WO2022145169A1

WO2022145169A1 - Optical film, production method therefor, and polarizing plate

Info

Publication number: WO2022145169A1
Application number: PCT/JP2021/044208
Authority: WO
Inventors: 恭輔井上
Original assignee: 日本ゼオン株式会社
Priority date: 2020-12-28
Filing date: 2021-12-02
Publication date: 2022-07-07
Also published as: CN116685610A; TW202232136A; KR20230121743A; JPWO2022145169A1

Abstract

The present invention produces an optical film by means of a production method involving, in the order given, a step for preparing a resin film comprising a resin that includes a crystalline polymer having a negative intrinsic birefringence and a thermoplastic polymer having a positive intrinsic birefringence, a step for bringing the resin film into contact with a solvent to cause the birefringence of the film in the thickness direction to change, and a step for stretching the resin film.

Description

Optical film and its manufacturing method, and polarizing plate

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

Conventionally, a film manufacturing technique using a resin has been proposed (Patent Documents 1 to 3).

Japanese Patent No. 4592004 International Publication No. 2017/145935 International Publication No. 2020/137409

A resin may be used to manufacture an optical film having anisotropy in the refractive index. Such an optical film having anisotropy in the refractive index may have birefringence. The optical film having birefringence can be provided in the display device as a film such as a reflection suppression film and a viewing angle compensation film.

When the optical film is provided in the display device, it is required 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 between 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 an optical film having an NZ coefficient of more than 0.0 and less than 1.0 is obtained, the optical film makes it possible to improve the display quality when the display surface is viewed from an inclined direction.

Further, the optical film is required to have reverse wavelength dispersibility. An optical film having a reverse wavelength dispersibility can usually exhibit its optical function in a wide wavelength range. For example, a wave plate as an optical film having anti-wavelength dispersibility can be used as a wide-band wave plate capable of functioning in a wide wavelength range.

Conventionally, a method for manufacturing an optical film having an NZ coefficient of more than 0.0 and less than 1.0 is known. Further, an optical film having a reverse wavelength dispersibility is conventionally known. However, it has not been conventionally achieved to realize an optical film having an NZ coefficient of more than 0.0 and less than 1.0 and having anti-wavelength dispersibility by a film having negative birefringence characteristics.

The present invention was devised in view of the above problems, and is an optic having a negative birefringence characteristic, a reverse wavelength dispersibility, and an NZ coefficient larger than 0.0 and less than 1.0. It is an object of the present invention to provide a film and a method for producing the same; and a polarizing plate provided with the above-mentioned optical film;

The present inventor has diligently studied to solve the above-mentioned problems. As a result, the present inventor has used a method including 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 step of stretching the resin film in this order. For example, they have found that the above-mentioned problems can be solved, and have completed the present invention.
That is, the present invention includes the following.

[1] An optical film containing a crystalline polymer.
The optical film has a negative birefringence characteristic and
The in-plane retardations Re (450), Re (550) and Re (650) of the optical film at the measurement wavelengths of 450 nm, 550 nm and 650 nm satisfy the formula (1).
An optical film in which the NZ coefficient Nz of the optical film satisfies the formula (2).
Re (450) <Re (550) <Re (650) (1)
0 <Nz <1 (2)
[2] The optical film according to [1], wherein the optical film has a single-layer structure.
[3] The optical film according to [1] or [2], wherein the optical film is a stretched film.
[4] The optical film according to any one of [1] to [3], wherein the optical film is a uniaxially stretched film.
[5] The optical film according to any one of [1] to [4], wherein the optical film has a long shape.
[6] The item according to any one of [1] to [5], which comprises a resin containing the crystalline polymer having a negative intrinsic birefringence and a thermoplastic polymer having a positive intrinsic birefringence. Optical film.
[7] When the weight ratio (thermoplastic polymer / crystalline polymer) of the thermoplastic polymer having positive intrinsic birefringence and the crystalline polymer having negative intrinsic birefringence is 3/7 or more. The optical film according to [6].
[8] The crystalline polymer having a negative intrinsic birefringence is a polystyrene-based polymer.
The optical film according to [6] or [7], wherein the thermoplastic polymer having positive intrinsic birefringence is a polyphenylene ether.
[9] A polarizing plate comprising the optical film according to any one of [1] to [8] and a polarizing film.
[10] The polarizing plate according to [9], wherein the slow axis of the optical film and the absorption axis of the polarizing film form an angle of 80 ° to 100 °.
[11] The method for producing an optical film according to any one of [1] to [8].
A step of preparing a resin film made of a resin containing a crystalline polymer having a negative intrinsic birefringence and a thermoplastic polymer having a positive intrinsic birefringence.
The step of bringing the resin film into contact with a solvent to change the birefringence in the thickness direction,
A method for producing an optical film, comprising the steps of stretching the resin film in this order.

According to the present invention, an optical film having negative birefringence characteristics, anti-wavelength dispersibility, and an NZ coefficient of more than 0.0 and less than 1.0; and a method for producing the same; A polarizing plate provided with an optical film; can be provided.

Hereinafter, the present invention will be described in detail by showing embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be arbitrarily modified and carried out without departing from the scope of claims of the present invention and the equivalent scope thereof.

In the following description, the in-plane retardation Re of the film is a value represented by Re = (nx-ny) × d unless otherwise specified. Further, the birefringence in the in-plane direction of the film is a value represented by (nx-ny), and is therefore 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], and is therefore represented by Rth / d, unless otherwise specified. Further, the NZ coefficient of the film is a value represented by (nx-nz) / (nx-ny) unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) and in the direction giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the film and perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. The measurement wavelength is 550 nm unless otherwise specified.

In the following description, the material having positive intrinsic birefringence means a material in which the refractive index in the stretching direction is larger than the refractive index in the direction perpendicular to it, unless otherwise specified. Therefore, a polymer having positive intrinsic birefringence means a polymer in which the refractive index in the stretching direction is larger than the refractive index in the direction perpendicular to the refractive index, unless otherwise specified. Further, the material having negative birefringence means a material in which the refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the refractive index, unless otherwise specified. Therefore, a polymer having negative intrinsic birefringence means a polymer in which the refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the refractive index, unless otherwise specified.

In the following description, the "long" shape means a shape having a length of 5 times or more, preferably 10 times or more, and specifically a roll. It refers to the shape of a film that has a length that allows it to be rolled up and stored or transported. There is no particular limitation on the upper limit of the length, but it is usually 100,000 times or less with respect to the width.

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

Unless otherwise specified, the angle formed by the optical axis (absorption axis, transmission axis, slow phase axis, etc.) of each film in the member including a plurality of films represents the angle when the film is viewed from the thickness direction.

Unless otherwise specified, the "polarizing plate", "circular polarizing plate", "wave plate" and "negative C plate" are not only rigid members but also flexible members such as resin films. Also includes. It was

[1. Overview of optical film]
The optical film according to an embodiment of the present invention contains a crystalline polymer. This optical film meets the following requirements (A) to (C) in combination.

Requirement (A): The optical film has negative birefringence characteristics.
Requirement (B): In-plane retardations Re (450), Re (550) and Re (650) of the optical film at the measurement wavelengths of 450 nm, 550 nm and 650 nm satisfy the formula (1).
Requirement (C): The NZ coefficient Nz of the optical film satisfies the equation (2).
Re (450) <Re (550) <Re (650) (1)
0 <Nz <1 (2)

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

[2. Birefringence characteristics of optical film]
The optical film according to this embodiment has a negative birefringence characteristic.
"The film has negative birefringence characteristics" means that when the film is stretched in one stretching direction, the amount of increase in the refractive index in the direction perpendicular to the stretching direction is larger than the amount of increase in the refractive index in the stretching direction. , Say big. Further, the film "has a positive birefringence characteristic" means that when the film is stretched in one stretching direction, the amount of increase in the refractive index in the stretching direction is the amount of increase in the refractive index in the direction perpendicular to the stretching direction. It means that it is bigger than. Since it is an increase amount, when the refractive index increases due to stretching, the increase amount of the refractive index becomes a positive value, and when the refractive index decreases due to stretching, the increase amount of the refractive index becomes negative. Is the value of. Here, the stretching direction is usually perpendicular to the thickness direction, and thus may be in-plane.

