KR20150037649A - Optical film - Google Patents

Abstract

The present invention relates to an optical film and a use thereof. In the present invention, a liquid crystal layer has reverse wavelength dispersibility even having a single layer and the low thickness through control of orientation state of a liquid crystal compound in the liquid crystal layer. An optical film including the liquid crystal layer can be used variously such as forming an optical device or three dimensional image which has optical modulation properties or improves light use efficiency in a display device such as liquid crystal display (LCD) or an organic light emitting device (OLED), and device for improving the quality.

Description

Optical film {Optical film}

The present invention relates to an optical film, an optical laminate, and a display device.

Films exhibiting optically anisotropic properties can be used for various applications. Such a film can be used, for example, for the purpose of adjusting optical characteristics of an LCD (Liquid Crystal Display), improving light utilization efficiency, or preventing reflection and visibility in an OLED (Organic Light Emitting Device). In addition, the film may be used to generate a stereoscopic image or to improve the quality of the stereoscopic image.

Patent Document 1: JP-A-1996-321381

The present application provides an optical film, an optical laminate, and a display device. It is an object of the present invention to provide an optical film having a so-called reverse wavelength dispersion characteristic while being a single layer by controlling the arrangement of liquid crystal compounds in the liquid crystal layer in an optical film including a liquid crystal layer.

This application relates to an optical film. An exemplary optical film may comprise a liquid crystal layer. The liquid crystal layer may include a twisted nematic liquid crystal compound, and the liquid crystal compound may be polymerized to form a liquid crystal layer in a state in which the liquid crystal compound is oriented as described above. Hereinafter, in this specification, a twist-oriented nematic liquid crystal compound is abbreviated as TN, and a liquid crystal layer containing TN is referred to as a TN layer.

TN is similar to a so-called cholesteric liquid crystal layer (CLC) in that an optical axis of a nematic liquid crystal compound has a helical structure in which layers are formed while being twisted along a virtual helix axis, It differs from CLC in that the twist angle is less than 360 degrees. In the above, the optical axis of the liquid crystal compound may mean the long axis direction of the liquid crystal compound. Due to this difference with the CLC of TN, the thickness of the TN layer is less than the pitch. In the above, the term pitch refers to the distance TN is required to complete 360 degrees of rotation.

To explain the alignment pattern of the TN, the alignment pattern of the CLC will first be described with reference to FIG.

Referring to FIG. 1, the CLC has a helical structure in which the optical axis direction (n in FIG. 1) of the liquid crystal compound is layered and aligned along a spiral axis (X in FIG. 1). In the above, the spiral axis is an imaginary line determined according to CLC. The distance (P in Fig. 1) until the optical axis of the liquid crystal compound completes the rotation of 360 degrees in the structure of CLC is referred to as " pitch ".

In the case of TN, the orientation form is similar to the CLC described above, but the liquid crystal compound has a rotation angle of less than 360 degrees because the thickness of the liquid crystal layer is less than the above pitch (P in FIG. 1).

The TN twist angle in the TN layer is May range from 50 degrees to 300 degrees. The twist angle of the term TN in the present application is the angle formed by the optical axis of the liquid crystal compound existing at the bottom of the TN layer and the optical axis of the liquid crystal compound located at the top of the TN layer. The term top or bottom of the term TN layer in this application is a concept for determining the relative positional relationship. That is, when one surface of the TN layer is referred to as a lower portion, the opposite surface may be defined as an upper portion, and the surface defined as the lower portion does not necessarily have to be underneath when the TN layer is applied. The twist angle may be greater than 60 degrees, greater than 70 degrees, or greater than 75 degrees in other examples. The twist angle may also be less than or equal to 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 190 Less than 180 degrees, less than 170 degrees, less than 160 degrees, less than 150 degrees, less than 140 degrees, less than 130 degrees, less than 120 degrees, or less than 110 degrees.

The twist angle may be appropriately changed to suit the application of the optical film.

