JP7096943B1 - Method for manufacturing stretched film and method for manufacturing optical laminate - Google Patents

Abstract

A long obliquely stretched film with reduced retardation unevenness (for example, retardation unevenness in an oblique direction) is provided. 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 held by left and right variable-pitch clips that change the clip pitch in the vertical direction. and stretching the resin film obliquely by changing the clip pitch of at least one of the left and right clips; 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. [Selection drawing] Fig. 1

Description

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

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

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

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

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

Patent No. 4845619

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

When the present inventors examined the above problems, the film thickness unevenness in the elongated direction of the diagonally stretched film was related to the phase difference unevenness, and when the film thickness unevenness was large, the visibility of the phase difference unevenness was improved. It turns out that the impact will also be greater. Based on this finding, the present inventors have stated that by increasing the uniformity of the film thickness in the long direction of the film before diagonally stretching, it is possible to reduce the film thickness unevenness of the film after diagonally stretching in the long direction. Inspired by the above, 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 the left and right ends of the resin film in the width direction are variable in which the clip pitch in the vertical direction changes. The resin film is stretched diagonally by grasping it with pitch-type left and right clips and changing the clip pitch of at least one of the left and right clips, and the amount of variation in the film thickness of the resin film in the long direction. Including measuring, when the fluctuation amount of the film thickness exceeds the first predetermined value, the fluctuation amount of the film thickness in the long direction of the resin film before being gripped by the left and right clips is reduced. , A method for producing a stretched film is provided.
In one embodiment, by reducing the film forming speed of the resin film, the amount of variation in the film thickness of the resin film in the long direction before being gripped by the left and right clips is reduced.
In one embodiment, the fluctuation amount of the film thickness is the moving average of the film thickness in the long direction of the resin film, and the peak and the adjacent peak when the bottom is detected on the moving average line of the film thickness. It is the difference from the bottom.
In one embodiment, the first predetermined value is 0.55 μm or less.
In one embodiment, it further comprises measuring the amount of variation in the film thickness of the resin film in the longitudinal direction before gripping with the left and right clips.
According to another aspect of the present invention, the elongated stretched film is obtained by the above-mentioned manufacturing method, and the elongated optical film and the elongated stretched film are conveyed in the elongated direction thereof. A method for manufacturing an optical laminate is provided, which comprises aligning and continuously laminating the two.
In one embodiment, the optical film is a polarizing plate and the stretched film is a λ / 4 plate or a λ / 2 plate.

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

It is a schematic diagram explaining the manufacturing method of the stretch film by embodiment of this invention. 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. It is a schematic diagram which shows the profile of the clip pitch in one embodiment of diagonal stretching. It is a schematic diagram which shows the profile of the clip pitch in one embodiment of diagonal stretching. It is a schematic diagram explaining the method of measuring a film thickness. It is the schematic sectional drawing of the circular polarizing plate using the retardation film obtained by the manufacturing method of this invention.

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

A. Method for Producing Stretched Film The method for producing a stretched film according to the embodiment of the present invention is as follows.
Forming a long resin film by extrusion molding (film forming process),
The left and right ends of the resin film in the width direction are gripped by left and right clips of a variable pitch type in which the clip pitch in the vertical direction changes, and at least one of the left and right clips is changed by changing the clip pitch of the resin film. (Diagonal stretching step), and
Including measuring the fluctuation amount of the film thickness in the long direction of the resin film (the first step of measuring the fluctuation amount of the film thickness).
When the fluctuation amount of the film thickness exceeds the first predetermined value, the fluctuation amount of the film thickness in the long 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 fluctuation in the film thickness in the long direction of the resin film is measured before being gripped by the left and right clips (second step of measuring the amount of variation in the film thickness). ) Can be further included. When the fluctuation amount of the film thickness measured in the measurement step of the fluctuation amount of the second film thickness exceeds the second predetermined value, before gripping with the left and right clips (typically, the second film). The effect of the present invention can be more preferably obtained by further reducing the amount of variation in the film thickness of the resin film in the long direction (before the step of measuring the amount of variation in thickness) (second film thickness adjustment). ..

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

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, the T-die method is typically used. For example, as shown in FIG. 1, the molten thermoplastic resin sent from the extruder 1 using the gear pump 7 is extruded from the T die 2 into a film shape, and the extruded film-like molten resin 300a is produced. The resin film 300b is obtained by bringing the nip roll 3 into close contact with the cooling roll 4 for cooling and solidification. The resin film 300b is conveyed to the stretching apparatus 100 by roll transport using the transport roll 5 as a raw film for diagonal stretching. The embodiment of the extrusion molding method is not limited to the illustrated example. For example, a plurality of cooling rolls 4 whose temperatures may be different from each other may be provided, and an air knife, an air chamber, or the like may be used instead of the nip roll 3.

