JP2020001284A - Manufacturing method of stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for obtaining a stretched film having sufficient peel strength while having an NZ coefficient of 1.3 or less. SOLUTION: (I) The lateral end portions 101a, 101b of a pre-stretched film 100 are spaced by a plurality of gripping tools 102a, 102b in a direction orthogonal to the lateral direction of the pre-stretched film. As L1, the step of gripping the pre-stretched film for each length L2 in the longitudinal direction, and then (II) moving the plurality of gripping tools laterally outward of the pre-stretched film to obtain the pre-stretched film. The step of stretching at a stretching ratio ETD times in the lateral direction to obtain a stretched film is included, the stretching ratio ETD satisfies the following formula (1), and the ratio (L1 / L2) of the L1 to the L2 is as follows. A method for producing a stretched film, which satisfies the formula (2). 1.6 ≤ ETD ≤ 2.2 (1) [Selection diagram] Fig. 1

Description

  The present invention relates to a method for producing a stretched film.

  Stretching the film can impart various optical properties, such as birefringence properties, to the film. Since different optical properties can be imparted to the film depending on the stretching method, a stretching method has been developed. For example, Patent Literature 1 and Patent Literature 2 disclose techniques for stretching a film in a lateral direction.

Japanese Patent No. 5371523 Japanese Patent No. 5503975

  A retardation film having a small NZ coefficient, for example, about 1.3 or less is being used advantageously as, for example, an optical compensation film of an image display device, and thus the demand is growing. In the following description, the NZ coefficient of a film is a value represented by (nx-nz) / (nx-ny) unless otherwise specified. nx represents the refractive index in the direction (in-plane direction) perpendicular to the thickness direction of the film and in the direction giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the film and orthogonal to the direction of nx. nz represents the refractive index in the thickness direction of the film. The measurement wavelength is 590 nm unless otherwise specified.

When the film is uniaxially stretched in the transverse direction, the NZ coefficient can be reduced by increasing the stretching ratio in the transverse direction.
However, when a stretched film having a large stretch ratio is bonded to another member such as a polarizing plate, the peel strength (peel strength) from the other member may not be sufficient.

  Therefore, there is a demand for a production method capable of obtaining a stretched film having a sufficient peel strength while having an NZ coefficient of 1.3 or less.

The present inventor has made intensive studies to solve the above-mentioned problems. As a result, it has been found that a stretched film having sufficient peel strength can be obtained while the NZ coefficient is small and 1.3 or less by a manufacturing method of performing stretching satisfying predetermined conditions while relaxing the film before stretching. The present invention has been completed.
That is, the present invention provides the following.

［２］ 前記工程（ＩＩ）を、前記延伸前フィルムを加熱しながら行う、［１］に記載の延伸フィルムの製造方法。
［３］ 前記延伸フィルムの厚みが、１５μｍ以上である、［１］又は［２］に記載の延伸フィルムの製造方法。
［４］ 下記式（３）が満たされる、［１］〜［３］のいずれか１項に記載の延伸フィルムの製造方法。
１．３０≦Ｅ_ＴＤ×（Ｌ１／Ｌ２）＜２．００ （３） [1] (I) The longitudinal end of the film before stretching is defined as a distance L1 between the plurality of gripping tools in a direction orthogonal to the horizontal direction of the film before stretching, using a plurality of gripping tools at both ends in the horizontal direction of the film before stretching. Gripping every length L2 in the direction,
(II) moving the plurality of gripping tools outward in the horizontal direction of the film before stretching, and stretching the film before stretching at a transverse stretching ratio of _ETD to obtain a stretched film;
The stretching ratio E _TD satisfies the following formula (1),
A method for producing a stretched film, wherein a ratio (L1 / L2) of the L1 to the L2 satisfies the following expression (2).
1.6 ≦ _ETD ≦ 2.2 (1)

[2] The method for producing a stretched film according to [1], wherein the step (II) is performed while heating the film before stretching.
[3] The method for producing a stretched film according to [1] or [2], wherein the thickness of the stretched film is 15 μm or more.
[4] The method for producing a stretched film according to any one of [1] to [3], wherein the following formula (3) is satisfied.
1.30 ≦ _ETD × (L1 / L2) <2.00 (3)

  According to the present invention, it is possible to provide a production method capable of obtaining a stretched film having a sufficient peel strength while having a small NZ coefficient of 1.3 or less.

