WO2017078290A1 - Polarizing plate and liquid crystal display device comprising same - Google Patents

Abstract

Provided are a polarizing plate and a liquid crystal display device comprising the same. The polarizing plate of the present invention comprises a polarizer and a protective film disposed on at least one surface of the polarizer. The in-plane retardation (Re) of the protective film is in the range of 0 nm to 200 nm, and the thickness-direction retardation (Rth) of the protective film is in the range of 0 nm to 1,200 nm. The polarizing plate has a rate of change of polarization represented by Formula 3 of about 10% or less after being left for 1,000 hours at a temperature of 60 ℃ and a relative humidity of 95%.

Description

Polarizing plate and liquid crystal display including the same

The present invention relates to a polarizing plate and a liquid crystal display including the same.

In recent years, the display field has been rapidly developed, and various flat panel displays having excellent performance of thinning, light weight, and low power consumption have been developed to replace the existing cathode ray tube (CRT). .

Specific examples of such a flat panel display include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display device (FED), and an organic light emitting display device ( Organic Electroluminescence Device).

Among these, the liquid crystal display is one of the flat panel displays that are most widely used at present. In general, a liquid crystal display device has a structure in which a liquid crystal layer is enclosed between a TFT (Thin Film Transistor) array substrate and a color filter substrate.

On the other hand, a polarizing plate composed of a polarizer and a polarizer protective film is used for the liquid crystal display, and rainbow stains may be recognized due to birefringence of the polarizer protective film, which may cause a problem of poor visibility.

Accordingly, the technical problem to be solved by the present invention is to provide a polarizing plate capable of preventing the above-mentioned rainbow stain and a liquid crystal display including the same.

The objects of the present invention are not limited to the above-mentioned technical problem, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

Polarizing plate according to an embodiment of the present invention for achieving the above object includes a polarizer, and a polarizer protective film disposed on at least one surface of the polarizer, the in-plane retardation (Re) of the polarizer protective film is about 0 to about 200 nm range, the thickness direction retardation (Rth) of the polarizer protective film is in the range of about 0 nm to about 1200 nm, the polarizing plate is left at a temperature of 60 ℃, 95% relative humidity for 1000 hours, the change in polarization degree is about 10% It is as follows.

The polarizer protective film may have a thickness in a range of about 10 μm to about 30 μm.

The polarizer protective film may include a polyester-based material.

The polarizer protective film may be polyethylene terephthalate-based, polyethylene naphthalate-based, or a copolymer including them.

The polarizer protective film may be a triple coextrusion structure including the polyethylene terephthalate-based, polyethylene naphthalate-based, or a copolymer including them.

The in-plane retardation (Re) of the polarizer protective film may range from about 0 nm to about 180 nm, and the thickness retardation (Rth) may range from about 0 nm to about 1150 nm.

The polarizer protective film may include an ultraviolet absorber.

Further comprising a functional layer disposed on one surface of the polarizer protective film, the functional layer is at least one of a hard coating layer (Hard-Coating Layer), an anti-reflection layer, an anti-glare layer and a diffusion layer It may include one or more.

The functional layer may include an ultraviolet absorbent.

According to an exemplary embodiment of the present invention, a liquid crystal cell, a backlight unit, a lower polarizer disposed between the liquid crystal cell and the backlight unit, and an upper polarizer disposed on a viewing side of the liquid crystal cell are provided. It includes, the upper polarizing plate comprises the polarizing plate.

Among the polarizers, a polarizer protective film having an in-plane retardation (Re) of about 0 nm to about 200 nm and a thickness retardation (Rth) of about 0 nm to about 1200 nm may be positioned at the viewer side of the upper polarizer. .

Further comprising a functional layer disposed on one surface of the polarizer protective film disposed on the viewing side of the upper polarizing plate, the functional layer is a hard coating layer (Hard-Coating Layer), anti-reflection layer (anti-reflection layer), anti-glare layer (Anti) -At least one of a Glare Layer) and a diffusion layer.

Specific details of other embodiments are included in the detailed description and the drawings.

According to embodiments of the present invention has at least the following effects.

That is, the polarizing plate of the present invention can be applied to the liquid crystal display device to prevent rainbow spots, thereby improving visibility.

In addition, the liquid crystal display of the present invention can prevent the rainbow spots visible from the side, thereby improving the visibility.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the present specification.

1 is a cross-sectional view schematically showing a polarizing plate according to an embodiment of the present invention.

2 is a schematic cross-sectional view of a polarizer according to another exemplary embodiment of the present invention.

3 and 4 are cross-sectional views schematically showing a polarizing plate according to another embodiment of the present invention.

