CN113474695A

CN113474695A - Polarizing plate and optical display device comprising same

Info

Publication number: CN113474695A
Application number: CN202080016123.8A
Authority: CN
Inventors: 郑利拉; 李正均; 金润定; 白一雄; 申东允; 郑姸周
Original assignee: Samsung SDI Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 2019-03-12
Filing date: 2020-02-20
Publication date: 2021-10-01
Also published as: KR102620956B1; KR102426168B1; TWI744819B; KR20200109190A; TW202040239A; WO2020184862A1; KR20220106940A

Abstract

A polarizing plate and an optical display device. The polarizing plate includes a polarizer; and a first retardation layer and a second retardation layer sequentially stacked on the lower surface of the polarizer. The first retardation layer has a regular wavelength dispersion characteristic and satisfies the relationship between refractive indices represented by relationship 5. The second retardation layer has a regular wavelength dispersion characteristic and satisfies the relationship between refractive indices represented by the relationship 8. The slow axis direction of the first retardation layer is inclined with respect to the lateral direction of the laminate of the first retardation layer and the second retardation layer, the laminate of the first retardation layer and the second retardation layer has reverse wavelength dispersion characteristics, and the polarizer has a degree of polarization of 99% or more than 99% and a single light transmittance (Ts) of 44% or more than 44%.

Description

Polarizing plate and optical display device comprising same

Technical Field

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 capable of achieving a significant reduction in front and side reflectance on a side surface thereof, particularly over the entire range of polar angle (θ) of 5 ° to 60 °, and an optical display device including the same.

Background

An organic electroluminescence panel includes a metal electrode layer having a high reflectance. Therefore, the organic EL panel suffers from visibility deterioration due to reflection of external light. Such deterioration in visibility can be improved by attaching a circular polarizing plate to the organic EL panel.

Generally, a circular polarizing plate is manufactured by attaching 1/4 retardation plates to a polarizer. When applied to a polarizing plate, a Cyclic Olefin Polymer (COP) based retardation sheet, in which retardation is substantially constant rather than depending on the wavelength of detected light, has a problem of a difference in reflection color due to its flat wavelength dispersion characteristic. To solve such a disadvantage of the flat wavelength dispersion characteristic, a circular polarizing plate including a Polycarbonate (PC) resin-based retardation film having a reverse wavelength dispersion characteristic is proposed, in which retardation of the PC resin-based retardation film increases according to the wavelength of detected light. However, although such a circularly polarizing plate can achieve a significant improvement in reflection of external light and reflection color in the front direction of a display panel including the circularly polarizing plate, the display panel provides a color different from that when viewed from the front direction when viewed in an oblique direction, thus causing a color difference problem.

The background art of the present invention is disclosed in Korean patent laid-open publication No. 10-2016-.

Disclosure of Invention

Technical challenge

An object of the present invention is to provide a polarizing plate capable of achieving a significant reduction in side reflectance.

Another object of the present invention is to provide a polarizing plate capable of ensuring a reduction in thickness and an improvement in handleability.

Means for solving the problems

1. One embodiment of the present invention relates to a polarizing plate.

The polarizing plate includes a polarizer; and a first retardation layer and a second retardation layer sequentially stacked on the lower surface of the polarizer,

wherein the first retardation layer has a regular wavelength dispersion characteristic and satisfies a relationship between refractive indices represented by relationship 5:

[ relationship 5]

nx>ny≒nz

(where nx, ny, and nz are refractive indices of the first retardation layer in a slow axis direction, a fast axis direction, and a thickness direction of the first retardation layer at a wavelength of 550 nm, respectively),

wherein the second retardation layer has a regular wavelength dispersion characteristic and satisfies a relationship between refractive indices represented by a relationship 8:

[ relationship 8]

nx≒nz>ny

(wherein nx, ny and nz are refractive indices of the second retardation layer in a slow axis direction, a fast axis direction and a thickness direction of the second retardation layer at a wavelength of 550 nm, respectively), and

wherein the slow axis direction of the first retardation layer is inclined with respect to a Transverse Direction (TD) of a laminate of the first and second retardation layers, the laminate of the first and second retardation layers has reverse wavelength dispersion characteristics, and the polarizer has a degree of polarization of 99% or more than 99% and a single transmittance (Ts) of 44% or more than 44%.

2. In 1, the laminate of the first retardation layer and the second retardation layer may be a monolithic film.

3. In 1-2, the laminate of the first retardation layer and the second retardation layer may have an in-plane retardation (Re) value of 140 nm to 200 nm at a wavelength of 550 nm.

4. In 1-3, the laminate of the first retardation layer and the second retardation layer may satisfy relations 1 and 2:

[ relationship 1]

0.8≤Re(450)/Re(550)<1.0

[ relationship 2]

1.0<Re(650)/Re(550)≤1.2

(wherein Re (450), Re (550) and Re (650) are in-plane retardation values of the laminates of the first retardation layer and the second retardation layer at wavelengths of 450 nm, 550 nm and 650 nm, respectively).

5. In 1-4, the slow axis direction of the first retardation layer may be inclined at an angle of 70 ° ± 10 ° with respect to the transverse direction of the multilayer body of the first retardation layer and the second retardation layer.

