JP2008255288A - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film having dimensional stability, particularly the dimensional stability against the environmental variation such as temperature and humidity and the dimensional stability at the time of processing, in a high degree. <P>SOLUTION: The biaxially oriented polyester film comprises an aromatic polyester between an aromatic dicarboxylic acid component and a gylcol component. The amount of ≥5 mol% and <50 mol% of the aromatic dicarboxylic acid component is 6,6'-(alkylene dioxy) di-2-naphthoic acid component, the aromatic polyester has a melting point in the range of 200-260°C, and at least one direction in the film planar direction has a Young's modulus of ≥6.0 GPa and a heat shrinkage ratio of ≤1.5% when treated at 105°C for 30 minutes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a film using an aromatic polyester copolymerized with 6,6 '-(alkylenedioxy) di-2-naphthoic acid.

  Aromatic polyesters typified by polyethylene terephthalate and polyethylene-2,6-naphthalate have excellent mechanical properties, dimensional stability and heat resistance, and thus are 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. in use. However, the demand for dimensional stability in high-density magnetic recording media and the like in recent years is increasing, and further improvement of characteristics is required.

  On the other hand, Patent Documents 1 to 4 are obtained from diethyl-6,6 ′-(alkylenedioxy) di-2-naphthoate, which is an ester compound of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid. Polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate has been proposed. According to this publication, polyethylene-6,6 '-(ethylenedioxy) di-2-naphthoate which is crystalline and has a melting point of 294 ° C. is specifically presented.

  However, since polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate presented in these patent documents has a very high melting point and very high crystallinity, it should be formed into a film or the like. Then, there was a problem that the fluidity in the molten state was poor and the extrusion became non-uniform, or even when trying to stretch after extrusion, crystallization progressed and the film would break when stretched at a high magnification.

In Patent Document 3, a film using polyethylene-6,6 ′-(ethylenedioxy) di-2-naphthoate has a maximum temperature expansion coefficient of 10 to 35 (ppm / ° C.) and a maximum humidity expansion coefficient. 0 to 8 (ppm /% RH), the difference between the maximum and minimum temperature expansion coefficient is 0 to 6.0 (ppm / ° C.), and the difference between the maximum and minimum humidity expansion coefficient is 0 to 4.0 (ppm /% RH) teaches that a magnetic recording flexible disk with small tracking deviation can be obtained. And, specifically in the embodiment, in the film forming direction of the Young's modulus 485kg ^/ mm 2 (4.8Gpa) and the Young's modulus in the transverse direction is 1100kg ^/ mm 2 (10.9GPa), the maximum temperature expansion coefficient 19 (ppm / ° C.), minimum temperature expansion 16.5 (ppm / ° C.), maximum humidity expansion 6 (ppm /% RH), and minimum humidity expansion 4.5 (ppm / % RH) film is disclosed.

  However, the demand for improvement in recording density in recent magnetic recording media and the like is severe, and accordingly, the dimensional stability required for the base film is presented in polyethylene-2,6-naphthalate and Patent Document 3 as well as polyethylene terephthalate. It has become a situation that can not be achieved even with such a film.

JP-A-60-135428 JP-A-60-212420 JP 61-145724 A JP-A-6-145323

  An object of the present invention is to provide a biaxially oriented polyester film having excellent moldability and excellent environmental change and dimensional stability in processing steps.

  In a biaxially oriented 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, when the same Young's modulus is used, it has been earnestly studied whether a film having an expansion coefficient with respect to a lower temperature and humidity can be obtained. Was considered as a suitable film because it exhibited a low coefficient of humidity expansion even when Young's modulus was low.

However, according to the above-mentioned Patent Documents 1 to 4, although a film made of polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate can have a very high Young's modulus, it is perpendicular to the film. There was a problem that the Young's modulus was extremely low. Moreover, although the humidity expansion coefficient was very small, there was also a problem that the temperature expansion coefficient was very high. Incidentally, when looking at the film disclosed in Example 1 of Patent Document 3, the Young's modulus is 1185 kg / mm ^{2 in the} width direction, but the film forming direction is only 485 kg / mm ² , and the coefficient of thermal expansion is 19 ( × 10 ⁻⁶ / ° C.) and a minimum of 16.5 (× 10 ⁻⁶ / ° C.), which was a very high value regardless of the Young's modulus.

  However, when the present inventors used 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component as a copolymerization component, surprisingly, polyalkylene-6,6 ′-(alkylenedioxy) It was found that a film having excellent characteristics of both di-2-naphthoate and an aromatic polyester which is a copolymerization partner thereof can be obtained. However, for example, when a coating liquid for forming a magnetic layer is applied and dried for use as a base film of a magnetic recording medium, it has been found that the base film contracts and spots are easily formed on the magnetic layer.

