Method for manufacturing phase difference films

Abstract

To provide a simple method for manufacturing a phase difference film that exhibits refractive index characteristics nx>nz>ny and suppresses appearance defects. [Solution] The method for manufacturing a phase difference film according to an embodiment of the present invention is a method for manufacturing a phase difference film in which the refractive index characteristics are in the relationship nx>nz>ny. This manufacturing method includes, in this order, a corona treatment step of applying corona treatment to at least one surface of an unstretched polymer film, a shrinkable film application step of attaching a shrinkable film to the corona-treated surface of the polymer film to obtain a laminate, and a stretching step of stretching the laminate. The discharge amount of the corona treatment is 20 W·min / m 2 That's all.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a phase difference film. [Background technology]

[0002] Image display devices (e.g., liquid crystal displays, organic EL displays, quantum dot displays) often have a polarizing plate on at least one side of the image display cell, depending on their image formation method. Furthermore, a phase difference film may be laminated on the image display cell side of the polarizing plate located on the viewing side of the image display device for purposes such as preventing external light reflection, background reflection, and hue improvement. As a phase difference film, a so-called Z film exhibiting refractive index characteristics nx>nz>ny is known (e.g., Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-091743 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, Z-films are difficult to manufacture because they require an increased refractive index in the thickness direction, and the resulting Z-films may have appearance defects.

[0005] The main objective of the present invention is to provide a simple method for manufacturing a phase difference film that exhibits refractive index characteristics nx>nz>ny and suppresses appearance defects. [Means for solving the problem]

[0006] [1] A method for producing a retardation film according to an embodiment of the present invention is a method for producing a retardation film having refractive index characteristics satisfying the relationship nx>nz>ny. The production method includes, in this order: a corona treatment step of performing corona treatment on at least one surface of an unstretched polymer film; a shrinkable film attaching step of attaching a shrinkable film to the corona-treated surface of the polymer film to obtain a laminate; and a stretching step of stretching the laminate. The discharge amount of the corona treatment is 20 W·min / m 2 or more. [2] In the production method according to [1] above, the corona treatment step includes performing corona treatment on both surfaces of an unstretched polymer film. [3] In the production method according to [1] or [2] above, the method includes heating the laminate after attaching the shrinkable film in the attaching step. [4] In the production method according to any one of [1] to [3] above, the thickness of the unstretched polymer film is 20 µm or more and 110 µm or less. [5] In the production method according to any one of [1] to [4] above, the birefringence Δn of the obtained retardation film is larger than 0.0025. [6] In the production method according to [5] above, the breaking force B in the stretching direction of the obtained retardation film M (N) and the breaking force B in the direction orthogonal to the stretching direction T (N), the ratio B M / B T is 1.300 or more.

Effects of the Invention

[0007] According to an embodiment of the present invention, a simple production method for a retardation film that exhibits refractive index characteristics of nx>nz>ny and has suppressed appearance defects can be provided.

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0009] (Definition of Terms and Symbols) The definitions of terms and symbols used in this specification are as follows: (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the refractive index in the plane is maximum (i.e., the direction of the slow axis). "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the direction of the fast axis), and "n "z" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference of the film measured with light of wavelength λnm at 23℃. Yes, there is. For example, "Re(550)" is measured using light with a wavelength of 550 nm at 23°C. This is the in-plane phase difference of the film. Re(λ) is given by the formula, where d(nm) is the thickness of the film. :Re can be calculated using the formula Re = (nx - ny) × d. (3) Phase difference in the thickness direction (Rth) "Rth(λ)" is the thickness direction of the film measured with light of wavelength λnm at 23℃. It is the phase difference. For example, "Rth(550)" is the phase difference of light with a wavelength of 550 nm at 23°C. This is the phase difference in the thickness direction of the measured film. Rth(λ) is the film thickness d(n When m is given, it can be found by the formula: Rth = (nx - nz) × d. (4)Angle In this specification, when angles are mentioned, unless otherwise specified, those angles are clockwise. It encompasses angles in both clockwise and counterclockwise directions. Therefore, for example, "45°" is ±45 ° includes

