TW202232136A - Optical film, production method therefor, and polarizing plate - Google Patents

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, method for producing the same, and polarizing plate

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

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

"Patent Documents" "Patent Document 1": Japanese Patent No. 4592004 "Patent Document 2": International Patent Publication No. 2017/145935 "Patent Document 3": International Patent Publication No. 2020/137409

Optical films having anisotropy in refractive index are sometimes produced using resins. Such an optical film having anisotropy in refractive index must have birefringence. The optical film having birefringence may be provided in a display device as a film such as a reflection suppression film, a viewing angle compensation film, or the like.

When an optical film is provided in a 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 represented 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 can be obtained, it becomes possible to improve the display quality when the display surface is viewed from an oblique direction by the optical film.

In addition, the optical film is required to have reverse wavelength dispersion. Optical films with inverse wavelength dispersibility generally exhibit their optical functions in a broad wavelength range. For example, a wavelength plate that is an optical film having reverse wavelength dispersion can be used as a broadband wavelength plate that can function in a wide wavelength range.

Conventionally, the manufacturing method of the optical film whose NZ coefficient is more than 0.0 and less than 1.0 is known. In addition, optical films having reverse wavelength dispersion properties have been conventionally known. However, in the past, it has not been possible to realize an optical film having an NZ coefficient greater than 0.0 and less than 1.0 and having an inverse wavelength dispersion by a film having negative birefringence characteristics.

The present invention is initiated in view of the aforementioned problems, and aims to provide an optical film having negative birefringence characteristics, inverse wavelength dispersion, and a NZ coefficient greater than 0.0 and less than 1.0, a method for producing the same, and an optical film having the aforementioned optical film. polarizer.

The present inventors have made intensive studies to solve the aforementioned problems. As a result, the present inventors have found that the aforementioned problems can be solved by using a method including a step of bringing a resin film containing a crystalline polymer into contact with a solvent and changing the birefringence in the thickness direction and a step of stretching the resin film in order. Thus, the present invention has been completed.

That is, the present invention includes the following.

[1] An optical film comprising a crystalline polymer, The aforementioned optical films have negative birefringence properties, The in-plane retardation Re(450), Re(550) and Re(650) of the aforementioned optical film at the measurement wavelengths of 450 nm, 550 nm and 650 nm satisfy the formula (1), The NZ coefficient Nz of the aforementioned 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 an elongated shape.

[6] The optical film according to any one of [1] to [5], comprising a resin comprising the aforementioned crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence made.

[7] The optical film according to [6], 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.

[8] The optical film according to [6] or [7], wherein The aforementioned crystalline polymer having negative intrinsic birefringence is a polystyrene polymer, The aforementioned thermoplastic polymer having positive intrinsic birefringence is polyphenylene ether.

[9] A polarizing plate comprising the optical film and polarizing film according to any one of [1] to [8].

[10] The polarizing plate according to [9], wherein the slow axis of the optical film and the absorption axis of the polarizing film comprise an angle of 80° to 100°.

[11] A method for producing an optical film, which is the method for producing an optical film as described in any one of [1] to [8], which sequentially comprises: A step of preparing a resin film made of a resin containing a crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence, a step of bringing the aforementioned resin film into contact with a solvent and changing the birefringence in the thickness direction, and The step of extending the aforementioned resin film.

According to the present invention, there can be provided an optical film having negative birefringence properties, inverse wavelength dispersion, and an NZ coefficient greater than 0.0 and less than 1.0, a method for producing the same, and a polarizing plate including the optical film.

Embodiments and examples are disclosed below to describe the present invention in detail. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with arbitrary changes without departing from the scope of the patent application of the present invention and the scope of its equivalents.

In the following description, the in-plane retardation Re of the film is a value represented by Re=(nx−ny)×d unless otherwise noted. In addition, the birefringence in the in-plane direction of the film, unless otherwise noted, is the value shown by (nx-ny), and accordingly is shown by Re/d. In addition, the retardation Rth of the thickness direction of a film is the value shown by Rth={[(nx+ny)/2]-nz}*d unless otherwise noted. In addition, unless otherwise noted, the birefringence in the thickness direction of the film is represented by {[(nx+ny)/2]-nz}, and is represented by Rth/d accordingly. In addition, the NZ coefficient of a thin film is the value shown by (nx-nz)/(nx-ny) unless otherwise noted. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the thin film (in-plane direction) and in the direction in which the maximum refractive index is given. ny represents the refractive index in the direction perpendicular to the direction of nx, which is the in-plane direction of the thin film. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. Measurement wavelength, unless otherwise noted, is 550 nm.

In the following description, unless otherwise noted, a material having positive intrinsic birefringence means a material whose refractive index in the extending direction becomes larger than the refractive index in the direction perpendicular thereto. Accordingly, a polymer having positive intrinsic birefringence means a polymer whose refractive index in the extending direction becomes larger than the refractive index in the direction perpendicular thereto, unless otherwise noted. In addition, unless otherwise noted, a material having negative intrinsic birefringence means a material whose refractive index in the extending direction becomes smaller than the refractive index in the direction perpendicular thereto. Accordingly, a polymer having negative intrinsic birefringence, unless otherwise noted, means a polymer whose refractive index in the extending direction becomes smaller than the refractive index in the direction perpendicular thereto.

In the following description, the so-called "strip-shaped" shape refers to a shape having a length of 5 times or more relative to the width, preferably 10 times or more in length, and specifically refers to a shape that can be retracted The shape of a length of film to the extent that it is stored or transported in a roll. The upper limit of the length is not particularly limited, but is usually 100,000 times or less the width.

In the following description, the directions of the so-called requirements are "parallel", "perpendicular" and "orthogonal", and unless otherwise noted, within the range that does not impair the effects of the present invention, for example, the directions of ±5° may be included. error within the range.

The angle contained by the optical axis (absorption axis, transmission axis, slow axis, etc.) of each film in a member having a plurality of films indicates the angle when the aforementioned film is viewed from the thickness direction unless otherwise noted.

The so-called "polarizing plate", "circular polarizing plate", "wavelength plate" and "negative C plate", unless otherwise noted, include not only rigid parts but also flexible parts such as resin films.

[1. Outline of Optical Films]

The optical film according to one embodiment of the present invention includes a crystalline polymer. This optical film satisfies a combination of the following requirements (A) to (C). Requirement (A): The optical film has negative birefringence characteristics. Requirement (B): The in-plane retardation 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 formula (2). Re(450)＜Re(550)＜Re(650) (1) 0＜Nz＜1 (2)

The aforementioned optical film has been difficult to manufacture in the past, but can be easily manufactured by using a specific manufacturing method to be described later.

[2. Birefringence properties of optical films]

The optical film related to this embodiment has negative birefringence characteristics.

The so-called film "has negative birefringence characteristics" means that when the film is extended in an extension direction, the increase in the refractive index in the direction perpendicular to the extension direction is greater than the increase in the refractive index in the extension direction. still big. In addition, when the film "has a positive birefringence characteristic", it means that when the film is extended in an extending direction, the increase in the refractive index in the extending direction is greater than the increase in the refractive index in the direction perpendicular to the extending direction. The amount is still large. In terms of the amount of increase, when the refractive index is increased by stretching, the increase in the refractive index is positive, and when the refractive index is decreased by stretching, the increase in the refractive index is negative. value. Here, the extending direction is generally vertical with respect to the thickness direction, and accordingly, it is referred to as the in-plane direction.

