JP2012067239A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film excellent in coating properties, reduced in error rate and further excellent in film-forming abilities, with small dimensional change due to environmental variation when employed as a magnetic recording medium.SOLUTION: The biaxially oriented polyester film has characteristics such that: Young's modulus in the width direction of the film is 6 to 10 GPa; the birefringence Δn (nMD-nTD) expressed by the difference between the refractive index nMD in film length direction and the refractive index nTD in film width direction is -0.10 to -0.02; and the enthalpy relaxation amount ΔHe of the film is 0.15 to 3.0 J/g.

Description

  The present invention relates to a support used for a magnetic recording medium such as a magnetic tape, and a magnetic recording medium provided with a magnetic layer on the support.

  Biaxially oriented polyester films are used in various applications because of their excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, especially magnetic recording media that have been strengthened using stretching technology, etc. Its usefulness as a support is well known. In recent years, magnetic recording media such as magnetic tapes are required to have high density recording in order to reduce the weight, size, and capacity of equipment. For high density recording, it is useful to shorten the recording wavelength and the recording track. However, if the recording track is made small, there is a problem that the recording track is liable to shift due to deformation caused by heat during tape running or temperature and humidity changes during tape storage. Therefore, there is an increasing demand for improvement in characteristics such as dimensional stability in the width direction in the tape use environment and storage environment. In order to enhance the dimensional stability in the width direction, when the orientation is increased in the width direction by a conventional film forming method, the thermal shrinkage becomes large and the coating property and the film forming property are deteriorated. In addition, there is a method of aging as a technique for improving dimensional stability (Patent Documents 1 to 4), but even if the aging treatment in these documents is performed, the alignment balance of molecular chains in the width direction and the longitudinal direction is poor. The currently required dimensional stability cannot be achieved. Therefore, it is difficult to improve the dimensional stability in the width direction while maintaining excellent coating properties, film forming properties, and error rates.

  Therefore, as a result of intensive studies, MD stretching, TD stretching, and TD stretching were sequentially performed in order, and there was a specific magnification difference between MD stretching and TD stretching. By performing an aging treatment under a specific tension using a highly oriented process having the above three features having a temperature difference, the Young's modulus and birefringence in the width direction are controlled within a certain range, and the enthalpy relaxation amount ΔHe is It has been found that it can be within a certain range, and when it is used as a magnetic tape, it has excellent dimensional stability, applicability, and error rate reduction, and can solve the above-mentioned many problems.

JP-A-11-110735 JP 2005-346865 A JP 2009-87470 A JP 2009-87471 A

  An object of the present invention is to solve the above problems and provide an excellent biaxially oriented polyester film. More specifically, it is an object of the present invention to provide a biaxially oriented polyester film that has little dimensional change due to environmental changes when used as a magnetic recording medium, is excellent in coating properties and film forming properties, and has a good error rate. In the following description, the width direction, TD, and the horizontal direction are used in the same meaning, and the longitudinal direction, MD, and the vertical direction are used in the same meaning.

  The present invention for solving the above-described problems is characterized by the following (1) to (5).

  (1) The Young's modulus in the width direction is 6 to 10 GPa, and the birefringence Δn (nMD−nTD) indicated by the difference between the refractive index nMD in the longitudinal direction and the refractive index nTD in the width direction is −0.10 to −0. A biaxially oriented polyester film having an enthalpy relaxation amount ΔHe of 0.1 to 3.0 J / g.

  (2) The biaxially oriented polyester film according to (1), wherein the humidity expansion coefficient in the width direction is 0 to 6 ppm /% RH.

  (3) The biaxially oriented polyester film according to (1) or (2), wherein the heat shrinkage rate in the width direction at 100 ° C for 30 minutes is 0 to 2%.

  (4) The biaxially oriented polyester film according to any one of the above (1) to (3), wherein the minute melting peak temperature T-meta is (Tm-105) to (Tm-50) ° C.

  An object of the present invention is to provide an excellent biaxially oriented polyester film. Specifically, when a magnetic recording medium is used, it is possible to obtain a biaxially oriented polyester film with little dimensional change due to environmental changes, excellent coating properties and film forming properties, and a good error rate.

  In the present invention, the polyester film is composed of, for example, a polymer having an acid component or a diol component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid as a structural unit (polymerization unit). .

  Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyldicarboxylic acid. Acid, 4,4′-diphenyl ether dicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, and the like can be used. Among them, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be preferably used. . As the alicyclic dicarboxylic acid component, for example, cyclohexane dicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. These acid components may be used alone or in combination of two or more.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, , 6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2'-bis (4'- -Hydroxyethoxyphenyl) propane and the like can be used, among which ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like can be preferably used, and particularly preferably ethylene glycol and the like The It is possible to have. These diol components may be used alone or in combination of two or more.

  The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, or a trifunctional compound such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, or 2,4-dioxybenzoic acid. A compound or the like may be copolymerized within a range in which the polymer is substantially linear without excessive branching or crosslinking. In addition to the acid component and diol component, the present invention includes aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 2,6-hydroxynaphthoic acid, p-aminophenol, and p-aminobenzoic acid. As long as the effect is not impaired, the copolymerization can be further carried out.

  Polyester is preferably polyethylene terephthalate or polyethylene naphthalate (polyethylene-2,6-naphthalate). Further, these copolymers and modified products may be used, and polymer alloys with other thermoplastic resins may be used. The polymer alloy here refers to a polymer multi-component system, which may be a block copolymer by copolymerization or a polymer blend by mixing. In particular, a polymer compatible with polyester is preferable, and a polyetherimide resin is preferable. As the polyetherimide resin, for example, those shown below can be used.

(Wherein R ¹ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R ² is a divalent aromatic residue having 6 to 30 carbon atoms, From the group consisting of alkylene groups having 2 to 20 carbon atoms, cycloalkylene groups having 2 to 20 carbon atoms, and polydiorganosiloxane groups chain-terminated with alkylene groups having 2 to 8 carbon atoms Selected divalent organic group.)
As said R < ¹ >, R < ² >, the aromatic residue shown by the following formula group can be mentioned, for example.

