JP2010173261A - Method of forming stretched optical film - Google Patents

Abstract

A method for efficiently producing a stretched optical film having a slow axis inclined with respect to the extending direction of the film and having little variation in thickness and optical properties.
The moving distance of the gripper X1 and the gripping of the gripper X1 are measured using a stretching machine having a pair of gripping parts each composed of a gripper X1 and a gripper Y1, each gripping both ends of a long film before stretching. Based on the moving distance of the child Y1, the stretched optical film having a slow axis at an angle of more than 0 ° and less than 90 ° with respect to the longitudinal direction is produced by obliquely stretching the film before stretching. A stretched optical film manufacturing method comprising the step of obliquely stretching the pre-stretch film, wherein the total thickness of the pre-stretch film or at least one of the layers constituting the pre-stretch film is the gripping A method for producing a stretched optical film, wherein the side gripped by the child X1 has a thickness gradient in the width direction that is thicker than the side gripped by the gripper Y1.
[Selection] Figure 1

Description

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

  In the liquid crystal display device, an optical member such as a retardation film is used to improve performance. The retardation film is usually required to have an angle that the slow axis is neither parallel nor perpendicular to the transmission axis of the polarizer. On the other hand, the transmission axis of the polarizer is parallel to the long side or short side direction of the rectangular display surface of the normal device. Therefore, there is a demand for a rectangular retardation film having a slow axis in an oblique direction with respect to its side.

  Conventionally, a retardation film is produced by longitudinally stretching (that is, stretching in the extending direction of a long film) or laterally stretching (that is, stretching in the width direction of a long film) a long film before stretching. Yes. In order to obtain a rectangular film having a slow axis in an oblique direction from such a long film, it is necessary to cut out the film so that the side faces in an oblique direction from the extending direction of the long film. Such production increases the amount of film discarded and makes roll-to-roll production impossible, resulting in lower production efficiency.

  In order to improve production efficiency, it has been proposed to stretch a long, unstretched film in an oblique direction. However, when the stretching in the oblique direction is performed, there is a problem that the thickness and optical characteristics of the obtained film are likely to be non-uniform compared to a film manufactured by longitudinal stretching and lateral stretching. As means for solving such a problem, Patent Document 1 and Patent Document 2 propose a tenter rail pattern in which the feeding direction during oblique stretching and the winding direction of the product after stretching satisfy a specific relationship. ing. Furthermore, in Patent Document 3 and Patent Document 4, an attempt is made to match the orientation of the stretched film with the angle between the oven stretching, heat setting, and cooling zone boundaries as much as possible. The problem has not been solved.

JP 2007-90532 A JP 2007-153926 A Japanese Patent Laid-Open No. 2003-311823 JP 2007-175974 A

  Accordingly, it is an object of the present invention to provide a method for efficiently producing a stretched optical film having a slow axis inclined with respect to the extending direction of the film and having little variation in thickness and optical properties.

  As a result of studying to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by setting the relationship between the stretching mode and the pre-stretching film to be supplied in the oblique stretching to a predetermined mode, The present invention has been completed. That is, according to the present invention, the following is provided:

[1] Using a stretching machine that includes a pair of gripping portions including a gripper X1 and a gripper Y1 that grips both ends of a long pre-stretching film, the moving distance of the gripper X1 and the gripper Based on the moving distance of Y1, the stretched optical film having a slow axis at an angle of more than 0 ° and less than 90 ° with respect to the longitudinal direction is produced by obliquely stretching the pre-stretched film. A method for producing a stretched optical film, comprising:
A step of continuously supplying the pre-stretching film to the stretching machine (A);
A step (B) of gripping the ends of the pre-stretch film with the grippers X1 and Y1, respectively;
A step of stretching the pre-stretching film by moving the grippers X1 and Y1, so that the travel distance of the gripper X1 during stretching is longer than the travel distance of the gripper Y1 during stretching Including the step (C) of oblique stretching,
The thickness gradient in the width direction is such that the total thickness of the film before stretching or the thickness of at least one layer constituting the film before stretching is thicker on the side gripped by the gripper X1 than on the side gripped by the gripper Y1. A process for producing a stretched optical film.
[2] The method for producing a stretched optical film according to [1], wherein the pre-stretch film includes a plurality of layers, and at least one of the plurality of layers has a thickness gradient in the width direction.
[3] The method for producing a stretched optical film according to [2], wherein the layer having a thickness gradient in the width direction is a layer to which optical anisotropy is imparted in the step (C).

