KR20210004981A - Broadband wavelength film and its manufacturing method, and manufacturing method of circular polarizing film - Google Patents

Abstract

A first step of preparing the layer (A) as a resin film having a slow axis; A second step of forming a layer (B) of a resin having a positive intrinsic birefringence on the layer (A) to obtain a multilayer film; A third step of stretching the multilayer film in a direction not perpendicular and not parallel to the slow axis of the layer (A) to obtain a long broadband wavelength film having a λ/2 layer and a λ/4 layer; in this order And the λ/2 layer and the λ/4 layer of the broadband wavelength film satisfy Formula (1).
θ(λ/4) = {45° + 2 × θ(λ/2)} ± 5° (1)
(θ(λ/2) represents the angle formed by the slow axis of the λ/2 layer with respect to the length direction of the broadband wavelength film, and θ(λ/4) is the ground level of the λ/4 layer with respect to the length direction of the broadband wavelength film. It represents the angle formed by the axis.)

Description

Broadband wavelength film and its manufacturing method, and manufacturing method of circular polarizing film

The present invention relates to a broadband wavelength film, a manufacturing method thereof, and a manufacturing method of a circular polarizing film.

Various studies have been made in the past about a method of manufacturing an optical film including two or more layers (see Patent Documents 1 to 3).

International Publication No. 2016/047465 International Publication No. 2009/031433 Japanese Patent Application Publication No. 2009-237534

As a broadband wavelength film capable of functioning as a wavelength plate in a wide wavelength band, a film including a λ/2 plate and a λ/4 plate in combination is known. Conventionally, such a broadband wavelength film is a process of stretching a certain film to obtain a λ/2 plate, a process of stretching another film to obtain a λ/4 plate, and bonding these λ/2 and λ/4 plates to obtain a broadband It was common to manufacture by a manufacturing method including a process of obtaining a wavelength film.

Further, a technique for obtaining a circularly polarizing film is known by combining the above broadband wavelength film with a linearly polarizing film as a film capable of functioning as a linearly polarizing plate. In general, a long linear polarizing film has an absorption axis in the longitudinal direction or the width direction. Therefore, in the case of obtaining a circular polarizing film by combining a long linear polarizing film with a broad-band wavelength film, the slow axis of the λ/2 plate is required to be in an oblique direction not parallel to the longitudinal direction but not perpendicular to the longitudinal direction.

In order to easily manufacture a desired λ/2 plate having a slow axis in the oblique direction as described above, the applicant has developed a technique for performing stretching two or more times as described in Patent Document 1. Then, in the entire manufacturing method of a broadband wavelength film, one or more stretching to obtain a λ/4 plate and two or more stretching to obtain a λ/2 plate are performed, so that the total number of stretching is 3 or more. . However, when the number of times of stretching was 3 or more, the operation was complicated.

The present invention is invented in view of the above problems, and a broadband wavelength film that can be efficiently manufactured with a small number of steps, and a manufacturing method thereof; And, it is an object to provide a circular polarizing film manufacturing method including the manufacturing method of the broadband wavelength film.

In order to solve the above problems, the present inventors have studied intensively. As a result, the present inventor has a first step of preparing a layer (A) as a resin film having a slow axis in the plane; A second step of forming a layer (B) of a resin having a positive intrinsic birefringence on the layer (A) to obtain a multilayer film; A third step of stretching the multilayer film in a direction not perpendicular and not parallel to the slow axis of the layer (A) to obtain a long broadband wavelength film having a λ/2 layer and a λ/4 layer; in this order According to the included manufacturing method, it was found out that a broadband wavelength film can be efficiently produced with a small number of steps, and the present invention was completed.

That is, the present invention includes the following.

[1] a first step of preparing a layer (A) as a resin film having a slow axis in the plane;

A second step of forming a layer (B) of a resin having a positive intrinsic birefringence on the layer (A) to obtain a multilayer film;

A third step of stretching the multilayer film in a direction not perpendicular and not parallel to the slow axis of the layer (A) to obtain a long broadband wavelength film including a λ/2 layer and a λ/4 layer; Include in order,

The λ/2 layer and the λ/4 layer of the broadband wavelength film satisfy the following formula (1).

θ(λ/4) = {45° + 2 × θ(λ/2)} ± 5° (1)

(In the above formula (1),

θ(λ/2) represents an angle formed by the slow axis of the λ/2 layer with respect to the length direction of the broadband wavelength film,

θ (λ/4) represents an angle formed by the slow axis of the λ/4 layer with respect to the length direction of the broadband wavelength film.)

[2] The method for producing a broadband wavelength film according to [1], wherein the layer (A) prepared in the first step is a long resin film having a slow axis that is not perpendicular to the length direction of the layer (A). .

[3] The production of the broadband wavelength film according to [1] or [2], wherein the third step includes stretching the multilayer film in a direction forming an angle of 45° or more with respect to the longitudinal direction of the multilayer film. Way.

[4] The method for producing a broadband wavelength film according to any one of [1] to [3], wherein the angle θ (λ/2) is in the range of 20° ± 10°.

[5] The method for producing a broadband wavelength film according to any one of [1] to [4], wherein the angle θ (λ/4) is in the range of 85° ± 20°.

[6] The method for producing a broadband wavelength film according to any one of [1] to [5], wherein the λ/2 layer is a layer obtained by stretching the layer (A).

[7] The method for producing a broadband wavelength film according to any one of [1] to [6], wherein the λ/4 layer is a layer obtained by stretching the layer (B).

[8] a step of producing a broadband wavelength film by the production method according to any one of [1] to [7];

The manufacturing method of a circular polarizing film containing; the process of bonding the said broadband wavelength film and a long linear polarizing film.

[9] The method for producing a circularly polarizing film according to [8], wherein the linearly polarizing film has an absorption axis in the longitudinal direction of the linearly polarizing film.

[10] As a long broadband wavelength film,

Λ/2 layer having a slow axis forming an angle of 20° ± 10° with respect to the length direction of the broadband wavelength film,

A long-length broadband wavelength film comprising a λ/4 layer having a slow axis forming an angle of 85° ± 20° with respect to the length direction of the broadband wavelength film.

According to the present invention, a broadband wavelength film that can be efficiently manufactured with a small number of steps and a manufacturing method thereof; And, a manufacturing method of a circular polarizing film including the manufacturing method of the broadband wavelength film; can be provided.

1 is a perspective view schematically showing a layer (A) as a resin film prepared in a first step of a method for producing a broadband wavelength film according to an embodiment of the present invention.
2 is a perspective view schematically showing a multilayer film obtained in a second step of a method for producing a broadband wavelength film according to an embodiment of the present invention.
3 is a perspective view schematically showing a broadband wavelength film obtained in a third step of the method for manufacturing a broadband wavelength film according to an embodiment of the present invention.

Hereinafter, the present invention is 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 carried out with arbitrary changes within the scope not departing from the claims of the present invention and their equivalent ranges.

In the following description, the term "long" film refers to a film having a length of 5 times or more with respect to the width, preferably has a length of 10 times or more, and specifically, the degree to which it is wound in rolls and stored or transported. Refers to a film having a length of. The upper limit of the length of the film is not particularly limited, and may be, for example, 100,000 times or less with respect to the width.

In the following description, the slow axis of a film or layer refers to a slow axis in the plane of the film or layer unless otherwise stated.

In the following description, the orientation angle of the film or layer represents an angle formed by the slow axis of the film or layer with respect to the longitudinal direction of the film or layer, unless otherwise noted.

In the following description, the angle formed by the optical axis (ground axis, transmission axis, absorption axis, etc.) of each layer in a member having a plurality of layers, unless otherwise noted, refers to the above layer in the thickness direction. Shows the angle when viewed.

In the following description, the angle of the direction of the optical axis (ground axis, transmission axis, absorption axis, etc.) and geometrical direction (length direction and width direction of the film, etc.) in the plane of a product (wideband wavelength film, circular polarizing film, etc.) Unless otherwise noted, the relationship is defined as a positive shift in one direction and a negative shift in the other direction, and the positive and negative directions are commonly defined in the components in the product. For example, in a broadband wavelength film, ``the angle formed by the slow axis of the λ/2 layer with respect to the length direction of the broadband wavelength film is 20°, and the slow axis of the λ/4 layer with respect to the length direction of the broadband wavelength film That the angle formed by this is 85° indicates the following two cases:

When the broadband wavelength film is observed from either surface, the slow axis of the λ/2 layer is shifted by 20° clockwise from the longitudinal direction of the broadband wavelength film, and the slow axis of the λ/4 layer is , Shifted by 85° clockwise from the longitudinal direction of the broadband wavelength film.

When the broadband wavelength film is observed from either side, the slow axis of the λ/2 layer is shifted by 20° counterclockwise from the longitudinal direction of the broadband wavelength film, and the slow axis of the λ/4 layer It is shifted by 85 degrees counterclockwise from the longitudinal direction of this broadband wavelength film.

