JP2010031174A - Polyester resin composition and biaxially oriented film using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester resin composition which has excellent dimensional stability and is also excellent in hydrolysis resistance when formed into a film or the like; and to provide a biaxially oriented film using the polyester resin composition. <P>SOLUTION: The polyester resin composition includes a modifying agent consisting of a cyclic imino ether compound or a carbodiimide compound in an amount of 0.05-10 parts by mass based on 100 parts by mass of copolyester in which the total rate of dicarboxylic acid represented by following formula (I) or (II) is 90-100 mol% of dicarboxylic acid in total, a dicarboxylic acid constituent represented by following formula (I) is 5 mol% or more but less than 50 mol% of the dicarboxylic acid in total, and 90-100 mol% of the diol constituent in the total is a 2-10C alkylene glycol. Formula (I) is HO(O)C-R<SP>2</SP>-OR<SP>1</SP>O-R<SP>2</SP>-C(O)OH. [In the formula, R<SP>1</SP>represents a 2-10C alkylene group; and R<SP>2</SP>represents a 2,6-naphthalenediyl group]. Formula (II) is HO(O)C-R<SP>3</SP>-C(O)OH. [In the formula, R<SP>3</SP>represents a phenylene group or a naphthalenediyl group]. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a novel polyester resin composition having excellent dimensional stability and good hydrolysis resistance, and a biaxially oriented film using the same.

  Aromatic polyesters typified by polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN) have excellent mechanical properties, dimensional stability and heat resistance, so they are widely used in films. Has been. In particular, since polyethylene-2,6-naphthalenedicarboxylate has mechanical properties, dimensional stability and heat resistance superior to those of polyethylene terephthalate, it is used in demanding applications such as a base for high-density magnetic recording media. Used for films. 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, in Patent Documents 1 to 5, polyesters composed of an acid component mainly composed of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid and a diol component mainly composed of alkylene glycol are proposed. A polyester having a melting point of 294 ° C. is also specifically disclosed.

  However, the polyesters disclosed in these documents have a very high melting point and very high crystallinity, so when trying to form a film or the like, the fluidity in the molten state is poor and the extrusion becomes non-uniform. In addition, there is a problem that even when trying to stretch after extrusion, crystallization progresses and breaks when stretched at a high magnification. Furthermore, when the Example of patent document 3 was seen, there also existed a problem that a temperature expansion coefficient was high although the humidity expansion coefficient was low.

  In order to improve such a problem, the present inventors previously added a predetermined amount of 6,6 ′-(alkylenedioxy) dioxy to a polyester having terephthalic acid, naphthalene-2,6-dicarboxylic acid or the like as a dicarboxylic acid component. A copolyester obtained by copolymerizing 2-naphthoic acid component was proposed. Certainly, according to such a copolyester, a film having excellent mechanical strength and excellent temperature expansion coefficient (αt) and humidity expansion coefficient (αh) can be provided with excellent film forming properties. However, long-term durability over time is required for applications such as solar cell backsheet films, for example, which may be insufficient in terms of hydrolysis resistance, and further improvements are desired.

JP-A-60-135428 JP-A-60-212420 JP 61-145724 A JP-A-6-145323 International Publication No. 2008/010607 Pamphlet

  An object of the present invention is to provide a polyester resin composition having excellent dimensional stability when molded into a film or the like and having excellent hydrolysis resistance, and a biaxially oriented film using the same. .

  As a result of repeated studies to achieve the above object, the present inventor has found that when a predetermined amount of a cyclic iminoether compound or a carbodiimide compound is added to the copolymer polyester, a temperature expansion coefficient (αt) and a humidity expansion coefficient (αh) The present inventors have found that a molded article having excellent durability over time such as hydrolysis resistance can be easily obtained while maintaining the excellent performance of a copolyester such as

Thus, according to the present invention, “the total proportion of the dicarboxylic acid components represented by the following formula (I) or the following formula (II) is 90 to 100 mol% of the total dicarboxylic acid components, and the following formula (I): Copolyester in which the dicarboxylic acid component represented by the formula occupies 5 mol% or more and less than 50 mol% of the total dicarboxylic acid component, and 90 to 100 mol% of the total diol component is an alkylene glycol having 2 to 10 carbon atoms. A polyester resin composition containing 0.05 to 10 parts by mass of a modifier composed of a cyclic imino ether compound or a carbodiimide compound with respect to 100 parts by mass. "
HO (O) C—R ² —OR ¹ O—R ² —C (O) OH (I)
[In the above formula (I), R ¹ represents an alkylene group having 2 to 10 carbon atoms, and R ² represents a 2,6-naphthalenediyl group. ]
HO (O) C—R ³ —C (O) OH (II)
[In the above formula (II), R ³ represents a phenylene group or a naphthalenediyl group. ]

  Molded articles such as films obtained using the composition of the present invention have low temperature expansion coefficient (αt) and humidity expansion coefficient (αh) and high mechanical strength. Since it has excellent dimensional stability and also has excellent durability over time such as hydrolysis resistance, it is suitably used as a base film such as a back sheet of a solar cell, which requires these performances. be able to.