  In the present invention, the “movement distance” of the grippers X1 and Y1 is from when the gripper grips the film until the film is released, unless it is clearly different from the context and unless otherwise noted. Is the distance that the gripper moves.

  According to the production method of the present invention, a stretched optical film with little variation in thickness and optical properties can be produced by oblique stretching, and thus has a slow axis inclined with respect to the extending direction of the film, and A stretched optical film with little variation in thickness and optical properties can be produced efficiently.

FIG. 1 is a top view schematically showing a stretching mechanism by a link device in an example of a stretching machine for oblique stretching for carrying out the manufacturing method of the present invention. FIG. 2 is a longitudinal sectional view schematically showing a cross section of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS1 and is perpendicular to the film surface direction. FIG. 3 is a longitudinal sectional view schematically showing a cross section of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS2 and is perpendicular to the film surface direction. FIG. 4 is a longitudinal cross-sectional view schematically showing a cross section of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS3 and is perpendicular to the film surface direction. FIG. 5 is a longitudinal sectional view schematically showing a cross section of another example of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS1 and is perpendicular to the film surface direction. FIG. 6 is a longitudinal sectional view schematically showing a cross section of another example of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS2 and is perpendicular to the film surface direction. FIG. 7 is a longitudinal sectional view schematically showing a cross section of another example of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS3 and is perpendicular to the film surface direction. FIG. 8 is a graph showing the measurement results of the total thickness of the film before stretching in Example 1 of the present application. FIG. 9 is a graph showing the measurement results of the inner layer thickness of the film before stretching in Example 1 of the present application. FIG. 10 is a graph showing the measurement results of the total thickness of the stretched optical film in Example 1 of the present application. FIG. 11 is a graph showing the measurement results of the inner layer thickness of the stretched optical film in Example 1 of the present application. FIG. 12 is a graph showing the measurement results of the retardation Re in the in-plane direction of the stretched optical film in Example 1 of the present application. FIG. 13 is a graph showing the measurement results of the total thickness of the film before stretching in Comparative Example 1 of the present application. FIG. 14 is a graph showing the measurement results of the inner layer thickness of the pre-stretch film in Comparative Example 1 of the present application. FIG. 15 is a graph showing the measurement results of the total thickness of the stretched optical film in Comparative Example 1 of the present application. FIG. 16 is a graph showing the measurement results of the inner layer thickness of the stretched optical film in Example 1 of the present application. FIG. 17 is a graph showing measurement results of retardation Re in the in-plane direction of the stretched optical film in Example 1 of the present application. 18 is a longitudinal cross-sectional view schematically showing a cross section of another example of the films 11B to 11A shown in FIG. 1 cut along a plane that passes through the dotted line CS1 and is perpendicular to the film surface direction. FIG. 19 is a longitudinal sectional view schematically showing a cross section of another example of the films 11B to 11A shown in FIG. 1 cut along a plane passing through the dotted line CS3 and perpendicular to the film surface direction.

Hereinafter, the present invention will be specifically described with reference to the drawings.
The method for producing a stretched optical film of the present invention is a method for producing a long stretched optical film. “Long” means a film having a length of at least about 5 times the width of the film, and preferably has a length of 10 times or more, specifically wound in a roll shape. It may be one having a length that can be stored or transported (film roll). In the manufacturing method of a long film, a film can be manufactured to desired arbitrary length by manufacturing a film continuously.

  In the method for producing a stretched optical film of the present invention, a stretched optical film having a slow axis at an angle of more than 0 ° and less than 90 ° with respect to the extending direction of the film is produced. Here, the angle with respect to the extending direction of the film is an angle in the film plane. Since the slow axis is usually expressed in the stretching direction or a direction perpendicular to the stretching direction, in the production method of the present invention, by stretching at an angle of more than 0 ° and less than 90 ° with respect to the film extension direction, A stretched optical film having such a slow axis can be produced.

  The angle formed by the extension direction of the film and the slow axis can be arbitrarily set to a desired angle in the range of more than 0 ° and less than 90 °, preferably 40 to 50 °. Can be 45 °.

