CN116685610A

CN116685610A - Optical film, method for producing same, and polarizing plate

Info

Publication number: CN116685610A
Application number: CN202180085915.5A
Authority: CN
Inventors: 井上恭辅
Original assignee: Zeon Corp
Current assignee: Zeon Corp
Priority date: 2020-12-28
Filing date: 2021-12-02
Publication date: 2023-09-01
Also published as: JPWO2022145169A1; WO2022145169A1; TW202232136A; KR20230121743A

Abstract

The present invention produces an optical film by a production method comprising, in order: a step of preparing a resin film formed of a resin containing a crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence; a step of bringing the resin film into contact with a solvent to change birefringence in the thickness direction; and a step of stretching the resin film, thereby producing an optical film.

Description

Optical film, method for producing same, and polarizing plate

Technical Field

The present invention relates to an optical film, a method for producing the same, and a polarizing plate.

Background

Techniques for producing a film using a resin have been proposed (patent documents 1 to 3).

Prior art literature

Patent literature

Patent document 1: japanese patent No. 4592004;

patent document 2: international publication No. 2017/145935;

patent document 3: international publication No. 2020/137409.

Disclosure of Invention

Problems to be solved by the invention

Resins are sometimes used to produce optical films having anisotropic refractive indices. Such an optical film having an anisotropic refractive index can have birefringence. An optical film having birefringence can be provided as a film such as a reflection suppressing film, a viewing angle compensating film, or the like in a display device.

When the optical film is provided in a display device, it is necessary to appropriately adjust the balance between the birefringence in the thickness direction and the birefringence in the in-plane direction perpendicular to the thickness direction. The balance of the birefringence in the thickness direction and the birefringence in the in-plane direction can be expressed by the NZ coefficient of the optical film. For example, if the NZ coefficient of the obtained optical film is more than 0.0 and less than 1.0, the display quality when the display surface is viewed from an oblique direction can be improved by the optical film.

In addition, the optical film is required to have inverse wavelength dispersion. Optical films having inverse wavelength dispersion are generally capable of performing their optical functions over a wide wavelength range. For example, a wave plate that is an optical film having inverse wavelength dispersion can be used as a broadband wave plate that functions in a wide wavelength range.

Methods for producing optical films having NZ coefficients of greater than 0.0 and less than 1.0 are currently known. In addition, optical films having inverse wavelength dispersion are also currently known. However, it has not been achieved so far to realize an optical film having an NZ coefficient of more than 0.0 and less than 1.0 and having inverse wavelength dispersion by a film having negative birefringence characteristics.

The present invention has been made in view of the above-described problems, and an object thereof is to provide an optical film having negative birefringence characteristics, having inverse wavelength dispersion, and having an NZ coefficient of more than 0.0 and less than 1.0, and a method for producing the same; a polarizing plate having the above optical film.

Solution for solving the problem

The present inventors have conducted intensive studies in order to solve the above-mentioned problems. As a result, the present inventors found that if a method comprising, in order: a step of bringing a resin film containing a crystalline polymer into contact with a solvent to change birefringence in the thickness direction; and a process for stretching the resin film, the above problems can be solved, and the present invention has been completed.

Namely, the content of the present invention includes:

[ 1 ] an optical film comprising a crystalline polymer, the optical film having negative birefringence characteristics, the optical film having in-plane retardation Re (450), re (550) and Re (650) at measurement wavelengths of 450nm, 550nm and 650nm satisfying formula (1), the optical film having an NZ coefficient Nz satisfying formula (2):

Re(450)＜Re(550)＜Re(650) (1)

0＜Nz＜1 (2)。

the optical film according to [ 2 ], wherein the optical film has a single-layer structure.

The optical film according to [ 1 ] or [ 2 ], wherein the optical film is a stretched film.

The optical film according to any one of [ 1 ] to [ 3 ], wherein the optical film is a uniaxially stretched film.

The optical film according to any one of [ 1 ] to [ 4 ], wherein the optical film has a long shape.

The optical film according to any one of [ 1 ] to [ 5 ], which is formed of a resin containing the crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence.

The optical film according to [ 7 ], wherein the weight ratio of the thermoplastic polymer having positive intrinsic birefringence to the crystalline polymer having negative intrinsic birefringence (thermoplastic polymer/crystalline polymer) is 3/7 or more.

The optical film according to [ 8 ], wherein the crystalline polymer having negative intrinsic birefringence is a polystyrene-based polymer, and the thermoplastic polymer having positive intrinsic birefringence is polyphenylene ether.

[ 9 ] a polarizing plate having the optical film according to any one of [ 1 ] to [ 8 ], and a polarizing film.

The polarizing plate according to item [ 10 ], wherein the slow axis of the optical film forms an angle of 80℃to 100℃with the absorption axis of the polarizing film.

The method for producing an optical film according to any one of [ 1 ] to [ 8 ], comprising, in order: a step of preparing a resin film formed of a resin containing a crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence; a step of bringing the resin film into contact with a solvent to change birefringence in the thickness direction; and stretching the resin film.

Effects of the invention

According to the present invention, an optical film having negative birefringence characteristics, having inverse wavelength dispersion, and having an NZ coefficient of greater than 0.0 and less than 1.0, and a method of manufacturing the same can be provided; a polarizing plate having the above optical film.

Detailed Description

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and the present invention can be arbitrarily modified and implemented without departing from the scope of the claims and the scope of equivalents thereof.

In the following description, unless otherwise specified, the in-plane retardation Re of the film is a value represented by re= (nx-ny) ×d. Further, the birefringence in the in-plane direction of the film is a value represented by (nx-ny) and thus represented by Re/d, unless otherwise specified. Further, the retardation Rth in the thickness direction of the film is a value represented by rth= [ { (nx+ny)/2 } -nz ] ×d, unless otherwise specified. Further, the birefringence in the thickness direction of the film is a value represented by [ { (nx+ny)/2 } -nz ] unless otherwise specified, and thus, is represented by Rth/d. Further, unless otherwise indicated, the NZ coefficient of a film is a value represented by (nx-NZ)/(nx-ny). Here, nx denotes a refractive index in a direction that provides the maximum refractive index among directions (in-plane directions) perpendicular to the film thickness direction. ny represents the refractive index in the direction perpendicular to the direction of nx in the above-mentioned in-plane direction of the film. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. Unless otherwise indicated, the measurement wavelength was 550nm.

In the following description, unless otherwise specified, a material having positive intrinsic birefringence means a material having a refractive index in the stretching direction larger than that in the direction perpendicular thereto. Thus, unless otherwise indicated, a polymer having positive intrinsic birefringence means a polymer having a refractive index in the stretching direction that is greater than the refractive index in the direction perpendicular thereto. Further, unless otherwise specified, a material having negative intrinsic birefringence means a material having a refractive index in the stretching direction smaller than that in the direction perpendicular thereto. Thus, unless otherwise indicated, a polymer having negative intrinsic birefringence means a polymer having a refractive index in the stretching direction that is smaller than the refractive index in the direction perpendicular thereto.

In the following description, the "long shape" refers to a shape having a length of 5 times or more, preferably 10 times or more, relative to the width, and specifically refers to a shape of a film having a length of a degree of storage or transportation that can be wound into a roll. The upper limit of the length is not particularly limited, and is usually 10 ten thousand times or less with respect to the width.

In the following description, unless otherwise specified, directions "parallel", "perpendicular", and "orthogonal" of elements may include errors within a range of, for example, ±5°, within a range that does not impair the effects of the present invention.

Unless otherwise specified, the angle made by the optical axis (absorption axis, transmission axis, slow axis, etc.) of each film in the member having a plurality of films means the angle when the films are viewed from the thickness direction.

Unless otherwise specified, "polarizer", "circularly polarizer", "wave plate" and "negative C plate" include not only rigid members but also flexible members such as resin films.

[1. Outline of optical film ]

The optical film according to one embodiment of the present invention contains a crystalline polymer. The optical film satisfies the following conditions (a) to (C) at the same time.

Condition (a): the optical film has negative birefringence characteristics.

Condition (B): the optical film satisfies the formula (1) in terms of in-plane retardation Re (450), re (550) and Re (650) at measurement wavelengths of 450nm, 550nm and 650 nm.

Condition (C): the NZ coefficient NZ of the optical film satisfies the formula (2).

Re(450)＜Re(550)＜Re(650) (1)

0＜Nz＜1 (2)

The optical film is difficult to manufacture in the past, but can be easily manufactured when a specific manufacturing method described later is used.

[2 ] birefringent Properties of optical film ]

The optical film of the present embodiment has negative birefringence characteristics.

