JP2020151960A - Method of producing stretched film - Google Patents

Abstract

To reduce sagging occurring in an obliquely stretched film.SOLUTION: A method of producing a stretched film includes: gripping the right and left ends in the crosswise direction of a long film with right and left variable-pitch-type clips whose longitudinal clip pitches vary, respectively; traveling the right and left clips while varying at least one clip pitch to obliquely stretch the film; releasing the film from the right and left clips; performing roll-transportation of the film and detecting the amount of sagging of the film between transport rolls and a site at which the sagging occurs; and performing compensation in which at least one clip pitch of the right and left clips in an upper transportation line is varied on the basis of the results of the detection.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a stretched film and a method for producing an optical laminate.

In image display devices such as a liquid crystal display device (LCD) and an organic electroluminescence display device (OLED), a circular polarizing plate is used for the purpose of improving display characteristics and preventing reflection. In a circular polarizing plate, typically, a polarizer and a retardation film (typically a λ / 4 plate) form an angle of 45 ° between the absorption axis of the polarizer and the slow axis of the retardation film. It is laminated in this way. Conventionally, retardation films are typically produced by uniaxially or biaxially stretched in the longitudinal and / or lateral directions, so that the slow axis is often a long film. It appears in the horizontal direction (width direction) or the vertical direction (long direction) of the original fabric. As a result, in order to produce a circularly polarizing plate, it was necessary to cut the retardation film at an angle of 45 ° with respect to the width direction or the length direction and bond them one by one.

Further, in order to secure the wide bandwidth of the circularly polarizing plate, two retardation films, a λ / 4 plate and a λ / 2 plate, may be laminated. In that case, the λ / 2 plates are laminated so as to form an angle of 75 ° with respect to the absorption axis of the polarizer, and the λ / 4 plates are laminated so as to form an angle of 15 ° with respect to the absorption axis of the polarizer. There is a need. Even in this case, when producing the circularly polarizing plate, it was necessary to cut the retardation films at 15 ° and 75 ° and bond them one by one.

In yet another embodiment, in order to prevent the light from the notebook PC from being reflected on the keyboard or the like, the direction of the linearly polarized light emitted from the polarizing plate is rotated by 90 ° on the visual side of the polarizing plate. A λ / 2 plate may be used. Even in this case, it was necessary to cut the retardation film at 45 ° and bond the films one by one.

In order to solve such a problem, the left and right edges of the long film in the width direction are gripped by the left and right clips of the variable pitch type in which the clip pitch in the vertical direction changes, respectively, and at least the left and right clips are held. A technique has been proposed in which the slow axis of a retardation film is expressed in an oblique direction by changing one clip pitch and stretching in an oblique direction (hereinafter, also referred to as “oblique stretching”) (for example, a patent). Document 1). However, in the diagonally stretched film obtained by such a technique, slack may occur at the end portion in the width direction. When a film having such slack is wound up, wrinkles or kneading may occur on the obtained film roll. In addition, when the loosened film is attached to another optical film, uneven coating of the adhesive or adhesive or uncoated parts may occur, or wrinkles or kneading may occur in the obtained optical laminate. There is.

Patent No. 4845619

The present invention has been made to solve the above problems, and a main object thereof is to reduce the slack generated in the obliquely stretched film.

According to one aspect of the present invention, the left and right ends of the long film in the width direction are gripped by the left and right clips of the variable pitch type in which the clip pitch in the vertical direction changes, respectively. Stretching the film diagonally while changing at least one clip pitch, releasing the film from the left and right clips, transporting the film, and the amount of slack of the film between the transport rolls. And the manufacture of a stretched film, which comprises detecting a site where slack is occurring, and making a correction for changing at least one of the left and right clips upstream of the transport line based on the detection result. A method is provided.
In one embodiment, after cutting and removing the left and right ends of the film released from the left and right clips, the amount of slack and the portion where the slack occurs are detected.
In one embodiment, the correction that changes the clip pitch includes increasing the clip pitch of the clip that grips the far end with respect to the slackened portion.
In one embodiment, the correction for changing the clip pitch causes the film to move to the left and right from the time when the clip traveling in advance passes the position of 1/2 to 9/10 of the traveling section in the oblique stretching. It is done from the clip to the release.
In one embodiment, the correction for changing the clip pitch is performed with a correction amount larger than the difference L'(unit: mm) in the lengths of the left and right ends of the film between the transport rolls, where L. 'Is calculated by substituting the length L (unit: mm) of the film between the transport rolls calculated based on the following formulas (1) and (2) into the following formula (3).
(In the above formula, d represents the detected amount of slack (unit: mm), W represents the mass per 1 m of the film (unit: g), g represents the gravitational acceleration, and S represents the above. The distance between the transport rolls (unit: mm) is represented, and H represents the tension (unit: N / m) applied to the end side where the slack is generated, which is calculated from the formula (1).
In one embodiment, the correction for changing the clip pitch is performed in the diagonal stretching, and the atmospheric temperature at that time is Tg to Tg + 20 ° C. of the film.
According to another aspect of the present invention, a long stretched film is obtained by the above-mentioned method for producing a stretched film, and the long optical film and the long stretched film are conveyed while being conveyed. A method for manufacturing an optical laminate is provided, which comprises aligning the elongated directions and continuously laminating them.
In one embodiment, the optical film is a polarizing plate and the stretched film is a λ / 4 plate or a λ / 2 plate.

In the method for producing a stretched film of the present invention, the amount of slack generated in the diagonally stretched film and the portion where the slack is generated are detected, and based on the detection result, at least one of the left and right clips upstream of the transport line is clipped. Correct the pitch. As a result, the difference in length between the left and right ends of the film is reduced, and as a result, a long diagonally stretched film with reduced slack can be obtained.

It is the schematic explaining an example of the manufacturing method of the stretch film of this invention. It is a schematic plan view explaining the whole structure of the example of the stretching apparatus which can be used in the manufacturing method of the stretched film of this invention. FIG. 5 is a schematic plan view of a main part for explaining a link mechanism for changing a clip pitch in the stretching device of FIG. FIG. 5 is a schematic plan view of a main part for explaining a link mechanism for changing a clip pitch in the stretching device of FIG. It is a schematic diagram explaining the method of measuring a slack amount. It is the schematic which shows the profile of the clip pitch in one Embodiment of the manufacturing method of the stretch film of this invention. It is the schematic which shows the profile of the clip pitch in another embodiment of the manufacturing method of the stretch film of this invention. It is the schematic sectional drawing of the circular polarizing plate using the retardation film obtained by the manufacturing method of this invention.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments. In addition, in this specification, "the clip pitch in the vertical direction" means the distance between the centers in the traveling direction of clips adjacent in a vertical direction. Further, the left-right relationship in the width direction of the long film means the left-right relationship in the transport direction of the film unless otherwise specified.

