CN112105970A

CN112105970A - Broadband wavelength film, method for producing same, and method for producing circularly polarizing film

Info

Publication number: CN112105970A
Application number: CN201980026053.1A
Authority: CN
Inventors: 石原次郎; 大里和弘
Original assignee: Zeon Corp
Current assignee: Zeon Corp
Priority date: 2018-04-27
Filing date: 2019-04-22
Publication date: 2020-12-18
Anticipated expiration: 2039-04-22
Also published as: TW201945773A; TWI798426B; CN112105970B; JPWO2019208512A1; KR20210004985A; JP7413997B2; WO2019208512A1

Abstract

The invention provides a method for manufacturing a broadband wavelength film, which sequentially comprises the following steps: a first step of preparing a layer (A) which is a resin film having a slow axis parallel or perpendicular to the longitudinal direction; a second step of forming a layer (B) of a resin having a negative intrinsic birefringence on the layer (a) to obtain a multilayer film; a third step of obliquely stretching the multilayer film to obtain a long broadband wavelength film having λ/2 layers and λ/4 layers; the lambda/2 layer and the lambda/4 layer of the broadband wavelength film satisfy formula (1). θ (λ/4) {45 ° +2 × θ (λ/2) } ± 5 ° (1) (θ (λ/2) represents an angle formed by the slow axis of the λ/2 layer and the longitudinal direction of the broadband wavelength film, and θ (λ/4) represents an angle formed by the slow axis of the λ/4 layer and the longitudinal direction of the broadband wavelength film.

Description

Broadband wavelength film, method for producing same, and method for producing circularly polarizing film

Technical Field

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

Background

Various methods for producing an optical film having 2 or more layers have been conventionally studied (see patent documents 1 to 3).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2016/047465;

patent document 2: international publication No. 2009/031433;

patent document 3: japanese patent laid-open No. 2009-237534.

Disclosure of Invention

Problems to be solved by the invention

As a broadband wavelength film that can function as a wavelength plate in a wide wavelength band, a film including a combination of a λ/2 wave plate and a λ/4 wave plate is known. Such a broadband wavelength film has been conventionally produced by a production method including the following steps: a step of stretching a certain film to obtain a lambda/2 wave plate, a step of stretching another film to obtain a lambda/4 wave plate, and a step of laminating the lambda/2 wave plate and the lambda/4 wave plate to obtain a broadband wavelength film.

Further, the following techniques are known: the circularly polarizing film is obtained by combining the above-described broadband wavelength film with a linear polarizing film which is a film capable of functioning as a linear polarizer. In general, a long linear polarizing film has an absorption axis in a longitudinal direction or a width direction thereof. Therefore, when a circular polarizing film is obtained by combining a broadband wavelength film and a long linear polarizing film, the slow axis of the λ/2 wave plate is required to be inclined neither parallel nor perpendicular to the width direction thereof.

In order to easily produce a desired λ/2 wave plate having a slow axis in an oblique direction as described above, the applicant developed a technique of performing stretching 2 times or more as described in patent document 1. Accordingly, in the entire method for producing a broadband wavelength film, since stretching is performed 1 or more times for obtaining the λ/4 wave plate and 2 or more times for obtaining the λ/2 wave plate, the total number of times of stretching is 3 or more times. However, when the number of times of stretching is as large as 3 or more, the operation is troublesome.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a broadband wavelength film which can be efficiently produced by a small number of steps, and a method for producing the same; and a method for producing a circular polarizing film comprising the method for producing a broadband wavelength film.

Means for solving the problems

The present inventors have conducted intensive studies in order to solve the above problems. As a result, the present inventors have found that a broadband wavelength film can be efficiently produced with a small number of steps by a production method comprising the following steps in this order: a first step of preparing a layer (A) which is a resin film having a slow axis parallel or perpendicular to the longitudinal direction; a second step of forming a layer (B) of a resin having a negative intrinsic birefringence on the layer (A) to obtain a multilayer film; and a third step of stretching the multilayer film in an oblique direction which is neither parallel nor perpendicular to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film having λ/2 layers and λ/4 layers.

That is, the present invention includes the following.

[1] A method for manufacturing a broadband wavelength film, comprising the following steps in this order:

a first step of preparing a layer (A) which is a long resin film;

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

a third step of stretching the multilayer film in an oblique direction which is neither parallel nor perpendicular to the longitudinal direction of the multilayer film to obtain a long broadband wavelength film having λ/2 layers and λ/4 layers;

the layer (A) prepared in the first step has a slow axis parallel or perpendicular to the longitudinal direction of the layer (A),

the lambda/2 layer and the lambda/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-mentioned formula (1),

θ (λ/2) represents an angle formed between the slow axis of the λ/2 layer and the longitudinal direction of the broadband wavelength film,

θ (λ/4) represents an angle formed by the slow axis of the λ/4 layer and the longitudinal direction of the broadband wavelength film)

[2] The method of producing a broadband wavelength film according to [1], wherein the third step includes a step of stretching the multilayer film in an oblique direction at an angle of 45 ° or less to a longitudinal direction of the multilayer film.

[3] The method for producing a broadband wavelength film according to [1] or [2], wherein the angle θ (λ/2) is in a 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 a 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 method for manufacturing a circular polarizing film, comprising the steps of:

a step of producing a broadband wavelength film by the production method according to any one of [1] to [6 ]; and

and a step of bonding the broadband wavelength film to the long linear polarizing film.

[8] The method for producing a circular polarizing film according to [7], wherein the linear polarizing film has an absorption axis in a longitudinal direction of the linear polarizing film.

[9] A long, broadband wavelength film which is a co-stretched film having lambda/2 layers and lambda/4 layers,

the lambda/2 layer has a slow axis forming an angle of 27.5 DEG + -10 DEG with the longitudinal direction of the broadband wavelength film,

The λ/4 layer has a slow axis that makes an angle of 100 ° ± 20 ° with the longitudinal direction of the broadband wavelength film.

Effects of the invention

According to the present invention, there can be provided: a broadband wavelength film which can be efficiently produced with a small number of steps and a method for producing the same; and a method for producing a circular polarizing film comprising the method for producing a broadband wavelength film.

Drawings

Fig. 1 is a perspective view schematically showing a layer (a) as a resin film prepared by a first step of a method for manufacturing a broadband wavelength film according to an embodiment of the present invention.

Fig. 2 is a perspective view schematically showing a multilayer film obtained by the second step of the method for producing a broadband wavelength film according to one embodiment of the present invention.

Fig. 3 is a perspective view schematically showing a broadband wavelength film obtained by a third step of the method for manufacturing a broadband wavelength film according to an embodiment of the present invention.

Detailed Description

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be modified and implemented arbitrarily without departing from the scope and range of equivalents of the claims of the present invention.

In the following description, a "long" film is a film having a length of 5 times or more, preferably 10 times or more, with respect to the width, and more specifically, a film having a length enough to be stored or transported in a roll form. The upper limit of the length of the film is not particularly limited, and may be, for example, 10 ten thousand times or less with respect to the width.

In the following description, the slow axis of a film or layer means the in-plane slow axis of the film or layer unless otherwise specified.

In the following description, unless otherwise specified, the orientation angle of a film or layer means the angle that the slow axis of the film or layer makes with the longitudinal direction of the film or layer.

