Method for manufacturing phase difference film

Abstract

The present invention provides a method for producing a retardation film having excellent appearance and excellent phase difference expression. The method for producing a retardation film of the present invention comprises a first step of heating a resin film to obtain an interlayer film and a second step of stretching the interlayer film.

Description

Technical Field

[0001] The present invention relates to a method for producing a phase difference film. Background Art

[0002] In recent years, image display devices with a retardation film positioned on the visual confirmation side have become widely used. The production of such retardation films typically involves extruding or coating a resin to form a resin film, and then stretching the resulting resin film to obtain the retardation film. However, existing methods for producing retardation films have problems such as poor appearance and insufficient phase difference visualization.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 3325560 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a method for producing a retardation film having excellent appearance and phase difference expression properties.

[0008] Means used to solve problems

[0009] The method for producing a retardation film of the present invention comprises a first step of heating a resin film to obtain an interlayer film, and a second step of subjecting the interlayer film to a stretching treatment.

[0010] In one embodiment, a step of winding up the intermediate film is further included between the first step and the second step.

[0011] In one embodiment, the heating temperature in the first step is (Tg+25° C.) / 2 or higher.

[0012] In one embodiment, the heating temperature in the first step is equal to or higher than Tg, and an increase in Re(550) of the intermediate film relative to that of the resin film before heating is equal to or less than 10 nm.

[0013] In one embodiment, the heating time in the first step is 10 seconds to 180 seconds.

[0014] In one embodiment, the heating time in the first step is 30 seconds to 120 seconds.

[0015] In one embodiment, the heating temperature in the first step is higher than the stretching temperature in the second step.

[0016] In one embodiment, a step of adhering a shrinkable film to form a laminate is included between the first step and the second step.

[0017] In another embodiment, before the above-mentioned first step, the step of bonding the above-mentioned resin film and a shrinkable film to form a laminated body is included, or the step of applying a coating liquid obtained by dissolving or dispersing the resin in a solvent to the shrinkable film is included, wherein the increase in Re (550) of the above-mentioned intermediate film relative to the above-mentioned resin film before heating is less than 10 nm.

[0018] Effects of the Invention

[0019] According to an embodiment of the present invention, a method for producing a retardation film includes a first step of heating a resin film to obtain an interlayer film and a second step of stretching the interlayer film, thereby achieving a retardation film having excellent appearance and retardation expression properties. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0021] (Definition of terms and symbols)

[0022] The definitions of terms and symbols in this specification are as follows.

[0023] (1) Refractive index (nx, ny, nz)

[0024] “nx” is the refractive index in the direction where the refractive index in the plane is maximum (ie, the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis in the plane (ie, the fast axis direction), and “nz” is the refractive index in the thickness direction.

[0025] (2) In-plane retardation (Re)

[0026] "Re(λ)" is the in-plane retardation measured with light of a wavelength of λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light of a wavelength of 550 nm at 23°C. Re(λ) is calculated using the formula: Re(λ) = (nx - ny) × d, assuming the thickness of the layer (film) is d (nm).

[0027] (3) Retardation in the thickness direction (Rth)

[0028] "Rth(λ)" is the retardation in the thickness direction measured with light of a wavelength of λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of a wavelength of 550 nm at 23°C. Rth(λ) is calculated using the formula: Rth(λ) = (nx - nz) × d, assuming the thickness of the layer (film) is d (nm).

[0029] (4) Nz coefficient

[0030] The Nz coefficient is obtained by Nz=Rth / Re.

[0031] A. Method for manufacturing phase difference film

[0032] The method for producing a retardation film in the present invention includes a step of preparing a resin film, a step of heating the resin film to obtain an interlayer film (a first step), and a step of stretching the interlayer film (a second step).

[0033] The method for producing a retardation film may further include a step of winding up the intermediate film between the first step and the second step, as needed.

[0034] In one embodiment, the method for manufacturing a phase difference film may further include a step of laminating an intermediate film and a shrinkable film between the first step and the second step. In another embodiment, with respect to the method for manufacturing a phase difference film, a resin film and a shrinkable film may be bonded to form a laminate, and then the laminate is heated to obtain an intermediate film. In yet another embodiment, with respect to the method for manufacturing a phase difference film, a coating liquid obtained by dissolving or dispersing a resin in a solvent may be applied to a shrinkable film to form a laminate, and then the laminate is heated to obtain an intermediate film. Below, each step of the method for manufacturing a phase difference film is described in detail.

