JP2023066617A - Method for manufacturing stretched film, and method for manufacturing optical laminate - Google Patents

Abstract

To provide a long-sized obliquely stretched film in which retardation unevenness (for example, retardation unevenness in oblique direction) is reduced.SOLUTION: A method for manufacturing a stretched film includes: manufacturing a long-sized resin film by an extrusion molding method; gripping each of right and left ends in a width direction of the resin film by right and left variable pitch type clips whose a clip pitch in a longitudinal direction changes, changing at least one clip pitch of the right and left clips, and obliquely stretching the resin film; and measuring a variation amount of film thickness in a longer direction of the resin film, wherein when the variation amount of the film thickness exceeds a first predetermined value, the variation amount of the film thickness in the longer direction of the resin film before the resin film is gripped by the right and left clips is reduced.SELECTED DRAWING: Figure 1

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, retardation unevenness (for example, retardation unevenness in an oblique direction) may occur in an obliquely stretched film obtained by such a technique.

Patent No. 4845619

A main object of the present invention is to provide a long obliquely stretched film in which retardation unevenness (for example, retardation unevenness in an oblique direction) is reduced.

When the present inventors examined the above problem, the film thickness unevenness in the longitudinal direction of the obliquely stretched film is related to the retardation unevenness, and when the film thickness unevenness is large, the visibility of the retardation unevenness is affected. It turns out that the impact is greater. Based on this knowledge, the present inventors believe that by increasing the uniformity of the film thickness in the longitudinal direction of the film before diagonal stretching, the film thickness unevenness in the longitudinal direction of the film after diagonal stretching can be reduced. With this idea, the present invention was completed.

That is, according to one aspect of the present invention, a long resin film is formed by an extrusion molding method, and left and right ends in the width direction of the resin film are respectively provided with a variable clip pitch in the vertical direction. Gripping by left and right pitch-type clips, changing the clip pitch of at least one of the left and right clips to stretch the resin film obliquely, and adjusting the amount of variation in film thickness in the longitudinal direction of the resin film. measuring, and reducing the amount of variation in film thickness in the longitudinal direction of the resin film before being gripped by the left and right clips when the amount of variation in film thickness exceeds a first predetermined value. , a method for producing a stretched film is provided.
In one embodiment, the amount of variation in film thickness of the resin film in the longitudinal direction before being gripped by the left and right clips is reduced by reducing the deposition speed of the resin film.
In one embodiment, the amount of change in the film thickness is the moving average of the film thickness in the longitudinal direction of the resin film, and the peak and bottom of the moving average line of the film thickness are detected. It is the difference from the bottom.
In one embodiment, the first predetermined value is 0.55 μm or less.
In one embodiment, the method further includes measuring a film thickness variation in the longitudinal direction of the resin film before gripping the resin film with the left and right clips.
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.

According to the stretched film manufacturing method according to the embodiment of the present invention, a long obliquely stretched film with reduced retardation unevenness can be provided.

It is the schematic explaining the manufacturing method of the stretched film by embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic plan view explaining the whole structure of an example of the film stretching apparatus used for diagonal stretching in embodiment 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. 2; 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. 2; 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. It is the schematic explaining the measuring method of a film thickness. 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.

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 distance between the centers of vertically adjacent clips in the traveling direction, and the vertical clip pitch is sometimes simply referred to as clip pitch. 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:
Forming a long resin film by an extrusion molding method (film forming process);
The left and right ends of the resin film in the width direction are respectively held by left and right variable-pitch clips whose clip pitch in the vertical direction changes, and the clip pitch of at least one of the left and right clips is changed to change the resin film. diagonally stretching (diagonally stretching step), and
measuring the amount of change in film thickness in the longitudinal direction of the resin film (first step of measuring the amount of change in film thickness),
When the film thickness variation exceeds a first predetermined value, the film thickness variation in the longitudinal direction of the resin film before being gripped by the left and right clips is reduced (first film thickness adjustment ).

In the method for producing a stretched film according to the embodiment of the present invention, the amount of change in the film thickness in the longitudinal direction of the resin film is measured before it is held by the left and right clips (second film thickness change amount measurement step ) can be further included. When the film thickness variation measured in the second film thickness variation measurement step exceeds a second predetermined value, before gripping by the left and right clips (typically, the second film thickness The effect of the present invention can be obtained more preferably by further reducing the amount of variation in the film thickness in the longitudinal direction of the resin film (second film thickness adjustment) before the step of measuring the amount of variation in thickness. .

