Retardation film manufacturing method

Abstract

Provided is a retardation film manufacturing method with which it is possible to stably manufacture a retardation film having a desired in-plane retardation and to suppress concentration of stress on a first clip and a second clip for gripping a film in a stretching step. A retardation film manufacturing method according to one embodiment of the present invention includes a gripping step, a stretching step, and an opening step. In the gripping step, a first end part of a film having an Δn(550) of 0.002-0.009 is gripped by a plurality of first clips, and a second end part is gripped by a plurality of second clips. The gripping area of the film gripped by each of the first clips and the second clips is 10 cm2 to 300 cm2. In the stretching step, the plurality of first clips and the plurality of second clips are moved while changing the pitch of the plurality of first clips, and the film is stretched in an oblique direction at 180°C or less. In the opening step, the film is released from the clips.

Description

Method for manufacturing retardation film

[0001] The present invention relates to a method for producing a retardation film.

[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 longitudinal and / or transverse directions, and therefore the slow axis is often expressed in the transverse (width) or longitudinal (length) direction of a long raw film. As a result, to produce a circular polarizing plate, it is necessary to cut the retardation film so that it forms a 45° angle with respect to the width or length direction and then bond the films 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 / 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 leading side and the other is set as the lagging side, and the clip pitch of the leading 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).

[0004] Patent No. 4845619

[0005] In recent years, the range of materials available for retardation films has expanded with the diversification of their applications. Therefore, it may be desirable to construct a retardation film from a material with relatively low in-plane birefringence (hereinafter referred to as a "low birefringence material"). In this case, in order to achieve sufficient in-plane retardation in the retardation film, it is necessary to stretch a film made of a low birefringence material at a relatively low temperature (typically 180°C or lower). However, in the oblique stretching method for sheet films described in Patent Document 1, if a film made of a low birefringence material is obliquely stretched at a relatively low temperature, stress may be concentrated on the clips holding the film, making it difficult to stably stretch the film. The main object of the present invention is to provide a method for producing a retardation film that can suppress stress concentration on the first and second clips holding the film during the stretching process and can stably produce a retardation film having a desired in-plane retardation.

[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 end in the width direction of a long film is gripped by a plurality of first clips aligned in the longitudinal direction of the film, and a second end in the width direction 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 changing the pitch of the first clips, thereby stretching the film in an oblique direction intersecting both the longitudinal direction and the width 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. The in-plane birefringence Δn(550) of the film is 0.002 to 0.009. The temperature in the stretching step is 180°C or lower. The gripping area of ​​the film of each of the plurality of first clips is substantially the same as the gripping area of ​​the film of each of the plurality of second clips. The gripping area of ​​the film of each of the plurality of first clips is 10 cm ２ ~300cm ２ is.

[0007] According to an embodiment of the present invention, it is possible to suppress the concentration of stress on the first clip and the second clip that grip the film in the stretching step, and to stably produce a retardation film having a desired in-plane retardation.

[0008] 5 is a schematic configuration diagram of an example of a stretching apparatus capable of carrying out a method for producing a retardation film according to an embodiment of the present invention. FIG. 6 is a schematic plan view for explaining a gripping process carried out by the stretching apparatus of FIG. 1. FIG. 7 is a schematic cross-sectional view for explaining a gripping process carried out by the stretching apparatus of FIG. 1. FIG. 8 is a schematic view showing a profile of a clip pitch in a stretching process carried out by the stretching apparatus of FIG. 1. FIG. 9 is a schematic plan view for explaining a link mechanism provided in the stretching apparatus of FIG. 1. FIG. 10 is a schematic plan view for explaining the operation of the link mechanism of FIG. 5. FIG. 6 is a schematic plan view of an upstream pitch control wheel provided in the stretching apparatus of FIG. 1.

[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 in-plane direction perpendicular to the slow axis (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 a wavelength of λ nm at 23°C. For example, "Δn(550)" is the in-plane birefringence measured with light of a wavelength of 550 nm at 23°C. The in-plane birefringence (Δn) is calculated from the formula: Δn = nx - ny. (3) Substantially Parallel or Orthogonal The expressions "substantially orthogonal" and "approximately orthogonal" include cases where the angle between the 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, in this specification, when simply referring to "orthogonal" or "parallel," this can include a state of being substantially orthogonal or substantially parallel.

