Retardation film manufacturing method

Abstract

To provide a retardation film manufacturing method that allows a manufacturing facility to be simplified.SOLUTION: A retardation film manufacturing method includes a step of bringing a resin film into contact with a solvent in order to stretch the resin film. The resin film is preferably brought into contact with the solvent by immersing the resin film in the solvent. Further, the resin film is preferably an embodiment composed from resin with a positive intrinsic birefringence.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a retardation film. [Background technology]

[0002] Conventionally, techniques for producing retardation films have been proposed (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 065222 (Corresponding Publication: U.S. Patent Application Publication No. 2020 / 292742) [Patent Document 2] JP 2016-212171 A Summary of the Invention [Problem to be solved by the invention]

[0004] A retardation film has retardation in at least one of the in-plane direction and the thickness direction. As a method for obtaining such a retardation film, a method in which a resin film is heated to a temperature equal to or higher than the glass transition temperature Tg of the resin and stretched is known (see, for example, Patent Document 1). However, when such a method is adopted, a device or equipment for heating the resin film is required, and there is a problem that the manufacturing equipment becomes large. There is also a problem that the energy consumption is large.

[0005] An object of the present invention is to provide a method for producing a retardation film, which can simplify the production equipment. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that retardation can be produced in at least one of the in-plane direction and the thickness direction by contacting a resin film with a solvent and stretching the resin film without heating the resin film, thereby solving the above-mentioned problems and completing the present invention. That is, the present invention includes the following.

[0007] [1] A method for producing a retardation film, comprising the steps of: A method for producing a retardation film, comprising a step of contacting a resin film with a solvent and stretching the resin film. [2] The method for producing a retardation film according to [1], wherein the resin film is brought into contact with the solvent by immersing the resin film in the solvent. [3] The method for producing a retardation film according to [1] or [2], wherein the resin film is made of a resin having a positive intrinsic birefringence value. [4] The method for producing a retardation film according to any one of [1] to [3], wherein the resin film is made of a resin containing a polymer having crystallinity. [5] The method for producing a retardation film according to [4], wherein the polymer having crystallinity is a hydrogenated product of a ring-opening polymer of dicyclopentadiene. [6] The method for producing a retardation film according to any one of [1] to [5], wherein the solvent is a hydrocarbon-based solvent. [7] The method for producing a retardation film according to any one of [1] to [6], wherein the stretching step is carried out without heating the resin film. Effect of the Invention

[0008] According to the present invention, a method for producing a retardation film that can simplify production equipment can be provided. [Brief description of the drawings]

[0009] [Figure 1] 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. [Diagram 2] FIG. 2 is a plan view diagrammatically illustrating a roll stretching machine that can be used in the method for producing the retardation film of Comparative Example 1. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] 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, 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.

[0012] 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 that in the direction perpendicular thereto. Also, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is smaller than that in the direction perpendicular thereto. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0013] In the following description, unless otherwise specified, the oblique 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.

[0014] In the following description, a "long" film refers to a film having a length of 5 times or more, preferably 10 times or more, the width, specifically a film having a length that can 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 the width.

[0015] 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 the 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 the long film.

[0016] 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°.

[0017] [Outline of the method for producing the retardation film of the present invention] The method for producing a retardation film of the present invention includes a step of contacting a resin film with a solvent and stretching it.

[0018] The method for producing a retardation film of the present invention includes a step of contacting a resin film, which is a material for the retardation film, with a solvent and stretching the resin film, and by including the step, the retardation can be expressed without heating the resin film. As a result, according to the present invention, a device for heating the resin film is not required, and therefore a method for producing a retardation film that can simplify the production equipment can be provided.

[0019] [Embodiment 1] Hereinafter, the method for producing a retardation film according to the first embodiment of the present invention will be specifically described with reference to Fig. 1. Fig. 1 is a side view that illustrates a schematic diagram of an apparatus that can be used in the method for producing a retardation film according to the first embodiment.

[0020] [Outline of the method for producing the retardation film of this embodiment] In 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 15 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 arranged at a position to sandwich the film 11 in the thickness direction.

[0021] Next, the resin film 15 is stretched while passing through a bath 102 filled with a solvent and contacting the resin film 15. In this embodiment, the resin film 15 is stretched in the film transport direction by the difference in peripheral speed between the nip rolls 101A, 101B arranged on the upstream side in the film transport direction and the nip rolls 104A, 104B arranged on the downstream side in the film transport direction. By stretching the resin film 15 while contacting it with a solvent, it is possible to develop retardation in at least one of the in-plane direction and the thickness direction of the film without heating the resin film. Therefore, the stretched film 10 obtained in this manner can be used as a retardation film as it is.

