METHOD FOR MANUFACTURING OPTICALLY ANISOTROPIC FILM

Abstract

A method for producing an optically anisotropic film. The optically anisotropic film produced using this method has a reverse wavelength dispersion property, which can control retardation deterioration at high temperature, and can be used in polarizing plates and display devices.

Claims

1. A method for producing an optically anisotropic film comprising: a step of forming an overcoat layer on one side of an optically anisotropic layer; and a step of aging the overcoat layer at a temperature of 100° C. or higher after the step of forming the overcoat layer, wherein the overcoat layer comprises a photoreactive compound having three or more photoreactive groups, and wherein the anisotropic layer comprises a polymerizable liquid crystal compound satisfying Equation 1:
R(450)/R(550)<R(650)/R(550),  [Equation 1] wherein, R (λ) is an in-plane retardation of a liquid crystal layer for light having a wavelength of λ nm, wherein the liquid crystal layer comprises the polymerizable liquid crystal compound oriented in a planar state.

2. The method for producing an optically anisotropic film according to claim 1, wherein the optically anisotropic layer has an in-plane retardation value for light having a wavelength of 550 nm in a range of 100 nm to 180 nm.

3. The method for producing an optically anisotropic film according to claim 1, wherein the three or more photoreactive groups of the photoreactive compound are selected from cinnamate groups or (meth)acryl groups.

4. The method for producing an optically anisotropic film according to claim 1, wherein the photoreactive compound is a polymer having three or more cinnamate groups.

5. The method for producing an optically anisotropic film according to claim 1, wherein the photoreactive compound is a monomer having three or more (meth)acryl groups.

6. The method for producing an optically anisotropic film according to claim 1, wherein the overcoat layer has a thickness in a range of 0.1 μm to 10 μm.

7. The method for producing an optically anisotropic film according to claim 1, wherein the overcoat layer has an in-plane retardation value for light having a wavelength of 550 nm in a range of 0 nm to 3 nm.

8. The method for producing an optically anisotropic film according to claim 1, wherein the overcoat layer exhibits no adhesive force.

9. The method for producing an optically anisotropic film according to claim 1, further comprising: a step of applying a liquid crystal composition on a base layer and then curing it to form the optically anisotropic layer, wherein the liquid crystal composition comprises the polymerizable liquid crystal compound.

10. The method for producing an optically anisotropic film according to claim 9, wherein an alignment film is formed on the base layer on which the liquid crystal composition is applied.

11. The method for producing an optically anisotropic film according to claim 1, wherein the step of forming an overcoat layer is performed by applying an overcoat composition on one side of the optically anisotropic layer, wherein the overcoat composition comprises the photoreactive compound and a solvent.

12. The method for producing an optically anisotropic film according to claim 1, wherein the aging is performed at a temperature range of 100° C. or higher to 200° C. or lower.

13. The method for producing an optically anisotropic film according to claim 1, wherein the aging is performed for 1 minute to 30 minutes.

14. The method for producing an optically anisotropic film according to claim 1, wherein an absolute value of a retardation change rate (ΔR) of the optically anisotropic film is calculated by Equation 3 below:
ΔR=(R.sub.1−R.sub.2)/R.sub.1×100%,  [Equation 3] wherein, ΔR is an in-plane retardation change rate of the optically anisotropic film after standing at high temperature, R.sub.1 is an initial in-plane retardation value of the optically anisotropic film, and R.sub.2 is an in-plane retardation value after leaving the optically anisotropic film at 85° C. for 500 hours, and wherein the ΔR value is 5% or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0109] FIG. 1 is a schematic illustration of an optically anisotropic film according to an exemplary embodiment of the present application.

[0110] FIG. 2 is a representation of the x-axis, the y-axis and the z-axis.

[0111] FIG. 3 is a schematic illustration of an optically anisotropic film according to an exemplary embodiment of the present application.

[0112] FIG. 4 is a schematic illustration of a polarizing plate according to an exemplary embodiment of the present application.

[0113] FIG. 5 is a schematic illustration of a polarizing plate according to another exemplary embodiment of the present application.

[0114] FIG. 6 is a schematic illustration of a polarizing plate according to another exemplary embodiment of the present application.

[0115] FIG. 7 is a graphical representation of high temperature reliability evaluation results.

