JP2007010883A - Method for manufacturing retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a retardation film having high retardation and uniform retardation in the plane and thickness directions, and without causing substantial display irregularity within the plane when built in a liquid crystal display device. <P>SOLUTION: The method for manufacturing a retardation film is characterized in that an amorphous thermoplastic resin film having substantially no orientation is uniaxially stretched in the width direction by a tenter, heat treated, cooled, and then the stretched film is released from clips gripping the film ends, and the film is further re-heat treated by an air floating type sheet heat treating device at a temperature T (°C) and a conveyance tension F (N/m/μm) satisfying formulae (1):Tg-20≤T≤Tg+20 and (2) 0<F≤0.5, wherein Tg (°C) represents a glass transition temperature of the amorphous thermoplastic resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an optically biaxial retardation film having a uniform retardation and high optical compensation used for a liquid crystal display device.

  In recent years, a liquid crystal display device has been widely used in place of a CRT of a cathode ray tube system. A liquid crystal display device realizes display by utilizing the electro-optical characteristics of liquid crystal molecules. However, since liquid crystals inherently have optical anisotropy, optical distortion due to birefringence and visual direction Viewing angle dependency such as coloration of the display occurs due to the modulation by. In order to eliminate such drawbacks, a retardation plate is widely used as an optical compensation film, and generally has a retardation (phase difference) value in the range of 50 to 800 nm when light having a wavelength of 550 nm is incident. Has been.

  The display quality of liquid crystal display devices has been remarkably improved. In particular, in large screen applications such as liquid crystal televisions and monitors, vertical alignment type liquid crystals generally known as VA liquid crystals having features such as a wide viewing angle and high contrast are becoming mainstream. .

  However, as the name suggests, this liquid crystal is oriented vertically, so that the refractive index ellipsoid is short in length to compensate for the light that has passed through it, and generally has a biaxiality called negative ampange. It is necessary to have. The retardation film here specifically refers to a film having an Nz coefficient of 1.3 or more.

  Conventionally, various methods for producing such a biaxial retardation film have been proposed, but it is not possible to obtain a retardation film having satisfactory quality by a method using only longitudinal uniaxial stretching or lateral uniaxial stretching. From the viewpoint of emphasizing production efficiency, a sequential biaxial stretching method in which a thermoplastic resin film is stretched in the longitudinal direction and then in the transverse direction has become the mainstream (see, for example, Patent Document 1).

  In particular, as the horizontal uniaxial stretching method, the two ends of the thermoplastic resin film in the width direction are gripped by a plurality of pairs of clips, and the two rails installed so as to be gradually widened on both sides of the thermoplastic resin film are A tenter transverse uniaxial stretching method that orients the molecular main chain of the thermoplastic resin in the width direction by running the clip is widely used. However, this method has a problem that uniform stretching cannot be performed over the entire width of the film. It has been.

  That is, when the film is heated and stretched, the hot air ejected from the nozzle arranged in the film width direction has a non-uniform temperature distribution in the width direction. In other words, the central portion of the nozzle is high, but the end portion becomes lower. Therefore, since the material temperature of the heated film is high in the center and low at the end, the center of the film is preferentially stretched immediately after the start of film widening, and the stretching of the end is delayed. For this reason, at the end of widening, in an arbitrary part in the width direction, each becomes a non-uniform stretch with different substantial stretch ratios. As a result, different retardations appear at the center and the end in the width direction, and non-uniform optical in the film plane. Therefore, sufficient optical compensation performance cannot be exhibited.

  As a method of uniformly controlling the hot air temperature in the width direction, mainly for heating equipment, such as installing a hot air rectifying plate in the drawing furnace, diversifying the flow of hot air from the heat source, and devising the nozzle shape and mounting position However, it is not always sufficient in the retardation film drawing process that requires high temperature distribution accuracy (see, for example, Patent Document 2).

  In this way, in the tenter transverse uniaxial stretching method in which unstable and non-uniform temperature distribution is unavoidable in the width direction of the film, it has a uniform retardation and optically biaxiality with high optical compensation accuracy. It was difficult to obtain a stretched film.

Japanese Patent Laid-Open No. 2002-148438 (particularly, column of conventional technology) Japanese Patent Laid-Open No. 5-96619

  The present invention has been made in view of the above-described problems of the prior art, and the in-plane and thickness-direction retardation is uniform, and substantial display unevenness does not occur in the surface when incorporated in a liquid crystal display device. It aims at providing the manufacturing method of retardation film.

