JP3232139B2 - Liquid crystal optical element and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission / scattering type liquid crystal optical element and a method for manufacturing the same, and more particularly to a liquid crystal optical element having a high response speed and a small hysteresis, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A liquid crystal display, which is a typical example of a liquid crystal optical element, has features such as low power consumption, light weight, and thinness.
It is widely used for displaying images on calculators, personal computers, televisions, etc. In general TN- and STN-liquid crystal displays, a liquid crystal is sealed in a liquid crystal cell in which a predetermined seal or the like is provided between glass plates having transparent electrodes on which an alignment film is formed, and further, a polarizing plate is used on both sides. It is a sandwich.

[0003]

[Problems to be solved by the invention]
The above-mentioned liquid crystal display requires (1) a narrow viewing angle because two polarizing plates are required, and a backlight with high power consumption because brightness is insufficient. (2) The cell thickness dependency is large, and it is difficult to increase the area. (3) Since the structure is complicated and it is difficult to enclose the liquid crystal in the cell,
High manufacturing cost. However, there are limitations in reducing the weight, thickness, area, power consumption, and cost of a liquid crystal display. As a liquid crystal display that solves such problems, application of a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer matrix is expected, and research and development thereof have been activated.

The main method for producing such a liquid crystal / polymer composite film is as follows. (1) A method of impregnating liquid crystal into a polymer porous body. (2) A method of casting and drying an emulsion in which a liquid crystal is dispersed in an aqueous solution of polyvinyl alcohol (hereinafter abbreviated as PVA) (see Japanese Patent Publication No. 58-501631). (3) A method in which a solution in which a liquid crystal and a polymer are dissolved in a common solvent is cast, and the liquid crystal and the polymer are phase-separated with the removal of the solvent (see Japanese Patent Application Laid-Open No. 61-502128). (4) A method in which a monomer is polymerized from a mixture of a liquid crystal and a monomer to obtain a phase-separated structure between the liquid crystal and the polymer (Japanese Patent Application Laid-Open No. Sho 61-61)
-502128). Among them, the above (2)
The method is advantageous in that manufacturing is simple, control of the structure and control of the film thickness are easy, and the area can be increased.
It is already used as a light control glass.

However, a problem of the liquid crystal / polymer composite film obtained by this method is that it has a large voltage history, and more specifically, has the following characteristics. (1) When the applied voltage is increased and when the applied voltage is decreased, the voltage-transmittance curve is not the same, and a large hysteresis is observed. (2) The longer the voltage application time, the longer the fall response time. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a liquid crystal optical element having high response speed and small hysteresis, and a method for manufacturing the same.

[0006]

The above object is achieved by the present invention described below. That is, the present invention provides a liquid crystal in which liquid crystal particles are dispersed in a polymer matrix between a pair of electrode substrates.
In a transmission scattering type liquid crystal optical element having a polymer composite film sandwiched therebetween, the polymer matrix has a degree of polymerization of 300 or more.
1,200 or less and saponification degree is 50% or more and 85% or less
Liquid crystal optical element, which is an electron beam crosslinked product of polyvinyl alcohol , and a method for producing the same.

[0007]

The liquid crystal optical element having high responsiveness and small hysteresis is provided by cross-linking the PVA matrix of the liquid crystal / polymer composite film constituting the liquid crystal display element with an electron beam.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail with reference to preferred embodiments. The liquid crystal referred to in the present invention is an organic mixture showing a liquid crystal state at around normal temperature, and includes a nematic liquid crystal, a cholesteric liquid crystal, and a smectic liquid crystal. Among them, a nematic liquid crystal or a nematic liquid crystal to which a cholesteric liquid crystal is added is preferable in terms of characteristics. A dye may be included in the liquid crystal to improve contrast or color tone. When a dichroic dye is added, it can be used not only as a scattering-transmission type composite film, but also as a composite film that switches between light absorption (coloring) and a transparent state due to the guest-host effect of the dye. .

The PVA which can be used in the present invention has a degree of polymerization of 300 to 1,200 and a saponification degree of 50.
It is of 85% or less than%. Further, PVA having a polymerization degree of preferably 500 or more and 1,000 or less and a saponification degree of 60% or more and 80% or less is more preferable. The liquid crystal emulsifying ability of PVA is
It can be estimated by measuring the surface tension of the aqueous solution. For example, the surface tension of a PVA aqueous solution tends to decrease from a low concentration region with a decrease in the degree of polymerization and the degree of saponification. This indicates that the lower the degree of polymerization and the degree of saponification, the higher the ability of PVA to adsorb to the gas-liquid interface. That is, PV
In the aqueous solution A, the lower the degree of polymerization and the lower the degree of saponification,
This indicates that the ability to disperse the liquid crystal in the emulsion is high.

