Liquid crystal device

Abstract

Provided are a liquid crystal device, a composition capable of forming a liquid crystal layer, a method of manufacturing the liquid crystal device, a system for manufacturing the liquid crystal device, and a use of the liquid crystal device. The liquid crystal device is a device capable of exhibiting, for example, a normally transparent or black mode, exhibiting a high contrast ratio, being driven with a low driving voltage, and exhibiting excellent durability such as thermal stability. Such a liquid crystal device may be applied to various optical modulators such as a smart window, a window protective film, a flexible display device, an active retarder for displaying 3D images, or a viewing angle control film.

Claims

1. A liquid crystal device, which comprises a liquid crystal layer comprising an alignable polymer network and a liquid crystal compound which is orientationally ordered in the polymer network and of which the ordering direction is changeable by an external action, and which is configured to be switchable between a light transmission mode and a light blocking mode according to the ordering direction of the liquid crystal compound, wherein the liquid crystal device further comprises an alignment layer adjacent to the liquid crystal layer, and polarizing layers on both sides of the liquid crystal layer, and wherein the liquid crystal layer satisfies Equation B:
(1a){(2n.sub.o.sup.2+n.sub.e.sup.2)/3}.sup.0.5n.sub.p(1+a)n.sub.e[Equation B] wherein the a is a number within a range from 0 to 0.5, the n.sub.o is an ordinary refractive index of the liquid crystal compound, the n.sub.e is an extraordinary refractive index of the liquid crystal compound, and the n.sub.p is a refractive index of the polymer network.

2. The liquid crystal device according to claim 1, wherein hazes in the light transmission mode and the light blocking mode are 10% or less.

3. The liquid crystal device according to claim 1, wherein the maximum value of a ratio (T/B) of a brightness (T) of the light transmission mode with respect to a brightness (B) of the light blocking mode is 200 or more.

4. The liquid crystal device according to claim 1, which is configured to maintain a normally transparent mode or a normally black mode.

5. The liquid crystal device according to claim 4, wherein a voltage required for realizing a transmittance of 10% from the normally transparent mode or a voltage required for realizing a transmittance of 90% from the normally black mode is 30 V or less.

6. The liquid crystal device according to claim 1, wherein the liquid crystal layer satisfies the following Equation A after thermal treatment in which it is maintained at 70 C. for 200 hours:
|100(X.sub.2X.sub.1)/X.sub.1|10%[Equation A] wherein the X is a retardation of the liquid crystal layer before the thermal treatment, and the X.sub.2 is a retardation of the liquid crystal layer after the thermal treatment.

7. The liquid crystal device according to claim 1, wherein the liquid crystal layer satisfies Equation C:
(n.sub.e+n.sub.o)/2b{(2n.sub.o.sup.2+n.sub.e.sup.2)/3}.sup.0.5(n.sub.e+n.sub.o)/2+b[Equation C] where the n.sub.e is an extraordinary refractive index of the liquid crystal compound, the n.sub.o is an ordinary refractive index of the liquid crystal compound, and the b is a number within a range from 0.1 to 1.

8. The liquid crystal device according to claim 1, wherein the polymer network is a network of a precursor comprising at least one selected from the group consisting of a bifunctional acrylate compound, a multifunctional acrylate compound that is a tri- or more functional compound and a monofunctional acrylate compound such that they satisfy Equations 1 to 3:
A1.3B[Equation 1]
AC[Equation 2]
A0.6(B+C)[Equation 3] wherein the A, B and C are weight ratios, respectively, between the compounds obtained after converting the sum of weights of the bifunctional acrylate compound, the multifunctional acrylate compound and the monofunctional acrylate compound present in the precursor to be 100.

9. The liquid crystal device according to claim 8, wherein the precursor comprises at least one selected from the group consisting of the bifunctional acrylate compound, the multifunctional acrylate compound that is a tri- or more functional compound and the monofunctional acrylate compound such that they further satisfy Equations 4 to 6:
A40[Equation 4]
B30[Equation 5]
C50[Equation 6] wherein the A, B and C are weight ratios, respectively, between the compounds obtained after converting the sum of weights of the bifunctional acrylate compound, the multifunctional acrylate compound and the monofunctional acrylate compound present in the precursor to be 100.