FIG. 1 is a schematic diagram schematically showing the upper surface of a film before stretching held by a plurality of holding tools in step (I) of the manufacturing method according to one embodiment of the present invention. FIG. 2 is a schematic diagram schematically illustrating a side surface of the film before stretching held by the plurality of holding tools in step (I) of the manufacturing method according to one embodiment of the present invention. FIG. 3 is an explanatory diagram schematically showing the step (II) in the manufacturing method according to the embodiment of the present invention.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and examples, and may be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and equivalents thereof.

  In the following description, the “long” film refers to a film having a length of 5 times or more with respect to the width, preferably having a length of 10 times or more, and specifically, a roll. A film having a length that can be wound up and stored or transported. The upper limit of the length of the film is not particularly limited, and may be, for example, 100,000 times or less with respect to the width.

  In the following description, the in-plane retardation Re of the film is a value represented by Re = (nx−ny) × d unless otherwise specified, and the retardation Rth in the thickness direction of the film is unless otherwise specified. , Rth = [{(nx + ny) / 2} −nz] × d. Here, nx, ny, and nz are as described above. d represents the thickness of the film. The measurement wavelength is 590 nm unless otherwise specified.

  In the following description, unless the element direction is "parallel" and "orthogonal", unless otherwise specified, within the range that does not impair the effects of the present invention, for example, within the range of ± 3 °, ± 2 ° or ± 1 ° May be included.

  In the following description, the lateral direction of the film means a direction orthogonal to the longitudinal direction of the film. The longitudinal direction of the film is generally the transport direction of the film.

[1. Outline of manufacturing method of stretched film]
According to one embodiment of the present invention, the method for producing a stretched film comprises: (I) forming a plurality of gripping tools on both ends of the unstretched film in the transverse direction so that the plurality of grippers are arranged in a direction orthogonal to the transverse direction of the unstretched film. A step of gripping each longitudinal length L2 of the film before stretching, with the distance between the grippers as L1,
(II) a step of moving the plurality of grippers outward in the horizontal direction of the film before stretching, and stretching the film before stretching at a transverse stretching ratio of _ETD to obtain a stretched film.

[1.1. Step (I)]
The film before stretching means a film before being stretched in the manufacturing method of the present embodiment.
The film before stretching is usually a film formed from a resin containing a thermoplastic polymer. Examples of thermoplastic polymers that can be included in the resin include alicyclic structure-containing polymers such as norbornene-based polymers, cellulose esters, polyvinyl alcohol, polyimide, polycarbonate, polysulfone, polyethersulfone, epoxy polymers, polystyrene, Acrylic polymers, methacrylic polymers, polyethylene, polypropylene, polyester and combinations thereof.
Among these, an alicyclic structure-containing polymer is preferred because of its excellent mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability and light weight.

  The film before stretching may be a single-sheet film or a long film. The film before stretching is preferably a long film, and is usually fed out of a roll form and subjected to each step.

The width of the film before stretching may be, for example, a width according to the use of the stretched film, and is preferably 200 mm or more, more preferably 300 mm or more, preferably 1500 mm or less, more preferably 1300 mm or less. Here, the width of the film before stretching means the length of the film before stretching in a direction orthogonal to the longitudinal direction of the film before stretching.
The thickness of the film before stretching may be, for example, a thickness according to the required retardation of the stretched film, preferably 20 μm or more, more preferably 22 μm or more, still more preferably 25 μm or more, preferably 60 μm or less, more preferably 55 μm or less. The thickness is more preferably 50 μm or less.

Next, the step (I) will be described in more detail with reference to FIGS.
FIG. 1 is a schematic diagram schematically showing the upper surface of a film before stretching held by a plurality of holding tools in step (I) of the manufacturing method according to one embodiment of the present invention.
FIG. 2 is a schematic diagram schematically illustrating a side surface of the film before stretching held by the plurality of holding tools in step (I) of the manufacturing method according to one embodiment of the present invention.