  The method for producing a stretched optical film of the present invention uses the stretcher provided with a pair of gripping parts each composed of a gripper X1 and a gripper Y1 for gripping both ends of a long unstretched film. Based on the moving distance of X1 and the moving distance of the gripper Y1, the manufacturing method of obliquely stretching the film before stretching, the step of continuously supplying the film before stretching to a stretching machine (A), A step (B) of gripping both ends of the film before stretching with the grippers X1 and Y1, respectively, and a step of stretching the film before stretching in a stretching line by moving the grippers X1 and Y1, A step (C) of obliquely stretching so that the moving distance of the gripper X1 during stretching is longer than the moving distance of the gripper Y1 during stretching.

  Below, the specific example of the manufacturing method of this invention is demonstrated with reference to the specific example of the apparatus which performs diagonal stretch. FIG. 1 is a top view schematically showing a stretching mechanism by a link device in an example of a stretching machine for oblique stretching for carrying out the manufacturing method of the present invention.

  In FIG. 1, the stretching machine 1 has a pair of link devices 101R and 101L, and each of the link devices 101R and 101L has grippers 110R and 110L. Although the link devices 101R and 101L are ring-shaped devices, some of them are omitted in FIG. The link device 101R is driven by the sprockets 12R and 13R, the link device 101L is driven by the sprockets 12L and 13L, and an appropriate rail (not shown) moves the film to the left when observing from the upstream to the downstream in the flow direction. Guided to bend the direction of travel.

  The unstretched film 11B is continuously supplied from the upstream (upper left side in FIG. 1) to the stretching machine 1 along the direction of the arrow D1 (step (A)), and the grippers 110R and 110L included in the link devices 101R and 101L. (Step (B)).

  When each of the link devices 101R and 101L is driven to circulate along the rail, the traveling direction of the film bends to the left, so that the length of the track that the link device 101R conveys while holding the film 11B is It becomes longer than the length of the track | orbit which the apparatus 101L conveys while holding the film 11B. Thereby, the length by which the link device 101R extends the film 11B is longer than the length by which the link device 101L extends the film 11B, and oblique stretching is achieved (step (C)). The obtained stretched optical film is released when the gripper is opened, and is carried out in the direction of the arrow D3.

  Specifically, when the grippers 110R and 110L on the dotted line CS1 move and reach the position indicated by the dotted line CS2, the film is stretched in the direction of the dotted line CS2, and the arrow AA1 is a direction orthogonal to the dotted line CS2. Optical anisotropy having a slow axis in the direction occurs. When the grippers 110R and 110L further move and reach the position indicated by the dotted line CS3, the stretch ratio further increases, and the optical anisotropy has a slow axis in the direction of the arrow AA2 that is the direction orthogonal to the dotted line CS3. A stretched optical film 11A is obtained.

  In the present invention, the total thickness of the film before stretching or the thickness of at least one of the layers constituting the film before stretching is such that the side gripped by the gripper X1 is thicker than the side gripped by the gripper Y1 It has a directional thickness gradient. By supplying such an unstretched film in the step (A), a stretched optical film with little variation in thickness and optical properties can be produced.

  In the example of the stretching machine 1 shown in FIG. 1, as the pre-stretch film, the side gripped by the gripper of the link device 101R has a thickness gradient in the width direction that is thicker than the side gripped by the gripper of the link device 101L. Film is supplied.

  Such a film and changes when it is stretched will be described with reference to FIGS. 2, 3, and 4 are cross-sections of the films 11 </ b> B to 11 </ b> A shown in FIG. 1 cut along planes that pass through dotted lines CS <b> 1, CS <b> 2, and CS <b> 3, respectively, and are perpendicular to the film surface direction. FIG. 6 is a longitudinal sectional view schematically showing a cross section CS2 ”and a“ cross section CS3 ”.

  As shown in the cross-section CS1 shown in FIG. 2, in the unstretched film 11B, the total thickness T1R of the right end E1R when observed from the upstream to the downstream in the flow direction is thicker than the total thickness T1L of the left end E1L. There is a gradient of the total thickness from the end E1R to the left end E1L. When such a pre-stretching film 11B is stretched by the stretching machine 1 shown in FIG. 1, the position closer to the right end E1R is longer due to the length of the track that the link device 101R conveys while stretching the film 11B. The magnification at which the film is stretched in both the film extension direction and the film width direction increases, and as a result, the total thickness of the film decreases. Therefore, as shown in the cross-section CS2 shown in FIG. 3, the total thickness of the right end E1R and the left end E1L becomes thinner as indicated by T2R and T2L and the difference therebetween becomes smaller as the stretching proceeds.