The method for producing a retardation film of the present invention comprises: stretching an amorphous thermoplastic resin film uniaxially in the width direction by a tenter; after passing through heat treatment and cooling treatment, releasing the stretched film from a clip that holds the film edge; The heat treatment is performed again at a temperature T (° C.) and a conveying tension F (N / m / μm) satisfying the following expressions (1) and (2) by an air floating sheet heat treatment apparatus.
Tg-20 ≦ T ≦ Tg + 20 (1)
0 <F ≦ 0.5 (2)
However, Tg shows the glass transition temperature of an amorphous thermoplastic resin.

  The amorphous thermoplastic resin used in the present invention is excellent in transparency, heat resistance and matching properties with liquid crystal, has a low intrinsic birefringence, a low photoelastic coefficient, etc., and has suitable characteristics as an optical member. The resin is not particularly limited as long as it is a resin having substantially no crystallinity. For example, a cyclic olefin resin having an alicyclic hydrocarbon structure in the main chain or side chain and a maleimide resin having a maleimide structure are particularly preferably used.

  The norbornene resin, which is a kind of the above cyclic olefin resin, is a resin that has been conventionally studied as an optical material, for example, a ring-opening (co) polymer of a norbornene monomer, a norbornene monomer, and an olefin monomer. Addition copolymers, norbornene-based addition copolymers, and derivatives thereof. These norbornene resins may be used alone or in combination of two or more. Of the norbornene-based resins, a ring-opening (co) polymer in which a carbon-carbon unsaturated double bond necessarily remains in the molecule or a carbon-carbon unsaturated double bond in the molecule depending on the monomer species used. In the case of employing an addition (co) polymer in which is remained, it is preferably saturated by hydrogenation from the viewpoint of weather resistance.

  The norbornene-based monomer constituting the norbornene-based resin is not particularly limited as long as it is a monomer having a norbornene ring. For example, bicyclic rings such as norbornene and norbornadiene; tricyclic rings such as dicyclopentadiene and dihydrodicyclopentadiene Tetracycles such as tetracyclododecene; pentacycles such as cyclopentadiene trimer, heptacycles such as tetracyclopentadiene; alkyls such as methyl, ethyl, propyl and butyl, alkenyls such as vinyl, and ethylidene Substituents such as alkylidene such as phenyl, tolyl, naphthyl, etc .; further, ester groups, ether groups, cyano groups, halogen groups, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carboxylic acid groups, amino groups, Hydroxyl group, silyl group, epoxy group, acrylic group, methacrylic group Groups containing elements other than carbon and hydrogen etc., include substitution products having a so-called polar group.

  Among these norbornene monomers, a polycyclic norbornene monomer having three or more rings is preferable because it is easily available, has excellent reactivity, and has excellent heat resistance of the obtained retardation film. Ring, tetracycle and pentacycle norbornene monomers are more preferred. In addition, a norbornene-type monomer may be used independently and 2 or more types may be used together.

  Examples of the α-olefin monomer include ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, and 1-hexene. , 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like, α-olefin monomers having 2 to 10 carbon atoms having high copolymerizability are preferable, and ethylene is more preferable. is there. When other α-olefin monomers are copolymerized with norbornene monomers, the presence of ethylene is preferable because the copolymerizability is increased.

The ring-opening (co) polymer of the norbornene-based monomer can be obtained according to a known ring-opening polymerization reaction. For example, the norbornene-based monomer is a halide of a metal such as ruthenium, rhodium, palladium, osmium, iridium, platinum, Using a catalyst system comprising nitric acid or an acetylacetone compound and a reducing agent, or a catalyst system comprising a metal halide such as titanium, tungsten or molybdenum, or an acetylacetone compound and an organoaluminum compound, in a solvent or without solvent. Usually, it is obtained by reacting at a polymerization temperature of −50 to 100 ° C. and a polymerization pressure of 0 to 5 MPa / cm ² .

The addition polymer of the norbornene monomers or the addition copolymer of the norbornene monomer and the olefin monomer can be obtained according to a known addition polymerization reaction. For example, these monomers are used in a solvent or without a solvent, and a vanadium compound. And an organoaluminum compound, preferably in the presence of a catalyst system comprising a halogen-containing organoaluminum compound, usually obtained by a reaction at a polymerization temperature of −50 to 100 ° C. and a polymerization pressure of 0 to 5 MPa / cm ^2. .

