Method for manufacturing phase difference film

Abstract

The technical problem of the present application is to achieve both heating reliability and orientation axis accuracy in a retardation film showing reverse wavelength dispersion characteristics. The present application relates to a method for manufacturing a phase difference film, which satisfies the following formulas (1) and (2): 0.8<Re(450) / Re(550)<1(1), 1<Re(650) / Re(550)<1.2(2), in which Re(450), Re(550) and Re(650) are the front phase differences of the film measured with light having wavelengths of 450nm, 550nm and 650nm at 23°C, respectively. The method for manufacturing the phase difference film comprises moving a long strip of resin film in a longitudinal direction while clamping its left and right side edges in a width direction with left and right clamps, while sequentially performing a preheating step and a stretching step, wherein the preheating step comprises preheating the resin film, and the stretching step comprises gradually increasing the separation distance between the left and right clamps to stretch the resin film, and the angle formed between the moving direction of the resin film and the advancing direction of the left and right clamps in the stretching step is less than 6°.

Description

Technical Field

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

[0002] In the past, image display devices such as liquid crystal display devices (LCD) and organic electroluminescent display devices (OLED) used retardation films such as λ / 4 plates for the purpose of improving display characteristics and preventing reflection. Retardation films are usually made by stretching a resin film to control the phase difference in a plane (for example, Patent Documents 1 and 2).

[0003] As for the above-mentioned phase difference film, it can show different wavelength dispersion characteristics according to the constituent material of the film (specifically, the reverse wavelength dispersion characteristics in which the phase difference value increases according to the wavelength of the measured light, the forward wavelength dispersion characteristics in which the phase difference value decreases according to the wavelength of the measured light, or the flat wavelength dispersion characteristics in which the phase difference value hardly changes according to the wavelength of the measured light). Among these, the resin constituting the material of the phase difference film showing the reverse wavelength dispersion characteristic is brittle and has a tendency to have a low refractive index (Δn), so it is usually necessary to fully preheat before stretching, and from the perspective of ensuring heating reliability, the stretched resin film is contracted to relax the residual stress. According to such a manufacturing method, it is easy to produce uneven angles at the width direction ends and the central part of the obtained phase difference film at the orientation axis, so it is difficult to take into account both heating reliability and orientation axis accuracy for the phase difference film showing the reverse wavelength dispersion characteristic.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 5975776

[0007] Patent Document 2: Japanese Patent No. 5594125 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to achieve both heating reliability and orientation axis accuracy in a retardation film showing reverse wavelength dispersion characteristics.

[0010] Means used to solve problems

[0011] According to one aspect of the present invention, there is provided a method for manufacturing a retardation film, wherein the retardation film satisfies the following formulas (1) and (2):

[0012] 0.8<Re(450) / Re(550)<1 (1)

[0013] 1<Re(650) / Re(550)<1.2 (2)

[0014] (In formulas (1) and (2), Re(450), Re(550), and Re(650) are the front retardations of the film measured at 23°C with light having wavelengths of 450 nm, 550 nm, and 650 nm, respectively.)

[0015] The manufacturing method of the phase difference film includes moving a long strip of resin film in the length direction while clamping the left and right side edges in the width direction with left and right clamps, while performing a preheating process and a stretching process in sequence, the preheating process includes preheating the resin film, and the stretching process includes gradually increasing the separation distance between the left and right clamps to stretch the resin film, and the angle formed by the moving direction of the resin film and the traveling direction of the left and right clamps in the stretching process is less than 6°.

[0016] In one embodiment, a ratio of a moving distance of the resin film in the stretching step to a total moving distance of the resin film in the preheating step and the stretching step is 50% or more.

[0017] In one embodiment, the method for producing the retardation film includes a preheating step, a stretching step, and a relaxation step in sequence, wherein the relaxation step includes shrinking the resin film in a width direction.

[0018] In one embodiment, a ratio of a moving distance of the resin film in the stretching step to a total moving distance of the resin film in the preheating step, the stretching step, and the relaxation step is 50% or more.

[0019] In one embodiment, the method for producing a retardation film is a method for producing a retardation film further satisfying the following formula (3).

[0020] 100nm<Re(550)<160nm (3)

[0021] (In formula (3), Re(550) is the front retardation of the film measured with light having a wavelength of 550 nm at 23°C.)

[0022] Effects of the Invention

[0023] According to the present invention, by gradually increasing the distance between the left and right clips to stretch the resin film in the width direction, a retardation film showing reverse wavelength dispersion characteristics that achieves both heating reliability and orientation axis accuracy can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic plan view for explaining the overall structure of an example of a stretching device that can be used in the production method of the present invention.

[0025] Figure 2 It is a schematic diagram showing the structure of the left and right rails in each area of ​​the stretching device used in the example.

[0026] Figure 3 It is a schematic diagram showing the structure of the left and right rails in each area of ​​the stretching device used in the example.

