JP7567808B2 - Method for manufacturing retardation film - Google Patents

Description

The present invention relates to a retardation film and a method for manufacturing the same.

Technologies for manufacturing films using resins have been proposed in the past (Patent Documents 1 to 3).

International Publication No. 2017/065222 (corresponding publication: U.S. Patent Application Publication No. 2018/284333) JP 2016-212171 A JP 2017-107177 A (Corresponding Publication: U.S. Patent Application Publication No. S2018348419)

One type of film manufactured using resin is a retardation film. Retardation films have retardation in at least one of the in-plane and thickness directions, so they are generally required to have large birefringence in at least one of the in-plane and thickness directions.

The balance between the in-plane birefringence and the thickness birefringence can be expressed by the NZ coefficient. For example, if a retardation film with an NZ coefficient of less than 1.0 can be obtained, the retardation film can improve the display quality, such as the viewing angle characteristics of a display device.

For retardation films with an NZ coefficient of less than 1.0, a manufacturing method thereof is proposed in, for example, Patent Document 1. However, the manufacturing method described in Patent Document 1 requires manufacturing a film having multiple layers and carrying out a shrinking process and a heating process. This means that there are many control items and a large number of processes, and the manufacturing method tends to be complicated.

Furthermore, Patent Document 1 discloses a specific example of producing a sheet of retardation film, but from the standpoint of efficient production using the roll-to-roll method, a long retardation film is required.

The present invention was devised in consideration of the above-mentioned problems, and aims to provide a long-length retardation film with excellent viewing angle characteristics, and a method for manufacturing the same.

The present inventors have conducted extensive research to solve the above problems, and as a result, have found that a long retardation film having a slow axis at an angle of 10° to 80° with respect to the width direction and an NZ coefficient greater than 0 and smaller than 1 can be obtained by stretching a resin film having a predetermined NZ coefficient in an oblique direction, thereby solving the above problems and completing the present invention.
That is, the present invention includes the following.

[1] A long retardation film,
The slow axis is at an angle of 10° to 80° with respect to the width direction,
A retardation film having an NZ coefficient greater than 0 and less than 1.
[2] The retardation film according to [1], which is a half-wave plate or a quarter-wave plate.
[3] The retardation film according to [1] or [2], which is made of a resin having a positive intrinsic birefringence value.
[4] The retardation film according to any one of [1] to [3], which is made of a resin containing a polymer having crystallinity.
[5] The retardation film according to [4], wherein the crystalline polymer is a hydrogenated product of a ring-opening polymer of dicyclopentadiene.
[6] The retardation film according to any one of [1] to [5], wherein the retardation film has a birefringence Re/d in an in-plane direction of 3.0×10 ⁻³ or more and 2.0×10 ⁻² or less. [7] The retardation film according to any one of [1] to [6], wherein the retardation film has a retardation Rth in a thickness direction of −30 nm or more and 30 nm or less.
[8] The retardation film according to [4] or [5], having a crystallinity of 10% or more as measured by an X-ray diffraction method.
[9] A method for producing a long retardation film having a slow axis at an angle of 10° to 80° with respect to the width direction and an NZ coefficient greater than 0 and smaller than 1, comprising the steps of:
Step 1 of preparing a film _F0 having an NZ coefficient less than 0;
A process 2 of obliquely stretching the film _F0 .
[10] The method for producing a retardation film according to [9], wherein the step 1 includes contacting a resin film with a solvent, thereby changing the NZ coefficient of the resin film, and obtaining the film F ₀ .
[11] The method for producing a retardation film according to [10], wherein the solvent is a hydrocarbon-based solvent.

The present invention provides a long retardation film with excellent viewing angle characteristics, and a method for manufacturing the same.

FIG. 1 is a side view diagrammatically illustrating an apparatus that can be used in step 1 of the method for producing a retardation film according to the first embodiment. FIG. 2 is a plan view diagrammatically illustrating an oblique stretching machine that can be used in step 2 of the method for producing a retardation film according to the first embodiment. FIG. 3 is a plan view showing a schematic diagram of a longitudinal stretching machine that can be used in any step.

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 shown below, and may be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

In the following description, the in-plane retardation Re of the film is a value expressed by "Re = (nx - ny) x d" unless otherwise specified. The in-plane birefringence of the film is a value expressed by "(nx - ny)" unless otherwise specified, and is therefore expressed by "Re/d". The thickness-direction retardation Rth of the film is a value expressed by "Rth = [{(nx + ny) / 2} - nz] x d" unless otherwise specified. The thickness-direction birefringence of the film is a value expressed by "[{(nx + ny) / 2} - nz]" unless otherwise specified, and is therefore expressed by "Rth/d". The NZ coefficient of the film is a value expressed by "(nx - nz) / (nx - ny)" unless otherwise specified, and is therefore expressed by "0.5 + Rth/Re". nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the film and perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. The measurement wavelength is 590 nm unless otherwise specified.

In the following description, unless otherwise specified, a material with positive intrinsic birefringence means a material whose refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to the stretching direction. Furthermore, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction, unless otherwise specified. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

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

In the following description, a "long" film refers to a film that is 5 times or more longer than its width, preferably 10 times or more longer, specifically a film that is long enough to be wound into a roll for storage or transportation. There is no particular upper limit on the length, but it is usually 100,000 times or less longer than the width.

In the following description, the longitudinal direction of a long film is usually parallel to the film transport direction in the production line. The MD direction (machine direction) is the film transport direction in the production line, and is usually parallel to the longitudinal direction of a long film. The TD direction (transverse direction) is a direction parallel to the film surface, perpendicular to the MD direction, and usually parallel to the width direction of a long film.

In the following description, unless otherwise specified, the directions of elements as "parallel," "vertical," and "orthogonal" may include an error within a range that does not impair the effect of the present invention, for example within a range of ±5°.

[Outline of the Retardation Film of the Present Invention]
The retardation film of the present invention is a long retardation film having a slow axis at an angle of 10° or more and 80° or less with respect to the width direction thereof and an NZ coefficient of more than 0 and less than 1.

The retardation film of the present invention has a slow axis at an angle of 10° to 80° with respect to its width direction, and has an NZ coefficient greater than 0 and less than 1, so that reflection in the tilt direction can be reduced. As a result, a retardation film with excellent viewing angle characteristics can be achieved. In addition, since the retardation film of the present invention is long, it can be efficiently manufactured by the roll-to-roll method.

[Outline of the method for producing the retardation film of the present invention]
The method for producing a retardation film of the present invention is a method for producing a long retardation film having a slow axis at an angle of 10° or more and 80° or less with respect to the width direction and an NZ coefficient greater than 0 and smaller than 1. The method for producing a retardation film of the present invention includes a step 1 of preparing a film F ₀ having an NZ coefficient less than 0, and a step 2 of obliquely stretching the film F ₀ .

Conventionally, it has been difficult to manufacture a retardation film with an NZ coefficient greater than 0 and less than 1, but by obliquely stretching a film with an NZ coefficient less than 0, a retardation film with an NZ coefficient greater than 0 and less than 1 can be manufactured by a simple method. Therefore, according to the present invention, it is possible to easily manufacture a retardation film with an NZ coefficient greater than 0 and less than 1, a slow axis at an angle of 10° to 80° with respect to the width direction, and excellent viewing angle characteristics.

[Embodiment 1]
Hereinafter, the retardation film according to the first embodiment of the present invention and the manufacturing method thereof will be described in more detail.
The retardation film of the present embodiment is a long retardation film having a slow axis at an angle of 10° or more and 80° or less with respect to the width direction and an NZ coefficient greater than 0 and smaller than 1.

[Resin Constituting Retardation Film]
The retardation film may be made of a resin. The resin constituting the retardation film includes a polymer. The resin constituting the retardation film is preferably a resin containing a polymer having crystallinity. The term "polymer having crystallinity" refers to a polymer having a melting point Tm (i.e., the melting point can be observed by a differential scanning calorimeter (DSC)). In the following description, a polymer having crystallinity may be referred to as a "crystalline polymer". Also, a resin containing a crystalline polymer may be referred to as a "crystalline resin". This crystalline resin is preferably a thermoplastic resin.

In addition, the resin that constitutes the retardation film is preferably a resin with a positive intrinsic birefringence value. Unless otherwise specified, a resin with a positive intrinsic birefringence value means a resin whose refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to the stretching direction. The value of the intrinsic birefringence can be calculated from the dielectric constant distribution.

In this embodiment, it is more preferable that the polymer contained in the resin constituting the retardation film is a crystalline polymer and has positive intrinsic birefringence.

[Crystalline polymer]
The crystalline polymer preferably contains an alicyclic structure. By using a crystalline polymer containing an alicyclic structure, the mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability and light weight of the retardation film can be improved. The polymer containing an alicyclic structure refers to a polymer containing an alicyclic structure in the molecule. Such a polymer containing an alicyclic structure can be, for example, a polymer obtained by polymerization reaction using a cyclic olefin as a monomer, or a hydrogenated product thereof.

Examples of alicyclic structures include cycloalkane structures and cycloalkene structures. Among these, cycloalkane structures are preferred because retardation films having excellent properties such as thermal stability can be easily obtained. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the number of carbon atoms contained in one alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

In a crystalline polymer containing an alicyclic structure, the ratio of the structural units containing an alicyclic structure to all structural units is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight or more. By increasing the ratio of the structural units containing an alicyclic structure as described above, heat resistance can be improved. The ratio of the structural units containing an alicyclic structure to all structural units can be 100% by weight or less. In addition, in a crystalline polymer containing an alicyclic structure, the remainder other than the structural units containing an alicyclic structure is not particularly limited and can be appropriately selected depending on the purpose of use.

