JP5344980B2 - Method for stretching polymer web and method for producing polymer film - Google Patents

Abstract

An off-line stretching device is provided with an accepting chamber and a stretching frame. The accepting chamber accepts an advanced film roller and a subsequent film roller. The width of the advanced film roller is expanded while the stretching machine maintains the maintenance area of the advanced film roller sent out from the advanced film roller. After all advanced films are sent out, subsequent films are sent out to the stretching machine from the subsequent roller. In the jointing part installed in front of the stretching machine, the rear end of the advanced film is overlapped with the front end of the subsequent film so as to form an overlapped part. A deposition area is installed at the part of the overlapped part depart from the central part of the maintenance are in B direction. The jointing part is jointed and processed in the deposition area. After jointing and processing, the jointed film is sent to the stretching machine and stretched towards both sides in B direction at the state of maintaining the maintenance area.

Description

  The present invention relates to a method for stretching a polymer web and a method for producing a polymer film.

  Polymer films (hereinafter referred to as “films”) are widely used as optical films because of their features such as excellent light transmission, flexibility, and reduction in weight. Among them, a TAC film formed from cellulose acylate, particularly cellulose triacetate (hereinafter referred to as TAC) having an average degree of acetylation of 57.5% to 62.5% is a protective film for a polarizing plate of a liquid crystal display device, It is used as an optical film such as an optical compensation film (for example, a viewing angle widening film).

  A solution casting method is known as a main method for producing a film. The solution casting method is a method in which a polymer solution containing a polymer and a solvent (hereinafter referred to as a dope) is cast on a traveling support (hereinafter referred to as a casting step) and has a self-supporting property. The cast film thus formed is peeled off from the support to form a film (hereinafter referred to as a peeling step), and the film is dried (hereinafter referred to as a drying step). And when removing wrinkles, tarmi, etc. generated in the film, or when giving desired optical properties to the film, the film is transported at a predetermined transport speed using a stretching device such as a clip tenter. A process of stretching in the width direction (hereinafter referred to as a stretching process) is performed in a drying process. Finally, using a winder or the like, the film is wound around a winding core to form a film roll. And a film can be manufactured continuously and efficiently by performing a casting process, a peeling process, and a drying process continuously.

  In recent years, demand for optical films such as TAC films has increased due to rapid development and spread of liquid crystal displays and the like. With this increase in demand, it is desired to improve the productivity of optical films. From such a background, a cooling gelling solution film forming method that can develop self-supporting property in a cast film by cooling in a short time while improving the running speed of the support is adopted as a method for manufacturing an optical film. There are many cases.

  However, the optimum speed is different between the traveling speed of the support and the transport speed of the film in the stretching apparatus. In particular, when the cooling gelation method is adopted, the film forming speed of the solution film forming method is determined by the conveying speed by the stretching apparatus, and the substantial production efficiency cannot be improved. Therefore, a solution film-forming facility for producing a film without performing a stretching treatment and a separate stretching facility for performing a stretching treatment on the produced film (hereinafter referred to as off-line stretching facility) are separately provided, and these facilities are used in combination. A method has been proposed (see, for example, Patent Document 1).

  Moreover, as described in Patent Document 1, in an off-line stretching facility, it is preferable to perform a stretching process continuously on the film fed from the winding core. Therefore, when the film roll is switched, the rear end portion and the front end portion are joined at the overlapping portion where the rear end portion of the film fed from the winding core overlaps the front end portion of the new film (hereinafter referred to as a joining process). Is performed uniformly. By performing such a joining process with an off-line stretching facility, it becomes possible to continuously perform the stretching process of the film while switching the film roll.

JP 2008-238682 A

  However, as described in Patent Document 1, when the joining process is uniformly performed over the entire overlapping portion, the portion of the film that forms the overlapping portion extends compared to the portion of the film that does not form the overlapping portion. Hateful. Therefore, when the film that has been subjected to the bonding process is stretched, failures that cause the film to break frequently occur near the boundary between the two parts due to the difference in deformation.

  This invention solves the said subject, and aims at providing the extending | stretching method of a polymer web which can perform the extending | stretching process of a film efficiently, and the manufacturing method of a polymer film.

In the method for stretching a polymer web of the present invention, the longitudinal rear end of the preceding first polymer web and the longitudinal leading end of the subsequent second polymer web are overlapped, and the overlapping portion of the trailing end and the leading end is overlapped by the width of the overlapping portion. Divided into a first area belonging to both ends of the direction and a second area belonging to substantially the center in the width direction of the overlapping portion, and welding at a plurality of locations in at least a part of the second area and not welding in the first area or A joining step in which the first polymer web and the second polymer web are joined to form a series of joined webs by welding at least a part of the first area to a degree lower than that in the second area. When using a pair gripping members for gripping both ends in the width direction of the bonding web, the bonding web and a stretching step of stretching in the width direction, the first area, a pair of gripping portions after the bonding step Is an area consisting of a gripping region gripped by the gripping region and a region within a range of 0.05 to 0.25 times W in the width direction from the gripping region, and the second area has a length in the width direction, It is an area within the range of 0.5 to 0.9 times the length W in the width direction of the overlapping portion .

  The method for producing a polymer film of the present invention is characterized by using the above-described polymer web stretching method.

  According to the present invention, the overlapping portion is divided into a plurality of areas in the extending direction, and the joining step is performed in the remaining areas excluding at least one area among the plurality of areas. The overlapping part that has undergone such a bonding process tends to extend in the width direction as a whole as compared with the overlapping part that has been uniformly subjected to the bonding process over the entire region. For this reason, even if the film subjected to the above-described bonding treatment is stretched in the width direction, the difference in deformation amount between the overlapping portion and the portion other than the overlapping portion can be reduced, thereby preventing the film from being broken. it can. Therefore, according to this invention, since it becomes possible to perform an extending | stretching process efficiently in an off-line extending | stretching installation, a polymer film can be manufactured efficiently.

