Manufacturing method of stretched film

Abstract

To provide a manufacturing method of a stretched film that can easily reduce bowing by an operation with little influence on control of stretching.SOLUTION: A method for manufacturing a stretched film, in which a long transparent resin film is stretched by a stretching device, comprises: a stretching step of guiding the transparent resin film along a track from upstream to downstream while being held by clips, passing through a preheating zone, a stretching zone, and a heat-setting zone in this order, and stretching the transparent resin film in the stretching zone; a releasing step of releasing the stretched film from the clips; a bowing measurement step of measuring a distribution of orientation angles across a width direction of the stretched film and obtaining bowing information as an indicator of a degree of bowing of the stretched film; and a feedback step of reducing the bowing by adjusting operating conditions in the heat-setting zone based on the bowing information.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a stretched film, and more particularly to a method for producing a stretched film in which bowing is suppressed. [Background technology]

[0002] Stretching a long resin film to form a stretched film is widely practiced. In particular, as a film for optical applications, a stretched film is produced by stretching a transparent resin film to impart properties such as retardation. Such stretched films are widely used as retardation films in display devices such as liquid crystal display devices and electroluminescence display devices.

[0003] In general, optical films are required to have various properties, such as thickness, retardation, and slow axis direction, that are uniform in the plane. A stretched long film is theoretically expected to have a slow axis in the longitudinal or width direction over the entire surface of the film, but in reality, the direction of the slow axis may be non-uniform depending on the position in the plane.

[0004] Typical examples of such non-uniform slow axis distribution include so-called bowing and reverse bowing, i.e., a distribution in which the slow axis in the central part in the width direction of a long film differs from the slow axis at the end parts in the width direction. When such bowing and reverse bowing are observed in the production of a stretched film, it is known that their occurrence can be suppressed by appropriately adjusting the operating conditions of the stretching part in the transport path for production (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2014 / 073021 Summary of the Invention [Problem to be solved by the invention]

[0006] In the production of a stretched film, it is necessary to precisely control the properties of the resulting stretched film to the desired ones. Therefore, during the stretching, various conditions such as the stretching ratio must be precisely controlled. However, when the operating conditions of the stretching section are adjusted to suppress bowing, as in Patent Document 1, the variables of the other conditions change, making it difficult to easily suppress bowing and simultaneously perform control to meet other production requirements.

[0007] Therefore, an object of the present invention is to provide a method for producing a stretched film which can easily reduce bowing through an operation that has little effect on the control of stretching. [Means for solving the problem]

[0008] The present inventors have conducted studies to solve the above-mentioned problems, and as a result, have found that by adjusting the operating conditions in the heat setting zone after the completion of the stretching operation in the stretching zone, it is possible to reduce bowing without significantly affecting the control of the stretching, and have thus completed the present invention. That is, the present invention is as follows.

[0009] (1) A method for producing a stretched film, comprising stretching a long transparent resin film using a stretching device, The stretching device includes a pair of tracks and a clip guideably disposed along the tracks; The manufacturing method includes: a stretching step in which, while both ends of the transparent resin film in a width direction are held by the clips, the transparent resin film is guided from upstream to downstream along the track and passes through a preheating zone, a stretching zone, and a heat setting zone in this order, and the transparent resin film is stretched in the stretching zone to form the stretched film; a releasing step downstream of the stretching step, in which the stretched film is released from the clips; a bowing measurement step downstream of the releasing step, in which a distribution of orientation angles across the width direction of the stretched film is measured to obtain bowing information that is an index of the degree of bowing of the stretched film; and a feedback process for reducing the bowing by adjusting operating conditions within the heat setting zone based on the bowing information. A method for producing a stretched film, comprising: (2) The method for producing a stretched film according to (1), wherein the operating condition is a heat setting temperature in the heat setting zone. (3) The method for producing a stretched film according to (1), wherein the operating condition is a set value of tension applied to the stretched film in the transport direction at the outlet of the heat setting zone. (4) The method for producing a stretched film according to (1), wherein the operating condition is the distance between the tracks at the entrance of the heat setting zone. [Effects of the Invention]

[0010] According to the present invention, there is provided a method for producing a stretched film, which can easily reduce bowing through an operation that has little effect on the control of stretching. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a top view schematically showing an example of a stretching device that can be used in the production method of the present invention. [Figure 2] FIG. 2 is a top view showing in more detail the clip chain portion of the stretching device shown in FIG. [Figure 3] FIG. 3 is a top view showing an example of the distribution of orientation directions measured in the measurement area 130 shown in FIG. [Figure 4] FIG. 4 is a graph plotting the distribution shown in FIG. [Figure 5] FIG. 5 is an enlarged top view showing a more specific structure of the guide rails 220L and 220R of the manufacturing apparatus 100 shown in FIG. 1 near the region 150. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with any modifications within the scope of the claims and their equivalents.

[0013] In the following description, a "long" film refers to a film having a length at least 5 times its width, preferably 10 times or more, and more specifically, a film long enough to be wound into a roll for storage or transportation.

[0014] In the following description, unless otherwise specified, the oblique direction of a long film refers to an in-plane direction of the film that is neither parallel nor perpendicular to the longitudinal direction of the film.

[0015] In the following description, a resin having a positive intrinsic birefringence value means a resin whose refractive index in the stretching direction is greater than the refractive index in the direction perpendicular to the stretching direction. A resin having a negative intrinsic birefringence value means a resin whose refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction. The intrinsic birefringence value can be calculated from the dielectric constant distribution.

[0016] In the following description, unless otherwise specified, the in-plane retardation Re of a film is a value expressed as Re = (nx - ny) x d. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the in-plane direction of the film that is perpendicular to the nx direction. d represents the thickness of the film. The measurement wavelength is 590 nm unless otherwise specified.

[0017] (Outline of the equipment used in the manufacturing method) In the method for producing a stretched film of the present invention, a long transparent resin film is stretched by a stretching device, which includes a pair of tracks and clips that are arranged to be guided along the tracks.

[0018] Fig. 1 is a top view schematically showing an example of a stretching device that can be used in the manufacturing method of the present invention. In Fig. 1, an inner clip chain 210L and an outer clip chain 210R are omitted. Fig. 2 is a top view more specifically showing the clip chain-related parts of the stretching device shown in Fig. 1.

[0019] 1, the manufacturing apparatus 100 includes a tenter-stretching machine 200 and an oven 300. The manufacturing apparatus 100 is configured to produce a stretched film 10 by stretching a resin film 30 unwound from a feed roll 20 using the tenter-stretching machine 200.