[0011] A. Overview of the Method for Producing a Retardation Film FIG. 1 is a schematic diagram of an example of a stretching apparatus capable of implementing a method for producing a retardation film according to one embodiment of the present invention; FIG. 2 is a schematic plan view illustrating the gripping process performed by the stretching apparatus of FIG. 1; FIG. 3 is a schematic cross-sectional view illustrating the gripping process performed by the stretching apparatus of FIG. 1; and FIG. 4 is a schematic diagram illustrating the clip pitch profile in the stretching process performed by the stretching apparatus of FIG. 1. The method for producing a retardation film according to one embodiment of the present invention includes a gripping process, a stretching process, and a releasing process, in this order. As shown in FIGS. 2 and 3, in the gripping process, a first end 1R of the film 1 is gripped by a plurality of first clips 40R, and a second end 1L of the film 1 is gripped by a plurality of 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 (the direction perpendicular to the longitudinal direction). The in-plane birefringence Δn(550) of the film 1 is, for example, 0.002 to 0.009, preferably 0.003 to 0.007, and more preferably 0.003 to 0.005. In the holding process, the multiple first clips 40R are aligned in the longitudinal direction of the film 1, and the multiple second clips 40L are aligned in the longitudinal direction of the film 1. As shown in FIG. 4 , in the stretching process, the multiple first clips 40R and the multiple second clips 40L are moved in the longitudinal direction of the film 1 while changing the pitch of the multiple first clips 40R. In one embodiment, the pitch of the multiple first clips 40R is set larger than the pitch of the multiple second clips 40L. Note that, in this specification, "pitch" refers to the length of an imaginary line segment connecting the centers of adjacent members (clips, clip support members, etc.) among multiple members. The temperature in such a stretching step is not more than 180° C. In the releasing step, the first end 1R of the film 1 is released from the plurality of first clips 40R, and the second end 1L of the film 1 is released from the plurality of second clips 40L (see FIG. 3).In the above-described gripping process, the gripping area of ​​the film 1 of each of the first clips 40R is substantially the same as the gripping area of ​​the film 1 of each of the second clips 40L. The gripping area of ​​the film 1 of each of the first clips 40R is 10 cm. ２ ~300cm ２ According to this method, the area (gripping area) of the portion of the film gripped by one clip (first clip or second clip) is within the above-mentioned range, so even if a film having an in-plane birefringence Δn(550) of 0.009 or less is obliquely stretched at 180°C or less, excessive concentration of stress on the clip (first clip or second clip) can be suppressed. Therefore, the film can be smoothly stretched in the stretching step, and as a result, a retardation film having a desired in-plane retardation can be stably produced. In particular, when the in-plane birefringence Δn(550) of the film subjected to the gripping step is equal to or greater than the above-mentioned lower limit, the retardation film can stably exhibit sufficient in-plane retardation.

[0012] In one embodiment, the method for manufacturing a retardation film further includes a first pitch adjustment step. In the first pitch adjustment step, the pitch of the plurality of first clips 40R and the pitch of the plurality of second clips 40L are substantially matched before the holding step. This allows the first clips 40R and the second clips 40L to be sufficiently maintained in a desired relative positional relationship even if the pitch of the plurality of first clips 40R is changed during the stretching step. Furthermore, because the pitch of the plurality of first clips 40R and the pitch of the plurality of second clips 40L are adjusted before holding the film 1, the pitch adjustment can be prevented from affecting the pitch variability of the plurality of first clips 40R during the stretching step, and the first clips 40R and the second clips 40L can stably hold the film 1 during the holding step. As a result, the pitch of the plurality of first clips 40R can be sufficiently and smoothly changed during the stretching step, and a retardation film with reduced deviation in orientation angle can be stably manufactured.