（上記構造式（Ｉ）中のＲは、炭素数１〜１０のアルキレン基を示す。）
で表される６，６’−（アルキレンジオキシ）ジ−２−ナフトエ酸成分であって、
該芳香族ポリエステルは融点が２００〜２６０℃の範囲にあり、
フィルム面方向における少なくとも一方向は、ヤング率が６．０ＧＰａ以上で、かつ１０５℃で３０分間処理したときの熱収縮率が１．５％以下である二軸配向ポリエステルフィルムが提供される。 Thus, according to the present invention, a biaxially oriented polyester film comprising an aromatic polyester of an aromatic dicarboxylic acid component and a glycol component, wherein at least 5 mol% of the aromatic dicarboxylic acid component is represented by the following formula (I):

(R in the structural formula (I) represents an alkylene group having 1 to 10 carbon atoms.)
A 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by:
The aromatic polyester has a melting point in the range of 200 to 260 ° C.,
In at least one direction in the film surface direction, a biaxially oriented polyester film having a Young's modulus of 6.0 GPa or more and a thermal shrinkage rate of 1.5% or less when treated at 105 ° C. for 30 minutes is provided.

Moreover, according to this invention, as a preferable aspect of this invention, at least one direction in a film surface direction is the following formula | equation (1).
αh <−1.2Y + 17 (1)
(Αh in the above general formula (1) is the coefficient of humidity expansion (ppm /% RH), Y is Young's modulus (GPa
). ), The humidity expansion coefficient in at least one direction of the film is in the range of 1 to 7 ppm / RH, the temperature expansion coefficient in at least one direction of the film is 10 ppm / ° C. or less, 6, 6 The '-(alkylenedioxy) di-2-naphthoic acid component is 6,6'-(ethylenedioxy) di-2-naphthoic acid component, and the aromatic polyester is used as a repeating unit, alkylene-2,6- It has at least one selected from the group consisting of naphthalene dicarboxylate units and alkylene terephthalate units, 90 mol% or more of the glycol component is an ethylene glycol component, and a biaxially oriented polyester film is a magnetic recording medium, particularly linear Used as a base film for high density magnetic recording tape The biaxially oriented polyester film comprising either even without also provided.

  According to the present invention, while maintaining the excellent characteristics of polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate, the film forming property can be enhanced to a high degree, which is surprising as a result. A biaxially oriented polyester film made of an aromatic polyester that also has excellent environmental changes such as temperature and humidity that cannot be predicted from conventional technology, and excellent dimensional stability in further processing steps. Is played.

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

<Aromatic polyester>
In the present invention, the aromatic polyester forming the biaxially oriented polyester film is composed of an aromatic dicarboxylic acid component and a glycol component. Specific examples of the aromatic dicarboxylic acid component other than the aromatic dicarboxylic acid component represented by the formula (I) include terephthalic acid component, isophthalic acid component, 2,6-naphthalenedicarboxylic acid component, and 2,7-naphthalenedicarboxylic acid. An acid component etc. are mentioned. Examples of the glycol component include an ethylene glycol component, a trimethylene glycol component, a tetramethylene glycol component, and a cyclohexane dimethanol component.

  Specific aromatic polyesters formed from aromatic dicarboxylic acid components other than the aromatic dicarboxylic acid component represented by the above formula (I) include alkylene terephthalates such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. Polyalkylene- having a repeating unit of alkylene-2,6-naphthalate such as polyalkylene terephthalate, polyethylene-2,6-naphthalate, polytrimethylene-2,6-naphthalate, polybutylene-2,6-naphthalate, etc. 2,6-naphthalate is preferred, and among these, polyethylene terephthalate and polyethylene-2,6-naphthalate are preferred from the viewpoint of mechanical properties and the like, and polyethylene-2,6-naphthalate is particularly preferred. Arbitrariness. From such a viewpoint, 90 mol% or more of the glycol component is preferably an ethylene glycol component. The proportion of the ethylene glycol component is preferably in the range of 90 to 100 mol%, more preferably 95 to 100 mol%.

  By the way, one of the characteristics of the present invention is that the acid component of the aromatic polyester described above is 6,6 ′-(alkylenedioxy) di-2- (2) represented by the above formula (I) in the range of 5 mol% or more. The naphthoic acid component is copolymerized. When the ratio of the 6,6 '-(alkylenedioxy) di-2-naphthoic acid component is less than the lower limit, the effect of reducing the humidity expansion coefficient of the present invention due to copolymerization is hardly exhibited. The upper limit is not particularly limited, but is preferably less than 80 mol% and more preferably less than 50 mol% from the viewpoint of moldability and the like. Surprisingly, the effect of reducing the coefficient of humidity expansion by the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is expressed very efficiently even in a small amount, and the upper limit of the copolymerization amount described above. In the following, a humidity expansion coefficient equal to or lower than that of the film described in the example of Patent Document 3 has already been achieved particularly in a portion of less than 50 mol%. It can be said that the effect of becomes saturated. A preferable upper limit of the copolymerization amount of the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is 45 mol% or less, further 40 mol% or less, more 35 mol% or less, particularly 30 mol% or less. On the other hand, the lower limit is 5 mol% or more, further 7 mol% or more, further 10 mol% or more, particularly 15 mol% or more.

  By using an aromatic polyester copolymerized with such a specific amount of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, a molded product having both a low temperature expansion coefficient and a low humidity expansion coefficient, For example, a film etc. can be manufactured.

  In addition, as the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by the structural formula (I), the R portion is an alkylene group having 1 to 10 carbon atoms, Preferably, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid component and 6,6 ′-(butylenedioxy) di -2-naphthoic acid component, and the like. Among these, from the viewpoint of the effect of the present invention, those having an even number of carbon atoms of R in the general formula (I) are preferred, and in particular, 6,6 ′-(ethylene An oxy) di-2-naphthoic acid component is preferred.

