CN115122617A

CN115122617A - Method for producing stretched film

Info

Publication number: CN115122617A
Application number: CN202210298206.1A
Authority: CN
Inventors: 中原步梦; 清水享; 北岸一志
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-03-24
Filing date: 2022-03-24
Publication date: 2022-09-30
Also published as: JP2022151494A; JP7039757B1; KR20220133101A

Abstract

The present invention relates to a method for producing a stretched film, using a film stretching apparatus, the film stretching apparatus comprising: the method comprises the steps of providing a circular left and right reference rails, a left and right pitch setting rail provided on the inner peripheral side of the left and right reference rails, a plurality of left and right jig carrying members guided by the left and right reference rails to travel, left and right jigs carried by the left and right jig carrying members, and a connecting mechanism configured to adjust the pitch between the jig carrying members by the distance between the reference rails and the pitch setting rail, the method comprising: the left and right ends of the long film in the width direction are respectively clamped by the left and right clamps; moving the left and right clamps while changing the clamp pitch of at least one clamp to stretch the film in an oblique direction; releasing the film from the left and right clamps; detecting wrinkles of the film; and increasing the traveling speed of the left and right clamps when clamping the film 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

For the purpose of improving display characteristics and preventing reflection, a circularly polarizing plate is used in an image display device such as a liquid crystal display device (LCD) or an organic electroluminescence display device (OLED). The circularly polarizing plate is typically formed by laminating a polarizer and a retardation film (typically, a λ/4 plate) so that the absorption axis of the polarizer and the slow axis of the retardation film form an angle of 45 °. Conventionally, a retardation film is typically produced by uniaxially or biaxially stretching in the longitudinal direction and/or the transverse direction, and therefore the slow axis thereof is often expressed along the transverse direction (width direction) or the longitudinal direction (length direction) of a long film blank. As a result, in order to produce a circularly polarizing plate, it is necessary to cut the retardation film at an angle of 45 ° with respect to the width direction or the longitudinal direction and bond the retardation film one by one.

In order to secure broadband characteristics 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 at an angle of 75 ° with respect to the absorption axis of the polarizer, and laminate the λ/4 plates at an angle of 15 ° with respect to the absorption axis of the polarizer. In this case, in order to produce the circularly polarizing plate, the retardation film needs to be cut at an angle of 15 ° or 75 ° with respect to the width direction or the longitudinal direction and bonded one by one.

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

In order to solve such a problem, the following techniques are proposed: the slow axis of the retardation film is expressed in an oblique direction by holding the left and right ends of the long film in the width direction with a variable-pitch type left and right jig whose jig pitch varies in the longitudinal direction, and stretching the film in an oblique direction with respect to the longitudinal direction by varying the jig pitch of at least one of the left and right jigs (hereinafter, also referred to as "oblique stretching") (for example, patent document 1). However, in the obliquely stretched film obtained by such a technique, wrinkles sometimes occur.

Documents of the prior art

Patent document

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-described problems, and a main object thereof is to reduce wrinkles generated in a film after 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 using a film stretching apparatus having: a method for producing a stretched film, the method comprising the steps of providing a plurality of jig carrying members, a plurality of left and right jig carrying members guided by the left and right reference rails and moved in a traveling manner, and a connecting mechanism configured to adjust a pitch between the jig carrying members by a distance between the reference rails and the pitch setting rails, wherein the method comprises: the left and right ends of the long film in the width direction are respectively clamped by the left and right clamps; moving the left and right clamps while changing the clamp pitch of at least one clamp to obliquely stretch the film; releasing the film from the left and right clamps; detecting wrinkles of the film; and increasing the traveling speed of the left and right clamps when clamping the film based on the detection result.

In one embodiment, the traveling speed of the left and right jigs when the film is sandwiched is increased to 8 m/min to 40 m/min.

In one embodiment, the rate of increase in the traveling speed of the left and right jigs when sandwiching the film is 101% to 800%.

In one embodiment, the obliquely stretching includes: (i) while making the clamp pitch of one of the left and right clamps from P ₁ Increase to P ₂ While making the distance between the clamps of the other clamp from P ₁ Is reduced to P ₃ (ii) a And (ii) changing the jig pitch of each jig so that the reduced jig pitch and the increased jig pitch are equal to each other.

In one embodiment, P ₂ /P ₁ 1.25 to 1.75, P ₃ /P ₁ Is 0.50 or more and less than 1.

According to another aspect of the present invention, there is provided a method for manufacturing an optical laminate, including: a long stretched film obtained by the above-described manufacturing method; and continuously laminating the optical film and the stretched film while aligning the optical film and the stretched film in the longitudinal direction.

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

Effects of the invention

According to the method for producing a stretched film of the embodiment of the present invention, when a wrinkle occurs in an obliquely stretched film obtained by using a predetermined stretching device, the traveling speed of the left and right clamps is increased when the film is sandwiched. Thus, the obliquely stretched film having reduced wrinkles can be obtained without changing the distribution of the distance between the jigs, the heating temperature, and other conditions of the oblique stretching. The reason for such effects can be presumed as described below, but the present invention is not limited to this. That is, by increasing the linear velocity, the stress acting on the jig carrying member during oblique stretching is also increased, and as a result, the distance between the reference rail and the pitch setting rail (as a result, the jig pitch) is changed, and an appropriate tension can be applied to the film. As a result, an obliquely stretched film with reduced wrinkles can be obtained.

Drawings

Fig. 1 is a schematic plan view illustrating an 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. 2 is a schematic plan view of a main part for explaining a connection mechanism for changing a clip pitch in the stretching apparatus of fig. 1.

