JP2011245624A - Method for manufacturing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film which is free from occurrence of peeling unevenness in the film width direction produced upon roll vertical stretching regarding a process for subsequently producing biaxially stretched film for optical use.SOLUTION: The method for producing a film is used when a film 5 made of a thermoplastic resin is subjected to roll vertical stretching by two stretching rolls 1, 2 arranged at intervals. Nip rolls 3, 4 are arranged in such a manner that a holding part 6 is made into the edge part on the side of the stretching roll 2 in a contact region 8, and further, a holding part 7 is made into the edge part on the side of the stretching roll 1 in a contact region 9. In this way, the roll vertical stretching is performed in such a manner that the contact time t between the film and the stretching roll 1 when the film 5 is stretched satisfies 0.5s<t<2.5s, and also, the surface temperature T of the stretching roll 1 satisfies the film Tg-6°C<T<the film Tg.

Description

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

  In recent years, along with the downsizing, thinning, and weight reduction of notebook computers, word processors, mobile phones, personal digital assistants, etc., liquid crystal display devices that take advantage of the light weight and compactness of these electronic devices have come to be widely used. It is coming. In the liquid crystal display device, various films such as a polarizing film are used in order to maintain the display quality. In order to further reduce the weight of liquid crystal display devices for portable information terminals and mobile phones, liquid crystal display devices using resin films instead of glass substrates have been put into practical use.

  Plastic films used in devices that handle polarized light such as liquid crystal display devices are required to have appropriate mechanical characteristics and highly controlled in-plane and birefringence in the film thickness direction. Biaxial stretching is required to improve the mechanical properties of the plastic film and to impart birefringence in the film plane and in the film thickness direction with high control. In this case, the biaxial stretching is generally sequential biaxial stretching composed of longitudinal and lateral sequential stretching. Here, a roll longitudinal stretching method or a zone longitudinal stretching method is used as the first longitudinal stretching method in the sequential biaxial stretching.

  With the roll longitudinal stretching method, for example, Patent Document 1 describes a technique for stretching a polyamide film by a roll longitudinal stretching method. However, in this method, when the film heated by the roll peels from the stretching roll, peeling unevenness occurs in the width direction due to the adhesiveness of the film.

  The zone longitudinal stretching method is a method of conveying a film by two sets of nip rolls provided with a heating zone between them as described in Patent Document 2, for example. In this method, the film is stretched by heat in a heating zone provided between two sets of nip rolls. According to this method, since stretching is performed in a heating zone provided between two nip rolls, there is no need for heating with a roll being conveyed, and a film having good film surface properties can be obtained. However, in the zone longitudinal stretching method, it is difficult to precisely control the support of the film in the zone, and an expensive equipment cost is required to obtain optical homogeneity.

  As a method for solving peeling unevenness in roll longitudinal stretching, for example, as described in Patent Document 3, a method of longitudinal stretching of a film in which an infrared heater is installed between stretching rolls has been reported. In this method, an infrared heater is installed between the stretching rolls, and the film is warmed and stretched, so there is no need to heat the film with the rolls, so that peeling unevenness does not occur in the width direction when the film peels from the stretching roll. . However, in this method, the installation of the infrared heater makes the equipment complicated and expensive, and stretching unevenness occurs in the film width direction due to temperature variation of the infrared heater.

Japanese Patent Laid-Open No. 9-286054 JP 2000-147257 A JP 2007-268971 A

  An object of the present invention is to provide a method for producing an optical film in which there is no occurrence of peeling unevenness in the film width direction that occurs during roll longitudinal stretching in order to solve the above-described problems of the prior art.

  That is, the present invention relates to the following.

  (I) For a film made of an amorphous thermoplastic resin, roll longitudinal stretching using a first stretching roll and a first nip roll adjacent to the first stretching roll, a second stretching roll and a second nip roll adjacent to the first stretching roll In the method for producing an optical film including a stretching step for performing the treatment, the contact time t between the film and the first stretching roll is 0.5 seconds <t <2.5 seconds, and the surface temperature T of the first stretching roll is ( Tg-6) A method for producing an optical film, wherein the film is longitudinally stretched at a temperature of T ≦ T ≦ Tg ° C. (Tg is a glass transition temperature).

