CN111716691B

CN111716691B - Method for producing stretched film

Info

Publication number: CN111716691B
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: 2023-04-21
Anticipated expiration: 2040-03-19
Also published as: TW202035106A; CN111716691A; KR20200112650A; TWI780395B; JP2020151960A; JP7253413B2

Abstract

The invention provides a method for manufacturing a stretched film. The relaxation of the obliquely stretched film is reduced. The method for producing the stretched film comprises the following steps: gripping the left and right ends of the elongated film in the width direction by left and right grippers of variable pitch type whose gripper pitch varies in the longitudinal direction; the film is obliquely stretched by moving the left and right jigs while changing the jig pitch of at least one of the left and right jigs; releasing the membrane from the left and right clamps; carrying out roller conveying on the film, and detecting the relaxation amount of the film between conveying rollers and the part generating relaxation; and performing correction of changing a jig pitch of at least one of the left and right jigs located upstream of the conveying 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 electroluminescence display devices (OLEDs), circular polarizing plates are used for the purpose of improving display characteristics and preventing reflection. Typically, a circularly polarizing plate is laminated with a polarizer and a retardation film (typically, a λ/4 plate) so that the absorption axis of the polarizer and the retardation axis of the retardation film form an angle of 45 °. Conventionally, a retardation film is typically produced by uniaxial stretching or biaxial stretching in the machine direction and/or the transverse direction, and therefore, its slow axis is often exhibited in the transverse direction (width direction) or the longitudinal direction (length direction) of a long film roll. As a result, when manufacturing a circularly polarizing plate, it is necessary to cut the phase difference film so as to form an angle of 45 ° with respect to the width direction or the length direction and attach the phase difference film to the polarizing plate (polarizer) one by one.

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

In other embodiments, in order to prevent light from the notebook PC from being reflected on a keyboard or the like, a λ/2 plate may be used on the viewing side of the polarizing plate for the purpose of rotating the direction of the linearly polarized light from the polarizing plate by 90 °. In this case, it is also necessary to cut the retardation film so as to form an angle of 45 ° with respect to the width direction or the length direction and attach the retardation film to a polarizing plate (polarizer) one by one.

In order to solve such a problem, the following techniques have been proposed: the retardation axis of the retardation film is developed in the oblique direction by gripping the left and right ends of the elongated film in the width direction by left and right grippers whose grip pitch varies in the longitudinal direction, and stretching in the oblique direction by varying the grip pitch of at least one of the left and right grippers (hereinafter also referred to as "oblique stretching") (for example, patent document 1). However, in the obliquely-stretched film obtained by such a technique, there is a case where the end portion in the width direction is loosened (relaxed). When such a film having slack is wound, wrinkles and scratches may occur in the resulting film roll. When the film having the slack is bonded to another optical film, there are cases where an adhesive, uneven application of an adhesive, or an uncoated portion is generated, and wrinkles or scratches are generated 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 its main object is to reduce the slack that occurs in a film that is drawn obliquely.

Solution for solving the problem

According to one aspect of the present invention, there is provided a method for producing a stretched film, comprising: gripping the left and right ends of the elongated film in the width direction by left and right grippers of variable pitch type whose gripper pitch varies in the longitudinal direction; moving at least one of the left and right jigs while changing a jig pitch of the at least one of the left and right jigs, and moving either one of the left and right jigs ahead of the other jig, thereby obliquely stretching the film; releasing the membrane from the left and right clamps; carrying out roller conveying on the film, and detecting the relaxation amount of the film between conveying rollers and the part generating relaxation; and performing correction of changing a jig pitch of at least one of the left and right jigs located upstream of the conveying line based on the detection result.

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

In one embodiment, the correction of the jig pitch variation includes the steps of: the clip pitch of the clip holding the end portion remote from the portion where the slack is generated is increased.

In one embodiment, the correction of the change in the pitch of the clips is performed from the time when the clip traveling in advance passes through the position of 1/2 to 9/10 of the traveling section of the oblique stretching until the film is released from the left and right clips.

In one embodiment, correction for changing 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 conveying rollers, and L' is calculated by substituting a 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)

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

In one embodiment, the correction for changing the pitch of the jigs is performed during the oblique stretching, 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 producing an optical laminate, the method comprising: obtaining a long stretched film by the above-mentioned method for producing a stretched film; and continuously bonding the elongated optical film and the elongated stretched film while aligning the longitudinal directions of the films while conveying 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.

ADVANTAGEOUS EFFECTS OF INVENTION

In the method for producing a stretched film according to the present invention, the amount of slack and the location of the slack that occurs in the film after oblique stretching are detected, and the clip pitch of at least one clip located on the left and right upstream of the transfer line is corrected based on the detection result. This reduces the difference in length between the left and right end portions of the film, and as a result, a long obliquely-stretched film with reduced sag can be obtained.

