JP5623445B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention relates to a method for producing an optical film.

  With the thinning of liquid crystal displays (LCD), the demand for thinning the individual optical films constituting the LCD is increasing. Retardation, which is one of the optical characteristics of the optical film, is expressed by the product of birefringence and thickness, and therefore it is necessary to control birefringence according to the thickness. That is, it is necessary to increase the birefringence, particularly the birefringence Rth in the thickness direction, as the optical film becomes thinner.

  On the other hand, film production methods include a melt extrusion method and a solution casting method. The melt extrusion method is a method for producing a film by melting a polymer and then extruding it with an extruder. This method has features such as high productivity and relatively low equipment cost. However, in the melt extrusion method, fine streaks often appear on the film surface. This fine streak has a greater influence on the optical properties of the film as the film becomes thinner.

  On the other hand, in the solution casting method, a polymer solution in which a polymer is dissolved in a solvent (hereinafter referred to as a dope) is flowed on a support to form a cast film, and the cast film is peeled off from the support and dried. This is a method for producing a film. In the solution casting method, the thickness of the film can be easily adjusted as compared with the melt extrusion method, and a film having a smoother film surface can be produced. Furthermore, the solution casting method can obtain a film with few contained foreign substances. For these reasons, many optical films used in LCDs are manufactured by a solution casting method. For example, for example, a cellulose acylate film is used as a polarizing plate protective film or a retardation film, and this cellulose acylate film is mainly produced by a solution casting method.

  As a method for increasing the retardation, there is a method in which a film includes a compound having an action of increasing the retardation, a so-called retardation increasing agent (for example, Patent Document 1). As other methods for increasing the retardation, there are methods for improving the material constituting the film and for incorporating a specific compound in the film (for example, Patent Documents 2 to 5). As a method for independently controlling Re and Rth, a layer having negative optical anisotropy due to molecular orientation birefringence and a layer that is optically isotropic are combined, and each of these layers is combined. There is a method of forming with a specific material (for example, Patent Document 6).

  Furthermore, in order to control the optical characteristics, a method has been proposed in which a plurality of polymers having different refractive indexes are used, and each layer is formed with each polymer to form a multilayer structure (for example, Patent Documents 7 and 8). .

JP 2002-131538 A JP 2008-238526 A JP 2010-262209 A JP 2011-002634 A JP 2011-1113026 A JP 2010-128378 A JP 2006-205729 A JP 2008-162289 A

  The method of Patent Document 1 has a certain effect on the increase in Re, but has little effect on the increase in Rth. Further, the methods of Patent Documents 1 and 2 require an addition line for adding the retardation increasing agent in-line into the dope in the dope production facility, and there is a problem of securing the equipment space and increasing the cost by adding the addition line. In addition, the use of the retardation increasing agent itself leads to a significant cost increase of the optical film.

  According to the methods of Patent Documents 3 to 5, for example, a film having an Rth of 280 nm and a thickness of 40 μm can be manufactured. However, since the methods of Patent Documents 3 to 5 require the use of specific materials and additives in predetermined amounts, the types of films produced are limited and the cost is increased. In the methods of Patent Documents 4 and 5, Re increases significantly as Rth increases. Although the method of Patent Document 6 can independently control Re and Rth, this method also requires the use of a specific material, which limits the types of films to be manufactured and increases costs.

  Moreover, since the method of patent document 7 and 8 is a method of manufacturing the reflective film which reflects light, for example, a film with a metallic luster, it combines in a layer form using a polymer with a big refractive index difference as a raw material. For this reason, the methods of Patent Documents 7 and 8 cannot produce an optical film that requires transparency, such as a polarizing plate protective film or a retardation film.

  This invention solves such a subject, and it aims at providing the manufacturing method of the optical film which selectively raises Rth of an optical film, without using specific compounds, such as a retardation increasing agent. To do.

The method for producing an optical film of the present invention comprises a flow dividing step of dividing a dope flow in which a polymer having a cyclic molecular structure is dissolved in a solvent, and a plurality of divided dope flows formed by the division of the flow dividing step in a layered manner. A merging step for merging so as to overlap, a compression step for compressing the layered dope flow formed by the merging of the merging step in the thickness direction, and casting the dope after the compression step on a traveling support A casting step of casting by flowing out of the die to form a casting membrane ; a stripping step of forming a wet film by continuously peeling the casting membrane from the support; and drying the wet film to a drying process possess, repeatedly performs dope stratification process comprising the diversion step and merging process and the compression process until the thickness of each layer in the layered dope becomes 50μm or less, the final pressure It is configured as characterized by supplying the dope casting process from step.

  In the branching step, it is preferable that the dope flow formed in a strip shape is divided in the width direction, and in the joining step, the plurality of divided dope flows are stacked in the thickness direction to form a layered dope flow.

  It is preferable that the dopes having different polymer concentrations are overlapped, a strip-like flow of the dope is formed so that the overlapping direction is a thickness direction, and the strip-like dope flow is subjected to the diversion step.

