JPH08194211A - Liquid crystal display element - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display element having high contrast ratio, low driving voltage and small consumption of electric power which enables gradation display. CONSTITUTION: The composite film of this element has such a structure that a dichroic dye is dispersed in a droplet state in a polymer matrix included in a liquid crystal having positive dielectric anisotropy. The number average particle size (d) of the droplet 1 ranges 0.5μm<=d<=1μm and more than half of the whole particles are <=1μm in size. The concn. of the dichroic dye in the droplet 1 is >=4wt.%. The composite film is 3 to 5μm thick and contains 1 to 20wt.% surfactant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a guest-host type polymer dispersion type liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal displays (LCD) are used for laptop personal computers, word processors,
It is used in various display devices such as automobile televisions. At present, what is mainly used in the LCD field is the so-called TN type and STN type using a nematic liquid crystal. A display device using these liquid crystals requires a polarizing plate, and thus has low light utilization efficiency. For this reason, the screen is dark and a backlight is required, which is an obstacle to thinning the element and reducing the power consumption.

In that respect, polymer dispersion type liquid crystal (hereinafter referred to as "PD
LC ”. Since the liquid crystal display element using (1) mainly uses the scattering of light, it is a very effective element that can solve the above problems. This device includes one having a structure in which liquid crystal droplets are dispersed in a polymer medium and one having a structure in which liquid crystals are dispersed in a polymer medium having a mesh structure. However, in any of the structures, when no voltage is applied, the liquid crystal is randomly oriented and a refractive index difference occurs at the liquid crystal / polymer interface, light is scattered, and when a voltage is applied, the liquid crystal is oriented in the electric field direction, The liquid crystal and polymer have the same refractive index, allowing light to pass through.

The PDLC element is considered to be applied to two types, a projection type (for projection) and a direct-view type. When the PDLC element is used as a direct-view display element,
An element including a dichroic dye in the liquid crystal (guest-host type element, hereinafter referred to as "GH type element") is required. This is because the contrast ratio cannot be sufficiently obtained in a system that does not include a dye that uses only light scattering.

The display characteristics of the GH type element are as follows: the thickness of the liquid crystal layer, the dye concentration, the size of the liquid crystal droplet, the Δn of the liquid crystal,
It is greatly affected by material properties such as the dichroic ratio of the dye.

The present inventors have studied the particle size of the liquid crystal droplets, the dye concentration, and the film thickness of the device, and in the region of small particle size, high color density, and thin film thickness, the PDLC is excellent in brightness and contrast ratio. It was found that a device can be obtained (Japanese Patent Application No. 6-2
5270).

Now, as a major problem of the PDLC element,
The driving voltage is high and the hysteresis is large. Various studies have been conducted on these, and they have been considerably improved.

The present inventors have found that low voltage driving and low hysteresis can be achieved by adding an appropriate amount of a surfactant (Japanese Patent Application No. 4-253122).

[0009]

However, the system to which the surfactant is added has lower resistance, higher power consumption, and poorer stability than the system to which the surfactant is not added. Further, since the fall response time is long, there is a problem that gradation display by pulse width modulation of the applied voltage cannot be performed.

On the other hand, there is a problem that the driving voltage becomes high in the system in which the surfactant is not added.

Therefore, a main object of the present invention is to solve the above-mentioned problems and to provide a liquid crystal display device having a high contrast ratio, a low driving voltage, a low power consumption, and a gray scale display. .

[0012]

In order to achieve the above object, the first invention is that a mixture containing a dichroic dye in a liquid crystal having a positive dielectric anisotropy is dropped in a polymer matrix. The number average particle diameter d of the droplets of the composite film having a structure dispersed in a matrix is 0.5 μm ≦ d ≦ 1 μ
m, the majority of the total number of particles is 1 μm or less, the concentration of dichroic dye contained in the droplets is 4% by weight or more, and the thickness of the composite film is 3 to 5 μm. The active agent is contained in an amount of 1 to 20% by weight.

In addition to the above structure, the present invention provides a liquid crystal display device having a specific resistance of 10 ¹² Ω · cm or more.

According to a second aspect of the invention, a nonionic surfactant is contained in a composite material in which a liquid crystal mixture containing a dichroic dye is dispersed in a polymer matrix in the form of droplets, and the liquid crystal is contained in the liquid crystal. In a liquid crystal display device using a material in which the droplet number average particle diameter d of the mixture is 0.5 μm ≦ d ≦ 1 μm, a rising response time is 5 msec or less in a range of an applied voltage pulse width of 2 msec or less,
The fall response time is set to 5 msec or less.