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

In the following description, unless otherwise specified, the angular relationship between the direction of the in-plane optical axis (slow axis, transmission axis, absorption axis, etc.) and the geometric direction (the longitudinal direction and the width direction of the film, etc.) of a certain product (a broadband wavelength film, a circular polarizing film, etc.) is such that the deviation in one direction is defined as positive and the deviation in the other direction is defined as negative, and the positive and negative directions are defined in the same manner in the constituent elements in the product. For example, in the broadband wavelength film, "an angle formed by the slow axis of the λ/2 layer and the longitudinal direction of the broadband wavelength film is 27.5 °, and an angle formed by the slow axis of the λ/4 layer and the longitudinal direction of the broadband wavelength film is 100 °" indicates the following 2 cases:

when the broadband wavelength film is viewed from one side, the slow axis of the λ/2 layer is shifted clockwise by 27.5 ° from the longitudinal direction of the broadband wavelength film, and the slow axis of the λ/4 layer is shifted clockwise by 100 ° from the longitudinal direction of the broadband wavelength film.

When the broadband wavelength film is viewed from one side thereof, the slow axis of the λ/2 layer is shifted counterclockwise by 27.5 ° from the longitudinal direction of the broadband wavelength film, and the slow axis of the λ/4 layer is shifted counterclockwise by 100 ° from the longitudinal direction of the broadband wavelength film.

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

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

In the following description, unless otherwise specified, the oblique direction of a certain film means a direction which is neither parallel nor perpendicular to the main surface of the film, and specifically means a direction in which the polar angle of the main surface is in a range of more than 0 ° and less than 90 °.

In the following description, unless otherwise specified, a material having positive intrinsic birefringence means a material having a refractive index in the stretching direction larger than that in the direction perpendicular thereto. Unless otherwise specified, a material having negative intrinsic birefringence means a material having a refractive index in the stretching direction smaller than that in the direction perpendicular thereto. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

In the following description, "(meth) acrylic group" includes "acrylic group", "methacrylic group", and combinations of these.

In the following description, unless otherwise specified, the in-plane retardation Re of the layer is a value expressed by Re ═ nx-ny × d. In addition, unless otherwise specified, the retardation Rth in the thickness direction of the layer is a value expressed by Rth [ { (nx + ny)/2} -nz ] × d. Further, unless otherwise specified, the NZ coefficient of the layer is a value represented by (nx-NZ)/(nx-ny). Here, nx represents a refractive index in a direction in which the maximum refractive index is given among directions (in-plane directions) perpendicular to the thickness direction of the layer. ny represents a refractive index in a direction orthogonal to the nx direction among the in-plane directions of the layer. nz represents a refractive index in the thickness direction of the layer. d represents the thickness of the layer. Unless otherwise specified, the measurement wavelength was 590 nm.

In the following description, unless otherwise specified, the directions of the elements "parallel", "perpendicular", and "orthogonal" may include errors in the range of ± 3 °, ± 2 °, or ± 1 °, for example, within a range that does not impair the effects of the present invention.

[1. summary ]

Fig. 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. 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 one embodiment of the present invention. Fig. 3 is a perspective view schematically showing a broadband wavelength film 300 obtained in a third step of the method for producing a broadband wavelength film according to an embodiment of the present invention.

The method for manufacturing the broadband wavelength film 300 according to one embodiment of the present invention includes the following steps in order:

(1) a first step of preparing a layer (a)100 as a long resin film as shown in fig. 1;

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

(3) the third step stretches the multilayer film 200 to obtain a long broadband wavelength film 300 shown in fig. 3.

As shown in FIG. 1, the layer (A)100 prepared in the first step has a slow axis A parallel or perpendicular to the longitudinal direction of the layer (A)100₁₀₀. In the second step, the layer (B)210 is formed on the layer (a)100 to obtain the multilayer film 200 shown in fig. 2, and then the multilayer film 200 is stretched in the third step. The stretching is performed in a diagonal direction which is neither parallel nor perpendicular to the length direction of the multilayer film 200 to obtain λ/2 layers and λ/4 layers having a slow axis in a desired direction.

By the stretching in the third step, co-stretching is performed in which the layer (a)100 and the layer (B)210 are simultaneously stretched. Thus, as shown in FIG. 3, a slow axis A is performed in layer (A)100₁₀₀And adjustment of the direction of the light source and adjustment of the optical characteristics. On the other hand, a slow axis A appears in the layer (B)210₂₁₀And optical characteristics are exhibited. The stretched layer (a)100 functions as one of a λ/2 layer and a λ/4 layer, and the stretched layer (B)210 functions as the other of a λ/2 layer and a λ/4 layer. Therefore, by the above manufacturing method, the broadband wavelength film 300 having the λ/2 layer and the λ/4 layer can be obtained. FIG. 3 shows that the stretched layer (A)100 functions as a lambda/2 layer and the stretched layer (B)210 functions as a lambda/4 layerThe structure of the broadband wavelength film 300 is not limited to this example.

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

θ(λ/4)＝{45°+2×θ(λ/2)}±5° (1)

The expression (1) indicates that 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. In the formula (1), θ (λ/2) represents the slow axis A of the λ/2 layer₁₀₀And the length direction A of the broadband wavelength film 300₃₀₀The angle formed. Further, θ (λ/4) represents the slow axis A of the λ/4 layer₂₁₀And the length direction A of the broadband wavelength film 300₃₀₀The angle formed. By including a combination of the λ/2 layer and the λ/4 layer satisfying the formula (1), the broadband wavelength film 300 can function as a broadband wavelength film that imparts an in-plane retardation of about 1/4 wavelengths of the wavelength of light transmitted through the film in a wide wavelength range.

In general, the longitudinal direction a of the broadband wavelength film 300₃₀₀The longitudinal direction of the λ/4 layer (not shown) and the longitudinal direction of the λ/2 layer (not shown) are aligned. Thus, the angle θ (λ/2) represents the slow axis A of the λ/2 layer₁₀₀The orientation angle formed with respect to the longitudinal direction of the λ/2 layer is hereinafter sometimes referred to as "orientation angle θ (λ/2)". Further, the angle θ (λ/4) represents the slow axis A of the λ/4 layer₂₁₀The orientation angle formed with respect to the longitudinal direction of the λ/4 layer is hereinafter sometimes referred to as "orientation angle θ (λ/4)".

[2. first step ]

In the first step, a layer (a) of a resin film which is long and has a slow axis in a predetermined direction in a plane is prepared. As the layer (a), a resin film having a multilayer structure including 2 or more layers can be used, but a resin film having a single-layer structure including only 1 layer is generally 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 can be used, but a resin having a positive intrinsic birefringence is preferably used in view of the fact that the production of a broadband wavelength film can be particularly easily performed.

Resins with positive intrinsic birefringence generally contain polymers with positive intrinsic birefringence. Examples of the polymer having positive intrinsic birefringence include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; a polycarbonate; a polyarylate; cellulose ester polymers, polyethersulfones; polysulfones; polyallyl sulfone; polyvinyl chloride; cyclic olefin polymers such as norbornene polymers; rod-like liquid crystal polymers, and the like. These polymers may be used alone in 1 kind, or may be used in combination in 2 or more kinds at an arbitrary ratio. The polymer may be a homopolymer or a copolymer. Among these, polycarbonate polymers are preferred in terms of excellent retardation development and stretchability at low temperatures. In addition, cyclic olefin polymers are preferred in terms of excellent mechanical properties, heat resistance, transparency, low hygroscopicity, dimensional stability, and lightweight properties.

The proportion of the polymer in the resin contained in the layer (a) is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and particularly preferably 90 to 100% by weight. In the case where the ratio of the polymer is within 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 above-mentioned polymers in combination with the polymers. Examples of the optional components include: colorants such as pigments and dyes; a plasticizer; a fluorescent whitening agent; a dispersant; a heat stabilizer; a light stabilizer; an ultraviolet absorber; an antistatic agent; an antioxidant; microparticles; surfactants, and the like. These components can be used alone in 1 kind, also can be used in any ratio of combination of 2 or more.

