JP5819876B2 - Method for producing stretched film - Google Patents

Description

The present invention relates to a method for producing a stretched film in which a film is stretched in the transport direction by a difference in peripheral speed between a pair of rollers.

  In general, the production of a thermoplastic resin film is roughly classified into a solution casting method and a melt casting method. In the solution casting method, a dope in which a thermoplastic resin is dissolved in a solvent is cast from a die onto a support, such as a cooling drum or a drying band, and then peeled to obtain a film. In the melt film-forming method, a thermoplastic resin is melted by an extruder, then extruded from a die onto a support, for example, a cooling drum, and then peeled to form a film.

  Thermoplastic films formed by these methods, for example, cellulose acylate films, are usually stretched in the longitudinal direction (conveying direction) and transverse direction (width direction) to achieve in-plane retardation (Re) and thickness direction. The retardation (Rth) is expressed. Thereby, when using as a phase difference film of a liquid crystal display device, viewing angle expansion can be aimed at (for example, refer to patent documents 1 and patent documents 2).

  When the thermoplastic film is stretched in the longitudinal direction, the thermoplastic film is preheated with a plurality of preheating rollers, and then stretched in the longitudinal direction due to a difference in peripheral speed between the pair of stretching rollers. In this case, there is a problem that the film comes into contact with a plurality of preheating rollers, and the surface of the film is scratched or wrinkled. For this reason, in the method for producing a stretched film of Patent Document 3, the peripheral speeds of the plurality of preheating rollers and the upstream stretch roller are gradually increased toward the downstream based on the temperature change before and after the film contact with each roller. The speed is increased and an appropriate tension is applied between the preheating rollers to suppress the generation of scratches and wrinkles. Specifically, the temperature difference ΔT before and after the film comes into contact with the preheating roller is multiplied by a certain coefficient to obtain the speed increase of the downstream preheating roller relative to the upstream preheating roller. In addition, the time for the film to contact each preheating roller is set in the range of 0.5 seconds to 10 seconds.

Japanese National Patent Publication No. 6-501040 JP 2001-42130 A JP 2008-213332 A

  By the way, recent liquid crystal display devices are required to be lightweight, thin, and high quality, and a film to be used is required to be thin and high quality of, for example, about 25 μm to 100 μm. When such a thin film is produced by longitudinal stretching, there is a limit to the preheating method using a preheating roller as in Patent Document 3, and the film surface may be scratched or wrinkled. There was a need for improvement.

This invention solves such a subject, and it aims at providing the manufacturing method of the stretched film which can respond to thinning of a film and does not generate | occur | produce an abrasion and a wrinkle on a film.

In order to achieve the above object, the method for producing a stretched film of the present invention is a method for producing a stretched film by stretching a film made of a strip-shaped thermoplastic resin having a glass transition temperature of Tg in the transport direction, and preheating. Including a process and a stretching process. The stretching step includes a low speed roller and a high speed roller that are spaced apart from each other in the transport direction, and stretches the film in the transport direction due to a difference in peripheral speed between them. The low speed roller contacts the film and heats the film to a stretching temperature Te of Tg ° C. or higher and (Tg + 20) ° C. or lower. The preheating step is performed before the stretching step. In this preheating step, heated air is supplied into the preheating chamber to preheat the film to (Te-40) ° C. or higher and (Tg-5) ° C. or lower. In the preheating step, the film is stretched over a plurality of free rollers that change the film transport direction, and the free rollers are set to a temperature or diameter that does not cause wrinkles due to thermal expansion due to the contact of the film.

  The high-speed roller preferably cools the film that has passed through the low-speed roller to (Tg-100) ° C. or higher and (Tg-5) ° C. or lower. The film tension in the preheating chamber is preferably 20 N / m or more and 200 N / m or less.

  The preheating chamber is divided into a plurality of preheating zones in the conveying direction, the preheating temperature is increased from the upstream side to the downstream side of each divided preheating zone, and the temperature difference between the adjacent downstream preheating zone and the upstream preheating zone is increased. Is preferably 50 ° C. or lower.

