JP2022155459A - Manufacturing method of stretched film - Google Patents

Abstract

To reduce looseness and/or wrinkles caused in a film which has been obliquely stretched.SOLUTION: A manufacturing method of a stretched film includes: holding right and left edges in a width direction of a long-sized film, by right and left clips of a variable pitch type in which a clip pitch in a machine direction changes, respectively; making the right and left clips travel and move while changing a clip pitch of at least one clip in a manner of tracing a right and left symmetrical trajectory to obliquely stretch the film; and heat setting the film. In the oblique stretch, the traveling and moving is performed so that one clip of the right and left clips precedes the other clip. In the heat setting, a temperature gradient region is formed in which temperature at an edge side held by the one preceding clip of the film is higher than temperature at an edge side of the other.SELECTED DRAWING: Figure 5

Description

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

BACKGROUND ART In image display devices such as liquid crystal display devices (LCD) and organic electroluminescence display devices (OLED), circularly polarizing plates are used for the purpose of improving display characteristics and preventing reflection. A circularly polarizing plate is typically a polarizer and a retardation film (typically a λ/4 plate), and the absorption axis of the polarizer and the slow axis of the retardation film form an angle of 45°. It is layered in this way. Conventionally, a retardation film is typically produced by uniaxial stretching or biaxial stretching in the machine direction and / or the transverse direction, so the slow axis is often a long film It develops in the horizontal direction (width direction) or the vertical direction (lengthwise direction) of the raw fabric. As a result, in order to produce a circularly polarizing plate, it was necessary to cut the retardation film so as to form an angle of 45° with respect to the width direction or the longitudinal direction, and to bond the films one by one.

Moreover, in order to secure the broadband property 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 plate is laminated so as to form an angle of 75° with respect to the absorption axis of the polarizer, and the λ/4 plate is laminated so as to form an angle of 15° with respect to the absorption axis of the polarizer. There is a need. Even in this case, when producing a 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 longitudinal direction, and to laminate one by one. .

In still another embodiment, in order to prevent light from a notebook PC from being reflected on a keyboard or the like, a A λ/2 plate may be used. Even in this case, it was necessary to cut the retardation film so as to form an angle of 45° with respect to the width direction or the longitudinal direction, and to bond the films one by one.

In order to solve such a problem, the left and right ends in the width direction of the long film are respectively gripped by left and right variable-pitch clips with variable clip pitches in the vertical direction. A technique has been proposed in which the slow axis of the retardation film is expressed in an oblique direction by changing one clip pitch and stretching in an oblique direction with respect to the longitudinal direction (hereinafter also referred to as "diagonal stretching"). (for example, Patent Document 1). However, in the obliquely stretched film obtained by such a technique, slackness and wrinkles may occur.

Patent No. 4845619

The present invention has been made to solve the above problems, and a main object thereof is to reduce slackness and/or wrinkles generated in an obliquely stretched film.

According to one aspect of the present invention, left and right ends in the width direction of a long film are respectively gripped by left and right variable-pitch clips with varying clip pitches in the vertical direction; The film is diagonally stretched by running and moving so as to draw a symmetrical trajectory while changing the clip pitch of at least one clip, and the film is heat-set, wherein in the diagonal stretching, One of the left and right clips is moved so that it precedes the other clip, and in the heat fixing, the temperature of the end of the film gripped by the preceding one clip is the same as that of the other end. A method for producing a stretched film is provided in which a temperature gradient region is formed that is higher than the side temperature.
In one embodiment, the maximum temperature difference between both ends in the width direction of the temperature gradient region is 0.3°C to 25°C.
In one embodiment, the temperature gradient region is formed such that the isothermal line extends obliquely with respect to the width direction of the film.
In one embodiment, forming the temperature gradient region is performed by supplying hot air toward the film.
In one embodiment, the wind speed of the hot air is 3m/min to 45m/min.
_In one embodiment, the diagonal stretching includes (i) increasing the clip pitch of the _one clip from P1 to P2 while decreasing the clip pitch of the _other clip from P1 to _P3 ; and (ii) varying the clip pitch of each clip such that the reduced clip pitch and the increased clip pitch are equal to a predetermined 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.
According to another aspect of the present invention, a long stretched film is obtained by the above-described production method, and the long optical film and the long stretched film are transported in the longitudinal direction. A method for manufacturing an optical laminate is provided, comprising aligning and successively laminating the layers.
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 stretched film manufacturing method of the present invention, heat setting is performed in a heat setting zone having a temperature gradient region in which the temperature of the end portion held by the preceding clip during diagonal stretching is higher than that of the other end portion. As a result, non-uniformity of residual stress generated due to diagonal stretching can be reduced, and as a result, a long diagonally stretched film in which slackness and/or wrinkles are eliminated or reduced can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic plan view explaining the whole structure of an example of the stretching apparatus which can be used for 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; FIG. 10 is a schematic diagram showing a profile of clip pitch in one embodiment of diagonal stretching. FIG. 10 is a schematic diagram showing a profile of clip pitch in one embodiment of diagonal stretching. 4 is a schematic plan view for explaining an example of a temperature gradient that a heat fixation zone D has; FIG. 1 is a schematic diagram illustrating a hot air heating device that can be used to create a temperature gradient region; FIG. FIG. 4 is a schematic plan view for explaining an arrangement example of a hot-air heating device that can be used to form a temperature gradient region; 1 is a schematic cross-sectional view of a circularly polarizing plate using a retardation film obtained by the manufacturing method of the present invention; FIG. It is the schematic explaining the measuring method of slack amount.

Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In this specification, the term "vertical clip pitch" means the center-to-center distance in the running direction of vertically adjacent clips. Further, the lateral relationship in the width direction of a long film means the lateral relationship in the transport direction of the film, unless otherwise specified.

A. Method for producing stretched film The method for producing a stretched film according to an embodiment of the present invention comprises:
gripping the left and right ends in the width direction of the elongated film with left and right variable-pitch clips in which the clip pitch in the vertical direction changes (gripping step);
diagonally stretching the film by running and moving the left and right clips so as to draw a symmetrical track while changing the clip pitch of at least one of the clips (diagonal stretching step);
heat setting the film (heat setting step).
In the manufacturing method of the present embodiment, in the diagonal stretching, one of the left and right clips is moved so as to precede the other clip, and in heat setting, the film is gripped by the preceding one clip. A temperature gradient region is formed in which the temperature on the side of the end to which the current is applied is higher than the temperature on the side of the other end. Typically, the manufacturing method of this embodiment further includes a preheating step. Specifically, the film held by the left and right clips is preheated and then diagonally stretched.