  (Ii) When the distance L between the contact area between the film and the first stretching roll and the contact area between the film and the second stretching roll is the radius R1 of the first stretching roll and the radius R2 of the second stretching roll (R1 + R2) ) <L <(R1 + R2) × 10. The method for producing an optical film as described in (i).

  (Iii) The production of the optical film as described in (i) or (ii), wherein the draw ratio of the roll longitudinal drawing treatment by two drawing rolls is about 1.1 times or more and about 3 times or less Method.

(Iv) The method for producing an optical film as described in (iii), wherein the amorphous thermoplastic resin is an acrylic resin.
(V) The acrylic resin is an imide resin having a unit represented by the following general formula (1) and a unit represented by the following general formula (2): (iv) Manufacturing method for optical film.

(However, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents hydrogen, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(However, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents hydrogen, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

  In the manufacturing method of the optical film which concerns on this invention, generation | occurrence | production of the peeling pattern which generate | occur | produces when a film peels from a 1st extending | stretching roll is suppressed, and there exists an effect that a beautiful external appearance film can be manufactured.

It is the schematic which shows an example of the roll longitudinal stretch method. It is the schematic which shows an example of the roll longitudinal stretch method. It shows an example of an embodiment of the present invention and is a schematic diagram showing a roll longitudinal stretching method.

  The method for producing an optical film according to the present invention includes a first stretching roll, a first nip roll adjacent to the first stretching roll, a second stretching roll, and a first stretching roll adjacent to the first stretching roll, with respect to the film made of an amorphous thermoplastic resin. In the method for producing an optical film including a stretching process in which a roll longitudinal stretching process is performed using a two-nip roll, the contact time t between the film and the first stretching roll is 0.5 seconds <t <2.5 seconds, and the first The surface temperature T of one stretching roll is characterized by performing roll longitudinal stretching treatment with film Tg−6 ° C. <T <film Tg.

  The present invention will be described below.

First, an unstretched melt-extruded acrylic resin film will be described. The acrylic resin is not particularly limited, and examples thereof include a glutaric anhydride resin, a resin having a lactone ring structure, and a glutarimide resin. Although it does not restrict | limit especially as glutaric anhydride resin, It can manufacture according to the method of Unexamined-Japanese-Patent No. 2007-254703, etc. The resin having a lactone ring structure can be produced according to the method described in JP-A-2008-9378.
The glutarimide resin will be described in detail below. Specific examples of the glutarimide resin include the following general formula (1).

(Wherein R1 and R2 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and R3 is an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or This is a substituent containing an aromatic ring having 5 to 15 carbon atoms.)
(Hereinafter also referred to as “glutarimide unit”),
The following general formula (2)

(Wherein R4 and R5 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and R6 is an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or This is a substituent containing an aromatic ring having 5 to 15 carbon atoms.)
A glutarimide resin containing a unit represented by (hereinafter also referred to as “(meth) acrylic acid ester unit”) can be suitably used.

  Moreover, the said glutarimide resin is the following general formula (3) as needed.

(In the formula, R7 is hydrogen or an alkyl group having 1 to 8 carbon atoms, and R8 is an aryl group having 6 to 10 carbon atoms.)
(Hereinafter also referred to as “aromatic vinyl unit”).

  In the general formula (1), R1 and R2 are each independently hydrogen or a methyl group, R3 is preferably hydrogen, a methyl group, a butyl group, or a cyclohexyl group, and R1 is a methyl group R2 is more preferably hydrogen and R3 is more preferably a methyl group.

  The glutarimide resin may include only a single type as a glutarimide unit, or may include a plurality of types in which R1, R2, and R3 in the general formula (1) are different.

  The glutarimide unit can be formed by imidizing the (meth) acrylic acid ester unit represented by the general formula (2).

  In addition, acid anhydrides such as maleic anhydride, or half esters of such acid anhydrides and linear or branched alcohols having 1 to 20 carbon atoms; acrylic acid, methacrylic acid, maleic acid, maleic anhydride, The glutarimide unit can also be formed by imidizing an α, β-ethylenically unsaturated carboxylic acid such as itaconic acid, itaconic anhydride, crotonic acid, fumaric acid or citraconic acid.

