JP5292265B2 - Manufacturing method of optical film - Google Patents

Abstract

The invention provides a method of manufacturing optical films.A clip stenter is successively equipped with a preheating zone, a stretching zone and a relaxing zone at the upstream of the transmission direction of a moistening film.In the relaxing zone, the internal stress of the moistening film stretched in the stretching zone is relaxed and the offset of the slow shaft of the side end part is corrected at the same time.The correction is performed by heating the side end part with a first heating device.In the preheating zone, the temperature of the moistening film is increased in advance and the heating for adjusting the offset of the slow shaft is performed by a second heating device.

Description

  The present invention relates to a method for producing an optical film, particularly an optical film used for a display device or the like.

  The required performance for display devices such as liquid crystal displays has been increasing in recent years, and the required performance for optical films used in display devices has only increased. For example, in liquid crystal displays, the brightness is increasing and the screen is becoming larger. With this, optical films such as retardation films are required to have stricter optical characteristics uniformity. ing.

  The optical film is manufactured by either a solution casting method or a melt casting method, and is manufactured by a continuous manufacturing method. That is, the optical film is made long. And the uniformity of said optical characteristic is calculated | required more strongly about the width direction of a long optical film. In addition, as the area of the display device is increased, the width for which the optical characteristics must be uniform is also increasing. Furthermore, in response to growing demand for display devices and cost reductions, it is necessary to increase the production speed while using existing film forming equipment. And the amount of the waste of the optical film which arises in a film forming process is also increasing, so that a manufacturing speed is improved.

  Among optical characteristics, the uniformity of the slow axis has been especially emphasized in recent years. The slow axis is observed in films that exhibit birefringence. Then, when the long film is stretched so as to expand in the width direction, the linear marking applied in the width direction before stretching becomes a convex shape in the long direction after stretching, and this is a stretched line or Called Boeing Line. In addition, when extending | stretching, conveying, an extending | stretching line may become convex in a conveyance direction, and may become convex in an anti-conveyance direction. The slow axis almost coincides with the tangent in the curved drawn line, and often coincides with the polymer main chain direction.

  A film made of a polymer usually exhibits birefringence, and even a cellulose acylate film said to have small anisotropy exhibits birefringence. It is difficult to make the slow axis of a film exhibiting such birefringence uniform in the width direction, and various proposals have been made so far.

  For example, when gripping each side with the gripping means and extending in the width direction, the track rails on which the gripping means on one side and the gripping means on the other side run respectively have different lengths. A method for independently changing the length has been proposed (see, for example, Patent Document 1). According to this method, since the left and right grip lengths of the film are independently changed, the slow axis can be controlled to be uniform to some extent in the width direction during stretching.

  Furthermore, it is a method for producing a film that is stretched in the width direction and is taken up by a take-up roll. The orientation angle of the film is observed in the width direction, and the tension in the running direction is controlled by the take-up roll according to the distribution of the observed orientation angle. A method has been proposed (see, for example, Patent Document 2).

  In addition, among the optical characteristics, the retardation that depends on the refractive index in the slow axis and the refractive index in the fast axis can be made uniform by providing a temperature gradient in the width direction in the thermal relaxation process. It is disclosed that it can be performed (see Patent Document 3).

JP 2006-182020 A JP 2006-150659 A Japanese Patent No. 3935570

  However, in order to achieve a uniform thickness or develop a desired retardation, the conditions for the stretching process for stretching in the width direction need to be strictly set. In addition to this, finding the setting conditions in the stretching process as in Patent Document 1 to achieve uniformity in the width direction of the slow axis makes the setting conditions in the stretching process more complicated. become. Furthermore, in Patent Document 1, it is necessary to change the structure of the stretching device so that the length of the track rail is variable. Further, in the method of Patent Document 1, even if the slow axis shift is reduced, it is around 1 °, and the level of uniformity of the slow axis as required in recent years is not achieved.

  Further, according to the method of Patent Document 2, the range in which the desired slow axis appears in the width direction can be widened to some extent, but the range has a limit. In particular, the larger the width of the optical film to be manufactured, the wider the range in which the shift of the slow axis is not eliminated.

  Furthermore, according to the method of Patent Document 3, the retardation can be made uniform in the width direction, but the slow axis cannot be made uniform in the width direction.

  Then, an object of this invention is to provide the manufacturing method of the optical film which can manufacture the optical film with a small shift | offset | difference of a slow axis in the width direction so that a width | variety may become wider.

  The method for producing an optical film of the present invention includes a stretching step of stretching a long polymer film being conveyed so as to expand in the width direction while heating, and for relaxing the internal stress of the stretched polymer film. A relaxation step of heating the polymer film in a state in which the width is regulated, and depending on the amount of deviation between the slow axis and the intended slow axis at the side end of the polymer film that has undergone the relaxation step, In the relaxation step, the side end portion is heated to a higher temperature to correct the slow axis shift.

  When the bowing shape at the start of the relaxation process is convex with respect to the transport direction, it is preferable to perform the correction in the subsequent relaxation process.

  The shift amount is determined in advance for each set condition in the stretching step, and the set condition is determined by the temperature of the polymer film, the width at the start of stretching of the polymer film and the stretch ratio at the end of stretching, It is preferable that it is the conveyance speed of a polymer film.

  The method for producing an optical film described above has a preheating step in which the polymer film being conveyed is heated in advance to raise the temperature before the stretching step, and the side end portion is heated at a higher temperature during the preheating step. It is preferable to adjust the amount of deviation by heating.

  When the bowing shape of the polymer film that has undergone the relaxation process is concave in the transport direction, it is more preferable to perform the adjustment in the subsequent preheating process so that the shape becomes convex.

The polymer film is arranged on a first layer made of cellulose acylate having a total acyl group substitution degree Z satisfying the following formula (I), and at least one surface of the first layer, and the total acyl group substitution degree Z Preferably has a second layer made of cellulose acylate satisfying the following formula (II).
2.0 ≦ Z <2.7 (I)
2.7 ≦ Z ≦ 3.0 (II)

  According to the present invention, an optical film having no slow axis shift in the width direction can be produced, and further, the slow axis can be produced with a uniform width.

It is the schematic which shows a solution casting apparatus. It is the schematic of a clip tenter. It is explanatory drawing of deviation | shift amount D and orientation angle | corner (theta) when convex bowing appears with respect to a conveyance direction. (A) is explanatory drawing of the Boeing line BL. (B) is a top view of a wet film. (C) is a graph of the deviation | shift amount D along the measurement line ML of (b). (D) is a graph of the orientation angle θ along the measurement line ML of (b). It is a side view which shows the cross-sectional outline of a clip tenter. It is explanatory drawing explaining the heating method of the side edge part in the clip tenter which is 1st Embodiment. It is a graph of orientation angle (theta) explaining the correction method by a 1st heating apparatus. It is a graph of orientation angle (theta) when the setting conditions in a extending process differ from each other. It is explanatory drawing of deviation | shift amount D and orientation angle | corner (theta) when concave bowing appears with respect to a conveyance direction. (A) is explanatory drawing of the Boeing line BL. (B) is a top view of a wet film. (C) is a graph of the deviation | shift amount D along the measurement line ML of (b). (D) is a graph of the orientation angle θ along the measurement line ML of (b). It is the schematic of the clip tenter which is 2nd Embodiment. It is a graph of orientation angle (theta) explaining the method of deviation | shift amount adjustment by a 2nd heating apparatus. It is a graph of orientation angle (theta) explaining the method of deviation correction by the 1st heating device. It is sectional drawing of an air supply type heating apparatus. It is sectional drawing of an air supply type heating apparatus.

  The solution casting apparatus 10 in FIG. 1 manufactures an optical film (hereinafter simply referred to as “film”) 22 from the dope 11. The dope 11 is obtained by dissolving a polymer in a solvent. The solution casting apparatus 10 includes a casting device 15 that forms a wet film 12 from a dope 11, a pin tenter 16 that holds each side of the wet film 12 with a pin (not shown), and dries the wet film 12, A first excision device 17 for excising each side portion having a retention mark, a clip tenter 20 for gripping each side portion of the wet film 12 with a clip 50 (see FIG. 2), and extending the wet film 12 in the width direction, A second excision device 21 that excises each side where there is a grip mark, a drying chamber 25 that further dries the wet film 12 into a film 22, a cooling chamber 26 that cools the film 22, and the film 22 is wound into a roll. The winding device 27 is provided in order from the upstream side.