The film "having negative birefringence" means that when the film is stretched in one stretching direction, the amount of increase in refractive index in the direction perpendicular to the stretching direction is larger than the amount of increase in refractive index in the stretching direction. In addition, the film "having positive birefringence" means that when the film is stretched in one stretching direction, the amount of increase in refractive index in the stretching direction is larger than the amount of increase in refractive index in the direction perpendicular to the stretching direction. Since the increase is a positive value in the case where the refractive index is increased by stretching, the increase is a negative value in the case where the refractive index is decreased by stretching. Here, the stretching direction may be an in-plane direction by being generally perpendicular to the thickness direction.

The birefringence properties of an optical film can be examined by stretching the optical film. In addition, the birefringent properties of an optical film generally depend on the composition of the optical film. In this way, when an optical film is produced by stretching a resin film having the same composition as the optical film as in the production method described later, the birefringent properties of the optical film can be examined by stretching the resin film. Specifically, when the resin film is stretched in one stretching direction, the birefringence of the optical film obtained from the resin film may be negative when the amount of increase in refractive index in the direction perpendicular to the stretching direction is larger than the amount of increase in refractive index in the stretching direction.

In general, when a film having negative birefringence characteristics is stretched in a direction perpendicular to the thickness direction, the birefringence in the thickness direction increases. Thus, it is generally difficult to produce a film having an NZ coefficient of greater than 0 by stretching, which would make the NZ coefficient 0 or less by stretching. Thus, it would be surprising to those skilled in the art that the optical film of the present embodiment having negative birefringence characteristics and having NZ coefficient satisfying the formula (2) was obtained. Therefore, the optical film of the present embodiment having both negative birefringence characteristics, in-plane retardation satisfying the formula (1), and NZ coefficient satisfying the formula (2) is an optical film which has not been conventionally known, and has high industrial value.

[3 wavelength Dispersion of optical film ]

The optical film of the present embodiment satisfies the formula (1) in the in-plane retardation Re (450) at the measurement wavelength of 450nm, the in-plane retardation Re (550) at the measurement wavelength of 550nm, and the in-plane retardation Re (650) at the measurement wavelength of 650 nm.

Re(450)＜Re(550)＜Re(650) (1)

The optical film having an in-plane retardation satisfying the formula (1) generally has inverse wavelength dispersion. Thus, the longer the measurement wavelength is, the larger the in-plane retardation of the optical film can be. Therefore, the optical film can exert its optical function in a wide wavelength range. For example, when the optical film can function as a 1/4 wave plate at one wavelength, the optical film can also function as a 1/4 wave plate in a wide wavelength range other than the one wavelength. For example, when the optical film can function as a 1/2 wave plate at one wavelength, the optical film can also function as a 1/2 wave plate in a wide wavelength range other than the one wavelength.

[4. NZ coefficient of optical film ]

The NZ coefficient NZ of the optical film of the present embodiment satisfies the formula (2). The three-dimensional birefringence nx, ny of the optical film having the NZ coefficient NZ satisfying the formula (2) can satisfy nx > NZ > ny.

0＜Nz＜1 (2)

In detail, the NZ coefficient NZ of the optical film is generally greater than 0.0, preferably greater than 0.1, more preferably greater than 0.2, and furthermore, is generally less than 1.0, preferably less than 0.9, more preferably less than 0.8.

The optical film having the NZ coefficient satisfying the formula (2) can appropriately change not only the polarization state of light passing through the optical film in the thickness direction but also the polarization state of light passing through the optical film in an oblique direction which is neither parallel nor perpendicular to the thickness direction. Thus, the optical film can exert its optical function not only for light in the thickness direction but also for light in the oblique direction. For example, in the case where the optical film can provide a phase difference of 1/4 wavelength for light passing in the thickness direction, the optical film can also provide a phase difference of 1/4 wavelength for light passing in the oblique direction. Further, for example, in the case where the optical film can provide a phase difference of 1/2 wavelength to light passing in the thickness direction, the optical film can also provide a phase difference of 1/2 wavelength to light passing in the oblique direction.

[5 composition of optical film ]

The optical film according to one embodiment of the present invention contains a crystalline polymer. The crystalline polymer means a polymer having crystallinity. The polymer having crystallinity means a polymer having a melting point Tm. That is, a polymer having crystallinity means a polymer in which the melting point Tm can be observed using a Differential Scanning Calorimeter (DSC). In the following description, a resin containing a crystalline polymer is sometimes referred to as "crystalline resin". The crystalline resin is preferably a thermoplastic resin. The optical film preferably contains a crystalline resin, and more preferably consists of only a crystalline resin.

The crystalline polymer preferably has negative intrinsic birefringence. The crystalline polymer having negative intrinsic birefringence can exhibit a large refractive index in a direction perpendicular to the stretching direction thereof when stretched. Thus, when a crystalline polymer having negative intrinsic birefringence is used, an optical film having negative birefringence can be easily obtained. In addition, in the case of using a crystalline polymer having negative intrinsic birefringence as described above, in-plane retardation satisfying the formula (1) and NZ coefficient satisfying the formula (2) can be easily achieved.

The crystalline polymer having negative intrinsic birefringence is preferably a polymer containing an aromatic ring, and examples thereof include polystyrene polymers. In the following description, a polystyrene-based polymer having crystallinity is sometimes referred to as "crystalline polystyrene-based polymer".

The crystalline polystyrene-based polymer may be a polymer of a styrene-based monomer. Thus, the crystalline polystyrene-based polymer may be a polymer including a structural unit having a structure formed by polymerizing a styrene-based monomer (hereinafter, appropriately referred to as "styrene-based unit").

The styrene monomer may be an aromatic vinyl compound such as styrene or a styrene derivative. Examples of the styrene derivative include compounds in which a substituent is substituted at the benzene ring, alpha-position or beta-position of styrene.

Examples of the styrene monomer include styrene, alkylstyrene, halostyrene, haloalkylstyrene, alkoxystyrene, vinyl benzoate, and hydrogenated polymers thereof.

Examples of the alkylstyrene include methylstyrene, ethylstyrene, isopropylstyrene, t-butylstyrene, 2, 4-dimethylstyrene, phenylstyrene, vinylnaphthalene, and vinylstyrene. Examples of the halogenated styrene include chlorostyrene, bromostyrene, and fluorostyrene. As an example of the haloalkylstyrene, chloromethylstyrene may be mentioned. Examples of the alkoxystyrenes include methoxystyrenes and ethoxystyrenes. Among the styrene monomers, styrene, methylstyrene, ethylstyrene, 2, 4-dimethylstyrene are preferred. The styrene monomer may be used in an amount of 1 or 2 or more.

The crystalline polystyrene-based polymer preferably has an isotactic structure or a syndiotactic structure, and more preferably has a syndiotactic structure. The crystalline polystyrene polymer having a syndiotactic structure means that the stereochemical structure of the crystalline polystyrene polymer is a syndiotactic structure. The syndiotactic structure means a steric structure in which phenyl groups as side chains are alternately located in opposite directions in the fischer projection with respect to a main chain formed by carbon-carbon bonds. The polystyrene-based polymer having a syndiotactic structure generally has a lower specific gravity and is excellent in hydrolysis resistance, heat resistance and chemical resistance than the polystyrene-based polymer having a random structure.

Can pass nuclear magnetic resonance method based on isotope carbon ¹³ C-NMR method) of the crystalline polystyrene-based polymer (tacticity: stereoregularity). By passing through ¹³ The stereoregularity measured by the C-NMR method can be shown by the presence ratio of a plurality of structural units in succession. Typically, for example, 2 consecutive building blocks are grouped together in two blocks, 3 in three blocks and 5 in five blocks. In this case, the crystalline polystyrene polymer having a syndiotactic structure has a syndiotacticity of usually 75% or more, preferably 85% or more in terms of a two-unit group (syndiotactic two-unit group), or a syndiotacticity of usually 30% or more, preferably 50% or more in terms of a five-unit group (syndiotactic five-unit group).

The crystalline polystyrene polymer may be a homopolymer or a copolymer. Thus, the crystalline polystyrene-based polymer may be a homopolymer of 1 kind of styrene-based monomer or a copolymer of 2 or more kinds of styrene-based monomers. When the crystalline polystyrene is a copolymer of 2 or more kinds of styrene monomers, the proportion of each styrene unit to 100% by weight of the crystalline polystyrene as a whole is preferably 5% by weight or more, more preferably 10% by weight or more, still more preferably 95% by weight or less, and still more preferably 90% by weight or less.