It is a schematic side view which shows an off-line extending | stretching installation. It is a top view which shows a tenter part. It is sectional drawing of a tenter part when a flapper exists in a grip open position. It is sectional drawing of a tenter part when a flapper exists in a holding position. It is a perspective view which shows the outline | summary of a junction part. It is the elements on larger scale of the receiving surface of a base. It is a top view which shows the outline | summary of the 1st welding area provided in an overlap part. It is explanatory drawing which shows the outline | summary of the 1st arrangement pattern of the welding part provided in a welding area. It is explanatory drawing which shows the outline | summary of the 2nd arrangement pattern of the welding part provided in a welding area. It is a top view which shows the outline | summary of the 2nd welding area provided in an overlap part. It is a top view which shows the outline | summary of the 3rd welding area provided in an overlap part. It is a top view which shows the outline | summary of the 4th welding area provided in an overlap part. It is a top view which shows the outline | summary of the 5th welding area provided in an overlap part. It is explanatory drawing which shows the outline | summary of solution casting apparatus. It is explanatory drawing which shows the outline | summary of a fusion | melting film forming facility. It is a perspective view which shows the arrangement | positioning state of the some roll in a heat processing zone. It is explanatory drawing which shows the roll wrap length (D) of a some roll in a heat processing zone, and the length (G) between rolls.

  As shown in FIG. 1, the off-line stretching equipment 2 includes a film storage chamber 4 for storing a long film 3, a reservoir 5, a tenter unit 6, a thermal relaxation chamber 7, a cooling chamber 8, a film winding The tenter unit 6 sequentially applies a stretching process to the film 3.

  The film storage chamber 4 includes a turret type film delivery section 10 and a joining section 11. The film delivery unit 10 has a turret arm 13. A pair of mounting shafts 12 a are provided at both ends of the turret arm 13. The turret arm 13 rotates intermittently by 180 degrees, thereby setting one attachment shaft 12 a at the film delivery position 16 and setting the other attachment shaft 12 a at the core replacement position 17. The film roll 14 is attached to the attachment shaft 12 a at the winding core replacement position 17, and the film roll 14 attached to the attachment shaft 12 a is set to the film delivery position 16 by the rotation of the turret arm 13. An empty core is taken out from the mounting shaft 12a at the core replacement position 17, and a new film roll 15 is set.

  The film sending unit 10 sends a film (hereinafter referred to as a preceding film) from the film roll 14 at the film sending position 16 to the joining unit 11. When the film delivery unit 10 detects that the film roll 14 set at the film delivery position 16 has run out, the turret arm 13 is rotated 180 degrees to deliver a new film roll 15 at the core replacement position 17 to the film delivery. Set to position 16. Then, a film (hereinafter referred to as a subsequent film) is sent out from the new film roll 15 to the joint portion 11.

  In the joining portion 11, a joining process is performed in which the rear end portion of the preceding film and the leading end portion of the subsequent film are welded to form one film 3. The film 3 is sent out to the tenter unit 6 through the reservoir 5, and the tenter unit 6 is subjected to a stretching process. The details of the bonding portion 11 and the bonding process will be described later.

  In the reservoir 5, a part of the preceding film is retained. The length of the preceding film retained in the reservoir 5 is equal to or more than the product of the time required for the joining process and the transport speed of the preceding film in the tenter unit 6.

  The tenter unit 6 grips both side edges of the film 3, stretches the film 3 in the width direction, and sends the film 3 to the edge-cutting device 21. The edge-cutting device 21 cuts off both side edges of the film 3. The film 3 as a product part from which both side edges have been cut off by the edge-cutting device 21 is sent to the heat relaxation chamber 7. On the other hand, both side edges separated from the film 3 are sent to the cut blower 22 and finely cut into small pieces. The cut ear dust pieces are sent to the crusher 23 by an air feeding device (not shown) and crushed into chips. This chip is reused for dope preparation.

  The heat relaxation chamber 7 is provided with a large number of rollers 25 and a drying duct (not shown). The film 3 is conveyed through the heat relaxation chamber 7 by the rollers 25 and is heat relaxed by heating, and then is transferred to the cooling chamber 8. Sent. In addition, it is preferable that the temperature of the wind from a dry wind duct is 20 degreeC or more and 250 degrees C or less.

  The film 3 after heat relaxation is cooled to 30 ° C. or less in the cooling chamber 8 and then sent to the film winding chamber 9. The film winding chamber 9 is provided with a winder 27 having a press roller 26. The film 3 is wound around the winding core 28 while being pressed against the winding core 28 by the press roller 26.

(Tenter part)
As shown in FIG. 2, the tenter unit 6 applies a tension in the width direction (hereinafter referred to as direction B) to the film 3 while transporting the film 3 in the longitudinal direction, so that the width 3 of the film 3 changes from W1 to W2. It is something to expand. The tenter unit 6 is provided with a preheating area 6a, a stretching area 6b, and a relaxation area 6c in order from the upstream side in the transport direction of the film 3 (hereinafter referred to as direction A). A duct (not shown) is provided in each of the areas 6a to 6c. Each duct sends a predetermined drying air to the film 3 in each area 6a-6c. Thereby, it adjusts so that the temperature of the film 3 in each area 6a-6c may become the optimal range.

  The tenter unit 6 includes a clip 31, rails 32 and 33, and chains 34 and 35. The rails 32 and 33 are installed on both sides of the conveyance path of the film 3, and the rails 32 and 33 are arranged so as to be separated at a predetermined rail interval. This rail interval is constant in the preheating area 6a, gradually increases in the extending area 6b in the direction A, and is constant in the relaxation area 6c. A driving sprocket 38 is provided in the vicinity of the downstream ends of the rails 32 and 33 in the direction A, and a driven sprocket 39 is provided in the vicinity of the upstream ends of the rails 32 and 33 in the direction A.

  As shown in FIG. 2, the chains 34 and 35 are spanned between the driving sprocket 38 and the driven sprocket 39 and are movably attached along the rails 32 and 33. A plurality of clips 31 are attached to the chains 34 and 35 at a predetermined interval. In order to avoid complication of the figure, only a part of the clip 31 is shown in FIG.

  As shown in FIGS. 3 and 4, the clip 31 includes a clip body 40 and a rail attachment portion 41. The clip main body 40 includes a substantially U-shaped frame 42 and a flapper 43 rotatably attached to the frame 42 by an attachment shaft 42a. The flapper 43 is provided so as to be freely displaceable between a grip open position (see FIG. 3) that stands obliquely (see FIG. 3) and a grip position (see FIG. 4) that stands up substantially vertically, and is not self-weighted or illustrated. The spring is biased to the gripping position.