[0020] As shown in FIG. 2, the tenter stretching machine 200 includes an inner clip chain 210L, an outer clip chain 210R, an inner guide rail 220L corresponding to the inner clip chain 210L, an outer guide rail 220R corresponding to the outer clip chain 210R, and sprockets (not shown) for driving the inner clip chain 210L and the outer clip chain 210R in a circular motion.

[0021] In addition to the above components, the tenter stretching machine 200 includes a position adjustment device for adjusting the positions of the guide rails 220L and 220R. The position adjustment device may include a servo motor and a shaft that transmits the displacement of the servo motor to the guide rails. While the position adjustment device is not shown in FIGS. 1 and 2, the configuration and function of the position adjustment device in region 150 will be described in detail below.

[0022] The inner clip chain 210L is an endless chain that can be rotated, and includes a plurality of inner clips 230L. These inner clips 230L are provided so as to be able to grip one end 30L of the resin film 30. On the other hand, the outer clip chain 210R is another endless chain that is provided so as to be able to rotate, and is provided with a plurality of outer clips 230R. These outer clips 230R are provided so as to be able to grip the other end 30R of the resin film 30. 1 and 2 show an example in which the inner clip 230L and the outer clip 230R are provided so as to be able to grip the left end 30L and the right end 30R, respectively, of the resin film 30. Here, for convenience of explanation, "right" and "left" refer to the directions when viewed from upstream to downstream in the film transport direction, unless otherwise specified.

[0023] The inner clip 230L is provided so as to be able to run along the inner guide rail 220L, and therefore the clip 230L can be guided along the track defined by the inner guide rail 220L.

[0024] The inner clips 230L are arranged to grip the end 30L of the resin film 30 at an inner gripping start position 240L set at the entrance 240 of the tenter stretching machine 200, and to release the end 30L of the resin film 30 at an inner release position 250L set at the exit 250 of the tenter stretching machine 200. Therefore, the inner clips 230L grip the end 30L of the resin film 30 at the inner gripping start position 240L, travel along the inner guide rail 220L while maintaining this gripped state, and release the end 30L of the resin film 30 at the inner release position 250L. Furthermore, the inner clips 230L are arranged to travel at a constant speed while maintaining a constant distance from the inner clips 230L before and after them.

[0025] The outer clip 230R is provided to run along the outer guide rail 220R. The outer clip 230R is provided to grip the end 30R of the resin film 30 at an outer gripping start position 240R set at the entrance 240 of the tenter stretching machine 200, and to release the end 30R of the resin film 30 at an outer release position 250R set at the exit 250 of the tenter stretching machine 200. Therefore, the outer clip 230R grips the end 30R of the resin film 30 at the outer gripping start position 240R, runs along the outer guide rail 220R while maintaining this gripped state, and releases the end 30R of the resin film 30 at the outer release position 250R. The outer clip 230R is provided to run at a constant speed, maintaining a constant distance from the outer clips 230R before and after it.

[0026] The inner guide rail 220L is provided on one side of the film transport path so as to guide the inner clip 230L. The inner guide rail 220L has an endless continuous track so that the inner clip 230L can move around a predetermined track. Therefore, after the inner clip 230L releases the end 30L of the resin film 30 at the inner release position 250L, it can be sequentially returned to the inner gripping start position 240L.

[0027] The outer guide rail 220R is provided on the other side of the film transport path so as to guide the outer clip 230R. The outer guide rail 220R also has an endless continuous track so that the outer clip 230R can move around a predetermined track. Therefore, after the outer clip 230R releases the end 30R of the resin film 30 at the outer release position 250R, it can be sequentially returned to the outer gripping start position 240R.

[0028] The tenter stretching machine 200 in the manufacturing apparatus 100 in FIGS. 1 and 2 is a device that performs oblique stretching. The inner guide rail 220L and the outer guide rail 220R have asymmetric shapes according to conditions such as the direction of the slow axis of the stretched film 10 to be produced and the stretching ratio. Therefore, the inner clip 230L and the outer clip 230R, which face each other in a direction perpendicular to the traveling direction of the resin film 30 at the entrance section 240 of the tenter stretching machine 200, can move in such a way that the inner clip 230L precedes the outer clip 230R at the exit section 250 of the tenter stretching machine 200. This allows the tenter stretching machine 200 to stretch the resin film 30 in an oblique direction that is neither parallel nor perpendicular to its longitudinal direction (dotted line L in FIG. 2). D1 ~L D3 reference).

[0029] The tenter stretching machine 200 also includes sprockets (not shown) for driving the inner clip chain 210L and the outer clip chain 210R in a circular motion. Typically, these sprockets are provided at the upstream and downstream ends of the inner clip chain 210L and the outer clip chain 210R, respectively. In the tenter stretching machine 200, these sprockets drive the inner clip chain 210L and the outer clip chain 210R in a circular motion, allowing the inner clips 230L and the outer clips 230R to travel along the inner guide rail 220L and the outer guide rail 220R.

[0030] The manufacturing apparatus 100 in Figures 1 and 2 may further include a measurement device for performing a bowing measurement step downstream of the tenter stretching machine 200. An example of the bowing measurement device is a device that measures the retardation and orientation angle of the stretched film 10 in-line. The bowing measurement device may be a device that can measure the orientation angle across the entire width direction by scanning the width direction of the stretched film 10 or simultaneously measuring across the entire width direction in the measurement region 130 downstream of the tenter stretching machine 200 shown in Figure 1.

[0031] The obliquely stretched film 10 produced by the production apparatus 100 and delivered downstream is usually wound up and collected as a film roll 40.

[0032] 1, the manufacturing apparatus 100 is provided with an oven 300 that covers the tenter stretching machine 200. The oven 300 is provided so as to heat the resin film 30, which passes through the oven 300 while both end portions 30L and 30R are held by the inner clip 230L and the outer clip 230R, to a desired temperature.

[0033] The oven 300 has, in this order from the upstream side, a preheating zone 310, a stretching zone 320, and a heat-setting zone 330. The oven 300 is provided with a partition wall 340 that can separate the preheating zone 310, the stretching zone 320, and the heat-setting zone 330 so that the temperatures in the preheating zone 310, the stretching zone 320, and the heat-setting zone 330 can be adjusted independently.

