JP2021049741A - Manufacturing method for biaxially oriented films - Google Patents

Abstract

To address the problem of providing a method for manufacturing biaxially oriented film that can predict in advance the occurrence of clip gripping failure in the tenter equipment and reduce such gripping failure and the resulting unevenness in stretching and film cutting over a long period of time.SOLUTION: The method for manufacturing biaxially oriented film comprises, in this order, a longitudinal stretching process in which the sheet is stretched in the longitudinal direction, a transverse stretching process in which the uniaxially oriented film obtained in the longitudinal stretching process is stretched in the width direction by the first tenter device, and a heat fixing process in which the biaxially oriented film obtained in the transverse stretching process is heat treated by the second tenter device. Between the roll located immediately before the entrance of the second tenter unit (Roll A) and the point where the clip of the second tenter unit first grasps the biaxially oriented film obtained in the transverse stretching process (grasping point), the amount of position change in the thickness direction of at least one widthwise edge of the biaxially oriented film obtained in the transverse stretching process is more than 0.00 mm to less than 2.50 mm.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for producing a biaxially oriented film.

As a method for producing a biaxially oriented film, a sequential biaxial stretching method is known in which a molten polymer is discharged, formed into a sheet with a die or the like, then longitudinally stretched, and then laterally stretched. For this lateral stretching, a tenter device that stretches the sheet in the width direction by increasing the interval between the clips while running the clips that grip both ends of the uniaxially oriented film obtained by the longitudinal stretching in the transport direction. Is used. The biaxially oriented film obtained through longitudinal stretching and transverse stretching has its molecules and crystals oriented in two directions, so that the mechanical strength is improved, the optical properties and gas permeability are improved, and the like before stretching. It has features that are not found in the sheet.

As a clip in the tenter device, for example, the clip having the configuration shown in FIG. 1 is well known. FIG. 1 is a schematic view of an example of a clip of a tenter device when observed from a traveling direction. As shown in FIG. 1, the clip (hereinafter, may be simply referred to as a clip) 1 of the tenter device is mounted on a clip base 3 slidably arranged with respect to the rail 2. The clip 1 has a base 4 and an upright portion 5 that stands up from the base 4 in an arch shape, 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 indicated by the dotted line by the elastic force of a spring (not shown) located between the upper portion (the portion above the support shaft 7) and the upright portion 5, and the lower portion (support shaft) thereof. The widthwise end of the uniaxially oriented film 9 can be gripped between the tip of (the portion below 7) and the liner 8 installed on the base 4.

In the longitudinal stretching step, a contraction force acts in the width direction of the sheet by stretching the non-oriented sheet in the longitudinal direction. Then, in the uniaxially oriented film obtained by longitudinal stretching, the surrounding constraints act on each other at the central portion in the width direction, while the film contracts freely at the end portion in the width direction. Therefore, curl occurs at the widthwise end portion of the uniaxially oriented film, and this tendency becomes remarkable particularly when the uniaxially oriented film is thin or when the tension in the widthwise direction applied along the guide roll decreases.

Usually, it is difficult to arrange the guide roll in the vicinity of 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 becomes small, and the widthwise end portion of the uniaxially oriented film may be curled. When the clip tries to grip the uniaxially oriented film in such a curled state, the lower portion of the clip lever 6 comes into contact with the widthwise end portion of the uniaxially oriented film 9. Therefore, gripping defects such as the gripping point of the clip shifting outward (FIG. 2-A) and the clip not being able to grip the uniaxially oriented film (FIG. 2-B) may occur. Further, when the impact caused by the closing operation of the clip is transmitted to the curl portion of the uniaxially oriented film, the curl portion vibrates, and the gripping defect may be further increased.

Further, in the production of the biaxially oriented film, it is also possible to re-stretch or heat-fix the film once laterally stretched by the tenter device by another tenter device. Then, in such an embodiment, the clip gripping failure due to the curl as described above may occur in this other tenter device as well.