[0013] In the opening process, the first clips 40R typically move in the longitudinal direction of the film 1 while releasing their grip on the first end 1R of the film 1 (see FIG. 3 ). In the opening process, the second clips 40L typically move in the longitudinal direction of the film 1 while releasing their grip on the second end 1L of the film 1 (see FIG. 3 ). In the stretching process, if the pitch of the first clips is made larger than the pitch of the second clips, the lagging second clip may be pulled by the leading first clip through the film. In this case, the pitch of the second clips may become excessively narrow during the opening process, causing clogging and hindering the smooth movement of the second clips. In response to this, in one embodiment, the method for manufacturing a retardation film further includes a second pitch adjustment process. In the second pitch adjustment process, the pitch of the first clips 40R and the pitch of the second clips 40L are adjusted after the opening process. This can prevent the second clips from becoming jammed during the opening process, and allows the second clips to move smoothly.

[0014] In one embodiment, the method for producing a retardation film further includes a preheating step and a heat setting step. The preheating step is performed 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 performed between the stretching step and the releasing step. In the heat setting step, the film 1 is heat set at any appropriate temperature.

[0015] B. Stretching Apparatus Next, a stretching apparatus 100 capable of continuously carrying out the above-described method for producing a retardation film will be described with reference to Fig. 1. The stretching apparatus 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.

[0016] 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). In the stretching device 100, between the first stretching unit 101R and the second stretching unit 101L, 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 an opening zone E where the opening step described above is performed are provided in this order. Note that these zones are not mechanically or structurally independent compartments. The length ratio of each zone in the stretching device shown in FIG. 1 may differ from the actual length ratio.

[0017] Furthermore, a zone for performing any appropriate treatment may be provided between the stretching zone C and the heat setting zone D, as needed. Such a treatment may include, for example, a 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.

[0018] The first stretching unit 101R has a configuration (variable pitch type) that allows the pitch of the multiple first clips 40R to be changed. In one embodiment, the first stretching unit 101R includes a reference rail 10, a pitch setting rail 20, multiple clip support members 30, a link mechanism 80 (see FIG. 5 ), multiple first clips 40R, a driving means 50, an upstream pitch control wheel 60, and a downstream pitch control wheel 70.

[0019] B-1. Reference Rail The reference rail 10 typically has an endless shape. The reference rail 10 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 up-down direction and in a second direction perpendicular to the first 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 in the second direction. The third curved portion 10c is located on the opposite side of the second curved portion 10b in the first direction. The fourth curved portion 10d is located on the opposite side of the third curved portion 10c in the second direction and on the opposite side of the first curved 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°.

[0020] 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, moving 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.

[0021] 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.

[0022] B-3. ​​Clip Support Member As shown in Figures 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. 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 extension direction supports the first clip 40R.

[0023] 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 .

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 .

[0028] 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.

[0029] B-4. Link Mechanism The link mechanism 80 is configured to change the pitch of the multiple clip support members 30 by changing the distance 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 multiple main link members 81 and multiple sub link members 82.

[0030] Each of the multiple main link members 81 connects the first shaft member 33 included in one of the adjacent clip support members 30 to the 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.

[0031] 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.

[0032] As shown in FIG. 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 adjacent clip support members 30 move closer to each other. As a result, the pitch between the multiple first clips 40R becomes smaller. On the other hand, as shown in FIG. 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 adjacent clip support members 30 move apart. As a result, the pitch between the multiple first clips 40R becomes larger.

[0033] B-5. Clips Each of the multiple 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.

[0034] As shown in Fig. 3, the first clip 40R is configured to be able to grip the first end 1R of the film 1. In one embodiment, the first clip 40R is able to clamp the first end 1R of the film 1 in the thickness direction of the film 1. In the illustrated example, the first clip 40R includes a base 401 and a pressing portion 402. The base 401 is fixed to one end of the first support member 30R in the extension direction. The pressing portion 402 is supported by one end of the first support member 30R in the extension direction so as to be movable relative to the base 401 in the thickness direction of the film 1.

[0035] B-6. Driving Means As shown in Fig. 1, the driving means 50 is configured to apply a driving force to the plurality of clip support members 30. The driving means 50 is 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 downstream pitch control wheel 70 from the second stretching unit 101L in the first direction, with a gap therebetween.

[0036] 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 the 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.