  The casting apparatus 15 peels off a drum 30 as a casting support, a casting die 31 that flows out the dope 11 toward the circumferential surface of the drum 30, and a casting film 32 that is formed on the circumferential surface of the drum 30. A take-off roller 35 that supports the wet film 12 is provided in a chamber 36 that partitions the external space.

  The drum 30 has a drive unit (not shown), and the drive unit rotates around a shaft 30a provided at the center of a circular cross section in the circumferential direction indicated by an arrow A1. When the dope 11 flows out of the casting die 31 toward the peripheral surface of the rotating drum 30, a casting film 32 is formed on the peripheral surface of the drum 30. A bead made of the dope 11 is formed from the casting die 31 to the drum 30. A chamber (not shown) that decompresses the upstream area of the bead by sucking air is provided upstream of the bead in the rotation direction A1 of the drum 30.

  The temperature of the peripheral surface of the drum 30 is controlled by a temperature controller 37. A flow path through which the heat transfer medium flows is formed inside the drum 30, and the temperature controller 37 adjusts the temperature of the heat transfer medium and circulates the heat transfer medium between the drum 30. For example, in the case of so-called cooling casting in which the casting film 32 is cooled and solidified (gelled), the temperature controller 37 cools the heat transfer medium and sends the cooled heat transfer medium to the drum 30. By continuously performing this feeding, the heat transfer medium goes around the flow path inside the drum 30 and returns to the temperature controller 37.

  The casting support is not limited to the drum 30. For example, in place of the drum 30, an endless band stretched around the backup roller pair may be used. When an endless band is used as a casting support, the temperature of the band is adjusted through the backup roller by passing a heat transfer medium through each backup roller. In the case of so-called dry casting in which the cast film is dried and solidified, a band is often used instead of the drum 30.

  The stripping roller 35 is disposed so that the longitudinal direction is parallel to the longitudinal direction of the drum 30. The wet film 12 is pulled in the transport direction Z1, and the wet film 12 is supported by the peeling roller 35 on the peripheral surface, whereby the casting film 32 is peeled off from the drum 30 at a predetermined position.

  Inside the casting apparatus 15, a condenser (condenser) is provided that condenses the solvent evaporated from each of the dope 11, the casting film 32, and the wet film 12. The solvent liquefied by the condenser is guided to a recovery device arranged outside the chamber 36 and recovered by the recovery device. In addition, illustration of a condenser and a collection | recovery apparatus is abbreviate | omitted.

  The wet film 12 is guided from the casting device 15 to the pin tenter 16 by the roller 40. The pin tenter 16 has a pin plate (not shown) for penetrating and holding a plurality of pins on the side of the wet film 12, and this pin plate travels on a predetermined track. The wet film 12 is conveyed by the travel of the pin plate. A duct (not shown) through which dry air flows out is provided above the transport path of the wet film 12. A slit-like air outlet that is long in the width direction of the wet film 12 is formed on the lower surface of the duct, and when the dry air is discharged from the air outlet, the transported wet film 12 is gradually dried. . The pin tenter 12 is preferably dried so that the residual solvent amount of the wet film 12 is in the range of 3% by mass to 20% by mass. The residual solvent amount in the present specification is determined by {(XY) / Y} × 100, where X is the mass of the wet film 12 and Y is the mass after the wet film 12 is dried. This is a so-called dry weight standard value.

  The first cutting device 17 includes a cutting blade that cuts each side of the wet film 12. The wet film 12 is continuously guided by the cutting blade, and each side portion is cut so that the retention mark by the pin plate is removed.

  In this embodiment, the wet film 12 is dried by the pin tenter 16 and then guided to the clip tenter 20. However, in the case of dry casting, the pin tenter 16 need not be used. That is, in the case of dry casting, the wet film 12 from the casting device 15 may be guided to the clip tenter 20 without providing the pin tenter 16 and the first cutting device 17.

  The wet film 12 whose both sides have been cut by the first cutting device 17 is guided to the clip tenter 20. The configuration and operation of the clip tenter 20 will be described later with reference to another drawing.

  The second excision device 21 has the same configuration as the first excision device 17. The wet film 12 is continuously guided to the cutting blade, and each side portion is cut so that the grip marks by the clip are removed.

  The drying chamber 25 is provided with a plurality of rollers 41 that support the wet film 12 on the peripheral surface. Among these rollers 41, there is a driving roller that rotates in the circumferential direction, and the wet film 12 is conveyed by the rotation of the driving roller. The drying chamber 25 is supplied with heated dry air. The wet film 12 is dried by passing through the drying chamber 25. The cooling chamber 26 is supplied with dry air at approximately room temperature. By passing through the cooling chamber 26, the obtained film 22 is cooled. The film 22 whose temperature has been lowered is guided from the cooling chamber 26 to the winding device 27 and wound around the core 42.

  As shown in FIG. 2, the clip tenter 20 includes a chamber 43 that surrounds the transport path of the wet film 12 and partitions the transport path and its periphery from the external space. The chamber 43 includes a preheating area 45, an extending area 46, a relaxation area 47, and a cooling area 48 in order from the upstream side in the transport direction Z1. However, the chamber 43 is not provided with a partition member that partitions the areas 45 to 48 so as to be independent spaces. As will be described later, each of the areas 45 to 48 is formed by the traveling track of the clip 50 and dry air flowing out from each of the first to fourth supply chambers 55a to 55d (see FIG. 3).

  The clip tenter 20 includes a plurality of clips 50 that grip the side of the wet film 12, rails 51 and 52 that form a travel path of the clip 50, a duct 55 that discharges dry air, and dry air that has a predetermined condition in the duct 55. And an air supply unit 56 for feeding the air. The rails 51 and 52 are installed on both sides of the transport path of the wet film 12.

  The rail 51 and the rail 52 are separated from each other by a predetermined rail width. The rail width is constant at the width W1 in the preheating area 45, gradually increases from the width W1 to the width W2 in the extending area 46 in the direction Z1, and in the relaxation area 47 from the width W2 to the width W3 in the direction Z1. The cooling area 48 has a constant width W3. By setting each rail width in this way, in the preheating area 45, the wet film 12 is conveyed in a state in which the width is regulated so as to maintain a constant width, and in the stretching area 46, the wet film being conveyed. The film 12 is stretched so as to expand in the width direction. In the relaxation area 47, the wet film 12 is transported in a state where the width is restricted while the width is reduced, and in the cooling area 48, the wet film 12 is transported in a state where the width is kept constant.

  However, the above “constant” regarding the rail width in the preheating area 45 and the cooling area 48 need not be strict. That is, in order to express the desired optical characteristics, the rail width is slightly changed in the preheating area 45 and the cooling area 48 from the upstream to the downstream so that the width W1 and the width W3 can be said to be substantially constant. Good. Also, the rail width in the relaxation area 47 does not necessarily need to be gradually narrowed from upstream to downstream. For example, in the relaxation area 47, the rail width may be slightly changed from upstream to downstream to an extent that the rail width is substantially constant at the width W2.

  The plurality of clips 50 are attached to a chain (not shown) with a predetermined interval. This chain is attached to a rail 51 and a rail 52, respectively, and is movable along the rails 51 and 52. The chain meshes with a turn wheel 57 disposed on the upstream side of the preheating area 45 and a sprocket 58 disposed on the downstream end of the cooling area 48. The chain runs continuously as the sprocket 58 rotates. As the chain travels, the clip 50 moves along the rails 51 and 52.

  Upstream from the preheating area 45, gripping start means (not shown) for starting gripping of the side of the wet film 12 by the clip 50 is provided, and downstream of the cooling area 48, the wet film 12 by the clip 50 is provided. A grip releasing means (not shown) for releasing the side grip is provided. As a result, the wet film 12 is gripped by the clip 50 upstream of the preheating area 45, and the clip 50 moves along the rails 51 and 52 to be conveyed in the Z1 direction, and sequentially passes through the areas 36 to 39. A predetermined process is performed in each of the areas 36 to 39, and the grip is released at the downstream end of the cooling area 48.

