JP2010000773A - Method of producing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce an optical film having a high Re and a low Rth value relative to the Re, and a low haze value compared to a conventional film. <P>SOLUTION: In a first tenter 55, a wet film 54 is stretched at an average atmospheric temperature of ≥70°C but ≤115°C until a residual solvent content is reduced to 25 wt.% to obtain an intermediate film 56. Further in the first tenter 55, the intermediate film 56 is dried at an average atmospheric temperature of ≥40°C but ≤90°C so as to reduce the residual amount of the solvent to ≥10 to <25 wt.% and thereafter, the intermediate film 56 is conveyed to a second tenter 57. In the second tenter 57, the intermediate film 56 after the residual solvent content is reached to 10 wt.% is stretched in an atmosphere having a set temperature of ≥160°C but ≤195°C to obtain an optical film 52 having a low Rth/Re, high Re and low haze value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  The required performance for liquid crystal displays has been increasing in recent years. The liquid crystal display has a structure in which a plurality of optical films are stacked, and an optical film having various optical characteristics corresponding to various display formats in the liquid crystal display is required. The optical film has an in-plane direction retardation (hereinafter referred to as “Re”) (nm) and a thickness direction retardation (hereinafter referred to as “Rth”) (nm), particularly depending on the type and model of the liquid crystal display. And various optical characteristics represented by haze value (%). The “in-plane direction” of Re is the direction of the plane perpendicular to the thickness direction of the film.

As is well known, Re is obtained by the following equation (1) and Rth is obtained by the following equation (2). In the formulas (1) and (2), nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction, nz is the refractive index in the film thickness direction, and d is the film thickness. Thickness (nm).
Re = (nx−ny) × d (1)
Rth = {(nx + ny) / 2−nz} × d (2)

  By the way, a polymer film, particularly a film made of cellulose acylate as a raw material, is adjusted to adjust the orientation of polymer molecules or the ratio of polymer molecules to crystallize, thereby adjusting the Re, Rth and haze values. Thereby, it is used especially as a polarizing plate retardation film of a liquid crystal display device. And as Re is made higher, the widening ratio in stretching is increased, thereby increasing Rth. Recently, however, the polarizing plate retardation film is required to have optical characteristics that are particularly high in Re and low in Rth relative to Re. Rth lower than Re means that the value of Rth / Re is smaller than that of the conventional product by 1 or more, that is, a value closer to 1. Such a film is also required to have a low haze value.

As a method for adjusting Re and Rth for a polymer film, a cellulose ester solution is cast on a support to produce a cast film, and the cast film is peeled off from the support as a wet film. While the amount is within a predetermined range, a method of producing a film having a large Re and Rth by stretching in the width direction while drying, or the residual solvent amount of the casting film is within the predetermined range There is a method in which a film having a small Re is produced by peeling it as a film for a while and stretching the film in two steps in the width direction (see, for example, Patent Document 2). Furthermore, there is a film manufacturing method (see, for example, Patent Document 3) in which a film having a large Re is manufactured by adding a retardation increasing agent to a polymer solution.
JP 2002-187960 A JP 2002-31245 A Special Table 2000-0665384

  In the method described in Patent Document 1, the casting film in the case where the solvent residual amount is large is easily broken, and thus the stretching speed in the width direction and the stretching ratio cannot be increased. Further, in the case of so-called cooling casting, when the casting film is solidified and peeled off using a drum on the casting support in order to increase productivity, the casting film is peeled off according to the method of Patent Document 1. Sometimes molecules are oriented in the transport direction of the wet film, and the Rth of the film after the stretching process is increased. Therefore, in the case of cooling casting, there is a problem that even if Re can be increased, the value of Rth / Re cannot be decreased.

  In the method described in Patent Document 2, the film is stretched by the first tenter and the second tenter downstream of the first tenter, but the residual amount of the solvent sent to the first tenter is 10 to 50% by mass. . Therefore, in order to dry the film so as to reach the above-mentioned solvent residual amount before reaching the first tenter, it is necessary to dry the cast film on the support. However, in the so-called dry casting in which the casting film is dried and peeled off on the support in this way, productivity as high as cooling casting cannot be expected. Also, with this method, a film having a high Re and a low haze value cannot be produced. On the other hand, in the method described in Patent Document 3, since a retardation increasing agent is added to the casting film, Re can be increased, but Rth also increases, and desired optical characteristics can be obtained. could not.

  In the present invention, in view of the above problems, a method for producing an optical film that has a high Re of 30 nm or more, a low Rth value relative to Re, and a low haze value as compared with the prior art. The purpose is to provide.

  In the method for producing a film of the present invention, a dope containing cellulose acylate and a solvent is cast on a traveling support to form a cast film, and the cast film has a self-supporting property by cooling. After the wet film forming step of peeling off from the support as a wet film and the gas having an average temperature in the range of 70 (° C.) to 115 (° C.), the residual solvent amount reaches 25% by weight. The wet film was dried, and during this drying, the wet film was stretched in the width direction to obtain an intermediate film, and the average temperature was in the range of 40 (° C.) to 90 (° C.). In the gas, the second step of drying the intermediate film so that the residual solvent amount is from 25% by weight to 10% by weight, and after the second step, the residual solvent amount reaches 10% by weight. The intermediate film is (℃) or 195 (℃) in a temperature set gas below, and having a third step of stretching in the width direction.

  It is preferable that the wet film widening ratio in the third step is 10% or more and 60% or less. The first step and the second step are preferably performed by a pin tenter that holds both side edges of the wet film or the intermediate film with pins. It is preferable to perform the third step by a clip tenter that holds both side edges of the intermediate film with clips.

  An optical film having Re of 30 (nm) or more, a low Rth value relative to Re, and a low haze value can be efficiently produced.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described here.

[Dope raw materials]
As the dope raw material, cellulose acylate is used as a solute. The solvent is not particularly limited as long as it dissolves or disperses cellulose acylate. Here, the dope refers to a polymer solution or dispersion obtained by dissolving a polymer in a solvent or dispersing in a dispersion medium. The details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148, and these descriptions can also be applied to the present invention.

  Specific examples of the dope solvent 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.), ethers (eg, tetrahydrofuran, methyl cellosolve, etc.) and the like.

  Among these solvents, halogenated hydrocarbons having 1 to 7 carbon atoms are preferable, and dichloromethane is most preferable. And from the viewpoint of properties such as solubility of cellulose acylate, peelability from a cast film support, mechanical strength of the film, and optical properties of the film, one or several kinds of alcohols having 1 to 5 carbon atoms are used. Is preferably mixed with dichloromethane. At this time, it is preferable that content of alcohol is 2-25 (weight%) with respect to the whole solvent, and it is more preferable that it is 5-20 (weight%). Preferable specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, etc. Among them, methanol, ethanol, n-butanol, or a mixture thereof is preferably used.

  Various additives are added to the dope. Examples of additives include plasticizers, deterioration inhibitors, ultraviolet absorbers, optical anisotropy control agents, dyes, matting agents, release agents, and retardation increasing agents.

