JP2009262528A - Film manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a film having such optical properties as Re higher than those of conventional films, Rth low relative to Re and a suppressed haze. <P>SOLUTION: A dope 21 is cast on a running drum 75 to give a cast film 76. After the cast film 76 gets a self-supporting function by cooling, the film is peeled off as a wet film 54 from the drum 75, wherein a residual solvent amount of the wet film 54 upon peeling off of the cast film is shown as W. In a first tenter 55, the wet film 54 is drawn in a width direction under drying to give an intermediate film 56. Drawing is conducted on the wet film 54 until 5 to 30% drawing in a width direction is attained while the residual solvent amount reaches to (W-100) wt.%. In a second tenter 57, drawing is conducted on the intermediate film 56 until 10 to 60% drawing in a with direction is attained. In this way, a film having such optical properties that Re is higher than conventional ones, Rth relative to Re is low and a haze is suppressed can be manufactured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  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. It is necessary to have various optical characteristics represented by haze value (%). The “in-plane direction” of Re is a direction 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). The “surface direction” of Re is the surface direction of the film, that is, the direction of the surface perpendicular to the film thickness direction.
Re = (nx−ny) × d (1)
Rth = {(nx + ny) / 2−nz} × d (2)

  By the way, polymer films, especially films made from cellulose acylate, are particularly used as polarizing plate retardation films for liquid crystal display devices by adjusting the orientation of polymer molecules by stretching and adjusting Re and Rth. Has been. Then, the higher the Re, the larger the expansion ratio in stretching, thereby increasing the Rth. However, recently, there has been a demand for an optical film having optical characteristics having a high Re and a low Rth relative to Re with respect to the polarizing plate retardation film. 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.

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 in a predetermined range, a manufacturing method (for example, see Patent Document 1) for producing a film having a large Re and Rth by stretching in the width direction while drying, or a solvent residual amount of a casting film in a predetermined range In the meantime, there is a method in which the film is peeled off as a film and the film is stretched in two stages in the width direction to produce a film having a small Re (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. In addition, this method cannot produce a film having a high Re. 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 addition, to increase Re, it is necessary to increase the stretching ratio. However, when a film having a small amount of solvent remaining after drying is stretched, the film tends to become cloudy due to the stretching, and the haze value is high. On the other hand, when the film is stretched while the residual solvent amount is large, high Re may be exhibited in the film while suppressing an increase in the haze value. However, as described in Patent Document 1, if the casting film is widened while the solvent residual amount is large, the film is easily broken. Therefore, it has been difficult to produce a high Re film while suppressing the haze value.

  In the present invention, in view of the above problems, the production of an optical film having a high molecular orientation in the width direction, a high Re, a low Rth value relative to Re, and a low haze value as compared with the prior art. It aims to provide a method. Here, the low haze value specifically means that the haze value is suppressed so that the Re / haze value is 130 or more.

  In the film production method 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 film is peeled off from the support as a film, the first stretching step of stretching the film in the width direction while drying the film, and the second stretching step of stretching in the width direction while heating the film after the first stretching step In the method for producing a film having the above, the first stretching step evaporates the solvent from the film when the residual amount of the solvent when the cast film is peeled off from the support is W (unit: wt%). And a first widening step for performing stretching to expand to 5% or more and 30% or less in the width direction until the solvent residual amount reaches (W-100)% by weight. 10% or more in the direction 60 And having a second widening step of performing stretching to expand below.

  An optical film having Re of 30 [nm] or more and controlled to have a low Rth value with respect to Re 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 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 can be 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.

  By the above manufacturing method, the dope 21 having a cellulose acylate concentration of 5 wt% or more and 40 wt% or more can be manufactured. The cellulose acylate concentration is more preferably in the range of 15% by weight to 30% by weight, and further preferably in the range of 17% by weight to 25% by weight. The concentration of the additive is preferably in the range of 1% by weight to 20% by weight with respect to the entire 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 wet film 54 is dried while being conveyed while being held on both sides. And extending | stretching to the width direction is implemented, implementing this drying. Hereinafter, this process, that is, the process of stretching while drying is referred to as a first stretching process. The film that has been dried by the first tenter 55 will be referred to as an intermediate film 56 in the following description. In the second tenter 57, the intermediate film 56 delivered from the first tenter 55 is transported and dried by heating, and the width is expanded by stretching during this heating, and the cellulose acylate film (hereinafter referred to as "film"). ) 52 is obtained. Hereinafter, this process, that is, the process of stretching while heating is referred to as a second stretching process. 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 rotational 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.

