JP3374817B2 - Biaxially oriented polyester film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film having significantly improved quality and its use.
More specifically, a magnetic recording film, a packaging film, which is excellent in thermal dimensional stability and transparency and has good productivity,
Film for condenser, film for thermal transfer ribbon,
The present invention relates to a polyester film suitable as a film for various industrial materials such as a film for photo / platemaking, a film for electrical insulation, and the use thereof.

[0002]

2. Description of the Related Art Polyester films such as polyethylene terephthalate films are widely used in various applications including magnetic recording applications and electrical applications because of their excellent mechanical, thermal and electrical properties. Magnetic recording tape, which is one of the application fields of such polyester film, is being made thinner and higher density for the purpose of downsizing and longer recording. The demand for improvement of elongation deformation is becoming stronger.

In the case of a polyethylene terephthalate film, in order to meet the above requirements, the film is stretched in two directions, a longitudinal direction (hereinafter, referred to as a longitudinal direction) and a width direction (hereinafter, referred to as a lateral direction), and then, again in the longitudinal direction or / Also, a method of stretching in the transverse direction to increase the strength is mainly used.
However, when the film is re-stretched to increase the strength,
At the same time, there is a problem that the dimensional change due to heat shrinkage becomes large. This dimensional change lowers the yield in the tape processing process and causes the recording tracks to shift when used as a tape to increase the error rate during playback, so polyethylene terephthalate film for high-density magnetic recording tape is used. Is a major issue for the application of.

On the other hand, polyethylene terephthalate (PE
No technical disclosure has been given in the past regarding the composition of T) and polyetherimide (PEI) (for example, “JO
URNAL of APPLIED POLYMER
SCIENCE 48 935-937 (199
3) ”,“ Macromolecules 28 28
45-2851 (1995), POLYMER 38
4043-4048 ”(1997)). However, there has been no report on a biaxially oriented film made of a compatible blend of PET and PEI, let alone the dimensional stability of the film, and it is the fact that it has not been studied yet.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high quality biaxially oriented polyester film which is excellent in thermal dimensional stability and transparency and is also excellent in productivity and its use. In addition, practical properties that have been emphasized in various applications of polyester film, such as deviation of recording tracks in magnetic recording tape applications, curl in magnetic recording card applications, printing deviation in ribbon applications, heat resistance in condenser applications, etc. It is to provide a biaxially oriented polyester film which can be improved.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a polyester composition containing a polyester (A) containing an ethylene terephthalate unit as a main component and a polyetherimide (B). In a film made of a material, it was found that the above object can be achieved by imparting a predetermined orientation to the film by a stretching / heat treatment step and keeping the density and the refractive index within specific ranges, and to complete the present invention. It has come. That is, the biaxially oriented polyester film of the present invention comprises a polyester composition containing a polyester (A) containing ethylene terephthalate units as main components and a polyetherimide (B), and has a density ρ of 1.35 to 1.42 g. /
cm ³ , and the refractive index n in at least one of the longitudinal direction and the width direction is 1.60 to 1.80.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester (A) referred to in the present invention is a polymer having an ethylene terephthalate unit as a main component, and preferably containing 70 mol% or more. The acid component is mainly terephthalic acid, but a small amount of other dicarboxylic acid component may be copolymerized,
The glycol component is mainly composed of ethylene glycol, but other glycol components may be added as a copolymerization component.

Examples of dicarboxylic acids other than terephthalic acid include naphthalene dicarboxylic acid, isophthalic acid,
Diphenyl sulfone dicarboxylic acid, benzophenone dicarboxylic acid, 4,4'-diphenyl dicarboxylic acid, 3,
Aromatic dicarboxylic acids such as 3'-diphenyldicarboxylic acid, adipic acid, succinic acid, azelaic acid, sebacic acid, dodecanedioic acid and other aliphatic dicarboxylic acids, hexahydroterephthalic acid, 1,3-adamantanedicarboxylic acid, etc. An alicyclic dicarboxylic acid can be mentioned.

Examples of glycol components other than ethylene glycol include chlorohydroquinone, methylhydroquinone, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenylsulfone,
4,4'-dihydroxydiphenyl sulfide, 4,4
′ -Dihydroxybenzophenone, aromatic diol such as p-xylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, etc., 1 , 4-butanediol, 1,6-
Examples thereof include aliphatic and alicyclic diols such as hexanediol and neopentyl glycol.

Further, in addition to the acid component and the glycol component, aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid and p-aminophenol and p-aminobenzoic acid. A small amount of acid or the like can be further copolymerized as long as the object of the present invention is not impaired.

The polyetherimide (B) referred to in the present invention is a polymer containing an aliphatic, alicyclic or aromatic ether unit and a cyclic imide group as repeating units, and is a polymer having melt moldability. There is no particular limitation as long as it exists. For example, U.S. Pat. No. 4,141,927, Japanese Patent No. 2,622,678, Japanese Patent No. 2606.
No. 912, Japanese Patent No. 2606914, Japanese Patent No. 2
Polyetherimides such as 596565, Japanese Patent No. 2596566, Japanese Patent No. 2598478,
Japanese Patent No. 2598536, Japanese Patent No. 2599171, Japanese Patent Laid-Open No. 9-48852, Japanese Patent No. 25655.
56, Japanese Patent No. 2564636, Japanese Patent No. 25
Japanese Patent No. 64637, Japanese Patent No. 2563548, Japanese Patent No. 2563547, Japanese Patent No. 2558341, Japanese Patent No. 2558339, Japanese Patent No. 283458.
Examples thereof include the polymers described in JP-A-0. Within the range in which the effects of the present invention are not impaired, the main chain of the polyetherimide (B) is a cyclic imide, a structural unit other than an ether unit, for example, an aromatic, aliphatic or alicyclic ester unit, an oxycarbonyl unit. It goes without saying that, etc. may be contained.

Specific examples thereof include polymers containing a unit having an ether bond represented by the following general formula (I). (I):

[Chemical 1] (Wherein R ₁ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms; R ₂ is a divalent aromatic residue having 6 to 30 carbon atoms, 2 to Selected from the group consisting of alkylene groups having 20 carbon atoms, cycloalkylene groups having 2 to 20 carbon atoms, and polydiorganosiloxane groups chain-terminated with alkylene groups having 2 to 8 carbon atoms. It is a divalent organic group.)

Examples of R ₁ and R ₂ include aromatic residues represented by the following formula group (II). (II):

[Chemical 2]

In the present invention, when a polyether imide having a glass transition temperature of 350 ° C. or lower, more preferably 250 ° C. or lower is used, the effect of the present invention is easily obtained, and from the viewpoints of cost and melt moldability, the following formula (III ) Or (IV) containing the structural unit
Most preferred is the polymer sold under the trade name TEM ".