Drawings

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

Fig. 2 is a schematic plan view illustrating the overall structure 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 a clip pitch 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 a clip pitch in the stretching apparatus of fig. 2.

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

Fig. 6A is a schematic diagram showing a curve of the jig pitch in one embodiment of the method for producing a stretched film according to the present invention.

Fig. 6B is a schematic view showing a curve of the jig pitch in another embodiment of the method for producing a stretched film according to 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, annular ring; 20. a clamp; 100. a stretching device; 200. a conveying roller; 300. a winding part; 400. an ultrasonic displacement sensor; 500. a circular polarizing plate.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments. In the present specification, the term "clip pitch in the longitudinal direction" refers to the center-to-center distance in the traveling direction of clips adjacent in the longitudinal direction. The left-right relationship in the width direction of the elongated film refers to the left-right relationship in the conveying 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 following steps: gripping the left and right ends of the elongated film in the width direction by left and right grippers of variable pitch type whose gripper pitch varies in the longitudinal direction; the film is obliquely stretched by moving the left and right jigs while changing the jig pitch of at least one of the left and right jigs; releasing the membrane from the left and right clamps; carrying out roller conveying on the film, and detecting the relaxation amount of the film between conveying rollers and the part generating relaxation; and performing correction of changing a jig pitch of at least one of the left and right jigs located upstream of the conveying 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 a method for producing a stretched film according to the present invention. The obliquely-stretched film 1 which is 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 roll-fed by the feed rolls 200a, 200b, 200c, 200d to be wound around the winding section 300. When the film 1 is conveyed by rollers, a slack amount 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 clip located on the left and right upstream of the conveying line. Thus, the difference in length between the left and right ends of the stretched film obtained after correction is reduced, and as a result, a long obliquely-stretched film with reduced sag can be obtained.

The gripping, preheating, oblique stretching, and releasing of the film by the clamp may be performed by using, for example, a tenter type simultaneous biaxial stretching apparatus having left and right clamps capable of moving at different speeds while gripping the left and right ends of the elongated film in the width direction.

Fig. 2 is a schematic plan view illustrating the overall structure of an example of a stretching apparatus that can be used in the manufacturing method of the present invention. The stretching device 100 has an annular ring 10L and an annular ring 10R symmetrically on the left and right sides in a plan view, and the annular ring 10L and the annular ring 10R have a plurality of jigs 20 for film gripping. In this 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 when viewed from the inlet side of the film. The jigs 20 of the left and right annular rings 10L, 10R are guided by the reference rails 70 to move in an annular cycle. 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. The stretching apparatus includes a grip region a, a preheating region B, an inclined stretching region C, and a release region D in this order from an inlet side to an outlet side of the sheet. These regions are regions for holding, preheating, obliquely stretching, and releasing a film to be stretched, and are not mechanically and 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.

Although not shown in fig. 2, a region for performing any appropriate process may be provided between the inclined stretching region C and the release region D as needed. Such a process includes a lateral shrinkage process and the like. The stretching apparatus includes a heating apparatus (for example, various ovens of a hot air type, a near infrared type, a far infrared type, and the like) for forming a heating environment from the preheating region B to the releasing region D, which is also not shown in the drawings.

In the grip region a and the preheating region B of the stretching apparatus 100, the left and right

annular rings

10L and 10R are formed so as 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 annular rings 10L, 10R gradually increases from the side of the preheating region B toward the releasing region D so as to correspond to the stretched width of the film. In the release region D, the left and right annular rings 10L, 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 annular rings 10L, 10R may be configured to be substantially parallel to each other from the holding region a to the releasing region D at a distance 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 respectively and independently circulated. For example, the driving

sprockets

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

electric motors

13, 14 to rotate in the counterclockwise direction, and the driving

sprockets

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

electric motors

13, 14 to rotate in the clockwise direction. 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. Thus, the left annular ring 10L is cyclically moved in the counterclockwise direction, and the right annular ring 10R is cyclically 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 circulated independently.

Further, the clamp (left clamp) 20 of the left annular ring 10L and the clamp (right clamp) 20 of the right annular ring 10R are each of a variable pitch type. That is, the left and

right jigs

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

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

As shown in fig. 3 and 4, a jig holding member 30 is provided that holds the jigs 20 and is elongated in the lateral direction in a plan view. Although not shown, the clip holding member 30 is formed into a firm frame structure having a closed cross section by using 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 to the clip). The jig holding member 30 is provided so as to roll on the running surfaces 81, 82 by the running wheels 38 at both ends thereof. In fig. 3 and 4, the front-wall-side travel wheel (travel wheel that rolls on the travel surface 81) is not shown. The traveling

