JP2007112122A - Manufacturing method of polymer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a polymer film having desired Re and Rth on-line. <P>SOLUTION: A dope is prepared from CAP, an additive and a solvent and cast on a casting band from a casting die to form a cast film on the casting band. After the dope becomes the cast film having self-supporting properties, the cast film is peeled as a wet film and the wet film is dried to obtain a first polymer film 14. The first polymer film 14 is taken up in a roll form. The first polymer film 14 is continuously fed to a tenter type stretching machine 18 from the roll and stretched by 25% (target draw ratio) in a width direction in a width direction stretching part 63. A relaxation start position 63b is set at a position where an advance degree EP1 is below 70% with respect to the target draw ratio R1. The first polymer film 14 is relaxed by 2% in a feed direction from the relaxation start position 63b to obtain a product polymer film 24. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer film, and more particularly to a method for producing a polymer film used as an optical functional film.

  Liquid crystal displays (hereinafter referred to as LCDs) are used in various applications taking advantage of their light weight, thinness, and low power consumption. For example, a large display such as a notebook personal computer or a television receiver may be used. It is also used as a small and medium display such as a mobile phone or a personal digital assistant (PDA). Particularly in recent years, it is often used for large display applications.

  For the LCD, an inexpensive polymer film having excellent flexibility is used. Examples of the polymer film include a protective film for a polarizing plate of an LCD and a support for a retardation plate for realizing a wide viewing angle of the LCD. Hereinafter, the film used in the LCD is referred to as an optical functional film. In addition, the research and development of LCD display modes such as the VA (Vertically Aligned) type and the OCB (Optically Compensated Bend) type, in which the viewing angle is expanded from the conventional TN (Twisted Nematic) type, are rapidly progressing. Many optical functional films are also used in these display mode LCDs. The optical functional film is manufactured by a solution casting method or a melt extrusion method in the same manner as a normal polymer film (see, for example, Non-Patent Document 1).

  In the solution casting method, a polymer solution (hereinafter referred to as a dope) is prepared by dissolving a polymer such as cellulose triacetate (hereinafter referred to as TAC) in a mixed solvent containing dichloromethane or methyl acetate as a main solvent. The dope is cast on a support by forming a casting bead from a casting die to form a casting film. After the cast film has a self-supporting property on the support, it is peeled off from the support as a film (hereinafter, this film is referred to as a wet film), dried and wound up as a film (for example, Non-patent document 2).

  By the way, an optical functional film, especially a protective film for a polarizing plate, requires high wet heat durability in addition to high transparency and strength. If the wet heat durability of the protective film is not sufficient, the protective film shrinks or deteriorates under high temperature and high humidity, or the adhesive material layer between the protective film and the glass substrate of the liquid crystal cell tends to deteriorate. And a protective film and a glass substrate will peel by such shrinkage | contraction and deterioration.

Against this background, in order to increase the wet heat durability of the film, it has also been proposed to use a polymer other than TAC in the solution casting method. For example, in the acylation of cellulose, acylation with an acetyl group (—CO—CH ₃ ) and acylation with a propionyl group (—CO—C ₂ H ₅ ) are performed, and cellulose acylate propionate (hereinafter referred to as CAP). ) And using CAP as a film raw material is known (see, for example, Patent Document 1).

On the other hand, the melt film forming method is performed by the following method. For example, a chip of polyethylene terephthalate (hereinafter referred to as PET) is manufactured from terephthalic acid and ethylene glycol. And it is a manufacturing method which heat-melts a PET chip and extrudes it from the extruder on the cooling drum which is a support body, and obtains a film. In addition, other polyester films, such as a polyethylene naphthalate film, and a cellulose film can also be manufactured by the same method. In addition, in the melt film forming method, a method of stretching in the width direction of the film and relaxing (relaxing) in the transport direction is known in order to make the optical characteristics of the film desired (for example, Non-Patent Document 2). reference). By stretching and relaxing the film, the birefringence of the film can be adjusted. A film having such a birefringence is used as a retardation film for LCD.
"Electronic Display Technology 2004", Industrial Research Committee, issued in June 2004 Japan Society for Invention and Innovation Public Technical Bulletin No. 2001-1745 JP 2001-188128 A JP 2000-309051 A

  By the way, in order to express desired optical properties, the polymer film is stretched or relaxed to control the orientation of the polymer molecules. Thereby, the in-plane or thickness direction retardation of the film is controlled. However, there is a problem in that the orientation of the polymer molecules forming the film is disturbed by the subsequent step of the stretching or relaxation step, and desired optical properties (for example, in-plane or thickness direction retardation) cannot be obtained. Yes.

  An optical functional film used for a VA LCD having a wide viewing angle and a high-speed response is required to have extremely high optical characteristics. In this VA-type LCD, in order to realize high-speed response, a technique for narrowing the distance (cell gap) between glass substrates sandwiching liquid crystal molecules is used. In this case, it is effective from the viewpoint of optical compensation by improving the in-plane retardation (Re) of the optical functional film. However, when the thickness direction retardation (Rth) is increased at approximately the same ratio as Re, it is compared with the cell gap. Therefore, it becomes too large, causing deterioration of the optical characteristics of the LCD.

  Therefore, it is required to perform the stretching relaxation process for adjusting the optical characteristics immediately before shipping the film as a product. For this reason, a batch type production method in which the produced polymer film (hereinafter referred to as the first polymer film) is stored in a roll shape and the first polymer film is stretched and relaxed immediately before shipment is suitable. Detailed knowledge of the experimental conditions has not been obtained.

  A first object of the present invention is to provide a polymer film production method for producing a polymer film having desired optical properties in a batch process.

  A second object of the present invention is to provide a method for producing a polymer film in which in-plane retardation is increased and thickness direction retardation is decreased.

  The present invention relates to a method for producing a polymer film comprising a polymer film polymer as a main component and stretching or relaxing a long strip-shaped first polymer film, wherein either the solution casting method or the melt extrusion method using the polymer as a main component is provided. The first polymer film is manufactured by, the first polymer film is wound up as a first film roll, the first polymer film is taken out from the first film roll, and the first polymer film is stretched in the width direction. In addition, relaxation of the first polymer film in the transport direction is started.

  When the progress of the stretching in the width direction of the first polymer film is less than 70% of the target stretching rate, it is preferable to start relaxation in the transport direction of the first polymer film. It is preferable that the relaxation rate in the conveyance direction of the first polymer film is 1% or more and 5% or less. The stretching ratio in the width direction of the first polymer film is preferably 10% or more and 40% or less. The polymer preferably contains at least one of cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate. The polymer film is preferably an optical functional film.

  According to the method for producing a polymer film of the present invention, the first polymer film is produced using either the solution casting method or the melt extrusion method with the polymer as a main component, and the first polymer film is used as a first film roll. Winding up, taking out the first polymer film from the first film roll, and starting the relaxation in the transport direction of the first polymer film when stretching the first polymer film in the width direction, Optical characteristics can be adjusted immediately before shipping as a product.

  According to the method for producing a polymer film of the present invention, when the progress of stretching in the width direction of the first polymer film is less than 70% of the target stretching rate, the transport direction of the first polymer film is performed. Therefore, the thickness direction retardation (Rth) can be lowered while increasing the in-plane retardation (Re).

  Next, an embodiment of the present invention will be described. First, the film manufacturing process using the solution casting method according to the first embodiment will be described. The outline of the film production process using the melt film-forming method will be described later.

  The first embodiment of the present invention will be described using CAP as an example. However, the raw material polymer used for this invention is not limited to CAP, You may use the other cellulose ester and well-known polymer which can be made into a film with a solution casting method. The present invention is not limited to the embodiments described below.

  As shown in FIG. 1, the film production process 2 using the solution casting method of the present invention has a dope production line, a film production line 4 (see FIG. 2), and a stretching relaxation line 5 (see FIG. 3), A predetermined process is performed on the line.

  Next, the detail of each line used by the film manufacturing process 2 is demonstrated. In the dope production line, a desired dope 11 can be obtained by performing the dope preparation step 10.

  In the film production line 4, the casting process 12 in which the dope 11 obtained in the dope preparation process 10 is cast on a support, the casting film obtained from the casting process 12 is peeled off as a wet film, and this wet film is removed. The drying process 13 to dry, the 1st film winding process 15 which winds up the 1st polymer film 14 obtained at the drying process 13, and the 1st film roll 16 obtained at the 1st film winding process 15 are stored in a predetermined place. A storage step 17 is performed. The solution casting method for producing the first polymer film 14 includes steps 10, 12 and 13.