When the refractive index in the longitudinal direction of the optical film is nx, the refractive index in the width direction is ny, the refractive index in the thickness direction is nz, and the thickness is d, Rth obtained by the following formula (1) by the dope flow stratification step is It is preferable to control. In the drying step, the wet film is dried by the drying air from the blower, the temperature of the wet film is changed, each side portion in the width direction of the wet film is gripped by the gripping means, and the track on which the gripping means travels is displaced. It is preferable to control the Re obtained by the following formula (2) by changing the widening ratio in the width direction of the wet film and controlling at least one of the widening ratio and the temperature of the wet film.
Rth = ((ny + nx) / 2−nz) × d (1)
Re = (ny−nx) × d (2)

  According to the present invention, it is possible to produce an optical film having a high Rth regardless of the level of Re without using a specific compound such as a retardation increasing agent.

It is explanatory drawing which shows the outline | summary of solution casting apparatus. It is a perspective view which shows the outline | summary of a die unit. It is an end view of the casting die in the cross section which follows the III-III line of FIG. It is sectional drawing of the casting die in XZ plane, and is sectional drawing which follows the IV-IV line of FIG. It is a perspective view which shows the outline of the flow path formed in the inside of a feed block. It is explanatory drawing of a layered dope flow. It is a perspective view which shows the outline | summary of a die unit. It is explanatory drawing of a layered dope flow.

(Solution casting equipment)
An optical film (hereinafter simply referred to as a film) is manufactured by, for example, a solution casting apparatus 10 shown in FIG. The solution casting apparatus 10 includes a casting apparatus 12, a clip tenter 13, a drying apparatus 15, a cooling apparatus 16, and a winding apparatus 17.

  The casting apparatus 12 includes a die unit 21, a band 22, a first roller 23 and a second roller 24, and a casting chamber 25. The die unit 21 includes a feed block 28 and a casting die 29, and the dope 31 supplied to the feed block 28 continuously flows out from the casting die 29. Details of the die unit 21 will be described later with reference to another drawing.

  The band 22 is an endless casting support body formed in an annular shape, and is wound around the peripheral surfaces of the first roller 23 and the second roller 24. The first roller 23 includes a rotation shaft 23 a at the center of a circular side surface, and the rotation shaft 23 a is rotated in the circumferential direction by a motor 32. As a result, the first roller 23 rotates in the circumferential direction. The drive of the motor 32 is controlled by the controller 33, whereby the rotational speed of the rotary shaft 23a is controlled. The band 22 travels in the longitudinal direction by the rotation of the first roller 23. The second roller 24 includes a rotating shaft 24a at the center of the circular side surface, and rotates around the rotating shaft 24a as the band 22 that is wound travels. In this embodiment, the band 22 is caused to travel by the rotation of the first roller 23. However, the traveling of the band 22 is caused by rotating at least one of the first roller 23 and the second roller 24 in the circumferential direction. Just do it.

  By continuously flowing out the dope 31 from the casting die 29 on the traveling band 22, the casting film 36 is continuously formed on the band 22. In this embodiment, the band 22 is used as a casting support, but the present invention is not limited to this. For example, instead of the band 22, a drum that rotates in the circumferential direction may be used.

  In the present embodiment, as shown in FIG. 1, the casting die 29 is placed so that the downstream end of the winding region of the band 22 wound around the first roller 23 and the outlet of the casting die 29 face each other. It is arranged. However, the position of the casting die 29 is not limited to this. For example, the casting die 29 may be disposed so that the outflow port faces the band 22 from the first roller 23 toward the second roller 24.

  A decompression chamber 37 for sucking air is disposed upstream of the die unit 21 in the rotation direction of the first roller 23. When the decompression chamber 37 sucks air, the dope extending from the casting die 29 to the band 22, that is, the area upstream of the bead in the rotation direction of the first roller 23 is decompressed. This stabilizes the bead shape.

  The first roller 23 and the second roller 24 include a temperature controller (not shown) that controls the peripheral surface temperature. By controlling the peripheral surface temperature of the first roller 23 and the second roller 24, the temperature of the band 22 is controlled. By controlling the temperature of the band 22, the temperature of the casting film 36 is controlled, and the drying speed of the casting film 36 is adjusted.

  A stripping roller 38 is disposed in the vicinity of the first roller 23. The stripping roller 38 is disposed so that the longitudinal direction is substantially parallel to the rotation shaft 23 a of the first roller 23. The stripping roller 38 supports the wet film 41 which is a casting film stripped in a state containing a solvent, and thereby maintains the stripping position where the casting film 36 is stripped from the band 22 at a constant level. To do.

  The casting chamber 25 accommodates the die unit 21, the first roller 23, the second roller 24, the band 22, and the peeling roller 38, so that the solvent evaporated from the casting film 36 is downstream of the clip tenter. Prevents diffusion to etc. A roller 42 that supports the wet film 41 from below and guides it to the clip tenter 13 is provided in the transition from the casting chamber 25 to the clip tenter 13 downstream of the casting chamber 25.

  The clip tenter 13 has a plurality of clips (not shown) that grip each side portion in the width direction of the wet film 41, and these clips travel on a track (not shown). The wet film 41 is conveyed by the traveling of the clip. A blower (not shown) is disposed on at least one of the upper and lower sides of the conveyance path of the wet film 41. Due to the outflow of drying air from the blower, the wet film 41 is dried while being conveyed.

