CN111716691A

CN111716691A - Method for producing stretched film

Info

Publication number: CN111716691A
Application number: CN202010198019.7A
Authority: CN
Inventors: 清水享; 村冈敦史; 平田聪
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2019-03-20
Filing date: 2020-03-19
Publication date: 2020-09-29
Anticipated expiration: 2040-03-19
Also published as: KR20200112650A; TW202035106A; TWI780395B; JP7253413B2; CN111716691B; KR102709058B1; JP2020151960A

Abstract

The invention provides a method for producing a stretched film. Reducing the sag of the obliquely stretched film. The method for producing a stretched film comprises the steps of: holding the left and right ends of the long film in the width direction by a variable-pitch left and right jig with a jig pitch varying in the longitudinal direction; moving the left and right clamps while changing the clamp pitch of at least one of the left and right clamps, thereby obliquely stretching the film; releasing the film from the left and right clamps; roll-conveying the film, detecting the amount of slack of the film between the conveying rollers and the location where the slack occurs; and correcting a change in the inter-clamp distance of at least one of the left and right clamps positioned upstream of the conveyance line based on the detection result.

Description

Method for producing stretched film

Technical Field

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

Background

In image display devices such as liquid crystal display devices (LCDs) and organic electroluminescent display devices (OLEDs), circularly polarizing plates are used for the purpose of improving display characteristics and preventing reflection. Typically, a polarizer and a retardation film (typically, a λ/4 plate) are stacked in a circular polarizing plate such that an absorption axis of the polarizer and a slow axis of the retardation film form an angle of 45 °. In the past, since a retardation film is typically produced by uniaxial stretching or biaxial stretching in the longitudinal direction and/or the transverse direction, the slow axis thereof appears in many cases in the transverse direction (width direction) or the longitudinal direction (longitudinal direction) of a long film web. As a result, when manufacturing a circular polarizing plate, it is necessary to cut the phase difference film at an angle of 45 ° with respect to the width direction or the length direction and attach the polarizing plates (polarizers) one by one.

In order to secure broadband properties of the circularly polarizing plate, two retardation films of a λ/4 plate and a λ/2 plate may be laminated. In this case, it is necessary to laminate λ/2 plates so as to form an angle of 75 ° with respect to the absorption axis of the polarizer, and to laminate λ/4 plates so as to form an angle of 15 ° with respect to the absorption axis of the polarizer. In this case, even when a circularly polarizing plate is manufactured, the retardation film needs to be cut so as to form an angle of 15 ° and an angle of 75 ° with respect to the width direction or the longitudinal direction, and the retardation film needs to be bonded to the polarizing plate (polarizer) one by one.

In another embodiment, in order to prevent light from the notebook PC from being reflected on the keyboard, a λ/2 plate may be used on the viewing side of the polarizing plate to rotate the direction of the linearly polarized light emitted from the polarizing plate by 90 °. In this case, the retardation film needs to be cut at an angle of 45 ° with respect to the width direction or the longitudinal direction, and bonded to a polarizing plate (polarizer) one by one.

In order to solve such problems, the following techniques have been proposed: a retardation film is stretched in an oblique direction by holding the left and right ends of a long film in the width direction with a variable-pitch left and right jig having a varying jig pitch in the longitudinal direction, and varying the jig pitch of at least one of the left and right jig to stretch the film in an oblique direction (hereinafter also referred to as "oblique stretching") (for example, patent document 1). However, in the obliquely-stretched film obtained by such a technique, a slack (slack) may be generated in the end portion in the width direction. When such a film with slack is wound, wrinkles or scratches may occur in the obtained film roll. When a film that has slackened is bonded to another optical film, uneven application of an adhesive or an uncoated portion may occur, or wrinkles or scratches may occur in the obtained optical laminate.

Patent document 1: japanese patent No. 4845619

Disclosure of Invention

Problems to be solved by the invention

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

Means for solving the problems

According to an aspect of the present invention, there is provided a method for producing a stretched film, the method comprising: holding the left and right ends of the long film in the width direction by a variable-pitch left and right jig with a jig pitch varying in the longitudinal direction; moving at least one of the left and right clamps while changing a clamp pitch of the clamp, and moving either clamp ahead of the other clamp to obliquely stretch the film; releasing the film from the left and right clamps; roll-conveying the film, detecting the amount of slack of the film between the conveying rollers and the location where the slack occurs; and correcting a change in the inter-clamp distance of at least one of the left and right clamps positioned upstream of the conveyance line based on the detection result.

In one embodiment, the left and right ends of the film released from the left and right clamps are cut and removed, and then the amount of slack and the locations where slack occurs are detected.

In one embodiment, the correcting the change in the jig pitch includes: the distance between the clamps holding the end portion far from the portion where the slack is generated is increased.

In one embodiment, the correction of the change in the distance between the clamps is performed from the time when the clamp traveling in advance passes through the positions 1/2 to 9/10 in the traveling section of the oblique stretching until the film is released from the left and right clamps.

In one embodiment, the correction of the change in the clip pitch is performed with a correction amount larger than a difference L '(unit: mm) in length between the left and right ends of the film between the transport rollers, and L' is calculated by substituting the length L (unit: mm) of the film between the transport rollers calculated based on the following equations (1) and (2) into the following equation (3),

[ expression 1 ]

d＝(H/(w＊g))＊(cosh(w＊g＊S/2H)-1)…(1)

L＝(2H/(w*g))＊sinh((w＊g＊S/2H)…(2)

L‘＝L-S…(3)

(in the above formula, d represents the detected amount of slack (unit: mm), W represents the mass per meter of the film (unit: g), g represents the gravitational acceleration, S represents the distance between the conveying rollers (unit: mm), and H represents the tension applied to the end portion side where the slack calculated according to the formula (1) occurs (unit: N/m)).

In one embodiment, the tilt stretching is performed with a correction to change the pitch of the jigs, and the ambient temperature at this time is Tg to Tg +20 ℃.

According to another aspect of the present invention, there is provided a method for manufacturing an optical laminate, the method comprising the steps of: obtaining a long stretched film by the above method for producing a stretched film; and continuously laminating the long optical film and the long stretched film while aligning the longitudinal directions thereof.

In one embodiment, the optical film is a polarizing plate, and the stretched film is a λ/4 plate or a λ/2 plate.

ADVANTAGEOUS EFFECTS OF INVENTION

In the method for producing a stretched film of the present invention, the amount of slack occurring in the obliquely stretched film and the locations where the slack occurs are detected, and the grip pitch of at least one of the left and right grips located upstream of the conveyance path is corrected based on the detection results. This reduces the difference in length between the left and right ends of the film, and as a result, a long obliquely-stretched film with reduced slack can be obtained.