  The rail attachment portion 41 includes an attachment frame 44 and a guide roller 45. The chain 34 or the chain 35 is attached to the attachment frame 44. The guide roller 45 rotates while contacting each support surface of each sprocket 38 to 39 (see FIG. 2) or the support surface of the rail 32 or the rail 33. Thus, the clip body 40 is guided along the rails 32 and 33 without dropping from the sprockets 38 to 39 and the rails 32 and 33.

  As shown in FIGS. 2 to 4, a grip start position Pi is provided in the vicinity of the upstream end in the direction A of the rails 32 and 33. Further, a grip release position Po is provided in the vicinity of the downstream end in the direction A of the rails 32 and 33. An opening member 48 of the clip 31 is provided on the upstream side in the direction A of the grip start position Pi, and an opening member 49 of the clip 31 is provided on the downstream side in the direction A of the grip release position Po. The release members 48 and 49 are in contact with the engaging head 43a of the flapper 43 of the clip 31 passing through the vicinity of the upstream side in the direction A of the grip start position Pi and the vicinity of the downstream side of the direction A of the grip release position Po. Arranged.

  When the engagement head 43a comes into contact with the release member 48 by the travel of the clip 31 along the rails 32 and 33, the flapper 43 is displaced to the grip release position (see FIG. 3). Thereby, the clip 31 is in a state in which the side edge portion of the film 3 can be received. Subsequently, when the traveling clip 31 passes the grip start position Pi, the contact between the release member 48 and the engagement head 43a is released, and the flapper 43 is displaced to the grip position (see FIG. 4). Thus, at the grip start position Pi, the clip 31 grips both side edges (hereinafter referred to as gripping area) 3w of the film 3 by the film gripping surface 42b and the flapper lower surface 43b. Thereafter, the film 3 is sequentially conveyed to each of the areas 6a to 6c in a state where the grip area 3w is gripped by the clip 31. In the stretching area 6b, a stretching process is performed in which the film 3 is stretched in the direction B and the width of the film 3 is expanded from W1 to W2. The stretching ratio ER (= W2 / W1) is preferably 1.1 or more and 2.0 or less. Thereafter, when the clip 31 passes the grip release position Po, the engaging head 43 a comes into contact with the release member 49. The flapper 43 is displaced to the grip opening position by the contact between the opening member 49 and the engaging head 43a. Thereby, the clip 31 releases the grip of the grip area 3w.

(Joining unit)
As shown in FIGS. 1 and 5, a nip roller 51 and a nip roller 52 are arranged in the joining portion 11 from the upstream side in the direction A, and an ultrasonic joining device 53 and a pedestal 54 are interposed between the nip roller 51 and the nip roller 52. Is arranged.

(pedestal)
The pedestal 54 has a receiving surface 55. As shown in FIG. 6, the receiving surface 55 is subjected to knurling, and numerous projections 56 are formed. The protrusion 56 is formed in a truncated pyramid shape. The shape of the protrusion 56 is not limited to a truncated pyramid, and may be a truncated cone, a cone, a pyramid, a cone, or other shapes. The pedestal 54 is provided so as to be movable in the direction C under the control of a control unit (not shown).

(Nip roller)
Returning to FIG. 1 and FIG. 5, the nip rollers 51 and 52 perform superposition processing under the control of a control unit (not shown). In the superimposing process, the nip rollers 51 and 52 sandwich the preceding film 3a and the succeeding film 3b, feed the films 3a and 3b in the direction A or the direction opposite to the direction A, and the position of the rear end 3ax of the preceding film 3a. And the position of the front-end | tip part 3bx of the subsequent film 3b is adjusted so that it may become on the receiving surface 55. FIG. Thus, an overlapping portion 60 where the rear end portion 3ax of the preceding film 3a and the front end portion 3bx of the subsequent film 3b overlap is formed on the receiving surface 55.

(Ultrasonic bonding equipment)
The ultrasonic bonding apparatus 53 uses a frictional heat caused by mechanical vibration to weld a target, and includes a vibrator 65, a horn 66, and an oscillator 67. Under the control of a control unit (not shown), the oscillator 67 mechanically vibrates the vibrator 65 at a predetermined frequency (10 kHz to 50 kHz). The horn 66 vibrates in the thickness direction of the film 3 (hereinafter referred to as direction C) as a result of resonating with the vibration of the vibrator 65.

  The ultrasonic bonding device 53 is attached to the pressing portion 71 via the attachment member 70. The pressing unit 71 makes the ultrasonic bonding apparatus 53 movable in the direction C under the control of the control unit.

  The pressing portion 71 is provided in the first slide mechanism 72 so as to be movable in the A direction. Further, the first slide mechanism 72 is provided in the second slide mechanism 73 so as to be movable in the direction B. The second slide mechanism 73 includes a pair of pulleys 76 that are rotatably provided, a belt 77 that spans the pair of pulleys 76, and a control unit that rotates the pulleys 76 in a predetermined direction by a predetermined amount. (Not shown). In this manner, the ultrasonic bonding apparatus 53 is movable in the direction A and the direction B by the first slide mechanism 72 and the second slide mechanism 73.

  The ultrasonic bonding device 53 and the pedestal 54 are movable between a holding position for holding the overlapping portion 60 with a predetermined pressure and a retreat position for retreating from the holding position under the control of the control unit. When the joining process is not performed, the ultrasonic joining device 53 and the base 54 are in the retracted position, and move to the clamping position only when the joining process is performed.

  Next, the joining process performed in the joining part 11 is demonstrated. As shown in FIGS. 1 and 5, the film delivery unit 10 sends the preceding film 3 a from the film roll 14 to the joining unit 11, and the nip rollers 51 and 52 send the preceding film 3 a to the reservoir 5. Thereafter, when the control unit detects that the film roll set at the film delivery position 16 has run out, the film delivery unit 10 rotates the turret arm 13 by 180 degrees to create a new film at the core replacement position 17. The roll 15 is set at the film delivery position 16. Then, the subsequent film 3b is sent out from the new film roll 15.

  The nip rollers 51 and 52 align the rear end portion 3ax and the front end portion 3bx by conveying the preceding film 3a and the subsequent film 3b. Thus, an overlapping portion 60 where the rear end 3ax of the preceding film 3a and the front end 3bx of the subsequent film 3b overlap is formed on the receiving surface 55.

