KR20170027467A

KR20170027467A - Optical film

Info

Publication number: KR20170027467A
Application number: KR1020150124108A
Authority: KR
Inventors: 김영진; 이대희; 장준원; 이은혜; 박문수
Original assignee: 주식회사 엘지화학
Priority date: 2015-09-02
Filing date: 2015-09-02
Publication date: 2017-03-10
Also published as: KR101959489B1

Abstract

The present invention relates to a method for producing an optical film, an optical film and an optical element including the same, and can provide an optical film exhibiting a reflection characteristic in a wide wavelength range and having excellent durability, It can be used as a reflection type polarizing plate capable of improving light utilization efficiency of a display device such as an LCD and improving brightness.

Description

Optical film {Optical film}

The present invention relates to a method for producing an optical film, an optical film and an optical element including the same.

The liquid crystal display (LCD) may include a liquid crystal panel and a polarizing plate disposed on the upper side and the lower side of the liquid crystal panel, and may include various functional optical elements in addition to the polarizing plate (Patent Document 1).

In the LCD, an image can be displayed by changing the orientation of the liquid crystal for each pixel of the liquid crystal panel. Since the LCD is not a self-luminous device, a light source such as a backlight unit (BLU) is usually placed on the back surface of the lower polarizer of the liquid crystal panel, and the light emitted from the light source is transmitted through the panel to display an image .

Patent Document 1: Korean Patent Publication No. 2013-0101327

The present application relates to a method for producing an optical film. The method comprises: forming a coating layer comprising a cholesteric liquid crystal composition on a substrate;

A first photocuring step of irradiating the coating layer with ultraviolet rays at 100 mJ / cm ² to 500 mJ / cm ² at 40 to 60 ° C for 5 to 10 seconds; And

And a second photo-curing step of irradiating ultraviolet rays at 1000 mJ / cm ² to 2500 mJ / cm ² at 40 to 70 ° C for 5 to 20 seconds to the application layer after the first photo-curing step,

(Hereinafter referred to as a " CLC layer ") including a cholesteric aligned liquid crystal region satisfying the following general formula (1).

[Formula 1]

150 <? _Max -? _Min <250

In the general formula 1,

? _max represents a minimum wavelength (nm) with a transmittance of 60% in a linear optical spectrum,

? _min represents a maximum wavelength (nm) with a transmittance of 60% in a linear optical spectrum.

In the present specification, a cholesteric liquid crystal or a cholesteric liquid crystal can be abbreviated as " CLC ".

In one example, the cholesteric liquid crystal composition (hereinafter " CLC composition ") may comprise a polymerizable mesogenic compound, a chiral agent, and a photoinitiator.

In one example, the cholesteric liquid crystal composition may further comprise a solvent or a surfactant.

As used herein, the term " CLC composition " may include any kind of composition that can be used to form a CLC layer comprising a liquid crystal region in a desired pattern. In one example, the composition may comprise a low molecular weight compound such as a CLC compound, a CLC polymer, or a monomer or oligomer capable of reacting to form a CLC polymer. In addition, the CLC composition may comprise one or more other additives, such as crosslinking agents, polymerization initiators, and the like. Polymerization initiators may be included in the CLC composition to initiate polymerization or crosslinking of monomers or other low molecular weight compounds. Suitable polymerization initiators include those capable of generating free radicals to initiate polymerization and crosslinking and to propagate. The free radical initiator may be selected, for example, depending on its stability or half life. Preferably, the free radical initiator does not generate additional color in the CLC layer by absorption or otherwise. Free radical initiators are typically thermal free radical initiators or photoinitiators. Thermally-free radical initiators include, for example, peroxide, persulfate or azonitrile compounds. Free radical initiators generate free radicals upon thermal degradation.

Photoinitiators can be activated by electromagnetic radiation or particle irradiation. Examples of suitable photoinitiators may include onium salt photoinitiators, organometallic photoinitiators, cationic metal salt photoinitiators, photodegradable organosilanes, latent sulfonic acids, phosphine oxides, cyclohexyl phenyl ketones, amine substituted acetophenones, and benzophenones have. In general, ultraviolet (UV) irradiation may be used to activate the photoinitiator, although other light sources may be used. The photoinitiator can be selected based on absorption of a specific wavelength of light. Ultraviolet light (UV) may be used herein to refer to light of a wavelength in the range of about 10 nm to about 400 nm.

The CLC composition typically can be part of a coating composition comprising at least one solvent. The coating composition may comprise, for example, dispersants, antioxidants and antiozonants. In addition, the coating composition may include various dyes and pigments to absorb ultraviolet, infrared or visible light, if desired. In some cases, it may be appropriate to add viscosity modifiers such as thickeners and fillers.

The CLC composition can be applied by various liquid coating methods. In some embodiments, after coating, the CLC composition is polymerized or converted into a CLC layer. This conversion can be accomplished by evaporation of the solvent, heating to align the CLC material, Crosslinking of the CLC composition; Or application of heat, such as, for example, actinic irradiation; Irradiation of light such as ultraviolet light, visible light or infrared light and irradiation of an electron beam, or a combination thereof, or curing of a CLC composition using a similar technique.

In one example, the CLC composition may comprise a compound of Formula 1, a photoinitiator, and a chiral agent.

In one example, the formation of the CLC layer comprises coating a CLC composition comprising a polymerizable liquid crystal compound or a polymerizable mesogenic compound, for example, a compound of formula 1 and a chiral agent, and polymerizing the liquid crystal compound can do.

[Chemical Formula 1]

Wherein A is a single bond, -COO- or -OCO-, R1 to R10 are each independently selected from the group consisting of hydrogen, a halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group, -OQP, , At least one of R ₁ to R ₁₀ is -OQP or a substituent of the following formula 2: wherein Q is an alkylene group or an alkylidene group, and P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, A methacryloyl group, an acryloyloxy group or a methacryloyloxy group.