The temperature of the resin (extrusion temperature) at the time of extrusion molding is a temperature at which the resin can be melted, and a temperature 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, and more preferably 240 ° C to 260 ° C.

The temperature of the cooling roll may be, for example, 150 ° C. or lower, 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, and 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 film-formed resin film 300b can be incorporated into the oblique stretching device at a film-forming speed and a constant velocity.

The film thickness of the resin film 300b can be appropriately set according to the retardation value, application, etc. desired for the stretched resin film (stretched film) 300c. The film thickness of the resin film 300b can be, for example, 10 μm to 200 μm, preferably 30 μm to 180 μm, and 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 ports 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 polyurethanes. Examples include based resins. Preferably, it is a polycarbonate-based resin, a cellulose ester-based resin, a polyester-based resin, a polyester carbonate-based resin, or a cycloolefin-based resin. This is because with these resins, a retardation film showing so-called reverse dispersion wavelength dependence can be obtained. These resins may be used alone or in combination according to desired characteristics.

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

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

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

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

If necessary, any suitable additive may be added to the resin film. Examples of the additive include an ultraviolet absorber, an antioxidant, a stabilizer, a lubricant and the like. The blending amount of the additive (the total blending amount when two or more kinds of additives are used) is usually 0.1 part by weight to 10 parts by weight, preferably 0, with respect to 100 parts by weight of the resin constituting the resin film. It is 1 part by weight to 5 parts by weight.

A-2. Diagonal stretching step In the diagonal stretching step, the left and right ends of the long resin film obtained in the film forming step in the width direction are gripped by the left and right clips of the variable pitch type in which the clip pitch in the vertical direction changes. The resin film (hereinafter, may be 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 the left and right edges of the long film in the width direction with variable-pitch type left and right clips that change the clip pitch in the vertical direction, respectively.
Preheating the film,
To stretch the film diagonally by moving the left and right clips while changing the clip pitch of at least one of the clips.
Thermally fixing the film and
Includes releasing the film from the left and right clips.

FIG. 2 is a schematic plan view illustrating an overall configuration of an example of a stretching device that can be used for the diagonal stretching. The stretching device 100 has an endless loop 10L and an endless loop 10R having a large number of clips 20 for gripping the film on both the left and right sides symmetrically in a plan view. In the present specification, the endless loop on the left side when viewed from the inlet side of the film is referred to as the endless loop 10L on the left side, and the endless loop on the right side is referred to as the endless loop 10R on the right side. The clips 20 of the left and right endless loops 10L and 10R are guided by the reference rail 70 and circulate in a loop shape, respectively. The clip 20 of the endless loop 10L on the left side circulates in the counterclockwise direction, and the clip 20 of the endless loop 10R on the right side circulates in the clockwise direction. In the stretching device, a gripping zone A, a preheating zone B, a stretching zone C, a heat fixing zone D, and an open zone E are provided in this order from the inlet side to the outlet side of the film. Each of these zones means a zone in which the film to be stretched is substantially gripped, preheated, diagonally stretched, heat-fixed and opened, and does not mean a mechanically or structurally independent section. Also note that the length ratio of each zone in the stretching device of FIG. 2 is different from the actual length ratio.

Although not shown in FIG. 2, a zone for performing arbitrary appropriate treatment may be provided between the stretching zone C and the heat fixing zone D, if necessary. Examples of such treatment include lateral shrinkage treatment and the like. Similarly, although not shown, the stretching device is typically a heating device (for example, a hot air type) for setting each zone from the preheating zone B to the heat fixing zone D or the open zone E as a heating environment. , Various ovens such as near-infrared type and far-infrared type). In one embodiment, preheating, diagonal stretching, heat immobilization and release from clips can each be performed in an oven set to a predetermined temperature.

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

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

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

3 and 4 are schematic plan views of a main part for explaining a link mechanism for changing the clip pitch in the stretching device of FIG. 2, FIG. 3 shows a state where the clip pitch is the minimum, and FIG. 4 shows a clip. Indicates the maximum pitch.

