JP2012071476A - Stretching equipment and method of polymer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of thickness unevenness in a width direction of a polymer film.SOLUTION: Stretching equipment grips a side edge in a width direction of the film 19 with a clip 35 and stretches and conveys the film 19. An upper blast head 40a is arranged at an upper surface side of the film 19 in a tenter 12. A lower blast head 40b is arranged at a lower surface side of the film 19 in the tenter 12. Heating wind is sprayed on the upper and lower surfaces of the film 19 from the upper blast head 40a and the lower blast head 40b. The blast volume of the lower blast head 40b is made larger than the blast volume of the upper blast head 40a and the wind pressure difference is given. Deflection in a width direction of the film 19 is suppressed according to the wind pressure difference. The film 19 is stretched in the condition of being held horizontally.

Description

  The present invention relates to an apparatus and method for stretching a polymer film.

  Polymer films such as cellulose ester films are widely used as polarizing films for liquid crystal displays. And in order to give a desired optical characteristic to the polymer film (henceforth a film) for such an optical use, a film may be extended, heating.

  In order to stretch a long film while heating, a tenter is used. The tenter is configured by arranging a stretching section and a heating section in a stretching chamber. The stretching section stretches in the width direction of the film while transporting the film, and a pair of rails whose distance is widened in the width direction of the film at a desired widening rate, and an endless chain that is travel-guided by this rail And a clip attached to the endless chain at a predetermined pitch. A heating part flows the heated gas to the vicinity of a film, and heats a film in order to extend | stretch in the width direction of a film. In the stretching chamber, the clip grips both side edges of the film, and the endless chain moves on the rail in the gripped state, whereby the film is stretched at a desired widening rate.

  In this way, stretching while heating the film may be performed in the film production process in solution casting, or may be performed on a film obtained by solution casting or melt casting. is there.

  By the way, a film for optical use is required to have a uniform retardation value and film thickness over the width direction. In view of this, there has been proposed a blower that uniformizes the conditions for stretching the film in the tenter, that is, the temperature of the gas for heating, the pressure for blowing the gas, and the like over the width direction of the film (for example, patents). Reference 1).

JP 2007-237560 A

  However, even if the temperature and pressure of the heating air are made uniform across the width direction of the film as in Patent Document 1, uneven thickness may occur at the side edge of the film, and improvement has been desired.

  Therefore, as a result of intensive studies on the behavior of the film in the tenter, the inventor of the present application has found that bending has occurred in the width direction due to the weight of the film, and this bending has caused uneven thickness. . When the bent film is stretched in the width direction to widen the width (hereinafter referred to as widening), the film then contracts in the width direction. It was found that the thickness unevenness occurs at the time of this contraction.

  Even though both side edges are held by the clip, the film is softened by heating by the heating unit. Moreover, when the film is wide due to a request for widening, it is impossible to maintain a flat state due to the influence of its own weight. This is considered to be the cause of thickness unevenness. In particular, compared to the central portion in the width direction of the film, both end portions are thinner due to their own weight, and thickness unevenness is likely to occur.

  As described above, when the film having the end portion thinner in the width direction than the center portion is heated and stretched in the width direction as in the past, the film is thinner near both ends than the center portion. turn into. And the thickness nonuniformity becomes more remarkable by shrinkage after extending in the width direction.

  The present invention is intended to solve the above-mentioned problems, and a stretching apparatus and method for a polymer film that suppresses bending due to the weight of the film and eliminates thickness unevenness in the width direction that occurs in the film during shrinkage. The purpose is to provide.

  The polymer film stretching apparatus of the present invention is gripped by the tenter main body having a plurality of clips that move in the running direction of the film while gripping both side edges of the film and stretch the film in the width direction. The upper blower that blows heated air against the upper surface of the film, the lower blower that blows heated air against the lower surface of the film held by the clip, and the heating blown from the upper blower and the lower blower And a horizontal holding control unit that holds the film horizontally due to a wind pressure difference.

  It is preferable that the horizontal holding control unit controls at least the air flow rate of the lower air blowing unit. The horizontal holding control unit includes a deflection sensor that measures a deflection amount of the film, and the horizontal holding control unit is configured to reduce the lower air blowing unit as the deflection amount increases based on a signal representing the deflection amount from the deflection sensor. It is preferable to increase the air blowing amount.

  The horizontal holding control unit measures a thickness distribution of the film in the width direction, and obtains a thickness difference between both end portions of the film with respect to a center portion of the film in the width direction based on the measured thickness distribution. When the thickness difference exceeds a certain value, it is preferable to increase the amount of air blown from the lower air blowing unit.