In addition to the above structure, the present invention provides a liquid crystal display device with a driving electric field of 2.0 Vrms / μm or less.

[0016]

According to the first invention, the number average particle diameter d of liquid crystal droplets is reduced to 0.5 .mu.m.ltoreq.d.ltoreq.1 .mu.m in order to obtain a high-dimensional and well-balanced brightness and contrast ratio, and the dye concentration is reduced. By appropriately selecting the liquid crystal, the polymer and the surfactant so that the specific resistance of the element becomes 10 ¹² Ω · cm or more in the element in which the film thickness is increased to 4% by weight or more and the film thickness is reduced to 3 to 5 μm. A liquid crystal display device having a high contrast ratio, a low driving voltage, and low power consumption can be obtained.

Further, the specific resistance ρ of the liquid crystal display element is ρ ≧ 10
^In order to obtain ¹² Ω · cm, it is not necessary that the specific resistance ρ of materials such as liquid crystal, polymer, and surfactant used for PDLC be 10 ¹² Ω · cm or more.

The specific resistance ρ of the liquid crystal display element changes depending on the type of material used and its composition ratio. For example, if the specific resistance ρ of liquid crystal or polymer is much higher than 10 ¹² Ω · cm,
Even if the specific resistance ρ of the surfactant is smaller than 10 ¹² Ω · cm, the specific resistance ρ ≧ 10 ¹² Ω · cm can be obtained for the liquid crystal display device.

On the other hand, the specific resistance ρ of liquid crystal and polymer is 10 ¹² ·
If it is about cm, the resistivity ρ of the surfactant is also 10 ¹² Ω ・
It should be at least cm.

The specific resistance ρ of the liquid crystal display element was measured using a unit cell. The resistance, film thickness, and electrode area of the liquid crystal display element were measured to determine the specific resistance ρ. L for resistance measurement
The measurement was performed at 20 ° C., 120 Hz, and 1 V using a CR meter.

The polymer applicable to this embodiment is not particularly limited as long as it is a water-soluble polymer. For example, methyl cellulose, polyvinyl alcohol, polyoxyethylene and the like can be mentioned.

As the dichroic dye, an azo mixture or an anthraquinone mixture is used, but it is not particularly limited.

The liquid crystal is not particularly limited as long as it has a positive dielectric anisotropy. For example, an azoxy compound,
Examples thereof include biphenyl compounds, azomethine compounds, Schiff base compounds, pyrimidine compounds, benzoic acid ester compounds, dioxane compounds, phenylcyclohexane compounds, cyclohexylcarboxylic acid ester compounds, and cyanobiphenyl compounds.

According to the second aspect of the present invention, in the PDLC element to which the surfactant is added, the number average particle diameter d of the liquid crystal droplets is 0.5 μm ≦ d ≦ 1 μm, and the applied voltage (square wave) pulse width is 2 msec or less. Rising response time is 5 in range
When it is set to msec or less and the fall response time is set to 5 msec or less, the brightness and the contrast ratio are excellent, the driving voltage is low, and gradation display is possible.

Here, the pulse width gradation modulation display method will be described.

FIG. 6 shows drive waveforms in the case of 10 gradations.
This is a method in which one frame time (t) is divided into a required number of gradations (10), and the applied pulse width (τ) is changed according to the required gradation, thereby performing the gradation display shown in FIG. .

The rising response time (t _r ) and the falling response time (t _d ) will be described.

The ideal optical response is a case where it immediately responds to the drive voltage waveform as shown in FIG. However, in an actual liquid crystal display element, optical response delay occurs. Therefore,
As shown in FIG. 4, the time required for the optical response to reach 90% of the maximum value (100%) from the initial value (0%) is the rise response time (t _r ), and the time until the optical response decays from the maximum value to 10% of the maximum value. Was defined as the fall response time (t _d ).

Next, the cause of defective gradation will be described.

PDL in Japanese Patent Application No. 4-253122
Driving voltage and hysteresis are reduced by adding an appropriate amount of a certain surfactant to C. However, a system to which a surfactant is added has a problem that gradation display by pulse width modulation cannot be performed.

