JP5209218B2 - Biaxially oriented polyester film - Google Patents

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. It is used. 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. Aromatic polyester resins have 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 polyethylene-6,6 ′-(ethylenedioxy) di-2-naphthoate presented in these patent documents has a very high melting point and very high crystallinity, it is intended to form a film or the like. As a result, there are problems such as poor fluidity in the molten state and non-uniform extrusion, and even if trying to stretch after extrusion, crystallization progresses and breaks 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 (× 10 ⁻⁶ / ° C.) and a maximum. The humidity expansion rate is 0 to 8 (× 10 ⁻⁶ /% RH), the difference between the maximum and minimum temperature expansion rates is 0 to 6.0 (× 10 ⁻⁶ / ° C.), and the maximum and minimum humidity expansion rates are It teaches that a magnetic recording flexible disk with a small tracking shift can be obtained by setting the difference to 0 to 4.0 (× 10 ⁻⁶ /% RH). 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 (× 10 ⁻⁶ / ° C.), minimum temperature expansion 16.5 (× 10 ⁻⁶ / ° C.), maximum humidity expansion 6 (× 10 ⁻⁶ /% RH), and minimum humidity A film having an expansion coefficient of 4.5 (× 10 ⁻⁶ /% RH) is disclosed.

  However, demands for improvement in recording density in recent magnetic recording media are severe, and accordingly, dimensional stability required for a 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 dimensional stability, particularly dimensional stability against environmental changes such as temperature and humidity.

  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 intensive studies were conducted to determine whether a film having an expansion coefficient with a lower temperature and humidity could be obtained with the same Young's modulus, a film made of the above-mentioned polyethylene-6,6 ′-(ethylenedioxy) di-2-naphthoate was obtained. The film was considered as a suitable film because it showed a low coefficient of humidity expansion regardless of Young's modulus.

However, as described above, a film made of polyethylene-6,6 ′-(ethylenedioxy) di-2-naphthoate has a problem that the temperature expansion coefficient is very high although the humidity expansion coefficient is small. Looking at the disclosed in Example 1 of Patent Document 3 film, yet the direction of film 485 kg / mm ² and the width direction 1110kg / mm ² Young's modulus, thermal expansion rate maximum 19 (× 10 ^{- 6} / ° C.) and the minimum was 16.5 (× 10 ⁻⁶ / ° C.), indicating a very high value regardless of the Young's modulus. That is, it was unlikely that the temperature expansion coefficient could be adjusted by molecular orientation.

  However, when the present inventors used 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component as a copolymerization component, surprisingly, polyalkylene-6,6 ′-(alkylenedioxy) ) The present inventors have 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, and the present invention has been achieved.

（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ること、芳香族ポリエステルの主たる繰り返し単位が、アルキレン−２，６−ナフタレートおよびアルキレンテレフタレートからなる群より選ばれた少なくとも一種であり、グリコール成分の９０モル％以上がエチレングリコールであること、そしてフィルム面方向における少なくとも一方向の温度膨張係数（αｔ）が１４×１０^−６／℃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 5 mol% or more and less than 50 mol% of the aromatic dicarboxylic acid component is represented by the following formula ( I)

(R in the above structural formula (I) represents an alkylene group having 1 to 10 carbon atoms.) Represented by 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, aromatic The main repeating unit of the group polyester is at least one selected from the group consisting of alkylene-2,6-naphthalate and alkylene terephthalate, 90 mol% or more of the glycol component is ethylene glycol, and at least in the film surface direction. A biaxially oriented polyester film having a unidirectional temperature expansion coefficient (αt) of 14 × 10 ⁻⁶ / ° C. or lower is provided.

