JP7106977B2 - polyester film - Google Patents

Description

The present invention is used in applications requiring extremely high dimensional stability, such as base films used in ultra-high-density recording media exceeding 10 Tb. The present invention relates to a polyester film which is easy to adjust and excellent in workability for magnetic recording media.

2. Description of the Related Art In recent years, as the amount of data that needs to be handled in computer systems and the like has increased, there has been a demand for a significant increase in the recording capacity of magnetic recording media. Conventionally, efforts have been made to improve the dimensional stability of substrates used in magnetic recording media (Reference 1), but improvements in substrate dimensional stability with inexpensive materials are reaching their limits. In addition, by adjusting the tape tension and matching the tape width during data recording and data playback, the track position during recording is within the range of the playback head. Proposals have also been made to reduce this (references 2-4). These techniques change the longitudinal dimension of the tape by changing the tension in the longitudinal direction of the tape. The purpose is to converge the tape width during playback within the allowable range. However, the adjustment range of the tape width by tape tension requires a large tension change when using a conventional high-rigidity magnetic recording medium substrate. In recent years, the tension in high-density recording tape playback devices has been set to be as small as possible in order to suppress irreversible changes due to creep deformation of magnetic recording media. However, the tape width adjustment range is limited to a very small area, and it becomes difficult to significantly improve the recording density by increasing the number of tracks. On the other hand, using a low-rigidity base material makes it easier to adjust the tape width by adjusting the tape tension. There is a problem that when a high tension is applied, the base material itself is stretched and easily buckled, making it impossible to obtain a good magnetic recording medium.

Japanese Patent Application Laid-Open No. 2010-31116 JP 2005-285196 A JP-A-2005-285261 JP 2006-099919 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a resin film for a magnetic recording medium substrate excellent in improving the track density by adjusting the tape tension as a means for achieving a significant improvement in the track density required for ultra-high density magnetic recording media. It is in.

As a result of intensive research by the inventors of the present invention to solve the above problems, copolymerization of a specific dimer component achieves both facilitation of width control by tape tension and suitability for processing to a magnetic recording medium at a high level. We have found that it is possible, and arrived at the present invention.

Thus, according to the present invention, the following formulas (I) and (II)
-C(O)-R ^A -C(O)- (I)
-OR ^A -O- (II)
(In the structural formulas (I) to (II) above, ^RA represents an alkylene group which may contain a cyclo ring having 31 to 51 carbon atoms and a branched chain.) is a repeating unit of the polyester. A polyester film formed from a copolymerized polyester copolymerized in the range of 0.3 to less than 5 mol% based on the number of moles of
The polyester film has a longitudinal Young's modulus of 1 GPa or more and 6 GPa or less, a thickness of 1 μm or more and 4.5 μm or less, and a product of the longitudinal Young's modulus and the thickness of 5 GPa·μm or more and 20 GPa·μm or less,
Provided is a polyester film having a longitudinal elongation of 3% or less when heated from 30° C. to 110° C. at a rate of 5° C./min under a load of 2 kg/mm ² in the longitudinal direction.

The polyester film of the present invention improves dimensional stability against environmental changes such as temperature and humidity in base films and the like used for ultrahigh-density recording media of 10 Tb or more, and the tape width can be easily adjusted by tape tension. The occurrence of wrinkles or the like during processing into a magnetic recording medium is also suppressed, making it possible to provide an excellent data storage tape.

1 is a perspective view of a dimension measuring device used in the present invention; FIG.

<Copolyester>
The copolymer polyester in the present invention consists of a dicarboxylic acid component and a glycol component.
First, the specific dicarboxylic acid component mentioned above is a phenylene group or a naphthalenediyl group. mentioned. Among these, the terephthalic acid component and the 2,6-naphthalenedicarboxylic acid component, which relatively tend to improve physical properties such as mechanical strength, are preferred, and the 2,6-naphthalenedicarboxylic acid component is particularly preferred, from the viewpoint of the effect of the present invention. .

Examples of the aforementioned glycol component mainly include alkylene glycols having 2 to 4 carbon atoms, and specific examples include ethylene glycol, trimethylene glycol, tetramethylene glycol and the like. Among these, from the viewpoint of the effect of the present invention, the ethylene glycol component is preferable because it relatively easily improves physical properties such as mechanical strength.

A feature of the present invention is that the dimer components having 31 to 51 carbon atoms represented by the above formulas (I) and (II), that is, aliphatic dimer acids or dimer diols are copolymerized. Specific dimer acids and dimer diols preferably contain a branched chain, preferably have an alicyclic moiety such as a cyclohexane ring structure, and particularly preferably have both a branched chain and a cyclohexane ring. Preferred dimer components range from 34 to 46 carbon atoms.

In addition, the copolymerized polyester in the present invention is a known copolymerized component such as an aliphatic dicarboxylic acid component, an alicyclic dicarboxylic acid component, and an alkylene that does not correspond to any of the above, as long as the effects of the present invention are not impaired. A glycol component, a hydroxycarboxylic acid component, an acid component having a trifunctional or higher functional group such as trimellitic acid, an alcohol component, or the like may be copolymerized.

The dimer component should be in the range of 0.3 to less than 5 mol % based on the number of moles of repeating units of the polyester. If the molar fraction of the dimer component is too high, the film formability will be significantly deteriorated, making it difficult to stably form a film. Therefore, the molar fraction of the dimer component is preferably in the range of 0.5 to 4.5 mol%, more preferably in the range of 0.7 to 4.0 mol, and particularly in the range of 0.9 to 3.5 mol%. preferable.