  In the stretching relaxation line 5, a first film feeding process 20 for feeding the first film roll 16 as the first polymer film 14 to the tenter type stretching machine 18 (see FIG. 3), and the first polymer film sent to the tenter type stretching machine 18. 14, a stretching relaxation process 21 for performing a stretching process or a relaxation process in a predetermined direction, and a product film winding process 23 for winding the product polymer film 22 obtained in the stretching relaxation process 21 are performed. Moreover, the product film roll 24 which is a final form can be obtained by this product film winding process 23. FIG.

[Dope production line]
The dope production line includes a solvent tank for storing the solvent, a mixing tank for mixing the solvent and CAP, a hopper for supplying CAP, and an additive tank for storing the additive. Is provided. Furthermore, the heating apparatus for heating the swelling liquid mentioned later, the temperature controller which adjusts the temperature of the prepared dope, and the filtration apparatus are provided. Furthermore, a flash device and a filtration device for concentrating the prepared dope are also provided. Further, a recovery device for recovering the solvent and a regeneration device for regenerating the recovered solvent are provided. The dope production line is connected to the film production line 4 (see FIG. 2) via a stock tank 25 (see FIG. 2).

[Film production line]
The film production line 4 shown in FIG. 2 includes a casting apparatus 26 that performs the casting process 12, a drying apparatus 27 that performs the drying process 13, and a first film winding apparatus 28 that performs the first film winding process 15. .

[Casting device]
The casting device 26 includes a stirrer 31 that is rotated by a motor, and stores a stock tank 25 that can store the dope 11, a filtration device 32 that is connected to the stock tank 25, a casting die 33 that is connected to the filtering device 32, and a casting die. A casting band 35 for forming a casting film 34 from the dope 11 cast from 33, and a peeling roller 37 for peeling the casting film 34 formed on the casting band 35 as a wet film 36 are provided. Yes.

  The rotating rollers 35a and 35b are rotated by a driving device (not shown). The casting band 35 is stretched around the rotating rollers 44 and 45. As the rotary rollers 35a and 35b rotate, the casting band 35 travels endlessly. Heat transfer medium flow paths (not shown) are formed in the rotation rollers 35a and 35b, and the heat transfer medium maintained at a predetermined temperature passes through the flow paths, whereby the rotation rollers 35a and 35b. Is maintained at a predetermined value.

[Drying equipment]
The drying device 27 includes a crossover portion 40 that sends out the wet film 36 from the casting device 26, a blower 41, an ear cutting device 42 that cuts the wet film 36 into a predetermined width, and a side end portion (referred to as an ear) of the cut wet film 36. The crusher 43 for finely cutting the waste and the wet film 36 are dried, and the drying chamber 44 for generating the first polymer film 14 is cooled to cool the first polymer film 14 to a predetermined temperature. It is comprised from the chamber 45 and the forced static elimination apparatus 50 which adjusts the charged voltage of the 1st polymer film 14 to a predetermined range. The drying chamber 44 is provided with a number of rollers 44a, and an adsorption / recovery device 44b for adsorbing / recovering the solvent gas generated by evaporation is attached.

[First film winding device]
The first film winding device 28 winds the first polymer film 14 to give a product film roll 24 by winding the first polymer film 14 and a knurling roller 51 for embossing both edges of the first polymer film 14. It is comprised from the intake chamber 52, and these are provided in the downstream of the drying apparatus 27 in order. Inside the winding chamber 52, a winding roller 52a for winding the first polymer film 14 and a press roller 52b for controlling the tension at the time of winding are provided.

  The first film roll 16 which is a precursor of the product film roll 24 which is the final form of the product is stored so that the polymer molecules in the first polymer film 14 are not decomposed by heat or water. By such storage, the optical properties of the first polymer film 14 and the quality as a film are maintained.

[Extension relaxation line]
The stretching relaxation line 5 shown in FIG. 3 includes a first film delivery device 60 that feeds the first polymer film 14 from the first film roll 16, a tenter stretching machine 18 that stretches or relaxes the first polymer film 14 in a predetermined direction, and The product polymer film 22 fed from the tenter-type stretching machine 18 is wound up to obtain a product film roll 24.

  As shown in FIG. 3, the simultaneous biaxial tenter type stretching machine 18 includes an inlet portion 62, a width direction stretching portion 63 that stretches the first polymer film 14 in the width direction X1, X2, and a width of the first polymer film 14. It is comprised from the width direction relaxation part 64 and the exit part 65 which relax in direction X1, X2.

  The tenter type stretching machine 18 has a number of clips connected to the chain. Both ends of the first polymer film 14 are gripped by this clip. This chain travels endlessly by meshing with the sprocket. Along with the movement of the chain connected to the clip, the first polymer film 14 is conveyed to the outlet portion 65 through the width direction extending portion 63 and the width direction relaxing portion 64 that are extended from the inlet portion 62 in the width direction X1, X2. The In addition, these clips include a roll-shaped clip, an abacus ball-shaped clip, a belt-shaped clip, and a drum-roll-shaped clip that can be moved in the transport direction Y1 and the direction opposite to the transport direction Y1 by releasing the grip portion of the self-locking portion of the clip. Disc-shaped clips, slide clips, etc. are used. In the width direction extending | stretching part 63, extending | stretching of the width direction X1, X2 of the 1st polymer film 14 and relaxation of the conveyance direction Y1 can be performed simultaneously by these clips.

  Next, the detail of the film manufacturing process 2 shown in FIG. 1 is demonstrated.

[Dope preparation process]
In the dope preparation process 10, a dope is manufactured by the following method using a dope manufacturing line. First, the solvent is sent from the solvent tank to the mixing tank. Next, the CAP placed in the hopper is fed into the mixing tank while being weighed. The required amount of additive solution is fed from the additive tank to the mixing tank.

  The mixing tank is provided with a jacket that wraps the outer surface thereof and a first stirrer that is rotated by a motor. By using the first stirrer, a swelling liquid in which CAP is swollen in a solvent is obtained.

  Next, the swelling liquid is sent to a heating device, and is heated to 50 ° C. to 120 ° C. by the heating device. The heating device is preferably a jacketed pipe, and further preferably has a configuration capable of pressurizing the swelling liquid. By using such a heating apparatus, the dope is obtained by dissolving the solid content in the swelling liquid under heating conditions or under pressure heating conditions. Hereinafter, this method is referred to as a heating dissolution method. Moreover, you may use the cooling dissolution method using the cooling device which cools swelling liquid to the temperature of -100 degreeC--30 degreeC. It is possible to sufficiently dissolve CAP in a solvent by appropriately selecting the heating dissolution method and the cooling dissolution method. After the dope is brought to about room temperature with a temperature controller, the impurities contained in the dope are removed by filtration with a filtration device. The dope 11 after filtration is sent to the stock tank 25 in the film production line 4 and stored therein.

  By the above method, a dope having a CAP concentration of 5 wt% to 40 wt% can be manufactured. In addition, about the raw material in the solution casting method which obtains a cellulose-ester film, a raw material, the dissolution method and addition method of an additive, the filtration method, and manufacturing methods of dope, such as defoaming, [0517] paragraph of Unexamined-Japanese-Patent No. 2005-104148 To [0616] paragraph. These descriptions are also applicable to the present invention.

[Casting process]
Next, the casting process 12 will be described. First, the dope 11 stored in the stock tank 25 is always made uniform by the rotation of the stirrer 31. The dope 11 may be mixed with additives such as a plasticizer and an ultraviolet absorber even during the stirring.

  The homogenized dope 11 is sent to the filtration device 32 by a pump. The filtered dope 11 is cast from the casting die 33 onto the casting band 35. The dope 11 on the casting band 35 forms a casting film 34.

  The casting film 34 moves as the casting band 35 travels. At this time, the evaporation of the solvent is promoted by the drying air from the blower opening provided in the vicinity of the casting band 35. And the wind-shielding board provided in the vicinity of the casting band 35 is suppressing that the surface shape of the casting film 34 is fluctuate | varied by blowing of this dry wind.

  The casting film 34 having a self-supporting property is peeled off from the casting band 35 while being supported by a peeling roller 37 as a wet film 36.

[Drying process]
Next, the drying process 13 will be described. The wet film 36 fed out from the peeling roller 37 is conveyed to the ear clip device 42 via the crossover 40. The crossover section 40 has a large number of rollers, and the wet film 36 on the crossover section 40 is conveyed to the ear clip device 42 by rotating these rollers in a predetermined direction. In the transition part 40, the drying of the wet film 36 is advanced by sending the drying air of desired temperature from the air blower 41. FIG.

  Both edges of the wet film 36 are cut at both edges by the edge-cutting device 42. The cut side end portion is sent to the crusher 43 by a cutter blower (not shown). The crusher 43 pulverizes the film side end portion into a chip. This chip is reused for dope preparation.