The crystalline polystyrene polymer may be a copolymer of 1 or 2 or more kinds of styrene monomers and a monomer other than the styrene monomers. From the viewpoint of obtaining an optical film having desired optical characteristics, the proportion of the styrene unit contained in the crystalline polystyrene polymer is preferably 80% by weight or more, more preferably 83% by weight or more, and still more preferably 85% by weight or more.

In general, the crystalline polystyrene polymer may contain a certain structural unit in a ratio that matches the ratio of the monomer corresponding to the structural unit to the entire monomers of the crystalline polystyrene polymer. Thus, the proportion of the styrene unit contained in the crystalline polystyrene polymer can be matched with the proportion of the styrene monomer to the entire monomers of the crystalline polystyrene polymer.

The crystalline polystyrene polymer can be produced, for example, by polymerizing a styrene monomer using a condensation product of a titanium compound and water with trialkylaluminum as a catalyst in an inert hydrocarbon solvent or in the absence of a solvent (see Japanese patent application laid-open No. 62-187708).

The crystalline polymer may be used alone or in combination of 2 or more kinds in any ratio.

The weight average molecular weight Mw of the crystalline polymer is preferably 130000 or more, more preferably 140000 or more, particularly preferably 150000 or more, preferably 500000 or less, more preferably 450000 or less, particularly preferably 400000 or less. The crystalline polymer having such a weight average molecular weight Mw can have a high glass transition temperature Tg, and thus can improve the heat resistance of the optical film.

The weight average molecular weight (Mw) of the polymer as a polystyrene equivalent can be measured by Gel Permeation Chromatography (GPC) using 1,2, 4-trichlorobenzene as a developing solvent.

The glass transition temperature Tg of the crystalline polymer is preferably 85℃or higher, more preferably 90℃or higher, particularly preferably 95℃or higher. In this way, when a crystalline polymer having a high glass transition temperature Tg is used, the heat resistance of the optical film can be improved. The glass transition temperature of the crystalline polymer is preferably 160 ℃ or lower, more preferably 155 ℃ or lower, and particularly preferably 150 ℃ or lower, from the viewpoint of smooth stretching in the process of producing an optical film.

The melting point Tm of the crystalline polymer is preferably 200 ℃ or higher, more preferably 210 ℃ or higher, particularly preferably 220 ℃ or higher, preferably 300 ℃ or lower, more preferably 290 ℃ or lower, particularly preferably 280 ℃ or lower. When the melting point Tm of the crystalline polymer is within the above range, it is possible to suppress the progress of crystallization of the undesirable crystalline polymer and the generation of foreign matter due to thermal decomposition when the crystalline resin is molded to obtain a resin film. Thus, an optical film having good appearance and optical characteristics can be easily obtained.

The glass transition temperature Tg and melting point Tm of the polymer can be determined by the following method. First, the polymer was melted by heating, and the melted polymer was quenched using dry ice. Next, using this polymer as a test body, the glass transition temperature Tg and the melting point Tm of the polymer can be measured at a temperature rise rate (temperature rise pattern) of 10 ℃/min using a Differential Scanning Calorimeter (DSC).

The amount of the crystalline polymer in 100 wt% of the crystalline resin is preferably 30 wt% or more, more preferably 40 wt% or more, particularly preferably 45 wt% or more, preferably 80 wt% or less, more preferably 70 wt% or less, particularly preferably 65 wt% or less, from the viewpoint of obtaining an optical film having desired optical characteristics.

The crystallinity of the crystalline polymer contained in the optical film is generally higher than a certain degree or more. The specific crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The crystallinity of the crystalline polymer can be measured by an X-ray diffraction method.

The crystalline resin may contain an amorphous polymer having no crystallinity in combination with a crystalline polymer. As the amorphous polymer, a thermoplastic polymer is generally used. Among them, the amorphous thermoplastic polymer preferably has positive intrinsic birefringence. When a polymer having positive intrinsic birefringence is used in combination with the crystalline polymer having negative intrinsic birefringence, the inverse wavelength dispersion of the optical film can be easily obtained.

From the viewpoints of transparency and toughness, the thermoplastic polymer having positive intrinsic birefringence is preferably polyphenylene ether. Polyphenylene ether is generally excellent in compatibility with crystalline polystyrene polymers.

Polyphenylene ether means a polymer having a phenylene ether skeleton. The benzene ring of the phenylene ether backbone may or may not be bonded to a substituent. Polyphenylene ethers generally have a phenylene ether backbone in their backbone. The polyphenylene ether is preferably a polymer comprising a phenylene ether unit represented by the following formula (I).

[ chemical formula 1]

In the formula (I), Q ¹ Each independently represents a halogen atom, a lower alkyl group (for example, an alkyl group having 1 to 7 carbon atoms), a phenyl group, a haloalkyl group, an aminoalkyl group, a hydrocarbyloxy group, or a halohydrocarbonoxy group (a group having at least 2 carbon atoms between a halogen atom and an oxygen atom). Wherein as Q ¹ Alkyl groups and phenyl groups are preferable, and alkyl groups having 1 to 4 carbon atoms are particularly preferable.

In formula (I), Q ² Each independently represents a hydrogen atom, a halogen atom, a lower alkyl group (for example, an alkyl group having 1 to 7 carbon atoms), a phenyl group, a haloalkyl group, a hydrocarbyloxy group, or a halohydrocarbonoxy group (a group having at least 2 carbon atoms between the halogen atom and the oxygen atom). Wherein as Q ² Preferably a hydrogen atom.

The polyphenylene ether may be a homopolymer having 1 kind of structural unit or a copolymer having 2 or more kinds of structural units.

When the polymer containing the structural unit represented by the formula (I) is a homopolymer, a preferable example of the homopolymer is a polymer having a 2, 6-dimethyl-1, 4-phenylene ether unit ("- (C) ₆ H ₂ (CH ₃ ) ₂ -O) - "structural units).

When comprising a structural unit represented by the formula (I)When the polymer of (a) is a copolymer, a preferable example of the copolymer is a copolymer having both a 2, 6-dimethyl-1, 4-phenylene ether unit and a 2,3, 6-trimethyl-1, 4-phenylene ether unit ("- (C) ₆ H(CH ₃ ) ₃ -O- ") structural units represented by the formula (i).

The polyphenylene ether may also contain structural units other than phenylene ether units. In this case, the polyphenylene ether can be a copolymer having a phenylene ether unit and a structural unit other than the phenylene ether unit. Among them, the ratio of the structural units other than the phenylene ether unit in the polyphenylene ether is preferably small in a range where desired optical characteristics can be obtained. Specifically, the content of the phenylene ether unit in 100% by weight of the polyphenylene ether is preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, still more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

Examples of the polyphenylene ether include polyphenylene ether having a polymer chain having other substituents grafted thereto. Such polyphenylene ethers can be synthesized by grafting other substituents onto the polyphenylene ether, for example, using an appropriate method. When specific examples are to be mentioned, polyphenylene ether grafted with a polymer such as polystyrene, polybutadiene, or other vinyl-containing polymer can be mentioned.

The method for producing polyphenylene ether is not limited, and it can be produced by the method described in, for example, japanese patent application laid-open No. 11-302529.

The amorphous polymer may be used alone or in combination of 1 or more than 2 kinds in any ratio.

The weight average molecular weight Mw of the amorphous polymer such as polyphenylene ether is preferably 15000 or more, more preferably 25000 or more, particularly preferably 35000 or more, preferably 100000 or less, more preferably 85000 or less, particularly preferably 70000 or less. When the weight average molecular weight Mw of the amorphous polymer is equal to or greater than the lower limit of the above range, the mechanical strength of the optical film can be improved. When the weight average molecular weight Mw of the amorphous polymer is equal to or less than the upper limit of the above range, the crystalline polymer and the amorphous polymer can be uniformly mixed at a high level.

The glass transition temperature of the amorphous polymer such as polyphenylene ether is preferably 100℃or higher, more preferably 110℃or higher, particularly preferably 120℃or higher, preferably 350℃or lower, more preferably 300℃or lower, particularly preferably 250℃or lower. When the glass transition temperature of the amorphous polymer is equal to or higher than the lower limit of the above range, the heat resistance of the optical film can be improved. In addition, when the glass transition temperature of the amorphous polymer is equal to or lower than the upper limit value of the above range, stretching can be smoothly performed in the process of manufacturing the optical film.

From the viewpoint of obtaining an optical film having desired optical characteristics, the amount of the amorphous polymer in the crystalline resin is preferably 20% by weight or more, more preferably 30% by weight or more, particularly preferably 35% by weight or more, preferably 70% by weight or less, more preferably 60% by weight or less, particularly preferably 55% by weight or less, based on 100% by weight of the crystalline resin.