As shown in FIGS. 3 and 4, a clip supporting member 30 having an elongated rectangular shape in the horizontal direction in a plan view is provided to individually support the clips 20. Although not shown, the clip-supporting member 30 is formed into a strong frame structure having a closed cross section by an upper beam, a lower beam, a front wall (a wall on the clip side), and a rear wall (a wall on the opposite side of the clip). The clip-supporting member 30 is provided so as to roll on the traveling road surfaces 81 and 82 by the traveling wheels 38 at both ends thereof. In addition, in FIGS. 3 and 4, the traveling wheel on the front wall side (the traveling wheel rolling on the traveling road surface 81) is not shown. The traveling road surfaces 81 and 82 are parallel to the reference rail 70 over the entire area. A long hole 31 is formed along the longitudinal direction of the clip-supporting member on the rear side of the upper beam and the lower beam of the clip-supporting member 30 (the opposite side of the clip side (hereinafter referred to as the anti-clip side)), and the slider 32 is long. It is slidably engaged in the longitudinal direction of the hole 31. In the vicinity of the clip 20 side end of the clip supporting member 30, one first shaft member 33 is vertically provided so as to penetrate the upper beam and the lower beam. On the other hand, the slider 32 of the clip-supporting member 30 is provided with a second shaft member 34 vertically penetrating. One end of the main link member 35 is pivotally connected to the first shaft member 33 of each clip-supporting member 30. The other end of the main link member 35 is pivotally connected to the second shaft member 34 of the adjacent clip-supporting member 30. In addition to the main link member 35, one end of the sub-link member 36 is pivotally connected to the first shaft member 33 of each clip-supporting member 30. The other end of the sub-link member 36 is pivotally connected to the intermediate portion of the main link member 35 by a pivot 37. As shown in FIG. 3, as the slider 32 moves to the rear side (anti-clip side) of the clip-supporting member 30 due to the link mechanism by the main link member 35 and the sub-link member 36, the clip-supporting members 30 are vertically aligned with each other. The pitch in the direction (as a result, the clip pitch) becomes smaller, and as shown in FIG. 4, the more the slider 32 moves to the front side (clip side) of the clip supporting member 30, the more the clip supporting members 30 are in the vertical direction. The pitch (as a result, the clip pitch) increases. Positioning of the slider 32 is performed by the pitch setting rail 90. As shown in FIGS. 3 and 4, the smaller the separation distance between the reference rail 70 and the pitch setting rail 90, the larger the clip pitch.

By diagonally stretching the film using the stretching device as described above, a diagonally stretched film, for example, a retardation film having a slow phase axis in the diagonal direction can be produced. A specific embodiment of the stretching device as described above is described in, for example, Japanese Patent Application Laid-Open No. 2008-44339, and the whole thereof is incorporated herein by reference. Hereinafter, the diagonal stretching step will be described in detail.

A-2-1. In the gripping zone A (the entrance of the film take-in of the stretching device 100), typically, the left and right endless loops 10L and 10R clips 20 have a constant clip pitch at which the left and right ends of the film to be stretched are equal to each other. Is gripped 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 °,). Even more preferably, it is 90 °). The clip pitch of the left and right clips at the time of gripping 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 fed to the preheating zone B by the movement of the clips 20 of the left and right endless loops 10L and 10R (substantially, the movement of each clip-carrying member guided by the reference rail).

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

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

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

A-2-3. Diagonal stretching In the stretching zone C, the left and right clips 20 are run and moved while changing the clip pitch in the vertical direction of at least one of the clips, and the film is stretched diagonally. More specifically, the left and right clips are moved by running and moving at different positions while increasing or decreasing the clip pitch, and by changing (increasing and / or decreasing) the clip pitch at different speeds. The film is stretched diagonally by such means. Of the pair of left and right clips that grip the left and right edges of the film by moving the left and right clips while changing the clip pitch in this way, one clip is preceded by the other clip to move the stretch zone. .. Such diagonal stretching results in the film being stretched diagonally between the preceding clip and the trailing clip, resulting in a desired orientation (eg, longitudinal) of the elongated film. The slow axis can be expressed in the direction of 45 ° with respect to the film.

Diagonal stretching may include transverse stretching. In this case, the diagonal stretching can be performed while increasing the distance between the left and right clips (distance in the width direction), for example, as shown in the illustrated example. Alternatively, unlike the illustrated example, diagonal stretching does not include lateral stretching and can be performed while maintaining the distance between the left and right clips.

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

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

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

In yet another embodiment, oblique stretching (i) increases the clip pitch of one of the left and right clips from P ₁ to P ₂ , while increasing the clip pitch of the other clip from P ₁ to P ₃ . It can be done by reducing to, and (ii) changing the clip pitch of each clip so that the reduced clip pitch and the increased clip pitch are at predetermined equal pitches. For the diagonal stretching of the embodiment, for example, the description in JP-A-2014-194484 can be referred to. Diagonal stretching of the embodiment increases the clip pitch of one clip from P ₁ to P ₂ while increasing the distance between the left and right clips, while reducing the clip pitch of the other clip from P ₁ to P ₃ . Then, while stretching the film diagonally (first diagonal stretching) and increasing the distance between the left and right clips, the clip pitch of one of the clips is set to P so that the clip pitches of the left and right clips are equal. It may include diagonally stretching the film _{( second} diagonal stretching) by maintaining at ₂ or reducing to P4 and increasing the clip pitch of the other clip to P2 or _P4 .