The diagonal stretching is performed, for example, by a tenter-type simultaneous two-way stretcher equipped with left and right clips that can move at different speeds so as to draw symmetrical trajectories while gripping the left and right ends in the width direction of the long film. It can be done using an axial stretching device. According to such a tenter-type simultaneous biaxial stretching apparatus, the right and left ends of the film can be stretched at different stretch ratios. Therefore, of the pair of left and right clips when gripping the film, the running speed of one clip is made higher than the running speed of the other clip (one end of the film has a higher draw ratio than the other end) By stretching with), one clip can be moved ahead of the other clip, and the film is stretched in an oblique direction between the preceding one clip and the other following clip. be. At this time, the side gripped by the clip that reached the end of the stretching zone earlier than the other is the side gripped by the preceding clip (the side with the higher stretching ratio).

FIG. 1 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the manufacturing method of the present invention. In the stretching apparatus 100, a gripping zone A, a preheating zone B, a stretching zone C, a heat setting zone D and an opening zone E are provided in this order from the film entrance side to the exit side. These respective zones mean zones in which the film to be stretched is substantially gripped, preheated, obliquely stretched, heat set and released, and do not mean mechanically and structurally independent compartments. Also note that the length ratios of the respective zones in the drawing apparatus of FIG. 1 differ from the actual length ratios.

Although not shown in FIG. 1, between the drawing zone C and the heat setting zone D, a zone for any suitable treatment may be provided as required. Examples of such processing include lateral contraction processing and the like. Also, although not shown, the stretching apparatus is typically a heating apparatus (e.g., hot air type, near infrared type, far infrared Equipped with various ovens such as external ovens).

The stretching apparatus 100 has endless loops 10L and 10R having a large number of clips 20 for gripping the film symmetrically on both left and right sides in a plan view. In this specification, the endless loop on the left side as viewed from the entrance side of the film is referred to as the left endless loop 10L, and the endless loop on the right side is referred to as the right endless loop 10R. 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. The clip 20 of the left endless loop 10L circulates counterclockwise, and the clip 20 of the right endless loop 10R circulates clockwise. At this time, as described above, since the endless loops 10L and 10R are bilaterally symmetrical in plan view, the clip 20 of the left endless loop 10L and the clip 20 of the right endless loop 10R are located in the gripping zone. From A to the open zone E, it runs and moves so as to draw a bilaterally symmetrical trajectory.

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

The clip (left clip) 20 of the left endless loop 10L and the clip (right clip) 20 of the right endless loop 10R can independently cyclically move. For example, the driving sprockets 11 and 12 of the left endless loop 10L are rotated counterclockwise by the electric motors 13 and 14, and the driving sprockets 11 and 12 of the right endless loop 10R are rotated clockwise by the electric motors 13 and 14. It is rotationally driven in the direction of rotation. As a result, a running force is applied to the clip carrying members of the driving rollers (not shown) engaged with the driving sprockets 11,12. As a result, the left endless loop 10L circulates counterclockwise, and the right endless loop 10R circulates clockwise. By independently driving the left electric motor and the right electric motor, the left endless loop 10L and the right endless loop 10R can be cyclically moved independently.

Further, the clip (left clip) 20 of the left endless loop 10L and the clip (right clip) 20 of the right endless loop 10R are each of variable pitch type. That is, the left and right clips 20, 20 can independently change their clip pitches in the vertical direction as they move. A variable pitch configuration can be realized by adopting a drive system such as a pantograph system, a linear motor system, a motor chain system, or the like. A link mechanism (pantograph mechanism) will be described below as an example.

2 and 3 are respectively schematic plan views of essential parts for explaining the link mechanism for changing the clip pitch in the drawing device of FIG. Indicates the maximum pitch.

As shown in FIGS. 2 and 3, there is provided an elongated rectangular clip carrying member 30 which carries the clips 20 individually in plan view. Although not shown, the clip carrying member 30 is formed into a rigid frame structure with a closed cross section by an upper beam, a lower beam, a front wall (the wall on the clip side), and a rear wall (the wall on the side opposite to the clip). The clip carrier member 30 is mounted to roll on the running surfaces 81, 82 by running wheels 38 at both ends thereof. 2 and 3, the running wheels on the front wall side (running wheels that roll on the running road surface 81) are not shown. The running road surfaces 81 and 82 are parallel to the reference rail 70 over the entire area. Long holes 31 are formed along the longitudinal direction of the clip carrier member 30 on the rear side of the upper and lower beams of the clip carrier member 30 (on the side opposite to the clip side (hereinafter referred to as the anti-clip side)), and the slider 32 is elongated. It is slidably engaged in the longitudinal direction of hole 31 . A single first shaft member 33 is provided vertically through the upper and lower beams in the vicinity of the clip 20 side end of the clip support member 30 . On the other hand, a single second shaft member 34 is provided vertically through the slider 32 of the clip carrier member 30 . One end of a main link member 35 is pivotally connected to the first shaft member 33 of each clip carrier member 30 . The main link member 35 is pivotally connected at its other end to the second shaft member 34 of the adjacent clip carrier member 30 . In addition to the main link member 35 , one end of a secondary link member 36 is pivotally connected to the first shaft member 33 of each clip carrier member 30 . The secondary link member 36 has its other end pivotally connected to the intermediate portion of the main link member 35 by a pivot 37 . As shown in FIG. 2, the link mechanism of the main link member 35 and the sub-link member 36 causes the clip support members 30 to move vertically toward each other as the slider 32 moves to the rear side (anti-clip side) of the clip support members 30 . The pitch in the direction (resultingly, the clip pitch) becomes smaller, and as shown in FIG. The pitch (resulting in clip pitch) increases. Positioning of the slider 32 is performed by a pitch setting rail 90 . As shown in FIGS. 2 and 3, the smaller the distance between the reference rail 70 and the pitch setting rail 90, the larger the clip pitch.

An obliquely stretched film, for example, a retardation film having a slow axis in the oblique direction can be produced by obliquely stretching the film using the stretching apparatus as described above. A specific embodiment of the stretching apparatus as described above is described, for example, in JP-A-2008-44339, the entirety of which is incorporated herein by reference. Each step will be described in detail below.

A-1. Gripping process In the gripping zone A (entrance of the film take-in of the stretching device 100), the clips 20 of the left and right endless loops 10L and 10R make the both ends of the film to be stretched have a constant clip pitch that is equal to each other, or clips that are different from each other. Grasped by pitch. The film is sent to the preheating zone B by movement of the clips 20 of the left and right endless loops 10L, 10R (substantially, movement of each clip carrying member guided by the reference rail 70).