  The ultrasonic bonding device 53 and the pedestal 54 are set in the retracted position in advance. The first slide mechanism 72 and the second slide mechanism 73 set the ultrasonic bonding device 53 at a predetermined position on the receiving surface 55 based on a welding area set in advance in the overlapping portion 60.

  Thereafter, when the ultrasonic bonding apparatus 53 and the base 54 in the retracted position are moved to the holding position by the control unit, the overlapping portion 60 is held by the vibrating horn 66 and the receiving surface 55, and the overlapping portion 60 vibrates. As a result of the frictional heat generated between the rear end 3ax of the preceding film 3a and the front end 3bx of the subsequent film 3b due to the vibration of the overlapping portion 60, the portion sandwiched between the vibrating horn 66 and the receiving surface 55, and The rear end 3ax and the front end 3bx in the vicinity are welded.

  Further, the first slide mechanism 72 and the second slide mechanism 73 move the ultrasonic bonding apparatus 53 in the direction B or the direction A within the welding area. As a result, the horn 66 comes into contact with the entire overlapping portion 60 in the welding area, and as a result, the welding of the rear end portion 3ax and the front end portion 3bx in the entire welding area is completed.

  After the welding of the rear end portion 3ax and the front end portion 3bx is completed in the entire welding area, the pressing portion 71 moves the ultrasonic bonding device 53 and the base 54 to the retracted position. Thus, the joining part 11 can weld the rear end part 3ax and the front end part 3bx in a desired welding area in the overlapping part 60.

  In the present invention, as shown in FIG. 7, a welding area 60y is set in a portion of the overlapping portion 60 away from the gripping area 3w toward the center side in the direction B, and an unwelded area 60z is formed on both sides in the direction B of the welding area 60y. And a joining process is performed in the welding area 60y. Even if the film 3 that has undergone such a bonding process is stretched, the unwelded area 60z between the gripping area 3w and the welded area 60y can be deformed in the same manner as the film 3 that does not constitute the overlapping portion 60.

  Therefore, according to the present invention, in the stretching process, it is possible to reduce the difference between the deformation amount of the overlapping portion 60 as a whole and the deformation amount of the portion of the film 3 that does not constitute the overlapping portion 60. The breakage of the film 3 due to the difference between the deformation amounts of the two in the process can be suppressed.

  The distance CL1 between the gripping area 3w and the welding area 60y in the direction B is preferably 0.05 times or more and 0.25 times or less of the width W1 of the film 3, for example, preferably 50 mm or more and 600 mm or less. The length Wy in the direction B of the welding area 60y is preferably 0.5 to 0.9 times the width W1 of the film 3, for example, 600 mm to 2200 mm. The length L1 in the direction A of the overlapping portion 60 is preferably, for example, not less than 10 mm and not more than 40 mm.

(Welding conditions)
In the bonding process, the bonding work W _TH per unit thickness is preferably 0.4 W / μm or more and 1.1 W / μm or less, and more preferably 0.6 W / μm or more and 0.9 W / μm or less. When the joining work W _TH is less than 0.4 W / μm, vibrations sufficient for welding are not transmitted to the overlapping portion 60, so that the rear end portion 3ax and the front end portion 3bx cannot be welded. If the joining work W _TH is larger than 1.1 W / μm, the vibration of the overlapping portion 60 becomes excessively large, which is not preferable. The joining work W _TH per unit thickness is obtained by dividing the work amount W given to the overlapping portion 60 by the horn 66 by the thickness of one film 3.

In the bonding process, the pressure P _TH per unit thickness applied to the overlapping portion 60 is preferably 1.0 × 10 ⁻³ MPa / μm or more and 3.5 × 10 ⁻³ MPa / μm or less. When the pressure P _TH per unit thickness is less than 1.0 × 10 ⁻³ MPa / μm, vibration sufficient for welding is not transmitted to the overlapping portion 60, and as a result, the rear end portion 3ax and the front end portion 3bx are welded. I can't. On the other hand, if the pressure _PTH per unit thickness is larger than 3.5 × 10 ⁻³ MPa / μm, the vibration of the overlapping portion 60 becomes excessively large and breaks. The pressure P _TH per unit thickness is obtained by dividing the pressure P applied to the overlapping portion 60 by the horn 66 by the thickness of one film 3.

It is preferable that the horn amplitude f _TH per unit thickness in the welding is 0.35 or more and 0.7 or less. If the horn amplitude f _TH per unit thickness is less than 0.35, the vibration sufficient for welding is not transmitted to the overlapping portion 60, so that the rear end portion 3ax and the front end portion 3bx cannot be welded. On the other hand, if the horn amplitude f _TH per unit thickness is larger than 0.7, it is not preferable because the vibration of the overlapping portion 60 becomes too large and breaks. The horn amplitude f _TH per unit thickness is obtained by dividing the amplitude f of the horn 66 by the thickness of one film 3.

Total area of the portion the rear end 3ax and the tip 3bx is welded is preferably 2000 mm ² or more 22000Mm ² or less.

(the film)
The width W1 of the film 3 is preferably 600 mm or more, more preferably 1300 mm or more and 2500 mm or less, and the effect of the present invention is exhibited even when it is larger than 2500 mm. Moreover, it is preferable that thickness TH1 of the film 3 is 20 micrometers or more and 200 micrometers or less, and it is more preferable that they are 30 micrometers or more and 100 micrometers or less.

(Welding pattern)
The arrangement pattern of the welding parts in the welding area 60y is a solid pattern in which welding parts are provided in the entire welding area 60y, and a pattern in which a plurality of welding parts 80 provided in the welding area 60y are arranged like a sea island structure as shown in FIG. In addition to this, a pattern in which the welded portion 81 provided in the welded area 60y is provided on the filament as shown in FIG. The line pattern shown in FIG. 9 is provided so as to extend in the direction B, but may be provided so as to extend in the direction A, or may be provided so as to extend in a direction intersecting the direction A or the direction B at an acute angle. . Further, the number of the line patterns shown in FIG. 9 is not limited to two, but may be three or more, or may be one.