  In the present invention, 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m-phenylenediamine from the viewpoint of affinity with polyester, cost, melt moldability, and the like, or A polymer having a repeating unit represented by the following formula, which is a condensate with p-phenylenediamine, is preferred.

Or

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This polyetherimide is available from SABIC Innovative Plastics under the trade name “Ultem” (registered trademark), and is “Ultem 1000”, “Ultem 1010”, “Ultem 1040”, “Ultem 5000”, “Ultem 6000” and “Ultem XH6050”. ”Series,“ Extreme XH ”, and“ Extreme UH ”registered trademark names.

  The biaxially oriented polyester film of the present invention has a Young's modulus in the width direction of 6 to 10 GPa. If the Young's modulus in the width direction is within the above range, dimensional stability due to environmental changes during recording / reproduction of the magnetic recording medium will be good when used for a magnetic recording medium. The upper limit of the Young's modulus in the width direction is more preferably 9.0 GPa, and even more preferably 8.5 GPa. The lower limit of the Young's modulus in the width direction is more preferably 6.5 GPa, and even more preferably 7.0 GPa. A more preferable range is 6.5 to 9 GPa, and a further preferable range is 7 to 8.5 GPa. The Young's modulus in the width direction can be controlled by the temperature and magnification of TD stretching 1 and 2. In particular, the total TD magnification influences, and the higher the total TD magnification, the higher the Young's modulus in the width direction.

  The biaxially oriented polyester film of the present invention has a birefringence index Δn (nMD−nTD) represented by the difference between the refractive index nMD in the film longitudinal direction and the refractive index nTD in the film width direction of −0.10 to −0.02. is there. Birefringence indicates the difference between the longitudinal direction and the width direction of the degree of molecular chain orientation, and the larger the negative number, the more the molecular chain is oriented in the width direction. When the birefringence Δn is within the above range, the dimensional stability in the width direction is good and the film forming property is also stable. A more preferable range of the birefringence is -0.09 to -0.025, and a more preferable range is -0.07 to -0.03. If it exceeds −0.02 or less than −0.10, even if an attempt is made to produce a biaxially oriented polyester film, the film is difficult to be formed because breakage frequently occurs. The birefringence Δn can be controlled by the magnification of TD stretching 1 and 2. In particular, the total TD magnification is affected, and the birefringence Δn decreases as the total TD magnification increases.

  Moreover, enthalpy relaxation amount (DELTA) He calculated | required from the differential scanning calorimetry (DSC) of the biaxially-oriented polyester film of this invention is 0.1-3.0 J / g. When ΔHe is within the above range, the structure of the molecular chain is stabilized, the thermal shrinkage rate and the humidity expansion coefficient are improved, and the dimensional stability is improved. More preferably, it is 0.12-2J / g, and a still more preferable range is 0.15-1J / g. If ΔHe is less than 0.1 J / g or exceeds 3.0 J / g, the dimensional stability tends to be lowered. When the temperature of the aging treatment is low, the tension is small, or the time is short, ΔHe becomes small.

  The biaxial polyester film of the present invention preferably has a humidity expansion coefficient in the range of 0 to 6 ppm /% RH. Since the polyester expands when humidity, that is, moisture, is added, generally the humidity expansion coefficient is often a positive value in a magnetic recording medium. Further, when the orientation is so high that the humidity expansion takes a negative value, the temperature expansion coefficient becomes too small, and when the temperature is changed from low to high, the film shrinks in the tape width direction and regenerative failure is likely to occur. Further, when the humidity expansion coefficient is larger than 6 ppm /% RH, the tape width direction expands when the environment for recording and reproducing magnetic data changes from low humidity to high humidity, which tends to cause reproduction failure. The humidity expansion coefficient is more preferably 0 to 5.5 ppm /% RH, and still more preferably 0 to 5.0 ppm /% RH. The humidity expansion coefficient increases when the difference between the TD stretching 1 temperature and the TD stretching 2 temperature is small.

  As for the thermal contraction rate of the width direction in 100 degreeC and 30 minutes of the polyester film of this invention, 0 to 2% is preferable. When the heat shrinkage rate exceeds 2%, when processing into a magnetic recording medium, process troubles such as “wrinkles” are caused, the coating property is lowered, and the heat shrinkage rate of the magnetic recording medium can be controlled within a preferable range. It becomes difficult and the error rate decreases. If it is less than 0%, the relaxation of the amorphous part has progressed too much, the temperature and humidity expansion coefficient becomes too high, and the quality may deteriorate. A more preferred upper limit is 1.0%, and a more preferred upper limit is 0.5%. The heat shrinkage rate can be controlled by the heat set temperature (hereinafter referred to as the HS temperature). If the HS temperature is too low, the heat shrinkage rate increases.

  The fine melting peak (T-meta) obtained from differential scanning calorimetry (DSC) of the biaxial polyester film of the present invention is preferably Tm−105 to Tm−50 ° C. when the melting point is Tm. More preferably, it is Tm-100-Tm-55 degreeC, More preferably, it is Tm-90-Tm-60 degreeC. When the temperature is lower than Tm-105 ° C., the coating property during processing into a magnetic recording medium tends to deteriorate due to relaxation of the amorphous part. On the other hand, when the temperature exceeds Tm-50 ° C., molecular chain orientation relaxation proceeds, the humidity expansion coefficient deteriorates, and the dimensional stability tends to deteriorate. T-meta can be controlled by the HS temperature. The higher the HS temperature, the higher the tendency.

