JPH11212070A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable practical low-voltage driving by reducing a driving electric field to a range capable of using a general-purpose driving circuit while balancing lightness and contrast by adding nonionic surfactants more than two kinds to composite materials. SOLUTION: The nonionic surfactants more than two kinds are added to the composite materials held between two substrates with transparent electrode. Namely, concerning a polymer distributed liquid crystal(PDLC) material distributing the small drops of nematic liquid crystal in a water soluble polymer matrix, in addition to the nematic liquid crystal and water soluble polymer, nonionic surfactants more than two kinds are added and one kind of these nonionic surfactant is a chemical compound (aromatic ring) having benzene structures more than one. Thus, since one kind of nonionic surfactants more than two kinds has the aromatic ring, the driving electric field is reduced not more than 1 V/μm.

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, and more particularly, to a liquid crystal display utilizing a polymer dispersed liquid crystal.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays (LCDs)
Due to advantages such as low voltage and low power driving, it is mounted on various display devices.

At present, nematic LCDs are mainly used for LCDs. Among them, direct drive type relatively inexpensive twisted nematic (TN) type and super twisted nematic (STN) type, and active matrix type expensive type are used. A thin film transistor (TFT) type has been widely put to practical use.

However, these TN type, STN type, and T
FT-type LCDs have an element in which a liquid crystal is sandwiched between substrates with transparent electrodes, and are further sandwiched between polarizing plates, and light is transmitted through the polarizing plates. Therefore, light use efficiency is low, and the display becomes dark. Light is needed. For this reason, the display is thick and heavy, and the power consumption is large, which is not suitable for a portable or reflective display.

On the other hand, other LCDs using nematic liquid crystals
A display device using a polymer dispersed liquid crystal (PDLC) is known.

A display element using this PDLC mainly uses light scattering without using a polarizing plate, and therefore has a high light use efficiency and does not require a backlight because the display is bright. Therefore, there is a possibility that the above problem can be solved.

[0007]

SUMMARY OF THE INVENTION However, PDL
One of the biggest technical issues in promoting widespread practical use of C is reduction of the driving electric field. However, in the current display device using PDLC, the magnitude of this driving electric field E ₉₀ (E ₉₀ = V ₉₀
/ Film thickness V ₉₀ is a drive voltage value that gives 90% of the maximum light transmittance. ) Is about 2.5 to 5 V / μm, and the general-purpose driving circuit for the liquid crystal display element is driven at 5 V, so that the practicability is low.

Accordingly, an object of the present invention is to reduce the driving electric field to 1 V / μm or less so that a general-purpose driving circuit can be used while maintaining the balance between brightness and contrast.
An object of the present invention is to provide a polymer dispersed liquid crystal display device that can be driven at a practical low voltage.

[0009]

In order to solve the above-mentioned problems, a first aspect of the present invention is a structure in which a composite material in which a nematic liquid crystal is dispersed in a water-soluble polymer medium is sandwiched between two substrates with transparent electrodes. In the above liquid crystal display device, two or more kinds of nonionic surfactants are added to the composite material.

According to a second aspect of the present invention, at least one of the two or more nonionic surfactants has an aromatic ring.

According to a third aspect of the present invention, the nonionic surfactant is added in an amount of 1 to 10 wt.
%.

That is, the gist of the present invention is that a nematic liquid crystal droplet is dispersed in a water-soluble polymer matrix.
In the DLC material, in addition to the nematic liquid crystal and the water-soluble polymer, two or more nonionic surfactants are added, and at least one of the nonionic surfactants is a compound having at least one benzene structure. (Hereinafter, referred to as an aromatic ring).

[0013]

Next, a preferred embodiment of the present invention will be described in detail.

The driving electric field E ₉₀ (E ₉₀ ) of the conventional PDLC element
= V ₉₀ / film thickness V ₉₀ is a drive voltage value that gives 90% of the maximum light transmittance. ) Is 2.5 to 5 V / μm.

As a result of various studies, the present inventors have found that a certain nonionic surfactant such as a nonionic surfactant having an aromatic ring is added to a PDLC material in which droplets of nematic liquid crystal are dispersed in a water-soluble polymer matrix. When a surfactant is added,
It has been found that the driving electric field E ₉₀ is reduced to about 1.5 V / μm.

In general, a surfactant forms an interfacial film, but a single surfactant often does not form a closely packed interfacial film. In this case, two types of surfactants are used instead of a single surfactant. Since the mixture of the above surfactants forms a more densely packed interfacial film, the present inventor has determined that the driving electric field E ₉₀ can be increased by adding two or more nonionic surfactants. Was found to decrease.