  The wet film 36 from which both ends have been removed is sent to the drying chamber 44 and dried in the drying chamber 44. Although the temperature in the drying chamber 44 is not specifically limited, It is preferable that it is the range of 50 to 160 degreeC. In the drying chamber 44, the wet film 36 is conveyed while being wound around a roller 44 a in the drying chamber 44 to become the first polymer film 14. The solvent gas generated by evaporation is adsorbed and recovered by the adsorption recovery device 44b. The air from which the solvent component has been removed is blown again as dry air inside the drying chamber 44. The first polymer film 14 is cooled to a predetermined temperature in the cooling chamber 45.

[First film winding process]
Next, the first film winding process 15 will be described. Inside the winding chamber 52, a winding roller 52a for winding the first polymer film 14 and a press roller 52b for controlling the tension at the time of winding are provided. The 1st film roll 16 is obtained by winding up the 1st polymer film 14 with the winding roller 52a.

[Storage process]
The first film roll 16 is stored so that polymer molecules are not decomposed by heat or water.

[First film delivery process]
As shown in FIG. 3, in the first film delivery step 20, the first film delivery device 60 continuously delivers the first polymer film 14 from the first film roll 16 to the tenter type stretching machine 18.

[Stretching relaxation process]
Next, the stretching relaxation step 21 will be described. The tenter type stretching machine 18 has predetermined stretching conditions in the width direction X1 and X2 and relaxation conditions in the transport direction Y1 and width directions X1 and X2. Under these conditions, the product polymer film 22 having a desired in-plane retardation (Re) and thickness direction retardation (Rth) can be formed by subjecting the first polymer film 14 to stretching or relaxation treatment. it can. Details of the conditions for the stretching relaxation treatment will be described later.

[Film winding process]
Finally, a product film winding step 23 for winding the product polymer film 22 is performed after the stretching relaxation step 21 has been performed. The product polymer film 22 having desired optical properties is wound around a winding roller 61 after both side ends (ear portions) are cut. In this way, since the stretching relaxation step 21 is performed on the first polymer film 14, the optical characteristics can be adjusted immediately before the shipment of the final product polymer film 22.

  Next, the detail of the extending | stretching relaxation process in the extending | stretching relaxation process 21 is demonstrated. The first polymer film 14 is gripped at both ends by clips at the inlet 18 a of the tenter type stretching machine 18. The width of the first polymer film 14 held by the clip at this time (hereinafter referred to as biting width) is L1. By movement of the chain to which the clip is connected, the first polymer film 14 is conveyed to the width direction extending portion 63 while holding the biting width L1.

  In the width direction extending | stretching part 63, the extending | stretching process which extends | stretches the 1st polymer film 14 to the width direction X1, X2 is performed because the clip holding the 1st polymer film 14 moves to the width direction X1, X2. By the stretching process in the width directions X1 and X2, the casting width of the first polymer film 14 becomes the maximum width direction stretching width L2. The first polymer film is between the relaxation start line 63b when the width of the first polymer film 14 is L1 ′ and the relaxation end line 63c when the width of the first polymer film 14 is L1 ″. 14 while moving in the width direction X1 and X2 while the clip holding 14 moves in the direction substantially opposite to the conveyance direction Y1, the stretching treatment in the width direction X1 and X2 and the relaxation treatment in the conveyance direction Y1 are performed in the first polymer film. 14 is applied. Details of the relaxation start line 63b and the relaxation end line 63c will be described later. Thereafter, the first polymer film 14 is sent to the width direction relaxation portion 64 that is relaxed in the width directions X1 and X2. In the width direction relaxation part 64, the casting width of the first polymer film 14 is relaxed to the separation width L3 by the relaxation process in the width directions X1 and X2. After the relaxation processing in the width directions X1 and X2, the first polymer film 14 having the separation width L3 is sent out from the outlet 18b as the product polymer film 22.

  A broken line CL represents the grip portion CL on the most central side among grip portions on the first polymer film 14 gripped by grip means such as a clip. As shown in FIG. 3, since both side ends of the first polymer film 14 are gripped by clips, a pair of gripped portions CL are shown at both side ends on the first polymer film 14. The biting widths L 1, L 1 ′, L 1 ″, L 2 and L 3 are all the distances between the grip portions CL on both sides of the first polymer film 14.

  In this stretching process, a part of the clip that holds the first polymer film 14 on the relaxation start line 63b moves in a direction substantially opposite to the transport direction Y1, and relaxes the transport direction of the first polymer film 14. That is, the movement of the clip makes it possible to stretch the first polymer film 14 in the width direction and relax the conveyance direction. Under such predetermined conditions, by performing the stretching process in the width direction of the first polymer film 14 and the relaxation process in the transport direction, the polymer molecules are stretched in the width directions X1 and X2 and contracted in the transport direction Y1. Therefore, the in-plane retardation (Re) value increases, and at the same time, the change in the thickness direction of the first polymer film 14 in this stretching relaxation treatment is small compared to the case where only the stretching treatment in the normal width direction is performed. The thickness direction retardation (Rth) value of the polymer film 14 decreases.

  In the present invention, the stretching in the width direction refers to applying tension in the width directions X1 and X2 to the first polymer film 14 using a clip or the like that holds both side ends. In this stretching, in addition to increasing the width of the first polymer film 14 by applying tension, the width of the first polymer film 14 is maintained, and further, the stretching is performed with a contraction force equal to or greater than the applied tension. The case where the width of one polymer film 14 shrinks is also included. In the present invention, “relaxation in the width direction” means relaxation of stress remaining in the first polymer film 14. Specifically, the tension in the width direction X1, X2 applied to the first polymer film 14 is reduced, or the tension is released, and the temperature of the first polymer film 14 or the atmosphere is kept within a predetermined range. Any method can be used as long as it can relieve the residual stress of the first polymer film 14 such as holding.

  Next, the conditions for the stretching process and the relaxation process in the relaxation stretching process 21 will be described. First, a stretching ratio R1 (hereinafter referred to as a target stretching ratio R1) in the stretching process in the width directions X1 and X2 is defined as R1 = (L2−L1) / L1 × 100. In the stretching relaxation step 21, when the target stretching ratio R1 is less than 10%, there is a possibility that the effect of improving the in-plane retardation (Re) value by arranging polymer molecules may not be exhibited. Moreover, there exists a possibility that the effect which correct | amends surface defects, such as a crack and wrinkles which generate | occur | produce on the film surface by an extending | stretching process may not express. On the other hand, when the target stretching ratio R1 exceeds 40%, the arrangement of polymer molecules proceeds excessively, and the in-plane retardation (Re) value is excessively improved, or the first polymer film 14 has defects such as tearing. There is a fear. That is, the target draw ratio R1 in the present invention is preferably in the range of 10% to 40%, more preferably 15% to 35%, and most preferably 25% to 30%.

In the present invention, the relaxation in the transport direction is to relieve the stress in the transport direction Y1 or the transport direction Y1 in the residual stress of the first polymer film 14, and specifically, the first polymer film. 14 is to reduce the interval in the transport direction Y1 of the clip gripping 14. The relaxation in the transport direction Y1 is preferably performed to such an extent that the first polymer film 14 does not sag. Further, since the relaxation in the transport direction Y1 needs to be started from the time when the elastic limit of the first polymer film 14 is not exceeded, the relaxation start line 63b needs to be set from the progress degree EP1 of the target stretching ratio R1. Here, the degree of progress EP1 of the target stretching ratio R1 is given by Equation 1, and Equation 2 is obtained from Equation 1. Therefore, the relaxation start line 63b is obtained from the progress degree EP1 of the target stretching ratio R1.
(Expression 1) EP1 = {(L1′−L1) / (L2−L1)} · 100
(Formula 2) L1 ′ = {(L2−L1) · EP1 / 100} + L1

  Then, the degree of progress EP1 in the relaxation start line 63b is preferably less than 70%, more preferably 1% or more and 40% or less, and most preferably 3% or more and 30% or less. In this case, if the biting width L1 (mm) is 1300 mm and the maximum conveying direction stretching width L2 (mm) is 1650 mm and the separation width L3 (mm) is 1620 mm, the target stretching is performed. The rate R1 is approximately 26.92%, and the width L1 ′ (mm) of the first polymer film 14 when starting the relaxation in the conveyance direction is 1300 mm (0% of the target stretch rate R1) or more and 1545 mm (target stretch rate) R1 is preferably less than 70%, more preferably 1303.5 mm (1% of the target stretch ratio R1) or more and 1440 mm (target stretch ratio R1 is 40%) or less, and 1310 mm (target stretch ratio R1). 3%) or more and 1405 mm (30% of the target draw ratio R1) or less. The relaxation end line 63c is determined by the set relaxation start line 63b and the relaxation rate RL1 in the transport direction Y1. The relaxation rate RL1 will be described later.