  Regarding additives such as plasticizers, deterioration inhibitors, ultraviolet absorbers, optical anisotropy control agents, dyes, matting agents, release agents, etc., paragraphs [0196] to [0516] of JP-A-2005-104148 are also used. These descriptions are also applicable to the present invention.

  The retardation increasing agent is described in paragraphs [0030] to [0142] of JP-A-2006-235383, and these descriptions can also be applied to the present invention.

[Dope production method]
FIG. 1 shows a dope manufacturing facility. However, the present invention is not limited to the dope manufacturing apparatus and method shown here. The dope production facility 10 includes a solvent tank 11, a hopper 12, an additive tank 13, a mixing tank 15, a heating device 16, a temperature regulator 17, a filtration device 18, a flash device 22, and a filtration device 23. With.

  The solvent tank 11 stores a solvent. The hopper 12 supplies cellulose acylate. The additive tank 13 stores the additive. In the mixing tank 15, the solvent, cellulose acylate, and additive are mixed to obtain a mixed solution 14. Then, the mixed solution 14 is heated by the heating device 16. In the temperature adjuster 17, the temperature of the heated mixed liquid 14 is adjusted. The dope 21 is obtained by filtering the mixed solution 14 from the temperature regulator 17 with the filtration device 18. In the flash device 22, the concentration of the dope 21 from the filtration device 18 is adjusted. The filtering device 23 filters the dope 21 whose concentration has been adjusted.

  The dope manufacturing facility 10 further includes a recovery device 24 for recovering the solvent and a regeneration device 25 for regenerating the recovered solvent. This dope manufacturing equipment 10 is connected to a solution casting equipment 27 via a stock tank 26. In addition, although the valves 31-33 for adjusting the amount of liquid feeding and the pumps 34 and 35 for liquid feeding are provided in dope manufacturing equipment 10, about the position where these are arranged, and increase / decrease in the number of pumps suitably Be changed.

  The dope 21 is manufactured by the following method by the dope manufacturing facility 10. By opening the valve 32, the solvent is sent from the solvent tank 11 to the mixing tank 15. Next, cellulose acylate is fed into the mixing tank 15 from the hopper 12. At this time, the cellulose acylate may be continuously sent to the mixing tank 15 by a sending unit that continuously measures and delivers, or the mixing tank 15 by a sending unit that measures and sends a predetermined amount. May be sent intermittently. In addition, the required amount of the additive solution is sent from the additive tank 13 to the mixing tank 15 by opening and closing the valve 31.

  In addition to the method of feeding the additive as a solution, for example, when the additive is liquid at room temperature, the additive can be fed into the mixing tank 15 in the liquid state. Further, when the additive is solid, a method of feeding into the mixing tank 15 using a hopper or the like is also possible. When a plurality of types of additives are added, a solution in which a plurality of types of additives are dissolved can be placed in the additive tank 13. Alternatively, it is also possible to use a plurality of additive tanks and put a solution in which the additive is dissolved into each of them and send them to the mixing tank 15 through independent pipes.

  In the above description, the order of putting in the mixing tank 15 is the solvent, cellulose acylate, and additive, but is not limited to this order. Moreover, an additive is not necessarily limited to mixing with a cellulose acylate and a solvent in the mixing tank 15, and may be mixed with the mixture of a cellulose acylate and a solvent by an in-line mixing system etc. at a next process.

  The mixing tank 15 includes a jacket 36 that covers the outer surface of the mixing tank 15 and is supplied with a heat transfer medium between the mixing tank 15, a first stirrer 38 that is rotated by a motor 37, and a second stirrer 42 that is rotated by a motor 41. It is preferable that it is attached. The temperature of the mixing tank 15 is adjusted by a heat transfer medium flowing into the inside of the jacket 36, and a preferable temperature range is −10 ° C. to 55 ° C. By appropriately selecting and using the types of the first stirrer 38 and the second stirrer 42, a mixed liquid 14 in which cellulose acylate is swollen with a solvent is obtained. The first stirrer 38 preferably has an anchor blade, and the second stirrer 42 is preferably a dissolver type eccentric stirrer.

  Next, the mixed liquid 14 is sent to the heating device 16 by the pump 34. The heating device 16 is preferably a jacketed tube having a tube main body (not shown) and a jacket for passing a heat transfer medium between the tube main body, and further pressurizing the mixed liquid 14. It is preferable to have a part (not shown). By using such a heating device 16, the solid content in the mixed solution 14 can be effectively and efficiently dissolved under heating conditions or pressure heating conditions. Hereinafter, such a method of dissolving a solid component in a solvent by heating is referred to as a heating dissolution method. In the heating dissolution method, it is preferable to heat the mixed solution 14 so as to be 0 ° C to 97 ° C.

  Note that the solid component may be dissolved in a solvent by a cooling dissolution method instead of the heating dissolution method. The cooling dissolution method is a method of proceeding dissolution while cooling the mixed solution 14 in a state where the temperature is maintained or even lower. In the cooling dissolution method, the mixed solution 14 is preferably cooled to a temperature of −100 ° C. to −10 ° C. The cellulose acylate can be sufficiently dissolved in the solvent by the heating dissolution method or the cooling dissolution method as described above.

  After the mixed liquid 14 is brought to about room temperature by the temperature controller 17, it is filtered by a filtration device 18 to remove foreign matters such as impurities and aggregates to obtain a dope 21. The filter used in the filtration device 18 preferably has an average pore diameter of 100 μm or less. The filtration flow rate is 50 liters / hr. The above is preferable.

  The dope 21 after filtration is sent to the stock tank 26 by the valve 33 and once stored, and then used for film production.

  By the way, as described above, the method in which the solid component is once swollen and then dissolved to form a solution increases the time required for the dope production as the concentration of the cellulose acylate in the solution increases. May be problematic in terms. In such a case, it is preferable to once make a dope having a concentration lower than the target concentration and then carry out a concentration step to achieve the target concentration. For example, the dope 21 can be concentrated by sending the dope 21 filtered by the filtering device 18 to the flash device 22 by the valve 33 and evaporating a part of the solvent of the dope 21 by the flash device 22. The concentrated dope 21 is extracted from the flash device 22 by the pump 35 and sent to the filtration device 23. The temperature of the dope 21 during filtration is preferably 0 ° C to 200 ° C. The dope 21 from which foreign substances have been removed by the filtration device 23 is sent to the stock tank 26 and once stored, and then used for film production. In addition, since the concentrated dope 21 may contain bubbles, it is preferable to perform a bubble removal process before sending it to the filtration device 23. As the bubble removal method, various known methods such as an ultrasonic irradiation method in which ultrasonic waves are applied to the dope 21 are applied.

  Further, the solvent gas generated by the flash evaporation in the flash device 22 is condensed and recovered as a liquid by a recovery device 24 having a condenser (not shown). The recovered solvent is regenerated and reused as a solvent for dope production by the regenerator 25. Such collection and recycling have advantages in terms of manufacturing costs and are effective in preventing adverse effects on the human body and the environment because they are implemented in a closed system.