  In the general formula (2), R4 and R5 are each independently hydrogen or a methyl group, R6 is preferably hydrogen or a methyl group, R4 is hydrogen, R5 is a methyl group, R6 is more preferably a methyl group.

  The glutarimide resin may contain only a single type as a (meth) acrylic acid ester unit, or a plurality of types in which R4, R5, and R6 in the general formula (2) are different. Also good.

  The glutarimide resin preferably contains styrene, α-methylstyrene or the like, more preferably styrene, as the aromatic vinyl structural unit represented by the general formula (3).

  Moreover, the said glutarimide resin may contain only the single kind as an aromatic vinyl structural unit, and may contain the several kind from which R7 and R8 differ.

  In the glutarimide resin, the content of the glutarimide unit represented by the general formula (1) is not particularly limited, and is preferably changed depending on, for example, the structure of R3.

  Generally, the content of the glutarimide unit is preferably 1% by weight or more of the glutarimide resin, more preferably 1% to 95% by weight, and 2% to 90% by weight. More preferably, it is more preferably 3 to 80% by weight.

  If the content of the glutarimide unit is within the above range, the heat resistance and transparency of the resulting glutarimide resin may decrease, or the moldability and mechanical strength when processed into a film may decrease. There is no.

  On the other hand, when the content of the glutarimide unit is less than the above range, the resulting glutarimide resin tends to be insufficient in heat resistance or impaired in transparency. On the other hand, if the amount is larger than the above range, the heat resistance and melt viscosity are unnecessarily increased, the molding processability is deteriorated, the mechanical strength during film processing becomes extremely brittle, or the transparency is impaired. Tend.

  In the glutarimide resin, the content of the aromatic vinyl unit represented by the general formula (3) is not particularly limited, and can be appropriately set according to required physical properties. Depending on the application used, the content of the aromatic vinyl unit represented by the general formula (3) may be zero. When the aromatic vinyl unit represented by the general formula (3) is included, it is preferably 10% by weight or more, preferably 10% by weight to 40% by weight, based on the total repeating unit of the glutarimide resin. More preferably, it is more preferably 15 to 30% by weight, and particularly preferably 15 to 25% by weight.

  If the content of the aromatic vinyl unit is within the above range, the resulting glutarimide resin will not have insufficient heat resistance, and the mechanical strength during film processing will not decrease.

  On the other hand, when there is more content of an aromatic vinyl unit than the said range, there exists a tendency for the heat resistance of the glutarimide resin obtained to be insufficient.

  The glutarimide resin may be further copolymerized with other units other than the glutarimide unit, the (meth) acrylic acid ester unit, and the aromatic vinyl unit, if necessary.

  As other units, for example, nitrile monomers such as acrylonitrile and methacrylonitrile, and maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide are copolymerized. A structural unit can be mentioned.

  These other units may be directly copolymerized or graft copolymerized in the glutarimide resin.

The weight average molecular weight of the glutarimide resin is not particularly limited, but is preferably 1 × 10 ^{4 to} 5 × 10 ⁵ . If it is in the said range, moldability will not fall or the mechanical strength at the time of film processing will not be insufficient.

  On the other hand, when the weight average molecular weight is smaller than the above range, the mechanical strength when formed into a film tends to be insufficient. Moreover, when larger than the said range, the viscosity at the time of melt-extrusion is high, there exists a tendency for the moldability to fall and for the productivity of a molded article to fall.

  The glass transition temperature of the glutarimide resin is not particularly limited, but is preferably 110 ° C. or higher, and more preferably 120 ° C. or higher. When the glass transition temperature is within the above range, the applicable range of the obtained thermoplastic resin composition can be expanded.

  Although the manufacturing method in particular of the said glutarimide resin is not restrict | limited, For example, the method etc. which are described in Unexamined-Japanese-Patent No. 2008-273140 are mention | raise | lifted.

  Next, an unstretched acrylic resin film is demonstrated. Although there is no restriction | limiting in particular regarding the manufacturing method of an unstretched acrylic resin film, It is preferable to use the method described in Unexamined-Japanese-Patent No. 2002-221312.

