JP6988014B1 - Method for manufacturing stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce slack and / or wrinkles generated in a diagonally stretched film. SOLUTION: The left and right ends of a long film in the width direction are gripped by left and right clips, respectively, the left and right clips are traveled and moved to diagonally stretch the film, and then from the left and right clips. A method of producing a stretched film, comprising opening and rolling the film using a curved roll, wherein the non-sagging end of the film is more curved than the loosening end. A method for producing a stretched film, in which the center of the film in the width direction and the center of the curved roll in the width direction are displaced so as to be closer to the center in the width direction of the roll, and the film is conveyed in a roll. [Selection diagram] FIG. 7

Description

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

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

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

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

In order to solve such a problem, the left and right ends of the long film in the width direction are gripped by the left and right clips of the variable pitch type in which the clip pitch in the vertical direction changes, respectively, and at least the left and right clips are held. A technique has been proposed in which the slow axis of the retardation film is expressed in the diagonal direction by changing one of the clip pitches and stretching in the diagonal direction with respect to the long direction (hereinafter, also referred to as "diagonal stretching"). (For example, Patent Document 1). However, the diagonally stretched film obtained by such a technique may have slack or wrinkles.

Patent No. 4845619

The present invention has been made to solve the above problems, and a main object thereof is to reduce slack and / or wrinkles caused in a diagonally stretched film.

According to one aspect of the present invention, the left and right edges of the elongated film in the width direction are gripped by the left and right clips, respectively, the left and right clips are moved to run and the film is stretched diagonally, and then the film is stretched diagonally. A method for producing a stretched film, comprising releasing the film from the left and right clips and rolling the film using a curved roll, wherein the end of the film on the non-sagging side is loosened. Provided is a method for producing a stretched film, in which the center in the width direction of the film and the center in the width direction of the curved roll are displaced so as to be closer to the center in the width direction of the curved roll than the end portion, and the film is conveyed in a roll. To.
In one embodiment, the amount of curvature of the curved roll is 5 mm to 15 mm.
In one embodiment, the distance between the center in the width direction of the film and the center in the width direction of the curved roll when passing through the curved roll is 10 mm to 40 mm.
In one embodiment, the distance between the center in the width direction of the film and the center in the width direction of the curved roll when passing through the curved roll is 40 mm to 120 mm.
In one embodiment, in addition to the curved rolls, flat expander rolls and / or concave rolls are used to roll the film.
In one embodiment, the clip is a variable pitch type clip in which the clip pitch in the vertical direction changes, and the clip pitch of at least one of the left clip that grips the left end portion of the film and the right clip that grips the right end portion. The film is diagonally stretched by moving the film while changing the above.
In one embodiment, the oblique stretching (i) increases the clip pitch of one of the left and right clips from P _{1 to P 2} , while increasing the clip pitch of the other clip from P _{1 to P 3.} It includes (ii) changing the clip pitch of each clip so that the reduced clip pitch and the increased clip pitch have a predetermined equal pitch.
In one embodiment, P ₂ / P ₁ is 1.25 to 1.75 and P ₃ / P ₁ is 0.50 or more and less than 1.
In one embodiment, the film is tilted by changing the transport direction of the film in the middle while moving the left clip that grips the left end portion of the film and the right clip that grips the right end portion at a constant speed. Stretch.
According to another aspect of the present invention, the elongated stretched film is obtained by the above-mentioned manufacturing method, and the elongated optical film and the elongated stretched film are conveyed in the elongated direction thereof. A method for manufacturing an optical laminate is provided, which comprises aligning and continuously laminating the two.
In one embodiment, the optical film is a polarizing plate and the stretched film is a λ / 4 plate or a λ / 2 plate.

In the method for producing a stretched film of the present invention, a slanted elongated film is passed through a curved roll in a state where the centers in the width direction are deviated from each other. Specifically, the center in the width direction of the film and the center in the width direction of the curved roll are shifted so that the end on the non-slack side of the film is closer to the center in the width direction of the curved roll than the end on the loose side. Roll transport. As a result, a greater tension is applied to the non-slack side of the film than to the slack side, and as a result, a long diagonally stretched film with reduced slack and / or wrinkles can be obtained.

It is a schematic plan view explaining the whole structure of the example of the stretching apparatus which can be used in the manufacturing method of the stretched film of this invention. FIG. 3 is a schematic plan view of a main part for explaining a link mechanism for changing a clip pitch in the stretching device of FIG. 1. FIG. 3 is a schematic plan view of a main part for explaining a link mechanism for changing a clip pitch in the stretching device of FIG. 1. It is a schematic plan view explaining the whole structure of another example of the stretching apparatus which can be used in the manufacturing method of the stretched film of this invention. It is a schematic diagram which shows the profile of the clip pitch in one embodiment of diagonal stretching. It is a schematic diagram which shows the profile of the clip pitch in one embodiment of diagonal stretching. (A) and (b) are schematic plan views and schematic side views explaining an example of roll transport, respectively. It is a schematic diagram which enlarged the curved roll part in the roll transport. It is a schematic plan view explaining the flat expander roll preferably used in embodiment of this invention. It is a schematic plan view explaining the concave roll preferably used in embodiment of this invention. It is the schematic sectional drawing of the circular polarizing plate using the retardation film obtained by the manufacturing method of this invention. It is a schematic diagram explaining the method of measuring a slack amount.

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

A. Method for manufacturing stretched film In the method for manufacturing stretched film according to the embodiment of the present invention, the left and right ends of the long film in the width direction are gripped by the left and right clips, respectively, and the left and right clips are moved by running. It comprises stretching the film diagonally and then releasing it from the left and right clips, and rolling the film using a curved roll. In the method for producing the stretched film, the center of the film and the curved roll so that the end of the film on the non-slack side is closer to the center of the curved roll in the width direction than the end on the loose side. The film is rolled and conveyed so as to be offset from the center in the width direction. Typically, the method for producing a stretched film according to the embodiment of the present invention further includes a preheating step. Specifically, the film gripped by the left and right clips is preheated and then subjected to diagonal stretching.