Drawings

Fig. 1 is a schematic diagram illustrating an example of the method for producing a stretched film of the present invention.

Fig. 2 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the method for producing a stretched film of the present invention.

Fig. 3 is a schematic plan view of a main part of a link mechanism for explaining a change in the distance between the clamps in the stretching apparatus of fig. 2.

Fig. 4 is a schematic plan view of a main part of a link mechanism for explaining a change in the distance between the clamps in the stretching apparatus of fig. 2.

Fig. 5 is a schematic diagram illustrating a method of measuring the slack amount.

Fig. 6A is a schematic view showing a curve of the clip pitch in one embodiment of the method for producing a stretched film of the present invention.

Fig. 6B is a schematic view showing a curve of the clip pitch in another embodiment of the method for producing a stretched film of the present invention.

Fig. 7 is a schematic cross-sectional view of a circularly polarizing plate using a retardation film obtained by the production method of the present invention.

Description of the reference numerals

1. Stretching the film; 10L, annular ring; 10R, an annular ring; 20. a clamp; 100. a stretching device; 200. a conveying roller; 300. a winding section; 400. an ultrasonic displacement sensor; 500. a circularly polarizing plate.

Detailed Description

Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In addition, in the present specification, the "clip pitch in the longitudinal direction" refers to an inter-center distance in the traveling direction of the clips adjacent in the longitudinal direction. 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 producing stretched film

The method for producing a stretched film of the present invention comprises the steps of: holding the left and right ends of the long film in the width direction by a variable-pitch left and right jig with a jig pitch varying in the longitudinal direction; moving the left and right clamps while changing the clamp pitch of at least one of the left and right clamps, thereby obliquely stretching the film; releasing the film from the left and right clamps; roll-conveying the film, detecting the amount of slack of the film between the conveying rollers and the location where the slack occurs; and correcting a change in the inter-clamp distance of at least one of the left and right clamps positioned upstream of the conveyance line based on the detection result. Typically, the film held by the jig is preheated and then subjected to oblique stretching.

Fig. 1 is a schematic diagram illustrating an example of the method for producing a stretched film of the present invention. The obliquely stretched film 1 obliquely stretched in the stretching apparatus 100 and then released from the jig is fed out from the outlet of the stretching apparatus 100, and is transported by rollers using

transport rollers

200a, 200b, 200c, and 200d and wound around the winding section 300. When the film 1 is roll-conveyed, the amount of slack or the like is detected between the conveying rollers, and based on the detection result, correction is performed to change the clip pitch of at least one of the left and right clips positioned upstream of the conveying path. This reduces the difference in length between the left and right ends of the stretched film obtained after correction, and as a result, a long obliquely stretched film with reduced slack can be obtained.

The film gripping, preheating, oblique stretching, and releasing from the clips can be performed, for example, by using a tenter type simultaneous biaxial stretching apparatus including left and right clips which can travel at different speeds while gripping left and right ends in the width direction of the long film.

Fig. 2 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the production method of the present invention. The stretching apparatus 100 includes, in a plan view, an annular ring 10L and an annular ring 10R which are bilaterally symmetrical on both left and right sides, and the annular ring 10L and the annular ring 10R include a plurality of jigs 20 for holding a film. In the present specification, the left annular ring is referred to as a left annular ring 10L and the right annular ring is referred to as a right annular ring 10R, as viewed from the inlet side of the membrane. The jigs 20 of the left and right

endless loops

10L, 10R are guided by the reference rails 70 to circularly move in a ring shape. The gripper 20 of the left annular ring 10L is cyclically moved in the counterclockwise direction, and the gripper 20 of the right annular ring 10R is cyclically moved in the clockwise direction. In the stretching apparatus, a gripping region a, a preheating region B, an inclined stretching region C, and a releasing region D are provided in this order from the entrance side toward the exit side of the sheet. These regions are regions for substantially holding, preheating, obliquely stretching, and releasing the film to be stretched, and do not mean mechanically or structurally independent regions. In addition, it is desirable to note that the ratio of the lengths of the respective regions in the stretching apparatus of fig. 1 is different from the ratio of the actual lengths.

In fig. 2, although not shown, an area for performing any appropriate processing may be provided between the oblique stretching area C and the releasing area D as necessary. Such a treatment may be a transverse shrinkage treatment. Also, although not shown, the stretching device typically includes a heating device (for example, various ovens such as a hot air oven, a near-infrared oven, and a far-infrared oven) for providing a heating environment from the preheating zone B to the releasing zone D.

In the gripping area a and the preheating area B of the stretching apparatus 100, the left and right

endless loops

10L, 10R are configured to be substantially parallel to each other at a distance corresponding to the initial width of the film to be stretched. In the inclined stretching region C, the distance between the left and right

endless loops

10L, 10R gradually increases from the preheating region B side toward the releasing region D to correspond to the stretched width of the film. In the release region D, the left and right

annular rings

10L and 10R are configured to be substantially parallel to each other at a distance corresponding to the stretched width of the film. However, the structure of the left and right annular rings 10L, 10R is not limited to the above-described example. For example, the left and right

endless loops

10L and 10R may be configured to be substantially parallel to each other at a distance from the holding region a to the releasing region D corresponding to the initial width of the film to be stretched.

The gripper (left gripper) 20 of the left annular ring 10L and the gripper (right gripper) 20 of the right annular ring 10R can be independently moved cyclically. For example, the driving

sprockets

11 and 12 of the left annular ring 10L are driven by the

electric motors

13 and 14 to rotate counterclockwise, and the driving

sprockets

11 and 12 of the right annular ring 10R are driven by the

electric motors

13 and 14 to rotate clockwise. As a result, a traveling force is applied to the jig holding member of the driving roller (not shown) engaged with the driving

sprockets

11 and 12. Thereby, the left annular ring 10L is circularly moved in the counterclockwise direction, and the right annular ring 10R is circularly moved in the clockwise direction. Since the left electric motor and the right electric motor are driven independently, the left annular ring 10L and the right annular ring 10R can be cyclically moved independently.

The jig (left jig) 20 of the left annular ring 10L and the jig (right jig) 20 of the right annular ring 10R are of variable pitch type. That is, the left and

right jigs

20, 20 can change the jig pitch in the longitudinal direction independently with the movement. The variable pitch type structure can be realized by adopting a drive system such as a pantograph system, a linear motor system, a motor-chain system, or the like. Hereinafter, a link mechanism (pantograph mechanism) will be described as an example.

