WO2023095863A1

WO2023095863A1 - Optical film, multilayer film and method for producing same, and polarizing plate

Info

Publication number: WO2023095863A1
Application number: PCT/JP2022/043507
Authority: WO
Inventors: 健作藤井
Original assignee: 日本ゼオン株式会社
Priority date: 2021-11-29
Filing date: 2022-11-25
Publication date: 2023-06-01
Also published as: TW202328230A

Abstract

The present invention provides an optical film which contains a copolymer that comprises a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit, wherein the proportion of the (meth)acrylic compound unit in the copolymer is 5% by weight to 40% by weight.

Description

Optical film, multilayer film, manufacturing method thereof, and polarizing plate

The present invention relates to an optical film, a multilayer film, a manufacturing method thereof, and a polarizing plate.

　Polymers produced using polycyclic aromatic vinyl compounds such as vinyl naphthalene are sometimes used as materials for optical films. The polymer can usually be a polymer containing a polycyclic aromatic vinyl compound unit, and can exhibit excellent optical properties. For example, Patent Literatures 1 and 2 describe techniques for using a polymer produced using vinylnaphthalene as a material for an optical film.

Japanese Patent Application Laid-Open No. 2006-111650 WO2020/066174

　Polymers containing polycyclic aromatic vinyl compound units are sometimes used as materials for optical films with in-plane retardation. In general, from the viewpoint of thickness reduction, an optical film is required to be excellent in retardation expression.

Also, an optical film containing a polymer containing a polycyclic aromatic vinyl compound unit may be used by bonding it to another member. However, such optical films have conventionally been susceptible to delamination. Delamination refers to delamination accompanied by internal failure (cohesive failure) of the membrane. Therefore, when delamination occurs in an optical film bonded to a member, the optical film is usually destroyed, and a portion of the optical film may remain on the member. If there is such a residue of the optical film, it may be a cause of poor reworkability of the optical film.

Specifically, there are cases where it is required to once attach an optical film to a member, peel off the optical film, and attach the optical film to the member again. The property of being easily peeled off from a member and reattached is called "reworkability". For example, when an optical film is attached to a display panel (for example, a liquid crystal panel) of an image display device, and then the optical film is peeled off from the display panel and reattached, excellent reworkability is required. However, if delamination occurs when the optical film is peeled off from the member, part of the destroyed optical film may remain on the surface of the member. If a part of the optical film remains on the surface of the member, even if the optical film is adhered again, it is difficult to obtain a product with the same quality as the first pasting.

Due to the above circumstances, there is a demand for the development of a technology that can effectively suppress delamination in optical films containing polymers containing polycyclic aromatic vinyl compound units.

The present invention was invented in view of the above problems, and an optical film containing a polymer containing a polycyclic aromatic vinyl compound unit and having excellent retardation property and delamination resistance; An object of the present invention is to provide a multilayer film, a method for producing the same, and a polarizing plate provided with the multilayer film.

The inventors have made extensive studies to solve the above problems. As a result, the present inventors have found that an optical film containing a copolymer containing a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit in a specific range has both retardation development property and delamination resistance. The present invention was completed by discovering that it is excellent in
That is, the present invention includes the following.

(1) including a copolymer containing a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit,
The optical film, wherein the proportion of the (meth)acrylic compound unit in the copolymer is 5% by weight or more and 40% by weight or less.
(2) The optical film according to (1), wherein the copolymer has a weight average molecular weight Mw of 50,000 to 500,000.
(3) The optical film according to (1) or (2), wherein the copolymer contains a repeating unit having a structure formed by polymerizing vinylnaphthalene.
(4) The optical film according to any one of (1) to (3), wherein the copolymer has a glass transition temperature of 110° C. or higher.
(5) Any one of (1) to (4), wherein the ratio Re/d between the in-plane retardation Re and the thickness d of the optical film at a measurement wavelength of 550 nm is 10.0×10 ⁻³ or more. The optical film according to .
(6) A multilayer film comprising a substrate film and the optical film according to any one of (1) to (5).
(7) The multilayer film according to (6), wherein the base film contains an alicyclic structure-containing polymer.
(8) A method for producing a multilayer film comprising a substrate film and an optical film, comprising:
Coating a coating liquid containing a copolymer on the base film,
The copolymer contains polycyclic aromatic vinyl compound units and (meth)acrylic compound units,
A method for producing a multilayer film, wherein the amount of the (meth)acrylic compound unit in the copolymer is 5% by weight or more and 40% by weight or less.
(9) A polarizing plate comprising the multilayer film according to (6) or (7) and a polarizing film.

According to the present invention, an optical film containing a polymer containing a polycyclic aromatic vinyl compound unit and having excellent retardation property and delamination resistance; a multilayer film comprising the optical film and a method for producing the same; A polarizing plate comprising the multilayer 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 can be arbitrarily modified without departing from the scope of the claims and their equivalents.

In the following description, the in-plane retardation Re represents a value represented by Re=(nx−ny)×d unless otherwise specified. The retardation Rth in the thickness direction represents a value represented by Rth={(nx+ny)/2−nz}×d unless otherwise specified. nx represents the refractive index in the direction (slow axis direction) that is perpendicular to the thickness direction (in-plane direction) and gives the maximum refractive index, and ny is the in-plane direction in the nx direction. represents the refractive index in the orthogonal direction, nz represents the refractive index in the thickness direction, and d represents the thickness. The measurement wavelength is 550 nm unless otherwise stated. Retardation such as in-plane retardation and retardation in the thickness direction can be measured using a phase difference meter (“AxoScan” manufactured by Axometrics).

In the following description, the slow axis represents the slow axis in the in-plane direction unless otherwise specified.

In the following description, unless otherwise specified, the angle formed by the optical axes (absorption axis, transmission axis, slow axis, etc.) of each layer in a member including a plurality of layers is the angle when the layer is viewed from the thickness direction. represents

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

In the following description, a "long" film refers to a film having a length of 5 times or more, preferably 10 times or more, with respect to the width, specifically a roll A film that is long enough to be rolled up into a shape and stored or transported. The upper limit of the length of the long film is not particularly limited, and can be, for example, 100,000 times or less the width.

In the following description, unless otherwise specified, "polarizing plate", "circularly polarizing plate", "λ/2 plate", and "λ/4 plate" refer not only to rigid members but also to resin films, for example Also includes flexible members such as .

In the following description, "a polymer having a positive intrinsic birefringence value" and "a resin having a positive intrinsic birefringence value" mean that "the refractive index in the stretching direction is higher than the refractive index in the direction perpendicular to the stretching direction. Polymers that become larger" and "resins that have a higher refractive index in the direction of stretching than in the direction orthogonal to the direction of stretching" respectively. In addition, "a polymer having a negative intrinsic birefringence value" and "a resin having a negative intrinsic birefringence value" are defined as "a polymer whose refractive index in the stretching direction is smaller than that in the direction orthogonal to the stretching direction. and "resin in which the refractive index in the stretching direction is smaller than the refractive index in the direction orthogonal to the stretching direction" respectively. Intrinsic birefringence values can be calculated from the dielectric constant distribution.

In the following description, adhesives include not only adhesives in a narrow sense, but also adhesives having a shear storage modulus of less than 1 MPa at 23°C unless otherwise specified. The narrowly defined adhesive means an adhesive having a shear storage modulus of 1 MPa to 500 MPa at 23° C. after irradiation with energy rays or after heat treatment.