Fig. 3 is a schematic plan view of a main part for explaining a connecting mechanism for changing the clip pitch in the stretching apparatus in fig. 1.

Fig. 4A is a schematic view showing the distribution of the clip pitch in one embodiment of oblique stretching.

Fig. 4B is a schematic diagram showing the distribution of the clip pitch in one embodiment of the oblique stretching.

Fig. 5 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 symbols

10 reference rail

20-pitch setting track

30 jig carrying member

40 clamp

50 driving mechanism

100 stretching device

500 circular polarizer

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" means a distance between centers of adjacent clips in the longitudinal direction in the traveling direction. The left-right relationship of the long film in the width direction means a left-right relationship in the film conveyance direction unless otherwise specified.

A. Method for producing stretched film

A method for producing a stretched film according to an embodiment of the present invention is performed using a film stretching apparatus including: the jig mounting device includes a ring-shaped left and right reference rails, left and right pitch setting rails provided on an inner peripheral side of the reference rails, a plurality of left and right jig carrying members guided by the reference rails and moved forward, left and right jigs carried on the jig carrying members, and a connecting mechanism configured to adjust a pitch between the jig carrying members by a distance between the reference rails and the pitch setting rails.

The method for producing a stretched film according to an embodiment of the present invention includes:

the left and right ends of the long film in the width direction are held by the left and right clamps (holding step);

moving the left and right jigs while changing the jig pitch of at least one of the jigs to obliquely stretch the film (oblique stretching step);

releasing the film from the left and right clamps (releasing step);

detecting wrinkles in the film (a wrinkle detection step); and

based on the detection result, the traveling speeds of the left and right jigs when the film is clamped are increased (linear speed changing step).

Typically, the manufacturing method of the present embodiment further includes a preheating step. Specifically, the film sandwiched by the left and right clamps is subjected to oblique stretching after preheating.

A-1 stretching device

The stretching apparatus used in the method for producing a stretched film according to the embodiment of the present invention includes: the jig mounting device includes a ring-shaped left and right reference rails, left and right pitch setting rails provided on an inner peripheral side of the reference rails, a plurality of left and right jig carrying members guided by the reference rails and moved forward, left and right jigs carried on the jig carrying members, and a connecting mechanism configured to adjust a pitch between the jig carrying members by a distance between the reference rails and the pitch setting rails.

Fig. 1 is a schematic plan view illustrating an overall configuration of an example of a stretching apparatus that can be used in the production method of the present invention. In the stretching apparatus 100, a nip area a, a preheating area B, a stretching area C, and a releasing area D are provided in this order from the inlet side toward the outlet side of the film. Each of the above-mentioned regions is a region for substantially holding, preheating, obliquely stretching, and releasing the film to be stretched, and does not mean a mechanically and structurally independent block. In addition, it is to be noted 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. 1, although not shown, a region for performing any appropriate process may be provided between the stretch region C and the release region D as needed. Examples of such treatment include transverse shrinkage treatment. Similarly, although not shown, the stretching apparatus 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 release zone D.

The stretching device 100 includes, in a left-right symmetrical manner in a plan view, annular left and right reference rails 10L, 10R on both left and right sides, and pitch setting

rails

20L, 20R provided on an inner peripheral side thereof along the left and right reference rails 10L, 10R. The stretching apparatus 100 further includes a plurality of left and right

jig carrying members

30L, 30R that carry the jig 40 and are guided by the left and right reference rails 10L, 10R to travel, and drive mechanisms (in the illustrated example, drive sprockets) 50L, 50R that apply a traveling force to the left and right

jig carrying members

30L, 30R. In the present specification, the reference track on the left side when viewed from the film entrance side is referred to as a left reference track 10L, and the reference track on the right side when viewed from the film entrance side is referred to as a right reference track 10R. The

jig carrying members

30L and 30R carrying the jig 40 are guided by the

reference rails

10L and 10R to circularly move. Specifically, the jig (left jig) 40 carried on the jig carrier guided by the left reference rail 10L is moved in a counterclockwise direction, and the jig (right jig) 40 carried on the jig carrier guided by the right reference rail 10R is moved in a clockwise direction.

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

right reference rails

10L and 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 stretching region C, the following configuration is adopted: the distance between the left and

right reference rails

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

right reference rails

10L and 10R are configured to be substantially parallel to each other at a distance corresponding to the width of the film after stretching. However, the configuration of the right and left

reference rails

10L, 10R is not limited to the above-described example. For example, the left and

right reference rails

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

The left jig 40 and the right jig 40 are configured to be independently movable in a circular manner. Specifically, the driving rollers 39 that can be selectively engaged with the driving

sprockets

50L and 50R are provided on the

jig carrying members

30L and 30R, and the driving rollers 39 are selectively engaged with the driving

sprockets

50L and 50R that are rotationally driven by the

electric motors

60L and 60R, thereby applying a traveling force to the

jig carrying members

30L and 30R. Thus, the driving sprocket 50L for the left reference rail 10L is rotationally driven in the counterclockwise direction, and the driving sprocket 50R for the right reference rail 10R is rotationally driven in the clockwise direction, whereby the left gripper is cyclically moved in the counterclockwise direction, and the right gripper is cyclically moved in the clockwise direction. By adjusting the output of the electric motor to change the traveling force transmitted from the driving sprocket to the jig carrier members, the traveling speeds of the left and right jig carrier members (and the left and right jig traveling speeds) can be independently controlled to arbitrary values. Further, on the film inlet side, jig

position adjustment sprockets

52L and 52R for synchronizing the film clamping timing by the jig to the left and right are disposed and are rotationally driven by

electric motors

62L and 62R, respectively, but these sprockets do not affect the traveling speed of the jig. In addition, unlike the illustrated example, a driving sprocket may be disposed on the film inlet side.

