Method for producing stretched film

Abstract

To provide a method for producing a stretched film, capable of sufficiently changing pitches of a plurality of first clips at a stretching step and, also, capable of smoothly moving a plurality of second clips after a releasing step.SOLUTION: A method for producing a stretched film in one embodiment includes a holding step, a stretching step and a releasing step in this order. In the holding step, a first end of a film is held by a plurality of first clips, and a second end of the film is held by a plurality of second clips. In the stretching step, the film is stretched in an oblique direction by moving the plurality of first clips and the plurality of second clips while making pitches of the plurality of first clips larger than pitches of the plurality of second clips. In the releasing step, the film is released from the plurality of first clips and the plurality of second clips. This method of producing a stretched film adjusts the pitches of the plurality of first clips and the pitches of the plurality of second clips after the releasing step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Circular polarizing plates are used in image display devices such as liquid crystal displays (LCDs) and organic electroluminescence displays (OLEDs) to improve display characteristics and prevent reflection. A circular polarizing plate typically comprises a polarizer and a retardation film (typically a λ / 4 plate) laminated together such that the absorption axis of the polarizer and the slow axis of the retardation film form a 45° angle. Conventionally, retardation films are typically produced by uniaxial or biaxial stretching in the machine and / or cross directions, and the slow axis is often expressed in the cross direction (width direction) or machine direction (length direction) of a long raw film. As a result, to produce a circular polarizing plate, it is necessary to cut retardation films so that they form a 45° angle with the machine or cross direction and then bond them together one by one.

[0003] Therefore, there is a demand for the production of a retardation film having a slow axis extending in a direction oblique to the longitudinal direction.As a method for producing such a retardation film, for example, a method for obliquely stretching a sheet or film has been proposed, in which the left and right ends of a long film in the width direction are held by left and right clips of a variable pitch type whose longitudinal clip pitch is variable, one of the left and right clips is set as the advancing side and the other is set as the lagging side, and the clip pitch of the advancing side is changed to be larger than the clip pitch of the lagging side, thereby stretching the film in a direction oblique to the longitudinal direction (hereinafter also referred to as "oblique stretching") (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4845619 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method for obliquely stretching a sheet or film described in Patent Document 1, the lagging clip is pulled by the leading clip through the film, which can cause the pitch of the lagging clip to become narrower than the desired pitch. In this case, after the lagging clip releases the film, a blockage can occur in the flow of the clip, making it difficult for the clip to move smoothly. The main object of the present invention is to provide a method for manufacturing a stretched film that can sufficiently change the pitch of multiple first clips during the stretching process and can smoothly move multiple second clips after the release process. [Means for solving the problem]

[0006] [1] A method for producing a stretched film according to one embodiment of the present invention includes a gripping step, a stretching step, and a releasing step, in this order. In the gripping step, a first widthwise end of a long film is gripped by a plurality of first clips aligned in the longitudinal direction of the film, and a second widthwise end of the film is gripped by a plurality of second clips aligned in the longitudinal direction. In the stretching step, the first clips and the second clips are moved in the longitudinal direction while the pitch of the first clips is made larger than the pitch of the second clips, thereby stretching the film in an oblique direction intersecting both the longitudinal direction and the widthwise direction. In the releasing step, the first end of the film is released from the first clips, and the second end of the film is released from the second clips. This method for producing a stretched film further includes a pitch adjusting step, in which the pitch of the first clips and the pitch of the second clips are adjusted after the releasing step. [2] In the method for producing a stretched film according to [1] above, in the opening step, the first clips may open the first end while moving in the longitudinal direction, and the second clips may open the second end while moving in the longitudinal direction.

[0007] According to the embodiment of the present invention, the pitch of the plurality of first clips can be sufficiently changed in the stretching step, and the plurality of second clips can be smoothly moved after the releasing step. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating an example of a stretching device capable of carrying out a stretched film manufacturing method according to one embodiment of the present invention. [Figure 2] 2 is a schematic plan view for explaining a gripping step carried out by the stretching device of FIG. 1. FIG. [Figure 3] FIG. 2 is a schematic cross-sectional view for explaining a gripping step carried out by the stretching device of FIG. [Figure 4] 2 is a schematic diagram showing a clip pitch profile in a stretching process carried out by the stretching device of FIG. 1. FIG. [Figure 5] 2 is a schematic plan view for explaining a link mechanism provided in the stretching device of FIG. 1. FIG. [Figure 6] 6 is a schematic plan view for explaining the operation of the link mechanism of FIG. 5. FIG. [Figure 7] 2 is a schematic plan view of a pitch control wheel provided in the drawing device of FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. Note that the drawings are drawn schematically or conceptually to facilitate visibility and understanding, and the length, width, shape, size, ratio, direction, number, etc. may differ from the actual ones, and there may be no correspondence between the drawings.