Free rollers are divided into a plurality of groups in the conveyance direction, the free rollers for each group, it is preferable that the temperature from the upstream side toward the downstream side is raised gradually.

  It is preferable that the temperature difference between the conveyance direction changing members between the adjacent downstream group and the upstream group is 50 ° C. or less.

  According to the present invention, before the stretching process, when the glass transition temperature of the film is Tg and the stretching temperature of the film is Te (Te is Tg ° C. or more (Tg + 20) ° C. or less), the heating air is supplied into the preheating chamber. By supplying and preheating the film to (Te-40) ° C. or higher and (Tg-5) ° C. or lower, the film is expanded on the preheating roller, unlike the conventional method in which the film is heated by contacting the preheating roller. The generation of corrugated wrinkles due to the phenomenon is eliminated.

It is a side view which shows the outline | summary of an example of the film extending equipment which enforces the manufacturing method of the stretched film of this invention. It is a side view which shows the outline | summary of an example of the film extending | stretching equipment of another embodiment which divided the preheating chamber into plurality. It is a side view which shows the outline | summary of the preheating chamber of another embodiment which adjusts the temperature of the free roller in a preheating chamber. It is a side view which shows the outline | summary of the preheating chamber of another embodiment using a turn bar. It is a graph which shows the appropriate range of extending | stretching temperature Te and preheating temperature Tp.

As shown in FIG. 1, the film stretching equipment 10 includes a preheating unit 11 and a longitudinal stretching unit 12. A pre-process device 13 is connected to the film stretching facility 10 on the inlet side, and a post-process device 14 is connected on the outlet side. Examples of the pre-process device 13 include a film forming facility and a film delivery device (not shown). As the film forming facility, a well-known solution film forming facility, a melt film forming facility, or the like is used. Unlike the case where the film 15 is directly sent from the film forming facility, the film delivery apparatus pulls out the film 15 from the roll film wound up in a roll shape after the film formation and supplies the film 15. Examples of the post-process device 14 include a clip tenter and a film winding device that are used in the case of lateral stretching after longitudinal stretching. When the transverse stretching is not performed continuously following the longitudinal stretching, the clip tenter is omitted, and the film 15 is wound in a roll shape by the film winding device.

  The film 15 to be stretched may be a thermoplastic resin film. For example, a film 15 made of cellulose acylate, norbornene-based resin, acrylic, or polycarbonate that is suitable for use in an optical film such as a retardation film is preferable.

  A tension adjusting unit 16 is provided between the pre-process device 13 and the film stretching equipment 10. The tension adjusting unit 16 moves the tension roller 18 between the free rollers 17a and 17b up and down by a shift mechanism 19 to maintain the tension of the film 15 in the preheating unit 11 constant. The film tension in the preheating part 11 is preferably 20 N / m or more and 200 N / m or less. If it is 20 N / m or more, rotation failure of the free roller 25 does not occur, and generation of scratches on the film 15 is suppressed. Further, when it is 200 N / m or less, no longitudinal stretching occurs in the preheating section 11, and proper longitudinal stretching is performed in the longitudinal stretching section 12.

  The preheating unit 11 includes a preheating chamber 20. A plurality of free rollers (conveying direction changing members) 25 are arranged in the preheating chamber 20 so as to be separated in the vertical direction. By alternately winding the film 15 between the free rollers 25, the film 15 is conveyed in the vertical direction between the rollers 25, and the film path (path) in the preheating chamber 20 is set long.

  The film path length of the preheating chamber 20 depends on the preheating temperature Tp and the transport speed of the film 15, but is preferably 5 m or more and 50 m or less, for example. The free roller 25 has a diameter of, for example, 80 mm, and a contact area between the film 15 and the free roller 25 by winding the film 15 is reduced. The diameter of the free roller 25 is preferably 40 mm or greater and 150 mm or less. If it is 40 mm or more, the free roller 25 will not be bent, and the occurrence of uneven rotation and scratches due to the bending can be suppressed. Moreover, when it is 150 mm or less, the contact time with the free roller 25 falls within an appropriate range, and wrinkles are suppressed. In addition, the occurrence of scratches on the film due to rotation failure of the free roller 25 can be suppressed. It is preferable that the outer peripheral surface of the free roller 25 is hard chrome plated. By applying the hard chrome plating, the adhesion with the film 15 is improved, and the film 15 is difficult to slip.