The left jig carrier (resulting in the left jig) and the right jig carrier (resulting in the right jig) are of variable pitch type. That is, the left and right jig carrying members (as a result, the left and right jigs) can change the jig pitch in the vertical direction independently of the movement. The variable pitch type configuration can be realized by employing a link mechanism configured to be able to adjust the pitch between the jig carrying members by the distance between the reference rail and the pitch setting rail. An example of the coupling mechanism (telescopic mechanism) will be described below.

Fig. 2 and 3 are schematic plan views of main portions for explaining a connection mechanism for changing the clip pitch in the stretching apparatus of fig. 1, respectively, fig. 2 showing a state where the clip pitch is minimum, and fig. 3 showing a state where the clip pitch is maximum.

As shown in fig. 2 and 3, the jig carrier members 30 are provided in a laterally elongated rectangular shape in plan view, and each carry a jig 40 at one end in the longitudinal direction. Although not shown, the jig carrier member 30 has a strong frame structure with a closed cross section formed by an upper beam, a lower beam, a front wall (a wall on the jig side), and a rear wall (a wall on the opposite side of the jig). The jig carrier members 30 are provided so as to be rotated on the

travel paths

81 and 82 by the travel wheels 38 at both ends thereof. In fig. 2 and 3, the traveling wheels on the front wall side (traveling wheels that rotate on the traveling road surface 81) are not shown. The traveling

road surfaces

81 and 82 run parallel to the reference rail 10 over the entire area. On the rear side of the upper beam and the lower beam of the jig carrying member 30 (the side opposite to the jig side (hereinafter referred to as the reverse jig side)), long holes 31 are formed along the longitudinal direction of the jig carrying member, and the slider 32 is engaged slidably in the longitudinal direction of the long holes 31. One first shaft member 33 is provided vertically through the upper beam and the lower beam in the vicinity of the end of the jig 40 side of the jig carrier member 30. Although not shown, a guide roller is rotatably provided at the lower end of the first shaft member 33, and the guide roller engages with a groove provided in the reference rail 10. Further, at the upper end of the first shaft member 33, a driving roller 39 is rotatably provided. On the other hand, the slider 32 of the jig carrier member 30 is provided with a single second shaft member 34 extending vertically therethrough. Although not shown, a pitch setting roller is rotatably provided at the lower end of the second shaft member 34, and the pitch setting roller engages with a groove provided in the pitch setting rail 20. One end of the main link member 35 is pivotally coupled to the first shaft member 33 of each jig carrier member 30. The other end of the main link member 35 is pivotally coupled to the second shaft member 34 of the adjacent jig carrier member 30. One end of a sub-link 36 is pivotally connected to the first shaft member 33 of each jig carrier member 30 in addition to the main link 35. The other end of the sub link member 36 is pivotally coupled to an intermediate portion of the main link member 35 via a pivot shaft 37. By the connection mechanism of the main connection member 35 and the sub connection member 36, as shown in fig. 2, the distance between the jig carrier members 30 in the longitudinal direction (and consequently the jig distance) becomes smaller as the slider 32 moves to the rear side (the opposite side) of the jig carrier member 30, and as shown in fig. 3, as the slider 32 moves to the front side (the jig side) of the jig carrier member 30, the distance between the jig carrier members 30 in the longitudinal direction (and consequently the jig distance) becomes larger. The positioning of the slider 32 is performed by the pitch setting rail 20. As shown in fig. 2 and 3, the smaller the distance between the reference rail 10 and the pitch setting rail 20, the larger the jig pitch.

According to the above stretching apparatus, when the clip pitch is maintained constant, the traveling speed of the clip is also maintained constant, and when the clip pitch is changed (increased or decreased), the traveling speed of the clip is also changed at a change rate substantially corresponding to the change rate of the clip pitch. Thus, the basic jig travel speed is the jig travel speed (the jig carrier travel speed) when the drive mechanism applies the travel force, and the jig pitch (and consequently the jig travel speed) can be changed arbitrarily by adjusting the distance between the reference rail and the pitch setting rail thereafter. Thus, by keeping the distance between the reference track and the pitch setting track constant from the installation point of the drive mechanism to the clamping area a, the jig can enter the clamping area a while substantially maintaining the basic travel speed. In the present specification, the traveling speed at which the film is nipped by the jig is sometimes referred to as "linear velocity".

By stretching the film in an oblique direction using the stretching apparatus as described above, a film stretched in an oblique direction, for example, a retardation film having a slow axis in an oblique direction can be produced. Further, a specific embodiment of the stretching device as described above is described in, for example, japanese patent application laid-open No. 2008-44339, the entirety of which is incorporated by reference in the present specification. The stretching apparatus applicable to the method for producing a stretched film according to the embodiment of the present invention is not limited to the illustrated example. For example, various stretching apparatuses having a connecting mechanism as described in japanese patent laid-open nos. 2003-71921 and 2017-113890 may be applied.

Hereinafter, each step will be described in detail.

A-2. clamping procedure

In the clamping area a (the entrance of the stretching apparatus 100 into which the film is taken), the left and right clamps 40 typically clamp both ends of the film to be stretched at the same time and at the same constant clamp pitch. The film is fed to the preheating zone B by the movement of the left and right jigs (substantially, the movement of each jig carrier member guided by the left and right reference rails 10L, 10R).

The traveling speeds of the left and right clamps at the time of sandwiching the film may be appropriately set in consideration of production efficiency, oblique stretching conditions (for example, a rate of change in the clamp pitch, timing, and heating temperature), and the like. The traveling speed of the left and right jigs is, for example, 3 m/min to 40 m/min, preferably 5 m/min to 35 m/min, and more preferably 8 m/min to 30 m/min.