  The wet film 41 may be expanded or narrowed in the width direction by displacing the track in the width direction of the wet film 41. For example, in the case of increasing Re, such as in the case of producing a retardation film, the wet film 41 may be expanded in the width direction to increase the expansion ratio. For example, when manufacturing a polarizing plate protective film with low Re, it is preferable to keep the width constant, for example, to keep the width expansion rate to 0 (zero) or small. Re is also controlled by controlling the temperature of the wet film 41 by controlling the temperature of the drying air from the blower. As described above, the Re level is controlled by controlling at least one of the widening rate in the clip tenter 13 and the temperature of the wet film 41. In the clip tenter 13, when the width is kept constant or widened, it is preferable to reduce the width of the wet film 41 after that, and after the stress relaxation, the clip tenter 13 wets the next process. Send film 41.

  A retention mark by the clip of the clip tenter 13 is formed on both side ends of the wet film 41 that has left the clip tenter 13. Therefore, it is preferable to provide an ear clip device 43 downstream of the clip tenter 13. The ear-cleaving device 43 cuts out both sides including the trace of the wet film 41 guided by the clip. Thereby, the drying apparatus 15 and the conveyance downstream thereof are stabilized. Both sides separated from the wet film 41 are sent to the crusher 46 by the wind to be crushed and reused as a raw material for the dope 31 and the like.

  The drying device 15 is provided with a number of rollers 15a, and a wet film 41 is wound around and conveyed. The temperature and humidity of the atmosphere in the drying device 15 are adjusted by an air conditioner (not shown) that is not shown, and the wet film 41 is dried while passing through the drying device 15 to obtain a dried film 47. It is done. Note that the temperature of the drying device 15 may be increased in order to promote drying of the wet film 41. In this case, a cooling device 48 having an internal temperature lower than that of the drying device 15 may be disposed downstream of the drying device 15. Thereby, the film 47 is cooled while passing through the inside of the cooling device 48, and becomes, for example, about room temperature.

  A knurling roller pair 51 is provided on the downstream side of the cooling device 48, whereby knurling is applied to both sides of the film 47.

  A winding core 52 is set in the winding device 17, and the winding device 17 rotates the winding core 52 to wind up the guided film 47 in a roll shape.

  As shown in FIG. 2, the die unit 21 includes a feed block 28 and a casting die 29. The feed block 28 is disposed on the upstream side of the casting die 29. In the following description, the width direction of the band 22 is referred to as the X direction, the traveling direction of the band 22 is referred to as the Y direction, and the direction perpendicular to the band surface is referred to as the Z direction. The X direction, the Y direction, and the Z direction are orthogonal to each other. In each of the feed block 28 and the casting die 29, a flow path for the dope 31 is formed. FIG. 2 shows an embodiment in which a feed block 28 is arranged on the upper surface of the casting die 29. An inlet 28b into which the dope 31 is inserted is formed on the upper surface of the feed block 28, and the dope 31 is placed in the inlet 28b. A pipe 56 (see FIG. 1) for guiding is connected. The casting die 29 is arranged so that the outlet 29a of the dope 31 faces the band 29, and the longitudinal direction of the slit-like outlet 29a is in the X direction. When the dope 31 is supplied through the pipe 56, the feed block 28 controls the flow of the dope 31 (hereinafter referred to as the dope flow) and sends it to the casting die 29 as will be described later. The casting die 29 flows the dope 31 guided from the feed block 28 toward the band 22 from the outlet 29a.

  As shown in FIGS. 3 and 4, the casting die 29 includes a pair of lip plates 57 and a pair of side plates 58. The pair of lip plates 57 are arranged side by side in the Y direction as shown in FIG. Each of the pair of side plates 58 is disposed in close contact with each side edge in the X direction of the pair of lip plates 57. As a result, a slot 59 surrounded by the pair of lip plates 57 and the pair of side plates 58 is formed, and this slot 59 becomes a flow path for the dope 31.

  The slot 59 in this embodiment is provided so as to penetrate the casting die 29 in the Z direction. In some cases, the casting die 29 is inclined in the Y direction. In this case, the direction through which the slot 59 penetrates may also be inclined in the Y direction. One end of the slot 59 opens to the upper surface of the casting die 29 to become the inlet 29b of the dope 31, and the other end opens to the lower end of the casting die 29 to become the outlet 29a.

  The slot 59 includes a first slot portion 61, a second slot portion 62, a third slot portion 63, and a fourth slot portion 64 from the inflow port 29b toward the outflow port 29a.

  Inner deckle plates 67 are provided at both ends in the X direction from the second slot 62 to the outlet 29a. The inner deckle plate 67 regulates the flow width (length in the X direction) of the dope 31. In the following description, the flow width of the dope 31 is referred to as a flow width.

  The cross-sectional shape of the slot 59 in the XY plane is a rectangular shape that is long in the X direction and short in the Y direction. The length of the slot 59 in the X direction is constant in each of the first slot portion 61, the third slot portion 63, and the fourth slot portion 64 from the upstream side to the downstream side in the flow direction. Then gradually increase. Further, the lengths in the X direction of the third slit portion 63 and the fourth slot portion 64 are equal to each other. Thereby, the flow width of the dope 31 becomes wider toward the downstream in the second slot portion 62, and becomes constant in the third slot portion 63 and the fourth slot portion 64.

