JP2020049738A - Method for producing biaxially oriented film - Google Patents

Abstract

To provide a method for producing a biaxially oriented film capable of predicting in advance an occurrence of a poor grip of a clip in a tenter device, and reducing such poor grip and accompanying stretching unevenness and film cutting over a long period of time.SOLUTION: A method for producing a biaxially oriented film includes, in this order, a longitudinal stretching step of stretching a sheet in a longitudinal direction, and a transverse stretching step of stretching an uniaxially oriented film obtained in the longitudinal stretching step, in a width direction using a tenter device. Between a roll (roll A) located immediately before an entrance of the tenter device and a point where a clip of the tenter device first grips the uniaxially oriented film (grip point), a position change amount in a thickness direction of at least one end of the uniaxially oriented film in a width direction is controlled to be 0.00 mm or more and 2.50 mm or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for producing a biaxially oriented film in which a uniaxially oriented film having a molecular orientation in the longitudinal direction is stretched in the width direction using a tenter device.

  As a method for producing a biaxially oriented film, there has been known a sequential biaxial stretching method in which a polymer in a molten state is discharged, formed into a sheet shape using a die or the like, longitudinally stretched, and then horizontally stretched. In this transverse stretching, a tenter device that stretches a sheet in the width direction by extending a gap between the clips while gripping both ends in the width direction of the uniaxially oriented film obtained by the longitudinal stretching in the transport direction. Is used. The biaxially oriented film obtained through the longitudinal stretching and the transverse stretching has its molecules and crystals oriented in two directions, so that the mechanical strength, optical properties and gas permeability are improved. It has features that are not found in this sheet.

  As the clip in the tenter device, for example, the clip having the configuration shown in FIG. 1 is well known. FIG. 1 is a schematic diagram when an example of a clip of a tenter device is observed from a running direction. As shown in FIG. 1, a clip (hereinafter simply referred to as a clip) 1 of the tenter device is mounted on a clip table 3 slidably disposed relative to a rail 2. The clip 1 has a base 4 and an upright portion 5 standing upright from the base 4, and a clip lever 6 is rotatably attached to the upright portion 5 by a support shaft 7. The clip lever 6 is rotated to the position shown by the dotted line by the elastic force of a spring (not shown) located between its upper part (part above the support shaft 7) and the upright part 5, and its lower part (support shaft). The widthwise end of the uniaxially oriented film 9 can be gripped between the front end of the lower part 5 and the liner 8 provided on the base 4.

  In the longitudinal stretching step, a non-oriented sheet is stretched in the longitudinal direction, so that a contraction force acts in the width direction of the sheet. Then, in the uniaxially oriented film obtained by longitudinal stretching, the peripheral constraint acts on each other at the center in the width direction, while the film contracts freely at the end in the width direction. For this reason, curling occurs at the width direction end of the uniaxially oriented film, and this tendency is particularly remarkable when the uniaxially oriented film is thin or when the tension in the width direction applied along the guide rolls decreases.

  Usually, it is difficult to arrange the guide roll near the clip of the tenter device. Therefore, at the point where the clip grips the uniaxially oriented film, the tension caused by the guide roll is reduced, and the widthwise end of the uniaxially oriented film may be curled. When the clip attempts to grip the uniaxially oriented film in such a curled state, the lower portion of the clip lever 6 contacts the end of the uniaxially oriented film 9 in the width direction. For this reason, a gripping point may be shifted outward (FIG. 2A), or a gripping failure may occur such that the clip cannot grip the uniaxially oriented film (FIG. 2B). Further, when an impact caused by the closing operation of the clip is transmitted to the curled portion of the uniaxially oriented film, the curled portion may vibrate, and the grip failure may be further increased.

  Usually, since the gripping position of the clip is continuous so as to be parallel to the longitudinal direction, stable film formation and uniform stretching are possible. However, when such poor gripping occurs, there may be a problem that the uniformity of the stretching is impaired or the film is cut during the stretching. More specifically, when the grip point of the clip is shifted outward as shown in FIG. 2-A, the stretching ratio in the width direction is slightly changed only at that portion, and the quality of the obtained biaxially oriented film is uneven. If the clip is not held as shown in FIG. 2B, the film may be cut from that portion.