A-2. Preheating Step In the preheating zone B, the left and right endless loops 10L and 10R are configured to be substantially parallel to each other with a separation distance corresponding to the initial width of the film to be stretched as described above. The film is heated without lateral 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 coming into contact with the nozzles in the oven.

In the preheating step, the film is heated to temperature T1 (°C). The temperature T1 is preferably the glass transition temperature (Tg) of the film or higher, 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. Depending on the film used, the temperature T1 is, for example, 70°C to 190°C, preferably 80°C to 180°C.

The heating time 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 manufacturing conditions (for example, transport speed of the film). These heating 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 Step In the stretching zone C, the film is diagonally stretched by moving the left and right clips 20 so as to draw a symmetrical trajectory while changing the vertical clip pitch of at least one of the clips. For example, the clip pitches of the left and right clips may be increased or decreased at different positions, or the clip pitches of the left and right clips may be changed (increased and/or decreased) at different change speeds. As a result of running and moving the left and right clips while changing the clip pitch in this way, one clip of the pair of left and right clips simultaneously transferred to the stretching zone runs and moves ahead of the other clip. one clip reaches the end of the drawing zone ahead of the other clip. According to such oblique stretching, the film is stretched in the oblique direction between the preceding clip and the following clip, and as a result, the desired direction of the long film (for example, the longitudinal direction A slow axis can be developed in the direction of 45° with respect to ).

Diagonal stretching may include lateral stretching. In this case, the diagonal stretching can be performed while enlarging the distance between the left and right clips (distance in the width direction), for example, as shown in the drawing. Alternatively, unlike the illustrated example, diagonal stretching may be performed while maintaining the distance between the left and right clips without lateral stretching.

When the diagonal stretching includes lateral stretching, the stretching ratio in the transverse direction (TD) (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. ~6.00, more preferably 1.10 to 5.00.

In one embodiment, the diagonal stretching is such that 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 are different in the vertical direction. This can be done by increasing or decreasing the clip pitch of each clip to a predetermined pitch while in position. For the oblique stretching in this embodiment, for example, reference can be made to the descriptions in Patent Document 1, JP-A-2014-238524, and the like.

In another embodiment, the diagonal stretching is performed by increasing or decreasing the clip pitch of one of the left and right clips while fixing the clip pitch of the other clip to a predetermined pitch, followed by can be done by returning to For the diagonal stretching of the embodiment, for example, reference can be made to the descriptions of JP-A-2013-54338, JP-A-2014-194482, and the like.

In yet another embodiment, diagonal stretching (i) increases the clip pitch of _one of the left and right clips from P1 to P2 _, while increasing the clip pitch of the _other clip from P1 to _P3 . and (ii) varying the clip pitch of each clip such that the reduced clip pitch and the increased clip pitch are equal to a predetermined pitch. For the oblique stretching of the embodiment, for example, the description of JP-A-2014-194484 can be referred to. _The diagonal stretching of this embodiment increases the clip pitch of _one clip from P1 to P2 while increasing the distance between the left and right clips _, while decreasing the clip pitch of the _other clip from P1 to P3. to stretch the film diagonally (first diagonal stretching), and while increasing the distance between the left and right clips, the clip pitch of the one clip is set to P so that the clip pitches of the left and right clips are equal. ₂ or reduced to P4 and increasing the clip pitch of the other clip to P2 or _P4 to diagonally stretch the film _{( second} diagonal stretch).

In the first diagonal stretching, one end of the film is stretched in the longitudinal direction and the other end is shrunk in the longitudinal direction while diagonally stretching to obtain a desired direction (e.g., longitudinal A slow axis can be expressed with high uniaxiality and in-plane orientation in the direction of 45° to the slender direction. Further, in the second diagonal stretching, the diagonal stretching is performed while reducing the difference between the left and right clip pitches, thereby allowing sufficient stretching in the diagonal direction while relieving excess stress.

In the diagonal stretching of the above three embodiments, the film can be released from the clips with the left and right clips moving at the same speed. Subsequent winding of the film can be suitably performed.

FIGS. 4A and 4B are schematic diagrams showing examples of clip pitch profiles in diagonal stretching including the first diagonal stretching and the second diagonal stretching, respectively. Hereinafter, the first oblique stretching will be specifically described with reference to these figures. 4A and 4B, the horizontal axis corresponds to the travel distance of the clip. At the start of the _first diagonal stretching, both left and right clip pitches are set to P1. _P1 is typically the clip pitch when the film is gripped. At the same time as the first diagonal stretching starts, one clip (hereinafter sometimes referred to as the first clip) starts increasing the clip pitch, and the other clip (hereinafter referred to as the second clip) start reducing the clip pitch of the In the first diagonal stretching, the clip pitch of the _first clip is increased to P2 and the clip pitch of the _second clip is decreased to P3. Therefore, at the end of the first diagonal stretching (at the start of the second diagonal stretching), the _second clip moves at clip pitch P3, and the _first clip moves at clip pitch P2. ing. Note that the clip pitch ratio can roughly correspond to the clip moving speed ratio. Therefore, the ratio of the clip pitches of the left and right clips can roughly correspond to the ratio of the draw ratios in the MD direction between the right end portion and the left end portion of the film.

In FIGS. 4A and 4B, 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 at the start of the first oblique stretching, but the illustrated example is different. Alternatively, the clip pitch of the second clip may begin to decrease after the clip pitch of the first clip begins to increase, and the clip pitch of the first clip may begin to decrease after the clip pitch of the second clip begins to decrease. You can start increasing it. In one preferred embodiment, the clip pitch of the second clip begins to decrease after the clip pitch of the first clip begins to increase. According to such an embodiment, since the film has already been stretched in the width direction to a certain degree (preferably about 1.2 to 2.0 times), even if the clip pitch of the second clip is greatly reduced, Wrinkles are less likely to occur. Therefore, more acute-angle oblique stretching becomes possible, and a retardation film with high uniaxiality and in-plane orientation can be suitably obtained.

Similarly, in FIGS. 4A and 4B, the clip pitch of the first clip continues to increase and the clip pitch of the second clip decreases until the end of the first diagonal stretching (the start 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

The clip pitch change rate (P ₂ /P ₁ ) of the first clip is preferably 1.25 to 1.75, more preferably 1.30 to 1.70, still more preferably 1.35 to 1.65. is. Further, the clip pitch change rate (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, more preferably 0.55 to 0.90, It is more preferably 0.55 to 0.85. If the change rate of the clip pitch is within such a range, the slow axis can be expressed with high uniaxiality and in-plane orientation in a direction approximately 45 degrees to the longitudinal direction of the film.