The liquid crystal response is considered to be the cause of the defective gradation. The ideal optical response would be an immediate response to the drive voltage waveform. In this case, when the display is performed while changing the pulse width (τ), the display characteristic as shown in FIG. 2 is obtained.

However, in reality, a response delay occurs at the fall, and as the response delay increases, the reflectance increases from a low duty as shown in FIG. 5, resulting in defective gradation.
In the surfactant-added system, this response delay (fall time) is considerably larger than in the non-added system.

The reason why the fall time of the surfactant addition system is long will be described.

In the PDLC element, when the voltage is off, the liquid crystal molecules 2 in the liquid crystal droplets 1 are arranged in an arrangement as shown in FIG. 1 (random alignment). At this time, it is considered that the liquid crystal molecules 2 are subjected to the alignment regulating force (stable state when the voltage is off, that is, the force for holding the random alignment) from the polymer / droplet interface. If it is considered that the system to which the surfactant is added has weaker regulation power than the system to which the surfactant is not added, it is explained that the system in which the surfactant is added has a large t _d .

That is, when the voltage is on, the liquid crystal molecules 2 are oriented by a large external force (electric field E), so that both the surfactant-added system and the surfactant-free system rise quickly, but when the voltage is off, only the regulating force is applied. The liquid crystal molecules 2 are returned to the random alignment. Therefore, when the regulation force is large (surfactant-added system), the random orientation returns in a short time, and t _d is small, but when the regulation force is small (surfactant-added system), the random orientation takes a long time. Therefore, it is considered that t _d becomes large. In addition, 3 is an electrode, 4 is a polymer, and 5 is a surfactant.

In the above, the present inventors have found that in a PDLC material containing a certain nonionic surfactant, the number average particle diameter d of liquid crystal droplets is 0.5 μm ≦ d ≦ 1 μ.
When the applied voltage pulse width is 2 msec or less, the falling response time (t _d ) is 5 msec or less, the brightness and the contrast ratio are excellent, the device can be driven at a low voltage, and the gradation display is excellent. We have developed a liquid crystal display device that can

[0037]

EXAMPLES Examples of the present invention will be described in detail below together with comparative examples.

Example 1 A liquid crystal (RDP-20081 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-429 manufactured by Mitsui Toatsu Co., Ltd.) was added thereto.
Was dissolved by 4%. 5 g of this solution, 10 g of a 10% aqueous solution of purified polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.), and a purified surfactant (SC-1 manufactured by Asahi Glass Co., Ltd.)
05) 0.2 g was mixed and stirred at a rotation speed of 1500 rpm using a homogenizer to prepare an emulsion. At this time, Coulter counter (made by Coulter)
The average particle diameter of the liquid crystal droplets measured by using a. Was 0.8 μm. This emulsion liquid was applied onto a glass substrate with an ITO electrode and dried, and then a counter substrate was laminated to produce a liquid crystal display element.

The film thickness of the liquid crystal display element was 4.1 μm. The specific resistance ρ of the liquid crystal display element is 7.4 × 10 ¹² Ω · cm
And the power consumption was 0.05 mW / cm ² . The driving voltage V ₉₀ was 6.5V. The reflectances R _ON and R _OFF of the device when the voltage was turned on and off were measured, and the contrast ratio (CR = R _ON / R _OFF ) was determined. As a result, the reflectance R _ON is 38.0%, and the reflectance R is
_OFF was 7.0%, and contrast ratio CR was 5.4.

Example 2 A liquid crystal (TL-204 manufactured by Rodic Co., Ltd.) was used, and 4.5% of a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was used.
% Dissolved. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.), and 0.25 g of a surfactant (SC-101 manufactured by Asahi Glass Co., Ltd.)
And were mixed together, and a liquid crystal display element was manufactured in the same manner as in Example 1. At this time, the average particle size of the liquid crystal droplets was 0.8 μm, and the film thickness was 4.1 μm.

The specific resistance ρ of the liquid crystal display element is 2.4 × 10 ¹¹
Ω · cm, and power consumption was 1.0 mW / cm ² . The driving voltage V ₉₀ was 7.0V. The reflectance R _ON of this device was 38.3%, the reflectance R _OFF was 7.4%, and the contrast ratio CR was 5.2.