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

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

5A and 5B are schematic views showing an example of the clip pitch profile in the diagonal stretching including the first diagonal stretching and the second diagonal stretching, respectively. Hereinafter, the first diagonal stretching will be specifically described with reference to these figures. In FIGS. 5A and 5B, the horizontal axis corresponds to the mileage of the clip. At the start of the _first diagonal stretching, the left and right clip pitches are both P1. P ₁ is typically a clip pitch when the film is gripped. At the same time as the first diagonal stretching is started, the clip pitch of one clip (hereinafter, may be referred to as the first clip) is started to be increased, and the other clip (hereinafter, the second clip) is started. (Sometimes referred to as) begins to reduce the clip pitch. In the first 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 beginning of the second diagonal stretching), the _second clip moves at the clip pitch P3 and the _first clip moves at the clip pitch P2. ing. The clip pitch ratio can roughly correspond to the clip moving speed ratio.

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

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

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

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

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

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

Next, one embodiment of the second diagonal stretching will be specifically described with reference to FIG. 5A. In the _second diagonal stretching of the present embodiment, the clip pitch of the _second clip is increased from P3 to P2. On the other hand, the clip pitch of the first clip is maintained at P2 during the _second diagonal stretching. Therefore, at the end of the _second diagonal stretching, both the left and right clips are supposed to move at the clip pitch P2.

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

Another embodiment of the second diagonal stretching will be specifically described with reference to FIG. 5B. In the second diagonal stretching of the present embodiment, the clip pitch of the first clip is decreased and the clip pitch of the second clip is increased. Specifically, the clip pitch of the first clip is decreased from P ₂ to P ₄ , and the clip pitch of the second clip is increased from P ₃ to P ₄ . Therefore, at the end of the second diagonal stretching, both the left and right clips are supposed to move at the clip pitch _P4 . In the illustrated example, the clip pitch of the first clip is decreased and the clip pitch of the second clip is increased at the same time as the start of the second diagonal stretching, but these can be started at different timings. .. Similarly, the decrease in the clip pitch of the first clip and the increase in the clip pitch of the second clip may end at different timings.

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

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

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

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

A-2-4. Heat-fixing In the heat-fixing zone D, the diagonally stretched film is heat-treated. In the heat-fixing 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 depends on the film to be stretched, and may be T2 ≧ T3 or T2 <T3. Generally, when the film is an amorphous material, T2 ≧ T3, and when the film is a crystalline material, the crystallization treatment may be performed by setting T2 <T3. When T2 ≧ T3, the difference between the temperatures T2 and T3 (T2-T3) is preferably 0 ° C to 50 ° C. The heat treatment time is typically 10 seconds to 10 minutes. The heat treatment time can be controlled by adjusting the length of the heat setting zone and / or the transfer rate of the film.

A-2-5. Clip Opening The film is released from the clip at any position in the open zone E. In the open zone E, the film is usually cooled to a desired temperature without performing lateral stretching or longitudinal stretching on the heat-fixed film, and then the film is released from the clip. The film temperature when released from the clip is, for example, 150 ° C. or lower, preferably 70 ° C. to 140 ° C., and more preferably 80 ° C. to 130 ° C.

The resin film released from the clip is sent out from the outlet of the stretching device, is used for measuring the fluctuation amount of the film thickness in the long direction, and then is rolled into a roll shape by a winder or a roll shape. It can be used for laminating with other optical films without being wound around.

A-3. First step of measuring the amount of variation in the film thickness In the first step of measuring the amount of variation in the film thickness, the amount of variation in the film thickness of the resin film (stretched film) after diagonal stretching is measured in the long direction. The measurement of the fluctuation amount of the film thickness is preferably performed continuously. With respect to the resin film after diagonally stretched, the fluctuation amount of the film thickness in the long direction is continuously measured (monitored), and when the measured fluctuation amount exceeds the first predetermined value, the fluctuation amount is preferable. Every time the first predetermined value is exceeded, the first film thickness adjustment described later is performed. As a result, the fluctuation amount of the film thickness is reduced (for example, the fluctuation amount of the film thickness is reduced to the first predetermined value or less), and as a result, a stretched film in which the retardation unevenness is also reduced can be obtained. ..

