JPH10206851A - Reflection type guest-host type liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the contrast and to eliminate problems of a double display by arranging a reflecting layer at an interval with a liquid crystal layer. SOLUTION: This device has a guest-host type liquid crystal layer 6 which has liquid crystal molecules oriented without being twisted or at a nearly constant twist angle at the right angles to a substrate surface and also has >=2 orientation directions distributed in parallel to the substrate surface and a light reflecting layer 8 which is arranged between the liquid crystal layer 6 and one of substrates 1a and 1b at the specific interval with the liquid crystal layer 6. Namely, an acrylic resin layer 7 is arranged between the liquid crystal layer 6 and reflecting layer 8, which is placed at the interval with the liquid crystal layer 6. When a liquid crystal layer in the path of incident light 9a and a liquid crystal layer in the path of reflected light 9b are considered to be different liquid crystal cells, the acrylic resin layer 7 put the positions of the incident light and reflected light away from each other in the cell, microdomains 4a and 4b that the incident light 9a and reflected light 9b pass through are different, and the orientation directions of both the microdomains 4a and 4b are different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a reflective guest-host type liquid crystal display device using a reflected light for display, which contains a dichroic dye.

[0002]

2. Description of the Related Art Various liquid crystal display elements are used in various industrial fields. In a liquid crystal display element, light is controlled by utilizing the property that liquid crystal molecules tend to align in a certain alignment state. Typically, light is on / off controlled according to the alignment state of liquid crystal controlled by an electric field.

In a normal liquid crystal display device, liquid crystal molecules themselves control the polarization direction and scattering of incident light. A polarizing plate is used to align the polarization directions of light incident on the liquid crystal layer.

[0004] The dichroic dye is usually composed of elongated rod-like molecules, and the light absorption characteristics vary depending on the direction of the dichroic dye molecules. The spectrum of the transmitted light changes depending on whether the major axis direction of the dichroic dye molecule is parallel or perpendicular to the electric vector of light.

In order to control the direction of dichroic dye molecules,
Liquid crystal molecules can be used. When a dichroic dye molecule (guest) also having an elongated shape is mixed into a liquid crystal molecule (host) having an elongated shape, the dichroic dye molecule becomes
The liquid crystal molecules are aligned according to the alignment of the surrounding liquid crystal molecules. By controlling the direction of the dichroic dye molecules, the absorption characteristics for incident light can be controlled.

As such a guest-host type liquid crystal display device, nematic liquid crystal, chiral nematic liquid crystal,
A device using cholesteric liquid crystal is known. The pair of substrates of the guest-host type liquid crystal display element is subjected to an alignment treatment such as rubbing so that the alignment directions of liquid crystal molecules on the substrates have a fixed relationship. The liquid crystal molecules of the guest-host type liquid crystal display device having been subjected to such an alignment process are aligned in a fixed direction over the entire surface of the substrate. The alignment direction is set so as to have a constant twist angle with respect to the thickness direction of the liquid crystal layer.

One of the features of the guest-host liquid crystal display element is that it is not necessary to use a polarizing plate.
Therefore, a bright display element can be realized in both the transmissive type and the reflective type since the light utilization factor is good. However, on the other hand, the contrast is low.

[0008] In the embodiment of the specification of Japanese Patent Application No. 7-26784 filed by the same applicant as the present application, a large number of microdomains are formed on the substrate surface without subjecting the substrate to active alignment treatment. It is shown that the contrast is improved by a guest-host type liquid crystal display element having a multi-domain structure in which the orientation directions of liquid crystal molecules are aligned between substrates in each micro domain.

In the reflection type liquid crystal display device, a reflection plate is arranged on the substrate surface outside the rear substrate or inside the rear substrate of the pair of substrates. Light that enters from the front side (display surface) substrate, passes through the liquid crystal layer, and is reflected by the reflector again passes through the liquid crystal layer again, exits from the front side substrate, and enters the viewer's eyes. The transmission state is controlled while the light passes through the liquid crystal layer twice.

[0010]

Problems to be Solved by the Invention Japanese Patent Application No. Hei 7-26784
In the specification of No. 2, when a guest-host liquid crystal display element having a multi-domain structure is of a reflection type, there are two examples of a structure in which a reflector is arranged outside a liquid crystal cell and a structure in which a reflector is arranged inside a liquid crystal cell. It is shown.

