US-12624142-B2 - Optical polymer material, optical film, display device, optical polymer material manufacturing method, and optical film manufacturing method

US12624142B2US 12624142 B2US12624142 B2US 12624142B2US-12624142-B2

Abstract

An optical polymer material includes an alternating copolymer made of a monomer of a styrene derivative and a monomer of a maleimide derivative, and has a nonlinear property in which the photoelastic coefficient of the optical polymer material decreases to a predetermined value with increase in composition ratio of the styrene derivative, and rises above the predetermined value with further increase in composition ratio of the styrene derivative. A composition ratio of the styrene derivative is within a predetermined range. An absolute value of the photoelastic coefficient is equal to or smaller than a first absolute value within the predetermined range of the composition ratio, and an absolute value of the intrinsic birefringence is equal to or smaller than a second absolute value of the optical polymer material within the predetermined range of the composition ratio.

Inventors

Yasuhiro Koike
Yuma Kobayashi
Kohei Watanabe

Assignees

YASUHIRO KOIKE
TOSOH CORPORATION

Dates

Publication Date: 20260512
Application Date: 20201224
Priority Date: 20191226

Claims (11)

1 . A low birefringence optical polymer material comprising an alternating copolymer comprising a monomer of a styrene derivative and a monomer of at least one maleimide derivative, wherein (a) the optical polymer material exhibits a nonlinear property in which a photoelastic coefficient of the optical polymer material decreases to a minimum value with an increase in composition ratio of the styrene derivative, and rises above the minimum value with a further increase in composition ratio of the styrene derivative, (b-1) an absolute value of the photoelastic coefficient is equal to or smaller than 2×10 −12 Pa −1 within a predetermined range of the composition ratio, and (b-2) an absolute value of an intrinsic birefringence of the optical polymer material is equal to or smaller than 20×10 −3 within the predetermined range of the composition ratio, and (b-3) an absolute value of a temperature coefficient of the intrinsic birefringence is 2×10 −5 ° C. −1 or less, and (c) the composition ratio of the maleimide derivative is more than the composition ratio of the styrene derivative, and wherein the alternating copolymer comprises (i) from 7 mol % to 27 mol % of the styrene derivative, (ii) from 27 mol % to 68 mol % of the maleimide derivative and (iii) the remainder being at least one monomer of a modified organic compound having a physical property related to mechanical strength, the physical property being different from those of the monomer of the styrene derivative and the monomer of the maleimide derivative.
2 . The low birefringence optical polymer material according to claim 1 , wherein the styrene derivative is styrene and the maleimide derivative is ethylmaleimide.
3 . A low birefringence optical polymer material comprising a polymer made of (i) a monomer of a styrene derivative, (ii) a monomer of at least a maleimide derivative, and (iii) a monomer of a modified organic compound having a physical property related to mechanical strength, the physical property being different from those of the monomer of the styrene derivative and the monomer of the at least one maleimide derivative, wherein (a) the optical polymer material exhibits a nonlinear property in which, in relation to the monomer of the styrene derivative and the monomer of the maleimide derivative, a photoelastic coefficient of the optical polymer material decreases to a minimum value with an increase in composition ratio of the styrene derivative, and rises above the minimum value with a further increase in composition ratio of the styrene derivative, and a composition ratio of the styrene derivative is within a predetermined range, (b-1) an absolute value of the photoelastic coefficient is equal to or smaller 2×10 −12 Pa −1 value within the predetermined range of the composition ratio, (b-2) an absolute value of an intrinsic birefringence of the optical polymer material is equal to or smaller than 20×10 −3 within the predetermined range of the composition ratio, and (b-3) an absolute value of a temperature coefficient of the intrinsic birefringence is 2×10 −5 °°C. −1 or less, and wherein the polymer comprises (i) from 7 mol % to 27 mol % of the styrene derivative, (ii) from 27 mol % to 68 mol % of the maleimide derivative where the maleimide derivative content exceeds that of the styrene derivative and (iii) the remainder being the at least one monomer of a modified organic compound having a physical property related to mechanical strength, the physical property being different from those of the monomer of the styrene derivative and the monomer of the maleimide derivative.
4 . The low birefringence optical polymer material according to claim 3 , wherein in a two-dimensional birefringence map defined by the intrinsic birefringence and the photoelastic coefficient, the composition ratio of the styrene derivative and a composition ratio of the maleimide derivative are set such that a coordinate point represented by a first photoelastic coefficient and a first intrinsic birefringence that are determined by the composition ratio of the styrene derivative and the composition ratio of the maleimide derivative, and a coordinate point represented by a second photoelastic coefficient and a second intrinsic birefringence of the modified organic compound are located with an origin point interposed therebetween, and a composition ratio of the modified organic compound is set such that the first photoelastic coefficient and the first intrinsic birefringence are canceled out with the second photoelastic coefficient and the second intrinsic birefringence.
5 . The low birefringence optical polymer material according to claim 4 , wherein a glass transition temperature of the optical polymer material is higher than that of acrylic resin and lower than that in a case in which the modified organic compound is not contained, or is higher than that in a case in which the modified organic compound is not contained.
