KR20200050750A - Polarizing plates and liquid crystal display devices - Google Patents

Abstract

The present application relates to a polarizing plate and to a liquid crystal display device. The polarizing plate of the present application can be applied to a horizontal electric field type liquid crystal display device by reducing luminance at a viewing angle through the use of a dichroic dye, thereby improving a contrast ratio at a viewing angle. The polarizing plate comprises: a polarizer; a dye layer disposed on one surface of the polarizer, and including a liquid crystal compound and a dichroic dye in a vertically aligned state; and a retardation layer disposed on the opposite side of the dye layer of the polarizer.

Description

Polarizing plates and liquid crystal display devices

The present application relates to a polarizing plate and a liquid crystal display device.

The horizontal electric field type liquid crystal display device refers to a liquid crystal display device in which the orientation of the initial liquid crystal is horizontal to the substrate and is oriented at a constant angle with respect to the electrode, and the direction of the electric field applied for driving is formed parallel to the substrate.

The liquid crystal display of the horizontal electric field method has a problem in that a color is seen in an oblique direction according to the characteristics of the panel, and as a result, light leakage is large in a dark state (black state) and visibility is deteriorated.

In order to improve the contrast ratio in the viewing angle and realize a display of excellent quality without distortion of image quality, a retardation film may be applied. However, a higher level contrast ratio may be required depending on the product applied to the liquid crystal display, and there is a limit in improving the contrast ratio in the viewing angle through adjustment of the phase difference value and optical axis of the retardation film.

Republic of Korea Patent Publication No. 2010-0106838

The present application provides a polarizing plate capable of exhibiting an excellent contrast ratio at a viewing angle through a reduction in luminance of a black state at a viewing angle, and a liquid crystal display device including the polarizing plate.

This application relates to a polarizing plate. 1 exemplarily shows the polarizing plate of the present application. As shown in FIG. 1, the polarizing plate may include a polarizer 10, a dye layer 20 disposed on one surface of the polarizer, and a retardation layer 30 disposed on opposite sides of the dye layer of the polarizer. The dye layer may include a liquid crystal compound and a dichroic dye in a vertically aligned state. The polarizing plate of the present application not only has a viewing angle compensation effect, but also applies the dye layer as described above to the top of the polarizer, so that the absorption axis of the polarizer and the absorption axis of the dye layer are in a cross state, resulting in a viewing angle. Since the luminance can be reduced in the black state, an excellent contrast ratio can be exhibited in the viewing angle.

In this application, the terms polarizer and polarizer refer to objects that are distinguished from each other. The term polarizer means a film, sheet, or device having a polarizing function itself, and the term polarizer means an object including the polarizer and other elements stacked on one or both surfaces of the polarizer. Other elements in the above may be exemplified by the liquid crystal layer, a protective film of a polarizer, a retardation layer, an adhesive layer, an adhesive layer, a surface treatment layer, etc., but is not limited thereto.

A polarizer is a functional element capable of extracting light oscillating in one direction from incident light oscillating in various directions. As the polarizer, for example, a known absorption type linear polarizer can be used. As such a polarizer, a poly (vinyl alcohol) (PVA) polarizer may be exemplified.

In one example, the polarizer included in the polarizing plate may be a PVA film or sheet in which a dichroic dye or iodine is adsorbed and oriented. The PVA can be obtained, for example, by gelling polyvinyl acetate. As polyvinyl acetate, a homopolymer of vinyl acetate; And copolymers of vinyl acetate and other monomers. In the above, as the other monomer copolymerized with vinyl acetate, an unsaturated carboxylic acid compound, an olefin compound, a vinyl ether compound, an unsaturated sulfonic acid compound, and an acrylamide compound having an ammonium group or the like may be exemplified. The degree of gelation of the polyvinyl acetate is generally about 85 mol% to about 100 mol% or 98 mol% to 100 mol%. The degree of polymerization of the polyvinyl alcohol of the linear polarizer may generally be about 1,000 to about 10,000 or about 1,500 to about 5,000.

The transmittance or polarization degree of the polarizer may be appropriately adjusted in consideration of the purpose of the present application. For example, the transmittance for the 550 nm wavelength of the polarizer may be a single transmittance in the range of 40% to 55%, and the polarization degree may be in the range of 65% to 99.9997%.

The dye layer may include a liquid crystal compound and a dichroic dye in a vertically aligned state. In the present application, the vertical alignment state means a state in which the direction of the liquid crystal compound is vertically arranged with respect to the plane of the dye layer or the liquid crystal layer, for example, an arrangement state of about 85 degrees to 95 degrees, preferably about 90 degrees. Can be. In the present application, the horizontal alignment state means a state in which the direction of the liquid crystal compound is arranged parallel to the plane of the dye layer or the liquid crystal layer, for example, an arrangement state of -5 degrees to 5 degrees, preferably about 0 degrees. Can be.