(III):

[Chemical 3]

(IV):

[Chemical 4]

In the biaxially oriented polyester film of the present invention, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, and the like, as long as the effects of the present invention are not impaired. A compound such as a whitening agent, a colorant, a conductive agent, or inorganic particles, organic particles, or another kind of polymer may be added.

The biaxially oriented polyester film of the present invention has a density ρ of 1.35 to 1.42 g / cm ³ , and a refractive index n of at least one of the longitudinal direction and the width direction of 1.60 to 1. Must be 80. By setting the density ρ and the refractive index n within the above ranges, a highly rigid biaxially oriented polyester film that is less likely to undergo heat shrinkage, has less deformation under load, and has excellent dimensional stability can be obtained. In addition, the frequency of tears is reduced and uneven thickness is reduced. Further, as a result of earnestly studying, preferably ρ is 1.36 to
1.39, and n is 1.65 to 1.75, more preferably ρ is 1.37 to 1.38, and n is 1.67 to 1.75.
It has been found that when the value is 72, the dimensional stability can be improved. The plane orientation coefficient fn of the film is 0.10 to 0.
When it is 18, the characteristics of the biaxially oriented polyester film of the present invention are easily obtained, which is preferable. fn is 0.12
˜0.17 is more preferable, and 0.14 to 0.16 is particularly preferable.

The haze value as referred to in the present invention is an internal haze value (%) in terms of 25 μm measured by immersing a film test piece in tetralin.

According to the present invention, the internal haze value of 25 μm is preferably 0.1 to 15% in order to obtain a polyester film having excellent transparency. According to the knowledge of the present inventors, it is extremely difficult industrially to set the haze value to less than 0.1%, and it is not a practical essential requirement in the case of a polyester film. A more preferable haze value range is 0.3 to 10%, and a more preferable range is 0.
5 to 3%.

The biaxially oriented polyester film of the present invention preferably has a single glass transition temperature (Tg). When the glass transition temperature of the film is single, the polyester (A) and the polyetherimide (B) are sufficiently compatible in the film, and the effects of the present invention can be sufficiently exhibited, which is preferable. .

The glass transition temperature (Tg) in the present invention is
From the heat flux gap at the time of temperature rise in differential scanning calorimetry, J
It can be determined according to IS K7121. When it is difficult to make a determination only by the method of differential scanning calorimetry, a morphological method such as dynamic viscoelasticity measurement or microscopic observation may be used together. When the glass transition temperature is determined by differential scanning calorimetry, it is also effective to use a temperature modulation method or a high sensitivity method.

In the biaxially oriented polyester film of the present invention, if the heat of fusion ΔH of the crystal determined from differential scanning calorimetry (DSC) is 15 to 45 J / g, the structure is stabilized by the presence of the crystal, It is preferable because heat shrinkage is small. ΔH is more preferably 25 to 40 J / g, further preferably 30 to 38 J / g.

The content of the polyetherimide (B) (ratio to the total resin constituting the film) is preferably 1% by weight or more, more preferably 5% by weight or more, further preferably 10% by weight or more. is there. Since the melt viscosities of the polyester (A) and the polyetherimide (B) are greatly different, the content of the polyetherimide (B) is 1% by weight or more in order to be kneaded with each other and compatibilized with each other in an extruder. It is preferable.

The content of polyester (A) (ratio to the total resin constituting the film) is 50% by weight.
It is preferable that the amount is above, more preferably 60% by weight.
The above is more preferable, and the more preferable is 70% by weight. In order to biaxially stretch the obtained polyester film to develop a desired strength, the content of the polyester (A) is 50.
It is preferably at least wt%.

As the method for measuring the content of polyetherimide, the following method is preferably used. The blended polymer of polyester (A) and polyetherimide (B) is dissolved in a suitable solvent such as hexafluoroisopropanol / chloroform which dissolves both, and under the following conditions, 1
The NMR spectrum of the H nucleus is measured. In the obtained spectrum, the absorption corresponding to the aromatic proton of terephthalic acid in the polyester (A) (8.1 ppm) and the absorption corresponding to the aromatic proton of bisphenol A of the polyetherimide (B) (7.0 ppm). ) Peak area intensity is calculated, and the molar ratio of the blend is calculated from the ratio and the number of protons. Further, the weight ratio is calculated from the formula weight corresponding to the unit unit of the polymer.

Further, the intrinsic viscosity (IV) of the polyester film of the present invention is preferably in the range of 0.6 to 1.0 dl / g from the viewpoint of film-forming property and dimensional stability of the film,
The range of 0.65 to 0.80 dl / g is more preferable.

The sum of the Young's modulus (Y _MD ) in the longitudinal direction and the Young's modulus (Y _TD ) in the width direction of the biaxially oriented polyester film of the present invention (Y _MD + Y _TD ) is in the range of 8 to 25 GPa. Preferably, more preferably 10 to 20 GP
a, particularly preferably 12-18 GPa. This is because if the sum of Young's moduli is 8 GPa or more, the elongation deformation due to stress also becomes small. From the viewpoint of tear resistance and heat shrinkage characteristics of the film, the sum of Young's moduli is preferably 25 GPa or less.

In the biaxially oriented polyester film of the present invention, in view of dimensional stability of the base and suitability for processing in various film applications, the heat shrinkage rate at 100 ° C. in at least one of the longitudinal direction and the width direction is high. It is preferably 2% or less. More preferably, the heat shrinkage at a temperature of 100 ° C. is 1.0% or less in both the longitudinal direction and the width direction, and most preferably 0.5.
% Or less.

In the present invention, the temperature is 50 ° C. and the load is 28 MPa.
The creep compliance after lapse of 30 minutes under the conditions of 0.1 to 0.55 GPa ^-1 is preferable, and 0.12 to 0.30 GPa is more preferable.
^-1 , most preferably 0.15 to 0.20 GPa ^-1 . Especially, the creep compliance is 0.55GPa
If it is ^-1 or less, elongation deformation of the tape due to tension during running or storage of the tape is unlikely to occur, and track deviation and reproduction error during recording / reproduction can be reduced. From the viewpoint of tape breakage, the creep compliance is preferably 0.10. The creep compliance referred to in the present invention is described in "Introduction to High Polymer Chemistry (2nd Edition)" (published by Kagaku Dojin Co., Ltd.), p150.

The biaxially oriented polyester film of the present invention is not particularly limited, but it can be suitably used for magnetic recording medium applications, electric capacitor applications, heat-sensitive transfer ribbon applications and the like. Of these, magnetic recording medium applications are particularly preferable.