The birefringence properties of an optical film can be adjusted by extending the optical film. Also, the birefringence properties of an optical film generally depend on the composition of the optical film. Accordingly, in the case of producing an optical film by extending a resin film having the same composition as that of the optical film by the production method described later, the birefringence characteristic of the optical film can also be generally adjusted by extending the resin film. Specifically, when the resin film is extended in an extending direction, in the case where the increase in the refractive index in the direction perpendicular to the extending direction is larger than the increase in the refractive index in the extending direction, the self- The birefringence characteristic of the optical film obtained from this resin film was negative.

In general, when a film having negative birefringence properties extends in a direction perpendicular to the thickness direction, the birefringence in the thickness direction increases. According to this, the NZ coefficient usually becomes 0 or less by stretching, and it is difficult to manufacture a thin film having a NZ coefficient greater than 0 by stretching. Accordingly, it is quite surprising to those skilled in the art that the optical film of the present embodiment having negative birefringence characteristics and having the NZ coefficient satisfying the formula (2) can be obtained. Therefore, the optical film of the present embodiment having a combination of negative birefringence characteristics, in-plane retardation satisfying the formula (1), and NZ coefficient satisfying the formula (2) is an optical film not seen in the past, and has high industrial value.

[3. Wavelength Dispersion of Optical Films]

The in-plane retardation Re(450) at the measurement wavelength of 450 nm, the in-plane retardation Re(550) at the measurement wavelength of 550 nm, and the in-plane retardation Re at the measurement wavelength of 650 nm of the optical film related to this embodiment (650) satisfies Equation (1). Re(450)＜Re(550)＜Re(650) (1)

Optical films having in-plane retardation satisfying the formula (1) generally have inverse wavelength dispersion. Accordingly, the in-plane retardation of the optical film can be larger as the measurement wavelength is longer. Therefore, the optical film can exert its optical function in a wide wavelength range. For example, when the optical film can function as a quarter-wave plate at one wavelength, the optical film can also function as a quarter-wave plate in a wide wavelength range other than the aforementioned one wavelength. Furthermore, for example, when the optical film can function as a 1/2 wavelength plate at one wavelength, the optical film can also function as a 1/2 wavelength plate in a wide wavelength range other than the aforementioned one wavelength.

[4. NZ coefficient of optical films]

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 formula (2) may satisfy nx>nz>ny. 0＜Nz＜1 (2)

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

The optical film having the NZ coefficient satisfying the formula (2) can not only change the polarization state of the light passing through the optical film along the thickness direction, but also moderately change the polarization state of the light passing through the oblique direction that is neither parallel nor perpendicular to the thickness direction. . Accordingly, the optical film exhibits its optical function not only for the light in the thickness direction but also for the light in the oblique direction. For example, in the case where the optical film can impart a phase difference of 1/4 wavelength to the light passing in the thickness direction, the optical film can also impart a retardation of 1/4 wavelength to the light passing in the oblique direction. Further, for example, when the optical film is required to impart a retardation of 1/2 wavelength to light passing in the thickness direction, the optical film must also impart a retardation of 1/2 wavelength to light passing in an oblique direction.

[5. Composition of optical films]

The optical film according to one embodiment of the present invention includes a crystalline polymer. The crystalline polymer refers to a polymer having crystallinity. A polymer having crystallinity means a polymer having a melting point Tm. That is, a polymer having crystallinity means a polymer whose melting point Tm can be observed by a differential scanning calorimeter (DSC). In the following description, a resin containing a crystalline polymer may be referred to as a "crystalline resin". The crystalline resin is preferably a thermoplastic resin. It is preferable that an optical film contains a crystalline resin, and it is preferable that it consists only of a crystalline resin.

The crystalline polymer preferably has a negative intrinsic birefringence. A crystalline polymer having negative intrinsic birefringence can exhibit a large refractive index in a direction perpendicular to its extending direction when extended. Accordingly, in the case of using a crystalline polymer having negative intrinsic birefringence, an optical film having negative birefringence characteristics can be easily obtained. Furthermore, when a crystalline polymer having such a negative intrinsic birefringence is used, the in-plane retardation satisfying the formula (1) and the NZ coefficient satisfying the formula (2) can be easily achieved.

As a crystalline polymer which has a negative intrinsic birefringence, the polymer containing an aromatic ring is preferable, for example, a polystyrene-type polymer is mentioned. In the following description, a polystyrene-based polymer having crystallinity may be referred to as a "crystalline polystyrene-based polymer".

The crystalline polystyrene-based polymer is obtained as a polymer of a styrene-based monomer. Accordingly, the crystalline polystyrene-based polymer is a polymer including a structural unit having a structure formed by polymerizing a styrene-based monomer (hereinafter referred to as a "styrene-based unit" as appropriate).

The styrene-based monomer may be an aromatic vinyl compound such as styrene or a styrene derivative. As a styrene derivative, the compound which substituted the benzene ring of styrene or the alpha-position or β-position, for example, is mentioned.

Examples of the styrene-based monomers include styrene, alkylstyrenes, halogenated styrenes, halogenated alkylstyrenes, alkoxystyrenes, vinylbenzyl esters, and hydrogenated polymers thereof.

Examples of alkylstyrenes include methylstyrene, ethylstyrene, isopropylstyrene, tertiary butylstyrene, 2,4-dimethylstyrene, phenylstyrene, ethylene Naphthalene and vinyl styrene. Examples of halogenated styrenes include chlorostyrene, bromostyrene, and fluorostyrene. Examples of halogenated alkylstyrenes include methylchlorostyrene. As an example of alkoxystyrene, methoxystyrene and ethoxystyrene are mentioned. Among the styrene-based monomers, styrene, methylstyrene, ethylstyrene, and 2,4-dimethylstyrene are preferred. In addition, a styrene-based monomer may be used by 1 type, and may be used in combination of 2 or more types.

The crystalline polystyrene polymer preferably has the same row structure or the opposite row structure, and preferably has the opposite row structure. The so-called crystalline polystyrene-based polymer has an opposite row structure, and it means that the stereochemical structure of the crystalline polystyrene-based polymer is a paired row structure. The so-called opposite structure refers to a three-dimensional structure in which the phenyl groups of the side chains are alternately located in opposite directions in the Fisher projection formula with respect to the main chain formed by carbon-carbon bonds. Compared with the polystyrene-based polymer with the hetero-row structure, the polystyrene-based polymer with the opposite-row structure generally has a low specific gravity, and is excellent in hydrolysis resistance, heat resistance and chemical resistance.

Stereoisomerism (tacticity: stereoisomerism) of the crystalline polystyrene polymer can be quantitatively analyzed by nuclear magnetic resonance method ( ¹³ C-NMR method) using isotopic carbon. Stereoisomerism measured by the ¹³ C-NMR method can be represented by the existence ratio of a plurality of consecutive structural units. In general, when the number of continuous structural units is two, it is a dyad, 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 an opposite structure is usually 75% or more in terms of diads (racemic diads), so that the opposite tacticity of 85% or more is Preferably, it is usually 30% or more in terms of pentads (racemic pentads), so that it is better to have an opposite tacticity of 50% or more.

The crystalline polystyrene-based polymer may be a homopolymer or a copolymer. Accordingly, the crystalline polystyrene-based polymer may be a homopolymer of one type of styrene-based monomer, or may be a copolymer of two or more types of styrene-based monomers. When the crystalline polystyrene-based polymer is a copolymer of two or more styrene-based monomers, the ratio of each styrene-based unit to 100% by weight of the entire crystalline polystyrene-based polymer is It is preferably 5% by weight or more, more preferably 10% by weight or more, more preferably 95% by weight or less, more preferably 90% by weight or less.

