JP5788729B2 - Oriented polyester film - Google Patents

Description

  The present invention relates to an oriented polyester film using an aromatic polyester comprising an aromatic dicarboxylic acid component and a glycol component and copolymerized with a 4,4'-diphenylene dialkylene glycol component as a glycol component.

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

  Therefore, Patent Document 1 discloses a high-density magnetic recording medium in which the coefficient of humidity expansion can be reduced and the dimensional stability is improved by copolymerizing a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component. A film suitable for the base film has been proposed. However, the production of the 6,6 '-(alkylenedioxy) di-2-naphthoic acid component has a problem in terms of productivity because a very large amount of solvent is required.

  On the other hand, in Patent Document 2, when polyethylene-2,6-naphthalenedicarboxylate is blown and used when forming into a bottle or the like, the forming processability is poor, and the forming processability by blow-drawing is poor. In order to improve the above, it has been proposed to copolymerize structural units derived from an alkylene oxide adduct of dihydroxynaphthalene or an alkylene oxide adduct of biphenol.

JP 2008-189801 A JP-A-10-204166

  An object of the present invention is to provide an oriented polyester film excellent in dimensional stability, particularly dimensional stability against environmental changes such as temperature and humidity.

  In the oriented polyester film, the temperature expansion coefficient and the humidity expansion coefficient are very closely related to the Young's modulus, and generally the lower the Young's modulus, the lower. However, the Young's modulus is not increased as much as possible, and there is a limit in terms of film forming properties and securing the Young's modulus in the orthogonal direction. For this reason, when the same Young's modulus is used, it has been studied whether a film having a lower expansion coefficient with respect to temperature and humidity can be obtained. It was found that an oriented polyester film having extremely excellent dimensional stability can be obtained by making the temperature expansion coefficient in the most oriented direction and the thermal shrinkage rate at 105 ° C. into a specific range. .

（上記構造式（１）中の、Ｒ_１、Ｒ_２は炭素数２〜１０のアルキレン基もしくは炭素数８〜１０のシクロアルキレン基を示す。）で表される４，４’−ジフェニレンジアルキレングリコール成分とエチレングリコール成分で、４，４’−ジフェニレンジアルキレングリコールール成分とエチレングリコール成分のモル比が、３５：６５〜５：９５の範囲にあること、そして
（２）配向フィルムは、直交する２方向の１０５℃３０分での熱収縮率が１％以下であること
を同時に具備する配向ポリエステルフィルムが提供される。 Thus, according to the present invention, an oriented polyester film comprising an aromatic polyester,
(1) The aromatic polyester is one kind selected from the group consisting of a terephthalic acid component and a naphthalenedicarboxylic acid component with 95 mol% or more of the total acid component, and 95 mol% or more of the total glycol component is represented by the following formula ( 1)

(In the structural formula (1), R ₁ and R ₂ represent an alkylene group having 2 to 10 carbon atoms or a cycloalkylene group having 8 to 10 carbon atoms.) The molar ratio of the 4,4′-diphenylene dialkylene glycol component and the ethylene glycol component in the alkylene glycol component and the ethylene glycol component is in the range of 35:65 to 5:95, and (2) the oriented film is There is provided an oriented polyester film simultaneously having a heat shrinkage rate of 1% or less at 105 ° C. for 30 minutes in two orthogonal directions.

Further, according to the present invention, as a preferred embodiment of the present invention, the 4,4′-diphenylene dialkylene glycol component is such that R ₁ and R ₂ are ethylene groups, the film thickness is 10 μm or less, DSC The glass transition temperature measured in (1) is 100 ° C. or higher, the Young's modulus in at least one direction in the film surface direction is 4.5 GPa or higher, and the humidity expansion coefficient in at least one direction in the film surface direction is 1 to 7.5. There is also provided an oriented polyester film having at least one of being in the range of (× 10 ⁻⁶ /% RH) and being used as a base film of a magnetic recording medium.

  ADVANTAGE OF THE INVENTION According to this invention, the oriented film excellent in the dimensional stability with respect to a temperature or humidity change is provided. Therefore, if the oriented film of the present invention is used, a high-density magnetic recording medium having excellent dimensional stability against changes in temperature and humidity can be provided.