In the case where the crystalline resin contains both a thermoplastic polymer having positive intrinsic birefringence and a crystalline polymer having negative intrinsic birefringence, their weight ratio (thermoplastic polymer/crystalline polymer) is preferably in a specific range. Specifically, the weight ratio (thermoplastic polymer/crystalline polymer) is preferably 3/7 or more, more preferably 3.5/6.5 or more, particularly preferably 4/6 or more, preferably 8/2 or less, more preferably 7.5/2.5 or less, particularly preferably 7/3 or less. When the weight ratio (thermoplastic polymer/crystalline polymer) is in the above range, the inverse wavelength dispersion of the optical film can be easily obtained.

The crystalline resin may contain any component in combination with the crystalline polymer and the amorphous polymer. Examples of the optional component include: a lubricant; a lamellar crystal compound; particles such as inorganic particles; stabilizers such as antioxidants, heat stabilizers, light stabilizers, weather stabilizers, ultraviolet light absorbers, and near infrared light absorbers; a plasticizer; colorants such as dyes and pigments; antistatic agents, and the like. 1 kind of optional component may be used, or 2 or more kinds may be used in combination. The amount of any component can be appropriately set within a range that does not significantly impair the effects of the present invention. The amount of any component may be, for example, a range that maintains the total light transmittance of the optical film at 85% or more.

[6. Layer Structure of optical film ]

The optical film may have a multilayer structure including a plurality of layers, but preferably has a single-layer structure. The single-layer structure means a structure having only a single layer containing the same composition, and having no layer containing a composition different from the above composition. Accordingly, the optical film preferably has a layer formed of the crystalline resin alone.

[7. Properties of optical film ]

The optical film preferably has an in-plane retardation in an appropriate range corresponding to its use.

For example, the specific in-plane retardation Re of the optical film can be preferably 100nm or more, more preferably 110nm or more, particularly preferably 120nm or more, and further preferably 180nm or less, more preferably 170nm or less, particularly preferably 160nm or less at a measurement wavelength of 550 nm. In this case, the optical film can function as a 1/4 wave plate.

For example, the specific in-plane retardation Re of the optical film can be preferably 245nm or more, more preferably 265nm or more, particularly preferably 270nm or more, and further preferably 320nm or less, more preferably 300nm or less, particularly preferably 295nm or less at a measurement wavelength of 550 nm. In this case, the optical film can function as a 1/2 wave plate.

Retardation of the film can be measured using a phase difference meter (e.g., "AxoScan OPMF-1" manufactured by axso Mei Teli g).

The optical film preferably has high transparency. The specific total light transmittance of the optical film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The total light transmittance of the film can be measured in the wavelength range of 400nm to 700nm using an ultraviolet/visible spectrophotometer.

The optical film preferably has a small haze. The haze of the optical film is preferably less than 1.0%, more preferably less than 0.8%, particularly preferably less than 0.5%, and ideally 0.0%. In this way, when the optical film having a small haze is provided in a display device, the sharpness of an image displayed on the display device can be improved. The haze of the film can be measured using a haze meter (for example, "NDH5000" manufactured by japan electric color industry corporation).

The optical film can comprise a solvent. The solvent may be a solvent introduced into the resin film in the step of bringing the film into contact with the solvent in the production method described later. In detail, all or a part of the solvent introduced into the resin film by contact with the film can enter the inside of the polymer. Therefore, even if the drying is performed at a temperature equal to or higher than the boiling point of the solvent, the solvent is not easily removed completely. Thus, the optical film can contain a solvent.

The optical film is preferably a stretched film. The stretched film is a film produced by stretching treatment. Among them, the optical film is preferably a uniaxially stretched film. The uniaxially stretched film is a film in which the stretching treatment is positively performed only in one direction and the stretching treatment is not positively performed in the other directions. The uniaxially stretched film can be produced by stretching in only one direction, whereby the production process can be simplified and simple production can be achieved.

The optical film may be a sheet-like film or a long film having a long shape. When the optical film has a long shape, the optical film is bonded to the long polarizing film, whereby the polarizing plate can be continuously manufactured.

The thickness of the optical film can be appropriately set according to the use of the optical film. The specific thickness of the optical film is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 30 μm or more, preferably 400 μm or less, more preferably 300 μm or less, particularly preferably 200 μm or less.

[8 ] outline of method for producing optical film ]

The optical film may be manufactured by a manufacturing method comprising the steps of: a step (i) of preparing a resin film formed of a resin containing a crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence; a step (ii) of bringing the resin film into contact with a solvent to change the birefringence in the thickness direction; and (iii) stretching the resin film.

In the following description, the resin film before the resin film is brought into contact with the solvent in the step (ii) may be referred to as a "raw material film", and the resin film after the resin film is brought into contact with the solvent in the step (ii) may be referred to as a "pre-stretching film".

The present inventors speculate that the mechanism of obtaining the above optical film by the above manufacturing method is as follows. However, the technical scope of the present invention is not limited to the following mechanism.

In this manufacturing method, a resin film containing a crystalline polymer having negative intrinsic birefringence is used to manufacture an optical film. When a crystalline polymer having negative intrinsic birefringence is oriented in a certain orientation direction, a small refractive index can be exhibited in the orientation direction, and a large refractive index can be exhibited in a direction perpendicular to the orientation direction. Thus, the resin film and the optical film containing the crystalline polymer can have negative birefringence characteristics as represented by the condition (a).

In addition, the optical film can contain a thermoplastic polymer having positive intrinsic birefringence in combination with a crystalline polymer having negative intrinsic birefringence. When a thermoplastic polymer having positive intrinsic birefringence is oriented in a certain orientation direction, a large refractive index can be exhibited in the orientation direction, and a small refractive index can be exhibited in a direction perpendicular to the orientation direction. Thus, when the crystalline polymer is oriented in a certain orientation direction, the direction in which the refractive index of the crystalline polymer is the largest and the direction in which the refractive index of the thermoplastic polymer is the largest can be perpendicular. In this way, the birefringence of the entire optical film including both the crystalline polymer and the thermoplastic polymer can reflect the difference between the birefringence of the crystalline polymer and the birefringence of the thermoplastic polymer. In the optical film, the difference between the birefringence of the crystalline polymer and the birefringence of the thermoplastic polymer is small at a short measurement wavelength and large at a long measurement wavelength. Therefore, the optical film obtained by the above-described production method can have inverse wavelength dispersion as represented by the condition (B).

Further, when the raw material film containing the crystalline polymer is brought into contact with the solvent in the step (ii), the solvent is immersed in the raw material film. Under the action of the immersed solvent, microscopic brownian motion of the molecules of the crystalline polymer in the film occurs, resulting in orientation of the molecular chains thereof. According to the studies of the present inventors, it is considered that the solvent-induced crystallization phenomenon of the crystalline polymer can be performed at the time of the molecular chain orientation.

In general, the surface area of the film is large on the front and back sides as the main surfaces. Thus, the solvent immersion speed is high in the thickness direction passing through the front surface or the rear surface. Thus, the molecules of the crystalline polymer can be oriented in the thickness direction. In this way, in the step (ii), the molecules of the crystalline polymer can be oriented in the thickness direction.

In the production method of the present embodiment, in the step (iii), the pre-stretching film, which is the resin film in which the molecules of the crystalline polymer are oriented in the thickness direction in the step (ii), is stretched. By stretching, molecules of the polymer contained in the film before stretching can be oriented in a direction perpendicular to the thickness direction. Thus, by combining the orientation in the thickness direction in the step (ii) and the orientation in the direction perpendicular to the thickness direction in the step (iii), the orientation direction of the molecules of the polymer can be adjusted in three dimensions. Thus, the optical film obtained by the above-described production method can have an NZ coefficient in an appropriate range as represented by the condition (C).

[9 ] step (i) of preparing a resin film ]

The method for producing an optical film includes a step of preparing a raw material film that is a resin film before contact with a solvent.

As a material of the raw material film prepared in the step (i), a crystalline resin containing a crystalline polymer can be used. The raw material film is preferably formed of only a crystalline resin. The crystalline resin contained in the raw material film may be the same as the crystalline resin contained in the optical film. Among them, the crystallinity of the crystalline polymer contained in the raw material film is preferably small. The specific crystallinity is preferably less than 10%, more preferably less than 5%, particularly preferably less than 3%. When the crystallinity of the crystalline polymer contained in the raw material film before contact with the solvent is low, a large number of molecules of the crystalline polymer are oriented in the thickness direction by contact with the solvent, and thus the NZ coefficient can be adjusted in a wide range.