[0022] The stretched film 10 thus obtained is wound up while being laminated with the masking film 13 unwound from the roll 113. This produces the stretched film roll 110. The lamination of the stretched film 10 and the masking film 13 is performed while pressing the film with nip rolls 104A and 104B disposed at positions sandwiching the film from the thickness direction.

[0023] The method for producing a retardation film of the present embodiment includes a step of contacting a resin film with a solvent and stretching the resin film. In the following description, this step may be referred to as “step 1.”

[0024] [Process 1] Step 1 is a step of contacting a resin film with a solvent and stretching it. By contacting a resin film with a solvent and stretching it, retardation can be developed in the resin film. 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.

[0025] When the 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 polymer molecules in the film are oriented. Here, the surface area of ​​the resin film is large on the front surface and the back surface, which are the main surfaces. Therefore, the penetration speed of the solvent is high in the thickness direction through the front surface or back surface. Then, the orientation of the polymer molecules can proceed so that the polymer molecules are oriented in the thickness direction. When a resin film with molecules oriented in the thickness direction is stretched, the orientation of the molecules in the film in the stretching direction proceeds, and the degree of orientation increases. When the degree of orientation of the molecules increases in this way, the birefringence of the film changes, and the retardation increases.

[0026] Step 1 can be performed by an apparatus 100 shown in Fig. 1. The apparatus 100 includes upstream nip rolls 101A and 101B arranged on the upstream side in the film transport direction, downstream nip rolls 104A and 104B arranged on the downstream side in the film transport direction, and a bath 102 that brings the resin film 15 into contact with a solvent.

[0027] Step 1 includes step 1A of contacting the resin film with a solvent and step 1B of stretching the resin film. In this embodiment, step 1A is performed while step 1B is performed. That is, the resin film is brought into contact with the solvent in a region of the resin film path where tension is applied to the resin film by stretching. However, the method for producing a retardation film of the present invention is not limited thereto. The production method of the present invention includes an embodiment in which a part of step 1B overlaps with step 1A, for example, an embodiment in which step 1B of stretching the resin film is started halfway through step 1A of contacting the resin film with the solvent. In addition, the production method of the present invention also includes an embodiment in which step 1B of stretching the resin film is performed after step 1A of contacting the resin film with the solvent is performed, with the resin film being attached and / or impregnated with the solvent.

[0028] [Process 1A] Step 1A is a step of contacting a resin film with a solvent.

[0029] Examples of the method for contacting the resin film with the solvent include 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 a dipping method in which the resin film is dipped in the solvent. Among these methods, the dipping method is preferred from the viewpoint of easily expressing retardation in the thickness direction even when the resin film is thick, and from the viewpoint of easily performing continuous contact. Figure 1 shows the dipping method.

[0030] [Resin film] The resin film is a film that is a material for producing a retardation film, and can be made of a resin. The resin that constitutes the resin film includes a polymer.

[0031] The resin constituting the resin film is preferably a resin having a positive intrinsic birefringence value. Unless otherwise specified, a resin having a positive intrinsic birefringence value means a resin whose refractive index in the stretching direction is greater than that in the direction perpendicular thereto. The value of the intrinsic birefringence can be calculated from the dielectric constant distribution.

[0032] Moreover, the resin constituting the resin 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., a melting point that 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". Furthermore, a resin containing a crystalline polymer may be referred to as a "crystalline resin". This crystalline resin is preferably a thermoplastic resin.

[0033] In the present invention, the resin film is preferably a film made of a resin having a positive intrinsic birefringence value, and more preferably the resin is a resin containing a crystalline polymer.

[0034] [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 obtained 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.

[0035] Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure. Among these, a cycloalkane structure is preferred because it is easy to obtain a retardation film having excellent properties such as thermal stability. 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.

[0036] In the crystalline polymer containing an alicyclic structure, the ratio of the structural unit 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 unit containing an alicyclic structure as described above, heat resistance can be improved. The ratio of the structural unit containing an alicyclic structure to all structural units can be 100% by weight or less. In addition, in the crystalline polymer containing an alicyclic structure, the remainder other than the structural unit containing an alicyclic structure is not particularly limited and can be appropriately selected according to the purpose of use.

[0037] Examples of the crystalline polymer containing an alicyclic structure include the following polymer (α) to polymer (δ). Among these, polymer (β) is preferred because a retardation film having excellent heat resistance can be easily obtained. 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.