  On the other hand, the length of the slot 59 in the Y direction is constant in the first slot portion 61, the second slot portion 62, and the fourth slot portion 64 from the upstream side to the downstream side in the flow direction. In part 63, it gradually decreases. The lengths of the first slot portion 61 and the second slot portion 62 in the Y direction are equal to each other. As a result, the flow thickness (the length in the Y direction) of the dope 31 is constant from the first slot portion 61 to the second slot portion 62, becomes thin at the third slot portion 63, and is third at the fourth slot 64. The thinness reached in the slot is retained. In the following description, the flow thickness of the dope 31 is referred to as the flow thickness.

  Inside the feed block 28, a flow path 70 (see FIG. 5) of the dope 31 is formed. As shown in FIG. 5, the flow path 70 includes a first section 71, a second section 72, and a third section 73 in order from the upstream side, and the first section 71, the second section 72, and the third section 73. The section 73 has the same configuration as each other.

  The first section 71 communicates with the inflow port 28b, and the cross-sectional shape of the flow path 74 from the substantially square inflow port 28b to the first section 71 changes so as to become a long rectangle in the X direction toward the downstream. . In addition, although the shape of the cross section in the XY plane of the inflow port 28b is substantially square in this embodiment, it is not limited to this shape, For example, a polygon other than a circle, a rectangle, and a rectangle may be sufficient.

  The first section 71 includes a dividing unit 71a, a converting unit 71b, and a merging / compressing unit 71c arranged in order from the upstream side. The division part 71a branches the rectangular flow path 75 long in the X direction into four in the X direction which is the longitudinal direction. This branch is substantially equally divided in the X direction, and the lengths of the formed branch flow paths 76a to 76d in the X direction are substantially equal. The branch channels 76a to 76d are referred to as a first branch channel 76a, a second branch channel 76b, a third branch channel 76c, and a fourth branch channel 76d in order from the left side in FIG.

  The conversion unit 71 b converts the first branch flow channel 76 a to the fourth branch flow channel 76 d so as to be aligned in the Y direction that matches the thickness direction of the flow channel 75. The inner second branch channel 76b and third branch channel 76c in the X direction are in the Y direction so that the outer first branch channel 76a and the fourth branch channel 76d in the X direction are inside in the Y direction. Each branch flow path 76a-76d is converted so that it may become an outer side.

  The merging / compressing unit 71c overlaps the first branch flow channel 76a to the fourth branch flow channel 76d in the Y direction of the flow channel 75 and merges them, and decreases the length in the Y direction toward the downstream and in the X direction. Increase the length of The thickness of the downstream end of the confluence compression section 71c, that is, the length in the Y direction, is substantially equal to the thickness of the flow path 75 and the first branch flow path 76a to the fourth branch flow path 76d in the division section 71a. .

  The second section 72 and the third section 73 have the same configuration as the first section 71. The second section 72 includes a dividing unit 72a, a converting unit 72b, and a merging / compressing unit 72c, and the third section 73 includes a dividing unit 73a, a converting unit 73b, and a merging / compressing unit 73c. The merging and compressing portion 73 c of the third section communicates with the outflow port 28 a, and the outflow port 28 a is connected to the inflow port 29 b of the casting die 29. The thicknesses of the downstream ends of the merging / compressing part 72c and the merging / compressing part 73c, that is, the respective lengths in the Y direction, are determined by the flow path 75 and the first branch flow path 76a to the fourth branch flow path 76d in the division part 71a. It is approximately equal to each thickness.

  As a feed block having the above flow path, there is a multiplier manufactured by EDI. Although this is a product used for producing a film by a melt extrusion method, it is useful in that it has the above-mentioned flow path.

  The flow of the dope 31 supplied to the die unit 21 composed of the feed block 28 and the casting die 29 is controlled as follows. When the dope 31 is continuously guided to the inflow port 28, the cross-sectional shape of the dope flow changes so as to be a long rectangle in the X direction by the flow path 74, whereby the flow of the dope 31 becomes a band shape.

  When the dope flow formed in a strip shape is guided to the first section 71, the dope flow is divided into four substantially equally by the dividing portion 71 in the X direction which is the width direction. Dividing the dope flow is referred to as a diversion in the following description. The individual dope flows formed by the division are referred to as divided dope flows in the following description, and the divided dope flows flowing through the first branch channel 76a to the fourth branch channel 76d are referred to as the first to fourth divided dopes. This is called a flow. In addition, since the dividing unit 71 has four branch channels, the first to fourth branch channels 76a to 76d, the dope flow is divided into four in this embodiment, but the number of branch channels is 2, 3, By setting it to 5 or more, the dope stream can be divided into 2, 3 and 5 or more.

  The paths of the first and fourth divided dope flows outside in the X direction are controlled to be inside in the Y direction, and the second and third divided dope flows inside in the X direction are The route is controlled to be outside in the Y direction.

  The first to fourth divided dope flows whose paths are controlled are guided by the merging / compressing portion 71c and merged so as to overlap in the Y direction, thereby forming a layered dope flow in which the dope flows are layered. The layered dope flow formed in the first section 71 will be referred to as the first layered dope flow in the following description.

  The split dope flow is merged by the merge compression unit 71 into a layered dope flow and is compressed in the thickness direction. That is, the layered dope stream is compressed in thickness. As a result, the individual dope streams of the layered dope stream are compressed in thickness, and the contained polymer molecules are oriented along the XZ plane. The layered dope stream is compressed in the thickness direction and expanded in the X direction, which is the width direction, so that the layered dope stream has a wider band shape than the point of joining. For this reason, the orientation of the molecules of the polymer along the XZ plane is more reliably promoted.