  While holding the both ends of the wet film 54 and conveying the wet film 54, the wet film 54 is stretched and dried to obtain the intermediate film 56. Is provided.

  The second tenter 57 that holds the both side ends of the intermediate film 56, conveys the intermediate film 56, and heats the intermediate film 56 to stretch the intermediate film 56 to obtain the film 52. Similarly to the above, an air duct 80 for supplying dry air is provided.

  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 59. 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 is further provided between the drying chamber 60 and the cooling chamber 61. Good.

  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, the method of 1st Embodiment of this invention which manufactures the film 52 with the solution casting apparatus 27 is demonstrated 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 ° C. 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 if the cast film 76 has sufficient hardness for conveyance, regardless of the amount of solvent remaining in the cast film 76, but until the solvent residual quantity reaches 200% by weight. Preferably. 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 a film 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 solvent can be removed even if the residual solvent amount is 140% or more. When the cooling temperature is low, the drum 75 may have to be enlarged in order to extend the time for transporting the casting film 76. When the residual solvent amount is higher than 320%, it is difficult to make the cast film 76 sufficiently hard to transport even if the cast film 76 is cooled.

  From the above, it is preferable that the weight ratio W of the solvent is 140% or more and 320% or less when the weight of the solid content of the cast film 76 at the time of stripping is 100%. More preferably, it is 170% or more and 310% or less. Furthermore, it is preferably 200% or more and 300% or less.

  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 has a large number of pins 101 arranged along the conveyance path of the wet film 54 at positions on both side ends of the wet film 54. 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 101 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.

  The solvent gradually evaporates from the wet film 54 peeled off from the drum 75, and the solvent residual amount tends to be lower than the solvent residual amount W at the time of stripping. It is preferable to start stretching to apply tension to Y2 as soon as possible.

  The stretching in the first tenter 55 is preferably performed so that the stretching is completed until the solvent residual amount W of the wet film 54 reaches at least (W−200) wt%. More preferably, the stretching is finished by (W-150)% by weight, and more preferably, the stretching is finished by (W-100)% 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, 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. 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, particularly to increase Re significantly in the width direction, it is necessary to relax the molecular orientation in the transport direction X of the wet film 54 and increase the molecular orientation in the width direction. There is.

  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”). This process is referred to as a first widening process in the following description. Thereafter, the second width L2 is held so as not to change. When the second width L2 is held, tension is applied to the wet film 54 in the width directions Y1 and Y2. This is because the wet film 54 tends to shrink when the solvent of the wet film 54 volatilizes. The case of increasing the width is referred to as “widening”. In FIG. 4, reference sign KL represents the position of the most central portion in the width direction of the wet film 54 among the holding target parts of the wet film 54 held by the pins, and the first width to the second widths L1 to L2. Is the distance between the holding target lines KL on both sides.

  The widening ratio from the third position P3 to the fourth position P4 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 solvent residual amount is early and starts widening from W wt%, preferably until (W-100) wt%, more preferably (W-90) wt%, still more preferably (W− 80) By the end of widening, the molecular orientation in the width direction can be increased while the molecular orientation in the transport direction is relaxed by ending the widening. There is almost no effect on the widening after the solvent residual amount becomes smaller than (W-100)% by weight. This is because the wet film 54 is solidified by drying.

  On the other hand, when the expansion ratio is less than 5%, there is almost no effect of 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 Y direction of the wet film 54, the wet film 54 is stretched only in a range corresponding to 30% of the widening rate, and the molecular orientation in the width direction is not increased beyond the value corresponding to the widening rate of 30%.

  In the first stretching step, it is preferable to have a non-widening step that advances drying until the residual solvent amount reaches 20% by weight while maintaining the width after the first widening step. This is because the non-widening step provides an effect that the intermediate film 56 and the film 52 can be stably conveyed without being broken in the subsequent conveying path.

  And in the process after the 1st tenter 55, since the intermediate film 56 is conveyed, the tension | tensile_strength of the conveyance direction X is applied to the intermediate film 56, and it is difficult to prevent that molecular orientation extends in the conveyance direction X. However, since the wet film 54 can be given molecular orientation in the width direction Y1, Y2 by stretching with the first tenter 55, the intermediate film 56 has molecular orientation in the transport direction X and molecular orientation in the width direction Y1, Y2. A certain equilibrium can be established between the two.

  Next, the intermediate film 56 is sent to the second tenter 57 and undergoes a second stretching 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 holding the intermediate film 56 is a first position P11, and a position where the holding is released is a second 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 second position P12.