<1. Outline of optical film>
An optical film according to one embodiment of the present invention includes a copolymer containing polycyclic aromatic vinyl compound units and (meth)acrylic compound units. A polycyclic aromatic vinyl compound unit represents a repeating unit having a structure formed by polymerizing a polycyclic aromatic vinyl compound. Moreover, the (meth)acrylic compound unit represents a repeating unit having a structure formed by polymerizing a (meth)acrylic compound. However, the method for forming the polycyclic aromatic vinyl compound unit and the (meth)acrylic compound unit is not limited. Therefore, the polycyclic aromatic vinyl compound unit may be formed by a method other than polymerizing the polycyclic aromatic vinyl compound. Also, the (meth)acrylic compound unit may be formed by a method other than polymerizing the (meth)acrylic compound.

In the copolymer containing polycyclic aromatic vinyl compound units and (meth)acrylic compound units, the amount of (meth)acrylic compound units is within a specific range. Such a copolymer containing (meth)acrylic compound units in a specific range may be hereinafter referred to as a "specific copolymer". In general, the optical film according to this embodiment is made of a resin containing a specific copolymer. In the following description, the resin containing the specific copolymer may be referred to as "specific resin". Therefore, the optical film according to this embodiment usually contains the specific resin, and preferably contains only the specific resin. This specific resin is usually a thermoplastic resin.

The optical film according to this embodiment can be excellent in retardation expression and delamination resistance.

<2. Specific copolymer>
The specific copolymer contains polycyclic aromatic vinyl compound units and (meth)acrylic compound units. Since an optical film is usually formed of a specific resin containing this specific copolymer, the optical film contains the specific copolymer.

As described above, the polycyclic aromatic vinyl compound unit represents a repeating unit having a structure formed by polymerizing a polycyclic aromatic vinyl compound. A polycyclic aromatic vinyl compound is a compound containing a polycyclic aromatic group containing a plurality of aromatic rings and a vinyl group bonded to at least one aromatic ring of the polycyclic aromatic group. show. The aromatic ring usually follows Hückel's rule that the number of electrons contained in the π-electron system on the ring is 4n+2 (n represents an integer of 0 or more, preferably a natural number). Polymerization of this polycyclic aromatic vinyl compound usually proceeds as addition polymerization with a vinyl group. Thus, a polycyclic aromatic vinyl compound unit can contain a main chain formed by the polymerization reaction of vinyl groups and side chains containing polycyclic aromatic groups attached to the main chain.

In general, when the molecules of the specific copolymer are oriented by stretching, the main chain can be aligned parallel to the stretching direction, while the side chains can be aligned in a direction crossing the stretching direction (for example, a direction perpendicular to the stretching direction). . Therefore, the structure of the polycyclic aromatic group that can be included in the side chain can be reflected in the refractive index in the direction crossing the alignment direction of the optical film. Therefore, it is preferable to select the structure of the polycyclic aromatic group according to the refractive index desired to be expressed in the direction intersecting the orientation direction of the optical film. It is preferable to select according to optical characteristics such as gradation.

The polycyclic aromatic group may be, for example, a condensed aromatic group or a ring-assembled aromatic group. A condensed aromatic group represents a group containing an aromatic condensed ring. Moreover, the ring-assembled aromatic group represents a group containing a plurality of aromatic rings linked via a bond. The aromatic ring may be an aromatic heterocyclic ring, but is preferably an aromatic hydrocarbon ring. Moreover, the polycyclic aromatic group may contain one or more substituents other than the vinyl group. Examples of substituents include alkyl groups such as methyl group and ethyl group; alkoxy groups such as methoxy group and ethoxy group; and the like. Among them, the polycyclic aromatic group preferably does not have the substituents described above.

Polycyclic aromatic vinyl compounds containing condensed aromatic groups include, for example, vinylnaphthalenes such as 1-vinylnaphthalene and 2-vinylnaphthalene; vinyl compounds such as 1-vinylanthracene, 2-vinylanthracene and 9-vinylanthracene anthracene; and the like. Examples of polycyclic aromatic vinyl compounds containing ring-aggregated aromatic groups include vinylbiphenyl and vinylterphenyl. Among them, polycyclic aromatic vinyl compounds containing condensed aromatic groups are preferred, and vinylnaphthalene is particularly preferred. Therefore, the specific copolymer particularly preferably contains a repeating unit having a structure formed by polymerizing vinylnaphthalene (hereinafter sometimes referred to as "vinylnaphthalene unit").

The polycyclic aromatic vinyl compound may be used singly or in combination of two or more. Therefore, the specific copolymer may contain only one type of polycyclic aromatic vinyl compound unit, or may contain two or more types.

The ratio of the polycyclic aromatic vinyl compound unit in the specific copolymer is preferably 60% by weight or more, more preferably 65% by weight or more, and particularly preferably 70% by weight or more with respect to 100% by weight of the specific copolymer. preferably 95% by weight or less, more preferably 90% by weight or less, and particularly preferably 85% by weight or less. When the ratio of the polycyclic aromatic vinyl compound unit is within the above range, the optical film can have particularly excellent retardation development and delamination resistance. In particular, when the proportion of polycyclic aromatic vinyl compound units is at least the above lower limit, the retardation expressibility of the optical film can be effectively enhanced.

The ratio of the polycyclic aromatic vinyl compound units in the specific copolymer can be adjusted, for example, by the charging ratio of the polycyclic aromatic vinyl compound. Here, the charging ratio of the polycyclic aromatic vinyl compound represents the ratio of the amount of the polycyclic aromatic vinyl compound to the total monomers of the specific copolymer. Usually, the ratio of the polycyclic aromatic vinyl compound units in the specific copolymer can match the charging ratio of the polycyclic aromatic vinyl compound.

The (meth)acrylic compound unit represents a repeating unit having a structure formed by polymerizing a (meth)acrylic compound, as described above. A (meth)acrylic compound represents a compound containing a (meth)acryloyl group. Moreover, a (meth)acryloyl group includes an acryloyl group, a methacryloyl group, and combinations thereof. (Meth)acrylic compound, the carbon-carbon unsaturated bond contained in the (meth)acryloyl group is the carbon-carbon unsaturated bond of the vinyl group of the polycyclic aromatic vinyl compound or other (meth)acrylic compounds contain It can polymerize by reacting with carbon-carbon unsaturated bonds.

(Meth)acrylic compounds include acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, and the like. Examples of acrylic acid derivatives include acrylic acid esters and acrylic acid amides. Examples of methacrylic acid derivatives include methacrylic acid esters and methacrylic acid amides. Examples of acrylic esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, sec-butyl acrylate, t- Butyl, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate and the like. Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, sec-butyl methacrylate, and methacrylic acid. t-butyl, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, n-dodecyl methacrylate and the like. In addition, the (meth)acrylic acid esters such as the acrylic acid esters and methacrylic acid esters may have substituents such as hydroxyl groups and halogen atoms. Examples of substituted (meth)acrylic acid esters include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, glycidyl methacrylate and the like.

From the viewpoint of enhancing the adhesion between the optical film and other members, acrylic acid and methacrylic acid are preferable as the (meth)acrylic compound, and acrylic acid is particularly preferable. From the viewpoint of suppressing the hygroscopicity of the optical film and improving the water resistance and water vapor barrier properties, the (meth)acrylic compound is preferably an acrylic acid ester or a methacrylic acid ester, and particularly preferably an acrylic acid ester.

The (meth)acrylic compound may be used singly or in combination of two or more. Therefore, the specific copolymer may contain only one type of (meth)acrylic compound unit, or may contain two or more types.

The ratio of (meth)acrylic compound units in the specific copolymer is usually 5% by weight or more, preferably 10% by weight or more, particularly preferably 15% by weight or more, relative to 100% by weight of the specific copolymer. 40% by weight or less, preferably 35% by weight or less, particularly preferably 30% by weight or less. When the ratio of the (meth)acrylic compound unit is within the above range, the optical film can have particularly excellent retardation expressibility and delamination resistance. In particular, when the ratio of the (meth)acrylic compound units is equal to or higher than the lower limit, the delamination resistance of the optical film can be effectively increased.