In the case of the former structure, as shown in FIG. 2A, the light 9a incident from the front substrate 1a passes through the guest-host type liquid crystal layer 6, passes through the rear substrate 1b, and passes through the rear substrate 1b. The light is reflected by the reflector 10 arranged at a distance from the substrate. Then, the reflected light 9b passes through the rear substrate 1b,
The light passes through the guest-host type liquid crystal layer 6 and exits from the front substrate 1a.

In this case, since the rear glass substrate 1b is disposed in front of the reflector 10, when the liquid crystal display device is viewed from an oblique direction, the thickness of the rear glass substrate 1b is increased due to multiple reflection and refraction effects. However, there is a problem that only the parallax is generated and the display looks double.

Further, in the latter case of a structure in which a reflector is disposed inside a liquid crystal cell, as shown in FIG. 2B, light 9a incident from the front substrate 1a is applied to the guest-host type liquid crystal layer 6 as shown in FIG.
And is reflected by the reflector 11. Then, the reflected light 9b passes through the guest-host type liquid crystal layer 6 and exits from the front substrate 1a. In this case, there is no problem of double display as in the case of FIG. 2A, but the contrast ratio is lower than that of the structure of FIG. The reason is considered as follows.

In the structure shown in FIG. 2B, the obliquely incident light 9a and the reflected light 9b near the reflection point 12 of the reflection plate 11 are close to each other, and therefore the incident light 9a and the reflected light 9b are close to each other.
Will pass through the same microdomain 4. That is, since the orientation direction of the liquid crystal passes through the same domain, light absorption is reduced.

On the other hand, in the structure shown in FIG.
Is located away from the cell, the position of the incident light 9a and the position of the reflected light 9b in the cell are separated, and therefore, the micro domain 4a different from the incident light 9a and the reflected light 9b.
And 4b.

Since the orientation directions of a large number of microdomains change at random, the different microdomains 4a and 4b have a high probability of having mutually different orientation directions. Microdomains 4a and 4b with different orientations
Since the light 9b that has passed through is absorbed more, the structure of FIG.
It is considered that the contrast is higher in the former because it is lower than in the structure of (B).

An object of the present invention is to provide a double display when a guest-host liquid crystal display device having a multi-domain structure disclosed in an embodiment of the specification of Japanese Patent Application No. 7-26784 is used as a reflection type. An object of the present invention is to provide a reflection-type guest-host liquid crystal display element having no significant problem and high contrast.

[0018]

According to the present invention, there is provided a reflective guest-host liquid crystal display device comprising a pair of substrates opposed to each other at a predetermined interval, and a liquid crystal and a dichroic dye sandwiched between the pair of substrates. A guest-host type liquid crystal layer including, wherein the orientation direction of the liquid crystal molecules of the liquid crystal layer shows no twist or a substantially constant twist angle with respect to a direction perpendicular to the substrate surface,
A guest-host type liquid crystal layer in which two or more alignment directions are distributed in a direction parallel to the substrate surface, and a predetermined distance from the liquid crystal layer between the liquid crystal layer and one of the pair of substrates. And a light reflecting layer disposed.

[0019]

FIG. 1 shows a reflective guest-host liquid crystal display device according to an embodiment of the present invention. FIG. 1 (A)
FIG. 1 is a partial cross-sectional view of a liquid crystal display element, and FIG.
(C), (D) is a schematic diagram showing an alignment state of liquid crystal molecules on the substrate surface.

As shown in FIG. 1A, the liquid crystal display device comprises a pair of glass substrates 1a and 1b to form a liquid crystal cell, and a liquid crystal layer 6 is sandwiched inside. The upper glass substrate 1a is a front side serving as a display surface. The transparent electrode 2 is formed on the inner surface of the upper glass substrate 1a. Further, an alignment film (not shown) on which no alignment treatment is performed is formed thereon. The lower glass substrate 1b is a rear substrate. A reflection plate 8 is formed on the rear glass substrate 1b. The reflecting plate 8 is an aluminum layer also serving as a lower electrode, and the reflecting surface is roughened so that light is irregularly reflected.
A transparent acrylic resin film 7 is further formed on the reflection plate 8 by spin coating and baking. Then, on the transparent acrylic layer 7, an alignment film (not shown) which is not subjected to an alignment process is formed.

Since the alignment film has not been subjected to the alignment treatment, the liquid crystal layer 6 injected into the liquid crystal cell receives a force for aligning in parallel with the substrate surface, but receives an alignment force in the in-plane direction. Absent.

The liquid crystal layer 6 is formed by mixing dichroic dye molecules 5 into liquid crystal molecules 3 of a nematic liquid crystal, a chiral nematic liquid crystal or a cholesteric liquid crystal.

