GUEST-HOST TYPE LIQUID CRYSTAL COMPOSITION

Abstract

The present application relates to a liquid crystal composition, a polarizing element and a use of the polarizing element. Since the polarizing element may be prepared by a simple coating process, the guest host type liquid crystal composition of the present application allows not only for reducing the manufacturing cost and lightweight thinning of the polarizing element, but also for manufacturing the polarizing element showing an excellent heat resistant stability without changes of absorption spectrum to transmission spectrum even in a severe condition such as high temperature environment. Such a polarizing element can be applied to various display devices such as liquid crystal display devices, EL display devices, field emission display devices, display devices using electronic papers, projection display devices or piezoelectric ceramic display devices.

Claims

1. A guest host type liquid crystal composition comprising a cationic polymerizable liquid crystal compound and a dichroic dye and satisfying Equation 1 below:
−20≦100×(H−W)/W≦20   [Equation 1] wherein W is the maximum absorption wavelength of said dye immediately after said polymerizable liquid crystal compound is polymerized, and H is the maximum absorption wavelength of said dye after maintaining the liquid crystal composition having said liquid crystal compound polymerized at 100° C. for 100 hours.

2. The guest host type liquid crystal composition according to claim 1, wherein said cationic polymerizable liquid crystal compound has an epoxy group as the cationic polymerizable functional group.

3. The guest host type liquid crystal composition according to claim 1, wherein the polymerizable liquid crystal compound is a compound of Formula 1 below: ##STR00003## where, A is a single bond, —COO— or —OCO—, R.sub.1 to R.sub.10 are each independently hydrogen, halogen, an alkyl group, an alkoxy group, an alkoxycarbonyl group, a nitro group, an epoxy group, a cyano group, —OQP or a substituent of Formula 2 below, provided that at least one of R.sub.1 to R.sub.10 is an epoxy group, a cyano group, —O-Q-P or a substituent of Formula 2 below, or two adjacent substituents of R.sub.1 to R.sub.5 or two adjacent substituents of R.sub.6 to R.sub.10 are linked from each other to form a benzene substituted with —O-Q-P, Q is an alkylene group or an alkylidene group, and P is an epoxy group: ##STR00004## where, B is a single bond, —COO— or —OCO—, R.sub.11 to R.sub.15 are each independently hydrogen, halogen, an alkyl group, an alkoxy group, an alkoxycarbonyl group, a nitro group, an epoxy group, a cyano group or —O-Q-P, provided that at least one of R.sub.11 to R.sub.15 is an epoxy group, a cyano group, or —O-Q-P, or two adjacent substituents of R.sub.11 to R.sub.15 are linked from each other to form a benzene substituted with —O-Q-P, Q is an alkylene group or an alkylidene group, and P is an epoxy group.

4. The guest host type liquid crystal composition according to claim 1, wherein the maximum absorption wavelength of the dichroic dye is in the wavelength range of 400 nm to 700 nm.

5. The guest host type liquid crystal composition according to claim 1, wherein the dichroic dye comprises one or more dyes from a cyan dye, an anthraquinone dye, an acridine dye and a naphthalene dye.

6. The guest host type liquid crystal composition according to claim 1, wherein the dichroic dye is included in a ratio of 0.1 parts by weight to 20 parts by weight relative to 100 parts by weight of the polymerizable liquid crystal compound.

7. The guest host type liquid crystal composition according to claim 2, further comprising a cationic initiator.

8. A polarizing element comprising a polymerized layer of a guest host type liquid crystal composition comprising a cationic polymerizable liquid crystal compound and a dichroic dye and satisfying Equation 1 below:
−20≦100×(H−W)/W=20   [Equation 1] wherein W is the maximum absorption wavelength of said dye immediately after said polymerizable liquid crystal compound is polymerized, and H is the maximum absorption wavelength of said dye after maintaining the liquid crystal composition having said liquid crystal compound polymerized at 100° C. for 100 hours.

9. The polarizing element according to claim 8, wherein the polymerized layer is a coating layer of a polarizing material comprising the cationic polymerizable liquid crystal compound and the dichroic dye.

10. The polarizing element according to claim 8, wherein the polymerized layer has a thickness in a range of 0.5 μm to 10 μm.

11. The polarizing element according to claim 8, wherein the polymerizable liquid crystal compound is included in the polymerized layer in a horizontally oriented state.

12. The polarizing element according to claim 8, further comprising an alignment film adjacent to the polymerized layer.

13. The polarizing element according to claim 12, wherein the alignment film is a photo-alignment film.

14. The polarizing element according to claim 8, further comprising a substrate layer formed on one surface of the polymerized layer.

15. A method for manufacturing a polarizing element comprising polymerizing the liquid crystal composition of claim 1 coated on one surface of a substrate layer.

16. A display device comprising the polarizing element of claim 8.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0052] FIGS. 1 to 3 are schematic views of exemplary polarizing elements.

[0053] FIG. 4 shows the results evaluating heat resistant stability of Example and Comparative Example.