In addition, the crystalline polystyrene-based polymer may be a copolymer of one or two or more styrene-based monomers and monomers other than the styrene-based monomer. The ratio 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, from the viewpoint of obtaining an optical film having desired optical properties, More preferably, it is 85% by weight or more.

Usually, the ratio of a certain structural unit contained in the crystalline polystyrene-based polymer should be consistent with the ratio of the monomer corresponding to the aforementioned structural unit to all the monomers of the crystalline polystyrene-based polymer. Accordingly, the ratio of the styrene-based unit contained in the crystalline polystyrene-based polymer can be matched with the ratio of the styrene-based monomer to all the monomers of the crystalline polystyrene-based polymer.

Crystalline polystyrene-based polymers can be produced, for example, by polymerizing styrene-based monomers 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 (see Japanese Patent Publication No. S62-187708).

The crystalline polymer may be used alone or in combination of two or more 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, more preferably 150,000 or more, more preferably 500,000 or less, preferably 450,000 or less, and most preferably 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 improved.

The weight-average molecular weight (Mw) of the polymer can be measured in terms of polystyrene by gel permeation chromatography (GPC) using 1,2,4-trichlorobenzene as an eluent.

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 improved. From the viewpoint of smooth stretching during the production process of the optical film, the glass transition temperature of the crystalline polymer is preferably 160°C or lower, 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, preferably 210°C or higher, particularly preferably 220°C or higher, and preferably 300°C or lower, preferably 290°C or lower, and preferably 280°C The following are preferred. When the melting point Tm of the crystalline polymer is within the aforementioned range, when the crystalline resin is formed to obtain a resin film, the unintended progress of crystallization of the crystalline polymer and the occurrence of foreign matter due to thermal decomposition can be suppressed. produce. Accordingly, an optical film having good appearance and optical properties 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 by dry ice. Next, using this polymer as a sample, a differential scanning calorimeter (DSC) was used to measure the glass transition temperature Tg and melting point Tm of the polymer at a heating rate of 10°C/min (heating mode).

From the viewpoint of obtaining an optical film having desired optical properties, 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 45% by weight or more. The content is preferably not less than 80% by weight, preferably not more than 70% by weight, and more preferably not more than 65% by weight.

The crystallinity of the crystalline polymer contained in the optical film is usually high to a certain degree or more. The specific crystallinity range is preferably 10% or 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 also include an amorphous polymer having no crystallinity in combination with the crystalline polymer. As the amorphous polymer, a thermoplastic polymer is generally used. Among them, the amorphous thermoplastic polymer preferably has positive intrinsic birefringence. In the case where the polymer having positive intrinsic birefringence is used in combination with the crystalline polymer having negative intrinsic birefringence already described above, the reverse wavelength dispersion 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 are generally excellent in compatibility with crystalline polystyrene-based polymers.

Polyphenylene ether means a polymer having a phenylene ether skeleton. A substituent may be bonded to the benzene ring of the phenyl ether skeleton, or a substituent may not be bonded. Polyphenylene ether usually has a phenylene ether skeleton in its main chain. As this polyphenylene ether, a polymer containing a phenylene ether unit represented by the following formula (I) is preferable.

"Change 1"

In 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 halohydrocarbon Oxygen (group in which at least 2 carbon atoms separate its halogen atom from its oxygen atom). Among them, as Q ¹ , an alkyl group and a phenyl group are preferable, and an alkyl group having 1 or more and 4 or less carbon atoms is especially preferable.

In formula (I), Q ² each independently represents a hydrogen atom, a halogen atom, a lower alkyl group (eg, an alkyl group having 1 to 7 carbon atoms), a phenyl group, a haloalkyl group, a hydrocarbyloxy group, or a halohydrocarbyloxy group (A group in which at least 2 carbon atoms separate its halogen atom from its oxygen atom). Among them, as Q ² , a hydrogen atom is preferable.

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

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

In the case where the polymer containing the structural unit represented by the formula (I) is a copolymer, a preferred example of the copolymer is a copolymer having a combination of 2,6-dimethyl-1,4- Random copolymer of phenylene ether unit and 2,3,6-trimethyl-1,4-phenylene ether unit (structural unit represented by "-(C ₆ H(CH ₃ ) ₃ -O-)-") .

The polyphenylene ether may contain structural units other than the phenylene ether unit. In this case, the polyphenylene ether is a copolymer having a phenylene ether unit and other structural units. However, the ratio of the structural units other than the phenylene ether unit in the polyphenylene ether is preferably as small as possible in the range in which the desired optical properties can be obtained. Specifically, the content of phenylene ether units in 100% by weight of polyphenylene ether is preferably 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and more preferably 90% by weight or more More preferably, it is more preferably 95% by weight or more.

For example, polyphenylene ether having other substituents grafted to the polymer chain can also be mentioned. Such a polyphenylene ether can be synthesized by, for example, grafting other substituents onto the polyphenylene ether by a suitable method. Specific examples include polyphenylene ether grafted with polymers such as polystyrene, polybutadiene, and other vinyl-containing polymers.

The production method of polyphenylene ether is not limited, and it can be produced by, for example, the method described in Japanese Patent Laid-Open No. H11-302529.

The amorphous polymer may be used alone or in combination of two or more in any ratio.

The weight average molecular weight Mw of amorphous polymers such as polyphenylene ether is preferably 15,000 or more, preferably 25,000 or more, particularly preferably 35,000 or more, and preferably 100,000 or less, preferably 85,000 or less, Preferably below 70,000. When the weight average molecular weight Mw of the amorphous polymer is not less than the lower limit of the aforementioned range, the mechanical strength of the optical film can be improved. And when the weight average molecular weight Mw of an amorphous polymer is below the upper limit of the said range, it becomes possible to mix a crystalline polymer and an amorphous polymer highly uniformly.

The glass transition temperature of amorphous polymers such as polyphenylene ether is preferably 100°C or higher, preferably 110°C or higher, particularly preferably 120°C or higher, and preferably 350°C or lower, preferably 300°C or lower More preferably, it is 250 degrees C or less especially. When the glass transition temperature of the amorphous polymer is equal to or higher than the lower limit of the aforementioned 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 less than the upper limit value of the aforementioned range, the extension in the production 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, from the viewpoint of obtaining an optical film having desired optical properties, It is more preferably 35% by weight or more, more preferably 70% by weight or less, more preferably 60% by weight or less, and still more preferably 55% by weight or less.

In the case of a combination of crystalline resins comprising a thermoplastic polymer having positive intrinsic birefringence and a crystalline polymer having negative intrinsic birefringence, the weight ratio (thermoplastic polymer/crystalline polymer) is in a specific range is good. Specifically, the weight ratio (thermoplastic polymer/crystalline polymer) is preferably at least 3/7, more preferably at least 3.5/6.5, particularly preferably at least 4/6, and preferably at most 8/2 , preferably below 7.5/2.5, especially below 7/3. In the case where the weight ratio (thermoplastic polymer/crystalline polymer) is within the aforementioned range, the reverse wavelength dispersibility of the optical film can be easily obtained.

The crystalline resin may also contain any components in combination with the above-mentioned crystalline polymer and amorphous polymer. Examples of optional components include: lubricants; layered crystalline compounds; fine particles such as inorganic fine particles; stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, and near-infrared absorbers; plasticizers agents; colorants such as dyes and pigments; antistatic agents; etc. Arbitrary components may be used alone or in combination of two or more. The amount of the optional component is appropriately determined within a range that does not significantly impair the effects of the present invention. The amount of the arbitrary components is, for example, a range that can maintain the total light transmittance of the optical film at 85% or more.

