JP2019131706A - Polyester composition, polyester film, and magnetic recording medium - Google Patents

Abstract

To more easily provide a polyester film excellent in dimensional stability, especially dimensional stability to environmental change such as temperature or humidity.SOLUTION: There are provided a polyester composition containing a copolymer polyester of a dicarboxylic acid component represented by following formulae (I) and (II), and a glycol component represented by the following formula (III), and containing dimer acid represented by the following formula (I) of 0.5 to 3.5 mol% based on molar number of all dicarboxylic acid components constituting the copolymer polyester, and a polyester film using the same in at least one layer. -C(O)-RA-C(O)- (I) -C(O)-RB-C(O)- (II) -O-RC-O- (III). In above structural formulae (I) to (III), RA represents an alkylene group which has 31 to 51 carbon atoms and may contain a cyclo ring and a branched chain, RB represents a phenyl group or a naphthalenediyl group, and RC represents an alkylene group having 2 to 6 carbon atoms.SELECTED DRAWING: None

Description

  The present invention relates to a polyester composition, a polyester film and a magnetic recording medium using a copolyester obtained by copolymerizing a specific dimer acid.

  Aromatic polyesters typified by polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate have excellent mechanical properties, dimensional stability and heat resistance, and are therefore widely used for films and the like. In particular, polyethylene-2,6-naphthalate has mechanical properties, dimensional stability, and heat resistance superior to those of polyethylene terephthalate, so that it is used in demanding applications such as a base film for high-density magnetic recording media. It is used.

  In recent years, the demand for improvement in recording density in magnetic recording media and the like has been severe, and accordingly, the dimensional stability required for a base film cannot be achieved with polyethylene-2,6-naphthalate film as well as polyethylene terephthalate. It was.

  Therefore, in Patent Document 1, a 4,4 ′-(alkylenedioxy) bisbenzoic acid component is copolymerized. In Patent Document 2, a 2,6-naphthalenedicarboxylic acid component (Component A), a terephthalic acid component, and isophthalic acid are used. Dimension for humidity change by copolymerization of component, or 1,4-cyclohexanedicarboxylic acid component (component B), ethylene glycol component (component C) and aliphatic dimer diol component (component D) as glycol components It has been proposed to improve stability.

JP 2012-268375 A JP2013-173870A

  However, Patent Document 1 discloses that the 4,4 '-(alkylenedioxy) bisbenzoic acid component has a very complicated structure and it is difficult to obtain raw materials, and the method of Patent Document 2 is produced by copolymerization with four kinds of raw materials. Was very complex. Therefore, an object of the present invention is to provide a polyester film that is more easily dimensional stability, particularly excellent in dimensional stability against environmental changes such as temperature and humidity.

  In a polyester film, both the humidity expansion coefficient and the temperature expansion coefficient are very closely related to the Young's modulus, and generally lower as the Young's modulus is higher. However, the Young's modulus is not increased as much as possible, and there is a limit in terms of film forming properties and securing the Young's modulus in the orthogonal direction. For this reason, we have eagerly studied whether a film with a lower coefficient of expansion with respect to temperature and humidity can be obtained with the same Young's modulus. The inventors have found that a film having excellent characteristics can be obtained with a small amount, and have reached the present invention.

Thus, according to the present invention, the following polyester resin compositions described in (1) and (2), polyester films described in (3) to (7), and a magnetic recording medium described in (8) are provided.
(1) The number of moles of all dicarboxylic acid components constituting the copolymer polyester, including a copolymer polyester of a dicarboxylic acid component represented by the following formulas (I) and (II) and a glycol component represented by the following formula (III) Is a polyester composition characterized by containing 0.5 to 3.5 mol% of a dimer acid represented by the following formula (I).
-C (O) -RA-C (O)-(I)
-C (O) -RB-C (O)-(II)
-O-RC-O- (III)
In the structural formulas (I) to (III), RA is an alkylene group that may contain a C 31-51 cyclo ring and a branched chain, RB is a phenyl group or a naphthalenediyl group, and RC is a C 2-6 group. Represents an alkylene group.
(2) In addition to the copolyester, at least one selected from the group consisting of polyimide, polyetherimide, polyetherketone and polyetheretherketone is used, based on the mass of the copolyester, 0.5 to A polyester composition containing in the range of 25% by weight.
(3) A polyester film in which the polyester composition according to (1) or (2) is used in at least one layer.
(4) The polyester film according to (3), wherein the Young's modulus in at least one direction in the film surface direction is 4.5 GPa or more.
(5) The above (3), wherein the humidity expansion coefficient in at least one direction in the film surface direction is in the range of 1 to 8.5 (ppm /% RH) and the temperature expansion coefficient in at least one direction is 14 (ppm / ° C.) or less. -The polyester film in any one of (4).
(6) The polyester film according to any one of (3) to (5), wherein the water contact angle of at least one surface is in the range of 75 to 90 degrees.
(7) The polyester film according to any one of (3) to (6), which is used for a base film of a magnetic recording medium.
(8) A magnetic recording medium comprising the polyester film described in (7) above and a magnetic layer formed on one side thereof.

  According to the present invention, it is possible to provide a polyester film that is more easily dimensional stability, particularly excellent in dimensional stability against environmental changes such as temperature and humidity. It is also possible to provide a polyester film that is highly compatible with both properties and winding properties.

  Therefore, according to the present invention, there is provided a film suitable for applications requiring high dimensional stability in consideration of the influence of humidity and temperature, particularly for a base film of a high-density magnetic recording medium. If the film of the present invention is used, a high-density magnetic recording medium having excellent dimensional stability can be provided.