Examples of the crystalline polymer containing an alicyclic structure include the following polymer (α) to polymer (δ). Among these, polymer (β) is preferred because it is easy to obtain a retardation film having excellent heat resistance.
Polymer (α): A ring-opening polymer of a cyclic olefin monomer, which has crystallinity.
Polymer (β): A hydrogenated product of polymer (α) and has crystallinity.
Polymer (γ): An addition polymer of a cyclic olefin monomer, which has crystallinity.
Polymer (δ): A hydrogenated polymer (γ) having crystallinity.

Specifically, as the crystalline polymer containing an alicyclic structure, a ring-opening polymer of dicyclopentadiene having crystallinity and a hydrogenated ring-opening polymer of dicyclopentadiene having crystallinity are more preferable. Among them, a hydrogenated ring-opening polymer of dicyclopentadiene having crystallinity is particularly preferable. Here, a ring-opening polymer of dicyclopentadiene refers to a polymer in which the ratio of structural units derived from dicyclopentadiene to all structural units is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight.

The hydrogenated ring-opening polymer of dicyclopentadiene preferably has a high ratio of racemo dyads. Specifically, the ratio of racemo dyads in the repeating units of the hydrogenated ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high ratio of racemo dyads indicates high syndiotactic stereoregularity. Therefore, the higher the ratio of racemo dyads, the higher the melting point of the hydrogenated ring-opening polymer of dicyclopentadiene tends to be.
The ratio of the racemo dyads can be determined based on the ¹³ C-NMR spectrum analysis described in the Examples below.

As the above polymers (α) to (δ), polymers obtained by the manufacturing method disclosed in WO 2018/062067 can be used.

The melting point Tm of the crystalline polymer is preferably 200° C. or higher, more preferably 230° C. or higher, and preferably 290° C. or lower. By using a crystalline polymer having such a melting point Tm, a retardation film with an even better balance between formability and heat resistance can be obtained.

Typically, a crystalline polymer has a glass transition temperature Tg. The specific glass transition temperature Tg of a crystalline polymer is not particularly limited, but is typically 85°C or higher and typically 170°C or lower.

The glass transition temperature Tg and melting point Tm of a polymer can be measured by the following method. First, the polymer is melted by heating, and the molten polymer is rapidly cooled with dry ice. Next, using this polymer as a test specimen, the glass transition temperature Tg and melting point Tm of the polymer can be measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C/min (heating mode).

The weight average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, and preferably 1,000,000 or less, more preferably 500,000 or less. A crystalline polymer having such a weight average molecular weight has an excellent balance between moldability and heat resistance.

The molecular weight distribution (Mw/Mn) of the crystalline polymer is preferably 1.0 or more, more preferably 1.5 or more, and preferably 4.0 or less, more preferably 3.5 or less. Here, Mn represents the number average molecular weight. A crystalline polymer having such a molecular weight distribution has excellent moldability.

The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymer can be measured in polystyrene equivalent values by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent.

The degree of crystallinity of the crystalline polymer contained in the retardation film is not particularly limited, but is usually high to a certain degree. The specific range of the degree of crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The upper limit of the degree of crystallinity can be, for example, 70% or less.
The crystallinity of a crystalline polymer can be measured by X-ray diffraction.

The crystalline polymer may be used alone or in any combination of two or more types in any ratio.

The proportion of crystalline polymer in the crystalline resin is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of crystalline polymer is equal to or greater than the lower limit of the above range, the birefringence expression and heat resistance of the retardation film can be improved. The upper limit of the proportion of crystalline polymer can be 100% by weight or less.

The crystalline resin may contain optional components in addition to the crystalline polymer. Optional components include, for example, antioxidants such as phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants; light stabilizers such as hindered amine-based light stabilizers; waxes such as petroleum wax, Fischer-Tropsch wax, and polyalkylene wax; nucleating agents such as sorbitol-based compounds, metal salts of organic phosphoric acids, metal salts of organic carboxylic acids, kaolin, and talc; diaminostilbene derivatives, coumarin derivatives, and azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, benzoimide derivatives, and benzoyl esters). Examples of the optional components include fluorescent brighteners such as benzothiazole derivatives, carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolone derivatives; ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fibers; colorants; flame retardants; flame retardant assistants; antistatic agents; plasticizers; near-infrared absorbers; lubricants; fillers; and any polymer other than a crystalline polymer, such as a soft polymer. One type of optional component may be used alone, or two or more types may be used in combination at any ratio.

[NZ Coefficient of Retardation Film]
The NZ coefficient of the retardation film of this embodiment is greater than 0 and less than 1. The NZ coefficient of the retardation film is preferably 0.2 or more, more preferably 0.4 or more, and preferably 0.8 or less, more preferably 0.6 or less. When a retardation film having an NZ coefficient greater than 0 and less than 1 is provided in a display device, it is possible to improve the display quality of the display device, such as the viewing angle, contrast, and image quality. The NZ coefficient of the retardation film can be set arbitrarily according to the application of the retardation film.

The NZ coefficient of a retardation film can be calculated from the in-plane retardation Re and thickness direction retardation Rth of the film. The in-plane retardation Re and thickness direction retardation Rth of the film can be measured using a retardation meter (e.g., "AxoScan OPMF-1" manufactured by AXOMETRICS).

[Slow axis of retardation film]
The retardation film of this embodiment has a slow axis at an angle of 10° to 80° with respect to the width direction. The angle of the slow axis with respect to the width direction of the film can be adjusted by adjusting the stretching direction in step 2 (oblique stretching step) of the manufacturing method of this embodiment. The direction of the slow axis of the retardation film can be arbitrarily set depending on the application of the retardation film.

[Other characteristics of retardation film]
A retardation film usually has a large birefringence in one or both of the in-plane direction and the thickness direction. Specifically, a retardation film usually satisfies one or both of an in-plane birefringence Re/d of 1.0×10 ⁻³ or more and an absolute value of birefringence |Rth/d| of the thickness direction of 1.0×10 ⁻³ or more.

In detail, the birefringence Re/d in the in-plane direction of the retardation film is usually 1.0×10 ⁻³ or more, preferably 3.0×10 ⁻³ or more, particularly preferably 5.0×10 ⁻³ or more. There is no upper limit, and it can be, for example, 2.0×10 ⁻² or less, 1.5×10 ⁻² or less, or 1.0×10 ⁻² or less. However, when the absolute value |Rth/d| of the birefringence in the thickness direction of the retardation film is 1.0×10 ⁻³ or more, the retardation film can be a preferable retardation film even if the birefringence Re/d in the in-plane direction of the retardation film is outside the above range.

The absolute value of birefringence in the thickness direction of the retardation film |Rth/d| is usually 1.0×10 ⁻³ or more, preferably 3.0×10 ⁻³ or more, particularly preferably 5.0×10 ⁻³ or more. There is no upper limit, and it can be, for example, 2.0×10 ⁻² or less, 1.5×10 ⁻² or less, or 1.0×10 ⁻² or less. However, when the birefringence Re/d in the in-plane direction of the retardation film is 1.0×10 ⁻³ or more, even if the absolute value of birefringence in the thickness direction of the retardation film |Rth/d| is outside the above range, it can be a preferable retardation film.

The value of the in-plane retardation Re of the retardation film can be set depending on the application of the retardation film.
In an example, the specific in-plane retardation Re of the retardation film may be preferably 100 nm or more, more preferably 110 nm or more, particularly preferably 120 nm or more, and may be preferably 180 nm or less, more preferably 170 nm or less, particularly preferably 160 nm or less. In this case, the retardation film can function as a quarter-wave plate.

In another example, the specific in-plane retardation Re of the retardation film may be preferably 230 nm or more, more preferably 250 nm or more, particularly preferably 255 nm or more, and may be preferably 320 nm or less, more preferably 300 nm or less, particularly preferably 295 nm or less. In this case, the retardation film can function as a half-wave plate.

The retardation Rth value in the thickness direction of the retardation film can be set according to the application of the retardation film. The specific retardation Rth in the thickness direction of the retardation film is preferably -30 nm or more, more preferably -15 nm or more, and preferably 30 nm or less, more preferably 15 nm or less.

The haze of the retardation film according to this embodiment is usually less than 1.0%, preferably less than 0.8%, more preferably less than 0.5%, and ideally 0.0%. When a retardation film with such a small haze is installed in a display device, it can increase the clarity of the image displayed on the display device. The haze of the film can be measured using a haze meter (for example, "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

Since the retardation film is an optical film, it is preferable that it has high transparency. The specific total light transmittance of the retardation film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The total light transmittance of the retardation film can be measured in the wavelength range of 400 nm to 700 nm using an ultraviolet-visible spectrometer.

The thickness d of the retardation film can be appropriately set according to the application of the retardation film. The specific thickness d of the retardation film is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 15 μm or more, and preferably 200 μm or less, more preferably 100 μm or less, particularly preferably 50 μm or less. When the thickness d of the retardation film is equal to or greater than the lower limit of the above range, the handling properties can be improved and the strength can be increased. In addition, when the thickness d of the retardation film is equal to or less than the upper limit, it is easy to wind up a long retardation film.

[Solvents contained in retardation film]
The retardation film of the present embodiment may contain a solvent when produced by a production method including a solvent treatment step described later.