A. Method for manufacturing stretched film In the method for manufacturing stretched film of the present invention, the left and right ends of a long film in the width direction are gripped by left and right clips of a variable pitch type in which the clip pitch in the vertical direction changes. Running and moving the left and right clips while changing at least one clip pitch to diagonally stretch the film, releasing the film from the left and right clips, rolling the film, and between the transport rolls. This includes detecting the amount of slack in the film and the portion where the slack is occurring, and making corrections to change the clip pitch of at least one of the left and right clips upstream of the transport line based on the detection result. .. Typically, the film gripped by the clip is preheated and then subjected to oblique stretching.

FIG. 1 is a schematic view illustrating an example of a method for producing a stretched film of the present invention. The diagonally stretched film 1 that has been diagonally stretched in the stretching device 100 and then released from the clip is sent out from the outlet of the stretching device 100 and is rolled and transported using the transport rolls 200a, 200b, 200c and 200d to take up the winding unit 300. It is wound up with. When the film 1 is transported by rolls, the amount of slack or the like is detected between the transport rolls, and based on the detection result, correction is performed to change the clip pitch of at least one of the left and right clips upstream of the transport line. As a result, the difference in length between the left and right ends of the stretched film obtained after the correction is reduced, and as a result, a long diagonally stretched film with reduced slack can be obtained.

Gripping, preheating, diagonally stretching, and releasing from the clips by the clips include, for example, left and right clips that can travel and move at different speeds while gripping the left and right ends of the elongated film in the width direction. This can be done using a tenter type simultaneous biaxial stretching device.

FIG. 2 is a schematic plan view illustrating an overall configuration of an example of a stretching device that can be used in the manufacturing method of the present invention. The stretching device 100 has an endless loop 10L and an endless loop 10R having a large number of clips 20 for gripping the film symmetrically on the left and right sides in a plan view. In the present specification, the endless loop on the left side when viewed from the inlet side of the film is referred to as the endless loop 10L on the left side, and the endless loop on the right side is referred to as the endless loop 10R on the right side. The clips 20 of the left and right endless loops 10L and 10R are guided by the reference rail 70 and circulate in a loop shape, respectively. The clip 20 of the endless loop 10L on the left side circulates in the counterclockwise direction, and the clip 20 of the endless loop 10R on the right side circulates in the clockwise direction. In the stretching device, a gripping zone A, a preheating zone B, a stretching zone C, and an open zone D are provided in this order from the inlet side to the outlet side of the sheet. Each of these zones means a zone in which the film to be stretched is substantially gripped, preheated, diagonally stretched, and opened, not a mechanically or structurally independent compartment. Also note that the length ratio of each zone in the stretching device of FIG. 1 is different from the actual length ratio.

Although not shown in FIG. 2, a zone may be provided between the stretching zone C and the open zone D, if necessary, for performing arbitrary appropriate processing. Examples of such a treatment include a lateral shrinkage treatment. Similarly, although not shown, the stretching device is typically a heating device (for example, hot air type, near infrared type, far red) for setting a heating environment from the preheating zone B to the open zone D. It is equipped with various external ovens).

In the gripping zone A and the preheating zone B of the stretching device 100, the left and right endless loops 10L and 10R are configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the film to be stretched. In the stretching zone C, the distance between the left and right endless loops 10L and 10R gradually increases from the side of the preheating zone B toward the opening zone D until it corresponds to the width of the film after stretching. In the open zone D, the left and right endless loops 10L and 10R are configured to be substantially parallel to each other at a separation distance corresponding to the stretched width of the film. However, the configurations of the left and right endless loops 10L and 10R are not limited to the above illustrated example. For example, the left and right endless loops 10L and 10R may be configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the film to be stretched from the gripping zone A to the open zone D.

The clip (clip on the left side) of the endless loop 10L on the left side and the clip (clip on the right side) 20 of the endless loop 10R on the right side can be cyclically moved independently. For example, the drive sprockets 11 and 12 of the endless loop 10L on the left side are rotationally driven in the counterclockwise direction by the electric motors 13 and 14, and the drive sprockets 11 and 12 of the endless loop 10R on the right side are clocked by the electric motors 13 and 14. It is driven to rotate in the circumferential direction. As a result, a running force is applied to the clip-carrying members of the drive rollers (not shown) engaged with the drive sprockets 11 and 12. As a result, the endless loop 10L on the left side circulates in the counterclockwise direction, and the endless loop 10R on the right side circulates in the clockwise direction. By driving the electric motor on the left side and the electric motor on the right side independently, the endless loop 10L on the left side and the endless loop 10R on the right side can be cyclically moved independently.

Further, the clip (clip on the left side) of the endless loop 10L on the left side and the clip (clip on the right side) 20 of the endless loop 10R on the right side are each of a variable pitch type. That is, the left and right clips 20 and 20 can independently change the clip pitch in the vertical direction as they move. The variable pitch type configuration can be realized by adopting a drive system such as a pantograph system, a linear motor system, or a motor chain system. Hereinafter, the link mechanism (pantograph mechanism) will be described as an example.

3 and 4 are schematic plan views of a main part for explaining a link mechanism for changing the clip pitch in the stretching device of FIG. 1, FIG. 3 shows a state where the clip pitch is the minimum, and FIG. 4 shows a clip. Indicates the maximum pitch.

As shown in FIGS. 3 and 4, a clip supporting member 30 having an elongated rectangular shape in the horizontal direction in a plan view for individually supporting the clips 20 is provided. Although not shown, the clip-supporting member 30 is formed into a frame structure having a strong closed cross section by an upper beam, a lower beam, a front wall (a wall on the clip side), and a rear wall (a wall on the opposite side of the clip). The clip-carrying member 30 is provided so as to roll on the traveling road surfaces 81 and 82 by the traveling wheels 38 at both ends thereof. In addition, in FIGS. 3 and 4, the traveling wheel on the front wall side (the traveling wheel rolling on the traveling road surface 81) is not shown. The traveling road surfaces 81 and 82 are parallel to the reference rail 70 over the entire area. On the rear side of the upper beam and the lower beam of the clip-supporting member 30 (opposite side of the clip side (hereinafter, anti-clip side)), elongated holes 31 are formed along the longitudinal direction of the clip-supporting member, and the slider 32 is long. It is slidably engaged in the longitudinal direction of the hole 31. A first shaft member 33 is vertically provided in the vicinity of the clip 20 side end of the clip supporting member 30 so as to penetrate the upper beam and the lower beam. On the other hand, the slider 32 of the clip-supporting member 30 is provided with a second shaft member 34 vertically penetrating. One end of the main link member 35 is pivotally connected to the first shaft member 33 of each clip-carrying member 30. The other end of the main link member 35 is pivotally connected to the second shaft member 34 of the adjacent clip-supporting member 30. In addition to the main link member 35, one end of the sub-link member 36 is pivotally connected to the first shaft member 33 of each clip-carrying member 30. The other end of the sub-link member 36 is pivotally connected to the intermediate portion of the main link member 35 by a pivot 37. As shown in FIG. 3, the more the slider 32 moves to the rear side (anti-clip side) of the clip-supporting member 30 by the link mechanism by the main link member 35 and the sub-link member 36, the more the clip-supporting members 30 are vertically aligned with each other. The pitch in the direction (as a result, the clip pitch) becomes smaller, and as shown in FIG. 4, the more the slider 32 moves to the front side (clip side) of the clip supporting member 30, the more the clip supporting members 30 are in the vertical direction. The pitch (as a result, the clip pitch) increases. Positioning of the slider 32 is performed by the pitch setting rail 90. As shown in FIGS. 3 and 4, the smaller the distance between the reference rail 70 and the pitch setting rail 90, the larger the clip pitch.