  The aromatic polyester in the present invention may be copolymerized with other copolymerization components known per se within a range not impairing the effects of the present invention, or may be blended with polyetherimide or liquid crystalline resin. Also good.

  By the way, in the method of transesterifying an ester of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid) and alkylene glycol as shown in Patent Documents 1 to 4, a large amount of dialkylene glycol component and the like is present. It is likely to occur as a by-product. Therefore, esterification of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid and ethylene glycol is used to suppress the deterioration of physical properties due to by-products and to keep the amount of ethylene glycol as described above within the above range. It is preferable to employ a reaction method. The diethylene glycol content can be measured with a nuclear magnetic resonance apparatus.

  Next, the aromatic polyester in the present invention has a melting point measured by DSC in the range of 200 to 260 ° C., further in the range of 215 to 255 ° C., particularly in the range of 225 to 253 ° C. preferable. When the melting point exceeds the above upper limit, when melt extrusion is performed, the fluidity is inferior, and the discharge is likely to be non-uniform. On the other hand, when it is less than the above lower limit, although the film-forming property is excellent, the mechanical properties of the aromatic polyester are easily impaired. That is, if other acid components are usually copolymerized and the melting point is lowered, the mechanical properties and the like are also lowered at the same time. It is the present invention that the present inventors have found that the same mechanical properties as those of a polymer having an ester of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid as the main repeating unit described in 1-4 can be expressed. .

  Further, the aromatic polyester in the present invention has a glass transition temperature (hereinafter sometimes referred to as Tg) measured by DSC in the range of 90 to 115 ° C, more preferably in the range of 95 to 115 ° C, particularly 100 to 115 ° C. It is preferable from the viewpoint of heat resistance and dimensional stability. Such a melting point and glass transition temperature can be adjusted by controlling the type and amount of copolymerization component, dialalkylene glycol as a byproduct.

<Film>
The biaxially oriented polyester film of the present invention can be obtained by melt-forming the aforementioned aromatic polyester and extruding it into a sheet. And as above-mentioned, since the fluidity | liquidity at the time of a fusion | melting and subsequent crystallinity are improved, it becomes a uniform film excellent in film forming property, for example, without a thickness spot.
Of course, since it is a film obtained by melt-forming the above-mentioned aromatic polyester, an excellent machine of polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate and the aromatic polyester that is a copolymerization partner thereof. It also has special characteristics.

  By the way, the biaxially oriented polyester film of the present invention exhibits excellent dimensional stability when used as a base film such as a magnetic tape, so that at least one direction in the film surface direction has a Young's modulus of 6.0 GPa or more. It is necessary to have a high Young's modulus. In addition, by having such a high Young's modulus, it is possible to sufficiently reduce the coefficient of humidity expansion even when polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate is used as a copolymerization component. I can do it. The upper limit of the Young's modulus is not limited, but is usually 11 GPa. The preferred Young's modulus is 5.1 to 11 GPa in the longitudinal direction of the film, more preferably in the range of 5.2 to 10 GPa, particularly 5.5 to 9 GPa, and 5.0 to 11 GPa in the width direction of the film, further 6 to 10 GPa. In particular, it is in the range of 7-10 GPa.

  By the way, the biaxially oriented polyester film of the present invention is excellent in moldability and excellent in dimensional stability, and when heat-treated at 105 ° C. for 30 minutes in the direction where the Young's modulus is 6 GPa or more. Since the heat shrinkage rate is 1.5% or less, dimensional changes are suppressed even when high temperature heat is applied when processing into a magnetic recording medium, etc., and the Young's modulus decreases and the surface of the magnetic layer becomes non-uniform. Is suppressed. The upper limit of the preferable heat shrinkage rate is 1.0% or less, further 0.8% or less, particularly 0.5% or less, and the lower limit of the heat shrinkage rate is 0.0% or more from the viewpoint of suppressing tarmi and the like. It is preferable. That is, one of the features of the present invention is that when a biaxially oriented polyester film is formed from the specific polyester resin used in the present invention, the above-mentioned Young's modulus of 6.0 GPa or more is stretched at a higher magnification. It has been found that the heat shrinkage rate when heat-treated at 105 ° C. for 30 minutes is extremely large, and the Young's modulus is reduced by making the heat shrinkage rate not more than the above-mentioned upper limit. And the non-uniformity of the surface of the magnetic layer can be suppressed.

Furthermore, the preferable aspect of the biaxially-oriented polyester film of this invention is explained in full detail.
The biaxially oriented polyester film of the present invention has a humidity expansion coefficient (αh) and a Young's modulus (Y) of the film in at least one direction, preferably the direction in which the Young's modulus of the film is 6 GPa or more, particularly preferably in the width direction of the film. However, it is preferable to satisfy | fill the relationship of the following formula | equation (1).
αh <−1.2Y + 17 (1)
(Where αh is the humidity expansion coefficient (ppm /% RH) and Y is the Young's modulus (GPa).)