In the following description, the oblique direction of a long film is an in-plane direction of the film, unless otherwise stated, and indicates a direction that is neither parallel nor perpendicular to the longitudinal direction of the film.

In the following description, the front direction of any film means the normal direction of the main surface of the film, unless otherwise stated, and specifically refers to the direction of the declination angle 0° and the azimuth angle 0° of the main surface.

In the following description, the inclination direction of a film means a direction that is neither parallel nor perpendicular to the main surface of the film unless otherwise stated, and specifically, a range in which the declination angle of the main surface is greater than 0° and less than 90°. Points in the direction of

In the following description, a material having a positive intrinsic birefringence means a material in which the refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to it, unless otherwise stated. In addition, a material having a negative intrinsic birefringence means a material in which the refractive index in the stretching direction becomes smaller than the refractive index in the direction perpendicular to it, unless otherwise stated. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

In the following description, "(meth)acryl" includes "acrylic", "methacryl", and combinations thereof.

In the following description, the in-plane retardation Re of the layer is a value represented by Re = (nx-ny) x d unless otherwise noted. In addition, the retardation Rth in the thickness direction of the layer is a value represented by Rth = [{(nx + ny)/2}-nz] x d unless otherwise stated. In addition, the NZ coefficient of a layer is a value represented by (nx-nz)/(nx-ny) unless otherwise stated. Here, nx represents the refractive index in the direction in which the maximum refractive index is applied as a direction (in-plane direction) perpendicular to the thickness direction of the layer. ny represents the refractive index in a direction orthogonal to the direction of nx as the in-plane direction of the layer. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. The measurement wavelength is 590 nm unless otherwise stated.

In the following description, the directions of elements are "parallel", "vertical", and "orthogonal" unless otherwise stated, within a range that does not impair the effects of the present invention, for example ± 3°, ± 2 An error within the range of °, or ±1° may be included.

[One. summary]

1 is a perspective view schematically showing a layer (A) 100 as a resin film prepared in a first step of a method for manufacturing a broadband wavelength film according to an embodiment of the present invention. In addition, FIG. 2 is a perspective view schematically showing a multilayer film 200 obtained in a second step of a method for manufacturing a broadband wavelength film according to an embodiment of the present invention. In addition, FIG. 3 is a perspective view schematically showing a broadband wavelength film 300 obtained in a third step of a method for manufacturing a broadband wavelength film according to an embodiment of the present invention.

The manufacturing method of the broadband wavelength film 300 according to an embodiment of the present invention,

(1) As shown in Fig. 1, a first step of preparing a layer (A) 100 as a resin film having a slow axis A _{100 in the} plane;

(2) a second step of forming a layer (B) 210 of a resin having a positive intrinsic birefringence on the layer (A) 100 to obtain the multilayer film 200 shown in FIG. 2;

(3) a third step of stretching the multilayer film 200 to obtain a long broadband wavelength film 300 shown in FIG. 3;

Are included in this order.

As shown in Fig. 1, the layer (A) 100 prepared in the first step has a slow axis A _{100 in} its plane. In the second process, a layer (B) 210 is formed on the layer (A) 100, and as shown in FIG. 2, a multilayer including the layer (A) 100 and the layer (B) 210 After obtaining the film 200, the multilayer film 200 is stretched in a third process. This stretching is performed in an in-plane direction that is not perpendicular and not parallel to the slow axis A ₁₀₀ of the layer A so that a λ/2 layer and a λ/4 layer having a slow axis in a desired direction are obtained.

By stretching in the third step, air-performance stretching in which the layer (A) 100 and the layer (B) 210 are simultaneously stretched is performed. Therefore, as shown in FIG. 3, in the layer (A) 100, adjustment of the direction of the slow axis A ₁₀₀ and adjustment of the optical characteristics are performed. On the other hand, a slow axis (A ₂₁₀ ) appears on the layer (B) 210, and optical properties are expressed. The layer (A) 100 after stretching functions as one of the λ/2 layer and the λ/4 layer, and the layer (B) 210 after stretching functions as the other of the λ/2 layer and the λ/4 layer. Therefore, by the above manufacturing method, a broadband wavelength film 300 including a λ/2 layer and a λ/4 layer is obtained. 3 shows an example in which the layer (A) 100 after stretching functions as a λ/2 layer, and the layer (B) 210 after stretching functions as a λ/4 layer. The configuration is not limited to this example.

The λ/2 layer and the λ/4 layer satisfy the following formula (1).

θ(λ/4) = {45° + 2 × θ(λ/2)} ± 5° (1)

Equation (1) indicates that θ(λ/4) is "{45° + 2 × θ(λ/2)}-5°" or more "{45° + 2 × θ(λ/2)} + 5°" It shows what is in the following range. In equation (1), θ (λ/2) represents an angle formed by the slow axis A ₁₀₀ of the λ/2 layer with respect to the longitudinal direction A ₃₀₀ of the broadband wavelength film 300. Further, θ (λ/4) represents an angle formed by the slow axis A ₂₁₀ of the λ/4 layer with respect to the length direction A ₃₀₀ of the broadband wavelength film 300. By including a combination of a λ/2 layer and a λ/4 layer that satisfies this equation (1), the broadband wavelength film 300 is approximately 1/ of the wavelength of the light to the light passing through the film in a wide wavelength range. It can function as a broadband wavelength film capable of imparting 4-wavelength in-plane retardation.

Usually, the longitudinal direction A ₃₀₀ of the broadband wavelength film 300, the longitudinal direction of the λ/4 layer (not shown), and the longitudinal direction of the λ/2 layer (not shown) coincide. Therefore, the angle θ (λ/2) represents the orientation angle formed by the slow axis A ₁₀₀ of the λ/2 layer with respect to the length direction of the λ/2 layer, and thus, hereinafter, “the orientation angle θ (λ/2 )”. In addition, since the angle θ (λ/4) represents the orientation angle formed by the slow axis A ₂₁₀ of the λ/4 layer in the longitudinal direction of the λ/4 layer, hereinafter, “orientation angle θ (λ/4 )”.

[2. 1st process]

In the first step, the layer (A) as a resin film having a slow axis in the plane is prepared. From the viewpoint of obtaining a long broadband wavelength film, a long resin film is usually used as the layer (A). As the layer (A), a resin film having a multilayer structure including two or more layers may be used. Usually, a resin film having a single layer structure including only one layer is used.

As the resin forming the resin film, a thermoplastic resin containing a polymer and further containing an optional component can be used as necessary. In particular, as the resin contained in the layer (A), a resin having a negative intrinsic birefringence may be used, but it is preferable to use a resin having a positive intrinsic birefringence since the production of a broadband wavelength film can be carried out particularly easily. Do.

The resin having a positive intrinsic birefringence usually contains a polymer having a positive intrinsic birefringence. Examples of polymers having a positive intrinsic birefringence include polyolefins such as polyethylene and polypropylene; Polyesters such as polyethylene terephthalate and polybutylene terephthalate; Polyarylene sulfide such as polyphenylene sulfide; Polyvinyl alcohol; Polycarbonate; Polyarylate; Cellulose ester polymer, polyethersulfone; Polysulfone; Polyarylsulfone; Polyvinyl chloride; Cyclic olefin polymers such as norbornene polymers; A rod-shaped liquid crystal polymer, etc. are mentioned. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. In addition, the polymer may be a homopolymer or a copolymer. Among these, polycarbonate polymers are preferred from the viewpoints of excellent retardation expression properties and low-temperature stretchability. Further, from the viewpoint of excellent mechanical properties, heat resistance, transparency, low hygroscopicity, dimensional stability, and light weight, a cyclic olefin polymer is preferred.

The proportion of the polymer in the resin contained in the layer (A) is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, particularly preferably 90% by weight to 100% by weight to be. When the proportion of the polymer is in the above range, sufficient heat resistance and transparency can be obtained for the layer (A) and the broadband wavelength film.

The resin contained in the layer (A) may further contain arbitrary components other than the polymer in combination with the polymer. As an arbitrary component, for example, coloring agents, such as a pigment and a dye; Plasticizer; Optical brightener; Dispersant; Heat stabilizer; Light stabilizers; Ultraviolet absorbers; Antistatic agent; Antioxidants; Particulates; Surfactant etc. are mentioned. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The glass transition temperature TgA of the resin contained in the layer (A) is preferably 100°C or higher, more preferably 110°C or higher, particularly preferably 120°C or higher, preferably 190°C or lower, and more preferably It is 180°C or less, particularly preferably 170°C or less. When the glass transition temperature of the resin contained in the layer (A) is greater than or equal to the lower limit of the above range, the durability of the layer (λ/2 layer or λ/4 layer) obtained by stretching the layer (A) in a high-temperature environment can be improved. Further, when the glass transition temperature of the resin contained in the layer (A) is equal to or less than the upper limit of the above range, the stretching treatment can be easily performed.