Normally, 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 a poor grip occurs, the uniformity of stretching may be impaired, and problems such as the film being cut during stretching may occur. More specifically, when the gripping point of the clip shifts outward as shown in FIG. 2-A, the draw ratio in the width direction slightly fluctuates only in that portion, and the quality of the obtained biaxially oriented film becomes uneven. In some cases, if the clip is not gripped as shown in FIG. 2-B, the film may be cut from that portion.

As a method of overcoming such a problem, in order to increase the tension related to the uniaxially oriented film between the longitudinal stretching step and the transversely stretching step, a straightening roller is introduced before the transversely stretching step, and the width of the uniaxially oriented film is increased. Known methods include a method of flattening a directional end (Patent Document 1), a method of installing a slider on a clip of a tenter device, and pressing the conveyed film end (Patent Document 2).

Japanese Unexamined Patent Publication No. 2010-82854 Japanese Unexamined Patent Publication No. 2005-104081

However, if the traveling speed of the uniaxially oriented film, the composition and thickness of the film are different, the tension of the uniaxially oriented film between the longitudinal stretching step and the transverse stretching step also fluctuates. Further, when the heat fixing step by another tenter device is provided downstream of the transverse stretching step, the same tension fluctuation occurs in the biaxially oriented film between the two tenter devices. Therefore, the method described in Patent Document 1 has complicated adjustment of conditions for use in the production of a wide variety of films, and there is room for improvement in the effect of reducing gripping defects by the clip. Further, in the method of Patent Document 2, it is possible to reduce the gripping defect by installing the slider, but there is a problem in that the gripping defect occurs again when the equipment deteriorates in the process of continuing the production. Further, the method of Patent Document 2 cannot predict the occurrence of poor gripping in advance.

The present invention predicts in advance the occurrence of clip gripping failure in the tenter device (second tenter device) downstream of the transverse stretching step, and prolongs such gripping failure and the accompanying stretching unevenness and film cutting. An object of the present invention is to provide a method for producing a biaxially oriented film that can be reduced over a period of time.

In order to solve the above problems, the present invention has the following configurations.
(1) A longitudinal stretching step of stretching a sheet in the longitudinal direction, a transverse stretching step of stretching a uniaxially oriented film obtained in the longitudinal stretching step in the width direction by a first tenter device, and a biaxial orientation obtained in the transverse stretching step. A method for producing a biaxially oriented film having a heat-fixing step of heat-treating a film with a second tenter device in this order, in which a roll (roll A) located immediately before the inlet of the second tenter device and a clip of the second tenter device are clipped. In the thickness direction of at least one widthwise end of the biaxially oriented film obtained in the transversely stretched step between the point where the biaxially oriented film is first gripped (grasping point) obtained in the transversely stretched step. A method for producing a biaxially oriented film, which comprises controlling the amount of change in the position of the film to 0.00 mm or more and 2.50 mm or less.
(2) The biaxial orientation according to (1), wherein the amount of change in the position of the widthwise end portion of the biaxially oriented film obtained in the transverse stretching step in the thickness direction is measured by a displacement sensor. Film manufacturing method.
(3) The method for manufacturing a biaxially oriented film according to (2), wherein the displacement sensor is a laser type displacement sensor.
(4) When the measurement point is the point where the amount of change in the position of the widthwise end of the biaxially oriented film obtained in the transverse stretching step in the thickness direction is measured, the measurement point is between the measurement point and the gripping point. The method for producing a biaxially oriented film according to any one of (1) to (3), which comprises a pair of rotatable rolls.
(5) the roll A rotational speed _{V A} of the traveling speed of the clips of the second tenter apparatus is taken as _{V B,} to control the V B / _{V A} to 1.002 or 1.010 or less The method for producing a biaxially oriented film according to any one of (1) to (4), which is characterized.
(6) clips traveling speed _{V C} of the first tenter apparatus, the speed of the rolls (roll D) in contact with the first after the first tenter apparatus is taken as _{V D,} the V D / _{V C} 1.006 or 1. The method for producing a biaxially oriented film according to any one of (1) to (5), which comprises controlling to 010 or less.

