TWI750614B - Polarizing plate and optical display apparatus comprising the same - Google Patents

Abstract

A polarizing plate and an optical display apparatus including the same. The polarizing plate includes: an absorption type polarizer; and a first protective film and a reflection type polarizing film sequentially stacked on a lower surface of the absorption type polarizer, wherein a low refractivity axis of the first protective film in an in-plane direction thereof is disposed at an angle of about -5° to +5° with respect to a high refractivity axis of the reflection type polarizing film in an in-plane direction thereof.

Description

Polarizing plate and optical display device including the same

The present invention relates to a polarizing plate and an optical display device including the same. More particularly, the present invention relates to a polarizing plate with improved front contrast by a simple and economically feasible method and an optical display device including the same.

A liquid crystal display includes a liquid crystal panel and an electrode matrix disposed between a pair of absorbing polarizers. In a liquid crystal display, a liquid crystal panel includes liquid crystals that can be displaced to achieve variable optical states by an electric field generated when a voltage is applied to opposing electrodes. This treatment allows pixels containing data to display images using light polarized in a particular direction. To this end, the liquid crystal display includes a front absorption type polarizer and a rear absorption type polarizer that cause polarized light.

In a liquid crystal display, the absorbing polarizer absorbs 50% or more of the light received from the backlight unit. Therefore, it is difficult for the liquid crystal display to improve the use efficiency of light by using only the absorbing polarizer. Therefore, the liquid crystal display is further provided with a reflective polarizing film to improve the use efficiency of light. In recent years, with the development of large-scale liquid crystal displays, the demand for power consumption reduction has been increasing. To reduce power consumption, an absorbing polarizer is required to improve front contrast. However, despite the addition of a reflective polarizing film, there is still a limit in improving the front contrast.

The background art of the present invention is disclosed in Japanese Unexamined Patent Publication No. 2006-251659 and the like.

An object of the present invention is to provide a polarizing plate that achieves improved front contrast.

Another object of the present invention is to provide a polarizing plate that achieves improved front contrast by reducing the brightness in black mode.

Another object of the present invention is to provide a polarizing plate that has good handleability and economic feasibility, and can achieve reduced thickness.

One aspect of the present invention relates to a polarizing plate.

The polarizer includes: an absorbing polarizer; and a first protective film and a reflective polarizing film sequentially stacked on the lower surface of the absorbing polarizer, wherein the first protective film is in its in-plane direction The low refractive index axis of the reflective polarizing film is set at an angle of about -5° to +5° with respect to the high refractive index axis of the reflective polarizing film in its in-plane direction.

Another aspect of the present invention relates to an optical display device including the polarizing plate according to the present invention.

The present invention provides a polarizing plate with improved front contrast.

The present invention provides a polarizing plate that achieves improved front contrast by reducing the brightness in black mode.

The present invention provides a polarizing plate that has good handleability and economic feasibility, and can achieve reduced thickness.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. It should be understood that the present invention may be implemented in various ways and is not limited to the following examples. In the drawings, parts irrelevant to the present description will be omitted for clarity. Throughout this specification, the same components will be designated by the same reference numbers. Although the length, thickness or width of various components may be exaggerated in the drawings for understanding, it should be understood that the present invention is not limited thereto.

Herein, spatially relative terms such as "upper" and "lower" are defined with reference to the accompanying drawings. Thus, it will be understood that the term "upper surface" is used interchangeably with the term "lower surface" and that when an element such as a layer or film is referred to as being placed "on" another element, the element can be placed directly on the other element elements, or intervening elements may be present. On the other hand, when an element is referred to as being "directly on" another element, there are no intervening elements.

The "(meth)acrylic group" used herein refers to an acrylic group and/or a methacrylic group.

In this paper, "in-plane retardation (Re)", "out-of-plane retardation Rth" and "biaxiality NZ" are represented by Equation A, Equation B and Equation C, respectively: Re = (nx - ny) × d, ---(A) Rth = ((nx + ny)/2 - nz) × d,---(B) NZ = (nx - nz)/(nx - ny), ---(C) where nx, ny, and nz are the refractive indices of the respective optic in the x-, y-, and z-axis directions of the optic at a wavelength of about 550 nm, respectively, and d is the thickness of the optic (units: : Nano). Here, the x-axis direction is defined as the slow-axis direction of the optical device, and the y-axis direction is defined as the fast-axis direction of the optical device. The optical device may be a first protective film, a second protective film, or the like.

The inventors of the present invention have completed the present invention based on the confirmation that in a polarizing plate including an absorbing polarizer, a first protective film, and a reflective polarizing film, by adjusting the low refraction of the first protective film in the in-plane direction thereof The angle between the refractive index axis and the high refractive index axis of the reflective polarizing film in its in-plane direction can improve the front contrast of the polarizing plate.

Specifically, in the polarizing plate according to the present invention, the low refractive index axis of the first protective film in the in-plane direction thereof is at about −5° with respect to the high refractive index axis of the reflective polarizing film in the in-plane direction thereof Angle setting to +5° (the high refractive index axis of the reflective polarizing film in its in-plane direction is defined as 0°). The present invention can achieve an improvement in front contrast by reducing brightness in black mode only by adjusting the angle between the axes of the first protective film and the reflective polarizing film, and can improve processability and economic feasibility.

Hereinafter, a polarizing plate according to an embodiment of the present invention will be explained with reference to FIG. 1 .

Referring to FIG. 1 , the polarizing plate according to this embodiment includes an absorbing polarizer 100 , a first protective film 200 and a reflective polarizing film 300 .

In the polarizing plate, the first protective film and the reflective polarizing film are provided on the lower surface of the absorbing polarizer. The first protective film and the reflective polarizing film may be disposed on the light incident surface or the light exit surface of the absorbing polarizer. Preferably, the first protective film and the reflective polarizing film are disposed on the light incident surface of the absorbing polarizer to ensure further improvement of the front contrast.

In the polarizing plate, the first protective film and the reflective polarizing film are sequentially stacked on the lower surface of the absorbing polarizer, preferably on the light incident surface thereof. As another option, the reflective polarizing film and the first protective film may be sequentially disposed on the lower surface of the absorbing polarizer. Preferably, as shown in FIG. 1 , when the polarizing plate satisfies the relationship between the axes, the first protective film and the reflective polarizing film are sequentially arranged on the lower surface of the absorbing polarizer to further improve the front contrast.