road surfaces

81, 82 are parallel to the reference rail 70 over the entire area. A long hole 31 is formed in the rear side of the upper beam and the lower beam of the clip holding member 30 (the opposite side to the clip side (hereinafter referred to as the clip opposite side)) along the longitudinal direction of the clip holding member, and a slider 32 is engaged slidably in the longitudinal direction of the long hole 31. A 1 st shaft member 33 is provided vertically through the upper and lower beams in the vicinity of the clamp 20 side end of the clamp holding member 30. On the other hand, the slider 32 of the jig holding member 30 is provided with one 2 nd shaft member 34 vertically penetrating therethrough. One end of a main link member 35 is pivotally connected to the 1 st shaft member 33 of each clip holding member 30. The main link member 35 pivotally connects the other end to the 2 nd shaft member 34 of the adjacent clip holding member 30. The 1 st shaft member 33 of each clip holding member 30 is pivotally connected to one end of a sub link member 36 in addition to one end of a main link member 35. The sub link member 36 is pivotally connected at the other end 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 smaller the distance between the clip holding members 30 in the longitudinal direction (as a result of the clip distance) is, the larger the distance between the clip holding members 30 in the longitudinal direction (as a result of the clip distance) is, as shown in fig. 4, the larger the distance between the clip holding members 30 in the longitudinal direction (as a result of the clip distance) is, as the slider 32 moves toward the front side (clip side) of the clip holding members 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 separation distance between the reference rail 70 and the pitch setting rail 90, the larger the jig pitch.

By performing oblique stretching of the film using such a stretching device, an oblique stretched film can be produced, and for example, a retardation film having a retardation axis in an oblique direction can be produced. A specific embodiment of such a stretching device is described in, for example, japanese patent application laid-open No. 2008-44339, which is incorporated herein by reference in its entirety. Each step will be described in detail below.

A-1. Gripping of film by a clamp

In the holding region a (the entrance of film taking in of the stretching apparatus 100), both side edges of the film to be stretched are held at a constant or different clip pitch by the clips 20 of the left and right annular rings 10L, 10R. The film is transported to the preheating region B by the movement of the jigs 20 (substantially, the movement of the jig holding members guided by the reference rail 30) of the left and right annular rings 10L, 10R.

A-2. Preheating

In the preheating zone B, the left and right annular rings 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 as described above, and therefore the film is heated substantially without being stretched in the transverse direction or in the longitudinal direction. However, in order to avoid a problem such as the deflection of the film due to preheating and contact with the nozzle in the oven, the distance between the left and right jigs (the distance in the width direction) may be slightly increased.

During the preheating process, the film is heated to a temperature T1 (°c). The temperature T1 is preferably not less than the glass transition temperature (Tg) of the film, more preferably not less than tg+2℃, 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, 70℃to 190℃and preferably 80℃to 180 ℃.

The temperature rise time to the temperature T1 and the holding time of the temperature T1 can be appropriately set according to the constituent materials of the film and the manufacturing conditions (for example, the film conveyance 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. Oblique stretching

In the oblique stretching region C, the film is obliquely stretched by moving one of the left and right jigs 20 forward while changing the jig pitch in the longitudinal direction of at least one of the left and right jigs 20, and moving the other jig forward. More specifically, the film is obliquely stretched by increasing or decreasing the clip pitch of the left and right clips at different positions, changing (increasing and/or decreasing) the clip pitch of the left and right clips at different changing speeds, and the like, and advancing either clip over the other clip.

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

In the case where oblique stretching includes transverse stretching, the stretching ratio in the Transverse Direction (TD) (width W of the film after oblique stretching _final Relative to the initial width W of the film _initial Ratio (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 clip pitch of each clip to a predetermined pitch in a state where the clip pitch of one clip starts to increase or decrease from the clip pitch of the other clip starts to increase or decrease. For example, patent document 1 and japanese patent application laid-open No. 2014-238524 describe the oblique stretching of this embodiment.

In another embodiment, the oblique stretching may be performed by increasing or decreasing the clip pitch of one clip to a predetermined pitch and then returning the other clip to the original clip pitch in a state where the clip pitch of the one clip is fixed. For the oblique stretching in this embodiment, for example, refer to the descriptions of japanese patent application laid-open publication No. 2013-54338 and japanese patent application laid-open publication No. 2014-194482.

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

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

The above-described transverse shrinkage treatment is performed after the oblique stretching. For this treatment after the oblique stretching, refer to paragraphs 0029 to 0032 of Japanese patent application laid-open No. 2014-194483.