<Copolymerized polyester>
The copolyester in the present invention comprises a dicarboxylic acid component and a glycol component.
First, particular dimer acid moiety represented by the specific foregoing structural formula (I), the fat part of R ^A is an alkylene group having 31 to 51 carbon atoms, and some cyclohexane ring in the alkylene group The ring portion may be widened, and it may have a branched chain as well as a straight chain, and preferably includes an alkylene group having both a branched chain and a cyclohexane ring structure. Among these, from the viewpoint of the effect of the present invention, a dimer acid in which R ^A is an alkylene group having an alkyl branched chain having 33 to 49 carbon atoms and a cyclohexane ring is preferred, and an alkyl having 35 to 47 carbon atoms is also preferred. Dimer acid that is an alkylene group having a branched chain and a cyclohexane ring is particularly preferred.

Next, specific examples of the aromatic dicarboxylic acid component represented by the above formula (II) include those in which R ^B is a phenylene group or a naphthalenediyl group, a terephthalic acid component, an isophthalic acid component, 2 1,6-naphthalenedicarboxylic acid component, 2,7-naphthalenedicarboxylic acid component, and the like. Among these, from the viewpoint of the effect of the present invention, a terephthalic acid component and a 2,6-naphthalenedicarboxylic acid component that are relatively easy to improve physical properties such as mechanical strength are preferable, and a 2,6-naphthalenedicarboxylic acid component is particularly preferable. .

Finally, as the glycol component represented by the above formula (III), the ^RC portion is an alkylene group having 2 to 6 carbon atoms, such as an ethylene glycol component, a trimethylene glycol component, a tetramethylene glycol component, etc. Is mentioned. Among these, from the viewpoint of the effect of the present invention, an ethylene glycol component that is relatively easy to improve physical properties such as mechanical strength is preferable.

  The copolymer polyester in the present invention is a copolymer component known per se, for example, an aliphatic dicarboxylic acid component or an alicyclic dicarboxylic acid component not corresponding to the above-mentioned formula (I), as long as the effects of the present invention are not impaired. , An aromatic dicarboxylic acid component not corresponding to the above formula (II), an alkylene glycol component not corresponding to the above formula (III), a hydroxycarboxylic acid component, an acid component having a trifunctional or more functional group such as trimellitic acid, Alcohol components and the like may be copolymerized. Of course, based on the number of moles of all dicarboxylic acid components constituting the copolyester, the total number of moles of aromatic dicarboxylic acid components represented by the aforementioned formulas (I) and (II) and the aforementioned formula (III) It is preferable that the number of moles of the glycol component occupies 90 mol% or more, and more preferably 95 mol% or more.

  By the way, the characteristics of the copolyester in the present invention are characterized by the above formula (in the range of 0.5 mol% or more and 3.5 mol% or less based on the number of moles of all dicarboxylic acid components constituting the copolyester. The specific dimer acid component represented by I) is copolymerized. When the ratio of the specific dimer acid component is less than the lower limit, the effect of reducing the humidity expansion coefficient is difficult to be exhibited. On the other hand, when the upper limit is exceeded, film-forming properties are impaired, it is difficult to improve mechanical properties such as Young's modulus by stretching, it is difficult to lower the coefficient of thermal expansion, and in severe cases it breaks during film-forming processes such as stretching. Resulting in. Surprisingly, the effect of reducing the coefficient of humidity expansion by a specific dimer acid component is efficiently expressed even in a relatively small amount. From such a viewpoint, the upper limit of the content ratio of the preferred specific dimer acid component is 3.5 mol% or less, further 3.2 mol% or less, and further 2.9 mol% or less, while the lower limit is 0.5 mol%. As mentioned above, it is further 0.7 mol% or more, and further 0.9 mol% or more.

From such a viewpoint, the preferable ratio of the aromatic dicarboxylic acid component represented by the above formula (II) is 99.5 mol% or less, more preferably 99.3 mol% or less, particularly 99.1 mol% or less, and the lower limit is 99.5 mol% or less. It is 96.5 mol% or more, further 96.8 mol% or more, and further 97.1 mol% or more.
By using a copolyester obtained by copolymerizing such a specific amount of a specific dimer acid component, a molded product having a low temperature expansion coefficient and a low humidity expansion coefficient, such as a film, can be produced.

  The copolymerization amount of the specific dimer acid component is adjusted by adjusting the composition of the raw material so that the desired copolymerization amount is obtained in the polymerization stage, or a homopolymer using only the specific dimer acid component as the acid component or A polymer having a large amount of copolymerization and a non-copolymerized polymer or a polymer having a small amount of copolymerization can be prepared, and these can be adjusted by transesterification by melt-kneading so as to obtain a desired copolymerization amount.

<Method for producing copolymer polyester resin>
The production method of the copolyester in the present invention will be described in detail.
The specific dimer acid component represented by the structural formula (I) can be obtained by using dimer acid “Priplast 1838”, “Pripol 1009”, “Pripol 1004”, etc. manufactured by Croda.

  Moreover, the copolyester in this invention reacts a specific dimer acid and its alkylester derivative, for example, ethylene glycol, and manufactures a polyester precursor. In that case, it can also be made to react with other aromatic dicarboxylic acid components, for example, 2,6-naphthalenedicarboxylic acid, terephthalic acid or ester-forming derivatives thereof. And it can manufacture by superposing | polymerizing the polyester precursor obtained in this way in presence of a polymerization catalyst, You may give a solid phase polymerization etc. as needed. The intrinsic viscosity measured at 35 ° C. using a mixed solvent of aromatic polyester P-chlorophenol / 1,1,2,2-tetrachloroethane (weight ratio 40/60) thus obtained is 0.4. From the viewpoint of the effect of the present invention, it is preferably in the range of -1.5 dl / g, more preferably 0.5-1.2 dl / g, and particularly preferably 0.55-0.8 dl / g.

  The reaction temperature for producing the polyester precursor is preferably in the range of 190 ° C. to 250 ° C., and is carried out under normal pressure or under pressure. When the temperature is lower than 190 ° C., the reaction does not proceed sufficiently. When the temperature is higher than 250 ° C., diethylene glycol which is a side reaction product is likely to be generated.

  In the reaction step for producing a polyester precursor, a known esterification or transesterification reaction catalyst may be used. For example, manganese acetate, zinc acetate, alkali metal compounds, alkaline earth metal compounds, titanium compounds and the like can be mentioned. A titanium compound that can suppress high surface protrusions when formed into a film is preferred.