By using a copolyester obtained by copolymerizing such a specific amount of a specific dimer component, it is possible to produce a molded product, such as a film, having both a low temperature expansion coefficient and a low humidity expansion coefficient. Therefore, the tension control for adjusting the tape width to be constant becomes easier.

The copolymerization amount of the above-mentioned specific dimer component is obtained by adjusting the composition of the raw material so as to obtain the desired copolymerization amount in the polymerization stage, or, for example, when dimer diol is used, the above-mentioned specific dimer diol is used as the diol component. A homopolymer using only the components or a polymer with a large amount of copolymerization thereof and a polymer without copolymerization or a polymer with a small amount of copolymerization are prepared, and these are melt-kneaded to obtain the desired copolymerization amount to esterify. It can be adjusted by exchanging.

Specific dimer acid components include Croda's dimer acids "Priplast 1838", "Pripol 1009" and "Pripol 1004", and specific dimer diol components include Croda's dimer diol "Pripol 2033". ” and dimer diol “SOVERMOL 908” manufactured by Cognis.

From the viewpoint of the effect in the present invention, both dimer acid and dimer diol can be preferably used as the dimer component, but dimer diol is preferable from the viewpoint of handling during polymerization and less foreign matter present in the resin.

<Method for producing copolymerized polyester resin>
The method for producing the copolyester in the present invention will be described in detail.
The copolyester in the present invention can be obtained by subjecting a polyester precursor to a polycondensation reaction. Specifically, an aromatic dicarboxylic acid component having 6 or more carbon atoms, such as dimethyl 2,6-naphthalenedicarboxylate, is transesterified with a specific dimer acid or dimer diol and ethylene glycol to obtain a polyester precursor. After that, the polyester precursor thus obtained can be produced by polymerizing in the presence of a polymerization catalyst, and solid phase polymerization or the like may be performed as necessary. The intrinsic viscosity of the thus obtained aromatic polyester measured at 35° C. using a mixed solvent of P-chlorophenol/1,1,2,2-tetrachloroethane (weight ratio 40/60) was 0.4. From the viewpoint of the effects of the present invention, it is preferably in the range of up to 1.5 dl/g, more preferably 0.5 to 1.2 dl/g, particularly 0.55 to 0.8 dl/g.

The reaction temperature for producing the polyester precursor is preferably in the range of 190° C. to 250° C., and the reaction is carried out under normal pressure or under pressure. When the temperature is lower than 190°C, the reaction does not proceed sufficiently, and when the temperature is higher than 250°C, side-reactants such as diethylene glycol tend to form.

In addition, in the reaction step for producing the polyester precursor, a known esterification or transesterification reaction catalyst may be used. Examples include manganese acetate, zinc acetate, alkali metal compounds, alkaline earth metal compounds, and titanium compounds. A titanium compound is preferred because it can suppress high surface protrusions when formed into a film.

Next, the polycondensation reaction will be explained. First, the polycondensation temperature is higher than the melting point of the polymer to be obtained and 230 to 300° C., more preferably in the range from 5° C. higher than the melting point to 30° C. higher than the melting point. The polycondensation reaction is preferably carried out under a reduced pressure of 100 Pa or less.

Examples of polycondensation catalysts include metal compounds containing at least one metal element. The polycondensation catalyst can also be used in the esterification reaction. Metal elements include titanium, germanium, antimony, aluminum, nickel, zinc, tin, cobalt, rhodium, iridium, zirconium, hafnium, lithium, calcium, and magnesium. More preferable metals are titanium, germanium, antimony, aluminum, tin, and the like. It is preferred to use this as it is less

These catalysts may be used alone or in combination. The amount of such catalyst is preferably 0.001 to 0.1 mol %, more preferably 0.005 to 0.05 mol %, relative to the number of moles of repeating units in the copolyester.

Examples of titanium compounds as specific esterification catalysts, transesterification catalysts and polycondensation catalysts include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraisobutyl titanate, tetra-tert-butyl Titanate, tetracyclohexyl titanate, tetraphenyl titanate, tetrabenzyl titanate, lithium oxalate titanate, potassium oxalate titanate, ammonium oxalate titanate, titanium oxide, titanium orthoester or condensed orthoester, titanium orthoester or condensed orthoester Reaction products consisting of hydroxycarboxylic acids, titanium orthoesters or condensed orthoesters, reaction products consisting of hydroxycarboxylic acids and phosphorus compounds, titanium orthoesters or condensed orthoesters and polyhydric alcohols having at least two hydroxyl groups , 2-hydroxycarboxylic acid, or a reaction product consisting of a base.

As described above, the copolyester in the present invention may be polymerized so as to obtain a copolyester having a desired copolymerization amount. Aromatic polyesters with different amounts may be prepared and melt-kneaded to blend them to obtain the desired copolymerization amount.

The above-described polyester in the present invention may be blended with additives known per se or other resins to form a composition within a range that does not impair the effects of the present invention. Examples of additives include stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants, flame retardants, release agents, pigments, nucleating agents, fillers, glass fibers, carbon fibers, layered silicates, and the like. It may be selected as appropriate according to the requirements of the intended use. Other resins include aliphatic polyester resins, polyamide resins, polycarbonates, ABS resins, liquid crystalline resins, polymethyl methacrylate, polyamide elastomers, polyester elastomers, polyetherimides, polyimides, and the like.