Fig. 3 and 4 are schematic plan views of main portions of a link mechanism for explaining a change in the clip pitch in the stretching apparatus of fig. 1, respectively, fig. 3 showing a state in which the clip pitch is minimum, and fig. 4 showing a state in which the clip pitch is maximum.

As shown in fig. 3 and 4, jig holding members 30 that hold the jigs 20 and have a rectangular shape elongated in the lateral direction in a plan view are provided. Although not shown, the clip holding member 30 is formed into a firm frame structure having a 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 jig holding member 30 is provided so as to roll on the

travel paths

81 and 82 by the travel wheels 38 at both ends thereof. In fig. 3 and 4, the traveling wheels on the front wall side (traveling wheels that roll on the traveling road surface 81) are not shown. The

travel surface

81, 82 is parallel to the reference rail 70 over the entire area. A long hole 31 is formed along the longitudinal direction of the clip holding member on the rear side of the upper beam and the lower beam of the clip holding member 30 (on the opposite side to the clip side (hereinafter referred to as the opposite side to the clip)), and a slider 32 is engaged slidably in the longitudinal direction of the long hole 31. One 1 st shaft member 33 is vertically provided through the upper beam and the lower beam in the vicinity of the jig 20 side end portion of the jig holding member 30. On the other hand, one 2 nd shaft member 34 is provided to penetrate vertically through the slider 32 of the jig holding member 30. One end of a main link member 35 is pivotally connected to the 1 st shaft member 33 of each of the jig holding members 30. The main link member 35 pivotally couples the other end to the 2 nd shaft member 34 of the adjacent jig holding member 30. In addition to one end of the main link member 35, one end of the sub link member 36 is pivotally connected to the 1 st shaft member 33 of each of the jig holding members 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. With the link mechanism composed of the main link member 35 and the sub link member 36, as shown in fig. 3, the distance in the longitudinal direction between the jig holding members 30 (as a result, the jig distance) is smaller as the slider 32 moves to the rear side (the opposite side to the jig) of the jig holding member 30, and as shown in fig. 4, the distance in the longitudinal direction between the jig holding members 30 (as a result, the jig distance) is larger as the slider 32 moves to the front side (the jig side) of the jig holding member 30. The positioning of the slider 32 is performed by the pitch setting rail 90. As shown in fig. 3 and 4, the smaller the spacing distance between the reference rail 70 and the pitch setting rail 90, the larger the jig pitch.

By obliquely stretching the film using such a stretching apparatus, an obliquely stretched film, for example, a retardation film having a slow axis in an oblique direction can be produced. A specific embodiment of the stretching apparatus is described in, for example, japanese patent application laid-open No. 2008-44339, which is incorporated by reference in its entirety into the present specification. Hereinafter, each step will be described in detail.

A-1. Film gripping by a clamp

In the gripping region a (an entrance of the stretching apparatus 100 into which the film is taken), both side edges of the film to be stretched are gripped by the grippers 20 of the left and right

endless loops

10L, 10R at a constant gripper pitch equal to each other or at different gripper pitches from each other. The film is conveyed to the preheating region B by the movement of the jigs 20 of the left and right

endless loops

10L, 10R (substantially, the movement of the jig holding members guided by the reference rail 30).

A-2. Preheating

In the preheating region B, the left and right annular rings 10L, 10R are configured to be substantially parallel to each other at the interval distance corresponding to the initial width of the film to be stretched as described above, and therefore, the film is heated while being stretched substantially neither in the transverse direction nor in the longitudinal direction. However, in order to avoid a problem such as the film being deflected by preheating and coming into contact with the nozzle in the oven, the distance between the left and right jigs (distance in the width direction) may be slightly increased.

During the preheating, the film was heated to a temperature T1 (. degree. C.). The temperature T1 is preferably not less than the glass transition temperature (Tg) of the film, more preferably not less than Tg +2 ℃, and still more preferably not less than Tg +5 ℃. On the other hand, the heating temperature T1 is preferably Tg +40 ℃ or lower, more preferably Tg +30 ℃ or lower. The temperature T1 varies depending on the film used, but the temperature T1 is, for example, from 70 ℃ to 190 ℃ and preferably from 80 ℃ to 180 ℃.

The temperature rise time to the temperature T1 and the holding time at the temperature T1 can be appropriately set according to the material of the film and the production conditions (for example, the film transport speed). The temperature rise time and the holding time may be controlled by adjusting the moving speed of the jig 20, the length of the preheating region, the temperature of the preheating region, and the like.

A-3. Obliquely stretching

In the oblique stretching region C, the film is obliquely stretched by moving the left and right clamps 20 while changing the clamp pitch in the longitudinal direction of at least one clamp 20 of the left and right clamps 20, and moving one clamp ahead of the other clamp. More specifically, the film is obliquely stretched by advancing one of the left and right clamps ahead of the other clamp, for example, by increasing or decreasing the clamp pitch of the left and right clamps at different positions, or by changing (increasing and/or decreasing) the clamp pitch of the left and right clamps at different changing speeds.

The oblique stretching may comprise transverse stretching. In this case, for example, as shown in the illustrated example, the oblique stretching may be performed while the distance between the left and right jigs (the distance in the width direction) is increased. Alternatively, the oblique stretching may be performed while maintaining the distance between the left and right clamps, unlike the illustrated example.

In the case where the oblique stretching includes transverse stretching, the stretching ratio in the Transverse Direction (TD) (width W of the obliquely stretched film)_finalRelative to the initial width W of the film_initialRatio of (W)_final/W_initial) Preferably 1.05 to 6.00, more preferably 1.10 to 5.00.

In one embodiment, the oblique stretching may be performed by increasing or decreasing the jig pitch of each of the left and right jigs to a predetermined pitch in a state where a position where the jig pitch of one of the jigs starts to increase or decrease and a position where the jig pitch of the other jig starts to increase or decrease are set to different positions in the longitudinal direction. The oblique stretching in this embodiment can be described, for example, in patent document 1 and japanese patent application laid-open No. 2014-238524.

In another embodiment, the inclined stretching may be performed by increasing or decreasing the jig pitch of one of the left and right jigs to a predetermined pitch and then returning the jig pitch of the other jig to the initial jig pitch in a state where the jig pitch of the other jig is fixed. As for the oblique stretching in this embodiment, for example, the descriptions of japanese patent laid-open nos. 2013 and 54338 and 2014 and 194482 can be referred to.