6. In 1-5, the slow axis direction of the second retardation layer may be inclined at an angle of 0 ° ± 20 ° (excluding 0 °) with respect to the transverse direction of the multilayer body of the first retardation layer and the second retardation layer.

7. In 1-6, an angle defined between an absorption axis of the polarizer and the slow axis direction of the first retardation layer may be in a range of 10 ° to 30 °.

8. In 1-7, an angle defined between an absorption axis of the polarizer and the slow axis direction of the second retardation layer may be in a range of 70 ° to 90 °.

9. In 1-8, the first retarder layer may be a positive A retarder layer and the second retarder layer may be a negative A retarder layer.

10. In 1-9, the first retardation layer may comprise a film comprising a material selected from the group consisting of cyclic olefin polymers, such as norbornene polymers, and the like; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and the like; polyvinyl alcohol; polyvinyl chloride; a polyarylsulfone; polyolefin resins such as polyethylene, polypropylene, and the like; a polyarylate; and rod-like liquid crystal polymers.

11. In 1-10, the second retardation layer may comprise a coating comprising at least one selected from the group consisting of a homopolymer of styrene or a styrene derivative, a polystyrene polymer comprising a copolymer of styrene or a styrene derivative and a comonomer, a polyacrylonitrile polymer, a poly (methyl methacrylate) copolymer, and a cellulose copolymer such as a cellulose ester.

12. In 1-11, the first retardation layer may have an in-plane retardation value of 220 nm to 280 nm at a wavelength of 550 nm, and the second retardation layer may have an in-plane retardation value of 85 nm to 145 nm at a wavelength of 550 nm.

13. In 1-12, the polarizer may have an orthogonal transmittance of 0.001% to 0.7%.

14. In 1-13, the second retarder layer may be formed directly on the first retarder layer.

15. In 1-14, the polarizing plate may further include a protective layer formed on an upper surface of the polarizer.

16. Another embodiment of the present invention relates to an optical display device including the polarizing plate according to the present invention as described above.

Effects of the invention

The present invention provides a polarizing plate capable of achieving a significant reduction in side reflectance.

The invention provides a polarizing plate capable of ensuring thickness reduction and improved handling property.

Drawings

Fig. 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

Fig. 2 illustrates slow axis directions of a first retardation layer and a second retardation layer of the polarizing plate shown in fig. 1.

Fig. 3 shows the slow axis directions of the first and second retardation layers of the polarizing plate with respect to the absorption axis of the polarizer in fig. 1.

Detailed Description

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 practice the invention. It is to be understood that the present invention may be embodied in various forms and is not limited to the following embodiments. Although the 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. Throughout the drawings, like components will be denoted by like reference numerals.

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

Herein, "in-plane retardation (Re)" is represented by equation a, "out-of-plane retardation (Rth)" is represented by equation B, and "biaxial degree (NZ)" is represented by equation C:

[ equation A ]

Re＝(nx-ny)×d

[ equation B ]

Rth＝((nx+ny)/2-nz)×d

[ equation C ]

NZ＝(nx-nz)/(nx-ny)

(where nx, ny, and nz are refractive indices of the optical device in a slow axis (slow axis) direction, a fast axis (fast axis) direction, and a thickness direction of the optical device at the measurement wavelength, and d is a thickness (unit: nm) of the optical device)),

in equations a to C, the "optical device" means the first retardation layer, the second retardation layer, or the laminate of the first retardation layer and the second retardation layer. In equations a through C, the "measurement wavelength" may refer to a wavelength of 450 nm, 550 nm, or 650 nm.

Herein, "(meth) acrylic group" means an acrylic group and/or a methacrylic group.

The expression "X to Y" as used herein to denote a particular numerical range means "greater than or equal to X and less than or equal to Y (X ≦ and ≦ Y)".

"X + -Y" as used herein to denote a particular range of values means "X + Y" to "X-Y".

The inventors of the present invention confirmed that a polarizing plate formed by stacking a laminate of a first retardation layer and a second retardation layer, described below, on the lower surface of a polarizer having a polarization degree and a single light transmittance within specific ranges can achieve a significant reduction in side reflectance on the side surface thereof, particularly over the entire range of polar angles (θ) of 5 ° to 60 °, when applied to an optical display device. The inventors of the present invention achieved a significant reduction in the lateral reflectance by adjusting the retardation of the retardation layer together with the degree of polarization and single transmittance of the polarizer.

Next, a polarizing plate according to one embodiment of the present invention will be described with reference to fig. 1, 2, and 3.

Referring to fig. 1, a polarizing plate according to one embodiment of the present invention includes a protective layer (400), a polarizer (300), a first retardation layer (110), and a second retardation layer (210). The protective layer (400) is stacked on the upper surface of the polarizer (300), and the first retardation layer (110) and the second retardation layer (210) are sequentially stacked on the lower surface of the polarizer (300). The first retardation layer (110) is stacked on the second retardation layer (210) without an adhesive layer (or adhesive layer) therebetween. With this structure, the polarizing plate can be reduced in thickness.