6 . The low birefringence optical polymer material according to claim 3 , wherein the styrene derivative is styrene, the maleimide derivative is ethylmaleimide or cyclohexylmaleimide, and the modified organic compound is a methacrylic acid derivative or t-butylmaleimide.
7 . The low birefringence optical polymer material according to claim 6 , wherein the predetermined range of the composition ratio of the styrene derivative is a range including 6%, 17%, 23%, or 25% in terms of mass ratio, and a range including 7%, 18.8% or 27% in terms of mole fraction.
8 . The low birefringence optical polymer material according to claim 1 , further comprising a homopolymer of the maleimide derivative.
9 . An optical film comprising the low birefringence optical polymer material according to claim 1 .
10 . A display device comprising the optical film according to claim 9 .
11 . The low birefringence optical polymer material of claim 1 wherein the alternating copolymer comprises on a weight basis more maleimide derivative than styrene derivative such that the intrinsic birefringence is 20×10-3 or lower.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a 35 U.S.C. § 371 national stage application of International patent application PCT/JP2020/048579, filed Dec. 24, 2020, which is based on and claims the benefit of priority to Japanese Application 2019-237326, filed Dec. 26, 2019. The entire contents of these applications are incorporated herein by reference. FIELD The present invention relates to an optical polymer material, an optical film, a display device, a method for manufacturing the optical polymer material, and a method for manufacturing the optical film. BACKGROUND In recent years, display devices including, as typical examples, liquid crystal display devices (LCDs) and organic light-emitting diode (OLED) display devices have been used as display devices for various devices. For example, these display devices are used in computer display devices, TV receivers, instrument panels and navigation devices in automobiles, airplanes, ships, and the like, mobile information terminals such as smartphones, or digital signage (electronic signage) used for advertisements and guidance displays. Several types of optical polymer films are used in these display devices to contribute to excellent image quality. Among them, a polarizer protection film, for example, is required such that birefringence thereof is reduced to a very low level. Low birefringence is also required in polymers used for pickup lenses and LCD backlights. To reduce the birefringence to a low level, it is preferable that intrinsic birefringence and photoelastic birefringence be low. In consideration of use under a wide range of environmental temperatures, it is preferable that the temperature dependence of the intrinsic birefringence be low (e.g., Non Patent Literature 1). In order to produce such an optical polymer material having low temperature dependence and low birefringence, quaternary and quintet optical polymer materials have been conventionally required. CITATION LIST Non Patent Literature Non Patent Literature 1: M. D. Shikanai, A. Tagaya, and Y. Koike, Appl. Phys. Lett. 108 pp. 131902 (2016). SUMMARY Technical Problem However, the quintet optical polymer material has a practical problem because of its complex composition and complicated design to obtain desired properties. In view of this, the present invention has been made, and it is an object thereof to provide an optical polymer material and an optical film that have a simple composition and low birefringence and can be easily designed to obtain desired properties, methods for manufacturing them, and display devices using them. Solution to Problem To solve the problem described above and to achieve the object, an optical polymer material according to one aspect of the present invention includes an alternating copolymer made of a monomer of a styrene derivative and a monomer of a maleimide derivative. The optical polymer material has a nonlinear property in which a photoelastic coefficient of the optical polymer material decreases to a first value with an increase in composition ratio of the styrene derivative, and rises above the first value with a further increase in composition ratio of the styrene derivative, and a composition ratio of the styrene derivative is within a predetermined range, an absolute value of the photoelastic coefficient is equal to or smaller than a first absolute value within the predetermined range of the composition ratio, and an absolute value of an intrinsic birefringence of the optical polymer material is equal to or smaller than a second absolute value within the predetermined range of the composition ratio. An optical polymer material according to one aspect of the present invention includes a polymer made of a monomer of a styrene derivative, a monomer of a maleimide derivative, and a monomer of a modified organic compound having a physical property related to mechanical strength, the physical property being different from those of the monomer of the styrene derivative and the monomer of the maleimide derivative. The optical polymer material has a nonlinear property in which, in relation to the monomer of the styrene derivative and the monomer of the maleimide derivative, a photoelastic coefficient of the optical polymer material decreases to a second value with an increase in composition ratio of the styrene derivative, and rises above the second value with a further increase in composition ratio of the styrene derivative, and a composition ratio of the styrene derivative is within a predetermined range, an absolute value of the photoelastic coefficient is equal to or smaller than a third absolute value within the predetermined range of the composition ratio, and an absolute value of an intrinsic birefringence of the optical polymer material is equal to or smaller than a fourth absolute value within the predetermined range of the composition ratio. An optical film according to one aspect of the present invention includes the opti