JP2017144693A - Flow casting apparatus and solution film formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow casting apparatus and a solution film formation method for further suppressing an accompanying wind and producing an optical film having more uniform thickness.SOLUTION: The flow casting apparatus includes a casting belt 22, a die 19, a box-like wind shielding box 20, and a suction mechanism 21. The die 19 allows a dope to flow out from a slit-like exit 40. The wind shielding box 20 is disposed upstream the die 19 in a traveling direction X of the casting belt 22, and blocks an accompanying wind. The suction mechanism 21 sucks gas inside the wind shielding box 20. The wind shielding box 20 has a counter plate 45 opposing to the casting belt 22; and the counter plate 45 extends along the traveling direction X. In the counter plate 45, a second opening 47 extending in a longitudinal direction of the exit 40 is formed at a downstream end in the traveling direction X and each at one end and the other end in the longitudinal direction of the exit 40.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a casting apparatus and a solution casting method.

  A solution casting method is known as a method for producing an optical film such as a protective film for a polarizing plate. In the solution casting method, a casting film is formed on a support by flowing out from a die toward a support that travels a dope in which a solvent is dissolved in a solvent, and the casting film is peeled off from the support and dried. It is the manufacturing method of the film to do. The exit of the die from which the dope comes out is formed in a slit shape, so that a film of dope called a bead is formed over the support from the exit of the die.

  When the bead vibrates and is unstable, the resulting film has uneven thickness, that is, uneven thickness. As what causes such bead instability, there is a so-called accompanying wind that flows along the traveling direction of the support. In order to suppress the influence of the accompanying wind on the bead, there is a method in which the upstream side of the die in the traveling direction of the support is decompressed by a decompression chamber, and this method has a certain effect. However, in reality, the thinner the film to be produced and the higher the production speed, the more difficult it is to control the bead using the vacuum chamber.

  Therefore, for example, Patent Document 1 and Patent Document 2 are provided with a wind shielding member that blocks the accompanying wind at a position upstream of the die in the traveling direction of the support and in the vicinity of the die. In Patent Document 1, a small amount of accompanying air that was not blocked on the upstream surface of the wind shielding member was guided to the upstream surface of the die, and the guided accompanying wind was formed between the die and the wind shielding member. A method is described for feeding to the top of the die via a suction passage. Further, Patent Document 1 also describes a method in which a porous layer or a suction groove is formed on the surface of the windshield member facing the support, and the above-mentioned trace of accompanying air is guided to them. The method described in Patent Document 1 is excellent in terms of suppressing the influence of the accompanying wind on the bead.

  In addition, the windshield member of Patent Document 2 has an opening formed on the facing surface facing the die. This opening is the entire width direction of the wind shielding member. In the windshield member, a partition plate that partitions into a plurality of regions in the width direction is provided, and gas is sucked in a specific region of the side section partitioned by the partition plate. In recent years, with the further thinning of displays, it has been desired that the optical film used suppresses a slight thickness unevenness that has not been regarded as a problem in the past. The methods described in Patent Documents 1 and 2 are excellent in that the generation of a slight thickness unevenness due to the influence of the accompanying wind is suppressed.

Japanese Patent Application Laid-Open No. 2015-066742 JP2015-168062A

  However, when the difference between the maximum value and the minimum value of the thickness is very small, there is one that appears at a substantially constant pitch in the longitudinal direction of the film. Thus, the thickness unevenness having periodicity tends to appear when the bead is formed thin in order to manufacture the optical film thinner.

  Then, an object of this invention is to provide the casting apparatus and solution casting method which manufacture an optical film with more uniform thickness.

  The casting apparatus of the present invention includes a traveling support, a die, a wind shielding box, and a suction mechanism. The die flows out of the dope from the slit-shaped outlet toward the support. The wind-shielding box is formed in a box shape, and is disposed upstream of (i) in the travel direction of the support, and blocks the accompanying wind that flows along with the travel of the support. The suction mechanism sucks the gas inside the wind shielding box. The wind shielding box has a counter plate that faces the support and extends along the traveling direction of the support. The counter plate is formed with an opening extending in the longitudinal direction of the outlet at the downstream end in the running direction of the support and at one end and the other end in the longitudinal direction of the outlet.

  In the width direction orthogonal to the running direction of the support, the edge of the wind shielding box is preferably outside the edge of the outlet. The outer edge of the opening is in the range of 40 mm or more and 100 mm or less from the edge of the outlet, and the inner edge of the opening is in the range of 140 mm or more and 450 mm or less from the edge of the outlet. It is preferable to be within.

  The length in the longitudinal direction of the opening is preferably in the range of 5% to 25% of the length in the longitudinal direction of the die outlet. The length of the opening in the short direction is preferably in the range of 5 mm to 80 mm.

  Of the intermediate between the windshield box and the bead formed over the support from the die outlet, when the pressure at the center in the width direction of the support is PC, the suction mechanism draws the gas inside the windshield box. It is preferable that the differential pressure determined by PC-atmospheric pressure be within a range of -40 Pa to 0 Pa by suction.

  It is preferable that the wind shielding box is opposed to the die with a gap, and the casting apparatus includes an extending member. The extending member extends along the longitudinal direction of the die outlet, and closes the end of the gap on the support side.