The glass transition temperature TgA of the resin contained in the layer (a) is preferably 100 ℃ or higher, more preferably 110 ℃ or higher, particularly preferably 120 ℃ or higher, preferably 190 ℃ or lower, more preferably 180 ℃ or lower, and particularly preferably 170 ℃ or lower. When the glass transition temperature of the resin contained in the layer (a) is not less 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 (a) in a high-temperature environment can be improved. In addition, when the glass transition temperature of the resin contained in the layer (a) is not more than the upper limit of the above range, the stretching treatment can be easily performed.

The layer (a) prepared in the first step has a slow axis parallel or perpendicular to the longitudinal direction of the layer (a). Therefore, the orientation angle formed by the slow axis of the layer (a) and the longitudinal direction of the layer preferably satisfies any one of the following (a1) and (a 2).

(a1) The method comprises the following steps 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, more preferably 2 ° or less, and particularly preferably 1 ° or less.

(a2) The method comprises the following steps 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, more preferably 92 ° or less, and particularly preferably 91 ° or less.

When the layer (a) having such a slow axis is used, a broadband wavelength film having preferable optical characteristics can be easily obtained.

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

For example, when it is desired to stretch the layer (a) to obtain a λ/2 layer, the in-plane retardation of the layer (a) is preferably 150nm or more, more preferably 180nm or more, particularly preferably 200nm or more, preferably 400nm or less, more preferably 380nm or less, and particularly preferably 350nm or less. The NZ coefficient of the layer (a) is preferably 1.0 or more, more preferably 1.1 or more, and particularly preferably 1.15 or more, preferably 1.7 or less, more preferably 1.65 or less, and 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 broadband 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 a step of stretching an appropriately long resin film to develop a slow axis in the resin film. In the following description, the resin film before the stretching treatment is sometimes referred to as a "pre-stretched film", and the resin film obtained after stretching is sometimes referred to as a "stretched film".

The film before stretching can be produced by, for example, 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 the layer (a) excellent in mechanical strength and surface accuracy, an extrusion molding method, an inflation molding method, or a press molding method is preferable, and among them, an extrusion molding method is particularly preferable from the viewpoint of enabling efficient and easy production of the layer (a).

After preparing a long film before stretching, the long film before stretching can be stretched to obtain a layer (a) as a stretched film.

The slow axis of layer (a) is typically developed by stretching the film prior to stretching. Therefore, the stretching direction of the film before stretching is preferably set in accordance with the direction of the slow axis of the layer (a). For example, in the case where the film before stretching is formed of a resin having positive intrinsic birefringence, the stretching direction of the film before stretching is preferably set to a direction parallel to the slow axis of the layer (a) to be prepared in the first step. In addition, for example, in the case where the film before stretching is formed of a resin having a negative intrinsic birefringence, the stretching direction of the film before stretching is preferably set to a direction perpendicular to the slow axis of the layer (a) to be prepared in the first step. Therefore, the stretching direction of the film before stretching is preferably a direction parallel or perpendicular to the longitudinal direction of the film before stretching. In particular, the direction of the film before stretching is preferably a direction perpendicular to the longitudinal direction of the film before stretching, from the viewpoint of easy production of a desired broadband wavelength film.

The stretch 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, more preferably 3.0 times or less. When the stretch ratio is equal to or higher than the lower limit of the above range, the refractive index in the stretching direction can be increased. In addition, when the stretching magnification is equal to or less than 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 more, more preferably "TgA +2 ℃", particularly preferably "TgA +5 ℃", preferably "TgA +40 ℃", more preferably "TgA +35 ℃", and particularly preferably "TgA +30 ℃". Here, TgA refers to the glass transition temperature of the resin contained in the layer (a). When the stretching temperature is within the above range, the molecules contained in the film before stretching can be reliably oriented, and thus the layer (a) having desired optical properties can be easily obtained.

The stretching can be performed by using an appropriate stretching machine such as a roll stretcher or a tenter, while continuously conveying the film in the longitudinal direction before stretching. For example, when the film before stretching is stretched in the longitudinal direction of the film before stretching, a roll stretcher is preferably used. The free uniaxial stretching can be easily performed by a roll stretcher. The uniaxial free stretch is a stretch in a certain direction, and a control force is not applied in a direction other than the stretched direction. As these stretching machines, for example, a stretching machine described in patent document 1 can be used.

[3. fourth step ]

The method for producing a broadband wavelength film may include a step of preparing the layer (a) in the first step and then forming a thin film layer on the layer (a) as necessary. By forming an appropriate thin film layer, the thin film layer can function as an easy-adhesion layer, and the adhesion between the layer (a) and the layer (B) can be improved. Further, the thin film layer preferably has solvent resistance. Such a film layer is generally formed of a resin.

Examples of the material of the film layer include acrylic resin, urethane resin, acrylic urethane resin, ester resin, and ethylene imine resin. The acrylic resin is a resin containing a propylene-based polymer. Further, the polyurethane resin is a resin containing polyurethane. Polymers such as propylene-based polymers and polyurethanes generally have high adhesion to a wide variety of resins, and thus the adhesion between the layer (a) and the layer (B) can be improved. These polymers may be used alone in 1 kind, or may be used in combination in 2 or more kinds at an arbitrary ratio.

The resin used as the film layer material may contain any component in combination with the polymer, such as a heat-resistant stabilizer, a weather-resistant stabilizer, a leveling agent, an antistatic agent, a slip agent, an antiblocking agent, an antifogging agent, a slip agent, a dye, a pigment, a natural oil, a synthetic oil, a wax, and a particle. Any of the components may be used alone in 1 kind, or may be used in combination in 2 or more kinds at any ratio.

The glass transition temperature of the resin as the film layer material 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 contained in the layer (B) whose intrinsic birefringence is negative. In particular, the temperature difference between the glass transition temperature of the resin as the film layer material and the lower one of the glass transition temperatures TgA and TgB is preferably 5 ℃ or more, more preferably 10 ℃ or more, and particularly preferably 20 ℃ or more. This can suppress retardation of the thin film layer due to stretching in the third step, and therefore the thin film layer in the broadband wavelength film can have optical isotropy. Therefore, the optical characteristics of the broadband wavelength film can be easily adjusted.

The thin film layer can be formed by, for example, a method including a step of coating a coating liquid including 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, 1 kind of solvent may be used alone, or 2 or more kinds may be used in combination at an arbitrary ratio.

Further, the coating liquid may contain a crosslinking agent. By using the crosslinking agent, the mechanical strength of the film layer can be improved, or the adhesiveness of the film layer to the layer (a) and the layer (B) can be improved. As the crosslinking agent, for example, an epoxy compound, an amino compound, an isocyanate compound, a carbodiimide compound, etc. can be usedA substance,

Oxazoline compounds, and the like. These may be used alone in 1 kind, or may be used in combination in 2 or more kinds at an arbitrary ratio. 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, and more preferably 65 parts by weight or less, relative to 100 parts by weight of the polymer in the coating liquid.

Examples of the coating method of the coating liquid include the same methods as those applicable to formation of the layer (B) described later.

By applying the coating liquid to the layer (a), a thin film layer can be formed. The thin film layer may be subjected to curing treatment such as drying and crosslinking, if necessary. Examples of the drying method include heat drying using an oven. Examples of the crosslinking method include heat treatment and irradiation treatment with active energy rays such as ultraviolet rays.