According to the present invention, as a preferred embodiment of the present invention, the Young's modulus and the humidity expansion coefficient in at least one direction in the film surface direction are represented by the following general formula (1):
αh <−1.2Y + 17 (1)
(In the general formula (1), αh is a humidity expansion coefficient (× 10 ⁻⁶ /% RH), Y is Young's modulus (GPa)), and at least in one direction in the film surface direction. The Young's modulus 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 7 (× 10 ⁻⁶ /% RH), and the temperature expansion coefficient of the film is 14 × 10. ^The direction of ⁻⁶ / ° C. or lower is the film width direction, the melting point is in the range of 200 to 260 ° C., the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is 6, 6 '- it is (ethylenedioxy) di-2-naphthoic acid component, biaxially oriented polyester film, a magnetic recording medium, that of less that specifically used in the base film of high-density magnetic recording tape of linear recording system A biaxially oriented polyester film comprising at least either is 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. In addition, a particularly remarkable effect is obtained in that a biaxially oriented polyester film made of an aromatic polyester having dimensional stability that cannot be predicted from the prior art is obtained.

  Therefore, according to the present invention, a film suitable for a base film of a high-density magnetic recording medium, which is used for applications requiring a high degree of dimensional stability including the influence of humidity and temperature, is provided. If 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.

  Among these, as specific aromatic polyesters formed of the aromatic dicarboxylic acid component shell other than the aromatic dicarboxylic acid component represented by the aforementioned formula (I), polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, etc. And polyalkylene-2,6-naphthalate such as polyalkylene terephthalate, polyethylene-2,6-naphthalate, polytrimethylene-2,6-naphthalate, and polybutylene-2,6-naphthalate. From the viewpoint of characteristics and the like, polyethylene terephthalate and polyethylene-2,6-naphthalate in which ethylene terephthalate units and ethylene-2,6-naphthalate units are the main repeating units are preferred. 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) represented by the above formula (I) in the range of 5 mol% or more and less than 50 mol%. The di-2-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 less than 50 mol% because the present invention improves the dimensional stability by copolymerization of the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, thereby reducing the temperature expansion coefficient. can do. 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 already in the portion below the upper limit. The humidity expansion coefficient equivalent to or lower than that of the film described in the example of Patent Document 3 is achieved, and it can be said that the effect from the viewpoint of the humidity expansion coefficient is saturated even when the upper limit is added. 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 a method in which an ester of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid and an alkylene glycol as shown in Patent Documents 1 to 4 are transesterified, a large amount of a dialkylene glycol component or the like is added. It tends to occur as a living organism. 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. A preferable amount of diethylene glycol is 5 mol% or less, further 3 mol% or less, particularly 2 mol% or less, based on the number of moles of all glycol components.

  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 205 to 255 ° C., particularly in the range of 210 to 250 ° 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 has also been found that the same mechanical properties as those of a polymer having an ester of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid as described in 1 to 4 as the main repeating unit can be expressed. 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 80 to 120 ° C., more preferably in the range of 82 to 118 ° C., particularly 85 to 118 ° 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 film with the uniform film thickness excellent in film forming property, for example.

  Of course, since it is a film obtained by melt-forming the above-mentioned aromatic polyester, polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate and the aromatic dicarboxylic acid component which is a copolymerization partner thereof are 6 , 6 '-(alkylenedioxy) di-2-naphthoic acid and other aromatic polyesters that are aromatic dicarboxylic acids have excellent mechanical properties.

By the way, the biaxially oriented polyester film of the present invention has a temperature expansion coefficient (αt) in at least one direction in the plane direction of the film, preferably a temperature expansion in the width direction of the film, from the viewpoint of exhibiting excellent dimensional stability. The coefficient (αt) needs to be 14 × 10 ⁻⁶ / ° C. or less. When the temperature expansion coefficient in at least one direction of the film is not more than the upper limit, for example, it can be expressed in a film that can obtain excellent dimensional stability against environmental changes by matching with the direction of the film in which dimensional stability is most required. I can do it. From the results of Patent Document 3, it is expected that when polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate is copolymerized, the temperature expansion coefficient is expected to increase. The present invention has surprisingly been able to reduce the coefficient of thermal expansion by copolymerizing within the range of the polymerization amount and stretching it. The lower limit of the temperature expansion coefficient is not limited, but is usually −15 × 10 ⁻⁶ / ° C. The preferred temperature expansion coefficient (αt) is −10 × 10 ⁻⁶ / ° C. or higher, further −7 × 10 ⁻⁶ / ° C. or higher, particularly −5 × 10 ⁻⁶ / ° C. or higher, and 10 × 10 ⁻⁶ / ° C. In the following, the range of 7 × 10 ⁻⁶ ° C. or lower, particularly 5 × 10 ⁻⁶ / ° C. or lower is excellent in dimensional stability against dimensional changes due to changes in the temperature and humidity of the atmosphere, for example, when used as a magnetic recording tape. It is preferable because sex can be expressed.