  As shown in FIG. 7, the relaxation rate RL1 in the transport direction Y1 is such that the component in the transport direction Y1 is Z1 in the interval between the adjacent clips 108 before relaxation in the transport direction Y1, and the adjacent clip 108 after relaxation in the transport direction. When the component in the transport direction Y1 in the interval is Z2, RL1 = (Z1−Z2) / Z1 · 100. Note that Z1 and Z2 may be intervals between adjacent clips 108 without using the components in the transport direction Y1.

  The relaxation rate RL1 in the transport direction is not particularly limited, but if the relaxation rate RL1 is less than 1%, the effect of lowering the thickness direction retardation (Rth) value may not be exhibited. On the other hand, if the relaxation rate RL1 exceeds 5%, the first polymer film 14 may sag, which may cause manufacturing troubles such as conveyance failure. That is, the relaxation rate RL1 in the transport direction is preferably 1% or more and 5% or less, more preferably 2% or more and 5% or less, and most preferably 3% or more and 5% or less. The rate of relaxation in the transport direction, that is, the rate of change of the relaxation rate RL1 per unit time is preferably 0.015% / second or more and 2.000% / second or less, and 0.050% / second or more and 1 More preferably, it is 0.000% / second or less.

  In the present invention, when the first polymer film 14 is stretched in the width directions X1 and X2, the transport direction Y1 is relaxed, and thereby the tension in the transport direction Y1 generated in the first polymer film 14 by this stretching is reduced. It is possible to control the orientation of polymer molecules in the first polymer film 14 to increase the in-plane retardation (Re) value and to decrease the thickness direction retardation (Rth) value.

  In addition, as the tenter type stretching machine 18 used in the present invention, a linear motor type or pantograph type tenter type dryer can be used in addition to the type in which the clip is driven using the endless running chain described above. The linear motor type tenter dryer includes a carriage having secondary windings and clips, guide rails for guiding a number of carriages in a predetermined direction, and primary windings arranged in the vicinity of the guide rails. The carriage on the guide rail can be individually conveyed at a predetermined speed by controlling the magnitude and direction of the current flowing through the primary winding. On the other hand, a pantograph-type tenter dryer includes a clip, a guide rail, and a pantograph mechanism disposed therebetween. By controlling the pantograph mechanism, the distance between the clips in the transport direction Y1, the direction substantially opposite to the transport direction Y1, and the width directions X1 and X2 can be adjusted. Therefore, even if these linear motor type or pantograph type tenter dryers are used, the first polymer film 14 is stretched or relaxed in the transport direction Y1 as well as stretched or relaxed in the width directions X1 and X2. Processing can be performed. The details of the linear motor type tenter dryer are disclosed in JP-A-2002-507501 and JP-A-6-57618, and the details of the pantograph-type tenter dryer are disclosed in JP-A-2003-236927. Etc. are described.

  The temperature in the tenter type stretching machine 18 when the relaxation treatment in the transport direction Y1 is performed is preferably 80 ° C. or higher and 160 ° C. or lower, and more preferably 100 ° C. or higher and 150 ° C. or lower.

  Note that a plurality of relaxation start lines 63b and relaxation end lines 63c may be set, and the relaxation process in the transport direction may be performed a plurality of times. The relaxation rate in this case may be the sum of the relaxation rates of the respective relaxation processes in the carrying direction, or may be the relaxation rate for the most upstream relaxation start line 63b and the most downstream relaxation end line 63c. In FIG. 7, the relaxation end line 63 c is described in the width direction extending portion 63, but may be set in the width direction relaxing portion 64 regardless of this.

  Next, the raw material of the 1st polymer film 14 used by this invention is demonstrated.

[material]
The polymer used in the present invention is a cellulose ester. Among them, it is preferable to use a cellulose ester that satisfies the following formulas (I) and (II).
(I) 2.5 ≦ A + B ≦ 3.0
(II) 1.25 ≦ B ≦ 3.0
In the formula, A and B represent the degree of substitution of the acyl group (—CO—R) substituted with a hydrogen atom of the hydroxyl group of cellulose, and A represents the degree of substitution of the acetyl group (—CO—CH ₃ ). ing. B represents propionyl group (—CO—C ₂ H ₅ ), butyryl group (—CO—C ₃ H ₇ ), pentanoyl group (—CO—C ₄ H ₉ ), hexanoyl group (— a degree of substitution of _{CO-C 5 H 11).} In addition, when B is a propionyl group, it is called CAP (cellulose acetate propionate), and when B is a butyryl group, it is called CAB (cellulose acetate butyrate). The formula (II) is more preferably 1.3 ≦ B ≦ 2.97, and most preferably 1.4 ≦ B ≦ 2.97. 90% by weight or more of CAP and CAB are preferably particles having a particle size of 0.1 mm to 4 mm.

  Solvents for preparing the dope include aromatic hydrocarbons (eg, benzene, toluene, etc.), halogenated hydrocarbons (eg, dichloromethane, chlorobenzene, etc.), alcohols (eg, methanol, ethanol, n-propanol, n-butanol, Diethylene glycol, etc.), ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl acetate, ethyl acetate, propyl acetate, etc.) and ethers (eg, tetrahydrofuran, methyl cellosolve, etc.). In the present invention, the dope means a polymer solution or dispersion obtained by dissolving or dispersing a polymer in a solvent.

  Among these, it is preferable to use a C1-C7 halogenated hydrocarbon as a solvent, and it is more preferable to use a dichloromethane. From the viewpoints of physical properties such as solubility of CAP, peelability of the cast film from the support, mechanical strength of the film, and optical properties of the film, alcohol having 1 to 5 carbon atoms is added in addition to dichloromethane. It is preferable to mix seeds or several kinds. The content of the alcohol is preferably 2% by weight to 25% by weight and more preferably 5% by weight to 20% by weight with respect to the whole solvent. Specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like, but methanol, ethanol, n-butanol or a mixture thereof is preferably used.

  By the way, recently, for the purpose of minimizing the influence on the environment, studies have been conducted on the solvent composition when dichloromethane is not used. Examples of the solvent for this purpose include ethers having 4 to 12 carbon atoms, carbon There are ketones having 3 to 12 atoms, esters having 3 to 12 carbon atoms, alcohols having 1 to 12 carbon atoms, and the like, which are appropriately mixed. For example, a mixed solvent of methyl acetate, acetone, ethanol, and n-butanol can be mentioned. These ethers, ketones, esters and alcohols may have a cyclic structure. A compound having two or more functional groups of ether, ketone, ester, and alcohol (that is, —O—, —CO—, —COO—, and —OH) can also be used as the solvent.

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

[Melt casting method]
Next, a second embodiment of the present invention will be described. In the description of this embodiment, CAP (cellulose acylate propionate) is used as a raw material, and a method for producing a polymer film produced by using a melt film-forming method is exemplified. The raw material for the polymer film according to the present invention is as follows. It is not limited to CAP, and other raw materials may be used. Examples of other materials include cellulose derivatives such as CAB, polyesters such as PEN (polyethylene naphthalate), and polyamides such as nylon.

  A film manufacturing process 70 shown in FIG. 4 includes a raw material preparation process 71 for generating a CAP chip as a film raw material, a melt extrusion process 73 for generating a first polymer film 72 from the CAP chip, a cooling process 74, and a first polymer film 72. A first film winding step 76 that winds up to generate the first film roll 75, a storage step 77 that stores the first film roll 75 obtained in the first film winding step 15 in a predetermined place, and a first film roll 75. A first film sending step 80 for sending the first polymer film 72 to the tenter-type stretching machine 18 (see FIG. 3), a stretching relaxation step 81 for subjecting the first polymer film 72 to stretching or relaxation treatment in a predetermined direction, and From the product film winding step 83 for winding the product polymer film 82 obtained in the stretching relaxation step 81. It is. Moreover, the product film roll 84 which is a final form can be obtained by this product film winding process 83. FIG.

  The melt film-forming method for producing the first polymer film is composed of steps 71, 73 and 74. Further, since the steps 76, 77, 80, 81, and 83 are substantially the same as the steps 15, 17, 20, 21, and 23 described above, detailed description of the steps is omitted.

(Thermoplastic resin)
The thermoplastic resin for performing the stretching described above is not particularly limited, but a cellulose acylate film and a saturated norbornene film are more preferable. These are because they have moderate Re and Rth developability due to stretching, and are excellent in uneven stretching. Hereinafter, the cellulose acylate resin will be described.