5 is a cross-sectional view schematically illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

6 is a cross-sectional view schematically illustrating a liquid crystal cell in the liquid crystal display of FIG. 5.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

References to elements or layers "on" other elements or layers include all instances where another layer or other element is directly over or in the middle of another element. Like reference numerals refer to like elements throughout.

Although the first, second, etc. are used to describe various components, these components are of course not limited by these terms. These terms are only used to distinguish one component from another. Therefore, of course, the first component mentioned below may be a second component within the technical spirit of the present invention.

In addition, unless the steps constituting the manufacturing method described herein are sequential or sequential, or unless otherwise stated, one step and another step constituting one manufacturing method in the order described in the specification It is limited and not interpreted. Therefore, the order of construction steps of the manufacturing method can be changed within a range that can be easily understood by those skilled in the art, in which case the obvious changes to those skilled in the art will be included within the scope of the present invention.

In the present specification, "in-plane retardation (Re)" and "thickness retardation (Rth)" are defined as values at a wavelength of 550 nm unless specifically mentioned.

Polarizer

Hereinafter, a polarizer according to an embodiment of the present invention will be described with reference to FIG. 1. 1 is a cross-sectional view schematically showing a polarizing plate according to an embodiment of the present invention.

Referring to FIG. 1, a polarizer 100 according to an embodiment of the present invention includes a polarizer 110 and a polarizer protective film 120 disposed on at least one surface of the polarizer 110. In addition, the in-plane retardation (Re) of the polarizer protective film 120 ranges from about 0 nm to about 200 nm, for example, about 0 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 110 nm, about 120 nm, about 130 nm, about 140 nm, about 150 nm, about 160 nm, about 170 nm, about 180 nm, about 190 nm, about 200 nm, and the polarizer protective film 120 of Thickness direction retardation (Rth) is about 0 nm to about 1200 nm, for example about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm , About 1050 nm, about 1100 nm, about 1150 nm, about 1200 nm. Within this range, rainbow spots can be prevented from occurring.

In addition, the polarizing plate, that is, the polarizing plate in the state that the polarizer protective film 120 is laminated on the polarizer 110, the amount of change in polarization degree of the following formula 3 after being left for 1000 hours at a temperature of 60 ℃, 95% relative humidity About 10% or less, preferably about 5% or less, about 4% or less, about 3% or less, about 2% or less, about 1% or less. It is possible to implement excellent durability in the above range, it is possible to prevent the optical properties of the polarizing plate is lowered under various use conditions of the polarizing plate.

<Equation 3>

Change in polarization degree = ｜ P1-P0 ｜ x 100

(Equation 3, P0 is the initial polarization degree (unit:%) of the polarizing plate,

P1 is the polarizing degree (unit:%) after leaving the polarizer for 1000 hours at 60 ℃, 95% relative humidity conditions)

In addition, the polarizing plate, that is, the polarizing plate in the state in which the polarizer protective film 120 is laminated on the polarizer 110 has a polarization degree change rate of Equation 4 after being left for 1000 hours at a temperature of 60 ° C. and a relative humidity of 95%. About 0.1% or less, preferably about 0.05% or less, about 0.04% or less, about 0.03% or less, about 0.02% or less, about 0.01% or less. It is possible to implement excellent durability in the above range, it is possible to prevent the optical properties of the polarizing plate is lowered under various use conditions of the polarizing plate.

<Equation 4>

Polarization degree change rate = ｜ P1-P0 | / P0 x 100

(Equation 4, P0 is the initial polarization degree (unit:%) of the polarizing plate,

P1 is a polarization degree (unit:%) after leaving the polarizing plate for 1000 hours at a temperature of 60 ℃, 95% relative humidity.

When the polarizing plate 100 is applied to the display device to be described later in the phase difference range of the polarizer protective film 120, it is possible to prevent the occurrence of rainbow spots. More specifically, the polarizer protective film having the phase difference range may be more useful to prevent the rainbow spots located on the upper side of the display device.

The in-plane retardation (Re) and the thickness direction retardation (Rth) is the thickness of the polarizer protective film 120, d _x the refractive index in the in-plane slow axis direction, n _{y the} in-plane fast axis direction in the plane, n _y , the thickness direction When the refractive index is defined as n _z , it may be defined by Equations 1 and 2, respectively.

<Equation 1>

Re = (n _x -n _y ) xd

<Equation 2>

Rth = ((n _x + n _y ) / 2-n _z ) xd

In addition, the retardation value may be defined as a positive value as an absolute value.

The slow axis may be defined as a direction in which the in-plane refractive index of the polarizer protective film 120 is maximized, and the fast axis may be defined as a direction perpendicular to the slow axis in the plane.