  In the present invention, the thickness of the biaxially oriented polyester film can be appropriately determined according to the use, but usually 1 to 7 μm is preferable for the magnetic recording medium. When this thickness is smaller than 1 μm, electromagnetic conversion characteristics may be deteriorated when a magnetic tape is used. On the other hand, when the thickness is larger than 7 μm, the tape length per one tape is shortened, so that it may be difficult to reduce the size and increase the capacity of the magnetic tape. Therefore, in the case of high-density magnetic recording medium applications, the lower limit of the thickness is preferably 2 μm, more preferably 3 μm, and the upper limit is preferably 6.5 μm, more preferably 6 μm. A more preferable range is 2 to 6.5 μm, and a more preferable range is 3 to 6 μm.

  The above-described biaxially oriented polyester film of the present invention is produced, for example, as follows.

  First, a polyester film constituting a biaxially oriented polyester film is manufactured. In order to produce a polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, and then cooled and solidified to form a sheet. At this time, it is preferable to filter the polymer with a fiber-sintered stainless metal filter in order to remove unmelted material in the polymer. In addition, it is preferable to add inert particles in order to control the surface properties of the polyester film and to impart easy slipping, wear resistance, scratch resistance, and the like. Inert particles are inorganic particles, organic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, etc., acrylic Examples thereof include organic particles containing acid, styrene resin, thermosetting resin, silicone, imide compound and the like, particles precipitated by a catalyst added at the time of polyester polymerization reaction (so-called internal particles), and the like. Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, and the like, provided that they do not inhibit the present invention. Conductive agents, crystal nucleating agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments, dyes, and the like may be added.

  Then, after extending | stretching the said sheet | seat to the biaxial of a longitudinal direction and the width direction, it heat-processes. In order to improve the dimensional stability in the width direction, the stretching step is preferably divided into two or more stages in the width direction. That is, it is easy to obtain a film with high dimensional stability that is optimal as a magnetic tape having high dimensional stability by the method of performing re-TD stretching. As the stretching method, a sequential biaxial stretching method in which stretching in the longitudinal direction and then stretching in two steps in the width direction is preferable.

  Hereinafter, the method for producing the support of the present invention will be described as an example in which polyethylene terephthalate (PET) is used as polyester. Of course, the present application is not limited to a support using a PET film, but may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalenedicarboxylate having a high glass transition temperature or a high melting point, it may be extruded or stretched at a temperature higher than the following temperature.

  First, polyethylene terephthalate is prepared. Polyethylene terephthalate is manufactured by one of the following processes. (1) Using terephthalic acid and ethylene glycol as raw materials, a low molecular weight polyethylene terephthalate or oligomer is obtained by direct esterification reaction, and then a polymer is obtained by polycondensation reaction using antimony trioxide or titanium compound as a catalyst. Process (2) A process in which dimethyl terephthalate and ethylene glycol are used as raw materials, a low molecular weight product is obtained by transesterification, and then a polymer is obtained by polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. Here, the reaction proceeds even without a catalyst, but the transesterification usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium, titanium as a catalyst, and the transesterification reaction is carried out. After the completion of the reaction, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction.

  In order to contain the inert particles in the polyester constituting the film, a method in which the inert particles are dispersed in a predetermined proportion in the form of a slurry in ethylene glycol and this ethylene glycol is added during polymerization is preferable. When adding inert particles, for example, water sol or alcohol sol particles obtained at the time of synthesis of the inert particles are added without drying once, the dispersibility of the particles is good. It is also effective to mix an aqueous slurry of inert particles directly with PET pellets and knead them into PET using a vented biaxial kneading extruder. As a method for adjusting the content of the inert particles, a master pellet of a high concentration of inert particles is prepared by the above method, and this is diluted with PET that does not substantially contain inert particles during film formation. A method for adjusting the content of the active particles is effective.

  Next, the obtained PET pellets are dried under reduced pressure at 180 ° C. for 3 hours or more, and then supplied to an extruder heated to 270 to 320 ° C. under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease. The film is extruded from a slit-shaped die and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh, in order to remove foreign substances and altered polymers. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. To laminate the film, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merge blocks.

  Next, the unstretched film thus obtained is stretched in the longitudinal direction using the difference in peripheral speed of the roll (MD stretching) using an MD stretching machine in which several rolls are arranged. A biaxial stretching method in which stretching is performed in two stages with a stenter (TD stretching 1, TD stretching 2) will be described.

  First, the unstretched film is MD stretched. The stretching temperature for MD stretching varies depending on the type of polymer used, but can be determined using the glass transition temperature Tg of the unstretched film as a guide. It is preferable that it is the range of Tg-10-Tg + 15 degreeC, More preferably, it is TgC-Tg + 10 degreeC. When the stretching temperature is lower than the above range, film tearing frequently occurs and the productivity is lowered, and it may be difficult to stably stretch in the two-stage TD stretching after MD stretching, which is a feature of the present application. . The MD draw ratio is preferably 2.5 to 4.0 times. More preferably, it is 2.8 to 3.8 times, and still more preferably 3.0 to 3.5 times. In order to stably stretch the two-stage TD stretching, the film structure after the MD stretching ratio is important. If the film is oriented too much in the MD direction, the molecular chains are entangled during TD stretching, and stress is locally generated, so that the film is easily broken. In order to prevent the local generation of stress, it is necessary to create a microcrystalline state that acts as a stress propagation portion and to have an appropriate MD orientation.

  Next, TD stretching is performed using a stenter. In order to improve the dimensional stability in the width direction and to obtain a biaxially oriented polyester film having good storage stability, slit property and film forming property, it is preferable to stretch in two steps in the width direction. First, the draw ratio of the first-stage drawing (TD drawing 1) is preferably 3.0 to 5.0 times, more preferably 3.2 to 4.5 times, and even more preferably 3.5 to 5.0 times. It is 4.0 times. The stretching temperature of TD stretching 1 is preferably in the range of 65 to 120 ° C, more preferably 75 to 110 ° C, and further preferably 80 to 105 ° C. Next, the second stage stretching (TD stretching 2) is performed in the stenter as it is. The draw ratio of TD stretch 2 is preferably 1.01 to 2 times, more preferably 1.1 to 1.8 times, and still more preferably 1.2 to 1.6 times. The stretching temperature of TD stretching 2 is preferably in the range of 160 to 210 ° C, more preferably 165 to 205 ° C, and further preferably in the range of 170 to 200 ° C.