[0037] B-7. Upstream Pitch Control Wheel The upstream pitch control wheel 60 is configured to adjust the pitch of the plurality of first clips 40R. The upstream pitch control wheel 60 is typically located upstream of the gripping zone A (i.e., on the opposite side of the stretching zone C from the gripping zone A) in the direction of orbital movement of the plurality of clip support members 30. In one embodiment, the upstream pitch control wheel 60 is located between the gripping zone A and the fourth curved portion 10d in the direction of orbital movement of the plurality of clip support members 30. In the illustrated example, the upstream pitch control wheel 60 is arranged along the first curved portion 10a of the reference rail 10.

[0038] As shown in Figure 7, the upstream pitch control wheel 60 is rotatable about an axis extending in the vertical direction. Although not shown, the upstream pitch control wheel 60 is configured so that a driving force from a motor is input. The outer diameter of the upstream pitch control wheel 60 is, for example, 10 cm to 120 cm, and preferably 30 cm to 100 cm.

[0039] In the illustrated example, a plurality of recesses 61 are provided on the circumferential surface of the upstream pitch control wheel 60. Each of the recesses 61 is typically configured to receive the end of the frame 31 opposite the first clip 40R. The recesses 61 are positioned at equal intervals around the circumference of the upstream pitch control wheel 60. When viewed from the top and bottom, each of the recesses 61 has a generally V-shape that opens toward the radially outer side of the upstream pitch control wheel 60. The number of recesses 61 is not particularly limited. The number of recesses 61 is, for example, 2 to 10, and preferably 4 to 6. The depth of the recesses 61 (the radial dimension of the upstream pitch control wheel 60) is, for example, 5 cm to 100 cm, and preferably 20 cm to 80 cm.

[0040] B-8. Downstream Pitch Control Wheel As shown in FIG. 1 , the downstream pitch control wheel 70 is configured to adjust the pitch of the plurality of first clips 40R. The downstream pitch control wheel 70 is typically located downstream of the open zone E (i.e., on the opposite side of the stretching zone C from the open zone E) in the orbital movement direction of the plurality of clip support members 30. In one embodiment, the downstream pitch control wheel 70 is located between the open zone E and the third curved portion 10c in the orbital movement direction of the plurality of clip support members 30. In the illustrated example, the upstream pitch control wheel 60 is disposed along the second curved portion 10b of the reference rail 10.

[0041] 7, the downstream pitch control wheel 70 typically has a configuration similar to that of the above-described upstream pitch control wheel 60. Therefore, a detailed description of the downstream pitch control wheel 70 will be omitted.

[0042] B-9. Second Stretching Unit As shown in FIG. 1, the second stretching unit 101L has a configuration in which the pitch of the multiple second clips 40L can be changed (variable pitch type). The second stretching unit 101L typically has a configuration that is linearly symmetrical to the first stretching unit 101R with respect to the second direction. The second stretching unit 101L can be described in the same manner as the first stretching unit 101R, except that it includes multiple second clips 40L instead of multiple first clips 40R. Therefore, a description of the configuration of the second stretching unit 101L will be omitted.

[0043] C. Details of the Method for Producing Retardation Film Next, a description will be given of the method for producing a retardation film using the stretching apparatus 100. In one embodiment, the stretching apparatus 100 continuously performs a first pitch adjusting step, a gripping step, a preheating step, a stretching step, a heat setting step, a releasing step, and a second pitch adjusting step in this order.

[0044] C-1. First Pitch Adjustment Step In the first pitch adjustment step, the upstream pitch control wheel 60 is used to make the pitch of the plurality of first clips 40R and the pitch of the plurality of second clips 40L substantially coincident with each other.

[0045] More specifically, 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. In the illustrated example, the driving force is transmitted from the sprocket 50a to the multiple clip support members 30 included in the first stretching unit 101R, causing them to orbit in a clockwise direction as viewed from above. As a result, the multiple first clips 40R, like the multiple clip support members 30, also orbit in a clockwise direction as viewed from above. Similarly, the driving force is transmitted from the sprocket 50a to the multiple clip support members 30 included in the second stretching unit 101L, causing them to orbit in a counterclockwise direction as viewed from above. As a result, the multiple second clips 40L, like the multiple clip support members 30, also orbit in a counterclockwise direction as viewed from above. 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 each 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.