In general, when the fast axis of the polarizer protective film 120 is Θr and the absorption axis is Θp, when the Θr-p value is not 90 ° or 0 °, that is, the slow axis r of the polarizer protective film 120 ) And the absorption axis p of the polarizer are not vertical (90 °) or parallel (0 °), the rainbow spots are visually recognized by the influence of the phase difference birefringence. When the polarizer protective film of the present invention is located at the end of the viewing direction, the rainbow stain may not be recognized without being affected by the Θr-p value.

In an exemplary embodiment, for the same reason, the in-plane retardation Re may be in the range of about 0 nm to about 200 nm, in the range of about 0 nm to 180 nm, or in the range of about 0 nm to about 100 nm. . In addition, the thickness direction retardation (Rth) may range from about 0 nm to about 1150 nm, and may range from about 0 nm to about 500 nm. Within this range, rainbow mura visibility can be further reduced.

Preferably, the polarizer protective film 120 may be disposed on the light exit surface of the polarizer 110 to transmit polarized light passing through the polarizer 110.

The polarizer 110 is a film that can be converted from natural light or polarized light into arbitrary polarized light, and can generally be converted to specific linearly polarized light. As the polarizer 110, a dichroic substance such as iodine or dichroic dye is adsorbed and stretched onto a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene-vinyl acetate copolymer-based partially saponified film. Although polyene type oriented films, such as the thing of the dehydration process of filivinyl alcohol, and the dehydrochlorination process of polyvinyl chloride, etc. are mentioned, it is not limited only to these. In an exemplary embodiment, a polyvinyl alcohol-based film containing iodine, which may have a high degree of polarization and has excellent adhesion with the polarizer protective film 120, may be mentioned, but is not limited thereto.

The polarizer protective film 120 may include a polyester-based material. As said polyester, for example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5- Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfoncarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclo Hexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2 Dicarboxylic acids such as dimethyl glutaric acid, adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid, Ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexane Methanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4 Although diols, such as -hydroxyphenyl) sulfone, can be mentioned, It is not limited only to these. A homopolymer obtained by polycondensing each of the above substances, or a copolymer obtained by polycondensing at least one dicarboxylic acid with at least two diols, or by condensing two or more dicarboxylic acids with at least one diol. The polyester resin in any one of the copolymer and the blend resin which blends 2 or more types of these homopolymers and copolymers is mentioned.

In an exemplary embodiment, in view of the polyester exhibiting crystallinity, aromatic polyesters can be used, for example, polyethylene terephthalate (PET) -based, polyethylene naphthalate (PEN) -based, or copolymers containing them. Although these are mentioned, It is not limited only to these.

In addition, the polarizer protective film 120 may be a triple coextrusion structure including a polyethylene terephthalate-based, polyethylene naphthalate-based, or a copolymer resin containing them.

A polyester film is obtained by the method etc. which melt-extrude the above-mentioned polyester resin into a film form, for example, cool-solidify with a casting drum, and form a film. In this invention, a stretched polyester film, especially a biaxially stretched polyester film can be used suitably from a viewpoint of providing crystallinity to a polyester film and achieving the said characteristic. In addition, when using what has aromatic polyester as a main component as a 1st protective film, such a film may contain resin, additives, etc. other than aromatic polyester.

In the case where the polarizer protective film 120 is a stretched film, the stretching method is not particularly limited, and a longitudinal uniaxial stretching method, a lateral uniaxial stretching method, a longitudinal transverse biaxial stretching method, a longitudinal transverse simultaneous biaxial stretching method, and the like can be adopted. In an exemplary embodiment, it may be by the simultaneous biaxial stretching method, but is not limited thereto. As the stretching means, any suitable stretching machine such as a roll stretching machine, a tenter stretching machine, or a biaxial stretching machine of a pantograph type or a linear motor type can be used.

On the other hand, the thickness of the polarizer protective film 120 may be in the range of about 10 ㎛ to about 30 ㎛ for thinning. However, it is not limited to this.

The polarizer protective film 120 may include an ultraviolet absorber. The transmittance of light having a wavelength of 380 nm of the polarizer protective film 120 may be controlled by the ultraviolet absorber in a range of about 1% to about 55%.

The first adhesive layer 10 may be interposed between the polarizer 110 and the polarizer protective film 120 to stack the polarizer 110 and the polarizer protective film 120 with each other. The first adhesive layer 10 may include an aqueous adhesive, but is not limited thereto and may include an ultraviolet curable adhesive.

The water-based adhesive may include at least one selected from the group consisting of polyvinyl alcohol-based resins and vinyl acetate-based resins, or may include polyvinyl alcohol-based resins having a hydroxyl group, but is not limited thereto.

In addition, the ultraviolet curing adhesive may include an acrylic compound, for example, may be acrylic, urethane-acrylic, epoxy-based. However, the present invention is not limited thereto.