[0010] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is greatest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane birefringence (Δn) "Δn(λ)" is the in-plane birefringence measured with light of wavelength λ nm at 23° C. For example, "Δn(550)" is the in-plane birefringence measured with light of wavelength 550 nm at 23° C. In-plane birefringence (Δn) is calculated from the formula: Δn=nx-ny. (3) Substantially parallel or perpendicular The expressions "substantially perpendicular" and "approximately perpendicular" include the case where the angle between two directions is 90°±10°, preferably 90°±7°, and more preferably 90°±5°. The expressions "substantially parallel" and "approximately parallel" include the case where the angle between two directions is 0°±10°, preferably 0°±7°, and more preferably 0°±5°. Furthermore, when simply referring to "orthogonal" or "parallel" in this specification, this can include the state of being substantially perpendicular or substantially parallel.

[0011] A. Overview of the stretched film manufacturing method FIG. 1 is a schematic diagram of an example of a stretching device capable of carrying out a method for producing a stretched film according to one embodiment of the present invention; FIG. 2 is a schematic plan view illustrating the gripping process carried out by the stretching device of FIG. 1; FIG. 3 is a schematic cross-sectional view illustrating the gripping process carried out by the stretching device of FIG. 1; and FIG. 4 is a schematic diagram showing the clip pitch profile in the stretching process carried out by the stretching device of FIG. 1. A method for producing a stretched film according to one embodiment of the present invention includes a gripping step, a stretching step, and a releasing step in this order. As shown in Figures 2 and 3, in the holding process, a first end 1R of the film 1 is held by multiple first clips 40R, and a second end 1L of the film 1 is held by multiple second clips 40L. The film 1 has a long shape. The first end 1R is located at one end in the width direction (direction perpendicular to the long direction) of the film 1. The second end 1L is located at the other end of the film 1 opposite the first end 1R in the width direction (direction perpendicular to the long direction). In the holding process, the multiple first clips 40R are lined up in the long direction of the film 1, and the multiple second clips 40L are lined up in the long direction of the film 1. 4, in the stretching process, the pitch of the first clips 40R is made larger than the pitch of the second clips 40L, and the first clips 40R and the second clips 40L are moved in the longitudinal direction of the film 1. This causes the film 1 to be stretched in an oblique direction that intersects both the longitudinal direction and the width direction. In the releasing process, the first end 1R of the film 1 is released from the multiple first clips 40R, and the second end 1L of the film 1 is released from the multiple second clips 40L (see FIG. 3). In the releasing process, typically, the multiple first clips 40R move in the longitudinal direction of the film 1 to release the first end 1R of the film 1, and the multiple second clips 40L move in the longitudinal direction of the film 1 to release the second end 1L of the film 1 (see FIG. 3). As shown in Figure 1, this method of producing a stretched film includes a pitch adjustment step in addition to the gripping, stretching, and opening steps described above. In the pitch adjustment step, the pitch of the first clips 40R and the pitch of the second clips 40L are adjusted after the opening step described above. Therefore, after the opening step, the pitch of the second clips 40L can be adjusted to a suitable range. As a result, blockages in the flow of the second clips 40L can be suppressed after the opening step. Furthermore, because the pitch of the first clips 40R and the pitch of the second clips 40L are adjusted after the film 1 is released, it is possible to prevent the pitch adjustment from affecting the pitch variability of the first clips 40R during the stretching process. As a result, it is possible to sufficiently and smoothly change the pitch of the first clips 40R during the stretching process, and it is possible to smoothly move the second clips 40L after the release process. In this specification, the term "pitch" refers to the length of an imaginary line segment connecting the centers of adjacent members among a plurality of members (clips, clip support members, etc.).

[0012] In one embodiment, the method for producing a stretched film further includes a preheating step and a heat setting step. The preheating step is carried out between the holding step and the stretching step. In the preheating step, the film 1 is preheated to any appropriate temperature. The heat setting step is carried out between the stretching step and the releasing step. In the heat setting step, the film 1 is heat set at any appropriate temperature.

[0013] B. Stretching device Next, with reference to FIG. 1, a stretching apparatus 100 capable of continuously carrying out the above-described method for producing a stretched film will be described. The stretching device 100 includes a first stretching unit 101R including a plurality of first clips 40R, and a second stretching unit 101L including a plurality of second clips 40L.