  Next, roll longitudinal stretching will be described. Roll longitudinal stretching is a method in which a film is stretched in the traveling direction while being heated to a predetermined temperature by a low peripheral speed roll and a high peripheral speed roll which are close to each other. The method of roll longitudinal stretching is not particularly limited, and examples thereof include single-stage stretching in which stretching is performed with a pair of rolls having different circumferential speed differences, and multi-stage stretching in which stretching is performed with two or more pairs of stretching rolls. The stretching is preferably performed by one-stage stretching.

  For example, as shown in FIG. 1, when the film 5 is sandwiched by the nip roll 3 and the nip roll 4 that are close to the stretching roll 1 and the stretching roll 2, respectively, as shown in FIG. There are a method in which the film is in contact with each roll between the sandwiching portions and a method in which the film is not in contact with each roll between the sandwiching portions as shown in FIG. 2, but in the present invention, as shown in the latter A method is used in which the film does not come into contact with each roll between the holding parts. In particular, as shown in FIG. 3, the surface including the rotation axis of the stretching roll 1 and the stretching roll 2 and the film transport surface are parallel to each other, and the rotation direction of the stretching roll 1 and the stretching roll 2 is the same direction. It is preferable to use such a stretching method.

  Even if it is multistage stretching, it is within the scope of the present invention as long as a set of stretching rolls is configured such that the film does not contact each roll between the sandwiching portions as described above.

  In the present invention, the contact time t of the first stretching roll is 0.5 seconds ≦ t ≦ 2.5 seconds. “Contact time” is defined as the time during which the film being conveyed is in contact with the first stretching roll. That is, it is defined by the following formula.

(Contact time) = (Distance where the film is in contact with the first stretching roll) / (Speed of the first stretching roll)
Here, the speed of the first stretching roll is the outer peripheral speed of the first stretching roll, and is defined by the following equation.

(Speed of first stretching roll) = (Outer peripheral length of first stretching roll) × (Rotation speed of first stretching roll)
The distance that the film is in contact with the first stretching roll is the point at which the film starts to contact the first stretching roll (contact), that is, the point at which the film is separated from the first stretching roll (contact), that is, the nipping with the nip roll. The distance to the part.

  The contact time is particularly preferably 0.5 seconds ≦ t ≦ 2.5 seconds. If it is less than 0.5 seconds, the film breaks due to insufficient preheating, and if it is more than 2.5 seconds, uneven peeling occurs.

  In the present invention, the surface temperature T of the first stretching roll is (Tg−6) ° C. ≦ T ≦ Tg ° C. (Tg is a glass transition temperature). When the temperature is lower than (Tg-6) ° C., the film breaks due to insufficient preheating, and when the temperature is higher than Tg, peeling unevenness occurs.

  In the present invention, peeling unevenness (peeling pattern) is a phenomenon in which stripes in the film width direction occur at equal intervals in the film longitudinal direction, and the film thickness is not stabilized by stretching in a state where the film temperature is not uniform. Such stretching unevenness is different.

In the present invention, the distance L between the contact area between the film and the first stretching roll and the contact area between the film and the second stretching roll is set such that the radius of the first stretching roll is R1, and the radius of the second stretching roll is R2. Then
(R1 + R2) <L <(R1 + R2) × 10
It is preferable that

  Next, the definition of the distance L between clamping parts is demonstrated using FIG. In the present invention, the film is conveyed and longitudinally stretched by sandwiching the film by both stretching rolls arranged at regular intervals and the nip rolls respectively close to the stretching rolls. At this time, the distance between the both sandwiching portions is L.

  The draw ratio is defined by the peripheral speed ratio between the first draw roll and the second draw roll. That is, it is expressed by the following formula.