  The polymer film stretching method of the present invention includes a stretching step of stretching the film in the width direction while gripping both side edges of the film with a plurality of clips and moving in the running direction of the film, and the gripping with the clips. A heating step of blowing the upper surface heating air to the upper surface of the film and blowing the lower surface heating air to the lower surface of the film held by the clip to heat the film; and the upper surface heating air and the lower surface heating air And a horizontal holding step for holding the film horizontally due to a difference in wind pressure.

  According to the present invention, since the film is held horizontally by the wind pressure difference between the upper air blowing part and the lower air blowing part, the thickness unevenness in the width direction generated in the film at the time of shrinkage is suppressed due to the deflection of the film due to its own weight. can do.

It is a schematic side view of an off-line extending | stretching installation. It shows the inside of the tenter where the film is stretched, and is a cross-sectional view of the upper blowing head. It is a schematic front view which shows the state which has hold | maintained the film horizontally in the width direction within a tenter by the difference in the ventilation volume by an upper ventilation head and a lower ventilation head. Schematic showing a second embodiment in which a deflection sensor is provided in the tenter, the deflection of the film is measured online, and the blower is controlled to hold the film horizontally in the width direction based on the measured deflection. It is a front view. FIG. 5 is a schematic plan view showing a main part of a third embodiment in which a movable wind shielding plate is provided so as to be swingable, covers a part of a blowout port of a blower nozzle, and can control the air volume distribution in the width direction of the film. .

  As shown in FIG. 1, the off-line stretching equipment 10 includes a film delivery chamber 11, a tenter 12, an ear clip device 13, a stress relaxation chamber 14, a cooling chamber 15, and a film winding chamber 16 in order.

  The film delivery chamber 11 is provided with a film delivery machine 17 having an attachment shaft 17a. A film roll 18 is set on the mounting shaft 17a. The film 19 is continuously drawn from the film roll 18 by the film delivery machine 17 and sent to the tenter 12.

  In the tenter 12, the film 19 is gripped by a plurality of clips 35 (see FIG. 2) at both side edges. As these clips 35 run inside the tenter 12, the film 19 is transported. As the distance between the clip 35 that holds one side edge and the clip 35 that holds the other side edge increases toward the downstream, the film 19 is stretched with tension applied in the width direction. Moreover, the film 19 is heated while the film 19 is conveyed. This heating raises the temperature of the film 19. The draw ratio is appropriately set according to desired optical characteristics and the like.

  The film 19 stretched by the tenter 12 is sent to the ear clip device 13. The side edges of the film 19, which is the portion gripped by the clip 35, are cut off by the ear clip device 13. The ear dust, which is the slit-like side edge portion, is cut into small pieces by the cut blower 21. The cut small pieces are sent to the crusher 22 and further cut into thin pieces to form chips. This chip is reused for dope preparation.

  The film 19 from which both side edges are cut off by the edge-cutting device 13 is sent to the stress relaxation chamber 14. A number of rollers 23 are provided in the stress relaxation chamber 14 so as to be aligned in the transport direction of the film 19. The film 19 is guided in the longitudinal direction inside the stress relaxation chamber 14 by a roller 23. When passing through the stress relaxation chamber 14 by the roller 23, the film 19 is relieved of stress strain caused by stretching. The film 19 after the stress relaxation is sent to the cooling chamber 15. In addition, the temperature inside the stress relaxation chamber 14 is set to a constant value in a range of 20 ° C. to 250 ° C., for example.

  The film 19 is cooled to, for example, 30 ° C. or less in the cooling chamber 15 and then sent to the film winding chamber 16. The film winding chamber 16 is provided with a film winding machine 24 having a winding shaft 24a. A winding core (not shown) is attached to the winding shaft 24a. The winding shaft 24a is rotated by the film winder 24, and the film 19 is wound around the winding core to form a film roll.

  As shown in FIG. 2, the tenter 12 includes a stretching unit 31, a heating unit 32, and a stretching chamber 33. In the stretching chamber 33, the film 19 is stretched. The stretching unit 31 is provided with a tenter chain 34 that runs on a pair of rails. A large number of clips 35 are attached to the tenter chain 34 at a constant pitch. The tenter chain 34 circulates on the rail when the chain sprocket 36 is rotated.