[0038] Specifically, the crystalline polymer containing an alicyclic structure is preferably a dicyclopentadiene ring-opening polymer having crystallinity, and a dicyclopentadiene ring-opening polymer hydrogenation product having crystallinity. Among them, a dicyclopentadiene ring-opening polymer hydrogenation product having crystallinity is particularly preferred. Here, the dicyclopentadiene ring-opening polymer refers to a polymer in which the ratio of dicyclopentadiene-derived structural units 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.

[0039] 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 racemo-dyads is described in the Examples below. 13 It can be determined based on C-NMR spectrum analysis.

[0040] As the polymer (α) to polymer (δ), polymers obtained by the production method disclosed in WO 2018 / 062067 can be used.

[0041] 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 having an even better balance between formability and heat resistance can be obtained.

[0042] Usually, a crystalline polymer has a glass transition temperature Tg. The specific glass transition temperature Tg of the crystalline polymer is not particularly limited, but is usually 80° C. or higher and usually 170° C. or lower. The glass transition temperature of the crystalline polymer is preferably 85° C. or higher, more preferably 90° C. or higher, and preferably 150° C. or lower, more preferably 130° C. or lower.

[0043] 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 melted polymer is quenched with dry ice. Then, 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).

[0044] The weight average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, and is 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.

[0045] The molecular weight distribution (Mw / Mn) of the crystalline polymer is preferably 1.0 or more, more preferably 1.5 or more, and is 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.

[0046] The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer can be measured in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a developing solvent.

[0047] The crystalline polymer may be used alone or in combination of two or more kinds in any ratio.

[0048] The proportion of the 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 the crystalline polymer is equal to or more 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 the crystalline polymer can be 100% by weight or less.

[0049] The crystalline resin may contain optional components in addition to the crystalline polymer. Examples of the optional components include 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-based derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, and benzimide derivatives). 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.

[0050] When the resin contained in the resin film is a crystalline resin, the crystallinity of the crystalline polymer contained in the resin film before carrying out step 1 is preferably small. The specific crystallinity is preferably less than 10%, more preferably less than 5%, and particularly preferably less than 3%. When the crystallinity of the crystalline polymer contained in the resin film before contacting with the solvent is low, many molecules of the crystalline polymer can be oriented in the thickness direction by contacting with the solvent, making it possible to adjust the retardation in a wide range.

[0051] The in-plane retardation Re of the resin film before step 1 is preferably 20 nm or less, more preferably 10 nm or less, and particularly preferably 0 nm. 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 nm. When Re and Rth of the resin film before step 1 are each within the above range, the retardation of the resin film after step 1 is easily adjusted.

[0052] The resin film before contacting with the solvent preferably has a small solvent content, more preferably does not contain any 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 contact with the solvent, so that the retardation can be adjusted in a wide range. The solvent content of the resin film can be measured by density.

[0053] The thickness of the resin film is preferably set according to the thickness of the retardation film to be produced. 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. Therefore, the thickness of the resin film may be set in consideration of the change in thickness in step 1, which is the contact with the solvent and the stretching.

[0054] It is preferable to use a long resin film as the resin film, which enables continuous production of the retardation film by a roll-to-roll method, and therefore effectively increases the productivity of the retardation film.

[0055] There is no limitation on the method for producing the resin film. Since a resin film that does not contain a solvent can be obtained, resin molding methods such as injection molding, extrusion molding, press molding, inflation molding, blow molding, calendar molding, cast molding, and compression molding are preferred. Among these, extrusion molding is preferred because it is easy to control the thickness.

[0056] 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. 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.

[0057] In this embodiment, a masking film is attached to a long resin film and wound into a roll, and the film roll is subjected to step 1. As the masking film, known masking films (e.g., "FF1025" and "FF1035" manufactured by Tredegar Co., Ltd.; "SAT116T", "SAT2038T-JSL" and "SAT4538T-JSL" manufactured by San-A Chemical Co., Ltd.; "NBO-0424", "TFB-K001", "TFB-K0421" and "TFB-K202" manufactured by Fujimori Kogyo Co., Ltd.; "DT-2200-25" and "K-6040" manufactured by Hitachi Chemical Co., Ltd.; "6010#75", "6010#100", "6011#75" and "6093#75" manufactured by Teraoka Manufacturing Co., Ltd.) can be used.

[0058] [solvent] In step 1A, the solvent to be brought into contact with the resin film may be a solvent that can penetrate into the resin film without dissolving the polymer contained in 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.