[4. second step ]

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

The resin having negative intrinsic birefringence is generally a thermoplastic resin, and includes a polymer having negative intrinsic birefringence. When a polymer having negative intrinsic birefringence is exemplified, there can be mentioned homopolymers and copolymers of styrene or styrene derivatives, and polystyrenic polymers comprising a copolymer of styrene or styrene derivatives and an optional monomer; a polyacrylonitrile polymer; a polymethyl methacrylate polymer; or a multipolymer of these; and cellulose compounds such as cellulose esters. Further, as the above-mentioned arbitrary monomer capable of copolymerizing styrene or a styrene derivative, for example, acrylonitrile, maleic anhydride, methyl methacrylate and butadiene are exemplified as preferable monomers. Among them, polystyrene-based polymers and cellulose compounds are preferable. These polymers may be used alone in 1 kind, or may be used in combination in 2 or more kinds at an arbitrary ratio.

The proportion of the polymer in the resin having a negative intrinsic birefringence value is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and particularly preferably 90 to 100% by weight. In the case where the ratio of the polymer is within 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 the plasticizer, the glass transition temperature TgB of the resin contained in the layer (B) can be appropriately adjusted. Examples of the plasticizer include phthalic acid esters, fatty acid esters, phosphoric acid esters, and epoxy derivatives. Specific examples of the plasticizer include plasticizers described in Japanese patent application laid-open No. 2007-233114. Further, 1 kind of the plasticizer may be used alone, or 2 or more kinds may be used in combination at an arbitrary ratio.

Among the plasticizers, phosphate esters are preferred in terms of availability and low cost. Examples of the phosphate ester include trialkyl phosphates such as triethyl phosphate, tributyl phosphate, and trioctyl phosphate; halogen-containing trialkyl phosphates such as trichloroethyl phosphate; triaryl phosphates such as triphenyl phosphate, tricresyl phosphate, tri (isopropylphenyl) phosphate, and cresyldiphenyl phosphate; alkyl-diaryl phosphates such as octyl diphenyl phosphate; and tris (alkoxyalkyl) phosphate such as tris (butoxyethyl) phosphate.

The amount of the plasticizer is preferably 0.001% by weight or more, more preferably 0.005% by weight or more, particularly preferably 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, relative to 100% by weight of the amount of the resin having a negative intrinsic birefringence contained in the layer (B). When the amount of the plasticizer is within the above range, the glass transition temperature TgB of the resin contained in the layer (B) can be appropriately adjusted, and thus appropriate stretching that can obtain a desired broadband wavelength film can be easily performed in the third step.

The resin whose intrinsic birefringence is negative may further contain any component other than the above-mentioned polymer and plasticizer in combination with the above-mentioned polymer and plasticizer. Examples of the optional component include the same optional components as those that can be contained in the resin contained in the layer (a). Any of the components may be used alone in 1 kind, or may be used in combination in 2 or more kinds at any ratio.

The glass transition temperature TgB of the resin having a negative intrinsic birefringence included in the layer (B) is preferably 80 ℃ or higher, more preferably 90 ℃ or higher, still more preferably 100 ℃ or higher, particularly preferably 110 ℃ or higher, and particularly preferably 120 ℃ or higher. When the glass transition temperature TgB of the resin having negative intrinsic birefringence is as high as this, the orientation relaxation of the resin having negative intrinsic birefringence can be reduced. The upper limit of the glass transition temperature TgB of the resin having a negative intrinsic birefringence is not particularly limited, but is usually 200 ℃.

From the viewpoint of adjusting the optical characteristics of both the layer (a) and the layer (B) to an appropriate range by stretching in the third step, 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) are preferably close to each other. Specifically, the absolute value | TgA-TgB | of the difference between the glass transition temperature TgA and the glass transition temperature TgB is preferably 20 ℃ or less, more preferably 15 ℃ or less, and particularly preferably 10 ℃ or less.

Layer (B) may have an in-plane retardance and a slow axis. When the layer (B) has an in-plane retardation and a slow axis, the in-plane retardation and the slow axis direction of the layer (B) can be adjusted by stretching in the third step. However, setting of the stretching conditions for such adjustment is liable to become complicated. Therefore, from the viewpoint of easily obtaining desired optical characteristics and slow axis direction in the layer (B) after stretching in the third step, the layer (B) formed in the second step preferably has no in-plane retardation and slow axis, or has a small in-plane retardation even if it has. Specifically, the in-plane retardation of the layer (B) is preferably 0nm to 20nm, more preferably 0nm to 15nm, and particularly preferably 0nm 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 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. In the case where 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 coating method, an extrusion method, a bonding method, or the like can be used.

In the case of forming the layer (B) by a coating method, the second step includes a step of coating a composition containing a resin having a negative intrinsic birefringence on the layer (a). The composition is usually a liquid composition containing a solvent and 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, 1, 4-dioxanone

Alkanes, 2-pentanone, N-dimethylformamide, and the like. Further, 1 kind of solvent may be used alone, or 2 or more kinds may be used in combination at an arbitrary ratio. The solvent may cause phenomena such as dissolution and orientation relaxation of the layer (a), but the liquid composition is generally applied to a small thickness and is dried quickly after application, and thus the above phenomena are negligible.

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

In the coating method, the second step includes a step of drying the composition to be coated as necessary after the composition is coated on the layer (a). By removing the solvent by drying, a layer (B) of a resin having a negative intrinsic birefringence can be formed on the layer (a). The drying can be carried out by a drying method such as natural drying, heat drying, drying under reduced pressure, and heat drying under reduced pressure.

In the case where the layer (B) is formed by an extrusion method, the second step includes a step of extruding a resin having a negative intrinsic birefringence on the layer (a). The extrusion of the resin is usually performed in a state where the resin is molten. Further, the resin is generally extruded into a film shape using a die. By adhering the resin having negative intrinsic birefringence thus extruded to the layer (a) or the film layer, the layer (B) of the resin having negative intrinsic birefringence can be formed on the layer (a). In addition, in the case of forming the layer (B) by an extrusion method, the second step generally includes a step of cooling and solidifying the resin having a negative intrinsic birefringence extruded and adhered to the layer (a).

In the case where the layer (B) is formed by a laminating method, the second step includes a step of laminating a film containing a resin having a negative intrinsic birefringence to the layer (a). Examples of the method for producing a film of a resin having negative intrinsic birefringence include melt molding methods such as extrusion molding, inflation molding, and press molding; solution casting method. In the lamination of the layer (a) and the film of the resin having negative intrinsic birefringence, an adhesive or a bonding agent may be used as needed.

Among the methods for forming the layer (B), a coating method is preferable. Generally, a resin having negative intrinsic birefringence tends to have low mechanical strength. However, by the coating method, even if such a resin having low mechanical strength is used, the layer (B) can be easily formed. In this regard, for example, in the case of using a bonding method, when the layer (B) is formed on an appropriate support film and the layer (B) is bonded to the layer (a), the layer (B) can be formed on the layer (a) while suppressing breakage of the layer (B). However, the coating method can reduce the number of steps required for forming the layer (B) as compared with a bonding method in which a plurality of steps of forming the layer (B) on a support film and transferring the layer (B) from the support film to the layer (a) are performed. Furthermore, by the coating method, an adhesive or a bonding agent is not required. In addition, the coating method 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. third step ]

After the multilayer film having the layer (a) and the layer (B) is obtained in the second step, a third step of stretching the multilayer film to obtain a long broadband wavelength film is performed. 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, whereby one of the λ/2 layer and the λ/4 layer can be obtained. Further, by stretching in the third step, the layer (B) exhibits a slow axis and the layer (B) exhibits optical characteristics, and 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 which is neither parallel nor perpendicular to the longitudinal direction of the multilayer film. The specific stretching direction is set from the in-plane direction of the multilayer film so that a desired broadband wavelength film can be obtained.

