JP2015068965A - Manufacturing method of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an optical film capable of manufacturing, at a target thickness, an optical film achieving a target retardation and haze regardless of the manufacturing speed.SOLUTION: Superheated steam is supplied to a film 12 by a steam supply device 14. By the supply, the moisture content of the film 12 at an extension start point in a tenter device 15 is controlled. A haze detecting unit 53 detects the haze of the wound film 12. A control unit 55 controls a steam supply unit 56 of the steam supply device 14 on the basis of the detected haze and the target haze, and controls the amount of superheated steam supplied from the steam supply unit 56 to blowout units 58a-58c and 59a-59c.

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.

  With the thinning of display devices such as liquid crystal displays, there is a demand for further thinning of optical films used in display devices. Examples of the optical film include a retardation film having a retardation function, and the retardation film is produced by subjecting a polymer film to stretching so as to exhibit a predetermined retardation function.

  The retardation function is evaluated by retardation such as in-plane retardation Re and thickness direction retardation Rth, and the retardation is controlled by combining various conditions in the stretching process. For example, the higher the target retardation, the lower the temperature of the polymer film being stretched. The retardation is a value depending on the thickness of the film. When the conditions such as the temperature of the polymer film and the stretching ratio in the stretching process are made constant, the retardation decreases as the thickness of the polymer film decreases. Therefore, when manufacturing an optical film having a high retardation with a smaller thickness, it is necessary to set the temperature of the polymer film during stretching to be lower. However, the lower the temperature of the polymer film during stretching, the higher the haze of the resulting optical film.

  Moreover, in order to improve the manufacturing speed of a long optical film using the existing equipment, the time of the extending | stretching process which extends | stretches a polymer film in the width direction with a tenter apparatus becomes short. Therefore, in order to express the target retardation, the time for passing through the tenter device is shortened without changing the draw ratio. Thus, the haze of the obtained optical film will go up, so that the draw ratio in unit time, ie, a draw speed, is raised. Therefore, the higher the retardation of the optical film to be manufactured, the higher the haze increases as the manufacturing speed is increased.

  In order to increase the production rate, that is, increase the production efficiency, for example, Patent Document 1 describes a method for increasing the temperature rise rate of a polymer film by applying normal-pressure superheated steam to the polymer film in a tenter device. ing. Moreover, the method of applying superheated steam to a polymer film within a tenter device is also described in Patent Document 2, for example. In the method of Patent Document 2, superheated steam is applied to the polymer film being stretched, thereby suppressing variations in optical characteristics in the width direction.

  Moreover, the method of applying water vapor | steam with respect to a polymer film in a production line is described also in other literature. For example, each method described in Patent Document 3 and Patent Document 4 supplies water vapor to the polymer film before the stretching treatment by the tenter device, thereby suppressing curling of the film. In the method described in Patent Document 4, the stretching process is performed twice, and water vapor is supplied before the second stretching process. Patent document 5 supplies water vapor | steam before extending | stretching to a longitudinal direction, and, thereby, manufactures the optical compensation film as an optical film excellent in the viewing angle characteristic.

JP 2008-213265 A JP 2013-067134 A JP 2011-189616 A JP 2007-051210 A Japanese Patent Laid-Open No. 2003-090915

  However, even if the methods of Patent Documents 1 to 5 are used, the haze increases as the production speed is increased as the temperature of the polymer film during stretching is lowered and the retardation of the optical film to be produced is higher.

  Then, this invention aims at providing the manufacturing method of the optical film which manufactures the optical film which expresses the target retardation and haze with the target thickness irrespective of a manufacturing speed.

  The present invention relates to an optical film manufacturing method in which a polymer film is stretched in the width direction to form an optical film, and a stretching process in which the continuous polymer film is stretched in the width direction while heating is continuously stretched. A water vapor supply step of supplying an amount of water vapor determined from a target haze of the polymer film after stretching by the step to the polymer film before stretching by the stretching step, and adjusting a moisture content of the polymer film at the start of stretching. It is configured.

  The first relationship between the haze of the polymer film after stretching in the stretching step and the glass transition point of the polymer film at the start of stretching, the second relationship between the moisture content and the glass transition point at the start of stretching, and the water vapor supply step The glass transition point corresponding to the target haze is obtained as the target glass transition point based on the first relationship in advance, based on the first relationship, the amount of water vapor supplied in step 3 and the moisture content at the start of stretching. Based on the relationship, the water content corresponding to the target glass transition point is obtained as the target water content, and on the basis of the third relationship, the amount of water vapor for achieving the target water content is determined. It is preferable to have a control step of controlling the amount of water vapor supplied in the water vapor supply step.

  The first relationship exists for each set condition in the stretching step, and the control step preferably obtains the target glass transition point based on the first relationship corresponding to the set condition set in the stretching step.

  The stretching process heats the polymer film by blowing a heated gas onto the polymer film, and the setting conditions are the transport speed of the polymer film being stretched in the stretching process, the width at the start of stretching of the polymer film, and the end of stretching It is preferable that it is the draw ratio calculated | required from the width | variety in, and the temperature of gas.

  It is preferable that a control process controls the quantity of the water vapor | steam supplied by a water vapor | steam supply process based on the difference of the haze of a polymer film after extending | stretching, and a target haze.

  The steam is preferably superheated steam. In the water vapor supply step, it is preferable to supply water vapor continuously or intermittently to the polymer film so that the temperature of the water vapor on the downstream side in the transport direction of the polymer film is equal to or higher than the temperature of the water vapor on the upstream side.

  In the water vapor supply step, it is preferable to supply water vapor to the polymer film independently from one side and the other side of the polymer film.

  According to the present invention, an optical film that exhibits a target retardation and haze can be manufactured with a target thickness regardless of the manufacturing speed.