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

The draw 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 to 2.5 times, more preferably 1.25 to 2.0 times. If the draw ratio is less than 1.1 times, corrugated iron-like wrinkles may occur at the ends on the contracted side. On the other hand, if the draw ratio exceeds 3.0 times, the biaxiality of the obtained retardation film becomes high, and viewing angle characteristics may deteriorate when the film is applied to a circularly polarizing plate or the like.

In one embodiment, in the first diagonal stretching, the product of the clip pitch change rate of the first clip and the clip pitch change rate of the second clip is preferably 0.7 to 1.5, more It is preferably 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 with high uniaxiality and in-plane orientation can be obtained.

Next, one embodiment of the second oblique stretching will be specifically described with reference to FIG. 4A. In the _second diagonal stretching of this embodiment, the clip pitch of the _second clip is increased from P3 to P2. Meanwhile, the clip pitch of the first clip remains at P2 during the _second diagonal stretch. Therefore, at the end of the _second oblique stretching, both the left and right clips are supposed to move at a clip pitch of P2.

The rate of change (P ₂ /P ₃ ) of the clip pitch of the second clip in the second oblique stretching of the embodiment shown in FIG. 4A is not limited as long as it does not impair the effects of the present invention. 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 is specifically described with reference to FIG. 4B. In the second diagonal stretching of this 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 P2 to _{P4 ,} and the clip pitch of the _second clip is increased from _P3 to P4. Therefore, both the left and right clips are supposed to move at a clip pitch of P4 at the end of the _second oblique stretching. In the illustrated example, the decrease in the clip pitch of the first clip and the increase in the clip pitch of the second clip are started simultaneously with the start of the second oblique stretching, but these can be started at different timings. . Similarly, the clip pitch decrease of the first clip and the clip pitch increase of the second clip may end at different timings.

The clip pitch change rate (P ₄ /P ₂ ) of the first clip and the clip pitch change rate (P ₄ /P ₃ ) of the second clip in the second diagonal stretching of the embodiment shown in FIG. 4B are There is no limitation as long as it does not impair the effects of the present invention. 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. Also, 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, P4 is greater _than or _equal to P1. If P ₄ <P ₁ , problems such as wrinkles at the ends and increased biaxiality may occur.

The draw 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, 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, corrugated iron-like wrinkles may occur at the ends on the contracted side. On the other hand, if the draw ratio exceeds 3.0 times, the biaxiality of the obtained retardation film becomes high, and viewing angle characteristics may deteriorate when the film is applied to a circularly polarizing plate or the like. Further, the stretch 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, from the same viewpoint as above, It is preferably 1.2 to 4.0 times, more preferably 1.4 to 3.0 times.

Diagonal stretching can typically be performed at temperature T2. The temperature T2 is preferably Tg−20° C. to Tg+30° C., more preferably Tg−10° C. to Tg+20° C., particularly preferably about Tg relative to the glass transition temperature (Tg) of the film. Depending 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 more, more preferably ±5° C. or more. In one embodiment, T1>T2, so the film heated to temperature T1 in the preheat zone can be cooled to temperature T2.

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

A-4. Heat-setting process In the heat-setting zone D, the obliquely stretched film is heat-treated. If desired, the longitudinal clip pitch may be reduced during heat treatment, thereby relieving stress. The stretched state is fixed by heat treatment and optional stress relaxation.

In the embodiment of the present invention, in the heat setting zone _D , the temperature of the end side ( _SH side) gripped by the preceding clip during diagonal stretching is higher than the temperature of the other end side (SL side). A high temperature gradient region is formed. FIG. 5 is a schematic plan view illustrating an example of the temperature gradient formed in the heat fixation zone D, and dotted lines indicate isotherms (a° C.>b° C.>c° C.>d° C.). As shown in FIG. 5, the heat setting zone D has regions D1 and D3 with uniform temperature distributions on the drawing zone C side and the release zone E side, respectively, and the region having the predetermined temperature gradient therebetween ( temperature gradient region) D2. Note that, unlike the illustrated example, the heat setting zone D may omit one or both of the regions D1 and D3. Also, the temperature gradient region is formed in the heat setting zone as the ambient temperature of the film (e.g., the temperature of the region spaced 250 mm from the film surface), but the temperature of the temperature gradient region is substantially the film temperature. can cope.

In region D2, the isothermal line preferably extends obliquely to the width direction of the temperature gradient region (substantially, the width direction of the film). The direction in which the isothermal line extends (the direction in which the straight line connecting the _SH side and the _SL side of the isothermal line extends) may gradually change from upstream to downstream in the temperature gradient region in the conveying direction. It may be constant throughout. Also, in the temperature gradient region in the illustrated example, the isothermal line is formed in a curved line, but the isothermal line may be linear. When the direction in which the isothermal line extends gradually changes from upstream to downstream in the conveying direction of the temperature gradient region, the angle formed by the extending direction of the isothermal line and the width direction gradually increases from the upstream side in the conveying direction to the downstream side. obtain. The angle (the maximum value of the angle when the direction in which the isothermal line extends) is preferably 10° to 80° or 100° to 170°, more preferably 20° to 70° or 110° to 160°, It is more preferably 30° to 60° or 120° to 150°. In one embodiment, the direction in which the isothermal line extends (when the direction in which the isothermal line extends changes, the direction in which the isothermal line forms the largest angle with respect to the width direction extends ( _SL3 and _SH3 in the illustrated example) or the direction in which the straight line connecting S _L4 and _SH4 extends)) is the diagonal stretching direction (the slow axis direction if the film 1 is a resin film having positive birefringence) with respect to X , preferably 0° to 60° or 120° to 180°, more preferably 0° to 50° or 130° to 180°, even more preferably 0° to 45° or 135° to 180°, even more preferably 0 ° to 30° or 150° to 180°, even more preferably 0° to 20° or 160° to 180°, even more preferably 0° to 10° or 170° to 180°. Preferably, the direction in which the isothermal line extends is inclined to the same side as the diagonal stretching direction X with respect to the longitudinal direction of the film (in other words, the inclination has the same sign). By passing through such a temperature gradient region D2, non-uniformity of residual stress caused by oblique stretching can be reduced, and as a result, slackness and/or wrinkles can be preferably reduced. Further, when the direction in which the isothermal line extends gradually changes from upstream to downstream in the temperature gradient region in the conveying direction, the minimum value of the angle formed by the extending direction of the isothermal line and the width direction exceeds 0°, for example, 1°. can do.