[6. Layer structure of optical films]

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 means 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. Accordingly, it is preferable for the optical film to have a layer formed of the aforementioned crystalline resin alone.

[7. Characteristics of optical films]

The optical film preferably has an in-plane retardation in an appropriate range according to the application.

Specifically, the specific in-plane retardation Re of the optical film is at the measurement wavelength of 550 nm, preferably 100 nm or more, preferably 110 nm or more, more preferably 120 nm or more, and preferably 180 nm or less. Preferably, it is preferably below 170 nm, particularly preferably below 160 nm. In this case, the optical film can function as a quarter wave plate.

For example, the specific in-plane retardation Re of the optical film is at the measurement wavelength of 550 nm, preferably above 245 nm, preferably above 265 nm, particularly preferably above 270 nm, and preferably below 320 nm. Preferably, it is preferably below 300 nm, particularly preferably below 295 nm. In this case, the optical film can function as a half wavelength plate.

The retardation of the film is measured using a phase difference meter (for example, "AxoScan OPMF-1" manufactured by AXOMETRIC Corporation).

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

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%, more preferably less than 0.5%, and ideally 0.0%. When the optical film with such a small haze is installed in a display device, the vividness of the image displayed by the display device can be improved. The haze of the film is measured using a haze meter (for example, "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

Optical films may contain solvents. The solvent may be incorporated into the film in the step of contacting the resin film with the solvent in the production method described later. In detail, all or part of the solvent incorporated into the resin film by contacting the film may enter the interior of the polymer. Therefore, even if drying is performed above the boiling point of the solvent, it is difficult to easily and completely remove the solvent. Accordingly, the optical film may contain a solvent.

The optical film is preferably a stretched film. The stretched film refers to a film produced by a stretching process. Among them, the optical film is preferably a uniaxially stretched film. The uniaxially stretched film refers to a film that is actively stretched in only one direction and not actively stretched in directions other than this direction. Since the uniaxially stretched film can be produced by stretching only in one direction, the production process can be simplified, and thus simple production can be realized.

The optical film may be a cut-to-sheet film, or a long-striped film having an elongated shape. When the optical film has an elongated shape, the optical film and the elongated polarizing film can be bonded together to continuously manufacture a polarizing plate.

The thickness of the optical film can be appropriately set according to the application of the optical film. The specific thickness of the optical film is preferably above 5 μm, preferably above 10 μm, particularly preferably above 30 μm, preferably below 400 μm, preferably below 300 μm, preferably below 200 μm for the best.

[8. Outline of the manufacturing method of the optical film]

The optical films described above can be manufactured by the following manufacturing methods, which sequentially include: Step (i) of preparing a resin film made of a crystalline resin comprising a crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence; the step (ii) of bringing the resin film into contact with a solvent and changing the birefringence in the thickness direction; and Step (iii) of extending the resin film.

In the following description, among the resin films, the resin film before contact with the solvent in step (ii) is referred to as "raw material film", and the resin film after contact with the solvent in step (ii) is referred to as "before stretching" film".

The present inventors presume that the mechanism by which the above-mentioned optical film can be obtained by the above-mentioned production method is as follows. However, the technical scope of the present invention is not limited to the following mechanisms.

In this production method, an optical film is produced using a resin film containing a crystalline polymer having negative intrinsic birefringence. When a crystalline polymer with negative intrinsic birefringence is oriented in a certain orientation direction, it exhibits a small refractive index in the orientation direction and a large refractive index in the direction perpendicular to the orientation direction. Accordingly, the resin film and the optical film containing the crystalline polymer can have negative birefringence characteristics as shown in the requirement (A).

Also, the optical film may comprise a thermoplastic polymer having positive intrinsic birefringence combined with a crystalline polymer having negative intrinsic birefringence. If a thermoplastic polymer having positive intrinsic birefringence is oriented in a certain orientation direction, it exhibits a large refractive index in the orientation direction and a small refractive index in a direction perpendicular to the orientation direction. Accordingly, when oriented in a certain orientation direction, the direction in which the refractive index of the crystalline polymer becomes the largest and the direction in which the refractive index of the thermoplastic polymer becomes the largest are perpendicular to each other. If so, the overall birefringence of an optical film comprising these crystalline polymers in combination with thermoplastic polymers should 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 reverse wavelength dispersion as shown in the requirement (B).

Next, when the raw material film containing the crystalline polymer is brought into contact with the solvent in the step (ii), the solvent is impregnated into the raw material film. Through the action of the immersed solvent, the molecules of the crystalline polymer in the film will undergo micro-Brownian motion, and their molecular chains will be oriented. According to the research of the present inventors, it is conceivable that the solvent-induced crystallization phenomenon of the crystalline polymer may occur when the molecular chain is oriented.

In general, the surface area of the film is larger than the front and back of the main surface. According to this, the immersion speed of the solvent in the thickness direction through the front surface or the back surface is as large as that. If so, the orientation of the molecules of the aforementioned crystalline polymer is carried out in such a way that the molecules of the polymer are oriented in the thickness direction. Accordingly, in the step (ii), the molecules of the crystalline polymer can be oriented in the thickness direction.

Further, in the production method according to the present embodiment, the pre-stretching film, which is 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). By stretching, the molecules of the polymer contained in the film before stretching can be oriented in a direction perpendicular to the thickness direction. Accordingly, by combining the orientation in the thickness direction in the step (ii) with 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 three-dimensionally. Accordingly, the optical film obtained by the above-mentioned manufacturing method can have an NZ coefficient in an appropriate range as shown in the requirement (C).

[9. Step (i) of preparing resin film]

The manufacturing method of an optical film includes the process of preparing the raw material film which 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 made of only crystalline resin. The crystalline resin contained in the raw material 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 material film is preferably small. The specific crystallinity is preferably less than 10%, preferably less than 5%, and particularly preferably less than 3%. If the crystallinity of the crystalline polymer contained in the raw material film before contact with the solvent is low, most of the molecules of the crystalline polymer can be oriented in the thickness direction by the contact with the solvent, so that a wide range of Range adjustment NZ factor.

The raw material film is preferably optically isotropic. Accordingly, it is preferable that the birefringence Re/d in the in-plane direction of the raw material film is small, and the absolute value |Rth/d| of the birefringence in the thickness direction is preferably small. Specifically, the birefringence Re/d in the in-plane direction of the raw material film is preferably less than 1.0×10 ⁻³ , preferably less than 0.5×10 ⁻³ , and especially less than 0.3×10 ⁻³ good. Furthermore, the absolute value of the birefringence in the thickness direction of the raw material film |Rth/d| is preferably less than 1.0×10 ⁻³ , preferably less than 0.5×10 ⁻³ , and preferably less than 0.3×10 ⁻³ for the best. Such optical isotropy means that the orientation of the molecules of the crystalline polymer contained in the raw material film is low, and the orientation is substantially non-oriented. In the case of using such an optically isotropic raw material film, it is not necessary to precisely control the optical properties of the raw material film. Accordingly, since it is not necessary to precisely control the orientation of the molecules of the crystalline polymer, the production of the optical film can be simplified. method. In addition, when an optically isotropic raw material film is used, an optical film with a small haze is usually obtained.

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

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

The thickness of the raw material film is preferably set according to the thickness of the optical film to be produced. Usually, the thickness is increased by contacting with a solvent in the step (ii). By extending in the step (iii), the thickness can be reduced. Therefore, the thickness of the raw material film can also be set in consideration of the change in thickness in the aforementioned steps (ii) and (iii).

The raw material film may also be a cut film, but a long film is preferred. By using the elongated raw material film, since the optical film can be continuously produced by the roll-to-roll method, the productivity of the optical film can be effectively improved.