[0035] B. Resin film production process

[0036] The resin film can be formed from any appropriate resin. Examples of the resin forming the resin film include polycarbonate resins, cyclic olefin resins, cellulose resins, polyester resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, acrylic resins, and polyester carbonate resins. Among these, polycarbonate resins and cyclic olefin resins are preferably used.

[0037] As a polycarbonate resin, any appropriate polycarbonate resin can be used as long as the effect of the present invention can be obtained. Preferably, the polycarbonate resin comprises a structural unit derived from an isosorbide-based dihydroxy compound and a structural unit derived from at least one dihydroxy compound selected from alicyclic diols, alicyclic dimethanol, diethylene glycol, triethylene glycol or polyethylene glycol and an alkylene glycol or spiro glycol. More preferably, the polycarbonate resin comprises a structural unit derived from an isosorbide-based dihydroxy compound and a structural unit derived from alicyclic dimethanol and / or a structural unit derived from diethylene glycol, triethylene glycol or polyethylene glycol. As needed, the polycarbonate resin may also include a structural unit derived from other dihydroxy compounds. In addition, the details of the method for manufacturing the polycarbonate resin and phase difference film applicable to the present invention are, for example, recorded in International Publication Gazette No. 2011 / 062239, and the contents of the description are incorporated herein by reference.

[0038] Cyclic olefin resins are a general term for resins that are polymerized using cyclic olefins as polymerization units. Examples include the resins described in Japanese Patent Application Laid-Open No. 1-240517, Japanese Patent Application Laid-Open No. 3-14882, and Japanese Patent Application Laid-Open No. 3-122137. Specific examples include: ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins with α-olefins such as ethylene and propylene (representatively random copolymers), and grafted modified products modified with unsaturated carboxylic acids and their derivatives, as well as hydrogenated products thereof. Specific examples of cyclic olefins include norbornene monomers. Examples of norbornene monomers include monomers described in Japanese Patent Application Laid-Open No. 2015-210459, etc. Various products of the above-mentioned cyclic olefin resins are commercially available. Specific examples include "ZEONEX" and "ZEONOR" manufactured by Zeon Corporation of Japan, "Arton" manufactured by JSR Corporation, "TOPAS" manufactured by TICONA Corporation, and "APEL" manufactured by Mitsui Chemicals, Inc.

[0039] As a method for forming the resin film, any appropriate method can be adopted. For example, melt extrusion (e.g., T-die molding), casting and coating (e.g., tape casting), calendaring, hot pressing, co-extrusion, co-melting, multi-layer extrusion, inflation molding, etc. are mentioned. T-die molding, tape casting, and inflation molding are preferably used.

[0040] The thickness of the resin film can be set to any appropriate value depending on desired optical properties, stretching conditions described below, etc. It is preferably 30 μm to 300 μm, and more preferably 40 μm to 250 μm.

[0041] C. Step of heating the resin film to obtain an interlayer film (first step)

[0042] An interlayer film can be obtained by heating the resin film obtained in B. According to an embodiment of the present invention, heating the resin film under predetermined conditions as a separate step (i.e., preheating other than stretching) before stretching can provide a retardation film having excellent appearance and phase difference expression properties.

[0043] The heating temperature of the resin film in this step is preferably at least (Tg + 25°C) / 2, more preferably at least Tg. When the heating temperature is within this range, an interlayer film having the desired orientation state and / or Re(550) can be obtained. In one embodiment, the heating temperature in the first step is higher than the stretching temperature of the interlayer film.

[0044] The heating time of the resin film is preferably 10 to 180 seconds, more preferably 30 to 120 seconds. When the heating time is within this range, an interlayer film having a desired orientation state and / or Re(550) can be obtained.

[0045] The Re(550) of the interlayer film obtained by this process is preferably 0 nm to 30 nm, more preferably 0 nm to 20 nm, and even more preferably 0 nm to 10 nm. According to the present invention, an interlayer film having such a Re(550) can be obtained by heating the resin film under the above-described heating conditions. If the heating temperature is above Tg, the Re(550) can be further reduced.