DETAILED DESCRIPTION

[0116] Hereinafter, the present application will be described in detail through examples according to the present application and comparative examples not complying with the present application, but the scope of the present application is not limited to the following examples.

Example 1

[0117] 20 g of 5-norbornene-2-methyl-(4-methoxy cinnamate) as a photo-alignment polymer, 20 g of dipentaerythritol hexaacrylate as a reactive compound and 5 g of a photoinitiator (Irgacure OXE02, Ciba-Geigy (Switzerland)) were dissolved in 980 g of toluene to prepare a composition for forming an alignment film, and the composition for forming the alignment film was applied on a PET (polyethylene terephthalate) film so as to have a thickness of about 1,000 Å or so after drying, and then hot-air dried in a drying oven at 80° C. for 2 minutes. After drying, it was irradiated with ultraviolet rays linearly polarized in the direction perpendicular to the travel direction of the film via a wire grid polarizing plate (manufactured by Moxtek) at a light quantity of 150 mJ/cm.sup.2, using a high-pressure mercury lamp as a light source, to impart orientation, thereby producing the alignment film.

[0118] A liquid crystal composition was prepared by dissolving an UCL-R17 mixture (manufactured by DIC) comprising a polymerizable liquid crystal compound capable of planar orientation and having a reverse wavelength dispersion property in toluene as a solvent so as to have 35 parts by weight of the solid content relative to 100 parts by weight of the total composition (solvent+UCL-R17 mixture). The liquid crystal composition was applied on the alignment film so as to have a thickness of 2 μm after drying, and hot-air dried in a drying oven at 80° C. for 2 minutes. Then, it was irradiated with unpolarized ultraviolet rays by a high-pressure mercury lamp (80 w/cm) and cured, thereby forming an optically anisotropic layer. The ultraviolet rays are ultraviolet rays having a wavelength of about 150 nm to 350 nm, which are irradiated with a light quantity of 50 mJ/cm.sup.2 to 5000 mJ/cm.sup.2 as the total irradiance level. The produced optical film is a laminated optical film comprising the PET film, the alignment film formed on the film, and the optically anisotropic layer formed on the alignment film.

[0119] Overcoat Layer Formation

[0120] An overcoat composition was prepared by mixing 0.5 g of PETA (pentaerythritol triacrylate) and 0.05 g of an initiator (Irgacure 907, manufactured by Ciba-Geigy, Switzerland) in 10 g of a toluene solvent. The overcoat composition was coated on the optically anisotropic layer in a thickness of 0.2 μm to 0.5 μm, followed by drying at 60° C. for 2 minutes, and then irradiated with ultraviolet rays at an intensity of 300 mJ and cured to form an overcoat layer. The overcoat layer was formed, and then further subjected to aging at 120° C. for 3 minutes to produce an optically anisotropic film.

Example 2

[0121] An optically anisotropic film was produced in the same method as in Example 1, except that the overcoat layer was formed on the optically anisotropic layer in the following method.

[0122] Formation of Overcoat Layer

[0123] An overcoat composition was prepared by mixing 0.2 g of a material of Formula A below, 0.02 g of PETA (pentaerythritol triacrylate) and 0.002 g of an initiator (oximer ester) in 10 g of a toluene solvent. The overcoat composition was coated on the optically anisotropic layer in a thickness of 0.2 μm to 0.3 μm, followed by drying at 80° C. for 2 minutes, and then irradiated with ultraviolet rays at an intensity of 300 mJ and cured to form an overcoat layer. The overcoat layer was formed, and then further subjected to aging at 120° C. for 3 minutes.

##STR00007##

[0124] (weight average molecular weight: about 10,000 to 100,000)

Example 3

[0125] An optically anisotropic film was produced in the same method as in Example 1, except that the overcoat layer was formed in the following method.

[0126] Formation of Overcoat Layer

[0127] An overcoat composition was prepared by mixing 2 g of tris(acryloxyethyl) isocyanurate, 1 g of isophorone diamine diisocyanate, 2 g of tetrahydro furfuryl acrylate, 2 g of a polyester oligomer and 0.35 g of an initiator (Darocur TPO) in 3 g of a MEK solvent. The overcoat composition was coated on the optically anisotropic layer in a thickness of 1p m to 5 μm, and then a TAC film was bonded together onto the coating layer of the overcoat composition. Next, the side of the TAC film was irradiated with ultraviolet rays at an intensity of 150 mJ and the overcoat composition was cured to form an overcoat layer. The overcoat layer was formed and then further subjected to aging at 120° C. for 3 minutes.