INDUSTRIAL APPLICABILITY The present invention provides a method for producing a biaxially oriented film, which can predict the occurrence of clip gripping defects in a tenter device in advance and reduce such gripping defects and associated stretching unevenness and film cutting over a long period of time. can do.

It is the schematic when observing an example of a clip of a tenter device from a traveling direction. It is the schematic which shows the gripping failure of a clip in a tenter device. It is the schematic which shows the movement of a clip and a film in a tenter device. It is a side view which shows an example between two tenter devices.

The method for producing a biaxially oriented film of the present invention includes a longitudinal stretching step of stretching a sheet in the longitudinal direction, a transverse stretching step of stretching the uniaxially oriented film obtained in the longitudinal stretching step in the width direction by a first tenter device, and a lateral stretching step. A method for producing a biaxially oriented film having a heat-fixing step of heat-treating the biaxially oriented film obtained in the stretching step with a second tenter device in this order, and a roll (roll) located immediately before the inlet of the second tenter device. At least one of the biaxially oriented films obtained in the transversely stretched step between A) and the point at which the clip of the second tenter device first grips the biaxially oriented film obtained in the transversely stretched step (grasping point). It is characterized in that the amount of change in the position of the end portion in the width direction in the thickness direction is controlled to 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 a sheet in the longitudinal direction, a transverse stretching step of stretching a uniaxially oriented film obtained in the longitudinal stretching step in the width direction by a first tenter device, and a lateral stretching step. It is important to have a heat fixing step in which the biaxially oriented film obtained in the stretching step is heat-treated by the second tenter device in this order. Here, the sheet refers to a sheet obtained by cooling and solidifying a molten thermoplastic resin into a sheet. The longitudinal direction refers to the direction in which the sheet or film travels in the manufacturing process of the biaxially oriented film, and the width direction refers to the direction orthogonal to the longitudinal direction in the sheet surface or the film surface. The "biaxially oriented film obtained in the transverse stretching step" means a biaxially oriented film between the transverse stretching step and the heat fixing step. Further, "having a longitudinal stretching step, a transverse stretching step, and a heat fixing step in this order" means that before the longitudinal stretching step, between the longitudinal stretching step and the transverse stretching step, and between the transverse stretching step and the heat fixing step. And regardless of whether or not there is another step after the heat fixing step, it refers to all aspects in which the transverse stretching step is downstream of the longitudinal stretching step and the heat fixing step is downstream of the transverse stretching step. With such an embodiment, the widthwise end of the biaxially oriented film is curled, which causes poor gripping of the clip of the second tenter device used in the heat fixing step, so that the advantage of applying the invention is great. Become.

The lateral stretching by the first tenter device is to widen the interval in the width direction of the clips while running the uniaxially oriented film in the longitudinal direction by running the clips gripping both ends in the width direction of the uniaxially oriented film along the rail. Can be done by. The details will be described later with reference to the clip of the first tenter device.

In the longitudinal stretching step, a contraction force acts in the width direction of the sheet by stretching the non-oriented sheet in the longitudinal direction. Then, at the outlet of the first tenter device, the temperature of the biaxially oriented film obtained in the transverse stretching step may be equal to or higher than the glass transition temperature, and the contraction force in the width direction is promoted. As a result, in the biaxially oriented film obtained in the transverse stretching step, the surrounding restraints work with each other at the central portion in the width direction, whereas the film contracts freely at the end portion in the width direction, so that curl is formed at the end portion in the width direction. It is easy to occur. As a result, for example, when the clip of the aspect of FIG. 1 grips the widthwise end portion of the biaxially oriented film obtained in the transverse stretching step, the clip lever comes into contact with the widthwise end portion lifted by the curl. Poor grip of the clip occurs. On the other hand, in a non-oriented sheet or a uniaxially oriented film, the shrinkage force acting in the width direction is extremely small as compared with the biaxially oriented film. The frequency of poor gripping is also low.