Since the substrate has no orientation direction, the liquid crystal layer 6
Are oriented in random directions. However, since the cell thickness of the liquid crystal cell is as small as at most a few μm, the liquid crystal layer 6 is oriented according to the properties of the liquid crystal in the cell thickness direction. The figure shows a case where chiral nematic liquid crystal is injected.
The liquid crystal molecules 3 exhibit a constant twist from one substrate 1a to the other substrate 1b according to the chirality. The dichroic dye molecules 5 are oriented according to the orientation of the liquid crystal molecules 3.

Without performing such a positive alignment treatment,
A method of manufacturing a liquid crystal cell having a multi-domain structure including a large number of microdomains is disclosed in Japanese Patent Application No. 4-236652 or Japanese Patent Application No. 6-19 filed by the same applicant as the present applicant.
No. 4,655, or Japanese Patent Application No. 6-53639, and the methods disclosed in the examples in the specification of Japanese Patent Application No. 7-26784 in which they are applied to a guest-host type liquid crystal display device can be used. That is, when using the methods disclosed in these specifications, the gap between the cell substrates and the chiral pitch of the liquid crystal are arranged so as to have a specific relationship, and the liquid crystal is oriented using the thermo-optic effect of the liquid crystal. I have. In other words, a liquid crystal material is heated to a temperature higher than the phase transition temperature of the liquid crystal and is injected into the cell in a state of an isotropic liquid, that is, isotropic phase, and then gradually cooled to undergo a phase transition to a liquid crystal state, that is, a liquid crystal phase to be oriented. Things. Thereby, a large number of minute alignment regions, that is, microdomains can be formed at random.

FIGS. 1B, 1C and 1D show alignment states of liquid crystal molecules generated when an alignment process is not performed on a substrate.

In the case of FIG. 1B, a large number of microdomains 4 are formed in the substrate surface, and the liquid crystal molecules 3 are substantially aligned in a certain direction inside each microdomain 4 as shown by arrows. Parallel alignment. The orientation direction differs for each microdomain 4, and the orientation is random when viewed over the entire surface of the substrate.

In FIG. 1C, the alignment direction of the liquid crystal molecules 3 changes continuously in the plane of the substrate. There is no rule in this continuity, and the orientation is random when viewed over the entire surface of the substrate.

In FIG. 1D, the micro domain 4
Are scattered. In each microdomain 4, liquid crystal molecules are aligned in a substantially constant direction. Micro domain 4
In the region between, the liquid crystal molecules 3 exist with the alignment direction continuously changed. The orientation state of FIG.
It can be considered as a combination of (B) and (C).

[0029]

EXAMPLE A guest-host type liquid crystal cell having a multi-domain structure as shown in FIG. 1A was manufactured by using the method of the prior application. At this time, the thickness of the acrylic resin film 7 on the aluminum reflection film 8 was set to 1 μm, 3 μm, 10 μm, 50 μm
And four types of cells were created. However, 50 μm
Those were overcoated.

Further, in this embodiment, the maximum absorption wavelength 600
guest host liquid crystal obtained by mixing 0.75 wt% of a chiral nematic liquid crystal having a natural pitch of 15.43 μm with a dark blue dye (G256 manufactured by Japan Photographic Dye Laboratories) having a thickness of 9 nm. Injected above the transition temperature (120 ° C.)
The method disclosed in Examples in the specification of 236652).

The liquid crystal molecules in the reflective guest-host liquid crystal display device prepared under such conditions have a 210 ° angle between the upper and lower substrates.
Will be twisted. For comparison with the display element of the present example, a display element (same as FIG. 2B) to which the acrylic resin film 7 was not applied was also prepared. Table 1 shows the measurement results of the contrasts of these display elements.

[0032]

[Table 1]

As can be seen from the results shown in Table 1, those having the acrylic resin layer 7 provided, particularly those having a thickness of 3 μm or more, were compared with those having no acrylic resin layer (the structure of FIG. 2B). As a result, the contrast ratio was improved. Moreover, since the reflector 8 is disposed inside the cell, double display does not occur when the reflector such as the liquid crystal display element of FIG. 2A is disposed outside the cell.

The acrylic resin layer 7 having a constant thickness is formed on the liquid crystal layer 6.
By disposing the reflective layer 8 between the liquid crystal layer 6 and the reflective layer 8, the contrast is improved and the problem of double display is solved.

