JP2010082992A - Method of manufacturing retardation film - Google Patents

Abstract

A long retardation film having a uniform thickness, Re, and Rth in the width direction is manufactured.
A tenter unit 12 includes a preheating area 36, an extension area 37, a relaxation area 38, and a cooling area 39 in order from the upstream side in the transport direction Z1. In the preheating area 36, the film 20 is heated so that the temperature increases from the ear 20a of the film 20 toward the center in the width direction Z2. Thereby, the stress in the width direction Z2 of the film 20 in the stretching area 37 becomes constant in the width direction. The temperature difference between the ear 20a and the center is in the range of 2 ° C. or higher and 20 ° C. or lower. In the stretching area 37, the film 20 is widened while maintaining the temperature distribution in the width direction Z2 obtained in the preheating area.
[Selection] Figure 3

Description

  The present invention relates to a method for producing a retardation film, particularly a retardation film used for a liquid crystal display device or the like.

  The required performance for liquid crystal displays has been increasing in recent years, and the required performance is only increasing for a plurality of polymer films constituting the liquid crystal display. In recent years, the brightness of liquid crystal displays has become higher and the screen has become larger, and this has led to stricter demands on the uniformity of optical properties for polymer films such as retardation films. It is becoming

  The retardation film is produced by either a solution casting method or a melt casting method, and is a continuous production method. That is, the retardation film is formed in a long shape. And the uniformity of said optical characteristic is calculated | required more strongly about the width direction of a long retardation film.

  In the past, in order to eliminate non-uniformity in optical properties, a method of making the film flatter by making the thickness more uniform and smoothing the surface has been proposed in order to eliminate optical unevenness. For example, Patent Document 1 discloses a step of cooling and solidifying a film made of a polymer which has been melted and extruded by sandwiching the film by a cooled roller and a pressing roller provided so as to be pressed against the roller. And the melt film-forming method including the process of extending | stretching this film is proposed, and the improvement of thickness precision is aimed at by this.

Further, attention has been paid to optical characteristics such as in-plane retardation Re and thickness direction retardation Rth, and proposals have been made to make these in the width direction uniform. For example, Patent Document 2 discloses a melt film-forming method in which a film peeled off from a metal support has a side edge at a temperature higher by 1 ° C. to 30 ° C. than the central portion in the width direction and is spread in the width direction to form a retardation film. suggest. And patent document 3 proposes the manufacturing method of retardation film including the process of extending | stretching a thermoplastic film to the width direction, and the process of changing the temperature to the width direction and heat-processing after this extending | stretching.
JP 2007-137028 A JP 2002-296422 A JP-A-11-77822

  However, the non-uniformity of the optical characteristics cannot be eliminated simply by making the thickness uniform as in Patent Document 1. Further, in the method of Patent Document 2, there is no effect on the uniformity in the width direction among the non-uniformity of the optical characteristics, and the non-uniformity in the width direction may be serious. Although the method of Patent Document 3 has a certain effect in making the optical characteristics in the width direction uniform, it cannot make the liquid crystal display uniform enough to meet the recent increase in brightness and screen size.

  Accordingly, an object of the present invention is to provide a method for producing a long retardation film having a uniform thickness, Re, and Rth in the width direction.

  The method for producing a retardation film of the present invention includes a heating step of heating the film so that a temperature gradient increases as it goes from a side end portion of a long film made of a polymer toward a central portion in the width direction; The widening step is performed in a state in which the temperature gradient is maintained, and the holding means that holds each side end of the film is displaced in the width direction of the film to widen the width of the film to form a retardation film. It is characterized by having.

  It is preferable that a temperature difference between the side end portion and the central portion is in a range of 2 ° C. or more and 20 ° C. or less.

  The dope in which the polymer is dissolved in a solvent flows out from a casting die to a traveling support to form a casting film, and the casting film is removed from the support as a wet film containing the solvent. It has a casting process for peeling and a drying process for drying a wet film to form the film, or a polymer melted by heating is continuously extruded into a thin film shape and stretched in the transport direction while transporting. A film is preferred.

  The polymer is preferably a cyclic olefin or cellulose acylate.

  According to the present invention, it is possible to produce a long retardation film having a uniform thickness, Re, and Rth in the width direction.

(Offline stretching device)
As shown in FIG. 1, the offline stretching apparatus 10 unwinds a film 20 wound in a roll shape and sends it to the next process, and a tenter unit 12 that widens the film 20 to form a retardation film 18. The thermal relaxation unit 13 that relaxes the stress by heating the retardation film 18, the cooling unit 14 that cools the retardation film 18, and the winding unit 15 that winds the retardation film 18 are provided. The supply unit 11 is set with a film 20 that is manufactured by a solution film forming method or a melt film forming method, which will be described later, and is wound around the winding core 21 in a roll shape. The film 20 is guided to the tenter unit 12 by the supply roller 22 and then sequentially sent to the heat relaxation unit 13, the cooling unit 14, and the winding unit 15, and predetermined processing is performed in each unit 12 to 15. The

  The tenter unit 12 grips each side end (hereinafter referred to as “ear part”) of the film 20 and performs a stretching process of stretching and widening the film 20 in the width direction while conveying the film 20. In FIG. 1, the conveyance direction is indicated by an arrow Z1.