The ratio of (meth)acrylic compound units in the specific copolymer can be adjusted, for example, by the charging ratio of the (meth)acrylic compound. Here, the charge ratio of the (meth)acrylic compound represents the ratio of the amount of the (meth)acrylic compound to the total monomers of the specific copolymer. Usually, the ratio of (meth)acrylic compound units in the specific copolymer can match the charge ratio of the (meth)acrylic compound.

The specific copolymer may contain any structural unit in combination with the polycyclic aromatic vinyl compound unit and the (meth)acrylic compound unit. Any structural unit usually has a structure different from the polycyclic aromatic vinyl compound unit and the (meth)acrylic compound unit. For example, any structural unit can have a structure formed by polymerizing any compound other than a polycyclic aromatic vinyl compound containing a carbon-carbon unsaturated bond and a (meth)acrylic compound.

The specific copolymer preferably has a weight average molecular weight Mw within a specific range. Specifically, the weight average molecular weight Mw of the specific copolymer is preferably 50,000 or more, more preferably 100,000 or more, and preferably 500,000 or less, more preferably 300,000 or less. When the weight-average molecular weight Mw of the specific copolymer is within the above range, the optical film can have particularly excellent retardation expressibility and delamination resistance.

The weight average molecular weight Mw of the polymer can be measured in terms of polyisoprene or polystyrene by gel permeation chromatography (GPC) using cyclohexane as a solvent. Toluene may be used as a solvent for GPC if the polymer is not soluble in cyclohexane.

The specific copolymer preferably has a glass transition temperature Tg within a specific range. Specifically, the glass transition temperature Tg of the specific copolymer is preferably 110° C. or higher, more preferably 115° C. or higher, particularly preferably 120° C. or higher, and preferably 180° C. or lower, more preferably 170° C. °C or less, particularly preferably 160°C or less. When the weight-average molecular weight Mw of the specific copolymer is within the above range, the optical film can have particularly excellent retardation expressibility and delamination resistance. The range of the glass transition temperature Tg of the specific copolymer may be the same as the range of the glass transition temperature of the specific resin containing the specific copolymer.

The glass transition temperature Tg can be measured using a differential scanning calorimeter ("DSC7000X" manufactured by Hitachi High-Tech Science Co., Ltd.) under the condition of a heating rate of 10°C/min. This glass transition temperature Tg can be measured based on JIS K 6911.

A specific copolymer usually has a negative intrinsic birefringence value. Therefore, a particular resin containing that particular copolymer can also have a negative intrinsic birefringence value.

There are no particular restrictions on the method of manufacturing the specific copolymer. The specific copolymer can be produced, for example, by a method including copolymerizing a polycyclic aromatic vinyl compound, a (meth)acrylic compound, and, if necessary, any compound. In this copolymerization, a polymerization initiator may be used as necessary. Examples of polymerization initiators include organic compounds such as lauroyl peroxide, diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, t-butylperoxypivalate, and 3,3,5-trimethylhexanoyl peroxide. Peroxides; azo compounds such as α,α'-azobisisobutyronitrile; ammonium persulfate; and potassium persulfate. One polymerization initiator may be used alone, or two or more polymerization initiators may be used in combination at an arbitrary ratio.

The ratio of the specific copolymer contained in the specific resin forming the optical film is preferably 80% by weight or more, more preferably 90% by weight or more, and still more preferably 95% by weight or more with respect to 100% by weight of the specific resin. be. The specific resin may contain only the specific copolymer. Therefore, the optical film may contain only the specific copolymer.

<3. Optional component>
The specific resin forming the optical film may further contain optional components in combination with the specific copolymer. Examples of optional components include stabilizers such as antioxidants, heat stabilizers, light stabilizers, weather stabilizers, ultraviolet absorbers, and near-infrared absorbers; plasticizers; and the like. One type of optional component may be used alone, or two or more types may be used in combination.

<4. Characteristics and Dimensions of Optical Film>
The optical film can have high retardation expressibility. The retardation development property of an optical film can be represented by the ratio Re/d between the in-plane retardation Re and the thickness d of the optical film. The measurement wavelength of the in-plane retardation Re is 550 nm unless otherwise specified. Specifically, the ratio Re/d of the optical film is preferably 10.0×10 ⁻³ or more, more preferably 11.0×10 ⁻³ or more, still more preferably 12.0×10 ⁻³ or more, Particularly preferably, it is 13.0×10 ⁻³ or more. The upper limit of the ratio Re/d of the optical film is not particularly limited, and may be, for example, 20.0×10 ⁻³ or less, 18.0×10 ⁻³ or less, or 16.0×10 ⁻³ or less.

The optical film can have high delamination resistance. The delamination resistance of an optical film can be expressed by the amount of force required to peel off a member after the optical film has been adhered to the member. This force may be hereinafter referred to as "peel strength". Specifically, the peel strength range is preferably 1.0 N/15 mm or more, more preferably 2.0 N/15 mm or more, and particularly preferably 5.0 N/15 mm or more. The upper limit of the peel strength of the optical film is not particularly limited, and may be, for example, 20.0 N/15 mm or less, 15.0 N/15 mm or less. The peel strength of the optical film can be measured by the method described in <Method for measuring delamination resistance> in Examples described later.

The optical film preferably has an in-plane retardation suitable for its application.
For example, the optical film may have low in-plane retardation. As a specific example, the in-plane retardation Re of the optical film at a measurement wavelength of 550 nm may be, for example, 10 nm or less, 7 nm or less, 5 nm or less, or 0 nm. Since the optical film has excellent advantages other than the retardation expressibility, for example, when the optical film is used for an application that utilizes the advantages other than the retardation expressibility, the optical film should have a small in-plane retardation Re as described above. It may be an optically isotropic film having a The optical film may be an optically anisotropic film having a small in-plane retardation Re as described above and a large retardation Rth in the thickness direction.

The in-plane retardation Re of the optical film may be, for example, within a range in which the optical film can function as a λ/4 plate. When the optical film can function as a λ/4 plate, the in-plane retardation Re of the optical film at a measurement wavelength of 550 nm is preferably 80 nm or more, more preferably 100 nm, particularly preferably 110 nm or more, and preferably 170 nm or less. It is more preferably 150 nm or less, particularly preferably 140 nm or less.

The in-plane retardation Re of the optical film may be, for example, within a range in which the optical film can function as a λ/2 plate. When the optical film can function as a λ/2 plate, the in-plane retardation Re of the optical film at a measurement wavelength of 550 nm is preferably 220 nm or more, more preferably 240 nm, particularly preferably 250 nm or more, and preferably 310 nm or less. It is more preferably 290 nm or less, particularly preferably 280 nm or less.

The optical film may have a slow axis. There is no particular limitation on the direction of the slow axis of the optical film. For example, the slow axis of the long optical film may be parallel or perpendicular to the width direction of the optical film. Further, the slow axis of the elongated optical film may form an angle in the range close to 45° with respect to the width direction of the optical film. As a specific example, the angle formed by the slow axis of the long optical film with respect to the width direction of the optical film is preferably 40° or more, more preferably 42° or more, still more preferably 43° or more, particularly It can be preferably 44° or more, preferably 50° or less, more preferably 48° or less, even more preferably 47° or less, and particularly preferably 46° or less.

The total light transmittance of the optical film is preferably 80% or higher, more preferably 85% or higher, and particularly preferably 90% or higher. The total light transmittance can be measured in a wavelength range of 400 nm to 700 nm using an ultraviolet/visible spectrometer.