In the present invention, development for various film applications,
From the viewpoint of stable film formation, the thickness unevenness in the longitudinal direction of the film is preferably less than 15%. The thickness unevenness of the film is more preferably less than 10%, further preferably less than 8%, most preferably less than 6%.

The thickness of the film can be appropriately determined according to the use and purpose, but is preferably in the range of 0.5 to 300 μm. From the viewpoint of achieving the object of the present invention, the film thickness is more preferably less than 150 μm, further preferably less than 20 μm. In particular, for magnetic recording medium applications, it is suitable for high-density magnetic recording tapes, particularly base films for data storage, and has a magnetic recording density of preferably 30 GB (gigabytes) or more, more preferably 70 GB or more, Even more preferably, it is 100 GB or more. In addition, the film thickness is usually in the range of 1 μm to 15 μm for magnetic recording material use, 2 μm to 10 μm for data coating magnetic recording medium use, and 3 μm to 9 μm for data evaporation type magnetic recording medium use. .

The biaxially oriented polyester film of the present invention is preferably a film having a thickness of 1 to 6 μm for use in a thermal transfer ribbon, and has no wrinkles at the time of printing, uneven printing or excessive transfer of ink. High-definition printing can be performed.

The biaxially oriented polyester film of the present invention is preferably used in an electric capacitor for 0.5%.
A film having a thickness of up to 15 μm is applied, and the dielectric breakdown voltage and the dielectric properties are excellent in stability.

The resin component constituting the film of the present invention is
Polyester (A) and polyetherimide (B) are essential components, and other polymers, compatibilizers, inorganic particles and organic particles, and various other additives such as antioxidants, antistatic agents, crystal nucleating agents, etc. However, a small amount can be added so long as the effects of the present invention are not impaired.

The film of the present invention can be produced by a conventional biaxial stretching method, and the production method is not particularly limited.

For example, as a preferred method for producing the film of the present invention, a resin composition obtained by blending a predetermined ratio of polyester (A) and polyetherimide (B) is melt-extruded and discharged from a die, and the molten polymer is cooled and solidified. And molded into a sheet, and the sheet-shaped molded product is stretched in the longitudinal direction and the transverse direction, and the total area ratio (the product of the stretching ratio in the longitudinal direction and the stretching ratio in the transverse direction) is stretched to 9 to 100 times, Then, at a temperature of 150 ° C to 260 ° C for 0.3 seconds to 10 seconds.
Examples include a method of heat setting for 0 seconds. Here, the stretching in the machine direction and the transverse direction may be either a sequential biaxial stretching method or a simultaneous biaxial stretching method. Further, in order to make the polyester (A) and the polyetherimide (B) compatible with each other in the melt extrusion step, it is preferable to prepare a blend chip by melt kneading in advance before the melt extrusion step.
From the viewpoint of dimensional stability, thickness unevenness, and film breakage frequency, the total area ratio is more preferably 10 to 70 times,
30 to 50 times is most preferable. The temperature of heat treatment is
Depending on the use of the film, 180 ° C to 245 ° C is more preferable, and 190 ° C to 230 ° C is most preferable. From the viewpoint of dimensional stability and productivity of the film, the heat treatment time is
0.5 second to 10 seconds is more preferable, and 1 second to 5 seconds is most preferable.

Next, specific examples of the method for producing the biaxially oriented polyester film of the present invention will be described, but it goes without saying that the invention is not limited to the following description.

The polyethylene terephthalate pellets (A) obtained by the usual method and the polyetherimide pellets (B) are mixed at a predetermined ratio to give 270 to 3
The mixture is fed to a vent type twin-screw kneading extruder heated to 00 ° C. to be melt-extruded into chips. The shear rate at this time is 50
~ 300 sec ^-1 is preferable, and more preferably 100-
200 sec ⁻¹ , and the residence time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes.

The obtained polyetherimide-containing chip was vacuum-dried at 180 ° C. for 3 hours or more, then placed in an extruder, melt-extruded at 280-320 ° C., and passed through a fiber-sintered stainless metal filter. Then, the sheet is discharged from the T die. In addition, the surface temperature of this sheet 2
The film is brought into close contact with a cooling drum of 5 to 30 ° C. to be cooled and solidified to obtain a film in a substantially non-oriented state.

Next, this unstretched film is biaxially stretched,
Orient biaxially. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. here,
Using a longitudinal stretching machine in which several rolls are arranged, stretching is performed in the longitudinal direction by utilizing the peripheral speed difference of the rolls (MD stretching 1), and then transverse stretching is performed by a stenter (TD stretching 1). A biaxial stretching method in which re-longitudinal stretching is performed by a roll longitudinal stretching machine (MD stretching 2) and transverse stretching is performed again by a stenter (TD stretching 2) will be described.

First, an unstretched film (Tg-100)
To (Tg + 100) (° C), preferably (Tg-
50) to (Tg + 50) (° C), more preferably (Tg-30) to (Tg + 30) (° C) in the range of heating rolls in the range of 1.1 to 5.0 times in the longitudinal direction.
Preferably 1.5 to 4.0 times, more preferably 2.0.
˜3.5 times, and cooled with a cooling roll group at 20 to 50 ° C. (MD stretching 1). Next, stretching in the width direction is performed using a stenter. The draw ratio is 2.0 to 6.0 times, preferably 3.0 to 5.5 times, and more preferably 4.0.
5.0 times, temperature is (Tg-100) ~ (Tg + 100)
(C) range, preferably (Tg-50) to (Tg + 5)
0) (° C) range, more preferably (Tg-30) to
It is performed in the range of (Tg + 30) (° C.) (TD stretching 1).

Further, the film is (Tg-100)
(Tg + 100) (° C) range, preferably (Tg-5
0) to (Tg + 50) (° C), more preferably (Tg-30) to (Tg + 30) (° C) in a range of heating rolls, and 1.1 to 4.0 times in the longitudinal direction, Preferably 1.4-3.0 times, more preferably 1.6-
It is re-longitudinal stretched 2.5 times and cooled with a cooling roll group at 20 to 50 ° C. (MD stretching 2). Next, stretching in the width direction is performed again using a stenter.

The draw ratio is 1.1 to 3.0 times, preferably 1.2 to 2.5 times, and more preferably 1.3 to 2.0.
Times, the temperature is in the range of Tg to 250 (° C.), preferably (T
g + 20) to 240 (° C.), more preferably (Tg + 40) to 220 (° C.) (TD stretching 2). If necessary, the stretched film is relaxed under tension or in the width direction while being 150 to 250 ° C, preferably 170 to 240 ° C, more preferably 160 to 220 ° C.
Heat treatment within the range.