[0046] The increase in Re(550) of the interlayer film in this step relative to the pre-heated resin film is preferably 10 nm or less, more preferably 5 nm or less, and even more preferably 3 nm or less. The smaller the increase in Re(550) of the interlayer film, the better, and its lower limit is preferably substantially 0 nm. According to the present invention, by heating the resin film under the above-described heating conditions, the increase in Re(550) before and after heating can be reduced. If the heating temperature is above Tg, the increase in Re(550) can be further reduced.

[0047] This process is preferably performed under tension-free conditions and low wind speed. Examples of tension-free processes include lining the resin film with a protective film and transporting it using a tenter or belt conveyor. Examples of low wind speed processes include using an IR heater. This is to prevent the resin film from being blown by the airflow generated by the fan.

[0048] D. Intermediate film winding process

[0049] If necessary, the interlayer film obtained in step C. is wound onto an axis perpendicular to the conveying direction to form a roll. This roll may be directly subjected to the stretching step or stored for a predetermined period of time. When the roll is stored, the storage period is preferably 12 to 96 hours, more preferably 24 to 48 hours.

[0050] E. Intermediate Film Stretching Step (Second Step)

[0051] In one embodiment, the retardation film is produced by uniaxially stretching or fixed-end uniaxially stretching the interlayer. A specific example of fixed-end uniaxial stretching is a method in which the interlayer is stretched in the width direction (transverse direction) while being moved in the longitudinal direction. The stretching ratio is preferably 1.1 to 3.5 times, more preferably 1.3 to 2.0 times.

[0052] The stretching temperature of the interlayer film is preferably Tg-30°C to Tg+30°C, more preferably Tg-20°C to Tg+20°C, and even more preferably Tg-15°C to Tg+15°C. Stretching at such a temperature yields a retardation film having suitable properties for the present invention. Tg is the glass transition temperature of the film's constituent material.

[0053] In this step, by stretching the interlayer film heated in the above C., a so-called positive A plate (nx>ny=nz) or a negative B plate (nx>ny>nz) can be obtained.

[0054] In another embodiment, the retardation film is produced by continuously stretching the intermediate film obliquely along a direction at an angle θ relative to the longitudinal direction. Examples of stretching machines used for oblique stretching include tenter-type stretching machines that can apply feed forces, stretching forces, or pulling forces at different speeds in the transverse and / or longitudinal directions. Examples of tenter-type stretching machines include transverse uniaxial stretching machines and simultaneous biaxial stretching machines. Any suitable stretching machine can be used as long as it can continuously stretch the intermediate film obliquely.

[0055] F. Embodiment using shrink film

[0056] F-1. Embodiment using shrink film after the first step

[0057] In one embodiment, between step C. (first step) and step E. (second step), a step of bonding the interlayer film and the shrinkable film to form a laminate is included. This bonding of the interlayer film and the shrinkable film can be performed before or after the interlayer film is wound up in step D. By bonding the interlayer film and the shrinkable film and stretching the resulting laminate, a retardation film having a refractive index characteristic of nx>nz>ny can be obtained.

[0058] The shrinkage ratio of the shrinkable film in the direction perpendicular to the stretching direction in the intermediate film stretching step (second step) is preferably in the range of 0.50 to 0.99 times, more preferably 0.60 to 0.98 times, and even more preferably 0.75 to 0.95 times.

[0059] As the forming material of the above-mentioned shrinkable film, there is no particular limitation, but from the perspective of being suitable for stretching treatment, thermoplastic resins are preferred. Specifically, for example, acrylic resins and polyolefin resins such as polyethylene and polypropylene (PP), polyester resins such as polyethylene terephthalate (PET), polyamides, polycarbonate resins, norbornene resins, polystyrene, polyvinyl chloride, polyvinylidene chloride, cellulose resins such as triacetyl cellulose, polyether sulfone, polysulfone, polyimide, polyacrylic acid, acetate resin, polyarylate, polyvinyl alcohol and mixtures thereof can be listed. In addition, liquid crystal polymers etc. can also be used. The shrinkable film is preferably a uniaxial or biaxial stretched film formed by one or more of the above-mentioned forming materials. For example, commercially available products can also be used for the shrinkable film. Examples of commercially available products include “Spaceclean” manufactured by Toyobo Co., Ltd., “Fancy Wrap” manufactured by Gunze Co., Ltd., “Torayfan” manufactured by Toray Industries, Ltd., “Lumirror” manufactured by Toray Industries, Ltd., “Arton” manufactured by JSR Corporation, “ZEONOR” manufactured by Nippon Zeon Co., Ltd., and “Suntec” manufactured by Asahi Kasei Corporation.