In the region D2, the temperature may monotonically rise from the _SL side to the _SH side in parallel with the width direction, and the pattern may be linear or curved. In addition, in the downstream region of the region D2, there may exist a portion where the temperature is constant in the width direction as the temperature gradient is eliminated.

The maximum value of the temperature difference between both ends in the width direction in the region D2 (for example, the maximum value of the temperature difference 250 mm above the film 1 end on the _SH side and the _SL side on a line parallel to the width direction) is, for example, 0.3. °C to 25 °C. If the temperature difference between the SH side and the _SL side is within this range, the effect of reducing _slackness and/or wrinkles can be preferably obtained.

In one embodiment, the maximum temperature difference is preferably between 1°C and 20°C, more preferably between 3°C and 17°C. If the temperature difference between the SH side and the _SL side is within this range, the effect of reducing _slackness can be obtained more preferably.

In one embodiment, the maximum temperature difference is preferably between 0.5°C and 25°C, more preferably between 5°C and 20°C. If the temperature difference between the _SH side and the _SL side is within this range, the effect of reducing wrinkles can be obtained more preferably.

In one embodiment, the maximum temperature difference is preferably between 5°C and 17°C, more preferably between 7°C and 15°C. If the temperature difference between the SH side and the _SL side is within this range, the effect of reducing _slackness and wrinkles can be obtained more preferably.

In the transport direction (longitudinal direction of the film) of the region D2, the temperature gradually decreases from upstream to downstream. The temperature at the beginning of the region D2 (the most upstream point having a temperature gradient in the width direction) and the temperature at the end of the region D2 (the most downstream point having a temperature gradient in the width direction) depend on the type of resin forming the film. can be set appropriately. In one embodiment, the temperature at the beginning of zone D2 is for example 80°C to 180°C, preferably 90°C to 170°C, more preferably 100°C to 160°C. The temperature at the end of region D2 is, for example, 30°C to 150°C, preferably 40°C to 140°C, more preferably 50°C to 130°C. The temperature difference between the start and end of the region D2 is, for example, 10°C to 70°C, preferably 20°C to 60°C, more preferably 30°C to 50°C. In addition, in the downstream region of the region D2, there may exist a portion where the temperature is constant in the transport direction as the temperature gradient is eliminated.

The heat treatment time in the region D2 is, for example, 10 seconds to 600 seconds, preferably 30 seconds to 360 seconds.

A method for forming the region D2 having a temperature gradient is not particularly limited. For example, a temperature gradient in the conveying direction is provided in which the temperature decreases from the starting end side to the terminal end side of the region D2 (that is, from the upstream side to the downstream side in the conveying direction), and at the starting end of the region D2, from the _SH side to the _SL side. By providing a temperature gradient in the width direction in which the temperature decreases toward the edge, it is possible to suitably form the temperature gradient region D2 in which the isothermal line extends obliquely. As a method for forming a temperature gradient in the conveying direction, the D2 area is divided into a plurality of sections, and the ambient temperature of each section is adjusted using means such as heaters and hot air so that the temperature decreases from the start end side to the end side. There is a method of adjustment. Examples of the method for forming a temperature gradient in the width direction include a method of supplying hot air having a temperature gradient in the width direction toward the film, and a method of irradiating the film with an infrared heater with different outputs in the width direction. A method of supplying hot air to the film can be preferably used because the temperature gradient can be easily controlled.

A method of supplying hot air having a temperature gradient in the width direction toward the film is, for example, as illustrated in FIG. These can be mixed in various ratios in the main body 230, and hot air with different temperatures can be blown out from a plurality of nozzles 240 arranged at predetermined intervals in the width direction. . The main body 230 is connected to, for example, the piping 210 and connected to a high-temperature air distribution header (not shown), the flow rate of which decreases toward the piping 220 side. It has low-temperature air distribution headers (not shown), and by adjusting the ratio of high-temperature air and low-temperature air distributed from these distribution headers, it is possible to supply hot air having a desired temperature gradient.

In one embodiment, in the heat setting zone where the temperature gradient is formed in the transport direction, a hot air heater is placed at the beginning of the region D2 to supply hot air having a temperature gradient in the width direction to the film. At this time, by arranging a plurality of hot-air heating devices in parallel and controlling the temperature gradient of the hot air supplied by each hot-air heating device, hot air having a temperature gradient in both the conveying direction and the width direction (as a result, A hot air having a temperature gradient such that the isothermal line extends in an oblique direction) can be supplied. For example, in the embodiment shown in FIG. 6B, first to fourth hot air heating devices 200a to 200d are arranged in parallel in this order from upstream to downstream in the conveying direction. Each of the first to fourth hot air heating devices 200a to 200d supplies hot air having a temperature gradient in which the temperature decreases from the right end ( _SH side) to the left end ( _SL side) in the width direction, Also, the temperature of the hot air on the _SH side and the _SL side is lowered from the first hot air heating device 200a toward the fourth hot air heating device 200d (that is, downstream in the conveying direction). is set. The hot air supply time can be, for example, 10 seconds to 600 seconds, preferably 30 seconds to 360 seconds. The hot air having a temperature gradient in the width direction or the hot air having a temperature gradient in both the conveying direction and the width direction is gradually cooled downstream in the conveying direction to the zone temperature, forming a temperature gradient region in which the isothermal line extends obliquely. can be

The air velocity of the hot air supplied from the hot air heating device 200 toward the film is, for example, 3 m/min to 45 m/min. If the wind speed of the hot air is within this range, the temperature gradient region can be spread to the ends of the film to perform the desired temperature control on the film, and as a result, the effect of reducing slackness and / or wrinkles can be preferably obtained. can be obtained.

In one embodiment, the wind speed of the hot air is preferably 5m/min to 30m/min, more preferably 10m/min to 25m/min. If the wind speed of the hot air is within this range, the effect of reducing slackness can be obtained more preferably.

In one embodiment, the wind speed of the hot air is preferably 15m/min to 40m/min, more preferably 20m/min to 35m/min. If the wind speed of the hot air is within this range, the effect of reducing wrinkles can be obtained more preferably.

In one embodiment, the wind speed of the hot air is preferably 15m/min to 30m/min, more preferably 20m/min to 25m/min. If the wind speed of the hot air is within this range, the effect of reducing slackness and wrinkles can be obtained more preferably.

As long as the temperature gradient region is formed, the angle at which the hot air is blown is not limited. In one embodiment, the hot air is blown at a 90° angle to the film plane.

The temperature of region D1 is typically the same temperature as the beginning of region D2. Also, the heat treatment time in the region D1 is, for example, 3 seconds to 120 seconds.