Then, after cooling to room temperature, the film edge is removed to obtain the biaxially stretched film of the present invention.

[Measurement Method of Physical Properties and Evaluation Method of Effects] The measurement method of characteristic values and the evaluation method of effects are as follows.

(1) Refractive index According to the method specified in JIS-K7105, the D-line was measured using an Abbe refractometer as a light source. The mount solution used was methylene iodide, and
It was measured at 65 ° C. and 65% RH. The surface orientation coefficient fn is a value defined by 1/2 (na + nb) -nc, where na, nb, and nc are the refractive indices in the longitudinal direction, the width direction, and the thickness direction.

(2) Haze According to JIS-K-6714, a haze meter (manufactured by Suga Test Instruments Co., Ltd.) was used. The internal haze was measured in the state of being immersed in tetralin, and expressed by the following formula in terms of 25 μm. Haze (%) = internal film haze (%) x (25 (μ
m) / film thickness (μm))

(3) Young's modulus Measured using an Instron type tensile tester according to the method specified in ASTM-D882. The measurement was performed under the following conditions. Measuring device: Orientec Co., Ltd. film strength and elongation automatic measuring device "Tensilon AMF / RTA-100" Sample size: Width 10 mm x test length 100 mm, tensile speed: 200 mm / min Measuring environment: temperature 23 ° C, humidity 65 % RH.

(4) Heat shrinkage ratio Measured according to JIS-C2318. Sample size: width 10 mm, marked line interval 200 mm Measurement conditions: temperature 100 ° C., treatment time 30 minutes, unloaded state 100 ° C. Thermal shrinkage was calculated from the following formula. Thermal contraction rate (%) = [(L ₀ −L) / L ₀ ] × 100 L ₀ : Mark interval before heat treatment L: Mark interval after heat treatment

(5) TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. so that the creep compliance film was sampled in a width of 4 mm and the test length was 15 mm.
And the heating control unit TA-1500. Fifty
A load of 28 MPa was applied to the film under conditions of ° C and 65% RH and kept for 30 minutes, and the film elongation amount at that time was measured. The amount of expansion and contraction (% display, ΔL) of the film is measured by a personal computer PC manufactured by NEC Corporation via an AD converter ADX-98E manufactured by Canopus Electronics Co., Ltd.
The creep compliance was calculated from the following formula. Creep compliance (GPa ^-1 ) = (ΔL / 10
0) /0.028

(6) Intrinsic viscosity Measured at a concentration of 0.1 g / ml in orthochlorophenol at 25 ° C. The unit is [dl / g]. (7) Density The density of the film was measured using an aqueous sodium bromide solution by the density gradient tube method of JIS-K-7112.

(8) Glass transition temperature (Tg) The specific heat was measured by the following apparatus and conditions, and JIS K71
21. Equipment: Temperature modulation DSC manufactured by TA Instrument Measuring conditions: Heating temperature: 270-570K (RCS cooling method) Temperature calibration: High-purity indium and tin melting points Temperature modulation amplitude: ± 1K Temperature modulation cycle: 60 seconds Temperature raising step: 5K Sample weight: 5 mg Sample container: Aluminum open-type container (22 mg) Reference container: Aluminum open-type container (18 mg) The glass transition temperature was calculated by the following formula. Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2

(9) Heat of fusion (ΔH) It was measured according to JIS K7122. Device: "Robot DSC-R" manufactured by Seiko Instruments Inc.
DC220 "Data Analysis" Disc Session SSC /
5200 "Sample mass: 5 mg Heating rate: 20 ° C / min

(10) Breakage frequency Film breakage due to film formation was observed and judged according to the following criteria. ◎: When there is no film tear ○: When film tear occurs extremely rare △: When film tear occurs occasionally ×: When film tear occurs frequently

(11) Thickness unevenness in the longitudinal direction of the film Film thickness tester "KG manufactured by Anritsu Corporation
Using a "601A" and an electronic micrometer "K306C", the thickness of a film sampled in the longitudinal direction of the film to a width of 30 mm and a length of 10 m is continuously measured. The transport speed of the film was 3 m / min. R = Tmax-Tmin was obtained from the maximum thickness Tmax (μm) and the minimum value Tmin (μm) at 10 m length, and the thickness unevenness was obtained from R and the average thickness Tave (μm) at 10 m length by the following formula. Thickness unevenness (%) = (R / Tave) × 100

(12) Center line average surface roughness (Ra) Measured using a high precision thin film step gauge ET-10 manufactured by Kosaka Laboratory Ltd. and measured according to JIS B0601. ) Was asked. The probe tip radius was 0.5 μm, the needle pressure was 5 mg, the measurement length was 1 mm, and the cutoff was 0.08 mm.

(13) Electromagnetic conversion characteristics (C /
N) On the surface of the film of the present invention, a magnetic coating material and a non-magnetic coating material having the following compositions are multilayer coated by an extrusion coater (the upper layer is a magnetic coating material having a coating thickness of 0.1 μm, and the thickness of the non-magnetic lower layer is appropriately changed), Magnetically orient and dry. Then, after forming a back coat layer having the following composition on the opposite surface, a small test calender device (steel / steel roll, 5 steps) was used, temperature: 85 ° C., linear pressure: 200 kg /
After calendering in cm, cure at 70 ° C. for 48 hours. The raw tape is slit into a width of 8 mm to prepare a pancake. Then, a length of 200 m from this pancake is incorporated into a cassette to form a cassette tape.

On this tape, a commercially available Hi8 VTR (S
7MHz using ONY EV-BS3000)
The C / N (carrier to noise ratio) of +1 MHz is measured. This C / N is a commercially available Hi8 video tape (SON
Compared with 120 minutes MP made by Y company, +3 dB or more is ○,
It is determined that Δ is +1 or more and less than +3 dB, and x is less than +1 dB. A circle is desirable, but a triangle can also be practically used.