[0059] The temperature of the solvent to be brought into contact with the resin film can be any temperature within a range in which the solvent can maintain a liquid state, and therefore can be set within a range from the melting point to the boiling point of the solvent. In particular, in the present application, even when the temperature of the solvent is adjusted to room temperature (for example, 15°C or higher and lower than 40°C, more preferably 18°C ​​or higher and lower than 35°C, and even more preferably 23°C or higher and lower than 30°C), or even when adjusted to a temperature range close to room temperature, good stretching can be performed. When the solvent is heated, the temperature can be adjusted to a temperature higher than room temperature as necessary. However, even in this case, good stretching can be performed with simpler equipment than when the temperature around the film transported during stretching is heated by an oven in a general stretching device.

[0060] 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 making the contact time equal to or more than the lower limit of the above range, the molecules contained in the resin film can be effectively oriented. On the other hand, even if the contact time is extended, the degree of molecular orientation tends not to change significantly. Therefore, by making the contact time equal to or less than the upper limit of the above range, the productivity can be increased without impairing the quality of the retardation film.

[0061] [Process 1B] Step 1B is a step of stretching a resin film.

[0062] In the manufacturing method of this embodiment, the resin film is stretched using a stretching machine that performs longitudinal stretching by the difference in peripheral speed between multiple sets of rolls. The upstream nip rolls 101A, 101B and the downstream nip rolls 104A, 104B are rotated by a driving means (not shown) so that the resin film 15 can be transported in the transport direction A1. In this embodiment, the peripheral speed of the downstream nip rolls 104A, 104B is set faster than the peripheral speed of the upstream nip rolls 101A, 101B. Therefore, there is a peripheral speed difference between the upstream nip rolls 101A, 101B and the downstream nip rolls 104A, 104B, and the resin film 15 can be continuously stretched in the transport direction (travel direction) due to this peripheral speed difference. In addition, the stretch ratio of the resin film 15 can be adjusted by adjusting the peripheral speed difference.

[0063] In the manufacturing method of the present embodiment, since the resin film is stretched by contacting it with a solvent, even if the stretching is performed at a low stretch ratio, retardation can be easily expressed. The stretch ratio of the resin film in step 1 is preferably 1.05 or more, more preferably 1.1 or more, and preferably 5.00 or less, more preferably 3.00 or less. When the stretch ratio is equal to or more than the lower limit of the above range, retardation can be effectively expressed in the resin film. When the stretch ratio is equal to or less than the upper limit of the above range, productivity can be increased without impairing the quality of the retardation film obtained by the present invention.

[0064] According to the manufacturing method of this embodiment, since retardation can be developed without heating the resin film during stretching, it is not necessary to heat the resin film during stretching, but the resin film may be heated during stretching. In this case, the resin film before stretching may be preheated. When the resin film is heated during stretching, the stretching temperature 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 resin film 15.

[0065] The stretched film 10 obtained after carrying out step 1 can be used as a retardation film as it is, but a film obtained by carrying out a further step (for example, a further stretching step, etc.) may also be used as a retardation film.

[0066] [Effects of this embodiment] In the method for producing a retardation film according to the present embodiment, the resin film is brought into contact with a solvent and stretched, so that retardation can be produced in at least one of the in-plane direction and the thickness direction without heating the resin film. As a result, according to the present embodiment, a heating device such as an oven for heating the resin film is not required, so that the production equipment for the retardation film can be simplified. In addition, according to the present embodiment, the resin film is brought into contact with the solvent and the resin film is stretched at the same time, so that the production efficiency of the retardation film can be improved.

[0067] [Optional process] The method for producing the retardation film of the present invention may include any of the steps described below.

[0068] The method for producing a retardation film of the present invention may include a step of removing the solvent from the resin film after the resin film has been brought into contact with the solvent. Examples of the method for removing the solvent from the resin film include drying and wiping.

[0069] When the solvent is removed by drying from the resin film after contacting with the solvent, there is no limitation on the method, and for example, a heating device such as an oven can be used. Specifically, the solvent can be removed by conveying the resin film after contacting with the solvent in a heating device for a predetermined time. Heating for removing the solvent can be performed at a relatively low temperature, unlike heating performed during stretching in a general stretching device, and can be performed without strict temperature control and can be completed in a relatively short time. In addition, by appropriately selecting the type of solvent, it is also possible to achieve drying by simply conveying at room temperature without performing any particular heating operation.

[0070] When the solvent is removed by drying, the film may be subjected to tension. Drying in such a state is preferable because it can effectively increase the uniformity of the optical properties of the film after contact with the solvent. The magnitude and direction of the tension applied to the resin film can be set in consideration of the material of the resin film. When tension is applied to the resin film, for example, the resin film may be held by an appropriate holder, and the resin film may be pulled by the holder to apply tension. The holder may be capable of continuously holding the entire length of the side of the resin film, or may be capable of holding the side intermittently at intervals. For example, the side of the resin film may be held intermittently by holders arranged at a predetermined interval.