By diagonally stretching the film using the stretching device as described above, a diagonally stretched film, for example, a retardation film having a slow axis in the diagonal direction can be produced. Specific embodiments of the stretching apparatus as described above are described in, for example, Japanese Patent Application Laid-Open No. 2008-44339, and the whole thereof is incorporated herein by reference. Hereinafter, each step will be described in detail.

A-1. Gripping the film with clips In the grip zone A (the entrance of the film take-up of the stretching device 100), the clips 20 of the left and right endless loops 10L and 10R have a constant clip pitch or a constant clip pitch in which both edges of the film to be stretched are equal to each other. , Are gripped at different clip pitches. The film is sent to the preheating zone B by the movement of the clips 20 of the left and right endless loops 10L and 10R (substantially, the movement of each clip supporting member guided by the reference rail 30).

A-2. Preheating In the preheating zone B, the left and right endless loops 10L and 10R are basically configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the film to be stretched as described above. The film is heated without stretching or longitudinal stretching. However, the distance between the left and right clips (distance in the width direction) may be slightly increased in order to avoid problems such as the film bending due to preheating and contacting the nozzle in the oven.

In preheating, the film is heated to a temperature of T1 (° C.). The temperature T1 is preferably equal to or higher than the glass transition temperature (Tg) of the film, more preferably Tg + 2 ° C. or higher, and further preferably Tg + 5 ° C. or higher. On the other hand, the heating temperature T1 is preferably Tg + 40 ° C. or lower, more preferably Tg + 30 ° C. or lower. Although it depends on the film used, the temperature T1 is, for example, 70 ° C. to 190 ° C., preferably 80 ° C. to 180 ° C.

The temperature raising time up to the temperature T1 and the holding time at the temperature T1 can be appropriately set according to the constituent materials of the film and the manufacturing conditions (for example, the transport speed of the film). These temperature raising time and holding time can be controlled by adjusting the moving speed of the clip 20, the length of the preheating zone, the temperature of the preheating zone, and the like.

A-3. Diagonal Stretching In the stretching zone C, the left and right clips 20 are run and moved while changing the clip pitch in at least one of them in the vertical direction to diagonally stretch the film. More specifically, by increasing or decreasing the clip pitches of the left and right clips at different positions, or by changing (increasing and / or decreasing) the clip pitches of the left and right clips at different speeds of change, etc. The film is stretched diagonally.

Diagonal stretching may include transverse stretching. In this case, the oblique stretching can be performed while increasing the distance between the left and right clips (distance in the width direction), for example, as shown in the illustrated example. Alternatively, unlike the illustrated example, it can be performed while maintaining the distance between the left and right clips.

When the oblique stretching includes lateral stretching, the ratio of the lateral (TD) stretching ratio (the ratio of the width W _final of the film after diagonal stretching to the initial width W _initial of the film (W _final / W _initial ) is preferably 1.05. It is ~ 6.00, more preferably 1.10 to 5.00.

In one embodiment, the oblique stretching differs in the longitudinal direction from the position where the clip pitch of one of the left and right clips starts to increase or decrease and the position where the clip pitch of the other clip starts to increase or decrease. This can be done by increasing or decreasing the clip pitch of each clip to a predetermined pitch while in position. For the diagonal stretching of the embodiment, for example, the description of Patent Document 1, Japanese Patent Application Laid-Open No. 2014-238524, etc. can be referred to.

In another embodiment, oblique stretching increases or decreases the clip pitch of the other clip to a predetermined pitch while keeping the clip pitch of one of the left and right clips fixed, and then increases or decreases the original clip pitch. Can be done by returning to. For the diagonal stretching of the embodiment, for example, the description of JP2013-54338A, JP2014-194482A, and the like can be referred to.

In yet another embodiment, oblique stretching reduces the clip pitch of one of the left and right clips while increasing the clip pitch of the other clip, and (ii) the decrease. This can be done by changing the clip pitch of each clip so that the clip pitch and the increased clip pitch have a predetermined equal pitch. For the diagonal stretching of the embodiment, for example, the description of JP-A-2014-194484 can be referred to. The oblique stretching of the embodiment is to diagonally stretch the film by increasing the clip pitch of one clip and decreasing the clip pitch of the other clip while increasing the distance between the left and right clips (the first). 1), and while increasing the distance between the left and right clips, the clip pitch of one clip is maintained or reduced so that the clip pitches of the left and right clips are equal, and the clip pitch of the other clip is maintained or reduced. Increasing the clip pitch of the clip may include diagonally stretching the film (second diagonal stretching step).

Diagonal stretching can typically be done at temperature T2. The temperature T2 is preferably Tg-20 ° C. to Tg + 30 ° C., more preferably Tg-10 ° C. to Tg + 20 ° C., and particularly preferably about Tg, with respect to the glass transition temperature (Tg) of the film. Although it depends on the film used, the temperature T2 is, for example, 70 ° C. to 180 ° C., preferably 80 ° C. to 170 ° C. The difference (T1-T2) between the temperature T1 and the temperature T2 is preferably ± 2 ° C. or higher, more preferably ± 5 ° C. or higher. In one embodiment, T1> T2, so the film heated to temperature T1 in the preheating zone can be cooled to temperature T2.

The lateral shrinkage treatment is performed after diagonal stretching. For the treatment after the diagonal stretching, paragraphs 0029 to 0032 of JP2014-194483A can be referred to.