  As shown in FIGS. 1 and 2, the pre-stretched film 100 includes a plurality of grippers 102 a and a plurality of grippers 102, each of which is an end portion 101 a and an end portion 101 b which are both ends in the transverse direction D <b> 1 of the unstretched film 100. 102b. The distance between the plurality of grippers 102a in the transport direction D2, which is a direction orthogonal to the lateral direction D1, is L1. The distance between the plurality of gripping tools 102b in the transport direction D2 is L1.

  Here, the distance between the gripping tools 102a is the distance between the centers P1a of the portions of the adjacent gripping tools 102a, 102a that grip the film 100 before stretching. The distance between the gripping tools 102b is the distance between the centers P1b of the portions of the adjacent gripping tools 102b, 102b that grip the film 100 before stretching.

  The ends 101a of the unstretched film 100 are gripped by the adjacent gripping tools 102a for each longitudinal length L2. Specifically, the length of the unstretched film 100 between the centers P1a and P1a of the adjacent gripping tools 102a is L2.

  The other end portion 101b of the film 100 before stretching is also gripped by the adjacent gripping tools 102b for each length L2 in the longitudinal direction (not shown). Specifically, the length of the unstretched film 100 between the centers P1b and P1b of the adjacent gripping tools 102b is L2.

  Here, the distance L1 between the adjacent gripping tools is shorter than the length L2 of the film before stretching 100 between the centers of the adjacent gripping tools. Therefore, the pre-stretched film 100 gripped by the adjacent gripping tools is in a relaxed state in the longitudinal direction. The relationship between L1 and L2 will be described later in detail.

In the step (I), the film before stretching may be heated in advance. Thereby, in step (II), stretching can be performed under stable temperature conditions. For example, the film before stretching can be heated by performing all or a part of the step (I) in an oven set at a predetermined temperature. The heating temperature may be the same as the temperature range described later as a preferred heating temperature in step (II).
When the step (I) is performed in multiple stages as described later, it is preferable that, of the steps included in the step (I), the step immediately before the step (II) is performed while heating. For example, it is preferable to perform the below-described step (I-2) while heating.

  Step (I) may be performed in a single step or in multiple steps.

  For example, the process (I) may be performed in a single step by holding the undrawn film unwound from the roll with a plurality of holding tools whose intervals are set to L1 for each length L2 of the undrawn film. Good.

Step (I) may include a plurality of steps.
For example, the step (I) may include the following steps (I-1) and (I-2) in this order.

(I-1) The length in the longitudinal direction of the film before stretching, where L2 is the distance between the plurality of gripping tools in a direction orthogonal to the film before stretching, using a plurality of gripping tools. Step of gripping every L2.
(I-2) a step of reducing the interval between the plurality of gripping tools from L2 to L1.

  The step (I) can be performed by a film stretching device provided with a conventionally known gripping device, for example, a film stretching device described in Japanese Patent No. 5371523.

[1.2. Step (II)]
In the step (II), the pre-stretched film gripped for each length L2 in the longitudinal direction by the plurality of gripping tools obtained in the step (I) and having an interval L1 between adjacent gripping tools is transferred in the transverse direction. Stretch.
FIG. 3 is an explanatory diagram schematically showing the step (II) in the manufacturing method according to the embodiment of the present invention.

In step (I), the gripper 102a and stretched before film 100 is gripped by the gripper 102b, while conveying the conveying direction D2, is drawn at a draw ratio _{E TD} magnification in the horizontal direction D1. Specifically, the stretched film 1000 is obtained by moving the gripper 102a and the gripper 102b to the outside in the lateral direction together with the transport of the film 100 before stretching.

Here, the laterally outer side means a lateral direction and a direction away from a line CL passing through a central point in the lateral direction of the film before stretching. Further, the stretching ratio E _TD means the stretching ratio in the transverse direction, and is usually the width of the film (stretched film) after stretching in the transverse direction and the width of the film before stretching in the transverse direction (film before stretching). It is the ratio to the width.

