TWI798426B - Broad-band wavelength film and its manufacturing method, and circular polarizing film manufacturing method - Google Patents

Abstract

A method of manufacturing a broadband wavelength film, which sequentially includes: the first process of preparing a layer (A) as a "resin film having a slow axis parallel to or perpendicular to the long-side direction"; on the layer (A) The second process of forming a layer (B) of a resin with a negative intrinsic birefringence to obtain a multilayer film; and extending the multilayer film obliquely to obtain a strip-shaped broadband with a λ/2 layer and a λ/4 layer The third process of the wavelength film; wherein the λ/2 layer and the λ/4 layer of the broadband wavelength film satisfy the formula (1). θ(λ/4)=[45°+2×θ(λ/2)]±5° (1) (θ(λ/2) represents the angle between the slow axis of the λ/2 layer and the long-side direction of the broadband wavelength film, θ(λ/4) represents the slow axis of the λ/4 layer relative to the broadband wavelength film The angle included in the direction of the long side.)

Description

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

The invention relates to a broadband wavelength film and its manufacturing method, as well as a circular polarizing film manufacturing method.

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

"Patent Documents" "Patent Document 1": International Patent Publication No. 2016/047465 "Patent Document 2": International Patent Publication No. 2009/031433 "Patent Document 3": Japanese Patent Laid-Open No. 2009-237534

As a broadband wavelength film capable of functioning as a wavelength plate in a wide wavelength band, a film comprising a combination of a λ/2 plate and a λ/4 plate is known. In the past, such a wide-band wavelength film was generally obtained by extending a certain film to obtain a λ/2 plate, extending another film to obtain a λ/4 plate, and combining these λ/2 plates and λ/4 plates. Manufactured by the manufacturing method of the process of laminating 4 plates to obtain a broadband wavelength film.

Furthermore, there is known a technique for obtaining a circular polarizing film by combining "the aforementioned broadband wavelength film" with "a linear polarizing film which is a film that functions as a linear polarizing plate". A strip-shaped linear polarizing film generally has an absorption axis in its long-side direction or width direction. Accordingly, in the case of combining a broadband wavelength film into a strip-shaped linear polarizing film to obtain a circular 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 its long side direction .

In order to easily manufacture a desired λ/2 plate having a slow axis in an oblique direction as described above, the applicant has developed a technique of stretching twice or more as described in Patent Document 1. If so, in the overall manufacturing method of the broadband wavelength film, one or more stretches for obtaining a λ/4 plate and two or more stretches for obtaining a λ/2 plate are performed, so the total stretching The number of times becomes more than 3 times. However, if the number of extensions is three or more, the operation will be complicated.

The present invention is created in view of the aforementioned problems, and its purpose is to: provide a broadband wavelength film that can be efficiently manufactured with a small number of steps and a manufacturing method thereof, and a method of manufacturing a circular polarizing film including the manufacturing method of the aforementioned broadband wavelength film.

The inventors of the present invention have devoted themselves to research in order to solve the aforementioned problems. As a result, the present inventors found that according to the sequence including: the first step of preparing the layer (A) as a resin film having a slow axis parallel to or perpendicular to the longitudinal direction; the second step of preparing the layer (A) on the layer (A) Forming a layer (B) of a resin with negative intrinsic birefringence to obtain a multilayer film; and the third step, extending the multilayer film along an oblique direction that is neither parallel nor perpendicular to the long side direction of the multilayer film to obtain a multilayer film with λ/2 layer and λ/4 layer elongated broadband wavelength film; the manufacturing method can efficiently manufacture broadband wavelength film with a small number of steps, and further complete the present invention.

That is, the present invention includes the following.

[1] A method of manufacturing a broadband wavelength thin film, which sequentially includes: The first step is to prepare the layer (A) as a strip-shaped resin film; the second step is to form a layer (B) of resin with inherently negative birefringence on the aforementioned layer (A) to obtain a multilayer film; With the third process, the aforementioned multilayer film is extended along a diagonal direction that is neither parallel nor perpendicular to the long side direction of the aforementioned multilayer film to obtain a strip-shaped broadband wavelength film with a λ/2 layer and a λ/4 layer ; wherein the aforementioned layer body (A) prepared in the aforementioned first process has a slow axis parallel or perpendicular to the long side direction of the layer body (A), the aforementioned λ/2 layer and the aforementioned λ of the aforementioned broadband wavelength film The /4 layer satisfies the following formula (1). θ(λ/4)=[45°+2×θ(λ/2)]±5° (1) (In the aforementioned formula (1), θ(λ/2) represents the relative slow axis of the aforementioned λ/2 layer In the angle included in the long-side direction of the aforementioned broadband wavelength film, θ(λ/4) represents the angle included by the slow axis of the aforementioned λ/4 layer relative to the long-side direction of the aforementioned broadband wavelength film.)

[2] The method for producing a broadband wavelength film as described in [1], wherein the third step includes: stretching the multilayer film obliquely at an angle of 45° or less with respect to the long side direction of the multilayer film .

[3] The method for producing a broadband wavelength film as described in [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 as described in 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 method for manufacturing a circular polarizing film, comprising: A step of manufacturing a broadband wavelength film by the manufacturing method described in any one of [1] to [6]; and a step of laminating the aforementioned broadband wavelength film and a strip-shaped 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 the longitudinal direction of the linear polarizing film.

[9] A strip-shaped broadband wavelength film, which is a co-extended film, and the co-extended film has: The λ/2 layer has a slow axis with an angle of 27.5°±10° relative to the long-side direction of the aforementioned broadband wavelength film, and the λ/4 layer has a 100° angle relative to the long-side direction of the aforementioned broadband wavelength film Slow axis at an angle of ±20°.

According to the present invention, it is possible to provide a broadband wavelength film that can be efficiently manufactured with a small number of steps, a method for manufacturing the same, and a method for manufacturing a circular polarizing film including the method for manufacturing the broadband wavelength film.

Embodiments and examples are disclosed below to describe the present invention in detail. However, the present invention is not limited to the implementation forms and examples disclosed below, and can be implemented with arbitrary changes within the scope not departing from the scope of the patent application of the present invention and its equivalent scope.

In the following description, the so-called "strip-shaped" film refers to a film having a length of 5 times or more relative to the width, preferably 10 times or more in length, and specifically refers to a film having a length that can be rolled into Roll-shaped film with a length sufficient for storage or handling. The upper limit of the length of the film is not particularly limited, and may be, for example, 100,000 times or less relative to the width.

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

In the following description, the so-called orientation angle of a film or layer, unless otherwise noted, means the angle formed by the slow axis of the film or layer relative to the long side direction of the film or layer.

In the following description, the angles formed by the optical axes (slow axis, transmission axis, absorption axis, etc.) of each layer in a part with multiple layers represent the layers viewed from the thickness direction unless otherwise noted. time angle.

In the following description, the direction of the optical axis (slow axis, transmission axis, absorption axis, etc.) and width direction, etc.), unless otherwise noted, the offset in one direction is defined as positive, and the offset in the other direction is defined as negative. The positive and negative directions are the constituent elements of the product Made the same in China. For example, in a broadband wavelength film, the so-called "the angle between the slow axis of the λ/2 layer and the long side direction of the broadband wavelength film is 27.5°, and the slow axis of the λ/4 layer relative to the broadband The angle formed by the longitudinal direction of the wavelength film is 100°", which means the following two situations. ・If viewed from one side of the broadband wavelength film, the slow axis of the λ/2 layer is shifted clockwise by 27.5° from the long side of the broadband wavelength film, and the slow axis of the λ/4 layer is offset from the broadband wavelength film The direction of the long side of the wavelength film is shifted clockwise by 100°. ・If viewed from one side of the broadband wavelength film, the slow axis of the λ/2 layer is offset 27.5° counterclockwise from the long side of the broadband wavelength film, and the slow axis of the λ/4 layer is offset from the broadband wavelength film The direction of the long side of the wavelength film is offset 100° counterclockwise.

In the following description, unless otherwise noted, the oblique direction of the strip-shaped film refers to the in-plane direction of the film and is neither parallel nor perpendicular to the long side direction of the film.

In the following description, the so-called frontal direction of a film, unless otherwise noted, means the normal direction of the main surface of the film, specifically the direction of the polar angle 0° and azimuth angle 0° of the aforementioned main surface.

