JP2009298101A - Optical polyethylene-2,6-naphthalate film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyethylene-2,6-naphthalate film formed by stretching and orientating polyethylene-2,6-naphthalate, small in the angle of a slow phase axis, excellent in appearance such as hue and transparency, and useful for optical application. <P>SOLUTION: The optical polyethylene-2,6-naphthalate film is formed by biaxially orienting an aromatic polyester in which polyethylene-2,6-naphthalate units occupy at least 80% of all of the repeating units, and its retardation value is 1,200 nm or larger and the angle of the slow phase axis is ±2 degrees to the film width direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film formed using polyethylene-2,6-naphthalate. More specifically, a slow axis obtained by stretching and orienting using polyethylene-2,6-naphthalate having a high intrinsic viscosity, which is suppressed in crystallinity using an antimony compound as a polycondensation catalyst, and has excellent hue and transparency. The present invention relates to a highly heat-resistant optical film having a small angle. In particular, the present invention relates to a film used as a base film for optical applications.

  Polyethylene-2,6-naphthalate film is being used for heat-resistant film materials because it has excellent basic characteristics such as heat resistance and chemical resistance compared to polyethylene terephthalate film. Attracted attention in the field of optics. In particular, for optical applications, quality with excellent appearance such as hue and transparency is strongly required from the viewpoint of commercial value.

  Polyethylene-2,6-naphthalate can be obtained by reacting with a catalyst similar to polyethylene terephthalate. When a germanium compound is used as a polycondensation catalyst, it is excellent in terms of hue and transparency, but cost is high and polymerization activity is high. There is also a problem such as low. On the other hand, when an antimony compound is used as a polycondensation catalyst, there is no problem in terms of cost and polymerization activity. However, when the obtained polymer is formed into a sheet or the like due to precipitation of metal antimony and its nucleating agent effect, transparency, etc. There is a problem that the appearance is deteriorated or the color is inferior such as blackening of the polymer due to precipitation of metal antimony. As described above, polyethylene-2,6-naphthalate and a film obtained by molding the polyethylene-2,6-naphthalate are not necessarily sufficient in terms of appearance such as strength, hue and transparency.

  The following techniques have been proposed as related public literatures. Patent Document 1 discloses an application in which polyethylene-2,6-naphthalate is used as a bottle, and Patent Document 2 discloses a technique in which a biaxially stretched polyethylene-2,6-naphthalate film or sheet is used as a light diffusion application or a release film for inspection. And Patent Document 3.

JP 2000-026586 A JP 2002-080621 A Japanese Patent Application Laid-Open No. 07-101026

  The first object of the invention is polyethylene-2,6-naphthalate stretched and oriented, polyethylene-2,6-useful for optical applications with a small slow axis angle and excellent appearance such as hue and transparency. It is to provide a naphthalate film.

  The second object of the present invention is to provide a polyethylene-2,6-naphthalate film, particularly a release film for optical substrate inspection, useful for optical applications having high intrinsic viscosity and excellent appearance such as hue and transparency. It is to provide.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor specified polyethylene-2,6-naphthalate obtained by specifying the degree of crystallinity and intrinsic viscosity using an antimony compound as a polycondensation catalyst. By biaxially stretching and heat-fixing by this method, an optical polyethylene-2,6-naphthalate film for optical use with high strength, excellent hue and transparency, high retardation, and a small slow axis angle is obtained. The present invention has been reached.

That is, according to the present invention,
(1) A film in which an aromatic polyester in which ethylene-2,6-naphthalate unit occupies at least 80 mol% of all repeating units is biaxially oriented, has a retardation value of 1200 nm or more, and a slow axis angle of the film. An optical polyethylene-2,6-naphthalate film characterized by being ± 2 degrees with respect to the width direction;
(2) The aromatic polyester is obtained by a solid phase polymerization method using an antimony compound as a polymerization catalyst, and has an intrinsic viscosity (IV) in the range of 0.40 to 0.80 dl / g. Polyethylene-2,6-naphthalate film for
(3) An aromatic polyester film in which unstretched ethylene-2,6-naphthalate units occupy at least 80 mol% of all repeating units has a stretching ratio of 3.0 to 5.0 times in both the longitudinal and lateral directions, and a longitudinal stretching ratio. The film is stretched biaxially and horizontally so that the stretch ratio of the film and the transverse stretch ratio (transverse stretch ratio / longitudinal stretch ratio) is 1.2 to 1.5, and the film after biaxial stretching is heat-set. A process for producing an optical polyethylene-2,6-naphthalate film as described in (1) above, and (4) an optical film formed from the film as described in (1) or (2) above. Release film for substrate inspection,
Is provided.