Meanwhile, FIG. 2 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention. Referring to FIG. 2, the polarizing plate 101 further includes a functional layer 150 disposed on one surface of the polarizer protective film 120. It may include. The functional layer 150 may include at least one of a hard-coating layer, an anti-reflection layer, an anti-glare layer, and a diffusion layer.

More specifically, the functional layer 150 may be formed on one surface of the polarizer protective film 120, that is, the surface opposite to the surface on which the polarizer 110 of the polarizer protective film 120 is disposed. The functional layer 150 will be described in more detail. For example, the hard coating layer may improve the wet heat durability of the polarizing plate and prevent dimensional change, and the anti-reflection layer dissipates light of light incident from the outside to provide reflection. The anti-glare layer may prevent glare by inducing diffusion and reflection of light incident from the outside.

On the other hand, the functional layer 150 may include a UV absorber. As a result, the transmittance of light having a wavelength of 380 nm among the light passing through the functional layer 150 may be adjusted in a range of about 1% to about 55%.

On the other hand, the other components are the same as described above, overlapping description will be omitted.

3 is a cross-sectional view of a polarizer according to another embodiment of the present invention. Referring to FIG. 3, in the polarizing plate 102, the polarizer protective film 120 may be disposed on one surface of the polarizer 110 with the first adhesive layer 10 interposed therebetween, and the primer may be disposed on the other surface of the polarizer 110. Layer 30 and adhesive layer 130 may be disposed. In addition, not shown separately, a release film is disposed on the outer surface of the adhesive layer 130, it may be easy to store and transport the polarizing plate. In addition, the adhesive layer 130 may be used for attaching a polarizing plate to a display panel which will be described later. In addition, the primer layer 30 may protect the polarizer 110 and may improve adhesion between the polarizer 102 and the display panel to be described later. The primer layer 30 may be formed by coating and drying a coating liquid including a water dispersible polymer resin, water dispersible fine particles, and water on the polarizer 110 using a bar coating method, a gravure coating method, or the like. .

On the other hand, the other components are the same as described above, overlapping description will be omitted.

4 is a cross-sectional view of a polarizer according to another embodiment of the present invention. Referring to FIG. 4, the polarizers 103 are in a state in which polarizer protective films 120 and 140 are laminated on both sides of the polarizer 110 with the first adhesive layer 10 and the second adhesive layer 20 interposed therebetween. Can be. In addition, although not separately illustrated, an adhesive layer is formed on one surface of the polarizer protective film 120. 140, and may be attached to the display panel.

On the other hand, the other components are the same as described above, overlapping description will be omitted.

Liquid crystal display

5 is a cross-sectional view schematically illustrating a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 6 is a cross-sectional view schematically illustrating a liquid crystal cell included in the liquid crystal display of FIG. 5.

5 and 6, the liquid crystal display device 1 includes a liquid crystal cell 200, a backlight unit 500, a lower polarizer 400 and a liquid crystal disposed between the liquid crystal cell 200 and the backlight unit 500. The upper polarizer 300 is disposed on the viewer side of the cell 200, and the upper polarizer 300 disposed on the viewer side includes the polarizer described above. Preferably, the polarizer protective film 120 is disposed on the light exit surface of the polarizer 110, the light from the backlight unit 500 passes through the lower polarizing plate 400, the liquid crystal cell 200, the upper polarizing plate ( When passing through 300, the light passing through the polarizer may be disposed to be transmitted.

That is, the upper polarizer 300 may include a polarizer protective film having an in-plane retardation (Re) of about 0 to about 200 nm, a thickness retardation (Rth) of about 0 nm to about 1200 nm, and more Specifically, the polarizer protective film satisfying the retardation range may be located on the viewing side of the upper polarizing plate, thereby preventing the rainbow mura phenomenon from occurring.

In addition, the upper polarizer 300 may further include a functional layer disposed on one surface of the polarizer protective film disposed on the viewing side of the upper polarizer 300, the functional layer is a hard coating layer (Hard-Coating Layer), It may include at least one or more of an anti-reflection layer, an anti-glare layer, and a diffusion layer. Since these functional layers have already been described above, overlapping descriptions will be omitted.

Referring to FIG. 6, the liquid crystal cell 200 includes a liquid crystal layer 220 encapsulated between the first substrate 210, the second substrate 230, the first substrate 210, and the second substrate 230. The upper polarizer 300 may be stacked on one surface (upper surface) of the first substrate 210.

The lower polarizer 400 may be stacked on the lower surface of the second substrate 230, and when the two polarizers 300 and 400 are positioned above and below the liquid crystal cell 200, the transmission axes of the polarizers of the respective polarizers are mutually different. It can be orthogonal or parallel. In an exemplary embodiment, the lower polarizer 400 may also be configured as the polarizer of the present invention, and in this case, the protective film having a specific phase difference described above is a lower surface of the lower polarizer 400, that is, the backlight unit 400 side. Can be placed in.