The birefringence characteristics of the optical film can be examined by stretching the optical film. Also, the birefringence characteristics of an optical film usually depend on the composition of the optical film. Therefore, when a resin film having the same composition as an optical film is stretched to produce an optical film as in the manufacturing method described later, the birefringence characteristics of the optical film are usually examined by stretching the resin film as well. be able to. Specifically, when the resin film is stretched in one stretching direction, if the amount of increase in the refractive index in the direction perpendicular to the stretching direction is larger than the amount of increase in the refractive index in the stretching direction, it is obtained from the resin film. The birefringence characteristic of the optical film to be obtained can be negative.

Generally, when a film having a negative birefringence characteristic is stretched in a direction perpendicular to the thickness direction, the birefringence in the thickness direction becomes large. Therefore, according to stretching, the NZ coefficient is usually 0 or less, and it is difficult to produce a film having an NZ coefficient larger than 0 by stretching. Therefore, it is surprising to those skilled in the art that an optical film of the present embodiment having a negative birefringence characteristic and an NZ coefficient satisfying the formula (2) can be obtained. Therefore, the optical film of the present embodiment having a combination of negative birefringence characteristics, an in-plane retardation satisfying the formula (1), and an NZ coefficient satisfying the formula (2) is an optical film that has never existed before. Its industrial value is high.

[3. Wavelength dispersibility of optical film]
The in-plane retardation Re (450) at a measurement wavelength of 450 nm, the in-plane retardation Re (550) at a measurement wavelength of 550 nm, and the in-plane retardation Re (650) at a measurement wavelength of 650 nm according to the present embodiment are Equation (1) is satisfied.
Re (450) <Re (550) <Re (650) (1)

An optical film having an in-plane retardation satisfying the formula (1) usually has a reverse wavelength dispersibility. Therefore, the in-plane retardation of this optical film can be larger as the measurement wavelength is longer. Therefore, the optical film can exhibit 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. Further, 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 according to the present embodiment satisfies the formula (2). The three-dimensional birefringence nx, ny and nz of the optical film having the NZ coefficient Nz satisfying this equation (2) can satisfy nx>nz> ny.
0 <Nz <1 (2)
Specifically, the NZ coefficient Nz of the optical film is usually greater than 0.0, preferably greater than 0.1, more preferably greater than 0.2, and usually less than 1.0, preferably less than 0.9. , More preferably less than 0.8.

An optical film having an NZ coefficient satisfying the formula (2) is not only in the polarized state of light passing through the optical film in the thickness direction, but also in the polarized state of light passing in an inclined direction that is neither parallel nor perpendicular to the thickness direction. Can be changed appropriately. Therefore, the optical film can exert its optical function not only for light in the thickness direction but also for light in the tilt direction. For example, when the optical film can give a phase difference of 1/4 wavelength to the light passing in the thickness direction, the optical film also gives a phase difference of 1/4 wavelength to the light passing in the tilt direction. sell. Further, for example, when the optical film can give a phase difference of 1/2 wavelength to the light passing in the thickness direction, the optical film has a phase difference of 1/2 wavelength to the light passing in the tilt direction. Can be given.

[5. Optical film composition]
The optical film according to an embodiment of the present invention contains a crystalline polymer. The crystalline polymer represents a polymer having crystallinity. The crystalline polymer represents a polymer having a melting point Tm. That is, the crystalline polymer represents a polymer whose melting point Tm can be observed with a differential scanning calorimeter (DSC). In the following description, a resin containing a crystalline polymer may be referred to as a "crystalline resin". This crystalline resin is preferably a thermoplastic resin. The optical film preferably contains a crystalline resin, and more preferably consists only of the crystalline resin.

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

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

The crystalline polystyrene-based polymer can be a polymer of a styrene-based monomer. Therefore, the crystalline polystyrene-based polymer can be a polymer containing a structural unit having a structure formed by polymerizing a styrene-based monomer (hereinafter, appropriately referred to as “styrene-based unit”).

The styrene-based monomer may be an aromatic vinyl compound such as styrene or a styrene derivative. Examples of the styrene derivative include compounds in which the benzene ring of styrene or the α-position or β-position is substituted with a substituent.

Examples of the styrene-based monomer include styrene, alkylstyrene, halogenated styrene, halogenated alkylstyrene, alkoxystyrene, vinyl benzoic acid ester, and hydrogenated polymers thereof.

Examples of alkyl styrene include methyl styrene, ethyl styrene, isopropyl styrene, t-butyl styrene, 2,4-dimethyl styrene, phenyl styrene, vinyl naphthalene, and vinyl styrene. Examples of halogenated styrene include chlorostyrene, bromostyrene, and fluorostyrene. Examples of halogenated alkyl styrenes include chloromethyl styrene. Examples of alkoxystyrene include methoxystyrene and ethoxystyrene. Among the styrene-based monomers, styrene, methylstyrene, ethylstyrene, and 2,4-dimethylstyrene are preferable. Further, one type of styrene-based monomer may be used, or two or more types may be used in combination.

The crystalline polystyrene-based polymer preferably has an isotactic structure or a syndiotactic structure, and more preferably has a syndiotactic structure. The fact that the crystalline polystyrene-based polymer has a syndiotactic structure means that the stereochemical structure of the crystalline polystyrene-based polymer has a syndiotactic structure. The syndiotactic structure is a three-dimensional structure in which phenyl groups, which are side chains, are alternately located in opposite directions with respect to the main chain formed by a carbon-carbon bond in the Fischer projection formula. Compared with the polystyrene-based polymer having an atactic structure, the polystyrene-based polymer having a syndiotactic structure usually has a low specific density and is excellent in hydrolysis resistance, heat resistance and chemical resistance.

The tacticity of a crystalline polystyrene-based polymer can be quantified by a nuclear magnetic resonance method ( ¹³ C-NMR method) using isotope carbon. ¹³ The tacticity measured by the C-NMR method can be indicated by the abundance ratio of a plurality of consecutive constituent units. In general, for example, when there are two consecutive building blocks, it is a diad, when there are three, it is a triad, and when there are five, it is a pentad. In this case, the crystalline polystyrene-based polymer having a syndiotactic structure may have a syndiotacticity of usually 75% or more, preferably 85% or more in diad (racemic diad), or pentad (racemic pen). (Tad) may have a syndiotacticity of usually 30% or more, preferably 50% or more.

The crystalline polystyrene-based polymer may be a homopolymer or a copolymer. Therefore, the crystalline polystyrene-based polymer may be a homopolymer of one kind of styrene-based monomer, or may be a copolymer of two or more kinds of styrene-based monomers. When the crystalline polystyrene-based polymer is a copolymer of two or more types of styrene-based monomers, the ratio of each styrene-based unit to 100% by weight of the entire crystalline polystyrene-based polymer is preferably 5% by weight. As described above, it is more preferably 10% by weight or more, preferably 95% by weight or less, and more preferably 90% by weight or less.

Further, the crystalline polystyrene-based polymer may be a copolymer of one or more types of styrene-based monomers and a monomer other than the styrene-based monomers. The proportion of the styrene-based unit contained in the crystalline polystyrene-based polymer is preferably 80% by weight or more, more preferably 83% by weight or more, still more preferably 85% by weight or more from the viewpoint of obtaining an optical film having desired optical properties. Is.

Normally, the ratio of a certain structural unit contained in the crystalline polystyrene-based polymer can match the ratio of the monomer corresponding to the structural unit to all the monomers of the crystalline polystyrene-based polymer. Therefore, the ratio of the styrene-based unit contained in the crystalline polystyrene-based polymer may match the ratio of the styrene-based monomer to all the monomers of the crystalline polystyrene-based polymer.