  The dope 21 having a cellulose acylate concentration in the range of 5 (wt%) or more and 40 (wt%) or less is manufactured by the above manufacturing method. The cellulose acylate concentration is more preferably in the range of 15 (wt%) to 30 (wt%), and still more preferably in the range of 17 (wt%) to 25 (wt%). Moreover, it is preferable to make the density | concentration of an additive into the range of 1 (weight%) or more and 20 (weight%) or less with respect to the whole solid content.

  In addition, about the raw material in the solution casting method which obtains a cellulose acylate film, a raw material, the dissolution method of the additive, the filtration method, defoaming, and the addition method, [0517] Paragraph [0617] of JP, 2005-104148, A The paragraphs are detailed and these descriptions can also be applied to the present invention.

[Film production equipment and method]
FIG. 2 is a schematic view showing the solution casting apparatus 27 according to the first embodiment of the present invention. However, the present invention is not limited to the solution casting apparatus 27. The solution casting equipment 27 includes a filtration device 51, a casting chamber 53, a first tenter 55, a second tenter 57, and an edge-cutting device 58 that separates both side ends of the film 52 sent from the second tenter 57. And a drying chamber 60 that dries the film 52 while being conveyed over a plurality of rollers 59, a cooling chamber 61, a static elimination device 62, a knurling roller pair 63, and a winding chamber 64.

  The filtration device 51 removes foreign substances from the dope 21 sent from the stock tank 26. In the casting chamber 53, the dope 21 filtered by the filtration device 51 is cast into a casting film 76, and the casting film 76 is peeled off to obtain the wet film 54. In the first tenter 55, the intermediate film 56 is obtained by drying while holding both side ends of the wet film 54 while being conveyed. In the second tenter 57, the intermediate film 56 delivered from the first tenter 55 is dried while being transported to obtain a film 52 that is a cellulose acylate film. In the cooling chamber 61, the film 52 is cooled, and the charge removal amount of the film 52 is reduced by the static eliminator 62. Embossing is performed on the side end portion of the film 52 by the knurling roller pair 63, and then the film 52 is wound in the winding chamber 64.

  An agitator 72 that is rotated by a motor 71 is attached to the stock tank 26, and the dope 21 is agitated by the rotation of the agitator 72. The dope 21 in the stock tank 26 is sent to the filtration device 51 by the pump 73.

  The casting chamber 53 is provided with a casting die 74 that flows out of the dope 21 and a drum 75 as a support on which the dope 21 is cast on the peripheral surface.

  The drum 75 is provided with a heat transfer medium circulation device 77 that supplies a heat transfer medium into the drum 75 to control the surface temperature of the drum 75. A heat transfer medium flow path (not shown) is formed inside the drum 75, and the heat transfer medium maintained at a predetermined temperature passes through the flow path, so that the drum 75 The temperature of the peripheral surface is held at a predetermined value. The surface temperature of the drum 75 is appropriately set according to the type of solvent, the type of solid component, the concentration of the dope 21, and the like.

  A decompression chamber 78 is provided in the vicinity of the casting die 74. The decompression chamber 78 sucks and decompresses air in the upstream area of the casting bead formed from the casting die 74 to the drum 75 in the rotation direction of the drum 75.

  The casting chamber 53 is provided with a temperature control device 81 for keeping the internal temperature at a predetermined value, and a condenser (condenser) 82 for condensing and recovering the solvent evaporated from the dope 21 and the casting film 76. It is done. A recovery device 83 for recovering the condensed and liquefied solvent is provided outside the casting chamber 53.

  An air blower (not shown) may be provided in the transition portion 84 from the casting chamber 53 to the first tenter 55.

  The first tenter 55 that stretches and dries the wet film 54 while transporting the wet film 54 while holding both side ends of the wet film 54 with holding means is provided with a blower duct 79 that supplies dry air. ing. The temperature of the atmosphere (gas) inside the first tenter 55 is adjusted by controlling the temperature of the drying air to be sent out from the air duct 79.

  The second end of the intermediate film 56 guided from the first tenter 55 is held, the intermediate film 56 is conveyed, and the intermediate film 56 is heated while being stretched to obtain the film 52. As with the first tenter 55, the tenter 57 is provided with a blower duct 80 for supplying dry air.

  Further, the ear clip device 58 is provided with a crusher 85 for finely cutting the side edge scraps of the cut film 52.

  An adsorption recovery device 86 for adsorbing and recovering the solvent gas generated by evaporation from the film 52 is attached to the drying chamber 60. A cooling chamber 61 is provided downstream of the drying chamber 60, and a humidity control chamber (not shown) for adjusting the water content of the film 52 may be further provided between the drying chamber 60 and the cooling chamber 61. .

  The static eliminator 62 is a so-called forced static eliminator such as a static eliminator, and adjusts the charged voltage of the film 52 to be within a predetermined range. The position of the static eliminating device 62 is not limited to the downstream side of the cooling chamber 61. The knurling imparting roller pair 63 imparts knurling to both end portions of the film 52 by embossing. Inside the take-up chamber 64, a take-up roll 87 for taking up the film 52 and a press roller 88 for controlling the tension during the take-up are provided.

  Next, 1st Embodiment of this invention of the method of manufacturing the film 52 with the solution casting apparatus 27 is described below. The dope 21 is sent to the stock tank 26 and is always made uniform by the rotation of the stirrer 72 therein. Thereby, precipitation of solid content and aggregation are suppressed until it uses for casting. Various additives can be appropriately mixed in the dope 21 during the stirring. And the foreign material of a size more than a predetermined particle size and a gel-like foreign material are removed by filtration with the filtration apparatus 51. FIG.

  The dope 21 after being filtered is cast from the casting die 74 to the drum 75. The temperature of the dope 21 at the time of casting is preferably constant in the range of 30 to 35 (° C.), and the surface temperature of the drum 75 is preferably constant in the range of −10 to 10 (° C.). The temperature of the casting chamber 53 is preferably set to 10 to 30 (° C.) by the temperature control device 81. The solvent evaporated in the casting chamber 53 is recovered by the recovery device 83 and then regenerated and reused as a solvent for dope production.

  A casting bead is formed from the casting die 74 to the drum 75, and a casting film 76 is formed on the drum 75. The cast film 76 is cooled by a drum 75 to be gelled and solidified. When the casting film 76 has self-supporting properties, it is peeled off from the drum 75 while being supported by the peeling roller 91 to obtain the wet film 54. The stripping can be performed as long as the casting film 76 has sufficient hardness for conveyance, regardless of the amount of solvent remaining in the casting film 76. Here, in the present invention, the solvent residual amount is a value based on the dry amount. Specifically, when the weight of the solvent is x and the weight of the casting film 76 or an intermediate film 56 described later is y, {x / (Y−x)} × 100. Hereinafter, the solvent residual amount of the casting film 76 at the time of peeling is referred to as “W”.