A-4. Releasing of clamps

The film is released from the jig at an arbitrary position in the release area D. In the release region D, generally, neither transverse stretching nor longitudinal stretching is performed, but the film is heat-treated as needed to fix (heat-fix) the stretched state, and/or the film is cooled to below Tg, followed by release of the film from the jig. Further, at the time of heat setting, the clamp 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 varies depending on the film to be stretched, and may be T2. Gtoreq.T3 or T2 < T3. In general, the crystallization treatment may be performed with T2 being equal to or greater than T3 when the film is an amorphous material, or with T2 < T3 when the film is a crystalline material. In the case where T2. Gtoreq.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 jig is sent out from the outlet of the stretching device and fed to a roller described later.

A-5. Roller transport

In the roll conveying step, the amount of relaxation of the stretched film between the conveying rolls and the site where the relaxation occurs are detected.

In one embodiment, after the left and right end portions in the width direction of the stretched film released from the jig are cut off and removed, the amount of slack and the portion where the slack is generated are detected. By detecting the amount of the above-described slack and the portion where the slack is generated in a state where both end portions are removed, a more accurate detection result can be obtained.

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

In one embodiment, the detection of the amount of slack and the occurrence of slack may be performed by detecting a difference between an original film travel position and an actual film travel position during the roller conveyance. For example, the detection may be performed by detecting a difference in position (conveying height) of the film in the width direction at an intermediate point between the conveying rollers.

Fig. 5 is a schematic diagram illustrating an example of a detection method for detecting a slack amount and a portion where the slack occurs. As shown in fig. 5, ultrasonic displacement sensors 400 are disposed below the center portion and the right and left end portions of the stretched film 1 in the width direction at the intermediate points of the two adjacent conveying

rollers

200b, 200c, and the distance from the ultrasonic displacement sensors 400 to the stretched film 1 is measured so that the maximum distance (L _MAX ) From the minimum distance (L _MIN ) Difference (L) _MAX －L _MIN ) The relaxation amount was set. In addition, the portion at which the minimum distance is generated is detected as the portion at which the relaxation is generated. Further, as a cause of the occurrence of the relaxation of the obliquely stretched film, there is a case where the stretching process (time, number of times, order, thermal history, etc. of stretching or shrinking) of the left and right end portions of the film at the time of oblique stretching is different from each other, and as a result, the deformation amount of both end portions after releasing the clamp is uneven, and therefore the portion where the relaxation occurs is usually one end portion. Therefore, the loose detection portion can be made to be a stretched film only1, left and right end portions in the width direction. In this case, the film having no slack can be transported in advance and the distance (L ₀ ) And the distance between the left and right end parts and the ultrasonic displacement sensor is equal to L ₀ The difference is set as the relaxation amount. Further, although an ultrasonic displacement sensor is described as an example of the slack detection device, any suitable detection device (for example, a laser doppler velocimeter may be used to calculate the difference in length by obtaining the film passing speed between the normal portion and the slack portion) may be used to detect the slack.

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

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

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

A-6. Correction of variations in fixture spacing

The correction of the jig pitch change is so-called feedback correction, and is performed by changing the jig pitch of at least one of the left and right jigs located upstream of the transfer line so as to reduce the amount of slack based on the amount of slack and the detection result of the portion where the slack is generated. For example, when the detected slack amount is equal to or larger than a predetermined value, correction for changing the clamp pitch is performed, and when the detected slack amount is smaller than the predetermined value, the tilt stretching can be continued without correction. Specifically, the above correction can be performed when the amount of relaxation detected at the inter-roller distance of 1000mm is, for example, 3mm or more, 5mm or more, 10mm or more, or 15mm or more.

The correction of the jig pitch change (hereinafter also simply referred to as "feedback correction") may be performed by any suitable method as long as the effects of the present invention can be obtained. The feedback correction can be performed, for example, by: increasing a clip pitch of clips holding an end portion remote from a portion where slack is generated; the clamp pitch of clamps for holding the end part near the part where the looseness is generated is reduced; or a combination of both. However, even if the clip pitch is reduced, the film may not shrink but may be just loose, and thus it is preferable to perform feedback correction by increasing the clip pitch of the clip holding the end portion that is far from the portion where the slack occurs. More specifically, when the portion where the slack occurs is one of the left and right end portions of the stretched film, the feedback correction can be preferably performed by increasing the clip pitch of the clips that hold the other end portion.

In the feedback correction, the timing of changing the clip 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 from the clip release after the transfer of the film upstream of the transfer line to the oblique stretching region. Preferably, the corrected clip pitch is applied from an arbitrary time after the clip advanced upstream of the transfer line passes through the intermediate point of the advancing section of the oblique stretching section until the film is released from the clip, more preferably, the corrected clip pitch is applied from a time when the advanced clip passes through 1/2 to 9/10 of the advancing section of the oblique stretching section until the film is released from the clip. More specifically, the above-described feedback correction is applied from an arbitrary timing after the jig advanced upstream of the conveying line passes through the intermediate point of the advancing section of the oblique stretching region, preferably from 1/2 to 9/10 of the timing when the advanced jig passes through the advancing section of the oblique stretching region, so that the jig pitch is changed to obtain a desired correction amount at the end point of the oblique stretching region. Further, it is preferable that the correction amount is maintained until the film is released from the jig after the transfer from the inclined stretching region to the release region. In the latter half of the oblique stretching, particularly in the final stage, the jig pitch of at least one jig is maintained constant or limited to a change at a small rate of change, and therefore, by correcting the jig pitch at this time, the effect of the present invention can be preferably obtained.