For example, when the layer (a) is a resin layer having positive intrinsic birefringence, the slow axis direction of the layer (a) changes so as to approach the stretching direction by stretching in the third step. For example, when the layer (a) is a resin layer having a negative intrinsic birefringence, the slow axis direction of the layer (a) is changed so as to approach a direction perpendicular to the stretching direction by stretching in the third step. In this way, the direction of the slow axis of the layer (a) generally changes with the stretching in the third step. Further, in the layer (B), generally, by stretching in the third step, a slow axis appears in a direction perpendicular to the stretching direction. Therefore, the stretching direction in the third step is preferably set so that λ/2 layers and λ/4 layers having slow axes in desired directions can be obtained by the above-described change in the direction of the slow axes in the layer (a) and the development of the slow axes in the layer (B).

The specific angle formed by the stretching direction of the multilayer film in the third step and the longitudinal direction of the multilayer film is preferably 4 ° or more, particularly preferably 5 ° or more, preferably 45 ° or less, more preferably 30 ° or less, and particularly preferably 20 ° or less. In the case of stretching the multilayer film in such a stretching direction, the direction of the slow axis of the λ/2 layer and the λ/4 layer can be easily controlled.

The size of the angle (absolute value of the angle) formed between the stretching direction of the multilayer film in the third step and the slow axis of the layer (a) is preferably 45 ° or more, more preferably 60 ° or more, particularly preferably 70 ° or more, preferably 86 ° or less, and particularly preferably 85 ° or less. In the case of stretching the multilayer film in such a stretching direction, the slow axes of the λ/2 layer and the λ/4 layer can be easily adjusted so as to satisfy the relationship of the formula (1).

The stretching 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 or less, and particularly preferably 2.0 times or less. When the stretch ratio in the third step is not less than the lower limit of the above range, the occurrence of wrinkles can be suppressed. In addition, when the stretch ratio in the third step is equal to or less than the upper limit of the above range, the slow axis directions of the λ/2 layer and the λ/4 layer can be easily controlled.

The stretching temperature in the third step preferably satisfies both of the following conditions (C1) and (C2) 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) whose intrinsic birefringence is negative.

(C1) The stretching temperature is preferably a temperature of TgA-20 ℃ or higher, more preferably a temperature of TgA-10 ℃ or higher, particularly preferably a temperature of TgA-5 ℃ or higher, preferably a temperature of TgA +30 ℃ or lower, more preferably a temperature of TgA +25 ℃ or lower, and particularly preferably a temperature of TgA +20 ℃ or lower.

(C2) The stretching temperature is preferably a temperature of TgB-20 ℃ or higher, more preferably a temperature of TgB-10 ℃ or higher, particularly preferably a temperature of TgB-5 ℃ or higher, preferably a temperature of TgB +30 ℃ or lower, more preferably a temperature of TgB +25 ℃ or lower, and particularly preferably a temperature of TgB +20 ℃ or lower.

By stretching at such a stretching temperature, the optical properties of the layer (a) can be appropriately adjusted, and the layer (B) can be made to exhibit desired optical properties. Thus, a broadband wavelength film having desired optical characteristics can be obtained.

The stretching in the third step may be performed using any stretching machine, and may be performed using, for example, a spread stretching machine or a roll stretching machine. Stretching using these stretching machines is preferably performed while continuously conveying a long multilayer film in the longitudinal direction.

[6. optional Process ]

The method for producing a broadband wavelength film may further include any process in combination with the above process.

For example, the method for manufacturing the broadband wavelength film may include a step of providing a protective layer on the surface of the broadband wavelength film.

Further, for example, the method for producing a broadband wavelength film may include a step of performing a surface treatment such as corona treatment or plasma treatment on the surface of 1 or 2 or more of the layer (a), the layer (B), and the thin film layer at an arbitrary timing. Thus, for example, after the surface of the layer (a) is subjected to surface treatment, the layer (B) or the thin film layer can be formed on the treated surface. Further, for example, after the surface of the thin film layer is subjected to surface treatment, the layer (B) may be formed on the treated surface. By performing the surface treatment, the adhesiveness between the layers on the surface after the surface treatment can be improved.

The first to fourth steps and any of the steps described above can be performed while continuously conveying a film such as the layer (a), a multilayer film, and a broadband wavelength film. The direction of transport of such a film is generally the longitudinal direction of the film. Thus, during 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 the conveyance.

[7. broadband wavelength film ]

By the above-described manufacturing method, a co-stretched film having a λ/2 layer and a λ/4 layer can be obtained. The lambda/2 layer and the lambda/4 layer of the co-stretched film satisfy the above formula (1). The combination of the λ/2 layer and the λ/4 layer satisfying the relationship expressed by the formula (1) can function as a broadband wavelength film that imparts an in-plane retardation of about 1/4 wavelengths of the wavelength of light transmitted through the film in a wide wavelength range (see japanese patent application laid-open No. 2007-004120). Thus, by the above-mentioned production method, a long broadband wavelength film can be obtained as a co-stretched film having λ/2 layers and λ/4 layers. From the viewpoint of realizing a broadband wavelength film capable of functioning in a wider wavelength range, the λ/2 layer and the λ/4 layer preferably satisfy formula (2), and more preferably satisfy formula (3). The expression (2) indicates that theta (lambda/4) is in the range of "{ +45 DEG +2 Xtheta (lambda/2) } -4 DEG" or more and "{ +45 DEG +2 Xtheta (lambda/2) } +4 DEG" or less. Further, the expression (3) indicates that θ (λ/4) is in the range of "{ +45 ° +2 × θ (λ/2) } -3 °" or more and "{ +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 production method, the stretching of the layer (a) and the stretching of the layer (B) are not performed separately as in the conventional method, but performed together in the third step. Therefore, the number of times of stretching treatment can be reduced as compared with the conventional one, and therefore, the number of steps required for producing a broadband wavelength film can be reduced, and thus, efficient production can be achieved. In the above-described production method for obtaining a broadband wavelength film by co-stretching the layer (a) and the layer (B) by stretching the multilayer film, displacement in the slow axis direction due to bonding does not occur unlike the conventional production method in which the λ/2 layer and the λ/4 layer are separately produced and then bonded. Therefore, since the directions of the slow axes of the λ/2 layer and the λ/4 layer are easily and precisely controlled, a high-quality wide-band wavelength film capable of realizing a circular polarizing film in which coloring can be effectively suppressed 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 a layer obtained by stretching the other of the layer (a) and the layer (B). Among these, in terms of ease of production of the broadband wavelength film, 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). Thus, the λ/2 layer is preferably a layer formed of the same resin as the layer (a), and the λ/4 layer is preferably a layer formed of the same resin as the layer (B).

The λ/2 layer is a layer having an in-plane retardation of usually 220nm or more and usually 300nm or less at a measurement wavelength of 590 nm. In the case where the λ/2 layer has such an in-plane retardation, a broadband wavelength film can be realized by combining the λ/2 layer and the λ/4 layer. Among these, from the viewpoint of obtaining a circular polarizing film excellent in the function of suppressing coloration in an oblique direction, the in-plane retardation of the λ/2 plate at a measurement wavelength of 590nm is preferably 230nm or more, more preferably 240nm or more, preferably 280nm or less, and more preferably 270nm or less.