  In the case where correction of the shift of the slow axis, which will be described later, is not performed, bowing is usually generated in the wet film 12 that has undergone the relaxation process in the relaxation area 47. Here, the shape of the bow and the shift of the slow axis will be described with reference to FIG. In addition, the elongate direction of the wet film 12 corresponds to the conveyance direction Z1 and a counter conveyance direction. Reference numeral 12e (R) is attached to the right edge of the wet film 12 when the transport direction Z1 is upward, and 12e (L) is attached to the left edge.

  The bowing line BL in FIG. 3A has a convex shape with respect to the transport direction Z1. Thus, the slow axis is measured for the wet film 12 in which the convex bowing occurs in the transport direction Z1. The slow axis is measured along a measurement line ML taken in the width direction Z2 as shown in FIG. The intended slow axis is the width direction Z2.

  The slow axis of the central portion 12c in the width direction Z2 substantially coincides with the width direction Z2. Accordingly, the slow axis of the central portion 12c is the intended slow axis. The slow axis gradually shifts from the width direction Z2 toward the right edge 12e (R) from the central portion 12c and the left edge 12e (L) from the central portion 12c. The range showing the deviation is the side end portion 12s as the correction target region.

  Here, as shown in FIG. 3C, the amount of deviation D between the slow axis at the side end portion 12s and the slow axis of the center portion 12c between the side end portions 12s is taken as the vertical axis, and the conveying direction Z2 Is the horizontal axis. In this specification, when the bowing appears in a convex shape as shown in FIG. 3A with respect to the transport direction Z1, the deviation amount D is set to a positive (+) as shown in FIG. Define as value. That is, when the bowing line BL is convex with respect to the transport direction Z1, and the slow axis at the point P on the measurement line ML is shifted from the intended slow axis, the deviation amount D (P) at the point P is set as follows. In this specification, it is a positive value.

  The shift amount D can be represented by, for example, an angle formed by the slow axis at the side end portion 12s and the slow axis of the center portion 12c. Therefore, the angle formed is hereinafter referred to as an orientation angle θ (where −90 ° ≦ θ ≦ 90 °). As shown in FIGS. 3C and 3D, in the present specification, the orientation angle θ when the shift amount D is positive is defined as a positive (+) value. In other words, the orientation angle θ in this specification is positive on the left edge 12e (L) side, and the angle taken clockwise from the intended slow axis toward the shifted slow axis is positive, and the right edge 12e. On the (R) side, the angle taken counterclockwise is positive. For example, when the shift amount D (P) is positive as shown in FIG. 3C, the orientation angle θ (P) at the point P is set positive as shown in FIG. Note that the orientation angle θ is 0 (zero) when the slow axis of the side end portion 12s is not displaced from the slow axis of the central portion 12c, which is the intended slow axis (deviation amount = 0). . In addition, the code | symbol "c" in the horizontal axis of (c), (d) shows the center in the width direction Z2 of the wet film 12. FIG.

  When the film is stretched so as to have a stretching ratio symmetric with respect to the center in the width direction Z2 of the wet film 12 as shown in FIG. 2, the graph of the symmetrical displacement amount D and the graph of the orientation angle θ as shown in FIG. Usually it is obtained.

  In the following first embodiment, for the wet film 12 that has undergone the relaxation process in the relaxation area 47 without being corrected by the first heating device 63 (see FIGS. 4 and 5) described later, the slow axis shift is corrected. When the orientation angle θ at the side end 12s is positive as shown in FIG. 3D, that is, when the bowing is convex in the transport direction, the slow axis deviation is corrected. In the present specification, “passed through the relaxation process” means after the end of the relaxation process. Therefore, the case where the bow of the wet film 12 after the end of the relaxation process or the film 22 after drying in the drying chamber 25 is convex with respect to the transport direction may be used. In the present embodiment, the wet film 12 at the end of the relaxation process will be described as an example of the film that has undergone the relaxation process. The wet film 12 at the end of the relaxation process is the wet film 12 at the downstream end of the relaxation area 47.

  As shown in FIG. 4, the duct 55 is provided above the conveyance path so that the distance between the wet film 12 and the conveyance path is substantially constant. A duct having the same configuration as that of the duct 55 is provided below the transport path so that the distance from the transport path is substantially constant, but the illustration is omitted. A slit 61 extending in the width direction Z2 of the wet film 12 is formed in the lower portion of the duct 55, and a plurality of slits 61 are provided in the Z1 direction. On the other hand, in the duct (not shown) below the conveyance path, each slit is formed in the upper part. In addition, the conveyance direction Z1 and the width direction Z2 shall be orthogonally crossed. Further, the inside of the duct 55 is partitioned into first to fourth air supply chambers 55 a to 55 d by a plurality of partition plates 62. In FIG. 4, there are a plurality of slits 61 in each of the first and second supply chambers 55a and 55b, and there is one slit 61 in each of the third and fourth supply chambers 55c and 55d. However, the number of the slits 61 in each of the air supply chambers 55a to 55d is not limited to this. That is, one slit 61 may be provided in the first supply chamber 55a and the second supply chamber 55b, and a plurality of slits 61 may be provided in the third supply chamber 55c and the fourth supply chamber 55d.

  The air supply unit 56 supplies dry air to the first to fourth supply chambers 55 a to 55 d of the duct 55. The air supply unit 56 includes a temperature controller (not shown) that independently controls the temperature of each dry air supplied to the first to fourth supply chambers 55a to 55d. By this temperature controller, the dry air adjusted to a predetermined temperature is supplied to each of the areas 45 to 48 through the first to fourth supply chambers 55a to 55d, respectively.

  Due to the supply of dry air from the second air supply chamber 55b, the wet film 12 is heated to a predetermined temperature in the stretching area 46. The temperature of the wet film 12 in the stretched area 46 is determined based on optical characteristics such as retardation of the optical film to be manufactured.

  Further, the wet film 12 before entering the stretching area 46 is heated in advance by the supply of dry air from the first air supply chamber 55a. By the heating by the preheating area 45, stretching in the stretching area 46 is started quickly, and more uniform tension is applied in the width direction Z2 when stretching in the stretching area 46. .

  In the relaxation area 47, in addition to the restriction of the width by gripping both sides, the stress (residual stress) remaining inside is appropriately relaxed by heating with the dry air from the third supply chamber 55c. In this relaxation step, the molecular orientation in the wet film 12 is brought into an intended state. This relaxation process will be described in more detail later.

  In the cooling area 48, the wet film 12 having the desired molecular orientation in the relaxation process is cooled with dry air. This cooling fixes the molecules in the desired orientation. In FIG. 4, illustration of the clip 50, the turn wheel 57, and the sprocket 58 is omitted to avoid complication.

  In the first embodiment, as shown in FIG. 4, a first heating device 63 is provided in the relaxation area 47. The first heating device 63 is arranged between the third air supply chamber 55 c and the transport path of the wet film 12, and the lower part is a heater 64. The first heating devices 63 each have a controller 71 that controls the amount of heat generated from the heater 64. In FIG. 4, for convenience of explanation, the heaters 64 and their arrangement pitch are greatly drawn with respect to the wet film 12.

  The first heating device 63 may be disposed on the opposite side of the third air supply chamber 55 c with respect to the conveyance path of the wet film 12, that is, below the wet film 12. In this case, the first heating device 63 is provided so that the heater 64 faces upward. However, when the heater 64 is disposed below the wet film 12, if the wet film 12 is broken for some reason, it is assumed that the broken wet film 12 contacts the heater 64. Therefore, it is more preferable that the heater 64 is disposed above the conveyance path of the wet film 12.

  As shown in FIG. 5, a plurality of first heating devices 63 are provided in the relaxation area 47, and are arranged above the respective side end portions 12 s of the wet film 12. The first heating device 63 includes a plurality of heaters 64, and a plurality of heaters 64 are arranged in the width direction of the wet film 12. In FIG. 5, illustration of a duct, a clip 50, a turn wheel 57, and a sprocket 58 disposed below the conveyance path of the wet film 12 is omitted.

  The controller 71 controls these heaters 64 independently, and controls the amount of heat generated from each heater 64 including on / off switching of each heater 64. The controller 71 is preliminarily input with a signal related to information on the on / off of each heater 64 and a signal related to information about the amount of heat to be generated by the heater 64 to be turned on, and controls each heater 64 based on these signals. .

