JPS6017722A - Guest-host liquid crystal display element - Google Patents

Abstract

PURPOSE:To reduce a change in the absorbance in the visible light region with the lapse of time by using at least one kind of anthraquinone dye having its light absorption maximum in a specified wavelength range. CONSTITUTION:Plural kinds of polychromatic dyes to be used are one or more kinds of azo dyes each having its absorption maximum in the wavelength range of 340-500nm and one or more kinds of anthraquinone dyes each having its absorption maximum in the wavelength range of 500-740nm, and at least one of the anthraquinone dyes has its absorption maximum in the wavelength range of 500-550nm. An azo dye having its absorption maximum in the wavelength range of <=500nm contributes to the improvement of order parameter, and an anthraquinone dye having its absorption maximum in the wavelength range of 500-550nm eliminates the instability of absorbance at about 550nm. An anthraquinone dye having its absorption maximum in the wavelength range of >=550nm provides a desired hue and contributes to the stability of light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a guest-host liquid crystal display element in which a liquid crystal layer is formed by dissolving a plurality of types of pleochroic dyes in a liquid crystal base material to form a 4VI liquid crystal layer.

A guest-host type liquid crystal display element is an element in which a so-called pleochroic dye, which is a so-called gelatin, is dissolved in a liquid crystal base material, which is a so-called host material.
The molecular axis of the dichroic dye is displaced in accordance with the 'a-crystalline orientation, which is changed by an externally applied voltage, and the optical anisotropy of the dichroic dye is utilized to polarize light in a specific direction. This is an element that absorbs light with a specific range of spectrum and enables color tone modulation using voltage. Regarding the performance of guest-host type liquid crystal display elements, from the viewpoint of Hun 1-Last, the ratio of absorbance to light polarized parallel and perpendicular to the molecular axis of the aligned liquid crystal, that is, the ratio of the two colors. It is desirable that the sex ratio or order parameter be as large as possible, the better, and that the dichroism ratio should be as close as possible to the dichroism ratio of the dye solid ira.

On the other hand, from the perspective of use x 1 life, visible light and ultraviolet rays are 3
It is desirable that the change in absorbance over time is as small as possible. It is desirable that the material be stable against washing.

Accordingly, host type liquid crystal display elements are based on conventional Gess 1 and 8 from the viewpoint of these contrasts 1 to 8 and photostability.
J) The types of body substances and pleochroic pigments are selected.

Conventionally, azo (Am and an-1-laquinone) dyes have been used as one of these pleochroic dyes. Among these,
Although azo dyes have excellent order parameters, they exhibit maximum absorption in the long wavelength region.1-Azo dyes have the disadvantage of large changes in absorbance over time, that is, they are unstable to light. are doing.

On the other hand, anthraquinone dyes are stable to light [However, atraquinone dyes, which have an absorption maximum in the short wavelength region, have the disadvantage of having a hot order parameter, and are susceptible to color switching caused by voltage application. There is a problem with insufficient contrast.

Therefore, a proposal for improving such conventional drawbacks is disclosed in Japanese Patent Application Laid-open No. 55-127485. It is a guest-host type dye that is a mixture of at least two types of dyes: an azo dye that has an absorption maximum in the wavelength range of 340 to 550 nm, and an atraquinone dye that has an absorption maximum in the wavelength range of 550 to 750 nm. It is a liquid crystal display element. According to the report, accelerated tests using ultraviolet irradiation showed that the device had far greater photostability than a guest-host liquid crystal display device composed only of azo dyes. Furthermore, it is said that a product with greater contrast than a product containing only anthraquinone dyes was obtained.

However, when the present inventors conducted a photostability experiment using J3 in the visible light region, it was found that good photostability was not necessarily obtained. That is, although the photostability of electrons disclosed in the above-mentioned special report is remarkable in the ultraviolet region, there is no photostability in the visible light region, and there is a large change in absorbance over time near Ei E50 nm (J). It has become clear that this occurs.

Therefore, the present invention was made with the aim of improving the shortcomings related to photon stability in the visible light region of conventional devices. The purpose is to provide a type of liquid crystal display element.