A reflective polarizing film is stacked on the lower surface of the first protective film. Although not shown in FIG. 1 , an adhesive layer, an adhesive layer or an adhesive/adhesion layer may be stacked between the first protective film and the reflective polarizing film to integrate the first protective film and the reflective polarizing film. The integration allows the thickness of the polarizer to be reduced. Alternatively, the reflective film may simply be stacked on the first protective film without an adhesive layer, adhesive layer, or adhesive/adhesive layer. Preferably, the adhesive layer, the adhesive layer or the adhesive/adhesive layer is stacked between the first protective film and the reflective polarizing film. Reflective polarizing film

The reflective polarizing film 300 may include a brightness enhancement film disposed on the lower surface of the first protective film to enhance brightness by preventing loss of light that has passed through the lower surface of the first protective film.

The reflective polarizing film has a high refractive index axis and a low refractive index axis in the in-plane direction. Here, the "high refractive index axis" and the "low refractive index axis" are defined by the relative comparison between the two axes in the in-plane direction of the reflective polarizing film, that is, the x-axis and the y-axis. Although not particularly limited, the high refractive index axis and the low refractive index axis of the reflective polarizing film can be determined by stretching the reflective polarizing film during its manufacture.

In one embodiment, the reflective polarizing film may comprise a matrix and a plurality of plate polymers dispersed in the matrix. Although not particularly limited, the high-refractive index axis and the low-refractive index axis in the in-plane direction may be formed by stretching in the process of manufacturing the reflective polarizing film.

In one embodiment, in a reflective polarizing film, the high refractive index axis may be the reflection axis, and the low refractive index axis may be the transmission axis. In one embodiment, the high refractive index axis of the reflective polarizing film may be the machine direction (MD) of the reflective polarizing film corresponding to its stretching direction, and the low refractive index axis of the reflective polarizing film may be reflective The transverse direction (TD) of the reflective polarizing film corresponds to a direction perpendicular to the stretching direction of the reflective polarizing film.

In one embodiment, the reflective polarizing film may include a diffuse reflection type polarizing film. Hereinafter, the diffuse reflection type polarizing film will be explained.

When light reaches the reflective polarizing film, the reflective polarizing film allows polarized light (P-polarized light) traveling perpendicular to its stretching direction to pass therethrough, while passing polarized light traveling in the stretching direction (S-polarized light) is reflected toward the lower surface of the reflective polarizing film. In this process, the S-polarized light is again reflected by the lower surface of the reflective polarizing film to re-enter the reflective polarizing film after the polarization state is changed, so that in the polarized light after the polarization state is changed, the P-polarized light The light passing through the reflective polarizing film, and the S-polarized light is again reflected by the reflective polarizing film, thereby improving the brightness by recycling the light.

In one embodiment, the reflective polarizing film includes a core layer, which may include a matrix and a plurality of plate-like polymers dispersed in the matrix. The plate-like polymer has a different refractive index from the core layer in at least one axial direction, and the core layer is stretched in at least one axial direction. Each of the plate-like polymers is formed into a plurality of groups reflecting shear waves of predetermined wavelengths, respectively, and the plate-like polymers in one group have an average optical thickness different from that of the other groups. With this structure, in the light emitted from the light source that has reached the reflective polarizing film, the reflective polarizing film only allows some polarized light components (P-polarized light) traveling perpendicular to its stretching direction to pass therethrough. pass and reflect the other polarized light component in the stretching direction (S-polarized light) towards its lower surface. During this process, the S-polarized light is repeatedly reflected by the lower surface of the reflective polarizing film again, and the P-polarized light passes through the reflective polarizing film, thereby improving brightness. In a reflective polarizer, the plate-like polymer has a different refractive index from the matrix, where the transmitted light exhibits scattering properties. Reflective polarizing films are available from commercially available products.

The plate-like polymer may include at least one selected from the group consisting of polyethylene naphthalate, copolyethylene naphthalate, polyethylene terephthalate, polycarbonate, polycarbonate Alloys, polystyrene, heat-resistant polystyrene, poly(methyl methacrylate), polybutylene terephthalate, polypropylene, polyethylene, acrylonitrile butadiene styrene, polyurethane , polyimide, polyvinyl chloride, styrene acrylonitrile, ethylene vinyl acetate, polyamide, polyacetal, phenol, epoxy resin, urea, melamine, unsaturated ester, silicone and cyclic olefin polymers. Preferably, the plate polymer includes polyethylene naphthalate.

The matrix may comprise at least one selected from the group consisting of polyethylene naphthalate, copolyethylene naphthalate, polyethylene terephthalate, polycarbonate, polycarbonate alloys , polystyrene, heat-resistant polystyrene, poly(methyl methacrylate), polybutylene terephthalate, polypropylene, polyethylene, acrylonitrile butadiene styrene, polyurethane, Polyimide, polyvinyl chloride, styrene acrylonitrile, ethylene vinyl acetate, polyamide, polyacetal, phenol, epoxy resin, urea, melamine, unsaturated ester, silicone and cyclic olefin polymers. Preferably, the matrix can be dimethyl-2,6-naphthalene dicarboxylate, dimethyl terephthalate and copolynaphthalene obtained by polymerization of ethylene glycol, cyclohexanedimethanol, etc. Ethylene Glycol Diformate.

A reflective polarizing film according to an embodiment of the present invention will be explained with reference to FIG. 2 .

Referring to FIG. 2 , the reflective polarizing film includes a core layer 10 . The core layer 10 includes a group A and a group B sequentially formed in the thickness direction of the core layer 10 , wherein the group A and the group B are integrally formed with each other. Group A includes plate polymers 11 , 12 , and group B includes plate polymers 13 , 14 . Each of the plate polymers 11, 12 and the plate polymers 13, 14 is impregnated in a matrix (not shown in Figure 2). The optical thickness between the plate-like polymers included in the group A is different from the optical thickness between the plate-like polymers 13 , 14 included in the group B. With this structure, groups A and B can reflect light in different wavelength bands. Although two groups are shown in FIG. 2 , the number of groups included in the core layer is not particularly limited as long as luminance enhancement can be achieved.