In the following description, the so-called inclination direction of a film, unless otherwise noted, means a direction that is neither parallel nor perpendicular to the main surface of the film, specifically refers to the polar angle of the aforementioned main surface greater than 0° and less than The direction of the range of 90°.

In the following description, unless otherwise noted, a material having a positive intrinsic birefringence means a material in which the refractive index in the extending direction becomes larger than that in the direction perpendicular thereto. And, unless otherwise noted, a material having negative intrinsic birefringence means a material in which the refractive index in the extending direction becomes smaller than the refractive index in the direction perpendicular thereto. The value of intrinsic birefringence can be calculated from the permittivity distribution.

In the following description, "(meth)acrylic acid" includes "acrylic acid", "methacrylic acid" 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 noted. In addition, the retardation Rth in the thickness direction of the layer is a value represented by Rth={[(nx+ny)/2]−nz}×d unless otherwise noted. In addition, unless otherwise noted, the NZ coefficient of a layer is a value represented by (nx-nz)/(nx-ny). Here, nx represents the refractive index which is the direction (in-plane direction) perpendicular to the thickness direction of a layer body, and the direction which gives a maximum refractive index. ny represents the refractive index in the above-mentioned in-plane direction of the layer body and in the direction perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer body. Measurement wavelength, unless otherwise noted, is 590 nm.

In the following description, the directions of the so-called elements are "parallel", "perpendicular" and "orthogonal". Unless otherwise noted, it may also include, for example, ±3°, ±2° within the scope of not impairing the effect of the present invention. ° or within ±1°.

[1. Summary]

FIG. 1 is a schematic perspective view of a layer body (A) 100 prepared as a resin film in the first step of the manufacturing method of a broadband wavelength film related to an embodiment of the present invention. Moreover, FIG. 2 is a schematic perspective view of a multilayer film 200 obtained in the second process of the manufacturing method of a broadband wavelength film related to an embodiment of the present invention. Furthermore, FIG. 3 is a schematic perspective view of a broadband wavelength film 300 obtained in the third process of the manufacturing method of a broadband wavelength film related to an embodiment of the present invention.

The manufacturing method of the wide-band wavelength film 300 related to an embodiment of the present invention includes in sequence: (1) As shown in Fig. 1, the first process of preparing the layer body (A) 100 as a strip-shaped resin film; (2) Forming a layer (B) 210 of a resin with negative intrinsic birefringence on the layer (A) 100 to obtain the second process of the multilayer film 200 shown in FIG. 2 ; and (3) The third process of stretching the multilayer film 200 to obtain the strip-shaped broadband wavelength film 300 shown in FIG. 3 .

As shown in FIG. 1 , the layer body (A) 100 prepared in the first step has a slow axis A 100 parallel to or perpendicular to the long side direction of the layer body (A) ₁₀₀ . 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 extension is performed in an oblique direction that is neither parallel nor perpendicular to the long side direction of the multilayer film 200 in such a way that the λ/2 layer and the λ/4 layer with the slow axis in the desired direction are obtained.

By the stretching in the third step, co-extension in which the layer body (A) 100 and the layer body (B) 210 are simultaneously stretched can be performed. Therefore, as shown in FIG. 3 , adjustment of the direction of the slow axis A ₁₀₀ and adjustment of optical characteristics can be performed in the layer body (A) 100 . On the other hand, a slow axis A ₂₁₀ appears in the layer body (B) 210 and exhibits optical properties. The stretched layer body (A) 100 functions as one of the λ/2 layer and the λ/4 layer, and the stretched layer body (B) 210 functions as the other of the λ/2 layer and the λ/4 layer function. Accordingly, the broadband wavelength film 300 having the λ/2 layer and the λ/4 layer can be obtained by the aforementioned manufacturing method. In FIG. 3, although the stretched layer body (A) 100 functions as a λ/2 layer and the stretched layer body (B) 210 functions as a λ/4 layer is shown, the broadband wavelength film The configuration of 300 is not limited to this example.

The aforementioned λ/2 layer and λ/4 layer satisfy the following formula (1): θ(λ/4)=[45°+2×θ(λ/2)]±5° (1) Formula (1) represents θ( λ/4) is in the range of “[45°+2×θ(λ/2)]−5°” to “[45°+2×θ(λ/2)]+5°”. In formula (1), θ(λ/2) represents the angle formed by the slow axis A ₁₀₀ of the λ/2 layer relative to the long-side direction A ₃₀₀ of the broadband wavelength film 300 . In addition, θ(λ/4) represents the angle formed by the slow axis A ₂₁₀ of the λ/4 layer with respect to the long-side direction A ₃₀₀ of the broadband wavelength film 300 . By including the combination of the λ/2 layer and the λ/4 layer satisfying this formula (1), the broadband wavelength film 300 can function as a broadband wavelength film capable of operating in a wide wavelength range An in-plane retardation of approximately 1/4 wavelength of the wavelength of the light is imparted to light passing through the film.

Usually, the long-side direction A ₃₀₀ of the broadband wavelength film 300 , the long-side direction (not shown) of the λ/4 layer and the long-side direction (not shown) of the λ/2 layer are consistent. Accordingly, the angle θ(λ/2) is sometimes referred to as “orientation angle θ(λ) since it represents the orientation angle of the slow axis A ₁₀₀ of the λ/2 layer relative to the long-side direction of the λ/2 layer. /2)". Also, the angle θ(λ/4) is sometimes referred to as “orientation angle θ(λ/4) hereinafter because it represents the orientation angle formed by the slow axis A ₂₁₀ of the λ/4 layer relative to the long-side direction of the λ/4 layer. 4)".

[2. The first process]

In the first step, a layer body (A) is prepared as a long resin film having a slow axis in a predetermined in-plane direction. As the layer (A), a resin film having a multilayer structure including two or more layers can also be used, but a resin film having a single layer structure including only one layer is usually used.

As the resin for forming the resin film, a thermoplastic resin containing a polymer and, if necessary, an optional component may be used. In particular, as the resin contained in the layer body (A), a resin having a negative intrinsic birefringence can also be used, but a resin having a positive intrinsic birefringence is preferably used because it is particularly easy to manufacture a wide-band wavelength film. .

Intrinsically positive birefringence resins generally comprise intrinsically positive birefringence polymers. To give examples of polymers with positive inherent birefringence, polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene sulfide, etc. Polyaryl sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester polymer; polyether; liquid crystal polymers, etc. These polymers may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios. In addition, the polymer may be a homopolymer or a copolymer. Among them, polycarbonate polymers are preferable in terms of retardation development and low-temperature elongation. Furthermore, cycloolefin polymers are preferable in terms of excellent 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 most preferably 90% by weight to 100% by weight. When the ratio of the polymer is within the above range, sufficient heat resistance and transparency can be obtained for the layer body (A) and the broadband wavelength film.

The resin contained in the layer body (A) may further contain any components other than the aforementioned polymers combined into the polymer. Examples of optional components include: colorants such as pigments and dyes; plasticizers; fluorescent whitening agents; dispersants; heat stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; antioxidants; fine particles; interfaces Active agents, etc. These components may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios.

The glass transition temperature TgA of the resin contained in the layer (A) is preferably 100°C or higher, more preferably 110°C or higher, more preferably 120°C or higher, and preferably 190°C or lower, and 180°C or lower. Preferably, it is especially preferably below 170°C. In the case where the glass transition temperature of the resin contained in the layer (A) is above the lower limit of the aforementioned range, the layer (λ/2 layer or λ/4 layer) obtained by extending the layer (A) can be increased ) for durability in high temperature environments. Furthermore, when the glass transition temperature of the resin contained in a layer body (A) is below the upper limit of the said range, stretching process can be performed easily.

The layer body (A) prepared in the first step has a slow axis parallel to or perpendicular to the long side direction of the layer body (A). Accordingly, the orientation angle formed by the slow axis of the layer (A) relative to the longitudinal direction of the layer preferably satisfies either of the following (a1) and (a2). (a1): The orientation angle of the layer (A) is preferably not less than -3°, more preferably not less than -2°, more preferably not less than -1°, and preferably not more than 3°, and not more than 2° More preferably, it is especially preferably below 1°. (a2): The orientation angle of the layer (A) is preferably above 87°, more preferably above 88°, especially above 89°, preferably below 93°, more preferably below 92° , preferably below 91°.

In the case of using the layer body (A) having such a slow axis, a broadband wavelength film having good optical characteristics can be easily obtained.