  An ear clip device 25 is provided between the tenter unit 12 and the heat relaxation unit 13. The ear clip device 25 cuts the ear portion of the retardation film 18. The cut ear is cut into small pieces by the cut blower 26. The cut ear portion is sent to the crusher 27 by an air feeding device (not shown) and crushed into chips.

  A number of rollers 28 are provided in the heat relaxation unit 13, and the retardation film 18 is conveyed to the cooling unit 14 by these rollers 28. Moreover, in the thermal relaxation part 13, dry wind is sprayed with respect to the retardation film 18 in conveyance. In the cooling unit 14, the retardation film 18 is cooled to a predetermined temperature. The cooled retardation film 18 is sent to the winding unit 15. The winding unit 15 is provided with a winding roller 30 and a press roller 31, and the phase difference film 18 is wound around the winding roller 30 while being pressed by the press roller 31.

(Tenter part)
As shown in FIGS. 2 and 3, the tenter unit 12 includes, in order from the upstream side in the transport direction Z1, a preheating area 36 for heating the film 20 before widening, a stretching area 37 for stretching so as to widen, and for stress relaxation. These are the relaxation area 38 and the cooling area 39 for cooling. The relaxation area 38 and the cooling area 39 are not necessarily provided.

  The tenter unit 12 includes a clip 40, rails 41 and 42, a duct 43, and an air supply unit 45. The rails 41 and 42 are installed on both sides of the transport path of the film 20, and the rails 41 and 42 are separated by a predetermined rail width. This rail width is constant at the width L1 in the preheating area 36, gradually increases from the width L1 to the width L2 in the extending area 37 in the direction Z1, and in the relaxation area 38, from the width L2 to the width L3 in the direction Z1. The cooling area 39 has a constant width L3.

  A chain (not shown) is movably attached along the rails 41 and 42. The plurality of clips 40 are attached to the entire chain at a predetermined interval. In FIG. 3, only a part of the clip 40 is shown to avoid complication of the drawing. The chain meshes with sprockets 48 and 49. As the sprockets 48 and 49 rotate, the clip 40 moves along the rails 41 and 42. On the upstream side of the preheating area 36 in the Z1 direction, grip start means (not shown) for starting the gripping of the ear portion 20a of the film 20 by the clip 40 is provided, and on the downstream side of the cooling area 39 in the Z1 direction by the clip 40. A grip releasing means (not shown) for releasing the grip of the ear portion 20a of the film 20 is provided. As the clip 40 moves along the rails 41 and 42, the film 20 is transported in the Z1 direction, sequentially passes through the areas 36 to 39, and predetermined processing is performed in the areas 36 to 39.

  The duct 43 is provided above the transport path of the film 20. The interval between the duct 43 and the transport path of the film 20 is substantially constant. On the lower surface of the duct 43, a plurality of slits 53 extending in the width direction Z2 of the film 20 are formed in the transport direction Z1. Further, the inside of the duct 43 is partitioned into first to fourth air supply chambers 43 a to 43 d by a partition plate 54. FIG. 2 shows a case where a plurality of slits 53 are provided in the first and second supply chambers 43a and 43b, and only one slit 53 is provided in the third and fourth supply chambers 43c and 43d. However, the present invention is not limited to this, and one slit 53 is provided in the first supply chamber 43a and the second supply chamber 43b, and a plurality of slits 53 are provided in the third supply chamber 43c and the fourth supply chamber 43d. May be provided.

  The air supply unit 45 supplies air to the first to fourth supply chambers 43 a to 43 d of the duct 43. The air supplied to the first to fourth supply chambers 43a to 43d is adjusted to a temperature within a predetermined range by a temperature controller (not shown). The air in the first to fourth supply chambers 43 a to 43 d becomes wind 56 to 59 and is blown against the film 20 passing through the areas 36 to 39 through the slits 53.

  Next, the operation of the present invention will be described. As shown in FIG. 1, the supply roller 22 sends the film 20 that has been rolled up and taken up by the winding core 21 to the tenter unit 12. As shown in FIG. 3, the film 20 sent to the tenter unit 12 is sent to the preheating area 36. On the upstream side in the Z1 direction of the preheating area 36, the clip 40 traveling along the rails 41 and 42 grips the ear portion 20a of the film 20 by gripping start means (not shown). The clip 40 travels in the Z1 direction while grasping the ear portion 20a, so that the film 20 sequentially passes through the preheating area 36, the stretching area 37, the relaxation area 38, and the cooling area 39 from the upstream side in the Z1 direction. The film 20 that has passed through the tenter unit 12 is cut at the ear part 20a by the ear-cutting device 25, and the product part 20b from which each ear part 20a is removed passes through the thermal relaxation part 13 and the cooling chamber 14 as the retardation film 18, and is wound. It is sent to the collecting unit 15.