The clip of the first 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 effect of the present invention is not impaired, and is known. Can be appropriately selected from. Specific examples thereof include the embodiment shown in FIG. This will be described in detail below. In this embodiment, the clip (hereinafter, may be simply referred to as a clip) 1 of the tenter device is mounted on a clip base 3 slidably arranged with respect to the rail 2. The clip 1 has a base 4 and an upright portion 5 that stands up from the base 4 in an arch shape, 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 indicated by the dotted line by the elastic force of a spring (not shown) located between the upper portion (the portion above the support shaft 7) and the upright portion 5, and the lower portion (support shaft) thereof. The widthwise end of the uniaxially oriented film 9 can be gripped between the tip of (the portion below 5) and the liner 8 installed on the base 4. The clip of such an aspect can also be suitably used as a clip in the second tenter device (however, in this case, the uniaxially oriented film 9 is referred to as "the biaxially oriented film 9 obtained in the transverse stretching step". It shall be read as ".).

Subsequently, stretching (transverse stretching) by the tenter device provided with the clip of the aspect of FIG. 1 will be specifically described with reference to the drawings. FIG. 3 is a schematic view showing the movement of the clip and the film in the tenter device. The uniaxially oriented film 9 whose widthwise ends are gripped by the clips 1 at the entrance of the tenter device is stretched in the width direction by the clips 1 traveling along the rail 2 so as to widen the width direction, and the tenter device of the tenter device. By the time it reaches the outlet, it becomes a biaxially oriented film. At this time, when the upper portion of the clip lever 6 in the clip 1 comes into contact with the clip closer 10 at the entrance, the clip lever 6 rotates as shown by the dotted line in FIG. 1 to grip the uniaxially oriented film 9. After that, the clip travels while gripping 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. To do. Upon contact with the clip opener 11 and the wear ring 12, the clip lever 6 rotates against the spring force of the spring as shown by the solid line in FIG. 1 to release the biaxially oriented film from gripping by the clip 1. Then, the clip 1 that has released the biaxially oriented film then travels along the rail 2 and returns to the entrance again. Further, the number of clips in the tenter device is not particularly limited as long as the effect of the present invention is not impaired, and can be appropriately set according to the scale of the device, the stretching ratio, etc. It is about 500 pieces.

In the method for producing a biaxially oriented film of the present invention, the roll (roll A) located immediately before the inlet of the second tenter device and the biaxially oriented film obtained by the lateral stretching step of the clip of the second tenter device are first used. The amount of change in the position of at least one of the biaxially oriented films obtained in the transverse stretching step in the thickness direction between the gripping point (grasping point) is controlled to 0.00 mm or more and 2.50 mm or less. It is important to. By adopting such an aspect, the vertical vibration of the biaxially oriented film obtained in the lateral stretching step traveling near the gripping point is suppressed, and when the clip of the second tenter device grips the end portion in the width direction of the film. In addition, the risk of the clip lever being hit by the film is reduced. Here, the roll (roll A) located immediately before the entrance of the second tenter device is a drive roll having a holding angle of 10 ° or more of the biaxially oriented film obtained in the transverse stretching step, and is the first roll. (Ii) The device that exists at the position closest to the entrance of the second tenter device on the upstream side of the entrance of the second tenter device. The hugging angle of the biaxially oriented film is located at the end of contact between the biaxially oriented film obtained in the transverse stretching step and the roll A when the roll A is observed from a direction parallel to the rotation axis. The angle formed when a straight line is drawn from the center of the axis of rotation at each of the two points.

From the above viewpoint, in the method for producing a biaxially oriented film of the present invention, between the roll A and the gripping point, in the thickness direction of at least one widthwise end of the biaxially oriented film obtained in the transverse stretching step. It is preferable to control the amount of change in the position of the above to 0.00 mm or more and 2.30 mm or less. On the other hand, when the distance between the roll A and the grip portion is secured to some extent in order to install the displacement sensor described later, the amount of change in the position of the biaxially oriented film width direction end portion in the thickness direction becomes large unless the tension is increased. .. Considering this point as well, the amount of change in the position of at least one of the biaxially oriented films obtained in the transverse stretching step in the thickness direction between the roll A and the gripping point in the thickness direction is 1.60 mm or more. It is more preferable to control it to .30 mm or less. Further, from the viewpoint of reducing such a risk on both sides in the width direction, in the method for producing a biaxially oriented film of the present invention, the biaxially oriented film obtained in the transverse stretching step between the roll A and the gripping point. It is preferable to control the amount of change in the position of both widthwise ends in the thickness direction to 0.00 mm or more and 2.50 mm or less or the above-mentioned preferable range. The method for measuring the amount of change in the position of the widthwise end of the biaxially oriented film obtained in the transverse stretching step in the thickness direction will be described later together with the displacement sensor that can be used for the measurement.