[0046] 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 upstream pitch control wheel 60 and the downstream pitch control wheel 70. As a result, the upstream pitch control wheel 60 and the downstream pitch control wheel 70 of the first stretching unit 101R rotate clockwise as viewed from above. In addition, the upstream pitch control wheel 60 and the downstream pitch control wheel 70 of the second stretching unit 101L rotate counterclockwise as viewed from above. The rotation speed of the upstream pitch control wheel 60 of the first stretching unit 101R and the rotation speed of the upstream pitch control wheel 60 of the second stretching unit 101L are typically substantially the same. In addition, the rotation speed of the downstream pitch control wheel 70 of the first stretching unit 101R and the rotation speed of the downstream pitch control wheel 70 of the second stretching unit 101L are typically substantially the same.

[0047] In the first pitch adjustment step, when the upstream pitch control wheel 60 rotates in each of the first stretching unit 101R and the second stretching unit 101L, the ends of the frames 31 of the multiple clip support members 30 fit sequentially into the recesses 61 of the upstream pitch control wheel 60. This causes the pitch of the multiple first clips 40R in the first stretching unit 101R to substantially match the pitch of the multiple second clips 40L in the second stretching unit 101L. In other words, the phases of the multiple first clips 40R and the multiple second clips 40L are aligned at a predetermined pitch. At this time, as shown in FIG. 4 , an imaginary line segment connecting the centers of the first clips 40R and the second clips 40L is typically substantially perpendicular to the film transport direction (second direction). The angle between the virtual line segment and the film conveyance direction (second direction) is, for example, 87° to 93°, preferably 89° to 91°, more preferably 89.5° to 90.5°, and even more preferably 90°. The pitch of the multiple first clips 40R adjusted in the first pitch adjustment process is, for example, 100 mm to 200 mm, preferably 125 mm to 175 mm, and more preferably 140 mm to 160 mm. The pitch of the multiple second clips 40L adjusted in the first pitch adjustment process is, for example, 97% to 103%, preferably 99% to 101%, more preferably 99.5% to 100.5%, and even more preferably 100%, when the pitch of the multiple first clips 40R is 100%.

[0048] C-2. Gripping Step As shown in FIG. 1, in the gripping step, the long film 1 is typically supplied along the second direction to a gripping zone A located between the first stretching unit 101R and the second stretching unit 101L.

[0049] 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.

[0050] As the polycarbonate-based resin, preferably, a polycarbonate-based resin containing a structural unit derived from a dihydroxy compound is used. Specific examples of the dihydroxy compound include 9,9-bis(4-hydroxyphenyl)fluorene, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3-ethylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-propylphenyl)fluorene, 9,9-bis(4-hydroxy-3-isopropylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-sec-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-tert-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-cyclohexylphenyl)fluorene, 9,9-bis(4-hydroxy-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, 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.

[0051] Details of the polycarbonate resins described above are described, for example, in JP-A-2012-67300 and Japanese Patent No. 3325560. The descriptions in these patent documents are incorporated herein by reference.

[0052] 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).

[0053] 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.

[0054] 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 whose pitches have been aligned in the first pitch adjustment step are lined up in the second direction (the longitudinal direction of the film 1), and a plurality of second clips 40L whose pitches have been aligned in the first pitch adjustment step are lined up in the second direction (the longitudinal direction of the film 1).

[0055] 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.

[0056] 3, in one embodiment, the gripping area of ​​the film 1 in each of the plurality of first clips 40R is substantially the same as the gripping area of ​​the film 1 in each of the plurality of second clips 40L. Specifically, the gripping area of ​​the first clip 40R is the area of ​​the portion of the film 1 that is sandwiched between the base 401 and the holding portion 402, and is preferably 50 cm ２ ~200cm ２ 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%, of the gripping area of ​​the first clip 40R, taken as 100%. When the gripping areas of the first clip and the second clip are within these ranges, stress concentration on the film during the stretching process can be stably suppressed, even if the film has the above-mentioned in-plane birefringence Δn(550). As a result, load on the stretching device can be suppressed, and, for example, bending of the reference rail can be suppressed.

