CN115139503A

CN115139503A - Method for producing stretched film

Info

Publication number: CN115139503A
Application number: CN202210328682.3A
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: 2021-03-30
Filing date: 2022-03-30
Publication date: 2022-10-04
Also published as: JP6990790B1; KR20220136227A; JP2022154341A

Abstract

The present invention reduces the sag and/or wrinkle of the film resulting from the oblique stretching. The present invention relates to a method for producing a stretched film, including the steps of: 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 to stretch the film in an oblique direction, and then releasing the film from the left and right clamps; and roll-conveying the film using a planar stretching roll having: a pair of ring members that are disposed so as to face each other so as to be spread at an angle exceeding 0 ° with respect to the film conveying direction, and that are rotatable in the circumferential direction; and a plurality of elastic bands that are stretchable and contractible and that are attached between the ring members so as to be spaced apart from each other in the circumferential direction.

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

Circularly polarizing plates are used in image display devices such as liquid crystal display devices (LCDs) and organic electroluminescence display devices (OLEDs) for the purpose of improving display characteristics and preventing reflection. 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 properties of the circularly polarizing plate, two retardation films of a λ/4 plate and a λ/2 plate may be laminated. In this case, it is necessary to laminate 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 for the purpose of rotating 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 developed 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 having a jig pitch that 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, the obliquely stretched film obtained by such a technique may be subjected to sagging or wrinkling.

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 the sag and/or the wrinkle of a film generated after oblique stretching.

Means for solving the problems

According to an aspect of the present invention, there is provided a method for producing a stretched film, including the steps of: clamping left and right ends of the long film in the width direction by left and right clamps, respectively; moving the left and right clamps to stretch the film in an oblique direction, and then releasing the film from the left and right clamps; and roll-conveying the film using a plane-expanding roller having: a pair of ring members that are disposed so as to face each other so as to be spread at an angle exceeding 0 ° with respect to the film conveying direction, and that are rotatable in the circumferential direction; and a plurality of elastic bands that are stretchable and contractible and that are attached between the ring members so as to be spaced apart from each other in the circumferential direction.

In one embodiment, the angle is more than 0 ° and 4.0 ° or less.

In one embodiment, the film has a rockwell hardness of R100 to M120.

In one embodiment, the film is roll-conveyed by using a concave roller and/or a curved roller in addition to the plane-expanding roller.

In one embodiment, the jig is a variable pitch type jig in which a jig pitch in a longitudinal direction is changed, and the film is obliquely stretched by moving the jig while changing a jig pitch of at least one of a left jig for holding a left end portion of the film and a right jig for holding a right end portion of the film.

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

In one embodiment, the film is obliquely stretched by changing the transport direction of the film halfway while moving a left gripper that grips the left end portion of the film and a right gripper that grips the right end portion of the film at equal speeds.

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

In the method for producing a stretched film of the present invention, a long obliquely stretched film is roll-fed using a plane stretching roll. Thus, a long obliquely-stretched film with reduced sagging and/or wrinkling 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 pitch of clamps 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. 4 is a schematic plan view illustrating the overall configuration of another example of a stretching apparatus that can be used in the method for producing a stretched film of the present invention.

Fig. 5A is a schematic view showing the distribution of the clip pitch in one embodiment of oblique stretching.

Fig. 5B is a schematic diagram showing the distribution of the clip pitch in one embodiment of the oblique stretching.

Fig. 6 (a) and (b) are a schematic top view and a schematic side view, respectively, illustrating an example of roll conveyance.

Fig. 7 is a schematic plan view illustrating a planar stretching roll preferably used in the embodiment of the present invention.

Fig. 8 is a schematic plan view illustrating a concave roller preferably used in the embodiment of the present invention.

Fig. 9 is a schematic plan view illustrating a bending roll preferably used in the embodiment of the present invention.

Fig. 10 is a schematic cross-sectional view of a circularly polarizing plate using a retardation film obtained by the production method of the present invention.

Fig. 11 is a schematic diagram illustrating a method of measuring the amount of slack.

Description of the symbols

1. Stretched film

10L Ring

10R cyclic ring

20. Clamp apparatus

51. Plane expanding roller

60. Coiling part

100. Stretching device

200. Circular polarizing film

300. Ultrasonic displacement sensor

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

The method for producing a stretched film according to an embodiment of the present invention includes the steps of: 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 to stretch the film in an oblique direction, and then releasing the film from the left and right clamps; and roll-conveying the film using a flat-surface stretching roller. In the present embodiment, the plane-expanding roller includes: a pair of ring members that are disposed facing each other so as to be spread out at an angle exceeding 0 ° with respect to the film conveying direction, and that are rotatable in the circumferential direction; and a plurality of elastic bands that are stretchable and contractible and that are attached between the ring members so as to be spaced apart from each other in the circumferential direction. Typically, the method for producing a stretched film 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.