That is, the present invention provides a guest-host type liquid crystal display layer including a plurality of types of pleochroic dyes, wherein the plurality of types of pleochroic dyes have a wavelength range of 340 to 5QQI1.
consisting of one or more azo dyes having an absorption maximum at J5 m and one or more anthraquinone dyes having an absorption maximum in the wavelength range of 500 to 740 rv, at least one of the anthraquinone dyes It is characterized by having an absorption maximum in the wavelength range of 500 to 550 nm.

Here, as the liquid crystal matrix, P-type or N-type nematic liquid crystal, P-type cholesteric liquid crystal, mixed crystal liquid crystal of P-type cholesteric liquid crystal and P-type nematic liquid crystal, etc. can be used. system dye (wavelength range 340-500
It has an absorption maximum in the nm range.

The azo dye may be composed of multiple types. However, wavelength range 5
00 nm or more does not contain dyes with an absorption of 44 degrees. Also, anthraquinone pigments are 500 to 740
It has an absorption maximum in the wavelength range of nm,
At least one of them always has an absorption maximum in the wavelength range of 500 to 550 nm. Azo dyes that have an absorption maximum in the wavelength range of 500 nm or less contribute to improving the A-ta parameter, and anthraquinone dyes that have an absorption maximum in the wavelength range of 500 to 550 nm contribute to the improvement of the A-ta parameter.
It acts to eliminate the instability of light absorbance around 5Q nm. In addition, there is absorption in the wavelength region of 5501 m or more.
The anthraquinone-based colored threads that make up the 1v pole provide the desired hue (17) and contribute to photostability.

Hereinafter, the present invention will be explained based on Examples.

FIG. 1: Guest host 1 according to an embodiment of the present invention.
FIG. 4 is a cross-sectional view showing the configuration of a liquid crystal display element. J
'7S1.11III11 plate glass substrates 2 and 1
Indium oxide thin film layers 4 and 10 are formed on the end face of each of the liquid crystal layers by vacuum evaporation. These indium oxide thin film layers have a sheet resistance of 1000/S.
O. Next, this indium oxide R? Il
Polyimide film layers 6 and 8 were formed on the inner end surfaces of 'AY'l 4 and 10, respectively. The surfaces of this polyimide film layer (3 and 8) were rubbed in one direction with a cloth,
Parallel alignment processing is performed.

Both ends of the two substrates formed in this manner are supported by suberes 16 and 18 to form a liquid crystal layer! A constant interval of gears/tubes was obtained for the rotation. This substrate spacing 1; C1
It is 0 μm. All of these items, except for a few, are sealed with epoxy adhesive.

Next, a liquid crystal mixed with a pleochroic dye, which will be described later, was injected into the gap between the substrates by a reduced pressure injection method to form a liquid crystal layer, thereby constructing a guest-host type liquid crystal display element. The material of the liquid crystal layer is phenylcyclohexane mixed liquid crystal, L
0N9016 (Chisso Corporation), the first
A pleochroic dye having an absorption maximum in the predetermined wavelength range shown in the table was dissolved in a predetermined mixing ratio.

In addition, in a liquid crystal element similar to the structure shown in Fig. 1, the pleochroic dye is
As is conventionally known, a comparative example was prepared in which materials having absorption maximums in a predetermined wavelength range were mixed at a predetermined ratio.

That is, the substances constituting the liquid crystal layer according to the comparative example are phenylcyclohexane-based mixed liquid crystal, LIXO
It was composed of a liquid crystal matrix N9016 (Chisso Corporation) in which a dye having maximum absorption in the wavelength range shown in Table 2 was dissolved at a predetermined mixing ratio.

Here, the difference between the example and the comparative example is that in the comparative example, an azo color iG 20 having an absorption maximum at 542 nm is used.
2, whereas in this example, 546 nm is used.
Which anthraquinone color has the right absorption maximum? (j l)
52 is used. Also, tl/go; 'i'
Although each color is different, it is selected based on the relationship between the molecular extinction coefficient of each color thread.