[0057] C-3. Preheating Step As shown in FIG. 1 , the film 1 is transported to the preheating zone B by the movement of the first clip 40R and the second clip 40L. In the preheating zone B, a preheating step is carried out, and the film 1 is heated (preheated) while being transported by the first clip 40R and the second clip 40L. In the preheating zone B, 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 preheating zone B, the film 1 is heated without being stretched transversely or longitudinally. However, to avoid problems such as the film bending due to preheating and contact with the nozzle in the oven, the distance (widthwise distance) between the first clip 40R and the second clip 40L may be slightly increased.

[0058] 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.

[0059] 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 (e.g., 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.

[0060] C-4. Stretching Process Next, the film 1 is sent to the stretching zone C as the first clip 40R and the second clip 40L move. In the stretching zone C, the stretching process is carried out to obliquely stretch the film 1. This produces a retardation film. In the stretching process, the first clips 40R and the second clips 40L are moved at least in the second direction (the longitudinal direction of the film 1) while changing (increasing and / or decreasing) the pitch of the first clips 40R. In the illustrated example, the pitch of the first clips 40R is made larger than the pitch of the second clips 40L. In the stretching process, the pitch of the second clips 40L may be changed (increasing and / or decreasing), or the pitch of the second clips 40L may be maintained constant. As a result, of the first clip and the second clip that arrive at the stretching zone simultaneously, one clip (the first clip in the illustrated example) reaches the end of the stretching zone first. By such oblique stretching, the end of film 1 on the leading clip side is stretched at a higher stretch ratio than the end on the trailing (lagging) clip side, and as a result, a slow axis can be developed in the desired direction of film 1 (for example, a direction at 45° to the longitudinal direction).

[0061] 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.

[0062] The stretching step may include transverse stretching. In this 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, for example, as shown in FIG.

[0063] When the stretching step includes transverse stretching, the stretching ratio in the transverse direction (TD) (initial width W of the film) ｉｎｉｔｉａｌ ) The width W of the film after oblique stretching ｆｉｎａｌ The ratio (W ｆｉｎａｌ / W ｉｎｉｔｉａｌ ) is, for example, 1.05 to 6.00, preferably 1.10 to 5.00.

[0064] 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.

[0065] The stretching temperature T2 in the stretching step is, for example, Tg-20°C to Tg+30°C relative to the glass transition temperature (Tg) of the film, 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 preferably 160°C or less, more preferably 150°C or less. On the other hand, the stretching temperature T2 is, for example, 130°C or more, preferably 140°C or more. If the stretching temperature is within this range, film breakage in the stretching step can be stably suppressed. 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.

[0066] C-5. Heat Setting Step Next, the stretched film 1 (retardation film) is sent to the heat setting zone D along with the movement of the first clip 40R and the second clip 40L. In the heat setting zone D, a heat setting step is carried out, and the stretched film 1 (retardation 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.

[0067] The heat setting temperature T3 in the heat setting step varies depending on the film being stretched, and may be either T2 ≥ T3 or T2 < T3. Generally, if the film is an amorphous material, T2 ≥ T3, and if the film is a crystalline material, crystallization can be performed by setting T2 < T3. When T2 ≥ T3, the difference between 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 film transport speed.

[0068] C-6. Release Step Next, the heat-set retardation film 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 step is performed, and at an arbitrary position, the first end 1R of the retardation film is released from the first clip 40R, and the second end 1L of the retardation film is released from the second clip 40L. More specifically, when the first clip 40R reaches an arbitrary position, the first end 1R of the film 1 is released, and when the second clip 40L reaches an arbitrary position, 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, the heat-set retardation film is cooled to a desired temperature without being stretched transversely or longitudinally, and then released from the first clip and the second clip.

[0069] The temperature of the retardation film when released from the first clip and the second clip is, for example, 150°C or lower, preferably 70°C to 140°C, and more preferably 80°C to 130°C.

[0070] In this manner, a retardation film is obtained by stretching the film 1. The retardation film will be described in detail later.