FIG. 1 is a schematic diagram illustrating a method for producing a stretched film according to an embodiment of the invention. In the embodiment shown in FIG. 1, the resin film formed in the film forming step is subjected to the oblique stretching step without being wound on a roll, and a series of steps are continuously performed. Differently, the film-forming process and the oblique stretching process can be performed on separate lines. In this case, the resin film formed in the film forming step is wound on a roll, the resin film is unwound from the obtained roll, and subjected to a diagonal stretching step, a first film thickness variation measurement step, and an optional first A film thickness variation amount measurement step is performed, and the first film thickness adjustment and the optional second film thickness adjustment can be performed in the film forming step based on the measurement result. Each step will be specifically described below.

A-1. Film Forming Process In the film forming process, a long resin film is formed by an extrusion molding method. As the extrusion molding method, a T-die method is typically used. For example, as shown in FIG. 1, a molten thermoplastic resin sent from an extruder 1 using a gear pump 7 is extruded into a film shape from a T-die 2, and the extruded film-shaped molten resin 300a is The resin film 300b is obtained by bringing the resin film 300b into close contact with the cooling roll 4 by the nip roll 3 and cooling and solidifying it. The resin film 300b is transported to the stretching device 100 by roll transport using the transport rolls 5 as a raw film for diagonal stretching. In addition, embodiment of an extrusion molding method is not limited to the example of illustration. For example, a plurality of cooling rolls 4 that may have different temperatures may be provided, and instead of the nip rolls 3, air knives, air chambers, or the like may be used.

As the temperature of the resin (extrusion temperature) at the time of extrusion molding, a temperature at which the resin can be melted and suitable for molding can be appropriately set. The extrusion temperature may vary depending on the type of resin, but may be, for example, 200°C to 300°C, preferably 220°C to 280°C, more preferably 240°C to 260°C.

The temperature of the chill roll can be, for example, 150°C or less, preferably 40°C to 140°C, more preferably 50°C to 130°C. If the temperature of the cooling roll is too high, the resulting resin film may have a poor appearance.

The film forming speed (extrusion speed for extruding the film-shaped molten resin 300a from the T die 2) is, for example, 1 m/min to 30 m/min, preferably 3 m/min to 25 m/min, more preferably 5 m/min to 20 m/min. is. The film forming speed may be the same as or different from the transport speed of the resin film 300b. In one embodiment, the formed resin film 300b can be taken into an oblique stretching device at the same speed as the film forming speed.

The film thickness of the resin film 300b can be appropriately set according to the retardation value desired for the resin film (stretched film) 300c after stretching, the application, and the like. The film thickness of the resin film 300b can be, for example, 10 μm to 200 μm, preferably 30 μm to 180 μm, more preferably 50 μm to 150 μm. The film thickness of the resin film 300b can be controlled to a desired value by adjusting the gap between the ejection openings of the T-die.

The resin constituting the resin film 300b is not particularly limited, but a resin applicable as a retardation film can be preferably used. Examples of such resins include polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, acrylic resins, cellulose ester resins, cellulose resins, polyester resins, polyester carbonate resins, olefin resins, and polyurethane. system resin and the like. Preferred are polycarbonate-based resins, cellulose ester-based resins, polyester-based resins, polyester carbonate-based resins, and cycloolefin-based 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-based 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.

Any suitable additive may be blended into the resin film as necessary. Examples of additives include ultraviolet absorbers, antioxidants, stabilizers, lubricants, and the like. The amount of additives (the total amount when two or more additives are used) is generally 0.1 to 10 parts by weight, preferably 0.1 part by weight, per 100 parts by weight of the resin constituting the resin film. 1 to 5 parts by weight.

A-2. Diagonal stretching process In the diagonal stretching process, the left and right ends in the width direction of the long resin film obtained in the film forming process are respectively held by left and right variable-pitch clips whose clip pitch in the vertical direction changes, The resin film (hereinafter sometimes simply referred to as "film") is obliquely stretched by changing the clip pitch of at least one of the left and right clips.