As a method of obliquely stretching the film by the traveling movement of the left and right jigs, any appropriate method may be used that can stretch the left and right end portions of the film at different stretching ratios from each other (as a result, stretching in an oblique direction with respect to the longitudinal direction is possible). For example, mention may be made of: a method of performing oblique stretching by moving a jig for holding the left end portion of the film and a jig for holding the right end portion at different speeds from each other, and a method of performing oblique stretching by moving a jig for holding the left end portion of the film and a jig for holding the right end portion at different distances from each other. In the former embodiment of the oblique stretching, the film can be stretched in an oblique direction by moving the clamps while changing the clamp pitch of at least one of the left clamp holding the left end portion of the film and the right clamp holding the right end portion of the film using a variable pitch type clamp in which the clamp pitch in the longitudinal direction is changed. In the latter embodiment of the oblique stretching, the film can be stretched in an oblique direction by changing the film conveyance direction in the middle while moving the left gripper that grips the left end portion of the film and the right gripper that grips the right end portion at the same speed (as a result, the conveyance path lengths of the left and right end portions are made different). In addition, in the obliquely-stretched film obtained by the above oblique stretching, the film tends to be easily loosened and wrinkled on the side having a smaller stretching magnification. Thus, in one embodiment, in the obliquely-stretched film, the side having a smaller stretching ratio in the oblique stretching may be the slack side. The obliquely stretched film is preferably a lambda/4 plate or a lambda/2 plate.

Fig. 1 is a schematic plan view illustrating an overall configuration of an example of a stretching apparatus that can be used for the above-described former oblique stretching. The stretching apparatus 100a includes an annular ring 10L and an annular ring 10R symmetrically on both left and right sides in a plan view, and the annular ring 10L and the annular ring 10R include a plurality of jigs 20 for film clamping. In the present specification, the ring-shaped ring on the left side when viewed from the inlet side of the membrane is referred to as a left ring-shaped ring 10L, and the ring-shaped ring on the right side when viewed from the inlet side of the membrane is referred to as a right ring-shaped ring 10R. The jigs 20 of the left and right

annular rings

10L and 10R are guided by the reference rails 70 to move circularly. 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 moved in the clockwise direction. In the stretching apparatus, 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 to the outlet side of the sheet. 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 processing may be provided between the stretch region C and the release region D as necessary. 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 setting each region from the preheating region B to the release region D as a heating environment. In one embodiment, the preheating, the diagonal stretching, and the releasing from the jig may be performed in an oven set to a predetermined temperature, respectively.

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

endless loops

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

annular rings

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

annular rings

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

annular rings

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

annular rings

10L and 10R may be arranged to be substantially parallel to each other from the nip region a to the release region D by 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 independently move around. For example, the driving

sprockets

11 and 12 of the left annular ring 10L are rotationally driven in the counterclockwise direction by the

electric motors

13 and 14, and the driving

sprockets

11 and 12 of the right annular ring 10R are rotationally driven in the clockwise direction by the

electric motors

13 and 14. As a result, a traveling force can be applied to the jig carrier (not shown) of the driving roller (not shown) engaged with the driving

sprockets

11 and 12. Thereby, the left annular ring 10L is moved in a counterclockwise direction, and the right annular ring 10R is moved in a clockwise direction. The left annular ring 10L and the right annular ring 10R can be independently moved by independently driving the left electric motor and the right electric motor, respectively.

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

right jigs

20, 20 may be moved independently to change the jig pitch in the longitudinal direction. The variable pitch type configuration can be realized by employing a driving method such as a telescopic method, a linear motor method, and a motor chain method. For example, patent document 1, japanese patent application laid-open No. 2008-44339 and the like describe in detail a tenter type simultaneous biaxial stretching apparatus using a stretching type link mechanism. Hereinafter, the connection mechanism (telescopic mechanism) will be described as an example.

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, a jig carrier member 30 having a horizontally elongated rectangular shape in a plan view is provided to carry each jig 20. 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 member 30 is 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 travel wheels on the front wall side (the travel wheels that rotate on the travel surface 81) are not shown. The

travel surface

81, 82 is parallel to the reference rail 70 over the entire area. On the rear sides of the upper beam and the lower beam of the jig carrier 30 (on the opposite side to the jig side (hereinafter referred to as the "opposite jig side")), long holes 31 are formed along the longitudinal direction of the jig carrier, and the sliders 32 are 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 20 side of the jig carrier member 30. 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. One end of the main link member 35 is pivotally coupled to the first shaft member 33 of each of the jig carrier members 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 using 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 jig 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 90. As shown in fig. 2 and 3, the smaller the distance between the reference rail 70 and the pitch setting rail 90, the larger the jig pitch.

Fig. 4 is a schematic plan view illustrating an overall configuration of an example of a stretching apparatus that can be used for the above-described latter oblique stretching. The stretching apparatus 100b includes

annular rings

10L and 10R on both left and right sides in a plan view, and the

annular rings

10L and 10R include a plurality of clamps 20 for clamping the film. The jigs 20 of the left and right

annular rings

10L and 10R are guided by the reference rails 40 to move in an annular orbit (in the illustrated example, a part of the

annular rings

10L and 10R is omitted). The gripper 20 of the left annular ring 10L is cyclically moved in the counterclockwise direction, and the gripper 20 of the right annular ring 10R is cyclically moved in the clockwise direction. In the stretching apparatus, a nip area a, a preheating area B, a stretching area C, and a releasing area D are arranged in this order from the inlet side to the outlet side of the sheet. These respective regions are regions for substantially holding, preheating, obliquely stretching, and releasing the film to be stretched, and do not mean mechanically or structurally independent blocks. In addition, it is to be noted that the ratio of the lengths of the respective regions in the stretching apparatus of fig. 4 is different from the ratio of the actual lengths.