By the way, the polyester film in the present invention further contains at least one selected from the group consisting of polyimide, polyetherimide, polyetherketone, and polyetheretherketone in addition to the above-described copolymerized polyester, and the mass of the resin composition is As a standard, it may be contained in the range of 0.5 to 25% by weight. By containing such a resin in the above range, the glass transition temperature of the polyester resin composition can be increased, and as a result, the dimensional stability can be more easily improved. Among these, polyetherimide is preferable because it is easier to disperse more uniformly and it is easier to raise the glass transition temperature. If the content is too small, the effect of improving the heat resistance is small, and if it is too large, phase separation occurs. From such a viewpoint, the content is preferably 2 to 20% by weight, more preferably 4 to 18% by weight, still more preferably 5 to 15% by weight, based on the mass of each film layer. Specific examples of polyetherimide include those disclosed in JP-A-2000-355631. In addition, from the viewpoint of further improving dimensional stability against environmental changes, 6,6'-(ethylenedioxy)di-2-naphthoic acid component, 6,6'-( A copolymer of a trimethylenedioxy)di-2-naphthoic acid component and a 6,6'-(butylenedioxy)di-2-naphthoic acid component is also preferred.

In the case of the polyester film containing the above polyetherimide, a polyetherimide having a glass transition temperature of 350° C. or less, more preferably 250° C. or less is preferred, and 2,2-bis[4-(2,3-dicarboxyphenoxy ) A condensate of phenyl]propane dianhydride and m-phenylenediamine or p-phenylenediamine is most preferred from the viewpoints of compatibility with polyester, cost, melt moldability and the like. This polyetherimide is known from the "Ultem® 1000 or 5000 series" manufactured by SABIC.

<Polyester film>
The polyester film of the present invention will be described in detail below. For convenience of explanation, the film-forming direction of the film may be referred to as the machine axis direction, the longitudinal direction, the longitudinal direction, and the MD direction, and the direction orthogonal to the film-forming direction and the thickness direction may be referred to as the width direction, the lateral direction, and the direction perpendicular to the thickness direction. It may be called TD direction.

The polyester film of the present invention has a Young's modulus in the longitudinal direction of the film of 1 GPa or more and 6 GPa or less. If the Young's modulus is less than the lower limit, it is very difficult to handle a thin film. A large tension change must be applied. A preferable lower limit of Young's modulus in the longitudinal direction is 1.5 GPa or more, further 2 GPa or more, particularly 2.5 GPa or more, and a preferable upper limit is 5.5 GPa or less, further 5 GPa or less, particularly 4.5 GPa or less.

The polyester film of the present invention has a thickness of 1 µm or more and 4.5 µm or less. If the thickness is less than the lower limit, the handling becomes very difficult, and the film tends to break during film formation, which is not suitable. If the thickness exceeds the upper limit, it becomes necessary to give a greater change in tension when adjusting the tape tension of a reproducing apparatus to control the dimension in the width direction when the magnetic recording medium is used. A more preferable lower limit of the thickness is 1.5 μm or more, further 2 μm or more, and a preferable upper limit is 4 μm or less, furthermore 3.5 μm or less.

By the way, the value of the product of Young's modulus in the longitudinal direction and the thickness of the polyester film of the present invention is 5 GPa·μm or more and 20 GPa·μm or less. If this value is less than the lower limit, it is very difficult to handle, and if this value exceeds the upper limit, the tape tension of the reproducing device is adjusted to control the dimension in the width direction when used as a magnetic recording medium. At that time, a larger tension change must be applied. More preferably, the lower limit of the value of the product of Young's modulus in the longitudinal direction and the thickness is 8 GPa·μm or more, furthermore 10 GPa·μm or more, and the preferable upper limit is 18 GPa·μm or less, furthermore 16 GPa·μm or less.

Furthermore, the polyester film of the present invention has a longitudinal elongation of 3% or less when heated from 30° C. to 110° C. under a load of 2 kg/mm ² in the longitudinal direction. If the amount of elongation in the longitudinal direction exceeds the upper limit, it tends to elongate in the longitudinal direction when the magnetic paint is applied, causing wrinkles due to the buckling phenomenon. More preferably, the upper limit of the elongation in the longitudinal direction of the film is 2.8% or less, 2.6% or less, 2.5% or less, 2.4% or less, 2.0% or less, and 1.5% or less. preferable.

The value of tan δ obtained by measuring with a dynamic viscoelasticity measuring device (DMA), which will be described later, is preferably as high as possible, preferably 100° C. or higher. The higher the tan δ, the more difficult it is for the film to stretch in the longitudinal direction during the coating process of the magnetic layer, etc., and the less troubles such as cutting and uneven coating occur. The lower limit of tan δ is more preferably 115°C or higher, more preferably 120°C or higher, and particularly preferably 125°C or higher. As described above, the higher the value of tan δ is, the more preferable it is, so the upper limit is not particularly limited.

In addition, the polyester film of the present invention has a temperature expansion coefficient (αt) in the width direction of the film of −8.0 to 10 ppm/° C., further −7.5 to 9 ppm/° C., from the viewpoint of exhibiting excellent dimensional stability. , particularly preferably in the range of -7.0 to 8 ppm/°C.

In addition, the polyester film of the present invention has a humidity expansion coefficient (αh) in the width direction of the film from 1 to 8.5 ppm/% RH, further from 3 to 8.5 ppm/% RH, from the viewpoint of exhibiting excellent dimensional stability. , particularly preferably in the range of 4 to 7 ppm/% RH. Outside this range, the dimensional change due to the change in humidity becomes large. Such temperature expansion coefficient and humidity expansion coefficient can be adjusted by the blend or copolymer composition described above and the stretching described below.