  As a method for overcoming such a problem, a straightening roller is introduced before the transverse stretching step to increase the tension on the uniaxially oriented film between the longitudinal stretching step and the transverse stretching step, and the width of the uniaxially oriented film is increased. There are known a method of flattening an end in the direction (Patent Document 1), a method of installing a slider on a clip of a tenter device and pressing an end of a conveyed film (Patent Document 2).

JP 2010-82854 JP 2005-104081A

  However, if the running speed of the uniaxially oriented film, the composition and the thickness of the film, and the like are different, the tension of the uniaxially oriented film between the longitudinal stretching step and the transverse stretching step also varies. For this reason, the method described in Patent Document 1 requires complicated adjustment of conditions for manufacturing various kinds of films, and there is room for improvement in the effect of reducing gripping defects by clips. In addition, the method of Patent Document 2 can reduce gripping failure by installing a slider, but there is a problem in that gripping failure occurs again when equipment deteriorates in the course of continuing production. Further, the method disclosed in Patent Document 2 cannot predict occurrence of gripping failure in advance.

  The present invention provides a method for producing a biaxially oriented film capable of predicting in advance the occurrence of poor grip of a clip in a tenter device and reducing such poor grip and accompanying stretching unevenness and film cutting over a long period of time. Is the task.

In order to solve such a problem, the present invention has the following configuration.
(1) A method for producing a biaxially oriented film having a longitudinal stretching step of stretching a sheet in a longitudinal direction and a transverse stretching step of stretching a uniaxially oriented film obtained in the longitudinal stretching step in a width direction by a tenter device in this order. Between the roll (roll A) located immediately before the entrance of the tenter device and the point where the clip of the tenter device first grips the uniaxially oriented film (grip point), at least one end of the uniaxially oriented film width direction end portion. A method for producing a biaxially oriented film, characterized in that a position change amount in a thickness direction is controlled to be 0.00 mm or more and 2.50 mm or less.
(2) The method for producing a biaxially oriented film according to (1), wherein the amount of change in the position of the end of the uniaxially oriented film in the width direction in the thickness direction is measured by a displacement sensor.
(3) The method for producing a biaxially oriented film according to (2), wherein the displacement sensor is a laser displacement sensor.
(4) A pair of rotatable rolls is provided between the measuring point and the gripping point when a point for measuring the amount of positional change in the thickness direction of the end of the uniaxially oriented film in the width direction is set as a measuring point. The method for producing a biaxially oriented film according to any one of (1) to (3), wherein
(5) the roll A rotational speed _{V A} of the traveling speed of the clip when the _{V B,} and controls the V B / _{V A} to 1.006 or 1.010 or less, ( The method for producing a film according to any one of 1) to (4).

  According to the present invention, there is provided a method for producing a biaxially oriented film capable of predicting in advance occurrence of gripping failure of a clip in a tenter device, and reducing such gripping failure, accompanying stretching unevenness and film cutting over a long period of time. can do.

It is the schematic at the time of observing an example of the clip of a tenter apparatus from a driving direction. It is the schematic which shows the holding | grip defect of a clip in a tenter apparatus. It is a schematic diagram showing movement of a clip and a film in a tenter device. It is a side view showing an example of a section from a roll A to a grip point.

  The method for producing a biaxially oriented film of the present invention includes a longitudinal stretching step of stretching the sheet in the longitudinal direction, and a transverse stretching step of stretching the uniaxially oriented film obtained in the longitudinal stretching step in the width direction with a tenter device in this order. A method for producing a biaxially oriented film, wherein at least one of a roll (roll A) located immediately before an entrance of a tenter device and a point where a clip of the tenter device first grips the uniaxially oriented film (gripping point). The amount of positional change in the thickness direction of the end portion in the width direction of the uniaxially oriented film is controlled to be 0.00 mm or more and 2.50 mm or less.