In the present application, the orientation of the TN layer can be further adjusted in order to secure a desired effect. That is, the change in the angle of rotation of the liquid crystal compound rotating along the helical axis in the TN layer, that is, the angle of the optical axis of the liquid crystal compound with respect to the optical axis of the lowermost liquid crystal compound in the TN layer, may be non-linear. By such an orientation, a liquid crystal layer having the object described later, that is, a so-called reverse wavelength dispersion characteristic can be formed.

For example, when the change in thickness from the lower portion to the upper portion of the TN layer is defined as x-axis, and the angle formed by the optical axis direction of the liquid crystal compound present in the thickness with the optical axis direction of the liquid crystal compound existing at the lowermost portion of the TN layer is defined as y The graph plotted as an axis may be a nonlinear graph. Referring to FIG. 2, if the graph is linear (201 in FIG. 2), that is, when the change in the rotation angle of the liquid crystal compound occurs constantly, the desired effect may not be easily secured. On the other hand, when the graph is non-linear (for example, 202 in FIG. 2), that is, when the change in the rotation angle of the liquid crystal compound occurs unevenly, the desired effect can be secured. The non-linear graph type TN layer can be manufactured by controlling the twisting powder of the nematic liquid crystal compound to vary in thickness during the manufacturing process, and this can be performed by adjusting the concentration of the chiral agent as described below .

In order to achieve the desired properties more effectively, in the graph of the TN layer of the present application, the slope of the graph includes a portion that increases together as the thickness of the TN layer increases (i.e., as the x-axis value of the graph increases) As shown in Fig.

The TN layer of the present application exhibits a so-called reverse wavelength dispersion according to the specific orientation as described above. The reverse wavelength dispersion characteristic in the present application may mean a state satisfying the following expression (1).

 [Equation 1]

R (550) / R (550)> R (450) / R (550)

R (550) is a phase difference of the liquid crystal layer with respect to light having a wavelength of 550 nm, and R (450) is a phase difference of 450 (nm) plane retardation of the liquid crystal layer with respect to light having a wavelength of 10 nm.

The phase retardation for each wavelength in the above can be determined according to the following equation (2).

[Equation 2]

R (?) = D x (Nx - Ny)

In the formula (2), R (?) Is the phase difference of the TN layer with respect to the light having a wavelength of? Nm, d is the thickness of the TN layer, and Nx is the refractive index in the slow axis direction of the TN layer, Ny is the refractive index for light in the fast phase axis direction of the TN layer, that is, in the direction perpendicular to the slow axis on the plane, with respect to light having a wavelength of? Nm.

The specific range of R (450) / R (550) and R (650) / R (550) in the formula 1 is not particularly limited. In one example, R (450) / R (550) in the formula 1 is from 0.81 to 0.99, 0.82 to 0.98, 0.83 to 0.97, 0.84 to 0.96, 0.85 to 0.95, 0.86 to 0.94, 0.87 to 0.93, 0.88 to 0.92 May be in the range of 0.89 to 0.91. Further, it is preferable that R (650) / R (550) is within the range of 1.01 to 1.19, 1.02 to 1.18, 1.03 to 1.17, 1.04 to 1.16, 1.05 to 1.15, 1.06 to 1.14, 1.07 to 1.13, 1.08 to 1.12, Can be. In this range, desired reverse wavelength dispersion characteristics can appropriately be secured.

The TN layer of the optical film may have quarter-wave or half-wave phase retardation characteristics. The term " n-wavelength phase delay characteristic " in this specification can mean a characteristic that, within at least a part of the wavelength range, the incident light can be phase-delayed by n times the wavelength of the incident light. When the TN layer has a quarter-wave retardation, the phase retardation of the TN layer with respect to light having a wavelength of 550 nm may be about 110 nm to 220 nm or 140 nm to 170 nm. Further, if the TN layer has half-wave retardation, the phase retardation of the TN layer for light of a wavelength of 550 nm may be in the range of 240 nm to 350 nm or 250 nm to 340 nm.