Although not shown in FIG. 2, a skin layer may be additionally formed on one or both surfaces of the core layer to protect the core layer. In this case, the skin layer may have a refractive index of about 1.4 to about 1.8, preferably about 1.5 to 1.7. Within this range, the layer contacting the coating has a higher refractive index than the coating, thus minimizing loss of brightness and contrast.

The skin layer may comprise at least one selected from the group consisting of polyethylene terephthalate, polycarbonate, polycarbonate alloys, polystyrene, heat resistant polystyrene, poly(methyl methacrylate), poly Butylene terephthalate, polypropylene, polyethylene, acrylonitrile butadiene styrene, polyurethane, polyimide, polyvinyl chloride, styrene acrylonitrile, ethylene vinyl acetate, poly Amides, polyacetals, phenols, epoxy resins, ureas, melamines, unsaturated esters, silicones and cyclic olefin polymers. Preferably, the skin layer comprises polycarbonate or a polycarbonate alloy.

Although not shown in FIG. 1 , a low refractive index layer may be further stacked on the lower surface of the reflective polarizing film. The low refractive index layer improves the hardness of the reflective polarizing film and thus improves the durability of the reflective polarizing film and the polarizing plate. The low-refractive-index layer serves as a low-reflection layer and can further improve front contrast, as described below.

The low refractive index layer may have a smaller refractive index than the outermost layer of the reflective polarizing film. For example, the low refractive index layer may have a refractive index of about 1.52 or less, specifically about 1.0 to 1.5, more specifically about 1.10 to 1.44, still more specifically about 1.18 to 1.36. Within this range, by further improving the transmittance of light incident on the polarizing plate, the low refractive index layer can further improve the front contrast by further improving the brightness. The low refractive index layer may have a thickness of about 5 microns or less, specifically greater than about 0 microns to 5 microns or less. The low-refractive index layer may have any composition as long as the low-refractive index layer can secure the refractive index within the above-mentioned range. first protective film

The first protective film is stacked on the lower surface of the absorbing polarizer to protect the absorbing polarizer. The first protective film improves front contrast by adjusting the angle between the axes explained below.

The first protective film may include a film formed of an optically transparent resin. For example, the first protective film may include at least one selected from the group consisting of cellulose ester resins, including triacetylcellulose (TAC); and cyclic polyolefin resins, including amorphous cyclic olefin polymers (cyclic olefin polymers). olefin polymer, COP), etc.; polycarbonate resin; polyester resin, including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene naphthalate Butylene glycol esters, etc.; polyether resins; polyamide resins; polyimide resins; polyimide resins; resin, etc.; polyvinyl alcohol resin; polyvinyl chloride resin; and polyvinylidene chloride resin, but not limited thereto.

Preferably, the first protective film is a polyester resin, including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. esters, etc.

In one embodiment, the first protective film may have about 80 grams/(square meter day) or less than 80 grams/(square meter day) (eg, 0 grams/(square meter day), 10 grams/(square meter day) square meter day), 20 grams/(square meter day), 30 grams/(square meter day), 40 grams/(square meter day), 50 grams/(square meter day), 60 grams/( square meter day), 70 grams/(square meter day) or 80 grams/(square meter day)), specifically about 0 grams/(square meter day) to 80 grams/(square meter day) , more specifically about 65 grams/(square meter day) or less than 65 grams/(square meter day), more specifically about 50 grams/(square meter day) or less than 50 grams/(square meter day) days) moisture permeability. Within this range, the first protective film has low moisture permeability to improve the durability of the polarizer, and can prevent deterioration of the bonding strength between the reflective polarizer and the polarizer to prevent separation of the reflective polarizer and the polarizer. Here, the "moisture permeability" can be measured by the method of KS T 1305, but is not limited thereto.

The first protective film may be a single layer or may be composed of a plurality of resin films integrally formed with each other by co-extrusion.

The first protective film may have a thickness of about 10 to 100 microns, specifically, about 40 to 80 microns. Within this thickness range, the first protective film can be used in polarizers.

The first protective film has a high refractive index axis and a low refractive index axis in the in-plane direction. Here, the "high refractive index axis" and the "low refractive index axis" are defined by the relative comparison between the two axes in the in-plane direction of the first protective film, that is, the x-axis and the y-axis thereof. Although not particularly limited, the high refractive index axis and the low refractive index axis of the first protective film in the in-plane direction thereof can be determined by stretching the first protective film in the production of the first protective film. For example, the high refractive index axis may be the slow axis, and the low refractive index axis may be the fast axis.

3 , assuming that the high refractive index axis 310 of the reflective polarizing film 300 in the in-plane direction thereof is defined as 0°, the low refractive index axis 210 of the first protective film 200 relative to the high refractive index axis 310 is approximately - Angle settings from 5° to +5°. Within this range, polarizers ensure improved front contrast. Herein, in the expression of angles, "+" means an angle in a clockwise direction, and "-" means an angle in a counterclockwise direction with reference to 0°.

3, the angle may be between about -4° to about +4°, about -3° to about +3°, -2° to about +2°, or about -1° to about In the range of +1°, more specifically 0°. Within this range, the polarizing plate can be manufactured by a roll-to-roll process, thereby improving the handleability and economic feasibility of the polarizing plate.

In one embodiment, the low refractive index axis of the first protective film in its in-plane direction may be the machine direction (MD) of the first protective film, and the high refractive index axis of the first protective film in its in-plane direction It can be the transverse direction (TD) of the first protective film.

In another embodiment, the low refractive index axis of the first protective film in its in-plane direction may be the transverse direction (TD) of the first protective film, and the high refractive index of the first protective film in its in-plane direction The axis may be the machine direction (MD) of the first protective film.

In a further embodiment, the low refractive index axis of the first protective film in its in-plane direction may be a direction inclined with respect to the lateral direction of the first protective film, and the first protective film in its in-plane direction has a high refractive index axis. The refractive index axis may be a direction inclined with respect to the machine direction of the first protective film.

Preferably, the low refractive index axis of the first protective film in its in-plane direction is the machine direction (MD) of the first protective film, and the high refractive index axis of the first protective film in its in-plane direction is the first protective film. The transverse direction (TD) of the protective film thus improves the handleability and economic feasibility of the polarizer by allowing the polarizer to be manufactured by a roll-to-roll process by taking into account the axial relationship with respect to the absorbing polarizer.