  In the step (I), the pre-stretched film 100 is gripped by the gripper 102a and the gripper 102b to make the pre-stretched film 100 slack in the longitudinal direction, and in the step (II), the pre-stretched film 100 is horizontally stretched. Thus, transverse stretching close to free uniaxial stretching can be performed.

  Step (II) can be performed using a conventionally known film stretching apparatus.

  Step (II) is preferably performed while heating the film before stretching. For example, the film before stretching can be heated by performing the step (II) in an oven set at a predetermined temperature. The heating temperature can be appropriately set according to the stretching ratio and the like. When the glass transition temperature of the material of the film before stretching is Tg (° C.), the heating temperature is preferably (Tg−10) ° C. or higher, more preferably (Tg−5) ° C. or higher, and preferably (Tg + 20) ° C. Or less, more preferably (Tg + 15) ° C. or less.

  The glass transition temperature Tg (° C.) of the material of the film before stretching was determined by using a differential operation calorimeter (DSC) to rapidly cool a sample heated to 300 ° C. in a nitrogen atmosphere with liquid nitrogen and increasing the temperature at a rate of 10 ° C./min. Can be obtained by measuring under the following conditions.

[1.3. Conditions for gripping and stretching]
In the step (II), the stretching ratio E _TD in the transverse direction satisfies the following expression (1).
1.6 ≦ _ETD ≦ 2.2 (1)

  In the step (I), the ratio (L1 / L2) of L1 to L2 satisfies the following equation (2).

In the following description, the term in the leftmost of the formula (2), may be referred to as "1 / √E _TD".

  In the steps (I) and (II), by satisfying the expressions (1) and (2), a stretched film having a sufficient peel strength while having an NZ coefficient of 1.3 or less can be obtained.

_ETD is usually 1.6 or more, preferably 1.7 or more, more preferably 1.8 or more, and still more preferably, from the viewpoint of reducing wrinkles of the stretched film and reducing the NZ coefficient. It is 1.9 or more, and from the viewpoint of improving the peel strength, it is usually 2.2 or less, preferably 2.1 or less, and more preferably 2.0 or less.

Ratio L2 of L1 (L1 / L2), from the viewpoint of reducing wrinkles of the stretched film, usually greater than 1 / √E _TD, from the viewpoint of reducing the NZ coefficient, usually less than 0.90, preferably 0. It is 85 or less, more preferably 0.82 or less.

It is preferable that the draw ratio _ETD and the ratio of L1 to L2 (L1 / L2) satisfy the following expression (3).
1.30 ≦ _ETD × (L1 / L2) <2.00 (3)
By satisfying the expression (3), wrinkles of the stretched film can be reduced, the NZ coefficient can be reduced to 1.3 or less, and the peel strength of the stretched film can be effectively improved.

Reducing the wrinkles of the stretched film, from the viewpoint of reducing the NZ _{coefficient, E TD × (L1 / L2} ) is preferably 1.30 or more, more preferably 1.35 or more, more preferably 1. _ETD × (L1 / L2) is preferably less than 2.00, more preferably 1.90 or less, further preferably 1.90 or more, from the viewpoint of effectively improving the peel strength. 85 or less.

  As in the method of the present embodiment, the step (I) and then the step (II) may be continuously performed on the unstretched film while the long unstretched film is being unwound to form a stretched film. Step (I) may be performed on the film before stretching, and then step (II) may be performed.

[1.4. Optional process]
The manufacturing method of the present embodiment may include an optional step other than the above-described step (I) and step (II).
For example, such an optional step includes, for example, a step of cooling the stretched film, and a step of cutting a portion held by the gripper from the stretched film obtained by stretching in the step (II) after the step (II) And a step of winding a stretched film and a step of cutting a long stretched film.

[2. Stretched film obtainable by the production method of the present embodiment]
The stretched film obtained by the production method of the present embodiment may have, for example, the following characteristics.

  The in-plane retardation Re of the stretched film is preferably 100 nm or more, more preferably 105 nm or more, further preferably 110 nm or more, preferably 150 nm or less, more preferably 145 nm or less, and even more preferably 140 nm or less.