(2)

R ₁₁ to R ₁₅ each independently represents hydrogen, halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group or -OQP, R ₁₁ to R ₁₅ each independently represent a hydrogen atom, At least one of them is -OQP wherein Q is an alkylene group or an alkylidene group and P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group, It is a sunny season.

In the above formula (2), "-" to the left of B means that B is directly connected to benzene of formula (1).

The term "single bond" in the above formulas (1) and (2) means a case where there is no separate atom in the part represented by A or B. For example, when A is a single bond in formula (I), benzene on both sides of A may be directly connected to form a biphenyl structure.

As the halogen in the formulas (1) and (2), chlorine, bromine or iodine and the like can be exemplified.

The alkyl group in the general formulas (1) and (2) is preferably a linear or branched alkyl group having from 1 to 20 carbon atoms, from 1 to 16 carbon atoms, from 1 to 12 carbon atoms, from 1 to 8 carbon atoms or from 1 to 4 carbon atoms or from 3 to 20 carbon atoms, A cycloalkyl group having 4 to 12 carbon atoms may be exemplified. In addition, the alkyl group may be optionally substituted by one or more substituents.

In the general formulas (1) and (2), an alkoxy group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms may be exemplified. The alkoxy group may be linear, branched or cyclic. In addition, the alkoxy group may be optionally substituted with one or more substituents.

The alkylene group or the alkylidene group in the formulas (1) and (2) may be an alkylene group or an alkylidene group having 1 to 12 carbon atoms, 4 to 10 carbon atoms, or 6 to 9 carbon atoms. The alkylene group or alkylidene group may be linear, branched or cyclic. The alkylene or alkylidene group may be optionally substituted by one or more substituents.

The alkenyl groups in the general formulas (1) and (2) include an alkenyl group having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms or 2 to 4 carbon atoms. The alkenyl group may be linear, branched or cyclic. In addition, the alkenyl group may be optionally substituted with one or more substituents.

Examples of the substituent which may be substituted in the above alkyl group, alkoxy group, alkenyl group, alkylene group or alkylidene group include alkyl group, alkoxy group, alkenyl group, epoxy group, cyano group, carboxyl group, acryloyl group, methacryloyl group, Acryloyloxy group, methacryloyloxy group, aryl group, and the like, but the present invention is not limited thereto.

In the general formulas (1) and (2), P may be an acryloyl group, a methacryloyl group, an acryloyloxy group or a methacryloyloxy group, or an acryloyloxy group or a methacryloyloxy group. In another example, acryloyloxy Time.

The -OQP or the moiety of formula 2 which may be present in at least one of the formulas 1 and 2 may be present, for example, at the position of R ₃ , R ₈ or R ₁₃ , for example, Can exist. Further, substituents other than -OQP or the residue of the formula (2) in the compound of the formula (1) or the residue of the formula (2) include, for example, hydrogen, halogen, a straight or branched alkyl group of 1 to 4 carbon atoms, An alkyl group, a cyano group, an alkoxy group having 1 to 4 carbon atoms, a cyano group or a nitro group, preferably a chlorine, a straight or branched alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 4 to 12 carbon atoms, Or an alkoxy group or a cyano group.

In one example, the CLC layer may comprise a liquid crystal polymer. An exemplary method for producing a CLC layer is a method of coating a composition comprising a polymerizable liquid crystal compound and a polymerizable or non-polymerizable chiral agent, The CLC layer may comprise a polymerized liquid crystal polymer.

In one example, the chiral agent that can be included in the CLC composition is not particularly limited as long as it does not impair liquid crystallinity, such as nematic regularity, and can induce a desired spiral pitch. have. The chiral agent for causing the helical pitch in the liquid crystal needs to include at least the chirality in the molecular structure. Chiral agents include, for example, a compound having one or more asymmetric carbons, a compound having an asymmetric point on a heteroatom such as a chiral amine or a chiral sulfoxide, or a compound having an asymmetric carbon atom such as cumulene ) Or an axially asymmetric (optically active site) having an axial-reducing agent such as binaphthol. The chiral agent may be, for example, a low molecular weight compound having a molecular weight of 1,500 or less. As the chiral agent, a commercially available chiral nematic liquid crystal, for example, a chiral dopant liquid crystal S-811 available from Merck Co., Ltd. or LC756 manufactured by BASF may be used.

The CLC composition may contain the chiral agent in an amount of 1 part by weight to 10 parts by weight based on 100 parts by weight of the compound of the formula (1). By controlling the content of chiral agent as described above, effective twisting of CLC can be induced.

The photoinitiator is used for initiating the polymerization or crosslinking of the compound of formula (1). As long as there is no problem in compatibility with the above compound, general components known in this field can be appropriately selected and used. Examples of the photoinitiator include 2-methyl-1- [4- (methylthio) phenyl] -2- (4-morpholinyl) phenyl-2- (4-morpholinyl) -1-propanone, 2-dimethoxy-1,2-diphenylethan-1- 1-hydroxy-cyclohexyl-phenyl-ketone, triarylsulfonium hexafluoroantimonate salts, and diphenyl (2,4,6-trimethyl Benzoyl) -phosphine oxide (diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide) may be used, but the present invention is not limited thereto. The CLC composition may include 0.1 to 10 parts by weight of the photoinitiator relative to 100 parts by weight of the compound of Formula 1. By controlling the content of the photoinitiator as described above, it is possible to induce effective polymerization and crosslinking of the liquid crystal compound and to prevent deterioration of physical properties due to the residual initiator after polymerization and crosslinking. Unless otherwise specified, the unit weight portion in the present specification may mean the weight ratio of each component.

The CLC composition may further comprise a solvent if desired. Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, tetrachloroethane, trichlorethylene, tetrachlorethylene and chlorobenzene; Aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene; Alcohols such as methanol, ethanol, propanol, isopropanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone; Cellosolve such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; And ethers such as diethylene glycol dimethyl ether (DEGDME) and dipropylene glycol dimethyl ether (DPGDME). The content of the solvent is not particularly limited and may be suitably selected in consideration of coating efficiency, drying efficiency, and the like.