  When the number average molecular weight of the norbornene-based resin is small, the mechanical strength of the obtained retardation film is lowered. When the number average molecular weight is large, the moldability of the film may be hindered. It is preferably 5000 to 50000, more preferably 8000 to 30000, as measured by an association chromatography.

  The norbornene-based resin is, for example, the product name “ZEONOR” series from ZEON CORPORATION, the product name “ARTON” series from JSR, the product name “APEL” series from Mitsui Chemicals, and the product name “TOPAS” from TICONA. (TOPAS) "series etc.

  The maleimide-based resin is also a resin that has been conventionally studied as an optical application material, and includes, for example, a maleimide-olefin copolymer including the following component (A) and component (B), It can be obtained by a radical copolymerization reaction with olefins.

  Examples of the compound that gives component (A) include maleimide, N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn-butylmaleimide, Ni-butylmaleimide , N-s-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, and the like, and N- Methyl maleimide is preferred. Furthermore, these compounds can be used alone or in combination.

  Examples of the compound that gives the component (B) include olefins such as isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, 2-methyl-1-hexene, and of these, heat resistance, mechanical properties Isobutene is particularly preferred from the viewpoint of properties and transparency. Moreover, these compounds can be used 1 type or in combination of 2 or more types. The content of the component (A) is preferably 40 to 60 mol%, and more preferably 45 to 55 mol% of the entire copolymer.

  For the polymerization of these monomers, any known polymerization method such as bulk polymerization method, solution polymerization method, suspension polymerization method, or emulsion polymerization method can be employed. The precipitation polymerization method is particularly preferred from the viewpoint of the transparency and color tone of the obtained film.

  The maleimide-olefin copolymer described above can also be obtained by post-amidating a resin obtained by copolymerization of maleic anhydride and olefins with ammonia or alkylamine.

  The weight average molecular weight of the maleimide resin is not particularly limited, but is more preferably about 1,000 to 500,000 considering sheet formability and stretchability and the quality of the obtained film as a retardation film.

  In the above amorphous thermoplastic resin, UV absorbers such as benzophenone, benzotriazole, salicylic acid ester, cyanoacrylate, acrylonitrile, etc., phenol, phosphorus, etc. within the range that does not deteriorate the function of the retardation film Antioxidants of lactones; thermal degradation inhibitors such as lactones and phenols; aliphatic alcohol esters, polyhydric alcohol partial esters, partial ethers and other lubricants; amines and other antistatic agents May be.

  When the average thickness of the amorphous thermoplastic resin film is thin, it is difficult to develop a phase difference, and when it is thick, when used in a liquid crystal display device, the thickness of the liquid crystal panel is thick, so generally 30 to 200 μm is preferable. Preferably it is 40-150 micrometers.

  The amorphous thermoplastic resin film can be produced by, for example, supplying an amorphous thermoplastic resin to an extruder, melting and kneading it, and extruding it from a mold attached to the tip of the extruder into a thin film. Conventionally known methods such as a melt extrusion method for forming a film, a solution casting method in which a solution obtained by dissolving an amorphous thermoplastic resin in an organic solvent is cast on a drum, an endless belt, etc., and then the organic solvent is evaporated to form a film. Any molding method may be employed.

  When the thickness of the amorphous thermoplastic resin film is 80 μm or more, it is difficult to sufficiently evaporate and remove the organic solvent by the solution casting method. Therefore, it is preferable to manufacture the amorphous thermoplastic resin film by a melt extrusion method.

  In the method for producing a retardation film of the present invention, the amorphous thermoplastic resin film is uniaxially stretched in the width direction by a tenter (hereinafter simply referred to as lateral uniaxial stretching). At this time, it is preferable that the amorphous thermoplastic resin is substantially non-oriented, that is, the retardation value in the film plane and in the film thickness direction is close to zero. More specifically, each is preferably 20 nm or less, more preferably 10 nm or less.

  For the horizontal uniaxial stretching by the tenter, any conventionally known horizontal uniaxial tenter stretching method may be employed.For example, both ends of the amorphous thermoplastic resin film in the width direction are held by a tenter clip, and the tenter clip A method of widening and stretching the amorphous thermoplastic resin film in the width direction by gradually separating the interval in the width direction can be mentioned.