  As described above, in the first section 71, the single-layer dope flow 80 ((A) in FIG. 6) becomes the first layer-like dope flow 81 in which the flow overlaps in the Y direction on the XY plane, and the flow thickness of each layer Is compressed and smaller than the flow thickness of the dope flow 80 introduced into the dividing portion 71a ((B) of FIG. 6). In FIG. 6, the flow thickness is greatly exaggerated with respect to the flow width. In the present embodiment, the thickness of the downstream end of the merging / compressing portion 71c and the thickness of the flow path 75 at the dividing portion 71a are substantially equal, so the flow thickness of each layer of the first layered dope flow 81 is equal to the dividing portion 71a. The dope stream 80 introduced into is compressed to about ¼ of the flow thickness. As described above, in the first section 71, a laminar flow process including the processes of diversion, merging, and dope flow compression is performed.

  The first layered dope stream 81 compressed in the thickness direction is subjected to a series of processes of shunting, merging, and compressing the dope stream in the second section 72, that is, a laminarization process. Thereby, the first layered dope stream 81 becomes a second layered dope stream 82, and the flow thickness of each layer is compressed and smaller than the flow thickness of each layer of the first layered dope stream 81 ((C )). In the present embodiment, the thickness of the downstream end of the merging / compressing part 72c and the thickness of the downstream end of the merging / compressing part 71c are made substantially equal, so the flow thickness of each layer of the second layered dope stream 82 is the merging / compressing part 71c. The first layered dope stream 81 that has exited is compressed to about ¼ of the flow thickness of each layer. Thereby, the flow thickness of each layer of the second layered dope stream 82 is compressed to about 1/16 of the flow thickness of the dope stream 80 introduced into the dividing portion 71a. Since the second layered dope stream 82 is formed by dividing the first layered dope stream 81 into four parts in the X direction and overlapping in the Y direction, it is a layered dope stream in which 16 layers overlap.

  The second layered dope stream 82 is guided to the third section 73 and similarly shunted, merged, and compressed in the dope stream to become a third layered dope stream 83 in which the dope streams are overlapped by 64 layers. The thickness is compressed and smaller than the flow thickness of each layer of the second layered dope flow 82 (see FIG. 6D). In the present embodiment, since the thickness of the downstream end of the merging / compressing portion 73c and the thickness of the downstream end of the merging / compressing portion 72c are substantially equal, the flow thickness of each layer of the third layered dope flow 83 is equal to the merging / compressing portion 71c. The second layered dope stream 82 exiting from the center is compressed to about 1/4 of the flow thickness of each layer. Thereby, the flow thickness of each layer of the third layered dope flow 83 is compressed to about 1/64 of the flow thickness of the dope flow 80 introduced into the dividing portion 71a.

  As described above, the laminar flow process is repeatedly performed in the feed block 29.

  The third layered dope stream 83 formed by repeating the laminar flow process three times is guided by the casting die 29 and flows out from the outlet 29b of the casting die 29. In the present embodiment, the third layered dope flow 83 is also compressed in the thickness direction in the third slot portion 63 of the casting die 29, and this compression is the final compression step. Therefore, when using the casting die 29 that compresses the layered dope flow in the thickness direction in this way, the confluence compression portion 73c of the third section of the feed block may be replaced with another mode. As another aspect, there is a single flow path that is connected to the downstream end of the conversion unit 73b and has the same length in the X direction and the Y direction as the downstream end of the conversion unit 73b. When such a flow path is used, the divided dope flows formed by the dividing portions 73a merge to form the third layered dope flow 83, and the formed third layered dope flow 83 flows without being compressed. It is guided to the drawing die 29 and compressed by the third slot portion 63 of the casting die 29.

  As described above, since each of the divided portions 71a, 72a, 73a of the present embodiment branches the flow path 75 into four, the number of layers of the obtained third layered dope stream 73 is 4 to the third power. (= 64). Thus, the number of layers of each layered dope flow can be set by the number of branches in the divided portions of each section.

  The number of sections is not limited to 3 as in this embodiment. For example, when forming a layered dope flow having more layers, a similar section may be added in series downstream of the third section 73.

  The number of layered dope streams used for casting is preferably 50 or more and 2000 or less, and the flow thickness of each layer is preferably in the range of 10 nm or more and 50 μm or less. The flow thickness of each layer corresponds to a range in which the thickness of each layer in the film 47 is 4 nm or more and 1 μm or less when each layer is found in the obtained film 47. When the flow thickness of each layer is larger than 50 μm, the degree of improvement of Rth is extremely small even if the orientation of the polymer proceeds.

  According to the above method, a film 47 having a remarkably high Rth can be obtained without using a retardation increasing agent. Further, according to the above method, it is possible to produce a film 47 having a remarkably high Rth without increasing Re or suppressing it with a slight increase even if it increases. For this reason, for example, a film 47 for polarizing plate protective film that requires low Re and high Rth can be produced. In addition, Re can be set to a target value by controlling the widening rate in the width direction in the clip tenter 13 with the wet film 41 at a predetermined temperature. For example, in the case of manufacturing a film 47 for use in a retardation film that requires high Re, it is preferable to increase the width expansion rate in the width direction of the clip tenter 13. Thus, the present invention can selectively increase only Rth independently of Re. In addition, according to the present invention, Rth is controlled before casting and Re is controlled after casting. Therefore, the conditions of each process can be set independently. Furthermore, according to the present invention, high Rth can be expressed using the existing dope 31 without using a specific compound for controlling Rth. Further, the film 47 having a greatly increased elastic modulus is obtained by the layering step.