[0014] The first stretching unit 101R and the second stretching unit 101L are spaced apart from each other in a first direction perpendicular to the up-down direction (typically the vertical direction). Between the first stretching unit 101R and the second stretching unit 101L, the following zones are provided in this order: a gripping zone A where the gripping step described above is performed; a preheating zone B where the preheating step described above is performed; a stretching zone C where the stretching step described above is performed; a heat setting zone D where the heat setting step described above is performed; and a release zone E where the release step described above is performed. These zones are not mechanically or structurally independent. The length ratio of each zone in the stretching device shown in FIG. 1 may differ from the actual length ratio.

[0015] Furthermore, a zone for performing any appropriate treatment may be provided between the stretching zone C and the heat-setting zone D, as needed. Examples of such treatments include transverse shrinkage treatment. Furthermore, the stretching device typically includes a heating device (e.g., various types of hot air, near-infrared, or far-infrared ovens) for creating a heated environment from the preheating zone B to the heat-setting zone D or the release zone E.

[0016] The first stretching unit 101R has a configuration in which the pitch of the plurality of first clips 40R can be changed (variable pitch type). In one embodiment, the first stretching unit 101R includes a reference rail 10, a pitch setting rail 20, a plurality of clip support members 30, a link mechanism 80 (see FIG. 5), a plurality of first clips 40R, a driving means 50, and a pitch control wheel 70.

[0017] B-1. Reference rail The reference rail 10 typically has an endless shape and has a first curved portion 10a, a second curved portion 10b, a third curved portion 10c, and a fourth curved portion 10d. The first curved portion 10a and the second curved portion 10b are spaced apart in the vertical direction and in a second direction perpendicular to the first direction. In the second direction, the first curved portion 10a is located on the opposite side of the stretching zone C from the gripping zone A. In the second direction, the second curved portion 10b is located on the opposite side of the stretching zone C from the open zone E. The third bending portion 10c is positioned away from the second bending portion 10b in the first direction. The fourth bending portion 10d is positioned away from the third bending portion 10c in the second direction and away from the first bending portion 10a in the first direction. The central angle of each of the first curved portion 10a, the second curved portion 10b, the third curved portion 10c and the fourth curved portion 10d is typically 90°.

[0018] In the illustrated example, the portions of the reference rail 10 corresponding to the gripping zone A and the preheating zone B extend along the second direction. Furthermore, the portion of the reference rail 10 corresponding to the stretching zone C extends in a direction intersecting the second direction so as to move away from the second stretching unit 101L as it approaches the heat setting zone D from the preheating zone B. Furthermore, the portions of the reference rail 10 corresponding to the heat setting zone D and the release zone E extend along the second direction. The configuration of the reference rail 10 is not limited to the illustrated example. For example, the portion of the reference rail 10 corresponding to the gripping zone A to the release zone E may extend linearly along the second direction.

[0019] B-2. Pitch setting rail The pitch setting rail 20 is typically arranged at a predetermined interval inside the reference rail 10. The pitch setting rail 20 is movable relative to the reference rail 10. In the illustrated example, the pitch setting rail 20 has an endless shape that follows the reference rail 10.

[0020] B-3. ​​Clip support member 5 and 6, in one embodiment, a plurality of clip support members 30 are arranged above the reference rail 10 and the pitch setting rail 20. The plurality of clip support members 30 are typically lined up along the reference rail 10 and are guided by the reference rail 10 to move around in a loop shape. Each of the plurality of clip support members 30 typically extends in a direction perpendicular to the reference rail 10. Each of the plurality of clip support members 30 supports a first clip 40R. More specifically, one end of the first support member 30R in the extending direction supports the first clip 40R.

[0021] In the illustrated example, the clip support member 30 includes a frame 31 , a first shaft member 33 , a second shaft member 34 , and a slider 32 .

[0022] The frame 31 extends in a direction perpendicular to the reference rail 10. In one embodiment, the frame 31 has a substantially rectangular frame shape when viewed from the movement direction of the clip support member 30. The frame 31 has a long hole 31a. The long hole 31a is formed in an upper beam of the frame 31. The long hole 31a extends in the same direction as the upper beam of the frame 31.

[0023] The first shaft member 33 extends in the vertical direction. The first shaft member 33 penetrates the clip support member 30 between the first clip 40R and the elongated hole 31a. A guide roller (not shown) is rotatably provided at the lower end of the first shaft member 33. The guide roller is fitted into a recessed groove (not shown) provided in the reference rail 10.