  And this horizontal uniaxial tenter stretching method was a preheating step for heating the amorphous thermoplastic resin film to a film temperature at which the amorphous thermoplastic resin film can be stretched, a stretching step for widening and stretching the amorphous thermoplastic resin film in the width direction, and a stretched process. It consists of a heat treatment step for reducing the bowing of the amorphous thermoplastic resin film and aligning the orientation, and a cooling step for fixing the orientation of the amorphous thermoplastic resin.

  In the preheating step, the amorphous thermoplastic resin film is heated to near the temperature at which it can be stretched, and may be heated to near the stretching temperature set in the stretching step. The substantially non-oriented amorphous thermoplastic resin sheet expands and deforms by heating and widens the sheet width, so that it relaxes up and down by its own weight while passing through the preheating step, and the inside of the furnace including the hot air nozzle In some cases, the material may come into contact with the material, but such a traveling trouble can be avoided by preliminarily expanding the clip rail width with respect to the seat width.

  If the temperature of the amorphous thermoplastic resin film in the widening region during the stretching process is low, the film may be cut during stretching or the tenter clip may be gripped. Therefore, when the glass transition temperature of the amorphous thermoplastic resin is Tg, Tg to Tg + 20 ° C. is preferable, and Tg + 2 to Tg + 10 ° C. is more preferable. Tg was measured by using a differential scanning calorimeter (trade name “DSC2920 Modulated DSC” manufactured by TA Instruments) under the following temperature program conditions as the glass transition temperature of the present invention. .

(Temperature program conditions)
Temperature was raised from room temperature to 50 ° C. at 10 ° C./min and held for 5 minutes, temperature from 50 ° C. to 200 ° C. was raised at 10 ° C./min and held at 200 ° C. for 5 minutes, from 200 ° C. to −50 ° C. The temperature was lowered at 10 ° C / min and held at -50 ° C for 5 minutes, and the temperature was raised from -50 ° C to 200 ° C at 10 ° C / min and held at 200 minutes for 5 minutes.

  In the present invention, the stretching time from the start of widening to the end of widening is preferably 10 to 100 seconds, more preferably 20 to 60 seconds. By setting the stretching time within this range, it is possible to correct the bowing that occurs in the widening step without significantly reducing the retardation due to thermal relaxation. If the length is longer than this, the retardation due to thermal relaxation becomes remarkable. If the length is shorter, the optical axis cannot be controlled to be parallel to the film width direction due to the remarkable bowing phenomenon. The film running stability in the stretching process is impaired.

  The draw ratio in the present invention may be determined as appropriate depending on the compensation retardation amount of the obtained retardation film, but if the draw ratio is low, the orientation direction may not be uniform, and conversely if too high, the center of the film Part is slack, the retardation value varies in the width direction, and the main orientation axis and thickness are non-uniform, so 1.2 to 2.5 times are preferable, more preferably 1.5 to 2.0 times. It is.

  If the stretching strain rate in the stretching step becomes small, the retardation value decreases due to thermal relaxation or the effect of controlling the bowing phenomenon decreases. Therefore, the stretching strain rate is preferably 300% / min or more. Since the thermoplastic resin film is cut or the tenter clip is detached, it is more preferably 400 to 1000% / min. In addition, by performing stretching at a high strain rate, it becomes possible to increase the rail opening angle and shorten the furnace length of the stretching zone.

  The heat treatment step is a step for reducing the bowing of the stretched amorphous thermoplastic resin film and aligning the orientation parallel to the film width direction. If the temperature of this step is too high, the retardation value decreases. Therefore, the temperature of this process is Tg-Tg + 10 degreeC, Comprising: It is preferable that it is temperature lower than the said extending | stretching temperature. In this step, it is also possible to further enhance the treatment effect by slightly relaxing or slightly stretching the film in the width direction.

  The cooling step is a step for fixing the orientation of polymer molecules formed in the stretched film by rapidly cooling the stretched amorphous thermoplastic resin film, and the temperature of this step is Tg-5 to Tg. -50 degreeC is preferable, More preferably, it is Tg-40-Tg-50 degreeC.