[ laminate of first retardation layer and second retardation layer ]

The laminate of the first retardation layer (110) and the second retardation layer (210) exhibits wavelength dispersion characteristics in which the value of in-plane retardation (Re) gradually decreases as the wavelength decreases from longer wavelengths to shorter wavelengths. That is, the laminate of the first retardation layer and the second retardation layer exhibits reverse wavelength dispersion characteristics. As a result, the polarizing plate can achieve an improvement in screen quality on its side surface when applied to an optical display device. Specifically, the laminate of the first retardation layer and the second retardation layer may satisfy relations 1 and 2:

[ relationship 1]

0.8≤Re(450)/Re(550)<1.0

[ relationship 2]

1.0<Re(650)/Re(550)≤1.2，

For example, the laminate of the first retardation layer and the second retardation layer may have Re (450)/Re (550) of 0.8 to 0.99, specifically 0.81 to 0.95. The laminate of the first retardation layer and the second retardation layer may have Re (650)/Re (550) of more than 1.0 to less than 1.2, 1.01 to 1.15, specifically 1.04 to 1.13. Within this range, the polarizing plate can achieve an improvement in screen quality and a significant reduction in side reflectance.

In one embodiment, the laminate of the first and second retardation layers may have an in-plane retardation value of 140 nm to 200 nm (e.g., 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm) at a wavelength of 550 nm, specifically 140 nm to 195 nm, more specifically 140 nm to 190 nm, and even more specifically 150 nm to 190 nm. Within this range, the polarizing plate can achieve a reduction in side reflectance.

In another embodiment, the laminate of the first and second retardation layers may have an in-plane retardation value of 130 nm to 190 nm at a wavelength of 450 nm, specifically 135 nm to 185 nm, more specifically 140 nm to 180 nm. Within this range, the polarizing plate may exhibit the above-described wavelength dispersion characteristics, thereby providing a desired circular polarization effect while preventing the display panel from exhibiting blue color. In one embodiment, the laminate of the first and second retardation layers may have an in-plane retardation value of 150 nm to 210 nm at a wavelength of 650 nm, specifically 155 nm to 205 nm, more specifically 160 nm to 200 nm. Within this range, the polarizing plate can exhibit the above-described wavelength dispersion characteristics, and can prevent the display panel from appearing red.

The laminate of the first and second retardation layers may have a thickness of greater than 0 to 70 microns or less than 70 microns, specifically 5 to 60 microns, more specifically 10 to 60 microns. Within this thickness range, the laminate can be used in a polarizing plate.

The second retardation layer is formed directly on the first retardation layer. Herein, the expression "directly formed" means that no adhesive layer, adhesive layer or adhesive/adhesive layer is formed between the second retardation layer and the first retardation layer. The second retardation layer is formed by depositing a composition for the second retardation layer on the first retardation layer, and drying and/or curing the composition, followed by stretching. Therefore, the laminate of the first retardation layer and the second retardation layer is a single-layer film. With this structure, the polarizing plate allows roll-to-roll bonding when bonding the laminate of the first retardation layer and the second retardation layer to the polarizer, thereby improving the handleability and the production yield by reducing the defect rate. Although the first retardation layer and the second retardation layer have different retardation values, the first retardation layer is directly formed on the second retardation layer, and thus it is possible to reduce the thickness and improve the handleability of the polarizing plate.

Next, the first retardation layer and the second retardation layer will be described.

[ first retardation layer ]

The first retardation layer (110) exhibits wavelength dispersion characteristics in which the in-plane retardation (Re) value gradually increases as the wavelength decreases from longer wavelengths to shorter wavelengths. That is, the first delay layer exhibits regular wavelength dispersion characteristics. In this way, the polarizing plate is manufactured by forming a first retardation layer having a regular chromatic dispersion characteristic on the lower surface of the polarizer and forming a second retardation layer having a regular chromatic dispersion characteristic on the lower surface of the first retardation layer. With this structure, the polarizing plate can improve the screen quality of an optical display device including the polarizing plate.

Specifically, the first retardation layer may satisfy relation 3 and relation 4:

[ relationship 3]

1.0<Re(450)/Re(550)≤1.1

[ relationship 4]

0.9≤Re(650)/Re(550)<1.0

(where Re (450), Re (550), and Re (650) are in-plane retardation values of the first retardation layer at wavelengths of 450 nm, 550 nm, and 650 nm, respectively).

In one embodiment, the first retardation layer may have Re (450)/Re (550) of greater than 1.0 to 1.05 or less than 1.05. In another embodiment, the first retardation layer may have Re (650)/Re (550) of 0.95 or more than 0.95 to less than 1.0. Within this range, the polarizing plate can achieve a significant reduction in front reflectance and side reflectance.

In one embodiment, the first retarder layer may have an in-plane retardation value of 220 nm to 280 nm (e.g., 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, or 280 nm) at a wavelength of 550 nm, specifically 225 nm to 275 nm, more specifically 230 nm to 270 nm. Within this range, the polarizing plate can achieve a significant reduction in side reflectance.