  The solution casting method of the present invention includes a step of forming a casting film made of a dope on a support using the above casting apparatus, a step of forming a film by peeling the casting film from the support, and Drying the film.

  Among the intermediate between the wind shielding box and the bead formed from the die outlet to the support, the PC, which is the pressure at the center in the width direction of the support, is in the range of −40 Pa to 0 Pa, and the bead and die PS, which is the pressure between the openings, is in the range of −300 Pa to −10 Pa, and PC-PS is preferably in the range of 5 Pa to 250 Pa.

  According to the present invention, an entrained wind is more reliably suppressed and an optical film having a more uniform thickness can be obtained.

It is the schematic of the solution casting apparatus which implemented this invention. It is a partial cross section schematic diagram of a casting die and a wind shielding box. It is a perspective view of a windshield box. It is explanatory drawing of the opposing board of a windshield box.

  In FIG. 1, a solution casting apparatus 10 embodying the present invention is for continuously producing an optical film (hereinafter simply referred to as “film”) 11. The thickness of the film 11 to be manufactured is 30 μm or 60 μm in the present embodiment, but is not particularly limited, and is in the range of 10 μm or more and 70 μm or less. In each of the embodiments shown below, as the thickness of the film 11 is thinner, the effect of suppressing the thickness unevenness and the effect of suppressing the accompanying wind are more remarkable. For example, when the film 11 in the range of 10 μm to 50 μm is manufactured. Has been confirmed to be particularly effective compared to the prior art.

  The solution casting apparatus 10 includes a casting device 12, a clip tenter 13, a drying chamber 15, a cooling chamber 16, and a winding chamber 17 in order from the upstream side. In addition, in this example, although the film 11 used as a protective film of the polarizing plate of a liquid crystal display is manufactured, it is not restricted to this, For example, the film used as a phase difference film which has a protective function of a polarizing plate, or a low moisture-permeable film Can be manufactured.

  The casting apparatus 12 is for forming a film 11 containing a solvent from a dope 18 which is a polymer solution in which a polymer is dissolved in a solvent. In this example, the polymer of the dope 18 is cellulose triacetate (hereinafter referred to as TAC), and the solvent is a mixture of dichloromethane and methanol. However, the polymer of the dope 18 and the solvent are not limited to this. Other examples of the polymer include cellulose acylate different from TAC, polymethyl methacrylate (PMMA), and the like. Examples of cellulose acylate different from TAC include cellulose diacetate and cellulose acetate propionate. Other examples of the solvent include methanol, butanol, acetone, chloroform, and the like. These substances may be used alone or in combination, depending on the type of polymer used. Can be decided.

  The casting apparatus 12 includes a die 19, a wind shielding box 20, a suction mechanism 21, a casting belt 22, rotating rollers 23 and 24, and a peeling roller 25 that peels the casting film 33 from the casting belt 22. And a temperature controller 26 and blowers 27a and 27b.

  The die 19 forms the flow of the dope 18 in a film shape while guiding the supplied dope 18 inside, and flows out. The casting belt 22 supports the dope 18 flowing out from the die 19 and forms a casting film 33.

  A casting belt 22 as a support formed in an annular shape is stretched around the rotating rollers 23 and 24. The rotating rollers 23 and 24 have rotating shafts 23a and 24a, and the rotating shafts 23a and 24a rotate in the circumferential direction by being rotated by a driving device (not shown). With this rotation, the casting belt 22 continuously runs in the longitudinal direction. The die 19 is provided on the rotating roller 23 in the present embodiment, but may be provided on the casting belt 22 from the rotating roller 23 toward the rotating roller 24. As the dope 18 continuously flows out of the die 19 toward the traveling belt 22 that travels, a casting film 33 is formed on the casting belt 22. The dope 18 flowing out from the outlet 40 of the die 19 is applied to the casting belt 22 to form a film-like bead 18a (see FIG. 2). In this example, the casting belt 22 is used as a support that is stretched around the rotation rollers 23 and 24 and travels by the rotation of the rotation rollers 23 and 24. However, the present invention is not limited to this, and a casting drum (not shown) is used. May be used.

  The casting belt 22 has a running speed in the range of 25 m / min to 80 m / min, and thus the production speed of the film 11 is in the range of 25 m / min to 80 m / min. In this embodiment, the running speed of the casting belt 22 and the production speed of the film 11 are set to 60 m / min.

  The temperature controller 26 is for setting the temperature of the belt surface of the casting belt 22 that supports the casting film 33 to a predetermined value. The temperature controller 26 is attached to the rotating rollers 23 and 24 and includes a temperature adjusting unit (not shown) that adjusts the temperature of the heat transfer medium. The temperature adjusting unit and the rotating rollers 23 and 24 are provided inside the casting film 33. A heat transfer medium adjusted to a desired temperature is circulated between the flow path provided in the pipe. By the circulation of the heat transfer medium, the temperature of the casting belt 22 is adjusted via the rotating rollers 23 and 24.

