JP5107193B2 - Method for stretching polymer film - Google Patents

Description

  The present invention relates to a method for stretching a polymer film.

  In recent years, due to the rapid development and spread of liquid crystal displays and the like, the demand for cellulose acylate films, particularly triacetyl cellulose films (TAC films) used as protective films for these liquid crystal displays is increasing. With this increase in demand, improvement in productivity is desired. The TAC film is supported by casting a dope containing a TAC and a solvent on a continuously running support using a casting die, and providing the casting film with self-supporting property by drying or cooling. It is manufactured by peeling off from the body, drying and winding up. In such a solution casting method, a film having no foreign matter and excellent optical characteristics can be obtained as compared with a film forming method by melt extrusion.

  In the solution casting method, the support for receiving the dope includes a band and a drum. The drum system is easier to improve the casting speed than the band. Moreover, in order to give self-supporting property on a support body, methods, such as acceleration | stimulation of drying and cooling gelation, are used. On the other hand, stretching is carried out as a method for adjusting the optical properties of the TAC film, particularly the retardation.

  The optimum speed is different between the film-forming speed and the stretching speed, and the film-forming speed is the rate-determining. Therefore, if the film-forming speed is adjusted to the film-forming speed, the stretching for improving the optical properties cannot be performed sufficiently. Therefore, it has been proposed to extend off-line separately from the solution casting line.

When stretching is performed off-line separately from the solution casting line, it is preferable to stretch the film continuously in order to perform the stretching process efficiently. Off-line stretching equipment is a process of joining the preceding film and the succeeding film, and while continuously transporting the joined film, the film is heated and the side edges of the film are gripped by a plurality of clips, and the film width A stretching process for stretching in the direction, a thermal relaxation process for heat-treating the stretched film for stress relaxation, and the like (for example, see Patent Document 1). In the joining process, a double-sided joining tape is used as a simple joining means. In general, a double-sided bonding tape has a sheet-like base material and adhesive layers provided on both sides of the base material, and a material different from the TAC film is used for the base material.
Japanese Patent Application No. 2007-084424

  When a double-sided bonding tape is used in the joining process of the offline stretching equipment, if the stretching process and the thermal relaxation process are performed, the amount of thermal expansion and contraction of the base material constituting the double-sided bonding tape and the amount of thermal expansion and contraction of the film are different. As shown in FIG. 12, in the joining region 501 between the preceding film 500a and the following film 500b (here, it is assumed that a double-sided joining tape is applied to the entire region where the films overlap), the film There is a problem that a force acts in the transport direction, and this force becomes stronger in the center than in the end in the film width direction (the length of the arrow indicates the magnitude of the force), causing a bowing phenomenon. In other words, the bowing phenomenon is a phenomenon in which a straight line drawn in the film width direction on the film before the stretching process is curved like a bow after the stretching process and the thermal relaxation process. When such a bowing phenomenon occurs, there arises a problem that the optical characteristics (delay axis) vary in the film width direction in the film.

  Since the joining area 301 joined by the double-sided joining tape contains the base material of the double-sided joining tape, it cannot be reused as a film raw material, and the joining area 301 needs to be cut and discarded. Along with the joining area 301, the surrounding area 302 affected by the bowing phenomenon must be discarded. For this reason, there was a problem that the area which can be made into a product decreases.

  An object of this invention is to provide the film extending method which can suppress the bowing phenomenon of the joining area | region vicinity of a film to the minimum.

The present invention includes a joining step in which a rear end portion of a preceding polymer film and a front end portion of a succeeding polymer film are overlapped and joined, and the polymer film is heated while continuously transporting the joined polymer film. A stretching step of gripping both side edges of the polymer film with a plurality of clips and stretching in the film width direction, and a thermal relaxation step of performing heat treatment for stress relaxation while continuously transporting the stretched polymer film. In the method for stretching a polymer film, the joining step is characterized by joining with a double-sided adhesive tape having only an adhesive layer having no substrate.

In the joining step, it is preferable that the length of the joining region of the preceding polymer film and the succeeding polymer film in the transport direction of the polymer film be in the range of 0.2% to 2.2% of the film width.

According to the present invention, since the films are bonded together using a double-sided pressure-sensitive adhesive tape having only a pressure-sensitive adhesive layer having no base material, the base material of the double-sided pressure-sensitive adhesive tape does not exist in the joining region, so that the bowing phenomenon is suppressed.

According to the present invention, since the length in the film transport direction of the joining region to be joined using the double-sided pressure-sensitive adhesive tape is within the range of 0.2% to 2.2% of the film width, the bowing phenomenon can be further suppressed. .

[First Embodiment]
As shown in FIG. 1, the offline stretching equipment 2 stretches a TAC film 3 (hereinafter referred to as film 3), and includes a film supply chamber 4, a tenter unit 5, a thermal relaxation chamber 6, and a cooling chamber 7. And a winding chamber 8, and these are arranged in order along the film transport direction A. The film supply chamber 4 is provided with a film roll 9 manufactured by a solution casting apparatus. The film roll 9 is obtained by winding the film 3 around a core to form a roll. The film 3 is sent out from the film roll 9 provided in the film supply chamber 4, and the film 3 is stretched in the film width direction while being heated by the tenter unit 5, and the stretched film 3 includes the heat relaxation chamber 6 and the cooling chamber 7. After that, the temperature is lowered and the film is wound in the winding chamber 8. In the tenter unit 5, the film 3 is stretched by 100.5% to 300% in the width direction.

