TW201436996A - Stretched film production method and film stretching apparatus - Google Patents

Abstract

An object of the present invention is to provide a stretched film production method and a film stretching apparatus for stretching a film in a transporting direction thereof without generating scratches and corrugated wrinkles on the film. A film is stretched in a transporting direction thereof by utilizing circumferential velocity difference between a low-speed roller pair and a high-speed roller pair. The film before being stretched is preheated by heated air blown thereto in a preheating chamber. According to the present invention, since the film is heated by the heated air, corrugated wrinkles due to thermal expansion are not generated on the film, in comparison with a conventional case where a film is directly heated by conduction of heat from a preheating roller. Since wrinkles are not generated, it is possible to prevent generation of scratches on the film.

Description

Method for producing stretched film and film stretching device

The present invention relates to a method for producing a stretched film which stretches a film in a conveying direction by a circumferential speed difference of a pair of rolls, and a film stretching apparatus.

Generally, a method for producing a thermoplastic resin film is roughly classified into a solution film forming method and a melt film forming method. In the solution film forming method, a dope in which a thermoplastic resin is dissolved in a solvent is cast from a mold onto a support such as a cooling drum or a drying belt, and then peeled off to obtain a thermoplastic resin. Further, the melt film forming method melts the thermoplastic resin by an extruder, and then extrudes it from a mold onto a support such as a cooling roll, and then peels it off as a thermoplastic resin.

A thermoplastic resin film, such as a cellulose oxime film, which is formed by the above-mentioned methods, is described in, for example, Japanese Patent Publication No. Hei 6-501040, Japanese Patent Publication No. 2001-42130, which is generally in the longitudinal direction (transport direction) and the lateral direction ( Stretching in the width direction, thereby exhibiting an in-plane retardation (Re) and a thickness direction retardation (Rth). Thereby, when used as a retardation film of a liquid crystal display device, the viewing angle can be enlarged.

When the thermoplastic resin film is longitudinally stretched, the thermoplastic resin film is preheated by a plurality of preheating rolls, and then longitudinally stretched by a peripheral speed difference of a pair of stretching rolls. At this time, the thermoplastic resin film is in contact with a plurality of preheating rolls, so that there is a problem that the surface of the film is scratched or wrinkled. Therefore, in the method for producing a stretched film of Japanese Laid-Open Patent Publication No. 2008-213332, the peripheral speeds of the plurality of preheating rolls and the stretching rolls are made to face downstream depending on the temperature change before and after the thermoplastic resin film contacts the respective rolls. Gradually accelerated, and appropriate tension is applied between the preheating rolls to suppress the generation of scratches and wrinkles. Specifically, the temperature difference ΔT before and after the thermoplastic resin film is brought into contact with the preheating roll is multiplied by a constant coefficient to determine the amount of increase in the preheating roll on the downstream side with respect to the preheating roll on the upstream side. Further, the time during which the thermoplastic resin film is brought into contact with each of the preheating rolls is set to be in the range of 0.5 second or more and 10 or less.

However, in recent years, the liquid crystal display device has been increasingly required to be lighter, thinner, and higher in quality, and a high-quality film having a thickness of, for example, about 25 μm to 100 μm is required for the thermoplastic resin film to be used. When the thin thermoplastic resin film is produced by longitudinal stretching, there is a limitation in the method of preheating by a preheating roll as disclosed in Japanese Patent Laid-Open Publication No. 2008-213332, which causes scratching or generation on the surface of the film. Wrinkles, so it is required to improve it.

An object of the present invention is to provide a method and a film stretching apparatus for a stretched film which can correspond to a reduction in thickness of a thermoplastic resin film and which does not cause scratches or wrinkles on a thermoplastic resin film.

The method for producing a stretched film of the present invention comprises a stretching step (step A) and a preheating step (step B), and stretching a strip-shaped film made of a thermoplastic resin having a glass transition temperature of Tg in a transport direction to produce an extruded film. film. In the step A, the film is stretched in the conveying direction by a low speed roller which is disposed separately in the conveying direction and a high speed roller which is rotated at a peripheral speed higher than the low speed roller. The low speed roll is in contact with the film to heat the film to a stretching temperature Te in the range of Tg ° C or more (Tg + 20) ° C or less. In the step B, the heating air is supplied to the inside of the preheating chamber before the step A to preheat the film to a range of (Te - 40) ° C or more (Tg - 5) ° C or less.