In the present application, the direction of the liquid crystal compound may mean a long axis when the liquid crystal compound is in a rod shape, or may mean an axis in a normal direction of the plane of the disc when the liquid crystal compound is a discotic shape.

The dichroic dye may be aligned according to the orientation of the liquid crystal compound. Therefore, when the liquid crystal compound is included in a vertically oriented state, a dichroic dye may also be included in a vertically oriented state. When the dichroic dye is included in a vertically oriented state, the contrast ratio at the viewing angle can be improved due to the anisotropic absorption characteristics at the viewing angle.

The liquid crystal compound may be a polymerizable or curable liquid crystal compound. In the present application, the polymerizable or curable liquid crystal compound may mean a molecule including a site capable of exhibiting liquid crystallinity, for example, a mesogen skeleton, and one or more polymerizable or curable functional groups. The polymerizable or curable functional group is not particularly limited, but examples thereof include 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. have.

The dye layer may include the liquid crystal compound in a cured state or a polymerized state. In addition, including the polymerizable liquid crystal material in a cured state or a polymerized state may mean a state in which the liquid crystal compound is polymerized to form a skeleton such as a main chain or a side chain of the liquid crystal polymer in the dye layer. The dye layer may include a liquid crystal compound in a state in which vertical alignment is fixed. Therefore, in the dye layer, the vertical alignment state of the liquid crystal compound is not switched by the application of external energy such as an electric field.

The term "dye" in the present application intensively absorbs light within at least a part or the entire range within a visible light region, for example, a wavelength range of 380 nm to 780 nm, 380 nm to 750 nm, 400 nm to 750 nm, 380 nm to 700 nm or 400 nm to 700 nm, and / Alternatively, it may mean a material that can be deformed, and the "dichroic dye" may mean a material capable of anisotropically absorbing light in at least a part or the entire range of a visible light region.

In the dye layer, the dichroic dyes are arranged together according to the arrangement of the liquid crystal compound, and thus the anisotropic light absorbing properties may be exhibited with respect to the alignment direction of the dichroic dye and the vertical direction of the alignment direction. In one example, the dichroic dye may have a rod shape. For example, a dichroic dye is a material whose absorption rate of light varies depending on the polarization direction. If the absorption rate of light polarized in the long axis direction is large, it is called a p-type dye, and when the absorption rate of light polarized in the short axis direction is large, it is called an n-type dye. It can be called. In one example, when a p-type dye is used, polarization vibrating in the long axis direction of the dye is absorbed, and polarization vibrating in the short axis direction of the dye is less absorbed and can be transmitted. It is assumed that the dichroic dye is a p-type dye unless otherwise specified.

As the dichroic dye, for example, a known dye known to have properties that can be arranged according to the orientation of the liquid crystal compound can be selected and used. Such dichroic dyes include, for example, azo dyes, anthraquinone dyes, methine dyes, azomethine dyes, oxadine dyes, azo dyes, styryl dyes, coumarin dyes, porphyrin dyes, di It is possible to use one or more dyes selected from the group consisting of benzofuranone-based dyes, ketetophyllophyllor-based dyes, rhodamine-based dyes, chisanthene-based dyes, and phylomethenic-based dyes. As for the dichroic dye, one dye may be used or a mixture of two or more dyes may be used within a range in which the dye layer exhibits a desired transmittance.

In the polarizing plate of the present application, a contrast ratio characteristic may be adjusted at a viewing angle according to a dichroic ratio of a dichroic dye. The dichroic ratio of the dichroic dye may be appropriately selected within a range capable of achieving the object of the present application. The term "dichroic ratio" in the present application means, for example, in the case of a p-type dye, the value obtained by dividing the absorption of polarized light parallel to the long axis direction of the dye by the absorption of polarized light parallel to the direction perpendicular to the long axis direction. Can be.

In this specification, the dichroic ratio of the dichroic dye can be obtained by measuring the transmittance to the dye layer containing the dichroic dye and the liquid crystal compound. In one example, with respect to the dye layer containing the dichroic dye and the liquid crystal compound in a horizontally aligned state, among light incident in the normal direction of the dye layer, measured for polarization parallel to the direction of the horizontal alignment After measuring the transmittance (Te) and the transmittance (To) for the polarization parallel to the direction of the horizontal orientation and the in-plane vertical direction, a dichroic ratio may be determined by a ratio of log10 (Te) / log10 (To). The dichroic ratio for a specific wavelength may be obtained by substituting a value for a specific wavelength in Te and To, and a dichroic ratio for a specific wavelength range can be obtained by substituting the average value of a specific wavelength range for Te and To.