[0071] The method for producing a retardation film of the present invention may include a step of further stretching the film obtained after carrying out step 1. The stretching conditions in this step, such as the stretching direction, stretching device, and stretching ratio, are not particularly limited and may be set in consideration of the intended use of the retardation film, etc.

[0072] In addition, in the case of producing a long retardation film, the method for producing a retardation film of the present invention may include a step of cutting the long retardation film into a desired shape.

[0073] [Retardation film] Next, the retardation film obtained by the method for producing a retardation film of the present invention will be described.

[0074] [Retardation of phase difference film] The in-plane retardation Re of the retardation film can be set according to its application. The in-plane retardation Re of the retardation film is preferably 10 nm or more, more preferably 30 nm or more, and is preferably 1000 nm or less, more preferably 800 nm or less.

[0075] The specific in-plane retardation Re value of the retardation film is, for example, preferably 100 nm or more, more preferably 110 nm or more, particularly preferably 120 nm or more, and 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.

[0076] Furthermore, the specific in-plane retardation Re value of the retardation film can be, for example, preferably 230 nm or more, more preferably 250 nm or more, particularly preferably 255 nm or more, and 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 1 / 2 wavelength plate.

[0077] 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 −500 nm or more, more preferably −400 nm or more, and preferably 300 nm or less, more preferably 150 nm or less.

[0078] [NZ coefficient of retardation film] The NZ coefficient of the retardation film is preferably -10 or more, more preferably -8 or more, and preferably 10 or less, more preferably 8 or less. When a retardation film having an NZ coefficient within the above range is provided in a display device, it can 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 depending on the application of the retardation film.

[0079] The NZ coefficient of a retardation film can be calculated from the in-plane retardation Re and the thickness direction retardation Rth of the film. The in-plane retardation Re and the thickness direction retardation Rth of the film can be measured using a retardation meter (for example, "AxoScan OPMF-1" manufactured by AXOMETRICS).

[0080] [Birefringence of retardation film] A retardation film usually has a large birefringence in at least one of the in-plane direction and the thickness direction. -3 The birefringence Re / d in the in-plane direction is 1.0×10 -3 At least one of the absolute values ​​of birefringence in the thickness direction, |Rth / d|, is satisfied.

[0081] In detail, the birefringence Re / d in the in-plane direction of the retardation film is usually 1.0×10 -3 More than 3.0×10 -3 More preferably, 5.0×10 -3 That's it. There is no upper limit. For example, 2.0×10 -2 Below, 1.5 x 10 -2 or less, or 1.0 x 10 -2 However, the absolute value of birefringence in the thickness direction of the retardation film |Rth / d| is 1.0×10 or less. -3 If it is equal to or greater than this range, the birefringence Re / d in the in-plane direction of the retardation film may be outside the above range.

[0082] The absolute value of birefringence in the thickness direction of the retardation film, |Rth / d|, is usually 1.0×10-3 More than 3.0×10 -3 More preferably, 5.0×10 -3 That's it. There is no upper limit. For example, 2.0×10 -2 Below, 1.5 x 10 -2 or less, or 1.0 x 10 -2 However, the birefringence Re / d in the in-plane direction of the retardation film may be 1.0×10 or less. -3 If it is equal to or greater than this range, the absolute value |Rth / d| of birefringence in the thickness direction of the retardation film may be outside the above range.

[0083] [Other characteristics of retardation film] The haze of the retardation film 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 provided in a display device, the image displayed on the display device can be made more clear. The haze of the film can be measured using a haze meter (for example, "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

[0084] Since the retardation film is an optical film, it is preferable that the retardation film 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.

[0085] 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 more than the lower limit of the above range, the handling property 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.

[0086] In the retardation film manufactured using a resin film containing a crystalline polymer, the crystallinity of the crystalline polymer is not particularly limited, but is usually high to a certain degree. The specific range of the crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The crystallinity of a crystalline polymer can be measured by X-ray diffraction.

[0087] [Solvents contained in retardation film] Since the method for producing a retardation film of the present invention includes a step of contacting a resin film with a solvent and stretching it, the retardation film produced by the production method may contain a solvent.

[0088] When the resin film is brought into contact with the solvent, all or part of the solvent taken into the resin film may penetrate into the polymer contained in the resin constituting the film. Therefore, even if the film is dried at a temperature equal to or higher than the boiling point of the solvent, it is difficult to completely remove the solvent. Therefore, the retardation film produced by the production method including the step of bringing the film into contact with the solvent may contain the solvent.