  The blowers 27 a and 27 b are for drying the casting film 33. The blowers 27 a and 27 b are provided downstream of the die 19 in the traveling direction of the casting belt 22. The traveling direction of the casting belt 22 (hereinafter simply referred to as “traveling direction”) is indicated by an arrow X in the drawing. In the present embodiment, the blowers 27a and 27b are configured to send dry air toward the casting film 33 that passes therethrough. However, the blowers 27a and 27b are not limited thereto, and for example, dry air is applied onto the casting film 33 in the traveling direction X. May be provided.

  An airflow is generated on the casting belt 22 along with the traveling. The wind shielding box 20 for blocking the accompanying wind, which is the air flow, is disposed upstream of the die 19 in the traveling direction X. The wind shielding box 20 is a wind shielding member formed in a hollow box shape. Therefore, the wind shielding box 20 is configured to partition the space on the upstream side of the die 19 in the traveling direction X and in the vicinity of the casting belt 22 from the external space. The suction mechanism 21 is connected to the wind shielding box 20 and sucks the gas inside the wind shielding box 20.

  The stripping roller 25 is arranged with its rotation axis parallel to the rotation shaft 23 a of the rotation roller 23. In this example, the peeling roller 25 is disposed on the side opposite to the casting belt 22 with respect to the conveyance path of the film 11, and the film 11 is wound around the circumferential surface. The stripping roller 25 rotates following the conveyance of the film 11. With the film 11 wound around the stripping roller 25, the film 11 is pulled toward the downstream side of the solution casting equipment 10, whereby the casting film 33 is peeled off from the casting belt 22 at a predetermined stripping position. Note that the peeling roller 25 may be rotated in synchronization with the conveyance of the film 11 by a motor.

  A plurality of rollers 28 are arranged on the conveyance path from the casting device 12 to the clip tenter 13, and these rollers 28 guide the film 11 to the clip tenter 13. A blower (not shown) may be provided in the vicinity of the conveyance path of the film 11 set by the plurality of rollers 28. This blower applies air to the film 11 in a state containing a solvent and proceeds to dry the film 11.

  The clip tenter 13 is a stretching device that stretches the film 11 in the width direction, and includes a plurality of clips 29 as holding members that hold the side ends of the film 11. Note that the holding member may be a pin plate having a plurality of pins on a table. The plurality of clips 29 are attached to a chain (not shown) formed in an annular shape at a predetermined interval. The chain is movably attached along a rail (not shown), and the clip 29 circulates along the rail as the chain moves. The clip 29 starts holding the guided film 11 in the vicinity of the inlet of the clip tenter 13, moves toward the outlet, and releases the holding in the vicinity of the outlet. The clip 29 released from the holding moves again to the vicinity of the entrance and holds the newly guided film 11. The clip tenter 13 extends in the width direction while transporting the film 11 in the longitudinal direction by moving the clip 29 in the longitudinal direction and the width direction of the film 11. The clip tenter 13 is provided with a blowing device 30, and drying air is sent from the blowing device 30 to the film 11 being conveyed.

  An ear clip device 31 may be provided downstream of the clip tenter 13 as in the present embodiment. The edge-cutting device 31 cuts off both end portions in the width direction of the film 11. The separated both end portions are sent to the crusher 32 by air blowing, crushed by the crusher 32, and reused as a raw material such as a dope.

  The drying chamber 15 is for further drying while conveying the film 11. A large number of rollers 34 are provided in the drying chamber 15, and the film 11 is conveyed while being wound around each of the rollers 34. The temperature and humidity of the atmosphere in the drying chamber 15 are adjusted by an air conditioner (not shown).

  The cooling chamber 16 is provided downstream of the drying chamber 15 and is for cooling the film 11 to, for example, room temperature. In the cooling chamber 16, the temperature and humidity of the atmosphere are adjusted by an air conditioner (not shown).

  In the present embodiment, a knurling roller 35 is provided downstream of the cooling chamber 16. The knurling roller 35 applies knurling composed of a large number of irregularities to both end portions of the film 11. The winding chamber 17 includes a winding machine 36, and the winding machine 36 has a press roller 38. A winding core 37 for winding the film 11 is set in the winding machine 36, and the winding core 37 is rotated in the circumferential direction by a drive unit (not shown) to hold the film 11 on the winding core 37 while being pressed by the press roller 38. Wind up.

  As shown in FIG. 2, the wind shielding box 20 faces the die 19 with a gap. In addition, according to the kind of film 11 to manufacture, the distance of the exit 40 which takes out the dope 18 of the die | dye 19, and the casting belt 22 is set. The outlet 40 is formed in a slit shape extending in the depth direction of FIG. 2, and the die 19 is provided so that the longitudinal direction of the outlet 40 coincides with the width direction of the casting belt 22. The die 19 and the wind-shielding box 20 are each formed of metal, and the dimensions thereof change slightly depending on the temperature. Therefore, the gap CL, that is, the distance between the die 19 and the wind shielding box 20 is set so that the die 19 and the wind shielding box 20 do not come into contact with each other even if the dimensions of the die 19 and the wind shielding box 20 change. The For example, the gap CL is set within a range of 0.5 mm or more and 5.0 mm or less, and is 1.0 mm in this embodiment.