The raw material film preferably has optical isotropy. Accordingly, the birefringence Re/d in the in-plane direction of the raw material film is preferably small, and the absolute value |Rth/d| of the birefringence in the thickness direction is preferably small. Specifically, the material film preferably has a birefringence Re/d in the in-plane direction of less than 1.0X10 ^-3 More preferably less than 0.5X10 ^-3 Particularly preferably less than 0.3X10 ^-3 . The absolute value |Rth/d| of birefringence in the thickness direction of the raw material film is preferably less than 1.0X10 ^-3 More preferably less than 0.5X10 ^-3 Particularly preferably less than 0.3X10 ^-3 . As described above, the optical isotropy indicates that the molecules of the crystalline polymer contained in the raw material film have low orientation properties and are substantially unoriented. In the case of using such an optically isotropic raw material film, since it is not necessary to precisely control the optical characteristics of the raw material film, it is not necessary to precisely control the molecular orientation of the crystalline polymer, and therefore the method for producing an optical film can be simplified. Further, when an optically isotropic raw material film is used, an optical film having a small haze can be obtained.

The raw material film preferably contains a small amount of solvent, and more preferably contains no solvent. The ratio of the solvent (solvent content) contained in the raw material film is preferably 1% or less, more preferably 0.5% or less, particularly preferably 0.1% or less, and desirably 0.0% or less, based on 100% by weight of the raw material film. Since the amount of the solvent contained in the raw material film before the contact with the solvent is small, and a large amount of molecules of the crystalline polymer are oriented in the thickness direction by the contact with the solvent, the NZ coefficient can be adjusted in a wide range. The solvent content of the raw material film can be measured based on the density.

The haze of the raw material film is preferably less than 1.0%, preferably less than 0.8%, more preferably less than 0.5%, and desirably 0.0%. The smaller the haze of the raw material film, the easier the haze of the obtained optical film is made small.

The thickness of the raw material film is preferably set according to the thickness of the optical film to be produced. In general, the thickness increases by contact with the solvent in step (ii). By stretching in the step (iii), the thickness is reduced. Therefore, the thickness of the raw material film may be set in consideration of the variation in the thickness in the steps (ii) and (iii) described above.

The raw material film may be a sheet-like film, preferably a long film. By using the long raw material film, the optical film can be continuously produced by the roll-to-roll method, and therefore, the productivity of the optical film can be effectively improved.

From the viewpoint of obtaining a raw material film containing no solvent, a resin molding method such as an injection molding method, an extrusion molding method, a compression molding method, a blow molding method, a calender molding method, an injection molding method, or a compression molding method is preferable as a method for producing the raw material film. Among these, the extrusion molding method is preferable from the viewpoint of easy control of thickness.

The production conditions of the extrusion molding method are preferably as follows. The barrel temperature (molten resin temperature) is preferably not less than Tm, more preferably not less than "tm+20℃", preferably not more than "tm+100℃", more preferably not more than "tm+50℃". The cooling body with which the molten resin extruded into a film shape first contacts is not particularly limited, and a casting roll is generally used. The casting roll temperature is preferably "Tg-50deg.C" or higher, preferably "Tg+70deg.C" or lower, and more preferably "Tg+40deg.C" or lower. When the raw material film is produced under such conditions, the raw material film having a thickness of 1 μm to 1mm can be easily produced. Here, "Tm" means the melting point of the crystalline polymer, and "Tg" means the glass transition temperature of the crystalline polymer.

[10 ] step (ii) of contacting the resin film with the solvent

The method for producing an optical film includes a step (ii) of bringing a resin film as a raw material film into contact with a solvent after the step (i). By this step (ii), the birefringence of the raw material film in the thickness direction is changed, and a stretched film having a different birefringence from the raw material film in the thickness direction is obtained.

As the solvent, an organic solvent is generally used. As a specific type of the solvent, a solvent which does not dissolve the crystalline polymer contained in the resin film and can be immersed in the resin film can be used, and examples thereof include: hydrocarbon solvents such as cyclohexane, toluene, limonene, decalin, and the like; carbon disulphide. The types of the solvents may be 1 or 2 or more.

The method of contacting the resin film with the solvent is not limited. Examples of the contact method include a spraying method in which a solvent is sprayed onto a resin film; a coating method of coating a resin film with a solvent; an impregnation method in which the resin film is immersed in a solvent, and the like. Among them, the dipping method is preferable from the viewpoint of facilitating continuous contact.

The temperature of the solvent in contact with the resin film is arbitrary in a range in which the solvent can be maintained in a liquid state, and thus can be set in a range of not less than the melting point and not more than the boiling point of the solvent.

The contact time is preferably 0.5 seconds or more, more preferably 1.0 seconds or more, and particularly preferably 5.0 seconds or more. The upper limit is not particularly limited, and may be, for example, 24 hours or less. However, since the degree of orientation does not change greatly even if the contact time is prolonged, the contact time is preferably short in a range where desired optical characteristics can be obtained.

The birefringence Rth/d of the resin film in the thickness direction changes by contact with the solvent. The amount of change in the birefringence Rth/d in the thickness direction by contact with the solvent is preferably 0.1X10 ^-3 The above is more preferably 0.2X10 ^-3 The above is particularly preferably 0.3X10 ^-3 The above is preferably 50.0X10 ^-3 Hereinafter, more preferably 30.0X10 ^-3 Hereinafter, it is particularly preferably 20.0X10 ^-3 The following is given. The amount of change in the birefringence Rth/d in the thickness direction represents the absolute value of the change in the birefringence Rth/d in the thickness direction of the resin film. The amount of change in the specific thickness-direction birefringence Rth/d can be obtained as an absolute value by subtracting the thickness-direction birefringence Rth/d of the raw material film from the thickness-direction birefringence Rth/d of the film before stretching. It is preferable that the birefringence Rth/d in the thickness direction is increased by the contact of the resin film with the solvent.

By contact with solventsThe birefringence Re/d of the resin film in the in-plane direction may or may not be changed. In order to simplify the control of the in-plane retardation Re of the optical film, it is preferable that the change in the birefringence Re/d in the in-plane direction of the resin film is small by contact with the solvent, and it is more preferable that no change is generated. The amount of change in the in-plane direction birefringence Re/d by contact with the solvent is preferably 0.0X10 ^-3 ～0.2×10 ^-3 More preferably 0.0X10 ^-3 ～0.1×10 ^-3 Particularly preferably 0.0X10 ^-3 ～0.05×10 ^-3 . The amount of change in the in-plane direction birefringence Re/d represents the absolute value of the change in the in-plane direction birefringence Re/d of the resin film. The amount of change in the birefringence Re/d in the specific in-plane direction can be obtained as an absolute value by subtracting the in-plane direction birefringence Re/d of the raw material film from the in-plane direction birefringence Re/d of the film before stretching.

The film before stretching, which is a resin film after contact with a solvent, is preferably a negative C plate. Thus, the refractive index nz in the thickness direction of the film before stretching is preferably smaller than the refractive indices nx and ny in the in-plane direction. Further, the refractive indices nx and ny in the in-plane direction of the film before stretching are preferably the same value or a value close to each other. Therefore, the film before stretching preferably has a relatively small difference between the refractive index nx and the refractive index ny, a relatively large difference between the refractive index nx and the refractive index nz, and a relatively large difference between the refractive index ny and the refractive index nz.

At this time, the difference between the refractive index nz in the thickness direction and the refractive indices nx and ny in the in-plane direction can be represented by the birefringence Rth/d in the thickness direction. That is, since "Rth/d= { (nx+ny)/2 } -nz" can represent the birefringence Rth/d in the thickness direction of the film before stretching, the difference between the refractive index nz in the thickness direction and the refractive indices nx and ny in the in-plane direction can be represented by the birefringence Rth/d in the thickness direction. The birefringence Rth/d in the thickness direction of the film before stretching is preferably 0.05X10 ^-3 The above is preferably 0.1X10 ^-3 The above is particularly preferably 0.2X10 ^-3 The above is preferably 10×10 ^-3 Hereinafter, more preferably 6.0X10 ^-3 Hereinafter, it is particularly preferably 4.0X10 ^-3 The following is given.

Furthermore, it can be represented by the birefringence Re/d in the in-plane directionThe difference between the refractive indices nx and ny in the in-plane direction. That is, since "Re/d=nx-ny" can represent the birefringence Re/d in the in-plane direction of the film before stretching, the difference between the refractive indices nx and ny in the in-plane direction can be represented by the birefringence Re/d in the in-plane direction. In general, the difference between the refractive indices nx and ny in the in-plane direction is smaller than the difference between the refractive index nz in the thickness direction and the refractive indices nx and ny in the in-plane direction. Thus, the in-plane direction birefringence Re/d of the film before stretching can be a value smaller than the thickness direction birefringence Rth/d of the film before stretching. The specific range of the birefringence Re/d in the in-plane direction of the film before stretching is preferably 0.01X10 ^-3 The above is preferably 0.05X10 ^-3 The above is particularly preferably 0.1X10 ^-3 The above is preferably 1.0X10 ^-3 Hereinafter, more preferably 0.5X10 ^-3 Hereinafter, it is particularly preferably 0.2X10 ^-3 The following is given.

