Method for manufacturing a stretch film

Abstract

The technical problem of the present application is to achieve both heating reliability and precision of an orientation axis for a phase difference film showing a reverse wavelength dispersion characteristic. A manufacturing method of a stretched film of the present application includes a first process and a second process, the first process includes the following processes in this order: preheating while moving a long thermoplastic resin film in the length direction, stretching in the width direction, shrinking in the width direction, and winding into a roll shape, and the second process includes the following processes in this order: preheating while unwinding the thermoplastic resin film in the roll shape and moving it in the length direction, stretching in the width direction, and shrinking in the width direction, wherein the stretched film satisfies the following equation (1) when the stretching ratio in the width direction in the first process is E1 and the total stretching ratio in the width direction is set to E, E x 0.55 < E1 < E x 0.75 (1).

Description

TECHNICAL FIELD

[0001] The present application relates to a method for manufacturing a stretched film. BACKGROUND

[0002] Conventionally, in image display devices such as liquid crystal display devices (LCD), organic electroluminescent display devices (OLED), and the like, phase difference films such as λ / 4 plates have been used for the purpose of improving display characteristics and preventing reflection. Phase difference films are generally manufactured by stretching a resin film to control the in-plane phase difference (for example, Patent Documents 1 and 2).

[0003] In the above phase difference film, different wavelength dispersion characteristics (specifically, a reverse wavelength dispersion characteristic in which the phase difference value increases as the wavelength of the measuring light increases, a positive wavelength dispersion characteristic in which the phase difference value decreases as the wavelength of the measuring light increases, or a flat wavelength dispersion characteristic in which the phase difference value hardly changes as the wavelength of the measuring light changes) can be exhibited depending on the constituent material of the film. Among these, the resin of the constituent material of the phase difference film exhibiting the reverse wavelength dispersion characteristic is generally brittle. Therefore, in the manufacturing thereof, from the viewpoint of imparting a desired phase difference, sufficient preheating before stretching is required, and from the viewpoint of ensuring heating reliability, relaxation of the residual stress due to shrinkage is performed after stretching. However, according to such a manufacturing method, the orientation angle is likely to be uneven, and the orientation property of the obtained phase difference film has room for further improvement.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

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

[0007] Patent Document 2: Japanese Patent No. 5594125 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] The present application has been achieved in order to solve the above conventional problems, and aims to provide a manufacturing method of a phase difference film that improves both the orientation axis precision and the uniaxiality.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] According to one aspect of the present application, there is provided a method for manufacturing a stretched film, which includes a first process and a second process, the first process including, in this order, a preheating step, a stretching step in the width direction, a shrinking step in the width direction, and a winding step into a roll shape, while moving a long thermoplastic resin film in the length direction, and the second process including, in this order, a preheating step, a stretching step in the width direction, and a shrinking step in the width direction, while unwinding the thermoplastic resin film in the roll shape and moving it in the length direction, wherein the stretched film satisfies the following expression (1) when the stretching ratio in the width direction in the first process is E1 and the total stretching ratio in the width direction is E.

[0012] E x 0.55 < E1 < E x 0.75 (1)

[0013] In one embodiment, the method for manufacturing a stretched film is a method for manufacturing a stretched film satisfying the following expressions (A) and (B).

[0014] 0.8 < R(450) / R(550) < 1 (A)

[0015] 1 < R(650) / R(550) < 1.2 (B)

[0016] (In expressions (A) and (B), R(450), R(550), and R(650) are the front surface phase difference of the film measured with light having a wavelength of 450 nm, 550 nm, and 650 nm at 23°C, respectively.)

[0017] In one embodiment, the total stretching ratio in the width direction is 2.4 times to 3.2 times.

[0018] In one embodiment, the stretching ratio in the width direction in the first process is 1.4 times to 2.2 times.

[0019] In one embodiment, the thermoplastic resin film includes at least one selected from the group consisting of polycarbonate-based resins, polyvinyl acetal resins, cellulose ester-based resins, polyester-based resins, and polyester carbonate-based resins.

[0020] Effects of the Invention

[0021] According to the method for manufacturing a stretched film of the present application, by moving a long thermoplastic resin film in opposite directions in the first process and the second process, respectively, while stretching and shrinking it in the width direction, and further setting the ratio of the stretching ratio in the first process to the total stretching ratio to a prescribed range, a phase difference film improved in both the orientation axis precision and the uniaxiality can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1is a schematic plan view for explaining the first step in one embodiment of the present application.

[0023] Figure 2 is a schematic plan view for explaining the second step in one embodiment of the present application.

[0024] Figure 3 is a graph showing the relationship between the stretching ratio and the birefringence in the first step.

[0025] Figure 4 is a graph showing the relationship between the stretching ratio and the orientation angle unevenness in the first step.

[0026] Symbol explanation

[0027] 1 thermoplastic resin film

[0028] 10 track

[0029] 20 jig

[0030] 100 stretching device DETAILED DESCRIPTION

[0031] Hereinafter, preferred embodiments of the present application will be explained, but the present application is not limited to these embodiments.