In the exemplary optical film, the helical axis of the TN layer may be formed to be parallel to the thickness direction of the TN layer. The term thickness direction of the TN layer may refer to a direction parallel to an imaginary line connecting the lowermost portion and the uppermost portion of the TN layer at the shortest distance. In one example, when the optical film further includes a base layer as described later, and the TN layer is formed on one surface of the base layer, the thickness direction of the TN layer is such that the TN 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.

The TN layer may have a thickness in the range of, for example, 0.1 탆 to 10 탆. The other lower limit of the thickness may be 0.5, 1, or 1.5 microns, and the other upper limits may be 9, 8, 7, 6, 5, or 4 microns. By controlling the thickness of the TN layer to the above range, it is possible to optically control the retardation dispersion characteristics.

In one example, the TN layer may comprise a liquid crystal polymer. Exemplary methods for producing a TN layer include coating a composition comprising a polymerizable liquid crystal compound and a polymerizable or non-polymerizable chiral agent, and bringing the liquid composition into contact with the composition . In this case, the TN layer may include a polymerized liquid crystal polymer.

One exemplary TN layer may include a compound represented by the following formula (1) in a polymerized form.

 [Chemical Formula 1]

In Formula 1 A is a single bond, -COO- or -OCO-, R ₁ to R ₁₀ are each independently hydrogen, halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group, or a -OQP chihwangiyi of formula (II) Wherein at least one of R ₁ to R ₁₀ is -OQP or a substituent of the following formula 2, Q is an alkylene group or an alkylidene group, P is an alkenyl group, an epoxy group, a cyano group, a carboxyl group, , A methacryloyl group, an acryloyloxy group, or a methacryloyloxy group.

(2)

R ₁₁ to R ₁₅ are each independently hydrogen, a halogen, an alkyl group, an alkoxy group, a cyano group, a nitro group or -OQP, R ₁₁ to R ₁₅ is -OQP, 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 meta Lt; / RTI >

"는 B가 화학식 1의 벤젠에 직접 연결되는 것을 의미한다.In the formula (2), "

Means that B is directly linked to the benzene of formula (1).

The term "single bond" in formulas (1) and (2) means a case where no separate atom is present at the portion 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.

Examples of the alkylene group or the alkylidene group in the formulas (1) and (2) include 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.

As the alkenyl groups in the formulas (1) and (2), 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 may be exemplified. 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 group .

The -OQP or the moiety of formula 2 which may be present in at least one of the formulas 1 and 2 may for example be present at the position of R ₃ , R ₈ or R ₁₃ , for example 1 or 2 above 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.

The chiral agent that can be included in the liquid crystal layer is not particularly limited as long as it can induce the desired rotation without deteriorating the liquid crystallinity, for example, the nematic regularity. The chiral agent for inducing rotation 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

In one example, the optical film may further comprise a base layer, and a TN layer may be formed on one side of the base layer.

As the base layer, a transparent base layer such as a glass or transparent plastic base layer 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.

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 alignment layer may refer to a layer exhibiting surface alignment properties that improve or provide alignment uniformity in the process of forming the liquid crystal 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 alignment layer 102 may be formed on the surface of the base layer 101, for example, the base layer 101 when the optical film 100 includes the base layer 101 as shown in Fig. And the TN layer 103, 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 a property capable of controlling the TN to the intended range without the orientation layer.

The present application also relates to a method for producing such an optical film. The production method includes, for example, a step of inducing a change in concentration of the chiral agent to a liquid crystal coating layer containing a nematic liquid crystal compound, a chiral agent and a polymerization initiator according to the thickness of the coating layer, And then polymerizing the nematic liquid crystal compound.

The liquid crystal coating layer can be formed by coating a nematic liquid crystal compound, for example, a coating liquid (TN composition) containing the compound of Formula 1 and a chiral agent together with a polymerization initiator.

The TN composition typically may be part of a coating composition comprising at least one solvent. The coating composition may optionally comprise additional components such as, 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 TN composition can be applied by various liquid coating methods. In some embodiments, after coating, the TN composition is polymerized or converted into a TN layer. This conversion can be accomplished by evaporation of the solvent, heating to align the TN material; Crosslinking the TN 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 TN composition using a similar technique.