  In consideration of production efficiency, it is preferable to cool the cast film 76 so that the cast film 76 is sufficiently hard even if the solvent residual amount W of the cast film 76 is high. The exposed surface of the cast film 76 is sufficiently solidified by cooling. If so, by taking measures such as flowing dry air in the vicinity of the casting film 76, it is possible to further improve the transport stability after peeling. When the production speed is set to 50 m / min or higher, it is preferable that the cooling is performed rapidly so that the cast film 76 can be stripped even if the residual solvent amount is 140 wt% or more. If the cooling temperature cannot be set low and cannot be rapidly cooled, the drum 75 may have to be enlarged in order to extend the transport time of the casting film 76. Further, when the residual amount of the solvent in the casting film 76 is higher than 320% by weight, it is difficult to make the casting film 76 sufficiently hard to carry even if the casting film 76 is cooled.

  The wet film 54 containing a large amount of solvent is sent to the first tenter 55. Both ends of the wet film 54 are held by pins, and are conveyed by the travel of the pins. The wet film 54 is dried by the drying air from the air duct 79 provided in the first tenter 55 while being conveyed.

  FIG. 3 is a schematic diagram of the inside of the first tenter 55. The first tenter 55 includes a pin plate 102, a chain 103, a rail 104, and a drying duct 79 (see FIG. 1). The pin plate 102 is disposed at the position of both end portions of the wet film 54 along the conveyance path of the wet film 54. The pin plate 102 has a large number of pins 101. The multiple pin plates 102 are attached to the chain 103. The chain 103 travels endlessly. The track of the chain 103 is determined by the rail 104. The rail 104 is provided with a shift mechanism 105.

  When the wet film 54 sent to the first tenter 55 reaches a predetermined position, the pins 101 are inserted and held at both end portions. The shift mechanism 105 moves the rail 104 in the width direction of the wet film 54, whereby the chain 103 moves. The pin plate 102 on the chain 103 moves in the width direction of the wet film 54 while holding the wet film 54, and tension is applied to the wet film 54 in the width direction.

  The wet film 54 immediately after being peeled off from the drum 75 contains a large amount of solvent and is very unstable. Therefore, the wet film 54 is difficult to transport with a roller and cannot withstand gripping with a clip. Therefore, as in this embodiment, when the both ends of the wet film 54 are pierced with the pins 101, the wet film 54 can be stably held and transported.

  FIG. 4 is an explanatory view showing a stretched state of the wet film 54 in the first tenter 55. The arrow line X is the conveyance direction of the wet film 54. In the first tenter 55, a position where the holding of the wet film 54 by the pin 101 (see FIG. 3) is started is a first position P1, and a position where the holding is released is a second position P2. The inlet of the first tenter 55 is on the upstream side of the first position P1, and the outlet is on the downstream side of the second position P2, but the illustration is omitted in FIG.

  Although the solvent gradually evaporates from the wet film 54 peeled off from the drum, the solvent residual amount tends to be lower than the solvent residual amount W at the time of peeling, but the width direction Y1, Y2 of the wet film 54 Stretching is started as soon as possible.

  The stretching is completed until the residual solvent amount of the wet film 54 is at least 25% by weight. More preferably, the stretching is finished by 35% by weight. More preferably, the stretching is completed up to 40% by weight. Here, the position where stretching is started is defined as a third position P3. A position at which the stretching is finished is set as a fourth position P4.

  In the first tenter 55, the wet film 54 is dried until the wet film 54 reaches a predetermined solvent residual amount, specifically 25% by weight, and a first step of stretching during the drying is performed. The wet film obtained in the first step is referred to as an intermediate film 56. And after this 1st process, the 2nd process which carries out the drying of the intermediate film 56 used as the solvent residual amount of 25 weight%, and is 10 weight% is implemented.

  In the first tenter 55, tension is applied to the wet film 54 in the width directions Y1 and Y2. When the tension is not applied in the width direction Y1, Y2 in the first tenter 55, the wet film 54 is slackened by its own weight or contracts in the width direction Y1, Y2 as the solvent evaporates. Therefore, in order to prevent slack, tension is applied to the wet film 54 in the width directions Y1 and Y2 (first stretching step). The tension is preferably applied to the wet film 54 symmetrically with respect to the center in the width direction of the wet film 54. This is because the molecular orientation is uniformly controlled in the width direction of the wet film 54.

  Since the wet film 54 is transported, tension is always applied in the transport direction X, and the cellulose acylate molecules of the wet film 54 tend to be oriented in the transport direction X. Therefore, in order to increase Re while suppressing an increase in Rth, the molecular orientation in the width direction is increased after relaxing the molecular orientation in the transport direction X of the wet film 54.

  In addition to the purpose of preventing loosening, the wet film 54 can be tensioned in the width directions Y1 and Y2 to increase the molecular orientation in the width directions Y1 and Y2. Thereby, the molecular orientation in the width directions Y1 and Y2 can be increased with respect to the molecular orientation extending in the conveyance direction X of the cellulose acylate of the wet film 54.

  In general, the molecular orientation in the thickness direction of the film is difficult to adjust unless the thickness of the film is adjusted. Since the film is manufactured to have a predetermined thickness, the molecular orientation in the thickness direction is limited to a predetermined value. Therefore, Rth is controlled by adjusting the molecular orientation in the transport direction and the molecular orientation in the width direction.

  By applying tension to the wet film 54 in the width direction Y1, Y2, the width of the wet film 54 that was the width L1 (hereinafter referred to as “first width”) when entering the first tenter 55 is reduced to L2 (hereinafter referred to as “first width”). (Referred to as “second width”) (first stretching step). Thus, the first step includes a first stretching step. That is, the start timing may coincide with each other and the end timings may coincide with each other so that the first step and the first stretching step overlap with each other, or the start of the first step and the first stretching may be performed. The aspect implemented in order of the start of a process, completion | finish of a 1st extending | stretching process, and completion | finish of a 1st process may be sufficient.

  Next, the second width L2 of the intermediate film 56 is increased to L3 (hereinafter referred to as “third width”) (second stretching step). In the second step, stretching may not be performed, but it is preferable that the second step includes a second stretching step as in the present embodiment. When the second step includes the second stretching step, the start timings coincide with each other and the end timings coincide with each other so that the second step and the second stretching step overlap in time. Alternatively, it may be implemented in the order of the start of the second step, the start of the second stretching step, the end of the second stretching step, and the end of the second step.

  And in the 1st tenter 55, it is preferable after this 2nd process to implement the holding process which hold | maintains this width | variety L3 so that it may not change after this. When the third width L3 is held, tension is applied to the intermediate film 56 in the width directions Y1 and Y2. This is because the intermediate film 56 tends to shrink when the solvent of the intermediate film 56 volatilizes. In the following description, the case of increasing the width is referred to as “widening”. In FIG. 4, reference numeral KL represents the position of the wet film 54 or intermediate film 56 held by a pin on the most central side in the width direction of the wet film 54 or the intermediate film 56. Each of the width to the third widths L1 to L3 is a distance between the holding target lines KL on both sides. A point where the width of the wet film 54 is extended to L2 is defined as a fifth position P5.