  With the above control, for the wet film 12 subjected to the subsequent relaxation process, the side end 12s to be corrected whose slow axis is deviated from the intended slow axis is removed from the first supply chamber 55c. It heats so that it may become predetermined temperature higher than only spraying of dry air. By this heating, the side end portion 12 s is contracted in the transporting direction Z <b> 1 and the counter-transporting direction in the relaxation area 47 to be larger than the central portion 12 c. By increasing the amount of contraction of the side end portion 12s beyond the center portion 12c by a predetermined amount, the wet film 12 in which the shift between the slow axis of the side end portion 12s and the intended slow axis is corrected at the end of the relaxation process. It becomes. By this correction, the slow axis of the wet film 12 becomes uniform in the width direction Z2.

  The deviation between the slow axis of the side end 12s of the wet film 12 that has undergone the relaxation process in the relaxation area 47 and the intended slow axis is effective because the side end 12s is heated while the width is regulated. Is to be corrected. Therefore, in the relaxation process performed without restricting the width, for example, in the relaxation process of removing the residual stress by heating the wet film 12 being conveyed while being supported by the peripheral surfaces of the plurality of rollers. Even if the portion 12s is heated, the shift of the slow axis is not sufficiently corrected.

  A method of correcting the shift of the slow axis at the side end 12s using the first heating device 63 will be described with reference to FIG. When extending symmetrically with respect to the center, as shown in FIG. 3D, the orientation angle θ is substantially symmetrical on the left and right. 6 shows only the range from the left edge 12e (L) of the wet film 12 to the center. That is, in FIG. 6, the left end of the horizontal axis is the left edge 12 e (L) of the wet film 12, and the right end indicated by “c” on the horizontal axis is the center of the wet film 12. A curve L1 is a graph of the orientation angle θ when the bowing at the end of the relaxation process has a convex shape with respect to the transport direction Z1. The bow shape of the film obtained by guiding it to the drying chamber 25 without correcting the shift of the slow axis as it is is substantially equal to L1.

  Since the position where the orientation angle θ is positive in the curve L1 is a position indicating a slow axis that deviates from the intended slow axis (θ = 0 °), it is the side end 12s as a correction target. In this way, for the wet film 12 stretched in the width direction Z2 under predetermined setting conditions, the side end 12s as the correction target is specified based on the profile of the orientation angle θ at the end of the relaxation process. The heater 64 (see FIG. 4) through which the side end 12s to be corrected passes is turned on, and the amount of heat generated is controlled. By heating the side end 12s to a predetermined temperature due to the heat generated by the heater 64 during the relaxation process, it is possible to correct so that the slow axis shift is eliminated.

  As shown by the curve L1, the orientation angle θ of the side end portion 12s when the bowing appears in a convex shape with respect to the transport direction Z1 is positive (+). Therefore, the curve L1 has a curved shape that is more inclined toward the positive (+) side as it approaches the left edge 12e (L). The temperature of the side end 12s to be reached by the heating of the heater 64 is determined according to the magnitude of the orientation angle θ at the end of the relaxation process. First, the relationship between the orientation angle θ at the end of the relaxation step and the temperature when the side end 12s having this orientation angle θ is heated is obtained. Then, the temperature of the side end portion 12s is determined so that the orientation angle θ of the position to be corrected becomes 0 °. For example, when correcting the orientation angle θ (P) at the end of the relaxation process of the point P located at a distance P from the left edge 12e (L) to 0 °, it shrinks so that θ (P) becomes 0 °. The temperature at the point P is obtained in advance, the heater 64 through which the point P has passed is turned on, and the amount of heat generated is adjusted. Thereby, in the wet film 12 guided to the first heating device 63 thereafter, the point P located at a distance P from the left edge 12e (L) passes through the heater 64 which is turned on. By adjusting the amount of heat generated by the heater 64, the temperature of the point P is raised to a predetermined temperature obtained in advance. Accordingly, θ (P) at the end of the relaxation process becomes 0 °. Thus, the graph of the orientation angle θ of the film 22 obtained by heating with the heater 64 through which the side end portion 12s passes becomes a curve L2.

  As described above, in the relaxation area 47, the wetness guided thereafter to the first heating device 63 according to the amount of deviation D between the slow axis of the side end 12s and the intended slow axis at the end of the relaxation process. The side end portion 12s of the film 12 is heated by applying more heat energy than the central portion 12c so as to reach a higher temperature, and the shift of the slow axis is corrected. In this way, the amount of deviation D in the wet film 12 that has finished the relaxation process in the relaxation area 47 is obtained, and the deviation of the wet film 12 that is subsequently provided to the relaxation process in the relaxation area 47 is determined according to the amount of deviation D. to correct. In addition, it is good to obtain | require previously the relationship between the emitted-heat amount of the heater 64, and the temperature of the side edge part 12s reached by this heat_generation | fever for every conveyance speed of the wet film 12. FIG. This is because the amount of heat energy transmitted to the side end portion 12s changes according to the conveyance speed.

  If the amount of heat generated by the heater 64 is too large, the temperature of the side end portion 12s becomes higher than the expected value. Thus, if the temperature of the side end portion 12s is set to be higher than the expected value, the orientation angle θ (P) at the end of the relaxation step becomes a negative value beyond the line L2. As described above, if the temperature of the side end 12s is too high, the graph of the orientation angle θ at the end of the relaxation process has an inclination in the negative (−) region having the opposite sign as the curve L3. And the inclination of the curve L3 becomes steeper so that the temperature of 12s of side edges is made too high. In this way, when the temperature of the side end portion 12s is excessively raised by the heater 64 and the orientation angle θ (P) at the point P turns negative as shown by the curve L3, the point P passes. It is preferable to lower the temperature of the side end 12s by reducing the amount of heat generated by the heater 64.

  With respect to the wet film 12 at the end of the relaxation step, the slow axis shift amount D confirmed by the shape of the curve L1 varies depending on the setting conditions in the stretching area 46. Specifically, the range of the side end portion 12s to be corrected and the slope of the curve of the side end portion 12s change when the setting conditions in the extending area 46 are changed. Therefore, the relationship between the orientation angle θ at the end of the relaxation step and the temperature when the side end portion 12 s having this orientation angle θ is heated is determined for each set condition in the stretching area 46. The setting conditions in the stretched area 46 are the temperature of the wet film 12 in the stretched area 46, the stretch ratio, and the conveyance speed of the wet film 12 described above. The draw ratio is obtained from the width of the wet film 12 at the start of the drawing process in the drawing area 46 and the width of the wet film 12 at the end of the drawing process, and is a value obtained by, for example, W2 / W1.

  The setting conditions of the stretched area 46 are determined based on the optical characteristics of the target retardation value. If the slow axis shift of the side end 12s is completely corrected in the stretched area 47, the retardation value and the like are determined. It will affect the control. Even if the slow axis deviation can be corrected in addition to the optical characteristics such as the retardation value in the stretched area 46, the setting conditions are a very complicated combination. On the other hand, in the present invention, the setting condition of the stretched area 46 is determined based on optical characteristics such as a target retardation value, and the slow axis shift of the side end 12s is corrected in the relaxation area 47. The setting conditions of the stretching area 46 are relatively simple, and the retardation value and the like can be easily controlled. Furthermore, in the present invention, the shift amount D is detected for the wet film 12 that has undergone the relaxation process, and the shift is corrected based on the detected value, so that the shift is more reliably corrected.

  Furthermore, even if the slow axis deviation is corrected in the stretching process, the slow axis deviation amount D can be corrected only to about 1.5 °. This is because the slow axis is likely to change even in the relaxation process. However, in the present invention, in the relaxation process in the relaxation area 47, the side end portion 12s to be corrected is heated, and this correction is performed in a state where the width of the wet film 12 is regulated. Detecting is performed on the wet film 12 that has already undergone the relaxation process. Thereby, in this invention, even if it is a shift | offset | difference of a slow axis smaller than 1 degree, it can correct | amend precisely. As a result, the area that can be used as a product can be greatly increased, and the amount of the side portion to be excised with the second excision device 21 (see FIG. 1) can be greatly reduced. Therefore, even if a conventional production line is used, an optical film having a larger width can be produced, and an optical film that can be applied to a display device having a larger screen can be obtained.

  In this embodiment, the deviation and deviation amount D between the intended slow axis and the slow axis of the side end portion 12S are detected by the angle of the orientation angle θ, but the presence or absence of deviation and the deviation amount D are not necessarily the orientation. The angle θ may not be detected. For example, assume that the intended slow axis and the slow axis at the side end are simply detected, and the deviation is detected when the directions of the two slow axes do not match. The displacement D may be detected based on the magnitude.