[0032] A. Method for manufacturing stretched film

[0033] The method for manufacturing a stretched film of the embodiment of the present application includes a first step and a second step, the above-mentioned first step includes the following steps in order: preheating while moving a long thermoplastic resin film in the length direction, stretching in the width direction, shrinking in the width direction, and winding into a roll shape, the above-mentioned second step includes the following steps in order: preheating while unwinding the thermoplastic resin film in the roll shape and moving it in the length direction, stretching in the width direction, and shrinking in the width direction, wherein, when the stretching ratio in the width direction in the first step is El and the total stretching ratio in the width direction is set to E, the above-mentioned stretched film satisfies the following equation (1).

[0034] E x 0.55 < El < E x 0.75 (1)

[0035] According to the above-described manufacturing method of the stretched film, the starting end portion in the first process of the long strip-shaped thermoplastic resin film becomes the terminal end portion in the second process, and the moving direction in the first process of the thermoplastic resin film and the moving direction in the second process become opposite directions. In this way, by moving the long strip-shaped thermoplastic resin film in opposite directions in the first process and the second process, respectively, while stretching and contracting in the width direction, and by setting the ratio of the stretching ratio in the first process with respect to the total stretching ratio in the width direction to a prescribed range, a phase difference film that improves both the orientation axis precision and the uniaxiality can be obtained. The reason why such an effect is obtained is considered as follows, but does not constitute any limitation on the present application. That is, it is considered that by dividing the stretching and contracting into a plurality of stages and setting the stretching ratio at the time of the primary stretching to a high level, the in-plane orientation of the resin molecular chain can be improved, as a result of which the uniaxiality is improved. In addition, it is considered that by setting the moving direction at the time of each stretching and contracting to opposite directions, the orientation angle unevenness caused by the bowing phenomenon and the like can be canceled out, and the orientation axis precision can be improved.

[0036] The total stretching ratio in the width direction E in the above-described manufacturing method of the stretched film can be appropriately set according to the purpose. In an embodiment of the phase difference film that exhibits the reverse wavelength dispersion characteristic as the target stretched film, the total stretching ratio in the width direction E can be, for example, 2.4 times to 3.2 times, preferably can be 2.6 times to 3.0 times, and more preferably can be 2.7 times to 2.9 times. In addition, the total stretching ratio is the product of the respective stretching ratios in the stretching in the entire width direction that is performed in the manufacturing method of the stretched film. Therefore, for example, in the case where the manufacturing method of the stretched film only includes the stretching in the first process and the stretching in the second process as the stretching in the width direction, the total stretching ratio E is found as the product of the stretching ratio in the width direction El in the first process and the stretching ratio in the width direction E2 in the second process.

[0037] A-1. Thermoplastic resin film

[0038] As the forming material of the thermoplastic resin film, any appropriate thermoplastic resin can be used according to the purpose. For example, polycarbonate-based resins, polyvinyl acetal resins, cyclic olefin-based resins, acrylic-based resins, cellulose ester-based resins, cellulose-based resins, polyester-based resins, polyester carbonate-based resins, olefin-based resins, polyurethane-based resins, and the like can be cited. Polycarbonate resins, polyvinyl acetal-based resins, cellulose ester-based resins, polyester-based resins, and polyester carbonate-based resins are preferred. This is because, as long as these resins, a phase difference film that exhibits the so-called reverse dispersion of wavelength dependence can be obtained. These resins can be used alone or in combination according to the desired characteristics.

[0039] As the polycarbonate-based resin described above, any appropriate polycarbonate-based resin can be used. For example, a polycarbonate-based resin containing a structural unit derived from a dihydroxy compound is preferred. As specific examples of the dihydroxy compound, 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-t-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-(2-hydroxyethoxy)-3-methylphenyl)fluorene, 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-t-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-t-butyl-6-methylphenyl)fluorene, 9,9-bis(4-(3-hydroxy-2,2-dimethylpropoxy)phenyl)fluorene, and the like can be listed. The polycarbonate-based resin can contain, in addition to the structural unit derived from the dihydroxy compound described above, a structural unit derived from a dihydroxy compound such as isosorbide, isomannide, isoidide, spiroglycol, dioxanediol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), bisphenols, and the like.

[0040] Details of the polycarbonate-based resin described above are described, for example, in Japanese Patent Application Publication No. 2012-67300 and Japanese Patent No. 3325560. The description of this patent document is incorporated herein by reference.

[0041] The polycarbonate-based resin preferably has a glass transition temperature of 110°C to 250°C, and more preferably 120°C to 230°C. When the glass transition temperature is too low, there is a tendency for heat resistance to deteriorate, and dimensional changes can occur after film formation. When the glass transition temperature is too high, there are cases where the stability of molding during film formation deteriorates, and cases where the transparency of the film is impaired. Furthermore, the glass transition temperature is determined based on JIS K 7121 (1987).

[0042] As the above polyvinyl acetal resin, any appropriate polyvinyl acetal resin can be used. Typically, the polyvinyl acetal resin can be obtained by subjecting at least two aldehyde compounds and / or ketone compounds to a condensation reaction with a polyvinyl alcohol-based resin. Specific examples of the polyvinyl acetal resin and detailed manufacturing methods thereof are described, for example, in Japanese Patent Application Publication No. 2007-161994. The description thereof is incorporated herein by reference.