  Unlike the first tenter, 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 holding that holds both end portions of the intermediate film 56. A tenter device having means may be used.

Since the solvent is evaporated in the first tenter 55, the residual amount of the solvent in the intermediate film 56 when entering the second tenter 57 is not less than 0.01% by weight and not more than 20% by weight. Preferably, the solvent residual amount is 0.05% by weight or more and 15% by weight or less. More preferably, the residual solvent amount is 0.1 wt% or more and 10 wt% or less. Since the intermediate film 56 is more solidified than the wet film 54, the second tenter 57 softens the intermediate film 56 by applying heat to the intermediate film 56. Then, the intermediate film 56 is softened and stretched to apply tension in the width direction of the intermediate film 56.

  By applying tension, the width of the intermediate film 56, which was the width L11 (hereinafter referred to as “first width”) when entering the second tenter 57, is increased to L12 (hereinafter referred to as “second width”). (Second widening step). The second width L12 may be held so as not to change thereafter, but the second width L12 may be reduced. When the width of the intermediate film 56 having the second width L12 is reduced, the width after the reduction is set to L13 (hereinafter referred to as “third width”). Even when the second width L12 is maintained and when the width is reduced from the second width L12 to the third width L13, tension is applied to the film 52 in the width directions Y1 and Y2. In the case of reducing the width, the width is controlled by applying a tension that naturally contracts and applying tension thereto. In addition, in FIG. 5, code | symbol KM represents the position of the center part side in the width direction of the intermediate film 56 among the holding | maintenance parts of the intermediate film 56 hold | maintained by a holding means, and 1st width-3rd width L11- L13 is the distance between the holding target lines KM on both sides.

  The position at which the first width L11 starts to be expanded to the second width L12 is the fifth position P15, the position at which the expansion is finished is the sixth position P16, and the position at which the second width L12 starts to be contracted to the third width L13 is the seventh position P17. The position at which the reduction width is finished is defined as an eighth position P18.

  The widening ratio from the fifth position P15 to the sixth position P16 is 10% or more and 60% or less. Furthermore, it is preferably 15% or more and 55% or less, and more preferably 20% or more and 50% or less. When the expansion ratio is 10% or less, there is almost no effect of extending the molecular orientation in the width direction. Further, if the widening ratio is set to 60% or more, the intermediate film 56 may be torn.

  The solvent residual amount of the intermediate film 56 is smaller than the solvent residual amount of the wet film 54, and the intermediate film 56 is hardened and is not easily broken. Therefore, the widening rate of the second tenter 57 can be made larger than the widening rate of the first tenter 55. Furthermore, the intermediate film 56 when it exits the first tenter 55 has a specific ratio between the molecular orientation in the transport direction and the molecular orientation in the width direction due to stretching by the first tenter 55. This ratio is determined by the stretching of the first tenter 55 in the width direction. Due to the stretching by the first tenter 55, the orientation in the transport direction is relaxed. When the molecular orientation in the width direction of the intermediate film 56 is increased by the second tenter 57, a film 52 having a large molecular orientation in the width direction with respect to the molecular orientation in the transport direction can be obtained. Thereby, large Re can be expressed in the width direction in the film 52.

  Therefore, the second tenter 57 does not stretch the intermediate film 56 in the width direction, or the first tenter 55 does not stretch the wet film 54 in the width direction in a state where the residual solvent amount is high. Thus, it is possible to obtain the film 52 having the optical characteristics that Re is large, haze is small, and Rth is small with respect to Re.

  On the other hand, the contraction may be performed after the expansion regardless of the residual solvent amount. Therefore, the seventh position P17 is the same as the sixth position P16 or downstream of the sixth position P16. The end position of the reduced width may be an arbitrary position up to the eighth position P18.

  The reduction ratio is preferably 10% or less. In the present invention, since the second width L12 may be held without performing the reduction, the reduction ratio is not less than zero and not more than 10. 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 width reduction ratio is a value obtained by {(L12−L13) / L13} × 100.

  In the present embodiment, the first stretching process is performed by the first tenter 55 and the second stretching process is performed by the second tenter 57. However, the first stretching process and the second stretching process are performed in one tenter. Also good.

  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 either from the casting process to the process of winding up a 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 50-160 degreeC. The drying chamber 60 is more preferably divided into a plurality of sections in the film transport direction in order to change the air 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.