[0034] The preheating zone 310 is a section provided upstream of the stretching zone 320. The temperature of this preheating zone 310 is set so that the resin film 30 can be heated to a desired preheat temperature. Typically, the preheating zone 310 is configured so that the inner clip 230L and the outer clip 230R, which hold both ends 30L and 30R of the resin film 30, can travel while maintaining a constant distance D (see Figure 2). Therefore, the guide rails 220L and 220R, which define the trajectories of the clips 230L and 230R, are arranged approximately parallel within this zone. The guide rails being "approximately parallel" means that the angular deviation from an exactly parallel arrangement is within 3.5°. The guide rails being "non-parallel" means that the angular deviation from an exactly parallel arrangement exceeds 3.5°.

[0035] As shown in FIG. 2 , the stretching zone 320 is a section where the gap between the inner clip 230L and the outer clip 230R gripping both ends 30L and 30R of the resin film 30 widens. In the stretching zone 320, the inner guide rail 220L and the outer guide rail 220R are non-parallel, and the gap between the inner clip 230L and the outer clip 230R increases downstream. In this embodiment, the inner guide rail 220L and the outer guide rail 220R are shaped so that the resin film 30 is bent with the inner clip 230L facing inward in the traveling direction. Therefore, in the stretching zone 320, the travel distance of the outer clip 230R is set longer than the travel distance of the inner clip 230L, thereby achieving oblique stretching. The temperature in the stretching zone 320 is typically set so that the resin film 30 can be heated to the desired stretching temperature.

[0036] The heat setting zone 330 is a section downstream of the stretching zone 320 where the outer gripper 110R and the inner gripper 110L can travel while maintaining a constant gap between them again. Therefore, the guide rails 220L and 220R that define the paths of the clips 230L and 230R are arranged substantially parallel to each other within this zone. The temperature of this heat setting zone 330 is usually set so that the resin film 30 can be heated to a desired heat setting temperature.

[0037] (Manufacturing method steps) The manufacturing method of the present invention includes a stretching step, a releasing step, a bowing measurement step, and a feedback step.

[0038] (Stretching process) In the stretching process, while both ends of the transparent resin film in the width direction are held by clips, the transparent resin film is guided from upstream to downstream along a track, passing through a preheating zone, a stretching zone, and a heat-fixing zone in that order, and the transparent resin film is stretched in the stretching zone to form a stretched film.

[0039] Explaining with reference to the example of Figures 1 and 2, in the stretching step, a long resin film 30 is unwound from a feed roll 20 and continuously supplied to a tenter stretching machine 200. When the resin film 30 is supplied to the tenter stretching machine 200, the tenter stretching machine 200 sequentially grips both end portions 30L and 30R of the resin film 30 with inner clips 230L and outer clips 230R at an inner gripping start position 240L and an outer gripping start position 240R at an entrance section 240 of the tenter stretching machine 200.

[0040] By driving the clip chains 210R and 210L and causing them to rotate along the guide rails 220R and 220L, which serve as tracks, the resin film 30 is guided from upstream to downstream along the tracks, passing through the preheating zone 310, the stretching zone 320, and the heat setting zone 330 in that order. The shapes of the guide rails 220R and 220L in the stretching zone 320 are set to the shape described above (i.e., a shape in which the distance between the inner clip 230L and the outer clip 230R becomes wider the further downstream, and in which the traveling direction of the resin film 30 is curved), and therefore, the resin film 30 is obliquely stretched in the stretching zone 320.

[0041] The preheating temperature in the preheating zone, the stretching temperature in the stretching zone, and the heat setting temperature in the heat setting zone can be appropriately set so as to achieve the desired stretching. The preheating temperature and stretching temperature can be temperatures equal to or higher than the glass transition temperature (Tg) of the resin constituting the resin film. A specific preheating temperature is, for example, preferably (Tg + 60)°C or higher, more preferably (Tg + 70)°C or higher, and preferably (Tg + 250)°C or lower, more preferably (Tg + 230)°C or lower. A specific stretching temperature is, for example, preferably (Tg + 60)°C or higher, more preferably (Tg + 70)°C or higher, and preferably (Tg + 240)°C or lower, more preferably (Tg + 220)°C or lower.

[0042] On the other hand, the heat setting temperature may be a temperature below Tg. The heat setting temperature may be adjusted to adjust the operating conditions in the feedback step (described later). Specific examples of the heat setting temperature include preferably (Tg-50)°C or higher, more preferably (Tg-60)°C or higher, and preferably (Tg-200)°C or lower, more preferably (Tg-190)°C or lower.

[0043] When the transparent resin film includes multiple layers each having a different glass transition temperature, the preheating temperature, stretching temperature, and heat setting temperature can be determined, for example, by taking the weighted average of the glass transition temperatures based on the thickness of each layer as the Tg.

[0044] The stretching ratio in the stretching zone can be appropriately adjusted so as to obtain a stretched film having the desired properties. Specific stretching ratios are, for example, preferably 1.1 times or more, more preferably 1.2 times or more, and preferably 3.0 times or less, more preferably 2.5 times or less.

[0045] (Release process) A releasing process is carried out downstream of the stretching process. In the releasing process, the stretched film is released from the clips. In the example of FIGS. 1 and 2, after passing through the heat setting zone 330, the resin film 30 exits the oven 300. When the resin film 30 is transported to the exit section 250 of the tenter stretching machine 200, the tenter stretching machine 200 releases the resin film 30 from the inner clips 230L and the outer clips 230R at the inner release position 250L and the outer release position 250R.

[0046] (Boeing measurement process) Downstream of the releasing step, a bowing measurement step is carried out, in which the distribution of orientation angles across the width of the stretched film is measured to obtain bowing information that is an index of the degree of bowing of the stretched film.

[0047] Bowing refers to a phenomenon in which the widthwise center of a long film is distorted in either direction along the longitudinal direction relative to the widthwise ends of the film. In particular, in a long film being transported, a state in which the widthwise ends lead and the widthwise center lags, resulting in distortion with the widthwise center shifted upstream is called forward bowing, and a state in which the widthwise ends lag and the widthwise center leads and the widthwise center lags, resulting in distortion with the widthwise center shifted downstream is called reverse bowing.

[0048] Bowing information is information on the measurement results of the properties of a stretched film that reflects the direction of bowing (whether forward bowing or reverse bowing) and its degree. A suitable example of bowing information for a transparent stretched film is the distribution of the orientation direction of the stretched film in the width direction. Here, the orientation direction of a stretched film can be defined as the in-plane slow axis direction for a stretched film made of a material with a positive intrinsic birefringence, or as the in-plane fast axis direction for a stretched film made of a material with a negative intrinsic birefringence.