A-4. Clip Opening The film is released from the clip at any position in the opening zone D. In the open zone D, neither lateral stretching nor longitudinal stretching is usually performed, and if necessary, the film is heat-treated to fix the stretched state (heat-fixed) and / or cool to Tg or less, and then the film. Release from the clip. At the time of heat fixing, the clip pitch in the vertical direction may be reduced to relieve the stress.

The heat treatment can typically be performed at temperature T3. The temperature T3 depends on the film to be stretched, and may be T2 ≧ T3 or T2 <T3. Generally, when the film is an amorphous material, T2 ≧ T3, and when the film is a crystalline material, T2 <T3 may be set to perform the crystallization treatment. When T2 ≧ T3, the difference between the temperatures T2 and T3 (T2-T3) is preferably 0 ° C to 50 ° C. The heat treatment time is typically 10 seconds to 10 minutes.

The stretched film released from the clip is sent out from the outlet of the stretching device and is used for roll transport described later.

A-5. Roll transfer In roll transfer, the amount of slack in the stretched film between the transfer rolls and the portion where the slack occurs are detected.

In one embodiment, after cutting and removing the left and right ends of the stretched film released from the clip in the width direction, the amount of slack and the portion where the slack occurs are detected. More accurate detection results can be obtained by detecting the amount of slack and the portion where the slack is occurring with both ends removed.

The width of each end to be cut and removed can be independently, for example, 20 mm to 600 mm, preferably 100 mm to 500 mm. Cutting and removal of the end portion can be performed by ordinary slit processing.

In one embodiment, the amount of slack and the portion where the slack is generated can be detected by detecting the difference between the original running position of the film and the actual running position of the film during roll transfer. For example, the detection can be performed by detecting a difference in position (transport height) in the width direction of the film at an intermediate point between the transport rolls.

FIG. 5 is a schematic view illustrating an example of a method of detecting a slack amount and a slackened portion. As shown in FIG. 5, at the midpoint between the two adjacent transport rolls 200b and 200c, the ultrasonic displacement sensor 400 is arranged below the central portion and the left and right end portions in the width direction of the stretched film 1 to obtain ultrasonic waves. The distance from the displacement sensor 400 to the stretched film 1 can be measured, and the difference between the maximum distance (L _MAX ) and the minimum distance (L _MIN ) (L _MAX- L _MIN ) can be used as the amount of slack. In addition, the part given the minimum distance is detected as the part where slack occurs. The cause of the slack in the diagonally stretched film is that the stretching processes (timing, number of times, order, heat history, etc.) of the left and right ends of the film are different from each other during diagonal stretching, and as a result, both ends after the clip is opened. Since the amount of deformation of the film may be non-uniform, the site where the slack occurs is usually one of the ends. Therefore, the slack can be detected only at the left and right ends of the stretched film 1 in the width direction. In this case, a film without slack is conveyed in advance, the distance (L ₀ ) from the ultrasonic displacement sensor to the film is measured and placed, and the difference between the distance between the left and right ends and the ultrasonic displacement sensor and L _0. Can be used as the amount of slack. Although the ultrasonic displacement sensor has been described as an example of the slack detecting means, the slack can be obtained by determining the film passing speed of the normal part and the slack part by using an arbitrary appropriate detecting means (for example, a laser Doppler velocimeter). It can be detected using (calculating the difference in length, etc.).

The distance (D) between the transport rolls at the time of the above detection is not particularly limited, but can be, for example, 500 mm to 2000 mm, preferably 700 mm to 1500 mm.

The film tension at the time of the above detection is not particularly limited, but can be, for example, 50 N / m to 400 N / m, preferably 100 N / m to 200 N / m. If the transport tension is too high, the film being transported may be elastically deformed, making it difficult to detect slack. On the other hand, if the transport tension is too low, the tension itself may not be stable and the measured value of slack may not be stable.

The roll transfer can be performed in a non-heated environment. The atmospheric temperature during roll transfer may be, for example, about 15 ° C. to 40 ° C., or for example, about 20 ° C. to 30 ° C.

A-6. Correction to change the clip pitch The correction to change the clip pitch is so-called feedback correction, and is upstream of the transport line so as to reduce the amount of slack based on the detection result of the amount of slack and the portion where the slack is occurring. This is done by changing the clip pitch of at least one of the left and right clips. For example, if the detected amount of slack is equal to or greater than a predetermined value, a correction for changing the clip pitch can be performed, and if it is less than a predetermined value, diagonal stretching can be continued without correction. Specifically, the above correction can be performed when the amount of slack detected at a distance between rolls of 1000 mm is, for example, 3 mm or more, 5 mm or more, 10 mm or more, or 15 mm or more.

The correction for changing the clip pitch (hereinafter, also simply referred to as “feedback correction”) can be performed by any suitable method as long as the effect of the present invention can be obtained. Feedback correction, for example, increases the clip pitch of the clip that grips the far end with respect to the slackened portion, and increases the clip pitch of the clip that grips the end near the slackened portion. It can be done by reducing or combining these. However, even if the clip pitch is reduced, the film may not shrink but only loosen. Therefore, by increasing the clip pitch of the clip that grips the end far from the slackened portion, , It is preferable to perform feedback correction. More specifically, when the slackened portion is one of the left and right ends of the stretched film, feedback correction is preferably performed by increasing the clip pitch of the clip that grips the other end. Can be done.

In the feedback correction, the timing of changing the clip pitch is not particularly limited as long as the effect of the present invention can be obtained. In one embodiment, after the film upstream of the transport line shifts to the oblique stretching zone, the corrected clip pitch can be changed at an arbitrary timing until the film is released from the clip. Preferably, from any point in time after the clip traveling ahead in the upstream of the transport line passes through the intermediate point of the traveling section of the diagonally stretched zone until the film is released from the clip, the clip traveling ahead is more preferably The corrected clip pitch is applied from the time when the film passes from 1/2 to 9/10 of the traveling section of the obliquely stretched zone until the film is released from the clip. More specifically, from any point in time after the clip traveling ahead of the transport line passes through the intermediate point of the traveling section of the diagonal extension zone, preferably the clip traveling ahead is 1 / of the traveling section of the oblique extension zone. The application of the feedback correction is started from the time of passing 2 to 9/10, and the clip pitch is changed so that a desired correction amount can be obtained at the end point of the oblique stretching zone. Further, it is preferable to maintain the correction amount until the film is released from the clip even after the transition from the oblique stretching zone to the open zone. In the latter half of the diagonal stretching, particularly in the final stage, at least one of the clip pitches is maintained constant or changes at a small rate of change. Therefore, the present invention is made by correcting the clip pitch at that timing. The effect of can be preferably obtained.