Hereinafter, the present invention will be described in detail.
(Creation of polymer)
The polyethylene-2,6-naphthalate of the present invention has naphthalenedicarboxylic acid as the main acid component and ethylene glycol as the main diol component.

  The naphthalenedicarboxylic acid as the main acid component in the present invention is 2,6-naphthalenedicarboxylic acid and its lower alkyl ester derivative. “Main” means 80 mol% or more, preferably 95 mol% or more of the total dicarboxylic acid component.

  Components that can be copolymerized within a range of 20 mol% or less include aromatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, isophthalic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonedicarboxylic acid, and diphenyletherdicarboxylic acid. Examples thereof include alicyclic dicarboxylic acids such as acid, cyclohexanedicarboxylic acid and decalin dicarboxylic acid, oxyacids such as glycolic acid and p-oxybenzoic acid.

  The main diol component in the present invention is composed of 80 mol% or more, preferably 95 mol% or more of ethylene glycol. Trimethylene glycol, tetramethylene glycol, hexamethylene glycol, triethylene glycol, neopentyl glycol, cyclohexanedimethanol, bisphenol A and the like may be copolymerized within a range of 20 mol% or less.

  When the acid component and the glycol component are copolymerized in excess of 20 mol%, the original properties of polyethylene-2,6-naphthalate, such as heat resistance and gas barrier properties, are poor. In the present invention, diethylene glycol is an example of a diol component present as a copolymer component in the polymer. The amount of copolymerization is preferably 3.0% by weight or less of the total amount of the polymer. When the diol component is copolymerized in an amount of more than 3.0% by weight in the polyester, the resulting polyester has a remarkable decrease in heat resistance, mechanical strength, etc. Since the width is narrow, it is not preferable.

  In the present invention, an antimony compound is preferably used as the polycondensation catalyst. Examples of the antimony compound include antimony oxide, antimony acetate, antimonic acid glycolate, etc. Among them, antimony trioxide is preferably used.

  The addition amount of the antimony compound is preferably in the range of 5 to 20 mmol% with respect to the total acid component in terms of antimony trioxide. When the addition amount of the antimony compound is less than 5 mmol%, not only is the polymerization activity low, the polycondensation time becomes long, and it is not preferable from an economic viewpoint such as a decrease in productivity, but also the side reaction product due to an increase in the polycondensation time. This is not preferable because quality is inferior, such as an increase and deterioration of hue. When the added amount of the antimony compound exceeds 20 mmol%, the crystallinity increases due to the crystal nucleating agent effect of the precipitated metal antimony, the appearance of the resulting polyester film is impaired, and the decomposition reaction occurs at the time of remelting during film formation. Accelerating is undesirable because undesirable side reaction products such as acetaldehyde increase.

  Polyethylene-2,6-naphthalate is preferably subjected to a transesterification method or a direct esterification method as a pre-stage for performing a polycondensation reaction using the antimony compound as a catalyst.

  In the case of producing by the transesterification method, a transesterification reaction catalyst is required. The transesterification catalyst is not particularly limited, and manganese compounds, calcium compounds, magnesium compounds, titanium compounds, zinc compounds, sodium compounds, potassium compounds, cerium compounds, lithium compounds, etc. that are generally widely used as transesterification catalysts for polyethylene terephthalate Is mentioned. Further, a cobalt compound may be contained as a transesterification reaction catalyst that also acts as a color adjusting agent.

