JP2012030481A - Drying device and solution film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly dry a wide casting film.SOLUTION: The second drying unit for drying the casting film 30 has a box-shaped supply duct, vertical nozzle 32b for sending out a drying wind 402 and a suction duct 32c for sucking the drying wind 402. The supply duct is provided above the casting film 30. The vertical nozzle 32b is projected from the supply duct toward the casting film 30 in the lower surface of the supply duct. The suction duct 32c is provided in both sides in the B-direction of the vertical nozzle 32b arranged in the A-direction. A suction port 32cx for sucking the drying wind 402 is provided to the suction duct 32c. The suction port 32cx is disposed at a position apart from the casting film 30 more than a wind sending slit 32bx provided in the vertical nozzle 32b. A suction route for the drying wind is formed among a plurality of the vertical nozzles 32b.

Description

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

  Polymer films having light permeability (hereinafter referred to as films) are lightweight and easy to mold, and thus are widely used as optical films. Among them, cellulose ester films using cellulose acylate and the like are optical films (for example, retardation film and polarizing plate protection) which are constituent members of liquid crystal display devices whose market has been expanding in recent years, including photographic photosensitive films. Used in film, etc.).

  Such a film is manufactured by a solution casting method. The outline of the solution casting method is as follows. First, a polymer solution containing a polymer and a solvent (hereinafter referred to as a dope) is poured to form a cast film on the support. Secondly, the solvent is evaporated from the casting film until the casting film becomes self-supporting and transportable. Third, the cast film is peeled off from the support to form a wet film. Thereafter, the film can be obtained from the wet film by evaporating the solvent from the wet film.

  As a method for drying a cast film, a method of blowing dry air from above the cast film is known (for example, Patent Document 1). In the drying method described in Patent Document 1, a drying device 202 is provided above a casting film 201 conveyed by a casting band 200 as a support, as shown in FIG. The drying device 202 is provided with air blowing slits 202 a for sending the drying air 203 toward the casting film 201 and suction ports 202 b for sucking the drying air 203 alternately in the transport direction of the casting film 201. Using such a drying apparatus 202, the solvent contained in the casting film 201 is evaporated by applying the drying air 203 to the casting film 201.

JP 2007-290375 A

  In recent years, with the increase in demand for liquid crystal display devices and the increase in size of LCD display panels and the like, the production of wide optical films has become a new issue for optical film providers.

  When the method described in Patent Document 1 is used, it is necessary to lengthen the blow slit 202a and the suction port 202b in the width direction of the casting film in accordance with the widening of the casting film. However, by making the suction port 202b longer, it becomes difficult to make the suction amount of the drying air uniform in the width direction, so that the drying conditions vary in the width direction of the cast film. The optical film that has undergone the drying process under such conditions has optical characteristics (for example, Re, Rth) that vary in the width direction.

  This invention solves such a subject, and it aims at providing the drying apparatus which performs a drying process on a casting film on the conditions uniform in the width direction, and the solution film forming method which has this drying process. .

  The drying device of the present invention is provided with a duct disposed so as to face a belt-shaped cast film that contains a polymer and a solvent and is conveyed in the longitudinal direction, and is protruded from the duct toward the cast film. A nozzle arranged in the moving direction, and a blower slit that is formed so as to extend long in the width direction of the casting film at the tip of the nozzle, and sends dry gas from the duct to the casting film as dry air And a suction port that is located between the nozzles in the moving direction and located on both sides of the casting film in the width direction, and sucks the dry air sent from the blower slit, and the suction port The distance between the casting film and the casting film is larger than the distance between the blower slit and the casting film.

  It is preferable that the air blowing slits and the suction ports are alternately arranged from the upstream side to the downstream side in the moving direction. In addition, the suction port may be formed from the upstream side in the movement direction with respect to the one nozzle to the downstream side in the movement direction with respect to the one nozzle.

  The suction port preferably faces the casting band. The suction port may face the center side in the width direction.

  It is preferable that the residual solvent amount of the cast film to which the dry air hits is 150% by mass or more and 350% by mass or less. Moreover, it is preferable that the said duct is provided above the said casting film. Furthermore, the width of the cast film is preferably 600 mm or more and 2000 mm or less.

