JPWO2019208512A1 - Wideband wavelength film and its manufacturing method, and circularly polarizing film manufacturing method - Google Patents

Abstract

In the first step of preparing a layer (A) as a resin film having a slow axis parallel or perpendicular to the longitudinal direction; a layer (B) of a resin having a negative intrinsic compound refraction is formed on the layer (A). The second step of obtaining the multilayer film; and the third step of stretching the multilayer film in an oblique direction to obtain a long broadband wavelength film having λ / 2 layer and λ / 4 layer; in this order. A method for producing a wideband wavelength film, which comprises, and in which the λ / 2 layer and the λ / 4 layer of the wideband wavelength film satisfy the formula (1). θ (λ / 4) = {45 ° + 2 × θ (λ / 2)} ± 5 ° (1) (θ (λ / 2) is the slow axis of the λ / 2 layer with respect to the longitudinal direction of the broadband wavelength film. Represents the angle formed by, and θ (λ / 4) represents the angle formed by the slow axis of the λ / 4 layer with respect to the longitudinal direction of the broadband wavelength film.)

Description

The present invention relates to a broadband wavelength film, a method for producing the same, and a method for producing a circularly polarizing film.

Various studies have been made conventionally on a method for producing an optical film having two or more layers (see Patent Documents 1 to 3).

International Publication No. 2016/0474665 International Publication No. 2009/031433 Japanese Unexamined Patent Publication No. 2009-237534

As a broadband wavelength film that can function as a wave plate in a wide wavelength band, a film containing a combination of a λ / 2 plate and a λ / 4 plate is known. Conventionally, such a broadband wavelength film has a step of stretching a certain film to obtain a λ / 2 plate, a step of stretching another film to obtain a λ / 4 plate, and these λ / 2 plates and λ /. It was generally manufactured by a manufacturing method including a step of laminating four plates to obtain a broadband wavelength film.

Further, there is known a technique for obtaining a circularly polarizing film by combining the above-mentioned broadband wavelength film with a linearly polarizing film as a film capable of functioning as a linear polarizing plate. Generally, a long linear polarizing film has an absorption axis in the longitudinal direction or the width direction thereof. Therefore, when a wide-band wavelength film is combined with a long linearly polarizing film to obtain a circularly polarizing film, the slow axis of the λ / 2 plate is required to be in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction. ..

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

The present invention has been devised in view of the above problems, and is a wideband wavelength film and a method for producing the same, which can be efficiently produced with a small number of steps; and a method for producing a circularly polarizing film including the above method for producing a wideband wavelength film. Aim to provide.

The present inventor has diligently studied to solve the above-mentioned problems. As a result, the present inventor has a first step of preparing a layer (A) as a resin film having a slow axis parallel or perpendicular to the longitudinal direction; a resin having a negative intrinsic birefringence on the layer (A). In the second step of forming the layer (B) of the above to obtain a multi-layer film; the multi-layer film is stretched in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the multi-layer film, and λ / According to the manufacturing method including the third step of obtaining a long wideband wavelength film having two layers and λ / 4 layers in this order, it has been found that the wideband wavelength film can be efficiently manufactured with a small number of steps, and the present invention is made. Completed.
That is, the present invention includes the following.

[1] With the first step of preparing the layer (A) as a long resin film;
A second step of forming a resin layer (B) having a negative intrinsic birefringence on the layer (A) to obtain a multi-layer film;
The multilayer film is stretched in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film having λ / 2 layer and λ / 4 layer. Steps and; are included in this order,
The layer (A) prepared in the first step has a slow axis parallel to or perpendicular to the longitudinal direction of the layer (A).
A method for producing a broadband wavelength film, wherein 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 the angle formed by the slow axis of the λ / 2 layer with respect to the longitudinal 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 longitudinal direction of the broadband wavelength film. )
[2] The broadband wavelength film according to [1], wherein the third step includes stretching the multilayer film in an oblique direction forming an angle of 45 ° or less with respect to the longitudinal direction of the multilayer film. Manufacturing method.
[3] The method for producing a broadband wavelength film according to [1] or [2], wherein the angle θ (λ / 2) is in the range of 27.5 ° ± 10 °.
[4] The method for producing a broadband wavelength film according to any one of [1] to [3], wherein the angle θ (λ / 4) is in the range of 100 ° ± 20 °.
[5] The method for producing a broadband wavelength film according to any one of [1] to [4], wherein the λ / 2 layer is a layer obtained by stretching the layer (A).
[6] The method for producing a broadband wavelength film according to any one of [1] to [5], wherein the λ / 4 layer is a layer obtained by stretching the layer (B).
[7] A step of manufacturing a broadband wavelength film by the manufacturing method according to any one of [1] to [6];
A method for producing a circularly polarizing film, which comprises a step of laminating the broadband wavelength film and a long linearly polarizing film;
[8] The method for producing a circularly polarizing film according to [7], wherein the linearly polarizing film has an absorption axis in the longitudinal direction of the linearly polarizing film.
[9] A long wideband wavelength film.
A λ / 2 layer having a slow phase axis at an angle of 27.5 ° ± 10 ° with respect to the longitudinal direction of the broadband wavelength film, and
A long broadband wavelength film, which is a co-stretched film including a λ / 4 layer having a slow axis having an angle of 100 ° ± 20 ° with respect to the longitudinal direction of the broadband wavelength film.

According to the present invention, it is possible to provide a broadband wavelength film and a method for producing the same, which can be efficiently produced with a small number of steps; and a method for producing a circularly polarizing film including the method for producing the broadband wavelength film.

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

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

In the following description, the "long" film means a film having a length of 5 times or more, preferably 10 times or more, and specifically a roll. A film that has a length that allows it to be rolled up and stored or transported. 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 the film or layer represents the slow axis in the plane of the film or layer unless otherwise specified.

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

In the following description, the angles formed by the optical axes (slow phase axis, transmission axis, absorption axis, etc.) of each layer in a member having a plurality of layers are angles when the layers are viewed from the thickness direction unless otherwise specified. Represents.

In the following description, the in-plane optical axis (slow phase axis, transmission axis, absorption axis, etc.) direction and geometric direction (longitudinal direction and width of the film) of a certain product (broadband wavelength film, circularly polarizing film, etc.) Unless otherwise specified, the angular relationship of (direction, etc.) is defined as positive for a shift in one direction and negative for a shift in another direction, and the positive and negative directions are commonly defined in the components in the product. To. For example, in a broadband wavelength film, "the angle formed by the slow axis of the λ / 2 layer with respect to the longitudinal direction of the broadband wavelength film is 27.5 °, and the λ / 4 layer with respect to the longitudinal direction of the broadband wavelength film. The angle formed by the slow axis of is 100 ° "represents the following two cases:
When the wideband wavelength film is observed from one side thereof, the slow axis of the λ / 2 layer is shifted clockwise by 27.5 ° from the longitudinal direction of the wideband wavelength film, and the λ / 4 layer The slow axis is shifted 100 ° clockwise from the longitudinal direction of the broadband wavelength film.
-Observing the wideband wavelength film from one side, the slow axis of the λ / 2 layer is shifted counterclockwise by 27.5 ° from the longitudinal direction of the wideband wavelength film, and the λ / 4 layer. The slow axis of is shifted 100 ° counterclockwise from the longitudinal direction of the broadband wavelength film.

In the following description, the diagonal direction of a long film is an in-plane direction of the film, which is neither parallel nor perpendicular to the longitudinal direction of the film, unless otherwise specified.