It is preferred to cool the film passing through the low speed roll to a range of (Tg - 100) ° C or more (Tg - 5) ° C or less by a high speed roller.

The tension of the film in the preheating chamber is preferably in the range of 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, and the preheating temperature rises from the upstream side divided into a plurality of preheating zones toward the downstream side, and the adjacent downstream side preheating zone and the upstream side preheating zone The temperature difference is preferably 50 ° C or less.

Preferably, the film in step B is wound around a plurality of conveying direction changing members that change the conveying direction.

It is preferable that the conveying direction changing member is a free roller or a steering lever.

The conveying direction changing member is divided into a plurality of groups in the conveying direction, and the temperature is gradually increased from the upstream side of each group to the downstream side.

It is preferable that the temperature difference of the conveyance direction changing member of the group on the downstream side and the group on the upstream side is 50 ° C or less.

The film stretching apparatus of the present invention comprises a longitudinal stretching portion, a low-speed roller, a high-speed roller, and a preheating portion, and is stretched by stretching a strip-shaped film made of a thermoplastic resin having a glass transition temperature of Tg in a conveying direction. film. The longitudinal stretching portion stretches the film in the conveying direction. The low speed roller is present in the longitudinal stretching portion, and the film is heated to a stretching temperature Te of Tg ° C or more (Tg + 20) ° C or less by contact with the film. The high speed roller is rotated at a peripheral speed higher than the low speed roller to stretch the film in the conveying direction. The high speed roller is disposed in the longitudinal stretching portion separately from the low speed roller in the conveying direction. The preheating section supplies a heating wind to the inside of the preheating chamber to preheat the film to (Te - 40) ° C or more (Tg - 5) ° C or less. The preheating portion is disposed upstream of the longitudinal stretching portion.

Unlike the conventional method of heating a thermoplastic resin film by contact with a preheating roll, according to the present invention, it does not cause scratches or corrugated plate-like wrinkles due to film expansion on the preheating roll, and can be combined with a thermoplastic resin film. Corresponding to thin walling.

10‧‧‧film stretching equipment

11, 51, 63, 71‧ ‧ preheating department

12‧‧‧ longitudinal stretching

13‧‧‧Pre-process equipment

14‧‧‧ late process equipment

15‧‧‧film

16‧‧‧Tensile adjustment department

17a, 17b‧‧‧ free roll

18‧‧‧ Tension roller

19‧‧‧displacement mechanism

20, 50, 60, 74‧‧‧ preheating room

25, 61‧‧‧ free roll

31‧‧‧Air supply nozzle

32‧‧‧Exhaust nozzle

33‧‧‧ catheter

34, 72‧‧‧ blower

35, 73‧‧‧temperature regulator

36‧‧‧heating wind

41‧‧‧Low speed roller set

41a‧‧‧low speed roller

41b, 42b‧‧‧ pinch roller

42‧‧‧High speed roller set

42a‧‧‧High speed roller

43‧‧‧Cooling roller

49‧‧‧Baffle

50a, 50b, 50c‧‧‧ preheating area

62a, 62b, 62c‧ ‧ tempering mechanism

70‧‧‧ steering rod

Fig. 1 is a schematic side view showing an example of a film stretching apparatus of the present invention.

Fig. 2 is a schematic side view showing an example of a film stretching apparatus in which a plurality of preheating chambers are divided into a plurality of embodiments.

Fig. 3 is a schematic side view showing a preheating chamber of another embodiment for adjusting the temperature of the free roller in the preheating chamber.

Fig. 4 is a schematic side view showing a preheating chamber of another embodiment using a steering column.

Fig. 5 is a graph showing an appropriate range of the stretching temperature Te and the preheating temperature Tp.

As shown in FIG. 1, the film stretching apparatus 10 of the present invention includes a preheating portion 11 and a longitudinal stretching portion 12. The front side of the film stretching apparatus 10 is connected to the front process unit 13, and the outlet side is connected to the post-process apparatus 14. As the pre-processing apparatus 13, there are a film forming apparatus (not shown), a film feeding apparatus, and the like. A well-known solution film forming apparatus, a melt film forming apparatus, etc. are used as a film forming apparatus. When the film 15 is directly fed out from the film forming apparatus, the film feeding device winds up the roll film roll pulling film 15 from the film forming film to supply the film 15. As the post-process apparatus 14, there are a clip tenter and a film take-up apparatus which are used for the transverse stretching after the longitudinal stretching. Immediately after the longitudinal stretching, the clip tenter is omitted, and the film 15 is taken up in a roll shape by the film winding device.

