JP5824081B2 - Manufacturing method of optical film - Google Patents

Description

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

  Polymer films are widely used as optical films because of their excellent light transmittance, flexibility, and the ability to reduce the weight of light films. Among polymer films, cellulose acylate films are used for optical films such as protective films and retardation films for polarizing plates of liquid crystal display devices.

  The main production methods for polymer films include a melt extrusion method and a solution casting method. The melt extrusion method is a method for producing a polymer film by heating and dissolving a polymer as it is and then extruding it with an extruder. The melt extrusion method has features such as high polymer film productivity and relatively low equipment costs. On the other hand, in the solution casting method, a polymer solution in which a polymer is dissolved in a solvent (hereinafter referred to as a dope) is cast on a support to form a cast film. Then, the solution casting method is a method of forming a film by peeling the casting film containing the solvent from the support after the casting film has self-supporting property, and drying the film. It is. This solution casting method is particularly suitable for a method for producing an optical film because it is excellent in thickness uniformity and can obtain a film with few contained foreign substances as compared with a melt extrusion method.

  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 LCDs, the thickness is increasingly thinner, the screen is increasingly larger, and the brightness is getting higher. With this, optical films such as retardation films have uniform optical properties and are transparent. There are more stringent requirements for sex.

  In addition, optical films used for liquid crystal display devices and the like are required to ensure certain characteristics and quality under predetermined environmental conditions. For example, the retardation of the polymer film may change due to a durability test (hereinafter referred to as a wet heat durability test) under high temperature and high humidity conditions (for example, a temperature of 60 ° C. or higher and a relative humidity of 90% RH). There is a demand for a small change in retardation due to a wet heat durability test.

  Various proposals have been made so far in order to suppress the decrease in transparency as described above and the change in retardation caused by the wet heat durability test. For example, Patent Document 1 proposes a method for producing a cellulose acylate film having a three-layer structure by co-casting. In this patent document 1, the center core layer in the thickness direction and the first surface layer provided on one surface of the core layer include cellulose acylate, an organic solvent, and an additive, and the content of the additive is The second surface layer formed from different dopes and provided on the other surface of the core layer is formed from a dope containing cellulose acylate, fine particles, and an organic solvent. And the film formed by peeling the cast film from the support in a state containing the solvent while the residual solvent amount is in the range of 3% by mass or more and 50% by mass or less, or of the film at the time of stretching Stretching at least in the width direction while keeping the temperature in the range of 140 ° C. or higher and 200 ° C. or lower. Patent document 1 manufactures the film excellent in transparency by this.

  Moreover, patent document 2 performs the water vapor | steam contact process and heat processing to the polymer film which passed through the extending | stretching process, and suppresses the change of the retardation by a wet heat endurance test small by this. In the steam contact process for performing the steam contact treatment, the steam is brought into contact with the polymer film after the stretching process, and the temperature of the polymer film is maintained within a range of 100 ° C. or more and 150 ° C. or less. In the heat treatment step, the dried gas is brought into contact with the polymer film that has undergone the water vapor contact step, and the temperature of the polymer film is maintained within a range of 120 ° C. or higher and 130 ° C. or lower.

  Furthermore, in order to express the target optical characteristics in the polymer film, the long polymer film is often subjected to, for example, a stretching treatment for stretching in the width direction.

Japanese Patent No. 4686916 JP 2010-107949 A

  In order to express the desired retardation in the optical film, it is necessary to stretch the polymer film at a higher stretching ratio in the stretching process as the thickness is thinner. However, the higher the stretching ratio, the lower the transparency of the polymer film. In order to maintain transparency, it is necessary to stretch the polymer film at a higher temperature in the stretching process. However, in the stretching process, the change in retardation due to the wet heat endurance test becomes larger as the stretching ratio is increased while the temperature of the polymer film is increased. Such a change in retardation due to the wet heat durability test cannot be suppressed by the method of Patent Document 1.

  In addition, according to the method of Patent Document 2, a film having excellent transparency can be obtained, and there is a certain effect in that the change in retardation due to the wet heat durability test is suppressed to be small. However, the method of Patent Document 2 has not yet achieved the level that has recently been required for the change in retardation due to the wet heat durability test.

  Therefore, an object of the present invention is to provide a method for producing an optical film having a small change in retardation by a wet heat durability test and excellent in transparency.

The present invention relates to a method for producing an optical film that is made into an optical film by stretching in the width direction while conveying a long cellulose acylate film, wherein the glass transition point of the cellulose acylate film is Tg (° C.), Preheat cellulose acylate films that are arranged in order from the upstream side of the cellulose acylate film transport direction when the angle between the transport direction of the rate film and the passage between the side edges of the cellulose acylate film is the stretching angle. In the tenter preheating area comprising a preheating area, a first stretching area and a second stretching area extending in the width direction, and a cooling area for cooling, while maintaining the width of the cellulose acylate film constant. The preheating process for preheating the rate film and the preheating process are performed continuously, and the first rolling In area, the spread of the cellulose acylate film (Tg + 10 ℃) or more (Tg + 50 ℃) 1.8 times or less the width 1.5 times or more by stretching in the width direction while the temperature in the range A second stretching step is carried out continuously with the first stretching step and the first stretching step, and in the second stretching area, the cellulose acylate film is stretched in the width direction at a stretching angle θ2 smaller than the stretching angle θ1 in the first stretching step. The cellulose acylate film has a stretching step and a cooling step that is performed continuously with the second stretching step and is cooled while being conveyed in a cooling area while keeping the width of the cellulose acylate film constant. The time passing through the preheating area is Ta, the time passing through the first stretching area is Tb, the time passing through the second stretching area is Tc, and the time passing through the cooling area is Td. To, and is configured as satisfying the following (1) and (2).
0.5 ≦ (Ta + Td) / (Tb + Tc) ≦ 3.0 (1)
0.2 ≦ (Tb / Tc) ≦ 4.5 (2)

In the second stretching step, it is preferable to stretch the cellulose acylate film in the width direction while lowering the temperature of the cellulose acylate film. It is preferable that the angle change rate (unit:%) obtained by (θ2 / θ1) × 100 is in the range of 0.5% to 40%. Prior to the first stretching step, by stretching the cellulose acylate film in the width direction in a state of 140 ° C. or lower, the prestretching step expands the width within the range of 1.01 times or more and 1.20 times or less. It is preferable to have.