[0027] Figure 4 It is a schematic diagram showing the structure of the left and right rails in each area of ​​the stretching device used in the example.

[0028] Figure 5 It is a schematic diagram showing the structure of the left and right rails in each area of ​​the stretching device used in the example.

[0029] Figure 6 It is a schematic diagram showing the structure of the left and right rails in each area of ​​the stretching device used in the comparative example.

[0030] Figure 7 It is a schematic diagram showing the structure of the left and right rails in each area of ​​the stretching device used in the comparative example.

[0031] Explanation of symbols

[0032] 10L, 10R tracks

[0033] 20L, 20R clamp

[0034] 100 stretching device DETAILED DESCRIPTION

[0035] Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0036] According to one aspect of the present invention, there is provided a method for manufacturing a retardation film, wherein the retardation film satisfies the following formulas (1) and (2):

[0037] 0.8<Re(450) / Re(550)<1 (1)

[0038] 1<Re(650) / Re(550)<1.2 (2)

[0039] (In equations (1) and (2), Re(450), Re(550), and Re(650) are the front phase differences at wavelengths of 450 nm, 550 nm, and 650 nm, respectively)

[0040] The manufacturing method of the phase difference film includes moving a long strip of resin film in the length direction while holding the left and right side edges in the width direction with left and right clamps while sequentially performing a preheating process and a stretching process, wherein the preheating process includes preheating the resin film, and the stretching process includes gradually increasing the separation distance between the left and right clamps to stretch the resin film. In the manufacturing method of the phase difference film of this embodiment, the angle formed by the moving direction of the resin film and the traveling direction of the left and right clamps in the stretching process is less than 6°.

[0041] A.Stretching device

[0042] First, refer to Figure 1 A stretching device that can be used in the production method according to the embodiment of the present invention will be described. Figure 1 This is a schematic plan view for explaining the overall structure of an example of a stretching device used in the production method according to the embodiment of the present invention. Figure 1 The stretching device 100 shown includes: a pair of left and right rails 10L, 10R and a plurality of pairs of left and right clamps 20L, 20R that move along the left and right rails 10L, 10R and clamp the edges of the resin film on both sides in the width direction. In addition, although not shown in the figure, the stretching device 100 is representatively also equipped with a heating mechanism (oven, etc.) that can adjust the resin film to a specified temperature in each area described later. In addition, in this specification, when observing from the inlet side of the film, the track on the left is referred to as the left track 10L, and the track on the right is referred to as the right track 10R. In the stretching device 100, a preheating area A, a stretching area B and a relaxation area C are sequentially arranged from the inlet side to the outlet side of the film. In addition, these respective areas refer to areas where the resin film to be stretched is substantially preheated, stretched and relaxed (contracted / stabilized), and do not necessarily refer to mechanically and structurally independent partitions. In addition, it should be noted that: Figure 1 The ratio of the lengths of the various regions in the stretching device may be different from the ratio of the actual lengths.

[0043] In the stretching device 100, the left and right rails 10L and 10R are configured to be symmetrical in a top view; in the preheating area A, the left and right rails 10L and 10R are configured to extend approximately parallel to the longitudinal direction of the resin film at a distance corresponding to the initial width of the resin film to be stretched. In the stretching area B, the distance between the left and right rails 10L and 10R is gradually expanded from the preheating area A side to the relaxation area C to correspond to the width of the resin film after stretching. The relaxation area C includes a shrinkage area C1 and a stabilization area C2 in sequence downstream in the conveying direction. In the shrinkage area C1, the distance between the left and right rails 10L and 10R is gradually reduced from the stretching area B side to the stabilization area C2 side. In the stabilization area C2, the left and right rails 10L and 10R are configured to be approximately parallel to each other at a distance corresponding to the width of the resin film after shrinkage. In addition, as described above, the left and right clamps 20L and 20R move along a pair of rails 10L and 10R, respectively, so in one embodiment, the angle θ formed by the extension direction of the rail in the preheating area and the extension direction of the rail in the stretching area can correspond to the angle formed by the moving direction of the resin film and the traveling direction of the left and right clamps in the stretching process. The angle θ formed by the extension direction of the rail in the preheating area and the extension direction of the rail in the stretching area can be representatively 6° or less, preferably greater than 0° and 5.5° or less, more preferably 1.0° to 5.0°, and further preferably 2.0° to 4.5°.

[0044] The stretching device used in the manufacturing method of the embodiment of the present invention is not limited to the stretching device shown in the above figure. For example, the stretching device may be provided with a preheating area A and a stretching area B in sequence from the inlet side to the outlet side of the film and may not have a relaxation area. In addition, the relaxation area may also be composed of only a shrinkage area or a stabilization area.

[0045] B. Method for manufacturing phase difference film

[0046] According to the manufacturing method of the phase difference film using the stretching device as described above, the resin film to be stretched is clamped by multiple pairs of left and right clamps at the left and right side edges of the entrance of the stretching device and preheated, and then stretched in a manner of moving through the stretching area with an enlarged track width to achieve the desired phase difference, and then the residual stress caused by shrinkage is relaxed and / or stabilized as needed and released by the clamps.