[Copolyester]
The copolymer polyester forming the polyester resin composition of the present invention is a copolymer comprising a dicarboxylic acid component represented by the formula (I) or the formula (II) and a diol component which is an alkylene glycol having 2 to 10 carbon atoms. Polymerized polyester.

[Dicarboxylic acid component]
Dicarboxylic acid component represented by the formula (I) is an alkylene group ^{R 1} is from 2 to 10 carbon atoms in the formula are those ^{wherein R 2} is 2,6-naphthalene-diyl group, among others of ^{R 1} 6,6 ′-(ethylenedioxy) di-2-naphthoic acid having 2 to 4 carbon atoms, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, 6,6 ′-(butylene) oxy) di-2-naphthoic acid are preferable, the carbon number of R ¹ include the even number is preferable. Among these, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, in which R ¹ has 2 carbon atoms, is particularly preferable from the viewpoint of dimensional stability against environmental changes such as temperature and humidity.

On the other hand, the dicarboxylic acid component represented by the formula (II) is one in which R ³ is a phenylene group or a naphthalenediyl group, such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2, Examples include 7-naphthalenedicarboxylic acid. Among these, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferable from the viewpoint of mechanical properties and the like, and 2,6-naphthalenedicarboxylic acid is particularly preferable.

  The total proportion of the dicarboxylic acid components represented by the above formulas (I) and (II) is 90 to 100 mol%, preferably 95 to 100 mol%, particularly preferably based on the total dicarboxylic acid components of the copolyester. Is 100 mol% and may be copolymerized with other dicarboxylic acid components such as adipic acid, sebacic acid, diphenyldicarboxylic acid, etc., as long as the ratio is 10 mol% or less. When the total proportion of the dicarboxylic acid components represented by the above formulas (I) and (II) is less than 90 mol%, the dimensional stability and mechanical properties are deteriorated and the object of the present invention cannot be achieved.

  In the present invention, it is further important that the dicarboxylic acid component represented by the formula (I) accounts for 5 mol% or more and less than 50 mol% of the total dicarboxylic acid component. The proportion of the dicarboxylic acid component represented by the formula (I) is preferably 7 mol% or more, more preferably 10 mol% or more, particularly preferably 15 mol% or more, and in the case of less than 5 mol%, The effect of reducing the humidity expansion coefficient is insufficient. On the other hand, in the case of 50 mol% or more, not only the effect of reducing the coefficient of humidity expansion does not increase any more, but also the film forming property decreases. In addition, since the humidity expansion coefficient reducing effect by the component (I) is expressed very efficiently even in a small amount, it is preferable from the viewpoint that film forming property can be improved in addition to the viewpoint of the humidity expansion coefficient. The copolymerization ratio of the (alkylenedioxy) di-2-naphthoic acid component is preferably less than 40 mol%, more preferably 35 mol% or less, and particularly preferably 30 mol% or less.

  By using such a specific amount of the copolymerized polyester in which the dicarboxylic acid component represented by the formula (I) and the formula (II) is copolymerized, the dimensional stability having a small temperature expansion coefficient and a low humidity expansion coefficient is excellent. Molded articles, for example films, can be produced.

[Diol component]
The diol component is 90 to 100 mol%, preferably 95 to 100 mol%, particularly preferably 98 to 100 mol%, of alkylene glycol having 2 to 10 carbon atoms based on the total diol component. If it is a ratio of 10 mol% or less, other diol components such as diethylene glycol and bisphenol A may be copolymerized.

  Preferred examples of the alkylene glycol having 2 to 10 carbon atoms include ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Among these, ethylene glycol is particularly preferable.

  The copolyester comprising the dicarboxylic acid component and the diol component has an intrinsic viscosity measured at 35 ° C. using a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (weight ratio 40/60). Is preferably in the range of 0.4 to 3 dl / g, more preferably in the range of 0.4 to 1.5 dl / g, and particularly preferably in the range of 0.5 to 1.2 dl / g.