A-3 preheating step

In the preheating region B, as described above, the left and right reference rails 10L, 10R are configured such that the distance intervals corresponding to the initial width of the film to be stretched are substantially parallel to each other, and therefore, the film is heated without being stretched substantially in the transverse direction and without being stretched in the longitudinal direction. However, in order to avoid troubles such as deflection of the film due to preheating and contact with a nozzle in the oven, the distance between the left and right jigs (distance in the width direction) may be slightly increased.

In the preheating step, the film is 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 is, for example, 70 ℃ to 190 ℃ and preferably 80 ℃ to 180 ℃, although it varies depending on the film used.

The temperature rise time to the temperature T1 and the holding time at the temperature T1 may be appropriately set depending on the material constituting the film and the production conditions (for example, the film transport speed). The heating time and the holding time can be controlled by adjusting the moving speed of the jig 40, the length of the preheating region, the temperature of the preheating region, and the like.

A-4. oblique stretching step

In the stretching region C, the film is obliquely stretched by moving the left and right clamps 40 while changing the clamp pitch in the longitudinal direction of at least one of the left and right clamps 40. More specifically, the film is obliquely stretched by increasing or decreasing the clip pitch of each of the left and right clips at different positions, changing (increasing and/or decreasing) the clip pitch of each of the left and right clips at different changing speeds, and the like.

The oblique stretching may comprise transverse stretching. In this case, the oblique stretching can be performed while increasing the distance between the left and right jigs (the distance in the width direction), for example, as in the configuration shown in fig. 1. Alternatively, the process may be performed directly while maintaining the distance between the left and right jigs, unlike the configuration shown in fig. 1.

In the case where the oblique stretching includes transverse stretching, the stretching ratio in the Transverse Direction (TD) (width W of the film after the oblique stretching) _final And the initial width W of the film _initial Ratio of (W) _final /W _initial ) Preferably 1.05 to 6.00, and more preferably 1.10 to 5.00.

In one embodiment, the bias stretching may be performed as follows: the position where the jig pitch of one of the left and right jigs starts to increase or decrease is set to a position where the jig pitch of the other jig starts to increase or decrease, which is different in the longitudinal direction, and in this state, the jig pitch of each jig is increased or decreased to a predetermined pitch. As for the oblique stretching in this embodiment, for example, patent document 1 and japanese patent application laid-open No. 2014-238524 and the like can be cited.

In another embodiment, the diagonal stretching may be performed as follows: in a state where the jig pitch of one of the left and right jigs is fixed, the jig pitch of the other jig is increased or decreased to a predetermined pitch, and then returned to the original jig pitch. For the oblique stretching in this embodiment, for example, the contents described in japanese patent laid-open nos. 2013 and 54338 and 2014 and 194482 can be referred to.

In yet another embodiment, the bias stretching may be performed as follows: (i) while making the clamp pitch of one of the left and right clamps from P ₁ Increase to P ₂ While moving the distance between the clamps of the other clamp from P ₁ Is reduced to P ₃ (ii) a And (ii) changing the jig pitch of each jig so that the reduced jig pitch and the increased jig pitch are equal to each other. For the oblique stretching of this embodiment, for example, refer to the disclosure of japanese patent application laid-open publication No. 2014-194484. The diagonal stretching of this embodiment may include: the distance between the left and right clamps is enlarged, and the clamp pitch of one clamp is increased from P ₁ Increase to P ₂ And the clamp pitch of the other clamp is from P ₁ Is reduced to P ₃ And the film is subjected to oblique stretching (first oblique stretching); and maintaining the clamp pitch of the one clamp at P so that the clamp pitches of the left and right clamps become equal while expanding the distance between the left and right clamps ₂ Or reduced to P ₄ And increasing the clamp pitch of the other clamp to P ₂ Or P ₄ And the film is obliquely stretched (second oblique stretching).

In the first oblique stretching, the film is stretched in the longitudinal direction at one end portion thereof while being shrunk in the longitudinal direction at the other end portion thereof, and the oblique stretching is performed, whereby a slow axis can be expressed with high uniaxiality and in-plane orientation in a desired direction (for example, a direction of 45 ° with respect to the longitudinal direction). In addition, in the second oblique stretching, the oblique stretching is performed while reducing the difference between the left and right jig pitches, and thus the stretching can be sufficiently performed in the oblique direction while relaxing the excessive stress.

In the oblique stretching of the three embodiments described above, since the film can be released from the clamps in a state where the moving speeds of the left and right clamps are equal, a deviation in the film conveyance speed or the like is less likely to occur when the left and right clamps are released, and the subsequent winding of the film can be appropriately performed.

Fig. 4A and 4B are schematic views each showing an example of the distribution of the inter-jig distances in the oblique stretching including the first oblique stretching and the second oblique stretching. Hereinafter, the first oblique stretching will be specifically described with reference to these drawings. In fig. 4A and 4B, the horizontal axis corresponds to the travel distance of the jig. When the first oblique stretching is started, the left and right clamp spaces are set to be P ₁ 。P ₁ Typically the clip pitch when gripping the film. At the same time as the first oblique drawing is started, an increase in the clip pitch of one clip (hereinafter sometimes referred to as a first clip) is started, and a decrease in the clip pitch of the other clip (hereinafter sometimes referred to as a second clip) is started. In the first oblique stretching, the clamp pitch of the first clamp is increased to P ₂ Reducing the clamp pitch of the second clamp to P ₃ . Therefore, at the end of the first oblique stretching (at the start of the second oblique stretching), the second jig is set at the jig pitch P ₃ Moving the first clamp at a clamp pitch P ₂ And (4) moving. Further, the ratio of the jig pitches may substantially correspond to the ratio of the moving speeds of the jigs.