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

For example, in the case of extending the layer body (A) to obtain a λ/2 layer, the in-plane retardation of the layer body (A) is preferably 150 nm or more, more preferably 180 nm or more, and 200 nm or more Especially preferably, it is preferably below 400 nm, more preferably below 380 nm, and most preferably below 350 nm. In addition, the NZ coefficient of the layer body (A) is preferably at least 1.0, more preferably at least 1.1, more preferably at least 1.15, preferably at most 1.7, more preferably at most 1.65, and most preferably at most 1.6. .

The thickness of the layer (A) prepared in the first step can be set arbitrarily within the range in which a desired broadband wavelength film can be obtained. The specific thickness of the layer (A) is preferably above 20 μm, more preferably above 25 μm, especially above 30 μm, preferably below 100 μm, preferably below 95 μm, preferably below 90 μm The following are preferred. In the case where the thickness of the layer body (A) is within the aforementioned 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 appropriately long resin film so that the resin film exhibits a slow axis". In the following description, the resin film before being stretched may be referred to as "pre-stretched film", and the resin film obtained after stretching may be referred to as "stretched film".

The film before stretching can be produced by, for example, a melt forming method or a solution casting method. More specific examples of the melt molding method include extrusion molding, press molding, inflation molding, injection molding, blow molding, and stretch molding. Among these methods, in order to obtain a layer (A) excellent in mechanical strength and surface precision, extrusion molding, inflation molding, or press molding are preferable, and among them, the layer (A) can be manufactured efficiently and easily. From the point of view, the extrusion molding method is particularly preferable.

After the elongated film before stretching is prepared, the elongated film before stretching is stretched to obtain a layer (A) as a stretched film.

The slow axis of the layer (A) is usually displayed by stretching the film before stretching. Accordingly, the stretching direction of the film before stretching is preferably set in a direction corresponding to the slow axis of the layer (A). For example, in the case where the film before stretching is formed of a resin with positive intrinsic birefringence, the stretching direction of the film before stretching is set to be parallel to the slow axis of the layer (A) to be prepared in the first process direction is better. And, for example, in the case where the unstretched film is formed of a resin whose inherent birefringence is negative, the stretching direction of the unstretched film is set to be slower than that of the layer (A) to be prepared in the first step. The direction perpendicular to the axis is preferred. Therefore, the stretching direction of the film before stretching is preferably a direction parallel to or perpendicular to the long side direction of the film before stretching. In particular, it is preferable that the stretching direction of the film before stretching be perpendicular to the long side direction of the film before stretching from the viewpoint of easy production of a desired broadband wavelength film.

The stretching ratio of the film before stretching is preferably at least 1.1 times, more preferably at least 1.2 times, preferably at most 4.0 times, more preferably at most 3.0 times. When the stretching magnification is more than the lower limit of the aforementioned range, the refractive index in the stretching direction can be increased. In addition, when the stretch ratio is not more than the upper limit of the aforementioned 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 above TgA, preferably above "TgA+2°C", especially above "TgA+5°C", preferably below "TgA+40°C", and below "TgA+35°C" Good, especially below "TgA+30°C". Here, TgA refers to the glass transition temperature of the resin contained in the layer (A). When the stretching temperature is in the above-mentioned range, the molecules contained in the film before stretching can be surely oriented, so that the layer body (A) having desired optical characteristics can be easily obtained.

The above-mentioned stretching can usually be carried out using an appropriate stretching machine such as a roll stretching machine or a tenter stretching machine while continuously conveying the film before stretching in the longitudinal direction. For example, when stretching the unstretched film in the longitudinal direction of the unstretched film, it is preferable to use a roll stretcher. With the roll stretching machine, free uniaxial stretching can be easily performed. The so-called free uniaxial extension refers to the extension in a certain direction without exerting a binding force in directions other than the extended direction. As such stretching machines, those described in Patent Document 1 can be used, for example.

[3. The fourth process]

The manufacturing method of the broadband wavelength thin film may also include: after the layer body (A) is prepared in the first step, a step of forming a thin film layer on the layer body (A) as required. By forming a suitable thin film layer, the thin film layer can function as an easy bonding layer and improve the binding force between the layer body (A) and the layer body (B). In addition, the film layer preferably has solvent resistance. Such film layers are usually formed of resin.

Examples of the material of the film layer include acrylic resins, urethane resins, acrylic urethane resins, ester resins, and ethyleneimine resins. Acrylic resins are resins containing acrylic polymers. In addition, the urethane resin is a resin containing polyurethane. Polymers such as acrylic polymers and polyurethanes generally have a high binding force to a wide variety of resins, so the binding force between the layer (A) and the layer (B) can be increased. Moreover, these polymers may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios.

The resin used as the material of the film layer may also contain heat stabilizers, weather stabilizers, leveling agents, antistatic agents, slip agents, anti-adhesive agents, anti-fogging agents, slip agents, dyes, pigments, natural oils, synthetic oils , waxes, particles, etc., are combined into polymers. Optional components may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.

The glass transition temperature of the resin used as the material of the film layer is equal to the glass transition temperature TgA of the resin contained in the layer (A) and the glass transition temperature TgB of the resin with a negative intrinsic birefringence contained in the layer (B). Low is better. In particular, the difference between the glass transition temperature of the resin used as the material of the film layer and the lower of the glass transition temperatures TgA and TgB is preferably 5°C or higher, more preferably 10°C or higher, and 20°C or higher. Excellent. Thereby, the occurrence of retardation in the thin film layer due to the stretching in the third step can be suppressed, so that the thin film layer in the broadband wavelength film can have optical isotropy. Therefore, the optical properties of the broadband wavelength film can be easily adjusted.

The thin film layer can be formed by, for example, a method comprising applying a coating solution containing a resin and a solvent as materials of the thin film layer onto the layer body (A). As a solvent, water can be used, and an organic solvent can also be used. As an organic solvent, the same thing as the solvent used for formation of the layer body (B) mentioned later is mentioned, for example. Moreover, a solvent may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios.

Furthermore, the aforementioned coating liquid may also contain a crosslinking agent. By using the crosslinking agent, the mechanical strength of the film layer can be improved, or the binding property to the layer body (A) and the layer body (B) of the film layer can be improved. As the crosslinking agent, for example, epoxy compounds, amine compounds, isocyanate compounds, carbodiimide compounds, oxazoline compounds and the like can be used. In addition, these may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios. The amount of the crosslinking agent is preferably at least 1 part by weight, preferably at least 5 parts by weight, and preferably not more than 70 parts by weight, more preferably not more than 65 parts by weight, relative to 100 parts by weight of the polymer in the coating liquid. good.

As the coating method of the coating liquid, for example, the same method as the coating method used for the formation of the layer body (B) described later can be mentioned.

A thin film layer can be formed by apply|coating a coating liquid on a layer body (A). The film layer can also be cured such as drying and cross-linking as required. As a drying method, heating drying using an oven is mentioned, for example. Moreover, as a crosslinking method, methods, such as heat processing and irradiation processing of active energy rays, such as an ultraviolet-ray, are mentioned, for example.

[4. Second process]

In the first step, a layer (A) is prepared, and a thin film layer is formed if necessary, followed by a second step of forming a layer (B) of a resin with negative intrinsic birefringence to obtain a multilayer film. In this second step, the layer body (B) is formed directly on the layer body (A) or indirectly through any layer body such as a thin film layer. Here, the so-called "directly" means that there is no any layer between the layer (A) and the layer (B).

Intrinsically negative birefringence resins are typically thermoplastic resins and include polymers that are inherently negative in birefringence. To give examples of polymers with negative intrinsic birefringence, homopolymers and copolymers of styrene or styrene derivatives, and copolymers containing styrene or styrene derivatives and arbitrary monomers Polystyrene-based polymers; polyacrylonitrile polymers; polymethyl methacrylate polymers; or multi-polymers of these; and cellulose compounds such as cellulose esters, etc. In addition, examples of the optional monomer capable of copolymerizing styrene or a styrene derivative include acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene as good ones. Among them, polystyrene-based polymers and cellulose compounds are preferable. Moreover, these polymers may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios.

The proportion of the polymer in the resin with negative intrinsic birefringence is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and most preferably 90% by weight to 100% by weight. When the ratio of the polymer is within the aforementioned range, the layer (λ/2 layer or λ/4 layer) obtained by stretching the layer (B) can exhibit suitable optical characteristics.