In addition, the CLC composition may further comprise a surfactant. The surfactant is dispersed on the surface of the liquid crystal to make the surface even and stabilizes the liquid crystal alignment so that the surface of the film can be smoothly maintained after the formation of the CLC layer. As a result, the appearance quality can be improved.

As the surfactant, for example, a fluorocarbon surfactant and / or a silicon surfactant may be used. Fluorad FC4430 (TM), Fluorad FC4432 (TM), Fluorad FC4434 (TM) manufactured by 3M Company and Zonyl produced by Dupont Co., Ltd. can be used as the fluorocarbon surfactant, and silicone surfactants BYK 占 manufactured by BYK-Chemie, etc. may be used. The content of the surfactant is not particularly limited and may be suitably selected in consideration of coating efficiency, drying efficiency, and the like.

After the application of the CLC composition as described above, for example, the components of the composition may be polymerized to form a CLC layer in a state where CLC orientation of the liquid crystal compound is induced in the composition.

In one example, the formation of the CLC layer is performed by irradiating a coating layer of the CLC composition with a relatively weak ultraviolet ray to primarily expand the reflection bandwidth, and irradiate ultraviolet light having a relatively strong intensity to the coating layer, So that the reflection bandwidth can be further extended.

In the present specification, the term " reflection bandwidth " may mean a width of a wavelength region representing a reflection characteristic. In one example, when describing the reflection bandwidth by the transmittance according to the wavelength of the optical film, the reflection bandwidth means the width of the wavelength region having a low transmittance. Specifically, the reflection bandwidth is the shortest It can be displayed as the absolute value of the difference between the wavelength and the long wavelength.

For example, the reflection bandwidth can be expressed by the following Formula 1-1.

[Formula 1-1]

λ _max - λ _min

In the above formula,? _Max represents the shortest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less, and? _Min represents the longest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or shorter.

The step of extending the reflection bandwidth with a primary may be carried out with UV light for 5 to 10 seconds at 40 to 60 ℃ the coating layer by irradiation with 100 mJ / cm ² to 500 mJ / cm ^2. The reflection bandwidth of the coating layer of 50 to 60 nm is extended to 100 to 200 nm, for example, 130 to 190 nm by the primary expansion step. In one specific example, a primary expansion step may be performed by irradiating UV light for 7 to 9 seconds at 45 to 55 ℃ to 100 mJ / cm ² to 400 mJ / cm ^2. According to one embodiment of the present invention, the primary expansion step may be performed by irradiating ultraviolet light at 150 mJ / cm ² to 300 mJ / cm ² at 48 to 52 캜 for about 8 seconds. Further, according to one embodiment of the present invention, the ultraviolet light irradiated in the first expansion step may be ultraviolet light within a wavelength range of about 210 nm to 400 nm.

The step of secondarily expanding the reflection bandwidth can be performed by irradiating the application layer with ultraviolet rays at 1000 mJ / cm ² to 2500 mJ / cm ² at 40 to 70 캜 for 5 to 20 seconds. By the secondary expansion step, the reflection bandwidth of the coating layer of 100 to 200 nm is extended to 170 to 250 nm, for example, 190 to 230 nm. A secondary expansion step in the specific examples of can be carried out by irradiation of ultraviolet rays for 8 to 12 seconds from 45 to 60 ℃ to 1300mJ / cm ² to 2200 mJ / cm ^2. Uihamyeo to one embodiment of the invention, the second extension step may be performed by irradiating UV light for about 10 seconds at 45 to 50 ℃ to 1500 mJ / cm ² to 2000 mJ / cm ^2. Also, according to one embodiment of the present invention, the ultraviolet light irradiated in the second expansion step may be ultraviolet light within a wavelength range of about 210 nm to 400 nm.

The optical film having undergone the step of secondarily extending the reflection bandwidth satisfies the condition of the following general formula (1).

[Formula 1]

150 <? _Max -? _Min <250

In the general formula 1,

? _max represents the shortest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less,

lambda _min represents the longest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less.

In one example, the liquid crystal layer having the extended reflection bandwidth can be further photo-cured to increase the degree of curing of the film while maintaining the reflection bandwidth. Through this, the durability of the optical film can be improved. The third photo-curing step may be performed by irradiating ultraviolet rays at 500 mJ / cm ² to 2000 mJ / cm ² at room temperature to 60 ° C for 5 to 20 seconds to the application layer after the second photo-curing step. The third photo-step in one specific example may be performed by irradiation of ultraviolet rays for 8 seconds to 12 seconds at room temperature to 40 ℃ to 800mJ / cm2 to 1700 mJ / cm ^2. According to one embodiment of the present invention, the third photocuring step may be performed by irradiating ultraviolet light at 1000 mJ / cm ² to 1500 mJ / cm ² for about 10 seconds at room temperature. As used herein, the term " ambient temperature " refers to a temperature of natural or unheated or non-warmed state at any temperature within the range of about 15 캜 to 40 캜, such as about 20 캜, about 25 캜, . &Lt; / RTI > Also, according to one embodiment of the present invention, the ultraviolet light irradiated in the third photo-curing step may be ultraviolet light within a wavelength range of about 300 nm to 400 nm.

In one example, the application layer of the CLC composition may be formed on a suitable substrate layer. The substrate layer may be, for example, an optically isotropic or anisotropic substrate layer as described above, or a polarizing element or the like.

In one example, the method for producing an optical film may further include the step of imparting an orientation to the substrate surface before the step of forming the application layer. The surface of the substrate layer on which the coating layer of the CLC composition is formed may be provided with an orientation property. The orientation can be imparted, for example, by using a base layer of a hydrophilic surface as described above, by rubbing or stretching the base layer, or by forming an orientation layer on the surface of the base layer. The effect of forming the wide band CLC layer can be enhanced by giving the surface of the base layer with proper orientation. The manner of forming the alignment layer in the base layer is not particularly limited, and any suitable method known in the art can be used.