It is the schematic which shows a solution casting apparatus. It is the schematic of a tenter apparatus. It is the schematic of a water vapor | steam supply apparatus. It is a graph which shows the relationship between the amount of superheated steam to supply, and the haze of the film after extending | stretching. It is a graph which shows the relationship between the glass transition point Tg in the extending | stretching start time, and the haze of the film after extending | stretching. It is a graph which shows the relationship between the moisture content of the film in the extending | stretching start time, and the glass transition point Tg. It is a graph which shows the relationship between the amount of superheated steam to supply, and the moisture content of the film in the extending | stretching start time.

  In FIG. 1, a solution casting apparatus 10 continuously produces a cellulose acylate film (hereinafter simply referred to as “film”) 12. The film 12 is an optical film having a retardation function (birefringence) by being subjected to a stretching process in the film forming process.

The dope 11 is obtained by dissolving a polymer in a solvent. In this embodiment, the dope 11 is formed by dissolving cellulose acylate as a transparent thermoplastic polymer in a solvent. 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).

  Examples of the polymer component of the optical film having a retardation function include transparent thermoplastic polymers such as polycarbonate, polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polymethyl methacrylate. Since these polymers have the property of easily absorbing water, they may be used as the polymer component of the dope 11 instead of cellulose acylate.

  The solution casting apparatus 10 includes a casting device 13, a water vapor supply device 14, a tenter device 15, a cutting device 16, a drying chamber 17, a cooling chamber 18, and a winding device 19.

  The casting apparatus 13 continuously forms the film 12 containing the solvent from the dope 11. The casting apparatus 13 includes a belt 21, a pair of backup rollers 22, a casting die 23, a peeling roller 25, and a chamber 26 in which these are accommodated. The belt 21 is an endless casting support body that is formed into an annular shape. The belt 21 is stretched over a pair of backup rollers 22 so that the space between the backup rollers 22 is horizontal. One of the pair of backup rollers 22 has a drive unit (not shown) connected to the drive shaft 22a, and is rotated in the circumferential direction indicated by the arrow A1 by the drive unit. The belt 21 circulates by the rotation of the backup roller 22.

  The casting die 23 flows out to the surface of the belt 21 running on the dope 11. As a result, the casting film 27 is continuously formed on the surface of the belt 21. The decompression chamber 28 depressurizes the area upstream of the dope 11 from the outlet of the casting die 23 to the surface of the belt 21 in the belt traveling direction to prevent vibration and breakage of the outflowed dope 11. To do.

  The temperature controller 29 supplies the temperature-adjusted heat transfer medium into each backup roller 22. Thereby, the temperature of the casting film 27 is controlled via each backup roller 22 and the belt 21. In this embodiment, the dry casting, that is, the cast film is dried and gelled, and the temperature controller 29 controls the temperature so as to promote the evaporation of the solvent of the cast film 27.

  Instead of dry casting, so-called cooling casting in which the casting film is cooled and gelled may be used. In this case, the temperature controller 29 cools the belt 21 by supplying the cooled heat transfer medium to the backup roller 22, and reduces the fluidity of the casting film 27 by this cooling. Further, the casting support is not limited to the belt 21. For example, instead of the belt 21, a drum may be used, and the dope 11 may be flowed out and cast onto the peripheral surface of the rotating drum. In the case of so-called dry casting in which the cast film is dried and gelled, the belt 21 is often used, and in the case of cooling casting, a drum is often used. A belt may be used for cooling casting. When the temperature of the casting film is controlled using the drum as a casting support, the temperature of the peripheral surface of the drum may be lowered by flowing a cooled heat transfer medium through the drum.

  The casting film 27 is dried while being conveyed by the belt 21, is peeled off from the belt 21 at the position of the peeling roller 25, and is conveyed downstream as the film 12. The stripping roller 25 is for stripping the casting film 27 from the belt 21 while keeping the stripping position constant, and its rotation axis is arranged in parallel with the rotation axis of the backup roller 22. In a state where the film 12 is wound around the peeling roller 25, the film 12 is pulled toward the downstream side of the solution casting equipment 10, whereby the casting film 27 is peeled off from the belt 21 at a predetermined peeling position. The film 12 is sent out of the chamber 26 and sent to the water vapor supply device 14.

  In the chamber 26, a condenser (condenser) is disposed by condensing the solvent evaporated from each of the dope 11, the casting film 27, and the film 12 into a gas. The solvent liquefied by this condenser is sent to a recovery device and recovered. In addition, illustration of a condenser and a collection | recovery apparatus is abbreviate | omitted.

  The film 12 from the casting apparatus 13 is sent to the water vapor supply apparatus 14. In this embodiment, the film 12 is supplied directly from the casting apparatus 13 to the water vapor supply apparatus 14. However, for example, it may be a case of so-called off-line stretching in which the film 12 is drawn from a film roll wound up with a predetermined length of the film 12 before stretching and supplied to the tenter device 15 for stretching. In this case, the film 12 drawn from the film roll is guided to the water vapor supply device 14 to supply water vapor, and then guided to the tenter device 15.

  The steam supply device 14 is for adjusting the moisture content at the start of stretching in the tenter device 15 by supplying a predetermined amount of superheated steam to the film 12. It is preferable to start supplying superheated steam to the film 12 whose residual solvent amount is in the range of 0.3% by mass to 40% by mass. The residual solvent amount at the end of the supply may be 0.3% by mass or less. When the amount of residual solvent at the start of supplying superheated steam is larger than 40% by mass, for example, a drying apparatus for drying the cast film is provided in the cast apparatus 13, or the casting apparatus 13 and the steam supply apparatus 14 The residual solvent amount of the film 12 may be adjusted by providing a drying device for drying the film 12 therebetween.