  The melting point measured by DSC is preferably in the range of 200 to 260 ° C, more preferably 210 to 255 ° C, particularly preferably 220 to 253 ° C. When this melting point exceeds the upper limit, when melt extrusion is performed, it is necessary to make the temperature higher in order to increase fluidity, and thermal degradation is likely to occur. On the other hand, when the melting point is lower than the lower limit, the film forming property is excellent. However, the mechanical properties of polyester are easily impaired.

  In general, copolymerized polyesters have a lower melting point than homopolyesters and tend to decrease mechanical strength. However, the copolyester of the present invention is a copolyester in which the total proportion of the dicarboxylic acid components represented by the formula (I) or the formula (II) occupies 90 mol% or more with respect to the total dicarboxylic acid components, Although the melting point is lower than that of the homopolyester of the dicarboxylic acid component represented by the formula (I), the molded article has an excellent characteristic that the mechanical strength is the same.

  The glass transition temperature (hereinafter sometimes referred to as Tg) measured by DSC of the copolymerized polyester in the present invention is preferably 80 to 125 ° C, more preferably 95 to 123 ° C, and particularly preferably 110 to 120 ° C. Is in range. When Tg is in this range, a molded article such as a film having excellent heat resistance and dimensional stability can be obtained. The melting point and glass transition temperature can be adjusted by controlling the type of copolymerization component and the amount of copolymerization.

[Method for producing copolymer polyester]
The copolyester can be produced according to a known polyester production method. For example, ester 6,6 ′-(alkylenedioxy) di-2-naphthoic acid or an ester-forming derivative thereof such as 2,6-naphthalenedicarboxylic acid or terephthalic acid or an ester-forming derivative thereof and ethylene glycol, for example. The polyester precursor is produced by the reaction of esterification or transesterification. Then, the obtained polyester precursor can be produced by polycondensation in the presence of a polycondensation catalyst and, if necessary, solid phase polymerization. Two types of polymers having different ratios of the above formulas (I) and (II) may be prepared and melt-kneaded so that the ratios of the above formulas (I) and (II) are aimed. In this case, one polyester that does not contain the aromatic dicarboxylic acid component represented by the formula (I) may be used.

  In the step of producing the polyester precursor, it is possible to use ethylene glycol in an amount of 1.1 to 6 times, more preferably 2 to 5 times, particularly 3 to 5 times the number of moles of the total acid component. It is preferable from the point.

  Moreover, as reaction temperature at the time of manufacturing a polyester precursor, it is preferable to carry out above the boiling point of ethylene glycol, and it is preferable to carry out especially in the range of 190-250 degreeC. 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 may be performed under pressure to further increase productivity. More specifically, the absolute pressure is 10 kPa to 200 kPa, the reaction temperature is usually 150 ° C. to 250 ° C., preferably 180 ° C. to 230 ° C., and the reaction time is 10 minutes to 10 hours, preferably 30 minutes to 7 hours. Preferably it is done.

  In the step of producing this 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 temperature is in the range of a temperature not lower than the melting point of the obtained copolyester 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 copolymer polyester having a high degree of polymerization.

  Examples of the polycondensation catalyst include metal compounds containing at least one metal element. In addition, you may use together a polycondensation catalyst as a catalyst of esterification reaction or transesterification. 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 preferable because it exhibits high activity in both the esterification reaction, the transesterification 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 total acid component of the copolyester.

[Composition]
The polyester resin composition of this invention needs to contain the modifier which consists of a cyclic imino ether compound or a carbodiimide compound in said copolymer polyester.

[Cyclic imino ether compound]
The cyclic imino ether compound used in the present invention is not particularly limited as long as it has a cyclic imino ether group in the molecule. For example, a compound having an oxazoline group or an oxazine group as the cyclic imino ether group is preferable. Examples of the cyclic imino ether compound preferably used include 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline), and 2,2′-bis (4,4- Dimethyl-2-oxazoline), 2,2′-p-phenylenebis (2-oxazoline), 2,2′-m-phenylenebis (2-oxazoline), 2,2′-o-phenylenebis (2-oxazoline) ) 2,2′-ethylenebis (2-oxazoline), 2,2′-tetramethylenebis (2-oxazoline), 2,2′-hexamethylenebis (2-oxazoline), 2,2′-octamethylene Such as bis (2-oxazoline), 2,2′-decamethylenebis (2-oxazoline), 2,2′-cyclohexylenebis (2-oxazoline), 2,2′-diphenylenebis (2-oxazoline), etc. Bisoxazo Compounds, 2,2′-bis (5,6-dihydro-4H-1,3-oxazine), 2,2′-methylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2 '-Ethylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2'-propylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2'-butylenebis ( 5,6-dihydro-4H-1,3-oxazine), 2,2'-hexamethylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2'-p-phenylenebis (5 , 6-Dihydro-4H-1,3-oxazine), 2,2′-m-phenylenebis (5,6-dihydro-4H-1,3-oxazine), 2,2′-naphthylenebis (5,6- Bihydroxazine compounds such as dihydro-4H-1,3-oxazine) can be used.