The temperature of region D3 is typically the same temperature as the end of region D2. Also, the heat treatment time in the region D3 is, for example, 3 seconds to 120 seconds.

A-5. Release Step At any position in the release zone E, the film is released from the clip. In release zone E, the film is usually cooled to a desired temperature without laterally stretching or longitudinally stretching the heat-set film, and then the film is released from the clips. Typically, the open zone has a uniform temperature distribution.

The film temperature when released from the clip is, for example, 150°C or less, preferably 70°C to 140°C, more preferably 80°C to 130°C.

The stretched film released from the clip is sent out from the exit of the stretching device and subjected to detection of the amount of slackness and/or the presence or absence of wrinkles.

B. Film to be Stretched Any appropriate film can be used in the production method of the present invention. For example, a resin film applicable as a retardation film is mentioned. Examples of materials constituting such films include polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, acrylic resins, cellulose ester resins, cellulose resins, polyester resins, polyester carbonate resins, and olefin resins. resins, polyurethane resins, and the like. Preferred are polycarbonate resins, cellulose ester resins, polyester resins, polyester carbonate resins, and cycloolefin resins. This is because, with these resins, it is possible to obtain a retardation film exhibiting so-called inverse wavelength dependence of dispersion. These resins may be used alone or in combination depending on the desired properties.

Any appropriate polycarbonate-based resin is used as the polycarbonate-based resin. For example, a polycarbonate resin containing a structural unit derived from a dihydroxy compound is preferred. Specific examples of dihydroxy compounds 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. Polycarbonate resin, in addition to structural units derived from the dihydroxy compound, isosorbide, isomannide, isoidet, spiroglycol, dioxane glycol, diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG), cyclohexanedimethanol ( CHDM), tricyclodecanedimethanol (TCDDM), and structural units derived from dihydroxy compounds such as bisphenols.

Details of the above polycarbonate resins are described, for example, in JP-A-2012-67300 and JP-A-3325560. The description of the patent document is incorporated herein by reference.

The glass transition temperature of the polycarbonate-based 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 be poor, and there is a possibility that dimensional change will occur after film formation. If the glass transition temperature is excessively high, the molding stability during film molding may deteriorate, and the transparency of the film may be impaired. The glass transition temperature is obtained according to JIS K 7121 (1987).

Any appropriate polyvinyl acetal-based resin can be used as the polyvinyl acetal-based resin. Typically, a polyvinyl acetal-based resin can be obtained by condensation reaction of at least two kinds of aldehyde compounds and/or ketone compounds and a polyvinyl alcohol-based resin. Specific examples and detailed production methods of polyvinyl acetal-based resins are described, for example, in JP-A-2007-161994. The description is incorporated herein by reference.

The stretched film (retardation film) obtained by stretching the film to be stretched preferably exhibits 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 this specification, nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow axis direction), and ny is the direction orthogonal to the slow axis in the plane (that is, the fast is the refractive index in the axial direction), and nz is the refractive index in the thickness direction. Re(λ) is the in-plane retardation of the film measured at 23° C. with light having a wavelength of λ nm. Therefore, Re(550) is the in-plane retardation of the film measured at 23° C. with light having a wavelength of 550 nm. 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 within a desired range by appropriately setting the diagonal stretching conditions. For example, a method for producing a retardation film having an in-plane retardation Re (550) of 100 nm to 180 nm by diagonal stretching is disclosed in JP-A-2013-54338, JP-A-2014-194482, and JP-A-2014-238524. This is disclosed in detail in publications such as JP-A-2014-194484. Therefore, those skilled in the art can set appropriate diagonal stretching conditions based on the disclosure.

When producing 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 to 137°, particularly preferably about 45° or 135°.

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

The retardation film preferably exhibits so-called inverse wavelength dependence of 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, more preferably 0.8 to 0.95. Re(550)/Re(650) is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.97.

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

C. Optical Laminate and Method for Producing the Optical Laminate The stretched film obtained by the production method of the present invention can be used as an optical laminate by being laminated 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 attached to a polarizing plate.

FIG. 7 is a schematic cross-sectional view of an example of such a circularly polarizing plate. The illustrated circularly polarizing plate 500 includes a polarizer 510, a first protective film 520 arranged on one side of the polarizer 510, a second protective film 530 arranged on the other side of the polarizer 510, and a second protective film 530 arranged on the other side of the polarizer 510. and a retardation film 540 arranged outside the protective film 530 of No. 2. The retardation film 540 is a stretched film (for example, a λ/4 plate) obtained by the manufacturing method described in Section A. The second protective film 530 may be omitted. In that case, the retardation film 540 can function as a protective film for the polarizer. The angle between the absorption axis of the polarizer 510 and the slow axis of the retardation film 540 is preferably 30° to 60°, more preferably 38° to 52°, still more preferably 43° to 47°, particularly preferably It is about 45°.

The retardation film obtained by the production method of the present invention is elongated and has a slow axis in an oblique direction (for example, a direction at 45° to the elongated direction). Also, in many cases, a long polarizer has an absorption axis in the length direction or the width direction. Therefore, by using the retardation film obtained by the production method of the present invention, so-called roll-to-roll can be used, and a circularly polarizing plate can be produced with extremely excellent production efficiency. In addition, roll-to-roll refers to a method in which long films are conveyed in a roll and continuously pasted together with their longitudinal directions aligned.

In one embodiment, the method for producing an optical laminate of the present invention comprises obtaining a long stretched film by the method for producing a stretched film described in Section A, and While transporting the stretched film, the longitudinal direction is aligned and continuously pasted together.

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 Measured using a dial gauge (manufactured by PEACOCK, product name “DG-205 type pds-2”).
(2) Retardation value In-plane retardation Re (550) was measured using Axoscan manufactured by Axometrics.
(3) Orientation angle (development direction of slow axis)
A sample was prepared by cutting out a central portion of the film to be measured into a square having a width of 50 mm and a length of 50 mm with one side parallel to the width direction of the film. This sample was measured using Axoscan manufactured by Axometrics to measure the orientation angle θ at a wavelength of 590 nm.
(4) Glass transition temperature (Tg)
Measured according to JIS K 7121.
(5) Amount of slackness As shown in FIG. 8, an ultrasonic displacement sensor 400 is arranged below the transport path of the film 1 at the midpoint between the transport rolls 300a and 300b (distance between the rolls: 912 mm), and the transport tension is 150 N/ Measure the distance from the ultrasonic displacement sensor to the stretched film at the center and end in the width direction when conveyed at m, and the difference between the maximum distance (L _MAX ) and the minimum distance (L _MIN ) (L _MAX -L _MIN ) was taken as the slack amount (mm). The amount of slack was measured by cutting the tension applied to correct the slack using a suction roll or the like, and then conveying the film with rolls at a conveying tension of 150 N/m.