The direction of the slow axis of the layer (A) prepared in the first step can be arbitrarily set within a range in which a desired broadband wavelength film is obtained. For example, when the intrinsic birefringence of the resin contained in the layer (A) is positive, the slow axis of the layer (A) is usually close to the stretching direction of the multilayer film due to the stretching of the multilayer film in the third step. Change to lose. In addition, for example, when the intrinsic birefringence of the resin contained in the layer (A) is negative, the slow axis of the layer (A) is usually the stretching direction of the multilayer film by stretching of the multilayer film in the third step. It changes to get closer to the direction perpendicular to and. Therefore, the direction of the slow axis of the layer (A) prepared in the first step can be set according to the stretching direction of the multilayer film in the third step.

It is preferable that the slow axis of the layer (A) prepared in the first step is not perpendicular to the longitudinal direction of the layer (A), and more preferably has a relationship parallel to or close to the longitudinal direction of the layer (A). Therefore, the orientation angle formed by the slow axis of the layer (A) with respect to the length direction of the layer (A) is preferably greater than -87°, more preferably -45° or more, even more preferably -30° It is more, particularly preferably -15° or more, preferably less than 87°, more preferably 45° or less, still more preferably 30° or less, and particularly preferably 15° or less. When the layer (A) having such a slow axis is used, a broadband wavelength film having desirable optical properties can be easily obtained.

Optical properties such as retardation and NZ coefficient of the layer (A) prepared in the first step can be set according to the optical properties of the layer obtained by stretching the layer (A).

For example, in the case of stretching the layer (A) to obtain a λ/2 layer, the in-plane retardation of the layer (A) is preferably 200 nm or more, more preferably 250 nm or more, particularly preferably 300 nm or more. And, preferably 500 nm or less, more preferably 450 nm or less, and particularly preferably 400 nm or less. In addition, the NZ coefficient of the layer (A) is preferably 1.00 or more, preferably 1.20 or less, more preferably 1.15 or less, particularly preferably 1.10 or less.

The thickness of the layer (A) prepared in the first step can be arbitrarily set within a range in which a desired broadband wavelength film is obtained. The specific thickness of the layer (A) is preferably 20 μm or more, more preferably 25 μm or more, particularly preferably 30 μm or more, preferably 100 μm or less, more preferably 95 μm or less, particularly preferably 90 μm or less. . When the thickness of the layer (A) is within the above range, a λ/2 layer or a λ/4 layer having desired optical properties can be easily obtained by stretching in the third step.

The layer (A) can be obtained by a production method including stretching an appropriate resin film to express a slow axis in the resin film. In the following description, the resin film before the stretching treatment is performed is referred to as "pre-stretching film", and the resin film obtained after stretching is sometimes referred to as "stretched film".

The film before stretching can be produced, for example, by a melt molding method or a solution casting method. More specific examples of the melt molding method include an extrusion molding method, a press molding method, an inflation molding method, an injection molding method, a blow molding method, and a stretch molding method. Among these methods, in order to obtain a layer (A) having excellent mechanical strength and surface accuracy, an extrusion molding method, an inflation molding method, or a press molding method is preferable, and among them, the extrusion molding method from the viewpoint of being able to easily produce the layer (A) with high efficiency. This is particularly preferred. Moreover, it is preferable to obtain the film before extending|stretching as a long film.

After preparing the pre-stretching film, the pre-stretching film is stretched to obtain a layer (A) as a stretched film.

The slow axis of the layer (A) is usually expressed by stretching the film before stretching. Therefore, it is preferable to set the stretching direction of the film before stretching according to the direction of the slow axis of the layer (A). For example, if the film before stretching is formed of a resin having a positive intrinsic birefringence, the stretching direction of the film before stretching is set to be parallel to the slow axis of the layer (A) to be prepared in the first step. desirable. In addition, for example, if the film before stretching is formed of a resin having a negative intrinsic birefringence, the stretching direction of the film before stretching is set to a direction perpendicular to the slow axis of the layer (A) to be prepared in the first step. It is desirable to do.

In addition, it is preferable that the stretching direction of the film before stretching is not perpendicular to the longitudinal direction of the film before stretching. Therefore, it is preferable that the extending direction of the film before extending|stretching is in the longitudinal direction or the oblique direction of the said pre-stretching film. By using a stretched film obtained by a production method including stretching in such a longitudinal direction or an oblique direction as the layer (A), a broadband wavelength film having desirable optical properties can be easily obtained.

The draw ratio of the film before stretching is preferably 1.1 times or more, more preferably 1.2 times or more, preferably 4.0 times or less, and more preferably 3.0 times or less. When the draw ratio is more than the lower limit of the above range, the refractive index in the stretching direction can be increased. In addition, when the draw ratio is less than or equal to the upper limit of the above range, the direction of the slow axis of the layer obtained by stretching the layer (A) can be easily controlled.

The stretching temperature of the film before stretching is preferably TgA or higher, more preferably "TgA + 2°C" or higher, particularly preferably "TgA + 5°C" or higher, and preferably "TgA + 40°C" or lower, More preferably, it is "TgA + 35 degreeC" or less, Most preferably, it is "TgA + 30 degreeC" or less. Here, TgA refers to the glass transition temperature of the resin contained in the layer (A). When the stretching temperature is in the above range, the molecules contained in the film before stretching can be reliably oriented, so that the layer (A) having desired optical properties can be easily obtained.

Stretching in the first step may be performed as free uniaxial stretching. Free uniaxial stretching refers to stretching in one direction, and in which a binding force is not applied to a direction other than the stretching direction. Therefore, for example, free uniaxial stretching in the longitudinal direction of the film before stretching refers to stretching in the longitudinal direction performed without restraining the end of the film in the width direction before stretching.

The above-described stretching can usually be performed using an appropriate stretching machine such as a roll stretching machine and a tenter stretching machine while continuously conveying the film before stretching in the longitudinal direction. For example, in the case of stretching the film before stretching in the longitudinal direction of the film before stretching, it is preferable to use a roll stretching machine. Free uniaxial stretching can be easily performed by the roll stretching machine. As these stretching groups, those described in Patent Document 1 can be used, for example.

[3. 4th process]

The manufacturing method of a broadband wavelength film may include a step of forming a thin film layer on the layer (A) as necessary after preparing the layer (A) in the first step. By forming an appropriate thin film layer, the thin film layer functions as an easily adhesive layer, and the binding force between the layer (A) and the layer (B) can be enhanced. In addition, it is preferable that the thin film layer has solvent resistance. Such a thin film layer is usually formed of a resin.

As a material of the thin film layer, an acrylic resin, a urethane resin, an acrylic urethane resin, an ester resin, an ethyleneimine resin, etc. are mentioned, for example. Acrylic resin is a resin containing an acrylic polymer. In addition, the urethane resin is a resin containing polyurethane. Polymers such as acrylic polymers and polyurethanes usually have high binding strength to a wide variety of resins, so that the bonding strength between the layer (A) and the layer (B) can be increased. In addition, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Resin as the material of the thin film layer is combined with a polymer, such as heat-resistant stabilizer, weather stabilizer, leveling agent, antistatic agent, slip agent, anti-blocking agent, anti-fogging agent, lubricant, dye, pigment, natural oil, synthetic oil, wax, particle, etc. Arbitrary components may be included. An arbitrary component may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The glass transition temperature of the resin as a material of the thin film layer is preferably lower than the glass transition temperature TgA of the resin contained in the layer (A) and the glass transition temperature TgB of the resin in which the intrinsic birefringence contained in the layer (B) is positive. In particular, the difference between the glass transition temperature of the resin as a material for the thin film layer and the lower one of the glass transition temperatures TgA and TgB is preferably 5°C or higher, more preferably 10°C or higher, and particularly preferably 20°C or higher. Thereby, since it is possible to suppress the occurrence of retardation in the thin film layer due to stretching in the third step, the thin film layer in a broadband wavelength film can have optical isotropy. Therefore, it is possible to facilitate adjustment of the optical properties of the broadband wavelength film.

The thin film layer can be formed, for example, by a method including coating a coating liquid containing a resin and a solvent as a material of the thin film layer on the layer (A). As the solvent, water may be used or an organic solvent may be used. As the organic solvent, for example, the same solvents that can be used for forming the layer (B) described later are mentioned. In addition, a solvent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Moreover, the said coating liquid may contain a crosslinking agent. By using a crosslinking agent, the mechanical strength of the thin film layer can be increased, or the binding properties of the thin film layer to the layers (A) and (B) can be improved. As a crosslinking agent, an epoxy compound, an amino compound, an isocyanate compound, a carbodiimide compound, an oxazoline compound, etc. can be used, for example. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The amount of the crosslinking agent is preferably 1 part by weight or more, more preferably 5 parts by weight or more, preferably 70 parts by weight or less, more preferably 65 parts by weight or less, based on 100 parts by weight of the polymer in the coating liquid.