The amount of change in the position of at least one of the biaxially oriented films obtained in the transverse stretching step in the thickness direction between the roll A and the gripping point in the thickness direction is 0.00 mm or more and 2.50 mm or less, or the above-mentioned preferable amount. The means for controlling the range is not particularly limited as long as the effect of the present invention is not impaired. For example, a pair of rotatable films are sandwiched between the roll A and the gripping point so as to sandwich the biaxially oriented film obtained in the transverse stretching step. Examples include a method of installing a pair of rolls and a method of adjusting the distance between the roll A and the gripping point. More specifically, by installing such a pair of rotatable rolls and narrowing the distance between the roll A and the gripping point, the widthwise end portion of the biaxially oriented film obtained in the transverse stretching step. The amount of change in the position of the film in the thickness direction can be reduced.

In the method for producing a biaxially oriented film of the present invention, it is preferable to measure the amount of change in the position of the widthwise end portion of the biaxially oriented film obtained in the transverse stretching step in the thickness direction with a displacement sensor. With such an embodiment, it is possible to easily measure the amount of change in the position of the biaxially oriented film widthwise end portion in the thickness direction obtained in the transverse stretching step in the manufacturing process. Normally, the displacement sensor is installed between the roll A and the gripping point at at least one of the upper part and the lower part of the biaxially oriented film obtained in the transverse stretching step, so that the displacement sensor is within 10 mm from the outermost end in the width direction. Measure the amount of position change. 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 effect of the present invention is not impaired, and for example, an ultrasonic type, an eddy current type, a laser type and 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 type mutation sensor, it becomes easy to reduce the influence of other displacement sensors when a plurality of sensors are installed, and to reduce the disadvantage that detailed 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 the measurement itself is possible, and for example, LHG500A manufactured by KEYENCE Corporation can be preferably used.

When using the LHG500A laser mutation sensor manufactured by KEYENCE Co., Ltd. to measure the amount of change in the position of the biaxially oriented film width direction end in the thickness direction, the measurement conditions are a sampling period of 100 μs, an accumulation period of 1, and an accumulation point of 65536. Can be set to. 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 biaxially oriented film width direction end portion obtained in the transverse stretching step.

In the method for producing a biaxially oriented film of the present invention, a measurement point is set as a measurement point where the amount of change in the position of the widthwise end of the biaxially oriented film obtained in the transverse stretching step in the thickness direction is measured. It is preferable to provide a pair of rotatable rolls between the gripping point and the gripping point. In other words, as shown in FIG. 4, which is a side view showing an example between the two tenter devices, the roll A13, the measurement point 14, the pair of rotatable rolls 15, and the gripping point 16 are located in this order. preferable. By adopting such an embodiment, the vertical movement of the pair of rotatable rolls can be reduced by sandwiching the biaxially oriented film obtained in the transverse stretching step, so that the resulting roll can be obtained in the transverse stretching step at the measurement point. The value of the amount of change in the position of the widthwise end of the biaxially oriented film in the thickness direction can be reduced. Here, the provision of a pair of rotatable rolls means that the rolls, which have no power but can be passively rotated by an external force, sandwich the biaxially oriented film obtained in the transverse stretching step. In addition, it refers to the state of being located above and below it. In addition, a cover may be attached in front of the gripping point to prevent the lubricating oil of the clip from scattering to the surroundings. 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 1.002 or 1.010 or less It is preferable, and it is more preferable to control it to 1.006 or more and 1.010 or less. By _{setting V B} / _VA to 1.002 or more, it is possible to suppress the slackening of the biaxially oriented film obtained in the transverse stretching step in the section from the roll A to the gripping point. It is possible to reduce the curl of the widthwise end portion of the axially oriented film and the resulting poor gripping of the clip. On the other hand, by _{setting V B} / _VA to 1.010 or less, it is possible to reduce film tearing in the second tenter device caused by excessive tension.