The haze of the optical film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. Haze can be measured using a haze meter in accordance with JIS K7361-1997.

The optical film may be a sheet film or a long film.

Although there is no particular limitation on the thickness of the optical film, it is preferably thin from the viewpoint of obtaining a thin optical film by utilizing excellent retardation expression. The specific thickness range of the optical film is preferably 0.5 µm or more, more preferably 1 µm or more, particularly preferably 5 µm or more, and preferably 100 µm or less, more preferably 80 µm or less, and particularly preferably 70 µm or less. .

There are no restrictions on the uses of the optical film described above. Optical films, alone or in combination with other components, can be used in a wide variety of applications in the optical field. Examples of applications of optical films include retardation films, viewing angle compensation films, polarizing plate protective films, and the like. Among them, the optical film is preferably used as a multilayer film in combination with the base film from the viewpoint of effectively utilizing the excellent delamination resistance.

<5. Method for producing an optical film>
A method for manufacturing the optical film is not particularly limited. The optical film is formed by molding a specific resin by a resin molding method such as injection molding, extrusion molding, press molding, inflation molding, blow molding, calendar molding, cast molding, compression molding, and the like. It can be manufactured by a method including In addition, the optical film is formed by a method including, for example, applying a coating liquid containing a specific resin and a solvent to an appropriate surface, and drying the applied coating liquid to remove the solvent. , may be manufactured.

The method for manufacturing the optical film may include stretching the optical film. By stretching, the desired retardation can be expressed in the optical film and the thickness of the optical film can be adjusted. There are no restrictions on the stretching direction, 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. Moreover, the stretching direction may be one direction or two or more directions. Therefore, the stretching method includes, for example, a method of uniaxially stretching an optical film in the longitudinal direction (longitudinal uniaxial stretching method), a method of uniaxially stretching an optical film in the width direction (horizontal uniaxial stretching method), and the like. Biaxial stretching methods such as a simultaneous biaxial stretching method in which the film is stretched in the longitudinal direction and the width direction at the same time, and a sequential biaxial stretching method in which the optical film is stretched in one of the longitudinal direction and the width direction and then stretched in the other direction. a method of stretching an optical film in an oblique direction (diagonal stretching method); and the like.

The draw ratio is preferably 1.1 times or more, more preferably 1.2 times or more, preferably 5.0 times or less, more preferably 3.0 times or less, and particularly preferably 2.0 times or less. .
The stretching temperature is preferably “Tg−5° C.” or higher, more preferably “Tg+5° C.” or higher, and preferably “Tg+50° C.” or lower, more preferably “Tg+30° C.” or lower. Here, "Tg" represents the glass transition temperature of the specific copolymer.

<6. Multilayer film>
A multilayer film according to one embodiment of the present invention includes a base film and the optical film described above.

A resin film can be used as the base film. Therefore, the base film usually contains a resin, preferably only a resin. The resin forming the resin film is preferably a thermoplastic resin, more preferably a thermoplastic resin having a positive intrinsic birefringence value.

The resin that forms the base film usually contains a polymer. Since the resin forming the base film preferably has a positive intrinsic birefringence value, the polymer contained in the resin also preferably has a positive intrinsic birefringence value. Examples of polymers having a positive intrinsic birefringence value include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polyether sulfone; polysulfone; polyallyl sulfone; polyvinyl chloride; alicyclic structure-containing polymer; These polymers may be used singly or in combination of two or more. Among them, alicyclic structure-containing polymers, cellulose esters, and polycarbonates are preferred, and alicyclic structure-containing polymers are particularly preferred.

A polymer containing an alicyclic structure is a polymer containing an alicyclic structure in a repeating unit, and is usually an amorphous polymer. As the alicyclic structure-containing polymer, both a polymer containing an alicyclic structure in the main chain and a polymer containing an alicyclic structure in the side chain can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and a cycloalkane structure is preferable from the viewpoint of thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, particularly preferably 6 or more, preferably 30 or less, more preferably 20 or less, Particularly preferably, it is 15 or less.

In the alicyclic structure-containing polymer, the proportion of repeating units containing an alicyclic structure is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of repeating units containing an alicyclic structure is within the above range, a multilayer film with excellent heat resistance can be obtained.

Examples of alicyclic structure-containing polymers include (1) norbornene polymers, (2) monocyclic cyclic olefin polymers, (3) cyclic conjugated diene polymers, and (4) vinyl alicyclic hydrocarbon polymers. coalescence, hydrogenated products thereof, and the like. Among these, cyclic olefin polymers and norbornene-based polymers are preferred, and norbornene-based polymers are particularly preferred. Norbornene-based polymers include, for example, ring-opening polymers of monomers containing a norbornene structure, ring-opening copolymers of monomers containing a norbornene structure and other ring-opening copolymerizable monomers, and their hydrogen compounds: addition polymers of norbornene structure-containing monomers, addition copolymers of norbornene structure-containing monomers and other copolymerizable monomers, and the like. Among these, a hydride of a ring-opening polymer of a monomer containing a norbornene structure is particularly preferable from the viewpoint of transparency. The alicyclic structure-containing polymer can be selected from polymers disclosed in JP-A-2002-321302, for example.

The range of the weight average molecular weight Mw of the polymer contained in the resin forming the base film is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100, 000 or less, more preferably 80,000 or less, and particularly preferably 50,000 or less. When the weight average molecular weight Mw is within the above range, the mechanical strength and moldability of the base film are highly balanced.

The molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of the polymer contained in the resin forming the base film is preferably 1.2 or more, more preferably 1.5 or more, and particularly preferably It is 1.8 or more, preferably 3.5 or less, more preferably 3.0 or less, and particularly preferably 2.7 or less. When the molecular weight distribution is at least the lower limit of the above range, the productivity of the polymer can be enhanced and the production cost can be suppressed. Further, when the molecular weight distribution is equal to or less than the upper limit, the amount of low-molecular-weight components is small, so relaxation during high-temperature exposure can be suppressed, and the stability of the base film can be enhanced.

The proportion of the polymer in the resin forming the base film is preferably 50% to 100% by weight, more preferably 70% to 100% by weight, and particularly preferably 90% to 100% by weight. When the proportion of the polymer is within the above range, the base film may have high heat resistance and transparency.

The resin forming the base film may further contain optional components in combination with the polymer. Optional components include, for example, the same examples as optional components that the optical film may contain. One type of optional component may be used alone, or two or more types may be used in combination.

The glass transition temperature Tg of the resin forming the base film is preferably 110° C. or higher, more preferably 115° C. or higher, particularly preferably 120° C. or higher, preferably 180° C. or lower, more preferably 170° C. or lower, especially Preferably, it may be 160° C. or less. The glass transition temperature of the resin can be measured by the same method as the glass transition temperature of the polymer.

The substrate film preferably has an in-plane retardation suitable for the use of the multilayer film.
For example, the base film may have small in-plane retardation. As a specific example, the in-plane retardation Re of the substrate film at a measurement wavelength of 550 nm may be, for example, 10 nm or less, 7 nm or less, 5 nm or less, or 0 nm. A substrate film having such a small in-plane retardation can be an optically isotropic film in the in-plane direction.

Further, for example, the in-plane retardation Re of the substrate film at a measurement wavelength of 550 nm is preferably 80 nm or more, more preferably 100 nm, particularly preferably 110 nm or more, preferably 170 nm or less, more preferably 150 nm or less, and particularly preferably can be 140 nm or less. A base film having an in-plane retardation in such a range can function as a λ/4 plate.