  As shown in FIG. 2, the air supplied to the duct 43 by the air supply unit 45 becomes wind 56 to 59 through the slit 53 and blows against the film 20 passing through the areas 36 to 39. It is done. Thereby, the temperature of the film 20 in the preheating area 36 and the extending | stretching area 37 rises until it becomes in a predetermined range. In the relaxation area 38 and the cooling area 39, the temperature of the film 20 decreases until it falls within a predetermined range.

  As shown in FIG. 3, the film 20 passes through the preheating area 36 while maintaining the length in the Z2 direction, that is, the width L1. Thereafter, in the stretching area 37, the film 20 is stretched. By the stretching process, the film 20 is given a tension in the Z2 direction, and the length in the Z2 direction gradually increases from L1 to L2. The residual solvent amount of the film 20 passing through the stretching area 37 is preferably 0% by weight or more and 3% by weight or less. The amount of residual solvent in the film 20 is determined by taking the sample film from the target film, x is the weight of the sample film at the time of collection, and y is the weight after drying the sample film {(xy) / y} × 100.

  In the relaxation area 38, the film 20 is subjected to a relaxation process. The stress remaining in the film 20 is removed by the relaxation treatment, and the length of the film 20 in the Z2 direction gradually decreases from L2 to L3. Thereafter, the film 20 passes through the cooling area 39 with the length in the Z2 direction being L3. The width L3 is preferably not less than 500 mm and not more than 4000 mm. The residual solvent amount of the film 20 that passes through the cooling area 39 is preferably 0 wt% or more and 3 wt% or less. Then, gripping by the clip 40 is released by gripping release means (not shown).

  In the present invention, the temperature of the film 20 is controlled by the duct 43 provided in the preheating area 36 and the stretching area 37 so that the temperature gradually increases from the ear portion 20a toward the center in the width direction Z2 of the film 20. . That is, the temperature of the product part 20b is increased as the product part 20b is closer to the ear part 20a. This is because, in the conventional method, it can be seen that the stress during stretching increases toward the center in the width direction Z2, and in the present invention, the stress during stretching is made constant in the width direction. That is, in the present invention, the temperature of the film 20 is increased as the stress increases under conventional stretching conditions, and the temperature of the film 20 is decreased as the stress decreases. Thereby, since the stress during stretching in the width direction can be made constant, the retardation film 18 having a uniform thickness, Re, and Rth in the width direction Z2 can be formed. Specifically, the thickness unevenness in the width direction Z2 can be 10%, the Re unevenness can be within 10 nm, and the Rth unevenness can be 20 nm. The temperature distribution of the film 20 in the width direction Z2 may be stepwise or continuous.

  The thickness unevenness is a value (unit:%) obtained by 100 × (T1−T2) / TA, where T1 is the maximum thickness in the width direction Z2, T2 is the minimum value, and TA is the average value. . Further, each of the irregularities of Re and Reh is a value obtained by the following method. Twenty samples in the width direction were cut out from the obtained retardation film 18 at equal intervals. For each sample, Re was KOBRA21DH (manufactured by Oji Scientific Instruments), and Rth was an ellipsometer (M150 JASCO). (Made by Co., Ltd.). Of the 20 Re values and 20 Rth values, the maximum values are Re1 and Rth1, the minimum values are Re2 and Rth2, Re1-Re2 is Re unevenness, and Rth1-Rth2 is Rth unevenness. .

  The in-plane retardation Re is a value obtained by | n1-n2 | · d, where n1 and n2 are the refractive indexes in the Z1 direction and Z2 direction of the film, and d is the film thickness. Rth is a value obtained by {(n1 + n2) / 2−n3} · d, where n3 is a refractive index in the thickness direction of the film.

  The above-described effects of the present invention are particularly significant when a retardation film having Re of 20 nm to 300 nm and Rth in the thickness direction of −100 nm to 300 nm is produced. The present invention is more effective as the width of the retardation film 18 to be manufactured is increased and the manufacturing speed is increased.

  Therefore, in the present invention, the stress at the time of stretching at a predetermined value is preset in the width direction of the film for each setting condition in the tenter part, for example, the stretching ratio, the stretching speed, and the temperature of the film at the time of stretching. In particular, the stress difference between the ear portion 20a and the center 20b and the stress distribution in the width direction Z2 are obtained, and the temperature control in the preheating area 36 and the extending area 37 is performed based on the obtained stress difference and stress distribution. . The temperature of the film 20 when obtaining such a stress difference or stress distribution is preferably the highest temperature among the temperatures of the film 20 to be set by the tenter unit 12.

  The draw ratio (unit:%) is obtained by 100 × (L2−L1) / L1 based on the width L1 before widening and the width L2 after widening, and the stretching speed is the time from the start of widening to the end of widening ( It is determined as a value (unit:% / min) obtained by dividing the draw ratio by (min).

  In the preheating area 36, the wind 56 is caused to flow out of the slit 53 toward the film 20 so that the temperature distribution in the width direction Z2 of the film 20 is in the above-described manner. The film 20 having the desired temperature distribution in the width direction is widened at the desired draw ratio and draw speed while the temperature distribution is maintained in the draw area 37. In the stretching area 37, the temperature distribution is maintained by causing the wind 57 to flow out of the slit 53 toward the film 20.