<Aromatic polyester>
One of the features of the present invention is that (1) 95 mol% or more of the total acid component is one selected from the group consisting of a terephthalic acid component and a naphthalenedicarboxylic acid component, and (2) 95 of all glycol components. More than mol% is the 4,4′-diphenylene dialkylene glycol component (hereinafter sometimes referred to as DPA component) represented by the formula (1) and the ethylene glycol component, and the moles of the DPA component and the ethylene glycol component. An aromatic polyester satisfying that the ratio is in the range of 35:65 to 5:95. When the proportion of either the terephthalic acid or naphthalenedicarboxylic acid component is less than the lower limit of the total acid components, sufficient Young's modulus and dimensional stability cannot be ensured.

  Moreover, about a glycol component, when the ratio of the DPA component and ethylene glycol component in all the glycol components is less than the said minimum, dimensional stability is not ensured. Further, when the DPA component of the glycol component is not more than the above lower limit, sufficient dimensional stability is not ensured, and when it is not less than the above upper limit, it is difficult to ensure a sufficient Young's modulus. The ratio of the copolymerization amount of the glycol component (DPA component: ethylene glycol component) is in the range of 35: 65-5: 95, preferably 35: 65-6: 94, more preferably 30: 70-6: 94. It is a range.

The R ₁ and R ₂ moieties represented by the formula (1) are an alkylene group having 2 to 10 carbon atoms or a cycloalkylene group having 8 to 10 carbon atoms, preferably an ethylene group, a propylene group, or a butylene group. Among these, from the viewpoint of the effect of the present invention, those having an even number of carbon atoms of R ₁ and R ₂ in the general formula (1) are preferable, and an ethylene group is particularly preferable. Of course, the aromatic polyester in the present invention may be copolymerized with other copolymerization components known per se as long as the effects of the present invention are not impaired.

  By the way, the aromatic polyester in the present invention has a film forming property that the melting point measured by DSC is in the range of 200 to 270 ° C., further in the range of 210 to 270 ° C., particularly in the range of 230 to 265 ° C. From the viewpoint of the mechanical properties of Further, the aromatic polyester in the present invention has a glass transition temperature (hereinafter sometimes referred to as Tg) measured by DSC in the range of 80 to 120 ° C, more preferably in the range of 90 to 118 ° C, particularly 95 to 116 ° C. It is preferable from the viewpoint of the stretchability, heat resistance and dimensional stability of the film. 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. Further, from the viewpoint of improving workability at high temperature after forming into a film, for example, workability such as coating of a magnetic layer, Tg is preferably as high as possible, and glass transition temperature is within the range not impairing the object of the present invention. Copolymerization with a copolymer component capable of increasing the viscosity, or blending with a polyetherimide or a liquid crystal resin (for example, JP-A 2000-355631, JP-A 2000-141475 and JP-A-11-1568) Is also a preferred embodiment. The copolymerization amount of the 4,4′-diphenylene dialkylene glycol component is adjusted by adjusting the composition of the raw material so that a desired copolymerization amount is obtained in the polymerization stage, or the 4,4′-dialkylene glycol component as the glycol component. Prepare a homopolymer using only the phenylene dialkylene glycol component or a polymer with a high copolymerization amount, a non-copolymerization polymer or a polymer with a low copolymerization amount, and add these to the desired copolymerization amount. It can be adjusted by transesterification by melt kneading.

<Oriented film>
The oriented film of the present invention is a film made of the above-described resin composition and stretched in at least one direction of the film surface direction, that is, a molecular chain is oriented.
The two directions perpendicular to the film surface direction, that is, the direction in which the molecular chain is most oriented (hereinafter referred to as the main orientation direction) and the direction perpendicular to the direction are measured at 105 ° C. for 30 minutes under no load. The heat shrinkage rate is 1% or less. If the thermal shrinkage rate is larger than this, the film shrinks in the main orientation direction during processing at high temperature, and even if the elongation during high-temperature processing is suppressed, the deformation is large, the workability decreases, and the post-processing Characteristics such as the coefficient of humidity expansion and Young's modulus may be easily impaired. From such a viewpoint, the upper limit of the preferred thermal shrinkage rate in the main orientation direction is 1.0% or less, further 0.9% or less, and 0.8% or less. Such a heat shrinkage rate can be reduced by performing a heat setting treatment after stretching and increasing the temperature at that time or relaxing the heat shrinkage in a direction in which the heat shrinkage rate is desired to decrease. The lower limit of the heat shrinkage rate is not particularly limited, but under normal film forming conditions, if it is intended to be a negative value that expands, wrinkle is likely to occur in the process. .1% or more is preferable.