When the above-described feedback correction is applied to the oblique stretching region, the film to be subjected is preferably heated to Tg 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 feedback correction at a temperature equal to or slightly higher than Tg. In one embodiment, the film transferred to the release area through the oblique stretching area while receiving the feedback correction at the above temperature is heat-treated in a state in which the correction amount performed in the oblique stretching area is maintained, then cooled, and then released from the jig. The heat treatment and cooling are as described in item A-4.

Fig. 6A is a schematic diagram showing a curve of the jig pitch in one embodiment of the method for producing a stretched film according to the present invention. In the illustrated example, the pitch of the left and right clamps X, Y in the preheating zone B is P ₁ In the initial oblique stretching before the feedback correction, the clamp pitch of the one clamp X starts to be increased and the clamp pitch of the other clamp Y starts to be decreased while entering the oblique stretching region C, and the clamp pitch of the clamp X is increased to P ₂ Reducing the clamp pitch of the clamp Y to P ₃ Thereafter, the jig pitch of the jig X is maintained at P ₂ And increases the jig pitch of the jig Y to P ₂ . Left and right clamps X, Y are arranged at a clamp distance P ₂ Moves toward 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, in the inclined stretching region C, the clip pitch of the clip X is adjusted from P ₂ Gradually increase to P ₂ '. As will be described later, in the release region, the clip pitch of the clips X, Y is maintained at P ₂ ' and P ₂ The correction amount (P at the end point of the inclined stretching region is maintained ₂ ’－P ₂ )。

Fig. 6B is a schematic view of a curve showing a jig pitch in another embodiment of the method for producing a stretched film according to the present invention. In the illustrated embodiment, the oblique stretching is performed in the same manner as in the embodiment shown in fig. 6A, and the left and right clamps X, Y are separated from P together at the time of thermosetting in the release region D ₂ Reduced to P ₃ The membrane was 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, in the inclined stretching region C, the clip pitch of the clip X is adjusted from P ₂ Gradually increase to P ₂ ' in the release region, the clip pitch of the clip X is from P ₂ ' reduce to P ₃ ' the clamp pitch of the clamp Y is from P ₂ Reduced to P ₃ . In addition, as will be described later, in the release region, the correction amount (P ₂ ’－P ₂ ) The manner of (a) is to reduce the clip pitch of the clips X, Y to satisfy P ₃ ’－P ₃ ＝P ₂ ’－P ₂ Is a relationship of (3).

In the inclined stretching region, the variation of the clamp pitch after correction (P ₂ ' variation) is preferably gradually performed from the point where the application of the feedback correction is started to the end point (from the point of time when 2/3 of the oblique stretching region has passed to the end point in fig. 6A and 6B). Further, the correction amount of the oblique stretching end time (|the clip pitch before correction of the oblique stretching end time-the clip pitch after correction of the oblique stretching end time|) is preferably maintained in the range from the end point of the oblique stretching region to the release of the clip. For example, in the curves 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 in the range from the end point of the inclined stretching region to the release of the clip (i.e., P ₂ ’－P ₂ ). By thus varying the clip spacing, the effects of the present invention can be preferably obtained.

The above-described change in the clip pitch can be performed by adjusting the distance between the reference rail and the pitch setting rail, or the like, as described above. These adjustments can be made without temporarily stopping or stopping the conveying line.

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

The difference L' (unit: mm) in length between the left and right ends of the stretched film between the conveying rollers can be calculated by substituting the length L (unit: mm) of the stretched film between the conveying rollers calculated based on the following formula (1) and formula (2) into the following formula (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 above-described 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 conveying 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, still more preferably 5mm or less, and still more preferably less than 3mm.

B. Film to be stretched

In the production method of the present invention, any suitable film can be used. For example, a resin film that can be applied as a retardation film can be exemplified. Examples of the material constituting such a film include polycarbonate-based resins, polyvinyl acetal-based resins, cycloolefin-based resins, acrylic resins, cellulose ester-based resins, cellulose-based resins, polyester-carbonate-based resins, olefin-based resins, and polyurethane-based resins. Preferably, the resin is a polycarbonate resin, a cellulose ester resin, a polyester carbonate resin, or a cycloolefin resin. This is because, if the resin is used, a so-called retardation film exhibiting a wavelength dependence of inverse dispersion can be obtained. These resins may be used alone or in combination according to desired characteristics.