When the obtained biaxially oriented polyester film does not satisfy the relationship of the above formula (1), it becomes only αh for Young's modulus equivalent to a film made of conventional polyethylene terephthalate or polyethylene-2,6-naphthalate, and polyalkylene- The effect of reducing humidity expansion due to the copolymerization of 6,6 ′-(alkylenedioxy) di-2-naphthoate is not sufficiently exhibited. The coefficient “−1.2” in the above relational expression is derived from the relationship between the Young's modulus and αh of the polyethylene-2,6-naphthalate film described in Comparative Examples 1 to 3 of the present specification. is there. Moreover, as an aromatic polyester copolymerized with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid, polyethylene-2,6-naphthalate is particularly preferable because Young's modulus is easily increased. The relationship between the preferred humidity expansion coefficient (αh) and Young's modulus (Y) is
αh <−1.2Y + 16.5 (1 ′)
Αh <−1.2Y + 16.0 (1 ″)
It is.

The lower limit of the relational expression between the Young's modulus and αh is not particularly limited.
αh> −1.2Y + 12.0 (1 ′ ″)
Degree. The Young's modulus, αh, and αt described later can be adjusted by the copolymerization composition described above and the stretching described later.

The biaxially oriented polyester film of the present invention preferably has a temperature expansion coefficient (αt) in at least one direction, preferably in the width direction of the film, of 10 ppm / ° C. or less from the viewpoint of exhibiting excellent dimensional stability. When the temperature expansion coefficient in at least one direction of the film is 10 ppm ⁶ / ° C. or less, excellent dimensional stability against environmental changes can be exhibited. From the results of Patent Document 3, it is expected that when polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthalate is copolymerized, the temperature expansion coefficient is expected to increase, but the specific copolymerization. The present invention has surprisingly been able to reduce the coefficient of thermal expansion by copolymerizing within a range of amounts and stretching it. The lower limit of the temperature expansion coefficient is not limited, but is usually −15 × 10 ⁻⁶ / ° C. A preferable temperature expansion coefficient (αt) is in the range of −10 to 10 ppm / ° C., further −7 to 7 ppm / ° C., particularly −5 to 5 ppm / ° C. It is preferable because it can exhibit excellent dimensional stability against dimensional changes due to.

  The biaxially oriented polyester film of the present invention has a humidity expansion coefficient in the range of 3 to 7 ppm /% RH and 3 to 6 ppm /% RH in the direction satisfying the relationship of the temperature expansion coefficient in at least one direction, preferably the width direction of the film. It is preferable from the viewpoint of dimensional stability when a magnetic recording tape is used. In particular, when used as a base film for a magnetic recording tape, it is preferable that the direction is the width direction of the biaxially oriented polyester film because track deviation and the like can be extremely suppressed.

  Further, for the direction in which the temperature expansion coefficient is 10 ppm / ° C. or less, at least one direction, preferably as described above, the width direction should be satisfied, but the direction orthogonal thereto is also dimensional stability point, It is preferable that the same temperature expansion coefficient, humidity expansion coefficient, and Young's modulus are satisfied.

<Method for producing aromatic polyester resin>
Next, a method for producing the aromatic polyester in the present invention will be described in detail.
First, 6,6 ′-(alkylenedioxy) di-2-naphthoic acid is reacted with, for example, 2,6-naphthalenedicarboxylic acid, terephthalic acid or an ester-forming derivative thereof, for example, ethylene glycol, and a polyester precursor is obtained. To manufacture. 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 in the range of 0.5-1.3 dl / g. As described above, by reacting 6,6 ′-(alkylenedioxy) di-2-naphthoic acid directly with glycol without passing through its ester compound, a by-product such as diethylene glycol, which is a reaction by-product, is produced. The content can also be reduced.

  Further, in the step of producing the above-mentioned polyester precursor, the ethylene glycol component is used in an amount of 1.1 to 6 times, further 2 to 5 times, particularly 3 to 5 times the number of moles of the total acid component. From the point of view, it is preferable.

  The reaction temperature for producing the polyester precursor is preferably at or above the boiling point of ethylene glycol, particularly preferably in the range of 190 ° C to 250 ° C. When the temperature is lower than 190 ° C., the reaction does not proceed sufficiently. When the temperature is higher than 250 ° C., diethylene glycol as a side reaction product is likely to be generated. In addition, the reaction can be performed under normal pressure, but the reaction may be performed under pressure in order to further increase productivity. More specifically, the reaction pressure is 10 to 200 kPa in absolute pressure, the reaction temperature is usually 150 to 250 ° C., preferably 180 to 230 ° C., the reaction time is 10 to 10 hours, preferably 30 to 7 minutes. It is preferable to be performed for less than an hour. A reaction product as a polyester precursor is obtained by this esterification reaction.

  In the reaction step for producing the polyester precursor, a known esterification or transesterification reaction catalyst may be used. For example, an alkali metal compound, an alkaline earth metal compound, a titanium compound, and the like can be given.

  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 280 ° 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 50 Pa or less. If it is higher than 50 Pa, the time required for the polycondensation reaction becomes long and it becomes difficult to obtain a copolymerized aromatic polyester resin having a high degree of polymerization.

  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, etc. Among them, a titanium compound is particularly preferable because it exhibits high activity in both the esterification reaction and the polycondensation reaction.

  These catalysts may be used alone or in combination. The amount of the catalyst is preferably 0.001 to 0.5 mol%, more preferably 0.005 to 0.2 mol%, based on the number of moles of the repeating unit of the copolymerized aromatic polyester.