  When the oriented film of the present invention is used as a base film such as a magnetic tape, it is preferable that at least one direction in the film surface direction has a high Young's modulus of 4.5 GPa or more so that the base film does not stretch. . Moreover, the humidity expansion coefficient can be further reduced by increasing the Young's modulus in this way. The upper limit of the Young's modulus is not limited, but is usually 11 GPa. Preferred Young's modulus is 3 to 11 GPa in the longitudinal direction of the film, more preferably 3.5 to 10 GPa, particularly 4.0 to 9 GPa, and 4 to 11 GPa, further 5 to 11 GPa, and further 6 to 10 GPa in the width direction of the film. In particular, it is in the range of 7-10 GPa.

  The oriented film of the present invention preferably has a humidity expansion coefficient in the main orientation direction of 7.5 ppm /% RH or less, more preferably 7.4 ppm /% RH or less, particularly 7.2 ppm /% RH or less, while the lower limit is Although not particularly limited, it is preferably 1 ppm /% RH or more, more preferably 2 ppm /% RH or more, particularly 3 ppm /% RH from the viewpoint of imparting excellent dimensional stability against humidity changes to the target product. In particular, when used for a base film of a linear recording magnetic recording medium, it is preferable that the direction satisfying the humidity expansion coefficient is the width direction because track deviation and the like can be extremely suppressed. In the present invention, the width direction of the film is a direction orthogonal to the film forming direction of the film (also referred to as a longitudinal direction or a longitudinal direction), and is sometimes referred to as a lateral direction.

  The oriented film of the present invention has a coefficient of thermal expansion in the main orientation direction of −10 to +10 ppm / ° C., more preferably −7 to +5 ppm / ° C., particularly −5 to −1 ppm / ° C. This is preferable in terms of dimensional stability. In particular, when used as a base film for a magnetic recording tape, it is preferable that the direction satisfying the above-mentioned temperature expansion coefficient is the width direction because track deviation and the like can be extremely suppressed.

The thickness of the oriented film of the present invention may be appropriately determined depending on the application. When used for a base film of a magnetic recording tape, the thickness is preferably 2 to 10 μm, more preferably 3 to 7 μm, and particularly preferably 4 to 6 μm.
By the way, as for the oriented film of this invention, it is preferable that one surface roughness (Ra) is 1 nm-20 nm, More preferably, it is 2 nm-10 nm.

  In general, in order to increase the surface roughness of the film, inert particles may be included to form protrusions. As the inert particles to be contained, (1) heat resistant polymer particles (for example, crosslinked silicone resin, crosslinked polystyrene, crosslinked acrylic resin, melamine-formaldehyde resin, aromatic polyamide resin, polyimide resin, polyamideimide resin, crosslinked polyester, etc.) Particles), (2) metal oxides (eg, aluminum oxide, titanium dioxide, silicon dioxide (silica), magnesium oxide, zinc oxide, zirconium oxide, etc.), metal carbonates (eg, magnesium carbonate, calcium carbonate, etc.) Particles made of inorganic compounds such as metal sulfates (eg calcium sulfate, barium sulfate etc.), carbon (eg carbon black, graphite, diamond etc.) and clay minerals (eg kaolin, clay, bentonite etc.) And more (3) and the like inside precipitated particles formed by precipitation, such as externally added particles are added in the form of composite particles such as particles, such as different materials shell type using for example the core and the shell or (4) a catalyst. Among these, at least one kind of particles selected from the group consisting of a crosslinked silicone resin, a crosslinked acrylic resin, a crosslinked polyester, a crosslinked polystyrene, aluminum oxide, titanium dioxide, silicon dioxide, kaolin and clay is particularly preferable. At least one kind of particles selected from the group consisting of silicone resin, cross-linked acrylic resin, cross-linked polyester, cross-linked polystyrene, and silicon dioxide (excluding porous silica etc.) reduces the variation in particle size. It is preferable because it is easy. Of course, these may be used in combination of two or more.