  Next, the polycondensation reaction will be described. First, the polycondensation temperature is in the range of a temperature not lower than the melting point of the obtained polymer and not higher than 230 to 300 ° C, more preferably not lower than 5 ° C and higher than the melting point by 30 ° C. The polycondensation reaction is usually preferably performed under a reduced pressure of 100 Pa or less.

  Examples of the polycondensation catalyst include metal compounds containing at least one metal element. The polycondensation catalyst can also be used in the esterification reaction. Examples of the metal element 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. As described above, particularly when a titanium compound is used, a high protrusion on the surface due to the influence of the residual metal used in the catalyst when a film is formed. It is preferable to use this because it is suppressed.

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

  Specific examples of the esterification catalyst, the transesterification catalyst, and the titanium compound as the polycondensation catalyst include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraisobutyl titanate, and tetra-tert-butyl. Titanate, tetracyclohexyl titanate, tetraphenyl titanate, tetrabenzyl titanate, lithium oxalate titanate, potassium oxalate titanate, ammonium oxalate titanate, titanium oxide, titanium ortho ester or condensed ortho ester, titanium ortho ester or condensed ortho ester Reaction product comprising hydroxycarboxylic acid, reaction product comprising titanium orthoester or condensed orthoester, hydroxycarboxylic acid and phosphorus compound, titanium orthoester Or polyhydric alcohols having at least two hydroxyl groups and condensed orthoesters, 2-hydroxy carboxylic acid, or a reaction product comprising a base and the like.

  And, as described above, the copolymerized polyester in the present invention may be polymerized so as to be a copolymerized polyester having a desired copolymerization amount, and since the transesterification proceeds at the time of melt-kneading, two or more kinds of copolymers are copolymerized. Aromatic polyesters having different amounts may be prepared, and they may be melt-kneaded and blended to obtain a desired copolymerization amount.

<Polyester composition>
The polyester composition of the present invention is characterized by containing the above-mentioned copolymer polyester. In addition, as long as the effect of the present invention is not inhibited, a known additive or other resin may be blended to form a composition. Additives include stabilizers such as UV absorbers, antioxidants, plasticizers, lubricants, flame retardants, mold release agents, pigments, nucleating agents, fillers or glass fibers, carbon fibers, layered silicates, etc. And may be appropriately selected according to the requirements of the intended use. Examples of other resins include aliphatic polyester resins, polyamide resins, polycarbonates, ABS resins, liquid crystal resins, polymethyl methacrylate, polyamide elastomers, polyester elastomers, polyether imides, and polyimides.

  By the way, the polyester composition of the present invention contains at least one selected from the group consisting of polyimide, polyetherimide, polyetherketone and polyetheretherketone in addition to the above-mentioned copolymerized polyester. It is good also as a polyester composition by making it contain in 0.5 to 25weight% of a range on the basis of mass. By containing such a resin in the above range, the glass transition temperature as the polyester resin composition can be increased, and as a result, the dimensional stability can be further improved. Among these, polyetherimide is preferable because it can be more uniformly dispersed and the glass transition temperature can be easily increased. Specific examples of the polyetherimide include those disclosed in JP-A No. 2000-355631. Further, from the viewpoint of further improving the dimensional stability against environmental changes, the 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component described in International Publication No. 2008/096612 pamphlet, 6,6 ′-( Those obtained by copolymerizing a trimethylenedioxy) di-2-naphthoic acid component and a 6,6 ′-(butylenedioxy) di-2-naphthoic acid component are also preferred.

<Film>
The polyester film of the present invention is preferably a stretched oriented film because it is easy to increase the Young's modulus, which will be described later, and is particularly preferably a biaxially oriented polyester film oriented in two orthogonal directions. For example, the above-mentioned polyester composition is melt-formed and extruded into a sheet, and the film-forming direction (hereinafter, sometimes referred to as the longitudinal direction, the longitudinal direction, or the MD direction) and the direction orthogonal thereto (hereinafter, the width direction). , Sometimes referred to as the transverse direction or the TD direction).

  Of course, since it is a film obtained by melt-forming the above-mentioned copolymerized polyester, it also has excellent mechanical properties of the specific dimer acid component and the aromatic polyester composed of the above formulas (II) and (III). Yes. The polyester film of the present invention is not limited to a single layer, and may be a laminated film. In that case, it is easy that at least one layer is a film layer made of the above-described copolymerized polyester of the present invention. Will be understood.

  By the way, the polyester film of the present invention preferably has a temperature expansion coefficient (αt) in at least one direction in the plane direction of the film of 14 ppm / ° C. or less from the viewpoint of exhibiting excellent dimensional stability. Preferably, the temperature expansion coefficient (αt) in the width direction of the film is equal to or less than the upper limit of the temperature expansion coefficient in at least one direction of the film, for example, by matching with the direction of the film for which dimensional stability is most required. It can be expressed in a film that can obtain excellent dimensional stability against changes. The lower limit of the preferred temperature expansion coefficient (αt) is −10 ppm / ° C. or more, further −7 ppm / ° C. or more, particularly −5 ppm / ° C. or more, and the upper limit is 10 ppm / ° C. or less, further 7 ppm / ° C. or less, particularly 5 ppm / It is below ℃. Further, for example, when a magnetic recording tape is used, it is possible to develop excellent dimensional stability against dimensional changes due to changes in the temperature and humidity of the atmosphere, and therefore the direction satisfying the temperature expansion coefficient is the width direction of the polyester film. preferable.