  The temperature distribution in the width direction Z2 is divided into a method in which the air volume and speed from each slit are changed in the longitudinal direction of the slit, and the first supply chamber 43a and the second supply chamber 43b are divided into a plurality of portions in the width direction Z2. In addition, there is a method in which air is sent from the air supply unit 45 at different temperatures and air volumes for each area, and the wind from each area is controlled independently, but the present invention is not limited to these methods.

  The temperature difference between the center and the ear portion 20a in the width direction Z2 is preferably in the range of 2 ° C. or more and 20 ° C. or less. Thereby, said effect is acquired more reliably. Then, the Re unevenness may be within 8 nm, the Rth unevenness may be within 15 nm, the Re unevenness may be within 6 nm, and the Rth unevenness may be within 10 nm. May be within 4 nm and Rth unevenness may be within 6 nm. If the temperature difference is smaller than 2 ° C., the portion where the stress is small during stretching is excessively stretched during stretching, and the unevenness in thickness, Re, and Rth in the width direction Z2 may not be sufficient. When the temperature difference is larger than ° C., a portion having a small stress during stretching may not achieve the desired elongation during stretching, and the thickness, re, and Rth in the width direction Z2 may not be sufficiently different. A more preferable range of the temperature difference is a range of 3 ° C. to 15 ° C., and a more preferable range is a range of 4 ° C. to 12 ° C.

  Although the duct 43 is provided above the transport path of the film 20, it may be provided below the transport path of the film 20 or may be provided above and below the transport path of the film 20. When the duct 43 is provided below the conveyance path of the film 20, a slit 53 is provided on the upper surface of the duct 43.

  The stretching ratio in the stretching area 37 is preferably 5% to 150%, and the stretching speed is preferably 5% / min to 600% / min.

  The present invention also includes a solution casting method in which the stretching process using the tenter part is performed. FIG. 4 is a schematic view of the solution casting apparatus 80. In addition, about the apparatus and member same as the said embodiment, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted. The solution casting apparatus 80 includes a casting chamber 82, a pin tenter 112, a tenter unit 12, a drying chamber 83, a cooling chamber 14, and a winding unit 15.

  In the casting chamber 82, a casting die 95, a casting drum 96 as a support, a peeling roller 97, temperature control devices 98 and 99, and a decompression chamber 100 are installed. The casting drum 96 is rotated in a circumferential direction indicated by an arrow A1 around a shaft 96a by a driving device (not shown). When the dope 91 flows out of the casting die 95 toward the circumferential surface of the rotating casting drum 96, a casting film 103 is formed on the circumferential surface of the casting drum 96.

  The temperature in the casting chamber 82 and the casting drum 96 is set to a temperature at which the casting film 103 is easily cooled and solidified (gelled) by the temperature control devices 98 and 99. Then, while the casting drum 96 rotates about 3/4, the casting film 103 reaches a gel strength having self-supporting properties, and is peeled off from the casting drum 96 by the peeling roller 97 to become a wet film 104. .

  The temperature control device 99 circulates the heat transfer medium through the casting drum 96 in order to keep the temperature of the peripheral surface of the casting drum 96 at a desired temperature. The heat transfer medium is maintained at a desired temperature, and the temperature of the peripheral surface of the casting drum 96 is maintained at the desired temperature by passing through the heat transfer medium flow path in the casting drum 96.

  The decompression chamber 100 is arranged on the upstream side in the A1 direction with respect to the casting die 95, and maintains the inside of the decompression chamber 100 at a negative pressure. As a result, the back side of the casting bead (the surface that comes into contact with the circumferential surface of the casting drum 96 later) is reduced to a desired pressure, and the influence of the accompanying wind generated by the casting drum 96 rotating at high speed is reduced. Then, a stable casting bead is formed between the casting die 95 and the casting drum 96, and the casting film 103 with little film thickness unevenness is formed.

  In the casting chamber 82, a condenser (condenser) 109 for condensing and recovering the evaporated organic solvent and a recovery device 110 for recovering the condensed and liquefied solvent are provided. The organic solvent condensed and liquefied by the condenser 109 is recovered by the recovery device 110. The recovered solvent is regenerated by a regenerator and then reused as a dope preparation solvent.

  On the downstream side of the casting chamber 82, a crossover part 111, a pin tenter 112, and a tenter part 12 are installed in this order. In the transfer section 111, the wet film 104 is introduced into the pin tenter 112 using the transport roller 113. The pin tenter 112 has a large number of pin plates that pass through and hold both ends of the wet film 104, and the pin plates travel on a track. During the traveling, the drying air is sent to the wet film 104, and the wet film 104 is dried while traveling to become the film 20.

  The wet film 104 is preferably dried with a pin tenter 112 until the residual solvent amount is 0.1 wt% or more and 10 wt% or less. The cast film 103 is peeled off when the residual solvent amount is in the range of 150 wt% or more and 320 wt% or less, and dried by the pin tenter 112 until the residual solvent amount falls within the above range, whereby cellulose acylate molecules in the tenter section 12 are obtained. Is more effectively controlled. That is, the effect of controlling the direction of the slow axis, the effect of increasing Re and Rth, and the effect of improving optical unevenness in the stretching process in the tenter unit 12 are enhanced. However, in the present invention, drying with the pin tenter 112 may not be performed until the residual solvent amount falls within the above range. That is, the wet film 104 having a residual solvent amount higher than 10% by weight may be fed into the tenter unit 12.