Furthermore, for example, the in-plane retardation Re of the substrate film at a measurement wavelength of 550 nm is preferably 220 nm or more, more preferably 240 nm, particularly preferably 250 nm or more, preferably 310 nm or less, more preferably 290 nm or less, and particularly preferably can be 280 nm or less. A base film having an in-plane retardation in such a range can function as a λ/2 plate.

The in-plane retardation of the base film and the in-plane retardation of the optical film may be the same or different. When the in-plane retardation of the base film and the in-plane retardation of the optical film are different, the difference between them may be within a specific range. For example, the difference between the in-plane retardation of the base film and the optical film may be preferably 100 nm or more, more preferably 110 nm or more, and preferably 180 nm or less, more preferably 160 nm or less. At this time, the in-plane retardation of the base film may be larger than the in-plane retardation of the optical film, or the in-plane retardation of the base film may be smaller than the in-plane retardation of the optical film.

The base film may have a slow axis. There is no particular limitation on the direction of the slow axis of the substrate film. For example, the slow axis of the base film may be substantially perpendicular to the slow axis of the optical film. The slow axis of the base film and the slow axis of the optical film being “substantially perpendicular” means that the angle formed by the slow axis of the base film and the slow axis of the optical film is close to 90°. represents Specifically, the angle formed by the slow axis of the base film and the slow axis of the optical film is preferably 85° or more, more preferably 87° or more, still more preferably 88° or more, and particularly preferably 89°. ° or more, preferably 95° or less, more preferably 93° or less, still more preferably 92° or less, particularly preferably 91° or less.

There are no particular restrictions on the thickness of the base film. The specific thickness range of the base film is preferably 0.5 µm or more, more preferably 1 µm or more, particularly preferably 5 µm or more, and preferably 100 µm or less, more preferably 70 µm or less, and particularly preferably 50 µm or less. be.

The multilayer film may, if necessary, have any layers other than the base film and the optical film. Examples of optional layers include any layer having optical isotropy. Any layer having this optical isotropy can generally have an in-plane retardation of 10 nm or less at a measurement wavelength of 550 nm. The optional optically isotropic layer includes, for example, a protective film layer for protecting the substrate film and the optical film; an adhesive layer for bonding each layer such as the substrate film and the optical film; and the like. Another example of the arbitrary layer is an arbitrary layer having optical anisotropy. The optical properties of the optional layers having this optical anisotropy are preferably set so that the multilayer film as a whole has the desired retardation. As a specific example, a combination of any layer having optical anisotropy and one or both of the base film and the optical film can function as a λ/4 plate or a λ/2 plate. Optical properties of the layer may be set.

The multilayer film preferably has an in-plane retardation suitable for its application.
For example, the range of in-plane retardation Re of the multilayer film at a measurement wavelength of 550 nm is preferably 100 nm or more, more preferably 115 nm or more, particularly preferably 125 nm or more, and preferably 180 nm or less, more preferably 160 nm or less. , particularly preferably 150 nm or less. A multilayer film having an in-plane retardation Re within such a range can function as a λ/4 plate. A multilayer film having an in-plane retardation in such a range can be obtained, for example, by appropriately adjusting the in-plane retardation and slow axis direction of the base film and the in-plane retardation and slow axis direction of the optical film. can be obtained by

In-plane retardation Re (450), Re (550) and Re (650) of the multilayer film at measurement wavelengths of 450 nm, 550 nm and 650 nm preferably satisfy the relationship Re (450) < Re (550). More preferably, the relationship (450)<Re(550)<Re(650) is satisfied. A multilayer film having in-plane retardations Re(450), Re(550) and Re(650) satisfying such a relationship can exhibit reverse wavelength dispersion. Specifically, the multilayer film can generally have a larger in-plane retardation as the measurement wavelength is longer. Therefore, this multilayer film can function as a broadband wavelength plate capable of uniformly converting the polarization state of light passing through the multilayer film in a wide wavelength range. A multilayer film having in-plane retardations Re(450), Re(550) and Re(650) that satisfy such a relationship is, for example, the in-plane retardation and slow axis direction of the base film and the optical film. It can be obtained by appropriately adjusting the in-plane retardation and slow axis direction.

The total light transmittance of the multilayer film is preferably 80% or higher, more preferably 85% or higher, and particularly preferably 90% or higher.
The haze of the multilayer film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%.
The multilayer film may be a sheet film or a long film.

There are no particular restrictions on the thickness of the multilayer film. The specific thickness of the multilayer film is preferably 5 µm or more, more preferably 10 µm or more, particularly preferably 15 µm or more, and preferably 150 µm or less, more preferably 120 µm or less, and particularly preferably 80 µm or less.

<7. Method for producing multilayer film>
The method for producing the multilayer film is not particularly limited. The multilayer film may be produced, for example, by a method including a step of preparing a base film, a step of preparing an optical film, and a step of laminating the base film and the optical film. Also, the multilayer film may be produced by a method including, for example, a step of co-extrusion of the resin forming the base film and the specific resin forming the optical film. From the viewpoint of manufacturing a multilayer film with high productivity, the multilayer film is preferably manufactured by a manufacturing method including applying a coating liquid containing a specific copolymer onto a substrate film. This preferred manufacturing method will be described below.

A method for manufacturing a multilayer film according to a preferred example includes applying a coating liquid containing a specific copolymer onto a base film. The base film can be produced, for example, by a melt molding method or a solution casting method. Among them, the melt molding method is preferable. Among the melt molding methods, extrusion molding, inflation molding and press molding are preferred, and extrusion molding is particularly preferred. The substrate film thus produced can be an optically isotropic film having an in-plane retardation of usually 10 nm or less at a measurement wavelength of 550 nm. A coating liquid may be applied to an optically isotropic base film. Further, if necessary, the substrate film may be stretched before the application of the coating liquid to develop in-plane retardation in the substrate film.

After preparing the base film, a coating liquid containing the specific copolymer is applied onto the base film. A coating liquid is a liquid composition containing a specific copolymer, and may contain a specific copolymer and a solvent. Moreover, the coating liquid may contain any component in combination with the specific copolymer and the solvent. As the solvent, those capable of dissolving or dispersing the specific copolymer are preferred, and those capable of dissolving the specific copolymer are particularly preferred. Moreover, a solvent may be used individually by 1 type, and may be used in combination of 2 or more types. The concentration of the specific copolymer in the coating liquid is preferably adjusted so that the viscosity of the coating liquid is within a range suitable for coating, and may be, for example, 1 wt % to 50 wt %.

There are no restrictions on the coating method of the coating liquid. Examples of coating methods include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, and die coating. method, gap coating method, and dipping method.

By applying the coating liquid, a layer of the coating liquid is formed on the base film. Therefore, by drying the coating liquid to remove the solvent as necessary, an optical film containing the specific copolymer is formed on the substrate film, and a multilayer film can be obtained. The drying method is not particularly limited, and drying methods such as heat drying and reduced pressure drying can be used.

The method for producing a multilayer film may include stretching the multilayer film, if necessary. In the following description, the multilayer film before being stretched may be referred to as "pre-stretching multilayer film", and the multilayer film after being stretched may be referred to as "multilayer stretched film". Stretching may be performed only once, or may be performed twice or more.

The stretch ratio of the multilayer film before stretching can be set according to the optical properties that the multilayer stretched film is desired to exhibit. The range of the specific stretch ratio of the multilayer film before stretching is preferably 1.05 times or more, more preferably 1.1 times or more, still more preferably 1.2 times or more, and particularly preferably 1.3 times or more. It is preferably 3.0 times or less, more preferably 2.5 times or less, and still more preferably 2.0 times or less. When stretching is performed twice or more, it is preferable that the stretching ratio of each stretching is within the above range. Moreover, when extending|stretching twice or more, the draw ratio of each time of extending|stretching may be the same, and may differ.