[0047] Therefore, in one embodiment, the method for manufacturing the phase difference film includes the following steps. The left and right side edges of the long strip of resin film are clamped by left and right clamps respectively (clamping process); the resin film is preheated (preheating process); the separation distance between the left and right clamps is gradually expanded to stretch the resin film (stretching process); and the resin film is released by the left and right clamps (releasing process). As needed, the method for manufacturing the phase difference film may further include a relaxation process after the stretching process and before the releasing process, and the relaxation process may include shrinking the resin film in the width direction and / or stabilizing the orientation state of the resin film. Below, each process is described in detail.

[0048] B-1. Clamping process

[0049] For the long strip of resin film, the edges on both sides of the film inlet of the stretching device are clamped by left and right clamps. Typically, for the resin film, the edges on both sides are clamped by left and right clamps at a certain clamp spacing that is equal to each other. It is preferred that the edges on both sides are clamped in a manner such that the line connecting the pair of left and right clamps is substantially orthogonal to the moving direction of the resin film when the edges on both sides are clamped. The resin film with the edges on both sides clamped by the left and right clamps is transported to the preheating area A by the movement of the clamps.

[0050] B-2. Preheating process

[0051] As for the preheating area (preheating process) A, as described above, the left and right rails 10L and 10R are configured to be substantially parallel to each other (extending in a direction substantially parallel to the moving direction of the resin film) at a distance corresponding to the initial width of the resin film to be stretched, so that the resin film is heated without substantially stretching it in the transverse direction or in the longitudinal direction. However, in order to avoid problems such as bending of the resin film and contact with the nozzle in the oven due to preheating, the distance between the left and right clamps may be slightly increased.

[0052] In the preheating step, the resin film is heated to a temperature T1 (°C). The temperature T1 is preferably above the glass transition temperature (Tg) of the resin film, more preferably above Tg+2°C, and further preferably above Tg+5°C. On the other hand, the heating temperature T1 is preferably below Tg+40°C, and more preferably below Tg+30°C. The temperature T1 varies depending on the resin film used, and is, for example, 70°C to 190°C, and preferably 80°C to 180°C.

[0053] The heating time to the above-mentioned temperature T1 and the holding time at the temperature T1 can be appropriately set according to the constituent material of the resin film and the manufacturing conditions (for example, the conveying speed of the resin film). In addition, the resin film can be heated step by step. These heating time and holding time can be controlled by adjusting the moving speed of the clamp, the length of the preheating area, the temperature of the preheating area, etc. The preheating time can be, for example, 8 seconds to 180 seconds.

[0054] B-3. ​​Stretching process

[0055] As for the stretching area B (stretching process), a pair of left and right clamps 20L, 20R can move at a speed equal to each other, or they can move at different speeds. As described above, the left and right tracks 10L, 10R are constructed to be symmetrical in a top view, so when a pair of left and right clamps 20L, 20R move at a speed equal to each other, their moving distances are equal to each other, so that the resin film is stretched only in the width direction. On the other hand, when the moving speeds of the left and right clamps are different, since one clamp moves lagging behind, the resin film is stretched in the inclined direction. By using a clamp of a variable spacing type in which the clamp spacing in the moving direction can be changed, a pair of left and right clamps can be moved at different moving speeds. The variable spacing type structure can be realized by adopting a telescopic method, a linear motor method, a motor chain method and other driving methods. The telescopic variable spacing type structure is described in detail in, for example, Japanese Patent Publication No. 2008-23775. The stretching conditions of the oblique stretching are described in detail in, for example, Japanese Patent Application Laid-Open Nos. 2013-054338, 2014-194484, and 2014-238524.

[0056] As described above, in the stretching region B (stretching process), the distance between the left and right tracks (and the distance between the left and right clamps) is gradually expanded to correspond to the width of the film after stretching, and the angle θ between the moving direction of the resin film and the traveling direction of the left and right clamps in the stretching region (in other words, the extension direction of the left and right tracks in the stretching region) is typically 6° or less. By setting the angle θ to 6° or less, the stretching in the width direction is slowly performed, and as a result, the unevenness of the orientation axis in the width direction can be suppressed. The angle θ is preferably greater than 0° and less than 5.5°, more preferably 1.0° to 5.0°, and further preferably 2.0° to 4.5°.

[0057] The stretch ratio in the width direction (film width after stretching (W1) / initial film width (W0)) is preferably 2.4 to 3.2, more preferably 2.6 to 3.0, and further preferably 2.7 to 2.9. The film width refers to the film width including the portion clamped by the left and right clamps.

[0058] The stretching speed [(film width after stretching (W1) - initial film width (W0)) / time required for the stretching process] is preferably 30 mm / sec or less, more preferably 10 mm / sec to 25 mm / sec, and further preferably 12 mm / sec to 20 mm / sec. By setting such a stretching speed, both heating reliability and orientation axis accuracy can be appropriately taken into account.