  The polyester film of the present invention preferably has a Young's modulus of at least 4.5 GPa in at least one direction of the film surface direction, preferably the direction in which the temperature expansion coefficient is 14 ppm / ° C. or less, and the upper limit is not particularly limited. Is usually about 12 GPa. A particularly preferable Young's modulus is in the range of 5 to 11 GPa, particularly 6 to 10 GPa. If it is out of this range, it may be difficult to achieve the above-mentioned αt and αh, and the mechanical characteristics may be insufficient. Such Young's modulus can be adjusted by the blend or copolymer composition described above and the stretching described below. Further, the polyester film of the present invention has a humidity expansion coefficient of 1 to 8 in at least one direction of the film surface direction, preferably in the direction in which the temperature expansion coefficient is 14 ppm / ° C. or less, when used for a base film of a magnetic tape. 5 (ppm /% RH), more preferably 3 to 8.5 (ppm /% RH), particularly 4 to 7 (ppm /% RH), and the lower limit is not particularly limited. % RH) is preferred. Outside this range, the dimensional change with respect to the humidity change increases. Such a humidity expansion coefficient can be adjusted with the orientation by the below-mentioned extending | stretching using the above-mentioned polyester composition.

  As for the direction where the temperature expansion coefficient is 14 ppm / ° C. or less, it is sufficient that the width direction is satisfied in at least one direction, preferably as described above. Of course, the direction orthogonal to the width direction also preferably satisfies the same temperature expansion coefficient, humidity expansion coefficient, Young's modulus, and the like from the viewpoint of dimensional stability.

  By the way, the surface energy of the surface of the polyester composition varies depending on the content of dimer acid when it is formed into a film. Specifically, the contact angle of water increases as the content of dimer acid increases. And since the humidity expansion coefficient can be lowered by making the film surface more hydrophobic, the contact angle of water on at least one surface of the polyester film of the present invention is 75 degrees or more. Preferably, more preferably 77 degrees or more. More preferably, it is 78 degrees or more. Moreover, it is preferable that the upper limit of a contact angle is 90 degrees or less from a viewpoint of an application | coating process. This is because if the surface energy is too different from that of the polyester film, problems that did not occur in the past in the coating process may occur. The upper limit is more preferably 88 degrees or less, and still more preferably 86 degrees or less.

  By the way, when applying a magnetic layer, a backcoat layer, etc. to a polyester film, it heats in oven for drying. A film elongation at 110 ° C., which will be described later, can be considered as one index of the appropriate process capability in this drying process. When the film elongation is high, trough is generated in the process and causes smears. Therefore, the film elongation is preferably low and is preferably 3.0% or less. The film elongation is preferably 2.5% or less, more preferably 2.0% or less, and still more preferably 1.5% or less.

<Production method of polyester film>
As described above, the polyester film of the present invention is preferably an oriented polyester film, and particularly preferably a film in which the molecular orientation in each direction is enhanced by stretching in the film forming direction and the width direction. Such an oriented polyester film is preferably produced, for example, by the following method because the Young's modulus is increased and the temperature expansion coefficient and the humidity expansion coefficient are easily reduced while maintaining the film formability.

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

  In order to achieve αt, αh, Young's modulus, etc. defined 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 viewpoint, it is preferable to perform cooling by the cooling drum very quickly. From such a viewpoint, it is preferable to carry out at a low temperature of 20 to 60 ° C. By performing at such a low temperature, crystallization in the state of an unstretched film is suppressed, and subsequent stretching can be performed more smoothly.

As the biaxial stretching, those known per se can be adopted, and sequential biaxial stretching or simultaneous biaxial stretching may be employed.
Here, a manufacturing method of sequential biaxial stretching in which longitudinal stretching, lateral stretching, and heat treatment are performed in this order will be described as an example. First, the first longitudinal stretching is performed at a glass transition temperature (Tg: ° C.) to (Tg + 40) ° C. of the copolyester, which is stretched 3 to 8 times, and then at a higher temperature (Tg + 10) than the previous longitudinal stretching in the transverse direction. ) To (Tg + 50) ° C. at a temperature of 3 to 8 times, and further as a heat treatment at a temperature below the melting point of the copolyester and at a temperature of (Tg + 50) to (Tg + 150) ° C. for 1 to 20 seconds, and further 1 to 15 It is preferable to carry out a second heat fixing treatment.
In the above description, sequential biaxial stretching has been described. However, the polyester film of the present invention can be produced by simultaneous biaxial stretching in which longitudinal stretching and lateral stretching are simultaneously performed. For example, referring to the stretching ratio and the stretching temperature described above. do it.

  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 types of molten polyester are laminated in a die and then extruded into a film, preferably extruded at a temperature of the melting point (Tm: ° C.) to (Tm + 70) ° C. of each polyester, or two or more types. The molten polyester is extruded from a die and then 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 single-layer film described above. Further, when providing the above-mentioned coating layer, a desired coating solution is applied to one or both sides of the unstretched film or the uniaxially stretched film, and then the biaxial stretching and the same method as in the case of the single-layer film are performed. It is preferable to perform a heat treatment.

  According to the present invention, the above-described polyester film of the present invention is used as a base film, and a nonmagnetic layer and a magnetic layer are formed in this order on one side, and a back coat layer is formed on the other side. It can be set as a magnetic recording tape.

  By the way, the polyester film of this invention is not restricted to a single layer film as above-mentioned, A laminated | multilayer film may be sufficient, and it is easy to make flatness and winding property compatible by it. For example, by applying a magnetic layer on a flat surface with a small surface roughness and a backcoat layer on a rough surface with a large surface roughness, both required flatness and transportability can be achieved at a higher level. From such a viewpoint, when used for a base film of a magnetic recording medium, the upper limit of the surface roughness of a rough surface having a large surface roughness is preferably 8.0 nm, more preferably 7.0 nm, and particularly preferably 6.0 nm. On the other hand, the lower limit is preferably 2.0 nm, more preferably 3.0 nm, and particularly preferably 4.0 nm. Further, the upper limit of the surface roughness of a flat surface having a small surface roughness is preferably 5.0 nm, more preferably 4.5 nm, particularly 4.0 nm, while the lower limit is 1.0 nm, further 1.5 nm, It is preferably 2.0 nm. Such surface roughness can be adjusted by containing inert particles, adjusting the particle size and content of the inert particles, or providing a coating layer on the surface.