Therefore, by selecting an appropriate PVA, the proportion of liquid crystal present in the aqueous phase is small,
This means that the possibility of forming a liquid crystal / polymer composite film having a uniform particle diameter, which is encapsulated with VA, is increased. The PVA as described above is generally used as an aqueous solution of 1 to 20% by weight, and if necessary, a water-soluble organic solvent such as ethanol or ethyl cellosolve may be added. The above P
With respect to the use amount of the liquid crystal with respect to VA, the mixing ratio (weight ratio) of PVA / liquid crystal is 5/95 to 50/50. If the use amount of the liquid crystal is too small, the transparency at the time of turning on the voltage is insufficient. On the other hand, it is insufficient in that a large voltage is required to make the film transparent, and on the other hand, if the amount of liquid crystal used is too large, scattering (turbidity) when the voltage is turned off becomes insufficient. In addition, it is not preferable because the strength of the film is reduced, and when the emulsion is applied to an appropriate substrate, it causes repelling.

The method of dispersing the liquid crystal in the aqueous PVA solution is not particularly limited, but a mixing method using various stirring devices such as an ultrasonic disperser or a film emulsification method (Tadao Nakajima, Masataka Shimizu, PHARMTECH) JAPAN 4
Vol. 10, No. (1988)) is effective. The size of the liquid crystal emulsion particles depends on the dispersion method used, but is generally preferably in the range of 0.5 to 7 μm, and more preferably in the range of 1 to 5 μm.

A method for forming a liquid crystal / polymer composite film from the liquid crystal particle dispersion thus obtained is a method in which the above-mentioned emulsion is coated on a suitable substrate by a usual coating method and dried. The coating method may be a general coating method such as an electrodeposition method, blade coating, knife coating, slide coating, screen coating, extrusion coating, and fountain coating. The thickness of the composite film thus obtained is preferably about 5 to 15 μm.

In another preferred embodiment of the present invention, the liquid crystal emulsion is treated to produce microcapsules containing liquid crystals, and the microcapsule dispersion is separated or separated and then a coating liquid is prepared. A liquid crystal / polymer composite film can be produced by the method as described above. As a method for producing microcapsules from an emulsion in which liquid crystals are dispersed, both a chemical production method and a physicochemical production method can be used. As the chemical preparation method, there are an interfacial polymerization method using a synthesis reaction, an in situ polymerization method, and a curing-in-liquid coating method which causes a change in physical properties of a polymer. The interfacial polymerization method is a method in which a water-soluble monomer and an oil-soluble monomer are selected as two kinds of monomers that undergo a polycondensation or polyaddition reaction, and either of them is dispersed and reacted at the interface. i
The n situ polymerization method is a method in which a reactant (monomer and initiator) is supplied from one of the inside and the outside of the core material and reacted on the surface of the capsule wall film.

As physicochemical preparation methods, there are a coacervation method using phase separation, an interfacial sedimentation method, a submerged concentration method,
There are a submerged drying method and a secondary emulsion method. A simple coacervation method in which phase separation is caused by a decrease in solubility, and a complex coacervation method in which phase separation is caused by electrical interaction can also be used. The interface precipitation method is a method capable of encapsulation under mild conditions without vigorous reaction or rapid pH change, for example, by dispersing an emulsion in which a liquid crystal core material is dispersed in a solvent solution of a hydrophobic polymer. After that, it is further redispersed in an aqueous protective colloid solution.

A liquid crystal / polymer composite film is formed on a conventionally known electrode substrate for a liquid crystal display using the liquid crystal emulsion as described above. In the present invention, PVA as a matrix polymer is cross-linked by an electron beam. It is characterized by having The step of cross-linking PVA is preferably performed after applying the liquid crystal emulsion on the electrode substrate or after bringing another electrode substrate into close contact with the surface. If PVA is crosslinked before coating, film formation becomes extremely difficult, and in some cases, the insoluble polymer may precipitate in the liquid crystal emulsion before coating. PV
The simplest and most effective method for cross-linking A is to apply an emulsion to the electrode substrate and then cross-link by electron beam irradiation. For crosslinking, various crosslinking agents, for example, a dialdehyde, a methylol compound, a stabilized isocyanate compound, or the like are added in advance to a liquid crystal emulsion, and then an acetalization reaction, a methylolation reaction, a urethanization reaction, etc., by heat treatment or the like. In the method of generating and cross-linking, the ionic component may impart conductivity to the liquid crystal / polymer composite film.

When an electron beam is used, since a decomposition reaction occurs together with the crosslinking reaction, it is necessary to irradiate under conditions that give priority to the crosslinking reaction. Specifically, conditions such as heating and irradiating, irradiating in the presence of water, and irradiating in a state in which oxygen is hardly replenished are mentioned.
It is desirable to satisfy one or more conditions. The object of the present invention is achieved by cross-linking PVA as described above. In addition, the effect of imparting water resistance to the liquid crystal / polymer composite film is also obtained.