The first substrate 210 may be a color filter CF substrate. Although not specifically illustrated in the drawings, for example, a black matrix for preventing light leakage on a lower surface of a substrate made of a transparent insulating material such as glass or plastic, a color filter of red, green, and blue and a transparent conductive material such as ITO or IZO It may include a common electrode which is an electric field generating electrode formed of an oxide.

The second substrate 230 may be a thin film transistor (TFT) substrate. Although not specifically shown in the drawings, for example, a thin film transistor comprising a gate electrode, a gate insulating film, a semiconductor layer, an ohmic contact layer, and a source / drain electrode on a substrate made of a transparent insulating material such as glass or plastic, and ITO or It may include a pixel electrode which is an electric field generating electrode formed of a transparent conductive oxide such as IZO.

Plastic substrates that can be used for the first substrate 210 and the second substrate 230 include polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN), and polyether (PES) that can be used for displays. It may be a plastic substrate such as sulfone), PAR (polyarylate) and COC (cycloolefin copolymer), but the present invention is not limited thereto. In addition, the first substrate 210 and the second substrate 230 may be made of a flexible material.

The liquid crystal layer 220 may be a twisted nematic (TN) mode, a vertical alignment (VA) mode, a horizontal alignment (IPS, FFS) mode, or the like having positive dielectric anisotropy. In FIG. 6, the TN mode will be described as an example.

When there is no voltage difference between the pixel electrode and the common electrode, that is, the field generating electrode, and the electric field is not applied to the liquid crystal layer 220, as shown in FIG. 6, the liquid crystal of the liquid crystal layer 220 has a first long axis direction. It is arranged parallel to the surface of the substrate 210 and the second substrate 230, has a structure twisted 90 ° in a spiral from the first substrate 210 to the second substrate 230.

The polarization of the linearly polarized light changes due to retardation due to the refractive anisotropy of the liquid crystal while passing through the liquid crystal layer 220. When the dielectric anisotropy (Δε) and chiral pitch of the liquid crystal and the thickness of the liquid crystal layer 220, that is, the cell gap, are adjusted, the linearly polarized light direction of the light passing through the liquid crystal layer 220 is changed. Can be rotated 90 °.

The backlight unit 500 may generally include a light source, a light guide plate, a reflective film, and the like. According to the configuration of the backlight can be arbitrarily divided into a direct method, a side light method, a planar light source method.

Although not separately illustrated, the liquid crystal display device 1 may include an optical film or an optical sheet disposed between the lower polarizer 400 and the backlight unit 500. The optical film or the optical sheet may include at least one brightness enhancing film, a diffusion sheet, a prism sheet, and the like, which are well known in the art and will not be described in detail.

Manufacturing method of polarizing plate

Although not separately illustrated, a method of manufacturing a polarizer may include preparing a polarizer protective film and a polarizer, and laminating the polarizer protective film and the polarizer through an adhesive.

The preparing of the polarizer may include a dyeing step of dyeing a polyvinyl alcohol film with iodine or a dichroic dye, and a drawing step of stretching the polyvinyl alcohol film.

The dyeing step may be performed by impregnating a polyvinyl alcohol-based film in a solution of iodine or dichroic material. For example, the case of the dyeing using the iodine, the temperature of the iodine solution is in the range of about 20 ℃ to about 50 ℃, the impregnation time may be in the range of about 10 seconds to about 300 seconds. When the iodine solution is used as the iodine solution, an aqueous solution containing iodine (I ₂ ) and iodine ions, for example, potassium iodide (KI) used as a dissolution aid, may be used.

On the other hand, the dyeing step may further comprise the step of swelling the polyvinyl alcohol-based film in the swelling bath. In addition, the swelling step may be performed at a temperature range of about 40 ° C to about 80 ° C, for example, may range from about 50 ° C to about 75 ° C or about 60 ° C to about 70 ° C. The swelling step serves to soften the molecular chain of the polyvinyl alcohol-based film and to relax the molecular chain, thereby allowing the dichroic substance to be dyed into the polyvinyl alcohol-based film during the dyeing process, wherein polyvinyl By increasing the swelling temperature near the glass transition temperature of the alcohol-based film, it is possible to reduce the crystal content in the polyvinyl alcohol-based film and to increase the swelling rate by making the molecules move actively. As a result, the dyeability of the dichroic material is increased, and the dichroic material is homogeneously dyed to the polyvinyl alcohol-based film, and thus may have high optical properties and excellent orthogonal transmittance upon stretching.