  The polyethylene-2,6-naphthalate produced by the transesterification method and / or direct esterification method preferably contains a phosphorus compound as a stabilizer. As the phosphorous compound, at least one selected from orthophosphoric acid, phosphorous acid, phosphoric acid ester, phosphoric acid triester and the like can be used. Among them, normal phosphoric acid and phosphorous acid are preferably used from the viewpoint of transparency. It is done. Although the addition amount of a phosphorus compound changes with manufacturing methods, it is preferable to add so that it may become the following residual amount.

  When polyethylene-2,6-naphthalate is produced by a transesterification method, it is preferable to add such that the residual amount of the phosphorus compound is 0.7 to 2.0 mol times the transesterification reaction catalyst. When the content of the phosphorus compound is less than 0.7 mol times, the transesterification reaction catalyst cannot be sufficiently deactivated, and the obtained polyethylene-2,6-naphthalate is inferior in terms of thermal stability and hue. It is not preferable. Further, when the content of the phosphorus compound exceeds 2.0 mol times, it is not preferable because of poor heat stability and hue.

  On the other hand, when polyethylene-2,6-naphthalate is produced by a direct esterification method, a transesterification catalyst is not used as in the case of the above-described transesterification method. It is preferable to add so that the residual amount of the phosphorus compound is in the range of 5 to 100 mmol% with respect to the total acid component. When the content of the phosphorus compound is less than 5 mmol% or more than 100 mmol% with respect to the total acid component, it is not preferable in terms of poor thermal stability and hue of the obtained polyethylene-2,6-naphthalate. .

(Intrinsic viscosity of polymer (IV))
The polyethylene-2,6-naphthalate resin used as a raw material for film formation in the present invention is preferably produced by solid phase polymerization after obtaining a prepolymer by melt polymerization. It is preferable that the molten resin after the condensation reaction described above is chipped (pelletized) and subjected to solid phase polymerization under heating under reduced pressure or in an inert gas stream such as nitrogen. The pellet after the solid phase polymerization treatment is washed with distilled water (obtained by contacting with water, water vapor or water vapor-containing gas after solid phase polymerization). This washing removes fine powder and whiskers. In general, such powder and whiskers are difficult to remove in the melt extrusion and melt resin filtration process when forming into a film, so they may enter the film and become a quality defect as an internal foreign matter. . According to the solid phase polymerization, oligomers contained in the polyethylene-2,6-naphthalate resin can also be reduced, so that surface defects due to the oligomers existing on the film-formed film surface can be further reduced.

  The intrinsic viscosity of the polyethylene-2,6-naphthalate resin used in the present invention is preferably 0.40 to 0.80 dl / g. More preferably, it is 0.52-0.75 dl / g, Most preferably, it is 0.55-0.70 dl / g.

  When the intrinsic viscosity is less than 0.40 dl / g, there is a problem that the film after melt extrusion becomes brittle and breaks easily during stretching. Moreover, since the conditions of a predetermined draw ratio cannot be taken, it is not preferable. On the other hand, when the intrinsic viscosity of the polyethylene-2,6-naphthalate resin exceeds 0.80 dl / g, the normal synthesis method requires a long time for polymerization, and the productivity is deteriorated. Further, not only is the coloration during polymerization and an increase in side reaction products become remarkable, but also deterioration of the polymer is promoted by shear heat generation resulting from high melt viscosity when formed into a film, which is not preferable.

  The polyethylene-2,6-naphthalate resin used in the present invention is usually melt-extruded after drying the pellets with hot air. The drying conditions are a hot air temperature of 170 to 175 ° C. and 3 hours or longer. In this way, the moisture content of the pellets can be reduced to prevent a decrease in intrinsic viscosity due to hydrolysis during melt extrusion.

(Additive)
In the present invention, polyethylene-2,6-naphthalate contains various additives such as a stabilizer, an antioxidant, an inert fine particle, an ultraviolet absorber, an antistatic agent, a lubricant, a flame retardant, a dye, and a pigment as necessary. It may be contained. In order to impart slipperiness to the film, it is preferable to contain a small amount of inert particles.