In fig. 4, although not shown, a region for performing any appropriate process may be provided between the stretch region C and the release region D as necessary. Examples of such treatment include transverse stretching treatment and transverse shrinking 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 setting each region from the preheating region B to the release region D as a heating environment. In one embodiment, the preheating, the diagonal stretching, and the releasing from the jig may be performed in an oven set to a predetermined temperature, respectively.

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

annular rings

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 left annular ring 10L and the right annular ring 10R are stretched in a laterally asymmetric direction, and thus the distance between the left and right

annular rings

10L and 10R gradually increases from the preheating region B side toward the release region D while the film conveyance direction changes, until the distance corresponds to the stretched width of the film. In the release region D, the left and right

annular rings

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

The gripper (left gripper) 20 of the left annular ring 10L and the gripper (right gripper) 20 of the right annular ring 10R can independently move around. For example, similarly to the stretching apparatus shown in fig. 1, the driving sprocket 11 of the left annular ring 10L is driven to rotate counterclockwise by the electric motor 13, and the driving sprocket 11 of the right annular ring 10R is driven to rotate clockwise by the electric motor 13. Typically, the left gripper 20 and the right gripper 20 travel at equal speeds, and the gripper pitch in the longitudinal direction can be kept constant. When the difference between the traveling speeds of the pair of left and right jigs is 1% or less, the traveling speeds of the both are considered to be equal to each other, and the difference between the traveling speeds is preferably 0.5% or less, more preferably 0.1% or less.

By obliquely stretching the film using the stretching apparatus as described above, an obliquely stretched film, for example, a retardation film having a slow axis in an oblique direction can be produced. The respective steps of the method for producing the stretched film will be described in detail below.

A-1 clamping of a film by means of a clamp

In the holding region a (an inlet of the stretching apparatus 100a or 100b into which the film is taken), the film to be stretched is held at both ends thereof by the clamps 20 of the left and right

annular rings

10L and 10R at a constant clamp pitch equal to each other or at different clamp pitches from each other. The film is sent to the preheating region B by the movement of the jigs 20 of the left and right annular rings 10L, 10R (substantially, the movement of the jig carrying members guided by the reference rails).

A-2 preheating

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

In the preheating, 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 20, the length of the preheating region, the temperature of the preheating region, and the like.

A-3. Oblique stretching

A-3-1. Oblique stretching Using variable-Pitch type jig

In the stretching region C of the stretching apparatus 100a, the film is obliquely stretched by moving the left and right clamps 20 while changing the clamp pitch in the longitudinal direction of at least one of the left and right clamps 20. 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, or 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, more preferably 1.10 to 5.00.

In one embodiment, the diagonal 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. For the oblique stretching in this embodiment, for example, refer to the disclosure of patent document 1 and japanese patent application laid-open No. 2014-238524.

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. 2013-54338 and 2014-194482 can be referred to.

In yet another embodiment, the diagonal stretching may be performed as follows: (i) While the distance between the left and right clamps is 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) making each of the reduced jig pitches and the increased jig pitches equal to a predetermined pitchThe grip pitch of each grip varies. As for the oblique stretching in this embodiment, for example, refer to the description of japanese patent application laid-open No. 2014-194484 and the like. 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. 5A and 5B 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. 5A and 5B, the horizontal axis corresponds to the travel distance of the jig. At the start of the first oblique stretching, the left and right jig pitches are set to P together ₁ 。P ₁ Typically the clip pitch when gripping the film. At the beginning of the firstSimultaneously with the oblique stretching, 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. 5A and 5B, 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. 5A and 5B, the increase in the jig pitch of the first jig and the decrease in the jig pitch of the second jig are continued until the first oblique drawing is completed (at the start of the second oblique drawing), but unlike the illustrated example, either the increase or decrease in the jig pitch may be completed earlier than the other one, and the jig pitch may be maintained until the other one is completed (until the end of the first oblique 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 still more preferably 1.25 to 1.751.35 to 1.65. In addition, the rate of change of the clamp pitch (P) of the second clamp ₃ /P ₁ ) For example, the average particle diameter 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 draw ratio is less than 1.1 times, a wrinkle in the form of a scala wave may occur at the end portion on the contraction side. When the stretching ratio exceeds 3.0 times, the obtained retardation film may have high biaxial properties, 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 jig pitch of the first jig and the rate of change in the jig pitch 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. 5A. 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 stretching 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.