(Cellulose acylate resin)
The cellulose acylate used in the present invention preferably has the following characteristics. The substitution degree of the acyl group (—CO—R—) substituted with the hydrogen atom of the hydroxyl group of cellulose satisfies 2.5 ≦ A + B ≦ 3.0 and 1.25 ≦ B ≦ 3. Cellulose acylate film (A is the substitution degree of acetyl group, B is the sum of substitution degree of propionyl group, butyryl group, pentanoyl group and hexanoyl group). More preferable substitution degree is 2.6 ≦ A + B ≦ 2.95 and 2.0 ≦ B ≦ 2.95 when 1/2 or more of B is a propionyl group, and less than 1/2 of B is a propionyl group In this case, 2.6 ≦ A + B ≦ 2.95 and 1.3 ≦ B ≦ 2.5. Further preferable substitution degree is 2.7 ≦ A + B ≦ 2.95 and 2.4 ≦ B ≦ 2.9 when 1/2 or more of B is a propionyl group, and less than 1/2 of B is a propionyl group In this case, 2.7 ≦ A + B ≦ 2.95 and 1.3 ≦ B ≦ 2.0.

  The present invention is characterized in that the degree of substitution of the acetyl group is reduced and the sum of the degree of substitution of the propionyl group, butyryl group, pentanoyl group, and hexanoyl group is increased. As a result, unevenness of elongation is difficult to occur during stretching, unevenness of Re and Rth are difficult to occur, crystal melting temperature (Tm) can be lowered, and yellowing caused by thermal decomposition of molten film is suppressed. You can also. These effects can be achieved by using as large a substituent as possible. However, if it is too large, the glass transition temperature (Tg) and the elastic modulus are excessively lowered, which is not preferable. For this reason, a propionyl group, a butyryl group, a pentanoyl group, and a hexanoyl group larger than an acetyl group are preferable, a propionyl group and a butyryl group are more preferable, and a butyryl group is more preferable.

[Raw material preparation process]
As shown in FIG. 4, in the melt film forming method, a raw material preparation step 71 is first performed. The cellulose acylate resin may be used as a powder, but it is more preferable to use a pelletized one in order to reduce the variation in the thickness of the film. This resin has a moisture content of 1% or less, more preferably 0.5% or less, and is then put into a hopper of a melt extruder. At this time, the hopper is Tg-50 ° C. or higher and Tg + 30 ° C. or lower, more preferably Tg−40 ° C. or higher and Tg + 10 ° C. or lower, and further preferably Tg−30 ° C. or higher and Tg or lower. As a result, re-adsorption of moisture in the hopper can be suppressed, and the drying efficiency can be more easily expressed.

[Melt extrusion process and cooling process]
Next, a melt extrusion process 73 and a cooling process 74 are performed to obtain a first polymer film 72. The CAP chip is supplied to an extruder heated under a nitrogen atmosphere or under vacuum, and melt extrusion film formation is performed according to a conventional method. An extruder extrudes a CAP chip into a sheet and solidifies it on a roller that cools the CAP film. Thereby, the unstretched first polymer film 72 can be obtained. The melt extrusion step 73 and the cooling step 74 can also be performed in a series of steps as described above. Moreover, a laminated film can also be obtained by performing simultaneous extrusion using a plurality of extruders. Furthermore, an additive (for example, a mat material) can be simultaneously extruded and included in the first polymer film 72 during melt extrusion.

  In the melt extrusion step 73, the CAP chip is kneaded and melted at 120 ° C to 250 ° C, more preferably 140 ° C to 220 ° C, and even more preferably 150 ° C to 200 ° C. At this time, the melting temperature may be a constant temperature, or may be divided into several parts and controlled. The kneading time is preferably 2 minutes or more and 60 minutes or less, more preferably 3 minutes or more and 40 minutes or less, and further preferably 4 minutes or more and 30 minutes or less. Furthermore, it is also preferable to carry out the inside of the melt extruder in an inert (nitrogen or the like) air flow or while evacuating using a vented extruder.

  The melted resin is passed through a gear pump, and after removing the pulsation of the extruder, it is filtered with a metal mesh filter or the like, and extruded from a T-shaped die attached behind it onto a cooling drum. Extrusion may be performed in a single layer, or multiple layers may be extruded using a multi-manifold die or a feed block die. At this time, the thickness unevenness in the width direction can be adjusted by adjusting the distance between the lips of the die.

  Thereafter, it is extruded onto a casting drum. At this time, it is preferable to use a method such as an electrostatic application method, an air knife method, an air chamber method, a vacuum nozzle method, or a touch roll method to increase the adhesion between the casting drum and the melt-extruded sheet. Such an adhesion improving method may be performed on the entire surface of the melt-extruded sheet or a part thereof. In addition, it is preferable that the temperature of a casting drum is 60 degreeC or more and 150 degrees C or less.

[First film winding process]
Next, a first film (first polymer film) winding step 76 is performed. The unstretched first polymer film 72 is wound up by a winding roller to obtain a first film roll 75. The film formation width of the first polymer film 14 is preferably 1.3 m or more and 3 m or less. Thus, the thickness of the 1st polymer film 14 obtained is 50 micrometers or more and 200 micrometers or less.

  It is preferable that both ends of the first polymer film 14 thus obtained are trimmed and wound up. The trimmed part is recycled as a raw material for the same type of film or as a raw material for a film of a different type after being pulverized or after being subjected to a granulation process or a depolymerization / repolymerization process as necessary. May be used. Moreover, it is also preferable from a viewpoint of scratch prevention to attach a lami film to at least one surface before winding.

[Storage process]
The first film roll 75 which is a precursor of the product film roll 84 which is the final form of the product is stored so that the polymer molecules in the first polymer film 72 are not decomposed by heat or water. By such storage, the optical properties of the first polymer film 72 and the quality as a film are maintained.

[First film delivery step and stretching relaxation step]
In the first film delivery step 80, the first polymer film 72 is delivered to the tenter type stretching machine 18. In the stretching relaxation step 81, a stretching relaxation treatment is performed on the unstretched first polymer film 72 under predetermined conditions. This stretching relaxation condition can be performed under the same conditions as in the melt film-forming method described above. That is, when the progress degree EP1 of the stretching process of the first polymer film 72 is less than 70% of the target stretching rate, the relaxation process in the transport direction of the first polymer film 72 is started. Further, the stretching ratio R1 in the width direction of the first polymer film 72 is preferably in the range of 10% to 40%, more preferably 15% to 35%, and most preferably 25% to 30%. is there. Further, the relaxation rate RL1 in the transport direction is preferably 1% or more and 5% or less, more preferably 2% or more and 5% or less, and most preferably 3% or more and 5% or less. The other conditions in the stretching relaxation step 81 are preferably performed in the same manner as in the stretching relaxation step 21 described above.

  A product polymer film 82 having desired optical characteristics can be obtained by stretching and relaxing the first polymer film 72. As a specific example of the optical properties of the product polymer film 82, in the case of a CAP film having a thickness of 60 μm to 120 μm, an in-plane retardation (Re) is 30 nm to 150 nm, and a thickness direction retardation (Rth) is 100 nm to 250 nm. The product polymer film 82 obtained by the present invention is not limited to this.

[Film winding process]
A product film winding step 83 for winding the product polymer film 82 having desired optical properties is performed. A product polymer film 82 is taken up on a take-up roller, and a product film roll 84 is formed.

  Examples are given below, but the present invention is not limited thereto. The description will be made in detail in Experiment 1. For Experiment 2 according to the present invention and Experiments 3 to 6 which are comparative examples, descriptions of the same conditions as in Experiment 1 are omitted.