The coating method of the coating liquid includes, for example, a method similar to the coating method that can be used for forming the layer (B) described later.

A thin film layer can be formed by applying a coating liquid on the layer (A). If necessary, the thin film layer may be subjected to a curing treatment such as drying and crosslinking. As a drying method, heat drying using an oven is mentioned, for example. In addition, as a crosslinking method, methods, such as heat treatment and irradiation treatment with active energy rays, such as ultraviolet rays, are mentioned, for example.

[4. 2nd process]

After the layer (A) is prepared in the first step and a thin film layer is formed as necessary, a second step of forming a layer (B) of a resin having a positive intrinsic birefringence to obtain a multilayer film is performed. In this second step, the layer (B) is formed directly on the layer (A) or indirectly via an arbitrary layer such as a thin film layer. Here, "direct" means that there is no arbitrary layer between the layer (A) and the layer (B).

As the resin having a positive intrinsic birefringence forming the layer (B), an arbitrary resin can be selected and used from the range of resins having a positive intrinsic birefringence described as the material of the layer (A) in the first step. In addition, the resin contained in the layer (B) and the resin contained in the layer (A) may be the same or different.

The glass transition temperature TgB of the resin with positive intrinsic birefringence contained in the layer (B) is preferably 100°C or higher, more preferably 110°C or higher, particularly preferably 120°C or higher, and preferably 190°C or lower. , More preferably 180°C or less, particularly preferably 170°C or less. When the glass transition temperature of the resin contained in the layer (B) is equal to or higher than the lower limit of the above range, the durability of the layer (λ/2 layer or λ/4 layer) obtained by stretching the layer (B) in a high-temperature environment can be improved. In addition, when the glass transition temperature of the resin contained in the layer (B) is equal to or less than the upper limit of the above range, the stretching treatment can be easily performed.

From the viewpoint of adjusting the optical properties of both the layer (A) and the layer (B) to an appropriate range by stretching in the third step, the glass transition temperature TgA and the layer (B) of the resin contained in the layer (A) It is preferable that the glass transition temperature TgB of the resin contained in is close. Specifically, the absolute value |TgA-TgB| of the difference between the glass transition temperature TgA and the glass transition temperature TgB is preferably 20°C or less, more preferably 15°C or less, and particularly preferably 10°C or less.

Layer (B) may have in-plane retardation and slow axis. When the layer (B) has an in-plane retardation and a slow axis, the in-plane retardation and a slow axis direction of the layer (B) are adjusted by stretching in the third step. However, setting of the stretching conditions for performing such adjustment tends to be complicated. Therefore, from the viewpoint of easily obtaining desired optical properties and slow axis direction in the layer (B) after stretching in the third step, the layer (B) formed in the second step does not have in-plane retardation and slow axis, or Even if it has, it is preferable that the in-plane retardation is small. Specifically, the in-plane retardation of the layer (B) is preferably 0 nm to 20 nm, more preferably 0 nm to 15 nm, and particularly preferably 0 nm to 10 nm.

The thickness of the layer (B) formed in the second step can be arbitrarily set within a range in which a desired broadband wavelength film is obtained. The specific thickness of the layer (B) is preferably 3 μm or more, more preferably 4 μm or more, particularly preferably 5 μm or more, preferably 30 μm or less, more preferably 25 μm or less, particularly preferably 20 μm or less. . When the thickness of the layer (B) is in the above range, a λ/2 layer or a λ/4 layer having desired optical properties can be easily obtained by stretching.

There is no particular limitation on the method of forming the layer (B), and, for example, a forming method such as a coating method, an extrusion method, or a bonding method can be used.

In the case of forming the layer (B) by the coating method, the second step includes coating a composition containing a resin having a positive intrinsic birefringence on the layer (A). The above composition is usually a liquid composition further containing a solvent in combination with a resin having a positive intrinsic birefringence. As a solvent, for example, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, 3-methyl-2-butanone, methyl isobutyl ketone, tetrahydrofuran, cyclopentyl methyl ether, acetylacetone, cyclohexanone, 2-methylcyclohexanone, 1,3-dioxolane, 1,4-dioxane, 2-pentanone, N,N-dimethylformamide, etc. are mentioned. In addition, a solvent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The solvent may cause phenomena such as dissolution and orientation relaxation in the layer (A), but in general, the coating thickness of the liquid composition is thin, and since it dries quickly after coating, the degree of the above phenomenon is negligible. Small enough to be possible.

As a coating method of the above composition, for example, curtain coating method, extrusion coating method, roll coating method, spin coating method, dip coating method, bar coating method, spray coating method, slide coating method, printing coating method, gravure A coating method, a die coating method, a gap coating method, and a dipping method.

In addition, in the coating method, after coating the composition on the layer (A), the second process includes drying the coated composition as necessary. The solvent is removed by drying, and a layer (B) of a resin having a positive intrinsic birefringence can be formed on the layer (A). Drying can be performed by drying methods, such as natural drying, heat drying, vacuum drying, and vacuum heating drying, for example.

When forming the layer (B) by the extrusion method, the second step includes extruding a resin having a positive intrinsic birefringence on the layer (A). The extrusion of the resin is usually performed in a state in which the resin is melted. In addition, the resin is usually extruded into a film using a die. When the extruded resin having positive intrinsic birefringence is attached to the layer (A) or the thin film layer, a layer (B) of a resin having a positive intrinsic birefringence can be formed on the layer (A). In addition, in the case of forming the layer (B) by the extrusion method, the second step generally includes cooling and curing a resin having positive intrinsic birefringence, which is extruded and adhered to the layer (A).

When forming a layer (B) by a bonding method, the 2nd process includes bonding a film of a resin with a positive intrinsic birefringence to the layer (A). Examples of the method for producing a resin film having a positive intrinsic birefringence include melt molding methods such as extrusion molding, inflation molding, and press molding; The solution casting method; is mentioned. In addition, an adhesive or a pressure-sensitive adhesive may be used as necessary for bonding the film of the resin having a positive intrinsic birefringence and the layer (A).

Among the methods for forming the layer (B) described above, a coating method is preferable. For example, in the case of using a bonding method, when a layer (B) is formed on an appropriate support film and the layer (B) is bonded to the layer (A), the layer (A) is suppressed while the breakage of the layer (B) is suppressed. It is possible to form a layer (B) on top. However, compared to the bonding method in which a number of steps such as formation of the layer (B) on the support film and transfer of the layer (B) from the support film to the layer (A) are performed, the coating method is the formation of the layer (B). It can reduce the number of processes required for Further, according to the coating method, an adhesive and an adhesive are not required. In addition, in the coating method, it is easier to reduce the thickness of the layer (B) itself than the extrusion method. Therefore, from the viewpoint of obtaining a thin broadband wavelength film with a small number of steps, it is preferable to form the layer (B) by a coating method.

[5. 3rd process]

After obtaining the multilayer film including the layer (A) and the layer (B) in the second process, the multilayer film is stretched to perform a third process of obtaining a long broadband wavelength film. By stretching in the third step, the direction of the slow axis of the layer (A) is adjusted, and the optical properties of the layer (A) are adjusted, so that one of the λ/2 layer and the λ/4 layer is obtained. Further, by stretching in the third step, a slow axis appears in the layer (B), and optical properties are expressed in the layer (B), so that the other of the λ/2 layer and the λ/4 layer is obtained.

Stretching in the third step is performed in a direction that is not perpendicular and not parallel to the slow axis of the layer (A) included in the multilayer film. Thereby, in general, retardation can be expressed in the layer (B), and the slow axis of the layer (A) can be controlled in an arbitrary direction to obtain the angular relationship of the above formula (1).

The specific stretching direction is set so as to obtain a desired broadband wavelength film among the in-plane directions of the multilayer film.

For example, when the layer (A) is a layer of a resin having a positive intrinsic birefringence, the direction of the slow axis of the layer (A) changes so as to be closer to the stretching direction by stretching in the third step. In addition, for example, when the layer (A) is a layer of a resin whose intrinsic birefringence is negative, the direction of the slow axis of the layer (A) is close to a direction perpendicular to the stretching direction by stretching in the third step. Change to lose. In this way, usually, the direction of the slow axis of the layer (A) changes by stretching in the third step. In addition, in the layer (B), a slow axis usually appears in a direction parallel to the stretching direction by stretching in the third step. Therefore, the stretching direction in the third step is a λ/2 layer having a slow axis in a desired direction by the change in the direction of the slow axis in the layer (A) as described above, and the expression of the slow axis in the layer (B). It is preferable to set so that a λ/4 layer is obtained.

