Polyester composition, polyester film, and magnetic recording medium

Abstract

The invention provides a polyester composition in which the primary repeating units contain an aromatic dicarboxylic acid component (Component A) and an ethylene glycol component (Component C) and a long-chain alkyl dicarboxylic acid component having not less than 6 carbons (Component B) or a long-chain alkyl diol component having not less than 6 carbons (Component D), wherein a sum (WB+WD) of a relative amount (WB) of Component B as calculated based on a total number of moles of Component A and Component B plus a relative amount (WD) of Component D as calculated based on a total number of moles of Component C and Component D are within a range of 2-13 mol %. The invention also provides a polyester film prepared from the polyester composition and having excellent dimensional stability, as well as a magnetic recording medium utilizing the polyester film.

Claims

1. A polyester composition characterized in that primary repeating units therein comprise an aromatic dicarboxylic acid component (Component A) and an ethylene glycol component (Component C); a long-chain alkyl dicarboxylic acid component having from 6 to 14 carbons (Component B) or a long-chain alkyl diol component having from 6 to 14 carbons (Component D) is present therein; and a sum (WB+WD) of a relative amount (WB) of Component B as calculated based on a total number of moles of Component A and Component B plus a relative amount (WD) of Component D as calculated based on a total number of moles of Component C and Component D is within a range of 2 mol % to 13 mol %.

2. The polyester composition according to claim 1, wherein at least one species selected from the group consisting of polyimide, polyether imide, polyether ketone, and polyether ether ketone is present in an amount within a range of 0.5 wt % to 25 wt % as calculated based on mass of the polyester composition.

3. A polyester film wherein the polyester composition according to claim 1 is employed in at least one layer thereof.

4. The polyester film according to claim 3, having a Young's modulus in at least one surfacial direction of the film of not less than 4.5 GPa.

5. The polyester film according to claim 3, having a percent elongation in a long direction of the film at 110° C. of not greater than 3.0%.

6. The polyester film according to claim 3, having a coefficient of expansion due to humidity in at least one surfacial direction of the film of 1 ppm/% RH to 10.0 ppm/% RH, and a coefficient of expansion due to temperature in at least one direction of not greater than 14 ppm/° C.

7. The polyester film according to claim 3 that is capable of being used in a base film for a magnetic recording medium.

8. A magnetic recording medium comprising the polyester film according to claim 7 and a magnetic layer formed on one surface thereof.

9. A polyester film provided with a film layer comprising the polyester composition according to claim 1.

10. The polyester film according to claim 9, having a Young's modulus in at least one surfacial direction of the film of not less than 4.5 GPa.

11. The polyester film according to claim 9, having a percent elongation in a long direction of the film at 110° C. of not greater than 3.0%.

12. The polyester film according to claim 9, having a coefficient of expansion due to humidity in at least one surfacial direction of the film of 1 ppm/% RH to 10.0 ppm/% RH, and a coefficient of expansion due to temperature in at least one direction of not greater than 14 ppm/° C.

13. The polyester film according to claim 9, wherein at least one species selected from the group consisting of polyimide, polyether imide, polyether ketone, and polyether ether ketone is present in the polyester composition in an amount within a range of 0.5 wt % to 25 wt % as calculated based on mass of the polyester composition.

14. The polyester film according to claim 9, wherein the long-chain alkyl dicarboxylic acid component (Component B) has a structure that does not contain a branched chain.

15. A magnetic recording medium comprising the polyester film according to claim 9 and a magnetic layer formed on one surface thereof.

16. The polyester film according to claim 9, wherein the long-chain alkyl diol component (Component D) has a structure that does not contain a branched chain.

17. A laminated film wherein the polyester composition according to claim 1 is employed in at least two layers thereof.

18. The laminated film according to claim 17, having a Young's modulus in at least one surfacial direction of the laminated film of not less than 4.5 GPa.

19. The laminated film according to claim 17, having a percent elongation in a long direction of the laminated film at 110° C. of not greater than 3.0%.

Description

WORKING EXAMPLES

(1) The present invention is described in more specific terms by way of the Working Examples and Comparative Examples given below. Note that in accordance with the present invention the following methods were used to measure and evaluate the properties thereof.

(2) (1) Young's Modulus

(3) The film that was obtained was cut into samples of width 10 mm and length 15 cm, and a universal tension testing apparatus (product name: Tensilon; manufactured by Toyo Baldwin) was used to apply tension thereto under the conditions: 100 mm chuck separation, 10 mm/min elongation rate, and chart speed 500 mm/min. Young's modulus was calculated from the tangent at the rising portion of the load-elongation curve that was obtained.