The crystalline polystyrene-based polymer is obtained, for example, by polymerizing a styrene-based monomer in an inert hydrocarbon solvent or in the absence of a solvent, using a titanium compound and a condensation product of water and trialkylaluminum as a catalyst. It can be manufactured (see Japanese Patent Application Laid-Open No. 62-187708).

As the crystalline polymer, one type may be used alone, or two or more types may be used in combination at any ratio.

The weight average molecular weight Mw of the crystalline polymer is preferably 130,000 or more, more preferably 140,000 or more, particularly preferably 150,000 or more, preferably 500,000 or less, and more preferably 450,000 or less. Particularly preferably, it is 400,000 or less. Since the crystalline polymer having such a weight average molecular weight Mw can have a high glass transition temperature Tg, the heat resistance of the optical film can be enhanced.

The weight average molecular weight (Mw) of the polymer can be measured as a polystyrene-equivalent value 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 ° C. or higher, more preferably 90 ° C. or higher, and particularly preferably 95 ° C. or higher. When a crystalline polymer having such a high glass transition temperature Tg is used, the heat resistance of the optical film can be enhanced. From the viewpoint of smooth stretching in the manufacturing process of the optical film, the glass transition temperature of the crystalline polymer is preferably 160 ° C. or lower, more preferably 155 ° C. or lower, and particularly preferably 150 ° C. or lower.

The melting point Tm of the crystalline polymer is preferably 200 ° C. or higher, more preferably 210 ° C. or higher, particularly preferably 220 ° C. or higher, preferably 300 ° C. or lower, more preferably 290 ° C. or lower, and particularly preferably 280 ° C. or lower. Is. When the melting point Tm of the crystalline polymer is within the above range, when the crystalline resin is molded to obtain a resin film, unintended progress of crystallization of the crystalline polymer and generation of foreign substances due to thermal decomposition are suppressed. can. Therefore, 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 measured by the following methods. First, the polymer is melted by heating, and the melted polymer is rapidly cooled with dry ice. Subsequently, using this polymer as a test piece, the glass transition temperature Tg and melting point Tm of the polymer were measured at a heating rate of 10 ° C./min (heating mode) using a differential scanning calorimeter (DSC). Can be measured.

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

The crystallinity of the crystalline polymer contained in the optical film is usually higher than a certain level. The specific range of 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 X-ray diffraction.

The crystalline resin may contain an amorphous polymer having no crystallinity in combination with the crystalline polymer. As the amorphous polymer, a thermoplastic polymer is usually used. Above all, this amorphous thermoplastic polymer preferably has a positive intrinsic birefringence. When a polymer having positive intrinsic birefringence is used in combination with the above-mentioned crystalline polymer having negative intrinsic birefringence, the inverse wavelength dispersibility of the optical film can be easily obtained.

As the thermoplastic polymer having positive intrinsic birefringence, polyphenylene ether is preferable from the viewpoint of transparency and toughness. Polyphenylene ethers can usually have excellent compatibility with crystalline polystyrene-based polymers.

Polyphenylene ether represents a polymer having a phenylene ether skeleton. Substituents may or may not be attached to the benzene ring of the phenylene ether skeleton. Polyphenylene ether usually has a phenylene ether skeleton in its backbone. As the polyphenylene ether, a polymer containing a phenylene ether unit represented by the following formula (I) is preferable.

In formula (I), Q ¹ is independently a halogen atom, a lower alkyl group (for example, an alkyl group having 1 or more and 7 or less carbon atoms), a phenyl group, a haloalkyl group, an aminoalkyl group, a hydrocarbon oxy group, or Represents a halohydrocarbon oxy group (where the halogen atom and the oxygen atom are separated by at least two carbon atoms). Of these, an alkyl group and a phenyl group are preferable as Q ¹ , and an alkyl group having 1 or more and 4 or less carbon atoms is particularly preferable.

In the formula (I), Q ² is independently a hydrogen atom, a halogen atom, a lower alkyl group (for example, an alkyl group having 1 or more and 7 or less carbon atoms), a phenyl group, a haloalkyl group, a hydrocarbon oxy group, or a halo. Represents a hydrocarbon oxy group (where the halogen atom and the oxygen atom are separated by at least two carbon atoms). Of these, a hydrogen atom is preferable as ^Q2 .

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

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

When the polymer containing the structural unit represented by the formula (I) is a copolymer, preferred examples of the copolymer include 2,6-dimethyl-1,4-phenylene ether unit and 2,3. , 6-trimethyl-1,4-phenylene ether unit (structural unit represented by "-(C ₆ H (CH ₃ ) ₃ -O-)-") and a random copolymer having a combination thereof.

The polyphenylene ether may contain structural units other than the phenylene ether unit. In this case, the polyphenylene ether can be a copolymer having a phenylene ether unit and other structural units. However, the ratio of structural units other than the phenylene ether unit in the polyphenylene ether is preferably small as long as the desired optical properties 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. Particularly preferably, it is 95% by weight or more.

For example, polyphenylene ethers having other substituents grafted on the polymer chain can also be mentioned. Such polyphenylene ethers can be synthesized, for example, by grafting another substituent onto the polyphenylene ether by an appropriate method. Specific examples include polyphenylene ether grafted with a polymer such as polystyrene, polybutadiene, or other vinyl-containing polymer.

There are no restrictions on the method for producing polyphenylene ether, and for example, the polyphenylene ether may be produced by the method described in JP-A-11-302259.

As the amorphous polymer, one type may be used alone, or two or more types may be used in combination at any ratio.

The weight average molecular weight Mw of the amorphous polymer such as polyphenylene ether is preferably 15,000 or more, more preferably 25,000 or more, particularly preferably 35,000 or more, and preferably 100,000 or less. It is preferably 85,000 or less, and particularly preferably 70,000 or less. When the weight average molecular weight Mw of the amorphous polymer is not more than the lower limit of the above range, the mechanical strength of the optical film can be increased. Further, when the weight average molecular weight Mw of the amorphous polymer is not more 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 an amorphous polymer such as polyphenylene ether is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher, preferably 350 ° C. or lower, more preferably 300 ° C. or lower. Particularly preferably, it is 250 ° C. or lower. When the glass transition temperature of the amorphous polymer is at least the lower limit of the above range, the heat resistance of the optical film can be enhanced. Further, when the glass transition temperature of the amorphous polymer is not more than the upper limit of the above range, stretching in the manufacturing process of the optical film can be smoothly performed.

The amount of the amorphous polymer in 100% by weight of the crystalline resin is preferably 20% by weight or more, more preferably 30% by weight or more, and particularly preferably 35% by weight from the viewpoint of obtaining an optical film having desired optical properties. % Or more, preferably 70% by weight or less, more preferably 60% by weight or less, and particularly preferably 55% by weight or less.

When the crystalline resin contains a combination of a thermoplastic polymer having a positive intrinsic compound refraction and a crystalline polymer having a negative intrinsic compound refraction, the weight ratio (thermoplastic polymer / crystalline polymer) is , Preferably within 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, and particularly preferably 4/6 or more. Is 8/2 or less, more preferably 7.5 / 2.5 or less, and particularly preferably 7/3 or less. When the weight ratio (thermoplastic polymer / crystalline polymer) is in the above range, the inverse wavelength dispersibility of the optical film can be easily obtained.

The crystalline resin may contain any component in combination with the above-mentioned crystalline polymer and amorphous polymer. Optional components include, for example, lubricants; layered crystal compounds; fine particles such as inorganic fine particles; antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, stabilizers such as near-infrared absorbers; plastics. Agents; colorants such as dyes and pigments; antistatic agents; and the like. Any component may be used alone or in combination of two or more. The amount of any component can be appropriately determined as long as the effect of the present invention is not significantly impaired. The amount of any component may be, for example, in the range where the total light transmittance of the optical film can be maintained at 85% or more.

[6. Layer structure of optical film]
The optical film may have a multi-layer structure including a plurality of layers, but preferably has a single-layer structure. The single-layer structure represents a structure having only a single layer having the same composition and not having a layer having a composition different from the above-mentioned composition. Therefore, it is preferable that the optical film has a single layer formed of the crystalline resin.