  In this example, the amount of residual solvent means that the mass of the film 12 to be measured for which the amount of residual solvent is to be obtained is X, and the mass after the film 12 is completely dried is Y, {(XY) / Y} × 100%, which is a so-called dry weight reference value. Note that “completely dry” does not require that the residual amount of the solvent be strictly “0”. In the present embodiment, Y is the mass after the film 12 to be measured is subjected to a drying treatment for 3 hours or more in a constant temperature bath of 120 ° C. or higher and a relative humidity of 10% or lower. Details of the water vapor supply device 14 will be described later with reference to another drawing. The film 12 from the water vapor supply device 14 is sent to the tenter device 15.

  The tenter device 15 stretches the long film 12 in the width direction Z2 (see FIG. 2) perpendicular to the transport direction Z1. Although details will be described later, in the tenter device 15, the both sides of the film 12 are each gripped by the clips 30 and the clips 30 are moved in the transport direction Z <b> 1, and the interval between the opposed clips (hereinafter referred to as the opposed clip interval) is increased. By doing so, the film 12 is stretched in the width direction Z2. The film 12 stretched by the tenter device 15 is sent to the cutting device 16.

  The tenter device 15 includes an air supply unit 31 and a duct 32. The air supply unit 31 supplies dry air adjusted to various temperatures to the duct 32, and blows dry air from the duct 32 onto the film 12 in the tenter device 15. Thereby, the film 12 is heated and cooled in each section of the tenter device 15, and the temperature of the film 12 is adjusted by the heating and cooling. Note that heating and cooling of the film 12 may be performed by other methods.

  In this embodiment, a clip tenter is used as the tenter device 15, and the clip 30 is a holding member. 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 pin plate as a holding member moves to stretch the film 12 in the width direction.

  The cutting device 16 continuously guides the film 12 to the cutting blade and cuts off both side portions where the grip marks by the clips 30 are present. The film 12 whose both sides have been cut off by the cutting device 16 is sent to the drying chamber 17.

  A plurality of rollers 33 are provided in the drying chamber 17. The film 12 is wound around the rollers 33 in order, meandering through the drying chamber 17, and conveyed to the cooling chamber 18. The drying chamber 17 is supplied with heated dry air, and the film 12 is further dried while passing through the drying chamber 17.

  The cooling chamber 18 is supplied with dry air at room temperature, for example, about 15 to 35 ° C. The temperature of the film 12 is lowered by passing through the cooling chamber 18. The film 12 whose temperature has been lowered is sent from the cooling chamber 18 to the winding device 19 and wound around the winding core 35.

  As shown in FIG. 2, the tenter device 15 includes the above-described clip 30 and rails 41 and 42. Further, in the tenter device 15, the conveyance path is, in order from the upstream side, a preheating section 44 that performs a preheating process, an extending section 45 that performs an extending process, a relaxing section 46 that performs a relaxing process, and a cooling section 47 that performs a cooling process. It is divided. Further, a grip start position is set upstream of the preheating section 44, and a grip release position is set downstream of the cooling section 47.

  The rails 41 and 42 are disposed on both sides of the film 12 conveyance path. A plurality of clips 30 are provided on each of the rails 41 and 42. Each clip 30 is movable along the corresponding rail, and the moving direction is defined by the rails 41 and 42. Each rail 41, 42 is provided in an annular shape having an outward path portion that moves the clip 30 from the grip start position to the grip release position and a return path portion that returns the clip 30 moved to the grip release position to the grip start position. Yes. In addition, although the clip 30 exists in the perimeter of each rail 41 and 42 with a fixed space | interval, only a part of clip 30 is drawn in FIG.

  Each of the rails 41 and 42 is provided with an annular chain (not shown) in which a plurality of clips 30 are attached at predetermined intervals so as to be movable along the rails. The chain is hung on a turn wheel 49a disposed upstream of the grip start position and a sprocket 49b disposed downstream of the grip start position. As the sprocket 49b is rotated by a drive unit (not shown), the chain circulates along the rails 41 and 42. Due to the movement of the chain, each clip 30 moves along the rails 41 and 42 at a constant speed. In the following description, the forward portion is described as the rails 41 and 42 when the forward portion and the backward portion are not clearly shown.

  At the grip start position, a grip start member (not shown) that causes the clip 30 to start gripping the side edges of the film 12 is provided. In addition, a grip release member (not shown) is provided at the grip release position to release the clip 30 from the side of the film 12. As a result, the film 12 is gripped by the clip 30 at both gripping ends at the grip start position, transported in the transport direction Z1 by the movement of the clip 30, and sequentially passes through the sections 44 to 47. While passing through each section 44 to 47, the film 12 is processed for each section, and the grip of the clip 30 is released at the grip release position. The conveying speed of the film 12 by the clip 30 is set based on the target manufacturing speed, and the stretching speed changes according to the conveying speed. The stretching speed is a stretching ratio α per unit time. The draw ratio α will be described later.

  From the grip start position to the extending section 45, the rails 41 and 42 are parallel to the transport direction Z1, and the distance between them (hereinafter referred to as rail width) is constant. As a result, the clip 30 is moved in the transport direction Z1 in a state where the interval between the opposing clips 41 on the rail 41 and the clip 30 on the rail 42 is constant. Therefore, during this time, the film 12 is conveyed without being stretched.

  In the preheating section 44, the film 12 is heated (hereinafter referred to as preheating) before the stretching process. Accordingly, in the preheating section 44, the film 12 is preheated without being stretched. By this preheating, the stretching in the stretching section 45 is started quickly, and more uniform tension is applied to the film 12 in the width direction Z2 during the stretching.