In the first step of measuring the fluctuation amount of the film thickness, as illustrated in FIGS. 1 and 6, the resin film 300c delivered from the outlet of the stretching device 100 is rolled and conveyed to a predetermined position on the transfer line. The film thickness meter 200 provided in the above can be used to continuously measure the film thickness in-line. In this way, by continuously measuring the film thickness of the resin film 300c at the predetermined position in the long direction, the amount of variation in the film thickness of the resin film in the long direction can be measured.

In the embodiment shown in FIG. 6, in the transport line, a film thickness meter 200 is provided above the center portion in the width direction and the left and right ends of the resin film 300c, and the film thickness of the conveyed resin film is measured at three locations in the width direction. Fixed point measurement. The measurement point may be different from the illustrated example. For example, the film thickness may be measured at any one place such as the center portion in the width direction of the resin film, the left end portion (within 25 mm from the left end side), the right end portion (within 25 mm from the right end side), or the like. It can also be done at two, three or more locations at regular intervals or at random in the width direction. When the film thickness is measured at two or more points, the fluctuation amount of the film thickness is independently measured at each measurement point and can be used for determining the necessity of the first film thickness adjustment described later. Preferably, the film thickness is measured at the center of the resin film in the width direction.

The film thickness may be measured continuously or at predetermined intervals. For example, the film thickness can be measured 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 type film thickness meter, or a laser displacement meter can be preferably used.

The film thickness may be measured after cutting and removing the left and right edges of the stretched film released from the clip in the width direction. The widths of the edges to be cut and removed can be independently, for example, 20 mm to 600 mm, preferably 100 mm to 500 mm. Cutting and removal of the end portion can be performed by ordinary slit processing.

In one embodiment, the amount of variation 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 long direction. Can be.

In another embodiment, the amount of fluctuation in the film thickness is the moving average of the film thickness in the long direction of the resin film, and the adjacent peaks and bottoms when the peak and the bottom in the moving average line of the film thickness are detected. Can be the difference between. According to this embodiment, minute fluctuations in the film thickness are removed, and it becomes easy to grasp a large change. Since a large change in the film thickness can lead to a large phase difference unevenness and cause a decrease in visibility, according to the present embodiment, a large change in the film thickness can be accurately grasped, and the effect of the present invention can be obtained. Can be obtained more preferably.

In the moving average processing of the film thickness in the long direction, the operation of calculating the average of the film thickness (arithmetic mean) measured in the predetermined section is repeated while shifting the predetermined section by a predetermined distance in the long direction. Can be done by. The predetermined section may be, for example, a section in which 10 or more, preferably 30 to 100 film thickness data are acquired, for example, 1 mm to 1000 mm, preferably 3 mm to 500 mm, and more preferably 5 mm to 50 mm (for example). It can be in the range of 10 mm). When the predetermined section is within the range, the amount of fluctuation in the film thickness (phase difference unevenness) that may affect the visibility can be suitably detected. Specifically, if the predetermined section is too short, the difference between the peak and the bottom may be remarkably calculated and excessive detection may occur, and if the predetermined section is too long, the peak and the bottom may be smoothed. This may make it difficult to detect fluctuations in film thickness. Further, the predetermined distance may be, for example, 0.1 mm to 10 mm, preferably 0.5 mm to 5 mm. The peaks and bottoms of the moving average are detected as points where the slope of the moving average switches from positive to negative and points where the slope of the moving average switches from negative to positive, respectively.

A-4. First film thickness adjustment In the first film thickness adjustment, the amount of variation in the film thickness in the long 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 fluctuation amount of the film thickness measured in the measurement step of the fluctuation amount of the first film thickness exceeds the first predetermined value, and the fluctuation amount of the film thickness is the first. It does not need to be done if it is less than or equal to the predetermined value of 1 (as a result, it may 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 based on the amount of fluctuation in the film thickness measured in the first step of measuring the amount of variation in the film thickness is determined. It may include a step to determine.

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

Any appropriate method can be adopted as a method for reducing the fluctuation amount of the film thickness in the long direction 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 Japanese Patent Application Laid-Open No. 2013-137394 (rotating a gear pump at 5 rpm or more, setting an air gap to 200 mm or less, extrusion). Examples of the machine include a twin-screw extruder or a single-screw extruder having a double-flight screw type). In particular, a method of reducing the film forming speed of the resin film during extrusion molding is suitable for feedback control described later.

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

The rate of decrease in the film-forming rate can be appropriately set in consideration of the desired amount of variation in film thickness, 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 × 100) is, for example, 1% to 50%, preferably 1% to 30%, more preferably. Can be 1% to 10%. The film forming speed after the reduction can be, for example, 1 m / min to 20 m / min.