[0043] The thickness of the above thermoplastic resin film (thickness before stretching) is, for example, 10 μm to 300 μm, preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0044] A-2. First process

[0045] The first process includes, in order, the following processes: preheating while moving a long thermoplastic resin film (hereinafter sometimes referred to simply as "resin film") along the length direction, stretching in the width direction, shrinking in the width direction, and winding into a roll shape. As necessary, the first process can further include the following process: stabilizing the resin film after shrinking in the width direction. In addition, the end portion can be cut and the film width can be adjusted to a desired value before winding.

[0046] In one embodiment, the thermoplastic resin film is stretched in the width direction using a tenter stretching device while being moved along the length direction, and then shrunk in the width direction. Figure 1 is a schematic top view illustrating the first process in this embodiment. The thermoplastic resin film 1 is conveyed along the length direction at a predetermined speed while the width direction end portions are gripped by the left and right grippers 20L, 20R at the inlet of the stretching device 100a, so that the preheating region Al, the stretching region Bl, the shrinking region Cl, and the stabilizing region Dl move in order. Then, the thermoplastic resin film 1 is released from the gripping by the left and right grippers 20L, 20R and wound into a roll shape by the winding device 200.

[0047] A-2-1. Stretching device

[0048] Figure 1The illustrated stretching apparatus 100a is provided with 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 end portions in the width direction of the resin film 1. In addition, although not illustrated, the stretching apparatus 100a is typically further provided with a heating mechanism (an oven or the like) capable of adjusting the resin film to a prescribed temperature in each of the regions described below. Furthermore, in the present specification, the rail on the left side is referred to as the left rail 10L and the rail on the right side is referred to as the right rail 10R when viewed from the inlet side of the film. In the stretching apparatus 100a, a preheating region Al, a stretching region Bl, a shrinkage region Cl, and a stabilization region Dl are provided in this order from the inlet side to the outlet side of the film. Furthermore, these regions each refer to a region in which the resin film that is the object of stretching is substantially preheated, stretched, shrunk, and stabilized, and do not necessarily refer to a mechanically and structurally independent section. In addition, it should be noted that: Figure 1 The ratio of the lengths of the respective regions in the stretching apparatus can differ from the ratio of the actual lengths.

[0049] In the stretching apparatus 100a, the left and right rails 10L, 10R are configured to be left-right symmetrical in plan view; with respect to the preheating region Al, the left and right rails 10L, 10R are configured to extend substantially in parallel with the length direction of the resin film 1 at a separation distance corresponding to the initial width of the resin film 1 that is the object of stretching. With respect to the stretching region Bl, the left and right rails 10L, 10R are configured such that the separation distance thereof gradually increases from the preheating region Al side toward the shrinkage region Cl to correspond to the width of the resin film 1 after stretching. The shrinkage region Cl is configured such that the separation distance of the left and right rails 10L, 10R gradually decreases from the stretching region Bl side toward the stabilization region Dl side. With respect to the stabilization region Dl, the left and right rails 10L, 10R are configured to be substantially parallel to each other at a separation distance corresponding to the width of the resin film 1 after shrinkage. Typically, the pair of left and right clamps 20L, 20R move at substantially equal speeds to each other in a manner such that the line joining the pair of left and right clamps becomes substantially orthogonal to the direction of movement of the resin film.

[0050] The stretching apparatus used in the manufacturing method of the embodiment of the present application is not limited to the above-described illustrated example. For example, the stretching apparatus can be provided with a preheating region Al, a stretching region Bl, and a shrinkage region Cl in this order from the inlet side to the outlet side of the film, and can not have a stabilization region Dl.

[0051] A-2-2. Clamping

[0052] In the case of a long resin film, both end portions of the film at the film taking-in port of the stretching device are held by the left and right clamps. Typically, in the case of a resin film, both end portions are held by the left and right clamps at a certain clamp interval equal to each other. It is preferable to hold in a manner such that a line connecting a pair of left and right clamps when holding both end portions becomes substantially orthogonal to the moving direction of the resin film. The resin film whose both end portions are held by the left and right clamps is transported to the preheating region Al by movement of the clamps.

[0053] A-2-3. Preheating

[0054] In the preheating region Al, as described above, the left and right tracks 10L, 10R are configured to be substantially parallel to each other (extend in a direction substantially parallel to the moving direction of the resin film) at a separation distance corresponding to the initial width of the resin film that is the object of stretching, and thus the resin film is heated without substantially performing either lateral stretching or longitudinal stretching. However, in order to avoid problems such as deflection of the resin film due to preheating, contact with the nozzles in the oven, and the like, the separation distance between the left and right clamps can be slightly expanded.

[0055] In the preheating, the resin film is heated to a temperature T1 (°C). The temperature T1 is preferably equal to or higher than the glass transition temperature (Tg) of the resin film, more preferably equal to or higher than Tg + 2°C, and further preferably equal to or higher than Tg + 5°C. On the other hand, the heating temperature T1 is preferably equal to or lower than Tg + 40°C, and more preferably equal to or lower than Tg + 30°C. The temperature T1 varies depending on the resin film used, and is, for example, 70°C to 190°C, and is preferably 80°C to 180°C.

