US-12619021-B2 - Polarizing plate and optical display apparatus comprising the same

US12619021B2US 12619021 B2US12619021 B2US 12619021B2US-12619021-B2

Abstract

A polarizing plate and an optical display apparatus including the same are provided. A polarizing plate includes: a polarizer; a protective layer stacked on a surface of the polarizer; and a retardation layer stacked on another surface of the polarizer, and the protective layer has an in-plane retardation of 3,000 nm or more at a wavelength of 550 nm, an optical axis of the protective layer is tilted at an angle of −2° to +2° with respect to a light absorption axis of the polarizer, and the polarizer has a single transmittance of 44.0% or more and a minimum crossed transmittance of 0.005% or more at a wavelength of 400 nm to 700 nm.

Inventors

Il Woong Baek
Yeon Ju Jung
Seo Young Kang
Seon Oh HWANG
Kwang Ho Shin
Jong Kyu Choi

Assignees

SAMSUNG SDI CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20221019
Priority Date: 20211020

Claims (13)

1 . A polarizing plate comprising: a polarizer; a protective layer stacked on a surface of the polarizer; and a retardation layer stacked on another surface of the polarizer, wherein: the polarizer comprises a polyvinyl alcohol based film dyed in a dyeing solution containing 1 wt % to 5 wt % of at least one of iodine or a dichroic dye; the protective layer comprises at least one selected from among a polyester based resin, a cyclic olefin polymer based resin, and a (meth)acrylic based resin; the protective layer has an in-plane retardation of 3,000 nm or more at a wavelength of 550 nm; an optical axis of the protective layer is tilted at an angle of −2° to +2° with respect to a light absorption axis of the polarizer; the polarizer has a single transmittance of 44.0% or more; and the polarizer has a minimum crossed transmittance of 0.005% to 5% at a wavelength of 400 nm to 700 nm.
2 . The polarizing plate according to claim 1 , wherein the protective layer has a water vapor transmission rate of 30 g/m 2 ·day or less.
3 . The polarizing plate according to claim 1 , wherein the optical axis is a slow axis or a fast axis of the protective layer.
4 . The polarizing plate according to claim 1 , wherein the protective layer further comprises an antireflection layer, a low reflectivity layer, an antiglare layer, a hard coating layer, a fingerprint resistant layer, or a primer layer on a surface thereof or on another surface thereof.
5 . The polarizing plate according to claim 1 , wherein the protective layer has a reflectivity of 1% or less.
6 . The polarizing plate according to claim 1 , wherein the polarizer has a maximum crossed transmittance at a wavelength of 480 nm to 550 nm in a wavelength range of 450 nm to 580 nm.
7 . The polarizing plate according to claim 1 , wherein the retardation layer comprises a first retardation layer and a second retardation layer.
8 . The polarizing plate according to claim 7 , wherein an absolute value of a tilted angle of a slow axis of the first retardation layer with reference to the light absorption axis of the polarizer is in a range of 10° to 30°.
9 . The polarizing plate according to claim 7 , wherein an absolute value of a tilted angle of a slow axis of the second retardation layer with reference to the light absorption axis of the polarizer is in a range of 79° to 89°.
10 . The polarizing plate according to claim 7 , wherein an angle defined between a slow axis of the first retardation layer and a slow axis of the second retardation layer is in a range of 49° to 79°.
11 . The polarizing plate according to claim 7 , wherein the first retardation layer has an in-plane retardation of 210 nm to 270 nm at a wavelength of 550 nm, and the second retardation layer has an in-plane retardation of 60 nm to 150 nm at a wavelength of 550 nm.
12 . The polarizing plate according to claim 1 , wherein the polarizing plate has a deviation of crossed optical characteristics of 10% or less, as calculated by the following Equation 3: Deviation of crossed optical characteristics=|( A−B )/ B|× 100, where A is a value of the crossed optical characteristics, as measured on the polarizing plate including the protective layer stacked on an upper surface of the polarizer and having the optical axis, and B is a value of the crossed optical characteristics, as measured on a reference polarizing plate including a protective layer stacked on the upper surface of the polarizer and having no optical axis.