As the polycarbonate resin, any suitable polycarbonate resin can be used. For example, a polycarbonate resin containing a structural unit derived from a dihydroxy compound is preferable. As a specific example of the dihydroxy compound, examples thereof 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, 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, 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, 9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, 9-bis (4-hydroxy-3-phenylphenyl) fluorene, 9, 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 units derived from the above-mentioned dihydroxy compounds, structural units derived from dihydroxy compounds such as isosorbide, isomannide, isoidide, spiro ethylene glycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), cyclohexanedimethanol (CHDM), tricyclodecanedimethanol (TCDDM), bisphenols and the like.

Details of such polycarbonate resins are described in, for example, japanese patent application laid-open No. 2012-67300 and japanese patent No. 3325560. The description of this patent document is incorporated by reference into the present specification.

The glass transition temperature of the polycarbonate resin is preferably 110 ℃ to 250 ℃, more preferably 120 ℃ to 230 ℃. If the glass transition temperature is too low, the 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 at the time of film molding may be deteriorated, and the transparency of the film may be impaired. The glass transition temperature was determined based on 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 subjecting at least two aldehyde compounds and/or ketone compounds to a condensation reaction with a polyvinyl alcohol resin. Specific examples of polyvinyl acetal resins and detailed production methods are described in, for example, JP-A2007-161994. This description is incorporated by reference into this specification.

The retardation film obtained by stretching the film to be stretched preferably has refractive index characteristics showing a relationship of nx > ny. In one embodiment, the retardation film may preferably function as a λ/4 plate. In this embodiment, the in-plane retardation Re (550) of the retardation film (λ/4 plate) is preferably 100nm to 180nm, more preferably 135nm to 155nm. In another embodiment, the retardation film may preferably function as a λ/2 plate. In this embodiment, the in-plane retardation Re (550) of the retardation film (lambda/2 plate) is preferably 230nm to 310nm, more preferably 250nm to 290nm. In the present specification, nx is a refractive index in a direction in which the in-plane refractive index is largest (i.e., a slow axis direction), ny is a refractive index in a direction in which the in-plane refractive index is orthogonal to the slow axis (i.e., a fast axis direction), and nz is a refractive index in a thickness direction. Re (lambda) was the in-plane retardation of the film measured at 23℃by light having a wavelength of lambda nm. Thus, re (550) is the in-plane retardation of the film at 23℃as measured by light having a wavelength of 550 nm. When the film thickness is d (nm), re (λ) is obtained from 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, japanese patent application laid-open No. 2013-54338, japanese patent application laid-open No. 2014-194482, japanese patent application laid-open No. 2014-238524, japanese patent application laid-open No. 2014-194484 and the like disclose a method for producing a retardation film having an in-plane retardation Re (550) of 100nm to 180nm by oblique stretching. Thus, a person skilled in the art can set an appropriate oblique stretching condition based on this disclosure.

When a circularly polarizing plate is produced using 1 retardation film (specifically, λ/4 plate), or when the orientation of linearly polarized light is rotated by 90 ° using 1 retardation film, the retardation 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 °, still more preferably about 43 ° to 47 ° or 133 ° to 137 °, and particularly preferably about 45 ° or 135 ° with respect to the longitudinal direction of the film.

In the case of producing a circularly polarizing plate using two retardation films (specifically, a λ/2 plate and a λ/4 plate), the retardation axis direction of the retardation film (λ/2 plate) to be 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 retardation 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 so-called inverse dispersion wavelength dependence. Specifically, the in-plane retardation 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, more preferably 0.8 to 0.95.Re (550)/Re (650) is preferably 0.8 or more and less than 1.0, 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)～100×10 ^-12 (m ² N), more preferably 5X 10 ^-12 (m ² /N)～50×10 ^-12 (m ² /N)。

C. Optical laminate and method for producing the same

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

Fig. 7 is a schematic cross-sectional view of an example of such a circular 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 phase difference film 540 disposed outside the 2 nd protective film 530. The retardation film 540 is a stretched film (for example, λ/4 plate) obtained by the production method described in item a. The 2 nd protective film 530 may be omitted. In this case, the retardation film 540 can function as a protective film for the polarizer. The angle between the absorption axis of the polarizer 510 and the retardation axis of the retardation film 540 is preferably about 30 ° to 60 °, more preferably about 38 ° to 52 °, even 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 the oblique direction (direction at 45 ° to the longitudinal direction, for example). In addition, in many cases, the elongated 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 so-called roll-to-roll film can be used, and a circularly polarizing plate can be produced with extremely excellent production efficiency. The roll-to-roll method is a method of continuously bonding long films in a longitudinal direction while carrying out roll-to-roll conveyance of the films.