In one example, the application layer of the CLC composition is formed on the surface of the substrate layer with a wetting angle of 0 to 50 degrees, 0 to 40 degrees, 0 to 30 degrees, 0 to 20 degrees, or 0 to 10 degrees . As the base layer having such a wetting angle as described above, a substrate layer having been subjected to a suitable hydrophilizing treatment on its surface or a substrate layer having hydrophilic properties from the beginning including a hydrophilic functional group itself may be used. Examples of the hydrophilizing treatment include corona treatment, plasma treatment, alkali treatment, and the like. The treatment conditions are not particularly limited. In this field, various methods for imparting hydrophilicity to the substrate layer are known, and the hydrophilization treatment can be performed by employing the above-described method so that the substrate angle is represented by the wetting angle.

When the CLC layer is formed on the surface of the substrate layer having the wetting angle as described above, a CLC layer including the above described homeotropic or focal-conic CLC regions can be formed.

The present application relates to a method of manufacturing an optical element.

A method of manufacturing an optical element may include forming a quarter wavelength layer on the CLC layer produced by the above manufacturing method. The formation method of the 1/4 wavelength layer is not particularly limited, and the 1/4 wavelength layer can be formed on the CLC layer at an appropriate time during the process.

The formation of the 1/4 wavelength layer in the above can be achieved by, for example, (a) forming an orientation layer on a film or sheet, (b) applying, orienting and polymerizing a polymerizable liquid crystal compound on the orientation layer .

This application relates to an optical film. An exemplary optical film comprises a liquid crystal layer comprising a cholesteric aligned liquid crystal region and satisfies the following general formulas (1) to (3).

[Formula 1]

170 & lt _{;? Max} -? _Min < 250

[Formula 2]

T [(λ _max + λ _min ) / 2]> T [λ _min + (λ _max - λ _min ) / 4]

[Formula 3]

T [(λ _max + λ _min ) / 2]> T [λ _max - (λ _max - λ _min ) / 4]

In the general formulas 1 to 3,

lambda _min represents the longest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less,

T [(λ _max + λ _min ) / 2] represents the transmittance (%) at (λ _max + λ _min ) / 2 wavelength,

T [λ _min + (λ _max - λ _min ) / 4] represents the transmittance (%) at λ _min + (λ _max - λ _min ) / 4 wavelength,

T [λ _max - (λ _max - λ _min ) / 4] represents the transmittance (%) at λ _max - (λ _max - λ _min ) / 4 wavelength.

In one example, λ _max is any wavelength within the range of 650 to 750 nm, specifically 670 to 720 nm, and λ _min is any wavelength within the range of 450 to 550 nm, specifically 470 to 530 nm.

In one example of the _{T [(λ max + λ min} ) / 2] is 55, and to _{65%, T [λ min +} (λ max - λ min) / 4] and _{T [λ max - (λ max} - λ min ) / 4] is 45 to 55%, respectively.

In the optical film produced by the manufacturing method of the present application, the transmittance at an intermediate wavelength (λ _max + λ _min ) / 2 of the reflection band is different from the wavelength at the other wavelength within the reflection bandwidth, for example, the _{λ min + (λ max - λ} min) / 4 of the wavelength λ _max corresponding to 3/4 of the point or reflection bandwidth _{- (λ max - λ min)} / 4 shows a larger transmittance than the unique behavior of the point.

In the optical film, the CLC layer may be a single layer. Herein, the CLC layer may be formed as a single layer by laminating or adhering two or more CLC layers, or may exclude a CLC layer formed by coating the CLC composition a plurality of times.

The CLC layer may include a cholesteric liquid crystal region, and the liquid crystal region may include two or more types of liquid crystal regions having different center wavelengths of reflected light. Referring to FIG. 1, the CLC has a helical structure in which a waveguide (n in FIG. 1) of liquid crystal molecules is layered and aligned along a spiral axis (X in FIG. 1). The distance (P in Fig. 1) until the waveguide of the liquid crystal molecules completes the rotation of 360 degrees in the structure of CLC is called " pitch ". As used herein, the term " liquid crystal region or CLC region " may mean a CLC region in which a CLC waveguide completes a 360 degree rotation. In this specification, each CLC region can be divided, for example, according to the central wavelength of reflected light of each CLC region.

In this specification, the term " thickness direction of the CLC layer " may refer to a direction parallel to a virtual line connecting the one major surface of the CLC layer and the major surface opposite to the major surface. In one example, when the optical film further includes a base layer as described later, and the CLC layer is formed on one side of the base layer, the thickness direction of the CLC layer is such that the CLC layer is formed And may be a direction parallel to an imaginary line formed in a direction perpendicular to the surface of the substrate layer. In this specification, when defining the angle and using terms such as vertical, parallel, orthogonal, or horizontal, it means a substantial vertical, parallel, orthogonal, or horizontal range without impairing the desired effect. For example, it includes an error considering manufacturing error or variation. For example, each of the above cases may include an error within about +/- 15 degrees, an error within about +/- 10 degrees, or an error within about +/- 5 degrees.

2 is a schematic diagram schematically illustrating the CLC layer 2 in which the central wavelength of the reflected light from the main surface 21 side to the other main surface 22 side of the CLC layer 2 is red A CLC region 231 belonging to the category of light, a CLC region 232 belonging to the category of green light and a CLC region 233 belonging to the category of blue light are sequentially arranged.

In one example, the CLC layer comprises a first region having a central wavelength of reflected light of 400 nm to 500 nm, a second region having a central wavelength of reflected light of 500 nm to 600 nm, and a second region having a center wavelength of reflected light of 600 to 700 nm Region. &Lt; / RTI > For example, the first to third regions may be arranged so that the center wavelength of the reflected light of each region sequentially changes along the thickness direction of the CLC layer, but the present invention is not limited thereto. The center wavelength of the reflected light in the CLC region can be measured according to a method known in the art.