  The clip 35 grips the side edge of the film 19 by being closed at the film gripping position. Further, the clip 35 is opened at the film opening position to release the grip of the side edge portion of the film 19. The pair of rails is set such that the distance between the rails gradually increases from the entrance to the exit of the extension chamber 33. Therefore, when the tenter chain 34 runs on the pair of rails while the both side edges of the film 19 are gripped by the clips 35, the clips 35 facing each other on the pair of rails are gradually separated. The film 19 is stretched in the width direction. In addition, a pair of rail space | interval can be changed corresponding to the width change of the film 19, and can be hot-stretched with respect to the film from which a width | variety differs.

  The heating unit 32 includes an upper blower 37, a lower blower 38, and a horizontal holding controller (hereinafter referred to as a controller) 39 (see FIG. 3). The upper blower unit 37 includes a large number of upper blower heads 40a, a blower duct 41a, a circulation duct 42a, a heated air blower unit 43a, and an exhaust duct 44a. The upper blowing head 40a is provided so as to face the upper surface of the film 19, and is provided side by side in the conveyance direction (arrow line A) of the film 19.

  The upper blowing head 40a includes, for example, five nozzles 45a. Each nozzle 45a is formed long in the width direction of the film 19, and a wind regulating plate (not shown) for adjusting the amount of heated air blown is arranged inside the nozzle 45a. This air conditioning plate is provided with round holes that are spaced apart in the width direction of the film 19. By changing the aperture ratio of the air conditioning plate, the amount of air blown out is adjusted, and a substantially uniform air blowing amount in the width direction of the film 19 is obtained. The shape and quantity of the air conditioning plate holes and the shape and quantity of the nozzles are not limited to those shown in the drawings, and may be changed as appropriate.

  The blower duct 41a is connected to the side surface of the upper blower head 40a, and sends heated air to each upper blower head 40a. The circulation duct 42a is connected to the other side surface of the blower head 40a facing the blower duct 41a, and sends a part of the air sent from the blower duct 41a to the heated wind blower 43a.

  The exhaust duct 44a is connected to the inside of the stretching chamber 33, exhausts the air accumulated in the stretching chamber 33, and sends it to the heated air blowing section 43a. The heated air blowing unit 43a includes a blower fan 46a for circulating air and a temperature adjusting unit 47a that heats the air to adjust the temperature, and connects the circulation duct 42a to one side to collect the air. The blower duct 41a is connected to the other side surface facing each other, and heated air is sent out.

  The lower air blower 38 (see FIG. 3) is also configured in the same manner as the upper air blower 37. The lower air blower 38, the air blower duct, the circulation duct, the nozzle, the exhaust duct, the heated air blower, and other components 40b to 45b are arranged. I have. The upper air blower 37 and the lower air blower 38 are different in that the upper air blower 37 blows the heated air toward the upper surface of the film 19 and the lower air blower 38 blows the heated air toward the lower surface of the film 19. Only. Therefore, the same reference numerals 40 to 47 as the respective constituent members of the upper blower portion 37 are attached to the respective constituent members of the lower blower portion 38, b is attached instead of a as a subscript, and the same drawing as FIG. Description is omitted.

  Next, characteristic portions of the present invention will be described. As shown in FIG. 3, in the tenter 12, both side edges of the film 19 are held by clips 35. Blower ducts 41a and 41b and circulation ducts 42a and 42b are connected to the upper blower head 40a and the lower blower head 40b, respectively. The heated air is sent from the heated air blowing sections 43a and 43b (see FIG. 2) to the blower ducts 41a and 41b. Then, heated air is blown toward the upper surface and the lower surface of the film 19 through the nozzles 44 a and 44 b from the upper air blowing head 40 a on the upper surface side of the film 19 and the lower air blowing head 40 b on the lower surface side of the film 19.

  The controller 39 makes a difference in the wind pressure with respect to the upper and lower surfaces of the film 19 by controlling the amount of air blown from the upper and lower blow heads 40a and 40b. Due to the wind pressure difference, the film 19 is kept horizontal without being bent due to its own weight. The setting of the wind pressure difference is performed by making the blowing amount of the lower blowing head 40b larger than the blowing amount of the upper blowing head 40a. In addition to or in addition to increasing the air flow rate of the lower air blowing head 40b, the air flow rate of the upper air blowing head 40a may be reduced.

  In this way, the film 19 can be stretched in the width direction while keeping the film 19 horizontal. Thereby, the film 19 can be stretched with a uniform force along the width direction. As a result, thickness unevenness does not occur during shrinkage. Furthermore, the degree of molecular orientation adjusted by stretching can be prevented from greatly differing between the both ends and the center of the film 19 in the width direction, and the optical characteristics can also be made uniform in the width direction of the film 19. it can.