It is preferable that the resin contained in the layer (B) has a negative intrinsic birefringence to contain a plasticizer. By using the plasticizer, the glass transition temperature TgB of the resin contained in the layer body (B) can be appropriately adjusted. Examples of the plasticizer include phthalates, fatty acid esters, phosphoric acid esters, and epoxy derivatives. As a specific example of a plasticizer, what was described in Unexamined-Japanese-Patent No. 2007-233114 is mentioned. Moreover, plasticizers may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.

Among the plasticizers, phosphate esters are preferable in terms of easy availability and low price. Examples of phosphoric acid esters include trialkyl phosphates such as triethyl phosphate, tributyl phosphate, and trioctyl phosphate; halogen-containing trialkyl phosphates such as trichloroethyl phosphate; triphenyl phosphate, tricresyl phosphate, etc. Triaryl phosphates such as esters, tris(cumyl phosphate), cresyl diphenyl phosphate and other triaryl phosphates; diaryl phosphates such as diphenyl octyl phosphate and other alkyl esters; Alkyl esters); etc.

The amount of the plasticizer is 100% by weight relative to the amount of resin with negative intrinsic birefringence contained in the layer (B), preferably 0.001% by weight or more, more preferably 0.005% by weight or more, and 0.1% by weight or more It is especially preferred, and preferably less than 20% by weight, more preferably less than 18% by weight, and most preferably less than 15% by weight. When the amount of the plasticizer is within the aforementioned range, the glass transition temperature TgB of the resin contained in the layer (B) can be appropriately adjusted, so that the third process can be easily performed to obtain the desired broadband wavelength film. extension.

The resin with inherently negative birefringence may further include an optional component other than the aforementioned polymer and plasticizer in combination with the aforementioned polymer and plasticizer. As an arbitrary component, the example similar to the arbitrary component contained in the resin contained in a layer body (A) is mentioned, for example. Optional components may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.

The glass transition temperature TgB of the resin with negative inherent birefringence contained in the layer (B) is preferably 80°C or higher, more preferably 90°C or higher, more preferably 100°C or higher, especially 110°C or higher , preferably above 120°C. In the case where the glass transition temperature TgB of the inherently negative birefringence resin is so high, the orientational relaxation of the inherently negative birefringence resin can be reduced. The upper limit of the glass transition temperature TgB of the resin having negative intrinsic birefringence is not particularly limited, but is usually 200°C or less.

From the viewpoint of adjusting the optical properties of both the layer (A) and the layer (B) to an appropriate range by extension in the third step, the glass transition of the resin contained in the layer (A) The temperature TgA is preferably close to the glass transition temperature TgB of the resin contained in the layer (B). 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 most preferably 10°C or lower.

Layers (B) may also have in-plane retardation and a slow axis. In the case where the layer body (B) has an in-plane retardation and a slow axis, the in-plane retardation and the direction of the slow axis of the layer body (B) can be adjusted by stretching in the third step. However, the setting of extension conditions for such an adjustment tends to become complicated. Therefore, from the viewpoint of easily obtaining the desired optical characteristics and the direction of the slow axis in the layer body (B) after stretching in the third step, the layer body (B) formed in the second step does not have an in-plane Retardation and slow axis, or even if there is, in-plane retardation is preferably small. Specifically, the in-plane retardation of the layer body (B) is preferably 0 nm to 20 nm, more preferably 0 nm to 15 nm, and especially preferably 0 nm to 10 nm.

The thickness of the layer body (B) formed in the second step can be set arbitrarily within the range obtained by the desired broadband wavelength film. The specific thickness of the layer (B) is preferably above 3 μm, preferably above 5 μm, especially preferably above 7 μm, preferably below 30 μm, preferably below 25 μm, and preferably below 20 μm The following are preferred. In the case where the thickness of the layer body (B) is within the aforementioned 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 methods such as coating method, extrusion method, and bonding method can be used.

In the case where the layer (B) is formed by a coating method, the second step includes: coating the layer (A) with a composition including a resin whose inherent birefringence is negative. The aforementioned composition is generally a liquid composition further comprising a solvent combined with a resin with inherently negative birefringence. Examples of solvents include methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, 3-methyl-2-butanone, methyl isobutyl ketone, tetrahydrofuran, cyclopentyl methyl ether, ethyl Acyl acetone, cyclohexanone, 2-methylcyclohexanone, 1,3-dioxomethanone, 1,4-dioxomethanone, 2-pentanone, N,N-dimethylformamide, etc. Moreover, a solvent may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios. Solvents may cause phenomena such as dissolution and orientation loosening of the layer (A), but usually the coating thickness of the liquid composition is thin, and it dries quickly after coating, so the degree of the above phenomenon is negligible.

Examples of coating methods for the aforementioned composition include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, inclined plate coating, print coating, gravure coating, etc. Plate coating method, mold coating method, gap coating method and dipping method, etc.

In addition, in the coating method, the second step includes: after coating the composition on the layer (A), drying the coated composition if necessary. The solvent is removed by drying, and a layer (B) of a resin with inherently negative birefringence can be formed on the layer (A). Drying can be carried out by a drying method such as natural drying, heating drying, reduced-pressure drying, and reduced-pressure heating drying.

In the case of forming the layer (B) by extrusion, the second step includes: extruding a resin with negative intrinsic birefringence on the layer (A). Extrusion of resin is usually carried out in a molten state of the resin. Also, the resin is usually extruded into a film form using a die. By attaching the thus-extruded resin having negative intrinsic birefringence to the layer (A) or the film layer, the layer (B) of resin having negative intrinsic birefringence can be formed on the layer (A). Furthermore, when the layer (B) is formed by extrusion, the second step usually includes cooling and solidifying a resin having a negative intrinsic birefringence that is extruded and attached to the layer (A).

In the case of forming the layer body (B) by a bonding method, the second step includes bonding a film of a resin whose inherent birefringence is negative to the layer body (A). Examples of methods for producing a resin film of inherently negative birefringence include melt molding methods such as extrusion molding, inflation molding, and pressure molding, and solution casting methods. In addition, an adhesive or an adhesive may be used for bonding the film of the resin having a negative intrinsic birefringence to the layer (A).

Among the methods for forming the layer (B) described above, the coating method is preferable. A resin with negative intrinsic birefringence generally tends to have low mechanical strength. However, according to the coating method, the layer body (B) can be easily formed while using a resin having such low mechanical strength. For example, in the case of using the bonding method, if the layer (B) is formed on a suitable support film, and the layer (B) is bonded to the layer (A), then the layer (A) can be formed on the layer (A). The layer (B) is formed, and the damage of the layer (B) is suppressed at the same time. However, the coating method can reduce the number of layers compared to the lamination method in which the layer (B) is formed on the support film, and the layer (B) is transferred from the support film to the layer (A). (B) The number of processes required for the formation. Furthermore, according to the coating method, a joint agent and an adhesive are not required. In addition, in the coating method, it is easier to reduce the thickness of the layer body (B) itself than in the extrusion method. Accordingly, from the viewpoint of obtaining a thin broadband wavelength film with a small number of steps, it is preferable to form the layer body (B) by a coating method.

[5. The third process]

After the multilayer film comprising the layer (A) and the layer (B) is obtained in the second step, the third step of stretching the multilayer film to obtain a long broadband wavelength film is performed. By extending in the third step, the direction of the slow axis of the layer body (A) can be adjusted and the optical properties of the layer body (A) can be adjusted to obtain one of the λ/2 layer and the λ/4 layer. And, by extension in the third step, the slow axis appears in the layer body (B) and the optical characteristics appear in the layer body (B), 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 carried out in an oblique direction which is neither parallel nor perpendicular to the long side direction of the multilayer film. The specific stretching direction is set from among the in-plane directions of the multilayer film so that a desired broadband wavelength film can be obtained.

For example, when the layer body (A) is a layer body of a resin whose inherent birefringence is positive, the direction of the slow axis of the layer body (A) will be closer to the extending direction due to the extension in the third step. Ways change. And, for example, in the case where the layer body (A) is a layer body of a resin whose inherent birefringence is negative, the direction of the slow axis of the layer body (A) is extended in the third process to be perpendicular to The way in which the direction of its extending direction approaches changes. In this way, the direction of the slow axis of the layer body (A) usually changes due to the stretching in the third step. Furthermore, in the layer body (B), usually, due to the stretching in the third step, a slow axis appears in a direction perpendicular to the stretching direction. Therefore, the direction of extension in the third process is set so that by changing the direction of the slow axis in the layer body (A) and the appearance of the slow axis in the layer body (B) as described above, it is possible to obtain Lambda/2 layers and lambda/4 layers having a slow axis in the desired direction are preferred.