In one example, the CLC layer may comprise a CLC region formed such that the helical axis of the waveguide of the liquid crystal molecules is not parallel to the thickness direction of the CLC layer. For example, the CLC layer may include a CLC region in which the helical axis is parallel to the thickness direction and a CLC region in which the helical axis is formed in a direction not parallel to the thickness direction.

The arrangement of the helical axes of the CLC region will be described below with reference to FIG.

Typically, the CLC region comprises a spirally-rotating CLC molecule, and the director of the CLC molecule, for example, the helical axis of the long axis of the CLC molecule, is aligned to be parallel to the thickness direction of the CLC layer. The CLC region is generally oriented such that the helical axis HA of the CLC is parallel to the thickness direction 31 of the CLC layer, as shown in Fig. In FIG. 3, the direction 32 perpendicular to the thickness direction 31 may mean, for example, the plane direction of the base layer as described above. In this specification, the CLC region in which the helical axis is oriented parallel to the thickness direction of the CLC layer as described above may be referred to as a planar oriented CLC region.

The direction of the helical axis of the waveguide of the CLC molecule may be aligned in a direction not parallel to the thickness direction of the CLC layer depending on the orientation condition of the CLC or the surface of the base layer on which the CLC is formed. For example, as shown in FIG. 3B, the helical axis HA of the CLC may be oriented in a direction perpendicular to the thickness direction 31 of the CLC layer, or may be oriented in a direction perpendicular to the thickness direction 31 of the CLC layer, (HA) may be oriented in a direction other than the direction perpendicular and parallel to the thickness direction 31 of the CLC layer. In this specification, the CLC region in which the helical axis is oriented perpendicular to the thickness direction of the CLC layer is referred to as a homeotropic oriented CLC region, and the helical axis is perpendicular and parallel to the thickness direction of the CLC layer The CLC region oriented in a direction other than one direction may be referred to as a focal conic oriented CLC region.

In a CLC layer formed in a conventional manner, the CLC region is oriented with the helical axis parallel to the thickness direction of the CLC layer. However, the CLC layer of the optical film may include a CLC region in which a helical axis is artificially formed in a direction other than the thickness direction of the CLC layer. The CLC region in which the helical axis is formed in a direction other than the direction parallel to the thickness direction of the CLC layer can control the haze characteristics of the optical film.

The amount, position or distribution state in the CLC layer of the homeotropic or focal-conical CLC region or the angle formed by the spiral axis in the thickness direction of the CLC layer in the focal-conic orientation is not particularly limited, Lt; / RTI >

The homeotropic or focal-coked CLC region can be formed, for example, by adjusting the surface characteristics of the surface on which the CLC layer is formed, or by appropriately setting the orientation conditions of the CLC, as described later.

The CLC layer may have a thickness of, for example, 3 占 퐉 to 8 占 퐉 or 4 占 퐉 to 6 占 퐉. By controlling the thickness of the CLC layer to the above range, the wide band CLC layer can be effectively implemented and, if necessary, the above-described homeotropic or focal-conicted CLC region can be effectively formed.

Fig. 4 is a cross-sectional view showing an exemplary optical film 4, which shows a case where the CLC layer 41 as described above is formed on the base material 42. Fig.

The present application relates to optical elements. Wherein the optical element comprises an optical film including the liquid crystal layer; And a 1/4 wavelength layer formed on the liquid crystal layer of the optical film.

As the 1/4 wavelength layer, for example, a polymer film or a liquid crystal film may be used, and it may be a single layer or a multilayer structure. Examples of the polymer film include polyolefins such as polycarbonate (PC), norbonene resin, polyvinyl alcohol (PVA), polystyrene (PS), poly (methyl methacrylate) (poly (arylate), PA (polyamide), PET (poly (ethylene terephthalate)) or PS (polysulfone). The polymer film may be stretched or shrunk under appropriate conditions to impart birefringence and used as the 1/4 wavelength layer.

The 1/4 wavelength layer may be a liquid crystal layer. In one example, the liquid crystal layer as the 1/4 wavelength layer is formed on the surface of the substrate. An alignment layer may be present between the substrate and the liquid crystal layer.

There is no particular limitation on the base material or orientation film of the liquid crystal layer which is the 1/4 wavelength layer or the kind of the liquid crystal which forms the 1/4 wavelength layer. In one example, a substrate of the above-described CLC layer, for example, an optically isotropic substrate, or the like can be used. As the alignment film, for example, a known alignment film such as a photo alignment film or a rubbing alignment film can be used. As the liquid crystal, a suitable material can be used in consideration of the orientation film at the bottom and the desired retardation characteristics. For example, RM (Reactive Mesogen) from Merk or LC242 from BASF can be exemplified.

In one example, the optical film may further comprise a substrate layer, and a CLC layer may be formed on one side of the substrate layer. When the optical film further comprises a base layer and a CLC layer is formed on one side of the base layer, for example, as described above, the center wavelength of the reflected light is reflected on one main surface side of the CLC layer, And a CLC region having a center wavelength of reflected light belonging to the blue light region is arranged on the other main surface side so that the center wavelength of the reflected light of each CLC region sequentially changes along the thickness direction of the CLC layer, A CLC region belonging to the red light region or a CLC region belonging to the blue light region may be disposed on the main surface side of the CLC layer contacting the base layer. In another example, a CLC region having a center wavelength of the reflected light belonging to the red light region may be formed on the main surface side of the CLC layer contacting the base layer.