Method for controlling the V _B / _{V A} to 1.010 or less or the preferred range of 1.002 is not particularly limited as long as it does not impair the effects of the present invention, for example, traveling speed _{V A} and clip roll A A method of adjusting the speed V _{B can be mentioned.} More specifically, and by increasing the _{V B,} such as by reducing the _{V A,} it can be increased _V B / V _A.

Method for producing a biaxially oriented film of the present invention, the clip running speed V _C of the first tenter _apparatus, the speed of the rolls (roll D) in contact with the first after the first tenter apparatus is taken as V _D, V _D / it is preferable to control the V _C to 1.006 or 1.010 or less. Here, the roll D is a drive roll having a holding angle of 10 ° or more of the biaxially oriented film obtained in the transverse stretching step, and is a downstream side of the first tenter device and an outlet of the first tenter device. The one that exists closest to. In other words, as shown in FIG. 4, it is located between the clip 17 of the first tenter device and the clip 19 of the second tenter device, and the size of the holding angle of the biaxially oriented film is 10 ° or more, and the first tenter device has a size of 10 ° or more. The roll closest to the clip 17 of the one tenter device is the roll D18. With V D _/ V _C of 1.006 or more, immediately after the first tenter apparatus, to suppress the widthwise contraction of the obtained biaxially oriented film in the transverse stretching step, the clip of the first tenter lateral Since the slack from the release of the biaxially oriented film obtained in the stretching step to the roll D can be suppressed, the curl of the widthwise end portion of the biaxially oriented film obtained in the lateral stretching step and the second resulting cause thereof. It is possible to reduce poor gripping of the clip in the tenter device. _Meanwhile, the V D / _{V C} by 1.010 or less, it is possible to reduce a film tear occurs in the tension becomes excessive.

Method for controlling the V _D / _{V C} 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 the running of the clip of the rotational speed _{V D} and the first tenter roll D and a method of adjusting the speed V _C. More specifically, and by increasing the _{V D,} such as by reducing the _{V C,} it is possible to increase the _V D / V _C.

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

First, PET pellets are supplied to the raw material input section of the extruder, and this is heated and melted. After that, the extrusion amount is made uniform with a gear pump or the like, and the PET melted by heating is extruded to remove foreign substances and gelled substances through a filter and the like. At this time, usually, when the film has a single-layer structure, one extruder can be used, and when the film has a laminated structure, a plurality of extruders can be used. When using a plurality of extruders, the thermoplastic resin that has passed through the filter is sent to the laminating apparatus. As the laminating device, a multi-manifold die, a feed block, a static mixer and the like can be used, and these may be arbitrarily combined.

The PET melt thus obtained is discharged as a sheet-like melt from a mouthpiece, extruded onto a cooling body such as a casting drum, and cooled and solidified to obtain an unoriented sheet. As a specific method for obtaining an unoriented sheet from a sheet-shaped melt, a wire-shaped, tape-shaped, needle-shaped or knife-shaped electrode is used to apply the sheet-shaped melt to a cooling body such as a casting drum by electrostatic force. A method of bringing them into close contact with each other and quenching and solidifying is preferable.

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

Further, after the longitudinal stretching step and before proceeding to the transverse stretching step described later, a step of applying a coating agent for forming a functional layer such as an easy-adhesion layer is provided on both sides or one side of the obtained uniaxially oriented film. 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, or the like can be used.