[0024] The second shaft member 34 extends in the vertical direction. The second shaft member 34 is located on the opposite side of the first clip 40R from the first shaft member 33, and passes through the clip support member 30. A pitch setting roller (not shown) is rotatably provided at the lower end of the second shaft member 34. The pitch setting roller is fitted into a recessed groove (not shown) provided in the pitch setting rail 20. In the illustrated example, the upper end of the second shaft member 34 is inserted into the elongated hole 31a.

[0025] The slider 32 is guided by the inner surface of the elongated hole 31a and is slidable relative to the frame 31. In the illustrated example, the slider 32 is provided at the upper end of the second shaft member .

[0026] The clip support member 30 may further include a drive roller 39. The drive roller 39 is engageable with a drive means 50. In the illustrated example, the drive roller 39 is provided at the upper end of the first shaft member 33.

[0027] B-4. Link mechanism The link mechanism 80 is configured to change the pitch of the multiple clip support members 30 by changing the spacing between the reference rail 10 and the pitch setting rail 20. In one embodiment, the link mechanism 80 has a pantograph structure. As shown in FIG. 6, the link mechanism 80 includes a plurality of main link members 81 and a plurality of sub-link members 82.

[0028] Each of the multiple main link members 81 connects a first shaft member 33 included in one of the adjacent clip support members 30 to a second shaft member 34 included in the other of the adjacent clip support members 30. In the illustrated example, one end of the main link member 81 is connected to the first shaft member 33 so as to be rotatable relative to the first shaft member 33. The other end of the main link member 81 is connected to the second shaft member 34 so as to be rotatable relative to the second shaft member 34.

[0029] Each of the multiple sub-link members 82 connects the main link member 81 to the first shaft member 33 to which the main link member 81 is not connected. In the illustrated example, one end of the sub-link member 82 is connected to the main link member 81 by a pivot 87 so as to be rotatable relative to the main link member 81. The other end of the sub-link member 82 is connected to the first shaft member 33 so as to be rotatable relative to the main link member 81.

[0030] 5, when the gap between the reference rail 10 and the pitch setting rail 20 becomes relatively large, the slider 32 moves within the elongated hole 31a away from the reference rail 10. This causes the main link member 81 and the sub-link member 82 to tilt, and the adjacent clip support members 30 move closer to each other. As a result, the pitch of the multiple first clips 40R becomes smaller. 6, when the gap between the reference rail 10 and the pitch setting rail 20 becomes relatively small, the slider 32 moves within the elongated hole 31a toward the reference rail 10. This causes the main link member 81 and the sub-link member 82 to stand up, and the adjacent clip support members 30 move away from each other. As a result, the pitch of the multiple first clips 40R increases.

[0031] B-5. Clip Each of the plurality of first clips 40R is supported by a corresponding clip support member 30. The first clips 40R are located on the opposite side of the reference rail 10 from the pitch setting rail 20 in a direction perpendicular to the reference rail 10.

[0032] 3, first clip 40R is configured to be able to grip first end 1R of film 1. In one embodiment, first clip 40R is able to clamp first end 1R of film 1 in the thickness direction of film 1. In the illustrated example, first clip 40R includes a base 401 and a pressing portion 402. Base 401 is fixed to one end of first support member 30R in the extension direction. Pressing portion 402 is supported by one end of first support member 30R in the extension direction so as to be movable relative to base 401 in the thickness direction of film 1.

[0033] B-6. Driving means 1, the driving means 50 is configured to apply a driving force to the plurality of clip support members 30. The driving means 50 may be disposed in any appropriate position. In the illustrated example, the driving means 50 is disposed inside the pitch setting rail 20. The driving means 50 is positioned on the opposite side of the pitch control wheel 70 from the second stretching unit 101L in the first direction, with a gap therebetween.

[0034] In one embodiment, the driving means 50 is a sprocket 50a. The sprocket 50a is rotatable about an axis extending in the vertical direction. A driving force from a motor 90 is input to the sprocket 50a. In the illustrated example, when a driving force from the motor 90 is input to the sprocket 50a, the sprocket 50a is driven to rotate and selectively engages with the driving rollers 39 provided on the clip support members 30. As a result, the driving force is transmitted to the multiple clip support members 30 in sequence, causing the multiple clip support members 30 to move in a circular motion.

[0035] B-7. Pitch control wheel 1, the pitch control wheel 70 is configured to adjust the pitch of the plurality of first clips 40R. The pitch control wheel 70 is typically located downstream of the open zone E in the direction of orbital movement of the plurality of clip support members 30 (i.e., on the opposite side of the extension zone C from the open zone E). In one embodiment, the pitch control wheel 70 is located between the open zone E and the third curved portion 10c in the direction of orbital movement of the plurality of clip support members 30. In the illustrated example, the pitch control wheel 70 is arranged along the second curved portion 10b of the reference rail 10.