10. The liquid crystal device according to claim 1, wherein the alignable polymer network has a double refraction of 20 nm or less.

11. The liquid crystal device according to claim 1, further comprising two base layers which are disposed opposite to each other, and between which the liquid crystal layer is.

12. The liquid crystal device according to claim 11, wherein an electrode layer is formed on a surface facing the liquid crystal layer of at least one base layer.

13. An optical modulator comprising the liquid crystal device of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 show an illustrative liquid crystal device.

(2) FIGS. 3 through 5 are diagrams illustrating a process of manufacturing the illustrative device.

(3) FIG. 6 is a diagram showing a system for manufacturing the illustrative liquid crystal device.

(4) FIGS. 7 to 17 show evaluation results for the liquid crystal device in Examples and Comparative Examples.

EXPALANATION OF THE MARKS IN THE DRAWINGS

(5) 101: the alignment layer

(6) 102: the liquid crystal layer

(7) 1021: the polymer network

(8) 1022: the liquid crystal region

(9) 201A, 201B: base layers

(10) 301: the polymerizable composition

(11) 302: the pressure roller

ILLUSTRATIVE EMBODIMENT

(12) Hereinafter, the above will be described in more detail by Examples and Comparative Examples; however the scope of the above is not limited to the below.

EXAMPLE 1

(13) Formation of Alignment Layer

(14) A precursor of an alignment layer was prepared by dissolving a mixture of polynorbornene (PNBCi, molecular weight (Mw): 85,000, polydispersity index (PDI): approximately 4.75) including the repeating unit of Formula A and a photoinitiator (Irgacure 907) as an alignment compound in a toluene solvent to have a solid content of the polynorbornene of 2 wt %. An alignment layer was formed by coating the precursor of the alignment layer on a transparent electrode layer of a polycarbonate (PC) film on which an indium tin oxide (ITO) transparent electrode layer is formed, and applying linearly-polarized UV rays (1,200 mJ/cm.sup.2) by means of a wire grid polarizer (WGP).

(15) ##STR00004##

(16) Manufacture of Liquid Crystal Device

(17) A precursor of a liquid crystal layer (polymerizable composition; nematic temperature (Tni): approximately 50 C.) was prepared by mixing 1.6-hexanediol diacrylate as a polymer network precursor with a liquid crystal compound (Merck, MAT-12-529, ne: 1.6092, no: 1.4820) in a weight ratio (polymer network precursor:liquid crystal compound) of 1:9, and dissolving the mixture in toluene with a suitable amount of an initiator. Afterward, the precursor of the liquid crystal layer was coated on a surface of the manufacture alignment layer to have a thickness of a final liquid crystal layer of 2.5 m. A liquid crystal layer was formed by stacking a surface of the alignment layer of the PC film on one surface of which the alignment layer was formed to be in contact with the coating layer on the coated precursor of the liquid crystal layer, and polymerizing a polymer network precursor by radiating UV rays (300 mW/cm.sup.2). A temperature during the UV radiation was maintained at approximately 25 C., and thus the precursor of the liquid crystal layer was maintained in a nematic phase. A refractive index of a polymer network for forming the liquid crystal layer measured with a prism coupler was approximately 1.456, and a phase retardation (measured retardation) of the liquid crystal layer measured using Axostep (Axometrics) equipment according to the manual of a manufacturer based on a wavelength of 550 nm was approximately 288 nm. FIG. 7 is an optical microscope image of the liquid crystal layer, and FIG. 8 is a scanning electron microscope (SEM) image of the liquid crystal layer.

EXAMPLE 2

(18) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 50 parts by weight of 1,6-hexanediol diacrylate and 50 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 45 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.446, and the measured retardation of the liquid crystal layer was approximately 286.7 mm.

EXAMPLE 3

(19) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 40 parts by weight of 1,6-hexanediol diacrylate, 20 parts by weight of trimethylolpropane triacrylate, and 40 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 45 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.452, and the measured retardation of the liquid crystal layer was approximately 285.3 mm.