[0056] The temperature increase time up to the above temperature T1 and the holding time at the temperature T1 can be appropriately set depending on the constituent material of the resin film, the manufacturing conditions (for example, the conveyance speed of the resin film). In addition, the resin film can be heated stepwise. These temperature increase time and holding time can be controlled by adjusting the moving speed of the clamps, the length of the preheating region, the temperature of the preheating region, and the like. The preheating time can be, for example, 8 seconds to 180 seconds.

[0057] A-2-4. Stretching

[0058] In the stretching region Bl, stretching of the resin film in the width direction is performed. Specifically, by moving the stretching region Bl configured as a left and right track whose separation distance gradually expands downstream in the conveyance direction, the resin film is stretched in the width direction.

[0059] The stretching ratio in the width direction E1 (E1 = film width after stretching (W1) / initial film width (W0)) can be appropriately selected depending on the final stretching ratio E. Specifically, it is preferable to select such that the stretching ratio in the width direction E1 satisfies the following equation (1), more preferably to select such that it satisfies equation (2), and even more preferably to select such that it satisfies equation (3). Further, the film width described above refers to the film width including the portion held by the left and right clamps.

[0060] E x 0.55 < E1 < E x 0.75 (1)

[0061] E x 0.6 < E1 < E x 0.7 (2)

[0062] E x 0.6 < E1 < E x 0.65 (3)

[0063] In one embodiment, the stretching ratio in the width direction E1 can be, for example, 1.4 to 2.2 times, preferably 1.5 to 2.1 times, and more preferably 1.6 to 2.0 times.

[0064] The stretching speed [(film width after stretching (W1) - initial film width (W0)) / required time for the stretching process] is preferably 30 mm / sec or less, more preferably 10 to 25 mm / sec, and even more preferably 12 to 20 mm / sec. By setting the stretching speed to such a value, it is possible to appropriately balance the heating reliability and the precision of the orientation axis.

[0065] The stretching described above can be performed at a temperature T2. The temperature T2 is preferably Tg - 20°C to Tg + 30°C, more preferably Tg - 10°C to Tg + 20°C, and particularly preferably around Tg, with respect to the glass transition temperature (Tg) of the resin film. The temperature T2 varies depending on the resin film used, and is, for example, 70°C to 180°C, and preferably 80°C to 170°C. The difference between the temperature T1 and the temperature T2 (T1 - T2) is preferably ±2°C or more, and more preferably ±5°C or more. In one embodiment, T1 > T2, and thus it is possible to cool the resin film heated to the temperature T1 in the preheating to the temperature T2.

[0066] A-2-5. Shrinkage

[0067] In the shrinkage region C1, the resin film is shrunk in the width direction. Specifically, the resin film is shrunk in the width direction by moving the shrinkage region C1 configured such that the separation distance of the left and right tracks gradually decreases toward the downstream in the conveyance direction. By such a shrinkage process, the residual stress in the resin film is relaxed, and as a result, it is possible to improve the heating reliability.

[0068] The shrinkage ratio in the width direction [shrunken film width (W2) / stretched film width (Wl)] is preferably 0.92 to 1.0, more preferably 0.95 to 1.0, and further preferably 0.98 to 1.0. If the shrinkage ratio is such, high heating reliability can be obtained.

[0069] The above-mentioned shrinking is typically performed at a temperature T3. The temperature T3 is typically the glass transition temperature (Tg) of the resin film or less, preferably Tg - 20°C to Tg°C, more preferably Tg - 15°C to Tg°C, and further preferably Tg - 10°C to Tg°C.

[0070] A-2-6. Stabilization

[0071] In the stabilization region Dl, the resin film is typically maintained at a temperature T4 without being stretched or shrunk. By this, the orientation state of the resin film is stabilized. The temperature T4 is typically the glass transition temperature (Tg) of the resin film or less, preferably 1°C or less than Tg, and more preferably room temperature to 3°C less than Tg. In one embodiment, the temperature T4 is equal to the temperature T3°C. Further, the stabilization treatment time can be appropriately set depending on the constituent material of the resin film and the manufacturing conditions (e.g., the conveyance speed of the resin film). The stabilization time can be, for example, 5 seconds to 60 seconds.

[0072] A-2-7. Release

[0073] The resin film subjected to the above-mentioned shrinking and optional stabilization is released by the left and right clamps in the vicinity of the outlet of the stretching device. The release by the clamps can be performed, for example, in a room temperature (around 25°C) environment.

[0074] A-2-8. Winding

[0075] The resin film released by the above-mentioned clamps is wound into a roll shape by a winding device according to a conventional method.

[0076] A-3. Second Process

[0077] The second process includes, in order, the following processes: preheating while unwinding and moving the roll-shaped thermoplastic resin film wound in the first process in the length direction, stretching in the width direction, and shrinking in the width direction. The second process can further include stabilizing the resin film after the shrinking in the width direction, as necessary.

[0078] In one embodiment, the roll-shaped thermoplastic resin film wound in the first process is unwound and moved in the length direction while being stretched in the width direction using a tenter stretching device, and then shrunk in the width direction. Figure 2This is a top view schematic diagram illustrating the second step of this embodiment. While the thermoplastic resin film 1, which has been wound into a roll in the first step, is wound out of the winding device 300 and conveyed along its length at a predetermined speed, the film is held at the width end by left and right clamps 20L and 20R at the entrance of the stretching device 100b and moved sequentially towards the preheating zone A2, the stretching zone B2, the shrinking zone C2, and the stabilization zone D2. Then, the thermoplastic resin film 1 is released from the clamping based on the left and right clamps 20L and 20R.