It is preferable that the film before stretching, which is a resin film after contact with a solvent, has an NZ coefficient of more than 1.0. The specific NZ coefficient of the film before stretching is preferably greater than 1.0, more preferably greater than 5.0, particularly preferably greater than 10, furthermore preferably less than 50, more preferably less than 40, particularly preferably less than 30.

The resin film is immersed in the solvent in contact with the resin film, and the thickness of the resin film is generally increased in the step (ii). The lower limit of the rate of change in the thickness of the resin film at this time may be, for example, 1% or more, 2% or more, or 3% or more. The upper limit of the rate of change of the thickness may be, for example, 80% or less, 50% or less, or 40% or less. The rate of change in the thickness of the resin film is a ratio obtained by dividing the difference between the thicknesses of the raw material film and the film before stretching by the thickness of the raw material film.

[11 step (iii) of stretching resin film ]

The method for producing an optical film includes a step (iii) of stretching a resin film as a film before stretching after the step (ii). By stretching, the molecules of the polymer contained in the resin film can be oriented in a direction corresponding to the stretching direction. Thus, by stretching in the step (iii), the optical characteristics such as the birefringence Re/d in the in-plane direction, the in-plane retardation Re, the birefringence Rth/d in the thickness direction, the retardation Rth in the thickness direction, and the NZ coefficient of the resin film are adjusted, and the optical film can be obtained.

The stretching direction is not limited. Examples thereof include a longitudinal direction, a width direction, and an oblique direction. Here, the diagonal direction refers to a direction that is neither parallel nor perpendicular to the width direction among directions perpendicular to the thickness direction. The stretching direction may be one direction or two or more directions, and is preferably one direction. Further, in the stretching in one direction, free uniaxial stretching in which a restraining force is not applied in a direction other than the stretching direction is more preferable. By these stretching, the optical film can be easily produced.

Since the film before stretching generally has negative birefringence, when stretching is performed in one direction, an optical film having a slow axis in a direction perpendicular to the stretching direction can be obtained. Thus, the slow axis direction of the optical film can be adjusted by the stretching direction, and therefore the stretching direction can be selected according to the direction of the slow axis that is intended to appear in the optical film. Generally, a long polarizing film has an absorption axis in its longitudinal direction and a transmission axis in its width direction. Thus, for example, when an optical film having a slow axis perpendicular to the absorption axis of the polarizing film is desired, the film before stretching may be stretched in the longitudinal direction to obtain an optical film having a slow axis in the width direction. In this case, the polarizing plate can be efficiently manufactured in a roll-to-roll manner by using a long optical film and a long polarizing film.

The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, still more preferably 20.0 times or less, still more preferably 10.0 times or less, still more preferably 5.0 times or less, and particularly preferably 2.0 times or less. The specific stretching ratio is preferably set appropriately according to factors such as optical characteristics, thickness, and mechanical strength of the optical film to be produced. When the stretching ratio is equal to or greater than the lower limit of the above range, the birefringence can be greatly changed by stretching. In addition, when the stretching ratio is equal to or less than the upper limit of the above range, the direction of the slow axis can be easily controlled, and film breakage can be effectively suppressed.

The stretching temperature is preferably "Tg _R "above", more preferablyIs "Tg _R +10 ℃ or higher, preferably "Tg _R Below +100℃, more preferably "Tg _R Below +90℃. Here, "Tg _R "means the glass transition temperature of the crystalline resin. When the stretching temperature is equal to or higher than the lower limit of the above range, the resin film can be sufficiently softened and stretched uniformly. In addition, when the stretching temperature is equal to or lower than the upper limit of the above range, curing of the resin film due to the progress of crystallization of the crystalline polymer can be suppressed, and therefore, stretching can be smoothly performed, and, in addition, large birefringence can be exhibited by stretching. Further, in general, the haze of the obtained optical film can be reduced, and the transparency can be improved.

By performing the stretching treatment described above, an optical film which is a stretched resin film can be obtained. As described above, since the birefringence can be changed by stretching, the balance between the birefringence Rth/d in the thickness direction and the birefringence Re/d in the in-plane direction can be adjusted to obtain a desired NZ coefficient. Further, since the polymer is oriented by contact with the solvent in the step (ii) and the polymer is oriented by stretching in the step (iii), optical characteristics such as retardation are exhibited, and thus the optical film can have desired optical characteristics.

[12. Optional procedure ]

The method for producing an optical film may further include any step in combination with the steps (i) to (iii). Examples of the optional step include: a step of preheating the film before stretching before the step (iii); a step of performing a heat treatment on the optical film obtained in the step (iii) to promote crystallization of the crystalline polymer; a step of drying the optical film to reduce the amount of the solvent in the film; and a step of removing residual stress in the film by thermally shrinking the optical film.

Further, according to the above-described production method, a long optical film can be produced using a long raw material film. The method for producing an optical film may include a step of winding the long optical film produced in this manner into a roll. The method for producing an optical film may further include a step of cutting the long optical film into a desired shape.

[13. Polarizer ]

The polarizing plate according to one embodiment of the present invention has the above-described optical film and polarizing film. Polarizing films generally function as linear polarizers. Thus, the polarizing plate transmits a part of polarized light and blocks the other polarized light.

The polarizing film generally has an absorption axis and a transmission axis perpendicular to the absorption axis. Further, it is possible to absorb the linearly polarized light having the vibration direction parallel to the absorption axis and transmit the linearly polarized light having the vibration direction parallel to the transmission axis. The vibration direction of the linearly polarized light refers to the vibration direction of the electric field of the linearly polarized light. In this case, the absorption axis of the polarizing film is preferably at a specific angle to the slow axis of the optical film.

In one example, the angle between the absorption axis of the polarizing film and the slow axis of the optical film is preferably 80 ° or more, more preferably 85 ° or more, particularly preferably 88 ° or more, preferably 100 ° or less, more preferably 95 ° or less, particularly preferably 92 ° or less. In this case, the optical film preferably has an in-plane retardation capable of functioning as a 1/2 wave plate. In the case of being provided to an image display device, the polarizing plate of this example can be used as a polarizing plate capable of compensating for viewing angle.

In another example, the angle between the absorption axis of the polarizing film and the slow axis of the optical film is preferably 40 ° or more, more preferably 42 ° or more, particularly preferably 44 ° or more, preferably 50 ° or less, more preferably 48 ° or less, particularly preferably 46 ° or less. In this case, the optical film preferably has an in-plane retardation capable of functioning as a 1/4 wave plate. The polarizing plate in this example can be used as a circularly polarizing plate that is capable of transmitting circularly polarized light in one rotation direction and blocking circularly polarized light in the other rotation direction. The circularly polarizing plate is provided on a display surface of a display device, whereby reflection of external light can be suppressed.

As the polarizing film, any polarizing film can be used. Examples of the polarizing film include a film obtained by uniaxially stretching a polyvinyl alcohol film after adsorbing iodine or a dichroic dye in a boric acid bath; the polyvinyl alcohol film is stretched after adsorbing iodine or a dichroic dye, and a part of the polyvinyl alcohol units in the molecular chain is modified into polyethylene units. Among them, a polarizing film containing polyvinyl alcohol is preferable as the polarizing film.

When natural light is incident into the polarizing film, only polarized light in one direction is transmitted. The polarization degree of the polarizing film is not particularly limited, but is preferably 98% or more, and more preferably 99% or more. Further, the thickness of the polarizing film is preferably 5 μm to 80 μm.

The polarizing plate may further include any layer. Examples of the optional layer include: a polarizer protective film layer; an adhesive layer for bonding the polarizing film and the optical film; a hard coat layer such as an impact-resistant polymethacrylate resin layer; a roughened layer that improves film slidability; a reflection suppressing layer; an anti-fouling layer; a charge suppressing layer, and the like. These arbitrary layers may be provided in 1 layer or 2 layers or more.

Examples

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented within a scope not departing from the scope of the claims and the equivalents thereof.

In the following description, unless otherwise indicated, "%" and "parts" representing amounts are weight basis. In addition, unless otherwise indicated, the operations described below were carried out under conditions in the atmosphere of normal temperature and normal pressure (23 ℃,1 atm).