From the viewpoint of runnability, the average particle diameter of the inert particles contained in the film layer is preferably in the range of 0.05 to 1.0 μm, more preferably 0.1 to 0.8 μm, particularly as a magnetic recording medium. When used, it is preferably in the range of 0.05 to 0.5 μm, more preferably 0.05 to 0.3 μm. The content of the inert particles contained in the film layer may be in the range of 0.005 to 1.0% by weight, more preferably 0.01 to 0.5% by weight, based on the weight of the film layer. preferable.
Of course, the oriented film of the present invention may be laminated with another film layer or provided with a coating layer as long as the effects of the present invention are not impaired.

<Method for producing aromatic polyester resin>
Next, a method for producing an aromatic polyester copolymerized with a 4,4′-diphenylene dialkylene glycol component in the present invention will be described in detail. In addition, as the aromatic polyester not copolymerized with the 4,4′-diphenylene dialkylene glycol component, those produced by a method known per se can be suitably used.

First, 4,4′-diphenylene dialkylene glycol may be obtained by reacting biphenol with the desired alkylene glycol as R ₁ or R ₂ to obtain an alkylene oxide adduct of the desired biphenol. Then, 4,4′-diphenylene dialkylene glycol, for example, 2,6-naphthalenedicarboxylic acid, terephthalic acid or an ester-forming derivative thereof, and ethylene glycol are reacted to produce a polyester precursor. And it can manufacture by superposing | polymerizing the polyester precursor obtained in this way in presence of a polymerization catalyst, You may give a solid phase polymerization etc. as needed. The intrinsic viscosity measured at 35 ° C. using a mixed solvent of aromatic polyester P-chlorophenol / 1,1,2,2-tetrachloroethane (weight ratio 40/60) thus obtained is 0.4. From the viewpoint of the effect of the present invention, it is preferably in the range of -1.5 dl / g, more preferably in the range of 0.5-1.3 dl / g. In addition, in the process of manufacturing 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 all acid components. From this point, 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., and the reaction time is 10 to 10 hours, preferably 30 or more. It is preferably performed for 7 hours or less. By such a transesterification reaction or esterification reaction, a reactant as a polyester precursor is obtained.

  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 a copolymerized aromatic polyester resin having a high degree of polymerization.

  Examples of the polycondensation catalyst include metal compounds containing at least one metal element. The polycondensation catalyst can also be used in transesterification and esterification reactions. Examples of the metal element include titanium, germanium, antimony, aluminum, nickel, zinc, tin, cobalt, rhodium, iridium, zirconium, hafnium, lithium, calcium, and magnesium. More preferable metals are titanium, germanium, antimony, aluminum, tin, and the like. Among these, titanium compounds are particularly preferable because they exhibit high activity in both 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 number of moles of the repeating unit of the copolymerized aromatic polyester.

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

  In the aromatic polyester that forms the film layer in the present invention, other thermoplastic polymers, stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants, flame retardants, as long as the effects of the present invention are not impaired. A mold release agent, pigment, nucleating agent, filler, glass fiber, carbon fiber, layered silicate and the like may be blended as necessary. Examples of other thermoplastic polymers include aliphatic polyester resins, polyamide resins, polycarbonates, ABS resins, polymethyl methacrylate, polyamide elastomers, polyester elastomers, polyether imides, polyimides, and the like.

<Film production method>
The oriented film of the present invention is one in which the molecular orientation in each direction is enhanced by stretching in the film forming direction and the width direction, and for example, it can be produced by the following method while maintaining the film forming property. It is preferable because the Young's modulus is easily improved. First, the aromatic polyester forming the film is used as a raw material, and after drying, these are extruded into a film form from a die in a molten state, preferably at a temperature not lower than the melting point (Tm: ° C.) of the polyester (Tm + 70) ° C. and unstretched. A film is prepared and biaxially stretched. In order to satisfy the aforementioned Young's modulus, αt, αh, and the like, it is preferable to perform cooling with a cooling drum very quickly in order to facilitate the subsequent stretching. From such a viewpoint, the temperature of the cooling drum 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 the aromatic polyester at 2 to 7 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 10 times, and further heat treatment is preferably 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. . A particularly preferable heat setting treatment is performed at a temperature of 180 to 220 ° C., further 190 to 210 ° C., and a time of 1 to 15 seconds.