By the way, the biaxially oriented polyester film of the present invention has a humidity expansion coefficient (αh) and a Young's modulus (αh) of the film in at least one direction of the film surface direction, preferably in the direction where the temperature expansion coefficient is 14 × 10 ⁻⁶ / ° C. or less. Y) preferably satisfies the relationship of the following formula (1).
αh <−1.2Y + 17 (1)
(Here, αh represents a humidity expansion coefficient (× 10 ⁶ /% RH), and Y represents a 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 relational expression (1) 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. It is a thing. The aromatic polyester copolymerized with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid is preferably polyethylene-2,6-naphthalate because the Young's modulus tends to increase and the other Young's modulus is preferred. On the other hand, polyethylene terephthalate is preferable because the humidity expansion coefficient can be easily reduced. 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, αt and αh as described above can be adjusted by the composition of the copolymer and the stretching described later.

Furthermore, the preferable aspect of the biaxially-oriented polyester film of this invention is explained in full detail.
In the biaxially oriented polyester film of the present invention, the upper limit of the humidity expansion coefficient (αh) in at least one direction in the plane direction of the film is preferably 8 × 10 ⁻⁶ /% RH or less. ^{X10 −6} /% RH or less, more preferably 7 × 10 ⁻⁶ /% RH or less, particularly 6 × 10 ⁻⁶ /% RH or less, particularly in terms of dimensional stability when a magnetic recording tape is used. Is preferable. The lower limit is not particularly limited, but is about 1 × 10 ⁻⁶ /% RH from the viewpoint of film forming properties. In particular, when the magnetic recording tape is used as a base film, the direction satisfying the above formula (1) is the width direction of the biaxially oriented polyester film. preferable. In the present invention, the surface direction of the film is a direction orthogonal to the thickness of the film, and the width direction of the film is a direction orthogonal to the film-forming direction of the film (sometimes referred to as a longitudinal direction or a longitudinal direction). And may be referred to as the lateral direction.

By the way, the biaxially oriented polyester film of the present invention has a Young's modulus of at least 4.5 GPa or more in a direction in which the temperature expansion coefficient is at most 14 × 10 ⁻⁶ /% RH in at least one direction of the film surface direction. The upper limit is not particularly limited, but is usually about 12 GPa. The particularly preferable Young's modulus is in the range of 5 to 11 GPa, more preferably 6 to 10 GPa, and particularly preferably 7 to 10 GPa. If it is out of this range, it may be difficult to achieve the above-mentioned αt and αh, or the mechanical characteristics may be insufficient. Such Young's modulus can be adjusted by the copolymerization composition described above and the stretching described below.

Further, for the direction in which the temperature expansion coefficient is 14 × 10 ⁻⁶ or less, it is sufficient that the width direction is satisfied as described above in at least one direction, preferably as described above. Preferably satisfies the same temperature expansion coefficient, humidity expansion coefficient, Young's modulus, and the like.

<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 0.5-1.2 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 from a temperature higher than the melting point of the polymer to be obtained and 230 to 280 ° C. or lower, more preferably 5 ° C. higher than the melting point to 30 ° C. higher than the melting point. The polycondensation reaction is usually preferably performed under a reduced pressure of 30 Pa or less. If it is higher than 30 Pa, the time required for the polycondensation reaction becomes long and it becomes difficult to obtain an aromatic polyester 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 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 obtained by stretching in the film forming direction and the width direction to increase the molecular orientation in each direction. For example, the following method maintains the film forming property. However, it is preferable because the temperature and humidity expansion coefficient can be easily reduced.