[0059] The stretching process can be typically carried out at temperature T2. Temperature T2 is preferably Tg-20°C to Tg+30°C relative to the glass transition temperature (Tg) of the resin film, more preferably Tg-10°C to Tg+20°C, and particularly preferably around Tg. Temperature T2 varies depending on the resin film used, and is, for example, 70°C to 180°C, preferably 80°C to 170°C. The difference (T1-T2) between the above-mentioned temperature T1 and temperature T2 is preferably ±2°C or more, more preferably ±5°C or more. In one embodiment, T1>T2, so the resin film heated to temperature T1 in the preheating process can be cooled to temperature T2.

[0060] B-4. Relaxation process

[0061] The relaxation process is performed after the stretching process and is an optional process that can be omitted depending on the purpose. The relaxation process includes shrinking the resin film in the width direction (shrinking treatment) and / or stabilizing the orientation state of the resin film (stabilization treatment).

[0062] B-4-1. Shrinkage treatment

[0063] As for the shrinkage treatment, the resin film is shrunk in the width direction. Specifically, the resin film is shrunk in the width direction by passing through the shrinkage area C1, and the shrinkage area C1 is configured such that the separation distance between the left and right tracks gradually decreases toward the downstream of the conveying direction. Through such shrinkage treatment, the residual stress in the resin film is relaxed, and as a result, the heating reliability can be improved.

[0064] The shrinkage ratio of the resin film in the shrinkage treatment [film width after shrinkage (W2) / film width after stretching (W1)] is preferably 0.92 to 1.0, more preferably 0.95 to 1.0, and even more preferably 0.98 to 1.0. With such a shrinkage ratio, high heating reliability can be obtained.

[0065] The shrinkage treatment can be typically performed at a temperature T3. The temperature T3 is typically lower than the glass transition temperature (Tg) of the resin film, preferably Tg-20°C to Tg°C, more preferably Tg-15°C to Tg°C, and further preferably Tg-10°C to Tg°C.

[0066] B-4-2. Stabilization treatment

[0067] For the stabilization treatment, the resin film is typically maintained at a temperature T4 without stretching or shrinking, so that its orientation state is stabilized. Temperature T4 is typically below the glass transition temperature (Tg) °C of the resin film, preferably below Tg-1 °C, and more preferably room temperature to Tg-3 °C. In one embodiment, temperature T4 is equal to temperature T3 °C. In addition, the stabilization treatment time can be appropriately set according to the constituent materials of the resin film and the manufacturing conditions (such as the conveying speed of the resin film). The stabilization time can be, for example, 5 seconds to 60 seconds.

[0068] B-5. Release process

[0069] Next, the resin film is released from the left and right clamps near the exit of the stretching device. The release from the clamps can be performed at room temperature (about 25°C), for example.

[0070] B-6. Ratio of stretching step in heating process (oven ratio)

[0071] With regard to the method for manufacturing the phase difference film of the embodiment of the present invention, the preheating process, the stretching process, and the relaxation process in the presence of the condition are preferably carried out in the form of a continuous heating process. Specifically, the resin film temperature T1 in the preheating process can be Tg+2°C or more, the resin film temperature T2 in the stretching process can be Tg-20°C~Tg+30°C, the resin film temperature T3 in the shrinkage process can be Tg-20°C~Tg°C, and the resin film temperature T4 in the stabilization process can be the same temperature as T3, and these processes can be carried out continuously. The moving distance of the resin film in the stretching process and the total moving distance of the resin film in the continuous heating process (for example, a heating process that maintains the resin film temperature at Tg-20°C or more, preferably Tg-5°C or more) (that is, the total moving distance of the resin film in the preheating process, the stretching process, and the shrinkage process and / or the stabilization process in the presence of the condition) is preferably 50% or more, more preferably 60% or more, further preferably 70% or more, and further more preferably 75% or more. In addition, the upper limit of the ratio can be, for example, 90%. When the ratio of the moving distance in the stretching step in the heating process is within such a range, a retardation film that satisfies both heating reliability and axis accuracy appropriately can be obtained.

[0072] C. Resin film to be stretched and phase difference film obtained by stretching

[0073] As a resin film suitable for the method for manufacturing a phase difference film described in item B, any appropriate resin film that can be used as a phase difference film can be listed. As materials constituting the resin film, for example, polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, acrylic resins, cellulose ester resins, cellulose resins, polyester resins, polyester carbonate resins, olefin resins, polyurethane resins, etc. are listed. Preferred are polycarbonate resins, polyvinyl acetal resins, cellulose ester resins, polyester resins, and polyester carbonate resins. This is because: as long as these resins are used, a phase difference film showing wavelength dependence of so-called reverse dispersion can be obtained. These resins can be used alone or in combination according to the desired properties.