In one embodiment, the first retarder layer may have an in-plane retardation value of 220 nm to 280 nm (e.g., 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, or 280 nm) at a wavelength of 450 nm, specifically 225 nm to 275 nm, more specifically 230 nm to 270 nm. Within this range, the polarizing plate can exhibit the above-described wavelength dispersion characteristics, and can reduce the front reflectance and the side reflectance. In one embodiment, the first retarder layer may have an in-plane retardation value of 220 nm to 280 nm at a wavelength of 650 nm, specifically 225 nm to 275 nm, more specifically 230 nm to 270 nm. Within this range, the polarizing plate can exhibit the above-described wavelength dispersion characteristics, and can reduce the front reflectance and the side reflectance.

The first retardation layer has a relationship between refractive indices represented by relationship 5. By such a relationship, the polarizing plate can have a better effect in reducing the side reflectance.

[ relationship 5]

nx>ny≒nz

(where nx, ny, and nz are refractive indices of the first retardation layer in a slow axis direction, a fast axis direction, and a thickness direction of the first retardation layer at a wavelength of 550 nm, respectively).

In one embodiment, the first retarder layer is a positive a retarder layer. With this structure, the polarizing plate can have a better effect in reducing the side reflectance.

The first retardation layer includes a film formed of a composition containing a resin having positive intrinsic birefringence. Therefore, the first retardation layer can be easily formed to have a refractive index in the stretching direction larger than that in the direction orthogonal to the stretching direction.

Resins having positive intrinsic birefringence include polymers having positive intrinsic birefringence. Polymers having positive intrinsic birefringence may include polymers selected from the group consisting of, for example, cyclic olefin polymers, such as norbornene polymers, and the like; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and the like; polyvinyl alcohol; polyvinyl chloride; a polyarylsulfone; polyolefin resins such as polyethylene, polypropylene, and the like; a polyarylate; and rod-like liquid crystal polymer, but not limited thereto. Specifically, polycarbonate resins having good properties in terms of retardation and high elongation at low temperatures, polyolefin resins having good properties in terms of mechanical properties, heat resistance, transparency and dimensional stability, and cycloolefin copolymers are preferable. The polymers having positive intrinsic birefringence may be used alone or in a mixture thereof.

The first retardation layer may further contain typical additives in addition to the resin having positive intrinsic birefringence. For example, the additives may include, but are not limited to, anti-coloring agents such as pigments and dyes, heat stabilizers, light stabilizers, Ultraviolet (UV) absorbers, antistatic agents, antioxidants, fine particles, and surfactants.

The first retardation layer has a slow axis in a direction oblique to a Transverse Direction (TD) of the laminate of the first retardation layer and the second retardation layer. Herein, the "oblique direction" is one in-plane direction of the first retardation layer, and means a direction which is not parallel and perpendicular to the TD of the laminated body of the first retardation layer and the second retardation layer. As such, since the slow axis direction of the first retardation layer is inclined with respect to the TD of the laminate of the first and second retardation layers, the laminate can be bonded to the polarizer by a roll-to-roll method, thereby preventing yield deterioration.

In one embodiment, referring to FIG. 2, the slow axis direction (SA) of the first retardation layer (110)₁₁₀) The TD of the laminate of the first retardation layer (110) and the second retardation layer (210) may be inclined at an angle of 70 DEG + -10 DEG, specifically 70 DEG + -5 DEG, more specifically 70 DEG + -3 deg. Within this range, the polarizing plate can achieve a reduction in front reflectance and side reflectance.

The first retardation layer (110) may have a thickness of 5 to 100 micrometers, in particular 5 to 60 micrometers. Within this thickness range, the first retardation layer may be used in a polarizing plate.

The first retardation layer may be formed by preparing a non-stretched film by melt molding, injection molding or compression molding a composition comprising a resin having positive intrinsic birefringence, and then stretching the non-stretched film in an oblique direction. Stretching of the non-stretched film may be performed to 1.1 times or more than 1.1 times, 4.0 times or less than 4.0 times, specifically 1.3 times to 3.0 times the original length of the non-stretched film. In this range, the slow axis direction of the first retardation layer can be controlled, and the refractive index of the first retardation layer in the stretching direction can be increased. Stretching may be carried out at a temperature of the glass transition temperature (Tg) +2 ℃ of the non-stretched film or greater to Tg +30 ℃ or less than Tg +30 ℃ of the non-stretched film. The stretching direction may be inclined at an angle smaller than an angle defined between the TD of the laminate of the first retardation layer and the second retardation layer and the slow axis direction of the first retardation layer with respect to the TD of the non-stretched film. For example, the stretching direction may be inclined at an angle of greater than 15 ° to less than 50 °, specifically greater than 17 ° to less than 48 °, relative to the TD of the non-stretched film.

Although the first retardation layer may be used alone in the polarizing plate, a primer layer may be further formed on the first retardation layer to improve adhesive strength between the first and second retardation layers. The primer layer may include at least one selected from the group consisting of an acrylic resin, a urethane resin, an acrylic urethane resin, an ester resin, and an ethylene imine resin, but is not limited thereto.

[ second retardation layer ]

The second retardation layer (210) exhibits wavelength dispersion characteristics in which the in-plane retardation (Re) value gradually increases as the wavelength decreases from longer wavelengths to shorter wavelengths. That is, the second retardation layer exhibits regular wavelength dispersion characteristics. With this structure, the polarizing plate can improve the screen quality of an optical display device including the polarizing plate. Specifically, the second retardation layer may satisfy relationship 6 and relationship 7:

[ relationship 6]

1.0<Re(450)/Re(550)≤1.2

[ relationship 7]

0.9≤Re(650)/Re(550)<1.0

(where Re (450), Re (550), and Re (650) are in-plane retardation values of the second retardation layer at wavelengths of 450 nm, 550 nm, and 650 nm, respectively).