  In the preheating unit 11, for example, an air supply nozzle 31 is disposed on the upper side, and an exhaust nozzle 32 is disposed on the lower side. A blower 34 and a temperature controller 35 are connected to the air supply nozzle 31 and the exhaust nozzle 32 via a duct 33. The temperature controller 35 heats the heating medium, for example, air to a desired temperature. The blower 34 sends air, the temperature of which has been adjusted by the temperature controller 35, to the air supply nozzle 31 through the duct 33. Heated air is sent out from the air supply nozzle 31, and the film 15 in the preheating unit 11 is preheated to a constant temperature by the heating air 36. The heating air 36 circulates from the side of the film 15 in the preheating chamber 20 and preheats the entire upper and lower surfaces of the film 15.

  The preheating temperature Tp by the heating air 36 needs to be lower than the temperature (stretching temperature) Te that enables stretching. Therefore, when the glass transition temperature of the film 15 is set to Tg, the heating air 36 is supplied into the preheating unit 11 to preheat the film 15 to (Te-40) ° C. or higher and (Tg-5) ° C. or lower. The stretching temperature Te is Tg ° C. or higher and (Tg + 20) ° C. or lower. The blowing speed of the heated air from the air supply nozzle 31 is preferably 2 m / sec or more and 15 m / sec or less. When it is 2 m / sec or more, the temperature of the preheating chamber 20 can be kept uniform, and the occurrence of stretching unevenness is eliminated. Further, when it is 15 m / sec or less, the generation of scratches due to flapping of the film 15 is eliminated.

  The film 15 preheated to a constant temperature through the preheating unit 11 is sent to the longitudinal stretching unit 12. The longitudinal stretching unit 12 includes a low speed roller pair 41, a high speed roller pair 42, and a cooling roller 43. The low speed roller pair 41 includes a low speed roller 41a and a nip roller 41b. The high speed roller pair 42 includes a high speed roller 42a and a nip roller 42b. The low-speed roller 41a, the high-speed roller 42a, and the cooling roller 43 are individually supplied with a temperature control medium such as oil or pressurized steam from the temperature control medium circulation unit. Each roller 41a, 42a, 43 is set to a desired surface temperature by circulating supply of the temperature control medium. For example, the temperature of the low speed roller 41a is Tg ° C. or more and (Tg + 20) ° C. or less, the temperature of the high speed roller 42a is (Tg−100) ° C. or more and (Tg−5) ° C. or less, and the temperature of the cooling roller 43 is 20 ° C. Above (Tg-100) ° C. When the film 15 comes into contact with these rollers 41a, 42a, 43, the film 15 is heated or cooled to the same temperature as the surface temperature of the rollers 41a, 42a, 43.

  Although not shown in the drawings, each of the rollers 41a, 42a, 43 is connected to a motor, and can rotate at a desired rotation speed. The film 15 is stretched in the transport direction and longitudinally stretched by the difference in peripheral speed between the low speed roller 41a and the high speed roller 42a. The peripheral speed difference between the low speed roller 41a and the high speed roller 42a is appropriately changed depending on the draw ratio, and the peripheral speed of the low speed roller 41a is preferably set in the range of 20 m / min to 80 m / min. By making it 20 m / min or more, the production efficiency is not lowered. Moreover, by setting it as 80 m / min or less, the contact time of the film 15 and the low speed roller 41a is ensured, and it can heat reliably.

  When performing longitudinal stretching, the longitudinal stretching ratio is preferably in the range of 1.0 to 1.5. When the longitudinal draw ratio is in the range of more than 1.0 and 1.5 or less, it is possible to suppress the occurrence of thickness unevenness, and to suppress the variation of the retardation that appears.