The dichroic dye, for example, may have a dichroic ratio of 5 or more. The dichroic dye is, for example, within the wavelength range of the visible light region, for example, at least a portion of the wavelength or at any one wavelength within a wavelength range of about 380 nm to 780 nm, about 400 nm to 750 nm or about 400 nm to 700 nm. You can satisfy the rain. The upper limit of the dichroic ratio may be, for example, 25 or less. Since the difference in luminance in the viewing angle tends to increase as the dichroic ratio of the dichroic dye increases, the dichroic ratio can be appropriately adjusted within the above range according to the needs of the final product.

The dichroic dye may be included in the dye layer in an amount of 0.1 to 1 part by weight based on 100 parts by weight of the liquid crystal compound. When the content of the dichroic dye is within the above range, it may be more advantageous to improve the contrast ratio by reducing the luminance of the black state at the viewing angle.

In the polarizing plate of the present application, the dichroic dye may have an absorption band within the entire range of visible light. In the present specification, the entire range of visible light may mean the entire range of 400 nm to 700 nm, the entire range of 400 nm to 750 nm, or the entire range of 380 nm to 780 nm. The dye having the above absorption band may be referred to as a neutral dye, and the color may indicate black. In the present application, by applying the dye layer containing the dichroic dye having such an absorption band to the upper portion of the polarizer, it is possible to improve the contrast ratio by reducing the luminance of the black state at the viewing angle.

In the present application, the absorption band of the dichroic dye is the point at which the absorbance is highest when the absorbance or transmittance for wavelengths in the entire range of visible light is measured for the dye layer containing the dichroic dye in a horizontally oriented state. Alternatively, it may mean a wavelength band including a wavelength at a point where transmittance is lowest. In the present application, the absorption band of a dichroic dye has a wavelength range in which the transmittance is about 20% or less, 15% or less, 10% or less, 7% or less, 5% or less, 3% or less, or 1% or less within the entire wavelength range. Can mean In addition, wavelength regions other than the absorption band may exhibit higher transmittance than the transmittance of the absorption band.

In one example, the dichroic dye may have a transmittance of 20% or less, 15% or less, 10% or less, 7% or less, 5% or less, 3% or less, or 1% or less in the entire range of visible light. The transmittance may be a transmittance measured for a dye layer containing a dichroic dye in a horizontally oriented direction. The dye layer may further include a liquid crystal compound in a horizontally oriented state in order to horizontally align the dichroic dye. The transmittance is a percentage of the intensity of light passing through the dye layer with respect to the intensity of light incident on the dye layer. The transmittance may mean transmittance to polarization parallel to an axis representing maximum absorbance or minimum transmittance with respect to the dye layer, based on light incident in a normal direction. The axis in which the dye layer exhibits maximum absorbance or minimum transmittance may be parallel to the direction of the horizontal orientation.

Since the dye layer includes the dichroic dye in a vertically oriented state, the dye layer itself included in the polarizing plate may exhibit high transmittance. In one example, the dye layer may be 90% or more within the entire range of visible light for the light incident in the normal direction of the dye layer.

The method for obtaining a dichroic dye having an absorption band in the entire visible light range is not particularly limited, and may be, for example, a mixture of dyes showing different colors or dyes having different chromophores in a dye molecule. .

In one example, the dichroic dye may be a mixture of two or more dichroic dyes having different absorption bands. As a specific example, the dichroic dye may be a mixture of a dichroic dye having an absorption band of a red wavelength, a dichroic dye having an absorption band of a green wavelength, and a dichroic dye having an absorption band of a blue wavelength. In the present application, the red wavelength region may mean about 620 nm to 780 nm, the green wavelength region may mean about 500 nm to 610 nm, and the blue wavelength region may mean about 380 nm to 495 nm. The dichroic dye having an absorption band of a red wavelength, a dichroic dye having an absorption band of a green wavelength, and a dichroic dye having an absorption band of a blue wavelength each exhibit a maximum absorbance within the wavelength range, and have a half width of about 50 nm to 200 nm or It may be in the range of about 50nm to 100nm. When the dichroic dye is a mixture as described above, it may be more advantageous to obtain a neutral black color.

The thickness of the dye layer may be appropriately adjusted in consideration of the purpose of the present application. The thickness of the dye layer may be, for example, 1 μm or more. When the thickness of the dye layer is within the above range, it may sufficiently contain a vertically oriented dichroic dye, and thus it may be more advantageous to exhibit an excellent contrast ratio in a viewing angle. In addition, when the thickness of the dye layer is too thick, the vertical alignment of the liquid crystal may collapse, so in view of realizing stable vertical alignment and reducing cost, the upper limit of the thickness is, for example, 1.8 μm or less, 1.5 μm or less, or 1.3 μm. It may be:

In the present application, the in-plane retardation value may be defined by Equation 1 below, and the thickness direction retardation value may be defined by Equation 2 below.