In the following description, the front direction of a film means the normal direction of the main surface of the film unless otherwise specified, and specifically, the direction of the polar angle 0 ° and the azimuth angle 0 ° of the main surface. Point to.

In the following description, the tilting direction of a film means a direction that is neither parallel nor perpendicular to the main surface of the film unless otherwise specified. Specifically, the polar angle of the main surface is greater than 0 ° and 90. Refers to a direction smaller than °.

In the following description, a material having a positive intrinsic birefringence means a material in which the refractive index in the stretching direction is larger than the refractive index in the direction orthogonal to the material, unless otherwise specified. Further, a material having a negative intrinsic birefringence means a material in which the refractive index in the stretching direction is smaller than the refractive index in the direction orthogonal to the material, unless otherwise specified. The value of the intrinsic birefringence can be calculated from the permittivity distribution.

In the following description, "(meth) acrylic" 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) × d unless otherwise specified. Further, the retardation Rth in the thickness direction of the layer is a value represented by Rth = [{(nx + ny) / 2} -nz] × d unless otherwise specified. Further, the NZ coefficient of the layer is a value represented by (nx-nz) / (nx-ny) unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer (in-plane direction) and in the direction in which the maximum refractive index is given. ny represents the refractive index in the in-plane direction of the layer and orthogonal to the nx direction. 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 specified.

In the following description, the directions of the elements are "parallel", "vertical" and "orthogonal", unless otherwise specified, within a range that does not impair the effect of the present invention, for example, ± 3 °, ± 2 ° or ± 1 °. It may include an error within the range of.

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

The method for producing the wideband wavelength film 300 according to the embodiment of the present invention is
(1) As shown in FIG. 1, the first step of preparing the layer (A) 100 as a long resin film;
(2) A second step of forming a resin layer (B) 210 having a negative intrinsic birefringence on the layer (A) 100 to obtain the multilayer film 200 shown in FIG.
(3) In the third step of stretching the multilayer film 200 to obtain the long broadband wavelength film 300 shown in FIG.
Are included in this order.

As shown in FIG. 1, the layer (A) 100 prepared in the first step has a slow-phase axis A ₁₀₀ parallel or perpendicular to the longitudinal direction of the layer (A) 100. After forming the layer (B) 210 on the layer (A) 100 in the second step to obtain the multilayer film 200 shown in FIG. 2, the multilayer film 200 is stretched in the third step. This stretching is performed in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the multilayer film 200 so that a λ / 2 layer and a λ / 4 layer having a slow phase axis in a desired direction can be obtained.

By stretching in the third step, co-stretching is performed in which the layer (A) 100 and the layer (B) 210 are stretched at the same time. Therefore, as shown in FIG. 3, in the layer (A) 100, _{the direction of the slow phase axis A 100} and the optical characteristics are adjusted. On the other hand, the slow-phase axis A ₂₁₀ appears on the layer (B) 210, and the optical characteristics are exhibited. The stretched layer (A) 100 functions as one of the λ / 2 layer and the λ / 4 layer, and the stretched layer (B) 210 functions as the other of the λ / 2 layer and the λ / 4 layer. Therefore, the wideband wavelength film 300 including the λ / 2 layer and the λ / 4 layer can be obtained by the above-mentioned manufacturing method. FIG. 3 shows an example in which the stretched layer (A) 100 functions as a λ / 2 layer and the stretched layer (B) 210 functions as a λ / 4 layer. Not limited to the 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)
In equation (1), θ (λ / 4) is in the range of “{45 ° + 2 × θ (λ / 2)} -5 °” or more and “{45 ° + 2 × θ (λ / 2)} + 5 °” or less. Indicates that it is in. In the formula (1), θ (λ / 2) represents an angle formed by _{the slow-phase 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 longitudinal direction A 300 of the broadband wavelength film 300.} By including the combination of the λ / 2 layer and the λ / 4 layer satisfying the formula (1), the broadband wavelength film 300 has a wavelength of approximately 1/4 of the wavelength of the light transmitted through the film in a wide wavelength range. Can function as a wideband wavelength film capable of providing in-plane retardation.

The longitudinal _{A 300} of the broadband wave film 300, lambda / 4 layers of longitudinal (not shown), and, lambda / 2 layer in the longitudinal direction (not shown) is consistent. Therefore, the angle θ (λ / 2) represents the orientation angle formed by _{the slow-phase axis A 100} of the λ / 2 layer with respect to the longitudinal direction of the λ / 2 layer. ) ”. Further, the angle θ (λ / 4) represents the orientation angle formed by _{the slow-phase axis A 210} of the λ / 4 layer with respect to the longitudinal direction of the λ / 4 layer. ) ”.

[2. First step]
In the first step, a layer (A) as a long resin film having a slow phase axis in a predetermined direction in the plane is prepared. As the layer (A), a resin film having a multi-layer structure including two or more layers may be used, but 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, if necessary, further containing an arbitrary component can be used. In particular, as the resin contained in the layer (A), a resin having a negative intrinsic birefringence may be used, but since a wideband wavelength film can be produced particularly easily, a resin having a positive intrinsic birefringence should be used. Is preferable.

A resin having a positive intrinsic birefringence usually contains a polymer having a positive intrinsic birefringence. Examples of polymers having a positive intrinsic compound refraction include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfide such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyallylate; cellulose ester weight. Coalescence, polyethersulfone; polysulfone; polyallyl sulphon; polyvinyl chloride; cyclic olefin polymer such as norbornene polymer; rod-shaped liquid crystal polymer and the like. One of these polymers may be used alone, or two or more of these polymers may be used in combination at any ratio. Further, the polymer may be a homopolymer or a copolymer. Among these, a polycarbonate polymer is preferable because it is excellent in the expression of retardation and the stretchability at a low temperature. Further, a cyclic olefin polymer is preferable because it is excellent in mechanical properties, heat resistance, transparency, low hygroscopicity, dimensional stability and light weight.

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, and particularly preferably 90% by weight to 100% by weight. When the proportion of the polymer is in the above range, the layer (A) and the broadband wavelength film can obtain sufficient heat resistance and transparency.

The resin contained in the layer (A) may further contain any component other than the polymer in combination with the polymer. Optional components include, for example, colorants such as pigments and dyes; plasticizers; optical brighteners; dispersants; heat stabilizers; light stabilizers; UV absorbers; antistatic agents; antioxidants; fine particles; surfactants. Activators and the like can be mentioned. One of these components may be used alone, or two or more of these components may be used in combination at any ratio.

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, more preferably 180 ° C. or lower. Especially preferably, it is 170 ° C. or lower. When the glass transition temperature of the resin contained in the layer (A) is equal to or higher than the lower limit of the above range, the layer (λ / 2 layer or λ / 4 layer) obtained by stretching the layer (A) under a high temperature environment. Durability can be increased. Further, when the glass transition temperature of the resin contained in the layer (A) is not more than the upper limit value in the above range, the stretching treatment can be easily performed.

The slow-phase axis of the layer (A) prepared in the first step is parallel or perpendicular 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 longitudinal direction of the layer preferably satisfies any of the following (a1) and (a2).
(A1): The orientation angle of the layer (A) is preferably -3 ° or more, more preferably -2 ° or more, particularly preferably -1 ° or more, preferably 3 ° or less, still more preferably 2 ° or less. , Especially preferably 1 ° or less.
(A2): The orientation angle of the layer (A) is preferably 87 ° or more, more preferably 88 ° or more, particularly preferably 89 ° or more, preferably 93 ° or less, still more preferably 92 ° or less, particularly preferably. Is 91 ° or less.
When the layer (A) having such a slow phase axis is used, a wideband wavelength film having preferable optical characteristics can be easily obtained.