[0010] A. Overview of the manufacturing method for phase difference film The method for manufacturing a phase difference film according to an embodiment of the present invention is a method for manufacturing a phase difference film (hereinafter sometimes referred to as a Z film) whose refractive index characteristics are in the relationship nx>nz>ny. The manufacturing method includes, in this order, a step of applying corona treatment to at least one surface of an unstretched polymer film (corona treatment step), a step of attaching a shrinkable film to the corona-treated surface of the polymer film to obtain a laminate (shrinkable film attachment step), and a step of stretching the laminate (stretching step). In the embodiment of the present invention, the discharge amount for corona treatment is 20 W·min / m 2 That's all.

[0011] The inventors of this invention diligently investigated defects in the appearance of Z films and found that in the production of Z films with a large birefringence Δn (=nx-ny), minute folds that are visible as streaks in the stretching direction are prone to occur. Furthermore, the inventors found that such minute folds may be caused by insufficient adhesion between the base film (unstretched polymer film) and the shrinkable film used to increase the refractive index in the thickness direction. After trial and error in improving the adhesion between the base film and the shrinkable film, the inventors found that corona treatment of the base film with a discharge amount above a predetermined value is optimal, leading to the completion of the present invention. It should be noted that in the production of Z films with a small birefringence Δn, such minute folds do not occur in most cases.

[0012] B. Details of the manufacturing method for phase difference film Each step of the method for manufacturing a phase difference film according to an embodiment of the present invention will be described.

[0013] B-1.Preparation process First, a raw material film is prepared. Typically, the raw material film is an unstretched polymer film. Any suitable resin film can be used as the polymer film. The glass transition temperature (Tg) of the resin film can be any suitable temperature. The Tg of the resin film may be, for example, 135°C or higher, preferably 140°C or higher, more preferably 145°C or higher, and even more preferably 150°C or higher. The upper limit of the Tg of the resin film may be, for example, 200°C. When the Tg of the resin film (essentially a polymer film) is within this range, it is easy to adjust the temperature during stretching (stretching temperature) to a temperature near the Tg. Examples of resins that make up the resin film include cyclic polyolefin resins, polycarbonate resins, polyarylate, polyamide, polyimide, polyester, polyaryletherketone, polyamideimide, polyesterimide, polyvinyl alcohol, polyfumarate ester, polyethersulfone, polysulfone, polycarbonate resin, cellulose resin, and polyurethane. These resins may be used individually or in combination. Details of the resin constituting the polymer film are described, for example, in Japanese Patent Application Publication No. 2014-010291. This description may be incorporated herein by reference. The polymer film is preferably composed of a cyclic olefin resin. A typical example of a cyclic olefin resin is norbornene resin.

[0014] Cyclic olefin resins are resins polymerized using norbornene monomers as polymerization units. Examples of cyclic olefin resins include those described in Japanese Patent Publication No. 1-240517, Japanese Patent Publication No. 3-14882, and Japanese Patent Publication No. 3-122137. Specific examples of cyclic olefin resins 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 (typically random copolymers), graft-modified products obtained by modifying these with unsaturated carboxylic acids and their derivatives, and their hydrides. Specific examples of cyclic olefins include norbornene monomers. Examples of norbornene monomers include those described in Japanese Patent Publication No. 2015-210459, etc.Examples of norbornene monomers include norbornene and its alkyl and / or alkylidene substituted derivatives, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, etc., and their halogen and other polar group substituted derivatives; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc. Tanooctahydronaphthalene, its alkyl and / or alkylidene substituted derivatives, and polar group substituted derivatives such as halogens, e.g., 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7 ,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano Examples include tano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, and tripers and tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentanthracene. The above norbornene-based resin may also be a copolymer of norbornene-based monomers and other monomers. The birefringence Δn of the polymer film can be adjusted by adjusting the copolymerization ratio of norbornene-based monomers. By using a polymer film (raw film) with a large birefringence Δn, a Z film with a desired in-plane phase difference Re(550) can be produced at a thinner thickness. A stretched film with good optical uniformity and small variation in phase difference values ​​can be produced. Various cyclic olefin resins are commercially available. Specific examples include "Zeonex" and "Zeonor" from Nippon Zeon Corporation, "Arton" from JSR Corporation, "Topas" from TICONA Corporation, and "APEL" from Mitsui Chemicals Corporation.