The reason for the improvement of the contrast will be described more clearly with reference to FIG. When the liquid crystal layer on the path of the incident light 9a and the liquid crystal layer on the path of the reflected light 9b are considered as separate liquid crystal cells, the acrylic resin layer 7 separates the positions of the incident light and the reflected light in the cell. , Incident light 9
Unlike the micro domain 4a through which a passes, and the micro domain 4b through which the reflected light 9b passes, the orientation directions of both micro domains are different from each other.

Accordingly, this corresponds to a case where two guest-host type liquid crystal display elements having different alignment directions are overlapped. Light absorption is maximized when the orientation directions of the two guest-host type liquid crystal display elements are perpendicular to each other. Since the orientation direction of the microdomain 4 is randomly and continuously changed as a whole in the cell, light absorption is increased in the entire cell, and the reflectance when no voltage is applied is substantially reduced.

When the thickness of the acrylic resin layer 7 is small, the effect of improving the contrast is small. The reason for the small thickness is that the incident light 9a and the reflected light 9b with respect to the light obliquely incident. This is considered to be due to the fact that the change in the orientation direction of the micro domain through which light passes is small.

Therefore, it is desirable that the thickness of the acrylic resin layer 7 is larger than the average diameter of the micro domains constituting the multi-domain structure. However, if the thickness of the acrylic resin layer 7 is too large, the problem of double display as described in the case of FIG. 2A will occur. Therefore, the maximum thickness of the acrylic resin layer 7 will be about 200 μm. Since the diameter of the microdomain is small and slightly smaller than the cell thickness, that is, about 3 μm, the thickness of the acrylic resin layer 7 is about 3 μm to 200 μm.
A range of about m is considered to be good.

It is to be noted that a layer made of a transparent material other than the acrylic resin layer or a means for providing a space may be employed in order to set the above-mentioned space between the liquid crystal layer and the reflection plate. .

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0041]

According to the reflection type guest-host liquid crystal display device, by disposing the reflection layer in the cell at a distance from the liquid crystal layer, the contrast is improved and the problem of double display is eliminated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a reflective guest-host type liquid crystal display device according to an embodiment of the present invention and a schematic diagram showing a configuration of a substrate-like micro domain.

FIG. 2 is a sectional view of two types of reflective guest-host type liquid crystal display devices disclosed in the specification of Japanese Patent Application No. 7-26784.

[Explanation of symbols]

 1a, 1b Glass substrate 2 Transparent electrode 3 Liquid crystal molecule 4, 4a, 4b Micro domain 5 Dichroic dye molecule 6 Liquid crystal layer 7 Acrylic resin layer 8 Reflector (also used as electrode) 9a Incident light 9b Reflected light

Claims (7)

[Claims] 1. A guest-host type liquid crystal layer sandwiched between a pair of substrates disposed opposite to each other at a predetermined interval and including a liquid crystal and a dichroic dye, wherein liquid crystal molecules of the liquid crystal layer are provided. The orientation direction of the guest-host type liquid crystal layer in which there is no twist or a substantially constant twist angle in the direction perpendicular to the substrate surface, and two or more orientation directions are distributed in the direction parallel to the substrate surface, A reflective guest-host type liquid crystal display device, comprising: a liquid crystal layer and a light reflective layer disposed at a predetermined distance from the liquid crystal layer between one of the pair of substrates. 2. The reflection type guest-host type liquid crystal display device according to claim 1, further comprising a transparent thin film having a thickness corresponding to the predetermined interval, disposed between the light reflection layer and the liquid crystal layer. 3. The guest-host type liquid crystal layer has a large number of microdomains in a direction parallel to a substrate surface, and liquid crystal molecules are aligned in each microdomain.
3. The reflective guest-host type liquid crystal display device according to claim 1, wherein the predetermined interval is larger than an average diameter of the micro domains. 4. The reflective guest-host type liquid crystal display device according to claim 3, wherein the predetermined interval is set to a value in a range of 3 μm to 200 μm. 5. The guest-host type liquid crystal layer includes a region in which the orientation direction of liquid crystal molecules changes almost continuously between a number of microdomains in a direction parallel to the substrate surface.
The reflective guest-host type liquid crystal display device according to the above. 6. The reflective guest-host type liquid crystal display according to claim 1, wherein the orientation direction of the liquid crystal molecules of the guest-host type liquid crystal layer changes microscopically and substantially continuously in a direction parallel to the substrate surface. element. 7. The reflective guest-host type liquid crystal display device according to claim 1, wherein said pair of substrates does not have a positive alignment structure for said liquid crystal molecules.