  Further, in the cross-section CS3 at the position where the stretching has progressed and the stretching has been completed, the total thickness of the right end E1R and the left end E1L is the same as shown by T3R and T3L as shown in FIG. The production of a stretched optical film having a uniform total thickness is achieved by stretching.

  The thickness gradient of the pre-stretch film that can achieve the most uniform film thickness at the position where stretching has been completed can be determined empirically by stretching films with various thickness gradients experimentally. it can. The thickness gradient of the film before stretching can be adjusted, for example, so that the thickness of the end portion on the thick side is about 0.5 to 3% thicker than the end portion on the thin side.

  On the other hand, as is done in the prior art, when the total thickness of the film before stretching is uniform, the cross-sections at dotted lines CS1, CS2, and CS3 are as shown in FIGS. 5, 6, and 7, respectively. In the cross section CS3 at the completed position, the total thickness of the stretched optical film becomes non-uniform.

  In the production method of the present invention, the draw ratio can be appropriately adjusted according to the desired conditions, but the oblique draw ratio is preferably 1.3 to 3.0 times, more preferably 1.5. ~ 2.5 times. Here, the stretching ratio in the oblique direction is the ratio of the distance between the pair of grippers opposed to each other at the stretching start position when the pair of grippers moved to the stretching end position moves. In the example of the stretching machine 1 shown, the distance between the pair of grips on the dotted line CS3 is the distance between the pair of grips on the dotted line CS1.

  The pre-stretch film used in the production method of the present invention has a predetermined gradient in the total thickness as shown in FIG. 2, and at least one of the layers constituting the pre-stretch film has a predetermined gradient. It may have. In this case, it is preferable that all the layers constituting the pre-stretch film have a predetermined gradient, but some of the layers constituting the pre-stretch film may not have a predetermined gradient. An example of such a film before stretching is shown in FIG.

  The film before stretching in the cross section CS1 shown in FIG. 18 has a two-layer / three-layer structure including an inner layer 2 and an outer layer 3 provided on both surfaces of the inner layer 2. In the inner layer 2, in the inner layer 2, the thickness T4R at the right end E2R when observed from the upstream to the downstream in the flow direction is thicker than the thickness T4L at the left end E2L, and the left end from the right end E2R. It has a thickness gradient over E2L. On the other hand, in the outer layer 3, the thickness T5R at the right end E2R and the thickness T5L at the left end E2L do not have such a relationship, and thus have no thickness gradient.

  When such a pre-stretched film is stretched, a stretched optical film having a cross section CS3 shown in FIG. 19 can be obtained. In the inner layer 2, the stretched optical film has the same thickness T6R at the right end E2R and the same thickness T6L at the left end E2L. Therefore, the stretched optical film is a stretched optical film having a uniform inner layer thickness by oblique stretching. . On the other hand, in the outer layer 3, the thickness T7R at the right end E2R is thinner than the thickness T7L at the left end E2L, and therefore the thickness is not uniform. However, in the case where the inner layer 2 is required to have a uniform thickness and optical characteristics, while the outer layer 3 is not required to have a uniform thickness and optical characteristics, such a stretched optical film can also be used effectively. .

  For example, the material of the inner layer 2 and the outer layer 3 and the stretching conditions are appropriately selected, and the stretching is performed at a temperature lower than the glass transition temperature of the inner layer 2 and higher than the glass transition temperature of the outer layer 3, so that only the inner layer 2 is homogeneous. Optical anisotropy can be imparted. In this case, even if the thickness of the outer layer 3 is not uniform, it can be useful as a stretched optical film if the stretched optical film has properties such as mechanical strength and total light transmittance within an allowable range. .

  Although the width | variety of the film before extending | stretching used for the manufacturing method of this invention is not specifically limited, 450-2000 mm, Preferably it can be 1000-1500 mm. The total thickness of the film is not particularly limited, but may have a gradient within the range of 40 to 400 μm, preferably 60 to 300 μm.