As the production method of the raw material film, in order to obtain the raw material film without solvent, there are injection molding method, extrusion molding method, pressure molding method, inflation molding method, blow molding method, calender molding method, die casting method, etc. Resin molding methods such as molding methods and compression molding methods are preferable. Among these, the extrusion molding method is preferable in terms of easy thickness control.

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

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

The manufacturing method of an optical film includes the process (ii) of making the resin film which is a raw material film contact a solvent after a process (i). By this step (ii), the birefringence in the thickness direction of the raw material film is changed, and a pre-stretching film having a birefringence in the thickness direction different from that of the raw material film can be obtained.

As the solvent, an organic solvent is usually used. The specific type of solvent can be a solvent that can be immersed in the resin film without dissolving the crystalline polymer contained in the resin film, such as hydrocarbon solvents such as cyclohexane, toluene, azylene, decalin, etc.; carbon disulfide. One kind of solvent may be sufficient as it, and two or more types may be sufficient as it.

The contact method of the resin film and the solvent is not limited. As a contact method, the spray method of spraying a solvent to a resin film, the coating method of apply|coating a solvent to a resin film, the dipping method of immersing a resin film in a solvent, etc. are mentioned, for example. Among them, the dipping method is preferable in that continuous contact can be easily performed.

The temperature of the solvent in contact with the resin film is arbitrary within the range in which the solvent can maintain a liquid state, and accordingly, it can be set in the range of the melting point of the solvent or more and the boiling point or less.

The contact time is preferably at least 0.5 seconds, more preferably at least 1.0 seconds, and particularly preferably at least 5.0 seconds. The upper limit is not particularly limited, and may be, for example, 24 hours or less. However, since there is a tendency that the degree of orientation does not change significantly even if the contact time is prolonged, the contact time is preferably as short as possible within the range in which the desired optical properties can be obtained.

By contact with the 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 due to contact with the solvent is preferably 0.1×10 ⁻³ or more, preferably 0.2×10 ⁻³ or more, and particularly preferably 0.3×10 ⁻³ or more , and preferably below 50.0×10 ⁻³ , preferably below 30.0×10 ⁻³ , particularly preferably below 20.0×10 ⁻³ . The amount of change in the birefringence Rth/d in the thickness direction refers to the absolute value of the change in birefringence Rth/d in the thickness direction of the resin film. The specific variation of birefringence Rth/d in the thickness direction is obtained by subtracting the birefringence Rth/d in the thickness direction of the raw material film from the birefringence Rth/d in the thickness direction of the film before stretching and its absolute value. Preferably, the birefringence Rth/d in the thickness direction increases due to the 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 be changed by contact with the solvent. From the viewpoint of simplifying the control of the in-plane retardation Re of the optical film, the change in birefringence Re/d in the in-plane direction of the resin film due to contact with the solvent is preferably small, and preferably not changed. The amount of change in birefringence Re/d in the in-plane direction due to contact with the solvent is preferably 0.0×10 ⁻³ to 0.2×10 ⁻³ , preferably 0.0×10 ⁻³ to 0.1×10 ⁻³ , preferably 0.0×10 ⁻³ to 0.05×10 ⁻³ . The amount of change in birefringence Re/d in the in-plane direction refers to the absolute value of the change in birefringence Re/d in the in-plane direction of the resin film. The specific variation of the birefringence Re/d in the in-plane direction is calculated by subtracting the birefringence Re/d in the in-plane direction of the raw material film from the birefringence Re/d in the in-plane direction of the film before stretching and its absolute value. have to.

It is preferable that the film before stretching as the resin film after contact with the solvent is a negative C plate. Accordingly, the refractive index nz in the thickness direction of the thin film before stretching is preferably smaller than the refractive indices nx and ny in the in-plane direction. In addition, the refractive indices nx and ny in the in-plane direction of the film before stretching are preferably the same or close to each other. Therefore, in the pre-stretching film, the difference between the refractive index nx and the refractive index ny is relatively small, the difference between the refractive index nx and the refractive index nz is relatively large, and the difference between the refractive index ny and the refractive index nz is relatively large.

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 the birefringence Rth/d in the thickness direction of the film before stretching is represented by "Rth/d=[(nx+ny)/2]-nz", the thickness direction can be represented by the birefringence Rth/d in the thickness direction. The difference between the refractive index nz of , and the refractive indices nx and ny in the in-plane direction. The birefringence Rth/d in the thickness direction of the film before stretching is preferably 0.05×10 ⁻³ or more, preferably 0.1×10 ⁻³ or more, more preferably 0.2×10 ⁻³ or more, and 10×10 ⁻³ or less is preferable, 6.0×10 ⁻³ or less is more preferable, and 4.0×10 ⁻³ or less is more preferable.

Furthermore, 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. That is, since the birefringence Re/d in the in-plane direction of the film before stretching is represented by "Re/d=nx-ny", the refractive index in the in-plane direction can be represented by the birefringence Re/d in the in-plane direction. The difference between nx and ny. In general, the difference between the refractive indices nx and ny in the in-plane direction is smaller than the difference between the refractive indices nz in the thickness direction and the refractive indices nx and ny in the in-plane direction. Accordingly, the birefringence Re/d in the in-plane direction of the film before stretching can be set to a value smaller than the birefringence Rth/d in the thickness direction 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 0.01×10 ⁻³ or more, more preferably 0.05×10 ⁻³ or more, particularly preferably 0.1×10 ⁻³ or more, And it is preferably 1.0×10 ⁻³ or less, more preferably 0.5×10 ⁻³ or less, and particularly preferably 0.2×10 ⁻³ or less.

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

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

[11. Step (iii) of extending the resin film]

The manufacturing method of an optical film includes the process (iii) of extending|stretching the resin film which is a pre-stretching film after a process (ii). By extending, the molecules of the polymer contained in the resin film can be oriented in the direction corresponding to the extending direction. According to this, by stretching in the step (iii), 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 can be adjusted in the in-plane direction. and other optical properties to obtain the above-mentioned optical films.

The extending direction is not limited, and examples thereof include the longitudinal direction, the width direction, and the oblique direction. Here, the oblique direction means a direction perpendicular to the thickness direction and neither parallel nor perpendicular to the width direction. In addition, the extending direction may be a single direction, or may be two or more directions, but a single direction is preferable. Furthermore, among the extension in a single direction, it is more preferable to use a free uniaxial extension in a direction other than the extension direction without exerting a restraining force. By extending like this, the optical film as described above can be easily produced.

Since the film before stretching generally has a negative birefringence characteristic, when stretching in a single direction, an optical film having a slow axis in a direction perpendicular to the stretching direction can be obtained. Accordingly, since the slow axis direction of the optical film can be adjusted by the extending direction, the extending direction can also be selected according to the slow axis direction of the optical film to be exhibited. Generally, a long polarizing film has an absorption axis in its longitudinal direction and a transmission axis in its width direction. Accordingly, for example, in the case of obtaining an optical film having a slow axis perpendicular to the absorption axis of the polarizing film, the film before stretching can also be extended along the longitudinal direction to obtain a slow axis in the width direction. axis of optical films. In this case, the polarizing plate can be efficiently produced by the roll-to-roll method using the elongated optical film and the elongated polarizing film.

The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, more preferably 20.0 times or less, more preferably 10.0 times or less, more preferably 5.0 times or less, and particularly preferably 2.0 times or less. The specific stretching ratio is appropriately set to meet expectations according to factors such as the optical properties, thickness, and mechanical strength of the optical film to be produced. When the stretching magnification is equal to or more than the lower limit value of the aforementioned 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-mentioned range, the direction of the slow axis can be easily controlled and film breakage can be effectively suppressed.