  The film supply chamber 4 includes a turret type film delivery device 10 and a joining portion 11. The film delivery apparatus 10 has a turret arm 13 provided with attachment shafts 12 at both ends. A film roll 9 is attached to each attachment shaft 12. The turret arm 13 rotates intermittently by 180 degrees, positions one attachment shaft 12 at the delivery position (on the joint 11 side), and positions the other attachment shaft 12 at the core replacement position. The film 3 is sent out from the film roll 9 mounted on the mounting shaft 12 at the sending position to the joint portion 11. When all the films 3 are sent out, the turret arm 13 rotates, the empty core is removed from the mounting shaft 12 located at the core replacement position, and a new film roll is mounted.

  As shown in FIG. 2 and FIG. 3, in order to supply the continuous film 3 to the tenter unit 5, the joining unit 11 is fed back and sent to the rear end portion of the preceding film 3 a sent out in advance. Then, the leading end portion of the succeeding film 3b is overlapped and joined via a double-sided joining tape 20 having elasticity. Examples of the double-sided adhesive tape include No. manufactured by Nitto Denko Corporation. In 532, a polyester material is used as a base material, and a tape having an adhesive layer formed on both sides of the base material is used.

  When the region where the preceding film 3a and the succeeding film 3b are overlapped is defined as the overlapping region 22 and the region bonded by the double-sided bonding tape 20 is defined as the bonding region 21, the length L1 of the bonding region 21 in the film transport direction A is The length of the overlapping region 22 in the film transport direction A is shorter (see FIG. 3). The length L1 of the joining region 21 may be equal to the length of the overlapping region 22 in the film transport direction A.

  The dimension in the film conveyance direction A of the bonding region 21 (the dimension in the film conveyance direction A of the double-sided bonding tape 20) is set within the range of 0.2% to 2.2% of the film width. That is, when the film width is Wa and the dimension of the bonding region 21 in the film transport direction A is L1, L1 is set so as to satisfy the condition of 0.002Wa ≦ L1 ≦ 0.022Wa. By securing the dimension of the joining region 21 to 0.2% or more of the film width, the leading film 3a and the succeeding film 3b are reliably joined and will not come off. Moreover, it can prevent that the bowing phenomenon reaches other than the joining area | region 21 by making the dimension of the joining area | region 21 into 2.2% or less of a film width. In this embodiment, Wa = 2500 mm and L1 = 50 mm (= 0.02 Wa) are set.

  When joining the preceding film 3a and the succeeding film 3b, the double-sided adhesive tape 20 is attached to the upper surface of the rear end of the preceding film 3a, and then the leading end of the succeeding film 3b is overlapped with the double-sided joining tape 20 Crimp. The joining of the film may be performed automatically, or may be performed manually when a simple configuration is used.

  As shown in FIG. 1, a reservoir 24 is disposed between the film supply chamber 4 and the tenter unit 5, and this reservoir 24 forms a loop of the film 3 that is longer than the length necessary for the film bonding process. To do. Therefore, at the time of film bonding, the film 3 stored in the reservoir 24 is sent out to the tenter unit 5, so that the film 3 can be bonded without stopping the tenter unit 5.

  As shown in FIG. 4, the tenter unit 5 extends the film 3 in the width direction while transporting the film 3 in the film transport direction A, and includes a first rail 30, a second rail 31, and a first rail. A first chain 32 guided by the rail 30 and a second chain 33 guided by the second rail 31 are provided. The tenter unit 5 is disposed in a drying chamber (not shown). The drying chamber is divided into a preheating zone 27, a heating zone 28, and a thermal relaxation zone 29 in order along the film conveyance direction A, and the drying air is sent by a duct (not shown) so as to obtain an optimum film temperature for each zone. It has been.

  The first chain 32 is spanned between the driving sprocket 35 and the driven sprocket 36, and the second chain 33 is spanned between the driving sprocket 37 and the driven sprocket 38. Each driving sprocket 35, 37 is rotationally driven by a drive mechanism (not shown).

  A number of clips 39 are attached to the first chain 32 and the second chain 33 at regular intervals. These clips 39 extend along the width direction of the film 3 by moving along the rails 30 and 31 while gripping the side edges of the film 3. A point PA indicates a film grip start position of the clip 39, and a point PB indicates a film grip open position of the clip 39. Further, the point PC represents the stretching start position by the clip 39, and the point PD represents the stretching end position by the clip 39. By the stretching process, the film width of the film 3 is changed from Wa to Wb (> Wa). In addition, the draw ratio of the film 3 is appropriately changed according to desired optical characteristics and the like.

  Returning to FIG. 1, the film 3 is stretched by the tenter unit 5, and then sent out to the ear clip device 40. The side edges of the film 3 are cut off by the cut-off line 23 (see FIG. 2) by the edge-cutting device 40, and the parts including the double-sided bonding tape 20 are removed from the cut-off side edges of the slits. After that, it is cut into small pieces by the cut blower 41. The cut ear dust pieces are sent to the crusher 42 by an air feeding device (not shown) and crushed into chips. This chip is reused as a film raw material. The film 3 from which both side edges are cut off by the edge-cutting device 40 is sent to the thermal relaxation chamber 6.

  The heat relaxation chamber 6 is provided with a large number of rollers 43, and the film 3 is conveyed through the heat relaxation chamber 6 by the rollers 43. The film 3 is heat-treated by sending wind at a desired temperature from the blower (not shown) into the heat relaxation chamber 6. The temperature of the wind at this time is preferably 20 ° C to 250 ° C. The film 3 gradually decreases in temperature.