  Preheating is performed by the heated dry air from the air supply unit 31. In the preheating, when the temperature of the film 12 is T (unit: ° C) and the glass transition point of the film 12 is Tg (unit: ° C), the film 12 is formed at the downstream end of the preheating section 44, that is, at the upstream end of the stretching section 45. The film 12 is heated so that the temperature T and the glass transition point Tg satisfy -40 ° C. ≦ T-Tg ≦ 20 ° C. Since the time at which the boundary between the preheating section 44 and the stretching section 45 passes is the stretching start time, the preheating heats the film 12 so as to satisfy −40 ° C. ≦ T−Tg ≦ 20 ° C. at the stretching start time. Means that.

  In the present embodiment, the temperature of the film surface is detected as the temperature T. The temperature of the film surface is detected by the temperature detector 61 provided above the boundary between the preheating section 44 and the stretching section 45 with a temperature detector 61 that detects the temperature of the film surface without contacting the film 12.

  The glass transition point Tg of the film 12 at the start of stretching cannot be measured online with respect to the film 12 being conveyed, and varies depending on the amount of solvent and the amount of water contained in the film 12, so that Looking for. The amount of residual solvent at the start of stretching is specified from the processing conditions for the casting film 27 and the film 12 from the formation to the downstream end of the preheating section 44.

  Further, the moisture content of the film is determined by an infrared moisture meter 62 that detects the moisture content of the film 12 without contacting the film 12. The infrared moisture meter 62 irradiates the film 12 with infrared rays, and optically obtains the moisture content of the film 12 from the reflected light. The infrared moisture meter 62 has a plurality of irradiation detection units 62a that detect reflected light by irradiating infrared rays. The plurality of irradiation detectors 62a are provided side by side in the width direction Z2 above and / or below the boundary between the preheating section 44 and the extending section 45. The irradiation detector 62a detects reflected light at a plurality of locations in the width direction, and the infrared moisture meter 62 obtains each moisture content from these detection signals based on the absorption wavelength related to the reflected light. In this embodiment, the average value of each moisture content calculated | required in the several position of the width direction is made into the moisture content of the film 12 in the extending | stretching start time. And based on the relationship between the glass transition point Tg of the film 12 determined in advance and the moisture content considering the residual solvent amount, the glass transition point corresponding to the moisture content specified in consideration of the residual solvent amount as described above. Tg is determined as the glass transition point Tg at the start of stretching. In addition, the moisture content is specified to a smaller value as the residual solvent amount is lower.

  In the extending section 45, the rails 41 and 42 are arranged in a straight line, but are arranged at an angle outward so as to form an extending angle θ with respect to the transport direction Z1, and the rail width toward the downstream. Gradually becomes wider. Thus, the moving direction of the clip 30 is directed outward by the stretching angle θ with respect to the transport direction Z1, and the film 12 is stretched in the width direction Z2 by gradually increasing the distance between the opposing clips as the clip 30 moves in the transport direction Z1. In the stretching section 45, the film 12 having the width W0 before stretching is expanded to the width W1. The process of expanding the width in this way is the stretching process, and the stretching process is performed in the stretching section 45. In the preheating section 44, since the rails 41 and 42 are parallel to the transport direction Z1, the stretching angle θ is an increment angle in the moving direction of the clip 30 in the stretching section 45 with respect to the preheating section 44.

  The draw ratio α is obtained by α = (W1 / W0) × 100%. The draw ratio α is set based on the target in-plane retardation Re and retardation Rth.

  In the stretching section 45, the film 12 is heated by the heated drying air from the air supply unit 31. The temperature of the film 12 in the stretching section 45 is set based on the target in-plane retardation Re and retardation Rth. The higher the target Re or Rth, the lower the temperature T of the film 12 is set.

  In the relaxation section 46 and the cooling section 47, as in the preheating section 44, the rails 41 and 42 are parallel to the transport direction Z1 and the rail width is constant. Therefore, in these relaxation and cooling sections 46 and 47, the clip 30 moves with the opposing clip interval kept constant, and the film 12 is conveyed while maintaining the width W1. In the relaxation section 46, the film 12 is heated in a state where the width thereof is constant, thereby relaxing the distortion caused by the stretching process in the stretching section 45. In the cooling section 47, the film 12 is cooled to fix the molecules of the film 12. The relaxation section 46 may not be provided.

  The steam supply device 14 supplies superheated steam in an amount corresponding to the haze of the film that has undergone the stretching process in the stretching section 45 to a new film 12 that is used in the subsequent stretching process, and is stretched in the tenter device 15. This is for adjusting the moisture content at the start. As shown in FIG. 3, the water vapor supply device 14 includes a plurality of rollers 51, a chamber 52, a haze detection unit 53, a storage unit 54, a control unit 55, a steam supply unit 56, and blowing units 58 a to 58 c. , 59a to 59c.

  In addition, the tenter device 15 includes a setting unit 61, and the setting unit 61 outputs a stretching condition, which is a setting condition in the above-described stretching process, to the tenter device 15. The stretching conditions are the conveyance speed of the film 12 in the stretching step, the stretching ratio α, and the temperature of the drying air from the air supply unit 31. That is, the conditions in the stretching process are determined from the conveyance speed of the film 12 in the stretching process, the stretching ratio α, and the temperature of the drying air from the air supply unit 31. In the stretching process, at least one of the stretching ratio α in the stretching conditions and the temperature of the drying air from the air supply unit 31 is the target retardation and thickness of the film 12, and the transport speed of the film 12 in the stretching process. It can be changed each time at least one of is changed. When the stretching condition is input, the tenter device 15 stretches the film 12 in the stretching section 45 under this stretching condition. The setting unit 61 also outputs the stretching conditions to the control unit 55.