[Equation 1]

Rin = (nx-ny) × d

[Equation 2]

Rth = (nz-ny) × d

In Equation 1, Rin means an in-plane retardation value, and in Equation 2, Rth means a thickness direction retardation value, and nx, ny, and nz are dye layers, liquid crystal layers, A plates, and B plates for wavelengths of 550 nm, respectively. The refractive index of the x-axis, y-axis and z-axis of the retardation layer such as C plate, and d is the thickness of the retardation layer such as dye layer, liquid crystal layer, A plate, B plate, and C plate.

In the present application, unless the x-axis, y-axis and z-axis of the retardation layers such as dye layer, liquid crystal layer, A plate, B plate, and C plate are described, the x axis is a dye layer, a liquid crystal layer, an A plate, The direction parallel to the in-plane slow axis of the retardation layer such as the B plate and the C plate, and the y axis refers to the direction parallel to the in-plane advancing axis of the retardation layer such as the dye layer, the liquid crystal layer, the A plate, the B plate, and the C plate. The z-axis means the thickness direction of a retardation layer such as a dye layer, a liquid crystal layer, an A plate, a B plate, and a C plate. The x-axis and the y-axis may be orthogonal to each other in a plane. In the present application, when the dye layer, the liquid crystal layer, or the retardation layer includes rod-shaped liquid crystal molecules, the slow axis may mean the long axis direction of the rod shape, and when the disc-shaped liquid crystal molecules are included, the slow axis is the disk-shaped normal line. Can mean direction. In the present application, the optical axis of the retardation layer such as a dye layer, a liquid crystal layer, an A plate, a B plate, and a C plate is described, and unless otherwise specified, it means a slow axis. In the present application, the refractive index of the retardation layer such as a dye layer, a liquid crystal layer, an A plate, a B plate, and a C plate is described, and unless otherwise specified, it means a refractive index for light having a wavelength of about 550 nm.

The dye layer may be formed, for example, by applying a composition comprising a liquid crystal compound and a dichroic dye to one surface of the base layer, followed by curing or polymerization.

The coating method of the composition on the substrate layer is not particularly limited, and known coating methods such as, for example, roll coating, printing, inkjet coating, slit nozzle method, bar coating, comma coating, spin coating or gravure coating, etc. It can be carried out by coating through.

The polymerization method of the composition is not particularly limited, and can be performed by a known liquid crystal compound polymerization method. For example, it may be performed by a method of maintaining an appropriate temperature or a method of irradiating an appropriate active energy ray so that a polymerization reaction can be initiated. If maintenance at an appropriate temperature and irradiation of active energy rays are required simultaneously, the process can be performed sequentially or simultaneously. In the above, irradiation of the active energy ray may be performed using, for example, a high-pressure mercury lamp, an electrodeless lamp, or a xenon lamp, and the conditions such as wavelength, light intensity, or light amount of the active energy ray to be irradiated are described above. It can be selected within a range in which polymerization of the polymerizable liquid crystal compound can be appropriately achieved.

As the base layer, a known material can be used without particular limitation. For example, inorganic films such as glass films, crystalline or amorphous silicon films, quartz, or indium tin oxide (ITO) films, plastic films, or the like can be used. As the substrate layer, an optically anisotropic substrate layer or an optically anisotropic substrate layer such as a retardation layer can also be used. As a plastic film, TAC (triacetyl cellulose); COP (cyclo olefin copolymer) such as norbornene derivatives; PMMA (poly (methyl methacrylate); PC (polycarbonate); PE (polyethylene); PP (polypropylene); PVA (polyvinyl alcohol); DAC (diacetyl cellulose); Pac (Polyacrylate); PES (poly ether sulfone); PEEK (polyetheretherketon) ); PPS (polyphenylsulfone), PEI (polyetherimide); PEN (polyethylenemaphthatlate); PET (polyethyleneterephtalate); PI (polyimide); PSF (polysulfone); PAR (polyarylate) or an amorphous fluorine resin may be used. The substrate layer may include a coating layer of a silicon compound such as gold, silver, silicon dioxide or silicon monoxide, or a coating layer such as an antireflection layer, if necessary.

A vertical alignment layer for vertically aligning the liquid crystal compound may be formed on the substrate layer. As the alignment film, for example, an alignment film known to be a contact alignment film such as a rubbing alignment film or a photo-alignment film compound that can exhibit alignment characteristics by a non-contact method such as irradiation of linearly polarized light can be used. Can be.

The polarizing plate may further include a retardation layer. The retardation layer may be disposed on the opposite side of the dye layer of the polarizer. The retardation layer may be a single retardation film or a laminate of two or more retardation films. 2 exemplarily shows a structure of a polarizing plate including a laminate of two retardation films. As shown in FIG. 2, the dye layer 20 may be disposed on one surface of the polarizer 10, and the first retardation film 301 and the second retardation film may be disposed on opposite sides of the dye layer 20 of the polarizer 10. 302 can be deployed.