The first protective film may include a stretched film to have the above-described low refractive index axis and high refractive index axis. Specifically, the first protective film may be a uniaxially stretched film or a biaxially stretched film, preferably a uniaxially stretched film. For example, the first protective film may be a TD uniaxially stretched film, an MD uniaxially stretched film or an MD/TD biaxially stretched film, preferably a TD uniaxially stretched film.

In TD uniaxial stretching, the first protective film may be produced by a method including stretching the resin for melt extrusion of the first protective film only in TD to about 2 times to 10 times its original length . Within this elongation ratio range, the first protective film may have a low refractive index axis and a high refractive index axis according to the present invention. Specifically, the first protective film may be stretched to an elongation of about 3 times to about 8 times.

In MD uniaxial stretching, the first protective film may be produced by a method including stretching the resin for melt extrusion of the first protective film only in MD to about 2 to 10 times its original length . Within this elongation ratio range, the first protective film may have a low refractive index axis and a high refractive index axis according to the present invention. Specifically, the first protective film may be stretched to an elongation of about 3 times to about 8 times.

At the time of biaxial stretching, the first protective film may be produced by a method including sequentially or simultaneously stretching the resin for melt extrusion of the first protective film in TD and MD. MD stretching may be performed to an elongation of about 1.0 to 3.5 times, and TD stretching may be performed to an elongation of about 2.5 to 6.0 times. Within this elongation ratio range, the first protective film may have a low refractive index axis and a high refractive index axis according to the present invention.

The stretching may be performed by at least one selected from dry stretching and wet stretching. The stretching may be performed at a temperature of (Tg - 20)° to (Tg + 50)°, wherein Tg is the glass transition temperature of the first protective film, specifically about 70°C to 150°C, and more specifically About 80°C to 130°C, still more specifically about 90°C to 120°C. Within this temperature range, stretching can be performed to provide the same stretching effect.

After stretching, the first protective film is subjected to heat treatment at a predetermined temperature to ensure the above axis and retardation of the first protective film. In particular, the first protective film subjected to TD uniaxial stretching may be subjected to heat treatment under the above-mentioned conditions to ensure the above axis and retardation of the first protective film. During the heat treatment, the temperature and time can be appropriately adjusted according to the material of the first protective film.

With the above-mentioned low refractive index axis and high refractive index axis, the first protective film may have a retardation value within a predetermined range. The retardation value of the first protective film may depend on the degree of stretching of the first protective film, the refractive index of the low refractive index axis, the refractive index of the high refractive index axis, and the like.

In one embodiment, the first protective film may have a wavelength of about 3,000 nanometers or greater, specifically about 3,000 nanometers to about 13,000 nanometers, more specifically about 5,000 nanometers, at a wavelength of about 550 nanometers The in-plane retardation Re is from about 13,000 nm to about 13,000 nm, still more specifically from about 5,000 nm to about 10,000 nm. Within this range, the first protective film can improve front contrast while suppressing the generation of rainbow mura.

In one embodiment, the first protective film may have a wavelength of about 15,000 nanometers or less, specifically about 3,000 nanometers to about 15,000 nanometers, more specifically about 6,000 nanometers, at a wavelength of about 550 nanometers meters to about 12,000 nm out-of-plane retardation Rth. Within this range, the first protective film can suppress the generation of speckles by birefringence, and at the same time improve the viewing angle characteristics of the liquid crystal display.

In one embodiment, the first protective film may have a wavelength of about 2.5 or less, specifically about 1.0 to about 2.2, more specifically about 1.2 to about 2.0, still more specifically about 2.5 at a wavelength of about 550 nanometers Biaxiality (NZ) of about 1.4 to about 1.8, most preferably about 1.45 to about 1.75. Within this range, the first protective film can suppress the generation of spots by birefringence while maintaining the mechanical strength of the film.

For example, the first protective film may be a TD uniaxially stretched film.

For example, the first protective film may have a refractive index nx or ny of 1.65 or more at a wavelength of about 550 nm in one of the x-axis direction and the y-axis direction in the in-plane direction. If the two refractive indices nx, ny of the first protective film are both less than about 1.65, or if the two refractive indices nx, ny of the first protective film are both about 1.65 or greater than 1.65, the first protective film may depend on the incident Speckle is caused by birefringence caused by changes in retardation of angle and wavelength. In one embodiment, the refractive index nx of the first protective film in the x-axis direction may be about 1.65 or more, specifically about 1.67 to about 1.75, and the refractive index of the first protective film in the y-axis direction ny It can be from about 1.45 to about 1.55. In other embodiments, the first protective film may have a refractive index ny of about 1.65 or greater, specifically about 1.67 to about 1.75, more specifically about 1.69 to 1.72, and a refractive index nx of about 1.45 to about 1.55. The absolute difference between nx and ny (|nx-ny|) may be in the range of about 0.1 to about 0.2, specifically about 0.12 to about 0.18, to ensure an improvement in viewing angle without generating rainbow spots.

In another embodiment, the first protective film may have a wavelength of about 500 nanometers or less, specifically about 50 nanometers to about 500 nanometers, more specifically about 100 nanometers, at a wavelength of about 550 nanometers. In-plane retardation Re from nanometers to about 350 nanometers. Within this range, the first protective film can improve the front contrast while suppressing the generation of rainbow streaks.

In another embodiment, the first protective film may have a wavelength of about 10,000 nanometers or less, specifically about 300 nanometers to about 900 nanometers, more specifically about 450 nanometers, at a wavelength of about 550 nanometers Out-of-plane retardation Rth from nanometers to about 750 nanometers. Within this range, the first protective film can suppress the generation of speckles by birefringence, and at the same time improve the viewing angle characteristics of the liquid crystal display.

In another embodiment, the first protective film may have a biaxiality ( NZ). Within this range, the first protective film can suppress the generation of spots by birefringence while maintaining the mechanical strength of the film.

For example, the first protective film may be a TD/MD biaxially stretched film.