When applying the feedback correction in the oblique stretching zone, the film of interest is preferably heated to Tg + 3 ° C to Tg + 20 ° C, more preferably Tg + 3 ° C to Tg + 10 ° C, and even more preferably Tg + 4 ° C to Tg + 8 ° C. By applying the feedback correction at a temperature equal to or slightly higher than Tg, the effects of the present invention can be preferably obtained. In one embodiment, the film that has passed through the oblique stretching zone while receiving feedback correction at the above temperature and has transitioned to the open zone is heat-treated and then cooled while maintaining the correction amount performed in the oblique stretching zone. After that, it is released from the clip. The heat treatment and cooling are as described in Section A-4.

FIG. 6A is a schematic view showing a profile of the clip pitch in one embodiment of the method for producing a stretched film of the present invention. In the illustrated example, the clip X of the right and left in the preheating zone B, clip pitch Y is the P ₁ both in the initial oblique stretching before being feedback correction, while at the same time enters the oblique stretching zone C, one clip starts the increase in X clip pitch, starts to decrease in the clip pitch of the other clips Y, the clip pitch of the clip X is increased to P _2, after the clip pitches of clips Y was reduced to P ₃ is , While maintaining the clip pitch of clip X at P ₂ , the clip pitch of clip Y is increased to P ₂ . Left and right clips X, Y opens the film moves to the left opening zone D of the clip pitch P _2. Then, a result of the feedback based on the amount of looseness or the like during roll conveyance of the film correction, clip pitch of the clip X is gradually increased from P ₂ to P _{2 'in} the oblique stretching zone C. Incidentally, as described later, the open zone, clips X, Y of clip Pucci _'is maintained and P _2, the correction amount in the oblique stretching zone ending point (P _2' P ₂ each -P ₂₎ is maintained.

FIG. 6B is a schematic view showing a profile of the clip pitch in another embodiment of the method for producing a stretched film of the present invention. In the embodiment of the illustrated example, diagonal stretching is performed in the same pattern as that of the embodiment shown in FIG. 6A, and the clip pitches of the left and right clips X and Y are both P ₂ to P ₃ during heat fixing in the open zone D. Release the film after it has decreased. Then, the result of the roll during conveyance of the slack amount such as based on the feedback correction of the film, the clip pitch of the clip X in the oblique stretching zone C is increased gradually from P ₂ to P _{2 ',} the open zone, the clip X Clip pitch is reduced to _{'P 3 from'} P _2, clip pitches of clips Y is reduced from P ₂ to P _3. Incidentally, as described later, the open zone, the correction amount in the oblique stretching zone ending point _{(P 2} 'Clip X as -P ₂₎ is maintained, Y clip Puig is decreased, _{P 3' -P 3} = _P satisfy the ₂ '-P ₂ relationship.

In the oblique stretching zone, changes to the clip pitch corrected (changed to P 2 _') is in the feedback end point from the point where the application of the correction is started (FIGS. 6A and 6B, 2/3 of oblique stretching zone It is preferable to gradually proceed from the time of passing to the end point). In addition, the correction amount at the end of diagonal stretching (| clip pitch before correction at the end of diagonal stretching-clip pitch after correction at the end of diagonal stretching |) remains from the end point of the diagonal stretching zone until the clip is released. It is preferably maintained. For example, in the profile shown in FIGS. 6A and 6B, during the period from the end point of the oblique stretching zone to the opening of the clip, the difference between the clip pitch and Clip Y Clip pitch of the clip X is constant (i.e., P ₂ '-P ₂ (To) is maintained. By changing the clip pitch in this way, the effect of the present invention can be preferably obtained.

The change in the clip pitch can be performed by adjusting the separation distance between the reference rail and the pitch setting rail as described above. These adjustments can be made with or without stopping the transport line.

The correction amount of the clip pitch at the end of diagonal stretching in the above feedback correction (| clip pitch before correction at the end of diagonal stretching-clip pitch after correction at the end of diagonal stretching |) is appropriately adjusted according to the amount of slack and the like. Can be set. The correction amount of the clip pitch is preferably an amount that exceeds the difference in length between the left and right end portions of the stretched film between the transport rolls, and more preferably 1.4 times to 5.0 times the difference in length. The correction amount may be more preferably 1.6 times to 4.0 times, and even more preferably 1.8 times to 3.0 times. If the amount of correction for the clip pitch is less than or equal to the difference in length between the left and right ends, the amount of reduction in slack may be insufficient.

The difference L'(unit: mm) in the lengths of the left and right ends of the stretched film between the transport rolls is the length of the stretched film between the transport rolls calculated based on the following formulas (1) and (2). It can be calculated by substituting L (unit: mm) into the following equation (3).
(In the above formula, d represents the detected amount of slack (unit: mm), W represents the mass per 1 m of the film (unit: g), g represents the gravitational acceleration, and S represents the above. The distance between the transport rolls (unit: mm) is represented, and H represents the tension (unit: N / m) applied to the end side where the slack is generated, which is calculated from the formula (1).

In one embodiment, the amount of slack reduced by the feedback correction (the amount of slack of the stretched film obtained before the feedback correction-the amount of slack of the stretched film obtained after the feedback correction: however, it is measured at a distance between the transport rolls of 1000 mm. The amount of slack) can be, for example, 3 mm or more, preferably 5 mm or more, more preferably 8 mm or more, still more preferably 10 mm or more. The amount of slack in the stretched film obtained after feedback correction may be, for example, less than 15 mm, preferably 10 mm or less, more preferably 8 mm or less, still more preferably 5 mm or less, and even more preferably less than 3 mm.

B. Film to be stretched In the production method of the present invention, any suitable film can be used. For example, a resin film applicable as a retardation film can be mentioned. Examples of the material constituting such a film include polycarbonate resin, polyvinyl acetal resin, cycloolefin resin, acrylic resin, cellulose ester resin, cellulose resin, polyester resin, polyester carbonate resin, and olefin. Examples thereof include based resins and polyurethane resins. Preferably, it is a polycarbonate resin, a cellulose ester resin, a polyester resin, a polyester carbonate resin, or a cycloolefin resin. This is because with these resins, a retardation film showing so-called inverse dispersion wavelength dependence can be obtained. These resins may be used alone or in combination according to desired properties.