Then, the uniaxially oriented film obtained in the longitudinal stretching step is stretched in the width direction by the first tenter device, and the process proceeds to a transverse stretching step. In the transverse stretching step, the clips that grip both ends of the uniaxially oriented film in the width direction are run along the rail to run the uniaxially oriented film in the longitudinal direction, and the distance between the clips in the width direction is widened to achieve uniaxial orientation. The film is stretched laterally. The ratio of lateral stretching can be appropriately adjusted within a range that does not impair 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 rotation speed of the roll D is adjusted from the viewpoint of maintaining an appropriate tension immediately after the first tenter, reducing gripping defects of the clip due to curling of the widthwise end portion of the biaxially oriented film, and reducing film breakage. V _D, the traveling speed of the clips of the first tenter apparatus is taken as _{V C,} it is also preferable to control the V D / _{V C} to 1.006 or 1.010 or less.

Further, in order to stabilize the structure of PET by crystallization, the process proceeds to a heat fixing step of heat-treating the biaxially oriented film obtained in the transverse stretching step with a second tenter device. In this heat fixing step, the biaxially oriented film obtained in the transverse stretching step may be heat-treated, and then relaxed if necessary. At this time, in order to reduce the gripping failure of the clip due to the curl of the widthwise end portion of the biaxially oriented film obtained in the transverse stretching step, the roll (roll A) located immediately before the inlet of the second tenter device and the first roll (roll A). At least one widthwise end of the biaxially oriented film obtained in the transversely stretched step with the point where the clip of the bitenter device first grips the biaxially oriented film obtained in the transversely stretched step (grasping point). The amount of change in the position of the portion 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 1.002 or more and 1.010 or less.

It is preferable to use a displacement sensor for measuring the amount of change in the position of the widthwise end of the biaxially oriented film obtained in the transverse stretching step in the thickness direction. Considering the measurement accuracy, a laser mutation sensor should be used. Is more preferable. As a means for controlling the amount of change in the position of the biaxially oriented film widthwise end obtained in the transverse stretching step in the thickness direction to 0.00 mm or more and 2.50 mm or less, for example, between the roll A and the gripping point, Examples thereof include a method of installing a pair of rotatable rolls so as to sandwich the film, a method of adjusting the distance between the roll A and the gripping point, and the like.

The biaxially oriented film thus obtained is cooled in the subsequent transfer process, once wound as an intermediate roll by a wide winder, and then cut into a required width and length by a slitter to form a final product. Become.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to this. The measurement methods and the like of each item in the examples and comparative examples are as follows.

(Measuring method)
(1) Amount of position change in the thickness direction of the widthwise end of the biaxially oriented film obtained in the transverse stretching step (indicated as "position change amount" in the table)
Distance from one side of the biaxially oriented polyester film obtained in the transverse stretching step while traveling between the speed-adjustable roll A located upstream of the inlet of the second tenter device and the pair of rotatable rolls. A displacement sensor (manufactured by Keyence) with the position in the width direction being 0 to 10 mm from the end and the position in the longitudinal direction being the midpoint between the pair of rolls that can rotate and the roll A from a position 500 mm away. It was measured using LHG500A). 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 amount was obtained by the transverse stretching step. The amount of change in position (mm) of the end portion in the width direction in the thickness direction.

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

(3) Film-forming stability The film-forming stability for 24 hours was performed three times, and the film-forming stability was evaluated according to the following criteria, and ○ and Δ were evaluated as acceptable. The cause of the film breakage was identified from the images of the film taken by the video cameras installed at the outlets of the first and second tenter devices. Specifically, when a torn film comes out at the outlet of each tenter device, if the clip is not detached, the film is broken due to film breakage, and if the clip is detached, the film is broken due to poor gripping of the clip. Identified.
◯: Film tearing due to poor clip grip and film tearing due to film breakage both occurred less than twice.
Δ: Film tearing due to poor clip grip occurred twice or less, but film tearing caused by film breakage occurred twice or more.
×: Neither ○ nor △ was applicable.