  The method for producing a biaxially oriented film of the present invention includes a longitudinal stretching step of stretching the sheet in the longitudinal direction, and a transverse stretching step of stretching the uniaxially oriented film obtained in the longitudinal stretching step in the width direction with a tenter device in this order. This is very important. Here, the sheet refers to a sheet obtained by cooling and solidifying a molten thermoplastic resin to form a sheet. The longitudinal direction refers to a direction in which a sheet or a film travels in a manufacturing process of a biaxially oriented film, and the width direction refers to a direction orthogonal to the longitudinal direction in a sheet plane or a film plane. Further, having a longitudinal stretching step and a transverse stretching step in this order means that before the longitudinal stretching step, between the longitudinal stretching step and the transverse stretching step, and whether or not there is another step after the transverse stretching step. , Refers to all aspects in which a transverse stretching step is provided downstream of the longitudinal stretching step. By adopting such a mode, curling of the end portion in the width direction of the uniaxially oriented film that causes gripping failure with the clip occurs, so that the advantage of applying the invention is increased.

  The transverse stretching by the tenter device is performed by extending the width of the clip in the width direction while running the uniaxially oriented film in the longitudinal direction by running the clips gripping both ends of the uniaxially oriented film in the width direction along the rail. be able to. The details will be described later with reference to the drawings together with the clip of the tenter device.

  In the longitudinal stretching step, a non-oriented sheet is stretched in the longitudinal direction, so that a contraction force acts in the width direction of the sheet. Then, in the uniaxially oriented film obtained by longitudinal stretching, the peripheral constraint acts mutually at the center in the width direction, while the film contracts freely at the end in the width direction, so that the curl is likely to occur at the end in the width direction. As a result, for example, when the clip of the embodiment of FIG. 1 grips the width direction end of the uniaxially oriented film, the clip lever comes into contact with the width direction end of the uniaxially oriented film that has risen due to curling, resulting in poor grip of the clip. Occurs. On the other hand, since the non-oriented sheet has a very small shrinkage force acting in the width direction as compared with the uniaxially oriented film, the frequency of such curling is usually low, and the frequency of occurrence of clip holding defects due to the curling is low.

  In the manufacturing method of the biaxially oriented film of the present invention, from the viewpoint of reducing the gripping failure of the clip, the roll (roll A) located immediately before the entrance of the tenter device and the clip of the tenter device first grip the uniaxially oriented film. It is important to control the amount of position change in the thickness direction of at least one end of the uniaxially oriented film in the width direction between the point (gripping point) and the thickness (0.001 mm or more and 2.50 mm or less). By adopting such an aspect, the vertical vibration of the uniaxially oriented film traveling near the grip point is suppressed, and when the clip grips the width direction end of the uniaxially oriented film, the clip lever is elastically moved by the uniaxially oriented film. The risk of erosion is reduced. Here, the roll (roll A) located immediately before the entrance of the tenter device is a drive roll having a holding angle of the uniaxially oriented film of 10 ° or more, and is located upstream of the entrance of the tenter device. The one that is closest to the entrance. In addition, the holding angle of the uniaxially oriented film means that the roll A is observed from a direction parallel to the rotation axis, and the two points located at the most end where the uniaxially oriented film and the roll A are in contact with each other from the center of the rotation axis. The angle formed when each line is drawn.

  In view of the above, in the method for producing a biaxially oriented film of the present invention, between the roll A and the gripping point, at least one of the uniaxially oriented film width direction end portions in the thickness direction is 0.00 mm or more. It is preferable to control it to 2.30 mm or less. On the other hand, when the gap between the roll A and the gripping portion is secured to some extent in order to install a displacement sensor to be described later, the amount of change in the thickness direction of the end of the uniaxially oriented film in the width direction increases unless the tension is increased. In consideration of this point, it is more preferable to control the amount of position change in the thickness direction of at least one end of the uniaxially oriented film in the width direction between the roll A and the gripping point to 1.60 mm or more and 2.30 mm or less. preferable. Further, from the viewpoint of reducing such a risk on both sides in the width direction, in the method for manufacturing a biaxially oriented film of the present invention, between the roll A and the gripping point, the thickness of the uniaxially oriented film width direction ends on both sides. It is preferable that the amount of change in the position in the direction is controlled to be 0.00 mm or more and 2.50 mm or less or the above preferable range. The method for measuring the amount of positional change in the thickness direction of the end of the uniaxially oriented film in the width direction will be described later together with a displacement sensor that can be used for the measurement.