（式中、Ｒ_１〜Ｒ_８はそれぞれ水素原子または１価の有機基であり、Ｘは２価の有機基であり、ｎは０または１である。） Of these, bisoxazoline compounds represented by the following formula (A) are preferable, and 2,2′-bis (2-oxazoline) is particularly preferable.

(In the formula, R _{1 to} R ₈ are each a hydrogen atom or a monovalent organic group, X is a divalent organic group, and n is 0 or 1.)

[Carbodiimide compound]
On the other hand, the carbodiimide compound may be a monofunctional carbodiimide or a bifunctional or higher polycarbodiimide as long as it has a carbodiimide bond in the molecule. For example, monofunctional carbodiimide compounds include dimethylcarbodiimide, diisopropylcarbodiimide, diisobutylcarbodiimide, di-t-butylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, dicyclohexylcarbodiimide, diphenylcarbodiimide, di-β-naphthylcarbodiimide, and the like. . Examples of the polycarbodiimide compound include polycarbodiimide obtained by reacting an aromatic diisocyanate compound, an aliphatic diisocyanate compound or an alicyclic diisocyanate compound. For example, 1,5-naphthalenecarbodiimide, 4,4′-diphenylmethanecarbodiimide. 4,4'-diphenyldimethylmethane carbodiimide, 1,3-phenylene carbodiimide, 1,4-phenylene carbodiimide, 2,4-tolylene carbodiimide, 2,6-tolylene carbodiimide, 2,4-tolylene carbodiimide and 2 , 6-Tolylenecarbodiimide, hexamethylenecarbodiimide, cyclohexane-1,4-carbodiimide, xylylenecarbodiimide, isophoronecarbodiimide, dicyclohexylmethane-4,4 ' Carbodiimide, methylcyclohexane carbodiimide, tetramethylxylylene carbodiimide, 2,6-diisopropylphenyl carbodiimide, such as 1,3,5-triisopropyl-phenylene-2,4-carbodiimide and the like.

  Moreover, in the case of the said polycarbodiimide compound, it can also control to a suitable polymerization degree using the compound which reacts with the terminal isocyanate of polycarbodiimide compound, such as monoisocyanate. Examples of the monoisocyanate for sealing the end of such a polycarbodiimide compound and controlling the degree of polymerization thereof include phenyl isocyanate, tolyl isocyanate, dimethylphenyl isocyanate, cyclohexyl isocyanate, butyl isocyanate, naphthyl isocyanate and the like. be able to.

（式中、Ｒは水素原子または炭素数１〜５の分岐を有していても良いアルキル基であり、ｎは３〜１５０の整数である。）
特に式（Ｂ）で表されるポリカルボジイミドが好ましい。ポリカルボジイミドの平均重合度としては３〜１５０であることが好ましい。なお、１官能性のカルボジイミド化合物の場合には、本発明の目的である経時耐久性の改善効果が小さくなることがあるので、ポリカルボジイミドであることが好ましい。しかしながら、平均重合度が大きくなりすぎると、カルボジイミドの合成において反応物の固化やゲル化が生じたり、またポリエステル樹脂組成物中での分散性が低下して十分な耐久性改善効果が得られないことがある。 Among these polycarbodiimide compounds, 4,4′-dicyclohexylmethane carbodiimide, tetramethylxylylene carbodiimide, and for example, 1,3,5-triisopropylphenylene-2,4-carbodiimide represented by the following formula (B) are preferable. ,

(In the formula, R is a hydrogen atom or an alkyl group which may have 1 to 5 carbon atoms, and n is an integer of 3 to 150.)
In particular, polycarbodiimide represented by the formula (B) is preferable. The average degree of polymerization of polycarbodiimide is preferably 3 to 150. In the case of a monofunctional carbodiimide compound, polycarbodiimide is preferred because the effect of improving durability over time, which is the object of the present invention, may be reduced. However, if the average degree of polymerization becomes too large, solidification or gelation of the reaction product occurs in the synthesis of carbodiimide, and the dispersibility in the polyester resin composition decreases, so that a sufficient durability improvement effect cannot be obtained. Sometimes.