As the polycarbonate resin, any suitable polycarbonate resin is used. For example, a polycarbonate resin containing a structural unit derived from a dihydroxy compound is preferable. Specific examples of the dihydroxy compound include 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, and 9,9-bis (4-hydroxy-3-3). Ethylphenyl) fluorene, 9,9-bis (4-hydroxy-3-n-propylphenyl) fluorene, 9,9-bis (4-hydroxy-3-isopropylphenyl) fluorene, 9,9-bis (4-hydroxy) -3-n-butylphenyl) fluorene, 9,9-bis (4-hydroxy-3-sec-butylphenyl) fluorene, 9,9-bis (4-hydroxy-3-tert-butylphenyl) fluorene, 9, 9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, 9,9-bis (4-hydroxy-3-phenylphenyl) fluorene, 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene, 9,9-bis (4- (2-hydroxyethoxy) -3-methylphenyl) fluorene, 9,9-bis (4- (2-hydroxyethoxy) -3-isopropylphenyl) fluorene, 9,9-bis ( 4- (2-Hydroxyethoxy) -3-isobutylphenyl) fluorene, 9,9-bis (4- (2-hydroxyethoxy) -3-tert-butylphenyl) fluorene, 9,9-bis (4- (2) -Hydroxyethoxy) -3-cyclohexylphenyl) fluorene, 9,9-bis (4- (2-hydroxyethoxy) -3-phenylphenyl) fluorene, 9,9-bis (4- (2-hydroxyethoxy) -3 , 5-Dimethylphenyl) Fluorene, 9,9-bis (4- (2-hydroxyethoxy) -3-tert-butyl-6-methylphenyl) fluorene, 9,9-bis (4- (3-hydroxy-2) , 2-Dimethylpropoxy) phenyl) fluorene and the like. In addition to the structural units derived from the above dihydroxy compounds, the polycarbonate resin contains isosorbide, isomannide, isoidet, spiroglycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), cyclohexanedimethanol ( It may contain structural units derived from dihydroxy compounds such as CHDM), tricyclodecanedimethanol (TCDDM) and bisphenols.

Details of the polycarbonate-based resin as described above are described in, for example, Japanese Patent Application Laid-Open No. 2012-67300 and Japanese Patent No. 3325560. The description of the patent document is incorporated herein by reference.

The glass transition temperature of the polycarbonate resin is preferably 110 ° C. or higher and 250 ° C. or lower, more preferably 120 ° C. or higher and 230 ° C. or lower. If the glass transition temperature is excessively low, the heat resistance tends to deteriorate, which may cause a dimensional change after film molding. If the glass transition temperature is excessively high, the molding stability during film molding may be deteriorated, and the transparency of the film may be impaired. The glass transition temperature is determined according to JIS K 7121 (1987).

As the polyvinyl acetal-based resin, any suitable polyvinyl acetal-based resin can be used. Typically, the polyvinyl acetal-based resin can be obtained by subjecting at least two types of aldehyde compounds and / or ketone compounds to a condensation reaction with a polyvinyl alcohol-based resin. Specific examples and detailed production methods of the polyvinyl acetal-based resin are described in, for example, Japanese Patent Application Laid-Open No. 2007-161994. This description is incorporated herein by reference.

The retardation film obtained by stretching the film to be stretched preferably has a refractive index characteristic of nx> ny. In one embodiment, the retardation film can preferably function as a λ / 4 plate. In the present embodiment, the in-plane retardation Re (550) of the retardation film (λ / 4 plate) is preferably 100 nm to 180 nm, more preferably 135 nm to 155 nm. In another embodiment, the retardation film can preferably function as a λ / 2 plate. In the present embodiment, the in-plane retardation Re (550) of the retardation film (λ / 2 plate) is preferably 230 nm to 310 nm, more preferably 250 nm to 290 nm. In the present specification, nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and ny is the in-plane direction orthogonal to the slow-phase axis (that is, phase-advance). It is the refractive index in the axial direction), and nz is the refractive index in the thickness direction. Re (λ) is an in-plane phase difference of the film measured with light having a wavelength of λ nm at 23 ° C. Therefore, Re (550) is the in-plane phase difference of the film measured with light having a wavelength of 550 nm at 23 ° C. Re (λ) can be obtained by the formula: Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the film.

The in-plane retardation Re (550) of the retardation film can be set to a desired range by appropriately setting the oblique stretching conditions. For example, methods for producing a retardation film having an in-plane retardation Re (550) of 100 nm to 180 nm by diagonal stretching are described in JP2013-54338, JP2014-194482, and JP2014-238524. It is disclosed in detail in Japanese Patent Application Laid-Open No. 2014-194484 and the like. Therefore, those skilled in the art can set appropriate diagonal stretching conditions based on the disclosure.

When a circular polarizing plate is manufactured using one retardation film, or when the direction of linearly polarized light is rotated by 90 ° using one retardation film, the slow axis direction of the retardation film used is , Preferably 30 ° to 60 ° or 120 ° to 150 °, more preferably 38 ° to 52 ° or 128 ° to 142 °, still more preferably 43 ° to 47 ° or 133 ° with respect to the longitudinal direction of the film. It is ~ 137 °, particularly preferably about 45 ° or 135 °.

Further, when a circular polarizing plate is produced using two retardation films (specifically, λ / 2 plate and λ / 4 plate), the slow axis of the retardation film (λ / 2 plate) used is used. The direction is preferably 60 ° to 90, more preferably 65 ° to 85, and particularly preferably about 75 ° with respect to the long direction of the film. The slow axis direction of the retardation film (λ / 4 plate) is preferably 0 ° to 30 °, more preferably 5 to 25 °, and particularly preferably about 15 ° with respect to the long direction of the film. is there.

The retardation film preferably exhibits so-called inverse dispersion wavelength dependence. Specifically, the in-plane phase difference satisfies the relationship of Re (450) <Re (550) <Re (650). Re (450) / Re (550) is preferably 0.8 or more and less than 1.0, and more preferably 0.8 to 0.95. Re (550) / Re (650) is preferably 0.8 or more and less than 1.0, and more preferably 0.8 to 0.97.

The absolute value of the photoelastic coefficient of the retardation film is preferably 2 × 10 ^-12 (m ² / N) to 100 × 10 ^-12 (m ² / N), and more preferably 5 × 10 ^-12. It is (m ² / N) to 50 × 10 ^-12 (m ² / N).

C. Optical laminate and method for producing the optical laminate The stretched film obtained by the production method of the present invention can be bonded to another optical film and used as an optical laminate. For example, the retardation film obtained by the production method of the present invention can be bonded to a polarizing plate and suitably used as a circular polarizing plate.

FIG. 7 is a schematic cross-sectional view of an example of such a circularly polarizing plate. The circular polarizing plate 500 of the illustrated example includes a polarizing element 510, a first protective film 520 arranged on one side of the polarizer 510, a second protective film 530 arranged on the other side of the polarizer 510, and a second. It has a retardation film 540 arranged outside the protective film 530 of 2. The retardation film 540 is a stretched film (for example, λ / 4 plate) obtained by the production method according to the item A. The second protective film 530 may be omitted. In that case, the retardation film 540 can function as a protective film for the polarizer. The angle formed by the absorption axis of the polarizer 510 and the slow axis of the retardation film 540 is preferably 30 ° to 60 °, more preferably 38 ° to 52 °, still more preferably 43 ° to 47 °, and particularly preferably. It is about 45 °.