[0074] Any appropriate polycarbonate resin can be used as the polycarbonate resin, and for example, a polycarbonate resin containing a structural unit derived from a dihydroxy compound is preferred. Specific examples of the dihydroxy compound include 9,9-bis(4-hydroxyphenyl)fluorene, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3-ethylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-propylphenyl)fluorene, 9,9-bis(4-hydroxy-3-isopropylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-sec-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-tert-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-cyclohexylphenyl)fluorene, 9,9-bis(4-hydroxy-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, 9,9-bis(4- 9,9-bis(4-(2-hydroxyethoxy)-3-isopropylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-isobutylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-cyclohexylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3,5-dimethylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butyl-6-methylphenyl)fluorene, 9,9-bis(4-(3-hydroxy-2,2-dimethylpropyloxy)phenyl)fluorene, etc. The polycarbonate resin may contain structural units derived from dihydroxy compounds such as isosorbide, isomannide, isoidide, spiroglycol, dioxanediol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), and bisphenols in addition to the structural units derived from the above-mentioned dihydroxy compounds.

[0075] The details of the polycarbonate resin described above are described in, for example, Japanese Patent Application Laid-Open No. 2012-67300 and Japanese Patent No. 3325560. The contents of the description of these patent documents are incorporated herein by reference.

[0076] The glass transition temperature of the polycarbonate resin is preferably 110°C to 250°C, more preferably 120°C to 230°C. When the glass transition temperature is too low, there is a tendency for heat resistance to deteriorate, which may cause dimensional changes after film formation. When the glass transition temperature is too high, there is a situation where the molding stability during film formation deteriorates, and there is also a situation where the transparency of the film is impaired. In addition, the glass transition temperature can be obtained based on JIS K 7121 (1987).

[0077] As the polyvinyl acetal resin, any appropriate polyvinyl acetal resin can be used. Typically, the polyvinyl acetal resin can be obtained by condensing at least two aldehyde compounds and / or ketone compounds with a polyvinyl alcohol resin. Specific examples of polyvinyl acetal resins and detailed production methods are described in, for example, Japanese Patent Application Publication No. 2007-161994. This description is incorporated herein by reference.

[0078] The thickness of the resin film to be stretched is, for example, 10 μm to 300 μm, preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0079] For the phase difference film obtained by stretching the resin film of the above-mentioned stretching object, it is preferred that the refractive index characteristics show the relationship of nx>ny. In addition, the phase difference film preferably has high in-plane orientation, for example, the birefringence Δn (Δn=nx-ny) when measured at a wavelength of 550nm is preferably 0.002~0.005, and more preferably 0.0025~0.004. Furthermore, the phase difference film can preferably act as a λ / 4 plate. The front phase difference Re (550) of the phase difference film is preferably 100nm~160nm, more preferably greater than 100nm and less than 160nm, and further preferably 135nm~155nm. In addition, in this specification, nx is the refractive index in the direction where the refractive index in the plane becomes the largest (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. In addition, Re (λ) is the front phase difference of the film measured with light of a wavelength of λnm at 23°C. Therefore, Re(550) is the front retardation of the film measured with light having a wavelength of 550 nm at 23° C. Re(λ) is obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the film is set to d (nm).

[0080] As long as the phase difference film has the relationship of nx>ny, it can show any appropriate refractive index ellipsoid. The refractive index ellipsoid of the phase difference film preferably shows the relationship of nx>ny≥nz. The Nz coefficient of the phase difference film is preferably 1 to 1.3, more preferably 1 to 1.25, and further preferably 1 to 1.2. The Nz coefficient is calculated by Nz=Rth(λ) / Re(λ). Here, Rth(λ) is the phase difference in the thickness direction of the film measured by light with a wavelength of λnm at 23°C, and is calculated by the formula: Rth(λ)=(nx-nz)×d.

[0081] The phase difference film typically shows the wavelength dependence of the so-called reverse dispersion. Specifically, its front phase difference satisfies the relationship of Re(450)<Re(550)<Re(650). Re(450) / Re(550) is typically greater than 0.8 and less than 1, preferably greater than 0.8 and less than 0.95. Re(650) / Re(550) is typically greater than 1 and less than 1.2.

[0082] The absolute value of the photoelastic coefficient of the retardation film is preferably 2×10 -12 (m 2 / N)~100×10 -12 (m 2 / N), more preferably 2×10 -12 (m 2 / N)~50×10 -12 (m 2 / N).

[0083] The orientation axis precision of the phase difference film is excellent. The difference between the orientation axis (slow axis) angle at the end in the width direction and the orientation axis (slow axis) in the center in the width direction can be within ±2°, preferably within ±1.5°, and more preferably within ±1.0°. In addition, the shrinkage rate in the TD direction of the phase difference film after heat treatment at Tg-30°C for 30 minutes can be within 6%, preferably within 5.5%, and more preferably within 5%.