In fig. 4A and 4B, the first oblique drawing start is set to be the timing at which the jig pitch of the first jig starts to increase and the first oblique drawing start is set to be the timing at which the jig pitch of the second jig starts to decrease, but unlike the illustrated example, the jig pitch of the first jig may start to increase and then the jig pitch of the second jig may start to decrease, or the jig pitch of the first jig may start to increase after the jig pitch of the second jig starts to decrease. In a preferred embodiment, the gripper pitch of the second gripper is started to decrease after the gripper pitch of the first gripper is started to increase. According to such an embodiment, the film is already stretched to some extent (preferably, about 1.2 to 2.0 times) in the width direction, and therefore, even if the clip pitch of the second clip is greatly reduced, wrinkles are less likely to occur. This makes it possible to realize more acute-angle oblique stretching and to suitably obtain a retardation film having high uniaxiality and in-plane orientation.

Similarly, in fig. 4A and 4B, the increase in the jig pitch of the first jig and the decrease in the jig pitch of the second jig continue until the first oblique drawing ends (when the second oblique drawing starts), but either the increase or decrease in the jig pitch may be ended earlier than the other, and the jig pitch may be maintained until the other ends (until the first oblique drawing ends), unlike the example shown in the drawing.

Rate of change of grip spacing (P) of first grip ₂ /P ₁ ) Preferably 1.25 to 1.75, more preferably 1.30 to 1.70, and further preferably 1.35 to 1.65. In addition, the rate of change of the clamp pitch (P) of the second clamp ₃ /P ₁ ) For example, the content is 0.50 or more and less than 1, preferably 0.50 to 0.95, more preferably 0.55 to 0.90, and still more preferably 0.55 to 0.85. If the rate of change of the chuck pitch is within such a range, the slow axis can be expressed with high uniaxiality and in-plane orientation in a direction of approximately 45 degrees with respect to the longitudinal direction of the film.

As described above, the distance between the pitch setting rail of the stretching device and the reference rail is adjusted to position the slider and adjust the jig pitch.

The stretching ratio of the film in the width direction during the first oblique stretching (film width at the end of the first oblique stretching/film width before the first oblique stretching) is preferably 1.1 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.25 to 2.0 times. If the stretch ratio is less than 1.1 times, a sheet-like wrinkle may occur at the end on the contraction side. When the stretching ratio exceeds 3.0 times, the biaxial property of the retardation film obtained may be high, and the viewing angle characteristics may be deteriorated when the retardation film is applied to a circularly polarizing plate or the like.

In one embodiment, the first oblique stretching is performed such that the product of the rate of change in the inter-jig distance of the first jig and the rate of change in the inter-jig distance of the second jig is preferably 0.7 to 1.5, more preferably 0.8 to 1.45, and still more preferably 0.85 to 1.40. When the product of the change rates is within such a range, a retardation film having high uniaxiality and in-plane orientation can be obtained.

Next, an embodiment of the second oblique stretching will be specifically described with reference to fig. 4A. In the second oblique stretching of the present embodiment, the clip pitch of the second clip is set from P ₃ Increase to P ₂ . On the other hand, the clamp pitch of the first clamp is maintained at P between the second oblique tensions ₂ . Therefore, when the second oblique stretching is finished, the left and right clamps are all arranged at the clamp pitch P ₂ And (4) moving.

The rate of change (P) of the clip pitch of the second clip in the second diagonal stretching of the embodiment shown in FIG. 4A ₂ /P ₃ ) There is no limitation as long as the effects of the present invention are not impaired. The rate of change (P) ₂ /P ₃ ) For example, 1.3 to 4.0, preferably 1.5 to 3.0.

Another embodiment of the second oblique stretching will be specifically described with reference to fig. 4B. In the second oblique stretching of the present embodiment, the jig pitch of the first jig is decreased and the jig pitch of the second jig is increased. Specifically, the clamp pitch of the first clamp is set to be P ₂ Is reduced to P ₄ And the clamp pitch of the second clamp is from P ₃ Increase to P ₄ . Therefore, when the second oblique stretching is finished, the left and right clamps are all arranged at the clamp pitch P ₄ And (4) moving. In the illustrated example, the reduction of the jig pitch of the first jig and the increase of the jig pitch of the second jig are started simultaneously with the start of the second oblique stretching, but they may be started at different timings. Similarly, the decrease in the jig pitch of the first jig and the increase in the jig pitch of the second jig may be finished at different timings.

The rate of change (P) of the clip pitch of the first clip in the second oblique stretching of the embodiment shown in FIG. 4B ₄ /P ₂ ) And rate of change of clamp pitch (P) of the second clamp ₄ /P ₃ ) There is no limitation as long as the effects of the present invention are not impaired. Rate of change (P) ₄ /P ₂ ) For example, 0.4 or more and less than 1.0, preferably 0.6 to 0.95. In addition, the rate of change (P) ₄ /P ₃ ) For example, it exceeds 1.0 and is 2.0 or less, preferably 1.2 to 1.8. P ₄ Preferably P ₁ As described above. If P ₄ ＜P ₁ There are cases where problems such as wrinkles occur at the end portions and biaxial deformation occur.

The stretching ratio of the film in the width direction during the second oblique stretching (film width at the end of the second oblique stretching/film width at the end of the first oblique stretching) is preferably 1.1 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.25 to 2.0 times. If the stretch ratio is less than 1.1 times, a sheet-like wrinkle may occur at the end on the contraction side. When the stretching ratio exceeds 3.0 times, the obtained retardation film may have high biaxiality, and the viewing angle characteristics may be deteriorated when the retardation film is applied to a circularly polarizing plate or the like. From the same viewpoint as described above, the stretching ratio in the width direction in the first oblique stretching and the second oblique stretching (the film width at the end of the second oblique stretching/the film width before the first oblique stretching) is preferably 1.2 times to 4.0 times, and more preferably 1.4 times to 3.0 times.