Stretch ratio = (peripheral speed of second stretch roll) / (peripheral speed of first stretch roll)
The preferred stretching ratio depends on the stretching temperature, but is preferably selected in the range of about 1.1 times to about 3.0 times, more preferably about 1.3 times to about 2.5 times, About 1.5 times or more and about 2.0 times or less are particularly preferable. For example, when the draw ratio is about 1.1 times or less, the film is not substantially stretched in the stretching step, and thus the mechanical properties of the film cannot be sufficiently improved. Thereby, the stretched film is easily broken. Moreover, when a draw ratio is about 3.0 times or more, the film before extending | stretching will become too thick, and will fracture | rupture at the time of unstretched film manufacture.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by this.
(Production Example 1)
A resin was produced using a tandem reaction extruder in which two extrusion reactors were arranged in series. As for the tandem type reactive extruder, the first extruder (1) and the second extruder (2) are both in the same direction meshing type with a diameter of 75 mm and L / D (ratio of the length L to the diameter D of the extruder) of 74. Using a twin-screw extruder, the raw material resin was supplied to the raw material supply port of the first extruder using a constant weight feeder (manufactured by Kubota Corporation). Moreover, the pressure reduction degree of each vent in the 1st extruder and the 2nd extruder was set to -0.095 MPa. Furthermore, the pressure control mechanism in the part connects the first extruder and the second extruder with a pipe having a diameter of 38 mm and a length of 2 m, and connects the resin discharge port of the first extruder and the raw material supply port of the second extruder. A constant flow pressure valve was used. The resin (strand) discharged from the second extruder was cooled by a cooling conveyor and then cut by a pelletizer to form pellets. Here, the outlet of the first extruder, the first extruder and the second extruder are used to adjust the pressure in the part connecting the resin discharge port of the first extruder and the raw material supply port of the second extruder, or to determine the fluctuation of the extrusion. A resin pressure gauge was provided at the center of the machine connecting part and at the outlet of the second extruder.

   Regarding the first extruder, a polymethyl methacrylate resin (Mw: 105,000) was used as a raw material resin, and monomethylamine was used as an imidizing agent to produce an imide resin intermediate 1. At this time, the maximum temperature of the extruder was 280 ° C., the screw rotation speed was 55 rpm, the raw material resin supply amount was 150 kg / hour, and the addition amount of monomethylamine was 2.0 parts with respect to 100 parts of the raw material resin. Moreover, the constant flow pressure valve was installed just before the 2nd extruder raw material supply port, and the 1st extruder monomethylamine press-fit part pressure was adjusted so that it might be set to 8 Mpa. Regarding the second extruder, after devolatilizing the imidization reaction reagent and by-products remaining in the rear vent and vacuum vent, a mixed solution of dimethyl carbonate and triethylamine is added as an esterifying agent to produce an imide resin intermediate 2 did. At this time, each barrel temperature of the extruder was 260 ° C., the screw rotation speed was 55 rpm, the addition amount of dimethyl carbonate was 3.2 parts with respect to 100 parts of the raw material resin, and the addition amount of triethylamine was 0.2 parts with respect to 100 parts of the raw material resin. 8 parts. Furthermore, after removing the esterifying agent with a vent, the resin composition was obtained by extruding from a strand die, cooling in a water tank, and pelletizing with a pelletizer. The imidation ratio of this resin composition was 3.7%, the acid value was 0.29 mmol / g, and the amount of carboxylic acid was 0.05 mmol / g.

Here, the imidization rate is a value derived from O-CH3 proton of methyl methacrylate in the vicinity of 3.5 to 3.8 ppm by performing 1H-NMR measurement of resin using ¹ H-NMR BRUKER Avance III (400 MHz). From the peak area A and the peak area B derived from the N—CH 3 proton of glutarimide in the vicinity of 3.0 to 3.3 ppm, it was determined by the following formula.

I% = B / (A + B) × 100
The obtained pellets were dried at 100 ° C. for 5 hours and then extruded at 240 ° C. using a 40 mm single screw extruder and a 400 mm wide T-die to obtain an unstretched acrylic resin film having an average thickness of 130 μm and a width of 300 mm. . After forming this unstretched film, the film may be temporarily stored or moved as necessary, and then the film may be stretched.

(Examples 1-4) and (Comparative Examples 1-3)
The obtained film was subjected to roll longitudinal stretching by the longitudinal stretching step in the present invention. The first stretching roll, the second stretching roll, and the nip roll in the longitudinal stretching process of this example were in the positional relationship described in FIG. The film width is 1000 mm. The radius R1 of the first stretching roll and the radius R2 of the second stretching roll are both 100 mm. As shown in FIG. 3, a stretching roll and a nip roll having a smaller radius than the stretching roll are arranged so that the film transport path is parallel to the plane including the rotation axis of both stretching rolls. The film was sandwiched by nip rolls close to the rolls, respectively, so that the film was transported and longitudinally stretched. And both extending | stretching rolls were the conveyance directions of a film, and were mutually rotated in the same direction. Further, the sandwiching portion interval L was set to 250 mm.