  A cellulose acylate film is formed by casting a casting film in which a cellulose acylate is dissolved in a solvent to form a casting film by casting the dope on a moving support, and peeling off the casting film containing the solvent. It is preferable to stretch the cellulose acylate film having a residual solvent amount of 20% by mass or less in the first stretching step.

  It is preferable to have a water vapor contact step of bringing the optical film into contact with the optical film after the second stretching step and maintaining the temperature of the optical film within a range of 100 ° C. or higher and lower than 150 ° C.

The cellulose acylate film is disposed 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 has a total acyl group substitution degree. Z is not preferable to have a second layer of cellulose acylate satisfying the following formula (II). In the first stretching step, it is preferable to widen the width of the cellulose acylate film from 1.6 times to 1.8 times.
2.0 ≦ Z <2.7 (I)
2.7 ≦ Z ≦ 3.0 (II)

  According to this invention, the change of the retardation by a wet heat endurance test is suppressed small, and the optical film excellent in transparency is obtained.

It is the schematic which shows a solution casting apparatus. It is the schematic of a 2nd tenter. It is a schematic sectional drawing in alignment with the III-III line of FIG. It is the schematic of a water vapor contact apparatus.

  The polymer in the optical film produced according to the present invention is a transparent thermoplastic polymer. The present invention is effective when the thermoplastic polymer has a hygroscopic property, and the higher the hygroscopic property, the greater the effect of the present invention. In the present embodiment, cellulose acylate is used as such a hygroscopic thermoplastic polymer.

Among cellulose acylates, the present invention is particularly effective when TAC (cellulose triacetate) is used in which the substitution degree of the acyl group to the hydroxyl group of cellulose satisfies the following formulas (1) to (3). 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 also particularly effective when using DAC (cellulose diacetate) 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

  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).

  The solution casting apparatus 10 in FIG. 1 is for producing a cellulose acylate film (hereinafter simply referred to as “film”) 12 from a dope 11. The dope 11 is obtained by dissolving a polymer in a solvent. The solution casting apparatus 10 includes a casting device 15, a first tenter 16, a first excision device 17, a second tenter 20, a second excision device 21, a drying chamber 25, a cooling chamber 26, a winding chamber. The take-up device 27 is provided in order from the upstream side.

  The casting apparatus 15 is for forming the film 12 containing the solvent from the dope 11. The casting apparatus 15 includes a belt 30, a casting die 31, a backup roller 33, and a peeling roller 35 in a chamber 36 that partitions the external space. The casting die 31 flows out the dope 11 toward the belt 30. The belt 30 is an endless casting support formed in an annular shape, and is stretched around a pair of backup rollers 33.

  At least one of the pair of backup rollers 33 has a drive unit (not shown), and the drive unit rotates in a circumferential direction indicated by an arrow A1 around a shaft 33a provided at the center of a circular cross section. . By this rotation, the belt 30 stretched around the peripheral surface is conveyed in the longitudinal direction. As the dope 11 flows out from the casting die 31 toward the circumferential surface of the belt 30 being conveyed, the dope is cast on the circumferential surface of the belt 30 to form a casting film 32. A bead made of the dope 11 is formed from the casting die 31 to the belt 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 backup roller 33.

  The temperature of the peripheral surface of each backup roller 33 is controlled by a temperature controller 33b. Inside the backup roller 33, a flow path through which the heat transfer medium flows is formed. The temperature controller 33 b adjusts the temperature of the heat transfer medium and circulates the heat transfer medium between the backup roller 33. By adjusting the peripheral surface temperature of the backup roller 33, the temperature of the casting film 32 is controlled via the belt 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 33 b cools the heat transfer medium and sends the cooled heat transfer medium to the backup roller 33. For example, by continuously performing this feeding, the heat transfer medium goes around the flow path inside the backup roller 33 and returns to the temperature controller 33b. In the case of so-called dry casting in which the casting film 32 is dried and solidified, the temperature controller 33b heats the backup roller 33.

  The casting support is not limited to the belt 30. For example, instead of the belt 30, a drum (not shown) that rotates in the circumferential direction may be used as the casting support. In the case of dry casting, the belt 30 is often used, and in the case of cooling casting, a drum is often used. When the drum is used as a casting support, the temperature of the peripheral surface of the drum is adjusted by passing a heat transfer medium through the drum, and the temperature of the casting film 32 is controlled through this drum.

  The stripping roller 35 is for maintaining a stripping position at which the casting film 32 is stripped from the belt 30, and is arranged so that the axial direction is parallel to the axial direction of the backup roller 33. The film 12 is pulled in the transport direction Z1, and the peeling film 35 supports the film 12 on the peripheral surface, whereby the casting film 32 is peeled off from the belt 30 at a predetermined position. By this continuous peeling, the film 12 is formed to be long.

  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 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.

  When TAC is used as the polymer, the film 12 preferably has a single layer structure made of TAC. On the other hand, when DAC is used as the polymer, the film 12 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. The casting die 31 in the case of simultaneous co-casting is a known multi-manifold die. Instead of a multi-manifold die, a feed block and a single manifold die may be used in combination. The feed block joins a plurality of types of supplied dopes inside, and sends the joined flow to a single manifold die.

  The film 12 is guided from the casting device 15 to the first tenter 16 by the roller 40. The first tenter 16 is for performing a pre-stretching process (a pre-stretching step) before a first stretching step and a second stretching step by a second tenter 20 described later. The first tenter 16 is a so-called clip tenter that holds each side portion of the film 12 by holding (gripping) the plurality of clips 16a, and the clip 16a travels on a predetermined track. The film 12 is conveyed by the travel of the clip 16a.