  In the drying chamber 83, the film 20 is dried by applying a drying air of 50 ° C. or more and 200 ° C. or less to the film 20. In the drying chamber 83, it is preferable to dry the film 20 until the residual solvent amount becomes 0.01 wt% or more and 5 wt% or less.

  Although the tenter unit 12 is provided between the pin tenter 112 and the drying chamber 83, the present invention is not limited to this, and the tenter unit 12 may be provided between the cooling chamber 14 and the winding unit 15. The tenter unit 12 may be provided both between the 112 and the drying chamber 83 and between the cooling chamber 14 and the winding unit 15.

  The film 20 of the present invention is not limited to the film obtained by the solution casting method as described above, but also includes a film obtained by the melt casting method. FIG. 5 is a schematic view of a melt film-forming facility. In the melt film-forming facility 410, the retardation film 18 that can be used for a liquid crystal display device or the like is manufactured. The pellet-shaped polymer that is the raw material of the retardation film 18 is introduced into the dryer 412 and dried, and then the pellet is extruded by the extruder 414 and supplied to the filter 418 by the gear pump 416. Next, foreign matters are filtered by the filter 418, and a molten polymer (hereinafter referred to as a molten polymer) is extruded from the die 420.

  The molten polymer is sandwiched between the first casting roll 428 and the touch roll 424 and press-molded. Then, the molten polymer is cooled and solidified by the first casting roll 428 to form a film having a predetermined surface roughness, and then the second casting. The film 20 is obtained by being conveyed by the roll 426 and the third casting roll 427.

  As shown in FIG. 6, the longitudinal stretching zone 446 is provided with rollers 448 a to 448 d that transport the film 20 in contact with the circumferential surface by rotational driving. By subjecting the film 20 to heat treatment and stretching in the longitudinal direction in the longitudinal stretching zone 446, the orientation angle, Re, Rth, and thickness are adjusted to some extent, but the unevenness in the width direction is eliminated. Not. Therefore, the film 20 is guided to the tenter unit 12, and preheating and widening are performed as described above, and relaxation and cooling are performed as appropriate. As a result, the retardation film 18 having a uniform thickness, Re, and Rth in the width direction is obtained, and the retardation film 18 is wound up by the winding unit 449.

  The film 20 exiting the longitudinal stretching zone 446 may be wound once at this stage and then sent to the tenter unit 12 or may be guided to the tenter unit 12 without being wound. Further, even if the film 20 once wound is supplied to the tenter unit 12, the same effect as that obtained when the film 20 is guided to the tenter unit 12 without being wound can be obtained.

  The film 20 is stretched in the transport direction Z1 in the longitudinal stretching zone 446. You may extend | stretch the conveyance direction Z1 before or after extending | stretching to the width direction Z2. The present invention is particularly effective for preheating and stretching in the tenter unit 12 when stretching in the transport direction Z1 is performed. The stretching in the transport direction Z1 is performed by transporting the film in the transport direction Z1 using a plurality of nip roll pairs arranged in the transport direction Z1, and by making the peripheral speed of the nip roll pair on the downstream side faster than the peripheral speed of the nip roll pair on the upstream side. Can be implemented. The stretching method differs depending on the distance (L) between the nip rolls in the transport direction Z1 and the ratio (L / W) of the film width W between the pair of nip rolls on the upstream side, and if L / W is small, JP-A-2005-330411 A stretching method in the transport direction Z1 as described in Japanese Patent Laid-Open No. 2006-348114 can be employed. This method tends to increase Rth, but can make the apparatus compact. On the other hand, when L / W is large, a stretching method in the transport direction Z1 as described in JP-A-2005-301225 can be used. Although this method can reduce Rth, the apparatus tends to be long.

(polymer)
The polymer in the present invention is a thermoplastic polymer. The present invention is particularly effective when, for example, cellulose acylate or cyclic polyolefin is used as the thermoplastic polymer.

Cellulose triacetate (TAC) is particularly preferable as the cellulose acylate when the film 20 is produced by solution casting or when the retardation film 18 is produced by solution casting. Among the cellulose acylates, the substitution degree of the acyl group to the hydroxyl group of cellulose is represented by the following formulas (I) to (III), and 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 degree of substitution of the acetyl group, and B is the degree of substitution of the acyl group having 3 to 22 carbon atoms. In addition, it is preferable that 90 weight% or more of TAC is a particle | grain of 0.1-4 mm. However, the polymer that can be used in the present invention is not limited to cellulose acylate.
(I) 2.5 ≦ A + B ≦ 3.0
(II) 0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.9