[0015] The thickness of the unstretched polymer film can be set to any appropriate value depending on the desired optical properties, the stretching conditions described later, etc. The thickness of the polymer film may preferably be 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more. On the other hand, the thickness of the polymer film may preferably be 110 μm or less, more preferably 105 μm or less, and even more preferably 100 μm or less. Within this range, it is easy to obtain a thin Z film having the desired in-plane phase difference Re(550).

[0016] An unstretched polymer film may have a surface protection film temporarily attached to one or both sides. The surface protection film can be peeled off from the polymer film before corona treatment.

[0017] B-2. Corona treatment process Corona treatment can typically be applied to the surface of a polymer film using a corona treatment device. The corona treatment involves a discharge rate (electron irradiation amount due to corona discharge) of 20 W·min / m². 2Any appropriate apparatus can be used as long as the above requirements are satisfied. For example, when a surface protective film is attached to a polymer film, corona treatment can be performed on the surface of the polymer film (the peeled surface of the surface protective film) after peeling off the surface protective film. By performing corona treatment on an unstretched polymer film, the corona-treated surface of the polymer film can be modified. As a result, the adhesion between the polymer film and the shrinkable film can be satisfactorily improved. Corona treatment may be performed on one side or both sides of an unstretched polymer film, and is preferably performed on both sides of an unstretched polymer film. By performing corona treatment on both sides of the polymer film, the adhesion of both sides to the shrinkable film can be improved, so that even after stretching, better conformability to the shrinkable film in the direction perpendicular to the stretching direction and good shrinkage properties can be achieved. As a result, nz can be satisfactorily increased while suppressing poor appearance.

[0018] As described above, the discharge amount of corona treatment is typically 20 W·min / m 2 or more, for example 30 W·min / m 2 or more, or for example 40 W·min / m 2 or more, or for example 50 W·min / m 2 or more, or for example 60 W·min / m 2 or more. The upper limit of the discharge amount for corona treatment is not particularly limited, and is, for example, 300 W·min / m 2 .

[0019] B-3. Step of attaching shrinkable film Next, a shrinkable film is attached to the corona-treated surface of the polymer film to obtain a laminate. The shrinkable film can be used to increase nz by applying a shrinking force in a direction perpendicular to the stretching direction during stretching. The shrinkable film can have any appropriate shrinkage rate (dimensional change rate). The dimensional change rate of the shrinkable film before attachment (e.g., the shrinkable film alone) is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. On the other hand, the dimensional change rate of the shrinkable film before stretching is preferably 60% or less, more preferably 50% or less, and even more preferably 45% or less. The shrinkage rate of the shrinkable film after attachment (e.g., as a laminate) is preferably 20% or more, more preferably 25% or more. On the other hand, the shrinkage rate of the shrinkable film after attachment is preferably 40% or less, more preferably 35% or less. When the dimensional change rate of the shrinkable film is within this range, the shrinkage uniformity can be further improved. As a result, a Z film with good optical uniformity can be produced. The dimensional change rate of the shrinkable film and / or laminate is the dimensional change rate in the longitudinal direction at 150°C, and is measured in accordance with JIS K7133:1999.

[0020] Examples of materials used for shrinkable films include polypropylene, polyester, polystyrene, polyvinyl chloride, and polyvinylidene chloride. The shrinkable film is preferably made of polypropylene. When the shrinkable film is made of polypropylene, it exhibits particularly excellent shrinkage uniformity and heat resistance. In one embodiment, shrinkable films may be laminated to both sides of a polymer film.