  In the solution casting method for obtaining a film by evaporating the solvent from a casting film containing a polymer and a solvent, the present invention faces the belt-shaped casting film conveyed in the longitudinal direction, and the casting film Using a blowing slit extending long in the width direction and arranged in the conveying direction, and having a supply step of sending dry air to the casting film, and a suction step of sucking the dry air, in the suction step, The distance from the casting film is further away from the blower slit, and the drying air is sucked from positions on both sides in the width direction than the casting film.

  According to the present invention, since the suction ports for sucking the drying air are provided at both ends in the width direction from the casting film, the drying air is sucked uniformly even when the width of the casting film is widened. be able to. Furthermore, since the distance between the suction port and the casting film is larger than the distance between the blower slit and the casting film, it is possible to suppress adverse effects caused by suction of the drying air. Therefore, according to the present invention, it is possible to manufacture an optical film in which variations in optical characteristics are suppressed.

It is explanatory drawing which shows the outline | summary of solution casting apparatus. It is a side view which shows the outline | summary of a 1st drying unit and a 2nd drying unit. It is a perspective view which shows the outline | summary of a 2nd drying unit. It is a perspective view which shows the outline | summary of a 2nd ventilation duct and a vertical nozzle. It is a VV line sectional view showing the outline of the 2nd drying unit. It is sectional drawing which shows the outline | summary of the front-end | tip of a vertical nozzle. It is a perspective view which shows the outline | summary in which a vertical nozzle sends out 2nd drying wind, and a suction duct suck | inhales 2nd drying wind. It is sectional drawing which shows the outline | summary of the suction sectional area provided between the vertical nozzles. It is sectional drawing which shows the outline | summary of the 2nd drying unit which has a 1st windshield. It is sectional drawing which shows the outline | summary of the 2nd drying unit which has a 2nd windshield. It is sectional drawing which shows the outline | summary of a 2nd suction duct. It is sectional drawing which shows the outline | summary of a 3rd suction duct. It is sectional drawing which shows the outline | summary of a 4th suction duct. It is a perspective view which shows the outline | summary of the conventional drying apparatus.

(Solution casting method)
As shown in FIG. 1, the solution casting apparatus 10 includes a casting chamber 12, a clip tenter 13, a drying chamber 15, a cooling chamber 16, and a winding chamber 17. In the casting chamber 12, a casting die 21, a casting band 22, rotating rollers 23a and 23b, and a peeling roller 24 are provided.

  The casting band 22 is formed by connecting both ends in the longitudinal direction of a band body formed in a band shape, and has an annular shape. The rotating rollers 23a and 23b that are rotatable about the shaft are arranged so that the axial direction is horizontal. An annular casting band 22 is wound around the rotating rollers 23a and 23b. When at least one of the rotating rollers 23a and 23b rotates by driving a motor (not shown), the casting band 22 wound around the rotating rollers 23a and 23b circulates in a predetermined direction (hereinafter referred to as A direction). To do.

  The casting die 21 continuously flows out the dope 28 containing the polymer and the solvent, and has a slit outlet through which the dope 28 flows out at the tip. The casting die 21 is positioned above the rotating roller 23 a and is arranged so that the slit outlet faces the casting band 22.

  The casting die 21, the casting band 22, and the rotating rollers 23a and 23b are preferably made of stainless steel, and more preferably made of SUS316 from the viewpoint of having sufficient corrosion resistance and strength.

  The dope 28 continuously flowing out from the slit exit of the casting die 21 is extended on the casting band 22, thereby forming a belt-like casting film 30 extending in the A direction. The casting film 30 is conveyed in the A direction by the circulating band 22 that circulates and moves.

  The first drying unit 31 to the third drying unit 33 are sequentially arranged downstream of the casting die 21 in the A direction in the vicinity of the casting band 22. The first drying unit 31 to the second drying unit 32 are provided above the rotating rollers 23a and 23b, and the third drying unit 33 is provided below the rotating rollers 23a and 23b.

  The first drying unit 31 to the third drying unit 33 send out a predetermined drying air toward the casting film 30. As a result of the evaporation of the solvent from the casting film 30 by the drying air from the first drying unit 31 to the third drying unit 33, it becomes a state where it can be conveyed independently.

  The stripping roller 24 is disposed in the vicinity of the casting band 22 and between the third drying unit 33 and the casting die 21. The casting film 30 that is in a state where it can be independently conveyed is peeled off by the peeling roller 24 and guided to the downstream side of the casting chamber 12 as a wet film 37.