[0049] Specifically, bowing information can be expressed as a graph plotting the distance from one end in the width direction on the horizontal axis and the orientation angle on the vertical axis. That is, a graph in which either the left or right end in the width direction of a stretched film is taken as the starting point and the other end as the end point, the distance from the starting point is taken as the horizontal axis, and the angle between the orientation direction at that distance and the width direction of the film is taken as the vertical axis, or the slope of an approximated line obtained by approximating the coordinates on the graph using an appropriate method such as the least squares method, can be used as bowing information. When the above-mentioned graph is plotted such that the angle direction of the part extending toward the end point of the line indicating the orientation direction at the starting point, relative to the width direction, is defined as a positive direction when the angle direction is inclined upstream and a negative direction when the angle direction is inclined downstream, the slope of the approximated curve will be negative in the case of forward bowing, and positive in the case of reverse bowing.

[0050] Fig. 3 is a top view showing an example of the distribution of orientation directions measured in measurement region 130 shown in Fig. 1, and Fig. 4 is a graph plotting the distribution shown in Fig. 3. In Fig. 3, line 390 indicates the width direction of the stretched film, and lines 321 to 325 indicate the orientation directions of stretched film 10 at each of measurement points 331 to 335.

[0051] The graph shown in Figure 4 was obtained by plotting the distance from end 30R to measurement points 331-335 on the horizontal axis (x-axis) and the angle between line 390 and lines 321-325 at each measurement point on the vertical axis (y-axis). In this example, at measurement point 331 near the starting point, the portion of line 321 extending toward end point 30L is tilted downstream. The angle shown is the angle when the direction of this tilt (indicated by arrow A3) is defined as negative. In Figure 4, line 410 is an approximation of the plot. In this example, this approximation has a negative slope, indicating the occurrence of forward bowing. The greater the absolute value of this slope, the greater the degree of forward bowing.

[0052] (Feedback process) In the feedback process, the operating conditions in the heat setting zone are adjusted based on the bowing information obtained in the bowing measurement process, and such adjustments can reduce bowing in subsequent stretched films.

[0053] In the production method of the present invention, the operating conditions in the heat setting zone after the completion of the stretching operation in the stretching zone are adjusted based on the bowing information measured in-line after the end of the stretching step. Therefore, adjustments can be made to reduce bowing without significantly affecting the control of stretching, and as a result, bowing can be easily reduced by operations that have little effect on the control of stretching.

[0054] The operating conditions in the heat setting zone that are adjusted in the feedback step include the following: In the production method of the present invention, the operating conditions that are adjusted may be only one of (1) to (3), or a combination of two or more thereof. Operating conditions (1): Heat setting temperature in the heat setting zone. Operating condition (2): Tension applied in the conveying direction of the stretched film at the exit of the heat setting zone. Operating condition (3): Track spacing at the entrance to the thermal fixation zone.

[0055] The adjustment of the operating condition (1) can be performed by adjusting the set temperature in the heat setting zone, which in the example of Figure 1 can be performed by adjusting the set temperature in zone 330 of oven 300.

[0056] In many cases, setting the heat setting temperature at a lower temperature increases the degree of forward bowing of the stretched film, while setting the heat setting temperature at a higher temperature increases the degree of reverse bowing of the stretched film. Therefore, although not necessarily limited thereto, a feedback process can be carried out by adjusting the heat setting temperature to increase if the bowing information obtained in the bowing measurement process indicates the occurrence of forward bowing, or by adjusting the heat setting temperature to decrease if the bowing information indicates the occurrence of reverse bowing.

[0057] The operating condition (2) can be adjusted by adjusting the amount of tension applied by a device that applies tension to the stretched film in the longitudinal direction, such as a take-up roll, nip roll, or suction roll, which is provided downstream of the stretching machine. In the example of Figure 1, the operating condition (2) can be adjusted by adjusting the tension applied to the stretched film 10 downstream of the tenter stretching machine 200 using a take-up device that takes up the film roll 40.

[0058] In many cases, the degree of reverse bowing of the stretched film increases as the applied tension increases, and the degree of forward bowing of the stretched film increases as the applied tension decreases. Therefore, although not necessarily limited to this, the feedback process can usually be carried out by adjusting the tension to decrease when the bowing information obtained in the bowing measurement process indicates the occurrence of reverse bowing, or by adjusting the tension to increase when the bowing information obtained in the bowing measurement process indicates the occurrence of forward bowing.

[0059] The operating condition (3) can be adjusted by adjusting the position of the track at the entrance of the heat fixation zone using a position adjusting device.

[0060] Fig. 5 is an enlarged top view showing a more specific structure of guide rails 220L and 220R of manufacturing apparatus 100 shown in Fig. 1 near region 150. As shown more specifically in Fig. 5, guide rail 220L, which was shown schematically in Fig. 1, includes guide rail 220LD that guides clip chain 210L moving from upstream to downstream while gripping resin film 30, and guide rail 220LU that guides clip chain 210L moving from downstream to upstream after releasing resin film 30. Similarly, guide rail 220R, which was shown schematically in Fig. 1, includes guide rail 220RD that guides clip chain 210R moving from upstream to downstream while gripping resin film 30, and guide rail 220RU that guides clip chain 210R moving from downstream to upstream after releasing resin film 30.

[0061] In this example, the guide rails are supported by a plurality of support members. Support members 511L, 512L, and 513L are provided within region 150 to support guide rails 220LD and 220LU, and support members 511R, 512R, and 513R are provided to support guide rails 220RD and 220RU. Support members 512L and 512R are support members located at the boundary between stretching zone 320 and heat setting zone 330. Support members 511L and 511R are support members located in stretching zone 320 upstream of support members 512L and 512R. Support members 513L and 513R are support members located in heat setting zone 330 downstream of support members 512L and 512R.

[0062] In this example, the support members 512L and 512R are connected to position adjustment devices 520L and 520R, respectively. The position adjustment device 520L includes a shaft 521L and a servo motor 522L, and the support member 512L is connected to the servo motor 522L via the shaft 521L. Similarly, the position adjustment device 520R includes a shaft 521R and a servo motor 522R, and the support member 512R is connected to the servo motor 522R via the shaft 521R.