  The first tenter 16 includes an air supply portion 16b and a duct (air outflow portion) 16c. The air supply unit 16b sends dry air of a predetermined temperature (hereinafter referred to as dry air) to the duct 16c, and the dry air is sent to the film 12 from the duct 16c. Accordingly, the film 12 is dried while passing through the first tenter 16. In the first tenter 16, it is preferable that the residual solvent amount of the film 12 be within a range of 3% by mass or more and 20% by mass or less by promoting the drying of the film 12. In this specification, the residual solvent amount means that the mass of the film 12 to be measured for which the residual solvent amount is to be obtained is X, and the mass after completely drying the film 12 is Y ({(X− Y) / Y} × 100. Note that “completely dry” does not require the amount of the solvent to be strictly 0 (zero). For example, the mass after drying the film 12 to be measured at 110 ° C. for 3 hours may be Y.

  In the present embodiment, a clip tenter is used as the first tenter 16, but a pin tenter may be used instead of the clip tenter. The pin tenter has a pin plate for penetrating and holding a plurality of pins on the side of the film 12, and the film 12 is conveyed by the pin plate traveling on a predetermined track. When the pin tenter is used as the first tenter 16, the residual solvent amount of the film 12 is set within the range of 3% by mass or more and 20% by mass or less by promoting the drying of the film 12 as in the case of using the clip tenter. Is preferred. When the film 12 is stretched in the width direction before being guided to the second tenter 20 described later, that is, when stretched in the width direction, the first tenter 16 is often a clip tenter.

  The first cutting device 17 includes a cutting blade (not shown) that cuts each side of the film 12. The film 12 is continuously guided by the cutting blade, and the holding marks by the clip 16a in the first tenter 16 are removed by cutting each side portion. As described above, when the pin tenter is used as the first tenter 16 instead of the clip tenter, the first excision device 17 removes the holding marks by the pins by separating each side portion.

  In this embodiment, the film 12 is dried by the first tenter 16 and then guided to the second tenter 20. However, the first tenter 16 is not necessarily used. However, when a multilayer film having a DAC layer between two TAC layers is manufactured, it is preferable to use the first tenter 16 and thereby stretch the film in the width direction. In the case of dry casting, a pin tenter need not be used.

  The film 12 having both sides cut by the first cutting device 17 is guided to the second tenter 20. The film 12 is guided to the second tenter 20 after the residual solvent amount is set to 20% by mass or less. In the present embodiment, as described above, the film 12 is dried by the first tenter 16 until the residual solvent amount becomes 20% by mass or less. The 2nd tenter 20 is for performing the below-mentioned 1st extending | stretching process and 2nd extending | stretching process. Details of the second tenter 20 and the first stretching process and the second stretching process 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 film 12 is continuously guided to the cutting blade, and each side portion is cut off so that the holding mark by the clip 50 (see FIG. 2) in the second tenter 20 is removed.

  The drying chamber 25 is provided with a plurality of rollers 41 that support the film 12 on the peripheral surface. Among the plurality of rollers 41, there is a driving roller that rotates in the circumferential direction, and the film 12 is conveyed by the rotation of the driving roller. The drying chamber 25 is supplied with heated dry air. The film 12 is further dried by passing through the drying chamber 25.

  Room-temperature dry air is supplied to the cooling chamber 26. Room temperature is a temperature within the range of 15 ° C. or higher and 30 ° C. or lower. The temperature of the film 12 is lowered by passing through the cooling chamber 26. The film 12 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 FIGS. 2 and 3, the second tenter 20 includes a chamber 43 that surrounds the transport path of the film 12 and partitions the transport path and its periphery from the external space. The chamber 43 includes a preheating area 45, a first extending area 46, a second extending 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 preheating area 45, the first extending area 46, the second extending area 47, and the cooling area 48 into independent spaces. The preheating area 45, the 1st extending | stretching area 46, the 2nd extending | stretching area 47, and the cooling area 48 flow out from each of the driving | running track of the clip 50, and the 1st-4th air supply chambers 55a-55d so that it may mention later. It is formed spatially by dry air.

  The second tenter 20 includes a plurality of clips 50 that grip the side portion of the film 12, rails 51 and 52 that form a running track of the clips 50, a duct (air outflow portion) 55 that discharges dry air, and a duct 55. And an air supply unit 56 for feeding dry air of a predetermined condition. The rails 51 and 52 are installed on both sides of the film 12 conveyance path.

  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, a grip start member (not shown) for starting the gripping of the side portion of the film 12 on the clip 50 is provided, and on the downstream side of the cooling area 48, the side portion of the film 12 on the clip 50 is provided. A grip release member (not shown) for releasing the grip is provided. Thereby, the film 12 is gripped by the clip 50 upstream from the preheating area 45, and the clip 50 is transported in the longitudinal direction by moving along the rails 51 and 52, and the preheating area 45 and the first stretching area 46 are The second extending area 47 and the cooling area 48 are sequentially passed. While passing through the preheating area 45, the first stretching area 46, the second stretching area 47, and the cooling area 48, the film 12 is described later in the preheating area 45, the first stretching area 46, the second stretching area 47, and the cooling area 48. The predetermined processing is performed, and the grip is released at the downstream end of the cooling area 48.

  The rail 51 and the rail 52 are separated from each other by a predetermined rail width. In this specification, since the clip 50 attached to the chain moves on the rail, the width of the film and the width of the rail are considered to be equal. The rail width is constant at the width W1 in the preheating area 45. Thereby, in the preheating area 45, the film 12 is conveyed, maintaining a fixed width | variety in the state by which the width | variety was controlled.

