JPH06202084A - Liquid crystal optical element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal optical element featuring a low driving voltage, high contrast and high reliability. CONSTITUTION:A mixture consisting of a liquid crystal 13, an uncured resin and conductive fillers 15 is held between a pair of upper and lower liquid crystal supporting plates 11 and 12 having transparent electrode layers 17. UV rays or heat is applied to this mixture, thereby the resin is polymerized and the liquid crystal optical element consisting of the high polymer dispersion type liquid crystal mixed with the conductive fillers 15 is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical element using a polymer dispersed liquid crystal in which liquid crystal is dispersed and held in a polymer resin matrix.

[0002]

2. Description of the Related Art In recent years, a polymer-dispersed liquid crystal in which a nematic liquid crystal is dispersed and held in a polymer having the same refractive index as that of liquid crystal molecules is sandwiched between a pair of upper and lower substrates having electrodes to detect the presence or absence of an electric field. The liquid crystal optical element that changes the refractive index of the liquid crystal to switch between the scattering state and the transmitting state has attracted much research and developer attention.
631, Japanese Patent Laid-Open No. 60-252687, and Japanese Patent Laid-Open No. 61-502128).

FIG. 2 is a schematic view showing the display principle of this liquid crystal optical element. In the state where no voltage is applied ((a) in the same figure), the molecular axis of the liquid crystal 24 is oriented in a random direction, so that the refractive index of the liquid crystal region is different from the refractive index of the surrounding polymer phase 25.
Incident light 22 entering the liquid crystal optical element becomes scattered light 23,
As a result, a scattering state is obtained. On the other hand, the transparent electrode layer 21
When an electric field is applied to the liquid crystal (FIG. 7B), the molecular axes of the liquid crystal 24 are aligned in the direction of the electric field, and for light incident perpendicularly to the substrate, the refractive index of the liquid crystal region is around the polymer phase 25. Since it substantially matches the refractive index of, the light is not scattered and becomes the transmitted light 26. As a result, a transmitted state is obtained.

Since the liquid crystal optical element using the polymer-dispersed liquid crystal utilizes light scattering, it is not necessary to use a polarizing plate, and unlike the conventional twisted nematic (TN) type liquid crystal optical element, Compared to liquid crystal optical elements that require the use of polarizing plates to obtain linearly polarized light,
A wide viewing angle display is possible. Further, the conventional TN type liquid crystal optical element or the like needs to accurately control the alignment treatment and the upper and lower substrate intervals, and thus has a problem that display unevenness is likely to occur when displaying a large area. The liquid crystal optical element using the molecular dispersion type liquid crystal is characterized in that alignment treatment is not necessary, the substrate spacing is not strictly controlled, and a large area liquid crystal optical element can be easily manufactured.

[0005]

As described above, the liquid crystal optical element using the polymer-dispersed liquid crystal has the advantage that it can realize a bright and wide viewing angle display because it does not use a polarizing plate. On the other hand, the driving voltage is considerably higher than that of a conventional TN type liquid crystal optical element. Further, in a liquid crystal optical element using polymer-dispersed liquid crystal, in order to obtain a high scattering state, it is necessary to increase the difference between the refractive index of the liquid crystal phase and the refractive index of the polymer phase. A cyano liquid crystal material having a refractive index must be used. However, cyano liquid crystal materials generally have poor reliability with respect to heat and light, and liquid crystal optical elements using these liquid crystal materials cannot provide sufficient reliability. In recent years, application of a highly reliable fluorine-based liquid crystal material to the above problems has been studied, and improvement of voltage response characteristics such as driving voltage and reliability has been reported (92 ′ Liquid Crystal Chemistry Debate, 92'SI
Regarding D), the scattering performance of the liquid crystal optical element is inferior to that using a cyano liquid crystal material.

A first object of the present invention is to realize a low driving voltage of a liquid crystal optical element using a polymer-dispersed liquid crystal, and at the same time, improve scattering performance and reliability, and achieve high performance and high reliability. It is to provide a liquid crystal optical element having excellent properties.

[0007]

As a cause of high driving voltage of a liquid crystal optical element using a polymer dispersed liquid crystal, a voltage drop due to a polymer phase holding a liquid crystal phase lowers an electric field applied to the liquid crystal phase. It is thought to be because of this.

Therefore, in order to lower the driving voltage of the liquid crystal optical element using the polymer dispersed liquid crystal, the specific resistance of the polymer phase is lowered or the dielectric constant is raised to suppress the voltage drop in the polymer phase. We must devise to increase the effective electric field applied to the phases. The present invention uses a polymer-dispersed liquid crystal in which a conductive filler is mixed with a polymer-dispersed liquid crystal as a means thereof, and a liquid crystal optical element uses a polymer-dispersed liquid crystal having a pair of electrodes. A liquid crystal optical element characterized by being produced by being sandwiched between substrates for forming.