The bias stretching may be typically performed at a temperature 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, relative to the glass transition temperature (Tg) of the film. The temperature T2 is, for example, 70 ℃ to 180 ℃ and preferably 80 ℃ to 170 ℃, although it varies 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, in the preheat zone, the film heated to temperature T1 may be cooled to temperature T2.

As described above, the transverse contraction treatment may be performed after the oblique stretching. Regarding this treatment after the oblique stretching, refer to paragraphs 0029 to 0032 in Japanese patent laid-open No. 2014-194483.

A-5. Release Process

In any position of the release region D, the film is released from the jig. In the release region D, the film is usually not stretched in the transverse direction nor in the longitudinal direction, but is heat-treated and the stretched state is fixed (heat-fixed) and/or the film is cooled to Tg or less and then released from the jig as necessary. Further, at the time of heat setting, the jig pitch in the longitudinal direction can be made small, thereby relaxing the stress.

The heat treatment may be typically performed at a temperature T3. The temperature T3 varies depending on the film to be stretched, and is sometimes T2. gtoreq.T 3, and also sometimes T2 < T3. In general, the crystallization treatment may be performed by setting T2 ≧ T3 in the case of an amorphous material and T2 < T3 in the case of 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 jig is sent out from the outlet of the stretching device and subjected to the detection of wrinkles.

A-6. detection of wrinkles

The detection of wrinkles can be performed, for example, by observing the membrane surface while irradiating light as necessary. The film surface may be visually observed or mechanically observed using a sensor or the like.

In one embodiment, the stretched film released from the jig is cut and removed at the left and right ends in the width direction, and then wrinkle detection is performed. The width of the end to be cut off can be, for example, 20mm to 600mm, preferably 100mm to 500mm, independently of one another. The end portions can be cut and removed by a usual slitting process.

A-7. line speed changing step

Based on the detection results, in the clamping process upstream of the conveyor line, the traveling speeds (linear speeds) of the left and right clamps at the time of clamping the film are increased. For example, when a wrinkle exceeding a predetermined reference is detected, the linear velocity is increased, and when the detected wrinkle is equal to or less than the predetermined reference, the production conditions of the stretched film up to now can be maintained without changing the linear velocity.

The rate of increase in linear velocity (linear velocity after increase/linear velocity before increase × 100) is not particularly limited as long as the effects of the present invention can be obtained. In one embodiment, the linear velocity increase rate is, for example, 101% to 800%, preferably 110% to 600%, and more preferably 120% to 500%. If the rate of increase in line speed is in this range, a stretched film with reduced wrinkles can be suitably obtained.

In one embodiment, the linear velocity after the increase is, for example, 8 m/min to 40 m/min, preferably 8 m/min to 35 m/min, and more preferably 8 m/min to 30 m/min. If the line speed is in this range, a stretched film with reduced wrinkles can be obtained while maintaining practically allowable production efficiency.

The linear velocity can be changed by increasing a traveling force (for example, changing the rotational speed of the driving sprocket) applied to the jig carrying member by the driving mechanism, changing the torque of the driving roller, or the like. The linear velocity is preferably increased gradually.

B. Film as stretching object

In the production method of the present invention, any appropriate film may be used. For example, a resin film which can be used as a retardation film is given. Examples of the material constituting such a film include: polycarbonate-based resins, polyvinyl acetal-based resins, cycloolefin-based resins, acrylic-based resins, cellulose ester-based resins, cellulose-based resins, polyester carbonate-based resins, olefin-based resins, polyurethane-based resins, and the like. Preferred are polycarbonate resins, cellulose ester resins, polyester carbonate resins, and cycloolefin resins. This is because: with these resins, a retardation film showing so-called wavelength dependence of reverse dispersion can be obtained. 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, 9-bis (4- (2-hydroxyethoxy) phenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-methylphenyl) fluorene, 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-phenylphenyl) fluorene, 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 units derived from the dihydroxy compound, structural units derived from dihydroxy compounds such as isosorbide, isomannide, isoidide, spiroglycol, dioxane glycol (dioxaneglycol), diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), Cyclohexanedimethanol (CHDM), Tricyclodecanedimethanol (TCDDM), and bisphenols.

Details of the polycarbonate-based resin are described in, for example, japanese unexamined patent publication nos. 2012 and 67300 and 3325560. The contents of the patent document are incorporated herein by reference.

The glass transition temperature of the polycarbonate resin is preferably 110 to 250 ℃ and 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 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 thereof are described in, for example, jp 2007-161994 a. The contents of this description are incorporated herein by reference.

The preferable refractive index characteristic of a stretched film (retardation film) obtained by stretching the film to be stretched exhibits a relationship of nx > ny. In one embodiment, the retardation film preferably functions as a λ/4 plate. In the present embodiment, the in-plane retardation Re (550) of the retardation film (. lamda./4 plate) is preferably 100 to 180nm, more preferably 135 to 155 nm. In another embodiment, the retardation film preferably functions 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 in the plane (i.e., a fast axis direction), and nz is a refractive index in a thickness direction. Re (. lamda.) is the in-plane retardation of the film measured at 23 ℃ with respect to light having a wavelength of. lamda.nm. Therefore, Re (550) is an in-plane retardation of the film measured with light having a wavelength of 550nm at 23 ℃. Re (λ) is represented by the formula when the film thickness is d (nm): 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, the person skilled in the art can set appropriate oblique stretching conditions based on this disclosure.