  The 1st extending | stretching area 46 is for performing a 1st extending | stretching process (1st extending | stretching process), and a rail width | variety becomes wide gradually as it goes to conveyance direction Z1, ie, downstream. Thereby, in the 1st extending | stretching area 46, the width | variety is expanded by extending | stretching the film 12 in the width direction, conveying. Specifically, when the width of the film 12 introduced into the first stretching area 46 is W1, and the width of the film 12 exiting the first stretching area 46 is W2, the rail width in the first stretching area 46 is adjusted. By doing so, the draw ratio calculated | required by W2 / W1 shall be 1.5 times or more, More preferably, it is 1.5 times or more and 2.2 times or less. Here, the angle between the transport direction Z1 and the passage through which the side edge 12e of the film 12 passes is referred to as a stretching angle, and the stretching angle in the first stretching area 46 is θ1.

  The stretching angle θ1 is constant. From the viewpoint of expressing the desired optical characteristics in the film 12, the stretching angle θ1 is preferably larger than 0 ° and not larger than 10 °. A stretching angle θ1 of 10 ° or less is preferable because the film 12 is not easily broken in the second tenter 20.

  The 2nd extending | stretching area 47 continuously provided in the 1st extending | stretching area 46 is for performing a 2nd extending | stretching process (2nd extending | stretching process). Here, the stretching angle in the second stretching area 47 is θ2. In the second extending area 47, the rail width gradually increases in the same direction as the first extending area 46 in the transport direction Z1, that is, downstream. Thereby, in the 2nd extending | stretching area 47, the film 12 is expanded by extending | stretching to the width direction, conveying. However, the stretching angle θ2 is set smaller than the stretching angle θ1. Therefore, the extent of the width per unit time in the second extending area 47 is smaller than that in the first extending area 46. In the present embodiment, the stretching angle θ2 in the second stretching area 47 is constant. Note that the width of the film 12 exiting the second stretching area 47 is W3.

  In the case of producing a multilayer film 12 having a DAC layer between two TAC layers, the draw ratio determined by W3 / W1 is in the range of 1.51 to 2.5. It is more preferable that it is in the range of 1.55 times or more and 2.2 times or less, and more preferably 1.6 times or more and 2.0 times or less. By making the draw ratio calculated | required by W3 / W1 1.51 times or more, the target retardation will express reliably compared with the case of less than 1.51 times. By setting the draw ratio determined by W3 / W1 to 2.5 times or less, an increase in the internal haze of the film 12, that is, a decrease in transparency, is suppressed as compared with a case where the draw ratio is larger than 2.5 times, and breakage occurs. Is also prevented.

  The cooling area 48 is for performing a cooling process (cooling process), and the rail width is constant. Thereby, in the cooling area 48, the film 12 is conveyed in a state where the width is kept constant at W3.

  However, the above “constant” regarding the rail width in the preheating area 45 and the cooling area 48 need not be strict. In other words, 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.

  As shown in FIG. 3, the duct 55 is provided above the conveyance path so that the distance between the 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 film 12 is formed below the duct 55, and a plurality of slits 61 are provided along the transport direction Z1. On the other hand, in the duct (not shown) below the conveyance path, each slit is formed in the upper part. The transport direction Z1 and the width direction Z2 are orthogonal to each other.

  The interior 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 the present embodiment, as shown in FIG. 3, a plurality of slits 61 are provided in each of the first to fourth supply chambers 55a to 55d. Specifically, the number of the slits 61 in the first supply chamber 55a is one, and the number of the slits 61 in the second to fourth supply chambers 55b to 55d is three. However, the number of the slits 61 in each of the air supply chambers 55a to 55d is not limited to this. That is, the number of slits 61 in the first air supply chamber 55a may be 1 or 3 or more, and the number of slits 61 in the second to fourth air supply chambers 55b to 55d may be 1, 2, 4 or more.

  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 the preheating area 45, the first extending area 46, the second extending area 47, and the cooling area 48 via the first to fourth supply chambers 55a to 55d, respectively. Supplied to. Note that the temperature in each of the air supply chambers 55a to 55d may be constant, or the temperature region may be further subdivided in the transport direction Z1 of the film 12.

  By supplying the dry air from the first air supply chamber 55a, the film 12 is heated in advance before entering the first stretching area 46. Due to the heating by the preheating area 45, the stretching in the first stretching area 46 is quickly started, and more uniform in the width direction Z2 with respect to the film 12 when stretching in the first stretching area 46. Tension is applied.

  Here, let the glass transition point of the film 12 be Tg (° C.). By supplying dry air from the second air supply chamber 55b, in the first stretching area 46, the film 12 is heated and the temperature of the film 12 is maintained within the range of (Tg + 10 ° C.) or more and (Tg + 50 ° C.) or less. By setting the temperature of the film 12 to (Tg + 10 ° C.) or higher in the first stretching area 46, an increase in internal haze is reliably suppressed. In addition, by setting the temperature of the film 12 to (Tg + 50 ° C.) or lower in the first stretched area 46, the target thickness direction retardation Rth is reliably expressed. Moreover, since it becomes difficult to sag by making it below (Tg + 50 degreeC), generation | occurrence | production of the damage | wound by a sag is prevented. In the case of producing a multilayer film 12 having a DAC layer between two TAC layers, the temperature of the film 12 in the first stretched area 46 is more preferably (Tg + 10 ° C.) or more (Tg + 40 ° C.). Within the following range, more preferably within the range of (Tg + 10 ° C.) or more and (Tg + 30 ° C.) or less.

  The temperature of the film 12 in the second stretched area 47 is a relaxation effect that relieves optical properties such as retardation of the optical film to be produced and stress (residual stress) remaining in the film 12 due to stretching in the first stretched area 46. Set based on the degree of. By this relaxation action, the molecular orientation in the film 12 is brought into a target state.