In still another embodiment, the oblique stretching may be performed by (i) increasing the jig pitch of one of the left and right jigs and decreasing the jig pitch of the other jig, and (ii) changing the jig pitches of the respective jigs such that the decreased jig pitch and the increased jig pitch become a predetermined equal pitch. As for the oblique stretching in this embodiment, for example, refer to the description of japanese patent application laid-open publication No. 2014-194484 and the like. The oblique stretching of this embodiment may include the following steps: obliquely stretching the film by increasing the distance between the left and right clamps and decreasing the clamp pitch of one clamp and the clamp pitch of the other clamp (1 st oblique stretching step); and obliquely stretching the film by increasing the jig pitch of the other jig while maintaining or decreasing the jig pitch of the one jig so that the jig pitches of the left and right jigs are equal to each other while increasing the distance between the left and right jigs (2 nd oblique stretching step).

Representatively, the inclined stretching may be performed at a temperature of T2. The temperature T2 is preferably from Tg-20 ℃ to Tg +30 ℃, more preferably from Tg-10 ℃ to Tg +20 ℃, and particularly preferably around Tg, with respect to the glass transition temperature (Tg) of the film. The temperature T2 is, for example, from 70 ℃ to 180 ℃ and preferably from 80 ℃ to 170 ℃ depending on the film used. The difference between the temperature T1 and the temperature T2 (T1-T2) is preferably. + -. 2 ℃ or more, more preferably. + -. 5 ℃ or more. In one embodiment, T1 > T2, and thus, a film that has been heated to a temperature T1 in the preheat zone can be cooled to a temperature T2.

The above-described transverse contraction treatment is performed after the oblique stretching. Regarding this process after the oblique stretching, reference can be made to paragraphs 0029 to 0032 of Japanese patent laid-open No. 2014-194483.

A-4. Releasing of the clamps

The film is released from the jig at an arbitrary position of the release area D. In the releasing zone D, normally neither transverse nor longitudinal stretching is performed, but the film is heat-treated as necessary to fix the stretched state (heat-set), and/or the film is cooled to Tg or less, and then the film is released from the jig. Further, when the thermosetting is performed, the jig pitch in the longitudinal direction can be reduced, thereby relaxing the stress.

Typically, the heat treatment may be performed at a temperature T3. The temperature T3 may be T2. gtoreq.T 3 or T2 < T3, depending on the film to be stretched. In general, the crystallization treatment may be performed so that T2 is T3 in the case where the film is an amorphous material and T2 < T3 in the case where the film is a crystalline material. When T2 is not less than T3, the difference between the temperatures T2 and T3 (T2-T3) is preferably 0 ℃ to 50 ℃. The heat treatment time is typically 10 seconds to 10 minutes.

The stretched film released from the clamp is sent out from the outlet of the stretching apparatus and is conveyed by a roller described later.

A-5. Roller conveying

In the roller conveying step, the amount of slack of the stretched film and the portion where the slack occurs between the conveying rollers are detected.

In one embodiment, the amount of slack and the locations where slack has occurred are detected after cutting and removing the left and right ends in the width direction of the stretched film released from the jig. By detecting the amount of slack and the portion where slack has occurred in the state where both end portions are removed, more accurate detection results can be obtained.

The width of the cut and removed end portion is independently, and may be, for example, 20mm to 600mm, and preferably 100mm to 500 mm. The end portions can be cut and removed by a usual slitting process.

In one embodiment, the amount of slack and the slack-occurring portion may be detected by detecting a difference between an original film advancing position and an actual film advancing position when the roller conveys the film. For example, the detection may be performed by detecting a difference in position (conveyance height) in the width direction of the film at an intermediate point between the conveyance rollers.

FIG. 5 is a view for explaining the detection of the amount of slack and the generation of the slackSchematic diagram of an example of the detection method (3). As shown in fig. 5, the ultrasonic displacement sensor 400 is disposed at the middle point between the two adjacent conveying

rollers

200b and 200c, below the center and the left and right ends of the stretched film 1 in the width direction, and the distance from the ultrasonic displacement sensor 400 to the stretched film 1 is measured, whereby the maximum distance (L) can be set_MAX) From a minimum distance (L)_MIN) Difference between (L)_MAX－L_MIN) The amount of slack is set. In addition, the portion where the minimum distance is generated is detected as the portion where the slack is generated. Further, as a cause of the occurrence of the sag in the obliquely-stretched film, there is a case where the stretching processes (timing, number, order, thermal history, and the like of stretching or shrinking) of the left and right end portions of the film are different from each other at the time of oblique stretching, and as a result, the amount of deformation is not uniform at both end portions after the release of the jig, and therefore, the portion where the sag occurs is usually one end portion. Therefore, the detection site of the sag can be only the left and right end portions in the width direction of the stretched film 1. In this case, the film having no slack can be conveyed in advance, and the distance (L) from the ultrasonic displacement sensor to the film can be measured in advance₀) And the distance between the left and right end parts and the ultrasonic displacement sensor is compared with L₀The difference is set as the amount of slack. Further, although the ultrasonic displacement sensor is described as an example of the slack detection device, the slack may be detected by using any appropriate detection device (for example, a difference in length or the like may be calculated by obtaining the film passing speed of the normal portion and the slack portion by using a laser doppler velocimeter).

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

The film tension at the time of detection is not particularly limited, and may be, for example, 50N/m to 400N/m, preferably 100N/m to 200N/m. If the conveying tension is too high, the film may be elastically deformed during conveyance, and it may be difficult to detect the slack. On the other hand, if the conveyance tension is too low, the tension itself may be unstable, and the measurement value of the slack may be unstable.

The roller conveyance described above may be performed in a non-heated environment. The ambient temperature during the roll conveyance is, for example, about 15 to 40 ℃ and may be, for example, about 20 to 30 ℃.

A-6. Correction for variations in fixture spacing

The correction of the change in the clip pitch is performed by changing the clip pitch of at least one of the left and right clips positioned upstream of the conveying line so as to reduce the slack amount based on the slack amount and the detection result of the portion where the slack occurs, so-called feedback correction. For example, when the detected slack amount is equal to or greater than a predetermined value, the correction for changing the jig pitch is performed, and when the detected slack amount is less than the predetermined value, the oblique stretching can be continued without performing the correction. Specifically, the above correction can be performed when the amount of slack detected at a distance between the rolls of 1000mm is, for example, 3mm or more, 5mm or more, 10mm or more, or 15mm or more.