[7. Characteristics of optical film]
The optical film preferably has an in-plane retardation in an appropriate range according to the application.

For example, the specific in-plane retardation Re of the optical film may be preferably 100 nm or more, more preferably 110 nm or more, particularly preferably 120 nm or more, and preferably 180 nm or less, more preferably 170 nm or less at a measurement wavelength of 550 nm. Particularly preferably, it may be 160 nm or less. 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 may be preferably 245 nm or more, more preferably 265 nm or more, particularly preferably 270 nm or more, and preferably 320 nm or less, more preferably 300 nm at a measurement wavelength of 550 nm. Hereinafter, it may be particularly preferably 295 nm or less. In this case, the optical film can function as a 1/2 wave plate.

The film retardation can be measured using a phase difference meter (for example, "AXoScan OPMF-1" manufactured by AXOMETRICS).

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 400 nm to 700 nm using an ultraviolet / visible spectrometer.

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%, ideally 0.0%. When the optical film having such a small haze is provided in the display device, the sharpness of the 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 Nippon Denshoku Kogyo Co., Ltd.).

The optical film may contain a solvent. This solvent may be incorporated into the film in the step of bringing the resin film into contact with the solvent in the production method described later. Specifically, all or part of the solvent incorporated into the film upon contact with the resin film can enter the interior of the polymer. Therefore, it is difficult to completely remove the solvent even if the drying is performed above the boiling point of the solvent. Therefore, the optical film may contain a solvent.

The optical film is preferably a stretched film. The stretched film represents a film produced through a stretching treatment. Above all, the optical film is preferably a uniaxially stretched film. The uniaxially stretched film represents a film that is positively stretched only in one direction and is not positively stretched in any other direction. Since the uniaxially stretched film can be manufactured by stretching in only one direction, the manufacturing process can be simplified, and thus simple manufacturing can be realized.

The optical film may be a single-wafer film or a long film having a long shape. When the optical film has a long shape, it is possible to continuously manufacture a polarizing plate by laminating the optical film and the long polarizing film.

The thickness of the optical film can be set appropriately according to the application 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, and particularly preferably 200 μm or less.

[8. Outline of manufacturing method of optical film]
The above-mentioned optical film is
The step (i) of preparing a resin film made of a crystalline resin containing a crystalline polymer having a negative intrinsic birefringence and a thermoplastic polymer having a positive intrinsic birefringence;
The step (ii) of bringing the resin film into contact with a solvent to change the birefringence in the thickness direction;
The step of stretching the resin film (iii) and
Can be manufactured by a manufacturing method containing the above in this order.
In the following description, among the resin films, the resin film before being brought into contact with the solvent in step (ii) is referred to as "raw film", and the resin film after being brought into contact with the solvent in step (ii) is referred to as "pre-stretched film". ".

The present inventor presumes that the mechanism for obtaining the above-mentioned optical film by the above-mentioned manufacturing method is as follows. However, the technical scope of the present invention is not limited by the following mechanism.

In this manufacturing method, an optical film is manufactured using a resin film containing a crystalline polymer having a negative intrinsic birefringence. When a crystalline polymer having a negative intrinsic birefringence is oriented in a certain orientation direction, it can exhibit a small refractive index in the orientation direction and a large refractive index in the direction perpendicular to the orientation direction. Therefore, the resin film and the optical film containing this crystalline polymer can have negative birefringence characteristics as represented by the requirement (A).

Further, the optical film may contain a thermoplastic polymer having a positive intrinsic birefringence in combination with a crystalline polymer having a negative intrinsic birefringence. When a thermoplastic polymer having positive intrinsic birefringence is oriented in a certain orientation direction, a large refractive index may be developed in the orientation direction, and a small refractive index may be developed in the direction perpendicular to the orientation direction. Therefore, when oriented in a certain orientation direction, the direction in which the refractive index of the crystalline polymer is maximized and the direction in which the refractive index of the thermoplastic polymer is maximized can be perpendicular to each other. Then, the entire birefringence of the optical film containing the combination of the crystalline polymer and the thermoplastic polymer may reflect the difference between the birefringence of the crystalline polymer and the birefringence of the thermoplastic polymer. In the above-mentioned 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-mentioned manufacturing method can have a reverse wavelength dispersibility as represented by the requirement (B).

Further, when the raw fabric film containing the crystalline polymer is brought into contact with a solvent in the step (ii), the solvent infiltrates into the raw fabric film. The action of the infiltrated solvent causes microBrownian motion in the molecules of the crystalline polymer in the film, and the molecular chains are oriented. According to the study of the present inventor, it is considered that the solvent-induced crystallization phenomenon of the crystalline polymer may proceed when the molecular chain is oriented.

Generally, the surface area of the film is large on the front surface and the back surface, which are the main surfaces. Therefore, as for the infiltration rate of the solvent, the infiltration rate in the thickness direction through the front surface or the back surface is high. Then, the orientation of the molecules of the crystalline polymer can proceed so that the molecules of the polymer are oriented in the thickness direction. Therefore, in the step (ii), the molecules of the crystalline polymer can be oriented in the thickness direction.

Then, in the production method according to the present embodiment, the pre-stretched film as a resin film in which the molecules of the crystalline polymer are oriented in the thickness direction in the step (ii) is stretched in the step (iii). According to stretching, the molecules of the polymer contained in the pre-stretched film can be oriented in a direction perpendicular to the thickness direction. Therefore, by combining the orientation in the thickness direction in the step (iii) and the orientation in the direction perpendicular to the thickness direction in the step (iii), the orientation direction of the polymer molecules can be three-dimensionally adjusted. can. Therefore, the optical film obtained by the above-mentioned manufacturing method can have an NZ coefficient in an appropriate range as represented by the requirement (C).

[9. Step of preparing a resin film (i)]
The method for producing an optical film includes a step of preparing a raw film as a resin film before contacting with a solvent.

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

The raw film preferably has optical isotropic properties. Therefore, the raw film preferably has a small birefringence Re / d in the in-plane direction, and preferably has a small absolute value | Rth / d | of the birefringence in the thickness direction. Specifically, the birefringence Re / d of the raw film in the in-plane direction is preferably less than 1.0 × 10 ^-3 , more preferably less than 0.5 × 10 ^-3 , and particularly preferably 0.3 ×. It is less than 10 ^-3 . Further, the absolute value | Rth / d | of the birefringence in the thickness direction of the raw film is preferably less than 1.0 × 10 ^-3 , more preferably less than 0.5 × 10 ^-3 , and particularly preferably 0.3. It is less than × 10 ^-3 . Having optical isotropic properties as described above indicates that the molecular orientation of the crystalline polymer contained in the raw film is low and is substantially non-oriented. When such an optically isotropic raw fabric film is used, it is not necessary to precisely control the optical properties of the raw fabric film, and therefore, it is not necessary to precisely control the orientation of the molecules of the crystalline polymer. Therefore, the manufacturing method of the optical film can be simplified. Further, when an optically isotropic raw film is used, it is usually possible to obtain an optical film having a small haze.

The raw film preferably has a small solvent content, and more preferably does not contain a solvent. The ratio (solvent content) of the solvent contained in the raw film to 100% by weight of the raw film is preferably 1% or less, more preferably 0.5% or less, and particularly preferably 0.1% or less. Ideally, it is 0.0%. Since the amount of the solvent contained in the raw film before contact with the solvent is small, many molecules of the crystalline polymer can be oriented in the thickness direction by the contact with the solvent, so that the NZ coefficient can be adjusted in a wide range. Is possible. The solvent content of the raw film can be measured by the density.

The haze of the raw film is preferably less than 1.0%, preferably less than 0.8%, more preferably less than 0.5%, and ideally 0.0%. The smaller the haze of the original film, the easier it is to reduce the haze of the obtained optical film.