[0021] In one embodiment, the process preferably involves attaching a shrinkable film to the corona-treated surface of a polymer film, followed by heating the laminate. More preferably, the heating (heat treatment) of the laminate is performed after attaching the shrinkable film and before the stretching process. By heat-treating the laminate after attaching the shrinkable film, the adhesion between the shrinkable film and the polymer film can be further enhanced. Therefore, the ability of the shrinkable film to follow the shrinkage in the stretching process can be further enhanced. As a result, this can contribute to further suppression of appearance defects in the Z film that may be ultimately obtained. The heat treatment can be performed by adjusting any appropriate heating temperature and heating time. The heating temperature may preferably be 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. On the other hand, the heating temperature may preferably be 75°C or lower, more preferably 70°C or lower, and even more preferably 65°C or lower. The heating time may preferably be 24 hours or more, more preferably 72 hours or more, and even more preferably 96 hours or more. The upper limit of the heating time may be, for example, 1000 hours.

[0022] B-4.Stretching process Next, the laminate is stretched. Any suitable stretching method can be used, as long as it can apply tension to the polymer film in the stretching direction and a shrinking force in a direction perpendicular to the stretching direction within the film plane. Examples of stretching methods include longitudinal uniaxial fixed-end stretching and longitudinal uniaxial free-end stretching.

[0023] When stretching a laminate, it is preferable to heat the laminate. Heating of the laminate can be performed, for example, in a heating furnace such as an oven while the laminate is being conveyed on rolls. The heating temperature during stretching (stretching temperature) can be appropriately adjusted according to the type of polymer film, the type of shrinkable film, its shrinkability, etc. The stretching temperature is preferably above the glass transition temperature (Tg) of the polymer film. When the stretching temperature is above Tg, the phase difference value of the resulting stretched film tends to be uniform, and the stretched film is less likely to crystallize (become cloudy). The stretching temperature is more preferably between Tg-15℃ and Tg+10℃ of the polymer film, and even more preferably between Tg-10℃ and Tg+8℃. When the stretching temperature is within this range, the laminate can be stretched at a temperature near the Tg of the polymer film, so excessive shrinkage of the shrinkable film can be suppressed. As a result, delamination of the shrinkable film from the polymer film can be suppressed. Therefore, it is presumed that by keeping the stretching temperature within this range, the birefringence Δn can be improved particularly well, and as a result, the thinning of the Z film can be further improved. Furthermore, in this embodiment, since the polymer film is corona treated as described above, the adhesion with the shrink film is enhanced, and by keeping the stretching temperature within this range, more uniform heat stretching of the laminate can be performed. As a result, it is possible to produce a Z film with a thinner thickness that has the same in-plane phase difference as conventional films. Moreover, it is preferable that the stretching temperature is constant in the film width direction. By doing so, it is possible to produce a stretched film with good optical uniformity and small variation in phase difference values.

[0024] The stretching ratio during the stretching process described above can be set to any appropriate value. The stretching ratio can be adjusted, for example, by appropriately adjusting the peripheral speed ratio between the downstream roll (e.g., nip roll) and the upstream roll (e.g., nip roll) when conveying the laminate via rolls. The stretching ratio is preferably 1.05 to 2.00 times, more preferably 1.10 to 1.50 times, even more preferably 1.20 to 1.40 times, and particularly preferably 1.22 to 1.35 times. By setting the stretching ratio within this range, a stretched phase difference film with minimal shrinkage of the film width and excellent mechanical strength can be obtained.

[0025] In this way, a Z film can be obtained. As described above, according to the embodiment of the present invention, a phase difference film exhibiting the refractive index characteristics nx>nz>ny and suppressing appearance defects can be obtained by a simple manufacturing method.

[0026] C. Characteristics of phase difference film The Z film obtained according to the embodiment of the present invention, when applied to an image display device, can effectively improve the oblique hue of the image display device. Furthermore, since the above hue improvement in the image display device can be achieved without separately providing a phase difference layer and an optical compensation layer by using the Z film, it can contribute to the thinning of image display devices and the like.

[0027] The birefringence Δn(nx-ny) of the Z film is preferably greater than 0.0025. More preferably, the birefringence Δn may be 0.0030 or greater, and even more preferably 0.0035 or greater. The upper limit of the birefringence Δn may be, for example, 0.0050. Having such a large birefringence Δn allows for the use of a thinner raw film to obtain the desired in-plane phase difference, thus enabling further thinning of the Z film. As a result, it can contribute to further thinning of image display devices to which the Z film is applied. The effects of the embodiments of the present invention can be particularly remarkable in the manufacture of Z films having such a large birefringence Δn.