The stretching temperature of the multilayer film before stretching can be set according to the optical properties that the multilayer stretched film is desired to exhibit. The specific stretching temperature range of the multilayer film before stretching is preferably Tg(low)-5°C or higher, more preferably Tg(low)-3°C or higher, and particularly preferably Tg(low)-1°C or higher. It is preferably Tg(high)+20° C. or less, more preferably Tg(high)+15° C. or less, and particularly preferably Tg(high)+12° C. or less. Here, Tg (low) represents the lower one of the glass transition temperature of the resin forming the base film and the glass transition temperature of the specific resin forming the optical film, and Tg (high) is the base film. and the glass transition temperature of the specific resin forming the optical film, whichever is higher. When stretching is performed twice or more, the stretching temperature for each stretching may be the same or different.

The stretching direction of the multilayer film before stretching can be set according to the optical properties that the multilayer stretched film is desired to exhibit. The stretching may be uniaxial stretching in which the film is stretched in only one direction, or may be biaxial stretching in which the film is stretched in two directions. Furthermore, when stretching is performed twice or more, the stretching direction of each stretching may be the same or different. For example, after uniaxially stretching in a certain first stretching direction, uniaxially stretching may be carried out in a second stretching direction substantially perpendicular to the first stretching direction. Specifically, the range of the angle formed by the first stretching direction and the second stretching direction is preferably 85° or more, more preferably 87° or more, still more preferably 88° or more, and particularly preferably 89° or more. preferably 95° or less, more preferably 93° or less, still more preferably 92° or less, and particularly preferably 91° or less.

According to the manufacturing method including stretching the multilayer film before stretching, birefringence can be expressed in one or both of the base film and the optical film by stretching. Therefore, a multilayer stretched film having desired optical properties can be obtained.

The method for producing a multilayer film may further include optional steps in combination with the steps described above. For example, when a long multilayer film is obtained, the method for manufacturing the multilayer film may include a trimming step of cutting the obtained multilayer film into a desired shape. According to the trimming process, a sheet-fed multilayer film having a desired shape can be obtained. Moreover, the method for producing a multilayer film may include, for example, a step of providing a protective layer on the multilayer film.

<8. Polarizing plate>
A polarizing plate according to one embodiment of the present invention includes the multilayer film and the polarizing film according to the above-described embodiments.

A film that can function as a linear polarizer can be used as the polarizing film. Examples of polarizing films include 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; films obtained by stretching and further modifying some of the polyvinyl alcohol units in the molecular chain to polyvinylene units; Among these, a film containing polyvinyl alcohol is preferable as the polarizing film.

When natural light is incident on a polarizing film, normally only one polarized light is transmitted. Although the degree of polarization of this polarizing film is not particularly limited, it is preferably 98% or more, more preferably 99% or more. Further, the thickness of the polarizing film is preferably 5 μm to 80 μm.

The polarizing plate preferably functions as a circularly polarizing plate. In this case, the multilayer film preferably has an in-plane retardation that can function as a λ/4 plate. Moreover, it is preferable that the angle formed by the polarization transmission axis of the polarizing film and the slow axis of one or both of the substrate film and the optical film is within a specific range close to 45°. Specifically, the angle is preferably 40° or more, more preferably 42° or more, still more preferably 43° or more, particularly preferably 44° or more, preferably 50° or less, more preferably 48°. Below, more preferably 47° or less, particularly preferably 46° or less. When a polarizing plate that can function as a circularly polarizing plate is provided on the display surface of the image display device, reflection of external light can be suppressed.

The polarizing plate may comprise a polarizing film, a base film and an optical film in this order. Also, the polarizing plate may comprise a polarizing film, an optical film and a substrate film in this order. A specific order can be set according to the in-plane retardation of the substrate film and the optical film.

The polarizing plate described above can further include any layer. Optional layers include, for example, a polarizer protective film layer; an adhesive layer for laminating a polarizing film and a multilayer film; a hard coat layer such as an impact-resistant polymethacrylate resin layer; antireflection layer; antifouling layer; antistatic layer; As for these optional layers, only one layer may be provided, or two or more layers may be provided.

<9. Image display device>
The optical film described above can be provided in an image display device. For example, a polarizing plate having an optical film may be prepared and provided in the image display device. A preferred example is an organic EL image display device (organic electroluminescence display device) having a polarizing plate that can function as a circularly polarizing plate. This organic EL image display device includes a circularly polarizing plate and an organic electroluminescence element (hereinafter sometimes referred to as an "organic EL element" as appropriate). This organic EL image display device usually comprises a polarizing film, a multilayer film and an organic EL element in this order.

An organic EL element usually comprises a transparent electrode layer, a light-emitting layer and an electrode layer in this order, and the light-emitting layer can emit light when a voltage is applied from the transparent electrode layer and the electrode layer. Examples of materials constituting the organic light-emitting layer include polyparaphenylenevinylene-based, polyfluorene-based, and polyvinylcarbazole-based materials. Further, the light-emitting layer may have a laminate of layers emitting light of different colors, or a mixed layer in which a certain dye layer is doped with a different dye. Furthermore, the organic EL element may have functional layers such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, an equipotential surface formation layer, and a charge generation layer.

The organic EL image display device can suppress reflection of external light on the display surface. Specifically, only a portion of linearly polarized light of the light incident from the outside of the device passes through the polarizing film, and then passes through the multilayer film to become circularly polarized light. Circularly polarized light is reflected by light-reflecting components (reflecting electrodes in organic EL elements, etc.) in the image display device, and passes through the multilayer film again, resulting in vibration perpendicular to the direction of vibration of the incident linearly polarized light. It becomes linearly polarized light with a direction and does not pass through the polarizing film. Here, the vibration direction of the linearly polarized light means the vibration direction of the electric field of the linearly polarized light. This achieves the antireflection function.

EXAMPLES 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 can be arbitrarily modified without departing from the scope of the claims and their equivalents.
In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. Further, the operations described below were carried out under normal temperature (23° C.), normal pressure (1 atm) conditions in the atmosphere, unless otherwise specified.

<Method for measuring molecular weight of polymer>
The weight average molecular weights of the polymers produced in Examples and Comparative Examples described later were measured in terms of polystyrene using a high-speed GPC apparatus "HLC-8420GPC" manufactured by Tosoh Corporation.

<Method for measuring glass transition temperature of polymer>
The glass transition temperatures Tg of the polymers produced in Examples and Comparative Examples described later were measured at a heating rate of 10°C/min using a differential scanning calorimeter (“DSC7000X” manufactured by Hitachi High-Tech Science).

<Method for measuring retardation expression>
A sheet having a thickness of 100 μm was produced by pressing 1 g of the polymer produced in Examples and Comparative Examples described later under conditions of 250° C., 5 MPa, and 1 minute using a press.

The obtained sheet was cut into a rectangular pre-stretched film with a size of 50 mm x 100 mm. The unstretched film was subjected to free width uniaxial stretching. Stretching was performed using a tensile tester with a constant temperature bath manufactured by INSTRON. The stretching conditions were a stretching temperature of Tg+10° C., a stretching ratio of 1.5 times, and a stretching rate of 33% per minute. As a result, a retardation film was obtained as an optical film.

The obtained retardation film was measured for in-plane retardation Re at a wavelength of 550 nm using a retardation meter ("AxoScan" manufactured by Axometrics). The obtained in-plane retardation Re was divided by the film thickness d to obtain Re/d.

<Method for measuring film thickness>
The thickness d of the film was measured with a film thickness measuring device (Mitutoyo "snap gauge").