Although it will not specifically limit if it is transparent as a material which can be used for each layer of the film before extending | stretching used for the manufacturing method of this invention, A thermoplastic resin, a thermoplastic elastomer, etc. can be mentioned.
Thermoplastic resins include alicyclic olefin resin (norbornene resin), polycarbonate resin, polyethersulfone resin, polyethylene terephthalate resin, polyimide resin, acrylic resin, polysulfone resin, polyarylate resin, polyethylene resin, polyvinyl chloride resin, styrene Examples thereof include resins.
Examples of thermoplastic elastomers include aromatic vinyl-conjugated diene block copolymers such as styrene-butadiene block copolymers, hydrogenated styrene-butadiene block copolymers, styrene-isoprene copolymers, and hydrogenated styrene-isoprene copolymers. Examples thereof include a polymer, an ethylene-propylene elastomer, a thermoplastic polyester elastomer, and an ethylene-based ethylene ionomer resin.
Here, the multilayer film is preferably a multilayer film including a layer made of an acrylic resin and a layer made of a styrene resin, from the viewpoint of easily obtaining a desired retardation.

  The pre-stretch film can be obtained by a known method such as a cast molding method, an extrusion molding method, or an inflation molding method. Of these, the extrusion method is preferable because it has a small amount of residual volatile components and is excellent in dimensional stability. In particular, when a laminated film of two or more layers is used as the pre-stretch film, the laminated film can be obtained by a known method such as a coextrusion molding method, a film lamination method, or a coating method. Of these, the coextrusion method is preferred. The film before stretching may be the film obtained by such a method as it is, or may be a film subjected to any treatment such as surface treatment or preliminary stretching.

  The stretched optical film obtained by the production method of the present invention can be used alone or in combination with other members as a retardation plate or a viewing angle compensation film, such as a liquid crystal display device, an organic EL display device, a plasma display device, an FED (electric field). The present invention can be widely applied to (emission) display devices, SED (surface electric field) display devices, and the like.

Although the foregoing disclosure has described the invention with reference to the preferred embodiments for purposes of illustration, the invention is intended to be limited only by the scope of the claims and their full scope of equivalents. Various modifications and changes can be further made in the above embodiment.
For example, in the above embodiment, the link device that moves the gripper X1 and the gripper Y1 does not have a function of expanding and contracting the distance between adjacent grippers on each link device, and the distance between the grippers is constant. Although a specific description has been made and illustrated about what circulates on the rail in a state, the link device and the link device used in the manufacturing method of the present invention are not limited to this, and adjacent to each link device such as a known pantograph structure The link device having a structure for expanding and contracting the gap between the grippers to be stretched may be used to perform the stretching in which the stretching in the longitudinal direction by the structure is performed. Further, in order to obtain a stretched optical film having a more uniform thickness, the thickness and optical characteristics of the stretched optical film to be carried out are measured, and according to the measurement results, the stretching conditions such as the rotation speed of the sprocket are determined according to Each of these may be controlled independently.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited only to the following Examples.

<Example 1>
(1-1: stretching machine)
As a stretching machine for carrying out biaxial stretching, an oblique stretching system stretching machine 1 schematically shown in FIG. 1 was prepared. The stretching machine 1 is installed in an oven that keeps the working environment temperature constant, and includes a pair of loop-shaped link devices 101L and 101R, and conveys the unstretched film 11B in the horizontal direction by the link device. This is an apparatus for obtaining the stretched optical film 11A. A rail (not shown) for guiding each link device was composed of 12 blocks connected by joints, and the length of each block was 2000 mm. As shown in FIG. 1, the rails were arranged to be obliquely stretched by bending the film traveling direction to the left.