  As the inert fine particles, spherical silica particles are preferable, the average particle size is preferably in the range of 0.05 to 5.0 μm, and more preferably in the range of 0.1 to 3.0 μm. Further, spherical silica fine particles having a particle size ratio (major axis / minor axis) of 1.0 to 1.2 are preferable.

  The spherical silica fine particles have a spherical shape very close to a true sphere, and have almost no coarse particles. Conventionally, silica fine particles (ultrafine particles of about 10 nm, or these Are aggregated to form aggregates (aggregated particles) of about 0.5 μm).

  If the average particle size of the spherical silica fine particles is larger than 5.0 μm, voids (voids, etc.) are likely to be generated in the polymer film around the protrusions due to the spherical silica fine particles, and the haze value is likely to increase. On the other hand, if the thickness is smaller than 0.05 μm, the film is inferior in slipperiness and difficult to handle.

  The content of the inert fine particles is preferably 0.001 to 1.0% by weight, and more preferably 0.03 to 0.5% by weight. If the content is more than 1.0% by weight, the slipperiness is sufficient, but the total number of voids increases and the haze value tends to increase, which is not preferable. When the content is less than 0.001% by weight, the film is inferior in slipperiness and difficult to handle.

  The inert fine particles may be added at any stage until polyethylene-2,6-naphthalate is formed. For example, the inert fine particles may be added at the polymerization stage or added during film formation. May be.

(Create melt-extruded film)
The crystallinity of the polyethylene-2,6-naphthalate polymer of the present invention is preferably 40% or less (here, the crystallinity is a value calculated from the density of the polymer).
When the degree of crystallinity of the polymer exceeds 40%, it is necessary to increase the extrusion temperature for melting the polymer, the deterioration of the hue and the increase of undesirable by-products such as acetaldehyde become remarkable, and the room for melt extrusion of the resin Cause environmental pollution. Moreover, when shape | molding without raising extrusion temperature, the transparency of the film obtained is impaired by the deterioration of the external appearance of the film by an unmelted polymer, and the crystallization promotion by a nucleating agent effect.

  In the unstretched polyethylene-2,6-naphthalate film used in the present invention, the resin is heated and melted in a melt extruder and uniformly kneaded and extruded. The temperature of the molten resin during extrusion is preferably in the range of 290 to 310 ° C, and more preferably in the range of 295 to 305 ° C. The resin melted by heating is filtered through a polymer filter to remove various foreign substances. As the filter element, one made of sintered metal or one made by pressing and thinning a fine metal wire can be used. Since various types with different openings and pressure resistance are commercially available, these are preferably selected. It is preferable to use a mixer for kneading to make the temperature distribution of the resin uniform in the polymer conduit for transporting the molten polymer. The mixer serves to reduce the temperature spots and viscosity spots of the resin to be extruded and to reduce the thickness spots of the film. Next, the molten resin is extruded into a molten sheet from, for example, an I die or a T die, and rapidly cooled on a cooling drum to form an unstretched film.

  When the obtained polyethylene-2,6-naphthalate is formed into a film, the haze is preferably 3% or less. When the haze exceeds 3%, the transparency is lowered and the appearance as a product is inferior, which is not preferable.

(Sequential stretching in length and width)
In the present invention, the unstretched (substantially unoriented) film is biaxially stretched and heat-set. Preferably, the unstretched film can be produced by biaxially stretching in the longitudinal and lateral directions and heat-setting.

  For example, when producing a biaxially stretched and heat-set film, the unstretched film is biaxially stretched at a temperature of Tg to (Tg + 60) ° C. in the machine direction and in the transverse direction at a magnification of 3.0 to 5.0 times. Heat-fix at 1 to 100 seconds at Tg + 50) to (Tg + 140) ° C. Stretching can be performed in a longitudinal direction by a generally used method, for example, a method using a roll or a lateral direction by a method using a tenter, and the stretching is sequentially performed in the longitudinal direction and the lateral direction.