[0089] 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 can be more than 0% by weight.

[0090] [Applications of retardation film] The retardation film produced by the production method of the present invention exhibits retardation in at least one of the in-plane direction and the thickness direction by contacting the resin film with a solvent and stretching it. Therefore, the retardation film obtained by the production method of the present invention can be used as a 1 / 2 wavelength plate or a 1 / 4 wavelength plate depending on its retardation value. A circular polarizing plate using the retardation film produced by the production method of the present invention as either or both of the 1 / 2 wavelength plate and the 1 / 4 wavelength plate can be used in a display device. EXAMPLES

[0091] 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 can be modified and carried out as desired without departing from the scope of the claims of the present invention and the scope of equivalents thereto.

[0092] In the following description, the units "%" and "parts" are by weight unless otherwise specified. The operations described below were performed at room temperature and pressure unless otherwise specified. In the following description, the wavelength for measuring retardation and birefringence was 590 nm unless otherwise specified.

[0093] [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 (Tosoh Corporation, "HLC-8320"). In the measurement, an H-type column (Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The temperature during the measurement was 40°C.

[0094] (Method for measuring hydrogenation rate of polymer) The hydrogenation rate of the polymer is 4 as a solvent at 145°C, 1 Measured by H-NMR measurement.

[0095] (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.

[0096] (Method for measuring the ratio of racemo-dyads in polymers) The ratio of racemo-dyads in the polymer was determined as follows. 4 The inverse-gated decoupling method was applied to the polymer at 200°C using 13 C-NMR measurements were performed. 13 The results of C-NMR measurement showed that o-dichlorobenzene-d 4 Using the peak at 127.5 ppm as the reference shift, the signal at 43.35 ppm from the meso-dyad and the signal at 43.43 ppm from the racemo-dyad were identified. The ratio of the racemo-dyads in the polymer was calculated based on the intensity ratio of these signals.

[0097] (Method of measuring film thickness) The thickness of the film was measured using a contact thickness meter (manufactured by MITUTOYO, Code No. 543-390).

[0098] (Method of measuring retardation and NZ coefficient) The in-plane retardation Re, thickness 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 in-plane retardation Re and thickness retardation Rth obtained.

[0099] [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 dicyclopentadiene), and 1.9 parts of 1-hexene were added to the metallic pressure-resistant reactor and heated to 53°C.

[0100] 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 a 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.

[0101] To 200 parts of the obtained solution of the ring-opening polymer of dicyclopentadiene, 0.037 parts of 1,2-ethanediol was added as a terminator, 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, heated to 60°C, and stirred for 1 hour. Thereafter, 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").

[0102] 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 hydrogenation reaction was carried out at 180°C and hydrogen pressure of 6 MPa for 4 hours. As a result, a reaction liquid containing a hydrogenated product of the ring-opening polymer of dicyclopentadiene was obtained. The reaction liquid was a slurry solution in which the hydrogenated product was precipitated.

[0103] The hydrogenated product and the solution contained in the reaction solution were separated using a centrifuge and dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a hydrogenated product of a crystalline ring-opening polymer of dicyclopentadiene. The hydrogenation rate of this hydrogenated product was 99% or more, the glass transition temperature (Tg) was 93°C, the melting point (Tm) was 262°C, and the ratio of racemo-dyads was 89%.

[0104] 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 put 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 mm. 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 temperature setting = 250℃ Screw speed: 145 rpm

[0105] [Example 1] (1-1) Manufacturing of resin films 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 50 μm. When the resin film was wound around a roll, it was protected with a masking film ("FF1025" manufactured by Tredegar). When the Re, Rth and NZ coefficient of the resin film were measured, Re was 1.7 nm, Rth was 1.9 nm, and NZ coefficient was 1.6. The operating conditions of the film forming machine are as follows. Barrel temperature setting: 280℃~300℃ Die temperature = 270℃ Cast roll temperature = 80℃