  In the above embodiment, the welding area 60y is set at the center of the direction B, but the present invention is not limited to this, and as shown in FIG. 10, the direction B is more than the pair of gripping areas 3w and the pair of gripping areas 3w. The welding area 60y may be set in the both end portions.

(Welding area)
In the above-described embodiment, the welding area 60y is set at a portion that is separated from the gripping area 3w toward the center of the direction B by CL1, but the present invention is not limited to this, and the overlapping portion 60 can be stretched in the direction B as a whole in the stretching process. To some extent, the welding area 60y may be set in a part of the overlapping portion 60.

  As an example of setting the welding area 60y, the overlapping portion 60 is divided into n (≧ 2) areas in the direction B, and at most (n−1) areas are set as the welding areas 60y, and the remaining areas are not welded. The area 60z may be used. Here, the non-welded area 60z is preferably provided in a portion of the film constituting the overlapping portion 60 where the amount of stretching in the stretching process is large. When performing the stretching process of gripping the gripping area 3w and stretching the film 3 in the direction B, the stretching amount of the film 3 in this stretching process gradually decreases from the gripping area 3w toward the center of the direction B. Therefore, when performing such a stretching process, the unwelded area 60z is provided on the side of the center portion in the direction B of the gripping area 3w. This is most preferable from the viewpoint of reducing the difference in the stretch amount of the part that is not configured.

In addition, as a setting example of the welding area 60y in the present invention, in addition to the forms shown in FIGS. 7 and 10, as shown in FIG. 11, welding areas 60y may be provided at both ends in the direction B of the overlapping portion 60.

  Further, when a plurality of welding areas 60y are provided in the overlapping portion 60, the length in the direction B of the welding area 60y may be different depending on the position where the welding area 60y is set as shown in FIG. Good. That is, it is preferable that the length of the welding area 60ya provided in the portion where the stretching amount in the stretching process is large is shorter than the length of the welding area 60yb provided in the portion where the stretching amount in the stretching process is small. Similarly, it is preferable that the length of the unwelded area provided in the portion where the stretching amount in the stretching process is large is longer than the length of the unwelded area provided in the portion where the stretching amount in the stretching process is small.

  In the above embodiment, the welding area 60y is set so as to be aligned in the direction A in the overlapping portion 60. However, the present invention is not limited to this, and the welding area 60y is aligned in a plurality of rows in the direction A. It may be set. Therefore, according to the present invention, a welding area 60y may be provided in the overlapping portion 60 as shown in FIG.

  In the said embodiment, although the extending | stretching process was performed in the width direction of the film 3, this invention is not limited to this. Also in this case, the overlapping portion 60 may be divided into a plurality of areas in the extending direction, and at least one area may be an unwelded area and the remaining area may be a welded area.

  In the above embodiment, the joining process is performed by sandwiching a predetermined portion of the overlapping portion 60 using the receiving surface 55 and the horn 66 that have been knurled, but the present invention is not limited to this. From the viewpoint of preventing breakage of the film 3, the portion sandwiched between the horn 66 and the receiving surface 55 is preferably a line or a point rather than a surface. From the above, as the receiving surface of the pedestal 54, any one of a flat surface, a flat surface provided with a linear groove, a linear protrusion provided, and a receiving surface 55 as shown in FIG. However, the receiving surface 55 as shown in FIG. 6 is the best.

  In the above embodiment, the overlapping portion 60 is joined using the horn 66 that vibrates in the direction C. However, the present invention is not limited to this, and vibrates in the direction A, the direction B, or the direction that intersects the direction A. The joining process of the overlapping portion 60 may be performed using the horn 66.

  Moreover, in the said embodiment, although the joining process was performed using the ultrasonic bonding apparatus 53, this invention is not limited to this, A heating head is made to contact a predetermined welding area like a heat sealer, and a joining process is carried out. Alternatively, after applying a solvent (acetone or the like) to a predetermined welding area of the rear end portion 3ax or the front end portion 3bx, the rear end portion 3ax and the front end portion 3bx are overlapped, and the rear end portion 3ax and the front end portion The part 3bx may be welded.

In the above-described embodiment, the unwelded area 60z is set in the overlapping portion 60. However, the present invention is not limited to this, and in the unwelded area 60z as long as the overlapping portion 60 can be stretched as a whole in the stretching process. The low bonding process may be performed. In the low bonding process, the rear end portion 3ax and the front end portion 3bx of the overlapping portion 60 are welded as in the normal bonding process, but the degree of welding is lower than that in the normal bonding process. The conditions for the low bonding process may be smaller than the conditions for the normal bonding process. When performing a low bonding process using an ultrasonic bonding apparatus, the bonding work W _TH is preferably 0.1 W / μm or more and 0.4 W / μm or less, and the pressure P _TH per unit thickness is 0. It is preferably 1 × 10 ⁻³ MPa / μm or more and 1.0 × 10 ⁻³ MPa / μm or less.

(Solution casting method)
The film in the above embodiment can be obtained by a solution casting method. As shown in FIG. 14, a solution casting apparatus 210 that performs the solution casting method includes a stock tank 211, a casting chamber 212, a pin tenter 213, a drying chamber 215, a cooling chamber 216, and a winding chamber 217.

  The stock tank 211 includes a stirring blade 211b and a jacket 211c that are rotated by a motor 211a. The stock tank 211 stores a dope 221 in which a polymer that is a raw material of the film 3 is dissolved in a solvent. The dope 221 in the stock tank 211 is adjusted by the jacket 211c so that the temperature becomes substantially constant. Further, the rotation of the stirring blade 211b keeps the dope 221 in a uniform quality while suppressing agglomeration of a polymer or the like. The pipe 222 connects the stock tank 211 and the casting die 230.

  In the casting chamber 212, a casting die 230, a casting drum 232 as a support, a peeling roller 234, temperature control devices 235 and 236, and a decompression chamber 237 are installed. The casting drum 232 is rotated in the direction Z1 about the shaft 232a by a driving device (not shown). The temperature in the casting chamber 212 and the casting drum 232 are set to temperatures at which the casting film 233 is easily cooled and solidified (gelled) by the temperature control devices 235 and 236.