13 . An optical display apparatus comprising the polarizing plate according to claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0139994, filed on Oct. 20, 2021 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. 1. FIELD Aspects of embodiments of the present invention relate to a polarizing plate and an optical display apparatus including the same. 2. DESCRIPTION OF THE RELATED ART An organic light emitting diode display can suffer from deterioration in visibility and contrast ratio due to reflection of external light. In order to solve such a problem, a polarizing plate for antireflection is used. The polarizing plate for antireflection includes a polarizer, a protective layer stacked on a surface of the polarizer, and a retardation layer stacked on another surface of the polarizer. External light entering the polarizer through the protective layer is extinguished through sequential reflection and/or transmission in the sequence of the retardation layer, an organic light emitting diode panel, the retardation layer and the polarizer, thereby solving the above problem. Since the protective layer does not directly participate in an antireflection function of the polarizing plate, a film substantially having an in-plane retardation of 0 nm at a wavelength of 550 nm, such as a triacetylcellulose (TAC) based film is used as the protective layer. However, since the TAC film has a high water vapor transmission rate and thus may reduce durability of the polarizing plate under high temperature/humidity conditions, a film having a low water vapor transmission rate such as polyethylene terephthalate (PET) based, cyclic olefin polymer (COP) based or acrylic based film may be used for the purpose of improving durability for the polarizing plate. However, these films have higher retardation values than the TAC based film and an optical axis due to a stretching process. In particular, the PET based film has problems due to birefringence thereof and, thus, when it does not have a high in-plane retardation, a rainbow mura may appear. The polarizing plate for antireflection requires an antireflective retardation film on one surface of the polarizer to convert linear polarization into circular polarization. However, in measurement of optical characteristics of the polarizing plate, when light is transmitted from the antireflective retardation film to the polarizer, the light is converted into circularly polarized light, thereby causing significant deterioration in measurement accuracy of the optical characteristics of the polarizing plate. Thus, the optical characteristics of the polarizing plate are measured while transmitting light in a direction from the protective layer to the polarizer. However, in a polarizing plate for antireflection including a protective layer having high in-plane retardation and a non-aligned optical axis, since the protective layer reduces an aligned state of linearly polarized light even upon transmission of light through the protective layer to the polarizer, the optical characteristics of the polarizing plate, particularly crossed optical characteristics measured with a low quantity of light, cannot be measured with high reliability. For polarizing plates for liquid crystal displays (LCDs), the crossed optical characteristics have a very high correlation with brightness and colors in a black mode. In particular, since a contrast ratio has a very high correlation with spectrum of crossed transmittance, it is important to perform accurate and reliable measurement of the corresponding performance such as the crossed optical characteristics. For polarizing plates for organic light emitting diodes (OLEDs), the crossed optical characteristics have a very high correlation with a reflected color that are included in the field of view. In particular, it is important to make accurate measurement of the crossed optical characteristics, since the crossed optical characteristics have a very high correlation with reflectivity. For the polarizing plates for OLEDs, inaccurate measurement of the crossed optical characteristics can make it very difficult to find and address problems when there is abnormality in reflection visibility of an OLED panel. Typically, the optical characteristics of the polarizing plate having a retardation layer and a protective layer on both surfaces thereof are measured before each of the retardation layer and the protective layer is bonded to the polarizer. However, since this method makes it difficult to check variation in optical characteristics after each of the retardation layer and the protective layer is bonded to the polarizer, this method is not regarded as accurate. As such, when the optical characteristics of the antireflective polarizing plate including the retardation layer and the protective layer providing phase retardation on both surfaces of the polarizer are not suitably measured or measured with low rel