[0036] 7, the pitch control wheel 70 is rotatable about an axis extending in the vertical direction. Although not shown, the pitch control wheel 70 is configured to receive a driving force from a motor. The outer diameter of the pitch control wheel 70 is, for example, 10 cm to 120 cm, and preferably 30 cm to 100 cm.

[0037] In the illustrated example, a plurality of recesses 71 are provided on the circumferential surface of the pitch control wheel 70. Each of the plurality of recesses 71 is typically configured to be able to receive the end of the frame 31 opposite the first clip 40R. The plurality of recesses 71 are positioned at equal intervals from one another in the circumferential direction of the pitch control wheel 70. When viewed from the top and bottom, each of the plurality of recesses 71 has a generally V-shape that opens outward in the radial direction of the pitch control wheel 70. There is no particular limitation on the number of the plurality of recesses 71. The number of the plurality of recesses 71 is, for example, 2 to 10, and preferably 4 to 6. The depth of the plurality of recesses 71 (the radial dimension of the pitch control wheel 70) is, for example, 5 cm to 100 cm, and preferably 20 cm to 80 cm.

[0038] B-8. Second extension unit As shown in FIG. 1, the second stretching unit 101L has a configuration in which the pitch of the plurality of second clips 40L can be changed (variable pitch type). The second stretching unit 101L typically has a configuration that is line-symmetrical to the first stretching unit 101R with respect to the second direction. The second stretching unit 101L will be described in the same manner as the first stretching unit 101R, except that the second stretching unit 101L includes a plurality of second clips 40L instead of a plurality of first clips 40R. Therefore, a description of the configuration of the second stretching unit 101L will be omitted.

[0039] C. Details of the manufacturing method of stretched film Next, a method for producing a stretched film using the stretching apparatus 100 will be described. In one embodiment, the stretching apparatus 100 performs a gripping step, a preheating step, a stretching step, a heat setting step, a releasing step, and a pitch adjusting step in this order.

[0040] C-1. Gripping process First, in each of the first stretching unit 101R and the second stretching unit 101L, the driving force from the motor 90 is input to the sprocket 50a. Then, in the illustrated example, the driving force is transmitted from the sprocket 50a to the multiple clip support members 30 provided in the first stretching unit 101R, and they move in a clockwise direction as viewed from above. As a result, the multiple first clips 40R, like the multiple clip support members 30, move in a clockwise direction as viewed from above. Furthermore, the plurality of clip support members 30 included in the second stretching unit 101L are driven by the sprocket 50a and move counterclockwise as viewed from above, causing the plurality of second clips 40L to move counterclockwise as viewed from above, similar to the plurality of clip support members 30. In addition, the movement speed of the multiple first clips 40R in the first stretching unit 101R and the movement speed of the multiple second clips 40L in the second stretching unit 101L can be independently controlled to any value by adjusting the output of the motor 90 and changing the driving force transmitted from the sprocket 50a to the clip support member 30.

[0041] In addition, in each of the first stretching unit 101R and the second stretching unit 101L, a driving force from a motor (not shown) is input to the pitch control wheel 70. As a result, the pitch control wheel 70 provided in the first stretching unit 101R rotates clockwise when viewed from above. Furthermore, the pitch control wheel 70 provided in the second stretching unit 101L rotates counterclockwise when viewed from above. The rotation speed of the pitch control wheel 70 provided in the first stretching unit 101R and the rotation speed of the pitch control wheel 70 provided in the second stretching unit 101L are typically substantially the same.

[0042] In the holding step, the long film 1 is typically supplied along the second direction to a holding zone A located between the first stretching unit 101R and the second stretching unit 101L.

[0043] The film 1 is made of any suitable resin material. Examples of the resin material include polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, acrylic resins, cellulose ester resins, cellulose resins, polyester resins, polyester carbonate resins, olefin resins, and polyurethane resins, and preferably polycarbonate resins. The resin materials may be used alone or in combination.

[0044] As the polycarbonate-based resin, preferably, a polycarbonate-based resin containing a structural unit derived from a dihydroxy compound is used. Specific examples of dihydroxy compounds 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, and 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-tert-butylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-cyclohexyl phenyl)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, and 9,9-bis(4-(3-hydroxy-2,2-dimethylpropoxy)phenyl)fluorene.In addition to the structural units derived from the above dihydroxy compounds, the polycarbonate resin may contain structural units derived from dihydroxy compounds such as isosorbide, isomannide, isoidet, spiroglycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), cyclohexanedimethanol (CHDM), tricyclodecanedimethanol (TCDDM), and bisphenols.

