Polarizing plate, image display apparatus, and method for improving bright-place contrast in image display apparatus

Patent metadata

Field	Value
Publication number	US-9989688-B2
Application number	US-201314779413-A
Country	US
Kind code	B2
Filing date	Dec 26, 2013
Priority date	Mar 29, 2013
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

There is provided a polarizing plate including: a polarizer; and a light transmissive film with a birefringent property in a plane, disposed on one surface of the polarizer, wherein the light transmissive film satisfies a relationship of the following expression (1):

n x >N>n y   (1)
where a refractive index in a slow-axis direction which is a direction with a greatest refractive index in a plane of the light transmissive film is n x , a refractive index in a fast-axis direction which is a direction orthogonal to the slow-axis direction in the plane is n y , and an average refractive index of the light transmissive film is N; and wherein the polarizer and the light transmissive film are placed so that both fast-axis direction of the light transmissive film and absorption-axis direction of the polarizer are along a horizontal direction.

First claim

The invention claimed is:

1. An image display apparatus comprising a polarizing plate, wherein the polarizing plate comprises:
a polarizer; and
a light transmissive film with a birefringent property in a plane, disposed on one surface of the polarizer, wherein the light transmissive film satisfies a relationship according to the following expression (1): n x >N>n y , wherein a refractive index in a slow-axis direction, which is a direction with a greatest refractive index in a plane of the light transmissive film, is n x , wherein a refractive index in a fast-axis direction, which is a direction orthogonal to the slow-axis direction in the plane, is n y , and wherein an average refractive index of the light transmissive film is N,
wherein the polarizer and the light transmissive film are placed so that both the fast-axis direction of the light transmissive film and an absorption-axis direction of the polarizer are parallel to each other,
wherein the polarizing plate is placed so that both the fast-axis direction of the light transmissive film and the absorption-axis direction of the polarizer are arranged along a horizontal direction, and
wherein the image display apparatus comprises a λ/4 phase difference plate and is an organic electroluminescence display, whereby the polarizing plate is placed on a side of the image display apparatus that is closer to an observer than the λ/4 phase difference plate.

2. The image display apparatus according to claim 1 , wherein the polarizing plate is placed so that the light transmissive film is located on a side of the image display apparatus that is closer to an observer than the polarizer.

3. The image display apparatus according to claim 2 , wherein the image display apparatus further comprises a display element, and the polarizing plate is placed on a side of the image display apparatus that is closer to an observer than the display element.

4. The image display apparatus according to claim 1 , wherein a difference (n x −n y ) between the refractive index (n x ) in the slow-axis direction of the light transmissive film, and the refractive index (n y ) in the fast-axis direction, which is a direction orthogonal to the slow-axis direction, is 0.01 or more and 0.30 or less.

5. The image display apparatus according to claim 4 , wherein the difference (n x −n y ) between the refractive index (n y ) in the slow-axis direction of the light transmissive film, and the refractive index (n y ) in the fast-axis direction, which is the direction orthogonal to the slow-axis direction, is 0.07 to 0.25.

6. The image display apparatus according to claim 1 , wherein the light transmissive film is one of a polyester film and a polycarbonate film.

7. The image display apparatus according to claim 1 , wherein the polarizing plate further comprises a functional layer, which is formed on a plane of the light transmissive film that is opposite to a plane on which the polarizer is formed, and of which a refractive index in a direction parallel to the fast-axis direction of the light transmissive film is lower than a refractive index in the fast-axis direction of the light transmissive film.

8. The image display apparatus according to claim 7 , wherein the functional layer is one of a hard coat layer and an antiglare layer.

9. The image display apparatus according to claim 7 , wherein the average refractive index of the light transmissive film is higher than an average refractive index of the functional layer.

10. A method for improving bright-place contrast in an image display apparatus comprising a polarizing plate and λ/4 phase difference plate, the method comprising the steps of:
providing the λ/4 phase difference plate;
providing polarizing plate, wherein the polarizing plate comprises a polarizer and a light transmissive film with a birefringent property in a plane that is disposed on one surface of the polarizer, wherein the light transmissive film satisfies a relationship according to the following expression (1): n x >N>n y , wherein a refractive index in a slow-axis direction, which is a direction with a greatest refractive index in a plane of the light transmissive film, is n x , wherein a refractive index in a fast-axis direction, which is a direction orthogonal to the slow-axis direction in the plane, is n y , and wherein an average refractive index of the light transmissive film is N;
placing the polarizer and the light transmissive film so that both the fast-axis direction of the light transmissive film and an absorption-axis direction of the polarizer are parallel to each other;
placing the polarizing plate in the image display apparatus so that both the fast-axis direction of the light transmissive film and the absorption-axis direction of the polarizer in the polarizing plate are arranged along a horizontal direction; and
wherein the image display apparatus is an organic electroluminescence display, whereby the polarizing plate is placed on a side of the image display apparatus that is closer to an observer than the λ/4 phase difference plate.

11. The method according to claim 10 , wherein the polarizing plate is placed so that the light transmissive film is located on a side of the image display apparatus that is closer to an observer than the polarizer.

12. The method according to claim 11 , wherein the image display apparatus further comprises a display element, and the polarizing plate is placed on a side of the image display apparatus that is closer to an observer than the display element.

13. The method according to claim 10 , wherein a difference (n x −n y ) between the refractive index (n y ) in the slow-axis direction of the light transmissive film and the refractive index (n y ) in the fast-axis direction, which is a direction orthogonal to the slow-axis direction, is 0.01 or more and 0.30 or less.

14. The method according to claim 13 , wherein the difference (n x −n y ) between the refractive index (n x ) in the slow-axis direction of the light transmissive film and the refractive index (n y ) in the fast-axis direction, which is the direction orthogonal to the slow-axis direction, is 0.07 to 0.25.

15. The method according to claim 10 , wherein the light transmissive film is one of a polyester film and a polycarbonate film.

16. The method according to claim 10 , wherein the polarizing plate further comprises a functional layer, which is formed on a plane opposite to a plane of the light transmissive film, on which the polarizer is formed, and of which a refractive index in a direction parallel to the fast-axis direction of the light transmissive film is lower than a refractive index in the fast-axis direction of the light transmissive film.

17. The method according to claim 16 , wherein the functional layer is one of a hard coat layer and an antiglare layer.

18. The method according to claim 16 , wherein the average refractive index of the light transmissive film is higher than an average refractive index of the functional layer.

Assignees

• Dainippon Printing Co Ltd

Inventors

• Kuroda Takashi

Classifications

• G02F1/133528

  Polarisers · CPC title

• G02F2201/50

  Protective arrangements · CPC title

• G02F1/133634

  the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis · CPC title

• G02B27/286

  for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another (G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34) · CPC title

• G02B1/14

  Protective coatings, e.g. hard coatings · CPC title