In one example, in order to form homeotropic or focal-conical oriented CLC regions, the side on which the CLC layer of the substrate layer is formed may be hydrophilic. In one example, the surface on which the CLC layer of the substrate layer is formed has a wetting angle to water of 0 to 50 degrees, 0 to 40 degrees, 0 to 30 degrees, 0 to 20 degrees, or 0 10 degrees to 50 degrees, 20 degrees to 50 degrees, and 30 degrees to 50 degrees. When the CLC layer is formed on the surface of the substrate layer having such a range of the wetting angle, the CLC regions that are homeotropic or focal-conical can be suitably formed. The method of measuring the wetting angle of the substrate layer with respect to water is not particularly limited and a wetting angle measurement method known in the art can be used. For example, by using a DSA100 device manufactured by KRUSS, Can be measured according to the manual.

As the base layer, various types of base layers may be used. In one example, the substrate layer may be an optically anisotropic substrate layer or a polarization element, such as an optically isotropic base layer, a retardation layer, or the like.

As the optically isotropic base layer, a transparent base layer such as a glass or transparent plastic base layer or the like may be used. The plastic substrate layer may be a cellulosic substrate layer such as a DAC (diacetyl cellulose) or TAC (triacetyl cellulose) substrate layer; A cycloolefin copolymer (COP) base layer such as a norbornene derivative resin base layer; An acrylic base layer such as PMMA (poly (methyl methacrylate) base layer, a polycarbonate base layer, an olefin base layer such as a PE (polyethylene) or a polypropylene (PB) base layer, a polyvinyl alcohol ether sulfone base layer, a polyetheretherketone (PEEK) base layer, a polyetherimide (PEI) base layer, a polyethylenenaphthatate (PEN) base layer, a polyester base layer such as a PET (polyethyleneterephtalate) base layer, a polyimide ) Base layer, a PAR (polyarylate) base layer, a fluororesin base layer, etc. The base layer may be, for example, in the form of a sheet or a film.

As the optically anisotropic base layer, for example, the phase retardation layer, for example, a 1/4 wavelength layer or a half wavelength layer or the like may be used. In the present specification, the term " quarter wavelength layer " means a phase delay element capable of phase-delaying incident light by 1/4 of its wavelength, and " half wavelength layer " And can be a phase delay element capable of delaying a phase by 1/2 of the wavelength. The retardation layer may be a liquid crystal polymer layer formed by aligning and polymerizing a polymerizable liquid crystal compound, or may be a plastic film imparted with birefringence by a stretching or shrinking process or the like.

As the polarizing element, a conventional element known in this field can be used. For example, as the polarizing element, an element manufactured by adsorbing and orienting a dichroic dye or the like on a polyvinyl alcohol resin can be used.

The substrate layer may be subjected to various surface treatments such as low reflection treatment, anti-reflection treatment, anti-glare treatment and / or high-resolution anti-glare treatment, if necessary.

The optical film may further include an orientation layer. The term " orientation layer " can refer to a layer exhibiting surface alignment properties that improve or provide alignment uniformity in the process of forming the CLC layer, or produce alignment of the liquid crystal waveguide. The alignment layer may be, for example, a resin film providing a plurality of patterned groove regions, a rubbing treatment film such as a photo alignment layer or rubbed polyimide, or the like. The orientation layer may be formed on the surface of the substrate 42, for example, between the substrate layer 42 and the CLC layer 41, if the optical film comprises a substrate 42 as shown in Fig. As shown in FIG. In some cases, a method of imparting orientation to the substrate layer by simply rubbing or stretching the base layer without imparting a separate orientation layer, or imparting hydrophilicity to the surface may be used. For example, if the base layer has the above-mentioned range of the wetting angle, the base layer may exhibit the property that the orientation of the CLC or the position of the helical axis of the CLC region can be controlled within a desired range without the orientation layer.

The optical element can be implemented in various structures. Figures 5 to 12 show an exemplary structure of the optical element.

In one example, the optical element 5 includes a first base material 54, a 1/4 wavelength layer 53 formed on one surface of the first base material 54, And the CLC layer 52 and the second substrate 51 adhered to the fourth wavelength layer 53. [ In the structure of FIG. 5, the 1/4 wavelength layer 53 may be the liquid crystal layer, and the 1/4 wavelength layer 53 may be formed in contact with the CLC layer 52. The above-described matters may be applied to the first or second base material 51, 54 in the same manner. In the structure of Fig. 5, the above-described homeotropic or focal-conic CLC region is present in the CLC layer 52, or the above-described haze layer is formed on one surface of the first or second substrate 51 or 54 , The haze of the overall film can be controlled.

The exemplary optical element 6 of FIG. 6 is a structure in which a 1/4 wavelength layer 53 and the CLC layer 52 are formed on both sides of one substrate 61. As the substrate 61, the same substrate as the substrate on which the CLC layer or the 1/4 wavelength layer is formed may be used. In the structure of FIG. 6, there is a homeotropic or focal-conic CLC region described above in the CLC layer 52, or the above-described haze layer is formed on one surface of the 1/4 wavelength layer 53 or the CLC layer 52 So that the haze of the entire film can be controlled.

The exemplary optical element 7 in Fig. 7 is a structure in which a CLC layer 52 and a 1/4 wavelength layer 53 are sequentially formed on one base material 71. Fig. As the substrate 71, the same substrate as the substrate on which the CLC layer or the 1/4 wavelength layer is formed can be used. In the structure of FIG. 7, there is a homeotropic or focal-conical CLC region in the CLC layer 52, or the above-described haze layer is formed on the 1/4 wavelength layer 53 or the substrate 71, Can be adjusted.

8 is a structure in which a 1/4 wavelength layer 53 and a CLC layer 52 are sequentially formed on one base material 81. In this case, The same substrate as the substrate 81, the CLC layer, or the substrate on which the 1/4 wavelength layer is formed can be used. In the structure of FIG. 8, there is a homeotropic or focal-conical CLC region in the CLC layer 52, or a haze layer is formed on the CLC layer 52 or the base material 81, Lt; / RTI >

The optical element exemplarily shown in Figs. 5 to 8 may also be integrated with the polarizing element to form an optical element. Usually, the polarizing plate used for an LCD or the like includes a polarizing element such as a polyvinyl alcohol polarizing element, and further includes a protective film formed on one or both surfaces of the polarizing element.