It is preferable to set the thickness of the raw film according to the thickness of the optical film to be manufactured. Usually, the thickness is increased by contacting with the solvent in the step (ii). By performing stretching in the step (iii), the thickness becomes smaller. Therefore, the thickness of the raw film may be set in consideration of the change in thickness in the step (ii) and the step (iii) as described above.

The raw film may be a single-wafer film, but it is preferably a long film. By using a long raw film, it is possible to continuously produce an optical film by a roll-to-roll method, so that the productivity of the optical film can be effectively increased.

As a method for producing the raw fabric film, since a raw fabric film containing no solvent can be obtained, an injection molding method, an extrusion molding method, a press molding method, an inflation molding method, a blow molding method, a calendar molding method, and a casting molding method. , A resin molding method such as a compression molding method is preferable. Among these, the extrusion molding method is preferable because the thickness can be easily controlled.

The manufacturing conditions in the extrusion molding method are preferably as follows. The cylinder temperature (molten resin temperature) is preferably Tm or higher, more preferably "Tm + 20 ° C" or higher, preferably "Tm + 100 ° C" or lower, and more preferably "Tm + 50 ° C" or lower. Further, the cooling body that the molten resin extruded into a film comes into contact with first is not particularly limited, but a cast roll is usually used. The cast roll temperature is preferably "Tg-50 ° C." or higher, preferably "Tg + 70 ° C." or lower, and more preferably "Tg + 40 ° C." or lower. When the raw fabric film is manufactured under such conditions, the raw fabric film having a thickness of 1 μm to 1 mm can be easily manufactured. Here, "Tm" represents the melting point of the crystalline polymer, and "Tg" represents the glass transition temperature of the crystalline polymer.

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

As the solvent, an organic solvent is usually used. As a specific type of solvent, a solvent that can penetrate into the resin film without dissolving the crystalline polymer contained in the resin film can be used, and for example, a hydrocarbon solvent such as cyclohexane, toluene, limonene, and decalin can be used. ; Carbon disulfide; The type of the solvent may be one type or two or more types.

There are no restrictions on the contact method between the resin film and the solvent. Examples of the contact method include a spray method in which a solvent is sprayed on a resin film; a coating method in which a solvent is applied to a resin film; a dipping method in which a resin film is immersed in a solvent; and the like. Above all, the dipping method is preferable because continuous contact can be easily performed.

The temperature of the solvent in contact with the resin film is arbitrary as long as the solvent can maintain the liquid state, and therefore can be set in the range of the melting point or more and the boiling point or less of the solvent.

The contact time is preferably 0.5 seconds or longer, more preferably 1.0 seconds or longer, and particularly preferably 5.0 seconds or longer. The upper limit is not particularly limited and may be, for example, 24 hours or less. However, since the degree of progress of orientation tends not to change significantly even if the contact time is lengthened, it is preferable that the contact time is short as long as the desired optical characteristics can be obtained.

By contacting with a solvent, the birefringence Rth / d in the thickness direction of the resin film changes. The amount of change in birefringence Rth / d in the thickness direction caused by contact with the solvent is preferably 0.1 × 10 ^-3 or more, more preferably 0.2 × 10 ^-3 or more, and particularly preferably 0.3 × 10 It is ^-3 or more, preferably 50.0 × 10 ^-3 or less, more preferably 30.0 × 10 ^-3 or less, and particularly preferably 20.0 × 10 ^-3 or less. The amount of change in the birefringence Rth / d in the thickness direction represents an absolute value of the change in the birefringence Rth / d in the thickness direction of the resin film. The specific amount of change in the birefringence Rth / d in the thickness direction is obtained by subtracting the birefringence Rth / d in the thickness direction of the original film from the birefringence Rth / d in the thickness direction of the unstretched film and obtaining it as an absolute value. Be done. Preferably, the birefringence Rth / d in the thickness direction is increased by contact between the resin film and the solvent.

The birefringence Re / d in the in-plane direction of the resin film may or may not change due to contact with the solvent. From the viewpoint of simplifying 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 caused by the contact with the solvent is small, and it is more preferable that the change does not occur. preferable. The amount of change in birefringence Re / d in the in-plane direction caused by contact with the solvent is preferably 0.0 × 10 ^-3 to 0.2 × 10 ^-3 , more preferably 0.0 × 10 ^-3 to 0. .1 × 10 ^-3 , particularly preferably 0.0 × 10 ^-3 to 0.05 × 10 ^-3 . The amount of change in the birefringence Re / d in the in-plane direction represents an absolute value of the change in the birefringence Re / d in the in-plane direction of the resin film. The specific amount of change in the in-plane birefringence Re / d is obtained by subtracting the in-plane birefringence Re / d of the raw film from the in-plane birefringence Re / d of the unstretched film. Obtained as a value.

Preferably, the pre-stretched film as the resin film after contact with the solvent is a negative C plate. Therefore, it is preferable that the refractive index nz in the thickness direction of the unstretched film is smaller than the refractive indexes nx and ny in the in-plane direction. Further, it is preferable that the refractive indexes nx and ny in the in-plane direction of the unstretched film are the same value or close to each other. Therefore, in the unstretched film, the difference between the refractive index nx and the refractive index ny is relatively small, the difference between the refractive index nz and the refractive index nz is relatively large, and the difference between the refractive index ny and the refractive index nz is relatively large. It is preferably relatively large.

At this time, the difference between the refractive index nz in the thickness direction and the refractive indexes nx and ny in the in-plane direction can be expressed by the birefringence Rth / d in the thickness direction. That is, since the birefringence Rth / d in the thickness direction of the unstretched film can be expressed by "Rth / d = {(nx + ny) / 2} -nz", the birefringence Rth / d in the thickness direction causes refraction in the thickness direction. The difference between the rate nz and the in-plane refractive indexes nx and ny can be expressed. The birefringence Rth / d in the thickness direction of the unstretched film is preferably 0.05 × 10 ^-3 or more, preferably 0.1 × 10 ^-3 or more, and particularly preferably 0.2 × 10 ^-3 or more. It is preferably 10 × 10 ^-3 or less, more preferably 6.0 × 10 ^-3 or less, and particularly preferably 4.0 × 10 ^-3 or less.

Further, the difference between the refractive indexes nx and ny in the in-plane direction can be expressed by the birefringence Re / d in the in-plane direction. That is, since the birefringence Re / d in the in-plane direction of the unstretched film can be expressed by "Re / d = nx-ny", the birefringence Re / d in the in-plane direction causes the refractive index nx in the in-plane direction. The difference from ny can be expressed. Normally, the difference between the in-plane refractive index nz and ny is smaller than the difference between the in-plane refractive index nz and the in-plane refractive index nx and ny. Therefore, the birefringence Re / d in the in-plane direction of the pre-stretched film may be smaller than the birefringence Rth / d in the thickness direction of the pre-stretched film. The specific range of birefringence Re / d in the in-plane direction of the unstretched film is preferably 0.01 × 10 ^-3 or more, preferably 0.05 × 10 ^-3 or more, and particularly preferably 0.1 × 10. It is ^-3 or more, preferably 1.0 × 10 ^-3 or less, more preferably 0.5 × 10 ^-3 or less, and particularly preferably 0.2 × 10 ^-3 or less.

Preferably, the pre-stretched film as the resin film after contact with the solvent has an NZ coefficient greater than 1.0. The specific NZ coefficient of the pre-stretched film is preferably greater than 1.0, more preferably greater than 5.0, particularly preferably greater than 10, and preferably less than 50, more preferably less than 40, particularly preferred. Is less than 30.

In the step (ii), the thickness of the resin film is usually increased due to the infiltration of the solvent in contact with the resin film into the resin film. 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. Further, the upper limit of the change rate 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 in thickness between the raw film and the unstretched film by the thickness of the raw film.

[11. Step of stretching the resin film (iii)]
The method for producing an optical film includes a step (iii) of stretching a resin film as a pre-stretching film after the step (iii). By stretching, the molecules of the polymer contained in the resin film can be oriented in a direction corresponding to the stretching direction. Therefore, according to the stretching in the step (iii), the in-plane birefringence Re / d, the in-plane retardation Re, the thickness direction birefringence Rth / d, the thickness direction birefringence Rth, and the NZ coefficient The above-mentioned optical film can be obtained by adjusting the optical characteristics such as.