In the solvent treatment process, all or part of the solvent absorbed into the film may penetrate into the polymer contained in the resin that constitutes the film. Therefore, even if drying is performed at or above the boiling point of the solvent, it is difficult to easily remove the solvent completely. Therefore, retardation films manufactured by a manufacturing method that includes a solvent treatment process may contain solvent.

Examples of the solvent include hydrocarbon solvents such as toluene, limonene, and decalin; and carbon disulfide. Of these, hydrocarbon solvents are preferred. The type of solvent may be one type or two or more types.

The ratio of the solvent contained in the retardation film to 100% by weight of the retardation film (solvent content) is preferably 10% by weight or less, more preferably 5% by weight or less, particularly preferably 0.1% by weight or less, and may be greater than 0% by weight.

The solvent content of the retardation film can be measured using the measurement method described in the examples.

The retardation film of this embodiment can be manufactured by the retardation film manufacturing method described below.

[Method of manufacturing phase difference film]
The method for producing a retardation film of the present embodiment includes a step 1 of preparing a film F ₀ having an NZ coefficient of less than 0, and a step 2 of obliquely stretching the film F ₀ .

Hereinafter, the method for producing a retardation film of this embodiment will be specifically described with reference to Figures 1 to 3. Figure 1 is a side view that shows a schematic diagram of an apparatus that can be used in step 1 of the method for producing a retardation film of embodiment 1. Figure 2 is a plan view that shows a schematic diagram of an oblique stretching machine that can be used in step 2 of the method for producing a retardation film of embodiment 1. Figure 3 is a plan view that shows a schematic diagram of a longitudinal stretching machine that can be used in any step.

[Outline of the method for producing the retardation film of this embodiment]
A long resin film is prepared, and a masking film is attached to the resin film while being wound up on a roll, to obtain a resin film roll 111. Next, as shown in Fig. 1, the masking film 12 is peeled off from the film 11 unwound from the resin film roll 111, and the long resin film 1 is transported in the direction indicated by A1. The masking film 12 is wound up on the roll 112 while being pressed by nip rolls 101A and 101B disposed at positions to sandwich the film 11 in the thickness direction.

Next, the resin film 1 is passed through a bath 102 filled with a solvent to bring the resin film 1 into contact with the solvent, and then conveyed into a heating device 103 to dry, thereby obtaining a solvent-treated film 10. By bringing the resin film 1 into contact with the solvent, the NZ coefficient of the resin film 1 changes, and the NZ coefficient becomes less than 0. In other words, by bringing the resin film 1 into contact with the solvent, a film _F0 is obtained (step 1).

The film F ₀ (solvent-treated film 10) obtained in step 1 is wound up while being laminated with the masking film 13 unwound from the roll 113, to obtain the solvent-treated film roll 110. The solvent-treated film 10 and the masking film 13 are laminated together while being pressed with nip rolls 104A and 104B arranged in a position to sandwich the film in the thickness direction.

Next, the masking film is peeled off from the film unwound from the roll 110 of the solvent-treated film, and the solvent-treated film 10 is transported. The solvent-treated film 10 is obliquely stretched by the stretching machine 200 shown in FIG. 2 (step 2). By obliquely stretching the solvent-treated film 10 (film F ₀ ), the NZ coefficient of the solvent-treated film changes, and the NZ coefficient becomes greater than 0 and less than 1. In addition, the average orientation angle of the film after the stretching process is 10° or more and 80° with respect to the film width direction. The stretched film 30 (stretched film 30) is wound up while the masking film is attached to it, and a roll 40 of the stretched film is obtained. The stretched film 30 can be used as a retardation film as it is.

Each step of the manufacturing method of this embodiment is described below.

[Step 1]
Step 1 is a step of preparing a film F ₀ having an NZ coefficient of less than 0. There is no limitation on the method of preparing the film F _0. Step 1 may include, for example, contacting a resin film with a solvent, thereby changing the NZ coefficient of the resin film, and obtaining the film F ₀ (solvent treatment step).

Step 1 can be performed by the apparatus shown in Figure 1. The apparatus 100 in Figure 1 includes nip rolls 101A, 101B, 104A and 104B, a bath 102 for contacting the resin film 1 with a solvent, and a heating device 103 for drying the resin film after contact with the solvent.

[Solvent treatment process]
The solvent treatment step is a step in which the resin film is brought into contact with a solvent, thereby changing the NZ coefficient of the resin film and obtaining a film F ₀ .

In the solvent treatment process, the resin film is brought into contact with the solvent, thereby changing its NZ coefficient, so that the NZ coefficient of the resin film after the solvent treatment process (film after solvent treatment) becomes less than 0. The mechanism by which such an effect is obtained is presumed to be as follows. However, the technical scope of the present invention is not limited by the mechanism described below.

When a resin film is brought into contact with a solvent, the solvent penetrates into the resin film. The action of the penetrating solvent causes micro-Brownian motion in the polymer molecules in the film, and the molecular chains of the film are oriented.
Here, although the resin film has side end faces in addition to the front and back surfaces which are the main surfaces, most of the surface area of the resin film is occupied by the front and back surfaces. Therefore, the penetration speed of the solvent is high in the thickness direction through the front or back surface. Then, the orientation of the polymer molecules can proceed so that the polymer molecules are oriented in the thickness direction.

[Resin film]
The resin film used in the solvent treatment process is a film that is a material for manufacturing a retardation film. Therefore, the resin constituting the resin film can be the same as the resin constituting the retardation film described in "1. Retardation film". From the viewpoint of easily manufacturing a retardation film having an NZ coefficient greater than 0 and smaller than 1, it is preferable that the polymer contained in the resin constituting the resin film is a crystalline polymer and has a positive intrinsic birefringence.

When the resin contained in the resin film is a resin containing a crystalline polymer, it is preferable that the crystallinity of the crystalline polymer contained in the resin is small. The specific crystallinity is preferably less than 10%, more preferably less than 5%, and particularly preferably less than 3%. If the crystallinity of the crystalline polymer contained in the resin film before contact with the solvent is low, many of the crystalline polymer molecules can be oriented in the thickness direction by contact with the solvent, making it possible to adjust the NZ coefficient over a wide range.

The in-plane retardation Re of the resin film is preferably 20 nm or less, more preferably 10 nm or less, and particularly preferably 0. The thickness-direction retardation Rth of the resin film is preferably 20 nm or less, more preferably 10 nm or less, and particularly preferably 0. By having the Re and Rth of the resin film before contact with the solvent each within the above range, it is easy to make the NZ coefficient of the resin film after contact with the solvent less than 0.

The resin film preferably has a small solvent content, and more preferably does not contain a solvent. The ratio of the solvent contained in the resin film to 100% by weight of the resin film (solvent content) is preferably 1% or less, more preferably 0.5% or less, particularly preferably 0.1% or less, and ideally 0.0%. Since the amount of solvent contained in the resin film before contacting with the solvent is small, many polymer molecules can be oriented in the thickness direction by contacting with the solvent, so that the NZ coefficient can be adjusted in a wide range.
The solvent content of the resin film can be measured by its density.

It is preferable to set the thickness of the resin film according to the thickness of the retardation film to be manufactured. Usually, the thickness of the film increases when it is brought into contact with a solvent. On the other hand, the thickness of the film decreases when it is stretched in step 2. Therefore, the thickness of the resin film may be set taking into account the change in thickness in steps after step 2.

In this embodiment, a long resin film is used as the resin film. This allows continuous production of the retardation film by the roll-to-roll method, effectively increasing the productivity of the retardation film.

There are no limitations to the method for producing the resin film. Resin molding methods such as injection molding, extrusion molding, press molding, inflation molding, blow molding, calendar molding, cast molding, and compression molding are preferred because they produce a resin film that does not contain solvent. Of these, extrusion molding is preferred because it is easy to control the thickness.

For example, when a resin film made of a resin containing a crystalline polymer is produced by an extrusion molding method, the production conditions are preferably as follows. The cylinder temperature (molten resin temperature) is preferably Tm or higher, more preferably "Tm + 20 ° C" or higher, and preferably "Tm + 100 ° C" or lower, more preferably "Tm + 50 ° C" or lower. In addition, the cooling body that the molten resin extruded into a film first comes into contact with is not particularly limited, but a cast roll is usually used. The cast roll temperature is preferably "Tg - 50 ° C" or higher, preferably "Tg + 70 ° C" or lower, more preferably "Tg + 40 ° C" or lower. Furthermore, the cooling roll temperature is preferably "Tg - 70 ° C" or higher, more preferably "Tg - 50 ° C" or higher, and preferably "Tg + 60 ° C" or lower, more preferably "Tg + 30 ° C" or lower. When a resin film is produced under such conditions, a raw film having a thickness of 1 μm to 1 mm can be easily produced. Here, "Tm" represents the melting point of the crystalline polymer, and "Tg" represents the glass transition temperature of the crystalline polymer.

In this embodiment, a masking film is laminated to a long resin film and wound into a roll, and the film roll is subjected to step 1. Known masking films (e.g., FF1025 and FF1035 manufactured by Tredegar; SAT116T, SAT2038T-JSL, and SAT4538T-JSL manufactured by San-A Chemical Industries; NBO-0424, TFB-K001, TFB-K0421, and TFB-K202 manufactured by Fujimori Kogyo; DT-2200-25 and K-6040 manufactured by Hitachi Chemical; and 6010#75, 6010#100, 6011#75, and 6093#75 manufactured by Teraoka Manufacturing Co., Ltd.) can be used.