(4) (2) Coefficient of Expansion Due to Temperature (αt)

(5) The film that was obtained was cut into pieces of length 15 mm and width 5 mm in such fashion as to cause the film forming direction of the film and the width direction thereof to respectively be the measured directions, these were placed in a TMA 3000 manufactured by Shinku-Riko, and pretreatment was carried out for 30 minutes at 60° C. in a nitrogen atmosphere (0% RH), following which temperature was decreased to room temperature. Temperature was thereafter increased by 2° C./minute from 25° C. to 70° C., sample lengths at respective temperatures were measured, and the following formula was used to calculate the coefficient of expansion due to temperature (αt). Note that the measured direction was the long direction of the cut samples, 5 measurements being made, the average thereof being used.
αt={(L.sub.60−L.sub.40)}/(L.sub.40×ΔT)}+0.5

(6) Here, at the foregoing formula, note that L.sub.40 is the sample length (mm) at 40° C., L.sub.60 is the sample length (mm) at 60° C., ΔT is 20 (=60−40)° C., and 0.5 is the coefficient of expansion due to temperature (×10.sup.−6/° C.) of quartz glass.

(7) (3) Coefficient of Expansion Due to Humidity (αh)

(8) The film that was obtained was cut into pieces of length 15 mm and width 5 mm in such fashion as to cause the film forming direction of the film and the width direction thereof to respectively be the measured directions, these were placed in a TMA 3000 manufactured by Shinku-Riko, sample lengths were respectively measured at humidity 30% RH and humidity 70% RH in a nitrogen atmosphere at 30° C., and the following formula was used to calculate the coefficient of expansion due to humidity. Note that the measured direction was the long direction of the cut samples, 5 measurements being made, the average thereof being taken to be αh.
αh=(L.sub.70−L.sub.30)/(L.sub.30×ΔH)

(9) Here, at the foregoing formula, note that L.sub.30 is the sample length (mm) at 30% RH, L.sub.70 is the sample length (mm) at 70% RH, and ΔH=40 (=70−30)% RH.

(10) (4) Identification of Long-Chain Diol Component and Long-Chain Dicarboxylic Acid Component

(11) A 20 mg sample was dissolved at room temperature in 0.6 mL of a 1:1 (vol % ratio) solvent mixture of deuterated trifluoroacetic acid:deuterated chloroform, and the amounts of the long-chain diol component and the long-chain dicarboxylic acid components within the film and polymer chips were calculated using .sup.1H-NMR at 500 MHz.

(12) (5) Intrinsic Viscosity (IV)

(13) Intrinsic viscosity of the film and polyester copolymer that were obtained was determined by using a P-chlorophenol/tetrachloroethane (40/60 wt % ratio) solvent mixture to dissolve the polymer, with measurement being carried out at 35° C.

(14) (6) Glass Transition Temperature (Tg) and Melting Point (Tm)

(15) Glass transition temperature (extrapolated onset temperature) and melting point were measured using a DSC (product name=Thermal Analyst 2100; manufactured by TA Instruments) at a temperature rise rate of 20° C./min with a 10 mg sample.

(16) (7) Percent Elongation of Film at 110° C.

(17) The film that was obtained was cut into pieces of length 20 mm and width 4 mm in such fashion as to cause the film forming direction of the film to be the measured direction, these were placed in an Exstar 6000 manufactured by SII and held at 30° C. in a nitrogen atmosphere (0% RH), following which temperature was increased by 2° C./minute to 150° C. while a stress of 20 MPa was applied thereto in the film forming direction, sample lengths at respective temperatures were measured, and the following formula was used to calculate the degree to which expansion occurred in the length direction based on the film length (L110) at 110° C. versus the film length (L30) after being held at 30° C. but before temperature was increased. The resulting percent elongations of the film that were obtained are shown in TABLE 2.
Percent elongation of film (%)={(L110−L30)/L30}×100
(8) Surface Roughness (Ra)

(18) A noncontact three-dimensional surface profiler (New View 5022 manufactured by Zygo Corporation) was used to carry out measurement under conditions such that measurement magnification was 10× and measurement area was 283 μm×213 μm (=0.0603 mm.sup.2), surface analysis software MetroPro internal to said profiler being used to obtain center plane average roughnesses (Ra) for the respective surfaces, average values being recorded such that surface roughness was deemed to be the same when the difference between center line average roughnesses (Ra) was not greater than 0.1 nm.