<Method for producing polyester film>
As described above, the polyester film of the present invention is preferably an oriented polyester film, and it is particularly preferred that the film is stretched in the film-forming direction and the width direction to enhance the molecular orientation in each direction. Such a polyester film is preferably produced by, for example, the following method, since it is easy to impart desired physical properties such as Young's modulus, temperature expansion coefficient, and humidity expansion coefficient while maintaining film formability.

First, the above-described polyester composition of the present invention is used as a raw material, dried, and then supplied to an extruder heated to a temperature of the melting point of the aromatic polyester (Tm: ° C.) to (Tm + 50) ° C., for example, T A sheet is extruded through a die such as a die. The extruded sheet material is rapidly cooled and solidified by a rotating cooling drum or the like to form an unstretched film, and the unstretched film is biaxially stretched.

In order to achieve the αt, αh, and Young's modulus specified in the present invention, it is necessary to facilitate the subsequent stretching, and the polyester composition of the present invention tends to have a high crystallization rate. From such a point of view, it is preferable to perform the cooling by the cooling drum very quickly. From such a point of view, it is preferable to carry out at a low temperature of 20 to 60°C. By carrying out at such a low temperature, crystallization in the state of the unstretched film is suppressed, and subsequent stretching can be carried out more smoothly.

As the biaxial stretching, one known per se can be employed, and sequential biaxial stretching or simultaneous biaxial stretching may be used.

Here, a manufacturing method of sequential biaxial stretching in which longitudinal stretching, transverse stretching and heat treatment are performed in this order will be described as an example. First, the first longitudinal stretching is carried out at a temperature of the glass transition temperature (Tg: ° C.) to (Tg + 40) ° C. of the copolymer polyester, and is stretched 3 to 8 times, and then in the transverse direction at a temperature higher than the previous longitudinal stretching (Tg + 10 ) ~ (Tg + 50) ° C. to stretch 3 to 8 times, further heat treatment at a temperature below the melting point of the copolymer polyester and at a temperature of (Tg + 50) ~ (Tg + 150) ° C. for 1 to 20 seconds, further 1 to 15 A second heat fixation treatment is preferred.

In the above description, sequential biaxial stretching is described, but the polyester film of the present invention can be produced by simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are performed simultaneously. do it.

Moreover, the polyester film of the present invention is not limited to a single-layer film, and may be a laminated film. In the case of a laminated film, two or more molten polyesters are laminated in a die and then extruded into a film, preferably at the melting point of each polyester (Tm: ° C.) to (Tm + 70) ° C., or two or more. After the molten polyester is extruded from a die, it is laminated, rapidly solidified to form a laminated unstretched film, and then biaxially stretched and heat-treated in the same manner as in the case of the monolayer film. Further, when a coating layer is provided on the surface of the polyester film, a desired coating liquid is applied to one or both sides of the unstretched film or uniaxially stretched film, and then two layers are formed in the same manner as in the case of the above-mentioned single layer film. Axial stretching and heat treatment are preferred.

According to the present invention, the polyester film of the present invention is used as a base film, a non-magnetic layer and a magnetic layer are formed on one surface of the base film in this order, and a back coat layer is formed on the other surface of the film to form data storage or the like. magnetic recording tape.

By the way, the polyester film of the present invention is not limited to a single-layer film as described above, and may be a laminated film, thereby easily achieving both flatness and windability. For example, by applying a magnetic layer on a flat surface with a small surface roughness and a back coat layer on a rough surface with a large surface roughness, both the required flatness and transportability can be achieved at a higher level. At this time, the types of inert particles to be added to the resin include inorganic particles such as spherical silica, aluminum silicate, titanium dioxide, and calcium carbonate, and other organic polymer particles include crosslinked polystyrene resin particles, crosslinked silicone resin particles, Crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, melamine resin particles and the like are preferred. One or more of these can be selected and used.

The size of the inert particles is preferably 0.01 μm or more and 1 μm or less, more preferably 0.05 μm or more and 0.7 μm or less, and particularly preferably 0.1 μm or more and 0.5 μm or less.

Regarding the method of adding inert particles to the resin, there are cases where particles are added to a part of the components constituting the resin and polymerized as it is in a slurry state, and addition using a twin-screw extruder after polymerization of the resin. There are multiple ways. The amount of inert particles added is preferably 0.001% to 2%, more preferably 0.01% to 1%, and particularly preferably 0.1% to 0.8%, based on the total weight of the film. is.

The magnetic recording tape of the present invention can be produced by forming a magnetic layer on the polyester film described above. On the surface of the resin film of the present invention, in order to improve adhesion to the magnetic layer or the like, a coating layer or the like having an easy-adhesion function known per se is formed within a range that does not impair the effects of the present invention. You can

The magnetic layer forming the magnetic recording tape of the present invention is not particularly limited. It is formed by uniformly dispersing in and applying the coating liquid. It can be a magnetic recording tape.

By the way, as mentioned above, it is necessary to miniaturize the magnetic material in order to increase the recording density. It became necessary to do in Then, the present inventors have newly discovered that when a film having an extremely flat surface is processed at a high temperature, problems such as wrinkles occur, and the present invention has been accomplished.