In one example, the TN composition may comprise the compound of Formula 1, a polymerization initiator, and a chiral agent.

As the polymerization initiator, for example, a radical initiator that generates a radical by heat or light may be used. Such a radical initiator is for initiating polymerization or crosslinking of a nematic liquid crystal compound, and as long as compatibility with the above compound is not problematic, general components known in this field can be appropriately selected and used. As the radical initiator, for example, 2-methyl-1- [4- (methylthio) phenyl] -2- (4-morpholinyl) 2-dimethoxy-1,2-diphenylethan-1-one), 2- 1-hydroxy-cyclohexyl-phenyl-ketone, triarylsulfonium hexafluoroantimonate salts, and diphenyl (2,4,6- (Diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide), and the like, but not limited thereto. The TN composition may contain the radical initiator in a ratio of 0.1 part by weight to 10 parts by weight based on 100 parts by weight of the liquid crystal compound. By controlling the content of the radical initiator as described above, it is possible to induce effective polymerization and crosslinking of the liquid crystal compound, and prevent deterioration of physical properties by 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.

As the chiral agent, for example, a compound of the above-described kind may be used. The TN composition may contain the chiral agent in a ratio of 0.1 part by weight to 10 parts by weight based on 100 parts by weight of the liquid crystal compound. By controlling the content of the chiral agent as described above, it is possible to induce the concentration gradient of the effective chiral agent and to polymerize the liquid crystal compound.

The TN 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 TN composition may further comprise a surfactant. The surfactant is distributed 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 TN 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. Fluorine surfactants of the carbon-based fluoro product manufactured by 3M rod (Fluorad) FC4430 ^{TM-fluoro-Rad TM} FC4432 fluoro-Rad ^TM and FC4434 Zonyl manufactured by Dupont Co., Ltd., and the silicone surfactant may be BYK-Chemie manufactured by BYK ^TM Back Can 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 TN composition is applied to form a liquid crystal coating layer, for example, a TN layer can be formed by polymerizing a liquid crystal compound in a state in which a concentration gradient of a chiral agent is induced.

In one example, the TN layer is formed by irradiating the application layer of the TN composition with a relatively weak ultraviolet ray to form a concentration gradient of the chiral agent, and irradiating the coating layer on which the concentration gradient is formed with relatively strong ultraviolet rays, To < / RTI >

When irradiating the coating layer of the TN composition with a relatively weak intensity of ultraviolet light at a predetermined temperature, it is possible to induce a concentration gradient of the chiral agent in the coating layer, that is, a change in the concentration of the chiral agent along the predetermined direction in the coating layer . In one example, the concentration gradient of the chiral agent may be formed along the thickness direction of the coating layer. The irradiation of ultraviolet rays having a concentration gradient of chiral agent can be performed at a temperature range of, for example, 40 캜 to 80 캜, 50 캜 to 70 캜 or about 60 캜. The irradiation of ultraviolet rays for formation of the concentration gradient may be performed by irradiating ultraviolet rays of the wavelength of the A region at a dose of about 10 mJ / cm ² to 500 mJ / cm ² . For the formation of a more efficient gradient of the light quantity is about 50 mJ / cm ² to 400 mJ / cm ^2, from about 50 mJ / cm ² to 300 mJ / cm ^2, from about 50 mJ / cm ² to 200 mJ / cm ^2, About 50 mJ / cm ² to about 150 mJ / cm ^2, or about 75 mJ / cm ² to about 125 mJ / cm ² .