  The casting die 230 has a slit formed so as to extend in the width direction. The casting die 230 discharges the dope 221 toward the peripheral surface 232b of the casting drum 232 rotating from the slit. Thereafter, a casting film 233 is formed from the dope 221 on the peripheral surface 232 b of the casting drum 232. Then, while the casting drum 232 rotates about 3/4, self-supporting property due to gelation is developed in the casting film 233, and the casting film 233 is peeled off from the casting drum 232 by the peeling roller 234, A wet film 238 is obtained. The residual solvent amount of the cast film 233 at the time of peeling is preferably 150% by weight or more and 320% by weight or less. Here, the residual solvent amount indicates the amount of solvent remaining in the casting film 233 or the like on a dry basis, and the measurement method is to take a sample from the target film or the like and calculate the weight of the sample. x, where y is the weight after drying the sample, it is calculated as {(xy) / y} × 100.

  The decompression chamber 237 is disposed upstream of the casting die 230 in the direction Z1, and maintains the inside of the decompression chamber 237 at a negative pressure, and the rear surface of the casting bead (later on the peripheral surface 232b of the casting drum 232). The surface to be contacted) is reduced to a desired pressure. By reducing the pressure on the back side of the casting bead, the influence of the accompanying air generated by the rotation of the casting drum 232 is reduced, and a stable casting bead is formed between the casting die 230 and the casting drum 232, and the membrane A cast film 233 with little thickness unevenness can be formed.

  The material of the casting die 230 is formed of a material having a high corrosion resistance against an electrolyte aqueous solution, a mixed liquid such as dichloromethane or methanol, and a low coefficient of thermal expansion. It is preferable to use a finishing accuracy of the wetted surface of the casting die 230 with a surface roughness of 1 μm or less and a straightness of 1 μm / m or less in any direction.

  The peripheral surface 232b of the casting drum 232 is subjected to a chrome plating process and has sufficient corrosion resistance and strength. The temperature control device 236 circulates the heat transfer medium through the casting drum 232 in order to keep the temperature of the peripheral surface 232b of the casting drum 232 at a desired temperature. The heat transfer medium is maintained at a desired temperature, and the temperature of the peripheral surface 232b of the casting drum 232 is maintained at a desired temperature by passing through the heat transfer medium flow path in the casting drum 232.

  The width of the casting drum 232 is not particularly limited, but it is preferable to use a casting drum in the range of 1.1 to 2.0 times the casting width of the dope. The material of the casting drum 232 is preferably made of stainless steel, and more preferably made of SUS316 so as to have sufficient corrosion resistance and strength. The chromium plating treatment applied to the peripheral surface 232b of the casting drum 232 is preferably so-called hard chromium plating with a Vickers hardness of Hv 700 or more and a film thickness of 2 μm or more.

  The casting chamber 212 includes a condenser (condenser) 239 for condensing the evaporated solvent and a recovery device 240 for recovering the condensed liquid. The solvent condensed and liquefied by the condenser 239 is recovered by the recovery device 240. The solvent is regenerated as a solvent for preparing a dope after being regenerated by a regenerator.

  A crossover 241 and a pin tenter 213 are sequentially installed downstream of the casting chamber 212. In the transfer section 241, the transport roller 242 introduces the wet film 238 into the pin tenter 213. The pin tenter 213 has a large number of pin plates that pass through and hold both side edges of the wet film 238, and the pin plates travel on a track. Dry air is sent to the wet film 238 traveling by the pin plate, and the wet film 238 is dried to be a film 220.

  An ear clip device 243 is provided downstream of the pin tenter 213. The edge-cutting device 243 cuts both side edges of the film 220. The cut side edges are sent to the crusher 244 by air blowing, pulverized, and reused as a raw material such as a dope.

  A large number of rollers 247 are provided in the drying chamber 215, and the film 220 is wound around and conveyed. A cooling chamber 216 is provided on the outlet side of the drying chamber 215, and the film 220 is cooled in this cooling chamber 216 until it reaches room temperature. A forced static elimination device (static elimination bar) 249 is provided downstream of the cooling chamber 216, and the film 220 is neutralized. Further, a knurling application roller 250 is provided on the downstream side of the forced static elimination device 249, and knurling is applied to both side edges of the film 220. In the winding chamber 217, a winding machine 251 having a press roller 252 is installed, and the film 220 is wound around the winding core in a roll shape, and a film roll 255 is obtained by the winding machine 251. The film roll 255 is stored in the film storage chamber 4 (see FIG. 1) of the off-line stretching equipment 2 from the winding chamber 217.

(polymer)
Hereinafter, the polymer that is a raw material of the film will be described. In the present embodiment, cellulose acylate is used as the polymer, and cellulose triacetate (TAC) is particularly preferable as the cellulose acylate. Among cellulose acylates, those in which the substitution degree of the acyl group to the hydroxyl group of cellulose satisfies all of the following formulas (I) to (III) are more preferable. In the following formulas (I) to (III), A and B represent the substitution degree of the acyl group with respect to the hydrogen atom in the hydroxyl group of cellulose, A is the substitution degree of the acetyl group, and B is 3 carbon atoms. The substitution degree of the acyl group of ˜22. In addition, it is preferable that 90 weight% or more of TAC is a particle | grain of 0.1-4 mm. However, the polymer that can be used in the present invention is not limited to cellulose acylate.
(I) 2.5 ≦ A + B ≦ 3.0
(II) 0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.9

  Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by esterifying some or all of these hydroxyl groups with an acyl group having 2 or more carbon atoms. The degree of acyl substitution means the ratio at which the hydroxyl groups of cellulose are esterified at each of the 2-position, 3-position and 6-position (the substitution degree is 1 in the case of 100% esterification).

  The total degree of acylation substitution, that is, the value of DS2 + DS3 + DS6 is preferably 2.00 to 3.00, more preferably 2.22 to 2.90, and particularly preferably 2.40 to 2.88. Further, the value of DS6 / (DS2 + DS3 + DS6) is preferably 0.28 or more, more preferably 0.30 or more, and particularly preferably 0.31 to 0.34. Here, DS2 is the ratio of the hydrogen of the hydroxyl group at the 2-position in the glucose unit (hereinafter referred to as the acyl substitution degree at the 2-position), and DS3 is the hydroxyl group at the 3-position in the glucose unit. This is the rate at which hydrogen is substituted by an acyl group (hereinafter referred to as the 3-position acyl substitution degree), and DS6 is the rate at which the hydrogen at the 6-position hydroxyl group is substituted by an acyl group in a glucose unit (hereinafter, (Referred to as the degree of acyl substitution at the 6-position).