In one embodiment, the diagonal stretching step is
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;
preheating the film;
diagonally stretching the film by moving the left and right clips while changing the clip pitch of at least one of the clips;
heat setting the film; and
releasing the film from the left and right clips.

FIG. 2 is a schematic plan view illustrating the overall configuration of an example of a stretching device that can be used for the diagonal stretching. 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. In the stretching apparatus, 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. 2 are different from the actual length ratios.

Although not shown in FIG. 2, between the stretching 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 in the drawings, the stretching apparatus typically includes a heating apparatus (for example, a hot air type , near-infrared, and far-infrared ovens). In one embodiment, preheating, diagonal stretching, heat setting and release from clips can each be performed in an oven set at a predetermined temperature.

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 clip rotates counterclockwise and the right clip rotates clockwise. By independently driving the left electric motor and the right electric motor, the left clip and the right clip 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.

3 and 4 are schematic plan views of essential parts for explaining the link mechanism for changing the clip pitch in the stretching device of FIG. Indicates the maximum pitch.

As shown in FIGS. 3 and 4, 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. 3 and 4, 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. 3, the link mechanism formed by 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. 3 and 4, 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. The diagonal stretching step will be described in detail below.

A-2-1. Gripping 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 typically hold the left and right edges of the film to be stretched at a constant clip pitch equal to each other. are grasped at the same time. At this time, the line connecting the centers of the left and right clips is substantially orthogonal to the film transport direction (for example, 90° ± 3°, preferably 90° ± 1°, more preferably 90° ± 0.5°, Still more preferably 90°). The clip pitch between the left and right clips when held is, for example, 100 mm to 200 mm, preferably 125 mm to 175 mm, and more preferably 140 mm to 160 mm.

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).

A-2-2. Preheating 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 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 preheating, 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-2-3. Diagonal Stretching In the stretching zone C, the left and right clips 20 are moved while changing the vertical clip pitch of at least one of the clips to diagonally stretch the film. More specifically, the left and right clips are moved while increasing or decreasing the clip pitch at different positions, or are moved while changing (increasing and/or decreasing) the clip pitch at different changing speeds. etc., to obliquely stretch the film. In this way, the left and right clips are moved while changing the clip pitch, and one of the pair of left and right clips grips the left and right ends of the film is moved ahead of the other clip to move in the stretching zone. . 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. 5A and 5B 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. 5A and 5B, the horizontal axis corresponds to the traveling 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.

In FIGS. 5A and 5B, both 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 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. 5A and 5B, 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. 5A. 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. 5A 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. 5B. 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. 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-2-4. Heat setting In the heat setting zone D, the obliquely stretched film is heat-treated. In the heat setting zone D, neither lateral stretching nor longitudinal stretching is normally performed, but if necessary, the clip pitch in the longitudinal direction may be reduced to relieve stress.

The heat treatment can typically be performed at temperature T3. The temperature T3 varies depending on the film to be stretched, and may be T2≧T3 or T2<T3. In general, if the film is an amorphous material, T2≧T3, and if the film is a crystalline material, the crystallization treatment may be performed by setting T2<T3. If T2≧T3, the difference between temperatures T2 and T3 (T2-T3) is preferably between 0.degree. C. and 50.degree. The heat treatment time is typically 10 seconds to 10 minutes. The heat treatment time can be controlled by adjusting the length of the heat setting zone and/or the transport speed of the film.

A-2-5. Releasing the Clip 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. 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 resin film released from the clip is sent out from the outlet of the stretching device, subjected to measurement of the variation in film thickness in the longitudinal direction, and then wound into a roll by a winder, or It can be used for lamination with other optical films without being wound up.

A-3. First Film Thickness Variation Measurement Step In the first film thickness variation measurement step, the thickness variation in the longitudinal direction of the resin film (stretched film) after being obliquely stretched is measured. The measurement of the film thickness variation is preferably performed continuously. With regard to the resin film after the oblique stretching, the amount of change in film thickness in the longitudinal direction is continuously measured (monitored), and when the measured amount of change exceeds a first predetermined value, preferably the amount of change is Each time the first predetermined value is exceeded, a first film thickness adjustment, which will be described later, is performed. Thereby, the amount of variation in the film thickness is reduced (for example, the amount of variation in the film thickness is reduced to a first predetermined value or less), and as a result, a stretched film with reduced retardation unevenness can be obtained. .