The magnetic layer should be coated so that its thickness is 1 μm or less, more preferably 0.1 to 1 μm. It is preferable from the viewpoint of providing a coated magnetic recording tape for high density recording with less dropout and less error rate. If necessary, it is also preferable to coat a non-magnetic layer containing fine titanium oxide particles or the like dispersed in the same organic binder as the magnetic layer as an underlayer of the coating type magnetic layer.

On the surface of the magnetic layer, a protective layer such as diamond-like carbon (DLC) and a fluorine-containing carboxylic acid-based lubricating layer are sequentially provided according to the purpose, application, and need, and a known back coat layer is provided on the other surface. may be provided.

The coated magnetic recording tape thus obtained is extremely useful as a magnetic tape for data applications such as LTO and enterprise. In particular, according to the present invention, since accurate tracking is possible by adjusting the tape tension, it is possible to dramatically improve the track density on the linear tape.

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below. In addition, in the present invention, the characteristics were measured and evaluated by the following methods.

(1) Young's modulus The obtained film was cut into a sample width of 10 mm and a length of 15 cm, and the chuck distance was 100 mm, the tensile speed was 10 mm/min, and the chart speed was 500 mm/min. Tensilon). The Young's modulus is calculated from the tangent to the rising portion of the obtained load-elongation curve.

(2) Thickness of Film Ten sheets of film are piled up so as not to contain dust, and the thickness is measured with a dot type electronic micrometer, and the thickness of one sheet is calculated.

(3) Film elongation under high temperature and high tension A film was cut into a lengthwise direction of 30mm and a widthwise direction of 4mm, and set in a thermomechanical property measurement tester EXSTR-6000 manufactured by Seiko Instruments Inc. so that the chuck distance was 20mm. With a load of 2 kg / mm ² applied in the longitudinal direction of the film, the temperature was raised from 30 ° C. to 170 ° C. at a heating rate of 5 ° C./min, and the length (L1) and 110 at 30 ° C. in the longitudinal direction of the sample Elongation (%) is calculated according to the following formula from the length (L2) in °C.
110°C elongation (%) = (L2-L1)/L1 x 100

(4) Dynamic viscoelasticity A sample cut to a length of 30 mm and a width of 5 mm was set in a viscoelasticity measuring device DMA-8000 manufactured by PerkinElmer, with a chuck interval of 11 mm and an amplitude of 0.1 mm. The temperature is raised at a temperature elevation rate of 2° C./min. Obtain the tan delta peak temperature at a frequency of 1 Hz.

(5) Temperature expansion coefficient (αt)
The resulting film was cut into a length of 15 mm and a width of 5 mm so that the film formation direction and the width direction of the film were the measurement directions, respectively, set in TMA3000 manufactured by Shinku Riko, and placed in a nitrogen atmosphere (0% RH) at 60 ° C. for 30 minutes and then allowed to cool to room temperature. After that, the temperature is raised from 25° C. to 70° C. at a rate of 2° C./min, the sample length is measured at each temperature, and the temperature expansion coefficient (αt) is calculated from the following equation. The measurement direction is the longitudinal direction of the cut sample, and the average value of five measurements was used.
αt={(L ₆₀ −L ₄₀ )}/(L ₄₀ ×ΔT)}+0.5
Here, L ₄₀ in the above formula is the sample length (mm) at 40 ° C., L ₆₀ is the sample length (mm) at 60 ° C., ΔT is 20 (= 60-40) ° C., 0.5 is the thermal expansion coefficient of quartz glass (×10 ⁻⁶ /° C.).

(6) Humidity expansion coefficient (αh)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the film forming direction and the width direction of the film were the measurement directions, respectively, set in TMA3000 manufactured by Shinku Riko, and placed in a nitrogen atmosphere at 30 ° C. and a humidity of 30%. The length of each sample is measured at RH and 70% RH, and the humidity expansion coefficient is calculated by the following formula. The measurement direction was the longitudinal direction of the cut sample, and the measurement was performed five times, and the average value was defined as αh.
αh=(L ₇₀ −L ₃₀ )/(L ₃₀ ×ΔH)
Here, L ₃₀ in the above formula is the sample length (mm) at 30% RH, L ₇₀ is the sample length (mm) at 70% RH, and ΔH is 40 (=70-30)% RH. be.

(7) Identification of dimer components (dimer acid, dimer diol) Dissolve 20 mg of a sample in 0.6 mL of a mixed solvent of deuterated trifluoroacetic acid: deuterated chloroform = 1:1 (volume ratio) at room temperature and perform ¹ H-NMR at 500 MHz. calculated the amounts of dimer acid and dimer diol in the polymer chips and films.

(8) Intrinsic viscosity (IV)
The intrinsic viscosity of the resulting polyester and film was obtained by dissolving the polymer in a mixed solvent of p-chlorophenol/tetrachloroethane (40/60 weight ratio) and measuring at 35°C.

(9) Glass transition point (Tg) and melting point (Tm)
The glass transition point (extrapolation starting point) and melting point were measured by DSC (manufactured by TA Instruments Co., Ltd., trade name: Thermal Analyst 2100) with a sample amount of 10 mg and a heating rate of 20° C./min.

(10) DMA tan δ
A film sample was cut into a width of 5 mm and a length of 35 mm, and measured using a dynamic viscoelasticity measuring device (DMA8000) manufactured by PerkinElmer Co., Ltd. at a frequency of 1 Hz from room temperature to 240° C. at a rate of 2° C./min. . Tan δ was obtained from the obtained chart.