The correction of the change in the jig pitch (hereinafter also simply referred to as "feedback correction") may be performed by any appropriate method as long as the effects of the present invention can be obtained. The feedback correction can be performed, for example, by the following procedure: increasing the clamp spacing of the clamp holding the end part far from the position where the looseness is generated; reducing the clamp spacing of the clamp holding the end part near the position where the slack is generated; or a combination of both procedures. However, even if the jig pitch is reduced, the film may be loosened without being shrunk, and therefore, it is preferable to perform feedback correction by increasing the jig pitch of the jig that grips the end portion that is distant from the portion where the slack is generated. More specifically, when the portion where the slack is generated is one of the left and right end portions of the stretched film, feedback correction can be preferably performed by increasing the clip pitch of the clip gripping the other end portion.

In the feedback correction, the timing of changing the jig pitch is not particularly limited as long as the effects of the present invention can be obtained. In one embodiment, the clip pitch can be changed to the corrected clip pitch at any time after the film upstream of the conveyance line is transferred to the inclined stretching region and before the film is released from the clips. Preferably, the corrected jig pitch is applied during a period from an arbitrary timing after the jig advanced upstream of the conveyance line passes through an intermediate point of the travel section of the inclined stretching region until the film is released from the jig, and more preferably, the corrected jig pitch is applied during a period from a timing when the jig advanced passes through 1/2 to 9/10 of the travel section of the inclined stretching region until the film is released from the jig. More specifically, the feedback correction is applied from an arbitrary timing after the jig traveling ahead on the upstream of the conveyance line passes through the middle point of the travel section of the inclined stretching region, preferably from the timing when the jig traveling ahead passes through 1/2 to 9/10 of the travel section of the inclined stretching region, and the inter-jig distance is changed so that a desired correction amount is obtained at the end point of the inclined stretching region. Preferably, the correction amount is also maintained during a period from when the film is released from the jig after the oblique stretching region is transferred to the releasing region. In the latter half of the oblique drawing, particularly in the final stage, the clip pitch of at least one clip is maintained constant or limited to a change at a small rate of change, and therefore, by correcting the clip pitch at that time, the effect of the present invention can be preferably obtained.

When the above feedback correction is applied to the oblique stretching region, the film to be subjected is preferably heated to Tg +20 ℃, more preferably Tg +3 ℃ to Tg +10 ℃, and still more preferably Tg +4 ℃ to Tg +8 ℃. The effect of the present invention can be preferably obtained by applying the feedback correction at a temperature equal to or slightly higher than Tg. In one embodiment, the film transferred to the release region through the obliquely stretched region while being subjected to the feedback correction at the above temperature is heat-treated in a state in which the amount of correction performed in the obliquely stretched region is maintained, then cooled, and then released from the jig. The heat treatment and cooling are as described in the section A-4.

Fig. 6A is a schematic view showing a curve of the clip pitch in the embodiment of the method for producing a stretched film of the present invention. In the illustrated example, the clamp pitches of the left and right clamps X, Y in the preheating region B are both P₁In the initial oblique stretching before the feedback correctionStarting to increase the clamp pitch of the clamp X on one side and starting to decrease the clamp pitch of the clamp Y on the other side while entering the inclined stretching region C, and increasing the clamp pitch of the clamp X to P₂Reducing the clamp pitch of the clamp Y to P₃Thereafter, the jig pitch of the jig X is maintained at P₂And the grip pitch of the grip Y is increased to P₂. Left and right clamps X, Y at a clamp pitch P₂Moves to the release area D and releases the film. Thereafter, as a result of feedback correction based on the amount of slack or the like at the time of roll conveyance of the film, the clamp pitch of the clamps X is changed from P in the oblique stretching region C₂Gradually increase to P₂'. As will be described later, the clip pitch of the clips X, Y is maintained at P in each of the release areas₂' and P₂The correction amount (P) at the end of the oblique stretching region is maintained₂’－P₂)。

Fig. 6B is a schematic view showing a curve of the clip pitch in another embodiment of the method for producing a stretched film of the present invention. In the illustrated embodiment, the inclined stretching is performed in the same manner as the embodiment shown in fig. 6A, and the clamp pitches of the left and right clamps X, Y are set together from P at the heat setting timing in the release area D₂Decrease to P₃The film is then released. Thereafter, as a result of feedback correction based on the amount of slack or the like at the time of roll conveyance of the film, the clamp pitch of the clamps X is changed from P in the oblique stretching region C₂Gradually increase to P₂', in the release area, the grip spacing of the grips X is from P₂' decrease to P₃', clamp Y with a clamp pitch from P₂Decrease to P₃. Further, as described later, in the drop-out region, the correction amount (P) at the end point of the oblique drawing region is maintained₂’－P₂) In such a manner that the clamp pitch of the clamp X, Y is reduced to satisfy P₃’－P₃＝P₂’－P₂The relationship (2) of (c).

In the inclined stretching region, the change toward the corrected clip pitch (toward P)₂Variation of' is preferred) from the point of starting application of feedback correction to the end point (in fig. 6A and 6B, from the point of passing through the tilt pullThe time of stretching 2/3 of the region to the end point). Further, it is preferable to maintain the correction amount of the oblique stretching end time (| the pre-correction clip pitch at the oblique stretching end time — the post-correction clip pitch at the oblique stretching end time |) also in the range from the end point of the oblique stretching region to the release of the clip. For example, in the graphs shown in fig. 6A and 6B, the difference between the clip pitch of the clip X and the clip pitch of the clip Y is maintained constant (i.e., P) in the range from the end point of the oblique stretching region to the release of the clip₂’－P₂). By thus changing the distance between the jigs, the effect of the present invention can be obtained preferably.

The jig pitch can be changed by adjusting the distance between the reference rail and the pitch setting rail as described above. These adjustments can be made without temporarily stopping or stopping the transport line.

The correction amount of the jig pitch at the end time of the oblique stretching in the feedback correction (i the jig pitch before correction at the end time of the oblique stretching — the jig pitch after correction at the end time of the oblique stretching) may be appropriately set in accordance with the amount of slack or the like. The correction amount of the clip pitch may preferably exceed the difference in length between the left and right end portions of the stretched film between the transport rollers, more preferably 1.4 to 5.0 times the difference in length, still more preferably 1.6 to 4.0 times the difference in length, and yet more preferably 1.8 to 3.0 times the difference in length. If the amount of correction of the chuck pitch is equal to or less than the difference in the lengths of the left and right end portions, the amount of reduction of the slack may be insufficient.

The difference L' (unit: mm) in the lengths of the left and right end portions of the stretched film between the transport rollers can be calculated by substituting the length L (unit: mm) of the stretched film between the transport rollers calculated based on the following equations (1) and (2) into the following equation (3).