Second bias stretching of the embodiment shown in FIG. 5A the rate of change of the jig pitch (P) of the second jig in (2) 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. 5B. 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. 5B 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, more than 1.0 and not more than 2.0, preferably 1.2 to 1.8.P ₄ Preferably P ₁ The above. If P is 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. When the draw ratio is less than 1.1 times, a wrinkle in a scala wave shape may occur at the end portion 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 to 4.0 times, and more preferably 1.4 to 3.0 times.

The oblique 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 (T1-T2) between the temperature T1 and the temperature T2 is preferably. + -. 2 ℃ or more, more preferably. + -. 5 ℃ or more. In one embodiment, T1 > T2, and thus, in the pre-heating 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-3-2. Oblique stretching Using a constant-pitch Clamp

In the stretching region C of the stretching device 100B, the left annular ring 10L and the right annular ring 10R are stretched in asymmetric directions, and as a result, the film conveyance direction is changed (specifically, the film conveyance direction in the preheating region B (the stretching direction of the arrow B) and the film conveyance direction in the release region D (the stretching direction of the arrow D) are configured to be nonparallel). With such a configuration, the lengths of the left and right annular rings 10L, R in the obliquely stretched region C (in other words, the travel distances of the left and right jigs in the obliquely stretched region C) are different. As a result, the pair of left and right grippers that travel at the same speed are advanced first (in fig. 4, the gripper on the left side is advanced first) to stretch the film in an oblique direction. For the oblique stretching of this embodiment, for example, the contents described in japanese patent application laid-open No. 2004-226686 and WO2007/111313 can be referred to.

The oblique stretching may be representatively 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 (T1-T2) between the temperature T1 and the temperature 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 the temperature T1 may be cooled to the temperature T2.

As described above, the transverse contraction treatment may be 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. Release of the clamps

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 performed typically at a temperature T3. The temperature T3 varies depending on the film to be stretched, and T2. Gtoreq.T 3 is sometimes used, and T2 < T3 is sometimes used. In general, the crystallization treatment may be performed by setting T2 ≧ T3 in the case where the film is an amorphous material and setting T2 < T3 in the case of a crystalline material. When T2. Gtoreq.T 3, 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.

In one embodiment, the width of the film released from the jig (as a result, the width of the film to be fed to a roller using a plane stretching roller described later) is, for example, 1500mm to 3000mm, preferably 1800mm to 2700mm, and more preferably 2000mm to 2400mm.

A-5 roller conveying

The above-described film released from the jig is subjected to roller conveyance using a flat-surface expanding roller. Fig. 6 (a) and 6 (b) are a schematic plan view and a schematic side view, respectively, illustrating an example of roller conveyance using the above-described flat stretching roller, and fig. 7 is a schematic plan view of a flat stretching roller that can be used in an embodiment of the present invention. In the roll conveyance of the illustrated example, the film 1 fed from the stretching apparatus 100 is conveyed by seven rolls (the plane stretching roll 51, the first to sixth plane rolls 52 to 57) and wound by the winding unit 60. In the present specification, a flat roller refers to a cylindrical conveying roller used for normal roller conveyance.

The flat stretching roller 51 shown in fig. 7 is a linear roller. The plane-expanding roller 51 has: the shaft 51a; a pair of support substrates 51b attached to both ends of the shaft 51a; a pair of ring members 51c attached to the inside of the support substrate 51b and arranged to face each other so as to extend at an angle θ with respect to the film transport direction; and a plurality of elastic belts (typically rubber belts) 51d which are attached between the pair of ring members 51c so as to be spaced apart from each other in the circumferential direction of the planar stretching roller 51 and are stretchable. The ring member 51c includes a bearing, and is configured to be rotatable in the circumferential direction together with the elastic belt 51d by receiving a frictional force between the elastic belt 51d and the film being conveyed. The ring member 51c is configured to be able to arbitrarily change the angle θ with respect to the film conveyance direction. In the illustrated example, the angle θ can be changed by the amount of insertion of the four adjustment bolts 51e, but the angle θ may be changed by another configuration. The larger the angle θ is, the greater the expandability can be exhibited in the flat stretching roll.

The angle θ may be set appropriately in a range exceeding 0 ° depending on the amount of relaxation of the stretched film and the degree of wrinkling. When the angle θ is 0 °, the flat stretching roller cannot exhibit the expandability, and functions as a flat roller. In addition, when the plane stretching roll is disposed so that the film overlaps the center in the width direction thereof, it is expected that the shape thereof exerts the stretchability in a bilaterally symmetric manner with respect to the center in the width direction of the film, but when the shape is applied to an obliquely stretched film having slack on one side and/or wrinkles caused by the slack, an excellent effect of substantially maintaining the intended axial angle and in-plane retardation and reducing the slack and/or wrinkles can be obtained. The reason for obtaining such an effect is not clear, but it is presumed that in the case where there is slack and/or wrinkles, the slack and/or wrinkles can be improved by a slight stretching effect, and in this case, since a uniform tension is applied in the film width direction, the surface uniformity characteristics can be maintained.

In one embodiment, the angle θ may exceed 0 ° and be 4.0 ° or less, and preferably may be 2.0 ° to 3.5 °. By using the plane-stretching roller at such an angle, a long stretched film with reduced sag can be more appropriately obtained while substantially maintaining the desired axial angle and in-plane retardation.