(11) Preparation of magnetic recording tape A film slit to a width of 1 m was transported under a tension of 2 kg/mm ² , and a magnetic coating and a non-magnetic coating were applied to one surface of the support according to the following description to obtain a tape having a width of 12.65 mm. Slit and create pancakes. Then, a 200 m long piece of this pancake was incorporated into a cassette to form a magnetic tape.

(Hereinafter, "parts" means "parts by mass.")
<Coating liquid for magnetic layer formation>
Barium ferrite magnetic powder 100 parts (plate diameter: 20.5 nm, plate thickness: 7.6 nm, tabular ratio: 2.7, Hc: 191 kA/m (≈2400 Oe)
Saturation magnetization: 44 Am2/kg, BET specific surface area: 60 m2/g)
Polyurethane resin 12 parts Mass average molecular weight 10,000
Sulfonic acid functionality 0.5 meq/g
α-Alumina HIT60 (manufactured by Sumitomo Chemical Co., Ltd.) 8 parts Carbon black #55 (manufactured by Asahi Carbon Co., Ltd.)
Particle size 0.015 μm 0.5 parts Stearic acid 0.5 parts Butyl stearate 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 parts

<Coating liquid for forming non-magnetic layer>
Non-magnetic powder α-iron oxide 85 parts Average major axis length 0.09 μm, specific surface area by BET method 50 m ² /g
pH 7
DBP oil absorption 27-38ml/100g
Surface treatment layer Al2O3 8% by mass
Carbon black 15 parts “Conductex” (registered trademark) SC-U (manufactured by Columbian Carbon)
Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 22 parts Phenylphosphonic acid 3 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 205 parts Cyclohexanone 135 parts

Each component of each of the above coating liquids (magnetic layer forming coating liquid and non-magnetic layer forming coating liquid) was kneaded with a kneader. The coating liquid was pumped through a horizontal sand mill filled with zirconia beads of 1.0 mmφ in an amount of 65% by volume with respect to the volume of the dispersion part, and was run at 2,000 rpm for 120 minutes (substantially retained in the dispersion part time), dispersed. Polyisocyanate was added to the resulting dispersion in 5.0 parts for the non-magnetic layer coating material and 2.5 parts for the magnetic layer coating material, and 3 parts of methyl ethyl ketone was added. The mixture was filtered through a filter to prepare a coating solution for forming a non-magnetic layer and a coating solution for forming a magnetic layer.

The resulting non-magnetic layer-forming coating solution was coated on a film so that the thickness after drying was 0.8 μm, and dried. It was coated to a thickness of 0.07 μm, and while the magnetic layer was still wet, it was oriented by a cobalt magnet with a magnetic force of 6,000 G (600 mT) and a solenoid with a magnetic force of 6,000 G (600 mT), and dried. rice field. Then, a back coat layer (carbon black average particle size: 17 nm 100 parts, calcium carbonate average particle size: 40 nm 80 parts, α-alumina average particle size: 200 nm 5 parts polyurethane resin was added so that the thickness after calendering was 0.5 μm. , dispersed in polyisocyanate) was applied. Next, after calendering with a calender at a temperature of 90° C. and a linear pressure of 300 kg/cm (294 kN/m), it was cured at 70° C. for 48 hours. Further, the nonwoven fabric and the razor blade were attached to a device having a slit product feeding and winding device so that the nonwoven fabric and the razor blade pressed against the magnetic surface, and the surface of the magnetic layer was cleaned with a tape cleaning device to obtain a magnetic tape.

(12) Dimensional change in the width direction when tension is applied to the magnetic recording tape In an atmosphere with a temperature of 23°C and a humidity of 50%, the magnetic material slit to a width of 12.65 mm (1/2 inch) prepared in (11) above. A tape (30 cm long) was measured with the apparatus shown in FIG. Specifically, the reference numerals in FIG. Stand 6: Dimension measuring machine 7: Cylindrical mounting surface, and magnetic tape was placed on the mounting surface as shown in FIG.

In this state, a weight of 0.2 N is attached to one side of the magnetic tape (the other side is fixed), and the width (T1) of the magnetic tape at that time is measured with a Keyence laser outer diameter measuring device (LS-9030N).

After that, the weight is changed to 1.2 N, and the width (T2) of the magnetic tape at that time is measured with a Keyence laser outer diameter measuring device (LS-9030N).
The amount of change in width dimension per 1N was calculated from the following equation.
Width dimensional change (ppm) = (T1-T2)/T1 x 1000,000
Furthermore, this measurement was repeated three times, and the average value was defined as the amount of change in dimension in the width direction per 1N.

(13) Processability In the step of applying and drying the magnetic paint in the above (11) production of the magnetic recording tape, the state of the web after drying was observed and evaluated according to the following criteria.
◎: 0 wrinkles after drying / 1 m width ○: 1 wrinkle after drying / 1 m width ×: 2 or more wrinkles after drying / 1 m width

(14) Ease of Tension Control A weight of 0.55 N was applied in the longitudinal direction of the magnetic tape in the same manner as in (12) above. Measure the dimensional change in the width direction of the 1/2-inch magnetic tape caused by the change in the following storage environment conditions, increase or decrease the load so that the dimensional change in the width direction becomes 0, and obtain the required amount of change in the load. The sum of the sums of the amounts of change in weight required for each environmental change A and environmental change B was obtained, and the easiness of tape tension control was evaluated. A smaller weight change amount indicates that the tape is easier to control the tension.
<Environmental change A: temperature = 15°C, humidity = 15% RH → temperature = 25°C, humidity = 75% RH>
<Environmental change B: temperature = 15°C, humidity = 75% RH → temperature = 40°C, humidity = 15% RH>

<Preparation of polyethylene naphthalate pellets A1>
Dimethyl 2,6-naphthalenedicarboxylate as a dicarboxylic acid component and ethylene glycol as a diol component were subjected to transesterification in the presence of titanium tetrabutoxide, followed by polycondensation to prepare polyethylene naphthalate pellets A1. (IV=0.58 dl/g, Tg=115°C, Tm=263°C).