Example 3 A liquid crystal (BL-015 manufactured by Merck & Co., Germany) was used.
A chromatic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved in 4.5%. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (405 manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (SP-030 manufactured by Kao Co., Ltd.) were mixed, and the same as in Example 1 below. Then, a liquid crystal display element was produced.

The liquid crystal droplets of this liquid crystal display device had an average particle diameter of 0.8 μm and a film thickness of 4.0 μm.
The specific resistance ρ of this element was 6.4 × 10 ¹² Ω · cm, and the power consumption was 0.08 mW / cm ² . The driving voltage V ₉₀ was 5.8V. The reflectance R _ON of this element is 38.0.
%, The reflectance R _OFF was 6.9%, and the contrast ratio CR was 5.5.

Example 4 A liquid crystal (BL-005 manufactured by Merck & Co., Inc.) was used and 4.5% of a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved therein. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (405, manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (SP-010, manufactured by Kao Co., Ltd.) were mixed, and the same as in Example 1 below. Then, a liquid crystal display element was produced.

The liquid crystal droplets of this liquid crystal display device had an average particle diameter of 0.9 μm and a film thickness of 4.0 μm.
The specific resistance ρ of this element was 2.0 × 10 ¹⁰ Ω · cm, and the power consumption was 0.12 mW / cm ² . The driving voltage V ₉₀ was 5.1V. The reflectance R _ON of this element is 39.7.
%, The reflectance R _OFF was 7.2%, and the contrast ratio CR was 5.5.

Comparative Example 1 A liquid crystal (RDP-20081 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-429 manufactured by Mitsui Toatsu Co., Ltd.) was used.
Was dissolved by 4%. 5 g of this solution was mixed with 10 g of a 10% aqueous solution of polyvinyl alcohol (205, manufactured by Kuraray Co., Ltd.), and then a liquid crystal display element was produced in the same manner as in Example 1.

The liquid crystal droplets of this liquid crystal element had an average particle diameter of 0.9 μm and a film thickness of 3.9 μm. The specific resistance ρ of this element was 3.0 × 10 ¹³ Ω · cm, and the power consumption was 0.01 mmW / cm ² . The driving voltage V ₉₀ was 32V. The reflectance R _ON of this element is 38.
5%, reflectance R _OFF was 7.1%, and contrast ratio CR was 5.4.

Comparative Example 2 A liquid crystal (RDP-20081 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-429 manufactured by Mitsui Toatsu Co., Ltd.) was used.
Was dissolved by 4%. 5 g of this solution and 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.)
And a surfactant (SC-105 manufactured by Asahi Glass Co., Ltd.) 0.
2 g was mixed and a liquid crystal display device was produced in the same manner as in Example 1.

The liquid crystal droplets of this liquid crystal element had an average particle diameter of 0.8 μm and a film thickness of 4.3 μm. The specific resistance ρ of this element was 2.1 × 10 ¹⁸ Ω · cm, and the power consumption was 1.1 mW. The driving voltage V ₉₀ was 6.4V. The reflectance R _ON of this element is 37.5%, and the reflectance R
_OFF was 6.7%, and contrast ratio CR was 5.6.

Comparative Example 3 A liquid crystal (403 manufactured by Rodic Co., Ltd.) was used, and 4.5% of a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved therein. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (205, manufactured by Kuraray Co., Ltd.), and 0.25 g of a surfactant (SC-101, manufactured by Asahi Glass Co., Ltd.) were mixed, and thereafter, in the same manner as in Example 2. A liquid crystal display device was produced by

The liquid crystal droplets of this liquid crystal display device had an average particle diameter of 0.8 μm and a film thickness of 4.1 μm. The specific resistance ρ of this element was 2.4 × 10 ¹¹ Ω · cm, and the power consumption was 1.0 mW / cm ² . The driving voltage V ₉₀ was 7.0V. The reflectance R _ON of this element is 3
8.3%, reflectance R _OFF is 7.4%, contrast ratio C
R was 5.2.

Comparative Example 4 A liquid crystal (BL-015 manufactured by Merck & Co., Inc.) was used, and 4.5% of a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved therein. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (405 manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (SP-030 manufactured by Kao Co., Ltd.) were mixed, and the same as in Example 3 below. Then, a liquid crystal display element was produced.