There is no limitation on the stretching direction, and examples thereof include a longitudinal direction, a width direction, and an oblique direction. Here, the diagonal direction is a direction perpendicular to the thickness direction and is neither parallel nor perpendicular to the width direction. Further, the stretching direction may be one direction or two or more directions, but one direction is preferable. Further, among the stretching in one direction, free uniaxial stretching in which no binding force is applied in a direction other than the stretching direction is further preferable. According to these stretchings, the above-mentioned optical film can be easily manufactured.

Since the pre-stretched film usually has negative birefringence characteristics, when stretching in one direction, an optical film having a slow axis in the direction perpendicular to the stretching direction can be obtained. Therefore, since the slow phase axis direction of the optical film can be adjusted by the stretching direction, the stretching direction may be selected according to the direction of the slow phase axis to be expressed 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. Therefore, for example, when it is desired to obtain an optical film having a slow phase axis perpendicular to the absorption axis of the polarizing film, the pre-stretched film is stretched in the longitudinal direction to obtain an optical film having a slow phase axis in the width direction. You may get it. In this case, it is possible to efficiently manufacture a polarizing plate by roll-to-roll using a long optical film and a long polarizing film.

The draw ratio is preferably 1.1 times or more, more preferably 1.2 times or more, preferably 20.0 times or less, more preferably 10.0 times or less, still more preferably 5.0 times or less, particularly. It is preferably 2.0 times or less. It is desirable to appropriately set the specific draw ratio according to factors such as the optical characteristics, thickness, and mechanical strength of the optical film to be manufactured. When the stretching ratio is equal to or higher than the lower limit of the above range, the birefringence can be significantly changed by stretching. Further, when the draw ratio is not more than the upper limit of the above range, the direction of the slow phase axis can be easily controlled and the film breakage can be effectively suppressed.

The stretching temperature is preferably "Tg _R " or higher, more preferably "Tg _R + 10 ° C" or higher, preferably "Tg _R + 100 ° C" or lower, and more preferably "Tg _R + 90 ° C" or lower. Here, "Tg _R " represents 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. Further, when the stretching temperature is not more than the upper limit of the above range, the curing of the resin film due to the progress of crystallization of the crystalline polymer can be suppressed, so that the stretching can be smoothly performed, and the stretching causes a large birefringence. Can be expressed. In addition, the haze of the resulting optical film can usually be reduced to increase transparency.

By performing the above stretching treatment, an optical film can be obtained as a stretched resin film. 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, the optical properties such as retardation are exhibited by the orientation of the polymer due to the contact with the solvent in the step (iii) and the orientation of the polymer due to the stretching in the step (iii), so that the optical film is desired. It can have optical properties.

[12. Arbitrary process]
The method for producing an optical film may be combined with the above-mentioned steps (i) to (iii) and further include any step. As an arbitrary step, for example, a step of preheating the pre-stretched film before the step (iii), a step of heat-treating the optical film obtained in the step (iii) to promote the crystallization of the crystalline polymer, and the like. Examples thereof include a step of drying the optical film to reduce the amount of the solvent in the film, a step of heat-shrinking the optical film to remove residual stress in the film, and the like.

Further, according to the above-mentioned manufacturing method, a long optical film can be manufactured by using a long raw film. The method for producing an optical film may include a step of winding the long optical film thus produced into a roll shape. Further, the method for producing an optical film may include a step of cutting a long optical film into a desired shape.

[13. Polarizer]
The polarizing plate according to the embodiment of the present invention includes the above-mentioned optical film and a polarizing film. The polarizing film can usually function as a linear splitter. Therefore, the polarizing plate can transmit a part of the polarized light and block the other polarized light.

The polarizing film usually has an absorption axis and a transmission axis perpendicular to the absorption axis. Then, it is possible to absorb the linear polarization having a vibration direction parallel to the absorption axis and transmit the linear polarization having a vibration direction parallel to the transmission axis. The vibration direction of linearly polarized light means the vibration direction of the electric field of linearly polarized light. At this time, it is preferable that the absorption axis of the polarizing film and the slow axis of the optical film form a specific angle.

In one example, the angle formed by 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, and preferably 100 ° or less. It is more preferably 95 ° or less, and particularly preferably 92 ° or less. In this case, the optical film preferably has an in-plane retardation that can function as a 1/2 wave plate. The polarizing plate according to this example can be used as a polarizing plate capable of compensating the viewing angle when provided in an image display device.

In another example, the angle formed by 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, and preferably 50 °. Below, it is more preferably 48 ° or less, and particularly preferably 46 ° or less. In this case, the optical film preferably has an in-plane retardation that can function as a 1/4 wave plate. The polarizing plate according to this example can be used as a circular polarizing plate capable of transmitting circular polarization in one rotation direction and blocking circular polarization in the other rotation direction. By providing this circularly polarizing plate on the display surface of the display device, it is possible to suppress the reflection of external light. It was

Any polarizing film can be used as the polarizing film. An example of a polarizing film is a film obtained by adsorbing iodine or a dichroic dye on a polyvinyl alcohol film and then uniaxially stretching it in a boric acid bath; adsorbing iodine or a dichroic dye on the polyvinyl alcohol film. Examples thereof include a film obtained by stretching and further modifying a part of polyvinyl alcohol units in the molecular chain to polyvinylene units. Of these, the polarizing film preferably contains polyvinyl alcohol. It was

When natural light is incident on the polarizing film, only one of the polarizations is transmitted. The degree of polarization of this polarizing film is not particularly limited, but is preferably 98% or more, more preferably 99% or more. The thickness of the polarizing film is preferably 5 μm to 80 μm. It was

The above-mentioned polarizing plate may further include an arbitrary layer. The optional layer may be, for example, a polarizing element protective film layer; an adhesive layer for bonding a polarizing film and an optical film; a hard coat layer such as an impact-resistant polymethacrylate resin layer; a matte layer for improving the slipperiness of the film; Examples thereof include a reflection suppressing layer; an antifouling layer; an antistatic layer; and the like. Any of these layers may be provided with only one layer, or may be provided with two or more layers.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples shown below, and may be arbitrarily modified and carried out without departing from the scope of claims of the present invention and the equivalent scope thereof.
In the following description, "%" and "part" representing quantities are based on weight unless otherwise specified. Further, the operations described below were performed under normal temperature and pressure (23 ° C., 1 atm) in the atmosphere unless otherwise specified.

[Measurement method of glass transition temperature Tg and melting point Tm]
The glass transition temperature Tg and the melting point Tm of the polymer were measured as follows. First, the polymer was melted by heating, and the melted polymer was rapidly cooled with dry ice. Subsequently, using this polymer as a test piece, the glass transition temperature Tg and melting point Tm of the polymer were measured at a heating rate of 10 ° C./min (heating mode) using a differential scanning calorimeter (DSC). It was measured.

[Measurement method of optical film retardation, NZ coefficient and slow phase axial direction]
The in-plane retardation Re of the optical film, the retardation Rth in the thickness direction, the NZ coefficient, and the slow phase axial direction were measured by a phase difference meter (“AXoScan OPMF-1” manufactured by AXOMETRICS).

[Manufacturing example 1. Manufacture of crystalline polystyrene]
17.8 g (71 mmol) of copper sulfate pentahydrate (CuSO 4.5H ₂ O), ₂₀₀ ml of toluene, and 24 ml (250 mmol) of trimethylaluminum were placed in a glass container having an internal volume of 500 ml and substituted with argon, and the temperature was 40 ° C. Was reacted for 8 hours. Then, the solid part was removed to obtain a solution. Toluene was further distilled off from the obtained solution under reduced pressure at room temperature to obtain 6.7 g of a contact product. The molecular weight of this contact product was measured by the freezing point lowering method and found to be 610.