Furthermore, among the two or more non-ionic surfactant, at least one is by the one having an aromatic ring, driving electric field E ₉₀ is we have found to drop to below 1V / [mu] m.

The reduction of the driving electric field E ₉₀ is caused by the PDLC
It is considered that the synergistic effect of a plurality of nonionic surfactants of different types worked even in the material.

In the present invention, applicable liquid crystals are not particularly limited, but include azoxy compounds, biphenyl compounds, azomethine compounds, pyrimidine compounds, benzoate compounds, dioxane compounds, phenylcyclohexane compounds, and cyclohexyl carboxylic acids. Ester compounds, cyanobiphenyl compounds and the like.

The water-soluble polymer applicable to the present invention is not particularly limited, but includes methylcellulose, polyvinyl alcohol, polyoxyethylene, polyvinyl butyral and the like.

The nonionic surfactants applicable to the present invention are not particularly limited, but include polyoxyethylene alkyl phenyl ethers and fluoroalkyl ethylene oxides having an aromatic ring, sorbitan fatty acid esters, and polyoxyethylene fatty acid. Esters and polyoxyethylene alkyl ethers.

However, the total addition amount is 1 to 10 w
t% is desirable, above which the effectiveness is greatly reduced.

The nematic liquid crystal may contain a dichroic dye or other additives.

[0024]

EXAMPLES Examples of the present invention and comparative examples will be described below.

Example 1 As a liquid crystal, BL003 manufactured by Merck was selected, and 4% of a red dichroic dye M-86 (anthraquinone) manufactured by Mitsui Toatsu was dissolved therein. 5 g of this solution is mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (405, Kuraray), and sorbitan monooleate (SPO-10, Kao Corporation) and polyoxyethylene nonyl phenyl ether (Emulgen) are used as nonionic surfactants. 903, Kao Corporation) was added at 3% each, and the mixture was stirred with a homogenizer at a rotation speed of 12,500 rpm to prepare an emulsion.
This was applied on a glass substrate with an ITO electrode using an applicator, and then a counter substrate was attached to produce an element.

Example 2 RO-TN-403 manufactured by Roddick Co., Ltd. was selected as a liquid crystal, and a blue dichroic dye M-137 manufactured by Mitsui Toatsu was selected.
(Anthraquinone type) was dissolved in 4%. 5 g of this solution is mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (405, Kuraray), and further as a nonionic surfactant,
Fluoroalkyl polyoxyethylene (DS-406,
(Daikin) and 4% of polyoxyethylene nonyl phenyl ether (Emulgen 903, Kao) were added, and the number of revolutions was 12,500 rpm using a homogenizer.
To prepare an emulsion. Then, Example 1
A device was produced in the same manner as described above.

Example 3 As liquid crystal, BL008 manufactured by Merck was selected, and 4% of a blue dichroic dye SI-497 (anthraquinone) manufactured by Mitsui Toatsu was dissolved therein. 5 g of this solution is mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (205, Kuraray), and fluoroalkyl polyoxyethylene (DS-406, Daikin) and polyoxyethylene octyl phenyl ether (Daikin) as nonionic surfactants OP-
3, Nikko Chemicals Co., Ltd.) was added in an amount of 3%, and the mixture was stirred at a rotation speed of 12,500 rpm using a homogenizer to prepare an emulsion. Thereafter, an element was manufactured in the same manner as in Example 1.

Comparative Example 1 BL003 manufactured by Merck was selected as a liquid crystal, and 4% of a red dichroic dye M-86 (anthraquinone) manufactured by Mitsui Toatsu was dissolved therein. 5 g of this liquid was mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (405, Kuraray), and 6% of sorbitan monooleate (SPO-10, Kao Corporation) was added as a nonionic surfactant.
The emulsion was prepared by stirring at 12,500 rpm using a homogenizer. Thereafter, an element was manufactured in the same manner as in Example 1.

Comparative Example 2 As a liquid crystal, BL003 manufactured by Merck was selected, and 4% of a red dichroic dye M-86 (anthraquinone) manufactured by Mitsui Toatsu was dissolved therein. 5 g of this solution was mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (405, Kuraray Co., Ltd.), and the mixture was stirred at 12,500 rpm using a homogenizer without adding a nonionic surfactant to prepare an emulsion. Thereafter, an element was manufactured in the same manner as in Example 1.

Comparative Example 3 RO-TN-403 manufactured by Roddick Co., Ltd. was selected as a liquid crystal, and a blue dichroic dye M-137 manufactured by Mitsui Toatsu Co., Ltd. was selected.
(Anthraquinone type) was dissolved in 4%. 5 g of this liquid was mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (405, Kuraray), and 6% of a fluoroalkylpolyoxyethylene (DS-406, Daikin) was added as a nonionic surfactant. Then, the mixture was stirred at 12,500 rpm to prepare an emulsion. Thereafter, an element was manufactured in the same manner as in Example 1.