In the third process, the specific angle between the extending direction of the multilayer film and the long side direction of the multilayer film is preferably more than 4°, more preferably more than 5°, and preferably less than 45°, preferably less than 30° It is better below 20°, especially preferably below 20°. In the case of stretching the multilayer film in such a stretching direction, the directions of the slow axes of the λ/2 layer and the λ/4 layer can be easily controlled.

In the third step, the angle between the extending direction of the multilayer film and the slow axis of the layer (A) (the absolute value of the angle) is preferably 45° or more, more preferably 60° or more, and 70° The above is especially preferable, and it is more preferably below 86°, and most preferably below 85°. When the multilayer film is stretched in such a stretching direction, it becomes easy to adjust the slow axes of the λ/2 layer and the λ/4 layer to satisfy the relationship of the formula (1).

The elongation ratio in the third step is preferably 1.1 times or more, more preferably 1.15 times or more, especially 1.2 times or more, and preferably 2.5 times or less, preferably 2.2 times or less, and 2.0 times The following are preferred. When the stretching ratio in the third step is equal to or greater than the lower limit of the aforementioned range, the occurrence of wrinkles can be suppressed. In addition, when the stretching ratio in the third step is not more than the upper limit of the aforementioned range, the directions of the slow axes of the λ/2 layer and the λ/4 layer can be easily controlled.

The stretching temperature in the third step is such that the following Both of conditions (C1) and (C2) are preferable. (C1) The extension temperature is preferably above TgA-20°C, preferably above TgA-10°C, especially preferably above TgA-5°C, preferably below TgA+30°C, preferably below TgA+25°C, The preferred temperature is below TgA+20°C. (C2) The extension temperature is preferably above TgB-20°C, preferably above TgB-10°C, especially preferably above TgB-5°C, preferably below TgB+30°C, preferably below TgB+25°C, The preferred temperature is below TgB+20°C.

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

The above-mentioned stretching in the third step can be performed using any stretching machine, for example, a tenter stretching machine and a roll stretching machine can be used. Stretching using these stretching machines is preferably performed while continuously conveying the elongated multilayer film in the longitudinal direction.

[6. Arbitrary process]

The manufacturing method of the above-mentioned broadband wavelength film may further include any combination of steps as the above-mentioned steps.

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

Furthermore, for example, the manufacturing method of the broadband wavelength thin film may also include applying corona treatment to the surface of one or more of the layers (A), layer (B) and film layers at any point in time , plasma treatment and other surface treatment processes. Accordingly, for example, after surface treatment is performed on the surface of the layer body (A), the layer body (B) or the film layer may be formed on the treated surface. Moreover, for example, after surface-treating the surface of a thin film layer, you may form a layer body (B) on this processing surface. By performing the surface treatment, the bonding property of the upper layer bodies on the surface treated can be improved.

The first step to the fourth step and any step mentioned above can be carried out while continuously conveying films such as the layer body (A), multilayer film, and broadband wavelength film. The conveying direction of such a conveying film is usually the long side direction of the film. Accordingly, during the aforementioned conveyance, the longitudinal direction and the width direction of the film generally coincide with the conveyed MD direction (Machine Direction) and TD direction (Transverse Direction).

[7. Broadband wavelength film]

By the above-mentioned manufacturing method, a co-extended 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-extended film satisfy the aforementioned 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 capable of penetrating the film in a wide wavelength range The ray of light imparts an in-plane retardation of approximately 1/4 wavelength of the wavelength of this ray. (Refer to Japanese Patent Laid-Open No. 2007-004120). Accordingly, according to the production method described above, a long broadband wavelength film can be obtained as a co-extended film having a λ/2 layer and a λ/4 layer. From the viewpoint of realizing a broadband wavelength film capable of functioning in a wider wavelength range, the λ/2 layer and the λ/4 layer preferably satisfy formula (2), and preferably satisfy formula (3). Equation (2) indicates that θ(λ/4) is in the range of “[+45°+2×θ(λ/2)]-4°” and “[+45°+2×θ(λ/2)]+4°” . In addition, formula (3) shows that θ(λ/4) is not less than [+45°+2×θ(λ/2)]-3° and not more than [[+45°+2×θ(λ/2)]+3°” range. 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 production method mentioned above, the stretching of the layer body (A) and the layer body (B) is carried out together in the third process, instead of being carried out separately as usual. Therefore, since the number of stretching processes can be reduced more than conventionally, the number of steps required for the manufacture of the broadband wavelength thin film can be reduced, so that efficient manufacture can be realized. Also, in the aforementioned production method of obtaining a broadband wavelength film by stretching the multilayer film thereby co-extending the layer body (A) and the layer body (B), it is not possible to produce the λ/2 layer and the λ/4 layer separately. In the conventional manufacturing method of laminating the two afterward, misalignment in the slow axis direction due to lamination generally occurs. Therefore, since it is easy to precisely control the directions of the respective slow axes of the λ/2 layer and the λ/4 layer, a high-quality broadband wavelength film capable of realizing a circularly polarizing film capable of effectively suppressing discoloration can be easily obtained.

In the broadband wavelength film obtained, one of the λ/2 layer system layer (A) and the layer body (B) is extended, and the λ/4 layer system layer body (A) and the layer body ( B) A layer obtained by extending the other. Among them, in terms of the ease of manufacturing broadband wavelength films, the layer obtained by stretching the layer (A) for the λ/2 layer is preferable, and the layer obtained by stretching the layer (B) for the λ/4 layer better. Accordingly, the λ/2 layer is preferably made of the same resin as the layer (A), and the λ/4 layer is preferably made of the same resin as the layer (B).

The λ/2 layer system is a layer body having an in-plane retardation of usually 220 nm or more and usually 300 nm or less at a measurement wavelength of 590 nm. In the case where the λ/2 layer has such an in-plane retardation, the λ/2 layer and the λ/4 layer can be combined to realize a broadband wavelength film. Among them, from the viewpoint of obtaining a circularly polarizing film with an excellent function of suppressing discoloration in the oblique direction, the in-plane retardation of the λ/2 layer at a measurement wavelength of 590 nm is preferably 230 nm or more, more preferably 240 nm or more , and preferably below 280 nm, preferably below 270 nm.

The retardation of the λ/2 layer in the thickness direction at the measurement wavelength of 590 nm is preferably 130 nm or more, more preferably 140 nm or more, especially 150 nm or more, and preferably 300 nm or less, and 280 nm or less More preferably, it is especially preferably below 270 nm. When the retardation in the thickness direction of the λ/2 layer is within the aforementioned range, a circularly polarizing film that is particularly excellent in the function of suppressing discoloration in the oblique direction can be obtained.

The NZ coefficient of the λ/2 layer is preferably not less than 1.0, more preferably not less than 1.05, more preferably not less than 1.10, preferably not more than 1.6, more preferably not more than 1.55, and most preferably not more than 1.5. In the case where the NZ coefficient of the λ/2 layer is in the aforementioned range, a circularly polarizing film that is particularly excellent in the function of suppressing discoloration in the oblique direction can be obtained. Also, a λ/2 layer with such an NZ coefficient can be easily fabricated.

Optical properties such as the retardation and NZ coefficient of the λ/2 layer can be determined by, for example, the retardation and thickness of the layer (A) prepared in the first process, and the stretching temperature, stretching ratio, stretching direction, etc. in the third process. Extend the conditions to adjust.

The orientation angle θ (λ/2) of the λ/2 layer is preferably in the range of 27.5°±10° (that is, the range of 17.5° to 37.5°), and preferably in the range of 27.5°±8° (that is, The range of 19.5°-35.5° is preferable, and the range of 27.5°±5° (that is, the range of 22.5°-32.5°) is more preferable. A general linear polarizing film has a transmission axis in its width direction and an absorption axis in its longitudinal direction. When the orientation angle θ(λ/2) of the λ/2 layer is within the aforementioned range, it can be combined with this general linear polarizing film to easily realize a circular polarizing film. Also, when the orientation angle θ(λ/2) of the λ/2 layer is in the aforementioned range, the function of suppressing discoloration in the front direction and oblique direction of the obtained circular polarizing film can be optimized.