The stretching temperature is preferably "TgR" or higher, preferably " _{TgR +} 10°C" or higher, and preferably "TgR ₊ 100°C" or lower, preferably "TgR ₊ 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 value of the aforementioned range, the resin film can be sufficiently softened to uniformly stretch. In addition, when the stretching temperature is below the upper limit of the above-mentioned range, since the curing of the resin film due to the progress of crystallization of the crystalline polymer can be suppressed, the stretching can be smoothly performed, and the stretching can be carried out smoothly. Makes large birefringence manifest. Furthermore, the haze of the optical film obtained can generally be reduced to improve transparency.

By applying the aforementioned stretching treatment, an optical film can be obtained in the form of a stretched resin film. As described above, since the birefringence varies by extension, the balance of 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. Furthermore, since optical properties such as retardation are exhibited by the orientation of the polymer in contact with the solvent in the step (ii) and the orientation of the polymer stretched in the step (iii), the optical film can have desired properties. optical properties.

[12. Arbitrary process]

The manufacturing method of an optical film may further comprise combining arbitrary processes in the process (i) - process (iii) already mentioned above. Examples of the optional steps include a step of preheating the pre-stretching film before step (iii), a step of subjecting the optical film obtained in step (iii) to heat treatment to promote crystallization of a crystalline polymer, and The process of drying the film to reduce the amount of solvent in the film, the process of thermally shrinking the optical film to remove the residual stress in the film, etc.

Furthermore, by the above-mentioned manufacturing method, a long-shaped optical film can be produced using a long-shaped raw material film. The manufacturing method of an optical film may also include the process of winding up the thus-produced elongated optical film into a roll shape. Furthermore, the manufacturing method of an optical film may include the process of cutting out a desired shape from a long optical film.

[13. Polarizing plate]

A polarizing plate according to an embodiment of the present invention is provided with the optical film and the polarizing film described above. Polarizing films generally function as linear polarizers. Accordingly, the polarizing plate can transmit a part of the polarized light and shield the other polarized light.

Polarizing films generally have an absorption axis and a transmission axis perpendicular to the absorption axis. Furthermore, linearly polarized light having a vibration direction parallel to the absorption axis can be absorbed and linearly polarized light having a vibration direction parallel to the transmission axis can be transmitted. The vibration direction of the linearly polarized light means the vibrational direction of the electric field of the 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 between the absorption axis of the polarizing film and the slow axis of the optical film is preferably more than 80°, preferably more than 85°, more preferably more than 88°, and preferably less than 100°, It is preferably 95° or less, and particularly preferably 92° or less. In this case, the optical film preferably has an in-plane retardation capable of functioning as a half-wavelength plate. The polarizing plate related to this example can be used as a polarizing plate capable of compensating the viewing angle when it is installed in an image display device.

In another example, the angle between the absorption axis of the polarizing film and the slow axis of the optical film is preferably greater than 40°, preferably greater than 42°, more preferably greater than 44°, and preferably less than 50° , preferably below 48°, particularly preferably below 46°. In this case, the optical film preferably has an in-plane retardation capable of functioning as a quarter-wave plate. The polarizing plate related to this example can be used as a circular polarizing plate that allows circularly polarized light in one rotational direction to pass through and shields circularly polarized light in another rotational direction. The circular polarizer can suppress the reflection of external light by being arranged on the display surface of the display device.

As the polarizing film, any polarizing film may be used. Examples of polarizing films include a film obtained by uniaxially stretching a polyvinyl alcohol film by adsorbing iodine or a dichroic dye in a boric acid bath, and a polyvinyl alcohol film by adsorbing iodine or a dichroic dye. A film obtained by further modifying a part of the polyvinyl alcohol unit in the molecular chain into a polyvinyl extension unit by dyeing and extending. Among these, it is preferable that the polarizing film contains polyvinyl alcohol.

If natural light is incident on the polarizing film, only one polarized light will penetrate. The degree of polarization of the polarizing film is not particularly limited, but preferably more than 98%, more preferably more than 99%. In addition, the thickness of the polarizing film is preferably 5 μm to 80 μm.

In the above-mentioned polarizing plate, any layer body may be further included. Examples of optional layers include: a polarizer protective film layer; a bonding layer for bonding a polarizing film and an optical film; a hard coat layer such as an impact-resistant polymethacrylic resin layer; a pad for optimizing the smoothness of the film layer; reflection inhibiting layer; antifouling layer; static inhibiting layer; etc. Only one layer of these arbitrary layers may be provided, or two or more layers may be provided.

"Example"

The following examples are disclosed to specifically illustrate the present invention. However, the present invention is not limited to the embodiments shown below, and can be implemented with arbitrary changes without departing from the scope of the patent application of the present invention and the scope of its equivalents.

In the following description, the "%" and "part" indicating the amount are based on weight unless otherwise noted. In addition, unless otherwise noted, the operation described below was performed under the conditions of normal temperature and normal pressure (23° C., 1 atmosphere) in the atmosphere.

[Measurement method of glass transition temperature Tg and melting point Tm]

The measurement of the glass transition temperature Tg and the melting point Tm of the polymer was carried out as follows. First, the polymer is melted by heating, and the melted polymer is rapidly cooled by dry ice. Next, using this polymer as a sample, a differential scanning calorimeter (DSC) was used to measure the glass transition temperature Tg and melting point Tm of the polymer at a heating rate of 10°C/min (heating mode).

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

The in-plane retardation Re of the optical film, the retardation Rth in the thickness direction, the NZ coefficient, and the slow axis direction were measured with a phase difference meter ("AxoScan OPMF-1" manufactured by AXOMETRIC Corporation).

[Production Example 1. Production of Crystalline Polystyrene]

Put 17.8 g (71 mmol) of copper sulfate pentahydrate (CuSO ₄ .5H ₂ O), 200 mL of toluene and 24 mL of trimethylaluminum (250 mL) into a glass vessel with an inner volume of 500 mL replaced with argon. molar) and allowed to react at 40°C for 8 hours. After that, the solid portion was removed to obtain a solution. Toluene was further distilled off under reduced pressure from the obtained solution at room temperature to obtain 6.7 g of a contact product. The molecular weight of the contact product was measured by the freezing point depression method, and the result was 610.

Subsequently, 5 mmol of the aforementioned contact product was added as an aluminum atom, 5 mmol of triisobutylaluminum, 0.025 mmol of pentamethylcyclopentadiene trimethoxytitanium and 1 mmol of high-purity styrene were added to the reaction vessel. ear, the polymerization was carried out at 90°C for 5 hours. After that, the product was decomposed with a methanol solution of sodium hydroxide to decompose the catalyst component, washed repeatedly with 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 with 1,2,4-trichlorobenzene as a solvent. As a result, the weight average molecular weight Mw of this polymer was 350,000. In addition, it was confirmed that the obtained polymer was a crystalline polystyrene having a tandem structure by measurement of melting point Tm and ¹³ C-NMR. The melting point Tm of the crystalline polystyrene was 270°C, and the glass transition temperature was 100°C.

This operation was repeated to prepare the crystalline polystyrene having the opposite row 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. This metal pressure-resistant reactor was charged with 154.5 parts of cyclohexane and 42.8 parts of a 70% concentration cyclohexane solution of dicyclopentadiene (with an endo-isomer content of 99% or more) (as the amount of dicyclopentadiene: 30 parts) and 1.9 parts of 1-hexene, heated to 53°C.