[0071] C-7. Second Pitch Adjustment Step In the second pitch adjustment step, the downstream pitch control wheel 70 adjusts the pitch of the multiple first clips 40R after releasing the first end 1R of the film 1 and the pitch of the multiple second clips 40L after releasing the second end 1L of the film 1. More specifically, the multiple first clips 40R that have passed through the release zone E reach the downstream pitch control wheel 70 of the first stretching unit 101R. Similarly, the multiple second clips 40L that have passed through the release zone E reach the downstream 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 multiple clip support members 30 fit sequentially into the recesses 61 of the downstream pitch control wheel 70. This allows the pitch of the plurality of first clips 40R in the first stretching unit 101R and the pitch of the plurality of second clips 40L in the second stretching unit 101L to be suitably adjusted. In one embodiment, the phases of the plurality of first clips 40R and the phases of the plurality of second clips 40L are aligned at a predetermined pitch.

[0072] The pitch of the plurality of first clips 40R adjusted in the second pitch adjustment 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 plurality of second clips 40L adjusted in the second pitch adjustment step 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 plurality of first clips 40R is 100%.

[0073] Thereafter, the plurality of first clips 40R, whose pitches have been adjusted in the second pitch adjustment process, move circumferentially along the reference rail 10 and are again subjected to the first pitch adjustment process. Also, the plurality of second clips 40L, whose pitches have been adjusted in the second pitch adjustment process, move circumferentially along the reference rail 10 and are again subjected to the first pitch adjustment process.

[0074] Such a stretching apparatus 100 can continuously produce a long retardation film having a desired in-plane retardation. In one embodiment, the refractive index of the retardation film exhibits 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.

[0075] Furthermore, the retardation film preferably exhibits wavelength dependence of so-called reverse dispersion. 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.

[0076] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. The methods for measuring each property in the examples and comparative examples are as follows.

[0077] (1) In-plane birefringence Δn(550) The in-plane birefringence of the films subjected to the holding step in the examples and comparative examples was automatically measured using an Axoscan (manufactured by Axometrics). The measurement wavelength was 550 nm and the measurement temperature was 23°C. The results are shown in Table 1.

[0078] (2) Rail Load A pressure gauge was installed on the reference rail after the opening process in the Examples and Comparative Examples, and the load on the reference rail during the stretching process was evaluated according to the following criteria. The results are shown in Table 1. Good: The load on the rail was 50 kN or less. Poor: The load on the rail exceeded 50 kN.

[0079] (3) Breaking The production of the retardation films in the examples and comparative examples was evaluated according to the following criteria. The results are shown in Table 1. Good: The resin film was stretched in the stretching device without breaking. Poor: The resin film was broken from the center or edge in the stretching device.

[0080] <<Film Preparation>> <Preparation Example 1> A PC resin film was prepared in the same manner as in Production Example 9 of JP 2022-150732 A. The PC resin film had a long shape, and the thickness of the PC resin film was 130 μm. The in-plane birefringence Δn of the PC resin film of Preparative Example 1 was 0.004. <Preparation Example 2> A PC resin (manufactured by Mitsubishi Chemical Corporation, product number "D5380R-3") was prepared, and film formation was carried out in the same manner as in Production Example 9 of JP 2022-150732 A, except for that, a PC resin film was prepared by film formation. The PC resin film had a long shape, and the thickness of the PC resin film was 100 μm. The in-plane birefringence Δn of the PC resin film of Preparative Example 2 was 0.006. <Preparation Example 3> A COP resin film (manufactured by Zeon Corporation, product number "ZF16") was prepared. The COP resin film had a long shape and a thickness of 120 μm. The in-plane birefringence Δn of the COP resin film of Preparative Example 3 was 0.007. <Preparative Example 4> An acrylic resin film (manufactured by Kaneka Corporation, product name "HTX-Z") was prepared. The acrylic resin film had a long shape and a thickness of 100 μm. The in-plane birefringence Δn of the acrylic resin film of Preparative Example 4 was 0.001.

[0081] Example 1 The PC resin film prepared in Preparation Example 1 was set in the stretching device shown in FIG. 1 . The stretching device included a first stretching unit including a plurality of first clips and a second stretching unit including a plurality of second clips. The reference rails included in each of the first stretching unit and the second stretching unit were made of high manganese steel. More specifically, a first end portion in the width direction of the PC resin film was held by a plurality of first clips, and a second end portion in the width direction of the PC resin film was held by a plurality of second clips (gripping process). The area (gripping area) of the portion of the PC resin film held by one clip (first clip or second clip) is shown in Table 1.