  Only one type of acyl group may be used in the cellulose acylate of the present invention, or two or more types of acyl groups may be used. When two or more kinds of acyl groups are used, it is preferable that one of them is an acetyl group. The sum of the degree of substitution of the hydroxyl groups at the 2nd, 3rd and 6th positions by acetyl groups is DSA, and the sum of the degree of substitution of the hydroxyl groups at the 2nd, 3rd and 6th positions by acyl groups other than acetyl groups When DSB is DSB, the value of DSA + DSB is preferably 2.22 to 2.90, and particularly preferably 2.40 to 2.88.

  The DSB is preferably 0.30 or more, particularly preferably 0.7 or more. Further, 20% or more of DSB is preferably a substituent at the 6-position hydroxyl group, more preferably 25% or more, further preferably 30% or more, and particularly preferably 33% or more. Further, the value of DSA + DSB at the 6-position of cellulose acylate is 0.75 or more, more preferably 0.80 or more, and particularly preferably cellulose acylate of 0.85 or more. These cellulose acylates By using, a solution (dope) having better solubility can be produced. In particular, when a non-chlorine organic solvent is used, a dope having excellent solubility, low viscosity and excellent filterability can be produced. Cellulose, which is a raw material for cellulose acylate, may be obtained from either linter or pulp.

  The acyl group having 2 or more carbon atoms of the cellulose acylate in the present invention may be an aliphatic group or an aryl group, and is not particularly limited. For example, cellulose alkylcarbonyl ester, alkenylcarbonyl ester, aromatic carbonyl ester, aromatic alkylcarbonyl ester and the like may be mentioned, and each may further have a substituted group. Preferred examples of these include propionyl group, butanoyl group, pentanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, iso-butanoyl group. , T-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a t-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and a propionyl group and a butanoyl group are particularly preferable. It is.

  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, release accelerators, etc. JP-A-2005-104148 describes in detail in paragraphs [0196] to [0516], and these descriptions can also be applied to the present invention.

(solvent)
Solvents for preparing the dope include aromatic hydrocarbons (eg, benzene, toluene, etc.), halogenated hydrocarbons (eg, dichloromethane, chlorobenzene, etc.), alcohols (eg, methanol, ethanol, n-propanol, n-butanol, Diethylene glycol, etc.), ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl acetate, ethyl acetate, propyl acetate, etc.) and ethers (eg, tetrahydrofuran, methyl cellosolve, etc.). In the present invention, the dope means a polymer solution or dispersion obtained by dissolving or dispersing a polymer in a solvent.

  Among these, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and dichloromethane is most preferably used. One kind of alcohol having 1 to 5 carbon atoms in addition to dichloromethane from the viewpoint of physical properties such as solubility of TAC, peelability of cast film from the support, mechanical strength of the film, and optical properties of the film It is preferable to mix several kinds. The content of the alcohol is preferably 2% by weight to 25% by weight and more preferably 5% by weight to 20% by weight with respect to the whole solvent. Specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like, but methanol, ethanol, n-butanol or a mixture thereof is preferably used.

  By the way, recently, for the purpose of minimizing the influence on the environment, studies have been conducted on the solvent composition when dichloromethane is not used. For this purpose, ethers having 4 to 12 carbon atoms, carbon atoms A ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and an alcohol having 1 to 12 carbon atoms are preferably used. These may be used in combination as appropriate. For example, a mixed solvent of methyl acetate, acetone, ethanol, and n-butanol can be mentioned. These ethers, ketones, esters and alcohols may have a cyclic structure. A compound having two or more functional groups of ether, ketone, ester, and alcohol (that is, —O—, —CO—, —COO—, and —OH) can also be used as the solvent.

  In the above-described embodiment, it has been described that cellulose acylate is used as a polymer as a raw material of the film. However, the present invention is not limited thereto, and is applicable to cyclic olefins and other cellulose esters such as cellulose acetate propionate. . Moreover, it can also apply to the polymer film manufactured by the melt film-forming method.

(Melting film forming equipment)
Next, a manufacturing facility for manufacturing a polymer film by a melt film forming method (hereinafter referred to as a melt film forming facility) will be described. As shown in FIG. 15, the melt film-forming facility 410 is an apparatus for producing a thermoplastic film F that can be used for a liquid crystal display device or the like. A pellet-shaped thermoplastic resin, which is a raw material of the thermoplastic film F, is introduced into a dryer 412 and dried, and then the pellet is extruded by an extruder 414 and supplied to a filter 418 by a gear pump 416. Next, foreign matters are filtered by the filter 418, and molten resin (molten thermoplastic resin) is extruded from the die 420. The molten resin is sandwiched between the first casting roll 428 and the touch roll 424 and press-molded, and then cooled and solidified by the first casting roll 428 to form a film having a predetermined surface roughness. Further, the second casting is performed. The unstretched film Fa is obtained by being conveyed by the roll 426 and the third casting roll 427. This unstretched film Fa may be wound up at this stage, or may be supplied to a lateral stretching section 442 that continuously performs long-span stretching. Further, even if the unstretched film Fa once wound up is supplied again to the transverse stretching section 442, the same effect as that obtained when the unstretched film Fa is supplied to the transverse stretching section 442 that performs continuous long span stretching can be obtained.

  In the laterally stretched portion 442, the unstretched film Fa is stretched in the width direction (hereinafter referred to as the direction Y) orthogonal to the transport direction (hereinafter referred to as the direction X) to obtain a laterally stretched film Fb. The preheating unit 436 may be provided on the upstream side of the lateral stretching unit 442, or the heat fixing unit 444 may be provided on the downstream side of the lateral stretching unit 442. Thereby, the bowing (shift of the optical axis) during stretching can be reduced. The preheating temperature is preferably higher than the transverse stretching temperature, and the heat setting temperature is preferably lower than the transverse stretching temperature. That is, normally, the center part in the width direction becomes concave toward the traveling direction, but bowing can be reduced by setting preheating temperature> lateral stretching temperature and transverse stretching temperature> heat setting temperature. Either pre-heat treatment or heat setting treatment may be performed, or both may be performed.