  An extending member 41 projects from the facing surface 20 s of the wind shielding box 20 facing the die 19. The extending member 41 is a closing member that closes an end of the gap CL (see FIG. 1) on the casting belt 22 side. As shown in FIG. 3, the extending member 41 extends along the width direction Y of the casting belt 22. As described above, the width direction of the casting belt 22 and the longitudinal direction of the outlet 40 coincide with each other. Therefore, in the following description, the longitudinal direction of the outlet 40 is also denoted by the symbol Y. The extending member 41 is for suppressing the atmospheric pressure wave having a very small wavelength generated in the air in the gap CL from being transmitted to the bead 18a. In the figure, Z is the vertical direction, and the longitudinal direction Y of the outlet 40 is orthogonal to the vertical direction Z. The extending member 41 is provided at the end of the facing surface 20s on the casting belt 22 side, that is, the lower end of the facing surface 20s in the vertical direction Z in FIGS. The extending member 41 closes the end of the gap CL on the casting belt 22 side. However, the extending member is not limited to this example, and the extending member 41 may close the entire gap CL. .

  Since the die 19 and the wind shielding box 20 are long in the longitudinal direction Y of the outlet 40 and are formed of metal, the die 19 and the shielding box 20 are shielded in order to close the gap CL over the entire area of the outlet 40 in the longitudinal direction Y. It is preferable that the wind box 20 is pressed and arranged with the extending member 41 interposed therebetween. Furthermore, the extending member 41 is preferably formed of a soft material. For example, a material whose elastic modulus is lower than that of the metal constituting the die 19 and the wind shielding box 20 is preferable, and examples of such a material include a fluorine-based polymer. Examples of the fluorine-based polymer include polytetrafluoroethylene. In this embodiment, polytetrafluoroethylene is also used. In addition, the raw material of the extending member 41 shall not melt | dissolve in the liquid used for the dope 18 as a solvent.

  The wind shielding box 20 includes a top plate 44 that partitions the upper external space in FIG. 2 and the internal space of the wind shielding box 20, and a counter plate 45 that faces the casting belt 22 in close proximity. The counter plate 45 extends along the traveling direction X. For this reason, the distance between the wind shielding box 20 and the casting belt 22 is substantially constant in the traveling direction X.

  A first opening 46 is formed in the top plate 44, and a second opening 47 is formed in the counter plate 45. The suction mechanism 21 is connected to the wind shielding box 20 at the first opening 46, and sucks the gas inside the wind shielding box 20 from the first opening 46. Thereby, the gas between the opposing plate 45 and the casting belt 22 flows in from the second opening 47 and is sucked into the suction mechanism 21 as the internal gas of the wind shielding box 20.

  Here, out of the pressure between the wind shielding box 20 and the bead 18a, the pressure at the center in the width direction Y of the casting belt 22 is defined as the center pressure PC. By sucking the gas inside the wind shielding box 20 using the suction mechanism 21, the PC-atmospheric pressure, which is the difference obtained by subtracting the atmospheric pressure from the central pressure PC, can be set within the range of -40 Pa to 0 Pa. Preferably, it is in the range of −25 Pa to 0 Pa, more preferably in the range of −15 Pa to 0 Pa. In this embodiment, it is set to -30 Pa or -100 Pa.

  The second opening 47 is formed at the downstream end of the facing plate 45 in the traveling direction X. As shown in FIG. 4, the second openings 47 are formed in the opposing plate 45 on one end side and the other end side in the longitudinal direction Y of the outlet 40. In addition, the windbreak box 20 shown in FIG. The second opening 47 is formed in, for example, a rectangle extending in the longitudinal direction Y of the outlet 40.

  The edge 20eL, 20eR of the wind shielding box 20 is preferably outside the edge 40, EL, ER of the outlet 40 in the width direction Y of the casting belt 22, and this is also the case in this embodiment. That is, the left edge 20eL of the windshield box 20 in FIG. 4 is outside the left edge EL of the outlet 40, and the right edge 20eR of the windshield box 20 is from the right edge ER of the outlet 40. Is also outside. As described above, the length of the wind shielding box 20 in the longitudinal direction Y of the outlet 40 is larger than the length of the outlet 40 in the longitudinal direction Y.

  The outer edge 47 о of each second opening 47 is preferably within the range of 40 mm or more and 100 mm or less on the inner side in the width direction Y of the casting belt 22 from the edges EL and ER of the outlet 40. That is, in the width direction Y of the casting belt 22, the edge 47o of the left second opening 47 in FIG. 4 is inside the edge EL, and the edge 47o of the right second opening 47 is inside the edge ER. It is preferable that the distance D1 between the edge 47o and the edges EL and ER is in the range of 40 mm to 100 mm. In the present embodiment, the distance D1 is 90 mm. The distance D1 is more preferably in the range of 50 mm to 95 mm, and still more preferably in the range of 60 mm to 90 mm.

  The inner edge 47 i of each second opening 47 is preferably within a range of 140 mm or more and 450 mm or less on the inner side in the width direction Y of the casting belt 22 from the edges EL and ER of the outlet 40. That is, in the width direction Y of the casting belt 22, the edge 47i of the left second opening 47 in FIG. 4 is inside the edge EL, and the edge 47i of the right second opening 47 is inside the edge ER. It is preferable that the distance D2 between the edge 47i and the edges EL and ER is in the range of 140 mm to 450 mm. In the present embodiment, the distance D2 is 300 mm. The distance D2 is more preferably in the range of 170 mm or more and 410 mm or less, and further preferably in the range of 200 mm or more and 300 mm or less.