The retardation of the lambda/2 layer in the thickness direction at a measurement wavelength of 590nm is preferably 130nm or more, more preferably 140nm or more, particularly preferably 150nm or more, preferably 300nm or less, more preferably 280nm or less, and particularly preferably 270nm or less. When the retardation in the thickness direction of the λ/2 layer is within the above range, a circularly polarizing film particularly excellent in the coloring suppressing function in an 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, and particularly preferably 1.5 or less. When the NZ coefficient of the λ/2 layer is within the above range, a circularly polarizing film particularly excellent in the coloring suppression function in an oblique direction can be obtained. Further, the λ/2 layer having such NZ coefficient can be easily manufactured.

The optical properties such as retardation and NZ coefficient of the λ/2 layer can be adjusted by, for example, the retardation and thickness of the layer (a) prepared in the first step, and the stretching conditions such as the stretching temperature, stretching ratio, and stretching direction in the third step.

The orientation angle θ (λ/2) of the λ/2 layer is preferably in the range of 27.5 ° ± 10 ° (i.e., in the range of 17.5 ° to 37.5 °), more preferably in the range of 27.5 ° ± 8 ° (i.e., in the range of 19.5 ° to 35.5 °), and particularly preferably in the range of 27.5 ° ± 5 ° (i.e., in the range of 22.5 ° to 32.5 °). A typical linear polarizing film has a transmission axis in its width direction and an absorption axis in its length direction. When the orientation angle θ (λ/2) of the λ/2 layer is within the above range, such a normal linear polarizing film can be combined to easily realize a circular polarizing film. In addition, 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 oblique direction of the obtained circularly polarizing film can be made good.

The orientation angle θ (λ/2) of the λ/2 layer can be measured, for example, in the direction of the slow axis of the layer (a) prepared in the first step; and adjusting the stretching conditions such as the stretching direction and the stretching ratio in the third step.

The thickness of the λ/2 layer is preferably 20 μm or more, more preferably 25 μm or more, further preferably 30 μm or more, preferably 80 μm or less, more preferably 70 μm or less, further preferably 60 μm or less. The mechanical strength of the lambda/2 layer can thereby be increased.

The λ/4 layer is a layer having an in-plane retardation of usually 90nm or more and usually 154nm or less at a measurement wavelength of 590 nm. In the case where the λ/4 layer has such an in-plane retardation, a broadband wavelength film can be realized by combining the λ/2 layer and the λ/4 layer. Among them, from the viewpoint of obtaining a circular polarizing film excellent in the function of suppressing coloration in an oblique direction, the in-plane retardation of the λ/4 layer at a measurement wavelength of 590nm is preferably 100nm or more, more preferably 110nm or more, preferably 140nm or less, and more preferably 130nm or less.

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

The NZ coefficient of the lambda/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, more preferably-0.05 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 particularly excellent in the coloring suppression function in an oblique direction can be obtained. Further, the λ/4 layer having such NZ coefficient can be easily manufactured.

The optical properties such as retardation and NZ coefficient of the λ/4 layer can be adjusted by, for example, the thickness of the layer (B) formed in the second step and the stretching conditions such as the stretching temperature, stretching ratio, stretching direction and the like in the third step.

The orientation angle θ (λ/4) of the λ/4 layer is preferably in the range of 100 ° ± 20 ° (i.e., in the range of 80 ° to 120 °), more preferably in the range of 100 ° ± 15 ° (i.e., in the range of 85 ° to 115 °), and particularly preferably in the range of 100 ° ± 10 ° (i.e., in the range of 90 ° to 110 °). When the orientation angle θ (λ/4) of the λ/4 layer is within the above range, it is possible to easily realize a circular polarizing film in combination with a normal linear polarizing film having a transmission axis in the width direction and an absorption axis in the length direction. In addition, 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 oblique direction of the obtained circularly polarizing film can be made good.

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

The thickness of the lambda/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 equal to or more than the lower limit of the above range, desired optical characteristics can be easily obtained. In addition, when the thickness of the λ/4 layer is equal to or less than the upper limit of the above range, the thickness of the broadband wavelength film can be reduced.

The lambda/2 layer and the lambda/4 layer are preferably in direct contact. This makes it possible to make the thickness of the broadband wavelength film thin.

In the case where the method for producing a broadband wavelength film includes the fourth step of forming a thin film layer, the broadband wavelength film has the thin film layer between the λ/2 layer and the λ/4 layer. The adhesive layer used in the conventional production method in which the λ/2 layer and the λ/4 layer are produced separately and then bonded to each other is generally as thick as 5 μm or more, whereas the thin film layer of the broadband wavelength film obtained by the above production method can be thinner than this. The thickness of the specific thin film layer is preferably less than 2.0. mu.m, more preferably less than 1.8. mu.m, and particularly preferably less than 1.5. mu.m. Since the thin film layer can be made thin, the thickness of the entire broadband wavelength film can be made thin. The lower limit of the thickness of the thin film layer is preferably as small as possible, and may be, for example, 0.1 μm.

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

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 accordance with JIS K0115 using an ultraviolet-visible spectrophotometer in the wavelength range of 400nm to 700 nm.

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%. The haze can be measured at 5 points using a haze meter NDH-300A manufactured by Nippon Denshoku industries Co., Ltd, according to JIS K7361-1997, and the average value obtained from these can be used.

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 manufacturing method, such a thin broadband wavelength film can be easily manufactured.

[8. circular polarizing film ]

The long circular polarizing film can be manufactured using the broadband wavelength film manufactured by the above-described method. Such a circular polarizing film can be produced by a production method including a step of producing a wide band wavelength film in the above production method and a step of laminating the wide band wavelength film to a long linear polarizing film. The lamination is usually performed by arranging a linear polarizing film, a λ/2 layer and a λ/4 layer in this order in the thickness direction. For the bonding, an adhesive layer or an adhesive layer may be used as necessary.

The linear 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 polarized light other than the linearly polarized light. Here, the vibration direction of linearly polarized light means a vibration direction of an electric field of linearly polarized light.

The linear polarizing film generally has a polarizer layer, and if necessary, a protective film layer for protecting the polarizer layer.

As the polarizer layer, for example, a polarizer layer in which an appropriate treatment is applied to a film of an appropriate vinyl alcohol polymer in an appropriate order and manner can be used. Examples of the polyvinyl alcohol include polyvinyl alcohol and partially acetalized polyvinyl alcohol. Examples of the treatment of the film include dyeing treatment with a dichroic substance such as iodine or a dichroic dye, stretching treatment, and crosslinking treatment. In general, in the stretching treatment for producing a polarizer layer, since the film before stretching is stretched in the longitudinal direction, the resulting polarizer layer can exhibit an absorption axis parallel to the longitudinal direction of the polarizer layer. The polarizer layer is a polarizer layer capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, and a polarizer layer having an excellent degree of polarization is particularly preferable. The thickness of the polarizer layer is usually 5 μm to 80 μm, but is not limited thereto.

As the protective film for protecting the polarizer layer, any transparent film can be used. Among them, a resin film excellent in transparency, mechanical strength, thermal stability, moisture resistance, 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. Among them, from the viewpoint of small birefringence, acetate resins, cyclic olefin resins, and (meth) acrylic resins are preferable, and from the viewpoint of transparency, low hygroscopicity, dimensional stability, lightweight property, and the like, cyclic olefin resins are particularly preferable.