The first film thickness adjustment may be feedback control based on the amount of fluctuation in the film thickness measured in the step of measuring the amount of fluctuation in the first film thickness. For example, in the embodiment in which the first film thickness adjustment is performed by reducing the film forming speed, an extruder 1 having a resin pressure adjusting unit (not shown), a resin temperature control unit (not shown), and a T-die 2 are used. , An extruded film forming apparatus including a nip roll 3, a cooling roll 4 and a film forming speed control unit 6. The film-forming speed control unit 6 is connected to a data analysis unit of the film thickness meter 200 that calculates the amount of change in film thickness from the film thickness data measured in the first step of measuring the amount of fluctuation in film thickness. The resin temperature control unit is, for example, a heater, and may be preferably provided inside the T-die and / or near the discharge port. The film-forming speed control unit 6 sends a signal for reducing the film-forming speed to a resin pressure adjusting unit when the amount of fluctuation in the film thickness continuously sent from the data analysis unit exceeds the first predetermined value. And / or output to the resin temperature control unit. Specifically, the resin temperature and / or the extrusion rate for obtaining the desired film formation rate or the rate of decrease in the film formation rate is calculated, and a signal for approaching the resin temperature and / or the extrusion rate is sent to the resin temperature control unit. Output to (heater) and / or pressure regulator. In this way, by adjusting the first film thickness by feedback control based on the fluctuation amount of the film thickness measured in the measurement step of the fluctuation amount of the first film thickness, the uniformity of the film thickness in the long direction can be obtained. Excellent, and 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, it is desired by the operator based on the amount of fluctuation in the film thickness measured in the first step of measuring the amount of variation in the film thickness without providing the film forming speed control unit. The resin temperature and / or the extrusion speed for obtaining the film forming speed may be calculated, and the settings of the resin pressure adjusting unit and / or the resin temperature controlling unit may be changed.

A-5. Second step of measuring the amount of variation in the film thickness In the second step of measuring the amount of variation in the film thickness, the amount of variation in the film thickness in the long direction of the resin film before being gripped by the left and right clips is measured. The second step of measuring the fluctuation amount of the film thickness can be performed at an arbitrary timing after the resin film is formed by the extrusion film formation (after cooling by the cooling roll) and before the oblique stretching.

The same description as in the first film thickness variation measurement step can be applied to the second film thickness variation measurement step, except for the timing at which the process is performed.

A-6. Second film thickness adjustment In the second film thickness adjustment, the fluctuation amount of the film thickness in the long 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 fluctuation amount of the film thickness measured in the measurement step of the fluctuation amount of the second film thickness exceeds the second predetermined value, and the fluctuation amount of the film thickness is the second. It does not need to be done if it is less than or equal to the predetermined value of 2 (as a result, it 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 second film thickness adjustment based on the amount of fluctuation in the film thickness measured in the second step of measuring the amount of variation in the film thickness is determined. It may include a step to determine.

The second predetermined value is, for example, 0.55 μm or less, preferably 0.50 μm or less, and more preferably 0.45 μm or less. When the second predetermined value is within the above range, the thickness unevenness of the resin film (stretched film) after diagonal stretching in the long direction can be more preferably reduced. The lower limit of the second predetermined value is not particularly limited, but may be 0.1 μm from the viewpoint of manufacturing efficiency.

As a method for reducing the fluctuation amount of the film thickness in the long direction before being gripped by the left and right clips, the same method as the first film thickness adjustment can be exemplified.

The second film thickness adjustment may be feedback control based on the fluctuation amount of the film thickness measured in the measurement step of the fluctuation amount of the second film thickness, similarly to the first film thickness adjustment. In this case, the film thickness control unit 6 is also connected to the data analysis unit of the film thickness meter that calculates the fluctuation amount of the film thickness from the film thickness data measured in the second measurement step of the fluctuation amount of the film thickness. , When the amount of fluctuation sent exceeds a second predetermined value, a signal for reducing the film thickness forming speed may be output to the resin pressure adjusting unit and / or the resin temperature controlling unit.

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

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

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

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

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

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

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, and more preferably 30 μm to 150 μm.

C. Optical laminate and method for manufacturing the optical laminate The stretched film obtained by the production method of the present invention can be bonded to another optical film and used as an optical laminate. For example, the retardation film obtained by the production method of the present invention can be suitably used as a circular polarizing plate by being bonded to a polarizing plate.

FIG. 7 is a schematic cross-sectional view of an example of such a circular polarizing plate. The circular polarizing plate 500 of the illustrated example includes a polarizing element 510, a first protective film 520 arranged on one side of the polarizing element 510, a second protective film 530 arranged on the other side of the polarizing element 510, and a second protective film. It has a retardation film 540 arranged on the outside of the protective film 530 of 2. The retardation film 540 is a stretched film (for example, a λ / 4 plate) obtained by the production method according to Item A. The second protective film 530 may be omitted. In that case, the retardation film 540 can function as a protective film for the stator. The angle formed by the absorption axis of the splitter 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 °, and particularly preferably. It is about 45 °.