In one embodiment, the angle θ may be, for example, 0.1 ° to 3 °, and preferably may be 0.5 ° to 2.5 °. By using the plane-expanding roller at such an angle, a long stretched film with reduced wrinkles while substantially maintaining the desired axial angle and in-plane retardation can be more appropriately obtained.

In one embodiment, the angle θ may be, for example, 1.5 ° to 3.5 °, and preferably may be 2.0 ° to 3.0 °. By using the plane-stretching roll at such an angle, a long stretched film with less sag and wrinkles can be obtained more appropriately while substantially maintaining the desired axial angle and in-plane retardation.

The wrap angle of the film when passing through the plane stretching roll is, for example, 45 ° to 135 °, preferably 70 ° to 100 °. If the wrap angle is within such a range, the effects of the present invention can be appropriately obtained.

As shown in the illustrated example, the roller conveyance may be performed using a plurality of rollers including a flat expansion roller. The total number of rollers (including the planar stretching rollers) through which the film passes in the roller conveyance may be, for example, 1 to 12, preferably 2 to 10, and more preferably 3 to 8. In this case, the order in which the film passes through the plane stretching rollers in all the rollers is not particularly limited, and the plane stretching rollers may be arranged at arbitrary positions.

In one embodiment, roller transport may be performed using a concave roller and/or a curved roller in addition to the planar expansion roller. By using these rollers in combination, the slack reduction effect can be more appropriately obtained. The arrangement positions of the concave roller and the curved roller are not particularly limited. These rollers may be disposed at any position upstream or downstream in the conveying direction from the plane stretching roller, respectively.

Fig. 8 is a schematic plan view illustrating a concave roller preferably used in the above embodiment. The concave roller 58 has: a central portion 58a, and an enlarged diameter portion 58b and an end portion 58c provided in this order from both ends of the central portion 58a toward the outside. The center portion 58a and the end portion 58C are each cylindrical, and the concave roller 58 has a point-symmetrical shape with the center C of the rotation axis a as a center of symmetry.

The difference X between the radius of the central portion 58a and the radius of the end portion 58c may be, for example, 0.2mm to 2.0mm, and preferably 0.3mm to 1.8mm. The width W4 of the end portion 58c may be, for example, 20mm to 200mm, preferably 30mm to 180mm. If the difference X and/or the width W4 is within this range, the effect of reducing the slack can be appropriately obtained. In the illustrated example, the central portion 58a has a width W2 and is cylindrical, but the width W2 of the central portion 58a may be 0mm, and in this case, the concave roller is configured to expand in diameter from the center in the width direction toward both end portions.

The diameter expansion ratio (X/W3 × 100) of the diameter expansion portion 58b is, for example, 0.1% to 6.0%, preferably 0.2% to 5.0%, and more preferably 1.0% to 4.5%. If the diameter expansion ratio is within this range, the relaxation reduction effect can be appropriately obtained while substantially maintaining the target axial angle and in-plane retardation. In the illustrated example, the diameter-enlarged portion is linearly enlarged, but the diameter-enlarged portion may be concavely curved.

Unlike the illustrated example, a concave roller having no enlarged diameter portion (i.e., a concave roller having end portions standing vertically from both ends of a central portion) may be used. The same description as for the concave roller having the enlarged diameter portion can be applied to the difference X between the radius of the central portion and the radius of the end portion and the width W4 of the end portion in the concave roller.

The total width W1 of the concave roller 58 and the width W2 of the central portion 58a can be appropriately set in accordance with the film width when the roller passes, the width W4 of the end portion, the diameter expansion ratio, the difference X, and the like. The overall width W1 of the concave roller 58 can be designed such that the left and right ends 58c overlap the film passing over the roller by, for example, 5mm to 195mm, or 10mm to 190mm, respectively.

The material for forming the concave roller is not particularly limited as long as the effect of the present invention can be obtained, and examples thereof include rubber and metal.

Fig. 9 is a schematic plan view illustrating a bending roll preferably used in the above embodiment. The bending rollers 59 shown in fig. 9 are bent symmetrically with respect to the center in the width direction (center line C1) so as to protrude in the conveying direction. When the bending roller is used, it is preferable that the center in the width direction of the film 1 (center line C2) is shifted from the center in the width direction of the bending roller (center line C1) so that the end portion on the non-slackened side of the film 1 is closer to the center in the width direction of the bending roller than the end portion on the slackened side, and the film 1 is roll-conveyed. By carrying out the conveyance as described above, a tension greater than that of the slackened side is applied to the slackened side of the film, and therefore, the slackening is favorably reduced.

The bending roller 59 has a structure in which a plurality of radial ball bearings (not shown) are attached around the bending shaft 59a, and the surface layer thereof is covered with a tube formed of an elastically deformable elastic material such as rubber, for example, and is configured to be rotatable about the bending shaft 59 b. The bending rollers may be of a fixed bending degree or of a variable bending degree, and any of the bending rollers may be used.