As a method of diagonally stretching the film by the traveling movement of the left and right clips, any arbitrary method capable of stretching the left and right ends of the film at different stretching ratios (as a result, stretching in the diagonal direction with respect to the elongated direction). Appropriate methods can be used. For example, a method in which a clip for gripping the left end of a film and a clip for gripping the right end are moved and diagonally stretched at different speeds, and a clip for gripping the left end of the film and a clip for gripping the right end of the film are used for each other. Examples thereof include a method of traveling a different distance and stretching diagonally. In one embodiment of the former diagonal stretching, at least one of a left clip for gripping the left end of the film and a right clip for gripping the right end is used with a variable pitch type clip in which the clip pitch in the vertical direction changes. By moving the clip while changing the clip pitch, the film can be stretched in an oblique direction. In one embodiment of the latter diagonal stretching, the film transport direction is changed in the middle while the left clip that grips the left end portion of the film and the right clip that grips the right end portion are moved at a constant speed (result). As a result, the film can be stretched in an oblique direction (by making the transport path lengths of the left and right ends different). In the diagonally stretched film obtained by the diagonal stretching, slack and wrinkles tend to occur on the side where the stretching ratio is small. Therefore, in one embodiment, in the diagonally stretched film, the side having a small draw ratio at the time of diagonal stretch may be the slack side. The diagonally stretched film is preferably a λ / 4 plate or a λ / 2 plate.

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

Although not shown in FIG. 1, a zone may be provided between the stretch zone C and the open zone D to perform any appropriate treatment, if necessary. Examples of such treatment include lateral shrinkage treatment and the like. Similarly, although not shown, the stretching device is typically a heating device (for example, a hot air type or a near infrared type) for setting each zone from the preheating zone B to the open zone D as a heating environment. , Various ovens such as far-infrared type). In one embodiment, preheating, diagonal stretching and opening from the clip can each be done in an oven set to a predetermined temperature.

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

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

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

2 and 3 are schematic plan views of a main part for explaining a link mechanism for changing the clip pitch in the stretching device of FIG. 1, FIG. 2 shows a state where the clip pitch is the minimum, and FIG. 3 shows a clip. Indicates the maximum pitch.

As shown in FIGS. 2 and 3, a clip supporting member 30 having an elongated rectangular shape in the horizontal direction in a plan view is provided to individually support the clips 20. Although not shown, the clip-supporting member 30 is formed into a strong frame structure having a closed cross section by an upper beam, a lower beam, a front wall (a wall on the clip side), and a rear wall (a wall on the opposite side of the clip). The clip-supporting member 30 is provided so as to roll on the traveling road surfaces 81 and 82 by the traveling wheels 38 at both ends thereof. In addition, in FIGS. 2 and 3, the traveling wheel on the front wall side (the traveling wheel rolling on the traveling road surface 81) is not shown. The traveling road surfaces 81 and 82 are parallel to the reference rail 70 over the entire area. A long hole 31 is formed along the longitudinal direction of the clip-supporting member on the rear side of the upper beam and the lower beam of the clip-supporting member 30 (opposite the clip side (hereinafter referred to as the anti-clip side)), and the slider 32 is long. It is slidably engaged in the longitudinal direction of the hole 31. In the vicinity of the clip 20 side end of the clip supporting member 30, one first shaft member 33 is vertically provided so as to penetrate the upper beam and the lower beam. On the other hand, the slider 32 of the clip-supporting member 30 is provided with a second shaft member 34 vertically penetrating. One end of the main link member 35 is pivotally connected to the first shaft member 33 of each clip-supporting member 30. The other end of the main link member 35 is pivotally connected to the second shaft member 34 of the adjacent clip-supporting member 30. In addition to the main link member 35, one end of the sub-link member 36 is pivotally connected to the first shaft member 33 of each clip-supporting member 30. The other end of the sub-link member 36 is pivotally connected to the intermediate portion of the main link member 35 by a pivot 37. As shown in FIG. 2, as the slider 32 moves to the rear side (anti-clip side) of the clip-supporting member 30 due to the link mechanism by the main link member 35 and the sub-link member 36, the clip-supporting members 30 are vertically aligned with each other. The pitch in the direction (as a result, the clip pitch) becomes smaller, and as shown in FIG. 3, the more the slider 32 moves to the front side (clip side) of the clip supporting member 30, the more the clip supporting members 30 are in the vertical direction. The pitch (as a result, the clip pitch) increases. Positioning of the slider 32 is performed by the pitch setting rail 90. As shown in FIGS. 2 and 3, the smaller the separation distance between the reference rail 70 and the pitch setting rail 90, the larger the clip pitch.

FIG. 4 is a schematic plan view illustrating an overall configuration of an example of a stretching device that can be used for the latter diagonal stretching. The stretching device 100b has a loop-shaped endless loop 10L and an endless loop 10R having a large number of clips 20 for gripping the film on both the left and right sides in a plan view. The clips 20 of the left and right endless loops 10L and 10R are guided by the reference rail 40 and circulate in a loop shape, respectively (in the illustrated example, a part of the endless loops 10L and 10R is omitted). The clip 20 of the endless loop 10L on the left side circulates in the counterclockwise direction, and the clip 20 of the endless loop 10R on the right side circulates in the clockwise direction. In the stretching device, a gripping zone A, a preheating zone B, a stretching zone C, and an open zone D are provided in this order from the inlet side to the outlet side of the seat. Each of these zones means a zone in which the film to be stretched is substantially gripped, preheated, diagonally stretched, and opened, and does not mean a mechanically or structurally independent section. Also note that the length ratio of each zone in the stretching device of FIG. 4 is different from the actual length ratio.

Although not shown in FIG. 4, a zone may be provided between the stretch zone C and the open zone D to perform any appropriate treatment, if necessary. Examples of such a treatment include a transverse shrinkage treatment such as a transverse stretching treatment. Similarly, although not shown, the stretching device is typically a heating device (for example, a hot air type or a near infrared type) for setting each zone from the preheating zone B to the open zone D as a heating environment. , Various ovens such as far-infrared type). In one embodiment, preheating, diagonal stretching and opening from the clip can each be done in an oven set to a predetermined temperature.