  Glucose units having β-1,4 bonds constituting cellulose have free 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 total degree of acylation substitution, that is, the value of DS2 + DS3 + DS6 is preferably 2.00 to 3.00, more preferably 2.22 to 2.90, and particularly preferably 2.40 to 2.88. Further, the value of DS6 / (DS2 + DS3 + DS6) is preferably 0.28, more preferably 0.30 or more, and particularly preferably 0.31 to 0.34. Here, DS2 is a ratio in which the hydrogen of the hydroxyl group at the 2-position in the glucose unit is substituted by an acyl group (hereinafter referred to as “acyl substitution degree at the 2-position”), and DS3 is the hydroxyl group at the 3-position in the glucose unit. The hydrogen is substituted with an acyl group (hereinafter referred to as “acyl substitution degree at the 3-position”), and DS6 is the ratio of the hydrogen at the 6-position hydroxyl group substituted with an acyl group (hereinafter referred to as “acyl substitution degree at the 3-position”). "The 6-position acyl substitution degree").

  Only one type of acyl group may be used in the cellulose acylate of the present invention, or two or more types of acyl groups may be used. When two or more kinds of acyl groups are used, it is preferable that one of them is an acetyl group. The sum of the degree of substitution of hydroxyl groups at the 2nd, 3rd and 6th positions by acetyl groups is DSA, and the sum of the degree of substitution of the hydroxyl groups at the 2nd, 3rd and 6th positions by acyl groups other than acetyl groups When DSB is DSB, the value of DSA + DSB is preferably 2.22 to 2.90, and particularly preferably 2.40 to 2.88.

  The DSB is preferably 0.30 or more, particularly preferably 0.7 or more. Further, 20% or more of DSB is preferably a substituent of a hydroxyl group at the 6-position, more preferably 25% or more, further preferably 30% or more, and particularly preferably 33% or more. Further, the DSA + DSB value at the 6-position of the cellulose acylate is 0.75 or more, more preferably 0.80 or more, and particularly preferably cellulose acylate of 0.85 or more. By using it, a dope with better solubility can be produced. In particular, when a non-chlorine organic solvent is used, a dope having excellent solubility, low viscosity and excellent filterability can be produced.

  Cellulose, which is a raw material for cellulose acylate, may be obtained from either linter or pulp.

  The acyl group having 2 or more carbon atoms of cellulose acylate in the present invention may be an aliphatic group or an aryl group, and is not particularly limited. For example, cellulose alkylcarbonyl ester, alkenylcarbonyl ester, aromatic carbonyl ester, aromatic alkylcarbonyl ester and the like may be mentioned, and each may further have a substituted group. Preferred examples of these include propionyl group, butanoyl group, pentanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, iso-butanoyl group. , T-butanoyl group, cyclohexanecarbonyl group, olenoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a t-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and a propionyl group and a butanoyl group are particularly preferable. It is.

  Solvent components of the dope 91 include aromatic hydrocarbons (eg, benzene, toluene, etc.), halogenated hydrocarbons (eg, dichloromethane, chlorobenzene, etc.), alcohols (eg, methanol, ethanol, n-propanol, n-butanol, etc.) Diethylene glycol, etc.), ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl acetate, ethyl acetate, propyl acetate, etc.) and ethers (eg, tetrahydrofuran, methyl cellosolve, etc.).

  Among the above halogenated hydrocarbons, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and dichloromethane is most preferably used. In the case of using TAC as a polymer component, in addition to dichloromethane, the number of carbon atoms is 1 to 5 from the viewpoint of physical properties such as solubility of TAC, peelability of the cast film from the support, mechanical strength and optical properties of the film. It is preferable to mix one kind or several kinds of alcohol. The content of alcohol is preferably 2 to 25% by weight, more preferably 5 to 20% by weight, based on the entire solvent. Examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, and n-butanol, but methanol, ethanol, n-butanol, or a mixture thereof is preferably used.

  Recently, a solvent composition that does not use dichloromethane has been studied for the purpose of minimizing the impact on the environment. In this case, an ether having 4 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and an alcohol having 1 to 12 carbon atoms are preferable. Sometimes used. For example, a mixed solvent of methyl acetate, acetone, ethanol, and n-butanol can be mentioned. These ethers, ketones, esters and alcohols may have a cyclic structure. In addition, a compound having two or more functional groups of ether, ketone, ester, and alcohol (that is, —O—, —CO—, —COO—, and —OH) can also be used as a solvent.

  Details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148, and these descriptions can also be applied to the present invention. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, UV absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, and release accelerators. It is described in detail in paragraphs [0196] to [0516] of Kai 2005-104148, and these descriptions can also be applied to the present invention.

  The polymer that can be used when the film 20 is produced by the melt film-forming method or when the melt-formed film 18 is produced is not particularly limited as long as it is a thermoplastic polymer. In addition to cellulose acylate, lactone ring-containing polymers, cyclic olefins, polycarbonates and the like can be mentioned. Of these, cellulose acylate and cyclic olefin are preferred, cellulose acylate containing an acetate group and propionate group, and cyclic olefin obtained by addition polymerization, more preferably cyclic olefin obtained by addition polymerization. It is.