  Means for controlling the amount of position change in the thickness direction of at least one end of the uniaxially oriented film in the width direction between the roll A and the gripping point within the range of 0.00 mm or more and 2.50 mm or less in the present invention The method is not particularly limited as long as the effect of (1) is not impaired. For example, between the roll A and the gripping point, a method of installing a pair of rotatable rolls so as to sandwich the uniaxially oriented film, A method of adjusting the distance may be used. More specifically, by installing such a rotatable pair of rolls, or by reducing the distance between the roll A and the gripping point, the amount of positional change in the thickness direction of the width direction end of the uniaxially oriented film is reduced. Can be smaller.

  The clip of the tenter device in the method for producing a biaxially oriented film of the present invention is not particularly limited as long as it can grip the uniaxially oriented film, as long as the effects of the present invention are not impaired. You can choose. A specific example thereof is, for example, the one shown in FIG. Hereinafter, this will be described specifically. In this embodiment, a clip (hereinafter simply referred to as a clip) 1 of the tenter device is mounted on a clip base 3 slidably disposed relative to a rail 2. The clip 1 has a base 4 and an upright portion 5 standing upright from the base 4, and a clip lever 6 is rotatably attached to the upright portion 5 by a support shaft 7. The clip lever 6 is rotated to the position shown by the dotted line by the elastic force of a spring (not shown) located between its upper part (part above the support shaft 7) and the upright part 5, and its lower part (support shaft). The widthwise end of the uniaxially oriented film 9 can be gripped between the front end of the lower part 5 and the liner 8 provided on the base 4.

  Subsequently, the stretching by the tenter device including the clip of the embodiment of FIG. 1 will be specifically described with reference to the drawings. FIG. 3 is a schematic view showing the movement of a clip and a film in the tenter device. The uniaxially oriented film 9 whose both ends in the width direction are gripped by the clip 1 at the entrance of the tenter device is stretched in the width direction by the clip 1 running so as to extend the distance in the width direction along the rail 2, and The film becomes a biaxially oriented film before reaching the outlet. At this time, when the upper portion of the clip lever 6 of the clip 1 comes into contact with the clip closer 10 at the entrance, the clip lever 6 rotates as shown by a dotted line in FIG. Thereafter, the clip travels while holding the uniaxially oriented film 9, and after the uniaxially oriented film 9 is stretched in the width direction to become a biaxially oriented film, the clip lever 6 contacts the clip opener 11 and the wear ring 12 at the outlet. I do. When the clip lever 6 comes into contact with the clip opener 11 and the wear ring 12, the clip lever 6 rotates as shown by the solid line in FIG. 1 against the spring force of the spring, and releases the biaxially oriented film from being gripped by the clip 1. Then, the clip 1 with the biaxially oriented film released, travels along the rail 2 and returns to the entrance again. The number of clips in the tenter device is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately set according to the scale of the device, the stretching ratio, and the like. The number is about 500.

  In the method for producing a biaxially oriented film of the present invention, it is preferable to measure the amount of positional change in the thickness direction of the end in the width direction of the uniaxially oriented film using a displacement sensor. By adopting such an embodiment, it is possible to easily measure the amount of positional change in the thickness direction of the end of the uniaxially oriented film in the width direction during the manufacturing process. Usually, the displacement sensor is disposed between the roll A and the gripping point, at least one of an upper portion and a lower portion of the traveling uniaxially oriented film, so that a position change amount within 10 mm from the end of the uniaxially oriented film width direction is obtained. Measure. The number of displacement sensors can be freely adjusted within a range that does not impair the effects of the present invention.

  The displacement sensor in the method for producing a biaxially oriented film of the present invention is not particularly limited as long as the effects of the present invention are not impaired. For example, an ultrasonic type, an eddy current type, a laser type, or the like can be used. However, from the viewpoint of measurement accuracy, the displacement sensor is preferably a laser displacement sensor. By using the laser displacement sensor, it is easy to reduce the influence of other displacement sensors when a plurality of displacement sensors are installed, and to reduce the disadvantage that fine setting cannot be performed due to the influence of noise. The laser displacement sensor used in the method for producing a biaxially oriented film of the present invention is not particularly limited as long as it can perform the measurement itself. For example, LHG500A manufactured by Keyence Corporation can be suitably used.