  In order to achieve the Young's modulus, birefringence index Δn, and enthalpy relaxation amount ΔHe of the present application, it is important to increase the total TD stretch ratio compared to the MD stretch ratio. In particular, in order to control Δn within the scope of the present application, it is necessary to increase the TD orientation.

  In addition, in order to perform stable film formation, it is important to perform TD stretching 1 and TD stretching 2 in the same tenter and stretch them with a specific stretching temperature difference. The temperature difference between TD stretching 1 and TD stretching 2 is preferably in the range of 60 to 105 ° C. More preferably, it is 65-103 degreeC, More preferably, it is 70-100 degreeC. When the temperature difference is smaller than 60 ° C., molecular chains that are intertwined and oriented at the time of stretching are difficult to unravel and re-stretching is difficult. When the temperature difference is larger than 105 ° C., the molecular chain oriented by TD stretching 1 is relaxed, and effective stretching cannot be performed by TD stretching 2, and dimensional stability may not be improved.

  Subsequently, the stretched film is heat-treated (heat set treatment, hereinafter referred to as HS treatment) while being relaxed under tension or in the width direction. Although HS treatment conditions vary depending on the type of polymer, the HS temperature is preferably 170 to 210 ° C, more preferably 180 to 200 ° C, and still more preferably 185 to 195 ° C. The HS time is preferably in the range of 0.5 to 10 seconds, and the relaxation rate is preferably 0 to 2%. After the HS treatment, the gripping clip is released to rapidly cool to room temperature while reducing the tension applied to the film. Thereafter, the film edge is removed and wound on a roll.

  In order for the film of the present invention to exhibit the effects of dimensional stability and storage stability, it is effective that the film after being wound on a roll is transported under tension and subjected to an aging treatment in a hot air oven. . The atmospheric temperature of the aging treatment is preferably Tg (glass transition point) -60 to Tg-22 ° C. More preferably, it is Tg-50-Tg-25 degreeC, More preferably, it is Tg-40-Tg-28 degreeC. When the atmospheric temperature is low, the enthalpy relaxation amount ΔHe is small. Rewinding and replacing the core side and the surface layer side to perform further aging processing, and this is repeated for the processing time. By repeating the rewinding, the physical property unevenness in the core portion and the surface layer portion of the roll can be reduced, and the storage stability can be further improved. The tension of the aging treatment is 8 to 16 MPa. More preferably, it is 9-15 MPa, More preferably, it is 10-14 MPa. If the tension of the aging treatment is too large, the molecular chain tends to extend in the longitudinal direction, which deteriorates the flatness. If the tension of the aging treatment is too small, the enthalpy relaxation amount ΔHe becomes small. The aging treatment takes strain of molecular chains, increases the degree of tension, and particularly improves dimensional stability. The aging treatment time is preferably in the range of 24 to 240 hours, more preferably in the range of 48 to 168 hours, and still more preferably in the range of 72 to 150 hours. If the aging treatment time is too long, the enthalpy relaxation amount ΔHe increases.

  In the present application, by performing the aging treatment under the MD-TD1-TD2 stretching process and the specific conditions described above, the film forming property is good and the Young's modulus, birefringence Δn, and enthalpy relaxation ΔHe are controlled within the scope of the present application. Can produce a biaxially oriented polyester film with good dimensional stability, applicability, and error rate when used as a magnetic tape. All processes such as MD-TD and MD1-TD1-MD2-TD2 It is difficult to obtain a biaxially oriented polyester film having good physical properties. In addition, simultaneous biaxial stretching makes it difficult to form an entanglement of molecular chains at the time of stretching in TD stretching, so that it is difficult to achieve orientation, and a similar biaxially oriented polyester film is difficult to obtain.

  Next, a method for manufacturing a magnetic recording medium will be described.

  The magnetic recording medium support (biaxially oriented polyester film) obtained as described above is slit into, for example, a width of 0.1 to 3 m, and conveyed at a speed of 20 to 300 m / min and a tension of 50 to 300 N / m. On the other hand, a magnetic paint and a non-magnetic paint are applied to one surface (A surface) with an extrusion coater. A magnetic paint is applied to the upper layer with a thickness of 0.1 to 0.3 μm, and a nonmagnetic paint is applied to the lower layer with a thickness of 0.5 to 1.5 μm. Thereafter, the support coated with the magnetic coating material and the nonmagnetic coating material is magnetically oriented and dried at a temperature of 80 to 130 ° C. Next, a back coat is applied to the opposite surface (B surface) with a thickness of 0.3 to 0.8 μm, and after calendar treatment, it is wound up. The calendering is performed using a small test calender (steel / nylon roll, 5 stages) at a temperature of 70 to 120 ° C. and a linear pressure of 0.5 to 5 kN / cm. Thereafter, the film is aged at 60 to 80 ° C. for 24 to 72 hours, slit to a width of 1/2 inch (1.27 cm), and a pancake is produced. Next, a specific length from this pancake is incorporated into a cassette to obtain a cassette tape type magnetic recording medium.

  Here, examples of the composition of the magnetic paint include the following compositions.

(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by weight Modified vinyl chloride copolymer: 10 parts by weight Modified polyurethane: 10 parts by weight Polyisocyanate: 5 parts by weight 2-ethylhexyl oleate: 1.5 parts by weight Palmitic acid: 1 Mass parts-Carbon black: 1 part by mass-Alumina: 10 parts by mass-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of back coat)
Carbon black (average particle size 20 nm): 95 parts by mass Carbon black (average particle size 280 nm): 10 parts by mass Alumina: 0.1 parts by mass Modified polyurethane: 20 parts by mass Modified vinyl chloride copolymer: 30 Mass parts: Cyclohexanone: 200 parts by mass Methyl ethyl ketone: 300 parts by mass Toluene: 100 parts by mass Magnetic recording media are, for example, data recording applications, specifically computer data backup applications (for example, linear tape recording media (LTO4 And LTO5))) and digital image recording applications such as video.