(19) (9) Film Layer Thickness

(20) For the unstretched film, a microtome (Ultracut-S) was used to a cut a section along the direction perpendicular to the film forming direction thereof, following which an optical microscope was used to calculate the respective thicknesses of Layers A and B. Furthermore, for the oriented laminated polyester film, cutting was carried out in similar fashion, following which a transmission electron microscope was used to calculate the respective thicknesses of Layers A and B, and the thickness ratio dA/dB was determined.

(21) (10) Fabrication of Magnetic Tape

(22) A die coater (tension at time of treatment=20 MPa; temperature=120° C.; speed=200 m/minute) was used to coat the surface on the rough surface layer side of the laminated biaxially oriented polyester film of width 1000 mm and length 1000 m that was obtained at each of the respective Working Examples and Comparative Examples with a back-coated layer coating having the following composition, and this was dried, following which a die coater was used to coat the surface on the flat layer side of the film with a nonmagnetic coating and a magnetic coating having the following compositions while simultaneously varying film thickness, magnetic orientation was performed, and drying was carried out. Moreover, a small-scale test calendaring apparatus (steel roller/nylon roller; 5-roller apparatus) was used to perform calendaring treatment at temperature=70° C. and linear load=200 kg/cm, following which curing was carried out at 70° C. for 48 hours. The foregoing tape was slit so as to be 12.65 mm and assembled in a cassette to obtain magnetic recording tape. Note that coated amounts were adjusted so as to obtain thicknesses of the back-coated layer, the nonmagnetic layer, and the magnetic layer that following drying were respectively 0.5 μm, 1.2 μm, and 0.1 μm.

(23) Composition of Nonmagnetic Coating

(24) Titanium dioxide microparticles: 100 parts by weight

(25) S-LEC A (vinyl chloride/vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.: 10 parts by weight

(26) Nippolan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane Industry Co., Ltd.): 10 parts by weight

(27) Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts by weight

(28) Lecithin: 1 part by weight

(29) Methyl ethyl ketone: 75 parts by weight

(30) Methyl isobutyl ketone: 75 parts by weight

(31) Toluene: 75 parts by weight

(32) Carbon black: 2 parts by weight

(33) Lauric acid: 1.5 parts by weight

(34) Composition of Magnetic Coating

(35) Iron (major axis=0.037 μm; acicular aspect ratio=3.5; 2350 oersteds): 100 parts by weight

(36) S-LEC A (vinyl chloride/vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.: 10 parts by weight

(37) Nippolan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane Industry Co., Ltd.): 10 parts by weight

(38) Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.): 5 parts by weight

(39) Lecithin: 1 part by weight

(40) Methyl ethyl ketone: 75 parts by weight

(41) Methyl isobutyl ketone: 75 parts by weight

(42) Toluene: 75 parts by weight

(43) Carbon black: 2 parts by weight

(44) Lauric acid: 1.5 parts by weight

(45) Composition of Back-Coated Layer Coating

(46) Carbon black: 100 parts by weight

(47) Thermoplastic polyurethane resin: 60 parts by weight

(48) Isocyanate Compound: 18 parts by weight (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.)

(49) Silicone oil: 0.5 part by weight

(50) Methyl ethyl ketone: 250 parts by weight

(51) Toluene: 50 parts by weight

(52) (11) Electromagnetic Transduction Characteristics

(53) A ½-inch linear system at which heads were secured was employed for measurement of electromagnetic transduction characteristics An electromagnetic induction head (25 μm track width; 0.1 μm gap) was used for recording, and an MR head (8 μm) was used for playback. A head/tape relative speed of 10 m/second was used, a signal of recorded wavelength 0.2 μm was recorded, a spectrum analyzer was used to carry out frequency analysis of the playback signal, the ratio of carrier signal (0.2 μm wavelength) output C and noise N integrated over the entire spectrum was taken to be the C/N ratio, and the value relative to a value of 0 dB for Working Example 1 fabricated according to the method at 11, above, was calculated, evaluation being carried out based on the following criteria.