The stretched film 15 is preferably a thermoplastic resin film. For example, a cellulose halide or a norbornene resin, an acrylic or polycarbonate film 15 suitable for use in an optical film such as a retardation film is preferable.

A tension adjusting portion 16 is provided between the preliminary processing device 13 and the film stretching device 10. The tension adjusting unit 16 raises and lowers the tension roller 18 between the free roller 17a and the free roller 17b by the displacement mechanism 19 to constantly maintain the tension of the film 15 in the preheating portion 11. The film tension in the preheating portion 11 is preferably in the range of 20 N/m or more and 200 N/m or less. When it is 20 N/m or more, the rotation failure of the free roller 25 does not occur, and the scratch on the film 15 is suppressed. In addition, when it is 200 N/m or less, longitudinal stretching does not occur in the preheating portion 11, and appropriate longitudinal stretching is performed on the longitudinally stretched portion 12. Further, the film tension (unit: N/m) is a tension per unit width (unit: N).

The preheating unit 11 includes a preheating chamber 20. A plurality of free rollers (transport direction changing members) 25 are disposed apart from each other in the vertical direction in the preheating chamber 20. The film 15 is alternately wound around the free rolls 25, whereby the film 15 is transported in the upward direction between the rolls 25, and the film path (channel) in the preheating chamber 20 is set longer.

The length of the film passage of the preheating chamber 20 is also dependent on the preheating temperature Tp and the conveying speed of the film 15, but it is preferably in the range of, for example, 5 m or more and 50 m or less. The free roller 25, for example, has a diameter of 80 mm, and the contact area between the film 15 and the free roller 25 becomes small due to the winding of the film 15. The diameter of the free roller 25 is preferably in the range of 40 mm or more and 150 mm or less. If it is 40 mm or more, the deflection does not occur on the free roller 25, and the unevenness of rotation due to the deflection and the flaw are suppressed. In addition, when it is 150 mm or less, the contact time with the free roller 25 is in an appropriate range, and in addition to the wrinkles being suppressed, the scratch of the film by the rotation failure of the free roller 25 is also suppressed. It is preferable that the outer peripheral surface of the free roller 25 is plated with hard chrome. By performing hard chrome plating, the adhesion to the film 15 is improved, and the film 15 becomes less slippery.

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 regulator 35 are connected to the air supply nozzle 31 and the exhaust nozzle 32 via a duct 33. The temperature regulator 35 heats, for example, air as a heating medium to a desired temperature. The blower 34 sends air whose temperature is adjusted by the temperature adjuster 35 to the air supply nozzle 31 via the duct 33. The heated air is sent from the air supply nozzle 31, and the film 15 in the preheating portion 11 is preheated to a constant temperature by the heated air 36. The heated air 36 is from the side of the film 15 in the preheating chamber 20. The winding is started and the entire upper surface and the lower surface of the film 15 are preheated.

It is necessary to set the preheating temperature Tp preheated by the heating air 36 to a temperature lower than the temperature (stretching temperature) Te which can be stretched. Therefore, when the glass transition temperature of the film 15 is Tg, the heating air 36 is supplied to the inside of the preheating section 11 to preheat the film 15 to a range of (Te - 40) ° C or more (Tg - 5) ° C or less. a certain temperature. The stretching temperature Te is in the range of Tg ° C or more (Tg + 20) ° C or less. Further, the speed of the heated air blown from the air supply nozzle 31 is preferably in the range of 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 uniformly maintained, and stretching unevenness does not occur. Further, if it is 15 m/sce or less, scratching due to the swing of the film 15 does not occur.