  In the solution casting method, various processes such as a drying process and a side edge cutting and removing process are performed until the film peeled off from the support is wound up. In each of these processes or between each process, the film is mainly supported or conveyed by a roller. These rollers include a driving roller and a non-driving roller, and the non-driving roller is mainly used for determining a film conveyance path and improving conveyance stability.

  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 100 m or more. The width of the film 52 to be wound is preferably 600 mm or more, and 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 93 is dried by the solution casting equipment 27 (see FIG. 2) by guiding the intermediate film 56 that has exited the first tenter 55 to the drying chamber 60 without passing through the second tenter 57. Then, it is obtained by sequentially feeding to the cooling chamber 61 and the winding chamber 64 and winding in the winding chamber 64. In the off-line drawing equipment 92 in FIG. 6, the same devices and members as in FIG.

  The offline stretching equipment 92 has 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, 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 is stretched under a predetermined condition in the second tenter 111 of the off-line stretching equipment 92, whereby the intermediate film 56 is obtained. The final Re and Rth corresponding to each of the above 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.

  In the present invention, by performing the first widening step on the wet film in a state where the solvent residual amount is high and performing the second widening step in which the intermediate film in the dried state is stretched in the width direction, Re / A film having a high Re and a low haze value such that the haze value is 130 or more can be produced.

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

A dope 24 having the following formulation was prepared by the dope manufacturing facility 10 shown in FIG.
Cellulose triacetate (degree of substitution 2.94, viscosity average polymerization degree 305.6%, viscosity of dichloromethane solution 6% by weight 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

  Using the dope, a plurality of films 52 were manufactured by the solution casting apparatus 40 of FIG. The speed at which the film 52 is conveyed was 35 [m / min]. The film 52 was manufactured so as to have a thickness of 45 μm. The residual amount of the solvent in the cast film at the time of stripping the cast film, that is, the wet film 54 at the time of stripping, was 250% by weight. The residual solvent amount of the wet film 54 when the stretching in the first tenter 55 was finished was 150% by weight. The first tenter 55 was stretched with a widening ratio of 20% and the second tenter 57 with a widening ratio of 40%. In Examples 1-8, the film 52 which satisfy | fills the manufacturing conditions of this invention was created. In the following Comparative Examples 1-7, the film 52 was created without satisfying the present invention.

  In Example 2, the conditions were the same as in Example 1 except that the second tenter 57 was stretched with a widening ratio of 10%.

  In Example 3, the conditions were the same as in Example 1 except that the second tenter 57 was stretched with a widening ratio of 60%.

  In Example 4, the conditions were the same as in Example 1 except that the first tenter 55 was stretched with a widening ratio of 5%.

  In Example 5, the same conditions as in Example 1 were used except that the first tenter 55 was stretched with a widening ratio of 30%.

  In Example 6, the conditions were the same as those in Example 1 except that stretching was performed with the residual amount of the solvent of the wet film 54 at the end of widening of the first tenter 55 being 200% by weight.

  In Example 7, the residual solvent amount of the wet film 54 when the cast film was peeled was 200% by weight. The conditions were the same as those in Example 1, except that stretching was performed with the residual amount of solvent in the wet film 54 at the end of widening of the first tenter 55 being 100% by weight.

  In Example 8, the residual solvent amount of the wet film 54 when the cast film was peeled was 180% by weight. The conditions were the same as those in Example 1, except that stretching was performed with the residual amount of solvent in the wet film 54 at the end of widening of the first tenter 55 being 80% by weight.

[Comparative Example 1]
In Comparative Example 1, the same conditions as in Example 1 were applied except that the first tenter 55 was stretched with a widening ratio of 2%.

[Comparative Example 2]
In Comparative Example 2, the solvent remaining amount of the wet film 54 at the time of stripping the casting film and at the end of the widening of the first tenter 55 was set to the same conditions as in Example 1, and the widening ratio of the first tenter 55 was stretched to 35%. Went. As a result, in the first tenter 55, the wet film 54 was torn off and could not be conveyed to the second tenter 57, and the film 52 could not be obtained.

[Comparative Example 3]
In Comparative Example 3, the conditions were the same as in Example 1 except that the residual amount of the solvent in the wet film 54 at the end of the widening of the first tenter 55 was 140% by weight.

[Comparative Example 4]
In Comparative Example 4, the solvent residual amount of the wet film 54 at the time of peeling off the cast film was 200% by weight. The conditions were the same as those in Example 1, except that stretching was performed with the residual amount of solvent in the wet film 54 at the end of widening of the first tenter 55 being 80% by weight.