(54) EXCELLENT=Greater than or equal to +1 dB

(55) GOOD=Greater than or equal to −1 dB but less than +1 dB

(56) BAD=Less than −1 dB

(57) (12) Error Rate

(58) The tape stock material fabricated at (10), above, was slit so as to be 12.65 mm (½ inch) in width, and this was assembled in an LTO case to fabricate a data storage cartridge at which the length of the magnetic recording tape was 850 m. An LTO 5 drive manufactured by IBM was used to carry out recording (0.55 μm recorded wavelength) at ambient conditions of 23° C. and 50% RH on this date storage, and the cartridge was then stored for 7 days at ambient conditions of 50° C. and 80% RH. After storing the cartridge at normal temperature for 1 day, the full length thereof was played back, and the error rate of the signal during playback was measured. The following formula was used to calculate the error rate based on error information (number of erroneous bits) output by the drive. Dimensional stability was evaluated based on the following criteria.

(59) Error rate=(Number of erroneous bits)/(number of bits written thereonto)

(60) EXCELLENT=Error rate was less than 1.0×10.sup.−6

(61) GOOD=Error rate was greater than or equal to 1.0×10.sup.−6 but less than 1.0×10.sup.−4

(62) BAD=Error rate was greater than or equal to 1.0×10.sup.−4

(63) (13) Dropouts (DO)

(64) The data storage cartridge for which error rate was measured at (12), above, was loaded into an LTO 5 drive manufactured by IBM, 14 GB of data signal was recorded thereonto, and this was played back. A signal in which amplitude (P-P value) was 50% or less of the average signal amplitude was taken to be a missing pulse, with four or more consecutive missing pulses being detected as a dropout. Note that dropouts were evaluated for one reel of length 850 m, these being converted into the equivalent number thereof per 1 m, determination being carried out based on the following criteria.

(65) EXCELLENT=Less than 3 dropouts/m

(66) GOOD=Greater than or equal to 3 dropouts/m but less than 9 dropouts/m

(67) BAD=Greater than or equal to 9 dropouts/m

(68) Preparation of Polyethylene Naphthalate Pellets A1

(69) Dicarboxylic acid component in the form of dimethyl 2,6-naphthalene dicarboxylate and diol component in the form of ethylene glycol were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare polyethylene naphthalate pellets A1 (IV=0.58 dl/g; Tg=115° C.; Tm=263° C.).

(70) Preparation of Polyethylene Terephthalate Pellets A2

(71) Dicarboxylic acid component in the form of dimethyl terephthalate and diol component in the form of ethylene glycol were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare polyethylene terephthalate pellets A2 (IV=0.58 dl/g; Tg=76° C.; Tm=254° C.).

(72) Preparation of Sebacic Acid Copolymerized Polyethylene Naphthalate Pellets B1

(73) Dicarboxylic acid component in the form of dimethyl 2,6-naphthalene dicarboxylate and dimethyl sebacate, and diol component in the form of ethylene glycol, were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare sebacic-acid-copolymerized polyethylene naphthalate pellets B1. Note that acid component in the form of sebacic acid was present in an amount that was 17 mol %. (IV=0.70 dl/g; Tg=75° C.; Tm=235° C.).

(74) Preparation of Sebacic Acid Copolymerized Polyethylene Terephthalate Pellets B2

(75) Dicarboxylic acid component in the form of dimethyl terephthalate and dimethyl sebacate, and diol component in the form of ethylene glycol, were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare sebacic-acid-copolymerized polyethylene terephthalate pellets B2. Note that acid component in the form of sebacic acid was present in an amount that was 17 mol %. (IV=0.65 dl/g; Tg=51° C.; Tm=230° C.).

(76) Preparation of Dodecanedioic Acid Copolymerized Polyethylene Naphthalate Pellets C1

(77) Dicarboxylic acid component in the form of 2,6-naphthalene dicarboxylic acid and dimethyl diol component in the form of ethylene glycol were subjected to transesterification reaction in the presence of titanium tetrabutoxide, dodecanedioic acid and ethylene glycol were added at the stage when distillation of methanol therefrom had ended and the transesterification reaction had ended, and this was subjected to esterification reaction while causing water to be distilled therefrom and then further subjected to polycondensation reaction to prepare dodecanedioic-acid-copolymerized polyethylene naphthalate pellets C1. Note that acid component in the form of dodecanedioic acid was present in an amount that was 16 mol %. (IV=0.77 dl/g; Tg=75° C.; Tm=238° C.).