The film 15 preheated to a certain temperature by the preheating portion 11 is sent to the longitudinal stretching portion 12. The longitudinal stretching portion 12 includes a low speed roller group 41, a high speed roller group 42, and a cooling roller 43. The low speed roller group 41 has a low speed roller 41a and a nip roller 41b. The high speed roller set 42 has a high speed roller 42a and a nip roller 42b. A temperature control medium such as oil and pressurized steam is supplied from the temperature control medium circulation portion to the low speed roller 41a, the high speed roller 42a, and the cooling roller 43, respectively. The low speed roller 41a, the high speed roller 42a, and the cooling roller 43 are set to a desired surface temperature by the cyclic supply of the temperature control medium. For example, the temperature of the low speed roller 41a is in the range of Tg ° C or more (Tg + 20) ° C or less, and the temperature of the high speed roller 42 a is in the range of (Tg - 100) ° C or more (Tg - 5) ° C or less, and the temperature of the cooling roller 43 is set. It is in the range of 20 ° C or more (Tg - 100) ° C or less. The film 15 is in contact with the low speed rolls 41a, the high speed rolls 42a, and the cooling rolls 43, whereby the film 15 is heated or cooled to the same temperature as the surface temperatures of the low speed rolls 41a, the high speed rolls 42a, and the cooling rolls 43.

Although not shown in the drawings, a motor is connected to each of the low speed roller 41a, the high speed roller 42a, and the cooling roller 43, and is rotatable at a desired number of revolutions. Further, the film 15 is elongated in the conveying direction by the difference in circumferential speed between the low speed roller 41a and the high speed roller 42a, and is longitudinally stretched. The "low speed" and "high speed" of the low speed roller 41a and the high speed roller 42a mean that the speed is relatively low and relatively high, respectively. That is, the peripheral speed of the high speed roller 42a is higher than the peripheral speed of the low speed roller 41a. The circumferential speed difference between the low speed roller 41a and the high speed roller 42a is appropriately changed depending on the longitudinal stretching magnification, and it is preferable to set the peripheral speed of the low speed roller 41a to, for example, 20 m/min or more and 80 m/min or less. By setting it to 20 m/min or more, the manufacturing efficiency is not reduced. Further, by setting it to 80 m/min or less, the contact time between the film 15 and the low speed roller 41a can be ensured, and heating can be reliably performed.

When longitudinally stretching, the longitudinal stretching ratio is greater than 1.0 and less than or equal to 1.5 The range is preferred. When the longitudinal stretching ratio is in the range of more than 1.0 and less than or equal to 1.5 or less, thickness unevenness can be suppressed, and variation in the retardation which appears can be suppressed.

In the preheating portion 11, by preheating the film 15 to (Te - 40) ° C or higher, the amount of temperature rise when the film 15 is heated by the low speed roller 41a of the longitudinal stretching portion 12 is not excessively increased, and The generation of corrugated plate wrinkles on the low speed roller 41a is suppressed. Further, in the preheating portion 11, the film 15 is preheated to (Tg - 5) ° C or lower, and the film 15 can be stretched in the longitudinal stretching portion 12 without stretching the film 15 in the preheating portion 11.

The film 15 which is longitudinally stretched in the longitudinal stretching portion 12 is taken up by a film winding machine of the post-processing apparatus 14 into a film roll.

In the present embodiment, since the heating air 36 is sent to the preheating chamber 20 and heated by the heating air 36, it is different from the conventional heat by the preheating roller, and the film 15 is not preheated. The roller is corrugated due to thermal expansion, and generation of wrinkles and scratches is suppressed. In particular, it is preferable that the wrinkles and scratches of the film are suppressed, that is, the thickness of the film 15 before stretching is in the range of 25 μm or more and 100 μm or less, and is in the range of 25 μm or more and 60 μm or less.

Further, if one preheating chamber 20 is preheated at the same temperature, the temperature of the free roller 25 can also become a temperature close to the room temperature of the preheating chamber 50. Therefore, the film 15 that has entered the preheating chamber 50 is in contact with the free roller 25 that is raised to the inlet side of the outlet temperature of the preheating chamber 50, so that the film 15 may be thermally expanded to become a corrugated plate shape in which the unevenness is repeated in the film width direction. The phenomenon of wrinkles. In order to prevent this, it is necessary to suppress the heating by the heat conduction of the free roller 25, to reduce the diameter of the free roller 25 as much as possible, and to reduce the wrap angle. Therefore, when the film transport speed is 40 m/min, the diameter of the free roller 25 is set in the range of 40 mm or more and 150 mm or less, so that even if the free roller 25 heated by the heated wind 36 contacts the film 15, it does not cause deformation due to thermal expansion. . Actually, sometimes the temperature of the free roller 25 becomes lower than the temperature in the preheating chamber 20 by contact with the continuously fed film 15 (the temperature is lower than the temperature of the preheating chamber 20), so that no cause is caused. The film is in contact with the free roller 25 to cause thermal deformation.

