Patent ID: 11971567
Assignee: DAI NIPPON PRINTING CO., LTD.
Field: Optics (Instruments)
Classification: CPC G  H | IPC G

Claim 0:
1. An optical film comprising a low-refractive index layer on a plastic film, wherein
the plastic film has a slow axis that is an axis with a largest refractive index in a plane, and a fast axis that is an axis orthogonal to the slow axis in the plane of the plastic film,
the low-refractive index layer is located on a surface of the optical film, and
the optical film comprises a region in which ΣT calculated from the following measurement condition 1 satisfies more than 0.04 and less than 0.20:, <Measurement Condition 1>
when linearly polarized light is incident from a surface on a side opposite to the low-refractive index layer of the optical film; the linearly polarized light that is incident light is defined as light L1; transmitted light that is the light L1 transmitting through the optical film is defined as light L2;
the light L1 is incident on the optical film at angles disposed such that an elevation angle in a vibration direction of the light L1 with respect to the plane of the optical film is 50 degrees or more and 70 degrees or less while an angle formed by the slow axis and the vibration direction of the light L1 is fixed at 45 degrees; the elevation angle is varied in a range of 50 degrees or more and 70 degrees or less by every 2 degrees, and the light L2 is subject to measurements at 11 different elevation angles; the light L2 is measured at 11 measurement points as in the measurements;
the light L2 is subject to conversion into conditions of a C light source and at a viewing angle of 2 degrees; a* value and b* value at an nth measurement point among the 11 measurement points of the light L2 and in an L*a*b* color system are defined as a*n and b*n, respectively; a* value and b* value at an (n+1)th measurement point among the 11 measurement points of the light L2 and in the L*a*b* color system are also defined as a*n1 and b*n1, respectively; and
the measurements at the 11 measurement points are used to calculate a sum of square of a difference in a* between adjacent measurement points and square of a difference in b* between the adjacent measurement points; and the sum is calculated for each of 10 adjacent points and ΣT indicating a total of the sums is calculated, the ΣT can be expressed by the following formula 1:

ΣT=Σ[{a*n−a*n1}2+{b*n−b*n1}2]  (formula 1).