[0106] (1-2) Process 1 Using the device shown in FIG. 1, step 1 was performed by the following method. The film 11 was pulled out from the roll 111 of the resin film obtained in (1-1), and the masking film 12 was continuously peeled off to transport the resin film 15. The resin film 15 was contacted with a solvent and stretched (step 1). Specifically, the resin film 15 was immersed in toluene by passing it through a bath 102 filled with toluene as a solvent. The time during which the resin film was transported through the solvent (solvent contact time) was 5 seconds. The room temperature at this time was 25° C., and therefore the temperature of the toluene in the bath 102 was also 25° C. The resin film 15 was stretched by providing a difference between the peripheral speed Ps1 of the nip rolls 101A and 101B on the upstream side and the peripheral speed Ps2 of the nip rolls 104A and 104B on the downstream side. Specifically, the peripheral speed ratio (Ps2 / Ps1) of the two pairs of nip rolls was set to 1.1, and the film was stretched in the conveying direction at a stretch ratio of 1.1. The stretched film 10 obtained after step 1 was wound up while being protected with a new masking film ("FF1025" manufactured by Tredegar) to obtain a stretched film roll 110. The Re, Rth, NZ coefficient, and thickness of the stretched film were measured, and the results were Re 56 nm, Rth -324 nm, NZ coefficient -5.29, and thickness 57 μm.

[0107] [Example 2] A roll of stretched film was obtained by the same operation as in (1-2) of Example 1, except that the peripheral speed ratio (Ps2 / Ps1) of the two pairs of nip rolls was set to 1.2, and the film was stretched in the conveying direction at a stretch ratio of 1.2 times. The stretched film was measured for Re, Rth, NZ coefficient, and thickness, and found to have an Re of 265 nm, an Rth of -295 nm, an NZ coefficient of -0.61, and a thickness of 56 μm.

[0108] [Example 3] A roll of stretched film was obtained by the same operation as in (1-2) of Example 1, except that the peripheral speed ratio (Ps2 / Ps1) of the two pairs of nip rolls was set to 1.5, and the film was stretched in the conveying direction at a stretch ratio of 1.5 times. The stretched film was measured for Re, Rth, NZ coefficient, and thickness, and found to have an Re of 650 nm, an Rth of 65 nm, an NZ coefficient of 0.6, and a thickness of 47 μm.

[0109] [Example 4] (4-1) Manufacturing of resin films A roll of resin film was obtained by the same operation as in Example 1 (1-1), except that in Example 1 (1-1), the line speed was adjusted to form the resin film to a thickness of 21 μm.

[0110] (4-2) Process 1 A roll of stretched film was obtained by the same procedure as in (1-2) of Example 1, except that the roll of resin film obtained in (1-1) was replaced with the roll of resin film obtained in (4-1), and the peripheral speed ratio (Ps2 / Ps1) of the two pairs of nip rolls was set to 1.5, so that the film was stretched at a stretch ratio of 1.5 in the conveying direction. The stretched film was measured for Re, Rth, NZ coefficient, and thickness, and found to have an Re of 275 nm, an Rth of 30 nm, an NZ coefficient of 0.61, and a thickness of 20 μm.

[0111] [Example 5] A roll of stretched film was obtained by the same procedure as in Example 1, except that in (1-2) of Example 1, the contact between the resin film and the solvent was carried out by the following coating method instead of passing the resin film through a bath filled with the solvent. The Re, Rth, NZ coefficient and thickness of the stretched film were measured, and the results were Re 62 nm, Rth -62 nm, NZ coefficient -0.5 and thickness 51 μm.

[0112] (Coating method) A coating device (reverse gravure type) was used instead of the bath 102, and toluene was applied to one side of the resin film by the coating device. The amount of the solvent applied was 30 g / m 2 (amount applied immediately after application).

[0113] [Comparative Example 1] The film was pulled out from the roll of the film obtained in (1-1) of Example 1, the masking film was peeled off from the film, and the resin film was transported. The resin film was passed through an oven heated to 110° C. for about 1 minute so as to be heated in the oven, whereby free longitudinal uniaxial stretching was performed at a stretching temperature of 110° C. This free longitudinal uniaxial stretching was performed by the following method using the roll stretching machine shown in FIG. 2.

[0114] The roll stretching machine 1 shown in Fig. 2 will be described. As shown in Fig. 2, the roll stretching machine 1 is a device for stretching a film 3 unwound from a film roll 2 in its longitudinal direction. The roll stretching machine 1 includes, in order from upstream in the transport direction, an upstream roll 6A and a downstream roll 6B as nip rolls capable of transporting the film 3 in the longitudinal direction. Here, the peripheral speed PsB of the downstream roll 6B is set to be faster than the peripheral speed PsA of the upstream roll 6A.