The size of the specific angle (absolute value of the angle) formed by the stretching direction of the multilayer film in the third step and the slow axis of the layer (A) is preferably 50° or more, more preferably 60° or more, particularly It is preferably 70° or more, preferably 86° or less, and particularly preferably 85° or less. When the multilayer film is stretched in such a stretching direction, it becomes easy to adjust the slow axes of the λ/2 layer and the λ/4 layer so as to satisfy the relationship of equation (1).

Especially, the 3rd process preferably includes extending|stretching the multilayer film in the extending direction which makes up an angle of 45 degrees or more with respect to the longitudinal direction of the said multilayer film. More specifically, the angle formed by the stretching direction in the third step with respect to the longitudinal direction of the multilayer film is preferably 45° or more, more preferably 60° or more, particularly preferably 70° or more, and preferably Is 135° or less, more preferably 110° or less, and particularly preferably 100° or less. When the multilayer film is stretched in such a stretching direction, it is possible to easily control the directions of the slow axis of the λ/2 layer and the λ/4 layer.

The draw ratio in the third step is preferably 1.1 times or more, more preferably 1.15 times or more, particularly preferably 1.2 times or more, preferably 3.0 times or less, more preferably 2.5 times or less, particularly Preferably it is 2.2 times or less. When the draw ratio in the third step is more than the lower limit of the above range, the occurrence of wrinkles can be suppressed. Further, when the draw ratio in the third step is less than or equal to the upper limit of the above range, it is possible to easily control the directions of the slow axes of the λ/2 layer and the λ/4 layer.

The stretching temperature in the third step is the following condition (C1) with respect to the glass transition temperature TgA of the resin contained in the layer (A) and the glass transition temperature TgB of the resin in which the intrinsic birefringence contained in the layer (B) is positive. It is preferable to satisfy both of) and (C2).

(C1) The stretching temperature is preferably TgA-20°C or higher, more preferably TgA-10°C or higher, particularly preferably TgA-5°C or higher, preferably TgA + 30°C or lower, more preferably TgA + 25°C or less, particularly preferably TgA + 20°C or less.

(C2) The stretching temperature is preferably TgB-20°C or higher, more preferably TgB-10°C or higher, particularly preferably TgB-5°C or higher, preferably TgB + 30°C or lower, more preferably TgB + 25°C or less, particularly preferably TgB + 20°C or less.

By performing stretching at such a stretching temperature, the optical properties of the layer (A) can be appropriately adjusted, and the desired optical properties can be expressed in the layer (B). Thus, a broadband wavelength film having desired optical properties can be obtained.

The stretching in the above-described third step can be performed using an arbitrary stretching machine, and for example, it can be performed using a tenter stretching machine or a roll stretching machine. It is preferable to perform stretching using these drawing machines, conveying a long multilayer film continuously in the longitudinal direction.

[6. Arbitrary process]

The manufacturing method of the above-described broadband wavelength film may further include an arbitrary process in combination with the above-described process.

For example, the manufacturing method of a broadband wavelength film may include a process of forming a protective layer on the surface of a broadband wavelength film.

In addition, for example, in the manufacturing method of a broadband wavelength film, at an arbitrary point in time, surface treatments such as corona treatment and plasma treatment are performed on the surface of one or two or more of the layer (A), layer (B), and thin film layer. You may include the process to perform. Therefore, for example, after performing a surface treatment on the surface of the layer (A), a layer (B) or a thin film layer may be formed on the treated surface. Further, for example, after performing a surface treatment on the surface of the thin film layer, a layer (B) may be formed on the treated surface. By performing the surface treatment, it is possible to improve the binding property between the layers on the surface to which the surface treatment has been performed.

All of the above-described first to fourth steps and arbitrary steps can be performed while continuously conveying films such as a layer (A), a multilayer film, and a broadband wavelength film. The conveyance direction of conveyance of such a film is usually the longitudinal direction of the said film. Therefore, at the time of the above conveyance, the longitudinal direction and the width direction of the film generally coincide with the MD direction (Machine Direction) and the TD direction (Transverse Direction) of conveyance.

[7. Broadband wavelength film]

By the above-described manufacturing method, a co-ordinated film having a λ/2 layer and a λ/4 layer can be obtained. The λ/2 layer and the λ/4 layer of this co-ordinated film satisfy the above formula (1). The combination of the λ/2 layer and the λ/4 layer that satisfies the relationship represented by Equation (1) provides in-plane retardation of approximately 1/4 of the wavelength of the light to the light transmitted through the film in a wide wavelength range. It can function as a broadband wavelength film that can be imparted (see Japanese Laid-Open Patent Publication No. 2007-004120). Therefore, according to the above-described manufacturing method, a broadband wavelength film can be obtained as a co-ordinated film having a λ/2 layer and a λ/4 layer. From the viewpoint of realizing a broadband wavelength film capable of functioning in a wider wavelength range, it is preferable that the λ/2 layer and the λ/4 layer satisfy equation (2), and more preferably satisfy equation (3). Do. Equation (2) shows that θ(λ/4) is "{+45° + 2 × θ(λ/2)}-4°" or more "{+45° + 2 × θ(λ/2)} + 4 It shows that it is in the range below. In addition, Equation (3) indicates that θ(λ/4) is "{+45° + 2 × θ(λ/2)}-3°" or more "{+45° + 2 × θ(λ/2)} + 3°" or less.

θ(λ/4) = {+45° + 2 × θ(λ/2)} ± 5° (1)

θ(λ/4) = {+45° + 2 × θ(λ/2)} ± 4° (2)

θ(λ/4) = {+45° + 2 × θ(λ/2)} ± 3° (3)

In the above-described manufacturing method, stretching of the layer (A) and the layer (B) is not performed separately as in the prior art, but is performed together in the third step. Therefore, since the number of stretching treatments can be reduced compared to the prior art, the number of steps required for manufacturing a broadband wavelength film can be reduced, and thus, efficient manufacturing can be realized. In addition, in the above production method for obtaining a broadband wavelength film by co-stretching the layers (A) and (B) by stretching the multilayer film, the conventional method of bonding both after the production of each of the λ/2 layer and the λ/4 layer Like the manufacturing method, a shift in the slow axis direction due to bonding is not caused. Therefore, since it is easy to precisely control the direction of the slow axis of each of the λ/2 layer and the λ/4 layer, it is possible to easily obtain a high-quality broadband wavelength film capable of realizing a circular polarizing film capable of effective coloring suppression.

In the obtained broadband wavelength film, the λ/2 layer is a layer obtained by stretching one of the layers (A) and (B), and the λ/4 layer is the other of the layers (A) and (B) stretching. It is a layer that is obtained. Among them, the λ/2 layer is preferably a layer obtained by stretching the layer (A), and the λ/4 layer is preferably a layer obtained by stretching the layer (B) from the viewpoint of particularly easy production of a broadband wavelength film. It is preferably a layer. Accordingly, the λ/2 layer is preferably a layer made of the same resin as the layer (A), and the λ/4 layer is a layer made of the same resin as the layer (B).

The λ/2 layer is a layer having an in-plane retardation of usually 220 nm or more and usually 300 nm or less at a measurement wavelength of 590 nm. When the λ/2 layer has such in-plane retardation, a broadband wavelength film can be realized by combining the λ/2 layer and the λ/4 layer. Especially, from the viewpoint of obtaining a circularly polarizing film excellent in color suppression function in the oblique direction, the in-plane retardation of the λ/2 layer at a measurement wavelength of 590 nm is preferably 230 nm or more, more preferably 240 nm or more, It is preferably 280 nm or less, more preferably 270 nm or less.

The retardation in the thickness direction at a measurement wavelength of 590 nm of the λ/2 layer is preferably 130 nm or more, more preferably 140 nm or more, particularly preferably 150 nm or more, preferably 300 nm or less, more preferably 280 nm Hereinafter, it is particularly preferably 270 nm or less. When the retardation in the thickness direction of the λ/2 layer is in the above range, a circularly polarizing film having particularly excellent color suppression function in the oblique direction can be obtained.

The NZ coefficient of the λ/2 layer is preferably 1.0 or more, more preferably 1.05 or more, particularly preferably 1.10 or more, preferably 1.6 or less, more preferably 1.55 or less, particularly preferably 1.5 or less. . When the NZ coefficient of the λ/2 layer is in the above range, a circularly polarizing film having particularly excellent color suppression function in the oblique direction can be obtained. Further, the λ/2 layer having such an NZ coefficient can be easily manufactured.

Optical properties, such as retardation of the λ/2 layer and NZ coefficient, include, for example, retardation and thickness of the layer (A) prepared in the first step; And it can be adjusted according to; stretching conditions, such as a stretching temperature, a stretching ratio, and a stretching direction in a 3rd process.