[0084] Example

[0085] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In addition, the measurement and evaluation methods in the examples are as follows.

[0086] (1) Orientation angle (direction of slow axis)

[0087] The sample was prepared by cutting the central part and both ends of the phase difference film in the width direction of the embodiment and the comparative example into a square shape with a width of 50 mm and a length of 50 mm in a way that one side was parallel to the width direction of the film. The sample was measured using a Mueller matrix polarimeter (product name "Axoscan" manufactured by Axometrics), and the orientation angle at 23°C was measured at a wavelength of 550nm. In addition, for the orientation angle, the sample was measured in a state where it was placed parallel to the measuring table. The difference between the orientation angle in the central part of the width direction and the orientation angle at both ends was obtained and evaluated as the orientation angle unevenness (orientation angle Δ).

[0088] (2) Front phase difference Re

[0089] In the same manner as in the above (1), measurement was performed at a wavelength of 550 nm at 23°C using "Axoscan" manufactured by Axometrics.

[0090] (3) Thickness

[0091] The thickness was measured using a micrometer thickness gauge (manufactured by Mitutoyo Corporation).

[0092] (4) Heating reliability evaluation

[0093] The retardation films obtained in the examples and comparative examples were placed in an oven at Tg-30°C, taken out after 30 minutes, and their dimensions before being placed in the oven (TD direction) and after being taken out were measured with a metal ruler. The dimensional shrinkage was calculated and evaluated as reliability Δ.

[0094] [Example 1]

[0095] (Production of polycarbonate resin film)

[0096] The polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux cooler controlled at 100° C. 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), isosorbide (ISB), diethylene glycol (DEG), diphenyl carbonate (DPC) and magnesium acetate tetrahydrate were prepared at a molar ratio of BHEPF / ISB / DEG / DPC / magnesium acetate=0.348 / 0.490 / 0.162 / 1.005 / 1.00×10 -5The reactor was fully substituted with nitrogen (oxygen concentration was 0.0005-0.001% by volume), and then heated by a heat medium. Stirring was started when the internal temperature reached 100°C. 40 minutes after the start of temperature increase, the internal temperature reached 220°C and was controlled to maintain this temperature. At the same time, the pressure was reduced and set to 13.3 kPa after 90 minutes after reaching 220°C. The phenol vapor produced as a by-product of the polymerization reaction was introduced into a 100°C reflux cooler, and a small amount of monomer components contained in the phenol vapor were returned to the reactor. The uncondensed phenol vapor was introduced into a 45°C condenser for recovery.

[0097] Nitrogen was introduced into the first reactor to temporarily restore it to atmospheric pressure, and then the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature and pressure reduction in the second reactor were started, and the internal temperature was set to 240°C and the pressure was set to 0.2 kPa for 50 minutes. Then, polymerization was carried out until the specified stirring power was reached. At the moment when the specified power was reached, nitrogen was introduced into the reactor to restore the pressure, and the reaction liquid was extracted in the form of strands, and pelletized with a rotary cutter to obtain a polycarbonate resin A with a copolymer composition of BHEPF / ISB / DEG=34.8 / 49.0 / 16.2 [mol %]. The reduced viscosity of the polycarbonate resin was 0.430 dL / g and the glass transition temperature was 140°C.

[0098] The obtained polycarbonate resin was vacuum dried at 80°C for 5 hours, and then a polycarbonate resin film with a thickness of 100 μm was produced using a film-making device equipped with a single-screw extruder (manufactured by Isuzu Chemical Machinery Co., Ltd., with a screw diameter of 25 mm and a cylinder set temperature of 220°C), a T-die (width of 900 mm, set temperature: 220°C), a cooling roller (set temperature: 120-130°C) and a winder.

[0099] (Manufacturing of Phase Difference Film)

[0100] Use as Figure 2 The stretching device shown in the figure performs a preheating step, a stretching step, and a relaxation step (shrinkage treatment) on the polycarbonate resin film obtained as described above, and releases it from the clamp under room temperature environment, thereby obtaining a retardation film. Figure 2 This is a diagram schematically showing the configuration of left and right rails in each area of ​​the stretching device, and the clamps are not shown. Figure 2The path length of each chamber in the stretching device shown is exactly the same (2000 mm), and the ratio of the stretching zone length to the sum of the preheating zone length, the stretching zone length and the shrinking zone length (oven ratio) is 50%. In addition, the angle θ formed by the extension direction of the track in the preheating zone and the extension direction of the track in the stretching zone (in other words, the angle formed by the moving direction of the resin film and the traveling direction of the left and right clamps in the stretching process) is 5.61°. The details of each process are as follows.

[0101] (Clamping process)

[0102] A long polycarbonate resin film (thickness: 100 μm, width ( W0 ): 650 mm) was moved in the longitudinal direction at a speed of 1500 mm / sec, while the left and right side edges were clamped by left and right clamps.