(1-2: Production and supply of film before stretching)
Polystyrene resin as inner layer resin (manufactured by NOVA CHEMICAL, trade name “DILARK D332”, maleic anhydride copolymer) and acrylic resin as outer layer resin (manufactured by Sumitomo Chemical, product name “SUMIPEX HT55Z”) in a molten state By extruding into a sheet form from a T-die and cooling, a multilayer film of two types and three layers having a width of 1200 mm and an inner layer resin sandwiched between outer layer resins was continuously produced as a film before stretching. The total thickness and inner layer thickness of the obtained unstretched film were measured using an in-line infrared film thickness meter (manufactured by Kurabo Industries, product name RX-200), with an in-line measurement interval of 5 mm in the width direction, and a line speed of 5 m / min. The results of average values measured 254 times in the film width direction are shown in FIGS. 8 and 9, respectively. 8 to 17, the “film width” on the horizontal axis indicates a value obtained by measuring the distance from the left end of the film to the measurement point in the width direction of the film when observing from the upstream to the downstream in the flow direction. As shown in these figures, the film before stretching had a thickness gradient that was thicker at the right end than at the left end.

(1-3: Production of stretched optical film)
The supplied unstretched film was supplied to a stretching machine, and oblique stretching by the stretching machine was started. The gripping with the gripper was performed so that at least a region of 200 to 1000 mm in the width direction of the film before stretching was included in the stretching region. The draw ratio was 1.8 times, and the ears on both sides were cut off, leaving a region corresponding to the region of 200 to 1000 mm in the width direction of the film before stretching to obtain a stretched optical film having a width of 1350 mm. The total thickness and inner layer thickness of the obtained stretched optical film were measured using an in-line infrared film thickness meter (trade name: RX-200, manufactured by Kurabo Industries Co., Ltd.) with an in-line measurement interval of 5 mm in the width direction and a line speed of 5 m / min. Then, the average value was obtained by measuring 254 times in the film width direction. In addition, the in-plane retardation Re of the obtained stretched engineering film was measured using an in-line phase difference meter (manufactured by Oji Scientific Instruments: KOBRA-WIST / 2RT). The results are shown in FIGS. The angle formed by the in-plane slow axis of the obtained stretched optical film and the length direction of the film was 45 °.

  As is apparent from the results of FIGS. 10 to 12, according to the method for producing a stretched optical film of the present invention, it is possible to obtain a film with little thickness gradient and Re variation in the width direction of the film by stretching by oblique stretching. it can.

<Comparative Example 1>
In the step (1-2), except that the shape of the opening of the T die was changed, the same operation as in Example 1 was performed to produce a pre-stretch film, which was stretched to obtain a stretched optical film. The total thickness and inner layer thickness of the film before stretching, and the measurement results of the total thickness, inner layer thickness and Re of the stretched optical film are shown in FIGS.

  As is clear from the results of FIGS. 13 to 17, in this comparative example in which the thickness gradient in the width direction of the film before stretching was not provided, the thickness gradient in the width direction of the obtained stretched optical film and the variation in Re were performed. It appeared larger than Example 1.

1 Stretcher 2 Film inner layer 3 Film outer layer 12R, 12L Sprocket 13R, 13L Sprocket 101R, 101L Link device 110R, 110L Gripper 11A Stretched optical film 11B Film before stretching D1 Film supply direction D3 Film unloading direction E1R, E2R Film right end E1L, E2L film left edge

Claims (3)

Using a stretching machine that includes a pair of gripping portions composed of a gripper X1 and a gripper Y1 that grips both ends of the long pre-stretch film, the movement distance of the gripper X1 and the movement of the gripper Y1 Stretching optical film for producing a long stretched optical film having a slow axis at an angle of more than 0 ° and less than 90 ° with respect to its longitudinal direction by obliquely stretching the pre-stretched film based on the distance A method for producing a film,
A step of continuously supplying the pre-stretching film to the stretching machine (A);
A step (B) of gripping the ends of the pre-stretch film with the grippers X1 and Y1, respectively;
A step of stretching the pre-stretching film by moving the grippers X1 and Y1, so that the travel distance of the gripper X1 during stretching is longer than the travel distance of the gripper Y1 during stretching Including the step (C) of oblique stretching,
The thickness gradient in the width direction is such that the total thickness of the film before stretching or the thickness of at least one layer constituting the film before stretching is thicker on the side gripped by the gripper X1 than on the side gripped by the gripper Y1. A process for producing a stretched optical film.   The method for producing a stretched optical film according to claim 1, wherein the pre-stretch film is composed of a plurality of layers, and at least one of the plurality of layers has a thickness gradient in the width direction.   The manufacturing method of the stretched optical film of Claim 2 whose layer which has the thickness gradient of the said width direction is a layer to which optical anisotropy is provided in the said process (C).

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