The orientation angle θ (λ/2) of the λ/2 layer is preferably in the range of 20° ± 10° (that is, in the range of 10° to 30°), and in the range of 20° ± 8° (that is, 12 It is more preferably in the range of ° to 28 °), and particularly preferably in the range of 20 ° ± 5 ° (that is, in the range of 15 ° to 25 °). A general linear polarizing film has a transmission axis in its width direction and an absorption axis in its longitudinal direction. When the orientation angle θ (λ/2) of the λ/2 layer is in the above range, a circular polarizing film can be easily realized in combination with such a general linear polarizing film. In addition, when the orientation angle θ (λ/2) of the λ/2 layer is in the above range, the color suppression function in the front direction of the circular polarizing film obtained can be improved.

The orientation angle θ (λ/2) of the λ/2 layer is, for example, the direction of the slow axis of the layer A prepared in the first step; And it can adjust according to; extending|stretching conditions, such as an extending|stretching direction in 3rd process, and a draw ratio.

The thickness of the λ/2 layer is preferably 20 μm or more, more preferably 25 μm or more, still more preferably 30 μm or more, preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less. Thereby, the mechanical strength of the λ/2 layer can be increased.

The λ/4 layer is a layer having an in-plane retardation of usually 90 nm or more and usually 154 nm or less at a measurement wavelength of 590 nm. When the λ/4 layer has such in-plane retardation, a broadband wavelength film can be realized by combining the λ/2 layer and the λ/4 layer. Especially, from the viewpoint of obtaining a circularly polarizing film excellent in color suppression function in the oblique direction, the in-plane retardation of the λ/4 layer at a measurement wavelength of 590 nm is preferably 100 nm or more, more preferably 110 nm or more, It is preferably 140 nm or less, more preferably 130 nm or less.

The retardation in the thickness direction of the λ/4 layer at a measurement wavelength of 590 nm is preferably 50 nm or more, more preferably 60 nm or more, particularly preferably 70 nm or more, preferably 135 nm or less, more preferably 125 nm Hereinafter, it is particularly preferably 115 nm or less. When the retardation in the thickness direction of the λ/4 layer is in the above range, a circularly polarizing film having particularly excellent color suppression function in the oblique direction can be obtained.

The NZ coefficient of the λ/4 layer is preferably 1.0 or more, more preferably 1.05 or more, particularly preferably 1.10 or more, preferably 1.6 or less, more preferably 1.55 or less, particularly preferably 1.5 or less. . When the NZ coefficient of the λ/4 layer is in the above range, a circularly polarizing film having particularly excellent color suppression function in the oblique direction can be obtained. Further, the λ/4 layer having such an NZ coefficient can be easily manufactured.

Optical properties such as retardation and NZ coefficient of the λ/4 layer may be determined, for example, by the thickness of the layer (B) formed in the second step; And it can be adjusted according to; stretching conditions, such as a stretching temperature, a stretching ratio, and a stretching direction in a 3rd process.

The orientation angle θ (λ/4) of the λ/4 layer is preferably in the range of 85° ± 20° (that is, in the range of 65° to 105°), and in the range of 85° ± 15° (that is, 70 It is more preferably in the range of ° to 100 °), and particularly preferably in the range of 85 ° ± 10 ° (that is, in the range of 75 ° to 95 °). When the orientation angle θ (λ/4) of the λ/4 layer is in the above range, a circular polarizing film can be easily realized by combining with a general linear polarizing film having a transmission axis in the width direction and an absorption axis in the length direction. I can. In addition, when the orientation angle θ (λ/4) of the λ/4 layer is in the above range, the color suppression function in the front direction of the circular polarizing film obtained can be improved.

The direction of the slow axis of the λ/4 layer can be adjusted by, for example, the stretching direction in the third step.

The thickness of the λ/4 layer is preferably 3 μm or more, more preferably 4 μm or more, particularly preferably 5 μm or more, preferably 15 μm or less, more preferably 13 μm or less, and particularly preferably 10 μm or less. When the thickness of the λ/4 layer is more than the lower limit of the above range, desired optical properties can be easily obtained. In addition, when the thickness of the λ/4 layer is below the upper limit of the above range, the thickness of the broadband wavelength film can be reduced.

It is preferable that the λ/2 layer and the λ/4 layer are in direct contact with each other. Thereby, the thickness of the broadband wavelength film can be made thin.

When the manufacturing method of the broadband wavelength film includes a fourth step of forming a thin film layer, the broadband wavelength film includes a thin film layer between the λ/2 layer and the λ/4 layer. While the adhesive layer used in the conventional manufacturing method of bonding both after the manufacture of each of the λ/2 layer and the λ/4 layer is generally thicker than 5 μm, the thin film layer of the broadband wavelength film obtained in the above manufacturing method is thinner than that. can do. The specific thickness of the thin film layer is preferably less than 2.0 μm, more preferably less than 1.8 μm, and particularly preferably less than 1.5 μm. Since the thin film layer can be made thin in this way, it is possible to make the entire thickness of the broadband wavelength film thin. The lower limit of the thickness of the thin film layer is preferably thinner, and may be, for example, 0.1 μm.

The broadband wavelength film may be provided with an arbitrary layer in combination with a λ/2 layer, a λ/4 layer, and a thin film layer. For example, an adhesive layer or an adhesive layer for bonding the λ/2 layer and the λ/4 layer may be provided.

The total light transmittance of the broadband wavelength film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The light transmittance can be measured in the range of 400 nm to 700 nm in wavelength using a spectrophotometer in accordance with JIS K0115.

The haze of the broadband wavelength film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. Here, in accordance with JIS K7361-1997, the haze is measured at five locations using "Turbidity Meter NDH-300A" manufactured by Nippon Denshoku Industries, and the average value obtained therefrom can be adopted.

The thickness of the broadband wavelength film is preferably 20 μm or more, more preferably 25 μm or more, particularly preferably 30 μm or more, preferably 120 μm or less, more preferably 100 μm or less, and particularly preferably 90 μm or less. According to the above-described manufacturing method, it is possible to easily manufacture such a thin broadband wavelength film.

[8. Circular polarizing film]

Using the broadband wavelength film manufactured by the above-described manufacturing method, a long circular polarizing film can be manufactured. Such a circular polarizing film can be manufactured by a manufacturing method including a step of manufacturing a broadband wavelength film by the above-described manufacturing method, and a step of bonding the broadband wavelength film and a long linear polarizing film. The above-mentioned bonding is usually performed so that a linear polarizing film, a λ/2 layer, and a λ/4 layer are arranged in this order in the thickness direction. Moreover, you may use an adhesive layer or an adhesive layer for bonding as needed.

The linearly polarizing film is a long film having an absorption axis, and has a function of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and allowing other polarized light to transmit. Here, the vibration direction of linearly polarized light means the vibration direction of the electric field of linearly polarized light.

A linear polarizing film is usually provided with a polarizer layer, and is provided with a protective film layer for protecting a polarizer layer as needed.

As the polarizer layer, for example, a film made of an appropriate vinyl alcohol-based polymer may be subjected to an appropriate treatment in an appropriate order and manner. Examples of such vinyl alcohol-based polymers include polyvinyl alcohol and partially formalized polyvinyl alcohol. Examples of the treatment of the film include dyeing treatment, stretching treatment, and crosslinking treatment with dichroic substances such as iodine and dichroic dyes. Usually, in the extending|stretching process for manufacturing a polarizer layer, since the film before extending|stretching is extended in the longitudinal direction, in the obtained polarizer layer, the absorption axis parallel to the longitudinal direction of the said polarizer layer can be expressed. This polarizer layer is capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and in particular, it is preferable to have excellent polarization degree. The thickness of the polarizer layer is generally 5 μm to 80 μm, but is not limited thereto.

An arbitrary transparent film can be used as a protective film layer for protecting a polarizer layer. Among them, a resin film excellent in transparency, mechanical strength, thermal stability, moisture shielding property, and the like is preferable. Examples of such resins include acetate resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, cyclic olefin resins, and (meth)acrylic resins. I can. Among them, acetate resins, cyclic olefin resins, and (meth)acrylic resins are preferable because of their small birefringence, and cyclic olefin resins are particularly preferable from the viewpoints of transparency, low hygroscopicity, dimensional stability, and light weight.

The said linear polarizing film can be manufactured by bonding a long polarizer layer and a long protective film layer, for example. At the time of bonding, you may use an adhesive as needed.

The linear polarizing film preferably has an absorption axis in the longitudinal direction of the linear polarizing film. Such a linear polarizing film is a λ/2 layer having an orientation angle θ (λ/2) of 20° ± 10° (ie, 10° to 30°), and 85° ± 20° (ie, 65° to 105°) It is preferable to bond with a broadband wavelength film including a λ/4 layer having an orientation angle θ (λ/4) of) to produce a circular polarizing film. According to the bonding of the combination as described above, since it is possible to manufacture a circular polarizing film by bonding a long linear polarizing film and a long broadband wavelength film in parallel with their length directions, the circular polarizing film is manufactured by a roll-to-roll method. It becomes possible to do. Therefore, it is possible to increase the manufacturing efficiency of the circular polarizing film.