EXAMPLE 4

(20) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 40 parts by weight of 1,6-hexanediol diacrylate, 30 parts by weight of trimethylolpropane triacrylate, and 30 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 50 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.455, and the measured retardation of the liquid crystal layer was approximately 286.1 mm.

EXAMPLE 5

(21) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 70 parts by weight of 1,6-hexanediol diacrylate and 30 parts by weight of trimethylolpropane triacrylate was used as a polymer network precursor. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 50 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.461, and the measured retardation of the liquid crystal layer was approximately 287 mm.

COMPARATIVE EXAMPLE 1

(22) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 40 parts by weight of 1,6-hexanediol diacrylate and 60 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor, and the polymer network precursor and the liquid crystal compound were mixed in a weight ratio (polymer network precursor:liquid crystal compound) of 10:90. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 45 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.444, and the measured retardation of the liquid crystal layer was approximately 124 mm.

COMPARATIVE EXAMPLE 2

(23) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 30 parts by weight of 1,6-hexanediol diacrylate, 20 parts by weight of trimethylolpropane triacrylate, and 50 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor, and the polymer network precursor and the liquid crystal compound were mixed in a weight ratio (polymer network precursor:liquid crystal compound) of 10:90. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 45 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.450, and the measured retardation of the liquid crystal layer was approximately 162 mm.

COMPARATIVE EXAMPLE 3

(24) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 30 parts by weight of 1,6-hexanediol diacrylate, 40 parts by weight of trimethylolpropane triacrylate, and 30 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor, and the polymer network precursor and the liquid crystal compound were mixed in a weight ratio (polymer network precursor:liquid crystal compound) of 10:90. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 45 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.457, and the measured retardation of the liquid crystal layer was approximately 166 mm.

COMPARATIVE EXAMPLE 4

(25) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 40 parts by weight of 1,6-hexanediol diacrylate, 40 parts by weight of trimethylolpropane triacrylate, and 20 parts by weight of 2-ethylhexyl acrylate was used as a polymer network precursor, and the polymer network precursor and the liquid crystal compound were mixed in a weight ratio (polymer network precursor:liquid crystal compound) of 10:90. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 50 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.459, and the measured retardation of the liquid crystal layer was approximately 157 mm.

COMPARATIVE EXAMPLE 5

(26) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 60 parts by weight of 1,6-hexanediol diacrylate and 40 parts by weight of trimethylolpropane triacrylate was used as a polymer network precursor, and the polymer network precursor and the liquid crystal compound were mixed in a weight ratio (polymer network precursor:liquid crystal compound) of 10:90. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 50 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C. A refractive index of the polymer network in the formed liquid crystal layer was approximately 1.463 and the measured retardation of the liquid crystal layer was approximately 182 mm.

COMPARATIVE EXAMPLE 6

(27) A liquid crystal layer was formed by the same method as described in Example 1, except that only a liquid crystal compound was injected between PC films having an alignment layer to form a liquid crystal layer without using a polymer network precursor. Here, a measured retardation of the liquid crystal layer was approximately 319 nm.

COMPARATIVE EXAMPLE 7

(28) A liquid crystal layer switched between a dispersing mode and a transparent mode was formed by forming a liquid crystal layer having a thickness of approximately 25 m between two PC films not having an alignment layer using a precursor of a liquid crystal layer prepared by mixing 40 parts by weight of a polymer network precursor (PN-393, Merck) and 60 parts by weight of a liquid crystal compound as a precursor capable of forming a device switched between a dispersing mode and a transparent mode. A haze in the dispersing mode of the layer crystal layer formed as described above was approximately 92.91%, and a retardation thereof was approximately 65 nm.

COMPARATIVE EXAMPLE 8

(29) A liquid crystal layer was formed by the same method as described in Example 1, except that a precursor of a liquid crystal layer prepared by mixing 10 parts by weight of a reactive liquid crystal compound and 90 parts by weight of a liquid crystal compound using the reactive liquid crystal compound (RM257, Merck) as a polymer network precursor was used. Here, a nematic temperature of the precursor of the liquid crystal layer was approximately 85 C., and the UV radiation was performed at a temperature maintaining the precursor in a nematic phase, for example, 25 C.

