CN-116685455-B - Birefringent film, method for producing same, and method for producing optical film

Abstract

The present invention relates to a birefringent film comprising a solvent A, a solvent B, and a polymer having crystallinity, wherein the boiling point Bp (SA) (DEGC) of the solvent A and the boiling point Bp (SB) (DEGC) of the solvent B satisfy Bp (SA) -Bp (SB) > 5, and the total content of the solvent A and the solvent B in the birefringent film is 0.01 wt% or more and 3wt% or less, and Rth is not more than-100 nm. The present invention relates to a method for producing a film, comprising a step of bringing a specific film into contact with a mixed solvent containing a solvent A and a solvent B, and changing the birefringence of the film in the thickness direction.

Inventors

• YUJI SHIBATA

Assignees

• 日本瑞翁株式会社

Dates

Publication Date

20260505

Application Date

20211215

Priority Date

20201228

Claims (8)

1. 1. A birefringent film comprising a solvent A, a solvent B, and a polymer having crystallinity, The boiling point Bp (SA) (° C) of the solvent A and the boiling point Bp (SB) (° C) of the solvent B meet the conditions of Bp (SA) -Bp (SB) of more than or equal to 5, The total content of the solvent A and the solvent B in the birefringent film is 0.01 wt% or more and 3 wt% or less, The birefringent film satisfies Rth less than or equal to-100 nm The weight ratio of the solvent A to the solvent B is 3:7-99:1.
2. 2. The birefringent film according to claim 1, wherein the birefringent film is a processed product of a melt extruded film.
3. 3. The birefringent film according to claim 1 or 2, wherein the polymer having crystallinity has an intrinsic birefringence value of positive.
4. 4. The birefringent film according to claim 1 or 2, wherein the polymer having crystallinity contains an alicyclic structure.
5. 5. The birefringent film according to claim 1 or 2, wherein the crystallinity obtained by X-ray diffraction measurement is 10% or more.
6. 6. The birefringent film according to claim 1 or 2, wherein the boiling point Bp (SA) of the solvent a, the boiling point Bp (SB) of the solvent B, and the glass transition temperature TgP of the polymer satisfy the relationship Bp (SA) No. TgP and Bp (SB) No. TgP.
7. 7. A method for producing the birefringent film according to any one of claims 1 to 6, comprising the steps of: a step (I) of melt-extruding a resin (pA) containing a polymer having crystallinity to form a film (pA), and And (II) bringing the film (pA) into contact with a mixed solvent containing the solvent A and the solvent B in a weight ratio of 3:7 to 99:1, and impregnating the resin (pA) with the mixed solvent to change the birefringence of the film (pA) in the thickness direction, thereby forming a film (qA).
8. 8. A method for producing an optical film, comprising the steps of: a process for producing a birefringent film by the production method according to claim 7, and And (III) stretching the birefringent film.

Description

Birefringent film, method for producing same, and method for producing optical film Technical Field The present invention relates to a birefringent film that can be usefully used for manufacturing an optical film, a method for manufacturing the birefringent film, and a method for manufacturing the optical film. Background Conventionally, resin films having specific optical characteristics have been used for optical applications. For example, a film whose NZ coefficient satisfies 0< NZ <1 is referred to as a three-dimensional phase difference film. It is known that when the three-dimensional retardation film is provided in a display device such as a liquid crystal display device, the three-dimensional retardation film can exhibit an effect of reducing coloring of a display surface viewed from an oblique direction. The three-dimensional retardation film has a larger retardation in the z-axis direction (i.e., thickness direction) than in the y-axis direction (i.e., in-plane direction orthogonal to the in-plane slow-axis direction). Therefore, a conventional method for producing a retardation film, such as a resin for an optical film having positive intrinsic birefringence, cannot be used by simply stretching the film. Therefore, it has been proposed to produce a three-dimensional retardation film or a film similar to the three-dimensional retardation film by combining a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence (for example, patent documents 1 to 2). Prior art literature Patent literature Patent document 1, international publication No. 2019/188205; patent document 2 International publication No. 2020/137409. Disclosure of Invention Problems to be solved by the invention The method for producing a three-dimensional retardation film, which has been proposed heretofore and which combines a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence, has the problems of requiring a complicated stretching step, requiring a bonding step after stretching, requiring a complicated positioning step, and the like. Accordingly, an object of the present invention is to provide a means for easily producing a three-dimensional retardation film that can exhibit a good effect. Solution for solving the problem If a film having a small retardation Rth in the thickness direction (particularly, a film having a negative Rth and a large absolute value) can be easily obtained, a three-dimensional retardation film can be easily produced by a simple operation (one-time uniaxial stretching or the like) based on this. Accordingly, the present inventors have studied a film which has a small Rth and can be easily produced in order to solve the above-described problems. In the course of this study, the inventors studied that a resin film containing a polymer having crystallinity was brought into contact with a solvent to form a state in which the solvent was impregnated into the resin, thereby changing the birefringence of the film in the thickness direction, and thus a film having a small Rth was produced. However, in the course of the investigation, when the solvent is impregnated into the resin, there is a problem that a large amount of solvent remains in the film. When a large amount of solvent remains, an undesirable phenomenon occurs in which, in a display device manufactured using the film, the solvent gradually volatilizes from the film, the film deteriorates with time in use, or other members of the device are adversely affected. In addition, since the film having a large amount of solvent remaining therein volatilizes the solvent in the subsequent step, an explosion-proof device must be used in the subsequent step. On the other hand, if drying is performed at high temperature for a long period of time in the film production process in order to reduce the amount of residual solvent, the quality of the film is degraded. In order to reduce the amount of residual solvent, it is considered to use a solvent having a low boiling point. However, according to the studies of the present inventors, a solvent which can sufficiently change birefringence in the thickness direction by acting on a polymer having crystallinity is limited to a solvent having a boiling point higher than the glass transition temperature of the polymer having crystallinity, and a solvent having both a large effect of changing birefringence and high volatility has not been found. However, the present inventors have further studied and as a result, have found that a combination of a plurality of specific solvents gives a good balance between the high level of birefringence change effect and the high volatility, and as a result, a film exhibiting a good effect as a member for producing a three-dimensional retardation film can be easily produced. The present invention has been completed based on this finding. Namely, the present invention includes the following. [1] A birefringe