In the first film thickness variation measurement step, as illustrated in FIGS. Continuous film thickness measurement can be performed in-line using the film thickness meter 200 provided in the . In this way, by continuously measuring the film thickness at the predetermined position of the resin film 300c in the longitudinal direction, it is possible to measure the variation in the film thickness of the resin film in the longitudinal direction.

In the embodiment shown in FIG. 6, film thickness gauges 200 are provided above the width direction central portion and left and right end portions of the resin film 300c in the transport line, and the film thickness of the transported resin film is measured at three points in the width direction. Fixed point measurement. The measurement points may differ from the illustrated example. For example, the measurement of the film thickness may be performed at any one location, such as the center of the resin film in the width direction, the left edge (within 25 mm from the left edge), or the right edge (within 25 mm from the right edge), or It can also be done at two, three or more locations equally spaced in the width direction or randomly. When the film thickness is measured at two or more locations, the film thickness variation amount is measured independently at each measurement location, and can be used to determine the necessity of the first film thickness adjustment, which will be described later. Preferably, the film thickness is measured at the central portion in the width direction of the resin film.

The film thickness measurement may be performed continuously or at predetermined intervals. For example, film thickness measurements can be made at intervals of 0.1 mm to 10 mm, preferably 0.5 mm to 5 mm.

As the film thickness meter, a non-contact film thickness meter such as an infrared film thickness meter, a spectroscopic interference film thickness meter, or a laser displacement meter can be preferably used.

The measurement of the film thickness may be performed after cutting and removing the left and right ends in the width direction of the stretched film released from the clip. The width of the cut off edges may independently be, for example, 20 mm to 600 mm, preferably 100 mm to 500 mm. Cutting off the ends can be done by normal slitting.

In one embodiment, the amount of change in film thickness is the difference between the maximum film thickness and the minimum film thickness per unit length (for example, a predetermined length set in the range of 0.5 mm to 10 mm) in the longitudinal direction. can be

In another embodiment, the amount of change in film thickness is obtained by taking a moving average of the film thickness in the longitudinal direction of the resin film, and detecting the peak and bottom of the moving average line of the film thickness. can be the difference between According to this embodiment, minute variations in the film thickness are removed, making it easier to grasp large variations. A large change in film thickness leads to large retardation unevenness and can cause a decrease in visibility. Therefore, according to the present embodiment, a large change in film thickness can be accurately grasped, and the effect of the present invention is achieved. can be obtained more preferably.

The moving average process of the film thickness in the longitudinal direction is to repeat the operation of calculating the average (arithmetic average) of the film thickness measured in a predetermined section while shifting the predetermined section in the longitudinal direction by a predetermined distance. can be done by The predetermined interval may be, for example, an interval in which 10 or more pieces, preferably 30 to 100 pieces of film thickness data are acquired, for example, 1 mm to 1000 mm, preferably 3 mm to 500 mm, more preferably 5 mm to 50 mm (for example 10 mm). If the predetermined section is within the range, it is possible to suitably detect the amount of film thickness variation (retardation unevenness) that may affect the visibility. Specifically, if the predetermined interval is too short, the difference between the peak and the bottom may be calculated significantly, resulting in over-detection. In some cases, it becomes difficult to detect variations in film thickness. Also, the predetermined distance can be, for example, 0.1 mm to 10 mm, preferably 0.5 mm to 5 mm. The peak and bottom of the moving average line are detected as points where the slope of the moving average line switches from positive to negative and from negative to positive, respectively.

A-4. First Film Thickness Adjustment In the first film thickness adjustment, the fluctuation amount of the film thickness in the longitudinal direction of the resin film before being gripped by the left and right clips is reduced. The first film thickness adjustment is performed when the film thickness variation amount measured in the first film thickness variation measurement step exceeds a first predetermined value. If it is less than or equal to a predetermined value of 1, it need not be done (and consequently can be omitted). Therefore, in the method for producing a stretched film according to the embodiment of the present invention, whether or not to perform the first film thickness adjustment is determined based on the amount of change in film thickness measured in the step of measuring the amount of change in the first film thickness. determining.