[Experiment 1]
The prescription of the compound used for dope preparation is shown below.
[composition]
Cellulose acetate propionate (acetyl substitution degree 1.00, propionyl substitution degree 1.70, total substitution degree 2.70, viscosity average polymerization degree 260, water content 0.2 wt%, viscosity of 6 wt% in dichloromethane solution 150 mPa S, powder having an average particle diameter of 1.5 mm and a standard deviation of 0.4 mm) 100 parts by weight dichloromethane (first solvent) 320 parts by weight methanol (second solvent) 83 parts by weight 1-butanol (third solvent) ) 3 parts by weight plasticizer A (triphenyl phosphate) 7.6 parts by weight plasticizer B (diphenyl phosphate) 3.8 parts by weight UV agent a: 2 (2′-hydroxy-3 ′, 5′-di-) tert-butylphenyl) benzotriazole 0.7 parts by weight UV agent b: 2 (2′-hydroxy-3 ′, 5′-di-tert-amylphenyl) -5
Chlorbenzotriazole 0.3 parts by weight Citric acid ester mixture (citric acid, monoethyl ester, diethyl ester, triethyl ester mixture) 0.006 parts by weight fine particles (silicon dioxide (average particle size 15 nm), Mohs hardness about 7) 05 parts by weight

  The cellulose acetate propinate (CAP) used here has a residual acetic acid content of 0.1 wt% or less, a residual propionic acid of 0.1 wt% or less, a Ca content of 60 ppm, and an Mg content of 10 ppm. The Fe content was 0.2 ppm, and the content of sulfur as a sulfate group was 65 ppm. The degree of substitution of the acetyl group with respect to hydrogen at the 6-position hydroxyl group was 0.32, the degree of substitution of the propionyl group with respect to hydrogen at the 6-position hydroxyl group was 0.58, and the proportion of all acyl groups was 33%. The methanol extract was 5% by weight, and the weight average molecular weight / number average molecular weight ratio was 2.5. The yellow index was 1.3, the haze was 0.08, the transparency was 92.9%, and the Tg (glass transition temperature; measured by DSC) was 133 ° C. This CAP is synthesized from cellulose collected from hardwood.

  First, the dope preparation step 10 was performed. The plurality of solvents were mixed in a 4000 L stainless steel mixing tank having stirring blades and stirred well to obtain a mixed solvent. In addition, as each raw material of a solvent, the thing whose water content is 0.5 weight% or less was used. Next, CAP flaky powder was gradually added from the hopper. The CAP powder is placed in a mixing tank and is initially stirred under a condition in which a dissolver type eccentric agitator that stirs at a peripheral speed of 5 m / sec and a stirrer having an anchor blade on the central shaft are agitated at a peripheral speed of 1 m / sec. Dispersed for minutes. The temperature at the start of dispersion was 25 ° C., and the final temperature reached 48 ° C. Further, an additive solution prepared in advance was supplied from the additive tank so that the total amount was 2000 kg. After finishing the dispersion of the additive solution, the high speed stirring was stopped. Then, the peripheral speed of the anchor blade of the stirrer was set to 0.5 m / sec, and the mixture was further stirred for 100 minutes to swell the CAP flakes to obtain a swelling liquid. Until the end of swelling, the inside of the mixing tank was pressurized to 0.12 MPa with nitrogen gas. At this time, the oxygen concentration in the mixing tank was less than 2 vol%, and the state of no problem in explosion prevention was maintained. The amount of water in the swelling liquid was 0.3% by weight.

  The swelling liquid was sent from the mixing tank to the jacketed pipe. The swelling liquid was heated to 50 ° C. with a jacketed pipe, and further heated to 90 ° C. under a pressure of 2 MPa to completely dissolve. The heating time at this time was 15 minutes. Next, the temperature of the dissolved liquid was lowered to 36 ° C. with a temperature controller, and the solution was passed through a filtration device having a filter medium having a nominal pore diameter of 8 μm to obtain a dope (hereinafter referred to as a dope before concentration). At this time, the primary pressure in the filtration device was 1.5 MPa, and the secondary pressure was 1.2 MPa. The filters, housings and pipes exposed to high temperatures were made of Hastelloy (trade name) alloy and had excellent corrosion resistance, and were equipped with a jacket for circulating a heat transfer medium for heat insulation and heating.

  The pre-concentration dope thus obtained was flash evaporated in a flash device at 80 ° C. and normal pressure, and the evaporated solvent was recovered by a condenser. The solid concentration of the dope 11 after the flash was 21.8% by weight. The condensed solvent was recovered with a recovery device to be reused as a dope preparation solvent. Then, after regenerating with a regenerator, the solution was sent to a solvent tank. Distillation and dehydration were performed in the recovery device and the regeneration device. The flash tank of the flash device was provided with a stirrer having an anchor blade on the stirring shaft, and the dope 11 flashed at a peripheral speed of 0.5 m / sec was stirred by the stirrer to perform defoaming. The temperature of the dope 11 in this flash tank was 25 ° C., and the average residence time of the dope in the tank was 50 minutes. The dope 11 was collected and the shear viscosity measured at 25 ° C. was 450 Pa · s at a shear rate of 10 (1 / sec).

  Next, bubbles were removed by irradiating the dope 11 with weak ultrasonic waves. Thereafter, it was passed through a filtration device while being pressurized to 1.5 MPa. In the filtration apparatus, first, a sintered fiber metal filter having a nominal pore diameter of 10 μm was passed, and then a sintered fiber filter having a same pore diameter of 10 μm was passed. Respective primary pressures were 1.5 MPa and 1.2 MPa, and secondary pressures were 1.0 MPa and 0.8 MPa. The dope temperature after filtration was adjusted to 36 ° C., and the dope 11 was sent and stored in a 2000 L stainless steel stock tank 25. The stock tank 25 has a stirrer 31 having an anchor blade on the central axis, and was constantly stirred at a peripheral speed of 0.3 m / sec. When preparing the dope 11 from the dope before concentration, no problem such as corrosion occurred at all in the wetted part of the dope.

  Moreover, the mixed solvent A of 86.5 weight part of dichloromethane, 13 weight part of acetone, and 0.5 weight part of 1-butanol was produced.

  The casting process 12, the drying process 13, and the first film winding process 15 were performed using the film production line 4 shown in FIG. 2 to produce the first polymer film 14. The dope 11 in the stock tank 25 was sent to the filtration device 32 with a high-precision gear pump. This gear pump has a function of increasing the pressure on the primary side of the pump, and feeds liquid by performing feedback control on the upstream side of the gear pump with an inverter motor so that the pressure on the primary side becomes 0.8 MPa. A gear pump having a volume efficiency of 99.2% and a discharge rate variation of 0.5% or less was used. The discharge pressure was 1.5 MPa. Then, the dope 11 that passed through the filtration device 32 was fed to the casting die 33.

  The casting die 33 was cast by adjusting the flow rate of the dope 11 at the discharge port of the casting die 33 so that the width of the casting die 33 was 1.8 m and the film thickness of the dried film was 80 μm. The casting width of the dope 11 from the discharge port of the casting die 33 was 1700 mm. In order to adjust the temperature of the dope 11 to 36 ° C., a jacket (not shown) was provided on the casting die 33 and the inlet temperature of the heat transfer medium supplied into the jacket was set to 36 ° C.

  The casting die 33 and the piping were all kept at 36 ° C. during film formation. As the casting die 33, a coat hanger type die was used. The casting die 33 was provided with thickness adjusting bolts at a pitch of 20 mm and equipped with an automatic thickness adjusting mechanism using a heat bolt. This heat bolt can also set a profile according to the pumping amount of the gear pump by a preset program, and feedback control by an adjustment program based on the profile of an infrared thickness meter (not shown) installed in the film production line 4 Also used were those having possible performance. In the film excluding the edge 20 mm, the thickness difference between two arbitrary points 50 mm apart was within 1 μm, and the thickness variation in the width direction was adjusted to 3 μm / m or less. The overall thickness was adjusted to ± 1.5% or less.

As the material of the casting die 33, precipitation hardening type stainless steel having a thermal expansion coefficient of 2 × 10 ⁻⁵ (° C. ⁻¹ ) or less was used. This had a corrosion resistance substantially equal to that of SUS316 in a forced corrosion test with an aqueous electrolyte solution. Further, even when immersed in a mixed solution of dichloromethane, methanol and water for 3 months, it had corrosion resistance that did not cause pitting (opening) at the gas-liquid interface. The finishing accuracy of the wetted surface of the casting die 33 was 1 μm or less in terms of surface roughness, the straightness was 1 μm / m or less in any direction, and the slit clearance was adjusted to 1.5 mm. About the corner | angular part of the liquid-contact part of the lip tip of the casting die 33, what was processed so that R might be set to 50 micrometers or less over the full width of a slit was used. The shear rate of the dope 11 inside the casting die 33 was in the range of 1 (sec ⁻¹ ) to 5000 (sec ⁻¹ ). Further, a WC (tungsten carbide) coating was performed on the lip end of the casting die 33 by a thermal spraying method to provide a cured film.

  Further, in order to prevent the dope 11 flowing out from being locally dried and solidified, a mixed solvent A for solubilizing the dope 11 is discharged from both ends of the casting bead to the discharge port of the casting die 33. Each 0.5 ml / min was supplied to the interface with the outlet. The pulsation rate of the pump supplying the mixed solvent was 5% or less. Further, the pressure on the back side of the casting bead was made 150 Pa lower than that of the front side by the decompression chamber. A jacket (not shown) was attached to keep the internal temperature of the vacuum chamber constant at a predetermined temperature. A heat transfer medium adjusted to 35 ° C. was supplied into the jacket. The edge suction device can adjust the edge suction air volume so as to be in the range of 1 L / min to 100 L / min, and in the present embodiment, this is in the range of 30 L / min to 40 L / min. Adjusted appropriately.