Comparative Example 4 RO-TN-403 manufactured by Roddick Co., Ltd. was selected as a liquid crystal, and a blue dichroic dye M-137 manufactured by Mitsui Toatsu Co., Ltd. was selected.
(Anthraquinone type) was dissolved in 4%. 5 g of this solution was mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (405, Kuraray Co., Ltd.), and the mixture was stirred at 12,500 rpm using a homogenizer without adding a nonionic surfactant to prepare an emulsion. Thereafter, an element was manufactured in the same manner as in Example 1.

Comparative Example 5 BL008 manufactured by Merck was selected as a liquid crystal, and 4% of a blue dichroic dye SI-497 (anthraquinone) manufactured by Mitsui Toatsu was dissolved therein. 5 g of this liquid was mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (205, Kuraray), and 6% of fluoroalkyl polyoxyethylene (DS-406, Daikin) was added as a nonionic surfactant. Rotational speed 125 using a homogenizer
The emulsion was prepared by stirring at 00 rpm. Thereafter, an element was manufactured in the same manner as in Example 1.

Comparative Example 6 BL008 manufactured by Merck was selected as a liquid crystal, and 4% of a blue dichroic dye SI-497 (anthraquinone) manufactured by Mitsui Toatsu was dissolved therein. 5 g of this solution was mixed with 10 g of a 5% aqueous solution of polyvinyl alcohol (205, Kuraray Co., Ltd.), and the mixture was stirred at a rotation speed of 12,500 rpm using a homogenizer without adding a nonionic surfactant to prepare an emulsion. Thereafter, an element was manufactured in the same manner as in Example 1.

The above-described Example 1, Example 2, and Example 3, in order to check for the effect of reducing the driving electric field E ₉₀ by non-ionic surface active agent, a liquid crystal applying type, water-soluble polymer A liquid crystal display device was prepared by changing the type, the type of dichroic dye, and the type of nonionic surfactant.

Comparative Example 1 is the same as Example 1 except that only one nonionic surfactant was added.
In Example 1, a nonionic surfactant was not added in Example 1.

Comparative Example 3 is the same as Example 2 except that only one nonionic surfactant was added.
In Example 2, the nonionic surfactant was not added.

Comparative Example 5 is the same as Example 3 except that only one nonionic surfactant was added.
In Example 3, a nonionic surfactant was not added.

For each of Examples 1 to 3 and Comparative Examples 1 to 6, the voltage dependence of the transmittance (555 nm) was measured using a spectrophotometer. The measurement frequency was 1000 Hz.

Table 1 shows the measurement results.

[0040]

[Table 1]

[0041] From Table 1, when comparing the Comparative Examples 1 and 2 in Example 1, driving electric field E ₉₀ of Example 1, 0.7 V / [mu] m than the driving electric field E ₉₀ of Comparative Example 1, Comparative Example 2 Drive electric field E ₉₀
1.9 V / μm lower than the above.

[0042] Comparing Comparative Examples 3 and 4 Example 2, the driving electric field E ₉₀ Example 2, 0.7 V / [mu] m than the driving electric field E ₉₀ Comparative Example 3, the driving electric field of the Comparative Example 4 E ₉₀ Than 1.
The value is lower by 9 V / μm.

[0043] Comparing Comparative Examples 5 and 6 Example 3, driving electric field E ₉₀ of the third embodiment, 0.9V / [mu] m than the driving electric field E ₉₀ Comparative Example 5, the driving electric field of Comparative Example 6 E ₉₀ Than 1.
The value is lower by 9 V / μm.

[0044] From the above, nonionic surfactant, by adding two or more, it is possible to reduce the driving electric field E _90, further having an aromatic ring in both two driving electric field becomes 1V / [mu] m or less , it is possible to reduce the most driving electric field E _90.

[0045]

In summary, according to the present invention, a low-cost liquid crystal display device which can realize a PDLC material having a low driving electric field and can be operated by a general-purpose driving circuit can be provided.

Claims (3)

[Claims] 1. A liquid crystal display device having a structure in which a composite material in which a nematic liquid crystal is dispersed in a water-soluble polymer medium is sandwiched between two substrates with transparent electrodes, wherein the composite material includes two or more nonionic A liquid crystal display device comprising a surfactant. 2. The liquid crystal display device according to claim 1, wherein at least one of the two or more nonionic surfactants has an aromatic ring. 3. The liquid crystal display device according to claim 1, wherein the amount of the nonionic surfactant added is 1 to 10 wt% based on the nematic liquid crystal.