<Example 1>
(Preparation of polyester carbonate resin film)
Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and reflux condensers 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. 139 mol), 63.77 parts by mass (0.298 mol) of DPC, and 1.19×10 ⁻² parts by mass (6.78×10 ⁻⁵ mol) of calcium acetate monohydrate as a catalyst were charged. After the interior of the reactor was replaced with nitrogen under reduced pressure, heating was performed with a heating medium, and stirring was started when the internal temperature reached 100°C. After 40 minutes from the start of heating, the internal temperature was allowed to reach 220°C, and the pressure was reduced at the same time as controlling to maintain this temperature. Phenol vapor produced as a by-product of the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and recovered. After nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and the internal temperature was brought to 240° C. and the pressure to 0.2 kPa in 50 minutes. After that, polymerization was allowed to proceed until a predetermined stirring power was obtained. When a predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, the polyester carbonate produced was extruded into water, and 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., cylinder set temperature: 250 ° C.), T die (width 200 mm, set temperature: 250 ° C.), chill roll (set temperature: 120 to 130° C.) and a film forming apparatus equipped with a winder was used to prepare a resin film having a thickness of 135 μm.

(Production of stretched film)
The polyester carbonate resin film obtained as described above was obliquely stretched using a stretching apparatus 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 held by left and right clips at the entrance of the stretching device, and preheated to 145°C in the preheating zone B. In the preheat zone, the clip pitch (P ₁ ) of the left and right clips was 125 mm.
Next, as the film enters stretching zone _C , it begins increasing the clip pitch of the right clip and decreasing the clip pitch of the left clip, increasing the clip pitch of the right clip to P2 and decreasing the clip pitch of the left clip. reduced to P ₃ (first oblique stretch). At this time, the clip pitch change rate (P ₂ /P ₁ ) of the right clip is 1.42, the clip pitch change rate (P ₃ /P ₁ ) of the left clip is 0.78, and the original width of the film is The transverse draw ratio for the film was 1.45 times. Next, while maintaining the clip pitch of the right clip at P2, the clip pitch of the left clip started to increase from _P3 to P2 _{( second} oblique stretching). The clip pitch change ratio (P ₂ /P ₃ ) of the left clip during this period was 1.82, and the transverse draw ratio to the original width of the film was 1.9 times. The stretching zone C was set at Tg+3.2°C (143.2°C).
Next, at the beginning of the heat setting zone D (the end of the stretching zone C) where the ambient temperature is set to 140° C., a hot air heating device is used so that the film has a temperature gradient that decreases from the right end side to the left end side. The film was heat-treated by blowing hot air onto the film for 180 seconds while adjusting the temperature from 140° C. to 125° C. on the right end side and from 140° C. to 115° C. on the left end side from upstream to downstream in the conveying direction. time 210 seconds). At this time, the speed of the hot air (the speed of the hot air blowing out from the hot-air heating device) was 20 m/min, and the hot air was blown from 200 mm below the film so as to form an angle of 90° with respect to the film surface. Note that the temperature at the end of the heat setting zone D was lowered to the ambient temperature (115° C.), and the temperature gradient in the width direction was eliminated.
Next, after the film was cooled to 100°C in the open zone E in which the temperature was set to 100°C, the left and right clips were released.
A stretched film was thus obtained. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.
When the temperature of the heat setting zone (the temperature at 250 mm above the film) was measured using a non-contact area thermometer, the temperature on the right side of the center in the width direction of the film was measured from the start to the end of the heat setting zone. A temperature gradient region higher than the temperature on the left was formed. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 10 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction). Also, the temperatures in the preheating zone, oblique stretching zone and open zone were uniform in the width direction, and no temperature gradient region was formed.

Prior to the production of the stretched film, hot air of 140 ° C. was blown uniformly in the width direction at the beginning of the heat setting zone D at a wind speed of 7 m / min, and then heat setting was performed according to the ambient temperature (result A stretched film was obtained in the same manner as in Example 1, except that a temperature gradient in the oblique direction was not formed). .

<Example 2>
At the beginning of the heat setting zone D, hot air of 140° C. was uniformly blown in the width direction for 180 seconds at a wind speed of 25 m / min, and then a temperature gradient was formed in the same manner as in Example 1 (specifically, a film Hot air (wind speed 25 m / min) having a temperature gradient that decreases from the right end side to the left end side is blown from upstream to downstream in the conveying direction from 140 ° C to 125 ° C on the right end side and from 140 ° C to 111 ° C on the left end side. A stretched film was obtained in the same manner as in Example 1, except that the film was sprayed for 180 seconds while adjusting to lower the temperature. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 14 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 3>
At the beginning of the heat setting zone D, hot air of 140° C. was uniformly blown in the width direction for 180 seconds at a wind speed of 23 m / min, and then a temperature gradient was formed in the same manner as in Example 1 (specifically, the film The hot air (wind speed 23 m / min) having a temperature gradient that decreases from the right end side to the left end side is blown from upstream to downstream in the conveying direction from 140 ° C. to 125 ° C. on the right end side and from 140 ° C. to 118 ° C. A stretched film was obtained in the same manner as in Example 1, except that the film was sprayed for 180 seconds while adjusting to lower the temperature. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 7 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 4>
At the beginning of the heat setting zone D, hot air of 140°C was uniformly blown in the width direction for 180 seconds at a wind speed of 20 m / min, and then a temperature gradient was formed in the same manner as in Example 1 (specifically, a film Hot air (wind speed 20 m / min) having a temperature gradient that decreases from the right end side to the left end side is blown from upstream to downstream in the conveying direction from 140 ° C to 130 ° C on the right end side and from 140 ° C to 115 ° C on the left end side. A stretched film was obtained in the same manner as in Example 1, except that the film was sprayed for 180 seconds while adjusting to lower the temperature. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 15 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 5>
At the beginning of the heat setting zone D, hot air of 140° C. was uniformly blown in the width direction for 180 seconds at a wind speed of 25 m / min, and then a temperature gradient was formed in the same manner as in Example 1 (specifically, a film Hot air (wind speed 25 m / min) having a temperature gradient that decreases from the right end side to the left end side of the conveying direction from upstream to downstream from 140 ° C to 115.5 ° C on the right end side and 140 ° C on the left end side. A stretched film was obtained in the same manner as in Example 1 except that the film was sprayed for 180 seconds while adjusting the temperature to decrease from 115°C. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 0.5 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (slow axis of the obtained stretched film direction at an angle of 3° to the direction).