In one example, the protective film of the polarizing plate may be used as a substrate in the structure of the optical element exemplarily shown in Figs. 5 to 8, or the optical element may be implemented as an integral optical element in the manner of attaching the protective film of the polarizing plate This is possible. In the construction of the integral element, the polarizing element can be arranged above the 1/4 wavelength layer. Figs. 9 to 12 show integral optical elements using the structures of the optical elements corresponding to Figs. 5 to 8, respectively. In each case, polarizing elements 91 such as polyvinyl alcohol polarizing elements are included.

The present invention also relates to a liquid crystal display (LCD). An exemplary LCD may include the optical element.

In one example, the LCD may further include a liquid crystal panel and a light source disposed on one side of the liquid crystal panel, and the optical element may be disposed between the liquid crystal panel and the light source. Further, the optical element may be arranged so that the optical film is located closer to the light source than the quarter-wavelength layer.

13, the LCD 13 includes, for example, a liquid crystal panel 132 in which polarizing plates 131 and 133 are disposed on both sides at upper and lower portions, respectively; And a light source 135 disposed below the lower polarizer 133. The optical element 134 may be disposed between the lower polarizer 133 and the light source 135. [ The optical element 134 may include a CLC layer 1342 and a 1/4 wavelength layer 1341 and the CLC layer 1342 may be formed on the light source 135 May be arranged to be closer to each other.

The CLC layer 1342 of the optical element 134 may transmit a part of the light emitted from the light source 135 to the lower polarizer 133 side and reflect the remaining light to the light source 135 side. The light transmitted to the lower polarizer 133 side may be converted into linearly polarized light by the 1/4 wavelength layer 1341 and transmitted to the upper portion. In this case, the light reflected by the CLC layer 1342 is reflected again inside the device, and the polarizing characteristic of the light is changed. Then, the light is incident on the polarizer 134 again.

In one example, when the optical element implements an integral structure with the polarizing element, the polarizing plate 133 and the optical element 134 are disposed in a region where the polarizing plate 133 and the optical element 134 exist in FIG. 13, The optical element of the integral structure may be located instead of the optical element 134.

In this case also, the light emitted from the light source 135 is first incident on the CLC layer in the optical element of the integral structure, partly reflected, and partially transmitted, and the transmitted light passes through the quarter wavelength layer The elements may be arranged so that the polarizing elements sequentially pass through the liquid crystal panel 132 and enter the liquid crystal panel 132.

As long as the LCD includes the optical element, other parts, structures, and the like are not particularly limited, and all contents well known in this field can be appropriately applied.

The present application can provide an optical film exhibiting a reflection characteristic in a wide wavelength range and having excellent durability. Such an optical film can improve the light utilization efficiency of a display device such as an LCD, for example, Can be used as the reflective polarizer.

1 is an exemplary diagram for explaining CLC.
Fig. 2 is an exemplary diagram for explaining the orientation of CLC. Fig.
3 is a diagram illustrating an exemplary arrangement of a CLC region in a CLC layer.
4 is a view showing an exemplary optical film.
5 to 12 are views showing an exemplary optical element.
13 is a diagram showing an exemplary LCD.
14 to 17 are views showing the results of measurement of the transmittance of the embodiment.
18 and 19 are diagrams showing the results of measurement of the transmittance before and after the heat resistance evaluation of the examples and the comparative example.

Hereinafter, the optical film will be specifically described with reference to Examples and Comparative Examples, but the scope of the film is not limited by the following examples.

Manufacturing example One. CLC Preparation of composition (A)

The CLC composition was prepared by mixing RMM856, RMM1520 or RMM1521, a CLC mixture available from Merck, with a solids content of about 40% by weight in a mixed solvent of toluene and xylene (weight ratio = 7: 3 (toluene: xylene) , And then the mixture was heated for about 60 to 1 hour to form a homogeneous solution and then sufficiently cooled.

Example 1. Preparation of reflective optical film

A CLC composition (A) of Production Example 1 was directly coated on one side of PET (poly (ethylene terephthalate), MRL38, Mitsubishi) as a substrate layer and dried at 100 ° C for 2 minutes to form a coating layer . Then, ultraviolet rays having a wavelength of about 210 nm to 400 nm were irradiated to the coating layer dried at a temperature of about 60 ° C. at about 48 to 52 ° C. for about 8 seconds to about 150 to 300 nm by ultraviolet irradiation equipment (TLK40W / 10R, Philips) mJ / cm < ² > for the first photo-curing. The coated layer after the first photo-curing step is then irradiated with ultraviolet light having a wavelength of about 210 nm to about 400 nm at about 45 to 50 DEG C for about 10 seconds to an intensity of about 1500 to 2000 mJ / cm ² And the second photo-curing was performed. Then, the coated layer after the second photo-curing step was irradiated with ultraviolet rays having a wavelength of about 300 nm to 400 nm at room temperature for about 10 seconds using the apparatus at the intensity of about 1000 to 1500 mJ / cm ² , Photo-curing was performed.

Comparative Example One.

The optical film of Comparative Example 1 was prepared in the same manner as in Example 1, except that the third photo-curing step was not performed after the second photo-curing.

Test Example 1. Evaluation of transmittance according to wavelength

Transmission ratios of the optical films of Example 1 and Comparative Example 1 were measured according to wavelength using an Axo Scan apparatus, and the results are shown in Figs. 14 to 17. Fig. Figs. 14 to 17 show transmittance graphs according to wavelengths immediately after coating each of the optical films of Example 1, after the first photo-curing step, the second photo-curing step and the third photo-curing step. 16 is the same as the graph of the transmittance according to the wavelength of the optical film of Comparative Example 1. Fig.