  The film 3 after heat relaxation is sent to the cooling chamber 7 and cooled to 30 ° C. or lower, and then sent to the winding chamber 8. Inside the winding chamber 8, a winding roller 44 and a press roller 45 are provided. The film 3 sent to the winding chamber 8 is wound up by a winding roller 44. At this time, it is pressed by the press roller 45 and wound up.

  The film 3 may be any film produced by a well-known solution casting method. For example, a TAC film described in JP-A-2005-104148 can be used. In particular, in order to improve the film forming speed, a dope containing TAC and a solvent is cast on the peripheral surface of a cooled casting drum, and the cast film is cooled and gelled to be self-supporting. The TAC film having excellent optical characteristics can be produced efficiently and without waste by carrying out the present invention with respect to the TAC film that has been taken and dried through the pin tenter.

  According to the offline stretching equipment 2 having the above-described configuration, since the dimension in the film transport direction A of the joining region 21 of the preceding film 3a and the succeeding film 3b is defined within a predetermined range, the stretching process and the thermal relaxation process are performed. Even in the film 3, as shown in FIG. 5, the force itself acting in the film transport direction A is small in the joining region 21, and the difference in force between the end portion and the central portion in the film width direction is small. Therefore, the Boeing phenomenon is minimized. For this reason, since the influence of the bowing phenomenon does not reach the periphery of the joining region 21, a region that can be made into a product can be widened as compared with the conventional case.

  In the above embodiment, the dimension in the film transport direction A of the joining region 21 of the preceding film 3a and the succeeding film 3b is defined within the range of 0.2% to 2.2% of the film width. It is more preferable to define the film width within the range of 0.2% to 1.0%. In this case, the bowing phenomenon can be further reduced.

[Second Embodiment]
In 1st Embodiment, in the junction part 11, although the double-sided bonding tape 20 was used for joining of the preceding film 3a and the succeeding film 3b, you may join by heat welding using a heat sealer instead. As shown in FIG. 6, the heat sealer apparatus 100 includes an upper welding head 101 and a lower welding head 102 provided so as to sandwich the conveyance path of the film 3 vertically. The upper welding head 101 has a heater 103 exposed from the lower surface, and the lower welding head 102 has a heater 106 exposed from the upper surface. The welding heads 101 and 102 are moved between a heating position where the heaters 103 and 106 are brought into contact with the film 3 and a retreat position where the heaters 103 and 106 are separated from the film 3 by a shift mechanism (not shown). The heaters 103 and 106 are temperature controlled by temperature controllers 104 and 107.

  A procedure for bonding films using the heat sealer apparatus 100 will be described. The leading end of the trailing film 3b is superimposed on the trailing end of the preceding film 3a. The upper welding head 101 and the lower welding head 102 are moved to the heating position. The temperature of each of the heaters 103 and 106 is set to a predetermined temperature that dissolves the film 3 but does not decompose it, for example, in the range of 150 ° C. to 299 ° C. Each of the heaters 103 and 106 is brought into contact with a region where the films are overlapped. A part of the film is melted and bonded by heating with the heaters 103 and 106 for a predetermined time. Each heater 103 and 106 stops heating after heating for a predetermined time, and naturally cools the bonding region 108 in a pressure state. Next, the upper welding head 101 and the lower welding head 102 are moved to the retracted position.

  Heating the bonding region 108 of the film 3 from the upper and lower surfaces enables efficient transfer of heat to the film 3, and welding and bonding while maintaining the temperature of the bonding region 108 below the decomposition temperature. be able to. Moreover, the opening of a melt | dissolution part and resin deterioration can also be prevented with respect to the polymer film with a melting point and a decomposition point near.

  When bonding is performed with the heat sealer apparatus 100 having the above-described configuration, since a different material does not exist in the bonding region 108, the bowing phenomenon of the film 3 after the stretching process and the thermal relaxation process are minimized. . Further, the bonding region 108 can be reused as a film raw material. Instead of the heat sealer device 100, the film may be heat-welded and bonded using an impulse sealer device.

[Third Embodiment]
In 1st Embodiment, although the film 3 was joined in the junction part 11 using the double-sided joining tape 20, you may join by heat welding using an ultrasonic bonding apparatus instead. As shown in FIG. 7, the ultrasonic bonding apparatus 200 includes a vibrator 201, a horn 202, and a transmitter 203, and mechanically moves the film 3 at an amplitude of 0.03 mm, for example, 20,000 to 28,000 times per second. Vibrate to generate heat and weld. Two vibrators 201 are provided, a permanent magnet 204 is disposed between the two vibrators 201, and a coil 205 is wound around each of the two vibrators 201. The transmitter 203 drives the vibrator 201 via the coil 205. The vibrator 201 converts electrical vibration into mechanical vibration. The horn 202 expands the mechanical vibration caused by the vibrator 201 and gives (vibrates) energy to the rear end portion of the preceding film 3a and the front end portion of the succeeding film 3b placed on the cradle 206.

  A procedure for bonding a film using the ultrasonic bonding apparatus 200 will be described. The leading end of the trailing film 3b is superimposed on the trailing end of the preceding film 3a. The transmitter 203 drives the vibrator 201, the mechanical vibration of the vibrator 201 is magnified by the horn 202, and the joining region 207 generates heat and is welded by the vibration.

  When the bonding process is performed by the ultrasonic bonding apparatus 200 having the above-described configuration, since a different material does not exist in the bonding region 207, the bowing phenomenon is minimized in the film 3 after the stretching process and the thermal relaxation process. Can be suppressed. Further, all of the bonding region 207 can be reused as a film raw material.