  In the above description, sequential biaxial stretching has been described. However, the oriented film of the present invention can be produced by simultaneous biaxial stretching in which longitudinal stretching and lateral stretching are simultaneously performed. For example, referring to the stretching ratio and the stretching temperature described above. do it. In addition, about the method of containing particle | grains, a publicly known method can be employ | adopted, for example, in the manufacturing process of polyester, you may add to a reaction system and may add to polyester by melt-kneading. From the viewpoint of the dispersibility of the particles, it is preferably added to a polyester reaction system to produce a polyester composition having a high particle concentration as a master polymer, which is mixed with a polyester composition containing no particles or having a low particle concentration. The method is preferred. According to the present invention, the oriented film of the present invention is used as a base film, and a nonmagnetic layer and a magnetic layer are formed in this order on one surface, preferably on a flatter surface, and the other surface, preferably A magnetic recording tape can be obtained by forming a backcoat layer on the surface that is less flat. Further, since it can exhibit a high degree of dimensional stability, it is particularly suitable as a base film for a linear recording magnetic recording tape.

  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 copolymerized aromatic polyester and film was measured at 35 ° C by dissolving the polymer using a mixed solvent of P-chlorophenol / tetrachloroethane (40/60 weight ratio). Asked.

(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 acid component, 50 mg of a sample was dissolved in 140 ml of a mixed solution of p-chlorophenol: heavy tetrachloroethane = 3: 1 (volume ratio) at 140 ° C., and 400 MHz ¹³ C-NMR (Hitachi Electronics) Manufactured by JEOL A600) at 140 ° C., and the amount of each acid component was measured. When DPA is an ethylene oxide adduct, the molar ratio of the DPA component to the ethylene glycol component in the present invention is that the ethylene glycol added to the biphenol is counted as the DPA component, and the amount of ethylene glycol compared to DPA is Do not add.

(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 measured using an Abbe refractometer at a pitch of 10 ° with the film forming direction being 0 ° and the width direction being 90 ° in the plane direction of the film. The measurement was performed as a value for the sodium D line at 23 ° C., and the direction with the highest refractive index was defined as the main orientation direction. And it cuts out to length 20mm and width 4mm so that a main orientation direction may turn into a measurement direction, and it sets to EXSTAR6000 made from SII, and pre-processes at 80 degreeC by nitrogen atmosphere (0% RH) for 30 minutes, Then, it reaches room temperature Let the temperature drop. Thereafter, the temperature is raised from 30 ° C. to 70 ° C. at 2 ° C./min, the sample length at each temperature is measured, and the temperature expansion coefficient (αt) is calculated from the following equation. In addition, the measurement direction is the longitudinal direction of the sample cut out, the measurement was performed 5 times, and the average value was used.
αt = {(L ₆₀ −L ₄₀ )} / (L ₄₀ × ΔT)} + 0.5
Here, L ₄₀ in the above formula is the sample length (mm) at 40 ° C., L ₆₀ is the sample length (mm) at 60 ° C., ΔT is 20 (= 60-40) ° C., 0.5 Is the temperature expansion coefficient of quartz glass (× 10 ⁻⁶ ppm / ° C.).

(6) Humidity expansion coefficient (αh)
Cut out into a length of 15 mm and a width of 5 mm so that the direction with the highest refractive index measured in (5) above is the measurement direction, set in a TMA4000SA manufactured by BRUKER, and a humidity of 20% RH and humidity in a nitrogen atmosphere at 30 ° C. The length of each sample at 80% RH is measured, and the humidity expansion coefficient is calculated by the following equation. In addition, the measurement direction is the longitudinal direction of the cut out sample, the measurement was performed 5 times, and the average value was αh (ppm /% RH).
αh = (L ₈₀ −L ₂₀ ) / (L ₈₀ × ΔH)
Here, L ₂₀ in the above formula is a sample length (mm) at 20% RH, and L ₈₀ is 80%.
Sample length at RH (mm), ΔH: 60 (= 80-20)% RH.

(7) Thermal shrinkage at 105 ° C. Cut into a length of 300 mm and a width of 300 mm so that the direction of the highest refractive index measured in (5) above and the direction orthogonal thereto are the measurement directions. And heat treatment at 105 ° C. for 30 minutes. And it cooled to room temperature after heat processing, the dimension after heat processing was subtracted from the dimension before heat processing, and what was divided by the dimension before heat processing was made into the thermal contraction rate.