For example, the first protective film may have a refractive index (nx or ny) of about 1.65 or more at a wavelength of about 550 nm in one of the x-axis direction and the y-axis direction in the in-plane direction. If the two refractive indices nx, ny of the first protective film are both less than about 1.65, or if the two refractive indices nx, ny of the first protective film are both about 1.65 or greater than 1.65, the first protective film may depend on the incident Speckle is caused by birefringence caused by changes in retardation of angle and wavelength. In one embodiment, the refractive index nx of the first protective film in the x-axis direction may be about 1.65 or more, specifically about 1.67 to about 1.75, and the refractive index of the first protective film in the y-axis direction ny It can be from about 1.45 to about 1.55. In other embodiments, the first protective film may have a refractive index nx of about 1.45 to about 1.55 and a refractive index ny of about 1.65 or greater, specifically about 1.67 to about 1.75, more specifically about 1.69 to about 1.72 . The absolute difference between nx and ny (|nx-ny|) may be in the range of about 0.1 to about 0.2, specifically about 0.12 to about 0.18, to ensure an improvement in viewing angle without generating rainbow spots. Absorptive polarizer

The absorptive polarizer 100 is used to split incident light into two polarized light components orthogonal to each other, and transmit one of the two polarized light components through the absorptive polarizer 100 while absorbing the other. The light component once polarized.

The absorptive polarizer may have a light transmittance of about 40% or more, specifically about 40% to about 45%, more specifically about 41% to about 45%. Absorptive polarizers may have a degree of polarization of about 95% or greater, specifically about 95% to about 100%, more specifically about 98% to about 100%. Within this range, the absorbing polarizer can further improve the front contrast and durability of the polarizing plate.

The absorbing polarizer may include at least one selected from the group of a dichroic dye-containing absorbing polarizer and a polyene functional group-containing absorbing polarizer. The dichroic dye-containing absorptive polarizer may include an absorptive polarizer manufactured by uniaxially stretching a base film for an absorptive polarizing film, followed by dyeing the stretched base film with iodine or a dichroic dye device. The polyene functional group-containing absorbing polarizer may include an absorbing polarizer manufactured by dehydrating and/or dechlorinating a base film for an absorbing polarizing film. The base film for the polarizing film may include a polyvinyl alcohol film or a derivative thereof, but is not limited thereto. Absorptive polarizers can be fabricated by typical methods well known to those skilled in the art.

The absorbing polarizer may have a thickness of about 1 micrometer to about 40 micrometers, specifically about 5 micrometers to about 30 micrometers, more specifically about 10 micrometers to about 25 micrometers. Within this thickness range, absorbing polarizers can be used in polarizers.

Although not shown in FIG. 1 , the polarizing plate may further include a second protective film on the upper surface of the absorbing polarizer 100 .

A second protective film may be stacked on the upper surface of the absorbing polarizer to protect the absorbing polarizer.

The second protective film may include an optical film formed of an optically transparent resin. The optical film may be formed of an optically transparent resin. The resin may include at least one selected from the group consisting of polyester resins, including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate Glycol esters, polybutylene naphthalate, etc.; acrylic resins; cyclic olefin polymer (COP) resins; cellulose ester resins, including triacetyl cellulose (TAC); polyvinyl acetate; polyvinyl chloride (polyvinyl chloride, PVC); polynorbornene; polycarbonate (PC); polyamide; polyacetal; polyphenylene ether; polyphenylene sulfide; Polyimide. The optical film may include a film manufactured after resin modification. Modification may include copolymerization, branching, cross-linking or modification of the terminal molecules. The optical film may be a stretched film or a non-stretched film. The second protective film may further include a coating layer formed on its upper surface to provide additional functions. The functional coating may be a hard coating, but is not limited thereto.

In one embodiment, the second protective film may have a wavelength of about 10 nanometers or less, specifically about 0 nanometers to about 10 nanometers, more specifically about 0 nanometers, at a wavelength of about 550 nanometers m to about 5 nm in-plane retardation Re. Within this range, the second protective film can improve the front contrast while suppressing the generation of rainbow streaks.

In one embodiment, the second protective film may have about 15 nanometers or less, specifically about -10 nanometers to about 15 nanometers, more specifically about -15 nanometers at a wavelength of about 550 nanometers Out-of-plane retardation Rth from 6 nm to about 10 nm. Within this range, the second protective film can suppress the generation of speckles by birefringence, and at the same time improve the viewing angle characteristics of the liquid crystal display.

In one embodiment, the second protective film may have a biaxiality (NZ) of about 50 or less, specifically about 0 to about 50, more specifically about 0 to about 30, at a wavelength of about 550 nanometers ). Within this range, the second protective film can suppress the generation of spots by birefringence while maintaining the mechanical strength of the film.

In another embodiment, the second protective film may have a wavelength of about 65 nanometers or less, specifically about 0 nanometers to about 60 nanometers, more specifically about 10 nanometers, at a wavelength of about 550 nanometers. In-plane retardation Re from nanometers to about 60 nanometers. Within this range, the second protective film can improve the front contrast while suppressing the generation of rainbow streaks.

In another embodiment, the second protective film may have a wavelength of about 150 nm or less, specifically greater than about 15 nm to about 150 nm, about 100 nm to about 150 nm at a wavelength of about 550 nm An out-of-plane retardation Rth of about 150 nm, more specifically about 120 nm to about 140 nm. Within this range, the second protective film can suppress the generation of speckles by birefringence, and at the same time improve the viewing angle characteristics of the liquid crystal display.

In another embodiment, the second protective film may have a biaxiality of about 10 or less, specifically about 0 to about 8, more specifically about 0 to about 5, at a wavelength of about 550 nm ( NZ). Within this range, the second protective film can suppress the generation of spots by birefringence while maintaining the mechanical strength of the film.

Although not shown in FIG. 1 , an adhesive layer, an adhesive layer or an adhesive/adhesive layer may be further formed on the upper surface of the second protective film. An adhesive layer, an adhesive layer, or an adhesive/adhesive layer can fix the polarizer to the adherend. The "adherent" may include, but is not limited to, a liquid crystal panel.

Next, a polarizing plate according to another embodiment of the present invention will be explained with reference to FIG. 4 .