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

For example, when the layer (A) is stretched to obtain a λ / 2 layer, the in-plane retardation of the layer (A) is preferably 150 nm or more, more preferably 180 nm or more, and particularly preferably 200 nm or more. It is preferably 400 nm or less, more preferably 380 nm or less, and particularly preferably 350 nm or less. The NZ coefficient of the layer (A) is preferably 1.0 or more, more preferably 1.1 or more, particularly preferably 1.15 or more, preferably 1.7 or less, and more preferably 1.65 or less. , Particularly preferably 1.6 or less.

The thickness of the layer (A) prepared in the first step can be arbitrarily set within a range in which a desired wideband wavelength film can be 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, and 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 characteristics can be easily obtained by stretching in the third step.

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

The pre-stretched film 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, an extrusion molding method, an inflation molding method or a press molding method is preferable in order to obtain a layer (A) having excellent mechanical strength and surface accuracy, and among these methods, a viewpoint that the layer (A) can be manufactured efficiently and easily. The extrusion molding method is particularly preferable.

After preparing a long pre-stretched film, the long pre-stretched film can be stretched to obtain a layer (A) as a stretched film.

The slow axis of layer (A) is usually expressed by stretching the pre-stretched film. Therefore, the stretching direction of the pre-stretched film is preferably set according to the direction of the slow axis of the layer (A). For example, when the pre-stretched film is made of a resin having a positive intrinsic birefringence, the stretching direction of the pre-stretched film is set to be parallel to the slow axis of the layer (A) to be prepared in the first step. It is preferable to do so. Further, for example, when the pre-stretched film is formed of a resin having a negative intrinsic birefringence, the stretching direction of the pre-stretched film is a direction perpendicular to the slow axis of the layer (A) to be prepared in the first step. It is preferable to set to. Therefore, the stretching direction of the pre-stretched film is preferably a direction parallel to or perpendicular to the longitudinal direction of the pre-stretching film. In particular, from the viewpoint of easily producing a desired wideband wavelength film, the stretching direction of the pre-stretched film is preferably a direction perpendicular to the longitudinal direction of the pre-stretching film.

The stretch ratio of the pre-stretched film 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 equal to or greater than the lower limit of the above range, the refractive index in the draw direction can be increased. Further, when the stretching ratio is not more than the upper limit value of the above range, the direction of the slow phase axis of the layer obtained by stretching the layer (A) can be easily controlled.

The stretching temperature of the pre-stretched film is preferably TgA or higher, more preferably "TgA + 2 ° C" or higher, particularly preferably "TgA + 5 ° C" or higher, preferably "TgA + 40 ° C" or lower, more preferably "TgA + 35 ° C" or lower, Particularly preferably, it is "TgA + 30 ° C." 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 pre-stretching film can be reliably oriented, so that the layer (A) having desired optical properties can be easily obtained.

The above-mentioned stretching can usually be carried out by using an appropriate stretching machine such as a roll stretching machine or a tenter stretching machine while continuously transporting the pre-stretching film in the longitudinal direction. For example, when the pre-stretched film is stretched in the longitudinal direction of the pre-stretched film, it is preferable to use a roll stretching machine. Free uniaxial stretching can be easily performed by the roll stretching machine. Free uniaxial stretching refers to stretching in a certain direction without applying a binding force in a direction other than the stretching direction. As these stretching machines, for example, those described in Patent Document 1 can be used.

[3. Fourth step]
The method for producing a broadband wavelength film may include, if necessary, a step of forming a thin film layer on the layer (A) after preparing the layer (A) in the first step. By forming an appropriate thin film layer, the thin film layer functions as an easy-adhesion layer, and the binding force between the layer (A) and the layer (B) can be enhanced. Further, the thin film layer preferably has solvent resistance. Such a thin film layer is usually formed of a resin.

Examples of the material of the thin film layer include acrylic resin, urethane resin, acrylic urethane resin, ester resin, and ethyleneimine resin. Acrylic resin is a resin containing an acrylic polymer. The urethane resin is a resin containing polyurethane. Polymers such as acrylic polymers and polyurethanes usually have a high binding force to a wide variety of resins, so that the binding force between the layer (A) and the layer (B) can be enhanced. In addition, one of these polymers may be used alone, or two or more of these polymers may be used in combination at any ratio.

Resin as a material for the thin film layer is combined with a polymer to be a heat-resistant stabilizer, weather-resistant stabilizer, leveling agent, antistatic agent, slip agent, anti-blocking agent, antifogging agent, lubricant, dye, pigment, natural oil, etc. It may contain any component such as synthetic oil, wax, particles and the like. As the arbitrary component, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The glass transition temperature of the resin as the material of the thin film layer is higher than the glass transition temperature TgA of the resin contained in the layer (A) and the glass transition temperature TgB of the resin contained in the layer (B) having a negative intrinsic birefringence. It is preferably low. In particular, the difference between the glass transition temperature of the resin as the material of the thin film layer and the lower temperature 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. preferable. As a result, it is possible to suppress the expression of retardation in the thin film layer due to stretching in the third step, so that the thin film layer in the broadband wavelength film can have optical isotropic properties. Therefore, it is possible to easily adjust the optical characteristics 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 as a material of the thin film layer and a solvent on the layer (A). As the solvent, water may be used, or an organic solvent may be used. Examples of the organic solvent include the same solvents as those that can be used for forming the layer (B) described later. Further, one type of solvent may be used alone, or two or more types may be used in combination at an arbitrary ratio.

Further, the coating liquid may contain a cross-linking agent. By using the cross-linking agent, the mechanical strength of the thin film layer can be increased, and the binding property of the thin film layer to the layers (A) and (B) can be enhanced. As the cross-linking agent, for example, an epoxy compound, an amino compound, an isocyanate compound, a carbodiimide compound, an oxazoline compound and the like can be used. In addition, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio. The amount of the cross-linking agent is preferably 1 part by weight or more, more preferably 5 parts by weight or more, preferably 70 parts by weight or less, and more preferably 65 parts by weight with respect to 100 parts by weight of the polymer in the coating liquid. It is as follows.

Examples of the coating method of the coating liquid include the same method as 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 hardening treatment such as drying and cross-linking. Examples of the drying method include heat drying using an oven. In addition, examples of the cross-linking method include heat treatment, irradiation treatment with active energy rays such as ultraviolet rays, and the like.

[4. Second step]
In the first step, a layer (A) is prepared, a thin film layer is formed if necessary, and then a resin layer (B) having a negative intrinsic birefringence is formed to obtain a multi-layer film. Do. 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, "directly" means that there is no arbitrary layer between the layer (A) and the layer (B).

A resin having a negative intrinsic birefringence is usually a thermoplastic resin and includes a polymer having a negative intrinsic birefringence. Examples of polymers having a negative intrinsic compound refraction include homopolymers and copolymers of styrene or styrene derivatives, and polystyrene-based polymers containing copolymers of styrene or styrene derivatives and arbitrary monomers; poly. Examples thereof include acrylonitrile polymers; polymethylmethacrylate polymers; or multiple copolymers thereof; and cellulose compounds such as cellulose esters. Further, as the arbitrary monomer copolymerizable with styrene or a styrene derivative, for example, acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene are preferable. Of these, polystyrene-based polymers and cellulosic compounds are preferable. In addition, one of these polymers may be used alone, or two or more of these polymers may be used in combination at any ratio.