Hereinafter, the case where the polyester film of the present invention is a laminated polyester film will be described.
When the polyester film of the present invention is a laminated polyester film obtained by laminating a film layer A and a film layer B, it is sufficient that at least one of the film layers A and B is made of the above-described polyester composition. The layer may be made of other polyester. At this time, from the viewpoint of curling, the film layer A and the film layer B preferably have substantially the same dimer acid content. From such a viewpoint, the film layer A and the film layer B are the same polyester. It is preferable that the difference in the content of the dimer acid contained is, for example, less than 0.3 mol%.

  Specific polyesters other than the above-mentioned copolymerized polyester include polyalkylene terephthalate having a repeating unit of alkylene terephthalate such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, poly Preferable examples include polyalkylene-2,6-naphthalate having repeating units of alkylene-2,6-naphthalate such as trimethylene-2,6-naphthalate and polybutylene-2,6-naphthalate. Among these, polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are preferable from the viewpoint of mechanical properties, and polyethylene-2,6-naphthalenedicarboxylate is particularly preferable.

  In addition, the aromatic polyester in which the specific dimer acid component is copolymerized in a specific amount and the polyester forming the other layer are other copolymer components known per se as long as the effects of the present invention are not impaired. May be copolymerized.

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

(1) Young's modulus The obtained film was cut out with a sample width of 10 mm and a length of 15 cm, and a universal tensile testing device (product name: manufactured by Toyo Baldwin, trade name: 100 mm between chucks, tensile speed 10 mm / min, chart speed 500 mm / min). Pull with Tensilon). The Young's modulus is calculated from the tangent of the rising portion of the obtained load-elongation curve.

(2) Temperature expansion coefficient (αt)
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 would be the measurement direction, and set in TMA3000 manufactured by Vacuum Riko, under a nitrogen atmosphere (0% RH), 60 ° C. For 30 minutes and then let it cool to room temperature. Thereafter, the temperature is raised from 25 ° C. to 70 ° C. at 2 ° C./min, the sample length at each temperature is measured, and the temperature expansion coefficient (αt) is calculated from the following equation. In addition, the measurement direction is the longitudinal direction of the sample cut out, the measurement was performed 5 times, and the average value 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 temperature expansion coefficient (× 10 ⁻⁶ / ° C.) of quartz glass.

(3) 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 would be the measurement direction, set in TMA3000 manufactured by Vacuum Riko, and a humidity of 30% under a nitrogen atmosphere at 30 ° C. The length of each sample at RH and humidity 70% RH is measured, and the humidity expansion coefficient is calculated by the following equation. In addition, the measurement direction is the longitudinal direction of the cut out sample, the measurement was performed 5 times, and the average value was αh.
αh = (L ₇₀ −L ₃₀ ) / (L ₃₀ × ΔH)
Here, L ₃₀ in the above formula is a sample length (mm) when 30% RH, L ₇₀ is a sample length (mm) when 70% RH, ΔH: 40 (= 70-30)% RH is there.

(4) Contact angle of water Using a contact angle measurement image analyzer (G-1-1000) manufactured by Elma Sales Co., Ltd., the contact angle 10 seconds after dropping water was measured.

(5) Identification of dimer acid 20 mg of a sample was dissolved in 0.6 mL of a mixed solvent of deuterated trifluoroacetic acid: deuterated chloroform = 1: 1 (volume ratio) at room temperature and ¹ H-NMR at 500 MHz in a polymer chip and a film. The amount of dimer acid was calculated.

(6) Intrinsic viscosity (IV)
The intrinsic viscosity of the obtained copolyester and film was determined by dissolving the polymer using a mixed solvent of P-chlorophenol / tetrachloroethane (40/60 weight ratio) and measuring at 35 ° C.

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

(8) Film elongation at 110 ° C. The obtained film was cut into a length of 20 mm and a width of 4 mm so that the film-forming direction of the film would be the measurement direction, set in SII EXSTAR6000, and under a nitrogen atmosphere (0% RH), held at 30 ° C., then heated to 2O 0 C / min to 150 ° C. with a stress of 20 MPa applied in the film forming direction, measured the sample length at each temperature, and held at 30 ° C. With respect to the film length (L30) before the subsequent temperature increase, the film length at 110 ° C. (L110) was calculated according to the following formula and how much the film length was expanded.
Application suitability (%) = (L110−L30) / L30 × 100

(9) Surface roughness (Ra)
Using a non-contact type three-dimensional surface roughness meter (manufactured by ZYGO: New View 5022), measurement was performed under conditions of a measurement magnification of 10 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ). Central surface average roughness (Ra) was performed on each surface by built-in surface analysis software MetroPro, and when the difference in surface roughness was 0.1 nm or less, the average value was described as the same surface roughness.

(10) Thickness of film layer In the case of an unstretched film, after cutting a section in a direction perpendicular to the film forming direction with a microtome (ULTRACUT-S), the thickness of each of layers A and B is determined using an optical microscope. Calculated. In the case of an oriented laminated polyester film, after cutting out in the same manner, the thicknesses of the layers A and B were calculated using a transmission electron microscope to obtain the thickness ratio dA / dB.

(11) Preparation of magnetic tape A back coat layer paint having the following composition was applied to the surface of the rough layer side of the laminated biaxially oriented polyester film having a width of 1000 mm and a length of 1000 m obtained in each of the examples and comparative examples. After coating and drying at a tension of 20 MPa, temperature: 120 ° C., speed: 200 m / min), the film thickness is simultaneously changed with a die coater on the flat layer side surface of the film with a nonmagnetic paint and magnetic paint having the following composition. And then magnetically oriented and dried. Further, after calendering with a small test calender (steel roll / nylon roll, 5 stages) at a temperature of 70 ° C. and a linear pressure of 200 kg / cm, curing is performed at 70 ° C. for 48 hours. The tape was slit to 12.65 mm and incorporated into a cassette to obtain a magnetic recording tape. The coating amount was adjusted so that the thicknesses of the dried backcoat layer, nonmagnetic layer and magnetic layer were 0.5 μm, 1.2 μm and 0.1 μm, respectively.