  Specific examples of the titanium compound as the polycondensation catalyst include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraisobutyl titanate, tetra-tert-butyl titanate, tetracyclohexyl titanate, tetraphenyl titanate, and the like. Eltitanate, tetrabenzyl titanate, lithium oxalate titanate, potassium oxalate titanate, ammonium oxalate titanate, titanium oxide, titanium orthoester or condensed orthoester, titanium orthoester or condensed orthoester and hydroxycarboxylic acid A reaction product comprising an orthoester or condensed orthoester of titanium, a hydroxycarboxylic acid and a phosphorus compound, an orthoester of titanium or a condensed orthoester and at least 2 Polyhydric alcohols having a hydroxyl group, 2-hydroxy carboxylic acid, or a reaction product comprising a base and the like.

  In the aromatic polyester in the present invention, other thermoplastic polymers, stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants, flame retardants, mold release agents, pigments, as long as the effects of the present invention are not impaired. Further, a nucleating agent, a filler or glass fiber, carbon fiber, layered silicate, etc. may be blended as necessary. Examples of other types of thermoplastic polymers include aliphatic polyester resins, polyamide resins, polycarbonates, ABS resins, polymethyl methacrylate, polyamide elastomers, polyester elastomers, polyetherimides, polyimides, and the like.

<Film production method>
The biaxially oriented polyester film of the present invention is one in which the molecular orientation in each direction is enhanced by stretching in the film forming direction and the width direction. For example, the film forming property can be maintained by the following method. However, it is preferable because the Young's modulus is easily improved.

  First, the above aromatic polyester is used as a raw material, dried, and then supplied to an extruder heated to a temperature of the melting point (Tm: ° C.) to (Tm + 50) ° C. of the aromatic polyester resin. Extrude into a sheet from the 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 satisfy the Young's modulus in both directions defined by the present invention, and αt and αh, it is necessary to facilitate the subsequent stretching. From such a viewpoint, the cooling by the cooling drum is very prompt. It is preferable to do so. From such a viewpoint, it is preferable to carry out at a low temperature of 20 to 60 ° C., not as high as 80 ° C. as described in Patent Document 3. 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.

Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching.
Here, a manufacturing method in which longitudinal stretching, lateral stretching, and heat treatment are performed in this order by sequential biaxial stretching will be described as an example. First, in the first longitudinal stretching, the glass transition temperature (Tg: ° C.) to (Tg + 40) ° C. of the copolymerized aromatic polyester is stretched 3 to 8 times, and then in the transverse direction at a higher temperature than the previous longitudinal stretching. The film is stretched 3 to 8 times at a temperature of (Tg + 10) to (Tg + 50) ° C., and further treated as a heat treatment at a temperature not higher than the melting point of the polymer 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.

  By the way, the reason why the above-mentioned heat shrinkage ratio is increased is that, since it is copolymerized, it is necessary to stretch at a higher magnification in order to obtain the same Young's modulus, and since the melting point is lowered, This is considered to be because the temperature of the heat setting treatment has to be lowered. Therefore, there is a trade-off between increasing the Young's modulus, reducing the dimensional change due to environmental changes such as temperature and humidity changes, and reducing the thermal shrinkage rate. It is preferable to adopt conditions.

  First, it is divided into four zones from transverse stretching after longitudinal stretching to cooling through heat setting treatment, and the first first zone is at a higher temperature than the previous longitudinal stretching (Tg + 10) to (Tg + 30) ° C. The stretching amount of the first zone ((width when leaving the first zone−width when entering the first zone) divided by the width of the unstretched film) at the temperature of The film is stretched to 70 to 90% with respect to (the width when exiting the fourth zone−the width when entering the first zone) divided by the width of the unstretched film). Zone 2 is the stretch amount of the second zone at the same temperature as the first zone or 20 ° C higher than the previous zone ((width when leaving the second zone-width when entering the second zone)) The value divided by the width of the unstretched film) is 10-30% of the total stretched amount, In zone 3, even if stretching is not performed or stretched at a temperature of (Tg + 70) to (Tg + 120) ° C. and lower than Tm, the stretch amount of the third zone ((width when leaving the third zone− The value obtained by dividing the width when entering the third zone by the width of the unstretched film) is 10% or less, further 7% or less, especially 5% or less with respect to the total stretched amount. It is preferable to perform heat setting treatment for 1 second and further for 1 to 15 seconds, and cool slowly at an ambient temperature of 120 to 170 ° C. without stretching in the fourth zone. By adopting such special stretching conditions, the thermal shrinkage rate can be further reduced even with the same Young's modulus.

  Normally, when the draw ratio is increased, the film-forming stability is impaired. However, in the present invention, the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is copolymerized, so that the drawability is increased. Is very high, so there is no such problem, and particularly the draw ratio can be further increased. Therefore, it is particularly useful for a thin film having a thickness of 10 μm or less, more preferably 8 μm or less. The lower limit of the thickness of the film is not particularly limited, but is usually about 1 μm, preferably 3 μm.

  Although the above description has been described for sequential biaxial stretching, the biaxially oriented 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, the stretching ratio and stretching temperature described above, etc. Should be referred to.