  In addition, the orientation angle θ of the side end portion 12s of the wet film 12 that has undergone the relaxation process varies depending on the type of polymer and the setting conditions of the stretching process. Even if the types of polymers are the same, if the setting conditions in the stretching process are different, the orientation angle θ becomes different from each other, for example, the positive and negative signs are reversed.

  For example, even when cellulose triacetate (TAC) is used as the polymer component, by changing the setting conditions in the stretching step, the graph of the orientation angle θ as shown by the curves (A), (B), and (C) in FIG. Are different from each other.

  For example, in offline stretching as described later, the polymer component is TAC, the film temperature in the stretching step is in the range of 200 ° C. or higher and lower than 220 ° C., and the draw ratio determined by W2 / W1 is 1.40 or higher and 1.55 or lower. If the range and the conveyance speed are 40 m / min or less, as shown in curves (A) and (B), the orientation angle θ of the side end portion 12s that has undergone the relaxation step becomes positive (+). Moreover, when only the temperature of the film in the stretching step is changed to a range of 220 ° C. or higher and 230 ° C. or lower, the orientation angle θ of the film that has undergone the relaxation step becomes negative (−) as shown in the curve (C). Further, as shown in FIG. 7, the magnitude | D | of the amount of deviation between the slow axis of the side end portion 12s and the slow axis of the central portion 12c, or the side end portion 12s where the slow axis is shifted from the central portion 12c. The ranges are also different from each other.

  Cellulose diacetate (DAC) has a greater temperature dependency of the change in molecular orientation than TAC. Therefore, in the case of DAC, the amount of heat generated by the heater 64 is reduced to correct the slow axis deviation than in the case where the polymer component is TAC.

  According to the present invention, the effect of correcting the shift of the slow axis can be obtained regardless of whether the bowing appears in the convex shape or the concave shape with respect to the transport direction Z1.

  In the second embodiment below, when the orientation angle θ at the side end portion 12s of the wet film 12 that has undergone the relaxation process is negative, that is, when the bowing is concave with respect to the transport direction Z1, Correct the deviation. In addition, the case where the bow of the film which dried the wet film 12 which passed through the relaxation process as it is in the drying chamber 25 with respect to a conveyance direction may be sufficient. In the following description of the second embodiment, an example in which the wet film 12 at the end of the relaxation process has a concave bowing shape will be described.

  In FIG. 8, as in FIG. 3, the right edge of the wet film 12 with the transport direction Z <b> 1 facing upward is denoted by 12 e (R), and the left edge is denoted by 12 e (L). Further, the reference symbol “c” on the horizontal axis of FIGS. 8C and 8D indicates the center of the wet film 12 in the width direction Z2. The positive / negative of the deviation D and the positive / negative of the orientation angle θ when bowing appears in a concave shape with respect to the transport direction Z1 are as follows according to the above definition.

  When the bowing line BL has a concave shape as shown in FIG. 8A with respect to the transport direction Z1, when the slow axis is measured along the measurement line ML in FIG. 8B, the shift amount D becomes (c). It is negative (−) as shown, and the orientation angle θ is also negative (−) as shown in (d). For example, in this case, the shift amount D (P) of the point P at the side end 12s and the orientation angle θ (P) are both negative. Thus, the correction of the shift when the shift amount D (P) and the orientation angle θ (P) are negative at the end of the relaxation process can be performed to some extent by controlling the setting conditions in the stretching process. However, the following clip tenter 120 is preferably used.

  9, the same devices and members as those in FIGS. 2, 4 and 5 are denoted by the same reference numerals as those in FIGS. 2, 4 and 5, and description thereof is omitted. The clip tenter 120 of FIG. 9 is used in place of the clip tenter 20 of the solution casting apparatus 10 of FIG. The clip tenter 120 includes a second heating device 67 having the same configuration as that of the first heating device 63 in the preheating area 45. The second heating device 67 is disposed between the first air supply chamber 55 a and the transport path of the wet film 12, and the lower portion is a heater 68, similar to the first heating device 63. In FIG. 9, for convenience of explanation, the heaters 64 and 48 and their arrangement pitch are greatly drawn with respect to the wet film 12.

  The second heating device 67 may be disposed on the opposite side of the first air supply chamber 55 a with respect to the conveyance path of the wet film 12, that is, below the wet film 12. In this case, the second heating device 64 is provided so that the heater 68 faces upward. However, the second heating device 67 is preferably provided above the conveyance path of the wet film 12 as in the case of the first heating device 63.

  The second heating device 67 is also connected to the controller 71 in the same manner as the first heating device 63. The controller 71 receives signals related to information on the amount of heat to be turned on and off and to generate heat so that the side end 12s is heated to a predetermined temperature for each of the plurality of heaters 64 and 68. The controller 71 independently controls the amount of heat generated from the heaters 64 and 68 based on these inputted signals.

  By the controller 71, the heater 68 controls the temperature of the side end portion 12s, which is a shift amount adjustment region described later, with a predetermined heat generation amount. Thereby, the shift | offset | difference amount D at the time of completion | finish of the relaxation process of the wet film 12 provided after that in a preheating process is adjusted. Due to the heating by the heater 68, the side end portion 12s is brought to a higher temperature as compared with heating only by the dry air from the first supply chamber 55a. Thereby, in the extending | stretching process implemented in the extending | stretching area 46, it is made for the side edge part 12s to extend more largely in the width direction Z2 compared with the case where only the heating by the dry air from the 1st air supply chamber 55a is carried out. Thus, by heating the side end portion 12s in the second heating device 67, the extension amount in the width direction Z2 of the side end portion 12s in the stretching process is increased, and by the increase in the extension amount, the first heating device 63 The orientation angle θ of the side end portion 12s to be corrected is adjusted. Therefore, the shift amount D to be corrected by the first heating device 63 is also adjusted.

  Each heater 68 adjusts the amount of heat generated in accordance with the slow axis deviation amount D at the end of the relaxation process. By adjusting the heat generation amount, the amount of increase in the extension amount of the side end portion 12s in the stretching step is adjusted, and the orientation angle θ of the side end portion 12s at the end of the relaxation step becomes the intended one. That the orientation angle θ is as intended means that the deviation amount D is as intended.

  The side end portion 12s that is the shift amount adjustment region corresponds to the side end portion 12s to be corrected in the relaxation process. As described later, the shift amount adjustment region obtains the relationship between the position in the width direction at the end of the relaxation process and the orientation angle θ, and further, the position in the width direction at the end of the relaxation process and the width direction at the start of the stretching process. It is good to specify by calculating | requiring the correspondence with the position of. Based on the specified shift amount adjustment region, it is determined which of the plurality of heaters 68 should be turned on, and a signal related to the determined information is input to the controller 71. The heater 68 through which the shift amount adjustment region passes is turned on.

  The wet film 12 adjusted so that the side end portion 12s at the end of the relaxation step has the desired orientation angle θ is guided to the first heating device 63 in the same manner as in the first embodiment, and the orientation angle θ. Is corrected to be 0 °. Thus, the film 22 in which the shift of the slow axis is corrected is obtained.

  A method of correcting the shift of the slow axis by the clip tenter 120 will be described with reference to FIG. When extending symmetrically with respect to the center, as shown in FIGS. 8C and 8D, the shift amount D and the orientation angle θ at the end of the relaxation process are substantially symmetrical on the left and right. 10 shows only the range from the left edge 12e (L) to the center of the wet film 12 as in FIG. A curve L4 is a graph of the orientation angle θ when the bowing at the end of the relaxation process is concave with respect to the transport direction Z1, and is a case where the deviation amount D is not adjusted by the second heating device 67. When the orientation angle θ at the end of the relaxation process is in the form of the curve L4, the first heating device 63 uses the side end portion 12s of the wet film 12 while the second heating device 67 is not used. When the heating is performed, the inclination of the curve of the orientation angle θ in the obtained film 22 becomes larger than the curve L4, and the bowing becomes a concave shape with a steeper inclination.

  The position where the orientation angle θ is negative on the curve L4 is the side end 12s to be adjusted for deviation. As described above, the side end portion 12s as the shift amount adjustment target is specified for the film stretched in the width direction Z2 under predetermined setting conditions. The heater 68 (see FIG. 9) through which the side end portion 12s that is the object of deviation adjustment passes is turned on to control the amount of heat generated. The amount of deviation D to be corrected by the first heating device 63 is adjusted by heating the wet film 12 to a predetermined temperature by the heat generated by the heater 68.