In one embodiment, the second retardation layer may have Re (450)/Re (550) of 1.05 to 1.15, more specifically 1.1 to 1.15. In one embodiment, the second retardation layer may have Re (650)/Re (550) of greater than 0.9 to 0.95. Within this range, the polarizing plate can achieve a significant reduction in front reflectance and side reflectance.

In one embodiment, the second retardation layer may have an in-plane retardation value of 85 to 145 nanometers at a wavelength of 550 nanometers, specifically 90 to 140 nanometers, more specifically 95 to 135 nanometers. Within this range, the polarizing plate can achieve a significant reduction in front reflectance and side reflectance.

In one embodiment, the second retardation layer may have an in-plane retardation value of 100 nm to 160 nm at a wavelength of 450 nm, specifically 105 nm to 155 nm, more specifically 110 nm to 150 nm. Within this range, the polarizing plate can exhibit the above-described wavelength dispersion characteristics, and can reduce the front reflectance and the side reflectance. In one embodiment, the second retardation layer may have an in-plane retardation value of 80 to 140 nanometers at a wavelength of 650 nanometers, specifically 85 to 135 nanometers, more specifically 90 to 130 nanometers. Within this range, the polarizing plate can exhibit the above-described wavelength dispersion characteristics, and can reduce the front reflectance and the side reflectance.

The second retardation layer has a relationship between refractive indices represented by relationship 8. By such a relationship, the polarizing plate can have a better effect in reducing the side reflectance.

[ relationship 8]

nx≒nz>ny

(where nx, ny, and nz are refractive indices of the second retardation layer in a slow axis direction, a fast axis direction, and a thickness direction of the second retardation layer at a wavelength of 550 nm, respectively).

In one embodiment, the second retarder layer is a negative a retarder layer. With this structure, the polarizing plate can have a better effect in reducing the side reflectance.

The second retardation layer is formed of a composition containing a resin having negative intrinsic birefringence.

The resin having negative intrinsic birefringence includes a polymer having negative intrinsic birefringence. The polymer having negative intrinsic birefringence may include at least one selected from the group consisting of, for example, a homopolymer of styrene or a styrene derivative, a polystyrene polymer including a copolymer of styrene or a styrene derivative and a comonomer, a polyacrylonitrile polymer, a poly (methyl methacrylate) copolymer, and a cellulose copolymer such as a cellulose ester, but is not limited thereto. The comonomer may include one of acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. Preferably, the second retardation layer comprises at least one selected from the group consisting of polystyrene polymers and cellulose copolymers, more preferably polystyrene polymers.

The second retardation layer may further contain typical additives in addition to the resin having negative intrinsic birefringence. For example, the additives may include plasticizers, anti-coloring agents such as pigments and dyes, heat stabilizers, light stabilizers, UV absorbers, antistatic agents, antioxidants, fine particles, and surfactants, but are not limited thereto.

The second retardation layer has a slow axis in a direction inclined with respect to the TD of the laminate of the first retardation layer and the second retardation layer. Herein, the "oblique direction" is one in-plane direction of the second retardation layer, and means a direction that is not parallel and perpendicular to the TD of the laminate of the first retardation layer and the second retardation layer. As such, since the slow axis direction of the second retardation layer is inclined with respect to the TD of the laminate of the first and second retardation layers, the laminate can be bonded to the polarizer by a roll-to-roll method, thereby preventing the production yield from deteriorating.

In one embodiment, referring to FIG. 2, the slow axis direction (SA) of the second retarder layer (210)₂₁₀) The TD of the laminate of the first retardation layer (110) and the second retardation layer (210) can be inclined at an angle of 0 ° ± 20 ° (excluding 0 °), specifically 0 ° ± 10 ° (excluding 0 °), more specifically 0 ° ± 5 ° (excluding 0 °). Within this range, the polarizing plate can achieve a reduction in front reflectance.

The second retardation layer may have an in-plane retardation value of-110 nm to-50 nm at a wavelength of 550 nm, specifically-105 nm to-60 nm, more specifically-100 nm to-70 nm. Within this range, the polarizing plate can achieve a significant reduction in front reflectance and side reflectance.

The second retardation layer may have a biaxial degree of-1.0 to 0.5 at a wavelength of 550 nm. Within this range, the polarizing plate can achieve a reduction in front reflectance and side reflectance.

The second retardation layer may have a thickness of 2 to 15 micrometers, specifically 3 to 10 micrometers. Within this thickness range, the second retardation layer can be used in a polarizing plate.

The second retardation layer is a coating layer formed of a composition containing a resin having negative intrinsic birefringence.

The laminate of the first retardation layer and the second retardation layer may be formed by coating the composition for the second retardation layer on the first retardation layer and drying the composition, and then stretching both the first retardation layer and the second retardation layer at the same time. By stretching the first retardation layer and the second retardation layer, the slow axis direction of the first retardation layer can be adjusted, the slow axis direction of the second retardation layer can be expressed, and retardation values of the first retardation layer and the second retardation layer can be achieved within a target range.