Next, to the reaction vessel, 5 millimoles of the contact product as an aluminum atom, 5 mmol of triisobutylaluminum, 0.025 mmol of pentamethylcyclopentadienyl titaniumtrimethoxyde, and 1 mmol of purified styrene were added, and 90 was added. The polymerization reaction was carried out at ° C. for 5 hours. Then, the product was repeatedly washed with methanol after decomposing the catalyst component with a solution of sodium hydroxide in methanol, and dried to obtain 308 g of a polymer (crystalline polystyrene).

The weight average molecular weight of this polymer was measured by gel permeation chromatography at 135 ° C. using 1,2,4-trichlorobenzene as a solvent. As a result, the weight average molecular weight Mw of this polymer was 350,000. Further, it was confirmed by measuring the melting point Tm and ¹³ C-NMR that the obtained polymer was crystalline polystyrene having a syndiotactic structure. The melting point Tm of crystalline polystyrene was 270 ° C., and the glass transition temperature was 100 ° C.
By repeating this operation, crystalline polystyrene having the syndiotactic structure required for evaluation was prepared.

[Manufacturing example 2. Production of crystalline polymer with positive intrinsic birefringence]
The pressure resistant reactor made of metal was sufficiently dried and then replaced with nitrogen. In this metal pressure resistant reactor, 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo content of 99% or more) (30 parts as the amount of dicyclopentadiene), and 1- 1.9 parts of hexene was added and heated to 53 ° C.

0.014 parts of the tetrachlorotungsten phenylimide (tetrahydrofuran) complex was dissolved in 0.70 parts of toluene to prepare a solution. To this solution, 0.061 part of a diethylaluminum ethoxide / n-hexane solution having a concentration of 19% was added and stirred for 10 minutes to prepare a catalytic solution. This catalyst solution was added to a pressure resistant reactor to initiate a ring-opening polymerization reaction. Then, the reaction was carried out for 4 hours while maintaining 53 ° C. to obtain a solution of a ring-opening polymer of dicyclopentadiene. The number average molecular weight (Mn) and weight average molecular weight (Mw) of the obtained ring-opening polymer of dicyclopentadiene are 8,750 and 28,100, respectively, and the molecular weight distribution (Mw / Mn) obtained from these. Was 3.21.

To 200 parts of the obtained solution of the ring-opening polymer of dicyclopentadiene, 0.037 parts of 1,2-ethanediol was added as a terminator, heated to 60 ° C., and stirred for 1 hour to stop the polymerization reaction. I let you. A part of a hydrotalcite-like compound (“Kyoward (registered trademark) 2000” manufactured by Kyowa Chemical Industry Co., Ltd.) was added thereto, and the mixture was heated to 60 ° C. and stirred for 1 hour. After that, 0.4 part of a filtration aid ("Radiolite (registered trademark) # 1500" manufactured by Showa Kagaku Kogyo Co., Ltd.) was added, and a PP pleated cartridge filter ("TCP-HX" manufactured by ADVANTEC Toyo Co., Ltd.) was used as an adsorbent. The solution was filtered off.

To 200 parts of a solution of a ring-opening polymer of dicyclopentadiene after filtration (polymer amount: 30 parts), 100 parts of cyclohexane is added, 0.0043 parts of chlorohydride carbonyltris (triphenylphosphine) ruthenium is added, and hydrogen is added. The hydrogenation reaction was carried out at a pressure of 6 MPa and 180 ° C. for 4 hours. As a result, a reaction solution containing a hydride of a ring-opening polymer of dicyclopentadiene was obtained. In this reaction solution, hydride was precipitated to form a slurry solution.

The hydride and the solution contained in the reaction solution were separated using a centrifuge and dried under reduced pressure at 60 ° C. for 24 hours to open dicyclopentadiene as a crystalline polymer having positive intrinsic birefringence. 28.5 parts of the hydride of the ring polymer was obtained. The hydrogenation rate of this hydride was 99% or more, the glass transition temperature Tg was 93 ° C., the melting point Tm was 262 ° C., and the ratio of racemo diad was 89%.

[Example 1]
(1-1. Preparation of crystalline resin)
60 parts of crystalline polystyrene having a syndiotactic structure obtained in Production Example 1, polyphenylene ether (“Noryl PPO640” manufactured by SABIC Innovative Plastics Japan Co., Ltd., weight average molecular weight Mw = 43,000, glass transition temperature Tg = 130 40 parts (° C.) was kneaded at 295 ° C. with a twin-screw extruder to produce transparent crystalline resin pellets.

(1-2. Extrusion film formation)
Crystalline resin pellets are melt-extruded using a thermal melt extrusion film forming machine equipped with a T-die (“Measuring Extruder Type Me-20 / 2800V3” manufactured by Optical Control Systems) and rolled at a speed of 1.5 m / min. A long raw film was obtained as a resin film having a width of about 120 mm before contacting with a solvent. The operating conditions of the film forming machine are itemized below.
・ Barrel temperature setting = 280 ° C to 300 ° C
・ Die temperature = 300 ℃
・ Screw rotation speed = 30 rpm
・ Cast roll temperature = 80 ℃

The thickness of the original film was 158 μm. When the retardation of the raw film was measured at a measurement wavelength of 550 nm, the in-plane retardation Re = 3 nm and the thickness direction retardation Rth = -18 nm.

(1-3. Solvent contact)
The raw film was cut into a rectangle of 120 mm × 120 mm. This rectangular raw film is immersed in cyclohexane as a solvent stored in a bat until the in-plane retardation Re = 2 nm and the thickness direction retardation Rth = 41 nm, and used as a resin film after contact with the solvent. A pre-stretched film was obtained. The pre-stretched film was taken out from cyclohexane, the cyclohexane adhering to the film surface was wiped off, and then the film was naturally dried in the air. The thickness of the obtained pre-stretched film was 160 μm.

(1-4. Stretching)
A batch type biaxial stretching device (manufactured by Eto'o) was prepared. The stretching device was equipped with an oven unit and a stretching clip capable of fixing the film. Using this stretching device, it is possible to stretch the film by pulling the film with a clip in the oven.

The unstretched film was cut into a rectangle of 100 mm x 100 mm. Both ends of this rectangular pre-stretched film were gripped by the five clips of the stretching device, respectively. The pre-stretched film was pulled with a clip and freely uniaxially stretched in the longitudinal direction of the long raw film obtained in the extrusion film formation step. The stretching temperature was 138 ° C. and the stretching ratio was 1.2 times. By this stretching, an optical film as a uniaxially stretched film was obtained.

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

[Example 2]
The line speed in step (1-2) was changed to change the thickness of the long raw film to 107 μm.
Further, in step (1-3), the immersion time of the raw film in the solvent was adjusted so that a pre-stretched film having an in-plane retardation Re = 2 nm and a thickness direction retardation Rth = 28 nm could be obtained. I went there.
Further, the draw ratio in the step (1-4) was changed to 1.3 times.
The optical film was manufactured by the same method as in Example 1 except for the above items.

[Example 3]
The line speed in step (1-2) was changed to change the thickness of the long raw film to 276 μm.
Further, in step (1-3), the immersion time of the raw film in the solvent was adjusted so that a pre-stretched film having an in-plane retardation Re = 4 nm and a thickness direction retardation Rth = 71 nm could be obtained. I went there.
Further, the draw ratio in the step (1-4) was changed to 1.1 times.
The optical film was manufactured by the same method as in Example 1 except for the above items.

[Example 4]
In step (1-1), the amount of crystalline polystyrene having a syndiotactic structure was changed to 50 parts, and the amount of polyphenylene ether was changed to 50 parts.
Further, the line speed in the step (1-2) was changed to change the thickness of the long raw film to 201 μm.
Further, in step (1-3), the immersion time of the raw film in the solvent was adjusted so that a pre-stretched film having an in-plane retardation Re = 42 nm and a thickness direction retardation Rth = 540 nm could be obtained. I went there.
Further, the stretching temperature in the step (1-4) was changed to 160 ° C., and the stretching ratio was changed to 1.6 times.
The optical film was manufactured by the same method as in Example 1 except for the above items.