[0045] Details of the polycarbonate resins described above are described, for example, in JP-A No. 2012-67300 and Japanese Patent No. 3325560. The descriptions in these patent documents are incorporated herein by reference.

[0046] The glass transition temperature of such a resin material is, for example, 110°C or higher and 250°C or lower, preferably 120°C or higher and 230°C or lower. If the glass transition temperature is too low, heat resistance tends to be poor, and dimensional changes may occur after film formation. If the glass transition temperature is too high, molding stability during film formation may be poor and the transparency of the film may be impaired. The glass transition temperature is determined in accordance with JIS K 7121 (1987).

[0047] The in-plane birefringence Δn(550) of such a film 1 is, for example, 0.002 to 0.009, and preferably 0.003 to 0.005. The width of the film 1 is, for example, 500 cm to 2000 cm, and preferably 650 cm to 1500 cm. The thickness of the film 1 is, for example, 30 μm to 200 μm, and preferably 60 μm to 150 μm.

[0048] In the illustrated example, in the gripping zone A, the reference rail 10 of the first stretching unit 101R and the reference rail 10 of the second stretching unit 101L extend along the second direction (the longitudinal direction of the film 1) and are substantially parallel to each other. Therefore, in the gripping zone A, a plurality of first clips 40R are lined up in the second direction (the longitudinal direction of the film 1), and a plurality of second clips 40L are lined up in the second direction (the longitudinal direction of the film 1).

[0049] In one embodiment, in gripping zone A, both widthwise ends of film 1 are gripped by first clip 40R and second clip 40L described above. More specifically, when first clip 40R moves to a desired position, it grips first end 1R of film 1, and when second clip 40L moves to a desired position, it grips second end 1L of film 1. At this time, the gripping timing of first clip 40R and the gripping timing of second clip 40L are preferably simultaneous.

[0050] 3, in one embodiment, the gripping area of ​​film 1 in each of multiple first clips 40R is substantially the same as the gripping area of ​​film 1 in each of multiple second clips 40L. Specifically, the gripping area of ​​first clip 40R is the area of ​​the portion of film 1 that is sandwiched between base 401 and pressing portion 402, and is, for example, 10 cm 2 ~300cm 2 and preferably 50 cm 2 ~200cm 2 is. When the gripping area of ​​the first clip 40R is taken as 100%, the gripping area of ​​the second clip 40L is, for example, 97% to 103%, preferably 99% to 101%, more preferably 99.5% to 100.5%, and even more preferably 100%. When the gripping area of ​​the first clip and the gripping area of ​​the second clip are within these ranges, even if the film has the above-mentioned in-plane birefringence Δn(550), stress concentration on the film during the stretching process can be suppressed, which in turn can suppress load on the stretching device and, for example, suppress bending of the reference rail.

[0051] C-2. Preheating process As shown in FIG. 1, film 1 is fed into preheating zone B as first clip 40R and second clip 40L move. In preheating zone B, a preheating step is carried out, and film 1 is heated (preheated) while being transported by first clip 40R and second clip 40L. In preheating zone B, reference rail 10 of first stretching unit 101R and reference rail 10 of second stretching unit 101L are substantially parallel. Therefore, in the illustrated example, film 1 is heated in preheating zone B without being stretched transversely or longitudinally. However, to avoid problems such as film bending due to preheating and contact with the nozzle inside the oven, the distance (distance in the width direction) between first clip 40R and second clip 40L may be slightly increased.

[0052] The preheating temperature T1 in the preheating step is, for example, equal to or higher than the glass transition temperature (Tg) of the film 1, preferably Tg + 2°C or higher, and more preferably Tg + 5°C or higher. On the other hand, the preheating temperature T1 is, for example, Tg + 40°C or lower, and preferably Tg + 30°C or lower. The preheating temperature T1 can be adjusted appropriately depending on the material of the film 1. The preheating temperature T1 is, for example, 70°C to 190°C, and preferably 80°C to 180°C.

[0053] The temperature rise time to the preheating temperature T1 and the holding time at the preheating temperature T1 can be appropriately set depending on the constituent material of the film and the manufacturing conditions (for example, the film conveying speed.) These temperature rise time and holding time can be controlled by adjusting the moving speed of the first clip 40R and the second clip 40L, the length of the preheating zone, the temperature of the preheating zone, etc.