  In the second stretching area 47, the temperature of the film 12 is preferably lowered from the temperature of the film 12 in the first stretching area 46 as it goes in the transport direction Z1. This temperature drop may be a continuous descent or a stepwise descent. The temperature of the film 12 in the second stretching area 47 is preferably in the range of (Tg−50 ° C.) or more and (Tg + 50 ° C.) or less. Thereby, even if it extends | stretches by the extending | stretching angle (theta) 2 smaller than (theta) 1 in the 2nd extending | stretching area 47, while an internal haze does not rise, while the target thickness direction retardation Rth expresses in the film 12, it is based on a wet heat endurance test. Retardation change is kept small. The temperature of the film 12 in the second stretched area 47 is more preferably in the range of (Tg−30 ° C.) to (Tg + 50 ° C.). More specifically, in the second stretched area 47, it is preferable to lower the temperature of the film 12 to (Tg-50 ° C), and more preferably to Tg-30 ° C.

  When the temperature of the film 12 in the first stretching area 46 is set to a high temperature within the range of (Tg + 10 ° C.) or more and (Tg + 50 ° C.) and this temperature is maintained in the second stretching area 47, the film 12 loosens and collides with each device. As a result, the film 12 may be damaged. However, when the temperature of the film 12 supplied from the first stretching area 46 is set to the above temperature in the second stretching area 47, the film 12 is not damaged.

  As described above, in the first stretching area 46, the film 12 is stretched in the width direction at a stretching angle θ1 in a state where the temperature of the film 12 is in the range of (Tg + 10 ° C.) to (Tg + 50 ° C.). The 1st extending | stretching process made into 1.5 times or more is performed (1st extending | stretching process). In the second stretching area 47, a second stretching process is performed in which the film 12 is stretched in the width direction at a stretching angle θ2 smaller than the stretching angle θ1 in the first stretching area 46 (second stretching step). Thereby, the obtained film 12 is excellent in transparency, and a change in retardation is suppressed to a small level even after a wet heat durability test. Moreover, suppression of the change of these retardation is more remarkable as the film 12 is thinner. The film 12 is further dried by heating with the dry air from the first to third supply chambers 55a to 55c in the preheating area 45, the first stretching area 46, and the second stretching area 47.

  In the cooling area 48, the film 12 having the target optical characteristics and molecular orientation in the second stretching area 47 is cooled with dry air to fix the molecules. In FIG. 3, the illustration of the clip 50, the turn wheel 57, and the sprocket 58 is omitted to avoid complexity.

The timing for switching from the first stretching step to the second stretching step, that is, the position of the boundary between the first stretching area 46 and the second stretching area 47 may be appropriately selected in order to obtain the desired performance. However, the length of the second tenter 20 in the transport direction Z1 is normally limited in length, and it is necessary to secure the time for the preheating process in the preheating area 45 and the cooling process in the cooling area 48. Therefore, the pre-heat treatment time Ta, the first stretching treatment time Tb, the second stretching treatment time Tc, and the cooling treatment time Td are set to times satisfying the following (1) and (2). . Thereby, the timing which switches from a 1st extending | stretching process to a 2nd extending | stretching process is set, and the change of the retardation by a wet heat endurance test is suppressed reliably. In addition, since each time Ta-Td is time when the film 12 passes each area 45-48, respectively, the following (1) and (( It is possible to set a time that satisfies 2).
0.5 ≦ (Ta + Td) / (Tb + Tc) ≦ 3.0 (1)
0.2 ≦ (Tb / Tc) ≦ 4.5 (2)

  The amount of change when the stretching angle changes from the stretching angle θ1 to the stretching angle θ2 may be appropriately selected in order to obtain the desired performance. However, when the angle change rate represented by (θ2 / θ1) × 100 (unit:%) is larger than 40%, the effect of suppressing the change in retardation by the wet heat durability test is reduced. When the angle change rate is 0%, θ1 = θ2 and the stretching conditions in the conventional tenter are the same, so the rate of change in retardation by the wet heat durability test is large. The angle change rate is preferably in the range of 0.5% to 40%, more preferably in the range of 1% to 30%, and particularly preferably in the range of 1.5% to 20%. By performing the 1st extending | stretching process and 2nd extending | stretching process in this 2nd tenter 20, the film 12 expresses the function as an optical film.

  In addition, when performing said 1st extending | stretching process and 2nd extending | stretching process in the 2nd tenter 20, the pre-stretching process in the 1st tenter 16 is the film 12 in the state which maintained the temperature of the film 12 at 140 degrees C or less. Is preferably stretched in the width direction. The stretching ratio of the preliminary stretching process in the first tenter 16 is preferably in the range of 1.01 times or more and 1.20 times or less. Thereby, the change rate of the retardation by a wet heat endurance test is suppressed more reliably small. The draw ratio in the first tenter 16 is determined by W5 / W4, where W4 is the width of the film 12 entering the first tenter 16 and W5 is the width of the film 12 exiting the first tenter 16.

  The first tenter 16 has a plurality of clips 16 a (refer to FIG. 1) that move on the rail like the second tenter 20. Therefore, the film 12 is stretched in the width direction by setting the distance between the rails so as to increase in the transport direction Z1. By this stretching, the width of the film 12 is expanded. Moreover, the 1st tenter 16 has the duct 16c (refer FIG. 1) and the air supply part 16b (refer FIG. 1) similarly to the 2nd tenter 20, and with the dry air from the air supply part 16b, the film 12 Adjust the temperature.

  The pre-stretching treatment of the above-described stretching ratio and temperature in the first tenter 16 reduces the rate of change in retardation due to the wet heat endurance test when manufacturing a multilayer film 12 having a DAC between two layers of TAC. This is particularly effective in terms of suppression.

  The above embodiment is a case where the film is stretched in the width direction Z2 in the solution film forming process, but the present invention is not limited to this aspect. For example, in the case of so-called off-line stretching in which a once produced polymer film is stretched in the width direction Z2, the first stretching process and the second stretching process by the second tenter 20 may be performed. Thereby, the film manufactured by off-line extending | stretching can suppress the rate of change of the retardation by a wet heat endurance test small, and can be used as an optical film. In particular, when a film having a multilayer structure including a DAC layer between two TAC layers is stretched off-line to obtain an optical film, a particularly remarkable effect can be obtained.