Comparative Example 1

[0128] In Example 1, an optically anisotropic film was produced in the same method as in Example 1, except that no overcoat layer was formed.

Comparative Example 2

[0129] In Example 1, an optically anisotropic film was produced in the same method as in Example 1, except that no overcoat layer was formed and the optically anisotropic layer was subjected to aging at 120° C. for 3 minutes.

Comparative Example 3

[0130] In Example 1, an optically anisotropic film was produced in the same method as in Example 1, except that the overcoat layer was formed and then no aging was performed.

Comparative Example 4

[0131] In Example 2, an optically anisotropic film was produced in the same method as in Example 2, except that the overcoat layer was formed and then no aging was performed.

Comparative Example 5

[0132] In Example 3, an optically anisotropic film was produced in the same method as in Example 3, except that the overcoat layer was formed and then no aging was performed.

Evaluation Example 1. High Temperature Reliability Evaluation

[0133] For the optically anisotropic films produced in Examples and Comparative Examples, the following samples were each produced to measure the initial in-plane retardation values and the in-plane retardation values after high temperature standing, and the results were graphically represented in FIG. 7 (x-axis: hour; y-axis: 100−ΔR (%)) and Table 1.

[0134] For Examples 1 and 2 and Comparative Examples 3 and 4, samples were prepared, in which the TAC films were attached to the overcoat layers via a pressure-sensitive adhesive, the PET film were peeled off, and then glass was attached to the alignment films via a pressure-sensitive adhesive.

[0135] For Example 3 and Comparative Example 5, samples were prepared, in which the PET films were peeled off, and then glass was attached to the alignment films via a pressure-sensitive adhesive.

[0136] For Comparative Examples 1 and 2, samples were prepared, in which the TAC films were attached to the optically anisotropic layers via a pressure sensitive adhesive, the PET films were peeled off, and then glass was attached to the alignment films via a pressure-sensitive adhesive.

[0137] The initial in-plane retardation value means the in-plane retardation value of the optically anisotropic film measured at a temperature of 25° C., and the in-plane retardation value after high temperature standing means the in-plane retardation value measured while applying heat to the optically anisotropic film at a temperature of 85° C. for 500 hours. In Table 1, ΔR means a retardation change rate (%), and is defined by Equation 3 below.

ΔR=(R.sub.1−R.sub.x)/R.sub.1×100%  [Equation 3]

[0138] In Equation 3, ΔR is the in-plane retardation change rate of the optically anisotropic film after high temperature standing, R.sub.1 is the initial in-plane retardation value of the optically anisotropic film, and R.sub.x is the in-plane retardation value of the optically anisotropic film after x hour standing at 85° C.

[0139] The in-plane retardation was measured for light having a wavelength of 550 nm using Axoscan equipment (manufactured by Axomatrics) capable of measuring 16 Muller matrices. Using Axoscan equipment, 16 Muller matrices were obtained according to the manufacturer's manual, through which the retardation was extracted.

TABLE-US-00001 TABLE 1 Initial 100 − ΔR (%) (25° C.) Initial 24 h 100 h 200 h 300 h 400 h 500 h Rin Value (25° C.) (85° C.) (85° C.) (85° C.) (85° C.) (85° C.) (85° C.) Comparative 1 139.2 100 97.8 97.0 96.5 96.4 96.0 95.8 Example 2 137.0 100 99.1 98.4 97.8 97.7 97.4 97.3 3 139.9 100 99.1 98.8 98.6 98.4 98.6 98.4 4 138.7 100 98.7 98.1 97.9 97.6 97.7 97.5 5 139.1 100 98.6 98.2 98.1 97.8 97.9 97.8 Example 1 137.8 100 99.8 99.6 99.3 99.3 99.2 99.1 2 137.1 100 99.7 99.2 98.7 98.6 98.7 98.5 3 137.3 100 99.7 99.3 98.8 98.7 98.7 98.7

REFERENCE NUMERALS USED HEREIN

[0140] 10: optically anisotropic layer [0141] 20: overcoat layer [0142] 30: alignment film [0143] 40: base layer [0144] 100: optically anisotropic film [0145] 200: polarizer