(Methods for measuring physical properties and methods for evaluating effects)
The characteristic value measurement method and effect evaluation method in the present invention are as follows.

(1) Young's modulus The Young's modulus of the film is measured according to ASTM D882 (1997). Instron type tensile tester is used and the conditions are as follows. The average value of the five measurement results is defined as the Young's modulus in the present invention.

・ Measuring device: Model 5848, an ultra-precision material testing machine manufactured by Instron
・ Sample size: Young's modulus measurement in the film width direction Film longitudinal direction 2 mm × film width direction 12.6 mm
(The gripping distance is 8mm in the film width direction)
・ Tensile speed: 1 mm / min ・ Measurement environment: Temperature 23 ° C., humidity 65% RH
-Number of measurements: 5 times.

(2) Birefringence index Δn
Δn (nMD-nTD) was measured using the following measuring instrument according to JIS-K7142 (2008).

・ Device: Abbe refractometer 4T (manufactured by Atago Co., Ltd.)
-Light source: Sodium D line-Measurement temperature: 25 ° C
・ Measurement humidity: 65% RH
Mount solution: methylene iodide, sulfur methylene iodide Average refractive index n_bar = ((nMD + nTD + nZD) / 3)
Birefringence Δn = (nMD−nTD)
nMD: Refractive index in the film longitudinal direction nTD: Refractive index in the film width direction (3) Melting point (Tm), minute melting peak temperature (T-meta)
According to JIS-K7121 (1987), a differential scanning calorimeter, DSC (RDC220) manufactured by Seiko Instruments Inc., and a disk station (SSC / 5200) manufactured by Seiko Instruments Inc. were used, and a sample 5 mg was placed on an aluminum tray 25 The temperature was raised from 0 ° C. to 300 ° C. at a heating rate of 20 ° C./min. At that time, the minute endothermic peak temperature appearing slightly on the low temperature side of the melting point (Tm), which is the endothermic peak temperature of melting observed, was defined as T-meta.

(4) Glass transition temperature (Tg)
Specific heat is measured with the following equipment and conditions, and determined according to JIS-K7121 (1987). The amount of heat calculated from the peak area of the endothermic peak due to enthalpy relaxation that appears slightly on the high temperature side of the glass transition point (Tg) is defined as enthalpy relaxation amount ΔHe.

・ Device: Temperature modulation DSC manufactured by TA Instrument
-Measurement conditions-Heating temperature: 270-570K (RCS cooling method)
・ Temperature calibration: Melting point of high purity indium and tin ・ Temperature modulation amplitude: ± 1K
・ Temperature modulation period: 60 seconds ・ Temperature increase step: 5K
・ Sample weight: 5mg
Sample container: Aluminum open container (22 mg)
Reference container: Aluminum open container (18mg)
The glass transition temperature is calculated by the following formula.

Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(5) Humidity expansion coefficient It measures on the following conditions with respect to the width direction of a film, and let the average value of three measurement results be a humidity expansion coefficient in this invention.

Measuring device: Thermomechanical analyzer TMA-50 manufactured by Shimadzu (humidity generator: humidity control device HC-1 manufactured by ULVAC-RIKO)
Sample size: 10 mm in the film longitudinal direction x 12.6 mm in the film width direction
・ Load: 0.5g
・ Number of measurements: 3 times ・ Measurement temperature: 30 ° C.
・ Measurement humidity: Measured dimensions by holding at 40% RH for 6 hours, increasing the humidity to 80% RH in 40 minutes and holding at 80% RH for 6 hours, and then measuring the dimensional change ΔL (mm) in the width direction of the support. taking measurement. The humidity expansion coefficient (ppm /% RH) is calculated from the following equation.

Humidity expansion coefficient (ppm /% RH) = 10 ⁶ × {(ΔL / 12.6) / (80-40)}
(6) Thermal contraction rate It measured according to JIS C2318 (2007).

Sample size: width 10 mm, marked line interval 200 mm
Measurement conditions: temperature 100 ° C., treatment time 30 minutes, no load state The heat shrinkage rate was determined from the following equation.

Thermal contraction rate (%) = {(L ₀ −L) / L ₀ } × 100
L ₀ : Marking interval before heat treatment L: Marking interval after heat treatment However, the sample size may be measured by reducing the mark interval depending on the size of the obtained sample.

(7) Stability of width dimension A film slit to a width of 1 m is conveyed with a tension of 200 N, and a magnetic paint and a non-magnetic paint having the following composition are applied on one surface (side A) of the support by an extrusion coater ( The upper layer is made of magnetic paint, the coating thickness is 0.2 μm, the lower layer is made of non-magnetic paint and the coating thickness is 0.9 μm), magnetically oriented, and dried at a drying temperature of 100 ° C. Next, a back coat having the following composition was applied to the opposite surface (B surface), and then at a temperature of 85 ° C. and a linear pressure of 2.0 × 10 ⁵ N / m using a small test calender device (steel / nylon roll, 5 steps). After calendaring with, take up. The original tape is slit to a width of 1/2 inch (12.65 mm) to make a pancake. Next, a length of 200 m from this pancake is incorporated into a cassette to form a cassette tape.