  The film 47 obtained by the above method has a single layer structure. This film 47 has an extremely high Rth as compared to a film manufactured using only the casting die 29 without using the feed block 28 and having the same thickness as the film 47. For example, Rth of the film when cellulose acylate is used as the polymer component of the dope 31 and the dope 31 is guided to the casting die 29 without using the feed block 28 and the widening ratio in the clip tenter 13 is 20%. Is about 110 nm. Compared to this, it is obtained by forming a third layered dope flow in which 64 layers of dope flows overlap using a feed block 28 in which three flow passage portions are formed in series without changing the polymer component and the widening ratio. The Rth of the film 47 is increased. Further, in place of the feed block 28, a feed block (not shown) in which two more flow passage portions are formed in series, that is, a feed block in which five flow passage portions are formed in series, is used. The Rth of the film obtained by forming the fifth layered dope stream in which the 1024 layer dope streams overlap is further increased to 180 nm.

  As the degree of compression of the dope flow in each of the confluence compression units 71c to 73c is increased, the degree of increase in Rth is increased. For example, the Rth of the film 47 obtained by compressing to 1/100 is higher than that of compressing the dope stream to 1/10, and the Rth of the film 47 obtained by compressing to 1/1000 is further increased. Thus, Rth can be controlled by controlling the degree of compression in the thickness direction of the dope flow. That is, the film 47 having a higher Rth is obtained by compressing the dope stream so as to be smaller in the thickness direction.

  In each layered dope flow, it is preferable that the layers do not mix and flow while maintaining the interface. Examples of the case where the layers are mixed include a case where the lengths of the confluence compression units 71c, 72c, 73c are too long, that is, a case where the flow time in the state of the layered dope flow is long. Thus, when each layer is mixed and Rth of the obtained film 47 does not rise so much, for example, the following method may be performed using the die unit 91 shown in FIG. In FIG. 7, the same members as those in FIG.

  The die unit 90 includes a casting die 29, a first feed block 91, and a second feed block 92. The first feed block 91 is disposed on the upstream side of the casting die 29, similarly to the feed block 28 of FIG. In the first feed block 91, the same flow path 70 as the feed block 28 of FIG. 2 is formed inside. The upstream end of the flow path 70 opens to the upper surface as an inlet (not shown) of the dopes 31a and 31b, and the downstream end of the flow path 70 opens to the upper face as an outlet (not shown) of the dopes 94 and 95. The outlet of the first feed block 91 is connected to the inlet 29 b of the casting die 29.

  The second feed block 92 is disposed on the upstream side of the first feed block 91, and is disposed on the upper surface of the first feed block 91 in the present embodiment. In the second feed block 92, an inlet 92b into which the dope 94 flows and an inlet 92c into which the dope 95 flows are formed. The inlet 92b and the inlet 92c are provided to face each other in the Y direction.

  Inside the second feed block 92, a flow path extending from the inflow port 92b, a flow path extending from the outflow port 92c, a merging portion where these flow paths merge, and a single flow path extending from the merging portion to the outflow port And are formed.

  Further, a concentration adjusting device 96 that adjusts the concentration of the dope 31 is provided upstream of the die unit 90. The concentration adjusting device 96 adjusts the concentration of the polymer component for the supplied dope 31 and prepares the dopes 94 and 95 having different concentrations. As a result, the dopes 94 and 95 having different viscosities are obtained. The method of adjusting the concentration is not particularly limited, and for example, a known method such as a method of increasing the concentration by concentrating the dope 31 or a method of decreasing the concentration by adding a solvent component of the dope 31 is used. In the present embodiment, two dopes 94 and 95 having different concentrations from each other are prepared from the dope 31, but either one of the dopes 94 and 95 is used without changing the concentration of the supplied dope 31. The other of the dopes 94 and 95 may be changed in concentration. Further, in this embodiment, the concentration of the polymer component is adjusted in order to create the dopes 94 and 95 having different viscosities. However, when other solid components may be added to the dopes 94 and 95, solids other than the polymer may be added. You may adjust the density | concentration of a component.

  The concentration adjusting device 96 is independently connected to the first inlet 92 b and the second inlet 92 c of the second feed block 92, and the prepared dopes 94 and 95 are independently supplied to the second feed block 92. Guided. For example, as shown in FIG. 2, the dope 94 is sent to the first inlet, and the dope 95 is sent to the second inlet 92c.

  The dopes 94 and 95 guided from the concentration adjusting device 96 to the second feed block 92 by the die unit 90 are merged so as to overlap in the Y direction at the merge portion in the second feed block. When a merge portion having a shape whose X direction is longer than the Y direction in the XY plane is formed, the merged dope 94 and dope 95 flow into a strip-like layered dope flow 100 ((A) in FIG. 8).