<Composition of non-magnetic paint>
-Titanium dioxide fine particles: 100 parts by weight-Esreck A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight-Nipponran 2304 (Nippon Polyurethane Polyurethane Elastomer): 10 parts by weight-Coronate L (Nippon Polyurethane Poly Isocyanate): 5 parts by weight, lecithin: 1 part by weight, methyl ethyl ketone: 75 parts by weight, methyl isobutyl ketone: 75 parts by weight, toluene: 75 parts by weight, carbon black: 2 parts by weight, lauric acid: 1.5 parts by weight <magnetic Composition of paint>
Iron (major axis: 0.037 μm, needle ratio: 3.5, 2350 oersted): 100 parts by weight Eslek A (vinyl chloride / vinyl acetate copolymer made by Sekisui Chemical: 10 parts by weight) Nipponan 2304 (Nippon Polyurethane) Polyurethane elastomer): 10 parts by weight, Coronate L (polyisocyanate made by Nippon Polyurethane): 5 parts by weight, lecithin: 1 part by weight, methyl ethyl ketone: 75 parts by weight, methyl isobutyl ketone: 75 parts by weight, toluene: 75 parts by weight, carbon Black: 2 parts by weight ・ Lauric acid: 1.5 parts by weight <Composition of back coat layer paint:>
Carbon black: 100 parts by weight Thermoplastic polyurethane resin: 60 parts by weight Isocyanate compound: 18 parts by weight (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.)
Silicone oil: 0.5 parts by weight Methyl ethyl ketone: 250 parts by weight Toluene: 50 parts by weight

(12) Electromagnetic conversion characteristics For measuring the electromagnetic conversion characteristics, a 1/2 inch linear system with a fixed head was used. Recording was performed using an electromagnetic induction head (track width 25 μm, gap 0.1 μm), and reproduction was performed using an MR head (8 μm). The relative speed of the head / tape is 10 m / sec, a signal with a recording wavelength of 0.2 μm is recorded, the reproduced signal is analyzed with a spectrum analyzer, the output C of the carrier signal (wavelength 0.2 μm), and the integration over the entire spectrum. The noise N ratio was defined as the C / N ratio, and a relative value was determined with 0 dB as Example 1 created by the above method 11, and evaluated according to the following criteria.
◎: +1 dB or more ○: −1 dB or more, less than +1 dB ×: less than −1 dB

(13) Error rate Data storage with the length of magnetic recording tape of 850 m, slitting the original tape produced in (11) above to a width of 12.65 mm (1/2 inch) and incorporating it into an LTO case. A cartridge was created. This data storage was recorded using an IBM LTO5 drive in an environment of 23 ° C. and 50% RH (recording wavelength 0.55 μm), and then the cartridge was stored in an environment of 50 ° C. and 80% RH for 7 days. After the cartridge was stored at room temperature for one day, the full length was reproduced, and the error rate of the signal at the time of reproduction was measured. 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.
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 ⁻⁴ ×: Error rate is 1.0 × 10 ⁻⁴ or more

(14) Dropout (DO)
The data storage cartridge whose error rate was measured in the above (13) was loaded into an IBM LTO5 drive, a data signal was recorded at 14 GB, and it was reproduced. A signal having an amplitude (PP value) of 50% or less with respect to the average signal amplitude was detected as a missing pulse, and four or more consecutive missing pulses were detected as dropouts. In addition, dropout evaluates 1 volume of 850m, converts into the number per 1m, and determines by the following references | standards.
◎: Dropout less than 3 pieces / m ○: Dropout of 3 pieces / m or more, less than 9 pieces / m ×: Dropout of 9 pieces / m or more

[Example 1]
A transesterification reaction of dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol as the diol component in the presence of titanium tetrabutoxide was carried out, followed by a polycondensation reaction to prepare polyethylene naphthalate pellets A1. (IV = 0.58 dl / g, Tg = 115 ° C., Tm = 263 ° C.).

  Dimer acid is copolymerized by performing a transesterification reaction in the presence of titanium tetrabutoxide with dimethyl 2,6-naphthalenedicarboxylate, Priplast 1838 as the dicarboxylic acid component, and ethylene glycol as the diol component, followed by a polycondensation reaction. Copolymer polyethylene naphthalate pellets B1 were prepared (IV = 0.58 dl / g, Tg = 58 ° C., Tm = 232 ° C.). The content of dimer acid as the acid component was found to be 10.6 mol% by NMR analysis.

  Pellets A1 and B1 were blended at a mass ratio of 90:10 to obtain resin C1. The dimer acid component contained in this resin C1 is 0.9 mol%. Further, for the resin C1, true spherical silica particles having an average particle diameter of 0.1 μm, and 0.25% by mass, and true spherical silica particles having an average particle diameter of 0.3 μm, based on the mass of the film, The content was 0.04% by mass on the basis of.

The resin C1 thus obtained was extruded at 280 ° C. on a rotating drum having a temperature of 60 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 130 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 130 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 210 ° C. for 3 seconds to give a thickness of 5.0 μm. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester are shown in Table 1.

[Example 2]
Pellets A1 and B1 were blended at a mass ratio of 84:16, respectively, to obtain Resin C2. The dimer acid component contained in this resin C2 is 1.5 mol%. Resin C2 contains true spherical silica particles having an average particle size of 0.1 μm, and 0.25% by mass of true spherical silica particles having an average particle size of 0.3 μm based on the mass of the film. The content was 0.04% by mass on the basis of.

The resin C2 thus obtained was extruded at 280 ° C. on a rotating cooling drum having a temperature of 60 ° C. to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 130 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.0 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 130 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-set at 200 ° C. for 3 seconds to obtain a thickness of 5.0 μm. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester are shown in Table 1.

[Example 3]
The unstretched film obtained in Example 2 was heated between two sets of rollers having different rotation speeds along the film forming direction with an IR heater from above so that the film surface temperature became 130 ° C. Stretching in the direction (film forming direction) was performed at a draw ratio of 5.0 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is led to a stenter, stretched at 130 ° C. in the transverse direction (width direction) at a stretch ratio of 4.0 times, and then heat-set at 200 ° C. for 3 seconds to give a thickness of 5.0 μm. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester are shown in Table 1.