[0079] A-3-1. Tensioning device

[0080] Figure 2 The tensioning device 100b shown has a similar function to... Figure 1 The stretching device 100b shown has a substantially the same configuration as the stretching device 100a. Specifically, the stretching device 100b includes a pair of left and right tracks 10L, 10R and multiple pairs of left and right clamps 20L, 20R that move along the left and right tracks 10L, 10R and clamp the end of the resin film 1 in the width direction. Typically, in each region described later, a heating mechanism (oven, etc.) (not shown) is further provided to adjust the resin film to a specified temperature. In the stretching device 100b, a preheating region A2, a stretching region B2, a shrinkage region C2, and a stabilization region D2 are arranged sequentially from the inlet side to the outlet side of the film. Furthermore, these regions, which substantially preheat, stretch, shrink, and stabilize the resin film to be stretched, are not necessarily mechanically or structurally independent partitions. In addition, it should be noted that: Figure 2 The ratio of the lengths of the different regions in the stretching device may differ from the ratio of the actual lengths.

[0081] Regarding the stretching device 100b, the left and right tracks 10L and 10R are configured to be symmetrical when viewed from above. Regarding the preheating zone A2, the left and right tracks 10L and 10R are configured to extend approximately parallel to the length direction of the resin film 1 with a separation distance corresponding to the initial width of the resin film 1 being stretched (the width of the resin film rolled out in step 2). Regarding the stretching zone B2, the separation distance of the left and right tracks 10L and 10R is configured to gradually increase from the preheating zone A2 towards the shrinkage zone C2 until it corresponds to the stretched width of the resin film 1. Regarding the shrinkage zone C2, the separation distance of the left and right tracks 10L and 10R is configured to gradually decrease from the stretching zone B2 towards the stabilization zone D2. Regarding the stabilization zone D2, the left and right tracks 10L and 10R are configured to be approximately parallel to each other with a separation distance corresponding to the shrunken width of the resin film 1. Typically, a pair of left and right clamps 20L and 20R move at approximately equal speeds with the line connecting them being approximately orthogonal to the direction of movement of the resin film.

[0082] The stretching device for the manufacturing method of the embodiments of the present application is not limited to the stretching device of the above-described illustrated example. For example, the stretching device can be provided with a preheating region A2, a stretching region B2, and a contraction region C2 in this order from the inlet side to the outlet side of the film without having a stabilization region D2.

[0083] A-3-2. Clamping

[0084] In the case of the long strip-shaped resin film, both ends of the film taking-in section of the stretching device are clamped by the left and right clamps. The clamping of the long strip-shaped resin film based on the left and right clamps can be performed in the same manner as in the first process.

[0085] A-3-3. Preheating

[0086] In the preheating region A2, preheating of the resin film is performed. As for the preheating of the resin film, the same description as in the preheating in the first process can be applied.

[0087] A-3-4. Stretching

[0088] In the stretching region B2, stretching of the resin film in the width direction is performed. Specifically, by moving the stretching region B2 configured so that the separation distance of the left and right tracks gradually increases toward the downstream of the conveyance direction, the resin film is stretched in the width direction.

[0089] The stretching ratio E2 in the width direction (E1 = film width (W4) after stretching / initial film width (W3)) can be appropriately set according to the final stretching ratio E. In one embodiment, the stretching ratio E2 in the width direction can be, for example, 1.3 to 1.9 times, preferably 1.4 to 1.8 times, and more preferably 1.5 to 1.7 times. In addition, the initial film width (W3) can be equivalent to the film width (W2) after contraction in the first process, but in the case where some contraction occurs at the time of stabilization or thereafter, the end portion can be cut off at times, and thus, it can be in a relationship of W3 ≤ W2.

[0090] As for the stretching speed and the stretching temperature, the same description as in the stretching in the first process can be applied.

[0091] A-3-5. Contraction

[0092] In the contraction region C2, contraction of the resin film in the width direction is performed. Specifically, by moving the contraction region C2 configured so that the separation distance of the left and right tracks gradually decreases toward the downstream of the conveyance direction, the resin film is contracted in the width direction. By such a contraction process, the residual stress in the resin film is relaxed, and as a result, the heating reliability can be improved.

[0093] The width direction shrinkage ratio [shrunken film width (W5) / stretched film width (W4)] is preferably 0.92 to 1.0, more preferably 0.95 to 1.0, further preferably 0.98 to 1.0. If the shrinkage ratio is such, high heating reliability can be obtained.

[0094] As for the shrinkage temperature, the same description as the shrinkage in the first process can be applied.

[0095] A-3-6. Stabilization

[0096] In the stabilization region D2, the resin film is typically maintained at a prescribed stabilization temperature without being stretched or shrunk. As for the stabilization temperature and the stabilization time, the same description as the stabilization in the first process can be applied.

[0097] A-3-7. Release

[0098] The resin film that has undergone the above-described shrinkage and optional stabilization is released from the left and right clamps in the vicinity of the outlet of the stretching device. The release from the clamps can be performed, for example, in a room temperature (around 25°C) environment.