[Fourth Embodiment]
In the first embodiment, the film 3 is bonded at the bonding portion 11 using the double-sided bonding tape 20. Instead, a polymer solvent (for example, acetone) is applied to the region where the double-sided bonding tape 20 is attached. And may be welded. In this case, since a different material does not exist in the joining region, the bowing phenomenon can be minimized in the film 3 after the stretching process and the thermal relaxation process. In addition, the entire joining region can be reused as a film raw material.

  In addition, as a solvent for joining the film 3, it is not restricted to acetone, What is necessary is just the solvent which can dissolve the polymer which makes the film 3 besides the solvent used for dope.

[Fifth Embodiment]
In 1st Embodiment, although the film 3 was joined using the double-sided bonding tape 20 with a base material in the junction part 11, instead of this, the double-sided bonding tape only of the adhesion layer without a base material is used. May be. The same material as that constituting the film is used for the adhesive layer of this double-sided adhesive tape. In this case, since a different material does not exist in the joining region, the bowing phenomenon can be minimized in the film 3 after the stretching process and the thermal relaxation process. In addition, the entire joining region can be reused as a film raw material.

(Solution casting method)
The film in the above embodiment can be obtained by a solution casting method. As shown in FIG. 8, a solution casting apparatus 210 that performs the solution casting method includes a stock tank 211, a casting chamber 212, a pin tenter 213, a drying chamber 215, a cooling chamber 216, and a winding chamber 217.

  The stock tank 211 includes a stirring blade 211b and a jacket 211c that are rotated by a motor 211a. Inside the stock tank 211, a dope 221 in which a polymer that is a raw material of the TAC film 3 is dissolved in a solvent is stored. The dope 221 in the stock tank 211 is adjusted by the jacket 211c so that the temperature becomes substantially constant. Further, the rotation of the stirring blade 211b keeps the dope 221 in a uniform quality while suppressing agglomeration of a polymer or the like. The pipe 222 connects the stock tank 211 and the casting die 230.

  In the casting chamber 212, a casting die 230, a casting drum 232 as a support, a peeling roller 234, temperature control devices 235 and 236, and a decompression chamber 237 are installed. The casting drum 232 is rotated in the direction Z1 about the shaft 232a by a driving device (not shown). The temperature in the casting chamber 212 and the casting drum 232 are set to temperatures at which the casting film 233 can be easily cooled and solidified (gelled) by the temperature control devices 235 and 236.

  The casting die 230 has a slit formed so as to extend in the width direction TD. The casting die 230 discharges the dope 221 toward the peripheral surface 232b of the casting drum 232 rotating from the slit. Thereafter, a casting film 233 is formed from the dope 221 on the peripheral surface 232 b of the casting drum 232. Then, while the casting drum 232 rotates about 3/4, self-supporting property due to gelation is developed in the casting film 233, and the casting film 233 is peeled off from the casting drum 232 by the peeling roller 234, A wet film 238 is obtained. The residual solvent amount of the cast film 233 at the time of peeling is preferably 150% by weight or more and 320% by weight or less. Here, the residual solvent amount indicates the amount of solvent remaining in the TAC film 3 or the like on a dry basis, and the measurement method is to take a sample from the target film and the weight of this sample is x When the weight after drying the sample is y, it is calculated as {(xy) / y} × 100.

  The decompression chamber 237 is disposed upstream of the casting die 230 in the direction Z1, and maintains the inside of the decompression chamber 237 at a negative pressure, and the rear surface of the casting bead (later on the peripheral surface 232b of the casting drum 232). The surface to be contacted) is reduced to a desired pressure. By reducing the pressure on the back side of the casting bead, the influence of the accompanying air generated by the rotation of the casting drum 232 is reduced, and a stable casting bead is formed between the casting die 230 and the casting drum 232, and the membrane A cast film 233 with little thickness unevenness can be formed.

  The material of the casting die 230 is formed of a material having a high corrosion resistance against an electrolyte aqueous solution, a mixed liquid such as dichloromethane or methanol, and a low coefficient of thermal expansion. It is preferable to use a finishing accuracy of the wetted surface of the casting die 230 with a surface roughness of 1 μm or less and a straightness of 1 μm / m or less in any direction.

  The peripheral surface 232b of the casting drum 232 is subjected to a chrome plating process and has sufficient corrosion resistance and strength. The temperature control device 236 circulates the heat transfer medium through the casting drum 232 in order to keep the temperature of the peripheral surface 232b of the casting drum 232 at a desired temperature. The heat transfer medium is maintained at a desired temperature, and the temperature of the peripheral surface 232b of the casting drum 232 is maintained at a desired temperature by passing through the heat transfer medium flow path in the casting drum 232.

  The width of the casting drum 232 is not particularly limited, but it is preferable to use a casting drum in the range of 1.1 to 2.0 times the casting width of the dope. The material of the casting drum 232 is preferably made of stainless steel, and more preferably made of SUS316 so as to have sufficient corrosion resistance and strength. The chromium plating treatment applied to the peripheral surface 232b of the casting drum 232 is preferably so-called hard chromium plating with a Vickers hardness of Hv 700 or more and a film thickness of 2 μm or more.

  The casting chamber 212 includes a condenser (condenser) 239 for condensing the evaporated solvent and a recovery device 240 for recovering the condensed liquid. The solvent condensed and liquefied by the condenser 239 is recovered by the recovery device 240. The solvent is regenerated as a solvent for preparing a dope after being regenerated by a regenerator.