The liquid crystal droplets of this liquid crystal display device had an average particle diameter of 0.8 μm and a film thickness of 4.0 μm.
The specific resistance ρ of this element was 9.4 × 10 ¹⁰ Ω · cm, and the power consumption was 0.95 mW / cm ² . The driving voltage V ₉₀ was 5.8V. The reflectance R _ON of this element is 38.0.
%, The reflectance R _OFF was 6.6%, and the contrast ratio CR was 5.8.

Comparative Example 5 A liquid crystal (BL-005 manufactured by Merck & Co., Inc.) was used and 4.5% of a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved therein. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (405 manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (SP-010 manufactured by Kao Co., Ltd.) were mixed, and the same as in Example 4 below. Then, a liquid crystal display element was produced.

The liquid crystal droplets of this liquid crystal display device had an average particle diameter of 0.9 μm and a film thickness of 4.0 μm.
The specific resistance ρ of this element was 4.0 × 10 ¹² Ω · cm, and the power consumption was 1.5 mW / cm ² . The driving voltage V ₉₀ is 5.
It was 1V. The reflectance R _ON of this element was 39.0%, the reflectance R _OFF was 7.0%, and the contrast ratio CR was 5.6.

As described above, according to Examples 1 to 4, since the surfactant is contained in an amount of 1 to 20% by weight, a liquid crystal display device having a high contrast ratio, a low driving voltage and low power consumption is realized. can do.

Next, Examples 5 to 7 and Comparative Examples 6 to 10 will be described.

Example 5 A liquid crystal (RO-TN-405 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was used.
Was dissolved by 4%. 5 g of this solution and 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.)
And a nonionic surfactant (SC-1 manufactured by Asahi Glass Co., Ltd.
05) 0.2g is mixed and, using a homogenizer,
The emulsion was prepared by stirring at a rotation speed of 1500 rpm. At this time, the average particle size of the liquid crystal droplets measured using a Coulter Counter (manufactured by Coulter, Inc.) was 0.8 μm. This emulsion liquid was applied onto a glass substrate with an ITO electrode using an applicator and dried, and then a liquid crystal display element produced by laminating a counter substrate had a film thickness of 4.9 μm.

The results of examining the pulse width dependence of the fall time of this liquid crystal display device are shown in Table 1 and FIG. The fall response time was 5 msec or less in the range of the applied voltage (square wave) pulse width of 2 msec or less. Rise response time is 5 ms in all range of pulse width 0.1 to 20 msec.
It was ec or less. The gradation display of this liquid crystal display device was substantially good as shown in FIG. The drive voltage V ₉₀
Was 7.8V. Furthermore, the voltage at full duty of this liquid crystal display element is turned on (20 V) and turned off (0 V).
Reflectance R _ON of 35.0%, reflectance R _OFF of 7.0%,
The contrast ratio CR was 5.0.

[0060]

[Table 1]

Comparative Example 6 The same material as in Example 5 was selected, and only the rotation speed was 5000r.
The emulsion was prepared by stirring at pm. At this time,
The average particle size of the liquid crystal droplets was 2.5 μm. A liquid crystal display device was produced in the same manner as in (Example 5) using this emulsion.

The film thickness of the liquid crystal display element was 5.1 μm.

The results of examining the pulse width dependence of the fall time of this liquid crystal display device are shown in Table 2 and FIG. Further, FIG. 10 shows gradation display characteristics. The gradation display was poor.
Although the driving voltage V ₉₀ was 4.8 V, which was superior to that of (Example 5), the reflectance and the contrast ratio were as follows.
The reflectance R _ON is 36.0%, the reflectance R _OFF is 16.0%,
The contrast ratio CR becomes 2.3, and the contrast ratio C
R has fallen to less than half.

[0064]

[Table 2]

Comparative Example 7 A liquid crystal (ZL1-1840 manufactured by Merck & Co., Inc.) was used and 2
4% of a color dye (S-429 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (Emulgen 906 manufactured by Asahi Glass Co., Ltd.) were mixed, and this was rotated at a rotation speed of 8000 rpm. Thereafter, a liquid crystal display element was produced in the same manner as in Example 5.

At this time, the liquid crystal droplets had an average particle diameter of 1.8 μm and a film thickness of 4.8 μm.

The results of examining the pulse width dependence of the fall time of this liquid crystal display element are shown in Table 3 and FIG. Further, FIG. 12 shows gradation display characteristics. The gradation display was poor.
Although the driving voltage V ₉₀ is 6.5 V, which is superior to that of the fifth embodiment, the reflectance R _ON is 39.0% and the reflectance R _{OFF is}
Is 9.0%, the contrast ratio CR is 3.9, and the contrast ratio CR is decreasing.