  When the draw ratio in the machine direction and the transverse direction is less than 3.0, it is not preferable because sufficient heat resistance and strength / elongation characteristics as a polyethylene-2,6-naphthalate film cannot be exhibited. Further, when the draw ratio in the longitudinal direction and the transverse direction exceeds 5.0 times, the film is liable to break, which is not preferable.

  Further, the stretching ratio in the machine direction and the transverse direction at this time is set to 1.2 to 1.5 as the ratio of stretching (transverse stretching ratio / longitudinal stretching ratio) (that is, the transverse stretching ratio is It is preferable that the height be higher than that in the vertical direction. A stretching ratio of 1.0 indicates a ratio in which the characteristics of the obtained film are substantially equal in the machine direction and the transverse direction, and 1.5 indicates a case where the orientation in the transverse direction is greatly superior.

  When the stretch ratio is less than 1.2, the variation in the angle of the slow axis in the transverse direction of the film becomes large, and the film characteristics of the present invention cannot be satisfied. When the stretching ratio exceeds 1.5, the film is easily broken during transverse stretching, which is not preferable.

  The polyethylene-2,6-naphthalate film obtained in the present invention has a retardation value of 1200 nm or more, preferably 1220 nm or more. Moreover, although an upper limit is not restrict | limited, 1650 nm or less has sufficient characteristics. If the retardation value is less than 1200 nm, the concentration of light interference in crossed Nicols increases rapidly, which is not preferable.

In addition, the polyethylene-2,6-naphthalate film obtained in the present invention has a slow axis angle of ± 2 degrees with respect to the film width direction, preferably ± 1.9 degrees, and more preferably. Is ± 1.8 degrees. If the angle of the slow axis exceeds ± 2 degrees with respect to the film width direction, the interference unevenness due to the axial unevenness in the crossed Nicols tends to appear as a cloud, which is not preferable.
The film of the present invention is particularly useful as a release film for optical substrate inspection.

(Winding)
When supplying the film of the present invention to the optical application field as a roll, particularly when there is no surface protrusion or the density of the surface protrusion is small or when no lubricant is added, unevenness is provided only at both ends of the film width. A so-called knurling winding or a roll winding method such as a method in which a spacer is wound only on both ends can be adopted. When a lubricant is not added, a method of imparting easy slipperiness to the film surface by in-line coating or the like and winding it up can also be employed.

  Since the oriented polyethylene-2,6-naphthalate film of the present invention is highly heat resistant and highly transparent, it can be used as various substrate films in the optical field. In particular, according to the present invention, light interference color in crossed Nicols is not substantially produced when laminated with a polarizing plate, a retardation polarizing plate, or a retardation plate, facilitating visual foreign matter inspection, and even for large-screen LCDs. It is possible to provide a release film that improves the accuracy of foreign matter inspection and prevents the generation of defective products, and a laminate having improved polarization characteristics by laminating the release film.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to these examples. Various characteristic values described in the examples are measured by the following methods. The longitudinal direction of the film means the extrusion direction in the production of the film, and the lateral direction means a direction orthogonal to the longitudinal direction in the film plane.

(Intrinsic viscosity IV)
It calculated from the solution viscosity measured at 35 degreeC using the mixed solvent of tetrachloroethane: phenol = 4: 6.

(Measurement of retardation value and angle of slow axis)
The measurement was performed using an automatic birefringence measuring device KOBRA-21SDH manufactured by Oji Scientific Co., Ltd.
The film sample was measured at a measurement interval of 5 mm by sampling 1000 mm in the full width and length directions. In addition, the length direction of the film took the sample from 100 mm inside from the center part of the film width direction and the both ends of the film width direction, and used for the measurement. Simultaneously with retardation, the slow axis angle was also measured and analyzed.

(Birefringence)
The birefringence Δn was calculated from the retardation Re determined from KOBRA-21SDH. The calculation formula is Re = Δn * d, where d is the thickness of the film where the retardation Re was measured.