[0061]   (Composition of magnetic paint)   ・ Ferromagnetic metal powder: 100 parts by weight   -Na sulfonate modified vinyl chloride copolymer: 10 parts by weight   ・ Na sulfonate modified polyurethane: 10 parts by weight   ・ Polyisocyanate: 5 parts by weight   ・ Stearic acid: 1.5 parts by weight   ・ Oleic acid: 1 part by weight   ・ Carbon black: 1 part by weight   ・ Alumina: 10 parts by weight   ・ Methyl ethyl ketone: 75 parts by weight   ・ Cyclohexanone: 75 parts by weight   ・ Toluene: 75 parts by weight

[0062] (Composition of non-magnetic lower layer paint)   ・ Titanium oxide: 100 parts by weight   ・ Carbon black: 10 parts by weight   -Na sulfonate modified vinyl chloride copolymer: 10 parts by weight   ・ Na sulfonate modified polyurethane: 10 parts by weight   ・ Methyl ethyl ketone: 30 parts by weight   Methyl isobutyl ketone: 30 parts by weight   ・ Toluene: 30 parts by weight (Backcoat composition)   ・ Carbon black (average particle size 20 nm): 95 parts by weight   Carbon black (average particle size 280 nm): 10 parts by weight   ・ Α-alumina: 0.1 part by weight   ・ Zinc oxide: 0.3 parts by weight   ・ Na sulfonate modified polyurethane: 20 parts by weight   -Na sulfonate modified vinyl chloride copolymer: 30 parts by weight   ・ Cyclohexanone: 200 parts by weight   ・ Methyl ethyl ketone: 300 parts by weight   Toluene: 100 parts by weight.

(14) A high-speed abradable film slit into a tape having a width of 1/2 inch is run on a guide pin (surface roughness: Ra of 100 nm) using a tape running tester ( Traveling speed 2
50m / min, 1 pass, wrapping angle: 60 °, running tension: 90g). At this time, visually observing the guide pin after the film has finished running, ○ shows no adhesion of white powder, △ shows slight adhesion of white powder, △ shows that a large amount of white powder adheres Judge as x. A circle is desirable, but a triangle can also be practically used.

(15) Running durability and storability of magnetic tape On the surface of the film of the present invention, a magnetic coating composition having the following composition is applied to a coating thickness of 2.0 μm, magnetically oriented and dried. Then, a back coat layer having the following composition is formed on the opposite surface, calendered, and then cured at 70 ° C. for 48 hours. The above tape raw material is slit into a width of 1/2 inch, and a magnetic tape having a length of 670 m is incorporated into a cassette to form a cassette tape.

[0065]   (Composition of magnetic paint)   ・ Ferromagnetic metal powder: 100 parts by weight   -Modified vinyl chloride copolymer: 10 parts by weight   -Modified polyurethane: 10 parts by weight   ・ Polyisocyanate: 5 parts by weight   ・ Stearic acid: 1.5 parts by weight   ・ Oleic acid: 1 part by weight   ・ Carbon black: 1 part by weight   ・ Alumina: 10 parts by weight   ・ Methyl ethyl ketone: 75 parts by weight   ・ Cyclohexanone: 75 parts by weight   ・ Toluene: 75 parts by weight (Backcoat composition)   ・ Carbon black (average particle size 20 nm): 95 parts by weight   Carbon black (average particle size 280 nm): 10 parts by weight   ・ Α-alumina: 0.1 part by weight   -Modified polyurethane: 20 parts by weight   -Modified vinyl chloride copolymer: 30 parts by weight   ・ Cyclohexanone: 200 parts by weight   ・ Methyl ethyl ketone: 300 parts by weight   ・ Toluene: 100 parts by weight

The prepared cassette tape is used as a Ma tape manufactured by IBM.
gstar3590 MODELB1A Tape D
The tape is run for 100 hours using a rive and the running durability of the tape is evaluated according to the following criteria. ○ is a passing product. ◯: There is no stretching or bending of the tape end face, and no trace of scraping is seen. Δ: There is no stretching or bending of the tape end surface, but some scraping marks are seen. X: A part of the tape end surface is stretched, wakame-like deformation is observed, and scratch marks are observed.

In addition, the cassette tape prepared above is IB
M made Magstar 3590 MODELB1A Ta
After reading the data into the pe Drive, the cassette tape is stored in an atmosphere of 50 ° C. and 80% RH for 100 hours, and then the data is reproduced to evaluate the storability of the tape according to the following criteria. ○ is a passing product. ◯: There was no track deviation, and normal reproduction was performed. Δ: There is no abnormality in the tape width, but it is partially unreadable. X: There is a change in the tape width, and the reading is unreadable.

(16) Printability of thermal transfer ribbon The biaxially oriented film of the present invention was coated with a thermal transfer ink having the following composition on a surface opposite to the anti-fusing layer with a hot melt coater so that the coating thickness was 3.5 μm. Process to make a thermal transfer ribbon. (Composition of thermal transfer ink) Carnauba wax: 60.6% by weight Microcrystalline wax: 18.2% by weight Vinyl acetate / ethylene copolymer: 0.1% by weight Carbon black: 21.1% by weight About the thermal transfer ribbon prepared A black solid is printed with a bar code printer (BC-8) manufactured by Oaks Co., Ltd. to evaluate the printability. ○ is a passing product. ○: Clearly printed. Δ: Pitch deviation occurs in printing. X: Ribbons are wrinkled, and the printing is disturbed. XX: The film was wrinkled during hot melt coating, and the thermal transfer ink could not be applied uniformly.

(17) Characteristic evaluation for capacitors A. A pair of symmetrical aluminum vapor-deposited films having an insulation resistance of 30 mm width and a margin of 1.5 mm width are overlapped and wound into a length having a capacitance of 1.5 μF. This roll is 150 ℃, 70kg
Press for 10 minutes at a pressure of / cm ² to mold. Metallicon is sprayed on both end faces to form electrodes, and lead wires are attached to make capacitor samples. Next, 1000 1.5 μF capacitor samples made here are
Measured as a 1-minute value at an applied voltage of 500 V with a super insulation resistance meter 4329A manufactured by YHP Co. in an atmosphere of 3 ° C. and 65% RH, and a capacitor sample having an insulation resistance of less than 5000 MΩ was regarded as a defective product, and the following criteria were used. judge. In the present invention, ⊚, ◯, and Δ are acceptable products. ◎: Less than 10 defective products ○: 10 or more and less than 20 defective products Δ: 20 or more and less than 50 defective products ×: 50 or more defective products

B. Dielectric breakdown voltage According to the method described in JIS-C-2318,
The film without metal deposition is used as a test piece and evaluated as follows. Laminate a rubber plate with a rubber shore hardness of about 60 degrees and a thickness of about 2 mm on a metal flat plate of an appropriate size, and place an aluminum foil with a thickness of about 6 μm on it.
A stack of 0 sheets is used as a lower electrode, and a brass cylinder having a diameter of 8 mm and a round bottom having a roundness of about 1 mm and a weight of about 50 g and having no scratch is used as an upper electrode. Then, the test is performed under the following two conditions to measure the dielectric breakdown voltage at room temperature and high temperature. First, after leaving in each atmosphere for 48 hours or more, a test piece is sandwiched between the upper electrode and the lower electrode, a DC voltage is applied between both electrodes in each atmosphere by a DC power source, and the DC voltage is applied for 1 second. It is raised from 0V at a speed of 100V until dielectric breakdown occurs. The test was conducted on 50 samples, and the average value of the dielectric breakdown voltage divided by the thickness of the test piece was obtained. Under the condition 1, the average value was 400 V / μm or more,
In Condition 2, 350 V / μm or more is passed (◯). Condition 1: Temperature 20 ± 5 ° C., relative humidity 65 ± 5% Condition 2: Temperature 125 ± 5 ° C., relative humidity 65 ± 5%