  By preheating the film 15 to (Te−40) ° C. or higher in the preheating unit 11, the amount of increase in temperature during heating of the film 15 by the low speed roller 41 a of the longitudinal stretching unit 12 does not become excessively large, and the speed is low. The generation of corrugated wrinkles on the roller 41a is suppressed. In addition, by preheating the film 15 to (Tg-5) ° C. or less in the preheating portion 11, the film 15 is not stretched in the preheating portion 11 and can be uniformly stretched in the longitudinal stretching portion 12. .

  The film 15 stretched in the longitudinal stretching section 12 is wound on a film roll by, for example, a film winder of the post-process device 14.

  In this embodiment, since the heating air 36 is sent into the preheating chamber 20 and heated by the heating air 36, unlike the heating by the heat conduction by the conventional preheating roller, the film 15 is thermally expanded on the preheating roller to be corrugated. The occurrence of wrinkles and scratches can be suppressed. In particular, the occurrence of wrinkles and scratches can be suppressed for a thin film having a thickness before stretching of the film 15 of 25 μm to 100 μm, preferably 25 μm to 60 μm.

  If one preheating chamber 20 is preheated at the same temperature, the temperature of the free roller 25 can be close to the room temperature of the preheating chamber 50. For this reason, since the film 15 entering the preheating chamber 50 contacts the free roller 25 on the inlet side raised to the outlet temperature of the preheating chamber 50, the film 15 is thermally expanded and the corrugated plate repeats unevenness in the film width direction. There is concern that it will be wrinkled. In order to prevent this, the diameter of the free roller 25 is made as thin as possible and the wrap angle is also made small in order to suppress the heating by the heat transfer of the free roller 25. Therefore, when the film transport speed is 40 m / min, the diameter of the free roller 25 is set to 40 mm or more and 150 mm or less, and even if the free roller 25 heated by the heating air 36 contacts the film 15, the film expands thermally. Avoid deformation. Actually, the free roller 25 is at a temperature lower than the temperature in the preheating chamber 20 due to the contact with the continuously fed film 15 (which is lower than the temperature of the preheating chamber 20). Therefore, thermal deformation may not occur due to film contact with the free roller 25.

  In the above embodiment, the film 15 is heated in one preheating chamber 20, but as shown in FIG. 2, preheating regions 50 a to 50 c in which the preheating chamber 50 is divided into a plurality of portions in the film conveyance direction by the partition walls 49. The preheating unit 51 may be used. In addition, the same code | symbol is attached | subjected to the same structural member as the said embodiment. In the case of the second embodiment, an air supply nozzle 31, an exhaust nozzle 32, a duct 33, a blower 34, and a temperature controller 35 are provided in each preheating area 50a to 50c, and the temperature in each preheating area 50a to 50c. Is set to gradually increase in the film transport direction. The temperature difference between the adjacent preheating chambers 20 is, for example, 20 ° C. or more and 50 ° C. or less. When this temperature difference is 20 ° C. or more, the number of sections can be reduced to an appropriate range, and the equipment efficiency is improved. Moreover, in the case of 50 degrees C or less, the temperature nonuniformity by the exchange of air does not generate | occur | produce between adjacent preheating areas, and it does not become a stretching nonuniformity.

  The number of sections in each preheating area 50a-50c increases or decreases according to the preheating temperature Tp. For example, when one preheating chamber 50 is preheated at the same temperature, the film 15 entering the preheating chamber 50 comes into contact with the free roller 25 on the inlet side raised to the outlet temperature of the preheating chamber 50, so that the film 15 is thermally expanded. However, there is a concern that wrinkled wrinkles that are repeatedly uneven in the film width direction. In order to prevent this, the preheating temperature Tp of each of the preheating regions 50a to 50c is set to be small enough that the free roller 25 heated by the heating air 36 does not expand and deform even if it contacts the film 15. And it preheats in steps to the temperature which can be longitudinally stretched by the some preheating area 50a-50c.