  Here, the length of the second opening 47 in the longitudinal direction is L1, and the length in the short direction, which is the length in the traveling direction Y, is L2. The length of the outlet 40 in the longitudinal direction Y is L3. The length L1 is preferably in the range of 5% to 25% of the length L3. That is, (L1 / L3) × 100 is preferably in the range of 5 to 25. In the present embodiment, the length L1 is 14% of the length L3. The length L1 is more preferably in the range of 9% to 22% of the length L3, and further preferably in the range of 14% to 20%.

  The length L2 is preferably within a range of 5 mm or more and 80 mm or less, and is 20 mm in the present embodiment. The length L2 is more preferably in the range of 5 mm to 60 mm, and still more preferably in the range of 5 mm to 45 mm.

  Here, an intermediate pressure between the bead 18a and the second opening 47 among the intermediate pressure between the wind shielding box 20 and the bead 18a is defined as a side pressure PS. The central PC is in the range of −40 Pa to 0 Pa, the side pressure PS is in the range of −300 Pa to −10 Pa, and the difference PC-PS obtained by subtracting the side pressure PS from the central pressure PC is 5 Pa. It is preferably within the range of 250 Pa or less. The second openings 47 extending in the longitudinal direction Y of the outlet 40 are formed at the downstream end in the traveling direction X of the counter plate 45 and at one end side and the other end side in the longitudinal direction Y of the outlet 40. The central part pressure PC, the side part pressure PS, and the difference PC-PS are within the above ranges, respectively, and in this embodiment, are also within the above ranges. Specifically, in this embodiment, the center pressure PC is −30 Pa, the side pressure PS is −100 Pa, and the difference PC-PS is 70 Pa. The bead 18a is further stabilized when the center pressure PC, the side pressure PS, and the difference PC-PS are within the above ranges, respectively. The central portion PC is more preferably in the range of −25 Pa to 0 Pa, and further preferably in the range of −15 Pa to 0 Pa. The side pressure PS is more preferably in the range of −250 Pa to −10 Pa, and still more preferably in the range of −200 Pa to −10 Pa. The difference PC-PS is more preferably in the range of 5 Pa to 210 Pa, and still more preferably in the range of 5 Pa to 190 Pa.

  The operation of the above configuration will be described. The dope 18 is continuously supplied to the die 19 by a pump (not shown). Inside the die 19, while the dope 18 is guided toward the outlet 40, the width of the flow is continuously increased to form a film, and the die 19 continuously flows out from the outlet 40. The dope 18 flows out toward the traveling casting belt 22, whereby a casting film 33 is formed on the casting belt 22. A bead 18 a is formed between the outlet 1 and the casting belt 22.

  The wind shielding box 20 is provided close to the casting belt 22, and the edges 20 eL and 20 eL of the wind shielding box 20 are located in the width direction Y of the casting belt 22 rather than the edges EL and ER of the outlet 40. Since it is outside, the accompanying wind that flows along with the running of the casting belt 22 is blocked by the upstream surface of the wind-shielding box 20 in the running direction X. As a result, the vibration of the bead 18a due to the accompanying wind is suppressed, and the film 11 in which the uneven thickness due to the accompanying wind is suppressed is obtained.

  Since the casting apparatus 12 includes the suction mechanism 21 and the second opening is formed in the opposing plate 45 of the wind shielding box 20, a small part of the accompanying wind is between the casting belt 22 and the opposing plate 45. Even if it flows into the air, it is guided to the suction mechanism 21 through the wind shielding box 20. Thereby, the influence of the accompanying wind with respect to the bead 18a is suppressed. As a result, the film 11 can suppress uneven thickness due to the accompanying wind. Since the second opening 47 is formed at the downstream end of the facing plate 45 in the traveling direction X, the accompanying wind newly generated as the casting belt 22 travels between the casting belt 22 and the facing plate 45. And the suction mechanism 21 is surely guided. As a result, it is possible to obtain the film 11 in which the uneven thickness due to the accompanying wind is reliably suppressed and the uneven thickness is also suppressed.

  By sucking the gas inside the wind shielding box 20 using the suction mechanism 21, the differential pressure obtained by PC-atmospheric pressure is set to -40 Pa or more, so that the bead 18a is sandwiched as compared with the case of making it less than -40Pa. However, the pressure difference between the upstream region and the downstream region increases, and the length of the bead 18a is expressed by the distance from the outlet 40 to the landing point of the casting belt 22 when the bead 18a is excessively drawn to the upstream side. Is suppressed from being shortened. When the length of the bead 18a is relatively long, the effect of absorbing the surrounding vibration received by the bead 18a is increased, and uneven thickness is suppressed. Since the differential pressure obtained by PC-atmospheric pressure is set to 0 Pa or less, the effect of removing the accompanying air by suction is greater than that when the pressure is greater than 0 Pa, and the effect of suppressing the vibration of the bead 18a by the accompanying air is increased. In other words, if the suction is not performed, the central pressure PC becomes greater than 0 due to the inflow of the accompanying air. If the central pressure PC is greater than 0 Pa even if the suction is performed, the accompanying air is not sufficiently sucked and the accompanying air is not It means that the wind remains.