  A temperature control device 39 is connected to the rotating rollers 23a and 23b. The temperature adjustment device 39 includes a temperature adjustment unit that adjusts the temperature of the heat transfer medium. The temperature control device 39 circulates the heat transfer medium adjusted to a desired temperature between the temperature adjusting unit and the flow path provided in the rotary rollers 23a and 23b. Due to the circulation of the heat transfer medium, the temperature of the casting band 22 can be maintained at a desired temperature.

  The temperature of the rotating roller 23a is preferably lower than the temperature of the rotating roller 23b. The temperature of the rotating roller 23a is preferably 3 ° C. or higher and 30 ° C. or lower, for example. Moreover, it is preferable that the temperature of the rotating roller 23b is 20 degreeC or more and 50 degrees C or less, for example.

  Although not shown, by providing a condensing device that condenses the solvent contained in the atmosphere in the casting chamber 12 and a collecting device that collects the condensed solvent, the solvent contained in the atmosphere in the casting chamber 12 is reduced. The concentration can be kept within a certain range.

  In addition, you may provide the pressure reduction chamber which attracts | sucks the gas of the upstream of the moving direction of the casting bead formed from the casting die 21 to the casting band 22 with the dope 28. FIG. The decompression chamber is preferably disposed adjacent to the casting die 21 on the upstream side in the A direction from the casting die 21. The suction of the gas by the decompression chamber can create a state where the pressure on the upstream side of the casting bead is lower than the pressure on the downstream side of the casting bead. The pressure difference between the upstream side and the downstream side of the casting bead is preferably 10 Pa or more and 2000 Pa or less.

  On the downstream side of the casting chamber 12, a clip tenter 13, a drying chamber 15, a cooling chamber 16, and a winding chamber 17 are installed in this order. A transition portion 51 between the casting chamber 12 and the clip tenter 13 is provided with a blower 51 a that applies dry air to the wet film 37 and a support roller 51 b that supports the wet film 37. The plurality of support rollers 51 b are arranged in the transport direction of the wet film 37. The support roller 51b is rotated around an axis by a motor (not shown). The support roller 51 b supports the wet film 37 sent out from the casting chamber 12 and guides it to the clip tenter 13. In the drawing, two support rollers 51 b are arranged in the transition part 51, but the present invention is not limited to this, and three or more support rollers 51 b may be arranged in the transition part 51.

  The clip tenter 13 performs a predetermined process on the wet film 37 and obtains the film 55 from the wet film 37. The film 55 sent from the clip tenter 13 is sent to the drying chamber 15.

  A large number of rollers 57 are provided in the drying chamber 15, and the film 55 is wound around and transported. The temperature and humidity of the atmosphere in the drying chamber 15 are adjusted by an air conditioner (not shown). In the drying chamber 15, the film 55 is dried. An adsorption recovery device 58 is connected to the drying chamber 15. The adsorption recovery device 58 recovers the solvent evaporated from the film 55 by adsorption.

  The cooling chamber 16 cools the film 55 until the temperature of the film 55 reaches substantially room temperature. Between the cooling chamber 16 and the winding chamber 17, a static elimination bar 59, a knurling roller 60, and an edge cutting device 61 are provided in order from the upstream side. The charge removal bar 59 is discharged from the cooling chamber 16 and performs a charge removal process for removing electricity from the charged film 55. The knurling application roller 60 applies a winding knurling to both ends of the film 55 in the width direction. The edge-cutting device 61 cuts both ends in the width direction of the film 55 so that knurling remains at both ends in the width direction of the film 55 after cutting.

  In the winding chamber 17, a press roller 64 and a winding machine 66 having a winding core 65 are installed. The film 55 sent to the winding chamber 17 is pressed against the winding core 65 while being pressed by the press roller 64. It is wound up into a roll shape.

  As shown in FIG. 2, the first drying unit 31 includes a first supply duct 31 a supplied with a dry gas by a supply unit (not shown), and the dry gas supplied to the first supply duct 31 a as a first drying air 401. It consists of the oblique nozzle 31b to send out. The oblique nozzle 31b is provided on the lower surface of the first supply duct 31a, and the plurality of oblique nozzles 31b are arranged in the A direction. A first drying air 401 having a predetermined temperature and a predetermined wind speed is sent from the oblique nozzle 31b toward the casting film 30 by a controller (not shown), and the solvent is evaporated from the casting film 30.