COMPARATIVE EXAMPLE 9

(30) A liquid crystal layer was formed by the same method as described in Example 1, except that a mixture of 20 parts by weight of 1,6-hexanediol diacrylate and 80 parts by weight of a liquid crystal compound was used as a polymer network precursor. Here, a nematic temperature (Tni) of the precursor of the liquid crystal layer was approximately 10 C., and the UV radiation was performed at a temperature in which the precursor was maintained in an isotropic phase, for example, 25 C. A retardation (measured retardation) of the liquid crystal layer measured using Axostep (Axometrics) equipment according to the manual of a manufacturer based on a wavelength of 550 nm was approximately 139 nm.

COMPARATIVE EXAMPLE 10

(31) A liquid crystal layer was formed by the same method as described in Example 1, except that UV radiation was performed at a temperature in which a precursor of a liquid crystal layer was maintained in an isotropic phase, for example, 60 C. Here, a refractive index of a polymer network in the manufactured liquid crystal layer measured using a prism coupler was approximately 1.456, and a retardation (measured retardation) of the liquid crystal layer measured using Axostep (Axometrics) equipment according to the manual of a manufacturer based on a wavelength of 550 nm was approximately 88 nm. FIG. 18 shows data of the liquid crystal layer, which was measured by Axostep.

COMPARATIVE EXAMPLE 11

(32) A liquid crystal layer was formed by the same method as described in Example 1, except that a PC film not having a photo-alignment layer was used. Here, a refractive index of a polymer network in the manufactured liquid crystal layer measured using a prism coupler was approximately 1.456, and a retardation (measured retardation) of the liquid crystal layer measured using Axostep (Axometrics) equipment according to the manual of a manufacturer based on a wavelength of 550 nm was approximately 46 nm. FIG. 18 shows data of the liquid crystal layer, which was measured by Axostep.

COMPARATIVE EXAMPLE 12

(33) A liquid crystal layer was formed by the same method as described in Example 1, except that a precursor of a liquid crystal layer was prepared by blending a polymer network precursor and a liquid crystal compound in a weight ratio (polymer network precursor:liquid crystal compound) of 4:6. A retardation (measured retardation) of the liquid crystal layer measured using Axostep (Axometrics) equipment according to the manual of a manufacturer based on a wavelength of 550 nm was approximately 139 nm.

EXPERIMENTAL EXAMPLE 1

Evaluation of Alignment Property of Polymer Network

(34) The liquid crystal layer manufactured in Example was placed between two polarizing plates disposed such that light absorption axes were perpendicular to each other or between two polarizing plates in which light absorption axes were disposed at 45 degrees, and an alignment property was evaluated by confirming whether the liquid crystal layer was switched between a transparent mode and a black mode while revolving. When the liquid crystal layer was switched between the transparent and black modes through the above-described process, it was evaluated that a liquid crystal compound was aligned in the liquid crystal layer due to the alignment property of a polymer network. According to the evaluation results, in Examples 1 to 5, switching between the transparent and black modes was confirmed, but in Comparative Examples 1 to 5 and Comparative Examples 9 to 12, polymer networks did not exhibit alignment properties. FIG. 9 shows evaluation results with respect to Examples 1 to 5, and FIG. 10 shows evaluation results with respect to Comparative Examples 1 to 5. In addition, FIG. 16 is a diagram showing the comparison between Example 1 and Comparative Example 9, and in Example 1 in which the formation of the liquid crystal layer was performed in a nematic phase of a precursor as confirmed from the drawings, a transparent mode (left) was exhibited when the liquid crystal layer was disposed at 45 degrees with a polarization axis, and a black mode (right) was exhibited when the liquid crystal layer was disposed at 90 degrees with a polarization axis. However, in Comparative Example 9 in which the formation of a liquid crystal layer was performed in a state in which a precursor was in an isotropic state, it was seen that switching between the transparent and black modes was impossible since light was blocked at both states in which the liquid crystal layer was disposed at 45 and 90 degrees (left and right) with a polarization axis.