According to the polarizing plate of the present application, the retardation layer does not include a dichroic dye. As described later, when the polarizing plate is applied to a liquid crystal display, a phase difference layer may be disposed closer to the liquid crystal panel compared to the dye layer. If, when the retardation layer disposed between the polarizer and the liquid crystal panel includes a dichroic dye, there is a problem in that the contrast ratio at the viewing angle decreases rather.

The retardation film may satisfy the refractive index relationship of any one of the following general formulas 1 to 7. When the retardation layer is a laminate of two or more retardation films, each retardation film may independently satisfy the refractive index relationship of any one of the following general formulas 1 to 7.

[Formula 1]

nx> ny = nz (+ A plate)

[Formula 2]

nx = nz> ny (-A plate)

[Formula 3]

nz> nx = ny (+ C plate)

[Formula 4]

nx = ny> nz (-C plate)

[Formula 5]

nz> nx> ny (+ B plate)

[Formula 6]

nx> ny> nz (-B plate)

[Formula 7]

nx> nz> ny (Z-axis orientation film)

In general formulas 1 to 7, nx, ny, and nz mean the refractive indexes in the x-axis, y-axis, and z-axis directions of the retardation film, respectively. In the present application, the x-axis direction may refer to the slow axis direction, the y-axis direction to the true axis direction, and the z-axis direction to the thickness direction. The refractive index may mean a refractive index for light having a wavelength of about 550 nm, unless otherwise specified in the present application.

The retardation film may be formed to satisfy any one of the following general formulas 8 to 10 wavelength dispersion. When the retardation layer is a laminate of two or more retardation films, each film may be independently formed to satisfy any one of the following general formulas 8 to 10. The following general formula 8 may be referred to as a reverse dispersion characteristic, the general formula 9 may be referred to as a regular dispersion characteristic, and the general formula 10 may be referred to as a flat dispersion characteristic.

[Formula 8]

R (450) / R (550) <R (650) / R (450)

[Formula 9]

R (450) / R (550)> R (650) / R (450)

[Formula 10]

R (450) / R (550) = R (650) / R (450)

In general formulas 8 to 10, R (λ) may mean a phase difference value for light having a wavelength of λnm in the phase difference film.

In one example, the retardation layer may include at least a + C plate. The phase difference in the thickness direction of the + C plate with respect to the wavelength of 550 nm may be, for example, 120 nm to 150 nm. Within this thickness direction retardation range, it may be applied to a liquid crystal display device to further improve viewing angle characteristics.

In one example, the retardation layer may further include a retardation film having an in-plane retardation value greater than 0 nm, for example, 100 nm to 140 nm. At this time, compared to the + C plate, the in-plane retardation value of more than 0 nm, the retardation film may be disposed closer to the polarizer or may be disposed farther away. For example, the retardation layer is a retardation film having an in-plane retardation value greater than 0 nm, and may further include a + A plate or a -B plate. Accordingly, the retardation layer may be a stack of + C plate and + A plate or a stack of + C plate and -B plate. In one example, the polarizing plate may sequentially include a polarizer, a -B plate, and a + C plate. In another example, the polarizing plate may sequentially include a polarizer, + C plate, and + A plate. The in-plane retardation for the 550 nm wavelength of the + A plate may be in the range of 100 nm to 140 nm. The angle formed by the slow axis of the + A plate and the light absorption axis of the polarizer may be within a range of -5 degrees to 5 degrees, -3 degrees to 3 degrees, or -1 degree to 1 degree. The in-plane retardation of the -B plate for the 550 nm wavelength may be in the range of 100 nm to 140 nm, and the retardation in the thickness direction for the 550 nm wavelength may be, for example, in the range of -20 nm to -50 m. The angle formed between the slow axis of the -B plate and the light absorption axis of the polarizer may be within a range of 85 degrees to 95 degrees, 87 degrees to 93 degrees, 89 degrees to 91 degrees to 89.5 degrees to 90.5 degrees. When further including such a retardation film, it may be applied to a liquid crystal display device to further improve viewing angle characteristics.

The retardation film may be a liquid crystal film or a polymer film.

In the case of a liquid crystal film, similar to that described for the liquid crystal layer, it can be produced by including a polymerizable or curable liquid crystal compound in a polymerized or cured state. In one example, the + C plate may be a liquid crystal film including a liquid crystal compound in a vertically oriented state. In one example, the + A plate may be a liquid crystal film including a liquid crystal compound in a horizontally oriented state. As described above, the retardation film does not contain a dichroic dye.

In the case of a polymer film, for example, a polyolefin film such as a polyethylene film or a polypropylene film, a cyclic olefin polymer (COP) film such as a polynorbornene film, a polyvinyl chloride film, a polyacrylonitrile film, poly A cellulose ester polymer film such as a sulfone film, a polyacrylate film, a polyvinyl alcohol film, or a triacetyl cellulose (TAC) film, or a copolymer film of two or more monomers among the monomers forming the polymer may be exemplified.