(78) Preparation of Dodecanedioic Acid Copolymerized Polyethylene Terephthalate Pellets C2

(79) Dicarboxylic acid component in the form of dimethyl terephthalate and diol component in the form of ethylene glycol were subjected to transesterification reaction in the presence of titanium tetrabutoxide, dodecanedioic acid and ethylene glycol were added at the stage when distillation of methanol therefrom had ended and the transesterification reaction had ended, and this was subjected to esterification reaction while causing water to be distilled therefrom and then further subjected to polycondensation reaction to prepare dodecanedioic-acid-copolymerized polyethylene terephthalate pellets C2. Note that acid component in the form of dodecanedioic acid was present in an amount that was 16 mol %. (IV=0.70 dl/g; Tg=50° C.; Tm=231° C.).

(80) Preparation of Hexanediol Copolymerized Polyethylene Naphthalate Pellets D1

(81) Dicarboxylic acid component in the form of dimethyl 2,6-naphthalene dicarboxylate and diol component in the form of ethylene glycol and hexanediol were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare hexanediol-copolymerized polyethylene naphthalate pellets D1. Note that diol component in the form of hexanediol was present in an amount that was 36 mol %. (IV=0.44 dl/g; Tg=87° C.; Tm=220° C.).

(82) Preparation of Hexanediol Copolymerized Polyethylene Terephthalate Pellets D2

(83) Dicarboxylic acid component in the form of dimethyl terephthalate and diol component in the form of ethylene glycol and hexanediol were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare hexanediol-copolymerized polyethylene terephthalate pellets D2. Note that diol component in the form of hexanediol was present in an amount that was 36 mol %. (IV=0.43 dl/g; Tg=52° C.; Tm=215° C.).

(84) Preparation of Decanediol Copolymerized Polyethylene Naphthalate Pellets E1

(85) Dicarboxylic acid component in the form of dimethyl 2,6-naphthalene dicarboxylate and diol component in the form of ethylene glycol and decanediol were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare decanediol-copolymerized polyethylene naphthalate pellets E1. Note that diol component in the form of decanediol was present in an amount that was 25 mol %. (IV=0.49 dl/g; Tg=81° C.; Tm=229° C.).

(86) Preparation of Decanediol Copolymerized Polyethylene Terephthalate Pellets E2

(87) Dicarboxylic acid component in the form of dimethyl terephthalate and diol component in the form of ethylene glycol and decanediol were subjected to transesterification reaction in the presence of titanium tetrabutoxide and then further subjected to polycondensation reaction to prepare decanediol-copolymerized polyethylene terephthalate pellets E2. Note that diol component in the form of decanediol was present in an amount that was 25 mol %. (IV=0.41 dl/g; Tg=50° C.; Tm=211° C.).

Working Example 1

(88) Pellets A1 and B1 were blended so as to cause sebacic acid to be present therein in an amount that was 7 mol %. In other words, pellets A1 nd B1 were blended so as to cause the relative amount (WB) to be 7 mol %, as a result of which the sum (WB+WD) was made to be 7 mol %. Furthermore, at the time that these were blended, true-sphere-shaped silica particles of average particle diameter 0.1 μm were made to be present therein in an amount that was 0.25 mass % as calculated based on the mass of the film, and true-sphere-shaped silica particles of average particle diameter 0.3 μm were made to be present therein in an amount that was 0.1 mass % as calculated based on the mass of the film.

(89) Resin C1 obtained in such fashion was extruded at 290° C. onto a rotating cooling drum, the temperature of which was 60° C., to produce unstretched film. In addition, between two sets of rollers of different rotational speeds in the film forming direction, the unstretched film was heated from above by an IR heater so as to cause the film surface temperature to be 130° C., stretching in the vertical direction (film forming direction) being carried out at a stretching ratio of 4.5× to obtain uniaxially stretched film. In addition, this uniaxially stretched film was guided to a stenter, stretching was carried out at a stretching ratio of 5.0× in the horizontal direction (width direction) at 130° C., and heat-setting treatment was thereafter carried out for 3 seconds at 210° C. to obtain biaxially oriented polyester film of thickness 5.0 μm.

(90) Results for the biaxially oriented polyester that was obtained are shown in TABLE 2.

Working Examples 2-12 and 14; Comparative Examples 1-5

(91) Except for the fact that the conditions shown in TABLE 1 were altered, a procedure similar to that at Working Example 1 was repeated to obtain biaxially oriented polyester film. Results for the biaxially oriented polyester film that was obtained are shown in TABLE 2.