  The NZ coefficient of the stretched film is preferably 1.0 or more, more preferably 1.05 or more, still more preferably 1.1 or more, preferably 1.3 or less, more preferably less than 1.3, and still more preferably. Is 1.25 or less, particularly preferably 1.25 or less.

  The thickness of the stretched film is preferably 15 μm or more, more preferably 17 μm or more, still more preferably 18 μm or more, preferably 30 μm or less, more preferably 28 μm or less, and still more preferably 26 μm or less.

  The stretched film obtained by the production method of the present embodiment has a sufficient peel strength while having an NZ coefficient of 1.3 or less, and thus is useful as, for example, an optical compensation film provided in an image display device.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and equivalents thereof.

  In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified. The operations described below were performed at normal temperature and normal pressure unless otherwise specified.

[Evaluation method]
(Method of measuring average in-plane retardation of film)
The in-plane retardation Re was measured at a plurality of points at 50 mm intervals in the width direction of the film using a phase difference measuring device (Axometric's product name “Axoscan”) at a wavelength of 590 nm. The average value of the in-plane retardation at these points was calculated, and this average value was defined as the average in-plane retardation of the film.

(Method of measuring film thickness)
The thickness of the film was measured at a plurality of points at 50 mm intervals in the width direction of the film using a film thickness measuring device (product name “Snap Gauge” manufactured by Mitutoyo Corporation). The average value of the film thickness at these points was calculated, and this average value was defined as the average thickness of the film.

(Method of measuring average NZ coefficient of film)
The NZ coefficient was measured at a plurality of points at 50 mm intervals in the width direction of the film using a phase difference measuring device (Axometric's product name “Axoscan”) at a wavelength of 590 nm. The average of the NZ coefficients at these points was calculated, and this average was defined as the average NZ coefficient of the film.
Here, the NZ coefficient was determined from the in-plane retardation Re and the retardation Rth in the thickness direction by the following equation.
NZ coefficient = (Rth / Re) +0.5

(Method of measuring peel strength)
An unstretched film (glass transition temperature: 160 ° C., thickness: 100 μm, manufactured by Zeon Corporation) made of a resin containing a norbornene-based polymer was prepared. One surface of the stretched film to be evaluated and one surface of the unstretched film were subjected to corona treatment. An adhesive was adhered to the corona-treated surface of the stretched film and the corona-treated surface of the unstretched film, and the surfaces to which the adhesive was adhered were adhered to each other. At this time, an ultraviolet curable adhesive was used as the adhesive. Thus, a sample film including a stretched film and an unstretched film was obtained.
Thereafter, the sample film was cut into a width of 15 mm, and the stretched film side was bonded to the surface of the slide glass with an adhesive. At this time, a double-sided adhesive tape (manufactured by Nitto Denko Corporation, product number “CS9621”) was used as the adhesive.
A 90-degree peel test was performed by sandwiching the unstretched film at the tip of a force gauge and pulling the unstretched film in the direction normal to the surface of the slide glass. At this time, the force measured when the unstretched film was peeled was a force required to peel the stretched film from the unstretched film, and the magnitude of this force was measured as the peel strength.

(Wrinkle evaluation method)
From the film taken out of the stretching machine, the area gripped by the clip was cut with a cutter or the like to remove a deformed portion of the film caused by gripping the clip.
The remaining film was visually observed to determine the presence or absence of wrinkles. The film was placed on a smooth table, and the film was observed from the side. When the film was waving at a height difference of 3 mm or more, it was determined that there was wrinkling.

[Production Example 1] Production of Film Before Stretching Pellets of a resin containing a norbornene-based polymer (“Zeonoa”: glass transition temperature 126 ° C, manufactured by Zeon Corporation) were dried at 100 ° C for 5 hours. The pellets were supplied to an extruder, melted in the extruder, and extruded in a sheet form from a T-die onto a casting drum through a polymer pipe and a polymer filter. The extruded resin was cooled and hardened on the casting drum, and a long elongate film having a thickness of 30 μm was obtained. The long film before stretching was wound up to obtain a film roll. From the film roll, a pre-stretched film (thickness 30 μm) having a rectangular shape of 200 mm × 200 mm was cut out.