  The plurality of rollers 51 set the transport path of the film 12 by supporting the film 12 on the peripheral surface. The chamber 52 covers the conveyance path of the film 12 set by these rollers 51 and partitions it from the external space, and prevents superheated steam described later from leaking to the external space. The film 12 guided from the casting device 13 to the chamber 52 is wound around each roller 51, passes through the chamber 52, and is guided to the tenter device 15.

  The haze detection unit 53 is for detecting the haze of the film 12 that has undergone the stretching process in the stretching section 45, and in the present embodiment, detects the haze of the wound film 12. The haze detection unit 53 outputs a detection signal of the detected haze to the control unit 55.

  The storage unit 54 stores the following first relationship, second relationship, and third relationship. The first relationship is a relationship between the haze of the film 12 after being stretched in the stretching step and the glass transition point Tg of the film 12 at the start of stretching. Since the first relationship exists for each stretching condition, the storage unit 54 stores a plurality of first relationships. The second relationship is a relationship between the glass transition point Tg at the start of stretching and the moisture content of the film 12 at the start of stretching. The third relationship is a relationship between the moisture content of the film 12 at the start of stretching and the amount of superheated steam supplied to the film 12 by the steam supply unit 56.

  The control part 55 is for controlling the temperature and flow volume of the superheated steam sent out from the steam supply part 56 to the blowing parts 58a-58c, 59a-59c. The flow rate is the amount of water vapor per unit time. The control unit 55 includes an input unit (not shown) to which a target haze (hereinafter referred to as target haze) of the film 12 after the stretching process is input, and the amount of superheated steam corresponding to the input target haze. Ask for. The control unit 55 controls the steam supply unit 56 so as to supply superheated steam in the determined amount. Actually, the control unit 55 obtains the flow rate supplied from the superheated steam supply unit 56 instead of the amount of superheated steam, and the superheat of the amount corresponding to the target haze is supplied by supplying this flow rate. Water vapor is supplied.

  The control unit 55 obtains the amount of superheated steam for achieving the target haze under the stretching conditions from the setting unit 61. The control unit 55 identifies the first relationship corresponding to the stretching condition from the setting unit 61 from the plurality of first relationships stored in the storage unit 54. The glass transition point Tg corresponding to the target haze is obtained as the target glass transition point TgP using the specified first relationship. The control part 55 calculates | requires the moisture content corresponding to a target glass transition point as the target moisture content GP using a 2nd relationship. The control unit 55 determines the amount of superheated steam for obtaining the target moisture content GP using the third relationship, and controls the amount of superheated steam supplied by the steam supply unit 56 to the determined amount.

  The control unit 55 obtains the difference between the target haze and the detected haze based on the haze detection signal from the haze detection unit 53, and minutely determines the amount of superheated steam supplied from the steam supply unit 56 according to this difference. adjust. This fine adjustment is performed based on the amount of superheated steam determined from the target haze.

  The steam supply part 56 is for supplying superheated steam to each blowing part 58a-58c, 59a-59c. The steam supply unit 56 generates superheated steam at a predetermined temperature under the control of the control unit 55 and supplies a predetermined amount of the generated superheated steam to each of the blowing units 58a to 58c and 59a to 59c. The steam supply unit 56 includes a steam generation unit 56a that generates steam and a hot air generation unit 56b that generates hot air adjusted to a predetermined temperature, and the steam and hot air generated by the generation units 56a and 56b. Superheated steam is generated by mixing. The temperature of superheated steam is adjusted by adjusting the temperature of hot air.

  In the present embodiment, the steam supply unit 56 generates superheated steam, that is, 100 ° C. or higher, but may generate steam of less than 100 ° C. instead of superheated steam. However, as will be described later, superheated steam is more preferable from the viewpoint of more reliably forming a water film on the film surface.

  The hot air is a gas heated to a predetermined temperature, and the gas may be air, nitrogen, or the like that does not alter the film 12, and the water content and temperature in the generated superheated steam are precisely adjusted. Therefore, it is preferable that the gas is a gas whose moisture content is kept constant at a low value. In this embodiment, the dehumidified dry air is used as hot air.

  Each of the blowing portions 58a to 58c and 59a to 59c is for blowing superheated steam onto the film 12. In the present embodiment, the blow-out portions 58a to 58c are respectively disposed so as to face a film surface peeled off from the belt 21 of the film 12 (hereinafter referred to as a peeling surface). Further, the blow-out portions 59a to 59c are respectively disposed so as to face a film surface opposite to the peeling surface of the film 12 (hereinafter referred to as an anti-peeling surface). In addition, although each blowing part 58a-58c, 59a-59c supplies superheated steam by spraying with respect to the film 12, it is not restricted to this. For example, water vapor such as superheated water vapor may be supplied to the chamber 52 so that water vapor is contained in the atmosphere around the conveyance path of the film 12, and water vapor may be supplied to the film 12 by passing the film 12. Further, the moisture content of the film 12 may be adjusted by bringing liquid water into contact with the film 12 instead of supplying water vapor. As a method of bringing liquid water into contact, there is a method of using a water tank and allowing the film 12 to pass through the water contained in the water tank.

  A plurality of outlets facing the film 12 are formed in each of the outlets 58a to 58c and 59a to 59c, and superheated steam is discharged from these outlets. The film 12 being transported is supplied with superheated steam by passing through each of the blowing portions 58a to 58c, 59a to 59c, and the moisture content at the time when the film reaches the upstream end of the stretching section 45, that is, at the time of starting stretching. Adjusted.

  All these blowing parts 58a-58c, 59a-59c may be distribute | arranged to any one of the peeling surface side and the anti-peeling surface side. However, depending on the balance of the amount of superheated steam supplied to the peeling surface side and the anti-peeling surface side of the film 12, the film 12 may curl on the film surface side where the moisture amount and the residual solvent amount are small. Therefore, from the viewpoint of preventing the curl, as in the present embodiment, the blowing portions are arranged on the peeling surface side and the anti-peeling surface side, respectively, so that the film 12 does not curl. It is preferable to supply superheated steam independently to the peeling surface side.