The proportion of the polymer in the resin having a negative intrinsic birefringence is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and particularly preferably 90% by weight to 100% by weight. When the proportion of the polymer is in the above range, the layer (λ / 2 layer or λ / 4 layer) obtained by stretching the layer (B) can exhibit appropriate optical characteristics.

The resin having a negative intrinsic birefringence contained in the layer (B) preferably contains a plasticizer. By using a plasticizer, the glass transition temperature TgB of the resin contained in the layer (B) can be appropriately adjusted. Examples of the plasticizer include phthalates, fatty acid esters, phosphoric acid esters, epoxy derivatives and the like. Specific examples of the plasticizer include those described in JP-A-2007-233114. Further, one type of plasticizer may be used alone, or two or more types may be used in combination at an arbitrary ratio.

Among the plasticizers, phosphoric acid ester is preferable because it is easily available and inexpensive. Examples of phosphate esters include trialkyl phosphates such as triethyl phosphate, tributyl phosphate, trioctyl phosphate; halogen-containing trialkyl phosphates such as trichloroethyl phosphate; triphenyl phosphate, tricresyl. Triaryl phosphates such as phosphates, tris (isopropylphenyl) phosphates, cresyldiphenyl phosphates; alkyl-diaryl phosphates such as octyldiphenyl phosphates; tri (alkoxyethyl) phosphates such as tri (butoxyethyl) phosphates. Alkoxy) phosphate; etc.

The amount of the plasticizer is preferably 0.001% by weight or more, more preferably 0.005% by weight or more, particularly preferably 0.001% by weight or more, based on 100% by weight of the resin having a negative intrinsic compound refraction contained in the layer (B). Is 0.1% by weight or more, preferably 20% by weight or less, more preferably 18% by weight or less, and particularly preferably 15% by weight or less. When the amount of the plasticizer is in the above range, the glass transition temperature TgB of the resin contained in the layer (B) can be appropriately adjusted, so that appropriate stretching to obtain a desired wideband wavelength film can be easily performed in the third step. It is possible to do.

The resin having a negative intrinsic birefringence may further contain any component other than the polymer and the plasticizer in combination with the polymer and the plasticizer. Examples of the optional component include the same examples as any component that can be contained in the resin contained in the layer (A). As the arbitrary component, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The glass transition temperature TgB of the resin having a negative intrinsic birefringence contained in the layer (B) is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, still more preferably 100 ° C. or higher, and particularly preferably 110 ° C. or higher. Is 120 ° C. or higher. When the glass transition temperature TgB of a resin having a negative intrinsic birefringence is such a high value, it is possible to reduce the orientation relaxation of the resin having a negative intrinsic birefringence. The upper limit of the glass transition temperature TgB of a resin having a negative intrinsic birefringence is not particularly limited, but is usually 200 ° C. or lower.

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 resin contained in the layer (A) is contained in the glass transition temperature TgA and the layer (B). It is preferable that the temperature is close to the glass transition temperature TgB of the resin. 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 lower, more preferably 15 ° C. or lower, and particularly preferably 10 ° C. or lower.

Layer (B) may have an in-plane retardation and a slow axis. When the layer (B) has an in-plane retardation and a slow-phase axis, the in-plane retardation and the slow-phase axial direction of the layer (B) are adjusted by stretching in the third step. However, setting stretching conditions for making such adjustments tends to be complicated. Therefore, from the viewpoint of easily obtaining the desired optical characteristics and the slow phase axial direction in the layer (B) after stretching in the third step, the layer (B) formed in the second step has an in-plane retardation and a slow phase. It is preferable that it does not have a shaft, or if it does, 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 as long as a desired broadband wavelength film can be obtained. The specific thickness of the layer (B) is preferably 3 μm or more, more preferably 5 μm or more, particularly preferably 7 μm or more, preferably 30 μm or less, more preferably 25 μm or less, and particularly preferably 20 μm or less. When the thickness of the layer (B) is within the above range, a λ / 2 layer or a λ / 4 layer having desired optical characteristics can be easily obtained by stretching.

The method for forming the layer (B) is not particularly limited, and for example, a forming method such as a coating method, an extrusion method, or a bonding method can be used.

When the layer (B) is formed by the coating method, the second step includes coating the layer (A) with a composition containing a resin having a negative intrinsic birefringence. The composition is usually a liquid composition that further contains a solvent in combination with a resin having a negative intrinsic birefringence. Examples of the solvent include 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, and 1 , 4-Dioxane, 2-pentanone, N, N-dimethylformamide and the like. Further, one type of solvent may be used alone, or two or more types may be used in combination at an arbitrary ratio. The solvent may cause phenomena such as dissolution and relaxation of orientation in the layer (A), but usually, the liquid composition has a thin coating thickness and dries quickly after coating. The degree of the phenomenon is negligible.

Examples of the coating method of the above composition include a curtain coating method, an extrusion coating method, a roll coating method, a spin coating method, a dip coating method, a bar coating method, a spray coating method, a slide coating method, a print coating method, and a gravure. Examples include a coating method, a die coating method, a gap coating method, and a dipping method.

Further, in the coating method, the second step includes coating the composition on the layer (A) and then drying the coated composition, if necessary. The solvent is removed by drying, and a layer (B) of a resin having a negative intrinsic birefringence can be formed on the layer (A). The drying can be performed by, for example, a drying method such as natural drying, heat drying, vacuum drying, and vacuum heating drying.

When the layer (B) is formed by the extrusion method, the second step involves extruding a resin having a negative intrinsic birefringence onto the layer (A). Extrusion of the resin is usually performed in a state where the resin is melted. In addition, the resin is usually extruded into a film using a die. By adhering the resin having a negative intrinsic birefringence to the layer (A) or the thin film layer in this way, a layer (B) of the resin having a negative intrinsic birefringence can be formed on the layer (A). it can. When the layer (B) is formed by an extrusion method, the second step usually involves cooling and curing a resin having a negative intrinsic birefringence that is extruded and adhered to the layer (A).

When the layer (B) is formed by the bonding method, the second step includes bonding a film of a resin having a negative intrinsic birefringence to the layer (A). Examples of the method for producing a film of a resin having a negative intrinsic birefringence include a melt molding method such as an extrusion molding method, an inflation molding method, and a press molding method; a solution casting method; Further, an adhesive or an adhesive may be used for bonding the film of the resin having a negative intrinsic birefringence to the layer (A), if necessary.

Among the methods for forming the layer (B) described above, the coating method is preferable. In general, resins with negative intrinsic birefringence tend to have low mechanical strength. However, according to the coating method, the layer (B) can be easily formed while using such a resin having low mechanical strength. In this respect, for example, when the bonding method is used, a layer (B) is formed on an appropriate support film, and when this layer (B) is bonded to the layer (A), damage to the layer (B) is suppressed. It is possible to form a layer (B) on top of the layer (A). However, compared to the laminating method in which the formation of the layer (B) on the support film and the transfer of the layer (B) from the support film to the layer (A) are performed, the coating method is the layer (B). The number of steps required for forming the above can be reduced. Further, according to the coating method, no adhesive and adhesive are required. Further, in the coating method, the thickness of the layer (B) itself can be easily reduced as compared with 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 the coating method.

[5. Third step]
In the second step, after obtaining a multi-layer film including the layer (A) and the layer (B), the multi-layer film is stretched to perform a third step 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 characteristics of the layer (A) are adjusted to obtain one of the λ / 2 layer and the λ / 4 layer. .. Further, by stretching in the third step, a slow phase axis appears in the layer (B), and optical characteristics are exhibited in the layer (B), so that the other of the λ / 2 layer and the λ / 4 layer can be obtained.