  The oblique nozzle 31b is preferably arranged so that the spray direction of the dry air 401 is an acute angle with the direction A. Thereby, it is possible to prevent the drying air 401 sent from the oblique nozzle 31b from flowing toward the casting die 21 and the casting bead formed between the casting die 21 and the casting band 22 from vibrating.

  As shown in FIGS. 2 and 3, the second drying unit 32 includes a second supply duct 32a to which a drying gas is supplied by a supply unit 32p, and the drying gas supplied to the second supply duct 32a to a second drying air. It consists of a vertical nozzle 32 b that feeds out as 402 and a suction duct 32 c that sucks in the second dry air 402.

  As shown in FIGS. 4 and 5, the second supply duct 32 a is formed in a box shape and is provided so as to cover the casting band 22. The vertical nozzle 32b is provided on the lower surface 32au of the second supply duct 32a, is arranged in the A direction on the lower surface 32au, and is provided so as to protrude from the lower surface 32au toward the casting film 30.

  A blower slit 32bx through which the second drying air 402 is sent out is provided at the tip of the vertical nozzle 32b. The blow slit 32bx extends long in the width direction of the casting film 30 (hereinafter referred to as the B direction). The vertical nozzle 32 b is provided so that the spraying direction of the drying air 402 is substantially perpendicular to the direction A. Thereby, compared with the case where it makes it diagonal, a heat transfer coefficient and a mass transfer coefficient can be made high, and, as a result, the efficiency of drying can be made high.

  The length L1 of the air blowing slit 32bx in the B direction is not limited as long as the drying air 402 can be sent to the entire area of the casting film 30 in the B direction. For example, the length L1 is equal to the width of the casting film 30 or It is preferable that the width is longer. The length of the second supply duct 32 a in the B direction is preferably equal to the width of the casting film 30 or longer than the width of the casting film 30.

  As shown in FIG. 6, when the second dry air 402 is sent out from the blow slit 32bx, the air in the vicinity of the blow slit 32bx is entrained, and as a result, the air hits the casting film 30 together with the second dry air 402 (FIG. 6). 6 (A)). As a result, it becomes difficult to adjust the drying conditions of the cast film 30 by adjusting the conditions of the second drying air 402. For this reason, in the vertical nozzle 32b, it is preferable to provide the folding | returning part 32by in the periphery of the ventilation slit 32bx (refer FIG. 6 (B)). The folded portion 32by can prevent air in the vicinity of the blowing slit 32bx from hitting the casting film 30 together with the second drying air 402.

  As shown in FIGS. 5 and 7, the suction duct 32c is preferably provided between the vertical nozzles 32b in the A direction and on both sides in the B direction with respect to the vertical nozzles 32b. The suction duct 32c is provided with a second suction port 32cx for sucking the second dry air 402. The second suction port 32cx is located above the blower slit 32bx. The opening direction of the second suction port 32cx is preferably the central side in the B direction.

  Returning to FIG. 1, the third drying unit 33 uses a parallel nozzle 33 a that sends the dry gas supplied from a supply unit (not shown) as the third drying air 403 toward the casting film 30, and the third drying air 403. It comprises a suction nozzle 33b for sucking. The parallel nozzle 33a and the suction nozzle 33b are sequentially provided from the upstream side in the A direction toward the downstream side. The parallel nozzle 33a has a third supply port 33ax that sends out the third drying air 403, and the third supply port 33ax opens toward the downstream side in the A direction. The suction nozzle 33b has a third suction port 33bx that sucks the third dry air 403, and the third suction port 33bx opens toward the upstream side in the A direction. By the parallel nozzle 33a and the suction nozzle 33b, the third dry air 403 can be made to flow substantially parallel to the casting film 30.

  Next, the operation of the present invention will be described. In the solution casting apparatus 10, a film forming process, a film drying process, and a stripping process are sequentially performed in the casting chamber 12. The clip tenter 13 and the drying chamber 15 perform a film drying process, and the winding chamber 17 performs a winding process. Details of each step will be described below.

(Film formation process)
In the casting chamber 12, the casting die 21 continuously flows out the dope 28 toward the casting band 22 that circulates in the A direction. A casting film 30 made of the dope 28 is formed on the casting band 22.