  Since the second opening 47 is formed on each of one end side and the other end side in the longitudinal direction Y of the outlet 40, and the second opening 47 extends in the longitudinal direction Y of the outlet 40, the center in the longitudinal direction of the outlet 40 One end side and the other end side of the part suck the accompanying air into the wind shielding box 20 with a stronger suction force. Thereby, the bead 18 a is formed in a mode along the longitudinal direction Y of the outlet 40.

  Since the second opening 47 extends in the longitudinal direction Y of the outlet 40, and the length in the traveling direction X is in the range of 5 mm or more and 80 mm or less, the area is thus suppressed to be small, It is easy to adjust the pressure in the upstream region of the bead 18a in the traveling direction X more precisely. For this reason, since the bead 18a becomes more stable, the film 11 can be more reliably obtained with a uniform thickness.

  Since each of the second openings 47 has an edge 47 о of 40 mm or more on the inner side in the width direction Y of the casting belt 22 from the edges EL and ER, the edge of the wind shielding box 20 is smaller than the case of less than 40 mm. Airflow flowing into the gap between the casting belt 22 and the counter plate 45 from the 20eL and 20eR toward the center in the width direction Y is suppressed. For this reason, the vibration of the end portion of the bead 18a in the width direction Y is more reliably suppressed by winds other than the accompanying wind. Further, the accompanying air rectified from the central portion in the width direction Y toward both ends by suction flows into the wind shielding box 20 from the second opening 47 without disturbing the flow. Further, since the edge 47о is not more than 100 mm on the inner side in the width direction Y of the casting belt 22 from the edge EL, ER, the accompanying air is suppressed on the upstream side of the bead 18a as compared with the case where it is larger than 100 mm. Precise control becomes possible more reliably to the end part of the bead 18a in the width direction Y. Each of the second openings 47 has an inner edge 47i that is not less than 140 mm on the inner side in the width direction Y of the casting belt 22 from the edges EL and ER. A sufficient area is ensured, so that suction leakage of the accompanying air is more reliably suppressed. Moreover, it is more reliably suppressed that the differential pressure between the upstream region and the downstream region of the bead 18a becomes too large due to excessive increase of the suction pressure for the purpose of preventing the accompanying air suction leakage. Further, since the edge 47i is set to 450 mm or less on the inner side in the width direction Y of the casting belt 22 from the edges EL and ER, the wind shielding box 20 and the casting belt 22 are compared with the case where the edge is larger than 450 mm. In the meantime, the accompanying wind flowing in from the upstream side in the traveling direction X is more reliably rectified from the central portion in the width direction Y to both ends and guided to the second opening 47. Thereby, in suppressing the influence of the accompanying wind on the bead 18a in the center portion in the width direction Y, the effect of rectifying the accompanying wind from the center portion to both ends is further improved.

  Since the length L1 is 5% or more of the length L3, compared with the case where the length L1 is less than 5%, the accompanying air is more reliably sucked over the entire area of the bead 18a in the width direction Y, and thereby the accompanying wind bead The influence on 18a is further suppressed. That is, when it is less than 5%, there is a possibility that a portion where the effect of removing the accompanying wind cannot be obtained in the width direction of the bead. Since the length L1 is 25% or less of the length L3, the entrained wind flowing from the upstream side in the traveling direction X between the wind shielding box 20 and the casting belt 22 is larger than the case where the length L1 is larger than 25%. The flow is more reliably rectified from the center portion in the width direction Y to both ends and guided to the second opening 47. Thereby, in suppressing the influence of the accompanying wind on the bead 18a in the center portion in the width direction Y, the effect of rectifying the accompanying wind from the center portion to both ends is further improved.

  Since length L2 is 5 mm or more, compared with the case where it is less than 5 mm, the area of the 2nd opening 47 is fully ensured, For this reason, the suction leak of an accompanying wind is suppressed more reliably. Moreover, it is more reliably suppressed that the differential pressure between the upstream region and the downstream region of the bead 18a becomes too large due to excessive increase of the suction pressure for the purpose of preventing the accompanying air suction leakage. Since the length L2 is 80 mm or less, the differential pressure between the upstream region and the downstream region, which has a small influence on the bead 18a, is more reliably maintained as compared with the case where the length L2 is greater than 80 mm.

  The central PC is in the range of −40 Pa to 0 Pa, the side pressure PS is in the range of −300 Pa to −10 Pa, and the difference PC-PS obtained by subtracting the side pressure PS from the central pressure PC is 5 Pa. Since it is in the range of 250 Pa or less, the bead 18 a is further stabilized, and as a result, the film 11 having a more uniform thickness can be obtained more reliably.

  Mechanical vibrations are generated during the operation of each device such as the drive system and the air blowing system of the solution casting apparatus 10, and these mechanical vibrations are amplified or resonated in the air in the gap CL. A very small wave pressure wave (hereinafter referred to as a micro-pressure wave) generated in the gap CL due to such amplification or resonance is more reliably transmitted to the bead 18a because the extending member 41 is provided. The vibration of the bead 18a and the change in the thickness of the bead 18a are more reliably suppressed. Thereby, the film 11 with a more uniform thickness is obtained. In addition, it is thought that the function of the extending member 41 which suppresses that a micro atmospheric pressure wave is transmitted to the bead 18a is both the attenuation function which attenuates a micro atmospheric wave, and the interruption | blocking function which interrupts | blocks.