When a circularly polarizing plate is produced using one retardation film or when the direction of linearly polarized light is rotated by 90 ° using one retardation film, the slow axis direction of the retardation film to be used is preferably 30 ° to 60 ° or 120 ° to 150 °, more preferably 38 ° to 52 ° or 128 ° to 142 °, further preferably 43 ° to 47 ° or 133 ° to 137 °, and 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 60 ° to 90 °, more preferably 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 0 ° to 30 °, more preferably 5 ° to 25 °, and particularly preferably about 15 ° with respect to the longitudinal direction of the film.

The retardation film preferably exhibits a 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 (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 same

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

Fig. 5 is a schematic cross-sectional view of an example of such a circularly polarizing plate. The circularly polarizing plate 500 illustrated in the figure has: the polarizer 510, the first protective film 520 disposed on one side of the polarizer 510, the second protective film 530 disposed on the other side of the polarizer 510, and the retardation film 540 disposed outside the second 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 second 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 polarizer 510 and the slow axis of retardation film 540 is preferably 30 ° to 60 °, more preferably 38 ° to 52 °, still more preferably 43 ° to 47 °, and particularly preferably about 45 °.

The retardation film obtained by the manufacturing method of the present invention is long and has a slow axis in an oblique direction (a direction of, for example, 45 ° with respect to the longitudinal direction). In many cases, the long polarizer has an absorption axis in the longitudinal direction or the width direction. Thus, if the retardation film obtained by the production method of the present invention is used, a so-called roll-to-roll process can be used to produce a circularly polarizing plate with extremely excellent production efficiency. The roll-to-roll method is a method of continuously laminating films in a state in which the films are aligned in the longitudinal direction while the films are roll-fed to each other.

In one embodiment, a method for manufacturing an optical laminate according to the present invention includes: a stretched film having a long length obtained by the method for producing a stretched film described in the item a; and continuously laminating the optical film and the stretched film while aligning the optical film and the stretched film in the longitudinal direction.

Examples

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

(1) Thickness of

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

(2) Phase difference value

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

(3) Orientation angle (slow axis expression direction)

A sample was prepared by cutting out a square 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 film was parallel to the width direction of the film. The sample was measured using an Axoscan manufactured by Axometrics, and the orientation angle θ at a wavelength of 590nm was measured.

(4) Glass transition temperature (Tg)

Measured according to JIS K7121.

< example 1 >

(preparation of a polyester carbonate resin film)

Polymerization was carried out using a batch polymerization apparatus comprising 2 vertical reactors each equipped with a stirring blade and a reflux cooler controlled to 100 ℃. Charging bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl]29.60 parts by mass (0.046mol) of 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 1.19X 10 of calcium acetate monohydrate as a catalyst ^-2 Mass portion (6.78X 10) ^-5 mol). After the inside of the reactor was replaced with nitrogen under reduced pressure, the reactor was heated with a heating medium, and stirring was started when the inside temperature reached 100 ℃.40 minutes after the start of the temperature increase, the internal temperature was set to 220 ℃ and the pressure reduction was started while controlling the temperature so as to be maintained, and the pressure was set to 13.3kPa for 90 minutes after the temperature reached 220 ℃. Phenol vapor by-produced in association with the polymerization reaction was introduced into a reflux condenser at 100 ℃ to return a small amount of monomer components contained in the phenol vapor to the reactor, and the phenol vapor that was not condensed was introduced into a condenser at 45 ℃ to be recovered. After nitrogen gas was introduced into the first reactor and the pressure was temporarily returned to atmospheric pressure, the reaction solution in the first reactor, which had been oligomerized, was transferred to the second reactor. Subsequently, the temperature and pressure in the second reactor were increased and reduced, and the internal temperature and pressure were set to 240 ℃ and 0.2kPa for 50 minutes. Then, the polymerization was carried out until a predetermined stirring power was obtained. When the predetermined power was reached, nitrogen gas was introduced into the reactor to recover the pressure, the produced polyester carbonate was extruded into water, and the strand was cut to obtain pellets. The Tg of the polyestercarbonate resin obtained was 140 ℃.

The obtained polyester carbonate resin was vacuum-dried at 80 ℃ for 5 hours, and then a film-forming apparatus equipped with a single-screw extruder (manufactured by Toshiba machine Co., Ltd., cylinder set temperature: 250 ℃), a T-die (width 200mm, set temperature: 250 ℃), a chill roll (set temperature: 120 to 130 ℃) and a winder was used to form a 135 μm thick resin film.

(production of stretched film)

The polyester carbonate resin film obtained as described above was obliquely stretched using a stretching apparatus shown in fig. 1 to 3, and a retardation film was obtained.

Specifically, the left and right ends of the polyester carbonate resin film were held between left and right clamps at the entrance of the stretching apparatus, and preheated to 145 ℃ in the preheating zone B. In the preheating region, the clamp pitch (P) of the left and right clamps ₁ ) Is 125 mm.

Then, the film enters the stretching region C, and the grip pitch of the right-side grip is increased to P while the increase of the grip pitch of the right-side grip and the decrease of the grip pitch of the left-side grip are started ₂ While reducing the clamp spacing of the left clamp to P ₃ (first oblique stretching). At this time, the rate of change of the clamp pitch (P) of the right clamp ₂ /P ₁ ) 1.42, rate of change of grip spacing (P) of left grip ₃ /P ₁ ) 0.78, and a transverse stretching magnification of 1.45 times the original width of the film. Then, the clamp pitch of the right clamp is maintained at P ₂ Starting the increase of the clamp pitch of the left clamp from P ₃ Increase to P ₂ (second oblique stretching). Rate of change of grip pitch (P) of left grip during this period ₂ /P ₃ ) The stretching ratio in the transverse direction to the original width of the film was 1.82, and 1.9. In addition, the stretching region C was set to Tg +3.2 deg.C (143.2 deg.C).