The linear polarizing film can be produced by laminating an elongated polarizer layer and an elongated protective film layer, for example. In the bonding, an adhesive may be used 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 preferably laminated with a broadband wavelength film comprising a λ/2 layer having an orientation angle θ (λ/2) of 27.5 ° ± 10 ° (i.e., 17.5 ° to 37.5 °) and a λ/4 layer having an orientation angle θ (λ/4) of 100 ° ± 20 ° (i.e., 80 ° to 120 °), to manufacture a circular polarizing film. In the lamination of the above-described combination, since the long linear polarizing film and the long broadband wavelength film can be laminated in a direction parallel to their longitudinal directions to produce the circular polarizing film, the circular polarizing film can be produced by a roll-to-roll (roll) method. Therefore, the manufacturing efficiency of the circular polarizing film can be improved.

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

The circular polarizing film may further have any of the layers in combination with the linear polarizing film and the broadband wavelength film.

For example, the circular polarizing film may have a protective film layer for suppressing damage. Further, for example, the circular polarizing film may have an adhesive layer or an adhesive layer for adhesion to the linear polarizing film and the broadband wavelength film.

When the circular 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 reflection of external light can be effectively reduced in a wide wavelength range in the visible light region. In addition, since reflection of external light in a wide wavelength range can be effectively reduced in this manner, the circular polarizing film can suppress coloring due to an increase in reflection intensity of light of a partial wavelength. The circularly polarizing film can obtain the above-described reflection suppressing and coloring suppressing effects at least in the front direction thereof, and can also obtain the above-described effects in the oblique direction thereof in general. In addition, the effects of reflection suppression and coloring suppression in the oblique direction can be generally obtained in all azimuthal directions of the film main surface.

[9. image display device ]

The circular polarizing film can be used as a reflection suppressing film of an organic electroluminescent display device (hereinafter, may be referred to as an "organic EL display device" as appropriate) by making full use of the function of suppressing reflection of external light as described above.

The organic EL display device has a circular polarizing film cut from a long circular polarizing film.

In the case where the organic EL display device has a circular polarizing film, the organic EL display device generally has a circular polarizing film on the display surface. By providing the circular polarizing film on the display surface of the organic EL display device so that the surface on the linear polarizing film side faces the viewing side, light incident from the outside of the device can be suppressed from being reflected inside the device and emitted to the outside of the device, and as a result, flicker of the display surface of the display device can be suppressed. Specifically, only a part of linearly polarized light of light incident from the outside of the device passes through the polarizing film, and then the light passes through the broadband wavelength film, thereby becoming circularly polarized light. The circularly polarized light is reflected by a component (such as a reflective electrode) that reflects light in the display device, and passes through the broadband wavelength film again, thereby becoming linearly polarized light having a vibration direction (polarization axis) in a direction orthogonal to the vibration direction (polarization axis) of the incident linearly polarized light, and no longer passing through the linear polarization film. Thereby achieving a reflection suppressing function. Further, by obtaining the above-described reflection suppressing function in a wide wavelength range, coloring of the display surface can be suppressed.

Further, the circular polarizing film may be provided on a liquid crystal display device. Such a liquid crystal display device has a circular polarizing film cut from a long circular polarizing film.

In the case where the liquid crystal display device has a circularly polarizing film sheet so that the surface on the linearly polarizing film side faces the viewing side, light incident from the outside of the device can be prevented from being reflected inside the device and emitted to the outside of the device, and as a result, flicker and coloring of the display surface of the display device can be prevented.

Further, in the case where the liquid crystal display device includes a circularly polarizing film sheet so as to include a broadband wavelength film, a linear 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 by circularly polarized light. Therefore, light emitted from the display surface can be stably viewed by the polarized sunglasses, and the image viewability when the polarized sunglasses are worn can be improved.

In particular, when the circularly polarizing film is provided in an image display device such as an organic EL display device or a liquid crystal display device so that the surface on the linearly polarizing film side faces the viewing side, the warpage of the display panel can be suppressed. This effect will be explained below.

Generally, an image display device has a display panel including display elements such as organic electroluminescence elements and liquid crystal cells. The display panel has a substrate such as a glass substrate for improving the mechanical strength of the display panel. In addition, a display panel provided with a circularly polarizing film sheet so that the surface on the linearly polarizing film side faces the viewing side generally includes a substrate, a broadband wavelength film, and a linearly polarizing film in this order.

In addition, the polarizer layer of the linear polarizing film is generally easily shrunk in the in-plane direction under a high-temperature environment. When the polarizer layer is to be shrunk as such, a display panel provided with the linear polarizing film including the polarizer layer may generate stress to bend the display panel. Since the warpage of the display panel can cause a reduction in image quality, it is desirable to suppress the warpage. Regarding this bending, it has been clarified that there is a tendency that the bending becomes larger as the distance between the polarizer layer and the substrate of the display panel becomes larger.

The wide wavelength film produced by the conventional production method in which the λ/2 layer and the λ/4 layer are produced separately and then bonded together is thick as a whole due to the thickness of the adhesive layer. Thus, in the conventional broadband wavelength film, the distance between the polarizer layer and the substrate of the display panel is increased, and thus the bending of the display panel tends to be increased.

In contrast, the wide-band wavelength film produced as a co-stretched film as described above can have the λ/2 layer and the λ/4 layer in direct contact, or can have a thin film layer provided between the λ/2 layer and the λ/4 layer. Therefore, the entire broadband wavelength film can be made thin, and thus the distance between the polarizer layer and the substrate of the display panel can be reduced. This can suppress the display panel from being bent.

Examples

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below, and can be modified and implemented arbitrarily within a range not departing from the scope and the equivalent range of the claims of the present invention.

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

[ evaluation method ]

[ method for measuring optical Properties of layer (A) ]

The in-plane retardation Re, the NZ coefficient, and the 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 corporation). The measurement wavelength was 590 nm.

[ method for measuring optical characteristics of respective layers of a broad band wavelength film ]

A broadband wavelength film to be evaluated was set on a stage of a phase difference meter ("Axoscan" manufactured by Axometrics). Then, the change in the polarization state of the polarized light transmitted through the broadband wavelength film before and after transmission through the broadband wavelength film was measured as the transmission polarization characteristic of the broadband wavelength film. The measurement was performed in a multi-directional manner in which the polar angle was in the range of-55 ° to 55 ° with respect to the main surface of the broadband wavelength film. The multi-directional measurement was performed in each azimuthal direction of 45 °, 90 °, 135 °, and 180 ° with a certain azimuthal angle of the main surface of the broadband wavelength film set to 0 °. The measurement wavelength of the above measurement was 590 nm.

Next, fitting calculation is performed based on the transmission polarization characteristics measured as described above, thereby obtaining the in-plane retardation Re, the retardation in the thickness direction Rth, the NZ coefficient, and the orientation angle of each layer. The fitting calculation is performed by setting the three-dimensional refractive index and the orientation angle of each layer included in the broadband wavelength film as fitting parameters. The fitting calculation was performed using software (Multi-Layer Analysis, manufactured by Axometrics) attached to the phase difference meter (AxoScan).

[ method for calculating color difference Δ Eab based on simulation ]

The circularly polarizing plates manufactured in the respective examples and comparative examples were modeled using "LCD Master" manufactured by Shintec corporation as software for simulation, and the color difference Δ E ab was calculated by the following setting.

In the model for simulation, a circular polarizing film is attached to the reflection surface of an aluminum mirror having a planar reflection surface so that the λ/4 layer side of the wide band wavelength film is in contact with the mirror. 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 is set.