The bending amount D (mm) and the total width W5 (mm) of the bending roller 59 may be set to appropriate values according to a desired amount of slack reduction, film width, and the like. The bending amount D may be, for example, 5mm to 15mm, preferably 8mm to 13mm. The bending ratio (D/W5X 100) of the bending roller 59 may be, for example, 0.1% to 1.5%, preferably 0.2% to 0.7%. If the amount of bending and/or the bending ratio are within this range, a long stretched film with reduced sag can be suitably obtained while substantially maintaining the intended axial angle and in-plane retardation and substantially maintaining the axial angle and in-plane retardation. Further, the total width W5 of the bending roller 59 may be, for example, 105% to 170%, and preferably may be 110% to 155% of the width of the film 1.

The distance L between the center of the film 1 in the width direction when passing through the bending roller 59 and the center of the bending roller 59 in the width direction (the distance between the center line C2 of the film 1 and the center line C1 of the bending roller) is, for example, 40mm to 120mm, preferably 45mm to 110mm, and more preferably 50mm to 100mm.

The roller conveyance is preferably performed while applying tension to the film released from the jig. In addition to the correction of the slack using the flat stretching roller, tension is applied to the entire film, and thus the slack and/or wrinkles can be more effectively reduced. The tension applied to the film is, for example, 100N/m or more, preferably 200N/m or more, and more preferably 250N/m to 500N/m. The tension can be applied by, for example, measuring the tension applied to the film between the transport rollers and controlling the rotation speed of the transport rollers so that the tension becomes a desired value.

The tension can be applied during a period from when the gripper is released to any of the transport rollers (for example, during a period from when the gripper is released to a roller downstream of the flat stretching roller).

The time for applying the tension can be appropriately set according to the film forming material, the amount of slack, and the like. This time may be, for example, 5 seconds to 60 seconds.

The roller conveyance may be performed in a heated environment or in a non-heated environment. Preferably, the roller transport is performed in a non-heated environment. By passing the plane stretching roller under a non-heated environment, it is possible to prevent the generation of a flaw and reduce sagging and/or wrinkles. The ambient temperature of the non-heating environment may be, for example, about 15 to 40 ℃ or, for example, about 20 to 30 ℃. The atmospheric temperature of the heating atmosphere may be set to be, for example, the same as the atmospheric temperature in the release region of the stretching device.

The film 1 conveyed by the roller can be wound by the winding section 60 to form a film roll. Alternatively, unlike the illustrated example, the optical laminate may be configured by continuously laminating the optical film and other long optical films while aligning the films in the longitudinal direction thereof and feeding the films without winding the films.

In one embodiment, when the amount of slack is measured and the amount of slack equal to or larger than a predetermined amount is detected while the stretched film released from the clips and sent out from the stretching apparatus is roll-fed by using only the flat rolls, the amount of slack of the stretched film obtained thereafter can be reduced by changing at least one of the flat rolls to a flat stretching roll and carrying out roll feeding.

A-6. Measurement of relaxation amount

The slack amount can be detected, for example, between the conveying rollers. Specifically, the amount of slack can be detected as a difference in position (conveyance height) in the width direction of the film at an intermediate point between the conveyance rollers.

The distance between the transport rollers in the detection is not particularly limited, and may be, for example, 500mm to 2000mm, and preferably 700mm to 1500mm.

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

The detection may be performed in a non-heated environment. The atmospheric temperature for detecting the amount of relaxation may be, for example, about 15 to 40 ℃ or, for example, about 20 to 30 ℃.

In one embodiment, the left and right ends in the width direction of the stretched film released from the jig are cut and removed, and then the amount of slack is detected. By detecting the amount of slack in the state where both ends have been removed, a more accurate detection result can be obtained.

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

The amount of relaxation reduction (the amount of relaxation of a film which is transported by a roll without using a flat stretching roll-the amount of relaxation of a film which is transported by a roll using a flat stretching roll: the amount of relaxation of a film which is transported by a roll with an inter-roll distance of 1000 mm) obtained by the method for producing a stretched film of the present invention may be, for example, 3mm or more, preferably 5mm or more, more preferably 8mm or more, and still more preferably 10mm or more. The amount of slack that may remain in the film after the film is conveyed by the roller using the above-described plane stretching roller may be, for example, less than 15mm, preferably 10mm or less, more preferably 8mm or less, still more preferably 5mm or less, and yet more preferably 3mm or less.

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

Details of the polycarbonate-based resin described above are described in, for example, japanese patent laid-open nos. 2012-67300 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 was 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 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 2007-161994 a. The contents of this description are incorporated herein by reference.

The Rockwell hardness of the film is preferably R100 to M120, more preferably R120 to M110, and still more preferably M70 to M100. In the roll conveyance using the flat stretching roll, although there may be a case where a flaw is generated in the film due to the press-in strength of the film, the occurrence of the flaw can be prevented by setting the hardness of the film within this range. Further, the effect of reducing sagging or wrinkling can be more appropriately obtained.