  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. 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 achieve αt, αh, Young's modulus, etc. defined in the present invention, it is necessary to facilitate the subsequent stretching, and 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, the first longitudinal stretching is performed at a glass transition temperature (Tg: ° C.) to (Tg + 40) ° C. of the aromatic polyester at 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 heat treatment is performed at a temperature below the melting point of the polymer and at a temperature of (Tg + 50) to (Tg + 150) ° C. for 1 to 20 seconds, and further for 1 to 15 seconds. It is preferable to perform the fixing process. The biaxially oriented polyester film of the present invention is extremely stretchable because the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is copolymerized, while the Young's modulus is the same at the same stretch ratio. In order to obtain the target Young's modulus, it is necessary to draw at a higher draw ratio. 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. There is no such problem.

  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 The glass transition point and melting point were measured by DSC (TA Instruments Co., Ltd., trade name: Thermal Analyst 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 (manufactured by Hitachi Electronics, JEOL A600), and the amount of each glycol component was measured.
As for the acid component, 50 mg of a sample was dissolved in 0.5 ml of a mixed solution of p-chlorophenol: heavy tetrachloroethane = 3: 1 (volume ratio) at 140 ° C. and 400 M ¹³ C-NMR (manufactured by Hitachi Electronics, JEOL A600). ) At 140 ° C., and the amount of each acid component was measured.

(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 (× 10 ⁻⁶ / ° C.) of quartz glass.

(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, 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.

[Example 1]
Esterification and transesterification of dimethyl terephthalate, 6,6 '-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol in the presence of titanium tetrabutoxide, followed by polycondensation reaction And the intrinsic viscosity is 0.73 dl / g, 65 mol% of the acid component is terephthalic acid component, 35 mol% of the acid component is 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, glycol component An aromatic polyester having 98.5 mol% of ethylene glycol component and 1.5 mol% of 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 233 ° C. and a glass transition temperature of 91 ° 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 temperature of 40 ° C. while rotating 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 110 ° C., and stretching in the longitudinal direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 4.0. And this uniaxially stretched film is led to a stenter, stretched at 120 ° C. in the transverse direction (width direction) at a stretch ratio of 4.5 times, and then heat-fixed at 210 ° C. for 3 seconds to be biaxially stretched with a thickness of 10 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 2]
Esterification and transesterification of dimethyl terephthalate, 6,6 '-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol in the presence of titanium tetrabutoxide, followed by polycondensation reaction And the intrinsic viscosity is 0.68 dl / g, 80 mol% of the acid component is terephthalic acid component, 20 mol% of the acid component is 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, glycol component An aromatic polyester having 98 mol% of ethylene glycol component and 2 mol% of 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 230 ° C. and a glass transition temperature of 85 ° 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 30 ° C. 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 105 ° C., and stretching in the longitudinal direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.0. Then, this uniaxially stretched film is guided to a stenter, stretched at 115 ° 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 be biaxially stretched with a thickness of 10 m. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[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, and the intrinsic viscosity was 0.78 dl / g, 73 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 27 mol% of the acid component was 6,6 ′-(alkylenedioxy). An aromatic polyester in which 98.5 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 1.5 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 112 ° C.

The aromatic polyester 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 45 ° C. during rotation 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 130 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 4.0. Then, this uniaxially stretched film is guided to a stenter, stretched at 140 ° C. in the transverse direction (width direction) at a stretch ratio of 6.0 times, and then heat-set at 200 ° C. for 10 seconds, and biaxially stretched with a thickness of 7 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 4]
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 performed, and the intrinsic viscosity was 0.81 dl / g, 94 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 6 mol% of the acid component was 6,6 ′-(alkylenedioxy). 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 0.5 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 255 ° 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 300 ° C. in a molten state onto a cooling drum having a rotating temperature of 55 ° C. 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 3.0. Then, this uniaxially stretched film is guided to a stenter, stretched at 135 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, then heat-set at 200 ° C. for 10 seconds, and biaxially stretched with a thickness of 10 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 5]
In Example 4, the stretching temperature in the film forming direction is 140 ° C., the stretching ratio in the film forming direction is 5.0 times, the stretching temperature in the width direction is 140 ° C., and the stretching ratio in the width direction is 4.2 times. The same operation was repeated except that the heat setting treatment temperature was changed to 210 ° C. to obtain a biaxially stretched film.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1. The obtained film had a very low Young's modulus in the width direction, had a large dimensional change in the width direction when used as a magnetic recording medium, and was very easily stretched when tension was applied in the width direction.