[0103] (Preheating process)

[0104] Next, the resin film was moved to the preheating area (the first chamber and the second chamber), and preheated while raising the film temperature from 144° C. to 146° C. in the first chamber and from 146° C. to 150° C. in the second chamber.

[0105] (Stretching process)

[0106] Next, the resin film was moved to the stretching area (chamber 3 to chamber 7) where the separation distance between the left and right clamps was expanded, thereby stretching in the width direction. The stretching temperature (film temperature) was reduced from 150°C to 138°C in chamber 3, and maintained at 138°C after chamber 4. The film width (W1) at the terminal end of the stretching area (exit of chamber 7) was 1838 mm, and the stretching ratio (W1 / W0) was 2.83 times.

[0107] (Shrinkage Processing)

[0108] Next, the resin film was moved to the shrinking area (chamber 8 to chamber 10) where the separation distance between the left and right clamps was reduced, thereby shrinking in the width direction. The film temperature was reduced from 138°C to 135°C in chamber 8, and maintained at 135°C in chambers 9 and 10. In addition, the film width (W2) at the terminal end of the shrinking area (exit of chamber 10) was 1803 mm, and the shrinkage ratio (W2 / W1) was 0.98.

[0109] (Release process)

[0110] Next, the resin film was released from the left and right clamps at the exit of the stretching device (atmosphere temperature: 25° C.) The clamp pitch in the moving direction of the left and right clamps did not substantially change from clamping to release and was constant.

[0111] The two ends (clamping parts) of the stretched film obtained as described above were cut to obtain a retardation film (thickness 37 μm, width 1410 mm, Re (550) 143 nm). The obtained retardation film was subjected to the evaluation of (1) above. The results are shown in Table 1.

[0112] [Example 2]

[0113] In addition to using Figure 3 Except for the stretching device shown, the preheating process, the stretching process and the relaxation process (shrinkage treatment) were carried out in the same manner as in Example 1, and the film was released from the clamp at room temperature to obtain a phase difference film (the stretching ratio and the shrinkage ratio were also the same as in Example 1). Figure 3 This is a diagram schematically showing the configuration of left and right rails in each area of ​​the stretching device, and the clamps are not shown. Figure 3 The path lengths of the chambers in the stretching device shown are all the same (2000 mm), the ratio of the stretching zone length to the sum of the preheating zone length, the stretching zone length and the shrinking zone length (oven ratio) is 60%. In addition, the angle θ formed by the extension direction of the track in the preheating zone and the extension direction of the track in the stretching zone is 4.72°.

[0114] The two ends (clamping parts) of the stretched film obtained as described above were cut to obtain a retardation film (thickness 37 μm, width 1410 mm, Re (550) 143 nm). The obtained retardation film was subjected to the evaluation of (1) above. The results are shown in Table 1.

[0115] [Example 3]

[0116] In addition to using Figure 4 Except for the stretching device shown, the preheating process, the stretching process and the relaxation process (shrinkage treatment) were carried out in the same manner as in Example 1, and the film was released from the clamp at room temperature to obtain a phase difference film (the stretching ratio and the shrinkage ratio were also the same as in Example 1). Figure 4 This is a diagram schematically showing the configuration of left and right rails in each area of ​​the stretching device, and the clamps are not shown. Figure 4 The path lengths of the chambers in the stretching device shown are all the same (2000 mm), the ratio of the stretching zone length to the sum of the preheating zone length, the stretching zone length and the shrinking zone length (oven ratio) is 70%. In addition, the angle θ formed by the extension direction of the track in the preheating zone and the extension direction of the track in the stretching zone is 4.21°.

[0117] The two ends (clamping parts) of the stretched film obtained as described above were cut to obtain a retardation film (thickness 37 μm, width 1410 mm, Re (550) 143 nm). The obtained retardation film was subjected to the evaluation of (1) above. The results are shown in Table 1.

[0118] [Example 4]

[0119] In addition to using Figure 5 Except for the stretching device shown, the preheating process, the stretching process and the relaxation process (shrinkage treatment) were carried out in the same manner as in Example 1, and the film was released from the clamp at room temperature to obtain a phase difference film (the stretching ratio and the shrinkage ratio were also the same as in Example 1). Figure 5 This is a diagram schematically showing the configuration of left and right rails in each area of ​​the stretching device, and the clamps are not shown. Figure 5 The path lengths of the chambers in the stretching device shown are all the same (2000 mm), the ratio of the stretching zone length to the sum of the preheating zone length, the stretching zone length and the shrinking zone length (oven ratio) is 80%. In addition, the angle θ formed by the extension direction of the track in the preheating zone and the extension direction of the track in the stretching zone is 3.13°.

[0120] The two ends (clamping parts) of the stretched film obtained as described above were cut to obtain a retardation film (thickness 37 μm, width 1410 mm, Re (550) 143 nm). The obtained retardation film was subjected to the evaluation of (1) above. The results are shown in Table 1.