  In the present embodiment, the blowing portions 58a, 58b, and 58c are arranged in order from the upstream side facing the peeling surface side, and the steam supply portion 56 blows out superheated steam having the same temperature at the same flow rate. You may send out to the parts 58a-58c. However, in the present embodiment, the steam supply unit 56 sends superheated steam having a higher temperature to the blowing units 58a to 58c in the order of the blowing units 58a, 58b, and 58c. Thereby, the supply of superheated steam fulfills at least a part of the function of the preheating process in the preheating section 44, so that the length of the preheating section 44 in the transport direction Z1 is set short. Since the length of the stretching section 45 in the transport direction Z1 is set to be longer by the amount that the preheating section 44 is set shorter, the stretching speed becomes smaller. For this reason, haze is suppressed smaller.

  In this example, the blow-out portions 58a, 58b, and 58c are spaced apart from each other in the conveyance direction of the film 12, and thereby superheated steam is intermittently supplied to the film 12 being conveyed. However, the outlets 58a, 58b, and 58c may be arranged adjacent to each other in the transport direction so that superheated steam is continuously supplied. In addition, although the number of the blowing parts distribute | arranged to the peeling surface side is set to 3 in this embodiment, 1, 2 or 4 or more may be sufficient.

  Further, the blowing portions 59a, 59b, 59c are arranged in order from the upstream side so as to face the anti-peeling surface side, and the steam supply portion 56 blows out superheated steam having the same temperature at the same flow rate to the blowing portions 59a to 59c. May be sent to However, in the present embodiment, the steam supply unit 56 supplies superheated steam having a high temperature in the order of the blowing parts 59a, 59b, and 59c to each blowing part 59a in the same manner as the feeding to the blowing parts 58a, 58b, and 58c on the peeling surface side. To 59c. Therefore, since the supply of superheated steam from the blowing parts 59a to 59c also fulfills at least a part of the function of the preheating process in the preheating section 44, the length of the stretching section 45 in the transport direction Z1 is set longer, and the haze is further increased. Can be kept small.

  In this example, the blowing portions 59a, 59b, and 59c are spaced apart from each other in the transport direction of the film 12, and thereby superheated steam is intermittently supplied to the film 12 being transported. However, the blowing portions 59a, 59b, and 59c may be arranged side by side in the transport direction so that superheated steam is continuously supplied. In addition, although the number of the blowing parts distribute | arranged to the peeling surface side is set to 3 in this embodiment, 1, 2 or 4 or more may be sufficient.

  The moisture content of the film 12 at the start of stretching is adjusted by the water vapor supply by the water vapor supply device 14 according to the haze detected by the haze detection unit 53. A method for adjusting the moisture content according to haze will be described below. In FIG. 4, the horizontal axis represents the haze of the film 12 that has undergone the stretching process (hereinafter simply referred to as haze), which means that the haze increases toward the right. The vertical axis represents the amount of superheated steam supplied to the unstretched film 12 (hereinafter simply referred to as superheated steam amount), which means that the amount increases as it goes upward.

There is a fixed relationship between the haze and the amount of superheated steam to be supplied. Specifically, as shown in FIG. 4, the greater the amount of superheated steam, the smaller the haze is and one-to-one correspondence. Therefore, the amount of superheated steam to be supplied is determined from the target haze. Then, the film 12 after extending | stretching expresses a target haze by supplying the superheated steam of the quantity corresponding to a target haze to the film 12 before extending | stretching. Incidentally, S-H curve L _S-H showing the relationship between the superheated steam amount and the haze is a downward convex curve, but the slope or the like is changed by stretching the above conditions change, overheating and the magnitude of the haze The trend of the relationship with the amount of water vapor does not change.

  Since the amount of superheated steam supplied as described above is determined from the target haze, the haze can be changed by increasing or decreasing the amount of superheated steam to be supplied. For example, when manufacturing the film 12 with smaller haze, the amount of superheated steam is increased. In addition, when the haze of the film 12 produced by supplying superheated steam is smaller than the target haze, energy saving can be achieved by reducing the amount of superheated steam within a range in which the target haze is expressed. . Thus, according to the haze of the obtained film 12, the haze of the film 12 to be produced later becomes the target haze without changing the stretching conditions by increasing or decreasing the amount of superheated steam, and energy saving is also achieved. Is done. In addition, the film 12 whose haze is larger than the target haze is used for other uses that can be discarded or used, for example.

  A case where the haze is controlled more precisely will be described. For example, the case where the haze of the film obtained without controlling the amount of superheated steam is set as the haze H1 before correction, and the case where the haze H1 before correction is larger than the target haze HP is taken as an example. The amount of superheated water vapor corresponding to the target haze HP is defined as a target water vapor amount SP, and the amount of superheated water vapor corresponding to the uncorrected haze H1 is defined as an uncorrected water vapor amount S1. The amount of superheated steam corresponding to the difference HP-H1 obtained by subtracting the uncorrected haze H1 from the target haze HP is the difference S1-SP obtained by subtracting the uncorrected steam amount S1 from the uncorrected steam amount S1. In this example, since the difference S1-SP is + (plus), the amount of superheated steam to be supplied is increased by the difference (= S1-SP). Although illustration is omitted, when the difference is-(minus), if the amount of water vapor to be supplied is decreased by the difference, energy saving can be achieved while achieving the target haze.

  The target water vapor amount SP can be obtained by directly matching the amount of superheated water vapor and haze, but may be obtained by the control unit 55 using the first relationship to the third relationship as described above. . The first to third relationships can be graphed, for example.