<Preparation of polyethylene terephthalate pellets A2>
Dimethyl terephthalate as a dicarboxylic acid component and ethylene glycol as a diol component were transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to prepare polyethylene terephthalate pellets A2 (IV=0.58 dl). /g, Tg = 76°C, Tm = 254°C).

<Preparation of Dimer Acid Copolymerized Polyethylene Naphthalate Pellets B1>
Dimethyl 2,6-naphthalenedicarboxylate, Priplast 1838 as a dicarboxylic acid component, and ethylene glycol as a diol component are subjected to a transesterification reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to copolymerize a dimer acid. Copolymerized polyethylene naphthalate pellets B1 were prepared (IV=0.60 dl/g, Tg=58° C., Tm=232° C.). NMR analysis revealed that the content of dimer acid as a dicarboxylic acid component was 10.6 mol %.

<Preparation of Dimer Acid Copolymerized Polyethylene Naphthalate Pellets B2>
2,6-naphthalenedicarboxylic acid and Pripol 1004 as dicarboxylic acid components and ethylene glycol as diol components were subjected to transesterification in the presence of titanium tetrabutoxide, followed by polycondensation to copolymerize dimer acid. A copolymerized polyethylene naphthalate pellet B2 was prepared (IV=0.58 dl/g). The content of dimer acid as an acid component was adjusted to 10.6 mol %.

<Preparation of dimer acid-copolymerized polyethylene terephthalate pellets B3>
Copolymerized polyethylene terephthalate obtained by subjecting dimethyl terephthalate and Priplast 1838 as a dicarboxylic acid component and ethylene glycol as a diol component to an ester exchange reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to copolymerize a dimer acid. A pellet B3 was prepared (IV=0.58 dl/g, Tg=47° C., Tm=244° C.). The content of dimer acid as a dicarboxylic acid component was adjusted to 10.6 mol %.

<Preparation of dimer diol-copolymerized polyethylene naphthalate pellets C1>
Dimethyl 2,6-naphthalenedicarboxylate as a dicarboxylic acid component, ethylene glycol as a diol component, and Pripol 2033 were subjected to an ester interchange reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to copolymerize the dimer diol. Copolymerized polyethylene naphthalate pellets C1 were prepared (IV=0.57 dl/g, Tg=77° C., Tm=250° C.). NMR analysis revealed that the content of dimer diol as a diol component was 10.3 mol %.

<Preparation of dimer diol-copolymerized polyethylene terephthalate pellets C2>
Copolymerized polyethylene terephthalate obtained by subjecting dimethyl terephthalate as a dicarboxylic acid component, ethylene glycol as a diol component, and Pripol 2033 to transesterification in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to copolymerize dimer diol. A pellet C2 was prepared (IV=0.56 dl/g, Tg=50° C., Tm=249° C.). The content of dimer diol as a diol component was adjusted to 10.3 mol %.

[Example 1]
Pellet A1 and pellet B1 were blended at a mass ratio of 84:16, respectively, so that the composition ratio of dimer acid was 1.2 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 130 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.0 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 130° C. at a stretch ratio of 5.8 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.0 μm. An axially oriented polyester film was obtained.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Example 2]
Pellet A1 and pellet B1 were blended at a mass ratio of 58:42, respectively, so that the composition ratio of dimer acid was 4.0 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 120 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.0 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 120° C. at a stretch ratio of 5.8 times, and then heat-set at 200° C. for 3 seconds to form a two-layer film with a thickness of 3.0 μm. An axially oriented polyester film was obtained.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Example 3]
Pellet A1 and pellet B2 were blended at a mass ratio of 79:21, respectively, so that the composition ratio of dimer acid was 1.5 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 130 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.0 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 130° C. at a stretch ratio of 5.8 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.0 μm. An axially oriented polyester film was obtained.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Example 4]
Pellets A1 and C1 were blended at a mass ratio of 86:14, respectively, so that the composition ratio of dimer diol was 1.2 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 130 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.0 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 130° C. at a stretch ratio of 5.8 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.0 μm. An axially oriented polyester film was obtained.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Example 5]
A biaxially oriented polyester film having a thickness of 3.0 μm was obtained in the same manner as in Example 4 except that the unstretched film of Example 4 was used and the stretching ratio was changed as shown in Table 1.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Example 6]
Pellets A1 and C1 were blended at a mass ratio of 56:44, respectively, so that the composition ratio of dimer diol was 4.0 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 120 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.0 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 120° C. at a stretch ratio of 5.8 times, and then heat-set at 200° C. for 3 seconds to form a two-layer film with a thickness of 3.0 μm. An axially oriented polyester film was obtained.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Examples 7, 8, 9]
Biaxially oriented polyester films were obtained in the same manner as in Example 4 except that the unstretched film of Example 4 was used and the stretching ratio and thickness were changed as shown in Table 1.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Example 10]
Pellets A2 and B3 were blended at a mass ratio of 83:17, respectively, so that the composition ratio of dimer acid was 1.5 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 25° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 90 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 3.6 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 90° C. at a draw ratio of 4.0 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.5 μm. An axially oriented polyester film was obtained.