The polarizing plate according to this embodiment includes an absorbing polarizer, a first protective film, and a reflective polarizing film, wherein a low refractive index axis of the first protective film in its in-plane direction is relative to the reflective polarizing film in its in-plane direction The high-refractive-index axis on the upper is set at an angle of about -5° to about +5°.

In addition, the high refractive index axis of the absorbing polarizer in the in-plane direction thereof is set at an angle of about −5° to +5° with respect to the high refractive index axis of the reflective polarizing film in the in-plane direction thereof. Except that the high refractive index axis of the absorbing polarizer in its in-plane direction is set at an angle of about -5° to +5° with respect to the high refractive index axis of the reflective polarizing film in its in-plane direction, according to this The polarizing plate of the embodiment is substantially the same as the polarizing plate shown in FIG. 1 . Here, the "high refractive index axis" and the "low refractive index axis" are defined by the relative comparison between the two axes in the in-plane direction of the absorbing polarizer, that is, the x-axis and the y-axis thereof. Although not particularly limited, the high refractive index axis and the low refractive index axis of the absorbing polarizer in its in-plane direction can be determined by stretching the absorbing polarizer in its manufacture.

Referring to FIG. 4 , in the polarizing plate, the high refractive index axis 110 of the absorbing polarizer 100 in the in-plane direction thereof is at about −5° with respect to the high refractive index axis 310 of the reflective polarizing film 300 in the in-plane direction thereof. to an angle setting of approximately +5°. Within this range, the polarizer ensures further improvement in front contrast. Specifically, in FIG. 4, the angle may be between about -4° to about +4°, about -3° to about +3°, about -2° to about +2°, or about -1° to In the range of about +1°, more specifically 0°. Within this range, the polarizing plate can be manufactured by a roll-to-roll process, thereby improving the handleability and economic feasibility of the polarizing plate.

In one embodiment, the high refractive index axis of the absorbing polarizer in its in-plane direction may be the absorption axis of the absorbing polarizer, and the low refractive index axis of the absorbing polarizer may be the transmission axis of the absorbing polarizer .

In one embodiment, the high index axis of the absorptive polarizer in its in-plane direction may be the machine direction (MD) of the absorptive polarizer, and the low index axis of the absorptive polarizer may be the absorptive polarizer the transverse direction (TD).

In one embodiment, an absorptive polarizer may be fabricated by uniaxially stretching a base film for an absorptive polarizing film, followed by dyeing the stretched base film with iodine or a dichroic dye.

Next, a polarizing plate according to a further embodiment of the present invention will be explained with reference to FIG. 5 .

The polarizing plate according to this embodiment includes an absorbing polarizer, a first protective film, and a reflective polarizing film, wherein a low refractive index axis of the first protective film in its in-plane direction is relative to the reflective polarizing film in its in-plane direction The high-refractive-index axis on the upper is set at an angle of about -5° to about +5°. In addition, in the polarizing plate, the high refractive index axis of the absorption type polarizer in the in-plane direction thereof is at an angle of about −5° to about +5° with respect to the low refractive index axis of the first protective film in the in-plane direction thereof. Angle setting. Further, except that the high refractive index axis of the absorbing polarizer in its in-plane direction is set at an angle of about -5° to about +5° with respect to the low refractive index axis of the first protective film in its in-plane direction , the polarizing plate according to this embodiment is substantially the same as the polarizing plate shown in FIG. 1 .

Referring to FIG. 5 , in the polarizing plate, the high refractive index axis 110 of the absorbing polarizer 100 in the in-plane direction thereof is at about −5° with respect to the low refractive index axis 210 of the first protective film 200 in the in-plane direction thereof. to an angle setting of approximately +5°. Within this range, the polarizer ensures further improvement in front contrast. 5, the angle may be between about -4° to about +4°, about -3° to about +3°, about -2° to about +2°, or about -1° to about In the range of +1°, more specifically 0°. Within this range, the polarizing plate can be manufactured by a roll-to-roll process, thereby improving the handleability and economic feasibility of the polarizing plate.

In one embodiment, the high refractive index axis of the absorbing polarizer in its in-plane direction may be the absorption axis of the absorbing polarizer or the machine direction (MD) of the absorbing polarizer.

In one embodiment, the low refractive index axis of the first protective film in its in-plane direction may be the machine direction (MD) of the second protective film.

Next, a polarizing plate according to still another embodiment of the present invention will be explained with reference to FIG. 6 .

The polarizing plate according to this embodiment includes an absorbing polarizer, a first protective film, and a reflective polarizing film, wherein a low refractive index axis of the first protective film in its in-plane direction is relative to the reflective polarizing film in its in-plane direction The high-refractive-index axis on the upper is set at an angle of about -5° to about +5°. The polarizing plate according to this embodiment is substantially the same as the polarizing plate shown in FIG. 1 except that the reflective polarizing film is a reflexive reflection type polarizing film.

Referring to FIG. 6 , the reflective polarizing film may have a multi-layered structure 20 in which first optical layers 24 and second optical layers 22 are alternately stacked on top of each other. Although not shown in FIG. 6 , a non-optical layer may be additionally formed on one or both surfaces of the multilayer structure constituting the brightness enhancement film to protect the optical film of the multilayer structure.

Each of the first optical layer and the second optical layer may comprise at least one selected from the group consisting of polyethylene naphthalate, copolyethylene naphthalate, polyethylene terephthalate Alcohol esters, polycarbonates, polycarbonate alloys, polystyrene, heat-resistant polystyrene, poly(methyl methacrylate), polybutylene terephthalate, polypropylene, polyethylene, acrylonitrile butadiene Ethylene styrene, polyurethane, polyimide, polyvinyl chloride, styrene acrylonitrile, ethylene vinyl acetate, polyamide, polyacetal, phenol, epoxy resin, urea, melamine, unsaturated Ester, silicone and cyclic olefin polymers. Preferably, the plate polymer includes polyethylene naphthalate. Preferably, each of the first optical layer and the second optical layer comprises polyethylene naphthalate.

The reflective polarizing film may be manufactured by stretching a multi-layer extruded film including a first optical layer and a second optical layer sequentially stacked thereon, but is not limited thereto.

The optical display according to the present invention may include the polarizing plate according to the present invention. In one embodiment, the optical display may comprise a liquid crystal display.