[solvent]
In the solvent treatment step, a solvent that can penetrate into the resin film without dissolving the polymer contained in the resin film can be used as the solvent to be brought into contact with the resin film. Examples of such solvents include hydrocarbon solvents such as toluene, limonene, and decalin; and carbon disulfide. When the resin film is made of a resin containing a crystalline polymer, a hydrocarbon solvent is preferred as the solvent from the viewpoint of being able to penetrate into the resin film without dissolving the crystalline polymer. The solvent may be one type or two or more types.

Methods for contacting the resin film with the solvent include, for example, a spray method in which the resin film is sprayed with the solvent, a coating method in which the resin film is coated with the solvent, and an immersion method in which the resin film is immersed in the solvent. Among these, the immersion method is preferred because it is easy to achieve continuous contact. Figure 1 shows the immersion method.

The temperature of the solvent that is brought into contact with the resin film may be any temperature within the range at which the solvent can remain liquid, and therefore may be set within the range above the melting point and below the boiling point of the solvent.

The time for contacting the resin film with the solvent is not particularly specified, but is preferably 1 second or more, more preferably 3 seconds or more, particularly preferably 5 seconds or more, and preferably 180 seconds or less, more preferably 120 seconds or less, particularly preferably 60 seconds or less. By having the contact time be equal to or greater than the lower limit of the above range, the NZ coefficient can be effectively adjusted by contact with the solvent. On the other hand, even if the contact time is extended, the amount of adjustment of the NZ coefficient tends not to change significantly. Therefore, by having the contact time be equal to or less than the upper limit of the above range, productivity can be increased without impairing the quality of the retardation film.

The solvent treatment step may include a step of removing the solvent from the resin film after contact with the solvent. Methods for removing the solvent from the resin film after contact with the solvent include, for example, drying and wiping. Among these, drying is preferred from the viewpoint of quickly removing the solvent to obtain a retardation film with stable characteristics.

When removing the solvent from the resin film after contact with the solvent by drying, there are no limitations on the method, and it can be done, for example, using a heating device such as an oven. Specifically, the solvent can be removed by transporting the resin film after contact with the solvent through a heating device for a predetermined time.

From the viewpoint of performing drying quickly, the drying temperature is preferably 50°C or higher, more preferably 60°C or higher, and particularly preferably 80°C or higher. Furthermore, from the viewpoint of suppressing orientation relaxation due to heat and maintaining uniformity of optical properties, the drying temperature is preferably Tg + 100°C or lower, more preferably Tg + 80°C or lower, and particularly preferably Tg + 50°C or lower. Here, "Tg" represents the glass transition temperature of the polymer contained in the resin film.

The drying time of the resin film after contact with the solvent is preferably 0.2 minutes or more, more preferably 0.5 minutes or more, particularly preferably 0.8 minutes or more, and preferably 10 minutes or less, more preferably 5 minutes or less, particularly preferably 3 minutes or less. By setting the drying time to the above lower limit or more, the amount of solvent remaining on the surface of the retardation film can be reduced, and by setting the drying time to the above upper limit or less, the time required for manufacturing the retardation film can be shortened and manufacturing efficiency can be improved.

The solvent treatment step may be carried out with the resin film under tension. The resin film may be under tension either or both when the resin film is brought into contact with the solvent and when the resin film is dried after contact with the solvent. In particular, drying the resin film under tension after contact with the solvent is preferred, since it is possible to effectively increase the uniformity of the optical properties of the film after solvent treatment.

In the solvent treatment process, the tension applied to the resin film is preferably set to a range in which the resin film is not substantially stretched by the tension. Substantially stretched means that the stretch ratio in either direction of the film is usually 1.1 times or more. The specific tension range is preferably 2 N/m or more, more preferably 5 N/m or more, particularly preferably 10 N/m or more, and preferably 100 N/m or less, more preferably 70 N/m or less, particularly preferably 50 N/m or less. The unit of tension "N/m" represents the magnitude of tension per 1 m of film dimension in the direction perpendicular to the tension direction. The magnitude of tension may be different or the same when the resin film is brought into contact with the solvent and when the resin film is dried after contact with the solvent.

The number of directions of tension applied to the resin film may be one or more. Typically, tension is applied in an in-plane direction perpendicular to the thickness direction of the resin film. Thus, the tension direction may be one or more in-plane directions. The direction of tension may be different or the same when the resin film is brought into contact with the solvent and when the resin film is dried after contact with the solvent.

When applying tension to the resin film as described above, for example, the resin film may be held by an appropriate holder, and tension may be applied to the resin film by pulling the resin film with this holder. The holder may be capable of continuously holding the entire length of the side of the resin film, or may be capable of holding it intermittently at intervals. For example, the side of the resin film may be held intermittently by holders arranged at predetermined intervals.

It is preferable that the resin film is tensioned by holding two or more sides of the resin film. In this case, tension can be applied to the resin film in the area between the held sides to improve the uniformity of the optical properties of the retardation film. In order to improve the uniformity of the optical properties over a wide area, it is preferable to hold the sides including the two opposing sides of the resin film and apply tension to the area between the held sides. In this embodiment, by holding two sides (i.e., the long sides) at the ends in the width direction of the long resin film and applying tension to the area between the two sides, the uniformity of the optical properties can be improved over the entire surface of the retardation film obtained from the resin film.

It is preferable for the holder to be one that does not come into contact with the resin film at any part other than the edges of the resin film. By using such a holder, a phase difference film with superior smoothness can be obtained.

In addition, the holder is preferably one that can fix the relative positions of the holders while the holders are holding the resin film. Such a holder makes it easier to suppress substantial stretching of the resin film because the positions of the holders do not move relative to each other. An example of a suitable holder is a gripper that is provided in a tenter stretching machine and can grip a film.

The NZ coefficient of the film _F0 is less than 0, and preferably -1 or less. By having an NZ coefficient in this range, the retardation film of the present invention can be easily produced. The lower limit of the NZ coefficient of the film _F0 is not particularly limited, but can be, for example, -40 or more.
Other optical properties of the film F ₀ can be appropriately adjusted so as to obtain a desired retardation film. For example, the retardation Re in the in-plane direction of the film F ₀ is preferably 300 nm or less, more preferably 200 nm or less. The lower limit of the retardation Re in the in-plane direction of the film F ₀ is not particularly limited, but may be, for example, 0 nm or more. The retardation Rth in the thickness direction of the film F ₀ is preferably −50 nm or less, more preferably −150 nm or less. The lower limit of the retardation Rth in the thickness direction of the film F ₀ is not particularly limited, but may be, for example, −500 nm or more.

The film _F0 obtained by carrying out step 1 is subjected to the next step (step 2).

[Step 2]
Step 2 is a step of obliquely stretching film F _0. Film F ₀ is a film obtained by carrying out step 1, and in this embodiment, film 10 after solvent treatment obtained in step 1 corresponds to film F _0. Here, "obliquely stretching" refers to stretching a long film in an oblique direction.

By obliquely stretching the film _F0 , a retardation film having a slow axis at an angle of 10° to 80° with respect to the film width direction and an NZ coefficient greater than 0 and smaller than 1 can be obtained.

The mechanism by which a film having an NZ coefficient greater than 0 and less than 1 can be obtained by obliquely stretching film _F0 is presumed to be as follows: By obliquely stretching film _F0 , the retardation Rth in the thickness direction of the film can be significantly changed from a negative value toward zero, and at the same time, the value of Re can be increased, and it is presumed that this allows a film having an NZ coefficient greater than 0 and less than 1 to be obtained.

Step 2 can be performed, for example, by an oblique stretching machine 200 shown in Fig. 2. Fig. 2 illustrates a tenter stretching machine as an example of the oblique stretching machine 200. The tenter stretching machine 200 is a device for stretching the solvent-treated film 10 (film F ₀ ), obtained by peeling the masking film from the film unwound from the unwound roll 110, in an oblique direction while transporting the film horizontally in a heating environment in an oven (not shown).

The tenter stretching machine 200 is equipped with a plurality of grippers 210R and 210L capable of gripping both end portions 10A and 10B, respectively, of the film 10 after solvent treatment, and a pair of guide rails 220R and 220L provided on both sides of the film transport path to guide the grippers 210R and 210L.

The grippers 210R and 210L are arranged to run along the guide rails 220R and 220L. The grippers 210R and 210L are arranged to run at a constant speed while maintaining a constant distance from the front and rear grippers 210R and 210L. The grippers 210R and 210L are arranged to grip both ends 10A and 10B in the width direction of the film 10 after the solvent treatment, which is sequentially supplied to the tenter stretching machine 200, at the entrance 230 of the tenter stretching machine 200 and release them at the exit 240 of the tenter stretching machine 200.

The guide rails 220R and 220L have asymmetric shapes according to conditions such as the direction of the slow axis of the retardation film to be manufactured and the stretching ratio. The tenter stretching machine 200 shown in FIG. 2 is provided with a stretching zone 250 in which the distance between the guide rails 220R and 220L becomes wider downstream. In this stretching zone 250, the shapes of the guide rails 220R and 220L are set so that the grippers 210R and 210L guided by the guide rails 220R and 220L can convey the film 10 after the solvent treatment so as to bend the traveling direction of the film 10 after the solvent treatment to the left, and the moving distance of one gripper 210R is longer than the moving distance of the other gripper 210L. Here, the traveling direction of the long film refers to the moving direction of the midpoint of the film in the width direction, unless otherwise specified. Additionally, unless otherwise specified, "right" and "left" refer to the directions when viewed from upstream to downstream in the conveying direction.