  The widening ratio from the third position P3 to the fifth position P5 is 5% or more and 30% or less. Here, the widening rate is the ratio of the length of the portion that has been widened and extended with respect to the length before widening. For example, the expansion ratio of the wet film 54 in the first tenter is a value obtained by {(L2-L1) / L1} × 100.

  The molecular orientation in the transport direction X is completed by ending the widening of the solvent residual amount from the W weight% until the widening starts to 25 weight%, more preferably 35 weight%. The molecular orientation in the width direction can be increased while relaxing. However, widening after the residual solvent amount is less than 25% by weight has little effect of relaxing the molecular orientation in the transport direction X. This is because the wet film 54 is solidified by drying.

  Further, when the width expansion ratio from the third position P3 to the fifth position P5 is less than 5%, there is almost no effect of extending the molecular orientation in the width directions Y1 and Y2. On the other hand, if the widening ratio is larger than 30%, the wet film 54 may be torn along the holding target line KL or the like depending on the amount of residual solvent. Therefore, in the Y1, Y2 direction of the wet film 54, the width expansion rate can be extended only in a range corresponding to 30%, and the orientation in the Y1, Y2 direction cannot be increased beyond the value corresponding to the width expansion rate of 30%. .

  When stripping from the drum 75 is performed when the residual solvent amount is 320% by weight, the residual solvent amount of the wet film 54 is from the third position P3 to the fifth position P5 inside the first tenter 55. Is 25 (wt%) or more and 320 (wt%) or less. In the first tenter 55, the temperature of the atmosphere (gas) in the conveyance path of the wet film 54 is set to 70 (° C.) or more and 115 (° C.) or less for at least the area from the third position P3 to the fifth position P5. Then, as described above, the wet film 54 is stretched. The temperature of the gas inside the first tenter 55 is more preferably 75 (° C.) to 110 (° C.), and still more preferably 80 (° C.) to 105 (° C.).

  The above temperature range for the atmosphere (gas) in the area from the third position P3 to the fifth position P5 is the average temperature in this area. Therefore, the temperature may be lower than a part of the area 70 ° C. included in this area or higher than 115 ° C.

  When the average temperature of the gas inside the first tenter 55 is lower than 70 (° C.), the effect of relaxing the molecular orientation in the transport direction does not occur even when the wet film 54 is stretched in the width directions Y1 and Y2. Therefore, Rth increases with respect to Re. When the average temperature of the gas inside the first tenter 55 is higher than 115 (° C.), the film may foam.

  In the fifth position P5 to the fourth position P4, the residual solvent amount of the intermediate film 56 is 10% by weight or more and less than 25% by weight. In the second step, as described above, it is preferable to perform the second stretching step in which the second width L2 is increased to the third width L3 by applying tension.

  The widening ratio from the fifth position P5 to the fourth position P4 is 0% or more and 20% or less. That is, it is not always necessary to perform the second stretching step, and the width may be maintained at a width of 0 (zero), but it is more preferable to perform the second stretching step in which the width expansion rate is greater than zero. The widening ratio in the second stretching step is preferably 1% or more and 15% or less, and more preferably 2% or more and 10% or less. When the expansion ratio is made smaller than 0%, that is, when the width is reduced, molecular orientation in the width direction may be reduced. Further, if the widening ratio is set to 20% or more, the intermediate film 56 may be torn. Here, the widening ratio of the intermediate film 56 in the first tenter is a value obtained by {(L3-L2) / L2} × 100.

  Between the fifth position P5 and the fourth position P4, the average temperature of the gas inside the first tenter 55 is set to 40 (° C.) or more and 90 (° C.) or less. The average temperature of the gas inside the first tenter 55 is more preferably 45 (° C.) or more and 85 (° C.) or less, and further preferably 50 (° C.) or more and 80 (° C.) or less.

  The above temperature range for the atmosphere (gas) in the area from the fifth position P5 to the fourth position P4 is the average temperature in this area. Therefore, some areas included in this area may have a temperature lower than 40 ° C. or a temperature higher than 90 ° C.

  When the average temperature of the gas inside the first tenter 55 between the fifth position P5 and the fourth position P4 is smaller than 40 (° C.), the haze value in the film 52 increases, so that the optical film emphasizes transparency. Unusable. Furthermore, the intermediate film 56 becomes hard and is easy to tear.

  When the average temperature of the gas inside the first tenter 55 between the fifth position P5 and the fourth position P4 is made larger than 90 (° C.), the intermediate film 56 is stretched in the Y1 and Y2 directions to change the molecular orientation in the width direction. Despite the increase, the side chains of the molecules are aligned in the transport direction X of the intermediate film 56 due to crystallization. Therefore, the film 52 obtained from the intermediate film 56 is a film having a high Rth value relative to Re.

  Here, the haze value (unit:%) is the degree of an unclear cloudy appearance inside or on the surface of a transparent film, and the numerical value is called a haze value. The haze test method measures the light transmittance of a test piece, and is represented by haze value Th = 100 × scattered light transmittance Td / total light transmittance Tt.

  After the second step, a width holding step may be further performed. In this width maintaining step, it is preferable to further dry. And it is good also considering the average temperature of the gas of the area which implements this width maintenance process, ie, the area from P4 to P2, as the 2nd process.

  The intermediate film 56 that has passed through the first tenter 55 is difficult to prevent the intermediate film 56 from being tensioned in the transport direction X due to the transport, and the molecular orientation in the transport direction X to proceed. However, since the wet film 54 can be given molecular orientation in the width directions Y1 and Y2 by the first stretching process in the first tenter 55 and also by the second stretching process, the transport direction X A certain balance can be established between the molecular orientations in the width direction and the molecular orientations in the width directions Y1 and Y2. In FIG. 4, the first step and the second step in the first tenter 55 are performed continuously, but a non-stretching area in which stretching is not performed may be provided between the first step and the second step. Good.

  Next, the intermediate film 56 whose residual solvent amount has reached 10 wt% in the first tenter 55 is sent to the second tenter 57. The solvent residual amount of the intermediate film 56 sent to the second tenter 57 may be 0 (zero). In the second tenter 57, the intermediate film 56 is placed in an atmosphere (gas) in a predetermined temperature range. It may be dried while stretching in the width direction.

  In the second tenter 57, a third step of stretching the intermediate film 56 in the width direction in an atmosphere (gas) whose temperature has been adjusted to be within a predetermined temperature range is performed. The third step preferably includes a third stretching step for widening the intermediate film 56 by stretching, but may include a width holding and a width reducing step. FIG. 5 is an explanatory diagram showing the widened and contracted state of the intermediate film 56 in the second tenter 57. The arrow line X is the conveyance direction of the intermediate film 56. In the second tenter 57, a position where the holding means starts to hold the intermediate film 56 is an eleventh position P11, and a position where the holding is released is a twelfth position P12. The inlet of the second tenter 57 is on the upstream side of the first position P11, and the outlet is on the downstream side of the twelfth position P12.