<Example 6>
A stretched film was obtained in the same manner as in Example 2, except that the speed of the hot air was 20 m/min. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 14 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 7>
A stretched film was obtained in the same manner as in Example 4, except that the hot air velocity was 25 m/min. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 15 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 8>
A stretched film was obtained in the same manner as in Example 3, except that the hot air velocity was 10 m/min. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 7 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 9>
A stretched film was obtained in the same manner as in Example 2, except that the hot air velocity was 30 m/min. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 14 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 10>
A stretched film was obtained in the same manner as in Example 2, except that the hot air velocity was 35 m/min. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 14 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Example 11>
A stretched film was obtained in the same manner as in Example 1, except that the speed of the hot air was 23 m/min. The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, a temperature gradient region was formed in which the temperature on the right side of the center in the width direction of the film was higher than the temperature on the left side. The maximum value of the temperature difference between both ends in the width direction in the temperature gradient region is 10 ° C., and the direction in which the isothermal line forming the largest angle with respect to the width direction extends is the oblique direction (in the slow axis direction of the obtained stretched film direction forming an angle of 3° with respect to the direction).

<Comparative Example 1>
At the beginning of the heat setting zone D, hot air of 140 ° C. was blown uniformly in the width direction at a wind speed of 20 m / min, and then heat setting was performed according to the ambient temperature (as a result, a diagonal temperature gradient was formed. A stretched film was obtained in the same manner as in Example 1, except that it was not done). The retardation Re (550) of the obtained stretched film was 147 nm, and the angle formed by the slow axis direction and the longitudinal direction was 45°.

Further, when the temperature of the heat setting zone was measured in the same manner as in Example 1, the temperature was uniform in the width direction, and no oblique temperature gradient region was formed (more specifically, the isotherm was A temperature gradient was formed in which the temperature was parallel to the width direction and decreased in the conveying direction).

[Appearance and handling evaluation]
A film laminate was obtained by laminating the stretched films obtained in the above Examples and Comparative Examples with a long masking film (manufactured by Toray Advanced Film Co., Ltd., product name "Toretec 7832C-30") by roll-to-roll. . Next, the masking film was peeled off from the film laminate, an adhesive was applied using a gravure coater, the laminate was attached to a polarizing plate, and UV irradiation was performed to obtain an optical laminate. The appearance (visual observation) of the optical laminate and the handleability of the stretched film were evaluated based on the following criteria.
◯: No wrinkles were observed after bonding the masking film (bonding tension: 150 N/m), and the adhesive could be applied to the entire surface of the film.
Δ: When bonding the masking film, bonding was possible without wrinkles by increasing the bonding tension to 300 N/m.
x: There are wrinkles and the appearance is deteriorated after bonding the masking film.

[Wrinkle evaluation]
The wrinkles of the obtained stretched film were evaluated based on the following criteria.
○: No wrinkles are visible even when irradiated with Polarion Light (manufactured by Polarion, product number “NP-1”).
Δ: No wrinkles are visually recognized even when irradiated with a fluorescent lamp, but wrinkles are visually recognized when irradiated with a Polarion light.
x: Wrinkles are visible when irradiated with a fluorescent lamp.

[Conveyance evaluation]
Regarding the obtained stretched film, whether or not the film was distorted or folded due to slackness and/or wrinkles was visually confirmed and evaluated based on the following criteria.
◯: The film is neither distorted nor folded.
x: The film is distorted and/or folded.

[Visibility evaluation]
The optical layered body produced in the evaluation of the appearance and handling properties was attached to the viewing side of the reflector or the organic EL panel via the adhesive layer. The obtained optical layered body was visually checked for irregularities in shape or light leakage caused by slackness or wrinkles, and evaluated according to the following criteria.
◯: No unevenness or light leakage was observed in both the reflector plate and the panel mounting.
Δ: Unevenness and/or light leakage are visible on the reflector plate, but are not visible on the panel mounting.
x: Unevenness and/or light leakage are visually recognized in both the reflector plate and the panel mounting.

Table 1 shows the amount of slackness and the evaluation results of the stretched films obtained in the above Examples and Comparative Examples.

<Evaluation>
As shown in Table 1, by performing heat setting in a heat setting zone having a temperature gradient region in which the temperature on the end side gripped by the preceding clip during diagonal stretching is higher than the temperature on the other end side , sagging and/or wrinkles are reduced.

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 image display devices such as liquid crystal displays (LCDs) and organic electroluminescence displays (OLEDs). .

1 stretched film 10L endless loop 10R endless loop 20 clip 100 stretching device 200 hot air heating device 300 transport roll 400 ultrasonic displacement sensor 500 circularly polarizing plate

Claims (9)

gripping left and right ends in the width direction of a long film by left and right variable-pitch clips with variable clip pitches in the vertical direction;
diagonally stretching the film by running and moving the left and right clips so as to draw a symmetrical trajectory while changing the clip pitch of at least one of the clips, and heat setting the film;
In the diagonal stretching, one of the left and right clips is moved so that it precedes the other clip,
A method for producing a stretched film, wherein in the heat setting, a temperature gradient region is formed in which the temperature of the end of the film gripped by the preceding one clip is higher than the temperature of the other end of the film. The method for producing a stretched film according to claim 1, wherein the maximum temperature difference between both ends in the width direction in the temperature gradient region is 0.3°C to 25°C. The method for producing a stretched film according to claim 1 or 2, wherein the temperature gradient region is formed so that the isothermal line extends obliquely to the width direction of the film. The method for producing a stretched film according to any one of claims 1 to 3, wherein the temperature gradient region is formed by supplying hot air toward the film. The method for producing a stretched film according to claim 4, wherein the hot air has a wind speed of 3 m/min to 45 m/min. The diagonal stretching (i) increases the clip pitch of the _one clip from P1 to P2 while decreasing the clip pitch of the _other clip from P1 to _P3 , and ( _ii ) the 6. The method for producing a stretched film according to any one of claims 1 to 5, comprising changing the clip pitch of each clip so that the reduced clip pitch and the increased clip pitch have a predetermined equal pitch. . 7. The method for producing a stretched film according to claim 6, 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. Obtaining a long stretched film by the production method according to any one of claims 1 to 7, and transporting the long optical film and the long stretched film, and A method for producing an optical laminate, comprising aligning and continuously laminating. the optical film is a polarizing plate,
9. The method for producing an optical laminate according to claim 8, wherein the stretched film is a λ/4 plate or a λ/2 plate.

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