The retardation film obtained by the production method of the present invention is long and has a slow axis in an oblique direction (for example, a direction of 45 ° with respect to the long direction). Also, in many cases, the elongated polarizer has an absorption axis in the elongated direction or the width direction. Therefore, if the retardation film obtained by the production method of the present invention is used, so-called roll-to-roll can be used, and a circularly polarizing plate can be produced with extremely excellent production efficiency. The roll-to-roll refers to a method in which long films are rolled and conveyed, and the long films are aligned and continuously bonded to each other.

In one embodiment, the method for producing an optical laminate of the present invention is to obtain an elongated stretched film by the method for producing a stretched film according to item A, and to obtain an elongated optical film and the elongated optical film. This includes aligning the elongated directions of the stretched film and continuously bonding the stretched film.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement and evaluation methods in the examples are as follows.

(1) Thickness Measured using a dial gauge (manufactured by PEACOCK, product name "DG-205 type pds-2").
(2) Phase difference value The in-plane phase difference Re (550) was measured using Axoscan manufactured by Axometrics.
(3) Orientation angle (expression direction of slow axis)
A sample was prepared by cutting out the central portion of the film to be measured into a square shape having a width of 50 mm and a length of 50 mm so that one side was parallel to the width direction of the film. This sample was measured using Axoscan manufactured by Axometrics, and the orientation angle θ at a wavelength of 590 nm was measured.
(4) Glass transition temperature (Tg)
Measured according to JIS K 7121.
(5) Amount of slack As shown in FIG. 5, an ultrasonic displacement sensor was placed at an intermediate point (distance between rolls: 912 mm) between two adjacent transport rolls under the transport path of the stretched film. While transporting the stretched film with a transport tension of 150 N / m, the distance from the ultrasonic displacement sensor to the stretched film is measured at the center and edges in the width direction, and the maximum distance (L _MAX ) and the minimum distance (L _MIN ) are obtained. The difference (L _MAX- L _MIN ) was defined as the amount of slack (mm). In addition, the part to which the minimum distance was given was determined to be the part where slack occurred.

<Example 1>
(Preparation of polyester carbonate resin film)
Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with a stirring blade and a reflux condenser controlled at 100 ° C. Bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl] methane 29.60 parts by mass (0.046 mol), ISB 29.21 parts by mass (0.200 mol), SPG 42.28 parts by mass (0. 139mol), were charged DPC 63.77 parts by weight (0.298 mol) and calcium acetate monohydrate 1.19 × ^{10 -2} parts by weight as a catalyst (6.78 × ¹⁰ -5 mol). After substituting nitrogen under reduced pressure in the reactor, heating was performed with a heat medium, and stirring was started when the internal temperature reached 100 ° C. The internal temperature was brought to 220 ° C. 40 minutes after the start of the temperature rise, and the depressurization was started at the same time as controlling to maintain this temperature, and the temperature was 13.3 kPa 90 minutes after reaching 220 ° C. The phenol vapor produced as a by-product of the polymerization reaction was guided to a reflux condenser at 100 ° C., the monomer component contained in a small amount in the phenol vapor was returned to the reactor, and the uncondensed phenol vapor was guided to a condenser at 45 ° C. for recovery. After introducing nitrogen into the first reactor and once restoring the pressure to atmospheric pressure, the oligomerized reaction solution in the first reactor was transferred to the second reactor. Then, the temperature rise and depressurization in the second reactor were started, and the internal temperature was 240 ° C. and the pressure was 0.2 kPa in 50 minutes. Then, the polymerization was allowed to proceed until the stirring power became a predetermined value. When the predetermined power was reached, nitrogen was introduced into the reactor to repressurize, the produced polyester carbonate was extruded into water, and the strands were cut to obtain pellets. The Tg of the obtained polyester carbonate resin was 140 ° C.

After vacuum-drying the obtained polyester carbonate resin at 80 ° C. for 5 hours, a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250 ° C.), T-die (width 200 mm, set temperature: 250 ° C.), chill roll A resin film having a thickness of 135 μm was produced using a film forming apparatus equipped with (set temperature: 120 to 130 ° C.) and a winder.

(Diagonal stretching before feedback correction)
The polyester carbonate resin film obtained as described above was obliquely stretched using a stretching device as shown in FIGS. 2 to 4 to obtain a retardation film. Specifically, the polyester carbonate resin film was preheated to 145 ° C. in the preheating zone of the stretching apparatus. In the preheating zone, the clip pitch (P ₁ ) of the left and right clips was 125 mm. Next, on the film enters the oblique stretching zone C, to start the reduction in the clip pitches increased and left clips clip pitch of the right clip, clip pitch of the left clip with increasing clip pitch of the right clip to the P ₂ the was reduced to _{P 3.} At this time, the clip pitch change rate (P ₂ / P ₁ ) of the right side clip is 1.42, the clip pitch change rate (P ₃ / P ₁ ) of the left side clip is 0.78, and the original width of the film. The lateral stretching ratio was 1.45 times. Then, while maintaining the clip pitch of the right clip at P ₂ , the increase of the clip pitch of the left clip was started and increased from P ₃ to P ₂ . During this period, the rate of change in the clip pitch of the left clip (P ₂ / P ₃ ) was 1.82, and the lateral stretching ratio with respect to the original width of the film was 1.9 times. The diagonally stretched zone C was set to Tg + 3.2 ° C. (143.2 ° C.).

Then, in the open zone D, the film was held at 125 ° C. for 60 seconds for heat fixation. After cooling the heat-fixed film to 100 ° C., the left and right clips were opened.

(Roll transfer)
Both end portions of the stretched film released from the clip and fed from the stretching device were cut off by 250 mm each. The film with both ends cut off was transported by roll, and the amount of slack between the transport rolls and the site where slack occurred were detected. As a result, slack was generated at the left end, and the amount of slack was 18.0 mm. Further, the difference L'of the lengths of both ends of the stretched film before correction calculated based on the above formulas (1) to (3) was 0.95 mm.

(Feedback correction)
The right clip clip pitch between the time which has passed through the 3/4 travel route of oblique stretching zone C until it reaches the end point P _{2 'is} gradually increased to (correction amount clip pitch (P _2' - P _2): 0.3 mm), similarly heat and above while maintaining the clip pitch (125 ° C., so as to open the clip for 60 seconds) and cooled (100 ° C.), the clip pitch The profile was changed and diagonal stretching was continued. That is, the clip pitch when oblique stretching the film after the feedback correction is released from the clip, the right is P _{2 ',} the left was P _2.