In the circularly polarized film thus obtained, linearly polarized light in a wide wavelength range that has passed through the linearly polarized film is converted into circularly polarized light by a broadband wavelength film. Therefore, the circularly polarized film has a function of absorbing one of the right circularly polarized light and the left circularly polarized light and transmitting the remaining light in a wide wavelength range.

The circularly polarizing film described above may further include an arbitrary layer in combination with a linear polarizing film and a broadband wavelength film.

For example, the circular polarizing film may be provided with a protective film layer for suppressing a flaw. Further, for example, the circular polarizing film may be provided with an adhesive layer or an adhesive layer in order to adhere a linear polarizing film and a broadband wavelength film.

When the circularly polarizing film is provided on a surface capable of reflecting light, reflection of external light can be effectively reduced. In particular, the circular polarizing film is useful in that it can effectively reduce reflection of external light in a wide wavelength range in the visible region. In addition, since reflection of external light can be effectively reduced in such a wide wavelength range, the circularly polarizing film can suppress coloration due to an increase in reflection intensity of light of a part of the wavelength. This circularly polarizing film can obtain the effect of suppressing the reflection and suppressing coloration described above at least in the front direction, and usually also in the oblique direction. In addition, the effect of suppressing reflection and suppressing coloring in the oblique direction can usually be obtained in all azimuth directions of the film main surface.

[9. Image display device]

By utilizing the function of suppressing reflection of external light as described above, the circular polarizing film can be used as a reflection suppressing film for an organic electroluminescent display device (hereinafter, it may be appropriately referred to as an "organic EL display device"). have.

The organic EL display device includes a circularly polarizing film piece obtained by cutting out from a long circularly polarizing film.

When the organic EL display device includes a circular polarizing film piece, usually, the organic EL display device includes a circular polarizing film piece on the display surface. By installing a circular polarizing film piece on the display surface of the organic EL display device so that the surface on the linear polarizing film side faces toward the viewer, light incident from the outside of the device is reflected in the device and emitted outside the device. And, as a result, it is possible to suppress glare of the display surface of the display device. Specifically, the light incident from the outside of the device becomes circularly polarized when only a part of the linearly polarized light passes through the linearly polarized film and then passes through the broadband wavelength film. Circularly polarized light is reflected by a component (reflective electrode, etc.) that reflects light in the display device and passes through a broadband wavelength film again, so that the direction of vibration (polarization axis) is perpendicular to the direction of vibration (polarization axis) of the incident linearly polarized light. ), and does not pass through the linearly polarized film. Thereby, a reflection suppression function is achieved. Further, since the above-described reflection suppression function is obtained in a wide wavelength range, coloration of the display surface can be suppressed.

Moreover, you may install the said circular polarizing film in a liquid crystal display device. Such a liquid crystal display device includes a circular polarizing film piece obtained by cutting out from a long circular polarizing film.

When the liquid crystal display device is provided with a circularly polarizing film piece and the surface of the linearly polarizing film side toward the viewing side, light incident from the outside of the device can be suppressed from being reflected in the device and emitted to the outside of the device. As a result, glare and coloring of the display surface of the display device can be suppressed.

In addition, when the liquid crystal display device includes a circularly polarized film piece, a broadband wavelength film, a linearly polarizing film, and a liquid crystal cell of the liquid crystal display device in this order from the viewing side, an image can be displayed in circularly polarized light. Therefore, it is possible to stably visually recognize the light emitted from the display surface with polarized sunglasses, and image visibility when wearing polarized sunglasses can be improved.

In addition, when a circularly polarizing film piece is provided in an image display device such as an organic EL display device and a liquid crystal display device so that the surface of the linearly polarizing film side faces toward the viewing side, warpage of the display panel can be suppressed. Hereinafter, this effect will be described.

BACKGROUND In general, an image display device includes a display panel including an organic electroluminescent element and a display element such as a liquid crystal cell. This display panel is provided with a substrate such as a glass substrate in order to increase the mechanical strength of the display panel. And in a display panel provided with a circularly polarizing film piece so that the surface on the linear polarizing film side faces toward the viewing side, a substrate, a broadband wavelength film, and a linearly polarizing film are usually provided in this order.

By the way, the polarizer layer of a linear polarizing film is generally easy to shrink in the in-plane direction in a high temperature environment. When the polarizer layer attempts to contract in this way, a stress to warp the display panel is generated in the display panel on which the linear polarizing film including the polarizer layer is installed. Since the warpage of the display panel may cause deterioration in image quality, it is desired to suppress it. As for this warpage, it has been found that the larger the distance between the polarizer layer and the substrate of the display panel, the larger the warpage tends to be.

In the broadband wavelength film manufactured by the conventional manufacturing method of bonding both after the manufacture of each of the λ/2 layer and the λ/4 layer, the adhesive layer was thick, so the entire broadband wavelength film was also thick. Accordingly, in the conventional broadband wavelength film, since the distance between the polarizer layer and the substrate of the display panel increases, the warpage of the display panel tends to increase.

On the other hand, as described above, in the broadband wavelength film manufactured as a co-ordinated film, the λ/2 layer and the λ/4 layer are in direct contact, or the thin film layer formed between the λ/2 layer and the λ/4 layer is thinned. I can. Therefore, since the entire broadband wavelength film can be made thin, the distance between the polarizer layer and the substrate of the display panel can be reduced. Therefore, it is possible to suppress the warpage of the display panel.

Example

Hereinafter, the present invention will be described in detail by showing examples. However, the present invention is not limited to the examples shown below, and can be carried out with arbitrary changes within the scope not departing from the claims of the present invention and its equivalent scope.

In the following description, "%" and "parts" indicating amounts are based on weight unless otherwise noted. In addition, the operation described below was performed under conditions of normal temperature and normal pressure, unless otherwise noted.

[Assessment Methods]

[Measurement method of optical properties of layer (A)]

The in-plane retardation Re, NZ coefficient, and orientation angle of the stretched film as the layer (A) obtained in the first step were measured using a retardation meter ("AxoScan" manufactured by Axometrics). The measurement wavelength was 590 nm.

[Measurement method of optical properties of each layer of a broadband wavelength film]

The broadband wavelength film to be evaluated was installed on a stage of a retardation meter ("AxoScan" manufactured by Axometrics). Then, the change of the polarization state before and after the polarization of the broadband wavelength film is transmitted through the broadband wavelength film was measured as the transmission polarization characteristic of the broadband wavelength film. This measurement was performed as a multidirectional measurement performed in a range of -55° to +55° of declination with respect to the main surface of the broadband wavelength film. In addition, the said multidirectional measurement was performed in each azimuth direction of 45 degrees, 90 degrees, 135 degrees, and 180 degrees, making any azimuth direction of the main surface of a broadband wavelength film 0 degrees. The measurement wavelength of the above measurement was 590 nm.

Next, from the transmitted polarization characteristics measured as described above, by performing fitting calculation, the in-plane retardation Re of each layer, the retardation Rth in the thickness direction, the NZ coefficient, and the orientation angle were obtained. The above fitting calculation was performed by setting the three-dimensional refractive index and orientation angle of each layer included in the broadband wavelength film as fitting parameters. In addition, for the above fitting calculation, the software attached to the phase difference meter (AxoScan) ("Multi-Layer Analysis" manufactured by Axometrics) was used.

[Calculation method of color difference ΔE*ab by simulation]

Using the "LCD Master" manufactured by Shintech Co. as software for simulation, the circularly polarizing films produced in each of the Examples and Comparative Examples were modeled, and the color difference ΔE*ab was calculated with the following settings.

In the model for simulation, a structure in which a circular polarizing film was attached to the reflective surface of an aluminum mirror having a planar reflecting surface so that the λ/4 layer side of the broadband wavelength film contacts the mirror was set. Therefore, in this model, a structure in which a linear polarizing film, a λ/2 layer, a λ/4 layer, and a mirror are provided in this order in the thickness direction was set.

And in the above model, the color difference ΔE*ab when light was irradiated from the D65 light source to the circular polarizing film was calculated in the front direction of the circular polarizing film. In the calculation of the color difference ΔE*ab, the reflected light in the directions of 0° of declination and 0° of azimuth of an aluminum mirror to which a circular polarizing film was not affixed was used as a reference. In addition, in the simulation, the surface reflection component actually generated on the surface of the circularly polarizing film is excluded from the calculation of the color difference ΔE*ab. The value of the color difference ΔE*ab is preferable because it means that the smaller the value is, the less change in color sense is.

[Visual evaluation of circular polarizing film]

The polarizing plate provided by the image display device (Apple's "AppleWatch" (registered trademark)) is peeled off, and the display surface of the image display device and the surface of the λ/4 layer of the circular polarizing film to be evaluated are attached to the adhesive layer (Nitto Denko Manufacturing "CS9621") was bonded through. The display surface was set to a black display state (a state in which black was displayed on the entire screen), and the display surface was observed from all directions of declination θ = 0° (front direction) and declination θ = 60° (tilting direction). The smaller the luminance and coloration due to reflection of external light, the better the result. The results of observation were evaluated according to the following criteria.