In particular, the stretching may be performed at an angle of 0 ° ± 20 °, in particular 0 ° ± 15 °, more in particular 5 ° ± 15 ° with respect to the TD of the first retardation layer and the coating. More preferably, the stretching may be performed at an angle of 90 ° with respect to the TD of the first retardation layer and the coating, i.e. in the longitudinal direction. In this case, control of the slow axis direction of the first retardation layer and the second retardation layer can be facilitated. The stretching may be performed to 1.1 to 2.0 times, specifically 1.2 to 1.8 times.

[ polarizer ]

A polarizer (300) is stacked on an upper surface of the first retardation layer to reduce side reflectance by linearly polarizing external light or light received from the first retardation layer.

The polarizer (300) may have a degree of polarization of 99% or more and a single transmittance (Ts) of 44% or more. By satisfying both the degree of polarization and the single transmittance, the polarizer can achieve a significant reduction in side reflectance on its side surface, particularly over the entire range of the polar angle (θ) of 5 ° to 60 °, when stacked on the laminate of the first retardation layer and the second retardation layer. Herein, "single light transmittance" means the light transmittance (Ts) measured in the visible spectrum, for example, at a wavelength of 400 to 700 nanometers, and can be measured by typical methods known to those skilled in the art.

The "degree of polarization" can be measured by typical methods known to those skilled in the art. Specifically, the polarizer may have a degree of polarization of 99% to 99.9999% and a light transmittance (Ts) of 44% to 50%.

The polarizer (300) may have an orthogonal transmittance (Tc) of 0.001% to 0.7%, specifically 0.01% to 0.2%, more specifically 0.05% to 0.2%, at a wavelength of 380 nm to 780 nm. Within this range, the polarizer may have an antireflection effect on its side surface, particularly in the entire range of the polar angle (θ) of 5 ° to 60 °.

The polarizer (300) is bonded to the laminate of the first retardation layer and the second retardation layer by a roll-to-roll method. Therefore, the laminate of the first retardation layer and the second retardation layer serves as a lower protective film of the polarizer, so that a separate protective film on the lower surface of the polarizer can be eliminated, and thus a reduction in thickness of the polarizer can be achieved.

Referring to fig. 3, the slow axis direction (SA) of the first retardation layer (110)₁₁₀) And a slow axis direction (SA) of the second retardation layer (210)₂₁₀) And (4) intersecting. In addition, in the slow axis direction (SA) of the first retardation layer (110)₁₁₀) And the absorption axis (A) of the polarizer (300)₃₀₀) May be in the range of 10 DEG to 30 DEG, particularly 15 DEG to 30 DEG, and in the slow axis direction (SA) of the second retardation layer (210)₂₁₀) And the absorption axis (A) of the polarizer (300)₃₀₀) The angle defined therebetween may range from 70 ° to 90 °, specifically 80 ° to 90 °, more specifically 80 ° to less than 90 °. Within this range, the polarizing plate can achieve a reduction in front reflectance.

The absorption axis of the polarizer corresponds to the Machine Direction (MD) of the polarizer, and may become the stretching direction in the manufacture of the polarizer.

The polarizer (300) may have a thickness of 5 to 40 microns. Within this range, the polarizer may be used in the polarizing plate.

The polarizer (300) may include a polyvinyl alcohol-based polarizer formed by unidirectionally pulling a polyvinyl alcohol film, or a polyene-based polarizer formed by dehydrating a polyvinyl alcohol film.

In one embodiment, the polarizer may be manufactured by dyeing, stretching, crosslinking, and color correcting a polyvinyl alcohol film. A polarizer having a degree of polarization and a light transmittance within the above ranges can be obtained by appropriately adjusting the conditions of dyeing, stretching, crosslinking, and color correction.

Although not shown in fig. 1, an adhesive layer, or an adhesive/adhesive layer, or a protective layer described below may be further formed between the polarizer (300) and the first retardation layer (110).

[ protective layer ]

A protective layer (400) may be stacked on an upper surface of the polarizer to protect the polarizer. The protective layer protects the polarizing film to improve the reliability and mechanical strength of the polarizing plate.

The protective layer (400) may include at least one selected from an optically transparent protective film and an optically transparent protective coating. The protective film may include at least one selected from the group consisting of a cellulose ester resin including triacetyl cellulose (TAC), a cyclic polyolefin including amorphous cycloolefin polymer (COP), a polycarbonate resin, a polyester resin including polyethylene terephthalate (PET), a polyether sulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, a non-cyclic polyolefin resin, a poly (meth) acrylate resin including poly (methyl methacrylate), a polyvinyl alcohol resin, a polyvinyl chloride resin, and a polyvinylidene chloride resin, but is not limited thereto. The protective coating may be formed from an actinic radiation curable resin composition including an actinic radiation curable compound and a polymerization initiator. The actinic radiation curable compound may include at least one selected from the group consisting of a cationically polymerizable curable compound, a radically polymerizable curable compound, a urethane resin, and a silicone resin.