[0054] C-3.Stretching process Next, the film 1 is fed into the stretching zone C as the first clip 40R and the second clip 40L move. In the stretching zone C, a stretching step is carried out to obliquely stretch the film 1. This prepares a stretched film. In the stretching process, the plurality of first clips 40R and the plurality of second clips 40L are moved at least in the second direction (the longitudinal direction of the film 1) while increasing the pitch of the plurality of first clips 40R. In the stretching process, the pitch of the plurality of first clips 40R is made larger than the pitch of the plurality of second clips 40L. In the stretching process, the pitch of the plurality of second clips 40L may be changed (increased and / or decreased), or the pitch of the plurality of second clips 40L may be maintained constant. As a result, of the first and second clips that arrive at the stretching zone simultaneously, the first clip reaches the end of the stretching zone first. This oblique stretching causes the end of film 1 near the leading first clip to be stretched at a higher stretch ratio than the end of film 1 near the trailing (lagging) second clip, resulting in the development of a slow axis in the desired direction of film 1 (for example, at 45° to the longitudinal direction).

[0055] Details of the above-described oblique stretching are described, for example, in JP-A-2023-46840, the disclosure of which is incorporated herein by reference.

[0056] The stretching step may include transverse stretching, in which case the stretching step is performed while increasing the distance (distance in the width direction) between the first clip 40R and the second clip 40L, as in the configuration shown in FIG.

[0057] If the stretching process includes transverse stretching, the stretching ratio in the transverse direction (TD) (the initial width W of the film) initial ) the width W of the film after oblique stretching final Ratio (W final / W initial ) is, for example, 1.05 to 6.00, and preferably 1.10 to 5.00.

[0058] The product of the rate of change in the clip pitch of the first clip 40R and the rate of change in the clip pitch of the second clip 40L in the stretching step is, for example, 0.7 to 1.5, preferably 0.8 to 1.45, and more preferably 0.85 to 1.40. If the product of the rates of change is within this range, a retardation film with high uniaxiality and in-plane orientation can be produced.

[0059] The stretching temperature T2 in the stretching step is, relative to the glass transition temperature (Tg) of the film, for example, Tg-20°C to Tg+30°C, preferably Tg-10°C to Tg+20°C, and more preferably Tg. The stretching temperature T2 can be adjusted appropriately depending on the material of the film 1. The stretching temperature T2 is, for example, 180°C or lower, preferably 160°C or lower, and more preferably 150°C or lower. On the other hand, the stretching temperature T2 is, for example, 130°C or higher, preferably 140°C or higher. The difference (T1-T2) between the preheating temperature T1 and the stretching temperature T2 is, for example, ±2° C. or more, preferably ±5° C. or more. In one embodiment, T1>T2, and therefore, the film heated to the preheating temperature T1 in the preheating zone can be cooled to the stretching temperature T2.

[0060] C-4. Heat setting process Next, the stretched film 1 (stretched film) is sent to the heat setting zone D as the first clip 40R and the second clip 40L move. In the heat setting zone D, a heat setting process is carried out, and the stretched film 1 (stretched film) is heat-treated while being transported by the first clip 40R and the second clip 40L. In the heat setting zone D, the reference rail 10 of the first stretching unit 101R and the reference rail 10 of the second stretching unit 101L are substantially parallel. Therefore, in the illustrated example, the film 1 is basically not stretched transversely or longitudinally in the heat setting zone D. However, if necessary, the pitch of the multiple first clips 40R may be reduced to relieve stress.

[0061] The heat setting temperature T3 in the heat setting process varies depending on the film to be stretched, and it can be either T2 ≧ T3 or T2 < T3. Generally, when the film is an amorphous material, T2 ≧ T3, and when it is a crystalline material, crystallization treatment can be performed by setting T2 < T3. When T2 ≧ T3, the difference between the temperatures T2 and T3 (T2 - T3) is, for example, 0°C to 50°C. The heat setting time is, for example, 10 seconds to 10 minutes. The heat treatment time can be controlled by adjusting the length of the heat treatment zone and / or the conveyance speed of the film.

[0062] C-5. Release Process Next, the stretched film after heat setting is sent to the release zone E as the first clip 40R and the second clip 40L move. In the release zone E, the release process is carried out, and at an arbitrary position, the first end 1R of the stretched film is released from the first clip 40R, and the second end 1L of the stretched film is released from the second clip 40L. More specifically, when the first clip 40R reaches an arbitrary position by movement, the first end 1R of the film 1 is released, and when the second clip 40L reaches an arbitrary position by movement, the second end 1L of the film 1 is released. In the release zone E, the reference rail 10 of the first stretching unit 101R and the reference rail 10 of the second stretching unit 101L are substantially parallel. Therefore, in the illustrated example, in the release zone E, after the stretched film after heat setting is cooled to a desired temperature without undergoing either horizontal stretching or vertical stretching, it is released from the first clip and the second clip.