Working Example 13

(92) Polyether imide in the form of “Ultem 1010” manufactured by SABIC Innovative Plastic was prepared. The polyether imide that was prepared and pellets A2 and E2 were blended, the amount of polyether imide that was added being 10 wt % by weight, this being carried out in such fashion as to cause decanediol to be present therein in an amount that was 7 mol %. Furthermore, at the time that these were blended, true-sphere-shaped silica particles of average particle diameter 0.1 μm were made to be present therein in an amount that was 0.25 mass % as calculated based on the mass of the film, and true-sphere-shaped silica particles of average particle diameter 0.3 μm were made to be present therein in an amount that was 0.1 mass % as calculated based on the mass of the film, and, except for the fact that the conditions shown in TABLE 1 were altered, a procedure similar to that at Working Example 1 was repeated to obtain biaxially oriented polyester. Results for the biaxially oriented polyester film that was obtained are shown in TABLE 2.

Working Example 15

(93) Pellets A1 and pellets E1 were blended so as to cause decanediol to be present therein in an amount that was 7 mol %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.1 μm to be present therein in an amount that was 0.08 mass % as calculated based on mass, to prepare resin 1. Furthermore, pellets A1 and pellets E1 were blended so as to cause decanediol to be present therein in an amount that was 7 mol %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.1 μm to be present therein in an amount that was 0.12 mass %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.3 μm to be present therein in an amount that was 0.13 mass %, as calculated based on mass, to prepare resin 2. Resin 1 and resin 2 were respectively extruded at 300° C., these being made to flow together so as to obtain a thickness ratio between resin 1 and resin 2 of 3:7 at the feedblock, these being extruded onto a rotating cooling drum, the temperature of which was 60° C. At this time, this was carried out in such fashion as to cause resin 1 to be surface A, and resin 2 to be surface B. Except for the fact that the conditions shown in TABLE 1 were altered, a procedure similar to that at Working Example 1 was repeated to form biaxially oriented laminated polyester film. Results for the biaxially oriented laminated polyester film that was obtained are shown in TABLE 2.

Working Example 16

(94) Resin 3 in which pellets A2 and true-sphere-shaped silica particles of average particle diameter 0.1 μm were blended so as to cause the true-sphere-shaped silica particles to be present therein in an amount that was 0.08 mass % as calculated based on mass was prepared. Furthermore, pellets A2 and pellets E2 were blended so as to cause decanediol to be present therein in an amount that was 10.3 mol %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.1 μm to be present therein in an amount that was 0.12 mass %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.3 μm to be present therein in an amount that was 0.13 mass %, as calculated based on mass, to obtain resin 4. Resin 3 and resin 4 were extruded at 280° C., these being made to flow together so as to obtain a thickness ratio between resin 3 and resin 4 of 3:7 at the feedblock, these being extruded onto a rotating cooling drum, the temperature of which was 25° C. At this time, the amount of decanediol present within the film was 7 mol %. Furthermore, this was carried out in such fashion as to cause resin 3 to be surface A, and resin 4 to be surface B. Except for the fact that the conditions shown in TABLE 1 were altered, a procedure similar to that at Working Example 15 was repeated to form biaxially oriented laminated polyester film. Results for the biaxially oriented laminated polyester film that was obtained are shown in TABLE 2.

Working Example 17

(95) Resin 5 in which pellets A2 and true-sphere-shaped silica particles of average particle diameter 0.1 μm were blended so as to cause decanediol to be 6.5 mol %, and so as to cause the true-sphere-shaped silica particles to be present therein in an amount that was 0.08 mass % as calculated based on mass, was prepared. Furthermore, pellets A2 and pellets E2 were blended so as to cause decanediol to be present therein in an amount that was 8.9 mol %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.1 μm to be present therein in an amount that was 0.12 mass %, and so as to cause true-sphere-shaped silica particles of average particle diameter 0.3 μm to be present therein in an amount that was 0.13 mass %, as calculated based on mass, to obtain resin 6. Resin 5 and resin 6 were extruded at 280° C., these being made to flow together so as to obtain a thickness ratio between resin 5 and resin 6 of 8:2 at the feedblock, these being extruded onto a rotating cooling drum, the temperature of which was 25° C. At this time, the amount of decanediol present within the film was 7 mol %. Furthermore, this was carried out in such fashion as to cause resin 5 to be surface A, and resin 6 to be surface B.