[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 0.78 dl / g, 57 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 43 mol% of the acid component was 6,6 ′-(alkylenedioxy). An aromatic polyester in which 98.5 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 1.5 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 253 ° 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 300 ° C. in a molten state onto a cooling drum at a temperature of 45 ° 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 4.5 times. And this uniaxially stretched film is led to a stenter, stretched at a stretching ratio of 5.2 times in the transverse direction (width direction) at 140 ° C., and then heat-set at 200 ° C. for 5 seconds, and biaxially stretched with a thickness of 10 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[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. And this uniaxially stretched film is led to a stenter, stretched at a stretching ratio of 4.3 times in the transverse direction (width direction) at 140 ° C., and then heat-set at 200 ° C. for 10 seconds to be biaxially stretched with a thickness of 10 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 2]
In Comparative Example 1, the stretching temperature in the film forming direction is 140 ° C., the stretching ratio in the film forming direction is 4.0 times, the stretching temperature in the width direction is 140 ° C., and the stretching ratio in the width direction is 4.0 times. The same operation was repeated except that the heat setting treatment temperature was changed to 200 ° C. to obtain a biaxially stretched film.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 3]
In Comparative Example 1, the stretching temperature in the film forming direction is 140 ° C., the stretching ratio in the film forming direction is 4.5 times, the stretching temperature in the width direction is 140 ° C., and the stretching ratio in the width direction is 3.4 times. The same operation was repeated except that the heat setting treatment temperature was changed to 200 ° C. to obtain a biaxially stretched film.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

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

  In Table 1, TA is a terephthalic acid component, NA is a 2,6-naphthalenedicarboxylic acid component, ENA is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, EG is an ethylene glycol component, and DEG is diethylene glycol. Components, Tg, glass transition temperature, MD, film forming direction, TD, film width direction. In addition, the Young's modulus of the reference example 1 shows what was converted into GPa.

  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 (9)

A biaxially oriented polyester film comprising an aromatic polyester of an aromatic dicarboxylic acid component and a glycol component,
5 mol% or more and less than 50 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.)
Selected from the group consisting of alkylene-2,6-naphthalate and alkylene terephthalate, wherein the main repeating unit of the aromatic polyester is a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by 90 mol% or more of the glycol component is ethylene glycol, and the temperature expansion coefficient (αt) in at least one direction in the film surface direction is 14 × 10 ⁻⁶ / ° C. or less. Biaxially oriented polyester film. The biaxially oriented polyester film according to claim 1, wherein the Young's modulus and the humidity expansion coefficient in at least one direction in the film surface direction satisfy the relationship of the following general formula (1).
αh <−1.2Y + 17 (1)
(In the general formula (1), αh represents a humidity expansion coefficient (× 10 ⁻⁶ /% RH), and Y represents a Young's modulus (GPa).)   The biaxially oriented polyester film according to claim 1, wherein the Young's modulus in at least one direction in the film surface direction is 4.5 GPa or more. The biaxially oriented polyester film according to claim 1, wherein the humidity expansion coefficient in at least one direction in the film surface direction is in the range of 1 to 7 (× 10 ⁻⁶ /% RH). The biaxially oriented polyester film according to claim 1, wherein the direction in which the temperature expansion coefficient is 14 × 10 ⁻⁶ / ° C. or less is the width direction of the film.   The biaxially oriented polyester film according to claim 1, wherein the aromatic polyester has a melting point in the range of 200 to 260 ° C.   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 biaxially oriented polyester film is used as a base film of a magnetic recording medium. 9. The biaxially oriented polyester film according to claim 8, wherein the magnetic recording medium is a linear recording type high-density magnetic recording tape.