  Further, when the biaxially oriented polyester film of the present invention is a laminated film, two or more types of molten polyester are laminated in a die and then extruded into a film, preferably the melting point (Tm: ° C.) to (Tm + 70) of each polyester. ) Extrude at a temperature of ° C. or extrude two or more types of molten polyester from a die, laminate them, quench and solidify them to form a laminated unstretched film, and then perform biaxial stretching and Heat treatment may be performed. 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 biaxially oriented polyester film of the present invention is used as a base film, a nonmagnetic layer and a magnetic layer are formed in this order on one side, and a backcoat layer is formed on the other side. Thus, a magnetic recording tape can be obtained.

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

(2) Glass transition point and melting point Glass transition point and melting point were measured by DSC (TA Instruments Co., Ltd., trade name: Thermal lyst 2100) at a heating rate of 20 ° C / min.

(3) Copolymerization amount For the glycol component, 10 mg of a sample was dissolved in 0.5 ml of a mixed solution of p-chlorophenol: heavy tetrachloroethane = 3: 1 (volume ratio) at 80 ° C. After adding isopropylamine and mixing well, it was measured at 80 ° C. with 600 M ¹ H-NMR (JEOL A600, manufactured by Hitachi Electronics), and the amount of each glycol component was measured.
As for the aromatic dicarboxylic acid component, 50 mg of a sample was dissolved in 0.5 ml of a mixed solution of p-chlorophenol: heavy tetrachloroethane = 3: 1 at 140 ° C., and 400 M ¹³ C-NMR (Hitachi Electronics JEOL A600) It measured at 140 degreeC and measured the amount of each acid component.

(4) 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: 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.

(5) Temperature expansion coefficient (αt)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the width direction of the film was a measurement direction, set in TMA3000 manufactured by Vacuum Riko, and pretreated at 60 ° C. for 30 minutes in a nitrogen atmosphere (0% RH). Then, the temperature is lowered 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 of quartz glass (× ^{10 -6} / ℃).

(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 width direction of the film would be the measurement direction, set in TMA3000 manufactured by Vacuum Riko, and a humidity of 30% RH and a humidity of 70% under a nitrogen atmosphere at 30 ° C. The length of each sample in RH is measured, and a 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, the sample length when the _{L 30} is RH 30% in the above formula _(mm), sample length of _{L 70} when the RH 70% (mm), △ H: with 40 (= 70-30)% RH is there.

(7) Thermal shrinkage (%)
Suspend a film with a length of approximately 30 cm and a width of 5 cm in an oven set at a temperature of 105 ° C., hold it for 30 minutes under no load, remove it, return to room temperature, Read changes. The thermal shrinkage rate is defined by the following formula.
Thermal contraction rate (%) = (ΔL / L0) × 100
Here, ΔL = | L0−L |, L0: length of the film before heat treatment, and L: length in the same direction of the film after heat treatment.
In addition, the said measurement produced the sample so that the film forming direction and the width direction might each be 30 cm in length, and measured each direction.

(8) Application spots On one surface of a 500 m long film slit to a width of 500 mm, a nonmagnetic coating and a magnetic coating having the following composition are simultaneously applied by a die coater, and the thicknesses of the nonmagnetic layer and the magnetic layer after drying are respectively The film thickness is changed so that the thickness becomes 1.2 μm and 0.1 μm, and the film is 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. And about the obtained film with a magnetic layer, the application | coating spot was evaluated by the following references | standards by visual determination. In addition, the visual judgment is performed by installing a fluorescent lamp on the back side of the film and counting light leakage due to the loss of the magnetic layer, and this film with a magnetic layer is provided with a back coat layer as necessary. , Slit to a width of 12.65 mm, and incorporated into a cassette to make a magnetic recording tape.
○: Application failure is less than 10 pieces / 250 m ²
Δ: coating omission 10 pieces / 250 m ² or more and less than 20 pieces / 250 m ²
×: Application missing 20 pieces / 250 m ² or more

Composition of non-magnetic paint
・ Titanium dioxide fine particles: 100 parts by weight
・ Sleek A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight
・ Nipporan 2304 (polyurethane elastomer made by Nippon Polyurethane): 10 parts by weight
Coronate L (Nippon Polyurethane Polyisocyanate): 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 magnetic paint
Iron (length: 0.3 μm, needle ratio: 10/1, 1800 oersted)
: 100 parts by weight
・ Sleek A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight
・ Nipporan 2304 (polyurethane elastomer made by Nippon Polyurethane): 10 parts by weight
Coronate L (Nippon Polyurethane Polyisocyanate): 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

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out to give an intrinsic viscosity of 0.66 dl / g, 73 mol% of the acid component being 2,6-naphthalenedicarboxylic acid component, and 27 mol% of the acid component being 6,6 ′-(alkylenedioxy). An aromatic polyester in which 98 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 2 mol% was a diethylene glycol component was obtained. The aromatic polyester contained silica particles having an average particle size of 0.5 μm so as to be 0.2% by weight based on the weight of the resin composition obtained before the polycondensation reaction. The aromatic polyester had a melting point of 240 ° C. and a glass transition temperature of 117 ° C.