MODE FOR CARRYING OUT INVENTION

[0054] Hereinafter, the polarizing element will be more specifically described through Example and Comparative Example, but the scope of the present application is not limited by the details shown below.

Example 1

[0055] A composition for forming a photo-alignment film was coated on one surface of a plastic substrate (TAC) to have a thickness after drying of about 200 Å, and dried in an oven of 80° C. for 2 minutes. In the above, as the composition for forming a photo-alignment film, a precursor composition of alignment film prepared by dissolving 2 parts by weight of poly(5-norbornene-2-methyl(4-methoxycinnamate)), 1 part by weight of dipentaerythritol hexaacrylate as a polar binder and 0.5 parts by weight of a photoinitiator (Igacure 907, manufactured by Ciba-Geigy AG, Switzerland) in about 96.8 parts by weight of a solvent (toluene) was used. After drying the composition for forming the photo-alignment film, the orientation process was carried out by irradiating UV light (100 mW/cm.sup.2) at a speed of 3 m/min

[0056] Subsequently, a liquid crystal composition comprising 1 part by weight of an azo-based cyan dye (G-472, manufactured by HAYABARA Company, absorption wavelength: 600 nm), 20 parts by weight of a polymerizable liquid crystal compound, p-phenylene-di[4-(2,3-epoxypropyloxy) benzoate], and 1 part by weight of a cationic initiator, triarylsulfonium hexafluorophosphate salts, mixed 50% in propylene carbonate (manufactured by Sigma-Aldrich AG), was coated on the oriented alignment layer to have a dry thickness of about 1.5 μm, oriented depending on the orientation of the lower alignment layer, and then irradiated with ultraviolet (300 mW/cm.sup.2) at a speed of 10 m/min, whereby liquid crystals were cross-linked and polymerized to prepare a polarizing element.

COMPARATIVE EXAMPLE 1

[0057] polarizing element was prepared by carrying out the same way as Example 1 except for using Acrylate RM (LC242, manufactured by BASF AG) of a radically polymerizable liquid crystal compound as the polymerizable liquid crystal compound.

TEST EXAMPLE 1

Evaluation of Heat Resistant Stability

[0058] For the polarizing elements prepared in Example 1 and Comparative Example 1, they were cut to a size of 10 mm×10 mm (width×length) to manufacture specimens, the absorbance depending on wavelengths of which was subsequently measured with N & K Analyer device, and the polarizing elements were left in a high temperature condition at 100° C. for 100 hours, the absorbance depending on wavelengths of which were again measured. The thus measured absorption spectra of the polarizing elements of Example 1 and Comparative Example 1 were shown in FIG. 4.

[0059] As shown in FIG. 4, before heat treatment, the polarization elements of Example 1 and Comparative Example 1 both show similar absorption spectra. However, after heat treatment, it can be confirmed that the polarizing element of Example 1 maintains the absorption spectrum, whereas in the polarizing element of Comparative Example lthe wavelength showing the maximum absorbance changes from about 580 nm to about 400 nm. In the case of using the liquid crystal compound comprising the acryloyl polymerizable group as in Comparative Example 1, the remaining radicals in the process causing the radical polymerization reaction attack the weak part of the azo-based dye in the high temperature condition to degrade the dye molecule so that the absorbance shifts toward the short wavelength, while in the case of using the liquid crystal compound having the cationic polymerizable group as in Example 1, it has no dye degradation by the radicals so that it is possible to secure the stable high temperature durability on using the azo-based dye. From this, it can be seen that the polarizing element according to Example has an excellent heat resistant stability without any change of the absorption spectrum even in a high temperature condition.

TEST EXAMPLE 2

Evaluation of Heat Resistant Light Characterization

[0060] The polarizing elements prepared in Example 1 and Comparative Example 1 were cut to a size of 10 mm×10 mm (width x length) to manufacture specimens, and then transmission spectra depending on wavelengths before and after heat treatment were measured with Jasco Spectrophotometer V-7100 device to evaluate heat resistant light characterization, and the results were summarized in Table 1 below.

[0061] As shown in Table 1, in the case of the polarizing element of Comparative Example 1 coated with the liquid crystal compound comprising the acryloyl polymerizable group, the single-plate transmittance (Ts: transmittance of one polarizing plate) changed from the initial 31.5% at 600 nm wavelength to 67.1% after 100° C. and 100 hours by about 53% and the wavelength showing the minimum transmission shifted from 600 nm to 460 nm. On the other hand, in the case of the polarizing element of Example 1 coated with the liquid crystal compound comprising the epoxy-based polymerizable group, Ts showed a change ratio of about 7% from the initial 39.6% to 42.6% after heat treatment at the same region of 600 nm. In addition, it was confirmed that the center wavelength did not shift at all from the existing 600 nm. Accordingly, it can be seen that when the cationic polymerizable liquid crystal compound is used, the heat resistant light characterization of the polarizing element is also more superior.

TABLE-US-00001 TABLE 1 Ts (initial) Ts (100° C.-100 hr) ΔTs Δλ (%) (%) (%) (nm) Comparative Example 1 31.5 67.1 53 120 Example 1 39.6 42.6 7 0