  A crossover 241 and a pin tenter 213 are sequentially installed downstream of the casting chamber 212. In the transfer section 241, the transport roller 242 introduces the wet film 238 into the pin tenter 213. The pin tenter 213 has a large number of pin plates that pass through and hold both side edges of the wet film 238, and the pin plates travel on a track. Dry air is sent to the wet film 238 traveling by the pin plate, and the wet film 238 is dried to be a film 220.

  The pin tenter 213 has a number of clips that grip both side edges of the film 220, and these clips travel on the stretching track. Dry air is sent to the film 220 traveling by the clip, and the film 220 is subjected to a drying process along with a stretching process in the film width direction TD.

  An ear clip device 243 is provided downstream of the pin tenter 213. The edge-cutting device 243 cuts both side edges of the film 220. The cut side edges are sent to the crusher 244 by air blowing, pulverized, and reused as a raw material such as a dope.

  A large number of rollers 247 are provided in the drying chamber 215, and the film 220 is wound around and conveyed. A cooling chamber 216 is provided on the outlet side of the drying chamber 215, and the film 220 is cooled in this cooling chamber 216 until it reaches room temperature. A forced static elimination device (static elimination bar) 249 is provided downstream of the cooling chamber 216, and the film 220 is neutralized. Further, a knurling application roller 250 is provided on the downstream side of the forced static elimination device 249, and knurling is applied to both side edges of the film 220. In the winding chamber 217, a winding machine 251 having a press roller 252 is installed, and the film 220 is wound around the winding core in a roll shape, and a film roll 255 is obtained by the winding machine 251. The film roll 255 is sent as the film roll 9 from the take-up chamber 217 to the film supply chamber 4 (see FIG. 1) of the off-line stretching equipment 2 and sent out as the film 3 from the film supply chamber 4.

  In the said 1st-5th embodiment, although demonstrated using a TAC film as a polymer film, this invention is applicable also to various polymer films, without being limited to a TAC film.

  As the polymer film that can be used in the present invention, for example, it is produced by a solution casting method in addition to a cellulose acylate film, and is produced by a polymer film made of another polymer such as a cyclic olefin or a melt casting method. There is a polymer film.

(Cellulose acylate)
As the cellulose acylate, triacetyl cellulose (TAC) is particularly preferable. Of the cellulose acylates, those in which the hydroxyl group of cellulose is esterified with carboxylic acid, that is, the substitution degree of the acyl group satisfies all of the following formulas (I) to (III) are more preferable. In the following formulas (I) to (III), A and B represent the substitution degree of the acyl group, the substitution degree A is the substitution degree of the acetyl group, and the substitution degree B is the acyl group having 3 to 22 carbon atoms. Is the degree of substitution. In addition, it is preferable that 90 weight% or more of TAC is a particle | grain of 0.1 mm-4 mm.
(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 of the hydroxyl group of cellulose esterified at each of the 2-position, 3-position and 6-position (100% esterification has a substitution degree of 1).

  The total acylation substitution degree, that is, 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, DS6 / (DS2 + DS3 + DS6) is preferably 0.28 or more, more preferably 0.30 or more, and particularly preferably 0.31 to 0.34. Here, DS2 is the degree of substitution of the hydroxyl group at the 2-position of the glucose unit with an acyl group (hereinafter also referred to as “degree of acyl substitution at the 2-position”), and DS3 is the degree of substitution of the hydroxyl group at the 3-position with an acyl group (hereinafter, referred to as “acyl group”). DS6 is the substitution degree of the hydroxyl group at the 6-position with an acyl group (hereinafter also referred to as “acyl substitution degree at the 6-position”).

  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. When the sum of the substitution degrees by the hydroxyl groups at the 2nd, 3rd and 6th positions is DSA, and the sum of the substitution degree by an acyl group other than the acetyl group at the 2nd, 3rd and 6th hydroxyl groups is DSB, the value of DSA + DSB is More preferably, it is 2.22 to 2.90, and particularly preferably 2.40 to 2.88. The DSB is 0.30 or more, particularly preferably 0.7 or more. Further, 20% or more of DSB is a substituent at the 6-position hydroxyl group, more preferably 25% or more is a substituent at the 6-position hydroxyl group, more preferably 30% or more, and particularly 33% or more is a 6-position hydroxyl group. It is preferable that it is a substituent. Furthermore, the cellulose acylate having a substitution degree of 6-position of cellulose acylate of 0.75 or more, further 0.80 or more, and particularly 0.85 or more can be mentioned. With these cellulose acylates, a solution having a preferable solubility (dope) can be produced. In particular, in a non-chlorine organic solvent, a good solution can be produced. Furthermore, it is possible to produce a solution having a low viscosity and good filterability.

  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 the cellulose acylate of the present invention may be an aliphatic group or an aryl group and is not particularly limited. These are, for example, cellulose alkylcarbonyl esters, alkenylcarbonyl esters, aromatic carbonyl esters, aromatic alkylcarbonyl esters, and the like, each of which may further have a substituted group. Preferred examples of these include propionyl, butanoyl, pentanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, iso-butanoyl, t-butanoyl, cyclohexanecarbonyl, oleoyl, benzoyl , Naphthylcarbonyl, cinnamoyl group and the like. Among these, propionyl, butanoyl, dodecanoyl, octadecanoyl, t-butanoyl, oleoyl, benzoyl, naphthylcarbonyl, cinnamoyl and the like are more preferable, and propionyl and butanoyl are particularly preferable.