[Comparative Example 1]
The line speed in step (1-2) was changed to change the thickness of the long raw film to 115 μm.
In addition, the raw film was not immersed in the solvent in step (1-3).
Further, in step (1-4), the raw film was stretched instead of the pre-stretched film, the stretching temperature was changed to 132 ° C., and the stretching ratio was changed to 2.2 times.
The optical film was manufactured by the same method as in Example 1 except for the above items.

[Comparative Example 2]
An antioxidant (tetrakis [methylene-3- (3', 5'-di-t-butyl-4'-hydroxyphenyl)] was added to 100 parts of the hydride of the ring-opening polymer of dicyclopentadiene obtained in Production Example 2. ) Propionate] Methane; BASF Japan's "Irganox (registered trademark) 1010") After mixing 1.1 parts, a twin-screw extruder equipped with four die holes with an inner diameter of 3 mmΦ (Toshiba Machine Co., Ltd. "TEM-37B" ”). A mixture of a hydride of a ring-opening polymer of dicyclopentadiene and an antioxidant was formed into a strand by hot melt extrusion molding, and then shredded with a strand cutter to obtain pellets of a crystalline resin.

This pellet was used in step (1-2). Further, the line speed in the step (1-2) was changed to change the thickness of the long raw film to 13 μm.
Further, in step (1-3), the type of solvent was changed to toluene. Further, the raw film was immersed in the solvent by adjusting the immersion time so that a pre-stretched film having an in-plane retardation Re = 8 nm and a thickness direction retardation Rth = −73 nm could be obtained.
Further, the stretching temperature in the step (1-4) was changed to 130 ° C., and the stretching ratio was changed to 1.5 times.
The optical film was manufactured by the same method as in Example 1 except for the above items.

[Evaluation of Optical Films Obtained in Examples 1 to 3 and Comparative Examples 1 and 2]
A polarizing film (“HLC2-5618S” manufactured by Sanritz Co., Ltd., a polarizing element having a thickness of 180 μm and a polarization transmission axis in the width direction) was prepared. With respect to one surface of the polarizing film and the optical films obtained in Examples 1 to 3 and Comparative Examples 1 and 2, the polarization transmission axis of the polarizing film and the slow axis of the optical film form an angle of 45 °. A circular polarizing plate was obtained by laminating with a pressure-sensitive adhesive layer (“CS9621” manufactured by Nitto Denko).

A mirror was prepared and the prepared circular polarizing plate was placed on the mirror so that the optical film was on the mirror side. The circularly polarizing plate was illuminated with a fluorescent lamp, and the reflected light from the mirror was observed in the front direction and in the tilt direction with a polar angle of about 60 °. The front direction is the front direction of the mirror and represents a direction parallel to the thickness direction of the circularly polarizing plate. In each observation direction, "○" if the coloring is not visible, "△" if the coloring is visible but very slight, and "×" if the coloring is visible at an unacceptable level. And said.

[Evaluation of Optical Film Obtained in Example 4]
Two polarizing films (“HLC2-5618S” manufactured by Sanritz, 180 μm in thickness, and a polarizing element having a polarizing transmission axis in the width direction) were prepared and placed on a cross Nicol. Cross Nicol means that the polarization transmission axis is vertical when viewed from the thickness direction. Between these polarizing films, the optical film obtained in Example 4 is placed on the polarizing transmission axis of the polarizing film on the viewing side (that is, the polarizing film on the viewing side when installed in a backlight described later) and the slow axis of the optical film. It was installed so that it matches. A polarizing film and an optical film were bonded to each other via an adhesive layer (“CS9621” manufactured by Nitto Denko) to obtain a laminated body.

A backlight was prepared in a dark room, and the prepared laminate was placed on the backlight. With the backlight turned on, the light transmitted through the laminate was observed in the front direction and in the tilting direction with a polar angle of about 60 °. At each observation position, "○" is visible if the tint is not visible, "△" if the tint is visible but very slight, and the tint and light leakage are visible at an unacceptable level. If it is, it is set as "x".

[result]
The results of the above-mentioned Examples and Comparative Examples are shown in the table below. In the table below, the meanings of the abbreviations are as follows.
SPS: Crystalline polystyrene.
PPE: Polyphenylene ether.
Cy: Cyclohexane.
Tl: Toluene.

[examination]
In the examples, crystalline polystyrene is used as the crystalline polymer having negative intrinsic birefringence to produce an optical film. When the pre-stretched film was freely uniaxially stretched to produce the optical film, the delayed phase axis was developed in the direction perpendicular to the stretching direction in all the examples, so that the obtained optical film was negatively birefringent. It can be confirmed that it has a refraction characteristic. Further, all of the optical films obtained in the examples have an in-plane retardation satisfying the formula (1) and an NZ coefficient satisfying the formula (2).

Since the optical film obtained in the examples has a reverse wavelength dispersibility, its optical function can be exhibited in a wide wavelength range.
Therefore, the optical films of Examples 1 to 3 can function as a quarter wave plate in a wide wavelength range. Therefore, the circularly polarizing plate provided with the optical film can suppress the reflection of light in a wide wavelength range as a reflection suppressing film. Therefore, it is possible to suppress the coloring caused by the light of a part of the wavelength passing through the circularly polarizing plate.
Further, 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 in a wide wavelength range transmitted through the optical film by 90 °. Therefore, it is possible to suppress coloring and light leakage due to the passage of light having a part of wavelengths through the laminate.

Further, since the optical film obtained in the examples has an appropriate NZ coefficient, not only the light transmitted through the optical film in the thickness direction but also the polarization of the light transmitted in the inclined direction which is neither parallel nor perpendicular to the thickness direction. The state can also be changed appropriately.
Therefore, since the optical films of Examples 1 to 3 can suppress the reflection of the light transmitted through the circularly polarizing plate in the tilting direction, the tinting can be suppressed not only in the front direction but also in the tilting direction.
Further, since the optical film of Example 4 can suppress the passage of light of the laminated body in the inclined direction, it is possible to suppress coloring and light leakage not only in the front direction but also in the inclined direction.

Claims

An optical film containing a crystalline polymer,
The optical film has a negative birefringence characteristic and
The in-plane retardations Re (450), Re (550) and Re (650) of the optical film at the measurement wavelengths of 450 nm, 550 nm and 650 nm satisfy the formula (1).
An optical film in which 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 according to claim 1, wherein the optical film has a single-layer structure.
The optical film according to claim 1 or 2, wherein the optical film is a stretched film.
The optical film according to any one of claims 1 to 3, wherein the optical film is a uniaxially stretched film.
The optical film according to any one of claims 1 to 4, wherein the optical film has a long shape.
The optical film according to any one of claims 1 to 5, comprising a resin containing the crystalline polymer having a negative intrinsic birefringence and a thermoplastic polymer having a positive intrinsic birefringence.
Claimed that the weight ratio (thermoplastic polymer / crystalline polymer) of the thermoplastic polymer having a positive intrinsic compound refraction to the crystalline polymer having a negative intrinsic compound refraction is 3/7 or more. Item 6. The optical film according to Item 6.
The crystalline polymer having a negative intrinsic birefringence is a polystyrene-based polymer.
The optical film according to claim 6 or 7, wherein the thermoplastic polymer having positive intrinsic birefringence is a polyphenylene ether.
A polarizing plate comprising the optical film according to any one of claims 1 to 8 and a polarizing film.
The polarizing plate according to claim 9, wherein the slow axis of the optical film and the absorption axis of the polarizing film form an angle of 80 ° to 100 °.
The method for manufacturing an optical film according to any one of claims 1 to 8.
A step of preparing a resin film made of a resin containing a crystalline polymer having a negative intrinsic birefringence and a thermoplastic polymer having a positive intrinsic birefringence.
The step of bringing the resin film into contact with a solvent to change the birefringence in the thickness direction,
A method for producing an optical film, comprising the steps of stretching the resin film in this order.