[ method for measuring glass transition temperature Tg and melting Point Tm ]

The glass transition temperature Tg and melting point Tm of the polymer were measured as follows. First, the polymer was melted by heating, and the melted polymer was quenched using dry ice. Next, using this polymer as a test body, the glass transition temperature Tg and the melting point Tm of the polymer were measured at a temperature rise rate (temperature rise pattern) of 10 ℃/min using a Differential Scanning Calorimeter (DSC).

[ retardation of optical film, NZ coefficient, and method for measuring slow axis direction ]

The in-plane retardation Re, the retardation in the thickness direction Rth, the NZ coefficient, and the slow axis direction of the optical film were measured using a retardation meter (AxoScan OPMF-1 manufactured by axso Mei Teli).

Production example 1 production of crystalline polystyrene

Into a glass vessel having an internal volume of 500ml replaced with argon, 17.8g (71 mmol) of copper sulfate pentahydrate (CuSO) ₄ ·5H ₂ O), 200ml of toluene, and 24ml (250 mmol) of trimethylaluminum were reacted at 40 ℃ for 8 hours. Then, the solid portion was removed to obtain a solution. Toluene was further removed from the resulting solution under reduced pressure at room temperature to give 6.7g of a contact product. The molecular weight of the contact product was measured by the freezing point depression method and found to be 610.

Next, 5 mmol of the above-mentioned contact product, 5 mmol of triisobutylaluminum, 0.025 mmol of pentamethylcyclopentadienyl titanium trimethoxyate and 1 mmol of purified styrene in terms of aluminum atom were charged into a reaction vessel, and polymerization was carried out at 90℃for 5 hours. Then, after decomposing the catalyst component in a methanol solution of sodium hydroxide, the product was repeatedly washed with methanol and dried, whereby 308g of a polymer (crystalline polystyrene) was obtained.

The weight average molecular weight of the polymer was determined by gel permeation chromatography at 135℃using 1,2, 4-trichlorobenzene as solvent. As a result, the weight average molecular weight Mw of the polymer was 350000. In addition, by measuring melting point Tm and ¹³ C-NMR confirmed that the obtained polymer was crystalline polystyrene having a syndiotactic structure. The crystalline polystyrene has a melting point Tm of 270℃and a glass transition temperature of 100 ℃.

This operation was repeated to prepare crystalline polystyrene having a syndiotactic structure required for evaluation.

Production example 2 production of crystalline Polymer having Positive intrinsic Birefringence

After the metal pressure-resistant reactor was sufficiently dried, nitrogen substitution was performed. To this metal pressure-resistant reactor were added 154.5 parts of cyclohexane, 42.8 parts (30 parts based on the amount of dicyclopentadiene) of a cyclohexane solution having a concentration of 70% of dicyclopentadiene (the content of the internal form of which is 99% or more), and 1.9 parts of 1-hexene, and the mixture was heated to 53 ℃.

A solution was prepared by dissolving 0.014 parts of a tungsten tetrachloride phenylimide (tetrahydrofuran) complex in 0.70 parts of toluene. To this solution, 0.061 part of a 19% strength diethyl aluminum ethoxide/n-hexane solution was added and stirred for 10 minutes to prepare a catalyst solution. The catalyst solution was added to a pressure-resistant reactor to initiate ring-opening polymerization. Then, the reaction was carried out for 4 hours while maintaining the temperature at 53℃to obtain a solution of a ring-opening polymer of dicyclopentadiene. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the obtained ring-opened polymer of dicyclopentadiene were 8750 and 28100, respectively, and the molecular weight distribution (Mw/Mn) obtained from these was 3.21.

To the resulting solution of 200 parts of the ring-opening polymer of dicyclopentadiene, 0.037 parts of 1, 2-ethylene glycol as a terminator was added, and the mixture was heated to 60℃and stirred for 1 hour to terminate the polymerization. Here, 1 part of a hydrotalcite-like compound (KYOWAAD (registered trademark) 2000, manufactured by the company of the chemical industry) was added, heated to 60 ℃, and stirred for 1 hour. Then, 0.4 part of a filter aid (manufactured by Showa chemical industry Co., ltd., "radio (registered trademark) # 1500") was added, and the adsorbent and the solution were separated by filtration using a polypropylene pleated cartridge filter (manufactured by ADVANTEC Toyo Co., ltd., "TCP-HX").

To 200 parts of the solution of the ring-opening polymer of dicyclopentadiene after filtration (30 parts of polymer amount) was added 100 parts of cyclohexane, 0.0043 parts of ruthenium tris (triphenylphosphine) carbonyl hydrochloride, and hydrogenation reaction was carried out at a hydrogen pressure of 6MPa and a temperature of 180℃for 4 hours. Thus, a reaction solution containing a hydrogenated product of a ring-opening polymer of dicyclopentadiene was obtained. The hydride in the reaction solution is precipitated to form a slurry solution.

The hydride contained in the reaction solution was separated from the solution by using a centrifugal separator, and dried at 60℃under reduced pressure for 24 hours to obtain 28.5 parts of a hydrogenated compound of a ring-opened polymer of dicyclopentadiene which is a crystalline polymer having positive intrinsic birefringence. The hydrogenation rate of the hydride is more than 99%, the glass transition temperature Tg is 93 ℃, the melting point Tm is 262 ℃, and the proportion of the syndiotactic diad is 89%.

Example 1

(1-1. Preparation of crystalline resin)

Using a biaxial extruder, 60 parts of the crystalline polystyrene having a syndiotactic structure obtained in production example 1 and 40 parts of polyphenylene ether (NORYL PPO640 "manufactured by japan sand foundation innovations plastics corporation, weight average molecular weight mw=43000, glass transition temperature tg=130℃) were kneaded at 295 ℃.

(1-2. Extrusion film formation)

Pellets of the crystalline resin were melt-extruded using a hot-melt extrusion film former (product of Optical Control Systems, inc. 'Measuring Extruder Type Me-20/2800V 3'), and wound at a speed of 1.5 m/min to obtain a long raw material film as a resin film before solvent contact with a width of about 120 mm. The operating conditions of the film forming machine are listed below one by one.

Barrel temperature setting = 280 ℃ to 300 DEG C

Die temperature=300℃

Screw speed = 30rpm

Casting roll temperature=80℃

The thickness of the raw material film was 158. Mu.m. The retardation of the raw material film was measured at a measurement wavelength of 550nm, and as a result, the in-plane retardation re=3 nm and the retardation rth= -18nm in the thickness direction.

(1-3. Solvent contact)

The raw material film was cut into a rectangular shape of 120mm by 120 mm. The rectangular raw material film was immersed in cyclohexane as a solvent stored in a tub until the in-plane retardation re=2 nm and the retardation rth=41 nm in the thickness direction, to obtain a film before stretching as a resin film after the solvent contact. The film before stretching was taken out of cyclohexane, and after the cyclohexane adhering to the film surface was wiped off, natural drying was performed in the atmosphere. The thickness of the resulting film before stretching was 160. Mu.m.

(1-4. Stretching)

A batch biaxial stretching apparatus (ETO co., ltd.) was prepared. The stretching device has an oven unit and a clamp capable of fixing the film for stretching. With this stretching device, the film can be pulled by a jig in an oven, thereby stretching the film.

The pre-stretched film was cut into 100mm by 100mm rectangles. The two ends of the rectangular stretched film were held by 5 jigs of the stretching device. The pre-stretched film is pulled by a jig and is free to uniaxially stretch along the longitudinal direction of the long raw material film obtained in the extrusion film forming step. The stretching temperature was 138℃and the stretching magnification was 1.2 times. By this stretching, an optical film as a uniaxially stretched film is obtained.

The in-plane retardation and NZ coefficient of the obtained optical film were measured, and as a result, the in-plane retardation Re (450), re (550), and Re (650) of wavelengths 450nm, 550nm, and 650nm were measured as Re (450) =128 nm, re (550) =140 nm, and Re (650) =144 nm. Further, the direction of the slow axis of the optical film is a direction perpendicular to the stretching direction. Further, the NZ coefficient at the measurement wavelength of 550nm was 0.45.

Example 2

The linear velocity in the step (1-2) was changed to 107 μm in thickness of the long raw material film.

In the step (1-3), the immersion time of the raw material film in the solvent was adjusted to obtain a stretched film having an in-plane retardation re=2 nm and a retardation rth=28 nm in the thickness direction.

Further, the stretching ratio in the step (1-4) was changed to 1.3 times.

Except for the above, the optical film was produced in the same manner as in example 1.

Example 3

The linear velocity in the step (1-2) was changed to 276 μm in thickness of the long raw material film.