(Film drying process)
The casting film 30 is conveyed in the A direction by the casting band 22. A conveyance speed is 10 m / min or more and 60 m / min or less, for example. The first to third drying units 31 to 33 send predetermined drying air 401 to 403 toward the casting film 30 conveyed by the casting band 22. The solvent evaporates from the casting film 30 by contact with each of the drying air 401 to 403. Details of the membrane drying step will be described later.

(Stripping process)
The peeling roller 24 peels off the casting film 30 which has been in a state where it can be independently carried through the film drying process as a wet film 37 and guides it to the clip tenter 13 through the crossing part 51.

  The residual solvent amount of the cast film 30 at the time of peeling is preferably 25% by weight or more and 50% by weight or less. In the present invention, the amount of the solvent remaining in the cast film 30 and each film is shown on the basis of the dry amount as the residual solvent amount. Moreover, the measurement method takes a sample from the target film, and when the weight of this sample is x and the weight after drying the sample is y, it is calculated as {(xy) / y} × 100. .

(Film drying process and winding process)
The clip tenter 13 conveys the wet film 37 while holding both ends of the wet film 37. Further, the clip tenter 13 applies dry air to the wet film 37 to evaporate the solvent from the wet film 37. As a result, the film 55 can be obtained from the wet film 37. The edge-cutting device 47 cuts both ends of the film 55 sent out from the clip tenter 13. The film 55 with both ends cut off sequentially passes through the drying chamber 15 and the cooling chamber 16, and is subjected to predetermined processing in each chamber. The film 55 delivered from the cooling chamber 16 is sequentially subjected to charge removal processing by the charge removal bar 59, knurling application processing by the knurling application roller 60, and ear cut processing by the ear cut device 61. The film 55 sent to the winding chamber 17 is wound around the winding core 65 while being pressed by the press roller 64 and becomes a roll.

  Next, the details of the film drying step will be described. In the film drying process, a first film drying process using the first drying air 401, a second film drying process using the second drying air 402, and a third film drying process using the third drying air 403 are sequentially performed.

(First film drying step)
As shown in FIGS. 1 and 2, the first drying unit 31 sends the first drying air 401 to the casting film 30. The solvent evaporates from the casting film 30 by contact with the first drying air 401. The first film drying step is preferably performed on the cast film 30 having a residual solvent amount of 250% by mass or more and 400% by mass or less, and is applied to the cast film 30 having a residual solvent amount of 300% by mass or more and 350% by mass or less. More preferably. It is preferable that the temperature of the 1st drying air 401 is 30 degreeC or more and 80 degrees C or less. Moreover, it is preferable that the wind speed of the 1st drying wind 401 is 5 m / sec or more and 25 m / sec or less.

(Second film drying step)
The vertical nozzle 32 b sends the second drying air 402 toward the casting film 30. The solvent evaporates from the casting film 30 by the contact with the second drying air 402. The second membrane drying step is preferably performed on the cast membrane 30 having a residual solvent amount of 150% by mass or more and 300% by mass or less. It is preferable that the temperature of the 2nd drying air 402 is 30 degreeC or more and 80 degrees C or less. Moreover, it is preferable that the wind speed of the 2nd drying wind 402 is 5 m / sec or more and 25 m / sec or less.

(Third film drying step)
The third drying unit 33 sends the third drying air 403 to the casting film 30. The solvent evaporates from the casting film 30 by the contact with the third drying air 403. The third film drying step is preferably performed on the cast film 30 having a residual solvent amount of 20% by mass or more and 150% by mass or less. The temperature of the third drying air 403 is preferably 40 ° C. or higher and 80 ° C. or lower. Moreover, it is preferable that the wind speed of the 3rd drying wind 403 is 5 m / sec or more and 20 m / sec or less.

  As shown in FIG. 7, the second suction ports 32cx for sucking the second dry air 402 are provided between the vertical nozzles 32b in the A direction and on both sides in the B direction with respect to the casting film 30, and from the blower slits 32bx. Is located above, the space between the casting film 30 and the second drying unit 32 and sandwiched between the vertical nozzles 32b aligned in the A direction becomes the suction route 70 (see FIG. 8) of the second drying air 402. .