  It should be noted that the amount of air blown from the heated air blowing sections 43a and 43b and the wind pressure sent from the upper blowing head 40a (hereinafter referred to as the first wind pressure) P1 and the lower part for suppressing the influence of the own weight and keeping the film 19 horizontal. Each set value such as the wind pressure (hereinafter referred to as the second wind pressure) P2 of the wind sent from the blower head 40b is obtained in advance for each type of film 19 in which the width, thickness, etc. of the film 19 are changed. Each set value is stored in a memory 39a in the controller 39 in a look-up table format. Therefore, it is possible to easily set different films having different widths and thicknesses by reading new set values from the data in the look-up table format stored in the memory 39a. Instead of the first wind pressure and the second wind pressure set values, the first wind pressure set value and the wind pressure difference, or the second wind pressure set value and the wind pressure difference may be stored. The wind pressure setting value may be obtained.

  In the so-called off-line stretching in which the once produced and dried film is guided again in the width direction as in this embodiment, the first wind pressure P1 is changed from the first wind pressure P1, the second wind pressure P2, and the second wind pressure P2. An example of the wind pressure difference (= P2−P1) obtained by subtracting is as follows. When the film width is 1800 mm and the film thickness is 80 μm, the set value of the first wind pressure P1 is, for example, 40 Pa or more and 240 Pa or less, the set value of the second wind pressure is 90 Pa or more and 390 Pa or less, and the wind pressure difference P2− P1 is 50 Pa or more and 150 Pa or less. In addition, by setting the wind pressure difference P2-P1 to 150 Pa or less, it is possible to more reliably prevent the film 19 from being bent toward the upper surface side as compared with a case where the pressure difference is larger than 150 Pa. On the other hand, by setting the wind pressure difference P2-P1 to 50 Pa or more, it is possible to more reliably prevent the film 19 from being bent to the lower surface side as compared with the case where it is smaller than 50 Pa.

  If the temperature of the glass transition point of the polymer that is the raw material of the film 19 is Tg (° C.), the temperature of the heated air blown to the film 19 is Tg ° C. or more (Tg + 100) ° C. or less, and the film 19 becomes soft. It becomes easy to heat stretch. For this reason, the present invention is particularly effective when the heated air in such a temperature range is blown onto the film 19. By setting the temperature of the heating air to (Tg + 100) ° C. or lower, the film 19 itself is more reliably prevented from being broken by stretching compared to the case where it is higher than (Tg + 100) ° C. By setting the temperature of the heating air to Tg or higher, the effect of adjusting the degree of orientation of the polymer molecules constituting the film 19 by stretching can be more reliably obtained than when the temperature is lower than Tg ° C.

  In addition, when cellulose triacetate (TAC) is used as a polymer as a raw material for a film for optical use, the film 19 becomes soft and stretched when the temperature of the heating air is in the range of 130 ° C. or higher and 230 ° C. or lower. It becomes easy. When polyethylene terephthalate (PET) is used, if the temperature of the heating air is in the range of 70 ° C. or higher and 170 ° C. or lower, the film 19 becomes soft and easily stretched. In addition, it is not restricted to these raw materials, Even if it is another polymer film, there exists an effect similarly.

  In addition, the present invention is particularly effective when the speed at which the film 19 is stretched in the width direction is 1% / second or more and 20% / second or less. By making the speed at which the film 19 is stretched 1% / second or more, the thickness in the width direction by stretching can be made more uniform than when the film 19 is made smaller than 1% / second, and the thickness unevenness at the time of shrinkage is reduced. Is more reliably prevented. By making the speed at which the film 19 is stretched 20% / second or less, the tension of the film is kept small and the deflection is increased compared with the case where the film 19 is made larger than 20% / second. Become. The value of “%” in the stretching speed is {(WE−WS) / WS} × 100, where WS is the width of the film at the start of stretching and WE is the width of the film at the end of stretching. It is the percentage calculated | required by.

  In the first embodiment, the deflection of the film 19 due to its own weight is eliminated by controlling the rotation of the blower fan motor of the heated air blowing unit 43a so that the wind pressure setting value obtained in advance through experiments or the like is obtained. However, instead of this, as shown in FIG. 4, the deflection of the film 19 in the width direction is performed online, that is, while the film 19 is being transported while being stretched by the tenter 12. When the measured amount of bending is within a predetermined range, the air blowing amount of the heated air blowing portions 43a and 43b may be controlled so that the film 19 is held horizontally.