  As a polymer film once produced, a polymer film produced by melt extrusion does not contain a polymer film, or produced by solution casting, and the amount of residual solvent is generally considered to be substantially free, such as less than a few percent. There is a good polymer film. In this case, the film 12 in the above-described embodiment is carried out in place of a polymer film which is regarded as containing no or substantially no solvent. As described above, the film to be subjected to off-line stretching may be produced by either a solution casting method or a melt extrusion method. When the present invention is applied to the polymer film manufactured by the solution casting method or the film 12 in the process of solution casting, it may have a single layer structure as in this embodiment. A multi-layer structure such as simultaneous co-casting and sequential casting may be used.

  In order to secure the transparency of the film 12 while suppressing the rate of change in retardation due to the wet heat durability test, for example, FIG. 4 is provided inside the drying chamber 25 or between the drying chamber 25 and the cooling chamber 26. It is preferable to provide the water vapor contact device 120 shown in FIG. In the present embodiment, the water vapor contact device 120 is provided inside the drying chamber 25.

  The water vapor contact device 120 is for performing water vapor contact treatment for bringing water vapor into contact with the film 12 and maintaining the film 12 in a temperature range described later. The water vapor contact device 120 includes a condensation prevention treatment casing 140 and a wet gas contact casing 141, and the wet gas contact casing 141 is provided in the condensation prevention treatment casing 140. Further, in the water vapor contact device 120, a plurality of rollers 41 for conveying the film 12 are disposed inside each of the dew condensation prevention treatment casing 140 and the wet gas contact casing 141.

  The dew condensation prevention casing 140 is formed with an inlet 140b for introducing the film 12 into the inside and an outlet 140c for letting the film 12 out. The wet gas contact casing 141 is formed with an inlet 141b for introducing the film 12 into the inside and an outlet 141c for letting the film 12 out. The film 12 is guided by the roller 41 and enters the dew condensation prevention treatment casing 140 from the inlet 140b, and then enters the wet gas contact casing 141 from the inlet 141b. The film 12 passes through the wet gas contact casing 141, exits from the outlet 141c, passes through the dew condensation prevention casing 140, and exits from the outlet 140c.

  The dew condensation prevention casing 140 is for performing a dew condensation prevention process, and is filled with a low dew point dry gas 404. The low dew point dry gas 404 is a dried gas whose dew point is lower than the temperature of the film 12. The wet gas contact casing 141 is for performing a wet gas contact process on the film 12, and is filled with the wet gas 400. The wet gas 400 is a gas containing water vapor.

  The wet gas contact casing 141 is connected to the wet gas supply equipment 145 by a feed duct 142 and a return duct 143. The wet gas supply facility 145 recovers the gas inside the wet gas contact casing 140 as the recovery gas 300 via the return duct 143. The wet gas supply equipment 145 creates the wet gas 400 adjusted to a predetermined condition from the recovered gas 300 and supplies the wet gas 400 to the wet gas contact casing 141 via the feed duct 142.

  The temperature of the film 12 in the wet gas contact casing 141 is adjusted by the wet gas 400. The wet gas contact treatment in the wet gas contact casing 141 is performed by holding the film 12 in a range of 100 ° C. or higher and 150 ° C. or lower while holding the film 12 with a wet gas 400 having a relative humidity of 20% RH or higher and 5 It is preferable to make contact within a range of seconds to 60 minutes. More preferably, while maintaining the temperature of the film 12 in the range of 100 ° C. or more and 140 ° C. or less, the film 12 is kept in a range of 30 seconds or more and 30 minutes or less with the wet gas 400 having a relative humidity of 25% RH or more. More preferably, while maintaining the temperature of the film 12 within a range of 100 ° C. or higher and 130 ° C. or lower, the film 12 is mixed with a wet gas 400 having a relative humidity of 30% RH or higher and 1 minute or longer and 15 minutes or longer. Contact within a range of less than a minute.

  The dew condensation prevention casing 140 is connected to the low dew point dry gas supply equipment 121 through ducts 122 and 123. The low dew point dry gas supply equipment 121 has the same configuration as the wet gas supply equipment 145, and collects a part of the low dew point dry gas 404 in the dew condensation prevention treatment casing 140 through the duct 123. The low dew point dry gas supply equipment 121 creates a new low dew point dry gas 404 having a predetermined temperature and supplies the new low dew point dry gas 404 to the dew condensation prevention treatment casing 140 through the duct 122. Thus, the dew condensation prevention treatment casing 140 is filled with the low dew point dry gas 404.

  The operation of the water vapor contact device 120 will be described. The film 12 that has undergone the first stretching process and the second stretching process in the second tenter 20 is guided to the drying chamber 25 and guided to the dew condensation prevention treatment casing 140 of the water vapor contact device 120 provided in the drying chamber 25. . When the film 12 is guided to the dew condensation prevention treatment casing 140, the dew condensation prevention process is performed in contact with the low dew point dry gas 404. Thereby, even if it enters into the wet gas contact casing 141, it is prevented that dew condensation arises in the film 12. FIG. Further, since the wet gas contact casing 141 is provided in the dew condensation prevention treatment casing 140, the dew condensation on the outer wall surface of the wet gas contact casing 141 is prevented, and water droplets generated by the dew condensation on the outer wall surface are dropped on the film. There is nothing.

  The film 12 is guided from the dew condensation prevention treatment casing 140 to the wet gas contact casing 141. The film 12 is subjected to wet gas contact treatment in which the film 12 is brought into contact with the wet gas 400 in the wet gas contact casing 141. When in contact with the wet gas 400, the film 12 absorbs water molecules. As a result, the glass transition point Tg of cellulose acylate contained in the film 12 is lowered and the diffusion of water molecules in the film 12 is promoted. By promoting the diffusion of water molecules in the film 12, the higher-order structure of the cellulose acylate molecule is likely to transition to a more stable structure. For this reason, the structure of the cellulose acylate molecule is stabilized in a short time as compared with a simple heat treatment. As a result, the film 12 having a smaller variation ΔRth of the retardation before and after the wet heat durability test, in particular, the thickness direction retardation Rth is obtained. As described above, the film 12 that has passed through the second tenter 20 is subjected to the water vapor contact process including the dew condensation prevention process and the wet gas contact process (water vapor contact process).