[0063] The servo motor 522L has an appropriate motor and screw structure, which can drive the shaft 521L in the directions of the arrows A531L and A532L. Similarly, the servo motor 522R has an appropriate motor and screw structure, which can drive the shaft 521R in the directions of the arrows A531R and A532R.

[0064] For example, when shaft 521L is driven in the direction of arrow 531L, the position of support member 512L is displaced from the solid line position to the dashed line position, and thereby the positions of guide rails 220LD and 220LU may also be displaced from the solid line position to the dashed line position. Similarly, when shaft 521R is driven in the direction of arrow 531R, the position of support member 512R is displaced from the solid line position to the dashed line position, and thereby the positions of guide rails 220RD and 220RU may also be displaced from the solid line position to the dashed line position. By such an operation, adjustment of operating condition (3) can be achieved to widen the track spacing at the entrance to the heat fixation zone.

[0065] In the example shown in FIG. 5, an adjustment is made to widen the gap between the tracks at the entrance to the heat fixation zone. However, conversely, an adjustment can also be made to narrow the gap between the tracks at the entrance to the heat fixation zone by driving shaft 521L in the direction of arrow 532L and driving shaft 521R in the direction of arrow 532L.

[0066] 5 is a schematic illustration, and the distance between the tracks shown in FIG. 5 is exaggerated, but adjustments to actual operating conditions (3) can affect the degree of bowing by making very small changes to the distance between the tracks, and such changes can be small relative to the length of the tracks. Such changes in the distance also change the stretch ratio at the exit of the stretching zone, but because the change is so small, the resulting effect on the optical properties of the stretched film 10 is usually negligible.

[0067] In many cases, increasing the gap between the tracks at the entrance to the heat setting zone increases the degree of forward bowing of the stretched film, while decreasing the gap increases the degree of reverse bowing of the stretched film. Therefore, although not necessarily limited to this, a feedback process can be carried out by typically adjusting the gap to be smaller when the bowing information obtained in the bowing measurement process indicates the occurrence of forward bowing, or adjusting the gap to be larger when the bowing information obtained in the bowing measurement process indicates the occurrence of reverse bowing.

[0068] The operating condition adjusted in the feedback step is preferably operating condition (3). When operating condition (3) is adjusted, it is particularly easy to effectively reduce bowing while maintaining the drawing conditions.

[0069] (Film material) In the present invention, the transparent resin film used to produce the stretched film is a single-layer or multi-layer film. A thermoplastic resin is preferred as the resin constituting the transparent resin film. Examples of thermoplastic resins include polyolefin resins such as polyethylene resins and polypropylene resins; alicyclic structure-containing polymer resins such as norbornene-based resins; cellulose-based resins such as diacetyl cellulose resins and triacetyl cellulose resins; polyimide resins, polyamideimide resins, polyamide resins, polyetherimide resins, polyetheretherketone resins, polyetherketone resins, polyketone sulfide resins, polyethersulfone resins, polysulfone resins, polyphenylene sulfide resins, polyphenylene oxide resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polyethylene naphthalate resins, polyacetal resins, polycarbonate resins, polyarylate resins, (meth)acrylic resins, polyvinyl alcohol resins, polypropylene resins, cellulose-based resins, epoxy resins, phenolic resins, (meth)acrylic acid ester-vinyl aromatic compound copolymer resins, isobutene / N-methylmaleimide copolymer resins, and styrene / acrylonitrile copolymer resins. These may be used alone or in combination of two or more in any ratio.

[0070] Among the thermoplastic resins, the alicyclic structure-containing polymer resin is preferred. The alicyclic structure-containing polymer resin is a resin containing an alicyclic structure-containing polymer, and has excellent properties such as transparency, low moisture absorption, dimensional stability, and light weight.

[0071] The alicyclic structure-containing polymer is a polymer having an alicyclic structure in its structural unit, and may be either a polymer having an alicyclic structure in the main chain or a polymer having an alicyclic structure in the side chain. The alicyclic structure-containing polymer may be used alone or in combination of two or more types in any ratio. Among these, polymers containing an alicyclic structure in the main chain are preferred from the viewpoints of mechanical strength, heat resistance, etc.

[0072] Examples of the alicyclic structure include saturated alicyclic hydrocarbon (cycloalkane) structures, unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structures, etc. Among these, from the viewpoints of mechanical strength, heat resistance, etc., cycloalkane structures and cycloalkene structures are preferred, and cycloalkane structures are particularly preferred.

[0073] The number of carbon atoms constituting each alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, particularly preferably 15 or less, per alicyclic structure. This is preferable because the mechanical strength, heat resistance, and formability of the resulting stretched film are well balanced.

[0074] The proportion of the structural units having an alicyclic structure in the alicyclic structure-containing polymer may be appropriately selected depending on the intended use, and is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of the structural units having an alicyclic structure in the alicyclic structure-containing polymer is within this range, it is preferable from the viewpoint of the transparency and heat resistance of the resulting stretched film.

[0075] Examples of the polymer containing an alicyclic structure include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof. Among these, norbornene polymers are preferred because of their good transparency and moldability.

[0076] Examples of norbornene polymers include ring-opening polymers of monomers having a norbornene structure and hydrogenated products thereof; and addition polymers of monomers having a norbornene structure and hydrogenated products thereof. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Among these, hydrogenated products of ring-opening polymers of monomers having a norbornene structure are particularly suitable from the viewpoints of transparency, moldability, heat resistance, low moisture absorption, dimensional stability, light weight, etc.

[0077] Examples of monomers having a norbornene structure include bicyclo[2.2.1]hept-2-ene (common name: norbornene), tricyclo[4.3.0.1 2,5 ]Deca-3,7-diene (common name: dicyclopentadiene), 7,8-benzotricyclo[4.3.0.1 2,5 ]dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo[4.4.0.1 2,5 .1 7,10 ]dodec-3-ene (trivial name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent on the ring). Examples of the substituent include an alkyl group, an alkylene group, and a polar group. These substituents may be the same or different, and a plurality of them may be bonded to the ring. The monomer having a norbornene structure may be used alone or in combination of two or more kinds in any ratio.

[0078] Examples of the polar group include a heteroatom or an atomic group having a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfonic acid group.

[0079] Examples of the optional monomer capable of ring-opening copolymerization with the monomer having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene, and derivatives thereof; cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene, and derivatives thereof; etc. The optional monomer capable of ring-opening copolymerization with the monomer having a norbornene structure may be used alone or in combination of two or more types in any ratio.