"A": There is no visible level of luminance and coloration.

"B": Brightness and coloring occur at a level that can be visually recognized.

"C": luminance and coloring are severely generated.

[Example 1]

(First Step: Preparation of Layer (A))

As a resin having a positive intrinsic birefringence, a pellet-shaped norbornene resin (manufactured by Nippon Xeon Corporation; glass transition temperature of 126°C) was prepared and dried at 100°C for 5 hours. The dried resin was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded from a T die onto a casting drum in a sheet form. The extruded resin was cooled to obtain a long pre-stretched film having a thickness of 110 μm. The obtained film before stretching was wound up on a roll and recovered.

The film before stretching was taken out from the roll and continuously supplied to the roll stretching machine. And free uniaxial stretching was performed on the film before extending|stretching by this roll stretching machine, and the elongate stretched film as a layer (A) was obtained. In this stretching, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the film before stretching was 0°, the stretching temperature was 132°C, and the stretching ratio was 1.9 times. In addition, the orientation angle of the obtained stretched film was 0°, the in-plane retardation Re was 350 nm, and the thickness was 80 μm. The obtained stretched film was wound up on a roll and recovered.

(Second step: formation of layer (B))

As a resin having a positive intrinsic birefringence, a liquid composition containing a norbornene resin (manufactured by Nippon Xeon Corporation; glass transition temperature of 135°C) was prepared. This liquid composition contained cyclohexanone as a solvent, and the concentration of norbornene-based resin in the liquid composition was 15.0% by weight.

The stretched film was taken out from the roll, and the liquid composition was applied onto the stretched film. Thereafter, the coated liquid composition was dried to form a layer (thickness of 10 μm) of norbornene-based resin as the layer (B) on the stretched film. Thereby, a multilayer film provided with the layer (A) and the layer (B) was obtained. The obtained multilayer film was wound up on a roll and recovered.

(3rd process: stretching of a multilayer film)

The multilayer film was taken out from the roll and continuously supplied to the tenter stretching machine. And the multilayer film was stretched by this tenter stretching machine. In this stretching, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was 75°, the stretching temperature was 140°C, and the stretching ratio was 2.0 times. Thereby, a broadband wavelength film was obtained as a co-stretched film including a λ/2 layer obtained by stretching the layer (A) and a λ/4 layer obtained by stretching the layer (B). The obtained broadband wavelength film was evaluated by the method described above.

(Production of circular polarizing film)

A long linear polarizing film having an absorption axis in the longitudinal direction was prepared. This linearly polarizing film and the said broadband wavelength film were bonded together by making mutual longitudinal directions parallel. This bonding was performed using an adhesive ("CS-9621" manufactured by Nitto Denko Corporation). Thereby, a circular polarizing film provided with a linear polarizing film, a λ/2 layer, and a λ/4 layer in this order was obtained. About the obtained circular polarizing film, it evaluated by the method mentioned above.

[Example 2]

In the third process, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 80°.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Example 3]

In the third step, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 85°.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Example 4]

As a resin having a positive intrinsic birefringence, a liquid composition containing a polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Ltd.; glass transition temperature of 137°C) was prepared. This liquid composition contained cyclopentanone as a solvent, and the concentration of the polycarbonate resin in the liquid composition was 15% by weight. In the second step, the liquid composition containing this polycarbonate resin was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third step, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 85°.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Example 5]

In the first step, as a stretching device for stretching the film before stretching, a tenter stretching machine was used instead of the roll stretching machine. The stretching using the tenter stretching machine was not free uniaxial stretching, but stretching in which a restraining force was applied in addition to the stretching direction. In addition, the stretching angle formed by the stretching direction with respect to the length direction of the film before stretching was changed to 10°. In addition, the draw ratio of the film before stretching was changed to 1.4 times.

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third process, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 90°.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Comparative Example 1]

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third process, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 90°.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Comparative Example 2]

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third step, as a stretching device for stretching the multilayer film, a roll stretching machine was used instead of the tenter stretching machine. In addition, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 0°. In addition, the draw ratio of the multilayer film was changed to 1.5 times.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Comparative Example 3]

In the first step, the stretching temperature of the film before stretching was changed to 138°C.

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third process, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 60°. In addition, the draw ratio of the multilayer film was changed to 1.5 times.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Comparative Example 4]

In the first step, the stretching temperature of the film before stretching was changed to 138°C.

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third step, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 30°. In addition, the draw ratio of the multilayer film was changed to 1.5 times.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Comparative Example 5]

In the first step, as a stretching device for stretching the film before stretching, a tenter stretching machine was used instead of the roll stretching machine. In addition, the stretching angle formed by the stretching direction with respect to the length direction of the film before stretching was changed to 10°. In addition, the draw ratio of the film before stretching was changed to 1.4 times.

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third process, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 60°. In addition, the draw ratio of the multilayer film was changed to 1.5 times.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[Comparative Example 6]

In the first step, as a stretching device for stretching the film before stretching, a tenter stretching machine was used instead of the roll stretching machine. In addition, the stretching angle formed by the stretching direction with respect to the length direction of the film before stretching was changed to 10°. In addition, the draw ratio of the film before stretching was changed to 1.4 times.

In the second step, the liquid composition containing the polycarbonate resin prepared in Example 4 was used instead of the liquid composition containing the norbornene resin used in Example 1.

In the third step, as a stretching device for stretching the multilayer film, a roll stretching machine was used instead of the tenter stretching machine. In addition, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the multilayer film was changed to 0°. In addition, the draw ratio of the multilayer film was changed to 1.5 times.

Except for the above matters, production and evaluation of a broadband wavelength film and a circular polarizing film were performed by the same operation as in Example 1.

[result]

The results of Examples and Comparative Examples are shown in Tables 1 and 2 below. In the following table, the meaning of the abbreviation is as follows.

COP: Norbornene resin.

PC: Polycarbonate resin.

Re: In-plane retardation.

Rth: retardation in the thickness direction.

Orientation angle: The angle made by the slow axis with respect to the longitudinal direction.

Total thickness: The total thickness of the λ/2 layer and the λ/4 layer.

Slope: Slope direction.

Portrait: longitudinal direction.

100th floor (A)
200 multilayer film
210th floor (B)
300 broadband wavelength film

Claims (10)

A first step of preparing the layer (A) as a resin film having a slow axis in the plane;
A second step of forming a layer (B) of a resin having a positive intrinsic birefringence on the layer (A) to obtain a multilayer film;
A third step of stretching the multilayer film in a direction not perpendicular and not parallel to the slow axis of the layer (A) to obtain a long broadband wavelength film including a λ/2 layer and a λ/4 layer; Include in order,
The λ/2 layer and the λ/4 layer of the broadband wavelength film satisfy the following formula (1).
θ(λ/4) = {45° + 2 × θ(λ/2)} ± 5° (1)
(In the above formula (1),
θ(λ/2) represents an angle formed by the slow axis of the λ/2 layer with respect to the length direction of the broadband wavelength film,
θ (λ/4) represents an angle formed by the slow axis of the λ/4 layer with respect to the length direction of the broadband wavelength film.) The method of claim 1,
The method for producing a broadband wavelength film, wherein the layer (A) prepared in the first step is a long resin film having a slow axis that is not perpendicular to the length direction of the layer (A). The method according to claim 1 or 2,
The third step includes stretching the multilayer film in a direction forming an angle of 45° or more with respect to the longitudinal direction of the multilayer film. The method according to any one of claims 1 to 3,
The method for producing a broadband wavelength film, wherein the angle θ (λ/2) is in the range of 20° ± 10°. The method according to any one of claims 1 to 4,
The above-described angle θ (λ/4) is in the range of 85° ± 20°, a method for producing a broadband wavelength film. The method according to any one of claims 1 to 5,
The λ/2 layer is a layer obtained by stretching the layer (A), a method for producing a broadband wavelength film. The method according to any one of claims 1 to 6,
The λ/4 layer is a layer obtained by stretching the layer (B), a method for producing a broadband wavelength film. A process of producing a broadband wavelength film by the production method according to any one of claims 1 to 7;
The manufacturing method of a circular polarizing film containing; the process of bonding the said broadband wavelength film and a long linear polarizing film. The method of claim 8,
The method for producing a circular polarizing film, wherein the linear polarizing film has an absorption axis in the longitudinal direction of the linear polarizing film. As a long broadband wavelength film,
Λ/2 layer having a slow axis forming an angle of 20° ± 10° with respect to the length direction of the broadband wavelength film,
A long-length broadband wavelength film comprising a λ/4 layer having a slow axis forming an angle of 85° ± 20° with respect to the length direction of the broadband wavelength film.

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