The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 290 ° C. onto a cooling drum having a rotating temperature of 50 ° C. in a molten state to form an unstretched film. Then, between two sets of rollers having different rotational speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 135 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 6.2. Then, this uniaxially stretched film is guided to a stenter, and subjected to transverse stretching, heat setting treatment (at 200 ° C. for 10 seconds) and cooling under the conditions of zones 1 to 4 shown in Table 1 to obtain a biaxially stretched film having a thickness of 6 μm. It was.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Example 2]
In Example 1, the stretching temperature in the film forming direction was changed to 135 ° C., the stretching ratio in the film forming direction was changed to 5.3 times, and the resulting uniaxially stretched film was led to a stenter. The same operation was repeated except that transverse stretching, heat setting treatment (210 ° C. for 10 seconds) and cooling were performed to obtain a biaxially stretched film.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Example 3]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out, the intrinsic viscosity was 0.72 dl / g, 94 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 6 mol% of the acid component was 6,6 ′-(ethylenedioxy). An aromatic polyester in which 99 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 1 mol% of a diethylene glycol component was obtained. The aromatic polyester contained silica particles having an average particle diameter of 0.4 μm so as to be 0.2% by weight based on the weight of the resin composition obtained before the polycondensation reaction. The aromatic polyester had a melting point of 255 ° C. and a glass transition temperature of 119 ° C.

The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 290 ° C. in a molten state onto a cooling drum having a rotating temperature of 60 ° C. to form an unstretched film. Then, between the two sets of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 140 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.3 times. Then, this uniaxially stretched film is guided to a stenter and subjected to transverse stretching, heat setting treatment (at 200 ° C. for 10 seconds) and cooling under the conditions of zones 1 to 4 shown in Table 1 to obtain a biaxially stretched film having a thickness of 8 μm. It was.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Example 4]
In Example 3, the stretching temperature in the film forming direction was changed to 135 ° C., the stretching ratio in the film forming direction was changed to 3.0 times, and the resulting uniaxially stretched film was led to a stenter, and zones 1 to 4 shown in Table 1 were used. The same operation was repeated except that transverse stretching, heat setting treatment (210 ° C. for 10 seconds) and cooling were performed to obtain a biaxially stretched film.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Example 5]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out, the intrinsic viscosity was 0.72 dl / g, 94 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 6 mol% of the acid component was 6,6 ′-(ethylenedioxy). An aromatic polyester in which 99 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 1 mol% of a diethylene glycol component was obtained. The aromatic polyester contained silica particles having an average particle size of 0.4 μm so as to be 0.1% by weight based on the weight of the resin composition obtained before the polycondensation reaction. The aromatic polyester had a melting point of 255 ° C. and a glass transition temperature of 119 ° C.

The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 290 ° C. onto a cooling drum having a rotating temperature of 50 ° C. in a molten state to form an unstretched film. Then, between two sets of rollers having different rotational speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 135 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.5. Then, this uniaxially stretched film is guided to a stenter and subjected to transverse stretching, heat setting treatment (210 ° C. for 10 seconds) and cooling under the conditions of zones 1 to 4 shown in Table 1 to obtain a biaxially stretched film having a thickness of 6 μm. It was.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Example 6]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out, the intrinsic viscosity was 0.77 dl / g, 80 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 20 mol% of the acid component was 6,6 ′-(ethylenedioxy). An aromatic polyester in which 99 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 1 mol% of a diethylene glycol component was obtained. The aromatic polyester contained silica particles having an average particle size of 0.4 μm so as to be 0.1% by weight based on the weight of the resin composition obtained before the polycondensation reaction. The aromatic polyester had a melting point of 247 ° C. and a glass transition temperature of 116 ° C.

The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 290 ° C. onto a cooling drum having a rotating temperature of 50 ° C. in a molten state to form an unstretched film. Then, between the two sets of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 140 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.5. Then, this uniaxially stretched film is guided to a stenter, and subjected to transverse stretching, heat setting treatment (210 ° C. for 10 seconds) and cooling under the conditions of zones 1 to 4 shown in Table 1 to obtain a biaxially stretched film having a thickness of 7 μm. It was.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Example 7]
In Example 1, the stretching temperature in the film forming direction was changed to 135 ° C., the stretching ratio in the film forming direction was changed to 4.8 times, and the resulting uniaxially stretched film was led to a stenter, and zones 1 to 4 shown in Table 1 were used. The same operation was repeated except that transverse stretching, heat setting treatment (at 190 ° C. for 10 seconds) and cooling were repeated to obtain a biaxially stretched film.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Comparative Example 1]
Dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol are subjected to an esterification reaction and a transesterification reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to obtain an intrinsic viscosity of 0.62 dl / g. Polyethylene-2,6-naphthalate in which 1.5 mol% of the glycol component was a diethylene glycol component was obtained. The polyethylene-2,6-naphthalate contains silica particles having an average particle diameter of 0.5 μm before the polycondensation reaction so that the amount is 0.2% by weight based on the weight of the resin composition obtained. Contained. This polyethylene-2,6-naphthalate had a melting point of 270 ° C. and a glass transition temperature of 120 ° C.