The swelling ratio can be from about 130% to about 270%. In this swelling process, the polyvinyl alcohol-based film can be stretched. When satisfying the swelling ratio and the elongation as described above, it is possible to achieve high permeability while preventing the occurrence of staining during the dyeing process without inhibiting the physical properties of the polarizing film and to improve the uniformity of the optical properties. The swelling step can be performed by a dry method or a wet method. In an exemplary embodiment, it may be carried out by a wet method in a swelling bath containing swelling liquid.

In another exemplary embodiment, a crosslinking process may further be included after the dyeing step.

When molecules of iodine or dichroic material are dyed in the polyvinyl alcohol-based film in the dyeing step, the dichroic molecules are adsorbed onto the polymer matrix of the polyvinyl alcohol-based film using boric acid, borate, or the like. Examples of the crosslinking method include a deposition method in which a polyvinyl alcohol-based film is deposited by dipping a boric acid solution or the like, but is not limited thereto, and may be performed by a coating method or a spraying method for applying or spraying a solution to a film. It may be.

On the other hand, in the stretching step, the polyvinyl alcohol-based film may be stretched using a wet stretching method and / or a dry stretching method common in the art. Further, the final draw ratio of the polyvinyl alcohol-based film may range from about 5.0: about 1 or more, for example, about 5.5: about 1 or more, or about 6.0: about 1 or more.

Non-limiting examples of the dry stretching method include an inter-roll stretching method, a heating roll stretching method, a compression stretching method, a tenter stretching method, and the like. Non-limiting examples include a tenter stretching method, an inter-roll stretching method, and the like.

In the case of the wet stretching method, stretching may be performed in alcohols, water or boric acid aqueous solution, and for example, a solvent such as methyl alcohol or propyl alcohol may be used, but is not limited thereto.

Stretching temperature and time can be suitably selected and used according to the material of a film, desired elongation rate, a usage method, etc. In addition, the stretching may be uniaxial stretching or biaxial stretching. However, biaxial stretching may be performed to produce a polarization film adhered to a liquid crystal cell of a liquid crystal display, which will be described later.

On the other hand, the steps of dyeing, stretching, crosslinking, swelling, etc. may be carried out in the state of laminating the polyvinyl alcohol-based film and the base film.

Preparing the polarizer protective film may include preparing a non-stretched polyester film and stretching the non-stretch polyester film.

The step of preparing the non-stretched polyester film is not particularly limited, but for example, a melt extrusion method may be used. After melting above the melting temperature of the polyester-based material, it can be discharged out of the extrusion facility to form a non-stretched film. Hereinafter, the melt extrusion method will be described in more detail.

If the content of moisture present in the raw material in the melt extrusion process is included in a certain level or more may cause product defects in the bubble state such as orange peel form, it should be managed to a water content below a certain level. The form of the dryer is not particularly limited, and examples thereof include a dehumidifying dryer and a hot air dryer, but are not limited thereto. The drying temperature may be carried out below the glass transition temperature of the film raw material. However, the drying temperature can be appropriately selected according to the type of resin and the glass transition temperature used. If the drying temperature is too low, there is no drying effect, on the contrary, if the drying temperature is higher than necessary, the properties of the raw material are changed, which is not appropriate. The drying time of the raw material may range from about 0.5 hours to about 5 hours, but may be easily selected in consideration of the ambient humidity.

The dried raw material may be fed to a raw material reservoir (hopper) located at the inlet of the extrusion facility. In some cases, the filter may be passed with air circulated primarily in the reservoir to primarily remove impurities that may be included in the raw material.

The input raw material is filled in the first section of the screw inside the extrusion plant. The first section serves to transfer the raw material to the extrusion plant cylinder.

Thereafter, the second section is a section in which melting of the raw material starts, preferably set to a temperature higher than the glass transition temperature of the film raw material.

The third section is the section in which the raw material is completely converted into the melt, and the temperature setting can be maintained in the same range as the second section.

The fourth section increases the density of the melt by increasing the pressure of the molten raw material, thereby ensuring a stable discharge amount. In this process, the temperature condition may be maintained in the same range as the second and third sections so that the melt discharged is not cured.

In some cases, it passes through a gear pump section that transfers the melt to the T-die in a fixed amount. If the raw material is transferred directly to the T-die through the screw in the cylinder of the extrusion facility, the instantaneous amount of raw material is irregular and a good quality product cannot be obtained. Therefore, the gear pump can store the raw material irregularly injected from the extrusion equipment cylinder in a certain space and stably supply a certain amount of melt to the T-die to minimize the change in pressure distribution.

The section in which the melt is finally discharged out of the extrusion facility is the T-die section. The shape and manufacturing thickness of the film are determined by the form of the T-die. The die die may be classified into a “T” die, a coat hanger die, a fish tail die, and the like, but is not limited thereto. The type of Ti die can be selectively used depending on the flowability of the melt.