  Further, instead of dividing the preheating chamber 50 into a plurality of parts, in one preheating chamber 60 as shown in FIG. 3, a temperature adjusting medium is supplied to each free roller 61 by the temperature adjusting mechanisms 62a to 62c. It is good also as the pre-heating part 63 which adjusts the surface temperature of 61 for every group. In this case, the surface temperature of the free roller 61 is increased for each group in order from the entrance side. The surface temperature of each free roller 61 is set to a temperature at which the film 15 contacts and does not generate corrugated wrinkles due to thermal expansion. The temperature adjustment may be performed for each free roller 61 as well as for each group. Furthermore, the temperature of the free roller 25 in the preheating chamber 50 partitioned as shown in FIG. The difference in temperature between the adjacent downstream group and the free roller 61 in the upstream group is 50 ° C. or less, and the temperature of the free roller 61 in the most upstream group is in the range of + 20 ° C. to 50 ° C. with respect to the outside room temperature of the preheating chamber 50. It is.

  In each of the above-described embodiments, the free roller 25, 61 is used to set the film path length in the preheating chamber 20, 50, 60 to be long, but instead of the free roller 25, 61, as shown in FIG. Alternatively, the preheating unit 71 using the turn bar 70 may be used. In this case, the blower 72 and the temperature controller 73 are connected to the turn bar 70 and the floating air is supplied to the turn bar 70. The floating air may be set to be the same as or lower than the preheating temperature Tp of the preheating chamber 74. 3 and 4, the preheating chambers 60 and 74 include the blower 34 and the temperature controller 35 as shown in FIG. 1, but are not shown. Similarly to the embodiment of FIG. 2, the preheating chambers 60 and 74 are divided into a plurality of sections, and a blower 34 and a temperature controller 35 are provided for each of the preheating chambers, and a preheating temperature Tp is set for each preheating chamber. The preheating temperature Tp may be gradually increased from the inlet side toward the outlet side. Further, similarly to the free roller 61 of the embodiment of FIG. 3, the temperature of the floating air from each turn bar 70 is changed individually for each turn bar 70 or for each group, and from the entrance to the exit of the preheating chamber 74, It may be gradually increased.

  In the above-described embodiment, the low-speed roller pair 41 and the high-speed roller pair 42 are used as the longitudinally extending portion 12. However, not only the nip method but also a high holding force roller such as a grooved processing roll may be used for the low-speed roller and the high-speed roller. Good. The longitudinal stretching unit 12 is a single-stage longitudinal stretching of the upstream low-speed roller pair 41 and the downstream high-speed roller pair 42, but may be a multi-stage longitudinal stretching.

  As the film 15, a cellulose acylate film having a thickness of 55 μm, a width of 600 mm, and a Tg of 145 ° C. was used, and preheating, longitudinal stretching, and cooling were performed. In the longitudinal stretching section 12, one-stage longitudinal stretching was performed by the upstream low-speed roller pair 41 and the downstream high-speed roller pair 42. A film delivery machine was used as the pre-process device 13 and the film 15 was pulled out from the film roll and sent to the preheating unit 11. A film winder was used as the post-process equipment 14 to wind up the film 15 to form a film roll. In the preheating unit 11, a free roller 25 having a diameter of 60 mm is arranged in the preheating chamber 20, and the film 15 is stretched over them to set the film path length in the preheating chamber 20 to 20 m. Then, preheating was performed by supplying heating air 36 so as to obtain a desired film temperature. The stretching ratio is 1.3 times, the stretching length Le (see FIG. 1) is 300 mm, the cooling temperature is 100 ° C., the film conveyance speed is 40 m / min, and as shown in Table 1, the preheating temperature Tp and the stretching temperature Te The experiment 1 to the experiment 17 were performed by changing the above. In Experiments 1 to 16, preheating was performed by supplying heated air using a heating chamber, and in Experiment 17, preheating was performed by contacting with a preheating roller.