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 (λ/4 plate) is preferably 100nm to 180nm, more preferably 135nm to 155nm. 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 290nm. In this specification, nx is a refractive index in a direction in which the in-plane refractive index is the largest (i.e., the slow axis direction), ny is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and nz is a refractive index in the 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 the 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 application 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 so-called wavelength dependence of 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 with 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 bonded to a polarizing plate.

Fig. 10 is a schematic cross-sectional view of an example of such a circularly polarizing plate. The circularly polarizing plate 200 illustrated in the figure has: the polarizer 210, the first protective film 220 disposed on one side of the polarizer 210, the second protective film 230 disposed on the other side of the polarizer 210, and the retardation film 240 disposed outside the second protective film 230. The retardation film 240 is a stretched film (for example, a λ/4 plate) obtained by the production method described in the item a. The second protective film 230 may be omitted. In this case, the retardation film 240 can function as a protective film for a polarizer. The angle formed by the absorption axis of the polarizer 210 and the slow axis of the retardation film 240 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 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-205type 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.

(5) Amount of relaxation

As shown in FIG. 11, an ultrasonic displacement sensor 300 was disposed below the film 1 conveyance path at the midpoint between the

conveyance rollers

50a and 50b (distance between rollers: 912 mm), and the distance from the ultrasonic displacement sensor to the stretched film was measured at the center and end in the width direction when the film was conveyed at a conveyance tension of 150N/m, and the maximum distance (L) was calculated _MAX ) From the minimum distance (L) _MIN ) Difference between (L) _MAX -L _MIN ) The amount of relaxation (mm) was set. Further, after the tension applied for correcting the slack is cut by a suction roller or the like, the amount of slack is measured while the roller is conveyed at a conveyance tension of 150N/m.

(6) Tension force

The tension applied to the film was measured by a film tension detector provided in the film transfer line.

(7) Rockwell hardness

The measurement was performed based on ASTM D785 using a nanoindenter (product name "Nano indexing-Tester NHT3" manufactured by Anton-Paar Co.).

< 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 (0.046 mol) of 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 1.19 × 10 parts by mass 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 ℃. Introducing phenol vapor by-produced in association with the polymerization reaction into a reflux cooler at 100 ℃ to make the phenol vaporThe monomer component contained in a small amount was returned to the reactor, and the uncondensed phenol vapor was introduced into a 45 ℃ condenser and 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 resin film having a thickness of 135 μm was produced using a film-producing apparatus equipped with a single-screw extruder (manufactured by Toshiba mechanical 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. The Rockwell hardness of the obtained film was M78.

(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 inlet of the stretching device was preheated to 145 ℃ in the preheating zone B while holding the left and right ends of the polycarbonate resin film by the left and right clamps. In the preheating region, the clamp pitch (P) of the left and right clamps ₁ ) Is 125mm.

Then, the film enters the stretching region C, and the gripper pitch of the right gripper is increased to P while the gripper pitch of the right gripper and the gripper pitch of the left gripper are increased ₂ While reducing the clamp pitch 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 pitch (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 right jig was held at a jig pitch of P ₂ Starting to increase the clamp pitch of the left clamp from P ₃ Increase to P ₂ (second bias 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 and heat-set. The heat-set film was cooled to 100 ℃, and then the left and right clamps were released and sent out from the outlet of the stretching apparatus.

(detection of relaxation)

As described above, in a room temperature environment, the film (width 2300 mm) fed out from the outlet of the stretching apparatus was conveyed by the conveying line using seven conveying rollers as shown in fig. 6 (a) and 6 (b), and the amount of slack was detected between the conveying rollers. During roller conveyance, a tension of 300N/m was applied to the film from the nip release point to the most downstream roller in the conveyance direction for 180 seconds by adjusting the torque of the most downstream roller in the conveyance direction. In addition, the rollers provided in the conveyor line are all flat rollers. As a result of the detection, the film fed from the outlet of the stretching device was slackened at the left end portion in the width direction, and the slackening amount was 23mm.

(roller feed)

In the roll conveyance, the roll through which the film fed out from the outlet of the stretching apparatus first passes is replaced with a flat stretching roll, and the roll conveyance is continued. At this time, the ring member was disposed so that the inclination angle θ of the ring member with respect to the film conveyance direction became 2.5 °.

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

< example 2 >

A stretched film was obtained in the same manner as in example 1, except that the angle θ was set to 2.0 °.

< example 3 >

A stretched film was obtained in the same manner as in example 1, except that the angle θ was 3.0 °.

< example 4 >

A stretched film was obtained in the same manner as in example 1, except that the angle θ was 3.5 °.

< example 5 >

After polypropylene (PP) resin (EG 7F, manufactured by Japan Polypropylene Co., ltd.) was vacuum-dried at 80 ℃ for 5 hours, a resin film having a thickness of 135 μm was produced using a film forming apparatus equipped with a single screw extruder (manufactured by Toshiba machine Co., ltd., cylinder set temperature: 220 ℃), a T die (width 200mm, set temperature: 250 ℃), a chill roll (set temperature: 120 to 130 ℃) and a winder. The rockwell hardness of the obtained film was R90.