  The modifiers comprising the cyclic imino ether compound or carbodiimide compound may be used singly or in combination of two or more, but the total is 0 with respect to 100 parts by mass of the copolyester. 0.05 to 10 parts by mass, preferably 0.08 to 8 parts by mass, more preferably 0.1 to 5 parts by mass, and particularly preferably 0.3 to 2 parts by mass. When the total content of the modifiers is less than 0.05 parts by mass, the effect of improving hydrolysis resistance is insufficient, whereas when it exceeds 10 parts by mass, the melt viscosity of the polyester resin is high. This is not preferable because the load increases during melt extrusion.

The polyester resin composition of the present invention preferably has a carboxyl end group amount of 1 to 20 equivalents / 10 ⁶ g, more preferably 1 to 18 equivalents / 10 ⁶ g, and particularly preferably 1 to 15 equivalents. / 10 ⁶ g. When the amount of this terminal group exceeds 20 equivalents / 10 ⁶ g, the effect of improving the durability over time such as hydrolysis resistance may be reduced, whereas to make it less than 1 equivalent / 10 ⁶ g Further, it is necessary to add a large amount of the modifying agent or to solid-phase polymerize the copolyester for a long time, and the productivity tends to be lowered.

  The method for producing a polyester resin composition of the present invention is such that, even if a modifier such as the cyclic imino ether compound or carbodiimide compound is added to the polymerization reaction system of the copolymerized polyester, it is melt-mixed after the polymerization reaction is completed. However, it is preferable to mix after the completion of the polymerization reaction. Alternatively, the copolyester once chipped may be melt mixed using a melt extruder. In this case, a polyester chip (so-called master batch) containing the modifier at a relatively high concentration is used as the chip. A method of mixing in a state and then melt mixing is preferable. In this case, two types of polymers having different ratios of the aforementioned formulas (I) and (II) may be melt-kneaded so that the ratios of the aforementioned formulas (I) and (II) are intended. One polyester that does not contain the aromatic dicarboxylic acid component represented by the formula (I) may be used.

  The polyester resin composition of the present invention thus obtained includes other thermoplastic polymers, stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants, difficult additives within the range not impairing the effects of the present invention. You may mix | blend a flame retardant, a mold release agent, a pigment, a nucleating agent, a filler or glass fiber, carbon fiber, a layered silicate as needed. Examples of other types of thermoplastic polymers include liquid crystalline resins, aliphatic polyester resins, polyamide resins, polycarbonates, ABS resins, polymethyl methacrylate, polyamide elastomers, polyester elastomers, polyether imides, polyimides, and the like. .

<Film production method>
The polyester resin composition of the present invention is used as a raw material, and after drying this, it is supplied to an extruder heated to a melting point (Tm: ° C.) to (Tm + 50) ° C. of the polyester resin composition. Extrude into a sheet from the die. In addition, the polyester resin composition to be used is not limited to one type. For example, a polymer having a large proportion of the above-described formula (I) and a polymer having a large amount of the above-described formula (II) are prepared. It may be used by being melt-kneaded with the modifying agent so that the ratio of (II) is within the target range, and by adopting such a method, the ratio of the aforementioned formulas (I) and (II) can be changed. It can be changed arbitrarily and conveniently. The extruded sheet can be rapidly cooled and solidified with a rotating cooling drum or the like to form an unstretched film, and the unstretched film can be biaxially stretched to obtain a biaxially oriented film.

  In addition, from the viewpoint of facilitating the later-described stretching, the cooling by the cooling drum is preferably performed very quickly, and is preferably performed at a low temperature of 20 to 60 ° C. By performing at such a low temperature, crystallization in the state of an unstretched film is suppressed, and subsequent stretching can be performed more smoothly.

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 polyester at 3 to 8 times, and then at a higher temperature than the previous longitudinal stretching (Tg + 10) in the transverse direction. It is preferable that the film is stretched 3 to 8 times at a temperature of (Tg + 50) ° C., and further heat-treated 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. The heat setting time is preferably 1 to 15 seconds.

Normally, when the draw ratio is increased, the film-forming stability is impaired. However, since the polyester resin composition of the present invention has high drawability, there is no such problem, and in particular, the draw ratio can be further increased. A thin film having a thickness of 10 μm or less, particularly 8 μm or less, can be stably formed. The lower limit of the film thickness is not particularly limited, but is usually about 1 μm, preferably 3 μm.
On the other hand, simultaneous biaxial stretching in which longitudinal stretching and lateral stretching are simultaneously performed can be similarly performed, and the stretching ratio, stretching temperature, and the like described in the sequential biaxial stretching may be referred to.