[Production Example 2] Production of film before stretching A rectangular pre-stretching film having a thickness of 60 µm was obtained in the same manner as in Production Example 1 except that the gap between the T dies was adjusted.

[Production Example 3] Production of film before stretching A rectangular pre-stretching film having a thickness of 25 µm was obtained in the same manner as in Production Example 1 except that the gap between the T dies was adjusted.

[Example 1]
The rectangular unstretched film (hereinafter referred to as cut film) obtained in Production Example 1 is stretched by a biaxial stretching apparatus (“biaxially stretched birefringence retardation measuring apparatus” manufactured by Eto Corporation) in the following procedure. Was.

(Gripping step: Step (I-1))
Four sides of the cut film were gripped by seven clips per side. The interval between the adjacent clips was set to 30 mm, and the length L2 of the cut film gripped by the adjacent clips was set to 30 mm so that the cut film was not loosened.

(Gripping step: Step (I-2))
The cut film was moved into an oven controlled at 135 ° C., and the cut film was preheated for 10 seconds. In the meantime, among the clips for gripping the cut film, the interval between the clips for gripping a pair of opposing sides was reduced from 30 mm to L1 along the direction of the gripping side. Hereinafter, for the sake of convenience, a direction parallel to the direction of one set of sides gripped by the clips with reduced intervals is referred to as a longitudinal direction, and a direction parallel to the directions of the other sides facing each other is referred to as a lateral direction. L1 was 25.5 mm. As a result, the sides of the cut film in the longitudinal direction (both ends in the horizontal direction) were gripped by the clips for each longitudinal length L2 (30 mm) of the cut film, with the interval L1 between the adjacent clips being 25.5 mm.

(Stretching step: Step (II))
With the cut film kept in an oven controlled at 135 ° C., the clips holding the longitudinal sides, the intervals of which were reduced in the step (I-2), were moved in the horizontal direction to the outside of the film. Moved in the direction to go. Here, the interval between adjacent clips that grip the side in the horizontal direction was increased from the original 30 mm to LT1. Here, LT1 was set to 54 mm. In addition, the interval between the facing clips that grip a pair of sides in the longitudinal direction was set to be _ETD times the original interval (20 mm). Here, E _TD = LT1 (mm) / 30 (mm).
As a result, the cut film was stretched at a stretch ratio (E _TD ) of 1.8.

(Cooling process)
After the stretching step, the stretched cut film was moved into an oven controlled at 120 ° C., cooled for 10 seconds, and taken out of the biaxial stretching apparatus. The cut film taken out was evaluated according to the evaluation method described above.

[Example 2]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
· In the stretching step, and 60mm the _LT1, was 2.0 _{E TD.}

[Example 3]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
In the gripping step (step (I-2)), L1 was set to 24.6 mm.
· In the stretching step, and 60mm the _LT1, was 2.0 _{E TD.}

[Example 4]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
In the gripping step (step (I-2)), L1 was set to 24.0 mm.
- in the stretching process, the LT1 and _66mm, was 2.2 _{E TD.}

[Comparative Example 1]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
-Instead of the rectangular pre-stretched film obtained in Production Example 1, the rectangular pre-stretched film having a thickness of 60 µm obtained in Production Example 2 was used.
In the gripping step (step (I-2)), L1 was set to 30.0 mm. That is, the interval between the clips gripping the longitudinal sides of the clips gripping the cut film was not reduced from 30 mm.
- in the stretching step, the LT1 and 105 _mm, and the _{E TD} 3.5.

[Comparative Example 2]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
In the gripping step (step (I-2)), L1 was set to 30.0 mm. That is, the interval between the clips gripping the longitudinal sides of the clips gripping the cut film was not reduced from 30 mm.
· In the stretching step, and 60mm the _LT1, was 2.0 _{E TD.}

[Comparative Example 3]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
-L1 was set to 28.5 mm in the gripping step (step (I-2)).
· In the stretching step, and 60mm the _LT1, was 2.0 _{E TD.}

[Comparative Example 4]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
In the gripping step (step (I-2)), L1 was set to 24.0 mm.
· In the stretching step, and 45mm the _LT1, was _{E TD} 1.5.