In the above embodiment, the film 15 is heated by one preheating chamber 20. However, as shown in Fig. 2, the preheating chamber 50 may be divided into a plurality of preheating directions in the film conveying direction by the partition plate 49. The preheating sections 51 of the regions 50a to 50c are heated. In FIG. 2, the same components as those of the above-described embodiment are denoted by the same reference numerals. In the second embodiment, An air supply nozzle 31, an exhaust nozzle 32, a duct 33, a blower 34, and a temperature regulator 35 are provided in each of the preheating zones 50a to 50c, and the temperatures in the respective preheating zones 50a to 50c are set to gradually increase in the film conveying direction. Raise. The temperature difference between the adjacent preheating zones 50a to 50c is, for example, in the range of 20 ° C or more and 50 ° C or less. When the temperature difference is 20 ° C or more, the number of divisions can be reduced to an appropriate range to improve equipment efficiency. Further, when the temperature is 50 ° C or less, temperature unevenness due to exchange of air is not generated between the adjacent preheating regions 50a to 50c, and stretching unevenness does not occur.

The number of divisions of each of the preheating zones 50a to 50c is increased or decreased according to the preheating temperature Tp. For example, if one preheating chamber 50 is preheated at the same temperature, the film 15 that has entered the preheating chamber 50 will come into contact with the free roller 25 that is raised to the inlet side of the outlet temperature of the preheating chamber 50, so that it is possible There is a phenomenon in which the film 15 is thermally expanded to form corrugated plate-like wrinkles which are irregular in the width direction of the film. In order to prevent this, the preheating temperature Tp of each of the preheating zones 50a to 50c is set to be small, so that even if the free roller 25 heated by the heating wind 36 comes into contact with the film 15, the degree of deformation due to thermal expansion does not occur. Further, the preheating is performed stepwise until the temperature in which the longitudinal stretching can be performed by the plurality of preheating zones 50a to 50c.

Further, instead of dividing the preheating chamber 50 into a plurality of portions, the preheating portion 63 of Fig. 3 may be employed. The preheating unit 63 supplies the temperature control medium to each of the rolls 61 by the temperature adjustment mechanisms 62a to 62c in one preheating chamber 60 to adjust the surface temperature of the free rolls 61 of each group. At this time, the surface temperature of the free roller 61 of each group is raised in order from the inlet side. The surface temperature of each of the rolls 61 is set so as not to cause a temperature of corrugated plate-like wrinkles due to thermal expansion due to contact with the film 15. Further, in addition to temperature adjustment for each group, each of the free rollers 61 can be tempered. Further, as shown in FIG. 2, the free roller 25 in the divided preheating chamber 50 can be similarly tempered. The temperature difference of the free roller 61 of the group on the downstream side and the group on the upstream side is 50 ° C or less, and the temperature of the free roller 61 of the most upstream group is +20 ° C or more and 50 ° C with respect to the outside room temperature of the preheating chamber 50 . Within the scope below.

In each of the above embodiments, the lengths of the film passages in the preheating chambers 20, 50, and 60 are set to be long by the free rollers 25, 61. However, as shown in FIG. 4, the preheating portion 71 of the steering lever 70 may be employed instead of the free rollers 25, 61. At this time, the blower 72 and the temperature adjuster 73 are connected to the steering lever 70 to supply the suspension air to the steering lever 70. The suspended air may be set to be the same as the preheating temperature Tp of the preheating chamber 74, or set to be lower than the preheating temperature Tp. In addition, in FIGS. 3 and 4, the preheating chambers 60 and 74 are provided with the blower 34 and the temperature regulator 35 shown in FIG. 1, but are omitted. The illustration. Further, as in the embodiment of FIG. 2, the preheating zone can be formed by dividing the preheating chambers 60, 74 into a plurality of, and the blower 34 and the temperature are provided in the preheating zones of the preheating chambers 60, 74. The regulator 35 sets the preheating temperature Tp for each of the preheating zones, and sets the preheating temperature Tp to gradually rise from the inlet side to the outlet side. Further, similarly to the free roller 61 of the embodiment of Fig. 3, the temperature of the suspended air from each of the steering levers 70 can be changed for each of the steering levers 70 or each group so as to be gradually moved from the entrance of the preheating chamber 74. Exports are rising.