  The resulting stretched film was evaluated for scratches, wrinkles, and stretch unevenness. The scratches were observed with a microscope, and the wrinkles were visually observed. Excellent A when there were no scratches or wrinkles, good B when there were scratches or wrinkles but acceptable, and no C when unacceptable scratches or wrinkles. Stretch unevenness is determined to be excellent A when the difference between the maximum thickness and the minimum thickness in the longitudinal direction of a sample piece having a length of 5 m is 3 μm or less, and acceptable B when exceeding 3 μm and 5 μm or less, and exceeding 5 μm. It was sometimes impossible C. According to the experimental results, in Experiments 1 to 16 in which preheating with heating air was performed, if the preheating temperature Tp was less than (stretching temperature Te-40) ° C. and (Tg-5) ° C., scratches, wrinkles, stretching unevenness From any of the evaluations, it was found that there was Impossible C. Therefore, it was found that the range of (Te-40) ° C. to (Tg-5) ° C. is appropriate for the preheating temperature Tp. Moreover, about extending | stretching temperature Te, when it was less than Tg and exceeded (Tg + 20) degreeC, it turned out that there is an unsatisfactory C by any evaluation of an abrasion, a wrinkle, and an extending | stretching nonuniformity. Therefore, it was found that the range of Tg ° C. or higher and (Tg + 20) ° C. or lower was appropriate for the stretching temperature Te. Further, in Experiment 17 in which the film was brought into contact with the preheating roller and preheating was performed, there was no stretching unevenness, but the evaluation was impossible C due to scratches and wrinkles.

  FIG. 5 is a graph of the appropriate range, and the hatched area is the appropriate condition range of the present invention. Thus, in order to perform uniform stretching, the stretching temperature Te needs to be Tg ° C. or more and (Tg + 20) ° C. or less, and the preheating temperature Tp needs to be (Tg−5) ° C. or less. I understand. It can also be seen that the preheating temperature Tp needs to be (Te-40) ° C. or higher in order not to cause wrinkles and scratches.

DESCRIPTION OF SYMBOLS 10 Film extending | stretching equipment 11, 51, 63, 71 Preheating part 12 Longitudinal extending part 15 Film 16 Tension adjusting part 20, 50, 60, 72 Preheating room 25, 61 Free roller 31 Air supply nozzle 32 Exhaust nozzle 33 Duct 34 Blower 35 Temperature Controller 41 Low-speed roller pair 41a Low-speed roller 41b, 42b Nip roller 42 High-speed roller pair 42a High-speed roller 43 Cooling rollers 50a, 50b, 50c Preheating zone 70 Turn bar

Claims (6)

In the method of producing a stretched film by stretching a film made of a strip-shaped thermoplastic resin having a glass transition temperature of Tg in the transport direction,
A low-speed roller that is spaced apart in the transport direction, contacts the film and heats the film to a stretching temperature Te of Tg ° C. or higher and (Tg + 20) ° C. or lower, and a high-speed roller having a peripheral speed difference with respect to the low-speed roller. A stretching step of stretching the film in the transport direction;
Before the stretching step, including a preheating step of supplying heating air into a preheating chamber to preheat the film to (Te-40) ° C. or higher and (Tg-5) ° C. or lower.
In the preheating step, the film is stretched around a plurality of free rollers that change the film conveyance direction, and the free rollers are set to a temperature or diameter that does not cause wrinkles due to thermal expansion due to the contact of the film. A method for producing a stretched film.   The manufacturing method of the stretched film of Claim 1 which cools the film which passed through the said low speed roller to (Tg-100) degreeC or more and (Tg-5) degreeC or less with the said high speed roller.   The method for producing a stretched film according to claim 1 or 2, wherein the tension of the film in the preheating chamber is 20 N / m or more and 200 N / m or less. The preheating chamber is partitioned into a plurality of preheating areas in the transport direction,
The preheating temperature is increased from the upstream side to the downstream side of each divided preheating region, and the temperature difference between the adjacent downstream preheating region and the upstream preheating region is 50 ° C or less. The manufacturing method of the stretched film of description.   5. The stretched film according to claim 1, wherein the free roller is divided into a plurality of groups in the transport direction, and the temperature of the free roller is gradually increased from the upstream side toward the downstream side for each group. Manufacturing method.   The method for producing a stretched film according to claim 5, wherein a temperature difference between the conveyance direction changing members of the adjacent downstream group and the upstream group is 50 ° C. or less.

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