  As shown by the curve L4, the orientation angle θ of the side end portion 12s when bowing appears in a concave shape at the end of the relaxation process with respect to the transport direction Z1 is negative (−). Therefore, the curve L4 has a curved shape that is more inclined to the negative (−) side as it approaches the left edge 12e (L). The temperature of the side end 12s to be reached by the heating of the heater 68 is determined according to the magnitude of the orientation angle θ. First, the relationship between the orientation angle θ and the temperature when the side end portion 12s having the orientation angle θ is heated is obtained. Then, the temperature of the side end portion 12s is determined so that the orientation angle θ at the position to be adjusted becomes positive (+). For example, when the orientation angle θ (P) of the point P on the side end 12s and at the distance P from the left edge 12e (L) is adjusted to be positive, the stretching process is performed so that θ (P) becomes positive. The temperature at the extending point P is obtained in advance, the heater 68 through which this point P has passed is turned on, and the amount of heat generated is adjusted. By adjusting the amount of heat generated by the heater 68, a point P at a distance P from the left edge 12e (L) of the wet film 12 guided to the second heating device 67 thereafter is set to a predetermined temperature obtained in advance. The temperature is raised to As a result, θ (P) at the end of the relaxation step becomes the adjusted orientation angle θa (P) which is a positive value. Thus, the wet film 12 heated by the heater 68 through which the side end portion 12s passes has a profile of the orientation angle θ as shown in the graph of the curve L5 at the end of the relaxation process. Therefore, the shift amount D has a similar profile. As described above, the second heating device 67 causes the bowing shape at the end of the relaxation process of the wet film 12 to be corrected by the first heating device 63 to be convex with respect to the transport direction Z1.

  As described above, in the preheating area 45, the preheating process in the preheating area 45 is subsequently applied according to the amount of deviation D between the slow axis of the side end 12s and the intended slow axis at the end of the relaxation process. The side end portion 12s of the wet film 12 is heated by applying more heat energy than the central portion 12c so as to reach a higher temperature, and the slow axis deviation amount D is adjusted to be positive. It should be noted that the relationship between the amount of heat generated by the heater 68 and the temperature of the side end portion 12s reached by this heat generation may be obtained in advance for each conveyance speed of the wet film 12. This is because the amount of heat energy transmitted to the side end portion 12s changes according to the conveyance speed.

  Since the amount of heat generated by the heater 68 is determined according to the shift amount D of the side end 12s at the end of the relaxation process, in the present embodiment, it is determined according to the orientation angle θ (P) at the end of the relaxation process. .

  At the end of the relaxation step, the side end portion 12s of the wet film 12 that is set to a positive adjustment orientation angle θa (P) like the curve L5 is heated by the first heating device 63 in the relaxation step. By this heating, the shift of the slow axis of the side end portion 12s is corrected. The correction by the first heating device 63 is the same as in the first embodiment. Therefore, the range in which the adjusted orientation angle θa (P) is positive is the side end portion 12s of the correction target region, and the amount of heat generated by the heater 64 through which the side end portion 12s passes is the positive adjusted orientation angle θa ( It is determined according to the size of P). According to the above method, the obtained film 22 has a graph of the orientation angle θ that is constant at θ = 0 ° in the width direction as indicated by a line segment L6 in FIG. Therefore, the film 22 having no slow axis deviation is obtained.

  In the second heating device 67, it is sufficient to heat the side end portion 12s so that the adjusted orientation angle θa (P) becomes positive, and it is not necessary to increase θa (P) so much in the positive region. Since the temperature of the side end portion 12s when correcting the shift by the first heating device 63 increases as the positive adjustment orientation angle θa (P) increases, the adjustment orientation angle θa (P) increases in the positive region. This is because if it becomes too much, the side end 12s in the relaxation area 47 must be heated to a higher temperature.

  When the adjustment orientation angle θa (P) exceeds the correctable amount that can be corrected by the first heating device 63, the calorific value of the predetermined heater 68 is lowered and the second heating device 67 reduces the side end portion. Lower the temperature reached by 12s. As a result, the adjusted orientation angle θa (P) becomes a smaller value. In this way, the shift amount D corrected by the first heating device 63 is adjusted by the second heating device 67.

  As described above, in the second embodiment, when the bow at the end of the relaxation process has a concave shape, the side end portion 12s is formed by the second heating device 67 so that the bow at the end of the relaxation process has a convex shape. It is heated. Also in the second embodiment, the setting condition of the stretching area 46 is determined based on the target optical characteristics such as the retardation value, and the shift of the slow axis of the side end 12s is corrected by the relaxation area 47, and the shift amount D Is adjusted based on the shift amount D after the end of the relaxation process after the stretching process. Thereby, the setting conditions of the extending area 46 are relatively simple, and the retardation value and the like can be easily controlled.

  Furthermore, according to this method, even if the film has a concave bowing shape, the side end 12s, which is the amount of deviation adjustment in the preheating process in the preheating area 45, is heated, and further corrected in the relaxation process. By heating the side end portion 12s that is the same as in the first embodiment, even if the amount of shift of the slow axis is negative and the magnitude | D | Can be precisely corrected. Thereby, while being able to increase the area which can be used as a product significantly, the quantity of the side part excised with the 2nd excision apparatus 21 (refer FIG. 1) can be reduced significantly. Therefore, even if a conventional production line is used, an optical film having a larger width can be produced, and an optical film that can be applied to a display device having a larger screen can be obtained.

  Also in the second embodiment, as in the first embodiment, the deviation and deviation amount D between the intended slow axis and the slow axis of the side end portion 12S are detected by an angle of the orientation angle θ. The presence / absence and the shift amount D are not necessarily detected as the orientation angle θ. For example, assume that the intended slow axis and the slow axis at the side end are simply detected, and the deviation is detected when the directions of the two slow axes do not match. The displacement D may be detected based on the magnitude.

  Cellulose diacetate (DAC) has a greater temperature dependency of the change in molecular orientation than TAC. Accordingly, the amount of heat generated by the heater 68 is made smaller in the DAC than in the case where the polymer component is TAC, and the shift amount D is adjusted.

  In some cases, the orientation angle θ of the side end 12s after the end of the relaxation process can be set to 0 ° by heating the side end 12s, which is the object of adjustment of the shift amount, with a predetermined heater 68. In this case, the first heating device 63 is not used.

  As described above, the tenter clip 120 includes the first heating device 63 and the second heating device 67. Therefore, by using this tenter clip 120, it is possible to correct the deviation even if the wet film 12 after the end of the relaxation process or the bowing shape of the film is uneven. That is, when the bowing shape of the wet film 12 or the film after the end of the relaxation process is convex, the second heating device 67 is not used, and only the first heating device 63 is used. On the other hand, when the shape of bowing in the wet film 12 or film after the end of the relaxation process is concave, the first heating device 63 and the second heating device 67 are used in combination.

  By using the second heating device 67 in combination with the first heating device 63, the effect that the desired slow axis is developed over the entire width of the optical film 22 may be more reliably obtained. For example, when the orientation angle θ (P) of the point P at the end of the relaxation process turns negative due to the heating by the first heating device 63, the side end 12s is made higher in the preheating process by the second heating device 67. By heating to the temperature, the film 22 in which the deviation is corrected can be obtained without further changing the temperature of the side end portion 12 reached by the first heating device 63.

  Since the temperature uniformity in the width direction Z2 of the wet film 12 is reduced only by heating only the first air supply chamber 55a (see FIG. 3) as the production speed is higher, that is, as the conveyance speed is higher, the second heating is performed. The effect of using the device 67 appears more remarkably. On the other hand, when the temperature distribution in the width direction Z <b> 2 in the relaxation process is difficult to be the intended one, the effect of using the first heating device 63 appears more significantly. Thus, it is preferable to adjust the balance of the heating of each side end by the first heating device 63 and the second heating device 67 in accordance with various conditions such as the manufacturing speed.