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

In the oblique stretching, the rotation of the driving sprocket of the stretching device was controlled so that the traveling speeds (hereinafter, referred to as linear speeds) of the left and right clamps at the time of sandwiching the film became 5 m/min.

(detection of wrinkles)

Both side end portions of the stretched film released from the above-mentioned clips and sent out from the stretching device were cut by 250mm, respectively. The film with both ends cut out was conveyed by a roller, and the presence or absence of wrinkles during the conveyance of the roller was visually confirmed while irradiating a fluorescent lamp. As a result, wrinkles are generated mainly on the left side of the stretched film.

(Change in Linear velocity)

The rotational speed of the driving sprocket was increased to set the linear velocity at 8 m/min, and the oblique stretching was continued. Further, the jig pitch of the left and right jigs is slightly increased by changing the linear velocity.

The retardation Re (550) of the obliquely stretched film obtained after the change of the linear velocity was 147nm, and the angle formed between the slow axis direction and the longitudinal direction was 45 °.

< example 2 >

A stretched film was obtained in the same manner as in example 1 except that the linear velocity was changed to 40 m/min. The retardation Re (550) of the obtained stretched film was 147nm, and the angle formed between the slow axis direction and the longitudinal direction was 45 °.

< example 3 >

A stretched film was obtained in the same manner as in example 1 except that the linear velocity was changed to 23 m/min. The retardation Re (550) of the obtained stretched film was 147nm, and the angle formed between the slow axis direction and the longitudinal direction was 45 °.

< comparative example 1 >

A stretched film was obtained in the same manner as in example 1 except that the line speed was not changed. The retardation Re (550) of the obtained stretched film was 147nm, and the angle formed between the slow axis direction and the longitudinal direction was 45 °.

[ evaluation of wrinkles ]

The obtained stretched film was evaluated for wrinkles based on the following criteria.

Good: no wrinkles were visually recognized even when polarized light (product number "NP-1" manufactured by polarin corporation) was irradiated.

And (delta): wrinkles were not visually recognized even when a fluorescent lamp was irradiated, but wrinkles were visually recognized when polarized light was irradiated.

X: wrinkles were visually recognized when the fluorescent lamp was irradiated.

[ evaluation of transportability ]

The obtained stretched film was visually checked for the occurrence of strain or bending of the film due to wrinkles, and evaluated based on the following criteria.

O: the film was not strained and bent.

X: the membrane is strained and/or bent.

[ evaluation of visibility ]

The stretched films obtained in the above examples and comparative examples were laminated on a long mask in a roll-to-roll manner (product name "TORETEC 7832C-30" manufactured by toray film processing corporation), to obtain a film laminate. Next, the mask was peeled off from the film laminate, an adhesive was applied by a gravure coater to be bonded to the polarizing plate, and UV irradiation was performed to obtain an optical laminate. The obtained optical laminate was bonded to the visible side of the reflector or the organic EL panel via the adhesive layer. The obtained optical laminate was visually checked for the presence or absence of shape unevenness due to wrinkles and light leakage, and evaluated based on the following criteria.

Good: both the reflector and the panel were mounted without visual unevenness and light leakage.

And (delta): unevenness and/or light leakage are visually recognized on the reflection plate, but are not visually recognized on the panel mounting.

X: unevenness and/or light leakage were visually recognized in both the reflection plate and the panel mounting.

The evaluation results of the stretched films obtained in the examples and comparative examples are shown in table 1.

TABLE 1

< evaluation >

As shown in table 1, in the examples in which the line speed was increased to 8 m/min to 40 m/min, the obliquely stretched film having reduced wrinkles was obtained.

Industrial applicability

The method for producing a stretched film of the present invention can be suitably used for producing a retardation film, and as a result, can contribute to 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, which is a method for producing a stretched film using a film stretching apparatus having: a ring-shaped left and right reference rails, a left and right pitch setting rail provided on an inner peripheral side of the reference rails, a plurality of left and right jig carrying members guided by the reference rails and moved in a traveling manner, left and right jigs carried on the jig carrying members, and a connecting mechanism configured to adjust a pitch between the jig carrying members by a distance between the reference rails and the pitch setting rail,

the method for producing the stretched film includes:

the left and right ends of the long film in the width direction are respectively clamped by the left and right clamps;

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

releasing the film from the left and right clamps;

detecting wrinkles of the film; and

based on the detection result, the traveling speed of the left and right clamps is increased when the film is clamped.

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

the traveling speeds of the left and right jigs when the film is clamped are increased to 8 m/min to 40 m/min.

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

the rate of increase in the traveling speed of the left and right jigs when holding the film is 101% to 800%.

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

the oblique stretching includes: (i) while making the clamp pitch of one of the left and right clamps from P ₁ Increase to P ₂ While making the distance between the clamps of the other clamp from P ₁ Is reduced to P ₃ (ii) a And (ii) changing the jig pitch of each jig so that the reduced jig pitch and the increased jig pitch are equal to each other.

5. The method for producing a stretched film according to claim 4,

P ₂ /P ₁ 1.25 to 1.75, P ₃ /P ₁ Is 0.50 or more and less than 1.

6. A method of manufacturing an optical stack, comprising:

a long stretched film obtained by the production method according to any one of claims 1 to 5; and

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

7. The method for manufacturing an optical laminate according to claim 6,

the optical film is a polarizing plate,

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