  Unlike the first tenter 55, the second tenter 57 transports the intermediate film 56 having a solvent residual amount lower than that of the wet film 54. Therefore, the second tenter 57 is not a pin-type holding means but a clip-type gripping both end portions of the intermediate film 56. It is preferable to use a tenter device having holding means.

  Since the intermediate film 56 is harder than the wet film 54, the second tenter 57 softens the intermediate film 56 by applying heat to the intermediate film 56. And a 3rd extending | stretching process is implemented about the intermediate | middle film 56 which softened the intermediate | middle film 56 or was softened.

  In the second tenter 57, when the intermediate film 56 in which the residual solvent amount has already reached 10% by weight is applied to the second tenter 57 by applying tension, the width L11 (hereinafter referred to as “11th width”). ) Is increased to L12 (hereinafter referred to as “12th width”).

  A position at which the eleventh width L11 starts to widen to the twelfth width L12 is defined as a thirteenth position P13, and a position at which the widening from the thirteenth position P13 is completed is defined as a fourteenth position P14.

  The widening ratio from the thirteenth position P13 to the fourteenth position P14 is 10% or more and 60% or less. Preferably they are 15% or more and 55% or less, More preferably, they are 20% or more and 50% or less. When the widening ratio is 10% or less, the effect of extending the molecular orientation in the width direction hardly occurs. Further, when the widening ratio is set to 60% or more, the intermediate film 56 may be torn and the haze value may be increased. Here, the widening ratio of the intermediate film 56 in the second tenter is a value obtained by {(L12−L11) / L11} × 100.

  Furthermore, in the thirteenth position P13 to the fourteenth position P14, the temperature of the gas inside the second tenter 57 is set to 160 (° C.) or more and 195 (° C.) or less. More preferably, the temperature of the gas inside the second tenter 57 is not less than 165 (° C.) and not more than 190 (° C.), and is not less than 170 (° C.) and not more than 185 (° C.).

  When the temperature of the gas around the intermediate film 56 in the thirteenth position P13 to the fourteenth position P14 is made smaller than 160 (° C.) and the intermediate film 56 is stretched, the haze value in the intermediate film 56 increases. This is because, when the temperature is low, the intermediate film 56 is not sufficiently softened, so that the stress due to stretching increases and the space between the molecules spreads. For this reason, it cannot be used as an optical film that places importance on transparency. Furthermore, the intermediate film 56 is easily torn.

  When the set temperature of the gas around the intermediate film 56 in the thirteenth position P13 to the fourteenth position P14 is larger than 195 (° C.), the intermediate film 56 is stretched in the Y1 and Y2 directions to increase the molecular orientation in the width direction. Nevertheless, the side chains of the molecules are aligned in the transport direction X of the intermediate film 56 due to crystallization. For this reason, the intermediate film 56 has a higher Rth value than Re.

  When the width of the intermediate film 56 having the twelfth width L12 is reduced, the width after the reduction is set to L13 (hereinafter referred to as “13th width”). A position at which the twelfth width L12 starts to be widened to the thirteenth width L13 is defined as a fifteenth position P15, and a position at which the widening from the fifteenth position P15 ends is defined as a sixteenth position P16.

  Even when the twelfth width L12 is held and when the width is reduced from the twelfth width L12 to the thirteenth width L13, the film 52 has a width direction Y1, Y2 between the fifteenth position P15 and the sixteenth position P16. A tension is applied to the. In the case of reducing the width, the width is controlled by applying tension to this while utilizing the force that naturally contracts while being held by the holding means. In addition, in FIG. 5, code | symbol KM represents the position of the center part side in the width direction of the intermediate | middle film 56 among the holding | maintenance parts of the intermediate | middle film 56 hold | maintained by a holding means, and the 11th width-13th width L11- L13 is the distance between the holding target lines KM on both sides.

  The reduction ratio is preferably 10% or less. In the present invention, since the twelfth width L12 may be held without performing the reduction, the reduction ratio is 0% or more and 10% or less. By performing the contraction after the expansion, the molecular orientation can be made more appropriate from the viewpoint of thermal shrinkage dimensional stability. If the width reduction ratio is larger than 10%, the effect of the widening performed previously may be lowered. Here, the reduction ratio of the intermediate film 56 in the second tenter is a value obtained by (L12−L13) / L13} × 100.

  By adjusting the temperature at which the wet film 54 and the intermediate film 56 are widened by the solvent residual amount, the side chains of the molecules are aligned in the transport direction X due to crystallization, thereby preventing the retardation in the width direction from being lowered. Since the molecular orientation in the width direction can be increased, Re can be widely adjusted. Moreover, it can prevent that a haze value becomes high by extending | stretching.

  As shown in FIG. 1, the film 52 is dried to a predetermined solvent residual amount by the second tenter 57, and then the both end portions thereof are cut and removed by the ear clip device 58. The separated both ends are sent to a crusher 85 by a cutter blower (not shown). The crusher 85 pulverizes the side edges to form chips. Since this chip is reused for dope manufacturing, the raw material can be effectively used. In addition, although it can also abbreviate | omit about the cutting process of this both-sides edge part, it is preferable to carry out in any one from the said casting process to the process of winding up the said film.

  On the other hand, the film 52 from which both side ends have been removed is sent to the drying chamber 60 and further dried. In the drying chamber 60, the film 52 is conveyed while being wound around the roller 59. Although the internal temperature of the drying chamber 60 is not specifically limited, It is preferable to set it as 50 to 160 degreeC. The drying chamber 60 is more preferably divided into a plurality of sections in the transport direction of the film 52 in order to change the blowing temperature. In addition, if a preliminary drying chamber (not shown) is provided between the ear opener 58 and the drying chamber 60 to preliminarily dry the film 52, the film temperature is prevented from rising sharply in the drying chamber 60. The shape change of the film 52 in the chamber 60 can be suppressed. The solvent gas generated by evaporation in the drying chamber 60 is adsorbed and recovered by the adsorption recovery device 86. The air from which the solvent component has been removed is sent again as drying air into the drying chamber 60.

  The film 52 is cooled to substantially room temperature in the cooling chamber 61. In the case where a humidity control chamber is provided between the drying chamber 60 and the cooling chamber 61, it is preferable to blow air adjusted to a desired humidity and temperature onto the film 52 in the humidity control chamber. Thereby, it is possible to suppress the occurrence of curling of the film 52 and winding failure when winding.

  The neutralizing device 62 sets the charged voltage while the film 52 is being conveyed to a predetermined value. The charged voltage after neutralization is preferably -3 kV to +3 kV. Further, the film 52 is preferably imparted with knurling by a knurling roller pair 63. In addition, it is preferable that the height of the unevenness | corrugation of the knurled location is 1 micrometer-200 micrometers.