In the step (1-3), the immersion time of the raw material film in the solvent was adjusted to obtain a stretched film having an in-plane retardation re=4 nm and a retardation rth=71 nm in the thickness direction.

Further, the stretching ratio in the step (1-4) was changed to 1.1 times.

Example 4

The amount of the crystalline polystyrene having the syndiotactic structure in the step (1-1) was changed to 50 parts, and the amount of the polyphenylene ether was changed to 50 parts.

The linear velocity in the step (1-2) was changed to change the thickness of the long raw material film to 201. Mu.m.

Further, in the step (1-3), the immersion time of the raw material film in the solvent was adjusted to obtain a stretched film having an in-plane retardation re=42 nm and a retardation rth=540 nm in the thickness direction.

The stretching temperature in the step (1-4) was changed to 160℃and the stretching ratio was changed to 1.6 times.

Comparative example 1

The linear velocity in the step (1-2) was changed to change the thickness of the long raw material film to 115. Mu.m.

In addition, the step (1-3) of immersing the raw material film in the solvent is not performed.

Further, in the step (1-4), instead of the film before stretching, the raw material film was stretched, the stretching temperature was changed to 132 ℃, and the stretching magnification was changed to 2.2 times.

Comparative example 2

100 parts of the hydrogenated ring-opening polymer of dicyclopentadiene obtained in production example 2 was mixed with 1.1 parts of antioxidant (tetrakis [ methylene-3- (3 ',5' -di-t-butyl-4 ' -hydroxyphenyl) propionate ] methane; irganox (registered trademark) 1010 by Baskikai Co., ltd.) and then fed into a biaxial extruder (TEM-37B by Toshiba machinery Co., ltd.) having four die holes with an inner diameter of 3 mm. Phi. The mixture of the hydrogenated ring-opening polymer of dicyclopentadiene and the antioxidant is molded into a strand by hot melt extrusion molding, and then chopped by a wire cutter to obtain crystalline resin pellets.

The particles are used in the step (1-2). The linear velocity in the step (1-2) was changed to change the thickness of the long raw material film to 13. Mu.m.

In the step (1-3), the type of the solvent is changed to toluene. Further, the immersion time of the raw material film in the solvent was adjusted to obtain a stretched film having an in-plane retardation re=8 nm and a retardation rth= -73nm in the thickness direction.

Further, the stretching temperature in the step (1-4) was changed to 130℃and the stretching ratio was changed to 1.5 times.

[ evaluation of optical films obtained in examples 1 to 3 and comparative examples 1 to 2 ]

Polarizing films (polarizers having a polarizing transmission axis in the width direction, manufactured by Santa Clara Co., ltd. "HLC2-5618S", 180 μm thick) were prepared. One surface of the polarizing film was bonded to the optical films obtained in examples 1 to 3 and comparative examples 1 to 2 via an adhesive layer (CS 9621, manufactured by solar electric Co., ltd.) so that the polarization transmission axis of the polarizing film was at an angle of 45 ° to the slow axis of the optical film, thereby obtaining a circularly polarizing plate.

A mirror was prepared, and the circular polarizing plate thus prepared was placed on the mirror so that the optical film was on the mirror side. The circularly polarizing plate was irradiated with a fluorescent lamp, and the reflected light of the mirror was observed in the front direction and in an oblique direction at a polar angle of about 60 °. The front direction is a direction parallel to the thickness direction of the circularly polarizing plate and the front direction of the mirror. In each observation direction, "good" if no coloration is observed, "delta" if weak coloration is observed, and "x" if an unacceptable level of coloration is observed.

[ evaluation of optical film obtained in example 4 ]

2 polarizing films (polarizer having a thickness of 180 μm and a polarization transmission axis in the width direction) were prepared and placed in crossed nicols (HLC 2-5618S, manufactured by san francisco). The crossed nicols prism means that the polarization transmission axis is perpendicular when viewed from the thickness direction. The optical film obtained in example 4 was disposed between these polarizing films so that the polarization transmission axis of the viewing-side polarizing film (i.e., the polarizing film on the viewing side when disposed in a backlight described later) was aligned with the slow axis of the optical film. The polarizing film and the optical film were bonded via an adhesive layer (CS 9621, manufactured by solar electric Co., ltd.) to obtain a laminate.

A backlight is prepared in a darkroom, and the fabricated laminate is placed over the backlight. In a state where the backlight is lit, light transmitted through the laminate is observed in a front direction and in an oblique direction at a polar angle of about 60 °. At each observation position, "good" if no coloration was observed, "delta" if weak coloration was observed, and "x" if unacceptable levels of coloration and light leakage were observed.

Results (results)

The results of the above examples and comparative examples are shown in the following table. In the following table, the meanings of the abbreviations are as follows.

SPS: crystalline polystyrene.

PPE: polyphenylene ether.

Cy: cyclohexane.

Tl: toluene.

TABLE 1

TABLE 1 results of examples and comparative examples

Discussion of the related art

In the examples, crystalline polystyrene is used as a crystalline polymer having negative intrinsic birefringence to manufacture an optical film. When the film before stretching was subjected to free uniaxial stretching in order to produce the optical film, all examples exhibited slow axes in the direction perpendicular to the stretching direction, and thus it was confirmed that the obtained optical film had negative birefringent properties. In addition, the optical films obtained in the examples each have an in-plane retardation satisfying the formula (1) and have NZ coefficients satisfying the formula (2).

The optical film obtained in the examples has inverse wavelength dispersion properties, and thus can exhibit its optical function in a wide wavelength range.

Thus, the optical films of examples 1 to 3 can function as 1/4 wave plates in a wide wavelength range. Therefore, the circularly polarizing plate having the optical film can suppress reflection of light in a wide wavelength range as a reflection suppressing film. Therefore, coloration due to the passage of light of a part of wavelengths through the circularly polarizing plate can be suppressed.

In addition, the optical film of example 4 can function as a 1/2 wave plate in a wide wavelength range. Therefore, the optical film can convert the vibration direction of linearly polarized light of a wide wavelength range transmitted through the optical film by 90 °. Therefore, coloring and light leakage due to the passage of light of a part of wavelengths through the laminate can be suppressed.

Further, since the optical film obtained in the examples has an appropriate NZ coefficient, the polarization state of light transmitted through the optical film in the thickness direction can be appropriately changed, and the polarization state of light transmitted through the optical film in an oblique direction which is neither parallel nor perpendicular to the thickness direction can be appropriately changed.

Thus, the optical films of examples 1 to 3 can suppress reflection of light transmitted through the circularly polarizing plate in the oblique direction, and therefore can suppress coloring not only in the front direction but also in the oblique direction.

In addition, the optical film of example 4 can suppress light from passing through the laminate in the oblique direction, and therefore can suppress coloring and light leakage not only in the front direction but also in the oblique direction.

Claims

1. An optical film comprising a crystalline polymer,

the optical film has negative birefringence characteristics,

the optical film has in-plane retardation Re (450), re (550) and Re (650) of 450nm, 550nm and 650nm measured at the wavelengths satisfying the formula (1),

the optical film has an NZ coefficient NZ satisfying the formula (2),

Re(450)＜Re(550)＜Re(650) (1)

0＜Nz＜1 (2)。

2. the optical film of claim 1, wherein the optical film has a single layer structure.

3. The optical film according to claim 1 or 2, wherein the optical film is a stretched film.

4. An optical film according to any one of claims 1 to 3, wherein the optical film is a uniaxially stretched film.

5. The optical film according to any one of claims 1 to 4, wherein the optical film has a long strip shape.

6. The optical film according to any one of claims 1 to 5, wherein the optical film is formed of a resin containing the crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence.

7. The optical film according to claim 6, wherein a weight ratio (thermoplastic polymer/crystalline polymer) of the thermoplastic polymer having positive intrinsic birefringence to the crystalline polymer having negative intrinsic birefringence is 3/7 or more.

8. The optical film according to claim 6 or 7, wherein the crystalline polymer having negative intrinsic birefringence is a polystyrene-based polymer,

the thermoplastic polymer having positive intrinsic birefringence is polyphenylene ether.

9. A polarizing plate having the optical film according to any one of claims 1 to 8 and a polarizing film.

10. The polarizing plate according to claim 9, wherein a slow axis of the optical film forms an angle of 80 ° to 100 ° with an absorption axis of the polarizing film.

11. A method for producing the optical film according to any one of claims 1 to 8, comprising the steps of:

a step of preparing a resin film formed of a resin containing a crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence;

a step of bringing the resin film into contact with a solvent to change birefringence in the thickness direction; the method comprises the steps of,

and stretching the resin film.