  Although the stress relaxation in the width direction can be achieved by the lateral relaxation treatment in the heat treatment step, the stress is not relaxed in the longitudinal direction of the film orthogonal to the width direction, and the in-plane retardation in the width direction is made more uniform. In order to do so, it is necessary to perform the relaxation treatment without restraining the width direction and the longitudinal direction. Therefore, after the film is released from the clip that restrains the free deformation in the width direction and the longitudinal direction, an unstretched grip portion at the end of the film is cut out, and a reheat treatment process is performed in which heat treatment is performed again.

The heat treatment temperature in the reheat treatment step needs to be in a range satisfying the following formula (1).
Tg-20 ≦ T ≦ Tg + 20 (1)
If the reheating temperature is lower than the above range, the effect of uniforming the retardation cannot be obtained sufficiently. On the other hand, when the length is high, the molecular orientation in the width direction obtained by the lateral uniaxial stretching is lost along with the extension in the longitudinal direction, or the conveyance failure due to the softening of the film occurs. The treatment temperature is preferably Tg-10 to Tg + 10 ° C, more preferably Tg-10 to Tg + 5 ° C.

Further, it is necessary to set the tension F (N / m / μm, unit tension at a film thickness of 1 μm and a film width of 1 m) in the film running direction at the time of reheat treatment in a range of 0 <F ≦ 0.5. When the tension is higher than 0.5, the film is stretched without stress relaxation along with the stretching in the longitudinal direction, the molecular orientation in the width direction obtained by transverse uniaxial stretching is broken, or the conveyance failure due to film softening occurs. .
In order to make film conveyance more stable, the conveyance tension F is preferably 0.3 ≦ F ≦ 0.5.

  As a method for performing the reheat treatment, an air floating method is preferred in which hot air is blown against the running film from nozzles arranged in a staggered manner along the upper and lower sides of the film running path, and the film is conveyed in a sine wave state (for example, JP-A-7-234070). The heat treatment equipment is installed between the tenter and the take-up equipment, and immediately after finishing the stretching, heat treatment and cooling processes in the tenter, a so-called in-line treatment in which the treated film is taken up by the take-up equipment, and a series of It is possible to select any of so-called off-line processing in which the film wound after the tenter process is finished is processed again by a heat treatment facility provided independently.

  The retardation film produced by the production method of the present invention having the above-described structure easily has a variation in in-plane retardation R0 of 6% in the center 80% of the film width direction excluding the tenter clip gripping part. The following can be controlled.

  The dispersion of the in-plane retardation R0 is controlled within the above range, and the retardation of the film is made to have a uniform distribution, so that when the retardation film is laminated on a liquid crystal panel, a stable image display without display unevenness can be obtained. Can do.

  In addition, according to the production method of the present invention, a retardation film in which the variation in retardation Rth in the thickness direction at the central portion 80% in the film width direction excluding the tenter clip gripping portion is easily controlled to 10 nm or less can be obtained. .

  Similar to the in-plane retardation, the variation in the thickness direction retardation Rth can be controlled within the above range, so that even when the retardation film is laminated on the liquid crystal panel, there is no display unevenness. By applying to a liquid crystal panel, the characteristics such as the wide viewing angle and high contrast inherent in the VA liquid crystal can be effectively enhanced.

  The retardation film obtained by the production method of the present invention preferably has an in-plane retardation R0 of 50 nm or more. When the value of the retardation R0 is small, birefringence when passing through the liquid crystal cannot be compensated when laminated on the liquid crystal panel, and the commercial value as a retardation film is lowered.

  Furthermore, the Nz coefficient of the retardation film obtained by the production method of the present invention is preferably 1.3 or more. When the Nz coefficient is lower than this, when laminated on a VA type liquid crystal panel, optical distortion due to birefringence and viewing angle dependence such as image quality modulation depending on the visual direction cannot be compensated for, and as a retardation film Product value is reduced.

  The retardation film of the present invention preferably has a deviation angle θ (°) of the slow axis, which is the orientation direction in the film plane of the amorphous thermoplastic resin molecular main chain, within ± 1 °. More preferably, it is within ± 0.5 °. When the deviation angle θ is within the above range, the optical axis becomes uniform over the entire surface of the film, so that the bonding angle with other members is stable, particularly when laminated on a liquid crystal panel with a large screen size. It is possible to obtain a high-quality image with no unevenness on the entire screen.