The orientation angle θ(λ/2) of the λ/2 layer can be extended by, for example, the direction of the slow axis of the layer (A) prepared in the first process, and the stretching direction and stretching ratio in the third process. conditions to adjust.

The thickness of the λ/2 layer is preferably above 20 μm, more preferably above 25 μm, more preferably above 30 μm, preferably below 80 μm, preferably below 70 μm, and below 60 μm better. Thereby, the mechanical strength of the λ/2 layer can be improved.

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

The retardation of the λ/4 layer in the thickness direction at the measurement wavelength of 590 nm is preferably above -150 nm, preferably above -140 nm, especially preferably above -130 nm, and preferably below -80 nm, It is preferably below -90 nm, especially preferably below -100 nm. When the retardation in the thickness direction of the λ/4 layer is within the aforementioned range, a circularly polarizing film that is particularly excellent in the function of suppressing discoloration in the oblique direction can be obtained.

The NZ coefficient of the λ/4 layer is preferably above -1.0, preferably above -0.8, especially above -0.7, preferably below 0.0, preferably below -0.05, and below -0.1. Excellent. In the case where the NZ coefficient of the λ/4 layer is within the aforementioned range, a circularly polarizing film that is particularly excellent in the function of suppressing discoloration in the oblique direction can be obtained. Also, a λ/4 layer with such an NZ coefficient can be easily fabricated.

Optical properties such as the retardation and NZ coefficient of the λ/4 layer can be determined by, for example, the thickness of the layer (B) formed in the second process, and the stretching conditions such as the stretching temperature, stretching ratio, and stretching direction in the third process to adjust.

The orientation angle θ (λ/4) of the λ/4 layer is preferably in the range of 100°±20° (that is, the range of 80° to 120°), and preferably in the range of 100°±15° (that is, The range of 85°-115°) is preferable, and the range of 100°±10° (that is, the range of 90°-110°) is more preferable. In the case where the orientation angle θ(λ/4) of the λ/4 layer is in the aforementioned range, it can be combined with a general linear polarizing film having a transmission axis in the width direction and an absorption axis in the long side direction, easily Realize circular polarizing film. Also, when the orientation angle θ(λ/4) of the λ/4 layer is in the aforementioned range, the function of suppressing discoloration in the front direction and oblique direction of the obtained circular polarizing film can be optimized.

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

The thickness of the λ/4 layer is preferably above 3 μm, more preferably above 4 μm, especially above 5 μm, preferably below 15 μm, preferably below 13 μm, and below 10 μm. Excellent. In the case where the thickness of the λ/4 layer is above the lower limit of the aforementioned range, desired optical characteristics can be easily obtained. Furthermore, when the thickness of the λ/4 layer is below the upper limit of the aforementioned range, the thickness of the broadband wavelength film can be reduced.

The λ/2 layer and the λ/4 layer are preferably connected directly. Thereby, the thickness of the broadband wavelength film can be thinned.

When the manufacturing method of the broadband wavelength film includes the fourth step of forming a thin film layer, the broadband wavelength film has a thin film layer between the λ/2 layer and the λ/4 layer. In contrast to the bonding layer used in the conventional manufacturing method in which the λ/2 layer and the λ/4 layer are produced separately and bonded together, the thickness is generally 5 μm or more. The film layer of the broadband wavelength film can be thinner than this. The thickness of the specific film layer is preferably less than 2.0 μm, more preferably less than 1.8 μm, and especially preferably less than 1.5 μm. Since the thin film layer can be thinned in this way, it is also possible to thin the thickness of the entire broadband wavelength thin film. 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 can also have any combination of layers up to λ/2 layer, λ/4 layer and thin film layer. For example, a bonding layer or an adhesive layer for bonding the λ/2 layer and the λ/4 layer may be provided.

The total light transmittance of the broadband wavelength film is preferably above 80%, preferably above 85%, and especially preferably above 88%. The total light transmittance must comply with JIS K0115 and be measured with a spectrophotometer at a wavelength of 400 nm to 700 nm.

The haze of the broadband wavelength film is preferably less than 5%, more preferably less than 3%, especially preferably less than 1%, ideally 0%. Here, the haze can be used: follow JIS K7361-1997, use Nippon Denshoku Kogyo Co., Ltd. "Nephelometer NDH-300A", measure at 5 places, and then calculate the average value.

The thickness of the broadband wavelength film is preferably above 20 μm, preferably above 25 μm, especially above 30 μm, preferably below 120 μm, preferably below 100 μm, and preferably below 90 μm Excellent. According to the above-mentioned manufacturing method, such a thin broadband wavelength film can be easily manufactured.

[8. Circular polarizing film]

A strip-shaped circular polarizing film can be produced by using the broadband wavelength film produced by the above-mentioned production method. This kind of circular polarizing film can be produced by a production method including "the process of manufacturing a broadband wavelength film by the above-mentioned production method" and "the process of bonding this broadband wavelength film to a long linear polarizing film". to manufacture. The aforementioned lamination is usually performed in such a manner that a linear polarizing film, a λ/2 layer, and a λ/4 layer are sequentially arranged in the thickness direction. Moreover, bonding layer or adhesive layer may also be used as required.

The linear polarizing film is a strip-shaped film with an absorption axis, which has the 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 the linearly polarized light means the vibration direction of the electric field of the linearly polarized light.

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

As the polarizer layer, for example, a film of an appropriate vinyl alcohol-based polymer that has been appropriately treated 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 the treatment of the film include dyeing treatment with a dichroic substance such as iodine and a dichroic dye, stretching treatment, and crosslinking treatment. Usually, in the stretching process for manufacturing the polarizer layer, the film before stretching is stretched in the longitudinal direction, so the absorption axis parallel to the longitudinal direction of the polarizer layer appears in the obtained polarizer layer. The polarizer layer is one capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, especially one having an excellent degree of polarization. The thickness of the polarizer layer is generally 5 μm˜80 μm, but not limited thereto.

As the protective film layer for protecting the polarizer layer, any transparent film may be used. Among them, films of resins excellent in transparency, mechanical strength, thermal stability, and moisture shielding properties are preferred. Examples of such resins include acetate resins such as cellulose triacetate, polyester resins, polyether resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and cycloolefin resins. , (meth)acrylic resin, etc. Among them, acetate resins, cycloolefin resins, and (meth)acrylic resins are preferable in terms of small birefringence. From the viewpoints of transparency, low hygroscopicity, dimensional stability, and light weight, etc., Cycloolefin resins are particularly preferred.

The aforementioned linear polarizing film, for example, can be manufactured by laminating a strip-shaped polarizer layer and a strip-shaped protective film layer. Adhesives can also be used as needed when laminating.

The linear polarizing film preferably has an absorption axis in the longitudinal direction of the linear polarizing film. This kind of linear polarizing film is preferably laminated with a broadband wavelength film comprising a λ/2 layer and a λ/4 layer to make a circular polarizing film, and the λ/2 layer has an angle of 27.5°±10° (that is, 17.5° ˜37.5°), the λ/4 layer has an orientation angle θ(λ/4) of 100°±20° (ie, 80°˜120°). According to the lamination of the combination as described above, the circular polarizing film can be manufactured by making the long-side direction of the elongated linear polarizing film and the elongated broadband wavelength film parallel and laminating them, so it becomes The circular polarizing film can be manufactured by the roll-to-roll method. Therefore, the production efficiency of the circular polarizing film can be improved.

In the circular polarizing film thus obtained, the linearly polarized light of a wide wavelength range that penetrates the linear polarizing film is converted into circularly polarized light by the broadband wavelength film. Therefore, the circular polarizing film has the function of absorbing light of one of right-handed circular polarization and left-handed circular polarization in a wide wavelength range and allowing the remaining light to pass through.

The aforesaid circular polarizing film may further have any combination of layers to linear polarizing film and broadband wavelength film.

For example, the circular polarizing film may also have a protective film layer for preventing damage. Furthermore, for example, the circular polarizing film may be provided with a bonding layer or an adhesive layer for bonding the linear polarizing film and the broadband wavelength film.

The aforementioned circular polarizing film can effectively reduce the reflection of external light when it is arranged on the surface capable of reflecting light. In particular, the aforementioned circularly polarizing film is useful in that it can effectively reduce the reflection of external light in a wide wavelength range in the visible light region. Moreover, since the reflection of external light in a wide wavelength range can be effectively reduced in this way, the aforementioned circular polarizing film can suppress discoloration caused by increased reflection intensity of light of a part of wavelengths. This circularly polarizing film can obtain the above-mentioned effects of suppressing reflection and suppressing discoloration at least in its front direction, and usually can further obtain it in its oblique direction. Also, the effects of suppressing reflection and suppressing discoloration in oblique directions can generally be obtained in all azimuthal directions of the main surface of the film.

