin flat type structure, the provision of such an illumination means impairs the thin structure. Even when performing monochrome display, if the backlight is not used,
The display quality is not sufficient due to the darkness of the display. In the so-called active matrix type configuration in which elements such as TFTs and MIMs are provided for each pixel, the active matrix is not used because the insufficient steepness in electro-optical characteristics in the TN mode can be covered. A display much brighter than that of the above-mentioned simple matrix type liquid crystal display device is possible, but it is still impossible to obtain sufficient brightness without using a backlight by using two polarizers. Further, since the polarizer is expensive, it is considerably disadvantageous in cost to use two polarizers. The process of attaching the polarizer (polarizing plate) to the liquid crystal display element is not easy, and it is difficult to attach it so that entrapment of bubbles and generation of wrinkles do not occur. The yield reduction due to this cannot be ignored. Further, in a general polarizing plate, stretched polyvinyl alcohol (PVA) contains iodine or P containing iodine.
Because it is made by stretching VA, heat resistance,
It is remarkably inferior in terms of moisture resistance, and it is no exaggeration to say that the reliability of the current liquid crystal display element is determined by the polarizing plate.

On the other hand, in recent years, a polymer-dispersed liquid crystal in which small spheres of liquid crystal are dispersed in a polymer matrix has been proposed (JP-A-58-501631), and it is difficult to be affected by the thickness of the liquid crystal layer and has a large area. However, it is attracting attention because it has features such as that it does not require a polarizing plate. Further, Japanese Patent Laid-Open No.
In 198725, a polymer network type liquid crystal in which a liquid crystal is dispersed in a three-dimensional network structure formed by a photocurable resin is used for a liquid crystal layer of a display element, and thus, in addition to the same characteristics as the polymer dispersion type liquid crystal, It has been shown that advantages such as voltage driving and excellent steepness can be obtained (hereinafter, a liquid crystal display device using a dispersion film of these polymers and liquid crystals is also referred to as PDLC). Since the PDLC performs light modulation and display by utilizing the light scattering property of the liquid crystal layer, it is very difficult to form a direct-view display device other than the guest-host type, and it has been developed as a projection display. Has been actively carried out. However, if it is used as a projection type, in addition to a powerful lamp, a projection optical system is also required, which is far from the original thin structure of the liquid crystal display element than when a backlight is used. In addition, the guest-host type is often inferior in reliability due to impurities contained in the dichroic dye and products generated by photolysis, and a dispersion structure of a polymer and a liquid crystal is formed using a photocurable resin. When attempting to do so, the dye often interferes with the photocuring reaction, which greatly limits the material system. Light-scattering type liquid crystal display elements are difficult to use as direct-viewing type liquid crystal display elements because of their light-scattering characteristics. In the case of a light scattering element that can be driven in a practical voltage range of several volts to ten and several volts, light is mainly scattered only forward. For this reason, the element itself is visually opaque, but a colored material (light-shielding layer, etc.) is formed immediately behind it.
When the element is arranged, the color of the colored material is visible even when the element is in the cloudy state, and clear contrast cannot be obtained even when the element is switched between the scattering state and the transparent state. For this reason, the PDLC, which has the most excellent characteristics among the light-scattering liquid crystal display devices at present, is mainly focused on the projection type and guest-host type applications, and the technology considering the direct-viewing type is considered. There are few announcements. A method has already been proposed (Japanese Patent Laid-Open No. 21215/1992) for increasing the reflection intensity even in a light-scattering liquid crystal display device having a large forward scattering intensity by using a selective light transmitting (reflecting) means. The outline of this method will be described with reference to FIG. The selective light transmission layer 2 is disposed between the display element 1 (light scattering type liquid crystal) and the light absorption layer 3. The light 4 vertically incident from the display element side is refracted by the selective transmission layer, but is finally transmitted and absorbed by the light absorption layer 3. On the other hand, the obliquely incident light 5 is
The light is totally reflected on the lower surface of the selective transmission layer and emitted toward the display element. This light is forward-scattered by the light-scattering display element 1 toward the observer, and as a result, the display element 1 looks bright. When the display element 1 is in the light-scattering state, the component of the light obliquely incident on the selective transmission layer is large, and thus the element is bright, and when the display element 1 is in the transparent state, the component transmitting the selective transmission layer. Is large, the color of the light absorption layer 3 is visible. Such a method has a great advantage that the display element is bright, but since it is necessary to provide an air layer between the selective reflection layer 2 and the light absorption layer 3, the distance between the display element 1 and the light absorption layer 3 is increased. Has a drawback that the display becomes large and the display is easy to see twice. Further, if the selective transmission layer 2 and the light absorption layer 3 are simply overlapped, the brightness at the portion where these two are in contact with each other is lowered, which causes uneven brightness. In other words, it is necessary to have a gap between the light absorption layer and the selective reflection layer, but if no means is used, the light absorption layer and the selective reflection layer are in partial contact and the brightness of that portion is Will fall. Further, since the distance between the light absorbing layer and the display element varies depending on the location, the degree of double image appearance also varies depending on the location.