  When the LHG500A laser-type mutation sensor manufactured by KEYENCE CORPORATION is used for measuring the amount of change in the position of the end of the uniaxially oriented film in the thickness direction, the measurement conditions are as follows: the sampling cycle is 100 μs, the accumulation cycle is 1, and the accumulation point is 65536 Can be set. Then, the difference (R) between the maximum value and the minimum value of the displacement amount measured under the same conditions can be used as the position change amount in the thickness direction of the end of the uniaxially oriented film in the width direction.

  The method for producing a biaxially oriented film of the present invention is characterized in that, when a point for measuring a position change amount in the thickness direction of the width direction end of the uniaxially oriented film is set as a measurement point, it is rotatable between the measurement point and the gripping point. It is preferable to provide a simple pair of rolls. In other words, as shown in FIG. 4 which is a side view of a section from the roll A to the gripping point, the roll A13, the measuring point 14, the pair of rotatable rolls 15, and the gripping point 16 may be located in this order. preferable. By adopting such an aspect, since a pair of rotatable rolls can reduce the vertical movement by sandwiching the uniaxially oriented film, the position of the end of the uniaxially oriented film in the width direction at the measurement point in the thickness direction can be reduced. The value of the amount of change can be reduced. Here, having a pair of rotatable rolls means that there is no power, but rolls that can be passively rotated by external force are positioned above and below the uniaxially oriented film. State. In addition, a cover may be attached in front of the gripping point to prevent the lubricating oil of the clip from scattering around. Therefore, if the positional relationship between the pair of rotatable rolls and the measurement point is reversed, the measurement point may have to be moved away from the gripping point and immediately after the pair of rotatable rolls, resulting in accurate measurement. Can be difficult.

Method for producing a biaxially oriented film of the present invention controls the rotation speed of the roll A _{V A,} the traveling speed of the clips when the _{V B,} the V B / _{V A} to 1.006 or 1.010 or less Is preferred. By setting V _B / V _A to 1.006 or more, since the slack of the uniaxially oriented film in the section from the roll A to the gripping point can be suppressed, the curl of the end in the width direction of the uniaxially oriented film and the clip caused by the curl of the end of the film. Poor gripping can be reduced. Meanwhile, the V B _/ V _A by 1.010 or less, it is possible to reduce the film breaking in the tenter generated by the tension becomes excessive.

Method for controlling the V _B / _{V A} to 1.006 or 1.010 or less is not particularly limited as long as it does not impair the effects of the present invention, for example, adjusting the rotational speed _{V A} and clip running speed _{V B} of the roll A Method. More specifically, and by increasing the _{V B,} such as by reducing the _{V A,} it can be increased _V B / V _A.

  Next, the method for producing a biaxially oriented film of the present invention will be described below, taking production of a polyethylene terephthalate (PET) film by a sequential biaxial stretching method as an example.

  First, PET pellets are supplied to a raw material charging section of an extruder, and are heated and melted. Thereafter, the extruded amount is made uniform by a gear pump or the like, and the PET which has been heated and melted is extruded, and foreign matter and gelled substances are removed through a filter or the like. At this time, usually, when the film has a single layer configuration, one extruder can be used, and when the film has a multilayer configuration, a plurality of extruders can be used. When a plurality of extruders are used, the thermoplastic resin that has passed through the filter is fed into the laminating apparatus. As the laminating apparatus, a multi-manifold die, a feed block, a static mixer, and the like can be used, and these may be arbitrarily combined.

  The thus obtained PET melt is discharged as a sheet-like melt from a die, extruded onto a cooling body such as a casting drum, and solidified by cooling to obtain a non-oriented sheet. As a specific method of obtaining a non-oriented sheet from a sheet-like melt, using a wire-like, tape-like, needle-like or knife-like electrode, the sheet-like melt is electrostatically applied to a cooling body such as a casting drum. It is preferable to use a method in which the solidification and the rapid solidification are performed.

  Next, the process proceeds to a longitudinal stretching step of stretching the non-oriented sheet in the longitudinal direction. In the longitudinal stretching step, the non-oriented sheet obtained by cooling and solidifying is longitudinally stretched to obtain a uniaxially oriented film. Longitudinal stretching can be performed in one stage using one or a plurality of stretching rolls having the same peripheral speed, or can be performed in multiple stages using a plurality of stretching rolls having different peripheral speeds, The magnification is preferably 3.0 to 5.0 times, and more preferably 3.5 to 3.8 times.