[ expression 2 ]

d＝(H/(w＊g))＊(cosh(w＊g＊S/2H)-1)…(1)

L＝(2H/(w*g))＊sinh((w＊g＊S/2H)…(2)

L‘＝L-S…(3)

In one embodiment, the amount of relaxation reduced by the feedback correction (the amount of relaxation of the stretched film obtained before the feedback correction-the amount of relaxation of the stretched film obtained after the feedback correction: wherein the amount of relaxation is measured in terms of the distance between the transport rollers of 1000 mm) may be, for example, 3mm or more, preferably 5mm or more, more preferably 8mm or more, and still more preferably 10mm or more. The relaxation amount of the stretched film obtained after the feedback correction may be, for example, less than 15mm, preferably 10mm or less, more preferably 8mm or less, further preferably 5mm or less, and further preferably less than 3 mm.

B. Film for stretching object

In the production method of the present invention, any appropriate film can be used. For example, a resin film that can be used as a retardation film is exemplified. Examples of the material constituting such a film include polycarbonate resin, polyvinyl acetal resin, cycloolefin resin, acrylic resin, cellulose ester resin, cellulose resin, polyester carbonate resin, olefin resin, and polyurethane resin. Polycarbonate-series resins, cellulose ester-series resins, polyester carbonate-series resins, and cycloolefin-series resins are preferred. This is because a retardation film showing wavelength dependence of the reverse dispersion can be obtained by using these resins. These resins may be used alone or in combination according to desired characteristics.

As the polycarbonate-based resin, any appropriate polycarbonate-based resin can be 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-bis ((4-hydroxy-3-methylphenyl) fluorene, 9-bis (4-hydroxy-3-ethylphenyl) fluorene, 9-bis (4-hydroxy-3-n-propylphenyl) fluorene, 9-bis (4-hydroxy-3-isopropylphenyl) fluorene, 9-bis (4-hydroxy-3-n-butylphenyl) fluorene, 9-bis (4-hydroxy-3-sec-butylphenyl) fluorene, 9-bis (4-hydroxy-3-tert-butylphenyl) fluorene, 9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, 9-bis (4-hydroxy-3-phenylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) phenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-methylphenyl) fluorene, 9, 9-bis (4- (2-hydroxyethoxy) -3-isopropylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-isobutylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-tert-butylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-cyclohexylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-phenylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3, 5-dimethylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-tert-butyl-6-methylphenyl) fluorene, 9-bis (4- (3-hydroxy-2, 2-dimethylpropoxy) phenyl) fluorene, and the like. The polycarbonate resin may contain, in addition to the structural unit derived from the above dihydroxy compound, a structural unit derived from a dihydroxy compound such as isosorbide, isomannide, isoidide, spiroglycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), Cyclohexanedimethanol (CHDM), Tricyclodecanedimethanol (TCDDM), or bisphenols.

The polycarbonate-series resin is described in detail in, for example, Japanese patent laid-open Nos. 2012 and 67300 and 3325560. The description of this patent document is incorporated herein by reference.

The glass transition temperature of the polycarbonate-based resin is preferably 110 ℃ or higher and 250 ℃ or lower, and more preferably 120 ℃ or higher and 230 ℃ or lower. If the glass transition temperature is too low, heat resistance tends to be poor, and dimensional change may occur after film formation. If the glass transition temperature is too 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 in accordance with JIS K7121 (1987).

As the polyvinyl acetal resin, any suitable polyvinyl acetal resin can be used. Typically, the polyvinyl acetal resin can be obtained by condensation reaction of at least two aldehyde compounds and/or ketone compounds with a polyvinyl alcohol resin. Specific examples of polyvinyl acetal resins and detailed production methods are described in, for example, Japanese patent laid-open No. 2007-161994. This description is incorporated by reference into this specification.

The retardation film obtained by stretching the film to be stretched preferably has a refractive index characteristic showing a relationship 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 100nm to 180nm, more preferably 135nm 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 (. lamda./2 plate) is preferably 230 to 310nm, more preferably 250 to 290 nm. In the present specification, nx is a refractive index in a direction in which an in-plane refractive index is maximum (i.e., a slow axis direction), ny is a refractive index in a direction orthogonal to the slow axis (i.e., a fast axis direction) in the plane, and nz is a refractive index in a thickness direction. Further, Re (. lamda.) is an in-plane retardation of the film measured at 23 ℃ by light having a wavelength of. lamda.nm. Thus, Re (550) is the in-plane retardation of the film obtained by measurement of light having a wavelength of 550nm at 23 ℃. When the film thickness is d (nm), Re (λ) is obtained by the formula Re (λ) ═ nx-ny) × d.

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 100nm to 180nm by oblique stretching are disclosed in detail in Japanese patent laid-open Nos. 2013-54338, 2014-194482, 2014-238524, 2014-194484, and the like. Thus, one skilled in the art can set appropriate oblique stretching conditions based on this disclosure.

When a circularly polarizing plate is produced using 1 sheet of retardation film (specifically, λ/4 plate) or when the orientation of linearly polarized light is rotated by 90 ° using 1 sheet of retardation film, the slow axis direction of the retardation film to be used is preferably about 30 ° to 60 ° or 120 ° to 150 °, more preferably about 38 ° to 52 ° or 128 ° to 142 °, further preferably about 43 ° to 47 ° or 133 ° to 137 °, particularly preferably about 45 ° or 135 °, with respect to the longitudinal direction of the film.

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

The retardation film preferably exhibits wavelength dependence of so-called reverse dispersion. Specifically, the in-plane retardation satisfies the relationship 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(m²/N)～100×10^-12(m²/N), more preferably 5 × 10^-12(m²/N)～50×10^-12(m²/N)。

C. Optical laminate and method for producing same

The stretched film obtained by the production method of the present invention can be used as an optical laminate by bonding to other optical films. For example, the retardation film obtained by the production method of the present invention can be preferably used as a circularly polarizing plate by being bonded to a polarizing plate.