  The inlet of the first feed block 91 is a rectangle longer in the X direction than the inlet 28b of the feed block 28, and the outlet of the second feed block 92 is the same as the inlet of the first feed block 91. As shape and size. As a result, the dope stream 100 formed by the second feed block 92 is guided to the first feed block 91 in a state where the formed two-layer structure is more reliably maintained.

  When the laminar dope stream 100 is guided from the second feed block 92 to the first feed block 91, the first section 71 (see FIG. 5) performs a series of stratification processes of shunting, merging, and dope stream compression. The first layered dope stream 101 ((B) of FIG. 8) in which the flows of the dope 94 and the dope 95 alternately overlap each other. In the present embodiment, the dope flow 100 having a two-layer structure is divided into four in the X direction, and the divided dope flows are overlapped and joined in the Y direction, so the number of layers of the first layered dope flow 101 is eight. The flow thickness of each layer of the first layered dope stream 101 is about ¼ of the flow thickness of each layer of the dope stream 101.

  The first layered dope stream 101 is similarly layered in the second section 72 (see FIG. 5) so that the flows of the dope 94 and the dope 95 are alternately overlapped, and the flow thickness of each layer is smaller. A two-layer dope flow 102 (FIG. 8C) is obtained. The number of layers of the second layered dope stream 102 is 32. The flow thickness of each layer of the second layered dope stream 102 is about ¼ of the flow thickness of each layer of the first layered dope stream 101.

  The second layered dope stream 102 is subjected to the same layering process in the second section 73 (see FIG. 5) so that the flows of the dope 94 and the dope 95 are alternately overlapped, and the flow thickness of each layer is further reduced. A three-layer dope flow 103 ((D) in FIG. 8) is obtained. The number of layers of the second layered dope stream 102 is 128. The flow thickness of each layer of the third layered dope stream 103 is about 1/4 of the flow thickness of each layer of the second layered dope stream 102.

  As described above, when the stratification process by the sections 71 to 73 is performed after the dopes 94 and 95 having different concentrations are overlapped, the movement of the polymer between layers in each layered dope flow is suppressed. For this reason, the effect of compressing the dope flow is less likely to be reduced, so that the effect of increasing Rth can be obtained more reliably. The film 47 thus obtained also has a single layer structure.

  In the present embodiment, the concentration of the dopes 94 and 95 is different from each other to suppress the movement of the polymer between the layers in each layered dope flow. However, this suppression effect can be obtained by other methods. For example, this is a method in which different polymer components are used as the polymer components of the dope 94 and the dope 95. However, in order to ensure the transparency of the film 47, the ratio of the refractive index of one of the polymer components to the other is preferably at most 1.01, that is, in the range of 1 to 1.01. When different polymer components are used as the polymer components of the dope 94 and the dope 95, a film having a multilayer structure having the number of layered dope flows to be cast may be obtained, or the affinity between different polymers may be obtained. When is high, a film having a multilayer structure or a single layer structure having a smaller number of layers may be obtained.

  Instead of the first feed block 91 and the second feed block 92, one feed in which the flow path (not shown) of the first feed block 91 and the flow path 70 of the second feed block 92 are connected in series from the upstream side. A block may be used.

  Each of the above embodiments is a mode in which the dope flow formed in a strip shape is divided in the width direction and the divided dope flow is overlapped in the thickness direction. However, the following modes may be used instead. For example, the following aspects can be implemented using Infinano manufactured by Krollen. First, the dope 31 is sent to the feed block, and the guided dope flow is divided into a plurality of divided dope flows. Each of the plurality of divided dope flows is formed into a band shape to form a band-shaped divided dope flow, and the plurality of divided dope flows formed into a band shape are joined so as to overlap in the thickness direction. By this merging, a strip-shaped layered dope flow having a multilayer structure is formed. This layered dope stream is compressed in the thickness direction. The compressed layered dope may be guided to the casting die 29, or may be guided to the feed block 28 before being guided to the casting die 29 for further layering.

  When a film having specific functional layers on both sides is manufactured, for example, a multi-manifold type casting die (not shown) may be used instead of the casting die 28. Examples of such a casting die include a slot 59 (see FIG. 3) and a casting die in which one flow path is formed on each side of the slot 59 in the Y direction. A manifold is formed in two flow paths formed on both sides in the Y direction of the slot 59. Using such a casting die, the layered dope flow that has undergone the layering process may be guided to the slot 59, and the dope forming the functional layer may be guided to the two flow paths having the manifolds. Thereby, Rth is raised by the dope flowing through the slot 59, and a film in which a functional layer is formed by the dope flowing through the two flow paths having the manifolds can be obtained. When the thickness of the obtained film is approximately 30 μm, the thickness of the functional layer is approximately 1 μm. As the functional layer, for example, when the polymer component of the layered dope flow guided to the slot 59 is cellulose diacetate, there is a peelability improving layer for facilitating peeling from the band 29. The polymer component of such a peelability improving layer is preferably cellulose triacetate.

  As the polymer of the dope 31, various known polymers used for solution casting can be used. A transparent polymer is used when manufacturing a film used as a polarizing plate protective film or a retardation film. For example, cellulose acylate is preferable. Further, the effect of increasing Rth due to compression of the dope flow is particularly noticeable when the polymer component of the dope 31 has a cyclic molecular structure.