[0009]

[Function] By mixing the conductive filler in the polymer dispersed liquid crystal, the specific resistance of the polymer phase is lowered. As a result, the voltage drop in the polymer phase can be suppressed, the effective electric field applied to the liquid crystal phase can be increased, and the drive voltage of the liquid crystal optical element can be reduced. It is desired that the conductive filler is uniformly mixed in the polymer matrix in a discontinuous or partially continuous state. When the conductive fillers are continuously connected in the polymer matrix, and when the upper and lower substrates of the liquid crystal optical element become completely conductive or close to it, it is one of the important characteristics for active matrix driving, that is, retention of accumulated charge. The problem of adverse effects arises. The amount of the conductive filler to be mixed in the polymer-dispersed liquid crystal from the above constraints is not particularly limited as long as the conductive filler is uniformly mixed in the polymer matrix in a discontinuous or partially continuous state,
As a rule of thumb, 0.01 is used for the composition of the liquid crystal forming the polymer-dispersed liquid crystal, the monomer, and the oligomer.
˜5.0 wt% is desirable. If it is 0.01% or less, the effect is insufficient. On the contrary, if it is 5.0% or more, the maximum transmittance of the liquid crystal display element is lowered or the retention of accumulated charges is deteriorated.
As the shape of the conductive filler, various shapes such as spherical shape and needle shape can be used alone or as a mixture, and the size is preferably 0.3 μm or less. Although it is desirable that these conductive fillers be present in the polymer phase, they may be present in the liquid crystal phase due to manufacturing problems.

According to the present invention, the driving voltage of the liquid crystal optical element can be lowered and the application to the active matrix liquid crystal element becomes possible. Furthermore, since the conductive filler itself has a scattering property, the scattering performance of the liquid crystal optical element is also improved, and as a result, it becomes possible to manufacture a liquid crystal optical element having a significantly improved contrast. Further, when an inorganic material is used as the conductive filler to be mixed, the material itself is stable, and there is no melting (compatibility) in the liquid crystal or polymer, so that a highly reliable liquid crystal optical element can be realized. .

[0011]

The liquid crystal optical element of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of a liquid crystal display device produced by using the polymer-dispersed liquid crystal of the present invention. Transparent electrode 17 made of indium / tin oxide
A pair of upper and lower substrates 11 and 12 on which the above are formed are prepared and bonded together with a spacer / sealing resin 16 therebetween to complete an empty cell. Then, the liquid crystal 13 and the uncured ultraviolet-curable or thermosetting uncured polymer material 1 through the opening of the empty cell
The conductive filler 15 is added to 4, and the heated and stirred melt is injected. After the injection, the injection port was sealed and the resin was polymerized by ultraviolet rays or heat to complete a liquid crystal cell composed of so-called polymer dispersed liquid crystal.

Hereinafter, specific examples will be described in more detail. (Example 1) Two pieces of glass on which a transparent electrode made of indium / tin oxide was formed were prepared, and a spacer / seal was formed on the surface of one of the supporting plates (for example, the lower substrate 32) as shown in (Fig. 3). As the resin 33, an acid anhydride-curable epoxy resin in which glass fibers having a diameter of 13 μm are dispersed is printed with a width of 5 mm at the center of one side and a width of 0.2 mm around the other side. The lower substrate 32 was pressed in a state of facing it, and heated at 140 ° C. for 4 hours to be cured and adhered to complete an empty cell.

Next, as a liquid crystal material, 8.200 g of liquid crystal (trade name: BL-002) manufactured by Merck Ltd., 0.954 g of 2-ethylhexyl acrylate as a polymer-forming monomer, and 0. 808 g, Darocur 1 as a photopolymerization initiator
0.038 g of 173 (manufactured by Merck Co., Ltd.) was prepared, and a tin oxide conductive filler (Ishihara Sangyo Co., Ltd .: trade name SN-100, average particle size 0.1 μm) was added to the mixture.
0.200 g (2.00% by weight to the composition consisting of liquid crystal, monomer and oligomer) was added, and the composition consisting of the above components was sufficiently stirred at 50 ° C. to obtain a dissolved product in which the conductive filler was uniformly dispersed. Was adjusted.

Further, this melt is injected into an empty cell prepared by the above-described manufacturing method at 50 ° C. through the opening 34, and after sealing the opening, ultraviolet rays (24.5%) are applied at 50 ° C.
mW / cm ² ) was irradiated for 10 seconds to complete a liquid crystal cell made of polymer dispersed liquid crystal. The electro-optical characteristics of the liquid crystal cell thus completed are shown in (a) of FIG. From the figure, it can be seen that the driving voltage is significantly improved, the transmittance is sufficiently low when no voltage is applied, the scattering performance is improved, and a sufficient scattering-transparent state is obtained. This excellent scattering-transparent state could be ensured even after the liquid crystal cell was left in an environment of 80 ° C. for 500 hours.