  As described above, since the second suction ports 32cx are provided between the vertical nozzles 32b in the A direction and on both sides in the B direction with respect to the casting film 30, the second suction ports 32cx according to the increase in the length of the blow slit 32bx. It is not necessary to lengthen the length. Therefore, according to the present invention, the second drying air 402 can be sucked uniformly in the B direction.

  Furthermore, it is necessary to increase the suction amount at the second suction port 32cx along with the increase in the length of the blow slit 32bx. However, when the second suction port 32cx and the casting film 30 are close to each other, the sucked drying air 402 As a result, streaks or the like are formed in the flowing direction, and the surface shape of the film 55 finally obtained is deteriorated. According to the present invention, since the second suction port 32cx is further away from the casting film 30 than the blower slit 32bx, even if the suction amount is increased, the planar shape of the film 55 caused by the suction of the dry air 402 is increased. Deterioration can be avoided.

  As shown in FIG. 8, between the second supply duct 32a and the casting band 22, a cross-sectional area (hereinafter referred to as an exhaust cross-sectional area) S1 of a suction route 70 sandwiched between adjacent vertical nozzles 23b, and a blow slit The ratio (= S1 / S2) with the opening area S2 of 32bx is preferably 15 or more, and more preferably 25 or more.

  The ratio of the distance CL1 between the suction port 32cx and the casting film 30 and the distance CL2 between the blow slit 32bx and the casting film 30 (= CL1 / CL2) is preferably 2 or more, and is 3 or more. It is more preferable.

  9 and 10, wind shielding plates 80 may be provided on both sides of the vertical nozzle 32b in the B direction. The wind shielding plate 80 may be provided so as to block the entire portion exposed from both sides in the B direction in the suction route (see FIG. 9), or provided so as to block a part of the portion exposed from both sides in the B direction. It is also possible (see FIG. 10). By providing the wind shielding plate 80 in this manner, it is difficult for the dry air to flow to the outside, so that the suction route pressure can be maintained higher than the pressure outside the second drying unit. And by maintaining the pressure of the suction route at a high state, air outside the second drying unit can be prevented from flowing into the suction route. As a result, the drying conditions can be maintained uniformly. It becomes easy. In place of the wind shield plate 80, a block-like wind shield member may be used.

  In the above embodiment, the suction port 32cx is provided on the inner side in the B direction. However, the present invention is not limited to this, and the suction port 32cx may be provided downward, that is, facing the casting band 22 (see FIG. 11). ).

  In the above embodiment, a plurality of suction ducts 32c are provided between the vertical nozzles 32b, but the present invention is not limited to this. A plurality of suction ducts 32c may be integrally provided (see FIGS. 12 and 13). In order to stabilize the flow of the second dry air 402, it is necessary to adjust the balance between the supply of the second dry air 402 in the vertical nozzle 32b and the suction of the second dry air 402 in the suction duct 32c. . From the viewpoint of easy adjustment of the balance between the supply of the second dry air 402 and the suction, it is preferable to provide the suction duct 32c for each vertical nozzle 32b.

  In the above embodiment, the suction duct 32c is provided on both sides in the B direction from the vertical nozzle 32b. However, the present invention is not limited to this, and the suction duct 32c may be provided on both sides in the B direction from the casting film 30.

  In the said embodiment, although the casting film 30 in the upper surface of the casting band 22 was dried using the 2nd drying unit 32, this invention is not restricted to this, The casting film in the lower surface of the casting band 22 30 may be dried. In the case of the solution casting apparatus 10 shown in FIG. 1, a structure having the same structure as the second drying unit 32 may be used instead of the third drying unit 33. That is, the suction port 32cx may be located between the vertical nozzles 32b.

  The film 55 obtained by the present invention can be used particularly for a retardation film or a polarizing plate protective film.

  The width of the film 55 is preferably 600 mm or more, and more preferably 1400 mm or more and 2500 mm or less. The present invention is also effective when the width of the film 55 is greater than 2500 mm. The film 55 preferably has a thickness of 30 μm or more and 120 μm or less.

  The in-plane retardation Re of the film 55 is preferably 20 nm or more and 300 nm or less, and the thickness direction retardation Rth of the film 55 is preferably −100 nm or more and 300 nm or less.