The stretching of the multilayer film in the third step is performed in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the multilayer film. The specific stretching direction is set so that a desired wideband wavelength film can be obtained from the in-plane direction 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 approach the stretching direction by stretching in the third step. To do. Further, for example, when the layer (A) is a layer of a resin having a negative intrinsic birefringence, the direction of the slow phase axis of the layer (A) is perpendicular to the stretching direction due to the stretching in the third step. It changes to approach the direction. As described above, the direction of the slow axis of the layer (A) is usually changed by stretching in the third step. Further, in the layer (B), the slow-phase axis usually appears in the direction perpendicular to the stretching direction by stretching in the third step. Therefore, the stretching direction in the third step is delayed in a desired direction due to the change in the direction of the slow axis in the layer (A) and the expression of the slow axis in the layer (B). It is preferable to set so that a λ / 2 layer and a λ / 4 layer having an axis can be obtained.

The specific angle formed by the stretching direction of the multilayer film in the third step with respect to the longitudinal direction of the multilayer film is preferably 4 ° or more, particularly preferably 5 ° or more, preferably 45 ° or less. It is more preferably 30 ° or less, and particularly preferably 20 ° or less. When the multilayer film is stretched in such a stretching direction, the directions of the slow-phase axes of the λ / 2 layer and the λ / 4 layer can be easily controlled.

The magnitude of the angle (absolute value of the angle) formed by the stretching direction of the multilayer film and the slow axis of the layer (A) in the third step is preferably 45 ° or more, more preferably 60 ° or more, particularly preferably. Is 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-phase axes of the λ / 2 layer and the λ / 4 layer so as to satisfy the relationship of the equation (1).

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 2.5 times or less, more preferably 2.2 times. It is twice or less, particularly preferably 2.0 times or less. When the draw ratio in the third step is equal to or greater than the lower limit of the above range, the occurrence of wrinkles can be suppressed. Further, when the stretching ratio in the third step is not more than the upper limit value of the above range, the directions of the slow axis of the λ / 2 layer and the λ / 4 layer can be easily controlled.

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 contained in the layer (B) having a negative intrinsic birefringence. ) And (C2) are both satisfied.
(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 lower, particularly preferably. Is a temperature of TgA + 20 ° C. or lower.
(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 lower, particularly preferably. Is a temperature of TgB + 20 ° C. or lower.
By stretching at such a stretching temperature, the optical characteristics of the layer (A) can be appropriately adjusted, and the desired optical characteristics can be exhibited in the layer (B). Therefore, a wideband wavelength film having desired optical characteristics can be obtained.

The stretching in the third step described above can be performed using an arbitrary stretching machine, for example, a tenter stretching machine or a roll stretching machine. Stretching using these stretching machines is preferably performed while continuously transporting a long multilayer film in the longitudinal direction.

[6. Arbitrary process]
The above-mentioned method for producing a broadband wavelength film may further include an arbitrary step in combination with the above-mentioned steps.
For example, the method for producing a broadband wavelength film may include a step of providing a protective layer on the surface of the broadband wavelength film.

Further, for example, in the method for producing a broadband wavelength film, at an arbitrary time point, one or two or more surfaces of the layer (A), the layer (B), and the thin film layer are subjected to surface treatment such as corona treatment and plasma treatment. It may include a step of applying. Therefore, for example, the surface of the layer (A) may be surface-treated, and then the layer (B) or the thin film layer may be formed on the treated surface. Further, for example, the surface of the thin film layer may be surface-treated, and then the layer (B) may be formed on the treated surface. By performing the surface treatment, it is possible to enhance the bondability between the layers on the surface treated.

The above-mentioned first step to fourth step and any step can be performed while continuously transporting a film such as a layer (A), a multilayer film and a broadband wavelength film. The transport direction for transporting such files is usually the longitudinal direction of the film. Therefore, at the time of the above-mentioned transport, the longitudinal direction and the width direction of the film usually coincide with the MD direction (Machine Direction) and the TD direction (Transverse Direction) of the transport.

[7. Wideband wavelength film]
By the manufacturing method described above, a co-stretched 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-stretched film satisfy the above formula (1). The combination of the λ / 2 layer and the λ / 4 layer satisfying the relationship represented by the formula (1) is an in-plane letter having approximately 1/4 wavelength of the wavelength of the light transmitted through the film in a wide wavelength range. It can function as a wide-band wavelength film capable of providing a substrate (see JP-A-2007-004120). Therefore, according to the above-mentioned manufacturing method, a long broadband wavelength film can be obtained as a co-stretched film having a λ / 2 layer and a λ / 4 layer. From the viewpoint of realizing a wideband wavelength film capable of functioning in a wider wavelength range, the λ / 2 layer and the λ / 4 layer preferably satisfy the formula (2), and more preferably the formula (3). In equation (2), θ (λ / 4) is in the range of “{+ 45 ° + 2 × θ (λ / 2)} -4 °” or more and “{+ 45 ° + 2 × θ (λ / 2)} + 4 °” or less. Indicates that it is in. Further, in the equation (3), θ (λ / 4) is “{+ 45 ° + 2 × θ (λ / 2)} -3 °” or more and “{+ 45 ° + 2 × θ (λ / 2)} + 3 °” or less. Indicates that it is in the range of.
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 manufacturing method described above, the layers (A) and the layer (B) are not stretched separately as in the conventional case, but are stretched together in the third step. Therefore, since the number of stretching treatments can be reduced as compared with the conventional case, the number of steps required for producing the broadband wavelength film can be reduced, and therefore efficient production can be realized. Further, in the above-mentioned production method of co-stretching the layer (A) and the layer (B) to obtain a broadband wavelength film by stretching the multilayer film, both are combined after the production of each of the λ / 2 layer and the λ / 4 layer. Unlike the conventional manufacturing method of laminating, there is no deviation in the slow axis direction due to laminating. 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, a high-quality wideband wavelength film capable of realizing a circularly polarizing film capable of effectively suppressing coloring. Can be easily obtained.

In the obtained broadband wavelength film, the λ / 2 layer is a layer obtained by stretching one of the layer (A) and the layer (B), and the λ / 4 layer is the layer (A) and the layer (B). The other is a layer obtained by stretching. Above all, since the production of a broadband wavelength film is particularly easy, it is preferable that the λ / 2 layer is a layer obtained by stretching the layer (A), and the λ / 4 layer is a layer (B). ) Is stretched to obtain a layer. Therefore, the λ / 2 layer is preferably a layer made of the same resin as the layer (A), and the λ / 4 layer is preferably 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 an in-plane retardation, a wideband wavelength film can be realized by combining the λ / 2 layer and the λ / 4 layer. Above all, from the viewpoint of obtaining a circularly polarizing film having an excellent function of suppressing coloring in the tilt 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, and preferably 240 nm or more. It is 280 nm or less, more preferably 270 nm or less.

The thickness direction retardation of the λ / 2 layer at the measurement wavelength of 590 nm 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 or less, and particularly preferably 270 nm. It is as follows. When the retardation of the λ / 2 layer in the thickness direction is within the above range, a circularly polarizing film having a particularly excellent function of suppressing coloring in the tilt 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. It is preferably 1.5 or less. When the NZ coefficient of the λ / 2 layer is in the above range, a circularly polarizing film having a particularly excellent function of suppressing coloring in the tilt direction can be obtained. Further, the λ / 2 layer having such an NZ coefficient can be easily manufactured.

Optical characteristics such as the retardation and NZ coefficient of the λ / 2 layer include, for example, the retardation and thickness of the layer (A) prepared in the first step; and the stretching temperature, stretching ratio, stretching direction, etc. in the third step. It can be adjusted according to the stretching conditions of.