[0099] The resin film (stretched film) released from the clamps can be wound into a roll shape by a winding device. Alternatively, the resin film can be supplied directly to the next process (e.g., punched to a prescribed size and laminated with other long optical film, etc.) without being wound.

[0100] B. Stretched Film

[0101] The stretched film obtained by the production method described in item A is typically a phase difference film having optical anisotropy. The thickness of the stretched film can be preferably 30 μm to 70 μm, more preferably 35 μm to 55 μm, further preferably 35 μm to 45 μm.

[0102] The refractive index characteristics of the phase difference film preferably show a relationship of nx > ny. In addition, the in-plane orientation of the phase difference film is preferably high, and, for example, the birefringence Δn (Δn = nx - ny) of the phase difference film measured at a wavelength of 550 nm is preferably 0.0020 to 0.0050, more preferably 0.0025 to 0.0050, further preferably 0.0030 to 0.0045, and more further preferably 0.0035 to 0.0045.

[0103] The phase difference film preferably functions as a λ / 4 plate. The front phase difference Re(550) of the phase difference film is preferably 100 nm to 160 nm, more preferably 135 nm to 155 nm. In the present specification, nx is the refractive index in the direction in which the in-plane refractive index is the largest (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., 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 having a wavelength of λ nm at 23°C. Thus, Re(550) is the front phase difference of the film measured with light having a wavelength of 550 nm at 23°C. Re(λ) is calculated from the formula: Re(λ) = (nx - ny) x d when the thickness of the film is set to d (nm).

[0104] The phase difference film can exhibit an arbitrary appropriate refractive index ellipsoid as long as it has a relationship of nx > ny. The refractive index ellipsoid of the phase difference film preferably exhibits a relationship of nx > ny > nz. The Nz coefficient of the phase difference film is preferably 1 to 1.20, more preferably 1 to 1.19, further preferably 1 to 1.18, and further more preferably 1 to 1.17. The Nz coefficient is calculated from Nz = Rth(λ) / Re(λ). Here, Rth(λ) is the thickness direction phase difference of the film measured with light having a wavelength of λ nm at 23°C, and is calculated from the formula: Rth(λ) = (nx - nz) x d.

[0105] The phase difference film typically exhibits a so-called reverse dispersion wavelength dependence. Specifically, the front phase difference thereof satisfies a relationship of Re(450) < Re(550) < Re(650). The phase difference film preferably satisfies the following formulas (A) and (B), and more preferably further satisfies (C).

[0106] 0.8 < R(450) / R(550) < 1 (A)

[0107] 1 < R(650) / R(550) < 1.2 (B)

[0108] 0.8 < R(450) / R(550) ≤ 0.95 (C)

[0109] The absolute value of the photoelastic coefficient of the phase difference film is preferably 2 x 10 -12 (m 2 / N) to 100 x 10 -12 (m 2 / N), more preferably 2 x 10 -12 (m 2 / N) to 50 x 10 -12 (m 2 / N).

[0110] The alignment axis of the phase difference film is excellent in accuracy. The difference between the angle of the alignment axis (slow axis) at the widthwise end portion and the angle of the alignment axis (slow axis) at the widthwise central portion can be, for example, within ±3°, preferably within ±2°, and more preferably within ±1.8°.

[0111] Examples

[0112] Hereinafter, the present application will be specifically described by way of examples, but the present application is not limited to these examples. Furthermore, the measurement and evaluation methods in the examples are described below.

[0113] (1) Orientation angle (direction in which the slow axis appears)

[0114] The widthwise central portion and both end portions of the phase difference film obtained in the examples and comparative examples were cut out in a square shape having a width of 50 mm and a length of 50 mm in such a manner that one side becomes parallel to the width direction of the film. The sample was measured using a Mueller matrix polarimeter (Axometrics Co., Ltd., product name "Axoscan"), and the orientation angle at 23°C was measured at a wavelength of 550 nm. Furthermore, the measurement was performed with the sample placed parallel to the measurement stage with respect to the orientation angle. The difference between the orientation angle of the widthwise central portion and the orientation angle of both end portions was calculated, and evaluated as the orientation angle unevenness (orientation angle Δ).

[0115] (2) Front phase difference Re, thickness direction phase difference Rth, and Δn

[0116] The measurement was performed at 23°C using the product name "Axoscan" manufactured by Axometrics Co., Ltd. in the same manner as in the above (1). Furthermore, Δn is the value at a wavelength of 550 nm.

[0117] (3) Nz coefficient

[0118] The calculation was performed based on the formula: Nz = Rth(550) / Re(550).

[0119] (4) Thickness

[0120] The measurement was performed using a micrometer thickness meter (manufactured by Mitutoyo Co., Ltd.).