  Even if the second heating device 67 is arranged upstream of the preheating area 45 and the side end portion is heated, the same effect as described above or an equivalent effect cannot be obtained. For example, when the side end portion 12s is heated upstream of the preheating area 45, the side end portion 12s contracts in the preheating area 45 more in the conveyance direction and the counter conveyance direction than the center portion in the width direction S2, and the side end The part 12s becomes thicker than the central part. When a wet film having such a thickness profile is stretched in the width direction Z2, the amount of extension of the side end portion becomes smaller than that of the central portion, and the amount of slow axis deviation D in the wet film that has undergone the relaxation process is more negative. It gets bigger. That is, the magnitude | D | becomes larger for the negative shift amount D.

  3, 6 to 8, 10, and 11, the range of the side end portion 12 s is greatly exaggerated with respect to the range of the central portion 12 c.

  In the clip tenters 20 and 120, the temperature around the clip 50 (see FIG. 2) tends to be lower than the central portion of the wet film 12 in the width direction Z2. In such a case, the use of the first heating device 63 and the second heating device 67 is particularly effective.

  The heaters 64 and 68 shown in FIGS. 4, 5 and 9 are so-called electric heaters used in a non-explosion-proof environment. However, when the stretching process is performed in the solution casting process, a solvent gas may exist in the preheating area 45 and the relaxation area 47. When explosion protection is taken into consideration, such as when the solvent gas is in the atmosphere, as shown in FIG. 12, a duct 155 that blows dry air heated to a predetermined temperature toward the side end portion 12s, and this duct 155 An air supply type heating device 163 having an air supply unit 156 that sends dry air heated to a predetermined temperature to the duct 161 may be used instead of the first heating device 63 and the second heating device 67.

  The inside of one duct 155 extending in the width direction Z2 is partitioned into a plurality in the width direction Z2 by a partition plate 162. The on / off control of each feed of dry air to the first to seventh air supply chambers 155a to 155g formed by the partition plate 162 is controlled. Further, the air supply unit 156 sends dry air whose temperature and air volume are independently controlled to the first to seventh air supply chambers 155a to 155g to which dry air is to be sent. The controller 177 controls the air supply unit 156 according to the air supply chamber into which the dry air is to be sent and the temperature of the dry air to be sent.

  The air supply chamber into which dry air is to be sent from the air supply unit 156 is an air supply chamber through which the side end portion 12s passes below. FIG. 12 shows a mode in which dry air is sent out from the third supply chamber 155c and the fourth supply chamber 155d. As a result, the side end portion 12s passing below the third supply chamber 155c and the fourth supply chamber 155d is heated to a predetermined temperature.

  As an air supply type heating device, a heating device 263 as shown in FIG. 13 may be used instead of the heating device 163. The heating device 263 includes a plurality of ducts 255, an air supply unit 256 that sends dry air whose temperature and air volume are independently controlled to the ducts 255, a duct 255 into which the dry air is to be sent, and the dry air And a controller 277 for controlling the air supply unit 256 with respect to temperature and air volume.

  When the stretching process is performed on a film produced by melt film formation, the heaters 64 and 68 as described above may be used because the film is in a non-explosion-proof environment. As the heaters 64 and 68 used in such a non-explosion-proof environment, a so-called ceramic heater which is commercially available is preferable. Regardless of the presence or absence of the clip tenters 20 and 120, the pin tenter 16 (see FIG. 1) may be used for stretching in the width direction Z2. The end 12s may be heated, and the side end 12s may be heated in a preheating step before the stretching step. When the stretching process is performed by using such a pin tenter 16, an air supply type heating is used instead of the first heating device 63 and the second heating device 67 having ceramic heaters according to the solvent gas concentration inside the pin tenter 16. It is preferable to use an apparatus.

  Note that a slow axis detection device that detects a slow axis and a shift of the slow axis on-line may be arranged downstream of the clip tenters 20 and 120 of the solution casting apparatus 10 (see FIG. 1). In this case, a control device is used in which the amount of deviation is obtained based on the detection result by the slow axis detection device, and a signal related to the information on the heat generation amount of the heaters 64 and 68 obtained according to the obtained amount of deviation is sent to the controller 71. Thus, online feedback control can be performed. Thereby, even when the solution casting apparatus 10 is in operation, the slow axis shift can be corrected and the shift amount can be adjusted.

  The first embodiment and the second embodiment described above are cases where the film is stretched in the width direction Z2 in the solution casting process, but the present invention is not limited to this aspect. For example, the present invention can also be applied to so-called off-line stretching in which a once produced polymer film is stretched in the width direction Z2. The polymer film once manufactured is usually considered to be substantially free of polymer film produced by melt casting without solvent, or produced by solution casting, and the residual solvent amount is less than several percent. There are such polymer films. In this case, the wet film 12 in the first and second embodiments described above is carried out in place of a polymer film that is regarded as containing no or substantially no solvent. As described above, the polymer film to be subjected to off-line stretching may be produced by either a solution casting method or a melt casting method. When the present invention is applied to the polymer film produced by the solution casting method or the wet film 12 in the process of solution casting, it may have a single layer structure as in this embodiment. However, it may have a multilayer structure by simultaneous co-casting and sequential casting.

  The optical film produced according to the present invention can be particularly preferably used as a retardation film that is used in a polarizing plate and optically compensates for light from a light source. In particular, when producing a retardation film for VA, the present invention is particularly effective. According to the present invention, since the slow axis becomes uniform, the contrast is further improved when this optical film is used in a display device. Display performance is obtained.

(polymer)
The polymer in the optical film produced according to the present invention is a thermoplastic polymer. The present invention is particularly effective when cellulose acylate is used as the thermoplastic polymer.

Among cellulose acylates, the present invention is particularly effective when a TAC in which the substitution degree of the acyl group to the hydroxyl group of cellulose satisfies the following formulas (1) to (3) is used. In the formulas (1) to (3), A and B represent the substitution degree of the acyl group with respect to the hydrogen atom in the hydroxyl group of cellulose, A is the substitution degree of the acetyl group, and B is the acyl having 3 to 22 carbon atoms. The degree of substitution of the group. The total acyl group substitution degree Z of cellulose acylate is a value determined by A + B.
(1) 2.7 ≦ A + B ≦ 3.0
(2) 0 ≦ A ≦ 3.0
(3) 0 ≦ B ≦ 2.9

The present invention is particularly effective when a DAC is used in which the substitution degree of the acyl group to the hydroxyl group of cellulose satisfies the following formula (4) instead of or in addition to TAC.
(4) 2.0 ≦ A + B <2.7

From the viewpoint of retardation wavelength dispersion, while satisfying the formula (4), the substitution degree A of the acetyl group of DAC and the total substitution degree B of the acyl group having 3 to 22 carbon atoms are represented by the following formula (5). It is preferable to satisfy (6) and (6).
(5) 1.0 <A <2.7
(6) 0 ≦ B <1.5

  When TAC is used as the polymer, the optical film 22 preferably has a single layer structure made of TAC. On the other hand, when DAC is used as the polymer, the optical film 22 preferably has a multilayer structure. A preferable multilayer structure is a structure in which a layer made of TAC is provided on one surface of a layer made of DAC. A more preferable multilayer structure is a structure in which a layer made of TAC is provided on one surface and the other surface of a layer made of DAC, respectively. Such an optical film having a multilayer structure having a DAC layer is preferably produced by a solution casting method, and is preferably produced by simultaneous co-casting or sequential casting.

  When offline stretching is performed using the clip tenters 20 and 120 on a multi-layered polymer film having a DAC layer between two layers of TAC, the polymer as a setting condition of the stretching area 46 The temperature of the film is preferably in the range of 160 ° C. or higher and 190 ° C. or lower, more preferably in the range of 165 ° C. or higher and 185 ° C. or lower, still more preferably in the range of 170 ° C. or higher and 180 ° C. or lower. The range of 0.0 to 1.5 is preferable, the range of 1.1 to 1.4 is more preferable, and the range of 1.15 to 1.35 is more preferable. When stretching is performed under such setting conditions using a DAC, and the shape of the bow of the polymer film at the start of stretching in the stretching area 46 is convex with respect to the transport direction Z1, 47, the temperature of the side end portion 12s is made higher than that of the central portion 12c. At this time, the side end portion 12s is heated by the heater 64 so that the temperature difference with the central portion 12c is 1 ° C. or more and 20 ° C. or less. Preferably, heating is performed to be 3 ° C. or more and 15 ° C. or less, and heating is further preferably performed to be 5 ° C. or more and 10 ° C. or less.

