Optically anisotropic film, optical element, and optical system

Patent metadata

Field	Value
Publication number	US-2023125215-A1
Application number	US-202218067250-A
Country	US
Kind code	A1
Filing date	Dec 16, 2022
Priority date	Jun 19, 2020
Publication date	Apr 27, 2023
Grant date	—

Abstract

An optically anisotropic film is formed of a liquid crystal composition including a liquid crystal compound and has a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction of the optically anisotropic film, and the optically anisotropic film satisfies predetermined requirements.

First claim

What is claimed is:

1 . An optically anisotropic film that is formed of a liquid crystal composition including a liquid crystal compound, the optically anisotropic film comprising:
a liquid crystal alignment pattern where a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction of the optically anisotropic film, wherein a requirement X described below and a requirement Y 1 or a requirement Y 2 described below are satisfied, the requirement X: in a case where any position on one surface of the optically anisotropic film in a cross-section of the optically anisotropic film taken along a direction in which the liquid crystal alignment pattern extends is represented by a position P 1 , a position at which a line and another surface of the optically anisotropic film intersect with each other is represented by a position P 2 , the line being formed by connecting positions at which directions of optical axes derived from the liquid crystal compounds are the same as a direction of an optical axis derived from the liquid crystal compound at the position P 1 from the position P 1 to the other surface of the optically anisotropic film, and a distance between the position P 1 and the position P 2 in the one in-plane direction of the optically anisotropic film is represented by a distance D, a first region where an angle between an optical axis derived from the liquid crystal compound at a position X on the one surface of the optically anisotropic film and an optical axis derived from the liquid crystal compound at a position Y on the other surface of the optically anisotropic film that is distant from the position X by the distance D in the direction in which the liquid crystal alignment pattern extends is less than 3° and a second region where the angle is 3° or more are provided in the optically anisotropic film, the requirement Y 1 : the optically anisotropic film is observed with a polarization microscope in a crossed nicols state, a direction of a dark line having a lowest brightness at each of positions in the direction in which the liquid crystal alignment pattern extends is specified, and a dark line at an outermost position in the polarization microscope observed region among some of the dark lines at the positions that are parallel to the direction in which the liquid crystal alignment pattern extends is set as a reference dark line, a rotation angle of the dark line at each of the positions in the direction in which the liquid crystal alignment pattern extends from the reference dark line with respect to the reference dark line is obtained, a point corresponding to the distance and the rotation angle at each of the positions is plotted at rectangular coordinates where a horizontal axis represents a distance from the reference dark line to each of the positions in the direction in which the liquid crystal alignment pattern extends and a vertical axis represents the rotation angle of the dark line at each of the positions with respect to the reference dark line, a regression line is formed with a least-squares method using the plurality of plotted points, and a difference between the rotation angle at each of the plotted points and a rotation angle of the regression line at the distance of each of the plotted points is less than 5°, the requirement Y 2 : the optically anisotropic film is observed with a polarization microscope in a crossed nicols state, a direction of a dark line having a lowest brightness at each of positions in the direction in which the liquid crystal alignment pattern extends is specified, and a dark line at an outermost position in the polarization microscope observed region among some of the dark lines at the positions that are parallel to the direction in which the liquid crystal alignment pattern extends is set as a reference dark line, a rotation angle of the dark line at each of the positions in the direction in which the liquid crystal alignment pattern extends from the reference dark line with respect to the reference dark line is obtained, a point corresponding to the distance and the rotation angle at each of the positions is plotted at rectangular coordinates where a horizontal axis represents a distance from the reference dark line to each of the positions in the direction in which the liquid crystal alignment pattern extends and a vertical axis represents the rotation angle of the dark line at each of the positions with respect to the reference dark line, an approximate curve is formed when quadratic function approximation is performed with a least-squares method using the plurality of plotted points, and a difference between the rotation angle at each of the plotted points and a rotation angle of the approximate curve at the distance of each of the plotted points is less than 5°.

2 . The optically anisotropic film according to claim 1 ,
wherein in a case where a length over which the optical axis derived from the liquid crystal composition rotates by 180° in a plane in the direction in which the liquid crystal alignment pattern extends is set as a single period, the length of the single period in the liquid crystal alignment pattern gradually decreases in the one in-plane direction in which the direction of the optical axis changes while continuously rotating in the liquid crystal alignment pattern, and the requirement Y 2 is satisfied.

3 . The optically anisotropic film according to claim 1 ,
wherein the first region and the second region are alternately provided in the direction in which the liquid crystal alignment pattern extends.

4 . The optically anisotropic film according to claim 1 ,
wherein in a case where a length over which the optical axis derived from the liquid crystal composition rotates by 180° in a plane in the direction in which the liquid crystal alignment pattern extends is set as a single period, the first region and the second region are alternately provided in the direction in which the liquid crystal alignment pattern extends and the single period includes at least two first regions and at least two second regions.

5 . The optically anisotropic film according to claim 1 ,
wherein in a case where a length over which the optical axis derived from the liquid crystal composition rotates by 180° in a plane in the direction in which the liquid crystal alignment pattern extends is set as a single period, a minimum value of the length of the single period is 20 μm or less.

6 . The optically anisotropic film according to claim 1 ,
wherein in a case where a length over which the optical axis derived from the liquid crystal composition rotates by 180° in a plane in the direction in which the liquid crystal alignment pattern extends is set as a single period, a thickness of the optically anisotropic film is more than ¼ times a minimum value of the length of the single period.

7 . The optically anisotropic film according to claim 1 ,
wherein the liquid crystal alignment pattern is a concentric circular pattern having a concentric circular shape where the one in-plane direction in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating moves from an inner side toward an outer side.

8 . The optically anisotropic film according to claim 1 ,
wherein the optically anisotropic film includes regions where twisted directions of the optical axes derived from the liquid crystal compounds in the thickness direction are different, the regions include a region A where the direction of the optical axis derived from the liquid crystal compound is twisted in a thickness direction and rotates and a region B where the direction of the optical axis derived fr

Assignees

• Fujifilm Corp

Inventors

• Yonemoto Takashi
• Saitoh Yukito
• Sato Hiroshi
• Fukushima Yuki
• Ichihashi Mitsuyoshi
• Kodama Keisuke
• Katoh Shunya
• Yanase Naoto

Classifications

• G02B5/1833

  comprising birefringent materials (birefringent elements per se G02B5/3083) · CPC title

• G02B5/1809

  with pitch less than or comparable to the wavelength · CPC title

• G02B5/3016 Primary

  involving passive liquid crystal elements (optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528) · CPC title

• G02F1/13706 Primary

  the liquid crystal having positive dielectric anisotropy · CPC title