In the gripping zone A and the preheating zone B of the stretching device 100b, the left and right endless loops 10L and 10R are configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the film to be stretched. In the stretch zone C, the left endless loop 10L and the right endless loop 10R extend in asymmetrical directions, whereby the film transport direction changes and the film is directed from the preheating zone B side toward the open zone D. Therefore, the distance between the left and right endless loops 10L and 10R is gradually expanded until it corresponds to the width of the film after stretching. In the open zone D, the left and right endless loops 10L and 10R are configured to be substantially parallel to each other at a separation distance corresponding to the stretched width of the film. However, the configuration of the left and right endless loops 10L and 10R is not limited to the above illustrated example.

The clip (clip on the left side) of the endless loop 10L on the left side and the clip (clip on the right side) 20 of the endless loop 10R on the right side can be cyclically moved independently. For example, similarly to the stretching device shown in FIG. 1, the drive sprocket 11 of the endless loop 10L on the left side is rotationally driven in the counterclockwise direction by the electric motor 13, and the drive sprocket 11 of the endless loop 10R on the right side is driven by the electric motor 13. Is driven to rotate clockwise. Typically, the clip 20 on the left side and the clip 20 on the right side travel at a constant speed, and the clip pitch in the vertical direction can be kept constant. When the difference between the traveling speeds of the pair of left and right clips is 1% or less, it can be said that the traveling speeds of the two are constant, and the difference between the traveling speeds is preferably 0.5% or less. It is preferably 0.1% or less.

By diagonally stretching the film using the stretching device as described above, a diagonally stretched film, for example, a retardation film having a slow phase axis in the diagonal direction can be produced. Hereinafter, each step of the method for producing the stretched film will be described in detail.

A-1. Clipping the film with clips In the gripping zone A (the entrance of the film capture of the stretching device 100a or 100b), the clips 20 of the left and right endless loops 10L and 10R allow both ends of the film to be stretched to have a constant clip pitch equal to each other. , Or they are gripped at different clip pitches. The film is fed to the preheating zone B by the movement of the clips 20 of the left and right endless loops 10L and 10R (substantially, the movement of each clip-carrying member guided by the reference rail).

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

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

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

A-3. Diagonal stretching A-3-1. Diagonal stretching using variable pitch type clips In the stretching zone C of the stretching device 100a, the left and right clips 20 are moved in a traveling manner while changing the clip pitch in at least one of them in the vertical direction to diagonally stretch the film. More specifically, by increasing or decreasing the clip pitch of the left and right clips at different positions, changing (increasing and / or reducing) the clip pitch of the left and right clips at different speeds of change, and the like. Stretch the film diagonally. As a result of running and moving the left and right clips while changing the clip pitch in this way, one of the pair of left and right clips simultaneously transferred to the stretching zone reaches the end of the stretching zone prior to the other clip. .. According to such diagonal stretching, the leading end of the clip side is stretched at a higher stretching ratio than the trailing end of the clip side, and as a result, the desired direction of the long film is obtained. The slow axis can be expressed (for example, in the direction of 45 ° with respect to the longitudinal direction).

Diagonal stretching may include transverse stretching. In this case, the diagonal stretching can be performed while increasing the distance between the left and right clips (distance in the width direction), for example, as shown in FIG. Alternatively, unlike the configuration shown in FIG. 1, it can be performed while maintaining the distance between the left and right clips.

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

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

In another embodiment, oblique stretching increases or decreases the clip pitch of the other clip to a predetermined pitch while keeping the clip pitch of one of the left and right clips fixed, and then increases or decreases the original clip pitch. Can be done by returning to. For the diagonal stretching of the embodiment, for example, the description of JP-A-2013-54338, JP-A-2014-194482, etc. can be referred to.

In yet another embodiment, oblique stretching (i) increases the clip pitch of one of the left and right clips from P _{1 to P 2} , while increasing the clip pitch of the other clip from P _{1 to P 3.} It can be done by reducing to, and (ii) changing the clip pitch of each clip so that the reduced clip pitch and the increased clip pitch are at predetermined equal pitches. For the diagonal stretching of the embodiment, for example, the description in JP-A-2014-194484 can be referred to. _{Diagonal stretching of the embodiment increases the clip pitch of one} clip from P 1 to P ₂ while increasing the distance between the left and right clips, while reducing the clip pitch of the other clip from P _{1 to P 3.} Then, while stretching the film diagonally (first diagonal stretching) and increasing the distance between the left and right clips, the clip pitch of one of the clips is set to P so that the clip pitches of the left and right clips are equal. ₂ was reduced to maintain or P ₄ in, and increase the clip pitch of the clip of the other side to P ₂ or P _4, may include the film obliquely stretched (second oblique stretching).

In the first diagonal stretching, the film is stretched in a desired direction (for example, length) by stretching one end of the film in the elongated direction and contracting the other end in the elongated direction. It is possible to develop a slow axis with high uniaxiality and in-plane orientation (in the direction of 45 ° with respect to the shaku direction). Further, in the second diagonal stretching, by performing the diagonal stretching while reducing the difference between the left and right clip pitches, it is possible to sufficiently stretch in the diagonal direction while relaxing the extra stress.

In the diagonal stretching of the above three embodiments, the film can be released from the clips in a state where the moving speeds of the left and right clips are equal, so that the film transport speed and the like are less likely to vary when the left and right clips are opened. Subsequent winding of the film can be preferably performed.

5A and 5B are schematic views showing an example of the clip pitch profile in the diagonal stretching including the first diagonal stretching and the second diagonal stretching, respectively. Hereinafter, the first diagonal stretching will be specifically described with reference to these figures. In FIGS. 5A and 5B, the horizontal axis corresponds to the mileage of the clip. At the start the first oblique stretching, the right and left clip pitch are both set to P _1. P ₁ is typically a clip pitch when the film is gripped. At the same time as the first diagonal stretching is started, the clip pitch of one clip (hereinafter, may be referred to as the first clip) is started to be increased, and the other clip (hereinafter, the second clip) is started. (Sometimes referred to as) begins to reduce the clip pitch. In the first oblique stretching, the clip pitch of the first clip is increased to P _2, to reduce the clip pitch of the second clip up to P _3. Thus, at the end of the first oblique stretching in (at the beginning of the second oblique stretching), the second clip moves the clip pitch P _3, the first clip is a moving clip pitch P ₂ ing. The clip pitch ratio can roughly correspond to the clip moving speed ratio.