[0121] [Example 1]

[0122] (Production of polycarbonate resin film)

[0123] Polymerization was performed using a batch polymerization apparatus composed of two vertical reactors equipped with stirring wings and reflux coolers controlled to 100°C. 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), isosorbide (ISB), diethylene glycol (DEG), diphenyl carbonate (DPC), and magnesium acetate tetrahydrate were charged in a molar ratio of BHEPF / ISB / DEG / DPC / magnesium acetate = 0.348 / 0.490 / 0.162 / 1.005 / 1.00 x 10 -5 The reactor was sufficiently subjected to nitrogen replacement (oxygen concentration: 0.0005 to 0.001 vol%) and then heated by a heating medium, and stirring was started at the time when the internal temperature became 100°C. The internal temperature was brought to 220°C 40 minutes after the start of temperature increase, and the temperature was controlled so as to maintain this temperature, and simultaneously, pressure reduction was started, and after reaching 220°C, the pressure was set to 13.3 kPa in 90 minutes. Phenol vapor produced as a byproduct of the polymerization reaction was introduced into a reflux cooler at 100°C, and the monomer components contained in a small amount in the phenol vapor were returned to the reactor, and the phenol vapor that was not condensed was introduced into a condenser at 45°C to be recovered.

[0124] The first reactor was temporarily returned to atmospheric pressure by introducing nitrogen, and then the oligomerized reaction solution in the first reactor was transferred to the second reactor. Subsequently, temperature increase 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 in 50 minutes. Then, polymerization was performed until a prescribed stirring power was reached. At the time when the prescribed power was reached, the pressure was returned by introducing nitrogen into the reactor, and the reaction solution was taken out in the form of a strand, and pelletized by a rotary cutter, and a polycarbonate resin A having a copolymer composition of BHEPF / ISB / DEG = 34.8 / 49.0 / 16.2 [mole %] was obtained. The specific viscosity of this polycarbonate resin was 0.430 dL / g, and the glass transition temperature was 140°C.

[0125] The obtained polycarbonate resin was vacuum-dried at 80°C for 5 hours, and then a film was produced using a film production apparatus equipped with a single-screw extruder (manufactured by Sumitomo Heavy Industries, Ltd., screw diameter: 25 mm, cylinder set temperature: 220°C), a T-die (width: 900 mm, set temperature: 220°C), a cooling roll (set temperature: 120 to 130°C), and a take-up machine, and a polycarbonate resin film having a thickness of 130 μm was produced.

[0126] (Making of phase difference film)

[0127] The polycarbonate resin film obtained as described above was subjected to the first step using a stretching apparatus as shown in Figure 1 Figure 2 ​The second process was performed using the stretching device shown, whereby a phase difference film was obtained. Details of each process are described below.

[0128] (First Process)

[0129] While moving the long polycarbonate resin film (thickness: 130 μm, width (W0): 610 mm) at a speed of 1500 mm / sec in the length direction, the left and right end portions were clamped with left and right clamps.

[0130] Next, while moving the preheating zone, the film temperature was raised in three stages (144°C, 149°C, and 154°C), and the resin film was preheated at each temperature for about 1.5 seconds.

[0131] Next, the stretching zone was moved to a zone in which the separation distance of the left and right clamps was expanded, whereby the resin film was stretched in the width direction. The stretching temperature (film temperature) was 143°C, and the stretching ratio (W1 / W0) was 1.55 times.

[0132] Next, the contraction zone was moved to a zone in which the separation distance of the left and right clamps was reduced, whereby the resin film was contracted in the width direction. The contraction temperature (film temperature) was 138°C, and the contraction ratio (W2 / W1) was 0.98 times.

[0133] Next, at the outlet of the stretching device (atmosphere temperature: 25°C), the resin film was released from the left and right clamps, the cutouts of the two end portions including the clamp portions were cut to about 100 mm, and the film was wound into a roll shape with a winding device.

[0134] (Second Process)

[0135] While the polycarbonate resin film obtained in the first process (thickness: 84 μm, width (W3): 767 mm) was unwound and moved at a speed of 1500 mm / sec in the direction opposite to the moving direction in the first process, the left and right end portions were clamped with left and right clamps.

[0136] Next, while moving the preheating zone, the film temperature was raised in three stages (144°C, 149°C, and 154°C), and the resin film was preheated at each temperature for about 1.5 seconds.

[0137] Next, the stretching zone was moved to a zone in which the separation distance of the left and right clamps was expanded, whereby the resin film was stretched in the width direction. The stretching temperature (film temperature) was 143°C, and the stretching ratio (W4 / W3) was 1.81 times (total stretching ratio: 2.8 times).

[0138] Next, the resin film was shrunk in the width direction by moving to a shrinkage region where the separation distance of the left and right clamps was reduced. The shrinkage temperature (film temperature) was 138°C, and the shrinkage ratio (W5 / W4) was 0.98 times.

[0139] Next, the resin film was released from the left and right clamps at the outlet of the stretching device (atmosphere temperature: 25°C).

[0140] A phase difference film (thickness: 47 μm) was obtained as described above.

[0141] [Example 2]

[0142] A phase difference film (thickness: 47 μm) was obtained as in Example 1, except that the stretching ratio (W1 / W0) in the first step was set to 1.75 times and the stretching ratio (W4 / W3) in the second step was set to 1.6 times.

[0143] [Example 3]

[0144] A phase difference film (thickness: 47 μm) was obtained as in Example 1, except that the stretching ratio (W1 / W0) in the first step was set to 1.95 times and the stretching ratio (W4 / W3) in the second step was set to 1.44 times.

[0145] [Example 4]

[0146] A phase difference film (thickness: 47 μm) was obtained as in Example 1, except that the stretching ratio (W1 / W0) in the first step was set to 2.1 times and the stretching ratio (W4 / W3) in the second step was set to 1.34 times.