(18) Tracking resistance of floppy disk Tracking deviation test due to temperature change The following method is used for the tracking deviation test. A magnetic recording layer was formed on both sides of a base film by sputtering a metal thin film, and a floppy disk made of a metal thin film punched out in a disk shape was formed at a temperature of 15 ° C and a humidity of 60%.
Magnetic recording is performed using a ring head at RH, and the maximum output and the output envelope of the magnetic sheet at that time are measured. Next, maintaining the ambient temperature at 60 ° C. and the humidity at 60% RH, and examining the maximum output and the output envelope at that temperature, the output envelope at the temperature of 15 ° C. and the humidity at 60% RH, the temperature of 60 ° C., and the humidity at 60% RH The output envelope at the time of% RH is compared to determine the tracking state.
The smaller the difference, the better the tracking resistance. If this difference exceeds 3 dB, the tracking is x, and if it is within 3 dB, it is evaluated as ◯. B. Tracking deviation test due to humidity change A floppy disk prepared in the same manner as the previous section was recorded in an atmosphere of temperature 25 ° C and relative humidity 20%, and the atmospheric conditions were maintained at temperature 25 ° C and relative humidity 70%. The output envelopes are compared to determine the tracking status. Similar to the previous item, if this difference exceeds 3 dB, the tracking is evaluated as x, and if the difference is within 3 dB, it is evaluated as o.

(19) Scratch resistance of floppy disk The same track magnetically recorded on a floppy disk obtained in the same manner as in (17) above was scanned 100,000 times or more at a relative running speed of 6 m / sec, and its output envelope was measured. Find out.
As an evaluation criterion, a mark in which a scratch generated on the surface of the magnetic layer is confirmed and the output envelope becomes unstable is marked with x. When the surface of the magnetic layer is not scratched and the output envelope is stable, it is evaluated as ◯.

[0073]

EXAMPLES The present invention will be described based on Examples and Comparative Examples.

Example 1 Polyethylene terephthalate obtained by conventional method (specific
Viscosity 0.85) pellets (50% by weight) and polite
Luimide pellets ("Ultem 1010 (Gene
(registered trademark of Ral Electric Company) ") (50 layers
(Amount%) is a vent type twin-screw kneading press heated to 280 ° C.
Supplied to the launch machine, shear rate 100 sec ^-1, Residence time 1
Melt-extruded in 50 minutes, containing 50% by weight of polyetherimide
Obtained chip (I) was obtained. The resulting polyether imie
Chip (I) containing polyethylene and polyethylene terephthalate (solid
Dry-blend a viscosity of 0.62) at a ratio of 40:60
It was After vacuum drying at 180 ° C for 3 hours, put in an extruder,
Melt extrusion at a set temperature of 285 ° C and a residence time of 300 seconds,
Fiber sintered stainless metal filter (10μm cut)
Shear speed within 10 seconds^-1After passing with, see from T die
It was ejected in the shape of a tooth. In addition, this sheet with a surface temperature of 25 ℃
Solidify by cooling on a cooling drum at a speed of 4 m / min.
20% by weight of substantially non-oriented polyetherimide
A% content film was obtained.

The obtained film was stretched under the conditions shown in Table 1. First, a longitudinal stretching machine in which several rolls are arranged is used to perform longitudinal stretching (MD stretching 1) by utilizing the peripheral speed difference of the rolls, and then transverse stretching (T stretching) by a stenter.
D-stretching 1), re-longitudinal stretching (MD stretching 2) with a roll longitudinal stretching machine, re-transverse stretching (TD stretching 2) with a stenter, heat treatment, cooling to room temperature, removal of film edges, and thickness A 6.9 μm biaxially stretched film was obtained. The characteristics of the obtained film are as shown in Table 2. The density ρ and the refractive index n were within the range of the present invention, and a high quality film excellent in dimensional stability could be stably formed.

Examples 2 and 3 In the same manner as in Example 1, the polyetherimide was mixed with 50
A chip (I) containing wt% was obtained. 40% by weight of polyetherimide was obtained by mixing the same chip (I) and polyethylene terephthalate (intrinsic viscosity 0.62) at a predetermined ratio and performing melt extrusion and biaxial stretching in the same manner as in Example 1.
Alternatively, a biaxially oriented polyester film containing 5% by weight was obtained. The obtained film was a high quality film having excellent dimensional stability. Further, as shown in Example 3, the dimensional stability was good even when the amount of the polyetherimide added was 5% by weight.

Example 4 Film formation was carried out in the same manner as in Example 1 except that the stretching and heat treatment were carried out under the conditions shown in Table 1. The density ρ and the refractive index n were within the range of the present invention, and the film was a high quality film having excellent dimensional stability. Example 5 Except that only MD stretching 1 and TD stretching 1 were used for biaxial stretching,
Film formation was carried out in the same manner as in Example 1. Also in this case, the density ρ and the refractive index n were within the range of the present invention, and the film was a high quality film excellent in dimensional stability.

Example 6 In the same manner as in Example 1, the polyetherimide was mixed with 50
A chip (I) containing wt% was obtained. The obtained polyetherimide-containing chip (I) and polyethylene terephthalate (intrinsic viscosity 0.62) were dry blended at a ratio of 80:20. After vacuum drying at 180 ° C. for 3 hours, it is put into an extruder, melt-extruded at a set temperature of 285 ° C. and a residence time of 60 seconds, and passed through a fiber-sintered stainless metal filter (10 μm cut) at a shear rate of 10 seconds ^−1. Then, the sheet was discharged from the T die. Further, apply this sheet to the surface temperature 2
Polyetherimide 4 in a substantially non-oriented state by being brought into close contact with a cooling drum at 5 ° C. at a speed of 4 m / min to be cooled and solidified.
A film containing 0% by weight was obtained. In this case, since the residence time was short, the film was a white turbid non-oriented film. afterwards,
By carrying out biaxial stretching and heat treatment under the conditions shown in Table 1, a biaxially oriented polyester film containing 40% by weight of polyetherimide was obtained. The obtained film had two glass transition temperatures of 108 ° C. and 161 ° C.