A stainless steel endless band having a width of 2.1 m and a length of 70 m was used as the casting band 35 as a support. The casting band 35 was polished so that the thickness was 1.5 mm and the surface roughness was 0.05 μm or less. The material is made of SUS316 and has sufficient corrosion resistance and strength. The thickness unevenness of the entire casting band 35 was 0.5% or less. The casting band 35 was driven by two rotating rollers 35a and 35b. At that time, the tension in the conveying direction of the casting band 35 was adjusted to 1.5 × 10 ⁵ N / m ² . Further, the relative speed difference between the casting band 35 and the rotating rollers 35a and 35b was adjusted to be 0.01 m / min or less. At this time, the speed fluctuation of the casting band 35 was set to 0.5% or less. Further, both end positions of the casting band 35 were detected and controlled so that the meandering in the width direction of one rotation was limited to 1.5 mm or less. The positional variation in the vertical direction between the tip of the die lip and the casting band 35 directly below the casting die 33 was set to 200 μm or less. The casting band 35 was installed in a casting chamber having wind pressure fluctuation suppressing means (not shown). The dope 11 was cast from the casting die 33 on the casting band 35.

As the rotating rollers 35a and 35b, those capable of feeding a heat transfer medium therein were used so that the temperature of the casting band 35 could be adjusted. A 5 ° C. heat transfer medium was passed through the rotary roller 35a on the casting die 33 side, and a 40 ° C. heat transfer medium was passed through the other rotary roller 35b for drying. The surface temperature of the central part of the casting band 35 immediately before casting was 15 ° C., and the temperature difference between both side ends was 6 ° C. or less. The casting band 35 preferably has no surface defects, has no pinholes of 30 μm or more, has no pinholes of 10 μm to 30 μm, 1 pin / m ² or less, and ² pinholes of less than 10 μm / Those with m ² or less were used.

The temperature of the casting chamber was kept at 35 ° C. using temperature control equipment. The casting film 34 formed from the dope 11 cast on the casting band 35 was first fed with a drying air flowing parallel to the casting film 34 to dry the casting film 34. The overall heat transfer coefficient from the dry air to the casting film 34 was 24 kcal / (m ² · hr · ° C.). As for the temperature of the drying air, 135 ° C. drying air was blown from the upstream air outlet at the upper part of the casting band 35. Further, 140 ° C. drying air was blown from the downstream air blowing port, and 65 ° C. drying air was blown from the air blowing port below the casting band 35. The saturation temperature of each drying wind was around -8 ° C. The oxygen concentration in the dry atmosphere on the casting band 35 was kept at 5 vol%. In order to maintain this oxygen concentration at 5 vol%, the air was replaced with nitrogen gas. Further, in order to condense and recover the solvent in the casting chamber, a condenser (condenser) was provided, and its outlet temperature was set to -10 ° C.

For 5 seconds after casting, a wind shielding plate was installed so that the dry wind did not directly hit the casting bead and the casting film 34, and the static pressure fluctuation in the vicinity of the casting die 33 was suppressed to ± 1 Pa or less. When the solvent ratio in the casting film 34 reached 50% by weight on a dry basis, the film was peeled off as a wet film 36 while being supported by the peeling roller 37 from the casting band 35. The stripping tension is 1 × 10 ² N / m ² , and the stripping speed (stripping roller draw) is 100.1% to 110% with respect to the speed of the casting band 35 in order to suppress stripping failure. Adjusted appropriately within the range. The surface temperature of the peeled wet film 36 was 15 ° C. The average drying speed on the casting band 35 was 60% by weight / min on a dry basis. The solvent gas generated by drying was condensed and liquefied by a -10 ° C. condenser and recovered by a recovery device. The recovered solvent was adjusted so that the water content was 0.5% or less. The drying air from which the solvent was removed was heated again and reused as drying air.

  The wet film 36 was conveyed through the roller of the crossing section 40. At the crossover 40, 40 ° C. dry air was blown from the blower 41 to the wet film 36. In addition, a tension of about 30 N was applied to the wet film 36 while being conveyed by the roller of the crossing section 40. Further, the residual amount of solvent in the wet film 36 on the most downstream side of the crossover 40 was 20% by weight on the dry basis.

Immediately before being transported to the drying chamber 44, the ear film is cut off at both ends of the wet film 36 by the ear clip device 42. Ears 50 mm on both sides were cut with an NT-type cutter, and the cut ears were blown to a crusher 90 with a cutter blower (not shown) and crushed into chips of about 80 mm ² on average. This chip was used again as a raw material for dope production together with CAP flakes as a raw material for dope preparation. Prior to drying at a high temperature in the drying chamber 44, the wet film 36 was preheated in a predrying chamber (not shown) supplied with 100 ° C. drying air.

  The wet film 36 was dried at a high temperature in the drying chamber 44. The drying chamber 44 was divided into four sections, and drying air at 120 ° C., 130 ° C., 130 ° C., and 130 ° C. was supplied from a blower (not shown) from the upstream side. The transport tension of the wet film 36 by the roller 44a was set to 100 N / m, and it was dried for about 10 minutes until the residual solvent amount finally reached 0.3% by weight to obtain the first polymer film 14. Here, the solvent content on the basis of the dry amount is calculated by {(xy) / y} × 100 where x is the film weight at the time of sampling and y is the weight after the sampling film is dried. Value. The wrap angle of the roller 91 (film winding center angle) was 90 degrees and 180 degrees. The material of the roller 44a was made of aluminum or carbon steel, and the surface was hard chrome plated. The roller 44a has a flat surface shape and a blasted matte surface. All film position fluctuations due to the rotation of the roller 44a were 50 μm or less. The roller deflection at a tension of 100 N / m was selected to be 0.5 mm or less.

  The solvent gas contained in the drying air was removed by adsorption using the adsorption / recovery device 44b. The adsorbent used here was activated carbon, and desorption was performed using dry nitrogen. The recovered solvent was reused as a dope preparation solvent after adjusting the water content to 0.3 wt% or less. The drying air contains plasticizers, UV absorbers and other high-boiling substances in addition to the solvent gas, so these were removed by a cooler and pre-adsorber to be removed by cooling and used for recycling. And adsorption / desorption conditions were set so that VOC (volatile organic compound) in the outdoor exhaust gas was finally 10 ppm or less. Moreover, the solvent amount collect | recovered by a condensation method among all the evaporation solvents was 90 weight%, and most of the remainder was collect | recovered by adsorption collection.

  The 1st polymer film 14 was conveyed to the 1st humidity control chamber (not shown). A drying air of 110 ° C. was supplied to the transition portion between the drying chamber 44 and the first humidity control chamber. Air having a temperature of 50 ° C. and a dew point of 20 ° C. was supplied to the first humidity control chamber. Furthermore, the 1st polymer film 14 was conveyed to the 2nd humidity control chamber (not shown) which suppresses generation | occurrence | production of the curl of the 1st polymer film 14. In the second humidity control chamber, air at 90 ° C. and 70% humidity was directly applied to the first polymer film 14.

  The first polymer film 14 after conditioning was cooled to 30 ° C. or lower in the cooling chamber 52. After that, the ears were cut again at both ends with an ear-cutting device (not shown). The forced static elimination device 50 was installed so that the charged voltage of the first polymer film 14 during conveyance was always in the range of -3 kV to +3 kV. Further, knurling was applied to both ends of the first polymer film 14 by a knurling roller 51. The knurling is applied by embossing from one side of the first polymer film 14, the width for applying the knurling is 10 mm, and the height of the unevenness is 12 μm higher than the average thickness of the first polymer film 14 on average. The pressing pressure by the knurling roller was set.

  And the 1st film winding-up process 15 was performed. The first polymer film 14 was conveyed to the winding chamber 52. The winding chamber 52 was kept at a room temperature of 28 ° C. and a humidity of 70%. An ion wind static elimination device (not shown) was also installed in the winding chamber 52 so that the charged voltage of the first polymer film 14 was −1.5 kV to +1.5 kV. The product width of the first polymer film 14 having a film thickness of 80 μm thus obtained was 1475 mm. The diameter of the winding roller 52a was 169 mm. The tension pattern was such that the winding start tension was 300 N / m and the winding end was 200 N / m. The total winding length was 3940 m. The fluctuation range of winding deviation at the time of winding (sometimes referred to as the oscillating width) was ± 5 mm, and the winding deviation period with respect to the winding roller 52a was 400 m. The pressing pressure of the press roller 52b against the winding roller 52a was set to 50 Pa. The temperature of the first polymer film 14 during winding was 25 ° C., the water content was 1.4% by weight, and the residual solvent amount was 0.3% by weight. The average drying rate was 20% by weight / min on the basis of the dry weight throughout the entire process. Moreover, there was no winding looseness and wrinkles, and no winding slip occurred in the impact test at 10G. The roll appearance was also good.