  When cellulose acylate is used as the polymer, only one type of acyl group of cellulose acylate may be used, or two or more types of acyl groups may be used. The cellulose acylate of the present invention preferably has an acyl group having 2 to 4 carbon atoms as a substituent. When two or more types of acyl groups are used, one of them is preferably an acetyl group, and the acyl group having 2 to 4 carbon atoms is preferably a propionyl group or a butyryl group. A dope can be prepared by dissolving these cellulose acylates in a solvent.

  Glucose units having a β-1,4 bond constituting cellulose acylate have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by acylating part or all of these hydroxyl groups with an acyl group. The degree of acyl substitution means the sum of the ratios of acylation of the hydroxyl groups of cellulose located at the 2-position, 3-position and 6-position (100% acylation at each position is substitution degree 1).

  The acyl group having 2 or more carbon atoms may be an aliphatic group or an allyl 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 acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, isobutanoyl group Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), more preferably an acetyl group (when the cellulose acylate is cellulose acetate).

(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 the above halogenated hydrocarbons, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and dichloromethane is most preferably used. From the viewpoint of physical properties such as solubility of TAC, peelability of cast film from the support, mechanical strength and optical properties of the film, one or several kinds of alcohols having 1 to 5 carbon atoms are mixed in addition to dichloromethane. It is preferable to do. The content of alcohol is preferably 2 to 25% by weight, more preferably 5 to 20% by weight, based on the entire solvent. Examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, etc., but methanol, ethanol, n-butanol, or a mixture thereof is preferably used. Moreover, the solvent composition which does not use a dichloromethane may be sufficient, and a well-known composition is applicable as such a solvent composition.

  The present invention is particularly effective when the film 47 having a thickness in the range of 10 μm to 50 μm is manufactured. For example, by setting the widening ratio in the clip tenter 13 to 3%, a film 47 having an Rth of 20 nm, an Re of 1 nm, and a thickness of 60 μm is obtained, and this film 47 can be used as a polarizing plate protective film. Further, for example, by setting the widening ratio in the clip tenter 13 to 25%, a film 47 having Rth of 130 nm, Re of 45 nm, and thickness of 60 μm is obtained, and this film 47 can be used as a retardation film.

Re is the optical anisotropy in the film plane, and Rth is the optical anisotropy in the film plane and in the film thickness direction. For a long film obtained by continuous film production, nx is the refractive index in the longitudinal direction of the film, ny is the refractive index in the width direction of the film, nz is the refractive index in the thickness direction of the film, and d is the film thickness. , Re and Rth are obtained by the following equations, respectively. In this specification, the values of Re and Rth are obtained by KOBRA 21ADH (manufactured by Oji Scientific Instruments).
Re = (ny−nx) × d
Rth = ((ny + nx) / 2−nz) × d

DESCRIPTION OF SYMBOLS 10 Solution film forming equipment 13 Clip tenter 21, 90 Die unit 22 Band 28 Feed block 29 Casting die 36 Casting film 41 Wet film 47 Film 70 Channels 71-73 First to third sections 71a, 72a, 73a Dividing part 71b, 72b, 73b Converters 71c, 72c, 73c Merge compressors 81-83 First to third layered dope flows

Claims (5)

A diversion process for dividing a flow of a dope in which a polymer having a cyclic molecular structure is dissolved in a solvent;
A merging step of merging a plurality of divided dope flows formed by dividing the diversion step so as to overlap in a layered manner;
A compression step of compressing the layered dope flow formed by the merging of the merging step in the thickness direction;
On the traveling support, a casting step of casting the dope that has undergone the compression step by flowing out of the casting die to form a casting film;
A peeling step of forming a wet film by continuously peeling the casting membrane from the support;
Possess a drying step of drying the wet film,
The dope flow stratification step consisting of the diversion step, the merging step and the compression step is repeated until the thickness of each layer in the layered dope flow becomes 50 μm or less, and the dope is transferred from the final compression step to the casting step. A method for producing an optical film, characterized by comprising: In the diversion step, the dope flow formed in a band shape is divided in the width direction;
The merging step method for producing an optical film according to claim 1, characterized in that the plurality of divided dope superimposed in the thickness direction to form the layered dope.   The dopes having different polymer concentrations are overlapped, a strip-like flow of the dope is formed such that the overlapping direction is a thickness direction, and the strip-like dope flow is subjected to the diversion step. The manufacturing method of the optical film of Claim 1 or 2. When the refractive index in the longitudinal direction of the optical film is nx, the refractive index in the width direction is ny, the refractive index in the thickness direction is nz, and the thickness is d,
The method for producing an optical film according to any one of claims 1 to 3, wherein Rth obtained by the following formula (1) is controlled by the dope flow stratification step.
Rth = ((ny + nx) / 2−nz) × d (1) When the refractive index in the longitudinal direction of the optical film is nx, the refractive index in the width direction is ny, and the thickness is d,
In the drying step, the wet film is dried by a dry air from a blower, the temperature of the wet film is changed, and each side portion in the width direction of the wet film is gripped by the gripping means, and the track travels by the gripping means. The width of the wet film in the width direction is changed by displacing the wet film, and Re obtained by the following formula (2) is controlled by controlling at least one of the widening ratio and the temperature of the wet film. The method for producing an optical film according to any one of claims 1 to 4.
Re = (ny−nx) × d (2)

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