  The extending member 41 is made of a material having a lower elastic modulus than that of the metal constituting the die 19 and the wind shielding box 20, for example, polytetrafluoroethylene in the present embodiment. When the die 19 and the wind shielding box 20 are pressed in the state, the gap CL is more reliably closed by the extending member 41 over the longitudinal direction Y of the outlet 40. As a result, the transmission of the micro-pressure wave to the bead 18a is more reliably suppressed, and the vibration of the bead 18a and the change in the thickness of the bead 18a are more reliably suppressed. Thereby, the film 11 with a more uniform thickness can be obtained more reliably.

  On the casting belt 22, the casting film 33 is dried by the drying air from the blowers 27 a and 27 b and gels before being peeled off. The stripping roller 25 continuously strips the casting film 33 that has been gelled to the extent that it can be transported from the casting belt 22 to form the belt-like film 11. The solvent content of the cast film 33 at the time of peeling is preferably in the range of 20% by mass to 250% by mass. In the present specification, the solvent content (unit:%) is a value based on the dry weight. Specifically, when the mass of the solvent is MS and the mass of the casting film 33 or the film 11 is MF, The percentage obtained by {MS / (MF-MS)} × 100.

  While being guided to the clip tenter 13, the film 11 is blown by a wind blower (not shown) to be dried. The temperature of the wind is preferably 20 ° C. or higher and 250 ° C. or lower. The film 11 is recommended to be dried while being transported in the clip tenter 13. During this drying, it is stretched and widened. The width may be reduced after stretching. Such a rate of change of the width is determined in accordance with a target optical characteristic, for example.

  The film 11 sent out from the clip tenter 13 is sent to the drying chamber 15 after the side end portion of the clip tenter 13 having a grip mark is cut off by the ear-cutting device 31. The drying chamber 15 sends the film 11 downstream while supporting the film 11 with the roller 34. The film 11 is further dried by passing through the drying chamber 15 in which the temperature and humidity of the atmosphere are adjusted. The film 11 is cooled to, for example, room temperature by passing through the cooling chamber 16.

  After the film 11 is cooled, knurling is applied to both side ends by a knurling roller 35. The film 11 provided with the knurling is wound up in a roll shape around the winding core 37 in the winding chamber 17.

  In this example, the self-supporting property is expressed in the casting film 33 by drying the solvent contained in the casting film 33, but the present invention is not limited to this. For example, the casting film 33 may exhibit self-supporting properties by cooling.

[Example 1] to [Example 3]
The film 11 was manufactured using the solution casting apparatus 10 shown in FIG. In each example, the differential pressure obtained from PC-atmospheric pressure was set to the value shown in the “Differential Pressure” column of Table 1. The thickness of the produced film 11 is shown in the “Thickness” column of Table 1.

About the uniformity of the thickness of the obtained film 11, and the entrainment failure of an accompanying wind, it evaluated with the following evaluation methods and evaluation criteria. In addition, about the uniformity of thickness, two of thickness fluctuation | variation and periodic thickness fluctuation | variation were evaluated as follows. Each evaluation result is shown in Table 1.
(1) Thickness uniformity (1-1) Thickness fluctuation About each film 11 wound up by the winder 36, the length of the central portion in the width direction is 1 mm or less over the length of 1 m or more in the longitudinal direction. The thickness was measured. A dot-type film thickness meter was used for the measurement. The difference between the maximum value and the minimum value of the measured thickness was defined as TS. Based on the following evaluation criteria, it evaluated as thickness fluctuation. A is acceptable and B and C are unacceptable.
A: TS is less than 0.3 μm.
B: TS is in the range of 0.3 μm or more and less than 0.7 μm.
C: TS is 0.7 μm or more.

(2-2) Periodic thickness fluctuation About each film 11, the thickness of the center part in the width direction was measured with the pitch of 1 mm or less over the length of 1 m or more in the longitudinal direction. A dot-type film thickness meter was used for the measurement. The difference between the maximum value and the minimum value of the measured thickness was defined as TS. Further, the obtained thickness measurement value was subjected to frequency analysis. In the frequency analysis, the frequencies are associated based on the running speed of the casting belt 22. By this analysis, a plurality of thickness values having frequencies in the range of 10 Hz to 80 Hz were specified. A plurality of vibrations having a thickness having a periodicity with a frequency in the range of 10 Hz to 80 Hz are specified. One of the plurality having the maximum thickness value was identified, and the thickness value TX was determined. And the value calculated | required by the calculation formula of TX / TSx100 was calculated | required as thickness change rate (a unit is%), and it evaluated as periodic thickness fluctuation | variation based on the following evaluation criteria.
A: The rate of change in thickness is 4% or less B: The rate of change in thickness is in the range of more than 4% and 8% or less.
C: The thickness change rate is in the range of 8% to 15%.
D: Thickness change rate is larger than 15%.