In FIGS. 5A and 5B, the timing at which the clip pitch of the first clip starts to increase and the timing at which the clip pitch of the second clip starts to decrease are both set as the start of the first diagonal stretching. Unlike, the clip pitch of the second clip may start to decrease after starting to increase the clip pitch of the first clip, and the clip pitch of the first clip may start to decrease after starting to decrease the clip pitch of the second clip. You may start increasing. In one preferred embodiment, the clip pitch of the first clip is started to be increased and then the clip pitch of the second clip is started to be decreased. According to such an embodiment, since the film has already been stretched to a certain extent (preferably about 1.2 to 2.0 times) in the width direction, even if the clip pitch of the second clip is greatly reduced. Wrinkles are less likely to occur. Therefore, it is possible to stretch diagonally at an acute angle, and a retardation film having high uniaxial and in-plane orientation can be preferably obtained.

Similarly, in FIGS. 5A and 5B, the clip pitch of the first clip continues to increase and the clip pitch of the second clip continues to decrease until the end of the first diagonal stretching (at the beginning of the second diagonal stretching). However, unlike the illustrated example, either the increase or decrease of the clip pitch ends earlier than the other, and the clip pitch is maintained as it is until the other ends (until the end of the first diagonal stretching). May be done.

The rate of change in the clip pitch (P ₂ / P ₁ ) of the first clip is preferably 1.25 to 1.75, more preferably 1.30 to 1.70, and even more preferably 1.35 to 1.65. Is. The rate of change in the clip pitch (P ₃ / P ₁ ) of the second clip is, for example, 0.50 or more and less than 1, preferably 0.50 to 0.95, and more preferably 0.55 to 0.90. More preferably, it is 0.55 to 0.85. When the rate of change of the clip pitch is within such a range, the slow axis can be developed with high uniaxial and in-plane orientation in the direction of approximately 45 degrees with respect to the longitudinal direction of the film.

As described above, the clip pitch can be adjusted by adjusting the separation distance between the pitch setting rail of the stretching device and the reference rail to position the slider.

The stretch ratio in the width direction of the film in the first diagonal stretching (film width at the end of the first diagonal stretching / film width before the first diagonal stretching) is preferably 1.1 times to 3.0 times, more. It is preferably 1.2 times to 2.5 times, more preferably 1.25 times to 2.0 times. If the draw ratio is less than 1.1 times, galvanized iron-like wrinkles may occur at the end on the contracted side. Further, if the draw ratio exceeds 3.0 times, the biaxiality of the obtained retardation film becomes high, and the viewing angle characteristics may deteriorate when applied to a circularly polarizing plate or the like.

In one embodiment, in the first diagonal stretching, the product of the rate of change in the clip pitch of the first clip and the rate of change in the clip pitch of the second clip is preferably 0.7 to 1.5. It is preferably performed so as to be 0.8 to 1.45, more preferably 0.85 to 1.40. If the product of the rate of change is within such a range, a retardation film having high uniaxial and in-plane orientation can be obtained.

Next, one embodiment of the second diagonal stretching will be specifically described with reference to FIG. 5A. In the second oblique stretching of this embodiment, the clip pitch of the second clip is increased from P ₃ to P _2. On the other hand, the clip pitch of the first clip, between the second oblique stretching, is maintained at P _2. Accordingly, at the time of termination second oblique stretching, the left and right clips together, there is a moving clip pitch P _2.

_{The rate of change in the clip pitch (P 2} / P ₃ ) of the second clip in the second diagonal stretching of the embodiment shown in FIG. 5A is not limited as long as the effect of the present invention is not impaired. The rate of change (P ₂ / P ₃ ) is, for example, 1.3 to 4.0, preferably 1.5 to 3.0.

Another embodiment of the second diagonal stretching will be specifically described with reference to FIG. 5B. In the second diagonal stretching of the present embodiment, the clip pitch of the first clip is decreased and the clip pitch of the second clip is increased. Specifically, the clip pitch of the first clip is _{decreased from P 2} to P _4, and the clip pitch of the second clip is increased from P _{3 to P 4.} Thus, at the end of the second oblique stretching, the right and left clip is a moving together with clips pitch P _4. In the illustrated example, the clip pitch of the first clip is decreased and the clip pitch of the second clip is increased at the same time as the start of the second diagonal stretching, but these can be started at different timings. .. Similarly, the decrease in the clip pitch of the first clip and the increase in the clip pitch of the second clip may end at different timings.

The rate of change in the clip pitch of the first clip (P ₄ / P ₂ ) and the rate of change in the clip pitch of the second clip (P ₄ / P ₃ ) in the second diagonal stretching of the embodiment shown in FIG. 5B are There is no limitation as long as the effect of the present invention is not impaired. The rate of change (P ₄ / P ₂ ) is, for example, 0.4 or more and less than 1.0, preferably 0.6 to 0.95. The rate of change (P ₄ / P ₃ ) is, for example, more than 1.0 and 2.0 or less, preferably 1.2 to 1.8. Preferably, P ₄ is P ₁ or higher. If P ₄ <P ₁ , problems such as wrinkles at the ends and high biaxiality may occur.

The stretching ratio in the width direction of the film in the second diagonal stretching (film width at the end of the second diagonal stretching / film width at the end of the first diagonal stretching) is preferably 1.1 times to 3.0 times. It is more preferably 1.2 times to 2.5 times, still more preferably 1.25 times to 2.0 times. If the draw ratio is less than 1.1 times, galvanized iron-like wrinkles may occur at the end on the contracted side. Further, if the draw ratio exceeds 3.0 times, the biaxiality of the obtained retardation film becomes high, and the viewing angle characteristics may deteriorate when applied to a circularly polarizing plate or the like. Further, the stretching ratio in the width direction in the first diagonal stretching and the second diagonal stretching (film width at the end of the second diagonal stretching / film width before the first diagonal stretching) is determined from the same viewpoint as above. It is preferably 1.2 times to 4.0 times, and more preferably 1.4 times to 3.0 times.