[0068]

[Table 3]

Example 6 A liquid crystal (TL-204 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was used in an amount of 3.5.
% Dissolved. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.), and 0.25 g of a surfactant (SP-010 manufactured by Kao Co., Ltd.) were mixed, and the same as in Example 5 below. Then, a liquid crystal display element was produced.

At this time, the average particle size of the liquid crystal droplets was 0.9 μm, and the film thickness was 4.8 μm.

Table 4 shows the results of examining the pulse width dependence of the fall time of this liquid crystal display element. The fall response time was 5 msec or less in the range of the applied voltage (square wave) pulse width of 2 msec or less. The rise response time was 5 msec or less in the entire range of the pulse width of 0.1 to 20 msec. The gradation display of this liquid crystal display element was good. The driving voltage V ₉₀ was 7.2V. Furthermore, the voltage is turned on (20
V) and off (0 V) reflectance R _ON was 40.0%, reflectance R _OFF was 7.5%, and contrast ratio CR was 5.3.

[0072]

[Table 4]

Comparative Example 8 A liquid crystal (TL-204 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was used in an amount of 3.5.
% Dissolved. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (DS-406 manufactured by Daikin Co., Ltd.) were mixed, and the rotation speed was 8000 rpm. A liquid crystal display device was produced in the same manner as in Example 6.

At this time, the average particle diameter of the liquid crystal droplets was 1.5 μm, and the film thickness was 4.7 μm.

The results of examining the pulse width dependence of the fall time of this liquid crystal display element have the values shown in Table 5,
This liquid crystal display element was defective in gradation display. The driving voltage V ₉₀ was 6.2V. Further, the reflectance R _ON of the liquid crystal display element when the voltage is on and off is 41.0.
%, The reflectance R _OFF was 7.9%, and the contrast ratio CR was 5.2.

[0076]

[Table 5]

Comparative Example 9 A liquid crystal (TL-204 manufactured by Rodic Co., Ltd.) was used, and a dichroic dye (S-344 manufactured by Mitsui Toatsu Co., Ltd.) was used in an amount of 3.5.
% Dissolved. 5 g of this solution was mixed with 10 g of a 10% aqueous solution of polyvinyl alcohol (205 manufactured by Kuraray Co., Ltd.), and a liquid crystal display element was produced in the same manner as in Example 6 below.

At this time, the average particle diameter of the liquid crystal droplets was 0.8 μm, and the film thickness was 4.7 μm.

The results of examining the pulse width dependence of the fall time of this liquid crystal display element have the values shown in Table 6,
The gradation display was good, but the drive voltage V ₉₀ was 32.2V.
Therefore, it was significantly higher than that of Example 6. The reflectance R _ON of the liquid crystal display element when the voltage is on and off is 41.5%, and the reflectance R _OFF is 7.6.
%, And the contrast ratio CR was 5.5.

[0080]

[Table 6]

Example 7 A liquid crystal (BL-015 manufactured by Merck & Co., Inc.) was used and 3.5% of a dichroic dye (S-428 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved therein. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (405 manufactured by Kuraray Co., Ltd.), and 0.3 g of a surfactant (SP-030 manufactured by Kao Co., Ltd.) were mixed, and the same as in Example 5 below. Then, a liquid crystal display element was produced.

At this time, the average particle size of the liquid crystal droplets was 1.0 μm, and the film thickness was 5.1 μm.

Table 7 shows the results of examining the pulse width dependence of the fall time of this liquid crystal display element. The fall response time was 5 msec or less in the range of the applied voltage (square wave) pulse width of 2 msec or less. The rise response time was 5 msec or less in the entire range of the pulse width of 0.1 to 20 msec. The gradation display of this liquid crystal display element was good. The driving voltage V ₉₀ was 8.6V. Furthermore, the voltage is turned on (20
V) and off (0 V) reflectance R _ON was 40.2%, reflectance R _OFF was 7.7%, and contrast ratio CR was 5.2.