It is considered that the reason why the hysteresis resistance of the liquid crystal display of the present invention is improved by crosslinking the PVA is that the molecular movement of the PVA forming the matrix is suppressed by the crosslinking. Further, the liquid crystal is dispersed in the form of droplets in the PVA matrix, but in the case of non-crosslinked PVA, the PVA molecules at the PVA / liquid crystal interface move according to the direct movement of the liquid crystal. However, since this movement is slower than the movement of the liquid crystal, a history is observed. However, in the present invention, when PVA, which is a liquid crystal matrix, is crosslinked with an electron beam,
It is considered that the history becomes small because this molecular motion is suppressed.

[0018]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Example 1 The following mixture was mixed at 5,000 rpm using a homomixer.
The mixture was stirred at rpm for 5 minutes to obtain a liquid crystal emulsion. Nematic liquid crystal: E-44 (manufactured by BDH) 3.0 g PVA (Gohsenol EG-05, manufactured by Nippon Synthetic Chemical) 10% aqueous solution 15 g The above liquid crystal emulsion is applied on a glass substrate coated with ITO by bar coating, and electron beam is applied. 1
Irradiated with 0 Mrad. After drying at room temperature and normal pressure for one day, the coated layer was sandwiched with a PET film coated with ITO to produce an optical element of the present invention. The thickness of the coating layer after drying was about 10 μm. The transmittance of the device was measured using PHOTAL5000 manufactured by Otsuka Electronics Co., Ltd. using a halogen lamp as a light source. The applied voltage used was a 1 kHz rectangular wave. Figure 1 is 10V / mi
n. 3 shows the change in transmittance when the voltage is increased or decreased at the speed shown in FIG. As is apparent from FIG. 1, the hysteresis of the liquid crystal optical element of the present invention is sufficiently small.

Comparative Example 1 A liquid crystal optical element of a comparative example was manufactured in the same manner as in Example 1 except that no electron beam was irradiated. The change in transmittance was measured in the same manner as in Example 1. FIG. 3 shows 10 V / min.
3 shows the change in transmittance when the voltage is increased or decreased at the speed shown in FIG. In the case of this liquid crystal optical element, a large hysteresis was observed. When the voltage application time and the fall response speed of each of the devices of Example 1 and Comparative Example 1 were measured, the results shown in FIG. 2 were obtained. FIG. 2A (Example 1)
When a voltage of 50 V was applied, the application time and the fall response speed (the change in transmittance was 9% of the total transmittance change).
Time required to transition from 0% to 10%) shows the relationship. FIG. 2B (the device of Comparative Example 1) has a voltage of 50V.
5 shows the relationship between the application time and the fall response speed when the voltage of (1) is applied. The fall response time increases significantly as the application time increases.

[0020]

According to the present invention as described above, a liquid crystal optical element having a high-speed response and a small hysteresis is obtained by cross-linking a PVA matrix of a liquid crystal / polymer composite film constituting a liquid crystal display element with an electron beam. Is provided.

[Brief description of the drawings]

FIG. 1 is a view for explaining hysteresis of a liquid crystal optical element of the present invention.

FIG. 2 is a view for explaining the relationship between the voltage application time and the fall response speed of each element of Example 1 (a) and Comparative example (b) 1.

FIG. 3 is a view for explaining hysteresis of a liquid crystal optical element of a comparative example.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masayuki Ando 1-1-1, Ichigaya-Kaga-cho, Shinjuku-ku, Tokyo Dai Nippon Printing Co., Ltd. (56) References JP-A-6-75206 (JP, A) JP-A-3-185422 (JP, A) JP-A-4-128821 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1334 C08L 29/04

Claims (2)

(57) [Claims] 1. A transmission-scattering liquid crystal optical element comprising a liquid crystal / polymer composite film in which liquid crystal particles are dispersed in a polymer matrix between a pair of electrode substrates, wherein the polymer matrix has a degree of polymerization. 300 or more and 1,200 or less, and
Polyvinyl alcohol having a saponification degree of 50% or more and 85% or less
Liquid crystal optical element, characterized in that it is an electron beam cross-linked product of 2. The method according to claim 1, wherein the liquid crystal particles have a degree of polymerization of 300 or more and
And a liquid crystal emulsion having a saponification degree of 50% or more and 85% or less, which is dispersed in an aqueous solution of polyvinyl alcohol, is applied to one electrode substrate and dried.
Forming a polymer composite film, in the method of manufacturing a transmission scattering type liquid crystal optical element in which the other electrode substrate is in close contact with the film surface,
A method for producing a liquid crystal optical element, comprising a step of crosslinking the polyvinyl alcohol with an electron beam.