The guide rails 220R and 220L have an endless continuous track so that the grippers 210R and 210L can move around a predetermined track. Therefore, the tenter stretching machine 200 has a structure that allows the grippers 210R and 210L, which have released the film 10 after the solvent treatment at the exit section 240 of the tenter stretching machine 200, to be sequentially returned to the entrance section 230.

In step 2, the film 10 after the solvent treatment is stretched using such a tenter stretching machine 200 as described below.
The film is unwound from a unwind roll 110 , and the solvent-treated film 10 obtained after peeling off the masking film (not shown) is continuously supplied to a tenter stretching machine 200 .
The tenter stretching machine 200 sequentially grips both ends 10A and 10B of the solvent-treated film 10 with the grippers 210R and 210L at the entrance 230. The solvent-treated film 10 with both ends 10A and 10B gripped is transported with the movement of the grippers 210R and 210L. As described above, in the tenter stretching machine 200 of this example, the guide rails 220R and 220L are shaped so that the traveling direction of the solvent-treated film 10 is bent to the left in the tenter stretching machine 200 of this example. Therefore, the distance of the path along which one gripper 210R travels while gripping the solvent-treated film 10 is longer than the distance of the path along which the other gripper 210L travels while gripping the solvent-treated film 10. Thus, of the pair of grippers 210R and 210L that faced each other in a direction perpendicular to the traveling direction of the solvent-treated film 10 at the entrance 230 of the tenter stretching machine 200, the left gripper 210L precedes the right gripper 210R at the exit 240 of the tenter stretching machine 200, so that the solvent-treated film 10 is stretched in an oblique direction to obtain a long stretched film 30 (see dashed lines L _D1 , L _D2 and L _D3 in FIG. 2 ). The obtained stretched film 30 is released from the grippers 210R and 210L at the exit 240 of the tenter stretching machine 200, taken up and collected as a roll 40.

The stretching ratio in step 2 is preferably 1.1 times or more, more preferably 1.2 times or more, and is preferably 5 times or less, more preferably 2 times or less. By setting the stretching ratio to the lower limit of the above range or more, the refractive index in the stretching direction can be increased. In addition, by setting the stretching ratio to the upper limit or less, the direction of the slow axis of the stretched film can be easily controlled.

The stretching temperature T1 in step 2 is preferably Tg°C or higher, more preferably Tg+2°C or higher, particularly preferably Tg+5°C or higher, and preferably Tg+40°C or lower, more preferably Tg+35°C or lower, particularly preferably Tg+30°C or lower. Here, Tg refers to the glass transition temperature of the polymer contained in the film 10 after the solvent treatment. In addition, the stretching temperature T1 in step 2 in the tenter stretching machine 200 refers to the temperature in the stretching zone 250 of the tenter stretching machine 200. By setting the stretching temperature T1 in step 2 in the above range, the molecules contained in the film 10 after the solvent treatment can be reliably oriented, so that a stretched film 30 having the desired optical properties can be easily obtained.

As a result of being stretched in step 2, the molecules contained in stretched film 30 are oriented. Therefore, stretched film 30 has a slow axis. Since stretching is performed in an oblique direction in step 2, the slow axis of stretched film 30 appears in the oblique direction of the stretched film. Specifically, stretched film 30 has a slow axis in the range of 5° to 85° with respect to its width direction.

The specific direction of the slow axis of the stretched film 30 can be set according to the direction of the slow axis of the wave plate to be manufactured.

Since the slow axis of the stretched film 30 is expressed by stretching the film 10 in an oblique direction, the specific direction of the slow axis of the stretched film 30 can be adjusted by the stretching conditions in the above-mentioned step 2. For example, the direction of the slow axis of the stretched film 30 can be adjusted by adjusting the payout angle φ between the payout direction D20 of the film 10 after the solvent treatment from the payout roll 110 and the winding direction D30 of the stretched film 30. Here, the payout direction D20 of the film 10 after the solvent treatment refers to the traveling direction of the film 10 after the solvent treatment that is paid out from the payout roll 110. Also, the winding direction D30 of the stretched film 30 refers to the traveling direction of the stretched film 30 that is wound into the roll 40.

The stretched film 30 obtained after performing step 2 can be used as the retardation film of the present invention as is, but the film obtained by performing a further step (e.g., a longitudinal stretching step, etc.) can also be used as the retardation film of the present invention.

[Optional steps]
The manufacturing method of this embodiment may include a step of performing a preheating treatment to heat the solvent-treated film to a stretching temperature before carrying out step 2. Usually, the preheating temperature and the stretching temperature are the same, but they may be different. The preheating temperature is preferably T1-10°C or more, more preferably T1-5°C or more, relative to the stretching temperature T1, and is also preferably T1+5°C or less, more preferably T1+2°C or less. The preheating time is optional, and is preferably 1 second or more, more preferably 5 seconds or more, and is also preferably 60 seconds or less, more preferably 30 seconds or less.

In addition, the manufacturing method of this embodiment may include a step of longitudinally stretching the film before or after step 2. Here, "longitudinal stretching" refers to stretching a long film in the machine direction.

Longitudinal stretching can be performed, for example, using a roll stretching machine 300 as shown in Figure 3. Figure 3 shows an example in which the stretched film 30 obtained by performing step 2 is further longitudinally stretched, but the film before performing step 2 (film 10 after solvent treatment) may be longitudinally stretched using the stretching machine before performing step 2.

As shown in FIG. 3, the roll stretching machine 300 is a device for stretching the film 30 unwound from the roll 40 in its longitudinal direction. The longitudinal stretching process may be performed in a heated environment using an oven (not shown).

The roll stretching machine 300 includes, in order from the upstream in the transport direction, an upstream roll 310 and a downstream roll 320 as nip rolls capable of transporting the film 30 in the longitudinal direction. Here, the rotation speed of the downstream roll 320 is set to be faster than the rotation speed of the upstream roll 310.

The film 30 is stretched using the roll stretching machine 300 as described below.
The film 30 is unwound from a roll 40 and continuously supplied to a roll stretching machine 300 .
The roll stretching machine 300 conveys the supplied film 30 in the order of the upstream roll 310 and the downstream roll 320. At this time, since the rotation speed of the downstream roll 320 is faster than that of the upstream roll 310, the film 30 is stretched in the longitudinal direction. In the stretching by the roll stretching machine 300, both ends 31 and 32 in the width direction of the film 30 are not restrained. Therefore, the width of the film 30 usually shrinks as it is stretched in the longitudinal direction, and a film 50 having a smaller width than the film 30 is obtained. The film 50 is obtained as a biaxially stretched film stretched in two directions, the longitudinal direction and the oblique direction.
The film 50 is then wound up and collected as a roll 60 after both ends have been trimmed if necessary.

It is preferable that the stretching ratio in the longitudinal stretching step is smaller than that in step 2. This makes it possible to stretch a film having a slow axis in an oblique direction while suppressing the occurrence of wrinkles. The stretching temperature in the longitudinal stretching step can be set taking into consideration the stretching temperature in step 2 and the in-plane retardation of the desired phase difference film.

The manufacturing method of this embodiment may include a step of removing the solvent adhering to the stretched film (retardation film) after step 2. The method of removing the solvent from the stretched film may be the same as the method of removing the solvent described in step 1.

According to the manufacturing method of this embodiment, a long retardation film can be manufactured, and the manufacturing method of the retardation film may also include a step of cutting the long retardation film thus manufactured into a desired shape.

[Uses of the Retardation Film of the Present Embodiment]
The retardation film of this embodiment and the retardation film manufactured by the manufacturing method of this embodiment have a slow axis at an angle of 10° to 80° with respect to the width direction, and the NZ coefficient is greater than 0 and smaller than 1. Therefore, the retardation film of this embodiment can be used as a 1/2 wavelength plate or a 1/4 wavelength plate. In a display device equipped with a circular polarizer using the retardation film of this embodiment as either or both of the 1/2 wavelength plate and the 1/4 wavelength plate, the reflectance in the tilt direction can be reduced. If both the 1/2 wavelength plate and the 1/4 wavelength plate are composed of the retardation film of this embodiment, the effect of reducing the reflectance in the tilt direction can be made more excellent.

[Effects of this embodiment]
The retardation film of this embodiment has a slow axis at an angle of 10° to 80° with respect to its width direction, and the NZ coefficient is greater than 0 and less than 1, so that reflection in the tilt direction can be reduced. As a result, a retardation film with excellent viewing angle characteristics can be achieved. In addition, since the retardation film of this embodiment is long, it can be efficiently manufactured by a roll-to-roll method.

In addition, in the method for producing a retardation film of the present embodiment, by obliquely stretching the film _F0 , a retardation film having an NZ coefficient greater than 0 and smaller than 1 can be produced in a simple manner. Therefore, according to the present embodiment, it is possible to easily produce a retardation film having an NZ coefficient greater than 0 and smaller than 1, a slow axis at an angle of 10° to 80° with respect to the width direction, and excellent viewing angle characteristics.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and may be modified as desired without departing from the scope of the claims of the present invention and the scope of equivalents thereto.

In the following description, the amounts of "%" and "parts" are by weight unless otherwise specified. Furthermore, the operations described below were performed at room temperature and pressure unless otherwise specified. Furthermore, in the following description, the wavelength for measuring retardation and birefringence was 590 nm unless otherwise specified.

[Evaluation method]
(Method of measuring weight average molecular weight Mw and number average molecular weight Mn of polymer)
The weight average molecular weight Mw and number average molecular weight Mn of the polymer were measured as polystyrene equivalent values using a gel permeation chromatography (GPC) system ("HLC-8320" manufactured by Tosoh Corporation). In the measurement, an H-type column (manufactured by Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The temperature during the measurement was 40°C.