  Further, after the longitudinal stretching step, before proceeding to the later-described transverse stretching step, a step of applying a coating agent for forming a functional layer such as an easily adhesive layer on both sides or one side of the obtained uniaxially oriented film is provided. Is also possible. The method for applying the coating agent is not particularly limited, and for example, a reverse coating method, a gravure coating method, a rod coating method, a bar coating method, a wire bar coating method, a die coating method, a spray coating method, and the like can be used.

  Thereafter, the process proceeds to a transverse stretching process in which the uniaxially oriented film obtained in the longitudinal stretching process is stretched in the width direction by a tenter device. In the transverse stretching step, the clips holding both ends in the width direction of the uniaxially oriented film are run along the rails, and while the uniaxially oriented film is running in the longitudinal direction, the gap in the width direction of the clips is widened so as to be uniaxially oriented. The film is stretched in the transverse direction. The magnification of the transverse stretching can be appropriately adjusted within a range not impairing the effects of the present invention, but is preferably 3.0 to 5.0 times, more preferably 4.0 to 4.3 times.

At this time, the roll (roll A) located immediately before the entrance of the tenter device and the clip of the tenter device first form the uniaxially oriented film in order to reduce the poor grip of the clip due to the curl of the width direction end of the uniaxially oriented film. At least one of the ends of the uniaxially oriented film in the width direction between the gripping point (grip point) and the position change amount in the thickness direction is controlled to 0.00 mm or more and 2.50 mm or less. Further, moderately maintain the tension in the vicinity of the gripping point from the viewpoint of reducing the breakage of the holding failure or film, the rotational speed of the rolls A V _A, the traveling speed of the clips when the V _B, V _{B /} V It is also preferable to control _A to be 1.006 or more and 1.010 or less.

  It is preferable to use a displacement sensor for measuring the amount of position change in the thickness direction of the end of the uniaxially oriented film in the width direction, and it is more preferable to use a laser-type mutation sensor in consideration of measurement accuracy. As means for controlling the amount of positional change in the thickness direction of the uniaxially oriented film width direction end to be 0.00 mm or more and 2.50 mm or less, for example, a pair of uniaxially oriented films is sandwiched between a roll A and a gripping point. And a method of adjusting the distance between the roll A and the gripping point.

  The biaxially oriented film obtained through the transverse stretching step may be subjected to a heat treatment for stabilizing the structure of the PET by crystallization and cooling, if necessary, thereafter. Means for performing these treatments is not particularly limited as long as the effects of the present invention are not impaired, but it is preferable to perform the treatment in a tenter device from the viewpoint of simplicity. The biaxially oriented film obtained in this way is cooled in the subsequent transport step, and once wound up as an intermediate roll by a wide winding machine, then cut by a slitter to a required width and length, and the final product and Become.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not construed as being limited thereto. The measuring method of each item in the examples and comparative examples is as follows.

(Measuring method)
(1) The amount of position change in the thickness direction of the end portion in the width direction of the uniaxially oriented film between the roll A and the gripping point (in the table, described as "the amount of position change")
From the position 500 mm away from one surface of the polyester film running between the roll A capable of speed adjustment and a pair of rotatable rolls located upstream of the entrance of the tenter device, the position in the width direction is the end. It was measured using a displacement sensor (Keyence's LHG500A) at a position between 0 and 10 mm, which is a midpoint between a pair of rolls and a roll A whose longitudinal position is freely rotatable. Regarding the measurement conditions, the sampling period was set to 100 μs, the accumulation period was set to 1, the number of accumulation points was set to 65536, and the difference (R) between the maximum value and the minimum value of the measured displacement was determined as the uniaxial orientation between the roll A and the gripping point. The amount of positional change (mm) in the thickness direction of the end in the film width direction was defined.

(2) Film thickness The biaxially oriented film is sampled from the roll of the finally obtained biaxially oriented film, and the thickness is measured by the micrometer method according to JIS-C-2330 (2001) 7.4.1.1. The obtained value was defined as the film thickness.