[0004]

The problem to be solved by the present invention is to provide a light-scattering liquid crystal display device using a selective light-reflecting layer, which is free from deterioration in brightness and uneven brightness.
Another object of the present invention is to provide a high quality liquid crystal display device by eliminating the drawback that the display is likely to appear double.

[0005]

According to the present invention, a light-scattering liquid crystal layer is sandwiched between two substrates provided with liquid crystal driving electrodes,
A selective light-reflecting layer is provided outside the liquid crystal layer, and a light-absorbing layer is provided on the surface of the light-reflecting layer opposite to the liquid crystal layer, and the light-scattering property of the liquid crystal layer is caused by an electric field applied to a liquid crystal driving electrode. In the liquid crystal display device that controls the size of the light to perform light modulation, the light reflection layer has an angle selectivity of transmitting light having an incident angle in a specific range and reflecting light having an incident angle outside the range. A liquid crystal display device and a liquid crystal driving electrode, wherein a gap is provided between the light reflection layer and the light absorption layer, and the thickness of the gap is constant in the display surface. A light-scattering liquid crystal layer is sandwiched between the two substrates provided, a selective light diffusing layer is provided outside the liquid crystal layer, and a light absorbing layer is provided on the opposite side of the light diffusing layer from the liquid crystal layer. A liquid crystal display device that is provided and controls the magnitude of light scattering of the liquid crystal layer by an electric field applied to the liquid crystal driving electrode to perform light modulation. In order to provide a liquid crystal display device, the light diffusing layer has an angle selectivity of transmitting light having an incident angle in a specific range and diffusing light having an incident angle outside the range. It was possible to solve the problems of the above technology. The selective light reflection layer of the liquid crystal display device of the present invention selectively transmits (reflects) only light having an incident angle in a predetermined range corresponding to the observation direction, and transmits light having incident angles other than that. It is reflected on the liquid crystal display side.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIG. As shown in FIG. 2, a light-scattering liquid crystal layer 7 is provided between the upper and lower substrates 6 and 8, and a selective light-reflecting layer 9 is arranged under the light-scattering liquid crystal layer 7 so that its convex portion is in contact with the lower substrate 8. Further, the light absorption layer 10 was placed therebelow. Selective light reflection layer 9
When the distance between the light absorbing layer 10 and the light absorbing layer 10 was kept constant and the structure as described in claim 1 was observed, the brightness was uniform.
In this configuration, in order to minimize the distance between the light-scattering liquid crystal layer 7 and the light absorption layer 10, the lower substrate 8 and the selective light reflection layer 9 are arranged in contact with each other. The selective light reflection layers 9 may be arranged separately. As the light-scattering liquid crystal layer 7, polymer dispersed liquid crystal (PDL) is used.
C), dynamic scattering type liquid crystal, transient scattering type liquid crystal, phase transition type liquid crystal and the like can be used. The selective light-reflecting layer 9 is made of a transparent material such as a glass plate or an acrylic plate, and has one surface substantially flat as shown in FIG. 1 or 2 and an uneven structure formed on the other surface. This is called a prism array sheet. The selective light-reflecting layer is arranged with the uneven surface facing the liquid crystal display element side. As an example of a member having such a shape and function, Brightn
ess Enhancement Film (BEF9
0, BEF100) [manufactured by 3M, trade name]. The cross section of the selective light reflection layer 9 does not necessarily have the triangular shape as described above, and may be a circular lenticular lens array sheet or a pyramid-shaped convex portion. The vertically incident light 4 and the obliquely incident light 5 are refracted by the uneven inclined surface of the selective light reflection layer 9. The vertically incident light 4 passes through the bottom surface of the selective light reflection layer 9 and is absorbed by the light absorption layer 3. On the other hand, the obliquely incident light 5 is totally reflected by the bottom surface of the selective light reflection layer 9. The range of the incident angle of transmission or reflection is determined by the refractive index of the selective light reflection layer 9 and the inclination angle of the uneven surface. If the light absorption layer 10 has a color other than white, it is possible to switch between that color and white. As the upper and lower substrates 6 and 8, glass substrates usually used for liquid crystal display devices, plastic substrates such as polyethylene terephthalate, polyethylene naphthalate, and polyether sulfone are used. As the light absorption layer, the same one as the conventional one is used. In the liquid crystal display device of the present invention, a color filter may be provided at any position on the light absorption layer 3 on the viewer side.