  Further, when the biaxially oriented film is a laminated film, two or more kinds of molten polyester resin compositions are laminated in a die and then extruded into a film, preferably the melting point (Tm: ° C.) of each polyester resin composition. Extrusion at a temperature of (Tm + 70) ° C. or extruding two or more molten polyester resin compositions from a die, laminating, rapidly solidifying to form a laminated unstretched film, and then the same method as in the case of the single-layer film described above Biaxial stretching and heat treatment may be performed. At this time, it is not necessary for all the film layers to be the polyester resin composition of the present invention, as long as at least one film layer is made of the polyester resin composition of the present invention. In addition, a coating layer may be provided on the surface of the biaxially oriented film. In that case, a desired coating solution is applied to one side or both sides of the unstretched film or the uniaxially stretched film described above, and after that, Biaxial stretching and heat treatment are preferably performed in the same manner as in the case.

The biaxially oriented film of the present invention obtained as described above preferably has a temperature expansion coefficient (αt) of at least one of the film forming direction (MD direction) and the width direction (TD direction), preferably 14 × 10 ^{−. 6} / ° C. or less, more preferably 10 × 10 ⁻⁶ / ° C. or less, further preferably 7 × 10 ⁻⁶ ° C. or less, and particularly preferably 5 × 10 ⁻⁶ / ° C. or less. It is preferable because it can exhibit excellent dimensional stability against dimensional changes due to.

The lower limit of the temperature expansion coefficient (αt) of at least one of the film forming direction and the width direction of the biaxially oriented film is preferably −15 × 10 ⁻⁶ / ° C., more preferably −10 × 10 ⁻⁶ / ° C., more preferably −7 × 10 ⁻⁶ / ° C.

  According to Patent Document 3, it is expected that the temperature expansion coefficient (αt) of the polyester film obtained by copolymerizing polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate is increased. However, according to the present invention, the temperature expansion coefficient (αt) can be reduced by employing a polyester having a specific copolymerization ratio and stretching.

The biaxially oriented film of the present invention has a humidity expansion coefficient (αh) of at least one of the film forming direction and the width direction of 1 × 10 ^{−6 to} 7 × 10 ⁻⁶ /% RH, and further 1 × 10 ⁻⁶ to It is preferably in the range of 6 × 10 ⁻⁶ /% RH.

Furthermore, the biaxially oriented film of the present invention preferably has a Young's modulus in the film forming direction of 4.5 GPa or more, more preferably 5 GPa or more from the viewpoint of suppressing elongation during high-temperature processing. The upper limit of the Young's modulus (Y) in the film forming direction of the film is preferably about 12 GPa because it is easy to provide a sufficient Young's modulus in the width direction of the film.
On the other hand, since the Young's modulus in the width direction of the film is in the range of 6 to 14 GPa, more preferably in the range of 7 to 12 GPa, it is easy to adjust the temperature expansion coefficient and humidity expansion coefficient in the width direction of the film within the above ranges. preferable.

  Hereinafter, the present invention will be described in more detail 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 measured at 35 ° C by dissolving the polymer using a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio). And asked.

(2) Glass transition point and melting point The glass transition point and the melting point were measured by DSC (TA Instruments, trade name: Q100) at a heating rate of 20 ° C / min.

(3) Copolymerization amount (glycol component) 10 mg of a sample was dissolved in 0.5 ml of a mixed solution of p-chlorophenol: 1,1,2,2-tetrachloroethane = 3: 1 (volume ratio) at 80 ° C., and isopropylamine Then, ¹ H-NMR of 600 MHz was measured at 80 ° C. using JEOL A600 manufactured by JEOL Ltd., and the amount of each glycol component was determined.
(Acid component) 60 mg of a sample was dissolved in a mixed solution of 0.5 ml of p-chlorophenol: 1,1,2,2-tetrachloroethane = 3: 1 (volume ratio) at 140 ° C., and ¹³ C-NMR of 150 MHz was obtained from Japan. It measured at 140 degreeC using the electronic company make and JEOL A600, and calculated | required each acid component amount.

(4) Temperature expansion coefficient (αt)
The obtained film was cut into a length of 20 mm and a width of 4 mm so that the TD direction (or MD direction) of the film would be the measurement direction, set in a TMA / SS6000 manufactured by Seiko Instruments, and under a nitrogen atmosphere (0% RH) , Pretreatment at 80 ° C. for 30 minutes, and then the temperature was lowered to room temperature. Thereafter, the temperature was raised from 30 ° C. to 80 ° C. at 2 ° C./min, the sample length at each temperature was measured, and the temperature expansion coefficient (αt) was 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 × 10 ⁻⁶
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 × 10 ⁻⁶ / ° C. is the temperature expansion coefficient (αt) of quartz glass.