EXPERIMENTAL EXAMPLE 2

Evaluation of Retardation, Haze, and Transmittance of Liquid Crystal Layer

(35) The retardation, haze, and transmittance of the liquid crystal layers manufactured in Examples 1 to 5 were evaluated. Here, the retardation (measurement wavelength: 550 nm) was measured according to the manual of a manufacturer based on a wavelength of 550 nm using Axostep (Axometrics) equipment, and the haze and transmittance were also measured according to the manual of a manufacturer using a hazemeter (NDH-5000SP). Here, the retardation was evaluated in a state in which a voltage was not applied to the liquid crystal layer, and the haze and transmittance were evaluated by applying a driving voltage. FIG. 11 is a diagram showing results obtained by evaluating retardations with respect to Examples, and FIG. 12 is a diagram showing results obtained by evaluating haze and transmittance with respect to Examples. FIG. 15 shows AXO-STEP measured data for Example 1 and Comparative Example 1.

EXPERIMENTAL EXAMPLE 3

(36) A contrast ratio was evaluated by evaluating a brightness by applying a voltage to the liquid crystal layers manufactured in Examples and Comparative Examples step by step. The brightness and contrast ratio were evaluated by converting values measured by LCMS-200 equipment (Sesim Photonics Technology). In the evaluation process, a distance between a measurement target and a light receiving part (detector) was maintained at approximately 10 cm, and a diameter of the light receiving part (detector) was approximately 1.5 mm. FIG. 13 shows evaluation results for Example 1, and Comparative Examples 1 and 7. For evaluation, the liquid crystal layers of Example 1 and Comparative Example 1 were placed between two polarizing plates in which light absorption axes were perpendicular to each other, and in the case of Comparative Example 7 configured to be switched between a dispersing mode and a transparent (white) mode, a contrast ratio between the dispersing mode and the transparent (white) mode was evaluated without using a polarizing plate. As seen from the drawings, in Example 1, while the maximum contrast ratio was 350 or more, in Comparative Examples 1 and 7, the contrast ratio was 100 or less. Meanwhile, the maximum contrast ratios in Examples 2 to 5 were all 350 or more, and the maximum contrast ratios in Comparative Examples 2 to 6, 8 and 9 were all less than 100.

EXPERIMENTAL EXAMPLE 4

(37) In Example 1 and Comparative Example 7, a transmittance according to a driving voltage was evaluated. In Example 1, the device exhibiting a normally transparent mode was configured by disposing the liquid crystal layer between two polarizing plates in which light absorption axes were perpendicular to each other to be aligned at 45 degrees with the light absorption axis of the polarizing plate, and then the transmittance was evaluated by applying a voltage and switching into a black mode, and in Comparative Example 7, a driving voltage was measured by applying a voltage to the device present in a normally dispersing mode to be converted into a transparent mode without using a polarizing plate. FIG. 14 shows the measurement results, and as seen from FIG. 14, in Example 1, a driving voltage for exhibiting a transmittance of 10% was 16.5 V, and in Comparative Example 7, a driving voltage for exhibiting a transmittance of 90% was 92.4 V. Meanwhile, as the evaluation was performed in the same manner in Examples 2 to 5, the driving voltages for exhibiting a transmittance of 10% were all less than 30 V, in Comparative Examples 1 to 6, 8 and 9, the driving voltages for exhibiting a transmittance of 10% were all 90V or more.

EXPERIMENTAL EXAMPLE 5

Evaluation of Thermal Stability

(38) Thermal stabilities of the liquid crystal layer (measured retardation: 288 nm) manufactured in Example 1 and the liquid crystal layer (measured retardation: 319 nm) manufactured in Comparative Example 6 were evaluated. Specifically, the thermal stability was evaluated by evaluating a retardation after each liquid crystal layer was maintained in an oven at 70 C. for 200 hours. Afterward, in Example 1, the minimum and maximum retardations were 254.4 nm and 278.9 nm, respectively, the average retardation was 263 nm, and a retardation change was 8.7%. In Comparative Example 6, the minimum and maximum retardations were 226.2 nm and 273.9 nm, respectively, the average retardation was 254.2 nm, a retardation change was 20.4%. In addition, as the result of evaluating thermal stabilities of Examples 2 to 5 in the same manner, the retardation changes were all less than 10%.