[Example 4]
The unstretched film obtained in Example 2 was heated between two sets of rollers having different rotation speeds along the film forming direction with an IR heater from above so that the film surface temperature became 130 ° C. Stretching in the direction (film forming direction) was performed at a stretch ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 130 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-set at 200 ° C. for 3 seconds to obtain a thickness of 5.0 μm. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester are shown in Table 1.

[Example 5]
Pellets A1 and B1 were blended in a mass ratio of 74:26 to obtain Resin C3. The dimer acid component contained in this resin C3 is 2.5 mol%. Further, for the resin C3, true spherical silica particles having an average particle diameter of 0.1 μm, based on the mass of the film, 0.25% by mass, true spherical silica particles having an average particle diameter of 0.3 μm, and the mass of the film The content was 0.04% by mass on the basis of.

The resin C3 thus obtained was extruded at 280 ° C. on a rotating cooling drum having a temperature of 60 ° C. to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotational speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 120 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.8 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 120 ° C. in the transverse direction (width direction) at a stretch ratio of 5.5 times, and then heat-set at 200 ° C. for 3 seconds. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester are shown in Table 1.

[Example 6]
Transesterification of dimethyl terephthalate as the dicarboxylic acid component and ethylene glycol as the diol component in the presence of titanium tetrabutoxide followed by a polycondensation reaction gave polyethylene naphthalate pellets A2 (IV = 0. 58 dl / g).

A copolymerized polyethylene naphthalate obtained by copolymerizing dimer acid by carrying out a transesterification reaction in the presence of titanium tetrabutoxide with dimethyl terephthalate, Priplast 1838 as a dicarboxylic acid component, and ethylene glycol as a diol component. Phthalate pellets B2 were prepared (IV = 0.58 dl / g). In addition, it prepared so that content of the dimer acid as an acid component might be 10.6 mol%.
Pellets A2 and B2 were blended at a mass ratio of 84:16, respectively, to obtain Resin C4. The dimer acid component contained in this resin C4 is 1.4 mol%. Resin C4 contains true spherical silica particles having an average particle diameter of 0.1 μm, and 0.25% by mass of true spherical silica particles having an average particle diameter of 0.3 μm based on the mass of the film. The content was 0.04% by mass on the basis of.

The resin C4 thus obtained was extruded at 280 ° C. onto a cooling drum having a temperature of 25 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotational speeds along the film forming direction so that the film surface temperature becomes 90 ° C. with an IR heater from above, and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 3.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched in the transverse direction (width direction) at 90 ° C. at a stretch ratio of 6.5 times, and then heat-set at 210 ° C. for 3 seconds. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 7]
“Ultem 1010” manufactured by SABIC Innovative Plastics was prepared as a polyetherimide. The prepared polyetherimide and pellets A2 and B2 were blended in a mass ratio of 5:79:16, respectively, to obtain Resin C5. The dimer acid component contained in this resin C5 is 1.6 mol%. Resin C5 contains true spherical silica particles having an average particle size of 0.1 μm, based on the mass of the film, and 0.25% by mass of true spherical silica particles having an average particle size of 0.3 μm. The content was 0.04% by mass on the basis of.

The resin C5 thus obtained was extruded at 280 ° C. onto a cooling drum having a temperature of 25 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 100 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 3.6 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is led to a stenter, stretched at 100 ° C. in the transverse direction (width direction) at a stretching ratio of 4.6 times, and then heat-set at 210 ° C. for 3 seconds to obtain a 5.0 μm thick two-piece film. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 8]
The prepared polyetherimide and pellets A2 and B2 were blended at a mass ratio of 20:64:16 to obtain Resin C6. The dimer acid component contained in this resin C6 is 1.9 mol%. Further, for the resin C6, true spherical silica particles having an average particle diameter of 0.1 μm, based on the mass of the film, 0.25% by mass, true spherical silica particles having an average particle diameter of 0.3 μm, and the mass of the film The content was 0.04% by mass on the basis of.

Resin C6 thus obtained was extruded at 280 ° C. onto a cooling drum having a temperature of 25 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 100 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 3.6 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched in the transverse direction (width direction) at 100 ° C. at a stretching ratio of 4.8 times, and then heat-set at 210 ° C. for 3 seconds to obtain a 5.0 μm thick two-piece film. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 9]
2,6-Naphthalenedicarboxylic acid, Pripol 1004 as the dicarboxylic acid component, and ethylene glycol as the diol component were transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to copolymerize the dimer acid. Copolymerized polyethylene naphthalate pellets B3 were prepared (IV = 0.58 dl / g). In addition, it prepared so that content of the dimer acid as an acid component might be 10.6 mol%.

  Pellets A1 and B3 were blended at a mass ratio of 84:16, respectively, to obtain Resin C7. The dimer acid component contained in this resin C7 is 1.5 mol%. Further, for the resin C8, true spherical silica particles having an average particle diameter of 0.1 μm, 0.25% by mass, and true spherical silica particles having an average particle diameter of 0.3 μm, based on the mass of the film, The content was 0.04% by mass on the basis of.

The resin C7 thus obtained was extruded at 280 ° C. onto a rotating drum at a temperature of 60 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 130 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is led to a stenter, stretched at 130 ° C. in the transverse direction (width direction) at a stretch ratio of 5.5 times, and then heat-fixed at 210 ° C. for 3 seconds to give a thickness of 5.0 μm. An axially oriented film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 10]
Resin C8 containing spherical silica particles having an average particle size of 0.1 μm as the lubricant composition of resin C2 based on the mass of film layer A was blended to 0.08% by mass. Similarly, when the spherical composition of the resin C2 is a spherical silica particle having an average particle diameter of 0.1 μm and the mass of the film layer B is a reference, 0.12% by mass of a spherical silica particle having an average particle diameter of 0.3 μm is obtained. Based on the mass of the film layer B, the resin C9 contained so as to be 0.13% by mass was blended. Resin C8 and Resin C9 were each extruded at 280 ° C., and merged with a feed block so that the thickness ratio of layer A to layer B was dA: dB = 3: 7.