(5) Humidity expansion coefficient (αh)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the TD direction (or MD direction) of the film would be the measurement direction, set in TMA4000SA manufactured by Bruker AXS, and a humidity of 20% under a nitrogen atmosphere at 30 ° C. The length of each sample at RH and humidity 80% RH was measured, and the humidity expansion coefficient (αh) was 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 ⁸⁰ −L ²⁰ ) / (L ²⁰ × ΔH)
Here, L ²⁰ in the above formula is a sample length (mm) when 20% RH, L ⁸⁰ is a sample length (mm) when 80% RH, ΔH: 60 (= 80-20)% RH is there.

(6) Carboxyl terminal group amount The obtained film was dissolved in benzyl alcohol at 200 ° C. in a nitrogen atmosphere, and then the carboxyl terminal group amount (equivalent / 10 ⁶ g) was measured by a titration method.

(7) Hydrolysis resistance The obtained film was cut into a length of 100 mm in the longitudinal direction (MD direction) and 10 mm in the lateral direction (HD direction) to obtain a strip-shaped sample piece, 121 ° C. · 2 atm · wet Saturation mode • Leave in an environmental tester set to 100% RH for a certain period (100 hours). Thereafter, the sample piece was taken out, its longitudinal breaking strength was measured 5 times, and the average value was obtained. The value obtained by dividing the average value by the measured value of the breaking strength before standing was defined as the breaking strength retention (%), and the hydrolysis resistance was evaluated according to the following criteria. In addition, it is judged that a thing with a high fracture strength retention is favorable for hydrolysis resistance.
Breaking strength retention rate (%) = (breaking strength after 100 hours of treatment time) / (breaking strength before treatment) × 100
◎: Breaking strength retention rate 75% or more ○: Breaking strength retention rate 60% or more and less than 75% Δ: Breaking strength retention rate 40% or more and less than 60% ×: Breaking strength retention rate 40% or less

[Reference 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, the intrinsic viscosity was 0.62 dl / g, 30 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 70 mol% of the acid component was 6,6 ′-(alkylenedioxy). An aromatic polyester (PB1) in which the di-2-naphthoic acid component and the glycol component were ethylene glycol was obtained. The aromatic polyester contained silica particles having an average particle diameter of 0.4 μm so as to be 0.3% by weight based on the weight of the resulting resin composition before the polycondensation reaction.

[Reference Example 2]
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 0.62 dl / g, 99.5 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 0.5 mol% of the acid component was 6,6 ′-( An aromatic polyester (PA1) in which the alkylenedioxy) di-2-naphthoic acid component and the glycol component were ethylene glycol was obtained. The aromatic polyester contained silica particles having an average particle diameter of 0.4 μm so as to be 0.3% by weight based on the weight of the resulting resin composition before the polycondensation reaction.

[Example 1]
The aromatic polyesters (PA1) and (PB1) obtained in Reference Examples 1 and 2 were mixed at a mass ratio of 61:39, and 2,2′-bis (2-oxazoline) was added as a modifier. 1 part by mass with respect to 100 parts by mass of the polyester group, supplied to an extruder, and on a cooling drum having a temperature of 55 ° C. during rotation in a molten state from a die at 295 ° C. (average residence time: 20 minutes) An unstretched film was extruded into a sheet shape. 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 133 ° C., and stretching in the longitudinal direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.0. And this uniaxially stretched film is led to a stenter, a transverse stretching temperature of 135 ° C., a transverse stretching ratio of 8.3 times, heat setting treatment (202 ° C. for 10 seconds) and cooling, and a biaxially stretched film having a thickness of 5.0 μm. Got. The characteristics of the obtained biaxially oriented film are shown in Table 1.

[Example 2]
In Example 1, the same operation was repeated except that the type of the modifier was changed to poly (1,3,5-triisopropylphenylene-2,4-carbodiimide) (molecular weight: about 10,000). The characteristics of the obtained biaxially oriented film are shown in Table 1.

[Example 3]
The aromatic polyesters (PA1) and (PB1) obtained in Reference Examples 1 and 2 were mixed at a mass ratio of 52:48 and poly (1,3,5-triisopropylphenylene-2 as a modifier). , 4-carbodiimide) (molecular weight: about 10,000) is mixed at a ratio of 1 part by mass with respect to 100 parts by mass of the aromatic polyester, supplied to an extruder and melted from the die at 300 ° C. (average residence time: 20 minutes). The sheet was extruded in the form of a sheet onto a cooling drum having a temperature of 55 ° C. during rotation to obtain 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 5.7. And this uniaxially stretched film is led to a stenter, a transverse stretching temperature of 130 ° C., a transverse stretching ratio of 8.3 times, heat setting treatment (194 ° C. for 10 seconds) and cooling, and a biaxially stretched film having a thickness of 5.0 μm. Got. The characteristics of the obtained biaxially oriented film are shown in Table 1.