[9. Video display device]

The circularly polarizing film utilizes the function of suppressing the reflection of external light as mentioned above, and can be used as a reflection suppressing film of an organic electroluminescent display device (hereinafter referred to as an "organic EL display device" as appropriate).

An organic EL display device includes a circularly polarizing film sheet cut from a long circularly polarizing film.

In the case where the organic EL display device is equipped with a circular polarizing film, the organic EL display device generally has a circular polarizing film on the display surface. By arranging the circular polarizing film on the display surface of the organic EL display device so that the side of the linear polarizing film faces the viewing side, it is possible to suppress the incident light from the outside of the device from being reflected in the device and exiting the device. As a result, it is possible to Suppresses glare on the display surface of a display device. Specifically, only a part of the linearly polarized light incident on the outside of the device passes through the linearly polarized film, and then passes through the broadband wavelength film to become circularly polarized light. Circularly polarized light is reflected by the components (reflective electrodes, etc.) that reflect light in the display device, and passes through the broadband wavelength film again, thereby becoming a direction perpendicular to the vibration direction (polarization axis) of the incident linearly polarized light. Linearly polarized light in the vibration direction (polarization axis) does not pass through the linear polarizing film. Thereby, the reflection suppression function is achieved. Furthermore, since the aforementioned reflection suppression function can be obtained over a wide wavelength range, discoloration of the display surface can be suppressed.

Furthermore, the aforementioned circular polarizing film can also be provided in a liquid crystal display device. Such a liquid crystal display device includes a circularly polarizing film sheet cut from a long circularly polarizing film.

In the case where the liquid crystal display device is equipped with a circular polarizing film with the surface of the linear polarizing film facing the viewing side, it is possible to suppress the incident light from outside the device from being reflected in the device and exiting the device. As a result, the display device can be suppressed. glare and discoloration of the display surface.

In addition, when a liquid crystal display device includes a circularly polarizing film sheet such that a broadband wavelength film, a linear polarizing film, and a liquid crystal cell of the liquid crystal display device are arranged sequentially from the viewing side, images can be displayed with circularly polarized light. Therefore, it is possible to stably see the light emitted from the display surface by using the polarized sunglasses, and the image visibility when wearing the polarized sunglasses is improved.

In addition, especially when the circular polarizing film sheet is installed so that the surface of the linear polarizing film faces the viewing side in an image display device such as an organic EL display device or a liquid crystal display device, warping of the display panel can be suppressed. This effect will be described below.

An image display device generally includes a display panel including display elements such as organic electroluminescent elements and liquid crystal cells. This display panel includes a base material such as a glass base material in order to increase the mechanical strength of the display panel. Furthermore, in a display panel in which a circular polarizing film sheet is provided so that the surface on the side of the linear polarizing film faces the viewing side, a base material, a broadband wavelength film, and a linear polarizing film are generally provided in this order.

Incidentally, the polarizer layer of the linear polarizing film generally tends to shrink in the in-plane direction under high-temperature environments. Once the polarizer layer shrinks in this way, a stress that warps the display panel will be generated on the display panel provided with the linear polarizing film including the polarizer layer. Since the warping of the display panel may cause image quality to be lowered, it is desirable to suppress it. Regarding this warpage, it has been found that the greater the distance between the polarizer layer and the base material of the display panel, the greater the warpage tends to be.

In the broadband wavelength film manufactured by the conventional manufacturing method of separately manufacturing the λ/2 layer and the λ/4 layer and then laminating them together, the overall broadband wavelength film is also thick because the bonding layer is thick. Accordingly, in the conventional broadband wavelength film, since the distance between the polarizer layer and the base material of the display panel increases, the warpage of the display panel tends to increase.

In contrast, the broadband wavelength film produced by making a co-extended film as described above, the λ/2 layer and the λ/4 layer can be directly connected, or it will be placed between the λ/2 layer and the λ/4 layer thinning of the interlayer film. Accordingly, since the entire broadband wavelength film can be thinned, the distance between the polarizer layer and the base material of the display panel can be reduced. Therefore, warping of the display panel can be suppressed.

"Example"

Examples are disclosed below to specifically illustrate the present invention. However, the present invention is not limited to the embodiments disclosed below, and can be implemented with arbitrary changes within the scope not departing from the scope of patent application and the scope of equivalents of the present invention.

In the following descriptions, "%" and "parts" indicating amounts are based on weight unless otherwise noted. In addition, the operations described below were carried out under the conditions of normal temperature and normal pressure unless otherwise noted.

[Evaluation method]

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

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

〔Measurement method of optical properties of each layer of broadband wavelength film〕

The broadband wavelength film to be evaluated was set on the stage of a retardation meter ("AxoScan" manufactured by Axometrics). Then, the change of the polarization state of the polarized light passing through the broadband wavelength film before and after passing through the broadband wavelength film is measured as the transmission polarization characteristic of the broadband wavelength film. This measurement is performed by multi-directional measurement in the range of polar angle -55° to 55° with respect to the main surface of the broadband wavelength film. In addition, the aforementioned multi-directional measurement is carried out in each azimuth direction of 45°, 90°, 135° and 180° by setting a certain azimuth direction of the main surface of the broadband wavelength film as 0°. The measurement wavelength of the aforementioned measurement is 590 nm.

Secondly, from the transmitted polarizing characteristics measured as mentioned above, the in-plane retardation Re, the retardation Rth in the thickness direction, the NZ coefficient and the orientation angle of each layer are obtained by fitting calculation. The aforementioned fitting calculation is performed by setting the three-dimensional refractive index and orientation angle of each layer contained in the broadband wavelength film as fitting parameters. In addition, the fitting calculation used software attached to the phase difference meter (AxoScan) (“Multi-Layer Analysis” manufactured by Axometrics Corporation).

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

Using "LCD Master" manufactured by Shintech Co., Ltd. as software for simulation, the circularly polarizing films produced in the respective examples and comparative examples were modeled, and the color difference ΔE*ab was calculated under the following settings.

In the simulation model, a configuration was set in which a circular polarizing film was attached to the reflective surface of an aluminum mirror having a planar reflective surface such that the λ/4 layer side of the broadband wavelength film was in contact with the mirror. Therefore, in this model, the following structure is set: a linear polarizing film, a λ/2 layer, a λ/4 layer, and a mirror are sequentially arranged in the thickness direction.

Then, in the aforementioned model, the color difference ΔE*ab when light is irradiated from the D65 light source to the circular polarizing film is calculated in the front direction of the aforementioned circular polarizing film. When calculating the chromatic aberration ΔE*ab, the reflected light of the aluminum mirror with no circular polarizing film attached in the direction of polar angle 0° and azimuth angle 0° is used as the reference. In addition, in the simulation, the surface reflection component that actually occurs on the surface of the circular polarizing film is excluded from the calculation of the color difference ΔE*ab. As for the value of color difference ΔE*ab, the smaller the value, the less the color change is, and it is better.

[Visual evaluation of circular polarizing film]

The polarizing plate of the image display device (“Apple Watch” (registered trademark) of Apple Inc.) was peeled off, and the display surface of the image display device was interposed with the λ/4 layer surface of the circular polarizing film to be evaluated. The adhesive layer (Nitto Denko Co., Ltd. Made "CS-9621") fit. Set the display surface to a black display state (a state where the entire screen displays black), and observe the display surface from all angles of polar angle θ = 0° (frontal direction) and polar angle θ = 60° (oblique direction). The smaller the brightness and discoloration caused by the reflection of external light, the better the result. The observed results were evaluated by the following criteria. "A": Brightness and discoloration to an extent not visible. "B": Brightness and discoloration occurred to a visible extent. "C": Brightness and discoloration occurred seriously.

[Example 1]

(First process: Manufacture of layer (A))

As a resin with positive intrinsic birefringence, a granular northylene-based resin (manufactured by Nippon Zeon Co., Ltd.; glass transition temperature: 126° C.) was prepared, and dried at 100° C. for 5 hours. The dried resin is supplied to the extruder, passes through the polymer tube and the polymer filter, and is extruded from the T-shaped die on the casting drum to form a sheet. The extruded resin was cooled to obtain a long unstretched film with a thickness of 160 μm. The obtained pre-stretched film is wound into a roll for recycling.