  In addition, when performing offline stretching using a clip tenter 120 on a multi-layered polymer film having a cellulose diacetate (DAC) layer between two TAC layers, stretching is performed under the above-mentioned setting conditions. When the shape of the polymer film bow at the start of stretching in the stretching area 46 is concave with respect to the transport direction Z1, in the preheating area 45, the temperature of the side end 12s is set higher than that of the central portion. In that case, it is preferable to heat the side end portion with the heater 68 so that the temperature difference from the center portion is 1 ° C. or more and 20 ° C. or less, and it is more preferable to heat the side end portion to 3 ° C. or more and 15 ° C. or less. More preferably, heating is performed so that the temperature is 5 ° C. or higher and 10 ° C. or lower.

  The glucose unit having β-1,4 bonds constituting cellulose has free hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by esterifying some or all of these hydroxyl groups with an acyl group having 2 or more carbon atoms. The degree of acyl substitution means the ratio at which the hydroxyl group of cellulose is esterified at each of the 2-position, 3-position and 6-position (the substitution degree is 1 in the case of 100% esterification).

  First, as shown in Table 1, two types of cellulose acylates having different types of acyl groups and different degrees of substitution were prepared. Sample names were C2 and C4, respectively. The cellulose acylate having a sample name of C2 is TAC, and the cellulose acylate having a sample name of C4 is DAC. In the preparation, sulfuric acid was used as a catalyst. The addition amount of this catalyst with respect to 100 mass parts of cellulose is 7.8 mass parts. Carboxylic acid as a raw material for the acyl substituent was added and an acylation reaction was performed at 40 ° C. The type of acyl group and the degree of substitution were adjusted by adjusting the type and amount of carboxylic acid. Moreover, it age | cure | ripened at 40 degreeC after acylation. Further, the low molecular weight component of the cellulose acylate was removed by washing with acetone.

  Two types of dopes having the following formulation were prepared.

(Dope C2)
Cellulose acylate: 100 parts by mass of C2 listed in Table 1 Additive A: 11.3 parts by mass of A-3 in Table 2 Compound D: 4 parts by mass of Compound D shown in Chemical Formula 1 406 parts by mass of dichloromethane 61 parts by mass of methanol

(Dope C4)
Cellulose acylate: 100 parts by mass of C4 described in Table 1 Additive A: 19 parts by mass of A-3 in Table 2 Compound D: 4 parts by mass of Compound D shown in Chemical Formula 1 406 parts by mass of dichloromethane 61 parts by mass of methanol

  Further, in both of the above two dopes, a matting agent (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., secondary average particle size of 1.0 μm or less) which is a fine particle with respect to 100 parts by mass of cellulose acylate 0.13 The matting agent dispersion was mixed and stirred so as to be part by mass.

  The additive A is a polyester, and this polyester is obtained by the combination and ratio of dicarboxylic acid and diol described in Table 2. In Table 2, “TPA” in the “aromatic dicarboxylic acid” column represents terephthalic acid, and “SA” in the “aliphatic dicarboxylic acid” column represents succinic acid.

  Experiments 1 to 12 were performed under the following conditions. Experiments 1 to 5 are for producing an optical film having a single layer structure made of TAC. “TAC” is described in “Optical film of Table 3”. In Experiments 6 to 12, an optical film having a three-layer structure in which a TAC layer is disposed on both sides of a DAC layer is manufactured. “DAC” is described in “Optical film of Table 3”. Experiments 6-12 were made by simultaneous co-casting. Two exposed surface layers of the three-layer structure were formed with the same dope. In the following description, a layer made of DAC in the three-layer structure is referred to as a main layer.

[Experiment 1] to [Experiment 5]
An optical film was manufactured by using the solution casting apparatus 10 with the dope C2. Since the solvent gas exists in the atmosphere inside the clip tenter 20, an air supply type heating device 163 shown in FIG. 12 was used instead of the first heating device 63 and the second heating device 67. . In Table 3, when the heating device 163 is used in the preheating area 45 and the relaxation area 47, the temperature of the side end portion 12s reached by the heating device 163 is indicated in the “Temperature of the side end portion in the preheating area” column. It is described in “Side end temperature in area”. In these columns, “-” indicates that heating by the air supply type heating device 163 was not performed. In Table 3, regarding the setting conditions in the stretching step, the temperature of the wet film is described in the “Temperature” column, and the stretching ratio is described in the “Stretching ratio W2 / W1” column.

  For each optical film obtained in Experiments 1 to 5, the orientation angle θ was measured to determine the degree of slow axis deviation, and the bowing shape was confirmed. In the “Boeing shape” column of Table 3, the shape with respect to the conveyance direction Z1 is described, and when it is recognized as being linear in the width direction Z2, “substantially flat” is described.

  The orientation angle θ was measured using KOBRA21ADH or WR (manufactured by Oji Scientific Instruments). Each manufactured optical film was set in this measuring apparatus, and light having a wavelength of λ nm was incident on the optical film from its normal direction to measure the orientation angle θ. In selecting the measurement wavelength λnm, a wavelength selection filter that passes a specific wavelength is exchanged manually or by a program. In this way, light having a specific wavelength λ nm was incident on the optical film. In this example, the orientation angle θ was measured by moving the optical film with respect to the light source. The orientation angle θ was measured at each selected location by selecting a plurality of arbitrary locations on the measurement line ML. When moving the optical film, the measurement line ML was made to coincide with the width direction Z2 in the solution casting apparatus 10. The measurement line ML has a position 20 mm from one side edge of the optical film as one end point, and a position 20 mm from the other side edge of the optical film as the other end point. However, the method for measuring the orientation angle θ is not limited to this method. For example, the orientation angle θ may be continuously measured in a direction corresponding to the width direction Z2 in the solution casting apparatus 10.

  For each orientation angle θ measured as described above, an absolute value | θ | The maximum value | θ | max was selected from all | θ | values. A value obtained by doubling the maximum value | θ | max, that is, | θ | max × 2 (unit: °), was set as the degree of shift of the slow axis. The degree of this slow axis deviation is shown in the “degree of deviation” column of Table 3.

[Experiment 6] to [Experiment 12]
Simultaneous co-casting was performed with the dope for the surface layer being the dope C2 and the dope for the main layer being the dope C4. About each obtained optical film, while calculating | requiring the grade of the shift | offset | difference of a slow axis, the shape of Boeing was confirmed.

DESCRIPTION OF SYMBOLS 10 Solution casting apparatus 12 Wet film 12s Side edge part 20,120 Clip tenter 22 Optical film 45 Preheating area 46 Stretching area 47 Relaxation area 50 Clip 55 Duct 56 Air supply parts 63, 67 First and second heating devices 64, 68 Heater 163,263 Heating device

Claims (6)

A stretching step of stretching the long polymer film being conveyed so as to expand in the width direction while heating,
In order to relieve the internal stress of the stretched polymer film, has a relaxation step of heating the polymer film in a state of regulating the width,
Depending on the amount of shift between the slow axis and the intended slow axis at the side end of the polymer film that has undergone the relaxation step, the side end is heated to a higher temperature during the subsequent relaxation step. A method for producing an optical film, characterized by correcting a shift of a slow axis.   The method for producing an optical film according to claim 1, wherein the correction is performed in the subsequent relaxation step when the shape of the bow of the polymer film that has undergone the relaxation step is convex with respect to the transport direction. The amount of deviation is obtained in advance for each set condition in the stretching step,
2. The setting conditions are a temperature of the polymer film, a draw ratio determined from a width at the start of stretching of the polymer film and a width at the end of stretching, and a conveyance speed of the polymer film. Or the manufacturing method of the optical film of 2. Before the stretching step, it has a preheating step of preheating and heating the polymer film being conveyed,
The method for producing an optical film according to any one of claims 1 to 3, wherein, in the preheating step, the side end portion is heated to a higher temperature to adjust the shift amount.   5. The adjustment is performed in the subsequent preheating step so that the shape becomes convex when the shape of the bow of the polymer film that has undergone the relaxation step is concave with respect to the transport direction. Manufacturing method of the optical film. The polymer film is arranged on a first layer made of cellulose acylate having a total acyl group substitution degree Z satisfying the following formula (I), and at least one surface of the first layer, and the total acyl group substitution degree Z And a second layer made of cellulose acylate satisfying the following formula (II).
2.0 ≦ Z <2.7 (I)
2.7 ≦ Z ≦ 3.0 (II)

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