[0084]

[Table 7]

Comparative Example 10 A liquid crystal (BL-015 manufactured by Merck & Co., Inc.) was used and 3.5% of a dichroic dye (S-428 manufactured by Mitsui Toatsu Co., Ltd.) was dissolved therein. 5 g of this solution, 10 g of a 10% aqueous solution of polyvinyl alcohol (405 manufactured by Kuraray Co., Ltd.), and 0.35 g of a surfactant (SP-030 manufactured by Kao Co., Ltd.) were mixed,
At 6000 rpm, a liquid crystal display device was manufactured in the same manner as in Example 7 below.

At this time, the average particle diameter of the liquid crystal droplets was 2.0 μm, and the film thickness was 5.1 μm.

The results of examining the pulse width dependence of the fall time of this liquid crystal display element have the values shown in Table 8,
The gradation display was poor. The driving voltage V ₉₀ is 5.8V
Met. The reflectance R _ON of the liquid crystal display element when the voltage was turned on and off was 40.2%, the reflectance R _OFF was 7.7%, and the contrast ratio CR was 5.2.

[0088]

[Table 8]

According to Examples 5 to 7, the average particle diameter d of the liquid crystal droplets is 0.5 μm ≦ d ≦ 1 μm, the applied voltage pulse width is 2 msec or less, and the rising response time is 5 msec or less. By setting the fall response time to 5 msec or less, it is possible to obtain a liquid crystal display element that is excellent in brightness and contrast ratio, has a low driving voltage, and can display gradation.

[0090]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) Since the surfactant is contained in an amount of 1 to 20% by weight, a liquid crystal display device having a high contrast ratio, a low driving voltage and low power consumption can be realized.

(2) The average particle diameter d of the liquid crystal droplets is 0.5 μm ≦
By setting d ≦ 1 μm and applying voltage pulse width of 2 msec or less, rising response time of 5 msec or less and falling response time of 5 msec or less, excellent brightness and contrast ratio, low driving voltage, and gradation A displayable liquid crystal display device can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a response of liquid crystal in PDLC.

FIG. 2 is an example of gradation display.

FIG. 3 is a schematic diagram showing an ideal optical response.

FIG. 4 is a schematic diagram showing an optical response of an actual element.

FIG. 5 is a gradation display of a liquid crystal display element having a defective gradation.

FIG. 6 is a drive voltage waveform when performing 10 gradation display.

FIG. 7 is a diagram showing the applied voltage pulse width dependence of the fall response time of the liquid crystal display element of Example 5;

FIG. 8 is a diagram showing gradation display characteristics of the liquid crystal display element of Example 5;

9 is a diagram showing the applied voltage pulse width dependence of the fall response time of the liquid crystal display element of Comparative Example 6. FIG.

10 is a diagram showing gradation characteristics of the liquid crystal display element of Comparative Example 6. FIG.

11 is a diagram showing the applied voltage pulse width dependence of the fall response time of the liquid crystal display element of Comparative Example 7. FIG.

12 is a diagram showing gradation display characteristics of the liquid crystal display element of Comparative Example 7. FIG.

[Explanation of symbols]

 1 Droplet (liquid crystal droplet) 2 Liquid crystal molecule 3 Electrode 4 Polymer

Claims (4)

[Claims] 1. An average number of droplets of a composite film having a structure in which a mixture containing a dichroic dye in a liquid crystal having a positive dielectric anisotropy is dispersed in a polymer matrix in a droplet shape. Particle diameter d is 0.5 μm ≦ d ≦ 1 μm
And the majority of the total number of particles is 1 μm or less, and the concentration of the dichroic dye contained in the droplet is 4% by weight.
The liquid crystal display device as described above, characterized in that the composite film has a thickness of 3 to 5 μm and contains a surfactant in an amount of 1 to 20% by weight. 2. The specific resistance of the liquid crystal display device is 10 ¹² Ω.multidot.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a size of at least cm. 3. A composite material in which a liquid crystal mixture containing a dichroic dye is dispersed in a polymer matrix in a droplet shape, and the nonionic surfactant is contained in an amount of 1 to 20% by weight. Number average particle size d of droplet
In a liquid crystal display element using a material having a value of 0.5 μm ≦ d ≦ 1 μm, the rise response time is 5 msec or less and the fall response time is 5 msec or less in the range of the applied voltage pulse width of 2 msec or less. A liquid crystal display device characterized by the above. 4. The driving electric field of the liquid crystal display device is 2.0 V.
The liquid crystal display device according to claim 3, wherein the liquid crystal display device has a rms / μm or less.