  And according to the conditions of Examples 1 to 4 in the table shown in Table 1, the film obtained in Production Example 1 was longitudinally stretched, and peeling unevenness evaluation in the film width direction during longitudinal stretching was performed. Comparative Examples 1 to 3 also performed the above evaluation.

In Table 1, “contact time” is defined as the time during which the film being conveyed is in contact with the first stretching roll. That is, it is defined by the following formula.
(Contact time) = (Distance where the film is in contact with the first stretching roll) / (Speed of the first stretching roll)
Here, the speed of the first stretching roll is the outer peripheral speed of the first stretching roll, and is defined by the following equation.
(Speed of first stretching roll) = (Outer peripheral length of first stretching roll) × (Rotation speed of first stretching roll)
In Table 1, “first stretching roll surface temperature” refers to a temperature obtained by measuring the surface of the first stretching roll with a contact thermometer.

  In Table 1, the “peeling pattern observation result” is a result of observing the surface of the stretched film in each Example and Comparative Example, where “◯” indicates a state where no peeling pattern is generated, and “×” indicates the entire film width direction. This is a state where a peeling pattern is generated, and Δ is an evaluation method in which a state where peeling unevenness is partially generated in the film width direction is observed. Here, peeling unevenness is a phenomenon in which stripes in the film width direction occur at regular intervals in the film longitudinal direction.

  From Table 1, the evaluation results in Examples 1 to 4 and Comparative Examples 1 to 3 are verified. First, in Examples 1 to 3 in which the surface temperature of the first stretching roll was Tg-6 ° C., no peeling unevenness occurred until the contact time was 0.5 seconds to 2.5 seconds. Further, in Example 4 in which the surface temperature of the first stretching roll was film Tg, no peeling unevenness occurred. However, in Comparative Examples 1 and 2 in which the surface temperature of the first stretching roll is film Tg + 2 ° C., peeling unevenness occurs at a contact time of 0.5 seconds to 2.5 seconds. In Comparative Example 3 in which the surface temperature of the first stretching roll was film Tg-8 ° C., the film was broken during stretching and could not be stretched. That is, when the contact time between the film and the first stretching roll is 0.5 seconds to 2.5 seconds, if the first stretching roll surface temperature is film Tg-6 ° C. to film Tg, the film is not broken and is stably stretched. It can be seen that no peeling unevenness occurs.

1. Stretching roll Stretch roll 2. Nip roll 4. 4. Nip roll Film 6. 6. Clamping part Nipping part 8. Contact area

Claims (5)

  The film made of an amorphous thermoplastic resin is subjected to roll longitudinal stretching using a first stretching roll and a first nip roll adjacent thereto, a second stretching roll and a second nip roll adjacent thereto. In the method for producing an optical film including a stretching step, the contact time t between the film and the first stretching roll is 0.5 seconds <t <2.5 seconds, and the surface temperature T of the first stretching roll is (Tg-6). ) A method for producing an optical film, wherein the film is longitudinally stretched at a temperature of C ≦ T ≦ Tg ° C. (Tg is a glass transition temperature).   When the distance L between the contact area between the film and the first stretching roll and the contact area between the film and the second stretching roll is the radius R1 of the first stretching roll and the radius R2 of the second stretching roll, (R1 + R2) <L <(R1 + R2) × 10> The method for producing an optical film according to claim 1, wherein:   The method for producing an optical film according to claim 1 or 2, wherein the draw ratio of the roll longitudinal drawing treatment by two drawing rolls is about 1.1 times or more and about 3 times or less.   The method for producing an optical film according to claim 3, wherein the amorphous thermoplastic resin is an acrylic resin. The acrylic resin is an imide resin having a unit represented by the following general formula (1) and a unit represented by the following general formula (2). A method for producing an optical film.

(However, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents hydrogen, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(However, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents hydrogen, an alkyl group having 1 to 18 carbon atoms, or a cycloalkyl having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

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