[0115] The resin film (corresponding to film 3 in FIG. 2) was stretched using the roll stretching machine 1 as follows. A film 3 was unwound from a film roll 2 and continuously supplied to a roll stretching machine 1. The roll stretching machine 1 transported the film 3 in the order of an upstream roll 6A and a downstream roll 6B. At this time, the ratio (PsB / PsA) of the peripheral speed PsB of the downstream roll 6B to the peripheral speed PsA of the upstream roll 6A was set to 1.5, so that the film 3 was stretched in the film transport direction (i.e., the longitudinal direction) at a stretching ratio of 1.5 times. Both ends of the stretched film in the width direction were trimmed by a trimming device (not shown) to obtain a long stretched film 4. This stretched film was wound up while being protected by a new masking film ("FF1025" manufactured by Tredegar Co., Ltd.) to obtain a roll 5 of stretched film. The Re, Rth, NZ coefficient, and thickness of the obtained stretched film were measured, and the results were Re of 75 nm, Rth of 38 nm, NZ coefficient of 1.01, and thickness of 40 μm.

[0116] Table 1 shows the resins constituting the resin films used in the examples and comparative examples, the thickness of the resin films, the conditions of contact with the solvent (type of solvent, contact method, contact time), the stretching ratio, and the physical properties of the stretched films (Re, Rth, NZ coefficient, thickness). For the comparative examples, the heating conditions (oven temperature) during stretching of the resin films are shown in Table 1. In Table 1, "crystalline COP" means a crystalline alicyclic structure-containing polymer. In Table 1, "immersion" means that the contact between the resin film and the solvent was performed by immersing the resin film in the solvent, and "coating" means that the contact between the resin film and the solvent was performed by coating the resin film with the solvent. In Table 1, "stretched film" means the resin film after stretching.

[0117] [Table 1]

[0118] As is clear from the results shown in Table 1, it is found that, according to the method of the embodiment, a film having retardation can be obtained even though the resin film is not heated during stretching. In other words, according to the production method of the present invention, since retardation can be exhibited without heating the resin film, a heating device for the resin film is not required, and the production equipment can be simplified.

[0119] [Other embodiments] (1) In the above embodiment and example, the resin film is uniaxially stretched in the film transport direction by the difference in peripheral speed between the nip rolls on the upstream side and downstream side of the transport direction, but the method of stretching the resin film (apparatus, stretching direction, etc.) is not limited to this. The stretching direction of the resin film may be an oblique direction or the film width direction. The stretching direction may be two or more directions, and in this case, the stretching in two or more directions may be performed simultaneously or sequentially. [Explanation of symbols]

[0120] 1...Roll stretching machine 2…Roll of resin film 3. Resin film 4... Stretched film 5…Roll of stretched film 6A…Upstream roll 6B…Downstream roll 10...Stretched film 11...Film (resin film with masking film attached) 12,13…Masking film 15...Resin film 100…device 101A, 101B...Upstream nip roll 102…Bathtub 104A, 104B... Downstream nip roll 110...Roll of stretched film 111...Roll of resin film 112,113…Rolls of masking film

Claims

1. A method for manufacturing a retardation film, comprising: a step 1 of stretching a resin film by bringing it into contact with a solvent, wherein the resin film is made of a resin containing a polymer having crystallinity, the step 1 includes a step 1A of bringing the resin film into contact with the solvent and orienting the molecules of the polymer having crystallinity in the thickness direction, and a step 1B of stretching the resin film, wherein the solvent is a hydrocarbon-based solvent or carbon disulfide, the polymer having crystallinity is polymer (α), polymer (β), polymer (γ), or polymer (δ), the polymer (α) is a ring-opening polymer of a cyclic olefin monomer and has crystallinity, the polymer (β) is a hydride of the polymer (α) and has crystallinity, the polymer (γ) is an addition polymer of a cyclic olefin monomer and has crystallinity, the polymer (δ) is a hydride of the polymer (γ) and has crystallinity, the Nz coefficient of the retardation film is 0.61 or less, the value of the in-plane retardation Re of the retardation film is 30 nm or more, A method for manufacturing a retardation film.

2. The method for manufacturing a retardation film according to claim 1, wherein the solvent is a hydrocarbon-based solvent.

3. The method for manufacturing a retardation film according to claim 2, wherein the hydrocarbon-based solvent is toluene, limonene, decalin, or a mixture thereof.

4. The method for manufacturing a retardation film according to any one of claims 1 to 3, wherein the solvent is a solvent that can penetrate into the resin film without dissolving the resin.

5. The method for manufacturing a retardation film according to any one of claims 1 to 4, wherein the contact between the resin film and the solvent is performed by immersing the resin film in the solvent.

6. The method for manufacturing a retardation film according to any one of claims 1 to 5, wherein the resin film is made of a resin having a positive specific birefringence value.

7. The method for manufacturing a retardation film according to any one of claims 1 to 6, wherein the polymer having crystallinity is a hydride of a ring-opening polymer of dicyclopentadiene.

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