A solution was prepared by dissolving 0.014 part of phenylimide tetrachloride (tetrahydrofuran) tungsten complex in 0.70 part of toluene. To this solution, 0.061 part of a diethyl ethoxyaluminum/n-hexane solution with a concentration of 19% was added, and the mixture was stirred for 10 minutes to prepare a catalyst solution. This catalyst solution was added to a pressure-resistant reactor to initiate ring-opening polymerization. Then, it was made to react for 4 hours while maintaining 53 degreeC, and the solution of the ring-opening polymer of dicyclopentadiene was obtained. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained ring-opened polymer of dicyclopentadiene were 8,750 and 28,100, respectively, and the molecular weight distribution (Mw/Mn) determined from these was 3.21.

To 200 parts of the obtained solution of the ring-opening polymer of dicyclopentadiene was added 0.037 part of 1,2-ethylene glycol as a terminator, heated to 60° C., and stirred for 1 hour to terminate the polymerization reaction. To this, 1 part of a hydrotalcite-like compound ("KYOWAAD (registered trademark) 2000" manufactured by Kyowa Chemical Industry Co., Ltd.) was added, heated to 60°C, and stirred for 1 hour. Then, 0.4 part of a filter aid (“RADIOLITE (registered trademark) #1500” manufactured by Showa Chemical Industry Co., Ltd.) was added, and the adsorbent and the solution were separated by filtration using a PP pleated cartridge filter (“TCP-HX” manufactured by ADVANTEC Toyo Corporation).

Add 100 parts of cyclohexane to 200 parts of the solution of the ring-opening polymer of dicyclopentadiene after filtration (30 parts of polymer amount), add 0.0043 part of chlorohydrocarbonyl (triphenylphosphine) ruthenium, under a hydrogen pressure of 6 MPa and 180°C for 4 hours of hydrogenation. Thereby, the reaction liquid containing the hydrogenated product of the ring-opening polymer of dicyclopentadiene can be obtained. The hydride of the reaction solution was precipitated to form a slurry solution.

The hydride contained in the reaction solution was separated from the solution using a centrifugal separator, and dried under reduced pressure at 60° C. for 24 hours to obtain 28.5 parts of the hydride of the ring-opening polymer of dicyclopentadiene as a compound with positive intrinsic birefringence. crystalline polymer. The hydrogenation rate of this hydride is 99% or more, the glass transition temperature Tg is 93°C, the melting point Tm is 262°C, and the ratio of the racemic diad is 89%.

[Example 1]

(1-1. Preparation of crystalline resin)

60 parts of crystalline polystyrene and polyphenylene ether (“NORYL PPO640” manufactured by SABIC Innovative Plastics Japan, weight average molecular weight Mw=43,000, glass transition temperature Tg=130°C) obtained in Production Example 1 40 parts were kneaded with a 2-axis extruder at 295° C. to produce transparent crystalline resin pellets.

(1-2. Extrusion into film)

The pellets of the crystalline resin were melt-extruded using a hot melt extrusion film forming machine equipped with a T-die (“Measuring Extruder Type Me-20/2800V3” manufactured by Optical Control Systems), and wound at a speed of 1.5 m/min. Roll to obtain a long strip of raw material film as a resin film with a width of about 120 mm before solvent contact. The operating conditions of the film forming machine are listed below. ． Tank temperature setting = 280℃～300℃ ． Mold temperature = 300℃ . Screw revolutions = 30 rpm . Casting roll temperature = 80°C

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

(1-3. Solvent contact)

The aforementioned raw material film was cut into a rectangle of 120 mm × 120 mm. This rectangular raw material film was immersed in cyclohexane as a solvent stored in a tank until the in-plane retardation Re=2 nm and the thickness direction retardation Rth=41 nm to obtain a resin film contacted with the film before stretching as a solvent. The pre-stretching film was taken out from cyclohexane, and after wiping off the cyclohexane adhering to the surface of the film, it was naturally dried in the air. The obtained pre-stretched film had a thickness of 160 μm.

(1-4. Extension)

A batch type biaxial stretching device (manufactured by ETO) was prepared. This stretching device includes an oven unit and a jig for stretching that can fix the film. If this stretching device is used, the film can be stretched by stretching the film through the jig in the oven.

Cut the pre-extension film into a rectangle of 100 mm × 100 mm. The two ends of the rectangular pre-stretching film are respectively clamped by the 5 clamps of the aforementioned stretching device. The pre-stretched film is stretched with a jig, and is freely uniaxially stretched in the longitudinal direction of the long-length raw material film obtained in the extrusion-forming process. 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 is obtained.

The in-plane retardation and NZ coefficient of the obtained optical film were measured, and the results were that the in-plane retardation Re(450), Re(550) and Re(650) at the measured wavelengths of 450 nm, 550 nm and 650 nm were Re(450). ) = 128 nm, Re(550) = 140 nm, Re(650) = 144 nm. In addition, the direction of the slow axis of the optical film is a vertical direction with respect to the extending direction. Furthermore, the NZ coefficient at the measurement wavelength of 550 nm is 0.45.

[Example 2]

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

In the step (1-3), the immersion time of the raw material film in the solvent was adjusted so that a pre-stretched film with an in-plane retardation Re=2 nm and a thickness direction retardation Rth=28 nm could be obtained.

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

Production of an optical film was carried out by the same method as in Example 1 except for the above.

[Example 3]

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

In the step (1-3), the immersion time was adjusted so that a pre-stretched film with in-plane retardation Re=4 nm and thickness direction retardation Rth=71 nm could be obtained to immerse the raw material film in the solvent.

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

Production of an optical film was carried out by the same method as in Example 1 except for the above.

[Example 4]

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

In addition, the line speed in the step (1-2) was changed so that the thickness of the elongated raw material film was changed to 201 μm.

Furthermore, in the step (1-3), the immersion time was adjusted so that the pre-stretching film with in-plane retardation Re=42 nm and thickness direction retardation Rth=540 nm was obtained to immerse the raw material film in the solvent.

In addition, the stretching temperature in the step (1-4) was changed to 160° C., and the stretching ratio was changed to 1.6 times.

Production of an optical film was carried out by the same method as in Example 1 except for the above.

[Comparative Example 1]

The line speed in the step (1-2) was changed to change the thickness of the long raw material film to 115 μm.

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

In the step (1-4), the raw material film was stretched instead of the pre-stretching film, the stretching temperature was changed to 132° C., and the stretching ratio was changed to 2.2 times.

Production of an optical film was carried out by the same method as in Example 1 except for the above.

[Comparative Example 2]

Antioxidant (4{3-[3',5'-bis(tertiarybutyl)-4'-hydroxyphenyl) was mixed with 100 parts of the hydrogenated product of the ring-opened polymer of dicyclopentadiene obtained in Production Example 2. ] Methylene propionate}methane propionate; 1.1 part of "Irganox (registered trademark) 1010" manufactured by BASF Japan) was placed in a biaxial extruder (manufactured by Toshiba Machinery Co., Ltd.) with four die holes with an inner diameter of 3 mm⌀ "TEM-37B"). The mixture of the hydrogenated product of the ring-opening polymer of dicyclopentadiene and the antioxidant is formed into strands by hot melt extrusion, and then finely chopped with a strand cutter to obtain pellets of a crystalline resin.

This pellet was used in the step (1-2). In addition, the line speed in the step (1-2) was changed so that the thickness of the elongated raw material film was changed to 13 μm.

In addition, in the step (1-3), the type of the solvent was changed to toluene. Furthermore, the immersion time was adjusted so that the pre-stretching film with in-plane retardation Re=8 nm and thickness direction retardation Rth=−73 nm could be obtained, and the immersion of the raw material film in the solvent was performed.