[0028] The in-plane phase difference Re(550) of the Z film can be adjusted to have any appropriate in-plane phase difference depending on the purpose. The in-plane phase difference Re(550) of the Z film may be, for example, between 100 nm and 350 nm. The in-plane phase difference Re(550) of the Z film may be, for example, 250 nm to 350 nm, preferably 260 nm to 330 nm, and more preferably 260 nm to 310 nm. Within this range, the Z film can function as a typical λ / 2 plate. Furthermore, with such an in-plane phase difference Re(550), the Z film has a short travel distance on the Poincaré sphere, resulting in excellent hue and brightness characteristics, and also reducing color shift of the image display panel and shifts due to the phase difference component of the TFT. When having such an in-plane phase difference Re(550), the thickness of the Z film may be, for example, 60 μm to 120 μm, preferably 70 μm to 100 μm. The in-plane phase difference Re(550) of the Z film may also be, for example, 100 nm to 200 nm, preferably 110 nm to 170 nm, and more preferably 130 nm to 150 nm. Within this range, the Z film can function as a typical λ / 4 plate. Furthermore, with such an in-plane phase difference Re(550), the Z film can have excellent oblique anti-reflective performance. When having such an in-plane phase difference Re(550), the thickness of the Z film may be, for example, 20 μm to 60 μm, preferably 30 μm to 50 μm.

[0029] The Z film obtained by the manufacturing method of the embodiment of the present invention may have a large birefringence Δn, and as a result, its mechanical properties may be anisotropic. For example, the breaking force of the Z film may have the following relationship: namely, the breaking force B in the stretching direction of the Z film. M [N] and the breaking force B in the direction perpendicular to the stretching direction T Ratio B to [N] M / B T The ratio B is preferably 1.300 or higher, more preferably 1.310 or higher. M / B TThe upper limit could be, for example, 1.500. Ratio B M / B T If it is within the above range, the Z film may have a greater birefringence Δn. The breaking force B in the stretching direction of the Z film. M This refers to the force (stress) applied to a Z film with dimensions of 100 mm in length and 10 mm in width, just before it breaks when pulled in the same direction as the stretching direction (typically the lengthwise direction) at a tensile speed of 1000 mm / min, 23°C, and 55% RH. Breaking force B is the force applied in the direction perpendicular to the stretching direction. T This refers to the force (stress) applied to a Z-film with dimensions of 100 mm in length and 10 mm in width, just before it breaks, when pulled in a direction perpendicular to both the stretching direction and the thickness direction (typically the width direction) at a tensile speed of 1000 mm / min, 23°C, and 55% RH. Bending force in the stretching direction M and the breaking force B in the direction perpendicular to the stretching direction T This can be measured by the method described in the examples below.

[0030] Furthermore, for example, the tensile modulus of a Z film may have the following relationship: namely, the tensile modulus E in the stretching direction of the Z film. M [N / mm 2 ] and the tensile modulus E in the direction perpendicular to the stretching direction T [N / mm 2 Ratio E M / E T The ratio E may preferably be 1.080 or higher, more preferably 1.100 or higher, and even more preferably 1.120 or higher. M / E T The upper limit could be, for example, 1.500. Ratio E M / E T If it is within this range, the Z film may have a larger birefringence Δn. Tensile modulus E in the stretching direction M [N / mm 2 ] and the tensile modulus E in the direction perpendicular to the stretching direction T [N / mm 2 This can be measured in accordance with JIS K7161-2.

[0031] The Nz coefficient of the Z film is preferably 0.3 to 0.7, more preferably 0.4 to 0.6, and even more preferably 0.45 to 0.55. Within this range of Nz coefficient, the hue from oblique directions can be further improved.

[0032] Z films typically exhibit flat wavelength dispersion characteristics, where the phase difference value hardly changes with the wavelength of the measured light.