[0080] A ring-opening polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of a known ring-opening polymerization catalyst.

[0081] Examples of any monomer capable of addition copolymerization with a monomer having a norbornene structure include α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, and 1-butene, and derivatives thereof; cycloolefins, such as cyclobutene, cyclopentene, and cyclohexene, and derivatives thereof; and non-conjugated dienes, such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene. Among these, α-olefins are preferred, and ethylene is more preferred. Furthermore, any monomer capable of addition copolymerization with a monomer having a norbornene structure may be used alone, or two or more may be used in combination at any ratio.

[0082] An addition polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of a known addition polymerization catalyst.

[0083] The hydrogenated products of the above-mentioned ring-opening polymers and addition polymers can be produced, for example, by hydrogenating the carbon-carbon unsaturated bonds in a solution of these ring-opening polymers and addition polymers, preferably to 90% or more, in the presence of a hydrogenation catalyst containing a transition metal such as nickel or palladium.

[0084] Among norbornene polymers, the structural units are X: bicyclo[3.3.0]octane-2,4-diyl-ethylene structure and Y: tricyclo[4.3.0.1 2,5 ]decane-7,9-diyl-ethylene structure, the amount of these structural units being 90% by weight or more of the total structural units of the norbornene polymer, and the ratio of X to Y being 100:0 to 40:60 by weight. By using such a polymer, the resulting stretched film can be made to have excellent stability of properties without dimensional change over the long term.

[0085] The weight-average molecular weight (Mw) of the polymer contained in the resin constituting the transparent resin film is preferably 10,000 or more, more preferably 15,000 or more, and particularly preferably 20,000 or more, and is preferably 100,000 or less, more preferably 80,000 or less, and particularly preferably 50,000 or less. Here, the weight-average molecular weight is the weight-average molecular weight in terms of polyisoprene or polystyrene measured by gel permeation chromatography using cyclohexane as a solvent (although toluene may be used if the sample is insoluble in cyclohexane). When the weight-average molecular weight is within this range, the mechanical strength and moldability of the stretched film are well balanced, making it ideal.

[0086] The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer contained in the resin constituting the transparent resin film is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, and preferably 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. By making the molecular weight distribution equal to or greater than the lower limit of the above range, polymer productivity can be increased and costs can be reduced. Furthermore, by making it equal to or less than the upper limit, low molecular weight components can be reduced, thereby extending the relaxation time. As a result, relaxation during exposure to high temperatures can be suppressed, and the stability of the stretched film can be improved.

[0087] The proportion of the polymer in the resin constituting the transparent resin film is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight. In particular, when an alicyclic structure-containing polymer resin is used as the resin, the proportion of the alicyclic structure-containing polymer contained in the alicyclic structure-containing polymer resin is preferably 80% by weight to 100% by weight, more preferably 90% by weight to 100% by weight.

[0088] The resin constituting the transparent resin film may contain optional components other than the polymer, as long as the effects of the present invention are not significantly impaired. Examples of optional components include additives such as colorants such as pigments and dyes; plasticizers; fluorescent whitening agents; dispersants; heat stabilizers; light stabilizers; UV absorbers; antistatic agents; antioxidants; lubricants; and surfactants. These components may be used alone or in combination of two or more in any ratio.

[0089] The glass transition temperature Tg of the resin constituting the transparent resin film is preferably 100°C or higher, more preferably 110°C or higher, and particularly preferably 120°C or higher, and is preferably 200°C or lower, more preferably 190°C or lower, and particularly preferably 180°C or lower. By making the glass transition temperature of the resin equal to or higher than the lower limit of the above range, the durability of the obliquely stretched film in a high-temperature environment can be improved. Furthermore, by making the glass transition temperature equal to or lower than the upper limit, stretching treatment can be easily carried out.

[0090] (Physical properties and dimensions of stretched film) The total light transmittance of the stretched film obtained by the production method of the present invention is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The light transmittance can be measured in accordance with JIS K0115 using a spectrophotometer (UV-visible-near-infrared spectrophotometer "V-570" manufactured by JASCO Corporation).

[0091] In some examples, the in-plane retardation Re of a stretched film in the longitudinal direction of the stretched film is preferably 100 nm or more, more preferably 120 nm or more, particularly preferably 140 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less, particularly preferably 150 nm or less. Having such an in-plane retardation Re allows the stretched film to be suitably used for useful applications such as λ / 4 wave plates. However, the in-plane retardation Re of the stretched film is not limited to this range and can be set to any appropriate value depending on the application.

[0092] The thickness of the stretched film is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more, and is preferably 100 μm or less, and more preferably 60 μm or less, which can increase the mechanical strength of the stretched film.

[0093] The width of the stretched film is preferably 1000 mm or more, more preferably 1300 mm or more, particularly preferably 1330 mm or more, and is preferably 1500 mm or less, more preferably 1490 mm or less. By widening the width of the stretched film in this way, it becomes possible to apply the stretched film to large display devices (such as organic EL display devices).

[0094] (Variation) The manufacturing method of the present invention is not limited to the above-described examples, and may be modified as appropriate to obtain a desired product. For example, in the example described above, the inner guide rail 220L and the outer guide rail 220R have an asymmetrical shape, and the resin film 30 is transported along a curved track to perform diagonal stretching, but the present invention is not limited to this, and for example, a pair of guide rails having symmetrical shapes may be used as the track to perform widthwise stretching of a long film. [Example]

[0095] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be implemented with any modifications within the scope of the claims and their equivalents. In the following examples and comparative examples, the units "%" and "parts" that represent amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out in air at room temperature and normal pressure unless otherwise specified.

[0096] (Evaluation method) (Method for measuring orientation angle) At the center of the width direction of the produced long obliquely stretched film, the orientation angle with respect to the width direction of the obliquely stretched film was measured in-line using a parallel Nicol rotation method retardation meter ("KOBRA-WIST-IE" manufactured by Oji Scientific Instruments Co., Ltd.) The orientation angle was measured at each position in the width direction, and the average value and standard deviation were also calculated.

[0097] (Method of measuring retardation) The in-plane retardation Re of the produced long obliquely stretched film was measured in-line at the center in the width direction of the obliquely stretched film using a parallel Nicol rotation method phase difference meter ("KOBRA-WIST-IE" manufactured by Oji Scientific Instruments).