Test Example 2. Evaluation of heat resistance

The optical films of Example 1 and Comparative Example 1 were allowed to stand at 80 DEG C for 100 hours, and a transmittance graph corresponding to the wavelength was measured using an Axo Scan apparatus. The results are shown in Fig. 18 (Example 1) and Fig. 19 1). In Example 1, there was almost no change in the transmittance graph according to the wavelengths before and after the heat resistance evaluation (a) and (b), but in Comparative Example 1, It can be confirmed that it moves about 20 nm towards the long wavelength side.

n: CLC waveguide
P: pitch
X, HA: Helical axis
21: thickness direction of the liquid crystal layer
22: direction perpendicular to the thickness direction of the liquid crystal layer
2: CLC layer 21, 22: main surface of CLC layer
231, 232, 233: CLC area
4: Optical film
41, 51, 54, 61, 71, 81: substrate 42: CLC layer
5, 6, 7, 8, 9, 10, 11, 12:
52, 1342: CLC layer
53, 1341: 1/4 wavelength layer 91: polarizing element
13: LCD
131, 133: polarizing plate 132: liquid crystal panel
134: reflective polarizer
135: Light source

Claims

Forming a coating layer comprising a cholesteric liquid crystal composition on a substrate;
A first photocuring step of irradiating the coating layer with ultraviolet rays at 100 mJ / cm ² to 500 mJ / cm ² at 40 to 60 ° C for 5 to 10 seconds; And
And a second photo-curing step of irradiating ultraviolet rays at 1000 mJ / cm ² to 2500 mJ / cm ² at 40 to 70 ° C for 5 to 20 seconds to the application layer after the first photo-curing step,
A method for producing an optical film comprising a liquid crystal layer comprising a cholesteric aligned liquid crystal region satisfying the following general formula:
[Formula 1]
170 & lt _{;? Max} -? _Min < 250
In the general formula 1,
? _max represents the shortest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less,
lambda _min represents the longest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less.

The method according to claim 1,
Wherein the cholesteric liquid crystal composition comprises a polymerizable mesogenic compound, a chiral agent, and a photoinitiator.

The method according to claim 1,
Wherein the cholesteric liquid crystal composition further comprises a solvent or a surfactant.

3. The method of claim 2,
Wherein the polymerizable mesogen compound is a compound represented by the following formula (1): < EMI ID =
[Chemical Formula 1]

In Formula 1,
A is a single bond, -COO- or -OCO-,
Wherein R ₁ to R ₁₀ are each independently selected from the group consisting of hydrogen, a halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group, -OQP or a substituent of the following general formula (2), at least one of R ₁ to R ₁₀ is -OQP, Lt; / RTI >
Wherein Q represents an alkylene group or an alkylidene group, and P represents an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group or a methacryloyloxy group,
(2)

In the formula (2)
B is a single bond, -COO- or -OCO-,
R ₁₁ to R ₁₅ each independently represent hydrogen, halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group or -OQP, provided that at least one of R ₁₁ to R ₁₅ is -OQP,
Wherein Q is an alkylene group or an alkylidene group, and P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group or a methacryloyloxy group.

The method according to claim 1,
Further comprising the step of imparting an orientation property to the substrate surface before the step of forming the coating layer.

The method according to claim 1,
Further comprising the step of surface treating the substrate so that the wetting angle of the substrate surface is 0 to 50 degrees before the step of forming the application layer.

The method according to claim 1,
And a third photo-curing step of irradiating ultraviolet rays at 500 mJ / cm ² to 2000 mJ / cm ² at room temperature to 60 ° C for 5 to 20 seconds to the application layer after the second photo-curing step Way.

A method for manufacturing an optical element, comprising the steps of: forming a 1/4 wavelength layer on a liquid crystal layer of an optical film manufactured by the manufacturing method of claim 1;

An optical film comprising a liquid crystal layer that satisfies the following general formulas 1 to 3 and includes a cholesteric aligned liquid crystal region:
[Formula 1]
170 & lt _{;? Max} -? _Min < 250
[Formula 2]
T [(λ _max + λ _min ) / 2]> T [λ _min + (λ _max - λ _min ) / 4]
[Formula 3]
T [(λ _max + λ _min ) / 2]> T [λ _max - (λ _max - λ _min ) / 4]
In the general formulas 1 to 3,
? _max represents the shortest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less,
lambda _min represents the longest wavelength (nm) at which the transmittance becomes 60% at a wavelength of 800 nm or less,
T [(λ _max + λ _min ) / 2] represents the transmittance (%) at (λ _max + λ _min ) / 2 wavelength,
T [λ _min + (λ _max - λ _min ) / 4] represents the transmittance (%) at λ _min + (λ _max - λ _min ) / 4 wavelength,
T [λ _max - (λ _max - λ _min ) / 4] represents the transmittance (%) at λ _max - (λ _max - λ _min ) / 4 wavelength.

10. The method of claim 9,
? _max is 650 to 750 nm, and? _min is 450 to 550 nm.

10. The method of claim 9,
T [(? _Max +? _Min ) / 2] is 55 to 65%
Wherein T [? _Min + (? _Max -? _Min ) / 4] and T [? _Max - (? _Max -? _Min ) / 4] are 45 to 55%.

An optical film according to claim 9; And a 1/4 wavelength layer formed on the liquid crystal layer of the optical film.

13. The method of claim 12,
The optical film comprises a substrate; An orientation film formed on the substrate, and a liquid crystal layer formed on the alignment film, wherein the 1/4 wavelength layer is in contact with the liquid crystal layer.

13. The method of claim 12,
An optical element further comprising a polarizing element disposed on top of the 1/4 wavelength layer.

13. A liquid crystal display device comprising the optical element of claim 12.

16. The method of claim 15,
A liquid crystal display device comprising: a liquid crystal panel; and a light source disposed on one side of the liquid crystal panel, wherein an optical element is disposed between the liquid crystal panel and the light source.

17. The method of claim 16,
Wherein the optical element is disposed so that the light source is located closer to the 1/4 wavelength layer than the optical film.