  The control part 55 calculates | requires target glass transition point TgP as follows using the specified 1st relationship. FIG. 5 shows the first relationship under certain stretching conditions. The horizontal axis is haze, which means that it is larger toward the right. The vertical axis represents the glass transition point Tg of the film 12 at the start of stretching (hereinafter, simply referred to as the glass transition point Tg), which means that it is higher toward the top. The H-Tg curve L1 indicating this first relationship is a proportional straight line rising to the right.

  The glass transition point corresponding to the uncorrected haze H1 is defined as a pre-correction glass transition point Tg1. The control unit 55 obtains the target glass transition point TgP and the pre-correction glass transition point Tg1 from the first relationship by setting the target haze input from the input unit and the haze from the haze detection unit 53 as the pre-correction haze H1. In this example, since the target haze is lower than the uncorrected haze H1, control is performed to lower the glass transition point Tg.

  The control part 55 calculates | requires the target moisture content GP as follows using the 2nd relationship. FIG. 6 shows the second relationship. The horizontal axis is the glass transition point Tg, which means that the value increases toward the right. The vertical axis represents the moisture content of the film 12 at the start of stretching (hereinafter simply referred to as the moisture content), which means that the higher the value is, the higher the value is. The Tg-G curve L2 indicating the second relationship is a right-down proportional line. Note that, as described above, the lower the residual solvent amount at the start of stretching, the smaller the moisture content, so that the Tg-G curve L2 is positioned further downward.

  Based on the second relationship, the control unit 55 obtains the moisture content corresponding to the target glass transition point TgP obtained from the first relationship as the target moisture content GP, and calculates the moisture content corresponding to the pre-correction glass transition point Tg1. Obtained as the moisture content G1 before correction. In this example, since the glass transition point Tg is lowered as described above, control for increasing the moisture content is performed. Further, when the polymer component of the dope 11 is cellulose acylate, the target moisture content GP is set in the range of 1% by mass to 20% by mass. In addition, when the polymer component of dope 11 is a cellulose acylate, it is more preferable that the water content of 1 mass% or more is maintained until the end of stretching.

  The control part 55 calculates | requires the quantity (henceforth target water vapor | steam quantity) SP of superheated steam which should be supplied as follows using the 3rd relationship. FIG. 7 shows the third relationship. The horizontal axis is the moisture content, which means that the water content increases toward the right. The vertical axis represents the amount of superheated steam, which means that the amount increases as it goes upward. The GS curve L3 indicating the third relationship is a curve that is convex to the right and downward.

Based on the third relationship, the control unit 55 obtains the water vapor amount corresponding to the target water content GP obtained from the second relationship as the target water vapor amount SP, and also calculates the water vapor amount corresponding to the pre-correction water content G1 before correction. Obtained as water vapor amount S1. In this example, as described above, control is performed to increase the amount of superheated steam in order to reduce the moisture content. The increment of superheated steam is the difference (SP-S1) between the target water vapor amount SP and the pre-correction water vapor amount S1 corresponding to the difference between the target water content GP and the pre-correction water content G1. When the polymer component of the dope 11 is cellulose acylate, the target water vapor amount SP is preferably set in the range of 30 g / m ³ or more and 500 g / m ³ or less, and 50 g / m ³ or more and 400 g / m. more preferably set in m ³ or less of the range, it is particularly preferably set at 100 g / ^{m 3} or more 350 g / ^{m 3} or less.

  As described above, by supplying water vapor to the unstretched film 12 and controlling the water content at the start of stretching, the film 12 having the target retardation and the target haze is manufactured. For example, when the existing tenter device 15 is used without changing the length of the tenter device 15 in the transport direction Z1, the effect of the expression of the target haze increases as the thickness of the film 12 to be manufactured decreases. The higher the (Re, Rth) and the higher the conveyance speed, the more prominent. For example, the thickness of the film 12 manufactured using the existing tenter device 15 is in the range of 15 μm or more and 100 μm or less. For example, the effect appears remarkably in the range of 15 μm to 50 μm. Moreover, even if the thickness of the film 12 to be manufactured is changed, the film 12 having the target haze and the target retardation is reliably manufactured.

  Further, the effect is remarkable when the in-plane retardation Re is in the range of 10 nm or more and 100 nm or less without changing the length of the tenter device 15 in the transport direction Z1, and the higher the range, the higher the effect, for example, 40 nm. The effect is particularly high when the thickness is in the range of 100 nm or less. Further, the effect is remarkable when the thickness direction retardation Rth is in the range of 10 nm or more and 300 nm or less, and the effect is higher as the thickness is higher in this range. For example, the effect is particularly high when the thickness direction retardation Rth is in the range of 80 nm or more and 300 nm or less. .

The in-plane retardation Re and the thickness direction retardation Rth are obtained as follows. nx is the refractive index in the longitudinal direction of the film 12 (corresponding to the transport direction Z1), ny is the refractive index in the width direction Z2 of the film 12, nz is the refractive index in the thickness direction of the film 12, and d is the thickness of the film. Each refractive index is measured with an automatic birefringence meter (KOBRA21DH, manufactured by Oji Scientific Instruments) after conditioning the sample film cut out from the film 12 at a temperature of 25 ° C. and a humidity of 60% RH for 2 hours. The
Re = (ny−nx) × d
Rth = {(nx + ny) / 2−nz} × d

  In addition, the effect is remarkable when the transport speed is in the range of 20 m / min to 100 m / min without changing the length of the tenter device 15 in the transport direction Z1, and the effect is higher as the range is larger. For example, the effect is particularly high when it is in the range of 40 m / min to 100 m / min. Moreover, even if the conveyance speed is changed, the film 12 having the target haze and the target retardation is reliably manufactured.