[0060] The thickness of the shrinkable film is not particularly limited, but is, for example, in the range of 10 μm to 300 μm, preferably in the range of 20 μm to 200 μm, and more preferably in the range of 40 μm to 150 μm. The surface of the shrinkable film may be subjected to a surface treatment, for example, to improve adhesion to the interlayer film. Examples of surface treatments include chemical or physical treatments such as chromic acid treatment, ozone exposure, flame exposure, high-voltage electric shock exposure, and ionizing radiation treatment. Furthermore, a primer layer may be formed by applying a primer (e.g., an adhesive) to the surface of the shrinkable film.

[0061] There are no particular restrictions on the method for laminating the shrinkable film to one side or both sides of the intermediate film. However, a method in which an acrylic adhesive layer having a (meth)acrylic polymer as a base polymer is provided between the intermediate film and the shrinkable film for bonding is preferred from the perspective of excellent workability and economic efficiency.

[0062] By laminating the interlayer obtained by heating in step C. above with the shrinkable film in step F. above, and stretching the resulting laminate as described in step E. above, a retardation film having a refractive index characteristic of nx>nz>ny can be obtained. The Nz coefficient of the obtained retardation film is preferably 0.3 to 0.9, and more preferably 0.4 to 0.8.

[0063] F-2. Embodiment using shrink film before the first step

[0064] F-2-1. Step of laminating resin film and shrinkable film

[0065] In another embodiment, a resin film and a shrinkable film may be bonded together to form a laminate, and the laminate may then be heated to obtain an intermediate film. Details of the shrinkable film are as described in F-1. above. The step of bonding the resin film and the shrinkable film to form a laminate may be performed using the same method as described in F-1. above.

[0066] F-2-2. Step of applying resin solution to shrinkable film

[0067] In another embodiment, a coating liquid obtained by dissolving or dispersing any appropriate resin in a solvent may be applied to a shrinkable film to form a laminate, and then the laminate may be heated to obtain an intermediate film. The details of the shrinkable film are as described in F-1. above.

[0068] Example

[0069] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. In addition, the measuring methods of various properties are as follows.

[0070] (1) Appearance

[0071] The retardation films obtained in the Examples and Comparative Examples described below were visually evaluated for appearance. Evaluation criteria included: absence of wrinkles and unevenness in reflection and transmission; and absence of wrinkles and unevenness when viewed from the front and oblique directions between crossed polarizers. The evaluation criteria were set on a scale of 1 to 5.

[0072] 1: No wrinkles or unevenness in reflection, transmission, or polarizing plate evaluation.

[0073] 2: No wrinkles or unevenness in the reflection and transmission evaluations, but slight wrinkles and unevenness were observed in the polarizing plate evaluation.

[0074] 3: There were no wrinkles or unevenness in the reflection and transmission evaluations, but there were strong wrinkles and unevenness in the polarizing plate evaluation.

[0075] 4: Slight wrinkles and unevenness were observed in the reflection and transmission evaluations.

[0076] 5: There are strong wrinkles and unevenness in the reflection and transmission evaluations.

[0077] (2) Phase difference Re(550) and Nz coefficient

[0078] 50 mm x 50 mm samples were cut from the retardation films obtained in the Examples and Comparative Examples described below. The in-plane retardation Re(550) was measured using an Axoscan manufactured by Axometrics. The measurement temperature was 23°C. Furthermore, the thickness-direction retardation Rth(550) was measured, and the Nz coefficient was calculated.

[0079] Hereinafter, an example of producing a resin film will be described.