(96) Except for the fact that the conditions shown in TABLE 1 were altered, a procedure similar to that at Working Example 15 was repeated to form biaxially oriented laminated polyester film. Results for the biaxially oriented laminated polyester film that was obtained are shown in TABLE 2.

(97) TABLE-US-00001 TABLE 1 Layer A Layer B Copolymer component Copolymer component Acid component Diol component Acid component Diol component Mol Mol Mol Mol Cooling frac- frac- frac- frac- Blended component drum Stretching Heat-set Number tion Number tion Number tion Number tion Amount temper- Ratio Temperature temper- Pellets Compo- of mol Compo- of mol Pellets Compo- of mol Compo- of mol added ature MD TD MD TD ature used nent carbons % nent carbons % used nent carbons % nent carbons % Resin wt % ° C. Ratio Ratio ° C. ° C. ° C. Working A1/B1 SA 10 7 — — — — — — — — — — — — 60 4.5 5.0 130 130 210 Example 1 Working A1/C1 DA 12 7 — — — — — — — — — — — — 60 4.5 5.0 130 130 210 Example 2 Working A1/D1 — — — HD  6 7 — — — — — — — — — 60 4.5 5.0 130 130 210 Example 3 Working A1/E1 — — — DD 12 4 — — — — — — — — — 60 4.5 5.0 130 130 210 Example 4 Working A1/E1 — — — DD 12 6 — — — — — — — — — 60 4.5 5.0 130 130 210 Example 5 Working A1/E1 — — — DD 12 7 — — — — — — — — — 60 4.5 5.0 130 130 210 Example 6 Working A1/E1 — — — DD 12 1 — — — — — — — — — 60 4.5 4.0 130 130 210 Example 7 Working A1/E1 — — — DD 12 10 — — — — — — — — — 60 4.5 5.0 130 130 210 Example 8 Working A2/B2 SA 10 7 — — — — — — — — — — — — 25 3.6 4.0 90 90 210 Example 9 Working A2/C2 DA 12 7 — — — — — — — — — — — — 25 3.6 4.0 90 90 210 Example 10 Working A2/D2 — — — HD  6 7 — — — — — — — — — 25 3.6 4.0 90 90 210 Example 11 Working A2/E2 — — — DD 12 7 — — — — — — — — — 25 3.6 4.0 90 90 210 Example 12 Working A2/E2 — — — DD 12 7 — — — — — — — PET 10 25 3.8 4.2 100 100 210 Example 13 Working A2/C2/E2 DA 12   3.5 DD 12 3.5 — — — — — — — — — 25 3.6 4.0 90 90 210 Example 14 Working A1/E1 — — — DD 12 7 A1/E1 — — — DD 12 7 — — 60 4.5 5.0 130 130 210 Example 15 Working A2 — — — — — — A2/E2 — — — DD 12  10.3 — — 25 3.6 4.0 90 90 210 Example 16 Working A2/12 — — — DD 12 6.5 A2/E2 — — — DD 12   8.9 — — 25 3.6 4.0 90 90 210 Example 17 Comparative A2 — — — — — — — — — — — — — — — 25 3.6 4.0 90 90 210 Example 1 Comparative A1 — — — — — — — — — — — — — — — 60 4.5 4.0 130 130 210 Example 2 Comparative A1/B1 SA 10 20  — — — — — — — — — — — — 60 3.5 4.5 120 120 200 Example 3 Comparative A1/E1 — — — DD 12 20 — — — — — — — — — 60 3.5 4.5 120 120 200 Example 4 Comparative A1/E1 — — — DD 12 1.5 — — — — — — — — — 60 4.5 4.0 130 130 210 Example 5