The phase difference Re (590) of the obtained stretched film was 147 nm, and the angle formed by the slow-phase axial direction and the elongated direction was 45 °.

<Example 2>
Except that the amount of correction of the clip pitch (P ₂ '-P ₂₎ to 0.6mm in the same manner as in Example 1 to obtain a stretched film by performing the oblique stretching.

<Example 3>
Except that the amount of correction of the clip pitch (P ₂ '-P ₂₎ to 0.95mm in the same manner as in Example 1 to obtain a stretched film by performing the oblique stretching.

<Example 4>
Except that the amount of correction of the clip pitch (P ₂ '-P ₂₎ to 1.8mm in the same manner as in Example 1 to obtain a stretched film by performing the oblique stretching.

<Example 5>
Except that the amount of correction of the clip pitch (P ₂ '-P ₂₎ to 2.6mm in the same manner as in Example 1 to obtain a stretched film by performing the oblique stretching.

<Example 6>
Correction amount clip pitch _{(P 2} '-P ₂₎ it has a 0.6mm to and set the 3/4 subsequent sections travel segment of oblique stretching zone C to Tg + 6.0 ℃ (146.0 ℃) A stretched film was obtained by diagonally stretching in the same manner as in Example 1 except for the above.

<Example 7>
Setting the correction amount clip pitch _{(P 2} '-P ₂₎ it was 0.95 mm, and the 3/4 subsequent sections travel segment of oblique stretching zone C to Tg + 6.0 ℃ (146.0 ℃) A stretched film was obtained by diagonally stretching in the same manner as in Example 1 except for the above.

<Example 8>
Correction amount clip pitch _{(P 2} '-P ₂₎ it has a 1.8mm to and set the 3/4 subsequent sections travel segment of oblique stretching zone C to Tg + 6.0 ℃ (146.0 ℃) A stretched film was obtained by diagonally stretching in the same manner as in Example 1 except for the above.

<Example 9>
Setting the correction amount clip pitch _{(P 2} '-P ₂₎ that was 2.6 mm, and the 3/4 subsequent sections travel segment of oblique stretching zone C to Tg + 6.0 ℃ (146.0 ℃) A stretched film was obtained by diagonally stretching in the same manner as in Example 1 except for the above.

<Comparative example 1>
A stretched film was obtained by diagonally stretching in the same manner as in Example 1 except that feedback correction was not performed.

With respect to the stretched films obtained in the above Examples and Comparative Examples, the amount of slack was measured by the above method.

Further, the stretched films obtained in the above Examples and Comparative Examples are bonded to a long masking film (manufactured by Toray Film Processing Co., Ltd., product name "Tretec 7832C-30") by roll-to-roll to form a film laminate. Obtained. Next, the masking film was peeled off from the film laminate, an adhesive was applied with a gravure coater, the film was bonded to the polarizing plate, and UV irradiation was performed to obtain an optical laminate. The appearance (visual) of the film laminate and the handleability of the stretched film were evaluated based on the following criteria.
〇: After the masking film is bonded (bonding tension 150 N / m), no wrinkles are found and the adhesive can be applied to the entire surface of the film.
Δ: When the masking film was bonded, the bonding could be performed without wrinkles by increasing the bonding tension to 300 N / m, but when the adhesive was applied, the adhesive could not be applied to the loosened portion.
X: After the masking film is attached, there are wrinkles and the appearance is deteriorated.

Table 1 shows the results of evaluation of the amount of slack and the appearance of the film laminate together with the manufacturing process. In Table 1, the "sag reduction amount" is the difference from the slack amount of the stretched film of Comparative Example 1 (slack amount of the stretched film obtained in Comparative Example 1-slack amount of the stretched film obtained in each example). Is.

<Evaluation>
As shown in Table 1, by detecting the amount of slack in the diagonally stretched film and appropriately changing the clip pitch upstream of the transport line based on the detection result, the slack in the stretched film obtained thereafter is reduced. You can see that.

The method for producing a stretched film of the present invention is suitably used for producing a retardation film, and as a result, can contribute to the production of an image display device such as a liquid crystal display device (LCD) and an organic electroluminescence display device (OLED). ..

1 Stretched film 10L Endless loop 10R Endless loop 20 Clip 100 Stretching device 200 Conveying roll 300 Winding part 400 Ultrasonic displacement sensor 500 Circularly polarizing plate

Claims (8)

The left and right edges of the long film in the width direction are gripped by the variable pitch type left and right clips whose clip pitch in the vertical direction changes, respectively.
To stretch the film diagonally by moving the left and right clips while changing at least one clip pitch.
Releasing the film from the left and right clips,
The film is transported by roll, and the amount of slack of the film between the transport rolls and the location where the slack occurs are detected, and
A method for producing a stretched film, which comprises performing a correction for changing at least one clip pitch of the left and right clips upstream of the transport line based on the detection result. The method for producing a stretched film according to claim 1, wherein the amount of slack and the portion where the slack is generated are detected after cutting and removing the left and right ends of the film released from the left and right clips. The method for producing a stretched film according to claim 1 or 2, wherein the correction for changing the clip pitch includes increasing the clip pitch of the clip that grips the end portion far from the slackened portion. .. The film is released from the left and right clips from the time when the correction for changing the clip pitch passes the position of 1/2 to 9/10 of the traveling section in the oblique stretching. The method for producing a stretched film according to any one of claims 1 to 3, which is carried out during the period up to. The correction for changing the clip pitch is performed with a correction amount larger than the difference L'(unit: mm) in the lengths of the left and right ends of the film between the transport rolls, where L'is expressed by the following formula ( Any of claims 1 to 4, which is calculated by substituting the length L (unit: mm) of the film between the transport rolls calculated based on 1) and (2) into the following formula (3). The method for producing a stretched film according to.
(In the above formula, d represents the detected amount of slack (unit: mm), W represents the mass per 1 m of the film (unit: g), g represents the gravitational acceleration, and S represents the said. The distance between the transport rolls (unit: mm) is represented, and H represents the tension (unit: N / m) applied to the end side where the slack is generated, which is calculated from the formula (1). The correction for changing the clip pitch is performed in the diagonal stretching.
The method for producing a stretched film according to any one of claims 1 to 5, wherein the atmospheric temperature at that time is Tg to Tg + 20 ° C. of the film. The elongated stretched film is obtained by the production method according to any one of claims 1 to 6, and the elongated optical film and the elongated stretched film are conveyed in the elongated direction. A method for manufacturing an optical laminate, which comprises aligning and continuously laminating. The optical film is a polarizing plate,
The method for producing an optical laminate according to claim 7, wherein the stretched film is a λ / 4 plate or a λ / 2 plate.