  The deflection sensor 51 may be attached anywhere as long as it can be attached, and is preferably in the tenter 12 or near the exit of the tenter 12. The deflection sensor 51 may be any sensor that can detect the amount of deflection of the film 19 in a non-contact manner, and various known non-contact displacement sensors and distance sensors are used.

  The air volume and the wind pressure difference are controlled by controlling the number of rotations of the fan drive motor. However, it is sufficient that the air volume or the wind pressure difference can be generated. For example, an air volume throttle device (not shown) is provided in the air ducts 41a and 41b. And the amount of blown air may be controlled by controlling the throttle amount by this device. In this case, the air flow control is performed on-line by obtaining an optimum relationship between the deflection amount and the air blowing amount in advance through experiments or the like, obtaining the control amount from the deflection amount detected based on this relationship. Thereby, compared with 1st Embodiment, it is controlled on-line and a bending can be eliminated and the film 19 can be hold | maintained horizontally. Thereby, the thickness nonuniformity in the width direction and optical characteristic nonuniformity which generate | occur | produce in the film 19 can be suppressed further.

  In the second embodiment, the deflection sensor 51 is positioned at the center of the film 19 in the width direction, and the optimum air flow rate is set based on the amount of deflection at the center. However, the present invention is not limited to this form, and although not shown in the drawings, a plurality of deflection sensors are arranged at appropriate intervals in the width direction of the film 19, and the deflection amount distribution in the width direction of the film 19 is detected online. You may perform control which hold | maintains the film 19 horizontally based on quantity distribution. In addition to the above-described method for controlling the air volume of the upper air blowing section 37 and the lower air blowing section 38, the control for holding the film 19 horizontally is made even more so as to distribute the blowing amount in the width direction of the film 19. The film 19 may be held horizontally with high accuracy.

  As shown in FIG. 5, the nozzle of the lower blowing head 40b is provided with a slit-shaped outlet 53. In order to distribute the blowout amount in the width direction of the film 19 (see FIG. 4), the movable wind shielding plate 54 is attached so as to be swingable around the rotary shaft 55 adjacent to the blowout port 53. Then, the swing angle of the movable wind shield 54 is adjusted by the wind shield rotating mechanism 56 via the controller 39 (see FIG. 4). Thereby, by changing the blowing amount in the width direction of the film 19, it is possible to obtain a wind pressure distribution in which the central portion is strong in the width direction of the film 19 and gradually weakens toward both ends. By appropriately changing the swing angle of the movable wind shield 54, the air volume distribution can be changed and the film 19 can be held more horizontally. Note that the film 19 can be held horizontally with higher accuracy by simultaneously performing the air volume distribution control by the movable wind shield 54 and the air volume control by the heated air blowing section.

  In the above embodiment, the deflection of the film 19 is detected using a non-contact type deflection sensor, but instead, a signal output from a thickness sensor that measures the thickness of the film 19 in the width direction online. Based on this, you may control the ventilation volume and wind pressure of the upper ventilation part 37 and the lower ventilation part 38 (refer FIG. 2). The signal output from the thickness sensor in the width direction of the film 19 is related to the amount of deflection of the film 19 in the tenter 12, and based on the thickness distribution in the width direction of the film 19 by the thickness sensor of the film 19, Control the air flow. Specifically, based on the thickness distribution in the width direction of the film 19, the relationship between the thickness difference between both ends in the width direction of the film 19 and the central portion and the amount of deflection of the film 19 in the tenter 12 is obtained. In accordance with the thickness difference, the air flow rate is controlled so as to eliminate the film deflection amount. Thereby, the upper air blower 37 and the lower air blower 38 can be controlled so as to hold the film 19 horizontally in the tenter 12. Moreover, when thickness distribution is calculated | required over the width direction of the film 19 from the measured thickness amount, thickness difference of the both ends with respect to the center part of the film 19 is calculated | required based on this thickness distribution, and this thickness difference exceeds a fixed value Alternatively, the controller 39 may control the amount of air blown by the lower air blowing unit 37 to be increased.

  Details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148, and these descriptions can also be applied to the present invention. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, UV absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, and release accelerators. It is described in detail in paragraphs [0196] to [0516] of Kai 2005-104148, and these descriptions can also be applied to the present invention.

  From the drying conditions of the stretching process, handling method, curling, winding method after flatness correction to film recovery method, it is described in detail in paragraphs [0617] to [0889] of JP-A-2005-104148. The description can also be applied to the present invention.