The orientation angle θ (λ / 2) of the λ / 2 layer is preferably in the range of 27.5 ° ± 10 ° (that is, in the range of 17.5 ° to 37.5 °), preferably 27.5 ° ±. It is more preferably in the range of 8 ° (ie, in the range of 19.5 ° to 35.5 °), preferably in the range of 27.5 ° ± 5 ° (ie, in the range of 22.5 ° to 32.5 °). It is particularly preferable to be in. A general linearly polarizing film has a transmission axis in the width direction thereof and an absorption axis in the longitudinal direction thereof. When the orientation angle θ (λ / 2) of the λ / 2 layer is within the above range, a circularly polarizing film can be easily realized in combination with such a general linearly polarizing film. Further, when the orientation angle θ (λ / 2) of the λ / 2 layer is within the above range, the coloring suppressing function in the front direction and the inclination direction of the obtained circularly polarizing film 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 the stretching conditions such as the stretching direction and the stretching ratio in the third step. Can be adjusted by.

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, still 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 an in-plane retardation, a wideband wavelength film can be realized by combining the λ / 2 layer and the λ / 4 layer. Above all, from the viewpoint of obtaining a circularly polarizing film having an excellent function of suppressing coloring in the tilt 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, and preferably 110 nm or more. It is 140 nm or less, more preferably 130 nm or less.

The thickness direction retardation of the λ / 4 layer at the measurement wavelength of 590 nm is preferably -150 nm or more, more preferably -140 nm or more, particularly preferably -130 nm or more, preferably -80 nm or less, and more preferably -90 nm or less. , Particularly preferably -100 nm or less. When the retardation of the λ / 4 layer in the thickness direction is within the above range, a circularly polarizing film having a particularly excellent function of suppressing coloring in the tilt direction can be obtained.

The NZ coefficient of the λ / 4 layer is preferably -1.0 or more, more preferably -0.8 or more, particularly preferably -0.7 or more, preferably 0.0 or less, and more preferably -0. It is 05 or less, particularly preferably −0.1 or less. When the NZ coefficient of the λ / 4 layer is within the above range, a circularly polarizing film having a particularly excellent function of suppressing coloring in the tilt direction can be obtained. Further, the λ / 4 layer having such an NZ coefficient can be easily manufactured.

Optical characteristics such as retardation and NZ coefficient of the λ / 4 layer include, for example, the thickness of the layer (B) formed in the second step; and stretching conditions such as the stretching temperature, stretching ratio, and stretching direction in the third step. Can be adjusted by.

The orientation angle θ (λ / 4) of the λ / 4 layer is preferably in the range of 100 ° ± 20 ° (that is, in the range of 80 ° to 120 °), and is preferably in the range of 100 ° ± 15 ° (that is, 85 °. It is more preferably in the range of ° to 115 °, and particularly preferably in the range of 100 ° ± 10 ° (that is, in the range of 90 ° to 110 °). When the orientation angle θ (λ / 4) of the λ / 4 layer is in the above range, it is combined with a general linear polarizing film having a transmission axis in the width direction and an absorption axis in the longitudinal direction to form a circle. A polarizing film can be easily realized. Further, when the orientation angle θ (λ / 4) of the λ / 4 layer is within the above range, the coloring suppressing function in the front direction and the inclination direction of the obtained circularly polarizing film 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 at least the lower limit of the above range, desired optical characteristics can be easily obtained. Further, when the thickness of the λ / 4 layer is not more than 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. As a result, the thickness of the broadband wavelength film can be reduced.

When the method for producing a 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 the λ / 2 layer and the λ / 4 layer after manufacturing each is generally as thick as 5 μm or more, the thin film layer of the broadband wavelength film obtained by the above-mentioned manufacturing method is , Can be made thinner than that. 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 thinned in this way, the thickness of the entire broadband wavelength film can also be thinned. The lower limit of the thickness of the thin film layer is preferably as thin as possible, for example, 0.1 μm.

The broadband wavelength film may be provided with any layer in combination with the λ / 2 layer, the λ / 4 layer and the thin film layer. For example, an adhesive layer or an adhesive layer for adhering 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 wavelength range of 400 nm to 700 nm 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, the haze can be measured at five points using a "turbidity meter NDH-300A" manufactured by Nippon Denshoku Kogyo Co., Ltd. in accordance with JIS K7361-1997, and the average value obtained from the measurements 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 manufacturing method described above, it is possible to easily manufacture such a thin broadband wavelength film.

[8. Circularly polarizing film]
A long circularly polarizing film can be produced by using the broadband wavelength film produced by the production method described above. Such a circularly polarizing film can be manufactured by a manufacturing method including a step of manufacturing a wideband wavelength film by the above-mentioned manufacturing method and a step of laminating the wideband wavelength film and a long linearly polarizing film. The bonding is usually performed so that the linearly polarizing film, the λ / 2 layer and the λ / 4 layer are arranged in this order in the thickness direction. Further, an adhesive layer or an adhesive layer may be used for bonding, if necessary.

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 transmitting other polarized light. Here, the vibration direction of linearly polarized light means the vibration direction of an electric field of linearly polarized light.

The linearly polarizing film usually includes a polarizer layer, and if necessary, a protective film layer for protecting the polarizer layer.
As the polarizer layer, for example, a film of a suitable vinyl alcohol-based polymer subjected to an appropriate treatment in an appropriate order and method can be used. Examples of such vinyl alcohol-based polymers include polyvinyl alcohol and partially formalized polyvinyl alcohol. Examples of film treatments include dyeing treatments with dichroic substances such as iodine and dichroic dyes, stretching treatments, and cross-linking treatments. Usually, in the stretching treatment for producing a polarizer layer, the film before stretching is stretched in the longitudinal direction, so that the obtained polarizing element layer can develop an absorption axis parallel to the longitudinal direction of the polarizer layer. This polarizer layer can absorb linearly polarized light having a vibration direction parallel to the absorption axis, and is particularly preferably one having an excellent degree of polarization. The thickness of the polarizer layer is generally, but is not limited to, 5 μm to 80 μm.

Any transparent film can be used as the protective film layer for protecting the polarizer layer. Among them, a resin film having excellent 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, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, cyclic olefin resins, (meth) acrylic resins and the like. Among them, acetate resin, cyclic olefin resin, and (meth) acrylic resin are preferable in terms of small birefringence, and cyclic olefin resin is particularly preferable from the viewpoint of transparency, low hygroscopicity, dimensional stability, and light weight.

The linearly polarizing film can be produced, for example, by laminating a long polarizer layer and a long protective film layer. At the time of bonding, an adhesive may be used if necessary.

The linearly polarizing film preferably has an absorption axis in the longitudinal direction of the linearly polarizing film. Such a linearly polarizing film has a λ / 2 layer having an orientation angle θ (λ / 2) of 27.5 ° ± 10 ° (that is, 17.5 ° to 37.5 °) and 100 ° ± 20. It is preferable to produce a circularly polarizing film by laminating with a broadband wavelength film containing a λ / 4 layer having an orientation angle θ (λ / 4) of ° (that is, 80 ° to 120 °). According to the combination as described above, it is possible to manufacture a circularly polarizing film by laminating a long linear polarizing film and a long wideband wavelength film with their longitudinal directions parallel to each other. Therefore, it becomes possible to manufacture a circularly polarizing film by a roll-to-roll method. Therefore, it is possible to increase the production efficiency of the circularly polarizing film.