The dye layer, polarizer and retardation layer of the polarizing plate may be attached to each other by an adhesive or an adhesive. The dye layer, the polarizer, and the polarizer and the retardation layer may be directly attached through an adhesive layer or an adhesive layer, respectively, and if necessary, may further include a primer layer. An adhesive or adhesive layer may be further formed on a side opposite to the polarizer of the retardation layer. Through this, the polarizing plate can be attached to the liquid crystal panel described later. As the pressure-sensitive adhesive or adhesive, known pressure-sensitive adhesives or adhesives such as acrylic, silicone, rubber, and urethane can be used.

The method of attaching the dye layer and / or the retardation layer and the polarizer is not particularly limited. In one example, the adhesive or pressure-sensitive adhesive composition is coated on one side of the polarizer or the dye layer, and the composition is cured after laminating the polarizer and the dye layer, or the adhesive or pressure-sensitive adhesive composition is dropped onto the polarizer by a dropping method. A method of laminating a dye layer and curing the composition may be used. In the above, curing of the composition may be performed by irradiating an active energy ray of an appropriate intensity with an appropriate amount of light, for example, taking into account the components included in the composition. In another example, the dye layer may be attached to the polarizer by a transfer method. In the present application, the transfer of the dye layer may mean a process of bonding the dye layer formed on the carrier substrate to a polarizer to be transferred through an adhesive or an adhesive, and then peeling and removing the carrier substrate. The retardation layer and the polarizer can also be attached in the same way as the dye layer and the polarizer.

The present application also relates to the use of the polarizing plate. The present application relates to, for example, a liquid crystal display device including the polarizing plate. 3 exemplarily shows a liquid crystal display device of the present application. The exemplary liquid crystal display device of the present application sequentially includes the upper polarizing plate 100, the liquid crystal panel 200, and the lower polarizing plate 300, and the upper polarizing plate may be the polarizing plate of the present application. At this time, the phase difference layer 30 may be disposed closer to the liquid crystal panel 200 than the dye layer 20.

The liquid crystal panel may be a horizontal electric field type liquid crystal panel. In the present application, the horizontal electric field type liquid crystal panel refers to a liquid crystal panel in which a liquid crystal compound is present in a horizontally aligned state in a state in which no voltage is applied or in an initial state, and when the voltage is applied, its orientation can be switched according to the horizontal electric field. Can be. An example of such a horizontal electric field type liquid crystal panel may be an in-plane switching (IPS) mode, a fringe field switching (FSF) mode, or a liquid crystal panel in a plane to line switching (PLS) mode.

The liquid crystal panel may include an upper substrate, a liquid crystal layer, and a lower substrate. The upper and lower substrates may be glass substrates or plastic substrates, respectively. According to an embodiment of the present invention, the liquid crystal panel may be an IPS mode (plane switching mode) liquid crystal panel.

The liquid crystal layer may include a liquid crystal whose dielectric anisotropy is positive or negative. The dielectric anisotropy of the liquid crystal layer may be appropriately selected according to a desired mode of the liquid crystal panel. In one example, the liquid crystal layer may include a liquid crystal panel having a positive dielectric anisotropy. In one example, the in-plane retardation value of the liquid crystal layer is 270 nm to 330 nm, and the thickness direction retardation value may be 0 nm to -40 nm.

The upper polarizing plate may be referred to as a viewer-side polarizing plate, and the lower polarizing plate may be referred to as a rear-side polarizing plate. The lower polarizing plate may include a polarizer. With respect to the polarizer included in the lower polarizing plate, the contents described in the items of the polarizing plate of the present application may be equally applied. If necessary, a protective film and a retardation film may be further included on one surface of the lower polarizer.

The absorption axis of the upper polarizing plate and the absorption axis of the lower polarizing plate may be within a range of 80 degrees to 100 degrees. The liquid crystal display device may further include a backlight. The backlight may be disposed under the lower polarizing plate.

In one example, the initial alignment direction of the liquid crystal of the liquid crystal layer may be parallel to each other or perpendicular to the absorption axis of the lower polarizer. When the angle is parallel, it can be defined as an O-mode liquid crystal panel, and when orthogonal, it can be defined as an E-mode liquid crystal panel.

The upper and lower substrates of the liquid crystal panel may further include an alignment layer toward the liquid crystal layer. The alignment direction of the liquid crystal may be determined by the alignment layer. The alignment layer may be a horizontal alignment layer. As the alignment layer, a rubbing alignment layer or a photo alignment layer may be used.