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

As described above, lateral shrinkage treatment may be performed after diagonal stretching. For the treatment after the diagonal stretching, paragraphs 0029 to 0032 of JP-A-2014-194483 can be referred to.

A-3-2. Diagonal stretching using a clip with a constant pitch In the stretching zone C of the stretching device 100b, the left endless loop 10L and the right endless loop 10R are stretched in asymmetric directions, so that the film transport direction changes. (Specifically, the transport direction of the film in the preheating zone B (the direction in which the arrow B extends) and the transport direction of the film in the release zone D (the direction in which the arrow D extends) are non-parallel). There is. Due to such a configuration, the lengths of the left and right endless loops 10L and R in the diagonally stretched zone C (in other words, the mileage of the left and right clips in the diagonally stretched zone C) are different. As a result, for the pair of left and right clips that travel at a constant speed, the clip with the shorter mileage travels in advance (in FIG. 4, the left clip travels in advance), and the film runs diagonally. It is stretched. For the diagonal stretching of the embodiment, for example, the description of JP-A-2004-226686, WO2007 / 111313 and the like can be referred to.

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

As described above, lateral shrinkage treatment may be performed after diagonal stretching. For the treatment after the diagonal stretching, paragraphs 0029 to 0032 of JP-A-2014-194483 can be referred to.

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

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

In one embodiment, the width of the film released from the clip (as a result, the width of the film used for roll transport using the curved roll described below) is, for example, 1500 mm to 3000 mm, preferably 1800 mm to 2700 mm. Yes, more preferably 2000 mm to 2400 mm.

A-5. Roll transport The film released from the clip is roll-conveyed using a curved roll. At this time, the film is rolled by shifting the center in the width direction of the film and the center in the width direction of the curved roll so that the end on the non-slack side of the film is closer to the center in the width direction of the curved roll than the end on the loose side. Transport. In the present specification, a cylindrical transport roll used for normal roll transport may be referred to as a straight roll.

6 (a) and 6 (b) are schematic plan views and schematic side views for explaining an example of roll transport using the curved roll, respectively, and FIG. 7 is an enlarged view of a curved roll portion in roll transport. It is a schematic diagram. In the roll transport of the illustrated example, the film 1 fed from the stretching device 100 is conveyed through seven rolls (curved roll 51, first to sixth straight rolls 52 to 57), and is conveyed by the winding unit 60. It is wound up with.

As shown in FIG. 7, the curved roll 51 is symmetrically curved around the center in the width direction (center line C1) so as to be convex in the transport direction. When the film 1 released from the clip passes over such a curved roll 51, it receives a frictional force so as to spread outward in the width direction. At this time, the film 1 is a curved roll so that the end portion on the non-slack side (right end portion in the illustrated example) is closer to the center in the width direction of the curved roll 51 than the end portion on the slack side (left end portion in the illustrated example). Since it passes through 51, a greater tension is applied to the non-slack side of the film than to the slack side. As a result, a long diagonally stretched film with reduced slack and / or wrinkles can be obtained.

The curved roll 51 has a structure in which a large number of radial ball bearings (not shown) are attached around the curved shaft 51a, and the surface layer thereof is covered with a cylinder made of an elastically deformable elastic material such as rubber. The cylinder is configured to be rotatable around 51b. The curved roll may have a fixed degree of curvature or a variable degree of curvature, and any of them may be used.

The bending amount D (mm) and the total width Wa (mm) of the bending roll 51 can be set to appropriate values according to the desired slack reduction amount, film width, and the like, respectively. The amount of curvature D can be, for example, 5 mm to 15 mm, preferably 8 mm to 13 mm. The curvature ratio (D / Wa × 100) of the curved roll 51 can be, for example, 0.1% to 1.5%, preferably 0.2% to 0.7%. If the amount of curvature and / or the curvature ratio is within the range, slack and / or slack and / or slack while substantially maintaining the desired axial angle and in-plane phase difference while substantially maintaining the axial angle and in-plane phase difference. Alternatively, a long stretched film with reduced wrinkles can be preferably obtained. The total width Wa of the curved roll 51 may be, for example, 105% to 170%, preferably 110% to 155% of the width of the film 1.

The distance (distance between the center line C2 of the film 1 and the center line C1 of the curved roll) L between the center in the width direction of the film 1 and the center in the width direction of the curved roll 51 when passing through the curved roll 51 is the effect of the present invention. Can be set to any value as long as is obtained.

In one embodiment, the distance L is, for example, 10 mm to 40 mm, preferably 15 mm to 30 mm. When the distance L is within the range, a long stretched film with reduced wrinkles can be preferably obtained while substantially maintaining the target axial angle and in-plane phase difference.

In one embodiment, the distance L is, for example, 40 mm to 120 mm, preferably 45 mm to 110 mm, more preferably 50 mm to 100 mm. When the distance L is within the range, a long stretched film with reduced slack can be preferably obtained while substantially maintaining the target axial angle and in-plane phase difference.

The hugging angle of the film as it passes through the curved roll is, for example, 45 ° to 135 °, preferably 70 ° to 100 °. If the hugging angle is within such a range, the effect of the present invention can be preferably obtained.

As shown in the illustrated example, the roll transfer can be performed using a plurality of rolls including a curved roll. In roll transport, the total number of rolls through which the film passes (including curved rolls) can be, for example, 1-12, preferably 2-10, more preferably 3-8. At that time, the order in which the film passes through the curved rolls is not particularly limited during all the rolls, and the curved rolls can be arranged at any position.

In one embodiment, in addition to the curved roll, a flat expander roll and / or a concave roll may be used in combination for roll transfer. By using these in combination, the effect of reducing slack can be obtained more preferably. There are no particular restrictions on the location of the flat expander roll and concave roll. Each of these rolls may be placed at any location upstream or downstream of the curved roll in the transport direction.