  Before and after the wet gas contact treatment, the film is brought into contact with a heated high-temperature dry gas having a low dew point and heat-treated at an arbitrary film temperature and conveying tension for a predetermined time. This heat treatment can be arbitrarily carried out within a generally known condition range.

  The film 12 is used as an optical film. Specifically, the film 12 can be particularly preferably used as a retardation film that is used for a polarizing plate and optically compensates for light from a light source. Especially, it is particularly effective as a retardation film for VA and a retardation film for IPS. In addition, the film 12 is excellent in transparency, and the change in retardation is suppressed to be small even when the temperature and humidity conditions change. Therefore, the display device using this film has a large screen and high brightness, and is resistant to environmental changes. And stable display performance.

  First, as shown in Table 1, two types of cellulose acylates having different acyl substitution degrees were prepared. Sample names were C2 and C4, respectively. The cellulose acylate whose sample name is C2 is TAC, and the cellulose acylate whose sample name is 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 acylate is 7.8 mass parts. A carboxylic acid serving as a raw material for the acyl substituent was added, and an acylation reaction was carried out 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, the matting agent dispersion was mixed and stirred in any of the above two dopes. The matting agent (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., secondary average particle size of 1.0 μm or less) as fine particles was 0.13 parts by mass with respect to 100 parts by mass of cellulose acylate.

  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. The “dicarboxylic acid ratio” column in Table 2 indicates aromatic dicarboxylic acid / aliphatic dicarboxylic acid, and the “diol ratio” column indicates diol 1 / diol 2.

  Experiments 1 to 9 were performed under the following conditions. In Experiments 1 to 4, a film 12 having a single layer structure made of TAC is manufactured, and “TAC” is described in the “cellulose acylate” column of “Film” in Table 3. Experiments 5 to 9 are to produce a film 12 having a three-layer structure in which layers of TAC are arranged on both sides of a layer of DAC, and “DAC” in the “cellulose acylate” column of “Film” in Table 3 ". Experiments 5-9 were produced 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 9]
The film 12 was manufactured with the dope C2 using the solution casting apparatus 10, and these were made into Experiments 1-4. Moreover, the film 12 was manufactured with the dope C2 and the dope C4 using the solution casting apparatus 10, and these were made into Experiments 5-9. In Experiments 5 to 9, dopes C2 and C4 were co-cast, and a main layer was formed from dope C4 and a surface layer was formed from dope C2. Each thickness of the film 12 manufactured in each experiment and the film manufactured in each comparative experiment described later is shown in the “Thickness” column of “Film” in Table 2.

  For each experiment, the temperature (° C.) and the draw ratio W2 / W1 of the film 12 in the first stretch area 46 of the second tenter 20 and the stretch angle θ2 and the stretch ratio W3 / W2 in the second stretch area 47 are shown in Table 3. It shows in each column. The stretch angle θ2 is described in the “stretch angle θ2” column of Table 1 as “= θ1” when it is the same as the stretch angle θ1 in the first stretch area 46, and “<θ1” when smaller than θ1. ". When the steam contact device 120 is disposed in the drying chamber 25 and the film 12 is subjected to the steam contact treatment, “Yes” is described in the “Presence / absence of steam contact step” column, and is not performed. Is described as “none”.

Each film 12 obtained in Experiment 1 to Experiment 9 was evaluated for changes in retardation by transparency and wet heat durability test by the following method. Each result is shown in Table 3.
(1) Evaluation of transparency The transparency was evaluated by the internal haze (unit:%). The internal haze was measured by the following method. First, a sample film was obtained by sampling from the obtained film 12. After the sample film was conditioned at 25 ° C. and 60% RH for 2 hours or more, it was sandwiched between two slide glass plates via liquid paraffin, and the haze was measured with a haze meter (HGM-2DP, manufactured by Suga Test Instruments). Further, only liquid paraffin was sandwiched between two slide glass plates without a sample film, and this was used as a blank sample. The haze of this blank sample was measured with the above-mentioned haze meter. And what subtracted the haze value of the blank sample from the haze value of the sample film was made into the internal haze. From a practical viewpoint used as an optical film, it can be said that the internal haze is 0.1% or less.

(2) Evaluation of change in retardation by wet heat durability test The wet heat durability test was performed on a sample film sampled from the film 12. Sampling was performed by cutting out a plurality of rectangular pieces with a predetermined size along cutting lines along the film transport direction Z1 and the width direction Z2, respectively.

For the sample film, the thickness direction retardation Rth was determined before and during the wet heat durability test. Thickness direction retardation Rth ₀ of the sample film before being subjected to the wet heat durability test, Thickness direction retardation Rth ₁ after the lapse of 1 day for the wet heat durability test, and Thickness direction retardation Rth ₅ of the lapse of 5 days for the wet heat durability test The value obtained by {(Rth ₁ −Rth ₀ ) / Rth ₀ } × 100 and the value obtained by {(Rth ₅ −Rth ₀ ) / Rth ₀ } × 100 were defined as the variation amount ΔRth. The value of ΔRth is described in the column “Change in retardation due to wet heat durability test” in Table 3.