[0147] [Example 5]

[0148] A phase difference film (thickness: 40 μm) was obtained as in Example 1, except that the thickness of the film before stretching was set to 110 μm.

[0149] [Example 6]

[0150] A phase difference film (thickness: 36 μm) was obtained as in Example 2, except that the thickness of the film before stretching was set to 100 μm.

[0151] [Example 7]

[0152] A phase difference film (thickness: 38 μm) was obtained as in Example 3, except that the thickness of the film before stretching was set to 105 μm.

[0153] [Example 8]

[0154] A phase difference film (thickness: 42 μm) was obtained in the same manner as in Example 4 except that the thickness of the film before stretching was set to 120 μm.

[0155] [Comparative Example 1]

[0156] A phase difference film (thickness: 47 μm) was obtained in the same manner as in Example 1 except that the stretching ratio (W1 / W0) in the first step was set to 2.8 times and the second step was not performed.

[0157] [Comparative Example 2]

[0158] A phase difference film (thickness: 47 μm) was obtained in the same manner as in Example 1 except that the stretching ratio (W1 / W0) in the first step was set to 1.4 times and the stretching ratio (W4 / W3) in the second step was set to 2.0 times.

[0159] [Comparative Example 3]

[0160] A phase difference film (thickness: 47 μm) was obtained in the same manner as in Example 1 except that the stretching ratio (W1 / W0) in the first step was set to 2.45 times and the stretching ratio (W4 / W3) in the second step was set to 1.14 times.

[0161] [Reference Example 1]

[0162] A phase difference film (thickness: 30 μm) was obtained in the same manner as in Example 1 except that an isosorbide polycarbonate resin film (manufactured by Mitsubishi Chemical Corporation, product name "Durabio", thickness: 85 μm, Tg = 124°C) was used, the preheating temperature in the first step was set to 140°C, the stretching temperature was set to 137°C, the stretching ratio (W1 / W0) was set to 2.8 times, and the second step was not performed.

[0163] [Reference Example 2]

[0164] A phase difference film (thickness: 18 μm) was obtained in the same manner as in Example 1 except that a cyclic olefin resin film (manufactured by JSR Corporation, product name "Arton", thickness: 50 μm, Tg = 137°C) was used, the preheating temperature in the first step was set to 147°C, the stretching temperature was set to 142°C, the stretching ratio (W1 / W0) was set to 2.8 times, and the second step was not performed.

[0165] The phase difference films obtained in the above examples, comparative examples, and reference examples were subjected to the measurement of (1) to (3) described above. The results are shown in Table 1. In addition, with respect to the phase difference films obtained in the examples and comparative examples, the relationship between the stretching ratio in the first step and the birefringence and the relationship between the stretching ratio in the first step and the orientation angle unevenness are shown in Figs. 1 and 2, respectively. Figure 3 andFigure 4 .

[0166] Table 1

[0167]

[0168] < Evaluation >

[0169] As shown in Table 1 and Figure 3 and Figure 4 , it was found that the phase difference film obtained in the examples was superior in both the orientation axis precision and the orientation property (in-plane orientation property and uniaxiality) compared to the phase difference film obtained in the comparative examples. In addition, as shown in Reference Example 1 and Reference Example 2, it was found that even a manufacturing method including only one stretching and one shrinking, respectively, did not easily cause orientation angle unevenness depending on the resin film showing positive wavelength dispersion characteristics and the resin film showing flat wavelength dispersion characteristics.

[0170] Industrial Applicability

[0171] The phase difference film obtained by the manufacturing method of the present application can be applied to an image display device such as a liquid crystal display device (LCD), an organic electroluminescence display device (OLED), and the like.

Claims

1. A method for producing a stretched film, the stretched film being a phase difference film, comprising a first process and a second process, the first process comprising, in this order, a preheating process, a stretching process in the width direction, a shrinkage process in the width direction, and a winding process into a roll shape, while moving a long thermoplastic resin film in the length direction, the second process comprising, in this order, a preheating process, a stretching process in the width direction, and a shrinkage process in the width direction, while unwinding the thermoplastic resin film in the roll shape and moving it in the length direction, the stretching ratio in the width direction in the first process being 1.4 times to 2.2 times, wherein when the stretching ratio in the width direction in the first process is El and the total stretching ratio in the width direction is set as E, the stretched film satisfies the following equation (1), E x 0.55 < El < E x 0.75 (1).

2. The method for producing a stretched film according to claim 1, which is a method for producing a stretched film satisfying the following equations (A) and (B), 0.8 < R(450) / R(550) < 1 (A) 1 < R(650) / R(550) < 1.2 (B) in the equations (A) and (B), R(450), R(550), and R(650) are the front surface phase difference of the film measured with light having a wavelength of 450 nm, 550 nm, and 650 nm at 23°C, respectively.

3. The production method according to claim 1 or 2, wherein the total stretching ratio in the width direction being 2.4 times to 3.2 times.

4. The production method according to claim 1 or 2, wherein the thermoplastic resin film contains at least one selected from the group consisting of polycarbonate-based resins, polyvinyl acetal resins, cellulose ester-based resins, polyester-based resins, and polyester carbonate-based resins.

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