[Example 11]
Pellets A2 and C2 were blended at a mass ratio of 86:14, respectively, so that the composition ratio of dimer diol was 1.2 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 25° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 90 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 3.6 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 90° C. at a draw ratio of 4.0 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.5 μm. An axially oriented polyester film was obtained.

[Example 12]
As the polyetherimide, "Ultem 1010" manufactured by SABIC Innovative Plastics was prepared.
Polyetherimide, pellets A2 and pellets B3 were blended at a mass ratio of 10:75:15 so that the composition ratio of dimer acid was 1.5 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 25° C. to form an unstretched film. Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds along the film forming direction so that the film surface temperature is 100 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 3.8 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 100° C. at a stretch ratio of 4.2 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.5 μm. An axially oriented polyester film was obtained.

[Example 13]
Polyetherimide, pellets A2 and pellets C2 were blended at a mass ratio of 10:77:13 so that the composition ratio of dimer diol was 1.2 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 25° C. to form an unstretched film. Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds along the film forming direction so that the film surface temperature is 100 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 3.8 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 100° C. at a stretch ratio of 4.2 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.5 μm. An axially oriented polyester film was obtained.

[Comparative Example 1]
Pellets A2 were extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 25° C. to form an unstretched film. Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 90 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 3.6 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched in the horizontal direction (width direction) at 90° C. at a draw ratio of 4.0 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 5.0 μm. An axially oriented polyester film was obtained.

[Comparative Example 2]
Pellets A1 were extruded at 300° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film. Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 150 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.5 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 150° C. at a draw ratio of 4.0 times, and then heat-set at 210° C. for 3 seconds to form a double layer with a thickness of 3.0 μm. An axially oriented polyester film was obtained.

[Comparative Example 3]
Biaxially oriented polyester films were obtained in the same manner as in Comparative Example 2 except that the unstretched film of Comparative Example 2 was used and the stretching ratio and thickness were changed as shown in Table 1.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Comparative Example 4]
Pellets A1 and C1 were blended at a mass ratio of 37:63, respectively, so that the composition ratio of dimer diol was 6.0 mol %. The blended resin was extruded at 280° C. and extruded into a sheet on a rotating cooling drum at a temperature of 60° C. to form an unstretched film.

Then, the unstretched film is heated from above by an IR heater between two sets of rollers having different rotation speeds in the film forming direction so that the film surface temperature is 110 ° C., and the longitudinal direction (film forming direction ) was carried out at a draw ratio of 4.0 to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter and stretched in the horizontal direction (width direction) at 110° C. at a stretch ratio of 5.8 times, and then heat-set at 200° C. for 3 seconds to form a double layer with a thickness of 3.5 μm. An axially oriented polyester film was obtained.
The obtained polyester film had a large film elongation during drying in the preparation of the magnetic tape described in (10), making it difficult to prepare a magnetic tape. Therefore, the characteristics were not evaluated.
Table 1 shows the results of the resulting biaxially oriented polyester film.

[Comparative Example 5]
A biaxially oriented polyester film having a thickness of 5.0 μm was obtained in the same manner as in Example 4 except that the unstretched film of Example 4 was used and the stretching ratio was changed as shown in Table 1.
Table 1 shows the results of the resulting biaxially oriented polyester film.

PEI in Table 1 means polyetherimide.

REFERENCE SIGNS LIST 1 Transmitting part 1a Light-emitting part of transmitting part 2 Laser beam 3 Magnetic tape 4 Receiving part 4b Light-receiving part of receiving part 5 Base 6 Dimension measuring machine 7 Mounting surface of cylindrical surface

Claims (6)

A polyester formed from a copolymerized polyester in which a dimer component represented by the following formula (I) or (II) is copolymerized in a range of 0.3 to less than 5 mol% based on the number of moles of repeating units of the polyester a film,
The polyester film has a Young's modulus in the longitudinal direction of 1 GPa or more and 6 GPa or less, a thickness of 1 μm or more and 4.5 μm or less, and a product of the Young's modulus in the longitudinal direction and the thickness of 5 GPa·μm or more and 20 GPa·μm or less.
A polyester film having a longitudinal elongation of 3% or less when heated from 30° C. to 110° C. at a rate of 5° C./min under a load of 2 kg/mm ² in the longitudinal direction.
-C(O)-R ^A -C(O)- (I)
-OR ^A -O- (II)
(In the structural formulas (I) to (II) above, R ^A represents a cyclo ring having 31 to 51 carbon atoms and an alkylene group which may contain a branched chain.) In addition to the copolyester, at least one selected from the group consisting of polyimide, polyetherimide, polyetherketone, and polyetheretherketone, based on the mass of the copolyester, 0.5 to 25% by weight The polyester film according to claim 1, containing in the range of. 3. The polyester film according to claim 1, which has a tan δ peak temperature of 100° C. or higher as measured by DMA. The polyester film according to any one of claims 1 to 3, which has a temperature expansion coefficient of -8 to 10 ppm/°C and a humidity expansion coefficient of 1 to 8.5 ppm/% RH in the width direction of the film. The polyester film according to any one of claims 1 to 4, which is used as a base film for magnetic recording tapes. 6. The polyester film according to claim 5, which is used as a base film for a high-density magnetic recording tape whose track position is adjusted by controlling the tension applied in the running direction of the magnetic recording tape.

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