Although not shown in fig. 1, the polarizing plate may further include a functional coating layer on the upper surface of the protective layer. The functional coating layer may include at least one selected from the group consisting of a hard coating layer, an anti-fingerprint layer, an anti-reflection layer, a low-reflectivity layer, and an ultra-low-reflectivity layer, but is not limited thereto.

Although not shown in fig. 1, an adhesive layer may be further formed on the lower surface of the second retardation layer to stack the polarizing plate on the optical display device.

Next, a polarizing plate according to another embodiment will be explained.

The polarizing plate includes a protective layer, a polarizer, a first retardation layer and a second retardation layer. The protective layer is stacked on an upper surface of the polarizer, and the first retardation layer and the second retardation layer are sequentially stacked on a lower surface of the polarizer. The polarizing plate according to the present embodiment is substantially the same as the polarizing plate according to the above-described embodiment shown in fig. 1, except for the first retardation layer and the second retardation layer according to the present embodiment.

The first retardation layer and the second retardation layer according to the present embodiment are the same as the retardation layer described with reference to fig. 1.

According to the present embodiment, the slow axis direction of the first retardation layer may be inclined at an angle of 22.5 ° ± 15 °, specifically 22.5 ° ± 10 °, more specifically 22.5 ° ± 5 ° with respect to the TD of the laminate of the first retardation layer and the second retardation layer. Within this range, the polarizing plate can achieve an improvement in circularly polarized light.

According to the present embodiment, the slow axis direction of the second retardation layer may be inclined at an angle of 90 ° ± 25 °, specifically 90 ° ± 20 °, more specifically 90 ° ± 10 ° with respect to the TD of the laminate of the first and second retardation layers. Within this range, the polarizing plate can achieve an improvement in circularly polarized light.

Next, an optical display device according to the present invention will be explained.

The optical display device according to the present invention may include at least one of the polarizing plates according to the present invention. In one embodiment, the optical display device may include a liquid crystal display and a light emitting diode display, preferably a light emitting diode display. The liquid crystal display may include a liquid crystal display including an In-plane Switching (IPS) liquid crystal. The light emitting diode display includes an organic light emitting diode display or an organic/inorganic light emitting diode display such as a Light Emitting Diode (LED), an Organic Light Emitting Diode (OLED), a quantum dot light emitting diode (QLED), and a light emitting material such as a phosphor.

The invention will be explained in more detail below with reference to some examples. It should be noted, however, that these examples are provided for illustration only and should not be construed as limiting the invention in any way.

Example 1

A polarizer 12 μm thick was manufactured by stretching a polyvinyl alcohol film to three times its original length at 60 ℃, dyeing the stretched film with iodine, and stretching the dyed film to 2.5 times in an aqueous boric acid solution at 40 ℃. The single transmittance and the orthogonal transmittance of the polarizer were measured at a wavelength of 380 nm to 780 nm using V7100 (JASCO). The degree of polarization of the polarizer was measured using V7100 (japan optical spectroscopy).

A triacetyl cellulose (TAC) film (KA25-HC, Konica Minolta Opto, Inc., thickness: 32 μm) with a hard coat was bonded to the upper surface of the polarizer.

A monolithic film (reverse wavelength dispersion property, Re (450)/Re (550) ═ 0.91, Re (650)/Re (550) ═ 1.06) was formed by bonding a first retardation layer (regular wavelength dispersion property, + a plate, polyolefin-based film, Re (450) ═ 253 nm, Re (550) ═ 251 nm, Re (650) ═ 250 nm) to a second retardation layer (regular wavelength dispersion property, -a plate, polystyrene-based film, Re (450) ═ 129 nm, Re (550) ═ 116nm, Re (650) ═ 110 nm) without an adhesive layer, and the monolithic film was bonded to the lower surface of a polarizer, thereby producing a polarizing plate in which a triacetyl cellulose (TAC) film having a hard coat layer, a polarizer, a first retardation layer, and a second retardation layer were stacked in this order.

The monolithic film is a film formed by obliquely stretching a polyolefin-based copolymer resin film at a specific elongation and coating a polystyrene copolymer on one surface of the obliquely stretched polyolefin-based copolymer resin film to form a laminate, and then stretching the laminate at a specific elongation.

Examples 2 and 3

Each polarizing plate was prepared in the same manner as in example 1, except that a film having the specifications listed in table 1 was used as a monolithic film or the degree of polarization and light transmittance of a polarizer were changed as listed in table 1.

Comparative example 1

A polarizing plate was prepared in the same manner as in example 2, except that a film having the specifications listed in table 1 was used as the monolithic film and a polarizer having a degree of polarization of 98.0% and a light transmittance of 44.5% was used.

Comparative example 2

A polarizing plate was prepared in the same manner as in example 2, except that a film having the specifications listed in table 1 was used as the monolithic film and a polarizer having a degree of polarization of 99.0% and a light transmittance of 43.5% was used.

The details of the polarizing plates of examples and comparative examples are shown in table 1.

[ Table 1]

Alignment angle: an angle defined between a slow axis direction of the first retardation layer and a TD of a laminate of the first retardation layer and the second retardation layer

The reflectance (unit:%) of each polarizing plate of examples and comparative examples was measured, and the results are shown in table 2. Reflectance is (SCE) reflectance data not including a specular component measured on a polarizing film attached to a Galaxy S7 panel using DMS803 (Instrument Systems, Germany).