The stretching of the non-stretched polyester-based film may use a general wet stretching method and / or dry stretching method in the art.

Non-limiting examples of the dry stretching method include an inter-roll stretching method, a heating roll stretching method, a compression stretching method, a tenter stretching method, and the like. Non-limiting examples include a tenter stretching method, an inter-roll stretching method, and the like.

In the case of the wet stretching method, stretching may be performed in alcohols, water or boric acid aqueous solution, and for example, a solvent such as methyl alcohol or propyl alcohol may be used, but is not limited thereto.

In addition, the stretching may be carried out by a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and horizontal axial biaxial stretching method, a longitudinal and lateral simultaneous biaxial stretching method, and the like.

In an exemplary embodiment, a biaxial stretching method may be used to have the above phase difference value, and for the same reason, a biaxial stretching method may be used, but is not limited thereto.

The stretching ratio (MD: TD) of the stretching step may vary depending on the desired thickness range and the like, but is not particularly limited. The stretching may be in the range of (2.0: 1.0-3.0) to (3.5: 2.0-4.5). That is, the TD direction elongation may be set in the range of about ± 1.0 times to about 1.5 times the MD direction elongation. In this case, the MD direction elongation may range from about 2.0 to about 4.5 times.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Hereinafter, the polarizing plate and the liquid crystal display of the present invention will be described in more detail with reference to Preparation Examples and Experimental Examples.

Production Example  1 to Production Example  10 and Comparative example  1 to Comparative example  5

Using polyethylene terephthalate, polyethylene terephthalate polarizer protective film was prepared by using a melt extrusion process and a simultaneous biaxial stretching method, respectively, in terms of thickness, in-plane retardation (Re) and thickness direction retardation (Rth), respectively. And it was bonded to a polyvinyl alcohol polarizer containing iodine to prepare a polarizing plate.

The in-plane retardation Re and the thickness direction retardation Rth may be defined as in Equations 1 and 2 below, and the retardation value may be defined as a positive value as an absolute value.

<Equation 1>

Re = (n _x -n _y ) × d

<Equation 2>

Rth = ((n _x + n _y ) / 2-n _z ) xd

In the above formula, n _x is the refractive index in the slow axis direction in the film plane, n _y is the refractive index in the fast axis direction in the film plane, n _z is the refractive index in the thickness direction, and d is the thickness of the polarizer protective film. In addition, the slow axis may be defined as a direction in which the in-plane refractive index of the protective film is maximum, and the fast axis may be defined as a direction perpendicular to the slow axis in the plane.

In-plane retardation (Re) and thickness direction retardation (Rth) were measured using a product name AxoScan manufactured by Axometrics, which is a retardation measurement system, at a measurement wavelength of 550 nm under an environment of 23 ° C. In addition, the order of the measured value of retardation was determined so that it might correspond with the wavelength dispersion of the retardation of the polyester film previously calculated | required.

Experimental Example  One

The polarizing plates prepared in Production Examples 1 to 10 and Comparative Examples 1 to 5 were applied to the viewing side of the liquid crystal cell, and the polarizer protective film was arranged on the light exit surface of the polarizer, and then tested for rainbow stains. 1 is shown.

	Thickness [㎛]	Re [nm]	Rth [nm]	Rainbow stain poet
Preparation Example 1	30	150	850	Level 0
Preparation Example 2	30	90	1200	Level 1
Preparation Example 3	30	180	1150	Level 0
Preparation Example 4	20	100	1050	Level 0
Preparation Example 5	20	120	1150	Level 0
Preparation Example 6	20	70	760	Level 0
Preparation Example 7	20	50	820	Level 0
Preparation Example 8	10	50	500	Level 0
Preparation Example 9	10	130	750	Level 0
Preparation Example 10	10	150	1100	Level 0
Comparative Example 1	40	150	5300	Level 2
Comparative Example 2	40	200	5500	Level 2
Comparative Example 3	38	4100	6500	Level 2
Comparative Example 4	30	150	4300	Level 2
Comparative Example 5	20	243	1689	Level 2

Level 0: Rainbow Stain Mischief

Level 1: Rainbow stains Unacknowledged, but a single color poet. Applicable Level

Level 2: Rainbow stain Poet 'Medium' or higher, not applicable

Referring to Table 1 above, in the case of the liquid crystal cell to which the polarizer protective film satisfying the retardation range of the present invention is applied, rainbow spots are not visible, whereas in the comparative example, rainbow spots are recognized.

Therefore, it can be seen that when the polarizing plate of the present invention is used in a liquid crystal display device, rainbow spots can be prevented and visibility can be improved.

Comparative example  6

A triacetyl cellulose (TAC) protective film was used as the polarizer protective film, and the TAC protective film was laminated on one side of the polarizer to prepare a polarizing plate.