(2) Entrainment wind entrainment failure Photograph the casting belt 22, the bead 18a and the casting film 33 with a high-speed camera, and enlarge the photographed image to a range of 5 to 15 times and display it on the monitor. It was observed visually. It is confirmed whether or not air is caught between the casting belt 22 and the casting film 33 on the downstream side of the landing line where the bead 18a lands on the casting belt 22, and entrainment of the accompanying wind is performed according to the following evaluation criteria. Evaluated as a failure. The evaluation criteria are as follows.
Pass: Air was not caught.
Fail: Air was caught.

[Comparative Example 1] to [Comparative Example 8]
The windshield box 20 of Example 1 was replaced with another windshield box to produce a film, and Comparative Examples 1 to 7 were obtained. The windshield box 20 of Example 1 was removed to produce a film, and Comparative Example 8 was obtained. . In Comparative Example 1 and Comparative Example 2, a wind shielding box was used in which the counter plate 45 provided with the second opening 47 was replaced with a counter plate having a second opening formed in the entire area along the longitudinal direction of the outlet 40. In Comparative Examples 3 to 6, a wind shielding box without the facing plate 45 was used. In Comparative Example 7, a plate having no opening is provided as an opposing plate facing the casting belt 22, and a plate having an opening formed on the opposing surface 20 s facing the die 19 is provided as a die opposing plate facing the die 19. A wind box was used. The shape and size of the opening formed in the die facing plate of Comparative Example 7 was the same as in Example 1, and the openings were formed on one end side and the other end side in the longitudinal direction of the outlet 40 in the die facing plate, respectively. These two openings were formed at the end of the die facing plate on the casting belt 22 side, that is, the lower end in the vertical direction Z. In Comparative Example 8, since there is no target position for obtaining the central pressure PC because no wind shielding box is used, the PC-atmospheric pressure was not obtained. Describe.

  Using the same method and criteria as in the examples, the thickness uniformity of the obtained film and entrainment failure of the accompanying wind were evaluated. The results are shown in Table 1.

DESCRIPTION OF SYMBOLS 10 Solution casting apparatus 11 Film 12 Casting device 13 Clip tenter 15 Drying chamber 16 Cooling chamber 17 Winding chamber 18 Dope 18a Bead 19 Die 20 Wind shield box 20s Opposing surface 21 Suction mechanism 22 Casting belt 23, 24 Rotating roller 23a , 24a Rotating shaft 25 Peeling roller 26 Temperature controller 27a, 27b Blower 28 Roller 29 Clip 30 Blower 31 Trimming device 32 Crusher 33 Casting film 34 Roller 35 Knurling roller 36 Winder 37 Winding core 38 Press roller 40 Exit 41 Extension member 44 Top plate 45 Opposite plate 46 1st opening 47 2nd opening 47i Inner edge 47о Outer edge D1, D2 Distance EL, ER Edge L1-L3 Length

Claims (8)

A traveling support;
A die that flows out the dope from the slit-shaped outlet toward the support, and
A wind shielding box that is arranged upstream of the die in the running direction of the support and is formed in a box shape that blocks the accompanying wind that flows along with the running of the support;
A suction mechanism for sucking the gas inside the windshield box;
With
The wind-shielding box has an opposing plate facing the support and extending along the traveling direction,
The counter plate is a casting apparatus in which an opening extending in the longitudinal direction of the outlet is formed at each of a downstream end in the traveling direction and one end side and the other end side in the longitudinal direction of the outlet. In the width direction orthogonal to the traveling direction of the support,
The edge of the windbreak box is outside the edge of the outlet,
The outer edge of the opening is within the range of 40 mm or more and 100 mm or less from the edge of the outlet,
2. The casting apparatus according to claim 1, wherein an inner edge of the opening is within a range of 140 mm or more and 450 mm or less from an inner edge of the outlet.   The casting apparatus according to claim 1 or 2, wherein a length of the opening in the longitudinal direction is within a range of 5% to 25% of a length of the outlet in the longitudinal direction.   The casting apparatus according to any one of claims 1 to 3, wherein a length in a short direction of the opening is in a range of 5 mm to 80 mm. Among the intermediate between the wind shielding box and the bead formed across the support from the outlet, when the pressure of the central portion in the width direction of the support is PC,
5. The suction mechanism according to claim 1, wherein the suction mechanism sucks the gas inside the wind-shielding box so that a differential pressure obtained by PC-atmospheric pressure is in a range of −40 Pa to 0 Pa. 5. Casting equipment. The windshield box is opposed to the die with a gap,
The casting apparatus according to any one of claims 1 to 5, further comprising an extending member that extends along a longitudinal direction of the outlet and closes an end of the gap on the support side. Forming a casting film made of the dope on the support using the casting apparatus according to any one of claims 1 to 6;
Forming a film by peeling the cast film from the support;
A solution casting method comprising: drying the film. Among the intermediate between the wind shielding box and the bead formed from the outlet to the support, the PC, which is the pressure at the center in the width direction of the support, is in the range of −40 Pa to 0 Pa, and the bead PS between the opening and the opening is within a range of −300 Pa to −10 Pa,
PC-PS is in the range of 5 Pa or more and 250 Pa or less, The solution casting method of Claim 7.

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