(Example 2) The same monomer, oligomer, photopolymerization initiator, and conductive filler as in Example 1 were used, and only the liquid crystal material was changed to ZLI-4792 (Merck KK). By the same operation as in Example 1, a liquid crystal cell made of polymer dispersed liquid crystal was completed (the ratio of each component is the same as in Example 1). The electro-optical characteristics of the liquid crystal cell thus completed are shown in (a) of FIG. From the figure, it can be seen that the driving voltage is significantly improved, the transmittance is sufficiently low when no voltage is applied, the scattering performance is improved, and a sufficient scattering-transparent state is obtained. This excellent scattering-transparent state could be ensured even after the liquid crystal cell was left in an environment of 80 ° C. for 500 hours.

Comparative Example 1 Polymer dispersion was carried out in the same manner as in Example 1 except that the same kind and amount of liquid crystal, monomer, oligomer and photo-curing initiator as those described in Example 1 were used and no conductive filler was used. Completed a liquid crystal cell made of mold type liquid crystal.
The electro-optical characteristics of the liquid crystal cell thus completed are shown in FIG.
As shown in Table 1, the driving voltage was high, the transmittance was not sufficient when no voltage was applied, the scattering performance was poor, and a sufficient scattering-transparent state was not obtained.

(Comparative Example 2) Polymer dispersion was carried out in the same manner as in Example 2 except that the same kind and the same amount of liquid crystal, monomer, oligomer and photocuring initiator as those described in Example 2 were used and no conductive filler was used. Completed a liquid crystal cell made of mold type liquid crystal.
The electro-optical characteristics of the liquid crystal cell thus completed are shown in FIG.
As shown in Table 1, the driving voltage was high, the transmittance was not sufficient when no voltage was applied, the scattering performance was poor, and a sufficient scattering-transparent state was not obtained.

The liquid crystal material used is the above-mentioned BL-
Not limited to 002 and ZLI-4792, various nematic liquid crystals, cholesteric liquid crystals, and the like may be used. In this example, the proportion of the liquid crystal in the polymer-dispersed liquid crystal is 82% by weight, but it is not limited to this. As a polymer-forming monomer,
2-Ethylhexyl acrylate was used, but not limited thereto, 2-hydroxyethyl acrylate, neopentyl glycol acrylate, hexanediol diacrylate, diethylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, triethyl glycol diacrylate. Generally commercially available acrylic monomers such as methylolpropane triacrylate, as well as a wide range of commercially available products other than acrylic monomers are applicable. The oligomer is not limited to the polyurethane acrylate described above, and polyester acrylate, epoxy acrylate, etc. can be used.

The polymerization initiator is also Darocur 1173.
The product is not limited to (Merck Co., Ltd.), and may be Darocur 1116 (Merck) or Irgacure 184 or Irgacure 651 (Ciba-Gaiki).

Further, the polymer material used is not limited to the photo-curable resin shown in the examples, and may be a thermosetting resin or a thermoplastic resin.

[0021]

As described above, by using a polymer-dispersed liquid crystal in which a conductive filler is mixed in a polymer-dispersed liquid crystal for a liquid crystal optical element, the driving voltage of the liquid crystal optical element can be significantly reduced, and the active voltage can be reduced. Application to matrix driving becomes possible. At the same time, the scattering performance and reliability of the liquid crystal optical element are improved, and a liquid crystal optical element having high contrast and excellent reliability can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a liquid crystal optical element manufactured using a polymer-dispersed liquid crystal of the present invention.

FIG. 2 is a schematic diagram showing the display principle of a liquid crystal optical element manufactured using polymer-dispersed liquid crystal.

FIG. 3 is a plan view showing the outline of a liquid crystal optical element produced using the polymer-dispersed liquid crystal of the present invention.

FIG. 4 is a graph showing electro-optical characteristics of the liquid crystal cells shown in Example 1 and Comparative Example 1 of the present invention.

FIG. 5 is a graph showing electro-optical characteristics of the liquid crystal cells shown in Example 2 of the present invention and Comparative Example 2.

[Explanation of symbols]

11 Transparent Electrode Layer 12 Incident Light 13 Scattered Light 14 Liquid Crystal Molecules 15 Polymer Phase 16 Transmitted Light 21 Upper Substrate 22 Lower Substrate 23 Liquid Crystal 24 Polymer Material 25 Conductive Filler 26 Spacer / Seal Resin 27 Transparent Electrode Layer 31 Upper Substrate 32 Lower substrate 33 Spacer and sealing resin 34 Opening 35 Polymer dispersed liquid crystal injection part mixed with conductive filler

Claims (2)

[Claims] 1. A liquid crystal optical element in which a polymer-dispersed liquid crystal in which liquid crystal is dispersed and held in a matrix made of a polymer material is sandwiched between substrates having a pair of electrodes, wherein the polymer-dispersed liquid crystal is a conductive filler. A liquid crystal optical element, which is a polymer-dispersed liquid crystal containing a mixture of: 2. A conductive filler in a polymer dispersed liquid crystal,
The liquid crystal optical element according to claim 1, which is present in a discontinuous or partially continuous state.