FIG. 8 is a schematic plan view illustrating a flat expander roll preferably used in the above embodiment. The flat expander roll 58 shown in FIG. 8 is a linear roll. The flat expander roll 58 is attached to the inside of the shaft 58a, a pair of support substrates 58b attached to both ends of the shaft 58a, and the support substrate 58b, and is arranged to face each other so as to expand at an angle θ with respect to the film transport direction. It has a pair of ring members 58c and a plurality of stretchable elastic bands (typically rubber bands) 58d attached between the pair of ring members 58c at predetermined intervals in the circumferential direction. The ring member 58c is provided with a bearing, and is configured to be rotatable in the circumferential direction together with the elastic band 58d on the inside thereof by receiving a frictional force between the elastic band 58d and the film to be conveyed. Further, the ring member 58c is configured so that the angle θ with respect to the transport direction of the film can be arbitrarily changed. In the illustrated example, the angle θ can be changed by the insertion amount of the four adjusting bolts 58e, but the angle θ may be changed by another configuration. The flat expander roll can exhibit greater expandability as the angle θ becomes larger.

The inclination angle θ of the ring member may be, for example, more than 0 ° and not more than ° 4.0 °, preferably 0.1 ° to 3.5 °. By using the flat expander roll together at such an inclination angle, a long stretched film with reduced slack can be more preferably obtained while substantially maintaining the desired axial angle and in-plane phase difference. ..

FIG. 9 is a schematic plan view illustrating a concave roll preferably used in the above embodiment. The concave roll 59 has a central portion 59a, an enlarged diameter portion 59b and an end portion 59c located in this order from both ends thereof toward the outside. The central portion 59a and the end portion 59c each have a cylindrical shape, and the concave roll 59 has a point-symmetrical shape with the center C of the rotation axis A as the center of symmetry.

The difference X between the radius of the central portion 59a and the radius of the end portion 59c can be, for example, 0.2 mm to 2.0 mm, preferably 0.3 mm to 1.8 mm. Further, the width W4 of the end portion 59c may be, for example, 20 mm to 200 mm, preferably 30 mm to 180 mm. When the difference X and / or the width W4 is within the range, the effect of reducing slack can be preferably obtained. In the illustrated example, the central portion 59a has a width W2 and has a cylindrical shape, but the width W2 of the central portion 59a may be 0 mm. In that case, the concave roll has both ends from the center in the width direction. It has a structure that expands in diameter toward the part.

The diameter expansion ratio (X / W3 × 100) of the diameter expansion portion 59b is, for example, 0.1% to 6.0%, preferably 0.2% to 5.0%, and more preferably 1.0% to 4. It is 5%. When the diameter expansion rate is within the range, the effect of reducing slack can be suitably obtained while substantially maintaining the target axial angle and in-plane phase difference. In the illustrated example, the diameter-expanded portion is linearly expanded, but the diameter-expanded portion may be concave.

Unlike the illustrated example, a concave roll having no enlarged diameter portion (that is, a concave roll whose ends rise vertically from both ends of the central portion) can also be used. The same description as for the concave roll 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 such a concave roll.

The total width W1 of the concave roll 59 and the width W2 of the central portion 59a can be appropriately set according to the film width at the time of passing through the roll, the width W4 at the end portion, the diameter expansion ratio, the difference X, and the like. The full width W1 of the concave roll 59 may be designed, for example, so that the left and right end portions 51c overlap with the film passing over the roll, for example, 5 mm to 195 mm, and for example, 10 mm to 190 mm.

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

It is preferable to carry out the roll transfer while applying tension to the film after it is released from the clip. By applying tension to the entire film in addition to correcting slack using a curved roll, slack and / or wrinkles can be reduced more effectively. The tension applied to the film is, for example, 100 N / m or more, preferably 200 N / m or more, and more preferably 250 N / m to 500 N / m. The tension can be applied, for example, by measuring the tension applied to the film between the transport rolls and controlling the rotation speed of the transport rolls so that the tension becomes a desired value.

Tension can be applied between the opening of the clip and any transport roll (eg, between the opening of the clip and the roll downstream of the curved roll).

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

The roll transfer may be performed in a heated environment or may be performed in a non-heated environment. Preferably, the roll transfer is carried out in a non-heated environment. By passing the curved roll in a non-heated environment, slack and / or wrinkles can be reduced while preventing the occurrence of scratches. The atmospheric temperature in the non-heated environment can be, for example, about 15 ° C to 40 ° C, or for example, about 20 ° C to 30 ° C. Further, the atmospheric temperature of the heating environment can be, for example, about the same as the atmospheric temperature in the open zone of the stretching device.

The roll-conveyed film 1 can be wound by the winding unit 60 to form a film roll. Alternatively, unlike the illustrated example, the film can be continuously bonded in the same length direction while being conveyed with another long optical film without being wound up to form an optical laminate. ..

In one embodiment, the stretched film released from the clip and sent out from the stretching device is rolled and conveyed using only a straight roll, and the amount of slack is measured, and when a slack amount of a predetermined amount or more is detected. By changing the at least one straight roll to a curved roll and carrying out the roll transfer, the amount of slack in the stretched film obtained thereafter can be reduced.

A-6. Detection of slack amount The slack amount can be detected, for example, between transport rolls. Specifically, the amount of slack can be detected as a difference in position (transport height) in the width direction of the film at an intermediate point between the transfer rolls.

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

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

The above detection can be performed in a non-heated environment. The atmospheric temperature at which the amount of slack is detected may be, for example, about 15 ° C to 40 ° C, or for example, about 20 ° C to 30 ° C.

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

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

The amount of slack reduction obtained by the method for producing a stretched film of the present invention (the amount of slack in a film transported by a roll without using a curved roll-the amount of slack in a film transported by a roll using a curved roll: However, the distance between rolls is 1000 mm. The amount of slack measured in 1) may be, for example, 3 mm or more, preferably 5 mm or more, more preferably 8 mm or more, still more preferably 10 mm or more. The amount of slack that can remain in the film after roll transfer using the curved roll is, for example, less than 15 mm, preferably 10 mm or less, more preferably 8 mm or less, still more preferably 5 mm or less, still more preferably less than 3 mm. obtain.