[0033] The change in in-plane phase difference when the Z film is left in an environment at 85°C for 750 hours is preferably -10 nm or more and 0 nm or less, more preferably -5 nm or more and 0 nm or less, and even more preferably -2 nm or more and 0 nm or less. Within this range, the Z film can exhibit particularly excellent heat resistance. The above change in in-plane phase difference of the Z film is the in-plane phase difference R0 at a measurement wavelength of 550 nm at 23°C and the in-plane phase difference R at a measurement wavelength of 550 nm after being left in an environment at 85°C for 750 hours. t We measured and R0 and R t The difference (R t It can be calculated as -R0). The in-plane phase difference can be measured by the method described in the examples below. [Examples]

[0034] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement and evaluation methods in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0035] (1) Thickness For thicknesses of 10 μm or less, an interferometer (MCPD9800 from Otsuka Electronics Co., Ltd.) was used for measurement; for thicknesses of 10 μm or more, a digital micrometer was used.

[0036] (2) Breaking force Test specimens were prepared by cutting the phase difference films obtained in the examples, comparative examples, and reference examples to dimensions of 100 mm in length and 10 mm in width. At this time, the cutting was performed so that the stretching direction was the length direction. Next, a tensile test was performed on the test specimens using a tensile testing machine (Shimadzu Corporation AUTGRAPH AG-X) conforming to JIS K7161-2, under the conditions of a tensile speed of 1000 mm / min, 23°C, and 55% RH, by pulling in the length direction. In the tensile test, the force (stress) applied to the test specimen just before fracture was defined as the fracture force B in the stretching direction. M [N] was defined as the fracture force B, which is perpendicular to the stretching direction. A tensile test was performed on a similar specimen under the same conditions as above, by pulling it in the width direction. The force (stress) applied to the specimen just before it fractured was defined as the fracture force B, which is perpendicular to the stretching direction. T [N] was used. From the obtained values, ratio B M / B T The result was calculated.

[0037] (3) Tensile modulus A test specimen was prepared in the same manner as in (2) above. Next, a tensile test was performed on the test specimen using a tensile testing machine in the same manner as in (2) above, in accordance with JIS K7161-2, under the conditions of a tensile speed of 1000 mm / min, 23°C, and 55% RH, by pulling it in the length direction. From the relationship between the obtained stress and strain in the tensile test, the tensile modulus of elasticity in the extension direction E was determined. M [N / mm 2 The tensile modulus E in the direction perpendicular to the stretching direction was calculated from the relationship between stress and strain obtained by tensile testing of the same specimen under the same conditions as above in the width direction. T [N / mm 2 The result was calculated.

[0038] (4) Refractive index, phase difference value, and phase difference value change The phase difference values ​​of the phase difference films obtained in the examples, comparative examples, and reference examples were automatically measured using an AXOSCAN manufactured by Axometrics. The measurement wavelength was 550 nm and the measurement temperature was 23°C. In addition, the average refractive index was measured using an Abbe refractometer manufactured by Atago, and the refractive indices nx, ny, and nz were calculated from the obtained phase difference values.

[0039] To confirm the change in phase difference values ​​under prolonged high-temperature conditions, test specimens (50 mm in length, 50 mm in width) of the phase difference films obtained in the examples, comparative examples, and reference examples were placed in an environment at 85°C for 750 hours. After this time, the phase difference values ​​of the phase difference films removed were measured under conditions of a wavelength of 550 nm and a temperature of 23°C. The phase difference value at 23°C was defined as R0, and the phase difference value after heating was defined as R t Let the change be ΔR0 = R t -R0 was calculated.

[0040] (5) Evaluation: Minor breakage The phase difference films obtained in the examples, comparative examples, and reference examples were visually inspected to check for the presence and number of minute folds. If minute folds were found, the number of minute folds per 100m length was counted.