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

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

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

(1) Thickness The in-line film thickness measurement was performed using a laser displacement sensor. Other film thickness measurements were performed using a dial gauge (manufactured by PEACOCK, product name "DG-205 type pds-2").
(2) Phase difference value The in-plane phase difference Re (550) was measured using Axoscan manufactured by Axometrics.
(3) Orientation angle (direction of expression of slow axis)
A sample was prepared by cutting out the central portion of the film to be measured into a square shape having a width of 50 mm and a length of 50 mm so that one side was parallel to the width direction of the film. This sample was measured using Axoscan manufactured by Axometrics, and the orientation angle θ at a wavelength of 550 nm was measured.
(4) Glass transition temperature (Tg)
It was 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 a stirring blade and a reflux condenser controlled at 100 ° C. Bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl] methane 29.60 parts by mass (0.046 mol), ISB 29.21 parts by mass (0.200 mol), SPG 42.28 parts by mass (0. 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 were charged as a catalyst. After substituting nitrogen under reduced pressure in the reactor, heating was performed with a heat medium, and stirring was started when the internal temperature reached 100 ° C. The internal temperature was brought to 220 ° C. 40 minutes after the start of the temperature rise, and the depressurization was started at the same time as controlling to maintain this temperature, and the temperature was 13.3 kPa 90 minutes after reaching 220 ° C. The phenol vapor produced by the polymerization reaction was guided to a reflux condenser at 100 ° C., the monomer component contained in a small amount in the phenol vapor was returned to the reactor, and the non-condensed phenol vapor was guided to a condenser at 45 ° C. for recovery. Nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, and then the oligomerized reaction solution in the first reactor was transferred to the second reactor. Then, the temperature rise and depressurization in the second reactor were started, and the internal temperature was 240 ° C. and the pressure was 0.2 kPa in 50 minutes. Then, the polymerization was allowed to proceed until the stirring power became a predetermined value. When the predetermined power was reached, nitrogen was introduced into the reactor to repressurize, the produced polyester carbonate was extruded into water, and the strands were cut to obtain pellets. The Tg of the obtained polyester carbonate resin was 140 ° C.

(Extruded film formation)
After vacuum-drying the obtained polyester carbonate resin at 80 ° C. for 5 hours, a single-screw extruder (manufactured by Toshiba Machinery Co., Ltd., cylinder set temperature: 250 ° C.), T-die (width 1500 mm, set temperature: 250 ° C.), chill roll A resin film having a thickness of 135 μm was produced at a film forming rate (extrusion rate) of 8 m / min using a film forming apparatus equipped with a film forming rate control unit (set temperature: 120 to 130 ° C.).

(Preparation of stretched film)
The polyester carbonate resin film obtained as described above was conveyed to a film stretching apparatus as shown in FIGS. 2 to 4 without being wound up, and diagonally stretched.
Specifically, at the entrance of the film of the stretching device, the left and right ends of the polyester carbonate resin film were gripped by the left and right clips at the same timing and at the same clip pitch. The line connecting the centers of the left and right clips when the film was gripped was orthogonal 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 preheating zone B and preheated to 145 ° C. In the preheating zone B, the distance between the clips of the left and right clips and the clip pitch at the time of gripping were maintained.
Next, as soon as the film enters the stretch 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 increasing the clip pitch of the left clip. It was reduced to P3 ₍ first diagonal 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 of the left clip (P ₃ / P ₁ ) is 0.78, and the original width of the film is 0.78. The lateral stretching ratio was 1.45 times. Then, while maintaining the clip pitch of the right clip at P ₂ , the clip pitch of the left clip was started to be increased and increased from P ₃ to P ₂ (second diagonal extension). During this period, the rate of change in the clip pitch (P ₂ / P ₃ ) of the left clip was 1.82, and the lateral stretching ratio with respect to the original width of the film was 1.9 times. The stretching zone C was set to Tg + 3.2 ° C. (143.2 ° C.).
Next, in the heat fixing zone D, the film was held at 125 ° C. for 60 seconds for heat fixing. The heat-fixed film was cooled to 100 ° C. in the open zone E, and then the left and right clips were opened.

(Measuring process of fluctuation amount of first film thickness)
The film thickness at the center in the width direction of the film was measured in-line at 100 μm intervals while the stretched film released from the clip and sent out from the stretching device was rolled and conveyed. The process of calculating the average value of the film thickness in a section of 10 mm in the long direction is repeated while shifting the section by 1 mm to obtain a moving average of the film thickness, and the difference between the adjacent peak and bottom on the moving average line is calculated. It was calculated as the amount of variation in film thickness in the long direction.