  The first film roll 16 was stored in a storage rack at 25 ° C. and 55% RH for 1 month and further examined in the same manner as described above. As a result, no significant change was observed. Further, no adhesion was observed in the roll. Further, after the first polymer film 14 was formed, no peeling residue of the casting film 34 formed from the dope 11 was found on the casting band 35.

  A first film delivery step 20 for delivering the first polymer film 14 was performed. The first polymer film 14 was sent to a tenter type stretching machine 18 shown in FIG. The conveyance speed was 50 m / min. Next, the stretching relaxation step 21 was performed. The first polymer film 14 sent to the tenter-type stretching machine 18 was conveyed into the tenter-type stretching machine 18 while both ends thereof were fixed with clips. The clip was cooled by supplying a heat transfer medium at 20 ° C. The clip was conveyed by a chain, and the speed fluctuation of the sprocket was 0.5% or less.

  Stretching was also performed in the width direction while being conveyed in the tenter type stretching machine 18. The biting width L1 of the first polymer film 14 was 1000 mm, the widthwise maximum stretching width L2 was 1250 mm (target stretching ratio R1 was 25%), and the separation width L3 was 1200 mm. When the width L1 ′ was 1050 mm, relaxation in the transport direction was started, and when relaxation of 2% in the transport direction was completed, the width L1 ″ was 1170 mm.

  The stretching ratio of the first polymer film 14 in the tenter-type stretching machine 18 is such that the difference between the substantial stretching ratios at any two points at a position 10 mm or more away from the biting start position by the clip is 10% or less, and The difference between the stretching ratios at two arbitrary points separated by 20 mm was 5% or less. The ratio of the length from the clip clamping start position to the clamping release position with respect to the length from the inlet to the outlet of the tenter type stretching machine 18 was 90%. And it sent out as the product polymer film 22 from the tenter type | mold extending machine 18. FIG.

  Finally, a product film winding process 23 was performed. The product polymer film 22 was wound around the take-up roller 52a to obtain a product film roll 24. At this time, in order to eliminate winding defects such as winding deviation, winding was performed using the press roller 52b while applying a pressing pressure of 50 Pa.

[Evaluation]
1. Measurement of in-plane retardation (Re) Cut the product polymer film 22 into 70 mm x 100 mm, adjust the humidity at a temperature of 25 ° C and a humidity of 60% RH for 2 hours, and use an automatic birefringence meter (KOBRA21DH Oji Scientific Co., Ltd.) From the extrapolated value of the retardation value measured from the vertical direction at 632.8 nm, it was calculated according to the following formula.
Re = | nMD−nTD | × d
nMD is the refractive index in the transport direction, nTD is the refractive index in the width direction, and d is the thickness (film thickness) of the film. The calculated value was 82 nm.

2. Measurement of Thickness Direction Retardation (Rth) The product polymer film 22 was cut into 30 mm × 40 mm, conditioned for 2 hours at a temperature of 25 ° C. and a humidity of 60% RH, and 632.8 nm with an ellipsometer (M150 manufactured by JASCO Corporation). Was calculated according to the following formula from the value measured from the vertical direction and the extrapolated value of the retardation value measured in the same manner while tilting the film surface.
Rth = {(nMD + nTD) / 2−nTH} × d
nMD is the refractive index in the transport direction, nTD is the refractive index in the width direction, nTH is the refractive index in the film thickness direction, and d is the thickness (film thickness) of the film. The calculated value was 192 nm.

[Experiment 2]
In Experiment 2, the target draw ratio R1 was 15%. When the degree of progress of the stretching process in the width direction was 6% with respect to the target stretching ratio R1, relaxation was performed by 2% in the transport direction. The other conditions were the same as in Experiment 1, and the Re and Rth were calculated. In Experiment 2, Re was 60 nm and Rth was 174 nm.

Comparative example

[Experiment 3 to Experiment 6]
In Experiment 3, the target stretching ratio R1 was 30%. In Experiment 4, the target stretch ratio R1 was 25%, in Experiment 5, 15%, and in Experiment 6, 35%. In Experiments 3 to 6, no relaxation in the transport direction was performed. The other conditions were the same as in Experiment 1, and the Re and Rth were calculated. In Experiment 3, Re was 80 nm, Rth was 202 nm, Re in Experiment 4 was 70 nm, Rth was 194 nm, Re in Experiment 5 was 50 nm, Rth was 175 nm, Re in Experiment 6 was 85 nm, and Rth was 205 nm.

  FIG. 5 shows the correlation between the in-plane retardation Re and the thickness direction retardation Rth for Experiments 1 to 6, and FIG. 6 shows the correlation between the target stretch ratio R1 and the retardation ratio (= Re / Rth).

  As shown in FIG. 5, when comparing Experiments 1 and 2 in which the stretching process was performed in the middle of the stretching process in the width direction and Experiments 3 to 6 in which only the stretching process in the width direction was performed, conveyance in the middle of the stretching process in the width direction was performed. It can be seen that the direction relaxation treatment increases the in-plane retardation Re and suppresses the increase in the thickness direction retardation Rth (arrow A in FIG. 5). In addition, in order to obtain Re / Rth equivalent to Experiment 1 with a conventional stretching method that does not relax in the transport direction, it was found that the target stretching ratio R1 was 35%, but the transparency of the film deteriorated. (Experiment 6). That is, by performing relaxation in the transport direction, the retardation ratio (= Re / Rth) can be improved with a low target stretching ratio R1 (arrow B in FIG. 6).

  From the comparison between Experiment 1 and Experiment 4 or Experiment 2 and Experiment 5 in FIG. 5, in the film produced at the same target stretch ratio R1, the retardation ratio (= Re / Rth) is obtained by performing relaxation in the transport direction. It can be seen that there is an improvement (arrow A in FIG. 6).

  If the film is subjected to a stretching process with a high stretching ratio, problems such as a decrease in the transparency of the film may occur, making it difficult to use as a display material. However, according to the present invention, it has been found that the film having the desired Re and Rth can be obtained and the retardation ratio of the film is improved by performing relaxation in the transport direction even if the stretching ratio in the width direction is low. It was also found that the film does not cause problems such as a decrease in transparency.

It is explanatory drawing which shows the process of 1st Embodiment of the manufacturing method of the polymer film of this invention. It is the schematic of the film manufacturing line for enforcing the manufacturing method of the polymer film which concerns on this invention. It is the schematic of a tenter type stretching machine. It is explanatory drawing which shows the process of 2nd Embodiment of the manufacturing method of the polymer film of this invention. It is a correlation diagram of Re and Rth of the polymer film obtained by the manufacturing method of the polymer film of this invention. It is a correlation diagram of the target draw ratio R1 and Re / Rth of the polymer film obtained by the manufacturing method of the polymer film of this invention. It is a principal part enlarged view of the tenter drawing machine used by this invention.

Explanation of symbols

2, 70 Film production process 4 Film production line 5 Stretch relaxation line 10 Dope preparation process 14, 72 First polymer film 18 Tenta stretching machine 21, 81 Stretch relaxation process 22, 82 Product polymer film 63b Relaxation start line 71 Raw material preparation process 73 Melting extrusion process 74 Cooling process R1 Target stretch ratio EP1 Progression

Claims (6)

In the method for producing a polymer film comprising a polymer as a main component and stretching or relaxing the first polymer film having a long strip shape,
The first polymer film is produced by either a solution casting method or a melt extrusion method with the polymer as a main component,
Winding the first polymer film as a first film roll;
Removing the first polymer film from the first film roll;
When stretching the first polymer film in the width direction,
A method for producing a polymer film, comprising starting relaxation in the transport direction of the first polymer film. When the progress of the stretching in the width direction of the first polymer film is less than 70% of the target stretching rate,
2. The method for producing a polymer film according to claim 1, wherein relaxation in the transport direction of the first polymer film is started.   The method for producing a polymer film according to claim 1 or 2, wherein a relaxation rate of the first polymer film in the transport direction is 1% or more and 5% or less.   The method for producing a polymer film according to any one of claims 1 to 3, wherein a stretching ratio in a width direction of the first polymer film is 10% or more and 40% or less.   5. The method for producing a polymer film according to claim 1, wherein the polymer contains at least one of cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate.   The method for producing a polymer film according to any one of claims 1 to 5, wherein the polymer film is an optical functional film.

Images