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

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

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

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

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

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

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

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

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

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

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

C. Optical laminate and method for manufacturing the optical laminate The stretched film obtained by the production method of the present invention can be bonded to another optical film and used as an optical laminate. For example, the retardation film obtained by the production method of the present invention can be suitably used as a circular 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 circular polarizing plate 200 of the illustrated example includes a polarizing element 210, a first protective film 220 arranged on one side of the polarizing element 210, a second protective film 230 arranged on the other side of the polarizing element 210, and a second protective film. It has a retardation film 240 arranged on the outside of the protective film 230 of 2. The retardation film 240 is a stretched film (for example, a λ / 4 plate) obtained by the production method according to Item A. The second protective film 230 may be omitted. In that case, the retardation film 240 can function as a protective film for the stator. The angle formed by the absorption axis of the polarizing element 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. It is about 45 °.

The retardation film obtained by the production method of the present invention is long and has a slow axis in an oblique direction (for example, a direction of 45 ° with respect to the long direction). Also, in many cases, the elongated polarizing element has an absorption axis in the elongated direction or the width direction. Therefore, if the retardation film obtained by the production method of the present invention is used, so-called roll-to-roll can be used, and a circularly polarizing plate can be produced with extremely excellent production efficiency. Note that roll-to-roll refers to a method of continuously laminating long films by aligning their long directions while transporting them in a roll.

In one embodiment, in the method for producing an optical laminate of the present invention, a elongated stretched film is obtained by the method for producing a stretched film according to item A, and the elongated optical film and the elongated film are obtained. This includes continuously laminating the stretched film in the shape of a stretched film while aligning its long direction.

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

(1) Thickness Measured using a dial gauge (manufactured by PEACOCK, product name "DG-205 type pds-2").
(2) Phase difference value The in-plane phase difference Re (550) was measured using Axoscan manufactured by Axometrics.
(3) Orientation angle (direction of expression of slow axis)
A sample was prepared by cutting out the central portion of the film to be measured into a square shape having a width of 50 mm and a length of 50 mm so that one side was parallel to the width direction of the film. This sample was measured using Axoscan manufactured by Axometrics, and the orientation angle θ at a wavelength of 590 nm was measured.
(4) Glass transition temperature (Tg)
It was measured according to JIS K 7121.
(5) Loose amount As shown in FIG. 11, the ultrasonic displacement sensor 300 is arranged below the transport path of the film 1 at the midpoint between the transport rolls 50a and 50b (distance between rolls: 912 mm), and the transport tension is 150 N / The distance from the ultrasonic displacement sensor to the stretched film is measured at the center and edges in the width direction when transported at m, and the difference between _{the maximum distance (L MAX} ) and the minimum distance (L _{MIN ) (L MAX-} L). _MIN ) was defined as the amount of slack (mm). The amount of slack was measured by using a suction roll or the like to cut the tension applied to correct the slack, and then carrying the roll at a transport tension of 150 N / m.
(6) Tension The tension applied to the film was measured by a film tension detector installed in the film transport line.

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

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

(Preparation of stretched film)
The polyester carbonate resin film obtained as described above was obliquely stretched using a stretching device as shown in FIGS. 1 to 3 to obtain a retardation film.
Specifically, the left and right ends of the polyester carbonate resin film were gripped by the left and right clips at the entrance of the stretching device, and preheated to 145 ° C. in the preheating zone B. In the preheating zone, the clip pitch (P ₁ ) of the left and right clips was 125 mm.
Next, on the film enters the stretching zone C, to start the reduction in the clip pitches increased and left clips clip pitch right clip, clip pitch of the left clip with increasing clip pitch of the right clip to the P ₂ until P ₃ was reduced (first oblique stretching). At this time, the clip pitch change rate (P ₂ / P ₁ ) of the right clip is 1.42, the clip pitch change rate of the left clip (P ₃ / P ₁ ) is 0.78, and the original width of the film is 0.78. The lateral stretching ratio was 1.45 times. Then, while maintaining the clip pitch of the right clip at P ₂ , the clip pitch of the left clip was started to be increased and increased from P _{3 to P 2} (second diagonal extension). During this period, the rate of change in the clip pitch (P ₂ / P ₃ ) of the left clip was 1.82, and the lateral stretching ratio with respect to the original width of the film was 1.9 times. The stretching zone C was set to Tg + 3.2 ° C. (143.2 ° C.).
Then, in the open zone D, the film was held at 125 ° C. for 60 seconds for heat fixation. The heat-fixed film was cooled to 100 ° C., the left and right clips were opened, and the film was fed from the outlet of the stretching device.

(Detection of slack)
As described above, the film (width 2300 mm) fed from the outlet of the stretching device is transferred in a transport line using seven transport rolls as shown in FIGS. 6 (a) and 6 (b) under a room temperature environment. It was transported and the amount of slack was detected between the transport rolls. During roll transfer, a tension of 300 N / m was applied to the film from the clip opening point to the most downstream roll in the transfer direction for 180 seconds by adjusting the torque of the roll most downstream in the transfer direction. Among the rolls installed in the transport line, the roll that was sent out from the stretching device and the film first passed through was a curved roll (curvature amount 10 mm, total width 2400 mm), and all the other rolls were straight rolls. Further, the film was conveyed so that the center line C2 of the film overlaps the center line C1 of the curved roll (the distance between the center line C1 and the center line C2 is 0 mm). In the obtained stretched film, slack was generated at the left end portion in the width direction, and the amount of slack was 18 mm.

(Roll transfer)
In the roll transfer, the curved roll was moved in parallel with the film transfer direction so that the center line C2 of the film was 70 mm to the left of the center line C1 of the curved roll, and the roll transfer was continued.

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

<Example 1-2>
The stretched film was formed in the same manner as in Example 1-1 except that the curved roll was translated in parallel with the film transport direction so that the center line C2 of the film was 100 mm to the left of the center line C1 of the curved roll. Obtained.

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

<Example 1-3>
The stretched film was formed in the same manner as in Example 1-1 except that the curved roll was translated in parallel with the film transport direction so that the center line C2 of the film was 50 mm to the left of the center line C1 of the curved roll. Obtained.