(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by mass [Fe: Co: Ni: Al: Y: Ca = 70: 24: 1: 2: 2: 1 (mass ratio)]
[Long axis length: 0.09 μm, axial ratio: 6, coercive force: 153 kA / m (1,922 Oe), saturation magnetization: 146 Am ² / kg (146 emu / g), BET specific surface area: 53 m ² / g, X-ray Particle size: 15 nm]
Modified vinyl chloride copolymer (binder): 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Modified polyurethane (binder): 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
Polyisocyanate (curing agent): 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass Carbon black (antistatic agent): 1 part by mass (average primary particle size: 0.018 μm)
Alumina (abrasive): 10 parts by mass (α alumina, average particle size: 0.18 μm)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of nonmagnetic paint)
Modified polyurethane: 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass-Polyisocyanate: 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
・ 2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass (composition of back coat)
Carbon black: 95 parts by mass (antistatic agent, average primary particle size 0.018 μm)
Carbon black: 10 parts by mass (antistatic agent, average primary particle size 0.3 μm)
Alumina: 0.1 part by mass (α alumina, average particle size: 0.18 μm)
Modified polyurethane: 20 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 30 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
• Cyclohexanone: 200 parts by mass • Methyl ethyl ketone: 300 parts by mass • Toluene: 100 parts by mass Take out the tape from the cassette tape cartridge, put the sheet width measuring device prepared as shown in FIG. Measure. The sheet width measuring device shown in FIG. 1 is a device that measures the width dimension using a laser, and fixes the magnetic tape 9 to the load detector 3 while setting it on the free rolls 5 to 8, and the end portion A weight 4 serving as a load is hung on. When this magnetic tape 9 is irradiated with the laser beam 10, the laser beam 10 oscillated linearly in the width direction from the laser oscillator 1 is blocked only by the portion of the magnetic tape 9, enters the light receiving unit 2, and the blocked laser beam The width is measured as the width of the magnetic tape. The average value of the three measurement results is defined as the width in the present invention.

・ Measuring device: Sheet width measuring device manufactured by Ayaha Engineering Co., Ltd. ・ Laser oscillator 1, light receiving unit 2: Laser dimension measuring device LS-5040 manufactured by Keyence Corporation
-Load detector 3: Load cell CBE1-10K manufactured by NMB
・ Constant temperature and humidity chamber: SE-25VL-A manufactured by Kato Corporation
・ Load 4: Weight (longitudinal direction)
・ Sample size: width 1/2 inch x length 250 mm
-Retention time: 5 hours-Number of measurements: 3 measurements.

(Width dimensional change rate: dimensional stability)
The width dimension (l _A , l _B ) is measured under two conditions, and the dimensional change rate is calculated by the following equation. Specifically, dimensional stability is evaluated according to the following criteria.

By measuring the lapse of 24 hours after _{l A} in A conditions, measuring the _{l B} after a lapse of 24 hours then B conditions. Three points were measured: a sample cut from the 30 m point from the beginning of the tape cartridge, a sample cut from the 100 m point, and a sample cut from the 170 m point. X is rejected.

A condition: 10 ° C, 10% RH, tension 0.8N
B condition: 29 ° C, 80% RH, tension 0.5N
Width dimensional change rate (ppm) = 10 ⁶ × ((l _B -l _A ) / l _A )
A: Maximum width change rate is less than 500 (ppm) ○: Maximum width change rate is 500 (ppm) or more and less than 600 (ppm) Δ: Maximum width change rate is 600 (ppm) or more Less than 700 (ppm) ×: The maximum value of the width dimensional change rate is 700 (ppm) or more. (8) Coating property The cassette tape produced in (7) above is obtained using a commercially available LTO drive 3580-L11 manufactured by IBM. The coating unevenness or coating omission was visually checked before running, and then run for 24 hours. After peeling, the coating properties of the magnetic layer of the tape were evaluated according to the following criteria.

  A: There is no unevenness, coating omission, or peeling at all, and coating properties are good.

  ○: There is almost no unevenness, missing coating, or peeling, and there is no problem in coating properties.

  Δ: Unevenness, coating omission, and peeling sometimes occur and there is a slight problem in coating properties.

  X: Unevenness, coating omission, and peeling frequently occur, and there is a problem in applicability.

(9) Error rate The cassette tape produced in (7) above is recorded and reproduced (recording wavelength 0.55 μm) in an environment of 23 ° C. and 50% RH using a commercially available IBM LTO drive 3580-L11. evaluate. The error rate is calculated from the error information (number of error bits) output from the drive by the following formula. The dimensional stability is evaluated according to the following criteria. X is rejected.

Error rate = (number of error bits) / (number of write bits)
A: Error rate is less than 1.0 × 10 ⁻⁶ ○: Error rate is 1.0 × 10 ⁻⁶ or more, less than 1.0 × 10 ⁻⁵ Δ: Error rate is 1.0 × 10 ⁻⁵ or more, 1 Less than 0.0 × 10 ⁻⁴ ×; error rate is 1.0 × 10 ⁻⁴ or more (10) Film-forming property The film-forming property of the film was evaluated according to the following criteria.

  (Double-circle): There is no generation | occurrence | production of a film tear and it is a stable film forming.

  ○: Stable film formation is possible with almost no film tearing.

  (Triangle | delta): Film tearing generate | occur | produces occasionally and film forming stability is a little low.

  X: Many film breaks occur and the film formation stability is low.

  Based on the following examples, embodiments of the present invention will be described. Here, polyethylene terephthalate is expressed as PET, polyetherimide is expressed as PEI, and polyethylene naphthalate is expressed as PEN.

(Reference Example 1)
194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, and the contents were heated to 140 ° C. and dissolved. Then, 0.1 mass part of magnesium acetate tetrahydrate and 0.05 mass part of antimony trioxide were added while stirring the contents, and a transesterification reaction was performed while distilling methanol at 140 to 230 ° C. Next, 1 part by mass (5 parts by mass as trimethyl phosphate) of 5 parts by mass ethylene glycol solution of trimethyl phosphate was added.