The first predetermined value is, for example, 0.55 μm or less, preferably 0.50 μm or less, more preferably 0.45 μm or less. If the first predetermined value is within this range, retardation unevenness caused by thickness unevenness can be reduced, and as a result, deterioration of visibility can be prevented. Although the lower limit of the first predetermined value is not particularly limited, it may be 0.1 μm from the viewpoint of manufacturing efficiency.

Any appropriate method can be adopted as a method for reducing the amount of film thickness variation in the longitudinal direction of the resin film before being gripped by the left and right clips. For example, a method of reducing the film forming speed of a resin film during extrusion molding, a method described in JP-A-2013-137394 (rotating the gear pump at 5 rpm or more, setting the air gap to 200 mm or less, extruding As a machine, a twin-screw extruder or a single-screw extruder with a double-flight screw type is used). Among others, the method of reducing the film-forming speed of the resin film during extrusion molding is suitable for feedback control, which will be described later.

When the amount of variation in the film thickness is reduced by reducing the film forming speed, the film forming speed is, for example, reducing the temperature of the resin inside the T die and / or at the discharge port (increasing the viscosity of the resin), extruding It can be lowered by lowering the pressure, lowering the discharge rate of the extruder, or the like.

The reduction rate of the film forming speed can be appropriately set in consideration of the desired film thickness variation amount, production efficiency, and the like. The rate of decrease in film formation rate (film formation rate before decrease - film formation rate after decrease)/film formation rate before decrease x 100) is, for example, 1% to 50%, preferably 1% to 30%, more preferably can be from 1% to 10%. Also, the film forming speed after the decrease may be, for example, 1 m/min to 20 m/min.

The first film thickness adjustment may be feedback control based on the film thickness variation amount measured in the first film thickness variation measurement step. For example, in an embodiment in which the first film thickness adjustment is performed by reducing the film forming speed, an extruder 1 having a resin pressure control unit (not shown), a resin temperature control unit (not shown), a T die 2 , a nip roll 3, a chill roll 4 and a film forming speed controller 6 can be used. The film formation speed control unit 6 is connected to the data analysis unit of the film thickness meter 200 for calculating the film thickness variation from the film thickness data measured in the first film thickness variation measurement step. The resin temperature control unit is, for example, a heater, and is preferably provided inside the T-die and/or near the ejection port. The film forming speed control unit 6 sends a signal for decreasing the film forming speed to the resin pressure adjusting unit when the film thickness fluctuation amount continuously sent from the data analysis unit exceeds a first predetermined value. and/or output to the resin temperature control unit. Specifically, the resin temperature and/or the extrusion speed for obtaining the desired film forming speed or the reduction rate of the film forming speed is calculated, and a signal for approaching the resin temperature and/or the extrusion speed is sent to the resin temperature control unit. (heater) and/or pressure regulator. In this manner, by performing the first film thickness adjustment by feedback control based on the film thickness variation amount measured in the first film thickness variation measurement step, the film thickness uniformity in the longitudinal direction can be improved. As a result, a stretched film with reduced retardation unevenness can be obtained. As long as the effect of the present invention can be obtained, the desired film thickness variation can be obtained by the operator based on the film thickness variation measured in the first film thickness variation measurement step without providing the film forming speed control section. The resin temperature and/or the extrusion speed for obtaining the film forming speed may be calculated, and the setting of the resin pressure control section and/or the resin temperature control section may be changed.

A-5. Second Film Thickness Variation Measurement Step In the second film thickness variation measurement step, the film thickness variation in the longitudinal direction of the resin film before being gripped by the left and right clips is measured. The second step of measuring the amount of variation in film thickness can be performed at any timing after the resin film is formed by extrusion film formation (after cooling by cooling rolls) and before oblique stretching.

For the second film thickness variation amount measurement step, the same description as the first film thickness variation measurement step can be applied, except for the timing at which this step is performed.