<Method for measuring delamination resistance>
A substrate film (a glass transition temperature of 160° C., a thickness of 100 μm, an unstretched film manufactured by Nippon Zeon Co., Ltd.) made of a resin containing a norbornene-based polymer was prepared. One side of this base film was subjected to corona treatment.

Corona treatment was applied to one side of the retardation film obtained in the above <Method for measuring retardation expression>. An adhesive was applied to the corona-treated surface of the retardation film and the corona-treated surface of the base film, and the adhesive-attached surfaces were bonded together to cure the adhesive. An ultraviolet curable adhesive was used as the adhesive. A sample film having a layer structure of retardation film/adhesive layer/base film was obtained by the lamination.

A sample piece was obtained by cutting the sample film into a width of 15 mm. The retardation film side of the sample piece was attached to the surface of a slide glass via an adhesive (double-sided adhesive tape "CS9621" manufactured by Nitto Denko Corporation).

A 90-degree peel test was performed by sandwiching the base film between the tip of the force gauge and pulling it in the direction normal to the surface of the slide glass. At this time, since the force measured when the base film was peeled off was the force required to separate the retardation film and the base film, the magnitude of this force was measured as the peel strength.

Generally, the higher the peel strength, the better the delamination resistance. The higher the peel strength, the more the retardation film is prevented from being damaged when the film is reapplied, which means that the reworkability is excellent. Therefore, when the peel strength was 5.0 N or more, the delamination resistance was determined as "excellent". Moreover, when the peel strength was 2.0 N or more and less than 5.0 N, the delamination resistance was determined to be "good". Moreover, when the peel strength was 1.0 N or more and less than 2.0 N, the delamination resistance was determined to be "good". Furthermore, when the peel strength was less than 1.0 N, the delamination resistance was determined as "improper".

Further, in each of the examples and comparative examples, when the surface of the retardation film after peeling was observed, it was confirmed that the surface layer of the retardation film had undergone cohesive failure and the surface had become rough. Therefore, in all Examples and Comparative Examples, it was confirmed that delamination of the retardation film occurred instead of peeling at the interface between the base film and the adhesive or the interface between the adhesive and the retardation film. was done.

<Example 1>
1.5 g of methyl acrylate, 28.5 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container and purged with nitrogen. After that, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 110,000. Further, the glass transition temperature of the polymer measured by a differential scanning calorimeter was 138°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 14.89×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Method for measuring delamination resistance> above, the result was "good".

<Example 2>
3.0 g of methyl acrylate, 27.0 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 109,000. The glass transition temperature of the polymer measured by a differential scanning calorimeter was 135°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 14.74×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Method for measuring delamination resistance> above, the result was "good".

<Example 3>
6.0 g of methyl acrylate, 24.0 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 119,000. Moreover, the glass transition temperature of the polymer measured by a differential scanning calorimeter was 124°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 14.66×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Delamination resistance measuring method> above, the result was "good".

<Example 4>
9.0 g of methyl acrylate, 21.0 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 10 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 250,000. Further, the glass transition temperature of the polymer measured by a differential scanning calorimeter was 117°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 13.75×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Delamination resistance measuring method> above, the result was "good".

<Example 5>
9.0 g of methyl acrylate, 21.0 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 97,000. Further, the glass transition temperature of the polymer measured by a differential scanning calorimeter was 117°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 13.55×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Delamination resistance measuring method> above, the result was "good".

<Example 6>
9.0 g of acrylic acid, 21.0 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 20 mg of AIBN (azobisisobutyronitrile) was added and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 126,000. Further, the glass transition temperature of the polymer measured by a differential scanning calorimeter was 179°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 13.63×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Method for measuring delamination resistance> above, the result was "excellent".

[Example 7]
(First step: preparation of base film)
As a resin having a positive intrinsic birefringence value, a resin containing a pellet-shaped norbornene-based polymer (hereinafter referred to as norbornene-based resin, manufactured by Nippon Zeon Co., Ltd.; glass transition temperature 126 ° C.) is prepared and dried at 100 ° C. for 5 hours. bottom. A dried norbornene-based resin was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded into a sheet from a T-die onto a casting drum. The sheet-shaped extruded norbornene-based resin was cooled to obtain a long unstretched film having a thickness of 60 μm as a base film. Thickness and optical properties were measured on the unstretched film. The obtained unstretched film was wound up on a roll and collected.

The polymer prepared in Example 1 was mixed with 1,3-dioxolane and dissolved to obtain a resin solution as a coating liquid. The resin concentration of this resin solution was 15% by weight.

(Coating process)
An unstretched film as a base film was pulled out from the roll, and the resin solution was applied onto the unstretched film.

(Drying process)
Thereafter, the coated resin solution was rapidly dried at 120° C. to form a layer (thickness: 30 μm) of the polymer prepared in Example 1 as an optical film on the unstretched film as the base film. As a result, a multilayer film including an unstretched film as a base film and a layer of the polymer prepared in Example 1 as an optical film was obtained.

(Third step: stretching of multilayer film)
The resulting multi-layer film was cut to obtain a rectangular pre-stretched multi-layer film having a size of 50 mm×100 mm. Free width uniaxial stretching was applied to the multilayer film before stretching. Stretching was performed using a tensile tester with a constant temperature bath manufactured by INSTRON. The stretching conditions were a stretching temperature of Tg+10° C., a stretching ratio of 1.5 times, and a stretching rate of 33% per minute. As a result, a multilayer stretched film including a stretched base film and a stretched retardation film as an optical film was obtained.

The retardation film was peeled off from the multilayer stretched film. This retardation film was a monolayer film of the polymer prepared in Example 1. This retardation film was measured for in-plane retardation at a wavelength of 550 nm using a retardation meter (“AxoScan” manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d. Re/d was 14.85×10 ⁻³ .

Further, the same as <Method for measuring delamination resistance> except that the retardation film produced in Example 7 was used instead of the retardation film obtained in <Method for measuring retardation expression>. When the delamination resistance was evaluated by the method, the result was "good".

[Example 8]
(First step: preparation of base film)
As a resin having a positive intrinsic birefringence value, a norbornene-based resin containing a pellet-shaped norbornene-based polymer (manufactured by Zeon Corporation; glass transition temperature 126° C.) was prepared and dried at 100° C. for 5 hours. A dried norbornene-based resin was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded into a sheet from a T-die onto a casting drum. The sheet-shaped extruded norbornene-based resin was cooled to obtain a long unstretched film having a thickness of 60 μm as a base film. Thickness and optical properties were measured on the unstretched film. The obtained unstretched film was wound up on a roll and collected.

The polymer prepared in Example 2 was mixed with 1,3-dioxolane and dissolved to obtain a resin solution as a coating liquid. The resin concentration of this resin solution was 15% by weight.

(Drying process)
Thereafter, the coated resin solution was rapidly dried at 120° C. to form a layer (thickness: 30 μm) of the polymer prepared in Example 2 as an optical film on the unstretched film as the base film. As a result, a multilayer film including an unstretched film as a base film and a layer of the polymer prepared in Example 2 as an optical film was obtained.

The retardation film was peeled off from the multilayer stretched film. This retardation film was a monolayer film of the polymer prepared in Example 2. This retardation film was measured for in-plane retardation at a wavelength of 550 nm using a retardation meter (“AxoScan” manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d. Re/d was 14.85×10 ⁻³ .

Further, the same as <Method for measuring delamination resistance> except that the retardation film produced in Example 8 was used instead of the retardation film obtained in <Method for measuring retardation expression>. When the delamination resistance was evaluated by the method, the result was "good".