[Comparative Example 5]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
-Instead of the rectangular pre-stretched film obtained in Production Example 1, the 25 μm-thick rectangular pre-stretched film obtained in Production Example 3 was used.
In the gripping step (step (I-2)), L1 was set to 27.6 mm.
· In the stretching step, and 42mm the _LT1, was _{E TD} 1.4.

[Comparative Example 6]
Except that the following items were changed, a stretched cut film was obtained and evaluated in the same manner as in Example 1.
In the gripping step (step (I-2)), L1 was set to 27.0 mm.
- in the stretching step, the LT1 and 69 _mm, was 2.3 _{E TD.}

The stretching conditions and evaluation results of the examples and comparative examples are shown in the following table.
The indications in the following table represent the following meanings.
"Average Re" represents an average in-plane retardation.
"Film thickness" represents the average thickness of the film.

According to the above results, the draw ratio _{E TD} is 1.6 or more and 2.2 or less, L1 / L2 is, 1 / √E _TD is greater than and less than _{0.90, E TD × (L1 /} L2 ) Is 1.30 or more and less than 2.00, it can be seen that the obtained stretched film has an average NZ coefficient of 1.3 or less and good peel strength. Further, in Examples 1 to 4, it can be seen that the average in-plane retardation of the obtained stretched film is 110 nm or more, which is sufficiently large, and that generation of wrinkles is suppressed.

On the other hand, in the production methods of Comparative Examples 4 and 5 in which the stretch ratio _ETD is smaller than 1.6, the obtained stretched films have wrinkles or the NZ coefficient is larger than 1.3.
Further, in the production methods of Comparative Examples 1 and 6 in which the stretching ratio E _TD is larger than 2.2, the peel strength is remarkably small.

L1 / L2 is in the 1 / √E _TD less is the manufacturing method of Comparative Example 4, there is a wrinkle in stretching film obtained.
In the production methods of Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 5, and Comparative Example 6 in which L1 / L2 is 0.90 or more, the peel strength of the obtained stretched film is remarkably large. Small, average NZ coefficient is greater than 1.3, or wrinkled.

In the production methods of Comparative Examples 4 and 5 in which E _TD × (L1 / L2) is less than 1.30, the obtained stretched film has wrinkles or the average NZ coefficient is larger than 1.3.
In the production methods of Comparative Example 1, Comparative Example 2, and Comparative Example 6 where E _TD × (L1 / L2) is 2.00 or more, the peel strength of the obtained stretched film is remarkably low.

  The above results show that a stretched film having a sufficient peel strength can be obtained by the production method of the present invention while having a small NZ coefficient and 1.3 or less.

100 Pre-stretching film 101a End 101b End 102a Gripping tool 102b Gripping tool 1000 Stretched film D1 Lateral direction D2 Transport direction P1a Center of gripping tool P1b Center of gripping tool

Claims (4)

(I) A longitudinal length of the pre-stretched film is defined as a distance between the plurality of grippers in a direction orthogonal to the lateral direction of the unstretched film, L1, which is determined by using a plurality of grippers at both lateral ends of the film before stretching. Step of gripping each L2,
(II) moving the plurality of gripping tools outward in the horizontal direction of the film before stretching, and stretching the film before stretching at a transverse stretching ratio of _ETD to obtain a stretched film;
The stretching ratio E _TD satisfies the following formula (1),
A method for producing a stretched film, wherein a ratio (L1 / L2) of the L1 to the L2 satisfies the following expression (2).
1.6 ≦ _ETD ≦ 2.2 (1)

  The method for producing a stretched film according to claim 1, wherein the step (II) is performed while heating the film before stretching.   The method for producing a stretched film according to claim 1, wherein the thickness of the stretched film is 15 μm or more. The method for producing a stretched film according to any one of claims 1 to 3, wherein the following formula (3) is satisfied.
1.30 ≦ _ETD × (L1 / L2) <2.00 (3)

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