A-6. Second Film Thickness Adjustment In the second film thickness adjustment, the variation in film thickness in the longitudinal direction of the resin film before being gripped by the left and right clips is further reduced. The second film thickness adjustment is performed when the film thickness variation amount measured in the second film thickness variation measurement step exceeds a second predetermined value, and the film thickness variation amount is equal to the second film thickness variation amount. If it is less than or equal to a predetermined value of 2, it need not be done (and consequently can be omitted). Therefore, in the stretched film manufacturing method according to the embodiment of the present invention, whether or not to perform the second film thickness adjustment is determined based on the film thickness variation amount measured in the second film thickness variation measurement step. determining.

The second predetermined value is, for example, 0.55 μm or less, preferably 0.50 μm or less, more preferably 0.45 μm or less. If the second predetermined value is within the above range, it is possible to more preferably reduce thickness unevenness in the longitudinal direction of the resin film (stretched film) after being obliquely stretched. Although the lower limit of the second predetermined value is not particularly limited, it may be 0.1 μm from the viewpoint of manufacturing efficiency.

A method similar to the first film thickness adjustment can be exemplified as a method for reducing the variation in the film thickness in the longitudinal direction of the resin film before being gripped by the left and right clips.

The second film thickness adjustment, like the first film thickness adjustment, can be feedback control based on the film thickness variation measured in the second film thickness variation measurement step. In this case, the film forming speed control unit 6 is also connected to the data analysis unit of the film thickness meter for calculating the film thickness variation from the film thickness data measured in the second film thickness variation measurement step. , a signal for reducing the film forming speed can be output to the resin pressure control section and/or the resin temperature control section when the amount of variation sent exceeds a second predetermined value.

B. Stretched Film The stretched film (retardation film) obtained by the method for producing a stretched film described in Section A 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).

The thickness of the stretched film can be appropriately set according to the desired retardation value, application, and the like. The thickness of the stretched film can be, for example, 10 μm to 200 μm, preferably 20 μm to 180 μm, more preferably 30 μm to 150 μm.

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 degrees.

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 In-line film thickness measurement was performed using a laser displacement meter. Other film thickness measurements were performed 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 550 nm.
(4) Glass transition temperature (Tg)
Measured according to JIS K 7121.

<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.

(Extrusion film formation)
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 1500 mm, set temperature: 250° C.), chill roll (set temperature: 120 to 130° C.) and a film forming apparatus equipped with a film forming speed control unit was used to prepare a resin film having a thickness of 135 μm at a film forming speed (extrusion speed) of 8 m/min.

(Production of stretched film)
The polyester carbonate resin film obtained as described above was conveyed to a film stretching apparatus as shown in FIGS.
Specifically, the right and left ends of the polyester carbonate resin film were gripped at the same timing and at the same clip pitch by the left and right clips at the entrance of the film of the stretching device. A line connecting the centers of the left and right clips when gripping the film was perpendicular to the film transport direction, and the clip pitch (P1) of the left and right clips was 125 mm.
The film was then transferred to preheat zone B and preheated to 145°C. In the preheating zone B, the inter-clip distance and clip pitch of the left and right clips were maintained during gripping.
Next, as soon as the film enters stretching zone C, it starts 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).
Then, in the heat setting zone D, the film was held at 125° C. for 60 seconds for heat setting. After cooling the heat-set film to 100° C. in the release zone E, the left and right clips were released.

(Step of measuring variation of first film thickness)
The film thickness at the center in the width direction of the film was measured inline at intervals of 100 μm while the stretched film released from the clip and sent out from the stretching device was transported by rolls. The process of calculating the average value of the film thickness in a section of 10 mm in the longitudinal direction is repeatedly performed while shifting the section by 1 mm to obtain the moving average of the film thickness, and the difference between the adjacent peaks and bottoms on the moving average line. It was obtained as the amount of film thickness variation in the longitudinal direction.

(First film thickness adjustment)
When the film thickness variation measured in the first film thickness variation measurement step exceeds 0.45 μm, the set temperature of the T-die is lowered to reduce the deposition rate by 5% compared to before. The first film thickness adjustment was continuously performed throughout the production of the elongated stretched film by setting the film forming speed control unit in advance so as to allow the film to be formed.

Table 1 shows the average thickness (average thickness in a section of 10 mm in the longitudinal direction) and the amount of change in film thickness measured in the first step of measuring the amount of change in film thickness after 1 hour from the start of diagonal stretching. . Moreover, Re (550) of the obtained stretched film was 140 nm, and the orientation angle was 45° with respect to the longitudinal direction. Regarding the resin film before being taken into the stretching apparatus, the amount of change in film thickness in the longitudinal direction was measured (second measurement step for the amount of change in film thickness), and the measured amount of change in film thickness was 0. 0.33 μm or less.