(3) Film-forming stability Film-forming stability was evaluated according to the following criteria by performing film-forming for 24 hours three times. In addition, the cause of the film breakage was specified from a film image taken by a video camera installed at the exit of the tenter device. Specifically, when a torn film comes out at the exit of the tenter device, if the clip did not come off, it was specified that the film was broken due to film breakage, and if the clip had come off, it was specified as film breakage due to poor gripping of the clip. did.
：: The film breakage due to the poor gripping of the clip and the film breakage due to the breakage of the film were both twice or less.
C: The film was torn twice or less due to the poor gripping of the clip, but the film was torn twice or more due to the broken film.
×: Neither ○ nor Δ.

(Example 1)
After drying PET under reduced pressure at 160 ° C. for 8 hours, the PET was supplied to a known extruder for melt lamination, melt-extruded at 275 ° C., and filtered with a high-precision filter having a collection efficiency of 5 μm or more and 95% of 95%. Subsequently, the obtained molten resin composition is extruded into a sheet shape from a slit die kept at 285 ° C., and cooled and solidified on a casting roll having a surface temperature of 25 ° C. by using an electrostatic application casting method to obtain a non-oriented film. Was. This non-oriented sheet was longitudinally stretched 4.2 times at a temperature of 110 ° C. using a stretching roll having a surface roughness Ra of 0.2 μm. Thereafter, V _B / V _A was set to 1.010 and led to a tenter device. After stretching 4.5 times in the width direction under hot air of 115 ° C., heat treatment and relaxation treatment were performed in this order at 215 ° C. under constant tension, and the thickness was increased. A biaxially oriented PET film having a thickness of 25 μm was obtained. Table 1 shows the evaluation results of each item.

(Examples 2 to 7, Comparative Examples 1 and 2)
The speed ratio V _{B /} V _A of the rotational speed and the clip traveling speed of the rolls A to obtain a biaxially oriented polyester film in the same manner except for changing in Example 1 as described in Table 1. Table 1 shows the evaluation results of each item.

  According to the present invention, there is provided a method for producing a biaxially oriented film capable of predicting in advance occurrence of gripping failure of a clip in a tenter device, and reducing such gripping failure, accompanying stretching unevenness and film cutting over a long period of time. can do. The biaxially oriented film obtained by the method for producing a biaxially oriented film of the present invention has high quality with little stretching unevenness and cutting, and is, for example, a magnetic recording medium, a heat-sensitive transfer material, an electric insulating material, a release material, a packaging material. It can be suitably used for such purposes.

DESCRIPTION OF SYMBOLS 1 Clip of tenter apparatus 2 Rail 3 Clip stand 4 Base 5 Standing part 6 Clip lever 7 Support shaft 8 Liner 9 Uniaxially oriented film 10 Clip closer 11 Clip opener 12 Wear ring 13 Roll A
14 Measurement point 15 Rotatable pair of rolls 16 Gripping point

Claims (5)

A longitudinal stretching step of stretching the sheet in the longitudinal direction, and a method for producing a biaxially oriented film having a transverse stretching step of stretching the uniaxially oriented film obtained in the longitudinal stretching step in the width direction by a tenter device in this order,
Between the roll (roll A) located immediately before the entrance of the tenter device and the point where the clip of the tenter device first grips the uniaxially oriented film (grip point), the thickness direction of the width direction end of at least one uniaxially oriented film A method for producing a biaxially oriented film, characterized by controlling the amount of change in position to 0.002 mm or more and 2.50 mm or less.   The method for producing a biaxially oriented film according to claim 1, wherein the amount of change in the position of the width direction end of the uniaxially oriented film in the thickness direction is measured by a displacement sensor.   The method for producing a biaxially oriented film according to claim 2, wherein the displacement sensor is a laser displacement sensor.   When a point for measuring the position change amount in the thickness direction of the uniaxially oriented film width direction end portion is a measurement point, between the measurement point and the gripping point, comprising a pair of rotatable rolls. The method for producing a biaxially oriented film according to claim 1. The rotational speed _{V A} of the roll A, the traveling speed of the clip when the _{V B,} and controls the V B / _{V A} to 1.006 or 1.010 or less, claim 1 5. The method for producing a film according to any one of 4.

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