[0007]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 Using the liquid crystal display device shown in FIG. 2, the liquid crystal layer 7 and the light absorbing layer 1 are used.
The degree of double image appearance was compared by parallax by changing the distance of 0. The pixel pitch of the liquid crystal display elements (6 to 8) was the usual 300 μm, and the display device was observed from a position 1 m away. The results are summarized in Table 1.

[Table 1] As can be seen from Table 1, when the distance between the liquid crystal layer 7 and the light absorption layer 10 is 1 mm or less and 3 mm or more, the double image appearance becomes small. When the distance between the liquid crystal layer 7 and the light absorption layer 10 is as small as 1 mm or less, the parallax is sufficiently small so that the double image is difficult to see. On the other hand, when the distance between the liquid crystal layer 7 and the light absorption layer 10 is 3 mm or more, it is considered that the double image is blurred and the double image looks small.

Example 2 In FIG. 2, a liquid crystal display device having a pixel pitch of 10 mm was prepared, the display device was observed from a position 3 m apart, and the sizes of double images were compared. The results are summarized in Table 2.

[Table 2] As can be seen from Table 2, when the distance between the liquid crystal layer 7 and the light absorption layer 10 is 2.0 mm or less and 5.0 mm or more, the double image appearance becomes smaller. When the distance between the liquid crystal layer 7 and the light absorption layer 10 is as small as 2.0 mm or less, the parallax is sufficiently small so that a double image is difficult to see. In contrast,
It is considered that when the distance between the liquid crystal layer 7 and the light absorption layer 10 is 5.0 mm or more, the double image is blurred and the double image looks small. The reason why the results are different from those in Table 1 of Example 1 is that the distance for observing the liquid crystal display device is mainly different. Generally, in a display with a large pixel pitch, the distance between the display unit and the observer is large.

Example 3 A black pigment was applied to a glass substrate and dried, and then a solution in which plastic beads 13 were dispersed in an alcohol mixed solvent was applied by spinner, and the selective light reflecting layer 12 was bonded.
FIG. 3 shows a cross section of the liquid crystal display device thus manufactured. The spacer 13 is not limited to plastic beads, but may be an oxide such as silica. Moreover, what grind | pulverized the plastic fiber and the glass fiber can also be used. In all cases, it can be applied in the same way as for plastic beads. In addition to the method described above, there is also a dry method in which the solution is sprayed in a high-temperature oven, the solvent is evaporated, and then the spacers are sprayed.

Example 4 A light absorbing layer 18 was formed by forming irregularities on the surface of a black resin with a stamper. Using this light absorbing layer 18, a liquid crystal display device was manufactured with a constant gap thickness between the light absorbing layer 18 and the selective light reflecting layer 16. A cross section of the liquid crystal display device is shown in FIG.
Shown in Since the convex portion of the light absorbing layer 18 is in contact with the selective light reflecting layer 16, the gap 17 (air layer) is formed except the convex portion. Since the total reflection does not occur in the convex portion in contact with the selective light reflection layer 16, the selective light reflection layer 16 and the lower substrate 15
When the structure is such that they contact each other, the selective light reflection layer 16
The reflection loss can be minimized by selecting a place where the upper and lower contacts of the are matched. An example of such a configuration is shown in FIG. Since the gap portion of the lower electrode 22 is a non-pixel portion, the contact point between the selective light reflection layer 24 and the lower substrate and the contact point of the light absorption layer are aligned with each other. As a method of providing irregularities on the light absorption layer, etching or the like can be used in addition to the method using a stamper. In addition to black resin, black glass, metal oxide, or the like can be used as the material.

Example 5 In FIG. 2, a liquid crystal display device was manufactured using a selective light diffusion layer instead of the selective reflection layer. The cross section is shown in FIG. Since there is no need to provide a gap between the selective light diffusion layer 32 and the substrate 33, the structure is simple. As an example of the selective light diffusion layer 32, a visual field selection glass manufactured by Nippon Sheet Glass Co., Ltd. can be cited. Pixel pitch light is 400
When the distance between the scattering liquid crystal layer 29 and the light absorption layer 33 was changed by using a liquid crystal display element of μm, and the degree of double image appearance due to parallax was compared, the same results as in Table 1 were obtained. Also in this case, the distance between the scattering liquid crystal layer 29 and the light absorbing layer 33 is 1
It is preferable that it is less than or equal to mm or greater than or equal to 3 mm. When the selective light diffusion layer 32 is used, the lower substrate 3 located above and below it
It is better that there is no gap between 1 and the light absorption layer 33,
It is advisable to stick them together using an adhesive or the like.