[0082] The PC resin film was then preheated to 150°C (preheating step). Next, the first clips and the second clips were moved in the longitudinal direction while changing the pitch of the first clips, and the PC resin film was stretched in an oblique direction intersecting both the longitudinal direction and the width direction (stretching step). The temperature (stretching temperature) in the stretching step is shown in Table 1. The ratio of the width of the PC resin film after oblique stretching to the initial width of the PC resin film was 1.84.

[0083] The stretched PC resin film was then heat-set at 140°C (heat-setting step). Next, the first end of the PC resin film was released from the first clips, and the second end of the PC resin film was released from the second clips (release step). This resulted in a retardation film. The thickness of the retardation film was 57 μm. The in-plane retardation Re(550) of the retardation film is shown in Table 1.

[0084] [Example 2] The PC resin film of Preparation Example 1 was changed to the COP resin film of Preparation Example 2, and the gripping area of ​​the clip was increased to 200 cm ２ and the stretching temperature was changed to 136° C. A retardation film was obtained in the same manner as in Example 1. The thickness of the retardation film was 53 μm.

[0085] [Example 3] A retardation film was obtained in the same manner as in Example 1, except that the PC resin film of Preparatory Example 1 was changed to the PC resin film of Preparatory Example 2 and the stretching temperature was changed to 134°C. The thickness of the retardation film was 45 µm.

[0086] [Comparative Example 1] The gripping area of ​​the clip is 100 cm ２ The same procedure as in Example 1 was carried out except that the temperature was changed to 185°C and the stretching temperature was changed to 185°C. As a result, the PC resin film was broken.

[0087] [Comparative Example 2] The gripping area of ​​the clip was 5 cm ２ The same procedure as in Example 1 was carried out except for changing the procedure to the above, and the PC resin film was broken.

[0088] [Comparative Example 3] A retardation film was obtained in the same manner as in Example 1, except that the PC resin film of Preparatory Example 1 was changed to the acrylic resin film of Preparatory Example 4 and the stretching temperature was changed to 125°C. The thickness of the retardation film was 44 µm.

[0089]

[0090] [Evaluation] As is clear from Table 1, when the gripping area of ​​the clip was 10 cm ２ ~300cm ２ When the film has an in-plane birefringence Δn(550) of 0.009 or less, even if the film is obliquely stretched at 180°C or less, stress concentration on the clips during the stretching process can be suppressed, and as a result, the load on the reference rail of the stretching device can be reduced. Furthermore, when the stretching temperature is 180°C or less, breakage of the retardation film during the stretching process can be stably suppressed. Furthermore, when the in-plane birefringence Δn(550) of the film subjected to the gripping process is 0.002 or more, the retardation film can exhibit sufficient in-plane retardation. These factors enable stable production of retardation films having the desired in-plane retardation.

[0091] The method for producing a retardation film of the present invention can contribute to the production of image display devices such as liquid crystal displays (LCDs) and organic electroluminescence displays (OLEDs).

[0092] 1 Film 40R First clip 40L Second clip

Claims

1. A method for stretching a film, comprising the steps of: a gripping step of gripping a first end of a long film in the width direction with a plurality of first clips aligned in the length direction of the film, and gripping a second end of the film in the width direction with a plurality of second clips aligned in the length direction; a stretching step of moving the plurality of first clips and the plurality of second clips in the length direction while changing the pitch of the plurality of first clips, thereby stretching the film in an oblique direction intersecting both the length direction and the width direction; and a releasing step of releasing the first end of the film from the plurality of first clips and the second end of the film from the plurality of second clips, in this order; wherein the in-plane birefringence Δn(550) of the film is 0.002 to 0.009; the temperature in the stretching step is 180°C or less; and in the gripping step, the gripping area of ​​the film of each of the plurality of first clips is substantially the same as the gripping area of ​​the film of each of the plurality of second clips, and the gripping area is 10 cm. ２ ~300cm ２ The method for producing a retardation film is as follows.

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