After forming the concentration gradient, the TN layer can be formed by irradiating with an ultraviolet ray in an amount sufficient to polymerize the components of the composition. By the ultraviolet irradiation, the coating layer can be fixed with different pitches according to the concentration gradient of the chiral agent to form the TN region. The conditions of the irradiation of the strong ultraviolet ray are not particularly limited as long as the polymerization of the components of the composition is sufficiently carried out. In one example, irradiation of the ultraviolet ray can be performed by irradiating with a light amount of about 0.5 J / cm ² to 10 J / cm ² . The wavelength of the ultraviolet ray to be irradiated at this time is not particularly limited as long as sufficient polymerization can take place. For example, light in the ultraviolet region A to V region can be irradiated.

In one example, a coating layer of the TN composition may be formed on a suitable substrate layer.

In one example, the application layer of the TN composition may be formed on the orientation layer formed on the base layer.

The orientation layer may be formed by, for example, forming a polymer film such as polyimide on a base layer and performing rubbing treatment, coating a photo-aligning compound, performing orientation treatment through irradiation of linearly polarized light, or imprinting such as a nanoimprinting method Can be formed.

The optical film including the TN layer as described above may be applied to various applications on its own or in combination with other elements.

This application is directed to an optical laminate comprising the optical film and other elements.

Such an optical laminate can be applied, for example, to an LCD, an OLED, or the like, or can be applied to realization of a stereoscopic image or improvement of its quality.

In one example, the optical laminate may include a retardation film as the other element. As the retardation film, various elements can be selected depending on the application without any particular limitation. As the retardation film, for example, an A plate known as HWP (Half Wave Plate) or QWP (Quarter Wave Plate) can be used. The retardation film may be a polymer film imparted with a retardation by stretching or the like, or may be a liquid crystal film.

In the case where the optical laminate includes the optical film and the retardation film, the optical axis of the liquid crystal of the TN layer of the optical film and the retardation axis of the retardation film may be variously set depending on the application.

For example, the angle formed by the optical axes of the nematic liquid crystal compound located nearest to the retardation film in the slow axis of the retardation film and the retardation film in the TN layer is about 5 to 90 degrees or about 10 to 70 degrees Lt; / RTI >

In one example, the optical stack may further comprise a polarizing layer.

Such an optical laminate can sequentially include, for example, a polarizing layer 401, a retardation film 402 and an optical film 403 as shown in Fig.

In the above structure, the angle formed by the light absorption axis of the polarizing layer 401 and the slow axis of the retardation film 402 may be in a range of 10 degrees to 20 degrees. The angle formed by the optical axis of the nematic liquid crystal compound located nearest to the retardation film in the TN layer of the optical film 403 and the slow axis of the retardation film 402 may be in a range of 8 degrees to 16 degrees . In such a structure, the twist angle of the TN layer may be in the range of 36 degrees to 50 degrees. The optical laminate having such a structure can be applied to various applications, and can be used, for example, as an antireflective polarizing plate of an OLED.

In another example, the optical laminate may include the polarizing layer 401, the optical film 403, and the retardation film 402 sequentially arranged as shown in Fig.

In this relationship, the light absorption axis of the polarizing layer 401 and the slow axis of the retardation film 402 may be perpendicular or horizontal to each other.

When the slow axis of the retardation film 402 and the light absorption axis of the polarizing layer 401 are perpendicular to each other, the optical axis of the liquid crystal compound closest to the retardation film in the TN layer of the optical film 403 is perpendicular to the retardation film 402 may be in a range of about 50 degrees to about 70 degrees or about 55 degrees to about 67 degrees. Also, in this case, the twist angle of the TN layer may be in the range of about 10 degrees to about 30 degrees.

When the slow axis of the retardation film 402 and the light absorption axis of the polarizing layer 401 are horizontal, the optical axis of the liquid crystal compound closest to the retardation film in the TN layer of the optical film 403 is the retardation The angle formed with the slow axis of the film 402 may be in the range of about 15 degrees to about 35 degrees or about 17 degrees to about 32 degrees. Also, in this case, the twist angle of the TN layer may be in the range of about 60 degrees to about 85 degrees. The optical laminate having such a structure can be applied to various applications, and can be used, for example, as an antireflective polarizing plate of an OLED.