Experimental Example  2

Hard coating layer (HC) was formed on the polarizer protective film outside of Preparation Examples 1, 2 and Comparative Example 6, and a separate layer was not formed on the polarizer protective film of Preparation Example 3. In order to test the reliability of the high temperature and high humidity, the polarizing plates of Preparation Examples 1, 2 and Comparative Example 6, in which the hard coating layer was formed, and the polarizing plates of Preparation Example 3, in which the hard coating layer was not formed, were laminated on the glass by using an adhesive, and the temperature was 60 ° C. , The amount of change in polarization degree before and after 1000 hours under the condition of 95% relative humidity was measured according to Equation 3 above, and the rate of change in polarization degree was measured according to Equation 4 above. Polarization degree was measured using a V-7100 model (Jasco, Inc.), and the results are shown in Table 2 below.

	Surface treatment on polarizer protective film	Polarization degree
		0h [%]	After 1000h [%]	% Change	% Change
Preparation Example 1	Hard Coating Layer	99.996	99.989	0.7	0.007
Preparation Example 2	Hard Coating Layer	99.989	99.970	1.9	0.019
Preparation Example 3	X	99.988	99.960	2.8	0.028
Comparative Example 6	Hard Coating Layer	99.996	99.881	11.5	0.115

As shown in Table 2, when using the polarizer protective film of the present invention, it was confirmed that the polarization degree change rate can be minimized even under harsh test conditions.

The embodiments described above are all exemplary, and different embodiments may be applied in combination.

<Description of the code>

1: liquid crystal display

10: first adhesive layer

20: second adhesive layer

100, 101, 102, 103: polarizer

110: polarizer

120, 140: polarizer protective film

130: adhesive layer

150: functional layer

200: liquid crystal cell

210: first substrate

220: liquid crystal layer

230: second substrate

300: upper polarizer

400: lower polarizer

500: backlight unit

Claims (12)

1. Polarizer; And

   It is a polarizing plate comprising a polarizer protective film disposed on at least one surface of the polarizer,

   In-plane retardation (Re) of the polarizer protective film ranges from about 0 nm to about 200 nm, thickness direction retardation (Rth) of the polarizer protective film ranges from about 0 nm to about 1200 nm,

   The polarizing plate is a polarizing plate of about 10% or less of the amount of change in the degree of polarization of the following formula 3 after 1000 hours at a temperature of 60 ℃, 95% relative humidity:

   <Equation 3>

   Change in polarization degree = ｜ P1-P0 ｜ x 100

   (Equation 3, P0 is the initial polarization degree (unit:%) of the polarizing plate,

   P1 is a polarization degree (unit:%) after leaving the polarizing plate for 1000 hours at a temperature of 60 ℃, 95% relative humidity.
2. The method of claim 1,

   The polarizer protective film has a thickness of about 10 μm to about 30 μm.
3. The method of claim 1,

   The polarizer protective film is a polarizing plate comprising a polyester-based material.
4. The method of claim 3, wherein

   The polarizer protective film is a polyethylene terephthalate-based, polyethylene naphthalate-based, or a polarizing plate which is a copolymer containing them.
5. The method of claim 4, wherein

   The polarizer protective film is a polarizing plate having a triple coextrusion structure comprising the polyethylene terephthalate-based, polyethylene naphthalate-based, or a copolymer containing them.
6. The method of claim 1,

   In-plane retardation (Re) of the polarizer protective film ranges from about 0 nm to about 180 nm, thickness direction retardation (Rth) is in the range of about 0 nm to about 1150 nm.
7. The method of claim 1,

   The polarizer protective film is a polarizing plate containing a ultraviolet absorber.
8. The method of claim 1,

   Further comprising a functional layer disposed on one surface of the polarizer protective film,

   The functional layer may include at least one of a hard coating layer, a anti-reflection layer, an anti-glare layer, and a diffusion layer.
9. The method of claim 8,

   The functional layer is a polarizing plate containing a ultraviolet absorber.
10. Liquid crystal cell;

    A backlight unit;

    A lower polarizer disposed between the liquid crystal cell and the backlight unit; And

    An upper polarizing plate disposed on the viewing side of the liquid crystal cell,

    The upper polarizer includes the polarizer of claim 1.
11. The method of claim 10,

    The polarizer protective film having an in-plane retardation (Re) of about 0 to about 200 nm and a thickness direction retardation (Rth) of about 0 nm to about 1200 nm in the polarizing plate is located on the viewer side of the upper polarizing plate. .
12. The method of claim 10,

    Further comprising a functional layer disposed on one surface of the polarizer protective film disposed on the viewing side of the upper polarizing plate,

    The functional layer may include at least one of a hard-coating layer, an anti-reflection layer, an anti-glare layer, and a diffusion layer.

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