In one embodiment, the method for producing an optical laminate of the present invention comprises the steps of: obtaining a stretched film in a long form by the method for producing a stretched film described in item A; and continuously bonding the long optical film and the long stretched film in alignment in the longitudinal direction while conveying them.

Examples

Hereinafter, the present invention will be specifically described 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 (L)

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

(2) Phase difference value

The in-plane phase difference Re was measured using Axoscan manufactured by Axometrics, inc. (550).

(3) Orientation angle (presentation direction of slow phase axis)

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

(4) Glass transition temperature (Tg)

The measurement was performed in accordance with JIS K7121.

(5) Amount of relaxation

As shown in FIG. 5, an ultrasonic displacement sensor was disposed at a point (inter-roll distance: 912 mm) below the transport path of the stretched film and at the middle of two adjacent transport rolls. While conveying the stretched film 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 _MAX ) From the minimum distance (L _MIN ) Difference (L) _MAX －L _MIN ) The amount of relaxation (mm) was set. The portion at which the minimum distance is generated is determined as the portion at which the slack is generated.

Example 1 >

(production of 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 (0.046 mol) of bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl ] are added ]Methane, 29.21 parts by mass (0.200 mol) of ISB, 42.28 parts by mass (0.139 mol) of SPG, 63.77 parts by mass (0.298 mol) of DPC and 1.19X10 as a catalyst ^-2 Parts by mass (6.78X10) ^-5 mol) of calcium acetate monohydrate. After the reduced pressure nitrogen gas was replaced in the reactor, the reactor was warmed by a heat transfer medium, and stirring was started at the time when the internal temperature became 100 ℃. After 40 minutes from the start of the temperature rise, the internal temperature was brought to 220℃and the pressure was reduced while maintaining the temperature, and after reaching 220℃the pressure was set to 13.3kPa for 90 minutes. The phenol vapor by-produced together with the polymerization reaction was introduced into a reflux condenser at 100℃to return a certain amount of monomer components contained in the phenol vapor to the reactor, and the uncondensed phenol vapor was introduced into a condenser at 45℃to be recovered. After nitrogen was introduced into the 1 st reactor and the pressure was temporarily returned to the atmospheric pressure, the reaction liquid obtained by oligomerization in the 1 st reactor was transferred to the 2 nd reactor. Then, the temperature rise and pressure reduction in the 2 nd reactor were started, and the internal temperature was 240℃and the pressure was 0.2kPa within 50 minutes. Thereafter, polymerization is performed until a predetermined stirring power is reached. At the time of reaching a predetermined power, nitrogen was introduced into the reactor and the pressure was recovered, and the produced polyester carbonate was extruded into water, and the strands were cut to obtain pellets. The Tg of the resulting polyester carbonate resin was 140 ℃.

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

(oblique stretching before feedback correction)

The polyester carbonate resin film thus obtained was obliquely stretched by 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 the preheating zone of the stretching apparatus. In the preheating zone, the clamp pitch (P ₁ ) 125mm. Then, at the same time as the film enters the inclined stretching region C, the clamp pitch of the right clamp starts to be increased and the clamp pitch of the left clamp starts to be decreased, and the clamp pitch of the right clamp starts to be increased to P ₂ And the clamp spacing of the left clamp is reduced to P ₃ . At this time, the jig pitch change rate (P ₂ /P ₁ ) 1.42, the clip pitch change rate (P ₃ /P ₁ ) The transverse stretching ratio was 0.78, and 1.45 times with respect to the original width of the film. Then, the clamp pitch of the right clamp is maintained at P ₂ In the state of (2), the clamp pitch of the left clamp is initially increased from P ₃ Increase to P ₂ . Rate of change of clamp pitch of left clamp during this period (P ₂ /P ₃ ) The transverse stretching ratio was 1.82, and 1.9 times relative to the original width of the film. The inclined stretching region C was set to tg+3.2 ℃ (143.2 ℃).

Next, in the release zone D, the film was held at 125 ℃ for 60 seconds for thermal fixation. After cooling the heat-set film to 100 ℃, the left and right clamps are released.

(roller transport)

The both side ends of the stretched film released from the above-mentioned jig and sent from the stretching device were cut off by 250mm, respectively. The film with both ends cut off is roll-fed, and the amount of slack between the feed rolls and the portion where the slack is generated are detected. As a result, a slack was generated at the left end, and the amount of the slack was 18.0mm. The difference L' between the lengths of the both ends of the stretched film before correction calculated based on the above formulas (1) to (3) was 0.95mm.