By applying the polarizing plate of the present application to the viewing side of the liquid crystal display device, it is possible to exhibit an excellent contrast ratio in the viewing angle through a reduction in the luminance of the black state in the viewing angle. The method of constructing the liquid crystal display device as described above is not particularly limited, and a conventional method may be applied as long as the polarizing plate is used.

The present application can provide a polarizing plate capable of exhibiting an excellent contrast ratio in a viewing angle through a reduction in luminance of a black state at a viewing angle, and a liquid crystal display device including the polarizing plate.

1 exemplarily shows the polarizing plate of the present application.
2 exemplarily shows the polarizing plate of the present application.
3 exemplarily shows a liquid crystal display device of the present application.
4 is a view angle contrast ratio evaluation results of Comparative Example 1 and Examples 1 to 5.

Hereinafter, the present application will be described in detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the examples presented below.

Example  1 to 5

For evaluation of the viewing angle contrast ratio, a polarizing plate including a dye layer, a polarizer, and a retardation layer in order was prepared.

The dye layer includes a birefringent liquid crystal compound having a birefringence value of 0.12 and a dichroic dye in a vertically aligned state, and has a thickness of 1.1 µm. The dichroic dye is a neutral dye (black dye) having an absorption band in the entire range of 400nm to 700nm wavelength. Specifically, the dichroic dye has a transmittance of 1% or less in the entire range of 400nm to 700nm wavelength. The transmittance is a transmittance measured with respect to a dye layer comprising the rod-like liquid crystal compound and a dichroic dye in a horizontally aligned state, and polarized light parallel to the direction of the horizontal alignment among light incident in the normal direction of the dye layer. (Te). To, which will be described later, refers to transmittance for polarization parallel to the direction of the horizontal orientation and the in-plane vertical direction. The transmittance is a percentage of the intensity of light transmitted through the dye layer to the intensity of light incident on the dye layer. As shown in Table 1, Examples 1 to 5 were prepared according to the dichroic ratio of the dichroic dye. The dichroic ratio in Table 1 below is a dichroic ratio for a wavelength of 400 nm to 700 nm. The dichroic ratio of the dichroic dye can be determined by the ratio of log10 (Te) / log10 (To), and the dichroic ratio for the 400nm to 700nm wavelength is the average To and the average for the 400nm to 700nm wavelength in the To and Te of the formula. It can be obtained by substituting Te value. The polarizer is a PVA-based polarizer having a polarization degree of 99.99% or more and light transmittance of 42.5% for light having a wavelength of 380 nm to 780 nm.

The retardation layer includes a -B plate and a + C plate, and the -B plate is disposed closer to the polarizer than the + C plate. The -B plate is a COP-based film having a Rin (550) value of 120 nm and a Rth (550) value of -40 nm. The + C plate is a liquid crystal film having a Rin (550) value of 0 nm and a Rth (550) value of 130 nm.

Comparative example  One

Same as Example 1 except that instead of the dye layer, a birefringent liquid crystal compound having a birefringence value of 0.12 was vertically aligned, and a liquid crystal layer having a thickness of 1.1 µm (not containing a dichroic dye) was applied. A polarizing plate was prepared.

Evaluation example  One. Dichroic  Dye In the unusual rain  Following viewing angle Contrast ratio  evaluation

Using the Techwiz LCD 1D, for a planar switching mode liquid crystal display device, the contrast ratio was simulated at azimuth angle 210 ° based on 175 ° azimuth angle and 45 ° inclination angle, for all azimuth angles of inclination angle, particularly 40 °. The azimuth angle of 0 degrees is based on the absorption axis of the polarizer. In the planar switching mode liquid crystal display, a liquid crystal panel is disposed between the upper polarizing plate and the lower polarizing plate, and the lower polarizing plate is disposed closer to the backlight than the upper polarizing plate.

As the upper polarizing plate, the polarizing plates of Examples 1 to 5 or Comparative Example 1 are used, and the dye layer of the example or the liquid crystal layer of the comparative example is disposed on the outer layer. The liquid crystal panel has a cell spacing of 2.9 μm, a pretilt angle of 0 °, a dielectric anisotropy Δε> 0, and a liquid crystal birefringence Δn = 0.1 at a wavelength of 550 nm. Rin (550): 290nm Rth (550): O mode IPS liquid crystal panel with 0nm. The lower polarizing plate is a PVA-based polarizer having a polarization degree of 99.99% or more and light transmittance of 42.5% for light having a wavelength of 380 nm to 780 nm.

Tables 1 and 4 below show the comparison results of the viewing angle contrast ratios of Comparative Example 1 and Examples 1 to 5. The contrast ratio is the ratio of the brightness in the on state to the brightness in the off state of the liquid crystal display. In Table 1 below, Lw (0 °) is the brightness measured at the front of the liquid crystal display, and Lw (40 °) is the brightness measured at the 40 ° inclination angle of the liquid crystal display. Lw (40 °) / Lw (0 °) is the ratio of Lw (40 °) to Lw (0 °). In Table 1 below, the upper (θ = 40 °, ф = 175 °) value and the lower (θ = 45 °, ф = 210 °) value refer to the contrast value at a position that is easily seen by the driver looking at the navigation of the vehicle. do. As the value increases, it means better visibility.