In another example, the optical stack may include a polarizing layer as the other element. In this case, the absorption type polarizing layer or the reflection type polarizing layer may be applied as the polarizing layer. The type of the absorption or reflection type polarizing layer that can be used in the above is not particularly limited. For example, a known polarizing layer of PVA (polyvinyl alcohol) film type can be used as the absorption type polarizing layer, and a reflective polarizing layer made of LLC (Lyotropic Liquid Crystal) or CLC (Cholesteric Liquid Crystal) , A so-called DBEF (Dual Brightness Enhancement Film) or a WGP (Wire Grid Polarizer).

6 is a cross-sectional view of an exemplary optical laminate and shows a case including the polarizing layer 601 and the optical film 602 disposed on one side of the polarizing layer 601. [ The polarizing layer 601 may be a reflective or absorptive polarizing layer as described above.

When the polarizing layer is included, the angle formed between the optical axis of the liquid crystal compound closest to the polarizing layer in the TN layer and the optical absorption axis or the optical reflection axis of the polarizing layer in the optical film is in the range of 5 to 15 degrees , And may be in the range of 95 degrees to 105 degrees. Further, the twist angle of the TN layer in the above may be in the range of 80 to 110 degrees.

In another example, the optical laminate may include an absorption type polarization layer and a reflection type polarization layer at the same time. 7 shows an exemplary structure of the optical laminate, in which the absorption type polarizing layer 6011, the reflection type polarizing layer 6012 and the optical film 602 are sequentially arranged. The absorption type polarizing layer 6011 may be arranged adjacent to the optical film 602 in comparison with the reflection type polarizing layer 6012, unlike the structure shown in Fig.

In such a case, the light absorption axis of the absorption type polarizing layer and the light reflection axis of the reflection type polarizing plate may be parallel to each other. In this case, the angle formed by the optical axis of the liquid crystal compound closest to the absorptive or reflective polarizing layer in the TN layer and the optical absorption axis or the optical reflection axis of the polarizing layer may be in the range of 5 degrees to 15 degrees, May be within a range of degrees. Further, the twist angle of the TN layer in the above may be in the range of 80 to 100 degrees.

The optical laminate having such a structure can be used, for example, as an antireflection film in an OLED or a reflective LCD, or as a brightness enhancement film in an LCD.

The optical laminate may be obtained by laminating the optical film of the present invention and the polarizing layer or the retardation film with an adhesive or an adhesive, or by directly coating the TN composition on the polarizing layer or the retardation film to form a coating layer Followed by polymerization.

The present application also relates to a display device. An exemplary display device may include the optical film or the optical laminate.

The specific kind of the display device including the optical laminate is not particularly limited. The apparatus may be, for example, an LCD or an OLED.

The arrangement form of the optical film or optical laminate in the display device is not particularly limited, and for example, a known form can be employed. For example, in such an apparatus, when the optical film or the optical laminate is changed for optical characteristics or applied for anti-reflection effect, the above may be disposed on the front surface of the display device or adjacent to the reflective electrode layer of the OLED. Further, when the optical film or the optical laminate is applied to a brightness enhancement film in an LCD or the like, the optical film or the optical laminate may be positioned between the display panel and the light source.

In the present application, it is possible to control the alignment state of the liquid crystal compound in the liquid crystal layer so that the liquid crystal layer exhibits a so-called reverse wavelength dispersion characteristic even at a thin thickness. The optical film including such a liquid crystal layer may exhibit optical modulation characteristics in a display device such as an LCD (Liquid Crystal Display) or OLED (Organic Light Emitting Device), or an optical element or stereoscopic image Or an element for improving the quality thereof.

1 is a conceptual diagram for explaining the orientation of a liquid crystal compound.
Fig. 2 is a conceptual graph for explaining the orientation of the liquid crystal compound.
3 is an exemplary cross-sectional view of an optical film.
Figs. 4 to 7 are views showing various structures of the optical laminate. Fig.
Fig. 8 is a chart comparing the wavelength dispersion characteristics of Examples and Comparative Examples. Fig.