  The average thickness of the retardation film of the present invention is not particularly limited, but does not impair the desired retardation development, has a certain mechanical strength, and is important when mounted on a liquid crystal display device. In view of reduction in the thickness of the member to be formed, the thickness is preferably 30 to 100 μm, and more preferably 30 to 70 μm.

  The constitution of the present invention is as described above, and a retardation film having a uniform retardation in the width direction can be obtained by the present invention. In addition, when the obtained retardation film is used in a liquid crystal display device, it effectively compensates for the birefringence of the liquid crystal substance to eliminate display unevenness, and also provides a high-quality liquid crystal display image with excellent contrast and excellent viewing angle characteristics. Can be provided.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Examples 1-4, Comparative Examples 1-3)
An amorphous thermoplastic resin, norbornene-based resin (manufactured by Nippon Zeon Co., Ltd., trade name “ZEONOR 1420”, glass transition temperature Tg = 142 ° C.) is supplied to an extruder with a T-die, melting temperature 230 ° C., take-up speed 20 m. The film was melt-extruded on a cooling roll at / min, continuously formed into a film, and wound into a roll on a vinyl chloride resin core to obtain a substantially non-oriented norbornene resin film. The resulting norbornene-based resin film had a width of 300 mm and an average thickness of 100 μm.

  The obtained norbornene-based resin film is continuously unwound and has a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone, and a heating temperature can be set for each zone in a horizontal uniaxial tenter stretching machine at 10 m / min. The both ends of the width direction were hold | gripped with the tenter clip, and it expanded and extended 2.0 times in the width direction, and obtained the phase difference film.

  The temperature of the preheating zone is set to 150 ° C., and the supplied resin film is heated to 150 ° C., then is uniaxially stretched in the stretching zone set to 145 ° C., and immediately relaxed to 140 ° C. in the heat treatment zone. After that, it was cooled to 100 ° C. in the cooling zone.

  Both ends of the obtained laterally uniaxially stretched amorphous thermoplastic resin film are released from the tenter clip, and immediately after trimming the unstretched remaining portion at the end, the heat treatment temperature and conveyance shown in Table 1 are carried out with an air floating heat treatment apparatus. The film was treated with tension for 20 seconds and immediately cooled to 100 ° C. in an attached cooling furnace to obtain a retardation film. Table 1 shows the results of observation of the film state during conveyance.

  The width of the obtained retardation film was about 560 mm excluding the tenter clip gripping part, and the average thickness was 48 μm. Further, the Nz coefficient, retardation values R0 and R0 variations of the obtained retardation film were measured, and the results are shown in Table 1.

  In addition, the measuring method of the retardation value R0 of retardation film, Nz coefficient, and the dispersion | variation in a molecular principal chain orientation angle is as follows.

<Measurement method of retardation value R0>
Using an automatic birefringence measuring device (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments Co., Ltd.), the retardation is measured at a central 450 mm width portion of the retardation film at intervals of 10 mm in the width direction, and the average value is written as a letter. The difference between the maximum value and the minimum value in the measured value was defined as R0 variation.

<Measurement method of Nz coefficient>
Using an automatic birefringence measuring device (manufactured by Oji Scientific Instruments Co., Ltd., trade name “KOBRA-WR”), the center 450 mm width portion of the retardation film is measured at intervals of 10 mm in the width direction, and the average value is calculated as Nz. Coefficient.

Claims (4)

Amorphous thermoplastic resin film is uniaxially stretched in the width direction with a tenter, and after undergoing heat treatment and cooling treatment, the stretched film is released from the clip that holds the film edge, and further, by the air floating type sheet heat treatment device, the following formula A method for producing a retardation film, characterized by heat-treating again at a temperature T (° C.) and a conveying tension F (N / m / μm) satisfying (1) and (2).
Tg-20 ≦ T ≦ Tg + 20 (1)
0 <F ≦ 0.5 (2)
However, Tg shows the glass transition temperature of an amorphous thermoplastic resin. A retardation film produced by the production method according to claim 1 and having a variation in in-plane retardation R0 of 6% or less at a central portion 80% in a film width direction excluding a tenter clip gripping portion. The retardation film according to claim 2, wherein the Nz coefficient is 1.3 or more. The retardation film according to claim 2 or 3, wherein the amorphous thermoplastic resin is a norbornene resin or a maleimide resin.