Dichroic Lw (0 °) Lw (40 °) / Lw (0 °) Phase (θ = 40 °, ф = 175 °) Phase (θ = 45 °, ф = 210 °) Comparative Example 1 - 1158 0.996 945 706 Example 1 5 1018 0.933 967 767 Example 2 10 1016 0.930 1106 818 Example 3 15 1016 0.930 1220 858 Example 4 20 1015 0.930 1369 908 Example 5 25 1014 0.930 1503 951

Evaluation example  2. Dye layer  Viewing angle according to thickness Contrast ratio  evaluation

Comparative example  2 to 6

In Examples 1 to 5, the polarizing plates of Comparative Examples 2 to 6 were prepared in the same manner, except that the thicknesses of the dye layers were changed to 0.5 μm, respectively, and the viewing angle contrast ratio was evaluated. Table 2 below shows the results of Evaluation Example 2.

Dichroic Dye layer thickness Lw (0 °) Lw (40 °) / Lw (0 °) Phase (θ = 40 °, ф = 175 °) Phase (θ = 45 °, ф = 210 °) Comparative Example 2 5 0.5㎛ 1049 0.96 1016 715 Comparative Example 3 10 0.5㎛ 1049 0.92 1070 737 Comparative Example 4 15 0.5㎛ 1048 0.92 1112 755 Comparative Example 5 20 0.5㎛ 1048 0.92 1165 777 Comparative Example 6 25 0.5㎛ 1047 0.91 1210 796 Example 1 5 1.1㎛ 1018 0.933 967 767 Example 2 10 1.1㎛ 1016 0.930 1106 818 Example 3 15 1.1㎛ 1016 0.930 1220 858 Example 4 20 1.1㎛ 1015 0.930 1369 908 Example 5 25 1.1㎛ 1014 0.930 1503 951

10: polarizer, 20: dye layer, 30: retardation layer 301: first retardation film 302: second retardation film 100: upper polarizing plate 200: liquid crystal panel 300: lower polarizing plate

Claims (15)

A polarizer, a dye layer disposed on one surface of the polarizer, and comprising a liquid crystal compound and a dichroic dye in a vertically aligned state, and a retardation layer disposed on the opposite side of the dye layer of the polarizer, wherein the thickness of the dye layer is 1 The polarizing plate having an absorption band in the entire range of 400 nm to 700 nm in the horizontally oriented state, wherein the dichroic dye is at least µm. The polarizing plate of claim 1, wherein the liquid crystal compound is included in the dye layer in a cured state. The polarizing plate of claim 1, wherein the dichroic ratio of the dichroic dye is in a range of 5 to 25. The polarizing plate of claim 1, wherein the dichroic dye is included in the dye layer in an amount of 0.1 to 1 part by weight based on 100 parts by weight of the liquid crystal compound. The polarizing plate of claim 1, wherein the dye layer has a transmittance to light incident in a normal direction of the dye layer in a range of 400 nm to 700 nm in a wavelength range of 90% or more. The polarizing plate of claim 1, wherein the dichroic dye is a mixture of two or more dichroic dyes having different absorption bands. The polarizing plate of claim 1, wherein the dichroic dye is a mixture of a dichroic dye having an absorption band of a red wavelength, a dichroic dye having an absorption band of a green wavelength, and a dichroic dye having an absorption band of a blue wavelength. The thickness of the dye layer is a polarizing plate in the range of 1㎛ to 1.8㎛. The polarizing plate of claim 1, wherein the retardation layer does not include a dichroic dye. The polarizing plate of claim 1, wherein the retardation layer comprises a + C plate. The polarizing plate of claim 10, wherein the retardation layer further comprises a + A plate or a -B plate. A liquid crystal display device comprising an upper polarizing plate, a liquid crystal panel of a horizontal electric field method, and a lower polarizing plate sequentially, wherein the upper polarizing plate is the polarizing plate of claim 1, and the retardation layer of the polarizing plate is disposed closer to the liquid crystal panel than the dye layer. The liquid crystal display of claim 12, wherein the liquid crystal panel sequentially includes an upper substrate, a liquid crystal layer, and a lower substrate, and the in-plane retardation value of the liquid crystal layer is 270 nm to 330 nm, and the thickness direction retardation value is 0 nm to -40 nm. Device. The liquid crystal display of claim 12, wherein the absorption axis of the upper polarizing plate and the absorption axis of the lower polarizing plate are within a range of 80 degrees to 100 degrees. The liquid crystal display device of claim 12, further comprising a backlight under the lower polarizing plate.

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