The thickness direction retardation Rth was determined by the following method. The sample film was conditioned at a temperature of 25 ° C. and a humidity of 60% RH for 2 hours, and then measured with an automatic birefringence meter (KOBRA21DH, manufactured by Oji Scientific Instruments) from the vertical direction of the film surface at 589.3 nm. The following formula was calculated from the refractive index and the refractive index measured while tilting the film surface. In the following formula, nZ2 is the refractive index in the direction of the sample film corresponding to the width direction Z2 of the film 12, nZ1 is the refractive index in the direction of the sample film corresponding to the transport direction Z1 of the film 12, and nTH is the refractive index in the thickness direction. The rate d is the thickness (unit: μm).
Rth = {(nZ2 + nZ1) / 2−nTH} × d

  In the wet heat durability test, the sample film is continuously placed in a fixed test environment for a fixed period. A constant test environment was established by keeping the inside of the test chamber in which the sample film was placed at a constant temperature of 60 ° C. and a relative humidity of 90% RH. A sample film was placed in the test chamber. Note that ΔRth tends to increase as the film 12 has a lower Rth before the wet heat durability test. Further, even if ΔRth is the same value, the lower Rth before the wet heat durability test means that the change in Rth is larger, and the higher Rth means that the change in Rth is smaller. Here, the film 12 produced in Experiment 3 has a lower Rth before the wet heat durability test than the film 12 produced in Experiment 1 and the film produced in Comparative Experiment 2 described later. From the viewpoint of practical use as an optical film, ΔRth is preferably as small as possible when the target Rth is the same. In addition, it can be seen from the results of each experiment in Table 3 and the following comparative experiments that Rth is increased by the wet heat durability test.

[Comparative example]
[Comparative Experiment 1] to [Comparative Experiment 7]
A film was produced with the dope C2 using the solution casting apparatus 10, and these were designated as comparative experiments 1 to 3. Moreover, the film was manufactured with dope C2 and dope C4 using the solution casting apparatus 10, and these were set as comparative experiments 4-7. In Comparative Experiments 4 to 7, dopes C2 and C4 were co-cast, and a main layer was formed from dope C4 and a surface layer was formed from dope C2.

  For each comparative experiment, the film temperature (° C.) and the draw ratio W2 / W1 in the first stretch area 46 of the second tenter 20 and the stretch angle θ2 and the stretch ratio W3 / W2 in the second stretch area 47 are shown in Table 3. It shows in each column. Conditions other than these are the same as in the example.

  About each film obtained by the comparative experiment 1-the comparative experiment 7, evaluation about the change of the retardation by transparency and a wet heat endurance test was performed by the same method as an Example. Each result is shown in Table 3.

DESCRIPTION OF SYMBOLS 10 Solution casting apparatus 12 Film 16, 20 1st, 2nd tenter 46, 47 1st, 2nd extending area 50 Clip 55 Duct 56 Air supply part 120 Water vapor contact apparatus

Claims (8)

In the method for producing an optical film that is made into an optical film by stretching in the width direction while conveying a long cellulose acylate film,
When the glass transition point of the cellulose acylate film is Tg (° C.), and the angle formed between the passage of the side edge of the cellulose acylate film and the transport direction is the stretching angle,
A preheating area for preheating the cellulose acylate film, a first stretching area and a second stretching area extending in the width direction, and a cooling area for cooling, which are arranged in order from the upstream side in the conveyance direction of the cellulose acylate film A preheating step of preheating the cellulose acylate film while keeping the width of the cellulose acylate film constant in the preheating area of the tenter comprising:
The cellulose acylate film is maintained at a temperature within the range of (Tg + 10 ° C.) or more and (Tg + 50 ° C.) or less in the first stretching area while maintaining the temperature at a constant stretching angle θ1. A first stretching step for expanding the width to 1.5 times or more and 1.8 times or less by stretching to
The continuously performed in the first stretching step at the second extending segment, wherein the stretching angle θ1 said in small yet stretching angle θ2 than the cellulose acylate film second expanding the width by stretching in the width direction Stretching process ;
A cooling step that is performed continuously with the second stretching step, and in the cooling area, cooling while transporting the cellulose acylate film while maintaining a constant width;
The time for the cellulose acylate film to pass through the preheating area is Ta, the time for passing through the first stretching area is Tb, the time for passing through the second stretching area is Tc, and the time for passing through the cooling area is Td. When manufacturing, the manufacturing method of the optical film characterized by satisfy | filling following (1) and (2) .
0.5 ≦ (Ta + Td) / (Tb + Tc) ≦ 3.0 (1)
0.2 ≦ (Tb / Tc) ≦ 4.5 (2) 2. The method for producing an optical film according to claim 1, wherein in the second stretching step, the cellulose acylate film is stretched in the width direction while lowering the temperature of the cellulose acylate film. 3. The method for producing an optical film according to claim 1, wherein an angle change rate (unit:%) obtained by (θ2 / θ1) × 100 is in a range of 0.5% to 40%. Prior to the first stretching step, the cellulose acylate film is stretched in the width direction in a state where the temperature is 140 ° C. or lower, thereby expanding the width within a range of 1.01 times to 1.20 times. The method for producing an optical film according to any one of claims 1 to 3, further comprising a stretching step. A casting process in which a cellulose acylate is cast on a support that moves a dope in which a solvent is dissolved to form a casting film;
A peeling step of forming the cellulose acylate film by peeling off the cast film containing the solvent;
5. The method for producing an optical film according to claim 1, wherein in the first stretching step, the cellulose acylate film having a residual solvent amount of 20% by mass or less is stretched. Wherein contacting the steam with the optical film after the second stretching step, the claims 1, characterized in that it has a water vapor contacting step of maintaining the temperature within the range of less than 100 ° C. or higher 0.99 ° C. of the optical film 5 The manufacturing method of the optical film of any one of Claims 1. The cellulose acylate film is disposed 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 is substituted with a total acyl group substitution. the method for producing an optical film according to any one of claims 1 to 6, characterized in that the degree Z is and a second layer consisting of cellulose acylate satisfying the following formula (II).
2.0 ≦ Z <2.7 (I)
2.7 ≦ Z ≦ 3.0 (II) The method for producing an optical film according to claim 7, wherein in the first stretching step , the width of the cellulose acylate film is expanded from 1.6 times to 1.8 times.

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