[0121] [Comparative Example 1]

[0122] In addition to using Figure 6 Except for the stretching device shown, the preheating process, the stretching process and the relaxation process (shrinkage treatment) were carried out in the same manner as in Example 1, and the film was released from the clamp at room temperature to obtain a phase difference film (the stretching ratio and the shrinkage ratio were also the same as in Example 1). Figure 6 This is a diagram schematically showing the configuration of left and right rails in each area of ​​the stretching device, and the clamps are not shown. Figure 6 The path lengths of the chambers in the stretching device shown are all the same (2000 mm), the ratio of the stretching zone length to the sum of the preheating zone length, the stretching zone length and the shrinking zone length (oven ratio) is 30%. In addition, the angle θ formed by the extension direction of the track in the preheating zone and the extension direction of the track in the stretching zone is 8.38°.

[0123] The two ends (clamping parts) of the stretched film obtained as described above were cut to obtain a retardation film (thickness 37 μm, width 1410 mm, Re (550) 143 nm). The obtained retardation film was subjected to the evaluation of (1) above. The results are shown in Table 1.

[0124] [Comparative Example 2]

[0125] In addition to using Figure 7 Except for the stretching device shown, the preheating process, the stretching process and the relaxation process (shrinkage treatment) were carried out in the same manner as in Example 1, and the film was released from the clamp at room temperature to obtain a phase difference film (the stretching ratio and the shrinkage ratio were also the same as in Example 1). Figure 7 This is a diagram schematically showing the configuration of left and right rails in each area of ​​the stretching device, and the clamps are not shown. Figure 7 The path lengths of the chambers in the stretching device shown are all the same (2000 mm), the ratio of the stretching zone length to the sum of the preheating zone length, the stretching zone length and the shrinking zone length (oven ratio) is 40%. In addition, the angle θ formed by the extension direction of the track in the preheating zone and the extension direction of the track in the stretching zone is 6.72°.

[0126] The two ends (clamping parts) of the stretched film obtained as described above were cut to obtain a retardation film (thickness 37 μm, width 1410 mm, Re (550) 143 nm). The obtained retardation film was subjected to the evaluation of (1) above. The results are shown in Table 1.

[0127] Table 1

[0128] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Angle θ 5.61 4.72 4.21 3.13 8.38 6.72 Oven ratio 50 60 70 80 30 40 Orientation angle Δ[°] 6 3 2 2 16 9 Reliability Δ[%] 5 6.7 7.1 3.4 11.2 7.2

[0129] <Evaluation>

[0130] As shown in the above table, the phase difference film obtained in the embodiment is superior to the phase difference film obtained in the comparative example in both heating reliability and orientation axis accuracy. In addition, it can be seen that by increasing the oven ratio and / or further reducing the angle θ within the range below 6°, heating reliability and orientation axis accuracy can be taken into account at a higher level.

[0131] Industrial Applicability

[0132] The retardation film obtained by the production method of the present invention can be suitably used in image display devices such as liquid crystal display devices (LCD) and organic electroluminescent display devices (OLED).

Claims

1. A method for producing a phase difference film, wherein the phase difference film satisfies the following formulas (1) and (2): 0.8<Re(450) / Re(550)<1 (1) 1<Re(650) / Re(550)<1.2 (2) In the formulas (1) and (2), Re(450), Re(550) and Re(650) are the front retardations of the film measured at 23°C with light having wavelengths of 450 nm, 550 nm and 650 nm, respectively. The method for manufacturing a phase difference film includes sequentially performing a preheating step, a stretching step, and a relaxation step while moving a long strip of resin film in a longitudinal direction while holding left and right side edges of the long strip of resin film in a width direction with left and right clamps. The preheating step includes preheating the resin film. The stretching step includes gradually increasing the separation distance between the left and right clamps to stretch the resin film. The relaxation step includes shrinking the resin film in the width direction and / or stabilizing the orientation state of the resin film. The angle formed by the moving direction of the resin film and the advancing direction of the left and right clamps in the stretching step is 6° or less, The stretching ratio of the resin film in the width direction in the stretching step is 2.4 to 3.

2. The resin film includes at least one selected from polycarbonate resin, polyvinyl acetal resin and polyester carbonate resin.

2. The manufacturing method according to claim 1, wherein: A ratio of a moving distance of the resin film in the stretching step to a total moving distance of the resin film in the preheating step, the stretching step, and the relaxing step is 50% or more.

3. The manufacturing method according to claim 2, wherein: A ratio of a moving distance of the resin film in the stretching step to a total moving distance of the resin film in the preheating step, the stretching step, and the relaxation step is 70% or more.

4. The manufacturing method according to claim 1, wherein: The shrinkage rate of the resin film in the relaxation step is 0.92 to 1.

0.

5. The production method according to any one of claims 1 to 4, wherein The phase difference film also satisfies the following formula (3): 100nm<Re(550)<160nm (3) In the formula (3), Re(550) is the front retardation of the film measured with light having a wavelength of 550 nm at 23°C.

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