In the above-described embodiment, the low-speed roller group 41 and the high-speed roller group 42 are used as the longitudinal stretching portion 12. However, the high-speed holding roller such as a fluted processing roller may be used as the low-speed roller and the high-speed roller. Further, as the longitudinal stretching portion 12, the first-stage longitudinal stretching by the upstream-side low-speed roller group 41 and the downstream-side high-speed roller group 42 is employed, but a plurality of longitudinal stretching may be employed.

[Examples]

As the film 15, a cellulose vaporized 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 carried out. In the longitudinal stretching portion 12, the first-stage longitudinal stretching by the upstream-side low-speed roller group 41 and the downstream-side high-speed roller group 42 is performed. The pre-process apparatus 13 is sent out from the film roll pulling film 15 to the preheating section 11 using a film feeder. As the post-processing device 14, a film winding machine is used, and the film 15 is taken up. For film rolls. In the preheating section 11, a free roller 25 having a diameter of 60 mm is disposed in the preheating chamber 20, and the film 15 is wound around the free rollers, and the length of the film passage in the preheating chamber 20 is set to 20 m. Also, heated wind 36 is supplied to preheat until the desired film temperature is reached. The longitudinal stretching ratio was set to 1.3 times, the stretching length Le (see FIG. 1) was set to 300 mm, the cooling temperature was set to 100 ° C, and the film conveying speed was set to 40 m/min, as shown in Table 1 above, the change was made. Experiment 1 to Experiment 17 were carried out at a thermal temperature Tp and a stretching temperature Te. Further, in Experiments 1 to 16, the preheating of the heated wind by the heating chamber was performed, and in Experiment 17, the preheating was performed by contact with the preheating roll.

The obtained stretched film was evaluated for scratches, wrinkles, and uneven stretching. The abrasion was observed by a microscope, and the wrinkles were visually observed to evaluate. When there is no scratch and wrinkle, it is excellent "A", and when the scratch and wrinkle are grades that can be allowed, it is good "B", and when scratches and wrinkles are not within the allowable range, it is regarded as unqualified "C". Regarding the unevenness of the stretching, when the difference between the maximum thickness and the minimum thickness in the longitudinal direction of the sample of 5 m length is 3 μm or less, it is excellent "A", and when it exceeds 3 μm and is less than or equal to 5 μm, it is a good "B" as an allowable grade. When it exceeds 5 μm, it is regarded as unqualified "C". According to the experimental results, it was found that in the experiments 1 to 16 in which the preheating was performed by heating the wind, the preheating temperature Tp was less than (stretching temperature Te-40) ° C and exceeded (Tg - 5) ° C, and the abrasion was evaluated. , wrinkles and uneven stretching are all unqualified "C". From this, it is understood that the preheating temperature Tp is suitably in the range of (Te - 40) ° C or more (Tg - 5) ° C or less. Further, when the stretching temperature Te was less than Tg and exceeded (Tg + 20) °C, it was found that the scratches, wrinkles, and stretching unevenness were all unacceptable "C". From this, it is understood that the stretching temperature Te is suitably in the range of Tg ° C or more (Tg + 20) ° C or less. Further, although the stretching unevenness was not observed in the experiment 17 in which the film was brought into contact with the preheating roll, the scratches and wrinkles were evaluated as poor "C".

Fig. 5 is a diagram in which the above-mentioned reasonable range is plotted as a graph, and the area indicated by hatching is a reasonable condition range of the invention of the present application. The vertical axis is the preheating temperature Tp (unit: °C), expressed as the difference from Tg. For example, "-10" means (Tg - 10) °C, and "5" means (Tg + 5) °C. In addition, when the difference from Tg is 0 (zero), it is referred to as "Tg". The horizontal axis is the stretching temperature Te (unit: °C), which is expressed as the difference from Tg. For example, "-5" means (Tg-5) °C, and "15" means (Tg + 15) °C. In addition, when the difference from Tg is 0 (zero), it is referred to as "Tg". Thus, it is understood that the stretching temperature Te needs to be in the range of Tg ° C or more (Tg + 20) ° C or less in order to perform uniform stretching, and it is necessary to set the preheating temperature Tp to (Tg - 5) ° C or less. Further, it is understood that the preheating temperature Tp needs to be (Te - 40) ° C or more in order to avoid generation of wrinkles and scratches.