Fig. 7 is a schematic cross-sectional view of an example of such a circularly polarizing plate. The circularly polarizing plate 500 illustrated in the figure includes a polarizer 510, a 1 st protective film 520 disposed on one side of the polarizer 510, a 2 nd protective film 530 disposed on the other side of the polarizer 510, and a retardation film 540 disposed outside the 2 nd protective film 530. The retardation film 540 is a stretched film (for example, a λ/4 plate) obtained by the production method described in the section a. The 2 nd protective film 530 may be omitted. In this case, the retardation film 540 can function as a protective film for a polarizer. The angle formed by the absorption axis of the polarizer 510 and the slow axis of the retardation film 540 is preferably about 30 ° to 60 °, more preferably about 38 ° to 52 °, still more preferably about 43 ° to 47 °, and particularly preferably 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 (direction at, for example, 45 ° to the longitudinal direction). In many cases, a long polarizer has an absorption axis in the longitudinal direction or the width direction. Therefore, when the retardation film obtained by the production method of the present invention is used, a circular polarizing plate can be produced with extremely excellent production efficiency by so-called roll-to-roll. The roll-to-roll method is a method of continuously laminating long films while aligning the films in the longitudinal direction while roll-feeding the films.

In one embodiment, a method for producing an optical laminate according to the present invention includes the steps of: a method for producing a stretched film according to item a, wherein a long stretched film is obtained; and continuously bonding the long optical film and the long stretched film while aligning the longitudinal directions thereof.

Examples

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

(1) Thickness of

The measurement was carried out using a dial gauge (product name "DG-205 type pds-2" manufactured by PEACOCK Co., Ltd.).

(2) Phase difference value

The in-plane retardation Re (550) was measured using an Axoscan manufactured by Axometrics.

(3) Orientation angle (display direction of slow axis)

A sample was prepared by cutting out a square shape having a width of 50mm and a length of 50mm from the center of a film to be measured so that one side of the center is parallel to the width direction of the film. The sample was measured by using an Axoscan manufactured by Axometrics, and the orientation angle θ at a wavelength of 590nm was measured.

(4) Glass transition temperature (Tg)

The measurement was carried out in accordance with JIS K7121.

(5) Amount of relaxation

As shown in FIG. 5, an ultrasonic displacement sensor was disposed below the conveyance path of the stretched film at a point between two adjacent conveyance rollers (inter-roller distance: 912 mm). While the stretched film was conveyed at a conveying tension of 150N/m, the distance from the ultrasonic displacement sensor to the stretched film was measured at the center and the end in the width direction, and the maximum distance (L) was measured_MAX) From a minimum distance (L)_MIN) Difference between (L)_MAX－L_MIN) The amount of relaxation (mm) was set. In addition, the portion where the minimum distance has occurred is determined as the portion where the slack has occurred.

< example 1 >

(preparation of a polyester carbonate resin film)

The polymerization was carried out using a batch polymerization apparatus comprising two vertical reactors equipped with stirring blades and a reflux cooler controlled at 100 ℃. 29.60 parts by mass (0.046mol) of bis [ 9- (2-phenoxycarbonylethyl) fluoren-9-yl group was added]Methane, 29.21 parts by mass (0.200mol) of ISB, 42.28 parts by mass (0.139mol) of SPG, 63.77 parts by mass (0.298mol) of DPC and 1.19 × 10 as a catalyst^-2Mass portion (6.78 × 10)^-5mol) of calcium acetate monohydrate. After the inside of the reactor was replaced with nitrogen gas under reduced pressure, the reactor was heated with a heat transfer medium, and stirring was started when the internal temperature became 100 ℃. The internal temperature was increased to 220 ℃ 40 minutes after the start of the temperature increase, and the pressure reduction was started while controlling the temperature, and was set to 13.3kPa after 90 minutes from the temperature increase to 220 ℃. Introducing phenol vapor by-produced together with the polymerization reaction into a reflux cooler at 100 ℃, returning some amount of monomer components contained in the phenol vapor to the reactor, introducing uncondensed phenol vapor into a condenser at 45 ℃ and returning the uncondensed phenol vapor to the reactorAnd (6) harvesting. After nitrogen was introduced into the 1 st reactor and the pressure was temporarily returned to atmospheric pressure, the reaction liquid obtained by oligomerization in the 1 st reactor was transferred to the 2 nd reactor. Subsequently, the temperature and pressure in the 2 nd reactor were increased to 240 ℃ and 0.2kPa internal temperature within 50 minutes. Thereafter, polymerization was carried out until a predetermined stirring power was reached. When the predetermined power is reached, nitrogen is introduced into the reactor to recover the pressure, the produced polyester carbonate is extruded into water, and the strand is cut to obtain pellets. The Tg of the polyester carbonate resin obtained was 140 ℃.

After the obtained polyester carbonate resin was dried in vacuum at 80 ℃ for 5 hours, a resin film having a thickness of 135 μm was produced using a film forming apparatus equipped with a uniaxial extruder (cylinder set temperature: 250 ℃ C., manufactured by Toshiba machine Co., Ltd.), a T-die (width 200mm, set temperature: 250 ℃ C.), a cold roll (set temperature: 120 ℃ C. -130 ℃ C.) and a winding device.

(Tilt stretching before feedback correction)

The polyester carbonate resin film thus obtained was obliquely stretched using a stretching apparatus shown in fig. 2 to 4 to obtain a retardation film. Specifically, the polyester carbonate resin film was preheated to 145 ℃ in a preheating zone of the stretching apparatus. In the preheating region, the clamp pitch (P) of the left and right clamps₁) Is 125 mm. Then, while the film entered the inclined stretching region C, the gripper pitch of the right gripper was increased and the gripper pitch of the left gripper was decreased, and the gripper pitch of the right gripper was increased to P₂And the clamp spacing of the left clamp is reduced to P₃. At this time, the rate of change of the clamp pitch (P) of the right clamp₂/P₁) 1.42, rate of change of grip pitch (P) of left grip₃/P₁) 0.78, and a transverse stretching magnification of 1.45 times with respect to the original width of the film. Then, the clamp pitch of the right clamp is maintained at P₂Starting to increase the clamp pitch of the left clamp from P₃Increase to P₂. Rate of change of grip pitch (P) of left grip during this period₂/P₃) 1.82, cross-directional stretch times relative to the original width of the filmThe ratio was 1.9 times. Further, the inclined stretching region C was set to Tg +3.2 ℃ (143.2 ℃).

Subsequently, in the release region D, the film was held at 125 ℃ for 60 seconds to be heat-set. After cooling the heat-fixed film to 100 ℃, the left and right clamps were released.

(roller transport)

Both side end portions of the stretched film released from the above-mentioned jig and sent out from the stretching device were cut by 250mm, respectively. The film with both ends cut off is conveyed by rollers, and the amount of slack between the conveying rollers and the portion where the slack occurs are detected. As a result, slack was generated in the left end, and the amount of slack was 18.0 mm. The difference L' between the lengths of both ends of the stretched film before correction, calculated based on the above equations (1) to (3), was 0.95 mm.