(Method of measuring hydrogenation rate of polymer)
The hydrogenation rate of the polymer was measured by ¹ H-NMR measurement at 145° C. using orthodichlorobenzene- ^d4 as a solvent.

(Method of measuring glass transition temperature Tg and melting point Tm)
The glass transition temperature Tg and melting point Tm of the polymer were measured as follows. First, the polymer was melted by heating, and the melted polymer was quenched with dry ice. Then, the glass transition temperature Tg and melting point Tm of the polymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 10° C./min (heating mode) using the polymer as a test specimen.

(Method for measuring the ratio of racemo-dyads in polymers)
The ratio of the racemo-dyad in the polymer was measured as follows. The polymer was subjected to ¹³ C-NMR measurement by applying the inverse-gated decoupling method at 200°C using orthodichlorobenzene- ^d4 as a solvent. In the results of this ¹³ C-NMR measurement, a signal at 43.35 ppm derived from the meso-dyad and a signal at 43.43 ppm derived from the racemo-dyad were identified, with the peak at 127.5 ppm of orthodichlorobenzene- ^d4 as the reference shift. The ratio of the racemo-dyad in the polymer was calculated based on the intensity ratio of these signals.

(Method of measuring film thickness)
The thickness of the film was measured using a contact thickness meter (manufactured by MITUTOYO Corporation, Code No. 543-390).

(Method of measuring the solvent content of the retardation film)
A rectangular reference film measuring 130 mm long x 130 mm wide was cut out from the long resin film (resin film before the solvent treatment process) used in each example and comparative example, and the weight of this reference film was measured by thermogravimetric analysis (TGA: under nitrogen atmosphere, heating rate 10°C/min, 30°C to 300°C). The weight of the reference film W _O (300°C) at 300°C was subtracted from the weight of the reference film W _O (30°C) at 30°C to obtain the weight loss ΔW _O of the reference film at 300°C. This reference film is stretched after being produced by the melt extrusion method, so it does not contain a solvent. Therefore, the weight loss ΔW _O of this reference film was adopted as a reference in the formula (X) described later.

In addition, a rectangular film measuring 130 mm in length and 130 mm in width was cut out from the long retardation film produced in each example, and its weight was measured by thermogravimetric analysis (TGA: in a nitrogen atmosphere, heating rate of 10° C./min, 30° C. to 300° C.) in the same manner as above. The weight W _R (300° C.) of the retardation film at 300° C. was subtracted from the weight W _R (30° C.) of the retardation film at 30° C. to obtain the weight reduction ΔW _R of the retardation film at 300° C.

From the weight loss amount ΔW _O of the reference film at 300° C. and the weight loss amount ΔW _R of the retardation film at 300° C., the solvent content of the retardation film was calculated by the following formula (X).
Solvent content (%)={(ΔW _R −ΔW _O )/W _R (30° C.)}×100 (X)

(Method of measuring retardation and NZ coefficient)
The in-plane retardation Re, thickness direction retardation Rth, and NZ coefficient of the film were measured by Axo Scan OPMF-1 manufactured by AXOMETRICS. The measurement was performed at a wavelength of 590 nm. The NZ coefficient was calculated from the obtained in-plane retardation Re and thickness direction retardation Rth.

(Measurement of Crystallinity)
The crystallinity of the film was measured by X-ray diffraction using a D8 DISCOVER (manufactured by BRUKER).

(Visual evaluation of reflection intensity)
A mirror having a flat reflective surface was prepared. The mirror was placed so that the reflective surface was horizontal and facing upward. A circular polarizing plate was attached to the reflective surface of the mirror so that the polarizing film side faced upward.

After that, on a sunny day, the circular polarizer was illuminated by sunlight and the circular polarizer on the mirror was visually observed. Observations were performed at a polar angle of 45° and an azimuth angle of 0° to 360°.

When observing in an inclined direction, we evaluated whether the reflectance and color changed depending on the azimuth angle.

The visual evaluation was carried out by 20 observers, who ranked the results of all the Examples and Comparative Examples and gave them a score corresponding to that rank (1st place: 6 points, 2nd place: 5 points, ... lowest: 1 point). The total scores given by each observer for each Example and Comparative Example were then arranged in order of score, and within that range of scores, the top groups were rated as A, B, C, and D. The range of scores was divided equally (A: 91-120 points, B: 61-90 points, C: 31-60 points, D: 0-30 points).

(Method of calculating reflectance through simulation)
The circularly polarizing plates produced in each of the Examples and Comparative Examples were modeled using "LCD Master" manufactured by Shintech Co., Ltd. as simulation software, and the reflectance was calculated.

In the simulation model, a structure was set in which a circular polarizer was attached to the reflective surface of a mirror having a flat reflective surface so that the ¼ wavelength plate side was in contact with the mirror. Therefore, in the models using ½ wavelength plates and ¼ wavelength plates (Circular Polarizer A, Circular Polarizer C, Circular Polarizer D, Circular Polarizer F), a structure was set in which a polarizing film, ½ wavelength plate, ¼ wavelength plate, and mirror were arranged in this order in the thickness direction, and in the models using only ¼ wavelength plates (Circular Polarizer B, Circular Polarizer E), a structure was set in which a polarizing film, ¼ wavelength plate, and mirror were arranged in this order in the thickness direction.

In the model, the reflectance when the circular polarizer is irradiated with light from a D65 light source was calculated in the tilt direction of the circular polarizer. Here, calculations were performed at a polar angle of 45° and at azimuth angles ranging from 0° to 360° in 5° increments in the azimuth direction in the tilt direction, and the average of the calculated values was used as the reflectance in the tilt direction of the modeled circular polarizer. In this simulation, the surface reflection component that actually occurs on the surface of the polarizing film was excluded from the reflectance.

[Production Example 1. Production of crystalline resin containing hydrogenated product of ring-opened polymer of dicyclopentadiene]
A metallic pressure-resistant reactor was thoroughly dried and then purged with nitrogen. 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo isomer content of 99% or more) (30 parts as the amount of dicyclopentadiene), and 1.9 parts of 1-hexene were added to the metallic pressure-resistant reactor, and the reactor was heated to 53°C.

0.014 parts of tetrachlorotungsten phenylimide (tetrahydrofuran) complex was dissolved in 0.70 parts of toluene to prepare a solution. 0.061 parts of a 19% diethylaluminum ethoxide/n-hexane solution was added to this solution and stirred for 10 minutes to prepare a catalyst solution. This catalyst solution was added to a pressure-resistant reactor to start the ring-opening polymerization reaction. The reaction was then continued for 4 hours while maintaining the temperature at 53°C to obtain a solution of a ring-opened polymer of dicyclopentadiene. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained ring-opened polymer of dicyclopentadiene were 8,750 and 28,100, respectively, and the molecular weight distribution (Mw/Mn) calculated from these was 3.21.

0.037 parts of 1,2-ethanediol was added as a terminator to 200 parts of the resulting solution of ring-opened dicyclopentadiene polymer, and the mixture was heated to 60°C and stirred for 1 hour to terminate the polymerization reaction. One part of a hydrotalcite-like compound (Kyowa Chemical Industry Co., Ltd.'s "Kyoward (registered trademark) 2000") was added to the solution, which was then heated to 60°C and stirred for 1 hour. After that, 0.4 parts of a filter aid (Showa Chemical Industry Co., Ltd.'s "Radiolight (registered trademark) #1500") was added, and the adsorbent and the solution were filtered using a PP pleated cartridge filter (Advantec Toyo Co., Ltd.'s "TCP-HX").

100 parts of cyclohexane was added to 200 parts of the filtered ring-opening polymer solution (polymer amount 30 parts), and 0.0043 parts of chlorohydridocarbonyltris(triphenylphosphine)ruthenium was added, and the hydrogenation reaction was carried out at 6 MPa hydrogen pressure and 180°C for 4 hours. This resulted in a reaction liquid containing the hydride of the ring-opening polymer of dicyclopentadiene. The hydride precipitated from this reaction liquid, forming a slurry solution.

The hydride and the solution contained in the reaction liquid were separated using a centrifuge and dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a crystalline ring-opening polymer of dicyclopentadiene. The hydrogenation rate of this hydride was 99% or more, the glass transition temperature (Tg) was 93°C, the melting point (Tm) was 262°C, and the racemo-dyad ratio was 89%.