Example 6 In Example 5, a liquid crystal display device having a pixel pitch of 2 mm was used, and the distance between the scattering liquid crystal layer 29 and the light absorbing layer 33 was changed to compare the degree of double image appearance due to parallax. did. When the distance between the display device and the observer is 3 m
Results similar to those in Table 2 were obtained.

[0014]

[Effect] A liquid crystal display device having no decrease in brightness and uneven brightness and less double image appearance was obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a known light-scattering liquid crystal display device using a selective light transmission (reflection) means.

FIG. 2 is a schematic sectional view showing a basic configuration of a liquid crystal display device of the present invention.

FIG. 3 is a schematic sectional view of a liquid crystal display device of Example 3.

FIG. 4 is a schematic cross-sectional view of a liquid crystal display device of one embodiment of Example 4.

FIG. 5 is a schematic cross-sectional view of a liquid crystal display device of another aspect of Example 4.

6 is a schematic sectional view of a liquid crystal display device of Example 5. FIG.

[Explanation of symbols]

 1 Light Scattering Liquid Crystal Display Element 2 Selective Light Reflecting Layer 3 Light Absorbing Layer 4 Vertical Incident Light 5 Oblique Incident Light 6 Upper Substrate 7 Light Scattering Liquid Crystal Layer 8 Lower Substrate 9 Selective Light Reflecting Layer 10 Light Absorbing Layer 11 Lower Substrate 12 Selective Light Reflection Layer 13 Spacer (Plastic Beads) 14 Light Absorption Layer 15 Lower Substrate 16 Selective Light Reflection Layer 17 Gap (Air Layer) 18 Light Absorption Layer (Stamper Molded Black Resin) 19 Upper Substrate 20 Upper Electrode 21 Light Scattering liquid crystal layer 22 Lower electrode 23 Lower substrate 24 Selective light reflecting layer 25 Gap (air layer) 26 Light absorbing layer 27 Upper substrate 28 Upper electrode 29 Light scattering liquid crystal layer 30 Lower electrode 31 Lower substrate 32 Selective light diffusing layer 33 Light absorbing layer

Claims (6)

[Claims] 1. A light-scattering liquid crystal layer is sandwiched between two substrates provided with liquid crystal driving electrodes, and a selective light-reflecting layer is provided outside the liquid crystal layer. In the liquid crystal display device in which a light absorption layer is provided on the opposite surface side and the light scattering property of the liquid crystal layer is controlled by an electric field applied to the liquid crystal driving electrode to perform light modulation, the selective light reflection layer is Having an angle selectivity of transmitting light with an incident angle in a specific range and reflecting light with an incident angle outside the range, and providing a gap between the selective light reflection layer and the light absorption layer, A liquid crystal display device, characterized in that the thickness of the gap is constant in the display surface. 2. The gap between the selective light reflecting layer and the light absorbing layer is
The liquid crystal display device according to claim 1, wherein a constant thickness is provided by providing a spacer in the gap. 3. The gap between the selective light reflecting layer and the light absorbing layer is
The liquid crystal display device according to claim 1 or 2, wherein a convex portion is formed on a surface of the light absorption layer having a spacer function so that the light absorption layer has a constant thickness. 4. A light-scattering liquid crystal layer is sandwiched between two substrates provided with liquid crystal driving electrodes, a selective light diffusing layer is provided outside the liquid crystal layer, and the liquid crystal layer of the light diffusing layer is provided. In the liquid crystal display device in which a light absorption layer is provided on the side opposite to the surface, and the light scattering property of the liquid crystal layer is controlled by an electric field applied to the liquid crystal drive electrode to perform light modulation, the light diffusion layer is specified. A liquid crystal display device having an angle selectivity of transmitting light having an incident angle within a range and diffusing light having an incident angle outside the range. 5. The liquid crystal display device according to claim 1, wherein the pixel pitch is 500 μm or less, and the distance between the liquid crystal layer and the light absorption layer is 1 mm or less or 3 mm or more. 6. The liquid crystal display device according to claim 1, wherein the pixel pitch is 1 mm or more, and the distance between the liquid crystal layer and the light absorption layer is 2 mm or less or 5 mm or more.