[0080] [Production Example 1]

[0081] 47.19 parts by mass of tricyclodecane dimethanol (hereinafter sometimes abbreviated as "TCDDM"), 175.1 parts by mass of diphenyl carbonate (hereinafter sometimes abbreviated as "DPC"), and 0.979 parts by mass of a 0.2% by mass aqueous solution of cesium carbonate as a catalyst were placed in a reaction vessel relative to 81.98 parts by mass of isosorbide (hereinafter sometimes abbreviated as "ISB"). Under a nitrogen atmosphere, as the first step of the reaction, the heating tank temperature was heated to 150°C and the raw materials were dissolved while stirring as needed (approximately 15 minutes). Next, the pressure was set from atmospheric pressure to 13.3 kPa, and the heating tank temperature was raised to 190°C over 1 hour while the generated phenol was extracted from the reaction vessel. The entire reaction vessel was maintained at 190°C for 15 minutes, and then as the second step, the pressure in the reaction vessel was set to 6.67 kPa, and the heating tank temperature was raised to 230°C over 15 minutes, and the generated phenol was extracted from the reaction vessel. As the stirring torque of the stirrer gradually increased, the temperature was raised to 250°C in 8 minutes, and the pressure in the reaction container was reduced to 0.200 kPa or less in order to remove the generated phenol. After reaching the specified stirring torque, the reaction was terminated and the generated reactant was extruded into water, thereby obtaining polycarbonate resin pellets. The obtained polycarbonate resin was vacuum dried at 80°C for 5 hours, and then a polycarbonate resin film (1) with a thickness of 90 μm was produced using a film forming apparatus equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-die (width 300 mm, set temperature: 250°C), a cooling roller (set temperature: 120-130°C) and a winder. Tg was 130°C.

[0082] [Production Example 2]

[0083] The polymerization was carried out using a batch polymerization apparatus comprising two vertical reactors equipped with stirring blades and a reflux cooler controlled at 100° C. 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), 42.28 parts by mass (0.139 mol) of spiroglycol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19×10 mol of calcium acetate monohydrate as a catalyst were charged. -2 Mass parts (6.78×10 -5 mol). The reactor was purged with nitrogen and then heated with a heat medium. Stirring began when the internal temperature reached 100°C. Forty minutes after the start of the temperature increase, the internal temperature reached 220°C and was maintained at this temperature. Simultaneously, the pressure was reduced to 13.3 kPa over 90 minutes after reaching 220°C. Phenol vapor, a by-product of the polymerization reaction, was introduced into a 100°C reflux cooler. A small amount of monomer contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was recovered by introducing it into a 45°C condenser. Nitrogen was introduced into the first reactor to temporarily return it to atmospheric pressure, and the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature and pressure in the second reactor were increased and reduced, reaching an internal temperature of 240°C and a pressure of 0.2 kPa over 50 minutes. Polymerization was then continued until the specified stirring power was achieved. Once the specified power was achieved, nitrogen was introduced into the reactor to restore the pressure. The produced polyester carbonate resin was extruded into water, and the strands were cut to obtain pellets.

[0084] The obtained polyester carbonate resin (pellets) was vacuum dried at 80°C for 5 hours, and then a film forming apparatus equipped with a single screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder setting temperature: 250°C), a T die (width 200 mm, setting temperature: 250°C), a cooling roll (setting temperature: 120-130°C), and a winder was used to produce a 130 μm thick long reverse dispersion polycarbonate resin film (2). Tg was 140°C.

[0085] [Production Example 3]

[0086] As the resin film (3), a commercially available cyclic olefin resin film (manufactured by Zeon Corporation of Japan, trade name "ZEONOR ZF14") was used. The film had a thickness of 40 μm and a Tg of 136°C.

[0087] [Production Example 4]

[0088] As the resin film (4), a commercially available cyclic olefin resin film (manufactured by JSR Corporation, trade name "Arton (R5000)") was used. The thickness was 130 μm and the Tg was 137°C.

[0089] [Example 1]

[0090] 1. Step of heating the resin film to obtain an interlayer film (first step)

[0091] The polycarbonate resin film (1) obtained in Production Example 1 was heated at 110°C for 60 seconds using a tenter and an IR heater to obtain an interlayer film. The obtained interlayer film was subjected to the evaluation described in (2). The Re(550) value of the heated interlayer film was 1 nm, and the increase in Re(550) was 0 nm.

[0092] 2. Intermediate film winding process

[0093] The interlayer film obtained in the above 1. was wound up along an axis perpendicular to the conveying direction to form a roll, and the roll was stored for 48 hours.