In addition, the stretching temperature in the step (1-4) was changed to 130° C., and the stretching ratio was changed to 1.5 times.

Production of an optical film was carried out by the same method as in Example 1 except for the above.

[Evaluation of Optical Films Obtained in Examples 1 to 3 and Comparative Examples 1 to 2]

A polarizing film (“HLC2-5618S” manufactured by SANRITZ, a polarizer having a thickness of 180 μm and a polarization transmission axis in the width direction) was prepared. One side of this polarizing film and the optical films obtained in Examples 1-3 and Comparative Examples 1-2 are interposed by an adhesive layer (Nitto) in such a way that the polarization transmission axis of the polarizing film and the slow axis of the optical film sandwich an angle of 45°. Electrotech Co., Ltd. "CS9621") was laminated to obtain a circular polarizer.

A reflector is prepared, and the prepared circular polarizer is placed on the reflector so that the optical film becomes the side of the reflector. Irradiate the circular polarizing plate with a fluorescent lamp, and observe the reflected light of the reflector in the frontal direction and the oblique direction with a polar angle of about 60°. The aforementioned front direction is the front direction of the reflector, and represents a direction parallel to the thickness direction of the circular polarizer. In each observation direction, if no discoloration was observed, it was rated as "○", if discoloration was observed but only a small amount, it was rated as "△", and if discoloration was observed to an unacceptable level, it was rated as "╳".

[Evaluation of Optical Film Obtained in Example 4]

Two polarizing films (“HLC2-5618S” manufactured by SANRITZ, 180 μm in thickness, polarizers having a polarization transmission axis in the width direction) were prepared, and they were arranged in crossed nicotinium. The so-called orthogonal nicotinium means that the transmission axis of polarized light is vertical when viewed from the thickness direction. The optical film obtained in Example 4 was set so that the polarization transmission axis of the polarizing film on the viewing side (that is, the polarizing film provided on the viewing side in the case of a backlight to be described later) coincided with the slow axis of the optical film. between these polarizing films. An intermediary adhesive layer (“CS9621” manufactured by Nitto Denko) adheres the polarizing film and the optical film to obtain a stack.

A backlight is prepared in a dark room, and the fabricated stack is placed on the backlight. In the state in which the backlight was turned on, the light penetrating the stacked body was observed in the frontal direction and the oblique direction of the polar angle of about 60°. In each observation position, if no discoloration was observed, it was rated as "○", if discoloration was observed but only a small amount, it was rated as "△", and if discoloration and light leakage were observed to an unacceptable level, it was rated as "╳".

[result]

The results of the foregoing Examples and Comparative Examples are disclosed in the following table. In the table below, 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] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 resin composition type PPE/SPS PPE/SPS PPE/SPS PPE/SPS PPE/SPS crystalline COP weight ratio 40/60 40/60 40/60 50/50 40/60 — Extruded into film Re[nm] of raw material film 3 2 4 4 2 2 Rth[nm] of raw material film −18 −15 −32 −30 −16 4 Thickness of raw material film [μm] 158 107 276 201 115 13 solvent exposure solvent Cy Cy Cy Cy — Tl Re[nm] of the film before stretching 2 2 4 42 — 8 Rth[nm] of the film before stretching 41 28 71 540 — −73 Thickness of film before stretching [μm] 160 110 280 210 — 17 extend Extension temperature [℃] 138 138 138 160 132 130 extension method free uniaxial free uniaxial free uniaxial free uniaxial free uniaxial free uniaxial Elongation ratio [times] 1.2 1.3 1.1 1.6 2.2 1.5 Optical film Re(450)[nm] 128 139 112 251 123 142 Re(550)[nm] 140 150 128 280 139 140 Re(650)[nm] 144 156 132 289 143 138 NZ coefficient 0.45 0.19 0.84 0.46 −0.1 0.5 Thickness [μm] 143 101 260 190 105 15 The direction of the slow axis relative to the extension direction vertical vertical vertical vertical vertical parallel Visual evaluation (front direction) ○ ○ ○ ○ ○ ╳ Visual evaluation (oblique direction) ○ △ △ ○ ╳ ○

[discuss]

In the examples, crystalline polystyrene was used as the crystalline polymer with negative intrinsic birefringence to manufacture the optical film. When the pre-stretching film was freely uniaxially stretched to manufacture the optical film, since any of the examples exhibited the slow axis in the direction perpendicular to the stretching direction, it was confirmed that the obtained optical film had negative birefringence characteristics. In addition, the optical films obtained in the examples all have in-plane retardation satisfying the formula (1) and NZ coefficients satisfying the formula (2).

Since the optical films obtained in the examples have reverse wavelength dispersion, they can exert their optical functions in a wide wavelength range.

Accordingly, 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 this optical film can be used as a reflection suppression film to suppress reflection of light in a wide wavelength range. Therefore, discoloration caused by passing 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 half wavelength plate in a wide wavelength range. Therefore, the optical film can change the vibration direction of linearly polarized light through a wide wavelength range of the optical film by 90°. Therefore, it is possible to suppress discoloration and light leakage caused by light of a part of wavelengths passing through the stack.

In addition, since the optical film obtained in the embodiment has a moderate NZ coefficient, not only the light passing through the optical film in the thickness direction, but also the light passing in the oblique direction that is neither parallel nor perpendicular to the thickness direction can be polarized. Moderate changes in status.

Accordingly, the optical films of Examples 1 to 3 can suppress the reflection of light penetrating the circularly polarizing plate in the oblique direction, so that discoloration can be suppressed not only in the front direction but also in the oblique direction.

Moreover, since the optical film of Example 4 can suppress the transmission of the light of the stack in the oblique direction, it can suppress discoloration and light leakage not only in the front direction, but also in the oblique direction.

none.

none.

none.

Claims (11)

An optical film, which is an optical film comprising a crystalline polymer, the optical film has negative birefringence characteristics, and the in-plane retardation Re(450), Re(550) and Re(650) satisfy Equation (1), the NZ coefficient Nz of the aforementioned optical film satisfies Equation (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, wherein the optical film is a stretched film. The optical film according to claim 1, wherein the optical film is a uniaxially stretched film. The optical film according to claim 1, wherein the optical film has an elongated shape. The optical film according to any one of claims 1 to 5, which is formed from a resin comprising the aforementioned crystalline polymer having negative intrinsic birefringence and a thermoplastic polymer having positive intrinsic birefringence. The optical film according to claim 6, wherein the weight ratio (thermoplastic polymer/crystalline polymer) of the aforementioned thermoplastic polymer having positive intrinsic birefringence to the aforementioned crystalline polymer having negative intrinsic birefringence (thermoplastic polymer/crystalline polymer) is 3 /7 or more. The optical film according to claim 6, wherein the crystalline polymer having negative intrinsic birefringence is a polystyrene-based polymer, and the thermoplastic polymer having positive intrinsic birefringence is polyphenylene ether. A polarizing plate comprising the optical film and polarizing film according to any one of claims 1 to 8. The polarizing plate according to claim 9, wherein the slow axis of the optical film and the absorption axis of the polarizing film comprise an angle of 80°˜100°. A method for producing an optical film, which is the method for producing an optical film according to any one of claims 1 to 8, comprising in sequence: preparing a crystalline polymer comprising a negative intrinsic birefringence and a positive The step of forming a resin film made of a thermoplastic polymer resin with inherent birefringence, the step of contacting the resin film with a solvent to change the birefringence in the thickness direction, and the step of stretching the resin film.