100 parts of the obtained hydrogenated ring-opening polymer of dicyclopentadiene was mixed with 1.1 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane;"Irganox (registered trademark) 1010" manufactured by BASF Japan Ltd.), and then the mixture was fed into a twin-screw extruder (product name "TEM-37B", manufactured by Toshiba Machine Co., Ltd.) equipped with four die holes having an inner diameter of 3 mmΦ. The mixture of the hydrogenated ring-opening polymer of dicyclopentadiene and the antioxidant was molded into a strand shape by hot melt extrusion molding, and then chopped with a strand cutter to obtain a crystalline resin in the form of pellets. This crystalline resin has a positive intrinsic birefringence value.
The operating conditions of the twin-screw extruder are as follows.
・Barrel temperature setting = 270-280℃
Die set temperature = 250°C
Screw rotation speed = 145 rpm

[Example 1]
(1-1) Production of resin film The pellet-shaped crystalline resin produced in Production Example 1 was molded using a hot melt extrusion film molding machine equipped with a T-die, and a resin film with a width of about 600 mm was wound around a roll at a predetermined speed to obtain a roll of resin film. In this example, the line speed was adjusted to mold the resin film to a thickness of 18 μm. In addition, when winding around a roll, the film was wound while being protected with a masking film ("FF1025" manufactured by Tredegar). When the Re, Rth and NZ coefficient of the resin film were measured, the Re was 1.7 nm, the Rth was 1.9 nm, and the NZ coefficient was 1.6.
The operating conditions of the film forming machine are as follows.
・Barrel temperature setting = 280℃ to 300℃
Die temperature = 270°C
Cast roll temperature = 80°C

(1-2) Solvent treatment step (step 1)
The film was drawn from the roll of the resin film obtained in (1-1), and the masking film was continuously peeled off to transport the resin film. The resin film was passed through a bath filled with toluene as a solvent to bring the toluene into contact with the resin film. The contact time with the solvent was 7 seconds. The resin film in contact with the solvent was passed through an oven heated to 110° C. so as to be heated in the oven for about 1 minute to obtain a film after solvent treatment. During this process, a tension of 20 N/m was applied to the resin film. The film after the solvent treatment was wound up while being protected with a new masking film ("FF1025" manufactured by Tredegar Co., Ltd.) to obtain a roll of the film after the solvent treatment. The Re, Rth, NZ coefficient, and thickness of the film after the solvent treatment were measured, and the results were Re 7 nm, Rth -202 nm, NZ coefficient -28.4, and thickness 23 μm. The slow axis of the film after the solvent treatment was parallel to the longitudinal direction of the film.

(1-3) Oblique stretching step (step 2)
The film was pulled out from the roll of the solvent-treated film obtained in (1-2), and the masking film was continuously peeled off to transport the solvent-treated film. The solvent-treated film was obliquely stretched using a tenter stretching machine shown in FIG. 2 to obtain a long stretched film (retardation film). The stretching conditions were a stretching ratio of 1.5 times and a stretching temperature of 130° C. The average orientation angle of the slow axis of the obtained retardation film with respect to the width direction of the film was 15°. The obtained retardation film was trimmed at both ends in the width direction, and then rolled up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection to obtain a roll of retardation film. The Re, Rth, NZ coefficient, thickness and solvent content of the retardation film were measured, and the Re was 140 nm, the Rth was -5 nm, the NZ coefficient was 0.5, the thickness was 15 μm, and the solvent content was 1%. The degree of crystallinity of the retardation film was measured and found to be 22%.

[Example 2]
(2-1) Production of Resin Film A roll of resin film was obtained by the same operation as in (1-1) of Example 1, except that in (1-1) of Example 1, the line speed was adjusted to form the resin film to a thickness of 35 μm.

(2-2) Solvent Treatment Step In (1-2) of Example 1, the roll of the resin film obtained in (2-1) was used instead of the roll of the resin film obtained in (1-1), and the tension applied to the resin film during step 1 was set to 40 N/m. The same operation as in (1-2) of Example 1 was performed to obtain a roll of film after solvent treatment. The Re, Rth, NZ coefficient, and thickness of the film after the solvent treatment were measured, and the results were Re: 114 nm, Rth: -299 nm, NZ coefficient: -2.1, and thickness: 44 μm. The slow axis of the film after the solvent treatment was parallel to the longitudinal direction of the film.

(2-3) Oblique Stretching Step The film was pulled out from the roll of the solvent-treated film obtained in (2-2), and the masking film was continuously peeled off to transport the solvent-treated film. The solvent-treated film was obliquely stretched using a tenter stretching machine shown in FIG. 2 to obtain a long retardation film. The stretching conditions were a stretching ratio of 1.3 times and a stretching temperature of 130° C. The average orientation angle of the slow axis of the obtained retardation film with respect to the width direction of the film was 75°. After trimming both ends in the width direction, the obtained retardation film was wound up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection, to obtain a roll of retardation film. When the Re, Rth, NZ coefficient, thickness and solvent content of the retardation film were measured, Re was 270 nm, Rth was 10 nm, NZ coefficient was 0.5, thickness was 34 μm, and solvent content was 1%. The degree of crystallinity of the retardation film was measured and found to be 20%.

[Example 3]
In (1-3) of Example 1, the same operation as in (1-3) of Example 1 was performed to obtain a retardation film, except that the slow axis of the retardation film was stretched to an average orientation angle of 45° with respect to the width direction of the film using the roll of the film after the solvent treatment obtained in (1-2) of Example 1. The retardation film obtained was trimmed at both ends in the width direction, and then rolled up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection. The retardation film was measured for Re, Rth, NZ coefficient, thickness, and solvent content, and found to be Re 135 nm, Rth 6 nm, NZ coefficient 0.5, thickness 15 μm, and solvent content 1%. The crystallinity of the retardation film was measured to be 22%.

[Comparative Example 1]
The film was pulled out from the roll of the resin film obtained in (1-1) of Example 1, and the masking film was continuously peeled off to transport the resin film. This resin film was obliquely stretched using a tenter stretching machine shown in FIG. 2 to obtain a long retardation film. The stretching conditions were a stretching ratio of 2.5 times and a stretching temperature of 110° C. The average orientation angle of the slow axis of the obtained retardation film with respect to the width direction of the film was 45°. After trimming both ends in the width direction of the obtained retardation film, the film was wound up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection to obtain a roll of retardation film. When the Re, Rth, NZ coefficient, thickness and solvent content of the retardation film were measured, Re was 140 nm, Rth was 79 nm, NZ coefficient was 1.1, thickness was 20 μm, and solvent content was 0%. When the crystallinity of the retardation film was measured, it was 0%.

[Comparative Example 2]
(C2-1) Production of resin film Pellets of a resin containing a norbornene polymer (ZEONOR (registered trademark), manufactured by Nippon Zeon Co., Ltd., glass transition temperature Tg = 126 ° C.) were molded using a hot melt extrusion film molding machine equipped with a T-die, and a resin film with a width of about 600 mm was wound around a roll at a predetermined speed to obtain a roll of resin film. In this example, the line speed was adjusted to mold the resin film to a thickness of 80 μm. In addition, when winding up the film around a roll, the film was wound up while being protected with a masking film (FF1025, manufactured by Tredegar). The resin constituting the obtained resin film was a resin with a positive intrinsic birefringence value. The resin was a resin containing an amorphous polymer.
The operating conditions of the film forming machine are as follows.
・Barrel temperature setting = 270℃ to 290℃
Die temperature = 270°C
Cast roll temperature = 100°C

(C2-2) Oblique Stretching Step The film was pulled out from the roll of the resin film obtained in (C2-1), and the masking film was continuously peeled off to transport the resin film. This resin film was obliquely stretched using a tenter stretching machine shown in FIG. 2 to obtain a long retardation film. The stretching conditions were a stretching ratio of 4 times and a stretching temperature of 120° C. The average orientation angle of the slow axis of the obtained retardation film with respect to the width direction of the film was 15°. The obtained retardation film was trimmed at both ends in the width direction, and was wound up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection, to obtain a roll of retardation film. When the Re, Rth, NZ coefficient, thickness and solvent content of the retardation film were measured, Re was 140 nm, Rth was 78 nm, NZ coefficient was 1.1, thickness was 20 μm, and solvent content was 0%. The degree of crystallinity of the retardation film was measured and found to be 0%.

[Comparative Example 3]
(C3-1) Oblique Stretching Step The film was pulled out from the roll of the resin film obtained in (C2-1), and the masking film was continuously peeled off to transport the resin film. This resin film was obliquely stretched using a tenter stretching machine shown in FIG. 2 to obtain a long obliquely stretched film. The stretching conditions were a stretching ratio of 1.5 times and a stretching temperature of 140°C. The average orientation angle of the slow axis of the obtained obliquely stretched film with respect to the width direction of the film was 45°. The obliquely stretched film was wound up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection, to obtain a roll of obliquely stretched film. The Re, Rth, NZ coefficient, thickness and solvent content of the obliquely stretched film were measured, and the results were Re: 190 nm, Rth: 115 nm, NZ coefficient: 1.1, thickness: 47 μm, and solvent content: 0%.

(C3-2) Longitudinal Stretching Step The film was pulled out from the roll of the obliquely stretched film obtained in (C3-1), the masking film was peeled off from the film, and the obliquely stretched film was subjected to free longitudinal uniaxial stretching. This free longitudinal uniaxial stretching was performed using a roll stretching machine shown in FIG. 3. The stretching direction was the longitudinal direction of the film, the stretching ratio was 1.4 times, and the stretching temperature was 125 ° C. Thereafter, both ends of the film in the width direction after the free longitudinal uniaxial stretching were trimmed to obtain a long retardation film. The average orientation angle of the slow axis of the obtained retardation film with respect to the width direction was 75 °, the NZ coefficient was 1.15, the in-plane retardation Re was 260 nm, and the thickness was 40 μm. The crystallinity of the retardation film was measured and found to be 0%. The obtained retardation film was wound up while being laminated with a new masking film ("FF1025" manufactured by Tredegar) for protection.

Table 1 shows the conditions (type of solvent, drying temperature, tension, stretch ratio, stretch temperature) for producing the retardation films of the examples and comparative examples, and the physical properties (Re, Rth, NZ coefficient, thickness, average orientation angle) of the films obtained after each process. In Table 1, "crystalline COP" means a crystalline alicyclic structure-containing polymer, "amorphous COP" means an amorphous alicyclic structure-containing polymer, and "orientation angle" means "average orientation angle in the width direction of the film." In Table 1, "film after oblique stretching process" means a stretched film after the oblique stretching process, and corresponds to the retardation film in Examples 1 to 3 and Comparative Examples 1 and 2, and corresponds to the obliquely stretched film in Comparative Example 3. In Table 1, "solvent content" means the solvent content of the retardation film produced in the examples and comparative examples.