[0041] [Manufacturing Example 1: Preparation of Polymer Film (COP1)] As an unstretched polymer film, a cyclic polyolefin film (COP1) with a thickness of 70 μm was prepared. In detail, the polymer film was prepared as follows. In a nitrogen-purged reaction vessel, 21 parts by weight of dicyclopentadiene, 78 parts by weight of 8-methyl-8-carboxymethyltetracyclo[4.4.0.12,5.17,10]-3-dodecene, and 1 part by weight of 2-norbornene were added as monomers, 14.7 parts by weight of 1-hexene as a molecular weight adjuster, and 150 parts by weight of toluene as a solvent. The mixture was heated to 107°C. To this solution, 0.4 parts by weight of a toluene solution of ethylaluminum (0.6 mol / l) and 1.8 parts by weight of a toluene solution of methanol-modified tungsten hexachloride (0.025 mol / l) were added, and the mixture was reacted at 107°C for 1 hour to obtain a ring-opening polymer. To 360 parts by weight of the obtained ring-opening polymer solution, 0.04 parts by weight of Ru[4-CH3(CH2)4C6H4CO2]H(CO)[P(C6H5)3] was added as a hydrogenation reaction catalyst. The reaction was carried out at a hydrogen gas pressure of 9-10 MPa and a temperature of 160-165°C for 3 hours. After the reaction was complete, the obtained product (hydrogenated product) was precipitated in methanol and vacuum dried to obtain a cyclic polyolefin resin (weight-average molecular weight: 46000, glass transition temperature: 155°C). Using a twin-screw extruder, the obtained resin was melt-kneaded, extruded into strands, and after water cooling, passed through a feeder-ruler to obtain pellets. Using these pellets, an unstretched film with a thickness of 70 μm was prepared by melt extrusion. This was designated as polymer film COP1. Surface protection films (polyolefin-based film, manufactured by Toray, product name "Toretec") were applied to both sides of this polymer film.

[0042] [Manufacturing Example 2: Preparation of Polymer Film (COP2)] As an unstretched polymer film, a polymer film containing a hydrogenated resin of a ring-opening polymer of norbornene-based monomer with a thickness of 130 μm (manufactured by JSR Corporation, product name "ARTON R5000", Tg: 136℃) was prepared. This was designated as polymer film COP2. Surface protective films (polyolefin-based film, manufactured by Toray Industries, product name "Toretec") were attached to both sides of this polymer film.

[0043] [Example 1] (Corona treatment process) The surface protective films attached to both sides of the polymer film COP1 in Manufacturing Example 1 were peeled off, and each peeled surface was subjected to corona treatment using a table-type corona treatment device manufactured by Kasuga Electric. The discharge amount (electron irradiation amount due to corona discharge) for corona treatment was 62.50 W·min / m 2 That's what I decided. (Shrinkable film application process) Next, a 15 μm layer of acrylic adhesive was applied to a shrinkable film (biaxially oriented polypropylene film, manufactured by Toray Industries, Inc., product name "Trefan", thickness 60 μm), and the corona-treated surfaces (both sides) of the polymer film COP1 were attached to it. In this way, a laminate was obtained in which shrinkable films were attached to both sides of the polymer film. The laminate was then subjected to heat treatment at 60°C for 96 hours. (Stretching process) Next, the laminate was stretched to 1.319 times its original size while being heated in a roll stretcher in an air-circulating constant-temperature oven at 154.5°C ± 1°C. After stretching, the shrinkable film was peeled off the laminate to obtain a phase difference film with a thickness of 75 μm. The resulting phase difference film exhibited refractive index characteristics of nx>nz>ny, with Re(550) being 270nm and the Nz coefficient being 0.5. The obtained phase difference films were subjected to the above measurements and evaluations. The results are shown in Table 1. [Examples 2-3, Comparative Example 1] A phase difference film was prepared in the same manner as in Example 1, except that the discharge amount during corona treatment was changed as shown in Table 1. The obtained phase difference film was subjected to the same measurement and evaluation as in Example 1. The results are shown in Table 1. [Examples 4-5] A phase difference film was prepared in the same manner as in Example 1, except that the heat treatment conditions for the laminate after the shrinkable film was applied were changed as shown in Table 1. In Table 1, the "-" notation in the "Heat Treatment Conditions (Temperature / Time)" column for Example 5 means that the heat treatment was not performed. The obtained phase difference film was subjected to the same measurement and evaluation as in Example 1. The results are shown in Table 1. [Comparative Example 2] A phase difference film was prepared in the same manner as in Example 1, except that corona treatment was not performed. The obtained phase difference film was subjected to the same measurement and evaluation as in Example 1. The results are shown in Table 1. [Comparative Example 3] A phase difference film was prepared in the same manner as in Example 1, except that the discharge amount during corona treatment and the heat treatment conditions for the laminate after the application of the shrinkable film were changed as shown in Table 1. The obtained phase difference film was subjected to the same measurements and evaluations as in Example 1. The results are shown in Table 1. [Reference example 1] (Shrinkable film application process) A 15 μm layer of acrylic adhesive was applied to a shrinkable film (biaxially oriented polypropylene film, manufactured by Toray Industries, Inc., product name "Trefan", thickness 60 μm), and the corona-treated surfaces (both sides) of the polymer film COP2 were attached to it. In this way, a laminate was obtained in which shrinkable films were attached to both sides of the polymer film. Next, the laminate was heat-treated at 60°C for 72 hours. (Stretching process) Next, the laminate was stretched to 1.233 times its original size while being heated in a roll stretcher in an air-circulating constant-temperature oven at 142.1°C ± 1°C. After stretching, the shrinkable film was peeled off the laminate to obtain a phase difference film with a thickness of 138 μm. The resulting phase difference film exhibited refractive index characteristics of nx>nz>ny, with Re(550) being 270nm and the Nz coefficient being 0.5. The obtained phase difference films were subjected to the above measurements and evaluations. The results are shown in Table 1.