<Example 2>
Same as Example 1, except that a resin film (original film) having a thickness of 110 μm was formed by reducing the gap between the discharge ports of the T-die, and the diagonal stretching was performed at a stretching temperature of Tg + 1.5 ° C. A stretched film was obtained in the same manner. The obtained stretched film had an Re (550) of 140 nm and an orientation angle of 45° with respect to the longitudinal direction.

<Example 3>
Same as Example 1, except that the gap between the discharge ports of the T-die was reduced to form a resin film (original film) with a thickness of 70 μm, and that diagonal stretching was performed under the conditions of Tg + 0.8 ° C. to obtain a stretched film. The obtained stretched film had an Re (550) of 100 nm and an orientation angle of 45° with respect to the longitudinal direction.

<Comparative Example 1>
A stretched film was obtained in the same manner as in Example 1, except that the first film thickness adjustment was not performed. The obtained stretched film had an Re (550) of 140 nm and an orientation angle of 45° with respect to the longitudinal direction.

[Retardation unevenness visibility]
After laminating the stretched films obtained in Examples and Comparative Examples and a polarizing plate so that the angle formed by the slow axis and the absorption axis is 45°, the stretched film side is laminated to the reflecting plate so as to be in contact with the reflecting plate. Then, the visibility of unevenness when visually confirmed from the polarizing plate side was evaluated based on the following criteria. Table 1 shows the results.
◯: No unevenness is visually recognized when laminated on the reflector.
x: When laminated on the reflector, unevenness is visually recognized along the orientation angle.

[Appearance and handling evaluation]
The stretched films obtained in Examples and Comparative Examples were visually evaluated for appearance and handleability based on the following criteria. Table 1 shows the results.
◯: No wrinkles or slack was observed in the stretched film during roll transport.
x: Wrinkles and/or slack are observed in the stretched film during roll transport.

As shown in Table 1, in a long obliquely stretched film, when the amount of variation in film thickness in the longitudinal direction is large, the visibility decreases due to retardation unevenness, but the amount of variation in the film thickness is Visibility can be improved by reducing it to a predetermined value or less.

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). .

Reference Signs List 1 extruder 2 T-die 6 film forming speed controller 10L endless loop 10R endless loop 20 clip 100 stretching device 200 film thickness meter 300 resin film 500 circularly polarizing plate

Claims (7)

Forming a long resin film by an extrusion molding method;
The left and right ends of the resin film in the width direction are respectively held by left and right variable-pitch clips whose clip pitch in the vertical direction changes, and the clip pitch of at least one of the left and right clips is changed to change the resin film. diagonally stretching the
measuring the amount of change in film thickness in the longitudinal direction of the resin film,
A method for producing a stretched film, wherein when the amount of variation in film thickness exceeds a first predetermined value, the amount of variation in film thickness in the longitudinal direction of the resin film before being gripped by the left and right clips is reduced. 2. The method for producing a stretched film according to claim 1, wherein the film-forming speed of the resin film is reduced to reduce variation in film thickness in the longitudinal direction of the resin film before being gripped by the left and right clips. . The variation amount of the film thickness is the difference between adjacent peaks and bottoms when the moving average of the film thickness in the longitudinal direction of the resin film is taken and the peak and the bottom of the moving average line of the film thickness are detected. , The method for producing a stretched film according to claim 1 or 2. The method for producing a stretched film according to any one of claims 1 to 3, wherein the first predetermined value is 0.55 µm or less. The method for producing a stretched film according to any one of claims 1 to 4, further comprising measuring a film thickness variation in the longitudinal direction of the resin film before the left and right clips grip the resin film. Obtaining a long stretched film by the production method according to any one of claims 1 to 5, and
A method for producing an optical layered body, comprising continuously laminating a long optical film and a stretched long film while aligning their longitudinal directions while transporting the long optical film. the optical film is a polarizing plate,
7. The method for producing an optical laminate according to claim 6, wherein the stretched film is a λ/4 plate or a λ/2 plate.

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