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

The circularly polarizing film may be further provided with an arbitrary layer in combination with the linearly polarizing film and the broadband wavelength film.
For example, the circularly polarizing film may include a protective film layer for suppressing scratches. Further, for example, the circularly polarizing film may include an adhesive layer or an adhesive layer for adhesion between the linearly polarizing film and the broadband wavelength film.

When the circularly polarizing film is provided on a surface capable of reflecting light, the reflection of external light can be effectively reduced. In particular, the circularly polarizing film is useful in that it can effectively reduce the reflection of external light in a wide wavelength range in the visible region. Since the reflection of external light can be effectively reduced in such a wide wavelength range, the circularly polarizing film can suppress coloring due to an increase in the reflection intensity of light of a part of wavelengths. The circularly polarizing film can obtain the above-mentioned effects of suppressing reflection and suppressing coloring at least in the front direction thereof, and usually can also be obtained in the inclination direction thereof. Further, the effects of reflection suppression and coloring suppression in the tilting direction can usually be obtained in all azimuth directions of the main surface of the film.

[9. Image display device]
Utilizing the function of suppressing the reflection of external light as described above, the circularly polarizing film can be used as a reflection suppressing film of an organic electroluminescence display device (hereinafter, may be appropriately referred to as an "organic EL display device"). ..

The organic EL display device includes a piece of a circularly polarizing film obtained by cutting out from a long circularly polarizing film.
When the organic EL display device includes a circularly polarizing film piece, the organic EL display device usually includes a circularly polarizing film piece on the display surface. By providing a circularly polarizing film piece on the display surface of the organic EL display device so that the surface on the linearly polarizing film side faces the viewing side, light incident from the outside of the device is reflected inside the device and emitted to the outside of the device. As a result, glare on the display surface of the display device can be suppressed. Specifically, the light incident from the outside of the apparatus becomes circularly polarized light 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 (reflecting electrode, etc.) that reflects light in the display device, and when it passes through the broadband wavelength film again, it vibrates in a direction orthogonal to the vibration direction (polarization axis) of the incident linearly polarized light. It becomes linearly polarized light having a direction (polarization axis) and does not pass through the linearly polarizing film. As a result, the reflection suppression function is achieved. Further, since the reflection suppression function can be obtained in a wide wavelength range, coloring of the display surface can be suppressed.

Further, the circularly polarizing film may be provided in a liquid crystal display device. Such a liquid crystal display device includes a piece of a circularly polarizing film obtained by cutting out from a long circularly polarizing film.
When the liquid crystal display device is provided with a circularly polarizing film piece so that the surface on the linearly polarizing film side faces the viewing side, it is possible to suppress the light incident from the outside of the device from being reflected inside 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.
Further, when the liquid crystal display device includes the circularly polarizing film pieces so that the broadband wavelength film, the linearly polarizing film, and the liquid crystal cells of the liquid crystal display device are arranged in this order from the viewing side, the image can be displayed in circularly polarized light. .. Therefore, the light emitted from the display surface can be stably visually recognized by the polarized sunglasses, and the image visibility when wearing the polarized sunglasses can be improved.

Further, in particular, when the 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 on the linearly polarizing film side faces the viewing side, the warp of the display panel can be suppressed. .. This effect will be described below.

Generally, an image display device includes a display panel including an organic electroluminescence element and a display element such as a liquid crystal cell. This display panel includes a base material such as a glass base material in order to increase the mechanical strength of the display panel. A display panel provided with a circularly polarizing film piece so that the surface on the linearly polarizing film side faces the viewing side is usually provided with a base material, a broadband wavelength film, and a linearly polarizing film in this order.

By the way, the polarizer layer of the linearly polarizing film generally tends to shrink in the in-plane direction in a high temperature environment. When the polarizer layer tries to shrink in this way, a stress that tends to warp the display panel is generated in the display panel provided with the linear polarizing film including the polarizing element layer. Warpage of the display panel can cause deterioration in image quality, and it is desirable to suppress it. Regarding this warp, it has been found that the larger the distance between the polarizer layer and the base material of the display panel, the larger the warp tends to be.

Since the adhesive layer was thick in the wideband wavelength film produced by the conventional manufacturing method in which both the λ / 2 layer and the λ / 4 layer were laminated after each production, the entire wideband wavelength film was also thick. Therefore, in the conventional wideband wavelength film, the distance between the polarizer layer and the base material of the display panel is large, so that the warp of the display panel tends to be large.
On the other hand, in the broadband wavelength film produced as a co-stretched film as described above, the λ / 2 layer and the λ / 4 layer are in direct contact with each other, or the λ / 2 layer and the λ / 4 layer are provided between the λ / 2 layer and the λ / 4 layer. The thin film layer to be formed can be thinned. Therefore, since the entire broadband wavelength film can be made thin, the distance between the polarizer layer and the base material of the display panel can be reduced. Therefore, it is possible to suppress the warp of the display panel.

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to the examples shown below, and can be arbitrarily modified and implemented without departing from the scope of claims of the present invention and the equivalent scope thereof.

In the following description, "%" and "part" representing quantities are based on weight unless otherwise specified. The operations described below were performed under normal temperature and pressure conditions unless otherwise specified.

[Evaluation method]
[Measuring method of optical characteristics 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 phase difference meter (“AxoScan” manufactured by Axometrics). The measurement wavelength was 590 nm.

[Measurement method of optical characteristics of each layer of broadband wavelength film]
The wideband wavelength film to be evaluated was installed on the stage of a phase difference meter (“AxoScan” manufactured by Axometrics). Then, the change in the polarization state of the polarized light transmitted through the wideband wavelength film before and after passing through the wideband wavelength film was measured as the transmitted polarization characteristic of the wideband wavelength film. This measurement was performed as a multi-directional measurement performed in a range of polar angles −55 ° to 55 ° with respect to the main surface of the broadband wavelength film. Further, the multi-directional measurement was performed in each of the azimuth directions of 45 °, 90 °, 135 ° and 180 °, with the azimuth direction of the main surface of the broadband wavelength film as 0 °. The measurement wavelength of the above measurement was 590 nm.

Next, the in-plane retardation Re of each layer, the retardation Rth in the thickness direction, the NZ coefficient, and the orientation angle were obtained by performing a fitting calculation from the transmitted polarization characteristics measured as described above. The fitting calculation was performed by setting the three-dimensional refractive index and the orientation angle of each layer included in the wideband wavelength film as fitting parameters. Further, for the 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 "LCD Master" manufactured by Shintec Co., Ltd. as simulation software, the circularly polarizing films manufactured in each Example and Comparative Example were modeled, and the color difference ΔE * ab was calculated with the following settings.
In the simulation model, a structure was set in which a circularly polarizing film was attached to the reflective surface of an aluminum mirror having a flat reflective surface so that the λ / 4 layer side of the broadband wavelength film was in contact with the mirror. Therefore, in this model, a structure in which a linearly polarizing film, a λ / 2 layer, a λ / 4 layer, and a mirror are provided in this order is set in the thickness direction.
Then, in the above model, the color difference ΔE * ab when the circularly polarizing film was irradiated with light from the D65 light source was calculated in the front direction of the circularly polarizing film. In calculating the color difference ΔE * ab, the reflected light of the aluminum mirror to which the circularly polarizing film was not attached was used as a reference in the directions of the polar angle of 0 ° and the azimuth angle of 0 °. Further, 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 means that the smaller the value is, the smaller the change in color is, which is preferable.