  The above embodiment is a film forming method having one stretching process by the solution film forming equipment 10 having one tenter device 15. However, the stretching step may be 2 or more. In this case, a plurality of tenter devices 15 are arranged in series, and the steam supply device 14 is arranged between the tenter device 15 arranged on the most downstream side and the tenter device on the front (upstream). Thereby, the moisture content of the film 12 at the start of the final stretching process is adjusted.

  In the said embodiment, the average value of each moisture content calculated | required in the multiple positions of the width direction in the boundary of the preheating area 44 and the extending | stretching area 45 is made into the moisture content of the film 12 at the time of extending | stretching start. However, when the haze of the stretched film 12 is not uniform in the width direction, the moisture content obtained at a plurality of positions in the width direction may be used as the moisture content of the film 12 at the start of stretching. In this case, as the blowing parts 58a to 58c and 59a to 59c, those that supply different amounts of water vapor in the width direction to the film 12 are used, and the moisture content at each position in the width direction is controlled.

  In the above embodiment, the moisture content of the film 12 at the start of stretching is controlled by controlling the amount of superheated steam. However, the moisture content of the film 12 can also be controlled by raising and lowering the temperature of the superheated steam and raising and lowering the pressure of the superheated steam when the superheated steam is supplied to the film 12. In order to increase the moisture content, the temperature and pressure of superheated steam should be increased. On the other hand, when the moisture content is lowered, the temperature or pressure of the superheated steam is preferably increased. The water content of the film 12 at the start of stretching may be controlled by combining the amount of superheated steam, the temperature, and the pressure at the time of supply.

  In the above embodiment, superheated steam is supplied to the film 12 only upstream from the tenter device 15, but the present invention is not limited to this. In order to control the moisture content of the film 12 at the start of stretching, for example, superheated steam may be supplied in the preheating section 44, and in this case, the blowing portions 58 a to 58 c and 59 a to 59 c are arranged in the preheating section 44. . In this case, the duct 32 is not provided in the preheating section 44, and the preheating in the preheating section 44 is performed by superheated steam. Further, in this case, a chamber surrounding the film conveyance path of the preheating section 44 and the blowing portions 58a to 58c and 59a to 59c is arranged so that the superheated steam does not diffuse into the stretching section 45, the relaxation section 46, and the cooling section 47. It is preferable to do.

  Further, by controlling the moisture content of the film 12 being stretched, the glass transition point Tg of the film 12 until the end of stretching is adjusted to a predetermined range. For this reason, you may supply superheated steam with respect to the film 12 during extending | stretching. In this case, similarly, the blowing sections 58a to 58c and 59a to 59c are arranged in the extending section 45, and the duct 32 may not be provided in the extending section. In the stretching section 45, by supplying superheated steam instead of water vapor of less than 100 ° C., the film 12 is brought to a temperature high enough for stretching, so that it is uniformly stretched in the width direction. Further, by using the steam supply device 14 and the blowing portions 58 a to 58 c and 59 a to 59 c in the tenter device 15 together, superheated steam is supplied both upstream from the tenter device 15 and in the preheating section 44. Also good.

DESCRIPTION OF SYMBOLS 10 Solution casting apparatus 12 Film 14 Water vapor | steam supply apparatus 15 Tenter apparatus 45 Stretching zone 53 Haze detection part 54 Memory | storage part 55 Control part 55
56 Steam supply part 56
58a-58c, 59a-59c

Claims (8)

In the method for producing an optical film in which a polymer film is stretched in the width direction to form an optical film,
Stretching step for stretching in the width direction while heating the long polymer film that is continuously conveyed,
A steam supply step of supplying an amount of water vapor determined from a target haze of the polymer film after stretching by the stretching step to the polymer film before stretching by the stretching step, and adjusting a moisture content of the polymer film at the start of stretching; ,
A method for producing an optical film, comprising: A first relationship between the haze of the polymer film after stretching by the stretching step and the glass transition point of the polymer film at the start of stretching;
A second relationship between the moisture content and the glass transition point at the start of stretching,
Obtaining the amount of water vapor supplied in the water vapor supply step and the third relationship between the moisture content at the start of stretching,
Based on the first relationship, a glass transition point corresponding to the target haze is obtained as a target glass transition point, and based on the second relationship, a moisture content corresponding to the target glass transition point is set as a target moisture content. Obtaining and determining the amount of water vapor to achieve the target moisture content based on the third relationship, and having the control step of controlling the amount of water vapor supplied in the water vapor supply step to the determined amount The method for producing an optical film according to claim 1. The first relationship is for each set condition in the stretching step,
The said control process calculates | requires the said target glass transition point based on the 1st relationship corresponding to the setting conditions set to the said extending process, The manufacturing method of the optical film of Claim 2 characterized by the above-mentioned. The stretching step heats the polymer film by blowing a heated gas onto the polymer film,
The setting condition is a stretching speed determined from a transport speed of the polymer film being stretched in the stretching step, a width at the start of stretching of the polymer film and a width at the end of stretching, and the temperature of the gas. The method for producing an optical film according to claim 3.   The said control process controls the quantity of the water vapor | steam supplied by the said water vapor | steam supply process based on the difference of the haze of the said polymer film after extending | stretching, and the said target haze, The any one of Claim 2 thru | or 4 characterized by the above-mentioned. The manufacturing method of the optical film of description.   6. The method for producing an optical film according to claim 1, wherein the water vapor is superheated water vapor.   The water vapor supply step supplies the water vapor continuously or intermittently to the polymer film so that the temperature of the water vapor on the downstream side in the transport direction of the polymer film is equal to or higher than the temperature of the water vapor on the upstream side. The method for producing an optical film according to any one of claims 1 to 6.   8. The optical film according to claim 1, wherein the water vapor supplying step supplies the water vapor to the polymer film independently from one side and the other side of the polymer film. Production method.

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