The polyethylene-2,6-naphthalate thus obtained was supplied to an extruder and extruded from a die at 300 ° C. in a molten state onto a cooling drum at a temperature of 60 ° C. during rotation to form an unstretched film. . Then, between the two sets of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 140 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 3.0. Then, this uniaxially stretched film is guided to a stenter, and subjected to transverse stretching, heat setting treatment (at 200 ° C. for 10 seconds) and cooling under the conditions of zones 1 to 4 shown in Table 1 to obtain a 10 μm thick biaxially stretched film. It was.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Comparative Example 2]
In Comparative Example 1, the stretching temperature in the film forming direction was changed to 140 ° C., the stretching ratio in the film forming direction was changed to 4.0 times, and the resulting uniaxially stretched film was led to a stenter. The same operation was repeated except that transverse stretching, heat setting treatment (at 200 ° C. for 10 seconds), and cooling were repeated to obtain a biaxially stretched film.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Comparative Example 3]
In Comparative Example 1, the stretching temperature in the film forming direction was 140 ° C., the draw ratio in the film forming direction was 4.5 times, and the uniaxially stretched film was guided to the stenter, and the film was horizontally stretched under the conditions of zones 1 to 4 shown in Table 1. A biaxially stretched film was obtained by repeating the same operations except for heat setting (at 200 ° C. for 10 seconds) and cooling.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Comparative Examples 4 and 5]
In Example 1, the obtained uniaxially stretched film was guided to a stenter, and the same operation was performed except that transverse stretching, heat setting treatment (at 200 ° C. for 10 seconds) and cooling were performed under the conditions of zones 1 to 4 shown in Table 1. Was repeated to obtain a biaxially stretched film. In addition, the stretching amount of -0.3 times in zone 4 in Comparative Example 5 means that the width is 0.3 times the width of the unstretched film and the film is relaxed in the width direction.
Table 1 shows the characteristics of the obtained polyester resin composition, and Table 2 shows the characteristics of the obtained biaxially oriented polyester film.

[Reference Example 1]
As a reference example, Table 2 shows the results of Young's modulus, temperature expansion coefficient, and humidity expansion coefficient described in Example 1 of Patent Document 3.

  In Tables 1 and 2, NA is 2,6-naphthalenedicarboxylic acid component, ENA is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, EG is ethylene glycol component, DEG is diethylene glycol component, Tg Indicates the glass transition temperature, MD indicates the film forming direction, and TD indicates the width direction of the film. In addition, the Young's modulus of the reference example 1 shows what was converted into GPa. The stretch amount in Table 1 is a value obtained by dividing the width expanded in each zone (width when exiting each zone-width when entering each zone) by the width of the unstretched film. The amount is the sum of the stretching amount of each zone. Accordingly, the total stretching amount plus 1 corresponds to a stretching ratio that is usually used, and the ratio (%) of each zone is a value obtained by dividing the stretching amount of each zone by the total stretching amount.

  The biaxially oriented polyester film of the present invention is excellent as cannot be achieved with conventional polyethylene terephthalate, polyethylene-2,6-naphthalate or polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate. It has dimensional stability and can be suitably used as a base film for applications requiring dimensional stability, particularly for high-density magnetic recording media.

Claims (10)

A biaxially oriented polyester film comprising an aromatic polyester of an aromatic dicarboxylic acid component and a glycol component,
At least 5 mol% of the aromatic dicarboxylic acid component is represented by the following formula (I)

(R in the structural formula (I) represents an alkylene group having 1 to 10 carbon atoms.)
A 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by:
The aromatic polyester has a melting point in the range of 200 to 260 ° C.,
At least one direction in the film surface direction is a biaxially oriented polyester film having a Young's modulus of 6.0 GPa or more and a thermal shrinkage rate of 1.5% or less when treated at 105 ° C. for 30 minutes. The biaxially oriented polyester film according to claim 1, wherein at least one direction in the film surface direction has a relationship represented by the following formula (1).
αh <−1.2Y + 17 (1)
(In the above general formula (1), αh represents a humidity expansion coefficient (ppm /% RH), and Y represents a Young's modulus (GPa).)   The biaxially oriented polyester film according to claim 1, wherein a humidity expansion coefficient in at least one direction of the film is in a range of 1 to 7 ppm /% RH.   The biaxially oriented polyester film according to claim 1, wherein a temperature expansion coefficient in at least one direction of the film is 10 ppm / ° C or less.   The biaxially oriented polyester film according to claim 1, wherein the 6,6 '-(alkylenedioxy) di-2-naphthoic acid component is a 6,6'-(ethylenedioxy) di-2-naphthoic acid component.   The biaxially oriented polyester film according to claim 1, wherein the aromatic polyester has at least one selected from the group consisting of an alkylene-2,6-naphthalenedicarboxylate unit and an alkylene terephthalate unit as a repeating unit.   The biaxially oriented polyester film according to claim 1, wherein 90 mol% or more of the glycol component is an ethylene glycol component.   The biaxial direction according to claim 1, wherein the direction in which the Young's modulus is 6.0 GPa or more and the thermal shrinkage rate when treated at 105 ° C for 30 minutes is 1.5% or less is the width direction of the biaxially oriented polyester film. Oriented polyester film.   The biaxially oriented polyester film according to claim 1, wherein the biaxially oriented polyester film is used as a base film of a magnetic recording medium.   The biaxially oriented polyester film according to claim 9, wherein the magnetic recording medium is a linear recording type high-density magnetic recording tape.