[Production Example A] Production of Circularly Polarizing Plate A (A-1) Production of Optical Laminate A retardation film obtained by pulling out the film from the roll of retardation film produced in Example 1 and continuously peeling off the masking film was used as a quarter-wave plate. A retardation film obtained by pulling out the film from the roll of retardation film produced in Example 2 and continuously peeling off the masking film was used as a half-wave plate.
The half-wave plate and the quarter-wave plate were laminated together with their longitudinal directions parallel to each other via an adhesive layer ("CS9621" manufactured by Nitto Denko Corporation). This resulted in a long optical laminate in which the slow axis of the half-wave plate and the slow axis of the quarter-wave plate were laminated together so as to intersect at 60° when viewed from the thickness direction.

(A-2) Manufacture of a circularly polarizing plate A polarizing film ("HLC2-5618S" manufactured by Sanritz Co., Ltd., 180 μm thick, polarizer having a polarization transmission axis in the direction of 0° to the width direction) was prepared as a long linear polarizer. One surface of this polarizing film and the surface of the ½ wavelength plate side of the optical laminate obtained in (A-1) were bonded together via a pressure-sensitive adhesive layer ("CS9621" manufactured by Nitto Denko Co., Ltd.) with the longitudinal direction of the polarizing film and the longitudinal direction of the optical laminate parallel to each other. As a result, a long circularly polarizing plate having a layer structure of (polarizing film)/(pressure-sensitive adhesive layer)/(½ wavelength plate)/(pressure-sensitive adhesive layer)/(¼ wavelength plate) was obtained. The reflection intensity and reflectance of the circularly polarizing plate thus obtained were evaluated by the above-mentioned method.

[Production Example B] Production of Circularly Polarizing Plate B (B-1) Preparation of Retardation Film A retardation film was prepared by pulling out the film from the roll of the retardation film produced in Example 3 and continuously peeling off the masking film.

(B-2) Production of a circularly polarizing plate In (A-2) of Production Example A, the same operation as in (A-2) of Production Example A was carried out except that the retardation film prepared in (B-1) was used as the ¼ wavelength plate instead of the optical laminate obtained in (A-1), to obtain a long circularly polarizing plate B having a layer structure of (polarizing film)/(adhesive layer)/(¼ wavelength plate). The reflection intensity and reflectance of the circularly polarizing plate B thus obtained were evaluated by the method described above.

[Production Example C] Production of Circularly Polarizing Plate C (C-1) Production of Optical Laminate A long optical laminate was obtained by performing the same operation as in (A-1) of Production Example A, except that in (A-1) of Production Example A, instead of the retardation film obtained from the retardation film roll of Example 1, a retardation film obtained by pulling out a film from the roll of retardation film produced in Comparative Example 2 and continuously peeling off the masking film was used as a quarter-wave plate.

(C-2) Production of Circularly Polarizing Plate In (A-2) of Production Example A, except that the optical laminate obtained in (C-2) was used instead of the optical laminate obtained in (A-1) in (A-2) of Production Example A, the same operation as in (A-2) of Production Example A was carried out to obtain a long circularly polarizing plate C having a layer structure of (polarizing film)/(adhesive layer)/(½ wavelength plate)/(adhesive layer)/(¼ wavelength plate). The reflection intensity and reflectance of the circularly polarizing plate C thus obtained were evaluated by the method described above.

[Production Example D] Production of Circularly Polarizing Plate D (D-1) Production of Optical Laminate A long optical laminate was obtained by the same operation as in (A-1) of Production Example A, except that in (A-1) of Production Example A, instead of the retardation film obtained from the retardation film roll of Example 2, a retardation film obtained by pulling out a film from the roll of retardation film produced in Comparative Example 3 and continuously peeling off the masking film was used as a half-wave plate.

(D-2) Production of Circularly Polarizing Plate In (A-2) of Production Example A, except that the optical laminate obtained in (D-2) was used instead of the optical laminate obtained in (A-1) in (A-2) of Production Example A, the same operation as in (A-2) of Production Example A was carried out to obtain a long circularly polarizing plate D having a layer structure of (polarizing film)/(adhesive layer)/(½ wavelength plate)/(adhesive layer)/(¼ wavelength plate). The reflection intensity and reflectance of the circularly polarizing plate D thus obtained were evaluated by the method described above.

[Production Example E] Production of Circularly Polarizing Plate E (E-1) Preparation of Retardation Film A retardation film was prepared by pulling out the film from the roll of the retardation film produced in Comparative Example 1 and continuously peeling off the masking film.

(E-2) Production of a circularly polarizing plate In (A-2) of Production Example A, except that the retardation film prepared in (E-1) was used as the ¼ wavelength plate instead of the optical laminate obtained in (A-1), the same operation as in (A-2) of Production Example A was carried out to obtain a long circularly polarizing plate E having a layer structure of (polarizing film)/(adhesive layer)/(¼ wavelength plate). The reflection intensity and reflectance of the circularly polarizing plate E thus obtained were evaluated by the method described above.

[Production Example F] Production of Circularly Polarizing Plate F (F-1) Production of Optical Laminate A long optical laminate was obtained by the same operation as in Production Example A (A-1), except for the following changes in Production Example A (A-1).
Instead of the retardation film obtained from the retardation film roll of Example 1, a retardation film obtained by pulling out the film from the retardation film roll produced in Comparative Example 2 and continuously peeling off the masking film was used as a quarter-wave plate.
Instead of the retardation film obtained from the retardation film roll of Example 2, a retardation film obtained by pulling out the film from the retardation film roll produced in Comparative Example 3 and continuously peeling off the masking film was used as a half-wave plate.

(F-2) Production of a circularly polarizing plate In (A-2) of Production Example A, except that the optical laminate obtained in (F-1) was used instead of the optical laminate obtained in (A-1), the same operation as in (A-2) of Production Example A was carried out to obtain a long circularly polarizing plate F having a layer structure of (polarizing film)/(adhesive layer)/(½ wavelength plate)/(adhesive layer)/(¼ wavelength plate). The reflection intensity and reflectance of the circularly polarizing plate F thus obtained were evaluated by the method described above.

Table 2 shows the evaluation results of each circular polarizer, along with the retardation film used to manufacture the circular polarizer and its physical properties (Re, Rth, NZ coefficient).

As is clear from the results shown in Table 2, the circular polarizer using the retardation film of the present invention has a low reflectance in the tilt direction. This shows that the present invention can provide a long retardation film with excellent viewing angle characteristics and a manufacturing method thereof.

[Other embodiments]
(1) In the above embodiment and example, a method for producing a _retardation film having a slow axis of 10° to 80° with respect to the film width direction and an NZ coefficient greater than 0 and smaller than 1 was shown by obliquely stretching the film F0, but the retardation film of the present invention is not limited to that produced by this production method. For example, a retardation film having a slow axis of 10° to 80° with respect to the film width direction and an NZ coefficient greater than 0 and smaller than 1 may be produced by a method in which a film having an NZ coefficient of 1 or more is prepared, the film is brought into contact with a solvent, and then stretched.

1... resin film 10... film after solvent treatment (film F ₀ )
11: Film unwound from roll 12, 13: Masking film 30: Stretched film (retardation film)
40...Roll of stretched film 50...Film (film obtained by longitudinally stretching the stretched film 30)
60...Roll of film 50 100...Apparatus (apparatus for performing step 1)
101A, 101B, 104A, 104B... Nip roll 102... Bath 103... Heating device 110... Roll of film after solvent treatment 111... Roll of resin film 112... Roll (roll of masking film)
113: Masking film roll 200: Tenter stretching machine 210R, 210L: Grippers 220R, 220L: Guide rails 230: Inlet section 240: Outlet section 250: Stretching zone 300: Roll stretching machine (longitudinal stretching machine)
310...upstream roll 320...downstream roll

Claims (10)

A method for producing a long retardation film having a slow axis at an angle of 10° to 80° with respect to the width direction and an NZ coefficient greater than 0 and smaller than 1, comprising the steps of:
Film F with NZ coefficient less than 0 ₀ A step 1 of preparing
The film F ₀ and a step 2 of obliquely stretching the film. The method for producing a retardation film according to claim 1 , wherein the retardation film is a half-wave plate or a quarter-wave plate. The method for producing a retardation film according to claim 1 or 2, wherein the retardation film is made of a resin having a positive intrinsic birefringence value. The method for producing a retardation film according to claim 1 , wherein the retardation film is made of a resin containing a polymer having crystallinity. The method for producing a retardation film according to claim 4 , wherein the polymer having crystallinity is a hydrogenated product of a ring-opening polymer of dicyclopentadiene. 3. The method for producing a retardation film according to claim 1, wherein the retardation film has an in-plane birefringence Re/d of 3.0×10 ⁻³ or more and 2.0×10 ⁻² or less. 3. The method for producing a retardation film according to claim 1, wherein the retardation film has a thickness direction retardation Rth of −30 nm or more and 30 nm or less. The method for producing a retardation film according to claim 4 , wherein the retardation film has a crystallinity of 10% or more as determined by an X-ray diffraction method. The method for producing a retardation film according to claim 1 or 2 , wherein the step 1 comprises contacting a resin film with a solvent, thereby changing the NZ coefficient of the resin film, and obtaining the film F ₀ . The method for producing a retardation film according to claim 9 , wherein the solvent is a hydrocarbon-based solvent.

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