[ Table 2]

Angle of observation (°)	5	10	20	30	40	50	60
								Example 1	0.36	0.36	0.39	0.47	0.60	0.81	0.99
Example 2	0.33	0.34	0.36	0.43	0.57	0.76	0.93
								Example 3	0.39	0.39	0.42	0.50	0.65	0.86	1.03
Comparative example 1	0.48	0.48	0.51	0.58	0.72	0.91	1.06
								Comparative example 2	0.45	0.45	0.50	0.56	0.70	0.91	1.06

As shown in table 2, the polarizing plate according to the present invention can achieve a significant reduction in side reflectance.

In contrast, although the front surface reflectance is not shown in table 2, the polarizing plate of comparative example 1 including a polarizer having a degree of polarization of less than 99.0% has higher front surface reflectance and side surface reflectance than the polarizing plate of the example. In addition, although the front surface reflectance is not shown in table 2, the polarizing plate of comparative example 2 including a polarizer having a polarization degree of less than 44% has higher front surface reflectance and side surface reflectance than the polarizing plate of the example.

It is to be understood that various modifications, alterations, adaptations, and equivalent embodiments may occur to one skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. A polarizing plate comprising:

a polarizer; and

a first retardation layer and a second retardation layer sequentially stacked on a lower surface of the polarizer,

[ relationship 5]

nx>ny≒nz

(wherein nx, ny, and nz are refractive indices of the first retardation layer in a slow axis direction, a fast axis direction, and a thickness direction of the first retardation layer at a wavelength of 550 nm, respectively);

[ relationship 8]

nx≒nz>ny

(wherein nx, ny, and nz are refractive indices of the second retardation layer in a slow axis direction, a fast axis direction, and a thickness direction of the second retardation layer at a wavelength of 550 nm, respectively); and is

Wherein a slow axis direction of the first retardation layer is inclined with respect to a Transverse Direction (TD) of a laminate of the first and second retardation layers, the laminate of the first and second retardation layers has an inverse wavelength dispersion characteristic, and the polarizer has a degree of polarization of 99% or more than 99% and a single light transmittance (Ts) of 44% or more than 44%.

2. The polarizing plate of claim 1, wherein the laminate of the first retardation layer and the second retardation layer is a monolithic film.

3. The polarizing plate of claim 1, wherein the laminate of the first retardation layer and the second retardation layer has an in-plane retardation (Re) value of 140 nm to 200 nm at a wavelength of 550 nm.

4. The polarizing plate of claim 1, wherein the laminate of the first retardation layer and the second retardation layer satisfies relation 1 and relation 2:

[ relationship 1]

0.8≤Re(450)/Re(550)<1.0

[ relationship 2]

1.0<Re(650)/Re(550)≤1.2

5. The polarizing plate according to claim 1, wherein a slow axis direction of the first retardation layer is inclined at an angle of 70 ° ± 10 ° with respect to a transverse direction of the laminate of the first retardation layer and the second retardation layer.

6. The polarizing plate according to claim 5, wherein a slow axis direction of the second retardation layer is inclined at an angle of 0 ° ± 20 ° (excluding 0 °) with respect to a transverse direction of the laminate of the first retardation layer and the second retardation layer.

7. The polarizing plate of claim 1, wherein an angle defined between an absorption axis of the polarizer and a slow axis direction of the first retardation layer is in a range of 10 ° to 30 °.

8. The polarizing plate of claim 1, wherein an angle defined between an absorption axis of the polarizer and a slow axis direction of the second retardation layer is in a range of 70 ° to 90 °.

9. The polarizing plate of claim 1, wherein the first retardation layer is a positive a retardation layer and the second retardation layer is a negative a retardation layer.

10. The polarizing plate of claim 1, wherein the first retardation layer comprises a film comprising a polymer selected from the group consisting of cyclic olefin polymers, including norbornene polymers; polyesters, including polyethylene terephthalate and polybutylene terephthalate; polyvinyl alcohol; polyvinyl chloride; a polyarylsulfone; polyolefins, including polyethylene and polypropylene; a polyarylate; and rod-like liquid crystal polymers.

11. The polarizing plate of claim 1, wherein the second retardation layer comprises a coating comprising at least one selected from the group consisting of a homopolymer of styrene or a styrene derivative, a polystyrene polymer comprising a copolymer of styrene or a styrene derivative and a comonomer, a polyacrylonitrile polymer, a poly (methyl methacrylate) copolymer, and a cellulose copolymer comprising a cellulose ester.

12. The polarizing plate of claim 1, wherein the first retardation layer has an in-plane retardation value of 220 to 280 nm at a wavelength of 550 nm, and the second retardation layer has an in-plane retardation value of 85 to 145 nm at a wavelength of 550 nm.

13. The polarizing plate of claim 1, wherein the polarizer has an orthogonal transmittance of 0.001% to 0.7%.

14. The polarizing plate of claim 1, wherein the second retardation layer is formed directly on the first retardation layer.

15. The polarizing plate of claim 1, further comprising:

a protective layer formed on an upper surface of the polarizer.

16. An optical display device comprising the polarizing plate according to any one of claims 1 to 15.