  After the transverse stretching, post-heat treatment is performed, and then the transversely stretched film Fb is contracted in the direction X in the heat treatment zone 446. In the heat treatment zone 446, as shown in FIG. 16, a plurality of rolls 448a are used so that only the contraction in the direction X occurs without contracting in the direction Y without holding the side end portion of the laterally stretched film Fb with the chuck. The horizontally stretched film Fb is conveyed at ˜448d. At this time, as shown in FIG. 17, the plurality of rolls 448a to 448d are arranged so that the ratio (G / D) of the roll wrap length (D) to the inter-roll length (G) is 0.01 or more and 3 or less. Is done. Thereby, the shrinkage | contraction of the direction Y is suppressed by the friction with the transversely stretched film Fb and each roll 448-448d. The laterally stretched film Fb is conveyed at a ratio (V2 / V1) of the peripheral speed (V1) by the upstream roll 448a and the peripheral speed (V2) by the downstream roll 448d at 0.6 or more and 0.999 or less. While being heat treated. That is, the laterally stretched film Fb shrinks in the direction X in the heat treatment zone.

  The transversely stretched film Fb is heat-treated in the heat treatment zone, whereby the thermoplastic film F, which is the final product with the adjusted orientation angle and retardation, is produced. The film F is taken up by a take-up unit 449.

  Stretching in the direction X may be performed before or after stretching in the direction Y. Stretching in the direction X can be achieved by transporting the film using a plurality of nip roll pairs aligned in the direction X and increasing the peripheral speed of the downstream nip roll pair from the peripheral speed of the upstream nip roll pair. The stretching method differs depending on the distance (L) between the nip rolls in the direction X and the ratio (L / W) of the film width W between the pair of nip rolls on the upstream side, and if L / W is small, Japanese Patent Application Laid-Open No. 2005-330411 A stretching method in the direction X as described in JP-A-2006-348114 can be employed. This method tends to increase Rth, but can make the apparatus compact. On the other hand, when L / W is large, a stretching method in the direction X as described in JP-A-2005-301225 can be used. Although this method can reduce Rth, the apparatus tends to be long.

  The polymer that can be used in the melt film-forming method is not particularly limited as long as it is a thermoplastic resin, and examples thereof include cellulose acylate, lactone ring-containing polymer, cyclic olefin, and polycarbonate. Of these, cellulose acylate and cyclic olefin are preferred, cellulose acylate containing an acetate group and propionate group, and cyclic olefin obtained by addition polymerization, more preferably cyclic olefin obtained by addition polymerization. It is.

(Cyclic olefin)
The cyclic olefin is preferably polymerized from a norbornene compound. This polymerization can be carried out by either ring-opening polymerization or addition polymerization. Examples of the addition polymerization include those described in Japanese Patent No. 3517471, Japanese Patent No. 3559360, Japanese Patent No. 3867178, Japanese Patent No. 3817721, Japanese Patent No. 3907908, Japanese Patent No. 3945598, Japanese Patent Publication No. 2005-527696, Japanese Patent Laid-Open No. 2006-2006. No. 28993 and International Publication No. 2006/004376 pamphlet. Particularly preferred is the one described in Japanese Patent No. 3517471.

  As the ring-opening polymerization, WO 98/14499 pamphlet, Japanese Patent No. 30605532, Japanese Patent No. 3320478, Japanese Patent No. 3273046, Japanese Patent No. 3404027, Japanese Patent No. 3428176, Japanese Patent No. 3687231, Japanese Patent No. 3873934, Patent No. 3912159 is mentioned. Among them, those described in WO98 / 14499 pamphlet and Japanese Patent No. 30605532 are preferable.

  Of these cyclic olefins, those of addition polymerization are more preferred.

(Lactone ring-containing polymer)
The thing which has the lactone ring structure represented by the following (general formula 1) is pointed out.

In (General Formula 1), R ¹ , R ² , and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The content ratio of the lactone ring structure of (General Formula 1) is preferably 5 to 90% by weight, more preferably 10 to 70% by weight, and still more preferably 10 to 50% by weight.

  In addition to the lactone ring structure represented by (General Formula 1), at least selected from (meth) acrylic acid esters, hydroxyl group-containing monomers, unsaturated carboxylic acids, and monomers represented by the following (General Formula 2). A polymer structural unit (repeating structural unit) constructed by polymerizing one kind is preferred.

In (General Formula 2), R ⁴ represents a hydrogen atom or a methyl group, X is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an —OAc group, a —CN group, a —CO—R ⁵ group, or an ^{-C-O-R 6} group, Ac group represents an acetyl group, ^{R 5} and ^{R 6} represents a hydrogen atom or an organic residue having 1 to 20 carbon atoms.

  For example, those described in International Publication No. 2006/025445, JP 2007-70607 A, JP 2007-63541 A, JP 2006-171464 A, and JP 2005-162835 A can be used. .

2 Offline Stretching Equipment 3 Film 3a Predecessor Film 3b Subsequent Film 3w Gripping Area 4 Film Storage Room 6 Tenter Part 11 Joint Part 53 Ultrasonic Joining Device 54 Base 60 Overlapping Part 60y Welding Area 60z Unwelded Area

Claims (2)

The rear end in the longitudinal direction of the preceding first polymer web and the front end in the longitudinal direction of the subsequent second polymer web are overlapped, and the overlapping portion of the rear end and the front end belongs to both ends in the width direction of the overlapping portion. It is divided into one area and a second area belonging to substantially the center in the width direction of the overlapping portion, and at least a part of the second area is welded at a plurality of locations, and the first area is not welded or the first area A step of joining the first polymer web and the second polymer web to form a series of joined webs by welding at least a part of the first polymer web to a lower degree as compared with welding in the second area When,
Using a pair of gripping members that grip both ends of the bonded web in the width direction, and extending the bonded web in the width direction ,
The first area is an area including a gripping region gripped by the pair of gripping members and a region within a range from 0.05 times to 0.25 times W in the width direction from the gripping region. ,
The second area is an area in which the length in the width direction is in the range of 0.5 to 0.9 times the width W in the width direction of the overlapping portion . Stretching method. A method for producing a polymer film, wherein the method for stretching a polymer web according to claim 1 is used.

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