The method for measuring the in-plane retardation Re is as follows. In-plane retardation Re is a letter obtained by conditioning a sample film at a temperature of 25 ° C. and a humidity of 60% RH for 2 hours, and measuring it from the vertical direction at 632.8 nm with an automatic birefringence meter (KOBRA21DH Oji Scientific Co., Ltd.). The foundation value was used. Re is expressed by the following equation.
Re = | n1-n2 | × d
n1 is the refractive index of the slow axis, n2 is the refractive index of the fast axis 2, and d is the thickness (film thickness) of the film.

The measuring method of the thickness direction retardation Rth is as follows. The sample film was conditioned at a temperature of 25 ° C. and a humidity of 60% RH for 2 hours, and measured in the same manner while tilting the film surface with an ellipsometer (M150 manufactured by JASCO Corporation) measuring 632.8 nm from the vertical direction. It calculated according to the following formula from the extrapolated value of the retardation value.
Rth = {(n1 + n2) / 2−n3} × d
n3 represents the refractive index in the thickness direction.

(polymer)
In the said embodiment, the polymer used as the raw material of a polymer film is not specifically limited, For example, there exist a cellulose acylate, cyclic polyolefin, etc.

(Cellulose acylate)
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 ratio in which the hydroxyl group of cellulose is esterified with carboxylic acid, that is, the substitution degree of the acyl group satisfies all of the following formulas (I) to (III) is preferable. In the following formulas (I) to (III), A and B represent the substitution degree of the acyl group, A is the substitution degree of the acetyl group, and B is the substitution degree of the acyl group having 3 to 22 carbon atoms. It is. In addition, it is preferable that 90 weight% or more of a triacetyl cellulose (TAC) is 0.1 mm-4 mm particle | grains.
(I) 2.0 ≦ A + B ≦ 3.0
(II) 1.0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.0

  The total substitution degree A + B of the acyl group is more preferably 2.20 or more and 2.90 or less, and particularly preferably 2.40 or more and 2.88 or less. Further, the substitution degree B of the acyl group having 3 to 22 carbon atoms is more preferably 0.30 or more, and particularly preferably 0.5 or more.

  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 of the present invention may be an aliphatic group or an aryl group and is not particularly limited. These are, for example, cellulose alkylcarbonyl esters, alkenylcarbonyl esters, aromatic carbonyl esters, aromatic alkylcarbonyl esters, and the like, each of which may further have a substituted group. Preferred examples of these include propionyl, butanoyl, pentanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, iso-butanoyl, t-butanoyl, cyclohexanecarbonyl, oleoyl, benzoyl , Naphthylcarbonyl, cinnamoyl group and the like. Among these, propionyl, butanoyl, dodecanoyl, octadecanoyl, t-butanoyl, oleoyl, benzoyl, naphthylcarbonyl, cinnamoyl and the like are more preferable, and propionyl and butanoyl are particularly preferable.

(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. In addition to dichloromethane, one kind of alcohol having 1 to 5 carbon atoms is used from the viewpoint of physical properties such as solubility of polymer, peelability from cast film support, mechanical strength of film and optical properties of 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.

  The details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148. These descriptions are also applicable to the present invention. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, ultraviolet absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, and release accelerators. JP-A-2005-104148 describes in detail in paragraphs [0196] to [0516].

(Experiment 1)
In the solution casting apparatus 10 shown in FIG. In the casting chamber 12, the dope was cast on the casting band 22 using the casting die 21, and the casting film 30 was formed on the casting band 22. The casting width at this time was 1800 mm. Thereafter, the cast film 30 was dried using the first to third drying units 31 to 33. The distance between the blow slits 32bx in the A direction is 5 mm, the length L1 (see FIG. 5) of the blow slits 32bx in the B direction is 1800 mm, CL1 (see FIG. 8) is 150 mm, and CL2 (see FIG. 8) is 150 mm. It was. And the 2nd drying wind 402 whose temperature is 50 degreeC was ejected from the nozzle 32b at the wind speed of 20 m / sec.

(Experiment 2)
A film 55 was produced in the same manner as in Experiment 1 except that CL1 was 250 mm.

(Experiment 3)
A film 55 was produced in the same manner as in Experiment 1 except that CL1 was 350 mm.

(Experiment 4)
A film 55 was made in the same manner as in Experiment 1 except that the suction duct 32c shown in FIG. 13 was used and that CL1 was 250 mm.

(Experiment 5)
A film 55 was made in the same manner as in Experiment 1 except that the drying device 202 shown in FIG. 14 was used as the second drying unit 32.