10‧‧‧film stretching equipment

11‧‧‧Preheating Department

12‧‧‧ longitudinal stretching

13‧‧‧Pre-process equipment

14‧‧‧ late process equipment

15‧‧‧film

16‧‧‧Tensile adjustment department

17a, 17b‧‧‧ free roll

18‧‧‧ Tension roller

19‧‧‧displacement mechanism

20‧‧‧Preheating room

25‧‧‧Free roll

31‧‧‧Air supply nozzle

32‧‧‧Exhaust nozzle

33‧‧‧ catheter

34‧‧‧Air blower

35‧‧‧temperature regulator

36‧‧‧heating wind

41‧‧‧Low speed roller set

41a‧‧‧low speed roller

41b‧‧‧Clamping roller

42‧‧‧High speed roller set

42a‧‧‧High speed roller

42b‧‧‧Clamping roller

43‧‧‧Cooling roller

Claims (10)

A method for producing a stretched film, which comprises producing a stretched film by stretching a film-shaped film composed of a thermoplastic resin having a glass transition temperature of Tg in a transport direction, and the method for producing the stretched film has the following steps: (A) a step of stretching the film in the conveying direction by a low speed roller disposed separately in the conveying direction and a high speed roller rotating at a peripheral speed higher than the low speed roller, wherein the low speed roller contacts the film to heat the film a stretching temperature Te in a range of Tg ° C or more (Tg+20) ° C or less; and (B) supplying a heating wind to the inside of the preheating chamber to preheat the film to (Te - 40) ° C before the aforementioned step A The above range (Tg-5) °C or less. The method for producing a stretched film according to claim 1, wherein the film passing through the low speed roll is cooled to a range of (Tg - 100) ° C or more (Tg - 5) ° C or less by the high speed roller. . The method for producing a stretched film according to the first or second aspect of the invention, wherein the tension of the film in the preheating chamber is in a range of from 20 N/m to 200 N/m. The method for producing a stretched film according to claim 1 or 2, wherein the preheating chamber is divided into a plurality of preheating zones in the conveying direction, and the preheating temperature is divided into the plurality of preheating temperatures. The upstream side of the preheating zone rises toward the downstream side, and the temperature difference between the adjacent downstream side preheating zone and the upstream side preheating zone is 50 ° C or less. The method for producing a stretched film according to the first or second aspect of the invention, wherein the film in the step B is hung on a plurality of conveying direction changing members that change the conveying direction. The method for producing a stretched film according to claim 5, wherein the transport direction changing member is a free roller. The method for producing a stretched film according to claim 5, wherein the conveying direction changing member is a steering rod. The method for producing a stretched film according to claim 5, wherein the transport direction changing member is divided into a plurality of groups in the transport direction, and the temperature is gradually increased from the upstream side to the downstream side of each group. The method for producing a stretched film according to the eighth aspect of the invention, wherein the temperature difference of the transport direction changing member of the group on the downstream side and the group on the upstream side is 50° C. or less. A film stretching apparatus for producing a stretched film by stretching a belt-shaped film composed of a thermoplastic resin having a glass transition temperature of Tg in a conveying direction, the stretched film apparatus comprising: a longitudinal stretching portion, which is conveyed as described above Stretching the film in the direction; the low-speed roll is present in the longitudinal stretching portion and is heated to a stretching temperature Te of Tg ° C or more (Tg+20) ° C or less by contact with the film; the high-speed roll is high Rotating at a peripheral speed of the low speed roller to stretch the film in the conveying direction, the high speed roller being disposed in the longitudinal direction in the conveying direction separately from the low speed roller; and a preheating portion in the preheating chamber The heating film is supplied to preheat the film to (Te - 40) ° C or more (Tg - 5) ° C or less, and the preheating portion is disposed upstream of the longitudinal stretching portion.