(8) Dimensional stability In order to evaluate the overall dimensional stability as a film, with respect to the measurement values of (5), (6) and (7) described above, the following criteria A to C are used. evaluated.
-Thermal contraction rate at 105 ° C .: Δ in the case where it exceeds 1% or less than 0% in any one of the main orientation direction and the two directions orthogonal thereto, and Δ if it is 0.9% or more and 1.0% or less , If 0.8% or more and less than 0.9%, ◯, both orthogonal directions are 0% or more and less than 0.8%.
・ Temperature expansion coefficient in the main orientation direction: ５〜 at -5 to -1 ppm / ° C, ○ at -7 to +5 ppm / ° C, △ at -10 to -10 ppm / ° C, less than -10 ppm / ° C or 10 ppm / ° C When exceeding
-Humidity expansion coefficient in the main orientation direction: ◎ when 7.2 ppm /% RH or less, ◯ when 7.4 ppm /% RH or less, △ when 7.5 ppm /% RH or less, exceeding 7.5 ppm /% RH When ×
And ◎ is three for AAA, ◎ for two and ○ for one, AA for one, ◎ for one and two for A, B for no △ and one for △ One was also C. When the above judgments were AAA, AA and A, the magnetic recording tape had excellent dimensional stability against temperature and humidity changes in that order. On the other hand, those with the above judgment of B were slightly inferior to those of the above judgment A, but could be used as a magnetic recording tape. However, when the above judgment is C, there is a problem in terms of dimensional stability when used as a magnetic tape.

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. As a result, an aromatic polyester having an intrinsic viscosity of 1.2 dl / g in which the 4,4′-diphenylenediethylene glycol component was 5 mol% was obtained. The aromatic polyester had a melting point of 265 ° C. and a glass transition temperature of 120 ° 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 60 ° 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 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 140 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 2]
Dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. As a result, an aromatic polyester having an intrinsic viscosity of 1.2 dl / g in which the 4,4′-diphenylenediethylene glycol component was 10 mol% was obtained. The aromatic polyester had a melting point of 264 ° C. and a glass transition temperature of 117 ° C.
The aromatic polyester thus obtained was supplied to an extruder, extruded from a die at 300 ° C. in a molten state onto a cooling drum having a temperature of 60 ° C. and rotating into a sheet 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 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 140 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 3]
Dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. As a result, an aromatic polyester having an intrinsic viscosity of 1.2 dl / g and a 4,4′-diphenylenediethylene glycol component content of 20 mol% was obtained. The aromatic polyester had a melting point of 264 ° C. and a glass transition temperature of 116 ° C.
The aromatic polyester thus obtained was supplied to an extruder, extruded from a die at 300 ° C. in a molten state onto a cooling drum having a temperature of 60 ° C. and rotating into a sheet 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 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. And this uniaxially stretched film is led to a stenter, stretched at a stretch ratio of 5.0 times in the transverse direction (width direction) at 140 ° C., and then heat-set at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 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 as the dicarboxylic acid component and ethylene glycol and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. As a result, an aromatic polyester having an intrinsic viscosity of 1.2 dl / g and a 4,4′-diphenylenediethylene glycol component content of 30 mol% was obtained. The aromatic polyester had a melting point of 260 ° C. and a glass transition temperature of 111 ° C.
The aromatic polyester thus obtained was supplied to an extruder, extruded from a die at 300 ° C. in a molten state onto a cooling drum having a temperature of 60 ° C. and rotating into a sheet 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 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 140 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 5]
Dimethyl terephthalate as the dicarboxylic acid component and ethylene glycol and 4,4′-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction, An aromatic polyester having an intrinsic viscosity of 1.1 dl / g in which the 4′-diphenylenediethylene glycol component was 5 mol% was obtained. The aromatic polyester had a melting point of 254 ° C. and a glass transition temperature of 78 ° C.
The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 280 ° C. in a molten state onto a cooling drum having a rotating temperature of 30 ° C. to form 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 95 ° 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 led to a stenter, stretched at 110 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 1]
Diester 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction, and an intrinsic viscosity of 0.6 dl / g Of polyethylene-2,6-naphthalenedicarboxylate was obtained. The aromatic polyester had a melting point of 265 ° C. and a glass transition temperature of 121 ° C.
The aromatic polyester thus obtained was supplied to an extruder, extruded from a die at 300 ° C. in a molten state onto a cooling drum having a temperature of 60 ° C. and rotating into a sheet 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 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 140 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 2]
Dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction, An aromatic polyester having a viscosity of 1.2 dl / g was obtained. The aromatic polyester had a melting point of 250 ° C. and a glass transition temperature of 114 ° C.
The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 280 ° C. in a molten state onto a cooling drum having a temperature of 60 ° C. and rotating into a sheet 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 120 ° C., and stretching in the longitudinal 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 130 ° C. in the transverse direction (width direction) at a stretching ratio of 3.0 times, and then heat-set at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 3]
Dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. As a result, an aromatic polyester having an intrinsic viscosity of 1.2 dl / g and a 4,4′-diphenylenediethylene glycol component of 40 mol% was obtained. This aromatic polyester had no melting point and a glass transition temperature of 110 ° C. Since it was an amorphous polymer, film evaluation was not performed.