[Visual evaluation of circularly polarizing film]
The polarizing plate provided in the image display device (Apple Watch "Apple Watch" (registered trademark)) is peeled off, and the display surface of the image display device and the λ / 4 layer surface of the circularly polarizing film to be evaluated are separated from each other by an adhesive layer (adhesive layer (registered trademark)). It was pasted together via Nitto Denko's "CS9621"). Set the display surface to the black display state (the state where black is displayed on the entire screen), and observe the display surface from all directions of the polar angle θ = 0 ° (front direction) and the polar angle θ = 60 ° (tilt direction). did. The smaller the brightness and coloring due to the reflection of external light, the better the result. The results of the observations were evaluated according to the following criteria.
"A": There is no visible level of brightness and coloring.
"B": Luminance and coloring occur at a visible level.
"C": Brightness and coloring occur severely.

[Example 1]
(First step: Manufacture of layer (A))
As a resin having a positive intrinsic birefringence, a pellet-shaped norbornene-based resin (manufactured by Zeon Corporation; glass transition temperature 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 the form of a sheet. The extruded resin was cooled to obtain a long pre-stretched film having a thickness of 160 μm. The obtained pre-stretched film was wound on a roll and recovered.

The pre-stretched film was pulled out of the roll and continuously fed to the tenter stretcher. Then, the pre-stretched film was stretched by this tenter stretching machine to obtain a long stretched film as the layer (A). In this stretching, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the pre-stretched film was 90 °, the stretching temperature was 135 ° C., and the stretching ratio was 2.0 times. The orientation angle of the obtained stretched film was 90 °, the in-plane retardation Re was 250 nm, and the thickness was 80 μm. The obtained stretched film was wound on a roll and recovered.

(Second step: Formation of layer (B))
A liquid composition containing a styrene-maleic anhydride copolymer (“Daylark D332” manufactured by Nova Chemical Co., Ltd., glass transition temperature 130 ° C., oligomer component content 3% by weight) was prepared as a resin having a negative intrinsic birefringence. This liquid composition contained methyl ethyl ketone as a solvent, and the concentration of the styrene-maleic anhydride copolymer in the liquid composition was 10% by weight.

The stretched film was pulled out from the roll, and the above-mentioned liquid composition was applied onto the stretched film. Then, the coated liquid composition was dried to form a layer (thickness 10 μm) of a styrene-maleic anhydride copolymer as a layer (B) on the stretched film. As a result, a multi-layer film including the layer (A) and the layer (B) was obtained. The obtained multi-layer film was wound on a roll and collected.

(Third step: Stretching of multi-layer film)
The multilayer film was pulled out from the roll and continuously supplied to the tenter stretching machine. Then, 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 15 °, the stretching temperature was 130 ° C, and the stretching ratio was 1.5 times. As a result, 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.

(Manufacturing of circularly polarizing film)
A long linear polarizing film having an absorption axis in the longitudinal direction was prepared. The linearly polarizing film and the wideband wavelength film were bonded together with their longitudinal directions parallel to each other. This bonding was performed using an adhesive (“CS-9621” manufactured by Nitto Denko KK). As a result, a linearly polarizing film, a circularly polarizing film having λ / 2 layers and λ / 4 layers in this order was obtained. The obtained circularly polarizing film was evaluated by the method described above.

[Example 2]
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 10 °.
Except for the above items, the broadband wavelength film and the circularly polarizing film were manufactured and evaluated 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 5 °.
Except for the above items, the broadband wavelength film and the circularly polarizing film were manufactured and evaluated by the same operation as in Example 1.

[Comparative Example 1]
As a resin having a positive intrinsic birefringence, a pellet-shaped norbornene-based resin (manufactured by Zeon Corporation; glass transition temperature 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 the form of a sheet. The extruded resin was cooled to obtain a long pre-stretched film having a thickness of 110 μm. The obtained pre-stretched film was wound on a roll and recovered.

The pre-stretched film was pulled out of the roll and continuously supplied to the roll stretching machine. Then, the unstretched film was freely uniaxially stretched by this roll stretching machine to obtain a long stretched film. In this stretching, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the pre-stretched film was 0 °, the stretching temperature was 135 ° C., and the stretching ratio was 1.9 times. The orientation angle of the obtained stretched film was 0 °, the in-plane retardation Re was 350 nm, and the thickness was 80 μm.

A broadband wavelength film and a circularly polarizing film were produced and evaluated by the same operation as in Example 1 except that the stretched film thus obtained was used as the layer (A).

[Comparative Example 2]
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 0 °. Further, the multi-layer film was stretched in the third step by free uniaxial stretching using a roll stretching machine.
Except for the above items, the broadband wavelength film and the circularly polarizing film were manufactured and evaluated by the same operation as in Example 1.

[Comparative 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 45 °.
Except for the above items, the broadband wavelength film and the circularly polarizing film were manufactured and evaluated by the same operation as in Example 1.

[Comparative Example 4]
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 60 °.
Except for the above items, the broadband wavelength film and the circularly polarizing film were manufactured and evaluated 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 table below, the meanings of the abbreviations are as follows.
COP: Norbornene resin.
ST: Styrene-maleic anhydride copolymer.
Re: In-plane lettering.
Rth: Lettering in the thickness direction.
Orientation angle: The angle formed by the slow axis with respect to the longitudinal direction.
Total thickness: Total thickness of λ / 2 layer and λ / 4 layer.
Vertical: Longitudinal direction.
Horizontal: Width direction.
Diagonal: Diagonal direction.

100 layers (A)
200 double glazing 210 layers (B)
300 wideband wavelength film

Claims (9)

With the first step of preparing the layer (A) as a long resin film;
A second step of forming a resin layer (B) having a negative intrinsic birefringence on the layer (A) to obtain a multi-layer film;
The multilayer film is stretched in an oblique direction that is neither parallel nor perpendicular to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film having λ / 2 layer and λ / 4 layer. Steps and; are included in this order,
The layer (A) prepared in the first step has a slow axis parallel to or perpendicular to the longitudinal direction of the layer (A).
A method for producing a broadband wavelength film, wherein 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 the angle formed by the slow axis of the λ / 2 layer with respect to the longitudinal 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 longitudinal direction of the broadband wavelength film. ) The method for producing a broadband wavelength film according to claim 1, wherein the third step comprises stretching the multilayer film in an oblique direction forming an angle of 45 ° or less with respect to the longitudinal direction of the multilayer film. .. The method for producing a broadband wavelength film according to claim 1 or 2, wherein the angle θ (λ / 2) is in the range of 27.5 ° ± 10 °. The method for producing a broadband wavelength film according to any one of claims 1 to 3, wherein the angle θ (λ / 4) is in the range of 100 ° ± 20 °. The method for producing a broadband wavelength film according to any one of claims 1 to 4, wherein the λ / 2 layer is a layer obtained by stretching the layer (A). The method for producing a broadband wavelength film according to any one of claims 1 to 5, wherein the λ / 4 layer is a layer obtained by stretching the layer (B). A step of manufacturing a broadband wavelength film by the manufacturing method according to any one of claims 1 to 6;
A method for producing a circularly polarizing film, which comprises a step of laminating the broadband wavelength film and a long linearly polarizing film; The method for producing a circularly polarizing film according to claim 7, wherein the linearly polarizing film has an absorption axis in the longitudinal direction of the linearly polarizing film. It is a long wideband wavelength film
A λ / 2 layer having a slow phase axis at an angle of 27.5 ° ± 10 ° with respect to the longitudinal direction of the broadband wavelength film, and
A long broadband wavelength film, which is a co-stretched film including a λ / 4 layer having a slow axis having an angle of 100 ° ± 20 ° with respect to the longitudinal direction of the broadband wavelength film.

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