<Comparative Example 1>
After 500 ml of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were put into a pressure-resistant reactor that was dried and purged with nitrogen, 35 g of 2-vinylnaphthalene was added and reacted at 25° C. for 1 hour. As a result, a reactant containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction was poured into a large amount of 2-propanol to precipitate poly(2-vinylnaphthalene) and separated. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC was 250,000. The glass transition temperature of poly(2-vinylnaphthalene) measured by a differential scanning calorimeter was 142.degree.

A retardation film was produced from the obtained poly(2-vinylnaphthalene) by the method described in <Method for measuring retardation expression> above, and the retardation was measured. Re/d was 15.04×10. ^-3 . Moreover, when the delamination resistance was evaluated by the method described in <Method for measuring delamination resistance> above, the result was "impossible".

<Comparative Example 2>
After 500 ml of toluene as a solvent and 0.60 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that was dried and purged with nitrogen, 35 g of 2-vinylnaphthalene was added and reacted at 25° C. for 1 hour. As a result, a reactant containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction was poured into a large amount of 2-propanol to precipitate poly(2-vinylnaphthalene) and separated. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC was 100,000. The glass transition temperature of poly(2-vinylnaphthalene) measured by a differential scanning calorimeter was 142.degree.

<Comparative Example 3>
0.6 g of methyl acrylate, 29.4 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 112,000. Moreover, the glass transition temperature of the polymer measured by a differential scanning calorimeter was 140°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 15.11×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Method for measuring delamination resistance> above, the result was "impossible".

<Comparative Example 4>
15 g of methyl acrylate, 15 g of vinylnaphthalene, and 6.0 g of tetrahydrofuran were placed in a pressure-resistant container, and nitrogen substitution was performed. After that, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was carried out at 60° C. for 24 hours. The reaction was poured into a large amount of 2-propanol to precipitate the polymer and collected. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 115,000. The glass transition temperature of the polymer measured by a differential scanning calorimeter was 100°C.

A retardation film was produced from the obtained polymer by the method described in <Method for measuring retardation expression> above, and the retardation was measured to find that Re/d was 9.02×10 ⁻³ . . Moreover, when the delamination resistance was evaluated by the method described in <Delamination resistance measuring method> above, the result was "good".

[Comparative Example 5]
(First step: preparation of base film)
As a resin having a positive intrinsic birefringence value, a norbornene-based resin containing a pellet-shaped norbornene-based polymer (manufactured by Zeon Corporation; glass transition temperature 126° C.) was prepared and dried at 100° C. for 5 hours. A dried norbornene-based resin was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded into a sheet from a T-die onto a casting drum. The sheet-shaped extruded norbornene-based resin was cooled to obtain a long unstretched film having a thickness of 60 μm as a base film. Thickness and optical properties were measured on the unstretched film. The obtained unstretched film was wound up on a roll and collected.

The poly(2-vinylnaphthalene) prepared in Comparative Example 2 was mixed with 1,3-dioxolane and dissolved to obtain a resin solution. The resin concentration of this resin solution was 15% by weight.

(Drying process)
Thereafter, the coated resin solution was rapidly dried at 120° C., and a layer of poly(2-vinylnaphthalene) prepared in Comparative Example 2 (thickness: 30 μm) was formed as an optical film on the unstretched film as the base film. ) was formed. As a result, a multilayer film including an unstretched film as a base film and a layer of poly(2-vinylnaphthalene) synthesized in Comparative Example 2 as an optical film was obtained.

The retardation film was peeled off from the multilayer stretched film. This retardation film was a monolayer film of poly(2-vinylnaphthalene) prepared in Comparative Example 2. This retardation film was measured for in-plane retardation at a wavelength of 550 nm using a retardation meter (“AxoScan” manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d. Re/d was 15.05×10 ⁻³ .

In addition, the same as <Method for measuring delamination resistance> except that the retardation film produced in Comparative Example 2 was used instead of the retardation film obtained in <Method for measuring retardation expression>. Method to evaluate the delamination resistance, the result was "fail".

<Results>
The results of the examples and comparative examples described above are shown in the table below. In the table below, the numerical values in the Re expression column represent the magnitude of the Re/d value of each example or comparative example when the Re/d value of Comparative Example 1 is taken as 100%. In the table below, abbreviations have the following meanings.
AA: acrylic acid.
MA: methyl acrylate.
VN: vinyl naphthalene.
Mw: Weight average molecular weight.
Tg: glass transition temperature.
Re/d: Ratio of in-plane retardation Re and thickness d at a measurement wavelength of 550 nm.

<Consideration>
From the results of Comparative Examples 1 and 2, it was confirmed that an optical film formed of a homopolymer of a polycyclic aromatic vinyl compound such as polyvinyl naphthalene is inferior in delamination resistance.
Further, from the results of Comparative Example 3, it was confirmed that the copolymer containing 2% by weight of the (meth)acrylic compound unit did not show any improvement in delamination resistance.
Furthermore, from the results of Comparative Example 4, it was confirmed that the copolymer containing 50% by weight of (meth)acrylic compound units was inferior in retardation development.
On the other hand, in Examples 1 to 6, since an appropriate amount of (meth)acrylic compound units are combined with polycyclic aromatic vinyl compound units, both retardation development and delamination resistance are excellent. In particular, Example 6 is particularly excellent in delamination resistance. It is considered that the particularly excellent delamination resistance of Example 6 was obtained because the (meth)acrylic compound unit had a carboxyl group derived from acrylic acid.

Also, in Examples 7 and 8 and Comparative Example 5, a pre-stretched multilayer film comprising a base film and an optical film was produced, and the pre-stretched multilayer film was stretched. By stretching the multilayer film before stretching, the base film and the optical film are co-stretched, so that a retardation film is obtained as a stretched optical film. From the results of Examples 7 and 8 and Comparative Example 5, even when a retardation film is produced by co-stretching the base film and the optical film, the same letter as the retardation film obtained by stretching the optical film alone It was found that a retardation film having resistance to delamination and delamination can be obtained as an optical film.

In the above Examples and Comparative Examples, the proportions of polycyclic aromatic vinyl compound units and (meth)acrylic compound units contained in the produced polymers were measured by ¹ H-NMR. From the above measurements, it was confirmed that the charging ratio of the polycyclic aromatic vinyl compound as a monomer and the ratio of the polycyclic aromatic vinyl compound unit contained in the polymer matched. It was also confirmed by the above measurement that the charging ratio of the (meth)acrylic compound as a monomer and the proportion of (meth)acrylic compound units contained in the polymer were consistent.

Claims

Including a copolymer containing polycyclic aromatic vinyl compound units and (meth) acrylic compound units,
The optical film, wherein the proportion of the (meth)acrylic compound unit in the copolymer is 5% by weight or more and 40% by weight or less.
The optical film according to claim 1, wherein the copolymer has a weight average molecular weight Mw of 50,000 to 500,000.
The optical film according to claim 1, wherein the copolymer contains a repeating unit having a structure formed by polymerizing vinyl naphthalene.
The optical film according to claim 1, wherein the copolymer has a glass transition temperature of 110°C or higher.
2. The optical film according to claim 1, wherein a ratio Re/d between an in-plane retardation Re and a thickness d of the optical film at a measurement wavelength of 550 nm is 10.0×10 −3 or more.
A multilayer film comprising a substrate film and the optical film according to claim 1.
The multilayer film according to claim 6, wherein the base film contains an alicyclic structure-containing polymer.
A method for producing a multilayer film comprising a substrate film and an optical film, comprising:
Coating a coating liquid containing a copolymer on the base film,
The copolymer contains polycyclic aromatic vinyl compound units and (meth)acrylic compound units,
A method for producing a multilayer film, wherein the amount of the (meth)acrylic compound unit in the copolymer is 5% by weight or more and 40% by weight or less.
A polarizing plate comprising the multilayer film according to claim 6 or 7 and a polarizing film.