Comparative Examples 1 and 2 By the same method as in Example 1, polyetherimide-containing substantially non-oriented polyester films were obtained. The obtained film was formed under the stretching and heat treatment conditions shown in Table 1. The density ρ in Comparative Example 1 and the density ρ in Comparative Example 2
And the refractive index n were out of the range of the present invention, and the dimensional stability was poor.

Comparative Example 3 In the same manner as in Example 1, 50% of polyetherimide was added.
A chip (I) containing wt% was obtained. The same chip (I) and polyethylene terephthalate (intrinsic viscosity 0.62) are mixed and melt-extruded at 330 ° C., and a shear rate of 10 seconds ^{−1 in} a fiber sintered stainless metal filter (10 μm cut).
Then, the sheet was discharged from the T die in a sheet form. Further, place this sheet on a cooling drum having a surface temperature of 25 ° C.
A film containing 20% by weight of polyetherimide in a substantially non-oriented state was obtained by bringing the films into contact with each other at a rate of m / min and solidifying by cooling. The obtained film was a cloudy film. The obtained film was stretched under the conditions shown in Table 1 in the same manner as in Example 1. Since the obtained film had a refractive index n outside the range of the present invention, the dimensional stability was poor.

Comparative Example 4 Polyether imide was not contained and only polyethylene terephthalate (intrinsic viscosity 0.62) was charged into the extruder, and 2
The mixture was melt extruded at 80 ° C., passed through a fiber-sintered stainless metal filter (10 μm cut) at a shear rate of 10 sec ⁻¹ , and then discharged from a T die in a sheet form. Further, this sheet was brought into close contact with a cooling drum having a surface temperature of 25 ° C. at a rate of 4 m / min to be cooled and solidified to obtain a polyester film in a substantially non-oriented state. Then, stretching and heat treatment were performed under the conditions shown in Table 1. The evaluation results of the film obtained here are shown in Table 2. The film of this comparative example consisting of PET alone had poor thermal stability.

[0082]

[Table 1]

[0083]

[Table 2]

Example 7 Spherical silica particles with an average diameter of 0.07 μm were added to PET.
A blend chip (PET / PEI (I)) containing 50% by weight of polyetherimide was obtained in the same manner as in Example 1 except that 40% by weight was used.
Example 1 was repeated except that 0.5% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm and 0.025% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were mixed in PET. In the same manner as in (1), blend chips containing 50% by weight of polyetherimide (PET /
PEI (II)) was obtained.

Next, using two extruders A and B, a laminated film was prepared so that the extruder A formed a magnetic surface and the extruder B formed a running surface. To the extruder A heated to 280 ° C., 40 parts by weight of PET / PEI (I) pellets and 60 parts by weight of PET having an intrinsic viscosity of 0.65 were vacuum dried at 180 ° C. for 3 hours and then fed. To the extruder B heated to 280 ° C., 40 parts by weight of PET / PEI (II) pellets and 60 parts by weight of PET having an intrinsic viscosity of 0.65 were vacuum-dried at 180 ° C. for 3 hours, and then fed into a T-die. After merging in (lamination ratio I / II = 10/1), surface temperature 2
A laminated unstretched film was obtained by statically adhering onto a casting drum at 5 ° C. and cooling and solidifying.

Then, the film obtained here is shown in Table 3.
Stretching was carried out under the conditions shown in to obtain a biaxially oriented film having a thickness of 7.5 μm. Table 4 shows the basic characteristics of the obtained film.
The magnetic tape characteristics are shown in Table 5. The film of this example containing polyetherimide was superior in strength and thermal dimensional stability to the film of Comparative Example 5 consisting of PET alone, and was excellent in running durability, storage stability, high speed abrasion resistance, and electromagnetic conversion. It was also far superior in terms of magnetic tape characteristics such as characteristics.

Examples 8 and 9, Comparative Example 5 A laminated unstretched film was prepared in the same manner as in Example 7 except that the polyetherimide content was changed as shown in Table 3. The amount of particles in the blended raw material was adjusted so that the proportion of particles added to the two layers of the film was the same as in Example 7. Then, a film was formed in the same manner as in Example 7 under the conditions shown in Table 3 to obtain a biaxially oriented film having a thickness of 7.5 μm. The evaluation results of the films obtained here are shown in Tables 4 and 5. PET
The film of this comparative example, which is made of a single material, has deteriorated practical properties as a magnetic tape.

[0088]

[Table 3]

[0089]

[Table 4]

[0090]

[Table 5]

Example 10 PET / PEI (50 / prepared in the same manner as in Example 1)
50) blend raw material and PET (intrinsic viscosity 0.65, glass transition temperature 75 ° C., melting point 255 ° C., average diameter 0.3 μm)
Agglomerated silica particles of 0.25% by weight).
An unstretched film obtained in the same manner as in Example 1 except that an unstretched film of ET / PEI (90 parts by weight / 10 parts by weight) was prepared. The coating was performed with a gravure coater so that the coating thickness after drying was 0.5 μm. (Composition of coating material) Acrylic ester: 14.0% by weight Amino-modified silicone: 5.9% by weight Isocyanate: 0.1% by weight Water: 80.0% by weight

Then, the unstretched film is stretched in the machine direction of the film at a temperature of 110 ° C. by using a longitudinal stretching machine consisting of a plurality of heated roll groups and utilizing the peripheral speed difference of the rolls.
It was stretched at a magnification of 8 times. After that, both ends of this film are grasped by clips, guided to a tenter, and stretched at a stretching temperature of 10
Stretched in the width direction of the film at 5 ° C and a stretch ratio of 4.2 times,
After subsequent heat treatment at a temperature of 235 ° C., 150
A 1% relaxation treatment was applied in the lateral direction in a cooling zone controlled at 0 ° C., and after cooling to room temperature, the film edge was removed to obtain a biaxially oriented polyester film having a thickness of 3.5 μm. When this film was processed and evaluated for practical properties as a thermal transfer ribbon, as shown in Table 6, as compared with the film of Comparative Example 6 consisting of PET alone,
It had excellent properties as a thermal transfer ribbon.

Comparative Example 6 PET containing no polyetherimide as a raw material to be charged into the extruder (intrinsic viscosity 0.65, glass transition temperature 75
C., melting point 255.degree. C., 0.20% by weight of agglomerated silica particles having an average diameter of 0.3 .mu.m) were used, and the stretching temperature in the longitudinal direction was 95.degree. C. and the stretching temperature in the width direction was 90.degree. A film was formed in the same manner as in No. 25 to obtain a biaxially oriented film having a thickness of 3.5 μm. The characteristics of the obtained film are as shown in Table 6. The film of this comparative example, which was composed of PET alone, was likely to have print wrinkles and could not be used for a thermal transfer ribbon.