The liquid crystal display includes a liquid crystal panel, a polarizer according to the present invention (light source side polarizer) stacked on a light incident surface of the liquid crystal panel, and a polarizer (viewer side polarizer) stacked on a light exit surface of the liquid crystal panel. The polarizing plate stacked on the light exit surface of the liquid crystal panel includes any polarizing plate known to those skilled in the art. The liquid crystal display includes a light source disposed below the polarizing plate on the light source side. The light source may comprise a light source having a continuous light emission spectrum. For example, the light source may include a white light-emitting diode (LED) light source, a quantum dot (QD) light source, a light source containing a metal fluoride red phosphor, specifically a light source containing KSF (K ₂ SiF ₆ :Mn ⁴⁺ ) phosphor or KTF (K ₂ TiF ₆ :Mn ⁴⁺ ) phosphor light source, etc. The liquid crystal panel may be a vertical alignment (VA) mode panel, but is not limited thereto.

Next, the invention will be explained in more detail with reference to some examples. It should be understood that these examples are provided for illustration only and should not be construed as limiting the invention in any way. Example 1

A polyvinyl alcohol film (VF-PS#6500, thickness: 60 μm (Kuraray Co., Ltd.)) was uniaxially stretched in MD to 2 times its original length at 30°C , the stretched film was dyed with iodine, and a polarizer with a thickness of 20 μm was prepared by stretching the dyed film in a boric acid solution at 60° C. The stretching was performed at a maximum elongation of 6.5 times, and the polarizer’s high The refractive index axis is its absorption axis (MD).

Triacetoxycellulose (TAC) film (KC4CT1W, thickness: 40 μm, Re: 0.10 nm, Rth: 0.30 nm and NZ: 0.8 at a wavelength of 550 nm, Konica Co., Ltd. Co., Ltd.)) is bonded to the upper surface (light exit surface) of the polarizer. PET film (thickness: 80 μm, at 550 nm wavelength, Re: 8,500 nm, Rth: 9,300 nm and NZ: 1.55, (Toyobo Co., Ltd.)) to polarized light A reflective polarizing film (NRP300, structure of Figure 2, diffuse reflective polarizing film, Toray Chemical Co., Ltd.) was attached to the bottom surface of the PET film (light incident surface). the lower surface, thereby preparing a polarizing plate in which the TAC film, the polarizer, the PET film, and the reflective polarizing film are sequentially stacked on top of each other and integrated with each other.

The low refractive index axis of PET is the fast axis and corresponds to its MD.

The high refractive index axis of the reflective polarizing film is the reflection axis and corresponds to its MD. Assuming that the high refractive index axis of the reflective polarizing film of the polarizing plate in its in-plane direction is defined as 0°, the relationship between the high refractive index axis of the polarizer and the low refractive index axis of the PET film is shown in Table 1 . Example 2

Except using norbornene-based retardation film (thickness: 51 μm, at a wavelength of 550 nm, Re: 52 nm, Rth: 125 nm, NZ: 2.9, Zeon Co., Ltd.) ) in place of the TAC film, a polarizing plate was produced in the same manner as in Example 1. Example 3

A polarizing plate was fabricated in the same manner as in Example 1 except that the TAC film was not stacked. Example 4 and Example 5

The relationship between the high refractive index axis of the polarizer and the low refractive index axis of the PET film is changed as listed in Table 1, in the same manner as in Example 1, except that the high refractive index axis of the reflective polarizing film is assumed to be defined as 0°. way to manufacture polarizers. Example 6

A polarizing plate was fabricated in the same manner as in Example 1, except that a self-reflective polarizing film (QV2, 3M Company) was used in place of the reflective polarizing film (diffuse reflection polarizing film). Comparative Example 1

A polarizing plate was produced in the same manner as in Example 1 except that the PET film was not stacked. Comparative Example 2

Except that the high refractive index axis of the reflective polarizing film is assumed to be defined as 0°, the low refractive index axis of the PET film is inclined at an angle of 90° with respect to the high refractive index axis of the reflective polarizing film, in the same manner as in Example 1. way to manufacture polarizers. Comparative Example 3

Except for using a triacetyl cellulose (TAC) film (KC8UAW, thickness: 80 μm, non-stretched film, no low refractive index axis and no high refractive index axis in the in-plane direction, in the x-axis direction and the y-axis direction A polarizing plate was fabricated in the same manner as in Example 1, except that the TAC film was replaced by Konica Co., Ltd. having the same refractive index. Comparative Example 4

Except that the high refractive index axis of the reflective polarizing film is assumed to be defined as 0°, the low refractive index axis of the PET film is inclined at an angle of 6° with respect to the high refractive index axis of the reflective polarizing film, in the same manner as in Example 1. way to manufacture polarizers. Comparative Example 5

Except that the high refractive index axis of the reflective polarizing film is assumed to be defined as 0°, the low refractive index axis of the PET film is inclined at an angle of 6° with respect to the high refractive index axis of the reflective polarizing film, in the same manner as in Example 1. way to manufacture polarizers.

Liquid crystal panels were fabricated by sequentially assembling each of the polarizing plates fabricated in the examples and comparative examples.

Specifically, in addition to using each of the polarizers fabricated in the Examples and Comparative Examples as the light source side polarizers, the LED light source, the light guide plate, and the liquid crystal display module were assembled to include an edge-type LED light source (with the same Samsung TV (55" Ultra High Definition TV (UHD TV) (2016 model) same configuration, model: UN55KS8000F) LCD monitor. Then, using EZContrast X88RC ( EZXL-176R-F422A4, Eldim Inc. (ELDIM) measures the front (0°, 0°) side of the fabricated liquid crystal display module in each of the white mode and the black mode in the spherical coordinate system The brightness in 1) × 100/front contrast of Example 1. Table 1 first angle (°) Second angle (°) Front brightness in black mode front contrast difference in front contrast Example 1 0 0 0.056 6,500 0 Example 2 0 0 0.056 6450 -0.77% Example 3 0 0 0.056 6470 -0.46% Example 4 -5 0 0.060 6410 -1.38% Example 5 +5 0 0.060 6410 -1.38% Example 6 0 0 0.057 6490 -0.15% Comparative Example 1 - - 0.063 5650 -13.08% Comparative Example 2 90 0 0.073 4900 -24.62% Comparative Example 3 - - 0.064 5600 -13.85% Comparative Example 4 +6 0 0.066 5700 -12.31% Comparative Example 5 -6 0 0.066 5700 -12.31% *First angle: the angle of the low refractive index axis of the PET film of the polarizing plate relative to the high refractive index axis of the reflective polarizing film, assuming that the high refractive index axis of the reflective polarizing film is defined as 0° *Second angle: polarized light The angle of the high refractive index axis of the absorbing polarizer of the plate relative to the high refractive index axis of the reflective polarizing film, assuming that the high refractive index axis of the reflective polarizing film is defined as 0°

As shown in Table 1, the polarizing plate according to the present invention achieves a significant improvement in front contrast. In contrast, the polarizing plate of the comparative example, which did not satisfy the axial relationship according to the present invention, had a much lower front contrast ratio than the polarizing plate of the example.