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

  Among these, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and dichloromethane is most preferably used. One kind of alcohol having 1 to 5 carbon atoms in addition to dichloromethane from the viewpoint of physical properties such as solubility of TAC, peelability of cast film from the support, mechanical strength of the film, and optical properties of the film It is preferable to mix several kinds. The content of the alcohol is preferably 2% by weight to 25% by weight and more preferably 5% by weight to 20% by weight with respect to the whole solvent. Specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like, but methanol, ethanol, n-butanol or a mixture thereof is preferably used.

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

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

(Melting film forming equipment)
Next, a manufacturing facility for manufacturing a polymer film by a melt film forming method (hereinafter referred to as a melt film forming facility) will be described. As shown in FIG. 9, the melt film-forming facility 410 is an apparatus for producing a thermoplastic film F that can be used for a liquid crystal display device or the like. A pellet-shaped thermoplastic resin, which is a raw material of the thermoplastic film F, is introduced into a dryer 412 and dried, and then the pellet is extruded by an extruder 414 and supplied to a filter 418 by a gear pump 416. Next, foreign matters are filtered by the filter 418, and molten resin (molten thermoplastic resin) is extruded from the die 420. The molten resin is sandwiched between the first casting roll 428 and the touch roll 424 and press-molded, and then cooled and solidified by the first casting roll 428 to form a film having a predetermined surface roughness. Further, the second casting is performed. The unstretched film Fa is obtained by being conveyed by the roll 426 and the third casting roll 427. This unstretched film Fa may be wound up at this stage, or may be supplied to a lateral stretching section 442 that continuously performs long-span stretching. Further, even if the unstretched film Fa once wound up is supplied again to the transverse stretching section 442, the same effect as that obtained when the unstretched film Fa is supplied to the transverse stretching section 442 that performs continuous long span stretching can be obtained.

  In the laterally stretched portion 442, the unstretched film Fa is stretched in the width direction (hereinafter referred to as the TD direction) orthogonal to the transport direction (hereinafter referred to as the MD direction) to obtain a laterally stretched film Fb. The preheating unit 436 may be provided on the upstream side of the lateral stretching unit 442, or the heat fixing unit 444 may be provided on the downstream side of the lateral stretching unit 442. Thereby, the bowing (shift of the optical axis) during stretching can be reduced. The preheating temperature is preferably higher than the transverse stretching temperature, and the heat setting temperature is preferably lower than the transverse stretching temperature. That is, normally, the center part in the width direction becomes concave toward the traveling direction, but bowing can be reduced by setting preheating temperature> lateral stretching temperature and transverse stretching temperature> heat setting temperature. Either pre-heat treatment or heat setting treatment may be performed, or both may be performed.

  After the transverse stretching, post-heat treatment is performed, and then the transversely stretched film Fb is contracted in the MD direction in the heat treatment zone 446. In the heat treatment zone 446, as shown in FIG. 10, a plurality of rolls 448a are used so that only the shrinkage in the MD direction occurs without shrinking in the TD direction without holding the side end portion of the laterally stretched film Fb with the chuck. The horizontally stretched film Fb is conveyed at ˜448d. At this time, as shown in FIG. 11, the plurality of rolls 448a to 448d are arranged so that the ratio (G / D) of the roll wrap length (D) to the inter-roll length (G) is 0.01 or more and 3 or less. Is done. Thereby, the shrinkage | contraction of a TD direction is suppressed by the friction with the transversely stretched film Fb and each roll 448-448d. The laterally stretched film Fb is conveyed at a ratio (V2 / V1) of the peripheral speed (V1) by the upstream roll 448a and the peripheral speed (V2) by the downstream roll 448d at 0.6 or more and 0.999 or less. While being heat treated. That is, the laterally stretched film Fb shrinks in the MD direction in the heat treatment zone.

  The transversely stretched film Fb is heat-treated in the heat treatment zone, whereby the thermoplastic film F, which is the final product with the adjusted orientation angle and retardation, is produced. The film F is taken up by a take-up unit 449.

  Stretching in the MD direction may be performed before or after stretching in the TD direction. Stretching in the MD direction can be achieved by transporting the film using a plurality of nip roll pairs arranged in the MD direction and increasing the peripheral speed of the downstream nip roll pair from the peripheral speed of the upstream nip roll pair. The stretching method differs depending on the distance (L) between the nip rolls in the MD direction and the ratio of the film width W (L / 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 MD direction as described in JP-A-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 MD direction as described in JP-A-2005-301225 can be used. Although this method can reduce Rth, the apparatus tends to be long.

  The polymer that can be used in the melt film-forming method is not particularly limited as long as it is a thermoplastic resin, and examples thereof include cellulose acylate, lactone ring-containing polymer, cyclic olefin, and polycarbonate. 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)
The thing which has the lactone ring structure represented by the following (general formula 1) is pointed out.

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 5} group, Ac group represents an acetyl group, ^{R 5} and ^{R 5} 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 1-3)
Next, Experiments 1 to 3 will be described. The formulation for preparing the polymer solution (dope) used for film production is shown below.