[0098] (Thickness measurement method) Using a snap gauge ("ID-C112BS" manufactured by Mitutoyo Corporation), the thickness was measured at 5 cm intervals in the width direction of the film, and the average value was taken as the thickness of the film.

[0099] Example 1 (1.1. Transparent resin film) Pellets of a thermoplastic resin containing a norbornene polymer, a type of polymer containing an alicyclic structure (ZEONOR manufactured by Zeon Corporation, glass transition temperature Tg 126°C) were dried at 100°C for 5 hours. The dried pellets were fed into an extruder, where they were heated and melted. They were then extruded into a film form from a T-die onto a casting drum after passing through a polymer pipe and a polymer filter. The extruded resin was cooled on the casting drum, yielding a long, transparent resin film 38 μm thick and 1350 mm wide.

[0100] (1.2. Stretching Process, Release Process, and Bowing Measurement Process) A manufacturing apparatus 100, as shown schematically in Figures 1, 2, and 5, was prepared. However, the heat-setting zone 330 was further divided into three equal zones, allowing independent temperature settings along the transport path. The temperature was lowered in 10°C steps from upstream to downstream. The transparent resin film 30 obtained in (1.1) was continuously fed into the manufacturing apparatus 100, held by clips 230L and 230R, and guided from upstream to downstream along guide rails 220L and 220R. It passed through the preheating zone 310, stretching zone 320, and heat-setting zone 330 in that order, where it underwent oblique stretching, continuously obtaining a stretched film 10. The stretching conditions were a preheating zone temperature of 145°C, a stretching zone temperature of 139°C, and a stretch ratio of 1.3. After exiting the heat-setting zone, the stretched film 10 was released from clips 230L and 230R and transported further downstream, where its orientation angle and retardation were measured. This resulted in the continuous production of a long obliquely stretched film having a thickness of 26 μm, a width of 1330 mm, Re of 140 nm, and an average orientation angle of 45°.

[0101] Based on the obtained orientation angle information, a graph was created showing the relationship between the distance from the starting point and the orientation angle from the starting end 30R to the ending end 30L, as illustrated in Figure 4.It was found that the approximate curve was inclined in the negative direction, indicating that forward bowing was occurring.

[0102] (1.3. Feedback process) While maintaining the continuous obliquely stretched film production process described in (1.2), the heat-setting zone temperature and the tenter exit conveying tension (the set value of the tension imposed in the conveying direction of the stretched film at the exit of the heat-setting zone) were adjusted. Furthermore, by operating the position adjustment devices 520L and 520R shown in FIG. 5, the positions of the guide rails 220L (220LD and 220LU) and 220R (220RD and 220RU) at the entrance of the heat-setting zone 300 were slightly moved in the directions of arrows A532L and A532R to narrow the gap between the guide rails. The orientation angle was then measured again, and the slope of the approximation curve was calculated. As a result, it was found that the slope had increased (it was a negative value, and the absolute value had decreased). Further adjustments of the heat-setting zone temperature, changes in the tenter exit conveying tension, and measurements of the orientation angle were repeated, ultimately resulting in a decrease in the slope of the approximation curve to -0.0001° / mm. At this time, the heat-setting zone temperatures were 120°C, 110°C, and 100°C, respectively, from the upstream side. The tenter outlet conveying tension (the set value of the tension imposed in the conveying direction of the stretched film at the outlet of the heat-setting zone) was 160 N. The position of the guide rail at this time was designated as the final reference position. The Re was 140 nm, and the average orientation angle was 45°, which was unchanged from the start of step (1.2). The standard deviation of the orientation angle at this time was 0.1°.

[0103] Example 2 (2.1. Transparent resin film) Pellets of the same thermoplastic resin as used in (1.1) of Example 1 were mixed with an ultraviolet absorber (ADEKA Corporation's "LA-31"), melted, and re-formed into pellets to obtain ultraviolet absorber-containing resin pellets. The proportion of the ultraviolet absorber in these pellets was 10% by weight. The glass transition temperature of the ultraviolet absorber-containing resin pellets was 120°C.

[0104] A two-kind, three-layer coextrusion film molding machine equipped with a feed block and a single-layer die was prepared. The feed block had flow paths capable of melt extrusion molding of two-kind, three-layer films. That is, by supplying resins for the outer and inner layers to its two inlets, the feed block was capable of forming a multilayer film with a layer structure of (outer layer 1) / (inner layer) / (outer layer 2).

[0105] Pellets of the thermoplastic resin not containing a UV absorber were fed into a coextrusion film molding machine as the outer layer resin, and resin pellets containing a UV absorber were fed into the inner layer resin. The resin was heated and melted in the extruder, passed through a polymer pipe and a polymer filter, and extruded into a film form through a feed block and die onto a casting drum. The extruded resin was cooled in the casting drum to obtain a long transparent resin film with a thickness of 38 μm and a width of 1350 mm. The resulting transparent resin film was a multilayer film with a layer structure of (outer layer 1) / (inner layer) / (outer layer 2). The thicknesses of outer layer 1, inner layer, and outer layer 2 were 10 μm, 18 μm, and 10 μm, respectively.

[0106] (2.2. Stretching Process, Release Process, and Bowing Measurement Process) The same procedures as in (1.2) of Example 1 were carried out to produce a stretched film, and the orientation angle and retardation were measured, except that the transparent resin film 30 obtained in (2.1) was used instead of the transparent resin film obtained in (1.1) and the stretching zone temperature was changed to 140°C. A long obliquely stretched film having a thickness of 26 μm, a width of 1330 mm, an Re of 140 nm, and an average orientation angle of 45° was continuously produced. The obtained obliquely stretched film was a multilayer film having a layer structure of (outer layer 1) / (inner layer) / (outer layer 2). The thicknesses of outer layer 1, inner layer, and outer layer 2 were 6 μm, 14 μm, and 6 μm, respectively.

[0107] Based on the obtained orientation angle information, a graph was created showing the relationship between the distance from the starting point and the orientation angle from the starting end 30R to the ending end 30L, as illustrated in Figure 4.It was found that the approximate curve was inclined in the negative direction, indicating that forward bowing was occurring.