  The film 52 is taken up by a take-up roll 87 in the take-up chamber 64 to form a film original. It is preferable to wind the film while applying a desired tension to the film 52 by the press roller 88. It is more preferable to gradually change the tension from the start to the end of winding, thereby preventing excessive winding in the film roll. The length of the film to be wound is preferably 1400 to 3400 mm or less. However, the present invention is applied even when the width is larger than 3400 mm. The present invention is also applied to the production of a thin film having a thickness of 15 μm to 100 μm.

  Next, a second embodiment of a method for producing the film 52 by the solution casting equipment 27 will be described below. In 2nd Embodiment, the same code | symbol is attached | subjected about the same member as 1st Embodiment. The description of the same member is also omitted.

  FIG. 6 is a schematic view showing an off-line stretching facility 92 according to the second embodiment of the present invention. In the first embodiment, the off-line stretching equipment 92 of the second embodiment has no second tenter 57 and the intermediate film 56 exits the first tenter 55 and then winds through the drying chamber 60 and the cooling chamber 61 in the first embodiment. When the intermediate film 56 is wound up (see FIG. 2), the intermediate film original 93 of the intermediate film 56 that has been wound is stretched in the width direction by the second tenter 111. That is, the intermediate film original fabric 93 is guided by the solution casting apparatus 27 (see FIG. 2), and the intermediate film 56 that has exited the first tenter 55 is guided to the drying chamber 60 without passing through the second tenter 57 to be dried. Then, it is obtained by sequentially feeding to the cooling chamber 61 and the winding chamber 64 and winding in the winding chamber 64. The same apparatus and members in FIG. 2 in the off-line drawing facility 92 in FIG.

  The offline stretching equipment 92 includes a film delivery chamber 94, a second tenter 111, a stress relaxation chamber 120, a cooling chamber 61, and a film take-up chamber 64 in order, and the intermediate film 56 is heated by the second tenter 111. Is added and stretched. In the stress relaxation chamber 120, the film 52 is heated in order to relieve the stress strain generated in the film 52 by stretching.

  The film delivery chamber 94 includes a film delivery machine 96 in which the intermediate film original fabric 93 is set. The film delivery machine 96 is provided with a mounting shaft (not shown). An intermediate film original fabric 93 is set on the mounting shaft. The intermediate film 56 is sent out. The intermediate film 56 of the intermediate film 93 has specific Re and Rth set by the first tenter 55 (see FIG. 2). In addition, a plurality of film feeders 96 may be provided in order to continuously send a plurality of intermediate film originals 93 having various specific Re and Rth to the second tenter 57.

  In the first embodiment, stretching by the first tenter 55 and stretching by the second tenter 57 are continuously performed, whereas in the second embodiment, the intermediate film 56 that has already been stretched by the first tenter is used. The intermediate film 93 is pulled out and stretched by the second tenter 111. Therefore, by stretching the intermediate film 56 having different ratios of the molecular orientation degree in the transport direction and the molecular orientation degree in the width direction with the second tenter 111 of the off-line stretching equipment 92 under predetermined conditions, The final Re and Rth corresponding to each can be adjusted. For example, an original film of an intermediate film having a predetermined Re and Rth is stored, and when necessary, it is thermally stretched by the second tenter 111 to have any necessary combination of Re and Rth as appropriate. A film can be created. When a plurality of film delivery machines 96 are provided, by switching the film delivery machine 96 that sends out the intermediate film 56 and changing the stretching conditions in the second tenter 111, various types of intermediate film 56 are provided. On the other hand, it is possible to efficiently produce many kinds of films in which Re and Rth are different from each other by performing stretching one after another.

  The film produced in the first and second embodiments described above is suitable for an optical film of a liquid crystal display, and more suitable for use as a polarizing plate retardation film.

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

A dope 21 having the following formulation was produced by the dope manufacturing facility 10 shown in FIG.
Cellulose triacetate (substitution degree 2.94, viscosity average degree of polymerization 305.6%, viscosity of dichloromethane solution 6% by weight, viscosity 350 mPa · s) 100 parts by weight dichloromethane (first component of solvent) 390 parts by weight methanol (second component of solvent) ) 60 parts by weight Citric acid ester mixture (citric acid, monoethyl ester, diethyl ester, triethyl ester mixture) 0.006 part by weight Fine particles (silicon dioxide (average particle size 15 nm), Mohs hardness about 7) 0.05 part by weight N -N-di-m-toluyl-NP-methoxyphenyl-1,3,5-triazine-2,4,6-triamine (retardation increasing agent) 8 parts by weight

  A plurality of films 52 were manufactured by the solution casting apparatus 27 in FIG. 2 using the dope. The thickness of the film 52 was 45 μm. The speed at which the film 52 is conveyed was 60 [m / min]. In Example 1, a film satisfying the present invention was produced. The temperature in the first tenter 55 until the residual solvent amount of the wet film 54 reached 25% by weight was 100 ° C. The stretching widening ratio in the first tenter 55 until the residual solvent amount of the wet film 54 reached 25% by weight was set to 10%. The stretching temperature set by the first tenter 55 when the solvent residual amount of the intermediate film 56 was 10 wt% or more and less than 25 wt% was 50 ° C. Here, the stretching temperature is the average temperature of the gas in the tenter when stretching is performed. When the residual amount of the solvent in the intermediate film 56 is 10% by weight or more and less than 25% by weight, the width expansion ratio of the first tenter 55 is 5%. The stretching temperature of the second tenter 57 when the residual solvent amount of the intermediate film 56 was less than 10% by weight was 180 ° C. When the solvent residual amount of the intermediate film 56 is less than 10% by weight, the widening ratio of the stretching of the second tenter 57 was set to 40%. In the following Examples 1-12, the manufacturing conditions of this invention were satisfy | filled, and the comparative example 1-7 produced the film 52, without satisfying the manufacturing conditions of this invention.

  In Example 2, the same conditions as in Example 1 were used except that the stretching temperature in the first tenter 55 until the solvent residual amount of the wet film 54 reached 25% by weight was set to 70 ° C.

  In Example 3, the same conditions as in Example 1 were used except that the stretching temperature in the first tenter 55 until the solvent residual amount of the wet film 54 reached 25% by weight was 115 ° C.

  In Example 4, the conditions were the same as in Example 1 except that the stretching temperature in the first tenter 55 was 40 ° C. when the solvent residual amount of the intermediate film 56 was less than 25% by weight and 10% by weight or more.

  In Example 5, the same conditions as in Example 1 were used except that the stretching temperature in the first tenter 55 was 90 ° C. when the solvent residual amount of the intermediate film 56 was less than 25% by weight and 10% by weight or more.

  In Example 6, the same conditions as in Example 1 were used except that the expansion ratio of the first tenter was 0% when the solvent residual amount of the intermediate film 56 was 10 wt% or more and less than 25 wt%.