(feedback correction)

3 in the traveling section from the passing inclined stretching region CGradually increasing the clamp pitch of the right clamp to P in the period from the time of/4 to the time of reaching the end point ₂ ' A correction amount of clip pitch (P ₂ ’－P ₂ ): 0.3 mm) and the clamp pitch was maintained, and the curve of the clamp pitch was changed and the oblique stretching was continued so that the clamp was released by performing heat fixation (125 ℃ C., 60 seconds) and cooling (100 ℃ C.) in the same manner as described above. That is, the pitch of the clips when the obliquely-stretched film after the feedback correction is released from the clips is the pitch of the clips on the right side is P ₂ ' the left clamp spacing is P ₂ 。

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

Example 2 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) Except for 0.6mm, a stretched film was obtained by obliquely stretching in the same manner as in example 1.

Example 3 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) Except for 0.95mm, a stretched film was obtained by obliquely stretching in the same manner as in example 1.

Example 4 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) Except for 1.8mm, a stretched film was obtained by obliquely stretching in the same manner as in example 1.

Example 5 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) Other than 2.6mm, a stretched film was obtained by obliquely stretching in the same manner as in example 1.

Example 6 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) A stretched film was obtained in the same manner as in example 1 except that the thickness was set to 0.6mm and the distance 3/4 of the travel distance of the oblique stretching region C was set to tg+6.0 ℃ (146.0 ℃).

Example 7 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) A stretched film was obtained in the same manner as in example 1 except that the thickness was set to 0.95mm and the distance 3/4 of the travel distance of the oblique stretching region C was set to tg+6.0 ℃ (146.0 ℃).

Example 8 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) A stretched film was obtained in the same manner as in example 1 except that the thickness was 1.8mm and the distance 3/4 of the travel distance of the oblique stretching region C was tg+6.0 ℃ (146.0 ℃).

Example 9 >

Except for the correction amount (P) of the clip pitch ₂ ’－P ₂ ) A stretched film was obtained in the same manner as in example 1 except that the thickness was set to 2.6mm and the distance from 3/4 of the travel distance of the oblique stretching region C was set to tg+6.0 ℃ (146.0 ℃).

Comparative example 1 >

A stretched film was obtained 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 above-described method.

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

And (2) the following steps: after the masking film (lamination tension 150N/m) was laminated, no wrinkles were visible, and the adhesive could be applied over the entire surface of the film.

Delta: when the masking film is bonded, the bonding tension is raised to 300N/m, so that the masking film can be bonded 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 are present 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 manufacturing process. In table 1, "relaxation decrease amount" is a difference between 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 amount of relaxation of the film after oblique stretching was detected, and the clamp pitch upstream of the transfer line was appropriately changed based on the detection result, thereby reducing the relaxation of the stretched film obtained later.

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 be useful for producing an image display device such as a liquid crystal display device (LCD) and an organic electroluminescence display device (OLED).

Claims

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

the method for producing the stretched film comprises the following steps:

gripping the left and right ends of the elongated film in the width direction by left and right grippers of variable pitch type whose gripper pitch varies in the longitudinal direction;

the film is obliquely stretched by moving the left and right jigs while changing the jig pitch of at least one of the left and right jigs and advancing either one of the jigs ahead of the other jig;

releasing the membrane from the left and right clamps;

carrying out roller conveying on the film, and detecting the relaxation amount of the film between conveying rollers and the part generating relaxation; and

based on the detection result, correction is performed to change the jig pitch of at least one of the left and right jigs located upstream of the conveying line.

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

after the left and right ends of the film released from the left and right jigs are cut and removed, the amount of slack and the portion where the slack is generated are detected.

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

the correction of the jig pitch variation includes the steps of: the clip pitch of the clip 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 claim 1 to 3, wherein,

correction of changing the clip pitch is performed from the time when the clip that advanced passes through the position of 1/2 to 9/10 of the advancing section of the oblique stretching until the film is released from the left and right clips.

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

correction for varying the clip pitch is performed with a correction amount larger than a difference L 'in length of left and right end portions of the film between the conveying rollers, and in addition, L' is calculated by substituting the length L 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)

In the above formula, d represents the detected amount of relaxation, W represents the mass per meter of the film, g represents the gravitational acceleration, S represents the distance between the conveying rollers, H represents the tension applied to the end side where the relaxation calculated according to formula (1) occurs,

the difference L' in length, the amount of relaxation, the distance in mm, the mass per meter of the film in g, and the tension in N/m.

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

correction to change the jig pitch is performed in the oblique stretching,

the ambient temperature at this time was Tg to tg+20℃.

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

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

obtaining an elongated stretched film by the production method according to any one of claims 1 to 6; and

while conveying the long optical film and the long stretched film, the long optical film and the long stretched film are continuously bonded in alignment in the longitudinal direction.

8. The method for producing an optical laminate according to claim 7, wherein,

the optical film is a polarizing plate and,

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