The laminated sheet was extruded at 280 ° C. onto a rotating cooling drum at a temperature of 60 ° C. to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 130 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched in the transverse direction (width direction) at 130 ° C. at a stretch ratio of 5.5 times, and then heat-set at 210 ° C. for 3 seconds to form a laminate having a thickness of 4.0 μm. A biaxially oriented polyester film was obtained.
The results of the obtained laminated biaxially oriented polyester film are shown in Table 1.

[Comparative Example 1]
Using the pellet A2, true spherical silica particles having an average particle diameter of 0.1 μm, based on the mass of the film, 0.25% by mass, true spherical silica particles having an average particle diameter of 0.3 μm, and the mass of the film Based on the above, resin C10 was blended so as to be 0.04% by mass.

Resin 10 was extruded at 280 ° C. into a cooling drum having a temperature of 25 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotational speeds along the film forming direction so that the film surface temperature becomes 90 ° C. with an IR heater from above, and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.0 times to obtain a uniaxially stretched film. The uniaxially stretched film is guided to a stenter, stretched at 90 ° C. in the transverse direction (width direction) at a stretch ratio of 3.5 times, and then heat-set at 200 ° C. for 3 seconds. An axially oriented polyester film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 2]
Using the pellet A1, true spherical silica particles having an average particle diameter of 0.1 μm, based on the mass of the film, 0.25% by mass, and true spherical silica particles having an average particle diameter of 0.3 μm Based on the above, resin C11 was blended so as to be 0.04% by mass.

Resin C11 was extruded at 300 ° C. into a cooling drum having a temperature of 60 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction so that the film surface temperature becomes 150 ° C. from above with an IR heater, and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 150 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 210 ° C. for 3 seconds. An axially oriented film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 3]
Pellets A1 and B1 were blended at a mass ratio of 97: 3 to obtain Resin C12. The dimer acid component contained in this resin C12 is 0.3 mol%. Further, for the resin C12, true spherical silica particles having an average particle diameter of 0.1 μm, based on the mass of the film, 0.25% by mass, true spherical silica particles having an average particle diameter of 0.3 μm, and the mass of the film Was blended so as to be 0.04% by mass.

Resin C12 thus obtained was extruded at 300 ° C. onto a cooling drum having a temperature of 60 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction so that the film surface temperature becomes 150 ° C. from above with an IR heater, and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 150 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 210 ° C. for 3 seconds. An axially oriented laminated polyester film was obtained.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 4]
Pellets A1 and B1 were blended in a mass ratio of 59:41 to obtain Resin C13. The dimer acid component contained in this resin C13 is 4.0 mol%. Further, for the resin C13, true spherical silica particles having an average particle diameter of 0.1 μm and 0.25% by mass, and true spherical silica particles having an average particle diameter of 0.3 μm, based on the mass of the film, Was blended so as to be 0.04% by mass.

The resin C13 thus obtained was extruded at 280 ° C. onto a cooling drum having a temperature of 40 ° C. during rotation to obtain an unstretched film. Then, the unstretched film is heated between two sets of rollers having different rotation speeds along the film forming direction from above with an IR heater so that the film surface temperature becomes 110 ° C., and the longitudinal direction (film forming direction) ) Was performed at a draw ratio of 4.5 times to obtain a uniaxially stretched film. Then, this uniaxially stretched film is guided to a stenter, stretched at 110 ° C. in the transverse direction (width direction) at a stretching ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds. An axially oriented polyester film was obtained.
Since the obtained polyester film had a large film elongation at the time of drying in the production of the magnetic tape (11) and it was difficult to produce the magnetic tape, the characteristics were not evaluated.
The results of the obtained biaxially oriented polyester film are shown in Table 1.

  In Table 1, PEN means polyethylene-2,6-naphthalene dicarboxylate, PET means polyethylene terephthalate, PEI means polyetherimide, MD means film forming direction, and TD means width direction.

  Since the polyester film of the present invention has excellent dimensional stability, it can be suitably used for a base film of a high-density magnetic recording medium.

Claims (8)

Based on the number of moles of all dicarboxylic acid components comprising the copolymerized polyester of the dicarboxylic acid component represented by the following formulas (I) and (II) and the glycol component represented by the following formula (III): A polyester composition comprising 0.5 to 3.5 mol% of a dimer acid represented by the following formula (I).
-C (O) -R ^A -C (O)-(I)
—C (O) —R ^B —C (O) — (II)
—O—R ^C —O— (III)
In the above structural formulas (I) to (III), R ^A is an alkylene group which may contain a C 31-51 cyclo ring and a branched chain, R ^B is a phenyl group or a naphthalenediyl group, and R ^C is a carbon number. 2-6 alkylene groups are shown.   In addition to the copolymerized polyester, at least one selected from the group consisting of polyimide, polyetherimide, polyetherketone and polyetheretherketone is 0.5 to 25% by weight based on the mass of the copolymerized polyester. The polyester composition according to claim 1, which is contained in the range described above.   A polyester film in which the polyester composition according to claim 1 or 2 is used in at least one layer.   The polyester film according to claim 3, wherein the Young's modulus in at least one direction in the film surface direction is 4.5 GPa or more.   The humidity expansion coefficient in at least one direction in the film surface direction is in the range of 1 to 8.5 (ppm /% RH), and the temperature expansion coefficient in at least one direction is in the range of 14 (ppm / ° C) or less. The polyester film of crab.   The polyester film according to any one of claims 3 to 5, wherein the water contact angle of at least one surface is in the range of 75 to 90 degrees.   The polyester film according to claim 3, which is used for a base film of a magnetic recording medium.   A magnetic recording medium comprising the polyester film according to claim 7 and a magnetic layer formed on one surface thereof.