[Comparative Example 4]
Dimethyl 2,6-naphthalenedicarboxylate as the dicarboxylic acid component and ethylene glycol and 4,4'-diphenylenediethylene glycol as the diol component are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. As a result, an aromatic polyester having an intrinsic viscosity of 1.2 dl / g and a 4,4′-diphenylenediethylene glycol component of 95 mol% was obtained. The aromatic polyester had a melting point of 245 ° C. and a glass transition temperature of 114 ° C.
The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 280 ° C. in a molten state onto a cooling drum having a temperature of 60 ° C. and rotating into a sheet to obtain an unstretched film. Then, the film is not stretched in the film forming direction, but is directly led to a stenter, stretched at a stretching ratio of 5.5 times in the transverse direction (width direction) at 140 ° C., and then heat-set at 200 ° C. for 3 seconds to obtain a thickness. A biaxially stretched film having a thickness of 5 μm was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Comparative Example 5]
In Example 1, a biaxially oriented polyester film having a thickness of 5 μm was obtained under the same conditions except that the film was not heat-set.
Table 1 shows the characteristics of the obtained biaxially oriented polyester film.

[Comparative Example 6]
A transesterification reaction between dimethyl terephthalate as the dicarboxylic acid component and ethylene glycol as the diol component in the presence of titanium tetrabutoxide, followed by a polycondensation reaction, gives an aromatic polyester having an intrinsic viscosity of 0.65 dl / g. Got. The aromatic polyester had a melting point of 254 ° C. and a glass transition temperature of 76 ° C.
The aromatic polyester thus obtained was supplied to an extruder and extruded from a die at 280 ° C. in a molten state onto a cooling drum having a rotating temperature of 30 ° C. to form 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 95 ° 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 led to a stenter, stretched at 110 ° C. in the transverse direction (width direction) at a stretch ratio of 5.0 times, and then heat-fixed at 200 ° C. for 3 seconds, and biaxially stretched with a thickness of 5 μm. A film was obtained.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

  In Table 1, DPDE is 4,4'-diphenylenediethylene glycol component, melting point and glass transition temperature are values of copolymerized aromatic polyester in the state of film, MD is film forming direction, TD is film width direction Indicates.

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

Claims (7)

An oriented polyester film made of an aromatic polyester,
(1) The aromatic polyester is one kind selected from the group consisting of a terephthalic acid component and a naphthalenedicarboxylic acid component with 95 mol% or more of the total acid component, and 95 mol% or more of the total glycol component is represented by the following formula ( In the 4,4′-diphenylene dialkylene glycol component and the ethylene glycol component represented by 1), the molar ratio of the 4,4′-diphenylene dialkylene glycol component and the ethylene glycol component is 35:65 to 5:95. (2) An oriented polyester film characterized in that the oriented film simultaneously has a heat shrinkage rate of 1% or less at 105 ° C. for 30 minutes in two orthogonal directions.

(R ₁ and R ₂ in the structural formula (1) represent an alkylene group having 2 to 10 carbon atoms or a cycloalkylene group having 8 to 10 carbon atoms.) The oriented polyester film according to claim ₁ , wherein in the 4,4'-diphenylene dialkylene glycol component, R ₁ and R ₂ are ethylene groups.   The oriented polyester film according to claim 1, wherein the film thickness is 10 μm or less.   The oriented polyester film according to claim 1, wherein the glass transition temperature measured by DSC is 100 ° C or higher.   The 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 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 7.5 (× 10 ⁻⁶ /% RH).   The oriented polyester film according to claim 1, wherein the oriented polyester film is used as a base film of a magnetic recording medium.