[0094] 3. Intermediate film stretching process (second process)

[0095] The intermediate film wound up in 2. above was subjected to uniaxial stretching to obtain a retardation film. The stretching temperature was set to 145°C and the stretching ratio was set to 1.5 times. The obtained retardation film was subjected to the evaluations of (1) and (2) above. The results are shown in Table 1.

[0096] [Examples 2 to 8 and 17 to 30 and Comparative Examples 2 to 4 and 9 to 10]

[0097] A retardation film was produced in the same manner as in Example 1, except that the resin films numbered (1) to (4) listed in Table 1 were used and the heating conditions for the first step and the stretching conditions for the second step described in Table 1 were adopted. The obtained retardation film was subjected to the evaluations (1) and (2) above. The results are shown in Table 1.

[0098] [Examples 9 to 16 and 31 to 44 and Comparative Examples 5 to 8 and 11 to 12]

[0099] A 60 μm thick shrinkable film (manufactured by Toray Industries, Ltd., trade name "Torayfan BO2873") was laminated to one side of the interlayer film wound up in step 3 above via an acrylic adhesive layer (15 μm thick). A retardation film was produced in the same manner as in Example 1, except that the interlayer film and the shrinkable film were laminated, the resin films numbered (1) to (4) listed in Table 1 were used, and the heating conditions for the first step and the stretching conditions for the second step listed in Table 1 were employed.

[0100] Table 1

[0101]

[0102] <Evaluation>

[0103] The retardation film subjected to the first heating step was found to have superior appearance and retardation performance compared to the retardation film not subjected to the first heating step (comparison of Examples 1-2 with Comparative Example 1, Examples 3-4 with Comparative Example 2, Examples 5-6 with Comparative Example 3, Examples 7-8 with Comparative Example 4, and Examples 17-23 with Comparative Example 9, and Examples 24-30 with Comparative Example 10). Furthermore, similar results were found when the lamination step with a shrinkable film was performed (comparison of Examples 9-10 with Comparative Example 5, Examples 11-12 with Comparative Example 6, Examples 13-14 with Comparative Example 7, Examples 15-16 with Comparative Example 8, and Examples 31-37 with Comparative Example 11, and Examples 38-44 with Comparative Example 12).

[0104] Furthermore, it was found that even when the heating temperature in the first step was below the Tg of the resin film, excellent appearance and phase difference display properties could be obtained by setting the heating time to 30 seconds or longer (Examples 19, 26, 33, and 40). Furthermore, it was found that when the heating temperature in the first step was above the Tg of the resin film, excellent appearance and phase difference display properties could be obtained by setting the heating time to 10 seconds or longer (Examples 23, 30, 37, and 44).

[0105] Industrial applicability

[0106] The retardation film according to the embodiment of the present invention can be suitably used in an image display device.

Claims

1. A method for producing a phase difference film, comprising a step of preparing a resin film, a first step of heating the resin film to obtain an intermediate film, and a second step of stretching the intermediate film. The increase in Re(550) of the intermediate film relative to the resin film before heating is 0 nm or more and 10 nm or less, wherein Re(550) is the in-plane phase difference measured with light of 550 nm wavelength at 23°C. A step of winding up the intermediate film is included between the first step and the second step.

2. The method for producing a phase difference film according to claim 1, wherein: The heating temperature in the first step is (Tg+25°C) / 2 or higher.

3. The method for producing a phase difference film according to claim 2, wherein: The heating temperature in the first step is equal to or higher than Tg.

4. The method for producing a phase difference film according to claim 2, wherein: The heating time of the first step is 10 seconds to 180 seconds.

5. The method for producing a phase difference film according to claim 4, wherein: The heating time of the first step is 30 seconds to 120 seconds.

6. The method for producing a phase difference film according to claim 2, wherein: The heating temperature in the first step is higher than the stretching temperature in the second step. 7 . The method for producing a retardation film according to claim 1 , further comprising, between the first step and the second step, a step of adhering a shrinkable film to form a laminate.

8. The method for producing a retardation film according to any one of claims 1 to 6, wherein The resin film production step includes a step of bonding the resin film and a shrinkable film to form a laminate before the first step, or a step of applying a coating liquid obtained by dissolving or dispersing a resin in a solvent to the shrinkable film.

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