(feedback correction)

Gradually increasing the clamp pitch of the right clamp to P in the period from the time point of passing 3/4 in the travel section of the inclined stretching region C to the time point of reaching the end point₂' (amount of correction of chuck Pitch (P)₂’－P₂): 0.3mm) was heated (125 c, 60 seconds) and cooled (100 c) in the same manner as described above while maintaining the jig pitch, and the curve of the jig pitch was changed to continue the oblique drawing. That is, the clamp pitch when the feedback-corrected obliquely-stretched film is released from the clamp is P, and the clamp pitch on the right side is P₂', left clamp spacing is P₂。

The retardation Re (590) of the obtained stretched film was 147nm, and the angle formed between the slow axis direction and the longitudinal direction was 45 °.

< example 2 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by oblique stretching in the same manner as in example 1 except that the thickness was changed to 0.6 mm.

< example 3 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by oblique stretching in the same manner as in example 1 except that the thickness was changed to 0.95 mm.

< example 4 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by oblique stretching in the same manner as in example 1 except that the thickness was changed to 1.8 mm.

< example 5 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by oblique stretching in the same manner as in example 1 except that the thickness was changed to 2.6 mm.

< example 6 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by stretching obliquely in the same manner as in example 1, except that the thickness was 0.6mm and the section 3/4 and thereafter of the travel section of the obliquely stretched zone C was Tg +6.0 ℃ (146.0 ℃).

< example 7 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by stretching obliquely in the same manner as in example 1, except that the thickness was 0.95mm and the section 3/4 and thereafter of the travel section of the obliquely stretched zone C was Tg +6.0 ℃ (146.0 ℃).

< example 8 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by stretching obliquely in the same manner as in example 1, except that the thickness was 1.8mm and the section 3/4 and thereafter of the travel section of the obliquely stretched zone C was Tg +6.0 ℃ (146.0 ℃).

< example 9 >

Except for correcting the distance between the jaws (P)₂’－P₂) A stretched film was obtained by stretching obliquely in the same manner as in example 1, except that the thickness was 2.6mm and the section 3/4 and thereafter of the travel section of the obliquely stretched zone C was Tg +6.0 ℃ (146.0 ℃).

< comparative example 1 >

A stretched film was obtained by oblique stretching in the same manner as in example 1, except that the feedback correction was not performed.

The stretched films obtained in the above examples and comparative examples were measured for the amount of relaxation by the method described above.

The stretched films obtained in the above examples and comparative examples were laminated to a long masking film (product name "Tortec 7832C-30" manufactured by toray film processing) in a roll-to-roll manner to obtain a film laminate. Next, the masking film was peeled off from the film laminate, an adhesive was applied by a gravure coater, the film was laminated with a polarizing plate, and UV irradiation was performed, thereby obtaining an optical laminate. The appearance (visual observation) of the film laminate and the handling properties of the stretched film were evaluated based on the following criteria.

Good: after the mask film was bonded (bonding tension 150N/m), the adhesive could be applied to the entire surface of the film without any wrinkles being observed.

And (delta): when the mask film is bonded, the bonding tension is raised to 300N/m, whereby the bonding can be performed without wrinkles, but when the adhesive is applied, the adhesive cannot be applied to a loose portion.

X: after the masking film is attached, wrinkles exist, and the appearance is poor.

The results of the evaluation of the relaxation amount, the appearance of the film laminate, and the like are shown in table 1 together with the production process. In table 1, "relaxation reduction amount" is a difference from the relaxation amount of the stretched film of comparative example 1 (relaxation amount of the stretched film obtained in comparative example 1 — relaxation amount of the stretched film obtained in each example).

TABLE 1

< evaluation >

As shown in table 1, the sag of the stretched film obtained thereafter was reduced by detecting the sag of the obliquely stretched film and appropriately changing the nip pitch upstream of the conveying line based on the detection result.

Industrial applicability

The method for producing a stretched film of the present invention can be preferably 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) or an organic electroluminescent display device (OLED).

Claims

1. A method for producing a stretched film, wherein,

the method for producing a stretched film comprises the steps of:

holding the left and right ends of the long film in the width direction by a variable-pitch left and right jig with a jig pitch varying in the longitudinal direction;

moving the left and right clamps while changing the clamp pitch of at least one of the left and right clamps, and moving either clamp ahead of the other clamp to obliquely stretch the film;

releasing the film from the left and right clamps;

roll-conveying the film, detecting the amount of slack of the film between the conveying rollers and the location where the slack occurs; and

based on the detection result, correction is performed to change the gripper pitch of at least one of the left and right grippers positioned upstream of the conveyance path.

2. The method for producing a stretched film according to claim 1,

after the left and right ends of the film released from the left and right clamps are cut and removed, the amount of slack and the locations where slack occurs are detected.

3. The method for producing a stretched film according to claim 1 or 2,

the correction of the jig pitch variation includes the steps of: the distance between the clamps holding the end portion remote from the portion where the slack is generated is increased.

4. The method for producing a stretched film according to any one of claims 1 to 3,

and correcting the change of the clamp pitch from the time when the clamp which advances in advance passes through the positions 1/2-9/10 in the advancing section of the inclined stretching to the time when the film is released from the left and right clamps.

5. The method for producing a stretched film according to any one of claims 1 to 4,

the correction of the change of the clip pitch is performed with a correction amount larger than a difference L '(unit: mm) in length of the left and right end portions of the film between the conveying rollers, and further, L' is calculated by substituting the length L (unit: mm) of the film between the conveying rollers calculated based on the following formula (1) and formula (2) into the following formula (3),

[ expression 1 ]

d＝(H/(w＊g))＊(cosh(w＊g＊S/2H)-1)…(1)

L＝(2H/(w＊g))＊sinh(w＊g＊S/2H)…(2)

L‘＝L-S··…(3)

6. The method for producing a stretched film according to any one of claims 1 to 5,

correction of the change in the clip pitch is performed in the oblique stretching,

the ambient temperature at this point is between Tg and Tg +20 ℃ of the film.

7. A method for manufacturing an optical laminate, wherein,

the method for manufacturing the optical laminate comprises the following steps:

a long stretched film obtained by the production method according to any one of claims 1 to 6; and

the long optical film and the long stretched film are continuously laminated while being aligned in the longitudinal direction thereof.

8. The method for manufacturing an optical stack according to claim 7,

the optical film is a polarizing plate,

the stretched film is a lambda/4 plate or a lambda/2 plate.