  Addition of trimethyl phosphoric acid in ethylene glycol reduces the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. When the temperature of the reaction contents in the transesterification reactor thus reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

After the transition, the reaction system was gradually heated from 230 ° C. to 290 ° C. and the pressure was reduced to 0.1 kPa. The time to reach the final temperature and final pressure was both 60 minutes. After reaching the final temperature and the final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the agitation torque of the polymerization apparatus was a predetermined value (specific values differ depending on the specifications of the polymerization apparatus. The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 was a predetermined value). Accordingly, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain polyethylene terephthalate PET pellets X having an intrinsic viscosity of 0.62. (Tm = 255 ° C., Tg = 78 ° C.)
(Reference Example 2)
In the same direction rotation type bent type biaxial kneading extruder heated to 280 ° C., 98 parts by mass of PET pellet X prepared in Reference Example 1 and 10 parts by mass of water of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm. The slurry is supplied in an amount of 20 parts by mass (2 parts by mass as spherical cross-linked polystyrene), the vent hole is maintained at a reduced pressure of 1 kPa or less to remove moisture, and 2 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm are contained. PET pellet Z _0.3 with a viscosity of 0.62 was obtained.

(Reference Example 3)
In the same direction rotation type vent type biaxial kneading extruder heated to 280 ° C., 98 parts by mass of PET pellet X prepared in Reference Example 1 and 10 parts by mass of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm The slurry is supplied in an amount of 20 parts by mass (2 parts by mass as a spherical cross-linked polystyrene), the vent hole is maintained at a reduced pressure of 1 kPa or less, moisture is removed, and 2 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.8 μm are contained. PET pellets Z _0.8 with a viscosity of 0.62 were obtained.

(Reference Example 4)
Bent-type twin-screw kneading and extruding machine of the same direction rotation type provided with three kneading paddle kneading parts heated to a temperature of 300 ° C. (manufactured by Nippon Steel Works, screw diameter 30 mm, screw length / screw diameter = 45.5) 50 parts by mass of the PET pellet X obtained in Reference Example 1 and 50 parts by mass of PEI “Ultem 1010” pellets manufactured by SABIC Innovative Plastics Co., Ltd. were melt-extruded at a screw speed of 300 rpm to form a strand. After discharging and cooling with water at a temperature of 25 ° C., it was immediately cut to produce a blend chip (I).

(Reference Example 5)
To a mixture of 100 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate salt is added and gradually increased from a temperature of 150 ° C. to a temperature of 240 ° C. The transesterification was carried out while raising the temperature. In the middle, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added. When the reaction temperature reached 220 ° C., 0.042 parts by mass of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (corresponding to 2 mmol%) was added. Thereafter, a transesterification reaction was carried out, and 0.023 parts by mass of trimethyl phosphoric acid was added. Next, the reaction product is transferred to a polymerization apparatus, heated to a temperature of 290 ° C., subjected to a polycondensation reaction under a high vacuum of 30 Pa, and the stirring torque of the polymerization apparatus is a predetermined value (specifically depending on the specifications of the polymerization apparatus). Although this value was different, the value indicated by polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65 in this polymerization apparatus was a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in the form of a strand, and immediately cut to obtain PEN pellet X ′ having an intrinsic viscosity of 0.65.

(Reference Example 6)
A PEN pellet X ′ prepared in Reference Example 5 is 98 parts by mass and 10 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm in a bent biaxial kneading extruder of the same direction rotation type heated to 280 ° C. 20 parts by mass of water slurry (2 parts by mass as spherical cross-linked polystyrene) is supplied, the vent hole is maintained at a reduced pressure of 1 kPa or less to remove water, and 2 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm are contained. PEN pellets Z ′ _0.3 having an intrinsic viscosity of 0.65 were obtained.

(Reference Example 7)
Two spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were obtained in the same manner as in Reference Example 6 except that spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were used instead of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm. PEN pellets Z ′ _0.8 having an intrinsic viscosity of 0.65 and contained by mass were obtained.

Example 1
In the extruder E heated to 295 ° C. using the two extruders E and F, 3 parts by mass of the PET pellet X97 obtained in Reference Examples 1 and 2 and 3 parts by mass of the PET pellet Z _0.3 were obtained at 180 ° C. In the extruder F, which was supplied after drying under reduced pressure for a period of time and heated to 295 ° C., 3 parts by weight of PET pellets X99 parts by mass obtained in Reference Examples 1 and 3 and 1 part by weight of PET pellets Z _0.8 were obtained at 180 ° C. It supplied after drying under reduced pressure for the time. Two layers are joined together in a T-die (lamination ratio E (A surface side) / F (B surface side) = 7/1), while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., It was closely cooled and solidified so as to come into contact with the casting drum to produce a laminated unstretched film.

  Subsequently, the obtained unstretched laminated film was preheated with a heated roll group, then stretched 3.3 times at a temperature of 90 ° C. (MD stretching), and cooled with a roll group at a temperature of 25 ° C. to be uniaxially stretched. A film was obtained. While holding both ends of the obtained uniaxially stretched film with clips, the tenter is guided to a preheating zone at a temperature of 85 ° C. in the tenter, and then continuously in the heating zone at a temperature of 90 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. Then, the film was stretched 3.5 times (TD stretch 1), and further stretched 1.4 times in the width direction in a heating zone at a temperature of 180 ° C. (TD stretch 2). Subsequently, heat treatment was performed for 5 seconds at a temperature of 190 ° C. in a heat treatment zone in the tenter. Subsequently, after uniformly cooling to 25 ° C., the film edge was removed, and the film was wound on a core to obtain a biaxially oriented polyester film having a thickness of 5 μm.

  The obtained biaxially oriented polyester film was set in a hot air oven having an atmospheric temperature of 50 ° C., and an aging treatment was performed while running at a tension of 11 MPa and a conveyance speed of 10 m / min. When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, it had excellent properties in dimensional stability, applicability, error rate, and film forming stability.

(Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, since the Young's modulus in the MD direction is low when used as a magnetic tape, the applicability of the film is slightly inferior in dimensional stability and film formation stability. It had excellent characteristics in error rate.

(Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, dimensional stability, applicability, and error due to high Young's modulus in the MD direction when used as a magnetic tape, although film formation was slightly inferior. It had excellent characteristics in rate.