  In the above embodiment, the case where a film is stretched in a so-called off-line stretching facility has been described as an example. The present invention is not limited to this embodiment, and the present invention can also be used for a tenter used in a so-called on-line drawing facility. On-line stretching is stretching in a film forming process, that is, a film forming process for manufacturing a film. In the film forming process in the case of producing a film by solution casting, the film contains a solvent. The more the film contains a solvent, the lower the strength of the film itself and the more the weight increases. For this reason, this invention has an effect also in an online extending | stretching installation.

  In online stretching in solution casting, examples of the wind pressure difference (= P2−P1) obtained by subtracting the first wind pressure P1 from the first wind pressure P1, the second wind pressure P2, and the second wind pressure P2 are as follows. When the film width is 1800 mm and the film thickness is 80 μm, the set value of the first wind pressure P1 is, for example, in the range of 30 Pa to 120 Pa, and the set value of the second wind pressure is in the range of 60 Pa to 210 Pa, The wind pressure difference P2-P1 is in the range of 30 Pa to 90 Pa.

  The present invention can also be applied to two on-line stretching equipments and stretching methods arranged in series when stretching is performed in two stages in the process of solution casting.

  In the said embodiment, although this invention was implemented to the clip tenter using the clip which hold | grips the both-sides edge part of a film, it may replace with this and may implement this invention to a pin tenter. In the pin tenter, a pin plate provided with a large number of pins is used, and the film is stretched in the width direction by piercing and holding both side edges of the film on the pin plate.

As described above, the present invention can be applied to the case where the stretching process is performed either online or offline. In any case, the wind pressure difference P2-P1 is in the range of 0.5 × (ρ × θ × g × L / D) to 1.5 × (ρ × θ × g × L / D). It is good to set. In this equation, ρ (unit: kg / m ³ ) is the film density, θ (unit: mm) is the film thickness, L (unit: mm) is the distance between the nozzle 45a and the nozzle 45a, and D (unit: mm). ) Is the slit clearance of the nozzle 45a, and g (unit: m / sec ² ) is the gravitational acceleration. Each of the heating air pressures P1 and P2 (the unit is “Pa”) is when the blown air velocity is V (unit: m / second) and the air density is ρa (unit: kg / m ³ ). to be calculated by ρa × ^V 2/2. Note that ρ and θ are the values in the film at the start of widening when obtaining the wind pressure difference during the widening of the film, and reduced when obtaining the wind pressure difference during narrowing (shrinking) the film. It is the value in the film at the start of the width.

12 Tenter 19 Film 32 Heating Unit 35 Clip 39 Controller 40a Upper Blower Head 40b Lower Blower Head 54 Movable Windshield

Claims (5)

A tenter body having a plurality of clips that move in the running direction of the film while gripping both side edges of the film and extend the film in the width direction;
An upper air blower that blows heated air against the upper surface of the film held by the clip;
A lower air blower that blows heated air against the lower surface of the film held by the clip;
A stretching apparatus for a polymer film, comprising: a horizontal holding control unit that horizontally holds the film by a difference in pressure of heating air blown from the upper blower and the lower blower.   The said horizontal maintenance control part controls the ventilation volume of the said lower ventilation part at least, The extending | stretching apparatus of the polymer film of Claim 1 characterized by the above-mentioned.   The horizontal holding control unit includes a deflection sensor that measures a deflection amount of the film, and the horizontal holding control unit is configured to reduce the lower air blowing unit as the deflection amount increases based on a signal representing the deflection amount from the deflection sensor. The apparatus for stretching a polymer film according to claim 1, wherein the air blowing amount is increased.   The horizontal holding control unit measures a thickness distribution of the film in the width direction, and obtains a thickness difference between both end portions of the film with respect to a center portion of the film in the width direction based on the measured thickness distribution. The apparatus for stretching a polymer film according to any one of claims 1 to 3, wherein when the difference in thickness exceeds a certain value, the amount of air blown from the lower air blowing section is increased. A stretching step of stretching the film in the width direction while gripping both side edges of the film with a plurality of clips and moving in the running direction of the film;
A heating step of blowing the upper surface heating air to the upper surface of the film held by the clip and heating the film by blowing the lower surface heating air to the lower surface of the film held by the clip;
A method for stretching a polymer film, comprising a horizontal holding step of holding the film horizontally by a difference in wind pressure between the upper surface heating air and the lower surface heating air.

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