FIG. 33 shows the characteristics of the rate of change of absorbance over time a and i of each liquid crystal display element of the present example and guest boss according to a comparative example. This is a graph. In Fig. 3, the curve 43 shows the example of the L axis, and the curve 43 shows the dimensions of this example. In this experiment, 2 kW of XO clamp light was applied to the liquid crystal display element at 23 kW.
Deterioration In of absorbance after time irradiation was measured based on the absorbance before irradiation.

C1 This is defined as the rate of change in the absorbance level and is shown on the vertical axis of Figure 3. As a result, after the 23:00 timetable, in the comparative example, a large change in absorbance occurred near 550 nl (J), and the deterioration of absorbance was significant.

It can be seen that the deterioration of absorbance is significantly reduced as shown in the 1;

In addition, in order to investigate the cause of the deterioration of the absorbance of the comparative sample,
The 2 kW XG clamp light emission was spectrally analyzed, and the change in absorbance with respect to the absorption light wavelength after irradiation with light of a single frequency was measured using the wavelength of the irradiation light as a parameter. FIG. 2 shows the rate of change in absorbance of the liquid crystal display element after 23 hours of irradiation for each irradiation wavelength as a function of wavelength. As is clear from these results, the liquid crystal display element absorbs light with a 1.
The inventors have revealed that there is a large change in quality over time.

In order to improve the change in absorbance over time due to ultraviolet irradiation with the conventional 13'N, it is sufficient to mix an 1-laquinone colored thread that has an absorption maximum in the wavelength range of 550 to 740 nm. .However, this 'C is for use!T!
It is not possible to prevent the absorbance from deteriorating due to visible light, which is the key factor. Therefore, from the results of the 4R experiment, 500~
It has become clear that in order to prevent deterioration of absorbance in the 550nIllri region, it is necessary to use colored threads that are highly stable against light even in the 500-550nm reIII range.

Table 1 Table 2 Therefore, the present invention uses an anthraquinone dye D52 (manufactured by BD+-), which has an absorption maximum in the range of 500 to 5501 m, so that the absorbance changes over time as shown in the curve shown in Figure 3. It was found that it was possible to significantly reduce the

In summary, the present invention is a guest-host liquid crystal display element which is made by always mixing one kind of anthraquinone dye having a light absorption maximum in the wavelength range of 500 to 550 nm.

By configuring in this way, it is possible to avoid deterioration of the change in absorbance over time in the visible light region. Further, the contrast can be made sufficiently high by using the azo dye contained in the element.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a guest-host liquid crystal display device according to a specific embodiment of the present invention. FIG. 2 shows a comparative example of a liquid crystal display device illuminated with light of various wavelengths. FIG. 3 is a dimensional characteristic diagram showing the relationship between the rate of change in absorbance and absorption wavelength after FIG. 3 shows the measured characteristics of the rate of change in absorbance of the guest-post liquid crystal display elements according to the present example and the comparative example with respect to absorption wave 1. 2.12...Crow substrate 4, ε3 ... Indicomb oxide thin film 6.8 ... Polyimide thin film 20 ... Liquid crystal 22 ... Pleochroic dye Q!+ ii'
lApplicant Nippondenso Co., Ltd. Agent br, ]ff!
+ Anama Okawa Patent attorney Sakudo Fujitani Patent attorney Akito Maruyama Figure 1 Figure 2 Figure 3 123

Claims (3)

[Claims] (1) A guest-host type liquid crystal display device having a liquid crystal layer containing multiple types of pleochroic dyes has a maximum absorption in a wavelength range of 340 to 500 nm. and one or more azo dyes having wave I
(Absorption in the region 500-74 Q nm (individual's right η
at least 1 (1(
, L, wavelength [500 to 550 nl11]
Small strike: 13i product display element. (2) The guest-post liquid crystal display element according to claim 1, which is a dye that exhibits an absorption pole in a wavelength range of 500 to 550 nm. (3) The liquid crystal display device according to claim 1 or 2, wherein the liquid crystal material constituting the liquid crystal layer is a phenylcyclohexane mixed liquid crystal.