(First film thickness adjustment)
When the fluctuation amount of the film thickness measured in the first film thickness fluctuation measurement step exceeds 0.45 μm, the set temperature of the T-die is lowered and the film forming speed is lowered by 5% from before. By setting the film forming speed control unit in advance, the first film thickness adjustment was continuously performed during the production of the elongated stretched film.

Table 1 shows the average thickness (average thickness in the section of 10 mm in the long direction) and the amount of change in film thickness measured in the first step of measuring the amount of change in film thickness one hour after the start of diagonal stretching. .. The Re (550) of the obtained stretched film was 140 nm, and the orientation angle was 45 ° with respect to the elongated direction. As for the resin film before being incorporated into the stretching apparatus, the amount of fluctuation in the film thickness in the long direction was measured (the second step of measuring the amount of variation in the film thickness), and the measured amount of the variation in the film thickness was 0. It was .33 μm or less.

<Example 2>
Example 1 except that a resin film (raw film) having a thickness of 110 μm was formed by reducing the gap between the discharge ports of the T-die and that the film was diagonally stretched at a stretching temperature of Tg + 1.5 ° C. A stretched film was obtained in the same manner. The Re (550) of the obtained stretched film was 140 nm, and the orientation angle was 45 ° with respect to the elongated 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 (raw film) with a thickness of 70 μm, and diagonal stretching was performed under the condition of Tg + 0.8 ° C. A stretched film was obtained. The Re (550) of the obtained stretched film was 100 nm, and the orientation angle was 45 ° with respect to the elongated 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 Re (550) of the obtained stretched film was 140 nm, and the orientation angle was 45 ° with respect to the elongated direction.

[Phase difference uneven visibility]
After laminating the stretched film and the polarizing plate obtained in Examples and Comparative Examples so that the angle between the slow axis and the absorption axis is 45 °, the stretched film side is laminated on 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. The results are shown in Table 1.
〇: When laminated on the reflector, unevenness is not visible.
X: When laminated on the reflector, unevenness is visually recognized along the orientation angle.

[Appearance and handleability evaluation]
The appearance and handleability of the stretched films obtained in Examples and Comparative Examples were visually evaluated based on the following criteria. The results are shown in Table 1.
〇: No wrinkles or slack are confirmed on the stretched film during roll transfer.
X: Wrinkles and / or slack are confirmed on the stretched film during roll transfer.

As shown in Table 1, in a long diagonally stretched film, when the fluctuation amount of the film thickness in the long length direction is large, the visibility is lowered due to the phase difference unevenness, but the fluctuation amount of the film thickness is determined. Visibility can be improved by reducing the value 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 an image display device such as a liquid crystal display device (LCD) and an organic electroluminescence display device (OLED). ..

1 Extruder 2 T-die 6 Film-forming speed control unit 10L Endless loop 10R Endless loop 20 Clip 100 Stretching device 200 Film thickness meter 300 Resin film 500 Circular polarizing plate

Claims (6)

Forming a long resin film by extrusion molding,
The left and right ends of the resin film in the width direction are gripped by left and right clips of a variable pitch type in which the clip pitch in the vertical direction changes, and at least one of the left and right clips is changed by changing the clip pitch of the resin film. And to stretch diagonally
Measuring the amount of change in the film thickness of the resin film in the long direction is included in this order .
When the fluctuation amount of the film thickness exceeds the first predetermined value, the film forming speed of the resin film is reduced, so that the film thickness of the resin film in the long direction before being gripped by the left and right clips. Reduce the amount of fluctuation of
A method for producing a stretched film, wherein the film forming speed is an extrusion speed for extruding a film-like molten resin from a T-die . The fluctuation amount of the film thickness is the difference between the adjacent peaks and the bottom when the moving average of the film thickness in the long direction of the resin film is taken and the peak and the bottom in the moving average line of the film thickness are detected. The method for producing a stretched film according to claim 1 . The method for producing a stretched film according to claim 1 or 2 , 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 3 , further comprising measuring the amount of variation in the film thickness of the resin film in the elongated direction before gripping with the left and right clips. Obtaining a long stretched film by the production method according to any one of claims 1 to 4 , and
A method for manufacturing an optical laminate, which comprises transporting a long optical film and the long stretched film while aligning the long directions thereof and continuously laminating them. The optical film is a polarizing plate, and the optical film is a polarizing plate.
The method for producing an optical laminate according to claim 5 , wherein the stretched film is a λ / 4 plate or a λ / 2 plate.

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