(98) TABLE-US-00002 TABLE 2 Coefficient of expansion Coefficient of expansion due to temperature due to humidity Film Young's modulus (αt) (αh) thickness GPa ×10.sup.6/° C. ×10.sup.6/% RH μm MD TD MD TD MD TD Working 5.0 5.5 7.6 22.7 8.0 11.7 8.9 Example 1 Working 5.0 5.5 7.6 22.2 5.5 10.9 8.3 Example 2 Working 5.0 5.8 7.7 18.2 8.0 11.8 8.7 Example 3 Working 5.0 5.9 7.9 15.9 5.4 11.6 8.8 Example 4 Working 5.0 5.8 7.8 18.4 6.5 11.0 8.7 Example 5 Working 5.0 5.8 7.7 18.4 7.0 10.5 8.6 Example 6 Working 5.0 6.6 5.5 13.2 20.5 9.6 10.8 Example 7 Working 5.0 5.5 7.5 19.1 4.4 10.2 8.5 Example 8 Working 5 0 4.8 5.8 15.6 8.6 11.5 9.4 Example 9 Working 5.0 4.8 5.8 15.4 8.4 11.6 9.5 Example 10 Working 5.0 4.9 5.8 14.4 8.1 11.4 9.6 Example 11 Working 5.0 4.9 5.8 14.8 8.5 11.2 9.4 Example 12 Working 5.0 4.9 5.8 15.0 8.7 11.3 9.5 Example 13 Working 5.0 4.9 5.8 14.7 8.4 11.1 9.3 Example 14 Working 5.0 5.8 7.7 18.4 7.0 10.5 8.6 Example 15 Working 5.0 5.0 5.8 13.8 8.3 10.8 9.2 Example 16 Working 5.0 4.8 5.7 15.2 8.8 11.0 9.1 Example 17 Comparative 5.0 5.0 6.0 12.6 5.8 12.1 10.2 Example 1 Comparative 5.0 7.6 6.1 4.8 11.9 9.5 11.9 Example 2 Comparative 5.0 5.2 7.0 18.1 8.5 12.9 9.7 Example 3 Comparative 5.0 5.3 7.2 17.5 7.5 12.7 9.3 Example 4 Comparative 5.0 7.5 6.0 5.4 12.7 9.4 11.8 Example 5 Percent elongation of film Electromagnetic % Ra transduction MD nm characteristics Error rate Dropouts Working 1.3 4.3 — EXCELLENT EXCELLENT Example 1 Working 1.3 4.3 GOOD EXCELLENT EXCELLENT Example 2 Working 1.1 4.2 GOOD EXCELLENT EXCELLENT Example 3 Working 1.0 4.1 GOOD EXCELLENT EXCELLENT Example 4 Working 1 1 4.2 GOOD EXCELLENT EXCELLENT Example 5 Working 1.1 4.2 GOOD EXCELLENT EXCELLENT Example 6 Working 1.0 4.3 GOOD EXCELLENT EXCELLENT Example 7 Working 1.2 4.4 GOOD EXCELLENT EXCELLENT Example 8 Working 1.6 4.2 GOOD EXCELLENT EXCELLENT Example 9 Working 1.6 4.3 GOOD EXCELLENT EXCELLENT Example 10 Working 1.4 4.3 GOOD EXCELLENT EXCELLENT Example 11 Working 1.4 4.2 GOOD EXCELLENT EXCELLENT Example 12 Working 1.2 4.3 GOOD EXCELLENT EXCELLENT Example 13 Working 1.1 4.2 GOOD EXCELLENT EXCELLENT Example 14 Working 1.1 2.6 (surface A) EXCELLENT EXCELLENT EXCELLENT Example 15 5.0 (surface B) Working 1.2 2.5 (surface A) EXCELLENT EXCELLENT EXCELLENT Example 16 4.9 (surface B) Working 1.3 2.3 (surface A) EXCELLENT EXCELLENT EXCELLENT Example 17 5.0 (surface B) Comparative 0.7 4.4 GOOD BAD BAD Example 1 Comparative 0.5 4.3 GOOD BAD BAD Example 2 Comparative 4.6 4.0 — — — Example 3 Comparative 3.9 4 0 — — — Example 4 Comparative 0.6 4.3 GOOD BAD BAD Example 5

(99) At TABLE 1, MD indicates the film forming direction of the film; TD indicates the width direction of the film; at Working Examples 15-17 in TABLE 1, the surface on the A layer side did not come in contact with the cooling drum, this being indicated as surface A at TABLE 2, and the surface on the B layer side came in contact with the cooling drum, this being indicated as surface B at TABLE 2; and at TABLE 1, SA refers to sebacic acid, DA refers to dodecanedioic acid, HD refers to hexanediol, DD refers to decanediol, and PEI refers to polyether imide.

INDUSTRIAL UTILITY

(100) Because the polyester composition of the present invention and a polyester film employing same more easily permit achievement of dimensional stability, and in particular excellent dimensional stability with respect to changes in environment, e.g., changes in temperature and/or humidity, and the percent elongation of the film at 110° C. is moreover low, and are such that uneven coating during coating operations tends not to occur, they are suitable for use in applications in which a high degree of dimensional stability—including with respect to the effects of humidity and temperature—is sought; e.g., as base film for high-density magnetic recording media or the like.