[0063] The temperature of the stretched film when released from the first clip and the second clip is, for example, 150°C or lower, preferably 70°C to 140°C, more preferably 80°C to 130°C.

[0064] As described above, a stretched film in which the film 1 is stretched is obtained. The stretched film will be described in detail later.

[0065] C-6. Pitch Adjustment Process In the pitch adjustment process, the pitch control wheel 70 adjusts the pitch of the multiple first clips 40R after the first end 1R of the film 1 has been released, and the pitch of the multiple second clips 40L after the second end 1L of the film 1 has been released. More specifically, the plurality of first clips 40R that have passed through the open zone E reach the pitch control wheel 70 of the first stretching unit 101R. Also, the plurality of second clips 40L that have passed through the open zone E reach the pitch control wheel 70 of the second stretching unit 101L. Then, in each of the first stretching unit 101R and the second stretching unit 101L, the ends of the frames 31 of the plurality of clip support members 30 fit in the recesses 71 of the pitch control wheel 70 in order. This allows the pitch of the multiple first clips 40R in the first stretching unit 101R and the pitch of the multiple second clips 40L in the second stretching unit 101L to be suitably adjusted. In one embodiment, the phases of the multiple first clips 40R and the phases of the multiple second clips 40L are aligned at a predetermined pitch.

[0066] The pitch of the plurality of first clips 40R adjusted in the pitch adjusting step is, for example, 40 mm to 200 mm, preferably 60 mm to 190 mm, and more preferably 80 mm to 180 mm. The pitch of the multiple second clips 40L adjusted in the pitch adjustment process is, for example, 30% to 100%, preferably 40% to 100%, more preferably 50% to 100%, and even more preferably 100%, when the pitch of the multiple first clips 40R is 100%.

[0067] Thereafter, the plurality of first clips 40R, whose pitches have been adjusted in the pitch adjustment process, move in a circle along the reference rail 10 and are again subjected to the gripping process. Also, the plurality of second clips 40L, whose pitches have been adjusted in the pitch adjustment process, move in a circle along the reference rail 10 and are again subjected to the gripping process.

[0068] In such a stretching device 100, typically, a long, obliquely stretched film with suppressed misalignment of the orientation angle can be continuously produced. The stretched film is typically a retardation film. In one embodiment, the refractive indices of the retardation film exhibit the relationship nx > ny. The retardation film can preferably function as a λ / 4 plate. When the retardation film functions as a λ / 4 plate, the in-plane retardation Re(550) of the retardation film (λ / 4 plate) is, for example, 100 nm to 180 nm, preferably 135 nm to 155 nm. In another embodiment, the retardation film can function as a λ / 2 plate. When the retardation film functions as a λ / 2 plate, the in-plane retardation Re(550) of the retardation film (λ / 2 plate) is, for example, 230 nm to 310 nm, preferably 250 nm to 290 nm.

[0069] Also, the retardation film preferably exhibits a so-called inverse dispersion wavelength dependence. Specifically, its in-plane retardation satisfies the relationship Re(450) < Re(550) < Re(650). Re(450) / Re(550) is, for example, 0.8 or more and less than 1.0, preferably 0.8 to 0.95. Re(550) / Re(650) is, for example, 0.8 or more and less than 1.0, preferably 0.8 to 0.97.

Industrial Applicability

[0070] The method for manufacturing the stretched film of the present invention is suitably used for manufacturing a retardation film, and as a result, it can contribute to the manufacture of image display devices such as liquid crystal display devices (LCDs) and organic electroluminescence display devices (OLEDs).

Explanation of Reference Numerals

[0071] 1 Film 40R First Clip 40L Second Clip 70 Pitch Control Wheel

Claims

1. a gripping step of gripping a first end portion of a long film in a width direction with a plurality of first clips aligned in the length direction of the film and gripping a second end portion of the film in the width direction with a plurality of second clips aligned in the length direction; a stretching step of moving the first clips and the second clips in the longitudinal direction while making the pitch of the first clips larger than the pitch of the second clips, thereby stretching the film in an oblique direction intersecting both the longitudinal direction and the width direction; a releasing step of releasing the first end of the film from the first clips and releasing the second end of the film from the second clips, in this order; The method for producing a stretched film further comprises, after the releasing step, a pitch adjusting step of adjusting the pitch of the plurality of first clips and the pitch of the plurality of second clips.

2. 2. The method for producing a stretched film according to claim 1, wherein in the opening step, the plurality of first clips open the first end portion while moving in the longitudinal direction, and the plurality of second clips open the second end portion while moving in the longitudinal direction.

Images