(Glass transition temperature Tg)
The measurement was performed using a DSC (differential scanning calorimeter) 220 manufactured by Seiko Denshi Kogyo Co., Ltd. The DSC measurement conditions are as follows. 10 mg of a sample film was set in a DSC apparatus, heated at a temperature rising rate of 20 ° C./min, melted at a temperature of 300 ° C., and then rapidly cooled in liquid nitrogen. The rapidly cooled sample was heated at 10 ° C./min, and the glass transition point was detected.

(Refractive index)
Using an Abbe refractometer, the refractive index nx in one direction in the film plane (for example, the refractive index nMD in the longitudinal direction of the film) and the refractive index ny in the direction orthogonal thereto (for example, the refractive index nTD in the lateral direction of the film) are Measurement was performed at 23 ° C. and 65% RH by using D-line (589 nm) and using methylene iodide or a mixture of methylene iodide and sulfur as the mounting solution.

(density)
Using a density gradient tube using a calcium nitrate aqueous solution, the measurement was carried out at 25 ° C. by the flotation method.

(Crystallinity)
It was determined by measuring the density of the polymer.

(Thickness)
Thickness: Using an electronic micrometer (K-312A type) manufactured by Anritsu Corporation, the film thickness was measured at a needle pressure of 30 g.

(Visual inspection status (effect of light interference under crossed Nicols))
The film was evaluated and tested according to the description in Example 1 and Example 4 of JP-A-07-101026. Visual inspection was performed with the configuration and method described in the above publication, and the occurrence of optical interference was evaluated according to the following criteria.
Good: No optical interference generated by visual inspection Slightly poor: Optical interference generated by visual inspection but inspection possible Poor: Optical interference generated by visual inspection not possible

(MOR value)
Using a microwave molecular orientation meter manufactured by Kanzaki Paper Co., Ltd., the MOR value was determined from the transmission microwave intensity pattern. The MOR value is a ratio (maximum value / minimum value) between the maximum value and the minimum value of transmitted microwave intensity measured by a transmission type molecular orientation meter.

Example 1
(Creation of polymer)
Transesterification of 100 parts by weight of 2,6-naphthalenedicarboxylic acid dimethyl ester and 51 parts by weight of ethylene glycol in the presence of 0.030 parts by weight (30 mmol%) of manganese acetate tetrahydrate was carried out by a conventional method to distill off methanol. After 20 minutes, 0.012 (10 mmol%) of antimony trioxide was added, and 0.020 part by weight (50 mmol%) of orthophosphoric acid was added before the end of the transesterification reaction. Subsequently, a polycondensation reaction was performed at 295 ° C. under a high vacuum of 1.3 × 10 ² PaHg or less to obtain a polyethylene-2,6-naphthalate polymer having an intrinsic viscosity of 0.47 dl / g. Furthermore, solid phase polymerization was performed by a conventional method using this prepolymer to obtain a polymer having an intrinsic viscosity of 0.65 dl / g and a crystallinity of 38%. The resin contained 0.2% by weight of substantially spherical silica particles having an average particle size of 0.3 μm as a lubricant.

(Create unstretched film)
The polyethylene-2,6-naphthalate resin is dried with hot air at 175 ° C. for 5 hours, then melted at 300 ° C. with a melt extruder, extruded from a die onto a cooling drum at 60 ° C. And solidified by cooling to obtain an unstretched film. The properties of the obtained unstretched film are: intrinsic viscosity IV is 0.62 dl / g, birefringence Δn is 0.003, triaxial refractive index is 1.645, density is 1.330 g / cm ³ , glass transition The temperature Tg was 125 ° C. The film was homogeneous and transparent.

(Creation and evaluation of inspection sheet)
The unstretched film was sequentially stretched at a stretching ratio of 3.1 times in the machine direction and at a magnification of 4.1 times in the transverse direction. Next, heat setting was performed in three zones, and heat setting was performed at 210 ° C., 230 ° C., and 180 ° C. for 10 seconds each. The obtained biaxially stretched heat-setting film had a thickness of 38 μm and a film width of 730 mm (the parent roll width was 2190 mm because three 730 mm-wide rolls were taken from the parent film roll).
This film was further coated with silicone in accordance with Example 4 of JP-A-07-101026 to obtain a release film having polyethylene-2,6-naphthalate as a substrate.