(Cyclic olefin)
The cyclic olefin is preferably polymerized from a norbornene compound. This polymerization can be carried out by either ring-opening polymerization or addition polymerization. Examples of the addition polymerization include those described in Japanese Patent No. 3517471, Japanese Patent No. 3559360, Japanese Patent No. 3867178, Japanese Patent No. 3817721, Japanese Patent No. 3907908, Japanese Patent No. 3945598, Japanese Patent Publication No. 2005-527696, Japanese Patent Laid-Open No. 2006-2006. No. 28993 and International Publication No. 2006/004376 pamphlet. Particularly preferred is the one described in Japanese Patent No. 3517471.

  As the ring-opening polymerization, WO 98/14499 pamphlet, Japanese Patent No. 30605532, Japanese Patent No. 3320478, Japanese Patent No. 3273046, Japanese Patent No. 3404027, Japanese Patent No. 3428176, Japanese Patent No. 3687231, Japanese Patent No. 3873934, Patent No. 3912159 is mentioned. Among them, those described in WO98 / 14499 pamphlet and Japanese Patent No. 30605532 are preferable.

  Of these cyclic olefins, those of addition polymerization are more preferred.

(Lactone ring-containing polymer)
This refers to those having a lactone ring structure represented by the following (General Formula 1).

In (General Formula 1), R ¹ , R ² , and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The content ratio of the lactone ring structure of (General Formula 1) is preferably 5 to 90% by weight, more preferably 10 to 70% by weight, and still more preferably 10 to 50% by weight.

  In addition to the lactone ring structure represented by (General Formula 1), at least selected from (meth) acrylic acid esters, hydroxyl group-containing monomers, unsaturated carboxylic acids, and monomers represented by the following (General Formula 2). A polymer structural unit (repeating structural unit) constructed by polymerizing one kind is preferred.

In General Formula 2, R ⁴ represents a hydrogen atom or a methyl group, X is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an —OAc group, a —CN group, a —CO—R ⁵ group, or an -C-O-R ⁶ group, Ac group represents an acetyl group, R ⁵ and R ⁶ represents a hydrogen atom or an organic residue having 1 to 20 carbon atoms.

  For example, those described in International Publication No. 2006/025445, JP 2007-70607 A, JP 2007-63541 A, JP 2006-171464 A, and JP 2005-162835 A can be used. .

  Experiments 1 to 5 and Comparative Experiments 1 and 2 were performed under the following conditions, and the presence / absence of the effect of the present invention and the degree of the effect were examined.

[Experiment 1]
A predetermined solid content was appropriately added to a predetermined solvent and dissolved by stirring to prepare a dope 91. Dope 91 is
Cellulose triacetate (TAC, substitution degree 2.8) 89.3% by weight
Plasticizer A (triphenyl phosphate) 7.1% by weight
Plasticizer B (biphenyldiphenyl phosphate) 3.6% by weight
Solid content (solute) consisting of the composition ratio of
Dichloromethane 80% by weight
Methanol 13.5 wt%
n-butanol 6.5% by weight
The mixture was appropriately added to the solvent, and the mixture was dissolved by stirring. The concentration was adjusted so that the TAC concentration of the dope 91 was about 23% by weight. The dope 91 was filtered with a filter paper (Toyo Filter Paper Co., Ltd., # 63LB) and further filtered with a sintered metal filter (Nihon Seisen Co., Ltd. 06N, nominal pore size 10 μm), and further filtered with a mesh filter. I put it in a stock tank.

  The TAC used here has a residual acetic acid content of 0.1% by weight or less, a Ca content of 5 ppm, a Mg content of 42 ppm, a Fe content of 0.5 ppm, free acetic acid 40 ppm, and sulfuric acid. It contained 15 ppm of ions. The degree of substitution of the acetyl group with respect to the hydrogen at the 6-position hydroxyl group was 0.91. Further, 32.5% of all acetyl groups were acetyl groups in which the hydrogen of the hydroxyl group at the 6-position was substituted. Moreover, the acetone extraction part which extracted this TAC with acetone was 8 weight%, and the weight average molecular weight / number average molecular weight ratio was 2.5. The obtained TAC had a yellow index of 1.7, a haze of 0.08, and a transparency of 93.5%. This TAC is synthesized using cellulose collected from pulp as a raw material.

  The solution casting was performed in the solution casting equipment 80 that does not include the tenter unit 12 in the solution casting equipment 80 illustrated in FIG. 4, and the film 20 having a width of 1500 mm and a thickness of 100 μm was obtained from the dope 91.

  Using the offline stretching apparatus 10 shown in FIG. 1, the film 20 was stretched by the tenter unit 12. In the preheating area 36, the temperature of the film 20 was maintained in the range of 150 ° C. or higher and 180 ° C. or lower, and the temperature was continuously increased from the ear portion 20a of the film 20 toward the center in the width direction. As shown in the “Tc−Te” column of Table 1, the temperature difference obtained by subtracting the temperature Te (° C.) of the ear 20a from the temperature Tc (° C.) at the center in the width direction Z2 was 8.0 ° C. In the stretching area 37, the film 20 was stretched in the width direction Z2 while maintaining the temperature of the film 20 in the range of 180 ° C. or more and 200 ° C. or less and maintaining the temperature distribution in the width direction obtained in the preheating area 36. . The draw ratio was 40%. Next, in the relaxation area 38, relaxation treatment was performed while maintaining the temperature of the film 20 in the range of 150 ° C. or higher and 200 ° C. or lower.