[Comparative Example 5]
In Comparative Example 5, the residual solvent amount of the wet film 54 when the cast film was peeled was 180% by weight. The conditions were the same as those in Example 1, except that stretching was performed with the residual amount of solvent in the wet film 54 at the end of widening of the first tenter 55 being 60% by weight.

[Comparative Example 6]
In Comparative Example 6, the residual amount of solvent in the wet film 54 when the cast film was peeled was 240% by weight. The first tenter 55 was not widened. Therefore, the widening rate of the first tenter 55 is set to 0%. The second tenter 57 was stretched with a widening ratio of 40%. Other conditions are the same as those in Example 1.

[Comparative Example 7]
In Comparative Example 7, the residual solvent amount of the wet film 54 at the time of stripping the cast film was 120% by weight lower than that of the present invention. Accordingly, the residual solvent amount of the wet film in the first tenter 55 was also lowered. The first tenter was stretched with a widening ratio of 10% and the second tenter 57 with a widening ratio of 40%. Other conditions are the same as those in Example 1.

  Re, Rth, and haze values were determined for the films 52 obtained in Examples 1-8 and the films obtained in Comparative Examples 1-7. Each value is shown in Table 1. Re is the result of sampling a part of the film 52 taken up in the take-up chamber 64 and examining the value of Re for this sample piece. Specifically, it is a value (unit: nm) at 25 ° C. and 60% RH. Rth is a value (unit: nm) at 25 ° C. and 60% RH.

  A haze value is a value (unit:%) calculated | required by irradiating light to a film and measuring light transmittance, and haze value Th = 100x scattered light transmittance Td / total light transmittance Tt. The light transmittance was measured at 25 ° C. and 60% RH.

  A film having an Re value of 30 nm or more and an Rth / Re value of 1 or more and 2.5 or less is very excellent for use as a polarizing plate retardation film. A film having a Re value of 30 nm or more and an Rth / Re value of more than 2.5 and not more than 3.5 can be used as a polarizing plate retardation film. It cannot be said that a film having an Rth / Re value larger than 3.5 is preferably used as a polarizing plate retardation film.

  A film having a Re / haze value of 130 or more is excellent for use as a polarizing plate retardation film. On the other hand, a film having a Re / haze value smaller than 130 is equivalent to a conventional product as a polarizing plate retardation film.

Based on each value of Re, Rth / Re, and Re / haze value, the following criteria were evaluated, and the results shown in Table 1 were obtained.
A: 30 nm ≦ Re, 1 ≦ Rth / Re ≦ 2.5, and 130 ≦ Re / haze value are all satisfied.
○: All of 30 nm ≦ Re, 2.5 <Rth / Re ≦ 3.5, and 130 ≦ Re / haze value are satisfied.
X: Either 3.5 <Rth / Re or Re / haze value <130 is satisfied.

  Since the films of Comparative Examples 1 and 3 to 7 have a high Rth value, the Rth / Re value is larger than 3.5, which is not preferable as a polarizing plate retardation film. The Re / haze value was also smaller than 130. Moreover, in Comparative Example 2, since the widening ratio was increased in the first tenter, the wet film was torn off, and widening could not be performed in the second tenter. On the other hand, the films of Examples 1 to 8 satisfying the present invention have an Rth / Re value of 2.5 or less. Furthermore, the Re / haze value is 130 or more. Thus, according to the present invention, it is possible to obtain a film having a low haze such that Re is 30 or more, the Rth value is suppressed relative to Re, and the Re / haze value is 130 or more. Recognize.

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 27 Solution casting equipment 75 Drum 74 Casting die 76 Casting film 54 Wet film 55 First tenter 56 Intermediate film 57,111 Second tenter 92 Offline stretching equipment 101 Pin 105 Shift mechanism

Claims (1)

A dope containing cellulose acylate and a solvent is cast on a traveling support to form a cast film, and after the cast film has a self-supporting property by cooling, a film is formed from the support. In a method for producing a film having a first stretching step of stripping and stretching in the width direction while drying the film, and a second stretching step of stretching in the width direction while heating the film after the first stretching step,
When the residual solvent amount when peeling the cast film from the support is W (unit: wt%),
In the first stretching step, the solvent is evaporated from the film, and the stretching is performed so as to expand to 5% or more and 30% or less in the width direction until the solvent residual amount reaches (W-100) wt%. Has a widening process,
The said 2nd extending process has a 2nd widening process which performs extending | stretching which expands to 10% or more and 60% or less in the width direction, The manufacturing method of the film characterized by the above-mentioned.

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