A stretched film was obtained in the same manner as in example 1, except that the film produced as described above was used as a film to be stretched.

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

< example 6 >

A stretched film was obtained in the same manner as in example 1 except that the angle θ was set to 1.5 °.

< example 7 >

A stretched film was obtained in the same manner as in example 1, except that the angle θ was set to 1.0 °.

< example 8 >

Setting the angle θ to 1.5 °; a stretched film was obtained in the same manner as in example 1, except that the resin film obtained in example 5 was used as a film to be stretched.

< example 9 >

Replacing the flat roll through which the film fed out from the outlet of the stretching device first passes with a bending roll having a bending amount of 10mm, the flat roll being disposed such that the center line C2 of the film is 50mm to the left of the center line C1 of the bending roll, and the flat roll disposed third from the outlet of the stretching device with a concave roll; a stretched film was obtained in the same manner as in example 1, except that the flat roll disposed in the sixth stage was replaced with a flat stretching roll. Further, the inclination angle θ of the ring member of the plane-expanding roller was 3.5 °. The difference X between the radius of the end portion and the radius of the central portion of the concave roller was 0.9mm, the total width W1 was 2100mm, the width W2 of the central portion was 1800mm, the width W4 of each end portion was 100mm, and the diameter-expanded portion W3 was 50mm.

< comparative example 1 >

A stretched film was obtained in the same manner as in example 1, except that the angle θ was set to 0 °.

[ evaluation of appearance and handling ]

The stretched films obtained in the above examples and comparative examples were laminated on a mask having a long shape (manufactured by toratec 7832C-30, product name) in a roll-to-roll manner, 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 appearance (visual observation) of the optical laminate and the handling properties of the stretched film were evaluated based on the following criteria.

Good: after the mask was bonded (bonding tension 150N/m), no wrinkles were observed and the adhesive could be applied to the entire surface of the film.

And (delta): when the mask is bonded, bonding tension is increased to 300N/m, so that bonding can be performed without wrinkles, but when the adhesive is applied, the adhesive cannot be applied at a loose position.

X: after the mask is bonded, wrinkles are formed, and the appearance is deteriorated.

[ 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 a fluorescent lamp was irradiated.

[ evaluation of scars ]

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

Good: the visual inspection by an inspector shows no scar, and even if the scar is confirmed, the level is practically almost free from problems

And (delta): the scars were visually recognized by visual inspection of an inspector, but at a practically barely allowable level

X: the flaw was visually recognized by a visual inspection of an inspector at a level that could not be practically allowed.

[ evaluation of transportability ]

The obtained stretched film was visually checked for the occurrence of strain or bending due to relaxation and/or wrinkling, 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 optical laminate obtained in the above evaluation of appearance and handling properties was bonded to the visible side of the reflective plate or the organic EL panel via an adhesive layer. The obtained optical laminate was visually checked for the presence or absence of shape unevenness due to sagging or wrinkling or light leakage, and evaluated based on the following criteria.

Good: both the reflection plate and the panel were mounted without viewing unevenness and light leakage.

And (delta): unevenness and/or light leakage were visually recognized on the reflection plate, but were 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 relaxation amounts and the evaluation results of the stretched films obtained in the above examples are shown in table 1.

TABLE 1

< evaluation >

As shown in table 1, in the production of a long obliquely-stretched film, it was found that by passing the obliquely-stretched film through a plane stretching roll, the sag and/or the wrinkle were reduced. Specifically, it was confirmed that the slack is effectively reduced by using the flat stretching roller in which the inclination angle θ of the ring member is set to a large value, and the wrinkles are effectively reduced by using the flat stretching roller in which the inclination angle θ is set to a small value.

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, comprising the steps of:

clamping left and right ends of the long film in the width direction by left and right clamps, respectively;

moving the left and right clamps and stretching the film in an oblique direction, and then releasing the film from the left and right clamps; and

the film was subjected to roll conveyance using a flat stretching roll,

the plane spreading roller has:

a pair of ring members that are disposed so as to face each other so as to be spread at an angle exceeding 0 ° with respect to the film conveying direction, and that are rotatable in the circumferential direction; and

and a plurality of elastic bands that are stretchable and contractible, and that are attached between the ring members so as to be spaced apart from each other at predetermined intervals in the circumferential direction.

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

the angle exceeds 0 DEG and is 4.0 DEG or less.

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

the Rockwell hardness of the film is R100-M120.

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

the film is roll-conveyed using a concave roller and/or a curved roller in addition to the plane-expanding roller.

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

the jig is a variable pitch type jig in which the jig pitch varies in the longitudinal direction,

the film is obliquely stretched by moving the film while changing at least one of a left jig for holding the left end portion of the film and a right jig for holding the right end portion of the film.

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

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.

7. The method for producing a stretched film according to claim 6,

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

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

the film is obliquely stretched by changing the transport direction of the film halfway while moving a left gripper that grips the left end portion of the film and a right gripper that grips the right end portion at the same speed.

9. 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 8; and

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

10. The method for manufacturing an optical stack according to claim 9,

the optical film is a polarizing plate,

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