  As a result of evaluating the film by dividing it into B, C, and F for convenience in the width direction, the thermal shrinkage in the vertical and horizontal directions was 110 ° C. × 30 minutes, both 0%. The MOR values were 1.5, 1.5, and 1.5 in the order of B, C, and F, and the range (maximum value-minimum value) was 0.1 for both B, C, and F. The visual inspection state (influence of light interference under crossed Nicols) was good for B, C, and F. The range of the slow axis angle of the entire width of the parent roll film (2190 mm) was ± 1.8 degrees with respect to the lateral direction of the film. The retardation of the film was 1240 to 1260 nm.

  Reference characters B, C, and F are slits of the entire width (2190 mm) of the film-forming film into three equal parts (730 mm). B: film portion on the left side (blank side) when viewed from the film-forming film winding position, C: film-forming A central film portion (center portion) as viewed from the film winding position, and F: a right film portion (feed (drive) side) as viewed from the film-forming film winding position.

Example 2
The unstretched film obtained in Example 1 was sequentially stretched at a stretch ratio of 3.1 times in the machine direction and at a stretch ratio of 4.5 times in the transverse direction. Next, heat setting was performed at 210 ° C., 230 ° C., and 180 ° C. for 10 seconds in three zones. The film characteristics after silicone coating obtained by the same method as in Example 1 were as follows. In three roll films taken in the width direction (all 730 mm width), the MOR value is 1.4 for all rolls, the visual inspection state (effect of light interference under crossed Nicols) is good, and the heat shrinkage rate is 110. The temperature at 30 ° C. for 30 minutes was 0 to 0.1% in both the vertical and horizontal directions. The angle of the slow axis of the entire width of the parent film roll was ± 1.5 degrees with respect to the film width direction. Moreover, the retardation of the film was 1350-1400 nm.

Comparative Example 1
The unstretched film obtained in Example 1 was sequentially stretched at a stretch ratio of 3.1 times in the machine direction and at a stretch ratio of 3.4 times in the transverse direction. Next, heat setting was performed at 210 ° C., 230 ° C., and 180 ° C. for 10 seconds in three zones. The film characteristics after silicone coating obtained by the same method as in Example 1 were as follows. Of the three roll films taken in the width direction (all 730 mm wide), the visual inspection state (influence of light interference under crossed Nicols) is good only in the center in the width direction, and the other two are It was bad. The MOR value was 1.5 at only one central portion in the width direction. The other two rolls were 1.7 and 2.0. The heat shrinkage rate of 110 ° C. × 30 minutes was 0 to 0.1% in both the vertical and horizontal directions. The angle of the slow axis of the entire width (2190 mm) of the parent film roll was ± 35 degrees with respect to the film width direction. The retardation of the film was 680 to 750 nm.

Claims (4)

  It is a film in which an aromatic polyester in which ethylene-2,6-naphthalate units occupy at least 80 mol% of all repeating units is biaxially oriented, its retardation value is 1200 nm or more, and the slow axis angle is in the film width direction. An optical polyethylene-2,6-naphthalate film, which is ± 2 degrees with respect to the film.   2. The optical polyethylene-2 according to claim 1, wherein the aromatic polyester has an intrinsic viscosity (IV) in the range of 0.40 to 0.80 dl / g, obtained by solid phase polymerization using an antimony compound as a polymerization catalyst. , 6-Naphthalate film.   An aromatic polyester film in which unstretched ethylene-2,6-naphthalate units occupy at least 80 mol% of all repeating units is stretched in the longitudinal and lateral directions at a stretching ratio of 3.0 to 5.0, and the longitudinal stretching ratio and the lateral stretching. Including a step of successively biaxially stretching in the longitudinal and transverse directions so that a ratio of stretching to the magnification (lateral stretching ratio / longitudinal stretching ratio) is 1.2 to 1.5, and a step of heat-setting the film after biaxial stretching. The method for producing an optical polyethylene-2,6-naphthalate film according to claim 1.   A release film for optical substrate inspection formed from the film according to claim 1.