[0108] (2.3. Feedback process) While maintaining the continuous obliquely stretched film production process described in (2.2), the heat-setting zone temperature and the tenter exit conveying tension (the set value of the tension imposed in the conveying direction of the stretched film at the exit of the heat-setting zone) were adjusted. Furthermore, by operating the position adjustment devices 520L and 520R shown in FIG. 5, the positions of the guide rails 220L (220LD and 220LU) and 220R (220RD and 220RU) at the entrance of the heat-setting zone 300 were slightly moved in the directions indicated by arrows A532L and A532R, narrowing the distance between the guide rails. The orientation angle was then measured again, and the slope of the approximation curve was calculated. As a result, it was found that the slope had increased (it was a negative value, and the absolute value had decreased). Further adjustments of the heat-setting zone temperature, changes in the tenter exit conveying tension, and measurements of the orientation angle were repeated, ultimately resulting in a decrease in the slope of the approximation curve to -0.0001° / mm. At this time, the heat setting zone temperatures were 120°C, 110°C, and 100°C, respectively, from the upstream side, and the tenter outlet conveying tension (the set value of the tension imposed in the conveying direction of the stretched film at the outlet of the heat setting zone) was 160 N. The Re was 140 nm, and the average orientation angle was 45°, which was unchanged from the start of step (2.2). The standard deviation of the orientation angle at this time was 0.1°.

[0109] Example 3 In the preparation process of (1.3) in Example 1, the set temperatures of the heat setting zones were set to 119°C, 109°C, and 99°C, respectively, from the upstream side, and the other conditions were the same as the final preparation state in (1.3). At this point, the Re, film thickness, and orientation angle of the resulting stretched film were measured. As a result, the Re was maintained at 140 nm and the average orientation angle was maintained at 45°, while the slope of the approximation curve was -0.0002° / mm, and a greater forward bowing was observed than in the final preparation state of Example 1. The standard deviation of the orientation angle at this point was 0.1°.

[0110] Example 4 During the preparation process of (1.3) in Example 1, the film was adjusted to the same final preparation state as in (1.3) except that the tenter outlet conveying tension was set to 260 N. At this point, the Re, film thickness, and orientation angle of the resulting stretched film were measured. As a result, the Re was maintained at 140 nm and the average orientation angle was maintained at 45°, while the slope of the approximation curve was 0.00009° / mm, and greater forward bowing was observed than in the final preparation state of Example 1. The standard deviation of the orientation angle at this point was 0.1°.

[0111] (Reference example 1) A long obliquely stretched film was continuously produced by the same procedures as in (1.1) to (1.3) of Example 1. Furthermore, while maintaining the continuous obliquely stretched film production process, the positions of guide rails 220L (220LD and 220LU) and 220R (220RD and 220RU) at the entrance of heat-setting zone 300 were moved 10 mm from their final reference positions in the directions of arrows A531L and A531R, respectively, to expand the guide rail spacing by 20 mm. As a result, Re remained at 140 nm and the average orientation angle was maintained at 45°, while the slope of the approximation curve decreased to -0.0006° / mm. The standard deviation of the orientation angle at this point was 0.1°.

[0112] (Reference example 2) The same operations as in (1.1) to (1.3) of Example 1 were carried out to continuously produce a long obliquely stretched film. Furthermore, while maintaining the continuous obliquely stretched film production process, the positions of guide rails 220L (220LD and 220LU) and 220R (220RD and 220RU) at the entrance of heat-setting zone 300 were moved 10 mm from their final reference positions in the directions of arrows A532L and A532R, respectively, to reduce the distance between the guide rails by 20 mm. As a result, Re remained at 140 nm and the average orientation angle was maintained at 45°, while the slope of the approximation curve became +0.0001° / mm. The standard deviation of the orientation angle at this point was 0.2°.

[0113] The results of the Examples and Reference Examples are summarized in Table 1.

[0114] [Table 1]

[0115] The results of the Examples and Reference Examples show that the degree of bowing can be changed by adjusting the operating conditions in the heat setting zone based on the bowing information. Therefore, it is clear that the production method of the present invention can change the degree of bowing and achieve a reduction in bowing. [Explanation of symbols]

[0116] 10 Stretched film 20 Payout roll 30 Resin film 40 film rolls 100 Manufacturing equipment 130 measurement area 150 areas 200 Tenter stretching machine 240 Entrance 250 Exit section 300 Oven 310 Preheating Zone 320 Extension Zone 321 Line indicating orientation direction 322 Orientation line 323 Orientation line 324 Orientation line 325 Orientation line 330 Heat Fixing Zone 331 measurement points 332 measurement points 333 measurement points 334 measurement points 335 measurement points 340 Bulkhead 390 Line indicating the width direction of the stretched film 410 Plot Approximation Line 210L Inner Clip Chain 210R outer clip chain 220L guide rail 220LD guide rail 220LU guide rail 220R guide rail 220RD guide rail 220RU guide rail 230L Inner Clip 230R outer clip 240L Inner grip start position 240R Outside grip start position 250L inner release position 250R outer release position 30L resin film edge 30R Resin film edge 511L Support member 511R Support member 512L Support member 512R Support member 513L Support Member 513R Support member 520L position adjustment device 520R position adjustment device 521L shaft 521R shaft 522L Servo Motor 522R Servo Motor A3 Tilt direction A531L Drive direction A531R Drive direction A532L Drive direction A532R Drive direction D interval LD1 Stretching direction LD2 Extension direction LD3 Extension direction

Claims

1. A method for producing a stretched film, comprising stretching a long transparent resin film using a stretching device, The stretching device includes a pair of tracks and a clip guideably disposed along the tracks; The manufacturing method includes: a stretching step in which, while both ends of the transparent resin film in a width direction are held by the clips, the transparent resin film is guided from upstream to downstream along the track and passes through a preheating zone, a stretching zone, and a heat setting zone in this order, and the transparent resin film is stretched in the stretching zone to form the stretched film; a releasing step downstream of the stretching step, in which the stretched film is released from the clips; a bowing measurement step downstream of the releasing step, in which a distribution of orientation angles across the width direction of the stretched film is measured to obtain bowing information that is an index of the degree of bowing of the stretched film; and a feedback process for reducing the bowing by adjusting operating conditions within the heat setting zone based on the bowing information. A method for producing a stretched film, comprising:

2. The method for producing a stretched film according to claim 1 , wherein the operating conditions include a heat setting temperature in the heat setting zone.

3. The method for producing a stretched film according to claim 1 , wherein the operating conditions include a set value of tension imposed in the transport direction of the stretched film at the exit of the heat setting zone.

4. The method for producing a stretched film according to claim 1 , wherein the operating conditions include the spacing of the tracks at the entrance of the heat setting zone.

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