Then, in the above model, the color difference Δ E ab when the circular polarizing film is irradiated with light from the light source D65 in the front direction of the circular polarizing film is calculated. For the calculation of the chromatic aberration Δ Ε ab, the reflected light in the directions of the polar angle 0 ° and the azimuth angle 0 ° of the aluminum mirror to which the circular polarizing film is not attached was taken as a reference. In the simulation, the surface reflection component actually generated on the surface of the circular polarizing film was removed from the calculation of the color difference Δ E × ab. For values of the color difference Δ Ε ab, smaller values mean less color change, more preferred.

[ visual evaluation of circular polarizing film ]

A polarizing plate included in an image display device (Apple Watch (registered trademark)) was peeled off, and the display surface of the image display device was bonded to the surface of the λ/4 layer of the circular polarizing film to be evaluated via an adhesive layer (CS 9621 manufactured by ritonavir electric corporation). The display surface is set to a black display state (a state where black is displayed on the entire screen), and the display surface is viewed from all directions at a polar angle θ of 0 ° (front direction) and at a polar angle θ of 60 ° (oblique direction). The smaller the luminance and coloration due to reflection of external light, the better the result. The results of the observation were evaluated by the following criteria.

"A": there was no visual level of brightness or coloration.

"B": the luminance and coloring were visually confirmed.

"C": luminance and coloration occur seriously.

[ example 1]

(first step: production of layer (A))

A norbornene resin (manufactured by Nippon Ralskikai Co., Ltd.; glass transition temperature 126 ℃ C.) in the form of pellets was prepared as a resin having positive intrinsic birefringence, and dried at 100 ℃ for 5 hours. The dried resin was fed to an extruder, passed through a polymer tube and a polymer filter, and extruded from a T-die into a sheet on a casting drum. The extruded resin was cooled to obtain a long film before stretching having a thickness of 160 μm. The obtained film before stretching was wound into a roll and recovered.

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

(second step of Forming 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 negative intrinsic birefringence. The liquid composition contains methyl ethyl ketone as a solvent, and the concentration of the styrene-maleic anhydride copolymer in the liquid composition is 10% by weight.

A stretched film is drawn from a roll, and the liquid composition is applied to the stretched film. Then, the applied liquid composition was dried to form a layer (thickness 10 μm) of a styrene-maleic anhydride copolymer as the layer (B) on the stretched film. Thus, a multilayer film having the layer (a) and the layer (B) was obtained. The obtained multilayer film was wound into a roll and recovered.

(third Process: stretching of multilayer film)

The multilayer film was drawn out of the roll and continuously fed to a tenter. Then, the multilayer film is stretched by the tenter stretcher. In this stretching, the stretching angle formed by the stretching direction and the longitudinal direction of the multilayer film was 15 °, the stretching temperature was 130 ℃, and the stretching ratio was 1.5 times. Thus, a broadband wavelength film was obtained as a co-stretched film having 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 above method.

(method for producing circular polarizing film)

A long linear polarizing film having an absorption axis in the longitudinal direction is prepared. The linear polarizing film and the broadband wavelength film are bonded to each other so that the longitudinal directions thereof are parallel to each other. The lamination was performed using an adhesive (CS-9621, manufactured by Ridong electric Co., Ltd.). Thus, a circular polarizing film having a linear polarizing film, a lambda/2 layer and a lambda/4 layer in this order was obtained. The obtained circular polarizing film was evaluated in accordance with the above-mentioned method.

[ example 2]

In the third step, the stretching angle formed by the stretching direction and the longitudinal direction of the multilayer film was changed to 10 °.

In addition to the above, the production and evaluation of the broadband wavelength film and the circular polarizing film were performed in the same manner as in example 1.

[ example 3]

In the third step, the stretching angle formed by the stretching direction and the longitudinal direction of the multilayer film was changed to 5 °.

Comparative example 1

A norbornene resin (manufactured by Nippon Ralskikai Co., Ltd.; glass transition temperature 126 ℃ C.) in the form of pellets was prepared as a resin having positive intrinsic birefringence, and dried at 100 ℃ for 5 hours. The dried resin was fed to an extruder, passed through a polymer tube and a polymer filter, and extruded from a T-die into a sheet on a casting drum. The extruded resin was cooled to obtain a long film before stretching having a thickness of 110 μm. The obtained film before stretching was wound into a roll and recovered.

The film before stretching was drawn from the roll and continuously fed to a roll stretcher. Then, the film before stretching was subjected to free uniaxial stretching by the roll stretcher to obtain a long stretched film. In this stretching, the stretching angle formed by the stretching direction and the longitudinal direction of the film before stretching was 0 °, the stretching temperature was 135 ℃, and the stretching ratio was 1.9 times. The orientation angle of the obtained stretched film was 0 °, the in-plane retardation Re was 350nm, and the thickness was 80 μm.

A broadband wavelength film and a circularly polarizing film were produced and evaluated in the same manner 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 and the longitudinal direction of the multilayer film was changed to 0 °. Further, the multilayer film in the third step is stretched by free uniaxial stretching using a roll stretcher.

Comparative example 3

In the third step, the stretching angle formed by the stretching direction and the longitudinal direction of the multilayer film was changed to 45 °.

Comparative example 4

In the third step, the stretching angle formed by the stretching direction and the longitudinal direction of the multilayer film was changed to 60 °.

[ results ]

The results of examples and comparative examples are shown in tables 1 and 2 below. In the following tables, the abbreviations mean as follows.

COP: a norbornene-based resin.

ST: styrene-maleic anhydride copolymers.

Re: in-plane retardation.

Rth: retardation in the thickness direction.

Orientation angle: the slow axis is at an angle to the length direction.

And (3) total thickness: the total thickness of the lambda/2 layer and the lambda/4 layer.

Longitudinal: and (4) the length direction.

Transverse: the width direction.

Inclining: and (4) inclining.

[ Table 1]

[ Table 1. results of examples ]

[ Table 2]

[ Table 2. results of comparative examples ]

Description of the reference numerals

100: layer (A)

200: multilayer film

210: layer (B)

300: broadband wavelength film

Claims

1. A method for manufacturing a broadband wavelength film, comprising the following steps in order:

a first step of preparing a layer a which is a long resin film;

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

the layer a prepared in the first process has a slow axis parallel or perpendicular to the length direction of the layer a,

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 formula (1), the reaction mixture is,

theta (lambda/2) represents an angle formed by the slow axis of the lambda/2 layer and the longitudinal direction of the broadband wavelength film,

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

2. The method of producing a broadband wavelength film according to claim 1, wherein the third step includes a step of stretching the multilayer film in an oblique direction at an angle of 45 ° or less to a longitudinal direction of the multilayer film.

3. The method of manufacturing a broadband wavelength film according to claim 1 or 2, wherein the angle θ (λ/2) is in a range of 27.5 ° ± 10 °.

4. The method for manufacturing a broadband wavelength film according to any one of claims 1 to 3, wherein the angle θ (λ/4) is in a range of 100 ° ± 20 °.

5. 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.

6. 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.

7. A method for manufacturing a circular polarizing film, comprising the steps of:

a step of producing a broadband wavelength film by the production method according to any one of claims 1 to 6; and

8. The method of manufacturing a circular polarizing film according to claim 7, wherein the linear polarizing film has an absorption axis in a longitudinal direction of the linear polarizing film.

9. A long, broadband wavelength film which is a co-stretched film having lambda/2 layers and lambda/4 layers,

the lambda/2 layer has a slow axis at an angle of 27.5 DEG + -10 DEG to the longitudinal direction of the broadband wavelength film,

The λ/4 layer has a slow axis at an angle of 100 ° ± 20 ° to the length direction of the broadband wavelength film.