  In Example 7, the conditions were the same as in Example 1 except that the stretching temperature in the second tenter 57 when the solvent residual amount of the intermediate film 56 was less than 10% by weight was 160 ° C.

  In Example 8, the conditions were the same as in Example 1 except that the stretching temperature in the second tenter 57 was 195 ° C. when the solvent residual amount of the intermediate film 56 was less than 10% by weight.

  In Example 9, the same conditions as in Example 1 were used except that the stretching ratio of the second tenter 57 when the residual solvent amount of the intermediate film 56 was less than 10% by weight was 10%.

  In Example 10, the same conditions as in Example 1 were used except that the stretching ratio of the second tenter 57 when the solvent residual amount of the intermediate film 56 was less than 10% by weight was 60%.

  In Example 11, the conditions were the same as in Example 1 except that the expansion ratio of the second tenter 57 when the solvent residual amount of the intermediate film 56 was less than 10% by weight was 9%.

  In Example 12, the conditions were the same as in Example 1 except that the stretching ratio of the second tenter 57 when the residual solvent amount of the intermediate film 56 was less than 10% by weight was 65%.

[Comparative Example 1]
In Comparative Example 1, the same conditions as in Example 1 were used except that the stretching temperature in the first tenter 55 until the solvent residual amount of the wet film 54 reached 25% by weight was 60 ° C.

[Comparative Example 2]
In Comparative Example 2, the same conditions as in Example 1 were used except that the stretching temperature in the first tenter 55 until the solvent residual amount of the wet film 54 reached 25% by weight was 120 ° C. As a result, the wet film 54 was foamed and could not be stretched, and was broken. For this reason, the next process could not be carried out and the film 52 could not be produced.

[Comparative Example 3]
In Comparative Example 3, the same conditions as in Example 1 were used except that the first tenter 55 until the residual amount of the solvent of the wet film 54 reached 25% by weight was not stretched and the stretching width was 0%. did.

[Comparative Example 4]
In Comparative Example 4, the conditions were the same as in Example 1 except that the stretching temperature in the first tenter 55 was set to 100 ° C. when the solvent residual amount of the intermediate film 56 was less than 25% by weight and 10% by weight or more.

[Comparative Example 5]
In Comparative Example 5, the same conditions as in Example 1 were used except that the stretching temperature in the first tenter 55 was 30 ° C. when the solvent residual amount of the intermediate film 56 was less than 25% by weight and 10% by weight or more.

[Comparative Example 6]
In Comparative Example 6, the same conditions as in Example 1 were used except that the stretching temperature in the second tenter 57 when the residual solvent amount of the intermediate film 56 was less than 10% by weight was 150 ° C.

[Comparative Example 7]
In Comparative Example 7, the conditions were the same as in Example 1 except that the stretching temperature in the second tenter 57 when the residual solvent amount of the intermediate film 56 was less than 10% by weight was 200 ° C.

  Table 1 shows the conditions and results of Examples 1 to 12 and Comparative Examples 1 to 7. The Re value is a result of sampling a part of the film 52 taken up in the take-up chamber 64 and examining the Re value for this sample piece. Specifically, it is a value (unit: nm) at 25 ° C. and 60% RH. The Rth value is a value (unit: nm) at 25 ° C. and 60% RH. The value of Rth / Re was determined and shown in the table. The haze value (unit:%) was determined by measuring the light transmittance of the test piece at 25 ° C. and 60% RH, and taking the value of (scattered light transmittance Td / total light transmittance Tt) × 100.

In Table 1,-in Comparative Example 2 indicates that the process could not be carried out, and the stretching temperature and the widening rate could not be set. Based on Re and Rth / Re and the haze value, the film was evaluated according to the following criteria.
A film having a haze value larger than 1.0 or Rth / Re larger than 3.0 could not be used as a polarizing plate retardation film, and was judged as poor. For convenience, the case where the process could not be carried out in Comparative Example 2 was also marked with x.
A film having a haze value of 1.0 or less, Re of 30 nm or more, and Rth / Re of 3.0 or less can be used as a polarizing plate retardation film. did;
Among them, in particular, a film having a haze value of 0.7 or less, Re of 30 nm or more, and Rth / Re of less than 2.5 is very excellent as a polarizing plate retardation film. It was judged as better and marked as ◎.

  About Comparative Examples 1-7 which does not satisfy | fill this invention, in Comparative Example 2, the film was not able to be obtained. In Comparative Examples 5 and 6, the Re value is 30 nm or more, the Rth value is also suppressed, and the Rth / Re value is 3.0 or less. However, since the haze value is larger than 1.0, it cannot be said that the film is a good film. In Comparative Examples 1 to 4 and 7, since the value of Rth / Re exceeded 3.0, a good film could not be obtained.

  On the other hand, in Examples 1 to 12 satisfying the present invention, Re is 30 nm or more, the Rth value relative to Re, the Rth / Re value is 3.0 or less, and the haze value is 1.0 or less. Therefore, it can be seen that according to the present invention, a film having Re of 30 nm or more, Rth / Re being suppressed, and a low haze value can be obtained.

It is the schematic of dope manufacturing equipment. It is the schematic of the solution casting apparatus which implements 1st Embodiment of this invention. It is the schematic which shows the holding | maintenance state of the wet film in a 1st tenter. It is explanatory drawing which shows the widened state of the wet film in a 1st tenter. It is explanatory drawing which shows the widening and shrinkage | contraction state of the intermediate film in a 2nd tenter. It is the schematic of the off-line extending | stretching equipment which implements 2nd Embodiment of this invention.

Explanation of symbols

21 Dope 54 Wet film 55 First tenter 56 Intermediate film 57 Second tenter 75 Drum 74 Casting die 76 Casting film 101 Pin 105 Shift mechanism

Claims (4)

A dope containing cellulose acylate and a solvent is cast on a running support to form a cast film, and after the cast film has self-supporting property by cooling, a wet film is formed from the support. A wet film forming process to peel off;
The wet film is dried in a gas whose average temperature is in the range of 70 (° C.) or more and 115 (° C.) or less until the residual solvent amount reaches 25% by weight. A first step of obtaining an intermediate film by stretching in the width direction;
A second step in which the intermediate film is dried so that the residual solvent amount is from 25 wt% to 10 wt% in a gas having an average temperature in the range of 40 (° C.) to 90 (° C.);
A third film is stretched in the width direction in a gas whose temperature is set to 160 (° C.) or more and 195 (° C.) or less after the solvent remaining amount reaches 10% by weight through the second step. Process,
A method for producing a film, comprising:   The method for producing a film according to claim 1, wherein the expansion ratio of the intermediate film in the third step is 10% or more and 60% or less.   The method for producing a film according to claim 1 or 2, wherein the first step and the second step are performed by a pin tenter that holds both side edges of the wet film or the intermediate film with pins. The method for producing a film according to any one of claims 1 to 3, wherein the third step is performed by a clip tenter that holds both side edges of the intermediate film with clips.

Images