It should be understood that various modifications, changes, alterations and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the present invention.

10: Core layer 11, 12, 13, 14: Plate polymers 20: Multilayer structure 22: Second Optical Layer 24: First Optical Layer 100: Absorptive polarizer 110: High refractive index axis 200: The first protective film 210: Low Refractive Index Axis 300: Reflective polarizing film 310: High refractive index axis A, B: group

FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. FIG. 2 is a conceptual diagram of a reflective polarizing film of the polarizing plate shown in FIG. 1 . 3 is a conceptual diagram illustrating the relationship between the low refractive index axis in the in-plane direction of the second protective film of the polarizing plate shown in FIG. 1 and the high refractive index axis in the in-plane direction of the reflective polarizing film. 4 is a diagram illustrating the relationship between the high refractive index axis in the in-plane direction of the absorbing polarizer of the polarizing plate and the high refractive index axis in the in-plane direction of the reflective polarizing film according to another embodiment of the present invention Concept map. 5 is a conceptual diagram illustrating the relationship between the high refractive index axis in the in-plane direction of the absorbing polarizer of the polarizing plate and the low refractive index axis in the in-plane direction of the second protective film according to a further embodiment of the present invention picture. FIG. 6 is a conceptual diagram of a reflective polarizing film according to still another embodiment of the present invention.

100: Absorptive polarizer

200: The first protective film

300: Reflective polarizing film

Claims (21)

A polarizing plate, comprising: an absorbing polarizer; a first protective film and a reflective polarizing film, which are sequentially stacked on the lower surface of the absorbing polarizer, wherein the first protective film is in the in-plane direction of the first protective film. The low refractive index axis is positioned at an angle of about -5° to +5° relative to the high refractive index axis of the reflective polarizing film in its in-plane direction, wherein the first protective film is at a wavelength of about 550 nm has a refractive index (nx or ny) of 1.65 or more in one of the high-refractive-index axis direction and the low-refractive-index axis direction in the in-plane direction thereof, and wherein the absorbing polarizer has a refractive index (nx or ny) of 1.65 or more in its in-plane direction The high refractive index axis in the in-plane direction is inclined at an angle of -5° to +5° with respect to the low refractive index axis of the first protective film in the in-plane direction thereof. The polarizing plate of claim 1, wherein the first protective film and the reflective polarizing film are sequentially stacked on a light incident surface of the absorbing polarizer. The polarizing plate of claim 1, wherein the first protective film is bonded to the reflective polarizing film by an adhesive layer, an adhesive layer or an adhesive/adhesive layer. The polarizing plate of claim 1, wherein the low refractive index axis of the first protective film in its in-plane direction is relative to the high refractive index of the reflective polarizing film in its in-plane direction Said angle of axis setting is in the range of -1° to +1° Inside. The polarizing plate of claim 1, wherein the high refractive index axis of the reflective polarizing film in the in-plane direction thereof corresponds to a machine direction (MD) of the reflective polarizing film. The polarizing plate of claim 1, wherein the reflective polarizing film comprises at least one selected from the group consisting of a diffuse reflective polarizing film and a self-reflective polarizing film. The polarizing plate of claim 6, wherein the diffusely reflective polarizing film comprises a core layer comprising a matrix and a plurality of plate-like polymers dispersed in the matrix. The polarizing plate of claim 7, wherein the self-reflective polarizing film comprises a multi-layer film comprising first optical layers and second optical layers alternately stacked on each other, the first optical layer The optical layer has a different refractive index than the second optical layer. The polarizing plate of claim 1, wherein the low refractive index axis of the first protective film in the in-plane direction thereof corresponds to a machine direction (MD) of the first protective film. The polarizing plate of claim 1, wherein the first protective film is a uniaxially stretched film. The polarizing plate of claim 1, wherein the first protective film has an in-plane retardation (Re) of 5,000 nm or more at a wavelength of 550 nm. The polarizing plate of claim 1, wherein the first protective film Has an out-of-plane retardation (Rth) of 15,000 nm or less at a wavelength of 550 nm. The polarizing plate of claim 1, wherein the first protective film has a moisture permeability of about 80 g/(m2·day) or less than 80 g/(m2·day). The polarizing plate of claim 1, wherein the first protective film comprises a material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polyethylene terephthalate. At least one polyester resin film in butylene naphthalate. The polarizing plate of claim 1, wherein a high refractive index axis of the absorbing polarizer in the in-plane direction thereof is relative to the high refractive index of the reflective polarizing film in the in-plane direction thereof The axis is tilted at an angle of -5° to +5°. The polarizing plate of claim 15, wherein the angle is in the range of -1° to +1°. The polarizing plate of claim 15, wherein the high refractive index axis of the absorptive polarizer in the in-plane direction thereof corresponds to a machine direction (MD) of the absorptive polarizer. The polarizing plate of claim 1, wherein the low refractive index axis of the first protective film in the in-plane direction thereof corresponds to a machine direction (MD) of the first protective film, and the The high refractive index axis of the absorbing polarizer in the in-plane direction thereof corresponds to the machine direction (MD) of the absorbing polarizer. The polarizing plate of claim 2, further comprising: a low refractive index layer stacked on the lower surface of the reflective polarizing film. The polarizing plate of claim 1, further comprising: a second protective film stacked on the upper surface of the absorbing polarizer. An optical display device comprising the polarizing plate according to any one of claims 1 to 20.

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