[Preparation of dope]
The prescription of the compound used for preparation of the raw material dope is shown below.
Cellulose triacetate (degree of substitution 2.86) 89.3% by weight
Plasticizer A (triphenyl phosphate) 7.1% by weight
Plasticizer B (biphenyldiphenyl phosphate) 3.6% by weight
80% by weight of solid content (solute) with a composition ratio of dichloromethane
Methanol 13.5 wt%
n-butanol 6.5% by weight
A raw material dope was prepared by appropriately adding to a mixed solvent consisting of The TAC concentration of the raw material dope was adjusted to be about 23% by weight. The raw material dope is filtered through a filter paper (Toyo Filter Paper Co., Ltd., # 63LB), further filtered through a sintered metal filter (Nihon Seisen Co., Ltd. 06N, nominal pore size 10 μm), and further filtered through a mesh filter. I put it in the tank.

[Cellulose triacetate]
The cellulose triacetate used here has a residual acetic acid content of 0.1% by weight or less, a Ca content of 57 ppm, a Mg content of 41 ppm, a Fe content of 0.4 ppm, free acetic acid of 38 ppm, It contained 13 ppm of sulfate ion. 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 cotton as a raw material.

[Preparation of matting agent solution]
A matting agent solution was prepared from the following formulation.
Silica (Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) 0.67% by weight
Cellulose triacetate 2.93% by weight
Triphenyl phosphate 0.23% by weight
Biphenyl diphenyl phosphate 0.12% by weight
Dichloromethane 88.37 wt%
Methanol 7.68% by weight
A matting agent solution was prepared from the above formulation, dispersed with an attritor so that the volume average particle size was 0.7 μm, and then filtered with an astropore filter manufactured by Fuji Film Co., Ltd. And it put into the tank for mat agent liquids.

[Preparation of UV absorber solution]
An ultraviolet absorber solution was prepared from the following formulation.
2 (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole 5.83% by weight
2 (2′-hydroxy 3 ′, 5′-di-tert-amylphenyl) benzotriazole 11.66% by weight
Cellulose triacetate 1.48% by weight
Triphenyl phosphate 0.12% by weight
Biphenyl diphenyl phosphate 0.06% by weight
Dichloromethane 74.38 wt%
Methanol 6.47% by weight
An ultraviolet absorber solution was prepared from the above formulation, filtered through an astropore filter manufactured by Fuji Film Co., Ltd., and then put into a tank for an ultraviolet absorber liquid method.

  As shown in FIG. 8, a film 220 was manufactured using a solution casting apparatus 210. The matting agent solution was mixed with the ultraviolet absorber solution and mixed and stirred with an in-line mixer to obtain a mixed additive. The additive supply line sent the mixed additive into the pipe. The in-line mixer obtained a casting dope by mixing and stirring the raw material dope and the mixed additive. The casting drum 232 rotates around the shaft 232a under the control of the control unit, and holds the speed of the peripheral surface 232b in the traveling direction Z1 so as to be substantially constant within a range of 50 m / min to 200 m / min. did. The temperature of the peripheral surface 232b of the casting drum 232 was maintained so as to be substantially constant within a range of −10 ° C. to 10 ° C. In the casting die 230, the casting dope was cast on the peripheral surface 232b, and a casting film 233 was formed on the peripheral surface 232b. After the casting film 233 became self-supporting by cooling, the casting film 233 was peeled off from the casting drum 232 as a wet film 238 using a peeling roller 234. In order to suppress the peeling failure, the peeling speed (peeling roller draw) relative to the speed of the casting drum 232 was appropriately adjusted in the range of 100.1% to 110%. The wet film 238 was sequentially guided to the transfer section 241, the pin tenter 213, and the drying chamber 215. In the crossover part 241, the pin tenter 213, and the drying chamber 215, a predetermined drying process was performed by applying dry air to the wet film 238. The film 220 obtained by this drying treatment was sent to the cooling chamber 216. In the cooling chamber 216, the film 220 was cooled to 30 ° C. or lower. Thereafter, the film 220 was subjected to static elimination processing, knurling application processing, and the like, and then transferred to the winding chamber 217. In the winding chamber 217, the film 220 was wound around the winding core of the winder 251 while being applied with a desired tension by the press roller 252 to become a film roll 255. The film roll 255 was sent to the offline stretching apparatus 2.

  The film 3 was stretched using the off-line stretching facility 2 of the first embodiment. After the thermal relaxation treatment of the film 3, the evaluation regarding the bowing phenomenon occurring in the film 3 was performed. Table 1 shows the film width Wa and the length L1 of the bonding region 21 in the film conveyance direction A in Experiments 1 to 3. The thickness of the film 3 is 80 μm, and the thickness of the double-sided bonding tape 20 is 60 μm. A polyester film is used for the base material of the double-sided bonding tape 20, and an acrylic type is used for the adhesive layer. The stretching ratio of the film 3 in the tenter unit 5 is 140%, and the film temperature during stretching is 200 ° C. The results are shown in Table 1.

  Here, the bowing phenomenon is a phenomenon in which a straight line drawn in the film width direction on the film 3 at the entrance of the tenter unit 5 changes to a bow-like curve through the tenter unit 5 and the thermal relaxation chamber 6, and the bowing amount is It shows the dimensional difference in the film transport direction between the most concave point (usually the center of the film) and the most projecting point (usually both edges of the film) of this bowed curve. Further, the bowing strain indicates the ratio of the bowing amount to the film width.

  In Experiment 1, the bowing strain is 0.16%. With this value, the influence of the bowing phenomenon does not reach the periphery of the bonding region 21. Experiment 1 is evaluated as “◯”. In Experiment 2, the bowing strain is 0.23%, and this value is a limit value at which the influence of the bowing phenomenon does not reach the periphery of the bonding region 21. That is, when the bowing strain exceeds 0.23%, the influence of the bowing phenomenon starts to be strong around the bonding region 21. Experiment 2 is evaluated as “◯”. In Experiment 3, the bowing strain was 1.09%, and the influence of the bowing phenomenon was exerted strongly around the bonding region 21. Experiment 3 is evaluated as “x”.