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 . Preparation of liquid crystal composition

A liquid crystal composition was prepared in the following manner. RM1230 and RM1231, which are RM (Reactive Mesogen), which are commonly known to be used in the production of CLC (Choresteric Liquid Crystal), are mixed in a weight ratio of 1: 1 and mixed in a mixed solvent of toluene and cyclohexanone (Weight ratio = 7: 3 (toluene: cyclohexanone)) were mixed so as to have a solid content of about 40% by weight. Then, a photopolymerization initiator (Irgacure 907) having a maximum absorption wavelength in the range of 280 nm to 320 nm as the radical initiator was blended at a ratio of 3% by weight of the solid content of RM, and the maximum absorption wavelength was 360 nm to 400 nm (Darocure TPO) was added in a proportion of 0.4% by weight of the solid content of RM. Thereafter, the mixture was heated at a temperature of about 60 DEG C for about 1 hour and sufficiently cooled to prepare a homogeneous solution.

Example  One.

After forming a known rubbing alignment film on one surface of a PET (poly (ethylene terephthalate)) film, the liquid crystal composition prepared above is placed on the alignment film. 6, and dried at 100 DEG C for about 2 minutes. Then, the coating layer was irradiated with ultraviolet light having a wavelength in the range of 350 nm to 400 nm at a temperature of about 60 캜 at an amount of about 100 mJ / cm ² using an ultraviolet irradiation equipment (TLK40W / 10R, manufactured by Philips) A concentration gradient of < RTI ID = 0.0 > Thereafter, a strong ultraviolet ray was irradiated at a light quantity of 1 mJ / cm ² or more so that the polymerization of RM could be sufficiently performed with an ultraviolet irradiation equipment (Fusion UV, 400 W) on the coating layer in which the concentration gradient was induced, . As a result of the optical polarizing microscope (manufactured by Leica), the twist angle of the TN layer was about 90 degrees, showing nonlinear characteristics as shown by 202 in FIG.

Comparative Example  One.

The process of irradiating the coating layer with ultraviolet light having a wavelength in the range of 350 nm to 400 nm at a temperature of about 60 캜 at an amount of about 100 mJ / cm ² by using an ultraviolet irradiation equipment (TLK40W / 10R, manufactured by Philips) is omitted Except that a strong ultraviolet ray was irradiated at a light quantity of 1 mJ / cm ² or more to form a liquid crystal layer having a thickness of about 3 탆 so that polymerization of RM with the ultraviolet irradiation equipment (Fusion UV, 400 W) A liquid crystal layer was formed in the same manner as in Example 1. As a result of checking with an optical polarizing microscope (manufactured by Leica), the twist angle of the TN layer was about 90 degrees and showed a linear characteristic as shown by 201 in FIG.

Property evaluation

The wavelength dispersion characteristics of the liquid crystal layers of the liquid crystal films prepared in Examples and Comparative Examples were confirmed using Axoscan (Axometrics) equipment. The results are shown in FIG. As shown in Fig. 8, the optical films of Examples and Comparative Examples have the same twist angle, but Example 1, which exhibits nonlinear graph characteristics through derivation of a concentration gradient of chiral agent, achieves the so-called reverse wavelength dispersion characteristic, It can be confirmed that the film has a constant wavelength characteristic. In addition, it can be seen that the optical film of Example 1 is applied to various applications requiring a 1/4 wavelength plate or a 1/2 wavelength plate through the reverse wavelength dispersion characteristic, and can exhibit excellent characteristics.