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

<Example 1-4>
The curved roll was translated in parallel with the film transport direction so that the center line C2 of the film was 50 mm to the left of the center line C1 of the curved roll, and the third straight roll from the outlet of the stretching device was used as a concave roller. A stretched film was obtained in the same manner as in Example 1-1 except that the 6th straight roll was replaced with a flat expander roll. The inclination angle θ of the ring member of the flat expander roll was 3.5 °. The difference X between the radius of the end of the concave roll and the radius of the center is 0.9 mm, the total width W1 of the concave roll is 2100 mm, the width W2 of the center is 1800 mm, and the width of each end is 1800 mm. The width W3 was 100 mm, and each enlarged diameter portion W4 was 50 mm.

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

<Comparative Example 1-1>
A stretched film was obtained in the same manner as in Example 1-1 except that a straight roll was used instead of the curved roll and the center in the width direction overlapped with the center in the width direction of the film.

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

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

Table 1 shows the amount of slack and the evaluation results for the stretched films obtained in Examples 1-1 to 1-4 and Comparative Example 1-1.

<Example 2-1>
The stretched film was formed in the same manner as in Example 1-1 except that the curved roll was translated in parallel with the film transport direction so that the center line C2 of the film was 40 mm to the left of the center line C1 of the curved roll. Obtained.

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

<Example 2-2>
The stretched film was formed in the same manner as in Example 1-1 except that the curved roll was translated in parallel with the film transport direction so that the center line C2 of the film was 25 mm to the left of the center line C1 of the curved roll. Obtained.

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

<Example 2-3>
The stretched film was formed in the same manner as in Example 1-1 except that the curved roll was translated in parallel with the film transport direction so that the center line C2 of the film was 10 mm to the left of the center line C1 of the curved roll. Obtained.

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

<Comparative Example 2-1>
The stretched film was formed in the same manner as in Example 1-1 except that the roll was conveyed with the center line C2 of the film and the center line C1 of the curved roll overlapping without moving the curved roll in parallel. Obtained.

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

<Comparative Example 2-2>
Similar to Example 1-1, except that a straight roll was used instead of the curved roll and the center line C2 of the film was arranged so as to be 25 mm to the left of the center line C1 of the straight roll. A stretched film was obtained.

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

[Wrinkle evaluation]
The wrinkles of the obtained stretched film were evaluated based on the following criteria.
〇: Wrinkles are not visible even when irradiated with Polarion light (manufactured by Polarion, product number "NP-1").
Δ: Wrinkles are not visible even when irradiated with a fluorescent lamp, but wrinkles are visible when irradiated with a polarion light.
X: Wrinkles are visually recognized when irradiated with a fluorescent lamp.

[Evaluation of transportability]
With respect to the obtained stretched film, it was visually confirmed whether or not the film was distorted or broken due to slack and / or wrinkles, and evaluated based on the following criteria.
〇: The film is not distorted or broken.
X: The film is distorted and / or broken.

[Visibility evaluation]
The optical laminate produced in the above appearance and handleability evaluation was bonded to the visible side of the reflector or the organic EL panel via the adhesive layer. With respect to the obtained optical laminate, the presence or absence of uneven shape or light leakage due to slack or wrinkles was visually confirmed and evaluated based on the following criteria.
〇: Unevenness and light omission are not visible on both the reflector and the panel mounting.
Δ: Unevenness and / or light omission are visible on the reflector, but not on the panel mounting.
X: Unevenness and / or light omission are visually recognized in both the reflector and the panel mounting.

The evaluation results of the stretched films obtained in Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-2 are shown in Table 2.

<Evaluation>
As shown in Tables 1 and 2, in the production of a long diagonally stretched film, the film after diagonally stretched is passed through the curved roll so that the end on the non-slack side is closer to the center line of the curved roll. This reduces slack and / or wrinkles.

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

1 Stretched film 10L Endless loop 10R Endless loop 20 Clip 50 Conveying roll 51 Curved roll 60 Winding part 100 Stretching device 200 Circular polarizing plate 300 Ultrasonic displacement sensor

Claims (11)

To grip the left and right edges of the long film in the width direction with the left and right clips, respectively.
The left and right clips are run and moved to stretch the film diagonally, and then released from the left and right clips, and
A method for producing a stretched film, which comprises rolling and transporting the film using a curved roll.
The curved roll is symmetrically curved around the center in the width direction so as to be convex in the transport direction.
The film is offset from the center in the width direction of the film and the center in the width direction of the curved roll so that the end on the non-slack side of the film is closer to the center in the width direction of the curved roll than the end on the loose side. A method for producing a stretched film. The method for producing a stretched film according to claim 1, wherein the bending amount of the curved roll is 5 mm to 15 mm. The method for producing a stretched film according to claim 1 or 2, wherein the distance between the center in the width direction of the film and the center in the width direction of the curved roll when passing through the curved roll is 10 mm to 40 mm. The method for producing a stretched film according to claim 1 or 2, wherein the distance between the center in the width direction of the film and the center in the width direction of the curved roll when passing through the curved roll is 40 mm to 120 mm. The method for producing a stretched film according to any one of claims 1 to 4, wherein the film is rolled and conveyed using a flat expander roll and / or a concave roll in addition to the curved roll. The clip is a variable pitch type clip in which the clip pitch in the vertical direction changes.
7. A method for producing a stretched film. The diagonal stretching (i) increases the clip pitch of one of the left and right clips from P _{1 to P 2} , while reducing the clip pitch of the other clip from P _{1 to P 3.} (Ii) The method for producing a stretched film according to claim 6, wherein the clip pitch of each clip is changed so that the reduced clip pitch and the increased clip pitch have a predetermined equal pitch. .. The method for producing a stretched film according to claim 7, wherein _{P 2} / P ₁ is 1.25 to 1.75 and P ₃ / P _{1 is 0.50 or more and less than 1.} 1 5. The method for producing a stretched film according to any one of 5. The elongated stretched film is obtained by the production method according to any one of claims 1 to 9, and the elongated optical film and the elongated stretched film are conveyed in the elongated direction. A method for manufacturing an optical laminate, which comprises aligning and continuously laminating. The optical film is a polarizing plate, and the optical film is a polarizing plate.
The method for manufacturing an optical laminate according to claim 10, wherein the stretched film is a λ / 4 plate or a λ / 2 plate.

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