Example 4
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, the birefringence Δn was low when used as a magnetic tape, but the film stability was slightly inferior, but the dimensional stability, applicability, and error rate were low. It had excellent characteristics.

(Example 5)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, because of its low Young's modulus in the TD direction when used as a magnetic tape, coatability, error rate, and film formation are slightly inferior in dimensional stability. It had excellent properties.

(Example 6)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the aging treatment conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, when used as a magnetic tape, the enthalpy relaxation is low and the heat shrinkage rate is large, so that the error rate, the dimensional stability of the coating is slightly inferior, The film had excellent film forming properties.

(Example 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the aging treatment conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, although the enthalpy relaxation is high when used as a magnetic tape, the error rate is slightly inferior, but the dimensional stability, applicability, and film forming property are low. It had excellent properties.

(Example 8)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions and the aging treatment conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, the Young's modulus was low when used as a magnetic tape, and although the coefficient of humidity expansion was high, the dimensional stability and film forming properties were slightly inferior, It had excellent coating properties and error rate.

Example 9
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the aging treatment conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, the heat shrinkage rate was high when used as a magnetic tape, but the applicability was slightly inferior, but excellent in dimensional stability and film formability. Had characteristics.

(Example 10)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the aging treatment conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, the flatness deteriorated due to the large tension, and when used as a magnetic tape as shown in Table 2, the applicability and error rate were slightly inferior, but the dimensional stability The film had excellent film forming properties.

(Example 11)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, the heat shrinkage rate was high when used as a magnetic tape, but the applicability was slightly inferior, but the dimensional stability, error rate, film forming property It had excellent characteristics.

(Example 12)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, it has a high coefficient of humidity expansion when used as a magnetic tape, but its dimensional stability is slightly inferior, but its applicability, error rate, film forming property It had excellent characteristics.

(Example 13)
In the extruder E heated to 295 ° C. using two extruders E and F, the PET pellets X87 parts by mass obtained in Reference Examples 1, 2 and 4, 3 parts by mass of PET pellets Z _0.3 , blended chips (I) Extruder F, which was supplied after drying 10 parts by weight at 180 ° C. under reduced pressure for 3 hours and heated to 295 ° C., was obtained by adding PET pellets X89 parts obtained in Reference Examples 1, 3, and 4, PET 1 part by weight of pellets Z _{0.8 and} 10 parts by weight of blend chip (I) were dried at 180 ° C. under reduced pressure for 3 hours and then supplied. Two layers are joined together in a T-die (lamination ratio E (A surface side) / F (B surface side) = 7/1), while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was solidified by cooling so as to be in contact with the casting drum to produce a laminated unstretched film and the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, it had excellent properties in dimensional stability, storage stability, slit property, and film forming property.

(Example 14)
PET pellets X ′, PEN pellets Z ′ _0.3 , PET pellets X ′, PET pellets Z _0.3 , and PET pellets Z _0.8 used in Example 1 were obtained in Reference Examples 5, 6, 7, and 8. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the PEN pellet Z ′ was changed to _0.8 and a laminated unstretched film was produced and the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, it had slightly superior characteristics in dimensional stability, storage stability, slit property, and film forming property.

(Comparative Example 1)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions in Table 1 were changed. Since the TD Young's modulus was low and the humidity expansion coefficient was large, the obtained biaxially oriented polyester film was greatly inferior in dimensional stability and film formability.

(Comparative Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions in Table 1 were changed. The TD Young's modulus was high, and the obtained biaxially oriented polyester film was greatly inferior in film formability.

(Comparative Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions in Table 1 were changed. The TD Young's modulus was low, and the obtained biaxially oriented polyester film was greatly inferior in dimensional stability.

(Comparative Example 4)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions in Table 1 were changed. Since the TD stretch ratio was high, the obtained biaxially oriented polyester film was greatly inferior in film formability.

(Comparative Example 5)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the aging treatment conditions in Table 1 were changed. Since the aging treatment was not performed, there was no enthalpy relaxation, and the obtained biaxially oriented polyester film was greatly inferior in applicability.

(Comparative Example 6)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the aging treatment conditions in Table 1 were changed. Since the aging treatment time is long, the enthalpy relaxation ΔHe is large, and the humidity expansion coefficient is also large. Thus, the obtained biaxially oriented polyester film was greatly inferior in dimensional stability and error rate.

(Comparative Example 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions in Table 1 were changed. Since the MD draw ratio was larger than the total TD draw ratio, the TD Young's modulus was low and the birefringence index Δn was also large. The resulting biaxially oriented polyester film was greatly inferior in dimensional stability and film formability.

(Comparative Example 8)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film-forming stretching method in Table 1 was changed. The TD Young's modulus was low, and the obtained biaxially oriented polyester film was greatly inferior in dimensional stability.

It is a schematic diagram of the sheet | seat width measuring apparatus used when measuring a width dimension.

1: Laser oscillator 2: Light receiving unit 3: Load detector 4: Load 5: Free roll 6: Free roll 7: Free roll 8: Free roll 9: Magnetic tape 10: Laser light

Claims (4)

Young's modulus in the width direction is 6 to 10 GPa, and birefringence Δn (nMD−nTD) indicated by the difference between the refractive index nMD in the longitudinal direction and the refractive index nTD in the width direction is −0.10 to −0.02. A biaxially oriented polyester film having an enthalpy relaxation amount ΔHe of 0.1 to 3.0 J / g. The biaxially oriented polyester film according to claim 1, wherein a humidity expansion coefficient in the width direction is 0 to 6 ppm /% RH. The biaxially oriented polyester film according to claim 1 or 2, wherein a heat shrinkage rate in the width direction at 100 ° C for 30 minutes is 0 to 2%. The biaxially oriented polyester film according to any one of claims 1 to 3, wherein a minute melting peak temperature T-meta is (Tm-105) to (Tm-50) ° C.

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