(Example 1)
The PET was dried under reduced pressure at 160 ° C. for 8 hours, then supplied to a known fused deposition modeling extruder, melt-extruded at 275 ° C., and filtered through a high-precision filter having a collection efficiency of 5 μm or more and 95%. Subsequently, the obtained molten resin composition was extruded into a sheet from a slit die kept at 285 ° C., and cooled and solidified on a casting roll having a surface temperature of 25 ° C. using an electrostatically applied casting method to obtain an unoriented film. It was. This non-oriented sheet was longitudinally stretched 4.2 times under the condition of a temperature of 110 ° C. using a stretching roll having a surface roughness Ra of 0.2 μm. Thereafter, leads after 4.5 times stretched in the width direction in hot air under 115 ° C. in the first _tenter, the V D / _{V C 1.010,} the V B / _{V A} Second tenter apparatus as 1.010, Heat treatment and relaxation treatment were performed in this order at 215 ° C. under constant tension to obtain a biaxially oriented PET film having a thickness of 25 μm. The evaluation results of each item are shown in Table 1.

(Examples 2 to 9, Comparative Examples 1 to 3)
Wherein the rotational speed and the second tenter clips travel speed of the speed ratio V _{B /} V A of the roll _A, the velocity ratio V _{D /} V _C of the rotational speed of the rolls D and clip traveling speed of the first tenter apparatus Table 1 A biaxially oriented PET film was obtained in the same manner as in Example 1 except that the above-mentioned changes were made. The evaluation results of each item are shown in Table 1.

INDUSTRIAL APPLICABILITY According to the present invention, a method for producing a biaxially oriented film that can predict the occurrence of clip gripping failure in the second tenter device in advance and reduce such gripping failure and the accompanying stretching unevenness and film cutting over a long period of time. Can be provided. The biaxially oriented film obtained by the method for producing a biaxially oriented film of the present invention is of high quality with less uneven stretching and cutting, and is, for example, a magnetic recording medium, a heat-sensitive transfer material, an electrically insulating material, a mold release material, and a packaging material. It can be suitably used for such applications.

1 Clip of tenter device 2 Rail 3 Clip base 4 Base 5 Standing part 6 Clip lever 7 Support shaft 8 Liner 9 Uniaxial alignment film / Biaxial alignment film obtained in the transverse stretching process 10 Clip closer 11 Clip opener 12 Wearing 13 Roll A
14 Measurement point 15 A pair of rotatable rolls 16 Grip point 17 Clip of the first tenter device 18 Roll D
19 Clip of the second tenter device

Claims (6)

Longitudinal stretching step of stretching the sheet in the longitudinal direction,
A transverse stretching step of stretching the uniaxially oriented film obtained in the longitudinal stretching step in the width direction by a first tenter device,
A method for producing a biaxially oriented film, which comprises a heat-fixing step of heat-treating the biaxially oriented film obtained in the transverse stretching step with a second tenter device in this order.
Lateral between the roll (roll A) located immediately before the entrance of the second tenter device and the point (grip point) where the clip of the second tenter device first grips the biaxially oriented film obtained in the transverse stretching step. Production of a biaxially oriented film, characterized in that the amount of change in the position of at least one of the widthwise ends of the biaxially oriented film obtained in the stretching step in the thickness direction is controlled to 0.00 mm or more and 2.50 mm or less. Method. The production of the biaxially oriented film according to claim 1, wherein the amount of change in the position of the widthwise end portion of the biaxially oriented film obtained in the transverse stretching step in the thickness direction is measured by a displacement sensor. Method. The method for manufacturing a biaxially oriented film according to claim 2, wherein the displacement sensor is a laser type displacement sensor. When the measurement point is the point where the amount of change in the position of the widthwise end of the biaxially oriented film obtained in the transverse stretching step in the thickness direction is measured, the biaxially oriented film is rotatable between the measurement point and the gripping point. The method for producing a biaxially oriented film according to any one of claims 1 to 3, further comprising a pair of rolls. Rotational speed _{V A} of the roll A, the traveling speed of the clip of the second tenter apparatus is taken as _{V B,} and controls the V B / _{V A} to 1.002 or 1.010 or less , The method for producing a biaxially oriented film according to any one of claims 1 to 4. Clip traveling speed _{V C} of the first tenter apparatus, the speed of the rolls (roll D) in contact with the first after the first tenter apparatus is taken as _{V D,} the V D / _{V C} 1.006 or 1.010 to less The method for producing a biaxially oriented film according to any one of claims 1 to 5, wherein the biaxially oriented film is controlled.

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