[0044] [Table 1]

[0045] (evaluation) As is clear from Table 1, in Examples 1-3, even with a large birefringence Δn, no minute folds occurred in the phase difference film (Z film), and appearance defects were significantly suppressed. As a result, the yield of the manufactured Z film can be significantly improved. In Examples 4-5, although slight minute folds occurred in the phase difference film, they were within an acceptable range, and it was found that appearance defects could be suppressed even with a large birefringence Δn. As a result, the yield of the manufactured Z film can be improved even with a large birefringence Δn. On the other hand, in Comparative Examples 1-3, appearance defects occurred due to an unacceptable degree of minute folds, and the yield of the manufactured Z film deteriorated. Note that no minute folds occurred in Reference Example 1, indicating that minute folds are a unique challenge in the manufacture of Z films with a large birefringence Δn. [Industrial applicability]

[0046] The phase difference film obtained by the manufacturing method according to the embodiments of the present invention can be suitably used as an optical film such as a circular polarizer, a phase difference plate, a λ / 2 plate, or a λ / 4 plate. The phase difference film can also be suitably used for anti-reflective applications or as a polarizer for organic EL displays.

Claims

1. A method for manufacturing a phase difference film whose refractive index characteristics are in the relationship nx > nz > ny, A corona treatment step in which corona treatment is applied to at least one surface of an unstretched polymer film, A shrinkable film application step is performed to obtain a laminate by attaching a shrinkable film to the corona-treated surface of the polymer film, The process includes, in this order, a stretching step for stretching the laminate, The discharge rate of the aforementioned corona treatment is 20 W・min / m ２ That's all. A method for manufacturing a phase difference film.

2. The method for producing a phase difference film according to claim 1, wherein the corona treatment step includes applying corona treatment to both sides of an unstretched polymer film.

3. A method for manufacturing a phase difference film according to claim 1, comprising heating the laminate after attaching the shrinkable film in the aforementioned bonding step.

4. The method for producing a phase difference film according to claim 1, wherein the thickness of the unstretched polymer film is 20 μm or more and 110 μm or less.

5. The method for manufacturing a phase difference film according to claim 1, wherein the birefringence Δn of the resulting phase difference film is greater than 0.0025.

6. The breaking force B in the stretching direction of the resulting phase difference film. Ｍ (N) and the breaking force B in the direction perpendicular to the stretching direction Ｔ (N) ratio B Ｍ / B Ｔ A method for manufacturing a phase difference film according to claim 5, wherein the value is 1.300 or more.

Images