101: substrate layer
102: orientation layer
103: TN layer
201: Linear graph
202: Nonlinear Graph
401, 601: Polarizing layer
402: retardation film
403, 602: optical film
6011: absorption type polarizing layer
6022: reflection type polarizing layer

Claims (20)

A liquid crystal layer comprising cholesteric aligned nematic liquid crystal compounds and having a thickness less than the pitch of the cholesteric aligned nematic liquid crystal compound and having a twist angle in a range of 50 to 300 degrees, An optical film satisfying the following formula (1); And
An optical laminate comprising a polarizing layer disposed on one side of the optical film;
[Equation 1]
R (550) / R (550)> R (450) / R (550)
R (550) is a phase difference of the liquid crystal layer with respect to light having a wavelength of 550 nm, and R (450) is a phase difference of 450 (nm) plane retardation of the liquid crystal layer with respect to light having a wavelength of 10 nm. The optical laminate according to claim 1, wherein R (650) / R (550) in the formula 1 is in the range of 1.01 to 1.19 and R (450) / R (550) is in the range of 0.81 to 0.99. 2. The liquid crystal display device according to claim 1, wherein the thickness of the liquid crystal layer is defined as x axis, and the angle formed by the optical axis of the liquid crystal compound present in the thickness and the optical axis of the liquid crystal compound present at the lowermost portion Wherein the graph shown is a nonlinear graph. The optical laminate according to claim 3, wherein the graph includes a portion where the tilt increases as the thickness of the liquid crystal layer increases. The optical laminate according to claim 1, wherein the liquid crystal layer has a phase retardation with respect to light at a wavelength of 550 nm within a range of 110 nm to 220 nm or within a range of 240 nm to 350 nm. The optical laminate according to claim 1, wherein the liquid crystal layer has a thickness in the range of 0.1 占 퐉 to 10 占 퐉. The optical laminate according to claim 1, wherein the liquid crystal layer further comprises a chiral agent. The optical laminate according to claim 1, wherein the polarizing layer is an absorption type polarizing layer or a reflection type polarizing layer. The optical laminate according to claim 1, wherein the angle formed by the optical axis of the liquid crystal compound closest to the polarizing layer in the liquid crystal layer and the optical absorption axis or the optical reflection axis of the polarizing layer is in the range of 5 to 15 degrees. The optical laminate according to claim 1, wherein the angle formed between the optical axis of the liquid crystal compound closest to the polarizing layer in the liquid crystal layer and the optical absorption axis or the optical reflection axis of the polarizing layer is in the range of 95 to 105 degrees. The optical laminate according to claim 9 or 10, wherein the twist angle of the liquid crystal layer is in the range of 80 to 100 degrees. The optical multilayer structure according to claim 1, wherein the polarizing layer comprises an absorption type polarizing layer and a reflection type polarizing layer, and the absorption type polarizing layer, the reflection type polarizing layer and the optical film are sequentially arranged. The optical multilayer structure according to claim 12, wherein the absorption axis of the absorption type polarizing layer and the optical reflection axis of the reflection type polarizing layer are arranged in parallel. The optical laminate according to claim 12, wherein the angle formed by the reflection type polarizing layer and the optical axis of the closest liquid crystal compound in the liquid crystal layer is within a range of 5 degrees to 15 degrees or a range of 95 degrees to 105 degrees. The optical laminate according to claim 12, wherein the twist angle of the liquid crystal layer is in the range of 80 to 110 degrees. A brightness enhancement film comprising the optical laminate of claim 1. An antireflection film comprising the optical laminate of claim 1. A step of inducing a change in concentration of the chiral agent depending on the thickness of the coating layer on a liquid crystal coating layer comprising a nematic liquid crystal compound, a chiral agent and a polymerization initiator, and polymerizing the nematic liquid crystal compound in a state in which the concentration of the chiral agent is changed ≪ / RTI > of claim 1. 19. The method according to claim 18, wherein the induction of the concentration change and the polymerization of the liquid crystal compound are carried out by irradiating ultraviolet rays of the ultraviolet ray A region to the liquid crystal coating layer at a light quantity of 10 mJ / cm ² to 500 mJ / cm ² at a temperature of 40 ° C to 80 ° C And irradiating ultraviolet rays to a liquid crystal coating layer having a change in the concentration of chiral agent at a light amount of 0.5 J / cm ² to 10 J / cm ² . A display device comprising the optical film of claim 1, the brightness enhancement film of claim 16, or the antireflection film of claim 17.

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