[Example 4]
The aromatic polyesters (PA1) and (PB1) obtained in Reference Examples 1 and 2 were mixed at a mass ratio of 76:24, and poly (1,3,5-triisopropylphenylene-2, 4-carbodiimide) (molecular weight: about 10000) is mixed at a ratio of 1 part by mass with respect to 100 parts by mass of the aromatic polyester, supplied to the extruder, and melted from the die at 300 ° C. (average residence time: 15 minutes). Then, the sheet was extruded into a sheet on a rotating drum at a temperature of 55 ° C. during rotation to obtain an unstretched film. Then, between 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 136 ° C., and stretching in the longitudinal direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.2. And this uniaxially stretched film is led to a stenter, a transverse stretching temperature of 138 ° C., a transverse stretching ratio of 8.2 times, heat setting (at 212 ° C. for 10 seconds) and cooling, and a biaxially stretched film having a thickness of 5.0 μm. Got. The characteristics of the obtained biaxially oriented film are shown in Table 1.

[Example 5]
The aromatic polyesters (PA1) and (PB1) obtained in Reference Examples 1 and 2 were used in a mass ratio of 40:60 and poly (1,3,5-triisopropylphenylene-2 as a modifier). , 4-carbodiimide) (molecular weight: about 10,000) is mixed at a ratio of 0.5 part by mass with respect to 100 parts by mass of the aromatic polyester, supplied to an extruder and die at 300 ° C. (average residence time: 20 minutes). Then, it was extruded into a sheet form on a cooling drum having a temperature of 55 ° C. while being rotated in a molten state to obtain an unstretched film. Then, between the 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 125 ° C., and stretching in the longitudinal direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 6.2. And this uniaxially stretched film is led to a stenter, a transverse stretch temperature of 125 ° C., a transverse stretch ratio of 9.5 times, heat setting treatment (190 ° C. for 10 seconds) and cooling, and a biaxially stretched film having a thickness of 4.5 μm Got. The characteristics of the obtained biaxially oriented film are shown in Table 1.

[Example 6]
In Example 2, the same operation was performed except that the addition amount of the modifier (poly (1,3,5-triisopropylphenylene-2,4-carbodiimide) (molecular weight: about 10,000)) was changed to 2 parts by mass. Repeated. The characteristics of the obtained biaxially oriented film are shown in Table 1.

[Comparative Example 1]
In Example 1, the same operation was repeated except that the modifier was not added.
The characteristics of the obtained biaxially oriented film are shown in Table 1.

  In Table 1, B component is 2,6-naphthalenedicarboxylic acid component, A component is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, Tg is glass transition temperature, Tm is melting point, and TD is The width direction of a film is shown.

  The biaxially oriented polyester film comprising the polyester resin composition of the present invention can be achieved with conventional polyethylene terephthalate, polyethylene-2,6-naphthalate and polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate. The base film for high-density magnetic recording media and the base film for back sheets of solar cells has excellent dimensional stability as never before, and also has superior performance over time such as hydrolysis resistance. As, it can be used suitably.

Claims (4)

The total proportion of the dicarboxylic acid component represented by the following formula (I) or the following formula (II) is 90 to 100 mol% of the total dicarboxylic acid component, and the dicarboxylic acid component represented by the following formula (I) is It is cyclic with respect to 100 parts by mass of the copolyester that occupies 5 mol% or more and less than 50 mol% of the total dicarboxylic acid component, and 90 to 100 mol% of the total diol component is alkylene glycol having 2 to 10 carbon atoms. A polyester resin composition containing 0.05 to 10 parts by mass of a modifier comprising an imino ether compound or a carbodiimide compound.
HO (O) C—R ² —OR ¹ O—R ² —C (O) OH (I)
[In the above formula (I), R ¹ represents an alkylene group having 2 to 10 carbon atoms, and R ² represents a 2,6-naphthalenediyl group. ]
HO (O) C—R ³ —C (O) OH (II)
[In the above formula (II), R ³ represents a phenylene group or a naphthalenediyl group. ] The polyester resin composition according to claim 1, wherein the modifier is an oxazoline compound represented by the following formula (A).

(In the formula, R _{1 to} R ₈ are each a hydrogen atom or a monovalent organic group, X is a divalent organic group, and n is 0 or 1.) The polyester resin composition according to claim 1, wherein the modifier is a carbodiimide compound represented by the following formula (B).

(In the formula, R is a hydrogen atom or an alkyl group optionally having 1 to 5 carbon atoms, and n is an integer of 3 to 150.)   The biaxially oriented film which consists of a polyester resin composition in any one of Claims 1-3.