(Experiment 6)
A film 55 was produced in the same manner as in Experiment 5 except that the time required for the second membrane drying step was increased by 40 seconds.

(Evaluation)
About the film 55 obtained in Experiments 1-6, the following items were evaluated.

1. Planar Evaluation Using a schlieren method, it was examined whether or not streaks could be observed in the obtained film. Evaluation was performed based on the following criteria.
○: Streaks could not be observed.
X: Streaks were observed.

2. Drying efficiency The residual solvent amount ZY1 in the cast film at the time of peeling was measured.

3. Rth Measurement The retardation Rth in the thickness direction of the film was measured in the width direction, and the value of the variation ΔRth of the retardation Rth was calculated. ΔRth is defined as {(Xmax−Xmin), where Xav is an average value of measured values of retardation Rth, Xmax is a maximum value of measured values of retardation Rth, and Xmin is a minimum value of measured values of retardation Rth. ) / Xav} × 100.

  Table 1 shows the time required for the membrane drying step and the evaluation results in Experiments 1 to 6.

  In Experiment 5, since the residual solvent amount ZY1 of the cast film at the time of peeling was 41% by mass, the obtained film showed variations in the slow axis due to the peeling tension. On the other hand, in Experiments 1 to 4, since the cast film at the time of peeling was dry, the film finally obtained showed no variation in the slow axis due to the peeling tension. In order for the residual solvent amount ZY1 of the cast film at the time of stripping to be approximately the same as in Experiments 1 to 4 under the conditions of Experiment 5, the time required for the second film drying process must be increased. From the results of Experiments 5 and 6, it can be said that according to the present invention, the second film drying step can be shortened by 40 seconds compared with the conventional drying method. Therefore, according to the present invention, it can be said that the cast film can be efficiently dried as compared with the prior art.

10 Solution Casting Equipment 22 Casting Band 30 Casting Film 32 Second Drying Unit 32a Second Supply Duct 32b Vertical Nozzle 32bx Blower Slit 32c Suction Duct 32cx Suction Port 55 Film 402 Second Drying Air

Claims (11)

A duct including a polymer and a solvent and disposed so as to face a belt-shaped cast film conveyed in a longitudinal direction;
Nozzles provided so as to protrude from the duct toward the casting membrane, and arranged in the moving direction;
A blower slit that is formed to extend long in the width direction of the casting membrane at the tip of the nozzle, and sends dry gas from the duct to the casting membrane as drying air;
In the moving direction, between the nozzles, located on both sides in the width direction than the casting film, and having a suction port for sucking the dry air sent from the blow slit,
The distance between the said suction port and the said casting film is larger than the distance between the said ventilation slit and the said casting film, The drying apparatus characterized by the above-mentioned.   The drying apparatus according to claim 1, wherein the air blowing slits and the suction ports are alternately arranged from the upstream side to the downstream side in the moving direction.   The drying apparatus according to claim 1, wherein the suction port is formed from an upstream side of the one nozzle in the movement direction to a downstream side of the one nozzle in the movement direction.   The drying apparatus according to any one of claims 1 to 3, wherein the suction port faces the casting band.   The drying apparatus according to any one of claims 1 to 3, wherein the suction port faces a center side in the width direction.   The drying apparatus according to any one of claims 1 to 5, wherein a residual solvent amount of the casting film to which the drying air is applied is 150% by mass or more and 350% by mass or less.   The drying apparatus according to any one of claims 1 to 6, wherein the duct is provided above the casting membrane.   The drying apparatus according to any one of claims 1 to 7, wherein a width of the casting film is 1500 mm or more and 2400 mm or less. In the solution casting method for obtaining a film by evaporating the solvent from a casting film containing a polymer and a solvent,
Supplying step of sending dry air to the casting film using the blow slits facing the belt-like casting film conveyed in the longitudinal direction and extending long in the width direction of the casting film and arranged in the conveying direction When,
A suction step for sucking the dry air,
In the suction step, the solution casting method is characterized in that the distance from the casting film is farther than the blowing slit, and the drying air is sucked from positions on both sides in the width direction of the casting film.   The solution casting method according to claim 9, wherein the amount of residual solvent in the cast film to which the dry air is applied is 150% by mass or more and 350% by mass or less.   The solution casting method according to claim 9 or 10, wherein a width of the casting film is 1500 mm or more and 2400 mm or less.

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