[Experiment 2] to [Experiment 5], [Comparative Experiment 1], [Comparative Experiment 2]
In Experiments 2 to 5, the film 20 in the preheating area 36 and the stretching area 37 is the same as the experiment 1 except that the temperature difference between the ear 20a and the center in the width direction Z2 is set to the values shown in Table 1. The retardation film 18 was obtained. In the comparative experiment 1, the temperature in the width direction Z2 of the film 20 in the preheating area 36 and the stretching area 37 was made constant. In Comparative Experiment 2, the temperature was continuously lowered from the ear 20a of the film 20 toward the center in the width direction, and the temperature difference obtained by Tc-Te was set to the values shown in Table 1.

[Evaluation]
The following evaluation was performed about the obtained film.

1. Evaluation of thickness unevenness Thickness unevenness is obtained by the above formula, and based on the obtained value, the retardation film 18 obtained in Experiments 1 to 5 and the films obtained in Comparative Experiments 1 and 2 are evaluated based on the following criteria, respectively. did.
A: Thickness unevenness is less than 2% and very good B: Thickness unevenness is 2% or more and less than 5% C: Thickness unevenness is 5% or more and less than 8% and practically no problem D: Thickness unevenness It is 8% or more and it cannot be said that it is practically preferable.

2. Evaluation of Re Unevenness Re1 and Re2 were obtained by the above-described method to obtain Re1-Re2, and obtained in the retardation film 18 obtained in Experiments 1 to 5 and Comparative Experiments 1 and 2 based on the following criteria. Each film was evaluated for unevenness of Re. In addition, each Re of the 20 samples cut out as described above was conditioned for 2 hours at a temperature of 25 ° C. and a humidity of 60% RH, and then with an automatic birefringence meter (KOBRA21DH Oji Scientific Instruments). Measurements were taken from the vertical direction at 632.8 nm.
A: Re1-Re2 is less than 4 nm and very good B: Re1-Re2 is from 4 nm to less than 8 nm, and C: Re1-Re2 is from 8 nm to less than 10 nm, and there is no practical problem D: Re1-Re2 is 10 % Or more, which is not preferable for practical use

3. Evaluation of Rth Unevenness Rth1 and Rth2 were obtained by the above-described method to obtain Rth1-Rth2, and obtained by the retardation film 18 obtained in Experiments 1 to 5 and Comparative Experiments 1 and 2 based on the following criteria. Each film was evaluated for Rth unevenness. Each Rth of the 20 samples cut out as described above was conditioned for 2 hours at a temperature of 25 ° C. and a humidity of 60% RH, and vertical at 632.8 nm using an ellipsometer (M150 manufactured by JASCO Corporation). It calculated from the value measured from the direction, and the extrapolation value of the retardation value measured similarly, inclining the film surface.
A: Rth1-Rth2 is less than 4 nm and very good B: Rth1-Rth2 is from 4 nm to less than 8 nm, and C: Rth1-Rth2 is from 8 nm to less than 10 nm, and there is no practical problem D: Rth1-Rth2 is 10 % Or more, which is not preferable for practical use

  The evaluation results in Experiments 1 to 5 and Comparative Experiments 1 and 2 are shown in Table 1.

It is the schematic which shows an offline extending | stretching apparatus. It is a side view which shows the outline | summary of a tenter part. It is a top view which shows the outline | summary of a tenter part. It is the schematic which shows a solution casting apparatus. It is the schematic of a melt film-forming facility. It is a perspective view which shows the arrangement | positioning state of the some roll in a longitudinal direction extending | stretching zone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Off-line extending | stretching apparatus 12 Tenter part 18 Phase difference film 20 Film 20a Ear | edge part 36 Preheating area 37 Stretching area 43 Duct 53 Slit

Claims (5)

A heating step of heating the film so as to be a temperature gradient in which the temperature increases from the side edge of the long film made of polymer toward the center in the width direction;
A widening step that is performed in a state where the temperature gradient is maintained, and that the holding means that holds each side end of the film is displaced in the width direction of the film to widen the width of the film to form a retardation film; A method for producing a retardation film, comprising:   The method for producing a retardation film according to claim 1, wherein a temperature difference between the side end portion and the central portion is in a range of 2 ° C. to 20 ° C. The dope in which the polymer is dissolved in a solvent flows out from a casting die to a traveling support to form a casting film, and the casting film is used as a wet film containing the solvent. Casting process to peel off from,
The method for producing a retardation film according to claim 1, further comprising a drying step of drying the wet film to form the film.   The method for producing a retardation film according to claim 1 or 2, wherein the polymer melted by heating is continuously extruded into a thin film shape and stretched in the transport direction while being transported to form the film.   The method for producing a retardation film according to any one of claims 1 to 4, wherein the polymer is a cyclic olefin or cellulose acylate.

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