The unstretched film was pulled out from the roll and continuously supplied to a tenter stretcher. Then, the unstretched film was stretched using this tenter stretching machine to obtain a long stretched film as a layer (A). In this stretching, the stretching angle formed by the stretching direction with respect to the longitudinal direction of the film before stretching was 90°, the stretching temperature was 135° C., and the stretching ratio was 2.0 times. In addition, the obtained stretched film had an orientation angle of 90°, an in-plane retardation Re of 250 nm, and a thickness of 80 μm. The stretched film obtained is wound into a roll for recycling.

(Second process: formation of layer (B))

Prepare a liquid composition containing styrene-maleic anhydride copolymer ("Daylark D332" manufactured by NOVA Chemicals, glass transition temperature 130°C, oligomer content 3% by weight) as a resin with negative intrinsic birefringence . The liquid composition contains methyl ethyl ketone as a solvent, and the concentration of styrene-maleic anhydride copolymer in the liquid composition is 10% by weight.

The stretched film is pulled out from the roll, and the aforementioned liquid composition is applied on the stretched film. Thereafter, the applied 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. Thereby, a multilayer film including the layer body (A) and the layer body (B) is obtained. The obtained multilayer film is wound into a roll for recycling.

(Third process: stretching of multilayer film)

The multilayer film is pulled out from the roll and continuously supplied to a tenter stretcher. Then, using this tenter stretching machine, the multilayer film is stretched. In this stretching, the stretching angle formed by the stretching direction relative to the long side direction of the multilayer film is 15°, the stretching temperature is 130° C., and the stretching ratio is 1.5 times. In this way, a co-extended film having a λ/2 layer obtained by stretching the layer body (A) and a λ/4 layer obtained by stretching the layer body (B) is produced, and a broadband wavelength film is obtained. The obtained broadband wavelength film was evaluated by the method described above.

(Manufacture of circular polarizing film)

A long linear polarizing film having an absorption axis in the longitudinal direction was prepared. This linear polarizing film and the long-side direction of the broadband wavelength film were bonded together in parallel. This bonding is performed using an adhesive ("CS-9621" manufactured by Nitto Denko Co., Ltd.). Thereby, a circular polarizing film comprising a linear polarizing film, a λ/2 layer, and a λ/4 layer in this order was obtained. The obtained circular polarizing film was evaluated by the method mentioned 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°.

Production and evaluation of the broadband wavelength film and the circularly polarizing film were carried out by the same operations as in Example 1 except for the above matters.

[Example 3]

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

Production and evaluation of the broadband wavelength film and the circularly polarizing film were carried out by the same operations as in Example 1 except for the above matters.

[Comparative Example 1]

As a resin with positive intrinsic birefringence, a granular northylene-based resin (manufactured by Nippon Zeon Co., Ltd.; glass transition temperature: 126° C.) was prepared, and dried at 100° C. for 5 hours. The dried resin is supplied to the extruder, passed through the polymer tube and the polymer filter, and extruded from the T-die on the casting drum to form a sheet. The extruded resin was cooled to obtain a long unstretched film with a thickness of 110 μm. The obtained pre-stretched film is wound into rolls for recycling.

The unstretched film is pulled out from the roll and continuously supplied to the roll stretching machine. Then, using this roller stretching machine, the film is stretched free uniaxially before stretching 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 film before stretching was 0°, the stretching temperature was 135° C., and the stretching ratio was 1.9 times. Furthermore, the obtained stretched film had an orientation angle of 0°, an in-plane retardation Re of 350 nm, and a thickness of 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 obtained in this way was used as the layer body (A).

[Comparative Example 2]

In the third step, the stretching angle formed by the stretching direction relative to the long side direction of the multilayer film is changed to 0°. And, the stretching of the multilayer film in the third step is performed by free uniaxial stretching using a roll stretcher.

Production and evaluation of the broadband wavelength film and the circularly polarizing film were carried out by the same operations as in Example 1 except for the above matters.

[Comparative Example 3]

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

Production and evaluation of the broadband wavelength film and the circularly polarizing film were carried out by the same operations as in Example 1 except for the above matters.

[Comparative Example 4]

In the third step, the stretching angle formed by the stretching direction relative to the long side direction of the multilayer film is changed to 60°.

Production and evaluation of the broadband wavelength film and the circularly polarizing film were carried out by the same operations as in Example 1 except for the above matters.

[result]

The results of Examples and Comparative Examples are shown in Table 1 and Table 2 below. In the following table, the abbreviations have the following meanings. COP: Norrene-based resin. ST: Styrene-maleic anhydride copolymer. Re: In-plane delay. Rth: Retardation in the thickness direction. Orientation angle: the angle formed by the slow axis relative to the direction of the long side. Total thickness: the total thickness of the λ/2 layer and the λ/4 layer. Length: Long side direction. Horizontal: width direction. Oblique: oblique.

"Table 1" [Table 1. Results of Examples]

<Table 2> [Table 2. Results of Comparative Examples]

100‧‧‧Layers (A) 200‧‧‧Multilayer film 210‧‧‧Layer (B) 300‧‧‧broadband wavelength film

<Fig. 1> Fig. 1 is a schematic perspective view showing a layer body (A) as a resin film prepared in the first step of the manufacturing method of a broadband wavelength film related to an embodiment of the present invention.

<FIG. 2> FIG. 2 is a schematic perspective view of the multilayer film obtained in the second process of the manufacturing method of the broadband wavelength film related to an embodiment of the present invention.

<FIG. 3> FIG. 3 is a schematic perspective view of the broadband wavelength film obtained in the third process of the manufacturing method of the broadband wavelength film related to an embodiment of the present invention.

100‧‧‧Layers (A)

A ₁₀₀ ‧‧‧direction

Claims (9)

A method for manufacturing a broadband wavelength film, which includes in sequence: the first process, preparing a layer (A) as a strip-shaped resin film; the second process, forming an intrinsic birefringence on the aforementioned layer (A) as Negative resin layer (B) to obtain a multilayer film; and the third step, extending the aforementioned multilayer film along an oblique direction that is neither parallel nor perpendicular to the long side direction of the aforementioned multilayer film to obtain a layer with λ/2 and a strip-shaped broadband wavelength film with λ/4 layers; wherein the aforementioned layer (A) prepared in the aforementioned first process has a slow axis parallel or perpendicular to the long side direction of the layer (A), The aforementioned λ/2 layer and the aforementioned λ/4 layer of the aforementioned broadband wavelength film satisfy the following formula (1): θ(λ/4)=[45°+2×θ(λ/2)]±5° (1) (In the aforementioned formula (1), θ(λ/2) represents the angle between the slow axis of the aforementioned λ/2 layer and the long-side direction of the aforementioned broadband wavelength film, and θ(λ/4) represents the aforementioned λ/ The angle between the slow axis of the four layers relative to the long-side direction of the aforementioned broadband wavelength film). The manufacturing method of the broadband wavelength film according to claim 1, wherein the third step includes: extending the multilayer film obliquely at an angle of 45° or less relative to the long side direction of the multilayer film. The manufacturing method of the broadband wavelength film as claimed in item 1, wherein the aforementioned angle θ(λ/2) is in the range of 27.5°±10°. The manufacturing method of the broadband wavelength film as claimed in item 1, wherein the aforementioned angle θ(λ/4) is in the range of 100°±20°. The manufacturing method of the broadband wavelength film according to Claim 1, wherein the aforementioned λ/2 layer is a layer obtained by extending the aforementioned layer (A). The manufacturing method of the broadband wavelength film according to Claim 1, wherein the aforementioned λ/4 layer is a layer obtained by extending the aforementioned layer (B). A method for manufacturing a circular polarizing film, comprising the step of manufacturing a broadband wavelength film according to any one of claims 1 to 6, and pasting the broadband wavelength film on a strip-shaped linear polarizing film combined process. The method of manufacturing a circular polarizing film according to claim 7, wherein the linear polarizing film has an absorption axis in the long side direction of the linear polarizing film. A strip-shaped broadband wavelength film, which is a co-extended film, and the co-extended film has: λ/2 layers, with a slow axis with an angle of 27.5°±10° relative to the long-side direction of the aforementioned broadband wavelength film , and the λ/4 layer have a slow axis with an angle of 100°±20° relative to the long-side direction of the aforementioned broadband wavelength film.

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