(Experiment 11 to Experiment 13)
Using a melt film-forming method, a cellulose acetate propionate (indicated as “CAP” in Table 1) film (thickness: 100 μm) of Example 1 of JP-A-2007-89817 was obtained, and each condition was shown. Experiments 11 to 13 were performed in the same manner as Experiments 1 to 3 except that the values shown in FIG.

(Experiment 21 to Experiment 23)
Using a melt film-forming method, a cellulose acylate film (thickness = 100 μm, Tg = 131 ° C.) was obtained according to Example 101 of Example B of JP-A-2007-169588, and the conditions are shown in Table 1. Experiments 21 to 23 were performed in the same manner as Experiments 1 to 3, except that the values shown were used.

(Experiment 31 to Experiment 33)
Using the solution casting method, the film No. described in Example 1 of JP-A-2001-188128 was used. Experiments 31 to 33 were performed in the same manner as Experiments 1 to 3, except that 1 (cellulose acetate propionate: thickness 100 μm) was obtained and the conditions were set to the values shown in Table 1.

(Experiment 41 to Experiment 43)
Experiment 1 except that the polymer film was obtained from the cycloolefin resin A (referred to as “cycloolefin” in Table 1) using the melt film-forming method and that the conditions were set to the values shown in Table 1. Experiments 41 to 43 were performed in the same manner as.
Cycloolefin resin A (addition polymerization system): TOPAS 6013 (Tg = 130 ° C.) manufactured by Polyplastics Co., Ltd.

  Details of the melt film-forming method in Experiments 41 to 43 are as follows. Cycloolefin resin A was dried with a vacuum dryer at 110 ° C. to a water content of 0.1% or less, melted at 260 ° C. using a single-screw kneading extruder, fed from a gear pump, and then a leaf disk with a filtration accuracy of 5 μm. Three cast rolls set at (Tg-5) ° C, Tg ° C, and (Tg-10) ° C from a hanger coat die with a slit interval of 0.8mm and 270 ° C via a static mixer. A melt (molten resin) was extruded on top. At this time, the touch roll was brought into contact with the most upstream cast roll at a surface pressure of 0.1 MPa to form an unstretched film having a thickness of 100 μm. The touch roll was the one described in Example 1 of JP-A-11-235747 (the one described as a double holding roll), and the temperature was adjusted to Tg-5 ° C. (however, the thickness of the thin metal outer cylinder was 2 mm) did).

  Then, after trimming both ends (each 3% of the total width) just before winding, the both ends were subjected to thicknessing (knurling) with a width of 10 mm and a height of 20 μm. In each level, the width was 1.5 m, and 3000 m was wound at 30 m / min.

(Experiment 51 to Experiment 53)
Except for obtaining a polymer film made of a lactone ring-containing polymer resin (indicated as “lactone” in Table 1) using a melt film-forming method, and setting each condition to the values shown in Table 1, Experiments 51 to 53 were performed in the same manner as Experiments 1 to 3. The melt film-forming method in Experiment 51 to Experiment 53 followed Example 1 described in the pamphlet of International Publication No. 2006/025445. However, the film width was 1.5 m. The thicknesses of these original fabrics (unstretched films) were all prepared at 100 μm.

  In Experiments 11 to 53, when Boeing distortion was evaluated, the same tendency results as in Experiments 1 to 3 could be obtained.

  From the above experiments, it was found that the bowing phenomenon can be minimized in various polymer films according to the present invention.

It is a schematic block diagram of an offline extending | stretching installation. It is a perspective view of a preceding film and a following film. It is sectional drawing of the joining area | region of a preceding film and a succeeding film. It is a schematic block diagram of a tenter part. It is a figure which shows the film after performing a extending | stretching process and a heat relaxation process. It is a schematic block diagram of a heat sealer apparatus. It is a schematic block diagram of an ultrasonic bonding apparatus. It is explanatory drawing which shows the outline | summary of solution casting apparatus. It is explanatory drawing which shows the outline | summary of a fusion | melting film forming facility. It is a perspective view which shows the arrangement | positioning state of the some roll in a heat processing zone. It is explanatory drawing which shows the roll wrap length (D) of a some roll in a heat processing zone, and the length (G) between rolls. It is a figure which shows the conventional film after performing a extending | stretching process and a thermal relaxation process.

Explanation of symbols

2 offline stretching equipment 3 film 3a preceding film 3b trailing film 5 tenter part 6 thermal relaxation chamber 20 double-sided bonding tape 21 bonding area 100 heat sealer 200 ultrasonic bonding apparatus

Claims (2)

A joining step of superposing and joining a rear end portion of a preceding polymer film and a leading end portion of a succeeding polymer film; and while continuously transporting the joined polymer film, heating the polymer film to A stretching process in which both side edges of the polymer film are gripped by a plurality of clips and stretched in the film width direction, and a thermal relaxation process in which heat treatment for stress relaxation is performed while continuously transporting the stretched polymer film. In the stretching method of the polymer film having,
The said joining process joins with the double-sided adhesive tape of only the adhesion layer which does not have a base material, The stretching method of the polymer film characterized by the above-mentioned. In the joining step, the length of the joining region between the preceding polymer film and the succeeding polymer film in the transport direction of the polymer film is set within a range of 0.2% to 2.2% of the film width. The method for stretching a polymer film according to claim 1.

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