[0094]

[Table 6]

Example 11 PET / PEI (50 / prepared in the same manner as in Example 1)
50) blended raw material and PET (intrinsic viscosity 0.65, glass transition temperature 75 ° C., melting point 255 ° C., average diameter 0.2 μm)
A film having a thickness of 1.5 μm was obtained in the same manner as in Example 10 except that a PET / PEI film containing 10% by weight of PEI was formed by using 0.125% by weight of calcium phosphate particles (1). Obtained. The film obtained in this way was evaluated for practical properties for capacitors. As shown in Table 7, the film of this example had very excellent properties for capacitors.

Comparative Example 7 PET containing no polyetherimide as a raw material to be charged into the extruder (intrinsic viscosity 0.65, glass transition temperature 75
C., melting point 255.degree. C., 0.10% by weight of calcium phosphate particles having an average diameter of 0.2 .mu.m) was used, and the stretching temperature in the longitudinal direction was 95.degree. C. and the stretching temperature in the width direction was 90.degree.
A film was formed in the same manner as in Example 11. As shown in Table 7, the properties of the obtained film were inferior in heat resistance to the film of Example 11.

[0097]

[Table 7]

Example 12 PET / PEI (50 / prepared in the same manner as in Example 1)
20 parts by weight of the blend raw material of 50) and 80 parts by weight of PET (0.25% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.65 and an average particle size of 0.3 μm) are vacuum dried at 180 ° C. for 3 hours, and then 280 ° C. Supply to the extruder heated to
After being discharged in a sheet form from the T-die, it is brought into close contact with a cooling drum having a surface temperature of 25 ° C by electrostatic force to be cooled and solidified, and PE
An unstretched film containing 10% by weight of I was obtained.

Next, this unstretched film was stretched 3.8 times in the machine direction of the film at a temperature of 100 ° C. by using a longitudinal stretching machine composed of a plurality of heated roll groups and utilizing the peripheral speed difference of the rolls. Was stretched at a magnification of. After that, both ends of this film are grasped by clips, guided to a tenter, and stretched in the width direction of the film at a stretching temperature of 110 ° C. and a stretching ratio of 3.9 times, and subsequently at temperatures of 130 ° C., 180 ° C. and 200 ° C. Then, the temperature was raised stepwise to perform heat treatment. Subsequently 1
2% in the width direction in a cooling zone controlled at 00 ° C
After the relaxation treatment, the film was cooled to room temperature, the film edge was removed, and the film was wound. The film thickness was set to 62 μm by adjusting the extrusion rate. Table 8 shows the results of evaluating the practical characteristics of a floppy disk by subjecting this film to processing for a magnetic recording medium. The film obtained in this example was superior in thermal dimensional stability to the film of Comparative Example 8 consisting of PET alone, and was very excellent for a floppy disk.

Comparative Example 8 PET (incorporating 0.20% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.65 and an average particle size of 0.3 μm) at 180 ° C.
After vacuum-drying for 3 hours, supply to an extruder heated to 280 ° C., and discharge in sheet form from a T-die.
An unstretched film was obtained by bringing it into close contact with a 5 ° C. cooling drum by electrostatic force to cool and solidify. Next, this unstretched film was formed under the same conditions as in Example 12 except that the stretching temperature in the longitudinal direction was 95 ° C. and the stretching temperature in the width direction was 90 ° C., and a biaxially oriented film having a thickness of 62 μm was formed. Got The obtained film was processed for a magnetic recording medium in the same manner as in Example 12, and the results of evaluating practical properties as a floppy disk are shown in Table 8.

[0101]

[Table 8]

[0102]

EFFECTS OF THE INVENTION According to the present invention, a high-quality biaxially stretched polyester film is obtained which has little deformation under load, is excellent in thermal dimensional stability and transparency, and has little thickness unevenness. The film of the present invention greatly improves running durability and storage stability when used as a base film of a magnetic tape. It can also be widely used for various applications such as ribbons, capacitors, and floppy disks.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI B29K 79:00 B29K 79:00 B29L 7:00 B29L 7:00 31:34 31:34 (56) References JP 2000-309651 (JP, JP, A) JP 2000-141475 (JP, A) JP 11-217448 (JP, A) JP 11-49872 (JP, A) JP 11-1568 (JP, A) JP 51- 143060 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08J 5/00-5/24 C08L 1/00-101/16 B29C 47/00-47/96

Claims (13)

(57) [Claims] 1. A polyester composition comprising a polyester (A) containing ethylene terephthalate units as main components and a polyetherimide (B) and having a density ρ of 1.3.
A biaxially oriented polyester film having a refractive index n of 1.60 to 1.80 in at least one of the longitudinal direction and the width direction, which is 5 to 1.42 g / cm ³ . 2. The haze of 25 μm is 0.1 to 15
%, The biaxially oriented polyester film according to claim 1. 3. The biaxially oriented polyester film according to claim 1, which has a single glass transition temperature (Tg). 4. The biaxially oriented polyester film according to claim 1, wherein the heat of fusion ΔH of the crystal obtained by differential scanning calorimetry (DSC) is 15 to 45 J / g. . 5. The content of polyetherimide (B) is 1.
% Or more and the content of polyester (A) is 50
The biaxially oriented polyester film according to any one of claims 1 to 4, which is at least wt%. 6. The sum (Y _MD + Y _TD ) of the Young's modulus (Y _MD ) in the longitudinal direction and the Young's modulus (Y _TD ) in the width direction is 8 to 25 GPa.
The biaxially oriented polyester film according to any one of claims 1 to 5, wherein 7. The biaxially oriented polyester film according to claim 1, wherein a heat shrinkage ratio at 100 ° C. in at least one of the longitudinal direction and the width direction is 2% or less. . 8. The creep compliance after 30 minutes at a temperature of 50 ° C. and a load of 28 MPa is 0.10.
Is 0.55 GPa ^-1 .
The biaxially oriented polyester film according to any one of 7 above. 9. The biaxially oriented polyester film according to claim 1, wherein the thickness unevenness of the film is less than 15%. 10. A film having a thickness of 0.5 μm or more and 3
The biaxially oriented polyester film according to any one of claims 1 to 9, which has a thickness of 00 µm or less. 11. A magnetic recording medium comprising the biaxially oriented polyester film according to any one of claims 1 to 10. 12. A thermal transfer ribbon comprising the biaxially oriented polyester film according to any one of claims 1 to 10. 13. A capacitor comprising the biaxially oriented polyester film according to any one of claims 1 to 10.